Identification of the Flavonoid Luteolin as a Repressor of the Transcription Factor Hepatocyte Nuclear Factor 4α

HNF4α is required for Tkfc promoter activation by ChREBP

Triokinase/FMN cyclase (Tkfc) is involved in fructose metabolism and is responsible for the phosphorylation of glyceraldehyde to glyceraldehyde-3-phosphate. In this study, we showed that refeeding induced hepatic expression of Tkfc in mice. Luciferase reporter gene assays using the Tkfc promoter revealed the existence of 2 hepatocyte nuclear factor 4α (HNF4α)-responsive elements (HNF4RE1 and HNF4RE2) and 1 carbohydrate-responsive element-binding protein (ChREBP)-responsive element (ChoRE1). Deletion and mutation of HNF4RE1 and HNF4RE2 or ChoRE1 abolished HNF4α and ChREBP responsiveness, respectively. HNF4α and ChREBP synergistically stimulated Tkfc promoter activity. ChoRE1 mutation attenuated but maintained HNF4α responsiveness, whereas HNF4RE1 and HNF4RE2 mutations abolished ChREBP responsiveness. Moreover, Tkfc promoter activity stimulation by ChREBP was attenuated upon HNF4α knockdown. Furthermore, Tkfc expression was decreased in the livers of ChREBP-/- and liver-specific HNF4-/- (Hnf4αΔHep) mice. Altogether, our data indicate that Tkfc is a target gene of ChREBP and HNF4α, and Tkfc promoter activity stimulation by ChREBP requires HNF4α.

Luteolin Mitigates Diabetic Dyslipidemia in Rats by Modulating ACAT-2, PPARα, SREBP-2 Proteins, and Oxidative Stress

Diabetic dyslipidemia is a crucial link between type-2 diabetes mellitus (T2DM) and atherosclerotic cardiovascular diseases (ASCVD). Natural biologically active substances have been advocated as complementary remedies for ASCVD and T2DM. Luteolin, a flavonoid, exhibits antioxidant, hypolipidemic, and antiatherogenic effects. Hence, we aimed to determine influence of luteolin on lipid homeostasis and hepatic damage in rats with T2DM induced by high-fat-diet (HFD) and streptozotocin (STZ). After being fed HFD for 10 days, male Wistar rats received 40 mg/kg STZ intraperitoneal injection on 11th day. Seventy-two hours later, hyperglycemic rats (fasting glucose > 200 mg/dL) were randomized into groups, and oral hydroxy-propyl-cellulose, atorvastatin (5 mg/kg), or luteolin (50 mg/kg or 100 mg/kg) administered daily, while continuing HFD for 28 days. Luteolin significantly ameliorated dyslipidemia levels and concomitantly improved atherogenic index of plasma in a dose-dependent manner. Increased levels of malondialdehyde and diminished levels of superoxide dismutase, catalase, and glutathione in HFD-STZ-diabetic rats were significantly regulated by luteolin. Luteolin significantly intensified PPARα expression while decreasing expression of acyl-coenzyme A:cholesterol acyltransferase-2 (ACAT-2) and sterol regulatory element binding protein-2 (SREBP-2) proteins. Moreover, luteolin effectively alleviated hepatic impairment in HFD-STZ-diabetic rats to near-normal control levels. The findings of the present study expound mechanisms by which luteolin mitigated diabetic dyslipidemia and alleviated hepatic impairment in HFD-STZ-diabetic rats by amelioration of oxidative stress, modulation of PPARα expression, and downregulation of ACAT-2 and SREBP-2. In conclusion, our results imply that luteolin may be efficacious in management of dyslipidemia in T2DM, and future research may be essential to substantiate our findings.

Luteolin directly binds to KDM4C and attenuates ovarian cancer stemness via epigenetic suppression of PPP2CA/YAP axis

Long-term use of low-toxic natural products holds the promise for eradicating cancer stem cells. In this study, we report that luteolin, a natural flavonoid, attenuates the stemness of ovarian cancer stem cells (OCSCs) by directly binding to KDM4C and epigenetic suppression of PPP2CA/YAP axis. Ovarian cancer stem like cells (OCSLCs) isolated by suspension culture and CD133 + ALDH+ cell sorting was employed as OCSCs model. The maximal non-toxic dose of luteolin suppressed stemness properties, including sphere-forming capacity, the expression of OCSCs markers, sphere-initiating and tumor-initiating capacities, as well as the percentage of CD133 + ALDH+ cells of OCSLCs. Mechanistic study showed that luteolin directly binds to KDM4C, blocks KDM4C-induced histone demethylation of PPP2CA promoter, inhibits PPP2CA transcription and PPP2CA-mediated YAP dephosphorylation, thereby attenuating YAP activity and the stemness of OCSLCs. Furthermore, luteolin sensitized OCSLCs to traditional chemotherapeutic drugs in vitro and in vivo. In summary, our work revealed the direct target of luteolin and the underlying mechanism of the inhibitory effect of luteolin on the stemness of OCSCs. This finding thus suggests a novel therapeutic strategy for eradicating human OCSCs driven by KDM4C.

