Intestinal absorption of dietary maize glucosylceramide in lymphatic duct cannulated rats

Sphingolipids are ubiquitous in all eukaryotic organisms. Various physiological functions of dietary sphingolipids, such as preventing colon cancer and improving the skin barrier function, have been recently reported. One of the common sphingolipids used as a foodstuff is glucosylceramide from plant sources, which is composed of sphingoid bases distinct from those of mammals. However, the fate of dietary sphingolipids derived from plants is still not understood. In this study, we investigated the absorption of maize glucosylceramide in the rat intestine using a lipid absorption assay of lymph from the thoracic duct. The free and complex forms of trans-4,cis-8-sphingadienine, the predominant sphingoid base of maize glucosylceramide, were found in the lymph after administration of maize glucosylceramide. This plant type of sphingoid base was detected in the ceramide fraction and N-palmitoyl-4,8-sphingadienine (C16:0-d18:2) and N-tricosanoyl-4,8-sphingadienine (C23:0-d18:2) were identified by LC-MS/MS. The cumulative recovery of 4t,8c-sphingadienine in the lymph was very low. These results indicate that dietary glucosylceramide originating from higher plants is slightly absorbed in the intestine and is incorporated into ceramide structures in the intestinal cells. However, it appears that the intact form of sphingoid bases is not reutilized well in the tissues.     

Widespread tissue distribution and synthetic pathway of polyunsaturated C24:2 sphingolipids in mammals

Sphingolipids are multifunctional lipids and a major constituent of the cell membranes of eukaryotes. Although the fatty acid (FA) moiety of sphingolipids is usually a saturated or monounsaturated FA, polyunsaturated FA (PUFA)-containing species also exist in mammalian tissues. In the present study, we showed that C24:2 PUFA-containing ceramide is one of the seven major ceramide species in a wide range of tissues. C24:2 ceramide levels were especially high in spleen and small intestine; in the former, it was the fourth most abundant ceramide species. However, both the synthetic pathway and the physiological function of C24:2 ceramide had yet to be identified. Tracer analysis using deuterium-labeled linoleic acid (C18:2) revealed that C24:2 ceramide is produced via elongation of linoleic acid. We also found that the FA elongase ELOVL1 and the ceramide synthase CERS2 were involved in C24:2 ceramide production. Sphingolipids are known to form lipid microdomains in membranes; however, in a detergent-resistant membrane (DRM) assay, we observed a lower proportion of C24:2 sphingomyelin in the DRM fraction than of saturated sphingomyelins, suggesting that C24:2 sphingolipids may act to negatively regulate lipid microdomain formation. Our findings expand our knowledge of sphingolipid diversity, and provide insight into how different sphingolipid molecular species play different functions in biological membranes.     

Characterization of neutral sphingolipids from chicken erythrocytes

The neutral sphingolipids from chicken erythrocytes were characterized. The total concentration of neutral sphingolipids was found to be 480 nmol/g of dry stroma. They were isolated and purified by droplet counter-current chromatography, Iatrobeads column chromatography, and preparative thin-layer chromatography. The major neutral sphingolipids were free ceramide, ceramide monohexoside, ceramide dihexoside, and ceramide pentahexoside, which represented 43%, 23.5%, 10.0%, and 3.6% of the long chain bases, respectively. Thus, free ceramide was the most abundant neutral sphingolipid in chicken erythrocytes. Ceramide monohexoside was composed of more galactosylceramide than glucosylceramide. Galabiosylceramide was found in the ceramide dihexoside fraction together with lactosylceramide. Ceramide pentahexoside was a Forssman glycolipid. There were two groups of neutral sphingolipids; one had mainly C16 fatty acid and the other had C22 and C24 fatty acids. In both groups sphingosine (d18:1) was predominant as a long chain base. 2-Hydroxy-C16 fatty acid was a major component of one of the ceramide monohexosides.     

