15 Vitamins and Minerals
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Fat Soluble Vitamins
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Water Soluble Vitamins
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Minerals
Definition
Vitamins are organic compounds occurring in small quantities in different natural foods and necessary for growth and maintenance of good health.
Vitamins are mainly classified into
•
Fat soluble vitamins: Vitamins A, D, E and K
•
Water soluble vitamins: B Complex Vitamins and Vitamin C.
Endogenously synthesized Vitamins
Vitamins are generally not synthesized by the humans, but some vitamins can be synthesized endogenously. They are:
•
Vitamin D from precursor steroids
•
Vitamin K, Biotin, and pantothenic acid by the intestinal microflora
•
Niacin from tryptophan, an essential amino acid.
Fat Soluble Vitamins
Vitamin A
•
Ring structure present in Vitamin A is β ionone ring
•
Provitamin A, β carotene contain 2 β ionone ring
•
Cleaved in the intestine by a dioxygenase.
Retinoids
All compounds chemically related to retinol are called retinoids. They are:
•
Retinal: 11 cis retinal for normal vision
•
Retinoic acid: Normal morphogenesis, growth and cell differentiation
•
Retinol: Reproduction.
Vitamin A, in the strictest sense, refers to Retinol
Carotenoids
•
They are provitamins of Vitamin A present in plants
•
More than 600 carotenoids in nature, and approximately 50 of them can be metabolized to vitamin A
•
β Carotene is the most prevalent carotenoid in the food supply that has provitamin A activity.
Nonprovitamin A Carotenoids
•
Lutein and Zeaxanthin: Protect against macular degeneration
•
LycopeneQ: Protect against prostate cancer.
Vitamin A Metabolism
Absorption and transport of Vitamin A
•
Beta Carotene from plant sources is absorbed and cleaved to two molecules of Retinal by Beta Carotene Dioxygenase. Retinal is reduced to retinol by Retinol Reductase
•
Retinol ester from animal sources is hydrolyzed in the intestinal lumen to Retinol and absorbed into the intestinal cells
•
Retinol from animal and plant sources is reesterified to retinol esters and transported in ChylomicronsQ to Liver
‒
Uptake takes place in liver cells by means of apo E receptors.
Fig. 15.1: Metabolism of Vitamin A
Storage of Vitamin A
Stored in the Liver Perisinusoidal Stellate (Ito) cells as Retinyl Ester (Retinol Palmitate).
Transport of Vitamin A from Liver to Target Organs Carried to target sites in the plasma as trimolecular complex bound to Retinol Binding Protein (RBP) and Transthyretin.
Functions of Vitamin A
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Vision
‒
Visual process involve 3 forms of Vitamin A containing pigments
‒
Rhodopsin
-
Most light sensitive pigment present in rods
-
Formed by covalent association between 11 cis retinal and 7-transmembrane rod protein called opsin.
Three iodopsin each responsive to specific colors in cones in bright light.
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Regulation of gene expression and differentiation
‒
Retinoic Acids are involved in this function
‒
Biologically important retinoic acids are all Trans- retinoic acid and 9 -cis retinoic acid
‒
They act like steroid hormones
‒
They bind to nuclear receptors.
Retinoic acid receptors
Retinoid receptors regulate transcription by binding to specific DNA site.
•
Retinoic Acid Receptors (RARs) binds with high affinity to all: Transretinoic acid and 9 cis retinoic acid
•
Retinoic X receptor (RXRs) binds only to 9 cis retinoic acid
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Normal reproduction
‒
Retinol is necessary for this function.
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Maintenance of normal epithelium of skin and mucosa
•
Antioxidant Properties and photo protective property is attributed to Beta Carotenes
•
Host resistance to infection.
Vitamin A deficiency manifestations
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Most common vitamin deficiency
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Most common cause of preventable blindness
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Eyes
‒
Loss of sensitivity to green light is the earliest manifestation
‒
All the ocular manifestations are collectively called as Xerophthalmia
‒
Impairment to adapt in dim light, i.e. night blindness or Nyctalopia is the earliest symptom
‒
Conjunctival Xerosis (Dryness of Conjunctiva)
‒
Bitot’s spots (white patches of keratinized epithelium appearing on the sclera)
‒
Blinding corneal ulceration and necrosis
‒
Keratomalacia (softening of the cornea)
‒
Corneal scarring that causes blindness.
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Skin and Mucosa
‒
Epithelial metaplasia and keratinization
‒
Hyperplasia and hyperkeratinization of the epidermis with plugging of ducts of adnexal gland produce Follicular HyperkeratosisQ or Papular dermatosis. This is called as Phrynoderma or Toad Skin
‒
Squamous Metaplasia in the mucus secreting epithelium of upper respiratory tract and urinary tract
‒
Loss of taste sensation.
Remember
•
Concurrent Zinc deficiency can interfere with mobilization of Vitamin A from liver stores.
•
Alcohol interferes with conversion of retinol to retinaldehyde in the eyes.
Vitamin A as therapeutic agent
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β Carotene used in cutaneous Porphyria
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All transretinoic acid in acute Promyelocytic Leukemia [called as differentiation therapy]
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13 cis retinoic acid [Isotretinoin] in cystic Acne
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13 cis retinoic acid in childhood neuroblastoma.
Hypervitaminosis A
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Common in arctic explorers who eat polar bear liver.
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Organelle damaged in hypervitaminosis is Lysosomes
•
Acute toxicity: Pseudotumor cerebriQ (headache, dizziness, vomiting, stupor, and blurred vision, symptoms that may be confused with a brain tumor) and exfoliative dermatitis. In the liver, hepatomegaly and hyperlipidemia
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Chronic toxicity: If intake of > 50,000 IU/day for > 3 months
•
Weight loss, anorexia, nausea, vomiting, bony exostosis, bone and joint pain, decreased cognition, hepatomegaly progresses to cirrhosis
•
Retinoic acid stimulates osteoclast production and activity leading to increased bone resorption and high risk of fractures, especially hip fractures
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In pregnancy retinoids causes teratogenic effects.
Carotenemia
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Persistent excessive consumption of foods rich in Carotenoids
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Causes yellow staining of skin but not sclera (Unlike Hyperbilirubinemia which stain both skin and sclera).
Required Daily Allowance of Vitamin AQ (μg of Retinol) (ICMR 2010)
Children (1–6 yrs)
400 µg/day
Men
600 µg/day
Women
600 µg/day
Pregnancy
800 µg/day
Lactation
950 µg/day
Units of Vitamin A
•
Vitamin A in food is expressed as micrograms of retinol equivalent
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6 µg of beta Carotene = 1 µg of preformed retinol
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Pure Vitamin A for pharmaceutical uses is expressed International Units (IU) 1 IU = 0.3 µg of Retinol
•
1 µg of Retinol = 3.33 IU
•
In 2001 USA Canadian Dietary Reference value introduced the term Retinol Activity Equivalent (RAE) 1 RAE = 1 µg of Retinol or 12 µg of Beta carotene.
Sources of Vitamin A
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Animal food (mainly as Retinol)
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Plant food as Carotenes.
Animal sources
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Fish liver oilsQ are the rich sources of Vitamin A
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Halibut liver oil is the richest source (900000 µg/100 g) followed by cod liver oil
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Other animal sources are liver, egg, butter, cheese, whole milk, fish and meat.
Plant sources
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Richest plant source is Carrot
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Others are GLV like Spinach, Amaranth, Green and yellow fruits like papaya, mango, pumpkin.
Treatment of Vitamin A deficiency
•
200000 IU or 110 mg of Retinol Palmitate orally in two successive days.
Prevention of Vitamin A deficiency
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Single massive dose 200000 IU to children (1–6 years) once in 6 months
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Single massive dose 100000 IU to children (6 mo– 1 year) once in 6 months.
Assay of vitamin A
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Dark adaptation time
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Serum Vitamin A by Carr and Price reaction.
Vitamin D
Group of sterols having a hormone like function
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Ergocalciferol (Vit D2): Commercial Vitamin D obtained from the fungus, ergot
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Cholecalciferol (Vit D3): Endogenous synthesis from 7 Dehydrocholesterol.
Vitamin D metabolism
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Sources of Vitamin D
‒
The major source of vitamin D for humans is its endogenous synthesis in the skin by photochemical conversion of a precursor, 7-dehydro-cholesterol, to Cholecalciferol or Vitamin D3 via the energy of solar or artificial UV light in the range of 290 to 315 nm (UVB radiation) in the stratum corneum of the epidermis of skin
‒
Absorption of vitamin D from foods and supplements in the gut
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Binding of vitamin D from both of these sources to plasma α1-globulin (D-binding protein or DBP) and transport into the liver.
Fig. 15.2: Metabolism of Vitamin D
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Conversion of vitamin D into 25-hydroxy cholecal-ciferol (25-OH-D) in the liver, through the effect of
25- Hydroxylases. Most abundant circulatory form of Vitamin D. This is because there is little regulation of this liver hydroxylation. The measurement of 25-OH D is the standard method for determining patients’ Vitamin D status
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Conversion of 25-OH-D into 1, 25-dihydroxy vitamin D, (1, 25 (OH)2D3) or Calcitriol in the kidneyQ, the biologically most activeQ form of vitamin D, through the activity of α1-hydroxylase. This is the rate limiting step. PTH and Hypophosphatemia upregulate 1 α Hydroxylase. Hyperphosphatemia and 1, 25 OH D inhibit the enzyme
•
When Ca2+ level is high, kidney produces the relatively inactive metabolite 24, 25 Dihydroxy Chole-calciferol (Calcitroic acid) excreted through urine.
