Metabolite profile and antiproliferative effects in HaCaT cells of a Salix reticulata extract

Phenolic constituents of Salix reticulata (Salicaceae) and antiproliferative activity of an extract and individual compounds was investigated in immortalized human non-tumorigenic keratinocytes (HaCaT). A MeOH extract from aerial parts afforded several flavonoids, including luteolin and apigenin glycosides (2-5 and 9) and catechin (1), two procyanidin fractions, and the phenolic glucosides picein (6), triandrin (7), and salicortin (8). In an ATP assay, the MeOH extract reduced cell viability by approx. 60% at a concentration of 100 µg/mL. Cell proliferation was assessed with a BrdU incorporation ELISA assay. The extract inhibited proliferation of HaCaT cells in a concentration dependent manner, with an approx. 50% inhibition at 100 µg/mL. In time lapse assays, the extract showed distinct inhibitory effects on cell migration at concentrations of 12.5, 25 and 50 µg/mL. The activity of selected constituents was also determined. Luteolin-7-O-β-glucuronide (3) significantly inhibited cell proliferation at concentrations of 10 and 50µM. In contrast, luteolin-7-O-β-glucopyranoside (2) and a procyanidin fraction (P1) had only weak effects, and picein (6) and salicortin (8) did not affect cell proliferation. Luteolin-7-O-β-glucuronide (10µM) and, to a lesser extent, the procyanidin fraction (10 µg/mL) also inhibited cell migration.