Elevated Plasma Free Fatty Acids Research Articles

Pancreastatin inhibitor PSTi8 ameliorates insulin resistance by decreasing fat accumulation and oxidative stress in high-fat diet-fed mice.

Abnormal fat accumulation, enhanced free fatty acids (FFA) release, and their metabolites cause insulin resistance (IR) in major glucose-lipid metabolic organs such as skeletal muscle and adipose tissue. However, excessive lipolysis and FFA release from adipose tissue elevate plasma FFA levels leading to oxidative stress and skeletal muscle IR. Indeed, in obese individuals, there is enhanced pro-inflammatory secretion from adipose tissue influencing insulin signaling in skeletal muscles. Here, we investigated the effect of PSTi8 on FFA-induced IR in both in vitro and in vivo models. Palmitate (Pal)-treated 3T3-L1 cells increased lipid accumulation as well as lipolysis, which reduced the insulin-stimulated glucose uptake. PSTi8 treatment significantly prevented Pal-induced lipid accumulation, and release and enhanced insulin-stimulated glucose uptake. It further reduced the release of pro-inflammatory cytokines from Pal-treated 3T3-L1 cells as well as from adipose tissue explants. In addition, PSTi8 treatment decreases M1 surface markers in Pal-treated bone marrow-derived monocytes (BMDM). PSTi8 treatment also significantly enhanced the Pal-mediated reduced skeletal muscle glucose disposal and reduced intracellular oxidative stress. In vitro effect of PSTi8 was consistent with in vivo HFD-fed mice IR model. PSTi8 treatment in HFD-fed mice significantly improved glucose metabolism and enhanced skeletal muscle insulin sensitivity with reduced adiposity and pro-inflammatory cytokines. Taken together, our results support that PSTi8 treatment can protect both adipose and skeletal muscles from FFA-induced IR.

1554-P: Carnosic Acid Protects against Short-Term Lipid-Infusion–Induced Glucose Intolerance in Mice

Background: Obesity and type 2 diabetes (T2D) are associated with elevated plasma free fatty acids (FFA). In vivo exposure to FFAs, such as palmitate, by lipid infusion results in insulin resistance as observed in obesity and T2D. In recent years, compounds found in herbs and plants have attracted attention for prevention and treatment of insulin resistance and T2D. In recent studies by our group, carnosic acid (CA), found in rosemary, increased glucose uptake and attenuated the FFA (palmitate)-induced insulin resistance in muscle cells and adipocytes. In addition, CA caused a robust activation of AMP-activated protein kinase (AMPK). Our present study aimed to examine the effects of CA in short-term FFA-induced glucose intolerance in mice. Material and Methods: C57Bl/6J mice were cannulated in their jugular veins and infused for 48h with ethylpalmitate (EtP, nontoxic method of elevating circulating palmitate because of hydrolysis to palmitate and ethanol by plasma esterases), mimicking elevated FFA levels seen in obesity. In addition, a group of mice were infused with EtP plus 50 mg/kg CA for 48h. Ethanol vehicle with or without CA were two additional control groups. At the end of the infusions, the mice were subjected to a 2 hr hyperglycemic clamp (20 mM glucose) and the glucose infusion rate was measured to assess glucose tolerance. Results: Preliminary data revealed that mice infused with EtP and CA had a higher glucose infusion rate (GIR; mg/kg*min) (66.5±10, mean±SEM) than mice infused with EtP alone (22.7±10). The EtP and CA was comparable to the GIR of ethanol vehicle infused mice (73±9). Future Directions: Further analysis of collected plasma and tissue will be used to assess insulin resistance and beta cell function in vivo and to elucidate the mechanisms of CA alleviation of FFA-induced insulin resistance. Conclusions: Our data indicate that CA has the potential to counteract FFA-induced glucose intolerance in mice. Disclosure N.Tsakiridis: None. F.Vlavcheski: None. E.Tsiani: None. A.Giacca: None.

An Overview of Hormone-Sensitive Lipase (HSL).

Hormone-sensitive lipase (HSL) is a pivotal enzyme that mediates triglyceride hydrolysis to provide free fatty acids and glycerol in adipocytes in a hormonally controlled lipolysis process. Elevated plasma-free fatty acids were accompanied by insulin resistance, type-2 diabetes, and obesity. Inhibition of lipolysis through HSL inhibition may provide a mechanism to prevent the accumulation of free fatty acids and to improve the affectability of insulin and blood glucose handling in type II diabetes. The published studies that examine the structure, regulation, and function of HSL and major inhibitors were reviewed in this paper.

