VITAMIN C

A. History: No other vitamin, with the possible exception of vitamin E, is as generally misunderstood as is vitamin C. It is ironic that the oldest therapeutically-used vitamin, urnished in 1750s in the form the lemons to British sailors to prevent scurvy, is still a subject of controversy. However, in 1928, Albert G. Szent-Györgyi isolated this crystalline vitamin from the paprika plant and named it hexuronic acid. Later in 1932, C. Glen King and W.A. Waugh in United States isolated this from lemon juice. It was synthesized by Reichstein in 1933. It is also called cevitamin. It has a curing action against scurvy and hence popularly called as antiscorbutic factor.

B. Occurrence: In general, ascorbic acid is not as widely distributed as other vitamins. Among plants, it is present in all fresh fruits and vegetables. The richest source of vitamin C, known uptodate, is the acerola fruit (Malpighia punctifolia). The fruit yeilds 1,000–4,000 mg of ascorbic acid per 100 g of edible matter. Citrus fruits (such as orange, lemon, lime), gooseberry, pineapple, guavas, tomatoes, melons, raw cabbage and green pepper are also rich sources of it. New potatoes contain relatively large amounts. Dried legumes and cereals contain very little vitamin C. Dry seeds, in general, are devoid of it but during their sprouting, the vitamin appears. Woody tissues also lack it. Vitamin C is synthesized by most mammals, but not by primates (such as apes, man) and guinea pigs which acquire it from their diets. In animals, the vitamin occurs in tissues and various glands or organs such as liver, adrenals, thymus, corpus luteum etc. Meat contains relatively low concentration. Human milk is 3 to 4 times richer in vitamin C contents than cow's milk. Vitamin C is, however, absent from fish, fats and oils. It is also not present in or required by microorganisms. Since this vitamin is a good reducing agent, it is lost under oxidizing conditions like aeration and heating. Thus, many cooked and canned foods contain little ascorbic acid. It is also found in the combined form as ascorbigen. The adrenal and lenses have particularly high contents of vitamin C. The infant is usually born with adequate stores of as corbic acid if the mother’s intake has been adequate; the ascorbic acid content of cord blood plasma is 2-4 times greater than that of maternal plasma. Under these conditions, the breast milk contains ca 4-7 mg/dL of ascorbic acid and is an adequate source of ascorbic acid.

The vitamin C content of some food items are presented in Table.

C. Structure: The structure of ascorbic acid (C6H8O6) was established mainly by Haworth.It is a derivative of a hexose called L-gulose. Chemically, it is 1-threo-2,4,5, 6-pentoxyhexen-2-carboxylic acid lactone (refer Fig Metabolism of vitamin C ). Although ascorbic acid is a small molecule when compared with DNA, RNA or proteins, its metabolic impact is no less considerable. The dienolic group consisting of hydroxyls on C2 and C3 with a double bond between them invests the ascorbic acid molecule with redox property.
D. Properties: Ascorbic acid is a colourless and odourless crystalline substance, slightly sour in taste and optically active. Only the L-isomer has antiscorbutic properties. It is soluble in water and alcohol but practically insoluble in chloroform, solvent ether and light petroleum. It is readily oxidized, particularly in the presence of copper and iron but not of aluminium. It is for this reason that the foods cooked in copper utensils lose ascorbic acid quickly.This vitamin is also rapidly destroyed by alkalies but is fairly stable in weak acid solutions. Therefore, baking soda has a deleterious effect but steam cooking destroys very little amount of ascorbic acid. Drying ofvegetables and also their storage results in a loss of their ascorbic acid. However, freezing has no detrimental effect on this vitamin. Citrus fruit juices and tomato juice may be canned with but little loss of ascorbic acid. On account of its easily oxidizable nature, the ascorbic acid is a powerful reducing agent.

