Inhibition of apoB secretion from HepG2 cells by insulin is amplified by naringenin, independent of the insulin receptor

Naringin and Naringenin: Potential Multi-Target Agents for Alzheimer's Disease

Alzheimer's disease (AD) is one of the most common forms of neurodegenerative dementia. The etiology of AD is multifactorial, and its complex pathophysiology involves tau and amyloid-β deposition, increased oxidative stress, neuroinflammation, metabolic disorders, and massive neuronal loss. Due to its complex pathology, no effective cure for AD has been found to date. Therefore, there is an unmet clinical need for the development of new drugs against AD. Natural products are known to be good sources of compounds with pharmacological activity and have potential for the development of new therapeutic agents. Naringin, a naturally occurring flavanone glycoside, is predominantly found in citrus fruits and Chinese medicinal herbs. Mounting evidence shows that naringin and its aglycone, naringenin, have direct neuroprotective effects on AD, such as anti-amyloidogenic, antioxidant, anti-acetylcholinesterase, and anti-neuroinflammatory effects, as well as metal chelation. Furthermore, they are known to improve disordered glucose/lipid metabolism, which is a high risk factor for AD. In this review, we summarize the latest data on the impact of naringin and naringenin on the molecular mechanisms involved in AD pathophysiology. Additionally, we provide an overview of the current clinical applications of naringin and naringenin. The novel delivery systems for naringin and naringenin, which can address their widespread pharmacokinetic limitations, are also discussed. The literature indicates that naringin and naringenin could be multilevel, multitargeted, and multifaceted for preventing and treating AD.

Exploration of potential targets and mechanisms of naringenin in the treatment of nonalcoholic fatty liver disease through network pharmacology

OBJECTIVE

This study aimed to use network pharmacology to investigate the molecular mechanisms and potential targets of naringenin (NR) for nonalcoholic fatty liver disease (NAFLD) treatment to offer new drug development ideas.

METHODS

The structure and compound information of NR were obtained from PubChem and the traditional Chinese medicine system pharmacology database and analysis platform. The traditional Chinese medicine system pharmacology database and analysis platform Database, Comparative Toxicogenomics Database and Encyclopedia of Traditional Chinese Medicine Database were then used to predict the related targets of NR. Online mendelian inheritance in man, Disgenet, Gene cards, The therapeutic target database and Drug bank were used to screen NAFLD targets, and the intersection analysis was performed with the targets of NR active components to obtain the targets of NR in the treatment of NAFLD. The protein-protein interaction network of therapeutic targets was constructed by protein-protein interaction networks functional enrichment analysis 11.0, and gene ontology (GO) functional enrichment analysis and Kyoto encyclopedia of genes and genomes pathway enrichment analysis of therapeutic targets was performed by Metascape platform.

RESULTS

In this study, 171 NR targets and 1748 potential targets of NAFLD were screened, and 89 crossover targets and 16 core targets were screened and finally obtained. A total of 176 GO items were obtained by GO enrichment analysis (P < .05), including 389 biological process, 6 cell composition and 30 molecular function. A total of 137 signaling pathways were obtained by Kyoto encyclopedia of genes and genomes pathway enrichment and screening (P < .05). The core targets of NR in the treatment of NAFLD are TP53, CASP3, PRKCA, AKT1, RELA, PPARG, NCOA2, CYP1A1, ESR1, MAPK3, STAT3, JAK1, MAPK1, TNF, PPARA and PRKCB. Enrichment analysis showed that NR mainly involved in biological processes such as cellular response to nitrogen compound, regulation of miRNA transcription and negative regulation of miRNA-mediated gene silencing. It regulates Hepatitis B, Lipid and atherosclerosis, cytomegalovirus infection, Hepatitis C, AGE-RAGE signaling pathway in diabetic patients complications and other ways play a role in the treatment of NAFLD.

CONCLUSIONS

The therapeutic effect of NR on NAFLD has the characteristics of multi-targets and multi-pathways, which provides a preliminary theoretical basis for clinical trials and the development of new drugs.

Natural Foods for the Treatment of Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is one of the most common chronic liver diseases worldwide. The etiology of NAFLD is highly heterogeneous, which occurs and develops under the joint action of metabolism, inflammation, genetics, environment, and gut microbiota. At present, the principal therapeutic modalities targeting NAFLD are lifestyle interventions such as weight loss through diet and exercise. At present, there is no established therapy for the treatment of NAFLD, and many therapies are associated with a variety of side effects. A great number of in vitro and in vivo experiments have indicated that there are many natural foods that have therapeutic potential for NAFLD. This review summarizes the natural foods and their mechanisms that were found in recent years, furthermore, provides further information relevant to the treatment of NAFLD.

Beneficial Effects of Citrus Flavanones Naringin and Naringenin and Their Food Sources on Lipid Metabolism: An Update on Bioavailability, Pharmacokinetics, and Mechanisms

Naringin and naringin's aglycone naringenin belong to a subclass of flavonoids called flavanones. While many studies of pure naringenin and naringin and their food sources have shown beneficial health effects, including improved lipid metabolism, in animals and humans, the mechanisms underlying the lipid-lowering effects have not been completely understood. In recent years, multiple studies using various in vitro and rodent models have revealed new mechanisms underlying the hypolipidemic effects of naringin and naringenin, including regulation of lipid digestion, reverse cholesterol transport, and LDL receptor expression. In addition, naringin and naringenin show diverse effects in populations with different health conditions, such as obesity and diabetes. Furthermore, a novel naringin and naringenin enriched food source citrus bergamia (bergamot) and other citrus fruits have recently been studied for lipid-lowering effects in animal models and human clinical trials. In this review, we provide an update on recent advances on naringin and naringenin and their enriched food sources on lipid metabolism and underlying mechanisms. Because absorption, distribution, metabolism, and excretion, particularly in the presence of food matrix, impact the bioavailability, which in turn affects the bioactivities of these flavonoids in vivo, we also summarize new findings from the pharmacokinetics studies and on interplays between naringin and naringenin and gut microbiota.

