Vasopressin type 1A receptor up-regulation by cyclosporin A in vascular smooth muscle cells is mediated by superoxide

Lower malignancy rates in renal allograft recipients converted to sirolimus-based, calcineurin inhibitor-free immunotherapy: 24-month results from the CONVERT trial

BACKGROUND

Long-term immunosuppression imposes increased malignancy risk in renal allograft recipients, significantly contributing to overall morbidity and mortality. This study examined malignancy rates in renal allograft recipients at 2 years after conversion to a sirolimus (SRL)-based, calcineurin inhibitor (CNI)-free regimen.

METHODS

This open-label, randomized, multicenter study (the CONVERT Trial) randomly assigned 830 patients to SRL conversion (n=555) or CNI continuation (n=275). Patients with history of posttransplant lymphoproliferative disease or known/suspected malignancy within 5 years before screening were excluded. As part of standard safety measurements, subjects were monitored for any malignancy occurrence; both skin and nonskin malignancies were reported, even if the patient discontinued from the therapy. Malignancy rates were analyzed based on exposure time to study drugs (i.e., number of events per 100 person-years of follow-up).

RESULTS

At 2 years postconversion, the total number of malignancies per 100 person-years of exposure was significantly lower among SRL conversion patients compared with CNI continuation (2.1 vs. 6.0, P<0.001). Patients undergoing SRL-based, CNI-free therapy had significantly lower rates of the subset of nonmelanoma skin carcinomas through 2 years postconversion (1.2 vs. 4.3, P<0.001). This difference persisted after excluding patients with a history of malignancy before randomization. The rate of all other malignancies was not significantly different between treatment groups (P=0.058).

CONCLUSION

In renal allograft recipients, SRL-based immunosuppression was associated with a lower rate of malignancy at 2 years postconversion compared with continuation of CNI-based immunosuppression. This reduction was driven by a significant reduction in nonmelanoma skin carcinoma rates; the rate of all other malignancies was numerically lower but did not achieve statistical significance.

Cyclophilin D modulates mitochondrial F0F1-ATP synthase by interacting with the lateral stalk of the complex

Blue native gel electrophoresis purification and immunoprecipitation of F(0)F(1)-ATP synthase from bovine heart mitochondria revealed that cyclophilin (CyP) D associates to the complex. Treatment of intact mitochondria with the membrane-permeable bifunctional reagent dimethyl 3,3-dithiobis-propionimidate (DTBP) cross-linked CyPD with the lateral stalk of ATP synthase, whereas no interactions with F(1) sector subunits, the ATP synthase natural inhibitor protein IF1, and the ATP/ADP carrier were observed. The ATP synthase-CyPD interactions have functional consequences on enzyme catalysis and are modulated by phosphate (increased CyPD binding and decreased enzyme activity) and cyclosporin (Cs) A (decreased CyPD binding and increased enzyme activity). Treatment of MgATP submitochondrial particles or intact mitochondria with CsA displaced CyPD from membranes and activated both hydrolysis and synthesis of ATP sustained by the enzyme. No effect of CsA was detected in CyPD-null mitochondria, which displayed a higher specific activity of the ATP synthase than wild-type mitochondria. Modulation by CyPD binding appears to be independent of IF1, whose association to ATP synthase was not affected by CsA treatment. These findings demonstrate that CyPD association to the lateral stalk of ATP synthase modulates the activity of the complex.

Cyclophilin and the regulation of symbiosis in Aiptasia pallida

The sea anemone Aiptasia pallida, symbiotic with intracellular dinoflagellates, expresses a peptydyl-prolyl cis-trans isomerase (PPIase) belonging to the conserved family of cytosolic cyclophilins (ApCypA). Protein extracts from A. pallida exhibited PPIase activity. Given the high degree of conservation of ApCypA and its known function in the cellular stress response, we hypothesized that it plays a similar role in the cnidarian-dinoflagellate symbiosis. To explore its role, we inhibited the activity of cyclophilin with cyclosporin A (CsA). CsA effectively inhibited the PPIase activity of protein extracts from symbiotic A. pallida. CsA also induced the dose-dependent release of symbiotic algae from host tissues (bleaching). Laser scanning confocal microscopy using superoxide and nitric oxide-sensitive fluorescent dyes on live specimens of A. pallida revealed that CsA strongly induced the production of these known mediators of bleaching. We tested whether the CsA-sensitive isomerase activity is important for maintaining the activity of the antioxidant enzyme superoxide dismutase (SOD). SOD activity of protein extracts was not affected by pre-incubation with CsA in vitro.

V1a vasopressin receptor expression is modulated during myogenic differentiation

Neurohypophyseal peptides potently stimulate myogenic differentiation by acting through different receptors of the same family. Here, we show that L6C5 myogenic cells express, at a high density, a single class of V1a Arg8-vasopressin (AVP) receptor. The expression of the vasopressin receptor of type 1a (V1aR) is significantly higher in proliferating myoblasts than in differentiated myotubes. The differentiation-related decrease of V1aR expression was evident both at the mRNA and at the protein level as shown by the reduction of [(3)H]-AVP binding. However, in L6C5 cells transfected with a synthetic construct containing the luciferase gene driven by the 2 kb upstream region of V1aR, we observed a stimulation of the activity of the promoter when the cells were cultured in differentiative medium. The down-regulation of the V1aR correlated with a decreased half-life of its mRNA (half-life 5.86+/-0.74 hr in 10% fetal bovine serum [FBS] versus 3.53+/-0.72 hr in 1% FBS). Cyclosporine A and dexamethasone, but not 5'-azacytidine, treatments of cells in differentiation medium restored the V1aR level to that measured in proliferating L6C5 cells, thus confirming the role of post-transcriptional mechanisms in the modulation of V1aR expression. Taken together, these data show that mRNA stability plays a role in modulating protein expression during the myogenic differentiation process.

