RESUMO
The cardiotoxicity of allylamine (AA) is considered to be mediated by metabolism to the highly reactive aldehyde, acrolein (ACR). The toxicity of AA to myocardial myocyte reaggregate cultures (MMR) was assessed by measuring percentage beating as a marker of functional viability. The studies demonstrated that AA toxicity could be prevented by inhibitors of benzylamine oxidase (BZO) but not by inhibitors of monoamine oxidase A or B. Addition of exogenous BZO markedly potentiated the toxicity, an effect that could be blocked by semicarbazide, an inhibitor of BZO. The present studies support the view that AA is metabolized by BZO to the proximate toxicant, ACR. In serum-free cultures, high concentrations (0.5-2.5 mm) of AA were required to cause any loss of viability, and as the concentration of serum in the medium was increased so the loss of viability was induced by AA; in MMR maintained in 50% foetal calf serum, all viability was lost after 3 hr of exposure to 100 mum-AA. Mercaptoethanesulphonate (MESNA), a scavenger of reactive species that is known not to penetrate myocytes, prevented the toxicity both of 100 mum-AA and 100 mum-ACR to MMR in serum-supplemented medium. In contrast, when MMR in serum-free medium were exposed to high concentrations of AA, MESNA had no moderating effect. These findings suggest that AA undergoes extracellular metabolism to ACR in serum-supplemented medium because of the presence of BZO in serum. It is clear that extracellular metabolism is of great importance in the pathogenesis of AA-induced toxicity to MMR in serum-supplemented medium. The toxicity of AA was also prevented by the iron chelator desferrioxamine (DF) at a concentration shown not to inhibit significantly the activity of BZO. ACR toxicity too, was inhibited by DF. This suggests a role for free radicals in the toxicity of AA to MMR, as DF chelates iron, thus preventing the catalysis of free radical reactions (Halliwell and Gutteridge, 1986). Addition of alpha-tocopherol succinate, an inhibitor or lipid peroxidation, to the cultures also reduced the toxicity of AA, which provides some evidence of the role of lipid peroxidation in the mechanism of AA toxicity to MMR. That process too, commonly involves free radical mechanisms. The results are discussed with reference to the action of AA in vivo, in order to consider whether extracellular metabolism might be of importance in the mechanism of toxicity to the whole animal.
RESUMO
This study investigated the response of chick myocardial myocyte reaggregates (MMR) to allylamine, which is specifically toxic to the cardiovascular system, and its putative toxic metabolite, acrolein. Toxicity was assessed by determining cellular ATP content, spontaneous beating and ultrastructural alterations. Both allylamine and acrolein caused a dose-dependent loss of beating and depletion of cellular ATP content. Treatment with either 10 or 100 mum-allylamine produced marked alterations in reaggregate tissue morphology at all times, which was characterized by widespread myocyte necrosis and a reduction in tissue compactness. Exposure of aggregates to acrolein produced generalized tissue destruction following administration of either 10 or 100 mum-acrolein. The concentration of allylamine required to cause loss of MMR beating was greatly increased when incubations were carried out in serum-free medium. It is suggested that the presence of benzylamine oxidase in serum contributes to the toxicity of allylamine to MMR, by metabolizing allylamine to acrolein. This proposal is supported by the finding that the related amines n-methylallylamine and diallylamine had no effect on spontaneous beating, which may be because they are very poor substrates for benzylamine oxidase. The data presented demonstrate that allylamine is highly toxic to MMR, and we believe that further investigations into the role of serum in allylamine toxicity would improve our understanding of the biochemical basis of its action.
