Phytochemical Characterization of Rhododendron ferrugineum and In Vitro Assessment of an Aqueous Extract on Cell Toxicity

Within a systematic phytochemical investigation of the leaves of Rhododendron ferrugineum L. (Ericaceae), the volatile oil was isolated (0.7%) and its constituents were characterized. Eleven flavonoids were isolated and characterized, with quercetin 3-O-[6 ''-O-(2-methyl-1-oxobutyl)]-beta-D-glucopyranoside and 2R, 3R-dihydromyricetin 3-O-beta-L-arabinopyranoside as new natural products. Beside monomeric flavan-3-ols (catechin, epicatechin, gallocatechin, epigallocatechin) from the tannin fraction (about 3.5% calculated as pyrogallol), the dimeric procyanidins B1 to B7 were identified, as well as the trimeric compounds procyanidin C1, epicatechin-(4 beta -> 8)-epicatechin-(4 beta -> 8)-catechin and the trimeric A type-linked cinnamtannin B1. Additionally, phloroacetophenon 4-O-beta-D-glucopyranoside and chlorogenic acid were isolated. Water-soluble carbohydrates comprised about 13.5% of the dried leaves, including fructans (3%), polysaccharides (1%) (mainly type II arabinogalactans), glucose, fructose, sucrose, stachyose and raffinose. The in vitro effects on cellular vitality (MTT test), proliferation (BrdU incorporation) and necrosis (LDH release) of an aqueous extract were investigated. The extract did not exert any toxic effects, while the vitality and the proliferation rates of epithelial HaCaT keratinocytes were significantly increased at 100 mu g/mL, indicating that the aqueous extract does not have negative effects against cellular activity.