Jan Górski

Exercise and training effects on ceramide metabolism in human skeletal muscle

In rat skeletal muscle prolonged exercise affects the content and composition of ceramides, but in human skeletal muscle no data are available on this compound. Our aim was to examine the content of ceramide‐ and sphingomyelin fatty acids and neutral, Mg2+‐dependent sphingomyelinase activity in skeletal muscle in untrained and trained subjects before and after prolonged exercise. Healthy male subjects were recruited into an untrained (n= 8, VO2,max 3.8 ± 0.2 l min1) and a trained (n= 8, VO2,max 5.1 ± 0.1 l min1) group. Before and after a 3‐h exercise bout (58 ± 1%VO2,max) a muscle biopsy was excised from the vastus lateralis. Ceramide and sphingomyelin were isolated using thin‐layer chromatography. The content of individual ceramide fatty acids and sphingomyelin fatty acids was measured by means of gas‐liquid chromatography. The activity of neutral, Mg2+‐dependent sphingomyelinase was measured using N‐[14CH3]‐sphingomyelin as a substrate. Prior to exercise, the muscle total ceramide fatty acid content in both groups was similar (201 ± 18 and 197 ± 9 nmol g−1 in the untrained and trained group, respectively) and after exercise a 25% increase in the content was observed in each group. At rest, the muscle total sphingomyelin fatty acid content was higher in untrained than in trained subjects (456 ± 10, 407 ± 7 nmol g−1, respectively; P < 0.05). After exercise a 20% increase (P < 0.05) in total sphingomyelin was observed only in the trained subjects. The muscle neutral, Mg2+‐dependent sphingomyelinase activity was similar in the two groups at rest and a similar reduction was observed after exercise in both groups (untrained from 2.19 ± 0.08 to 1.78 ± 0.08 and trained from 2.31 ± 0.12 to 1.80 ± 0.09 nmol (mg protein)−1 h−1; P < 0.05 in each case). In conclusion, we have reported, for the first time, the values for ceramide fatty acid content and neutral, Mg2+‐dependent sphingomyelinase activity in human skeletal muscle. The results indicate that acute prolonged exercise affects ceramide metabolism in human skeletal muscle both in untrained and in trained subjects and this may influence muscle cell adaptation and metabolism.

AMP-activated Protein Kinase α2 Subunit is Required for the Preservation of Hepatic Insulin Sensitivity by n-3 Polyunsaturated Fatty Acids

OBJECTIVE The induction of obesity, dyslipidemia, and insulin resistance by high-fat diet in rodents can be prevented by n-3 long-chain polyunsaturated fatty acids (LC-PUFAs). We tested a hypothesis whether AMP-activated protein kinase (AMPK) has a role in the beneficial effects of n-3 LC-PUFAs. RESEARCH DESIGN AND METHODS Mice with a whole-body deletion of the α2 catalytic subunit of AMPK (AMPKα2−/−) and their wild-type littermates were fed on either a low-fat chow, or a corn oil-based high-fat diet (cHF), or a cHF diet with 15% lipids replaced by n-3 LC-PUFA concentrate (cHF+F). RESULTS Feeding a cHF diet induced obesity, dyslipidemia, hepatic steatosis, and whole-body insulin resistance in mice of both genotypes. Although cHF+F feeding increased hepatic AMPKα2 activity, the body weight gain, dyslipidemia, and the accumulation of hepatic triglycerides were prevented by the cHF+F diet to a similar degree in both AMPKα2−/− and wild-type mice in ad libitum-fed state. However, preservation of hepatic insulin sensitivity by n-3 LC-PUFAs required functional AMPKα2 and correlated with the induction of adiponectin and reduction in liver diacylglycerol content. Under hyperinsulinemic-euglycemic conditions, AMPKα2 was essential for preserving low levels of both hepatic and plasma triglycerides, as well as plasma free fatty acids, in response to the n-3 LC-PUFA treatment. CONCLUSIONS Our results show that n-3 LC-PUFAs prevent hepatic insulin resistance in an AMPKα2-dependent manner and support the role of adiponectin and hepatic diacylglycerols in the regulation of insulin sensitivity. AMPKα2 is also essential for hypolipidemic and antisteatotic effects of n-3 LC-PUFA under insulin-stimulated conditions.

