Manganese-mediated increase in the rat brain mitochondrial cytochrome P-450 and drug metabolism activity: susceptibility of the striatum.

The present study describes the high degree of sensitivity of the mitochondrial fraction of the striatum to Mn++-mediated perturbations in mixed-function oxidase activity. This study also defines the brain mitochondrial cytochrome P-450 subject to increase by Mn++. In the striatum of Mn++-treated animals (7 days) hydroxylation of benzo(a)pyrene and D-amphetamine was significantly increased in both the mitochondrial and the microsomal fractions. The effects were more pronounced in the mitochondrial fraction where hydroxylation activities were increased by 2- to 3-fold. SKF-525A (2-diethylaminoethyl-2,2-di-phenylvalerate hydrochloride) effectively inhibited NADH-dependent hydroxylation of both substrates by the mitochondrial fraction. In the Mn++-treated animals, significant increases in mitochondrial and microsomal cytochrome P-450 concentration were also noted. In the mitochondria, the hemoprotein concentration was increased by nearly 2.5-fold; in the microsomes the concentration of the cytochrome was increased by about 1.6-fold. Mn++ appeared to selectively increase cytochrome P-450 concentration since that of other cytochromes including the mitochondrial b, c1, c and a, and the microsomal cytochrome b5 was not increased. In addition, the activity of mitochondrial delta-aminolevulinate synthetase was not increased and that of the microsomal heme oxygenase was inhibited by Mn++ treatment. It is suggested that increases in the microsomal and the mitochondrial cytochrome P-450 may reflect intrinsic properties of cytochrome P-450 isozymes in these organelles, including their turnover rate, preferential utilization of heme and/or susceptibility to degradation. The possible relevance of the findings to Mn++ neurotoxicity of dopamine pathways is discussed.

Selective vulnerability of glutathione metabolism and cellular defense mechanisms in rat striatum to manganese.

The present findings provide experimental evidence for the hypothesis that compromised cellular defense mechanisms, i.e., glutathione (GSH), GSH-peroxidase and catalase in the brain may be involved in neuronal degeneration caused by manganese (Mn) neurotoxicity. Moreover, data are presented demonstrating that the striatum is particularly susceptible to the deleterious effects of Mn. Specifically, exposure to subchronic MnCl2 produced significant reductions in GSH-peroxidase activity in the cytosol and mitochondrial fractions of the whole brain and the striatum. The decrease in GSH-peroxidase was most pronounced in the mitochondrial fraction of the striatum where the activity was reduced to 35% of the control. Catalase activity was also decreased in the striatum of rats treated with Mn but not in the whole brain. GSH content was markedly depleted (20% of the control) in the striatum, although only modestly decreased in whole brain (80% of the control). The alterations in the above parameters were accompanied by depletion of dopamine and dopamine metabolites in the striatum. The treatment of rats with Mn also decreased the activity of oxidized glutathione-reductase; the same treatment increased the activity of gamma-glutamyltranspeptidase. The activity of gamma-glutamylcysteine synthetase was not altered by Mn. The possible relevancy of the findings of this study to understanding the mechanism of Mn neurotoxicity of dopamine systems is discussed.

Different roles for type A and type B monoamine oxidase in regulating synaptic dopamine at D-1 and D-2 receptors associated with adenosine-3',5'-cyclic monophosphate (cyclic AMP) formation.

The roles of multiple forms of monoamine oxidase (MAO) in regulating the synaptic concentration of dopamine, in the vicinity of dopamine receptors associated with cyclic AMP formation, was examined in striatal slices of the rat. d-Amphetamine (0.1 mumol/l to 20 mumol/l) caused a concentration-related increase in cyclic AMP formation, which correlated (in superfusion experiments) with the release of endogenously-formed dopamine. In the presence of (-)sulpiride (50 mumol/l), cyclic AMP formation was significantly increased at every concentration of d-amphetamine tested. At the same time, this concentration of (-)sulpiride had no effect on DA release. Inhibition of type A MAO with clorgyline (0.1 mumol/l) significantly enhanced the increase in cyclic AMP formation seen after d-amphetamine. By contrast, inhibition of type B MAO with deprenyl (0.1 mumol/l) was without effect on this action of d-amphetamine. At high concentrations of d-amphetamine (20 mumol/l), however, deprenyl + clorgyline treatment enhanced cyclic AMP formation to a greater extent than with clorgyline alone. Similar results could be obtained at lower concentrations of d-amphetamine (5 mumol/l), but only after inhibition of the dopamine neuronal reuptake system with nomifensine (30 mumol/l). Furthermore, in the presence of nomifensine, deprenyl alone was also able to significantly increase the cyclic AMP formation seen after d-amphetamine (5 mumol/l). In the presence of (-)sulpiride, relatively similar results were obtained following all MAO inhibitor treatments. These findings support the notion that type A MAO plays the primary role in regulating dopamine concentrations at D-1 and D-2 receptors within synapses of rat striatal tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Opposing actions of D-1 and D-2 dopamine receptor-mediated alterations of adenosine-3',5'-cyclic monophosphate (cyclic AMP) formation during the amphetamine-induced release of endogenous dopamine in vitro.

Changes in the formation of cyclic AMP following d-amphetamine (0.1 to 20 mumol/l) were examined in vitro in striatal slices of the rat. d-Amphetamine caused a dose-related increase in cyclic AMP content. This action of d-amphetamine was abolished by tissue pretreatment with reserpine (2.5 mg/kg, i.p.) and 3-iodotyrosine (1 mmol/l). By contrast, both clorgyline (0.1 mumol/l) and nomifensine (30 mumol/l) enhanced the d-amphetamine-induced increase in cyclic AMP formation. In superfusion experiments, a strong correlation between endogenous dopamine and cyclic AMP release was observed before, during and after d-amphetamine exposure. Finally, Sch 23390 (10 mumol/l) abolished while (-)sulpiride (10 mumol/l) enhanced the amphetamine-induced increase in cyclic AMP content. These results suggest that d-amphetamine enhances the formation of cyclic AMP through the release of endogenous dopamine into the synapse where it can interact with both D-1 and D-2 dopamine receptors. These results provide direct evidence that the antagonistic properties of D-1 and D-2 receptors on cyclic AMP formation are apparent at striatal synapses during release of endogenous neuronal dopamine.