Functions of Vitamin D
Regulation of calcium and phosphorus homeostasis Action on intestine
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Vitamin D increases Ca2+ absorption
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By increasing the transcription of TRPV6 (a member of the transient receptor potential vanilloid family), which encodes a critical calcium transport channel. This increases Calcium absorption from duodenum.
Action on kidney
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Vitamin D increases Ca2+ and Phosphorus reabsorption
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Increases calcium influx in distal tubules of the kidney through the increased expression of TRPV5, another member of the transient receptor potential vanilloid family.
Action on bones
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1, 25-dihydroxy vitamin D and parathyroid hormone enhance the expression of RANKL (receptor activator of NF-κB ligand) on osteoblasts
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RANKL binds to its receptor (RANK) located in preosteoclasts, inducing the differentiation of these cells into mature osteoclasts
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They dissolve bone and release calcium and phosphorus into the circulation.
Immunomodulatory and antiproliferative effects
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Prevent infection by Mycobacterium tuberculosis
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Within macrophages, synthesis of 1, 25-dihydroxy-vitamin D occurs through the activity of CYP27B located in the mitochondria
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Pathogen-induced activation of Toll-like receptors in macrophages causes a transcription-induced increase in vitamin D receptor and CYP27B.
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The resultant production of 1, 25-dihydroxy vitamin D then stimulates the synthesis of cathelicidin, an antimicrobial peptide from the defensin family, which is effective against infection by Mycobacterium tuberculosis.
Antiproliferative role of Vitamin D
1, 25 (OH)2 D level less than 20 ng/mL is associated with increase in incidence of
•
Colon cancer
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Breast cancer
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Prostate cancer
Mineralization of bones
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Vitamin D contributes to mineralization of osteoid matrix and epiphyseal cartilage in both flat and long bones
•
It stimulates osteoblast to synthesize calcium binding protein osteocalcin involved in deposition of calcium during bone development.
Vitamin D deficiency
•
The normal reference range for circulating 25-(OH) D is 20 to 100 ng/mL
•
The concentration circulating 25-(OH) D < 20="" ng/ml="" is="" called="" vitamin="" d="" deficiency.="" />
Causes inadequate mineralization of bone osteoid
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Before closure of epiphysis: Rickets in children
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After closure of epiphysis: Osteomalacia in adults.
Biochemical defect of different types of rickets Nutritional Vitamin D Deficiency
Most common cause of rickets globally.
Concept of biochemical changes that occur in nutritional Vitamin D deficiency
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Due to Vitamin D deficiency, Serum Calcium level and Phosphorus level is low
•
This causes Secondary Hyperparathyroidism, so PTH level is high
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This increases the 1 α hydroxylation in kidney, so 1,25 D level increases
•
This will increase the Serum Calcium level, but Phosphorus level remain at low level
•
So, Serum Calcium level is variable, Serum Phosphorus is low, S PTH increase, 25 D is decreased,1,25 D is low initially but later increase due to secondary hyperparathyroidism.
Remember
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Serum calcium need not be always low in Rickets
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1,25 D level also need not be always low in Rickets
•
Serum Phosphorus remain low.
Vitamin D–dependent rickets type 1 (Pseudo-vitamin D–resistant rickets)
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An autosomal recessive disorder
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Mutations in the gene encoding renal 1α-hydroxylase
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Prevent conversion of 25 D to 1,25 D
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Even with high PTH, as 1 α Hydroxylase is defective, 1,25 D is low
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Usually presents in first 2 years of life
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With classic features of rickets.
Concept of biochemical changes in Vitamin D Dependent Rickets Type I
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Inspite of secondary hyperparathyroidism,1,25 D will remain decreased as 1 α hydroxylase gene is mutated.
Vitamin D–dependent rickets type 2 (True vitamin D– resistant rickets)
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An autosomal recessive disorder
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Due to mutations in the gene encoding the vitamin D receptor causing end-organ resistance to the active metabolite 1,25 D
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Presents in infancy with less severe manifestation
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50–70% of children have alopecia
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Epidermal cyst is also a common manifestation.
X-linked hypophosphatemic rickets
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X-linked dominant disorder
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The most common hypophosphatemic rickets
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The defective gene is called PHEX (PHosphate-regulating gene with homology to Endopeptidases on the X chromosome)
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The product of this gene have either a direct or an indirect role in inactivating a phosphatonin or phosphatonins (FGF-23)
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Mutation of PHEX gene lead to increased level of FGF-23
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Hypophosphatemia with normal PTH, normal calcium and low or inappropriately normal 1,25 D are the lab findings.
Phosphatonins (FGF-23)
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Humoral mediator that decrease renal tubular reabsorption of phosphate, therefore decreases serum phosphorus
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This also decreases the activity of 1 α hydroxylase, resulting in deficiency of 1,25 D
•
Fibroblast Growth Factor-23 (FGF-23) is the most well characterized phosphatonin
•
Increased level of phosphatonins causes increased excretion of phosphorus in urine
•
So serum Phosphorus is decreased.
Autosomal dominant hypophosphatemic rickets
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An autosomal dominant condition
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Due to a mutation in the gene encoding FGF-23 which prevents the degradation of FGF-23 by proteases. So there is increased levels of phosphatonins
‒
Hypophosphatemia with normal PTH, normal calcium and low or inappropriately normal 1,25 D are the lab findings.
Remember
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Biochemical findings of X linked and autosomal dominant Hypophosphatemic rickets is same as phosphatonins is excess in both
•
Hypophosphatemia is due to increased excretion of phosphates through kidney by phosphatonins
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Low or normal 1,25D is due to decreased activity of 1 α Hydroxylase.
Autosomal Recessive Hypophosphatemic rickets
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Extremely rare disorder due to mutation in the gene encoding dentin matrix protein 1, which results in elevated level of FGF-23.
Hereditary Hypophosphatemic rickets with hypercal-ciuria (HHRH)
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Autosomal recessive disorder due to mutation in the gene for a sodium phosphate cotransporter in the proximal renal tubules
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Hypophosphatemia, stimulates production of 1,25 D
•
This causes increased intestinal absorption of calcium
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Symptoms of rickets, along with muscle pain, bone pain short stature with disproportionate decrease in length of lower extremities, kidney stones.
Chronic Renal Failure
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There is decreased activity of 1α-hydroxylase in the kidney, leading to diminished production of 1,25-D.
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Unlike the other causes of vitamin D deficiency, patients have hyperphosphatemia as a result of decreased renal excretion.
Conditions causing over production of phosphatonins which causes rachitic findings
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Tumor-induced osteomalacia
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McCune-Albright Syndrome (entity that has triad of Polyostotic fibrous dysplasia, Hyperpigmented macules, polyendocrinopoathy)
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Epidermal nevus Syndrome
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Neurofibromatosis in children.
Requirement of Vitamin D
•
Children: 10 µg/day (400 IU)
•
Adults: 5 µg/day (200 IU)
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Pregnancy, Lactation: 10 µg/day (400 IU).
Vitamin D is toxic in excess
•
Upper limit of Vitamin D intake has been set 4000 IU/ day
•
Some infants are sensitive to intakes of vitamin D as low as 50 µg/dayQ , resulting in an elevated plasma concentration of calcium
•
This can lead to contraction of blood vessels, high bloodpressure, and calcinosis—the calcification of soft tissues
•
Although excess dietary vitamin D is toxic, excessive exposure to sunlight does not lead to vitamin D poisoning, because there is a limited capacity to form the precursor, 7-dehydrocholesterol, and prolonged exposure of previtaminD to sunlight leads to formation of inactive compounds.
Beneficial effects of Vitamin D
•
Protective against the cancer of Prostate, Colorectal cancer
•
Protective against Prediabetes, and metabolic Syndrome.
Laboratory findings in disorders causing rickets
Disorder
Serum Calcium
S Phosphorus
PTH
25 (OH)D
1,25 (OH)D
ALP
Vitamin D Deficiency
N/Decrease
Decrease
Increase
Decrease
Decrease, N,
Increase
Increase
Vitamin D Dependent Rickets Type I
N/Decrease
Decrease
Increase
N
Decrease
Increase
Vitamin D Dependent Rickets TypeII
N/Decrease
Decrease
Increase
N
Increased
Increase
Chronic renal Failure
N/Decrease
Increase
Increase
N
Decrease
Increase
XLinked Hypophosphatemic Rickets
N
Decrease
Normal
N
Relatively
Decrease
Increase
Autosomal Dominant Hypophosphatemic Rickets
N
Decrease
Normal
N
Relatively
Decreased
Increase
Sources of Vitamin D
•
Sunlight
•
Foods: Only animal sources Liver, Egg yolk, butter and liver oils. Out of the food sources Fish liver oils are the richest source
•
The richest source of Vitamin D is also Halibut Liver oil.
Assay of Vitamin D
•
The release into the circulation of osteocalcin provides an index of vitamin D status
•
25(OH) Vitamin D level is measured in the serum indicate Vitamin D status.
Vitamin E
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Vitamin E is a collective name for all stereoisomers of tocopherols and tocotrienols
•
The most powerful naturally occurring antioxidantQ .
Ring Structure present in Vitamin E
•
Chromane (Tocol) ring with isoprenoid side chain
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Vitamin E is carried to liver in Chylomicron.
