Fatty acid metabolism and insulin secretion in pancreatic beta cells

The effects of free fatty acid-free bovine serum albumin and palmitate on pancreatic β-cell function

Pancreatic β-cells release insulin in response to fluctuations in plasma glucose, amino acids, and free fatty acids (FFA). Clonal cell lines and isolated islets serve as essential early models for studying the impact of nutrients and evaluating potential therapies to address β-cell dysfunction. Acute and chronic changes in FFA levels have been shown to have positive and negative effects on β-cell function both in vivo and in vitro. A key problem in comparing islet lipid studies from different laboratories is that a wide variety of methods are used to isolate, culture, and assess islet function. The current study compares bovine serum albumin (BSA) types and lipid preparation methods in clonal 832/13 cells and human islets. Changing the percentage and culture conditions when using FFA-free BSA can negatively affect β-cell function compared to regular BSA. Preparing palmitate with FFA-free BSA can rescue insulin secretion compared to treating cells alone with FFA-free BSA. Different methods of preparing palmitate can have unique effects on insulin secretion. Overall, interpreting the effects of lipids on β-cell function is complicated by a number of variables that need to be controlled for in islet experiments.

Plin5: A potential therapeutic target for type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) is a kind of metabolic disease characterized by aberrant insulin secretion as a result of -cell loss or injury, or by impaired insulin sensitivity of peripheral tissues, which finally results in insulin resistance and a disturbance of glucose and lipid metabolism. Among them, lipid metabolism disorders lead to lipotoxicity through oxidative stress and inflammatory response, destroying the structure and function of tissues and cells. Abnormal lipid metabolism can lead to abnormal insulin signaling and disrupt glucose metabolism through a variety of pathways. Therefore, emphasizing lipid metabolism may be a crucial step in the prevention and treatment of T2DM. Plin5 is a lipid droplet surface protein, which can bi-directionally regulate lipid metabolism and plays an important role in lipolysis and fat synthesis. Plin5 can simultaneously decrease the buildup of free fatty acids in the cytoplasm, improve mitochondrial uptake of free fatty acids, speed up fatty acid oxidation through lipid drops-mitochondria interaction, and lessen lipotoxicity. In oxidative tissues like the heart, liver, and skeletal muscle, Plin5 is extensively expressed. And Plin5 is widely involved in β-cell apoptosis, insulin resistance, oxidative stress, inflammatory response and other pathological processes, which has important implications for exploring the pathogenesis of T2DM. In addition, recent studies have found that Plin5 is also closely related to T2DM and cancer, which provides a new perspective for exploring the relationship between T2DM and cancer.

Genome-Scale Metabolic Modeling of Human Pancreas with Focus on Type 2 Diabetes

Type 2 diabetes (T2D) is characterized by relative insulin deficiency due to pancreatic beta cell dysfunction and insulin resistance in different tissues. Not only beta cells but also other islet cells (alpha, delta, and pancreatic polypeptide [PP]) are critical for maintaining glucose homeostasis in the body. In this overarching context and given that a deeper understanding of T2D pathophysiology and novel molecular targets is much needed, studies that integrate experimental and computational biology approaches offer veritable prospects for innovation. In this study, we report on single-cell RNA sequencing data integration with a generic Human1 model to generate context-specific genome-scale metabolic models for alpha, beta, delta, and PP cells for nondiabetic and T2D states and, importantly, at single-cell resolution. Moreover, flux balance analysis was performed for the investigation of metabolic activities in nondiabetic and T2D pancreatic cells. By altering glucose and oxygen uptakes to the metabolic networks, we documented the ways in which hypoglycemia, hyperglycemia, and hypoxia led to changes in metabolic activities in various cellular subsystems. Reporter metabolite analysis revealed significant transcriptional changes around several metabolites involved in sphingolipid and keratan sulfate metabolism in alpha cells, fatty acid metabolism in beta cells, and myoinositol phosphate metabolism in delta cells. Taken together, by leveraging genome-scale metabolic modeling, this research bridges the gap between metabolic theory and clinical practice, offering a comprehensive framework to advance our understanding of pancreatic metabolism in T2D, and contributes new knowledge toward the development of targeted precision medicine interventions.

Pancreatic expression of CPT1A is essential for whole body glucose homeostasis by supporting glucose-stimulated insulin secretion

Pancreatic islet β-cells express the Cpt1a gene, which encodes the enzyme carnitine palmitoyltransferase 1A (CPT1A), an enzyme that facilitates entry of long-chain fatty acids into the mitochondria. Because fatty acids are required for glucose-stimulated insulin secretion, we tested the hypothesis that CPT1A is essential to support islet β-cell function and mass. In this study, we describe genetic deletion of Cpt1a in pancreatic tissue (Cpt1aPdx1-/-) using C57BL/6J mice. Islet morphology, β-cell transcription factor abundance, islet ATP levels, glucose transporter 2 abundance, and expression of the dedifferentiation marker ALDH1A3 were analyzed by immunofluorescent staining. Glucose and insulin tolerance were assessed to investigate the metabolic status of genetic reductions in Cpt1a. Glucose-stimulated insulin secretion was evaluated in vivo and in isolated islets ex vivo by perifusion. Pancreatic deletion of Cpt1a reduced glucose tolerance but did not alter insulin sensitivity. Glucose-stimulated insulin secretion was reduced both in vivo and in islets isolated from Cpt1aPdx1-/- mice relative to control islets. Pancreatic islets from Cpt1aPdx1-/- mice displayed elevations in ALDH1A3, a marker of dedifferentiation, but no reduction in nuclear abundance of the β-cell transcription factors MafA and Nkx6.1 or the GLUT2 glucose transporter. However, intracellular ATP abundance was markedly decreased in islets isolated from Cpt1aPdx1-/- relative to littermate control mice. We conclude that there is an important physiological role for pancreatic CPT1A to maintain whole body glucose homeostasis by supporting glucose-stimulated insulin secretion and maintaining intracellular ATP levels in male mice.

Interplay of fatty acids, insulin and exercise in vascular health

Fatty acid metabolism, exercise, and insulin action play critical roles in maintaining vascular health, especially relevant in metabolic disorders such as obesity, type 2 diabetes, and cardiovascular disease. Insulin, a vasoactive hormone, induces arterial vasodilation throughout the arterial tree, increasing arterial compliance and enhancing tissue perfusion. These effects, however, are impaired in individuals with obesity and type 2 diabetes, and evidence suggests that vascular insulin resistance contributes to the pathogenesis of type 2 diabetes and its cardiovascular complications. Elevated plasma levels of free fatty acids in people with insulin resistance engender vascular inflammation, endothelial dysfunction, and vascular insulin resistance. Importantly, these effects are both functionally and structurally dependent, with saturated fatty acids as the primary culprits, while polyunsaturated fatty acids may support insulin sensitivity and endothelial function. Exercise enhances fatty acid oxidation, reduces circulating free fatty acids, and improves insulin sensitivity, thereby mitigating lipotoxicity and promoting endothelial function. Additionally, exercise induces beneficial vascular adaptations. This review examines the complex interplay among fatty acid metabolism, exercise training-induced vascular adaptations, and insulin-mediated vascular changes, highlighting their collective impact on vascular health and underlying mechanisms in both healthy and insulin-resistant states. It also explores the therapeutic potential of targeted exercise prescriptions and fatty acid-focused dietary strategies for enhancing vascular health, emphasizing tailored interventions to maximize metabolic benefits. Future research should investigate the pathways linking fatty acid metabolism to vascular insulin resistance, with a focus on how exercise and dietary modifications can be personalized to enhance vascular insulin sensitivity, optimize vascular health, and reduce the risks of type 2 diabetes and associated cardiovascular complications.

Recent Developments in Drug Design of Oral Synthetic Free Fatty Acid Receptor 1 Agonists

Over the past two decades, synthetic FFAR1 agonists such as TAK-875 and TSL1806 have undergone meticulous design and extensive clinical trials. However, due to issues primarily related to hepatotoxicity, no FFAR1 agonist has yet received regulatory approval. Research into the sources of hepatotoxicity suggests that one potential cause lies in the molecular structure itself. These structures typically feature lipid-like carboxylic acid head groups, which tend to generate toxic metabolites. Strategies to mitigate these risks focus on optimizing chemical groups to reduce lipophilicity and prevent the formation of reactive metabolites. Recent studies have concentrated on developing low-molecular-weight compounds that more closely resemble natural products, with CPL207280 showing promising potential and liver safety, currently in Phase II clinical trials. Moreover, ongoing research continues to explore the potential applications of FFAR1 agonists in diabetes management, as well as in conditions such as non-alcoholic fatty liver disease (NAFLD) and cerebrovascular diseases. Utilizing advanced technologies such as artificial intelligence and computer-aided design, the development of compact molecules that mimic natural structures represents a hopeful direction for future research and development.

