Arachidonic acid actions on functional integrity and attenuation of the negative effects of palmitic acid in a clonal pancreatic β-cell line

Environmentally relevant exposure to cotinine induces neurobehavioral toxicity in zebrafish (Danio rerio): A study using neurobehavioral and metabolomic approaches

As an important psychoactive substance, cotinine is ubiquitous in aquatic environment and poses a threat to aquatic organisms. However, the mechanism of its adverse health impacts remains unclear. We evaluated the effects of cotinine exposure at environmentally relevant concentrations on the development and locomotor behavior of zebrafish (Danio rerio) larvae using neurotransmitters and whole endogenous metabolism. Mild developmental toxicity and significant neurobehavior disorder, such as spontaneous movement (1-1000 μg/L), 48 hpf tactile response (50, 100, and 1000 μg/L), and 144 hpf swimming speed (1, 10, 100, 500, and 1000 μg/L), were observed in zebrafish. Exposure to cotinine led to significant alterations in 11 neurotransmitters, including homogentisic acid, serotonin, glutamic acid and aspartic acid, etc. 298 metabolites were identified and two pathways - linoleic acid metabolism and taurine and hypotaurine metabolism - were delineated. In addition, amino acid neurotransmitters were significantly correlated with metabolites such as arachidonic acid as well as its derivatives, steroidal compounds, and amino acids. Serotonin demonstrates a noteworthy correlation with 31 out of 40 differentially expressed neurotransmitters, encompassing lipids, amino acids, and other compounds. These novel findings contribute to a comprehensive understanding of the ecological risks associated with cotinine contamination in surface waters.

Excessive Tryptophan and Phenylalanine Induced Pancreatic Injury and Glycometabolism Disorder in Grower-finisher Pigs

BACKGROUND

The increase in circulating insulin levels is associated with the onset of type 2 diabetes (T2D), and the levels of branched-chain amino acids and aromatic amino acids (AAAs) are altered in T2D, but whether AAAs play a role in insulin secretion and signaling remains unclear.

OBJECTIVES

This study aimed to investigate the effects of different AAAs on pancreatic function and on the use of insulin in finishing pigs.

METHODS

A total of 18 healthy finishing pigs (Large White) with average body weight of 100 ± 1.15 kg were randomly allocated to 3 dietary treatments: Con, a normal diet supplemented with 0.68% alanine; Phe, a normal diet supplemented with 1.26% phenylalanine; and Trp, a normal diet supplemented with 0.78% tryptophan. The 3 diets were isonitrogenous. There were 6 replicates in each group.

RESULTS

Herein, we investigated the effects of tryptophan and phenylalanine on pancreatic function and the use of insulin in finishing pigs and found that the addition of tryptophan and phenylalanine aggravated pancreatic fat deposition, increased the relative content of saturated fatty acids, especially palmitate (C16:0) and stearate (C18:0), and the resulting lipid toxicity disrupted pancreatic secretory function. We also found that tryptophan and phenylalanine inhibited the growth and secretion of β-cells, downregulated the gene expression of the PI3K/Akt pathway in the pancreas and liver, and reduced glucose utilization in the liver.

CONCLUSIONS

Using fattening pigs as a model, multiorgan combined analysis of the insulin-secreting organ pancreas and the main insulin-acting organ liver, excessive intake of tryptophan and phenylalanine will aggravate pancreatic damage leading to glucose metabolism disorders, providing new evidence for the occurrence and development of T2D.

UPLC-Q-TOF/MS based serum and urine metabolomics strategy to analyze the mechanism of nervonic acid in treating Alzheimer's disease

Nervonic acid is a natural component of breast milk and is frequently used as a food additive due to its excellent neuroprotective effects. Although it has been reported that nervonic acid may play a role in the recovery of human cognitive impairment, its specific mechanism of action is still unclear. In this study, the results of serum biochemical indexes showed that nervonic acid improved inflammation and reduced amyloid β peptide (Aβ) deposition and tau protein phosphorylation in Alzheimer's disease (AD) rats. Subsequently, we further used a metabolomics approach to investigate the potential mechanism of action of nervonic acid in the treatment of AD. The results of serum and urine metabolomics study showed that the intervention of nervonic acid significantly reversed the metabolic profile disorder in AD rats. A total of 52 metabolites were identified. They mainly involved linoleic acid metabolism, alpha-linolenic acid metabolism, phenylalanine metabolism and arachidonic acid metabolism, and all these metabolic pathways were associated with the emergence of inflammation in vivo. It suggests that the therapeutic effect of nervonic acid on AD is likely to be produced by ameliorating inflammation. The results obtained in this study provide new insights into the mechanism of nervonic acid treatment of AD and lay a foundation for the clinical application of nervonic acid in the treatment of Alzheimer's disease.

Arachidonic acid alleviates autoimmune diabetes in NOD mice

BACKGROUND

Arachidonic acid (AA) is considered to link nutrient metabolism, to inflammation and immunity, suggesting it may have a role in autoimmune diseases. Our previous study suggests that DPP-4 inhibitors (DPP-4i) might regulate AA - relative signaling in type 1 diabetes.

AIMS

To examine the effect of AA on autoimmune diabetes and its cross-talk with DPP-4i in The Non-Obese Diabetic (NOD) mice.

METHODS

The NOD mice were divided randomly and equally into three groups: AA group, AA plus DPP-4i group and control group. The incidence of diabetes, blood glucose, insulitis and cytokine profiles were monitored. At the end of the experiment, pancreatic tissues were stained by H&E. Serum cytokine profiles were examined using a Mesco Scale Discovery multiplexed-assay kit.

RESULTS

Even though AA or AA plus DPP-4i treatment has no effect on incidence of diabetes and weight, AA treatment reduces blood glucose, preserves islet morphology and alleviates inflammatory cell infiltration into pancreatic islets in NOD mice, accompanying with increased serum levels of IL-10, IL-1 β, IL-6, IL-5, KC/GRO and TNF-α and decreased serum levels of IL-2.

CONCLUSION

We observed that AA treatment alleviates autoimmune diabetes in NOD mice by reducing hyperglycemia, alleviating insulitis and improving cytokine profiles. DPP-4i might alleviate the effect of AA by cross-talk. We provide evidence of AA treatment to alleviate type 1 diabetes in NOD mice, which may provide a novel therapeutic option for type 1 diabetes.

