Flavonoids protect pancreatic beta-cells from cytokines mediated apoptosis through the activation of PI3-kinase pathway

Mango (Mangifera indica L.) seed kernel extract suppresses hyperglycemia by modulating pancreatic β cell apoptosis and dysfunction and hepatic glucose metabolism in diabetic rats

This study investigated the anti-hyperglycemic action of mango seed kernel extract (MKE) and various mechanisms involved in its actions to improve pancreatic β cells and hepatic carbohydrate metabolism in diabetic rats. An intraperitoneal injection of 60 mg/kg of streptozotocin (STZ) followed by 30 consecutive days of treatment with MKE (250, 500, and 1000 mg/kg body weight) was used to establish a study group of diabetic rats. Using liquid chromatography-electrospray ionization-quadrupole time-of-flight mass spectrometry (LC-ESI-QTOF-MS/MS) for identification, 26 chemical compounds were found in MKE and the high-performance liquid chromatography (HPLC) analysis of the MKE also revealed the existence of mangiferin, gallic acid, and quercetin. The results confirmed that in each diabetes-affected rat, MKE mitigated the heightened levels of fasting blood glucose, diabetic symptoms, glucose intolerance, total cholesterol (TC), and low-density lipoprotein-cholesterol (LDL-C). As demonstrated by a remarkable increment in serum and pancreatic insulin, the diabetic pancreatic β cell function was potentiated by treating with MKE. The effect of MKE on diabetic pancreatic apoptosis clearly reduced the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL)-positive cells, which was related to diminished levels of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and Bax and an increase in Bcl-xL protein expression. Furthermore, diabetes-induced liver damage was clearly ameliorated along with a notable reduction in serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels and abnormal liver histology. By enhancing anti-oxidant superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) activities, MKE alleviated diabetes-induced pancreatic and liver oxidative damage, as demonstrated by diminished levels of malondialdehyde. In minimizing the expression levels of glucose 6-phosphatase and phosphoenolpyruvate carboxykinase-1 proteins in the diabetic liver, MKE also enhanced glycogen content and hexokinase activity. Collectively, these findings indicate that by suppressing oxidative and inflammatory processes, MKE exerts a potent anti-hyperglycemic activity in diabetic rats which serve to protect pancreatic β cell apoptosis, enhance their function, and improve hepatic glucose metabolism.

Fortification of Fermented Camel Milk with Salvia officinalis L. or Mentha piperita Leaves Powder and Its Biological Effects on Diabetic Rats

The incorporation of fermented camel milk with natural additives possesses numerous benefits for the treatment of various pathological and metabolic conditions. The present study investigated the impact of fortification of fermented camel milk with sage or mint leaves powder (1 and 1.5%, respectively) on glucose and insulin levels, lipid profile, and liver and kidney functions in alloxan-induced diabetic rats. The gross chemical composition of sage and peppermint leaves powder was studied. The chemical composition of sage and mint extracts was performed using liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-MS) of sage and mint extracts. Furthermore, a total of forty-two adult normal male albino rats were included in this study, whereas one group was kept as the healthy control group (n = 6 rats) and diabetes was induced in the remaining animals (n = 36 rats) using alloxan injection (150 mg/kg of body weight). Among diabetic rats groups, a control group (n = 6 rats) was kept as the diabetic control group whereas the other 5 groups (6 rats per group) of diabetic rats were fed fermented camel milk (FCM) or fermented camel milk fortified with 1 and 1.5% of sage or mint leaves powder. Interestingly, the oral administration of fermented camel milk fortified with sage or mint leaves powder, at both concentrations, caused a significant decrease in blood glucose level and lipid profile, and an increase in insulin level compared to the diabetic control and FCM groups. Among others, the best results were observed in the group of animals that received fermented camel milk fortified with 1.5% sage powder. In addition, the results revealed that the fermented camel milk fortified with sage or mint leaves powder improved the liver and kidney functions of diabetic rats. Our study concluded that the use of sage and mint leaves powder (at a ratio of 1.5%) with fermented camel milk produces functional food products with anti-diabetic activity.

Naringenin: A flavanone with anti-inflammatory and anti-infective properties

Although a growing body of research has recently shown how crucial inflammation and infection are to all major diseases, several of the medications currently available on the market have various unfavourable side effects, necessitating the development of alternative therapeutic choices. Researchers are increasingly interested in alternative medications or active components derived from natural sources. Naringenin is a commonly consumed flavonoid found in many plants, and since it was discovered to have nutritional benefits, it has been utilized to treat inflammation and infections caused by particular bacteria or viruses. However, the absence of adequate clinical data and naringenin's poor solubility and stability severely restrict its usage as a medicinal agent. In this article, we discuss naringenin's effects and mechanisms of action on autoimmune-induced inflammation, bacterial infections, and viral infections based on recent research. We also present a few suggestions for enhancing naringenin's solubility, stability, and bioavailability. This paper emphasizes the potential use of naringenin as an anti-inflammatory and anti-infective agent and the next prophylactic substance for the treatment of various inflammatory and infectious diseases, even though some mechanisms of action are still unclear, and offers some theoretical support for its clinical application.

Network pharmacology and molecular docking analysis on the mechanism of Cordyceps militaris polysaccharide regulating immunity through TLR4/TNF-α pathwayss

The role of polysaccharide components in the immune system, especially immunomodulatory effects, has received increasing attention. In this context, in this study, network pharmacology was adopted to explore the hypothesis of a multitarget mechanism for immune modulation by Chrysalis polysaccharides. A total of 174 common targets were screened by network pharmacology, with the main ones being TNF, MAPK3, CASP3, VEGFA, and STAT3, mostly enriched in the Toll pathway. The molecular docking results showed that the polysaccharide fraction of Chrysalis binds well to TNF proteins. Besides, in vitro cellular assays were performed to verify the ability of Chrysalis polysaccharides to regulate macrophage polarization and to screen for macrophage surface receptors. Furthermore, in vivo experiments were conducted to prove the activation of TLR4 and TNF-α protein expression in mice by Chrysalis polysaccharide.