Nutritional activities of luteolin in obesity and associated metabolic diseases: an eye on adipose tissues

Obesity is characterized by excessive body fat accumulation and is a high-risk factor for metabolic comorbidities, including type 2 diabetes, nonalcoholic fatty liver disease, and cardiovascular disease. In lean individuals, adipose tissue (AT) is not only an important regulatory organ for energy storage and metabolism, but also an indispensable immune and endocrine organ. The sustained energy imbalance induces adipocyte hypotrophy and hyperplasia as well as AT remodeling, accompanied by chronic low-grade inflammation and adipocytes dysfunction in AT, ultimately leading to systemic insulin resistance and ectopic lipid deposition. Luteolin is a natural flavonoid widely distributed in fruits and vegetables and possesses multifold biological activities, such as antioxidant, anticancer, and anti-inflammatory activities. Diet supplementation of this flavonoid has been reported to inhibit AT lipogenesis and inflammation as well as the ectopic lipid deposition, increase AT thermogenesis and systemic energy expenditure, and finally improve obesity and associated metabolic diseases. The purpose of this review is to reveal the nutritional activities of luteolin in obesity and its complications with emphasis on its action on AT energy metabolism, immunoregulation, and endocrine intervention.

Laurel Attenuates Dexamethasone-Induced Skeletal Muscle Atrophy In Vitro and in a Rat Model

Prevention of muscle atrophy contributes to improved quality of life and life expectancy. In this study, we investigated the effects of laurel, selected from 34 spices and herbs, on dexamethasone (DEX)-induced skeletal muscle atrophy and deciphered the underlying mechanisms. Co-treatment of C2C12 myotubes with laurel for 12 h inhibited the DEX-induced expression of intracellular ubiquitin ligases—muscle atrophy F-box (atrogin-1/MAFbx) and muscle RING finger 1 (MuRF1)—and reduction in myotube diameter. Male Wistar rats were supplemented with 2% laurel for 17 days, with DEX-induced skeletal muscle atrophy occurring in the last 3 days. Laurel supplementation inhibited the mRNA expression of MuRF1, regulated DNA damage and development 1 (Redd1), and forkhead box class O 1 (Foxo1) in the muscles of rats. Mechanistically, we evaluated the effects of laurel on the cellular proteolysis machinery—namely, the ubiquitin/proteasome system and autophagy—and the mTOR signaling pathway, which regulates protein synthesis. These data indicated that the amelioration of DEX-induced skeletal muscle atrophy induced by laurel, is mainly mediated by the transcriptional inhibition of downstream factors of the ubiquitin-proteasome system. Thus, laurel may be a potential food ingredient that prevents muscle atrophy.

Bioactivity of Dietary Polyphenols: The Role in LDL-C Lowering

Cardiovascular diseases are the leading causes of the death around the world. An elevation of the low-density lipoprotein cholesterol (LDL-C) level is one of the most important risk factors for cardiovascular diseases. To achieve optimal plasma LDL-C levels, clinal therapies were investigated which targeted different metabolism pathways. However, some therapies also caused various adverse effects. Thus, there is a need for new treatment options and/or combination therapies to inhibit the LDL-C level. Dietary polyphenols have received much attention in the prevention of cardiovascular diseases due to their potential LDL-C lowering effects. However, the effectiveness and potential mechanisms of polyphenols in lowering LDL-C is not comprehensively summarized. This review focused on dietary polyphenols that could reduce LDL-C and their mechanisms of action. This review also discussed the limitations and suggestions regarding previous studies.

Nutraceutical Combinations in Hypercholesterolemia: Evidence from Randomized, Placebo-Controlled Clinical Trials

There is an increasing number of nutraceutical combinations (NCs) on the market for hypercholesterolemia, although clinical trials to verify their safety and efficacy are scarce. We selected fourteen randomized, placebo-controlled clinical trials (RCTs) on different lipid-lowering NCs in hypercholesterolemic subjects. We described each compound's mechanism of action and efficacy in the mixtures and summarized the clinical trials settings and NCs safety and efficacy results. Almost all NCs resulted efficient against hypercholesterolemia; only one reported no changes. Interestingly, red yeast rice (RYR) was present in eleven mixtures. It is not clear whether the lipid-lowering efficacy of these combinations derives mainly from the RYR component monacolin K "natural statin" single effect. Up to now, few RCTs have verified the efficacy of every single compound vs. NCs to evaluate possible additive or synergistic effects, probably due to the complexity and the high resources request. In conclusion, to manage the arising nutraceutical tide against hypercholesterolemia, it could be helpful to increase the number and robustness of clinical studies to verify the efficacy and safety of the new NCs.

