Background: Recently, the antinociceptive effect of LMH-2, a σ1 receptor antagonist, has been reported in diabetic mice with neuropathic pain. However, the mechanism by which this effect is produced is not completely clear. In this study, we explored the involvement of TRPV1 and the MOR-NMDAR complex in the antiallodynic effect of LMH-2 in hyperglycemic mice with neuropathic pain.

Methods: Hyperglycemia was induced in mice by administering streptozotocin-nicotinamide. Four weeks later, once neuropathic pain was established, the antiallodynic effect of LMH-2 (56.2 mg/kg) was evaluated using the up-down method with the von Frey filaments, both in the absence and the presence of capsazepine (8 mg/kg, ip), naloxone (NLX, 1 mg/kg, ip), NMDA (0.4 nM/10 µL, it), or their co-administration (NLX-NMDA). Gabapentin was used as positive control.

Results: Pretreatment with NLX did not alter the antiallodynic effect of LMH-2 in the up-down method with the von Frey filaments in hyperglycemic mice, whereas NMDA significantly reduced it. The addition of NLX to NMDA (NLX-NMDA) did not modify the effect of NMDA alone on the antiallodynic activity of LMH-2. Additionally, capsazepine completely blocked the antinociceptive effect of LMH-2 in hyperglycemic mice. Molecular docking analysis suggested a potential interaction between LMH-2 and TRPV1. Moreover, a higher dose of LMH-2 did not cause mortality or damage in healthy mice.

Conclusions: These results suggest the potential utility of LMH-2 in the treatment of diabetic neuropathy and highlight a key role for TRPV1 in LMH-2's antiallodynic mechanism, along with a possible, albeit limited, interaction with the MOR/NMDA complex.