The pharmacognosy of Humulus lupulus L. (hops) with an emphasis on estrogenic properties

Abstract

As the population ages, there is an ever-increasing need for therapeutic agents that can be used safely and efficaciously to manage symptoms related to postmenopausal estrogen deficiency. Endogenous estrogens, e.g., 17beta-estradiol, of exogenous mammalian origin, e.g., horses, have long been used to manage such symptoms. There are more than 20 different classes of phytochemicals that have demonstrated affinity for human estrogen receptors in vitro. Some studies on exogenous estrogenic substances of botanical origin (phytoestrogens), such as standardized formulations of plant extracts with in vitro and in vivo estrogenic activity from soy (Glycine max Merill.) and red clover (Trifolium pratense L.), suggest clinical efficacy. Few clinical data for phytoestrogens other than isoflavonoids are available. In an exhaustive review of the literature through 2003, only two clinical trials were identified that were designed to evaluate the effect of hops (Humulus lupulus L.) on symptoms related to menopause. Folkloric, chemical, and biological literature relating primarily to the use of hops for their estrogenic activity, and two human clinical trials, are reviewed.

Figure 1

Current and extended naming system for chalcones from hops. φ indicates that the given structure cannot occur in the XG series. Compounds in boldface font have been reported in the literature, or have recently been isolated by our group. It is likely that all of the compounds in this figure, and many more related structures, will eventually be isolated from hops. A less confusing situation will arise if this naming system is implemented. The name “xanthohumol E” was previously given to a member of the desmethylxanthohumol series. Therefore, it is proposed that the name “xanthohumol F” be reserved for the true xanthohumol analogue (5-O-Me) of this compound. In cases where a new compound is a simple derivative or xanthohumol or one of its named derivatives, we suggest that the compounds be named to reflect this relationship. The 1″,2″ dihydro derivative of the xanthohumol C has been isolated, for example, and rather than adding another letter to the xanthohumol series, the compound was simply named 1″,2″-dihydroxanthohumol C (inset below).