Brain inflammation enhances 1-methyl-4-phenylpyridinium-evoked neurotoxicity in rats

Experimental Parkinson's disease and Parkinson's disease in humans include a CNS inflammatory component that may contribute to the pathogenesis of the disease. CNS inflammation produces a loss in cytochrome P450 metabolism and may impair the brain's protection against neurotoxins. We have examined if preexisting inflammation in the brain could increase the toxicity of the dopaminergic toxin 1-methyl-4-phenylpyridinium (MPP⁺). Lipopolysaccharide (LPS, 25 μg) or saline (control) was injected into the left lateral cerebral ventricle. A single injection of MPP⁺ into the median forebrain bundle followed 48 h later and produced a reduction in striatal dopamine content that was dose and time dependant. Two-days after 5 μg of MPP⁺ was administered, a 90% decrease in striatal dopamine content was observed in saline- and LPS-pretreated rats. However, 4 and 7 days after 5 μg MPP⁺ treatment, striatal dopamine recovered up to 70-80% of control values in saline-pretreated rats but remained depressed (80-90%) in rats treated with LPS. These results suggested that CNS inflammation might create an increased risk factor for drug-induced CNS toxicity or chemically mediated Parkinson's disease. The prolonged toxicity of MPP⁺ may be due to a decrease in brain cytochrome P450 metabolism that occurs during inflammation. As a second objective for the study, we examined if the CNS lesion produced by MPP⁺ altered cytochrome P450 metabolic activity in the liver, kidney, and lung. We have demonstrated a novel mechanism whereby the brain pathology produced by MPP⁺ treatment contributes to a reduction in cytochrome P450 metabolism in the kidney but not the liver or lung. Therefore, a chemically evoked CNS disorder with a chronic inflammatory component might have major effects on the renal metabolism of drugs or endogenous substrates.