Rosmarinic acid attenuates development and existing pain in a rat model of neuropathic pain: An evidence of anti-oxidative and anti-inflammatory effects

Background: We aimed to investigate the potential prophylactic and curative effects of rosmarinic acid, one of the main constituents of rosemary, on the neuropathic pain induced by chronic constriction injury (CCI) in rats. Materials and methods: CCI was used to induce peripheral neuropathic pain. In prophylactic groups, rosmarinic acid (10, 20, and 40 mg/kg, i.p.) was administered from the day of surgery (day 0) for 14 days. In treatment group, rosmarinic acid (40 mg/kg) was given from day 5 (after the pain was established), for 7 days. The degree of mechanical allodynia, cold allodynia, and heat hyperalgesia were measured on days 0, 3, 5, 7, 10 and 14 post-surgery. The open field test was carried out to assess locomotor activity of animals. Lumbar spinal cord levels of astroglia activation marker, glial fibrillary acidic protein (GFAP), microglial activation marker, ionized calcium-binding adapter molecule 1 (Iba-1), toll-like receptor 4 (TLR-4), tumor necrosis factor alpha (TNF-alpha), inducible isoform of nitric oxide synthase enzyme (iNOS) and apoptotic factors were quantified via western blot on days 7 and 14. Results: CCI rats showed a significant mechanical allodynia, cold allodynia and thermal hyperalgesia, compared to sham ones on day 3, persisted up to day 14 post-CCI. Rosmarinic acid was able to prevent and also attenuate CCI-induced behavioral features in prophylactic as well as treatment groups, respectively. A significant increase in the levels of TNF-alpha, iNOS, apoptotic factors (Bax, caspases 3, 9), Iba-1, TLR-4, and GFAP was observed on both days 7 and 14, which was suppressed by 14 days administration of rosmarinic acid. Conclusion: These findings further support the use of rosemary in traditional medicine to alleviate pain. Rosmarinic acid could be a promising compound in prophylaxis and treatment of neuropathic pain. Anti-apoptotic and anti-inflammatory effects of rosmarinic acid may have important roles in the observed antinociceptive properties.