Establishment of a quantitative, qualitative, and high-throughput analysis of sulfatides from small amounts of sera by matrix-assisted laser desorption ionization-time of flight mass spectrometry

Investigation of Clinical Features and Association between Vascular Endothelial Injury Markers and Cytomegalovirus Infection Associated with Thrombotic Microangiopathy in Patients with Anti-Neutrophil Cytoplasmic Antibody (ANCA)-Associated Vasculitis: Case-Based Research

Anti-neutrophil cytoplasmic antibody-associated vasculitis (AAV) can occasionally trigger thrombotic microangiopathy (TMA). Cytomegalovirus (CMV) may be reactivated during intensive immunosuppressive therapy for AAV and cause TMA. Therefore, we aimed to evaluate the clinical features of and the association between vascular endothelial injury markers and TMA due to CMV in patients with AAV. A 61-year-old female was diagnosed with AAV and severe kidney injury. Immunosuppressive therapy gradually improved her symptoms and laboratory findings. However, 2 weeks after induction therapy initiation, she exhibited altered consciousness, a significant decrease in platelet count, and hemolytic anemia, resulting in a TMA diagnosis. Plasma exchange did not improve TMA findings and routine screening test revealed CMV infection. Ganciclovir injection improved the infection and TMA findings. Consequently, we diagnosed her with CMV-induced TMA. Both AAV and CMV may induce severe vascular endothelial injury, potentially leading to TMA development. CMV-induced TMA should be considered when TMA develops during induction therapy against AAV. Moreover, of the three serum markers of vascular injury-serum sulfatides, soluble thrombomodulin, and pentraxin 3-serum sulfatides may be associated with the development of TMA, and a high level of soluble thrombomodulin may be associated with the development of CMV viremia during the clinical course of AAV.

Serum sulfatide level is associated with severe systemic vasculitis with kidney involvement

Sulfatides are a type of sulfated glycosphingolipid that are secreted with lipoproteins into the serum. These molecules are involved in the inflammatory pathway of vessels in addition to coagulation and platelet aggregation. Previous studies have proposed that sulfatides play a pivotal role in regulating inflammation-related disorders. Systemic vasculitis (SV) diseases are generally caused by autoimmune diseases and often involve kidney vasculitis, which may lead to rapidly progressive kidney dysfunction and end-stage kidney disease. Our earlier pilot study revealed that the level of serum sulfatides (SSs) was significantly decreased in patients with anti-neutrophil cytoplasmic antibody-associated vasculitis (AAV), a representative disease-causing SV with kidney involvement (SVKI), especially in patients exhibiting active crescentic findings on kidney biopsy. To further explore the clinical significance of an association between SS and SVKI, we analyzed and compared the SS level of patients with various SVKI diseases in this retrospective cohort study. Among patients admitted to our hospital between 2008 and 2021, we ultimately enrolled 26 patients with IgA vasculitis (IgAV), 62 patients with AAV, and 10 patients with anti-glomerular basement membrane disease (GBM) as examples of SVKI diseases, as well as 50 patients with IgA nephropathy (IgAN) and 23 donors for living kidney transplantation as controls. The mean ± standard deviation SS level in the donor, IgAN, IgAV, AAV, and GBM groups was 8.26 ± 1.72, 8.01 ± 2.21, 6.01 ± 1.73, 5.37 ± 1.97, and 2.73 ± 0.99 nmol/mL, respectively. Analysis of patients in the SVKI disease group showed that those with the crescentic class kidney biopsy finding exhibited a significantly lower SS level than did those with other class biopsy features. Additionally, the SS level had a higher detection ability for SVKI patients with crescentic class kidney biopsy findings (area under the receiver operating characteristic curve 0.90, 95% confidence interval 0.82-0.99) than did several other predictor candidates. Our results indicate that the SS level is decreased in more severe SVKI diseases and may be associated with active glomerular lesions in SVKI kidney biopsy samples.

Serum sulfatide as a biomarker of carotid atherosclerosis in patients with rheumatoid arthritis

PURPOSE

Rheumatoid arthritis (RA) patients have accelerated atherosclerosis (AS) leading to excess cardiovascular morbidity and mortality, but traditional risk factors for cardiovascular disease (CVD) are invalid to explain the problem. Sulfatides, as major components of serum lipoproteins, are synthesized in the liver. These molecules are reported to play an important role in the development of AS, thrombogenesis, and inflammation. However, it is unclear whether sulfatides are responsible for such issue. To elucidate the possible association between serum sulfatide and the accelerated progress of AS, evaluated by carotid intima-media thickness (CIMT), and ascertain the related mechanism underlying the correlation in RA cases.

METHODS

We performed an observational study of 144 patients with RA and 120 sex and age-matched controls. Meanwhile, 107 patients (of the 144 RA patients enrolled at baseline) were invited to undergo a second measurement after 12 months. Serum sulfatide levels of all the enrolled subjects were quantified by mass spectrometry after they were converted into lysosulfatides (LS), and then calculated as the sum of the levels of seven LS molecular species. Serum oxidative stress marker, malondialdehyde (MDA) was detected by ELISA. We subsequently statistically analyzed the causalities between carotid AS and clinical parameters, and the association of serum sulfatide with other variables. Multivariable logistic regression analysis was finally employed by taking all factors to identify independent determinant for carotid atherosclerotic plaque and serum sulfatide level.

RESULTS

A gradual declined trend in serum sulfatide levels was observed in control subjects, non-plaque group, and the plaque group (8.56 ± 1.37 nmol/mL, 5.63 ± 1.57 nmol/mL, 3.18 ± 1.32 nmol/mL, respectively, p < 0.01), along with an increased value of CIMT (0.63 ± 0.07 mm, 0.92 ± 0.14 mm, 1.43 ± 0.22 mm, respectively, p < 0.01). Meanwhile, a negative linear correlation between CIMT and serum sulfatide was further confirmed by Spearman's analysis (r = -0.622, p < 0.01). Eventually, multivariate logistic regression analysis identified serum MDA as the only independent factor for the abnormal level of serum sulfatide, and serum sulfatide was detected as a significant protective factor for the occurrence of carotid plaques in RA cases (p < 0.01), which was confirmed repeatedly by our cross-sectional and longitudinal studies.

