Hepatic expression of cannabinoid receptors CB1 and CB2 correlate with fibrogenesis in patients with chronic hepatitis B

Background: The endocannabinoid system is involved in the pathogenesis of liver fibrosis. However, most of the findings in this area have come from experimental studies in animal models or clinical trials on chronic hepatitis C. The roles of cannabinoid receptor 1 (CB1) and cannabinoid receptor 2 (CB2) in hepatofibrosis in patients with chronic hepatitis B (CHB) have not been studied fully. This study aimed to explore the relationship between liver fibrosis and the expression of CB1 and CB2 in patients with CHB.

Methods: Eighty liver biopsy specimens from patients with CHB (52 male, 28 female) were analyzed in this study. Fibrosis was staged on a scale of 1 to 4 (F1 to F4, with F4 defining cirrhosis). There were 20 samples for each fibrosis stage. The expression of hepatic alpha-smooth muscle actin (α-SMA), CB1, and CB2 was detected by immunohistochemistry.

Results: Hepatic CB1 and CB2 were expressed in all patients with CHB. The degree of fibrosis was significantly associated with the increased expression of CB1 and CB2 in CHB. Furthermore a significant increase in cells positive for both CB1 and CB2 was detected in stage 3 and stage 4 disease compared to stage 1 and stage 2 disease. There was a strong positive association between CB1 expression and α-SMA expression. Moreover, double immunofluorescence staining for CB1 and α-SMA demonstrated that activated hepatic stellate cells (HSCs) express CB1.

Conclusions: The hepatic expression of CB1 and CB2 plays an important role during the progression of fibrosis induced by CHB. Endogenous activation of CB1 receptors in patients with CHB enhances fibrogenesis by direct effect on activated HSCs.