In vitro production of cytokines is influenced by sulfatide and its precursor galactosylceramide

Lipidomic Profiles in Diabetes and Dementia

Lipids are a diverse class of hydrophobic and amphiphilic molecules which make up the bulk of most biological systems and are essential for human life. The role of lipids in health and disease has been recognized for many decades, as evidenced by the early identification of cholesterol as an important risk factor of heart disease and the development and introduction of statins as a one of the most successful therapeutic interventions to date. While several studies have demonstrated an increased risk of dementia, including Alzheimer's disease (AD), in those with diabetes mellitus, the nature of this risk is not well understood. Recent developments in the field of lipidomics, driven primarily by technological advances in high pressure liquid chromatography and particularly mass spectrometry, have enabled the detailed characterization of the many hundreds of individual lipid species in mammalian systems and their association with disease states. Diabetes mellitus and AD have received particular attention due to their prominence in Western societies as a result of the ongoing obesity epidemic and the aging populations. In this review, we examine how these lipidomic studies are informing on the relationship between lipid metabolism with diabetes and AD and how this may inform on the common pathological pathways that link diabetes risk with dementia.

Role of sulfatide in normal and pathological cells and tissues

Sulfatide is 3-O-sulfogalactosylceramide that is synthesized by two transferases (ceramide galactosyltransferase and cerebroside sulfotransferase) from ceramide and is specifically degraded by a sulfatase (arylsulfatase A). Sulfatide is a multifunctional molecule for various biological fields including the nervous system, insulin secretion, immune system, hemostasis/thrombosis, bacterial infection, and virus infection. Therefore, abnormal metabolism or expression change of sulfatide could cause various diseases. Here, we discuss the important biological roles of sulfatide in the nervous system, insulin secretion, immune system, hemostasis/thrombosis, cancer, and microbial infections including human immunodeficiency virus and influenza A virus. Our review will be helpful to achieve a comprehensive understanding of sulfatide, which serves as a fundamental target of prevention of and therapy for nervous disorders, diabetes mellitus, immunological diseases, cancer, and infectious diseases.

Sulfatide inhibits α-galactosylceramide presentation by dendritic cells

Sulfatide-reactive type II NKT cells, the so-called non-invariant NKT (non-iNKT) cells, have been shown to counteract invariant NKT (iNKT) cell activity. However, the effects of sulfatide on activation of iNKT cells by α-galactocylceramide (αGC) in the context of CD1d have not been studied in detail. Therefore, we studied the blocking effect of sulfatide on αGC-induced iNKT cell activation by dendritic cells (DCs). Even in the absence of non-iNKT cells, sulfatide inhibited αGC-mediated iNKT cell activation by reducing αGC/CD1d complex formations in a dose-dependent manner. This was also confirmed in a cell-free setting using immobilized CD1d-Ig. Moreover, simultaneous injection of αGC with sulfatide decreased αGC/CD1d complex formations on DCs, accompanied by the reduced CD40L-up-regulation and IFN-γ production by iNKT cells and IL-12p70 production by DCs. However, sulfatide by itself did not interfere with the presentation of MHC class II-mediated antigen presentation to specific T cells. These results demonstrate that sulfatide competes with αGC to be loaded onto CD1d along the endocytic pathway in DCs, thereby inhibiting the iNKT cell response.

A subset of human pancreatic beta cells express functional CD14 receptors: a signaling pathway for beta cell-related glycolipids, sulfatide and β-galactosylceramide

BACKGROUND

T1DM is a T-cell-mediated autoimmune disease targeting insulin-producing beta-cells. Multiple factors may contribute to the development of T1DM. Among these, the metabolic state of beta-cells and pro-inflammatory cytokines, produced by infiltrating immune cells, have been implicated in the precipitation of T1DM.

METHODS AND RESULTS

In this study, confocal immunofluorescence microscopy of human pancreata revealed a distinct subset of beta-cells expressing the innate LPS co-receptor CD14. Human islets expressed fully functional CD14 as LPS stimulation led to a dose-dependent secretion of tumour necrosis factor (TNFα), interleukin (IL)-1β and IL-8, which were substantially inhibited by a blocking anti-CD14 mAb. In addition, LPS stimulation impaired the glucose-mediated insulin secretion in rat islets. β-GalCer and sulfatide, glycolipids that are related to insulin processing and secretion, are possibly interacting with the CD14 receptor complex. β-GalCer had an LPS-like, serum- and CD14-dependent effect on the induction of pro-inflammatory cytokines in a human monocyte cell line. In contrast, the LPS-mediated cytokine production was inhibited by sulfatide. Human islets also responded to β-GalCer (10 µg/mL) by secreting TNFα, IL-1β and IL-8, whereas sulfatide partly inhibited the effect of LPS.

