Anti-Inflammatory Effects of Sphingosine Kinase Modulation in Inflammatory Arthritis

Abstract

Sphingosine kinase (SphK) is a key enzyme in the sphingolipid metabolic pathway responsible for phosphorylating sphingosine into sphingosine-1-phosphate (S1P). SphK/S1P play a critical role in angiogenesis, inflammation, and various pathologic conditions. Recently, S1P1 receptor was found to be expressed in rheumatoid arthritis (RA) synovium, and S1P signaling via S1P1 enhances synoviocyte proliferation, COX-2 expression, and prostaglandin E2 production. Here, we examined the role of SphK/S1P in RA using a potent SphK inhibitor, N,N-dimethylsphingosine (DMS), and a molecular approach against one of its isoenzymes, SphK1. We observed that levels of S1P in the synovial fluid of RA patients were significantly higher than those of osteoarthritis patients. Additionally, DMS significantly reduced the levels of TNF-α, IL-6, IL-1β, MCP-1, and MMP-9 in cell-contact assays using both Jurkat-U937 cells and RA PBMCs. In a murine collagen-induced arthritis model, i.p. administration of DMS significantly inhibited disease severity and reduced articular inflammation and joint destruction. Treatment of DMS also down-regulated serum levels IL-6, TNF-α, IFN-γ, S1P, and IgG1 and IgG2a anti-collagen Ab. Furthermore, DMS-treated mice also displayed suppressed proinflammatory cytokine production in response to type II collagen in vitro. Moreover, similar reduction in incidence and disease activity was observed in mice treated with SphK1 knock-down via small interfering RNA approach. Together, these results demonstrate SphK modulation may provide a novel approach in treating chronic autoimmune conditions such as RA by inhibiting the release of pro-inflammatory cytokines.

Targeting the Metabolism and Receptors of Sphingosine-1- Phosphate for the Treatment of Rheumatoid Arthritis

“…The S1P content in RA synovial fluids was significantly higher than those in serum (400 pM/ml) or plasma (100 pM/ml) from normal people. Lai et al (2008) also measured the amount of S1P by a competitive ELISA and detected up to 17 M S1P in RA synovial fluids, which was more than five fold higher than that found in OA synovial fluids (3 M). The increased level of S1P could be responsible for the recruitment and the infiltration of immune cells into the synovium (see section 4.2.2).…”

“…Several studies reveal high levels of S1P in RA synovial tissues and fluids (Kitano et al, 2006;Lai et al, 2008). Kitano et al (2006) reported elevated levels of S1P in synovial fluids of RA patients (1078 pM/ml) in comparison to those of osteoarthritis (OA) patients (765 pM/ml).…”

“…The SphK1 signalling pathway is activated in RA (Limaye et al, 2009). In the mouse model of CIA, administration of a non-specific pharmacological inhibitor of SphKs, N,Ndimethylsphingosine (DMS), and a siRNA approach to knockdown the SphK1 isoform, markedly suppressed joint pathologies such as adjacent cartilage and bone erosion, synovial hyperplasia, and infiltration of inflammatory cells into the joint compartment (Lai et al, 2008). Moreover, SphK1 deficiency in hTNF- transgenic mice that develop arthritis at an early age was related to less synovial inflammation and bone erosion (Baker et al, 2010).…”

“…The role played by S1P in the autoimmune disease rheumatoid arthritis (RA) has recently emerged. Activated SphK and elevated levels of S1P have been detected in the synovium and synovial fluids of patients with RA, respectively (Kamada et al, 2009;Kitano et al, 2006;Lai et al, 2008). In addition, exogenously applied S1P in cultured synovial fibroblasts from RA patients causes cell migration, production of cytokines/chemokines, expression of cyclooxygenase-2 and prostaglandins, as well as cell proliferation and survival (Kitano et al, 2006;Zhao et al, 2008).…”

“…SphK/S1P signalling was also implicated in cell-contact-mediated proinflammatory cytokine/chemokine secretion in RA synovium without additional exogenous stimulation. Lai et al (2008) used peripheral blood mononuclear cells from RA patients in cell-cell contact experiments. They discovered that activated peripheral T lymphocytes from RA patients induced substantial production of TNF-, IL-1, IL-6, MCP-1 and MMP-9 by autologous peripheral monocytes.…”