Potentiation of beta-adrenoceptor agonist-mediated lipolysis by quercetin and fisetin in isolated rat adipocytes

Hibiscus sabdariffa Linn. Extract Increases the mRNA Expression of the Arcuate Nucleus Leptin Receptor and is Predicted in silico as an Anti-obesity Agent

BACKGROUND

Leptin is predominant in regulating body weight by stimulating energy expenditure through its neuronal action in the brain. Moreover, it is projected to adipose tissue and induces adipocyte browning by activating the β3-adrenergic receptor (β3AR). However, the expression of leptin receptor (Lep-R) and β3AR in people with obesity is downregulated.

AIM

We hypothesized that Hibiscus sabdariffa Linn. extract (HSE) would increase hypothalamus arcuate nucleus (ARC) Lep-R and white adipose tissue (WAT) β3AR mRNA expression in DIO rats. This study also analyzed the potency of H. sabdariffa bioactive compounds as activators of Lep-R and β3AR by an in-silico experiment.

METHODS

Twenty-four male Sprague-Dawley rats were divided into four groups: Control (standard food), DIO (high-fat diet), DIO-Hib200 (HFD+HSE 200 mg/kg BW), and DIO-Hib400 (HFD+HSE400 mg/kg BW). HSE was administered orally for five weeks, once a day.

RESULTS

HSE administration significantly (p <0,05) increased the ARC Lep-R expression. The Lee index significantly decreased to the normal range (≤ 310) with p <0,001 for DIO-Hib200 and p <0,01 for DIO-Hib400. Among 39 bioactive compounds, 5-O-caffeoyl shikimic acid exhibited high free binding scores (-8,63) for Lep-R, and myricetin_3_arabinogalactoside had high free binding scores (-9,39) for β3AR. These binding predictions could activate Lep-R and β3AR.

CONCLUSION

This study highlights that HSE could be a potential therapeutic target for obesity by increasing LepR mRNA and leptin sensitivity, enhancing energy expenditure, and reducing obesity.

Adipose and non-adipose perspectives of plant derived natural compounds for mitigation of obesity

ETHNOPHARMACOLOGICAL RELEVANCE

Phyto-preparations and phyto-compounds, by their natural origin, easy availability, cost-effectiveness, and fruitful traditional uses based on accumulated experiences, have been extensively explored to mitigate the global burden of obesity.

AIM OF THIS REVIEW

The review aimed to analyse and critically summarize the prospect of future anti-obesity drug leads from the extant array of phytochemicals for mitigation of obesity, using adipose related targets (adipocyte formation, lipid metabolism, and thermogenesis) and non-adipose targets (hepatic lipid metabolism, appetite, satiety, and pancreatic lipase activity). Phytochemicals as inhibitors of adipocyte differentiation, modulators of lipid metabolism, and thermogenic activators of adipocytes are specifically discussed with their non-adipose anti-obesogenic targets.

MATERIALS AND METHODS

PubMed, Google Scholar, Scopus, and SciFinder were accessed to collect data on traditional medicinal plants, compounds derived from plants, their reported anti-obesity mechanisms, and therapeutic targets. The taxonomically accepted name of each plant in this review has been vetted from "The Plant List" (www.theplantlist.org) or MPNS (http://mpns.kew.org).

RESULTS

Available knowledge of a large number of phytochemicals, across a range of adipose and non-adipose targets, has been critically analysed and delineated by graphical and tabular depictions, towards mitigation of obesity. Neuro-endocrinal modulation in non-adipose targets brought into sharp dual focus, both non-adipose and adipose targets as the future of anti-obesity research. Numerous phytochemicals (Berberine, Xanthohumol, Ursolic acid, Guggulsterone, Tannic acid, etc.) have been found to be effectively reducing weight through lowered adipocyte formation, increased lipolysis, decreased lipogenesis, and enhanced thermogenesis. They have been affirmed as potential anti-obesity drugs of future because of their effectiveness yet having no threat to adipose or systemic insulin sensitivity.

CONCLUSION

Due to high molecular diversity and a greater ratio of benefit to risk, plant derived compounds hold high therapeutic potential to tackle obesity and associated risks. This review has been able to generate fresh perspectives on the anti-diabetic/anti-hyperglycemic/anti-obesity effect of phytochemicals. It has also brought into the focus that many phytochemicals demonstrating in vitro anti-obesogenic effects are yet to undergo in vivo investigation which could lead to potential phyto-molecules for dedicated anti-obesity action.

Genetic and drug-induced hypomagnesemia: different cause, same mechanism

Magnesium (Mg2+) plays an essential role in many biological processes. Mg2+ deficiency is therefore associated with a wide range of clinical effects including muscle cramps, fatigue, seizures and arrhythmias. To maintain sufficient Mg2+ levels, (re)absorption of Mg2+ in the intestine and kidney is tightly regulated. Genetic defects that disturb Mg2+ uptake pathways, as well as drugs interfering with Mg2+ (re)absorption cause hypomagnesemia. The aim of this review is to provide an overview of the molecular mechanisms underlying genetic and drug-induced Mg2+ deficiencies. This leads to the identification of four main mechanisms that are affected by hypomagnesemia-causing mutations or drugs: luminal transient receptor potential melastatin type 6/7-mediated Mg2+ uptake, paracellular Mg2+ reabsorption in the thick ascending limb of Henle's loop, structural integrity of the distal convoluted tubule and Na+-dependent Mg2+ extrusion driven by the Na+/K+-ATPase. Our analysis demonstrates that genetic and drug-induced causes of hypomagnesemia share common molecular mechanisms. Targeting these shared pathways can lead to novel treatment options for patients with hypomagnesemia.

(-)-Epicatechin and Anthocyanins Modulate GLP-1 Metabolism: Evidence from C57BL/6J Mice and GLUTag Cells

BACKGROUND

Generated in intestinal L cells through cleavage of proglucagon (Gcg), glucagon-like peptide 1 (GLP-1) is secreted and rapidly inactivated by dipeptidyl peptidase IV (DPP-IV). GLP-1 regulates insulin secretion and overall glucose homeostasis. The capacity of dietary bioactives to increase GLP-1 circulating levels, and therefore increase insulin secretion and glucose metabolism, has gained significant interest of late.

OBJECTIVES

We evaluated the effects of (-)-epicatechin (EC) and different anthocyanins (ACs) and AC metabolites on GLP-1 metabolism in mice and on GLUTag cells.

