Insulin resistance is associated with nonalcoholic fatty liver disease (NAFLD) and is a major factor in the pathogenesis of type 2 diabetes. The development of hepatic insulin resistance has been ascribed to multiple causes, including inflammation, endoplasmic reticulum (ER) stress, and accumulation of hepatocellular lipids in animal models of NAFLD. However, it is unknown whether these same cellular mechanisms link insulin resistance to hepatic steatosis in humans. To examine the cellular mechanisms that link hepatic steatosis to insulin resistance, we comprehensively assessed each of these pathways by using flash-frozen liver biopsies obtained from 37 obese, nondiabetic individuals and correlating key hepatic and plasma markers of inflammation, ER stress, and lipids with the homeostatic model assessment of insulin resistance index. We found that hepatic diacylglycerol (DAG) content in cytoplasmic lipid droplets was the best predictor of insulin resistance (R = 0.80, P < 0.001), and it was responsible for 64% of the variability in insulin sensitivity. Hepatic DAG content was also strongly correlated with activation of hepatic PKCε (R = 0.67, P < 0.001), which impairs insulin signaling. In contrast, there was no significant association between insulin resistance and other putative lipid metabolites or plasma or hepatic markers of inflammation. ER stress markers were only partly correlated with insulin resistance. In conclusion, these data show that hepatic DAG content in lipid droplets is the best predictor of insulin resistance in humans, and they support the hypothesis that NAFLD-associated hepatic insulin resistance is caused by an increase in hepatic DAG content, which results in activation of PKCε.

Insulin resistance is associated with the circulating free fatty acid (FFA) level and intracellular lipid content in muscle and liver. We investigated the effect of 2-wk diet and exercise therapy on total adiposity, circulating FFA, intracellular lipid content in muscle and liver, and peripheral insulin sensitivity. Type 2 diabetic patients were divided into a diet group (n = 7) and a diet plus exercise group (n = 7). We performed a hyperinsulinemic-euglycemic clamp study before and after treatment. Intramyocellular lipid (IMCL) in the tibialis anterior muscle and intrahepatic lipid (IHL) were evaluated by (1)H-magnetic resonance spectroscopy. Fasting FFA were not altered, and total body fat showed a slight, but significant, decrease in both groups after treatment. IMCL was decreased by 19%, and the glucose infusion rate was increased by 57% in the diet plus exercise group, whereas neither IMCL nor glucose infusion rate was significantly altered in the diet group. However, IHL showed a significant decrease in both groups. In summary, we found that 2 wk of diet and exercise decreased IMCL and increased muscle insulin-mediated glucose uptake, whereas diet with or without exercise decreased IHL. These effects were evident despite a small decrease in body fat and were observed independently of fasting FFA levels.

Summary Leptin reverses hyperglycemia in T1D though reductions in HPA-mediated lipolysis resulting in reduced hepatic gluconeogenesis through both substrate delivery and allosteric mechanisms.

