Cyclosporin A inhibits nitric oxide production by L929 cells in response to tumor necrosis factor and interferon-gamma

Calcineurin: form and function

Calcineurin is a eukaryotic Ca(2+)- and calmodulin-dependent serine/threonine protein phosphatase. It is a heterodimeric protein consisting of a catalytic subunit calcineurin A, which contains an active site dinuclear metal center, and a tightly associated, myristoylated, Ca(2+)-binding subunit, calcineurin B. The primary sequence of both subunits and heterodimeric quaternary structure is highly conserved from yeast to mammals. As a serine/threonine protein phosphatase, calcineurin participates in a number of cellular processes and Ca(2+)-dependent signal transduction pathways. Calcineurin is potently inhibited by immunosuppressant drugs, cyclosporin A and FK506, in the presence of their respective cytoplasmic immunophilin proteins, cyclophilin and FK506-binding protein. Many studies have used these immunosuppressant drugs and/or modern genetic techniques to disrupt calcineurin in model organisms such as yeast, filamentous fungi, plants, vertebrates, and mammals to explore its biological function. Recent advances regarding calcineurin structure include the determination of its three-dimensional structure. In addition, biochemical and spectroscopic studies are beginning to unravel aspects of the mechanism of phosphate ester hydrolysis including the importance of the dinuclear metal ion cofactor and metal ion redox chemistry, studies which may lead to new calcineurin inhibitors. This review provides a comprehensive examination of the biological roles of calcineurin and reviews aspects related to its structure and catalytic mechanism.

Protective effects of cyclosporin-A in splanchnic artery occlusion shock

Cyclosporin A (CsA) is an immunosuppressant drug that inhibits nitric oxide (NO) synthase induction in vascular smooth muscle cells. Splanchnic artery occlusion (SAO) shock is a lethal type of shock characterized by a marked vascular dysfunction in which the L-arginine/nitric oxide pathway plays an important role. We investigated whether CsA exerts protective effects in SAO shock by interfering with the L-arginine/nitric oxide pathway. Male anaesthetized rats (n=156) were subjected to clamping of the splanchnic arteries for 45 min. This surgical procedure resulted in an irreversible state of shock (SAO shock). Sham operated animals were used as controls. SAO shocked rats had a decreased survival (86+/-6 min, while sham shocked rats survived more than 240 min), marked hypotension, increased serum levels of TNF-alpha, enhanced plasma nitrite/nitrate concentrations (75+/-7.1 microM; sham shocked rats=1.6+/-0.5 microM) and enhanced inducible NO synthase (iNOS) protein induction and activity in the aorta. Moreover aortic rings from shocked rats showed a marked hyporeactivity to phenylephrine (PE, 1 nM - 10 microM). CsA (0.25, 0.5 and 1 mg kg(-1), 5 min after reperfusion) increased survival rate (SAO+CsA=236+/-9 min following the highest dose), reverted the marked hypotension, reduced plasma nitrite/nitrate concentration (11+/-5.2 microM following the highest dose), restored to control values the hyporeactivity to PE, and blunted iNOS protein induction and activity in aortic rings. The present data indicate that in an experimental rat model CsA may have antishock properties related to inhibition of L-arginine/nitric oxide pathway.

Role of endothelin ET(A) receptors in the hypertension produced by 4-day L-nitroarginine methyl ester and cyclosporine treatment

Studies were designed to examine the influence of endothelin type A receptor (ETA) blockade on the hypertensive and renal response to 4 day treatment with the nitric oxide (NO) synthase inhibitor, L-nitroarginine methyl ester (L-NAME), and cyclosporine. In the first series of experiments, male Sprague-Dawley rats maintained in metabolic cages were given the L-NAME at 50 mg/100 ml in the drinking water with or without the ETA receptor antagonist, A-127722 (2-(4-methoxyphenyl)-4-(1,3-benzodioxol-5-yl)-1-[[(dibutyl amino)carbonyl]methyl]-pyrrolidine-3-carboxylic acid; 10 mg kg(-1) day(-1)), in either food or water. After 4 days, tail cuff estimates of systolic arterial pressure and a blood sample were obtained. A-127722 prevented the rise in tail cuff pressure produced by L-NAME. In the second series of experiments, rats were given cyclosporine at 20 mg kg(-1) day(-1) (i.p.) or cyclosporine plus L-NAME. Control groups were given olive oil (1 ml/kg i.p.). Treatment with cyclosporine alone had no effect on tail cuff pressure or plasma creatinine, but significantly attenuated the normal increase in body weight over the 4-day period. The combination of cyclosporine plus L-NAME significantly increased both tail cuff pressure and plasma creatinine and completely prevented any gain in body weight. L-NAME plus olive oil produced a significant increase in tail cuff pressure but changed no other variable. To determine the role of ETA receptors in this setting, a final series of rats were treated with cyclosporine and L-NAME along with A-127722 in the drinking water. ETA receptor blockade had no effect on the increase in tail cuff pressure, plasma creatinine or the attenuated weight gain. These results indicate that subchronic (4-day) L-NAME hypertension is maintained, at least in part, by activation of ETA receptors although the hypertensive and renal response to combined L-NAME and cyclosporine treatment does not involve ETA receptor activation. These results support the hypothesis that endothelial dysfunction predisposes the kidney to functional derangements associated with cyclosporine.

Cyclosporin A inhibits nitric oxide synthase induction in vascular smooth muscle cells

The effect of cyclosporin A on induction of nitric oxide synthase in rat aortic smooth muscle cells was examined. A combination of interleukin-1 alpha (100 U/mL) and tumor necrosis factor--alpha (5000 U/mL) induced accumulation of nitrite/nitrate, the stable end products of nitric oxide, in culture media within 48 hours. Cyclosporin A inhibited this nitrite/nitrate accumulation in a concentration-dependent manner with an IC50 of 4 x 10(-7) mol/L when applied simultaneously with the cytokines. The expression of inducible nitric oxide synthase messenger RNA (mRNA) induced by the combination of interleukin-1 alpha and tumor necrosis factor-alpha was inhibited by the cyclosporin A cotreatment. Cyclosporin A did not decrease inducible nitric oxide synthase mRNA stability in the presence of transcription inhibitor actinomycin D (5 micrograms/mL). Induction of nitrite/nitrate production by the combination of tumor necrosis factor-alpha and bacterial lipopolysaccharide or that of interleukin-1 alpha and interferon gamma (100 U/mL) was also inhibited by cyclosporin A cotreatment. Another inhibitor of calcineurin, FK506 (up to 10(-6) mol/L), had no effect on the induction of nitrite/nitrate production, suggesting the possibility that the inhibitory effect of cyclosporin A may be exerted by means of a novel pathway other than inhibition of calcineurin. These results indicate that cyclosporin A inhibits inducible nitric oxide synthase induction at the mRNA level and that inducible nitric oxide synthase in vascular smooth muscle cells can be a target for cyclosporin A, providing a possible mechanism for the interference of the drug with the balance of vasoactive substances.

Molecular mechanisms of tumor necrosis factor-induced cytotoxicity. What we do understand and what we do not

Although TNF plays an important role in several physiological and pathological conditions, the hallmark of this important cytokine has been its selective cytotoxic activity on tumor cells. Since its cloning in 1984, understanding of how TNF selectively kills tumor cells has been the subject of research in many laboratories. Here we review TNF-induced post-receptor signaling mechanisms which seem to be involved in the pathway to cytotoxicity.