Mitigation of chronic glucotoxicity-mediated skeletal muscle atrophy by arachidonic acid

Toxicity caused by chronic hyperglycemia is a significant factor affecting skeletal muscle myogenesis, resulting in diabetic myopathy. Chronic and persistent hyperglycemia causes activation of the atrophy-related pathways in the skeletal muscles, which eventually results in inflammation and muscle degeneration. To counteract this process, various bioactive compound has been studied for their reversal or hypertrophic effect. In this study, we explored the molecular mechanisms associated with reversing glucotoxicity's effect in C2C12 cells by arachidonic acid (AA). We found a substantial increase in the pro-inflammatory cytokines and ROS production in hyperglycemic conditions, mitigated by AA supplementation. We found that AA supplementation restored protein synthesis that was downregulated under glucotoxicity conditions. AA enhanced myogenesis by suppressing high glucose induced inflammation and ROS production and enhancing protein synthesis. These results imply that AA has cytoprotective actions against hyperglycemia-induced cytotoxicity.

A review on the relationship between Arachidonic acid 15-Lipoxygenase (ALOX15) and diabetes mellitus

Arachidonic acid 15-lipoxygenase (ALOX15), as one of the lipoxygenase family, is mainly responsible for catalyzing the oxidation of various fatty acids to produce a variety of lipid components, contributing to the pathophysiological processes of various immune and inflammatory diseases. Studies have shown that ALOX15 and its related products are widely distributed in human tissues and related to multiple diseases such as liver, cardiovascular, cerebrovascular diseases, diabetes mellitus and other diseases. Diabetes mellitus (DM), the disease studied in this article, is a metabolic disease characterized by a chronic increase in blood glucose levels, which is significantly related to inflammation, oxidative stress, ferroptosis and other mechanisms, and it has a high incidence in the population, accompanied by a variety of complications. Figuring out how ALOX15 is involved in DM is critical to understanding its role in diseases. Therefore, ALOX15 inhibitors or combination therapy containing inhibitors may deliver a novel research direction for the treatment of DM and its complications. This article aims to review the biological effect and the possible function of ALOX15 in the pathogenesis of DM.

Integrated metabolomics and transcriptomics reveal the neuroprotective effect of nervonic acid on LPS-induced AD model mice

Nervonic acid (NA) is one of the long-chain fatty acids with significant biological activity that has been widely studied in recent years. It is believed that NA may play a crucial role in the recovery of human cognitive disorders. Although many literatures have shown that NA has some neuroprotective effect in experimental animal models, the detailed neuroprotective mechanism of NA is still poorly understood. In this study, we applied behavioral, transcriptomic and metabolomic approaches to analyze the neuroprotective effect of NA and its molecular mechanism in AD (Alzheimer's disease) model mice. We demonstrated that NA improved motor skills and learning and memory abilities of mice at the behavioral level. To further understand the specific pathways involved in this protective effect, we applied the metabolomics and transcriptomics profilings and focused on the expression patterns of genes that NA might alter, particularly those related to the accumulation of metabolites in the brain. According to the results, pathways related to neuroinflammation were significantly increased in LPS (lipopolysaccharide)-induced AD mice compared with the normal control, and pathways related to neuronal growth and synaptic plasticity were significantly downregulated. When NA was used for protection, these signaling pathways induced by LPS were partially reversed. At the same time, compared with the AD model group, upregulation of arachidonic acid metabolism, purine metabolism, and primary bile acid biosynthesis and downregulation of amino acid metabolic pathways were particularly pronounced in the NA treatment group. We also verified the enzymes of some metabolic pathways were consistent with transcriptome result. In summary, our results show that NA can significantly ameliorate LPS-induced neuroinflammation and deterioration of learning and memory, and exerts a neuroprotective function through regulation of multiple gene transcription and metabolism pathways. In particular, the arachidonic acid metabolism which related to inflammation and the amino acids metabolism which related to the synthesis of neurotransmitters were most significant response to NA treatment. Our results provided the first preliminary evidences for molecular mechanism investigation of NA from a combined transcriptome and metabolome perspective.

Transcriptomic and metabolomic analyses provide insights into the attenuation of neuroinflammation by nervonic acid in MPTP-stimulated PD model mice

Nervonic acid is one of the most promising bioactive fatty acids, which is believed to be beneficial for the recovery of human cognitive disorders. However, the detailed neuroprotective effects and mode of action of nervonic acid have not yet been fully elucidated. In this study, we used an MPTP-stimulated mouse Parkinson's disease (PD) model as a target to investigate the neuroprotective effects by behavioral tests and integrative analysis of trancriptomes and metabolomes of PD mouse brain with nervonic acid injections. The KEGG pathway enrichment analysis of transcriptomes showed that the genes involved in neuroinflammation were significantly increased after MPTP induction and have been greatly inhibited by nervonic acid injection, while nervonic acid also greatly improved nerve growth and synaptic plasticity pathways which were significantly downregulated by MPTP. At the same time, the upregulation of oleic acid and arachidonic acid metabolism pathways and the downregulation of amino acid metabolism pathways in metabolomes were particularly highlighted in the nervonic acid protection groups compared with the PD model. Meanwhile, it was found that arachidonic acid, oleic acid and taurine play an important regulatory role in the neuroprotective mechanism of nervonic acid through fatty acid metabolism by integrative analysis. Therefore, our study laid a solid foundation for further studies on the specific role of nervonic acid in the inhibition of PD at the level of metabolic regulation.

Syntaxin interacts with arachidonic acid to prevent diabetes mellitus

Syntaxin regulates pancreatic β cell mass and participates in insulin secretion by regulating insulin exocytosis. In addition, syntaxin 4 reduces IFNγ and TNF-α signaling via NF-ĸB in islet β-cells that facilitates plasma glucose sensing and appropriate insulin secretion. Arachidonic acid (AA) has potent anti-inflammatory actions and prevents the cytotoxic actions of alloxan and streptozotocin (STZ) against pancreatic β cells and thus, prevents the development of type 1 diabetes mellitus (induced by alloxan and STZ) and by virtue of its anti-inflammatory actions protects against the development of type 2 diabetes mellitus (DM) induced by STZ in experimental animals that are models of type 1 and type 2 DM in humans. AA has been shown to interact with syntaxin and thus, potentiate exocytosis. AA enhances cell membrane fluidity, increases the expression of GLUT and insulin receptors, and brings about its anti-inflammatory actions at least in part by enhancing the formation of its metabolite lipoxin A4 (LXA4). Prostaglandin E2 (PGE2), the pro-inflammatory metabolite of AA, activates ventromedial hypothalamus (VMH) neurons of the hypothalamus and inhibits insulin secretion leading to reduced glucose tolerance and decreases insulin sensitivity in the skeletal muscle and liver. This adverse action of PGE2 on insulin release and action can be attributed to its (PGE2) pro-inflammatory action and inhibitory action on vagal tone (vagus nerve and its principal neurotransmitter acetylcholine has potent anti-inflammatory actions). High fat diet fed animals have hypothalamic inflammation due to chronic elevation of PGE2. Patients with type 2 DM show low plasma concentrations of AA and LXA4 and elevated levels of PGE2. Administration of AA enhances LXA4 formation without altering or reducing PGE2 levels and thus, tilts the balance more towards anti-inflammatory events. These results suggest that administration of AA is useful in the prevention and management of DM by enhancing the action of syntaxin, increasing cell membrane fluidity, and reducing VMH inflammation. Docosahexaenoic acid (DHA) has actions like AA: it increases cell membrane fluidity; has anti-inflammatory actions by enhancing the formation of its anti-inflammatory metabolites resolvins, protectins and maresins; interacts with syntaxin and enhance exocytosis in general and of insulin. But the DHA content of cell membrane is lower compared to AA and its content in brain is significant. Hence, it is likely DHA is important in neurotransmitters secretion and regulating hypothalamic inflammation. It is likely that a combination of AA and DHA can prevent DM.