Effects of naringenin supplementation in overweight/obese patients with non-alcoholic fatty liver disease: study protocol for a randomized double-blind clinical trial

Introduction

Non-alcoholic fatty liver disease (NAFLD) is one of the main causes of chronic liver disease worldwide. Flavonoids, a group of natural compounds, have garnered a great deal of attention in the management of NAFLD because of their profitable effects on glucose and lipid metabolism, inflammation, and oxidative stress which are the pivotal pathophysiological pathways in NAFLD. Naringenin is a citrus-derived flavonoid with a broad spectrum of potential biological effects including anti-inflammatory and antioxidant properties, which may exert protective effects against NAFLD. The present clinical trial aims to examine the efficacy of naringenin supplementation on plasma adiponectin and neurogulin-4 (NRG-4) concentrations, metabolic parameters, and liver function indices in overweight/obese patients with NAFLD.

Methods and analysis

This is a double-blind, randomized, placebo-controlled clinical study that will investigate the impacts of naringenin supplementation in overweight/obese patients with NAFLD. Liver ultrasonography will be applied to diagnose NAFLD. Forty-four eligible overweight/obese subjects with NAFLD will be selected and randomly assigned to receive naringenin capsules or identical placebo (each capsule contains 100 mg of naringenin or cellulose), twice daily for 4 weeks. Participants will be asked to remain on their usual diet and physical activity. Safety of naringenin supplementation was confirmed by the study pharmacist. The primary outcome of this study is changes in adiponectin circulating levels. The secondary outcomes include changes in NRG-4 levels, liver function indices, metabolic parameters, body weight, body mass index (BMI), waist circumference (WC), blood pressure, and hematological parameters. Statistical analysis will be conducted using the SPSS software (version 25), and P value less than 0.05 will be regarded as statistically significant.

Discussion

We hypothesize that naringenin administration may be useful for treating NAFLD by modulating energy balance, glucose and lipid metabolism, oxidative stress, and inflammation through different mechanisms. The current trial will exhibit the effects of naringenin, whether negative or positive, on NAFLD status.

Ethical aspects

The current trial received approval from the Medical Ethics Committee of Tehran University of Medical Sciences, Tehran, Iran (IR.TUMS.MEDICNE.REC.1399.439).

Trial registration

Iranian Registry of Clinical Trials IRCT201311250155336N12. Registered on 6 June 2020

Supplementary Information

The online version contains supplementary material available at 10.1186/s13063-021-05784-7.

Does naringenin supplementation improve lipid profile, severity of hepatic steatosis and probability of liver fibrosis in overweight/obese patients with NAFLD? A randomised, double-blind, placebo-controlled, clinical trial

BACKGROUND AND OBJECTIVES

Naringenin has been reported to have some promising pharmacological effects on the management of obesity and related metabolic complications including non-alcoholic fatty liver disease (NAFLD). Therefore, the present clinical trial study was done to assess the effects of naringenin supplementation on lipid profile, aminotransferase levels, severity of steatosis, as well as probability of fibrosis in overweight/obese patients with NAFLD.

MATERIALS AND METHODS

This placebo-controlled, parallel randomised, double-blind clinical trial study was conducted on 44 eligible overweight/obese patients with NAFLD (naringenin-treated group (n = 22), control group (n = 22)) referred to the national Iranian oil company (NIOC) Central Hospital, Tehran City, Tehran Province, Iran. Participants were randomly assigned to receive naringenin capsules (100 mg) and identical placebo capsules twice a day, before lunch and dinner, for 4 weeks. The primary outcomes were improvement of liver steatosis and NAFLD fibrosis score (NFS), and secondary outcomes included changes in levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST) and lipid profile.

RESULTS

Naringenin consumption significantly reduced percentages of NAFLD grades (P < .001), as well as, serum levels of triglyceride (TG) (P < .001), total cholesterol (TC) (P = .01), and low-density lipoprotein (LDL) (P = .02) and increased serum level of high-density lipoprotein (HDL) (P = .02) compared with the control group. Even after adjusting for the confounders, the results were significant. However, there were no significant changes in AST, ALT and NFS.

CONCLUSION

Our findings revealed that daily intake of 200 mg of naringenin for 4 weeks had beneficial effects on lipid profile and percentages of NAFLD grades as an indicator for the severity of hepatic steatosis. Although, NFS values and serum levels of aminotransferase enzymes including AST and ALT did not remarkably change.

Chronic Alcohol Exposure of Cells Using Controlled Alcohol-Releasing Capillaries

Alcohol is one of the main causes of liver diseases such as fatty liver, alcoholic hepatitis, and chronic hepatitis with liver fibrosis or cirrhosis. To reproduce the conditions of alcohol-induced liver diseases and to identify the disease-causing mechanisms at the cellular level, several methods have been used to expose the cells to ethanol. As ethanol evaporates easily, it is difficult to mimic chronic alcohol exposure conditions at the cellular level. In this study, we developed a glass capillary system containing ethanol, which could steadily release ethanol from the polyethylene tubing and hydrogel portion at both sides of the capillary. The ethanol-containing capillary could release ethanol in the cell culture medium for up to 144 h, and the concentration of ethanol in the cell culture medium could be adjusted by controlling the number of capillaries. A long-term exposure to ethanol by the capillary system led to an increased toxicity of cells and altered the cellular physiologies, such as increasing the lipid accumulation and hepatic transaminase release in cells, as compared to the traditional direct ethanol addition method. Ethanol capillaries showed different gene expression patterns of lipid accumulation- or chronic alcoholism-related genes. Our results suggest that our ethanol-containing capillary system can be used as a valuable tool for studying the mechanism of chronic alcohol-mediated hepatic diseases at the cellular level.

