Esculetin Inhibits Fat Accumulation Through Insulin/Insulin-like Growth Factor- and AMP-Activated Protein Kinase-Dependent Pathways in Caenorhabditis elegans

Background: Esculetin, 6,7-dihydroxycoumarin, is a bioactive compound found in various herbal plants, and is known to have health-beneficial properties including anti-obesity effects. However, there is a lack of in vivo studies to clearly determine esculetin&rsquo:s role in lipid metabolism. Objectives: In this study, we studied esculetin&rsquo:s effect on lipid accumulation using Caenorhabditis elegans and its underlying mechanisms. Methods:&nbsp:C. elegans were treated with esculetin (100 or 200 &mu:M) for 48 h, and their triglyceride and protein levels were measured. Additionally, behavioral patterns such as pharyngeal pumping rate, body bending rate, body sizes, and locomotive activity were analyzed. Genetic dependencies were examined by utilizing mutant worms and testing relative gene expressions. Results:&nbsp:C. elegans treated with esculetin displayed significantly reduced fat accumulation compared to the controls without effects on the pharyngeal pumping rate, body bending rate, or locomotive activity. Esculetin&rsquo:s fat-lowering effect was dependent on DAF-2 (insulin/insulin-like growth factor-1 [IGF-1] receptor homolog), DAF-16 (Forkhead box protein O homolog), and AAK-2 (5&prime:-adenosine monophosphate-activated protein kinase [AMPK] catalytic subunit &alpha:2) in the mutant experiments. Esculetin also significantly increased the relative expression of downstream targets of DAF-16 (hsp-16.2 and sod-3), AMPK-related genes (aak-1 and aak-2), a sirtuin gene, sir-2.1, and a lipolysis-related gene, atgl-1. Conclusions: These findings suggest that esculetin inhibited fat accumulation in C. elegans and this effect was dependent on the insulin/IGF-1 and 5&prime:-adenosine monophosphate-activated protein kinase signaling pathways.