Comparative gene identification 58 (CGI-58) is a lipid droplet-associated protein that promotes the hydrolysis of triglyceride by activating adipose triglyceride lipase. Loss-of-function mutations in CGI-58 in humans lead to Chanarin-Dorfman syndrome, a condition in which triglyceride accumulates in various tissues, including the skin, liver, muscle, and intestines. Therefore, without adequate CGI-58 expression, lipids are stored rather than used for fuel, signaling intermediates, and membrane biosynthesis. CGI-58 knockdown in mice using antisense oligonucleotide (ASO) treatment also leads to severe hepatic steatosis as well as increased hepatocellular diacylglycerol (DAG) content, a well-documented trigger of insulin resistance. Surprisingly, CGI-58 knockdown mice remain insulin-sensitive, seemingly dissociating DAG from the development of insulin resistance. Therefore, we sought to determine the mechanism responsible for this paradox. Hyperinsulinemic-euglycemic clamp studies reveal that the maintenance of insulin sensitivity with CGI-58 ASO treatment could entirely be attributed to protection from lipid-induced hepatic insulin resistance, despite the apparent lipotoxic conditions. Analysis of the cellular compartmentation of DAG revealed that DAG increased in the membrane fraction of high fat-fed mice, leading to PKCe activation and hepatic insulin resistance. However, DAG increased in lipid droplets or lipid-associated endoplasmic reticulum rather than the membrane of CGI-58 ASO-treated mice, and thus prevented PKCe translocation to the plasma membrane and induction of insulin resistance. Taken together, these results explain the disassociation of hepatic steatosis and DAG accumulation from hepatic insulin resistance in CGI-58 ASO-treated mice, and highlight the importance of intracellular compartmentation of DAG in causing lipotoxicity and hepatic insulin resistance.nonalcoholic fatty liver disease | type 2 diabetes N onalcoholic fatty liver disease (NAFLD) is now the most common chronic liver disease in the United States and is strongly associated with hepatic insulin resistance and type 2 diabetes (1, 2). Although NAFLD is characterized by excessively high triglycerides in the liver, the triglycerides do not appear to be detrimental to hepatic insulin sensitivity (3, 4). Rather, other lipid moieties, such as diacylglycerols (DAG) and ceramides, have been implicated as the molecular triggers of insulin resistance (5-7). The mechanism whereby these lipids cause insulin resistance are diverse: DAGs cause insulin resistance through activation of PKCe in liver, leading to the inhibition of insulin-receptor kinase activity (8, 9), and PKCθ in skeletal muscle, leading to insulinreceptor substrate-1 serine phosphorylation on sites that interfere with insulin action (10-12). Ceramides have been proposed to inhibit AKT2 activation by either activating PP2A, which dephosphorylates and deactivates AKT2, or activating PKCζ, which phosphorylates AKT on an inhibitory residue and prevents its translocation to the plasma ...

BackgroundRecent studies reported that sodium glucose cotransporter 2 (SGLT2) inhibitors can potentially reduce the risk of cardiovascular mortality in patients with type 2 diabetes mellitus (T2DM). However, there is little or no information on the therapeutic effects of SGLT2 inhibitors on the progression of atherosclerosis. This dapagliflozin effectiveness on vascular endothelial function and glycemic control (DEFENCE) study was designed to determine the effects of dapagliflozin, a SGLT2 inhibitor, on endothelial function in patients with early-stage T2DM.MethodsDEFENCE is a prospective, randomized, open-label, blinded-endpoint, parallel-group, comparative clinical trial. Between October 2015 and August 2016, 80 T2DM patients treated with 750 mg of metformin (hemoglobin A1c ≥6.0 and <8.0%, n = 80) were enrolled and randomized to receive either 1500 mg/day metformin (the metformin group, n = 40), or 750 mg/day metformin supplemented with 5 mg/day dapagliflozin (the dapagliflozin group, n = 40), for 16 weeks. The primary endpoint was a change in flow-mediated dilation (FMD) from baseline to the end of the 16-week treatment period. The secondary outcomes include changes in indexes of glycemic control, lipid metabolism, and oxidative stress, body composition, and safety evaluation.ResultsAlthough FMD tended to improve only in the dapagliflozin group, ΔFMD was comparable between the two groups. Analysis of patients with HbA1c >7.0% showed significant improvement of FMD in the dapagliflozin group than metformin group (P < 0.05). HbA1c, fasting plasma glucose, plasma glucagon, and body weight significantly decreased in both groups. Interestingly, urine 8-hydroxy-2′-deoxyguanosin, a biomarker of oxidative stress, was significantly lower in the dapagliflozin group than metformin group at 16 weeks (P < 0.001).ConclusionsDapagliflozin add-on therapy to metformin for 16 weeks improved endothelial function, as assessed by FMD, in patients with inadequately controlled early-stage T2DM. Improvement in oxidative stress may contribute to the improvement in FMD. Trial registration University Hospital Medical Information Network Clinical Trial Registry (UMIN000018754)Electronic supplementary materialThe online version of this article (doi:10.1186/s12933-017-0564-0) contains supplementary material, which is available to authorized users.

