Wasabi (Wasabia japonica Matsumura) is a perennial plant, and its rhizome is widely used as a pungent spice. Wasabi rhizome has been reported to have various physiological activities, but the flower has not been studied in depth. The aim of the present study was to isolate compounds from wasabi flowers and clarify their antioxidant and anti-inflammatory activities. Three phenylpropanoids, one alkaloid and seven flavonoids were isolated from wasabi flowers. Among them, 2"-O-trans sinapoyl isovitexin was identified as a novel compound. Five compounds inhibited 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity, with IC 50 values of less than 100 μM. Luteolin isolated in this study was found to inhibit nitric oxide production in macrophage-like J774.1 cells, with an IC 50 value of 24.1 ± 4.4 µM. Our results indicate that the phenolic compounds in wasabi flowers are effective ingredients for antioxidant and anti-inflammatory activities. For these reasons, wasabi flowers are expected to be used effectively as a functional food.

To investigate the compounds present in wasabi leaves (Wasabia japonica Matsumura) that inhibit the adipocyte differentiation, activity-guided fractionation was performed on these leaves. 5-Hydroxyferulic acid methyl ester (1: 5-HFA ester), one of the phenylpropanoids, was isolated from wasabi leaves as a compound that inhibits the adipocyte differentiation. Compound 1 suppressed the intracellular lipid accumulation of 3T3-L1 cells without significant cytotoxicity. Gene expression analysis revealed that 1 suppressed the mRNA expression of 2 master regulators of adipocyte differentiation, PPARγ and C/EBPα. Furthermore, 1 downregulated the expression of adipogenesis-related genes, GLUT4, LPL, SREBP-1c, ACC, and FAS. Protein expression analysis revealed that 1 suppressed PPARγ protein expression. Moreover, to investigate the relationship between the structure and activity of inhibiting the adipocyte differentiation, we synthesized 12 kinds of phenylpropanoid analog. Comparison of the activity among 1 and its analogs suggested that the compound containing the substructure that possess a common functional group at the ortho position such as a catechol group exhibits the activity of inhibiting the adipocyte differentiation. Taken together, our findings suggest that 1 from wasabi leaves inhibits adipocyte differentiation via the downregulation of PPARγ.