Diet-Induced Obesity in Cannabinoid-2 Receptor Knockout Mice and Cannabinoid Receptor 1/2 Double-Knockout Mice

Evidence suggests that cannabinoid-1 receptor (CB1R) activation is associated with increased food intake and body weight gain. Human epidemiological studies, however, show decreased prevalence of obesity in cannabis users. Given the overlapping and complementary functions of the cannabinoid receptors (CB1R and CB2R), mice lacking CB2R and mice lacking both CB1R and CB2R were studied.

A high-fat diet was used to study metabolic changes in male mice lacking CB2R (CB2^-/- ) or lacking both CB1R and CB2R (double-knockout [CB-DKO]) compared with wild-type mice.

When CB2^-/- mice were maintained on a high-fat diet, their weight gain was not different from wild-type mice (gaining 19 and 21 g, respectively), whereas CB-DKO mice gained only 5 g. There were no significant differences in food intake or locomotor activity between the three groups. Respiratory exchange rate and heat production were elevated in CB-DKO mice, with upregulation of adipose tissue thermogenic genes. Glucose tolerance test and insulin levels indicated increased insulin sensitivity in CB-DKO mice, whereas CB2^-/- displayed signs of impaired glucose clearance.

These results indicate that lacking both CB1R and CB2R protected mice from diet-induced obesity, possibly through the prominent role of CB1R in obesity or through an interactive effect of both receptors.