Ação da Phα1β, peptídeo purificado do veneno da aranha Phoneutria nigriventer, sobre os efeitos analgésicos e adversos causados pela morfina em camundongos

Abstract

Opioids are the most common drugs prescribed worldwide for alleviating moderate to severe pain. However, the use of opioids is associated with the development of tolerance to the analgesic effect and potential adverse effects, such as paradoxical hyperalgesia, withdrawal syndrome and constipation. An important target for morphine-induced analgesia is the blockade of voltage-gated calcium channels (VGCCs). However, the participation of VGCCs in the tolerance and adverse effects caused by morphine is poorly understood. Thus, the present study was conducted in order to evaluate the possible actions of Phα1β, a peptide inhibitor of VGCCs purified from the venom of the Phoneutria nigriventer spider on the antinociceptive and adverse effects produced by single or repeated administration of morphine. It was evaluated the effect of intrathecal injection Phα1β (0.01-30 pmol/site) on mechanical and heat hyperalgesia, tolerance, withdrawal syndrome and constipation induced throught single (10 mg/kg) or repeated (increasing doses, 3 times a day, for 3 consecutive days) subcutaneous treatment of morphine in C57BL/6 mice. We observed that a single administration of morphine was able to reduce heat but not mechanical nociception as well as decrease gastrointestinal transit. The antinociception, but not the constipation, caused by a single injection of morphine was slightly increased by an intrathecal injection of Phα1β. Repeated treatment with morphine caused not only tolerance to its antinociceptive effect but also induced paradoxical heat and mechanical hyperalgesia, withdrawal syndrome and constipation. Phα1β was able to reverse the tolerance, withdrawal syndrome, mechanical and heat hyperalgesia and constipation induced by repeated morphine treatment. Finally, the effects produced by the native form of Phα1β were fully mimicked by a recombinant version of this peptide in naïve mice. Our results suggest that Phα1β is effective in potentiating the analgesia as well as in reducing tolerance and the adverse effects induced by morphine, indicating its potential use as an adjuvant drug in combination with opioids.