Effects of probucol on rat carotid artery responses to balloon catheter injury

DNA aptamer raised against advanced glycation end products inhibits neointimal hyperplasia in balloon-injured rat carotid arteries

BACKGROUND

Advanced glycation end products (AGE) and their receptor (RAGE) interaction elicit inflammatory and proliferative reactions in arteries, thus playing a role in cardiovascular disease. We have recently found that high-affinity DNA aptamer directed against AGE (AGE-aptamer) prevents the progression of experimental diabetic nephropathy by blocking the harmful actions of AGEs in the kidney. However, effects of AGE-aptamer on vascular injury remain unknown. In this study, we examined whether and how AGE-aptamer inhibits neointimal hyperplasia in balloon-injured rat carotid arteries.

METHODS

Male Wistar rats (weighting ca. 400 g at 11 weeks old) were anesthetized with sodium pentobarbital. The left common carotid artery was balloon-injured 3 times with 2F Fogaty catheter inserted through the femoral artery. Then the rats received continuous intraperitoneal infusion (3 μg/day) of either AGE-aptamer or control-aptamer by an osmotic mini pump for 2 weeks. 14 days after the procedure, the left common carotid arteries were excised for morphometric, immunohistochemical and western blot analyses.

RESULTS

Compared with control-aptamer, AGE-aptamer significantly suppressed neointima formation after balloon injury and reduced AGE accumulation, oxidative stress generation, proliferation cell nuclear antigen-positive area, macrophage infiltration, RAGE and platelet-derived growth factor-BB (PDGF-BB) expression levels in balloon-injured carotid arteries.

CONCLUSION

The present study suggests that AGE-aptamer could prevent balloon injury-induced neointimal hyperplasia by reducing PDGF-BB and macrophage infiltration via suppression of the AGE-RAGE-mediated oxidative stress generation. AGE-aptamer might be a novel therapeutic strategy for suppressing neointima formation after balloon angioplasty.

Development of a novel model of hypertriglyceridemic acute pancreatitis in hamsters: protective effects of probucol

OBJECTIVES

The aim of the present study was to develop a model of hypertriglyceridemic (HTG) acute pancreatitis and to investigate the effects of probucol in this model.

METHODS

Hamsters were fed a high-fat diet (HFD) or a normal diet for 3 weeks. Probucol was added at 1% to the HFD in the treated group. Pancreatitis was induced by 7 peritoneal injections of cerulein to the normal and HFD hamster groups. The severity of the pancreatitis and whole body oxidative stress were assessed.

RESULTS

The HFD induced severe HTG (>1000 mg/dL) in the hamsters. A more severe pancreatitis was observed in the HFD group. The HFD did not influence plasma-reduced glutathione level, but there was a significant increase after 1% probucol was provided in the diet. Plasma malonaldehyde levels in the HFD group were significantly higher than the normal chow group, whereas probucol administration significantly decreased plasma hydrogen peroxide and malonaldehyde levels. We also found that probucol significantly reduced levels of amylase and lipase in the plasma and pathological scores in pancreatic tissue.

CONCLUSIONS

This study presents a novel model of severe HTG acute pancreatitis, and our results support the potential therapeutic application of probucol in HTG acute pancreatitis.

Increased expression of Nox1 in neointimal smooth muscle cells promotes activation of matrix metalloproteinase-9

OBJECTIVE

Vascular injury causes neointimal hypertrophy, which is characterized by redox-mediated matrix degradation and smooth muscle cell (SMC) migration and proliferation. We hypothesized that, as compared to the adjacent medial SMCs, neointimal SMCs produce increased superoxide via NADPH oxidase, which induces redox-sensitive intracellular signaling to activate matrix metalloproteinase-9 (MMP-9).

