Vascular neointimal formation and signaling pathway activation in response to stent injury in insulin-resistant and diabetic animals

Association between diabetes mellitus and primary restenosis following endovascular treatment: a comprehensive meta-analysis of randomized controlled trials

IMPORTANCE

Diabetes mellitus (DM) is thought to be closely related to arterial stenotic or occlusive disease caused by atherosclerosis. However, there is still no definitive clinical evidence to confirm that patients with diabetes have a higher risk of restenosis.

OBJECTIVE

This meta-analysis was conducted to determine the effect of DM on restenosis among patients undergoing endovascular treatment, such as percutaneous transluminal angioplasty (PTA) or stenting.

DATA SOURCES AND STUDY SELECTION

The PubMed/Medline, EMBASE and Cochrane Library electronic databases were searched from 01/1990 to 12/2022, without language restrictions. Trials were included if they satisfied the following eligibility criteria: (1) RCTs of patients with or without DM; (2) lesions confined to the coronary arteries or femoral popliteal artery; (3) endovascular treatment via PTA or stenting; and (4) an outcome of restenosis at the target lesion site. The exclusion criteria included the following: (1) greater than 20% of patients lost to follow-up and (2) a secondary restenosis operation.

DATA EXTRACTION AND SYNTHESIS

Two researchers independently screened the titles and abstracts for relevance, obtained full texts of potentially eligible studies, and assessed suitability based on inclusion and exclusion criteria.. Disagreements were resolved through consultation with a third researcher. Treatment effects were measured by relative ratios (RRs) with 95% confidence intervals (CIs) using random effects models. The quality of the evidence was assessed using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) criteria.

MAIN OUTCOMES AND MEASURES

The main observation endpoint was restenosis, including > 50% stenosis at angiography, or TLR of the primary operation lesion during the follow-up period.

RESULTS

A total of 31,066 patients from 20 RCTs were included. Patients with DM had a higher risk of primary restenosis after endovascular treatment (RR = 1.43, 95% CI: 1.25-1.62; p = 0.001).

CONCLUSIONS AND RELEVANCE

This meta-analysis of all currently available RCTs showed that patients with DM are more prone to primary restenosis after endovascular treatment.

Neointima abating and endothelium preserving - An adventitia-localized nanoformulation to inhibit the epigenetic writer DOT1L

Open vascular reconstructions such as bypass are common treatments for cardiovascular disease. Unfortunately, neointimal hyperplasia (IH) follows, leading to treatment failure for which there is no approved therapy. Here we combined the strengths of tailoring nanoplatforms for open vascular reconstructions and targeting new epigenetic mechanisms. We produced adhesive nanoparticles (ahNP) that could be pen-brushed and immobilized on the adventitia to sustainably release pinometostat, an inhibitor drug selective to the epigenetic writer DOT1L that catalyzes histone-3 lysine-79 dimethylation (H3K79me2). This treatment not only reduced IH by 76.8% in injured arteries mimicking open reconstructions in obese Zucker rats with human-like diseases but also avoided the shortcoming of endothelial impairment in IH management. In mechanistic studies, chromatin immunoprecipitation (ChIP) sequencing revealed co-enrichment of the histone mark H3K27ac(acetyl) and its reader BRD4 at the gene of aurora kinase B (AURKB), where H3K79me2 was also enriched as indicated by ChIP-qPCR. Accordingly, DOT1L co-immunoprecipitated with H3K27ac. Furthermore, the known IH driver BRD4 governed the expression of DOT1L which controlled AURKB's protein level, revealing a BRD4- > DOT1L- > AURKB axis. Consistently, AURKB-selective inhibition reduced IH. Thus, this study presents a prototype nanoformulation suited for open vascular reconstructions, and the new insights into chromatin modulators may aid future translational advances.

Effects of Isoprenaline on ventricular myocyte shortening and Ca2+ transport in the Zucker rat

Obesity is an important risk factor for diabetes mellitus (DM) which is a major global health problem. Electro-mechanical dysfunction has been extensively described in diabetic heart and cardiovascular complications are an important cause of mortality and morbidity in diabetic patients.

OBJECTIVES

To examine the effects of Isoprenaline (ISO) in obesity and diabesity on ventricular myocyte shortening and Ca²⁺ transport in Zucker fatty (ZF), Zucker diabetic fatty (ZDF) in comparison to Zucker lean (ZL) rats.

METHODS

Myocyte shortening and intracellular Ca²⁺ were investigated with video imaging and fluorescence photometry, respectively.

RESULTS

The amplitude of Isoprenaline stimulated shortening was significantly (p < 0.05) decreased in ZDF and ZF compared to ZL myocytes. The amplitude of Isoprenaline stimulated Ca²⁺ transient was also significantly (p < 0.05) reduced in ZF compared to ZL and modestly reduced in ZDF compared to ZL myocytes. Mean Isoprenaline stimulated time to peak along with time to half relaxation of shortening were unchanged in ZDF and ZF compared to ZL myocytes. Mean Isoprenaline stimulated time to peak Ca²⁺ transient was significantly shortened in ZF compared to ZL myocytes. Time to half decay of the Ca²⁺ transient was considerably prolonged in ZDF compared to ZL myocytes. Amplitude of Isoprenaline stimulated caffeine-evoked Ca²⁺ transients were significantly reduced in ZDF and ZF in comparison to ZL myocytes.

CONCLUSION

Isoprenaline was less effective at generating an increase in the amplitude of shortening in ZDF and ZF in comparison to ZL myocytes and defects in Ca²⁺ signaling, and in particular SR Ca²⁺ transport, might partly underlie these abnormalities.

Histopathologic response after hydrophilic polyethylene glycol-coating stent and hydrophobic octadecylthiol-coating stent implantations in porcine coronary restenosis model

Device-related problems of drug-eluting stents, including stent thrombosis related to antiproliferative drugs and polymers, can cause adverse events such as inflammation and neointimal hyperplasia. Stent surface modification, wherein the drug and polymer are not required, may overcome these problems. We developed hydrophilic polyethylene glycol (PEG)-coating and hydrophobic octadecylthiol (ODT)-coating stents without a drug and polymer and evaluated their histopathologic response in a porcine coronary restenosis model. PEG-coating stents (n = 12), bare-metal stents (BMS) (n = 12), and ODT-coating stents (n = 10) were implanted with oversizing in 34 porcine coronary arteries. Four weeks later, the histopathologic response, arterial injury, inflammation, and fibrin scores were analyzed. A p value < 0.05 was considered statistically significant. There were significant differences in the internal elastic lamina area, lumen area, neointimal area, percent area of stenosis, arterial injury score, inflammation score, and fibrin score among the groups. Compared to the BMS or ODT-coating stent group, the PEG-coating stent group had significantly increased internal elastic lamina and lumen area (all p < 0.001) and decreased neointimal area and percent area of stenosis (BMS: p = 0.03 and p < 0.001, respectively; ODT-coating: p = 0.013 and p < 0.001, respectively). Similarly, the PEG-coating group showed significantly lower inflammation and fibrin scores than the BMS or ODT-coating groups (BMS: p = 0.013 and p = 0.007, respectively; ODT-coating: p = 0.014 and p = 0.008, respectively). In conclusion, hydrophilic PEG-coating stent implantation was associated with lower inflammatory response, decreased fibrin deposition, and reduced neointimal hyperplasia than BMS or hydrophobic ODT-coating stent implantation in the porcine coronary restenosis model.

Coenzyme A and Its Thioester Pools in Obese Zucker and Zucker Diabetic Fatty Rats

Feeding behavior is closely related to hypothalamic malonyl-CoA level in the brain and diet-induced obesity affects total CoA pools in liver. Herein, we performed a comprehensive analysis of the CoA pools formed in thirteen tissues of Zucker and Zucker diabetic fatty (ZDF) rats. Hypothalamic malonyl-CoA levels in obese rats remained low and were almost the same as those of lean rats, despite obese rats having much higher content of leptin, insulin, and glucose in their sera. Regardless of the fa-genotypes, larger total CoA pools were formed in the livers of ZDF rats and the size of hepatic total CoA pools in Zucker rats showed almost one tenth of the size of ZDF rats. The decreased total CoA pool sizes in Zucker rats was observed in the brown adipose tissues, while ZDF-fatty rats possessed 6% of total CoA pool in the lean rats in response to fa deficiency. This substantially lower CoA content in the obese rats would be disadvantageous to non-shivering thermogenesis. Thus, comparing the intracellular CoA behaviors between Zucker and ZDF rats, as well as the lean and fatty rats of each strain would help to elucidate features of obesity and type 2 diabetes in combination with result (s) of differential gene expression analysis and/or comparative genomics.