Characterization of free and glyceride-esterified long chain fatty acids in different skeletal muscle types of the rat.

The plasma-borne long-chain free fatty acids (FFA) enter skeletal muscle cells. Upon entering they are oxidized or esterified and a fraction remains free (non-esterified). The data on free fatty acids in skeletal muscles remain highly controversial. Furthermore, the composition of individual fatty acids in various lipid fractions including free fatty acids, monoglyceride and diglyceride in muscles has not been characterized. Also data on the composition of fatty acids esterified into muscle triglycerides and phospholipids are incomplete. The present study was undertaken to examine a composition of fatty acids in lipid fractions of different skeletal muscle types. For this purpose, samples of the rat soleus, red and white portions of gastrocnemius were excised, trimmed of visible fat and fascias and immediately frozen in liquid nitrogen. Samples were then pulverized and, lipids were extracted and fractionated by thin-layer chromatography. Individual long-chain fatty acids in different fractions were identified, characterized and quantitated by gas-liquid chromatography. FFA composition in the plasma was also determined. The total FFA content in the soleus, red and white gastrocnemius was 69.1 ± 10.8, 49.0 ± 13.6 and 22.7 ± 8.6 nmol/g, respectively. Palmitic and oleic acids were the major fatty acids in the muscles FFA fraction. Monoglyceride fraction of each muscle contained palmitic, stearic and linoleic acid as the major fatty acids, Diglyceride fraction contained mostly palmitic and oleic acid whereas triglyceride fraction mostly palmitic and linoleic acid.. The fraction of phospholipids was composed mostly of palmitic and linoleic acid but contained also considerable percentage of archidonic acid. Total plasma FFA/muscle FFA ratio depended on a muscle type and was: 2.4 in the soleus, 3.5 in the red and 7.4 in the white gastrocnemius. This assured transport of FFA to the myocytes. However, there were great differences in the ratio between particular FFA within the same muscle as well between the muscles. It indicates that individual FFA are either selectively transported from the plasma to the muscles or selectively used within the myocytes or both.

Hypoxia-induced fatty acid transporter translocation increases fatty acid transport and contributes to lipid accumulation in the heart.

Protein‐mediated LCFA transport across plasma membranes is highly regulated by the fatty acid transporters FAT/CD36 and FABPpm. Physiologic stimuli (insulin stimulation, AMP kinase activation) induce the translocation of one or both transporters to the plasma membrane and increase the rate of LCFA transport. In the hypoxic/ischemic heart, intramyocardial lipid accumulation has been attributed to a reduced rate of fatty acid oxidation. However, since acute hypoxia (15 min) activates AMPK, we examined whether an increased accumulation of intramyocardial lipid during hypoxia was also attributable to an increased rate of LCFA uptake as a result AMPK‐induced translocation of FAT/CD36 and FABPpm. In cardiac myocytes, hypoxia (15 min) induced the redistribution of FAT/CD36 from an intracellular pool (LDM) (−25%, P < 0.05) to the plasma membranes (PM) (+54%, P < 0.05). Hypoxia also induced an increase in FABPpm at the PM (+56%, P < 0.05) and a concomitant FABPpm reduction in the LDM (−24%, P < 0.05). Similarly, in intact, Langendorff perfused hearts, hypoxia induced the translocation of a both FAT/CD36 and FABPpm to the PM (+66% and +61%, respectively, P < 0.05), with a concomitant decline in FAT/CD36 and FABPpm in the LDM (−24% and −23%, respectively, P < 0.05). Importantly, the increased plasmalemmal content of these transporters was associated with increases in the initial rates of palmitate uptake into cardiac myocytes (+40%, P < 0.05). Acute hypoxia also redirected palmitate into intracellular lipid pools, mainly to PL and TG (+48% and +28%, respectively, P < 0.05), while fatty acid oxidation was reduced (−35%, P < 0.05). Thus, our data indicate that the increased intracellular lipid accumulation in hypoxic hearts is attributable to both: (a) a reduced rate of fatty acid oxidation and (b) an increased rate of fatty acid transport into the heart, the latter being attributable to a hypoxia‐induced translocation of fatty acid transporters.

