Abstract 248: Comparative Transcriptomic Analysis of Smooth Muscle Cells and Endothelial Cells Identifies Distinct Signaling Networks Following Inflammatory Challenges

Background: Drug-eluting devices have shown promising outcomes in patients receiving endovascular procedures, particularly in managing post-intervention restenosis that often leads to failure of the reconstructions. However, emerging evidences have revealed increased thrombogenic risk associated with the use of drug-eluting stents and balloons. It has been widely acknowledged that the major culprit responsible for the observed thrombosis events is the non-selective damage of the anti-restenotic compounds on vascular endothelial cells (ECs), which, under physiological conditions, serve as the protective barrier for maintaining vascular homeostasis. Given the clinical relevance, there is an urgent need for a therapeutic agent that could confer selective management of smooth muscle cells (SMCs) without damaging ECs. However, by far the differential mechanisms in the two cell types underlying their distinct cellular behaviors toward pathogenic stimuli are poorly understood. Thus, a systematic and comparative analysis of their cellular dynamics at the transcriptomic level is needed.

Methods and Results: Human primary aortic SMCs and ECs were starved and then stimulated with 2 pro-inflammatory cytokines (TNF-α and IL-1β), which are well-established inducers of SMCs’ proliferative and migratory phenotypes while simultaneously damaging ECs. Samples were then subject to RNA sequencing. We developed a customized algorithm to evaluate the differential responses and transcriptomic network dynamics in the two cell types, and successfully identified multiple gene modules that contain functionally related genes that possibly are involved in the distinct regulations of SMCs versus ECs post inflammatory challenges.

Conclusions: Our study provides the first comprehensive analysis of the differential transcriptomic dynamics between SMCs and ECs following inflammatory challenges, which are prominent contributors to the pathogenesis of both restenosis and thrombosis following vascular injury. Our data identify several module groups of genes that could serve as potential targets to achieve differential modulation of the pathophysiologies of SMCs versus ECs. Further studies are warranted to validate the contributions of these genes.

TGF-β/Smad3 inhibit vascular smooth muscle cell apoptosis through an autocrine signaling mechanism involving VEGF-A

We have previously shown that in the presence of elevated Smad3, transforming growth factor-β (TGF-β) transforms from an inhibitor to a stimulant of vascular smooth muscle cell (SMC) proliferation and intimal hyperplasia (IH). Here we identify a novel mechanism through which TGF-β/Smad3 also exacerbates IH by inhibiting SMC apoptosis. We found that TGF-β treatment led to inhibition of apoptosis in rat SMCs following viral expression of Smad3. Conditioned media from these cells when applied to naive SMCs recapitulated this effect, suggesting an autocrine pathway through a secreted factor. Gene array of TGF-β/Smad3-treated cells revealed enhanced expression of vascular endothelial growth factor (VEGF), a known inhibitor of endothelial cell apoptosis. We then evaluated whether VEGF is the secreted mediator responsible for TGF-β/Smad3 inhibition of SMC apoptosis. In TGF-β/Smad3-treated cells, VEGF mRNA and protein as well as VEGF secretion were increased. Moreover, recombinant VEGF-A inhibited SMC apoptosis and a VEGF-A-neutralizing antibody reversed the inhibitory effect of conditioned media on SMC apoptosis. Stimulation of SMCs with TGF-β led to the formation of a complex of Smad3 and hypoxia-inducible factor-1α (HIF-1α) that in turn activated the VEGF-A promoter and transcription. In rat carotid arteries following arterial injury, Smad3 and VEGF-A expression were upregulated. Moreover, Smad3 gene transfer further enhanced VEGF expression as well as inhibited SMC apoptosis. Finally, blocking either the VEGF receptor or Smad3 signaling in injured carotid arteries abrogated the inhibitory effect of Smad3 on vascular SMC apoptosis. Taken together, our study reveals that following angioplasty, elevation of both TGF-β and Smad3 leads to SMC secretion of VEGF-A that functions as an autocrine inhibitor of SMC apoptosis. This novel pathway provides further insights into the role of TGF-β in the development of IH.

Mechanisms of post-intervention arterial remodelling

It has been appreciated over the past two decades that arterial remodelling, in addition to intimal hyperplasia, contributes significantly to the degree of restenosis that develops following revascularization procedures. Remodelling appears to be an adventitia-based process that is contributed to by multiple factors including cytokines and growth factors that regulate extracellular matrix or phenotypic transformation of vascular cells including myofibroblasts. In this review, we summarize the currently available information from animal models as well as clinical investigations regarding arterial remodelling. The factors that contribute to this process are presented with an emphasis on potential therapeutic methods to enhance favourable remodelling and prevent restenosis.

