Identification of bioactive compounds from flowers of black elder (Sambucus nigra L.) that activate the human peroxisome proliferator-activated receptor (PPAR) gamma.

Obesity is one of the predisposing factors for the development of overt Type 2 diabetes (T2D). T2D is caused by a combination of insulin resistance and beta-cell failure and can be treated with insulin sensitizing drugs that target the nuclear receptor peroxisome proliferator-activated receptor (PPAR) gamma. Extracts of elderflowers (Sambucus nigra) have been found to activate PPARgamma and to stimulate insulin-dependent glucose uptake suggesting that they have a potential use in the prevention and/or treatment of insulin resistance. Bioassay-guided chromatographic fractionation of a methanol extract of elderflowers resulted in the identification of two well-known PPARgamma agonists; alpha-linolenic acid and linoleic acid as well as the flavanone naringenin. Naringenin was found to activate PPARgamma without stimulating adipocyte differentiation. However, the bioactivities of these three metabolites were not able to fully account for the observed PPARgamma activation of the crude elderflower extracts and further studies are needed to determine whether this is due synergistic effects and/or other ligand-independent mechanisms. Elderflower metabolites such as quercetin-3-O-rutinoside, quercetin-3-O-glucoside, kaempferol-3-O-rutinoside, isorhamnetin-3-O-rutinoside, isorhamnetin-3-O-glucoside, and 5-O-caffeoylquinic acid were unable to activate PPARgamma. These findings suggest that flavonoid glycosides cannot activate PPARgamma, whereas some of their aglycones are potential agonists of PPARgamma.