Inhibition of ceramide de novo synthesis reduces liver lipid accumulation in rats with nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is an insulin resistance‐related hepatic disorder which can transform to cirrhosis. Insulin resistance deregulates hepatic lipid metabolism, leading to accumulation of cytotoxic lipids including ceramide and diacylglycerols. Myriocin, obtained from fungi traditionally used in Chinese medicine in an effort to attain eternal youth, is a potent pharmacological inhibitor of ceramide de novo synthesis. We examined whether inhibition of ceramide de novo synthesis with myriocin ameliorate hepatic lipid accumulation and reverse NAFLD.

Ceramide metabolism is affected by obesity and diabetes in human adipose tissue.

Ceramide is involved in development of insulin resistance. However, there are no data on ceramide metabolism in human adipose tissue. The aim of our study was to examine sphingolipid metabolism in fat tissue from obese nondiabetic (n = 11), obese diabetic (n = 11), and lean nondiabetic (n = 8) subjects. The content of ceramide (Cer), dihydroceramide (dhCer), sphingosine (SPH), sphinganine (SPA), sphingosine‐1‐phosphate (S1P; pmol/mg of protein), the expression (mRNA) and activity of key enzymes responsible for Cer metabolism: serine palmitoyltransferase (SPT), neutral and acidic sphingomyelinase (nSMase and aSMase, respectively), and neutral and acidic ceramidase (nCDase and aCDase, respectively) were examined in human adipose tissue. The contents of SPA and Cer were significantly lower whereas the content of dhCer was higher in both obese groups than the respective values in the lean subjects. The expression of examined enzymes was elevated in both obese groups. The SPT and CDases activity increased whereas aSMase activity deceased in both obese groups. We have found correlation between adipose tissue Cer content and plasma adiponectin concentration (r = 0.69, P < 0.001) and negative correlation between total Cer content and HOMA‐IR index (homeostasis model of insulin resistance) (r = −0.67, P < 0.001). We have found that both obesity and diabetes affected pathways of sphingolipid metabolism in the adipose tissue. J. Cell. Physiol. 227: 550–557, 2012.

Intrathecal increase of sphingosine 1-phosphate at early stage multiple sclerosis

Sphingosine 1-phosphate (S1P) is a pleiotropic mediator that is critically involved in the development of an inflammatory response in various pathological conditions. We hypothesize that during the course of multiple sclerosis (MS) development, chronic inflammation will result in the alteration of S1P levels in blood and cerebrospinal fluid (CSF). We evaluated S1P concentrations in blood and CSF obtained from 66 subjects, including 40 patients diagnosed with MS and 26 subjects of a control group that included patients diagnosed with idiopathic cephalgia and idiopathic (Bells) facial nerve palsy. HPLC techniques were used to determine S1P levels. We found that S1P concentrations in blood of the MS subject group (361.7+/-150.7 nM) did not differ from those of the control group (371.9+/-142.5 nM). However, S1P concentrations in CSF of the MS group were significantly higher (p<0.01) compared to the control group (2.2+/-2.7 versus 0.69+/-1.1 nM). The increase of S1P concentration in CSF of MS subjects suggests that this bioactive lipid is involved in chronic inflammation associated with MS and it may be useful to study S1P in a number of neurodegenerative diseases to provide better understanding of the mechanisms governing their development.

Effect of high fat diet enriched with unsaturated and diet rich in saturated fatty acids on sphingolipid metabolism in rat skeletal muscle

