New strategies to prevent restenosis

Farrerol maintains the contractile phenotype of VSMCs via inactivating the extracellular signal-regulated protein kinase 1/2 and p38 mitogen-activated protein kinase signaling

Farrerol, a dihydroflavone isolated from Rhododendron dauricum L., can inhibit vascular smooth muscle cell (VSMC) proliferation and exert a protective effect on H₂O₂-induced vascular endothelial cells injury. In this study, we investigated the effects of farrerol on VSMC phenotypic modulation and balloon injury-induced vascular neointimal formation and explored the underlying mechanisms. Serum-starved rat thoracic aorta SMCs (RASMCs) were first pretreated with farrerol (3, 10, and 30 μM, respectively), U0126 (a MEK kinase inhibitor), and SB203580 (a p38 kinase inhibitor), and followed by treatment with serum (10% FBS). The expression of several VSMC-specific markers, including α-SMA, SM22α, and OPN, were analyzed by western blot. Phosphorylation of extracellular signal-regulated protein kinase 1/2 (ERK 1/2) and p38 mitogen-activated protein kinase (MAPK) was also investigated. Farrerol inhibited the serum-induced transition of RASMCs from the contractile to the synthetic phenotype, and this was associated with a decrease in α-SMA and SM22α expression, and an increase in OPN expression. Farrerol also inhibited serum-induced phosphorylation of ERK1/2 and p38MAPK in RASMCs. Moreover, U0126 and SB203580 both inhibited the serum-induced phenotypic transition of RASMCs. These findings indicate that farrerol can maintain the contractile phenotype of VSMCs partly via inactivating the ERK1/2 and p38 MAPK signaling pathways. Using a rat model of carotid artery balloon injury, inhibition of VSMC phenotypic transition and suppression of neointimal formation were confirmed in vivo following the perivascular application of farrerol. Our results suggested that farrerol could be a promising lead compound for the treatment of vascular proliferative diseases.

Different Responses of Neointimal Cells to Imatinib Mesylate and Rapamycin Compared with Normal Vascular Smooth Muscle Cells

Purpose:

This study was designed to investigate whether vascular smooth muscle cells (VSMC) from the neointima showed any different response to anti-proliferative agents, such as rapamycin or imatinib mesylate, compared to VSMCs from normal artery.

Materials and Methods:

Intimal hyperplasia was made by carotid balloon in jury in male rats. Neointimal cells at 4 weeks after injury and normal VSMCs were extracted by enzymatic isolation method and cultured. Cell viability and proliferation were tested in VSMCs from injured left carotid artery and uninjured right carotid artery. Tests were repeated with rapamycin, imatinib mesylate or both in various concentrations.

Results:

Rapamycin decreased cell viability only at a high concentration of 10⁻⁵ M in uninjured VSMCs. Combined drugs decreased cell viability at a lower concentration of 10⁻⁷ M in uninjured VSMCs, and at a higher concentration of 10⁻⁵ M in neointimal cells. Overall, rapamycin showed cytocidal effects at a high concentration of 10⁻⁵ M, whereas imatinib did not. Cell proliferation of neointima was significantly decreased along with the drug concentration. Cell proliferation of uninjured VSMCs was significantly decreased at higher drug concentrations. Combined drug therapy showed synergistic effects. Overall, neointimal cells are more susceptible to the antiproliferative effects of the drugs.

Conclusion:

Neointimal cells from the injured carotid artery are more susceptible to the antiproliferative effect of imatinib and rapamycin. Both drugs can be a used for the prevention of intimal hyperplasia, which could be investigated through further in vivo studies.

Intimal hyperplasia in loop-injured carotid arteries is attenuated in transglutaminase 2-null mice

Arterial restenosis frequently develops after open or endovascular surgery due to intimal hyperplasia. Since tissue transglutaminase (TG2) is known to involve in fibrosis, wound healing, and extracellular matrix remodeling, we examined the role of TG2 in the process of intimal hyperplasia using TG2-null mice. The neointimal formation was compared between TG2-null and wild-type (C57BL/6) mice by two different injury models; carotid ligation and carotid loop injury. In ligation model, there was no difference in intimal thickness between two groups. In loop injury model, intimal hyperplasia developed in both groups and the intimal/medial area ratio was significantly reduced in TG2-null mice (P = 0.007). TG2 was intensely stained in neointimal cells in 2 weeks. In situ activity of TG2 in the injured arteries steadily increased until 4 weeks compared to uninjured arteries. Taken together, intimal hyperplasia was significantly reduced in TG2-null mice, indicating that TG2 has an important role in the development of intimal hyperplasia. This suggests that TG2 may be a novel target to prevent the arterial restenosis after vascular surgery.

