Vitamin C - ascorbic acid

Vitamin C or ascorbic acid is a water-soluble vitamin. It is mostly found in fresh fruits and vegetables.

Vitamin C is one of the most researched and most frequently described vitamins. It acts as a reducing agent in many biological processes. It is important for the synthesis of collagen and carnitine and for the metabolism of fatty acids. As a coenzyme, it participates in many hydroxylation and amidation reactions and acts as a reducing agent by electron transfer to the enzyme. It is the strongest antioxidant among water-soluble vitamins. It is most commonly used in the form of calcium and sodium salts. It can be given orally and parenterally.

The next important episode in the history of vitamin C is related to Holst's and Frohlich's research. In 1907, they found that a guinea pig could get scurvy if fed only bran and oats without the addition of fresh vegetables. This has shown that some mammals cannot synthesize vitamin C on their own (among them man, monkey, guinea pig). 3-6.7 In 1928, A. Szent-Gyorgyi isolated vitamin C as a reducing agent in pure form from cabbage and from the adrenal glands. '' 6 '"1 In 1932, Waugh and King identified the compound in lemon juice as an active antiscorbutic factor.' ° Later, the chemical structure was determined in several laboratories and the substance was given the trivial name ascorbic acid. scurvy.

CHEMICAL COMPOSITION AND PROPERTIES

Chemically, ascorbic acid is a ketolactone with six carbon atoms, the structure is similar to glucose and other hexoses. Only unsaturated lactone with two hydroxyl groups with strong reducing properties. It is reversibly oxidized in the body to dehydroascorbic acid, which has full vitamin activity.

The reversible redox reaction between dehydro-L-ascorbic acid and L-ascorbic acid is an important feature on which physiological

depend

SOLUBILITY

Ascorbic acid is a white, odorless, light-sensitive, crystalline powder that is sensitive to light. It can be dissolved in water and alcohol. It is almost insoluble in chloroform and ether. It should not be stored in metal containers. It must be protected from air and light.

STABILITY

Oxidizes rapidly, especially in air and under the influence of alkalis, iron and copper. With mild oxidation, it turns into dehydroacid, which is active but decomposes with strong oxidants. It changes color under the influence of light, but a slight change in color does not affect the therapeutic activity (especially in injectable).

At concentrations greater than 100 mg / ml, L-ascorbic acid is degraded by the release of CO ₂ . Due to the fact that prolonged storage may increase the pressure in the injection ampoule, care should be taken when opening. Ascorbic acid occurs in isomeric forms. The L-isomer has biological activity, while the D-isomer shows a poorer therapeutic effect in the treatment of scurvy, but has a similar redox potential. Both isomers are used to prevent the formation of nitrosamines from nitrates used as preservatives.

NATURAL RESOURCES

The richest source of vitamin C are various types of fruits and vegetables. These include rose hips, black currants, cherries, citrus fruits (lemons, oranges, mandarins), leafy vegetables, peppers, cabbage, tomatoes, potatoes, green and black pepper, and evergreen shrub needles. Milk and animal tissues contain only small amounts of vitamin C.

FATE IN THE BODY

Following oral administration, ascorbic acid is rapidly absorbed by active transport. Absorption may be limited at high doses. Some of the many studies in this area have shown that only 50 percent of ascorbic acid is absorbed at higher doses (1 to 5 g). When used in a single oral dose, absorption decreases with increasing dose (75% is absorbed at 1 g and only 20% at 5 g). Vitamin C ingested with food is completely absorbed.12 Absorption may be reduced in patients with diarrhea or intestinal disease. Ascorbic acid is in plasma and is distributed to all cells of the body. Plasma concentrations vary with dose.

High concentrations of vitamin C are found in the liver, leukocytes (diagnostic value), glandular tissue and lens of the eye. Approximately 25 percent of plasma ascorbic acid is protein bound. Ascorbic acid passes through the placenta and occurs in breast milk. Breast milk contains 40 to 70 mg / ml with a normal diet. Ascorbic acid is reversibly oxidized to dehydroascorbic acid. A small portion is metabolized to inactive compounds, which also include sulfuric-ascorbic acid and oxalic acid, which are excreted in the urine. If given in large doses, ascorbic acid is excreted unchanged in the urine, but only when all tissue reserves are saturated. It can also be lost by hemodialysis.1,2

PHYSIOLOGICAL ROLE AND PHARMACOLOGICAL EFFECT

Askorbinskbut the acid acts as a coenzyme in many hydroxylation and amidation reactions.1,3 With its dehydro form, it is a reversible oxidative-reducing component that plays an important role in oxidoreductive processes and in cellular respiration.

