Functional relevance of the cannabinoid receptor 2 - heme oxygenase pathway: a novel target for the attenuation of portal hypertension

Abstract

Aims: In liver cirrhosis, inflammation triggers portal hypertension. Kupffer cells (KC) produce vasoconstrictors upon activation by bacterial constituents. Here, we hypothesize that the anti-inflammatory action of the cannabinoid receptor 2 (CB2) agonists JWH-133 and GP 1a attenuate portal hypertension.

Main methods: In vivo measurements of portal pressures and non-recirculating liver perfusions were performed in rats 4weeks after bile duct ligation (BDL). Zymosan (150μg/ml, isolated liver perfusion) or LPS (4mg/kgb.w., in vivo) was infused to activate the KC in the absence or presence of JWH-133 (10mg/kgb.w.), GP 1a (2.5mg/kgb.w.) or ZnPP IX (1μM). Isolated KC were treated with Zymosan (0.5mg/ml) in addition to JWH-133 (5μM). The thromboxane (TX) B2 levels in the perfusate and KC media were determined by ELISA. Heme oxygenase-1 (HO-1) and CB2 were analyzed by Western blot or confocal microscopy.

Key findings: JWH-133 or GP 1a pre-treatment attenuated portal pressures following KC activation in all experimental settings. In parallel, HO-1 expression increased with JWH-133 pre-treatment. However, the inhibition of HO-1 enhanced portal hypertension, indicating the functional role of this novel pathway. In isolated KC, the expression of CB2 and HO-1 increased with Zymosan, LPS and JWH-133 treatment while TXB2 production following KC activation was attenuated by JWH-133 pre-treatment.

Significance: JWH-133 or GP 1a treatment attenuates portal hypertension. HO-1 induction by JWH-133 plays a functional role. Therefore, the administration of JWH-133 or GP 1a represents a promising new treatment option for portal hypertension triggered by microbiological products.

Keywords: (6aR,10aR)-3-(1,1-dimethylbutyl)-6a,7,10,10a-tetrahydro-6,6,9-trimethyl-6H-dibenzo[b,d]pyran; 2-Chloro-5-nitro-N-phenylbenzamide; BDL; Bile duct ligation (BDL); CB(2); GW 9662; Gp 1a; HO; Heme oxygenase (HO); JWH-133; KC; Kupffer cell; LDH; LPS; N-(Piperidin-1-yl)-1-(2,4-dichlorop­henyl)-1,4-dihydro-6-methylindeno[1,2-c]pyrazole-3­-carboxamide; TLR; TX; Thromboxane; Zy; Zymosan A; b. w; bile duct ligation; body weight; cannabinoid receptor 2; heme oxygenase; lactate dehydrogenase; lipopolysaccharide; thromboxane; toll like receptor.