Estudo dos efeitos antinociceptivos, comportamentais e regenerativos do tratamento com gabapentina em modelo experimental de dor neuropática

Abstract

Neurophatic pain conveys mechanisms of difficult understanding, which changes with the disease progress, jeopardizing the therapeutics. The chronic constriction of the sciatic nerve (CCSN) model mimics this condition. Gabapentin (GBP) is an anti-convulsive drug often used as analgesics to control neurophatic pain. Few reports exist on their effects in the inflammatory and regenerative activity of the nerve. TNF-α and IL-1β cytokines, although related to pain and inflammation, are also associated with early myelin and axonal fragmentos removal after nerve injury and thus contribute to nerve regeneration. This study aimed at evaluating the analgesics early treatment (80 min prior to CCSN and along 5-day treatment, 12h/12h) effects of GBP (30, 60, 120 mg/kg, given orally) by monitoring (before surgery, on the 3rd day and 5th day of post-surgery treatment, 12h to12h) the following behaviors (1) spontaneous behavior, suggestive of chronic pain: Scratching and Biting (2) motor and exploratory-related behaviors: Climbing, Rearing, and Walking, (3) induced-pain behaviors: mechanical allodynia (electronic von Frey) and cold allodynia (10ºC) in Wistar male rats (250-300g) with CCSN. CCSN animals treated with saline and pseudo-operated were used as controls. Another aim of this study was to evaluate the pro and anti-inflammatory effects of GBP (60 and 120mg/kg, given orally) by carragenin-induced paw edema in CCSN-free animals and yet nerve myeloperoxidase measurements under chronic constriction. The neural regenerative effects of GBP were indirectly evaluated by measuring TNF-α, IL-1β, IL-10, and myelin basic protein (PBM) expressions in the same protocol, as follows: 5th day of treatment following CCSN to draw nerves in order to quantify cytokines by ELISA and immunohistochemistry, and for MPB expression detected by Western blot and immunohistochemistry on the 5th and 15th. Results: On the 5th day, GBP, at doses of 30, 60 and 120mg, reduced the scratching time in the ipslateral paw of 86.76%*; 83.82%*; 80.09%* (*p<0.01) and an inhibition of the biting time of 56.27%; 90.53%*; 65.06% (*p<0.01) in the right side in comparison with the saline group. In addition, GBP alleviated mechanical allodynia causing increase paw retrieval thresholds of 225.42%*, 246.01%*, 309.20%* (*p <0.001) and the reduction of the pain scores for cold allodynia in the range of 18.19%; 21.29%; 42.26%* (*p < 0.01) in comparison with the saline group. GBP, at doses of 60 and 120mg, significantly increased spontaneous motricity in CCSN animals and controls suggesting excitatory effects rather than sedation. GBP (60 mg/kg) also caused relevant effects (p<0.001) in peritoneal cell migration, and a 982.16% increase in nerve myeloperoxidase expression and 53% increase in paw edema, as opposed to the saline control. Regarding nerve TNF-α expression, doses of 60 and 120mg caused significant increase of 120.95 % and 91.99% in comparison with the saline group (p<0.01). A dose of 60mg/kg caused 59.26% increase in IL-1β expression compared with the saline group (p<0.05). We found a 158% significant increase in PBM expression by western blots (0.298 ± 0.069 PBM/Act) on the 15th treatment-day with GPB in comparison with the saline control (0.116 ± 0.034 PBM/Act). Conclusions: 5-day GBP treatment, although with pro-inflammatory effects, was found to have significant pain killing effects by reducing chronic spontaneous pain behaviors and by alleviating mechanical and thermal allodynia in the early neuropathy course. By taking our relevant findings of increasing migration cell rates to the nerve injury site on the 5th day of the neuropathy and the nerve TNF and IL-1β expression with more macrophage and Schwann cell activation and supposedly more nerve growth factor release, along with higher PBM expression, altogether suggest that GBP may hasten the myelin and axonal fragmentos withdrawn, therefore contributing to axonal outgrowth and ultimately remyelinization.