Malonyl-CoA signaling, lipid partitioning, and glucolipotoxicity: role in beta-cell adaptation and failure in the etiology of diabetes

Endoplasmic reticulum stress in diseases

The endoplasmic reticulum (ER) is a key organelle in eukaryotic cells, responsible for a wide range of vital functions, including the modification, folding, and trafficking of proteins, as well as the biosynthesis of lipids and the maintenance of intracellular calcium homeostasis. A variety of factors can disrupt the function of the ER, leading to the aggregation of unfolded and misfolded proteins within its confines and the induction of ER stress. A conserved cascade of signaling events known as the unfolded protein response (UPR) has evolved to relieve the burden within the ER and restore ER homeostasis. However, these processes can culminate in cell death while ER stress is sustained over an extended period and at elevated levels. This review summarizes the potential role of ER stress and the UPR in determining cell fate and function in various diseases, including cardiovascular diseases, neurodegenerative diseases, metabolic diseases, autoimmune diseases, fibrotic diseases, viral infections, and cancer. It also puts forward that the manipulation of this intricate signaling pathway may represent a novel target for drug discovery and innovative therapeutic strategies in the context of human diseases.

Metabolomics Signature in Prediabetes and Diabetes: Insights From Tandem Mass Spectrometry Analysis

OBJECTIVE

This study investigates the metabolic differences between normal, prediabetic and diabetic patients with good and poor glycaemic control (GGC and PGC).

DESIGN

In this study, 1102 individuals were included, and 50 metabolites were analysed using tandem mass spectrometry. The diabetes diagnosis and treatment standards of the American Diabetes Association (ADA) were used to classify patients.

METHODS

The nearest neighbour method was used to match controls and cases in each group on the basis of age, sex and BMI. Factor analysis was used to reduce the number of variables and find influential underlying factors. Finally, Pearson's correlation coefficient was used to check the correlation between both glucose and HbAc1 as independent factors with binary classes.

RESULTS

Amino acids such as glycine, serine and proline, and acylcarnitines (AcylCs) such as C16 and C18 showed significant differences between the prediabetes and normal groups. Additionally, several metabolites, including C0, C5, C8 and C16, showed significant differences between the diabetes and normal groups. Moreover, the study found that several metabolites significantly differed between the GGC and PGC diabetes groups, such as C2, C6, C10, C16 and C18. The correlation analysis revealed that glucose and HbA1c levels significantly correlated with several metabolites, including glycine, serine and C16, in both the prediabetes and diabetes groups. Additionally, the correlation analysis showed that HbA1c significantly correlated with several metabolites, such as C2, C5 and C18, in the controlled and uncontrolled diabetes groups.

CONCLUSIONS

These findings could help identify new biomarkers or underlying markers for the early detection and management of diabetes.

Investigating the Impact of IL6 on Insulin Secretion: Evidence from INS-1 Cells, Human Pancreatic Islets, and Serum Analysis

Interleukin-6 (IL6) is a pleiotropic cytokine implicated in metabolic disorders and inflammation, yet its precise influence on insulin secretion and glucose metabolism remains uncertain. This study examined IL6 expression in pancreatic islets from individuals with/without diabetes, alongside a series of functional experiments, including siRNA silencing; IL6 treatment; and assessments of glucose uptake, cell viability, apoptosis, and expression of key β-cell genes, which were conducted in both INS-1 cells and human islets to elucidate the effect of IL6 on insulin secretion. Serum levels of IL6 from Emirati patients with type 2 diabetes (T2D) were measured, and the effect of antidiabetic drugs on IL6 levels was studied. The results revealed that IL6 mRNA expression was higher in islets from diabetic and older donors compared to healthy or young donors. IL6 expression correlated negatively with PDX1, MAFB, and NEUROD1 and positively with SOX4, HES1, and FOXA1. Silencing IL6 in INS-1 cells reduced insulin secretion and glucose uptake independently of apoptosis or oxidative stress. Reduced expression of IL6 was associated with the downregulation of Ins, Pdx1, Neurod1, and Glut2 in INS-1 cells. In contrast, IL6 treatment enhanced insulin secretion in INS-1 cells and human islets and upregulated insulin expression. Serum IL6 levels were elevated in patients with T2D and associated with higher glucose, HbA1c, and triglycerides, regardless of glucose-lowering medications. This study provides a new understanding of the role of IL6 in β-cell function and the pathophysiology of T2D. Our data highlight differences in the response to IL6 between INS-1 cells and human islets, suggesting the presence of species-specific variations across different experimental models. Further research is warranted to unravel the precise mechanisms underlying the observed effects of IL-6 on insulin secretion.

Insulin Resistance, Obesity, and Lipotoxicity

Lipotoxicity, originally used to describe the destructive effects of excess fat accumulation on glucose metabolism, causes functional impairments in several metabolic pathways, both in adipose tissue and peripheral organs, like liver, heart, pancreas, and muscle. Ectopic lipid accumulation in the kidneys, liver, and heart has important clinical counterparts like diabetic nephropathy in type 2 diabetes mellitus, obesity-related glomerulopathy, nonalcoholic fatty liver disease, and cardiomyopathy. Insulin resistance due to lipotoxicity indirectly lead to reproductive system disorders, like polycystic ovary syndrome. Lipotoxicity has roles in insulin resistance and pancreatic beta-cell dysfunction. Increased circulating levels of lipids and the metabolic alterations in fatty acid utilization and intracellular signaling have been related to insulin resistance in muscle and liver. Different pathways, like novel protein kinase c pathways and the JNK-1 pathway, are involved as the mechanisms of how lipotoxicity leads to insulin resistance in nonadipose tissue organs, such as liver and muscle. Mitochondrial dysfunction plays a role in the pathogenesis of insulin resistance. Endoplasmic reticulum stress, through mainly increased oxidative stress, also plays an important role in the etiology of insulin resistance, especially seen in non-alcoholic fatty liver disease. Visceral adiposity and insulin resistance both increase the cardiometabolic risk, and lipotoxicity seems to play a crucial role in the pathophysiology of these associations.

Interference of altered plasma trace elements profile with hyperhomocysteinemia and oxidative stress damage to insulin secretion dysfunction in Psammomys obesus: focus on the selenium

The objective of this study is to investigate the relationship between altered plasma trace elements, particularly selenium (Se), with Hyper-homocysteinemia (HhCys) as a predictive factor of insulin secretion dysfunction. The study is carried out on adult Psammomys obesus, divided in 4 experimental groups: (I) Normoglycemic/Normoinsulinemic; (II) Normoglycemic/Hyperinsulinemic; (III) Hyperglycaemic/Hyperinsulinemic and (IV) Hyperglycaemic/Insulin deficiency with ketoacidosis. The data showed that a drastic depletion of Se plasma levels is positively correlated with HhCys (>15 µmol/L; p < .001), concomitantly with decreased GPx activity, GSH levels, and GSH/GSSG ratio in group IV both in plasma and liver. In contrast, SOD activity is increased (p ≤ .001) in group IV both in plasma and liver. However, plasma Cu and Mn levels increased, while plasma Zn levels decreased in group IV (p < .001). Our study confirms the increase of plasma hCys levels seemed to be a major contributing factor to antioxidant capacities and alters the availability of selenium metabolism by interference with homocysteine synthesis in the insulin secretion deficiency stage.

Clearance of p16Ink4a-positive cells in a mouse transgenic model does not change β-cell mass and has limited effects on their proliferative capacity

Type 2 diabetes is partly characterized by decreased β-cell mass and function which have been linked to cellular senescence. Despite a low basal proliferative rate of adult β-cells, they can respond to growth stimuli, but this proliferative capacity decreases with age and correlates with increased expression of senescence effector, p16Ink4a. We hypothesized that selective deletion of p16Ink4a-positive cells would enhance the proliferative capacity of the remaining β-cells due to the elimination of the local senescence-associated secretory phenotype (SASP). We aimed to investigate the effects of p16Ink4a-positive cell removal on the mass and proliferative capacity of remaining β-cells using INK-ATTAC mice as a transgenic model of senolysis. Clearance of p16Ink4a positive subpopulation was tested in mice of different ages, males and females, and with two different insulin resistance models: high-fat diet (HFD) and insulin receptor antagonist (S961). Clearance of p16Ink4a-positive cells did not affect the overall β-cell mass. β-cell proliferative capacity negatively correlated with cellular senescence load and clearance of p16Ink4a positive cells in 1-year-old HFD mice improved β-cell function and increased proliferative capacity in a subset of animals. Single-cell sequencing revealed that the targeted p16Ink4a subpopulation of β-cells is non-proliferative and non-SASP producing whereas additional senescent subpopulations remained contributing to continued local SASP secretion. In conclusion, deletion of p16Ink4a cells did not negatively impact beta-cell mass and blood glucose under basal and HFD conditions and proliferation was restored in a subset of HFD mice opening further therapeutic targets in the treatment of diabetes.

