Sphingosine kinase inhibition exerts both pro- and anti-atherogenic effects in low-density lipoprotein receptor-deficient (LDL-R(-/-)) mice

Sphingosine-1-phosphate receptor 3 regulates the transendothelial transport of high-density lipoproteins and low-density lipoproteins in opposite ways

AIMS

The entry of lipoproteins from blood into the arterial wall is a rate-limiting step in atherosclerosis. It is controversial whether this happens by filtration or regulated transendothelial transport.Because sphingosine-1-phosphate (S1P) preserves the endothelial barrier, we investigated in vivo and in vitro, whether S1P and its cognate S1P-receptor 3 (S1P3) regulate the transendothelial transport of lipoproteins.

METHODS AND RESULTS

Compared to apoE-haploinsufficient mice (CTRL), apoE-haploinsufficient mice with additional endothelium-specific knock-in of S1P3 (S1P3-iECKI) showed decreased transport of LDL and Evan's Blue but increased transport of HDL from blood into the peritoneal cave. After 30 weeks of high-fat diet feeding, S1P3-iECKI mice had lower levels of non-HDL-cholesterol and less atherosclerosis than CTRL mice. In vitro stimulation with an S1P3 agonist increased the transport of 125I-HDL but decreased the transport of 125I-LDL through human aortic endothelial cells (HAECs). Conversely, inhibition or knock-down of S1P3 decreased the transport of 125I-HDL but increased the transport of 125I-LDL. Silencing of SCARB1 encoding scavenger receptor B1 (SR-BI) abrogated the stimulation of 125I-HDL transport by the S1P3 agonist. The transendothelial transport of 125I-LDL was decreased by silencing of SCARB1 or ACVLR1 encoding activin-like kinase 1 but not by interference with LDLR. None of the three knock-downs prevented the stimulatory effect of S1P3 inhibition on transendothelial 125I-LDL transport.

CONCLUSION

S1P3 regulates the transendothelial transport of HDL and LDL oppositely by SR-BI-dependent and SR-BI-independent mechanisms, respectively. This divergence supports a contention that lipoproteins pass the endothelial barrier by specifically regulated mechanisms rather than passive filtration.

Sphingosine-1-Phosphate (S1P) Lyase Inhibition Aggravates Atherosclerosis and Induces Plaque Rupture in ApoE−/− Mice

Altered plasma sphingosine-1-phosphate (S1P) concentrations are associated with clinical manifestations of atherosclerosis. However, whether long-term elevation of endogenous S1P is pro- or anti-atherogenic remains unclear. Here, we addressed the impact of permanently high S1P levels on atherosclerosis in cholesterol-fed apolipoprotein E-deficient (ApoE^−/−) mice over 12 weeks. This was achieved by pharmacological inhibition of the S1P-degrading enzyme S1P lyase with 4-deoxypyridoxine (DOP). DOP treatment dramatically accelerated atherosclerosis development, propagated predominantly unstable plaque phenotypes, and resulted in frequent plaque rupture with atherothrombosis. Macrophages from S1P lyase-inhibited or genetically deficient mice had a defect in cholesterol efflux to apolipoprotein A-I that was accompanied by profoundly downregulated cholesterol transporters ATP-binding cassette transporters ABCA1 and ABCG1. This was dependent on S1P signaling through S1PR3 and resulted in dramatically enhanced atherosclerosis in ApoE^−/−/S1PR3^−/− mice, where DOP treatment had no additional effect. Thus, high endogenous S1P levels promote atherosclerosis, compromise cholesterol efflux, and cause genuine plaque rupture.

Hepatic FoxOs link insulin signaling with plasma lipoprotein metabolism through an apolipoprotein M/sphingosine-1-phosphate pathway

Multiple beneficial cardiovascular effects of HDL depend on sphingosine-1-phosphate (S1P). S1P associates with HDL by binding to apolipoprotein M (ApoM). Insulin resistance is a major driver of dyslipidemia and cardiovascular risk. However, the mechanisms linking alterations in insulin signaling with plasma lipoprotein metabolism are incompletely understood. The insulin-repressible FoxO transcription factors mediate key effects of hepatic insulin action on glucose and lipoprotein metabolism. This work tested whether hepatic insulin signaling regulates HDL-S1P and aimed to identify the underlying molecular mechanisms. We report that insulin-resistant, nondiabetic individuals had decreased HDL-S1P levels, but no change in total plasma S1P. This also occurred in insulin-resistant db/db mice, which had low ApoM and a specific reduction of S1P in the HDL fraction, with no change in total plasma S1P levels. Using mice lacking hepatic FoxOs (L-FoxO1,3,4), we found that hepatic FoxOs were required for ApoM expression. Total plasma S1P levels were similar to those in controls, but S1P was nearly absent from HDL and was instead increased in the lipoprotein-depleted plasma fraction. This phenotype was restored to normal by rescuing ApoM in L-FoxO1,3,4 mice. Our findings show that insulin resistance in humans and mice is associated with decreased HDL-associated S1P. Our study shows that hepatic FoxO transcription factors are regulators of the ApoM/S1P pathway.