A Comprehensive Systematic Review of the Effects of Naringenin, a Citrus-Derived Flavonoid, on Risk Factors for Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) has become the most common cause of liver dysfunction worldwide. Recently, some natural compounds have attracted growing interest in the treatment of NAFLD. In this context, most attention has been paid to natural products derived from fruits, vegetables, and medicinal herbs. Naringenin, a natural flavanone, has been revealed to have pharmacological effects in the treatment of obesity and associated metabolic disorders such as NAFLD. The aim of this study was to examine the therapeutic effects of naringenin and its possible mechanisms of action in the management of NAFLD and related risk factors. The current systematic review was performed according to the guidelines of the 2015 PRISMA (Preferred Reporting Items for Systematic Review and Meta-Analysis) statements. We searched PubMed/Medline, Science Direct, Scopus, ProQuest, and Google Scholar databases up until February 2020. Of 1217 full-text articles assessed, 36 studies met the inclusion criteria. The evidence reviewed in the present study indicates that naringenin modulates several biological processes related to NAFLD including energy balance, lipid and glucose metabolism, inflammation, and oxidative stress by different mechanisms. Overall, the favorable effects of naringenin along with its more potency and efficacy, compared with other antioxidants, indicate that naringenin may be a promising therapeutic approach for the management of NAFLD and associated complications. However, due to the lack of clinical trials, future robust human randomized clinical trials that address the effects of naringenin on NAFLD and other liver-related diseases are crucial. Further careful human pharmacokinetic studies are also needed to establish dosage ranges, as well as addressing preliminary safety and tolerability of naringenin, before proceeding to larger-scale endpoint trials.

Flavonoids from Aurantii Fructus Immaturus and Aurantii Fructus: promising phytomedicines for the treatment of liver diseases

Background

Liver diseases and related complications are major sources of morbidity and mortality, which places a huge financial burden on patients and lead to nonnegligible social problems. Therefore, the discovery of novel therapeutic drugs for the treatment of liver diseases is urgently required. Aurantii Fructus Immaturus (AFI) and Aurantii Fructus (AF) are frequently used herbal medicines in traditional Chinese medicine (TCM) formulas for the treatment of diverse ailments. A variety of bioactive ingredients have been isolated and identified from AFI and AF, including alkaloids, flavonoids, coumarins and volatile oils.

Main body

Emerging evidence suggests that flavonoids, especially hesperidin (HD), naringenin (NIN), nobiletin (NOB), naringin (NRG), tangeretin (TN), hesperetin (HT) and eriodictyol (ED) are major representative bioactive ingredients that alleviate diseases through multi-targeting mechanisms, including anti-oxidative stress, anti-cytotoxicity, anti-inflammation, anti-fibrosis and anti-tumor mechanisms. In the current review, we summarize the recent progress in the research of hepatoprotective effects of HD, NIN, NOB, NRG, TN, HT and ED and highlight the potential underlying molecular mechanisms. We also point out the limitations of the current studies and shed light on further in-depth pharmacological and pharmacokinetic studies of these bioactive flavonoids.

Conclusion

This review outlines the recent advances in the literature and highlights the potential of these flavonoids isolated from AFI and AF as therapeutic agents for the treatment of liver diseases. Further pharmacological studies will accelerate the development of natural products in AFI and AF and their derivatives as medicines with tantalizing prospects in the clinical application.

Global view of the RAF-MEK-ERK module and its immediate downstream effectors

Small molecule inhibitors of BRAF and MEK have proven effective at inhibiting tumor growth in melanoma patients, however this efficacy is limited due to the almost universal development of drug resistance. To provide advanced insight into the signaling responses that occur following kinase inhibition we have performed quantitative (phospho)-proteomics of human melanoma cells treated with either dabrafenib, a BRAF inhibitor; trametinib, a MEK inhibitor or SCH772984, an ERK inhibitor. Over nine experiments we identified 7827 class I phosphorylation sites on 4960 proteins. This included 54 phosphorylation sites that were significantly down-modulated after exposure to all three inhibitors, 34 of which have not been previously reported. Functional analysis of these novel ERK targets identified roles for them in GTPase activity and regulation, apoptosis and cell-cell adhesion. Comparison of the results presented here with previously reported phosphorylation sites downstream of ERK showed a limited degree of overlap suggesting that ERK signaling responses may be highly cell line and cue specific. In addition we identified 26 phosphorylation sites that were only responsive to dabrafenib. We provide further orthogonal experimental evidence for 3 of these sites in human embryonic kidney cells over-expressing BRAF as well as further computational insights using KinomeXplorer. The validated phosphorylation sites were found to be involved in actin regulation, which has been proposed as a novel mechanism for inhibiting resistance development. These results would suggest that the linearity of the BRAF-MEK-ERK module is at least context dependent.

Antidiabetic Properties of Naringenin: A Citrus Fruit Polyphenol

Type 2 diabetes mellitus (T2DM) is a metabolic disease characterized by insulin resistance and hyperglycemia and is associated with personal health and global economic burdens. Current strategies/approaches of insulin resistance and T2DM prevention and treatment are lacking in efficacy resulting in the need for new preventative and targeted therapies. In recent years, epidemiological studies have suggested that diets rich in vegetables and fruits are associated with health benefits including protection against insulin resistance and T2DM. Naringenin, a citrus flavanone, has been reported to have antioxidant, anti-inflammatory, hepatoprotective, nephroprotective, immunomodulatory and antidiabetic properties. The current review summarizes the existing in vitro and in vivo animal studies examining the anti-diabetic effects of naringenin.

Beneficial Effects of Citrus Flavonoids on Cardiovascular and Metabolic Health

The prevalence of cardiovascular disease (CVD) is increasing over time. CVD is a comorbidity in diabetes and contributes to premature death. Citrus flavonoids possess several biological activities and have emerged as efficient therapeutics for the treatment of CVD. Citrus flavonoids scavenge free radicals, improve glucose tolerance and insulin sensitivity, modulate lipid metabolism and adipocyte differentiation, suppress inflammation and apoptosis, and improve endothelial dysfunction. The intake of citrus flavonoids has been associated with improved cardiovascular outcomes. Although citrus flavonoids exerted multiple beneficial effects, their mechanisms of action are not completely established. In this review, we summarized recent findings and advances in understanding the mechanisms underlying the protective effects of citrus flavonoids against oxidative stress, inflammation, diabetes, dyslipidemia, endothelial dysfunction, and atherosclerosis. Further studies and clinical trials to assess the efficacy and to explore the underlying mechanism(s) of action of citrus flavonoids are recommended.