Protein acylation: mechanisms, biological functions and therapeutic targets

Metabolic reprogramming is involved in the pathogenesis of not only cancers but also neurodegenerative diseases, cardiovascular diseases, and infectious diseases. With the progress of metabonomics and proteomics, metabolites have been found to affect protein acylations through providing acyl groups or changing the activities of acyltransferases or deacylases. Reciprocally, protein acylation is involved in key cellular processes relevant to physiology and diseases, such as protein stability, protein subcellular localization, enzyme activity, transcriptional activity, protein-protein interactions and protein-DNA interactions. Herein, we summarize the functional diversity and mechanisms of eight kinds of nonhistone protein acylations in the physiological processes and progression of several diseases. We also highlight the recent progress in the development of inhibitors for acyltransferase, deacylase, and acylation reader proteins for their potential applications in drug discovery.

Alterations in Microbiota and Metabolites Related to Spontaneous Diabetes and Pre-Diabetes in Rhesus Macaques

Spontaneous type 2 diabetes mellitus (T2DM) macaques are valuable resources for our understanding the pathological mechanism of T2DM. Based on one month’s fasting blood glucose survey, we identified seven spontaneous T2DM macaques and five impaired glucose regulation (IGR) macaques from 1408 captive individuals. FPG, HbA1c, FPI and IR values were significant higher in T2DM and IGR than in controls. 16S rRNA sequencing of fecal microbes showed the significantly greater abundance of Oribacterium, bacteria inhibiting the production of secondary bile acids, and Phascolarctobacterium, bacteria producing short-chain fatty acids was significantly lower in T2DM macaques. In addition, several opportunistic pathogens, such as Mogibacterium and Kocuria were significantly more abundant in both T2DM and IGR macaques. Fecal metabolites analysis based on UHPLC-MS identified 50 differential metabolites (DMs) between T2DM and controls, and 26 DMs between IGR and controls. The DMs were significantly enriched in the bile acids metabolism, fatty acids metabolism and amino acids metabolism pathways. Combining results from physiochemical parameters, microbiota and metabolomics, we demonstrate that the imbalance of gut microbial community leading to the dysfunction of glucose, bile acids, fatty acids and amino acids metabolism may contribute to the hyperglycaemia in macaques, and suggest several microbes and metabolites are potential biomarkers for T2DM and IGR macaques.

Contribution of Mitochondria to Insulin Secretion by Various Secretagogues

Significance: Mitochondria determine glucose-stimulated insulin secretion (GSIS) in pancreatic β-cells by elevating ATP synthesis. As the metabolic and redox hub, mitochondria provide numerous links to the plasma membrane channels, insulin granule vesicles (IGVs), cell redox, NADH, NADPH, and Ca²⁺ homeostasis, all affecting insulin secretion. Recent Advances: Mitochondrial redox signaling was implicated in several modes of insulin secretion (branched-chain ketoacid [BCKA]-, fatty acid [FA]-stimulated). Mitochondrial Ca²⁺ influx was found to enhance GSIS, reflecting cytosolic Ca²⁺ oscillations induced by action potential spikes (intermittent opening of voltage-dependent Ca²⁺ and K⁺ channels) or the superimposed Ca²⁺ release from the endoplasmic reticulum (ER). The ATPase inhibitory factor 1 (IF1) was reported to tune the glucose sensitivity range for GSIS. Mitochondrial protein kinase A was implicated in preventing the IF1-mediated inhibition of the ATP synthase. Critical Issues: It is unknown how the redox signal spreads up to the plasma membrane and what its targets are, what the differences in metabolic, redox, NADH/NADPH, and Ca²⁺ signaling, and homeostasis are between the first and second GSIS phase, and whether mitochondria can replace ER in the amplification of IGV exocytosis. Future Directions: Metabolomics studies performed to distinguish between the mitochondrial matrix and cytosolic metabolites will elucidate further details. Identifying the targets of cell signaling into mitochondria and of mitochondrial retrograde metabolic and redox signals to the cell will uncover further molecular mechanisms for insulin secretion stimulated by glucose, BCKAs, and FAs, and the amplification of secretion by glucagon-like peptide (GLP-1) and metabotropic receptors. They will identify the distinction between the hub β-cells and their followers in intact and diabetic states. Antioxid. Redox Signal. 36, 920-952.

Glucolipotoxicity induces endothelial cell dysfunction by activating autophagy and inhibiting autophagic flow

OBJECTIVES

This study aims to determine the role and mechanism of autophagy in endothelial cell dysfunction by glucolipotoxicity.

METHODS

Human umbilical vein endothelial cells (HUVECs) were treated with high glucose and high palmitic acid. The number of autophagosomes was evaluated by monodansylcadaverine (MDC) staining and transmission electron microscopy (TEM). The expression of autophagy-related proteins (LC3 and P62) was assessed by Western blotting. Capillary tube-like formation was evaluated on Matrigel. Reactive oxygen species (ROS) production was detected by DCFH-DA. Cell apoptosis was measured by Hoechst 33258 staining and flow cytometry. Phosphorylation of AMPK, mTOR, and ULK1 was also analyzed by Western blotting.

RESULTS

We found that glucolipotoxicity induced autophagy initiation and hindered autophagosomes degradation. Moreover, glucolipotoxicity increased the production of intracellular ROS, decreased the ability of tubular formation, and increased cell apoptosis. However, endothelial cell dysfunction was alleviated by 3-methyladenine, an early-stage autophagy inhibitor. Additionally, glucolipotoxicity promoted the phosphorylation of AMPK and ULK1 and inhibited the phosphorylation of mTOR.

CONCLUSIONS

Glucolipotoxicity initiates autophagy through the AMPK/mTOR/ULK1 signaling pathway and inhibits autophagic flow, leading to the accumulation of autophagosomes, thereby inducing apoptosis and impairing endothelial cell function.

Meals That Differ in Nutrient Composition and Inflammatory Potential Do Not Differentially Impact Postprandial Circulating Cytokines in Older Adults above a Healthy Weight

In this exploratory study, mixed meals specifically formulated to differ in inflammatory potential were tested to determine whether they could differentially impact circulating levels of inflammatory markers in adults above a healthy weight. Complete data were analyzed from 11 adults (6 males and 5 females) aged 54−63 years with median BMI of 30.0 (27.1−31.6) kg/m². In a crossover study design, each participant consumed an isocaloric (2.2 MJ) meal with either a low (Anti-meal), moderate (Neutr-meal), or high (Pro-meal) inflammatory potential. Fasting and postprandial blood samples were analyzed for plasma levels of IL-6, IL-1β, TNF-α, IL-10, and metabolic makers. Postprandial plasma IL-6, IL-1β, TNF-α, and IL-10 incremental areas under the curve (iAUC) were not different between the three meals (p > 0.05). There was a trend of an increase in IL-6 with time in all three meals, but no changes were obvious for the other measured cytokines. The Pro-meal induced an increased postprandial iAUC for triglycerides compared to the Anti-meal and Neutr-meal (p = 0.004 and p = 0.012, respectively). Single meals, regardless of their theoretical inflammatory potential, did not substantially shift circulating inflammatory markers, suggesting that longer-term dietary patterns are important rather than single dietary exposures in the pathology of metabolic conditions.

Mitochondrial Dysfunction and Acute Fatty Liver of Pregnancy

The liver is one of the richest organs in mitochondria, serving as a hub for key metabolic pathways such as β-oxidation, the tricarboxylic acid (TCA) cycle, ketogenesis, respiratory activity, and adenosine triphosphate (ATP) synthesis, all of which provide metabolic energy for the entire body. Mitochondrial dysfunction has been linked to subcellular organelle dysfunction in liver diseases, particularly fatty liver disease. Acute fatty liver of pregnancy (AFLP) is a life-threatening liver disorder unique to pregnancy, which can result in serious maternal and fetal complications, including death. Pregnant mothers with this disease require early detection, prompt delivery, and supportive maternal care. AFLP was considered a mysterious illness and though its pathogenesis has not been fully elucidated, molecular research over the past two decades has linked AFLP to mitochondrial dysfunction and defects in fetal fatty-acid oxidation (FAO). Due to deficient placental and fetal FAO, harmful 3-hydroxy fatty acid metabolites accumulate in the maternal circulation, causing oxidative stress and microvesicular fatty infiltration of the liver, resulting in AFLP. In this review, we provide an overview of AFLP and mitochondrial FAO followed by discussion of how altered mitochondrial function plays an important role in the pathogenesis of AFLP.

Glycerol-3-phosphate phosphatase operates a glycerol shunt in pancreatic β-cells that controls insulin secretion and metabolic stress

Objective

The recently identified glycerol-3-phosphate (Gro3P) phosphatase (G3PP) in mammalian cells, encoded by the PGP gene, was shown to regulate glucose, lipid and energy metabolism by hydrolyzing Gro3P and to control glucose-stimulated insulin secretion (GSIS) in β-cells, in vitro. However, whether G3PP regulates β-cell function and insulin secretion in vivo is not known.