The Role of Lymphangiogenesis in Coronary Atherosclerosis

Lymphatic circulation, a one-way channel system independent of blood circulation, collects interstitial fluid in a blind-end way. Existing widely in various organs and tissues, lymphatic vessels play important roles in maintaining tissue fluid homeostasis, regulating immune function, and promoting lipid transport. Recent studies have shown clear evidence that lymphangiogenesis has a strong mutual effect on coronary atherosclerosis (AS). In this study, we focus on this topic, especially in the aspects of relevant ligand/receptor, inflammation, and adipose metabolism. For the moment, however, the role of lymphangiogenesis and remodeling in coronary AS still remains controversial. The studies of our group and accumulating published evidence show that the pathological remodeling of lymphatic vessels in coronary AS may have a negative effect, but normal functional lymphangiogenesis is probably beneficial to the regression of coronary AS. Thus, the conclusion of this review is that lymphatic vessel function rather than its quantity determines its influence in AS, which needs more evidence to support.

S1P in the development of atherosclerosis: roles of hemodynamic wall shear stress and endothelial permeability

Atherosclerosis is characterized by focal accumulations of lipid within the arterial wall, thought to arise from effects of hemodynamic wall shear stress (WSS) on endothelial permeability. Identifying pathways that mediate the effects of shear on permeability could therefore provide new therapeutic opportunities. Here, we consider whether the sphingosine-1-phosphate (S1P) pathway could constitute such a route. We review effects of S1P in endothelial barrier function, the influence of WSS on S1P production and signaling, the results of trials investigating S1P in experimental atherosclerosis in mice, and associations between S1P levels and cardiovascular disease in humans. Although it seems clear that S1P reduces endothelial permeability and responds to WSS, the evidence that it influences atherosclerosis is equivocal. The effects of specifically pro- and anti-atherosclerotic WSS profiles on the S1P pathway require investigation, as do influences of S1P on the vesicular pathways likely to dominate low-density lipoprotein transport across endothelium.

Sphingosine kinase-2 prevents macrophage cholesterol accumulation and atherosclerosis by stimulating autophagic lipid degradation

Atherosclerosis is the major cause of ischemic coronary heart diseases and characterized by the infiltration of cholesterol-accumulating macrophages in the vascular wall. Although sphingolipids are implicated in atherosclerosis as both membrane components and lipid mediators, the precise role of sphingolipids in atherosclerosis remains elusive. Here, we found that genetic deficiency of sphingosine kinase-2 (SphK2) but not SphK1 aggravates the formation of atherosclerotic lesions in mice with ApoE deficiency. Bone marrow chimaera experiments show the involvement of SphK2 expressed in bone marrow-derived cells. In macrophages, deficiency of SphK2, a major SphK isoform in this cell type, results in increases in cellular sphingosine and ceramides. SphK2-deficient macrophages have increases in lipid droplet-containing autophagosomes and autolysosomes and defective lysosomal degradation of lipid droplets via autophagy with an impaired luminal acidic environment and proteolytic activity in the lysosomes. Transgenic overexpression of SphK1 in SphK2-deficient mice rescued aggravation of atherosclerosis and abnormalities of autophagosomes and lysosomes in macrophages with reductions of sphingosine, suggesting at least partial overlapping actions of two SphKs. Taken together, these results indicate that SphK2 is required for autophagosome- and lysosome-mediated catabolism of intracellular lipid droplets to impede the development of atherosclerosis; therefore, SphK2 may be a novel target for treating atherosclerosis.

Targeting Sphingosine Kinases for the Treatment of Cancer

Sphingosine kinases (SK1 and SK2) are key, druggable targets within the sphingolipid metabolism pathway that promote tumor growth and pathologic inflammation. A variety of isozyme-selective and dual inhibitors of SK1 and SK2 have been described in the literature, and at least one compound has reached clinical testing in cancer patients. In this chapter, we will review the rationale for targeting SKs and summarize the preclinical and emerging clinical data for ABC294640 as the first-in-class selective inhibitor of SK2.

