OXIDATIVE STRESS AND ALZHEIMER’S DISEASE

Introduction: Brain tissue is particularly susceptible to oxidative damage, which has been associated with pathological findings of Alzheimer’s disease (AD), such as amyloid plaques and protein fibrils. Oxidative stress alterations, including increased production of reactive oxygen metabolites, decline of antioxidant systems, and decreased efficiency in repairing damaged molecules, have been linked to the development of AD. Postmortem studies on brain tissue from AD patients have shown several oxidative damage markers, such as increased lipid peroxidation, oxidative damage of proteins, glyco-oxidation, and reduction of antioxidant enzyme systems. Methods: We studied 40 patients referred to our Geriatric Unit (age 78.2±1.1 years), 28 patients with AD according to DSM-IV and NINCDS-ADRDA criteria, and 12 controls. All patients were tested with measurements of 8-hydroxy-2'-deoxyguanosine (8-OHdG) in the urine to assess oxidative stress. Twenty AD patients from group 1 were supplemented with fermented papaya powder (FPP, 4.5 grams per day) for 6 months, while other 8 AD patients (group 2) did not receive any treatment. Results: At baseline, 8-OHdG was significantly higher in patients with AD vs. controls (13.7±1.61 ng/ml vs. 1.6±0.12 ng/ml). After supplementation with FPP, 8-OHdG was significantly reduced (from 14.1±1.7 ng/ml to 8.45±1.1 ng/ml, p<0.01), while in group 2 (AD patients, not supplemented) 8-OHdG did not significantly change, with a nonsignificant tendency to increase (from 12.5±1.9 ng/ml to 19.6±4.1 ng/ml, p=NS). Conclusion: Our data show that 1) AD is associated with increased oxidative stress, and 2) that antioxidant FPP may be helpful to counteract excessive production of free radicals in these patients.