The sphingosine-1-phosphate receptor agonist FTY720 prevents the development of anti-glomerular basement membrane glomerulonephritis

A Rheostat of Ceramide and Sphingosine-1-Phosphate as a Determinant of Oxidative Stress-Mediated Kidney Injury

Reactive oxygen species (ROS) modulate sphingolipid metabolism, including enzymes that generate ceramide and sphingosine-1-phosphate (S1P), and a ROS-antioxidant rheostat determines the metabolism of ceramide-S1P. ROS induce ceramide production by activating ceramide-producing enzymes, leading to apoptosis, while they inhibit S1P production, which promotes survival by suppressing sphingosine kinases (SphKs). A ceramide-S1P rheostat regulates ROS-induced mitochondrial dysfunction, apoptotic/anti-apoptotic Bcl-2 family proteins and signaling pathways, leading to apoptosis, survival, cell proliferation, inflammation and fibrosis in the kidney. Ceramide inhibits the mitochondrial respiration chain and induces ceramide channel formation and the closure of voltage-dependent anion channels, leading to mitochondrial dysfunction, altered Bcl-2 family protein expression, ROS generation and disturbed calcium homeostasis. This activates ceramide-induced signaling pathways, leading to apoptosis. These events are mitigated by S1P/S1P receptors (S1PRs) that restore mitochondrial function and activate signaling pathways. SphK1 promotes survival and cell proliferation and inhibits inflammation, while SphK2 has the opposite effect. However, both SphK1 and SphK2 promote fibrosis. Thus, a ceramide-SphKs/S1P rheostat modulates oxidant-induced kidney injury by affecting mitochondrial function, ROS production, Bcl-2 family proteins, calcium homeostasis and their downstream signaling pathways. This review will summarize the current evidence for a role of interaction between ROS-antioxidants and ceramide-SphKs/S1P and of a ceramide-SphKs/S1P rheostat in the regulation of oxidative stress-mediated kidney diseases.

Sphingosine-1-phosphate in anti-neutrophil cytoplasmic antibody-associated vasculitis: coagulation-related clinical indicators and complications

BACKGROUND

Sphingosine-1-phosphate (S1P) plays a significant role in anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV).

METHODS

We collected the plasma samples from 40 patients with AAV and 10 healthy volunteers. The plasma levels of S1P were tested by enzyme-linked immunosorbent assay (ELISA). The levels of serum creatinine (Scr) were tested by rate method, and then the estimated glomerular filtration rate (eGFR) of the patients was calculated from the Scr, age, and gender. Prothrombin time (PT), partial thromboplastin time (APTT), thrombin time (TT), fibrinogen (FIB), fibrinogen reduction product (FDP), D-dimer and C-reactive protein (CRP) were tested by turbidimetric inhibition immunoassays. Platelets (PLTs) were tested by fluorescently labeled electrical impedance method.

RESULTS

The plasma levels of S1P were significantly higher in AAV patients than in healthy volunteers. Correlation analysis showed that plasma levels of S1P were negatively correlated with glomerular filtration (P=0.022, r = -0.306), and positively correlated with circulating levels of Birmingham vasculitis activity score (BVAS), PLT and D-dimer, (P=0.004, r = 0.443; P<0.001, r = 0.654; P=0.006, r = 0.427). The 40 patients with AAV were classified into three groups: the thromboembolism group (with complications of cerebral infarction and myocardial infarction, n=6), cerebral ischemia group (n=4), and cerebral hemorrhage group (n=2). The plasma levels of S1P were highest in the thromboembolism group and lowest in the cerebral hemorrhage group (P=0.003).

CONCLUSIONS

Plasma levels of S1P were associated with circulating levels of D-dimer, PLT and BVAS in the patients with AAV. Hence, plasma S1P level can be used as a biomarker to predict coagulation-related complications in AAV.

Regulatory role of SphK1 in TLR7/9-dependent type I interferon response and autoimmunity

Plasmacytoid dendritic cells (pDCs) express Toll like receptors (TLRs) that modulate the immune response by production of type I interferons. Here, we report that sphingosine kinase 1 (SphK1) which produces the bioactive sphingolipid metabolite, sphingosine 1-phosphate (S1P), plays a critical role in the pDC functions and interferon production. Although dispensable for the pDC development, SphK1 is essential for the pDC activation and production of type I IFN and pro-inflammatory cytokines stimulated by TLR7/9 ligands. SphK1 interacts with TLRs and specific inhibition or deletion of SphK1 in pDCs mitigates uptake of CpG oligonucleotide ligands by TLR9 ligand. In the pristane-induced murine lupus model, pharmacological inhibition of SphK1 or its genetic deletion markedly decreased the IFN signature, pDC activation, and glomerulonephritis. Moreover, increases in the SphK1 expression and S1P levels were observed in human lupus patients. Taken together, our results indicate a pivotal regulatory role for the SphK1/S1P axis in maintaining the balance between immunosurveillance and immunopathology and suggest that specific SphK1 inhibitors might be a new therapeutic avenue for the treatment of type I IFN-linked autoimmune disorders.