Raw orange intake is associated with higher prevalence of non-alcoholic fatty liver disease in an adult population

OBJECTIVES

Non-alcoholic fatty liver disease (NAFLD) is one of the most common public health issues worldwide. Oranges are the most popular fruit consumed in the world. Admittedly, flavonoids in oranges act as antioxidants and improve liver steatosis. However, oranges also are rich in fructose, which is a risk factor in the progress of NAFLD. Therefore, we hypothesize that orange intake may be a double-edged sword in the development of NAFLD. To our knowledge, there currently is little evidence of the effect of dietary orange intake on NAFLD. The aim of this study was to investigate how orange intake is related to NAFLD in a general adult population.

METHODS

We randomly recruited 27,214 adults into the Tianjin Chronic Low-Grade Systemic Inflammation and Health Cohort Study. NAFLD was diagnosed by liver ultrasonography. Raw orange intake was assessed by a validated self-administered food frequency questionnaire. Multiple logistic regression analysis was used to evaluate the association between orange intake and the prevalence of NAFLD.

RESULTS

There was a 27.18% prevalence of NAFLD among the participants. Consumption of orange was positively associated with the prevalence of NAFLD after adjustment for all potential confounding factors (P_trend = 0.04). The odds ratios (95% confidence interval) of the categories of orange intake in the NAFLD were 1.00 (reference) for less than once per week, 1.02 (0.95-1.11) for 1 to 6 times per week, and 1.17 (1.03-1.33) for ≥7 times per week, respectively.

CONCLUSIONS

The present study demonstrated that orange intake is positively associated with the prevalence of NAFLD.

Intervention with citrus flavonoids reverses obesity and improves metabolic syndrome and atherosclerosis in obese Ldlr-/- mice

Obesity and its associated metabolic dysfunction and cardiovascular disease risk represent a leading cause of adult morbidity worldwide. Currently available pharmacological therapies for obesity have had limited success in reversing existing obesity and metabolic dysregulation. Previous prevention studies demonstrated that the citrus flavonoids, naringenin and nobiletin, protect against obesity and metabolic dysfunction in Ldlr^-/- mice fed a high-fat cholesterol-containing (HFHC) diet. However, their effects in an intervention model are unknown. In this report, we show that, in Ldlr^-/- mice with diet-induced obesity, citrus flavonoid supplementation to a HFHC diet reversed existing obesity and adipocyte size and number through enhanced energy expenditure and increased hepatic fatty acid oxidation. Caloric intake was unaffected and no evidence of white adipose tissue browning was observed. Reversal of adiposity was accompanied by improvements in hyperlipidemia, insulin sensitivity, hepatic steatosis, and a modest reduction in blood monocytes. Together, this resulted in atherosclerotic lesions that were unchanged in size, but characterized by reduced macrophage content, consistent with a more stable plaque phenotype. These studies further suggest potential therapeutic utility of citrus flavonoids, especially in the context of existing obesity, metabolic dysfunction, and cardiovascular disease.

Beneficial effects of naringenin in liver diseases: Molecular mechanisms

Liver diseases are caused by different etiological agents, mainly alcohol consumption, viruses, drug intoxication or malnutrition. Frequently, liver diseases are initiated by oxidative stress and inflammation that lead to the excessive production of extracellular matrix (ECM), followed by a progression to fibrosis, cirrhosis and hepatocellular carcinoma (HCC). It has been reported that some natural products display hepatoprotective properties. Naringenin is a flavonoid with antioxidant, antifibrogenic, anti-inflammatory and anticancer properties that is capable of preventing liver damage caused by different agents. The main protective effects of naringenin in liver diseases are the inhibition of oxidative stress, transforming growth factor (TGF-β) pathway and the prevention of the transdifferentiation of hepatic stellate cells (HSC), leading to decreased collagen synthesis. Other effects include the inhibition of the mitogen activated protein kinase (MAPK), toll-like receptor (TLR) and TGF-β non-canonical pathways, the inhibition of which further results in a strong reduction in ECM synthesis and deposition. In addition, naringenin has shown beneficial effects on nonalcoholic fatty liver disease (NAFLD) through the regulation of lipid metabolism, modulating the synthesis and oxidation of lipids and cholesterol. Moreover, naringenin protects from HCC, since it inhibits growth factors such as TGF-β and vascular endothelial growth factor (VEGF), inducing apoptosis and regulating MAPK pathways. Naringenin is safe and acts by targeting multiple proteins. However, it possesses low bioavailability and high intestinal metabolism. In this regard, formulations, such as nanoparticles or liposomes, have been developed to improve naringenin bioavailability. We conclude that naringenin should be considered in the future as an important candidate in the treatment of different liver diseases.

Identification and characterization of a FOXA2-regulated transcriptional enhancer at a type 2 diabetes intronic locus that controls GCKR expression in liver cells

BACKGROUND

Genome-wide association studies (GWAS) have identified more than 100 genetic loci associated with type 2 diabetes (T2D). However, the underlying biological mechanisms for many of these associations remain unknown. GWAS signals close to the glucokinase regulatory protein gene (GCKR) have been reported for lipid and glucose metabolism traits and the risk of T2D. We investigated the regulatory function of an intronic locus at GCKR represented by the lead single nucleotide polymorphism (SNP) rs780094.

METHODS

We used ENCODE project histone modification and transcription factor binding data to determine the regulatory features of a GCKR intronic locus formed by the high linkage disequilibrium rs780094(C/T), rs780095(G/A), and rs780096(G/C) SNPs. Characterization of the transcriptional activity of this region was assessed by luciferase reporter assays in HepG2 cells and mouse primary hepatocytes. ChIP-qPCR was used to determine the levels of haplotype specific transcription factor binding and histone marks. A CRISPR-dCas9 transcriptional activator system and qPCR were used to activate the locus and measure GCKR expression, respectively. Differential haplotype expression was measured from human liver biopsies.

