Chemistry and biology of hop flavonoids

The flavonoids of hops include flavonol glycosides, condensed tannins, and prenylflavonoids. The first two flavonoid classes are located intracellular ly, while the prenylflavonoids are secreted along with bitter acids and ess ential oils by the lupulin glands of the inflorescences. The chemistry and biological activities of prenylflavonoids isolated from the lupulin fractio n are reviewed. An LC-MS method was developed for quantitation of these phe nolics in hops, hop-derived products. and beer. The fate of xanthohumol and related prenylflavonoids during the brewing process was investigated by LC -MS. The partial carryover of the prenylflavonoids from hops into beer was attributed mainly to incomplete extraction and adsorption to insoluble prot eins and yeast. Moreover, the prenylchalcone-type flavonoids were largely c onverted into isomeric prenylflavanones during wort boiling. The biological activities of some of the prenyIflavonoids isolated were examined using in vitro techniques. Some of the prenylflavonoids inhibited the growth of bre ast cancer (MCF-7) cells in a dose-dependent manner. Xanthohumol and relate d prenylflavonoids also inhibited the cytochrome P450-mediated activation o f procarcinogens and induced the activity of the carcinogen-detoxifying enz yme, quinone reductase. The prenylflavonoids were not toxic to normal cells (rat hepatocytes) at the same concentrations. Recent literature reports of biological activities are briefly discussed: inhibition of bone resorption , inhibition of diacylglycerol acyltransferase, and antimicrobial activitie s.