Role of peroxynitrite in endothelial damage mediated by Cyclosporine A

Although Cyclosporine A (CsA) is an effective therapy for immunosuppression, its use encompasses serious side effects that have been associated with oxidative stress. We previously reported the intracellular formation of both peroxynitrite and 3-nitrotyrosine in cultured bovine aortic endothelial cells (BAEC) when exposed to CsA. Here we show that re-addition of CsA to BAEC increases peroxynitrite formation in a concentration-dependent manner. This effect is inhibited by the glutathione donor and antioxidant, N-acetylcysteine (NAC). BAEC exposed to CsA showed impaired integrity of plasma membranes and increased cytolysis, a phenomenon prevented by NAC. When CsA was administered to mice, the increased presence of 3-nitrotyrosine was detected in the aortic endothelium, an effect also abrogated by the concomitant administration of NAC. An increase in nitrated MnSOD was detected in BAEC treated with CsA and the peroxynitrite donor SIN-1 and recapitulated in recombinant MnSOD, exposed to the conditioned media from BAEC. We propose that CsA promotes nitration of specific molecular targets, such as MnSOD, within vascular endothelial cells. This may represent a pathogenetic mechanism of vascular injury. Inhibition of this process by clinically applicable antioxidants, such as NAC, lends a basis for the exploration of therapeutic alternatives in patients treated with CsA.

On mechanism of superoxide signaling under physiological and pathophysiological conditions

It has been demonstrated that in various physiological and pathophysiological processes superoxide functions as a signaling molecule by the way different from those mediated by hydrogen peroxide, hydroxyl radicals, or peroxynitrite. However, until now the mechanism of superoxide signaling remains obscure. A well known role of superoxide as a precursor of reactive hydroxyl radicals by the superoxide-dependent Fenton reaction or the formation of peroxynitrite must result in the damage of the target molecules and lead to pathological disorders. However, this mechanism is unlikely in such processes as the stimulation by superoxide of enzymatic phosphorylation and dephosphorylation. But, not being a "super-oxidant", superoxide possesses the frequently forgotten "super"-nucleophilic properties. Now, we propose a new mechanism for superoxide signaling depending on its nucleophilic reactions. Possible nucleophilic mechanisms of superoxide signaling in the hydrolysis of phosphatidylinositol to inositol 1,4,5-tris-phosphate and in the catalysis of phosphorylation by mitogen-activated protein kinases, phospholipase C and other enzymes are considered.

In vitro anti-parasitic activity of Cyclosporin A analogs on Trypanosoma cruzi

Cyclosporin A (CsA) nonimmunosuppressive analogs were evaluated against Trypanosoma cruzi and on TcCyP19, a cyclophilin of 19 kDa. Two out of eight CsA analogs, H-7-94 and F-7-62 showed the best anti-parasitic effects on all in vitro assays. Their IC(50) values were 0.82 and 3.41 microM, respectively, compared to CsA IC(50) value 5.39 microM on epimastigote proliferation; and on trypomastigote lysis their IC(50) values were 0.97 and 2.66 microM compared to CsA IC(50) value 7.19 microM. H-7-94 and F-7-62 were also more effective than CsA in inhibiting trypomastigote infection. The enzymatic activity of TcCyP19 was inhibited by all CsA derivatives, suggesting this target is involved in the trypanocidal effects observed.

Desensitization of the Permeability Transition Pore by Cyclosporin A Prevents Activation of the Mitochondrial Apoptotic Pathway and Liver Damage by Tumor Necrosis Factor-α

We studied the effects of cyclosporin A (CsA) administration 1) on the properties of the permeability transition pore (PTP) in mitochondria isolated from the liver and 2) on the susceptibility to hepatotoxicity induced by lipopolysaccharide of Escherichia coli (LPS) plus D-galactosamine (D-GalN) in rats. CsA exerted a marked PTP inhibition ex vivo, with an effect that peaked between 2 and 9 h of drug treatment and decayed with an apparent half-time of about 13 h. Administration of LPS plus D-GalN to naive rats caused the expected increased serum levels of tumor necrosis factor (TNF)-alpha, liver inflammation with BID cleavage, activation of caspase 3, appearance of terminal deoxynucleotidyltransferase-mediated dUTP nick-end labeling-positive nuclei, and release of alanine aminotransferase and aspartate aminotransferase into the bloodstream. Treatment with CsA before or within 5 h of the administration of LPS plus D-GalN protected rats from hepatotoxicity despite the normal increase of serum TNF-alpha and BID cleavage. These results indicate that CsA prevents the hepatotoxic effects of TNF-alpha by blocking the mitochondrial proapoptotic pathway through inhibition of the PTP and provides a viable strategy for the treatment of liver diseases that depend on increased production and/or liver sensitization to TNF-alpha.

Role of Superoxide as a Signaling Molecule

Superoxide is known to affect vascular physiology in several ways and has also been recognized to contribute significantly to vascular physiopathology. Here we discuss the emerging role of superoxide as an essential signaling molecule in normal physiology.