HNF4α Is a Covalent Bond-Forming Receptor

HNF4α is a nuclear receptor whose ligands are fatty acids. HNF4α is a target molecule for drug discovery research and thus we tested its covalent binding ability to investigate the possible development of covalent modifiers of HNF4α. Oxidized polyunsaturated fatty acids (oxo-PUFAs) have moderate flexibility and possess a Michael acceptor that participates in conjugate addition reactions with nucleophilic amino acid residues. Thus, oxo-PUFAs were used as probes and their covalent binding abilities to HNF4α were verified. Several oxo-PUFAs, such as 4-oxoDHA, were shown to be covalent modifiers of HNF4α and therefore we concluded that HNF4α can form covalent bonds to ligands.

Nutrigenomics in Regulating the Expression of Genes Related to Type 2 Diabetes Mellitus

Nutrigenomics is the study of the gene-nutrient interaction and it indicates that some nutrients, called bioactive compounds, can mold the genetic expression or change the nucleotide chain. Polyphenols are secondary metabolites found in plants that are regularly consumed in functional foods and help prevent or delay the onset of type 2 diabetes mellitus (T2DM) and its complications. This article objected to review studies about the interaction of diet with polyphenols and Mediterranean diet in the expression of human genes related to T2DM. Resveratrol acts as an antioxidant, anti-inflammatory, and increases mitochondrial function. Regular consumption of quercetin resulted in improvement of hypertension and suppression of diabetes-induced vasoconstriction. Genistein also showed positive results in T2DM, such as increased cell mass and improved glucose tolerance and insulin levels. Catechins showed efficiency in inducing genes in triacylglycerol biosynthesis, inhibition of fatty acids and cholesterol, and resulting in their participation in mitigating complications of diabetes. Lastly, curcumin was demonstrated to be a protector of the pancreatic islets against streptozotocin-induced oxidative stress. Growing evidence suggest that bioactive compounds such as polyphenols have an important role in T2DM and the prevention and treatment of its complication, as they cause activation or inhibition of related genes.

Identification of herbal components as TRPA1 agonists and TRPM8 antagonists

Transient receptor potential (TRP) channels are non-selective cation channels that are implicated in analgesia, bowel motility, wound healing, thermoregulation, vasodilation and voiding dysfunction. Many natural products have been reported to affect the activity of TRP channels. We hypothesize that numerous traditional herbal medicines (THMs) might exert their pharmacological activity through modulating the activity of TRP channels. The present study aimed to evaluate the effects of flavonoid aglycones and their glycosides, which are the main components of many THMs, on the TRP channel subtypes. A Ca²⁺ influx assay was performed using recombinant human TRPA1, TRPV1, TRPV4 and TRPM8 cell lines. Our findings showed that flavonoid aglycones and glycycoumarin activated TRPA1. In particular, isoflavone and chalcone compounds displayed potent TRPA1 agonistic activity. Furthermore, flavone aglycones showed concomitant potent TRPM8 inhibiting activity. Indeed, flavone, isoflavone aglycones, non-prenylated chalcones and glycycoumarin were found to be TRPM8 inhibitors. Hence, flavonoid aglycones metabolized by lactase-phlorizin hydrolase and β-glucosidase in the small intestine or gut microbiota of the large intestine could generate TRPA1 agonists and TRPM8 antagonists.

Short term transcriptional responses of P450s to phytochemicals in insects and mites

Cytochrome P450 monooxygenases (P450s) play a key role in the detoxification of phytochemicals in arthropod herbivores. We present here an overview of recent progress in understanding the breadth and specificity of gene expression plasticity of P450s in response to phytochemicals. We discuss experimental setups and new findings in mechanisms of P450 regulation. Whole genome transcriptomic analysis of arthropod herbivores, either after direct administration of phytochemicals or after host plant shifts, allowed to integrate various levels of chemical complexity and lead to the unbiased identification of responsive P450 genes. However, despite progress in identification of inducible P450s, the link between induction and metabolism is still largely unexplored, and to what extent the overall response is biologically functional should be further investigated. In the near future, such studies will be more straightforward as forward and reverse genetic tools become more readily available.

Recent Research on Flavonoids and their Biomedical Applications

Flavonoids, commonly found in various plants, are a class of polyphenolic compounds having a basic structural unit of 2-phenylchromone. Flavonoid compounds have attracted much attention due to their wide biological applications. In order to facilitate further research on the biomedical application of flavonoids, we surveyed the literature published on the use of flavonoids in medicine during the past decade, documented the commonly found structures in natural flavonoids, and summarized their pharmacological activities as well as associated mechanisms of action against a variety of health disorders including chronic inflammation, cancer, cardiovascular complications and hypoglycemia. In this mini-review, we provide suggestions for further research on the biomedical applications of flavonoids.