Biochemical functions of Vitamin E
•
Biologically most potent form of Vitamin E is α TocopherolQ
•
Chain-breaking antioxidantQ and is an efficient pyroxyl radical scavenger that protects low-density lipoproteins (LDLs) and polyunsaturated fats in membranes from oxidation
•
Lipid soluble antioxidant.
Relationship with Selenium
•
Selenium decrease the requirement of Vitamin EQ .
Vitamin E deficiency
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Axonal degeneration and of the large myelinated axons and result in posterior column and spinocere-bellar symptoms
•
Hemolytic anemia: The erythrocyte membranes are abnormally fragile as a result of poor lipid peroxida-tion, leading to hemolytic anemia
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Peripheral neuropathy initially characterised by Areflexia with progression to ataxic gait, decreased position and vibration sense
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Spinocerebellar ataxia
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Skeletal myopathy
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Pigmented retinopathy
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Ophthalmoplegia.
Vitamin E in high doses may protect against
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Oxygen-induced retrolental fibroplasia
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Bronchopulmonary dysplasia
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Intraventricular hemorrhage of prematurity
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Treat intermittent claudication
•
Slow the aging process.
Toxicity of Vitamin E
•
Reduce platelet aggregation and interfere with Vitamin K.
Required daily allowance
•
Males 10 mg/day
•
Females 8 mg/day
•
Pregnancy 10 mg/day
•
Lactation 12 mg/day.
Sources of Vitamin E
Vegetable oils like Wheat germ oil, sunflower oil, Cotton seed oil, etc.
Vitamin K
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Naphthoquinone derivative with long isoprenoid side chain
•
Letter K is the abbreviation of German word, Koagulation Vitamin.
Three forms of Vitamin K
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Vitamin K1: Phylloquinone from dietary sources
•
Vitamin K2: Menaquinone Synthesized by Bacterial Flora
•
Vitamin K3: Menadione (and Menadiol diacetate): Synthetic, Water Soluble.
Functions of Vitamin K
Vitamin K is required for the post-translational carboxy-lation of glutamic acid (Gamma Carboxylation), which is necessary for calcium binding to γ carboxylated proteins.
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Prothrombin (factor II)
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Factors VII, IX, and X
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Protein C, protein S
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Proteins found in bone (osteocalcin)
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Matrix Gla protein
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Nephrocalcin in kidney
•
Product of growth arrest specific gene Gas6.
Drugs causing Vitamin K deficiency
Warfarin and Dicoumoral inhibit γ carboxylation by competitively inhibiting the enzyme that convert vitamin K to its active hydroquinone form
•
Antiobesity drug orlistat.
Vitamin K Deficiency
•
Elevated prothrombin time, bleeding time
•
Newborns, especially premature infants are particularly susceptible to Vitamin K deficiency because of low fat stores, low breast milk levels of vitamin K, sterility of the infantile intestinal tract, liver immaturity, and poor placental transport.
Hypervitaminosis K
•
Hemolysis
•
Hyperbilirubinemia
•
Kernicterus and brain damage.
Water Soluble Vitamins
•
B Complex Vitamins
•
Vitamin C
Thiamin (Vitamin B1)
•
Thiamin is also called Aneurine
Sources
•
Aleurone layer of cereals. Hence whole wheat flour and unpolished hand pound rice has better nutritive value. Yeast is also a good source of thiamine.
Active form of Thiamin
Thiamine Pyrophosphate (TPP) also called Thiamine diphosphate (TDP).
Thiamine and nerve conduction
Thiamin triphosphate has a role in nerve conduction; it phosphory-lates, and so activates, a chloride channel in the nerve membrane.
Coenzyme Role of Thiamine PyrophosphateQ
Thiamine generally function in the decarboxylation reaction of alpha keto acids and branched chain amino acids
•
Pyruvate DehydrogenaseQ which convert Pyruvate to Acetyl CoA
•
αKetoGlutarate DehydrogenaseQ in Citric Acid Cycle which convert α KetoGlutarate to Succinyl CoA
•
Branched Chain Ketoacid DehydrogenaseQ which catalyses oxidative decarboxylation of Branched Chain Amino acids
•
Trans KetolaseQ in Pentose Phosphate PathwayQ . This is the biochemical basis of assay of Thiamine status of the body.
Deficiency of Vitamin B1 (Thiamin)
BeriBeriQ
Two types
1.
Wet beriberi: Marked peripheral vasodilatation, resulting in high output cardiac failure with dysp-noea, tachycardia, cardiomegaly, pulmonary and peripheral edema.
2.
Dry beriberi: Involves both peripheral and central nervous system.
Peripheral nervous system
•
Typically a symmetric motor and sensory neuropathy with pain, paraesthesia and loss of reflexes. The legs are affected more than the arms.
Central nervous system
Wernicke’s Encephalopathy–in alcoholics with chronic
Thiamine deficiency
•
Horizontal Nystagmus
•
Ophthalmoplegia
•
Truncal ataxia
•
Confusion
•
Wernicke- Korsakoff Syndrome
•
Along with features of Wernicke’s Encephalopathy
•
Amnesia
•
Confabulatory psychosis.
Acute pernicious (fulminating) beriberi (shoshin beriberi), in which heart failure and metabolic abnormalities predominate.
Biochemical assessment of thiamin deficiency
•
Erythrocyte Transketolase activity is reduced
•
Urinary Thiamine excretion.
Thiamin toxicity
•
There is no known toxicity of thiamine Recommended Daily Allowance (RDA) of Vitamin B1
•
1–1.5 mg/day.
Riboflavin (Vitamin B2)
•
Is called Warburg Yellow enzymeQ of cellular respiration
•
Riboflavin is heat stable
•
Enzymes containing riboflavin are called Flavo-proteins
•
Act as respiratory coenzyme and an electron donor.
Active forms of Riboflavin
•
They are FAD (Flavin Adenine Dinucleotide) and FMN (Flavin Mononucleotide)
Coenzyme Role of Riboflavin
Q
FMN Dependent Enzymes
•
L- Amino Acid Oxidase
•
NADH Dehydrogenase (Complex I of ETC)
•
Monoamino Oxidase
FAD Dependent Enzymes
•
Complex II (Succinate Dehydrogenase) of ETC
•
D Amino Acid Oxidase
•
Acyl CoA Dehydrogenase
Contd...
Contd...
•
Alpha Ketoglutarate Dehydrogenase
•
Pyruvate Dehydrogenase
•
Xanthine Oxidase.
Deficiency manifestation of Vitamin B2 (Riboflavin) Magenta tongue (Glossitis), angular stomatitis, Seborrheic Dermatitis, Cheilosis, Corneal vascularization, anemia Biochemical Assessment of Nutritional status of Riboflavin
•
Measurement of activation of erythrocyte Glutathione Reductase by FAD added in vitro
•
Urinary excretion of Riboflavin.
Riboflavin toxicity
•
Riboflavin toxicity is not reported yet because of limited absorption capacity of GIT.
RDA of Riboflavin
•
1.5 mg/day.
Niacin or Nicotinic Acid (Vitamin B3)
•
Not strictly a Vitamin
•
Can be synthesized from Tryptophan
•
60 mg of Tryptophan yield 1 mg of Niacin.
Active form of niacin
•
Two Coenzyme forms are NAD+(Nicotinamide Adenine Dinucleotide) and NADP+(Nicotinamide Adenine Dinucleotide Phosphate).
Coenzyme Role of Niacin
•
Important in numerous oxidation reduction reactions. NAD+ linked Enzymes
•
Lactate Dehydrogenase
•
Pyruvate Dehydrogenase
•
αKetoGlutarate Dehydrogenase
•
Isocitrate Dehydrogenase
•
Malate Dehydrogenase
•
βHydroxy Acyl CoA Dehydrogenase
•
Glycerol 3 Phosphate Dehydrogenase (cytoplasmic)
•
Glutamate Dehydrogenase
•
Glyceraldehyde 3 phosphate Dehydrogenase.
NADP + utilizing enzymes
Mainly for Reductive BiosynthesisQ of steroids and CholesterolQ, Free radical ScavengingQ, Formation of deoxyribonucleotides, One carbon metabolism.
•
3 Keto acyl reductase
•
Enoyl reductase
•
HMG CoA Reductase
•
Folatereductase
•
Glutathione Reductase
•
Ribonucleotide Reductase.
Contd...
Contd...
NADPH generating ReactionsQ
•
Glucose 6 Phosphate Dehydrogenase in HMP shunt pathway
•
6 PhosphoGluconate Dehydrogenase in HMP shunt pathway
•
Cytoplasmic Isocitrate Dehydrogenase
•
Malic Enzyme. (NADP Malate Dehydrogenase).
Other function of NAD
NAD is the source of ADP-ribose for the ADP-ribosylation of proteins and polyADP-ribosylation of nucleoproteins involved in the DNA repair mechanism.
Deficiency of niacin
Pellagra
•
Photosensitive Dermatitis: Symmetric dermatitis in the sun exposed areas
•
Skin lesions are dark, dry and scaling
•
Casal’s NecklaceQ The rash form a ring around the neck
•
Dementia
•
Insomnia, irritability, and apathy and progresses to confusion, memory loss, hallucination, and depressive psychosis
•
Diarhea can be severe resulting in malabsorption due to atrophy of intestinal villi
•
Advanced Pellagra can result in death
•
Depressive psychosis.
4 Ds of Pellagra
•
Dermatitis (Photosensitive Dermatitis)
•
Dementia
•
Diarrhea
•
Death.
