N-acetylcysteine downregulates phosphorylated p-38 expression but does not reverse the increased superoxide anion levels in the spinal cord of rats with neuropathic pain

Abstract

We determined the effect of N-acetylcysteine (NAC) on the expression of the phosphorylated p38 (p-p38) protein and superoxide anion generation (SAG), two important players in the processing of neuropathic pain, in the lumbosacral spinal cord of rats with chronic constriction injury (CCI)-induced neuropathic pain. The sciatic functional index (SFI) was also measured to assess the functional recovery post-nerve lesion. Thirty-six male Wistar rats were divided equally into the following groups: Naive (rats did not undergo surgical manipulation); Sham (rats in which all surgical procedures involved in CCI were used except the ligature), and CCI (rats in which four ligatures were tied loosely around the right common sciatic nerve), which received 2, 4, or 8 intraperitoneal injections of NAC (150 mg·kg-1·day-1) or saline beginning 4 h after CCI. Rats were sacrificed 1, 3, and 7 days after CCI. The SFI was measured on these days and the lumbosacral spinal cord was used for analysis of p-p38 expression and SAG. CCI induced a decrease in SFI as well as an increase in p-p38 expression and SAG in the spinal cord. The SFI showed a partial recovery at day 7 in saline-treated CCI rats, but recovery was improved in NAC-treated CCI rats. NAC induced a downregulation in p-p38 expression at all time-points evaluated, but did not reverse the increased SAG induced by CCI. Since p-p38 is a mediator in neuropathic pain and/or nerve regeneration, modulation of this protein may play a role in NAC-induced effects in CCI rats.

Effects of N-acetylcysteine on spinal cord oxidative stress biomarkers in rats with neuropathic pain

“…Adult male Wistar rats weighing 200–300 g were divided into three experimental groups (Naive, Sham, and CCI), and each one was further divided into two subgroups (n=6 each), which received NAC (Fluimucil®, Zambon Laboratórios Farmacêuticos Ltda., Brazil) at a dose of 150 mg·kg −1 ·day −1 or 0.9% saline solution intraperitoneally for 1, 3, or 7 days. Administration started on the day of surgery (beginning 4 h after recovery from anesthesia) and was performed daily at 5:00 pm by the same researcher ( 9 , 10 ). Rats were not anesthetized for the injections.…”

“…It has been demonstrated that NAC has neuroprotective roles ( 6 ) and inhibits nociceptive transmission in humans and mice ( 7 ). This molecule also induces antinociception in rats with chronic constriction injury (CCI) of the sciatic nerve ( 8 – 10 ). Rat CCI is one of the most commonly employed animal models of neuropathic pain; CCI simulates the symptoms of chronic nerve compression, which correspond to causalgia or complex regional pain syndrome in human patients ( 11 ).…”

“…GSH is a protective agent and detoxifies reactive oxygen species (ROS) both enzymatically and non-enzymatically ( 12 ). NAC has also a direct role in scavenging ROS in neurons ( 6 ), which seems to help normalize the oxidative status altered by neuropathic pain, because ROS such as superoxide radicals, hydrogen peroxide (H 2 O 2 ) and nitric oxide play an important role in the pathogenesis of neuropathic pain ( 8 , 9 , 10 , 13 ). In rats with CCI, NAC treatment reduced nitric oxide metabolites and increased the activity of antioxidant enzymes such as glutathione-S-transferase and glutathione peroxidase in the spinal cord ( 9 ).…”

“…Since neuropathic pain increases ROS ( 8 , 9 , 10 , 13 ) and NAC is a precursor of GSH ( 4 , 5 ), we postulated that NAC treatment would change the levels of lipid hydroperoxides and ascorbic acid in the lumbosacral spinal cord from CCI rats, the region where most afferent fibers of the sciatic nerve enter. Thus, our study assessed the effect of intraperitoneal administration of NAC (150 mg·kg −1 ·day −1 ), given for 1, 3, and 7, days, on the lipid hydroperoxide and ascorbic acid levels in the lumbosacral spinal cord of rats with CCI.…”

“…The dose of NAC (150 mg·kg −1 ·day −1 ) was chosen because it showed antinociceptive effect in rats with CCI ( 9 , 10 ). The time points of the study (1, 3, and 7 days) were based on our previous study with NAC treatment ( 10 ).…”