NITRIC OXIDE-MEDIATED MITOCHONDRIAL DAMAGE - A POTENTIAL NEUROPROTECTIVE ROLE FOR GLUTATHIONE

In this study we have investigated the mechanisms leading to mitochond rial damage in cultured neurons following sustained exposure to nitric oxide. Thus, the effects upon neuronal mitochondrial respiratory chai n complex activity and reduced glutathione concentration following exp osure to either the nitric oxide donor, S-nitroso-N-acetylpenicillamin e, or to nitric oxide releasing astrocytes were assessed. Incubation w ith S-nitroso-N-acetylpenicillamine (1 mM) for 24 h decreased neuronal glutathione concentration by 57%, and this effect was accompanied by a marked decrease of complex I (43%), complex II-III (63%), and comple x IV (41%) activities. Incubation of neurons with the glutathione synt hesis inhibitor, L-buthionine-[S,R]-sulfoximine caused a major depleti on of neuronal glutathione (93%), an effect that was accompanied by a marked loss of complex II-III (60%) and complex IV (41%) activities, a lthough complex I activity was only mildly decreased (34%). In an atte mpt to approach a more physiological situation, we studied the effects upon glutathione status and mitochondrial respiratory chain activity of neurons incubated in coculture with nitric oxide releasing astrocyt es, Astrocytes were activated by incubation with lipopolysaccharide/in terferon-gamma for 18 h, thereby inducing nitric oxide synthase and, h ence, a continuous release of nitric oxide. Coincubation for 24 h of a ctivated astrocytes with neurons caused a limited loss of complex IV a ctivity and had no effect on the activities of complexes I or II-III. However, neurons exposed to astrocytes had a 1.7-fold fold increase in glutathione concentration compared to neurons cultured alone. Under t hese coculture conditions, the neuronal ATP concentration was modestly reduced (14%). This loss of ATP was prevented by the nitric oxide syn thase inhibitor, N-G-monomethyl-L-arginine. These results suggest that the neuronal mitochondrial respiratory chain is damaged by sustained exposure to nitric oxide and that reduced glutathione may be an import ant defence against such damage. Copyright (C) 1996 Elsevier Science I nc.