Antinociceptive effects of AS1069562, the (+)-isomer of indeloxazine, on spinal hypersensitivity induced by intrathecal injection of prostaglandin in mice: Comparison with duloxetine and amitriptyline

The (+)-isomer of indeloxazine AS1069562 exerts multiple pharmacological actions including the inhibition of serotonin (5-HT) and norepinephrine reuptake and analgesia in experimental animal pain models. Here, we evaluated the antinociceptive effects of AS1069562 and the antidepressants duloxetine and amitriptyline in mouse models of prostaglandin-induced spinal hypersensitivity. Prostaglandin E2 (PGE2) and F2α (PGF2α) were intrathecally administered to induce spinal hypersensitivity, causing tactile allodynia in mice. Allodynia induced by PGF2α but not by PGE2 was suppressed by desensitization of C-fibers with systemic pretreatment with resiniferatoxin. C-fiber hyperexcitability might therefore play a role in allodynia induced by PGF2α but not PGE2. In the PGE2-induced allodynia model, AS1069562 and duloxetine significantly suppressed allodynia, whereas amitriptyline did not. In the PGF2α-induced allodynia model, AS1069562 and amitriptyline significantly ameliorated allodynia, whereas duloxetine did not. To demonstrate the broad effects of AS1069562 compared to duloxetine, additional studies were conducted to elucidate other target mechanisms of AS1069562 beyond 5-HT and norepinephrine reuptake inhibition. AS1069562 exhibited affinity for both 5-HT1A and 5-HT3 receptors, and the analgesic effect of AS1069562 on PGF2α-induced allodynia was significantly blocked by the 5-HT1A receptor antagonist (S)–WAY100135 and the 5-HT3 receptor agonist SR57227. Taken together, these results indicate that AS1069562 inhibits both C-fiber- and non-C-fiber-dependent prostaglandin-induced allodynia, while duloxetine inhibits only non-C-fiber-triggered allodynia, and amitriptyline inhibits only C-fiber-triggered allodynia. These broad antinociceptive effects of AS1069562 may be due not only to 5-HT and norepinephrine reuptake inhibition but also to its effects on 5-HT receptors such as 5-HT1A and 5-HT3 receptors.