Heterocyclic amines, also sometimes referred to asHCAs, are chemical compounds containing at least oneheterocyclic ring, which by definition has atoms of at least two different elements, as well as at least oneamine (nitrogen-containing) group. Typically it is a nitrogen atom of an amine group that also makes the ring heterocyclic (e.g.,pyridine), though compounds exist in which this is not the case (e.g., the drugzileuton). The biological functions of heterocyclic amines vary, includingvitamins andcarcinogens. Carcinogenic heterocyclic amines are created by high temperature cooking of meat and smoking of plant matter liketobacco. Some well known heterocyclic amines areniacin (vitamin B3), nicotine (psychoactive alkaloid and recreational drug), and thenucleobases that encode genetic information in DNA.
The compoundpyrrolidine is composed of molecules that contain a saturated ring of five atoms. This cyclic structure is composed of one atom of nitrogen and four carbon.Nicotine is a molecule containing a pyrrolidine ring attached to a ring of pyridine (other heterocyclic amine). Nicotine belongs to a group of compounds known asalkaloids, which are naturally occurring organic compounds with nitrogen in them.Pyrrole is another compound made up of molecules with a five-membered heterocyclic ring. These molecules are unsaturated and contain a nitrogen atom in the ring. Four pyrrole rings are joined in a ring structure called aporphyrin.The rings ofporphyrin are components ofhemoglobin,myoglobin,vitamin B12,chlorophyll, andcytochromes. In the centers ofheme in hemoglobin, myoglobin, and cytochromes, iron is an ion; in the first two, iron ion is bound to oxygen.
The structure ofpyridine is similar to that ofbenzene except that a nitrogen atom replaces one carbon atom. Pyridine is used as a flavoring agent. The pyridine ring is part of two B vitamins:niacin andpyridoxine.Niacin, also called nicotinic acid, is found in most organisms. Via metabolism, it becomes nicotinamide adenine dinucleotide NAD, acoenzyme which is involved in oxidation and reduction in metabolic cells. A deficiency of niacin leads to a disease calledpellagra.Pyridoxine or vitamin B6, it becomes a major compound in the metabolism ofamino acids.
Pyrimidine is a heterocyclic amine that contains two nitrogen atoms in an unsaturated six-membered ring. An example of a molecule that contains pyrimidine isthiamine, which is also known as vitamin B1. Thiamine deficiency producesberiberi.Pyrimidine is a component of thenucleobases cytosine, uracil, and thymine. The other two nucleobases,adenine andguanine, are also heterocyclic amines calledpurines; they are composed of a fused pyrimidine andimidazole.
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Some HCAs found in cooked and especially burned meat are knowncarcinogens. Research has shown thatheterocyclic amine formation in meat occurs at high cooking temperatures.[1] Heterocyclic amines are the carcinogenic chemicals formed from the cooking of muscle meats such asbeef,lamb,pork, fish and poultry.[1][2] HCAs form whenamino acids andcreatine (a chemical found in muscles) react at high cooking temperatures.[1]
Colorectal cancer is associated with high intakes of HCAs found in meat cooked at high temperature.[3]
Six hours of marinating in beer or red wine cut levels of two types of HCA in beef steak by up to 90% compared with unmarinated steak.[4]
Harmane, a β-carboline alkaloid found in meats is "highly tremorogenic" (tremor inducing).[5][6] While harmane has been found in roughly 50% higher concentrations in patients withessential tremor than in controls,[7] there is no direct correlation between blood-levels and levels of daily meat consumption, suggesting a difference in metabolism of this chemical plays a greater role.[6] These chemicals are formed during the cooking process of meat, particularly the longer they are cooked, and the more they are exposed to high temperatures during cooking.[8][9]