FX5 as a non-steroidal GR antagonist improved glucose homeostasis in type 2 diabetic mice via GR/HNF4α/miR-122-5p pathway

Type 2 diabetes mellitus (T2DM) is a chronic metabolic disease characterized by glucose metabolic disorders, and gluconeogenesis inhibiting is a promisingly therapeutic strategy for T2DM. Glucocorticoid receptor (GR) is tightly implicated in the regulation of gluconeogenesis, although the underlying mechanism remains obscure. Here, we discovered that small molecule, 5-chloro-N-[4-chloro-3-(trifluoromethyl)phenyl]thiophene-2-sulfonamide (FX5) as a new non-steroidal GR antagonist efficiently ameliorated glucose homeostasis in db/db and HFD/STZ-induced T2DM mice. The mechanism underlying the suppression of FX5 against gluconeogenesis was highly investigated. FX5 suppressed gluconeogenetic genes G6Pase and PEPCK in mouse primary hepatocytes and liver tissues of T2DM mice. Results of mammalian one-hybrid and transactivation as well as nuclear translocation assays totally evaluated the antagonistic features of FX5 against GR. Moreover, siRNA and overexpression related assays verified that FX5 alleviated gluconeogenesis either directly by antagonizing GR or indirectly through GR/HNF4α/miR122-5p signaling pathway. Our work has presented a new mode for GR antagonist in the regulation of gluconeogenesis, which is expected to highlight the potential of FX5 in the treatment of T2DM.

Natural Product Luteolin Rescues THAP-Induced Pancreatic β-Cell Dysfunction through HNF4α Pathway

Endoplasmic reticulum stress (ER stress) plays a main role in pancreatic [Formula: see text]-cell dysfunction and death because of intracellular Ca[Formula: see text] turbulence and inflammation activation. Although several drugs are targeting pancreatic [Formula: see text]-cell to improve [Formula: see text]-cell function, there still lacks agents to alleviate [Formula: see text]-cell ER stress conditions. Therefore we used thapsigargin (THAP) or high glucose (HG) to induce ER stress in [Formula: see text]-cell and aimed to screen natural molecules against ER stress-induced [Formula: see text]-cell dysfunction. Through screening the Traditional Chinese drug library ([Formula: see text] molecules), luteolin was finally discovered to improve [Formula: see text]-cell function. Cellular viability results indicated luteolin reduced the THAP or HG-induced [Formula: see text]-cell death and apoptosis through MTT and flow cytometry assay. Moreover, luteolin improved [Formula: see text]-cell insulin secretion ability under ER stress conditions. Also ER stress-induced intracellular Ca[Formula: see text] turbulence and inflammation activation were inhibited by luteolin treatment. Mechanically, luteolin inhibited HNF4[Formula: see text] signaling, which was induced by ER stress. Moreover, luteolin reduced the transcriptional level of HNF4[Formula: see text] downstream gene, such as Asnk4b and HNF1[Formula: see text]. Conversely HNF4[Formula: see text] knockdown abolished the effect of luteolin on [Formula: see text]-cell using siRNA. These results suggested the protective effect of luteolin on [Formula: see text]-cell was through HNF4[Formula: see text]/Asnk4b pathway. In conclusion, our study discovered that luteolin improved [Formula: see text]-cell function and disclosed the underlying mechanism of luteolin on [Formula: see text]-cell, suggesting luteolin is a promising agent against pancreatic dysfunction.

Metabolic Impact of Flavonoids Consumption in Obesity: From Central to Peripheral

The prevention and treatment of obesity is primary based on the follow-up of a healthy lifestyle, which includes a healthy diet with an important presence of bioactive compounds such as polyphenols. For many years, the health benefits of polyphenols have been attributed to their anti-oxidant capacity as free radical scavengers. More recently it has been described that polyphenols activate other cell-signaling pathways that are not related to ROS production but rather involved in metabolic regulation. In this review, we have summarized the current knowledge in this field by focusing on the metabolic effects of flavonoids. Flavonoids are widely distributed in the plant kingdom where they are used for growing and defensing. They are structurally characterized by two benzene rings and a heterocyclic pyrone ring and based on the oxidation and saturation status of the heterocyclic ring flavonoids are grouped in seven different subclasses. The present work is focused on describing the molecular mechanisms underlying the metabolic impact of flavonoids in obesity and obesity-related diseases. We described the effects of each group of flavonoids in liver, white and brown adipose tissue and central nervous system and the metabolic and signaling pathways involved on them.

