Polyphenols in alcoholic beverages activating constitutive androstane receptor CAR

Case-based discussion of the acute hepatic porphyrias: Updates on pathogenesis, diagnosis and management

The acute hepatic porphyrias (AHPs) include three autosomal dominant disorders, acute intermittent porphyria, variegate porphyria  and hereditary coproporphyria, and the ultra-rare autosomal recessive 5-aminolevulinic acid dehydratase-deficient porphyria. All four are characterized by episodic acute neurovisceral attacks that can be life-threatening if left untreated. The attacks are precipitated by factors that induce hepatic 5-aminolevulinic acid synthase 1 (ALAS1), resulting in accumulation of the porphyrin precursors, 5-aminolevulinic acid and porphobilinogen, which are believed to cause neurotoxicity. Diagnosis of these rare disorders is often delayed because the symptoms are non-specific with many common aetiologies. However, once clinical suspicion of an AHP is raised, diagnosis can be made by specialized biochemical testing, particularly during attacks. Moderate or severe attacks are treated with intravenous hemin infusions, together with supportive care to relieve pain and other symptoms. Prophylactic treatments are recommended in patients with confirmed recurrent attacks (≥4 attacks in a maximum period of 12 months), the most effective being givosiran, an RNAi therapeutic targeting hepatocyte ALAS1 mRNA. AHP patients with clinically and/or biochemically active disease are at elevated risk for developing long-term complications, including chronic kidney disease, chronic hypertension and hepatocellular carcinoma, thus, surveillance is recommended. Here, using a case-based format, we provide an update on the pathogenesis, diagnosis and treatment of the AHPs based on literature review and clinical experiences.

Activity difference of three labdane diterpenoids on human constitutive androstane receptor

The constitutive androstane receptor (CAR) regulates enzyme transcription related to drug metabolism; therefore, natural compound clarification in food that interacts with CAR is significant for drug development. We revealed that 13-epimanool, which is a compound found in the common sage, is bound to hCAR based on differential scanning fluorometry (DSF) measurements using recombinant hCAR protein. Similar labdane diterpenoids were examined, which revealed that manool and sclareol, which were both natural compounds contained in herbs, are bound to hCAR. They exhibited different effects for CAR activity in the luciferase assay despite the structural similarity. Manool was a partial agonist, 13-epimanool was a weak partial agonist, and sclareol was an antagonist. The activity of hCAR may be regulated by slight differences in the bound compound.

Bile acid metabolism and signaling: Emerging pharmacological targets of dietary polyphenols

Beyond their role as emulsifiers of lipophilic compounds, bile acids (BAs) are signaling endocrine molecules that show differential affinity and specificity for a variety of canonical and non-canonical BA receptors. Primary BAs (PBAs) are synthesized in the liver while secondary BAs (SBAs) are gut microbial metabolites of PBA species. PBAs and SBAs signal to BA receptors that regulate downstream pathways of inflammation and energy metabolism. Dysregulation of BA metabolism or signaling has emerged as a feature of chronic disease. Dietary polyphenols are non-nutritive plant-derived compounds associated with decreased risk of metabolic syndrome, type-2 diabetes, hepatobiliary and cardiovascular disease. Evidence suggests that the health promoting effects of dietary polyphenols are linked to their ability to alter the gut microbial community, the BA pool, and BA signaling. In this review we provide an overview of BA metabolism and summarize studies that link the cardiometabolic improvements of dietary polyphenols to their modulation of BA metabolism and signaling pathways, and the gut microbiota. Finally, we discuss approaches and challenges in deciphering cause-effect relationships between dietary polyphenols, BAs, and gut microbes.

Role of the constitutive androstane receptor (CAR) in human liver cancer

BACKGROUND

The constitutive androstane receptor (CAR) is a member of the nuclear receptor superfamily (subfamily 1, group I, member 3, also known as NR1I3) that is almost exclusively expressed in the liver. CAR interacts with key signalling pathways such as those involved in drug, energy and bilirubin metabolism. In mouse models, activation of CAR leads to tumorigenesis by inducing pro-proliferative and anti-apoptotic signalling. However, many previous reports have shown species differences between CAR activity in animal models and humans. Recent studies have demonstrated that the mode of action of CAR in rodent liver tumorigenesis is not applicable to humans. Despite this, many studies still continue to study the role of CAR in animal models, hence, there is a need to further explore the role of CAR in human diseases particularly cancers. While there is limited evidence for a role of CAR in human cancers, some studies have proposed a tumour-suppressive role of CAR in liver cancer. In addition, recent studies exploring CAR in human livers demonstrated a hepato-protective role for CAR in and more specifically, its ability to drive differentiation and liver regeneration. This review will discuss the role of CAR in liver cancer, with a focus on species differences and its emerging, tumour-suppressive role in liver cancer and its role in the regulation of liver cancer stem cells.

