Prenylflavonoids and phloroglucinol derivatives from hops (Humulus lupulus)

Antiviral and antibacterial properties of phloroglucinols: a review on naturally occurring and (semi)synthetic derivatives with potential therapeutic interest

Phloroglucinol and derived compounds comprise a huge class of secondary metabolites widely distributed in plants and brown algae. A vast array of biological activities, including antioxidant, anti-inflammatory, antimicrobial, and anticancer has been associated to this class of compounds. In this review, the available data on the antiviral and antibacterial capacity of phloroglucinols have been analyzed. Some of these compounds and derivatives show important antimicrobial properties in vitro. Phloroglucinols have been shown to be effective against viruses, such as human immunodeficiency virus (HIV), herpes or enterovirus, and preliminary data through docking analysis suggest that they can be effective against SARS-CoV-19. Also, some phloroglucinols derivatives have shown antibacterial effects against diverse bacteria strains, including Bacillus subtilis and Staphylococcus aureus, and (semi)synthetic development of novel compounds have led to phloroglucinols with a significantly increased biological activity. However, therapeutic use of these compounds is hindered by the absence of in vivo studies and scarcity of information on their mechanisms of action, and hence further research efforts are required. On the basis of this consideration, our work aims to gather data regarding the efficacy of natural-occurring and synthetic phloroglucinol derivatives as antiviral and antibacterial agents against human pathogens, which have been published during the last three decades. The recollection of results reported in this review represents a valuable source of updated information that will potentially help researchers in the development of novel antimicrobial agents.

Prenylated acylphloroglucinols from the fruits of Garcinia xanthochymus

Our continuous study of the dry fruits of Garcinia xanthochymus led to the isolation and structural characterization of four new prenylated acylphloroglucinols, xanthochymusones J-M (1-4), together with the known polycyclic polyprenylated acylphloroglucinols, garciniagifolone A (5) and garcinialiptone A (6). Their structures were elucidated by interpretation of NMR and MS spectroscopic data. Compound 1 bearing a similar core to that of hulupinic acid should be derived via oxidization and ring contraction of prenylated acylphloroglucinol. The inhibitory activities of all the compounds against three human hepatocellular carcinoma cell lines Huh-7, Hep 3B, and Hep G2 were evaluated, and compounds 4 and 5/6 exhibited moderate cytotoxic activities against Hep G2 cells with IC₅₀ values10.4 and 8.8 μM.

Progress of isolation, chemical synthesis and biological activities of natural chalcones bearing 2-hydroxy-3-methyl-3-butenyl group

Chalcones have a three-carbon α,β-unsaturated carbonyl system composed of two phenolic rings. Many chalcones have shown broad spectrum of biological activities with clinical potentials against various diseases. They are usually abundant in seeds, fruit skin, bark and flowers of most edible plants. Among them, chalcones bearing 2-hydroxy-3-methyl-3-butenyl (HMB) group have been reported several times in the past few decades due to their novel scaffolds and numerous interesting biological activities. In this paper, we reviewed the isolation of twelve natural chalcones and a natural chalcone-type compound bearing 2-hydroxy-3-methyl-3-butenyl group discovered so far, and reviewed their synthesis methods and biological activities reported in the literature. We anticipate that this review will inspire further research of natural chalcones.

Anti-Inflammatory Markers of Hops Cultivars (Humulus lupulus L.) Evaluated by Untargeted Metabolomics Strategy

Hops (Humulus lupulus L.) are edible flowers commonly used to add flavour and aroma to beer, besides they have rich chemical diversity and medicinal potential. In this work, an ex vivo anti-inflammatory assay via the LPS-induced signalling pathway and metabolomics approaches were performed to evaluate the ability of hops to inhibit the production of prostaglandin E2 (PGE2) inflammatory mediator and analyze which metabolites produced by the nine different hop cultivars are potential anti-inflammatory markers. Columbus, Chinook and Hallertau Mittelfrüh hop cultivars yielded extracts with PGE2 release inhibition rates of 86.7, 92.5 and 73.5 %, respectively. According to the multivariate statistical analysis, the majority of the metabolites correlated with the activity were prenylated phloroglucinol and phenolic homologs. These results suggest promissory anti-inflammatory hop metabolites.

Exploring two types of prenylated bitter compounds from hop plant (Humulus lupulus L.) against α-glucosidase in vitro and in silico

Hops are abundant in natural bioactive compounds. In this work, nine prenylated bitter compounds from hop were evaluated for their inhibitory activity against α-glucosidase. As a result, four flavonoids and one phloroglucinol (lupulone, LP) outperformed acarbose in inhibiting α-glucosidase. Isoxanthohumol (IX) and LP with two types of structures were selected for inhibition mechanism studies by spectroscopic methods and molecular dynamics simulation (MD). Results showed that IX acted as noncompetitive inhibitor and bound to α-glucosidase in allosteric sites via hydrogen bonds, hydrophobic, van der Waals (vdW), and electrostatic force, whereas LP was uncompetitive inhibitor and bound to catalytic sites via hydrophobic and vdW interactions. Notably, the conformation around binding site of α-glucosidase formed stable α-helix and tightened after binding IX and LP, respectively, which helped to elucidate noncompetitive and uncompetitive inhibitory mechanisms. This work demonstrated that two types of prenylated bitter compounds are discrepant in their mechanisms of interaction with α-glucosidase.