Assessment of Vascular Patency and Inflammation with Intravascular Optical Coherence Tomography in Patients with Superficial Femoral Artery Disease Treated with Zilver PTX Stents

PURPOSE

Zilver PTX nitinol self-expanding drug-eluting stent with paclitaxel coating is effective for treatment of superficial femoral artery (SFA) disease. However, as with any stent, it induces a measure of vascular inflammatory response. The current clinical trial (NCT02734836) aimed to assess vascular patency, remodeling, and inflammatory markers with intravascular optical coherence tomography (OCT) in patients with SFA disease treated with Zilver PTX stents.

METHODS

Serial OCT examinations were performed in 13 patients at baseline and 12-month follow-up. Variables evaluated included neointimal area, luminal narrowing, thrombus area, stent expansion as well as measures of inflammation including, peri-strut low-intensity area (PLIA), macrophage arc, neovascularization, stent strut apposition and coverage.

RESULTS

Percentage of malapposed struts decreased from 10.3 ± 7.9% post-intervention to 1.1 ± 2.2% at 12-month follow-up, but one patient showed late-acquired stent malapposition (LASM). The percent of uncovered struts at follow-up was 3.0 ± 4.5%. Average expansion of stent cross-sectional area from baseline to follow-up was 35 ± 19%. The average neointimal area was 7.8 ± 3.8 mm². Maximal luminal narrowing was 61.1 ± 25.0%, and average luminal narrowing was 35.4 ± 18.2%. Average peri-strut low-intensity area (PLIA) per strut was 0.017 ± 0.018 mm². Average number of neovessels per mm of stent was 0.138 ± 0.181. Average macrophage angle per frame at follow-up was 7 ± 11°. Average thrombus area at follow-up was 0.0093 ± 0.0184 mm².

CONCLUSION

At 12-month follow-up, OCT analysis of Zilver PTX stent shows outward remodeling and minimal neointimal growth, but evidence of inflammation including PLIA, neovessels, thrombus and macrophages.

SUMMARY

Thirteen patients with PAD had paclitaxel-coated stents implanted in their SFAs and were then imaged with OCT at baseline and 12-month follow-up. OCT proxy metrics of inflammation were quantified.

miRNA Regulation of the Hyperproliferative Phenotype of Vascular Smooth Muscle Cells in Diabetes

Harnessing the mechanisms underlying the exacerbated vascular remodeling in diabetes mellitus (DM) is pivotal to prevent the high toll of vascular diseases in patients with DM. miRNA regulates vascular smooth muscle cell (VSMC) phenotypic switch. However, miRNA modulation of the detrimental diabetic VSMC phenotype is underexplored. Streptozotocin-induced type 1 DM (T1DM) Wistar rats and type 2 DM (T2DM) Zucker rats underwent right carotid artery experimental angioplasty, and global miRNA/mRNA expression profiling was obtained by RNA sequencing (RNA-Seq). Two days after injury, a set of six miRNAs were found to be uniquely downregulated or upregulated in VSMCs both in T1DM and T2DM. Among these miRNAs, miR-29c and miR-204 were the most significantly misregulated in atherosclerotic plaques from patients with DM. miR-29c overexpression and miR-204 inhibition per se attenuated VSMC phenotypic switch in DM. Concomitant miR-29c overexpression and miR-204 inhibition fostered an additive reduction in VSMC proliferation. Epithelial membrane protein 2 (Emp2) and Caveolin-1 (Cav1) mRNAs were identified as direct targets of miR-29c and miR-204, respectively. Importantly, contemporary miR-29c overexpression and miR-204 inhibition in the injured artery robustly reduced arterial stenosis in DM rats. Thus, contemporaneous miR-29c activation and miR-204 inhibition in DM arterial tissues is necessary and sufficient to prevent the exaggerated VSMC growth upon injury.

Upregulation of miR-221 and -222 in response to increased extracellular signal-regulated kinases 1/2 activity exacerbates neointimal hyperplasia in diabetes mellitus

BACKGROUND AND AIMS

Diabetes is associated with accelerated arterial intimal thickening that contributes to the increased cardiovascular disease seen in this population. In healthy arteries, intimal thickening is inhibited by elevated levels of the cyclin-dependent kinase inhibitor, p27^Kip1, and intimal thickening is promoted by activation of the mammalian Target of Rapamycin to promote degradation of p27^Kip1 protein. Recently, we reported that two microRNAs, miR-221 and -222, which promote intimal thickening via down-regulation of mRNA encoding p27^Kip1, are elevated in the arteries of diabetic patients. To determine if these miRNAs are critical to the increased intimal thickening under diabetic conditions, we examined the regulation of p27^Kip1in a mouse model of diabetes.

METHODS

Comparisons of p27^Kip1 signaling in NONcNZO10 mice fed a diabetogenic versus control diet were performed using immunochemistry and real-time PCR.

RESULTS

Vascular smooth muscle cells and arteries of diabetic mice exhibited decreased levels of p27^Kip1 that derived from destabilization of p27^Kip1 mRNA in an extracellular signal response kinase-1/2 (ERK-1/2) dependent manner. The activity of ERK-1/2 is increased in the arteries of diabetic mice and promotes an increase in miR-221 and -222. Inhibition of miR-221 and -222 restores normal levels of p27^Kip1 mRNA and protein in the arteries of diabetic mice and reduces intimal thickening following wire injury.

CONCLUSIONS

These data suggest diabetes is accompanied by increases in arterial miR-221 and -222 expression that promotes intimal thickening. Inhibition of the increased miR-221 and -222 may be efficacious in the prevention of the cardiovascular complications of diabetes.

Alagebrium inhibits neointimal hyperplasia and restores distributions of wall shear stress by reducing downstream vascular resistance in obese and diabetic rats

Mechanisms of restenosis in type 2 diabetes mellitus (T2DM) are incompletely elucidated, but advanced glycation end-product (AGE)-induced vascular remodeling likely contributes. We tested the hypothesis that AGE-related collagen cross-linking (ARCC) leads to increased downstream vascular resistance and altered in-stent hemodynamics, thereby promoting neointimal hyperplasia (NH) in T2DM. We proposed that decreasing ARCC with ALT-711 (Alagebrium) would mitigate this response. Abdominal aortic stents were implanted in Zucker lean (ZL), obese (ZO), and diabetic (ZD) rats. Blood flow, vessel diameter, and wall shear stress (WSS) were calculated after 21 days, and NH was quantified. Arterial segments (aorta, carotid, iliac, femoral, and arterioles) were harvested to detect ARCC and protein expression, including transforming growth factor-β (TGF-β) and receptor for AGEs (RAGE). Downstream resistance was elevated (60%), whereas flow and WSS were significantly decreased (44% and 56%) in ZD vs. ZL rats. NH was increased in ZO but not ZD rats. ALT-711 reduced ARCC and resistance (46%) in ZD rats while decreasing NH and producing similar in-stent WSS across groups. No consistent differences in RAGE or TGF-β expression were observed in arterial segments. ALT-711 modified lectin-type oxidized LDL receptor 1 but not RAGE expression by cells on decellularized matrices. In conclusion, ALT-711 decreased ARCC, increased in-stent flow rate, and reduced NH in ZO and ZD rats through RAGE-independent pathways. The study supports an important role for AGE-induced remodeling within and downstream of stent implantation to promote enhanced NH in T2DM.

Leukotriene-C4 synthase, a critical enzyme in the activation of store-independent Orai1/Orai3 channels, is required for neointimal hyperplasia

Leukotriene-C4 synthase (LTC4S) generates LTC4 from arachidonic acid metabolism. LTC4 is a proinflammatory factor that acts on plasma membrane cysteinyl leukotriene receptors. Recently, however, we showed that LTC4 was also a cytosolic second messenger that activated store-independent LTC4-regulated Ca(2+) (LRC) channels encoded by Orai1/Orai3 heteromultimers in vascular smooth muscle cells (VSMCs). We showed that Orai3 and LRC currents were up-regulated in medial and neointimal VSMCs after vascular injury and that Orai3 knockdown inhibited LRC currents and neointimal hyperplasia. However, the role of LTC4S in neointima formation remains unknown. Here we show that LTC4S knockdown inhibited LRC currents in VSMCs. We performed in vivo experiments where rat left carotid arteries were injured using balloon angioplasty to cause neointimal hyperplasia. Neointima formation was associated with up-regulation of LTC4S protein expression in VSMCs. Inhibition of LTC4S expression in injured carotids by lentiviral particles encoding shRNA inhibited neointima formation and inward and outward vessel remodeling. LRC current activation did not cause nuclear factor for activated T cells (NFAT) nuclear translocation in VSMCs. Surprisingly, knockdown of either LTC4S or Orai3 yielded more robust and sustained Akt1 and Akt2 phosphorylation on Ser-473/Ser-474 upon serum stimulation. LTC4S and Orai3 knockdown inhibited VSMC migration in vitro with no effect on proliferation. Akt activity was suppressed in neointimal and medial VSMCs from injured vessels at 2 weeks postinjury but was restored when the up-regulation of either LTC4S or Orai3 was prevented by shRNA. We conclude that LTC4S and Orai3 altered Akt signaling to promote VSMC migration and neointima formation.