High-density lipoprotein (HDL) promotes angiogenesis via S1P3-dependent VEGFR2 activation

High-density lipoprotein (HDL) has previously been shown to promote angiogenesis. However, the mechanisms by which HDL enhances the formation of blood vessels remain to be defined. To address this, the effects of HDL on the proliferation, transwell migration and tube formation of human umbilical vein endothelial cells were investigated. By examining the abundance and phosphorylation (i.e., activation) of the vascular endothelial growth factor receptor VEGFR2 and modulating the activity of the sphingosine-1 phosphate receptors S1P1-3 and VEGFR2, we characterized mechanisms controlling angiogenic responses in response to HDL exposure. Here, we report that HDL dose-dependently increased endothelial proliferation, migration and tube formation. These events were in association with increased VEGFR2 abundance and rapid VEGFR2 phosphorylation at Tyr1054/Tyr1059 and Tyr1175 residues in response to HDL. Blockade of VEGFR2 activation by the VEGFR2 inhibitor SU1498 markedly abrogated the pro-angiogenic capacity of HDL. Moreover, the S1P3 inhibitor suramin prevented VEGFR2 expression and abolished endothelial migration and tube formation, while the S1P1 agonist CYM-5442 and the S1P2 inhibitor JTE-013 had no effect. Last, the role of S1P3 was further confirmed in regulation of S1P-induced endothelial proliferation, migration and tube formation via up-regulation and activation of VEGFR2. Together, these findings argue that HDL promotes angiogenesis via S1P3-dependent up-regulation and activation of VEGFR2 and also suggest that the S1P-S1P3-VEGFR2 signaling cascades as a novel target for HDL-modulating therapy implicated in vascular remodeling and functional recovery in atherosclerotic diseases such as myocardial infarction and ischemic stroke.

Effects of apolipoprotein M in uremic atherosclerosis

BACKGROUND AND AIMS

Chronic kidney disease is characterized by uremia and causes premature death, partly due to accelerated atherosclerosis. Apolipoprotein (apo) M is a plasma carrier protein for the lipid sphingosine-1-phosphate (S1P). The Apom-S1P complex associates with HDL, and may contribute to its anti-atherosclerotic effects. The role of Apom/S1P in atherosclerosis is presently controversial and has not been explored in a uremic setting. We aimed to explore whether plasma concentrations of Apom/S1P are altered by uremia and whether Apom overexpression or deficiency affects classical and uremic atherosclerosis.

METHODS

Mild to moderate uremia was induced by subtotal nephrectomy (NX) in 86-92 Apoe-deficient mice that were either Apom-wild type, Apom-deficient, or overexpressed Apom (∼10 fold). The effects of uremia on plasma Apom/S1P and atherosclerosis were evaluated and compared to non-nephrectomized controls.

RESULTS

Uremia increased plasma Apom by ∼25%, but not S1P. Plasma S1P was elevated by ∼300% in mice overexpressing Apom, and decreased by ∼25% in Apom-deficient mice. Apom overexpression augmented aortic root atherosclerosis and plasma cholesterol. In contrast, aortic arch atherosclerosis was unaffected by the Apom genotype. There was no effect of Apom-deficiency or Apom overexpression on uremic atherosclerosis.

CONCLUSIONS

This study highlights the complexity of Apom/S1P in atherosclerosis and challenges the notion that the Apom/S1P complex is anti-atherogenic, at least in Apoe-deficient mice.

Sphingosine-1-Phosphate Signaling in Endothelial Disorders

Numerous preclinical studies indicate that sustained endothelial activation significantly contributes to tissue edema, perpetuates the inflammatory response, and exacerbates tissue injury ultimately resulting in organ failure. However, no specific therapies aimed at restoring endothelial function are available as yet. Sphingosine-1-phosphate (S1P) is emerging as a potent modulator of endothelial function and endothelial responses to injury. Recent studies indicate that S1PR are attractive targets to treat not only disorders of the arterial endothelium but also microvascular dysfunction caused by ischemic or inflammatory injury. In this article, we will review the current knowledge of the role of S1P and its receptors in endothelial function in health and disease, and we will discuss the therapeutic potential of targeting S1PR not only for disorders of the arterial endothelium but also the microvasculature. The therapeutic targeting of S1PR in the endothelium could help to bridge the gap between biomedical research in vascular biology and clinical practice.