Andrographolide modulates HNF4α activity imparting on hepatic metabolism

Hepatic nuclear factor 4 alpha (HNF4α) drives the expression of apolipoprotein B (ApoB), microsomal triglyceride transfer protein (MTP) and phospholipase A2 G12B (PLA2G12B), governing hepatic very-low-density lipoprotein (VLDL) production and secretion. Andrographolide (AP) is a major constituent isolated from Andrographis paniculata. We found that AP can disrupt the interaction between HNF4α and its coactivator peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α). Virtual docking and mutational analysis indicated that arginine 235 of HNF4α is essential for binding to AP. As a consequence of antagonizing the activity of HNF4α, AP suppresses the expression of ApoB, MTP and PLA2G12B and reduces the rate of hepatic VLDL secretion in vivo. AP additionally reduced gluconeogenesis via down-regulating the expression of HNF4α target genes phosphoenolpyruvate carboxykinase (Pepck) and glucose-6-phosphatase (G6pc). Collectively, our results suggest that AP affects liver function via modulating the transcriptional activity of HNF4α.

18β-Glycyrrhetinic acid acts through hepatocyte nuclear factor 4 alpha to modulate lipid and carbohydrate metabolism

Hepatocyte nuclear factor 4 alpha (HNF4α) regulates the expression of essential genes involved in very-low-density lipoprotein (VLDL) homeostasis and gluconeogenesis.　18β-glycyrrhetinic acid (GA) is an active ingredient of Glycyrrhiza uralensis an herbal medicine used for treating liver aliments. In this study, we established that GA functions as a partial antagonist of HNF4α through HNF4α-driven reporter luciferase assay and co-immunoprecipitation experiments with co-activator PGC1α. By virtual docking and site-directed mutagenesis analysis, we confirmed that serine 190 and arginine 235 of HNF4α are both essential for GA to exert its antagonistic action on HNF4α. Importantly, GA suppressed the expression of HNF4α target genes such as apolipoprotein B (ApoB), microsomal triglyceride transfer protein (MTP) and phospholipase A₂ G12B (PLA2G12B) modulating hepatic VLDL secretion in mice fed on a high fat diet. In addition, GA also suppressed gluconeogenesis and ameliorated glucose intolerance via down-regulating the expression of HNF4α target genes glucose-6-phosphatase (G6pc) and phosphoenolpyruvate carboxykinase (Pepck). Furthermore, GA significantly lowered blood glucose and improved insulin resistance in db/db mice. In all, we established that GA acts as a partial HNF4α antagonist modulating lipid and carbohydrate metabolism.

Vitamin D receptor targets hepatocyte nuclear factor 4α and mediates protective effects of vitamin D in nonalcoholic fatty liver disease

Epidemiological studies have suggested a link between vitamin D deficiency and increased risk for nonalcoholic fatty liver disease (NAFLD); however, the underlying mechanisms have remained unclear. Here, using both clinical samples and experimental rodent models along with several biochemical approaches, we explored the specific effects and mechanisms of vitamin D deficiency in NAFLD pathology. Serum vitamin D levels were significantly lower in individuals with NAFLD and in high-fat diet (HFD)-fed mice than in healthy controls and chow-fed mice, respectively. Vitamin D supplementation ameliorated HFD-induced hepatic steatosis and insulin resistance in mice. Hepatic expression of vitamin D receptor (VDR) was up-regulated in three models of NAFLD, including HFD-fed mice, methionine/choline-deficient diet (MCD)-fed mice, and genetically obese (ob/ob) mice. Liver-specific VDR deletion significantly exacerbated HFD- or MCD-induced hepatic steatosis and insulin resistance and also diminished the protective effect of vitamin D supplementation on NAFLD. Mechanistic experiments revealed that VDR interacted with hepatocyte nuclear factor 4 α (HNF4α) and that overexpression of HNF4α improved HFD-induced NAFLD and metabolic abnormalities in liver-specific VDR-knockout mice. These results suggest that vitamin D ameliorates NAFLD and metabolic abnormalities by activating hepatic VDR, leading to its interaction with HNF4α. Our findings highlight a potential value of using vitamin D for preventing and managing NAFLD by targeting VDR.

Xanthohumol Suppresses NPC1L1 Gene Expression through Downregulation of HNF-4α and Inhibits Cholesterol Uptake in Caco-2 Cells

Xanthohumol (Xan) is a prenylated chalcone mainly found in hops; it has been demonstrated to function against hypercholesterolemia, hyperlipidemia, and atherosclerosis. In this study, we focused on the hypocholesterolemic effect of Xan on cholesterol uptake and the underlying molecular mechanisms of Xan in human intestinal Caco-2 cells. The microarray data showed that Niemann-Pick C1-like 1 (NPC1L1), an essential transporter for dietary cholesterol absorption, was significantly downregulated in Xan-treated Caco-2 cells. We demonstrated that Xan (10 and 20 μM) suppressed the mRNA and protein expression of NPC1L1 by 0.65 ± 0.12-fold and 0.54 ± 0.15-fold and 0.72 ± 0.04-fold and 0.44 ± 0.12-fold, respectively, compared to that of the vehicle-treated Caco-2 cells. Moreover, Xan (10 and 20 μM) significantly inhibited cholesterol uptake by approximately 12 and 32% in Caco-2 cells. NPC1L1 promoter activity was significantly suppressed by Xan, and a DNA element within the NPC1L1 promoter involved in Xan-mediated NPC1L1 reduction located between the -120 and -20 positions was identified. Moreover, Xan markedly decreased the mRNA and protein levels of hepatocyte nuclear factor 4α (HNF-4α), a critical activator of NPC1L1 transcription, and subsequently attenuated HNF-4α/NPC1L1 promoter complex formation, resulting in the suppression of NPC1L1 gene expression. Finally, we demonstrated that Xan markedly abolished lovastatin-induced NPC1L1 overexpression in Caco-2 cells. These findings reveal that Xan suppresses NPC1L1 expression via downregulation of HNF-4α and exerts inhibitory effects on cholesterol uptake in the intestinal Caco-2 cells. Our findings suggest Xan could serve as a potential cholesterol-lowering agent and supplement for statin therapy.