Extracellular vesicles-incorporated microRNA signature as biomarker and diagnosis of prediabetes state and its complications

Extracellular vesicles (EVs) are small anuclear vesicles, delimited by a lipid bilayer, released by almost all cell types, carrying functionally active biological molecules that can be transferred to the neighbouring or distant cells, inducing phenotypical and functional changes, relevant in various physio-pathological conditions. The microRNAs are the most significant active components transported by EVs, with crucial role in intercellular communication and significant effects on recipient cells. They may also server as novel valuable biomarkers for the diagnosis of metabolic disorders. Moreover, EVs are supposed to mediate type 2 diabetes mellitus (T2DM) risk and its progress. The T2DM development is preceded by prediabetes, a state that is associated with early forms of nephropathy and neuropathy, chronic kidney disease, diabetic retinopathy, and increased risk of macrovascular disease. Although the interest of scientists was focused not only on the pathogenesis of diabetes, but also on the early diagnosis, little is known about EVs-incorporated microRNA involvement in prediabetes state and its microvascular and macrovascular complications. Here, we survey the biogenesis, classification, content, biological functions and the most popular primary isolation methods of EVs, review the EVs-associated microRNA profiling connexion with early stages of diabetes and discuss the role of EVs containing specific microRNAs in prediabetes complications.

Effects of Arachidonic Acid and Its Metabolites on Functional Beta-Cell Mass

Arachidonic acid (AA) is a polyunsaturated 20-carbon fatty acid present in phospholipids in the plasma membrane. The three primary pathways by which AA is metabolized are mediated by cyclooxygenase (COX) enzymes, lipoxygenase (LOX) enzymes, and cytochrome P450 (CYP) enzymes. These three pathways produce eicosanoids, lipid signaling molecules that play roles in biological processes such as inflammation, pain, and immune function. Eicosanoids have been demonstrated to play a role in inflammatory, renal, and cardiovascular diseases as well type 1 and type 2 diabetes. Alterations in AA release or AA concentrations have been shown to affect insulin secretion from the pancreatic beta cell, leading to interest in the role of AA and its metabolites in the regulation of beta-cell function and maintenance of beta-cell mass. In this review, we discuss the metabolism of AA by COX, LOX, and CYP, the roles of these enzymes and their metabolites in beta-cell mass and function, and the possibility of targeting these pathways as novel therapies for treating diabetes.

Essential Fatty Acids and Their Metabolites in the Pathobiology of Inflammation and Its Resolution

Arachidonic acid (AA) metabolism is critical in the initiation and resolution of inflammation. Prostaglandin E2 (PGE2) and leukotriene B4/D4/E4 (LTB4/LD4/LTE4), derived from AA, are involved in the initiation of inflammation and regulation of immune response, hematopoiesis, and M1 (pro-inflammatory) macrophage facilitation. Paradoxically, PGE2 suppresses interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) production and triggers the production of lipoxin A4 (LXA4) from AA to initiate inflammation resolution process and augment regeneration of tissues. LXA4 suppresses PGE2 and LTs' synthesis and action and facilitates M2 macrophage generation to resolve inflammation. AA inactivates enveloped viruses including SARS-CoV-2. Macrophages, NK cells, T cells, and other immunocytes release AA and other bioactive lipids to produce their anti-microbial actions. AA, PGE2, and LXA4 have cytoprotective actions, regulate nitric oxide generation, and are critical to maintain cell shape and control cell motility and phagocytosis, and inflammation, immunity, and anti-microbial actions. Hence, it is proposed that AA plays a crucial role in the pathobiology of ischemia/reperfusion injury, sepsis, COVID-19, and other critical illnesses, implying that its (AA) administration may be of significant benefit in the prevention and amelioration of these diseases.

Lipotoxicity and β-Cell Failure in Type 2 Diabetes: Oxidative Stress Linked to NADPH Oxidase and ER Stress

A high caloric intake, rich in saturated fats, greatly contributes to the development of obesity, which is the leading risk factor for type 2 diabetes (T2D). A persistent caloric surplus increases plasma levels of fatty acids (FAs), especially saturated ones, which were shown to negatively impact pancreatic β-cell function and survival in a process called lipotoxicity. Lipotoxicity in β-cells activates different stress pathways, culminating in β-cells dysfunction and death. Among all stresses, endoplasmic reticulum (ER) stress and oxidative stress have been shown to be strongly correlated. One main source of oxidative stress in pancreatic β-cells appears to be the reactive oxygen species producer NADPH oxidase (NOX) enzyme, which has a role in the glucose-stimulated insulin secretion and in the β-cell demise during both T1 and T2D. In this review, we focus on the acute and chronic effects of FAs and the lipotoxicity-induced β-cell failure during T2D development, with special emphasis on the oxidative stress induced by NOX, the ER stress, and the crosstalk between NOX and ER stress.

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.

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.