Everolimus-eluting stents improve vascular response in a diabetic animal model

BACKGROUND

Preclinical evaluation of the vascular response of drug-eluting stents is limited especially in the setting of diabetes mellitus preventing the evaluation of changes in drug-eluting stent design and eluted drugs after clinical use.

METHODS AND RESULTS

Cultured human aortic endothelial cells were used to assess the differences between sirolimus and its analog, everolimus, in the setting of hyperglycemia on various cellular functions necessary for endothelial recovery. A diabetic rabbit model of iliac artery stenting was used to compare histological and morphometric characteristics of the vascular response to everolimus-eluting, sirolimus-eluting, and bare metal stent placement. Under hyperglycemic conditions, sirolimus impaired human aortic endothelial cell barrier function, migration, and proliferation to a greater degree compared with everolimus. In our in vivo model of diabetes mellitus, endothelialization at 28 days was significantly lower and endothelial integrity was impaired in sirolimus-eluting stent compared with both everolimus-eluting and bare metal stents. Neointimal area, uncovered struts, and fibrin deposition were significantly higher in sirolimus-eluting compared with everolimus-eluting and bare metal stents.

CONCLUSIONS

Use of everolimus-eluting stent results in improved vascular response in our preclinical models of diabetes mellitus.

Effect of metabolic syndrome on the response to arterial injury

BACKGROUND

Metabolic syndrome is now an epidemic in the United States population. Intimal hyperplasia remains the principal lesion in the development of restenosis after vessel wall injury. The aim of this study is to characterize the changes induced in wall morphology in the developing intimal hyperplasia within a murine model in the presence of diabetes (type 1) and metabolic syndrome.

METHODS

Control (wild type B6), Non Obese Diabetic, and metabolic syndrome (RCS-10) mice were used. The murine femoral wire injury model was used in which a micro wire is passed through a branch of the femoral and used to denude the common femoral and iliac arteries. Specimens were perfusion fixed and sections were stained with hematoxylin and eosin and Movat stains such that dimensional and compositional morphometry could be performed using an ImagePro system. Additional stains for proliferation and apoptosis were used.

RESULTS

In control mice, the injured femoral arteries develop intimal hyperplasia, which is maximal at 28 d and remains stable to day 56. Sham-operated vessels do not produce such a response. In diabetic mice, the intimal response increased 5-fold with a 2-fold increase in proteoglycan deposition, whereas in the metabolic syndrome mice there was a 6-fold increase in the intimal response and a similar increase in proteoglycan deposition. Collagen deposition was different with a 22-fold increase over control in collagen deposition in diabetes and a 100-fold increase over control in collagen deposition in metabolic syndrome as compared with the control injury mice. Maximal vascular smooth muscle cell (VSMC) proliferation was decreased in both diabetes and metabolic syndrome compared with controls, whereas early cell apoptosis in both diabetes and metabolic syndrome was sustained over a longer period of time compared with wild-type mice.

CONCLUSIONS

These data demonstrate that development of intimal hyperplasia is markedly different in diabetes and metabolic syndrome compared with controls, with an increase in collagen deposition, a reduction in VSMC proliferation, and an increase in early VSMC apoptosis. These findings suggest that preventative strategies against restenosis must be tailored for the diabetic and metabolic syndrome patients.

Role of metabolic environment on nitric oxide mediated inhibition of neointimal hyperplasia in type 1 and type 2 diabetes

Nitric oxide (NO) is well known to inhibit neointimal hyperplasia following arterial injury. Previously, we reported that NO was more effective at inhibiting neointimal hyperplasia in a type 2 diabetic environment than control. We also found that NO was ineffective in an uncontrolled type 1 diabetic environment; however, insulin restored the efficacy of NO. Thus, the goal of this study was to more closely evaluate the effect of insulin and glucose on the efficacy of NO at inhibiting neointimal hyperplasia in both type 1 and type 2 diabetic environments using different doses of insulin as well as pioglitazone. Type 1 diabetes was induced in male lean Zucker (LZ) rats with streptozotocin (60 mg/kg IP). Groups included control, moderate glucose control, and tight glucose control. Zucker diabetic fatty (ZDF) rats fed Purina 5008 chow were used as a type 2 diabetic model. Groups included no therapy, insulin therapy, or pioglitazone therapy. After 4 weeks of maintaining group assignments, the carotid artery injury model was performed. Treatment groups included: control, injury and injury plus NO. 2 weeks following arterial injury, in the type 1 diabetic rats, NO most effectively reduced the neointimal area in the moderate and tightly controlled groups (81% and 88% vs. 33%, respectively, p=0.01). In type 2 diabetic rats, the metabolic environment had no impact on the efficacy of NO (81-82% reduction for all groups). Thus, in this study, we show NO is effective at inhibiting neointimal hyperplasia in both type 1 and type 2 diabetic environments. A greater understanding of how the metabolic environment may impact the efficacy of NO may lead to the development of more effective NO-based therapies for patients with diabetes.

Histopathological Comparison among Biolimus, Zotarolimus and Everolimus-Eluting Stents in Porcine Coronary Restenosis Model

Background and Objectives

The aim of this study was to examine the histolopathogical effects among the biolimus, zotarolimus, and everolimus eluting stent (EES) in the porcine coronary restenosis model.

Subjects and Methods

Pigs were randomized into three groups in which the coronary arteries (15 pigs, 10 coronaries in each group) had either a biolimus A9 eluting stent (BES, n=10), zotarolimus eluting stent (ZES, n=10) or an EES (n=10). Histopathologic analysis was performed at 28 days after stenting.

Results

There were no significant differences in the injury score among the three groups. There was a significant difference in the internal elastic lamina, lumen area, neointima area, percent area stenosis, and the fibrin and inflammation score among the three groups (4.3±0.53 mm², 2.5±0.93 mm², 1.8±1.03 mm², 40.7±20.80%, 1.7±0.41, 1.4±0.72 in the BES group vs. 5.1±0.55 mm², 2.3±1.14 mm², 2.8±1.00 mm², 55.4±21.23%, 2.0±0.39, 1.6±0.76 in the ZES group vs. 4.4±0.53 mm², 1.7±1.22 mm², 2.8±1.23 mm², 64.0±26.00%, 1.8±0.76, 2.1±0.90 in the EES group, respectively). BES is more effective in inhibiting neointimal hyperplasia compared to ZES and EES (p<0.0001). According to the fibrin and inflammation score, BES and EES are more effective in decreasing the fibrin deposition compared to ZES (p<0.001). Moreover, BES and ZES are more effective in reducing the inflammatory reaction compared to EES (p<0.001).

Conclusion

The result demonstrates that BES shows better histopathological characteristics than ZES and EES at one month after stenting in the porcine coronary restenosis model.

Importance of insulin resistance to vascular repair and regeneration

Metabolic insulin resistance is apparent across a spectrum of clinical disorders, including obesity and diabetes, and is characterized by an adverse clustering of cardiovascular risk factors related to abnormal cellular responses to insulin. These disorders are becoming increasingly prevalent and represent a major global public health concern because of their association with significant increases in atherosclerosis-related mortality. Endogenous repair mechanisms are thought to retard the development of vascular disease, and a growing evidence base supports the adverse impact of the insulin-resistant phenotype upon indices of vascular repair. Beyond the impact of systemic metabolic changes, emerging data from murine studies also provide support for abnormal insulin signaling at the level of vascular cells in retarding vascular repair. Interrelated pathophysiological factors, including reduced nitric oxide bioavailability, oxidative stress, altered growth factor activity, and abnormal intracellular signaling, are likely to act in conjunction to impede vascular repair while also driving vascular damage. Understanding of these processes is shaping novel therapeutic paradigms that aim to promote vascular repair and regeneration, either by recruiting endogenous mechanisms or by the administration of cell-based therapies.