Conditions associated with Pellagra like symptoms
•
Hartnup Disease (Due to intestinal malabsorption and renal reabsorption of Tryptophan)
•
Carcinoid Syndrome (Over production of serotonin leads to diversion of Tryptophan from NAD+ pathway)
•
Vitamin B6 deficiency (Defective Kynureninase that lead to defective synthesis of Niacin)
•
Pellagra is common in people whose staple diet is maize and jowar. Maize-Niacin present in unavailable form Niacytin Sorghum vulgare (Jowar)-High Leucine content inhibit QPRTase, rate limiting enzyme in Niacin synthesis.
Recommended Daily Allowance of Niacin (RDA) 20 mg/day
Toxicity of niacin
•
Prostaglandin mediated cutaneous flushing due to binding of vitamin to a G Protein coupled receptor
•
Gastric irritation
•
Hepatic toxicity is the most serious toxic reaction with sustained release niacin presents with jaundice, elevated liver enzymes (AST and ALT) even fulmi-nant hepatitis
•
Other toxic reactions include glucose intolerance, hyperuricemia, macular edema and cysts.
Treatment of cutaneous flushing
•
Laropiprant, a selective Prostaglandin D2 receptor 1 antagonist
•
Premedication with Aspirin.
Therapeutic uses of Niacin (Nicotinic acid)
•
Used as Lipid modifying Drug
•
Niacin reduces plasma triglyceride and LDL-C levels and raises the plasma concentration of HDL-C.
Pyridoxine (Vitamin B6)
Family of 3 related Pyridine derivatives
•
Pyridoxine
•
Pyridoxal
•
Pyridoxamine
Remember
Some 80% of the body’s total vitamin B6 is pyridoxal phosphate in muscleQ, mostly associated with glycogen phosphorylase.
Active form of Pyridoxine
•
Pyridoxal Phosphate (PLP)
•
Mainly used for Amino Acid metabolismQ.
Coenzyme Role of Pyridoxal Phosphate (PLP)Q Transamination
•
Alanine Amino Transferase (ALT)
•
Aspartate Amino Transferase (AST)
•
Alanine Glyoxalate Amino Transferase.
Decarboxylation of amino acids
This results in the formation of Biogenic Amines
•
Glutamate: GABA
•
5-Hydroxy Tryptophan: Serotonin
•
Histidine: Histamine
•
Cysteine: Taurine
•
Serine: Ethanolamine
•
DOPA: Dopamine.
Transulfuration
•
Involved in the metabolism of Sulfur containing amino acids
•
Synthesis of Cysteine from methionine
•
Enzymes are Cystathionine Beta Synthase and Cystathioninase.
Tryptophan metabolism
•
Coenzyme of Kynureninase involved in the synthesis of niacin from Tryptophan
•
In Pyridoxine deficiency Xanthurenic acid is excreted because of defective Kyneureninase in Niacin synthesis.
Heme synthesis
•
ALA Synthase that catalyse condensation of Succinyl CoA and Glycine.
Glycogenolysis
•
Glycogen phosphorylase.
Deficiency of Vitamin B6 (Pyridoxine)
•
Neurological manifestation: Due to deficiency of Catecholamines
•
Peripheral neuropathy
•
Personality changes that include depression and confusion
•
Convulsions: Due to decreased synthesis of GABA
•
Microcytic hypochromic Anemia: Due to decreased heme synthesis
•
Pellagra due defective niacin synthesis.
Other conditions caused by PLP deficiency.
•
Oxaluria: Due to defective Alanine: Glyoxylate Amino Transferase. Glyoxylate converted to Oxalic acid
•
Homocystinuria: Due to defective Cystathionine Beta Synthase
•
Xanthurenic Aciduria: Due to defective Kynureninase
•
Cardiovascular risks: Because of homocysteinemia.
Drugs that interact with carbonyl group and causes PLP deficiencies are L-Dopa, Pencillamine, Cycloserine. Pyridoxine dependency syndromes that need pharmacological dose of PLP
•
Classic homocystinuria (due to cystathionine beta synthase deficiency)
•
Sideroblastic anemia (due to ALA Synthase deficiency)
•
Gyrate atrophy of retina and choroid in δ- ornthine amino transferase.
High doses of Pyridoxine given in
•
Carpal Tunnel syndrome
•
Premenstrual syndrome
•
Schizophrenia
•
Diabetic neuropathy.
Pyridoxine and Hormone dependent cancer
•
Pyridoxine is important in steroid hormone action
Contd...
Contd...
•
Pyridoxal phosphate removes the hormone-receptor complex from DNA binding, terminating the action of the hormones
•
In vitamin B6 deficiency, there is increased sensitivity to the actions of low concentrations of estrogens, androgens, cortisol, and vitamin D
•
Increased sensitivity to steroid hormone action may be important in the development of hormone-dependent cancer of the breast, uterus, and prostate, and vitamin B6 status may affect the prognosis.
Biochemical Assay of Vitamin B6
•
Erythrocyte Transaminase activity
•
Tryptophan load test-measurement of Xanthurenic acid following Tryptophan load
•
Measurement of PLP in the blood.
Toxicity of Vitamin B6
•
Excess Pyridoxine may lead to Sensory Neuropathy.
RDA of Pyridoxine
•
1–2 mg/day
•
RDA of Pyridoxine depends on Protein intake.
Pantothenic Acid (Vitamin B5)
•
Derived from the Greek word pantos means everywhere
•
Endogenously synthesized by bacterial flora in the intestine
•
Vitamin that contains Beta Alanine
•
Vitamin present in Coenzyme A (CoA) and Acyl Carrier Protein (ACP) in Fatty Acid Synthase Complex.
The important CoA Derivatives are
•
Acetyl CoA
•
Succinyl CoA
•
HMG CoA
•
Acyl CoA.
Pantothenic acid as a part of CoA take part in
•
Fatty acid Oxidation
•
Acetylation
•
Citric acid cycle
•
Cholesterol synthesis.
Deficiency of Pantothenic Acid
•
Gopalan’s Burning feet Syndrome or Nutritional Melalgia or Peripheral nerve damage.
RDA of Pantothenic acid 10 mg/day.
Pantothenate kinase associated neurodegeneration (PKAN) (formerly Hallervorden-Spatz syndrome)
•
Rare autosomal recessive neurodegenerative disorder
•
Chorea, dystonia, parkinsonian features, pyramidal tract features and MR
•
MRI-decreased T2 signal in the globuspallidus and substantianigra, ‘eye of the tiger’ sign (hyperintense area within the hypointense area)
•
Sometimes acanthocytosis
•
Neuropathologic examination indicates excessive accumulation of iron-containing pigments in the globuspallidus and substantianigra
•
Similar disorders are grouped as neurodegeneration with brain iron accumulation (NBIA).
Biotin or Vitamin H or Vitamin B7
•
Also known as anti-egg white injury factor
•
Endogenously synthesized by intestinal flora
•
Reactive form is the enzyme bound CarboxyBiocytin.
Coenzyme role of Biotin
Play a role in gene expression, fatty acid synthesis, gluconeogenesis and serve as a CO2 carrier for Carboxylases enzymes and gene regulation by histone biotinylation.
Coenzyme for ATP dependent Carboxylation reaction (Carbon Dioxide Fixation)
•
Pyruvate Carboxylase (Pyruvate to Oxaloacetate)
•
Propionyl CoA Carboxylase (Propionyl CoA to Methyl Malonyl CoA)
•
Acetyl CoA Carboxylase (Acetyl CoA to Malonyl CoA)
•
Methyl Crotonyl CoA Carboxylase.
Biotin independent Carboxylation reaction
•
Carbamoyl Phosphate Synthetase –I and II
•
Addition of CO2 to C6 in Purine ring (AIR Carboxylase)
•
Malic Enzyme (Pyruvate to Malate).
•
Gamma Carboxylation (Vitamin K dependent).
Biotin Antagonist
Avidin
•
Protein present in the raw egg white
•
Eating raw egg is harmful because of Avidin present in raw egg inhibit biotin
•
Affinity of Avidin to Biotin is stronger than most of the Antigen antibody reaction.
This property is used in
•
ELISA test
•
Labelling of DNA.
Streptavidin
•
Purified from Streptomyces avidinii
•
Bind 4 molecules of Biotin.
Deficiency of biotin
•
Mental changes (Depression, hallucination) paresthesia, anorexia, and nausea
•
A scaling, seborrheic and erythematous rash around nose, eyes and mouth.
Biochemical tests to diagnose Biotin deficiency
•
Decreased concentration of Urinary biotin
•
Increased urinary excretion of 3-hydroxyvaleric acid after leucine challenge
•
Decreased activity of biotin dependent enzymes in lymphocytes.
Folic Acid or Vitamin B9
•
Derived from latin word folium, which means leaf of vegetable
•
Folic Acid is abundant in leafy vegetables
•
Folic Acid is absorbed from upper part of JejunumQ.
Functions of folic acid
•
Active form of Folic acid is Tetra Hydro Folic Acid (THFA)
•
THFA is the carrier of One Carbon groups.
One carbon metabolism
One carbon units are:
•
Methyl (CH3)
•
Methylene (CH2)
•
Methenyl (CH)
•
Formyl (CHO)
•
Formimino (CH = NH).
One carbon groups bind to THF through
•
N5 are Formyl, Formimino or methyl
•
N10 are Formyl
•
Both N5 and N10 are Methylene and Methenyl.