Constitutive Pleiotrophin Deletion Results in a Phenotype with an Altered Pancreatic Morphology and Function in Old Mice

Pleiotrophin (PTN) is crucial for embryonic development and pancreas organogenesis as it regulates metainflammation, metabolic homeostasis, thermogenesis, and glucose tolerance. Pleiotrophin deletion is associated with a lipodystrophic phenotype in which adipose tissue plasticity is altered in late life. This study explored the impact of pleiotrophin deletion on pancreatic morphology and function in later life. We analyzed glucose tolerance and circulating parameters on female wild-type (Ptn+/+) and knock-out (Ptn-/-) mice. At 9 and 15 months, we conducted morphometric analyses of pancreatic islets and evaluated the levels of insulin, glucagon, somatostatin, glucose transporter 2 (GLUT2), vesicle-associated membrane protein 2 (VAMP2), and synaptosome-associated protein 25 (SNAP25) via immunofluorescence. The effect of PTN on glucose-stimulated insulin secretion (GSIS) was evaluated in INS1E cells and isolated islets. Ptn-/- mice showed hyperinsulinemia, impaired glucose tolerance, and increased homeostatic model assessment for insulin resistance (HOMA-IR) with age. While Ptn+/+ islets enlarge with age, in Ptn-/- mice, the median size decreased, and insulin content increased. Vesicle transport and exocytosis proteins were significantly increased in 9-month-old Ptn-/- islets. Islets from Ptn-/- mice showed impaired GSIS and decreased cell membrane localization of GLUT2 whereas, PTN increased GSIS in INS1E cells. Ptn deletion accelerated age-related changes in the endocrine pancreas, affecting islet number and size, and altering VAMP2 and SNAP25 levels and GLUT2 localization leading to impaired GSIS and insulin accumulation in islets.

The metabolic consequences of 'yo-yo' dieting are markedly influenced by genetic diversity

BACKGROUND

Weight loss can improve the metabolic complications of obesity. However, it is unclear whether insulin resistance persists despite weight loss and whether any protective benefits are preserved following weight regain (weight cycling). The impact of genetic background on weight cycling is undocumented. We aimed to investigate the effects of weight loss and weight cycling on metabolic outcomes and sought to clarify the role of genetics in this relationship.

METHOD

Both C57BL/6 J and genetically heterogeneous Diversity Outbred Australia (DOz) mice were alternately fed high fat Western-style diet (WD) and a chow diet at 8-week intervals. Metabolic measures including body composition, glucose tolerance, pancreatic beta cell activity, liver lipid levels and adipose tissue insulin sensitivity were determined.

RESULTS

After diet switch from WD (8-week) to chow (8-week), C57BL/6 J mice displayed a rapid normalisation of body weight, adiposity, hyperinsulinemia, liver lipid levels and glucose uptake into adipose tissue comparable to chow-fed controls. In response to the same dietary intervention, genetically diverse DOz mice conversely maintained significantly higher fat mass and insulin levels compared to chow-fed controls and exhibited much more profound interindividual variability than C57BL/6 J mice. Weight cycled (WC) animals were re-exposed to WD (8-week) and compared to age-matched controls fed 8-week WD for the first time (LOb). In C57BL/6 J but not DOz mice, WC animals had significantly higher blood insulin levels than LOb controls. All WC animals exhibited significantly greater beta cell activity than LOb controls despite similar fat mass, glucose tolerance, liver lipid levels and insulin-stimulated glucose uptake in adipose tissue.

CONCLUSION

Following weight loss, metabolic outcomes return to baseline in C57BL/6 J mice with obesity. However, genetic diversity significantly impacts this response. A period of weight loss does not provide lasting benefits after weight regain, and weight cycling is detrimental and associated with hyperinsulinemia and elevated basal insulin secretion.

Metformin restores prohormone processing enzymes and normalizes aberrations in secretion of proinsulin and insulin in palmitate-exposed human islets

AIM

To elucidate how proinsulin synthesis and insulin was affected by metformin under conditions of nutrient overstimulation.

MATERIALS AND METHODS

Isolated human pancreatic islets from seven donors were cultured at 5.5 mmol/L glucose and 0.5 mmol/L palmitate for 12, 24 or 72 h. Metformin (25 μmol/L) was introduced after initial 12 h with palmitate. Proinsulin and insulin were measured. Expression of prohormone convertase 1/3 (PC1/3) and carboxypeptidase E (CPE), was determined by western blot. Adolescents with obesity, treated with metformin and with normal glucose tolerance (n = 5), prediabetes (n = 14), or type 2 diabetes (T2DM; n = 7) were included. Fasting proinsulin, insulin, glucose, 2-h glucose and glycated haemoglobin were measured. Proinsulin/insulin ratio (PI/I) was calculated.

RESULTS

In human islets, palmitate treatment for 12 and 24 h increased proinsulin and insulin proportionally. After 72 h, proinsulin but not insulin continued to increase which was coupled with reduced expression of PC1/3 and CPE. Metformin normalized expression of PC1/3 and CPE, and proinsulin and insulin secretion. In adolescents with obesity, before treatment, fasting proinsulin and insulin concentrations were higher in subjects with T2DM than with normal glucose tolerance. PI/I was reduced after metformin treatment in subjects with T2DM as well as in subjects with prediabetes, coupled with reduced 2-h glucose and glycated haemoglobin.

CONCLUSIONS

Metformin normalized proinsulin and insulin secretion after prolonged nutrient-overstimulation, coupled with normalization of the converting enzymes, in isolated islets. In adolescents with obesity, metformin treatment was associated with improved PI/I, which was coupled with improved glycaemic control.

Mitochondrial regulation in human pluripotent stem cells during reprogramming and β cell differentiation

Mitochondria are the powerhouse of the cell and dynamically control fundamental biological processes including cell reprogramming, pluripotency, and lineage specification. Although remarkable progress in induced pluripotent stem cell (iPSC)-derived cell therapies has been made, very little is known about the role of mitochondria and the mechanisms involved in somatic cell reprogramming into iPSC and directed reprogramming of iPSCs in terminally differentiated cells. Reprogramming requires changes in cellular characteristics, genomic and epigenetic regulation, as well as major mitochondrial metabolic changes to sustain iPSC self-renewal, pluripotency, and proliferation. Differentiation of autologous iPSC into terminally differentiated β-like cells requires further metabolic adaptation. Many studies have characterized these alterations in signaling pathways required for the generation and differentiation of iPSC; however, very little is known regarding the metabolic shifts that govern pluripotency transition to tissue-specific lineage differentiation. Understanding such metabolic transitions and how to modulate them is essential for the optimization of differentiation processes to ensure safe iPSC-derived cell therapies. In this review, we summarize the current understanding of mitochondrial metabolism during somatic cell reprogramming to iPSCs and the metabolic shift that occurs during directed differentiation into pancreatic β-like cells.

The Physiological and Pathological Role of Acyl-CoA Oxidation

Fatty acid metabolism, including β-oxidation (βOX), plays an important role in human physiology and pathology. βOX is an essential process in the energy metabolism of most human cells. Moreover, βOX is also the source of acetyl-CoA, the substrate for (a) ketone bodies synthesis, (b) cholesterol synthesis, (c) phase II detoxication, (d) protein acetylation, and (d) the synthesis of many other compounds, including N-acetylglutamate-an important regulator of urea synthesis. This review describes the current knowledge on the importance of the mitochondrial and peroxisomal βOX in various organs, including the liver, heart, kidney, lung, gastrointestinal tract, peripheral white blood cells, and other cells. In addition, the diseases associated with a disturbance of fatty acid oxidation (FAO) in the liver, heart, kidney, lung, alimentary tract, and other organs or cells are presented. Special attention was paid to abnormalities of FAO in cancer cells and the diseases caused by mutations in gene-encoding enzymes involved in FAO. Finally, issues related to α- and ω- fatty acid oxidation are discussed.