METHODS

We fed 6-week-old C57BL/6J male mice a control diet or a control diet supplemented with either 40 mg AC or 20 mg EC/kg body weight for 14 weeks (AC) or 15 weeks (EC). Intestinal mRNA levels of Gcg and Dpp-iv were measured. In vitro, GLUTag cells were incubated in the presence or absence of different ACs, the AC metabolite protocatechuic acid (PCA), and EC. GLP-1 secretion and the main pathways involved in its release were assessed.

RESULTS

Long-term supplementation with EC or AC increased mouse GLP-1 plasma concentrations (55% and 98%, respectively; P < 0.05). In mice, 1) EC and AC increased Gcg mRNA levels in the ileum (91%) and colon (41%), respectively (P < 0.05); and 2) AC lowered ileum Dpp-iv mRNA levels (35%), while EC decreased plasma DPP-IV activity (15%; P < 0.05). In GLUTag cells, 1) cyanidin, delphinidin, PCA, and EC increased GLP-1 secretion (53%, 33%, 53%, and 68%, respectively; P < 0.05); and 2) cyanidin, delphinidin, EC, and PCA increased cyclin adenosine monophosphate levels (25-50%; P < 0.05) and activated protein kinase A (PKA; 100%, 50%, 80%, and 86%, respectively; P < 0.05).

CONCLUSIONS

In mice, EC and ACs regulated different steps in GLP-1 regulation, leading to increased plasma GLP-1. Cyanidin, delphinidin, PCA, and EC promoted GLP-1 secretion from GLUTag cells by activating the PKA-dependent pathway. These findings support the beneficial actions of these flavonoids in sustaining intestinal and glucose homeostasis through the modulation of the GLP-1 metabolism.

Feeding brown fat: dietary phytochemicals targeting non-shivering thermogenesis to control body weight

Excessive adipose accumulation, which is the main driver for the development of secondary metabolic complications, has reached epidemic proportions and combined pharmaceutical, educational and nutritional approaches are required to reverse the current rise in global obesity prevalence rates. Brown adipose tissue (BAT) is a unique organ able to dissipate energy and thus a promising target to enhance BMR to counteract a positive energy balance. In addition, active BAT might support body weight maintenance after weight loss to prevent/reduce relapse. Natural products deliver valuable bioactive compounds that have historically helped to alleviate disease symptoms. Interest in recent years has focused on identifying nutritional constituents that are able to induce BAT activity and thereby enhance energy expenditure. This review provides a summary of selected dietary phytochemicals, including isoflavones, catechins, stilbenes, the flavonoids quercetin, luteolin and resveratrol as well as the alkaloids berberine and capsaicin. Most of the discussed phytochemicals act through distinct molecular pathways e.g. sympathetic nerve activation, AMP-kinase signalling, SIRT1 activity or stimulation of oestrogen receptors. Thus, it might be possible to utilise this multitude of pathways to co-activate BAT using a fine-tuned combination of foods or combined nutritional supplements.

Antiobesity Efficacy of Quercetin-Rich Supplement on Diet-Induced Obese Rats: Effects on Body Composition, Serum Lipid Profile, and Gene Expression

The antiobesity effects of quercetin-rich supplement (QRS), which contain quercetin, lycopene, taurine, and litchi flower extract, on a high-fat diet (HFD)-induced obese rats were investigated. The rats that consume HFD with QRS (185 mg/kg rat) have significantly modulated the final body weights [490 ± 11 (HFD) → 441 ± 11 (HFD+QRS) g], total body fat [112.9 ± 4.5 (HFD) → 86.6 ± 5.7 (HFD+QRS) g], liver weights [14.8 ± 0.4 (HFD) → 12.6 ± 0.4 (HFD+QRS) g/rat], and the serum TG [102.5 ± 7.3 (HFD) → 90.7 ± 6.5 (HFD+QRS) mg/dL] to a level that resembled the regular diet-consumed rats (p < 0.05). The excretion of lipid in the faeces augmented in QRS groups as compared with the nonsupplemented HFD group [faecal total lipid: 62.43 ± 2.80 (HFD) → 73.15 ± 0.88 (HFD+QRS) mg/g dried faeces, p < 0.05]. In the histological analysis, quercetin-rich formulation supplemented groups presented a much less lipid accumulation and smaller size of adipocytes. Moreover, a decreased serum thiobarbituric acid reactive substances [1.55 ± 0.17 (HFD) → 0.78 ± 0.04 (HFD+QRS) nmol MDA eq/mL serum] increased levels of serum Trolox equivalent antioxidant capacity [3.89 ± 0.08 (HFD) → 6.46 ± 0.20 (HFD+QRS) μmol/mL serum], and more active hepatic antioxidant enzymes were observed in the supplemented groups (p < 0.05). The result of this work is a good demonstration of how a combination of bioactive compounds could work synergistically and become very effective in disease prevention.

The bioactivity of Hedysarum coronarium extracts on skin enzymes and cells correlates with phenolic content

CONTEXT

The search for bioactive compounds from botanical sources is attracting much interest. However, differences in chemical composition may occur within the same species depending on different geographical origins.

OBJECTIVES

We evaluated the properties on skin enzymes and cells of extracts from sulla legume crop Hedysarum coronarium L. (Fabaceae), collected at two Italian sites near Pisa and Ventimiglia, for possible dermatological and cosmetic applications.

MATERIAL AND METHODS

Plant aerial portions were extracted in MTBE/ethyl acetate/acetone, obtaining two extracts named Pisa sulla extract (PSE) and Ventimiglia sulla extract (VSE). Extracts were subjected to chemical characterization, LC-MS/MS analysis and biological assays.

RESULTS

PSE showed stronger antiradical scavenging and higher phenolic and flavonoid contents with respect to VSE. LC-MS/MS analysis revealed similar composition for the two extracts, but PSE was richer in condensed tannins and flavonoids, principally rhoifolin, quercetin, naringenin and derivatives. PSE induced stronger inhibition on collagenase and elastase by in vitro enzyme assays, possibly due to higher levels of condensed tannins and quercetin. ELISA bioassay on human dermal fibroblasts revealed stronger PSE induction of collagen production. Determination of glycerol release from adipocytes disclosed stronger stimulation of lipolysis by PSE, allegedly ascribed to higher charge of quercetin and derivatives. In summary, the higher richness in phenolics of PSE is strictly related to stronger bioactivity.