Clinical Significance in Oral Cavity Squamous Cell Carcinoma of Pathogenic Somatic Mitochondrial Mutations

Somatic mutations affecting the mitochondrial DNA (mtDNA) have been frequently observed in human cancers and proposed as important oncological biomarkers. However, the clinical significance of mtDNA mutations in cancer remains unclear. This study was therefore performed to explore the possible clinical use in assessing oral squamous cell carcinoma (OSCC) of pathogenic mtDNA mutations. The entire mitochondrial genome of 300 OSCC with their matched control DNAs was screened by direct sequencing and criteria were set to define a pathogenic somatic mutation. The patients'' TP53 R72P genotypes were determined by polymerase chain reaction-restriction fragment length polymorphism. The relationships between pathogenic somatic mutations, clinicopathogical features, TP53 R72P genotype and clinical prognosis were analyzed. Overall, 645 somatic mtDNA mutations were identified and 91 of these mutations were defined as pathogenic. About one quarter (74/300) of the OSCC tumor samples contained pathogenic mutations. Individuals with the TP53 R allele had a higher frequency of pathogenic somatic mutation than those with the PP genotype. Kaplan-Meier analysis indicated that TP53 R allele patients with pathogenic somatic mutations demonstrated a significant association with a poorer disease-free survival than other individuals (HR = 1.71; 95% CI, 1.15–2.57; p = 0.009) and this phenomenon still existed after adjusting for mtDNA haplogroup, tumor stage with treatment regimens, differentiation and age at diagnosis (HR = 1.59; 95% CI, 1.06–2.40; p = 0.03). Subgroup analyses showed that this phenomenon was limited to patients who received adjuvant radiotherapy/chemo-radiotherapy after surgery. The results strongly indicated that pathogenic mtDNA mutations are a potential prognostic marker for OSCCs. Furthermore, functional mitochondria may play an active role in cancer development and the patient''s response to radiotherapy/chemo-radiotherapy.     

Assessment of essential and toxic elemental concentrations in tumor and non-tumor tissues with risk of colorectal carcinoma in Pakistan

BackgroundColorectal tumor is a major cause of cancer morbidity and mortality both in USA and around the globe. Exposure to environmental toxicants such as toxic trace elements has been implicated in colorectal malignancy. However, data linking them to this cancer are generally lacking.MethodsAccordingly, the current study was to investigate the distribution, correlation and chemometric evaluation of 20 elements (Ca, Na, Mg, K, Zn, Fe, Ag, Co, Pb, Sn, Ni, Cr, Sr, Mn, Li, Se, Cd, Cu, Hg and As) in the tumor tissues (n = 147) and adjacent non tumor tissues (n = 147) of same colorectal patients which were analyzed by flame atomic absorption spectrophometry employing nitric acid-perchloric acid based wet digestion method.ResultsOn the average, Zn (p < 0.05), Ag (p < 0.001), Pb (p < 0.001), Ni (p < 0.01), Cr (p < 0.005) and Cd (p < 0.001) showed significantly higher levels in the tumor tissues compared with the non tumor tissues of patients, whereas mean levels of Ca (p < 0.01), Na (p < 0.05), Mg (p < 0.001), Fe (p < 0.001), Sn (p < 0.05) and Se (p < 0.01), were significantly elevated in the non tumor tissues than the tissues of tumor patients. Most of the elements revealed markedly disparities in their elemental levels based on food (vegetarian/nonvegetarian) habits and smoking (smoker/nonsmoker) habits of donor groups. The correlation study and multivariate statistical analyses demonstrated some significantly divergent associations and apportionment of the elements in the tumor tissues and non tumor tissues of donors. Noticeably, variations in the elemental levels were also noted for colorectal tumor types (lymphoma, carcinoids tumor and adenocarcinoma) and stages (I, II, III, & IV) in patients.ConclusionOverall, the study revealed that disproportions in essential and toxic elemental concentrations in the tissues are involved in pathogenesis of the malignancy. These findings provide the data base that helps to oncologist for diagnosis and prognosis of colorectal malignant patients.     