Venom Peptides, Polyphenols and Alkaloids: Are They the Next Antidiabetics That Will Preserve β-Cell Mass and Function in Type 2 Diabetes?

Improvement of insulin secretion by pancreatic β-cells and preservation of their mass are the current challenges that future antidiabetic drugs should meet for achieving efficient and long-term glycemic control in patients with type 2 diabetes (T2D). The successful development of glucagon-like peptide 1 (GLP-1) analogues, derived from the saliva of a lizard from the Helodermatidae family, has provided the proof of concept that antidiabetic drugs directly targeting pancreatic β-cells can emerge from venomous animals. The literature reporting on the antidiabetic effects of medicinal plants suggests that they contain some promising active substances such as polyphenols and alkaloids, which could be active as insulin secretagogues and β-cell protectors. In this review, we discuss the potential of several polyphenols, alkaloids and venom peptides from snake, frogs, scorpions and cone snails. These molecules could contribute to the development of new efficient antidiabetic medicines targeting β-cells, which would tackle the progression of the disease.

Phyto-targeting the CEMIP Expression as a Strategy to Prevent Pancreatic Cancer Metastasis

INTRODUCTION

Metastasis of primary pancreatic cancer (PC) to adjacent or distant organs is responsible for the poor survival rate of affected individuals. Chemotherapy, radiotherapy, and immunotherapy are currently being prescribed to treat PC in addition to surgical resection. Surgical resection is the preferred treatment for PC that leads to 20% of 5-year survival, but only less than 20% of patients are eligible for surgical resection because of the poor prognosis. To improve the prognosis and clinical outcome, early diagnostic markers need to be identified, and targeting them would be of immense benefit to increase the efficiency of the treatment. Cell migration-inducing hyaluronan-binding protein (CEMIP) is identified as an important risk factor for the metastasis of various cancers, including PC. Emerging studies have pointed out the crucial role of CEMIP in the regulation of various signaling mechanisms, leading to enhanced migration and metastasis of PC.

METHODS

The published findings on PC metastasis, phytoconstituents, and CEMIP were retrieved from Pubmed, ScienceDirect, and Cochrane Library. Computational tools, such as gene expression profiling interactive analysis (GEPIA) and Kaplan-Meier (KM) plotter, were used to study the relationship between CEMIP expression and survival of PC individuals.

RESULTS

Gene expression analysis using the GEPIA database identified a stupendous increase in the CEMIP transcript in PC compared to adjacent normal tissues. KM plotter analysis revealed the impact of CEMIP on the overall survival (OS) and disease-free survival (DFS) among PC patients. Subsequently, several risk factors associated with PC development were screened, and their ability to regulate CEMIP gene expression was analyzed using computational tools.

CONCLUSION

The current review is focused on gathering information regarding the regulatory role of phytocomponents in PC migration and exploring their possible impact on the CEMIP expression.

Fetuin-A secretion from β-cells leads to accumulation of macrophages in islets, aggravates inflammation and impairs insulin secretion

Elevated fetuin-A levels, chemokines and islet-resident macrophages are crucial factors associated with obesity-mediated type 2 diabetes (T2D). Here, the aim of the study was to investigate the effect of MIN6 (a mouse insulinoma cell line)-derived fetuin-A (also known as AHSG) in macrophage polarization and decipher the effect of M1 type pro-inflammatory macrophages in commanding over insulin secretion. MIN6 and islet-derived fetuin-A induced expression of the M1 type macrophage markers Emr1 (also known as Adgre1), Cd68 and CD11c (Itgax) (∼1.8 fold) along with increased cytokine secretion. Interestingly, suppression of fetuin-A in MIN6 successfully reduced M1 markers by ∼1.5 fold. MIN6-derived fetuin-A also induced chemotaxis of macrophages in a Boyden chamber chemotaxis assay. Furthermore, high-fat feeding in mice showed elevated cytokine and fetuin-A content in serum and islets, and also migration and polarization of macrophages to the islets, while β-cells failed to meet the increased insulin demand. Moreover, in MIN6 culture, M1 macrophages sharply decreased insulin secretion by ∼2.8 fold. Altogether our results support an association of fetuin-A with islet inflammation and β-cell dysfunction, owing to its role as a key chemoattractant and macrophage polarizing factor.

Encapsulation of Hydrophobic and Low-Soluble Polyphenols into Nanoliposomes by pH-Driven Method: Naringenin and Naringin as Model Compounds

Naringenin and naringin are a class of hydrophobic polyphenol compounds and both have several biological activities containing antioxidant, anti-inflammatory and anti-tumor properties. Nevertheless, they have low water solubility and bioavailability, which limits their biological activity. In this study, an easy pH-driven method was applied to load naringenin or naringin into nanoliposomes based on the gradual reduction in their water solubility after the pH changed to acidity. Thus, the naringenin or naringin can be embedded into the hydrophobic region within nanoliposomes from the aqueous phase. A series of naringenin/naringin-loaded nanoliposomes with different pH values, lecithin contents and feeding naringenin/naringin concentrations were prepared by microfluidization and a pH-driven method. The naringin-loaded nanoliposome contained some free naringin due to its higher water solubility at lower pH values and had a relatively low encapsulation efficiency. However, the naringenin-loaded nanoliposomes were predominantly nanometric (44.95–104.4 nm), negatively charged (−14.1 to −19.3 mV) and exhibited relatively high encapsulation efficiency (EE = 95.34% for 0.75 mg/mL naringenin within 1% w/v lecithin). Additionally, the naringenin-loaded nanoliposomes still maintained good stability during 31 days of storage at 4 °C. This study may help to develop novel food-grade colloidal delivery systems and apply them to introducing naringenin or other lipophilic polyphenols into foods, supplements or drugs.

