Cholesterol metabolism is modulated by quercetin in rats

Quercitrin alleviates lipid metabolism disorder in polycystic ovary syndrome-insulin resistance by upregulating PM20D1 in the PI3K/Akt pathway

BACKGROUND

Abnormal endocrine metabolism caused by polycystic ovary syndrome combined with insulin resistance (PCOS-IR) poses a serious risk to reproductive health in females. Quercitrin is a flavonoid that can efficiently improve both endocrine and metabolic abnormalities. However, it remains unclear if this agent can exert therapeutic effect on PCOS-IR.

METHODS

The present study used a combination of metabolomic and bioinformatic methods to screen key molecules and pathways involved in PCOS-IR. A rat model of PCOS-IR and an adipocyte IR model were generated to investigate the role of quercitrin in regulating reproductive endocrine and lipid metabolism processes in PCOS-IR.

RESULTS

Peptidase M20 domain containing 1 (PM20D1) was screened using bioinformatics to evaluate its participation in PCOS-IR. PCOS-IR regulation via the PI3K/Akt signaling pathway was also investigated. Experimental analysis showed that PM20D1 levels were reduced in insulin-resistant 3T3-L1 cells and a letrozole PCOS-IR rat model. Reproductive function was inhibited, and endocrine metabolism was abnormal. The loss of adipocyte PM20D1 aggravated IR. In addition, PM20D1 and PI3K interacted with each other in the PCOS-IR model. Furthermore, the PI3K/Akt signaling pathway was shown to participate in lipid metabolism disorders and PCOS-IR regulation. Quercitrin reversed these reproductive and metabolic disorders.

CONCLUSION

PM20D1 and PI3K/Akt were required for lipolysis and endocrine regulation in PCOS-IR to restore ovarian function and maintain normal endocrine metabolism. By upregulating the expression of PM20D1, quercitrin activated the PI3K/Akt signaling pathway, improved adipocyte catabolism, corrected reproductive and metabolic abnormalities, and had a therapeutic effect on PCOS-IR.

Molecular Mechanism of Crataegi Folium and Alisma Rhizoma in the Treatment of Dyslipidemia Based on Network Pharmacology and Molecular Docking

Background

Dyslipidemia has become a critical global issue for public health, with elevating prevalence and morbidity closely related to many cardiovascular diseases (CVD) with high incidence rates. Crataegi Folium (known as Shanzhaye in China, SZ, the leaves of Crataegus pinnatifida Bge. var. major N.E. Br. or Crataegus pinnatifida Bge) and Alisma rhizoma (known as Zexie in China, ZX, the dried tuber of Alisma orientale (Sam.) Juzep or Alisma plantago-aquatica Linn), a classic combination of herbs, have been widely used to treat dyslipidemia. However, the therapeutic mechanism of this pair still remains unclear. Hence, this study aimed to elucidate the molecular mechanism of the Shanzhaye-Zexie herb pair (SZHP) in the treatment of dyslipidemia with the use of a network pharmacology analysis approach.

Methods

Active compounds, targets of the SZHP, and targets for dyslipidemia were screened based on the public database. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment were performed on the database for annotation, visualization, and integrated discovery (DAVID 6.8). The compound-target-disease-pathway network was visualized using the Cytoscape software, and SYBYL was used for molecular docking.

Results

Twelve active compounds in the SZHP were screened out, which were closely connected to 186 dyslipidemia-related targets. The network analysis revealed that sitosterol, stigmasterol, isorhamnetin, kaempferol, and quercetin might be candidate agents and CCND1, CASP3, HIF1A, and ESR1 genes were potential drug targets. GO analysis revealed 856 biological processes (BP), 139 molecular functions (MF), and 89 cellular components (CC). The KEGG pathway enrichment analysis indicated that the lipid level and atherosclerosis might influence the treatment of dyslipidemia. Molecular docking showed that quercetin bound well to CCND1, HIF1A, MYC, AKT1, and EGFR genes. These findings were in accord with the prediction obtained through the network pharmacology approach.

Conclusions

This study revealed the primary pharmacological effects and relevant mechanisms of the SZHP in treating dyslipidemia. Our findings may facilitate the development of the SZHP or its active compounds as an alternative therapy for dyslipidemia. Still, more pharmacological experiments are needed for verification.

Polyphenols: benefits to the cardiovascular system in health and in aging

Numerous studies have demonstrated the importance of naturally occurring dietary polyphenols in promoting cardiovascular health and emphasized the significant role these compounds play in limiting the effects of cellular aging. Polyphenols such as resveratrol, epigallocatechin gallate (EGCG), and curcumin have been acknowledged for having beneficial effects on cardiovascular health, while some have also been shown to be protective in aging. This review highlights the literature surrounding this topic on the prominently studied and documented polyphenols as pertaining to cardiovascular health and aging.

