A spider derived peptide, PnPP-19, induces central antinociception mediated by opioid and cannabinoid systems
Daniela da Fonseca Pacheco, Ana Cristina Nogueira Freitas, Adriano Monteiro C. Pimenta, Igor Dimitri Gama Duarte and Maria Elena de Lima
Journal of Venomous Animals and Toxins including Tropical Diseases, 2016, 22, 34,
Doi : 10.1186/s40409-016-0091-6
Background : Some peptides purified from the venom of the spider Phoneutria nigriventer have been identified as potential sources of drugs for pain treatment. In this study, we characterized the antinociceptive effect of the peptide PnPP-19 on the central nervous system and investigated the possible involvement of opioid and cannabinoid systems in its action mechanism.
Methods : Nociceptive threshold to thermal stimulation was measured according to the tail-flick test in Swiss mice. All drugs were administered by the intracerebroventricular route.
Results : PnPP-19 induced central antinociception in mice in the doses of 0.5 and 1 μg. The non-selective opioid receptor antagonist naloxone (2.5 and 5 μg), μ-opioid receptor antagonist clocinnamox (2 and 4 μg), δ-opioid receptor antagonist naltrindole (6 and 12 μg) and CB1 receptor antagonist AM251 (2 and 4 μg) partially inhibited the antinociceptive effect of PnPP-19 (1 μg). Additionally, the anandamide amidase inhibitor MAFP (0.2 μg), the anandamide uptake inhibitor VDM11 (4 μg) and the aminopeptidase inhibitor bestatin (20 μg) significantly enhanced the antinociception induced by a low dose of PnPP-19 (0.5 μg). In contrast, the κ-opioid receptor antagonist nor-binaltorphimine (10 μg and 20 μg) and the CB2 receptor antagonist AM630 (2 and 4 μg) do not appear to be involved in this effect.
Conclusions : PnPP-19-induced central antinociception involves the activation of CB1 cannabinoid, μ- and δ-opioid receptors. Mobilization of endogenous opioids and cannabinoids might be required for the activation of those receptors, since inhibitors of endogenous substances potentiate the effect of PnPP-19. Our results contribute to elucidating the action of the peptide PnPP-19 in the antinociceptive pathway.
Keywords : Peptide PnPP-19, Central antinociception, Phoneutria nigriventer, μ-opioid receptor, δ-opioid receptor, CB1 receptor, CB2 receptor
PnPP-19 is a synthetic peptide that contains 19 amino acid residues . It represents a part of the primary structure of the native toxin PnTx2-6, also known as δ- ctenitoxin-Pn2a , which was isolated from the venom of the spider Phoneutria nigriventer . Some peptides purified from the venom of this spider have been identified as potential sources of drugs for pain treatment. For example, PnTx3-3, renamed ω-ctenitoxin- Pn2a , showed an antinociceptive effect in different models of neuropathic pain . Additionally, Phα1β neurotoxin, another toxin isolated from that same venom, induced antinociception in models of neuropathic and inflammatory pain .
Cannabinoids and opioids are two separate groups of psychoactive drugs that exhibit several similar pharmacological effects, including analgesia, sedation, hypothermia and inhibition of motor activity [6–8]. In recent years, our group has demonstrated the involvement of endogenous opioids and cannabinoids in the antinociceptive action of several substances [9, 10]. Receptors for both drugs are coupled to similar intracellular signaling mechanisms and the interaction between cannabinoid and opioid systems in the nociceptive pathway has been the focus of much attention [9, 11–15].
Interestingly, it has been shown that endogenous opioids are involved in antinociception induced by a scorpion toxin . Therefore, it is hypothesized that pain relief induced by alpha- or beta- scorpion toxins may implicate the activation of an endogenous opioid system. The analgesic effect of those toxins might be partially due to the activation of diffuse noxious inhibitory controls of supra-spinal origin, which are linked to a counter-irritation phenomenon and release of endogenous opioids . Thus, opioid peptides may be involved in the action mechanism of other toxins, particularly toxins from other arthropods, such as the spider Phoneutria nigriventer.
Recently we have shown that PnPP-19 induces antinociception in the peripheral nervous system . We suggested that this effect is attributable to an inhibition of the neutral endopeptidase (neprilysin), which may lead to an increase of enkephalin levels and may cause activation of both μ- and δ-opioid receptors. In addition, we showed evidence that the receptor CB1 is implicated in the antinociceptive effect induced by PnPP-19.
Given the lack of information concerning the antinociceptive effect of PnPP-19 on the central nervous system (CNS), the aim of the present study was to determine the possible effect of this peptide on the CNS and investigate whether there is an involvement of the cannabinoid and opioid systems.