Lisofylline mitigates cardiac inflammation in a mouse model of obesity through improving insulin secretion and activating cardiac AMPK signaling pathway

Obesity has emerged as a leading cause of death in the last few decades, mainly due to associated cardiovascular diseases. Obesity, inflammation, and insulin resistance are strongly interlinked. Lisofylline (LSF), an anti-inflammatory agent, demonstrated protection against type 1 diabetes, as well as reduced obesity-induced insulin resistance and adipose tissue inflammation. However, its role in mitigating cardiac inflammation associated with obesity is not well studied. Mice were divided into 4 groups; the first group was fed regular chow diet, the second was fed regular chow diet and treated with LSF, the third was fed high fat diet (HFD), and the fourth was fed HFD and treated with LSF. Cardiac inflammation was interrogated via expression levels of TNF α, interleukins 6 and 10, phosphorylated STAT4 and lipoxygenases 12 and 12/15. Apoptosis and expression of the survival gene, AMPK, were also evaluated. We observed that LSF alleviated obesity-induced cardiac injury indirectly by improving both pancreatic β-cell function and insulin sensitivity, as well as, directly via upregulation of cardiac AMPK expression and downregulation of cardiac inflammation and apoptosis. LSF may represent an effective therapy targeting obesity-induced metabolic and cardiovascular complications.

Flavonoids and Insulin-Resistance: From Molecular Evidences to Clinical Trials

Insulin-resistance is one of the main factors responsible for the onset and progression of Metabolic Syndrome (MetS). Among all polyphenols, the effects of flavonoids and their main food sources on insulin sensitivity have been widely evaluated in molecular and clinical studies. The aim of this review is to analyse the data observed in vitro, in vivo and in clinical trials concerning the effects of flavonoids on insulin resistance and to determine the molecular mechanisms with which flavonoids interact with insulin signaling.

Flavonoids for preserving pancreatic beta cell survival and function: A mechanistic review

Although the currently available antidiabetic medications are effective in managing hyperglycemia, vascular complications are common in diabetic patients. Cohort studies have shown preserved beta cell function has a protective role against the development of diabetic complications. Accordingly, beta cell mass and function are important pharmacological targets in the field of diabetes. Growing number of evidence supports the efficacy of flavonoids (e.g., quercetin, kaempferol, luteolin, and epicatechin) for prevention and attenuation of diabetes consequences. The focus of this paper is to give an overview regarding the effects of flavonoids on pancreatic beta cells. Experiments on insulin-releasing cell lines, isolated pancreatic islets, and diabetic animal models have shown that flavonoids strengthen the survival processes and insulin secretory capacity of beta cells. The proposed mechanisms by which flavonoids preserve beta cells survival (against cytokines, glucotoxicity, and lipotoxicity) include inhibition of NF-κB signaling, activation of PI3K/Akt pathway, inhibition of nitric oxide generation, and decrease of reactive oxygen species levels. Improving mitochondrial bioenergetic function and stimulating pathways of insulin secretion (e.g., PLC/PKC and/or cAMP/PKA signaling) are mechanisms by which flavonoids improve the secretory capacity of beta cells. These beneficial effects of flavonoids are of great importance because may protect beta cells of diabetic patients before dramatic dysfunction and degeneration.

Pharmacokinetic, pharmacodynamic and formulations aspects of Naringenin: An update

Phenolic compounds constitute one of the important classes of secondary metabolites in the plants. Flavonoids are primary phenolic compounds found in natural drugs. Naringenin is a flavanone, aglycone of Naringin, predominantly found in citrus fruits with various pharmacological activities. Large number of scientific papers has been published on Naringenin describing its structure, physicochemical properties and its therapeutic use in different diseases. This review provides highlights of Naringenin with respect to its distribution, pharmacokinetic and its use in conditions like oxidative stress, inflammation, cancer, diabetes, cardiovascular diseases and neurological disorders. Furthermore, the review also focuses on molecular level mechanisms of Naringenin for its therapeutic effect. Various attempts have been made to formulate advanced dosage forms to address issue of solubility of Naringenin. Systematic review of data published on formulation aspects of Naringenin has also been presented in the article.

Estimated daily quercetin intake and association with the prevalence of type 2 diabetes mellitus in Chinese adults

PURPOSE

Quercetin is one of potential antidiabetic substances because of its powerful antioxidant and anti-inflammatory actions. The purpose of this study is to estimate daily quercetin intake and assess the relationship between dietary quercetin intake and the prevalence of type 2 diabetes mellitus (T2DM) in a Chinese population.

METHODS

Dietary intake was investigated by a validated 100-item food frequency questionnaire. Daily intakes of quercetin and nutrients were calculated accordingly. T2DM was diagnosed based on the criteria of the American Diabetes Association. Adjusted logistic regression models were used to analyze the relationship between the quartiles of quercetin intake and the prevalence of T2DM.

RESULTS

The prevalences of T2DM were 8.35% in men and 4.68% in women. The main food sources of quercetin were apple, orange, and green tea. Daily intake of quercetin was 20.9 ± 2.32 mg/day (mean ± SD). After adjusting for potentially confounding factors, the odds ratios (95% CI) for T2DM across the ascending quartiles of quercetin intake were: 1.00 (reference), 0.75 (0.60-0.95), 0.76 (0.59-0.99), and 0.63 (0.51-0.94).