Exercise-induced recovery of plasma lipids perturbed by ageing with nanoflow UHPLC-ESI-MS/MS

Daily physical exercise is an essential part of life and is required for remaining healthy; it enhances therapeutic efficacy in the elderly and prevents age-related diseases associated with lipid profile alterations, such as cardiovascular disease, diabetes mellitus, and dementia. To more efficiently analyse the lipid profiles and unveil the effect of exercise in aged mice, we optimized our study by examining the effects of using ionization modifiers in the mobile phase and in-source fragmentation of lysophospholipids on the simultaneous analysis of fatty acids (FAs) including hydroxyl fatty acids, glycerophospholipids, sphingolipids, and glycerolipids using nanoflow ultrahigh performance liquid chromatography-electrospray ionization-tandem mass spectrometry. We applied the optimization to investigate the lipidomic plasma alterations in young (7 weeks old) and aged (84 weeks old) mice (C57BL/6) subjected to treadmill exercise. Of the 390 identified lipid species, 159 were quantified to investigate ageing-related lipid species responsive to physical exercise. In particular, circulating lysophosphatidylcholine and lysophosphatidylethanolamine levels showed a significant decrease, and lysophosphatidic acid showed a simultaneous increase with ageing. The saturated FA (16:0 and 18:0) increased with ageing while the unsaturated FA 22:6 decreased. Dihydroxy fatty acid (18:1_2OH) showed an exercise-induced recovery against ageing. It is notable that the levels of five triacylglycerol species significantly increased by as much as threefold with ageing, but their levels largely recovered to those observed in the young mice after exercise. These findings can help understand the influence of ageing on lipid perturbation and the role of physical exercise on lipidomic recovery in response to ageing-associated loss of physical status. Graphical abstract.

C2C12 cell model: its role in understanding of insulin resistance at the molecular level and pharmaceutical development at the preclinical stage

OBJECTIVES

The myoblast cell line, C2C12, has been utilised extensively in vitro as an examination model in understanding metabolic disease progression. Although it is indispensable in both preclinical and pharmaceutical research, a comprehensive review of its use in the investigation of insulin resistance progression and pharmaceutical development is not available.

KEY FINDINGS

C2C12 is a well-documented model, which can facilitate our understanding in glucose metabolism, insulin signalling mechanism, insulin resistance, oxidative stress, reactive oxygen species and glucose transporters at cellular and molecular levels. With the aid of the C2C12 model, recent studies revealed that insulin resistance has close relationship with various metabolic diseases in terms of disease progression, pathogenesis and therapeutic management. A holistic, safe and effective disease management is highly of interest. Therefore, significant efforts have been paid to explore novel drug compounds and natural herbs that can elicit therapeutic effects in the targeted sites at both cellular (e.g. mitochondria, glucose transporter) and molecular level (e.g. genes, signalling pathway).

SUMMARY

The use of C2C12 myoblast cell line is meaningful in pharmaceutical and biomedical research due to their expression of GLUT-4 and other features that are representative to human skeletal muscle cells. With the use of the C2C12 cell model, the impact of drug delivery systems (nanoparticles and quantum dots) on skeletal muscle, as well as the relationship between exercise, pancreatic β-cells and endothelial cells, was discovered.

MiRNAs profile as biomarkers of nutritional therapy for the prevention of type 2 diabetes mellitus: From the CORDIOPREV study

BACKGROUND AND AIM

The incidence of type 2 diabetes mellitus (T2DM) has increased worldwide. One of the first actions to reduce the risk of this disease is to implement healthy dietary models; however, no universal dietary strategies have so far been established. In addition, MicroRNAs (miRNAs) are emerging as new biomarkers to predict disease. We aimed to study whether miRNAs could be used to select the nutritional therapy to prevent T2DM development in patients with cardiovascular disease.

METHODS

All patients from the CORDIOPREV study without T2DM at baseline according to the American Diabetes Association (ADA) diagnostic criteria (n = 462) were included in the present study. Of them, after a median dietary intervention period of 60 months with two diets (Low fat or Mediterranean diets), 107 developed T2DM and 355 subjects did not develop the disease. The plasma levels of 24 miRNAs were measured at baseline by qRT-PCR. The risk of T2DM was evaluated by Cox regression analysis based on the plasma levels of the miRNAs at baseline and according to the dietary intervention. Finally, pathways analyses were carried out to identify target genes regulated by the miRNAs studied and cellular processes which could be associated with T2DM development.

RESULTS

Cox regression analyses showed that patients with low plasma levels of miR-145 at baseline showed a higher risk of developing T2DM after consumption of an LFHCC diet. In addition, patients with low levels of miR-29a, miR-28-3p and miR-126 and high plasma levels of miR-150 at baseline showed a higher risk of developing T2DM after consumption of the Med diet. Finally, pathways analysis showed an interaction of miR-126 and miR-29a in the modulation of FoxO, TNF-α, PI3K-AKT, p53 and mTOR signaling, associated with T2DM development.

CONCLUSION

Our results suggest that circulating miRNAs could be used in clinical practice as a new tool for selecting the most suitable diet to prevent type 2 diabetes mellitus development in patients with cardiovascular disease.

CLINICAL TRIALS NUMBER

NCT00924937.

Indomethacin decreases insulin secretion by reducing KCa3.1 as a biomarker of pancreatic tumor and causes apoptotic cell death

Insulinomas originate from pancreatic β cells and it is the most widely known tumor. Indomethacin is a nonsteroidal anti-inflammatory drug, which is used for blocking the production of some natural substances that cause inflammation and decrease pain. In this study, I aimed to investigate the effects of indomethacin on rat insulinoma INS-1 cells. The relationship between cell death and insulin metabolism was determined with the administration of indomethacin. The cell viability by WST-1; the apoptosis and necrosis levels by ELISA kits; malondialdehyde levels by spectrophotometer; and beclin, intracellular insulin, insulin secretion, KCa3.1, insulin receptor (IR), glucose transporter type 2 (GLUT2), activating transcription factor 2 (ATF2), Elk1, c-Jun, Akt and phosphorylated ATF2, Elk1, c-Jun, Akt, intracellular betacellulin and betacellulin secretion levels by Western blot analysis investigated. The Ins1, Ins2, IR, GLUT2, ATF2, Elk1, c-Jun, Akt, and Betacellulin gene expression levels were determined by the real-time quantitative reverse transcription-polymerase chain reaction method. Apoptotic cell death was observed with the administration of indomethacin. The insulin secretion and Ins1, Ins2 gene expression levels decreased. The insulin receptor and GLUT2 levels increased, while KCa3.1 (KCNN4) levels decreased with the administration of indomethacin to insulinoma INS-1 cells. A decrease was observed in the total c-Jun, phosphorylated ATF2, Elk1, c-Jun, and Akt levels. Betacellulin secretion levels increased. In insulinoma INS-1 cells, apoptotic cell death occurred in the following manner: (i) indomethacin might decrease insulin secretion by reducing KCa3.1, (ii) might inactivate the JNK/ERK pathway with the inactivity of transcription factors.