METHODS AND RESULTS

Two weeks after balloon injury, rat aorta developed a prominent neointima, containing increased expression of NADPH oxidase and reactive oxygen species (ROS) as compared to the medial layer. Next, SMCs were isolated from either the neointima or the media and studied in culture. Neointimal-derived SMCs exhibited increased Nox1 expression and ROS levels as compared to medial SMCs. Neointimal SMCs had higher cell growth rates than medial SMCs. ROS-dependent ERK1/2 phosphorylation was greater in neointimal SMCs. MMP-9 activity, as detected by gel zymography, was greater in neointimal SMCs under resting and stimulated conditions and was prevented by expression of an antisense to Nox1 or treatment with an ERK1/2 inhibitor.

CONCLUSIONS

Following vascular injury, the increased expression of Nox1 in SMCs within the neointima initiates redox-dependent phosphorylation of ERK1/2 and subsequent MMP-9 activation.

Succinobucol induces apoptosis in vascular smooth muscle cells

Probucol inhibits the proliferation of vascular smooth muscle cells in vitro and in vivo, and the drug reduces intimal hyperplasia and atherosclerosis in animals via induction of heme oxygenase-1 (HO-1). Because the succinyl ester of probucol, succinobucol, recently failed as an antiatherogenic drug in humans, we investigated its effects on smooth muscle cell proliferation. Succinobucol and probucol induced HO-1 and decreased cell proliferation in rat aortic smooth muscle cells. However, whereas inhibition of HO-1 reversed the antiproliferative effects of probucol, this was not observed with succinobucol. Instead, succinobucol but not probucol induced caspase activity and apoptosis, and it increased mitochondrial oxidation of hydroethidine to ethidium, suggestive of the participation of H(2)O(2) and cytochrome c. Also, succinobucol but not probucol converted cytochrome c into a peroxidase in the presence of H(2)O(2), and succinobucol-induced apoptosis was decreased in cells that lacked cytochrome c or a functional mitochondrial complex II. In addition, succinobucol increased apoptosis of vascular smooth muscle cells in vivo after balloon angioplasty-mediated vascular injury. Our results suggest that succinobucol induces apoptosis via a pathway involving mitochondrial complex II, H(2)O(2), and cytochrome c. These unexpected results are discussed in light of the failure of succinobucol as an antiatherogenic drug in humans.

Nox1 transactivation of epidermal growth factor receptor promotes N-cadherin shedding and smooth muscle cell migration

AIMS

In atherosclerosis and restenosis, vascular smooth muscle cells (SMCs) migrate into the subendothelial space and proliferate, contributing to neointimal formation. The goal of this study was to define the signalling pathway by which Nox1 NAPDH oxidase mediates SMC migration.

METHODS AND RESULTS

SMCs were cultured from thoracic aorta from Nox1(-/y) (Nox1 knockout, KO) and wild-type (WT) mice. In response to thrombin, WT but not Nox1 KO SMCs generated increased levels of reactive oxygen species (ROS). Deficiency of Nox1 prevented thrombin-induced phosphorylation of Src and the subsequent transactivation of the epidermal growth factor receptor (EGFR) at multiple tyrosine residues. Next, activation of extracellular signal-regulated kinase 1/2 (ERK1/2) and matrix metalloproteinase-9 (MMP-9) by thrombin was inhibited by the EGFR inhibitor AG1478 and in Nox1 KO SMCs. Thrombin-induced shedding of N-cadherin from the plasma membrane was dependent on the presence of Nox1 and was blocked by AG1478 and an inhibitor of metalloproteinases. Migration of SMCs to thrombin was impaired in the Nox1 KO SMCs and was restored by expression of Nox1. Finally, treatment of WT SMCs with AG1478 abrogated Nox1-dependent SMC migration.

CONCLUSIONS

The Nox1 NADPH oxidase signals through EGFR to activate MMP-9 and promote the shedding of N-cadherin, thereby contributing to SMC migration.

Inhibition of apoptotic signaling and neointimal hyperplasia by tempol and nitric oxide synthase following vascular injury

OBJECTIVES

We hypothesized that redox-mediated apoptosis of medial smooth muscle cells (SMC) during the acute phase of vascular injury contributes to the pathophysiology of vascular disease.