CONCLUSIONS

The results of the present study showed that quercetin intake was inversely related to the prevalence of T2DM in the Chinese population, suggesting a protective effect of quercetin in the development of T2DM.

Naringin Protects Pancreatic β-Cells Against Oxidative Stress-Induced Apoptosis by Inhibiting Both Intrinsic and Extrinsic Pathways in Insulin-Deficient Diabetic Mice

SCOPE

Oxidative stress has been suggested to play a central role in the pathogenesis of diabetes, as well as other metabolic disorders. Naringin, a major flavanone glycoside in citrus species, has been shown to display strong antioxidant potential in in vitro and in vivo models of oxidative stress; however, the underlying protective mechanisms in diabetes are unclear.

METHODS AND RESULTS

To study the protective effects and molecular mechanisms of naringin in preventing islet dysfunction and diabetes, we examined glucose homeostasis, β-cell apoptosis, and inflammatory response in insulin-deficient diabetic mice exposed to acute oxidative stress with streptozotocin (STZ). Naringin dose-dependently ameliorated hyperglycemia and islet dysfunction in insulin-deficient diabetic mice. Naringin counteracted STZ-induced β-cell apoptosis by inhibiting both the intrinsic (mitochondria-mediated) and extrinsic (death receptor-mediated) pathways. Furthermore, these protective effects were associated with suppression of DNA damage response and nuclear factor-kappa B- and mitogen-activated protein kinase-mediated signaling pathways, as well as reduction of reactive oxygen species accumulation and pro-inflammatory cytokine production in the pancreas.

CONCLUSION

Taken together, our study provides insights into the underlying mechanisms through which naringin protects the pancreatic β-cells against oxidative stress-induced apoptosis.

Sex- and Dose-Specific Effects of Maternal Bisphenol A Exposure on Pancreatic Islets of First- and Second-Generation Adult Mice Offspring

BACKGROUND

Exposure to the environmental endocrine disruptor bisphenol A (BPA) is ubiquitous and associated with the increased risk of diabetes and obesity. However, the underlying mechanisms remain unknown. We recently demonstrated that perinatal BPA exposure is associated with higher body fat, impaired glucose tolerance, and reduced insulin secretion in first- (F1) and second-generation (F2) C57BL/6J male mice offspring.

OBJECTIVE

We sought to determine the multigenerational effects of maternal bisphenol A exposure on mouse pancreatic islets.

METHODS

Cellular and molecular mechanisms underlying these persistent changes were determined in F1 and F2 adult offspring of F0 mothers exposed to two relevant human exposure levels of BPA (10μg/kg/d-LowerB and 10mg/kg/d-UpperB).

RESULTS

Both doses of BPA significantly impaired insulin secretion in male but not female F1 and F2 offspring. Surprisingly, LowerB and UpperB induced islet inflammation in male F1 offspring that persisted into the next generation. We also observed dose-specific effects of BPA on islets in males. UpperB exposure impaired mitochondrial function, whereas LowerB exposure significantly reduced β-cell mass and increased β-cell death that persisted in the F2 generation. Transcriptome analyses supported these physiologic findings and there were significant dose-specific changes in the expression of genes regulating inflammation and mitochondrial function. Previously we observed increased expression of the critically important β-cell gene, Igf2 in whole F1 embryos. Surprisingly, increased Igf2 expression persisted in the islets of male F1 and F2 offspring and was associated with altered DNA methylation.

CONCLUSION

These findings demonstrate that maternal BPA exposure has dose- and sex-specific effects on pancreatic islets of adult F1 and F2 mice offspring. The transmission of these changes across multiple generations may involve either mitochondrial dysfunction and/or epigenetic modifications. https://doi.org/10.1289/EHP1674.

Sulforaphane Protects against High Cholesterol-Induced Mitochondrial Bioenergetics Impairments, Inflammation, and Oxidative Stress and Preserves Pancreatic β-Cells Function

Cholesterol plays an important role in inducing pancreatic β-cell dysfunction, leading to an impaired insulin secretory response to glucose. This study aimed to determine the protective effects of sulforaphane, a natural isothiocyanate Nrf2-inducer, against cholesterol-induced pancreatic β-cells dysfunction, through molecular and cellular mechanisms involving mitochondrial bioenergetics. Sulforaphane prevented cholesterol-induced alterations in the coupling efficiency of mitochondrial respiration, improving ATP turnover and spare capacity, and averted the impairment of the electron flow at complexes I, II, and IV. Sulforaphane also attenuated the cholesterol-induced activation of the NFκB pathway, normalizing the expression of pro- and anti-inflammatory cytokines. In addition, it also inhibited the decrease in sirtuin 1 expression and greatly increased Pgc-1α expression in Min6 cells. Sulforaphane increased the expression of antioxidant enzymes downstream of the Nrf2 pathway and prevented lipid peroxidation induced by cholesterol. The antioxidant and anti-inflammatory properties of sulforaphane and its ability to protect and improve mitochondrial bioenergetic function contribute to its protective action against cholesterol-induced pancreatic β-cell dysfunction. Our data provide a scientifically tested foundation upon which sulforaphane can be developed as nutraceutical to preserve β-cell function and eventually control hyperglycemia.

