Antioxidant enzymes in red blood cells and lymphocytes of ataxia-telangiectasia patients.

Toxic oxygen metabolites may contribute to the development of tissue damage, and play a role in the pathogenesis of malignancies, some acute and chronic pulmonary diseases, and in cell damage by radiomimetic agents, which can be seen in patients with ataxia-telangiectasia (A-T). Oxidative stress resulting from increased free radical production and/or defects in antioxidant defences is also involved in neurodegenerative disorders. Thus, oxidative stress could account for several aspects of the pleiotropic phenotype of A-T patients. The aim of this study was to determine the activities of the enzymes involved in cellular antioxidant metabolism in A-T patients to see if there is any defect which may result in constant oxidative stress. Superoxide dismutase (SOD) and catalase activities of erythrocytes, in contrast to lymphocytes, were found to be significantly higher in patients than in healthy controls. Our results may be another indication for the presence of constant oxidative stress in A-T patients as suggested previously.

Mitochondrial complex I and IV activities in leukocytes from patients with parkin mutations.

The parkin protein functions as a RING-type ubiquitin protein ligase. Considering the possibility that impaired ubiquitin-proteosomal system activity may impair antioxidant defenses and enhance oxidative stress, we have investigated the activity of mitochondrial respiratory enzymes in patients with parkin gene mutations. A significant decrease in the leukocyte complex I activity was found both in patients with parkin mutations (62.5%) and idiopathic PD (64.5%) compared with age-matched controls (P < 0.001). Complex IV activity was also decreased significantly in idiopathic PD patients (60%), but no difference was detected between controls and patients with parkin mutations.