CONCLUSIONS

A subset of human beta-cells expresses functional CD14 receptor and thus is able to recognize both exogenous bacterial (LPS) as well as endogenous ligands (e.g. glycolipids of beta-cell origin). The CD14 expression on a subset of human beta-cells may play a role in the innate surveillance of the endocrine environment but may also contribute to innate immune mechanisms in the early stages of beta-cell aggression.

A variation in the cerebroside sulfotransferase gene is linked to exercise-modified insulin resistance and to type 2 diabetes

Aims. The glycosphingolipid β-galactosylceramide-3-O-sulfate (sulfatide) is present in the secretory granules of the insulin producing β-cells and may act as a molecular chaperone of insulin. The final step in sulfatide synthesis is performed by cerebroside sulfotransferase (CST) (EC 2.8.2.11). The aim of this study was to investigate whether two single nucleotide polymorphisms (SNP), rs2267161 located in an exon or rs42929 located in an intron, in the gene encoding CST are linked to type 2 diabetes (T2D). Methods. As a population survey, 265 male and female patients suffering from T2D and 291 gender matched controls were examined. Results. A higher proportion of T2D patients were heterozygous at SNP rs2267161 with both T (methionine) and C (valine) alleles present (49.8% versus 41.3%, P = .04). The calculated odd risk for T2D was 1.47 (1.01–2.15, P = .047). Among female controls, the homozygous CC individuals displayed lower insulin resistance measured by HOMA-IR (P = .05) than the C/T or TT persons; this was particularly prevalent in individuals who exercise (P = .03). Conclusion. Heterozygosity at SNP rs2267161 in the gene encoding the CST enzyme confers increased risk of T2D. Females with the CC allele showed lower insulin resistance.

Sulfatide increases adiponectin and decreases TNF-alpha, IL-6, and IL-8 in human adipose tissue in vitro

Type 2 diabetes is associated with decreased levels of the glycosphingolipid sulfatide, as well as a state of low-grade inflammation. Sulfatide is reported to have anti-inflammatory properties in other cell-types. In the present study, the effects of sulfatide on adipokine (adiponectin, TNF-alpha, IL-6, and IL-8) production in human adipose tissue (AT) was investigated in vitro. Isolated human adipocytes and AT cultures were incubated with sulfatide isolated from pig brain [sulfatide containing a variety of fatty acids or isoforms of sulfatide with defined, saturated fatty acids with 16 (C16:0) or 24 (C24:0) carbon atoms]. Adiponectin production was increased 50-80%, by all sulfatide preparations. Only the C16:0 isoform decreased TNF-alpha, IL-6, and IL-8 production 20-30%. The C16:0 sulfatide has been shown to activate potassium channels in beta-cells, and glibenclamide, an ATP-sensitive K+-(KATP) channel blocker, reversed the C16:0-induced decrement in stimulated TNF-alpha, IL-6, and IL-8 release in adipocytes. Glibenclamide on its own was without effect on the production of adiponectin, TNF-alpha, IL-6, and IL-8. In conclusion, this study shows that, sulfatide exerts anti-inflammatory effects in human adipocytes and AT in vitro. Accordingly, the reported low serum levels of sulfatide in patients with type 2 diabetes might be of importance in relation to the chronic low-grade inflammatory state found in this disease.

Regulatory effect of sulphatides on BKCa channels

BACKGROUND AND PURPOSE

Sulphatides are sulphated glycosphingolipids expressed on the surface of many cell types, particularly neurones. Changes in sulphatide species or content have been associated with epilepsy and Alzheimer's disease. As the large conductance, calcium sensitive K(+) channel (BK(Ca)) are modulated by membrane lipids, the aim of the study was to explore possible effects of sulphatides on BK(Ca) channels.