Sources of one carbon groups
•
The major point of entry of one carbon unit is Methylene THFQ
•
SerineQ is the most important source of One Carbon units
•
SerineQHydroxy Methyl TransferaseQ is the enzyme involved in this pathway.
Important sources of one carbon groups
Source of Methylene THF
•
Serine to Glycine by Serine Hydroxy Methyl Transferase
•
Glycine
•
Choline.
Source of Formimino THF
•
Histidine ---->FIGLU------->Formimino THF
Utilization of one carbon groups
•
Serine to Glycine
•
Homocysteine to Methionine
•
Synthesis of Purine Nucleotides
•
Synthesis of TMP
•
Synthesis of Choline.
Fig. 15.3: One carbon metabolism
Pharmaceutically used THFA derivative
•
5-Formyl-tetrahydrofolateQ2013 is more stable than folate and is therefore used pharmaceutically (known as folinic acid), and the synthetic (racemic) compound (leucovorin).
•
It is given orally or parenterally to overcome the toxic effects of methotrexate or other DHF reductase inhibitors.
Biochemical assessment of folate deficiency
•
Serum Folate (Normal level is 2–20 ng/ml)
•
Red Cell Folate
•
Histidine Load testQ or FIGLU excretion test
•
AICAR [Amino Imidazole Carboxamide Ribose 5 Phosphate] Excretion Test
•
Serum Homocysteine
•
Peripheral Blood Smear (Macrocytes, tear drop cells, hypersegmented neutrophils, anisopoikilocytosis).
Fig. 15.4: FIGLU excretion
Deficiency of folic acid
•
Reduced DNA Synthesis because THF derivatives are involved in purine synthesis and thymidylate Synthesis
•
Megaloblastic Anemia
‒
Vitamin B12 deficiency and Folate deficiency can lead to this condition
‒
In Vitamin B12 deficiency Megaloblasticanemia is due to folate trap
•
Homocysteinemia due decreased conversion of Homocysteine to Methionine. This is because Methyl THFA is the methyl donor for this reaction
•
Neural tube defects (like Spina bifida) during pregnancy
•
Atrophic glossitis
•
Depression.
Folic acid and cancer
•
Low folate status results in impaired methylation of CpG islands in DNA, which is a factor in the development of colorectal and other cancers
•
Prophylactic Folic Acid during pregnancy reduce chance of Acute Lymphoblastic Lymphoma
•
But, folate supplements increase the rate of transformation of preneoplastic colorectal polyps into cancers
•
Folic acid ‘feed’ tumors by increasing thymidine pools and ‘better’ quality DNA
•
So Folic Acid should be avoided in established tumors.
Vitamin B12 (Cobalamin)
•
Other name is Extrinsic factor of castle
•
Contain 4.35% cobalt by weight
•
Contain 4 pyrrole rings coordinated with a cobalt atom, called Corrin ring.
Active forms of Vitamin B12
•
Methyl Cobalamin and Adenosyl Cobalamin (Ado B12) Coenzyme Role of Cobalamin
•
Methyl Malonyl CoA Mutase
•
L Methyl Malonyl CoA → Succinyl CoA Methionine Synthase or Homocysteine Methyl Transferase
•
Homocysteine → Methionine
•
Leucine Amino Mutase
Vitamin B12 metabolism Absorption of cobalamin
•
99% of absorption of Cobalamin are active
•
Active mechanism: Site is IleumQ
•
1% passive occurs equally in Buccal cavity, Duodenum, Ileum.
Cobalamin binding proteins
•
Cobalamin binding proteins in the saliva are called Haptocorrins or Cobalophilin or R Binders
•
Intrinsic Factor of Castle from parietal cells of body and fundus of the stomach
‒
Vitamin B12 is freed from binding proteins in food through the action of pepsin in the stomach and binds to salivary proteins called cobalophilins, or R-binders
‒
In the duodenum, bound vitamin B12 is released by the action of pancreatic proteases. It then associates with intrinsic factor
‒
Actively absorbed from the ileumQ by binding to IF receptor
‒
IF receptor in the ileum is called CUBULIN.
Transport of Cobalamin to the target tissues
•
Major Cobalamin transport protein in plasma is Transcobalamin II (TC II)Q
•
Transcobalamin I [TC I] play a role in the transport of Cobalamin analogues
•
At the target tissues by receptor mediated endocytosis involving TC II receptor.
Causes of Vitamin B12 deficiency
Nutritional
•
Vitamin B12 is found only in foods of animal origin, there being no plant sources of this vitamin. This means that strict vegetarians (vegans) are at risk of developing B12 deficiency.
Malabsorption-pernicious anemia
•
Pernicious anemia is a specific form of megaloblas-ticanemia caused by autoimmune gastritis and an attendant failure of intrinsic factor production, which leads to vitamin B12 deficiency.
Gastric causes
•
Congenital absence of intrinsic factor or functional abnormality
•
Total or partial gastrectomy.
Intestinal causes
•
Intestinal stagnant loop syndrome: jejunal diverticulosis, ileocolic fistula, anatomic blind loop, intestinal stricture, etc.
•
Ileal resection and Crohn’s disease.
Selective malabsorption with proteinuria
•
Imerslund Syndrome
•
Imerslund-Gräsbeck Syndrome
•
Congenital Cobalamin Malabsorption
•
Autosomal Recessive Megaloblastic Anemia
•
Tropical sprue
•
Transcobalamin II deficiency.
Fish tapeworm
•
The fish tapeworm (Diphyllobothriumlatum) lives in the small intestine of humans and accumulates cobalamin from food, rendering the cobalamin unavailable for absorption.
Vitamin B12 deficiency and Folate trap
•
When acting as a methyl donor, S-adenosyl methionine forms homocysteine, which may be remethylated by methyl-tetrahydrofolate catalyzed by methionine synthase, a vitamin B12–dependent enzyme
•
The reduction of methylene-tetrahydrofolate to methyl-tetrahydrofolate is irreversible. This is the major source of tetrahydrofolate for tissues is methyltetrahydrofolate
•
Impairment of methionine synthase in vitamin B12 deficiency results in the accumulation of methyltetrahydrofolate—the ‘folate trap’
•
There is therefore functional deficiency of folate, secondary to the deficiency of vitamin B12.
Fig. 15.5: Folate trap
Deficiency manifestation of Vitamin B12
•
Megaloblasticanemia
•
Homocysteinemia: Due decreased conversion of Homocysteine to Methionine
•
Methyl Malonic Aciduria: Due to defective Methyl Malonyl CoA Mutase which leads to decreased conversion of L Methyl malonyl CoA to Succinyl CoA
•
Subacute Combined Degeneration
•
Cobalamin deficiency may cause a bilateral peripheral neuropathy or degeneration (demyelination) of the posterior and pyramidal tracts of the spinal cord.
Biochemical assessment of cobalamin deficiency
•
Serum Cobalamin
•
Serum Methyl Malonate (This helps to distinguish between Megaloblasticanemia due to Cobalamin deficiency and Folate deficiency)
•
Serum Homocysteine
•
Schilling Test using Radioactive labelled Cobalt-60
•
Urine Homocystine and MMA
•
Bone marrow and Peripheral Blood Smear.
Vitamin C (Ascorbic Acid)
•
Other name is antiscorbutic factor
•
Most animals synthesize Vitamin C from Glucose by uronic Acid PathwayQ
•
Humans and higher Primates cannot due to absence of Gulonolactone OxidaseQ.
Biochemical Functions of Ascorbic Acid
•
Acts as a good reducing agent and a scavenger of free radicals (Antioxidant)
•
In Collagen Synthesis: Vitamin C is required for the post-translational modification, Hydroxylation of lysine and Proline
•
Hydroxylation of Tryptophan
•
Tyrosine Metabolism: Oxidation of P hydroxyl Phenyl Pyruvate to Homogentisic Acid
•
Bile Acid Synthesis in 7 alpha Hydroxylase
•
Iron Absorption: Favor Iron absorption by conversion of Ferric ions to Ferrous ions
•
Folate Metabolism: Conversion of Folate to its active form
•
Adrenal steroid synthesis.
Vitamin C Deficiency
Scurvy
•
Petechiae, ecchymosis, coiled hairs, inflamed and bleeding gums, joint effusion, poor wound healing, fatigue
•
Perifollicular hemorrhages
•
Perifollicular hyperkeratotic papules, petechiae, purpura
•
Splinter hemorrhage, bleeding gums, hemarthroses, subperiosteal hemorrhage
•
Anemia
•
Late stage are characterized by edema, oliguria, neuropathy, intracerebral hemorrhage and death.
Barlows Syndrome (Infantile Scurvy)
•
In infants between 6-12 months, the diet if not supplemented with Vitamin C then deficiency will result.
Vitamin C toxicity
•
Gastric irritation, flatulence, diarrhea,
•
Oxalate stones are of theoretic concern.
Vitamins at a Glance
Vitamin deficiencies causing dementia
•
Thiamin
•
Niacin
•
Cobalamin
Sulfur Containing Vitamins
•
Biotin
•
Thiamin
Antioxidant Vitamin
•
Vitamin E
•
Vitamin C
•
Beta Carotene
Antioxidant vitamins are also Pro-oxidants • Vitamin C
•
Beta Carotene
•
Vitamin E
B complex Vitamins with Toxicity
•
Niacin
•
Pyridoxine
Redox Vitamins
Vitamins that take part in Oxidation reduction reaction
•
Niacin and Riboflavin
Endogenously Synthesized Vitamins
•
Niacin (Vitamin B3)
•
Biotin
•
Vitamin D
•
Pantothenic Acid
•
Vitamin K.