CONCLUSION

Excessive abnormal levels of oxidative stress decreased serum sulfatide levels, followed by a high occurrence of AS in RA patients. Serum sulfatide level might be useful as a predictor (biomarker) for the progression of AS in RA cases.

Serum Sulfatide Levels as a Biomarker of Active Glomerular Lesion in Patients with Anti-Neutrophil Cytoplasmic Antibody-Associated Vasculitis: A Single Center Pilot Study

Sulfatides are glycosphingolipids that are associated with coagulation and platelet aggregation. Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) activates platelet function and often leads to thrombotic complications. These facts suggest an association between serum sulfatides and AAV. We aimed to clarify the significance of serum sulfatide levels in patients with AAV. We conducted a retrospective, single-center, observational pilot study that included 35 patients who developed AAV and 10 control patients who were candidates for living-donor kidney transplantation. We compared serum sulfatide levels between the control and AAV patients. We analyzed the differences in serum sulfatide levels among four classes (focal, crescentic, mixed, and sclerotic class) of glomerular lesions that were categorized by histopathologic classification of ANCA-associated glomerulonephritis. Serum sulfatide levels in patients with AAV were significantly lower than those in the controls. Serum sulfatide levels were significantly different between the four classes. Additionally, serum sulfatide levels in the crescentic class were significantly lower than those in the other classes. Serum sulfatide levels were significantly correlated with albumin, cholesterol, C-reactive protein, and pentraxin 3. In conclusion, serum sulfatide levels are significantly correlated with inflammation, reflecting crescentic glomerulonephritis, which is an active glomerular lesion in AAV patients.

Gallbladder cancer with ascites in a child with metachromatic leukodystrophy

INTRODUCTION

Metachromatic leukodystrophy (MLD) refers to leukodystrophy caused by the accumulation of sulfatide from arylsulfatase A (ARSA) gene mutations. Sulfatide also accumulates in various organs, including the peripheral nerves, kidney, and gallbladder. Proliferative changes in the gallbladder have been reported in several patients, while gallbladder cancer is reported in only two adult MLD cases. We report what is likely the first pediatric case of MLD with gallbladder cancer.

CASE REPORT

The patient was a 5-year-old girl diagnosed with MLD using head magnetic resonance imaging and detecting a homozygous mutation of c.302G>A (p.Gly101Asp) in ARSA. Abdominal bloating was observed at the age of 4 years; CT revealed a giant tumor in the gallbladder and massive ascites. Cholecystectomy was performed and pathological examination revealed adenocarcinoma. Measurement of serum sulfatide revealed increased levels compared to the average healthy range.

DISCUSSION

Rapidly increased ascites and large polyps which are reported as risk factors for cancer were characteristic in our MLD case. When such lesions are detected, they should be removed immediately because of the possibility of cancer, even in a pediatric patient.

Polyunsaturated fatty acid deficiency affects sulfatides and other sulfated glycans in lysosomes through autophagy-mediated degradation

Metabolic changes in sulfatides and other sulfated glycans have been related to various diseases, including Alzheimer's disease (AD). However, the importance of polyunsaturated fatty acids (PUFA) in sulfated lysosomal substrate metabolism and its related disorders is currently unknown. We investigated the effects of deficiency or supplementation of PUFA on the metabolism of sulfatides and sulfated glycosaminoglycans (sGAGs) in sulfatide-rich organs (brain and kidney) of mice. A PUFA-deficient diet for over 5 weeks significantly reduced the sulfatide expression by increasing the sulfatide degradative enzymes arylsulfatase A and galactosylceramidase in brain and kidney. This sulfatide degradation was clearly associated with the activation of autophagy and lysosomal hyperfunction, the former of which was induced by suppression of the Erk/mTOR pathway. A PUFA-deficient diet also activated the degradation of sGAGs in the brain and kidney and that of amyloid precursor proteins in the brain, indicating an involvement in general lysosomal function and the early developmental process of AD. PUFA supplementation prevented all of the above abnormalities. Taken together, a PUFA deficiency might lead to sulfatide and sGAG degradation associated with autophagy activation and general lysosomal hyperfunction and play a role in many types of disease development, suggesting a possible benefit of prophylactic PUFA supplementation.

Characterization of galactosyl and lactosyl sulfatide species in human serum by MALDI-TOF mass spectrometry

Background

Sulfatides are found in a variety of tissues and serum lipoproteins. Sulfatide is a molecular species composed of various sphingoid bases, fatty acids and sugar chains; therefore, rapid analysis of the qualitative structure is important in clinical assessment.

Methods

In this study, sulfatide-rich fractions were isolated from serum lipids, and the sulfatide species were analysed by negative ion mode using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS).

Results

Sulfatide species identified in human serum included two different sugar chains, eight sphingoid molecules and various fatty acid side chains including hydroxy fatty acids. In total, 64 galactosyl sulfatides (SM4s) and 49 lactosyl sulfatides (SM3) were identified. Quantitatively, the amount of SM3 was less than 1% of the amount of SM4s. The fatty acids of SM4s of healthy serum ( n = 8) were predominantly C16:0 and a hydroxylation C16:0 (C16:0h), followed by very long chain fatty acids (VLCFAs) predominant species, and SM3 was a major component of VLCFAs.

Conclusion

This present study described a simple method of human serum sulfatide analysis using MALDI-TOF MS. This method is suitable for clinical laboratories and is likely to increase the understanding of the roles of sulfatide species in both physiological and disease states.