E. Metabolism:Higher plants (like pea) and all known mammals except man, the primates

ContentsWATER-SOLUBLE VITAMINS 1011 and guinea pig can synthesize ascorbic acid from L-gulonolactone. The rat, for example, is resistant to scurvy. In animals, the liver and adrenals (cortical portion) are the main sites of synthesis. The biosynthesis of ascorbic acid in animals takes place according to the scheme as depicted in Fig.(Biosynthesis of vitamin C). The scheme also probably applies to the plants. Man lacks the enzyme L-gulono-oxidaseand as such is incapable of synthesizing ascorbic acid. Ascorbic acid can be readily oxidized (Fig. Metabolism of vitamin C) to dehydroascorbic acid in the presence of metal ions. Dehydroascorbic acid is a much more powerful electron donor than even ascorbic acid by virtue of its unpaired electron. It is, in fact, the free radical form of ascorbic acid. Dehydroascorbic acid can be reduced, in the presence of H2S or cysteine, back to ascorbic acid. The reduced form (i.e., L-ascorbic acid) predominates in the plasma and also apparently in tissues
at a ratio of about 15 : 1 of the oxidized form (i.e., dehydro-L-ascorbic acid). Both of these are
biologically active and are equally potent in carrying out their metabolic functions. When dehydro- L-ascorbic acid is hydrated, 2,3-diketo-L-gulonic acid is formed which is biologically inactive and cannot be converted back to either of the active forms in the body. Since the hydration reaction takes place automatically in the neutral medium, the oxidation of ascorbic acid, in other words, means its biologic inactivation. These reactions have been shown to occur in vivo in man and guinea pigs.

Ascorbic acid functions in a number of enzymatic activities. A major function of ascorbic acid is the formation of tissue collagen or ‘intracellular cement substance’. In fact, ascorbic acid appears to be essential to the activity of the enzyme collagen proline hydroxylase, which catalyzesthe conversion of proline to hydroxyproline. Hydroxyproline (Hyp) is found exclusively in collagenand is vital in maintaining the tertiary structure of this major vertebrate protein, i.e., collagen.

Recent researches have established the role of ascorbic acid in the conversion of folic acid to

a physiologically active form, tetrahydrofolic acid.Ascorbic acid also plays a key role in tyrosine metabolism. One of the steps in tyrosine metabolism is the oxidation of p-hydrophenylpyruvic acid to homogentisic acid. The vitamin C protects the enzyme p-hydrophenylpyruvic acid oxidase from inhibition by excess substrate. Ascorbic acid is also involved in electron transport in the microsomal fraction. However, in none of the biological oxidation systems, ascorbic acid has been shown to act as a specific coenzyme. Vitamin C is found concentrated in certain parts of human body such as brain and the white blood cells. This body “pool” amounts to roughly 1,500 mg for a man and slightly more for a woman, which is normally enough for about a month's need. However, illness or stress can substantially decrease the body's vitamin C reserves, as also can smoking, drinking, and a variety of drugs such as aspirin. Vitamin C plays an important role in our body's wondrous immune system. It may enhance the body's production of interferon, prostaglandins, T-lymphocytes and immunoglobulins-weapons of the body's self-defence arsenal. However, huge doses of ascorbic acid can leach calcium and other needed minerals out of the body. It can act as a diuretic and laxative.The fact that in old age the deficiency of vitamin C is frequently observed point to a possiblerole of vitamin C as an anti-ageing agent. Free radicals are the major cause of ageing. These are oxygen molecules which lose an electron in the course of circulating through the blood-stream. These highly reactive molecules try to regain chemical stability by ‘snatching’ electrons from other molecules, a process which causes much damage. While normal metabolic processes produce some free radicals, their number increases by tissue injuries from infection, toxins, reduced blood flow, excessive exercise and environmental hazards like radiation, heat, and cold. And the antioxidants like vitamins A, C and E neutralize these free radicals by ‘donating’ electrons.vitamin C (and also vitamins A and E) have long been known to be beneficial for the skin. While vitamins A and E work by exfoliating the skin's surface cells, vitamin C works from the inside by boosting collagen production and repair. It also inhibits the excess production of melanin (C17H98O33N14S) which leads to a tan and hyperpigmentation. Some dermatologists encourage the use of vitamin C as an anti-inflammatory agent as its topical application speeds up the skin's healing process, reducing redness and irritation caused by sun exposure. Ascorbic acid plays an important role in germination, growth, metabolism and flowering of plants (Chenoy JJ, 1962, 1967–1973). During germination, embryo axis has higher ascorbic acid content as well as higher rate of ascorbic acid utilization compared with those of the endosperm or the cotyledons. Ascorbic acid stimulates amylase, protease and RNAase activity and RNA content in various crops including gram (Cicer arietinum). Free radical content of the endosperm/cotyledon has been shown to be higher during the initial stages of germination as compared to that in the embryo axis, suggesting an active participation of free radicals in the process of energy flow for transport of metabolites from storage organ to the embryo axis. Increase in free radical content of the embryo axis, at later stages of germination is highly suggestive of the important role of free radical in the biosynthesis of macromolecules and other cell constituents for seedling growth. Further, it was established that the ascorbic acid turnover is appreciably higher during the reproductive