Ring Structures of B-complex Vitamins
Vitamin
Ring structure
Vitamin B1 [Thiamine]
Pyrimidine + Thiazole
Vitamin B2 [Riboflavin]
Isoalloxazine
Vitamin B3 [Niacin]
Pyridine
Vitamin B6 [Pyridoxine]
Pyridine
Vitamin B12 [Cobalamin]
Corrin [Tetrapyrrole with Co at its center]
Folic Acid
Pteridine + PABA
Biotin
Imidazole + Thiophene
Pantothenic Acid
No ring Structure Contain Pantoic Acid and Beta AlanineQ in amide linkage
Deficiency of Vitamins
Principal clinical findings of vitamin malnutrition
Nutrient
Clinical finding
Thiamin
Peripheral nerve damage (beriberi) or central nervous system lesions (Wernicke-Korsakoff syndrome)
Riboflavin
Magenta tongue, angular stomatitis, cheilosis, seborrheic dermatitis
Niacin
Pellagra: pigmented rash of sun-exposed areas (photosensitive dermatitis), bright red tongue, diarrhea, apathy, memory loss, disorientation, depressive psychosis
Vitamin B6
Seborrhea, glossitis, convulsions, neuropathy, depression, confusion, microcytic anemia
Folate
Megaloblasticanemia, atrophic glossitis, depres-sion, ↑homocysteine
Vitamin B12
Pernicious anemia = megaloblasticanemia with degeneration of the spinal cord, loss of vibratory and position sense, abnormal gait, dementiaQ , impotence, loss of bladder and bowel control, ↑homocysteine, ↑methylmalonic acid
Pantothenic Acid
Peripheral nerve damage (nutritional melalgia or ‘burning foot syndrome’)
Vitamin C
Scurvy: petechiae, ecchymosis, coiled hairs, inflamed and bleeding gums, joint effusion, poor wound healing, fatigue
Vitamin A
Xerophthalmia, night blindness, Bitot’s spots, follicular hyperkeratosis, impaired embryonic development, immune dysfunction
Vitamin D
Rickets: skeletal deformation, rachitic rosary, bowed legs; osteomalacia
Vitamin E
Peripheral neuropathy, spinocerebellar ataxia, skeletal muscle atrophy, retinopathy
Vitamin K
Elevated prothrombin time, bleeding
Classified into
•
Macrominerals (Major elements)
‒
Daily requirement > 100 mg
‒
Calcium, Magnesium, Phosphorus, Sodium, Potassium, Chloride, Sulfur
•
Micromineral (Trace element)
‒
Daily requirement < 100="" mg="" />
‒
Iron, Iodine, Copper, Cobalt, Mangenese, Molybdenum, Selenium, Zinc, and Fluorine
•
Ultra trace elements
‒
Daily requirement < 1="" mg/day.="" />
Body distribution of Iron.
Iron content, mg
Adult male
Adult female
Hemoglobin
2500
1700
Myoglobin/Enzymes
500
300
Transferrin
3
3
Iron Stores
600–1000
0–300
Total Body Iron content
3603–4003
2003–2303
Iron Containing Proteins
Heme ContainingQ
•
•
•
•
•
•
•
Hemoglobin
Myoglobin
Cytochrome c
Cytochrome oxidase
Tryptophan pyrrolase
Catalase
Nitric Oxide Synthase
Nonheme –iron containing Proteins
•
Aconitase
•
Transferrin
•
Ferritin
•
Hemosiderin
Iron-Sulfur Complex
•
Complex I of ETC
•
Complex II of ETC
•
Complex III of ETC
•
Xanthine oxidase
Proteins that has role in Iron metabolism Storage form Ferritin and Hemosiderin Ferritin
•
The human body can typically store up to 1 g of iron, the vast majority of which is bound to ferritin
•
MW 440 kDa
•
Ferric iron + Apoferritin = Ferritin
•
Poly nuclear complex of hydrous ferric oxide
•
Ferritin is composed of 24 identical subunits, which surround as many as 3000 to 4500 ferric atoms
•
The subunits may be of the H (heavy) or the L (light) type
•
The H-subunit possesses ferroxidase activity, which is required for iron-loading of ferritin
•
The function of the L subunit is not clearly known but is proposed to play a role in ferritin nucleation and stability
•
Seen in Intestinal cells, Liver, Spleen and Bone marrow
•
Plasma ferritin levels thus are considered to be an indicator of body iron stores.
Hemosiderin
•
A partly degraded form of ferritin that contains iron is Hemosiderin
•
Iron is not easily mobilized from Hemosiderin unlike ferritin
•
It can be detected in tissues by histological stains (e.g. Prussian blue), under conditions of iron overload (hemosiderosis)
•
Hemosiderin is an Index of Iron OverloadQ .
Transport form Transferrin Transferrin and Transferrin receptors
•
Iron is transported in plasma in the Fe3+ form by the transport protein, transferrin
•
Ferric iron combines with apo transferrin to form transferrin
•
Synthesized in the Liver
•
Transferrin is a β1 globulin
•
Transferrin is a bilobed glycoprotein with two iron binding sites
•
Transferrin that carries iron exists in two forms— monoferric (one iron atom) or diferric (two iron atoms)
•
The turnover (half-clearance time) of transferrin-bound iron is very rapid—typically 60–90 min
•
Normal 1/3rd transferrin saturated with Iron
•
The iron-transferrin complex circulates in the plasma until it interacts with specific transferrin receptors
•
On the surface of marrow erythroid cells
•
Diferric transferrin has the highest affinity for transferrin receptors
•
The greatest number of transferrin receptors (300,000 to 400,000/cell) is the developing erythroblast
•
The Transferrin receptor 1 (TfR1) can be found on the surface of most cells
•
Transferrin receptor 2 (TfR2), by contrast, is expressed primarily on the surface of hepatocytes and also in the crypt cells of the small intestine
•
The affinity of TfR1 for Tf-Fe is much higher than that of TfR2
•
The major role of TfR2 is sensing iron level, rather than internalizing iron.
Reciprocal regulation of TfR1 and Ferritin
•
The rates of synthesis of TfR1 and ferritin are reciprocally linked to intracellular iron levels
•
When iron is low, TfR1 synthesis increases and that of ferritin declines
Contd...
•
The opposite occurs when iron is abundant
•
Control is exerted through the binding of iron regulatory proteins (IRPs) called iron response elements (IREs) located in the 5’ and 3’ untranslated regions of mRNA.
Concept
When iron level is low, tissue demand for iron is high, increased trans-ferrin receptors, help to internalize the available iron in the plasma. Decreased ferritin will help to mobilize the maximum iron stores to meet the demand of iron.
Fig. 15.6: Metabolism of iron
Iron Metabolism
•
Site of absorption: Enterocytes in the proximal duodenum
•
Heme iron is absorbed by a heme transporter
•
Iron is absorbed in the ferrous formQ
•
Inorganic dietary iron in the ferric state (Fe3+) is reduced to its ferrous form (Fe2+) by a brush border membrane-bound ferrireductase, duodenal cytochrome b (Dcytb)
•
Vitamin C in food also favors reduction of ferric iron to ferrous iron
•
The transfer of iron from the apical surfaces of enterocytes into their interiors is performed by a proton- coupled divalent metal transporter (DMT1)
•
This protein is not specific for iron, as it can transport a wide variety of divalent cations. (Co2+,Zn2+,Pb2+,Cu2+)
Carbohydrate Deficient Transferrin (CDT)
•
Glycosylation of transferrin is impaired in congenital disorders of glycosylation as well as in chronic
•
Alcoholism
•
The presence of carbohydrate-deficient transferring (CDT), which can be measured by isoelectric focussing (IEF)
•
This is used as a biomarker of chronic alcoholism and Congenital Disorders of Glycosylation (CDGs)
Fig. 15.7: Absorption of Iron
•
Once inside the enterocytes, iron can either be stored as ferritin or transferred across the basolateral membrane into the circulation by the iron exporter protein, ferroportin or iron-regulated protein 1 (IREG1 or SLC40A1)
•
This protein may interact with the copper-containing protein hephaestin, a protein similar to ceruloplasmin
•
Hephaestin is thought to have a ferroxidase activity, which is important in the release of iron from cells
•
Thus, Fe2+ is converted back to Fe3+ , the form in which it is transported in the plasma by transferrin.
Dietary Regulation of Iron by Mucosal Block at the Level of Enterocyte
Hepcidin
•
Hepcidin is the Chief Regulator of Systemic Iron Homeostasis
•
It is a 25-amino acid peptide
•
Synthesized in the liver as an 84-amino acid precursor (prohepcidin).
Mechanism of Iron regulation by hepcidin
•
Hepcidin binds to the cellular iron exporter, ferroportin, triggering its internalization and degradation
•
The consequent decrease in ferroportin results in decreased export of iron into circulation and depressed iron recycling by macrophages
•
Together, these result in a reduction in circulating iron levels (hypoferremia) as well as reduced placental iron transfer during pregnancy
•
When plasma iron levels are high, hepatic synthesis of hepcidin increases, thus reducing circulating iron level
•
The opposite occurs when plasma iron levels are low.