Methods

We now examined the role of G3PP in the control of insulin secretion in vivo, β-cell function and glucotoxicity in inducible β-cell specific G3PP-KO (BKO) mice. Inducible BKO mice were generated by crossing floxed-G3PP mice with Mip-Cre-ERT (MCre) mice. All the in vivo studies were done using BKO and control mice fed normal diet and the ex vivo studies were done using pancreatic islets from these mice.

Results

BKO mice, compared to MCre controls, showed increased body weight, adiposity, fed insulinemia, enhanced in vivo GSIS, reduced plasma triglycerides and mild glucose intolerance. Isolated BKO mouse islets incubated at high (16.7 mM), but not at low or intermediate glucose (3 and 8 mM), showed elevated GSIS, Gro3P content as well as increased levels of metabolites and signaling coupling factors known to reflect β-cell activation for insulin secretion. BKO islets also showed reduced glycerol release and increased O₂ consumption and ATP production at high glucose only. BKO islets chronically exposed to elevated glucose levels showed increased apoptosis, reduced insulin content and decreased mRNA expression of β-cell differentiation markers, Pdx-1, MafA and Ins-2.

Conclusions

The results demonstrate that β-cells are endowed with a “glycerol shunt”, operated by G3PP that regulates β-cell metabolism, signaling and insulin secretion in vivo, primarily at elevated glucose concentrations. We propose that the glycerol shunt plays a role in preventing insulin hypersecretion and excess body weight gain and contributes to β-cell mass preservation in the face of hyperglycemia.

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G3PP operates a glycerol shunt in β-cells to remove excess glucose as glycerol.

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Inducible β-cell specific G3PP-KO (BKO) mice show hyperinsulinemia.

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BKO mice show enhanced body weight and glucose induced insulin secretion.

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BKO isolated islets show elevated insulin secretion only at high glucose.

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Chronic exposure of BKO isolated islets to high glucose enhances glucotoxicity.

Maintaining Effective Beta Cell Function in the Face of Metabolic Syndrome-Associated Glucolipotoxicity-Nutraceutical Options

In people with metabolic syndrome, episodic exposure of pancreatic beta cells to elevated levels of both glucose and free fatty acids (FFAs)-or glucolipotoxicity-can induce a loss of glucose-stimulated insulin secretion (GSIS). This in turn can lead to a chronic state of glucolipotoxicity and a sustained loss of GSIS, ushering in type 2 diabetes. Loss of GSIS reflects a decline in beta cell glucokinase (GK) expression associated with decreased nuclear levels of the pancreatic and duodenal homeobox 1 (PDX1) factor that drives its transcription, along with that of Glut2 and insulin. Glucolipotoxicity-induced production of reactive oxygen species (ROS), stemming from both mitochondria and the NOX2 isoform of NADPH oxidase, drives an increase in c-Jun N-terminal kinase (JNK) activity that promotes nuclear export of PDX1, and impairs autocrine insulin signaling; the latter effect decreases PDX1 expression at the transcriptional level and up-regulates beta cell apoptosis. Conversely, the incretin hormone glucagon-like peptide-1 (GLP-1) promotes nuclear import of PDX1 via cAMP signaling. Nutraceuticals that quell an increase in beta cell ROS production, that amplify or mimic autocrine insulin signaling, or that boost GLP-1 production, should help to maintain GSIS and suppress beta cell apoptosis in the face of glucolipotoxicity, postponing or preventing onset of type 2 diabetes. Nutraceuticals with potential in this regard include the following: phycocyanobilin-an inhibitor of NOX2; agents promoting mitophagy and mitochondrial biogenesis, such as ferulic acid, lipoic acid, melatonin, berberine, and astaxanthin; myo-inositol and high-dose biotin, which promote phosphatidylinositol 3-kinase (PI3K)/Akt activation; and prebiotics/probiotics capable of boosting GLP-1 secretion. Complex supplements or functional foods providing a selection of these agents might be useful for diabetes prevention.

Gut Metabolite Trimethylamine N-Oxide Protects INS-1 β-Cell and Rat Islet Function under Diabetic Glucolipotoxic Conditions

Serum accumulation of the gut microbial metabolite trimethylamine N-oxide (TMAO) is associated with high caloric intake and type 2 diabetes (T2D). Impaired pancreatic β-cell function is a hallmark of diet-induced T2D, which is linked to hyperglycemia and hyperlipidemia. While TMAO production via the gut microbiome-liver axis is well defined, its molecular effects on metabolic tissues are unclear, since studies in various tissues show deleterious and beneficial TMAO effects. We investigated the molecular effects of TMAO on functional β-cell mass. We hypothesized that TMAO may damage functional β-cell mass by inhibiting β-cell viability, survival, proliferation, or function to promote T2D pathogenesis. We treated INS-1 832/13 β-cells and primary rat islets with physiological TMAO concentrations and compared functional β-cell mass under healthy standard cell culture (SCC) and T2D-like glucolipotoxic (GLT) conditions. GLT significantly impeded β-cell mass and function by inducing oxidative and endoplasmic reticulum (ER) stress. TMAO normalized GLT-mediated damage in β-cells and primary islet function. Acute 40µM TMAO recovered insulin production, insulin granule formation, and insulin secretion by upregulating the IRE1α unfolded protein response to GLT-induced ER and oxidative stress. These novel results demonstrate that TMAO protects β-cell function and suggest that TMAO may play a beneficial molecular role in diet-induced T2D conditions.

Free fatty acid receptor 1: a ray of hope in the therapy of type 2 diabetes mellitus

Free fatty acid receptor 1 (FFAR1) is a G-protein coupled receptor with prominent expression on pancreatic beta cells, bones, intestinal cells as well as the nerve cells. This receptor mediates a multitude of functions in the body including release of incretins, secretion of insulin as well as sensation of pain. Since FFAR1 causes secretion of insulin and regulates glucose metabolism, efforts were made to unfold its structure followed by discovering agonists for the receptor and the utilization of these agonists in the therapy of type 2 diabetes mellitus. Development of such functional FFAR1 agonists is a necessity because the currently available therapy for type 2 diabetes mellitus has numerous drawbacks, of which, the major one is hypoglycemia. Since the most prominent effect of the FFAR1 agonists is on glucose concentration in the body, so the major research is focused on treating type 2 diabetes mellitus, though the agonists could benefit other metabolic disorders and neurological disorders as well. The agonists developed so far had one major limitation, i.e., hepatotoxicity. Although, the only agonist that could reach phase 3 clinical trials was TAK-875 developed by Takeda Pharmaceuticals but it was also withdrawn due to toxic effects on the liver. Thus, there are numerous agonists for the varied binding sites of the receptor but no drug available yet. There does seem to be a ray of hope in the drugs that target FFAR1 but a lot more efforts towards drug discovery would result in the successful management of type 2 diabetes mellitus.

Novel advances in understanding fatty acid-binding G protein-coupled receptors and their roles in controlling energy balance

Diabetes, obesity, and other metabolic diseases have been recognized as the main factors that endanger human health worldwide. Most of these metabolic syndromes develop when the energy balance in the body is disrupted. Energy balance depends upon the systemic regulation of food intake, glucose homeostasis, and lipid metabolism. Fatty acid-binding G protein-coupled receptors (GPCRs) are widely expressed in various types of tissues and cells involved in energy homeostasis regulation. In this review, the distribution and biological functions of fatty acid-binding GPCRs are summarized, particularly with respect to the gut, pancreas, and adipose tissue. A systematic understanding of the physiological functions of the fatty acid-binding GPCRs involved in energy homeostasis regulation will help in identifying novel pharmacological targets for metabolic diseases.

Urolithin A, a pomegranate metabolite, protects pancreatic β cells from apoptosis by activating autophagy

ETHNOPHARMACOLOGICAL RELEVANCE

Urolithin A is an active metabolite of plant polyphenol ellagic acid generated by intestinal flora, which is derived from strawberry or traditional anti-diabetic Chinese medicine such as Punica granatum L. and Phyllanthus emblica. The present study aimed to whether urolithin A can protect against glycolipid-toxicity-induced apoptosis of pancreatic β-cells and the underlying mechanisms.

MATERIALS AND METHODS

Apoptosis was induced in the pancreas of mice with type 2 diabetes and MIN6 pancreatic β-cells. CC-8 assay was conducted to determine cell viability. Flow cytometry, JC-1 fluorescent probe, and western blot assays were performed to assess apoptosis. Immunofluorescence and western blot assays were used to detect changes in autophagy. The mechanism of apoptosis was elucidated using autophagy inhibitor chloroquine.

