(S)-4',5,7-Trihydroxy-6-prenylflavanone

Chemoprotective Effects of Xanthohumol against the Carcinogenic Mycotoxin Aflatoxin B1.[Pubmed:34207931]

Foods. 2021 Jun 9;10(6). pii: foods10061331.

The present study addresses the chemoprotective effects of xanthohumol (XN), a prenylated flavonoid found in the female inflorescences (hops) of the plant Humulus lupulus L., against the carcinogenic food contaminant aflatoxin B1 (AFB1). The chemical reactions of XN and its derivatives (isoxanthohumol (IXN), 8-prenylnaringenin (8-PN), and 6-prenylnaringenin (6-PN)) with the AFB1 metabolite, aflatoxin B1 exo-8,9-epoxide (AFBO), were investigated in silico, by calculating activation free energies (DeltaG(double dagger)) at the Hartree-Fock level of theory in combination with the 6-311++G(d,p) basis set and two implicit solvation models. The chemoprotective effects of XN were investigated in vitro in the metabolically competent HepG2 cell line, analyzing its influence on AFB1-induced cytotoxicity using the MTS assay, genotoxicity using the comet and gammaH2AX assays, and cell cycle modulation using flow cytometry. Our results show that the DeltaG(double dagger) required for the reactions of XN and its derivatives with AFBO are comparable to the DeltaG(double dagger) required for the reaction of AFBO with guanine, indicating that XN, IXN, 8-PN, and 6-PN could act as scavengers of AFBO, preventing DNA adduct formation and DNA damage induction. This was also reflected in the results from the in vitro experiments, where a reduction in AFB1-induced cytotoxicity and DNA single-strand and double-strand breaks was observed in cells exposed to combinations of AFB1 and XN, highlighting the chemoprotective effects of this phytochemical.

Humulone Modulation of GABAA Receptors and Its Role in Hops Sleep-Promoting Activity.[Pubmed:33177986]

Front Neurosci. 2020 Oct 14;14:594708.

Humulus lupulus L. (hops) is a major constituent of beer. It exhibits neuroactive properties that make it useful as a sleeping aid. These effects are hypothesized to be mediated by an increase in GABAA receptor function. In the quest to uncover the constituents responsible for the sedative and hypnotic properties of hops, recent evidence revealed that humulone, a prenylated phloroglucinol derivative comprising 35-70% of hops alpha acids, may act as a positive modulator of GABAA receptors at low micromolar concentrations. This raises the question whether humulone plays a key role in hops pharmacological activity and potentially interacts with other modulators such as ethanol, bringing further enhancement in GABAA receptor-mediated effects of beer. Here we assessed electrophysiologically the positive modulatory activity of humulone on recombinant GABAA receptors expressed in HEK293 cells. We then examined humulone interactions with other active hops compounds and ethanol on GABA-induced displacement of [(3)H]EBOB binding to native GABAA receptors in rat brain membranes. Using BALB/c mice, we assessed humulone's hypnotic behavior with pentobarbital- and ethanol-induced sleep as well as sedation in spontaneous locomotion with open field test. We demonstrated for the first time that humulone potentiates GABA-induced currents in alpha1beta3gamma2 receptors. In radioligand binding to native GABAA receptors, the inclusion of ethanol enhanced humulone modulation of GABA-induced displacement of [(3)H]EBOB binding in rat forebrain and cerebellum as it produced a leftward shift in [(3)H]EBOB displacement curves. Moreover, the additive modulatory effects between humulone, isoxanthohumol and 6-prenylnaringenin were evident and corresponded to the sum of [(3)H]EBOB displacement by each compound individually. In behavioral tests, humulone shortened sleep onset and increased the duration of sleep induced by pentobarbital and decreased the spontaneous locomotion in open field at 20 mg/kg (i.p.). Despite the absence of humulone effects on ethanol-induced sleep onset, sleep duration was increased dose-dependently down to 10 mg/kg (i.p.). Our findings confirmed humulone's positive allosteric modulation of GABAA receptor function and displayed its sedative and hypnotic behavior. Humulone modulation can be potentially enhanced by ethanol and hops modulators suggesting a probable enhancement in the intoxicating effects of ethanol in hops-enriched beer.

6-Prenylnaringenin from Hops Disrupts ERalpha-Mediated Downregulation of CYP1A1 to Facilitate Estrogen Detoxification.[Pubmed:32986415]

Chem Res Toxicol. 2020 Nov 16;33(11):2793-2803.

