Investigation on possible antioxidative properties of the NMDA-receptor antagonists ketamine, memantine, and amantadine in comparison to nicanartine in vitro.

Possible antioxidative properties of three N-methyl-D-aspartate (NMDA)-receptor antagonists, the anesthetic ketamine and the antiparkinson drugs memantine and amantadine were investigated in vitro on the microsomal cytochrome P450 (P450) system of rat livers and on rat whole blood chemiluminescence in comparison to nicanartine, a substance with known antiatherosclerotic, hypolipemic and antioxidative capacity. For this purpose, the effects on NADPH- and iron-stimulated lipid peroxidation (LPO), hydrogen peroxide (H2O2) production, and NADPH- and iron-stimulated lucigenin (LC) and luminol (LM) amplified chemiluminescence (CL) were examined using rat liver microsomes. Additionally, the influence on LM amplified whole blood chemiluminescence after zymosan activation of polymorphonuclear leukocytes (WB-CL) was investigated. Furthermore, binding to P450 and effects on P450 mediated monooxygenase function, as measured by the model reactions ethoxyresorufin O-deethylation (EROD), ethoxycoumarin O-deethylation (ECOD), and ethylmorphine N-demethylation (END), were assessed. Nicanartine concentration dependently reduced LPO and H2O2 production already at a concentration of 1 microM, whereas LC and LM amplified CL and WB-CL were not affected. EROD and END were concentration dependently diminished starting at 1 microM, and ECOD already at 0.1 microM. Ketamine decreased LPO, H2O2 production and LM and LC amplified CL, starting at 100 microM. WB-CL was significantly diminished already at 10 microM. EROD and ECOD were inhibited at 10 and 100 microM and END at 100 microM. With memantine a concentration dependent inhibition of LPO and WB-CL was seen at 100 and 1000 microM and a reduction of LC and LM amplified CL only at 1000 microM. H2O2 production was not affected. EROD and ECOD were significantly diminished by a concentration of 100 microM. No effect was observed on END. Amantadine significantly reduced LPO and WB-CL, but only at 1000 microM. H2O2 production and LC and LM amplified CL were not affected. EROD was significantly diminished at 100 microM, whereas no influence was seen on ECOD and END. Nicanartine displayed type II or reverse type I, ketamine, memantine and amantadine type I substrate binding to P450. The highest binding affinity to P450 was seen with nicanartine, followed by ketamine, memantine and then amantadine. These results demonstrate, that all four substances seem to act as radical scavengers and/or as inhibitors of the oxidative function of P450. All four substances seem to interfere with the monooxygenase function of P450. This may result in a possible influence on the biotransformation of endogenous as well as of foreign compounds. The effects of nicanartine were much more pronounced than those of ketamine, memantine, and amantadine.