Agomelatine-loaded nanostructured lipid carriers alleviate neuropathic pain in rats by Nrf2/HO-1 signalling pathway

Neuropathic pain arises from impairments or malfunctions within the nervous system, resulting in atypical transmission and interpretation of pain signals. In the present study, we examined the neuroprotective effects of agomelatine (AGM) and agomelatine-loaded nanostructured lipid carriers (AGM-NLCs) in neuropathic animal models induced by chronic constriction injury (CCI) of the sciatic nerve. Male Sprague Dawley rats were divided into seven experimental groups to compare the effects of AGM and AGM-NLCs, which were administered at 20 mg/kg for 14 consecutive days after CCI. Our finding demonstrated that CCI triggered the onset of analgesia in these animals, corroborated by mechanical allodynia and thermal hyperalgesia. Furthermore, CCI induced an elevation in inflammatory mediators such as interleukin (IL)-1β and inducible nitric oxide synthase (iNOS), and downregulated heme oxygenase-1 (HO-1) and nuclear factor E2-related factor (Nrf2). Treatment with AGM and AGM-NLCs reversed inflammatory cascades and elevated antioxidant enzyme levels, leading to a reduction in paw withdrawal latency and threshold in rats. To further investigate the effect of AGM and AGM-NLCs, all-trans retinoic acid (ATRA) was administered, which antagonizes Nrf2. ATRA substantially downregulated Nrf2 expression and exacerbated thermal hyperalgesia, whereas Nrf2 and HO-1 expressions were significantly upregulated after AGM-NLCs administration. Overall, the results demonstrated that AGM-NLCs offer promising antinociceptive and anti-inflammatory properties in alleviating neuropathic pain symptoms, which can be attributed to improved drug delivery and therapeutic outcomes compared with AGM alone.