Investigations of the mechanism of selective inhibition of type B mitochondrial monoamine oxidase by phosphatidylserine

90 years of monoamine oxidase: some progress and some confusion

It would not be practical to attempt to deal with all the advances that have informed our understanding of the behavior and functions of this enzyme over the past 90 years. This account concentrates key advances that explain why the monoamine oxidases remain of pharmacological and biochemical interest and on some areas of continuing uncertainty. Some issues that remain to be understood or are in need of further clarification are highlighted.

Halo lipids. 10. Synthesis and cytostatic activity of O-alkylglycerophospho-L-serine analogs

The synthesis of O-alkylglycerophospho-L-serine analogs is described, which represent a new class of cytostatically active agents based on phospholipids. The new compounds were obtained by conversion of O-alkylglycerophosphoric ester analogs by means of phospholipase D and by condensing O-alkylglycerophosphoric acid analogs with protected L-serine followed by the removal of protective groups of the resulting intermediates. The structure of the O-alkylglycerophospho-L-serines was confirmed by fast atom bombardment mass spectrometry. The compounds were found to inhibit the growth of Ehrlich ascites tumor cells in vitro. Half maximum inhibition was observed at concentrations between 7 and 15 microM. For the 1-O-alkyl-2-methoxy glycerophosphoserine only a higher value (30 microM) was found. With most of the substances tested growth was completely inhibited at a concentration of 40 microM.

Biochemistry and genetics of monoamine oxidase

This chapter reviews the two mitochondrial flavin containing isozymes of monoamine oxidase. Section 1, "Biochemistry" discusses assays, substrates and inhibitors, phylogenic and tissue distribution, interactions with lipids, nutritional studies, protein structure, kinetic and chemical mechanistic proposals, and biosynthesis. Section 2, "Inheritance" discusses possible genes involved in expression, genetic studies of platelet MAO-B and fibroblast MAO-A, and chromosomal location. Section 3, "Molecular Genetics" reviews the cloning of their cDNAs, their intra- and interspecies homology and structural inferences made from deduced amino acid sequences. Section 4, "Regulation" gives an overview of levels in development and aging, and effect of drugs. The final section 5, "Role in Human Disease" discusses physiological function and effects of altered levels in humans and animal models including complete absence due to a submicroscopic chromosomal deletion in several human patients.

Urinary trace amine excretion and platelet monoamine oxidase activity in schizophrenia

The relationship between subtypes of schizophrenia classified by ICD-9 and 24-hour urinary beta-phenylethylamine (PEA) and phenylacetic acid (PAA) excretion has been studied. Schizophrenia was divided into two types: paranoid and nonparanoid. Increased urinary PEA excretion was found in paranoid schizophrenics, but urinary PAA excretion did not show any significant difference between schizophrenics and normal subjects. A relationship between platelet monoamine oxidase (MAO) activity and urinary PEA excretion was found. These findings offer some indication that PEA may play a role in the pathogenesis of schizophrenia.

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.

Phosphatidylserine inhibition of monoamine oxidase in platelets of schizophrenics

Phosphatidylserine (PS) has recently been reported to be a specific inhibitor of B-type monoamine oxidase (MAO-B). The effect of added PS liposomes on platelet MAO-B activity was examined in two schizophrenic groups (paranoid and a mixture of residual/undifferentiated) and in normal controls. PS was a potent partial-mixed-uncompetitive inhibitor of the platelet enzyme, whereas other phospholipids tested were without effect. The PS concentration required for 50% inhibition was significantly higher for the paranoid relative to the residual/undifferentiated group and controls. This correlated with a lower mean basal MAO-B activity in this group. Hill plots, as a measure of the concentration dependence of PS sensitivity, however, revealed a similarity between the two schizophrenic groups in regard to inhibitor binding properties. Mean Hill coefficients for both groups were significantly different from the controls. The results were consistent with an in vivo role for PS as an allosteric regulator of platelet MAO-B.