Methylmalonic acidemias consist of a group of inherited metabolic disorders caused by deficiency of
methylmalonyl-CoA mutase activity and biochemically characterized by methylmalonate (MMA) accumulation, impairment mitochondrial oxidative metabolism and reactive species production. Preliminary studies with
nitric oxide synthase (NOS) inhibitors have suggested that
nitric oxide (NO) plays a role in the
convulsant effect of MMA. However, definitive biochemical and electrophysiological evidence of the involvement of NO in the convulsions induced by MMA are lacking. In this study, we investigated whether the inhibition of NOS by
7-nitroindazole (7-NI, 3-60mg/kg, i.p.) altered the convulsions,
protein oxidative damage, NO(x) (NO(2) plus NO(3)) production and Na(+),K(+)-
ATPase activity inhibition induced by MMA. 7-NI decreased striatal NO(x) content, but increased
seizures and protein carbonylation induced by MMA (6mumol/striatum). The intrastriatal injection of
l-arginine (50nmol/0.5mul), but not of d-
arginine (50nmol/0.5mul), increased striatal NO(x) content and protected against MMA-induced electroencephalographic
seizures, striatal protein carbonylation and Na(+),K(+)-
ATPase inhibition. Furthermore,
l-arginine (50nmol/0.5mul) and MMA had no additive effect on NO(x) increase. These results are experimental evidence that endogenous NO plays a protective role in the convulsions and acute neurochemical alterations induced by this organic
acid.