Higher serum sPD-L1 levels after radiotherapy indicate poor outcome in hepatocellular carcinoma patients

BackgroundOur preclinical research reveals that radiotherapy (RT) promoted PD-L1 upregulation in tumor tissues and that higher PD-L1 after RT worsened the prognosis through immunosuppression. We sought to validate our experimental results in clinical cohorts and promote clinical application.Patients and methodsIn cohort 1, formalin-fixed paraffin-embedded samples were obtained from 46 HCC patients, 23 of whom received preoperative RT and the other 23 received direct surgery. A prospectively collected database contained 122 HCC patients treated with liver RT were enrolled in cohort 2. Blood samples were taken a day before and two weeks after RT. Patients in cohort 2 were further divided into two groups, exploration (73 patients) and validation (49 patients) groups.ResultsIn cohort 1, RT increased the expression of PD-L1 in tumor tissues (p = 0.001), and PD-L1 levels were associated with decreased cytotoxic T-cell infiltration and a trend toward poor prognosis (p = 0.14). Moreover, PD-L1 expression in tumor tissue positively correlated with soluble (s) PD-L1 in serum (R = 0.421, p = 0.046). Then, in cohort 2, we revealed RT increased sPD-L1 in serum (p < 0.001), which was associated with the number of circulating CD8+ T cells (R = -0.24, p = 0.036), indicating poor survival. Furthermore, patients with higher rate of sPD-L1 increase after RT have better treatment response (p < 0.001), PFS (p = 0.032) and OS (p = 0.045).ConclusionHigher post-RT serum sPD-L1, which may potentiate immune suppression effects, indicates a poor prognosis for HCC patients treated with RT.     

Effect of ceramide N-acyl chain and polar headgroup structure on the properties of ordered lipid domains (lipid rafts)

Ceramides are sphingolipids that greatly stabilize ordered membrane domains (lipid rafts), and displace cholesterol from them. Ceramide-rich rafts have been implicated in diverse biological processes. Because ceramide analogues have been useful for probing the biological function of ceramide, and may have biomedical applications, it is important to characterize how ceramide structure affects membrane properties, including lipid raft stability and composition. In this report, fluorescence quenching assays were used to evaluate the effect of analogues of ceramide with different N-acyl chains or different sphingoid backbones on raft stability and sterol content. The effect of replacing 18 mol% of sphingomyelin (SM) with ceramide in vesicles composed of a 1:1 (mol:mol) mixture of SM and dioleoylphosphatidylcholine (DOPC), with or without 25 mol% sterol, was examined. In the absence of sterol, the thermal stability of the SM-rich ordered domains increased with ceramide N-acyl chain length in the order C2:0 ∼ C6:0 ∼ C8:0 < no ceramide < C12:0 < C16:0. In vesicles containing 25 mol% cholesterol (1:1:0.66 sphingolipid:DOPC:cholesterol), the dependence of raft stability on ceramide N-acyl chain length increased in the order C8:0 ∼ C6:0 < C2:0 < C12:0 ∼ no ceramide < C16:0. We also studied the stability of lipid rafts in the presence of N-lauroyl- and N-palmitoylsphingosine analogues containing altered structures in or near the polar portion of the sphingoid base. In almost all cases, the analogues stabilized rafts to about the same degree as a normal ceramide containing the same acyl chain. The only exception was N-palmitoyl-4D-ribophytosphingosine, which was very strongly raft-stabilizing. We conclude that variations in sphingoid base structure induce only insignificant changes in raft properties. N-Lauroyl and N-palmitoylsphingosine and their analogues displaced sterol from rafts to a significant degree. Both C12:0 and C16:0 analogues of ceramide may be good mimics of natural ceramide, and useful for cellular studies in which maintenance of the normal physical properties of ceramide are important.     

Plasma Sphingolipids as Potential Indicators of Hepatic Necroinflammation in Patients with Chronic Hepatitis C and Normal Alanine Aminotransferase Level

