Antinociceptive effect of thymoquinone in diabetic rats and the role of serum lipid peroxidation

Hyperalgesia is one of the signs of diabetes mellitus that affects the life quality of patients. Nigella sativa-derived thymoquinone exhibits antidiabetic and anti-inflammatory effects. This study was designed to investigate the antinociceptive effect of thymoquinone (TQ) in streptozotocin-diabetic rats. Rats were divided into control, high dose TQ-treated control, diabetic, sodium salicylate (SS)-treated control and diabetic, and high and low dose TQ-treated diabetic groups. TQ was administered i.p. at doses of 2.5 and 5 mg/kg one week after diabetes induction by streptozotocin for 5 weeks. TQ treatment of diabetic rats reduced pain score in acute and chronic phases of the formalin test (p<0.05). Meanwhile, SS administration significantly reduced pain score only at chronic phase of the test (p<0.01). Regarding hot tail immersion test, diabetic rats showed a significant reduction in tail flick latency as compared to control ones (p<0.05) and TQ treatment of diabetic rats slightly increased this latency relative to untreated diabetics but the existing difference was not statistically significant. In addition, high-dose TQ significantly reduced serum level of MDA in diabetic group (p<0.05). Taken together, administration of TQ could attenuate nociceptive score in both phases of formalin test in experimental model of diabetes mellitus and has no obvious effect on thermal pain threshold and part of this effect is exerted through attenuation of lipid peroxidation in peripoheral tissues of the body.