Regulation of expression of hepcidin The hepcidin level is influenzed by
•
Circulatory level of iron
•
Bone Morphogenic Proteins (BMPs) and Hemojuvelin
•
Erythropoietic signals
•
Inflammation
•
Hypoxia
Circulation level of Iron
•
Liver cells monitor iron levels using an iron sensing complex comprised of two transmembrane receptors
(TfR-1, TfR-2) and transmembrane protein HFE protein
•
TfR-1 binds to iron bound transferring (Tf-Fe) at the site where it binds to HFE protein
•
When iron is abundant, Tf-Fe are high, hence HFE is displaced from TfR-1
•
The displaced HFE binds to TfR-2
•
Binding of HFE to TfR-2 triggers intracellular signal cascade (ERK-MAPK cascade)
•
Which activate expression of HAMP gene that codes for Hepcidin.
Concept is increased level of iron→increased expression of hepcidin→which inturn decreases circulating iron.
Bone Morphogenic Proteins (BMPs) and Hemojuvelin (HJV)
•
BMP binds to a cell-surface receptor (BMPR) whose binding affinity is augmented by binding to a co- receptor, hemojuvelin (HJV)
•
The activation of the BMPR-HJV complex triggers the phosphorylation of intracellular signaling proteins called SMADs, which subsequently results in transcriptional activation of hepcidin.
Erythropoietic signals
•
Two molecules secreted by erythroblasts, growth differentiation factor 15 (GDF15) and twisted gastrulation 1 (TWSG1)
•
They inhibit expression of hepcidin in β-thalassemia major.
Inflammation
•
Hepcidin synthesis is induced by cytokines such as interleukin–6 (IL-6) that are released as part of an inflammatory response
•
Binding of IL-6 to its cell surface receptor stimulates gene expression by activating the JAK-STAT (Janus Kinase—Signal Transducer and Activator of Transcription) Pathway
•
Anemia that is associated with chronic inflammation (anemia of inflammation or AI) is probably due to inflammation-mediated upregulation of hepcidin.
Hypoxia
•
Hypoxia is suppress hepcidin expression
•
This effect is mediated by erythropoietin, whose synthesis is controlled by hypoxia-inducible transcription factors 1 and 2 (HIF-1 and HIF-2).
Fig. 15.8: Regulation ofExpression of Hepcidin
Conservation of Iron
•
Extracorpuscular hemoglobin is bound by haptoglobin
•
Hemopexin is a β1 globin that binds Heme
•
Albumin will bind some metheme (ferric heme) to form methemalbumin
•
Which then transfers the metheme to hemopexin
•
Transferrin bind free Iron (Fe 3+) in plasma.
Haptoglobin
•
Human haptoglobin exists in three polymorphic forms, known as Hp 1-1, Hp 2-1, and Hp 2-2
•
Haptoglobin is an acute phase protein, and its plasma level is elevated in a variety of inflammatory states
•
Haptoglobin scavenges hemoglobin that has escaped recycling.
Haptoglobin protects the kidneys from damage by extracorpus-cular hemoglobin
•
During the course of red blood cell turnover, approximately 10% of an erythrocytes hemoglobin is released into the circulation.
•
This free, extracorpuscular hemoglobin is sufficiently small at =65 kDa to pass through the glomerulus of the kidney into the tubules, where it tends to form damaging precipitates.
•
Haptoglobin (Hp) is a plasma glycoprotein that binds extra-corpuscular hemoglobin (Hb) to form a tight noncovalent complex (Hb-Hp).
•
Since the Hb-Hp complex is too large (≥155 kDa) to pass through the glomerulus, this protects the kidney from the formation of harmful precipitates and reduces the loss of the iron associated with extracorpuscular hemoglobin.
Contd...
Contd...
Haptoglobin level in hemolytic anemia
•
Patients suffering from hemolytic anemias exhibit low levels of haptoglobin
•
The half-life of haptoglobin is approximately 5 days
•
The Hb-Hp complex is removed rapidly by the hepatocytes (half-life 90 minutes)
•
Thus, when haptoglobin is bound to hemoglobin, it is cleared from the plasma about 80 times faster than normally
•
So the level of haptoglobin falls rapidly in situations where hemoglobin is constantly being released from red blood cells, such as occurs in hemolytic anemias.
Haptoglobin-related protein and cancer
A plasma protein that has a high degree of homology to haptoglobin, it is elevated in some patients with cancers, although the significance of this is not understood.
Iron Deficiency Anemia
Stages of iron deficiency
•
The progression to iron deficiency can be divided into three stages
•
The first stage is negative iron balance, in which the demands for (or losses of) iron exceed the body’s ability to absorb iron from the diet. Serum iron is normal and hemoglobin synthesis is unaffected
•
The second stage is iron-deficient erythropoiesis, transferrin saturation falls to 15–20%, Serum iron level begin to fall, hemoglobin synthesis becomes impaired
•
The third stage is Iron deficiency anemia, where hemoglobin and hematocrit falls. Microcytic Hypochromic anemia sets in.
Normal
Negative iron balance
Iron deficient erythro-poiesis
Iron deficiency anemia
Iron stores
Erythron iron
Marrow iron
stores
1–3 +
0–1 +
Serum
ferritin (µg/L)
50–200
< 20="" />
< 15="" />
< 15="" />
TIBC (µg/dL)
300–360
> 360
> 380
> 400
SI(µg/dL)
50–150
NL
< 50="" />
< 30="" />
Saturation
(%)
30–50
NL
< 20="" />
< 10="" />
Marrow
sideroblasts
(%)
40–60
NL
< 10="" />
< 10="" />
Protopor-phyrin (µg/ dL)
30–50
NL
> 100
> 200
RBC morphology
NL
NL
NL
Microcytic/ hypochronic
Laboratory iron studies in normal and different stages of evolution of iron deficiency
Parameter
Normal
Negative iron balance
Iron defi-cient eryth- ropoiesis
Iron deficiency anemia
Marrow Iron
stores
1–3+
0–1 +
Serum ferritin
(μg/dL)
50–200
Decreased
< 20="" />
Decreased
< 15="" />
Decreased
< 15="" />
Total iron binding capacity (TIBC) (μg/dL)
300–
360
Slightly increased
> 360
Increased >
380
Increased > 400
Serum iron (μg/ dL)
50–150
Normal
Decreased < 50="" />
Decreased
< 30="" />
Transferrin saturation(%)
30–50
Normal
Decreased
< 20="" />
Decreased
< 10="" />
RBC protopor-phyrin (μg/dL)
30–50
Normal
Increased
Increased
Soluble trans-ferrin receptor
(μg/L)
4–9
Increased
Increased
Increased
RBC morphol-ogy
Normal
Normal
Normal
Microcytic Hypochro-mic
Lab Parameters that increase in Iron Deficiency Anemia
• TIBC • RBC Protoporphyrin • s TR[TRP](Transferrin Receptor Protein) • RBC Distribution Width[RDW]
Diagnosing Microcytic anemia
Tests
Iron deficiency
Inflamma-tion
Thalas-semia
Sidero-blastic anemia
Peripheral
Smear
Microcytic Hypochro-mic
Normal/ Micro/
Hypo
Microcytic Hypochro-mic with targeting
Variable
S Iron (μg/ dL)
< 30="" />
< 50="" />
Normal to high
Normal to high
TIBC(μg/dL)
> 360
< 300="" />
Normal
Normal
Transferrin saturation(%)
< 10="" />
10–20
30–80
30–80
Ferritin(μg/L)
< 15="" />
30–200
50–300
50–300
Hb electrophoresis pattern
Normal
Normal
Abnormal pattern in beta Thal-assemia
Normal
Iron Overload Conditions
TYPE-I Hereditary Hemochromatosis (HFE related)
•
Mutation in HFE gene located on Chr 6p
•
Tightly linkedto the HLA-A locus
•
Most Common Hemochromatosis [80–90%]
Non HFE related Hereditary Hemochromatosis
•
Juvenile hemochromatosis(type 2A) (hemojuvelin mutations)
•
Juvenile hemochromatosis(type 2B) (hepcidin mutation)
•
Mutated transferrin receptor 2 TFR2 (type 3)
•
Mutated ferroportin 1 gene, SLC11A3 (type 4)
Secondary Hemochromatosis
•
Anemia characterized by ineffective erythropoiesis (eg, thalassemia major)
•
Repeated blood transfusions
•
Parenteral iron therapy
•
Dietary iron overload (Bantu siderosis)
Miscellaneous Conditions Associated with Iron Overload
•
Alcoholic liver disease
•
Nonalcoholic steatohepatitis
•
Hepatitis C infection.
Hemochromatosis
Inherited disorder of iron metabolism that lead to iron overload, leading to deposition of iron in the parenchymal cells leading to fibrosis and organ failure.
Hemosiderosis
•
Acquired condition
•
Presence of stainable iron in tissues
Hemochromatosis at a glance
•
The first organ to be affected in Hemochromatosis Liver
•
Maximum deposition of Hemosiderin is seen in Liver
•
Least Hemosiderin deposition is seen in Skin
Classical Triad of Hemochromatosis is
•
Cirrhosis with Hepatomegaly
•
Skin Pigmentation [Bronzing]
Due to the epidermis of the skin is thin, and melanin is increased in the cells of the basal layer and dermis
•
Diabetes Mellitus
•
First joint to be affected in hemochromatosis-2nd and 3rd MCP joint
•
Most common cause of death in treated patients-Hepatocellular Carcinoma
•
Role of HFE Mutations in other diseases
–
Nonalcoholic Steatohepatitis
–
Porphyria CutaneaTarda
Cofactor role of Copper
•
Amine oxidases
•
Ferroxidase (ceruloplasmin) (Iron metabolism, Copper Transport)
•
Cytochrome-c oxidase (in Complex IV of Electron Transport Chain)
•
Superoxide dismutase (Free Radical Scavenging enzyme)
•
Tyrosinase (Melanin Synthesis)
•
Component of ferroportin (Iron Metabolism)
•
Lysyl Oxidase (Cross linking in Collagen)
Copper Deficiency Anemia is a microcytic hypochromic type of Anemia.