phase of differentiation in many thermophobes (wheat, barley, oat), as well as in many thermophytes (maize, sesame). During the period of reproductive differentiation, the free radical content is enhanced.

F. Deficiency : Avitaminosis C leads to scurvy, which may occur at any stage but is rare in the newborn infant. The majority of cases appear in infants 6-24 months (mo) of age. Breast-fed infants are protected as the breast milk contains adequate amounts of vitamin C. Clinical manifestations require time to develop. However, after a variable period of vitamin C depletion, contain vague symptoms of irritability, tachypnea (very rapid respiration), digestive disturbancesand loss of appetite appear.
The main symptoms which later develop are listed below :

• Tender bones : There is evidence of general tenderness, esp., noticeable in the legs when the infant is picked up or when the diaper is changed. The legs assume the typical “froglike position”, in which the hips and knees are semiflexed with the feet rotated outward. This may be mistaken for paralysis and is hence aptly called pseudo-paralysis.
• Edematous swellings : These develop along the shafts of the legs and in some cases a subperiosteal hemorrhage can be palpated at the end of the femur.
• Petechial hemorrhages : The capillaries become brittle and burst, thus giving rise to red and purple spots (or petechiae) over the body. Petechiae may be seen in the skin and mucous membranes. Hematuria, melena, and orbital or subdural hemorrhages may be found.

Bleeding gums :.
Changes in the gums, most noticeable when the teeth are erupted, arecharacterizedby bluish-purple, spongy swellings of the mucous membrane, usually over the upper incisors (in Fig )

• Scorbutic rosary : The costochondral junctions become prominent and appear sharp and
  angular, giving rise to a beaded structure, called scorbutic rosary. The angulation of the scorbutic beads is usually sharper than that of the rachitic rosary because it is produced by a separation of epiphyses of ribs and backward displacement of sternum rather than by widening of the softened epiphyses as occurs in rickets, where the prominence of the costochondral junction is dome-shaped and semicircular.
• Delayed wound healing: The wound healing is delayed or, in many cases, even does not
  occur because of the failure of the cells to deposit collagen fibrils. The healed wounds may even break down.
• Cessation of bone growth : The bones cease to grow. The cells of growing epiphyses continue to proliferate but no new matrix is laid down between the cells. Consequently, bones fracture easily at the point of growth because they fail to ossify. Moreover, when an already ossified bone fractures in a scorbutic individual, the osteoblasts cannot secrete a new matrix for the deposition of new bone. With the result, the fractured bone does not heal.
• “Sicca” syndrome : Swollen joints and follicular hyperkeratosis may develop, as well as the “sicca” syndrome of Sjögren, which is usually associated with collagen disorders and includes xerostomia, keratoconjunctivitis sicca, and enlargement of the salivary glands.
• Anemia : Anemia may reflect inability to utilize iron or impaired folic acid metabolism.

• Pyrexia : Low-grade fever is usually present in scorbutic children.

