N-Acetylcysteine and Acetylsalicylic Acid Inhibit Alcohol Consumption by Different Mechanisms: Combined Protection

Abstract

Chronic ethanol intake results in brain oxidative stress and neuroinflammation, which have been postulated to perpetuate alcohol intake and to induce alcohol relapse. The present study assessed the mechanisms involved in the inhibition of: (i) oxidative stress; (ii) neuroinflammation; and (iii) ethanol intake that follow the administration of the antioxidant N-acetylcysteine (NAC) and the anti-inflammatory acetylsalicylic acid (ASA) to animals that had consumed ethanol chronically. At doses used clinically, NAC [40 mg/kg per day orally (p.o.)] and ASA (15 mg/kg per day p.o.) significantly inhibited chronic alcohol intake and relapse intake in alcohol-preferring rats. The coadministration of both drugs reduced ethanol intake by 65% to 70%. N-acetylcysteine administration: (a) induced the Nrf2-ARE system, lowering the hippocampal oxidative stress assessed as the ratio of oxidized glutathione (GSSG)/reduced glutathione (GSH); (b) reduced the neuroinflammation assessed by astrocyte and microglial activation by immunofluorescence; and (c) inhibited chronic and relapse ethanol intake. These effects were blocked by sulfasalazine, an inhibitor of the xCT transporter, which incorporates cystine (precursor of GSH) and extrudes extracellular glutamate, an agonist of the inhibitory mGlu2/3 receptor, which lowers the synaptic glutamatergic tone. The inhibitor of mGlu2/3 receptor (LY341495) blocked the NAC-induced inhibition of both relapse ethanol intake and neuroinflammation without affecting the GSSG/GSH ratio. Unlike N-acetylcysteine, ASA inhibited chronic alcohol intake and relapse via lipoxin A4, a strong anti-inflammatory metabolite of arachidonic acid generated following the ASA acetylation of cyclooxygenases. Accordingly, the lipoxin A4 receptor inhibitor, WRW4, blocked the ASA-induced reduction of ethanol intake. Overall, via different mechanisms, NAC and ASA administered in clinically relevant doses combine their effects inhibiting ethanol intake.

Oxidative Stress and Neuroinflammation as a Pivot in Drug Abuse. A Focus on the Therapeutic Potential of Antioxidant and Anti-Inflammatory Agents and Biomolecules

“…Interestingly, the activation of mGluR2/3 by NAC also restores the NAcc ability to recover neuronal synaptic adaptations. Consequently, the antagonists of mGluR2/3 prevent the rescuing effect of cocaine-seeking behavior and relapse to ethanol consumption by NAC [144,147,148].…”

“…Interestingly, aspirin treatment promotes additional anti-inflammatory mechanisms compared to other NSAIDs, as COX2 acetylated by aspirin can metabolize arachidonic acid to induce the generation of aspirin-induced lipoxins, with potent anti-inflammatory activity [191]. Recently, lipoxin administration was found to significantly inhibit chronic ethanol intake in rats and the administration of a lipoxin antagonist prevented the effect of aspirin in reducing ethanol intake [148], again showing a clear association between dug intake and inflammation.…”

Ethanol Induces Microglial Cell Death via the NOX/ROS/PARP/TRPM2 Signalling Pathway

“…These results, together, support a crucial role of the TRPM2 channel in mediating EtOH-induced microglial cell death. It is known that exposure to alcohol leads to oxidative stress and activation of PARP [ 8 , 9 , 10 ] and, as introduced earlier, PARP activation is the major signaling mechanism for oxidative stress-induced TRPM2 channel activation, including in microglial cells [ 25 , 26 , 27 , 28 , 29 , 31 , 32 , 33 ]. As described in our recent study examining cell death induced by ROS or Zn 2+ in primary microglial cells [ 25 ], and in this study showing H 2 O 2 -induced cell death in BV2 microglial cells ( Figure 2 e–h), EtOH-induced microglial cell death was remarkably attenuated by treatment with PJ34 and DPQ, two structurally different PARP inhibitors ( Figure 3 ), supporting that PARP activation is critical in EtOH-induced TRPM2-mediated microglial cell death.…”

“…ROS production is one of the common events involved in mediating TRPM2 channel activation [ 26 , 27 , 28 , 29 ]. It has been well documented that EtOH can stimulate ROS production [ 9 ] via induction of NOX [ 11 ]. Consistent with this notion, we showed that exposure to high concentrations of EtOH induced a significant increase in ROS production in microglial cells ( Figure 4 a,b) and, furthermore, that EtOH-induced microglial cell death was prevented by treatment with PKC and NOX inhibitors ( Figure 4 c–f), consistent with the notion that PKC/NOX-mediated ROS production acts as an upstream mechanism in mediating EtOH-induced TRPM2 channel activation and microglial cell death.…”

“…In addition, as has been well documented, alcohol intake causes the brain to promote further alcohol consumption [ 7 ]. Regarding how alcohol impacts the brain, multiple molecular and cellular mechanisms have been proposed, including increased poly(ADP-ribose) polymerase (PARP) activity and ensuing regulation of gene expression, induction of oxidative stress via NADPH oxidases (NOX)-mediated generation of reactive oxygen species (ROS), neurotoxicity, neuromodulation, and neuroinflammation [ 7 , 8 , 9 , 10 , 11 , 12 ].…”