Accurate estimation of hepatic necroinflammation caused by chronic hepatitis C (CHC) is crucial for prediction of prognosis and design of therapeutic strategy, which is particularly true for CHC patients with normal alanine aminotransferase (ALT) level. Recent studies have shown that sphingolipids have a close relationship with hepatitis C virus infection. The present study aimed to identify plasma sphingolipids related to hepatic necroinflammation. We included 120 treatment-naïve CHC patients and 64/120 had normal ALT levels (<40 U/L). CHC patients who underwent liver biopsies were subjected to Scheuer scoring analysis for scope of hepatic inflammation. Plasma sphingolipids were detected by high-performance liquid chromatography tandem mass spectrometry. Our results showed 44 plasma sphingolipids were detected altogether. Of all detected sphingolipids, hexosylceramide (HexCer) (d18∶1/22∶0) and HexCer (d18∶1/24∶0) showed a significant difference among G0/G1, G2, and G3/G4 (P<0.05). For identifying hepatic necroinflammation (G≥2), after adjusting other factors, the odds ratio (OR) of HexCer (d18∶1/22∶0) reached 1.01 (95% confidence interval [CI]: 1.00–1.02). Furthermore, the area under the curve (AUC) of HexCer (d18∶1/22∶0) was 0.7 (P = 0.01) and approached that of ALT (AUC = 0.78). However, in CHC patients with normal ALT, HexCer (d18∶1/22∶0) was an independent factor (OR: 1.02, 95% CI: 1.01–1.03) to identify the hepatic necroinflammation (G≥2). HexCer (d18∶1/22∶0) not only showed the largest AUC (0.78, P = 0.001), but also exhibited the highest specificity of all indicators. These results indicate that plasma HexCer (d18∶1/22∶0) is a potential indicator to distinguish hepatic necroinflammation in CHC patients. For CHC with normal ALT, the ability of HexCer (d18∶1/22∶0) to distinguish hepatic necroinflammation might be superior to conventional serum indicators.     

Inactivation of Ceramide Synthase 6 in Mice Results in an Altered Sphingolipid Metabolism and Behavioral Abnormalities

The N-acyl chain length of ceramides is determined by the specificity of different ceramide synthases (CerS). The CerS family in mammals consists of six members with different substrate specificities and expression patterns. We have generated and characterized a mouse line harboring an enzymatically inactive ceramide synthase 6 (CerS6KO) gene and lacz reporter cDNA coding for β-galactosidase directed by the CerS6 promoter. These mice display a decrease in C16:0 containing sphingolipids. Relative to wild type tissues the amount of C16:0 containing sphingomyelin in kidney is ∼35%, whereas we find a reduction of C16:0 ceramide content in the small intestine to about 25%. The CerS6KO mice show behavioral abnormalities including a clasping abnormality of their hind limbs and a habituation deficit. LacZ reporter expression in the brain reveals CerS6 expression in hippocampus, cortex, and the Purkinje cell layer of the cerebellum. Using newly developed antibodies that specifically recognize the CerS6 protein we show that the endogenous CerS6 protein is N-glycosylated and expressed in several tissues of mice, mainly kidney, small and large intestine, and brain.     

Prediction value of intercellular adhesion molecule-1 gene polymorphisms for epithelial ovarian cancer risk,clinical features,and prognosis

Intercellular adhesion molecule-1 (ICAM-1, encoded by ICAM-1) is implicated in tumorigenesis and tumor progression. ICAM-1 modulates the susceptibility to several types of cancer and the disease prognosis; however, its role in epithelial ovarian cancer (EOC) is unclear. Here, we evaluate single nucleotide polymorphisms (SNPs) in ICAM-1 as predictors of EOC risk and prognosis. Six ICAM-1 polymorphisms were genotyped in 408 patients with EOC and 520 controls using the MassARRAY system. The ICAM-1 mRNA levels in 89 EOC tissues and 35 normal ovarian tissues were examined using quantitative PCR. The ICAM-1 rs5498 G allele was associated with increased tumor grade (OR = 2.650) and EOC risk (OR = 1.405). This risk was more evident in females who had first-degree relatives (FDRs) with a tumor (OR = 3.475) or who experienced early menarche (OR = 2.774). The ICAM-1 expression in the cancerous tissue was elevated compared with that of normal ovarian tissues (p < 0.0001), and it was associated with an rs5498 genotype (p = 0.0002). ICAM-1 SNPs did not significantly predict the overall EOC survival (p > 0.05). However, the rs5498 G allele correlated with EOC survival time in patients whose FDRs suffered from a tumor (p = 0.001). ICAM-1 rs5498 likely confers a high risk for EOC in G allele carriers accompanied by up-regulation of ICAM-1 expression during carcinogenesis. The combination of ICAM-1 rs5498 and tumor history predicts the EOC prognosis.     