Differences in lipid metabolism in acquired versus preexisting glucose intolerance during gestation: role of free fatty acids and sphingosine-1-phosphate

BackgroundThe prevalence of gestational diabetes mellitus (GDM) is increasing worldwide. There is increasing evidence that GDM is a heterogeneous disease with different subtypes. An important question in this context is whether impaired glucose tolerance (IGT), which is a typical feature of the disease, may already be present before pregnancy and manifestation of the disease. The latter type resembles in its clinical manifestation prediabetes that has not yet manifested as type 2 diabetes (T2DM). Altered lipid metabolism plays a crucial role in the disorder's pathophysiology. The aim was to investigate the role of lipids which are relevant in diabetes-like phenotypes in these both models with different time of initial onset of IGT.MethodsTwo rodent models reflecting different characteristics of human GDM were used to characterize changes in lipid metabolism occurring during gestation. Since the New Zealand obese (NZO)-mice already exhibit IGT before and during gestation, they served as a subtype model for GDM with preexisting IGT (preIGT) and were compared with C57BL/6 N mice with transient IGT acquired during gestation (aqIGT). While the latter model does not develop manifest diabetes even under metabolic stress conditions, the NZO mouse is prone to severe disease progression later in life. Metabolically healthy Naval Medical Research Institute (NMRI) mice served as controls.ResultsIn contrast to the aqIGT model, preIGT mice showed hyperlipidemia during gestation with elevated free fatty acids (FFA), triglycerides (TG), and increased atherogenic index. Interestingly, sphingomyelin (SM) concentrations in the liver decreased during gestation concomitantly with an increase in the sphingosine-1-phosphate (S1P) concentration in plasma. Further, preIGT mice showed impaired hepatic weight adjustment and alterations in hepatic FFA metabolism during gestation. This was accompanied by decreased expression of peroxisome proliferator-activated receptor alpha (PPARα) and lack of translocation of fatty acid translocase (FAT/CD36) to the hepatocellular plasma membrane.ConclusionThe preIGT model showed impaired lipid metabolism both in plasma and liver, as well as features of insulin resistance consistent with increased S1P concentrations, and in these characteristics, the preIGT model differs from the common GDM subtype with aqIGT. Thus, concomitantly elevated plasma FFA and S1P concentrations, in addition to general shifts in sphingolipid fractions, could be an interesting signal that the metabolic disorder existed before gestation and that future pregnancies require more intensive monitoring to avoid complications.Graphical This graphical abstract was created with BioRender.com.

Title: Involvement of unsaturated fatty acid biosynthesis in CRC progression based on in vitro and in silico studies

Obesity is one of the risk factors concerns of colorectal cancer (CRC), the most common type of gastrointestinal cancer, due to the changing lifestyle and especially diet. There are various molecular pathways associated with obesity and the risk of CRC incidence, such as insulin resistance or elevated plasma free fatty acids, which alter the signaling pathways of intestinal epithelial cells. The aim of this study was to better understand the significance of unsaturated fatty acid biosynthesis on pathogenesis of colon cancer in obese. Based on GSE20931 dataset, obese individuals affected by CRC had higher increased gene expression than non-obese individuals. The analysis showed that in obese individuals, the 16 signaling pathway genes were activated and increased (FDR <0.05) significantly. The biosynthetic pathway of unsaturated fatty acids showed a cross-talk with the arachidonic acid metabolism pathway and the PPAR signaling pathway is influenced and regulated via these pathways. The biosynthetic pathway of unsaturated fatty acids consisting of 22 genes, were analyzed using GEO data and revealed that 4 genes (HSD17B12, TECR, FADS2, ELOVL5) from this pathway were significantly increased (FDR <0.05). These data were validated based on TCGA data (Adj.p.value <0.001). The expression level of candidate genes in HT-29 cells decreased significantly (P.value <0.01), and PPARγ expression increased under linoleic acid treatment (200 μM) compared to control cells. Moreover, in presence of linoleic acid treatment, migration, colony formation, and proliferation decreased (P.value <0.01) in presence of treatment. In summary, the Biosynthesis pathway of unsaturated fatty acids is an interesting and critical pathway in CRC.