Dysregulation of the Mammalian Target of Rapamycin and p27Kip1 Promotes Intimal Hyperplasia in Diabetes Mellitus

The proliferation and migration of vascular smooth muscle cells (VSMCs) in the intima of an artery, known as intimal hyperplasia, is an important component of cardiovascular diseases. This is seen most clearly in the case of in-stent restenosis, where drug eluting stents are used to deliver agents that prevent VSMC proliferation and migration. One class of agents that are highly effective in the prevention of in-stent restenosis is the mammalian Target of Rapamycin (mTOR) inhibitors. Inhibition of mTOR blocks protein synthesis, cell cycle progression, and cell migration. Key to the effects on cell cycle progression and cell migration is the inhibition of mTOR-mediated degradation of p27Kip1 protein. p27Kip1 is a cyclin dependent kinase inhibitor that is elevated in quiescent VSMCs and inhibits the G1 to S phase transition and cell migration. Under normal conditions, vascular injury promotes degradation of p27Kip1 protein in an mTOR dependent manner. Recent reports from our lab suggest that in the presence of diabetes mellitus, elevation of extracellular signal response kinase activity may promote decreased p27Kip1 mRNA and produce a relative resistance to mTOR inhibition. Here we review these findings and their relevance to designing treatments for cardiovascular disease in the presence of diabetes mellitus.

Nitric oxide differentially affects ERK and Akt in type 1 and type 2 diabetic rats

BACKGROUND

We have shown that nitric oxide (NO) is more effective at inhibiting neointimal hyperplasia in type 2 diabetic rats than in nondiabetic rats, but is not effective in type 1 diabetic rats. Insulin signaling is mediated by the ERK and Akt pathways, and thus we hypothesized that NO differentially affects ERK and Akt activity in type 1 versus type 2 diabetic rats.

MATERIALS AND METHODS

To investigate this hypothesis, we induced type 2 diabetes in Zucker diabetic fatty (ZDF) rats by feeding them Purina 5008 chow. To induce type 1 diabetes, lean Zucker (LZ) rats were injected with streptozotocin (STZ; 60 mg/kg). The carotid artery injury model was performed. Groups included injury and injury + PROLI/NO (20 mg/kg) (n = 6/group).

RESULTS

Three days following injury, all animal models exhibited an increase in pERK levels. Whereas NO reduced pERK levels in LZ and STZ rats, NO had no effect on pERK levels in ZDF rats. Following a similar pattern, NO reduced pAkt levels in LZ and STZ rats but increased pAkt levels in ZDF rats. Fourteen days following injury, NO increased total pERK levels throughout the arterial wall in both the STZ and ZDF rats. These changes were greatest in the adventitia. Interestingly, whereas NO decreased total pAkt levels in LZ and STZ rats, NO increased pAkt levels in ZDF rats. Evaluation of the pERK:pAkt ratio revealed that NO increased this ratio in LZ and STZ rats but decreased the ratio in ZDF rats.

CONCLUSIONS

We report that NO differentially affects the expression of pERK and pAkt in type 1 versus type 2 diabetic rats. Given that NO is more effective at inhibiting neointimal hyperplasia in type 2 diabetic animals, the pERK:pAkt ratio may be the best surrogate to predict efficacy.

Comparative vascular responses three months after paclitaxel and everolimus-eluting stent implantation in streptozotocin-induced diabetic porcine coronary arteries

BACKGROUND

Diabetes remains a significant risk factor for restenosis/thrombosis following stenting. Although vascular healing responses following drug-eluting stent (DES) treatment have been characterized previously in healthy animals, comparative assessments of different DES in a large animal model with isolated features of diabetes remains limited. We aimed to comparatively assess the vascular response to paclitaxel-eluting (PES) and everolimus-eluting (EES) stents in a porcine coronary model of streptozotocin (STZ)-induced type I diabetes.

METHOD

Twelve Yucatan swine were induced hyperglycemic with a single STZ dose intravenously to ablate pancreatic β-cells. After two months, each animal received one XIENCE V® (EES) and one Taxus Liberte (PES) stent, respectively, in each coronary artery. After three months, vascular healing was assessed by angiography and histomorphometry. Comparative in vitro effects of everolimus and paclitaxel (10-5 M-10-12 M) after 24 hours on carotid endothelial (EC) and smooth muscle (SMC) cell viability under hyperglycemic (42 mM) conditions were assayed by ELISA. Caspase-3 fluorescent assay was used to quantify caspase-3 activity of EC treated with everolimus or paclitaxel (10-5 M, 10-7 M) for 24 hours.

RESULTS

After 3 months, EES reduced neointimal area (1.60 ± 0.41 mm, p < 0.001) with trends toward reduced % diameter stenosis (11.2 ± 9.8%, p = 0.12) and angiographic late-loss (0.28 ± 0.30 mm, p = 0.058) compared to PES (neointimal area: 2.74 ± 0.58 mm, % diameter stenosis: 19.3 ± 14.7%, late loss: 0.55 ± 0.53 mm). Histopathology revealed increased inflammation scores (0.54 ± 0.21 vs. 0.08 ± 0.05), greater medial necrosis grade (0.52 ± 0.26 vs. 0.0 ± 0.0), and persistently elevated fibrin scores (1.60 ± 0.60 vs. 0.63 ± 0.41) with PES compared to EES (p < 0.05). In vitro, paclitaxel significantly increased (p < 0.05) EC/SMC apoptosis/necrosis at high concentrations (≥ 10-7 M), while everolimus did not affect EC/SMC apoptosis/necrosis within the dose range tested. In ECs, paclitaxel (10-5 M) significantly increased caspase-3 activity (p < 0.05) while everolimus had no effect.

CONCLUSION

After 3 months, both DES exhibited signs of delayed healing in a STZ-induced diabetic swine model. PES exhibited greater neointimal area, increased inflammation, greater medial necrosis, and persistent fibrin compared to EES. Differential effects of everolimus and paclitaxel on vascular cell viability may potentially be a factor in regulating delayed healing observed with PES. Further investigation of molecular mechanisms may aid future development of stent-based therapies in treating coronary artery disease in diabetic patients.

A role for MRP8 in in stent restenosis in diabetes

OBJECTIVE

The most common cause of death in diabetes mellitus is cardiovascular disease. Patients frequently undergo vascular intervention such as stenting. The occurrence of in stent restenosis (ISR) has been reduced by the use of drug eluting stents in non-diabetic patients but the incidence of restenosis and stent thrombosis remains higher in diabetic patients. We investigated the pathogenesis of in stent restenosis in an animal model of type 2 diabetes mellitus.

METHODS AND RESULTS

Stents were placed in Zucker Fatty rat (ZFR) and wild type rat carotid arteries, and tissues were harvested 14 days post surgery for morphometric analysis. Unstented carotid arteries from both groups were harvested for microarray analysis. In vitro apoptosis, proliferation and migration assays were performed on rat and human aortic endothelial cells (EC). ZFRs developed an exaggerated intimal response to stent placement compared to wild type controls 14 days post stent placement. MRP8 and MRP14 were up-regulated in unstented ZFR carotid arteries in comparison to controls. Expression of MRP8/14 was also elevated in EC exposed to high glucose conditions. EC function was impaired by high glucose concentrations, and this effect could be mimicked by MRP8 over-expression. MRP8 knockdown by shRNA significantly restored EC function after exposure to high glucose concentrations. MRP8 expression in glucose exposed cells was also inhibited using pharmacological blockade of glucose-induced pathways.

CONCLUSIONS

EC dysfunction caused by elevated glucose levels could be mimicked by MRP8/14 over-expression and reversed/prevented by MRP8 knockdown. Thus, MRP8/14 likely plays a role in exaggerated ISR in diabetes mellitus, and MRP8 inhibition may be useful in improving outcome after stent placement in diabetes mellitus.

