Amygdalin (Vitamin B17)
Amygdalin is a herbal constituent derived from the kernels of various fruits of the Genus Prunus (synonym amygdalus) , which includes the plum, prune, cherry, peach and apricot. The word is derived from the contraction of the chemical term LAE vo-mandeloni TRILE . Krebs also designated laetrile as vitamin B17.
Amygdalin is a naturally occurring glycoside that was originally isolated from apricot pits by the famous biochemist Forest T. Krebs in the 1920s. Other sources include the seeds and pits of apples, cherries, peaches, plums, almonds, papaya, and nectarines. An unusual feature of this carbohydrate is the presence of a cyanide substituent that yields HCN upon hydrolysis by intestinal bacteria. The more common name for amygdalin is "laetrile" and many investigations have been conducted to determine the potential anti-cancer activity of amygdalin. For the most part, it has been found that amygdalin is devoid of any significant activity against tumor cells and can be lethal if ingested in excessive amounts. Ernst Krebs conducted many of the anti-cancer studies of amygdalin and he ultimately named the compound vitamin B-17, although there is no established metabolic need for amygdalin and none of the common vitamin deficiency symptoms occur when this chemical is excluded from the diet of humans.
The most widespread theory ("cyanide theory") on the action of amygdalin was propounded by Ernest Krebs, Jr. in the seventies. Krebs hypothesis: The resulting end products of the hydrolysis of amygdalin are the hydrocyanic acid (HCN) and benzaldehyde. In order to produce these products B-glucuronidase is required. It has been demonstrated that this enzyme is present in cancerous tissue, about 1,000 to 3,600 times higher than in normal tissue. Rhodanase is an enzyme found in the liver cell and is known to be concerned with the conversion of toxic hydrocyanic acid to thiocyanate, a harmless substance. Rhodanase is part of the normal detoxification process of the body. However, it was found that normal cells contain a relatively high concentration of rhodanase and low concentration of B-gluco-ronidase, whereas cancerous cells are high in available B-glucoronidase and low in available rhodanase.
Amygdalin is extracted from almond cake by boiling alcohol; on evaporation of the solution and the addition of ether, amygdalin is precipitated as white minute crystals. Sulphuric acid decomposes it into d-glucose, benzaldehyde, and prussic acid (hydrogen cyanide); while hydrochloric acid gives mandelic acid, d-glucose, and ammonia. The decomposition induced by enzymes may occur in two ways. Maltase partially decomposes it, giving d-glucose and mandelic nitrile glucoside, C6H5CH(CN)O·C6H11O5; this compound is isomeric with sambunigrin, a glucoside found by E.E. Bourquelot and Danjou in the berries of the common elder, Sambucus nigra. Emulsin, on the other hand, decomposes it into benzaldehyde, cyanide, and two molecules of glucose; this enzyme occurs in the bitter almond, and consequently the seeds invariably contain free cyanide and benzaldehyde. An "amorphous amygdalin" is said to occur in the cherry-laurel. Closely related to these glucosides is dhurrin, C14H17O7N, isolated by W. Dunstan and T. A. Henry from the common sorghum or "great millet," Sorghum vulgare; this substance is decomposed by emulsin or hydrochloric acid into d-glucose, cyanide, and p-hydroxybenzaldehyde.
Amygdalin is also called laevomandelonitrile, or Laetrile (some claim that Laetrile is derived from a Latin word meaning "joyfulness") for short, and used to prevent cancer, though this is not approved by the FDA. The US government's National Institutes of Health reports that two clinical trials with laetrile have been published. One Phase I study found that amygdalin caused minimal side effects; the side effects that were seen were similar to the symptoms of cyanide poisoning. One Phase II study with 175 patients had some patients reporting improvements in symptoms, but all patients showed cancer progression 7 months after completing treatment, and it was determined no further tests were necessary. No double-blind, controlled clinical trials have been conducted.