In this article we will discuss about:- 1. Historical Review of Thiamine 2. Properties of Thiamine 3. Distribution 4. Functions 5. Deficiency 6. Daily Requirement.
Historical Review of Thiamine:
(Aneurine, Vitamin B1) (Antineuritic Factor, Antiberiberi Substance)
Beriberi, a disabling condition, was endemic for centuries in the Orient and Pacific islands and this was finally proved to be deficiency disease. An analogous condition was produced artificially in hens in 1890 when Eijkman found out that birds fed with polished rice developed polyneuritis.
In 1911 Dr. Casimir Funk cured polyneuritis in birds by administering concentrate of rice polishing. In 1926 this vitamin in pure form was isolated by Jansen and Donath and in 1936 the vitamin was synthesised by Williams and his coworkers.
Free thiamine is a basic substance containing a pyrimidine and a thiazole ring. It is generally prepared as a thiamine hydrochloride. In yeast it is found combined with a pyrophosphate. It contains sulphur and a primary amino group.
Properties of Thiamine:
It is a white crystalline substance, water-soluble and destroyed at elevated temperature unless the pH is low; but can stand short boiling up to 100°C. Hence, it is only partly lost in cooking or canning processes.
Autoclave, long boiling or boiling with alkali, destroys it. But it is stable in acid medium. On oxidation it produces thiochrome which gives fluorescence and its oxidation, under controlled condition, has become the basis of assay of this vitamin.
Distribution of Thiamine:
i. Vegetable Sources:
Cereals (in the husk and embryo), pulses, nuts and green vegetables, i.e., beets, carrots, turnip, lettuce, cauliflower, pears, beans, etc., are rich sources. Polished rice and white flour are poor in this vitamin content.
ii. Animal Sources:
Generally poor. Yeast and egg-yolk contain fair amount (100 i.u.).
Free thiamine is absorbed readily from the small intestine. It is not much stored in the body. About 25% of the ingested vitamin B1 is excreted in the urine. It has also been produced synthetically. An international unit of thiamine is equal to 3 µ gm of thiamine hydrochloride.
Functions of Thiamine:
i. The pyrophosphate ester of thiamine is a coenzyme (cocarboxylase) and being bound to a specific protein (apoenzyme) together with α-lipoic acid and Mg++ forms the active enzyme carboxylase, which is responsible for the oxidative decarboxylation of pyruvic acid, α-ketoglutaric acid and other keto acids.
It is an essential step in the final oxidation of sugar in the tissues and brain. In the absence of this vitamin, pyruvic and lactic acids fail to be broken down, and hence, accumulate in blood and tissues. Most of the deficiency signs are due to the abnormal accumulation of these acids (pyruvic and lactic acids).
ii. It also helps the enzyme system which is responsible for the synthesis of fats from carbohydrates and proteins. Thiamine pyrophosphate is also a coenzyme for the transketolase reaction in the phosphogluconate oxidative pathway of carbohydrate metabolism.
Deficiency of Thiamine:
Beriberi may be classified as dry, wet, cardiac or mixed type:
i. Dry beriberi is associated with disorders of the nervous system.
ii. In wet beriberi, the polyneuritis is accompanied by oedema.
iii. Cardiac beriberi is associated with signs of congestive cardiac and circulatory failure.
iv. The mixed type in which any combinations of the above may be found.
General Manifestations in Beriberi:
i. There is oedema specially in the legs.
ii. Loss of appetite, atony of the gastro-intestinal tract, hypochlorhydria, etc. All these are due to lack of energy derived from the imperfect metabolism of carbohydrate.
iii. Blood changes: Lactic and pyruvic acids accumulate in blood.
iv. Same changes are found to take place in peripheral nerves, brain and cerebrospinal fluid. The peripheral neuritis or polyneuritis, with the tenderness of muscles of feet and legs, ataxia and muscular weakness, is a characteristic feature. These defects are due to diminished utilisation of carbohydrate and production of energy. Pyruvic acid accumulates in the brain stem, brain and cerebrospinal fluid.
v. Heart also becomes weak and enlarged, which is obviously due to accumulation of pyruvic acid. Cardiac failure may also occur in some subjects. In rats, marked bradycardia occurs.
vi. Cerebral beriberi has also been reported. In this disease the grey matter of the cerebrum round the third ventricle is affected. In certain fishes there are heatlabile enzymes which destroy thiamine. Foxes, fed with raw uncooked fishes, develop a type of spastic paralysis (Chastek paralysis). This has been attributed to presence of a thiamine-splitting enzyme in raw fishes.
Daily Requirement of Thiamine:
About 1.8 mgm for a diet producing 3,000 calories. The requirement is increased in pregnancy, lactation, heavy muscular work, high carbohydrate diet, etc. Daily intake for children range from 0.4 mgm for infants to 1.3 mgm for pre-adolescents. Requirement of thiamine increases in shock, haemorrhage, serious illness or injury, during oral administration of antibiotics, etc.