The Effect of Polyphenols on Hypercholesterolemia through Inhibiting the Transport and Expression of Niemann-Pick C1-Like 1

The Niemann-Pick C1-like 1 (NPC1L1) protein is a cholesterol transporter that is expressed in the small intestine. This report describes the discovery of NPC1L1, its transport properties, and the inhibitory effects of polyphenols on NPC1L1. NPC1L1 was identified in 2004 while searching for ezetimibe molecular targets. Excessive synthesis of cholesterol results in hyperlipidemia, which increases the amount of bile cholesterol excreted into the duodenum. The inhibition of NPC1L1 decreases blood cholesterol because food and bile cholesterol are also absorbed from NPC1L1 in the intestine. Some polyphenols, particularly luteolin, have been reported as NPC1L1-mediated anti-dyslipidemia constituents. Luteolin affects NPC1L1 through two mechanisms. Luteolin directly inhibits NPC1L1 by binding to it, which occurs in a short timeframe similar to that for ezetimibe. The other mechanism is the inhibition of NPC1L1 expression. Luteolin reduced the binding of Sterol-regulatory element-binding protein 2 (SREBP2) in the promoter region of the NPC1L1 gene and decreased mRNA levels of SREBP2 and hepatocyte nuclear factor 4α. These data suggest that luteolin decreases the expression of NPC1L1 through regulation of transcription factors. This review also explores the effect of other polyphenols on NPC1L1 and hypercholesterolemia.

Adipose tissue as a possible therapeutic target for polyphenols: A case for Cyclopia extracts as anti-obesity nutraceuticals

Obesity is a significant contributor to increased morbidity and premature mortality due to increasing the risk of many chronic metabolic diseases such as type 2 diabetes, cardiovascular disease and certain types of cancer. Lifestyle modifications such as energy restriction and increased physical activity are highly effective first-line treatment strategies used in the management of obesity. However, adherence to these behavioral changes is poor, with an increased reliance on synthetic drugs, which unfortunately are plagued by adverse effects. The identification of new and safer anti-obesity agents is thus of significant interest. In recent years, plants and their phenolic constituents have attracted increased attention due to their health-promoting properties. Amongst these, Cyclopia, an endemic South African plant commonly consumed as a herbal tea (honeybush), has been shown to possess modulating properties against oxidative stress, hyperglycemia, and obesity. Likewise, several studies have reported that some of the major phenolic compounds present in Cyclopia spp. exhibit anti-obesity effects, particularly by targeting adipose tissue. These phenolic compounds belong to the xanthone, flavonoid and benzophenone classes. The aim of this review is to assess the potential of Cyclopia extracts as an anti-obesity nutraceutical as underpinned by in vitro and in vivo studies and the underlying cellular mechanisms and biological pathways regulated by their phenolic compounds.

Reviewing the mechanisms of natural product-drug interactions involving efflux transporters and metabolic enzymes

The World Health Organization (WHO) and other worldwide health agencies have recently taken initiatives to encourage the use of traditional medicine and/or complementary/alternative medicine in order to promote well-being and public health. In this way, one of the WHO's concerns is the safe use of these therapies. Phytotherapy is a strategy consisting of the use of medicinal plants (MP) and/or herbal medicinal products (HMP) for medicinal purposes. The use of phytotherapy concomitantly with drugs may cause interactions compromising the expected pharmacological action or generating toxic effects. These interactions are complex processes that may occur with multiple medications targeting different metabolic pathways, and involving different compounds present in MP and HMP. Thus, the aim of this review was to summarize the main MP- and HMP-drug interactions that involve specific transporters (P-glycoprotein and BCRP) and CYP450 enzymes (CYP3A4 and CYP2D6), which play relevant roles in the mechanisms of interactions. Firstly, multiple databases were used to search studies describing in vitro or in vivo MP and HMP-drug interactions and, after that, a systematic note-taking and appraisal of the literature was conducted. It was observed that several MP and HMP, metabolic pathways and transcription factors are involved in the transporters and enzymes expression or in the modulation of their activity having the potential to provide such interactions. Thus, the knowledge of MP- and HMP-drug interaction mechanisms could contribute to prevent harmful interactions and can ensure the safe use of these products to help the establishment of the therapeutic planning in order to certify the best treatment strategy to be used.