Nutritional Composition and Anti-Type 2 Diabetes Mellitus Potential of Femur Bone Extracts from Bovine, Chicken, Sheep, and Goat: Phytochemical and In Vivo Studies

Nutritional deficits in one's diet have been established as the key risk factor for T2DM in recent years. Nutritional therapy has been demonstrated to be useful in treating T2DM. The current study was carried out to assess the nutritional composition of bovine (12 months), chicken (4 months), sheep (13 months), and goat (9 months) femur bone extracts, as well as their potential therapeutic effects on T2DM regression in a Wistar albino rat model (500 mg/kg b.wt.). The proximate composition of the different extracts, their fatty acid composition, their amino acids, and their mineral contents were identified. In vivo data indicated considerably improved T2DM rats, as seen by lower serum levels of TL, TG, TC, ALT, AST, ALP, bilirubin, creatinine, urea, IL-6, TNF-α, sICAM-1, sVCAM-1, and MDA. Low levels of HDL-C, GSH, and total proteins were restored during this study. Histological investigations of liver and pancreatic tissue revealed that the distribution of collagen fibers was nearly normal. The bovine extract, on the other hand, was the most active, followed by the sheep, goat, and finally chicken extract. This research could result in the creation of a simple, noninvasive, low-cost, and reliable method for T2DM control, paving the way for potential early therapeutic applications in T2DM control.

Peroxisomes during postnatal development of mouse endocrine and exocrine pancreas display cell-type- and stage-specific protein composition

Peroxisomal dysfunction unhinges cellular metabolism by causing the accumulation of toxic metabolic intermediates (e.g. reactive oxygen species, very -chain fatty acids, phytanic acid or eicosanoids) and the depletion of important lipid products (e.g. plasmalogens, polyunsaturated fatty acids), leading to various proinflammatory and devastating pathophysiological conditions like metabolic syndrome and age-related diseases including diabetes. Because the peroxisomal antioxidative marker enzyme catalase is low abundant in Langerhans islet cells, peroxisomes were considered scarcely present in the endocrine pancreas. Recently, studies demonstrated that the peroxisomal metabolism is relevant for pancreatic cell functionality. During the postnatal period, significant changes occur in the cell structure and the metabolism to trigger the final maturation of the pancreas, including cell proliferation, regulation of energy metabolism, and activation of signalling pathways. Our aim in this study was to (i) morphometrically analyse the density of peroxisomes in mouse endocrine versus exocrine pancreas and (ii) investigate how the distribution and the abundance of peroxisomal proteins involved in biogenesis, antioxidative defence and fatty acid metabolism change during pancreatic maturation in the postnatal period. Our results prove that endocrine and exocrine pancreatic cells contain high amounts of peroxisomes with heterogeneous protein content indicating that distinct endocrine and exocrine cell types require a specific set of peroxisomal proteins depending on their individual physiological functions. We further show that significant postnatal changes occur in the peroxisomal compartment of different pancreatic cells that are most probably relevant for the metabolic maturation and differentiation of the pancreas during the development from birth to adulthood.

Lipotoxicity in a Vicious Cycle of Pancreatic Beta Cell Exhaustion

Hyperlipidemia is a common metabolic disorder in modern society and may precede hyperglycemia and diabetes by several years. Exactly how disorders of lipid and glucose metabolism are related is still a mystery in many respects. We analyze the effects of hyperlipidemia, particularly free fatty acids, on pancreatic beta cells and insulin secretion. We have developed a computational model to quantitatively estimate the effects of specific metabolic pathways on insulin secretion and to assess the effects of short- and long-term exposure of beta cells to elevated concentrations of free fatty acids. We show that the major trigger for insulin secretion is the anaplerotic pathway via the phosphoenolpyruvate cycle, which is affected by free fatty acids via uncoupling protein 2 and proton leak and is particularly destructive in long-term chronic exposure to free fatty acids, leading to increased insulin secretion at low blood glucose and inadequate insulin secretion at high blood glucose. This results in beta cells remaining highly active in the “resting” state at low glucose and being unable to respond to anaplerotic signals at high pyruvate levels, as is the case with high blood glucose. The observed fatty-acid-induced disruption of anaplerotic pathways makes sense in the context of the physiological role of insulin as one of the major anabolic hormones.

A PDX1 cistrome and single-cell transcriptome resource of the developing pancreas

Pancreatic and duodenal homeobox 1 (PDX1) is crucial for pancreas organogenesis, yet the dynamic changes in PDX1 binding in human or mouse developing pancreas have not been examined. To address this knowledge gap, we performed PDX1 ChIP-seq and single-cell RNA-seq using fetal human pancreata. We integrated our datasets with published datasets and revealed the dynamics of PDX1 binding and potential cell lineage-specific PDX1-bound genes in the pancreas from fetal to adult stages. We identified a core set of developmentally conserved PDX1-bound genes that reveal the broad multifaceted role of PDX1 in pancreas development. Despite the well-known dramatic changes in PDX1 function and expression, we found that PDX1-bound genes are largely conserved from embryonic to adult stages. This points towards a dual role of PDX1 in regulating the expression of its targets at different ages, dependent on other functionally congruent or directly interacting partners. We also showed that PDX1 binding is largely conserved in mouse pancreas. Together, our study reveals PDX1 targets in the developing pancreas in vivo and provides an essential resource for future studies on pancreas development.

Plin5, a New Target in Diabetic Cardiomyopathy

Abnormal lipid accumulation is commonly observed in diabetic cardiomyopathy (DC), which can create a lipotoxic microenvironment and damage cardiomyocytes. Lipid toxicity is an important pathogenic factor due to abnormal lipid accumulation in DC. As a lipid droplet (LD) decomposition barrier, Plin5 can protect LDs from lipase decomposition and regulate lipid metabolism, which is involved in the occurrence and development of cardiovascular diseases. In recent years, studies have shown that Plin5 expression is involved in the pathogenesis of DC lipid toxicity, such as oxidative stress, mitochondrial dysfunction, endoplasmic reticulum (ER) stress, and insulin resistance (IR) and has become a key target of DC research. Therefore, understanding the relationship between Plin5 and DC progression as well as the mechanism of this process is crucial for developing new therapeutic approaches and exploring new therapeutic targets. This review is aimed at exploring the latest findings and roles of Plin5 in lipid metabolism and DC-related pathogenesis, to explore possible clinical intervention approaches.

β-cell mitochondria in diabetes mellitus: a missing puzzle piece in the generation of hPSC-derived pancreatic β-cells?

Diabetes mellitus (DM), currently affecting 463 million people worldwide is a chronic disease characterized by impaired glucose metabolism resulting from the loss or dysfunction of pancreatic β-cells with the former preponderating in type 1 diabetes (T1DM) and the latter in type 2 diabetes (T2DM). Because impaired insulin secretion due to dysfunction or loss of pancreatic β-cells underlies different types of diabetes, research has focused its effort towards the generation of pancreatic β-cells from human pluripotent stem cell (hPSC) as a potential source of cells to compensate for insulin deficiency. However, many protocols developed to differentiate hPSCs into insulin-expressing β-cells in vitro have generated hPSC-derived β-cells with either immature phenotype such as impaired glucose-stimulated insulin secretion (GSIS) or a weaker response to GSIS than cadaveric islets. In pancreatic β-cells, mitochondria play a central role in coupling glucose metabolism to insulin exocytosis, thereby ensuring refined control of GSIS. Defects in β-cell mitochondrial metabolism and function impair this metabolic coupling. In the present review, we highlight the role of mitochondria in metabolism secretion coupling in the β-cells and summarize the evidence accumulated for the implication of mitochondria in β-cell dysfunction in DM and consequently, how targeting mitochondria function might be a new and interesting strategy to further perfect the differentiation protocol for generation of mature and functional hPSC-derived β-cells with GSIS profile similar to human cadaveric islets for drug screening or potentially for cell therapy.