Participates in collagen synthesis (conversion of some lysine and proline residues to hydroxylysine and hydroxyproline), carnitine synthesis (oxidation of the lysine side chain in protein to hydroxy-3-methyl lysine), conversion of folic acid to folinic acid, drug metabolism in microsomes and in the hydroxylation of dopamine to norepinephrine.

It also acts on certain peptide hormones (oxytocin, antidiuretic hormone, cholecystokinin) by promoting the activity of enzymes responsible for their action.

Ascorbic acid is required for the reduction of trivalent iron (Fe3 +) to divalent iron (Fe2 +) and for the reduction of copper. It is also involved in the synthesis of adrenocorticosteroids, as it was found that after stress and after the use of corticotropin, the concentration of ascorbic acid and cholesterol in the adrenal cortex decreases rapidly. Participates in the synthesis of intercellular substance from bone, teeth and capillary endothelium.

HYPOVITAMINOSIS

Too little vitamin C intake can lead to hypovitaminosis. ‘A pronounced deficiency of this vitamin causes a disease called scurvy. The pathogenetic basis of scurvy is the inability to produce collagen. The bundles of collagen in the intracellular substance disappear, which depolymerizes and becomes thin and watery. The most important changes occur in the bones and in the blood capillaries (the bones become brittle, the joints swell). Teeth become loose, gums swollen and bleeding. Scurvy is often accompanied by hypochromic anemia.1,17'19 Insufficient intake of vitamin C usually occurs in children, alcoholics and the elderly. As a result of vitamin C deficiency, symptoms occur that are mostly noticed quickly. These are: bleeding gums, joint and muscle pain, irritability and susceptibility to infections.3 5.6 RECOMMENDED DAILY QUANTITIES AND THERAPEUTIC USE The recommended daily allowance (RDA) for a healthy adult is 60 mg. Today, significantly higher doses are used in prophylaxis and therapy. In 2000, the American Food and Nutrition Board (FNB) published new recommended values ​​for antioxidants (vitamin C, vitamin E, selenium and carotenoids) based on the results of scientific research. According to these data, RDA values ​​increase from 60 to 90 mg for men and 20 from 60 to 75 mg for women. Smokers need to take another 35 mg of vitamin C more.

The use of ascorbic acid is strictly indicated in scurvy. In some conditions (infectious diseases, tuberculosis) increased consumption is justified. It is believed that this acid is effective in the treatment and prophylaxis of a whole range of diseases, from colds through dental caries, gingivitis, hemorrhagic diathesis to the prophylaxis of some cancers.

Many reputable scientists recommend the use of high doses of ascorbic acid even preventively for a healthier life ("mega" therapy or "orthomolecular" therapy). Certainly high doses of vitamin C increase calcium needs. It is also known that the absorption of iron from plant foods is greater if vitamin C is consumed at the same time.

The toxicity of ascorbic acid must be taken into account. High doses can lead to the formation of kidney stones. In addition, there is still a belief that therapies started with high doses do not need to be stopped quickly. The dose should be reduced gradually until the drug is completely discontinued. Rapid dose reduction or discontinuation may lead to scurvy. Vitamin C is mostly given orally. It is used parenterally in patients who eat exclusively parenterally, and in cases where absorption from the gastrointestinal tract is not possible. As vitamin C used in this way is excreted more rapidly in the urine, the daily dose is increased to 200 mg in several divided doses.

Increased vitamin C requirements occur in:

• pregnancy,
• lactating women,
• alcoholics,
• smokers,
• prolonged diarrhea,
• prolonged exposure to low temperatures,
• gastrectomy,
• tuberculosis,
• hyperthyroidism,
• stress,
• infections of various etiologies,
• trauma,
• therapies with certain drugs (estrogens, oral contraceptives, barbiturates, tetracyclines and salicylates).

INTERACTIONS

Interactions between ascorbic acid and different drugs may occur depending on the amount. High doses of ascorbic acid (but not sodium ascorbate) can lower urine pH and cause renal tubular reabsorption of acidic drugs (taken at the same time) or reduce the reabsorption of alkaline drugs (taken at the same time).

Desferioxamine
Concomitant use with ascorbic acid