INCREASED PROTEIN OXIDATION IN HUMAN SUBSTANTIA-NIGRA PARS COMPACTA IN COMPARISON WITH BASAL GANGLIA AND PREFRONTAL CORTEX MEASURED WITH ANIMPROVED DINITROPHENYLHYDRAZINE ASSAY

The dopaminergic phenotype of neurons inhuman substantia nigra deterio rates during normal aging, and loss of these neurons is prominent in P arkinson's disease. These degenerative processes are hypothesized to i nvolve oxidative stress. To compare oxidative stress in the nigra and related regions, we measured carbonyl modifications of soluble protein s in postmortem samples of substantia nigra, basal ganglia, and prefro ntal cortex from neurologically normal subjects, using an improved 2,4 -dinitrophenylhydrazine assay. The protein carbonyl content was found to be about twofold higher in substantia nigra pars compacta than in t he other regions. To further analyze this oxidative damage, the distri bution of carbonyl groups on soluble proteins was determined by wester n immunoblot analysis. This method revealed that carbonyl content of t he major proteins in each region was linearly dependent on molecular w eight. This distribution raises the possibility that protein carbonyl content is controlled by a size-dependent mechanism in vivo. Our resul ts suggest that oxidative stress is elevated in human substantia nigra pars compacta in comparison with other regions and that oxidative dam age is higher within the dopaminergic neurons. Elevated oxidative dama ge may contribute to the degeneration of nigral dopaminergic neurons i n aging and in Parkinson's disease.