Circulating Sulfatide, A Novel Biomarker for ST-Segment Elevation Myocardial Infarction

Aims: ST-segment elevation myocardial infarction (STEMI) is an acute inflammatory and thrombotic disease due to coronary artery atherosclerotic lesions. Studies have established the correlation of serum sulfatides with inflammation, thrombogenesis, and atherosclerosis. We observed that serum sulfatides level significantly increased in STEMI patients. In this study, we try to identify the relationship of serum sulfatides level on clinical outcomes of patients in STEMI.

Methods: Serum sulfatides level was monitored in 370 inpatients within 24 h of STEMI onset. On the basis of the level of serum sulfatides that was below 10 µmol/L in the normal population, the patients were divided into two groups with the median value of 15.2 µmol/L; low sulfatide group [serum sulfatides level ≤ 15.2 µmol/L (n = 200)] and high sulfatide group [serum sulfatides level > 15.2 µmol/L (n = 170)]. Patients' baseline characteristics, in-hospital outcomes, and late major adverse cardiovascular events (MACE) were analyzed. Independent incident for in-hospital death and late adverse events were modeled by multivariate logistic and Cox regression analysis.

Results: Between the two groups, there were no differences in the angiographic characteristics, percutaneous coronary intervention (PCI) results, and in-hospital recovery. However, high serum sulfatides level is positively correlated with increased rate of in-hospital death (OR 0.971; 95% CI 0.926–0.990, p = 0.019). In addition, this group of patients has more cumulative incidences of target vessel revascularization (TVR) (23% vs. 8%, p < 0.05) and increased overall MACE (28% vs. 10%, p < 0.05). Cox regression analysis indicated that high serum sulfatides level contributes to TVR and overall MACE.

Conclusions: Elevated serum sulfatides level positively correlate with in-hospital death and complications (TVR and MACE) in STEMI patients.

Impact of chronic kidney dysfunction on serum Sulfatides and its metabolic pathway in mice

Serum sulfatides are critical glycosphingolipids that are present in lipoproteins and exert anticoagulant effects. A previous study reported decreased levels of serum sulfatides in hemodialysis patients and suggested an association with cardiovascular disease. However, the mechanism of changes in serum sulfatides in chronic kidney dysfunction has not been well investigated. The current study examined whether a chronic kidney disease (CKD) state could decrease serum sulfatide levels using 5/6 nephrectomy (5/6NCKD) mice, an established CKD murine model, and studied the mechanisms contributing to diminished sulfatides. 5/6NCKD mice and sham operation control mice were sacrificed at the 4th or 12th postoperative week (POW) for measurement of serum sulfatide levels. Hepatic sulfatide content, which is the origin of serum sulfatides, and the expression of sulfatide metabolic enzymes in liver tissue were assessed as well. The 5/6NCKD mice developed CKD and showed increased serum creatinine and indoxyl sulfate. The serum levels and hepatic amounts of sulfatides were significantly decreased in 5/6NCKD mice at both 4 and 12 POW, while the degradative enzymes of sulfatides arylsulfatase A and galactosylceramidase were significantly increased. In a Hepa1-6 murine liver cell line, indoxyl sulfate addition caused intracellular levels of sulfatides to decrease and degradative enzymes of sulfatides to increase in a manner comparable to the changes in 5/6NCKD mice liver tissue. In conclusion, chronic kidney dysfunction causes degradation of sulfatides in the liver to decrease serum sulfatide levels. One explanation of these results is that indoxyl sulfate, a uremic toxin, accelerates the degradation of sulfatides in liver tissue.

Peroxisome proliferator-activated receptor α attenuates high-cholesterol diet-induced toxicity and pro-thrombotic effects in mice

Peroxisome proliferator-activated receptor α (PPARα) is involved in the regulation of fatty acid and cholesterol metabolism. A high-cholesterol (HC) diet increases the risk of developing cardiovascular diseases (CVD); however, it is unclear whether the toxic effects of cholesterol involve changes in thrombotic factor expression, and whether PPARα is necessary for such effects. To investigate this possibility, we fed a HC diet to wild-type (WT) and Ppara-null mice and measured cholesterol and triglyceride contents, liver histology, serum/plasma levels of coagulation factors, hepatic expression of the coagulation factors, liver/serum sulfatide levels, hepatic sulfatide metabolism, hepatic expression of lipid transporters, and hepatic oxidative stress and its relating enzymes. In Ppara-null mice, the HC diet caused triglyceride accumulation and exacerbated inflammation and oxidative stress in liver, increased levels of coagulation factors, including tissue factor, plasminogen activator inhibitor-1 and carboxypeptidase B2 in blood and liver, and decreased levels of anti-thrombotic sulfatides in serum and liver. These changes were much less marked in WT mice. These findings imply that cholesterol overload exerts its toxic effects at least in part by enhancing thrombosis, secondary to abnormal hepatic lipid metabolism, inflammation, and oxidative stress. Moreover, we reveal for the first time that PPARα can attenuate these toxic effects by transcriptional regulation of coagulation factors and sulfatides, in addition to its known effects of controlling lipid homeostasis and suppressing inflammation and oxidative stress. Therapies aimed at activating PPARα might prevent HC diet-induced CVD through modulating various pro- and anti-thrombotic factors.

