Purification of human blood platelet monoamine oxidase

Platelet Function in Alcoholics Treated with Disulfiram

Disulfiram is usually used in alcoholics as aversion therapy. It binds to various enzymes and pro teins in blood and in tissues. In particular, it inhibits the thromboxane synthetase in human platelets and, for this reason, it has been surmised that disulfiram has a possible effect on platelet function. So far, disulfiram failed to confirm this hypothesis in healthy volunteers. However, it appears able to decrease the threshold collagen concen tration for platelet aggregation. Our aim was to evaluate the effect of disulfiram on the platelet function of alco holics. In this study, 24 alcoholics, divided in group A (12 abstinent patients with disulfiram 200 mg/day), group B (12 abstinent patients without treatment), and 17 normal controls, are reported. Different tests were performed at time 0 (acute alcohol intoxication), time 2, and time 15 after the beginning of abstinence. A significant increase was observed in bleeding time (BT) of group B and in platelet count of both groups. No modification was seen in prothrombin time. In group A, a significant increase of platelet aggregation under adenosine diphosphate (ADP; 2 μ M) stimulus was observed. Whereas no difference was seen in platelet 5-hydroxytryptamine (5-HT), serum 5-HT increased significantly at time 15 in group A. We con clude that the increase in serum 5-HT was probably due to the inhibition of monoamine oxidase (MAO) promoted by disulfiram, followed by an activation of MAO induced by disulfiram.

Isoelectric focusing of monoamine oxidase subtypes as identified by MAO inhibitors

Monoamine oxidase from various human tissues from several individuals was labeled with [3H]pargyline and solubilized by means of Triton X-100 or Triton X-100 and urea. The specificity of the labeling was assessed using various selective, reversible and irreversible inhibitors as pharmacologic tools in competition experiments. The labeled material was submitted to isoelectric focusing on polyacrylamide gels according to one- and two-dimensional electrophoretic procedures and with fluorographic detection. While the differences in electrophoretic mobility of the two subtypes, MAO-A and MAO-B, could be replicated the subtypes showed identical although heterogeneous charges in isoelectric focusing. This contrasts with recent findings of clear differences in the primary structure of monoamine oxidase subtypes and thus needs further clarification.

In vivo relationship between monoamine oxidase type B and alcohol dehydrogenase: effects of ethanol and phenylethylamine

The role of acute ethanol (2.5 g/kg i.p.) and phenylethylamine (100 mg/kg i.p.) on the brain and platelet monoamine oxidase activities, hepatic cytosolic alcohol dehydrogenase, redox state and motor behaviour were studied in male rats. Ethanol on its own decreased the redox couple ratio, as well as, alcohol dehydrogenase activity in the liver whilst at the same time it increased brain and platelet monoamine oxidase activity due to lower Km with no change in Vmax. The elevation in both brain and platelet MAO activity was associated with ethanol-induced hypomotility in the rats. Co-administration of phenylethylamine and ethanol to the animals, caused antagonism of the ethanol-induced effects described above. The effects of phenylethylamine alone, on the above mentioned biochemical and behavioural indices, are more complex. Phenylethylamine on its own, like ethanol, caused reduction of the cytosolic redox ratio and elevation of monoamine oxidase activity in the brain and platelets. However, in contrast to ethanol, this monoamine produced hypermotility and activation of the hepatic cytosolic alcohol dehydrogenase activity in the animals. The results suggest that some of the toxic actions of ethanol in rats may be mediated through the activation of monoamine oxidase type B, with the consequent depletion of the endogenous levels of phenylethylamine. The data appear to support the concept of phenylethylamine involvement in affective disorders.