Chrysin reduces the activity and protein level of mature forms of sterol regulatory element-binding proteins

Sterol regulatory element-binding proteins (SREBPs) are transcription factors that regulate the expression of genes involved in fatty acid and cholesterol biosynthetic pathways. The present study showed that the flavonoid chrysin impairs the fatty acid synthase promoter. Chrysin reduces the expression of SREBP target genes, such as fatty acid synthase, in human hepatoma Huh-7 cells and impairs de novo synthesis of fatty acids and cholesterol. Moreover, it reduces the endogenous mature, transcriptionally active forms of SREBPs, which are generated by the proteolytic processing of precursor forms. In addition, chrysin reduces the enforced expressing mature forms of SREBPs and their transcriptional activity. The ubiquitin-proteasome system is not involved in the chrysin-mediated reduction of SREBPs mature forms. These results suggest that chrysin suppresses SREBP activity, at least partially, via the degradation of SREBPs mature forms. Abbreviations: ACC1: acetyl-CoA carboxylase 1; DMEM: Dulbecco's modified Eagle's medium; FAS: fatty acid synthase; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; 25-HC: 25-hydroxycholesterol; HMGCS: HMG-CoA synthase; LDH: lactate dehydrogenase; LPDS: lipoprotein-deficient serum; PI3K: phosphatidylinositol 3-kinase; SCD1: stearoyl-CoA desaturase; SREBPs: sterol regulatory element-binding proteins.

Flavonoids: New Frontier for Immuno-Regulation and Breast Cancer Control

Breast cancer (BC) remains the second most common cause of cancer-related deaths in women in the US, despite advances in detection and treatment. In addition, breast cancer survivors often struggle with long-term treatment related comorbidities. Identifying novel therapies that are effective while minimizing toxicity is critical in curtailing this disease. Flavonoids, a subclass of plant polyphenols, are emerging as promising treatment options for the prevention and treatment of breast cancer. Recent evidence suggests that in addition to anti-oxidant properties, flavonoids can directly interact with proteins, making them ideal small molecules for the modulation of enzymes, transcription factors and cell surface receptors. Of particular interest is the ability of flavonoids to modulate the tumor associated macrophage function. However, clinical applications of flavonoids in cancer trials are limited. Epidemiological and smaller clinical studies have been largely hypothesis generating. Future research should aim at addressing known challenges with a broader use of preclinical models and investigating enhanced dose-delivery systems that can overcome limited bioavailability of dietary flavonoids. In this review, we discuss the structure-functional impact of flavonoids and their action on breast tumor cells and the tumor microenvironment, with an emphasis on their clinical role in the prevention and treatment of breast cancer.

Dimerization defective MODY mutations of hepatocyte nuclear factor 4α

HNF4α is a culprit gene product for a monogenic and dominantly-inherited form of diabetes, referred to as MODY1 (Maturity Onset Diabetes of the Young type 1). Reduced HNF4α activities have been linked to impaired insulin secretion and β-cell function. Numerous mutations have been identified from the patients and they have been instructive as to the individual residue's role in protein structure-function and dysfunction. As a member of the nuclear receptor (NR) superfamily, HNF4α is made of characteristic modular domains and it functions exclusively as a homodimer despite its sequence homology to RXR, a common heterodimer partner of non-steroidal NRs. Transcription factors commonly dimerize to enhance their molecular functions mainly by facilitating the recognition of double helix target DNAs that display an intrinsic pseudo-2-fold symmetry and the recruitment of the remainder of the main transcriptional machinery. HNF4α is no exception and its dimerization is maintained by the ligand binding domain (LBD) mainly through the leucine-zipper-like interactions at the stalk of two interacting helices. Although many MODY1 mutations have been previously characterized, including DNA binding disruptors, ligand binding disruptors, coactivator binding disruptors, and protein stability disruptors, protein dimerization disruptors have not been formally reported. In this report, we present a set of data for the two MODY1 mutations found right at the dimerization interface (L332 P and L328del mutations) which clearly exhibit the disruptive effects of directly affecting dimerization, protein stability, and transcriptional activities. These data reinforced the fact that MODY mutations are loss-of-function mutations and HNF4α dimerization is essential for its optimal function and normal physiology.

