[Show abstract][Hide abstract] ABSTRACT: Purpose: Atherosclerotic plaques progress in a highly individual manner. Plaque eccentricity has been associated with a rupture-prone phenotype and adverse coronary events in humans. Endothelial shear stress (ESS) critically determines plaque growth and low ESS leads to high-risk lesions. However, the factors responsible for rapid disease progression with increasing plaque eccentricity have not been studied. We investigated in vivo the effect of local hemodynamic and plaque characteristics on progressive luminal narrowing with increasing plaque eccentricity in humans.
Methods: Three-dimensional coronary artery reconstruction using angiographic and intravascular ultrasound data was performed in 374 patients at baseline (BL) and 6-10 months later (FU) to assess plaque natural history as part of the PREDICTION Trial. A total of 874 coronary arteries were divided into consecutive 3-mm segments. We identified 408 BL discrete luminal narrowings with a throat in the middle surrounded by gradual narrowing proximal and distal to the throat. Local BL ESS was assessed by computational fluid dynamics. The eccentricity index (EI) at BL and FU was computed as the ratio of max to min plaque thickness at the throat. Mixed-effects logistic regression was used to investigate the effect of BL variables on the combined endpoint of substantial worsening of luminal narrowing (decrease in lumen area >1.8 mm2 or >20%) with an increase in plaque EI.
Results: Lumen worsening with an increase in plaque EI was evident in 73 luminal narrowings (18%). Independent predictors of worsening lumen narrowing with plaque EI increase were low BL ESS (<1 Pa) distal to the throat (odds ratio [OR] =2.2 [95% CI: 1.3-3.7]; p=0.003) and large BL plaque burden (>51%) at the throat (OR=1.7 [95% CI: 1.0-2.8]; p=0.051). The incidence of worsening lumen narrowing with increasing plaque eccentricity was 30% in the presence of both predictors versus 15% in luminal narrowings without this combination of characteristics (OR=2.4 [95% CI: 1.4-4.3]; p=0.002).
Conclusions: Low local ESS independently predicts areas with rapidly progressive luminal narrowing and increasing plaque eccentricity. Coronary regions manifesting an abrupt anatomic change, i.e., at highest risk to cause an adverse event, can be identified early by assessment of ESS and plaque burden.
[Show abstract][Hide abstract] ABSTRACT: 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.
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.
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).
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.
[Show abstract][Hide abstract] ABSTRACT: 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.
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, O(2) consumption in isolated heart muscle strips was decreased in nNOS-overexpressing nNOS(+)/αMHC-tTA(+) mice already under resting conditions. Additionally, we found that the reactive oxygen species concentration was significantly decreased in hearts of nNOS-overexpressing nNOS(+)/αMHC-tTA(+) mice compared with noninduced nNOS(+)/αMHC-tTA(+) animals.
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.
[Show abstract][Hide abstract] ABSTRACT: Calcineurin (Cn), a serine/threonine phosphatase, plays a crucial role in the development of myocardial hypertrophy. Cn is a cytosolic phosphatase which dephosphorylates various target molecules, e.g. the transcriptional factor nuclear factor of activated T cells (NFAT), thereby enabling its nuclear translocation. Recently, it was demonstrated that not only NFAT, but also Cn is translocated into the nucleus. The nuclear coexistence of Cn and NFAT is important for the full transcriptional activity of the Cn-NFAT signalling cascade. Once Cn and NFAT have entered the nucleus of cardiomyocytes, the transcription of genes characteristic for myocardial hypertrophy (e.g. BNP, ANP) is initiated. The nuclear localization sequence (NLS), a region spanning amino acids 172-183 of calcineurin Abeta (CnAbeta) is essential for recognition and shuttling of Cn into the nucleus by importinbeta (1). A synthetic import blocking peptide (IBP) that mimics the NLS of Cn was tested recently. The NLS analogon IBP saturates the Cn binding site of importinbeta(1) thereby preventing binding of Cn and importin. This inhibits the translocation of Cn into the nucleus. Inhibiting the Cn/importin interaction with competing synthetic peptides is one of several new approaches to prevent the development of myocardial hypertrophy. Several patents have also been filed on molecules related to inhibition of Cn-NFAT signalling.