Inhibition of De Novo Ceramide Synthesis Reverses Diet-Induced Insulin Resistance and Enhances Whole-Body Oxygen Consumption

OBJECTIVE - It has been proposed that skeletal muscle insulin resistance arises from the accumulation of intramyocellular lipid metabolites that impede insulin signaling, including diacylglycerol and ceramide. We determined the role of de novo ceramide synthesis in mediating muscle insulin resistance. RESEARCH DESIGN AND METHODS - Mice were subjected to 12 weeks of diet-induced obesity (DIO), and then treated for 4 weeks with myriocin, an inhibitor of serine palmitoyl transferase-1 (SPT1), the rate-limiting enzyme of de novo ceramide synthesis. RESULTS - After 12 weeks of DIO, C57BL/6 mice demonstrated a doubling in gastrocnemius ceramide content, which was completely reversed (141.5 ± 15.8 vs. 94.6 ± 10.2 nmol/g dry wt) via treatment with myriocin, whereas hepatic ceramide content was unaffected by DIO. Interestingly, myriocin treatment did not alter the DIO-associated increase in gastrocnemius diacyglycerol content, and the only correlation observed between lipid metabolite accumulation and glucose intolerance occurred with ceramide (R = 0.61). DIO mice treated with myriocin showed a complete reversal of glucose intolerance and insulin resistance which was associated with enhanced insulin-stimulated Akt and glycogen synthase kinase 3β phosphorylation. Furthermore, myriocin treatment also decreased intramyocellular ceramide content and prevented insulin resistance development in db/db mice. Finally, myriocin-treated DIO mice displayed enhanced oxygen consumption rates (3,041 ± 124 vs. 2,407 ± 124 ml/kg/h) versus their control counterparts. CONCLUSIONS - Our results demonstrate that the intramyocellular accumulation of ceramide correlates strongly with the development of insulin resistance, and suggests that inhibition of SPT1 is a potentially promising target for the treatment of insulin resistance. © 2010 by the American Diabetes Association.link_to_subscribed_fulltex

Inhibition of Soluble Epoxide Hydrolase Limits Mitochondrial Damage and Preserves Function Following Ischemic Injury

Aims: Myocardial ischemia can result in marked mitochondrial damage leading to cardiac dysfunction, as such identifying novel mechanisms to limit mitochondrial injury is important. This study investigated the hypothesis that inhibiting soluble epoxide hydrolase (sEH), responsible for converting epoxyeicosatrienoic acids to dihydroxyeicosatrienoic acids protects mitochondrial from injury caused by myocardial infarction. Methods: sEH null and WT littermate mice were subjected to surgical occlusion of the left anterior descending (LAD) artery or sham operation. A parallel group of WT mice received an sEH inhibitor, trans-4-[4-(3-adamantan-1-y1-ureido)-cyclohexyloxy]-benzoic acid (tAUCB; 10 mg/L) or vehicle in the drinking water 4 days prior and 7 days post-MI. Cardiac function was assessed by echocardiography prior- and 7-days post-surgery. Heart tissues were dissected into infarct, peri-, and non-infarct regions to assess ultrastructure by electron microscopy. Complexes I, II, IV, citrate synthase, PI3K activities, and mitochondrial respiration were assessed in non-infarct regions. Isolated working hearts were used to measure the rates of glucose and palmitate oxidation. Results: Echocardiography revealed that tAUCB treatment or sEH deficiency significantly improved systolic and diastolic function post-MI compared to controls. Reduced infarct expansion and less adverse cardiac remodeling were observed in tAUCB-treated and sEH null groups. EM data demonstrated mitochondrial ultrastructure damage occurred in infarct and peri-infarct regions but not in non-infarct regions. Inhibition of sEH resulted in significant improvements in mitochondrial respiration, ATP content, mitochondrial enzymatic activities and restored insulin sensitivity and PI3K activity. Conclusion: Inhibition or genetic deletion of sEH protects against long-term ischemia by preserving cardiac function and maintaining mitochondrial efficiency