1322-P: Role of Macrophage NOD1 in Fat-Induced ß-Cell Dysfunction

In individuals with obesity, free fatty acids (FFA) are chronically raised resulting in ß-cell dysfunction, leading to type 2 diabetes (T2D) . Recent data implicate the role of inflammation in developing ß-cell dysfunction, which is in part mediated by nucleotide-oligomerization domain 1 (NOD1) , an intracellular pattern recognition receptor. NOD1 is activated by peptidoglycans of bacterial cell walls; however, in vitro studies have documented that NOD1 can also be activated by saturated FFA. Previous data from our lab have shown that palmitate-induced ß-cell dysfunction was prevented in whole body and ß-cell specific NOD1 null mice. We have seen earlier reports on increased macrophage infiltration in islets after elevation in circulating palmitate, and much higher expression of NOD1 in macrophages than ß-cells. Hence, we hypothesized that macrophage NOD1 receptors play a pivotal role in FFA-induced ß-cell dysfunction. We have generated myeloid specific NOD1 null mice to target macrophage NOD1 receptors by crossing NOD1 floxed mice with Lyz2 Cre+ mice. Both knockouts and their controls (floxed and Cre) were infused for 48 h with ethylpalmitate (hydrolyzed to palmitate and ethanol in plasma) , to achieve elevated circulating FFA in a non-toxic manner. Ethanol vehicle was infused as control treatment. To assess in vivo ß-cell function, hyperglycemic clamp was performed following the 48 h infusion, and the disposition index (DI) was calculated. Ethylpalmitate resulted in elevated plasma FFA compared to vehicle infusion. Ethylpalmitate caused marked reduction in DI in control mice, while knockout mice displayed no significant changes in DI between ethylpalmitate and vehicle infused groups. These results suggest that macrophage NOD1 plays a causal role in palmitate-induced ß-cell dysfunction in vivo. Overall, our data reveal NOD1 as a key factor and a potential therapeutic target for obesity-associated diabetes. Disclosure S.Rahman: None. J.Yung: None. Y.Zhang: None. A.Giacca: None.

ATP10A has a protective and sex‐specific role in lipid metabolism

Genetic predisposition and environment play substantial roles in obesity, type 2 diabetes and cardiovascular disease (CVD). Genetic association studies have linked ATP10A, encoding a type IV P‐type ATPase (P4‐ATPase), to human metabolic disease. ATP10A is a lipid flippase that catalyzes the membrane translocation of phosphatidylcholine and glucosylceramide. These lipids and their respective metabolites have been independently implicated in metabolic dysfunction. To explore the role of this flippase in metabolism, we created a novel Atp10aknockout (KO) mouse model. Atp10a KO mice display a female‐specific weight gain during high‐fat diet feeding and this is attributable to increased adiposity. Female Atp10a KO mice also exhibit elevated plasma free fatty acids, cholesterol, and triglycerides, as well as a depletion in eicosanoid species compared to the wild type (WT) littermates. Additionally, female Atp10a KO mice exhibit elevated fasting blood glucose levels without compensatory elevation of insulin. We also found that the liver of female Atp10aKO mice displays larger lipid droplets, which was associated with increased diacylglycerol acyltransferase‐2 (DGAT2) expression and an attenuation of the insulin signaling pathway compared to the WT littermates. Thus far, our studies have shown that knocking out Atp10a in mice on a high fat diet results in sex‐specific perturbations to body composition, plasma lipid levels, glucose homeostasis, and liver metabolism. We have recently found that ATP10A is specifically expressed in the endothelial cells of multiple tissues. We are now exploring these metabolic phenotypes through the lens of endothelial cell dysfunction. These studies suggest mechanisms by which this flippase contributes to the development of CVD with obesity.