EXPERIMENTAL APPROACH

Using patch-clamp techniques, we studied effects of exogenous sulphatides on BK(Ca) channels expressed in Chinese hamster ovary cells.

KEY RESULTS

Sulphatides reversibly increased the whole-cell current and the single channel open probability of BK(Ca) channels dose-dependently. The EC(50) value on the channel at +10 mV was 1.6 microM and the Hill coefficient was 2.5. In inside-out patches, sulphatides increased the single channel open probability from both intra- and extra-cellular faces of the membrane, but more effectively with external application. Furthermore, activation of the channels by sulphatides was independent of intracellular Ca(2+) concentration. Sulphatides also shifted the activation curve of the channels to less positive membrane potentials. Mutant BK(Ca) channels lacking a 59 aminoacid region important for amphipath activation (STREX) were less activated by the sulphatides.

CONCLUSIONS AND IMPLICATIONS

Sulphatides are novel activators of BK(Ca) channels, independent of intracellular Ca(2+) or other signalling molecules but partly dependent on the STREX sequence of the channel protein. As changes of sulphatide content are associated with neuronal dysfunction, as in epilepsy and Alzheimer's disease, our results imply that these effects of sulphatides may play important pathophysiological roles in regulation of BK(Ca) channels.

Uptake of the glycosphingolipid sulfatide in the gastrointestinal tract and pancreas in vivo and in isolated islets of Langerhans

Background

The glycosphingolipid sulfatide has previously been found in several mammalian tissues, but information on the uptake of exogenously administered sulfatide in different organs in vivo is limited. In pancreatic beta cells, sulfatide has been shown to be involved in insulin processing and secretion in vitro. In this study, we examined the uptake of exogenously administered sulfatide and its distribution to the pancreatic beta cells. This might encourage future studies of the function(s) of sulfatide in beta cell physiology in vivo. Radioactive sulfatide was given orally to mice whereafter the uptake of sulfatide in the gastrointestinal tract and subsequent delivery to the pancreas was examined. Sulfatide uptake in pancreas was also studied in vivo by i.p. administration of radioactive sulfatide in mice, and in vitro in isolated rat islets. Isolated tissue/islets were analysed by scintillation counting, autoradiography and thin-layer chromatography-ELISA.

Results

Sulfatide was taken up in the gastrointestinal tract for degradation or further transport to other organs. A selective uptake of short chain and/or hydroxylated sulfatide fatty acid isoforms was observed in the small intestine. Exogenously administered sulfatide was found in pancreas after i.p, but not after oral administration. The in vitro studies in isolated rat islets support that sulfatide, independently of its fatty acid length, is endocytosed and metabolised by pancreatic islets.

Conclusion

Our study supports a selective uptake and/or preservation of sulfatide in the gastrointestinal tract after oral administration and with emphasises on pancreatic sulfatide uptake, i.p. administration results in sulfatide at relevant location.

Involvement of sulfatide in beta cells and type 1 and type 2 diabetes

Mammalian tissues express beta-isoforms of glycosphingolipids and, among these, sulfatide (sulphated galactosylceramide) is present in the beta cells, and it is here that the short fatty acid chain (C16) isoform is predominately found. In vitro studies have shown that sulfatide preserves insulin crystals and facilitates insulin monomerisation under certain biochemical conditions. It also activates beta cell potassium channels and moderates insulin secretion. Anti-sulfatide antibodies are seen in type 1 diabetes, and immunological presentation of glycosphingolipids by the non-classical CD1 molecules has recently been reported. It is via this mechanism that alpha-galactosylceramide and sulfatide are able to influence the innate immune system and inhibit autoimmunity, possibly through regulatory natural killer T cells. Administration of sulfatide substantially reduces the incidence of diabetes in non-obese diabetic mice and prevents antigen-induced experimental autoimmune encephalomyelitis in wild-type mice. Sulfatide has specific anti-inflammatory properties, increasing the number of CD3+CD25+ regulatory T cells and reducing production of several cytokines, including TNF-alpha. Patients with type 2 diabetes have low serum concentrations of sulfatide, and some animal models of type 2 diabetes have low pancreatic expression of C16:0 sulfatide; administration of this increases insulin secretion and improves first-phase insulin response in Zucker fatty rats. Glycosphingolipids in general, and sulfatide in particular, appear relevant to both type 1 and type 2 diabetes.

