Bradykinin receptor antagonists attenuate neointimal proliferation postangioplasty

Carbon-Coated Stent and the Role of the Kallikrein-Kinin System in Peripheral Angioplasty

OBJECTIVE

The purpose of this study was to investigate the clinical evolution of patients treated with carbon-coated stent, as well as its patency and the inflammatory response triggered by this process through the quantification of serum elements of the kallikrein-kinin system (KKS).

METHODS

This was a single-center prospective study with 27 patients with peripheral artery disease (PAD) who required percutaneous transluminal angioplasty and stenting of the iliacofemoropopliteal segment using carbon-coated stent grafts (carbostents). The blood concentrations of the total and kininogen fractions were evaluated using immunoenzymatic methods. Plasma kallikrein levels were assessed by the colorimetric method and tissue kallikrein levels were evaluated by the spectrophotometric method. The activity of kininase II was measured by -fluorometric analysis.

RESULTS

Of the 27 patients who completed the 6 months of the study (11 iliac territory, 16 femoropopliteal territory), only one experienced restenosis (3.7%) (femoropopliteal segment) and no patient had occlusion (96.3% of patency). In 1 year, four patients were lost to follow-up and all 23 patients evaluated maintained stent patency, except for the patient who had restenosis throughout the first 6 months. We report complete (100%) member salvage in 12 months of follow-up. The activity levels of high- and low-molecular-weight kininogens decreased significantly over time (before vs. 24 h, p < 0.01; before vs. 6 months, p < 0.001, and before vs. 24 h, p < 0.01; before vs. 6 months, p < 0.001; 24 h vs. 6 months, p < 0.001, respectively). Patients also had significantly lower levels of plasma and tissue kallikrein (before vs. 24 h, p < 0.001; before vs. 6 months, p < 0.001, and before vs. 24 h, p < 0.01; before vs. 6 months, p < 0.05, respectively). There was a significant increase in the enzymatic activity of kininase II at 24 h and after 6 months compared to the pre-treatment control (p < 0.001).

CONCLUSION

Our early experience shows that the use of carbon-coated stents in PAD appears to be safe, with low rates of early restenosis (3.7% in the first 6 months and 5% in the 12 months of follow-up). We concluded that KKS was involved in the inflammatory response caused by the placement of carbon-coated stents.

Upregulation of peroxisome proliferator-activated receptor-gamma and NADPH oxidases are involved in restenosis after balloon injury

Restenosis is a major complication of percutaneous transluminal coronary angioplasty (PTCA) and is characterized by increased superoxide formation and accumulation of smooth muscle cells (SMCs). The mechanisms through which peroxisome proliferator-activated receptor-gamma (PPAR-gamma) modulates the pathological process are incompletely defined. In this study, balloon injury of porcine coronary arteries in vivo and cell scraping model in vitro were used to elucidate the pathway via this molecule. PPAR-gamma and NADPH oxidase expression significantly increased both in neointimal hyperplasia after balloon injury or in the cultured SMCs after scraping injury. In vitro, PPAR-gamma agonist 15-deoxy-Delta(12,14)-prostagladlin J(2) (15d-PGJ2) decreased cell-scraping-induced superoxide generation through suppression of NADPH oxidase activity via down-regulation of p22(phox) and gp91(phox). Furthermore, 15d-PGJ2 could suppress scraping-stimulated proliferation of SMCs. These data demonstrate that upregulation of PPAR-gamma and NADPH oxidases are involved in restenosis and activation of PPAR-gamma can inhibit the NADPH oxidase-dependent superoxide generation in SMCs after injury. These findings will provide a new potential drug target for restenosis after balloon injury.

Valsartan versus ACE inhibition after bare metal stent implantation—results of the VALVACE trial

The use of ACE inhibitors (ACE-i) represents an Ia recommendation in the treatment of patients with STEMI and NSTEMI. However, results of smaller studies suggest an increase of in-stent-restenosis under ACE-i administration. The effects of ACE-i and valsartan after bare metal stent implantation of the culprit type B2/C lesion should be compared. Seven hundred patients were treated either by ACE-i in cases of LVEF<50% or 80 mg valsartan in cases of LVEF> or =50%. Restenosis rates after 6 months were analysed in 399 patients under valsartan and 224 patients under ACE-i with control angiography and major adverse cardiac events (death, infarction, reintervention) in a follow-up of up to 4 (mean 2.6) years in all patients. In-stent-restenosis was found in 19.5% under valsartan and in 34% under ACE-i (p<0.005). In diabetic patients, restenosis occurred in 24% under valsartan and in 43% under ACE-i (p<0.01). In initial acute coronary syndrome (ACS), restenosis rate was 14% under valsartan and 43% under ACE-i (p<0.0001). In stable angina, restenosis rates were 26.5% and 27.5%, respectively. Total MACE rates revealed significant differences in ACS due to reintervention rates of 22% and 7% under ACE-i and valsartan (p<0.0001). The administration of 80 mg valsartan after bare metal stent implantation leads to a reduction of in-stent-restenosis compared to ACE-i. This effect is mainly due to beneficial effects of valsartan in cases with initial ACS. Major differences between ACE-i and valsartan are discussed including inflammation, activation of neutrophils, mode of bradykinin activation, AT2 receptor stimulation and apoptosis of smooth muscle cells.