The impact of preprocedural hemoglobin A1c on the efficacy of sirolimus-eluting and paclitaxel-eluting stents

Several reports have shown contrary results regarding the efficacy of sirolimus-eluting stents (SES) and paclitaxel-eluting stents (PES) in diabetic patients. The association between hemoglobin A1c (A1c) before coronary intervention and the midterm clinical outcomes of patients treated with these stents is unclear. The enrolled population was 415 patients with diabetes or impaired glucose tolerance (IGT) who underwent follow-up angiography after being implanted with a SES (n = 282) or PES (n = 133). The enrolled population was classified into the optimal glycemic control group (n = 213) and suboptimal glycemic control group (n = 202), and the predictors of restenosis were examined in each group. In the optimal glycemic control group, the use of PES was an independent predictor of restenosis [odds ratio (OR) 9.98, 95% confidence interval (CI) 3.08-38.9, p < 0.0001]; on the other hand, the use of SES was a positive independent predictor of restenosis prevention (OR 0.10, 95% CI 0.03-0.32, p < 0.0001). In the suboptimal glycemic control group, neither stent was predictive of restenosis. In a subanalysis, preprocedural A1c (≥7.0%) was found to be an independent predictor of restenosis in the SES group (OR 3.61, 95% CI 1.14-12.8, p = 0.03), but not the PES group. Postprocedural A1c (≥7.0%) was not an independent predictor of restenosis in either stent group. This study showed that the superiority of SES compared to PES was attenuated in the suboptimal glycemic control group. Preprocedural A1c (≥7.0%) was found to be an independent predictor of restenosis in the SES group, but not in the PES group.

Insulin induces production of new elastin in cultures of human aortic smooth muscle cells

Diabetes mellitus accelerates atherosclerotic progression, peripheral angiopathy development, and arterial hypertension, all of which are associated with elastic fiber disease. However, the potential mechanistic links between insulin deficiency and impaired elastogenesis in diabetes have not been explored. Results of the present study reveal that insulin administered in therapeutically relevant concentrations (0.5 to 10 nmol/L) selectively stimulates formation of new elastic fibers in cultures of human aortic smooth muscle cells. These concentrations of insulin neither up-regulate collagen type I and fibronectin deposition nor stimulate cellular proliferation. Further, the elastogenic effect of insulin occurs after insulin receptor activation, which triggers the PI3K downstream signaling pathway and activates elastin gene transcription. In addition, the promoter region of the human elastin gene contains the CAAATAA sequence, consistent with the FoxO-recognized element, and the genomic effects of insulin occur after removal of the FoxO1 transcriptional inhibitor from the FoxO-recognized element in the elastin gene promoter. In addition, insulin signaling facilitates the association of tropoelastin with its specific 67-kDa elastin-binding protein/spliced form of β-galactosidase chaperone, enhancing secretion. These results are crucial to understanding of the molecular and cellular mechanisms of diabetes-associated vascular disease, and, in particular, endorse use of insulin therapy for treatment of atherosclerotic lesions in patients with type 1 diabetes, in which induction of new elastic fibers would mechanically stabilize the developing plaques and prevent arterial occlusions.

Adventitial contributions of the extracellular signal-regulated kinase and Akt pathways to neointimal hyperplasia

BACKGROUND

We recently reported that the efficacy of nitric oxide (NO) appears to be based on both sex and hormone status. The mechanism responsible for this differential efficacy is unknown. The aim of this study was to characterize the effect of sex, hormones, and NO on the extracellular signal-regulated kinase (ERK) and Akt signaling pathways after arterial injury.

METHODS

Male and female Sprague-Dawley rats underwent castration or sham surgery. Two weeks later, they underwent carotid artery balloon injury. Treatment groups included the following: control, injury, and injury + 1-[2-(carboxylato)pyrrolidin-1-yl]diazen-1-ium-1,2-diolate (PROLI/NO) (n = 5 per group). Arteries were harvested 2 weeks after injury and assessed for phospho-ERK (pERK) and phospho-Akt (pAkt) expression.

RESULTS

After injury, more pERK and pAkt activity was seen in the adventitia than media in both sexes, regardless of hormone status (P < .05). In hormonally intact males, NO further increased pERK (44%) and pAkt (120%) after injury (P < .001). Castration attenuated the effects of NO. In hormonally intact females, NO caused the opposite pattern with pERK activity but did not affect pAkt activity.

CONCLUSIONS

After arterial injury, ERK and Akt activity is significantly greater in the adventitia than the media, and depends on sex, hormone status, and NO. Understanding adventitial regulation of proliferative signaling pathways will allow the development of targeted therapies for neointimal hyperplasia.

Origin of restenosis after drug-eluting stent implantation in hyperglycemia is inflammatory cells and thrombus

AIMS

The cellular and molecular mechanisms and safety after drug-eluting stent (DES) implantation in diabetic patients are still poorly understood; therefore, in this study, we evaluated the pathologic responses of the sirolimus-eluting stent (SES) or paclitaxel-eluting stent (PES) in a type I diabetes mellitus (DM) rat model.

METHODS

The type I DM rat model was manipulated by intra-peritoneal streptozotocin injection. Two weeks later, DES was implanted in the aorta of rats with hyperglycemia or not as a control. Four weeks after DES implantation, the stented aorta was isolated and histomorphometric analysis was performed.

RESULTS

On histomorphometric analysis, increased thrombus, inflammatory cell infiltration, and neointimal hyperplasia (NIH) without change of the smooth muscle cell number after DES implantation were observed in DM rats compared with non-DM (NDM) rats. Furthermore, delayed coverage of mature endothelial cells defined as a von Willebrand factor expression and increased immature endothelial cells as a c-kit expression after DES implantation were observed in DM rats compared with NDM rats. Increased fibrin deposition and decreased hyaluronic acid accumulation at NIH after DES implantation were also observed in DM rats compared with NDM rats.

CONCLUSIONS

In conclusion, the main mechanism of restenosis after DES implantation under hyperglycemic conditions was initial thrombus with changes of the extracellular matrix rather than SMC proliferation. These results provided a therapeutic clue for the selection of DES and application of combination therapy using anti-thrombotic and anti-inflammatory drugs in diabetic patients.

Clinical science review article: understanding the implications of diabetes on the vascular system

Patients with diabetes comprise an extremely complex subset of patients for the vascular surgeon. Often, they have numerous comorbidities that can further complicate matters. The diabetic environment is highly complex and the interplay of various diseases makes this an extremely challenging condition to manage. Knowing the mechanisms by which diabetes inflicts adverse microscopic changes in the vasculature allows the clinician to anticipate problems and minimize the heightened risks observed in diabetic patients undergoing surgery. In this review, we will illustrate how diabetes affects the vasculature and how the molecular and cellular derangements that occur in diabetic environments lead to these pathophysiologic consequences.

Loss of canonical insulin signaling accelerates vascular smooth muscle cell proliferation and migration through changes in p27Kip1 regulation

Insulin resistance is associated with an accelerated rate of atherosclerosis. Vascular smooth muscle cell (VSMC) migration and proliferation are important components of atherosclerosis. To elucidate the effects of the loss of normal insulin receptor (IR) signaling on VSMC function, we compared the proliferation and migration of murine VSMCs lacking the IR (L2-VSMCs) with wild type (WT-VSMCs). We also examined changes in the response of L2-VSMCs to insulin stimulation and to inhibition of the mammalian target of rapamycin (mTOR), a kinase critical in VSMC proliferation and migration. The L2-VSMCs exhibit greater proliferation and migration rates compared with WT-VSMCs. L2-VSMCs also exhibit a resistance to the effects of rapamycin, an mTOR inhibitor, on proliferation, migration, and cell cycle progression. The resistance to mTOR inhibition is coupled with a loss of effect on the cyclin-dependent kinase inhibitor p27(Kip1), an inhibitor of cell cycle progression and VSMC migration. In response to stimulation with physiological insulin, the L2-VSMCs exhibit a loss of Akt phosphorylation and a significantly increased activation of the ERK-1/2 compared with WT-VSMCs. Insulin stimulation also decreased p27(Kip1) mRNA in L2-VSMCs but not in WT-VSMCs. The effect of insulin on p27(Kip1) mRNA was blocked by pretreatment with an ERK-1/2 pathway inhibitor. We conclude that loss of canonical insulin signaling results in increased ERK-1/2 activation in response to physiological insulin that decreases p27(Kip1) mRNA. These data demonstrate a potential mechanism where changes in IR signaling could lead to a decrease in p27(Kip1), accelerating VSMC proliferation and migration.

Modulation of TGF-β/BMP-6 expression and increased levels of circulating smooth muscle progenitor cells in a type I diabetes mouse model

Background

Diabetic patients experience exaggerated intimal hyperplasia after endovascular procedures. Recently it has been shown that circulating smooth muscle progenitor cells (SPC) contribute to intimal hyperplasia. We hypothesized that SPC differentiation would be increased in diabetes and focused on modulation of TGF-β/BMP-6 signaling as potential underlying mechanism.

