Background: Endocannabinoids acting via cannabinoid receptor 1 (CB1R) can elicit increased intestinal permeability (a condition also called ‘leaky gut’). Alcohol binge can adversely affect digestive functions, including intestinal permeability; however, the underlying mechanisms remain incompletely understood. The current study aimed at examining whether CB1R is involved in alcohol binge-induced intestinal permeability. Methods: We developed intestinal epithelial-specific CB1R knockout (CB1^IEC−/−) mice and evaluated the in vivo contribution of gut CB1R in alcohol binge-induced intestinal permeability. Results: Alcohol binge increased anandamide levels in the proximal small intestine in association with increased intestinal permeability. Radioligand binding and functional assays confirmed that the genetic deletion of intestinal epithelial CB1R did not alter the density or functionality of CB1R in the brain. Additionally, a peripheral CB1R antagonist, (S)-MRI-1891 (INV-202/monlunabant), exhibited comparable binding affinity to CB1R in brain homogenates. An acute oral administration of (S)-MRI-1891 (3 mg/kg) reduced alcohol binge-induced intestinal permeability in littermate control CB1^f/f (CB1 floxed/floxed) mice but had no effect in CB1^IEC−/− mice, underscoring the role of intestinal CB1R in this phenomenon. Mechanistically, we found that alcohol activated intestinal epithelial CB1R-ERK1/2 pathway with subsequent downregulation of tight junction proteins and reduction in villi length. In addition, targeting intestinal CB1R and downstream ERK1/2 was able to reverse this process, with subsequent upregulation of tight junction proteins and increased villi length, thus improving gut barrier function. Despite the effects on intestinal permeability, deletion of intestinal CB1R did not significantly affect metabolic parameters and liver disease. Conclusion: Our findings suggest that alcohol promotes leaky gut via the activation of gut epithelial CB1R and demonstrate that inhibition of CB1R with peripheral-restricted selective CB1R antagonists can prevent alcohol binge-induced intestinal permeability.

Alcohol consumption is associated with gut dysbiosis, increased intestinal permeability, endotoxemia, and a cascade that leads to persistent systemic inflammation, alcoholic liver disease, and other ailments. Craving for alcohol and its consequences depends, among other things, on the endocannabinoid system. We have analyzed the relative role of central vs. peripheral cannabinoid CB1 receptors (CB1R) using a “two-bottle” as well as a “drinking in the dark” paradigm in mice. The globally acting CB1R antagonist rimonabant and the non-brain penetrant CB1R antagonist JD5037 inhibited voluntary alcohol intake upon systemic but not upon intracerebroventricular administration in doses that elicited anxiogenic-like behavior and blocked CB1R-induced hypothermia and catalepsy. The peripherally restricted hybrid CB1R antagonist/iNOS inhibitor S-MRI-1867 was also effective in reducing alcohol consumption after oral gavage, while its R enantiomer (CB1R inactive/iNOS inhibitor) was not. The two MRI-1867 enantiomers were equally effective in inhibiting an alcohol-induced increase in portal blood endotoxin concentration that was caused by increased gut permeability. We conclude that (i) activation of peripheral CB1R plays a dominant role in promoting alcohol intake and (ii) the iNOS inhibitory function of MRI-1867 helps in mitigating the alcohol-induced increase in endotoxemia.

Gut-brain signaling influences alcohol consumption and addiction behaviors. We found that selectively deleting cannabinoid receptor 1 (CB ₁ R) from advillin ⁺ peripheral sensory neurons eliminates the inhibitory effect of the peripheral CB ₁ R antagonist JD5037 on voluntary ethanol intake (VEI). Similar results were seen in mice with CB ₁ R deletion in Phox2b ⁺ nodose ganglia (NGA), but not in Wnt ⁺ dorsal root ganglia. These findings were corroborated with MRI-1891, another non-brain penetrant CB ₁ R antagonist. The inhibition of VEI by JD5037 was lost in Gpr65 ^Cre ; Cnr1 ^lox/lox mice but remained intact in Glp1r ^Cre ; Cnr1 ^lox/lox mice. Additionally, deleting the ghrelin receptor (Ghsr) from Phox2b ⁺ NGA neurons blocked the inhibition of alcohol intake either by a Ghsr or by CB ₁ R antagonists. Thus, CB ₁ R on Gpr65 ⁺ NGA projections to the mucosa of the gastrointestinal tract is essential for VEI. These findings also suggest a mutual interdependence of endocannabinoid and ghrelin signaling in controlling VEI via a gut-brain axis.