Natural product modulators of human sensations and mood: molecular mechanisms and therapeutic potential

Humans perceive physical information about the surrounding environment through their senses. This physical information is registered by a collection of highly evolved and finely tuned molecular sensory receptors. A multitude of bioactive, structurally diverse ligands have evolved in nature that bind these molecular receptors. The complex, dynamic interactions between the ligands and the receptors lead to changes in our sensory perception or mood. Here, we review our current knowledge of natural products and their derived analogues that interact specifically with human G protein-coupled receptors, ion channels, and nuclear hormone receptors to modulate the sensations of taste, smell, temperature, pain, and itch, as well as mood and its associated behaviour. We discuss the molecular and structural mechanisms underlying such interactions and highlight cases where subtle differences in natural product chemistry produce drastic changes in functional outcome. We also discuss cases where a single compound triggers complex sensory or behavioural changes in humans through multiple mechanistic targets. Finally, we comment on the therapeutic potential of the reviewed area of research and draw attention to recent technological developments in genomics, metabolomics, and metabolic engineering that allow us to tap the medicinal properties of natural product chemistry without taxing nature.

Resveratrol Increases Hepatic SHBG Expression through Human Constitutive Androstane Receptor: a new Contribution to the French Paradox

Sex hormone-binding globulin (SHBG) carries sex steroids in blood regulating their bioavailability. Red wine consumption increases plasma SHBG levels, and we have discovered that resveratrol, a polyphenol enriched in red wine, acts specifically through the human constitutive androstane receptor (CAR), a drug/xenobiotic detoxification gene regulator, to increase hepatic SHBG production. Chromatin immunoprecipitation and luciferase reporter gene assays show that human CAR binds to a typical direct repeat 1 nuclear hormone receptor-binding element in the human SHBG proximal promoter. Resveratrol also increased hepatic SHBG production in humanized SHBG/CAR transgenic mice. Moreover, SHBG expression correlated significantly with CAR mRNA levels in human liver biopsies. We conclude that the beneficial effects of red wine on the metabolic syndrome and it associated co-morbidities, including cardiovascular disease and type 2 diabetes, may be mediated in part by resveratrol acting via CAR to increase plasma SHBG levels.

Effects of resveratrol on drug- and carcinogen-metabolizing enzymes, implications for cancer prevention

Resveratrol is a polyphenol found in grape skins and peanuts that has demonstrated many health benefits including protection against aging, cardiovascular and metabolic disease, neurological decline, and cancer. The anticancer properties of resveratrol have been attributed to a variety of mechanisms, including its general inhibition of phase I metabolism and induction of phase II metabolism. The effects of resveratrol on these enzymes, however, are still unclear, as in vitro evidence often contrasts with animal studies and clinical trials. Reasons for these variances could include the low bioavailability of resveratrol and the effects of resveratrol metabolites. Due to resveratrol's interactions with drug-metabolizing enzymes and drug transporters, individuals concurrently taking pharmacological doses of resveratrol with other supplements or medications could potentially experience nutrient-drug interactions. This review summarizes the known effects of resveratrol and its main metabolites on drug metabolism in order to help characterize which populations might benefit from resveratrol for the prevention of cancer, as well as those that may need to avoid supplementation due to potential drug interactions.

Development of pharmacophore-based classification model for activators of constitutive androstane receptor

Constitutive androstane receptor (CAR) is predominantly expressed in the liver and is important for regulating drug metabolism and transport. Despite its biological importance, there have been few attempts to develop in silico models to predict the activity of CAR modulated by chemical compounds. The number of in silico studies of CAR may be limited because of CAR's constitutive activity under normal conditions, which makes it difficult to elucidate the key structural features of the interaction between CAR and its ligands. In this study, to address these limitations, we introduced 3D pharmacophore-based descriptors with an integrated ligand and structure-based pharmacophore features, which represent the receptor-ligand interaction. Machine learning methods (support vector machine and artificial neural network) were applied to develop an in silico model with the descriptors containing significant information regarding the ligand binding positions. The best classification model built with a solvent accessibility volume-based filter and the support vector machine showed good predictabilities of 87%, and 85.4% for the training set and validation set, respectively. This demonstrates that our model can be used to accurately predict CAR activators and offers structural information regarding ligand/protein interactions.

2-(3-Methoxyphenyl)quinazoline Derivatives: A New Class of Direct Constitutive Androstane Receptor (CAR) Agonists

Constitutive androstane receptor (CAR) is a key regulator of xenobiotic and endobiotic metabolism. Together with pregnane X (PXR) and aryl hydrocarbon (AHR) receptors, it is referred to as "xenobiotic receptor". The unique properties of human CAR, such as its high constitutive activity, both direct (ligand-binding domain-dependent) and indirect activation have hindered the discovery of direct selective human CAR ligands. Herein, we report a novel class of direct human CAR agonists in a group of 2-(3-methoxyphenyl)quinazoline derivatives. The compounds are even more potent activators of human CAR than is prototype 6-(4-chlorophenyl)imidazo[2,1-b][1,3]thiazole-5-carbaldehyde O-(3,4-dichlorobenzyl)oxime (CITCO). The three most potent ligands are at the same time extremely potent activators of the other xenobiotic or hormonal receptors, namely PXR, AHR, and vitamin D receptor, which regulate major xenobiotic-metabolizing enzymes and efflux transporters. Thus, the novel CAR ligands can be also considered as constituting the first class of potent pan-xenobiotic receptor ligands that can serve as potential antidotes boosting overall metabolic elimination of xenobiotic or toxic compounds.