Age-Related Changes in Lipid and Glucose Levels Associated with Drug Use and Mortality: An Observational Study

Background: The pathogenesis of type 2 diabetes mellitus is complex and still unclear in some details. The main feature of diabetes mellitus is high serum glucose, and the question arises of whether there are other statistically observable dysregulations in laboratory measurements before the state of hyperglycemia becomes severe. In the present study, we aim to examine glucose and lipid profiles in the context of age, sex, medication use, and mortality. Methods: We conducted an observational study by analyzing laboratory data from 506,083 anonymized laboratory tests from 63,606 different patients performed by a regional laboratory in Slovenia between 2008 and 2019. Laboratory data-based results were evaluated in the context of medication use and mortality. The medication use database contains anonymized records of 1,632,441 patients from 2013 to 2018, and mortality data were obtained for the entire Slovenian population. Results: We show that the highest percentage of the population with elevated glucose levels occurs approximately 20 years later than the highest percentage with lipid dysregulation. Remarkably, two distinct inflection points were observed in these laboratory results. The first inflection point occurs at ages 55 to 59 years, corresponding to the greatest increase in medication use, and the second coincides with the sharp increase in mortality at ages 75 to 79 years. Conclusions: Our results suggest that medications and mortality are important factors affecting population statistics and must be considered when studying metabolic disorders such as dyslipidemia and hyperglycemia using laboratory data.

Synthetic Small Molecules to Induce Insulin Secretion and Pancreatic Beta Cell Specific Gene Expression

Despite various efficient pharmaceuticals which are already used to manage diabetes, new drugs are needed to preserve and restore the function of pancreatic β-cells (pβCs) including cell specific gene expression and insulin production and secretion. Newly developed small molecules (SMs) with potential anti-diabetic activity need to be preliminary tested. Mice insulinoma MIN6 cells (MIN6) can be utilized as an in vitro screening model. These cells have pancreatic β-cells characteristics and can secrete insulin in response to glucose level changes. As well, β-cell-specific gene expression pattern of these cells is similar to that of mouse pancreatic islet cells. It is possible to use this cell line as a research tool to study the function of the pancreatic β-cells. To date, approximately 60 genes have been identified which, are effective in the pβCs embryonic development and insulin production and secretion during puberty, including pancreas/duodenum homeobox protein 1 (Pdx1), neuronal differentiation 1 (Neurod1), neurogenin3 (Ngn3), and insulin-1 precursor (Ins1). In this study, a family of new SMs that are structurally similar to glinides was synthesized through three different synthetic methods and categorized into three categories (C1-C3). Then, these novel SMs were characterized by testing their effects on cell viability, pβCs-specific gene expression, and insulin secretion of MIN6 in four different concentrations and three time points. According to our results, SMs of C1 (1j, 1k, and 1l) and two SMs of C3 (1f, 1I), at 200 μM concentration, were able to increase the expression levels of Pdx1, Neurod1, Ngn3, and Ins1 as well as the insulin secretion after 24 hours. However, C2 (1a, 1b, 1c and 1d) did not show significant bio-activity of MIN6 cells. These investigated molecules can provide a tool for exploring pseudo-islet functionality in MIN6 cells or provide a possible basis for future therapeutic interventions for diabetes.

Analysis of the transcriptome and metabolome of pancreatic spheroids derived from human induced pluripotent stem cells and matured in an organ-on-a-chip

The differentiation of pancreatic cells from hiPSC is one of the emerging strategies to achieve an in vitro pancreas model. Here, hiPSC-derived β-like-cells spheroids were cultured in microfluidic environment and characterized using omics analysis.

Linoleic acid and the regulation of glucose homeostasis: A review of the evidence

The consumption of linoleic acid (LA, ω-6 18:2), the most common ω-6 polyunsaturated fatty acid (PUFA) in the Modern Western diet (MWD), has significantly increased over the last century in tandem with unprecedented incidence of chronic metabolic diseases like obesity and type 2 diabetes mellitus (T2DM). Although an essential fatty acid for health, LA was a very rare fatty acid in the diet of humans during their evolution. While the intake of other dietary macronutrients (carbohydrates like fructose) has also risen, diets rich in ω-6 PUFAs have been promoted in an effort to reduce cardiovascular disease despite unclear evidence as to how increased dietary LA consumption could promote a proinflammatory state and affect glucose metabolism. Current evidence suggests that sex, genetics, environmental factors, and disease status can differentially modulate how LA influences insulin sensitivity and peripheral glucose uptake as well as insulin secretion and pancreatic beta-cell function. Therefore, the aim of this review will be to summarize recent additions to our knowledge to refine the unique physiological and pathophysiological roles of LA in the regulation of glucose homeostasis.

Impact of Pancreatic β-Cell Function on Clopidogrel Responsiveness and Outcomes in Chinese Nondiabetic Patients Undergoing Elective Percutaneous Coronary Intervention

PURPOSE

Insulin resistance and β-cell dysfunction are fundamental defects contributing to type 2 diabetes development. Prior studies indicated that insulin resistance may be correlated with low responsiveness to clopidogrel. This study aimed to investigate the effects of β-cell function on clopidogrel-induced platelet P2Y12 inhibition and the clinical outcomes of nondiabetic patients undergoing elective percutaneous coronary intervention (PCI).

METHODS

Patients scheduled to undergo elective PCI and receive clopidogrel in addition to aspirin were recruited for this study. Homeostatic model assessment 2 of β-cell function (HOMA2-β%) was used to classify participants into quartiles. Thromboelastography (TEG) was used to calculate the quantitative platelet inhibition rate to assess clopidogrel-induced antiplatelet reactivity. The clinical outcome was major adverse cardiovascular and cerebrovascular events (MACCEs).

RESULTS

Of the 784 participants evaluated, 21.3% of them (169 of 784) had low responsiveness to clopidogrel. According to multivariate linear regression analysis, the first quartile of HOMA2-β% (19.9-78.1), indicating greater β-cell dysfunction, was independently associated with low responsiveness to clopidogrel compared with the fourth quartile (126.8-326.2) after adjustment for potential covariates [odds ratio 2.140, 95% confidence interval (CI) (1.336 to 3.570), P = 0.038]. In addition, at one year, the first quartile of HOMA2-β% was associated with an increased risk of 1-year MACCE occurrence compared with the fourth quartile [adjusted hazard ratio 4.989, 95% CI (1.571 to 15.845), P = 0.006].

CONCLUSION

Increased β-cell dysfunction, indicated by a low HOMA2-β%, was associated with low responsiveness to clopidogrel and an increased risk of one-year MACCEs in nondiabetic patients undergoing elective PCI.

Blocking TLR4-NF-κB pathway protects mouse islets from the combinatorial impact of high fat and fetuin-A mediated dysfunction and restores ability for insulin secretion

Lipid mediated pancreatic β-cell dysfunction during Type 2 diabetes is known to be regulated by activation of TLR4 (Toll Like Receptor 4) and NF-κB (Nuclear factor kappa B). Recently we have reported that MIN6 cells (mouse insulinoma cells) secrete fetuin-A on stimulation by palmitate that aggravates β-cell dysfunction, but the mechanism involved in-vivo has not been demonstrated and thus remained unclear. Here we attempted to dissect the role of palmitate and fetuin-A on insulin secretion using high fat diet (HFD) fed mice model. HFD islets showed curtailed insulin secretion after 20 weeks of treatment with activated TLR4-NF-κB pathway. Further treatment of islets with palmitate raised fetuin-A expression by ~2.8 folds and cut down insulin secretion by ~1.4 folds. However, blocking the activity of TLR4, fetuin-A and NF-κB using specific inhibitors or siRNAs not only restored insulin secretion by ~2 folds in standard diet fed mice islets and MIN6 cells but also evoke insulin secretory ability by ~2.3 folds in HFD islets. Altogether this study demonstrated that blocking TLR4, fetuin-A and NF-κB protect pancreatic β-cells from the negative effects of free fatty acid and fetuin-A and restore insulin secretion.