METHODS

Apoptosis of medial SMC (1-14 days following balloon injury) was identified in rat carotid arteries by in situ DNA labeling. NADPH-derived superoxide and expression of Bcl-xL, Bax, caspase-3 and caspase-9 were assessed. The antioxidant tempol was administered in drinking water throughout the experimental period, and local adenoviral-mediated gene transfer of eNOS was performed prior to vascular injury.

RESULTS

Balloon injury increased NADPH-dependent superoxide production, medial SMC apoptosis, Bax-positive medial SMC index, Bax/Bcl-xL ratio, and caspase-3 and caspase-9 expression in the injured arteries. Treatment with tempol or eNOS gene transfer decreased superoxide levels and medial SMC apoptosis, with a concomitant increase in medial SMC density. Inhibition of superoxide was associated with a decreased Bax/Bcl-xL ratio, and caspase-3 and -9 expression. Tempol treatment and eNOS gene therapy significantly reduced neointima formation.

CONCLUSION

Vascular generation of reactive oxygen species participates in Bax activation and medial SMC apoptosis. These effects likely contribute to the shedding of cell-cell adhesion molecules and promote medial SMC migration and proliferation responsible for neointimal hyperplasia.

Pharmacologic approaches to restenosis prevention

Despite significant advances in technology and technique, coronary restenosis remains the primary limitation of percutaneous transluminal coronary angioplasty (PTCA). Among patients undergoing PTCA, between 20% and 50% of patients who do not receive a stent and 10%-30% of those who do receive a stent develop restenosis within 6 months of the procedure. Drug-eluting stents, which release high local concentrations of antiproliferative or immunosuppressive agents directly into the vessel wall at the site of the lesion, have dramatically reduced the incidence of restenosis in patients undergoing PTCA. However, even with drug-eluting stents, a significant percentage of higher-risk patients develop in-stent restenosis. These data suggest that a role remains for effective, well-tolerated systemic pharmacologic therapies to further reduce the rate of restenosis. To date, the majority of systemic agents tested for restenosis prevention have failed to show significant benefit. Only 2 agents, probucol and cilostazol, have consistently demonstrated efficacy in preventing restenosis. In addition, the investigational agent AGI-1067 has demonstrated promising efficacy in early clinical trials. Together with drug-eluting stents, these therapies may for the first time reduce the rate of restenosis to near zero, even in high-risk patients, such as individuals with diabetes mellitus.

Probucol mediates vascular remodeling after percutaneous transluminal angioplasty via down-regulation of the ERK1/2 signaling pathway

Although probucol is known to prevent restenosis by regulating vascular remodeling after percutaneous transluminal coronary angioplasty, the mechanisms remain unclear. The present study was designed to investigate whether probucol mediates vascular remodeling via the extracellular signal-regulated kinase 1/2 (ERK1/2) signalling pathway. A rabbit restenosis model was used, in which the New Zealand white rabbits received angioplasty with a 3.5 F angioplasty balloon catheter and the proliferation and migration of smooth muscle cells (SMCs) was induced by oxidized low-density lipoprotein (ox-LDL). We evaluated several vascular remodeling parameters and found that probucol prevented lumen restenosis and mediated expansive remodeling with a remodeling index greater than 1 and that the proliferation and migration of SMCs was inhibited. Based on Western blot analyses, probucol decreased the expression of phospho-mitogen-activated protein kinase kinases 1 (p-MEK1) and phospho-ERK1/2 and enhanced the expression of mitogen-activated protein (MAP) kinase phosphatase-1 (MKP-1) and caveolin-1. Cells treated with the MEK1 inhibitor PD98059 demonstrated a remarkable suppression of the effects of probucol. Furthermore, immunofluorescence analysis showed that probucol inhibited the activation of ERK1/2 by preventing its translocation to the nucleus. It was also found that c-myc expression in aortic tissue after angioplasty and the activator protein 1 (AP1) activity in SMCs induced by ox-LDL were decreased with probucol treatment. In conclusion, probucol mediated vascular remodeling to prevent restenosis after angioplasty by down-regulating the ERK1/2 signaling pathway.

