Samuel Eiduson

Platelet glutathione peroxidase and monoamine oxidase activity in schizophrenics with CT scan abnormalities: relation to psychosocial variables

We have previously reported that the activity in platelets of the important antioxidant enzyme glutathione peroxidase (GPx) is inversely correlated with computed tomographic (CT) measures of brain atrophy in a population of patients with chronic schizophrenia, suggesting that low GPx may be a vulnerability factor in those schizophrenic patients with structural brain abnormalities. The significance of this finding has now been explored in a larger clinical population by examining the relation of GPx and CT parameters to psychosocial variables and to the activity of platelet monoamine oxidase (MAO), which has also been reported to be altered in certain schizophrenic populations. In the present study, low platelet GPx and high brain atrophy were found to be associated with DSM-III diagnoses of nonparanoid schizophrenia, a high degree of chronicity, and a predominance of negative symptoms. Contrary to some literature reports, atrophy also correlated with age and length of illness among the schizophrenic patients, although the contribution of these factors was less than that of low GPx, which was itself not age dependent. The ventricle-brain ratio (VBR) and atrophy were highly correlated in a control group of affective disorder patients, but not in the schizophrenic group, where large VBRs were found predominantly in the DSM-III undifferentiated subgroup. The low-GPx/high-atrophy schizophrenic patients had normal platelet MAO levels, and MAO was significantly lower only in the paranoid subgroup, consistent with reported observations. There was no evidence for a neuroleptic-induced effect on either enzyme.

5-hydroxytryptamine in the developing chick brain: its normal and altered development and possible control by end-product repression.

IT now appears to be generally accepted that the biosynthesis, tissue levels and metabolism of 5-hydroxytryptamine (5-HT) may play an important role in brain function (EIDUSON, GELLER, YUWILER and EIDUSON, 1964). Although WEISS (1955) clearly pointed out the importance of the developmental dynamism of the growing organism, few observations have been made on the normal developmental appearance of serotonin in the developing brain and almost none on the consequences of its relatively long-term alteration (KARKI, KUNTZMAN and BRODIE, 1962; HSIA, NISHIMURA and BRENCHLEY, 1963; BOURNE, 1965). In addition, there is little information to suggest the manner in which the biosynthesis of this presumed important biogenic amine is regulated in the brain (or elsewhere). In the course of our experiments, it became evident that our data suggested the possibility of regulation of the biosynthesis of 5-HT by way of end-product repression and (or) inhibition. There appear to be only a few examples in the literature of this type of control mechanism in animal tissues (DEMARS, 1958; WYNGAARDEN and ASHTON, 1959; WALKER, 1960; UMBARGER, 1964). We chose to study regional parts of the developing chick brain because we found the chick to be a very suitable organism especially since, in the embryonic stages, it is encased in its shell and thus virtually a closed system but one which could be entered at will without destroying the organism. Accordingly we first studied the changing levels of 5-HT in distinct regional parts of the normally developing brain. We then altered the normal appearance of 5-HT in the brain by making available to the embryo quantities of the precurser material, 5-HTP. Further, a study of the developing activities of some of the enzymes involved in the biosynthesis and metabolism of 5-HT led to suggestions concerning possible regulation of serotonin in the brain. The observations we have made during the course of these studies serve as the subject matter of this report.

MONOAMINE OXIDASE (EC 1.4.3.4): ISOLATION AND CHARACTERIZATION OF MULTIPLE FORMS OF THE BRAIN ENZYME

Monoamine oxidase (MAO) in crude mitochondrial preparations from rat brain was solubilized, and different MAO‐active fractions were separated by agarose columns and by Sephadex electrophoresis. Any combination of these techniques yielded at least three fractions possessing MAO activity as measured by assays using radioactive serotonin and benzylamine as substrates. The molecular weight of one of the MAO forms was found to be approximately 400,000 daltons while another was at least 1.5 × 106 daltons. The crude mitochondria1 MAO was inhibited by [14C]‐labelled pargyline and then solubilized and the radioactivity of the soluble and particulate MAO was compared to the enzyme activity found in the soluble and particulate fractions. Our studies suggest that appreciable MAO activity is lost upon solubilization and that the conformation of MAO may be altered.

