Japanese Leaf Burdock Extract Inhibits Adipocyte Differentiation in 3T3-L1 Cells

Burdock, Arctium lappa Linn. (Asteraceae), is cultivated in East Asian for its edible roots, and its seeds are used in a herbal medicine. Burdock seeds and roots exhibit anti-adipogenic activity. However, the anti-adipogenic activity of the aboveground parts of burdock remains underexplored. Therefore, this study determined the anti-adipogenic effects of burdock leaf extract on 3T3-L1 adipocytes. Seventy percent ethanol (EtOH) extract of burdock leaves, which inhibited lipid accumulation, was fractionated into five fractions using Diaion (R) HP-20. EtOH eluted fractions (40 and 80%) strongly inhibited lipid accumulation. A common compound in these fractions was onopordopicrin (OPP), and purified OPP suppressed lipid accumulation and inhibited adipocyte differentiation. alpha, beta-unsaturated carbonyl structure of OPP suggests potential electrophilic reactivity with polyfunctional thiol-trapping agents like cysteine residues. Indeed, the anti-adipogenic effects of OPP disappeared with the addition of cysteamine, which possesses a thiol group. Rhodamine-maleimide assay showed that OPP binds to the cysteine residues of adipocyte-specific transcription factor, peroxisome proliferator-activated receptor gamma (PPAR gamma). Hence, our findings suggest that OPP exerts its anti-adipogenic action via binding to cysteine residues in signal proteins like PPAR gamma, inhibiting their activation. Thus, burdock leaf extract is a potential source of OPP, a bioactive compound with anti-obesity activity.