Role of nerve growth factor in oxidant homeostasis: glutathione metabolism.

Free radicals are generated in the CNS by ongoing oxygen metabolism and biological events associated with injury and inflammation. Increased free radical levels may also persist in some chronic neurological diseases and in the aged. Nerve growth factor (NGF) is a member of the neurotrophin family of proteins that can regulate neuronal development, maintenance, and recovery from injury. NGF protected rat pheochromocytoma PC12 cells, an adrenal chromaffin-like NGF-responsive cell line, from the oxidant stress accompanying hydrogen peroxide treatment by stimulating GSH levels and enzymes in the GSH metabolism cycle and in the GSH/GSH peroxidase antioxidant redox system, a ubiquitous cellular antioxidant system. Specifically, NGF increased gamma-glutamylcysteine synthetase (GCS) activity, the rate-limiting enzyme for GSH synthesis, by 50% after 9 h and GSH levels by 100% after 24 h of treatment. NGF stimulated GSH peroxidase by 30% after 3 days and glucose 6-phosphate dehydrogenase by 50% after 2 days. Treatment with NGF and cycloheximide, or actinomycin D, which inhibit protein and RNA synthesis, respectively, blocked the NGF stimulation of GCS and glucose 6-phosphate dehydrogenase. Increased GSH levels due to NGF treatment were responsible for the significant protection of PC12 cells from hydrogen peroxide-induced stress. Pretreatment of PC12 cells with NGF for 24 h rescued cells from the toxic effects of the extracellular hydrogen peroxide generated by the glucose/glucose oxidase system but did not rescue cells that were subjected to GSH deprivation due to treatment with 10 microM L-buthionine-(S,R)-sulfoximine, an inhibitor of GCS.(ABSTRACT TRUNCATED AT 250 WORDS)