AM404, a metabolite of acetaminophen, inhibits transporters that transport the endogenous cannabinoid anandamide and stimulates transient receptor potential vanilloid (TRPV) 1 channels. We have reported that AM404 inhibits N-methyl-D-aspartic acid (NMDA)-induced neuronal injury in mice. The aim of this study was to determine whether cannabinoid receptors or TRPV1 channels are involved in the protective effect of AM404 on NMDA-induced neuronal injury.
Cg-Tg (Thy1-CFP) 23Jrs/J mice were subjected to intravitreal injection of NMDA. Mixture of AM404 and SR141716A (a cannabinoid CB₁ receptor antagonist), or SR144528 (a cannabinoid CB₂ receptor antagonist), or A784168 (a TRPV1 antagonist) were intravitreally administered simultaneously with NMDA. After 7 days, the number of ECFP-positive cells in the retina was measured and the percentage of retinal ganglion cells (RGC) remaining was determined. NMDA-induced RGC loss was significantly inhibited by AM404. The protective effect of AM404 against NMDA-induced RGC injury was almost completely suppressed by SR141617A, but not SR144528. Furthermore, the effect of AM404 was almost completely inhibited by A784168. These results suggest that activation of cannabinoid CB₁ receptors and TRPV1 channels are involved in the protective effect of AM404 on NMDA-induced retinal neuronal injury.