Training Does Not Alter Muscle Ceramide and Diacylglycerol in Offsprings of Type 2 Diabetic Patients Despite Improved Insulin Sensitivity

Ceramide and diacylglycerol (DAG) may be involved in the early phase of insulin resistance but data are inconsistent in man. We evaluated if an increase in insulin sensitivity after endurance training was accompanied by changes in these lipids in skeletal muscle. Nineteen first-degree type 2 diabetes Offsprings (Offsprings) (age: 33.1±1.4 yrs; BMI: 26.4±0.4 kg/m2) and sixteen matched Controls (age: 31.3±1.5 yrs; BMI: 25.3±0.7 kg/m2) performed 10 weeks of endurance training three times a week at 70% of VO2max on a bicycle ergometer. Before and after the intervention a hyperinsulinemic-euglycemic clamp and VO2max test were performed and muscle biopsies obtained. Insulin sensitivity was significantly lower in Offsprings compared to control subjects (p<0.01) but improved in both groups after 10 weeks of endurance training (Off: 17±6%; Con: 12±9%, p<0.01). The content of muscle ceramide, DAG, and their subspecies were similar between groups and did not change in response to the endurance training except for an overall reduction in C22:0-Cer (p<0.05). Finally, the intervention induced an increase in AKT protein expression (Off: 27±11%; Con: 20±24%, p<0.05). This study showed no relation between insulin sensitivity and ceramide or DAG content suggesting that ceramide and DAG are not major players in the early phase of insulin resistance in human muscle

The Crucial Role of C18-Cer in Fat-Induced Skeletal Muscle Insulin Resistance

Background/Aims: Muscle bioactive lipids accumulation leads to several disorder states. The most common are insulin resistance (IR) and type 2 diabetes. There is an ongoing debate which of the lipid species plays the major role in induction of muscle IR. Our aim was to elucidate the role of particular lipid group in induction of muscle IR. Methods: The analyses were performed on muscle from the following groups of rats: 1. Control, fed standard diet, 2 HFD, fed high fat diet, 3. HFD/Myr, fed HFD and treated with myriocin (Myr), an inhibitor of ceramide de novo synthesis. We utilized [U13C] palmitate isotope tracer infusion and mass spectrometry to measure content and synthesis rate of muscle long-chain acyl-CoA (LCACoA), diacylglycerols (DAG) and ceramide (Cer). Results: HFD led to intramuscular accumulation of LCACoA, DAG and Cer and skeletal muscle IR. Myr-treatment caused decrease in Cer (most noticeable for stearoyl-Cer and oleoyl-Cer) and accumulation of DAG, possibly due to re-channeling of excess of intramuscular LCACoA towards DAG synthesis. An improvement in insulin sensitivity at both systemic and muscular level coincided with decrease in ceramide, despite elevated intramuscular DAG. Conclusion: The improved insulin sensitivity was associated with decreased muscle stearoyl- and oleoyl-ceramide content. The results indicate that accumulation of those ceramide species has the greatest impact on skeletal muscle insulin sensitivity in rats

Insulin-Sensitizing Effect of LXR Agonist T0901317 in High-Fat Fed Rats is Associated with Restored Muscle GLUT4 Expression and Insulin-Stimulated AS160 Phosphorylation

Background/Aim: Liver X receptors (LXRs) are ligand-activated transcription factors that were shown to stimulate hepatic lipogenesis leading to liver steatosis and hypertriglyceridemia. Despite their pro-lipogenic action, LXR activators normalize glycemia and improve insulin sensitivity in rodent models of type 2 diabetes. Antidiabetic action of LXR agonists is thought to result from suppression of hepatic gluconeogenesis. However, it remains unclear whether LXR activation affects muscle insulin sensitivity. In the present study we attempted to answer this question. Methods: The experiments were performed on male Wistar rats fed for 5 weeks on either standard chow or high fat diet. The latter group was further divided into two subgroups receiving either selective LXR agonist - T0901317 (10mg/kg/d) or vehicle during the last week of the experiment. All animals were then anaesthetized and samples of the soleus as well as red and white sections of the gastrocnemius muscle were excised. Results: As expected, administration of T0901317 to high-fat fed rats augmented diet-induced hyperlipidemia. Nevertheless, it also normalized glucose tolerance and improved insulin-stimulated glucose uptake in isolated soleus muscle. In addition, LXR agonist completely restored glucose transporter 4 expression and insulin-stimulated Akt substrate of 160 kDa phosphorylation in all investigated muscles. Insulin-sensitizing effect of T0901317 was not related to changes in intramuscular level of lipid mediators of insulin resistance, since neither diacylglycerols nor ceramide content was affected by the treatment. Conclusion: We conclude that improvement in muscle insulin sensitivity is one of the mechanisms underlying the antidiabetic action of LXR activators

Inhibition of Ceramide De Novo Synthesis Affects Adipocytokine Secretion and Improves Systemic and Adipose Tissue Insulin Sensitivity

Ceramide accumulation in muscle and in liver is implicated in the induction of insulin resistance. Much less in known about the role of ceramide in adipose tissue. The aim of the present study was to elucidate the role of ceramide in adipose tissue and to clarify whether lipids participate in the regulation of adipocytokine secretion. The experiments were performed on male Wistar rats divided into three groups: 1. Control, 2. fed high fat diet (HFD), and 3. fed HFD and treated with myriocin. Ceramide (Cer) and diacylglycerol (DAG) content were analyzed by LC/MS/MS. Hormone sensitive lipase (HSL) phosphorylation was analyzed by Western Blot. Plasma adiponectin and tumor necrosis factor alpha (TNF-&#945;) concentration were measured by enzyme-linked immunosorbent assay. An oral glucose tolerance test (OGTT) and insulin tolerance test (ITT) was also performed. In HFD group, total DAG and Cer content was elevated in both subcutaneous and visceral adipose tissue, which was accompanied by increased glucose, insulin, and HOMA-IR value. Myriocin treatment restored HOMA-IR as well as glucose and insulin concentration to control values. Moreover, myriocin decreased not only Cer, but also DAG levels in both fat depots. Furthermore, we observed a strong correlation between adiponectin (negative) and TNF-&#945; (positive) and Cer in both fat tissues, which suggests that Cer is involved in the regulation of adipocytokine secretion