Small-molecule modulators of the constitutive androstane receptor

INTRODUCTION

The constitutive androstane receptor (CAR) induces drug-metabolizing enzymes for xenobiotic metabolism.

AREAS COVERED

This review covers recent advances in elucidating the biological functions of CAR and its modulation by a growing number of agonists and inhibitors.

EXPERT OPINION

Extrapolation of animal CAR function to that of humans should be carefully scrutinized, particularly when rodents are used in evaluating the metabolic profile and carcinogenic properties of clinical drugs and environmental chemicals. Continuous efforts are needed to discover novel CAR inhibitors, with extensive understanding of their inhibitory mechanism, species selectivity, and discriminating power against other xenobiotic sensors.

Inhibitory action of Epilobium hirsutum extract and its constituent ellagic acid on drug-metabolizing enzymes

Epilobium hirsutum (EH) is a medicinal plant for treating various diseases. Despite its wide usage, there is no available information about its potential influences on drug metabolism. The present study was undertaken to determine the in vivo effects of EH on hepatic CYP2B, CYP2C, CYP2D, and CYP3A enzymes that are primarily involved in drug metabolism. Male Wistar rats were injected intraperitoneally with EH water extract (EHWE) and ellagic acid (EA) at a daily dose of 37.5 and 20 mg/kg, respectively, for 9 days and hepatic drug-metabolizing enzymes were assessed at activity, protein and mRNA levels. Erythromycin N-demethylase activity was inhibited by 53 and 21 % in EHWE- and EA-treated rats, respectively. Benzphetamine N-demethylase and 7-benzyloxyresorufin-O-debenzylase activities were decreased by 53 and 43 %, and 57 and 57 % in EHWE-and EA-treated rats, respectively. Moreover, protein levels of CYP2B1, CYP2C6, CYP2D2, and CYP3A1 also decreased by 55, 15, 33, and 82 % as a result of EHWE treatment of rats, respectively. Similarly, CYP2B1, CYP2C6, CYP2D2, and CYP3A1 protein levels decreased by 62, 63, 49, and 37 % with EA treatment, respectively. qRT-PCR analyses also showed that mRNA levels of these enzymes were significantly inhibited with bothEHWE and EA treatments. In conclusion, inhibition of drug clearances leading to drug toxicity because of the lowered activity and expression of drug-metabolizing enzymes might be observed in the people who used EH as complementary herbal remedy that might be contributed by its EA content.

Nuclear receptor-mediated alleviation of alcoholic fatty liver by polyphenols contained in alcoholic beverages

To elucidate the effect of the polyphenols contained in alcoholic beverages on the metabolic stress induced by ethanol consumption, four groups of mice were fed for five weeks on Lieber's diet with or without ethanol, with ethanol plus ellagic acid, and with ethanol plus trans-resveratrol. Alcoholic fatty liver was observed in the group fed the ethanol diet but not in those fed the ethanol plus polyphenol diets. Liver transcriptome analysis revealed that the addition of the polyphenols suppressed the expression of the genes related to cell stress that were up-regulated by ethanol alone. Conversely, the polyphenols up-regulated the genes involved in bile acid synthesis, unsaturated fatty acid elongation, and tetrahydrofolate synthesis that were down-regulated by ethanol alone. Because parts of these genes were known to be regulated by the constitutive androstane receptor (CAR), we performed the same experiment in the CAR-deficient mice. As a result, fatty liver was observed not only in the ethanol group but also with the ethanol plus polyphenol groups. In addition, there was no segregation of the gene expression profiles among these groups. These results provide a molecular basis for the prevention of alcohol-induced stress by the polyphenols in alcoholic beverages.

Targeting xenobiotic receptors PXR and CAR for metabolic diseases

The pregnane X receptor (PXR) and the constitutive androstane receptor (CAR) are two closely related and liver-enriched nuclear hormone receptors originally defined as xenobiotic receptors. Recently, an increasing body of evidence suggests that PXR and CAR also have endobiotic functions that impact glucose and lipid metabolism, as well as the pathogenesis of metabolic diseases. These new findings suggest that PXR and CAR not only regulate the transcription of drug-metabolizing enzymes and transporters, but also orchestrate energy metabolism and immune responses to accommodate stresses caused by xenobiotic exposures. The effectiveness of targeting PXR and CAR in the treatment of metabolic disorders, such as obesity, type 2 diabetes (T2D), dyslipidemia, and atherosclerosis, have been suggested in animal models. However, translation of these basic research results into clinical applications may require further investigation to determine the human relevance, and to obtain better understanding of the mechanisms through which PXR and CAR affect energy metabolism. Given a wide variety of natural or synthetic compounds that are PXR and CAR modulators, it is hoped that these two 'xenobiotic receptors' can be harnessed for therapeutic potentials in managing metabolic diseases.