Antiproliferative and palliative activity of flavonoids in colorectal cancer

Flavonoids are plant bioactive compounds of great interest in nutrition and pharmacology, due to their remarkable properties as antioxidant, anti-inflammatory, antibacterial, antifungal and antitumor drugs. More than 5000 different flavonoids exist in nature, with a huge structural diversity and a plethora of interesting pharmacological properties. In this work, five flavonoids were tested for their potential use as antitumor drugs against three CRC cell lines (HCT116, HT-29 and T84). These cell lines represent three different stages of this tumor, one of which is metastatic. Xanthohumol showed the best antitumor activity on the three cancer cell lines, even better than that of the clinical drug 5-fluorouracil (5-FU), although no synergistic effect was observed in the combination therapy with this drug. On the other hand, apigenin and luteolin displayed slightly lower antitumor activities on these cancer cell lines but showed a synergistic effect in combination with 5-FU in the case of HTC116, which is of potential clinical interest. Furthermore, a literature review highlighted that these flavonoids show very interesting palliative effects on clinical symptoms such as diarrhea, mucositis, neuropathic pain and others often associated with the chemotherapy treatment of CRC. Flavonoids could provide a double effect for the combination treatment, potentiating the antitumor effect of 5-FU, and simultaneously, preventing important side effects of 5-FU chemotherapy.

(±)-hyperzewalsins A-D, four pairs of nor-monocyclic polyprenylated acylphloroglucinols with immunosuppressive activity from hypericum przewalskii maxim

Three pairs of previously undescribed 2,3-nor-monocyclic polyprenylated acylphloroglucinols (MPAPs), (±)-hyperzewalsins A-C, a pair of 1,2,3,4-nor-MPAPs, (±)-hyperzewalsins D, along with one undescribed precursor, hyperzewalsin E, were isolated and identified from the aerial parts of Hypericum przewalskii Maxim. (Hypericaceae), and their structures were confirmed by extensive spectroscopic analyses, and quantum-chemical calculations including electronic circular dichroism calculations and NMR calculations with a DP4+ analysis. Significantly, (±)-hyperzewalsins A-D represented the first nor-MPAPs bearing carbon chain constitutions based on diverse highly degraded phloroglucinols. (±)-Hyperzewalsins A-C were the rare nor-MPAPs characterized by degradations of C-2 and C-3 in the core decorated by scissions of C-3/C-4 and C-1/C-2 bonds through Retro-Claisen reactions. (±)-Hyperzewalsins D were the first examples of naturally occurring MPAPs with the loss of C-1/2/3/4 in the phloroglucinol ring formed by cleavages of C-3/C-4 and C-1/C-6 bonds via Retro-Claisen and decarboxylation reactions. Plausible biogenetic pathways for the isolates were proposed. The isolates were evaluated for their immunosuppressive activity in lipopolysaccharide-stimulated murine splenocytes.

Redox and Anti-Inflammatory Properties from Hop Components in Beer-Related to Neuroprotection

Beer is a fermented beverage widely consumed worldwide with high nutritional and biological value due to its bioactive components. It has been described that both alcoholic and non-alcoholic beer have several nutrients derived from their ingredients including vitamins, minerals, proteins, carbohydrates, and antioxidants that make beer a potential functional supplement. Some of these compounds possess redox, anti-inflammatory and anticarcinogenic properties making the benefits of moderate beer consumption an attractive way to improve human health. Specifically, the hop cones used for beer brewing provide essential oils, bitter acids and flavonoids that are potent antioxidants and immune response modulators. This review focuses on the redox and anti-inflammatory properties of hop derivatives and summarizes the current knowledge of their neuroprotective effects.

Hop bitter acids: resources, biosynthesis, and applications

Diversified members of hop bitter acids (α- and β-acids) have been found in hop (Humulus lupulus). Mixtures of hop bitter acids have been traditionally applied in brewing and food industries as bitterness flavors or food additives. Recent studies have discovered novel applications of hop bitter acids and their derivatives in medicinal and pharmaceutical fields. The increasing demands of purified hop bitter acid promoted biosynthesis efforts for the heterologous biosynthesis of objective hop bitter acids by engineered microbial factories. In this study, the updated information of hop bitter acids and their representative application in brewing, food, and medicine fields are reviewed. We also speculate future trends on the development of robust microbial cell factories and biotechnologies for the biosynthesis of hop bitter acids. KEY POINTS: • Structures and applications of hop bitter acids are summarized in this study. • Biosynthesis of hop bitter acids remains challenging. • We discuss potential strategies in the microbial production of hop bitter acids.