Intercellular Communication in the Islet of Langerhans in Health and Disease

Blood glucose homeostasis requires proper function of pancreatic islets, which secrete insulin, glucagon, and somatostatin from the β-, α-, and δ-cells, respectively. Each islet cell type is equipped with intrinsic mechanisms for glucose sensing and secretory actions, but these intrinsic mechanisms alone cannot explain the observed secretory profiles from intact islets. Regulation of secretion involves interconnected mechanisms among and between islet cell types. Islet cells lose their normal functional signatures and secretory behaviors upon dispersal as compared to intact islets and in vivo. In dispersed islet cells, the glucose response of insulin secretion is attenuated from that seen from whole islets, coordinated oscillations in membrane potential and intracellular Ca2+ activity, as well as the two-phase insulin secretion profile, are missing, and glucagon secretion displays higher basal secretion profile and a reverse glucose-dependent response from that of intact islets. These observations highlight the critical roles of intercellular communication within the pancreatic islet, and how these communication pathways are crucial for proper hormonal and nonhormonal secretion and glucose homeostasis. Further, misregulated secretions of islet secretory products that arise from defective intercellular islet communication are implicated in diabetes. Intercellular communication within the islet environment comprises multiple mechanisms, including electrical synapses from gap junctional coupling, paracrine interactions among neighboring cells, and direct cell-to-cell contacts in the form of juxtacrine signaling. In this article, we describe the various mechanisms that contribute to proper islet function for each islet cell type and how intercellular islet communications are coordinated among the same and different islet cell types. © 2021 American Physiological Society. Compr Physiol 11:2191-2225, 2021.

Secretin activates brown fat and induces satiation

Brown adipose tissue (BAT) thermogenesis is activated by feeding. Recently, we revealed a secretin-mediated gut-BAT-brain axis, which stimulates satiation in mice, but the purpose of meal-induced BAT activation in humans has been unclear. In this placebo-controlled, randomized crossover study, we investigated the effects of intravenous secretin on BAT metabolism (measured with [18F]FDG and [15O]H2O positron emission tomography) and appetite (measured with functional magnetic resonance imaging) in healthy, normal weight men (GUTBAT trial no. NCT03290846). Participants were blinded to the intervention. Secretin increased BAT glucose uptake (primary endpoint) compared to placebo by 57% (median (interquartile range, IQR), 0.82 (0.77) versus 0.59 (0.53) μmol per 100 g per min, 95% confidence interval (CI) (0.09, 0.89), P = 0.002, effect size r = 0.570), while BAT perfusion remained unchanged (mean (s.d.) 4.73 (1.82) versus 6.14 (3.05) ml per 100 g per min, 95%CI (-2.91, 0.07), P = 0.063, effect size d = -0.549) (n = 15). Whole body energy expenditure increased by 2% (P = 0.011) (n = 15). Secretin attenuated blood-oxygen level-dependent activity (primary endpoint) in brain reward circuits during food cue tasks (significance level false discovery rate corrected at P = 0.05) (n = 14). Caloric intake did not significantly change, but motivation to refeed after a meal was delayed by 39 min (P = 0.039) (n = 14). No adverse effects were detected. Here we show in humans that secretin activates BAT, reduces central responses to appetizing food and delays the motivation to refeed after a meal. This suggests that meal-induced, secretin-mediated BAT activation is relevant in the control of food intake in humans. As obesity is increasing worldwide, this appetite regulating axis offers new possibilities for clinical research in treating obesity.

Involvement of aquaglyceroporins in energy metabolism in health and disease

Aquaglyceroporins are a group of the aquaporin (AQP) family of transmembrane water channels. While AQPs facilitate the passage of water, small solutes, and gases across biological membranes, aquaglyceroporins allow passage of water, glycerol, urea and some other solutes. Thanks to their glycerol permeability, aquaglyceroporins are involved in energy homeostasis. This review provides an overview of what is currently known concerning the functional implication and control of aquaglyceroporins in tissues involved in energy metabolism, i.e. liver, adipose tissue and endocrine pancreas. The expression, role and (dys)regulation of aquaglyceroporins in disorders affecting energy metabolism, and the potential relevance of aquaglyceroporins as drug targets to treat the alterations of the energy balance is also addressed.

Identification of MEDAG as a Hub Candidate Gene in the Onset and Progression of Type 2 Diabetes Mellitus by Comprehensive Bioinformatics Analysis

Objectives

We conducted the present study to identify novel hub candidate genes in the pathogenesis of type 2 diabetes mellitus (T2DM) and provide potential biomarkers or therapeutic targets for dealing with the disease.

Methods

We conducted weighted gene coexpression network analysis on a series of the expression profiles of the pancreas islet of T2DM patients obtained from the Gene Expression Omnibus database to construct a weighted coexpression network. After dividing genes into separated coexpression modules, we identified a T2DM-related module using Pearson's correlation analysis. Then, hub genes were identified from the T2DM-related module using the Maximal Clique Centrality method and validated by correlation analysis with clinical traits, differentially expressed gene analysis, validation in other datasets, and single-gene gene set enrichment analysis (GSEA).

Results

Genes were divided into 16 coexpression modules, and one module was identified as a T2DM-related module. Four hub candidate genes were identified, and MEDAG was a novel hub candidate gene. The expression level of MEDAG was positively correlated with hemoglobin A1c (HbA1c) and was evidently overexpressed in the pancreas islet tissue of T2DM patients compared with normal control. Analyses on two other datasets supported the results. GSEA verified that MEDAG plays essential roles in T2DM.

Conclusions

MEDAG is a novel hub candidate of T2DM, and its irregular expression in the pancreas islet plays vital roles in the pathogenesis of T2DM. MEDAG is a potential target of intervention in the future for the treatment of T2DM.

β-Cell Dysfunction, Hepatic Lipid Metabolism, and Cardiovascular Health in Type 2 Diabetes: New Directions of Research and Novel Therapeutic Strategies

Cardiovascular disease (CVD) remains a major problem for people with type 2 diabetes mellitus (T2DM), and dyslipidemia is one of the main drivers for both metabolic diseases. In this review, the major pathophysiological and molecular mechanisms of β-cell dysfunction and recovery in T2DM are discussed in the context of abnormal hepatic lipid metabolism and cardiovascular health. (i) In normal health, continuous exposure of the pancreas to nutrient stimulus increases the demand on β-cells. In the long term, this will not only stress β-cells and decrease their insulin secretory capacity, but also will blunt the cellular response to insulin. (ii) At the pre-diabetes stage, β-cells compensate for insulin resistance through hypersecretion of insulin. This increases the metabolic burden on the stressed β-cells and changes hepatic lipoprotein metabolism and adipose tissue function. (iii) If this lipotoxic hyperinsulinemic environment is not removed, β-cells start to lose function, and CVD risk rises due to lower lipoprotein clearance. (iv) Once developed, T2DM can be reversed by weight loss, a process described recently as remission. However, the precise mechanism(s) by which calorie restriction causes normalization of lipoprotein metabolism and restores β-cell function are not fully established. Understanding the pathophysiological and molecular basis of β-cell failure and recovery during remission is critical to reduce β-cell burden and loss of function. The aim of this review is to highlight the link between lipoprotein export and lipid-driven β-cell dysfunction in T2DM and how this is related to cardiovascular health. A second aim is to understand the mechanisms of β-cell recovery after weight loss, and to explore new areas of research for developing more targeted future therapies to prevent T2DM and the associated CVD events.

Pathways Enrichment Analysis of Gene Expression Data in Type 2 Diabetes

Profiling genome-wide transcriptional changes with advanced high-throughput transcriptional profiling techniques has led to a revolution in biomedical science. It has been challenging to handle the massive data generated by these techniques and draw meaningful conclusions from it. Therefore, computational biologists have developed a number of innovative methods of varying complexity and effectiveness to analyze such complex data. Over the past decade, rich information in pathway repositories has attracted and motivated researchers to incorporate such existing biological knowledge into computational analysis tools to develop what is known as pathway enrichment analysis tools. This chapter describes a new sophisticated pathway enrichment tool that exploits topology of pathway as well as expression of significantly changed genes to identify biologically significant pathways for high-dimensional gene expression datasets. Also, we demonstrate the use of this tool to analyze gene expression data from a type 2 diabetes dataset to identify a list of significantly enriched metabolic pathways.

Hormone-sensitive lipase: sixty years later

Hormone-sensitive lipase (HSL) was initially characterized as the hormonally regulated neutral lipase activity responsible for the breakdown of triacylglycerols into fatty acids in adipose tissue. This review aims at providing up-to-date information on structural properties, regulation of expression, activity and function as well as therapeutic potential. The lipase is expressed as different isoforms produced from tissue-specific alternative promoters. All isoforms are composed of an N-terminal domain and a C-terminal catalytic domain within which a regulatory domain containing the phosphorylation sites is embedded. Some isoforms possess additional N-terminal regions. The catalytic domain shares similarities with bacteria, fungus and vascular plant proteins but not with other mammalian lipases. HSL singularity is provided by regulatory and N-terminal domains sharing no homology with other proteins. HSL has a broad substrate specificity compared to other neutral lipases. It hydrolyzes acylglycerols, cholesteryl and retinyl esters among other substrates. A novel role of HSL, independent of its enzymatic function, has recently been described in adipocytes. Clinical studies revealed dysregulations of HSL expression and activity in disorders, such as lipodystrophy, obesity, type 2 diabetes and cancer-associated cachexia. Development of specific inhibitors positions HSL as a pharmacological target for the treatment of metabolic complications.