MULTIPLE FORMS OF MONOAMINE OXIDASE IN DEVELOPING BRAIN: TISSUE AND SUBSTRATE SPECIFICITIES

Brains, hearts and livers from newborn and adult rats were assayed for monoamine oxidase activity using gel electrophoretic techniques. The results suggest that each of the tissues possesses multiple forms (isoenzymes) of monoamine oxidase and that these forms are different for the various tissues. Further, the forms of monoamine oxidase in the neonatal tissues differ from those in the corresponding adult tissue. These different forms of monoamine oxidase have different substrate specificities. Using 5‐hydroxy[14C]tryptamine as substrate, we have demonstrated that the monoamine oxidase patterns appearing on the gel do indeed possess monoamine oxidase activity.

EFFECT OF PYRIDOXINE DEFICIENCY ON AROMATIC l-AMINO ACID DECARBOXYLASE IN THE DEVELOPING RAT LIVER AND BRAIN

—Maternal pyridoxine deficiency begun 2 weeks before mating and continued throughout pregnancy and the nursing period resulted in diminished wt. gains in the brain, the liver and the body in the first 16 days of life, as well as lowered levels of the aromatic l‐amino acid decarboxylase in both brain and liver tissue. The fetus was protected from the effect of vitamin B6 deficiency during pregnancy, since at birth the body wt., organ weights, and decarboxylase levels in these tissues were comparable to those of control litters. The brain was affected less than the liver, both in rate of wt. increase and decarboxylase activity.

Corticoid response to stress in the steroid-inhibited rat.

Summary A method is described which permits both the ascorbic acid and corticosteroid content of the same adrenal gland to be determined. Adrenal response to the stress of unilateral adrenalectomy was investigated in normal and hydrocortisone-inhibited rats. Hydrocortisone administration prevented the ascorbic acid depletion which occurred in untreated animals in response to stress. The steroid-inhibited animals, however, exhibited an increase in adrenal corticosterone concentrations equal to that of the saline treated controls, although the basal level from which this increase occurred was markedly lower. It is suggested that pre-treatment with hydrocortisone may alter the physiological “set” at which the corticoid component of the stress response is operating, but does not inhibit the response itself.

Interaction of 1-methyl-4-phenylpyridinium ion with human platelets

When uptake of the Parkinsons syndrome inducing neurotoxin MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) and its major brain metabolite MPP+ (1-methyl-4-phenylpyridinium ion) by human platelets were compared in platelet rich plasma, a much higher rate was observed for the metabolite. The uptake process was saturable (Km = 6.8 microM; Vmax = 0.064 nmole/min/mg protein) and could be blocked by inhibitors of serotonin uptake. The accumulation of MPP+ by the platelets was accompanied by a decrease in intracellular ATP and an inhibition of mitochondrial state 3 respiration. These findings are consistent with earlier reports of the effect of MPP+ on isolated mitochondria as a potential cytotoxic mechanism, but also demonstrate that the dopamine uptake system is not the only means by which this metabolite can be efficiently transported into cells.

Platelet monoamine oxidase in a pedigree with schizophrenia: an interlaboratory project.

Conflicting reports on the association between platelet MAO activity and schizophrenia prompted a critical review and determinations on identical samples at one laboratory in Sweden and one in the USA. Samples originated from eight schizophrenics and 27 relatives belonging to a large pedigree, thus ensuring biological homogeneity.

Oxidation of p-phenylenediamine and adrenaline in enzymic and copper-catalysed reactions.

THE study of the oxidation of amines by serum has taken two directions. One, involving the measurement of the oxygen consumed in reactions of this type, is characterized by the studies of the enzyme, ceruloplasmin (HOLMBERG and LAURELL, 1948, 1951~1, b). The second, based upon colour formation, is mainly concerned with whole serum and the amines, p-phenylenediamine, N,N-dimethyl-p-phenylenediamine, and adrenaline (LEACH and HEATH, 1956; LEACH et al., 1956; AKFRFELDT, 1957~1, 6 ; ABOOD, 1957), Of late, these two lines have merged, with the suggestion that the colour forming component of serum could be ceruloplasmin (LEACH et at., 1956). Recent reports (subsequently disputed) that the blood of schjzophrenics is high in oxidase activity (AKERFELDT, 1957a, b; ABOOD, 1957; BROWN, 1957; ANGEL et a/., 1957; ABOOD et al., 1957) stimulated in this laboratory a study of the properties of ceruloplasmin. In the course of this investigation, findings contrary to some of the published results came to light and they are reported below.

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.