Human metabolic transformation of quercetin blocks its capacity to decrease endothelial nitric oxide synthase (eNOS) expression and endothelin-1 secretion by human endothelial cells

The major dietary flavonol quercetin, which has been shown to improve endothelial function and decrease blood pressure, is extensively metabolized during absorption. This study examined the relative abilities of quercetin and its human metabolites to modulate the expression of eNOS and ET-1, which are involved in regulating endothelial homeostasis. Quercetin aglycone significantly reduced both eNOS protein and gene expression in HUVEC, mirroring the effects of the pro-inflammatory cytokine TNFα. In the presence of TNFα the aglycone caused further reductions in eNOS, whereas the metabolites were without effect in either TNFα-stimulated or unstimulated cells. ET-1 expression was significantly reduced by quercetin in both TNFα-stimulated or unstimulated HUVECs. The metabolites had no effect on ET-1 expression with the exception of quercetin-3'-sulfate, which caused a moderate increase in TNFα-stimulated cells. These results suggest that metabolic transformation of quercetin prevents it from causing a potentially deleterious decrease in eNOS in endothelial cells.

Advances in Nutritional Metabolomics

Metabolomics is maturing as an experimental approach in nutrition science, and it is a useful analysis for revealing systems biology outcomes associated with changes in diet. A major goal of this review is to present the rapidly evolving body of scientific literature that seeks to reveal connections between an individual's metabolic profile and experimentally manipulated or naturally varied dietary intakes. Metabolite profiles in tissue, serum, urine, or stool reflect changes in metabolic pathways that respond to dietary intervention which makes them accessible samples for revealing metabolic effects of diet. Three broadly defined areas of investigation related to dietary-metabolomic strategies include: (1) describing the metabolite variation within and between dietary exposures or interventions; (2) characterizing the metabolic response to dietary interventions with respect to time; and (3) assessing individual variation in baseline nutritional health and/or disease status. An overview of metabolites that were responsive to dietary interventions as reported from original research in human or animal studies is provided and illustrates the breadth of metabolites affected by dietary intervention. Advantages and drawbacks for assessing metabolic changes are discussed in relation to types of metabolite analysis platforms. A combination of targeted and non-targeted global profiling studies as a component of future dietary intervention trials will increase our understanding of nutrition in a systems context.

Protective effect of dietary flavonoid quercetin against lipemic-oxidative hepatic injury in hypercholesterolemic rats

CONTEXT

Quercetin, a dietary-derived flavonoid, is ubiquitous in fruits and vegetables and plays important roles in human health by virtue of its antioxidant activity.

OBJECTIVE

This study was conducted to investigate the possible modulatory effect of quercetin against hepatic lipemic-oxidative injury in rats fed with a high cholesterol diet (HCD), and to highlight the underlying mechanisms of such effect.

MATERIALS AND METHODS

Different groups of male Sprague-Dawley rats were used; one group was treated by gavage with HCD cocktail (1 mL/100 g) whereas another group was orally administered HCD-enriched with quercetin (15 mg/kg). Corresponding control animals were also used.

RESULTS

Quercetin administration significantly decreased liver triglycerides (24%), liver total cholesterol (TC) (22%), serum TC (20%), serum low-density lipoprotein cholesterol (31%), and duplicated serum high-density lipoprotein cholesterol (HDL-C). This study also revealed that quercetin administration significantly reduced the activity of serum alanine aminotransferase (41%), aspartate aminotransferase (51%), and γ-glutamyl transpeptidase (G-GT) (35%). Significant inhibition of thiobarbituric acid-reacting substances (40%), together with a valuable enhancement of reduced glutathione (GSH) content (53%) in the liver homogenates, was observed. In addition, quercetin-treated hypercholesterolemic animals exhibited a reasonable improvement of hepatic antioxidant enzymes. Moreover, serum and liver content of nitric oxide (NO) were markedly decreased in this model (26 and 25%, respectively), and were almost normalized following quercetin administration.

DISCUSSION AND CONCLUSION

These data revealed that quercetin has the ability to ameliorate HCD-induced lipemic-oxidative injury in rat liver possibly through its antioxidant potential and/or increased NO bioavailability.

Quercetin up-regulates LDL receptor expression in HepG2 cells

Quercetin, an abundant flavonol found in fruits and vegetable, has been implicated in lowering the risk of cardiovascular disease that is often associated with high plasma levels of low density lipoprotein (LDL) cholesterol. Here we investigated whether quercetin could modulate the expression of LDL receptors (LDLR) in HepG2 cells and the possible underlying mechanisms to exert quercetin's effects. We found that quercetin was able to induce LDLR expression with at least a 75 µ m concentration, which was accompanied by an increase in nuclear sterol regulatory element binding protein 2 (SREBP2). This effect was mediated by activation of c-jun-N-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK) signalling pathways as implicated by experiments using chemical inhibitors of each pathway. When cells were challenged with protein synthesis inhibitors in quercetin-activated LDLR transcription, LDL mRNA levels were not significantly affected by cycloheximide but puromycin abolished quercetin-induced LDLR transcription. Taken together, we conclude that quercetin can initiate LDLR transcription by enhancing SREBP2 processing, but new protein synthesis might be necessary to exert a maximum effect of quercetin in the up-regulation of the LDLR gene. Our findings demonstrate that quercetin strongly up-regulated LDLR gene expression, which might elicit hypolipidemic effects by increasing the clearance of circulating LDL cholesterol levels from the blood.