RESULTS

The ENCODE data suggest the existence of a liver-specific intragenic enhancer at the locus represented by s780094. We observed that FOXA2 increased the transcriptional activity of this region in a haplotype specific way (CGG > TAC; rs780094, rs780095, and rs780096). In addition, the CGG haplotype showed higher binding to FOXA2 and higher levels of the H3K27Ac histone mark. The epigenetic activation of this locus increased the expression of endogenous GCKR in HepG2 cells, confirming that GCKR is the direct target gene of the enhancer. Finally, we confirmed that the CGG haplotype exhibits higher levels of transcription in human liver.

CONCLUSIONS

Our results demonstrate the existence of a liver-specific FOXA2-regulated transcriptional enhancer at an intronic T2D locus represented by rs780094, rs780095, and rs780096 SNPs that increases GCKR expression. Differential haplotype regulation suggests the existence of cis regulatory effects that may contribute to the associated traits at this locus.

Naringenin ameliorates streptozotocin-induced diabetic rat renal impairment by downregulation of TGF-β1 and IL-1 via modulation of oxidative stress correlates with decreased apoptotic events

CONTEXT

Naringenin, a flavonone and a nutritive antioxidant which is mostly obtained from grapefruit, orange or tomato skin, has been extensively studied due to its radical scavenging activity.

OBJECTIVE

The present study investigates the protective effect of naringenin on rat kidney after streptozotocin-induced diabetes.

MATERIALS AND METHODS

Sixty male Wistar rats were divided into six groups. Diabetes was induced by a single intraperitoneal injection of streptozotocin (50 mg/kg) in groups II, III and IV. Naringenin 5 mg/kg body weight was given to groups III and V, but 10 mg/kg was given to groups IV and VI, orally once a day for 10 weeks. After which all animals were sacrificed, and the biochemical, histopathological, immunohistochemical and apoptotic assays were conducted.

RESULTS

Naringenin treatment with 5 and 10 mg/kg significantly decreased (p < 0.05) the serum biochemical parameters, elevated tissue malondialdehyde levels and increased (p < 0.01) the reduced superoxide dismutase, catalase and reduced glutathione enzyme activities in the diabetic kidney. Diabetes-induced naringenin-treated groups showed an improved histology and revealed a significant reduction in apoptosis activity (7.2 ± 0.01 and 1.8 ± 0.05) and in expression of TGF-β1 (18.9 ± 3.4 and 10.2 ± 2.1) at a dose of 5 and 10 mg/kg, respectively. Similarly, in contrast to the diabetic group, a significant difference was observed in the IL-1 expression (15.68 ± 4.3) in 5 mg/kg and (9.85 ± 2.1) in 10 mg/kg naringenin-treated groups.

CONCLUSION

Naringenin acts as a protective agent in diabetic renal impairment by altering oxidative stress, modulation of cytokines expression and apoptotic events.

Citrus Flavonoids as Regulators of Lipoprotein Metabolism and Atherosclerosis

Citrus flavonoids are polyphenolic compounds with significant biological properties. This review summarizes recent advances in understanding the ability of citrus flavonoids to modulate lipid metabolism, other metabolic parameters related to the metabolic syndrome, and atherosclerosis. Citrus flavonoids, including naringenin, hesperitin, nobiletin, and tangeretin, have emerged as potential therapeutics for the treatment of metabolic dysregulation. Epidemiological studies reveal an association between the intake of citrus flavonoid-containing foods and a decreased incidence of cardiovascular disease. Studies in cell culture and animal models, as well as a limited number of clinical studies, reveal the lipid-lowering, insulin-sensitizing, antihypertensive, and anti-inflammatory properties of citrus flavonoids. In animal models, supplementation of rodent diets with citrus flavonoids prevents hepatic steatosis, dyslipidemia, and insulin resistance primarily through inhibition of hepatic fatty acid synthesis and increased fatty acid oxidation. Citrus flavonoids blunt the inflammatory response in metabolically important tissues including liver, adipose, kidney, and the aorta. The mechanisms underlying flavonoid-induced metabolic regulation have not been completely established, although several potential targets have been identified. In mouse models, citrus flavonoids show marked suppression of atherogenesis through improved metabolic parameters as well as through direct impact on the vessel wall. Recent studies support a role for citrus flavonoids in the treatment of dyslipidemia, insulin resistance, hepatic steatosis, obesity, and atherosclerosis. Larger human studies examining dose, bioavailability, efficacy, and safety are required to promote the development of these promising therapeutic agents.

Activity and mRNA Levels of Enzymes Involved in Hepatic Fatty Acid Synthesis in Rats Fed Naringenin

We investigated the physiological activity of naringenin in affecting hepatic lipogenesis and serum and liver lipid levels in rats. Rats were fed diets containing 0, 1, or 2.5 g/kg naringenin for 15 d. Naringenin at a dietary level of 2.5 g/kg significantly decreased the activities and the mRNA levels of various lipogenic enzymes and sterol regulatory element binding protein-1c (SREBP-1c) mRNA level. The activities and the mRNA levels were also 9-22% and 12-38% lower, respectively, in rats fed a 1 g/kg naringenin diet than in the animals fed a naringenin-free diet, although the differences were not significant in many cases. Naringenin at 2.5 g/kg significantly lowered serum triacylglycerol, cholesterol, and phospholipid and hepatic triacylglycerol and cholesterol. This flavonoid at 1.0 g/kg also significantly lowered these parameters except for serum triacylglycerol. Naringenin levels in serum and liver dose-dependently increased, and hepatic concentrations reached levels that can affect various signaling pathways.

