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

Aerobic Training in Rats Increases Skeletal Muscle Sphingomyelinase and Serine Palmitoyltransferase Activity, While Decreasing Ceramidase Activity

Sphingolipids are important components of cell membranes that may also serve as cell signaling molecules; ceramide plays a central role in sphingolipid metabolism. The aim of this study was to examine the effect of 5 weeks of aerobic training on key enzymes and intermediates of ceramide metabolism in skeletal muscles. The experiments were carried out on rats divided into two groups: (1) sedentary and (2) trained for 5 weeks (on a treadmill). The activity of serine palmitoyltransferase (SPT), neutral and acid sphingomyelinase (nSMase and aSMase), neutral and alkaline ceramidases (nCDase and alCDase) and the content of sphingolipids was determined in three types of skeletal muscle. We also measured the fasting plasma insulin and glucose concentration for calculating HOMA-IR (homeostasis model assessment) for estimating insulin resistance. We found that the activities of aSMase and SPT increase in muscle in the trained group. These changes were followed by elevation in the content of sphinganine. The activities of both isoforms of ceramidase were reduced in muscle in the trained group. Although the activities of SPT and SMases increased and the activity of CDases decreased, the ceramide content did not change in any of the studied muscle. Although ceramide level did not change, we noticed increased insulin sensitivity in trained animals. It is concluded that training affects the activity of key enzymes of ceramide metabolism but also activates other metabolic pathways which affect ceramide metabolism in skeletal muscles

Characterising the inhibitory actions of ceramide upon insulin signaling in different skeletal muscle cell models:a mechanistic insight

International audienceCeramides are known to promote insulin resistance in a number of metabolically important tissues including skeletal muscle, the predominant site of insulin-stimulated glucose disposal. Depending on cell type, these lipid intermediates have been shown to inhibit protein kinase B (PKB/Akt), a key mediator of the metabolic actions of insulin, via two distinct pathways: one involving the action of atypical protein kinase C (aPKC) isoforms, and the second dependent on protein phosphatase-2A (PP2A). The main aim of this study was to explore the mechanisms by which ceramide inhibits PKB/Akt in three different skeletal muscle-derived cell culture models; rat L6 myotubes, mouse C2C12 myotubes and primary human skeletal muscle cells. Our findings indicate that the mechanism by which ceramide acts to repress PKB/Akt is related to the myocellular abundance of caveolin-enriched domains (CEM) present at the plasma membrane. Here, we show that ceramide-enriched-CEMs are markedly more abundant in L6 myotubes compared to C2C12 myotubes, consistent with their previously reported role in coordinating aPKC-directed repression of PKB/Akt in L6 muscle cells. In contrast, a PP2A-dependent pathway predominantly mediates ceramide-induced inhibition of PKB/Akt in C2C12 myotubes. In addition, we demonstrate for the first time that ceramide engages an aPKC-dependent pathway to suppress insulin-induced PKB/Akt activation in palmitate-treated cultured human muscle cells as well as in muscle cells from diabetic patients. Collectively, this work identifies key mechanistic differences, which may be linked to variations in plasma membrane composition, underlying the insulin-desensitising effects of ceramide in different skeletal muscle cell models that are extensively used in signal transduction and metabolic studies

Editorial: The Role of Sphingolipid Metabolism in the Development of Type 2 Diabetes and Obesity

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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

Sphingolipid Analysis Indicate Lactosylceramide as a Potential Biomarker of Inflammatory Bowel Disease in Children