Preclinical restenosis models and drug-eluting stents: still important, still much to learn

Percutaneous coronary intervention continues to revolutionize the treatment of coronary atherosclerosis. Restenosis remains a significant problem but may at last be yielding to technologic advances. The examination of neointimal hyperplasia in injured animal artery models has helped in our understanding of angioplasty and stenting mechanisms, and as drug-eluting stent (DES) technologies have arrived, they too have been advanced through the study of animal models. These models are useful for predicting adverse clinical outcomes in patients with DESs because suboptimal animal model studies typically lead to problematic human trials. Similarly, stent thrombosis in animal models suggests stent thrombogenicity in human patients. Equivocal animal model results at six or nine months occasionally have been mirrored by excellent clinical outcomes in patients. The causes of such disparities are unclear but may result from differing methods, including less injury severity than originally described in the models. Ongoing research into animal models will reconcile apparent differences with clinical trials and advance our understanding of how to apply animal models to clinical stenting in the era of DESs.

Effects of candesartan and probucol on restenosis after coronary stenting: results of insight of stent intimal hyperplasia inhibition by new angiotensin II receptor antagonist (ISHIN) trial

The purpose of this study was to determine whether candesartan and its combination with probucol reduce restenosis after coronary stenting. A total of 132 patients who successfully underwent stenting were randomly assigned to a control group (n=45), a candesartan group (8 mg daily, n=43), or a candesartan plus probucol group (+ probucol 500 mg daily, n=44). No differences in late loss were observed between the control and candesartan groups. In the candesartan plus probucol group, late loss was significantly smaller than in the control and candesartan groups (p=0.003, 0.015). The restenosis rate was 27% in the control group, 26% in the candesartan group (p>0.99), and 11% in the candesartan plus probucol group (p=0.104 vs the control group and p=0.103 vs the candesartan group). Intravascular ultrasound revealed no differences in stent area among the 3 groups, and no differences in lumen area or in intimal hyperplasia area between the control and candesartan groups. However, the intimal hyperplasia area in the candesartan plus probucol group was significantly less than that in the control and candesartan groups (p<0.001, p<0.001). This study demonstrated that candesartan failed to inhibit the neointimal hyperplasia and although the combination treatment did reduce neointimal hyperplasia, it did not statistically reduce the restenosis rate.

Effect of antioxidant probucol for preventing stent restenosis

Probucol is a lipid-lowering drug that has an antioxidant effect. The authors sought to investigate the effect of probucol on stent restenosis after the usual 3-day pretreatment protocol. From March 1999 to August 2000, 78 patients (mean age, 56 +/- 8; 49 male) with coronary artery disease who underwent coronary stenting were enrolled. After a diagnostic angiography was done, each eligible patient was randomized to either the probucol or the control group. Following the procedure, ticlopidine was administered for 1 month; aspirin and probucol continuously. Angiographic follow-up was done in 81% (57/70) and angiographic restenosis was not different between the two groups (21% vs. 24%; P = 0.81). In conclusion, antioxidant probucol did not show a beneficial effect on stent restenosis with 3 days of premedication protocol.

Mechanisms of angioplasty and stent restenosis: implications for design of rational therapy

Restenosis after angioplasty or stenting remains the major limitation of both procedures. A vast array of drug therapies has been used to prevent restenosis, but they have proven to be predominantly unsuccessful. Recent trends in drug therapy have attempted to refine the molecular and biological targets of therapy, based on the assumption that a single biological process or molecule is critical to restenosis. In contrast, both stenting and brachytherapy, which are highly nonspecific, can successfully reduce restenosis after angioplasty or stenting, respectively. This review examines the biology of both angioplasty and stent stenosis, focussing on human studies. We also review the landmark human trials that have definitively proven successful therapies, such as stenting and brachytherapy. We suggest that the successful trials of stenting and brachytherapy and the failure of other treatments have highlighted the shortcomings of conventional animal models of arterial intervention, and gaps in our knowledge of human disease. In contrast to arguments advocating gene therapy, these studies suggest that the most likely successful drug therapy will have a wide therapeutic range, targeting as many of the components or biological processes contributing to restenosis as possible.