Metformin prevents morphine‑induced apoptosis in rats with diabetic neuropathy: a possible mechanism for attenuating morphine tolerance

Abstract

Morphine is a drug of choice for the treatment of severe and chronic pain, but tolerance to the antinociceptive efect limits its use. The development of tolerance to morphine has recently been associated with neuronal apoptosis. In this study, our aim was to investigate the efects of metformin on morphine-induced neuronal apoptosis and antinociceptive tolerance in diabetic rats. Three days of cumulative dosing were administered to establish morphine tolerance in rats. The antinocicep tive efects of metformin (50 mg/kg) and test dose of morphine (5 mg/kg) were considered at 30-min intervals by thermal antinociceptive tests. To induce diabetic neuropathy, streptozotocin (STZ, 65 mg/kg) was injected intraperitoneally. ELISA kits were used to measure caspase-3, bax, and bcl-2 levels from dorsal root ganglion (DRG) tissue. Semi-quantitative scor ing system was used to evaluate apoptotic cells with the the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) method. The fndings suggest that co-administration of metformin with morphine to diabetic rats showed a signifcant increase in antinociceptive efect compared to morphine alone. The antinociceptive tests indicated that metformin signifcantly attenuated morphine antinociceptive tolerance in diabetic rats. In addition, metformin decreased the levels of apoptotic proteins caspase 3 and Bax in DRG neurons, while signifcantly increased the levels of antiapoptotic Bcl-2. Semi-quantitative scoring showed that metformin provided a signifcant reduction in apoptotic cell counts in diabetic rats. These data revealed that metformin demonstrated antiapoptotic activity in diabetic rat DRG neurons and attenuated morphine tolerance. The antiapoptotic activity of metformin probably plays a signifcant role in reducing morphine tolerance.