Protective Effect of Polyphenol-Rich Extract from Bee Pollen in a High-Fat Diet

We have studied a preventive effect of polyphenol-rich bee pollen ethanol extract (EEP) against histological changes in the liver and cardiac blood vessels, abnormalities of lipid profile, and the levels of oxidized low density lipoproteins (ox-LDL), asymmetric dimethylarginine (ADMA), angiotensin-converting enzyme (ACE), and angiotensin II (ANG II) caused by a high-fat diet in C₅₇BL₆ mice. Supplementing the diet with EEP in the doses of 0.1 g/kg body mass (BM) and 1 g/kg BM resulted in a decrease of total cholesterol by 31% and 35%, respectively. It also decreased the level of low density lipoproteins by 67% and 90%, respectively. No differences in the levels of high density lipoprotein and triacylglycerols were observed. EEP reduced the level of ox-LDL by 33% and 47%, ADMA by 13% and 51%, ACE by 17% and 30%, as well as ANG II by 11% and 15% in a dose-dependent manner, which proves a protective effect of EEP in a high-fat diet. EEP reduces and/or prevents hepatic steatosis and degenerative changes caused by a high-fat diet in C₅₇BL₆ mice, which indicates its hepatoprotective effect. EEP used with standard feed does not disturb a normal concentration of the assayed parameters.

Effect of Grifola frondosa 95% ethanol extract on lipid metabolism and gut microbiota composition in high-fat diet-fed rats

This study aimed to investigate the effects of 95% ethanol extract of G. frondosa (GF95) on lipid metabolism and gut microbiota composition in high-fat diet (HFD) fed rats.

The flavonoid derivative 4′-nitro-6-hydroxyflavone suppresses the activity of HNF4α and stimulates the degradation of HNF4α protein through the activation of AMPK

Hepatocyte nuclear factor 4α (HNF4α) is a nuclear receptor that regulates the expression of genes involved in a number of critical metabolic pathways. The modulation of HNF4α activity is thought to be a promising drug target pathway for hyperlipidemia. To identify compounds that reduce the activity of HNF4α, we conducted luciferase reporter assays using the promoter region of microsomal triglyceride transfer protein (MTP) gene, which contains an HNF4α-responsive element. Using this system, we show here that the flavonoid derivative 4′-nitro-6-hydroxyflavone (NOHF) suppresses MTP promoter activity. Treatment with NOHF caused a decrease in the expression of the HNF4α target gene. We also identified that NOHF triggers the AMP-activated protein kinase (AMPK) and accelerates the degradation of HNF4α protein. Knock-down of AMPK diminishes the effect of NOHF. These results indicate that NOHF is an AMPK activator and attenuates the transcriptional activity of HNF4α, at least in part, by accelerating HNF4α protein degradation.

BCL11B gene heterozygosity causes weight loss accompanied by increased energy consumption, but not defective adipogenesis, in mice

BCL11B is a zinc finger-type transcription factor that regulates the development of the white adipose tissue (WAT), skin, central nervous system, and immune system. BCL11B is required for proper adipocyte differentiation, and BCL11B−/− embryos at E19.5 have very low amounts of the subcutaneous WAT. Here, we demonstrated that BCL11B+/− mice have lower body weight than BCL11B+/+ mice, whereas the expression of adipogenic marker genes in the WAT was comparable between BCL11B+/+ and BCL11B+/− mice. Histological analysis indicated that BCL11B+/− mice fed a high-fat diet have much smaller white adipocytes and lipid droplets in the WAT and liver, respectively. In addition, BCL11B+/− mice had increased energy consumption under both standard and high-fat diets. Thus, this study identifies BCL11B as a regulator of energy metabolism, and it is unlikely that BCL11B functions in the WAT contribute to energy metabolism in BCL11B+/− mice.

Differentially expressed genes and gene networks involved in pig ovarian follicular atresia

Ovarian folliculogenesis corresponds to the development of follicles leading to either ovulation or degeneration, this latter process being called atresia. Even if atresia involves apoptosis, its mechanism is not well understood. The objective of this study was to analyze global gene expression in pig granulosa cells of ovarian follicles during atresia. The transcriptome analysis was performed on a 9,216 cDNA microarray to identify gene networks and candidate genes involved in pig ovarian follicular atresia. We found 1,684 significantly regulated genes to be differentially regulated between small healthy follicles and small atretic follicles. Among them, 287 genes had a fold-change higher than two between the two follicle groups. Eleven genes ( DKK3, GADD45A, CAMTA2, CCDC80, DAPK2, ECSIT, MSMB, NUPR1, RUNX2, SAMD4A, and ZNF628) having a fold-change higher than five between groups could likely serve as markers of follicular atresia. Moreover, automatic confrontation of deregulated genes with literature data highlighted 93 genes as regulatory candidates of pig granulosa cell atresia. Among these genes known to be inhibitors of apoptosis, stimulators of apoptosis, or tumor suppressors INHBB, HNF4, CLU, different interleukins ( IL5, IL24), TNF-associated receptor ( TNFR1), and cytochrome-c oxidase ( COX) were suggested as playing an important role in porcine atresia. The present study also enlists key upstream regulators in follicle atresia based on our results and on a literature review. The novel gene candidates and gene networks identified in the current study lead to a better understanding of the molecular regulation of ovarian follicular atresia.