Botanical dietary supplements (BDS) containing hops are sold as women's health supplements due to the potent hop phytoestrogen, 8-prenylnaringenin (8-PN), and the cytoprotective chalcone, xanthohumol. Previous studies have shown a standardized hop extract to beneficially influence chemical estrogen carcinogenesis in vitro by fostering detoxified 2-hydroxylation over genotoxic 4-hydroxylation estrogen metabolism. In this study, hop extract and its bioactive compounds were investigated for its mechanism of action within the chemical estrogen carcinogenesis pathway, which is mainly mediated through the 4-hydroxylation pathway catalyzed by CYP1B1 that can form gentoxic quinones. Aryl hydrocarbon receptor (AhR) agonists induce CYP1A1 and CYP1B1, while estrogen receptor alpha (ERalpha) inhibits transcription of CYP1A1, the enzyme responsible for 2-hydroxylated estrogens and the estrogen detoxification pathway. An In-Cell Western MCF-7 cell assay revealed hop extract and 6-prenylnaringenin (6-PN) degraded ERalpha via an AhR-dependent mechanism. Reverse transcription PCR and xenobiotic response element luciferase assays showed hop extract and 6-PN-mediated activation of AhR and induction of CYP1A1. A reduction in estrogen-mediated DNA (cytosine-5)-methyltransferase 1 (DNMT1) downregulation of CYP1A1 accompanied this activity in a chromatin immunoprecipitation assay. Ultimately, hop extract and 6-PN induced preferential metabolism of estrogens to their detoxified form in vitro. These results suggest that the standardized hop extract and 6-PN activate AhR to attenuate epigenetic inhibition of CYP1A1 through degradation of ERalpha, ultimately increasing 2-hydroxylated estrogens. A new mechanism of action rationalizes the positive influence of hop BDS and 6-PN on oxidative estrogen metabolism in vitro and, thus, potentially on chemical estrogen carcinogenesis. The findings underscore the importance of elucidating various biological mechanisms of action and standardizing BDS to multiple phytoconstituents for optimal resilience promoting properties.

Semi-Synthetic Approach Leading to 8-Prenylnaringenin and 6-Prenylnaringenin: Optimization of the Microwave-Assisted Demethylation of Xanthohumol Using Design of Experiments.[Pubmed:32887388]

Molecules. 2020 Sep 2;25(17). pii: molecules25174007.

The isomers 8-prenylnaringenin and 6-prenylnaringenin, both secondary metabolites occurring in hops, show interesting biological effects, like estrogen-like, cytotoxic, or neuro regenerative activities. Accordingly, abundant sources for this special flavonoids are needed. Extraction is not recommended due to the very low amounts present in plants and different synthesis approaches are characterized by modest yields, multiple steps, the use of expensive chemicals, or an elaborate synthesis. An easy synthesis strategy is the demethylation of xanthohumol, which is available due to hop extraction industry, using lithium chloride and dimethylformamide, but byproducts and low yield did not make this feasible until now. In this study, the demethylation of xanthohumol to 8-prenylnaringenin and 6-prenylnaringenin is described the first time and this reaction was optimized using Design of Experiment and microwave irradiation. With the optimized conditions-temperature 198 degrees C, 55 eq. lithium chloride, and a reaction time of 9 min, a final yield of 76% of both prenylated flavonoids is reached.

Quantitative Analysis of Prenylated Constituents in Commercial Hops Samples Using Ultrahigh-Performance Supercritical Fluid Chromatography.[Pubmed:32182624]

Planta Med. 2020 Oct;86(15):1140-1147.

The importance of hops (the flowers of Humulus lupulus) as food and an herbal remedy is reflected by a large number of analytical methods published. However, supercritical fluid chromatography, a highly efficient, rapid, and "green" separation technique, has not been considered for hops samples so far. This prompted us to establish the first supercritical fluid chromatography-based protocol for the separation, identification, and quantitation of five prenylated constituents of hops. Hulupinic acid ( 1: ), a prominent oxidation product of hop acids, three flavanones, i.e., 8-prenylnaringenin ( 2: ), 6-prenylnaringenin ( 3: ), and isoxanthohumol ( 4: ), as well as the chalcone xanthohumol ( 5: ) could be baseline separated in less than 5 minutes using a Viridis BEH 2-EP column (3.0 x 100 mm; 1.7 microm particle size) and a mobile phase consisting of CO2 and isopropanol. Good results regarding selectivity, accuracy (recovery rates: 85.0 - 113.1%), precision (intra-day /= 0.99) were obtained for both photodiode array and mass detection. The lowest detection limit at 220 nm was at 0.1 microg/mL ( 1, 3: , and 4: ), with mass detection even at 0.001 microg/mL ( 4: ). As an application example of the validated method, the five hops constituents were quantified in three dietary supplements, one herbal medicinal product, and two batches of hop flowers (Lupuli flos). In most samples analyzed, the major component was 5: (0.01 - 1.02%), whereas the major component in Lupuli flos samples was compound 1: (0.12 - 0.21%). This protocol offers a fast and environmentally friendly alternative to liquid chromatography for the quality control of hops.