Wilson’s Disease
Autosomal recessive Biochemical defect
•
ATP7 B mutation, a gene encoding for Copper transporting ATPase in the cells
•
Defective Biliary Copper Excretion from liver cells
•
Defective Copper incorporation into Apoceruloplas-min
•
Copper accumulate in cells leading to copper deposits in the liver and brain.
Quick glance: Wilson’s disease
•
The most common presentation in Wilson’s disease: Acute or Chronic Liver Disease
•
Neuropsychiatric manifestation in Wilson’s resembles: Parkinson’s Disease like Syndrome
•
Most Sensitive test in Wilson’s disease is or gold standard investigation is liver biopsy quantitative copper assay
•
False positive is liver biopsy quantitative copper assay in obstructive liver disease
•
The most specific Screening Test: Urinary Excretion of Copper
Diagnosis of Wilson’s Disease
•
99% of cases Kayser-Fleischer ring is present, but absence of KF ring does not excludes the disease
•
Serum Ceruloplasmin [18–35 mg/dL] decreased
•
But normal in 10% of affected individuals and decreased in 20% of carriers
•
24 hour Urinary Copper > 100 µg/24 hr
•
Gold Standard investigationQ is Liver BiopsyQ with quantitative Copper assays (> 200 µg/g dry weight of Liver)
Test
Usefulness
Normal Value
Wilson disease
Serum Ceru-loplasmin
+
180–350
mg/L
(18–35 mg/dL)
Lowin 90%
Kayser-
Fleischer
ring
++
Absent
Present in > 99% if neurologic or psychiatric symptoms are present. Present 30–50% in hepatic presentation and presymptomatic patients
Urine Copper (24h)
+++
0.3–0.8 μmol (20– 50 μg)
> 100 μg in symptomatic patients
60–100 μg in pres-ymptomatic
Liver Copper
++++
0.3–0.8 μmol/g (20–50 μg/g of tissue)
> 3.1 μmol (> 200 μg)
Treatment
Disease status
First line
Second line
Hepatitis or Cirrhosis without decom-pensation
Zinc
Trientene
Hepatic decompensation
Mild
Trientene and Zinc
Penicillamine and Zinc
Moderate
Trientene and Zinc
Hepatic Transplantation
Severe
Hepatic Transplantation
Trientene and Zinc
Initial neurologic/ psychiatric
Tetrathiomolybdate and Zinc
Zinc
Maintenance / Pre-symptomatic/ Pregnant/ Pediatric
Zinc
Trientene
Method to assess severity of Hepatic Decompensation in Wilson’s disease
Nazer’s Prognostic Index
•
Serum Bilirubin
•
Serum Aspartate Transferase [AST]
•
Prolongation of Prothrombin Time
‒
Score < 7="" medical="" management="" />
‒
Score > 9 Liver Transplantation
Menke’s (Kinky or Steely) Hair Syndrome
•
Mutation in ATP7A gene
•
X linked recessive condition
•
Defective Copper binding P-type ATPase
•
Copper is not mobilized from Intestine
MEDNIK Syndrome
•
A rare multisystem disorder of copper metabolism with features of both Wilson’s and Menke’s disease
•
Caused by mutation in AP1S1 gene, which encodes an adaptor protein necessary for intracellular trafficking of ATP7 A and ATP7B.
•
MEDNIK stands for Mental retardation, Enteropathy, Deafness, Neuropathy, Icthyosis, Keratodermia
•
Zincisan integral component of many metalloenzymes in the body
•
It is involved in the synthesis and stabilization of proteins, DNA, and RNA and plays a structural role in ribosomes and membranes
•
Zinc is necessary for the binding of steroid hormone receptors and several other transcription factors to DNA
•
Zinc is absolutelyrequired for normalspermatogenesis, fetal growth, and embryonic development.
Zn Deficiency
•
Mild chronic zinc deficiency can cause stunted growth in children, decreased taste sensation (hypogeusia), impaired immune function
•
Severe chronic zinc deficiency can cause hypogonadism, dwarfism, hypopigmented hair.
Acrodermatitis enteropathica
•
Rare autosomal recessive disorder characterized by abnormalities in zinc absorption
•
Clinical manifestations include diarrhea, alopecia, muscle wasting, depression, irritability, and a rash involving the extremities, face, and perineum
•
The rash is characterized by vesicular and pustular crusting with scaling and erythema
•
The diagnosis of zinc deficiency is usually made by a serum zinc level < 12="" mol/l="" />< 70="" g/dl).="" />
Zn Toxicity
•
Acute zinc toxicity after oral ingestion causes nausea, vomiting, and fever
•
Zinc fumes from welding may also be toxic and cause fever, respiratory distress, excessive salivation, sweating, and headache.
•
Selenium, in the form of selenocysteine, is a component of the all the enzymes that contain Selenocysteine
•
Selenium is being actively studied as a chemo-preventive agent against certain cancers, such as prostate cancer.
Keshan disease
An endemic cardiomyopathy found in children and young women residing in regions of China where dietary intake of selenium is low (< 20="" g/d).="" />
Selenium toxicity (Kashinbeck Disease)
Chronic ingestion of high amounts of selenium leads to selenosis (Kashinbeck Disease)
It is characterized by hair and nail brittleness and loss, garlic breath odor (Due to Dimethyl selenide), skin rash, myopathy, irritability, and other abnormalities of the nervous system.
•
Chromium potentiates the action of insulin in patients with impaired glucose tolerance, by increasing insulin receptor–mediated signalling.
Chromium -6
•
Chromium in the trivalent state is found in supplements and is largely nontoxic
•
Chromium-6 is a product of stainless steel welding and is a known pulmonary carcinogen as well as a cause of liver, kidney, and CNS damage.
•
An essential function for fluoride in humans has not been described, although it is useful for the maintenance of structure in teeth and bone
•
Adult fluorosis results in mottled and pitted defects in tooth enamel as well as brittle bone (skeletal fluorosis).
Minerals at a Glance
•
Zinc containing protein present in the Saliva: GustenQ
•
Mineral stabilize hormone insulinQ: Zinc
•
Mineral that potentiates action of Insulin: ChromiumQ Contd...
•
Mineral deficiency that leads to impaired Glucose tolerance: ChromiumQ
•
Highest concentration of Zn seen in Hippocampus and Prostatic Secretion
•
The mineral deficiency leads to impaired Spermato-genesis: Zinc
•
Garlicky odor in breath is seen in: Selenosis (Due to Dimethyl selenide)
•
Selenium toxicity lead to Kaschinbeck Disease
•
Low Selenium level leads to Keshan disease (Endemic Cardiomyopathy)
•
Calcium dependent Cysteine Protease are called Calpain
•
Calpain associated with Type II Diabetes Mellitus: Calpain 10
•
Normal Blood Calcium level-9: 11 mg/dl
•
Total Calcium level in the bodyQ is 1.5 kg.
Recommended Daily Allowances (RDA) of important Minerals
Mineral
RDA
CalciumQ
Adult-0.5g Children-1g
Pregnancy and Lactation-1.5g
IronQ
Males-15–20 mg
Females-20–25 mg
Pregnancy-40–50 mg
IodineQ
150–200 μg
200–250 μg
Phosphorus
500 mg
Magnesium
400 mg
Mangenese
5–6 mg
Sodium
5–10 g
Potassium
3–4 g
Copper
1.5–3 mg
Mineral
RDA
ZincQ
8–10 mg
SeleniumQ
50–200 μg
Other important Minerals: Functions and Deficiency manifestation
Mineral
Function
Deficiency
Cobalt
Constituent of Vitamin
B12
Macrocytic Anemia
Chromium
Potentiate the action of Insulin
Impaired Glucose Tolerance
Fluoride
Constituent of Bone and teeth
Dental caries
Iodine
Thyroid Hormone Synthesis
Thyroid enlargement,
↓T4, cretinism
Molybdenum
Cofactor forXan-thine oxidase and Sulfite oxidase, Aldehyde oxidase
Severe neurologic abnormalities, Xanthinuria
Selenium
Cofactor forGlutathione
Peroxidase Deiodinase, ThioredoxinReductase Antioxidant along with
Vitamin E
Keshan’s Disease (Cardiomyopathy),
heart failure, striated muscle degeneration
Zinc
Cofactor for Carbonic Anhydrase Carboxy Peptidase
Lactate Dehydrogenase Alcohol Dehydrogenase Alkaline Phosphatase
Growth retardation,
↓taste and smell, alope-cia, dermatitis, diarrhea, immune dysfunction, failure to thrive, gonadal atrophy, congenital malformation Impaired
wound healing
Mangenese
Cofactor for Arginase, Carboxylase, Kinase, Enolase, Glucosyl Tran-ferase,
PhosphoGlucoMutase Required for RNA Polymerase
Impaired growth and skeletal development, reproduction, lipid and carbohydrate metabolism; upper body rash
Contd...