Naturally occurring prenylated chalcones from plants: structural diversity, distribution, activities and biosynthesis

Covering: up to July 2020Naturally occurring chalcones carrying up to three modified or unmodified C5-, C10-, and C15-prenyl moieties on both rings A and B as well as at the α- and β-carbons are widely distributed in plants of the families of Fabaceae, Moraceae, Zingiberaceae and Cannabaceae. Xanthohumol and isobavachalcone being the most investigated representatives, exhibit diverse and remarkable biological and pharmacological activities. The present review deals with their structural characters, biological activities and occurrence in the plant kingdom. Biosynthesis of prenylated chalcones and metabolism of xanthohumol are also discussed.

In Vitro and In Vivo Effects of Flavonoids on Peripheral Neuropathic Pain

Neuropathic pain is a common symptom and is associated with an impaired quality of life. It is caused by the lesion or disease of the somatosensory system. Neuropathic pain syndromes can be subdivided into two categories: central and peripheral neuropathic pain. The present review highlights the peripheral neuropathic models, including spared nerve injury, spinal nerve ligation, partial sciatic nerve injury, diabetes-induced neuropathy, chemotherapy-induced neuropathy, chronic constriction injury, and related conditions. The drugs which are currently used to attenuate peripheral neuropathy, such as antidepressants, anticonvulsants, baclofen, and clonidine, are associated with adverse side effects. These negative side effects necessitate the investigation of alternative therapeutics for treating neuropathic pain conditions. Flavonoids have been reported to alleviate neuropathic pain in murine models. The present review elucidates that several flavonoids attenuate different peripheral neuropathic pain conditions at behavioral, electrophysiological, biochemical and molecular biological levels in different murine models. Therefore, the flavonoids hold future promise and can be effectively used in treating or mitigating peripheral neuropathic conditions. Thus, future studies should focus on the structure-activity relationships among different categories of flavonoids and develop therapeutic products that enhance their antineuropathic effects.

Substrate specificity change of a flavonoid prenyltransferase AhPT1 induced by metal ion

Prenylated flavonoids are good drug candidates due to multiple biological activities and health benefits. Prenyltransferase is an important enzyme involved in the biosynthesis of prenylated flavonoids. In this work, a flavonoid prenyltransferase (AhPT1) from Artocarpus heterophyllus showed an unexpectedly metal ion-induced specificity to flavonoid substrates. AhPT1 could catalyse 6-C-prenylation of genistein when Mg²⁺ serving as cofactor. Its catalytic activity to 6-hydroxyflavone was undetectable. However, when Mn²⁺ was used instead of Mg²⁺, 5-C-prenylated 6-hydroxyflavone was generated with a high conversion rate. Mn²⁺ altered the regiospecificity of AhPT1 and turned it into a 5-C-prenyltransferase. 2'-Hydroxyl could improve the conversion rate of 6-hydroxyflavone, whereas 3'- or 4'-hydroxyl impaired the catalysis efficiency of AhPT1. NQIFDADID174 and DLTDVEGD305 were active motifs involved in substrate binding and catalysis. Asn166, Asp170, Asp174, Asp298, Asp301 and Asp305 in the active center were critical to the prenylation reaction.

Phytochemical Characterization of Wild Hops (Humulus lupulus ssp. lupuloides) Germplasm Resources From the Maritimes Region of Canada

A survey was conducted in the Maritimes region of eastern Canada to measure the phytochemical diversity of prenylchalcone, soft resins (alpha & beta acids), and flavonol constituents from 30 unique wild-growing populations of hops (Humulus lupulus L.). Based on cone chemometrics, the majority of accessions (63.3%) are native Humulus lupulus ssp. lupoloides, with cones containing both xanthogalenol and 4'-O-methyl xanthohumol as chemotaxonomic indicator molecules. Interestingly, the leaves of all verified Humulus lupulus ssp. lupulus accessions accumulated high proportions (>0.20 total flavonols) of two acylated flavonol derivatives (kaempferol-3-O-(6''-O-malonyl)-β-D-glucopyranoside; quercetin-3-O-(6''-O-malonyl)-β-D-glucopyranoside), both previously unreported from hops leaves. The native lupuloides accessions examined possess only trace amounts of this compound in their leaves (<0.10 total flavonols), suggesting its potential utility as a novel, leaf-derived chemotaxonomic marker for subspecies identification purposes. A leaf-derived taxonomic marker is useful for identifying wild-growing accessions, as leaves are present throughout the entire growing season, whereas cones are only produced late in summer. Additionally, the collection of cones from 10-meter tall wild plants in overgrown riparian habitats is often difficult. The total levels of alpha acids, beta acids, and prenylchalcones in wild-collected Maritimes lupuloides cones are markedly higher than those previously reported for lupuloides individuals in the westernmost extent of its native range and show potentially valuable traits for future cultivar development, while some may be worthy of immediate commercial release. The accessions will be maintained as a core germplasm resource for future cultivar development.