Genetic variation rs10484761 on 6p21.1 derived from a genome-wide association study is associated with gastric cancer survival in a Chinese population

A recent genome-wide association study (GWAS) on esophageal squamous-cell carcinoma (ESCC) among Chinese people has discovered a novel single nucleotide polymorphism (SNP) rs10484761 on 6p21.1 region. We hypothesized that SNP rs10484761 T/C is associated with survival of gastric cancer. We genotyped SNP rs10484761 in 940 gastric cancer patients treated with surgical resection. Kaplan–Meier survival analysis, log-rank test, and Cox proportional hazard models were used to evaluate the association between the SNP rs10484761 and gastric cancer survival. In the dominant model, those who carry TC/CC genotypes had a significant shorter survival time (log-rank P = 0.005), especially in the subgroups of aged male patients, cardia intestinal tumor (HR = 1.41, 95% CI = 1.08–1.84 for cardia cancer and HR = 1.64, 95% CI = 1.14–2.37 for intestinal-type), tumor size ≤ 5 cm (HR = 1.41, 95% CI = 0.56–0.99), T1 depth invasion (HR = 2.34, 95% CI = 1.20–4.56), lymph node metastasis (HR = 1.51, 95% CI = 1.19–1.96), no distant metastasis (HR = 1.33, 95% CI = 1.05–1.68), TNM stage III + IV (HR = 1.50, 95% CI = 1.13–1.98), and with chemotherapy (HR = 1.53, 95% CI = 1.17–1.99). The results indicated that SNP rs10484761 was associated with prognosis of gastric cancer, suggesting that this genetic variant may serve as a potential marker to predict the survival of gastric cancer in Chinese population.     

Thermotropic behavior and lateral distribution of very long chain sphingolipids

Sphingolipids containing very long acyl chains are abundant in certain specialized tissues and minor components of plasma membranes in most mammalian cells. There are cellular processes in which these sphingolipids are required, and the function seems to be mediated through sphingolipid-rich membrane domains. This study was conducted to explore how very long acyl chains of sphingolipids influence their lateral distribution in membranes. Differential scanning calorimetry showed that 24:0- and 24:1-sphingomyelins, galactosylceramides and glucosylceramides exhibited complex thermotropic behavior and partial miscibility with palmitoyl sphingomyelin. The T_m was decreased by about 20 °C for all 24:1-sphingolipids compared to the corresponding 24:0-sphingolipids. The ability to pack tightly with ordered and extended acyl chains is a necessity for membrane lipids to partition into ordered domains in membranes and thus the 24:1-sphingolipids appeared less likely to do so. Fluorescence quenching measurements showed that the 24:0-sphingolipids formed ordered domains in multicomponent membranes, both as the only sphingolipid and mixed with palmitoyl sphingomyelin. These domains had a high packing density which appeared to hinder the partitioning of sterols into them, as reported by the fluorescent cholesterol analog cholestatrienol. 24:0-SM was, however, better able to accommodate sterol than the glycosphingolipids. The 24:1-sphingolipids could, depending on head group structure, either stabilize or disrupt ordered sphingolipid/cholesterol domains. We conclude that very long chain sphingolipids, when present in biological membranes, may affect the physical properties of or the distribution of sterols between lateral domains. It was also evident that not only the very long acyl chain but also the specific molecular structure of the sphingolipids was of importance for their membrane properties.     

Ceramide acyl chain length markedly influences miscibility with palmitoyl sphingomyelin in bilayer membranes