Methods

We isolated SPC from C57Bl/6 mice with streptozotocin-induced diabetes and controls. SPC differentiation was evaluated by immunofluorescent staining for αSMA and collagen Type I. SPC mRNA expression of TGF-β and BMP-6 was quantified using real-time PCR. Intima formation was assessed in cuffed femoral arteries. Homing of bone marrow derived cells to cuffed arterial segments was evaluated in animals transplanted with bone marrow from GFP-transgenic mice.

Results

We observed that SPC differentiation was accelerated and numeric outgrowth increased in diabetic animals (24.6 ± 8.8 vs 8.3 ± 1.9 per HPF after 10 days, p < 0.05). Quantitative real-time PCR showed increased expression of TGF-β and decreased expression of the BMP-6 in diabetic SPC. SPC were MAC-3 positive, indicative of monocytic lineage. Intima formation in cuffed arterial segments was increased in diabetic mice (intima/media ratio 0.68 ± 0.15 vs 0.29 ± 0.06, p < 0.05). In GFP-chimeric mice, bone marrow derived cells were observed in the neointima (4.4 ± 3.3 cells per section) and particularly in the adventitia (43.6 ± 9.3 cells per section). GFP-positive cells were in part MAC-3 positive, but rarely expressed α-SMA.

Conclusions

In conclusion, in a diabetic mouse model, SPC levels are increased and SPC TGF-β/BMP-6 expression is modulated. Altered TGF-β/BMP-6 expression is known to regulate smooth muscle cell differentiation and may facilitate SPC differentiation. This may contribute to exaggerated intimal hyperplasia in diabetes as bone marrow derived cells home to sites of neointima formation.

Sera from patients with diabetes do not alter the effect of mammalian target of rapamycin inhibition on smooth muscle cell proliferation

Clinical studies of drug-eluting stents delivering the mammalian target of rapamycin (mTOR) inhibitor, rapamycin (Sirolimus), have demonstrated a reduced efficacy for these devices in patients with diabetes, which suggests that the mTOR pathway may cease to be dominant in mediating the vascular response to injury under diabetic conditions. We hypothesized that changes in serum composition accompanying diabetes may reduce the role of mTOR in mediating the vascular response to injury. We measured the ability of a median dose of rapamycin (10 nM) to inhibit the proliferation of human coronary artery smooth muscle cells (huCASMCs) stimulated with serum obtained from donors with diabetes (n = 14) and without diabetes (n = 16). In an additional analysis, we compared the effects of rapamycin on huCASMCs stimulated with the serum of donors with metabolic syndrome (n = 15) versus those without (n = 7). There was no difference in the effect of rapamycin on huCASMC proliferation after stimulation with serum from either donors with diabetes or donors with metabolic syndrome compared with the respective controls. We conclude that the changes in the serum composition common to diabetes and metabolic syndrome are insufficient to diminish the role of mTOR in the progression of cardiovascular disease.

Insulin enhances the effect of nitric oxide at inhibiting neointimal hyperplasia in a rat model of type 1 diabetes

Diabetes confers greater restenosis from neointimal hyperplasia following vascular interventions. While localized administration of nitric oxide (NO) is known to inhibit neointimal hyperplasia, the effect of NO in type 1 diabetes is unknown. Thus the aim of this study was to determine the efficacy of NO following arterial injury, with and without exogenous insulin administration. Vascular smooth muscle cells (VSMC) from lean Zucker (LZ) rats were exposed to the NO donor, DETA/NO, following treatment with different glucose and/or insulin concentrations. DETA/NO inhibited VSMC proliferation in a concentration-dependent manner to a greater extent in VSMC exposed to normal-glucose vs. high-glucose environments, and even more effectively in normal-glucose/high-insulin and high-glucose/high-insulin environments. G(0)/G(1) cell cycle arrest and cell death were not responsible for the enhanced efficacy of NO in these environments. Next, type 1 diabetes was induced in LZ rats with streptozotocin. The rat carotid artery injury model was performed. Type 1 diabetic rats experienced no significant reduction in neointimal hyperplasia following arterial injury and treatment with the NO donor PROLI/NO. However, daily administration of insulin to type 1 diabetic rats restored the efficacy of NO at inhibiting neointimal hyperplasia (60% reduction, P < 0.05). In conclusion, these data demonstrate that NO is ineffective at inhibiting neointimal hyperplasia in an uncontrolled rat model of type 1 diabetes; however, insulin administration restores the efficacy of NO at inhibiting neointimal hyperplasia. Thus insulin may play a role in regulating the downstream beneficial effects of NO in the vasculature.

Akt pathway is hypoactivated by synergistic actions of diabetes mellitus and hypercholesterolemia resulting in advanced coronary artery disease

Atherosclerosis is an inflammatory process leading to enhanced cellular proliferation, apoptosis, and vasa vasorum (VV) neovascularization. While both diabetes mellitus (DM) and hypercholesterolemia (HC) predispose to atherosclerosis, the precise interaction of these risk factors is unclear. Akt is a central node in signaling pathways important for inflammation, and we hypothesized that DM/HC would lead to aberrant Akt signaling and advanced, complex atherosclerosis. DM was induced in pigs by streptozotocin and HC by a high-fat diet. Animals were randomized to control (non-DM, non-HC), DM only, HC only, and DM/HC groups. Coronary artery homogenates were analyzed by immunoblotting for proteins involved in the Akt pathway, including phosphorylated (p)-Akt (Ser473), p-GSK-3beta (Ser9), activated NF-kappaB p65, and VEGF. Immunohistochemical staining for Ki67 (cell proliferation), terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling (TUNEL) (apoptosis), and von Willebrand factor (vWF) (neovascularization) was performed. Neovascularization was visualized with micro-computerized tomography (CT). Only DM/HC animals developed advanced atherosclerosis and showed decreased p-Akt (Ser473) and p-GSK-3beta (Ser9) levels (P < 0.01 and P < 0.05, respectively). DM/HC arteries demonstrated increased cellular proliferation (P < 0.001), apoptosis (P < 0.01), and activation of NF-kappaB p65 (P < 0.05). Induction of DM/HC also resulted in significant VV neovascularization by enhanced VEGF expression (P < 0.05), increased vWF staining (P < 0.01), and increased density by micro-CT. In conclusion, DM and HC synergistically resulted in complex atherosclerosis associated with attenuated p-Akt (Ser473) levels. Aberrant Akt signaling correlated with increased inflammation, cellular proliferation, apoptosis, and VV neovascularization. Our results revealed a synergistic effect of DM and HC in triggering abnormal Akt signaling, resulting in advanced atherosclerosis.

Smooth muscle cells orchestrate the endothelial cell response to flow and injury

BACKGROUND

Local modulation of vascular mammalian target of rapamycin (mTOR) signaling reduces smooth muscle cell (SMC) proliferation after endovascular interventions but may be associated with endothelial cell (EC) toxicity. The trilaminate vascular architecture juxtaposes ECs and SMCs to enable complex paracrine coregulation but shields SMCs from flow. We hypothesized that flow differentially affects mTOR signaling in ECs and SMCs and that SMCs regulate mTOR in ECs.

METHODS AND RESULTS

SMCs and/or ECs were exposed to coronary artery flow in a perfusion bioreactor. We demonstrated by flow cytometry, immunofluorescence, and immunoblotting that EC expression of phospho-S6 ribosomal protein (p-S6RP), a downstream target of mTOR, was doubled by flow. Conversely, S6RP in SMCs was growth factor but not flow responsive, and SMCs eliminated the flow sensitivity of ECs. Temsirolimus, a sirolimus analog, eliminated the effect of growth factor on SMCs and of flow on ECs, reducing p-S6RP below basal levels and inhibiting endothelial recovery. EC p-S6RP expression in stented porcine arteries confirmed our in vitro findings: Phosphorylation was greatest in ECs farthest from intact SMCs in metal stented arteries and altogether absent after sirolimus stent elution.

CONCLUSIONS

The mTOR pathway is activated in ECs in response to luminal flow. SMCs inhibit this flow-induced stimulation of endothelial mTOR pathway. Thus, we now define a novel external stimulus regulating phosphorylation of S6RP and another level of EC-SMC crosstalk. These interactions may explain the impact of local antiproliferative delivery that targets SMC proliferation and suggest that future stents integrate design influences on flow and drug effects on their molecular targets.

