The methanolic extract from the flowers of Mesua ferrea Linn. (Calophyllaceae) showed significant hyaluronidase inhibitory activity. Following a bioassay-guided separation of the extract, two biflavonoids, viz., mesuaferrone-A (1) and mesuaferrone-B (2), were isolated, along with ten flavonoids (3–12), two xanthones (13 and 14), three triterpenes (15–17), a phenylpropanoid (18), and five aromatics (19–24). Among the isolates, 1 and 2 (IC50 = 51.1 µM and 54.7 µM, respectively) exhibited hyaluronidase inhibitory activity equivalent to that of the commercially available antiallergic agents disodium cromoglycate (64.8 μM) and ketotifen fumarate (76.5 μM). These biflavonoids (1 and 2) are 8-8′′ linked dimers that are composed of naringenin (1a) or apigenin (3), with their corresponding monomers lacking inhibitory activity (IC50 > 300 μM). In addition, 1 and 2 (IC50 = 49.4 µM and 49.2 µM, respectively) inhibited the release of β-hexosaminidase, which is a marker of antigen-IgE-mediated degranulation, in rat basophilic leukemia (RBL-2H3) cells. These inhibitory activities were more potent than those of the antiallergic agents tranilast and ketotifen fumarate (IC50 = 282 μM and 158 μM, respectively), as well as one of the corresponding monomers (1a; IC50 > 100 μM). Nonetheless, these effects were weaker than those of the other monomer (3; IC50 = 6.1 μM).

A methanol extract of rhizomes of Picrorhiza kurroa Royle ex Benth. (Plantaginaceae) showed hepatoprotective effects against D-galactosamine (D-GalN)/lipopolysaccharide (LPS)-induced liver injury in mice. We had previously isolated 46 compounds, including several types of iridoid glycosides, phenylethanoid glycosides, and aromatics, etc., from the extract. Among them, picroside II, androsin, and 4-hydroxy-3-methoxyacetophenone exhibited active hepatoprotective effects at doses of 50-100 mg/kg, per os (p.o.) To characterize the mechanisms of action of these isolates and to clarify the structural requirements of phenylethanoid glycosides for their hepatoprotective effects, their effects were assessed in in vitro studies on (i) D-GalN-induced cytotoxicity in mouse primary hepatocytes, (ii) LPS-induced nitric oxide (NO) production in mouse peritoneal macrophages, and (iii) tumor necrosis factor-α (TNF-α)-induced cytotoxicity in L929 cells. These isolates decreased the cytotoxicity caused by D-GalN without inhibiting LPS-induced macrophage activation and also reduced the sensitivity of hepatocytes to TNF-α. In addition, the structural requirements of phenylethanoids for the protective effects of D-GalN-induced cytotoxicity in mouse primary hepatocytes were evaluated.