Zinc-alpha2-glycoprotein, dysglycaemia and insulin resistance: a systematic review and meta-analysis

To systematically review the current literature investigating associations between zinc-alpha2-glycoprotein (ZAG) and dysglycaemia (including type 2 diabetes (T2DM), poly-cystic-ovary syndrome (PCOS), pre-diabetes or insulin resistance). This included relationships between ZAG and continuous measures of insulin and glucose. Additionally, we performed a meta-analysis to estimate the extent that ZAG differs between individuals with or without dysglycaemia; whilst examining the potential influence of adiposity. A systematic search was performed on four databases for studies on circulating ZAG concentrations in adult human populations, comparing healthy controls to individuals with dysglycaemia. Key characteristics, including the mean ZAG concentrations (mg∙L^-1), and any correlational statistics between ZAG and continuous measures of glucose, glycated haemoglobin (HbA1c) or insulin were extracted. Meta-analyses were performed to compare metabolically healthy controls to cases, and on studies that compared controls and cases considered overweight or obese (body mass index (BMI) ≥25 kg^.m²). 1575 papers were identified and 14 studies (16 cohorts) were considered eligible for inclusion. Circulating ZAG was lower in individuals with dysglycaemia compared to metabolically healthy controls (-4.14 [-8.17, -0.11] mg^.L^-1; I² = 98.5%; p < 0.001). When using data from only studies with overweight or obese groups with or without dysglycaemia (three studies (four cohorts); pooled n = 332), the difference in circulating ZAG was no longer significant (-0.30 [-3.67, 3.07] mg^. L^-1; I² = 28.0%; p = 0.225). These data suggest that ZAG may be implicated in dysglycaemia, although there was significant heterogeneity across different studies and the mediating effect of adiposity cannot be excluded. Therefore, more research is needed before robust conclusions can be drawn.

Effect of omega-3 fatty acids on glucose homeostasis: role of free fatty acid receptor 1

Insulin resistance is a worldwide health problem. This study investigated the acute effects of eicosapentanoic acid (EPA) on glucose homeostasis focusing on the role of free fatty acid receptor 1 (FFAR1) and the chronic effects of fish oil omega-3 fatty acids on insulin resistance. Insulin resistance was induced by feeding mice high-fructose, high-fat diet (HFrHFD) for 16 weeks. In the first part, the acute effects of EPA alone and in combination with GW1100 and DC260126 (FFAR1 blockers) on glucose homeostasis and hepatic phosphatidyl-inositol 4,5-bisphosphate (PIP2) and diacylglycerol (DAG) were investigated in standard chow diet (SCD)- and HFrHFD-fed mice. In the second part, mice were treated with fish oil omega-3 fatty acids for 4 weeks starting at the week 13 of feeding HFrHFD. Changes in the blood- and liver tissue-insulin resistance markers and FFAR1 downstream signals were recorded at the end of experiment. Results showed that EPA increased 0 and 30 min blood glucose levels after glucose load in SCD-fed mice but improved glucose tolerance in HFrHFD-fed mice. Moreover, FFAR1 blockers reduced EPA effects on glucose tolerance and hepatic PIP2 and DAG levels. On the other hand, chronic use of fish oil omega-3 fatty acids increased FBG levels and decreased serum insulin and triglycerides levels without improving the index of insulin resistance. Also, they increased hepatic β-arrestin-2, PIP2, and pS473 Akt levels but decreased DAG levels. In conclusion, EPA acutely improved glucose homeostasis in HFrHFD-fed mice by modulating the activity of FFAR1. However, the chronic use of fish oil omega-3 fatty acids did not improve the insulin resistance.

Adipose Triglyceride Lipase Is a Key Lipase for the Mobilization of Lipid Droplets in Human β-Cells and Critical for the Maintenance of Syntaxin 1a Levels in β-Cells

Lipid droplets (LDs) are frequently increased when excessive lipid accumulation leads to cellular dysfunction. Distinct from mouse β-cells, LDs are prominent in human β-cells. However, the regulation of LD mobilization (lipolysis) in human β-cells remains unclear. We found that glucose increases lipolysis in nondiabetic human islets but not in islets in patients with type 2 diabetes (T2D), indicating dysregulation of lipolysis in T2D islets. Silencing adipose triglyceride lipase (ATGL) in human pseudoislets with shRNA targeting ATGL (shATGL) increased triglycerides (TGs) and the number and size of LDs, indicating that ATGL is the principal lipase in human β-cells. In shATGL pseudoislets, biphasic glucose-stimulated insulin secretion (GSIS), and insulin secretion to 3-isobutyl-1-methylxanthine and KCl were all reduced without altering oxygen consumption rate compared with scramble control. Like human islets, INS1 cells showed visible LDs, glucose-responsive lipolysis, and impairment of GSIS after ATGL silencing. ATGL-deficient INS1 cells and human pseudoislets showed reduced SNARE protein syntaxin 1a (STX1A), a key SNARE component. Proteasomal degradation of Stx1a was accelerated likely through reduced palmitoylation in ATGL-deficient INS1 cells. Therefore, ATGL is responsible for LD mobilization in human β-cells and supports insulin secretion by stabilizing STX1A. The dysregulated lipolysis may contribute to LD accumulation and β-cell dysfunction in T2D islets.

Live-cell lipid biochemistry reveals a role of diacylglycerol side-chain composition for cellular lipid dynamics and protein affinities

Every cell produces thousands of lipid species, but studying the function of individual lipids in living cells is almost impossible with existing methodologies. Addressing this experimental bottleneck, we developed a strategy to quantify dissociation constants for lipid–protein interactions and transmembrane flip-flop rates of native lipids in live-cell experiments. Using a combination of plasma membrane-specific photochemical probes and mathematical modeling, we demonstrate that, for diacylglycerols as a model lipid class, the inherent lipid structural diversity caused by variations in acyl chain composition determines lipid protein affinities and transbilayer kinetics. In fact, subtle chemical differences change these values by orders of magnitude. Our approach represents a generally applicable method for elucidating the biological function of single lipid species on subcellular scales.

Every cell produces thousands of distinct lipid species, but insight into how lipid chemical diversity contributes to biological signaling is lacking, particularly because of a scarcity of methods for quantitatively studying lipid function in living cells. Using the example of diacylglycerols, prominent second messengers, we here investigate whether lipid chemical diversity can provide a basis for cellular signal specification. We generated photo-caged lipid probes, which allow acute manipulation of distinct diacylglycerol species in the plasma membrane. Combining uncaging experiments with mathematical modeling, we were able to determine binding constants for diacylglycerol–protein interactions, and kinetic parameters for diacylglycerol transbilayer movement and turnover in quantitative live-cell experiments. Strikingly, we find that affinities and kinetics vary by orders of magnitude due to diacylglycerol side-chain composition. These differences are sufficient to explain differential recruitment of diacylglycerol binding proteins and, thus, differing downstream phosphorylation patterns. Our approach represents a generally applicable method for elucidating the biological function of single lipid species on subcellular scales in quantitative live-cell experiments.

Exposure of Pancreatic β-Cells to Excess Glucose Results in Bimodal Activation of mTORC1 and mTOR-Dependent Metabolic Acceleration

Chronic exposure of pancreatic β-cells to excess glucose can lead to metabolic acceleration and loss of stimulus-secretion coupling. Here, we examined how exposure to excess glucose (defined here as concentrations above 5 mM) affects mTORC1 signaling and the metabolism of β-cells. Acute exposure to excess glucose stimulated glycolysis-dependent mTORC1 signaling, without changes in the PI3K or AMPK pathways. Prolonged exposure to excess glucose led to hyperactivation of mTORC1 and metabolic acceleration, characterized by higher basal respiration and maximal respiratory capacity, increased energy demand, and enhanced flux through mitochondrial pyruvate metabolism. Inhibition of pyruvate transport to the mitochondria decelerated the metabolism of β-cells chronically exposed to excess glucose and re-established glucose-dependent mTORC1 signaling, disrupting a positive feedback loop for mTORC1 hyperactivation. mTOR inhibition had positive and negative impacts on various metabolic pathways and insulin secretion, demonstrating a role for mTOR signaling in the long-term metabolic adaptation of β-cells to excess glucose.