Nrg4 promotes fuel oxidation and a healthy adipokine profile to ameliorate diet-induced metabolic disorders

OBJECTIVE: Brown and white adipose tissue exerts pleiotropic effects on systemic energy metabolism in part by releasing endocrine factors. Neuregulin 4 (Nrg4) was recently identified as a brown fat-enriched secreted factor that ameliorates diet-induced metabolic disorders, including insulin resistance and hepatic steatosis. However, the physiological mechanisms through which Nrg4 regulates energy balance and glucose and lipid metabolism remain incompletely understood. The aims of the current study were: i) to investigate the regulation of adipose Nrg4 expression during obesity and the physiological signals involved, ii) to elucidate the mechanisms underlying Nrg4 regulation of energy balance and glucose and lipid metabolism, and iii) to explore whether Nrg4 regulates adipose tissue secretome gene expression and adipokine secretion. METHODS: We examined the correlation of adipose Nrg4 expression with obesity in a cohort of diet-induced obese mice and investigated the upstream signals that regulate Nrg4 expression. We performed metabolic cage and hyperinsulinemic-euglycemic clamp studies in Nrg4 transgenic mice to dissect the metabolic pathways regulated by Nrg4. We investigated how Nrg4 regulates hepatic lipid metabolism in the fasting state and explored the effects of Nrg4 on adipose tissue gene expression, particularly those encoding secreted factors. RESULTS: Adipose Nrg4 expression is inversely correlated with adiposity and regulated by pro-inflammatory and anti-inflammatory signaling. Transgenic expression of Nrg4 increases energy expenditure and augments whole body glucose metabolism. Nrg4 protects mice from diet-induced hepatic steatosis in part through activation of hepatic fatty acid oxidation and ketogenesis. Finally, Nrg4 promotes a healthy adipokine profile during obesity. CONCLUSIONS: Nrg4 exerts pleiotropic beneficial effects on energy balance and glucose and lipid metabolism to ameliorate obesity-associated metabolic disorders. Biologic therapeutics based on Nrg4 may improve both type 2 diabetes and non-alcoholic fatty liver disease (NAFLD) in patients

Obesity and type 2 diabetes have additive effects on left ventricular remodelling in normotensive patients-a cross sectional study

BackgroundIt is unclear whether obesity and type 2 diabetes (T2D), either alone or in combination, induce left ventricular hypertrophy (LVH) independent of hypertension. In the current study, we provide clarity on this issue by rigorously analysing patient left ventricular (LV) structure via clinical indices and via LV geometric patterns (more commonly used in research settings). Importantly, our sample consisted of hypertensive patients that are routinely screened for LVH via echocardiography and normotensive patients that would normally be deemed low risk with no further action required.MethodsThis cross sectional study comprised a total of 353 Caucasian patients, grouped based on diagnosis of obesity, T2D and hypertension, with normotensive obese patients further separated based on metabolic health. Basic metabolic parameters were collected and LV structure and function were assessed via transthoracic echocardiography. Multivariable logistic and linear regression analyses were used to identify predictors of LVH and diastolic dysfunction.ResultsMetabolically healthy normotensive obese patients exhibited relatively low risk of LVH. However, normotensive metabolically non-healthy obese, T2D and obese/T2D patients all presented with reduced normal LV geometry that coincided with increased LV concentric remodelling. Furthermore, normotensive patients presenting with both obesity and T2D had a higher incidence of concentric hypertrophy and grade 3 diastolic dysfunction than normotensive patients with either condition alone, indicating an additive effect of obesity and T2D. Alarmingly these alterations were at a comparable prevalence to that observed in hypertensive patients. Interestingly, assessment of LVPWd, a traditional index of LVH, underestimated the presence of LV concentric remodelling. The implications for which were demonstrated by concentric remodelling and concentric hypertrophy strongly associating with grade 1 and 3 diastolic dysfunction respectively, independent of sex, age and BMI. Finally, pulse pressure was identified as a strong predictor of LV remodelling within normotensive patients.ConclusionsThese findings show that metabolically non-healthy obese, T2D and obese/T2D patients can develop LVH independent of hypertension. Furthermore, that LVPWd may underestimate LV remodelling in these patient groups and that pulse pressure can be used as convenient predictor of hypertrophy status.<br /

