Oxidative stress/PERK/apoptotic pathways interaction contribute to tramadol neurotoxicity in rat cerebral and cerebellar cortex and thyme enhances the antioxidant defense system: histological, immunohistochemical and ultrastructural study

Abstract

<p class="abstract"><strong>Background:</strong> Tramadol is an opioid analgesic with several adverse reactions. Oxidative and endoplasmic reticulum (ER) stresses have been involved in the molecular mechanisms underlying tramadol neurotoxicity. Importantly, protein kinase RNA-like ER kinase (PERK) is a key ER-downstream pathway that mediates apoptosis. We aimed to determine the cellular stresses interaction that mediates PERK-induced apoptosis in tramadol-treated rats and to assess the effect of thyme in enhancing the antioxidant defense system in the face of such stresses.</p><p class="abstract"><strong>Methods:</strong> Forty male Sprague Dawley rats were randomized into 4 groups. Control group, thyme group received thyme extract (500 mg/kg/day) orally. Tramadol group received tramadol HCL (40 mg/Kg/day) dissolved in saline orally. Tramadol + Thyme group received tramadol and thyme extract. After 30 days, frontal motor and cerebellar cortex specimens were biochemically assessed for oxidative stress biomarkers and evaluated for histological, ultrastructural and immunohistochemical changes. </p><p class="abstract"><strong>Results:</strong> Tramadol group showed a significant elevation in malondialdehyde level with a reduction in superoxide dismutase and catalase enzyme activities. Histologically and ultrastructurally, there were remarkable degenerative and apoptotic changes in the neurons and glial cells. In parallel, we detected a significant increase in integrated density for PERK immunostaining and number of caspase-3 positive cells/HPF compared to control. Tramadol + Thyme group showed improvement in oxidative stress parameters, histological and ultrastructural changes. Moreover, integrated density for PERK immunostaining and number of caspase-3 positive cells/HPF were significantly lower than Tramadol group.</p><p class="abstract"><strong>Conclusions:</strong> Oxidative and ER stress-mediated PERK/apoptosis axis corroborates to the tramadol-induced neurotoxicity. Therapeutic strategies enhancing antioxidant activity and/or blocking ROS-mediated ER stress pathway may resolve tramadol neurotoxicity.</p>