Hepatic Lipidomic Analysis of Dietary Different Type of Fats and Fructose Interactions in the Pathogenesis of Nonalcoholic Fatty Liver Diseases

ObjectiveDietary nutrient interactions are key determinants to the development of nonalcoholic fatty liver disease (NAFLD). Fat and fructose are two major components of Western diet. This study aimed to determine the combined effects of different type of dietary fats and fructose on the development of NAFLD in a murine model.MethodsMale adult C57BL/6J mice were assigned to six groups and fed with diets (AIN‐93G based) enriched with different types of fat, such as saturated fat (SF‐beef tallow), n‐6 polyunsaturated fat (n6USF‐corn oil), or n‐3 polyunsaturated fat (n3USF‐menhaden fish oil), respectively, with or without fructose supplementation through 10% fructose (w/v) in the drinking water ad lib for 20 weeks. 42% of calories was derived from the fat. Metabolic phenotypes were characterized by liver histology, plasma ALT and AST, glucose tolerance test, hepatic mRNA expression of genes involved in lipid metabolism, and lipidomic analysis of hepatic fatty acid composition.ResultsWhile both SF and n6USF fed mice developed obesity and hepatic steatosis with or without fructose, SFA fed mice were characterized with hepatomegaly, liver injury and fibrosis, which were further exacerbated by fructose; conversely, plasma triglyceride levels were lower compared to controls. Interestingly, n6USF fed mice exhibited steatosis without hepatomegaly, and this was associated with markedly elevated plasma triglyceride and free fatty acid levels, which were blunted by fructose. Moreover, fructose and n6USF led to markedly elevated glucose intolerance tests compared to controls. Hepatic lipidomic analysis revealed that total monounsaturated fatty acids, but not total SFA, exhibited a stepwise decrease from SF to n6USF and n3USF fed mice across most of the lipid pools, which parallels the hepatic triglyceride content, irrespective the presence of fructose. In line with this, hepatic mRNA levels of lipogenesis genes, including Srebf1, Scd1, Fasn, Acacaand Acacb, displayed a similar pattern of alterations (SF&gt;n6USF&gt;n3USF), suggesting that increased lipogenesis contributes to hepatic steatosis in SF and n6USF fed mice. Of note, fructose play a mild, but significant role in the alterations of specific individual fatty acids in certain fatty acid pools, despite the predominant role played by the dietary fats.ConclusionOur data suggest that excess energy from SF intake results in fat storage in the liver, likely due to impaired triglyceride secretion; whereas excess energy from n6USF intake is stored in the periphery. Both effects were exacerbated by fructose supplementation. n3USF is beneficial even in the presence of fructose.

Effects of Individual Circulating FFAs on Plasma Oxylipin Levels: Implications for FFA Epoxide‐diol Ratios as Indices of Soluble Epoxide Hydrolase Activity

Oxylipins, oxidation products of essential free fatty acids (FFAs), are involved in various cellular signaling. Among them, FFA epoxides are associated with beneficial effects in metabolic and cardiovascular health. FFA epoxides are metabolized to usually biologically less active diols by soluble epoxide hydrolase (sEH). Inhibition of sEH, which increases FFA epoxides, improves glucose homeostasis and cardiovascular health. Plasma epoxide‐diol ratios have been used as indices of sEH activity.Objective and HypothesisThe objective of this study was to examine the effects of acute elevation of plasma FFAs on oxylipins, particularly, epoxides, diols, and their ratios. We tested if FFA epoxide‐diol ratios are altered by circulating FFA levels (i.e., substrate availability) independent of sEH activity.MethodsMale Wistar rats received a constant intravenous infusion of olive (70% oleic acid [OA]), safflower seed (72% linoleic acid [LA]), and fish (rich in w‐3 FFAs) oils (20% wt/vol emulsion, 0.5 ml/h; n = 6 for each infusion) for 2 hours to selectively raise OA, LA, and w‐3 FFAs (eicosapentaenoic acid [EPA] and docosahexaenoic acid [DHA]), respectively. Blood samples were collected before and after the infusions and analyzed for oxylipins using LC‐MS and individual FFAs using GC‐MS. As LA, DHA, and EPA are metabolized to epoxides and diols, we evaluated their mass‐action effects to alter epoxides, diols, or their ratios. In contrast, OA is not metabolized to epoxides and diols detected in our assays, and the olive oil infusion served as control for any non‐mass‐action effects.ResultsAs expected, olive, safflower seed, and fish oil infusions selectively raised plasma OA (57%), LA (87%), and EPA (70%) and DHA (54%), respectively (P &lt; 0.05 for all). Interestingly, olive oil infusion had significant effects to decrease FFA epoxides and diols with more dramatic effects on epoxides than diols (P &lt; 0.01), resulting in large (up to 6‐fold) increases in diol‐to‐epoxide ratios. We found similar effects with safflower seed and fish oil infusions, although these infusions also showed mass action effects to increase epoxide and diol levels derived from LA (safflower seed oil) and DHA and EPA (fish oil). The decreases in FFA epoxides with acute elevation of circulating FFAs (i.e., increased substrate availability) were unexpected and appeared to be due to increased epoxide metabolism independent of sEH. We are currently examining the possibility that acute elevation of plasma FFAs stimulates glucuronidation of FFA epoxides to increase their removal via urinary excretion.ConclusionsRaising plasma FFAs has profound effects to decrease plasma FFA epoxides, significantly altering plasma epoxide‐diol ratios. These data suggest that caution should be taken in comparing epoxide‐diol ratios, as indices of sEH activity, between conditions with different circulating FFA levels. Our data also suggest that plasma FFAs regulate epoxide levels by stimulating a metabolic process independent of sEH, possibly glucuronidation followed by renal excretion.