The role of Cox-2 and prostaglandin E2 receptor EP3 in pancreatic β-cell death

Elevated levels of lipids, in particular saturated fatty acids, are known to be associated with type 2 diabetes (T2D) and to have a negative effect on β-cell function and survival. We bring new evidence indicating that palmitate up-regulates cyclooxygenase-2 (COX-2) expression levels in human islets and in MIN6 β cells, and that it is elevated in islets isolated from T2D donors. Both small interfering specific cyclooxygenase-2 small interfering RNA (siRNA) or the COX-2 inhibitor celecoxib significantly inhibited apoptosis induced by palmitate. Prostaglandin E₂ (PGE₂), the predominant product of COX-2 enzymatic activity, activates membrane receptors, which are members of the GPCR-family (EP1-EP4). In the present study, elevated expression of the PGE₂ receptor subtype 3 (EP3) receptor was observed in β cells exposed to palmitate and in islets from individuals with T2D. Down-regulation of the pathway using EP3 siRNA or the specific L-798,106 antagonist markedly decreased the levels of palmitate-induced apoptosis. Altogether, our data put forward the COX-2-PGE₂-EP3 pathway as one of the mediators of palmitate-induced apoptosis in β-cells.-Amior, L., Srivastava, R., Nano, R., Bertuzzi, F., Melloul, D. The role of Cox-2 and prostaglandin E₂ receptor EP3 in pancreatic β-cell death.

Fatty Acid-Stimulated Insulin Secretion vs. Lipotoxicity

Fatty acid (FA)-stimulated insulin secretion (FASIS) is reviewed here in contrast to type 2 diabetes etiology, resulting from FA overload, oxidative stress, intermediate hyperinsulinemia, and inflammation, all converging into insulin resistance. Focusing on pancreatic islet β-cells, we compare the physiological FA roles with the pathological ones. Considering FAs not as mere amplifiers of glucose-stimulated insulin secretion (GSIS), but as parallel insulin granule exocytosis inductors, partly independent of the K_ATP channel closure, we describe the FA initiating roles in the prediabetic state that is induced by retardations in the glycerol-3-phosphate (glucose)-promoted glycerol/FA cycle and by the impaired GPR40/FFA1 (free FA1) receptor pathway, specifically in its amplification by the redox-activated mitochondrial phospholipase, iPLA2γ. Also, excessive dietary FAs stimulate intestine enterocyte incretin secretion, further elevating GSIS, even at low glucose levels, thus contributing to diabetic hyperinsulinemia. With overnutrition and obesity, the FA overload causes impaired GSIS by metabolic dysbalance, paralleled by oxidative and metabolic stress, endoplasmic reticulum stress and numerous pro-apoptotic signaling, all leading to decreased β-cell survival. Lipotoxicity is exerted by saturated FAs, whereas ω-3 polyunsaturated FAs frequently exert antilipotoxic effects. FA-facilitated inflammation upon the recruitment of excess M1 macrophages into islets (over resolving M2 type), amplified by cytokine and chemokine secretion by β-cells, leads to an inevitable failure of pancreatic β-cells.

Association of APOB and LIPC polymorphisms with type 2 diabetes in Chinese Han population

BACKGROUND

Apolipoprotein B (APOB), and hepatic lipase (LIPC) genes have been shown to play a key role in lipid metabolism in type 2 diabetes (T2D). This study aimed to investigate the association of the three polymorphisms (rs679899 in APOB and rs6078 and rs6083 in LIPC) with T2D and related clinical quantitative traits.

METHODS

We conducted a case-control study in Chinese Han population, with a total of 929 T2D patients and 1044 healthy subjects in Chinese Han population. Polymorphisms were genotyped by MassARRAY Genotyping System.

RESULTS

The risk allele G of the polymorphism rs679899 was related to T2D (odds ratio (OR): 1.207, 95% confidence interval (CL): 1.006-1.448, P = 0.043) and the polymorphism rs679899 was associated with glutamyl transpeptidase (GGT) levels (P = 0.001). We also showed that the polymorphism rs6083 was associated with cholesterol (CHOL) levels (P = 0.012), triglyceride (TG) levels (P = 0.040), and low-density lipoprotein cholesterol (LDL) levels (P = 0.033). No significant difference in genotypic frequencies of rs6078 and rs6083 was observed between T2D patients and controls.

CONCLUSION

This study suggests that the APOB polymorphism rs679899 is associated with type 2 diabetes and GGT levels, while the LIPC polymorphism rs6083 may influence CHOL, TG, and LDL levels in Chinese Han population.

Fatty Acid-Induced Lipotoxicity in Pancreatic Beta-Cells During Development of Type 2 Diabetes

Type 2 diabetes is caused by chronic insulin resistance and progressive decline in beta-cell function. Optimal beta-cell function and mass is essential for glucose homeostasis and beta-cell impairment leads to the development of diabetes. Elevated levels of circulating fatty acids (FAs) and disturbances in lipid metabolism regulation are associated with obesity, and they are major factors influencing the increase in the incidence of type 2 diabetes. Chronic free FA (FFA) treatment induces insulin resistance and beta-cell dysfunction; therefore, reduction of elevated plasma FFA levels might be an important therapeutic target in obesity and type 2 diabetes. Lipid signals via receptors, and intracellular mechanisms are involved in FFA-induced apoptosis. In this paper, we discuss lipid actions in beta cells, including effects on metabolic pathways and stress responses, to help further understand the molecular mechanisms of lipotoxicity-induced type 2 diabetes.

Long-chain polyunsaturated fatty acids amend palmitate-induced inflammation and insulin resistance in mouse C2C12 myotubes

Intramuscular lipid accumulation results in inflammation, which is correlated with impaired insulin action in the skeletal muscle, an important organ for glucose uptake in the body. In this study, we explored the effects of docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), arachidonic acid (AA), and long-chain polyunsaturated fatty acids (PUFAs) on palmitic acid (PA)-induced inflammatory responses and insulin resistance in C2C12 myotubes. The mRNA expression of the pro-inflammatory cytokines interleukin-6 and tumor necrosis factor-α in PA-treated myotubes was suppressed by these three test long-chain PUFAs. Moreover, the addition of long-chain PUFAs decreased PA-induced insulin resistance as evidenced by increases in phosphorylated AKT and glucose uptake. In PA-treated myotubes, long-chain PUFAs improved glucose transporter 4 expression, basal glucose uptake without insulin, and the AMP-activated protein kinase pathway. Of note, the long-chain PUFAs obstructed the effects of PA on the activation of extracellular-signal-regulated kinase and protein kinase C-θ as well as nuclear factor-κB (NF-κB) and activator protein-1. The inhibitory effect of AA but not of DHA and EPA on PA-induced inflammation and impaired insulin action was cancelled in C2C12 myotubes transfected with a constitutively active mutant IκB kinase-β plasmid. These data suggest that long-chain PUFAs may be useful in the management of PA-induced inflammation and insulin resistance in myotubes. In addition to the NF-κB pathway, other mechanisms are involved in the health benefits of DHA and EPA in PA-treated myotubes.