Revascularization for coronary artery disease in diabetes mellitus: angioplasty, stents and coronary artery bypass grafting

Patients with diabetes mellitus (DM) are prone to a diffuse and rapidly progressive form of atherosclerosis, which increases their likelihood of requiring revascularization. However, the unique pathophysiology of atherosclerosis in patients with DM modifies the response to arterial injury, with profound clinical consequences for patients undergoing percutaneous coronary intervention (PCI). Multiple studies have shown that DM is a strong risk factor for restenosis following successful balloon angioplasty or coronary stenting, with greater need for repeat revascularization and inferior clinical outcomes. Early data suggest that drug eluting stents reduce restenosis rates and the need for repeat revascularization irrespective of the diabetic state and with no significant reduction in hard clinical endpoints such as myocardial infarction and mortality. For many patients with 1- or 2-vessel coronary artery disease, there is little prognostic benefit from any intervention over optimal medical therapy. PCI with drug-eluting or bare metal stents is appropriate for patients who remain symptomatic with medical therapy. However, selection of the optimal myocardial revascularization strategy for patients with DM and multivessel coronary artery disease is crucial. Randomized trials comparing multivessel PCI with balloon angioplasty or bare metal stents to coronary artery bypass grafting (CABG) consistently demonstrated the superiority of CABG in patients with treated DM. In the setting of diabetes CABG had greater survival, fewer recurrent infarctions or need for re-intervention. Limited data suggests that CABG is superior to multivessel PCI even when drug-eluting stents are used. Several ongoing randomized trials are evaluating the long-term comparative efficacy of PCI with drug-eluting stents and CABG in patients with DM. Only further study will continue to unravel the mechanisms at play and optimal therapy in the face of the profoundly virulent atherosclerotic potential that accompanies diabetes mellitus.

Enhanced proliferation and migration of vascular smooth muscle cells in response to vascular injury under hyperglycemic conditions is controlled by beta3 integrin signaling

Atheroma formation and restenosis following percutaneous vascular intervention involve the growth and migration of vascular smooth muscle cells (SMCs) into neointimal lesions, in part due to changes in the extracellular matrix. While some clinical studies have suggested that, in comparison to non-diabetics, beta3 integrin inhibition in diabetic patients confers protection from restenosis, little is known regarding the role of beta3 integrin inhibition on SMC responses in this context. To understand the molecular mechanisms underlying integrin-mediated regulation of SMC function in diabetes, we examined SMC responses in diabetic mice deficient in integrin beta3 and observed that the integrin was required for enhanced proliferation, migration and extracellular regulated kinase (ERK) activation. Hyperglycemia-enhanced membrane recruitment and catalytic activity of PKCbeta in an integrin beta3-dependent manner. Hyperglycemia also promoted SMC filopodia formation and cell migration, both of which required alphaVbeta3, PKCbeta, and ERK activity. Furthermore, the integrin-kinase association was regulated by the alphaVbeta3 integrin ligand thrombospondin and the integrin modulator Rap1 under conditions of hyperglycemia. These results suggest that there are differences in SMC responses to vascular injury depending on the presence or absence of hyperglycemia and that SMC response under hyperglycemic conditions is largely mediated through beta3 integrin signaling.

A novel mouse model of in situ stenting

AIMS

Animal models of stenting are mostly limited to larger animals or involve substantial abdominal surgery in rodents. We aimed to develop a simple, direct model of murine stenting.

METHODS AND RESULTS

We designed a miniature, self-expanding, nitinol wire coil stent that was pre-loaded into a metal stent sheath. This was advanced into the abdominal aorta of the mouse, via femoral access, and the stent deployed. In-stent restenosis was investigated at 1, 3, 7, and 28 days post-stenting. The model was validated by investigation of neointima formation in mice deficient in signalling via the interleukin-1 receptor (IL-1R1), compared with other injury models. Ninety-two per cent of mice undergoing the procedure were successfully stented. All stented vessels were patent. Inflammatory cells were seen in the adventitia and around the stent strut up to 3 days post-stenting. At 3 days, an early neointima was present, building to a mature neointima at 28 days. In mice lacking IL-1R1, the neointima was 64% smaller than that in wild-type controls at the 28-day timepoint, in agreement with other models.

CONCLUSION

This is the first description of a successful model of murine in situ stenting, using a stent specifically tailored for use in small thin-walled arteries. The procedure can be undertaken by a single operator without the need for an advanced level of microsurgical skill and is reliable and reproducible. The utility of this model is demonstrated by a reduction in in-stent restenosis in IL-1R1-deficient mice.

Contribution of insulin resistance to vascular dysfunction

Insulin is a vascular hormone, able to influence vascular cell responses. In this review, we consider the insulin actions on vascular endothelium and on vascular smooth muscle cells (VSMC) both in physiological conditions and in the presence of insulin resistance. In particular, we focus the relationships between activation of insulin signalling pathways of phosphatidylinositol-3 kinase (PI3-K) and mitogen-activated protein kinase (MAPK) and the different vascular actions of insulin, with a particular attention to the insulin ability to activate the pathway nitric oxide (NO)/cyclic GMP/PKG via PI3-K, owing to the peculiar relevance of NO in vascular biology. We also discuss the insulin actions mediated by the MAPK pathway (such as endothelin-1 synthesis and secretion and VSMC proliferation and migration) and by the interactions between the two pathways, both in insulin-sensitive and in insulin-resistant states. Finally, we consider the influence of free fatty acids, cytokines and endothelin on vascular insulin resistance.

New mechanism of rosiglitazone to reduce neointimal hyperplasia: activation of glycogen synthase kinase-3beta followed by inhibition of MMP-9

OBJECTIVE

Mechanism of neointimal hyperplasia after vascular injury includes activation of signaling pathways and matrix metalloproteinases (MMPs) that are involved in cell proliferation and migration. Rosiglitazone, a synthetic peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonist, was reported to inhibit neointimal hyperplasia in diabetic animals and humans. But the underlying mechanism has not been clarified. In this study, we examined how rosiglitazone inhibited neointimal hyperplasia.

METHODS AND RESULTS

The proliferation and survival of cultured rat VSMCs were reduced by rosiglitazone, which was mediated by inhibition of ERK and activation GSK-3beta, without change of Akt. The antiproliferative effect of rosiglitazone was reversed by GSK-3beta inactivation. The migration of VSMCs was also suppressed by rosiglitazone that inhibited the expression and activity MMP-9 through GSK-3beta activation. Thus migration of MMP-9(-/-) VSMCs from MMP-9 knockout mice was not affected by rosiglitazone. The underlying mechanism of MMP-9 suppression by rosiglitazone was that it inhibited NF-kappaB DNA binding activity, which was also dependent on GSK-3beta. In rat carotid artery, balloon injury significantly inactivated GSK-3beta with induction of MMP-9, which was effectively prevented by rosiglitazone. Thus, rosiglitazone significantly decreased the ratio of intima to media by reducing proliferation and inducing apoptosis of VSMCs at neointima, which was reversed by inactivation of GSK-3beta with adenoviral transfer of catalytically-inactive GSK-KM gene.

CONCLUSIONS

Rosiglitazone activates GSK-3beta, which inhibits not only proliferation of VSMCs but also migration of VSMCs through blocking NF-kappaB-dependent MMP-9 activation.

Heparanase alters arterial structure, mechanics, and repair following endovascular stenting in mice

Heparan sulfate proteoglycans (HSPGs) are potent regulators of vascular remodeling and repair. Heparanase is the major enzyme capable of degrading heparan sulfate in mammalian cells. Here we examined the role of heparanase in controlling arterial structure, mechanics, and remodeling. In vitro studies supported that heparanase expression in endothelial cells serves as a negative regulator of endothelial inhibition of vascular smooth muscle cell (vSMC) proliferation. Arterial structure and remodeling to injury were also modified by heparanase expression. Transgenic mice overexpressing heparanase had increased arterial thickness, cellular density, and mechanical compliance. Endovascular stenting studies in Zucker rats demonstrated increased heparanase expression in the neointima of obese, hyperlipidemic rats in comparison to lean rats. The extent of heparanase expression within the neointima strongly correlated with the neointimal thickness following injury. To test the effects of heparanase overexpression on arterial repair, we developed a novel murine model of stent injury using small diameter self-expanding stents. Using this model, we found that increased neointimal formation and macrophage recruitment occurs in transgenic mice overexpressing heparanase. Taken together, these results support a role for heparanase in the regulation of arterial structure, mechanics, and repair.