Adipocyte Gq signaling is a regulator of glucose and lipid homeostasis in mice

Obesity is the major driver of the global epidemic in type 2 diabetes (T2D). In individuals with obesity, impaired insulin action leads to increased lipolysis in adipocytes, resulting in elevated plasma free fatty acid (FFA) levels that promote peripheral insulin resistance, a hallmark of T2D. Here we show, by using a combined genetic/biochemical/pharmacologic approach, that increased adipocyte lipolysis can be prevented by selective activation of adipocyte Gq signaling in vitro and in vivo (in mice). Activation of this pathway by a Gq-coupled designer receptor or by an agonist acting on an endogenous adipocyte Gq-coupled receptor (CysLT2 receptor) greatly improved glucose and lipid homeostasis in obese mice or in mice with adipocyte insulin receptor deficiency. Our findings identify adipocyte Gq signaling as an essential regulator of whole-body glucose and lipid homeostasis and should inform the development of novel classes of GPCR-based antidiabetic drugs.

Діабетична дисліпідемія: фокус на патогенез і лікування

Atherosclerotic cardiovascular diseases are the most common cause of death in the developed countries of the world. Patients with diabetes mellitus 2 type are 2-4 times more likely to die from these diseases compared to patients without diabetes. This review discusses the pathophysiology of lipid disorders, which are the main cause of cardiovascular disease in patients with diabetes mellitus 2 type, and the current approaches to the medical therapy of these disorders. Obesity, metabolic syndrome, and diabetes mellitus 2 type are characterized by insulin resistance, which leads to excessive lipolysis of visceral adipose tissue. The consequence of this disorder is the excessive production of free fatty acids, which become the source for excessive synthesis of proatherogenic lipoproteins saturated with triglycerides. These lipid profile abnormalities are the main pathogenetic link between diabetes and increased risk of atherosclerosis. Chronically elevated levels of free fatty acids reduce insulin synthesis, glucose-stimulated insulin secretion, and β-cell sensitivity to glucose, resulting in a very high risk of developing diabetes mellitus 2 type. Numerous factors contribute to elevated plasma free fatty acid levels and subsequent impairment of metabolic health, such as unhealthy diet, obesity, low physical activity, obstructive sleep apnea, sleep deprivation, and smoking. Currently, lifestyle changes are the best tool for long-term normalization of the concentration of free fatty acids in the blood plasma. The results of modern research have proven that a healthy lifestyle and glycemic control, treatment with statins, ezetimibe, and hypoglycemic drugs improve the lipid profile, reduce insulin resistance and inflammation, which reduces the risk of cardiovascular diseases.

Nicotinamide Mononucleotide Prevents Free Fatty Acid-Induced Reduction in Glucose Tolerance by Decreasing Insulin Clearance.

The NAD-dependent deacetylase SIRT1 improves β cell function. Accordingly, nicotinamide mononucleotide (NMN), the product of the rate-limiting step in NAD synthesis, prevents β cell dysfunction and glucose intolerance in mice fed a high-fat diet. The current study was performed to assess the effects of NMN on β cell dysfunction and glucose intolerance that are caused specifically by increased circulating free fatty acids (FFAs). NMN was intravenously infused, with or without oleate, in C57BL/6J mice over a 48-h-period to elevate intracellular NAD levels and consequently increase SIRT1 activity. Administration of NMN in the context of elevated plasma FFA levels considerably improved glucose tolerance. This was due not only to partial protection from FFA-induced β cell dysfunction but also, unexpectedly, to a significant decrease in insulin clearance. However, in conditions of normal FFA levels, NMN impaired glucose tolerance due to decreased β cell function. The presence of this dual action of NMN suggests caution in its proposed therapeutic use in humans.

