Effects Of A Novel CB₁R Antagonist Or Inverse Agonist, MJ08 On Glucose And Lipid Metabolism In Mice

Objective:To explore the effects of a novel CB1R antagonist or inverse agonist on weight loss and insulin sensitivity, the pharmacodynamics mechanisms of MJ08 were performed on two kinds of models, C57BL/6J and KKAy mice, with rimonabant as control drug. According to the phenomenon of MJ08 elevated fasting blood glucose, we used the liver tissue as the object to further explore the role of inverse agonistic effect on the regulatory mechanism of glucose metabolism.Methods:(1) C57BL/6J and KKAy mice were randomly divided into three groups respectively:the vehicle control group, rimonabant (10mg/kg) treatment group and MJ08 (10mg/kg) treatment group, the mice were treated for 26 days. Changes in body weight were monitored everyday and fasting blood glucose was tested regularly. At the end of the experiments, serum triglyceride (TG), and total cholesterol (TCH) were measured. Insulin, glucagon and leptin concentrations were determined by multiplex. (2) The protein expression of cannabinoid receptor 1 (CB1R),β2-adrenergic receptor (ADRB2), glucagon receptor (GlucR), a subunit of the stimulatory G protein (Gsa), phosphate Carboxylase kinase (PEPCK), glucose-6-phosphatase (G6Pase) in liver tissue were detected by western blot. (3) The cyclic adenosine monophosphate (cAMP) content in the liver was measured by dual-wavelength fluorescence. (4) The method of Anthrone was applied to detect the liver glycogen content. (5) The PEPCK and G6Pase mRNA levels were detected by RT-PCR.Results:(1) SR141716 could lower weight and lipid profile, increase insulin sensitivity, and ease the symptoms of hyperglycemia in KKAy mice; having been treated with MJ08, the C57BL/6J and KKAy mice exhibited the effect of weight loss, and which was stronger than rimonabant. Moreover, MJ08 could reduce the index of fat and serum triglycerides in KKAy mice, indicating that MJ08 also relieved the symptoms of obesity. However, the effects on C57BL/6J mice were weak. MJ08 could reduce insulin sensitivity in mice, which was more obvious in C57BL/6J mice, mainly due to its glycemic effect. (2) In KKAy mice, SR141716 could decrease insulin hypersecretion without affecting the fold increase in glucose-stimulated insulin secretion. However, it decreased the fold increase in glucose-stimulated insulin secretion without affecting basal secretion in C57BL/6J mice; MJ08 had no effects on basal and fold increased insulin levels in KKAy mice, but it had the same effects with SR141716 in C57BL/6J mice, and the effect was more intense. (3) MJ08 mainly up-regulated the expression of GlucR, which activated Gsa system, then cAMP level increased in liver, eventually leading to the liver PEPCK, G6Pase gene and protein levels increased, resulting in increased hepatic glucose output and elevated blood glucose.Conclusions:MJ08 could significantly lower the body weight, which had more obvious inverse agonistic effect, especially on the regulation of glucose; MJ08 could activate the Gsa system, then up-regulated gluconeogenesis, resulting in increased hepatic glucose output.