Leukemia inhibitory factor is upregulated in coronary arteries of Ossabaw miniature swine after stent placement

Leukemia inhibitory factor (LIF), an IL-6 class cytokine, is reported to be antiatherosclerotic. Thus, we hypothesized that LIF expression might be altered during in-stent neointimal hyperplasia. Ossabaw miniature swine, a unique large-animal model of metabolic syndrome and cardiovascular disease, were used for these studies. Bare-metal stents were deployed in the left anterior descending and left circumflex coronary arteries. Stents were expanded to either 1.0 x luminal diameter (in accordance with current clinical practice) or 1.3 x (overexpansion). The development of in-stent neointimal hyperplasia was assessed 28-day postimplantation using intravascular ultrasound. The atherosclerotic coverage of the vessel wall was approximately five-fold higher in 1.0 x stents and approximately nine-fold higher in 1.3 x stents 4 weeks after deployment, compared with the same segments before stenting. LIF mRNA was elevated approximately 11-fold in stented segments, relative to unstented epicardial coronary arteries. LIF expression and the intima : media ratio were strongly correlated in 1.0 x stented vessels. Further studies to investigate the nature of the association between LIF and neointimal hyperplasia revealed that vascular smooth muscle cell proliferation was inhibited by LIF treatment in an in-vitro model of atherosclerosis (coronary artery organ culture). These novel and clinically relevant studies show that elevated LIF gene expression is predictive for in-stent neointimal hyperplasia, and suggest that LIF upregulation may be a compensatory mechanism in this setting.

Transition from bare metal to drug eluting stenting in contemporary US practice: effect on incidence and predictors of clinically driven target lesion revascularization

BACKGROUND

The performance of drug eluting stents (DES) and impact on every day practice in the USA, where complex, nonselective cases are the rule, remain unknown.

METHODS

The Brigham and Women's Hospital interventional experience in the bare metal stents (BMS) (6/2002 to 2/2003) and after abrupt and near universal adoption of DES (4/2003 to 9/2004) were compared. Demographic, procedural and in-hospital outcomes for all consecutive cases where investigated. Predictors and angiographic characteristics of patients returning for clinically driven target lesion revascularization (TLR) in both eras were analyzed.

RESULTS

Of 2,555 DES cases (3,061 lesions, 87.9% Cypher, 12.1% Taxus), 47 underwent TLR during follow-up (68 lesions, 2.2%). Of the 1,731 BMS cases (1,798 lesions), 162 underwent clinically indicated TLR (209 lesions, 11.6%), representing an 81% DES era TLR risk reduction. Multivariate predictors of TLR in the DES era: left main lesion (LM) (odds ratio (OR) 7.65, 95% confidence interval (CI) 3.33-17.53, P<0.01, treatment of restenosis (OR 5.96, CI 3.21-11.08, P<0.01), and diabetes (OR 1.68, CI 0.92-3.04, P=0.07). Predictors of restenosis in the BMS era included additional clinical, lesion, and stent characteristics, while LM lesion was absent. Angiographic patterns of stent restenosis differed in the DES (focal) and BMS (diffuse) era.

CONCLUSIONS

The transition from BMS to DES in the setting of a large USA hospital practice is safe and associated with significant reduction in clinically driven TLR. Treatment of specific lesions types (repeat restenosis, distal LM) and diabetic patients remain suboptimal and warrant further investigation.

Neointimal hyperplasia persists at six months after sirolimus-eluting stent implantation in diabetic porcine

Background

Observational clinical studies have shown that patients with diabetes have less favorable results after percutaneous coronary intervention compared with the non-diabetic counterparts, but its mechanism remains unclear. The aim of this study was to examine the changes of neointimal hyperplasia after sirolimus-eluting stent (SES) implantation in a diabetic porcine model, and to evaluate the impact of aortic inflammation on this proliferative process.

Methods

Diabetic porcine model was created with an intravenous administration of a single dose of streptozotocin in 15 Chinese Guizhou minipigs (diabetic group); each of them received 2 SES (Firebird, Microport Co, China) implanted into 2 separated major epicardial coronary arteries. Fifteen non-diabetic minipigs with SES implantation served as controls (control group). At 6 months, the degree of neointimal hyperplasia was determined by repeat coronary angiography, intravascular ultrasound (IVUS) and histological examination. Tumor necrosis factor (TNF)-α protein level in the aortic intima was evaluated by Western blotting, and TNF-α, interleukin (IL)-1β and IL-6 mRNA levels were assayed by reverse transcription and polymerase chain reaction.

Results

The distribution of stented vessels, diameter of reference vessels, and post-procedural minimal lumen diameter were comparable between the two groups. At 6-month follow-up, the degree of in-stent restenosis (40.4 ± 24.0% vs. 20.2 ± 17.7%, p < 0.05), late lumen loss (0.33 ± 0.19 mm vs. 0.10 ± 0.09 mm, p < 0.001) by quantitative angiography, percentage of intimal hyperplasia in the stented area (26.7 ± 19.2% vs. 7.3 ± 6.1%, p < 0.001) by IVUS, and neointimal area (1.59 ± 0.76 mm² vs. 0.41 ± 0.18 mm², p < 0.05) by histological examination were significantly exacerbated in the diabetic group than those in the controls. Significant increases in TNF-α protein and TNF-α, IL-1β and IL-6 mRNA levels were observed in aortic intima in the diabetic group.

Conclusion

Neointimal hyperplasia persisted at least up to 6 months after SES implantation in diabetic porcine, which may be partly related to an exaggerated inflammatory response within the blood vessel wall. Our results provide theoretical support for potential direct beneficial effects of anti-diabetic and anti-inflammation medications in reducing the risk of restenosis after stenting.

Insulin augments matrix metalloproteinase-9 expression in monocytes

OBJECTIVE

Insulin resistance and hyperinsulinemia are major causes of cardiovascular morbidity and mortality. Matrix metalloproteinases (MMPs), highly expressed in activated mononuclear cells in vulnerable atherosclerotic lesions, are the main proteolytic enzymes controlling plaque stability. The aim of this study was to investigate the regulation of monocyte MMP-9 by insulin.

METHODS AND RESULTS

Stimulation of MMP-9 expression by insulin was time- and concentration-dependent in human monocytic THP-1 cells. Inhibition of insulin receptor (IR) maturation via inhibition of its activating convertase furin with the pharmacological furin-inhibitor decanoyl-RVKR-chloromethylketone, as well as blocking of IGF-1R function with a IGF-1R blocking antibody, demonstrated that insulin mediates increases in MMP-9 via IR activation. Inhibition of insulin's "metabolic" phosphatidylinositol 3-kinase signaling with wortmannin (50 nmol/L) or LY294002 (2.5 micromol/L) did not prevent insulin-dependent MMP-9 induction. In contrast inhibition of insulin's "mitogenic" Ras-Raf-mitogen-activated protein kinase-kinase pathways with PD98059 (15 micromol/L) or U0126 (2 micromol/L) inhibited insulin-induced MMP-9 gelatinolytic activity in THP-1 cells. Likewise, PD98059 inhibited insulin augmented MMP-9 levels in primary human monocytes, whereas wortmannin had no effect.

CONCLUSION

This study demonstrates that insulin can induce MMP-9 via mitogenic signaling pathways in monocytes, whereas phosphatidylinositol 3-kinase-dependent signaling, typically altered in insulin resistance, is not required. Induction of MMP-9 by insulin may potentially contribute to a pro-inflammatory state and the increased cardiovascular morbidity and mortality in type 2 diabetics.

Increased neointimal formation after surgical vein grafting in a murine model of type 2 diabetes

BACKGROUND

Diabetes is an independent risk factor for the development of neointimal hyperplasia and subsequent vein graft failure after coronary or peripheral artery bypass grafting. We evaluate a new mouse model of surgical vein grafting to investigate the mechanisms of neointimal formation in the setting of type 2 diabetes.

METHODS AND RESULTS

Surgical vein grafts were created by inserting vein segments from age-matched C57BL/KsJ wild-type mice into the infra-renal aorta of lepr(db/db) diabetic and C57BL/KsJ wild-type mice. Mice were euthanized &4 weeks later, and vein grafts were analyzed using morphometric and immunohistochemical techniques. A significant increase in neointimal formation was noted in lepr(db/db) mice (139+/-64 versus 109+/-62 mm2; P=0.008) after 4 weeks. This difference was mainly secondary to an increase in collagen formation within the lesion in the vein grafts from lepr(db/db) mice (0.53+/-0.4 versus 0.44+/-0.05; P<0.001), whereas only slight increases (P=not significant) in alpha actin-stained smooth muscle cells were noted in the lepr(db/db) mice.

CONCLUSIONS

We established a new physiologically relevant model of surgical vein grafting in mice. In this report, type 2 diabetes was associated with significant increase in extracellular matrix deposition in addition to increased smooth muscle cell deposition. This new model may allow mechanistic studies of cellular and molecular pathways of increased neointimal formation in the setting of diabetes.