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

Modulation of monoamine oxidase activity in different brain regions and platelets following exposure of rats to methylmercury

Monoamine oxidase (MAO; EC 1.4.3.4) is known to have an important role in the regulation of biogenic amines in the brain and peripheral tissues. It is also known that circulating platelets represent an excellent model for an easy assessment of the effect of MAO-B inhibitors in extracerebral tissue. The present study was carried out to determine the effects of methylmercury (MeHg) on the activity of MAO in synaptosomes of different brain regions of male Sprague-Dawley rats as well as in rat blood platelets both in vitro and in vivo. MeHg pretreatment inhibited the activity of MAO in the synaptosomes of the cortex, hypothalamus, hippocampus, striatum, cerebellum, and brain stem in a concentration-dependent (0-10 microM) manner. The threshold concentration of MeHg for such inhibition in different brain synaptosomes was found to be the same (i.e., 1 microM) except for in the rat striatum it was 2.5 microM, and the IC50 value for MeHg was found to be around 2.1 microM. Significant inhibition of the MAO activity was also observed in synaptosomes of the cortex, cerebellum, hypothalamus, and hippocampus as well as in platelets of rats 24 h after treatment by gavage with a total cumulative dose of 35 mg/kg (5 mg/kg/day for 7 days). The decrease of such activity was found to be at maximum in different brain synaptosomes and platelets 24 h following treatment with a cumulative total dose of 75 mg/kg (7.5 mg/kg/day for 10 days); the treated animals showed signs of ataxia under these conditions. The data have further shown that methylmercury is capable of inhibiting the MAO activity in different brain synaptosomes to different degrees but without showing any specificity towards any specific brain region. The present in vivo results suggest that the platelet MAO activity may be used as a potential biomarker of early neurotoxicity due to repeated exposure to MeHg in rats.

Monoamine oxidase gene transcription in human cell lines: treatment with psychoactive drugs and ethanol

In the present study transcriptional activities has been measured with different fragments of the 5'-flanking sequence of the human monoamine oxidase (MAO) genes linked to human growth hormone which was used as a reporter gene. SH-SY5Y neuroblastoma cells and 1242 MG glioma cells were compared under basal conditions as well as after treatments with different drugs. Under basal conditions, the relative reporter activities of the different promoter fragments were similar for both cell lines. No changes in promoter activities, were observed when cells were treated with L-deprenyl, lithium chloride or raclopride. In contrast, increases (2-3-fold) in both reporter gene expression and enzyme activity were observed after ethanol treatment of cells transfected with MAO-B fragments. Gel retardation analysis showed that ethanol caused changes in transcription factor binding to the MAO-B core promoter in both the SH-SY5Y and 1242 MG cell lines in a cell-type specific fashion.

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.

Modulation of the stress response by ethanol in the rat frontal cortex

Microdialysis was used to characterize the effects of two doses of ethanol, stress, and their interaction on the dopaminergic system. Saline-treated animals showed no changes in levels of dopamine (DA) or dihydroxyphenylacetic acid (DOPAC). Neither a 0.5- nor a 2-g/kg IP injection of ethanol had an effect on DA or DOPAC in resting animals. Immobilization caused marked increases in DA levels and smaller increases in DOPAC. Pretreatment with 0.5 g/kg ethanol did not reduce the stress-induced increase in DA or DOPAC. However, pretreatment with 2 g/kg ethanol strongly reduced and antagonized the stress-induced increases in DA and potentiated the stress-induced increase in extracellular DOPAC. Our data show that ethanol can have different, dose-dependent effects in resting vs. stressed animals, that it has different effects on DA and DOPAC, and that the high dose antagonized stress-induced increases in DA. The latter adds biochemical evidence to the tension-reduction hypothesis of ethanol by perhaps implicating a reduction in the DA stress response by ethanol as a contributing factor in the development of alcoholism.