An altered ceramide composition in patients with inflammatory bowel disease (IBD) has been reported recently. The aim of this study was to evaluate the concentrations of sphingolipids in the serum of treatment-naive children with newly diagnosed IBD and to determine the diagnostic value of the tested lipids in pediatric IBD. The concentrations of sphingolipids in serum samples were evaluated using a quantitative method, an ultra-high-performance liquid chromatography-tandem mass spectrometry in children with Crohn&rsquo;s disease (CD) (n=34), ulcerative colitis (UC) (n = 39), and controls (Ctr) (n = 24). Among the study groups, the most significant differences in concentrations were noted for C16:0-LacCer, especially in children with CD compared to Ctr or even to UC. Additionally, the relevant increase in C20:0-Cer and C18:1-Cer concentrations were detected in both IBD groups compared to Ctr. The enhanced C24:0-Cer level was observed only in UC, while C18:0-Cer only in the CD group. The highest area under the curve (AUC), specificity, and sensitivity were determined for C16:0-LacCer in CD diagnosis. Our results suggest that the serum LacC16-Cer may be a potential biomarker that distinguishes children with IBD from healthy controls and differentiates IBD subtypes. In addition, C20:0-Cer and C18:0-Cer levels also seem to be closely connected with IBD

Maternal plasma and amniotic fluid sphingolipids profiling in fetal Down syndrome.

INTRODUCTION:Sphingolipids can be potentially involved in the formation of the central and peripheral nervous systems, which are particularly connected with the pathogenesis of Down syndrome. The aim of the study was to determine the concentration of selected sphingolipids in the plasma and amniotic fluid of pregnant patients with fetal Down syndrome. MATERIAL AND METHODS:Out of 190 amniocentesis we had 10 patients with confirmed Down syndrome. For the purpose of our control we chose 14 women without confirmed chromosomal aberration. To assess the concentration of 11 sphingolipids in the blood plasma and amniotic fluid we used an ultra-high performance liquid chromatography coupled with triple quadrupole mass spectrometry (UHPLC/MS/MS). RESULTS:We showed a significant increase in the concentration of 2 ceramides, C22-Cer and C24:1-Cer, in the plasma of women with fetal Down syndrome. Furthermore we showed a decrease in the concentration of 7 ceramides--C16-Cer, C18-Cer, C18:1-Cer, C20-Cer, C22-Cer, C24:1-Cer, and C24-Cer--in the amniotic fluid of women with fetal Down syndrome. We created ROC curves for all significant sphingolipids in maternal plasma, which set the threshold values and allowed for predicting the likelihood of Down syndrome in the fetus with specific sensitivity and specificity. We demonstrated a significantly higher risk of Down syndrome when the plasma concentration of C22-Cer > 12.66 ng/100 ul (sens. 0.9, sp. 0.79, P value = 0.0007) and C24:1-Cer > 33,19 ng/100 ul (sens. 0.6, sp. 0.86, P value = 0.0194). CONCLUSION:On the basis of our findings, it seems that the sphingolipids may play a role in the pathogenesis of Down syndrome. Defining their potential as biochemical markers of Down syndrome requires further investigation on a larger group of patients

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

Sphingolipids as a new factor in the pathomechanism of preeclampsia - Mass spectrometry analysis.

OBJECTIVE(S) AND DESIGN:The aim of the study was to analyse a panel of 11 sphingolipids in plasma and three blood fractions (platelet-poor plasma, platelets and red blood cells) of women with mild preeclampsia. MATERIALS AND METHODS:We recruited 21 women between 25-40 weeks gestation with diagnosed mild preeclampsia to the study group and 36 healthy women with uncomplicated pregnancies, who corresponded with the study group according to gestational age, to the control group. To assess the concentration of 11 sphingolipids in the blood plasma and blood fractions, we used ultra-high performance liquid chromatography coupled with triple quadrupole mass spectrometry (UHPLC/MS/MS). RESULTS:We showed a significant increase in the concentration of eight sphingolipids in the plasma of women with preeclampsia in comparison to the control group: Sph (p = 0.0032), S1P (p = 0.0289), C20-Cer (p < 0.0001), C18-Cer (p < 0.0001), C16-Cer (p = 0.012), C18:1-Cer (p = 0.003), C22-Cer (p = 0.0071), and C24:1-Cer (p = 0.0085). CONCLUSION:We showed that selected sphingolipids, especially C20-Cer and C18-Cer, are totally new factors in the pathomechanism of PE and that these bioactive lipids may play an important role in apoptosis and autophagy