Decreased Fatty Acid β-Oxidation Is the Main Cause of Fatty Liver Induced by Polyunsaturated Fatty Acid Deficiency in Mice

Insufficient intake of polyunsaturated fatty acids (PUFA) causes fatty liver. The mechanism responsible is primarily related to increased lipogenesis and decreased FA degradation based on rodent studies. However, these studies were limited by the fact that the typical PUFA-deficient diets contained insufficient amounts of long-chain FA, the PUFA-containing diets were primarily composed of n-3 PUFA-enriched oil, and the intake of PUFA was excessive compared with the physiological requirement. To address these issues, mice were fed a PUFA-deficient diet containing long-chain FA at a standard fed level and then were orally fed a n-3/n-6-balanced PUFA-containing oil [PUFA (+)] or a PUFA-deficient oil [PUFA (-)] at physiological relevant levels (0.1 mL/mouse/2d). We compared these groups and examined whether fatty liver in PUFA deficiency was attributable to both the effects of increased lipogenesis and decreased FA catabolism. Compared with the PUFA (+) group, the PUFA (-) group showed increases in liver triglyceride and serum FA content. Hepatic gene expression of several mitochondrial β-oxidation enzymes, the serum 3-hydroxybutyrate level, and DNA-binding ability of peroxisome proliferator-activated receptor α (PPARα) were increased in the PUFA (+) group, whereas these adaptive responses were significantly attenuated in the PUFA (-) group. The hepatic expression of typical lipogenesis genes did not differ between the groups. Therefore, fatty liver in PUFA deficiency is attributable to suppression of the FA-degrading system probably from decreased PPARα adaptive responsiveness, and PUFA may be an essential factor for PPARα functioning. This finding is helpful for managing clinical situations having a risk of PUFA deficiency.

Port-to-port delivery: Mobilization of toxic sphingolipids via extracellular vesicles

The discovery that most cells produce extracellular vesicles (EVs) and release them in the extracellular milieu has spurred the idea that these membranous cargoes spread pathogenic mechanisms. In the brain, EVs may have multifold and important physiological functions, from deregulating synaptic activity to promoting demyelination to changes in microglial activity. The finding that small EVs (exosomes) contain α-synuclein and β-amyloid, among other pathogenic proteins, is an example of this notion, underscoring their potential role in the brains of patients with Parkinson's and Alzheimer's diseases. Given that they are membranous vesicles, we speculate that EVs also have an intrinsic capacity to incorporate sphingolipids. In conditions under which these lipids are elevated to toxic levels, such as in Krabbe's disease and metachromatic leukodystrophy, EVs may contribute to spread disease from sick to healthy cells. In this essay, we discuss a working hypothesis that brain cells in sphingolipidoses clear some of the accumulated lipid material to attempt restoring cell homeostasis via EV secretion. We hypothesize that secreted sphingolipid-loaded EVs shuttle pathogenic lipids to cells that are not intrinsically affected, contributing to establishing non-cell-autonomous defects. © 2016 Wiley Periodicals, Inc.

High-throughput analysis of sulfatides in cerebrospinal fluid using automated extraction and UPLC-MS/MS

Sulfatides (STs) are a group of glycosphingolipids that are highly expressed in brain. Due to their importance for normal brain function and their potential involvement in neurological diseases, development of accurate and sensitive methods for their determination is needed. Here we describe a high-throughput oriented and quantitative method for the determination of STs in cerebrospinal fluid (CSF). The STs were extracted using a fully automated liquid/liquid extraction method and quantified using ultra-performance liquid chromatography coupled to tandem mass spectrometry. With the high sensitivity of the developed method, quantification of 20 ST species from only 100 μl of CSF was performed. Validation of the method showed that the STs were extracted with high recovery (90%) and could be determined with low inter- and intra-day variation. Our method was applied to a patient cohort of subjects with an Alzheimer's disease biomarker profile. Although the total ST levels were unaltered compared with an age-matched control group, we show that the ratio of hydroxylated/nonhydroxylated STs was increased in the patient cohort. In conclusion, we believe that the fast, sensitive, and accurate method described in this study is a powerful new tool for the determination of STs in clinical as well as preclinical settings.

Tandem Mass Spectrometry of Sphingolipids: Applications for Diagnosis of Sphingolipidoses

In recent years, mass spectrometry (MS) has become the dominant technology in lipidomic analysis. It is widely used in diagnosis and research of lipid metabolism disorders including those characterized by impairment of lysosomal functions and storage of nondegraded-degraded substrates. These rare diseases, which include sphingolipidoses, have severe and often fatal clinical consequences. Modern MS methods have contributed significantly to achieve a definitive diagnosis, which is essential in clinical practice to begin properly targeted patient care. Here we summarize MS and tandem MS methods used for qualitative and quantitative analysis of sphingolipids (SL) relative to the diagnostic process for sphingolipidoses and studies focusing on alterations in cell functions due to these disorders. This review covers the following topics: Tandem MS is sensitive and robust in determining the composition of sphingolipid classes in various biological materials. Its ability to establish SL metabolomic profiles using MS bench-top analyzers, significantly benefits the first stages of a diagnosis as well as metabolic studies of these disorders. It can thus contribute to a better understanding of the biological significance of SL.

Age-dependent PPARα activation induces hepatic sulfatide accumulation in transgenic mice carrying the hepatitis C virus core gene

Sulfatides, a type of glycosphingolipid, are associated with carcinogenesis. Peroxisome proliferator-activated receptor α (PPARα) is involved in the regulation of sulfatide metabolism as well as in cancer development. We previously reported that transgenic (Tg) mice expressing hepatitis C virus core protein (HCVcp) exhibited age-dependent PPARα activation and carcinogenesis in liver. However, the metabolism of sulfatides in hepatocellular carcinoma is unknown. To examine the relationship between sulfatide metabolism, carcinogenesis, HCVcp, and PPARα, age-dependent changes of these factors were examined in HCVcpTg, PPARα inhibitor-treated HCVcpTg, and non-Tg mice. The sulfatide content in liver, the hepatic expression of two key enzymes catalyzing the initial and last reactions in sulfatide synthesis, the hepatic expression of known sulfatide-transferring protein, oxidative stress, and hepatic PPARα expression and its activation were age-dependently increased in HCVcpTg mice. The increased synthesis and accumulation of sulfatides and PPARα activation were significantly enhanced in liver cancer lesions. These changes were attenuated by PPARα inhibitor treatment and not observed in non-Tg mice. These results suggest that HCVcp-induced age-dependent PPARα activation increases synthesis of sulfatides and the resulting sulfatide accumulation affects HCV-related liver cancer. The monitoring of hepatic sulfatide content and the modulation of sulfatide generation by intervention using a PPARα inhibitor might be useful for the prediction and prevention of HCV-related hepatocarcinogenesis, respectively.