New Male Specific Markers for Hop and Application in Breeding Program

Male specific DNA sequences were selected from a Diversity Arrays Technology (DArT) mapping study to evaluate their suitability for determination of the sex phenotype among young seedlings in a hop (Humulus lupulus L.) breeding program. Ten male specific DArT markers showed complete linkage with male sex phenotype in three crossing families. Following optimization, four were successfully converted into PCR markers and a multiplex PCR approach for their use was developed. Among 197 plants (97 from the world collection; 100 from three segregating families), 94-100% positive correlation with sex phenotypic data was achieved for the single PCR amplification, whereas the multiplex approach showed 100% correlation. To develop a fast and low-cost method, crude sample multiplex PCR was evaluated in 253 progenies from 14 segregating populations without losing accuracy. The study describes, for the first time, the routine application of molecular markers linked to male sex in an intensive Slovenian hop breeding program. The methods described could be employed for screening of sex at the seedling stage in other hop programs worldwide, thereby saving resources for desirable female plants.

Acetophenone derivatives from the roots of Melicope ptelefolia

Five new prenylated acetophenones, melicoptelins A-E (1-5), along with one known congener (6) were isolated from the roots of Melicope ptelefolia. Among them, compounds 2a/2b, 3a/3b, and 4a/4b were obtained as inseparable interconverting mixtures of keto and enol tautomers. Their structures were elucidated on the basis of extensive spectroscopic methods, including 1D, 2D NMR and HRESIMS. Compouds 2a/2b, 4a/4b and 5 exhibit protein tyrosine phosphatase 1B (PTP1B) inhibitory activity with IC₅₀ values of 34.4, 55.2 and 66.6 μM, respectively.

Modeling of α-acids and xanthohumol extraction in dry-hopped beers

The practice of dry-hopping has been used by the brewing industry to obtain beers with increased contents of flavor and bitterness compounds. Notwithstanding this, other compounds such as α-acids (AA) and xhanthohumol (XN) are co-extracted influencing the final characteristics of the beer, particularly its beneficial bioactivity. In this context a model for the understanding of AA and XN extraction by dry-hopping is proposed. The varieties Chinook (CHI), East Kent Goldings (EKG) and Tettnanger (TET) were assayed and robust statistical approaches were applied for data interpretation. Concentration of AA in beers post-maturation reached values higher than 20 mg/L using 2.8 g/L of CHI hops and 10 days of maturation. For XN, a similar behavior was verified. The maximum efficiency of AA and XN extraction (transfer rate) were reached at 13.5 days with dose rates of 147 and 13.9 mg/L, respectively.

In Vitro Antidiabetic Effects of Isolated Triterpene Glycoside Fraction from Gymnema sylvestre

A triterpene glycoside (TG) fraction isolated and purified from ethanolic extract of Gymnema sylvestre (EEGS) was investigated for blood glucose control benefit using in vitro methods. The HPLC purified active fraction TG was characterized using FTIR, LC-MS, and NMR. The purified fraction (TG) exhibited effective inhibition of yeast α-glucosidase, sucrase, maltase, and pancreatic α-amylase with IC₅₀ values 3.16 ± 0.05 μg/mL, 74.07 ± 0.51, 5.69 ± 0.02, and 1.17 ± 0.24 μg/mL, respectively, compared to control. TG was characterized to be a mixture of triterpene glycosides: gymnemic acids I, IV, and VII and gymnemagenin. In vitro studies were performed using mouse pancreatic β-cell lines (MIN6). TG did not exhibit any toxic effects on β-cell viability and showed protection against H₂O₂ induced ROS generation. There was up to 1.34-fold increase in glucose stimulated insulin secretion (p<0.05) in a dose-dependent manner relative to standard antidiabetic drug glibenclamide. Also, there was further one-fold enhancement in the expression of GLUT2 compared to commercial standard DAG (deacylgymnemic acid). Thus, the present study highlights the effective isolation and therapeutic potential of TG, making it a functional food ingredient and a safe nutraceutical candidate for management of diabetes.

New Polyisoprenylated Polycyclic Phloroglucines from Clusia gundlachii

A bioassay-guided fractionation yielded five new polycyclic phloroglucines derivatives, namely, gundlachiione A (1), gundlachiione B (2), gundlachiione C (3), gundlachiione D (4) and gundlachiione E (5) from the fruits of Clusia gundlachii, collected in Puerto Rico, USA. Their structures were determined by full spectroscopic data, including 2D NMR COSY, HMQC, HMBC, and NOESY experiments, and HRESIMS. Compounds 1 and 3 demonstrated activities against Leishmania donovani intracellular macrophage amastigotes in THP1 cultures, comparable to those observed for the standard drug pentamidine (IC50 and IC90 values 0.84 and 6.13 μg/mL, 2.32 and 3.01 μg/mL, 0.77 and 2.99 μg/mL, respectively). Both compounds, 1 and 3, also showed weak activities against L. donovani promastogotes and absence of cytotoxicity against transformed THP 1 cells.