Myricetin: a potent approach for the treatment of type 2 diabetes as a natural class B GPCR agonist

The physiologic properties of glucagon-like peptide 1 (GLP-1) make it a potent candidate drug target in the treatment of type 2 diabetes mellitus (T2DM). GLP-1 is capable of regulating the blood glucose level by insulin secretion after administration of oral glucose. The advantages of GLP-1 for the avoidance of hypoglycemia and the control of body weight are attractive despite its poor stability. The clinical efficacies of long-acting GLP-1 derivatives strongly support discovery pursuits aimed at identifying and developing orally active, small-molecule GLP-1 receptor (GLP-1R) agonists. The purpose of this study was to identify and characterize a novel oral agonist of GLP-1R (i.e., myricetin). The insulinotropic characterization of myricetin was performed in isolated islets and in Wistar rats. Long-term oral administration of myricetin demonstrated glucoregulatory activity. The data in this study suggest that myricetin might be a potential drug candidate for the treatment of T2DM as a GLP-1R agonist. Further structural modifications on myricetin might improve its pharmacology and pharmacokinetics.-Li, Y., Zheng, X., Yi, X., Liu, C., Kong, D., Zhang, J., Gong, M. Myricetin: a potent approach for the treatment of type 2 diabetes as a natural class B GPCR agonist.

The deleterious effect of cholesterol and protection by quercetin on mitochondrial bioenergetics of pancreatic β-cells, glycemic control and inflammation: In vitro and in vivo studies

Studying rats fed high cholesterol diet and a pancreatic β-cell line (Min6), we aimed to determine the mechanisms by which quercetin protects against cholesterol-induced pancreatic β-cell dysfunction and impairments in glycemic control. Quercetin prevented the increase in total plasma cholesterol, but only partially prevented the high cholesterol diet-induced alterations in lipid profile. Quercetin prevented cholesterol-induced decreases in pancreatic ATP levels and mitochondrial bioenergetic dysfunction in Min6 cells, including decreases in mitochondrial membrane potentials and coupling efficiency in the mitochondrial respiration (basal and maximal oxygen consumption rate (OCR), ATP-linked OCR and reserve capacity). Quercetin protected against cholesterol-induced apoptosis of Min6 cells by inhibiting caspase-3 and -9 activation and cytochrome c release. Quercetin prevented the cholesterol-induced decrease in antioxidant defence enzymes from pancreas (cytosolic and mitochondrial homogenates) and Min6 cells and the cholesterol-induced increase of cellular and mitochondrial oxidative status and lipid peroxidation. Quercetin counteracted the cholesterol-induced activation of the NFκB pathway in the pancreas and Min6 cells, normalizing the expression of pro-inflammatory cytokines. Quercetin inhibited the cholesterol-induced decrease in sirtuin 1 expression in the pancreas and pancreatic β-cells. Taken together, the anti-apoptotic, antioxidant and anti-inflammatory properties of quercetin, and its ability to protect and improve mitochondrial bioenergetic function are likely to contribute to its protective action against cholesterol-induced pancreatic β-cell dysfunction, thereby preserving glucose-stimulated insulin secretion (GSIS) and glycemic control. Specifically, the improvement of ATP-linked OCR and the reserve capacity are important mechanisms for protection of quercetin. In addition, the inhibition of the NFκB pathway is an important mechanism for the protection of quercetin against cytokine mediated cholesterol-induced glycemic control impairment. In summary, our data highlight cellular, molecular and bioenergetic mechanisms underlying quercetin's protective effects on β-cells in vitro and in vivo, and provide a scientifically tested foundation upon which quercetin can be developed as a nutraceutical to preserve β-cell function.

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Quercetin prevents the impairment in glycemic control induced by cholesterol.

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Quercetin prevents cholesterol-impaired insulin secretion in pancreatic β-cells.

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Quercetin improves mitochondrial bioenergetics impaired by cholesterol.

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Quercetin prevents the decrease in SIRT1 expression induced by cholesterol.

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Quercetin prevents NF-kB activation and prevents cholesterol-induced inflammation.

Hexarelin Protects Rodent Pancreatic Β-Cells Function from Cytotoxic Effects of Streptozotocin Involving Mitochondrial Signalling Pathways In Vivo and In Vitro

Mitochondrial functions are crucial for pancreatic β-cell survival and glucose-induced insulin secretion. Hexarelin (Hex) is a synthetic small peptide ghrelin analogue, which has been shown to protect cardiomyocytes from the ischemia-reperfusion process. In this study, we used in vitro and in vivo models of streptozotocin (STZ)-induced β-cell damage to study the protective effect of Hex and the associated mechanisms. We found that STZ produced a cytotoxic effect in a dose- and time-dependent manner in MIN6 cells (a mouse β-cell line). Hex (1.0 μM) decreased the STZ-induced damage in β-cells. Rhodamine 123 assay and superoxide DHE production assay revealed that Hex ameliorated STZ-induced mitochondrial damage and excessive superoxide activity in β-cells. In addition, Hex significantly reduced STZ-induced expression of cleaved Caspases-3, Caspases-9 and the ratio of pro-apoptotic protein Bax to anti-apoptotic protein Bcl-2 in MIN6 cells. We further examined the in vivo effect of Hex in a rat model of type 1 diabetes induced by STZ injection. Hex ameliorated STZ-induced decrease in plasma insulin and protected the structure of islets from STZ-induced disruption. Hex also ameliorated STZ-induced expression of cleaved Caspase-9 and the Bax in β-cells. In conclusion, our data indicate that Hex is able to protects β-cell mass from STZ-caused cytotoxic effects involving mitochondrial pathways in vitro and in vivo. Hex may serve as a potential protective agent for the management of diabetes.