Infants 6–12 months of age, who are fed on processed milk only, are very susceptible to this disese (infantile scurvy). Adult cases appear less frequently. Elderly bachelors and widowers who have to cook their own foods are especially prone to the development of vitamin C deficiency– a syndrome termed ‘bachelor scurvy’. Food faddists may also develop scurvy if their diet lacks fruits and vegetables.
In 1975, Prof. Olaf Skinsnes of the University of Hawaii, Honolulu, has succeeded in obtaining almost pure cultures of leprosy bacillus that afflicts human beings. This work has, however, raised the possibility of a vaccine against this dreaded scourge. As an important sidelight of his work, it appears that vitamin C tends to slow down the growth of the bacilli by inhibiting enzyme action. Vitamin C may, thus, have a minor but an important role to play in leprosy treatment.
G. Human requirements: Since vitamin C is continuously oxidized in the body, the daily requirement of this vitamin is rather high. The recommended daily dose for children is 40 mg and for men and women, 50–60 mg. Formula-fed infants should, however, receive even lower doses, i.e., 30 mg of ascorbic acid daily. Lactating mothers should take higher doses, i.e., 100 mg daily. According to a report published by the British Nutrition Foundation, the RDA for vitamin C on which most nutritionists base diets, is far too low. The 30 mg daily that is usually recommended in most countries is way below the United States at 60 mg, Germany at 75 mg and Russia at 100 mg. Ante diluvian though it sounds, the figure of 30 mg is based on the amount of vitamin C needed to prevent that scourge of seafarers, scurvy. The Nutrition Foundation believes that a more contemporary approach to vitamin C would be to consider at what level it actually promotes good health. Besides, vitamin C requirement in humans may vary with the time of day and time of year. Early autumn, for example, is when most poeple’s vitamin C levels are at their lowest.

H. Treatment : Scurvy is prevented by a diet rich in ascorbic acid; citrus fruits and juices are excellent sources. The administration of orange juice or tomato juice daily will quickly produce healing but ascorbic acid is preferable. The daily therapeutic dose is 100-200 mg or more, orally or parenterally.

CHOLINE and INOSITOL

CHOLINE

A. History: Choline is an essential component of the diet of animals and is, therefore, usually included among the vitamins. Best, for the first time, pointed out the role of choline in nutrition. He also showed that choline prevented the development of fatty livers in depancreatized dogs.

B. Occurrence: Choline is widely distributed. Therichest source is egg yolk. Liver, kidney, meats, cereals and many vegetables such as beans and peanuts are other good sources. It is an important constituent of lecithins.

C. Structure: Choline (C5H15O2N) is a quaternary ammonium compound, where out of the 4 H atoms, one is replaced by hydroxy ethyl group and the other three by 3 methyl groups

D. Properties: Choline is water soluble and has very strong basic properties.
E. Metabolism: Choline can be synthesized in the body by methylation of ethanolamine and, therefore, strictly speaking, this is not a vitamin.

Choline may function in many ways :

(a) It is an important constituent of phospholipids like lecithin.

(b) It undergoes esterification with acetyl-CoA to form acetyl-choline. This is an endergonic

reaction, the energy being derived from ATP. Acetylcholine is responsible for the transmission of nerve impulses in the central nervous system (CNS).

(c) It acts as an important methyl group donor in intermediary metabolism.
(d) It is an important lipotropic agent and participates in the mobilization of fat from the liver. Its absence, henceforth, causes accumulation of fat in the hepatic tissues. Using mutants of Neurospora, Horowitz has shown that the inability of the fungus to synthesize choline is due to a deficiency in the formation of an intermediate compound, N-monomethyl aminoethanol. The synthesis involves the following steps :F. Deficiency: In the deficiency of choline, puppies develop anorexia, hens do not lays eggs and mice do not lactate normally. A low-choline diet also develops hemorrhages of the kidneys and eyes, in addition to fatty livers, in young rats. No definite symptoms of choline deficiency have been established in man. However, alcoholic cirrhosis of the liver in man is largely a result of dietary deficiency of many lipotropic agents, of which choline is an important example.