Elevated Plasma Free Fatty Acid Susceptible to Early Cognitive Impairment in Type 2 Diabetes Mellitus.

Elevated free fatty acid (FFA) induces lipotoxicity, attributed to diabetes and cognitive decline. Sterol regulatory element-binding protein-1c (SREBP-1c) regulates lipid metabolism. We investigated the roles of FFA in mild cognitive impairment (MCI) of type 2 diabetes mellitus (T2DM) patients and determine its association with rs11868035 polymorphism. We recruited 191 Chinese T2DM patients into two groups through Montreal Cognitive Assessment. Demographic and clinical data were collected, multiple domain cognitive functions were tested, plasma FFA levels were measured through ELISA, and SREBP-1c rs11868035 genotype was detected using the Seqnome method. In comparison with the healthy-cognition group (n = 128), the MCI group (n = 63) displayed lower glucose control (p = 0.012) and higher plasma FFA level (p = 0.021), which were independent risk factors of MCI in T2DM patients in multivariate regression analysis (OR = 1.270, p = 0.003; OR = 1.005, p = 0.036). Additionally, the plasma FFA levels of MCI patients were positively correlated with Stroop color word test-C time scores (r = 0.303, p = 0.021) and negatively related to apolipoprotein A1 levels (r = -0.311, p = 0.017), which are associated positively with verbal fluency test scores (r = 0.281, p = 0.033). Both scores reflected attention ability and executive function. Moreover, the G allele carriers of rs11868035 showed higher digit span test scores than non-carriers in T2DM patients (p = 0.019) but without correlation with plasma FFA levels. In T2DM, elevated plasma level of FFA, when combined with lower apolipoprotein A1 level portends abnormal cholesterol transport, were susceptible to early cognitive impairment, especially for attention and execution deficits. The G allele of SREBP-1c rs11868035 may be a protective factor for memory.

Plasma Free Fatty Acid Concentration as a Modifiable Risk Factor for Metabolic Disease.

Plasma free fatty acid (FFA) concentration is elevated in obesity, insulin resistance (IR), non-alcoholic fatty liver disease (NAFLD), type 2 diabetes (T2D), and related comorbidities such as cardiovascular disease (CVD). Furthermore, experimentally manipulating plasma FFA in the laboratory setting modulates metabolic markers of these disease processes. In this article, evidence is presented indicating that plasma FFA is a disease risk factor. Elevations of plasma FFA can promote ectopic lipid deposition, IR, as well as vascular and cardiac dysfunction. Typically, elevated plasma FFA results from accelerated adipose tissue lipolysis, caused by a high adipose tissue mass, adrenal hormones, or other physiological stressors. Reducing an individual’s postabsorptive and postprandial plasma FFA concentration is expected to improve health. Lifestyle change could provide a significant opportunity for plasma FFA reduction. Various factors can impact plasma FFA concentration, such as chronic restriction of dietary energy intake and weight loss, as well as exercise, sleep quality and quantity, and cigarette smoking. In this review, consideration is given to multiple factors which lead to plasma FFA elevation and subsequent disruption of metabolic health. From considering a variety of medical conditions and lifestyle factors, it becomes clear that plasma FFA concentration is a modifiable risk factor for metabolic disease.

4-Phenylbutyric acid improves free fatty acid-induced hepatic insulin resistance in vivo.

Plasma free fatty acids (FFAs) are elevated in obesity and can induce insulin resistance via endoplasmic reticulum (ER) stress. However, it is unknown whether hepatic insulin resistance caused by the elevation of plasma FFAs is alleviated by chemical chaperones. Rats received one of the following i.v. treatments for 48 h: saline, intralipid plus heparin (IH), IH plus the chemical chaperone 4-phenylbutyric acid (PBA), or PBA alone and a hyperinsulinemic-euglycemic clamp was performed during the last 2 h. PBA co-infusion normalized IH-induced peripheral insulin resistance, similar to our previous findings with an antioxidant and an IκBα kinase β (IKKβ) inhibitor. Different from our previous results with the antioxidant and IKKβ inhibitor, PBA also improved IH-induced hepatic insulin resistance in parallel with activation of Akt. Unexpectedly, IH did not induce markers of ER stress in the liver, but PBA prevented IH-induced elevation of phosphorylated eukaryotic initiation factor-2α protein in adipose tissue. PBA tended to decrease circulating fetuin-A and significantly increased circulating fibroblast growth factor 21 (FGF21) without affecting markers of activation of hepatic protein kinase C-δ or p38 mitogen-activated protein kinase that we have previously involved in hepatic insulin resistance in this model. In conclusion: (i) PBA prevented hepatic insulin resistance caused by prolonged plasma FFA elevation without affecting hepatic ER stress markers; (ii) the PBA effect is likely due to increased FGF21 and/or decreased fetuin-A, which directly signal to upregulate Akt activation.

