Cyclosporin A, but not FK506, increases arachidonic acid release and inhibits proliferation of pituitary corticotrope tumor cells

Combination of N, N'-dicyclohexyl-N-arachidonic acylurea and tacrolimus prolongs cardiac allograft survival in mice

Current immunosuppressive agents for organ transplantation are not ideal because of their strong toxicity and adverse effects. Hence, there is an urgent need to develop novel immunosuppressive agents. The compound N, N'-dicyclohexyl-N-arachidonic acylurea (DCAAA) is a novel highly unsaturated fatty acid from the traditional Chinese medicinal plant Radix Isatidis. In this study, we systematically investigated the toxicity, immunosuppressive effect and mechanisms underlying the activity of DCAAA. The toxicity tests showed that DCAAA treatment did not lead to red blood cell hemolysis and did not affect the liver and kidney functions in mice. The lymphocyte transformation test showed that DCAAA treatment inhibited lymphocyte proliferation in a dose-dependent manner. An in vivo cardiac allotransplantation experiment showed that DCAAA treatment could suppress the immune rejection and significantly prolong the survival of cardiac allografts in recipient mice by reducing the proportion of CD4⁺ T cells in the spleen and grafts, concentration of interferon-γ in the supernatant and serum and infiltration of inflammatory cells into the grafts. Moreover, a combination treatment with DCAAA and tacrolimus had a synergistic effect in preventing acute rejection of heart transplants. In vitro molecular biology experiments showed that DCAAA treatment inhibited activation of the T-cell receptor-mediated phosphoinostide 3-kinase-protein kinase B pathway, thereby arresting cell cycle transition from the G₁ to the S phase, and inhibiting lymphocyte proliferation. Overall, our study reveals a novel, low-toxicity immunosuppressive agent that has the potential to reduce the toxic side effects of existing immunosuppressive agents when used in combination with them.

Strain-specific differences in the effects of cyclosporin A and FK506 on the survival and regeneration of axotomized retinal ganglion cells in adult rats

The immune response can influence neuronal viability and plasticity after injury, effects differing in strains of rats with different susceptibility to autoimmune disease. We assessed the effects of i.p. injections of cyclosporin A (CsA) or FK506 on adult retinal ganglion cell (RGC) survival and axonal regeneration into peripheral nerve (PN) autografted onto the cut optic nerve of rats resistant (Fischer F344) or vulnerable (Lewis) to autoimmune disease. Circulating and tissue CsA and FK506 levels were similar in both strains. Three weeks after autologous PN transplantation the number of viable beta-III tubulin-positive RGCs was significantly greater in CsA- and FK506-treated F344 rats compared with saline-injected controls. RGC survival in Lewis rats was not significantly altered. In F344 rats, retrograde labeling of RGCs revealed that CsA or FK506 treatment significantly increased the number of RGCs that regenerated an axon into a PN autograft; however these agents had no beneficial effect on axonal regeneration in Lewis rats. PN grafts in F344 rats also contained comparatively more pan-neurofilament immunoreactive axons. In both strains, 3 weeks after transplantation CsA or FK506 treatment resulted in increased retinal macrophage numbers, but only in F344 rats was this increase significant. At this time-point PN grafts in both strains contained many macrophages and some T cells. T cell numbers in Lewis rats were significantly greater than in F344 animals. The increased RGC axonal regeneration seen in CsA- or FK506-treated F344 but not Lewis rats shows that modulation of immune responses after neurotrauma has complex and not always predictable outcomes.

Relationship between Plasma Phospholipid Polyunsaturated Fatty Acid Composition and Bone Disease in Renal Transplantation

To investigate the relationship between polyunsaturated fatty acid (PUFA) and bone metabolism in renal transplant patients, plasma phospholipid (PP) PUFA levels, biochemical markers of bone turnover and bone mineral density (BMD) were determined in 22 recipients of a first renal allograft at baseline and after a mean 24.4 month follow-up. A significant increase in PP n-3 PUFA content, in the [n-3 PUFA/ arachidonic acid] ratio and in BMD values was observed, as well as a close correlation between the increase in PP n-3 PUFA content and femoral neck BMD. Multivariate regression analysis showed that BMD improvement was positively related to PP n-3 PUFA variation and baseline PP eicosapentaenoic acid levels, and negatively to PP arachidonic acid modification. Tacrolimus- versus cyclosporine-treated patients demonstrated a significant increase in femoral neck BMD and PP n-3 PUFA content. This is the first longitudinal study showing a link between PP-PUFA composition and bone disease in renal transplantation.

Cyclosporin A attenuates skeletal muscle damage induced by crotoxin in rats

This work was undertaken to determine the role of the calcineurin pathway on the necrosis of skeletal muscle induced by crotoxin, the major component of the venom of Crotalus durissus terrificus. Rats were treated with cyclosporin A (CsA), a calcineurin inhibitor, for 5 days and, in the 6th day, received an intramuscular injection of crotoxin into the tibialis anterior muscle. Rats were also treated with diclofenac, a non-steroidal anti-inflammatory drug, for 5 days and, on the 6th day, injected with crotoxin. All treated groups were sacrificed 24 h after injection of crotoxin. Tibialis anterior and soleus muscles were removed, frozen and stored in liquid nitrogen. Histological sections were stained with Toluidine Blue and assayed for acid phosphatase. The results show that CsA, but not diclofenac, is able to significantly minimize myonecrosis promoted by crotoxin. In conclusion, CsA attenuates skeletal muscle necrosis induced by crotoxin, indicating that the calcineurin pathway is essential for crotoxin myotoxic activity. The myoprotective effect of CsA is not related to its anti-inflammatory effect since diclofenac, a cyclo-oxygenase inhibitor, was not able to produce myoprotection.

Melittin exerts multiple effects on the release of free fatty acids from L1210 cells: lack of selective activation of phospholipase A2 by melittin

Melittin is known as a phospholipase A2 (PLA2) activator, but the selectivity of its effect on PLA2 is uncertain. We examined the selectivity of melittin effect on the release of free fatty acids (FFAs) from L1210 cells using various inhibitors. A systemic lipid analysis by HPLC and GLC revealed that melittin induced release of various FFAs including saturated, monounsaturated, and polyunsaturated FFAs. Various PLA2 inhibitors examined exerted only minimal effects on the melittin-induced arachidonic acid (AA) and palmitic acid (PAL) releases. Specific inhibitors of phosphatidylinositol-phospholipase C (U73122) and diacylglycerol lipase (RHC80267) exerted significant inhibitory effects on both AA and PAL releases. These results suggest that melittin-induced FFA release is most likely due to multiple participations of various types of lipases. Since BAPTA/AM, an intracellular Ca2+ chelator, did not influence the FFA release, the Ca2+ influxed by melittin appeared not to be a key factor for the FFA release. The mimicking of the melittin-induced FFA release by digitonin, a membrane-permeabilizing agent, implies that the membrane-perturbing action of melittin is likely the cause of the FFA release. Melittin also induced release of multiple FFAs from other cell lines including P388D1 and HL60. The rapid melittin-stimulated phospholipase D (PLD) observed in L1210 cells appeared not directly related to the steady release of FFA, as indicated by the fact that the PLD was not blocked by RHC80267. In view of melittin's multiple effects on the composition of cellular lipids, we conclude that melittin does neither exclusively release any single FFA nor selectively activate PLA2 in L1210 cells. The problem of using melittin as a PLA2 activator is discussed.