Multiple Sclerosis Drug Fingolimod Induces Thrombotic Microangiopathy in Deoxycorticosterone Acetate/Salt Hypertension

We examined whether fingolimod (FTY720), an S1PR (sphingosine-1-phosphate receptor) modulator, has beneficial or harmful effects on mineralocorticoid/salt-induced renal injury. Uninephrectomized rats on 0.9% NaCl/0.3% KCl drinking solution were randomly divided into control, control+FTY720, deoxycorticosterone acetate (DOCA), and DOCA+FTY720 groups and administered vehicle, vehicle+FTY720, DOCA+vehicle, and DOCA+FTY720 for 4 weeks, respectively. Only the DOCA+FTY720 group had reduced survival rates and showed hemolysis because of intravascular mechanical fragmentation of erythrocytes and thrombocytopenia. Both the DOCA+FTY720 and DOCA groups developed malignant hypertension, which was more severe in the DOCA+FTY720 group. In the DOCA+FTY720 group only, thrombotic microangiopathy involving severe renal arteriole endothelial cell injury was observed and was characterized by fibrinoid necrosis and onion-skin lesions in arterioles. There were fewer circulating endothelial progenitor cells in the DOCA+FTY720 group but more in the DOCA group compared with the control group. Expression levels of VEGF (vascular endothelial growth factor), S1PR1, and S1PR3 in renal arteriole endothelial cells were significantly greater in the DOCA+FTY720 and DOCA groups compared with the control group, with levels being similar between the 2 groups. Expression levels of endothelial nitric oxide synthase in renal arteriole endothelial cells were significantly lower in the DOCA+FTY720 group only. The control+FTY720 group showed reduced circulating endothelial progenitor cells but no significant functional or pathological changes in kidneys or changes in blood pressure. Exposure of uninephrectomized rats to DOCA/salt+FTY720 for 4 weeks induced renal arteriolar endothelial cell injury, resulting in the development of thrombotic microangiopathy. Consideration of this possibility is recommended when prescribing FTY720.

Sphingolipid signaling in renal fibrosis

Over the last decade, various sphingolipid subspecies have gained increasing attention as important signaling molecules that regulate a multitude of physiological and pathophysiological processes including inflammation and tissue remodeling. These mediators include ceramide, sphingosine 1-phosphate (S1P), the cerebroside glucosylceramide, lactosylceramide, and the gangliosides GM3 and Gb3. These lipids have been shown to accumulate in various chronic kidney diseases that typically end in renal fibrosis and ultimately renal failure. This review will summarize the effects and contributions of those enzymes that regulate the generation and interconversion of these lipids, notably the acid sphingomyelinase, the acid sphingomyelinase-like protein SMPDL3B, the sphingosine kinases, the S1P lyase, the glucosylceramide synthase, the GM3 synthase, and the α-galactosidase A, to renal fibrotic diseases. Strategies of manipulating these enzymes for therapeutic purposes and the impact of existing drugs on renal pathologies will be discussed.

FTY720 inhibits tubulointerstitial inflammation in albumin overload-induced nephropathy of rats via the Sphk1 pathway

AIM

FTY720, a new immunomodulatory drug with low cytotoxicity, is currently used to treat multiple sclerosis. In this study, we investigated the effects of FTY720 on inflammatory cell infiltration in albumin overload-induced nephropathy of rats.

METHODS

Male Wistar rats were subjected to right-side nephrectomy and divided into 3 groups. One week after the surgery, albumin overload (AO) group was treated with BSA (5 g·kg(-1)·d(-1), ip) for 9 weeks; AO+FTY720 group was given BSA (5 g·kg(-1)·d(-1), ip) plus FTY720 (0.5 g·kg(-1)·d(-1), ip) for 9 weeks; and control group received daily ip injection of equivalent volume of saline. All rats were killed 9 weeks after nephrectomy.

RESULTS

AO rats exhibited gradually increased urinary protein excretion accompanied by elevated urinary N-acetyl-β-O-glucosaminidase activity, and both reached their peak values at week 7. Furthermore, AO significantly increased lymphocytes and monocytes in circulation and the inflammatory cells recruited to tubulointerstitium, and the expression of inflammatory cytokines MCP-1, TNF-α and IL-6, as well as sphingosine 1-phosphate (S1P) receptors S1pr1 and S1pr3, and S1P-synthesizing enzyme sphingosine kinase 1 (Sphk1) in the kidney. Concomitant administration of FTY720 significantly attenuated all the AO-induced pathological changes.

CONCLUSION

FTY720 alleviates tubulointerstitium inflammation in an AO rat model of nephropathy via down-regulation of the Sphk1 pathway.

Treatment with the immunomodulator FTY720 (fingolimod) significantly reduces renal inflammation in murine unilateral ureteral obstruction

PURPOSE

The S1P signaling pathway represents an important potential target for the modulation of tissue inflammation/injury. The immunomodulator FTY720, also known as fingolimod, is a potent agonist for multiple S1P receptors that was approved by the Food and Drug Administration to treat multiple sclerosis. We examined the therapeutic role of FTY720 for renal injury secondary to unilateral ureteral obstruction.

