Oxidative/nitrosative stress and protein damages in aqueous humor of hyperglycemic rabbits: effects of two oral antidiabetics, pioglitazone and repaglinide.

The present study was undertaken to determine oxidative/nitrosative stress in aqueous humor of alloxan-induced hyperglycemic rabbits and to investigate the effects of two oral antidiabetic drugs, pioglitazone from peroxisome proliferator-activated receptor gamma (PPARγ) agonists and repaglinide from nonsulfonylurea K(ATP) channel blockers. Ascorbic acid (AA), glutathione (GSH), total antioxidant status (TAS), lipid peroxidation products (LPO), total nitrites (NO(2)), advanced oxidized protein products (AOPP), and protein carbonyl groups (PCG) were determined using respective colorimetric and ELISA methods. In our hyperglycemic animals, AA decreased by 77%, GSH by 45%, and TAS by 66% as compared to control animals. Simultaneously, LPO increased by 78%, PCG by 60%, AOPP by 84%, and NO(2) by 70%. In pioglitazone-treated animals, AA and TAS increased above control values while GSH and PCG were normalized. In turn, LPO was reduced by 54%, AOPP by 84%, and NO(2) by 24%, in relation to hyperglycemic rabbits. With repaglinide, AA and TAS were normalized, GSH increased by 20%, while LPO decreased by 45%. Our results show that pioglitazone and repaglinide differ significantly in their ability to ameliorate the parameters like NO(2), PCG, and AOPP. In this area, the multimodal action of pioglitazone as PPARγ agonist is probably essential.