1161-P: NOD1-JNK1 Axis Plays a Causal Role in Palmitate-Induced ß-Cell Dysfunction

Chronic elevation of free fatty acids (FFA) in obesity may cause ß-cell dysfunction leading to type 2 diabetes (T2D). Recent studies have focused on innate immunity receptors due to evidence implicating inflammation in obesity-induced T2D. While several of these receptors have been implicated in FFA-induced ß-cell dysfunction, the nucleotide-binding oligomerization domain (NOD) receptors have not been investigated. Our previous work showed that whole-body NOD1-null mice were protected from palmitate-induced ß-cell dysfunction in vivo. This may be due to lack of NOD1 in ß-cells and/or macrophages infiltrating islets. Also, islets of whole-body NOD1-null and JNK1-null mice were protected from ß-cell dysfunction induced by palmitate but not oleate in vitro, suggesting NOD1 activation is likely in ß-cells, is specific to saturated FFA and may cause ß-cell dysfunction via JNK1. Thus, we hypothesized that ß-cell NOD1 mediates palmitate-induced ß-cell dysfunction in vivo, and that JNK1 is downstream of NOD1 activation. Addition of an ethyl group on palmitate reduces toxicity of unbound palmitate, thus ethylpalmitate (EtPAL) was used. Ethyl esterases in mouse plasma hydrolyze EtPAL into palmitate and ethanol. ß-cell specific NOD1-null (ßKO) mice (using Ins1- and RIP-Cre) and their controls were infused with EtPAL or ethanol vehicle (Veh) for 48 hours, followed by a hyperglycemic clamp to evaluate ß-cell function in vivo from the disposition index (DI). Islets of JNK1-null and wildtype (WT) mice were isolated and treated with a NOD1 activator to investigate the NOD1-JNK1 axis. As expected, EtPAL infusion elevated plasma FFA. EtPAL decreased DI in control mice, while EtPAL-infused ßKO mice had similar DI to Veh-infused mice. Further, the NOD1 activator reduced insulin secretion in WT islets but not in JNK1-null islets. These data implicate ß-cell NOD1-JNK1 axis in palmitate-induced ß-cell dysfunction and reveal a novel pathway that could be targeted for manipulation in order to preserve ß-cell function. Disclosure J. Yung: None. A. Ivovic: None. I. Clark: None. F. Li: None. B. Lin: None. Y. Tan: None. A. Giacca: None. Funding Canadian Institutes of Health Research (CIHR50748)

Adipocyte P2Y14 receptors play a key role in regulating whole-body glucose and lipid homeostasis.

Obesity is the major driver of the worldwide epidemic in type 2 diabetes (T2D). In the obese state, chronically elevated plasma free fatty acid levels contribute to peripheral insulin resistance, which can ultimately lead to the development of T2D. For this reason, drugs that are able to regulate lipolytic processes in adipocytes are predicted to have considerable therapeutic potential. Gi-coupled P2Y14 receptor (P2Y14R; endogenous agonist, UDP-glucose) is abundantly expressed in both mouse and human adipocytes. Because activated Gi-type G proteins exert an antilipolytic effect, we explored the potential physiological relevance of adipocyte P2Y14Rs in regulating lipid and glucose homeostasis. Metabolic studies indicate that the lack of adipocyte P2Y14R enhanced lipolysis only in the fasting state, decreased body weight, and improved glucose tolerance and insulin sensitivity. Mechanistic studies suggested that adipocyte P2Y14R inhibits lipolysis by reducing lipolytic enzyme activity, including ATGL and HSL. In agreement with these findings, agonist treatment of control mice with a P2Y14R agonist decreased lipolysis, an effect that was sensitive to inhibition by a P2Y14R antagonist. In conclusion, we demonstrate that adipose P2Y14Rs were critical regulators of whole-body glucose and lipid homeostasis, suggesting that P2Y14R antagonists might be beneficial for the therapy of obesity and T2D.

