Fat Browning Effects of Catalpol and Rhoifolin from Rehmannia glutinosa (Gaertn.) and Lonicera japonica (Thunb.) in 3T3-L1 Adipocytes via the β3-AR Signaling Pathway

Background/Objectives: Promoting white adipose tissue (WAT) browning into thermogenic beige adipocytes is a promising anti-obesity strategy. Yanggyeoksanhwa-tang (YST) has been used traditionally to alleviate obesity-related conditions. Catalpol and rhoifolin are major bioactive components of Rehmannia glutinosa (Gaertn.) and Lonicera japonica (Thunb.) with known metabolic or anti-inflammatory effects. However, their direct roles in adipocyte browning and the mechanisms via β3-adrenergic receptor (β3-AR) signaling are not well defined, and this study addresses this gap. Methods: To evaluate browning potential, 3T3-L1 adipocytes were treated with catalpol and rhoifolin during differentiation. The expression of browning markers and lipid metabolism or catabolism transcription factors was analyzed using Western blotting and quantitative real-time polymerase chain reaction. The involvement of the β3-AR and adenosine monophosphate–activated protein kinase (AMPK) signaling pathways was further validated using specific agonists and antagonists. Results: Both compound treatments significantly upregulated beige-specific (Cd137, Cited, Tbx1, Cidea, Fgf21, Tmem26) and mitochondrial biogenesis markers (Cox4, Nrf1, Tfam), accompanied by a marked increase in thermogenic markers (UCP1, PGC-1α, Prdm16). Concurrently, lipolysis-related genes such as Atgl, Hsl, and Plin1 were elevated, while lipogenesis targets (Fasn, Lpl, Srebf1, Acaca) were downregulated through activation of the β3-AR signaling pathway. Conclusions: These findings suggest that catalpol and rhoifolin, key phytochemicals of YST, promote WAT browning and lipolysis. Our findings indicate that these compounds induce browning and modulate metabolism via the β3-AR pathway. These results serve as a cornerstone for natural anti-obesity therapy, pending further validation in vivo and clinical studies.