Inhibition of intimal hyperplasia by local perivascular application of rapamycin and imatinib mesilate after carotid balloon injury

Purpose

Inhibition of the intimal hyperplasia after vascular surgery is an important issue. The purpose of this study is to define whether perivascular application of rapamycin, imatinib mesylate or cysteamine can reduce intimal hyperplasia in a carotid balloon injury model.

Methods

Each drug was mixed with 40% pluronic gel solution and was topically applied over the injured carotid artery evenly. Two or four weeks after injury, the arteries were harvested and morphometric analysis was done.

Results

The medial areas were not significantly different in each group and a thinning of the media as a toxic drug effect was not observed in any treatment group. The intimal area and intima-to-media (I/M) ratio were significantly reduced in rapamycin-treated group and imatinib-treated group (P < 0.05). But cysteamine-treated group showed a trend of decrease in I/M ratio in 2 weeks, but no difference in 4 weeks.

Conclusion

Perivascular delivery of imatinib or rapamycin with pluronic gel attenuated the development of intimal hyperplasia. But cysteamine did not. Further studies are needed to refine the optimal drug dosages in large animal models.

Interactions between stainless steel, shear stress, and monocytes

Angioplasty with stent placement is commonly used to treat coronary atherosclerosis. However, 20-40% of stainless steel stents restenose within 6 months via a prolonged inflammatory response mediated by monocytic infiltration and cytokine secretion. In the current study, we tested a hypothesis that blood flow and monocytes interact to alter stent corrosion. We assessed the effects of THP1 monocytes on the corrosion rate of 316L stainless steel (316LSS) under shear stress (0.5-50 dyn/cm(2)). In addition, THP1 cytokine secretion was determined using cytokine arrays and ELISA analyses. Data were compared using ANOVA and Tukey post hoc analysis (alpha = 0.05). Monocytes significantly lowered 316LSS corrosion rates without limiting current density. However, shear stress alone did not alter the corrosion rate of 316LSS. THP1 cells adhered to the 316LSS surface at all flow rates. Exposure to the 316LSS/corrosion test under high fluid flow rates increased (>twofold) the secretion of 7 of the 42 cytokines tested (angeogenin, GRO, I309, interleukin 8, interleukin 6, interleukin 1beta, and macrophage chemoattractant protein-1). Each of these cytokines play a role in wound healing, macrophage differentiation, and cell proliferation, all hallmarks of in-stent restenosis. Furthermore, only IL8 levels were significantly higher than any of the system controls during the 316LSS/corrosion test conditions. The IL8 levels from the 316LSS/corrosion tests were not significantly different from the +LPS control. Together, these data suggest that monocytic cells maybe activated by exposure to 316LSS stents and could contribute to in-stent restenosis and altered corrosion of the stent.

Induction of vascular atrophy as a novel approach to treating restenosis. A review

Regardless of the type of arterial reconstruction, luminal narrowing (stenosis or restenosis) develops in approximately one third of the vessels. In the past, the focus of research has been on the mechanisms of stenosis (intimal hyperplasia, pathologic remodeling) and pharmacologic approaches to prevention. An alternative approach is to induce intimal atrophy after luminal narrowing has developed, thus limiting treatment to only those patients that develop a problem. This approach to treat established disease by reducing wall mass through induction of cell death and extracellular matrix removal would be particularly useful for treating stenosis in synthetic bypass grafts or stented vessels, in which intimal hyperplasia is the primary mechanism of stenosis. This approach may be applicable as well to other vascular proliferative disorders, such as pulmonary hypertension and chronic transplant arteriopathy. Proof of principle has been shown in experiments with antibodies to platelet-derived growth factor (PDGF) receptors that cause neointimal regression in baboon polytetrafluoroethylene (PTFE) grafts and with angiotensin-converting enzyme inhibitors that induce medial atrophy in hypertensive arteries. Possible molecular targets could include PDGF receptors, A20, and BMP4. Further studies are needed to determine the utility of such a therapeutic approach to vascular disease.

