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

Activation of pregnane X receptor (PXR) and constitutive androstane receptor (CAR) by herbal medicines

Pregnane X receptor (PXR) and constitutive androstane receptor (CAR) are transcription factors that control the expression of a broad array of genes involved not only in transcellular transport and biotransformation of many drugs, other xenochemicals, and endogenous substances, such as bile acid, bilirubin, and certain vitamins, but also in various physiological/pathophysiological processes such as lipid metabolism, glucose homeostasis, and inflammation. Ligands of PXR and CAR are chemicals of diverse structures, including naturally occurring compounds present in herbal medicines. The overall aim of this article is to provide an overview of our current understanding of the role of herbal medicines as modulators of PXR and CAR.

Hop (Humulus lupulus)-derived bitter acids as multipotent bioactive compounds

Hop acids, a family of bitter compounds derived from the hop plant (Humulus lupulus), have been reported to exert a wide range of effects, both in vitro and in vivo. They exhibit potential anticancer activity by inhibiting cell proliferation and angiogenesis, by inducing apoptosis, and by increasing the expression of cytochrome P450 detoxification enzymes. Furthermore, hop bitter acids are effective against inflammatory and metabolic disorders, which makes them challenging candidates for the treatment of diabetes mellitus, cardiovascular diseases, and metabolic syndrome. This review summarizes the current knowledge on hop bitter acids, including both phytochemical aspects, as well as the biological and pharmacological properties of these compounds.

DNA sequence and expression variation of hop (Humulus lupulus) valerophenone synthase (VPS), a key gene in bitter acid biosynthesis

BACKGROUND

The hop plant (Humulus lupulus) is a source of many secondary metabolites, with bitter acids essential in the beer brewing industry and others having potential applications for human health. This study investigated variation in DNA sequence and gene expression of valerophenone synthase (VPS), a key gene in the bitter acid biosynthesis pathway of hop.

METHODS

Sequence variation was studied in 12 varieties, and expression was analysed in four of the 12 varieties in a series across the development of the hop cone.

RESULTS

Nine single nucleotide polymorphisms (SNPs) were detected in VPS, seven of which were synonymous. The two non-synonymous polymorphisms did not appear to be related to typical bitter acid profiles of the varieties studied. However, real-time quantitative reverse-transcription polymerase chain reaction (qRT-PCR) analysis of VPS expression during hop cone development showed a clear link with the bitter acid content. The highest levels of VPS expression were observed in two triploid varieties, 'Symphony' and 'Ember', which typically have high bitter acid levels.

CONCLUSIONS

In all hop varieties studied, VPS expression was lowest in the leaves and an increase in expression was consistently observed during the early stages of cone development.

Pharmacognostic and pharmacological profile of Humulus lupulus L

The present review describes the morphological, phytochemical and ethnopharmacological aspects of Humulus lupulus L. (Cannabinaceae) and summarizes the most interesting findings obtained in the preclinical and clinical research related to the plant. The female inflorescences of Humulus lupulus (hops), well-known as bittering agent in brewing industry, have long been used in traditional medicine mainly to treat sleep disturbances. However the sedative activity is still under investigation in order to recognize the active principles responsible for the neuropharmacological effects observed in laboratory animals, and their mechanism of action. Here we report the data from our experiments as well as those obtained from other researchers, focusing on the variability of the results. Other traditional applications of hops as stomachic, antibacterial and antifungal remedy have been supported by in vivo and/or in vitro investigations. In recent years some prenylated chalcones present in hops have received much attention for their biological effects: in particular, xanthohumol has been shown to exert cancer chemopreventive activity in in vitro experiments, while 8-prenylnaringenin has been characterized as one of the most potent phytoestrogens isolated until now. Nevertheless much additional work is needed to open up new biomedical application of these compounds.

