Metabolic alterations produced by 3-nitropropionic acid in rat striata and cultured astrocytes: Quantitative in vitro ¹H nuclear magnetic resonance spectroscopy and biochemical characterization

Quantitative high resolution in vitro ¹H nuclear magnetic resonance spectroscopy was employed to study the metabolic effects of 3-nitropropionic acid associated with aging from perchloric acid extracts of rat striata. Systemic injection of 3-nitropropionic acid in rats at a dose of 10 mg/kg/day for seven consecutive days significantly impaired energy metabolism in rats one, four and eight months of age as evidenced by a marked elevation of succinate and lactate levels. However, a significant decrease in N-acetyl-L- aspartate level, a neuronal marker, was observed in four- and eight-month- old rats but not in one-month-old rats. This would indicate that rats at four to eight months are more susceptible to 3-nitropropionic acid than those at one month. A significant decrease in GABA level was observed in four-month- old 3-nitropropionic acid-treated rats, which is consistent with the literature that GABAergic neurons are particularly vulnerable to 3- nitropropionic acid treatment. In addition, glutamine and glutamate levels were markedly decreased at four and eight months in 3-nitropropionic acid- treated rats. Since glutamine is synthesized predominantly in glia, the observation above suggests that 3-nitropropionic acid intoxication may involve perturbation of energy metabolism, glial injury and consequent neuronal damage. Astrocytes which are essential in the metabolism of glutamate and glutamine were used to further assess 3-nitropropionic acid- induced toxicity. Glial proliferation, mitochondrial metabolism and glutamine synthetase activity were all reduced by 3-nitropropionic acid treatment with a concomitant increase, in a dose-dependent manner, of lactate levels, suggesting that 3-nitropropionic acid is also detrimental to astrocytes in vivo and thus may affect metabolic interaction between neurons and glia. These results not only imply that 3-nitropropionic acid blocks energy metabolism prior to exerting neurotoxic damage but also demonstrate that the degree of energy depletion determines the detrimental effects of 3- nitropropionic acid. In the present study, we also demonstrate that glutamate and glutamine levels as well as astrocytic functions may play pivotal roles in 3-nitropropionic acid-induced striatal lesions.