Antinociceptive effect of Brazilian armed spider venom toxin Tx3-3 in animal models of neuropathic pain.

Venoms peptides have produced exceptional sources for drug development to treat pain. In this study we examined the antinociceptive and side effects of Tx3-3, a peptide toxin isolated from Phoneutria nigriventer venom, which inhibits high-voltage-dependent calcium channels (VDCC), preferentially P/Q and R-type VDCC. We tested the effects of Tx3-3 in animal models of nociceptive (tail-flick test), neuropathic (partial sciatic nerve ligation and streptozotocin-induced diabetic neuropathy), and inflammatory (intraplantar complete Freund's adjuvant) pain. In the tail-flick test, both intrathecal (i.t.) and intracerebroventricular (i.c.v.) injection of Tx3-3 in mice caused a short-lasting effect (ED(50) and 95% confidence intervals of 8.8 [4.1-18.8] and 3.7 [1.6-8.4] pmol/site for i.t. and i.c.v. injection, respectively), without impairing motor functions, at least at doses 10-30 times higher than the effective dose. By comparison, ω-conotoxin MVIIC, a P/Q and N-type VDCC blocker derived from Conus magus venom, caused significant motor impairment at doses close to efficacious dose in tail flick test. Tx3-3 showed a long-lasting antinociceptive effect in neuropathic pain models. Intrathecal injection of Tx3-3 (30 pmol/site) decreased both mechanical allodynia produced by sciatic nerve injury in mice and streptozotocin-induced allodynia in mice and rats. On the other hand, i.t. injection of Tx3-3 did not alter inflammatory pain. Taken together, our data show that Tx3-3 shows prevalent antinociceptive effects in the neuropathic pain models and does not cause adverse motor effects at antinociceptive efficacious doses, suggesting that this peptide toxin holds promise as a novel therapeutic agent for the control of neuropathic pain. The Brazilian armed spider Tx3-3, a new P/Q and R-type calcium channel blocker, effectively alleviates allodynia in animal neuropathic pain models.