Stimulation of uncoupling protein 1 expression in brown adipocytes by naturally occurring carotenoids

OBJECTIVE: To assess the effect of naturally occurring carotenoids on brown adipocyte proliferation and differentiation. The rationale behind is that certain carotenoids have provitamin A activity in mammals, and that one of the active forms of vitamin A, (retinoic acid) is known to behave as a tran scriptional activator of the key gene for brown fat thermogenesis, the one encoding the uncoupling protein thermogenin (UCP1). DESIGN: Confluent primary cultures of mice brown adipocytes were treated wi th various concentrations of carotenoids. Cell morphology, total culture pr otein content, the DNA synthesis rate, and the levels of UCP1, retinoic aci d receptor alpha (RAR alpha) and retinoid X receptor alpha (RXR alpha) were analysed. RESULTS: Treatment with beta-carotene, alpha-carotene and lutein promoted U CP1 expression in a dose-dependent manner, with an effectiveness that was r elated to their potency as vitamin A precursors. Cell morphology, total cul ture protein content at confluence and DNA synthesis rate were unaffected a fter carotenoid treatment up to 10 mu M. CONCLUSION: The results indicate that carotenoids can positively affect the expression of UCP1 without altering brown adipocyte proliferation.