RESULTS

Urolithin A intervention significantly reduced pancreatic cell apoptosis in diabetic mice and MIN6 β cells. This was achieved by the downregulation of cleaved-caspase 3, cleaved-caspase 1, and restoration of cell viability, cell morphology and mitochondrial membrane potential, accompanied with the downregulation of autophagic protein SQSTM1/p62 and upregulation of LC3II. Chloroquine, an autophagy inhibitor, reversed the anti-glucolipotoxic and anti-apoptotic effects of urolithin A.

CONCLUSION

These findings suggest that urolithin A protects against glucolipotoxicity-induced apoptosis in pancreatic β-cells by inducing activation of autophagy.

miR-375 induces adipogenesis through targeting Erk1 in pancreatic duct cells under the influence of sodium palmitate

The goal of this study was to research long-term saturated fatty acid overexposure that can induce differentiation of pancreatic duct cells into adipocytes and also into β-cells. The important findings can be summarized as follows: (i) adipogenesis and early stage β-cell differentiation were stimulated in duct cells under lipotoxicity and glucolipotoxicity conditions, (ii) miR-375 expression was upregulated while its target Erk1 was downregulated and miR-375 inhibitor upregulated Erk1 while expression of adipogenesis markers was downregulated in duct cells under both conditions, (iii) apoptosis was induced in β and duct cells under both conditions, (iv) lipotoxicity induced proliferation of co-cultured β-cells. These findings suggest that long-term saturated fatty acid overexposure may cause intrapancreatic fat accumulation by inducing differentiation of duct cells into adipocytes and it may contributes to β-cell compensation by stimulating the early stage of β-cell differentiation in duct cells. In addition, miR-375 may have the potential to be a new target in the treatment of Type 2 diabetes, and NAFPD due to its role in the adipogenesis of duct cells.

Bilobalide Enhances AMPK Activity to Improve Liver Injury and Metabolic Disorders in STZ-Induced Diabetes in Immature Rats via Regulating HMGB1/TLR4/NF-κB Signaling Pathway

This study was aimed at examining the effect and underlying mechanisms of bilobalide (BB) on hepatic injury in streptozotocin- (STZ-) induced diabetes mellitus (DM) in immature rats. Immature rats (one day old) were randomly divided into five groups: group I, control nondiabetic rats; group II, STZ-induced, untreated diabetic rats; groups III/IV/V, STZ-induced and BB-treated diabetic rats, which were intraperitoneally injected with BB (2.5 mg/kg, 5 mg/kg, or 10 mg/kg) after 3 days followed by STZ treatment. We observed that BB improved the histopathological changes and maintained normal glucose metabolism, blood lipid, and liver function indicators, such as fasting blood glucose, obesity index, HbA1c, HOMA-IR, fast serum insulin, adiponectin, total cholesterol (TC), triglyceride (TG), high-density lipoprotein (HDL), low-density lipoprotein (LDL), aspartate transaminase (AST), and alanine transaminase (ALT) in STZ-induced DM in immature rats by a biochemical analyzer or ELISA. Meanwhile, Western blot analysis showed that in STZ-induced DM immature rats, BB decreased the expression of apoptosis-related proteins Bax, cleaved caspase-3, and cleaved caspase-9 while enhancing the Bcl-2 expression; BB downregulated the expression of ACC related to fat anabolism, while upregulating the expression of CPT-1 related to fat catabolism. Strikingly, treatment with BB significantly increased the expression of AMPKα1 as well as inhibited HMGB1, TLR4, and p-P65 expression in hepatic tissues of immature DM rats. AMPK inhibitor (compound C, CC) cotreated with BB undermined the protective effect of BB on the liver injury. The results of the present study suggested BB may have a significant role in alleviating liver damage in the STZ-induced immature DM rats.

Elevated Expression of Glycerol-3-Phosphate Phosphatase as a Biomarker of Poor Prognosis and Aggressive Prostate Cancer

The limitations of the biomarker prostate-specific antigen (PSA) necessitate the pursuit of biomarkers capable of better identifying high-risk prostate cancer (PC) patients in order to improve their therapeutic management and outcomes. Aggressive prostate tumors characteristically exhibit high rates of glycolysis and lipogenesis. Glycerol 3-phosphate phosphatase (G3PP), also known as phosphoglycolate phosphatase (PGP), is a recently identified mammalian enzyme, shown to play a role in the regulation of glucose metabolism, lipogenesis, lipolysis, and cellular nutrient-excess detoxification. We hypothesized that G3PP may relieve metabolic stress in cancer cells and assessed the association of its expression with PC patient prognosis. Using immunohistochemical staining, we assessed the epithelial expression of G3PP in two different radical prostatectomy (RP) cohorts with a total of 1797 patients, for whom information on biochemical recurrence (BCR), metastasis, and mortality was available. The association between biomarker expression, biochemical recurrence (BCR), bone metastasis, and prostate cancer-specific survival was established using log-rank and multivariable Cox regression analyses. High expression of G3PP in PC epithelial cells is associated with an increased risk of BCR, bone metastasis, and PC-specific mortality. Multivariate analysis revealed high G3PP expression in tumors as an independent predictor of BCR and bone metastasis development. High G3PP expression in tumors from patients eligible for prostatectomies is a new and independent prognostic biomarker of poor prognosis and aggressive PC for recurrence, bone metastasis, and mortality.

Molecular mechanisms of lipotoxicity-induced pancreatic β-cell dysfunction

Type 2 diabetes (T2D), a heterogeneous disorder derived from metabolic dysfunctions, leads to a glucose overflow in the circulation due to both defective insulin secretion and peripheral insulin resistance. One of the critical risk factor for T2D is obesity, which represents a global epidemic that has nearly tripled since 1975. Obesity is characterized by chronically elevated free fatty acid (FFA) levels, which cause deleterious effects on glucose homeostasis referred to as lipotoxicity. Here, we review the physiological FFA roles onto glucose-stimulated insulin secretion (GSIS) and the pathological ones affecting many steps of the mechanisms and modulation of GSIS. We also describe in vitro and in vivo experimental evidences addressing lipotoxicity in β-cells and the role of saturation and chain length of FFA on the potency of GSIS stimulation. The molecular mechanisms underpinning lipotoxic-β-cell dysfunction are also reviewed. Among them, endoplasmic reticulum stress, oxidative stress and mitochondrial dysfunction, inflammation, impaired autophagy and β-cell dedifferentiation. Finally therapeutic strategies for the β-cells dysfunctions such as the use of metformin, glucagon-like peptide 1, thiazolidinediones, anti-inflammatory drugs, chemical chaperones and weight are discussed.

Glucolipotoxicity and GLP-1 secretion

INTRODUCTION

The concept of glucolipotoxicity refers to the combined, deleterious effects of elevated glucose and/or fatty acid levels.

RESEARCH DESIGN AND METHODS

To investigate the effects of chronic glucolipotoxicity on glucagon-like peptide-1-(7-36) amide (GLP-1) secretion, we generated glucolipotoxic conditions in human NCI-H716 enteroendocrine cells using either 5 or 25 mM glucose with or without 500 µM palmitate for 72 hours. For in vivo study, we have established a chronic nutrient infusion model in the rat. Serial blood samples were collected for 2 hours after the consumption of a mixed meal to evaluate insulin sensitivity and β-cell function.

RESULTS

Chronic glucolipotoxic conditions decreased GLP-1 secretion and the expressions of pCREB, pGSK3β, β-catenin, and TCF7L2 in NCI-H716 cells. Glucolipotoxicity conditions reduced glucose transporter expression, glucose uptake, and nicotinamide-adenine dinucleotide phosphate (NADPH) levels in L-cells, and increased triglyceride accumulation. In contrast, PPARα and ATP levels were reduced, which correlated well with decreased levels of SUR1 and Kir6.2, cAMP contents and expressions of pCAMK2, EPAC and PKA. We also observed an increase in reactive oxygen species production, UCP2 expression and Complex I activity. Simultaneous treatment with insulin restored the GLP-1 secretion. Glucolipotoxic conditions decreased insulin secretion in a time-dependent manner in INS-1 cells, which was recovered with exendin-4 cotreatment. Glucose and SMOFlipid infusion for 6 hours decreased GLP-1 secretion and proglucagon mRNA levels as well as impaired the glucose tolerance, insulin and C-peptide secretion in rats.

CONCLUSION

These results provide evidence for the first time that glucolipotoxicity could affect GLP-1 secretion through changes in glucose and lipid metabolism, gene expressions, and proglucagon biosynthesis and suggest the interrelationship between glucolipotoxicities of L-cells and β-cells which develops earlier than that of L-cells.

