Anti-atherosclerotic properties of telmisartan in advanced atherosclerotic lesions in apolipoprotein E deficient mice.

Clinical studies have demonstrated that the inhibition of the renin-angiotensin system (RAS) by either an angiotensin-converting enzyme (ACE)-inhibitor or an angiotensin II receptor type 1 (AT(1))-antagonist reduces cardiovascular disease. The objective of this study was to evaluate underlying mechanisms of the AT(1)-antagonist telmisartan in comparison to the ACE-inhibitor ramipril on advanced atherosclerotic lesions. Thirty-two-week-old apolipoprotein E deficient mice (n=60) exhibiting advanced atherosclerotic lesions were fed a chow diet supplemented with ramipril or telmisartan for 16 weeks. Twenty mice received a standard diet. Mice receiving telmisartan had a 38% and mice receiving ramipril had a 18% reduction in progression of atherosclerotic lesion size within the innominate artery. Signs of plaque instability such as frequency of intra-plaque hemorrhage and size of the necrotic cores were reduced in mice receiving telmisartan. Furthermore, telmisartan-treated mice had fewer macrophages and reduced expression of early growth response gene-1 (Egr-1) within the lesions. Electrophoretic mobility shift assays revealed reduced DNA-binding activity of nuclear factor kappaB (NFkappaB) in the aorta of telmisartan-treated mice. In vitro studies in mouse macrophages demonstrated enhanced promoter activation of the nuclear transcription factor peroxisome proliferators-activated receptor gamma (PPARgamma). Target genes of PPARgamma, such as inducible nitric oxide synthase, NFkappaB and Egr-1, showed reduced activity after telmisartan pretreatment. These data suggest that chronic inhibition of the RAS by telmisartan prevails in reducing advanced atherosclerosis and promoting plaque stability over ramipril, possibly through the reduced activity of the pro-inflammatory transcription factors NFkappaB and Egr-1 and through the activation of PPARgamma.

Endothelin-1 induces functionally active CD40 protein via nuclear factor-kappaB in human vascular smooth muscle cells.

A plethora of evidence supports a link between inflammation and atherogenesis. The vasoactive peptide endothelin-1 (ET-1) has both proatherogenic and proinflammatory properties. The CD40-CD154 signaling pathway exhibits a direct influence on atherogenesis. We therefore tested the hypothesis that ET-1 induces CD40 in human vascular smooth muscle cells (SMC). ET-1 concentration-dependently stimulated CD40 protein in SMC. The specific ET-A-receptor antagonist BQ-123 prevented CD40 induction demonstrating receptor specificity of the ET-1 effect. Experiments with PI-1, an inhibitor of the IkappaB-a-degrading proteasome complex, demonstrated involvement of the transcription factor NF-kappaB in ET-1-induced CD40 expression. Specific decoy oligodeoxynucleotides with the consensus binding sequence for NF-kappaB and AP-1 supported a NF-kappaB-dependent and AP-1-independent induction pathway. Functional relevance of ET-1-induced CD40 expression was demonstrated by an increase in IL-6 secretion after stimulation with CD154 of cells preactivated with ET-1. The data show a link between a proatherogenic vasoactive peptide and cell-cell contact mediated inflammatory pathways and may implicate novel therapeutic options for vascular disease.

Angiotensin II promotes the inflammatory response to CD40 ligation via TRAF-2.

A plethora of evidence supports a link between inflammation and atherogenesis. Both the vasoactive peptide angiotensin II (ANG II) as well as the CD40/CD154 signaling pathway exhibit proinflammatory properties with a direct influence on atherogenesis. We therefore tested the hypothesis that ANG II interacts with CD40/CD154 in human vascular smooth muscle cells (SMC). ANG II did not increase expression of CD40 in human SMC. However, when SMC were prestimulated with ANG II and thereafter stimulated with CD154, the ligand for CD40, the release of IL-6 as a marker of inflammatory activation was augmented compared to cells not primed with ANG II. TNF receptor-associated factor 2 (TRAF-2), an important adaptor protein involved in CD40 signaling, but not TRAF-5 or -6, was increased by ANG II via activation of the angiotensin II type 1 (AT1) receptor subtype. These results suggest that a signaling pathway downstream of CD40 may be altered by ANG II prestimulation. Thus, ANG II can also indirectly cause inflammatory activation of vascular SMC. The data show a novel link between the proatherogenic vasoactive peptide ANG II and cell-cell contact-mediated inflammatory pathways and implicate options for the prevention and therapy of atherosclerotic disease.