G. Human requirements: In the case of choline, the dietary requirement for human beings
has not been established.

INOSITOL

A. History: Woolley (1940) discovered that the mice, when fed on a synthetic diet containing
all the known vitamins even, failed to grow and their hair growth was arrested. The addition of pantothenic acid, the absence of which may also cause hair changes, however, proved futile. Neither biotin nor p-aminobenzoic acid could also cure them. The curative effects were, however, obtained by the addition of phytin (obtained from cereal grain) or inositol (isolated from liver). Thus, it was
established as a vitamin of B group. This is also called as mouse antialopecia factor.
B. Occurrence: Inositol is found in muscles (hence, its nomenclature as muscle sugar),
liver, kidneys, brain, erythrocytes and tissues of the eye. Among plants, it occurs in furits, vegetables, whole grains and nuts. Milk and yeast contain appreciable quantities. Inositol is found in nature in at least 4 forms : free inositol, phytin, phosphatidylinositol and a nondialyzable complex. Inositol containing phosphatide or phosphoinositide ( = lipositol of Woolley) has been isolated in pure form from soyabeans and is also known to be present in brain and spinal cord.
C. Structure: Inositol, C6H12O6 or betterC6H6(OH)6,is a carbocyclic hexahydric alcohol. It has 9 possible stereoisomers, of which only one myoinositol found in muscles, is biologically active and happens to be a symmetric, optically inactive mesoform.
D. Properties: Although not a sugar, inositol is sweet in taste. This is, in fact, a common
property to many polyatomic alcohols including glycerol. Inositol is soluble in water.
E. Metabolism: Inositol as phosphoinositide helps in transport processes in cells.Inositol stimulates the growth of many microorganisms such as Saccharomyces cerevisiae and
Neurospora.
It also acts as a lipotropic agent and prevents the formation of fatty livers.
Possibly, it is an intermediate between carbohydrates and aromatic substances.
F. Deficiency: Inositol deficiency results in retarded growth and a peculiar hairlessness in
mice. Lack of inositol also causes insufficient lactation in experimental animals. Deficiency of
inositol, however, does not occur in man.
G. Human requirements: The amount of inositol needed by man is not known.

PARA-AMINOBENZOIC ACID and ALPHA-LIPOIC ACID

PARA-AMINOBENZOIC ACID
A. History: Ansbacher demonstrated that depigmentation of the hair (achromotrichia) in mouse could be cured by feeding rice polishings or by adding p-aminobenzoic acid (PABA) to the diet. PABA also appeared essential for the growth of rat and chick and also for bacterial multiplication.
B. Occurrence:PABA is widely distributed in nature. The good sources are liver, yeast, rice bran and whole wheat. PABA occurs in conjugated form as a part of folic acid and its derivatives
C. Structure: he structural formula of p-aminobenzoic acid
D. Properties:PABA is a white crystalline substance. It is sparingly soluble in cold water but freely soluble in hot water and alcohol.
E. Metabolism: Woods, for the first time, observed that PABA blocks the bacteriostatic properties of sulfanilamide . PABA is synthesized from shikimic acid via chorismic acid.
F. Deficiency: The deficiency of PABA affects adversely the growth and the maintenance of a normal fur coat in rats.
G. Human requirements: There is, at present, no evidence that PABA is an essential dietary factor for man.
ALPHA-LIPOIC ACID

A. History: Lipoic acid is a relatively newly-discovered factor. This factor supports the growth of a number of bacteria and protozoa. It has been variously called as pyruvate oxidation factor (POF) or acetate replacement factor or protogen. Lester J. Reed et al (1951) isolated this factor in crystalline form from the insoluble residue of liver. When first isolated, lipoic acid was believed to be a B-vitamin because of its coenzyme function.However,the current opinion is in favour of treating lipoic acid as a pseudovitamin since it is synthesized by most animals.
B. Occurrence: It is found in many biologic materials including yeast and liver.

C. Structure: α-lipoic acid (C8H14O2S2) is a cyclic disulfide, derived from 6, 8-dimercapton-
caprylic acid

D. Properties: Lipoic acid is an exception of the vitamins of B series in that it is fat-soluble rather than water-soluble.

E. Metabolism: Lipoic acid acts as a catalytic agent for the oxidative decarboxylation of pyruvic acid and α-ketoglutaric acid by certain microorganisms. It is probably a coenzyme or part of a coenzyme, called as lipothiamide pyrophosphate (LTPP), for this reaction.

