Background and Objective: CB1 antagonism may have potential benefits in the metabolic syndrome, with effects mediated through central orexigenic mechanisms and peripheral action on adipose tissue. We have previously described the effects of CB1 activation/inactivation on murine white preadipocyte 3T3-L1 proliferation; we now extend these studies to human tissue.
Method: Ethical approval was obtained for this study. Human preadipocytes were isolated from whole (paired subcutaneous & omental, n=4) tissue by collagenase digest. Both populations were exposed to varying concentrations of CB1 agonists (anandamide and ACEA) or antagonist (AM251) and proliferation assessed by direct cell counting (Coulter). Cells were also cultured in differentiation medium containing PPARγ agonist alone, or supplemented with 100 nM ACEA or AM251. mRNA was extracted at various time points and reverse transcribed. Transcripts for CB1, PPARγ, and GPDH (mouse) or LPL (human) were measured by QPCR.
Results: In both 3T3-L1 and human studies CB1 expression was upregulated during differentiation peaking at days 68 (104 copies) coincident with the rise in PPARγ. ACEA further increased both PPARγ and CB1 expression while AM251 resulted in higher levels of terminal markers of differentiation, but this was not accompanied by visible lipid droplet accumulation. CB1 agonists caused a concentration dependent stimulation of proliferation (peak effect 10−8M vs. 10−7M, 3T3 vs. human, P<0.001). The effect was inhibited by AM251, which was without effect alone in 3T3-L1. In human studies, however, AM251 inhibited proliferation by up to 30% with a greater response in omental cells than in subcutaneous (P<0.001), particularly those from individuals with the highest BMI.
Conclusion: AM251 resulted in higher responses in human cells with a preferential effect on omental preadipocyte proliferation, which may explain some of the antiobesity effects of CB1 antagonist therapy.