A central paradox in type 2 diabetes is the apparent selective nature of hepatic insulin resistance-wherein insulin fails to suppress hepatic glucose production yet continues to stimulate lipogenesis, resulting in hyperglycemia, hyperlipidemia, and hepatic steatosis. Although efforts to explain this have focused on finding a branch point in insulin signaling where hepatic glucose and lipid metabolism diverge, we hypothesized that hepatic triglyceride synthesis could be driven by substrate, independent of changes in hepatic insulin signaling. We tested this hypothesis in rats by infusing [U-13 C] palmitate to measure rates of fatty acid esterification into hepatic triglyceride while varying plasma fatty acid and insulin concentrations independently. These experiments were performed in normal rats, high fat-fed insulin-resistant rats, and insulin receptor 2′-O-methoxyethyl chimeric antisense oligonucleotide-treated rats. Rates of fatty acid esterification into hepatic triglyceride were found to be dependent on plasma fatty acid infusion rates, independent of changes in plasma insulin concentrations and independent of hepatocellular insulin signaling. Taken together, these results obviate a paradox of selective insulin resistance, because the major source of hepatic lipid synthesis, esterification of preformed fatty acids, is primarily dependent on substrate delivery and largely independent of hepatic insulin action.nonalcoholic fatty liver disease | hepatic insulin resistance | lipogenesis | esterification | mass spectrometry

Our results suggest that moderate weight reduction in obese subjects decreased IHL and augmented splanchnic glucose uptake. This mechanism is at least in part involved in improvement of glucose metabolism by moderate weight reduction in obese subjects.

Background: Few prospective studies have compared the cardiovascular benefits of sodium-glucose cotransporter-2 (SGLT2) inhibitors and dipeptidyl peptidase 4 (DPP-4) inhibitors. We aimed to clarify the efficacy of dapagliflozin versus sitagliptin for modulating cardiometabolic risk factors including high glycated hemoglobin (HbA1c) levels, hypoglycemia, and body weight. Methods: This prospective, randomized, open-label, blinded-endpoint, parallel-group trial enrolled 340 Japanese patients with early-stage type 2 diabetes receiving metformin alone or no glucose-lowering agents, who were randomized to receive dapagliflozin or sitagliptin for 24 weeks. The primary endpoint was the proportion of patients who achieved the composite endpoint of HbA1c level maintenance < 7.0% (53 mmol/mol), avoidance of hypoglycemia (maintenance of sensor glucose ≥ 3.0 mmol/L or ≥ 54 mg/dL), and ≥ 3.0% body weight loss from baseline. Secondary endpoints included components of the primary endpoint, other metabolic indices, and glucose variability indices measured using flash glucose monitoring. Results: Clinical characteristics of patients were age, 58.1 ± 12.2 years; known duration of diabetes, 5.8 ± 6.1 years; body weight, 74.7 ± 14.2 kg; body mass index, 27.9 ± 4.1 kg/m 2 ; and HbA1c level, 7.8 ± 0.8% at baseline. The achievement ratio of primary endpoint was significantly higher in the dapagliflozin group than in the sitagliptin group (24.4% vs. 13.8%, P < 0.05). While the rates of HbA1c level maintenance < 7.0% (53 mmol/mol) and avoidance of hypoglycemia were comparable between the groups (49.4 vs. 50.0% and 88.7 vs. 92.3% for dapagliflozin vs. sitagliptin, respectively), body weight loss of ≥ 3.0% was significantly achieved in the dapagliflozin group (54.4 vs. 19.6%, P < 0.001). Moreover, dapagliflozin was superior to sitagliptin regarding several secondary endpoints that modulate cardiometabolic risk, namely reducing fasting plasma glucose, insulin, uric acid, increasing high-density lipoprotein cholesterol, and suppressing the increase in serum creatinine and the decrease in estimated glomerular filtration rate. On the other hand, sitagliptin was superior to dapagliflozin in suppressing glucose variability.