Characteristic α-Acid Derivatives from Humulus lupulus with Antineuroinflammatory Activities

Twenty compounds, including 14 new α-acid derivatives, a new chromone, and five known compounds, were identified from the pistillate inflorescence of Humulus lupulus (hops), and their structures were elucidated via physical data analysis. The absolute configurations of new α-acid derivatives 1-11b were determined by comparing their computed and experimental electronic circular dichroism spectra using TDDFT and NMR spectroscopic data. A putative biosynthetic pathway for the identified components was deduced. Their antineuroinflammatory effects were assayed systematically, and their structure-activity relationships are discussed briefly. Among the identified compounds, compound 14 displayed moderate inhibitory effects against nitric oxide production with an IC₅₀ value of 7.92 μM.

Glandular hair constituents of Mallotus philippinensis Muell. fruit act as tyrosinase inhibitors: Insights from enzyme kinetics and simulation study

The glandular hair extracts from the fruit rind of Mallotus philippinensis Muell. is employed to treat various skin infections, however the anti-tyrosinase activity remains unknown. Hence the present study inspected on the anti-melanogenic activity of M. philippinensis constituents. Lineweaver Burk plot revealed mixed inhibition for Rottlerin; non-competitive type of inhibition for mallotophilippen A and B respectively. Thermodynamic studies resulted in static quenching forming ground state complex with higher binding constant temperature dependently. Fluorescence and circular dichroism study implicated conformational change in secondary and tertiary structure of tyrosinase. Molecular docking suggests rottlerin has high binding affinity to the active site pocket of tyrosinase. Simulation study further proved that the compactness of inhibitor with tyrosinase by hydrogen bonding influenced the stability of the enzyme. Depigmentation efficacy is further proved in Aspergillus niger spores. Thus our findings delineate that rottlerin could be utilized as a depigmentation agent in food pharmaceutical and agricultural industries.

Insecticidal effects of extracts of Humulus lupulus (hops) L. cones and its principal component, xanthohumol

Insecticidal effects of the dichloromethane, ethyl acetate, acetone, ethanol and methanol extracts of Humulus lupulus (hops) L. cones and its principal components, xanthohumol was investigated on five stored pests, Sitophilus granarius (L.), Sitophilus oryzae (L.), Acanthoscelides obtectus (Say.), Tribolium castaneum (Herbst) and Lasioderma serricorne (F.). The mortality of adults of the insects treated with 2, 5, 5, 10 and 20 mg ml̠-1 concentrations of the extracts and xanthuhumol was counted after 24, 48, 72, 96 and 120 h. In order to determine the toxic effects of the substances tested against all tested insects, durations for 50% mortality of the adults, and LD50 values were also determined in the first 48 h by probit analysis. Our results also showed that xanthohumol was more toxic against the pests in comparison with the extracts applications. LD50 values for xanthohumol were found to be low dose as compared with the extracts. Xanthohumol was more toxic against S. granarius (L.) with 6.8 µg of LD50 value. Among the extracts, methanol extract was less effective than other extracts against all tested insects. The ethyl acetate extract of H. lupulus cones was the most effective extract against the tested pests. The quantitative amounts of xanthohumol in the extracts were determined using a high-performance liquid chromatography. The quantitative data indicated that amount of xanthohumol in the extracts increased with increase of polarity of the solvents used from methanol to dichloromethane. The methanol extract contained the high amount of xanthohumol with 5.74 g/100 g extract (0.46 g/100 g plant sample).

Chemical Compounds in Natural Medicines That Affect Macropharges and Adipocyte Cells

Macrophages play major roles in inflammation, immunity and host defense mechanisms. Once activated they produce and release cytokines, oxygen and nitrogen species, and eicosanoids. The best characterized stimuli to induce the transcription of genes encoding pro-inflammatory proteins in macrophages in vitro is bacterial lipopolysaccharide (LPS). LPS could be used alone or in combination with recombinant mouse interferon-γ (IFN-γ). Such stimulation results in cytokine release and the synthesis of enzymes such as cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS). The nitric oxide (NO) radical is known to play a central role in inflammatory and immune reactions for self-protection. However, the excessive production of NO may lead to tissue damage. In inflammatory diseases such as rheumatoid arthritis, excessive NO production by activated macrophages has been observed. Adipose tissue is composed of various cell types such as mature adipocytes, preadipocytes, fibroblasts, endothelial cells, vascular cells, and macrophages. Recent studies indicate that obesity is associated with low-grade chronic inflammation of adipose tissues, and that such inflammation is one of the potential mechanisms leading to the insulin resistance. It has been demonstrated that obese adipose tissue is characterized by the increased infiltration of macrophages. Therefore, we attempted to identify natural anti-inflammatory compounds that not only inhibit the secretion of NO from RAW 264.7 cells, but also inhibit triglyceride accumulation in 3T3-L1 adipocytes. This review describes the NO prpduction inhibitory activity or the TG accumulation inhibitory activity of the compounds obtained from 18 plants and a fungi that have been used as traditional medicines.