The Pancreatic β-Cell: The Perfect Redox System

Pancreatic β-cell insulin secretion, which responds to various secretagogues and hormonal regulations, is reviewed here, emphasizing the fundamental redox signaling by NADPH oxidase 4- (NOX4-) mediated H₂O₂ production for glucose-stimulated insulin secretion (GSIS). There is a logical summation that integrates both metabolic plus redox homeostasis because the ATP-sensitive K⁺ channel (K_ATP) can only be closed when both ATP and H₂O₂ are elevated. Otherwise ATP would block K_ATP, while H₂O₂ would activate any of the redox-sensitive nonspecific calcium channels (NSCCs), such as TRPM2. Notably, a 100%-closed K_ATP ensemble is insufficient to reach the -50 mV threshold plasma membrane depolarization required for the activation of voltage-dependent Ca²⁺ channels. Open synergic NSCCs or Cl^- channels have to act simultaneously to reach this threshold. The resulting intermittent cytosolic Ca²⁺-increases lead to the pulsatile exocytosis of insulin granule vesicles (IGVs). The incretin (e.g., GLP-1) amplification of GSIS stems from receptor signaling leading to activating the phosphorylation of TRPM channels and effects on other channels to intensify integral Ca²⁺-influx (fortified by endoplasmic reticulum Ca²⁺). ATP plus H₂O₂ are also required for branched-chain ketoacids (BCKAs); and partly for fatty acids (FAs) to secrete insulin, while BCKA or FA β-oxidation provide redox signaling from mitochondria, which proceeds by H₂O₂ diffusion or hypothetical SH relay via peroxiredoxin "redox kiss" to target proteins.

Role of mitochondria in liver metabolic health and diseases

The liver is a major organ that coordinates the metabolic flexibility of the whole body, which is characterized by the ability to adapt dynamically in response to fluctuations in energy needs and supplies. In this context, hepatocyte mitochondria are key partners in fine-tuning metabolic flexibility. Here we review the metabolic and signalling pathways carried by mitochondria in the liver, the major pathways that regulate mitochondrial function and how they function in health and metabolic disorders associated to obesity, i.e. insulin resistance, non-alcoholic steatosis and steatohepatitis and hepatocellular carcinoma. Finally, strategies targeting mitochondria to counteract liver disorders are discussed.

Integration of single-cell datasets reveals novel transcriptomic signatures of β-cells in human type 2 diabetes

Pancreatic islet β-cell failure is key to the onset and progression of type 2 diabetes (T2D). The advent of single-cell RNA sequencing (scRNA-seq) has opened the possibility to determine transcriptional signatures specifically relevant for T2D at the β-cell level. Yet, applications of this technique have been underwhelming, as three independent studies failed to show shared differentially expressed genes in T2D β-cells. We performed an integrative analysis of the available datasets from these studies to overcome confounding sources of variability and better highlight common T2D β-cell transcriptomic signatures. After removing low-quality transcriptomes, we retained 3046 single cells expressing 27 931 genes. Cells were integrated to attenuate dataset-specific biases, and clustered into cell type groups. In T2D β-cells (n = 801), we found 210 upregulated and 16 downregulated genes, identifying key pathways for T2D pathogenesis, including defective insulin secretion, SREBP signaling and oxidative stress. We also compared these results with previous data of human T2D β-cells from laser capture microdissection and diabetic rat islets, revealing shared β-cell genes. Overall, the present study encourages the pursuit of single β-cell RNA-seq analysis, preventing presently identified sources of variability, to identify transcriptomic changes associated with human T2D and underscores specific traits of dysfunctional β-cells across different models and techniques.

Mitochondrial Carriers Regulating Insulin Secretion Profiled in Human Islets upon Metabolic Stress

Chronic exposure of β-cells to nutrient-rich metabolic stress impairs mitochondrial metabolism and its coupling to insulin secretion. We exposed isolated human islets to different metabolic stresses for 3 days: 0.4 mM oleate or 0.4 mM palmitate at physiological 5.5 mM glucose (lipotoxicity), high 25 mM glucose (glucotoxicity), and high 25 mM glucose combined with 0.4 mM oleate and/or palmitate (glucolipotoxicity). Then, we profiled the mitochondrial carriers and associated genes with RNA-Seq. Diabetogenic conditions, and in particular glucotoxicity, increased expression of several mitochondrial solute carriers in human islets, such as the malate carrier DIC, the α-ketoglutarate-malate exchanger OGC, and the glutamate carrier GC1. Glucotoxicity also induced a general upregulation of the electron transport chain machinery, while palmitate largely counteracted this effect. Expression of different components of the TOM/TIM mitochondrial protein import system was increased by glucotoxicity, whereas glucolipotoxicity strongly upregulated its receptor subunit TOM70. Expression of the mitochondrial calcium uniporter MCU was essentially preserved by metabolic stresses. However, glucotoxicity altered expression of regulatory elements of calcium influx as well as the Na⁺/Ca²⁺ exchanger NCLX, which mediates calcium efflux. Overall, the expression profile of mitochondrial carriers and associated genes was modified by the different metabolic stresses exhibiting nutrient-specific signatures.

Carbohydrate and fat intake associated with risk of metabolic diseases through epigenetics of CPT1A

BACKGROUND

Epigenome-wide association studies identified the cg00574958 DNA methylation site at the carnitine palmitoyltransferase-1A (CPT1A) gene to be associated with reduced risk of metabolic diseases (hypertriglyceridemia, obesity, type 2 diabetes, hypertension, metabolic syndrome), but the mechanism underlying these associations is unknown.

OBJECTIVES

We aimed to elucidate whether carbohydrate and fat intakes modulate cg00574958 methylation and the risk of metabolic diseases.

METHODS

We examined associations between carbohydrate (CHO) and fat (FAT) intake, as percentages of total diet energy, and the CHO/FAT ratio with CPT1A-cg00574958, and the risk of metabolic diseases in 3 populations (Genetics of Lipid Lowering Drugs and Diet Network, n = 978; Framingham Heart Study, n = 2331; and REgistre GIroní del COR study, n = 645) while adjusting for confounding factors. To understand possible causal effects of dietary intake on the risk of metabolic diseases, we performed meta-analysis, CPT1A transcription analysis, and mediation analysis with CHO and FAT intakes as exposures and cg00574958 methylation as the mediator.

RESULTS

We confirmed strong associations of cg00574958 methylation with metabolic phenotypes (BMI, triglyceride, glucose) and diseases in all 3 populations. Our results showed that CHO intake and CHO/FAT ratio were positively associated with cg00574958 methylation, whereas FAT intake was negatively correlated with cg00574958 methylation. Meta-analysis further confirmed this strong correlation, with β = 58.4 ± 7.27, P = 8.98 x 10-16 for CHO intake; β = -36.4 ± 5.95, P = 9.96 x 10-10 for FAT intake; and β = 3.30 ± 0.49, P = 1.48 x 10-11 for the CHO/FAT ratio. Furthermore, CPT1A mRNA expression was negatively associated with CHO intake, and positively associated with FAT intake, and metabolic phenotypes. Mediation analysis supports the hypothesis that CHO intake induces CPT1A methylation, hence reducing the risk of metabolic diseases, whereas FAT intake inhibits CPT1A methylation, thereby increasing the risk of metabolic diseases.

CONCLUSIONS

Our results suggest that the proportion of total energy supplied by CHO and FAT can have a causal effect on the risk of metabolic diseases via the epigenetic status of CPT1A.Study registration at https://www.clinicaltrials.gov/: the Genetics of Lipid Lowering Drugs and Diet Network (GOLDN)-NCT01023750; and the Framingham Heart Study (FHS)-NCT00005121.

Metabolic Syndrome Pathophysiology and Predisposing Factors

Metabolic syndrome (MetS) is a cluster of cardiometabolic risk factors with high prevalence among adult populations and elevated costs for public health systems worldwide. Despite the lack of consensus regarding the syndrome definition and diagnosis criteria, it is characterized by the coexistence of risk factors such as abdominal obesity, atherogenic dyslipidemia, elevated blood pressure, a prothrombotic and pro-inflammatory state, insulin resistance (IR), and higher glucose levels, factors indubitably linked to an increased risk of developing chronic conditions, such as type 2 diabetes (T2D) and cardiovascular disease (CVD). The syndrome has a complex and multifaceted origin not fully understood; however, it has been strongly suggested that sedentarism and unbalanced dietary patterns might play a fundamental role in its development. The purpose of this review is to provide an overview from the syndrome epidemiology, costs, and main etiological traits from its relationship with unhealthy diet patterns and sedentary lifestyles.

Autocrine C-peptide protects INS1 β cells against palmitic acid-induced oxidative stress in peroxisomes by inducing catalase

AIMS

C-peptide, produced by pancreatic β cells and co-secreted in the bloodstream with insulin, has antioxidant properties in glucose- and hydrogen peroxide (H2O2)-exposed INS1 β cells. Palmitic acid, the most physiologically abundant long-chain free fatty acid in humans, is metabolized in peroxisomes of β cells accumulating H2O2 that can lead to oxidative stress. Here, we tested the hypothesis that C-peptide protects β cells from palmitic acid-induced stress by lowering peroxisomal H2O2.