Naringenin prevents obesity, hepatic steatosis, and glucose intolerance in male mice independent of fibroblast growth factor 21

The molecular mechanisms and metabolic pathways whereby the citrus flavonoid, naringenin, reduces dyslipidemia and improves glucose tolerance were investigated in C57BL6/J wild-type mice and fibroblast growth factor 21 (FGF21) null (Fgf21(-/-)) mice. FGF21 regulates energy homeostasis and the metabolic adaptation to fasting. One avenue of this regulation is through induction of peroxisome proliferator-activated receptor-γ coactivator-1α (Pgc1a), a regulator of hepatic fatty acid oxidation and ketogenesis. Because naringenin is a potent activator of hepatic FA oxidation, we hypothesized that induction of FGF21 might be an integral part of naringenin's mechanism of action. Furthermore, we predicted that FGF21 deficiency would potentiate high-fat diet (HFD)-induced metabolic dysregulation and compromise metabolic protection by naringenin. The absence of FGF21 exacerbated the response to a HFD. Interestingly, naringenin supplementation to the HFD robustly prevented obesity in both genotypes. Gene expression analysis suggested that naringenin was not primarily targeting fatty acid metabolism in white adipose tissue. Naringenin corrected hepatic triglyceride concentrations and normalized hepatic expression of Pgc1a, Cpt1a, and Srebf1c in both wild-type and Fgf21(-/-) mice. HFD-fed Fgf21(-/-) mice displayed greater muscle triglyceride deposition, hyperinsulinemia, and impaired glucose tolerance as compared with wild-type mice, confirming the role of FGF21 in insulin sensitivity; however, naringenin supplementation improved these metabolic parameters in both genotypes. We conclude that FGF21 deficiency exacerbates HFD-induced obesity, hepatic steatosis, and insulin resistance. Furthermore, FGF21 is not required for naringenin to protect mice from HFD-induced metabolic dysregulation. Collectively these studies support the concept that naringenin has potent lipid-lowering effects and may act as an insulin sensitizer in vivo.

SREBP-1c overexpression induces triglycerides accumulation through increasing lipid synthesis and decreasing lipid oxidation and VLDL assembly in bovine hepatocytes

The natural incidence of fatty liver in ruminants is significantly higher than in monogastric animals. Fatty liver is associated with sterol regulatory element-binding protein 1c (SREBP-1c). The aim of this study was to investigate the regulatory network effects of SREBP-1c on the lipid metabolic genes involved in fatty acid uptake, activation, oxidation, synthesis, and very low-density lipoprotein (VLDL) assembly in bovine hepatocytes. In vitro, bovine hepatocytes were transfected with an adenovirus-mediated SREBP-1c overexpression vector. SREBP-1c overexpression significantly up-regulated the expression and activity of the fatty acid uptake, activation, and synthesis enzymes: liver fatty acid binding protein, fatty acid translocase, acyl-CoA synthetase long-chain 1, acetyl-CoA carboxylase 1, and fatty acid synthase, increasing triglyceride (TG) synthesis and accumulation. SREBP-1c overexpression down-regulated the expression and activity of the lipid oxidation enzymes: carnitine palmitoyltransferase 1 and carnitine palmitoyltransferase 2. Furthermore, the apolipoprotein B100 expression and microsomal triglyceride transfer protein activity were significantly decreased. SREBP-1c overexpression reduced lipid oxidation and VLDL synthesis, thereby decreasing TG disposal and export. Therefore, large amounts of TG accumulated in the bovine hepatocytes. Taken together, these results indicate that SREBP-1c overexpression increases lipid synthesis and decreases lipid oxidation and VLDL export, thereby inducing TG accumulation in bovine hepatocytes.

Effect of citrus flavonoids, naringin and naringenin, on metabolic syndrome and their mechanisms of action

Flavonoids are important natural compounds with diverse biologic activities. Citrus flavonoids constitute an important series of flavonoids. Naringin and its aglycone naringenin belong to this series of flavonoids and were found to display strong anti-inflammatory and antioxidant activities. Several lines of investigation suggest that naringin supplementation is beneficial for the treatment of obesity, diabetes, hypertension, and metabolic syndrome. A number of molecular mechanisms underlying its beneficial activities have been elucidated. However, their effect on obesity and metabolic disorder remains to be fully established. Moreover, the therapeutic uses of these flavonoids are significantly limited by the lack of adequate clinical evidence. This review aims to explore the biologic activities of these compounds, particularly on lipid metabolism in obesity, oxidative stress, and inflammation in context of metabolic syndrome.

Apolipoprotein B100 quality control and the regulation of hepatic very low density lipoprotein secretion

Apolipoprotein B (apoB) is the main protein component of very low density lipoprotein (VLDL) and is necessary for the assembly and secretion of these triglyceride (TG)-rich particles. Following release from the liver, VLDL is converted to low density lipoprotein (LDL) in the plasma and increased production of VLDL can therefore play a detrimental role in cardiovascular disease. Increasing evidence has helped to establish VLDL assembly as a target for the treatment of dyslipidemias. Multiple factors are involved in the folding of the apoB protein and the formation of a secretion-competent VLDL particle. Failed VLDL assembly can initiate quality control mechanisms in the hepatocyte that target apoB for degradation. ApoB is a substrate for endoplasmic reticulum associated degradation (ERAD) by the ubiquitin proteasome system and for autophagy. Efficient targeting and disposal of apoB is a regulated process that modulates VLDL secretion and partitioning of TG. Emerging evidence suggests that significant overlap exists between these degradative pathways. For example, the insulin-mediated targeting of apoB to autophagy and postprandial activation of the unfolded protein response (UPR) may employ the same cellular machinery and regulatory cues. Changes in the quality control mechanisms for apoB impact hepatic physiology and pathology states, including insulin resistance and fatty liver. Insulin signaling, lipid metabolism and the hepatic UPR may impact VLDL production, particularly during the postprandial state. In this review we summarize our current understanding of VLDL assembly, apoB degradation, quality control mechanisms and the role of these processes in liver physiology and in pathologic states.

Citrus flavanones: what is their role in cardiovascular protection?

Flavanones, including hesperidin and naringin, are polyphenolic compounds highly and almost exclusively present in citrus. Epidemiological studies reported an inverse relationship between their intake and the risk of cardiovascular diseases. Clinical and experimental data further showed their antihypertensive, lipid-lowering, insulin-sensitizing, antioxidative, and anti-inflammatory properties, which could explain their antiatherogenic action in animal models. Although flavanones may be promising compounds that are particularly active in cardiovascular disease prevention, clinical data are still scarce and most in vitro data have been obtained under nonphysiologically relevant conditions. Moreover, the mechanisms responsible for flavanone action are not fully elucidated. Therefore, further research is needed to better evaluate and understand the protective effects of flavanones in cardiovascular diseases.