Distribution of C16:0, C18:0, C24:1, and C24:0 sulfatides in central nervous system lipid rafts by quantitative ultra-high-pressure liquid chromatography tandem mass spectrometry

Sulfated galactosylceramides (sulfatides) are glycosphingolipids associated with cholesterol- and sphingolipid-enriched membrane microdomains (lipid rafts) and are highly expressed in brain tissue. Although it is known that sulfatide species show heterogeneity in their fatty acid acyl group composition throughout brain development, their lipid raft distribution and biological relevance is poorly understood. We validated a fast and sensitive ultra-high-pressure liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) method to measure developmentally regulated sulfatide species (C16:0, C18:0, C24:1, and C24:0) in central nervous system (CNS) lipid rafts isolated without using detergent. Our UHPLC-MS/MS assay showed good accuracy and precision with a linear range of 5 to 1,000 nM for C18:0 and C24:1 sulfatides and 10 to 1,000 nM for C16:0 and C24:0 sulfatides. We applied this quantitative analysis to detergent-free lipid rafts isolated from wild-type mice and arylsulfatase A-deficient (ASA knockout) mice that accumulate sulfatides. All four sulfatide species were more abundant in raft membranes than in non-raft membranes, with a significant increase in lipid rafts isolated from ASA knockout mice. This is the first description of an analytical method to study these sulfatide species in raft and non-raft membranes and has the potential to be applied to preparations from other tissues.

Association between serum sulfatide and carotid intima media thickness in patients with familial hypercholesterolemia

There is a positive association between sulfatide and atherosclerosis in an animal model for human familial hypercholesterolemia. Carotid intima-media thickness (IMT) is thought to be a marker of atherosclerosis in humans. We investigated the relationship between sulfatide and carotid IMT in heterozygous familial hypercholesterolemia (FH) patients. Thirty-five genetically-verified heterozygous patients with FH and 34 healthy controls were recruited into our study. We measured serum sulfatide levels, the carotid IMT, and conventional cardiovascular risk factors including obesity parameters, blood pressure, fasting blood glucose, and lipid profiles. Subjects with heterozygous FH had significantly elevated serum sulfatide, elevated total cholesterol, low-density lipoprotein cholesterol, and increased carotid IMT compared with control subjects. In patients with FH, univariate analysis showed that serum sulfatide was significantly correlated with carotid IMT. Multiple linear regression analysis indicated that serum sulfatide was the only independent predictor of carotid IMT in patients with FH. Patients with heterozygous FH had significantly higher carotid IMT and the level of serum sulfatide was independently associated with atherosclerotic progression. (R: 0.720, R(2): 0.503, p < 0.001).

Ultra-performance liquid chromatography/tandem mass spectrometry for determination of sulfatides in dried blood spots from patients with metachromatic leukodystrophy

RATIONALE

Metachromatic leukodystrophy (MLD) is a genetic autosomal recessive disease caused by a deficiency in arylsulfatase A. Accumulated sulfatides can be detected in the urine and detection of sulfatiduria is a useful test for diagnosis and monitoring. To our knowledge, no studies have explored the accumulation of sulfatides in dried blood spots (DBSs). We developed an ultra-performance liquid chromatography/tandem mass spectrometry (UPLC/MS/MS) method for measuring sulfatides in DBSs from patients with MLD.

METHODS

DBSs were eluted with internal standard. After mixing and centrifugation, the organic layer was transferred to a 96-well microplate and dried, then resuspended in methanol/propanol solution. Samples were analyzed on an UPLC system. Total running time was 4 min. Quantification was achieved by multiple reaction monitoring using a tandem mass spectrometer. We evaluated the precision, linearity, and ion suppression of the method and analyzed sulfatide concentrations in DBS specimens from MLD patients (n = 9), pseudodeficiency (PD) patient (n = 1), obligate heterozygotes (OH) (n = 2) and normal controls (n = 124).

RESULTS

In negative-ion mode, sulfatides species subjected to collision-induced dissociation readily fragment to produce an intense ion at m/z 96.8 (HSO4(-)). The precisions of low and high concentration controls ranged from 5.4 to 19.9%. The sulfatides produced linear responses. Molecular species of sulfatides were barely detected in DBSs from normal individuals and the PD-OH group [mean (range), 0.07 (<0.05-0.34) and 0.13 (<0.05-0.22) µg/mL, respectively]. In contrast, the DBSs from MLD patients showed a marked increase in several molecular species of sulfatide [mean (range), 2.02 (1.18-3.89) µg/mL].

CONCLUSIONS

Simultaneous detection for sulfatides using UPLC/MS/MS can be successfully applied to DBS analysis. This method provides a fast and effective screening and monitoring tool for the diagnosis and treatment of MLD.

