Biochemical and toxicological properties of the oxidation products of catecholamines

The normal catabolism of catecholamines proceeds through enzymatic pathways (monoaminooxidase, catechol-o-methyltranserase, and phenolsulphotransferase). In addition, nonenzymatic oxidative pathways might take place since catechols are readily oxidized. In this review article, the pathways of formation of the oxidation products of catecholamines and their reactions are described. The interactions of these products with different biological systems and their toxicity are examined. Among the reactions known to occur is that with sulfhydryls, which results in either a covalently linked adduct or disulfide production. Another interesting pathway to toxicity involves the oxidation of these catecholamine products by oxygen, with the formation of damaging oxygen-derived species. The action of the oxidation products of catecholamines is outlined, with special attention to the nervous and cardiac systems.

Toxicity of aminochromes

The first part of the present review deals with the chemical and enzymatic synthesis of adrenochrome and other aminochromes from the corresponding catecholamines. A description of the most significant pathways of formation and the reactivity of the aminochromes is presented. In the second part of the toxicity of aminochromes, mainly at the cardiac and CNS level, is described and some of the molecular mechanisms of the toxic action are outlined. The toxicity of the aminochromes appears to depend mainly on the production of reduced oxygen species through redox cycling. The interaction of aminochromes with sulfhydryl groups and the induced depletion of oxygen, ascorbate and glutathione are additional mechanisms resulting in noxious effects at a cellular level.