Modulation of neurotrophic signaling pathways by polyphenols

Polyphenols are an important class of phytochemicals, and several lines of evidence have demonstrated their beneficial effects in the context of a number of pathologies including neurodegenerative disorders such as Alzheimer’s and Parkinson’s disease. In this report, we review the studies on the effects of polyphenols on neuronal survival, growth, proliferation and differentiation, and the signaling pathways involved in these neurotrophic actions. Several polyphenols including flavonoids such as baicalein, daidzein, luteolin, and nobiletin as well as nonflavonoid polyphenols such as auraptene, carnosic acid, curcuminoids, and hydroxycinnamic acid derivatives including caffeic acid phentyl ester enhance neuronal survival and promote neurite outgrowth in vitro, a hallmark of neuronal differentiation. Assessment of underlying mechanisms, especially in PC12 neuronal-like cells, reveals that direct agonistic effect on tropomyosin receptor kinase (Trk) receptors, the main receptors of neurotrophic factors including nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) explains the action of few polyphenols such as 7,8-dihydroxyflavone. However, several other polyphenolic compounds activate extracellular signal-regulated kinase (ERK) and phosphoinositide 3-kinase (PI3K)/Akt pathways. Increased expression of neurotrophic factors in vitro and in vivo is the mechanism of neurotrophic action of flavonoids such as scutellarin, daidzein, genistein, and fisetin, while compounds like apigenin and ferulic acid increase cyclic adenosine monophosphate response element-binding protein (CREB) phosphorylation. Finally, the antioxidant activity of polyphenols reflected in the activation of Nrf2 pathway and the consequent upregulation of detoxification enzymes such as heme oxygenase-1 as well as the contribution of these effects to the neurotrophic activity have also been discussed. In conclusion, a better understanding of the neurotrophic effects of polyphenols and the concomitant modulations of signaling pathways is useful for designing more effective agents for management of neurodegenerative diseases.

Cilostazol attenuates murine hepatic ischemia and reperfusion injury via heme oxygenase-dependent activation of mitochondrial biogenesis

Hepatic ischemia-reperfusion (I/R) can cause hepatocellular injury associated with the inflammatory response and mitochondrial dysfunction. We studied the protective effects of the phosphodiesterase inhibitor cilostazol in hepatic I/R and the roles of mitochondria and the Nrf2/heme oxygenase-1 (HO-1) system. Wild-type, Hmox1(-/-), or Nrf2(-/-) mice were subjected to hepatic I/R in the absence or presence of cilostazol followed by measurements of liver injury. Primary hepatocytes were subjected to cilostazol with the HO-1 inhibitor ZnPP, or Nrf2-specific siRNA, followed by assessment of mitochondrial biogenesis. Preconditioning with cilostazol prior to hepatic I/R protected against hepatocellular injury and mitochondrial dysfunction. Cilostazol reduced the serum levels of alanine aminotransferase, TNF-α, and liver myeloperoxidase content relative to control I/R-treated mice. In primary hepatocytes, cilostazol increased the expression of HO-1, and markers of mitochondrial biogenesis, PGC-1α, NRF-1, and TFAM, induced the mitochondrial proteins COX III and COX IV and increased mtDNA and mitochondria content. Pretreatment of primary hepatocytes with ZnPP inhibited cilostazol-induced PGC-1α, NRF-1, and TFAM mRNA expression and reduced mtDNA and mitochondria content. Genetic silencing of Nrf2 prevented the induction of HO-1 and mitochondrial biogenesis by cilostazol in HepG2 cells. Cilostazol induced hepatic HO-1 production and mitochondrial biogenesis in wild-type mice, but not in Hmox1(-/-) or Nrf2(-/-) mice, and failed to protect against liver injury in Nrf2(-/-) mice. These results suggest that I/R injury can impair hepatic mitochondrial function, which can be reversed by cilostazol treatment. These results also suggest that cilostazol-induced mitochondrial biogenesis was mediated by an Nrf-2- and HO-1-dependent pathway.

Quercetin attenuates cyclooxygenase-2 expression in response to acute ureteral obstruction

Unilateral ureteral obstruction (UUO) is associated with increased hydrostatic pressure, inflammation, and oxidative stress in the renal parenchyma. Previous studies have demonstrated marked cyclooxygenase (COX)-2 induction in renal medullary interstitial cells (RMICs) in response to UUO. The aim of the present study was to evaluate the effect of quercetin, a naturally occurring antioxidant, on COX-2 induction in vivo and in vitro. Rats subjected to 24 h of UUO were treated intraperitoneally with quercetin (50 mg·kg(-1)·day(-1)). Quercetin partly prevented COX-2 induction in the renal inner medulla in response to UUO. Moreover, RMICs exposed to conditions associated with obstruction, inflammation (produced by IL-1β), oxidative stress (produced by H2O2), and mechanical stress (produced by stretch) showed increased COX-2 expression. Interestingly, quercetin reduced COX-2 induction in RMICs subjected to stretched. Similarly, PGE2 production was markedly increased in RMICs exposed to stretch and was reversed to control levels by quercetin treatment. Furthermore, stretch-induced phosphorylation of ERK1/2 was blocked by quercetin, and inhibition of ERK1/2 attenuated stretch-induced COX-2 induction in RMICs. These results indicate that quercetin attenuated the induction of COX-2 expression and activity in RMICs exposed to mechanical stress as a consequence of acute UUO and that the MAPK ERK1/2 pathway might be involved in this quercetin-mediated reduction in COX-2.