Cytosolic and Calcium-Independent Phospholipases A2 Activation and Prostaglandins E2 Are Associated with Escherichia coli-Induced Reduction of Insulin Secretion in INS-1E Cells

It is suspected that microbial infections take part in the pathogenesis of diabetes mellitus type 1 (T1DM). Glucose-induced insulin secretion is accompanied by the release of free arachidonic acid (AA) mainly by cytosolic- and calcium independent phospholipases A₂ (cPLA₂ and iPLA₂). Insulinoma cell line (INS-1E) was infected with E. coli isolated from the blood culture of a patient with sepsis. Invasion assay, Scanning Electron Microscopy and Transmission Electron Microscopy demonstrated the capacity of E. coli to enter cells, which was reduced by PLA₂ inhibitors. Glucose-induced insulin secretion was significantly increased after acute infection (8h) but significantly decreased after chronic infection (72h). PLA₂ activities, cPLA₂, iPLA₂, phospho-cPLA₂, and COX-2 expressions were increased after acute and, even more, after chronic E. coli infection. The silencing of the two isoforms of PLA₂s, with specific cPLA₂- or iPLA₂-siRNAs, reduced insulin secretion after acute infection and determined a rise in insulin release after chronic infection. Prostaglandins E₂ (PGE₂) production was significantly elevated in INS-1E after long-term E. coli infection and the restored insulin secretion in presence of L798106, a specific EP3 antagonist, and NS-398, a COX-2 inhibitor, and the reduction of insulin secretion in presence of sulprostone, a specific EP3 agonist, revealed their involvement in the effects triggered by bacterial infection. The results obtained demonstrated that cPLA₂ and iPLA₂ play a key role in insulin secretion process after E. coli infection. The high concentration of AA released is transformed into PGE₂, which could be responsible for the reduced insulin secretion.

Pigment epithelium-derived factor (PEDF) regulates metabolism and insulin secretion from a clonal rat pancreatic beta cell line BRIN-BD11 and mouse islets

Pigment epithelium-derived factor (PEDF) is a multifunctional glycoprotein, associated with lipid catabolism and insulin resistance. In the present study, PEDF increased chronic and acute insulin secretion in a clonal rat β-cell line BRIN-BD11, without alteration of glucose consumption. PEDF also stimulated insulin secretion from primary mouse islets. Seahorse flux analysis demonstrated that PEDF did not change mitochondrial respiration and glycolytic function. The cytosolic presence of the putative PEDF receptor - adipose triglyceride lipase (ATGL) - was identified, and ATGL associated stimulation of glycerol release was robustly enhanced by PEDF, while intracellular ATP levels increased. Addition of palmitate or ex vivo stimulation with inflammatory mediators induced β-cell dysfunction, effects not altered by the addition of PEDF. In conclusion, PEDF increased insulin secretion in BRIN-BD11 and islet cells, but had no impact on glucose metabolism. Thus elevated lipolysis and enhanced fatty acid availability may impact insulin secretion following PEDF receptor (ATGL) stimulation.

Role of cytosolic and calcium independent phospholipases A(2) in insulin secretion impairment of INS-1E cells infected by S. aureus

Cytosolic PLA2 (cPLA2) and Ca(2+)-independent PLA2 (iPLA2) play a significant role in insulin β-cells secretion. Bacterial infections may be responsible of the onset of diabetes. The mechanism by which Staphylococcus aureus infection of INS-1 cells alters glucose-induced insulin secretion has been examined. After acute infection, insulin secretion and PLA2 activities significantly increased. Moreover, increased expressions of phospho-cPLA2, phospho-PKCα and phospho-ERK 1/2 were observed. Chronic infection causes a decrease in insulin release and a significant increase of iPLA2 and COX-2 protein expression. Moreover, insulin secretion in infected cells could be restored using specific siRNAs against iPLA2 isoform and specific COX-2 inhibitor.

Cystine accumulation attenuates insulin release from the pancreatic β-cell due to elevated oxidative stress and decreased ATP levels

The pancreatic β-cell has reduced antioxidant defences making it more susceptible to oxidative stress. In cystinosis, a lysosomal storage disorder, an altered redox state may contribute to cellular dysfunction. This rare disease is caused by an abnormal lysosomal cystine transporter, cystinosin, which causes excessive accumulation of cystine in the lysosome. Cystinosis associated kidney damage and dysfunction leads to the Fanconi syndrome and ultimately end-stage renal disease. Following kidney transplant, cystine accumulation in other organs including the pancreas leads to multi-organ dysfunction. In this study, a Ctns gene knockdown model of cystinosis was developed in the BRIN-BD11 rat clonal pancreatic β-cell line using Ctns-targeting siRNA. Additionally there was reduced cystinosin expression, while cell cystine levels were similarly elevated to the cystinotic state. Decreased levels of chronic (24 h) and acute (20 min) nutrient-stimulated insulin secretion were observed. This decrease may be due to depressed ATP generation particularly from glycolysis. Increased ATP production and the ATP/ADP ratio are essential for insulin secretion. Oxidised glutathione levels were augmented, resulting in a lower [glutathione/oxidised glutathione] redox potential. Additionally, the mitochondrial membrane potential was reduced, apoptosis levels were elevated, as were markers of oxidative stress, including reactive oxygen species, superoxide and hydrogen peroxide. Furthermore, the basal and activated phosphorylated forms of the redox-sensitive transcription factor NF-κB were increased in cells with silenced Ctns. From this study, the cystinotic-like pancreatic β-cell model demonstrated that the altered oxidative status of the cell, resulted in depressed mitochondrial function and pathways of ATP production, causing reduced nutrient-stimulated insulin secretion.

Islet β-cell failure in type 2 diabetes--Within the network of toxic lipids

Obesity-related type 2 diabetes develops in individuals with the onset of β-cell dysfunction. Pancreatic islet lipotoxicity is now recognized as a primary reason for the onset and progression of the disease. Such dysfunction is reflected by the aberrant secretory capacity and detrimental loss of β-cell mass and survival. Elevated circulating serum fatty acid levels and disordered lipid metabolism management are particularly interesting in the search for biologically relevant triggers of β-cell demise. Herein, we review various types of toxic lipid metabolites that may play a significant role in pancreatic islet failure. The lipotoxic effect on β-cells depends on the type of lipid mediator (e.g., long-chain fatty acids, diacylglycerols, ceramides, phospholipids), cellular location of its action (e.g., endoplasmic reticulum, mitochondria), and associated-organelle conditions (e.g., membranes, vesicles). We also discuss various aspects of lipid action in β-cells, including effects on metabolic pathways, stress responses (e.g., oxidative stress, endoplasmic reticulum stress, and autophagy), and gene expression.

