Inhibitory effects of caffeine and its metabolites on intracellular lipid accumulation in murine 3T3-L1 adipocytes

To understand the mechanisms of the anti-obesity effects of dietary caffeine, the effects of caffeine and its metabolites on adipocyte differentiation and insulin-stimulated glucose uptake in murine 3T3-L1 adipocytes were investigated. Caffeine did not inhibit the differentiation of 3T3-L1 pre-adipocytes to mature adipocytes, but it did suppress the intracellular lipid accumulation after complete differentiation in a dose-dependent manner (0.125-1.0 mM). This effect was also observed in 1,3,7-trimethyluric acid-3,7-dimethyluric acid-and 5-acetylamino-6-formylamino-3-methyluracil-treated cells. Caffeine also inhibited insulin-stimulated glucose uptake in differentiated 3T3-L1 adipocytes in a dose-dependent manner. Treatment with theophylline, paraxanthine, 1-methylxanthine (MX), 3-MX, or 7-MX also inhibited glucose uptake in differentiated adipocytes. These results suggest that the anti-obesity activity of dietary caffeine is due to the additive and/or synergistic inhibitory effects of caffeine and its metabolites on intracellular lipid accumulation and that caffeine does not affect adipocyte differentiation.