Low serum concentration of sulfatide and presence of sulfated lactosylceramid are associated with Type 2 diabetes. The Skaraborg Project

AIMS

The glycosphingolipid sulfatide (sulfated galactosyl-ceramide) increases exocytosis of beta-cell secretory granules, activates K(ATP)-channels and is thereby able to influence insulin secretion through its presence in the islets. A closely related compound, sulfated lactosylceramide (sulf-lac-cer), is present in the islets during fetal and neonatal life when, as in Type 2 diabetes, insulin is secreted autonomically without the usual first phase response to glucose. The aim was to examine whether serum concentrations of these glycolipids are associated with Type 2 diabetes.

METHODS

A case-control study, comprising 286 women and 283 men, was designed using a population-based sample of patients with Type 2 diabetes and a population survey.

RESULTS

Low serum concentrations of sulfatide were associated with Type 2 diabetes, independent of traditional risk factors for diabetes in a sex-specific analysis: odds ratio (OR) 2.1 (95% confidence interval 1.1, 3.9) in men, and 2.3 (1.2, 4.3) in women, comparing the lowest and the highest tertiles. Type 2 diabetes was also associated with detectable amounts of sulf-lac-cer in serum: OR 1.7 (0.9, 3.4) in men, and 7.6 (3.8, 15.2) in women. After adjustment for confounding from other diabetes risk factors, these associations remained basically unchanged. The connections between sulfatide and Type 2 diabetes, and sulf-lac-cer and Type 2 diabetes were independent of each other. Insulin resistance (HOMA-IR) was negatively correlated with sulfatide concentration and positively correlated with sulf-lac-cer (both P < 0.0001, independently).

CONCLUSIONS

We report a new, robust and highly significant independent association between Type 2 diabetes and serum concentrations of sulfatide in both sexes, and sulf-lac-cer in females. The associations were also independent of other known diabetes risk factors.

C3 binding glycoprotein from Cuscuta europea induced different cytokine profiles from human PBMC compared to other plant and bacterial immunomodulators

The immunomodulatory properties of bioactive agents include the ability to induce cytokine production by the activated target cell. The effect of immunomodulatory C3 binding glycoprotein isolated from Cuscuta europea on the induction of human PBMC cytokine synthesis and the cell viability was investigated. Isolated PBMC from healthy donors were cultured for 24 h with C3bgp. We also studied the influence of C3bgp on the cytokine production in LPS, PHA, PWM and Dex treated PBMC. The quantitative determination of TNF-alpha, IL-12, IL-6 and IL-10 was performed in culture supernatant by ELISA. Results obtained demonstrated that C3bgp induced proinflammatory and immunoregulatory cytokine production, in the highest degree IL-12, followed by IL-6 and in lower degree TNF-alpha. IL-12 quantity was significantly increased in C3bgp stimulated cultures in comparison with LPS, PHA and PWM stimulated PBMC. C3bgp also increased IL-12 in PHA or PWM stimulated cultures, but not in LPS stimulated culture. C3bgp significantly increased IL-6 production compared to the PHA and PWM but not to LPS stimulation. On the other side, C3bgp inhibited IL-10 production after LPS, PHA and PWM stimulation. Cell viability in C3bgp stimulated cultures retained on the same level from 72 to 120 h of culturing, in contrast to LPS and PHA stimulated cultures. Based on the results presented, we conclude that the C3bgp exhibited immunomodulatory properties on the human PBMC. The ability of PDTC and Dex to down-regulate the effect of C3bgp on the proinflammatory cytokine production suggests that a part of the mechanism of action of C3bgp is mediated through NF-kB signal transduction pathway.