Nutrient regulation of insulin secretion and action

Pancreatic β-cell function is of critical importance in the regulation of fuel homoeostasis, and metabolic dysregulation is a hallmark of diabetes mellitus (DM). The β-cell is an intricately designed cell type that couples metabolism of dietary sources of carbohydrates, amino acids and lipids to insulin secretory mechanisms, such that insulin release occurs at appropriate times to ensure efficient nutrient uptake and storage by target tissues. However, chronic exposure to high nutrient concentrations results in altered metabolism that impacts negatively on insulin exocytosis, insulin action and may ultimately lead to development of DM. Reduced action of insulin in target tissues is associated with impairment of insulin signalling and contributes to insulin resistance (IR), a condition often associated with obesity and a major risk factor for DM. The altered metabolism of nutrients by insulin-sensitive target tissues (muscle, adipose tissue and liver) can result in high circulating levels of glucose and various lipids, which further impact on pancreatic β-cell function, IR and progression of the metabolic syndrome. Here, we have considered the role played by the major nutrient groups, carbohydrates, amino acids and lipids, in mediating β-cell insulin secretion, while also exploring the interplay between amino acids and insulin action in muscle. We also focus on the effects of altered lipid metabolism in adipose tissue and liver resulting from activation of inflammatory processes commonly observed in DM pathophysiology. The aim of this review is to describe commonalities and differences in metabolism related to insulin secretion and action, pertinent to the development of DM.

Group VIA phospholipase A2 mitigates palmitate-induced β-cell mitochondrial injury and apoptosis

Palmitate (C16:0) induces apoptosis of insulin-secreting β-cells by processes that involve generation of reactive oxygen species, and chronically elevated blood long chain free fatty acid levels are thought to contribute to β-cell lipotoxicity and the development of diabetes mellitus. Group VIA phospholipase A2 (iPLA2β) affects β-cell sensitivity to apoptosis, and here we examined iPLA2β effects on events that occur in β-cells incubated with C16:0. Such events in INS-1 insulinoma cells were found to include activation of caspase-3, expression of stress response genes (C/EBP homologous protein and activating transcription factor 4), accumulation of ceramide, loss of mitochondrial membrane potential, and apoptosis. All of these responses were blunted in INS-1 cells that overexpress iPLA2β, which has been proposed to facilitate repair of oxidized mitochondrial phospholipids, e.g. cardiolipin (CL), by excising oxidized polyunsaturated fatty acid residues, e.g. linoleate (C18:2), to yield lysophospholipids, e.g. monolysocardiolipin (MLCL), that can be reacylated to regenerate the native phospholipid structures. Here the MLCL content of mouse pancreatic islets was found to rise with increasing iPLA2β expression, and recombinant iPLA2β hydrolyzed CL to MLCL and released oxygenated C18:2 residues from oxidized CL in preference to native C18:2. C16:0 induced accumulation of oxidized CL species and of the oxidized phospholipid (C18:0/hydroxyeicosatetraenoic acid)-glycerophosphoethanolamine, and these effects were blunted in INS-1 cells that overexpress iPLA2β, consistent with iPLA2β-mediated removal of oxidized phospholipids. C16:0 also induced iPLA2β association with INS-1 cell mitochondria, consistent with a role in mitochondrial repair. These findings indicate that iPLA2β confers significant protection of β-cells against C16:0-induced injury.

Protection of palmitic acid-mediated lipotoxicity by arachidonic acid via channeling of palmitic acid into triglycerides in C2C12

Background

Excessive saturated fatty acids have been considered to be one of major contributing factors for the dysfunction of skeletal muscle cells as well as pancreatic beta cells, leading to the pathogenesis of type 2 diabetes.

Results

PA induced cell death in a dose dependent manner up to 1.5 mM, but AA protected substantially lipotoxicity caused by PA at even low concentration of 62 μM, at which monounsaturated fatty acids including palmitoleic acid (POA) and oleic acid (OA) did not protect as much as AA did. Induction of cell death by PA was resulted from mitochondrial membrane potential loss, and AA effectively blocked the progression of apoptosis. Furthermore, AA rescued significantly PA-impaired glucose uptake and -signal transduction of Akt in response to insulin.

Based on the observations that polyunsaturated AA generated competently cellular droplets at low concentration within the cytosol of myotubes compared with other monounsaturated fatty acids, and AA-driven lipid droplets were also enhanced in the presence of PA, we hypothesized that incorporation of harmful PA into inert triglyceride (TG) may be responsible for the protective effects of AA against PA-induced lipotoxicity. To address this assumption, C2C12 myotubes were incubated with fluorescent probed-PA analogue 4, 4-difluoro-5, 7-dimethyl-4-boro-3a,4a-diaza-s-indacene-3-hexadecanoic acid (BODIPY FL C16) in the presence of AA and their subsequent lipid profiles were analyzed. The analyses of lipids on thin layer chromatograpy (TLC) showed that fluorescent PA analogue was rapidly channeled into AA-driven TG droplets.

Conclusion

Taken together, it is proposed that AA diverts PA into inert TG, therefore reducing the availability of harmful PA into intracellular target molecules.

Metabolic regulation of insulin secretion

Regulation of metabolic fuel homeostasis is a critical function of β-cells, which are located in the islets of Langerhans of the animal pancreas. Impairment of this β-cell function is a hallmark of pancreatic β-cell failure and may lead to development of type 2 diabetes mellitus. β-Cells are essentially "fuel sensors" that monitor and react to elevated nutrient load by releasing insulin. This response involves metabolic activation and generation of metabolic coupling factors (MCFs) that relay the nutrient signal throughout the cell and induce insulin biosynthesis and secretion. Glucose is the most important insulin secretagogue as it is the primary fuel source in food. Glucose metabolism is central to generation of MCFs that lead to insulin release, most notably ATP. In addition, other classes of nutrients are able to augment insulin secretion and these include members of the lipid and amino acid family of nutrients. Therefore, it is important to investigate the interplay between glucose, lipid, and amino acid metabolism, as it is this mixed nutrient sensing that generate the MCFs required for insulin exocytosis. The mechanisms by which these nutrients are metabolized to generate MCFs, and how they impact on β-cell insulin release and function, are discussed in detail in this article.