Forest biorefinery: Potential of poplar phytochemicals as value-added co-products

The global forestry industry after experiencing a market downturn during the past decade has now aimed its vision towards the integrated biorefinery. New business models and strategies are constantly being explored to re-invent the global wood and pulp/paper industry through sustainable resource exploitation. The goal is to produce diversified, innovative and revenue generating product lines using on-site bioresources (wood and tree residues). The most popular product lines are generally produced from wood fibers (biofuels, pulp/paper, biomaterials, and bio/chemicals). However, the bark and other tree residues like foliage that constitute forest wastes, still remain largely an underexploited resource from which extractives and phytochemicals can be harnessed as by-products (biopharmaceuticals, food additives and nutraceuticals, biopesticides, cosmetics). Commercially, Populus (poplar) tree species including hybrid varieties are cultivated as a fast growing bioenergy crop, but can also be utilized to produce bio-based chemicals. This review identifies and underlines the potential of natural products (phytochemicals) from Populus species that could lead to new business ventures in biorefineries and contribute to the bioeconomy. In brief, this review highlights the importance of by-products/co-products in forest industries, methods that can be employed to extract and purify poplar phytochemicals, the potential pharmaceutical and other uses of >160 phytochemicals identified from poplar species - their chemical structures, properties and bioactivities, the challenges and limitations of utilizing poplar phytochemicals, and potential commercial opportunities. Finally, the overall discussion and conclusion are made considering the recent biotechnological advances in phytochemical research to indicate the areas for future commercial applications from poplar tree species.

Evaluation of antidiabetic, antioxidant and antiglycating activities of the Eysenhardtia polystachya

Background:

Many diseases are associated with oxidative stress caused by free radicals. The aim of the present study was to evaluate the antidiabetic, antioxidant and antiglycation properties of Eysenhardtia polystachya (EP) bark methanol-water extract.

Materials and Methods

: The antioxidant capacities were evaluated by studying in vitro the scavenging of DPPH and ABTS free radical, reactive oxygen species such as RO₂, O₂·^-, H₂O₂, OH^., H₂O₂, ONOO-, NO, HOCl,¹ O₂, chelating ability, ORAC, β-carotene-bleaching and lipid peroxidation. The antiglycation activities of EP were evaluated by haemoglobin, bovine serum albumin (BSA)-glucose, BSA-methylglyoxal and BSA-glucose assays. Oral administration of EP at the doses of 100 mg/kg, 200 mg/kg and 400 mg/g was studied in normal, glucose-loaded and antidiabetic effects on streptozotocin-induced mildly diabetic (MD) and severely diabetic (SD) mice.

Results:

EP showed Hdonor activity, free radical scavenging activity, metal chelating ability and lipid peroxidation Antioxidant activity may be attributed to the presence of phenolic and flavonoid compounds. EP is an inhibitor of fluorescent AGE, methylglyoxal and the glycation of haemoglobin. In STZ-induced diabetic mice, EP reduced the blood glucose, increased serum insulin, body weight, marker enzymes of hepatic function, glycogen, HDL, GK and HK while there was reduction in the levels of triglyceride, cholesterol, TBARS, LDL and G6Pase.

Conclusions:

Eysenhardtia polystachya possesses considerable antioxidant activity with reactive oxygen species (ROS) scavenging activity and demonstrated an anti-AGEs and hepatoprotective role, inhibits hyperglycemic, hyperlipidemic and oxidative stress indicating that these effects may be mediated by interacting with multiple targets operating in diabetes mellitus.

Caffeic acid, naringenin and quercetin enhance glucose-stimulated insulin secretion and glucose sensitivity in INS-1E cells

AIMS

Caffeic acid, naringenin and quercetin are naturally occurring phenolic compounds (PCs) present in many plants as secondary metabolites. The aim of this study was to investigate their effect on glucose-stimulated insulin secretion (GSIS) in INS-1E cells and to explore their effect on expression of genes involved in β-cell survival and function under normoglycaemic and glucotoxic conditions.

METHODS

For acute studies, INS-1E cells were grown in 11 mM glucose (72 h) and then incubated with the PCs (1 h) with 3.3/16.7 mM glucose; whereas, for chronic studies, the cells were grown in 11 mM glucose (72 h) with/without the PCs, and then incubated with 3.3/16.7 mM glucose (1 h); thereafter, GSIS was measured. For GSIS and gene expression studies (GES) under glucotoxic conditions, two sets of cells were grown in 11/25 mM glucose with/without the PCs (72 h): one was used for GES, using real time RT-PCR, and the other was exposed to 3.3/16.7 mM glucose, followed by measurement of GSIS.

RESULTS

The study demonstrated that the PCs can enhance GSIS under hyperglycaemic and glucotoxic conditions in INS-1E cells. Moreover, these compounds can differentially, yet distinctly change the expression profile of genes [Glut2 (glucose transporter 2), Gck (glucokinase), Ins1 (insulin 1), Ins2, Beta2 (neurogenic differentiation protein 1), Pdx1 (pancreatic and duodenal homeobox protein 1), Akt1 (RAC-α serine/threonine-protein kinase encoding gene), Akt2 (RAC-β serine/threonine-protein kinase encoding gene), Irs1 (insulin receptor substrate 1), Acc1 (acetyl CoA carboxylase 1), Bcl2 (β-cell lymphoma 2 protein), Bax (Bcl-2 associated X protein), Casp3 (Caspase 3), Hsp70 (heat shock protein 70), and Hsp90] involved in β-cell stress, survival and function.

CONCLUSION

The results indicate that the PCs tested enhance GSIS and glucose sensitivity in INS-1E cells. They also modulate gene expression profiles to improve β-cell survival and function during glucotoxicity.

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.

Low-dose cytokine-induced neutral ceramidase secretion from INS-1 cells via exosomes and its anti-apoptotic effect

It has been reported that the effect of inflammatory cytokines on β-cell destruction in type 1 diabetes is concentration-dependent. However, the underlying mechanisms remain unclear. In the present study, we found that a high concentration of cytokines promoted apoptosis in the rat β-cell line INS-1, whereas a low concentration of cytokines had no effect. We also found that cytokines at a low concentration stimulated neutral ceramidase (NCDase) release via exosomes from INS-1 cells, whereas cytokines at a high concentration inhibited NCDase release. Furthermore, the results showed that the NCDase-containing exosomes isolated from the culture medium of INS-1 cells treated with cytokines at a low concentration inhibited apoptosis induced by a high concentration of cytokines. Finally, the results also showed that the protective action of NCDase in the exosomes on apoptosis was mediated by the generation of sphingosine 1-phosphate (S1P) and its interaction with S1P receptor 2. Taken together, these findings revealed a novel NCDase-S1P-phosphate-S1P receptor 2-dependent mechanism by which a low level of inflammatory cytokines protects pancreatic β-cells from apoptosis induced by a high level of inflammatory cytokines.