Natural Prenylchalconaringenins and Prenylnaringenins as Antidiabetic Agents: α-Glucosidase and α-Amylase Inhibition and in Vivo Antihyperglycemic and Antihyperlipidemic Effects

Inhibition of α-glucosidase and α-amylase decreases postprandial blood glucose levels and delays glucose absorption, making it a treatment strategy for type 2 diabetes. This study examined in vivo and in vitro antidiabetic activities of natural prenylchalconaringenins 1 and 2 and prenylnaringenins 3 and 4, found in hops and beer. 3'-Geranylchalconaringenin (2) competitively and irreversibly inhibited α-glucosidase (IC₅₀ = 1.08 μM) with activity 50-fold higher than that of acarbose (IC₅₀ = 51.30 μM) and showed moderate inhibitory activity against α-amylase (IC₅₀ = 20.46 μM). Docking analysis substantiated these findings. In addition, compound 2 suppressed the increase in postprandial blood glucose levels and serum levels of total cholesterol and triglycerides in streptozotocin-induced diabetic mice. Taken together, these results suggest that 2 has dual inhibitory activity against α-glucosidase and α-amylase and alleviates diabetic hyperglycemia and hyperlipidemia, making it a potential functional food ingredient and drug candidate for management of type 2 diabetes.

New Polyprenylated Phloroglucinol and Other Compounds Isolated from the Fruits of Clusia nemorosa (Clusiaceae)

Clusia nemorosa has been widely used in folk medicine to treat various ailments, including headaches and inflammation. Investigation of the fruits of Clusia nemorosa (Clusiaceae) led to the isolation and characterization of a new phloroglucinol derivative, named 6S,8S,28S-nemorosic acid (1), together with seven known compounds: friedelin (2), β-sitosterol (3), stigmasterol (4), β-sitosterol glycoside (5), kaempferol (6), quercetin (7) and dimethyl citrate (8). The structures were determined by extensive 1D- and 2D-NMR, CD and MS spectroscopic analyses.

Sensomics analysis of key bitter compounds in the hard resin of hops (Humulus lupulus L.) and their contribution to the bitter profile of Pilsner-type beer

Recent brewing trials indicated the occurrence of valuable bitter compounds in the hard resin fraction of hop. Aiming at the discovery of these compounds, hop's ε-resin was separated by means of a sensory guided fractionation approach and the key taste molecules were identified by means of UV/vis, LC-TOF-MS, and 1D/2D-NMR studies as well as synthetic experiments. Besides a series of literature known xanthohumol derivatives, multifidol glucosides, flavon-3-on glycosides, and p-coumaric acid esters, a total of 11 bitter tastants are reported for the first time, namely, 1",2"-dihydroxanthohumol F, 4'-hydroxytunicatachalcone, isoxantholupon, 1-methoxy-4-prenylphloroglucinol, dihydrocyclohumulohydrochinone, xanthohumols M, N, and P, and isoxanthohumols M, N, and P, respectively. Human sensory analysis revealed low bitter recognition threshold concentrations ranging from 5 (co-multifidol glucopyranoside) to 198 μmol/L (trans-p-coumaric acid ethyl ester) depending on their chemical structure. For the first time, LC-MS/MS quantitation of these taste compounds in Pilsner-type beer, followed by taste re-engineering experiments, revealed the additive contribution of iso-α-acids and the identified hard resin components to be truly necessary and sufficient for constructing the authentic bitter percept of beer. Finally, brewing trails using the ε-resin as the only hop source impressively demonstrated the possibility to produce beverages strongly enriched with prenylated hop flavonoids.

The Draft Genome of Hop (Humulus lupulus), an Essence for Brewing

The female flower of hop (Humulus lupulus var. lupulus) is an essential ingredient that gives characteristic aroma, bitterness and durability/stability to beer. However, the molecular genetic basis for identifying DNA markers in hop for breeding and to study its domestication has been poorly established. Here, we provide draft genomes for two hop cultivars [cv. Saazer (SZ) and cv. Shinshu Wase (SW)] and a Japanese wild hop [H. lupulus var. cordifolius; also known as Karahanasou (KR)]. Sequencing and de novo assembly of genomic DNA from heterozygous SW plants generated scaffolds with a total size of 2.05 Gb, corresponding to approximately 80% of the estimated genome size of hop (2.57 Gb). The scaffolds contained 41,228 putative protein-encoding genes. The genome sequences for SZ and KR were constructed by aligning their short sequence reads to the SW reference genome and then replacing the nucleotides at single nucleotide polymorphism (SNP) sites. De novo RNA sequencing (RNA-Seq) analysis of SW revealed the developmental regulation of genes involved in specialized metabolic processes that impact taste and flavor in beer. Application of a novel bioinformatics tool, phylogenetic comparative RNA-Seq (PCP-Seq), which is based on read depth of genomic DNAs and RNAs, enabled the identification of genes related to the biosynthesis of aromas and flavors that are enriched in SW compared to KR. Our results not only suggest the significance of historical human selection process for enhancing aroma and bitterness biosyntheses in hop cultivars, but also serve as crucial information for breeding varieties with high quality and yield.

