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POINTS

History
Chemistry
Biosynthesis & Metabolism
Dietary sources & Requirement
Biochemical functions
Deficiency manifestations
Therapeutic use → Megadose of Vitamin C
Toxicity

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HISTORY

During the voyage of Vasco da Gama, around the cape hope good hope to India in 1498, he lost 2/3^rd of the crew due to scurvy.
The French explorer, Jaques Cartier, in 1536, during the voyages to discover eastern part of Canada, was laid up with Scurvy.
A friendly native gave an extract from the leaves of spruce tree, which produced remarkable cure to scurvy.
James Lind, published “Treatise on Scurvy”, in 1753.
Compulsory rationing of lime or lemon juice to all crew of British Royal Navy from 1795 onwards. So, the British Sailors were nicknamed as “Limeys”.

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CHEMISTRY

Water soluble
Structure resembles as Carbohydrates (C₆H₈O₆)
Comparatively strong acid, stronger than acetic acid, owing to dissociation of enolic H at C₂ & C₃
Strong reducing property due to double bonded (Enediol) form -OH group on C₂ & C₃
Easily destroyed by heat, alkali
Only L- ascorbic acid & Dehydro ascorbic acid have Antiscorbutic activity
D- ascorbic acid has no activity.

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Cooking vitamin C-rich foods or storing them for a long period of time can reduce the vitamin C content.
Microwaving and steaming vitamin C-rich foods may reduce cooking losses
Best food sources of vitamin C are Uncooked or raw fruits and vegetables.

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Ascorbic acid

(reduced form)

Dehydro ascorbic acid

(oxidized form)

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BIOSYNTHESIS

Most animals & plants can synthesize ascorbic acid from glucose.
Man, higher primates, guinea pigs, bats can not synthesize
Gulono lactone oxidase
Human lack L- gulonolactone oxidase, the enzyme that catalyzes the formation of 2-keto-L- gulonolactone, which spontaneously converted to L- ascorbic acid.

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SOURCES

All fruits and vegetables contain some amount of vitamin C.
Fruits:- Citrus fruits and juices, such as orange and grapefruit , Mango, lemon, Papaya, Pineapple, Strawberries, Raspberries, blue berries
Vegetables:-Cabbage, Cauliflower, Germinating seeds, Green peas, Beans, Tomatoes, Sweet and white potatoes
Amla (700 mgs/100 gms) is the richest source of Vitamin C.
Requirement:- 75 mg/day

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METABOLISM

Gastrointestinal Absorption of ascorbic acid occurs by a combination of,

Na⁺ dependent Active transport at low conc.

Simple diffusion at high conc.

70- 90 % of a usual dietary intake of ascorbic acid (up to 180 mg/day) is absorbed.
Absorbed ascorbic acid moves rapidly from intestinal cell into blood by a process of Facilitated diffusion.

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Ascorbate uptake by cells is mediated by specific transporters e.g. Na⁺dependent transporters (SVCT 1 & SVCT 2).
Vit C is found in glandular tissues like Pituitary, Adrenal cortex, Corpus luteum, Thymus have the highest amount and Retina has 20-30 times the plasma concentration.
Normal level in plasma:- 0.7 to1.2 mg/100 ml
25 mg/100 cc of WBC
From maternal blood it can cross the placental barriers & supplies the fetus

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Excreted in urine
Strong reducing agent so, Benedict’s test +ve
Very high concentration locally in healing wounds
Low level in blood is noted in women taking contraceptive pills & chronic alcoholics

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BIOCHEMICAL FUNCTIONS

Role in Cellular oxidation- reduction :-

Ascorbic acid ↔ Dehydroascorbic acid Slide 8

Role in Collagen synthesis:-

Hydroxyproline & Hydroxylysine

Functional activity of Fibroblasts/ Osteoblasts:-

MPS of connective tissue, osteoid tissue, dentine & intercellular substances of capillaries.

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Role in Tryptophan metabolism:-

as a cofactor for hydroxylation of tryptophan to

form 5-OH derivative (Serotonin)

Role in Tyrosine metabolism:-

oxidation of parahydroxy phenylpyruvate to Homogentisic acid

Formation of Tetrahydrofolate:-

it maintains ”Folic acid Reductase ” in its active state

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Absorption of Iron:-

Fe⁺⁺⁺ → Fe⁺⁺

Formation of Catecholamines:-

Dopamine → Norepinephrine (Dopamine Hydroxylase)

Formation of Carnitine:- γ-butyrobetaine hydroxylase
Role in oxidation of Fatty Acids:-

α- oxidation of long chain F.A. to form α- OH F.A.

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Action on certain enzymes:-

Arginase & Papain → Activated

Urease & β- Amylase → Inhibited

Hemoglobin metabolism:-

Met Hb → Hb

Bile acid Synthesis:-

Cholesterol → Bile acid

Phagocytic action of WBCs & formation of Antibody

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As an antioxidant:-
↓es DNA oxidation
Arrests protein damage
↓es lipid peroxidation
↓es production of extracellular oxidants from

neutrophils

Prevents atherosclerosis & CHD
Protective role in cancer by suppressing formation of carcinogenic nitrosamines
Synergistic effects with Vitamin E & carotenoids
Regular intake ↓es risk of Cataract.
Bone mineral metabolism

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Component of many drug metabolising enzyme system, particularly the mixed function oxidase system.

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DEFICIENCY

Scurvy
Infantile scurvy (Barlow's disease)
In infants between 6 to 12 months of age, (period in which weaning from breast milk), the diet should be supplemented with vitamin C sources. Otherwise, deficiency of vitamin C is seen.
Hemorrhagic tendency
Collagen is abnormal and the intercellular cement substance is brittle So capillaries are fragile, leading to the tendency to bleed even under minor pressure.
Subcutaneous hemorrhage: Petechiae in mild deficiency, ecchymoses or even hematoma in severe conditions

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Internal hemorrhage:- Conjunctiva & retina. Epistaxis, Hematuria, Melena
Gum becomes painful, swollen & spongy. The pulp is separated from the dentine & finally teeth are lost.
Wound healing
Bones:- failure of the Osteoblasts to form the intercellular substance, Osteoid. Weak bones, fractures, hemorrhage in joint cavities
Anemia:- Microcytic hypochromic anemia

1. Loss of blood by hemorrhage

2.↓ed iron absorption

3.↓ed Tetrahydrofolic acid

4. Accumulation of Met-Hb

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THERAPEUTIC USES

As an adjuvant in infections
In tuberculosis
Clinical dose:- 500 mg/day
Treatment of ulcer, trauma & burns
Megadose of vitamin C:- 2000-5000 mg/day
There is experimental evidence in animals that ageing process is prevented by megadoses of vitamin C.

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Detection of Deficiency in Man:-
Urine ascorbic acid “Saturation” test:-test dose of 5 mg per lb (pound) body wt. given. If 50 per cent or more excreted in next 24 hours, the Individual has no deficiency of the vitamin.
Intradermal test:-intradermal injection of 2, 6-dichlorophenol indophenol and determination of the time required for decolorisation. i.e.reduction of the dye.
Tourniquet test (capillary resistance or fragility test)

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TOXICITY

Since it is a water soluble substance, excess vitamin C is excreted, and not accumulated in the body. However, more than 2000 mg of vitamin C daily for a long time can cause iron overload, because vitamin C helps in absorption of iron.

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REVISION

Slide 2

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THANK YOU

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