Mitochondrial respiratory chain in brain homogenates:: activities in different brain areas in patients with Alzheimer's disease

Background and aims: The potential influence of impaired oxidative metabolism in the modulation of manifestations in sporadic Alzheimer's disease (AD) has attracted much attention in the last 50 years. Unfortunately, many clinical and experimental results aiming at proving this hypothesis are still controversial. The aim was to study the enzymatic activities of respiratory chain (RC) complexes I through V in three brain areas of a group of patients with definite AD, and to compare the results with a group of normal brains. We simultaneously assessed the lipid peroxidation of the samples as a measure of free radical damage. Methods: The specific activity of the individual complexes of the RC was measured spectrophotometrically, and the loss of cis-parinaric acid fluorescence was used to determine the chemical process of lipid peroxidation. Results: We were not able to detect differences in any of the analyzed RC enzymatic activities, or in the level of lipid peroxidation between patients with AD and controls. Instead, differences were found in the number of mitochondria and in the intrinsic enzymatic activities of complexes III and IV in various brain areas. Conclusions: Spectrophotometric enzymatic analyses of respiratory complexes in brain homogenates do not support the primary contribution of mitochondrial RC dysfunction in the pathogenesis of AD.