Chronic ethanol consumption decreases serum sulfatide levels by suppressing hepatic cerebroside sulfotransferase expression in mice

Epidemiological studies demonstrate a possible relationship between chronic ethanol drinking and thrombotic diseases, such as myocardial infarction and stroke. However, the precise mechanism for this association remains unclear. Sulfatides are endogenous glycosphingolipids composed of ceramide, galactose, and sulfate, known to have anti-thrombotic properties. Low (0.5 g/kg/day), middle (1.5 g/kg/day), and high (3.0 g/kg/day) doses of ethanol were administered for 21 days intraperitoneally to female wild-type mice, and serum/liver sulfatide levels were measured. No significant changes in cholesterol and triglycerides were seen in serum and liver by ethanol treatment. However, serum/liver sulfatide levels were significantly decreased by middle- and high-dose ethanol treatment, likely due to downregulation of hepatic cerebroside sulfotransferase (CST) levels. Marked decreases in the expression of catalase and superoxide dismutases and ensuing increases in lipid peroxides were also observed in the livers of mice with middle- and high-dose ethanol treatment, suggesting the association between the suppression of hepatic CST expression and enhancement of oxidative stress. Furthermore, serum levels of tissue factor, a typical pro-coagulant molecule, were significantly increased in the mice with middle- and high-dose ethanol treatment showing decreases in serum sulfatide levels. Collectively, these results demonstrate that chronic ethanol consumption reduces serum sulfatide levels by increasing oxidative stress and decreasing the expression of CST in the liver. These findings could provide a mechanism by which chronic ethanol drinking increases thrombotic events.

Peroxisome proliferator-activated receptor α mediates enhancement of gene expression of cerebroside sulfotransferase in several murine organs

Sulfatides, 3-O-sulfogalactosylceramides, are known to have multifunctional properties. These molecules are distributed in various tissues of mammals, where they are synthesized from galactosylceramides by sulfation at C3 of the galactosyl residue. Although this reaction is specifically catalyzed by cerebroside sulfotransferase (CST), the mechanisms underlying the transcriptional regulation of this enzyme are not understood. With respect to this issue, we previously found potential sequences of peroxisome proliferator-activated receptor (PPAR) response element on upstream regions of the mouse CST gene and presumed the possible regulation by the nuclear receptor PPARα. To confirm this hypothesis, we treated wild-type and Ppara-null mice with the specific PPARα agonist fenofibrate and examined the amounts of sulfatides and CST gene expression in various tissues. Fenofibrate treatment increased sulfatides and CST mRNA levels in the kidney, heart, liver, and small intestine in a PPARα-dependent manner. However, these effects of fenofibrate were absent in the brain or colon. Fenofibrate treatment did not affect the mRNA level of arylsulfatase A, which is the key enzyme for catalyzing desulfation of sulfatides, in any of these six tissues. Analyses of the DNA-binding activity and conventional gene expression targets of PPARα has demonstrated that fenofibrate treatment activated PPARα in the kidney, heart, liver, and small intestine but did not affect the brain or colon. These findings suggest that PPARα activation induces CST gene expression and enhances sulfatide synthesis in mice, which suggests that PPARα is a possible transcriptional regulator for the mouse CST gene.

Attenuation of kidney injuries maintains serum sulfatide levels dependent on hepatic synthetic ability: a possible involvement of oxidative stress

Serum sulfatides are the major glycosphingolipids in lipoproteins. Although serum sulfatides are mainly synthesized and secreted by the liver, they are significantly decreased when the kidneys are impaired. Our recent experimental study using a murine protein-overload nephropathy model suggested a hypothetical mechanism whereby serum sulfatides were reduced due to kidney dysfunction. This was the result of decreased hepatic expression of a sulfatide synthetic enzyme, cerebroside sulfotransferase (CST), which is associated with systemic enhancement of oxidative stress. However, there is a possibility that the experimental process, protein-overload itself, directly affected the sulfatide metabolism and oxidative stress in the liver. To determine whether kidney dysfunction actually reduces the hepatic synthesis of sulfatides via oxidative stress, we examined sulfatide levels, the hepatic content of metabolic sulfatide enzymes, and the degree of oxidative stress in protein-overload mice subjected to renoprotective therapy using clofibrate, a representative hypolipidemic medicine. Protein-overload mice exhibited marked kidney injuries, enhancement of hepatic oxidative stress, decreased levels of serum and hepatic sulfatides, and decreased expression of hepatic CST. The clofibrate treatment attenuated kidney damage and hepatic oxidative stress while maintaining serum/hepatic sulfatide levels and hepatic CST content in the mice. Because clofibrate monotherapy without protein-overload treatment only minimally affected these hepatic parameters, the hepatic synthesis of sulfatides appeared to be strongly influenced by kidney dysfunction and subsequent oxidative stress. This study suggests that the crosstalk between kidney dysfunction and hepatic sulfatide metabolism is mediated by oxidative stress. These results should help to understand the phenomenon in patients with end-stage kidney disease.

Hepatic Cerebroside Sulfotransferase Is Induced by PPARα Activation in Mice

Sulfatides are one of the major sphingoglycolipids in mammalian serum and are synthesized and secreted mainly from the liver as a component of lipoproteins. Recent studies revealed a protective role for serum sulfatides against arteriosclerosis and hypercoagulation. Although peroxisome proliferator-activated receptor (PPAR) α has important functions in hepatic lipoprotein metabolism, its association with sulfatides has not been investigated. In this study, sulfatide levels and the expression of enzymes related to sulfatide metabolism were examined using wild-type (+/+), Ppara-heterozygous (+/−), and Ppara-null (−/−) mice given a control diet or one containing 0.1% fenofibrate, a clinically used hypolipidemic drug and PPARα activator. Fenofibrate treatment increased serum and hepatic sulfatides in Ppara (+/+) and (+/−) mice through a marked induction of hepatic cerebroside sulfotransferase (CST), a key enzyme in sulfatide synthesis, in a PPARα-dependent manner. Furthermore, increases in CST mRNA levels were correlated with mRNA elevations of several known PPARα target genes, and such changes were not observed for other sulfatide-metabolism enzymes in the liver. These results suggest that PPARα activation enhances hepatic sulfatide synthesis via CST induction and implicate CST as a novel PPARα target gene.

