The Extract of Humulus japonicus Inhibits Lipogenesis and Promotes Lipolysis via PKA/p38 Signaling

Previous research has shown that an aqueous extract of Humulus japonicus (EH) can ameliorate hypertension, nonalcoholic fatty liver disease, and oxidative stress in adipocytes by activating the thermogenic pathway. However, the effects of an ethanol (30%) extract of EH on obesity are unknown.

Various protein expression levels in fully differentiated 3T3-L1 adipocytes were assessed by Western blotting. Lipid deposition in 3T3-L1 adipocytes was examined by oil red O staining. The MTT assay was used to evaluate adipocyte viability. Caspase 3 activity and glycerol release were determined using commercial assay kits.

In this study, we discovered that EH treatment inhibited lipogenesis and promoted lipolysis in both differentiated 3T3-L1 adipocytes and adipose tissue of mice fed a high-fat diet. EH treatment also increased phosphorylated protein kinase A (PKA) levels while reducing p38 phosphorylation. When H89, a PKA inhibitor, was used, the effects of EH on lipogenic lipid accumulation and lipolysis in 3T3-L1 adipocytes were eliminated. Treatment with luteolin 7-O-β-d-glucoside (LU), the major active compound in EH, also suppressed lipid deposition and p38 phosphorylation but enhanced lipolysis in 3T3-L1 adipocytes. These changes were abrogated by H89.

These findings indicate that EH containing LU reduces lipogenesis and stimulates lipolysis via the PKA/p38 signaling pathway, leading to an improvement in obesity in mice. Therefore, our study suggested that EH could be a promising therapeutic agent for treating obesity.