DISCUSSION AND CONCLUSIONS

Data indicate that aerial H. coronarium material is suitable for the development of dermatological and cosmeceutical products, but the geographical origin is an important factor for maximally exploiting the biological properties of this species.

Ethyl acetate fraction of Eclipta alba: a potential phytopharmaceutical targeting adipocyte differentiation

Natural products have always fascinated mankind for their miraculous properties. Eclipta alba (E. alba), a medicinal herb has long been used in traditional medicine for curing several pathologies. It has been shown to have anti-diabetic effect as well as hepato-protective activity. Here, in order to address metabolic derangements, the study was designed to evaluate the efficacy of E. alba and its fractions in adipogenesis inhibition and dyslipidemia. Of the crude extract and fractions screened, ethyl acetate fraction of E. alba inhibited adipocyte differentiation in 3T3-L1 pre-adipocytes and hMSC derived adipocytes. It inhibited mitotic clonal expansion and caused cell cycle arrest in G1 and S phase as suggested by western blot analysis and flow cytometry. It was also shown to have lipolytic effects. Oral administration of ethyl acetate fraction of E. alba to hamsters unveiled its anti-adipogenic as well as anti-dyslipidemic activity in-vivo. Mass spectrometry analysis of ethyl acetate fraction confirmed the presence of several bioactive components, projecting it as an effective phytopharmaceutical agent. In conclusion, ethyl acetate fraction of E. alba possesses potent anti-adipogenic as well as anti-dyslipidemic activity and could be projected as an herbal formulation towards obesity.

A common molecular motif characterizes extracellular allosteric enhancers of GPCR aminergic receptors and suggests enhancer mechanism of action

Several classes of compounds that have no intrinsic activity on aminergic systems nonetheless enhance the potency of aminergic receptor ligands three-fold or more while significantly increasing their duration of activity, preventing tachyphylaxis and reversing fade. Enhancer compounds include ascorbic acid, ethylenediaminetetraacetic acid, cortico-steroids, opioid peptides, opiates and opiate antagonists. This paper provides the first review of aminergic enhancement, demonstrating that all enhancers have a common, inobvious molecular motif and work through a common mechanism that is manifested by three common characteristics. First, aminergic enhancers bind directly to the amines they enhance, suggesting that the common structural motif is reflected in common binding targets. Second, one common target is the first extracellular loop of aminergic receptors. Third, at least some enhancers are antiphosphodiesterases. These observations suggest that aminergic enhancers act on the extracellular surface of aminergic receptors to keep the receptor in its high affinity state, trapping the ligand inside the receptor. Enhancer binding produces allosteric modifications of the receptor structure that interfere with phosphorylation of the receptor, thereby inhibiting down-regulation of the receptor. The mechanism explains how enhancers potentiate aminergic activity and increase duration of activity and makes testable predictions about additional compounds that should act as aminergic enhancers.

Effects of long-term feeding of the polyphenols resveratrol and kaempferol in obese mice

The effect of the intake of antioxidant polyphenols such as resveratrol and others on survival and different parameters of life quality has been a matter of debate in the last years. We have studied here the effects of the polyphenols resveratrol and kaempferol added to the diet in a murine model undergoing long-term hypercaloric diet. Using 50 mice for each condition, we have monitored weight, survival, biochemical parameters such as blood glucose, insulin, cholesterol, triglycerides and aspartate aminotransferase, neuromuscular coordination measured with the rotarod test and morphological aspect of stained sections of liver and heart histological samples. Our data show that mice fed since they are 3-months-old with hypercaloric diet supplemented with any of these polyphenols reduced their weight by about 5–7% with respect to the controls fed only with hypercaloric diet. We also observed that mice fed with any of the polyphenols had reduced levels of glucose, insulin and cholesterol, and better marks in the rotarod test, but only after 1 year of treatment, that is, during senescence. No effect was observed in the rest of the parameters studied. Furthermore, although treatment with hypercaloric diets induced large changes in the pattern of gene expression in liver, we found no significant changes in gene expression induced by the presence of any of the polyphenols. Thus, our data indicate that addition of resveratrol or kaempferol to mice food produces an initial decrease in weight in mice subjected to hypercaloric diet, but beneficial effects in other parameters such as blood glucose, insulin and cholesterol, and neuromuscular coordination, only appear after prolonged treatments.

A dietary pattern rich in lignans, quercetin and resveratrol decreases the risk of oesophageal cancer

Dietary lignans, quercetin and resveratrol have oestrogenic properties, and animal studies suggest that they synergistically decrease cancer risk. A protective effect of lignans on the development of oesophageal cancer in humans has recently been demonstrated, and the present study aimed to test whether these three phytochemicals synergistically decrease the risk of oesophageal cancer. Data from a Swedish nationwide population-based case-control study that recruited 181 cases of oesophageal adenocarcinoma (OAC), 158 cases of oesophageal squamous-cell carcinoma (OSCC), 255 cases of gastro-oesophageal junctional adenocarcinoma (JAC) and 806 controls were analysed. Exposure data were collected through face-to-face interviews and questionnaires. The intake of lignans, quercetin and resveratrol was assessed using a sixty-three-item FFQ. Reduced-rank regression was used to assess a dietary pattern, and a simplified dietary pattern score was categorised into quintiles on the basis of the distribution among the control subjects. Unconditional multivariable logistic regression provided OR with 95% CI, adjusted for all the potential risk factors. A dietary pattern rich in lignans, quercetin and resveratrol was mainly characterised by a high intake of tea, wine, lettuce, mixed vegetables, tomatoes, and whole-grain bread and a low intake of milk. There were dose-dependent associations between simplified dietary pattern scores and all types of oesophageal cancer (all P for trend < 0.05). On comparing the highest quintiles with the lowest, the adjusted OR were found to be 0.24 (95% CI 0.12, 0.49) for OAC, 0.31 (95% CI 0.15, 0.65) for OSCC, and 0.49 (95% CI 0.28, 0.84) for JAC. The results of the present study indicate that a dietary pattern characterised by the intake of lignans, quercetin and resveratrol may play a protective role in the development of oesophageal cancer in the Swedish population.

