Hydroxyframoside B, a Secoiridoid of Fraxinus rhynchophylla, Inhibits Adipocyte Differentiation in 3T3-L1 Cells

Fraxinus rhynchophylla showed significant inhibitory activity on adipocyte differentiation in the 3T3-L1 preadipocyte cell line as assessed by measuring fat accumulation using Oil Red O staining. Further fractionation led to the isolation of two secoiridoids, oleuropein and hydroxyframoside B. Hydroxyframoside B significantly reduced fat accumulation and triglyceride content in differentiated 3T3-L1 cells without affecting cell viability, whereas oleuropein showed little effect. Further studies with interval treatment demonstrated that hydroxyframoside B exerted inhibitory activity on adipocyte differentiation when treated within 2 days (days 0-2) after differentiation induction. In addition, hydroxyframoside B significantly blocked the induction of adipogenic transcription factors such as C/EBP alpha, C/EBP beta, and PPAR gamma. Taken together, these results suggest that hydroxyframoside B inhibited early/middle stage of adipogenic differentiation, in part, via inhibition of C/EBP alpha, C/EBP beta, and PPAR gamma-dependent pathways.