The Sphingosine Kinase 2 Inhibitor ABC294640 Reduces the Growth of Prostate Cancer Cells and Results in Accumulation of Dihydroceramides In Vitro and In Vivo

Despite recent advances in the development of novel therapies against castration-resistant prostate cancer, the advanced form of the disease remains a major treatment challenge. Aberrant sphingolipid signaling through sphingosine kinases and their product, sphingosine-1-phosphate, can promote proliferation, drug resistance, angiogenesis, and inflammation. The sphingosine kinase 2 inhibitor ABC294640 is undergoing clinical testing in cancer patients, and in this study we investigated the effects this first-in-class inhibitor in castration-resistant prostate cancer. In vitro, ABC294640 decreased prostate cancer cell viability as well as the expression of c-Myc and the androgen receptor, while lysosomal acidification increased. ABC294640 also induced a greater than 3-fold increase in dihydroceramides that inversely correlated with inhibition of dihydroceramide desaturase (DEGS) activity. Expression of sphingosine kinase 2 was dispensable for the ABC294640-mediated increase in dihydroceramides. In vivo, ABC294640 diminished the growth rate of TRAMP-C2 xenografts in syngeneic hosts and elevated dihydroceramides within tumors as visualized by MALDI imaging mass spectroscopy. The plasma of ABC294640-treated mice contained significantly higher levels of C16- and C24:1-ceramides (but not dihydro-C16-ceramide) compared with vehicle-treated mice. In summary, our results suggest that ABC294640 may reduce the proliferative capacity of castration-resistant prostate cancer cells through inhibition of both sphingosine kinase 2 and dihydroceramide desaturase, thereby providing a foundation for future exploration of this small-molecule inhibitor for the treatment of advanced disease.

SKI-II--a sphingosine kinase 1 inhibitor--exacerbates atherosclerosis in low-density lipoprotein receptor-deficient (LDL-R-/-) mice on high cholesterol diet

BACKGROUND

Sphingosine 1-phosphate (S1P) is a lysosphingolipid associated with high-density lipoproteins (HDL) that contributes to their anti-atherogenic potential. We investigated whether a reduction in S1P plasma levels affects atherosclerosis in low-density lipoprotein receptor deficient (LDL-R-/-) mice.

METHODS AND RESULTS

LDL-R-/- mice on Western diet containing low (0.25% w/w) or high (1.25% w/w) cholesterol were treated for 16 weeks with SKI-II, a sphingosine kinase 1 inhibitor that significantly reduced plasma S1P levels. SKI-II treatment increased atherosclerotic lesions in the thoracic aorta in mice on high but not low cholesterol diet. This compound did not affect body weight, blood cell counts and plasma total and HDL cholesterol, but decreased triglycerides. In addition, mice on high cholesterol diet receiving SKI-II showed elevated levels of tumor necrosis factor-α and endothelial adhesion molecules (sICAM-1, sVCAM-1).

CONCLUSION

Prolonged lowering of plasma S1P produces pro-atherogenic effects in LDL-R-/- mice that are evident under condition of pronounced hypercholesterolemia.

Apolipoprotein M in lipid metabolism and cardiometabolic diseases

PURPOSE

This review will address recent findings on apolipoprotein M (apoM) and its ligand sphingosine-1-phosphate (S1P) in lipid metabolism and inflammatory diseases.

RECENT FINDINGS

ApoM's likely role(s) in health and disease has become more diverse after the discovery that apoM functions as a chaperone for S1P. Hence, apoM has recently been implicated in lipid metabolism, diabetes and rheumatoid arthritis through in-vivo, in-vitro and genetic association studies. It remains to be established to which degree such associations with apoM can be attributed to its ability to bind S1P.

SUMMARY

The apoM/S1P axis and its implications in atherosclerosis and lipid metabolism have been thoroughly studied. Owing to the discovery of the apoM/S1P axis, the scope of apoM research has broadened. ApoM and S1P have been implicated in lipid metabolism, that is by modulating HDL particles. Also, the importance in regulating endothelial function is being investigated. Furthermore, both apoM and S1P have been linked to diabetes and glucose and insulin metabolism. Finally, genetic variations in the apoM gene are associated with lipid disturbances, diabetes and rheumatoid arthritis. These findings suggest not only diverse effects of apoM, but also the important question of whether apoM mainly acts as a S1P carrier, if apoM carries other substances with biological effects as well, or whether the apoM protein has effects on its own.