A network pharmacology approach to understanding the mechanisms of action of traditional medicine: Bushenhuoxue formula for treatment of chronic kidney disease

Traditional Chinese medicine (TCM) has unique therapeutic effects for complex chronic diseases. However, for the lack of an effective systematic approach, the research progress on the effective substances and pharmacological mechanism of action has been very slow. In this paper, by incorporating network biology, bioinformatics and chemoinformatics methods, an integrated approach was proposed to systematically investigate and explain the pharmacological mechanism of action and effective substances of TCM. This approach includes the following main steps: First, based on the known drug targets, network biology was used to screen out putative drug targets; Second, the molecular docking method was used to calculate whether the molecules from TCM and drug targets related to chronic kidney diseases (CKD) interact or not; Third, according to the result of molecular docking, natural product-target network, main component-target network and compound-target network were constructed; Finally, through analysis of network characteristics and literature mining, potential effective multi-components and their synergistic mechanism were putatively identified and uncovered. Bu-shen-Huo-xue formula (BSHX) which was frequently used for treating CKD, was used as the case to demonstrate reliability of our proposed approach. The results show that BSHX has the therapeutic effect by using multi-channel network regulation, such as regulating the coagulation and fibrinolytic balance, and the expression of inflammatory factors, inhibiting abnormal ECM accumulation. Tanshinone IIA, rhein, curcumin, calycosin and quercetin may be potential effective ingredients of BSHX. This research shows that the integration approach can be an effective means for discovering active substances and revealing their pharmacological mechanisms of TCM.

Beta-Glucan-Rich Extract from Pleurotus sajor-caju (Fr.) Singer Prevents Obesity and Oxidative Stress in C57BL/6J Mice Fed on a High-Fat Diet

Mushrooms have been used in folk medicine for thousands of years. In this study, the effect of β-glucan-rich extract of P. sajor-caju (GE) on lipid lowering and antioxidant potential was assessed in C57BL/6J mice fed on a high-fat diet. Obesity was induced in C57BL/6J mice by feeding a high-fat diet. The control groups in this study were ND (for normal diet) and HFD (for high-fat diet). The treated groups were ND240 (for normal diet) (240 mg/kg b.w) and HFD60, HFD120, and HFD240 (for high-fat diet), where the mice were administrated with three dosages of GE (60, 120, and 240 mg GE/kg b.w). Metformin (2 mg/kg b.w) served as positive control. GE-treated groups showed significantly reduced body weight, serum lipid, and liver enzymes levels. GE also attenuated protein carbonyl and lipid hydroperoxide levels by increasing the enzymic antioxidants (SOD, CAT, and GPx) activities in the mice. GE-treated groups induced the expression of hormone sensitive lipase (HSL) and adipose triglyceride lipase (ATGL) while downregulated the expression of peroxisome proliferator-activated receptor gamma (PPAR-γ), sterol regulatory binding protein-1c (SREBP-1c), and lipoprotein lipase (LPL). Hence, GE prevented weight gain in the mice by inducing lipolysis and may be valuable in the formulation of adjuvant therapy for obesity.

Butein is a novel anti-adipogenic compound

Rhus verniciflua Stokes (RVS) has been used as a traditional herbal medicine for its various biological activities including anti-adipogenic effects. Activity-guided separation led to the identification of the anti-adipogenic functions of butein. Butein, a novel anti-adipogenic compound, robustly suppressed lipid accumulation and inhibited expression of adipogenic markers. Molecular studies showed that activated transforming growth factor-β (TGF-β) and suppressed signal transducer and activator of transcription 3 (STAT3) signaling pathways were mediated by butein. Analysis of the temporal expression profiles suggests that TGF-β signaling precedes the STAT3 in the butein-mediated anti-adipogenic cascade. Small interfering RNA-mediated silencing of STAT3 or SMAD2/3 blunted the inhibitory effects of butein on adipogenesis indicating that an interaction between two signaling pathways is required for the action of butein. Upon butein treatments, stimulation of TGF-β signaling was still preserved in STAT3 silenced cells, whereas regulation of STAT3 signaling by butein was significantly impaired in SMAD2/3 silenced cells, further showing that TGF-β acts upstream of STAT3 in the butein-mediated anti-adipogenesis. Taken together, the present study shows that butein, a novel anti-adipogenic compound from RVS, inhibits adipocyte differentiation through the TGF-β pathway followed by STAT3 and peroxisome proliferator-activated receptor γ signaling, further implicating potential roles of butein in TGF-β- and STAT3-dysregulated diseases.

The isoflavone-rich fraction of the crude extract of the Puerariae flower increases oxygen consumption and BAT UCP1 expression in high-fat diet-fed mice

Puerariae flower extract (PFE) is a crude extract of the Kudzu flower. Previous studies have shown that PFE supplementation exerts anti-obesity and anti-fatty liver effects in high-fat diet-fed mice. In this study, we aimed to identify the PFE components responsible for these effects and to determine their influence on energy expenditure and uncoupling protein 1 (UCP1) expression. Experiments were conducted on C57BL/6J male mice classified into 3 groups: (1) high-fat diet-fed (HFD), (2) high-fat diet-fed given PFE (HFD + PFE), and (3) high-fat diet-fed given the PFE isoflavone-rich fraction (HFD + ISOF). All groups were fed for 42 days. The HFD + PFE and HFD + ISOF groups showed significant resistance to increases in body weight, hepatic triglyceride level, and visceral fat compared to the HFD group. These groups also exhibited significant increases in oxygen consumption and UCP1-positive brown adipose tissue (BAT) area. Our results demonstrate that the active ingredients in PFE are present in the ISOF and that these compounds may increase energy expenditure by upregulation of BAT UCP1 expression. These findings provide valuable information regarding the anti-obesity effects of isoflavones.

Quercetin inhibits IL-1β-induced inflammation, hyaluronan production and adipogenesis in orbital fibroblasts from Graves' orbitopathy

Management of Graves' orbitopathy (GO) is challenging, as no reliable, specific, and safe medical therapeutic agents have yet been developed. We investigated the effect of quercetin in primary cultured orbital fibroblasts from GO, targeting pathways of inflammation, aberrant accumulation of extracellular matrix macromolecules, and adipose tissue expansion. Quercetin significantly attenuated intercellular adhesion molecule-1 (ICAM-1), interleukin (IL) -6, IL-8, and cyclooxygenase (COX) -2 mRNA expression, and inhibited IL-1β-induced increases in ICAM-1, IL-6, and IL-8 mRNA. Increased hyaluronan production induced by IL-1β or tumor necrosis factor-α was suppressed by quercetin in a dose- and time-dependent manner. Treatment with noncytotoxic doses of quercetin inhibited accumulation of intracytoplasmic lipid droplets and resulted in a dose-dependent decrease in expression of peroxisome proliferator-activated receptor γ, CCAAT/enhancer-binding protein (C/EBP) α, and C/EBPβ proteins. In conclusion, inhibition of inflammation, hyaluronan production, and adipogenesis by the natural plant product quercetin in vitro provides the basis for further study of its potential use in the treatment of GO.