Long-term improvement of oxidative stress via kidney transplantation ameliorates serum sulfatide levels

BACKGROUND

Oxidative stress (OS) is a strong risk factor for cardiovascular disease (CVD). The incidence of CVD is lower among kidney transplantation (KT) recipients than hemodialysis patients, and the reduction in OS may be one reason for this difference. Recently, serum sulfatides were recognized as a candidate inhibitory factor of CVD affected by OS. However, the long-term changes in OS and serum sulfatide levels in KT recipients are unknown.

METHODS

We investigated the long-term changes in a serum OS marker, malondialdehyde (MDA), and the serum sulfatide levels in 17 KT recipients. Multiple regression analysis was used to analyze the factors correlated with serum sulfatide levels.

RESULTS

The high serum levels of MDA in the KT recipients decreased dramatically but were still high 1 year after KT surgery. MDA levels decreased further and reached near-normal levels more than 3 years after the surgery. Similarly, over the same 3 years, the low serum sulfatide levels increased to near-normal levels, reaching saturation. Multiple regression analysis showed that the most significant factors influencing serum sulfatide levels were MDA and total cholesterol content.

CONCLUSIONS

The current results show that over the long term, the internal improvement brought about by successful KT can normalize OS. Oxidative normalization was significantly correlated with the restoration of serum sulfatide levels, which were also influenced by lipoprotein metabolism. The amelioration of serum sulfatide levels might contribute to the low incidence of CVD in KT recipients.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: an update for 2007-2008

This review is the fifth update of the original review, published in 1999, on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2008. The first section of the review covers fundamental studies, fragmentation of carbohydrate ions, use of derivatives and new software developments for analysis of carbohydrate spectra. Among newer areas of method development are glycan arrays, MALDI imaging and the use of ion mobility spectrometry. The second section of the review discusses applications of MALDI MS to the analysis of different types of carbohydrate. Specific compound classes that are covered include carbohydrate polymers from plants, N- and O-linked glycans from glycoproteins, biopharmaceuticals, glycated proteins, glycolipids, glycosides and various other natural products. There is a short section on the use of MALDI mass spectrometry for the study of enzymes involved in glycan processing and a section on the use of MALDI MS to monitor products of the chemical synthesis of carbohydrates with emphasis on carbohydrate-protein complexes and glycodendrimers. Corresponding analyses by electrospray ionization now appear to outnumber those performed by MALDI and the amount of literature makes a comprehensive review on this technique impractical. However, most of the work relating to sample preparation and glycan synthesis is equally relevant to electrospray and, consequently, those proposing analyses by electrospray should also find material in this review of interest.

Kidney transplantation recovers the reduction level of serum sulfatide in ESRD patients via processes correlated to oxidative stress and platelet count

Sulfatide is a major component of glycosphingolipids in lipoproteins. Recently, we reported that a low serum level of sulfatide in hemodialysis patients might be related to the high incidence of cardiovascular diseases. However, the serum kinetics of sulfatide in kidney disease patients and the function of endogenous serum sulfatide are still unclear. To obtain novel knowledge concerning these issues, we investigated the serum kinetics of sulfatide in 5 adult kidney transplant recipients. We also analyzed the correlated factors influencing the serum sulfatide level, using multiple regression analysis. Kidney transplantation caused a dramatic increase of serum sulfatide without an alteration of its composition in all recipients in a time-dependent manner; however, the recovery speed was slower than that of the improvement of kidney function and the serum sulfatide reached a nearly normal level after 1 year. Multiple regression analysis showed that the significant correlated factor influencing the serum sulfatide level was log duration (time parameter) throughout the observation period, and the correlated factors detected in the stable phase were the decrease of serum concentration of malondialdehyde (an oxidative stress marker) as well as the elevation of platelet count. The current study results demonstrated the gradual but reliable recovery of the serum sulfatide level in kidney transplant recipients for the first time, suggesting a close correlation between serum sulfatide and kidney function. The recovery of serum sulfatide might derive from the attenuation of systemic oxidative stress. The normal level of serum sulfatide in kidney transplant recipients might affect platelet function, and contribute to the reduction of cardiovascular disease incidence.

Selective desorption/ionization of sulfatides by MALDI-MS facilitated using 9-aminoacridine as matrix

Recently, we used the favorable properties of 9-aminoacridine (9-AA) as matrix for the quantitative analysis of acidic metabolites and glycerophospholipids from extracts of biological materials [Sun, G., Yang, K., Zhao, Z., Guan, S., Han, X., and Gross, R.W. (2007) A shotgun metabolomics approach for rapid analysis of negatively-charged water-soluble cellular metabolites from mouse heart tissue. Anal. Chem. 79: 6629-6640; Sun, G., Yang, K., Zhao, Z., Guan, S., Han, X., and Gross, R.W. (2008) Matrix-assisted laser desorption/ionization-time of flight mass spectrometric analysis of cellular glycerophospholipids enabled by multiplexed solvent dependent analyte-matrix interactions. Anal. Chem. 80: 7576-7585.] by MALDI-MS. Herein, we extend this discovery and identified the selective desorption/ionization of sulfatides over other examined anionic lipids present in lipid extracts of biological samples by MALDI-MS using 9-AA as matrix. Through this approach, a high throughput method for the quantitative analysis of low to very low abundance sulfatide molecular species directly from crude lipid extracts has been developed. This method possessed a linear dynamic range of over 1,000-fold, a detection limit at the high attomole level, and a reproducibility of approximately 10% deviation. Many potential factors that might affect the quantitation of sulfatide species employing the method were examined and their effects were found to be negligible within experimental error. Collectively, these results demonstrate a powerful high throughput method for the measurement of sulfatides directly from extracts of biological samples, facilitating the study of sulfatide metabolism, trafficking, and homeostasis in health and disease.