Effects of traditionally used anxiolytic botanicals on enzymes of the gamma-aminobutyric acid (GABA) system

In Canada, the use of botanical natural health products (NHPs) for anxiety disorders is on the rise, and a critical evaluation of their safety and efficacy is required. The purpose of this study was to determine whether commercially available botanicals directly affect the primary brain enzymes responsible for gamma-aminobutyric acid (GABA) metabolism. Anxiolytic plants may interact with either glutamic acid decarboxylase (GAD) or GABA transaminase (GABA-T) and ultimately influence brain GABA levels and neurotransmission. Two in vitro rat brain homogenate assays were developed to determine the inhibitory concentrations (IC50) of aqueous and ethanolic plant extracts. Approximately 70% of all extracts that were tested showed little or no inhibitory effect (IC50 values greater than 1 mg/mL) and are therefore unlikely to affect GABA metabolism as tested. The aqueous extract of Melissa officinalis (lemon balm) exhibited the greatest inhibition of GABA-T activity (IC50 = 0.35 mg/mL). Extracts from Centella asiatica (gotu kola) and Valeriana officinalis (valerian) stimulated GAD activity by over 40% at a dose of 1 mg/mL. On the other hand, both Matricaria recutita (German chamomile) and Humulus lupulus (hops) showed significant inhibition of GAD activity (0.11-0.65 mg/mL). Several of these species may therefore warrant further pharmacological investigation. The relation between enzyme activity and possible in vivo mode of action is discussed.

Relevance of organic farming and effect of climatological conditions on the formation of alpha-acids, beta-acids, desmethylxanthohumol, and xanthohumol in hop (Humulus lupulus L.)

The concentrations of alpha-acids, beta-acids, desmethylxanthohumol, and xanthohumol were monitored in the hop varieties Admiral (A), Wye Challenger (WC), and First Gold (FG) during the harvest seasons of 2003 through 2005. Hops grown under an organic regimen were compared to plants grown conventionally in hop fields in close vicinity. The concentrations of the key compounds depended very much on climatological conditions showing, in general, highest levels in poorest weather conditions (2004). Of the three varieties studied, FG was the only one showing a clear trend for higher concentrations of secondary metabolites under organic growing conditions than under conventional farming conditions. Cultivation of A and WC seems to be very sensitive to climatic conditions and environmental stresses caused by pests and diseases, thereby leading to various results. WC proved to be a rich source of bioactive chalcones, particularly desmethylxanthohumol.

Prenylation enhances cytotoxicity of apigenin and liquiritigenin in rat H4IIE hepatoma and C6 glioma cells

Antioxidative as well as cytotoxic effects of the prenylated flavonoids licoflavone C (8-prenylapigenin) and isobavachin (8-prenylliquiritigenin) were investigated in comparison to the corresponding non-prenylated flavonoids (apigenin, liquiritigenin) and vitexin (apigenin-C8-glucoside) using metabolically active H4IIE hepatoma and metabolically poorly active C6 glioma cells. None of the substances showed radical scavenging activities in the 2,2-diphenyl-1-picrylhydrazyl (DPPH)-assay nor were they effective in protection against H2O2-induced intracellular 2',7'-dichlorodihydrofluorescein (H2DCF) oxidation (fluorescent probe for oxidative stress) in H4IIE and C6 cells. When the intrinsic effects of the substances were investigated, licoflavone C and isobavachin exerted a pronounced toxicity in both H4IIE (IC50 values of 42+/-5 and 96+/-19 micromol/L) and C6 cells (IC50 values of 37+/-6 and 69+/-3 micromol/L) while the non-prenylated analogues as well as the glycosylated derivate vitexin showed almost no cytotoxic effect up to 250 micromol/L. In H4IIE cells the induction of apoptotic cell death by licoflavone C and icobavachin was detected as an activation of caspase 3/7 (6- and 3.3-fold, respectively). Based on these experiments we suggest that C8-prenylation of a flavonoid enhances the cytotoxicity inducing an apoptotic cell death in H4IIE cells without affecting antioxidative properties.