Naringenin may prevent morphine-induced tolerance via inhibiting glycogen synthase kinase-3beta activity in mice

Background: Opioids are essential for pain treatment, but their long-term usage results in tolerance. Naringenin, a natural flavonoid found in fruit, inhibits the enzyme that causes opioid tolerance, making it effective in treating neurodegenerative diseases. Objective: In this study, we evaluate the role of naringenin in morphine-induced tolerance and the glycogen synthase kinase-3beta (GSK-3β) enzyme. Methods: To induce tolerance to morphine in mice, repeated injections of morphine were performed for five days, and on the fifth day, a single dose of morphine was injected intraperitoneally. Pain tests (hot plate and tail flick) were performed on the first, third, and fifth days of injections. To evaluate the impact of naringenin, 45 minutes before each morphine injection, doses of 25, 50, and 100 mg/kg were administrated orally. On the last day, brain tissues were checked for biochemical factors and changes in the phosphorylation of the enzyme by the immunohistochemical method. Results: The results indicated that the simultaneous use of naringenin significantly increases the analgesia delay compared to the morphine group (P 0.001) on the third and fifth days. Naringenin at all concentrations decreased the nitrite level caused by morphine. It showed protective effects on morphine tolerance (P 0.001) in the p-GSSer640 immunohistochemical assay and reduced the phosphorylation of p-GSSer640 by GSK-3β, activated by chronic morphine administration. Conclusion: Based on the results of the present study, the beneficial effect of naringenin on the GSK enzyme in morphine-induced tolerance is confirmed, but more studies are needed to investigate its impact mechanism.