Ceramides are precursors of major sphingolipids and can be important cellular effectors. The biological effects of ceramides have been suggested to stem from their biophysical effects on membrane structure affecting the lateral and transbilayer organization of other membrane components. In this study we investigated the effect of acyl chain composition in ceramides (C4-C24:1) on their miscibility with N-palmitoyl-sphingomyelin (PSM) using differential scanning calorimetry. We found that short-chain (C4 and C8) ceramides induced phase separation and lowered the T _m and enthalpy of the PSM endotherm. We conclude that short-chain ceramides were more miscible in the fluid-phase than in the gel-phase PSM bilayers. Long-chain ceramides induced apparent heterogeneity in the bilayers. The main PSM endotherm decreased in cooperativity and enthalpy with increasing ceramide concentration. New ceramide-enriched components could be seen in the thermograms at all ceramide concentrations above X _Cer = 0.05. These broad components had higher T _m values than pure PSM. C24:1 ceramide exhibited complex behavior in the PSM bilayers. The miscibility of C24:1 ceramide with PSM at low (X _Cer = 0.05–0.10) concentrations was exceptionally good according to the cooperativity of the transition. At higher concentrations, multiple components were detected, which might have arisen from interdigitated gel-phases formed by this very asymmetric ceramide. The results of this study indicate that short-chain and long-chain ceramides have very different effects on the sphingomyelin bilayers. There also seems to be a correlation between their miscibility in binary systems and the effect of ceramides of different hydrophobic length on sphingomyelin-rich domains in multicomponent membranes.     

Integrative Approach Detected Association between Genetic Variants of microRNA Binding Sites of TLRs Pathway Genes and OSCC Susceptibility in Chinese Han Population

Oral squamous cell carcinoma (OSCC) is a leading malignancy worldwide; the overall 5-year survival rate is approximately 50%. A variety of proteins in Toll-like receptors (TLRs) pathway have been related with the risk of OSCC. However, the influence of genetic variations in TLRs pathway genes on OSCC susceptibility is unclear. Previous studies mainly focused on the coding region of genes, while the UTR region remains unstudied. In the current study, a bioinformatics approach was performed to select candidate single nucleotide polymorphisms (SNPs) on microRNA binding sites of TLRs pathway genes related with OSCC. After screening 90 OSCC related TLRs pathway genes, 16 SNPs were selected for genotyping. We found that rs5030486, the polymorphisms on 3′ UTR of TRAF6, was significantly associated with OSCC risk. AG genotype of TRAF6 was strongly associated with a decreased risk of OSCC (OR = 0.252; 95% CI = 0.106, 0.598; p = 0.001). In addition, AG genotype was also related with a reduced risk of OSCC progression both in univariable analysis (HR = 0.303, 95% CI = 0.092, 0.995) and multivariable analysis (HR = 0.272, 95% CI = 0.082, 0.903). Furthermore, after detecting the mRNA expression level of TRAF6 in 24 OSCC patients, we found that TRAF6 expression level was significantly different between patients carrying different genotypes at locus rs5030486 (p = 0.013), indicating that rs5030486 of TRAF6 might contribute to OSCC risk by altering TRAF6 expression level. In general, these data indicated that SNP rs5030486 could be a potential bio-marker for OSCC risk and our results might provide new insights into the association of polymorphisms within the non-coding area of genes with cancers.     

A shift in sphingolipid composition from C24 to C16 increases susceptibility to apoptosis in HeLa cells

Sphingolipids, major lipid components of the eukaryotic plasma membrane, have a variety of physiological functions and have been associated with many diseases. They have also been implicated in apoptosis. Sphingolipids are heterogeneous in their acyl chain length, with long-chain (C16) and very long-chain (C24) sphingolipids being predominant in most mammalian tissues. We demonstrate that knockdown of ELOVL1 or CERS2, which catalyze synthesis of C24 acyl-CoAs and C24 ceramide, respectively, drastically reduced C24 sphingolipid levels with a complementary increase in C16 sphingolipids. Under ELOVL1 or CERS2 knockdown conditions, cisplatin-induced apoptosis significantly increased. Enhanced sensitivity to cisplatin-induced apoptosis exhibited close correlation with increases in caspase-3/7 activity. No significant alterations in sphingolipid metabolism such as ceramide generation were apparent with the cisplatin-induced apoptosis, and inhibitors of ceramide generation had no effect on the apoptosis. Apoptosis induced by UV radiation or C6 ceramides also increased in ELOVL1 or CERS2 knockdown cells. Changes in the composition of sphingolipid chain length may affect susceptibility to stimuli-induced apoptosis by affecting the properties of cell membranes, such as lipid microdomain/raft formation.     

