NADPH-oxidase 2 activation promotes opioid-induced antinociceptive tolerance in mice

Abstract

The analgesic effectiveness of long-term opioid therapies is compromised by the development of antinociceptive tolerance linked to the overt production of peroxynitrite (ONOO−, PN), the product of the interaction between superoxide (O2˙−, SO) and nitric oxide (NO), and to neuroinflammatory processes. We have recently reported that in addition to post-translational nitration and inactivation of mitochondrial MnSOD, activation of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase holoenzyme (NOX) in the spinal cord is a major source for the overt production of superoxide-derived PN during the development of morphine-induced antinociceptive tolerance. However, the NOX complex involved in these processes is not known. The objective of these studies is to identify a potential role for the NOX2 complex, an enzyme involved in inflammation. Mice lacking the catalytic subunit of NOX2 (Nox2−/−) or its regulatory subunit, p47phox (p47phox−/−), developed antinociceptive tolerance similar to wildtype (wt) mice after three days of continuous morphine. However, while wt mice continue to develop tolerance by day six, morphine analgesia was restored in both Nox2−/− and p47phox−/− mice. Moreover, the loss of Nox2 or p47 did not affect acute morphine analgesia in naïve mice. In wt mice, antinociceptive tolerance was associated with increased activation of NOX, nitration of MnSOD, and proinflammatory cytokines production in spinal cord. These events were markedly attenuated in Nox2−/− and p47phox−/− mice and instead, there was enhanced formation of antiinflammatory cytokine (IL4 and IL10) production. These results suggest that NOX2 activity provides a significant source of superoxide-derived PN to undertake post-translational modifications of mitochondrial MnSOD and to engage neuroinflammatory signaling in the spinal cord associated with opioid-induced antinociceptive tolerance. Thus, NOX2 may provide a potential target for adjuvant therapy to protect opioid analgesia.

Opioid‐Induced Central Immune Signaling: Implications for Opioid Analgesia

“…Inhibitor studies have implicated both mediators in morphine tolerance, which is due to dysregulation of glutamate homeostasis, activation of NFκB, and phosphorylation of p38 and ERK, leading to pro‐inflammatory cytokine release 82−84. This mechanism converges with other studies demonstrating that increased production of reactive oxygen and nitrogen species contributes to opioid tolerance 85−87…”

Attenuation of Remifentanil-Induced Hyperalgesia by Betulinic Acid Associates with Inhibiting Oxidative Stress and Inflammation in Spinal Dorsal Horn

“…Therefore, we determined the oxidative stress and inflammation in spinal dorsal horn 24 h after surgery to explore the underlying mechanisms by which BA alleviated RIH. Superoxide and peroxynitrite have been reported to result in the central sensitization and develop morphine-induced postoperative hyperalgesia [29,30]. Peroxynitrite is a short-lived (10 ms) ROS generated by the reaction of nitric oxide and superoxide, and easily diffuse through membranes to nitrate tyrosine residues to produce stable 3-NT [31].…”

Site-Specific Regulation of P2X7 Receptor Function in Microglia Gates Morphine Analgesic Tolerance

“…Y 382-384 may gate the P2X7R-mediated release of these signaling molecules that affect spinal microglia-to-neuron signaling in the development of morphine tolerance. Indeed, a complement of mechanisms in glia and neurons has been implicated in the development of opioid tolerance (Vanderah et al, 2001;Doyle et al, 2013). Whether these diverse mechanisms are causally linked through convergent or divergent pathways that modulate opioid analgesia are not known.…”

“…Drugs were administered by intrathecal injection under light anesthetic with 1% isoflurane (v/v) as described previously by De la Calle and Paíno (2002). Unless otherwise stated, intrathecal injections were delivered 30 min before intraperitoneal morphine or saline injections.…”