Hop (Humulus lupulus L.) Extract and 6-Prenylnaringenin Induce P450 1A1 Catalyzed Estrogen 2-Hydroxylation

Abstract

Humulus lupulus L. (hops) is a popular botanical dietary supplement used by women as a sleep aid and for postmenopausal symptom relief. In addition to its efficacy for menopausal symptoms, hops can also modulate the chemical estrogen carcinogenesis pathway and potentially protect women from breast cancer. In the present study, an enriched hop extract and the key bioactive compounds [6-prenylnarigenin (6-PN), 8-prenylnarigenin (8-PN), isoxanthohumol (IX), and xanthohumol (XH)] were tested for their effects on estrogen metabolism in breast cells (MCF-10A and MCF-7). The methoxyestrones (2-/4-MeOE1) were analyzed as biomarkers for the nontoxic P450 1A1 catalyzed 2-hydroxylation and the genotoxic P450 1B1 catalyzed 4-hydroxylation pathways, respectively. The results indicated that the hop extract and 6-PN preferentially induced the 2-hydroxylation pathway in both cell lines. 8-PN only showed slight up-regulation of metabolism in MCF-7 cells, whereas IX and XH did not have significant effects in either cell line. To further explore the influence of hops and its bioactive marker compounds on P450 1A1/1B1, mRNA expression and ethoxyresorufin O-dealkylase (EROD) activity were measured. The results correlated with the metabolism data and showed that hop extract and 6-PN preferentially enhanced P450 1A1 mRNA expression and increased P450 1A1/1B1 activity. The aryl hydrocarbon receptor (AhR) activation by the isolated compounds was tested using xenobiotic response element (XRE) luciferase construct transfected cells. 6-PN was found to be an AhR agonist that significantly induced XRE activation and inhibited 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induced XRE activity. 6-PN mediated induction of EROD activity was also inhibited by the AhR antagonist CH223191. These data show that the hop extract and 6-PN preferentially enhance the nontoxic estrogen 2-hydroxylation pathway through AhR mediated up-regulation of P450 1A1, which further emphasizes the importance of standardization of botanical extracts to multiple chemical markers for both safety and desired bioactivity.

A standardized Humulus lupulus (L.) ethanol extract partially prevents ovariectomy-induced bone loss in the rat without induction of adverse effects in the uterus

“…Although 8-PN was shown to be a potent ERα agonist and to promote proliferation in MCF-7 cells (Helle et al, 2014; Milligan et al, 2000), it is striking that no proliferation was observed in our study. This might be explained by the recently shown AhR agonistic activity of 6-PN (Wang et al, 2016) as several publications described a AhR-ER cross-talk in the uterus comprising a modulation of ER signaling by AhR activation (Buchanan et al, 2000; Shanle and Xu, 2011). The histological analysis of the mammary gland after this 8-week administration of the hops extract did not show any unwanted side effects providing further evidence for the safety of the hops extract (data not shown).…”

Evaluation of estrogenic potency of a standardized hops extract on mammary gland biology and on MNU-induced mammary tumor growth in rats

“…ER dependent activity of 8-PN may at least in part be functionally counterbalanced by the activation of AhR. As a molecular basis for this hypothesis, on one side we showed that the AhR family of genes is expressed in target tissues in a sex hormone dependent manner [47,48], and on the other side evidence exists that the hops extract may contain AhR activating, counterbalancing compounds with 6-PN [15] as an example.…”

“…Whereas 8-PN is the most potent ERα agonist known among the group of phytoestrogenic compounds [16,17], 6-PN has recently been identified as an AhR agonist thereby inducing cytochrome P450 enzyme 1A1 dependent 2-hydroxylation of estradiol, which is believed to be the non-toxic pathway of estrogen metabolism [15]. It is long known that AhR activation e.g.…”

“…It is prone to be metabolized to IX, desmethyl xanthohumol, 8-PN and 6-PN [13,14]. Enhancement of the nontoxic estrogen 2-hydroxylation pathway through AhR mediated up-regulation of the cytochrome P450 enzyme 1A1 has been shown for 6-PN [15]. 8-PN is the major estrogenic constituent in hops extracts [16], described before as 8-isopentenylnaringenin from heartwood of Anaxagorea luzonensis A.…”

In Vitro Effect of 8-Prenylnaringenin and Naringenin on Fibroblasts and Glioblastoma Cells—Cellular Accumulation and Cytotoxicity

“…Movement of the prenyl substituent from C-8 to C-6 results in a loss of estrogenic activity. Additionally, other prenyl derivatives of naringenin present in hops, such as 6-prenylnaringenin, may play an important role in post-menopausal hormonereplacement therapy, among others being catalysts of regioselective estrogene hydroxylation, which reduces the risk of breast cancer [16].…”