Franziska Panther

Conditional Overexpression of Neuronal Nitric Oxide Synthase Is Cardioprotective in Ischemia/Reperfusion

Background— We previously demonstrated that conditional overexpression of neuronal nitric oxide synthase (nNOS) inhibited L-type Ca2+ channels and decreased myocardial contractility. However, nNOS has multiple targets within the cardiac myocyte. We now hypothesize that nNOS overexpression is cardioprotective after ischemia/reperfusion because of inhibition of mitochondrial function and a reduction in reactive oxygen species generation. Methods and Results— Ischemia/reperfusion injury in wild-type mice resulted in nNOS accumulation in the mitochondria. Similarly, transgenic nNOS overexpression caused nNOS abundance in mitochondria. nNOS translocation into the mitochondria was dependent on heat shock protein 90. Ischemia/reperfusion experiments in isolated hearts showed a cardioprotective effect of nNOS overexpression. Infarct size in vivo was also significantly reduced. nNOS overexpression also caused a significant increase in mitochondrial nitrite levels accompanied by a decrease of cytochrome c oxidase activity. Accordingly, O2 consumption in isolated heart muscle strips was decreased in nNOS-overexpressing nNOS+/&agr;MHC-tTA+ mice already under resting conditions. Additionally, we found that the reactive oxygen species concentration was significantly decreased in hearts of nNOS-overexpressing nNOS+/&agr;MHC-tTA+ mice compared with noninduced nNOS+/&agr;MHC-tTA+ animals. Conclusion— We demonstrated that conditional transgenic overexpression of nNOS resulted in myocardial protection after ischemia/reperfusion injury. Besides a reduction in reactive oxygen species generation, this might be caused by nitrite-mediated inhibition of mitochondrial function, which reduced myocardial oxygen consumption already under baseline conditions.

Inhibition of nuclear translocation of calcineurin suppresses T-cell activation and prevents acute rejection of donor hearts.

Background. Inhibition of calcineurin (CnA) activity by cyclosporine A (CsA) is the mainstay in immunosuppressive therapy. CsA inhibits the phosphatase activity of the cytosolic phosphatase CnA and, therefore, prevents the dephosphorylation and subsequently nuclear translocation of the transcription factor nuclear factor of activated T cells (NFAT). However, CsA has multiple other targets within the cell and is, therefore, not specific. We developed a new approach to inhibit CnA/NFAT signaling. This synthetic peptide prevented CnA nuclear translocation in vitro. The purpose of this study was to demonstrate that this novel approach could potentially inhibit T-cell function in vitro and in vivo. Methods. T-cell activation (Jurkat T cells, naïve rat T cells, and peripheral human T cells) was assessed by protein synthesis, interleukin (IL)-2 promoter activity, and IL-2 levels after T-cell activation. Immunohistological stainings for CnA were performed to investigate nuclear localization of CnA. The immunosuppressive effects in vivo of the synthetic peptide were investigated in rats with heterotopic transplanted hearts. Results. The nuclear localization signal peptide significantly decreased alloantigen-specific T-lymphocyte proliferation, IL-2 promoter activity, and IL-2 production (338%±27% vs. 149%±11%, n=8, P<0.05) in cultured T cells by inhibition of CnA nuclear translocation. The synthetic peptide also significantly decreased the number of graft infiltrating CD8+ T lymphocytes. Moreover, treatment with the synthetic inhibitory inhibited acute graft rejection (5±0.6 days vs. 12±2 days, n=10, P<0.05). Conclusions. Inhibition of nuclear translocation of CnA is a novel approach to inhibit the activation of the CnA/NFAT signaling cascade. Further studies have to demonstrate the long-term use of this principle in vivo.

Lost central venous line caused tricuspid stenosis after 28 years

Sirs, A 45-year-old woman was referred for investigation because of dyspnoe on exertion. She had a history of Ebstein-Barr virus infection 28 years earlier. At that time she received oral analgetics for her sore throat with subsequent development of an anaphylactic shock. For the treatment of anaphylaxia she received a central venous line via the right subclavian vein. The patient fully recovered and was discharged after several days. Three years later a remaining central venous catheter ranging from the subclavian vein to the right ventricle was noted by X-ray examination. Since the patient was free of symptoms the catheter was left in place. The next 25 years were uneventful. Now echocardiography revealed signs of beginning right heart failure with dilation of the vena cava and the hepatic veins. MR imaging revealed interaction of the anterior tricuspid leaflet with the distal part of the central catheter (Fig. 1). Right heart catheterization showed calcification adherent to the catheter (Fig. 3). Simultaneous recording of right atrial and ventricular pressures demonstrated tricuspid stenosis with a mean pressure gradient of 5 mmHg (Fig. 2). Since MRI demonstrated adhesion of the proximal part of the catheter with the subclavian vein and adhesion of the distal part with the tricuspid valve no interventional approach to rescue the catheter was performed. The patient was transferred to the cardiac surgeons. The central line was removed surgically (Fig. 4). Intraoperatively Fig. 1 Cardiac MRI demonstrating the location of the catheter across the tricuspid valve. White arrows indicate catheter