Consumption of high fat diet leads to muscle lipid accumulation which is an important factor involved in induction of insulin resistance. Ceramide is likely to partially inhibit insulin signaling cascade. The aim of this study was to examine the effect of different high fat diets on ceramide metabolism in rat skeletal muscles. The experiments were carried out on rats fed for 5 weeks: (1) a standard chow and (2) high fat diet rich in polyunsaturated fatty acids (PUFA) and (3) diet enriched with saturated fatty acids (SAT). Assays were performed on three types of muscles: slow‐twitch oxidative (soleus), fast‐twitch oxidative–glycolytic, and fast‐twitch glycolytic (red and white section of the gastrocnemius, respectively). The activity of serine palmitoyltransferase (SPT), neutral and acid sphingomyelinase (n‐ and aSMase), and neutral and alkaline ceramidase (n‐ and alCDase) was examined. The content of ceramide, sphinganine, sphingosine, and sphingosine‐1‐phosphate was also measured. The ceramide content did not change in any muscle from PUFA diet group but increased in the SAT diet group by 46% and 52% in the soleus and red section of the gastrocnemius, respectively. Elevated ceramide content in the SAT diet group could be a result of increased SPT activity and simultaneously decreased activity of nCDase. Unchanged ceramide content in the PUFA diet group might be a result of increased activity of SPT and alCDase and simultaneously decreased activity of SMases. We conclude that regulation of muscle ceramide level depends on the diet and type of skeletal muscle. J. Cell. Physiol. 225: 786–791, 2010.

Myocardium of type 2 diabetic and obese patients is characterized by alterations in sphingolipid metabolic enzymes but not by accumulation of ceramide

Data from animal experiments strongly suggest that ceramide is an important mediator of lipotoxicity in the heart and that accumulation of ceramide contributes to cardiomyocyte apoptosis associated with type 2 diabetes and obesity. However, it remains unknown whether a similar relationship is present also in the human heart. Therefore, we aimed to examine whether myocardial apoptosis in obese and type 2 diabetic patients is associated with elevated ceramide level. The study included 11 lean and 26 overweight or moderately obese subjects without (n = 11, OWT) or with (n = 15, T2D-OWT) a history of type 2 diabetes. Samples of the right atrial appendage were obtained from patients at the time of coronary bypass surgery. Compared with lean subjects, the extent of DNA fragmentation (a marker of apoptosis) was significantly higher in the myocardium of OWT patients and increased further in T2D-OWT subjects. However, the content of ceramide and sphingoid bases remained stable. Interestingly, the mRNA level of enzymes involved in synthesis and degradation of ceramide including serine palmitoyltransferase, sphingosine kinase 1, neutral sphingomyelinase, and ceramidases was markedly higher in the myocardium of OWT and T2D-OWT patients compared with lean subjects. Our results indicate that in the human heart, or at least in the atrium, ceramide is not a major factor in cardiomyocyte apoptosis associated with obesity and type 2 diabetes.

Plasma gelsolin modulates cellular response to sphingosine 1-phosphate.

Hypogelsolinemia is observed in patients with different states of acute or chronic inflammation such as sepsis, rheumatoid arthritis, and multiple sclerosis. In animal models of sepsis, repletion of plasma gelsolin reduces septic mortality. However, the functions of extracellular gelsolin and the mechanisms leading to its protective nature are poorly understood. Potential mechanisms involve gelsolins extracellular actin scavenging function or its ability to bind bioactive lipids or proinflammatory mediators, which would limit inflammatory responses and prevent tissue damage. Here we report that human plasma gelsolin binds to sphingosine 1-phosphate (S1P), a pleiotropic cellular agonist involved in various immune responses, and to its synthetic structural analog FTY720P (Gilenya). The fluorescence intensity of a rhodamine B-labeled phosphatidylinositol 4,5-bisphosphate binding peptide derived from gelsolin and the optical density of recombinant human plasma gelsolin (rhpGSN) were found to decrease after the addition of S1P or FTY720P. Gelsolins ability to depolymerize F-actin also decreased progressively with increasing addition of S1P. Transient increases in phosphorylation of extracellular signal-regulated kinase in bovine aortic endothelial cells (BAECs) after S1P treatment were inhibited by rhpGSN. The ability of S1P to increase F-actin content and the elastic modulus of primary astrocytes and BAECs was also prevented by rhpGSN. Evaluation of S1P and gelsolin levels in cerebrospinal fluid reveals a low concentration of gelsolin and a high concentration of S1P in samples obtained from patients suffering from lymphatic meningitis. These findings suggest that gelsolin-mediated regulation of S1P bioactivity may be important to maintain immunomodulatory balance at inflammatory sites.