Cognitive and motor perturbations in elderly with longstanding diabetes mellitus

Type 2 diabetes mellitus is a chronic disease characterized by insulin resistance; inflammation; oxidative stress; vascular damage; and dysfunction of glucose, protein, and lipid metabolisms. However, comparatively less attention has been paid to neurologic alterations seen in elderly individuals with type 2 diabetes. We review clinical, metabolic, and biochemical aspects of diabetic encephalopathy (DE) and propose that quality of dietary lipids is closely linked to DE. This implies that preventive nutritional interventions may be designed to improve DE.

Evidence for the involvement of GPR40 and NADPH oxidase in palmitic acid-induced superoxide production and insulin secretion

G protein coupled receptor 40 (GPR40) and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase complex have been shown to be involved in the fatty acid amplification of glucose-stimulated insulin secretion (GSIS). The effect of palmitic acid on superoxide production and insulin secretion by INS-1E cells and the possible involvement of GPR40 and NADPH oxidase in these processes were examined in this study. Cells were incubated during 1 h with palmitic acid in low and high glucose concentrations, a GPR40 agonist (GW9508) and inhibitors of NADPH oxidase (diphenyleneiodonium, DPI) and PKC (calphostin C). GW9508 induced superoxide production at 2.8 and 5.6 mM glucose concentrations and stimulated insulin secretion at 16.7 mM glucose concentration involving both PKC and NADPH oxidase activation. Palmitic acid induced superoxide production through NADPH oxidase and GPR40-dependent pathways and the stimulation of insulin secretion in the presence of a high glucose concentration was reduced by knockdown of GPR40 using siRNA. Our results suggest that palmitic acid induces superoxide production and potentiates GSIS through NADPH oxidase and GPR40 pathways in pancreatic ? cells.

G-protein-coupled receptors as fat sensors

PURPOSE OF REVIEW

It has been demonstrated that fatty acids (FAs) are physiological ligands of G-protein-coupled receptors (GPRs). Activation of the GPRs (40, 41, 43, 84, 119 and 120) by FAs or synthetic agonists modulates several responses. In this review, we discuss the current knowledge on the actions of FA-activated GPRs and their relevance in normal and pathological conditions.

RECENT FINDINGS

Studies have shown that FA-activated GPRs modulate hormone secretion (incretin, insulin and glucagon), activation of leukocytes and several aspects of metabolism.

SUMMARY

Understanding GPR actions and their involvement in the development of insulin-resistance, β-cell failure, dyslipidemia and inflammation associated with obesity, type 2 diabetes, metabolic syndrome and cardiovascular diseases is important for the comprehension of the mechanisms underlying these pathological conditions and for the establishment of new and effective interventions.

A proteomic analysis of the functional effects of fatty acids in NIH 3T3 fibroblasts

Previous studies have demonstrated that long chain fatty acids influence fibroblast function at sub-lethal concentrations. This study is the first to assess the effects of oleic, linoleic or palmitic acids on protein expression of fibroblasts, as determined by standard proteomic techniques. The fatty acids were not cytotoxic at the concentration used in this work as assessed by membrane integrity, DNA fragmentation and the MTT assay but significantly increased cell proliferation. Subsequently, a proteomic analysis was performed using two dimensional difference gel electrophoresis (2D-DIGE) and MS based identification. Cells treated with 50 μM oleic, linoleic or palmitic acid for 24 h were associated with 24, 22, 16 spots differentially expressed, respectively. Among the identified proteins, α-enolase and far upstream element binding protein 1 (FBP-1) are of importance due to their function in fibroblast-associated diseases. However, modulation of α-enolase and FBP-1 expression by fatty acids was not validated by the Western blot technique.

Structure-activity relationships influencing lipid-induced changes in eIF2α phosphorylation and cell viability in BRIN-BD11 cells

Fatty acids influence the viability of eukaryotic cells differentially such that long chain saturated molecules are poorly tolerated, whereas unsaturated species are less detrimental and can be cytoprotective. The basis for these effects is unclear but studies in yeast imply that they reflect the spatial configuration of the molecules when incorporated into the ER membrane. Using BRIN-BD11 β-cells, we show that a wide range of unsaturated free fatty acids and their methyl-esters (having differing chain length and disposition of the double bonds) elicit cytoprotection and relief of protein kinase RNA-like endoplasmic reticulum kinase-dependent ER stress. Thus, both physical properties and specific signalling events may regulate fatty acid responses in β-cells.

A lipidomic screen of palmitate-treated MIN6 β-cells links sphingolipid metabolites with endoplasmic reticulum (ER) stress and impaired protein trafficking

Saturated fatty acids promote lipotoxic ER (endoplasmic reticulum) stress in pancreatic β-cells in association with Type 2 diabetes. To address the underlying mechanisms we employed MS in a comprehensive lipidomic screen of MIN6 β-cells treated for 48 h with palmitate. Both the overall mass and the degree of saturation of major neutral lipids and phospholipids were only modestly increased by palmitate. The mass of GlcCer (glucosylceramide) was augmented by 70% under these conditions, without any significant alteration in the amounts of either ceramide or sphingomyelin. However, flux into ceramide (measured by [3H]serine incorporation) was augmented by chronic palmitate, and inhibition of ceramide synthesis decreased both ER stress and apoptosis. ER-to-Golgi protein trafficking was also reduced by palmitate pre-treatment, but was overcome by overexpression of GlcCer synthase. This was accompanied by increased conversion of ceramide into GlcCer, and reduced ER stress and apoptosis, but no change in phospholipid desaturation. Sphingolipid alterations due to palmitate were not secondary to ER stress since they were neither reproduced by pharmacological ER stressors nor overcome using the chemical chaperone phenylbutyric acid. In conclusion, alterations in sphingolipid, rather than phospholipid, metabolism are more likely to be implicated in the defective protein trafficking and enhanced ER stress and apoptosis of lipotoxic β-cells.

Arachidonic acid fights palmitate: new insights into fatty acid toxicity in β-cells

Saturated fatty acids are toxic to pancreatic β-cells. By inducing apoptosis, they contribute to a decrease in β-cell mass, a hallmark of Type 2 diabetes. In the present issue of Clinical Science, Keane and co-workers show that the polyunsaturated fatty acid arachidonic acid protects the β-cell against the toxic effects of palmitate. As Type 2 diabetes is characterized by subclinical inflammation, and arachidonic acid and metabolites thereof are produced during states of inflammation, it is possible that pancreatic β-cells use arachidonic acid as a compound for self-protection.