Versican degradation and vascular disease

Versican is an abundant proteoglycan in the blood vessel wall that is increased after vascular injury and accumulates in advanced atherosclerotic plaques. Versican is a large molecule with domains that mediate binding to cytokines, enzymes, lipoproteins, other extracellular matrix molecules, and signaling receptors. There is evidence that versican exists in the normal, as well as the diseased, vessel wall as discrete fragments, which represent these functional domains. We review the literature on versican degradation in vascular tissue and the function of versican domains, all of which suggest that proteolytic modification of versican may have physiologic as well as pathologic implications for the vascular system.

Corrosion rates of stainless steel under shear stress measured by a novel parallel-plate flow chamber

A unique parallel-plate flow chamber has been engineered to assess the corrosion properties of implant materials in biological environments under shear flow. This parallel-plate flow chamber provides a novel approach to investigate hypotheses regarding cellular-material-mechanical-force interactions that influence the success or failure of implant devices. The results of the current study demonstrated that physiological stresses (0.5-50 dynes/cm2) from laminar flow from cell culture media did not significantly alter corrosion rates of stainless steel, providing baseline information for an extensive study of the cellular-material-mechanical-force interactions. Furthermore, this study demonstrated that this device is electrochemically stable and provides reproducible results within test parameters. In addition, the results were not significantly different from corrosion tests on bulk samples. Therefore, this system will be useful for investigating cell-material interactions under shear stress for implant alloys or other opaque materials. This information is currently lacking. The results of the present study also support further development of this test system to assess cellular responses to these materials under shear stresses.

Quinapril: a further update of its pharmacology and therapeutic use in cardiovascular disorders

Quinapril is rapidly de-esterified after absorption to quinaprilat (the active diacid metabolite), a potent angiotensin converting enzyme (ACE) inhibitor. Quinapril produces favourable haemodynamic changes, and improves ventricular and endothelial function in patients with various cardiovascular disorders; these effects are mediated through the binding of quinaprilat to both tissue and plasma ACE. Quinapril 10 to 40 mg/day provided effective blood pressure control in most patients with essential hypertension in clinical trials, but some patients required dosages of 80 mg/day and/or concomitant diuretic therapy. In general, quinapril provided similar blood pressure control to other standard antihypertensive therapies including other ACE inhibitors, calcium antagonists and beta-adrenoceptor antagonists in comparative clinical trials. Combined therapy with quinapril and hydrochlorothiazide had a significantly greater antihypertensive effect than either drug as monotherapy in two well designed studies. Quinapril has also been shown to reduce microalbuminuria in patients with hypertension and/or diabetes mellitus. In patients with congestive heart failure, quinapril <or=40 mg/day produced beneficial haemodynamic and echocardiographic changes and improved exercise tolerance, symptoms and functional class. Effects of quinapril on survival have not been investigated, but quinapril 10 to 20 mg/day showed comparable efficacy to captopril 25 to 50mg twice daily in two well designed trials. In patients with coronary artery disease, quinapril 40 mg/day significantly reduced the incidence of ischaemic events after coronary artery bypass grafting (CABG) in a well controlled study (n = 148). However, a lower dosage of quinapril (20 mg/day) showed no effect on ischaemic events or atherosclerotic progression with 3 years of treatment in a similarly designed study involving 1750 patients undergoing coronary angioplasty. The tolerability of quinapril is similar to that of other ACE inhibitors. In placebo-controlled trials, cough occurred in 2 and 4.3% and hypotension occurred in <1 and 2.9% of quinapril recipients with hypertension or congestive heart failure, respectively. No increase in adverse events was observed when the dosage was increased from 10 to 40 mg/day.

CONCLUSION

Quinapril is now firmly established as an effective and well tolerated ACE inhibitor for the treatment of patients with hypertension and congestive heart failure. Quinapril 40 mg/day also significantly reduced the incidence of ischaemic events in patients undergoing CABG in one study; however, a lower dosage of quinapril (20 mg/day) had no effect on ischaemic events in patients undergoing coronary angioplasty in another trial. Additional trials in patients with coronary artery disease receiving optimal dosages of quinapril (40 mg/day) would be useful.