Mechanisms of angiotensin II-induced expression of B2 kinin receptors

Although the primary roles of the kallikreinkinin system and the renin-angiotensin system are quite divergent, they are often intertwined under pathophysiological conditions. We examined the effect of ANG II on regulation of B(2) kinin receptors (B2KR) in vascular cells. Vascular smooth muscle cells (VSMC) were treated with ANG II in a concentration (10(-9)-10(-6) M)- and time (0-24 h)-dependent manner, and B2KR protein and mRNA levels were measured by Western blots and PCR, respectively. A threefold increase in B2KR protein levels was observed as early as 6 h, with a peak response at 10(-7) M. ANG II (10(-7) M) also increased B2KR mRNA levels twofold 4 h after stimulation. Actinomycin D suppressed the increase in B2KR mRNA and protein levels induced by ANG II. To elucidate the receptor subtype involved in mediating this regulation, VSMC were pretreated with losartan (AT(1) receptor antagonist) and/or PD-123319 (AT(2) receptor antagonist) at 10 microM for 30 min, followed by ANG II (10(-7) M) stimulation. Losartan completely blocked the ANG II-induced B2KR increase, whereas PD-123319 had no effect. In addition, expression of B2KR mRNA levels was decreased in AT(1A) receptor knockout mice. Finally, to determine whether ANG II stimulates B2KR expression via activation of the MAPK pathway, VSMC were pretreated with an inhibitor of p42/p44(mapk) (PD-98059) and/or an inhibitor of p38(mapk) (SB-202190), followed by ANG II (10(-7) M) for 24 h. Selective inhibition of the p42/p44(mapk) pathway significantly blocked the ANG II-induced increase in B2KR expression. These findings demonstrate that ANG II regulates expression of B2KR in VSMC and provide a rationale for studying the interaction between ANG II and bradykinin in the pathogenesis of vascular dysfunction.

Can angiotensin receptor antagonists prevent restenosis after stent placement?

Restenosis rates after coronary stent implantation in complex lesions are between 30 and 50%. Neointimal hyperplasia promoted by complex interaction between cellular and acellular elements, such as cytokines and growth factors, is thought to be the primary process responsible for restenosis. The risk of in-stent restenosis is increased in patients with a history of restenosis after percutaneous transluminal coronary angioplasty, in long lesions, in total occlusions, in patients with diabetes mellitus, in small vessels, in the proximal parts of the left anterior descending coronary artery and in cases of stent oversizing. In-stent restenosis represents a serious economic burden on society because treatment strategies include expensive approaches such as cutting-balloon angioplasty, rotational atherectomy and brachytherapy. A number of pharmacological agents, including ACE inhibitors, have been unsuccessful in preventing restenosis. Alternative procedures such as brachytherapy, radioactive stents and drug-eluting stents are under evaluation. Although sirolimus- or paclitaxel-eluting stents have been associated with very low restenosis rates over durations of 6 to 12 months, the long-term efficacy and tolerability of this approach is currently being investigated. Although ACE inhibitors have failed in reducing restenosis rates, the selective angiotensin II type 1 (AT(1)) receptor antagonist valsartan has shown encouraging results in the single-center Valsartan for Prevention of Restenosis after Stenting of Type B2/C lesions trial (ValPREST). The ValPREST trial is the first randomized, placebo-controlled study to have evaluated the effect of an angiotensin receptor antagonist on in-stent restenosis in a moderate number of patients. Compared with ACE inhibitors, angiotensin receptor blockers exert additional effects on the pathophysiological processes which lead to restenosis. Angiotensin receptor antagonists may affect several mechanisms involved in neointimal hyperplasia such as decreasing circulating cytokine and growth factor levels and reducing neutrophil activation, especially after stenting in acute coronary syndromes, but the results need to be confirmed in a large multicenter trial. The question whether long-term therapy, with an oral angiotensin receptor antagonist, is cost-effective and whether angiotensin receptor antagonists should be used as an add-on therapy to drug-eluting stents, requires clarification.