Dietary quercetin supplementation is not ergogenic in untrained men

Quercetin supplementation increases muscle oxidative capacity and endurance in mice, but its ergogenic effect in humans has not been established. Our study investigates the effects of short-duration chronic quercetin supplementation on muscle oxidative capacity; metabolic, perceptual, and neuromuscular determinants of performance in prolonged exercise; and cycling performance in untrained men. Using a double-blind, pretest-posttest control group design, 30 recreationally active, but not endurance-trained, young men were randomly assigned to quercetin and placebo groups. A noninvasive measure of muscle oxidative capacity (phosphocreatine recovery rate using magnetic resonance spectroscopy), peak oxygen uptake (V̇o2peak), metabolic and perceptual responses to submaximal exercise, work performed on a 10-min maximal-effort cycling test following the submaximal cycling, and voluntary and electrically evoked strength loss following cycling were measured before and after 7–16 days of supplementation with 1 g/day of quercetin in a sports hydration beverage or a placebo beverage. Pretreatment-to-posttreatment changes in phosphocreatine recovery time constant, V̇o2peak, substrate utilization, and perception of effort during submaximal exercise, total work done during the 10-min maximal effort cycling trial, and voluntary and electrically evoked strength loss were not significantly different ( P > 0.05) in the quercetin and placebo groups. Short duration, chronic dietary quercetin supplementation in untrained men does not improve muscle oxidative capacity; metabolic, neuromuscular and perceptual determinants of performance in prolonged exercise; or cycling performance. The null findings indicate that metabolic and physical performance consequences of quercetin supplementation observed in mice should not be generalized to humans.

Procyanidin effects on adipocyte-related pathologies

Procyanidins, a class of flavonoids, have clear and well-defined beneficial effects against several pathologies including cardiovascular heart disease. Now, studies in vivo are revealing the effects of procyanidins against obesity, where they prevent weight gain and adipose tissue mass increase, and against diabetes and insulin resistance, where they act as antihiperglycemic agents. Several mechanisms may be responsible for these effects. One of these, due to the key role of adipose tissue in the development of obesity and insulin resistance, is their effect on adipocytes. In this review we compile the studies that indicate a protective role for procyanidins in obesity and insulin resistance, focusing on their effects on the adipocyte, where procyanidins modify lipid synthesis, lipid degradation, glucose uptake, and adipose differentiation.

A Citrus Polymethoxy Flavonoid, Nobiletin Inhibits Sebum Production and Sebocyte Proliferation, and Augments Sebum Excretion in Hamsters

Acne vulgaris is characterized by excess sebum production, and apart from all-trans retinoic acid (atRA) or 13-cis retinoic acid (13-cisRA), there are few effective agents for acne therapy that directly suppresses sebaceous lipogenesis. In this study, we demonstrated that topical application of a citrus polymethoxy flavonoid, nobiletin, to hamster auricles decreased skin surface triacylglycerols (TG) level and the size of sebaceous glands along with inhibition of diacylglycerol acyltransferase (DGAT)-dependent TG synthesis and sebocyte proliferation. The inhibitory actions were similar to that observed with atRA and 13-cisRA in hamster sebocytes. The antilipogenic and antiproliferative actions of nobiletin were also reproduced in UVB (5.4 kJ/m2)-irradiated hamsters, which showed aberrant enhancement of sebum accumulation and sebaceous enlargement. Furthermore, nobiletin, but not 13-cisRA, augmented sebum excretion along with increases in intracellular cAMP level, protein kinase A (PKA) activation, and apoptosis-independent phosphatidylserine (PS) externalization in cell membrane. These phenomena were reproduced by forskolin and inhibited by a PKA inhibitor, H-89. These results provide early evidence that nobiletin is an effective candidate for acne therapy through mechanisms that include the inhibition of DGAT-dependent TG synthesis and sebocyte proliferation, and the progression of apoptosis-independent and PS-externalization-dependent sebum excretion by PKA activation.

The small polyphenolic molecule kaempferol increases cellular energy expenditure and thyroid hormone activation

Disturbances in energy homeostasis can result in obesity and other metabolic diseases. Here we report a metabolic pathway present in normal human skeletal muscle myoblasts that is activated by the small polyphenolic molecule kaempferol (KPF). Treatment with KPF leads to an approximately 30% increase in skeletal myocyte oxygen consumption. The mechanism involves a several-fold increase in cyclic AMP (cAMP) generation and protein kinase A activation, and the effect of KPF can be mimicked via treatment with dibutyryl cAMP. Microarray and real-time PCR studies identified a set of metabolically relevant genes influenced by KPF including peroxisome proliferator-activated receptor gamma coactivator-1alpha, carnitine palmitoyl transferase-1, mitochondrial transcription factor 1, citrate synthase, and uncoupling protein-3, although KPF itself is not a direct mitochondrial uncoupler. The cAMP-responsive gene for type 2 iodothyronine deiodinase (D2), an intracellular enzyme that activates thyroid hormone (T3) for the nucleus, is approximately threefold upregulated by KPF; furthermore, the activity half-life for D2 is dramatically and selectively increased as well. The net effect is an approximately 10-fold stimulation of D2 activity as measured in cell sonicates, with a concurrent increase of approximately 2.6-fold in the rate of T3 production, which persists even 24 h after KPF has been removed from the system. The effects of KPF on D2 are independent of sirtuin activation and only weakly reproduced by other small polyphenolic molecules such as quercetin and fisetin. These data document a novel mechanism by which a xenobiotic-activated pathway can regulate metabolically important genes as well as thyroid hormone activation and thus may influence metabolic control in humans.

