A comparison of platelet monoamine oxidase activity and phosphatidylserine content between chronic paranoid schizophrenics and normal controls.

Mitochondrial monoamine oxidase (MAO), type B, has been implicated in the etiology of schizophrenia. We have found the phospholipid, phosphatidylserine (PS) to be a highly specific inhibitor of MAO-B, which has led us to postulate that the PS-MAO interaction might offer a basis for the lower MAO levels observed in platelets from certain schizophrenic populations. In this study we compared platelet MAO activity with phospholipid composition in a group of normals and chronic paranoid schizophrenics. The phospholipids in platelets and erythrocytes were extracted and separated by high-performance liquid chromatography into major classes phosphatidylcholine (PC), phosphatidylethanolamine, lysophosphatidylethanolamine, phosphatidylinositol and PS. The paranoid subjects showed statistically significantly lower MAO activity as well as higher mean levels of PS and lower levels of PC in both platelets and erythrocytes, consistent with our hypothesis. The Ca2+-stimulated synthesis of serine-lipid in platelets was also monitored by incorporation of radioisotope into lipid extracts from 14C-labelled serine substrate, and no significant differences were found between subjects groups with respect to this parameter.