The novel N-type calcium channel blocker, AM336, produces potent dose-dependent antinociception after intrathecal dosing in rats and inhibits substance P release in rat spinal cord slices

Abstract

N-type calcium channels modulate the release of key pro-nociceptive neurotransmitters such as glutamate and substance P (SP) in the central nervous system. Considerable research interest has focused on the therapeutic potential of the peptidic omega-conopeptides, GVIA and MVIIA as novel analgesic agents, due to their potent inhibition of N-type calcium channels. Recently, the novel peptidic N-type calcium channel blocker, AM336, was isolated from the venom of the cone snail, Conus catus. Thus, the aims of this study were to (i) document the antinociceptive effects of AM336 (also known as CVID) relative to MVIIA following intrathecal (i.t.) bolus dosing in rats with adjuvant-induced chronic inflammatory pain of the right hindpaw and to (ii) quantify the inhibitory effects of AM336 relative to MVIIA on K+-evoked SP release from slices of rat spinal cord. Both AM336 and MVIIA inhibited the K+-evoked release of the pro-nociceptive neurotransmitter, SP, from rat spinal cord slices in a concentration-dependent manner (EC50 values=21.1 and 62.9 nM, respectively), consistent with the antinociceptive actions of omega-conopeptides. Following acute i.t. dosing, AM336 evoked dose-dependent antinociception (ED50 approximately 0.110 nmol) but the doses required to produce side-effects were an order of magnitude larger than the doses required to produce antinociception. For i.t. doses of MVIIA<or=0.07 nmol, dose-dependent antinociception was also produced (ED50 approximately 0.016 nmol). Unexpectedly, however, i.t. doses of MVIIA>0.07 nmol, produced a dose-dependent decrease in antinociception but the incidence and severity of the side-effects continued to increase for all doses of MVIIA investigated, suggesting that dose-titration with MVIIA in the clinical setting, may be difficult.

μO-conotoxin MrVIB selectively blocks Na v 1.8 sensory neuron specific sodium channels and chronic pain behavior without motor deficits

“…3A), these TTX-R currents were still at least 10-fold less than doses producing motor deficits. No other behavioral side effects, such as the ataxia produced by local anesthetics or the shaking produced by -conotoxins (18), were observed at the highest doses of MrVIB tested. By contrast, intrathecal lignocaine lacked selectivity for mechanical PWT and thermal PWL versus rotarod latency, with ED 50 s of 0.12 Ϯ 0.10, 0.2 Ϯ 0.14, and 0.20 Ϯ 0.40 mg, respectively (Fig.…”

Secondary hyperalgesia in the rat first degree burn model is independent of spinal cyclooxygenase and nitric oxide synthase

“…Lower doses of ziconotide were effective in this model than was necessary for the spinal nerve ligation model of nerve injury, although it must be remembered that in that case the agent was administered as a post-treatment (Chaplan et al, 1994a), but see (Bowersox et al, 1996). As N-type VGCC on the central terminals of primary afferent fibers (Westenbroek et al, 1995) regulates neurotransmitter release in the spinal cord, including that of substance P into the superficial dorsal horn (Smith et al, 2002), it was expected that ziconotide would block allodynia in the burn model. Intrathecal morphine, which has the same presynaptic actions is also highly effective given as both pre-and post-treatment (Nozaki-Taguchi and Yaksh, 2002b).…”

Developmental Biology of Neoplastic Growth

“…Since opiates also inhibit N-type calcium channels at the spinal level (indirectly via G proteins), it is not surprising that ω-conotoxins specific for N-type channels might be analgesic. Sub-nanomolar doses of ω-conotoxin MVIIA or ω-CVID ) delivered directly to the spinal cord (intrathecally) produce analgesia for up to 24 h in rats (Malmberg and Yaksh 1995;Smith et al 2002). Interestingly, the affinity of ω-conotoxins for N-type calcium channels is reduced upon co-expression with the auxilliary α2δ subunit protein (Mould et al 2004; see Fig.…”