Hops compounds modulatory effects and 6-prenylnaringenin dual mode of action on GABAA receptors.[Pubmed:32001220]

Eur J Pharmacol. 2020 Apr 15;873:172962.

Hops (Humulus lupulus L.), a major component of beer, contain potentially neuroactive compounds that made it useful in traditional medicine as a sleeping aid. The present study aims to investigate the individual components in hops acting as allosteric modulators in GABAA receptors and bring further insight into the mode of action behind the sedative properties of hops. GABA-potentiating effects were measured using [(3)H]ethynylbicycloorthobenzoate (EBOB) radioligand binding assay in native GABAA receptors. Flumazenil sensitivity of GABA-potentiating effects, [(3)H]Ro 15-4513, and [(3)H]flunitrazepam binding assays were used to examine the binding to the classical benzodiazepines site. Humulone (alpha acid) and 6-prenylnaringenin (prenylflavonoid) were the most potent compounds displaying a modulatory activity at low micromolar concentrations. Humulone and 6-prenylnaringenin potentiated GABA-induced displacement of [(3)H]EBOB binding in a concentration-dependent manner where the IC50 values for this potentiation in native GABAA receptors were 3.2 muM and 3.7 muM, respectively. Flumazenil had no significant effects on humulone- or 6-prenylnaringenin-induced displacement of [(3)H]EBOB binding. [(3)H]Ro 15-4513 and [(3)H]flunitrazepam displacements were only minor with humulone but surprisingly prominent with 6-prenylnaringenin despite its flumazenil-insensitive modulatory activity. Thus, we applied molecular docking methods to investigate putative binding sites and poses of 6-prenylnaringenin at the GABAA receptor alpha1beta2gamma2 isoform. Radioligand binding and docking results suggest a dual mode of action by 6-prenylnaringenin on GABAA receptors where it may act as a positive allosteric modulator at alpha+beta- binding interface as well as a null modulator at the flumazenil-sensitive alpha+gamma2- binding interface.

Antiproliferative Effects of Hop-derived Prenylflavonoids and Their Influence on the Efficacy of Oxaliplatine, 5-fluorouracil and Irinotecan in Human ColorectalC Cells.[Pubmed:31010128]

Nutrients. 2019 Apr 19;11(4). pii: nu11040879.

Beer, the most popular beverage containing hops, is also frequently consumed by cancer patients. Moreover, non-alcoholic beer, owing to its nutritional value and high content of biological active compounds, is sometimes recommended to patients by oncologists. However, the potential benefits and negatives have to date not been sufficiently evaluated. The present study was designed to examine the effects of four main hop-derived prenylflavonoids on the viability, reactive oxygen species (ROS) formation, activity of caspases, and efficiency of the chemotherapeutics 5-fluorouracil (5-FU), oxaliplatin (OxPt) and irinotecan (IRI) in colorectal cancer cell lines SW480, SW620 and CaCo-2. All the prenylflavonoids exerted substantial antiproliferative effects in all cell lines, with xanthohumol being the most effective (IC50 ranging from 3.6 to 7.3 microM). Isoxanthohumol increased ROS formation and the activity of caspases-3/7, but 6-prenylnaringenin and 8-prenylnaringenin exerted antioxidant properties. As 6-prenylnaringenin acted synergistically with IRI, its potential in combination therapy deserves further study. However, other prenylflavonoids acted antagonistically with all chemotherapeutics at least in one cell line. Therefore, consumption of beer during chemotherapy with 5-FU, OxPt and IRI should be avoided, as the prenylflavonoids in beer could decrease the efficacy of the treatment.