Intracellular mediators of procyanidin-induced lipolysis in 3T3-L1 adipocytes

We have previously reported that grape seed procyanidins stimulate long-term lipolysis on 3T3-L1 fully differentiated adipocytes. To unravel the molecular mechanism by which procyanidins exert this effect, we checked the involvement of two main cellular targets in adipose cells: protein kinase A (PKA) and peroxisome proliferator-activated receptor-gamma (PPAR-gamma). Procyanidin treatment increased intracellular cAMP levels in 3T3-L1 adipocytes, and their lipolytic effect was inhibited by simultaneous treatment with H89, a PKA specific inhibitor. BRL49653, a very highly specific ligand of PPAR-gamma, totally abolished the lipolytic effect of procyanidins. Simultaneous to this long-term lipolytic effect, the mRNA levels of some differentiation adipocyte markers decreased, although there were no changes in the triglyceride content of the cells. BRL49653 did not antagonize the decrements of differentiation markers. These results support a mediation of PPAR-gamma and PKA on the lipolytic effects of procyanidins on 3T3-L1 adipocytes.

Differential effects of flavonoids on 3T3-L1 adipogenesis and lipolysis

Flavonoids, polyphenolic compounds that exist widely in plants, inhibit cell proliferation and increase cell differentiation in many cancerous and noncancerous cell lines. Because terminal differentiation of preadipocytes to adipocytes depends on proliferation of both pre- and postconfluent preadipocytes, we predicted that flavonoids would inhibit adipogenesis in the 3T3-L1 preadipocyte cell line. The flavonoids genistein and naringenin inhibited proliferation of preconfluent preadipocytes in a time- and dose-dependent manner. When added to 2-day postconfluent preadipocytes at the induction of differentiation, genistein inhibited mitotic clonal expansion, triglyceride accumulation, and peroxisome proliferator-activated receptor-gamma expression, but naringenin had no effect. The antiadipogenic effect of genistein was not due to inhibition of insulin receptor subtrate-1 tyrosine phosphorylation. When added 3 days after induction of differentiation, neither flavonoid inhibited differentiation. In fully differentiated adipocytes, genistein increased basal and epinephrine-induced lipolysis, but naringenin had no significant effects. These data demonstrate that genistein and naringenin, despite structural similarity, have differential effects on adipogenesis and adipocyte lipid metabolism.

Changes in lipolysis and hormone-sensitive lipase expression caused by procyanidins in 3T3-L1 adipocytes

OBJECTIVE

To find out whether lipid stores are influenced by phenolic compounds in wine.

DESIGN

Differentiated 3T3-L1 cells were treated with catechin, epicatechin or procyanidin extracts with different degrees of polymerization at 150 microM for different periods of time (0.5-24 h).

SUBJECTS

Cell line 3T3-L1.

MEASUREMENTS

Cellular viability, glycerol-3-phosphate dehydrogenase activity, glycerol release in the medium, HSL mRNA levels, triacylglycerols and protein.

RESULTS

Catechin, epicatechin and procyanidin extracts were not toxic for the 3T3-L1 cells in the conditions assayed. Glycerol-3-phosphate dehydrogenase activity was markedly decreased by 150 microM procyanidin extracts. The release of glycerol into the medium was increased in 150 microM procyanidin extract-treated cells and reached a plateau after 15 h exposure. Procyanidins caused a time-dependent reduction in the HSL mRNA levels.

CONCLUSIONS

These results suggest that procyanidins from grape and wine affect lipid metabolism whilst their monomers (catechin and epicatechin) do not. This effect is more pronounced when the degree of polymerization is higher. Procyanidin extracts cause a time-dependent reduction in the HSL mRNA levels, inhibit triacylglycerol synthesis and also favour triacylglycerol hydrolysis until the HSL mRNA had reached very low levels.

Involvement of cAMP and beta-adrenoceptors in the relaxing effect elicited by flavonoids on rat uterine smooth muscle

1. The effect of the flavonoids genistein (3-100 microM), kaempferol (3-60 microM) and quercetin (1-100 microM) on KCl (60 mM)-induced tonic contraction in rat smooth muscle was assayed. In the same way, the modification of these effects in the presence of an inhibitor of protein kinase (PKA) (Rp-cAMPS), an inhibitor of phosphodiesterase (papaverine) and beta-adrenoreceptor blocking agents (propranolol and atenolol) was studied. 2. The flavonoids totally relaxed the KCl-induced tonic contraction (IC50: genistein 20.2 +/- 2.0 microM, n = 11; kaempferol 10.1 +/- 1.6 microM, n = 8; quercetin 13.2 +/- 1.2 microM, n = 8). 3. The incubation with Rp-cAMPS (10 and 100 microM) 30 min prior to KCl shifted the dose-response curve of the flavonoids to the right, increasing their IC50 up to 27.8 +/- 3.8 and 31.9 +/- 7.3 microM, respectively, for genistein; 24.7 +/- 0.2 and 19.6 +/- 4.9 microM, respectively, for kaempferol; 18.8 +/- 2.2 and 18.4 +/- 1.5 microM, respectively, for quercetin. 4. Papaverine (3-100 microM) also relaxed the contraction induced by KCl and this effect was significantly displaced to the right with Rp-cAMPS (10 microM) (IC50 12.1 +/- 2.2 vs. 16.5 +/- 3.1 microM). Papaverine (3 microM) added to the organ bath 15 min before the contractile agent increased the relaxing effect of the flavonoids and significantly decreased their IC50 (genistein 20.2 +/- 2.0 vs. 9.8 +/- 1.4 microM; kaempferol 10.1 +/- 1.6 vs. 6.6 +/- 0.7 microM; quercetin 13.2 +/- 1.2 vs. 7.8 +/- 1.4 microM). 5. The incubation with atenolol (10 microM) did not alter the relaxing effect of the flavonoids. In the same experimental conditions, propranolol (10 microM) did not modify the effect of genistein and kaempferol, but shifted the response curve of quercetin significantly to the right (13.2 +/- 1.2 vs. 17.7 +/- 3.4 microM). 6. The results suggest that genistein, kaempferol and quercetin produced the relaxation of uterine smooth muscle by increasing intracellular cAMP. Beta-adrenoceptors could also be involved in the effect of quercetin.