MATERIALS AND METHODS

We exposed INS1 β cells to palmitic acid and C-peptide in the setting of increasing glucose concentration and tested for changes in parameters of stress and death. To study the ability of C-peptide to lower peroxisomal H2O2, we engineered an INS1 β cell line stably expressing the peroxisomal-targeted H2O2 sensor HyPer, whose fluorescence increases with cellular H2O2. An INS1 β cell line stably expressing a live-cell fluorescent catalase reporter was used to detect changes in catalase gene expression.

RESULTS

C-peptide protects INS1 β cells from the combined effect of palmitic acid and glucose by reducing peroxisomal H2O2 to baseline levels and increasing expression of catalase.

CONCLUSIONS

In conditions of glucolipotoxicity, C-peptide increases catalase expression and reduces peroxisomal oxidative stress and death of INS1 β cells. Maintenance of C-peptide secretion is a pro-survival requisite for β cells in adverse conditions. Loss of C-peptide secretion would render β cells more vulnerable to stress and death leading to secretory dysfunction and diabetes.

Glucolipotoxicity, β-Cells, and Diabetes: The Emperor Has No Clothes

Reduction of β-cell mass and function is central to the pathogenesis of type 2 diabetes. The terms glucotoxicity, lipotoxicity, and glucolipotoxicity are used to describe potentially responsible processes. The premise is that chronically elevated glucose levels are toxic to β-cells, that elevated lipid levels in the form of circulating free fatty acids (FFA) also have toxic effects, and that the combination of the two, glucolipotoxicity, is particularly harmful. Much work has shown that high concentrations of FFA can be very damaging to β-cells when used for in vitro experiments, and when infused in large amounts in humans and rodents they produce suppression of insulin secretion. The purpose of this Perspective is to raise doubts about whether the FFA levels found in real-life situations are ever high enough to cause problems. Evidence supporting the importance of glucotoxicity is strong because there is such a tight correlation between defective insulin secretion and rising glucose levels. However, there is virtually no convincing evidence that the alterations in FFA levels occurring during progression to diabetes are pathogenic. Thus, the terms lipotoxicity and glucolipotoxicity should be used with great caution, if at all, because evidence supporting their importance has not yet emerged.

Nutrient-Induced Metabolic Stress, Adaptation, Detoxification, and Toxicity in the Pancreatic β-Cell

Paraphrasing the Swiss physician and father of toxicology Paracelsus (1493-1541) on chemical agents used as therapeutics, "the dose makes the poison," it is now realized that this aptly applies to the calorigenic nutrients. The case here is the pancreatic islet β-cell presented with excessive levels of nutrients such as glucose, lipids, and amino acids. The short-term effects these nutrients exert on the β-cell are enhanced insulin biosynthesis and secretion and changes in glucose sensitivity. However, chronic fuel surfeit triggers additional compensatory and adaptive mechanisms by β-cells to cope with the increased insulin demand or to protect itself. When these mechanisms fail, toxicity due to the nutrient surplus ensues, leading to β-cell dysfunction, dedifferentiation, and apoptosis. The terms glucotoxicity, lipotoxicity, and glucolipotoxicity have been widely used, but there is some confusion as to what they mean precisely and which is most appropriate for a given situation. Here we address the gluco-, lipo-, and glucolipo-toxicities in β-cells by assessing the evidence both for and against each of them. We also discuss potential mechanisms and defend the view that many of the identified "toxic" effects of nutrient excess, which may also include amino acids, are in fact beneficial adaptive processes. In addition, candidate fuel-excess detoxification pathways are evaluated. Finally, we propose that a more general term should be used for the in vivo situation of overweight-associated type 2 diabetes reflecting both the adaptive and toxic processes to mixed calorigenic nutrients excess: "nutrient-induced metabolic stress" or, in brief, "nutri-stress."

The relevance of AMP-activated protein kinase in insulin-secreting β cells: a potential target for improving β cell function?

AMP-activated protein kinase (AMPK) is present in different kinds of metabolically active cells. AMPK is an important intracellular energy sensor and plays a relevant role in whole-body energy homeostasis. AMPK is activated, among others, in response to glucose deprivation, caloric restriction and increased physical activity. Upon activation, AMPK affects metabolic pathways leading to increased formation of ATP and simultaneously reducing ATP-consuming processes. AMPK is also expressed in pancreatic β cells and is largely regulated by glucose, which is the main physiological stimulator of insulin secretion. Results of in vitro studies clearly show that glucose-induced insulin release is associated with a concomitant inhibition of AMPK in β cells. However, pharmacological activation of AMPK significantly potentiates the insulin-secretory response of β cells to glucose and to some other stimuli. This effect is primarily due to increased intracellular calcium concentrations. AMPK is also involved in the regulation of gene expression and may protect β cells against glucolipotoxic conditions. It was shown that in pancreatic islets of humans with type 2 diabetes, AMPK is downregulated. Moreover, studies with animal models demonstrated impaired link between glucose and AMPK activity in pancreatic islet cells. These data suggest that AMPK may be a target for compounds improving the functionality of β cells. However, more studies are required to better elucidate the relevance of AMPK in the (patho)physiology of the insulin-secreting cells.

Inborn errors of mitochondrial acyl-coenzyme a metabolism: acyl-CoA biology meets the clinic

The last decade saw major advances in understanding the metabolism of Coenzyme A (CoA) thioesters (acyl-CoAs) and related inborn errors (CoA metabolic diseases, CAMDs). For diagnosis, acylcarnitines and organic acids, both derived from acyl-CoAs, are excellent markers of most CAMDs. Clinically, each CAMD is unique but strikingly, three main patterns emerge: first, systemic decompensations with combinations of acidosis, ketosis, hypoglycemia, hyperammonemia and fatty liver; second, neurological episodes, particularly acute "stroke-like" episodes, often involving the basal ganglia but sometimes cerebral cortex, brainstem or optic nerves and third, especially in CAMDs of long chain fatty acyl-CoA metabolism, lipid myopathy, cardiomyopathy and arrhythmia. Some patients develop signs from more than one category. The pathophysiology of CAMDs is not precisely understood. Available data suggest that signs may result from CoA sequestration, toxicity and redistribution (CASTOR) in the mitochondrial matrix has been suggested to play a role. This predicts that most CAMDs cause deficiency of CoA, limiting mitochondrial energy production, and that toxic effects from the abnormal accumulation of acyl-CoAs and from extramitochondrial functions of acetyl-CoA may also contribute. Recent progress includes the following. (1) Direct measurements of tissue acyl-CoAs in mammalian models of CAMDs have been related to clinical features. (2) Inborn errors of CoA biosynthesis were shown to cause clinical changes similar to those of inborn errors of acyl-CoA degradation. (3) CoA levels in cells can be influenced pharmacologically. (4) Roles for acetyl-CoA are increasingly identified in all cell compartments. (5) Nonenzymatic acyl-CoA-mediated acylation of intracellular proteins occurs in mammalian tissues and is increased in CAMDs.

Effect of whole foods and dietary patterns on markers of subclinical inflammation in weight-stable overweight and obese adults: a systematic review

Context

Reduction of subclinical inflammation is a potential target for chronic disease management. Adiposity is a known modifier of meta-inflammation; however, the influence of dietary factors is less clear.

Objective

This review examines evidence from human trials evaluating effects of whole foods or dietary patterns on circulating inflammatory markers in weight-stable overweight and obese adults. It is the first review to investigate effects of diet on inflammation, independent of changes in adiposity.

Data Sources

The Ovid MEDLINE, EMBASE, CINAHL, and Cochrane databases were searched.

Data Extraction

Data extraction was conducted using the Cochrane Collaboration Handbook for Systematic Reviews of Interventions.

Data Analysis

Study quality was evaluated using the Cochrane Collaboration Risk of Bias Assessment tool. Thirty-three studies were included assessing effects of 17 foods and dietary patterns on 39 inflammatory markers.

Conclusions

Overall, foods and dietary patterns were not found to have significant effects on inflammatory markers in weight-stable individuals. Inconsistencies among studies were largely due to methodological limitations. Future research should invest in longer intervention periods and standardization of inflammatory marker panels paired with novel technologies, while ensuring anthropometric measures are monitored and adequately controls are used.

Systematic Review Registration

Prospero registration number CRD42017067765.