Supercritical carbon dioxide hops extracts with antimicrobial properties

Extracts obtained from hops (Humulus lupulus L., Cannabaceae) by supercritical fluid extraction (SFE), SFE followed by isomerization, as well as by conventional technique, were investigated for their chemical composition and antibacterial activity against selected foodborne pathogens and microorganisms capable to cause the food spoilage. The antibacterial activity of the extracts was compared with the antibacterial activity of xanthohumol, compound known for its broad pharmacological properties, isolated from the raw material remained after the SFE. Xanthohumol (XH, 96%) proved to posses the most prominent activity against all the tested strains, with the MIC values ranged between 2.5 and 20 μg mL-1. Supercritical hops extract and potassium isomerized supercritical hops extract showed strong antibacterial activity against the tested strains as well. Escherichia coli was not affected by the extracts, meaning that their oral admission would not cause the same problem as antibiotic application in intestinal flora. The chemical composition of the investigated hops extracts was analysed by GC-MS. Contents of α-acids, β-acids, iso-α-acids and xanthohumol in the samples were determined by HPLC.

K-targeted metabolomic analysis extends chemical subtraction to DESIGNER extracts: selective depletion of extracts of hops (Humulus lupulus)

This study introduces a flexible and compound targeted approach to Deplete and Enrich Select Ingredients to Generate Normalized Extract Resources, generating DESIGNER extracts, by means of chemical subtraction or augmentation of metabolites. Targeting metabolites based on their liquid-liquid partition coefficients (K values), K targeting uses countercurrent separation methodology to remove single or multiple compounds from a chemically complex mixture, according to the following equation: DESIGNER extract = total extract ± target compound(s). Expanding the scope of the recently reported depletion of extracts by immunoaffinity or solid phase liquid chromatography, the present approach allows a more flexible, single- or multi-targeted removal of constituents from complex extracts such as botanicals. Chemical subtraction enables both chemical and biological characterization, including detection of synergism/antagonism by both the subtracted targets and the remaining metabolite mixture, as well as definition of the residual complexity of all fractions. The feasibility of the DESIGNER concept is shown by K-targeted subtraction of four bioactive prenylated phenols, isoxanthohumol (1), 8-prenylnaringenin (2), 6-prenylnaringenin (3), and xanthohumol (4), from a standardized hops (Humulus lupulus L.) extract using specific solvent systems. Conversely, adding K-targeted isolates allows enrichment of the original extract and hence provides an augmented DESIGNER material. Multiple countercurrent separation steps were used to purify each of the four compounds, and four DESIGNER extracts with varying depletions were prepared. The DESIGNER approach innovates the characterization of chemically complex extracts through integration of enabling technologies such as countercurrent separation, K-by-bioactivity, the residual complexity concepts, as well as quantitative analysis by (1)H NMR, LC-MS, and HiFSA-based NMR fingerprinting.

Asymmetric, stereodivergent synthesis of (-)-clusianone utilizing a biomimetic cationic cyclization

We report a stereodivergent, asymmetric total synthesis of (-)-clusianone in six steps from commercial materials. We implement a challenging cationic cyclization forging a bond between two sterically encumbered quaternary carbon atoms. Mechanistic studies point to the unique ability of formic acid to mediate the cyclization forming the clusianone framework.

Hop water extract inhibits double-stranded RNA-induced thymic stromal lymphopoietin release from human nasal epithelial cells

BACKGROUND

Thymic stromal lymphopoietin (TSLP) acts as a master switch for allergic inflammation and plays a key role in allergic diseases, including allergic rhinitis. Double-stranded RNA (dsRNA) recognized by Toll-like receptor 3 (TLR3) strongly activates TSLP release from human nasal epithelial cells (HNECs). Hop (Humulus lupulus L.) extracts have been shown to have potent pharmacologic effects on inflammation.

METHODS

To investigate whether a hop water extract (HWE) prevents TSLP release from HNECs, human telomerase reverse transcriptase (hTERT)-transfected HNECs, used as a model of normal HNECs, were pretreated with HWE before treatment with the TLR3 ligand Polyinosine-polycytidylic acid (poly[I:C]).

RESULTS

In the hTERT-transfected HNECs, treatment with HWE significantly reduced poly(I:C)-induced production and release of TSLP in a dose-dependent manner, as well as dexamethasone. Treatment with the protein kinase C (PKC) inhibitor GF109203X and NF-κB inhibitor IMD-0354 also reduced poly(I:C)-induced TSLP release from hTERT-transfected HNECs. Treatment with HWE efficiently prevented up-regulation of PKC activity by 12-O-tetradecanoyl phorbol-13-acetate but not NF-κB activity induced by IL-1β in hTERT-transfected HNECs.

CONCLUSION

Our results clearly indicated that HWE inhibited dsRNA-induced production and release of TSLP via a PKC signal pathway in HNECs and it may have potent preventive effects against allergic rhinitis.

Anti-inflammatory and anti-tumor-promoting effects of 5-deprenyllupulonol C and other compounds from Hop (Humulus lupulus L.)