Flavonoids in modulation of cell survival signalling pathways

Flavonoids, a family of polyphenols, generally found in various fruits and vegetables, as well as in many plant beverages such as tea, pomegranate juice, raspberry, blueberries, and red wine. Recently, studies on flavonoids have attracted scientific attention as a potential nutritional strategy to prevent a broad range of chronic disorders. Many studies suggest that consumption of these flavonoids in sufficient amount plays neuroprotective, cardioprotective, anti-inflammatory, and chemopreventive roles. While there has been a major focus on the antioxidant properties, there is an emerging view that flavonoids and their in vivo metabolites do not act only as conventional antioxidants but may also exert modulatory actions on cellular system through direct action on various signalling pathways. These pathways include phosphoinositide 3-kinase, Akt/protein kinase B, mitogen-activated protein kinase, tyrosine kinases, and protein kinase C. Various inhibitory or stimulatory actions of flavonoids on these pathways greatly affect cellular functions by altering the phosphorylation state of targeted molecules. In addition, flavonoids also modulate various gene expressions through activation of various transcription factors. Thus, the present review will bestow a breathing overview regarding the prime role of flavonoids in modulation of survival signalling pathways at cellular system.

Carbonyl stress in aging process: role of vitamins and phytochemicals as redox regulators

There is a growing scientific agreement that the cellular redox regulators such as antioxidants, particularly the natural polyphenolic forms, may help lower the incidence of some pathologies, including metabolic diseases like diabetes and diabesity, cardiovascular and neurodegenerative abnormalities, and certain cancers or even have anti-aging properties. The recent researches indicate that the degree of metabolic modulation and adaptation response of cells to reductants as well as oxidants establish their survival and homeostasis, which is linked with very critical balance in imbalances in cellular redox capacity and signaling, and that might be an answer the questions why some antioxidants or phytochemicals potentially could do more harm than good, or why some proteins lose their function by increase interactions with glyco- and lipo-oxidation mediates in the cells (carbonyl stress). Nonetheless, pursue of healthy aging has led the use of antioxidants as a means to disrupt age-associated physiological dysfunctions, dysregulated metabolic processes or prevention of many age-related diseases. Although it is still early to define their exact clinical benefits for treating age-related disease, a diet rich in polyphenolic or other forms of antioxidants does seem to offer hope in delaying the onset of age-related disorders. It is now clear that any deficiency in antioxidant vitamins, inadequate enzymatic antioxidant defenses can distinctive for many age-related disease, and protein carbonylation can used as an indicator of oxidative stress associated diseases and aging status. This review examines antioxidant compounds and plant polyphenols as redox regulators in health, disease and aging processes with hope that a better understanding of the many mechanisms involved with these distinct compounds, which may lead to better health and novel treatment approaches for age-related diseases.

Quercetin Preserves β -Cell Mass and Function in Fructose-Induced Hyperinsulinemia through Modulating Pancreatic Akt/FoxO1 Activation

Fructose-induced hyperinsulinemia is associated with insulin compensative secretion and predicts the onset of type 2 diabetes. In this study, we investigated the preservation of dietary flavonoid quercetin on pancreatic β-cell mass and function in fructose-treated rats and INS-1 β-cells. Quercetin was confirmed to reduce serum insulin and leptin levels and blockade islet hyperplasia in fructose-fed rats. It also prevented fructose-induced β-cell proliferation and insulin hypersecretion in INS-1 β-cells. High fructose increased forkhead box protein O1 (FoxO1) expressions in vivo and in vitro, which were reversed by quercetin. Quercetin downregulated Akt and FoxO1 phosphorylation in fructose-fed rat islets and increased the nuclear FoxO1 levels in fructose-treated INS-1 β-cells. The elevated Akt phosphorylation in fructose-treated INS-1 β-cells was also restored by quercetin. Additionally, quercetin suppressed the expression of pancreatic and duodenal homeobox 1 (Pdx1) and insulin gene (Ins1 and Ins2) in vivo and in vitro. In fructose-treated INS-1 β-cells, quercetin elevated the reduced janus kinase 2/signal transducers and activators of transcription 3 (Jak2/Stat3) phosphorylation and suppressed the increased suppressor of cytokine signaling 3 (Socs3) expression. These results demonstrate that quercetin protects β-cell mass and function under high-fructose induction through improving leptin signaling and preserving pancreatic Akt/FoxO1 activation.

Beta cell dysfunction and insulin resistance

Beta cell dysfunction and insulin resistance are inherently complex with their interrelation for triggering the pathogenesis of diabetes also somewhat undefined. Both pathogenic states induce hyperglycemia and therefore increase insulin demand. Beta cell dysfunction results from inadequate glucose sensing to stimulate insulin secretion therefore elevated glucose concentrations prevail. Persistently elevated glucose concentrations above the physiological range result in the manifestation of hyperglycemia. With systemic insulin resistance, insulin signaling within glucose recipient tissues is defective therefore hyperglycemia perseveres. Beta cell dysfunction supersedes insulin resistance in inducing diabetes. Both pathological states influence each other and presumably synergistically exacerbate diabetes. Preserving beta cell function and insulin signaling in beta cells and insulin signaling in the glucose recipient tissues will maintain glucose homeostasis.