The Alberta Heart Failure Etiology and Analysis Research Team (HEART) study

Background Nationally, symptomatic heart failure affects 1.5-2% of Canadians, incurs $3 billion in hospital costs annually and the global burden is expected to double in the next 1–2 decades. The current one-year mortality rate after diagnosis of heart failure remains high at >25%. Consequently, new therapeutic strategies need to be developed for this debilitating condition. Methods/Design The objective of the Alberta HEART program (http://albertaheartresearch.ca) is to develop novel diagnostic, therapeutic and prognostic approaches to patients with heart failure with preserved ejection fraction. We hypothesize that novel imaging techniques and biomarkers will aid in describing heart failure with preserved ejection fraction. Furthermore, the development of new diagnostic criteria will allow us to: 1) better define risk factors associated with heart failure with preserved ejection fraction; 2) elucidate clinical, cellular and molecular mechanisms involved with the development and progression of heart failure with preserved ejection fraction; 3) design and test new therapeutic strategies for patients with heart failure with preserved ejection fraction. Additionally, Alberta HEART provides training and education for enhancing translational medicine, knowledge translation and clinical practice in heart failure. This is a prospective observational cohort study of patients with, or at risk for, heart failure. Patients will have sequential testing including quality of life and clinical outcomes over 12 months. After that time, study participants will be passively followed via linkage to external administrative databases. Clinical outcomes of interest include death, hospitalization, emergency department visits, physician resource use and/or heart transplant. Patients will be followed for a total of 5 years. Discussion Alberta HEART has the primary objective to define new diagnostic criteria for patients with heart failure with preserved ejection fraction. New criteria will allow for targeted therapies, diagnostic tests and further understanding of the patients, both at-risk for and with heart failure

Inhibition of Serine Palmitoyl Transferase I Reduces Cardiac Ceramide Levels and Increases Glycolysis Rates following Diet-Induced Insulin Resistance

Objective: Diet-induced obesity (DIO) leads to an accumulation of intra-myocardial lipid metabolites implicated in causing cardiac insulin resistance and contractile dysfunction. One such metabolite is ceramide, and our aim was to determine the effects of inhibiting de novo ceramide synthesis on cardiac function and insulin stimulated glucose utilization in mice subjected to DIO. Materials and Methods: C57BL/6 mice were fed a low fat diet or subjected to DIO for 12 weeks, and then treated for 4 weeks with either vehicle control or the serine palmitoyl transferase I (SPT I) inhibitor, myriocin. In vivo cardiac function was assessed via ultrasound echocardiography, while glucose metabolism was assessed in isolated working hearts. Results: DIO was not associated with an accumulation of intra-myocardial ceramide, but rather, an accumulation of intra-myocardial DAG (2.63±0.41 vs. 4.80±0.97 nmol/g dry weight). Nonetheless, treatment of DIO mice with myriocin decreased intra-myocardial ceramide levels (50.3±7.7 vs. 26.9±2.7 nmol/g dry weight) and prevented the DIO-associated increase in intra-myocardial DAG levels. Interestingly, although DIO impaired myocardial glycolysis rates (7789±1267 vs. 2671±326 nmol/min/g dry weight), hearts from myriocin treated DIO mice exhibited an increase in glycolysis rates. Conclusions: Our data reveal that although intra-myocardial ceramide does not accumulate following DIO, inhibition of de novo ceramide synthesis nonetheless reduces intra-myocardial ceramide levels and prevents the accumulation of intra-myocardial DAG. These effects improved the DIO-associated impairment of cardiac glycolysis rates, suggesting that SPT I inhibition increases cardiac glucose utilization. © 2012 Ussher et al.published_or_final_versio