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Acute glucose stimulates mTORC1 in β-cells through a glycolysis-dependent mechanism

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Chronic excess glucose promotes mTOR-dependent metabolic acceleration of β-cells

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Metabolic acceleration activates a positive feedback loop for mTORC1 hyperactivation

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mTOR hyperactivation disturbs the metabolism and insulin secretion patterns of β-cells

Connecting pancreatic islet lipid metabolism with insulin secretion and the development of type 2 diabetes

Obesity is the major contributing factor for the increased prevalence of type 2 diabetes (T2D) in recent years. Sustained positive influx of lipids is considered to be a precipitating factor for beta cell dysfunction and serves as a connection between obesity and T2D. Importantly, fatty acids (FA), a key building block of lipids, are a double-edged sword for beta cells. FA acutely increase glucose-stimulated insulin secretion through cell-surface receptor and intracellular pathways. However, chronic exposure to FA, combined with elevated glucose, impair the viability and function of beta cells in vitro and in animal models of obesity (glucolipotoxicity), providing an experimental basis for the propensity of beta cell demise under obesity in humans. To better understand the two-sided relationship between lipids and beta cells, we present a current view of acute and chronic handling of lipids by beta cells and implications for beta cell function and health. We also discuss an emerging role for lipid droplets (LD) in the dynamic regulation of lipid metabolism in beta cells and insulin secretion, along with a potential role for LD under nutritional stress in beta cells, and incorporate recent advancement in the field of lipid droplet biology.

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.

Aquaglyceroporins: Drug Targets for Metabolic Diseases?

Aquaporins (AQPs) are a family of transmembrane channel proteins facilitating the transport of water, small solutes, and gasses across biological membranes. AQPs are expressed in all tissues and ensure multiple roles under normal and pathophysiological conditions. Aquaglyceroporins are a subfamily of AQPs permeable to glycerol in addition to water and participate thereby to energy metabolism. This review focalizes on the present knowledge of the expression, regulation and physiological roles of AQPs in adipose tissue, liver and endocrine pancreas, that are involved in energy metabolism. In addition, the review aims at summarizing the involvement of AQPs in metabolic disorders, such as obesity, diabetes and liver diseases. Finally, challenges and recent advances related to pharmacological modulation of AQPs expression and function to control and treat metabolic diseases are discussed.

Liraglutide suppresses non-esterified free fatty acids and soluble vascular cell adhesion molecule-1 compared with metformin in patients with recent-onset type 2 diabetes

Background

It has been suggested that liraglutide could have an impact on glucose and lipid metabolism disorder and adhesion molecule activation, which may play important roles in the vascular damage of diabetes. In this study, we examined the effects of liraglutide versus metformin on non-esterified free fatty acids, beta-cell insulin secretion, and adhesion molecule levels in patients with recent-onset type 2 diabetes mellitus.

Methods

In this study, 60 patients newly diagnosed with type 2 diabetes mellitus (mean age 33.97 ± 5.67 years) were randomly assigned to receive once-daily subcutaneous liraglutide or oral metformin. Before the study and after the 8-week treatment period, a 75 g oral glucose tolerance test was performed. Plasma glucose, lipids and lipoprotein, plasma insulin, glycaemic and insulin responses, non-esterified free fatty acids (NEFA), and soluble vascular cell adhesion molecule-1 (sVCAM-1) levels were evaluated.

Results

After 8 weeks, 120 min of NEFA (155 ± 125 vs 99 ± 73 µmol/L, P = 0.026) and the levels of sVCAM-1 (465 ± 136 vs 382 ± 131 ng/ml, P = 0.013) significantly decreased, while the early phase insulin secretion index (24.94 [7.78, 38.89] vs. 31.13 [17.67, 59.09], P = 0.031), fasting plasma insulin (104 [51, 123] vs 113 [54, 171] mIU/L, P = 0.015), 60 min plasma insulin (326 [165, 441] vs 471 [334, 717] mIU/L, P = 0.005), 120 min plasma insulin (401 [193, 560] vs 500 [367, 960] mIU/L, P = 0.047), and insulin area under the curve (AUCins) (648 [321, 742] vs 738 [451, 1118] mIU/L, P = 0.005) remarkably increased for patients in the liraglutide treatment group. The levels of sVCAM-1 dramatically decreased after 8 weeks of liraglutide treatment (503 ± 182 vs 382 ± 131 ng/ml, P = 0.046) compared to that of the metformin treatment group. At the same time, the differences before and after liraglutide treatment in 120 min of NEFA (− 32 [− 96, − 5] vs 5 [− 35, 38] µmol/L, P = 0.033) and AUCins (738 [451, 1118] vs 594 [357, 1216] mIU/L, P = 0.014) were remarkably enhanced compared to that of the metformin therapy. Nevertheless, there were no significant differences in fasting NEFA after liraglutide or metformin treatment. The reduction of 120 min NEFA (ΔNEFA) was positively correlated with the decrease of sVCAM-1 (ΔsVCAM-1) after 8 weeks of liraglutide treatment (r = 0.523, P = 0.003).

Conclusions

Our results demonstrate that liraglutide administration is more effective than metformin in reducing 120 min NEFA and suppressing sVCAM-1 levels for recent-onset type 2 diabetes mellitus. We suggest that this outcome may be because liraglutide is associated with potentiating insulin secretion capacity, inhibiting vascular inflammatory cytokines, and antagonizing atherosclerosis.

Electronic supplementary material

The online version of this article (10.1186/s12933-018-0701-4) contains supplementary material, which is available to authorized users.

Effects of Dietary Fatty Acids in Pancreatic Beta Cell Metabolism, Implications in Homeostasis

Fatty acids are involved in several metabolic processes, including the development of metabolic and cardiovascular diseases. In recent years a disease that has received escalated interest is type 2 diabetes (T2D). Many contributing factors including a high-caloric diet rich in dietary saturated fats have been broadly characterized as triggers of T2D. Insulin resistance resulting from a high saturated fat diet leads to alterations in lipid cellular intake and accumulation which generate lipotoxic conditions, a key phenomenon in the metabolism of β-cells. Alternatively, unsaturated fatty acids have been described to show opposite effects in pancreatic β-cells. The purpose of this work is to perform a critical analysis of the complex role of saturated and unsaturated fatty acids in β-cell metabolism. We discuss the diverse effects main dietary fatty acids have upon pancreatic β-cell metabolism as a key factor to maintain homeostasis by focusing in the cellular and molecular mechanisms involved in the development and progression of T2D. For instance, modifications in protein homeostasis as well as the intracellular management of lipid metabolism which are associated with inflammatory pathways. These conditions initiate critical metabolic rearrangements, that in turn have repercussions on insulin β-cell metabolism. This review allows an integral and broad understanding of different functions of fatty acids inside β-cells, being important metabolites for novel therapeutic targets in T2D treatment.

Adiposity and fat metabolism during combined fasting and lactation in elephant seals

Animals that fast depend on mobilizing lipid stores to power metabolism. Northern elephant seals (Mirounga angustirostris) incorporate extended fasting into several life-history stages: development, molting, breeding and lactation. The physiological processes enabling fasting and lactation are important in the context of the ecology and life history of elephant seals. The rare combination of fasting and lactation depends on the efficient mobilization of lipid from adipose stores and its direction into milk production. The mother elephant seal must ration her finite body stores to power maintenance metabolism, as well as to produce large quantities of lipid and protein-rich milk. Lipid from body stores must first be mobilized; the action of lipolytic enzymes and hormones stimulate the release of fatty acids into the bloodstream. Biochemical processes affect the release of specific fatty acids in a predictable manner, and the pattern of release from lipid stores is closely reflected in the fatty acid content of the milk lipid. The content of the milk may have substantial developmental, thermoregulatory and metabolic consequences for the pup. The lactation and developmental patterns found in elephant seals are similar in some respects to those of other mammals; however, even within the limited number of mammals that simultaneously fast and lactate, there are important differences in the mechanisms that regulate lipid mobilization and milk lipid content. Although ungulates and humans do not fast during lactation, there are interesting comparisons to these groups regarding lipid mobilization and milk lipid content patterns.