Hedgehog Interacting Protein (Hhip) Regulates Insulin Secretion in Mice Fed High Fat Diets

Hedgehog interacting protein (Hhip) is essential for islet formation and beta-cell proliferation during pancreatic development; abnormally elevated Hhip expression has been linked to human pancreatitis. Here, we investigate the role of Hhip in modulating insulin secretion in adult Hhip mice (Hhip +/− vs. Hhip+/+) fed high fat diets (HFD). Both sexes of HFD-Hhip +/+ mice developed impaired glucose intolerance, that was only ameliorated in male HFD-Hhip +/− mice that had high levels of circulating plasma insulin, but not in female HFD-Hhip +/− mice. HFD stimulated Hhip gene expression, mainly in beta cells. Male HFD-Hhip +/+ mice had more large islets in which insulin content was reduced; islet architecture was disordered; and markers of oxidative stress (8-OHdG and Nox 2) were increased. In contrast, male HFD-Hhip +/− mice had more small islets with increased beta cell proliferation, enhanced GSIS, less oxidative stress and preserved islet integrity. In vitro, recombinant Hhip increased Nox2 and NADPH activity and decreased insulin-positive beta cells. siRNA-Hhip increased GSIS and abolished the stimulation of sodium palmitate (PA)-BSA on Nox2 gene expression. We conclude that pancreatic Hhip gene inhibits insulin secretion by altering islet integrity and promoting Nox2 gene expression in beta cells in response to HDF-mediated beta cell dysfunction, a novel finding.

Acceleration of β Cell Aging Determines Diabetes and Senolysis Improves Disease Outcomes

Type 2 diabetes (T2D) is an age-related disease. Although changes in function and proliferation of aged β cells resemble those preceding the development of diabetes, the contribution of β cell aging and senescence remains unclear. We generated a β cell senescence signature and found that insulin resistance accelerates β cell senescence leading to loss of function and cellular identity and worsening metabolic profile. Senolysis (removal of senescent cells), using either a transgenic INK-ATTAC model or oral ABT263, improved glucose metabolism and β cell function while decreasing expression of markers of aging, senescence, and senescence-associated secretory profile (SASP). Beneficial effects of senolysis were observed in an aging model as well as with insulin resistance induced both pharmacologically (S961) and physiologically (high-fat diet). Human senescent β cells also responded to senolysis, establishing the foundation for translation. These novel findings lay the framework to pursue senolysis of β cells as a preventive and alleviating strategy for T2D.

HCV Extrahepatic Manifestations

Hepatitis C virus (HCV) has been shown to affect many tissues other than liver. However, of the many extrahepatic manifestations (EMs) that have been associated with HCV, including cryoglobulinemia, lymphoma, insulin resistance, type 2 diabetes and neurological disorders, only a few have been shown to be directly related to HCV infection of extrahepatic tissues. HCV-triggered immune-mediated mechanisms account for most of the EMs. It is estimated that up to 74% of patients with chronic hepatitis C can develop at least one EM. All HCV patients with EMs should be considered for antiviral therapy, although not all will resolve with sustained virological response.

Heterogeneity of Metabolic Defects in Type 2 Diabetes and Its Relation to Reactive Oxygen Species and Alterations in Beta-Cell Mass

Type 2 diabetes (T2D) is a complex and heterogeneous disease which affects millions of people worldwide. The classification of diabetes is at an interesting turning point and there have been several recent reports on sub-classification of T2D based on phenotypical and metabolic characteristics. An important, and perhaps so far underestimated, factor in the pathophysiology of T2D is the role of oxidative stress and reactive oxygen species (ROS). There are multiple pathways for excessive ROS formation in T2D and in addition, beta-cells have an inherent deficit in the capacity to cope with oxidative stress. ROS formation could be causal, but also contribute to a large number of the metabolic defects in T2D, including beta-cell dysfunction and loss. Currently, our knowledge on beta-cell mass is limited to autopsy studies and based on comparisons with healthy controls. The combined evidence suggests that beta-cell mass is unaltered at onset of T2D but that it declines progressively. In order to better understand the pathophysiology of T2D, to identify and evaluate novel treatments, there is a need for in vivo techniques able to quantify beta-cell mass. Positron emission tomography holds great potential for this purpose and can in addition map metabolic defects, including ROS activity, in specific tissue compartments. In this review, we highlight the different phenotypical features of T2D and how metabolic defects impact oxidative stress and ROS formation. In addition, we review the literature on alterations of beta-cell mass in T2D and discuss potential techniques to assess beta-cell mass and metabolic defects in vivo.

Palmitate is not an effective fuel for pancreatic islets and amplifies insulin secretion independent of calcium release from endoplasmic reticulum

The aim of the study was to determine the acute contribution of fuel oxidation in mediating the increase in insulin secretion rate (ISR) in response to fatty acids. Measures of mitochondrial metabolism, as reflected by oxygen consumption rate (OCR) and cytochrome c reduction, calcium signaling, and ISR by rat islets were used to evaluate processes stimulated by acute exposure to palmitic acid (PA). The contribution of mitochondrial oxidation of PA was determined in the presence and absence of a blocker of mitochondrial transport of fatty acids (etomoxir) at different glucose concentrations. Subsequent to increasing glucose from 3 to 20 mM, PA caused small increases in OCR and cytosolic calcium (about 20% of the effect of glucose). In contrast, the effect of PA on ISR was almost 3 times that by glucose, suggesting that the metabolism of PA is not the dominant mechanism mediating PA's effect on ISR. This was further supported by lack of inhibition of PA-stimulated OCR and ISR when blocking entry of PA into mitochondria (with etomoxir), and PA's lack of stimulation of reduced cytochrome c in the presence of high glucose. Consistent with the lack of metabolic stimulation by PA, an inhibitor of calcium release from the endoplasmic reticulum, but not a blocker of L-type calcium channels, abolished the PA-induced elevation of cytosolic calcium. Notably, ISR was unaffected by thapsigargin showing the dissociation of endoplasmic reticulum calcium release and second phase insulin secretion. In conclusion, stimulation of ISR by PA was mediated by mechanisms largely independent of the oxidation of the fuel.

Maternal β-Cell Adaptations in Pregnancy and Placental Signalling: Implications for Gestational Diabetes

Rates of gestational diabetes mellitus (GDM) are on the rise worldwide, and the number of pregnancies impacted by GDM and resulting complications are also increasing. Pregnancy is a period of unique metabolic plasticity, during which mild insulin resistance is a physiological adaptation to prioritize fetal growth. To compensate for this, the pancreatic β-cell utilizes a variety of adaptive mechanisms, including increasing mass, number and insulin-secretory capacity to maintain glucose homeostasis. When insufficient insulin production does not overcome insulin resistance, hyperglycemia can occur. Changes in the maternal system that occur in GDM such as lipotoxicity, inflammation and oxidative stress, as well as impairments in adipokine and placental signalling, are associated with impaired β-cell adaptation. Understanding these pathways, as well as mechanisms of β-cell dysfunction in pregnancy, can identify novel therapeutic targets beyond diet and lifestyle interventions, insulin and antihyperglycemic agents currently used for treating GDM.

Cardiac Glucolipotoxicity and Cardiovascular Outcomes

Cardiac insulin signaling can be impaired due to the altered fatty acid metabolism to induce insulin resistance. In diabetes and insulin resistance, the metabolic, structural and ultimately functional alterations in the heart and vasculature culminate in diabetic cardiomyopathy, coronary artery disease, ischemia and eventually heart failure. Glucolipotoxicity describes the combined, often synergistic, adverse effects of elevated glucose and free fatty acid concentrations on heart structure, function, and survival. The quality of fatty acid shapes the cardiac structure and function, often influencing survival. A healthy fatty acid balance is therefore critical for maintaining cardiac integrity and function.

Protective role of the ELOVL2/docosahexaenoic acid axis in glucolipotoxicity-induced apoptosis in rodent beta cells and human islets

AIMS/HYPOTHESIS

Dietary n-3 polyunsaturated fatty acids, especially docosahexaenoic acid (DHA), are known to influence glucose homeostasis. We recently showed that Elovl2 expression in beta cells, which regulates synthesis of endogenous DHA, was associated with glucose tolerance and played a key role in insulin secretion. The present study aimed to examine the role of the very long chain fatty acid elongase 2 (ELOVL2)/DHA axis on the adverse effects of palmitate with high glucose, a condition defined as glucolipotoxicity, on beta cells.

METHODS

We detected ELOVL2 in INS-1 beta cells and mouse and human islets using quantitative PCR and western blotting. Downregulation and adenoviral overexpression of Elovl2 was carried out in beta cells. Ceramide and diacylglycerol levels were determined by radio-enzymatic assay and lipidomics. Apoptosis was quantified using caspase-3 assays and poly (ADP-ribose) polymerase cleavage. Palmitate oxidation and esterification were determined by [U-¹⁴C]palmitate labelling.

