Journal of Bioequivalence & Bioavailability

Brazilian toxins targeting channels involved in pain, ischemia and cardiac arrhythmias

International Conference and Exhibiton on Pharmaceutical Regulatory Affairs

6-7 September 2011 Baltimore, USA

Marcus Vinicius Gomez, A. H. Souza, C. Castro Junior, F.K. Rigo, I.A. Souza, M.A. M. Prado, V.F. Prado, J. Ferreira

Scientific Tracks Abstracts: JBB

Abstract:

O ne peptide toxin, purifi ed from the venom of the spider Phoneutria nigriventer Tx3-6 shows more specifi city for N-type calcium channels expressed in heterologous system HEK cells and was tested in diff erent models of pain. Tx3-6 was as eff ective and potent as  -conotoxin MVIIA to produce antinociception and was patented with the name of Ph  1  Comparing its antinociceptive action with morphine, Ph  1  showed higher potency and longer lasting eff ect. When administered before formalin injection (pretreatment), Ph  1  was as eff ective and potent as  -conotoxin MVIIA to produce antinociception but Pha1b was more eff ective to reverse an established nociceptive process (postreatment ) than conotoxin MVIIA. Pha1b had antinociceptive action in acute and chronic pain. In cancer pain of rodents, the treatment with Phα1β and MVIIA showed a long-lasting action. When side eff ects were assessed, Ph  1  had a therapeutic index 4 times wider than  -conotoxin MVIIA and this toxin were 2.2 times more toxic than Pha1b. In the spinal cord the neurotransmitter glutamate is an important mediator of pain. Formalin injection induces pain and increases glutamate levels in cerebrospinal fl uid (CSF) of rats. Ph  1  and  -conotoxin almost blocked the increase in CSF glutamate levels induced by formalin. Th e recombinant Phα1β repeats the eff ects of the native toxin. Capsaicin- stimulated glutamate release from spinal cord synaptosomes was inhibited by both Ph  1  and ω-conotoxin MVIIA but IC50 for the spider toxin was 2.2 times lower than that of ω-conotoxin MVIIA. Capsaicin is an agonist of TRPV1 receptor and we tested the action of the Phα1β on capsaicin-induced calcium transients of DRG neurons and HEK cells expressing TRPV1 receptor. Th e inhibitory actions of Phα1β and SB366791 (antagonist of TRPV1 receptor) on capsaicin-induced calcium transients in DRG neurons were not additive, suggesting they act on the same pathway.Th e specifi c binding of [ 3 H]-resiniferatoxin (3H-RTX) in DRG membranes decreased by capsaicin and neither SB366791, a TRPV1 antagonist nor Phα1β were able to alter [ 3 H]-RTX binding. Th us, the interaction of Phα1β with TRPV1 does not occur at the intracellular site of the TRPV1 receptor. Th e toxin prevents capsaicin-induced nociception using a TRPV1 pathway but without binding directly to this receptor. Th e spider toxin Tx3-4 is a calcium channel blocker N-and P/Q types and has neuroprotective eff ect of hippocampus and retinal tissues submitted to ischemia induced by oxygen and glucose deprivation. Th e toxin inhibits the glutamate release induced by the ischemia process and induces neuroprotection even whem applied aft er the onset of the ischemia in hippocampus and retinal tissues.