MATERIALS AND METHODS

CB57BL/6 mice underwent a sham procedure or unilateral ureteral obstruction and were treated with FTY720 by gavage for 1, 3 and 5 days. Control groups received vehicle. Ligated and unligated renal tissue was examined for histopathological changes, inflammatory and fibrotic markers, TGF-β1, α-SMA, and macrophage infiltration by Western blot and immunohistochemistry. Proinflammatory and profibrotic cytokines were profiled by quantitative reverse transcriptase-polymerase chain reaction.

RESULTS

Pathological evaluation revealed that FTY720 treatment resulted in a significant reduction in inflammatory infiltration in obstructed kidneys compared to controls. Immunohistochemical and Western blot showed that TGF-β1 and α-SMA protein levels were similarly decreased, as was macrophage infiltration into the renal interstitial space, compared to untreated mice. In agreement with these observations quantitative reverse transcriptase-polymerase chain reaction revealed that inflammatory and fibrotic cytokines (MCP-1, IL-1β, CXCL1, TNF-α and TGF-β1) were also significantly decreased in the FTY720 group.

CONCLUSIONS

This study suggests that in a murine ureteral obstruction model FTY720 significantly inhibited the production of inflammatory cytokines and factors regulating interstitial fibrosis and extracellular matrix accumulation. These findings were associated with decreased evidence of renal injury on pathological examination, suggesting that FTY720 or related compounds may be valuable modulators of obstruction induced renal injury.

Targeting the sphingosine kinase/sphingosine 1-phosphate pathway to treat chronic inflammatory kidney diseases

Chronic kidney diseases including glomerulonephritis are often accompanied by acute or chronic inflammation that leads to an increase in extracellular matrix (ECM) production and subsequent glomerulosclerosis. Glomerulonephritis is one of the leading causes for end-stage renal failure with high morbidity and mortality, and there are still only a limited number of drugs for treatment available. In this MiniReview, we discuss the possibility of targeting sphingolipids, specifically the sphingosine kinase 1 (SphK1) and sphingosine 1-phosphate (S1P) pathway, as new therapeutic strategy for the treatment of glomerulonephritis, as this pathway was demonstrated to be dysregulated under disease conditions. Sphingosine 1-phosphate is a multifunctional signalling molecule, which was shown to influence several hallmarks of glomerulonephritis including mesangial cell proliferation, renal inflammation and fibrosis. Most importantly, the site of action of S1P determines the final effect on disease progression. Concerning renal fibrosis, extracellular S1P acts pro-fibrotic via activation of cell surface S1P receptors, whereas intracellular S1P was shown to attenuate the fibrotic response. Interference with S1P signalling by treatment with FTY720, an S1P receptor modulator, resulted in beneficial effects in various animal models of chronic kidney diseases. Also, sonepcizumab, a monoclonal anti-S1P antibody that neutralizes extracellular S1P, and a S1P-degrading recombinant S1P lyase are promising new strategies for the treatment of glomerulonephritis. In summary, especially due to the bifunctionality of S1P, the SphK1/S1P pathway provides multiple target sites for the treatment of chronic kidney diseases.

FTY720 attenuates tubulointerstitial inflammation and fibrosis in subtotally nephrectomized rats

Tubulointerstitial fibrosis is a common pathway that leads to kidney failure, and persistent tubulointerstitial inflammation is a key event in the development of tubulointerstitial fibrosis. The new immunosuppressive drug FTY720 modifies lymphocyte migration into injured tissues by sequestering lymphocytes within secondary lymphoid organs. However, its therapeutic effect on tubulointerstitial inflammation and fibrosis had not been well understood. This study was designed to explore the effect of FTY720 on tubulointerstitial inflammation and fibrosis in subtotally nephrectomized (SNX) rats. In total, 24 male Sprague-Dawley rats were used. Seven days after 5/6 nephrectomy, rats were randomized to FTY720 (1 mg/kg/d) and placebo-treated groups. Sham-operated rats served as controls. FTY720 significantly attenuated the rise in proteinuria, serum creatinine, urea nitrogen and N-acetyl-β-D-glucosaminidase activity in SNX rats, and reduced the count of peripheral white blood cells and lymphocytes in SNX rats. Morphological analysis revealed that there was severe tubulointerstitial inflammation and fibrosis in SNX group and much more tubulointerstitial infiltrating inflammatory cells with high expression of CD3, CD4, CD8, CD20, CD68, CD163 and CCR-7 in SNX group, as compared with the controls, but the lesions were attenuated significantly by treatment with FTY720. Furthermore, the expressions of proinflammatory molecules (IL-6, TNF-α and MCP-1), profibrotic molecule (TGF-β1) and production of extracellular matrix proteins such as fibronectin and types I and III collagens were upregulated in SNX rats. FTY720 administration significantly reduced these abnormalities. In summary, FTY720 exerts therapeutic effects on tubulointerstitial fibrosis in SNX rats by inhibiting the tubulointerstitial inflammatory response.

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.