RESULTS

We found that glucolipotoxicity decreased ELOVL2 content in rodent and human beta cells. Downregulation of ELOVL2 drastically potentiated beta cell apoptosis induced by glucolipotoxicity, whereas adenoviral Elovl2 overexpression and supplementation with DHA partially inhibited glucolipotoxicity-induced cell death in rodent and human beta cells. Inhibition of beta cell apoptosis by the ELOVL2/DHA axis was associated with a decrease in ceramide accumulation. However, the ELOVL2/DHA axis was unable to directly alter ceramide synthesis or metabolism. By contrast, DHA increased palmitate oxidation but did not affect its esterification. Pharmacological inhibition of AMP-activated protein kinase and etomoxir, an inhibitor of carnitine palmitoyltransferase 1 (CPT1), the rate-limiting enzyme in fatty acid β-oxidation, attenuated the protective effect of the ELOVL2/DHA axis during glucolipotoxicity. Downregulation of CPT1 also counteracted the anti-apoptotic action of the ELOVL2/DHA axis. By contrast, a mutated active form of Cpt1 inhibited glucolipotoxicity-induced beta cell apoptosis when ELOVL2 was downregulated.

CONCLUSIONS/INTERPRETATION

Our results identify ELOVL2 as a critical pro-survival enzyme for preventing beta cell death and dysfunction induced by glucolipotoxicity, notably by favouring palmitate oxidation in mitochondria through a CPT1-dependent mechanism.

Endoplasmic Reticulum Stress in Metabolic Disorders

Metabolic disorders have become among the most serious threats to human health, leading to severe chronic diseases such as obesity, type 2 diabetes, and non-alcoholic fatty liver disease, as well as cardiovascular diseases. Interestingly, despite the fact that each of these diseases has different physiological and clinical symptoms, they appear to share certain pathological traits such as intracellular stress and inflammation induced by metabolic disturbance stemmed from over nutrition frequently aggravated by a modern, sedentary life style. These modern ways of living inundate cells and organs with saturating levels of sugar and fat, leading to glycotoxicity and lipotoxicity that induce intracellular stress signaling ranging from oxidative to ER stress response to cope with the metabolic insults (Mukherjee, et al., 2015). In this review, we discuss the roles played by cellular stress and its responses in shaping metabolic disorders. We have summarized here current mechanistic insights explaining the pathogenesis of these disorders. These are followed by a discussion of the latest therapies targeting the stress response pathways.

Cation-Independent Mannose 6-Phosphate Receptor Deficiency Enhances β-Cell Susceptibility to Palmitate

Palmitate attenuates insulin secretion and reduces the viability of insulin-producing cells. Previous studies identified the aberrant palmitoylation or mispalmitoylation of proteins as one mechanism by which palmitate causes β-cell damage. In this report, we identify a role for lysosomal protein degradation as a mechanism by which β cells defend themselves against excess palmitate. The cation-independent mannose 6-phosphate receptor (CI-MPR) is responsible for the trafficking of mannose 6-phosphate-tagged proteins to lysosomes via Golgi sorting and from extracellular locations through endocytosis. RINm5F cells, which are highly sensitive to palmitate, lack CI-MPR. The reconstitution of CI-MPR expression attenuates the induction of endoplasmic reticulum (ER) stress and the toxic effects of palmitate on RINm5F cell viability. INS832/13 cells express CI-MPR and are resistant to the palmitate-mediated loss of cell viability. The reduction of CI-MPR expression increases the sensitivity of INS832/13 cells to the toxic effects of palmitate treatment. The inhibition of lysosomal acid hydrolase activity by weak base treatment of islets under glucolipotoxic conditions causes islet degeneration that is prevented by the inhibition of protein palmitoylation. These findings indicate that defects in lysosomal function lead to the enhanced sensitivity of insulin-producing cells to palmitate and support a role for normal lysosomal function in the protection of β cells from excess palmitate.

Involvement of dying beta cell originated messenger molecules in differentiation of pancreatic mesenchymal stem cells under glucotoxic and glucolipotoxic conditions

Beta cell mass regulation represents a critical issue for understanding and treatment of diabetes. The most important process in the development of diabetes is beta cell death, generally induced by glucotoxicity or glucolipotoxicity, and the regeneration mechanism of new beta cells that will replace dead beta cells is still not fully understood. The aim of this study was to investigate the generation mechanism of new beta cells by considering the compensation phase of type 2 diabetes mellitus. In this study, pancreatic islet derived mesenchymal stem cells (PI-MSCs) were isolated from adult rats and characterized. Then, beta cells isolated from rats were co-cultured with PI-MSCs and they were exposed to glucotoxicity, lipotoxicity and glucolipotoxicity conditions for 72 hr. As the results apoptotic and necrotic cell death were increased in both PI-MSCs and beta cells especially by the exposure of glucotoxic and glucolipotoxic conditions to the co-culture systems. Glucotoxicity induced-differentiated beta cells were functional due to their capability of insulin secretion in response to rising glucose concentrations. Moreover, beta cell proliferation was induced in the glucotoxicity-treated co-culture system whereas suppressed in lipotoxicity or glucolipotoxicity-treated co-culture systems. In addition, 11 novel proteins, that may release from dead beta cells and have the ability to stimulate PI-MSCs in the direction of differentiation, were determined in media of glucotoxicity or glucolipotoxicity-treated co-culture systems. In conclusion, these molecules were considered as important for understanding cellular mechanism of beta cell differentiation and diabetes. Thus, they may be potential targets for diagnosis and cellular or therapeutic treatment of diabetes.

Mulberry leaf alleviates streptozotocin-induced diabetic rats by attenuating NEFA signaling and modulating intestinal microflora

Improvement of hyperglycemia through dietotherapy/herbal remedy is an effective approach to treating diabetes. In this study, mulberry leaf, famous for silkworm’s special food and therapeutic value without any side effects, alleviated diabetes by attenuating NEFA signaling and modulating intestinal microflora. Mulberry leaf treatment significantly reduce fasting blood-glucose and HbA1c, ameliorate the blood lipid profile and improve insulin resistance in streptozotocin-induced diabetic rats. Mechanistically, we found that mulberry leaf inhibited NEFA signaling by reducing downstream signaling in the NEFA pathway, further verified by reduced PKC and improved cellular energy homeostasis based on restored expression of PGC-1α, AK2, OXPHOS and adiponectin. Mulberry leaf treatment also restored the phyla Bacteroidetes and Proteobacteria and class Clostridia, which were associated with insulin resistance and diabetes. Our findings reveal that mulberry leaf is an edible with therapeutic potential for diabetes and may provide a novel dietotherapy/herbal remedy to the treatment of diabetes.

Insulin Resistance, Obesity and Lipotoxicity

Lipotoxicity , originally used to describe the destructive effects of excess fat accumulation on glucose metabolism, causes functional impairments in several metabolic pathways, both in adipose tissue and peripheral organs, like liver, heart, pancreas and muscle. Lipotoxicity has roles in insulin resistance and pancreatic beta cell dysfunction. Increased circulating levels of lipids and the metabolic alterations in fatty acid utilization and intracellular signaling, have been related to insulin resistance in muscle and liver. Different pathways, like novel protein kinase c pathways and the JNK-1 pathway are involved as the mechanisms of how lipotoxicity leads to insulin resistance in nonadipose tissue organs, such as liver and muscle. Mitochondrial dysfunction plays a role in the pathogenesis of insulin resistance. Endoplasmic reticulum stress, through mainly increased oxidative stress, also plays important role in the etiology of insulin resistance, especially seen in non-alcoholic fatty liver disease. Visceral adiposity and insulin resistance both increase the cardiometabolic risk and lipotoxicity seems to play a crucial role in the pathophysiology of these associations.

Comprehensive Analysis of Acylcarnitine Species in db/db Mouse Using a Novel Method of High-Resolution Parallel Reaction Monitoring Reveals Widespread Metabolic Dysfunction Induced by Diabetes

Acylcarnitines are exerting a variety of biological functions depending on the differences in lengths, saturation levels, and conjugation groups, which to a great extent contribute to the challenges of acylcarnitines quantifications due to various kinds of isomers. Here, we describe a novel method by using high-resolution parallel reaction monitoring (PRM) liquid chromatography-tandem mass spectrometry (LC-MS/MS). Both reversed-phase and normal-phase column were used in order to get accurate, reliable, widespread quantification of acylcarnitines, and without tedious sample preparation procedure. The method provided the most comprehensive acylcarnitine profile with high-resolution MS and MS/MS confirmation to date. A total of 117 acylcarnitines were detected from plasma and urine samples. The application of targeted profiling of acylcarnitines in db/m+ control and db/db diabetic mice indicated incomplete amino acid and fatty acid oxidation on diabetic mice. Interestingly, the reduction of medium odd-numbered chain acylcarnitines in urine samples was first observed between db/m+ and db/db mice. The high-resolution PRM method makes it possible to monitor the widespread metabolic changes of the acylcarnitines in response to stimuli. Besides, the accurate MS and MS/MS spectra data of the 117 acylcarnitines could be used as mass spectrometric resources for the identification of acylcarnitines.