Effects of topical sphingosine-1-phosphate 1 receptor agonist on corneal allograft in mice

Sphingosine 1-phosphate receptor modulators in multiple sclerosis and other conditions

The sphingosine 1-phosphate (S1P) signalling pathways have important and diverse functions. S1P receptors (S1PRs) have been proposed as a therapeutic target for various diseases due to their involvement in regulation of lymphocyte trafficking, brain and cardiac function, vascular permeability, and vascular and bronchial tone. S1PR modulators were first developed to prevent rejection by the immune system following renal transplantation, but the only currently approved indication is multiple sclerosis. The primary mechanism of action of S1PR modulators in multiple sclerosis is through binding S1PR subtype 1 on lymphocytes resulting in internalisation of the receptor and loss of responsiveness to the S1P gradient that drives lymphocyte egress from lymph nodes. The reduction in circulating lymphocytes presumably limits inflammatory cell migration into the CNS. Four S1PR modulators (fingolimod, siponimod, ozanimod, and ponesimod) have regulatory approval for multiple sclerosis. Preclinical evidence and ongoing and completed clinical trials support development of S1PR modulators for other therapeutic indications.

The purinergic receptor antagonist oxidized adenosine triphosphate suppresses immune-mediated corneal allograft rejection

Adenosine triphosphate (ATP) is released into the extracellular environment during transplantation, and acts via purinergic receptors to amplify the alloimmune response. Here, using a well-established murine model of allogeneic corneal transplantation, we investigated the immunomodulatory mechanisms of the purinergic receptor antagonist oxidized ATP (oATP). Corneal transplantation was performed using C57BL/6 donors and BALB/c hosts. oATP or sterile saline was administered via intraperitoneal injection for 2 weeks postoperatively. Frequencies of CD45+ leukocytes, CD11b+MHCII+ antigen presenting cells (APCs), CD4+IFN-γ+ effector Th1 cells and CD4+Foxp3+ regulatory T cells (Tregs) were evaluated by flow cytometry. Slit-lamp microscopy was performed weekly for 8 weeks to evaluate graft opacity and determine transplant rejection. Treatment with oATP was shown to significantly reduce graft infiltration of CD45+ leukocytes, decrease APC maturation and suppress effector Th1 cell generation relative to saline-treated control. No difference in Treg frequencies or Foxp3 expression was observed between the oATP-treated and control groups. Finally, oATP treatment was shown to reduce graft opacity and increase graft survival. This report demonstrates that oATP limits the alloimmune response by regulating APC maturation and suppressing the generation of alloreactive Th1 immunity.

Resolvin E1 Inhibits Corneal Allograft Rejection in High-Risk Corneal Transplantation

Purpose

To investigate the effects of Resolvin E1 (RvE1) on corneal allograft rejection in a high -risk corneal allograft transplantation model.

Methods

High-risk corneal beds were created via placement of intrastromal sutures in the corneas of BALB/c mice for 2 weeks. Allogeneic corneal transplantation was performed by transplanting corneas of C57BL/6 mice onto BALB/c hosts. RvE1 or normal saline (control) was subconjunctivally injected. Allograft survival was observed by slit lamp biomicroscope, and inflammatory cell infiltration was detected by hematoxylin and eosin and immunohistochemistry. The percentage of Th1, Th17, and Treg cells in draining lymph nodes (DLNs) were evaluated by flow cytometric analysis. The levels of Th1, Th2, and Th17-associated cytokines in the grafts were measured by cytometric bead array and real-time PCR.

Results

RvE1 treatment significantly improved allograft survival compared to the control group. After RvE1 treatment, the infiltration of neutrophils and CD4+ T (Th1/Th17) cells were decreased in corneal grafts, and the percentage of Th1/Th17 cells in DLNs were reduced. In addition, RvE1 treatment significantly reduced the mRNA expression of proinflammatory cytokines in the graft including IL-1α, IL-1β, TNF-α, IL-2, IL-6, IFN-γ, IL-17A, IL-17F, IL-21, and IL-22 as well as the protein level of the proinflammatory cytokines, including IL-2, TNF, IL-6, IFN-γ, and IL-17. However, RvE1 treatment did not alter the percentage of Treg cells in DLNs and the expression of IL-4, IL-5, and IL-10.

Conclusions

RvE1 treatment improves allogeneic corneal graft survival in a high-risk corneal transplantation model via inhibiting the Th1/Th17-related inflammation.

