This study was performed to assess whether mice lacking the cannabinoid receptor CB1, CB2 or both receptors show increased susceptibility to TNBS colitis in comparison to wildtype mice. Previously, activation of CB1 and CB2 receptors showed attenuation of TNBS colitis in mice. The aim of the study was to investigate the susceptibility of three mouse strains CB1-, CB2- and CB1+2 double knockout mice in the model of TNBS colitis. The different knockout mice were given each a single enema with TNBS 7 mg, volume 150 µl (in 50% ethanol solution) on day 1. Control group (C57BL/6 mice) received the same concentration of TNBS enema and each strain received vehicle application of 150 µl 50% ethanol solution. After a 3-day period, the animals were sacrificed and their colon excised. A scoring system was used to describe macroscopical and histological changes. Messenger RNA-expression of TNF- and IL-1ß as pro-inflammatory markers was measured by RT-PCR. All three knockout strains showed increased susceptibility to TNBS colitis quantified by macroscopical and histological scoring systems and pro-inflammatory cytokine expression in comparison to the TNBS control group (wild type C57BL/6 animals). Mice lacking the CB1-, CB2-receptor or both receptors showed aggravation of inflammation in the model of TNBS colitis. Lacking of both cannabinoid receptors did not result in potentiation of colitis severity compared to lacking of each CB1 or CB2, respectively. These results suggest that the endocannabinoid system may have tonic inhibitory effects on inflammatory responses in the colon.
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Previous studies have shown that stimulation of cannabinoid 1 (CB1) receptor protects the gastric mucosa against stress-induced lesion. Aim of the present study was to examine the influence of anandamide on lipid peroxidation and antioxidant defense system in gastric mucosa and the role of sensory nerves in gastroprotective effects of cannabinoids. Studies were performed on rats with intact or ablated sensory nerves (by neurotoxic doses of capsaicin). Gastric lesions were induced by water immersion and restrain stress (WRS). Anandamide was administered at the dose of 0.3, 1.5 or 3.0 µmol/kg, 30 min before exposure to WRS. CB1 receptor antagonist, AM251 (4.0 µmol/kg) was administered 40 min before WRS. WRS induced gastric lesions associated with the decrease in gastric blood flow, mucosal DNA synthesis and mucosal activity of superoxide dismutase (SOD). Serum level of interleukin-1ß (IL-1ß) and mucosal level of malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE) were increased. Administration of anandamide reduced the ulcers area, generation of MDA+4-HNE and serum level of IL-1ß, and this effect was associated with the reduction in the WRS-induced decrease in gastric mucosal blood flow, mucosal DNA synthesis and SOD activity. Ablation of sensory nerves increased the area of ulcers, serum level of IL-1ß and mucosal content of MDA+4-HNE, whereas mucosal DNA synthesis, SOD activity and blood flow were additionally decreased. In rats with ablation of sensory nerves, administration of anandamide at the high doses (1.5 and 3.0 µmol/kg) partly reduced deleterious effect of WRS on gastric mucosa, but this effect was weaker than in animals with intact sensory nerves. Low dose of anandamide (0.3 µmol/kg) was ineffective in the protection of gastric mucosa against the WRS-induced lesions in rats with ablation of sensory nerves. In rats with intact sensory nerves and exposed to WRS, administration of AM251 exhibited deleterious effect. In rats with ablation of sensory nerves and exposed to WRS, AM251 failed to affect mucosal injury in the stomach. We conclude that anandamide reduces the mucosal oxidative stress and exhibits gastroprotective effect against WRS-induced ulcers. These effects are partly mediated by sensory nerves.
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