Ceramides and Glucosylceramides Are Independent Antagonists of Insulin Signaling

Inhibitors of sphingolipid synthesis protect mice from diet induced-insulin resistance, and sphingolipids such as ceramides and glucosylated-ceramides (e.g., GM3) are putative nutritional intermediates linking obesity to diabetes risk. Herein we investigated the role of each of these sphingolipids in muscle and adipose tissue and conclude that they are independent and separable antagonists of insulin signaling. Of particular note, ceramides antagonize insulin signaling in both myotubes and adipocytes, whereas glucosyceramides are only efficacious in adipocytes: 1) In myotubes exposed to saturated fats, inhibitors of enzymes required for ceramide synthesis enhance insulin signaling, but those targeting glucosylceramide synthase have no effect. 2) Exogenous ceramides antagonize insulin signaling in myotubes, whereas ganglioside precursors do not. 3) Overexpression of glucosylceramide synthase in myotubes induces glucosylceramide but enhances insulin signaling. In contrast, glucosylated ceramides have profound effects in adipocytes. For example, either ganglioside addition or human glucosylceramide synthase overexpression suppresses insulin signaling in adipocytes. These data have important mechanistic implications for understanding how these sphingolipids contribute to energy sensing and the disruption of anabolism under conditions of nutrient oversupply.     

Quantification of ceramide species in biological samples by liquid chromatography electrospray ionization tandem mass spectrometry

We present an optimized and validated liquid chromatography electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) method for the simultaneous measurement of concentrations of different ceramide species in biological samples. The method of analysis of tissue samples is based on Bligh and Dyer extraction, reverse-phase high-performance liquid chromatography separation, and multiple reaction monitoring of ceramides. Preparation of plasma samples also requires isolation of sphingolipids by silica gel column chromatography prior to LC-ESI-MS/MS analysis. The limits of quantification were in a range of 0.01-0.50 ng/ml for distinct ceramides. The method was reliable for inter- and intraassay precision, accuracy, and linearity. Recoveries of ceramide subspecies from human plasma, rat liver, and muscle tissue were 78 to 91%, 70 to 99%, and 71 to 95%, respectively. The separation and quantification of several endogenous long-chain and very-long-chain ceramides using two nonphysiological odd chain ceramide (C17 and C25) internal standards was achieved within a single 21-min chromatographic run. The technique was applied to quantify distinct ceramide species in different rat tissues (muscle, liver, and heart) and in human plasma. Using this analytical technique, we demonstrated that a clinical exercise training intervention reduces the levels of ceramides in plasma of obese adults. This technique could be extended for quantification of other ceramides and sphingolipids with no significant modification.     

Characteristics of the rat cardiac sphingolipid pool in two mitochondrial subpopulations

Mitochondrial sphingolipids play a diverse role in normal cardiac function and diseases, yet a precise quantification of cardiac mitochondrial sphingolipids has never been performed. Therefore, rat heart interfibrillary mitochondria (IFM) and subsarcolemmal mitochondria (SSM) were isolated, lipids extracted, and sphingolipids quantified by LC-tandem mass spectrometry. Results showed that sphingomyelin (∼10,000 pmol/mg protein) was the predominant sphingolipid regardless of mitochondrial subpopulation, and measurable amounts of ceramide (∼70 pmol/mg protein) sphingosine, and sphinganine were also found in IFM and SSM. Both mitochondrial populations contained similar quantities of sphingolipids except for ceramide which was much higher in SSM. Analysis of sphingolipid isoforms revealed ten different sphingomyelins and six ceramides that differed from 16- to 24-carbon units in their acyl side chains. Sub-fractionation experiments further showed that sphingolipids are a constituent part of the inner mitochondrial membrane. Furthermore, inner membrane ceramide levels were 32% lower versus whole mitochondria (45 pmol/mg protein). Three ceramide isotypes (C₂₀-, C₂₂-, and C₂₄-ceramide) accounted for the lower amounts. The concentrations of the ceramides present in the inner membranes of SSM and IFM differed greatly. Overall, mitochondrial sphingolipid content reflected levels seen in cardiac tissue, but the specific ceramide distribution distinguished IFM and SSM from each other.