Amyloid growth and membrane damage: Current themes and emerging perspectives from theory and experiments on Aβ and hIAPP

Alzheimer's Disease (AD) and Type 2 diabetes mellitus (T2DM) are two incurable diseases both hallmarked by an abnormal deposition of the amyloidogenic peptides Aβ and Islet Amyloid Polypeptide (IAPP) in affected tissues. Epidemiological data demonstrate that patients suffering from diabetes are at high risk of developing AD, thus making the search for factors common to the two pathologies of special interest for the design of new therapies. Accumulating evidence suggests that the toxic properties of both Aβ or IAPP are ascribable to their ability to damage the cell membrane. However, the molecular details describing Aβ or IAPP interaction with membranes are poorly understood. This review focuses on biophysical and in silico studies addressing these topics. Effects of calcium, cholesterol and membrane lipid composition in driving aberrant Aβ or IAPP interaction with the membrane will be specifically considered. The cross correlation of all these factors appears to be a key issue not only to shed light in the countless and often controversial reports relative to this area but also to gain valuable insights into the central events leading to membrane damage caused by amyloidogenic peptides. This article is part of a Special Issue entitled: Protein Aggregation and Misfolding at the Cell Membrane Interface edited by Ayyalusamy Ramamoorthy.

The impact of insulin pump therapy to oxidative stress in patients with diabetic nephropathy

Background

The oxidative stress resulting from increased production of ROS plays a crucial role in the development of diabetic complications. We aim to explore the relationships between oxidative stress, diabetic nephropathy (DN) and short-term insulin pump intensive therapy (insulin therapy).

Methods

Levels of 8-hydroxy-deoxyguanosine (8-OHdG), 3-nitrotyrosine (3-NT), glutathione (GSH), superoxide dismutase (SOD) and Interleukin-6 (IL-6) were estimated before and after 2 weeks of insulin therapy in normal group (NC) and type 2 diabetic (DM) with normal albuminuria (NA), microalbuminuria (MA) and clinical albuminuria (CA).

Results

In DM group, levels of 8-OHdG and 3-NT were higher than those in NC group (P < 0.05); GSH and SOD were lower (P < 0.05). And their levels changed with urine albumin–creatinine ratio (P < 0.05). After insulin therapy, these derangements were significantly ameliorated and the changes in NA and MA groups were more significant than CA group (P < 0.05). Correlation analysis showed glycated hemoglobin, the course of disease, the HOME-IR and fasting plasma glucose were positively correlated with 8-OHdG and 3-NT, but negatively correlated with GSH and SOD.

Conclusions

The oxidative stress gradually increased with the magnitude of DN, and insulin pump intensive therapy can significantly ameliorate the derangements in the early stage of DN.

Trial registration NCT03174821

Comparative transcriptomic evidence for Tween80-enhanced biodegradation of phenanthrene by Sphingomonas sp. GY2B

Previous study of the effects of surfactants on the biodegradation of phenanthrene focused on investigating alterations of the cell characteristics of Sphingomonas sp. GY2B. However, genes regulation associated with biodegradation and biological processes in response to the presence of surfactants, remains unclear. In this study, comparative transcriptome analysis was conducted to observe the gene expression of GY2B during phenanthrene biodegradation in the presence and absence of Tween80. A diverse set of genes was regulated by Tween80, leading to increased biodegradation of phenanthrene by GY2B: (i) Tween80 increased expression of genes related to H⁺ transport in the plasma membrane to provide a driving force (i.e., ATP) for accelerating transmembrane transport of phenanthrene with increasing Tween80 concentrations, thereby enhancing the uptake and degradation of phenanthrene by GY2B; (ii) Tween80 (1 and 8 CMC) promoted intracellular biodegradation of phenanthrene by stimulating expression of genes encoding dioxygenases and monooxygenase, increasing expression of genes involved in intracellular metabolic processes (e.g., TCA cycle); and (iii) Tween80 likely increased GY2B vitality and growth by inducing expression of genes associated with ABC transporters and protein transport, regulating genes involved in other biological processes (e.g., transcription, translation).

The Role of Cholesterol in Driving IAPP-Membrane Interactions

Our knowledge of the molecular events underlying type 2 diabetes mellitus-a protein conformational disease characterized by the aggregation of islet amyloid polypeptide (IAPP) in pancreatic β cells-is limited. However, amyloid-mediated membrane damage is known to play a key role in IAPP cytotoxicity, and therefore the effects of lipid composition on modulating IAPP-membrane interactions have been the focus of intense research. In particular, membrane cholesterol content varies with aging and consequently with adverse environmental factors such as diet and lifestyle, but its role in the development of the disease is controversial. In this study, we employ a combination of experimental techniques and in silico molecular simulations to shed light on the role of cholesterol in IAPP aggregation and the related membrane disruption. We show that if anionic POPC/POPS vesicles are used as model membranes, cholesterol has a negligible effect on the kinetics of IAPP fibril growth on the surface of the bilayer. In addition, cholesterol inhibits membrane damage by amyloid-induced poration on membranes, but enhances leakage through fiber growth on the membrane surface. Conversely, if 1:2 DOPC/DPPC raft-like model membranes are used, cholesterol accelerates fiber growth. Next, it enhances pore formation and suppresses fiber growth on the membrane surface, leading to leakage. Our results highlight a twofold effect of cholesterol on the amyloidogenicity of IAPP and help explain its debated role in type 2 diabetes mellitus.

The Pancreatic β-Cell: A Bioenergetic Perspective

The pancreatic β-cell secretes insulin in response to elevated plasma glucose. This review applies an external bioenergetic critique to the central processes of glucose-stimulated insulin secretion, including glycolytic and mitochondrial metabolism, the cytosolic adenine nucleotide pool, and its interaction with plasma membrane ion channels. The control mechanisms responsible for the unique responsiveness of the cell to glucose availability are discussed from bioenergetic and metabolic control standpoints. The concept of coupling factor facilitation of secretion is critiqued, and an attempt is made to unravel the bioenergetic basis of the oscillatory mechanisms controlling secretion. The need to consider the physiological constraints operating in the intact cell is emphasized throughout. The aim is to provide a coherent pathway through an extensive, complex, and sometimes bewildering literature, particularly for those unfamiliar with the field.

Acute metabolic amplification of insulin secretion in mouse islets: Role of cytosolic acetyl-CoA

OBJECTIVE

Stimulation of the ß-cell metabolism by glucose and other fuels triggers insulin release by enhancing the mitochondrial ATP production and acutely amplifies the secretory response by increase in mitochondrial export of metabolites. We aimed to narrow down the uniform final reaction steps mediating fuel-induced acute amplification of insulin secretion.

MATERIAL/METHODS

Insulin secretion and metabolic parameters were measured in isolated mouse islets exposed to the sulfonylurea glipizide in high concentration (closing all ATP-sensitive K(+) channels) during the entire experiment. Fuel-induced effects were examined after treating the islets for one hour with medium devoid of fuels. This experimental design prevented acute amplification, but only when glucose was the sole fuel.

RESULTS

Strong amplification of insulin secretion by α-ketoisocaproate or glucose combined with α-ketoisovalerate (supplying mitochondrial oxaloacetate) was abolished within 14min after transition to medium devoid of fuels. After transition from medium containing glucose plus α-ketoisovalerate to medium containing solely glucose or α-ketoisovalerate, amplification (strong or weak, respectively) occurred until the end of the experiment. Glucose (alone or combined with α-ketoisovalerate) increased the total acetyl-CoA content as intensely as α-ketoisocaproate. Low concentrations of α-ketoisovalerate or α-ketoisocaproate were sufficient for saturation of acetyl-CoA increase, but caused no or only weak amplification, respectively. No acetyl-CoA increases occurred in the absence of glipizide.

CONCLUSIONS

Glucose and other fuels regulate acute amplification of insulin secretion by controlling the supply of acetyl-CoA to the ß-cell cytosol. Cytosolic acetyl-CoA does not amplify by serving as substrate for syntheses of metabolic intermediates, but amplifies by acting as substrate for cytosolic protein acetylation.