Envolvimento do peróxido de hidrogênio (H2O2) na modulação endógena periférica da dor inflamatória e neuropática em camundongos

Abstract

INTRODUCTION: Although essential, pain needs to be attenuated for the wellfare of the organism. The experience designated as pain is the final result of complex interactions, resulting from signaling via the nociceptive pathway and endogenous modulation of nociception, which functions in order to minimize the totality of this experience. Studies from our research group have demonstrated that inflammation and neuropathies are capable of activating peripheral endogenous systems that control pain, such as opioids and nitrergics. Our group has also stated, for the first time, that hydrogen peroxide (H2O2) is capable of arise peripheral antinociception through the NO/KATP pathway. Since H2O2 is produced endogenously, and it is a molecule present during inflammation and neuropathy, this study aims to evaluate whether H2O2 is mobilized in the periphery for endogenous pain control after stimulation by inflammatory and neuropathic pain. METHODS: Male Swiss mice (30-40 g) were used during the experiments. The nociceptive threshold was measured using the paw withdrawal test. To assess inflammatory pain, the hyperalgesic carrageenan (CG) and the inflammatory mediators TNFα, CXCL-1, IL-1β, NA, and PGE2 were administered. Neuropathic pain was induced using the sciatic nerve constriction (SNC) model. To assess opioid antinociception, the μ, δ, and κ agonists DAMGO, bremazocin, and SNC80 were used, and to assess CB1 and CB2 cannabinoid receptors, the agonists anandamide (AEA) and 2-arachidonoylglycerol (2-AG) were used. For the manipulation of endogenous hydrogen peroxide, the catalase enzyme inhibitor (ATZ) and inhibitors of the SOD 1, 2 and 3 enzymes (LCS-1, 2-ME and DETCA-3) were used. RESULTS: Inhibition of H2O2 degradation through the use of ATZ caused antinociception when injected during the 2nd hour of carrageenan action, but not during the 1st and 3rd hours. The same pattern of decreased nociception was observed during the 2nd hour of action of the CG-induced inflammatory cascade mediators: TNFα, IL-1β, CXCL-1, and PGE2, and at the peak of action of 5 minutes of noradrenaline. Inhibition of H2O2 synthesis in the cell cytosol through LCS-1 injection, as well as inhibition of its synthesis in mitochondria and the extracellular space with the use of 2-ME and DETCA-3, respectively, potentiated, in a dose-dependent manner, the pain caused by intermediate doses of CG when injected during the 2nd hour of carrageenan action, but not during the 1st and 3rd hours. The same pattern of decreased nociception was observed during the 2nd hour of action of the CG-induced inflammatory cascade mediators: TNFα, IL-1β, CXCL-1, and PGE2, and at the peak of action of 5 minutes of noradrenaline. Even the highest doses of SOD and catalase isoform inhibitors did not show a systemic effect. The drugs also did not exhibit hyperalgesic action by themselves. Inhibition of H2O2 degradation through ATZ injection reversed the pain on the 12th day of neuropathy. Inhibition of H2O2 synthesis in the cell cytosol through LCS-1 injection, as well as inhibition of its synthesis in mitochondria with the use of 2-ME, was not able to potentiate neuropathic pain. Inhibition of its synthesis in the extracellular space with the use of DETCA-3 potentiated submaximal pain during the decay of the nociceptive threshold in animals on the 6th day of neuropathy. Inhibition of H2O2 synthesis via DETCA-3 reversed the antinociception of the µ opioid agonist, DAMGO, but not of the δ and κ receptors bremazocin and SNC80. Its administration was also able to reverse analgesia induced by the classic opioid morphine. Inhibition of H2O2 degradation through the use of ATZ potentiated the submaximal dose of the µ agonist, DAMGO, but not the κ and δ opioid agonists bremazocin and SNC80. Its administration was also able to potentiate the analgesia of the submaximal dose of morphine. Inhibition of H2O2 synthesis through the use of DETCA-3 reversed the antinociception of the CB1 and CB2 receptor agonists AEA and 2-AG, as well as the phytocannabinoid Cannabidiol (CBD). Inhibition of H2O2 degradation through the use of ATZ potentiated the submaximal dose of the agonists AEA and 2-AG, as well as the phytocannabinoid CBD. CONCLUSION: Therefore, our study suggests that inflammatory pain induced by carrageenan (CG) and the inflammatory mediators TNFα, CXCL-1, IL-1β, NA, and PGE2, as well as neuropathic pain induced by chronic sciatic nerve constriction, promotes the mobilization of endogenous hydrogen peroxide (H2O2), which modulates nociception in the periphery. Additionally, we also suggest the participation of H2O2 as a mediator in analgesia arising from the agonism of opioid and cannabinoid receptors.