Evidence for adenosine- and serotonin-mediated antihyperalgesic effects of cizolirtine in rats suffering from diabetic neuropathy

Cizolirtine is a novel non-opioid drug which demonstrated antinociceptive activity in numerous pain models in rodents. Yet, its mechanism of action remains unknown. Several lines of evidence support the idea that adenosine (ADO) and serotonin (5-HT) modulate nociceptive signaling. Our study aimed at investigating whether these neuroactive molecules could be implicated in the mechanism of action of cizolirtine. Cizolirtine-induced antihyperalgesia was compared before and after pretreatment with ADO A1–A2A and 5-HT1B/1D receptor ligands in rats rendered diabetic by streptozotocin pretreatment and suffering from neuropathic pain. Cizolirtine alone (30–80 mg/kg, i.p.) significantly increased mechanical nociceptive thresholds. Acute pretreatment with the A1–A2A receptor antagonist caffeine (5 mg/kg, i.p.) or the 5-HT1B/1D receptor antagonist GR-127,935 (3 mg/kg, i.p.) significantly reduced the antihyperalgesic effects of cizolirtine. Conversely, cizolirtine-induced antihyperalgesia was promoted by pretreatment with either the selective A1 receptor agonist CPA (0.3 mg/kg, i.p.) or the selective 5-HT1B receptor agonist CP-94,253 (3 mg/kg, i.p.), and this potentiation was totally prevented by acute pretreatment with respective antagonists. Interestingly, A1 receptor blockade by DPCPX inhibited the promoting effect of CP-94,253 on cizolirtine-induced antihyperalgesia, suggesting that the adenosine A1-mediated step takes place downstream the serotonin 5-HT1B-mediated step in the neurobiological mechanisms underlying cizolirtine action.