Nobiletin attenuates VLDL overproduction, dyslipidemia, and atherosclerosis in mice with diet-induced insulin resistance

OBJECTIVE

Increased plasma concentrations of apolipoprotein B100 often present in patients with insulin resistance and confer increased risk for the development of atherosclerosis. Naturally occurring polyphenolic compounds including flavonoids have antiatherogenic properties. The aim of the current study was to evaluate the effect of the polymethoxylated flavonoid nobiletin on lipoprotein secretion in cultured human hepatoma cells (HepG2) and in a mouse model of insulin resistance and atherosclerosis.

RESEARCH DESIGN AND METHODS

Lipoprotein secretion was determined in HepG2 cells incubated with nobiletin or insulin. mRNA abundance was evaluated by quantitative real-time PCR, and Western blotting was used to demonstrate activation of cell signaling pathways. In LDL receptor-deficient mice (Ldlr(-/-)) fed a Western diet supplemented with nobiletin, metabolic parameters, gene expression, fatty acid oxidation, glucose homeostasis, and energy expenditure were documented. Atherosclerosis was quantitated by histological analysis.

RESULTS

In HepG2 cells, activation of mitogen-activated protein kinase-extracellular signal-related kinase signaling by nobiletin or insulin increased LDLR and decreased MTP and DGAT1/2 mRNA, resulting in marked inhibition of apoB100 secretion. Nobiletin, unlike insulin, did not induce phosphorylation of the insulin receptor or insulin receptor substrate-1 and did not stimulate lipogenesis. In fat-fed Ldlr(-/-) mice, nobiletin attenuated dyslipidemia through a reduction in VLDL-triglyceride (TG) secretion. Nobiletin prevented hepatic TG accumulation, increased expression of Pgc1α and Cpt1α, and enhanced fatty acid β-oxidation. Nobiletin did not activate any peroxisome proliferator-activated receptor (PPAR), indicating that the metabolic effects were PPAR independent. Nobiletin increased hepatic and peripheral insulin sensitivity and glucose tolerance and dramatically attenuated atherosclerosis in the aortic sinus.

CONCLUSIONS

Nobiletin provides insight into treatments for dyslipidemia and atherosclerosis associated with insulin-resistant states.

Enhancement of naringenin bioavailability by complexation with hydroxypropyl-β-cyclodextrin. [corrected]

The abundant flavonoid aglycone, naringenin, which is responsible for the bitter taste in grapefruits, has been shown to possess hypolipidemic and anti-inflammatory effects both in vitro and in vivo. Recently, our group demonstrated that naringenin inhibits hepatitis C virus (HCV) production, while others demonstrated its potential in the treatment of hyperlipidemia and diabetes. However, naringenin suffers from low oral bioavailability critically limiting its clinical potential. In this study, we demonstrate that the solubility of naringenin is enhanced by complexation with β-cyclodextrin, an FDA approved excipient. Hydroxypropoyl-β-cyclodextrin (HPβCD), specifically, increased the solubility of naringenin by over 400-fold, and its transport across a Caco-2 model of the gut epithelium by 11-fold. Complexation of naringenin with HPβCD increased its plasma concentrations when fed to rats, with AUC values increasing by 7.4-fold and C(max) increasing 14.6-fold. Moreover, when the complex was administered just prior to a meal it decreased VLDL levels by 42% and increased the rate of glucose clearance by 64% compared to naringenin alone. These effects correlated with increased expression of the PPAR co-activator, PGC1α in both liver and skeletal muscle. Histology and blood chemistry analysis indicated this route of administration was not associated with damage to the intestine, kidney, or liver. These results suggest that the complexation of naringenin with HPβCD is a viable option for the oral delivery of naringenin as a therapeutic entity with applications in the treatment of dyslipidemia, diabetes, and HCV infection.

Targeting metabolic syndrome: candidate natural agents

Following on from impressive economic development and urbanization, China is currently experiencing a high prevalence of metabolic syndrome. Patients with metabolic syndrome suffer from the "The Deadly Quartet" of hyperglycemia, hypertriglyceridemia, hypertension, and central (or upper body) obesity. Current treatment strategies directed towards metabolic syndrome tend to be limited to just one of these four conditions, so developing novel drugs to target multiple metabolic abnormalities could be preferable to current approaches. New insights suggest benefits of natural agents as treatments for metabolic syndrome. Herein, we review the evidence for using nine such agents developed on the basis of traditional medicine or herbal preparations.

Antiatherogenic properties of flavonoids: implications for cardiovascular health

Epidemiological studies suggest that higher flavonoid intake from fruits and vegetables is associated with decreased risk for the development of cardiovascular disease. The mechanisms explaining this observation remain unclear, but current evidence suggests that flavonoids may exert their effects through the improvement of cardiovascular risk factors. The present review summarizes data suggesting that flavonoids improve endothelial function. inhibit low-density lipoprotein oxidation, decrease blood pressure and improve dyslipidemia. A large number of studies have reported the impact of consuming flavonoid-rich foods on biomarkers of cardiovascular disease risk in healthy volunteers or at-risk individuals. Most studies have focused on cocoa, soy, and green and black tea. Recent evidence suggests that some polyphenols in their purified form, including resveratrol, berberine and naringenin, have beneficial effects on dyslipidemia in humans and/or animal models. In a mouse model of cardiovascular disease, naringenin treatment, through correction of dyslipidemia, hyperinsulinemia and obesity, attenuated atherosclerosis. Therefore, the beneficial effects of flavonoids on multiple risk factors may explain, in part, the observed beneficial effects of flavonoids on cardiovascular disease.

Naringenin decreases progression of atherosclerosis by improving dyslipidemia in high-fat-fed low-density lipoprotein receptor-null mice

OBJECTIVE

Naringenin is a citrus flavonoid that potently inhibits the assembly and secretion of apolipoprotein B100-containing lipoproteins in cultured hepatocytes and improves the dyslipidemia and insulin resistance in a mouse model of the metabolic syndrome. In the present study, we used low-density lipoprotein receptor-null mice fed a high-fat diet (Western, TD96125) to test the hypothesis that naringenin prevents atherosclerosis.