Oxidation of the flavonol fisetin by polyphenol oxidase

The present study demonstrates the antiradical efficiency of fisetin, a flavonol widely distributed in fruits and vegetables, by its ability to react with two different free radicals, ABTS; and DPPH;. The polyphenolic nature of fisetin led us to consider whether it might be oxidised by polyphenol oxidase (PPO), and the results reported show that it can be oxidised by PPO extracted and partially purified from broad bean seeds. The reaction was followed by recording spectral changes with time, with maximal spectral changes being observed at 282 nm (increase in absorbance) and at 362 nm (decrease). The presence of two isosbectic points (at 265 and 304 nm) suggested that only one absorbent product was formed. These spectral changes were not observed in the absence of PPO. The oxidation rate varied with the pH, reaching its highest value at pH 5.5. The fisetin oxidation rate increased in the presence of sodium dodecyl sulfate, an activator of polyphenol oxidase. Maximal activity was obtained at 0.87 mM sodium dodecyl sulfate. The following kinetic parameters were determined: Vmax=49 microM/min, Km=0.6 mM, Vmax/Km=8.2x10-2 min-1. Flavonol oxidation was inhibited by selective PPO inhibitors such as cinnamic acid (a classical competitive inhibitor, Ki=1.4 mM) and 4-hexylresorcinol, which behaved as a slow-binding inhibitor. The results reported show that fisetin oxidation was strictly dependent on the presence of polyphenol oxidase.

Depolarization-dependent effect of flavonoids in rat uterine smooth muscle contraction elicited by CaCl2

1. The effects of the flavonoids genistein (3-60 microM), kaempferol (3-60 microM) and quercetin (1-100 microM) on KCl (60 mM)-induced tonic contraction in rat uterus and their modifications with the inhibitor of cAMP-dependent protein kinases (TPCK, 3 microM), the inhibitor of ornithine decarboxylase [alpha-difluoromethyl ornithine (DFMO), 10 mM] and the polyamine spermine (1 mM) have been assayed. The effects of the three flavonoids were also studied on the contraction elicited by CaCl2 (30 microM to 10 mM) on rat uterus incubated in medium lacking calcium and supplemented with 33, 60 or 90 mM of KCl. For comparison, the effects of the calcium channel blockers nifedipine and verapamil and the activator of adenylyl cyclase forskolin were assayed on contractions induced by KCl and CaCl2. 2. Genistein (IC50: 20.2 +/- 1.0 microM, n = 11), kaempferol (IC50: 10.1 +/- 0.8 microM, n = 8) and quercetin (IC50: 13.2 +/- 0.5 microM, n = 8) relaxed the tonic contraction induced by KCl (60 mM) in a concentration-dependent way. Verapamil (IC50: 70.1 +/- 5.8 nM, n = 7), nifedipine (IC50: 8.4 +/- 0.7 nM, n = 6) and forskolin (IC50: 0.62 +/- 0.08 microM, n = 14) also relaxed the KCl-induced contraction. TPCK (3 microM) significantly antagonized the effect of quercetin, kaempferol and forskolin (P < 0.01) but did not modify the effect of genistein. 3. Spermine (1 mM) increased the effects of genistein and verapamil and antagonized the effect of quercetin but did not modify those of kaempferol and forskolin. DFMO (10 mM) did not modify the effect of quercetin but increased that of genistein and antagonized those of kaempferol and forskolin. The addition of spermine (1 mM) plus DFMO (10 mM) antagonized the effect of quercetin. Spermine counteracted the effect of DFMO on forskolin but not on genistein. 4. KCl (33, 60 or 90 mM) did not produce contraction in calcium-free solution, but CaCl2 (30 microM to 10 mM) induced concentration-dependent contraction after depolarizing with KCl. The EC50 values for CaCl2 were: 0.74 +/- 0.08 (n = 12), 0.34 +/- 0.03 (n = 14) and 0.48 +/- 0.02 (n = 12) mM in a medium with 33, 60 or 90 mM of KCl, respectively. 5. Genistein (20 microM), kaempferol (10 microM), quercetin (15 microM), verapamil (70 nM), nifedipine (10 nM) and forskolin (0.5 microM) inhibited the concentration-response curve to CaCl2 in medium supplemented with 33, 60 or 90 mM of KCl. The effect of kaempferol was independent of the concentration of KCl in the incubation medium. However, the inhibitory effect of genistein on CaCl2-induced contraction was inversely related to the concentration of KCl in the medium. On the contrary, the effect of quercetin was directly related to the concentration of KCl in the medium. 6. The antagonism of verapamil, nifedipine and forskolin on CaCl2-induced contraction seems to be related to the degree of depolarization because increasing the KCl in the medium counteracted their effects. 7. Our results suggest that (1) cAMP contributes to the relaxant effects of quercetin and kaempferol on KCl (60 mM)-induced tonic contraction; (2) polyamines are involved in the relaxant effects of forskolin and kaempferol on KCl-induced tonic contraction but not on CaCl2-induced contraction in the depolarized uterus, and (3) the flavonoids assayed also possess a calcium antagonist action but show a different behavior toward the calcium channel blockers and the cAMP enhancer forskolin.

Dissociation of phospholamban regulation of cardiac sarcoplasmic reticulum Ca2+ATPase by quercetin

Quercetin had a biphasic effect on Ca2+ uptake and calcium-stimulated ATP hydrolysis in isolated cardiac sarcoplasmic reticulum (SR). Stimulation of Ca2+ATPase was observed at low quercetin concentrations (<25 microM) followed by inhibition at higher concentrations. The effects were dependent upon the SR protein concentration, the MgATP concentration, and intact phospholamban regulation of cardiac Ca2+ATPase. Only the inhibitory effects at higher quercetin concentrations were observed in skeletal muscle SR which lacks phospholamban and in cardiac SR treated to remove phospholamban regulation. Stimulation was additive with monoclonal antibody 1D11 (directed against phospholamban) at submaximal antibody concentrations; however, the maximal antibody and quercetin stimulation were identical. Quercetin increased the calcium sensitivity of the Ca2+ATPase like that observed with phosphorylation of phospholamban or treatment with monoclonal antibody 1D11. In addition, low concentrations of quercetin increased the steady-state formation of phosphoenzyme from ATP or Pi, but higher quercetin decreased phosphoenzyme levels. Quercetin, even under stimulatory conditions, was a competitive inhibitor of ATP, but appears to relieve the Ca2+ATPase from phospholamban inhibition, thereby, producing an activation. The subsequent inhibitory action of higher quercetin concentrations results from competition of quercetin with the nucleotide binding site of the Ca2+ATPase. The data suggest that quercetin interacts with the nucleotide binding site to mask phospholamban's inhibition of the SR Ca2+ATPase and suggests that phospholamban may interact at or near the nucleotide binding site.

