Estudo sobre os mecanismos antinociceptivos periféricos induzidos pelo peróxido de hidrogênio (H2O2)

Abstract

ABSTRACT INTRODUCTION: Pain is a vital sensory phenomenon to the protection of tissues and the survival of the organism. Besides being essential in some cases, pain must be attenuated when it affects the system's welfare. Data from the literature describe different molecules with the ability to hyperpolarize the neuronal membrane potential to cause antinociception. Previously studies have shown that the administration of hydrogen peroxide (H2O2) can cause hyperpolarization in a variety of cells through opening the K+ channels, including neuronal cells. AIM: Thus, this study aimed to evaluate de peripheral antinociceptive effect of hydrogen peroxide in a prostaglandin E2 model of acute pain, and determine if the opioidergic and cannabinoidergic systems, as well as the nitric oxide pathway and potassium channels, are involved in the antinociceptive effect mediated by H2O2. METHODS: The paw compression test was used to measure the nociceptive threshold in mice (Swiss, male, 30-40 g, n = 5 / CEUA protocol: 212/2020). Acute pain was induced by PGE2 administration, and the study was conducted using pharmacological tools. All drugs were administrated intraplantar in a volume of 20 μl. RESULTS: The administration of PGE2 a 2 μg/paw efficiently decreased the nociceptive threshold of the animals. H2O2 (0,05; 0,1; 0,2 e 0,3 μg/paw) promotes dose-dependent antinociceptive effect in a PGE2 model of acute pain. This antinociceptive effect was not reversed by Naloxone (Nx - 50 μg/paw) a non-selective opioid receptor antagonist. The reversion did not occur by antagonizing the CB1 and CB2 receptors using the selective antagonists AM 251 (80 μg/paw) and AM 630 (100 μg/paw) respectively. The non-selective inhibition of nitric oxide synthase enzymes with L-NOarg (6, 12 e 24 μg/paw), dose-dependently reversed the H2O2-mediated antinociception. Thus, to evaluate which isoforms were responsible for the reversion was administered L-NIL (24 μg/paw), L-NPA (24 μg/paw) e L-NIO (24 μg/paw). Seletive inhibitors of iNOS, nNOS and eNOS respectively. The antinociceptive reversion occurs with the inhibition of the three isoforms, being total for iNOS and partial to nNOS and eNOS. The antinociception caused by H2O2 demonstrated to be involved with the potassium channels, given that tetraethylammonium (TEA), a selective voltage-gated potassium channel blocker (15, 30 e 60 μg/paw) fully reversed the H2O2 antinociception in a dose-dependent manner. The ATP- sensitive K+ channels selective blockers glibenclamide (40, 80 e 160 μg/paw), large and small conductance calcium-activated potassium channels paxiline (10, 20 e 40 μg/paw) and dequalinium (12,5; 25 e 50 μg/paw) respectively reversed the H2O2-mediated antinociception. Nonetheless, only dequalinium fully reversed the antinociception, and only paxiline didn't have a dose-dependent response. CONCLUSION: H2O2 has a peripheral antinociceptive effect on the acute pain model induced by PGE2 administration. It was demonstrated that the NO pathway and voltage-gated K+ channel, ATP-sensitive K+ channels, large and small conductance calcium-activated potassium channels take part in the antinociceptive mechanisms of H2O2. The role of the opioid and cannabinoid systems was not evidenced in this study.