METHODS AND RESULTS

Three groups (chow, Western, and Western plus naringenin) were fed ad libitum for 6 months. The Western diet increased fasting plasma triglyceride (TG) (5-fold) and cholesterol (8-fold) levels compared with chow, whereas the addition of naringenin significantly decreased both lipids by 50%. The Western-fed mice developed extensive atherosclerosis in the aortic sinus because plaque area was increased by 10-fold compared with chow-fed animals. Quantitation of fat-soluble dye (Sudan IV)-stained aortas, prepared en face, revealed that Western-fed mice also had a 10-fold increase in plaque deposits throughout the arch and in the abdominal sections of the aorta, compared with chow. Atherosclerosis in both areas was significantly decreased by more than 70% in naringenin-treated mice. Consistent with quantitation of aortic lesions, the Western-fed mice had a significant 6-fold increase in cholesterol and a 4-fold increase in TG deposition in the aorta compared with chow-fed mice. Both were reduced more than 50% by naringenin. The Western diet induced extensive hepatic steatosis, with a 10-fold increase in both TG and cholesteryl ester mass compared with chow. The addition of naringenin decreased both liver TG and cholesteryl ester mass by 80%. The hyperinsulinemia and obesity that developed in Western-fed mice was normalized by naringenin to levels observed in chow-fed mice.

CONCLUSIONS

These in vivo studies demonstrate that the citrus flavonoid naringenin ameliorates the dyslipidemia in Western-fed low-density lipoprotein receptor-null mice, leading to decreased atherosclerosis; and suggests a potential therapeutic strategy for the hyperlipidemia and increased risk of atherosclerosis associated with insulin resistance.

Naringenin prevents dyslipidemia, apolipoprotein B overproduction, and hyperinsulinemia in LDL receptor-null mice with diet-induced insulin resistance

OBJECTIVE

The global epidemic of metabolic syndrome and its complications demands rapid evaluation of new and accessible interventions. Insulin resistance is the central biochemical disturbance in the metabolic syndrome. The citrus-derived flavonoid, naringenin, has lipid-lowering properties and inhibits VLDL secretion from cultured hepatocytes in a manner resembling insulin. We evaluated whether naringenin regulates lipoprotein production and insulin sensitivity in the context of insulin resistance in vivo.

RESEARCH DESIGN AND METHODS

LDL receptor-null (Ldlr(-/-)) mice fed a high-fat (Western) diet (42% calories from fat and 0.05% cholesterol) become dyslipidemic, insulin and glucose intolerant, and obese. Four groups of mice (standard diet, Western, and Western plus 1% or 3% wt/wt naringenin) were fed ad libitum for 4 weeks. VLDL production and parameters of insulin and glucose tolerance were determined.

RESULTS

We report that naringenin treatment of Ldlr(-/-) mice fed a Western diet corrected VLDL overproduction, ameliorated hepatic steatosis, and attenuated dyslipidemia without affecting caloric intake or fat absorption. Naringenin 1) increased hepatic fatty acid oxidation through a peroxisome proliferator-activated receptor (PPAR) gamma coactivator 1alpha/PPARalpha-mediated transcription program; 2) prevented sterol regulatory element-binding protein 1c-mediated lipogenesis in both liver and muscle by reducing fasting hyperinsulinemia; 3) decreased hepatic cholesterol and cholesterol ester synthesis; 4) reduced both VLDL-derived and endogenously synthesized fatty acids, preventing muscle triglyceride accumulation; and 5) improved overall insulin sensitivity and glucose tolerance.

CONCLUSIONS

Thus, naringenin, through its correction of many of the metabolic disturbances linked to insulin resistance, represents a promising therapeutic approach for metabolic syndrome.

Inflammatory NF-kappaB activation promotes hepatic apolipoprotein B100 secretion: evidence for a link between hepatic inflammation and lipoprotein production

Insulin-resistant states are commonly associated with chronic inflammation and hepatic overproduction of apolipoprotein B100 (apoB100), leading to hypertriglyceridemia and a metabolic dyslipidemic profile. Molecular mechanisms linking hepatic inflammatory cascades and the pathways of apoB100-lipoprotein production are, however, unknown. In the present study, we employed a diet-induced, insulin-resistant hamster model, as well as cell culture studies, to investigate the potential link between activation of hepatic inflammatory nuclear factor-kappaB (NF-kappaB) signaling cascade and the synthesis and secretion of apoB100-containing lipoproteins. Using an established insulin-resistant animal model, the fructose-fed hamster, we found that feeding fructose (previously shown to induce hepatic inflammation) for as little as 4 days reduced hepatic IkappaB (inhibitor of NF-kappaB) level, indicating activation of the inflammatory NF-kappaB cascade. Importantly, IKK (IkappaB kinase) inhibition was found to suppress apoB100 overproduction in fructose-fed hamster hepatocytes. As IKK, the upstream activator of NF-kappaB has been shown to inhibit insulin signaling, and insulin is a major regulator of apoB100, we modulated IKK activity in primary hamster hepatocytes and HepG2 cells and assessed the effects on hepatic apoB100 biosynthesis. Inhibition of the IKK-NF-kappaB pathway by BMS345541 and activation of the pathway by adenoviral-mediated IKK overexpression decreased and increased newly synthesized apoB100 levels, respectively. Pulse-chase and metabolic labeling experiments revealed that IKK activation regulates apoB100 levels at the levels of apoB100 biosynthesis and protein stability. Inhibition of the IKK-NF-kappaB pathway significantly enhanced proteasomal degradation of hepatic apoB100, while direct IKK activation led to reduced degradation and increased apoB100 mRNA translation. Together, our results reveal important links between modulation of the inflammatory IKK-NF-kappaB signaling cascade and hepatic synthesis and secretion of apoB100-containing lipoproteins. Hepatic inflammation may be an important underlying factor in hepatic apoB100 overproduction observed in insulin resistance.