Structures and In Vitro Antihepatic Fibrosis Activities of Prenylated Dihydrostilbenes and Flavonoids from Glycyrrhiza uralensis Leaves.[Pubmed:30990886]

J Food Sci. 2019 May;84(5):1224-1230.

Glycyrrhiza uralensis is the major plant source of licorice. This study was to identify bioactive compounds from the plant's leaves in order to make better use of its aerial part. An ethanol extract of the leaves was subjected to repeated chromatography to yield 15 compounds. The structures were determined to be three novel dihydrostilbenes, based on their various spectroscopic data-glycypytilbene A (1), glycydipytilbene (2), and glycypytilbene B (3)-and 12 known compounds, alpha,alpha'-dihydro-3,5,4'-trihydroxy-4,3'-diisopentenylstilbene (4), alpha,alpha'-dihydro-3,5,3',4'-tetrahydroxy-2,5'-diisopentenylstilbene (5), 6-prenyleriodictyol (6), 5'-prenyleriodictyol (7), 6-prenylquercetin-3-Me ether (8), 5'-prenylquercetin (9), 6-prenylquercetin (10), 6-prenylnaringenin (11), 3'-prenylnaringenin (12), sigmoidin C (13), 8-[(E)-3-hydroxymethyl-2- butenyl]-eriodictyol (14), and quercetin-3-Me ether (15). Most of these chemical constituents inhibited alpha-glucosidase activity, with the two prenylated quercetin derivatives (9 to 10) being the greatest active (IC50 < 4.0 microg/mL). Compounds 1, 3 to 4, 6 to 7, 9 to 12 impeded the growth of human hepatic stellate cells, with the prenylated flavonoids (6 to 7, 9 to 12) being more robust than their unprenylated counterparts. PRACTICAL APPLICATIONS: This study found that Glycyrrhiza uralensis leaves contain prenylated dihydrostilbenes and flavonoids with inhibiting effects on alpha-glucosidase and on the proliferation of human hepatic stellate cells, which should prompt the development of G. uralensis leaves for healthy products with anti-diabetic or liver fibrosis-preventing effects.

Cytotoxic Activity and Related Mechanisms of Prenylflavonoids Isolated from Mallotus conspurcatus Croizat.[Pubmed:30779297]

Chem Biodivers. 2019 May;16(5):e1800465.

Five prenylflavonoids, 6-prenylnaringenin (1), 8-prenylnaringenin (2), 7-O-methyl-8-prenylnaringenin (3), 7-O-methyl-6-prenylnaringenin (4), and 4'-O-methyl-6-prenylnaringenin (5), were isolated from the traditional herb Mallotus conspurcatus Croizat (Euphorbiaceae). Compounds 1-5 revealed cytotoxic activity against cervical cancer (HeLa) cells with IC50 values ranging from 10.08 to 60.16 mum by MTT method, and interestingly, these prenylflavonoids were less toxic to normal HL-7702 cells. Furthermore, compounds 1 and 5 could inhibit the c-myc expression and telomerase activity and cause mitochondrial dysfunction. These findings might contribute to a better understanding of the biological activities of prenylflavonoids and lay the foundation for further studies on the cytotoxic activity of natural products isolated from M. conspurcatus.

The Multiple Biological Targets of Hops and Bioactive Compounds.[Pubmed:30608650]

Chem Res Toxicol. 2019 Feb 18;32(2):222-233.

Botanical dietary supplements for women's health are increasingly popular. Older women tend to take botanical supplements such as hops as natural alternatives to traditional hormone therapy to relieve menopausal symptoms. Especially extracts from spent hops, the plant material remaining after beer brewing, are enriched in bioactive prenylated flavonoids that correlate with the health benefits of the plant. The chalcone xanthohumol (XH) is the major prenylated flavonoid in spent hops. Other less abundant but important bioactive prenylated flavonoids are isoxanthohumol (IX), 8-prenylnaringenin (8-PN), and 6-prenylnaringenin (6-PN). Pharmacokinetic studies revealed that these flavonoids are conjugated rapidly with glucuronic acid. XH also undergoes phase I metabolism in vivo to form IX, 8-PN, and 6-PN. Several hop constituents are responsible for distinct effects linked to multiple biological targets, including hormonal, metabolic, inflammatory, and epigenetic pathways. 8-PN is one of the most potent phytoestrogens and is responsible for hops' estrogenic activities. Hops also inhibit aromatase activity, which is linked to 8-PN. The weak electrophile, XH, can activate the Keap1-Nrf2 pathway and turn on the synthesis of detoxification enzymes such as NAD(P)H-quinone oxidoreductase 1 and glutathione S-transferase. XH also alkylates IKK and NF-kappaB, resulting in anti-inflammatory activity. Antiobesity activities have been described for XH and XH-rich hop extracts likely through activation of AMP-activated protein kinase signaling pathways. Hop extracts modulate the estrogen chemical carcinogenesis pathway by enhancing P450 1A1 detoxification. The mechanism appears to involve activation of the aryl hydrocarbon receptor (AhR) by the AhR agonist, 6-PN, leading to degradation of the estrogen receptor. Finally, prenylated phenols from hops are known inhibitors of P450 1A1/2; P450 1B1; and P450 2C8, 2C9, and 2C19. Understanding the biological targets of hop dietary supplements and their phytoconstituents will ultimately lead to standardized botanical products with higher efficacy, safety, and chemopreventive properties.