Kidney dysfunction induced by protein overload nephropathy reduces serum sulfatide levels in mice

We recently proposed serum sulfatides as a novel biomarker for cardiovascular disease in patients with end-stage renal failure (ESRF), based on the possible antithrombotic properties of this molecule. In this earlier study, the level of serum sulfatides was gradually decreased in parallel with kidney dysfunction; however the precise mechanism underlying this decrease was unknown. The aim of the present study was to investigate the mechanism underlying the decrease in serum sulfatide levels caused by kidney dysfunction in an experimental animal model. To produce a kidney dysfunction animal model, we prepared a mouse model of protein overload nephropathy. Using high-throughput analysis combined with matrix-assisted laser desorption ionisation time-of-flight mass spectrometry, we measured the levels of sulfatides in the sera, livers, small intestines and kidneys of protein overload nephropathy mice. As the disease progressed, the levels of sulfatides in sera decreased. Also, the levels in livers and small intestines decreased in a similar manner to those in sera, to approximately 60% of the original levels. On the contrary, those in kidneys increased by approximately 1.4-fold. Our results indicate that kidney dysfunction affects the levels of sulfatides in lipoprotein-producing organs, such as livers and small intestines, and lowers the levels of sulfatides in sera.

Acute kidney injury induced by protein-overload nephropathy down-regulates gene expression of hepatic cerebroside sulfotransferase in mice, resulting in reduction of liver and serum sulfatides

Sulfatides, possible antithrombotic factors belonging to sphingoglycolipids, are widely distributed in mammalian tissues and serum. We recently found that the level of serum sulfatides was significantly lower in hemodialysis patients than that in normal subjects, and that the serum level closely correlated to the incidence of cardiovascular disease. These findings suggest a relationship between the level of serum sulfatides and kidney function; however, the molecular mechanism underlying this relationship remains unclear. In the present study, the influence of kidney dysfunction on the metabolism of sulfatides was examined using an established murine model of acute kidney injury, protein-overload nephropathy in mice. Protein-overload treatment caused severe proximal tubular injuries within 4days, and this treatment obviously decreased both serum and hepatic sulfatide levels. The sphingoid composition of serum sulfatides was very similar to that of hepatic ones at each time point, suggesting that the serum sulfatide level is dependent on the hepatic secretory ability of sulfatides. The treatment also decreased hepatic expression of cerebroside sulfotransferase (CST), a key enzyme in sulfatide metabolism, while it scarcely influenced the expression of the other sulfatide-metabolizing enzymes, including arylsulfatase A, ceramide galactosyltransferase, and galactosylceramidase. Pro-inflammatory responses were not detected in the liver of these mice; however, potential oxidative stress was increased. These results suggest that down-regulation of hepatic CST expression, probably affected by oxidative stress from kidney injury, causes reduction in liver and serum sulfatide levels. This novel mechanism, indicating the crosstalk between kidney injury and specific liver function, may prove useful for helping to understand the situation where human hemodialysis patients have low levels of serum sulfatides.

Serum sulfatides as a novel biomarker for cardiovascular disease in patients with end-stage renal failure

Sulfatides, normal components of serum lipoproteins, may play an important role in cardiovascular disease due to their various modulatory functions in haemostasis. The incidence of cardiovascular disease in patients with end-stage renal failure undergoing maintenance hemodialysis has been reported to be approximately 10 to 30 times higher than that in the general population. To elucidate the possible roles of serum sulfatides in this high incidence, we measured the level of sulfatides in 59 such patients, by converting them to lysosulfatides according to a recently developed quantitative, qualitative, high-throughput technique using matrix-assisted laser desorption ionization-time of flight mass spectrometry. The mean level of sulfatides in patients 3.58 +/- 1.18 nmol/ml was significantly lower than that in age-matched normal subjects (8.21 +/- 1.50 nmol/ml; P < 0.001). Patients receiving maintenance hemodialysis over a longer period had lower levels of sulfatides. When the mean levels of sulfatides were compared between patients with cardiovascular disease (N = 22) and those without the disease (N = 37), the level in the former group 2.85 +/- 0.67 nmol/ml was found to be significantly lower than that in the latter group 4.01 +/- 1.22 nmol/ml (P < 0.001). These findings reveal a close correlation between low levels of serum sulfatides and a high risk of cardiovascular disease in these patients. Determination of the level of serum sulfatides can contribute to predictions of the incidence of cardiovascular disease in patients with end-stage renal failure undergoing maintenance hemodialysis.

Pipette tip solid-phase extraction and gas chromatography – mass spectrometry for the determination of methamphetamine and amphetamine in human whole blood

Methamphetamine and amphetamine were extracted from human whole blood samples using pipette tip solid-phase extraction (SPE) with MonoTip C(18) tips, on which C(18)-bonded monolithic silica gel was fixed. Human whole blood (0.1 mL) containing methamphetamine and amphetamine, with N-methylbenzylamine as an internal standard, was mixed with 0.4 mL of distilled water and 50 microL of 5 M sodium hydroxide solution. After centrifugation, the supernatant was extracted to the C(18) phase of the tip (pipette tip volume, 200 microL) by 25 repeated aspirating/dispensing cycles using a manual micropipettor. Analytes retained in the C(18) phase were eluted with methanol by five repeated aspirating/dispensing cycles. After derivatization with trifluoroacetic anhydride, analytes were measured by gas chromatography - mass spectrometry with selected ion monitoring in the positive-ion electron impact mode. Recoveries of methamphetamine and amphetamine spiked into whole blood were more than 87.6 and 81.7%, respectively. Regression equations for methamphetamine and amphetamine showed excellent linearity in the range of 0.5-100 ng/0.1 mL. The limits of detection for methamphetamine and amphetamine were 0.15 and 0.11 ng/0.1 mL, respectively. Intra- and interday coefficients of variation for both stimulants were not greater than 9.6 and 13.8%, respectively. The determination of methamphetamine and amphetamine in autopsy whole blood samples is presented, and was shown to validate the present methodology.