Role of Sphingosine-1-Phosphate in Transplant Vasculopathy Evoked by Anti-HLA Antibody.

Transplant vasculopathy (TV) represents the main cause of late graft failure and limits the long-term success of organ transplantation. Cellular and humoral immune responses contribute to the pathogenesis of the concentric and diffuse intimal hyperplasia of arteries of the grafted organ. We recently reported that the mitogenic signaling, evoked in human vascular smooth muscle cells (hmSMC) by the anti-HLA class I monoclonal antibody W6/32, implicates neutral sphingomyelinase-2, suggesting a role for sphingolipids in intimal hyperplasia of TV. Here, we investigated whether the mitogenic sphingolipid, sphingosine-1-phosphate (S1P), is involved in intimal hyperplasia elicited by W6/32. Studies were done on cultured hmSMC and on an in vivo model of TV, consisting of human mesenteric arteries grafted into SCID/beige mice, injected weekly with W6/32. hmSMC migration and DNA synthesis elicited by W6/32 were inhibited by the sphingosine kinase-1 (SK1) inhibitor dimethylsphingosine, the anti-S1P antibody Sphingomab and the S1PR1/R3 inhibitor VPC23019. W6/32 stimulated SK1 activity, while siRNA silencing SK1, S1PR1 and S1PR3 inhibited hmSMC migration. In vivo, Sphingomab significantly reduced the intimal thickening induced by W6/32. These data emphasize the role of S1P in intimal hyperplasia elicited by the humoral immune response, and open perspectives for preventing TV with S1P inhibitors.

HLA class I antibodies provoke graft arteriosclerosis in human arteries transplanted into SCID/beige mice.

Antibodies toward HLA class I and/or MICA are commonly observed in transplanted patients suffering from allograft arteriosclerosis, also called chronic vascular rejection (CVR). The relative importance of cellular versus humoral alloreactivity for CVR is still disputed. We demonstrate that antibodies toward HLA class I provoke lesions typical for CVR in human arteries in vivo in the absence of cellular immunity. To show this, we grafted segments of human mesenteric arteries from 8 deceased organ donors into 36 immunodeficient SCID/beige mice in the infrarenal aortic position. Three mice died postoperatively. The remaining 33 mice received weekly i.v. injections of either a monoclonal antibody toward HLA class I, toward MICA or an irrelevant monoclonal antibody. At sacrifice after 6 weeks, mice receiving the HLA antibody showed a significant neointimal thickening in the grafted artery due to smooth muscle cell (SMC) proliferation while control mice receiving anti-MICA or irrelevant antibody showed little or no thickening. Whereas antibodies toward HLA class I were mitogenic to SMC in vitro, those directed toward MICA did not have any effect. Humoral alloreactivity toward HLA may thus play a causal role for the development of CVR and this opens new possibilities for the treatment of CVR.

FTY720 Inhibits Tumor Necrosis Factor-alpha-Induced Proliferation and Extracellular Signal-Regulated Kinase Phosphorylation of Human Smooth Muscle Cells.

We investigated the effects of the sphingolipid FTY720 on tumor necrosis factor-alpha (TNF-alpha)-induced proliferation and signal transduction in human smooth muscle cells (SMC). We showed that clinically relevant concentrations of FTY720 inhibited TNF-alpha-induced SMC proliferation and extracellular signal-regulated kinase (ERK) phosphorylation. We concluded that FTY720 may be a useful drug to inhibit chronic vascular rejection.

T-cell function in maintenance renal transplant patients receiving mycophenolate mofetil and steroids with or without tacrolimus.

Nephrotoxicity-sparing protocols, using mycophenolate mofetil (MMF) and steroids without calcineurin inhibitors (CNIs) or mammalian target rapamycin (mTOR), could be used to treat maintenance renal transplant patients. However, the risk for acute rejection seems to be high. The aim of this pharmacodynamic study was to analyze T-cell function, T-cell activation, and T-cell proliferation among patients receiving MMF and steroids (n = 15) compared with patients receiving immunosuppression with CNI-based therapy including tacrolimus, MMF, and steroids. Our data suggested that among stable maintenance patients, dual therapy with MMF and steroids might provide a similar reduction in T-cell proliferation and T-cell activation as that observed among patients on standard immunosuppressive therapy. As expected, intralymphocytic interleukin-2 (IL-2) and tumor necrosis factor-alpha (TNF-alpha) expressions were higher in patients not receiving CNIs.

Effect of FTY720 on apoptosis of smooth muscle cells.