Atheroprotective role of high-density lipoprotein (HDL)-associated sphingosine-1-phosphate (S1P)

Numerous epidemiological studies documented an inverse relationship between plasma high-density lipoprotein (HDL) cholesterol levels and the extent of atherosclerotic disease. However, clinical interventions targeting HDL cholesterol failed to show clinical benefits with respect to cardiovascular risk reduction, suggesting that HDL components distinct from cholesterol may account for anti-atherogenic effects attributed to this lipoprotein. Sphingosine-1-phosphate (S1P)-a lysosphingolipid exerting its biological activity via binding to specific G protein-coupled receptors and regulating a wide array of biological responses in a variety of different organs and tissues including the cardiovascular system-has been identified as an integral constituent of HDL particles. In the present review, we discuss current evidence from epidemiological studies, experimental approaches in vitro, and animal models of atherosclerosis, suggesting that S1P contributes to atheroprotective effects exerted by HDL particles.

Why targeting HDL should work as a therapeutic tool, but has not

Atherosclerosis is one of the most common causes of death and disability in the United States today despite the availability of statins, which reduce hyperlipidemia, a risk factor that predisposes individuals to this disease. Epidemiology of human populations has overwhelmingly demonstrated an inverse correlation between the concentration of plasma high-density lipoprotein (HDL) cholesterol (HDL-C) and the likelihood of developing cardiovascular disease (CVD). Decades of observations and mechanistic studies suggest that one protective function of HDL is its central role in reverse cholesterol transport. In this pathway, the ATP-binding cassette transporter A1 releases intracellular cholesterol, which is packaged with apolipoprotein A-I (apoA-I) into nascent HDL particles and released from the plasma membrane. Further lipidation and maturation of HDL occur in plasma with the eventual uptake by the liver where cholesterol is removed. It is generally accepted that CVD risk can be reduced if plasma HDL-C levels are elevated. Several different pharmacological approaches have been tried; the most popular approach targets the movement of cholesteryl ester from HDL to triglyceride-rich particles by cholesteryl ester transfer protein. Inhibition of cholesteryl ester transfer protein increases plasma HDL-C concentration; however, beneficial effects have yet to be demonstrated, likely the result of off-target effects. These revelations have led to a reevaluation of how elevating HDL concentration could decrease risk. A recent, landmark study showed that the inherent cholesterol efflux capacity of an individual's plasma was a better predictor of CVD status than overall HDL-C concentration. Even more provocative are recent studies showing that apoA-I, the principle protein component of HDL modulates cellular inflammation and oxidation. The following will review all these potential routes explaining how HDL apoA-I can reduce the risk of CVD.

Apolipoprotein M: bridging HDL and endothelial function

PURPOSE OF REVIEW

The review will address the potential roles of apolipoprotein M (apoM) as a carrier protein and modulator of sphingosine-1-phosphate (S1P) bioactivity.

RECENT FINDINGS

Recombinant apoM can bind small lipids such as retinoic acid, oxidized phospholipids, and S1P. Thus, the effects of apoM may be pleiotrophic. The S1P binding ability of apoM has biological impact. ApoM-bound S1P can activate S1P1 receptors on endothelial cells and deficiency of apoM abolishes the presence of S1P in HDL. In mice, the lack of apoM causes dysfunctional endothelial barrier function in the lungs. In humans, sepsis that is characterized by impaired endothelial function is associated with low plasma apoM.

SUMMARY

Plasma apoM is mainly bound to HDL. The roles of apoM in atherosclerosis and lipoprotein metabolism have been given much attention. New in the field is the discovery of apoM as a chaperone for S1P. S1P is a bioactive lipid with effects on angiogenesis, lymphocyte trafficking, endothelial cell migration, and inflammation. A drug targeting the S1P-system (fingolimod) is now used for treatment of multiple sclerosis. It improves the blood-brain barrier and inhibits migration of lymphocytes into the brain. Further exploration of the apoM/S1P axis may uncover its potential as a biomarker and target for new treatments.

Hematopoietic sphingosine 1-phosphate lyase deficiency decreases atherosclerotic lesion development in LDL-receptor deficient mice

AIMS

Altered sphingosine 1-phosphate (S1P) homeostasis and signaling is implicated in various inflammatory diseases including atherosclerosis. As S1P levels are tightly controlled by S1P lyase, we investigated the impact of hematopoietic S1P lyase (Sgpl1(-/-)) deficiency on leukocyte subsets relevant to atherosclerosis.

