Effects of combined treatment with zonisamide and diclofenac sodium on nerve regeneration following peripheral nerve injury

Peripheral nerve injury (PNI) is a significant health problem affecting over a million people worldwide. The widespread use of microsurgical techniques and advancements in histological and immunohistochemical methods have greatly enhanced the success of nerve repair. However, there is no existing literature on a study investigating the effects of combined treatment with zonisamide, a neuroprotective agent, and diclofenac sodium, an anti-inflammatory drug, after PNI. This study aimed to investigate the effects of zonisamide and diclofenac sodium treatments, both individually and in combination, on nerve regeneration using ultrastructural, immunohistochemical, histomorphometric, and molecular methods after crush-type injury to the sciatic nerve. A total of 84 male Wistar rats were randomly assigned to six groups: control group without any surgical procedures, sham operation group in which the sciatic nerve was exposed but not damaged, experimental control group without any treatment after nerve injury, treatment group receiving intraperitoneal injections of 2 mg/kg diclofenac sodium once daily for 7 days after nerve injury, treatment group receiving oral gavage of 100 mg/kg zonisamide once daily for 7 days after nerve injury, and combination treatment group receiving both intraperitoneal injections of 2 mg/kg diclofenac sodium and oral gavage of 100 mg/kg zonisamide once daily for 7 days after nerve injury. Nerve tissues were collected from the experimental and treatment groups on days 7, 14, and 21 to examine the time-dependent effects of the treatments. It was observed that the expressions of iNOS and COX-2 were significantly reduced in the zonisamide and combination treatment groups compared to the experimental control group, with the most significant reduction occurring on day 21. The number of myelinated nerve fibers was significantly increased in the combination treatment groups compared to the experimental control group. The expression level of Krox-20 decreased after injury but increased in the zonisamide and combination treatment groups. The expression level of p75NTR in the combination treatment group was significantly higher than the other treatment groups on day 14 and reached its highest level on day 21. Overall, considering all the findings, it can be concluded that the combined treatment with zonisamide and diclofenac sodium after experimental PNI can suppress inflammation and promote axonal growth and remyelination, thereby stimulating peripheral nerve regeneration. We suggested that further molecular studies can incorporate these treatment protocols into clinical practice.