A new phloroglucinol derivative, 5-deprenyllupulonol C (1), along with four other phloroglucinol derivatives, 2-5, five chalcones, 6-10, four flavanones, 11-14, two flavonol glycosides, 15 and 16, and five triterpenoids, 17-21, were isolated from the female inflorescence pellet extracts of hop (Humulus lupulus L.). Upon evaluation of these compounds against the Epstein-Barr virus early antigen (EBV-EA) activation induced by 12-O-tetradecanoylphorbol 13-acetate (TPA) in Raji cells, twelve compounds, i.e., 1-4, 11-14, 17-19, and 21, showed potent inhibitory effects on EBV-EA induction, with IC₅₀ values in the range of 215-393 mol ratio/32 pmol TPA. In addition, eleven compounds, i.e., 1-4, 6, 11, 12, 14, 17, 18, and 20, were found to inhibit TPA-induced inflammation (1 μg/ear) in mice, with ID₅₀ values in the range of 0.13-1.06 μmol per ear. Further, lupulone C (2) and 6-prenylnaringenin (14) exhibited inhibitory effects on skin-tumor promotion in an in vivo two-stage mouse-skin carcinogenesis test based on 7,12-dimethylbenz[a]anthracene (DMBA) as initiator and with TPA as promoter.

Biochemical basis for functional ingredient design from fruits

Functional food ingredients (nutraceuticals) in fruits range from small molecular components, such as the secondary plant products, to macromolecular entities, e.g., pectin and cellulose, that provide several health benefits. In fruits, the most visible functional ingredients are the color components anthocyanins and carotenoids. In addition, several other secondary plant products, including terpenes, show health beneficial activities. A common feature of several functional ingredients is their antioxidant function. For example, reactive oxygen species (ROS) can be oxidized and stabilized by flavonoid components, and the flavonoid radical can undergo electron rearrangement stabilizing the flavonoid radical. Compounds that possess an orthodihydroxy or quinone structure can interact with cellular proteins in the Keap1/Nrf2/ARE pathway to activate the gene transcription of antioxidant enzymes. Carotenoids and flavonoids can also exert their action by modulating the signal transduction and gene expression within the cell. Recent results suggest that these activities are primarily responsible for the health benefits associated with the consumption of fruits and vegetables.

Preparative isolation and purification of xanthohumol from hops (Humulus lupulus L.) by high-speed counter-current chromatography

Xanthohumol (XN) and related prenylflavonoids are the main bioactive components of hops (Humulus lupulus L.). The current work is to investigate the use of high-speed counter-current chromatography (HSCCC) in search for high isolation of xanthohumol from hops. A solvent system consisted of n-hexane-ethyl acetate-methanol-water at a volume ratio of 5:5:4:3 was employed. The results demonstrated that the constructed method could be well applied for the isolation of xanthohumol from hops extract. After HSCCC isolation procedure, the purity of xanthohumol was over 95% assayed by HPLC and the yield of extraction was 93.60%. The chemical structure identification of xanthohumol was carried out by UV, (1)H NMR and (13)C NMR. The present results demonstrated that xanthohumol could be efficiently obtained using a single HSCCC step from H. lupulus L. extract.

Production of phloroglucinol by Escherichia coli using a stationary-phase promoter

Escherichia coli was metabolically engineered using a new host-vector system to produce phloroglucinol. The key biosynthetic gene phlD (encoding a type III polyketide synthase) from Pseudomonas fluorescens was expressed in E. coli using the stationary-phase promoter of the fic gene and a high-copy plasmid. In shake-flasks, the engineered strain produced phloroglucinol up to 0.28 g/l with a productivity of 0.014 g/l h. About 9.2% of the glucose consumed was converted to phloroglucinol after 20 h. Compared with the widely used inducible T7 promoter system, this strain did not require IPTG induction and the final titer of phloroglucinol was 22% higher.

Acylphloroglucinol and xanthones from Hypericum ellipticum

An acylphloroglucinol, elliptophenone A, and two xanthones, elliptoxanthone A and elliptoxanthone B, were isolated from the aerial portions of Hypericum ellipticum together with three known xanthones, 1,3,7-trihydroxy-8-(3-methyl-2-butenyl)-9H-xanthen-9-one, 1,6-dihydroxy-4-methoxy-9H-xanthen-9-one, and 1,4,5-trihydroxy-9H-xanthen-9-one. Their structures were determined by spectroscopic analyses. The acylphloroglucinol and xanthones were evaluated for cytotoxicity using three human colon cancer cell lines cell lines (HT-29, HCT-116 and Caco-2) and a normal human colon cell line (CCD-18Co).

Chemistry and biochemistry of dietary polyphenols

Polyphenols are the biggest group of phytochemicals, and many of them have been found in plant-based foods. Polyphenol-rich diets have been linked to many health benefits. This paper is intended to review the chemistry and biochemistry of polyphenols as related to classification, extraction, separation and analytical methods, their occurrence and biosynthesis in plants, and the biological activities and implications in human health. The discussions are focused on important and most recent advances in the above aspects, and challenges are identified for future research.