Beta-galactosylceramide increases and sulfatide decreases cytokine and chemokine production in whole blood cells

The glycosphingolipid sulfatide and its immediate precursor beta-galactosylceramide (GalCer) are present in the pancreatic beta-cell in equimolar concentrations and may play a role in islet pathology. Previous studies of mononuclear cells have shown that sulfatide tends to decrease and GalCer tends to increase the production of proinflammatory cytokines. In this study we investigated the influence of various isoforms of sulfatide on the production of cyto- and chemokines and tested whether the opposing effects of GalCer and sulfatide could counter one another in competition assays. PHA-, LPS-, or unstimulated whole blood cultures were incubated with 30 microg/ml of native sulfatide (isolated from pig brains), C:16:0 and C:24:0 analogues of sulfatide, or native GalCer preparations. After 24 h, the supernatant levels of proinflammatory cytokines and chemokines were quantitated by ELISA. The general trend was for the sulfatides to lower the production of the cytokines, and for GalCer to increase it. In competition assays, native sulfatide dampened the stimulatory effects of GalCer but did not abolish cytokine release; GalCer, on the other hand, nullified the effect of native sulfatide at a ratio of four sulfatide molecules to one GalCer molecule. C:16:0 sulfatide appeared to have a stronger effect than C:24:0 sulfatide. The C:16:0 analogue decreased IL-1beta, IL-6, TNF-alpha, MIP-1alpha and IL-8 to 3-56% of control values (P < 0.05-0.01), while GalCer increased their production 2- to 10-fold (P < 0.01). In conclusion, sulfatide decreases the in vitro production of proinflammatory cytokines, whereas GalCer has the opposite effect.

Sulfatide controls insulin secretion by modulation of ATP-sensitive K(+)-channel activity and Ca(2+)-dependent exocytosis in rat pancreatic beta-cells

The glycosphingolipid sulfatide is present in secretory granules and at the surface of pancreatic beta-cells, and antisulfatide antibodies (ASA; IgG1) are found in serum from the majority of patients with newly diagnosed type 1 diabetes. Here we demonstrate that sulfatide produced a glucose- and concentration-dependent inhibition of insulin release from isolated rat pancreatic islets. This inhibition of insulin secretion was due to activation of ATP-sensitive K(+)-(K(ATP)) channels in single rat beta-cells. No effect of sulfatide was observed on whole-cell Ca(2+)-channel activity or glucose-induced elevation of cytoplasmic Ca(2+) concentration. It is interesting that sulfatide stimulated Ca(2+)-dependent exocytosis determined by capacitance measurements and depolarized-induced insulin secretion from islets exposed to diazoxide and high external KCl. The monoclonal sulfatide antibody Sulph I as well as ASA-positive serum reduced glucose-induced insulin secretion by inhibition of Ca(2+)-dependent exocytosis. Our data suggest that sulfatide is important for the control of glucose-induced insulin secretion and that both an increase and a decrease in the sulfatide content have an impact on the secretory capacity of the individual beta-cells.

[Transforming growth factor beta (TGF-beta) in Gaucher's disease. Preliminary results in a group of patients and their carrier and non-carrier relatives]

BACKGROUND

The poor phenotype/genotype correlation in Gaucher's disease makes difficult therapy-decision-making and prevention of complications. Gaucher's cells and tissue fibrosis are the earliest findings of the disease. Transforming growth factor ss (TGF-beta1) is the key cytokine involved in the regulation of tissular scarring and fibrosis. The aim of the study was to ascertain if there are differences in plasma TGF-beta1 between Gaucher's disease patients, carriers and non-carriers healthy people and whether there is any correlation between plasma TGF-beta1 and clinical phenotype among patients.

PATIENTS AND METHOD

Plasma TGF-beta1 was measured in 11 patients with Gaucher's disease, 12 carriers and 10 healthy people. Patients were further evaluated to know their liver and spleen size, bone involvement, hemoglobin, leukocyte and platelet count and the Zimran's severity score index (SSI). Plasma concentration of TGF-beta1 was determined by RIA phenotypic sandwich antibodies assay and quantified by a colorimetric procedure. Sensitivity was 25 pg/ml and specificity (cross reactivity) < 5% with beta2-TGF and beta3-TGF.

STATISTICS

ANOVA and T-test were applied for mean comparisons and subgroup analyses.

RESULTS

Plasma TGF-beta1 values were increased in Gaucher's disease patients (98.4 [91.4] pg/ml) over carriers (47.2 [21,7] pg/ml; p = 0.04) and healthy relatives (40.8 [9.8] pg/ml; p = 0.02). No differences in patients subgroups, with regard to SSI or bone involvement, were observed.

CONCLUSIONS

Plasma TGF-beta1 levels are increased in this group of patients with Gaucher's disease. Since there is no correlation between the plasma values and the phenotypic expression, TGF-beta1 could merely be a marker of macrophage activation.