Synthesis and biological activities of flavonoid derivatives as A3 adenosine receptor antagonists

A broad screening of phytochemicals has demonstrated that certain flavone and flavonol derivatives have a relatively high affinity at A3 adenosine receptors, with Ki values of > or = 1 microM (Ji et al. J. Med. Chem. 1996, 39, 781-788). We have further modified the flavone structure to achieve a degree of selectivity for cloned human brain A3 receptors, determined in competitive binding assays versus [125I]AB-MECA[N6-(4-amino-3-iodobenzyl)adenosine-5'-(N-methylur onamide)]. Affinity was determined in radioligand binding assays at rat brain A1 and A2a receptors using [3H]-N6-PIA ([3H]-(R)-N6-phenylisopropyladenosine) and [3H]CGS21680 [[3H]-2-[[4-(2-carboxyethyl)phenyl]ethylamino]-5'-(N-ethylcarbamoyl++ +)adenosine], respectively. The triethyl and tripropyl ether derivatives of the flavonol galangin, 4, had Ki values of 0.3 - 0.4 microM at human A3 receptors. The presence of a 5-hydroxyl group increased selectivity of flavonols for human A3 receptors. The 2',3,4',7-tetraethyl ether derivative of the flavonol morin, 7, displayed a Ki value of 4.8 microM at human A3 receptors and was inactive at rat A1/A2a receptors. 3,6-Dichloro-2'-(isopropyloxy)-4'-methylflavone, 11e, was both potent and highly selective (approximately 200-fold) for human A3 receptors (Ki = 0.56 microM). Among dihydroflavonol analogues, the 2-styryl instead of the 2-aryl substituent, in 15, afforded selectivity for human A3 vs rat A1 or A2A receptors. The 2-styryl-6-propoxy derivative, 20, of the furanochromone visnagin was 30-fold selective for human A3 receptors vs either rat A1 or A2A receptors. Several of the more potent derivatives effectively antagonized the effects of an agonist in a functional A3 receptor assay, i.e. inhibition of adenylyl cyclase in CHO cells expressing cloned rat A3 receptors. In conclusion, these series of flavonoids provide leads for the development of novel potent and subtype selective A3 antagonists.

Interactions of flavonoids and other phytochemicals with adenosine receptors

Flavone derivatives and other phytochemicals were found to bind to three subtypes of adenosine receptors in the micromolar range. Affinity was determined in radioligand binding assays at rat brain A1 and A2A receptors using [3H]-N6-PIA ([3H]-(R)-N6-phenylisopropyladenosine) and [3H]CGS21680 ([3H]-2-[[4-(2-carboxyethyl)phenyl]ethylamino]-5'- (N-ethylcarbamoyl)adenosine), respectively. Affinity was determined at cloned human and rat brain A3 receptors using [125I]-AB-MECA [N6-(4-amino-3-iodobenzyl)adenosine-5'-(N-methyluronamide)]. A structure-activity analysis indicated that the hydroxyl groups of naturally occurring flavones are not essential for affinity at adenosine receptors. Galangin, 14, displayed Ki values of 1 microM at both rat A1 and A2A receptors and 3 microM at human A3 receptors. Methylation but not acetylation of the hydroxyl groups of galangin enhanced A3 affinity. Pentamethylmorin, 20, appeared to bind with 14-17-fold selectivity for human A3 receptors vs rat A1 and A2A receptors, with a Ki value of 2.65 microM. Two flavone derivatives (14 and 15) showed 14-fold greater affinity at human vs rat A3 receptors. Reduction of the 2,3-olefinic bond, as in (+/-)-dihydroquercetin, or glycosidation, as in robinin, greatly diminished affinity. An isoflavone, genistein, also bound only very weakly at A3 receptors. alpha-Naphthoflavone had greater receptor affinity (0.79 microM at A1 receptors) than the beta-isomer. Other natural products of plant origin, including oxogalanthine lactam, hematoxylin, and arborinine were found to bind to A1 adenosine receptors with Ki values of 3-13 microM. These findings indicate that the flavones, flavonols, flavanones, and other phytochemicals may provide leads for the development of novel adenosine antagonists. The unexpected finding of considerable affinity of flavones at both rat and human A3 receptors may explain some of the previously observed biological effects of these compounds.

In vitro modulation of rat adipocyte ghost membrane fluidity by cholesterol oxysterols

The effects of cholesterol and cholesterol-derived oxysterols (cholestanone, cholestenone, coprostanone and epicoprostanol) on adipocyte ghost membrane fluidity were studied using a fluorescence depolarization method. The fluorescence anisotropy of the treated membranes was determined using 1,6-diphenyl-1,3,5-hexatriene (DPH) and 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH). Cholestanone and cholesterol decreased membrane fluidity at both the concentrations tested (10 & 50 microM) while the rest of the sterols did not exert any significant effect on membrane fluidity. In the presence of epinephrine, cholestanone partitioned more towards the lipid core but cholesterol partitioning was not affected. The fusion activation energies (delta E) obtained for membranes preincubated with cholestanone (8.6 kcal/mol) and cholesterol (8.2 kcal/mol) were not significantly different from that of untreated membranes (8.3 kcal/mol). Membranes preincubated with cholestanone and cholesterol did not exhibit any change in lipid phase throughout the temperature range (10-45 degrees C) tested. The sterols were found to inhibit fisetin-induced phospholipid methylation in isolated rat adipocytes in the rank order of cholesterol > epicoprostanol > cholestanone = cholestenone = coprostanone, while basal methylation was unaffected. When adipocytes were preincubated with the sterols before the addition of fisetin, cholestanone and cholestenone showed 74% and 66% inhibition of maximal methylation respectively. These results indicated that cholesterol oxysterols interact differently with rat adipocyte membranes, with cholestanone interacting more with phospholipids located at the inner lipid bilayer (e.g. phosphatidylethanolamine) while cholesterol interacts more with phosphatidylcholine located at the outer lipid bilayer. This differential interaction may cause selective changes in membrane fluidity at different depths of the bilayer and thus may modulate the activities of membrane-bound proteins such as enzymes and receptors.