No abstract

No abstract

Dietary flavonoids possess a wide spectrum of biochemical and pharmacological actions and are assumed to protect human health. These actions, however, can be antagonistic, and some health claims are mutually exclusive. The antiapoptotic actions of flavonoids may protect against neurodegenerative diseases, whereas their proapoptotic actions could be used for cancer chemotherapy. This study was undertaken to determine whether a cytoprotective dose range of flavonoids could be differentiated from a cytotoxic dose range. Seven structurally related flavonoids were tested for their ability to protect H4IIE rat hepatoma cells against H(2)O(2)-induced damage on the one hand and to induce cellular damage on their own on the other hand. All flavonoids proved to be good antioxidants in a cell-free assay. However, their pharmacologic activity did not correlate with in vitro antioxidant potential but rather with cellular uptake. For quercetin and fisetin, which were readily taken up into the cells, protective effects against H(2)O(2)-induced cytotoxicity, DNA strand breaks, and apoptosis were detected at concentrations as low as 10-25 micromol/L. On the other hand, these flavonoids induced cytotoxicity, DNA strand breaks, oligonucleosomal DNA fragmentation, and caspase activation at concentrations between 50 and 250 micromol/L. Published data on quercetin pharmacokinetics in humans suggest that a dietary supplement of 1-2 g of quercetin may result in plasma concentrations between 10 and 50 micromol/L. Our data suggest that cytoprotective concentrations of some flavonoids are lower by a factor of 5-10 than their DNA-damaging and proapoptotic concentrations.

Two new cyclic depsipeptide derivatives, kahalalides R (1) and S (2), together with two known congeners, kahalalides F (3) and D (4), were isolated from the Indian sacoglossan mollusk Elysia grandifolia. The structures of the new compounds were unambiguously established on the basis of NMR spectroscopic (1H, 13C, COSY, HMBC) and mass spectrometric (FABMS, ESIMS, MALDI-TOF/PSD) data, which also included Marfey amino acid analyses. The new derivative kahalalide R was found to exert comparable or even higher cytotoxicity than the potential drug candidate kahalalide F toward the MCF7 human mammary carcinoma cell line.