Synthetic cannabinoid ajulemic acid exerts potent antifibrotic effects in experimental models of systemic sclerosis

Background Cannabinoids modulate fibrogenesis in scleroderma. Ajulemic acid (AjA) is a non-psychoactive synthetic analogue of tetrahydrocannabinol that can bind the peroxisome proliferator-activated receptor-gamma (PPAR-gamma). Recent evidence suggests a key role for PPAR-gamma in fibrogenesis. Objective To determine whether AjA can modulate fibrogenesis in murine models of scleroderma. Material and methods Bleomycin-induced experimental fibrosis was used to assess the antifibrotic effects of AjA in vivo. In addition, the efficacy of AjA in pre-established fibrosis was analysed in a modified model of bleomycin-induced dermal fibrosis and in mice overexpressing a constitutively active transforming growth factor beta (TGF beta) receptor I. Skin fibrosis was evaluated by quantification of skin thickness and hydroxyproline content. As a marker of fibroblast activation, alpha-smooth muscle actin was examined. To study the direct effect of AjA in collagen neosynthesis, skin fibroblasts from patients with scleroderma were treated with increasing concentrations of AjA. Protein expression of PPAR-gamma, and its endogenous ligand 15d-PGJ2, and TGF beta were assessed before and after AjA treatment. Results AjA significantly prevented experimental bleomycin-induced dermal fibrosis and modestly reduced its progression when started 3 weeks into the disease. AjA strongly reduced collagen neosynthesis by scleroderma fibroblasts in vitro, an action which was reversed completely by co-treatment with a selective PPAR-gamma antagonist. Conclusions AjA prevents progression of fibrosis in vivo and inhibits fibrogenesis in vitro by stimulating PPAR-gamma signalling. Since therapeutic doses of AjA are well tolerated in humans, it is suggested that AjA as an interesting molecule targeting fibrosis in patients with scleroderma.