F. Deficiency: A deficiency of lipoic acid usually does not occur since it is synthesized by most animals.

G. Human requirements: α-lipoic acid is not an essential factor of the diet.

CARNITINE

CARNITINE:
A. History. Carnitine has long been known as a constituent of meat extractives. Its vitamin nature was first recognized when it was shown to be an essential food factor of certain insects such as the yellow mealworm, Tenebrio molitor. It was, however, first isolated from muscles.
B. Occurrence. Carnitine is widely distributed in most tissues including plants, animals and microorganisms. It occurs in the free state and also bound to lipid.
C. Structure. Carnitine is a betaine (pronounced as ‘bay-tah-een’).
D. Metabolism. Fatty acids are activated on the outer mitochondrial membrane whereas they
are oxidized in the mitochondrial matrix. Since the inner mitochondrial membrane is impermeable to long-chain acyl CoA molecules, a special transport mechanism is needed for them. It has been suggested that carnitine acts as a carrier of the activated long-chain fatty acids across the inner mitochondrial membrane. The acyl group is transferred from the S atom of acyl CoA to the OH group of carnitine to produce acyl carnitine, which traverses the inner mitochondrial membrane. In the mitochondrial matrix, the acyl group from acyl carnitine is transferred back to CoA so as to regenerate acyl CoA and free the carnitine. As the value of K is near 1, the O-acyl bond of carnitine is a high-energy bond. These transacylation reactions are reversible and are catalyzed by
fatty acyl CoA : carnitine fatty acid transferase.

BIOFLAVONOIDS and VITAMERS ( = ISOTELS)

BIOFLAVONOIDS:
A. History. Albert Szent-Györgyi and his associates, in 1936, reported the presence, inlemon peel, of a material which they named citrin. It consisted of a mixture of flavonoids and was shown to be associated with the maintenance of normal capillary permeability and fragility. The
active principle in citrin was found to be hesperidin. It shows physiologic roles similar to those
exhibited by other structurally-related compounds such as flavanones, flavones and flavonols. The term vitamin P (for permeability) was at first assigned to this group of compounds. They are now more commonly referred to as bioflavonoids.
B. Occurrence. The bioflavonoids are widely distributed in nature. They are always of plant
origin. They are present in the juice, peel and pulp of citrus fruits, in tobacco leaves, in buckwheat (Fagopyrum esculentum), in grapes and in many other fruits and vegetables.
C. Structure. Hesperidin is 5,3′-dihydroxy-4′-methoxy-7-rhamnoglucosidoflavanone. Its aglycone hesperitin, rutin (5,7,3′,4′- tetrahydroxy-3-glucorhamnosidoflavone) and its aglycone,
quercitin all have comparable physiologic roles.
D. Properties. The bioflavonoids are water-soluble.
E. Metabolism. The bioflavonoids act as antioxidants and thus protect ascorbic acid from
oxidative destruction (Clemetson and Andersen, 1966). The effect is indirect due to the chelation
of heavy metal ions (Cu2+ etc., ) that catalyze oxidative degradation of ascorbic acid. Bioflavonoids, thus, decrease oxidative losses of ascorbic acid from foods during storage or in intestinal tract.
F. Deficiency. Bioflavonoid deficiency in animals results in a syndrome characterized by increased capillary permeability and fragility. In man, however, the deficiency symptoms have not been observed.
G. Human requirements. The dietary allowances for man are not known.

VITAMERS ( = ISOTELS):
The various forms of any vitamin are referred to as vitamers. Williams, however, prefers to call these as isotels or isotelic vitamins, since the name vitamer is misleading. Although the isotels, in general, are not the isomers but a few of them may be isomers. All the fat-soluble vitamins and a few water-soluble vitamins (vitamins B5 and B6) have isotels. The various isotelic forms of a vitamin may differ with respect to either the β-ionone ring (vitamin A), the side chain attached at carbon 17 of the steroid nucleus (Vitamin D), the substituents present at carbon atoms 6, 7 and 8 in the chroman ring (vitamin E) or the side chain attached at carbon 3 of naphthoquinone radical (vitamin K). The study of isotels helps in a better understanding of the various physiologic functions which the vitamins perform.