METHODS AND RESULTS

LDL receptor deficient mice that were transplanted with Sgpl1(-/-) bone marrow showed disrupted S1P gradients translating into lymphopenia and abrogated lymphocyte mitogenic and cytokine response as compared to controls. Remarkably however, Sgpl1(-/-) chimeras displayed mild monocytosis, due to impeded stromal retention and myelopoiesis, and plasma cytokine and macrophage expression patterns, that were largely compatible with classical macrophage activation. Collectively these two phenotypic features of Sgpl1 deficiency culminated in diminished atherogenic response.

CONCLUSIONS

Here we not only firmly establish the critical role of hematopoietic S1P lyase in controlling S1P levels and T cell trafficking in blood and lymphoid tissue, but also identify leukocyte Sgpl1 as critical factor in monocyte macrophage differentiation and function. Its, partly counterbalancing, pro- and anti-inflammatory activity spectrum imply that intervention in S1P lyase function in inflammatory disorders such as atherosclerosis should be considered with caution.

The apolipoprotein m-sphingosine-1-phosphate axis: biological relevance in lipoprotein metabolism, lipid disorders and atherosclerosis

Apolipoprotein M (apoM) is a plasma apolipoprotein that mainly associates with high-density lipoproteins. Hence, most studies on apoM so far have investigated its effect on and association with lipid metabolism and atherosclerosis. The insight into apoM biology recently took a major turn. ApoM was identified as a carrier of the bioactive lipid sphingosine-1-phosphate (S1P). S1P activates five different G-protein-coupled receptors, known as the S1P-receptors 1–5 and, hence, affects a wide range of biological processes, such as lymphocyte trafficking, angiogenesis, wound repair and even virus suppression and cancer. The ability of apoM to bind S1P is due to a lipophilic binding pocket within the lipocalin structure of the apoM molecule. Mice overexpressing apoM have increased plasma S1P concentrations, whereas apoM-deficient mice have decreased S1P levels. ApoM-S1P is able to activate the S1P-receptor-1, affecting the function of endothelial cells, and apoM-deficient mice display impaired endothelial permeability in the lung. This review will focus on the putative biological roles of the new apoM–S1P axis in relation to lipoprotein metabolism, lipid disorders and atherosclerosis.

Sphingolipids and atherosclerosis

The atherosclerotic lesion contains a high amount of sphingolipids, a large group of structurally diverse lipids that regulate distinct biological functions beyond their role as structural membrane components. Assessment of their role in atherogenesis has been enabled after genes that regulate their metabolism had been identified and facilitated by the more wide availability of mass spectrometry. Here we discuss recent mechanistic insights obtained in animal and epidemiological studies that have greatly enhanced our understanding of mechanisms how sphingolipids affect the atherosclerotic process.

Increased serum concentration of sphingosine-1-phosphate in juvenile-onset systemic lupus erythematosus

PURPOSE

Sphingosine-1-phosphate (S1P) is an active sphingolipid with chemotactic abilities and has been linked to inflammatory mediators and autoimmune disease. The aim of this study was to assess whether children with juvenile-onset systemic lupus erythematosus (JSLE) express increased systemic and/or urinary concentrations of S1P.

METHODS

A subgroup of patients participating in the UK JSLE Cohort Study, were invited to participate. Cross sectional serum and urine samples were prospectively collected along with demographic and standard clinical data. Results were compared to a cohort of disease controls (Henoch Schonlein Purpura; HSP) and healthy controls (HC).

RESULTS

The median age of JSLE patients (n = 15) was 13.6 years (7.2-16.9 years). The serum concentrations of S1P in JSLE patients (7.4 uM, IQR 6.3-12.3 uM) were statistically significantly increased when compared to patients with HSP (n = 10; 5.2 uM, IQR 4.0-7.9 uM; p = 0.016) and HCs (n = 10; 3.8 uM, IQR 2.1-5.8 uM; p = 0.003). There was a trend towards increased serum S1P concentrations between patients with active lupus nephritis (n = 8; 8.7 uM, IQR 6.2-15.3 uM) compared to lupus non-nephritis (n = 7; 6.6 uM, IQR 6.3-10.6 uM; p = 0.355). No relationship was found between disease activity markers and S1P. Urine S1P concentrations were no different between JSLE patients (56.0 nM, IQR 40.3-96.6 nM) and HCs (58.7 nM, IQR 0-241.9 nM; p = 0.889).

CONCLUSIONS

We have demonstrated, for the first time, an increased serum concentration of S1P in a cohort of JSLE patients. These findings highlight a role of S1P in the pathophysiology of JSLE that warrants further investigation.