BACKGROUND: Hyperproliferation of smooth muscle cells (SMCs) plays a key role in allograft arteriosclerosis. This prompted us to investigate the effect of the novel immune modulator and synthetic sphingolipid FTY720 on apoptosis of SMCs. METHODS: Rabbit SMC cultures were treated with FTY720 and apoptosis and necrosis were detected by fluorescence microscopy. RESULTS: We investigated dose- and time-dependent effects of FTY720 and found that clinically relevant low doses of FTY720 (<1 micromol/L) did not induce apoptosis, whereas 10 micromol/L FTY720 induced apoptosis after 48 hours incubation. CONCLUSION: At doses of FTY720 used in clinics for treatment of renal allografts and multiple sclerosis. FTY720 did not induce SMC apoptosis.

Differential effects of dietary supplementation with fish oil or soy lecithin on human platelet adhesion.

To investigate the possible regulating role of omega-6 and of omega-3 fatty acids on platelet adhesiveness, we randomised 60 volunteers into three groups to take 20 ml (equivalent to 0.3 g omega-6, 3.6 g omega-3; omega-6/omega-3 ratio 0.1) per day of a fish oil supplement, or to take 25 g (equivalent to 1.5 g omega-6, 0.5 g omega-3; omega-6/omega-3 ratio 3) per day of a soy lecithin supplement, or to continue on their usual diet without any supplement (control group) for a period of 15 days. Platelet adhesion on fibrinogen-coated 96-well microtitre plates was evaluated in the resting condition and after stimulation with 2 microM ADP or 0.02 U/ml thrombin. Compared to the values before the experimental period, the fish oil group showed a significant reduction in stimulated adhesion (with ADP: from 18.8% to 15.6%, p<0.01; with thrombin: from 24.4% to 20.8%, p<0.005), whereas no difference was noted in the resting condition (from 3.6% to 3.5%, NS). In the soy lecithin group, platelet adhesion was increased in all test conditions (with ADP: from 18.7% to 23.2%, p<0.001; with thrombin: from 24.0% to 29.9% p<0.001; resting: from 3.5% to 6.6%, p<0.001). No significant changes were observed in the control group. A good correlation was found between platelet adhesion data and the changes in the platelet fatty acid omega-6/omega-3 ratio caused by the different supplementations. Our results indicate an inhibitory effect of fish oil rich in omega-3 fatty acids on stimulated human platelet adhesiveness and a stimulatory effect of soy lecithin rich in omega-6 fatty acids on resting and stimulated adhesion. They suggest moreover that the omega-6/omega-3 ratio is a determinant of platelet adhesion.

Effects of dietary fish oil and soy phosphatidylcholine on neutrophil fatty acid composition, superoxide release, and adhesion.

Fifty-seven healthy volunteers matched for sex and age were subdivided in 3 groups and their usual Western diets were supplemented according to three different protocols: group 1, fish oil supplement (20 ml/day); group 2, soybean phosphatidylcholine (PC) (25 g/day) and group 3, no supplementation (control group). After 2 weeks several important modifications of neutrophil fatty acid composition were observed: fish oil induced a significant decrease of linoleic (LA) and arachidonic acid (AA) and a significant increase of eicosapentaenoic (EPA) and docosahexaenoic acid (DHA), while soy PC induced significant increases of LA, total polyunsaturated fatty acid (PUFA) and PUFA/SFA ratio. Neutrophil superoxide generation and adhesion were not modified by fish oil diet, on the contrary a slight but significant increase of O2.- production in response to fMLP was measured after soy PC diet. Our study confirms the possibility of changing neutrophil fatty acid composition in vivo by dietary means, but also suggests that the manipulation of cell functions, like superoxide anion generation and adhesion, is not easily and directly achieved by controlling membrane lipid environment.

Erythrocyte membrane lipids and serum selenium in post-viral and alcoholic cirrhosis.

Erythrocyte-membrane fatty acid composition and cholesterol content were evaluated along with serum selenium in 33 patients with liver cirrhosis and in 40 normal subjects. Thirteen patients were suffering from post-viral (group V) and 20 from alcoholic (group A) cirrhosis. The aim of the study was to elucidate whether membrane lipid abnormalities in cirrhosis were linked to the aetiology of the disease or whether they were the results of the cirrhotic process itself. The patients presented a significant increase in membrane cholesterol, palmitic acid (C16:0) and saturated fatty acids (SFA), and a decrease in polyunsaturated fatty acids (PUFA) and polyunsaturated/saturated fatty acids ratio (P/S) compared with the control group. Serum selenium levels were significantly reduced. When patients were subdivided according to aetiology, the alcoholic patients showed greater lipid composition abnormalities than the viral cirrhotics (higher levels of SFA and lower PUFA and P/S), while pathologic palmitic acid, membrane cholesterol and serum selenium values were confirmed in both groups of patients. In conclusion, low serum selenium and a series of erythrocytes membrane lipid composition abnormalities would appear to be features peculiar to cirrhosis. Alcoholic cirrhotics, on the other hand, show a more deranged erythrocyte membrane lipid profile.