P2Y 14 receptor regulates adipocyte lipid mobilization and whole‐body glucose homeostasis

The incidence and prevalence of obesity and type 2 diabetes (T2D) is rapidly increasing worldwide. Obesity is associated with chronically elevated plasma free fatty acid (FFA) levels, causing peripheral insulin resistance and T2D. Drugs that are able to regulate adipocyte lipolytic processes, improving insulin sensitivity and whole-body glucose homeostasis, have considerable therapeutic potential. Gi-coupled P2Y14 receptor (P2Y14R), activated by UDP-glucose is abundantly expressed in mouse and human adipocytes. P2Y14R activation in primary mouse adipocytes decreased cAMP levels and CL-316,243 (β3-adrenoceptor agonist) induced lipolysis. To investigate the physiological relevance of adipocyte P2Y14Rs in regulating lipid and glucose homeostasis in-vivo, we generated a mouse model lacking P2Y14R specifically in adipocytes. Lack of adipocyte P2Y14R increased lipolysis only in the fasting state, resulting in decreased body weight, improved glucose tolerance and insulin sensitivity. Accordingly, high fat diet increased, whereas fasting decreased P2Y14R expression in visceral white adipocytes. Mechanistic studies suggested that activation of P2Y14R reduced the activity of lipolytic enzymes including ATGL and HSL, thereby inhibiting lipolysis. Supporting these findings, administration of P2Y14R agonist in control mice decreased lipolysis. Coadministration of P2Y14R antagonist with the P2Y14R agonist rescued the decrease in lipolysis. In conclusion, we demonstrate that lack of adipocyte P2Y14R decreased diet-induced obesity by enhancing lipolysis in the fasting state, suggesting that P2Y14R antagonists may prove beneficial for the therapy of obesity and T2D.

Exploring the role of ATP10A in diet‐induced obesity, insulin resistance, and type 2 diabetes

Type IV P-type ATPases (P4-ATPases) are enzymes that catalyze the translocation of lipids across plasma membranes. Our lab recently discovered that Atp10a, a mammalian P4-ATPase, can translocate glucosylceramide, a sphingolipid. Both Atp10a and glucosylceramide have been independently implicated in metabolic dysfunction. To explore the role of Atp10a in metabolic dysfunction and sphingolipid metabolism, we created a novel Atp10a knockout (KO) mouse model. Atp10a KO mice display a female-specific excess weight gain on standard chow that is exacerbated by 12 weeks of high fat feeding and this is attributable to increased adiposity. Additionally, they display an accumulation of neutral lipids and altered ceramide metabolism in their livers. After a 5 hour fast, these mice exhibit elevated blood glucose levels that are not coupled to a proportional elevation in insulin levels. Atp10a KO mice also exhibit elevated plasma free fatty acids, cholesterol, and triglycerides. Thus far, our studies have shown that knocking out Atp10a in a mouse results in sex-specific perturbations to body weight and composition, glucose homeostasis, plasma lipid levels, and liver metabolism.

Remodeling of whole-body lipid metabolism and a diabetic-like phenotype caused by loss of CDK1 and hepatocyte division.

Cell cycle progression and lipid metabolism are well-coordinated processes required for proper cell proliferation. In liver diseases that arise from dysregulated lipid metabolism, proliferation is diminished. To study the outcome of CDK1 loss and blocked hepatocyte proliferation on lipid metabolism and the consequent impact on whole-body physiology, we performed lipidomics, metabolomics, and RNA-seq analyses on a mouse model. We observed reduced triacylglycerides in liver of young mice, caused by oxidative stress that activated FOXO1 to promote expression of Pnpla2/ATGL. Additionally, we discovered that hepatocytes displayed malfunctioning β-oxidation, reflected by increased acylcarnitines (ACs) and reduced β-hydroxybutyrate. This led to elevated plasma free fatty acids (FFAs), which were transported to the adipose tissue for storage and triggered greater insulin secretion. Upon aging, chronic hyperinsulinemia resulted in insulin resistance and hepatic steatosis through activation of LXR. Here, we demonstrate that loss of hepatocyte proliferation is not only an outcome but also possibly a causative factor for liver pathology.