Activation of TGF-β/ALK5/SMAD signaling alleviates behavioral and neurochemical deficits in tramadol withdrawal.

Opioid withdrawal state poses profound neurobiological and clinical complications characterized by neuroinflammation, oxidative stress, and neurotransmitter imbalance. Tramadol, a widely used synthetic opioid, induces a distinct withdrawal syndrome with poorly understood mechanisms, limiting targeted therapeutic options. The current investigation evaluated the neuroprotective potential of SRI-011381 hydrochloride, a selective TGF-β receptor agonist, against neurobehavioral and biochemical changes in mice induced by tramadol withdrawal. Male albino mice were administered tramadol (50 mg/kg, s.c.) twice daily for 56 days to induce dependence; on day 57, only the morning dose was administrated followed by administration of naloxone (5 mg/kg) by intraperitoneal (i.p) route to precipitate the withdrawal symptoms. Behavioral parameters, including jumping frequency, withdrawal severity score (WSS), and hyperalgesia, were assessed. Biochemical evaluations measured oxidative stress (TBARS, GSH), inflammatory mediators (IL-1β, IL-6, TNF-α, NF-κB), and neurotransmitters (glutamate, serotonin, dopamine). Treatment with SRI-011381 hydrochloride (15 and 30 mg/kg, i.p.) significantly mitigated behavioral signs of withdrawal and restored biochemical homeostasis by enhancing antioxidant defenses, reducing lipid peroxidation, normalizing neurotransmitter levels, and attenuating inflammatory mediators. Co-administration of the SMAD4 inhibitor galnusertib (150 mg/kg, i.p.) reversed these effects, confirming the involvement of a SMAD-dependent mechanism. The standard drug clonidine (0.1 mg/kg, i.p.) exhibited comparable protective effects. These findings suggest that pharmacological activation of the TGF-β/ALK5/SMAD signaling pathway by SRI-011381 hydrochloride effectively ameliorates the neurobehavioral and biochemical disturbances associated with opioid withdrawal, highlighting this pathway as a potential therapeutic target for the treatment of opioid dependence and withdrawal syndromes.