Coronary stent thrombosis related to aspirin resistance: what are the underlying mechanisms?

Acute coronary stent thrombosis represents a serious complication for which aspirin resistance could be a potential cause. The actual case is a myocardial infarction treated with immediate stenting of the right coronary artery followed by elective stenting of the left anterior descending artery 4 days later. Despite standard antiplatelet therapy, stents in both arteries occluded 2 days after the last procedure. The patient's blood samples were analyzed and revealed the presence of aspirin resistance as well as elevated thromboxane B(2) plasma levels. No thrombophilic disorder was detected. Today the mechanism of aspirin resistance is mostly unknown. Further research as well as recommendations for laboratory screening and for alternative pharmacological treatment options are required.

Aspirin resistance in coronary artery disease is correlated to elevated markers for oxidative stress but not to the expression of cyclooxygenase (COX) 1/2, a novel COX-1 polymorphism or the PlA(1/2) polymorphism.

Aspirin resistance (AR) is estimated to be present in 5-75% of patients and is related to increased cardiovascular mortality. However, the underlying mechanisms are mostly unknown. In the present study, AR was detected in 14 out of 55 patients (25%) with coronary artery disease. The presence of concomitant anti-inflammatory drugs did not affect AR. Plasma levels of thromboxane B(2) as well as the markers for oxidative stress and known platelet activators 8-isoprostane and lipid peroxidation products were significantly higher in aspirin-resistant individuals (349.3 pg/ml, 53.9 pg/ml, and 538 micromol/l) compared to controls (113.7 pg/ml, 10.3 pg/ml, and 32.2 micromol/l; P < 0.05, respectively). Platelet cyclooxygenase-1 (COX-1) and COX-2 mRNA and protein expression were without significant differences between the two groups. DNA sequencing detected a novel platelet COX-1 single nucleotide polymorphism (SNP) resulting in amino acid exchange at position 8 (Arg8/Trp8). The wild-type as well as the heterozygous and homozygous SNP were present in both patient groups without significant differences. The aspirin binding (Arg120) and acetylation site (Ser529) were unaffected in the samples tested. Neither was AR related to the platelet integrin PlA(1)/A(2) polymorphism. In conclusion, AR appears to be unrelated to differences in platelet COX-1 and COX-2 expression or to a novel platelet COX-1 SNP and the PlA(1)/A(2) SNP. However, a correlation exists to elevated eicosanoids generated by oxidative stress indicating COX-1-independent pathways for the generation of platelet activating molecules represent a potential cause for AR.

Angiotensin II stimulates matrix metalloproteinase secretion in human vascular smooth muscle cells via nuclear factor-kappaB and activator protein 1 in a redox-sensitive manner.

The renin-angiotensin system contributes to atherogenesis. Matrix metalloproteinases (MMP) are thought to participate in plaque destabilization through degradation of extracellular matrix. This study tested whether angiotensin II (ANG II) induces MMP in human vascular smooth muscle cells (SMC). ANG II induced expression of MMP-1, -3, and -9, but not of MMP-2 in SMC. The expression of MMP-1, a key enzyme for collagen degradation, was studied in detail. SMC stimulated with ANG II concentration-dependently released enzymatically active MMP-1. The ANG II type 1 receptor antagonists losartan and candesartan blocked ANG-II-induced MMP-1 release. Inhibition experiments with actinomycin D suggest ANG-II-induced MMP-1 mRNA regulation at the transcriptional level. Decoy oligodeoxynucleotides against nuclear factor-kappaB and activator protein 1 inhibited MMP-1 secretion, demonstrating participation of these transcription factors in MMP-1 transcription. Stimulation of MMP-1 by ANG II depended on cyclooxygenase 2. The antioxidants pyrrolidine dithiocarbamate and N-acetylcysteine, the flavin protein inhibitor diphenylene iodonium, and the NADP(H) oxidase inhibitor apocynin blocked MMP-1 release, suggesting a redox-sensitive mechanism involving NADP(H) oxidase. The reactive oxygen species (ROS) donor 2,3-dimethoxy-1,4-naphthoquinone induced MMP-1 secretion and enhanced ANG-II-stimulated MMP-1 expression. These findings indicate that ROS may increase their own production by activation of NADP(H) oxidase. The capability of ANG II to induce functionally active MMP in human SMC may contribute to the altered plaque composition seen in complicated stages of atherosclerosis.