Critical role of Cav3.2 T-type calcium channels in the peripheral neuropathy induced by bortezomib, a proteasome-inhibiting chemotherapeutic agent, in mice.[Pubmed:30552955]

Toxicology. 2019 Feb 1;413:33-39.

Bortezomib, a first-line agent for treatment of multiple myeloma, exhibits anticancer activity through proteasome inhibition. However, bortezomib-induced peripheral neuropathy (BIPN) is one of the most serious side effects. Since decreased proteasomal degradation of Cav3.2 T-type calcium channels in the primary afferents is involved in persistent pain, we investigated whether BIPN involves increased protein levels of Cav3.2 in mice. Six repeated i.p. administrations of bortezomib for 12 days developed persistent mechanical allodynia. Systemic administration of novel T-type calcium channel blockers, (2R/S)-6-prenylnaringenin and KTt-45, and of TTA-A2, the well-known blocker, reversed the BIPN. Ascorbic acid, known to block Cav3.2, but not Cav3.1 or 3.3, and silencing of Cav3.2 gene also suppressed BIPN. Protein levels of Cav3.2 in the dorsal root ganglion (DRG) at L4-L6 levels increased throughout days 1-21 after the onset of bortezomib treatment. Protein levels of USP5, a deubiquitinating enzyme that specifically inhibits proteasomal degradation of Cav3.2, increased in DRG on days 3-21, but not day 1, in bortezomib-treated mice. In DRG-derived ND7/23 cells, bortezomib increased protein levels of Cav3.2 and T-channel-dependent currents, as assessed by a patch-clamp method, but did not upregulate expression of Cav3.2 mRNA or USP5 protein. MG-132, another proteasome inhibitor, also increased Cav3.2 protein levels in the cultured cells. Given the previous evidence for USP5 induction following nociceptor excitation, our data suggest that BIPN involves the increased protein levels of Cav3.2 in nociceptors through inhibition of proteasomal degradation of Cav3.2 by bortezomib itself and then by USP5 that is upregulated probably in an activity-dependent manner.

Highly Cancer Selective Antiproliferative Activity of Natural Prenylated Flavonoids.[Pubmed:30423918]

Molecules. 2018 Nov 9;23(11). pii: molecules23112922.

Xanthohumol (XN) and four minor hops prenylflavonoids: alpha,beta-dihydroxanthohumol (2HXN), isoxanthohumol (IXN), 8-prenylnaringenin (8PN), and 6-prenylnaringenin (6PN), were tested for antiproliferative activity towards human cancer and normal cell lines. Nonprenylated naringenin (NG) was used as a model compound. Xanthohumol, alpha,beta-dihydroxanthohumol and 6-prenylnaringenin were the most active compounds. Xanthohumol exhibited higher antiproliferative activity than cisplatin (CP) against five cancer cell lines: ovarian resistant to cisplatin A2780cis, breast MDA-MB-231 and T-47D, prostate PC-3, and colon HT-29. Isoxanthohumol was more potent than cisplatin against breast cancer cell lines MDA-MB-231 and T-47D whereas 6-prenylnaringenin was stronger than cisplatin against breast cancer cell line T-47D. It was found that tested chalcones possessed highly selective antiproliferative activity towards all tested breast cancer lines compared to the normal breast MCF 10A cell line (the calculated selectivity index ranged from 5 to 10). Low antiproliferative activity of naringenin indicates the importance of the prenyl group with respect to antiproliferative activity.