Corneal blindness and current major treatment concern-graft scarcity

According to World Health Organization, the global prevalence of blindness in 2010 was 39 million people, among which 4% were due to corneal opacities. Often, the sole resort for visual restoration of patients with damaged corneas is corneal transplantation. However, despite rapid developments of surgical techniques, instrumentations and immunosuppressive agents, corneal blindness remains a prevalent global health issue. This is largely due to the scarcity of good quality corneal grafts. In this review, the causes of corneal blindness, its major treatment options, and the major contributory factors of corneal graft scarcity with potential solutions are discussed.

Adverse Effect Profile of Topical Ocular Administration of Fingolimod for Treatment of Dry Eye Disease

Fingolimod is a promising prodrug in attenuating multiple sclerosis and prolonging survival of organ allograft, with many other protective effects. Its mechanism of action is related to the internalization of sphingosine 1-phosphate receptors (S1PRs). Our previous study indicated that fingolimod eyedrops was efficacious in inhibiting ocular inflammation in a dry eye disease (DED) model of non-obese diabetic (NOD) mice. In the current study, we evaluated potential adverse effects of fingolimod eyedrops. Inbred 10-week-old BALB/c mice were randomly divided into four groups, fingolimod-treated groups at three different concentrations (0.01%, 0.1% and 0.5%) and a negative control group without intervention. Our results showed that in the 0.5% fingolimod group, adverse effects such as photophobia, catacleisis and corneal oedema were observed after 1 week of treatment. 1 month later, corneal opacity, oedema and neovascularization persisted till the mice were killed 2 months later. In contrast, there was no significant abnormality in the negative control group, and 0.01% and 0.1% fingolimod-treated groups. During a 2-month treatment period, we did not detect fingolimod, nor significant change in blood cells in peripheral blood, nor pathological changes in retina and systemic organs. Combined with our previous study and the current results, we recommend that an optimal range of safe and effective concentration of fingolimod as eyedrops is between 0.005% and 0.1%.

Sphingosine-1-Phosphate Signaling in Immune Cells and Inflammation: Roles and Therapeutic Potential

Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid metabolite involved in many critical cell processes. It is produced by the phosphorylation of sphingosine by sphingosine kinases (SphKs) and exported out of cells via transporters such as spinster homolog 2 (Spns2). S1P regulates diverse physiological processes by binding to specific G protein-binding receptors, S1P receptors (S1PRs) 1-5, through a process coined as "inside-out signaling." The S1P concentration gradient between various tissues promotes S1PR1-dependent migration of T cells from secondary lymphoid organs into the lymphatic and blood circulation. S1P suppresses T cell egress from and promotes retention in inflamed peripheral tissues. S1PR1 in T and B cells as well as Spns2 in endothelial cells contributes to lymphocyte trafficking. FTY720 (Fingolimod) is a functional antagonist of S1PRs that induces systemic lymphopenia by suppression of lymphocyte egress from lymphoid organs. In this review, we summarize previous findings and new discoveries about the importance of S1P and S1PR signaling in the recruitment of immune cells and lymphocyte retention in inflamed tissues. We also discuss the role of S1P-S1PR1 axis in inflammatory diseases and wound healing.

Prolonging survival of corneal transplantation by selective sphingosine-1-phosphate receptor 1 agonist

Corneal transplantation is the most used therapy for eye disorders. Although the cornea is somewhat an immune privileged organ, immune rejection is still the major problem that reduces the success rate. Therefore, effective chemical drugs that regulate immunoreactions are needed to improve the outcome of corneal transplantations. Here, a sphingosine-1-phosphate receptor 1 (S1P1) selective agonist was systematically evaluated in mouse allogeneic corneal transplantation and compared with the commonly used immunosuppressive agents. Compared with CsA and the non-selective sphingosine 1-phosphate (S1P) receptor agonist FTY720, the S1P1 selective agonist can prolong the survival corneal transplantation for more than 30 days with a low immune response. More importantly, the optimal dose of the S1P1 selective agonist was much less than non-selective S1P receptor agonist FTY720, which would reduce the dose-dependent toxicity in drug application. Then we analyzed the mechanisms of the selected S1P1 selective agonist on the immunosuppression. The results shown that the S1P1 selective agonist could regulate the distribution of the immune cells with less CD4+ T cells and enhanced Treg cells in the allograft, moreover the expression of anti-inflammatory cytokines TGF-β1 and IL-10 unregulated which can reduce the immunoreactions. These findings suggest that S1P1 selective agonist may be a more appropriate immunosuppressive compound to effectively prolong mouse allogeneic corneal grafts survival.