Abstract P340: The Role of Osteoclast-like Cells in Abdominal Aortic Aneurysm

Increasing evidence suggests that arterial calcification is the result of highly organized processes resembling those seen in bone which relies upon a delicate balance between mineral deposition and resorption by osteoblasts and osteoclasts, respectively. Osteoclast-like cells (OLCs) are derived from the monocyte/macrophage lineage and share osteoclast features such as the ability to dissolve extracellular matrix. Although osteoclastogenesis, the development of OLCs, has been reported to occur in calcified arteries, its potential role in the development of abdominal aortic aneurysm (AAA) has yet to be explored. Firstly, we obtained aortic tissues from patients undergoing surgical repair for AAA (N = 5) and aortic occlusive disease (N = 5). Alizarin-Red staining showed calcification in both aneurysmal and occlusive aorta. In contrast, OLCs, recognized as multi-nucleated cells positive for enzymatic TRAP staining, were identified only in aneurysmal aorta (100%, 5 of 5). A time course experiment in mouse calcium chloride-induced AAA (CaCl 2 AAA) showed similarities in both spatial and temporal patterns of calcium deposition and monocyte/macrophage accumulation starting 48 hours followed by OLCs formation peaked at 7 days after CaCl 2 injury. Secondly, we administered bisphosphonate (pamidronate disodium, 1.25 mg/kg, weekly), an inhibitor of osteoclasts, or normal saline as a control, intravenously to mice after CaCl 2 injury (N = 5). Bisphosphonate-treated mice showed a significant reduction in aortic dilation compared to control mice after 7 and 42 days with mean fold change of 1.16 ± 0.04 (vs. 1.65 ± 0.05, P < 0.01) and 1.37 ± 0.12 (vs. 2.17 ± 0.08, P<0.01) respectively. We also studied the effect of bisphosphonate on “developed aneurysm” by delaying the injection of bisphosphonate until one week after the injury to allow the aneurysm to develop prior to injection (N = 5). The mice with delayed bisphosphonate injection also showed significant inhibition compared to the saline control at 42 days (1.56 ± 0.13 vs. 2.42 ± 0.06, P < 0.01). In conclusion, we have demonstrated the existence of OLCs in AAA. We also have demonstrated the inhibitory effect of bisphosphonate on aneurysm. These results indicate a novel approach for the pathogenesis and therapy of AAA.

Selecting stent grafts for the endovascular treatment of abdominal aortic aneurysms

Minimally invasive endovascular techniques for the treatment of abdominal aortic aneurysms (AAA) have significantly reduced the morbidity of these procedures as compared with standard surgical repair. In addition, patients with extensive comorbid medical illnesses in whom standard operative repair is contra-indicated, may be successfully treated using endovascular means. A variety of endovascular stent grafts are currently being used clinically for endovascular AAA repair. The characteristics of these stent grafts vary significantly. In selecting the specific stent graft to be used for endovascular AAA repair, these specific characteristics must be considered particularly with regard to the individual patient's anatomic and physiologic characteristics. In addition, the indications for use of endovascular grafts as compared to standard open surgery have not yet been fully defined. Endovascular stent grafts in current use have limitations and their use must be tempered accordingly, until their long-term effectiveness is more completely evaluated. This article describes the general principles of use for endovascular devices for the repair of AAA. It details the features and results for the devices in current use and highlights the factors that influence the selection of specific stent graft types.

Recessed elliptical-centric view-ordering for contrast-enhanced 3D MR angiography of the carotid arteries

Fast arterial-venous transit in the carotid arteries requires accurate, reliable timing of the acquisition to the bolus transit to maximize arterial signal and minimize venous artifacts. The rising edge of the bolus is not utilized in conventional elliptical-centric view-ordering because the critical k-space center must be acquired with full arterial enhancement. In this study, a recessed elliptical-centric view-ordering scheme is introduced in which the k-space center is acquired a few seconds following scan initiation. The recessed view-ordering is shown to be more robust to timing errors than the conventional scheme in a study of 37 patients.

Differential effects of protein kinase C on human vascular smooth muscle cell proliferation and migration

Vascular smooth muscle cell (SMC) migration and proliferation contribute to intimal hyperplasia, and protein kinase C (PKC) may be required for both events. In this report, we investigated the role of PKC in proliferation and migration of SMC derived from the human saphenous vein. Activation of PKC by phorbol-12,13-dibutyrate (PDBu) or (-)-indolactam [(-)-ILV] increases SMC proliferation. Downregulation of PKC activity by prolonged incubation with phorbol ester or inhibition of PKC with chelerythrine in SMC diminished agonist-stimulated proliferation. In contrast, stimulation of PKC with PDBu or (-)-ILV inhibited basal and agonist-induced SMC chemotaxis. Moreover, downregulation of PKC or inhibition with chelerythrine accentuated migration. We postulated that the inhibitory effect of PKC on SMC chemotaxis was mediated through cAMP-dependent protein kinase (protein kinase A, PKA). In support of this hypothesis, we found that activation of PKC in SMC stimulated PKA activity. The cAMP agonist forskolin significantly inhibited SMC chemotaxis. Furthermore, the inhibitory effect of PKC on SMC chemotaxis was completely reversed by cAMP or PKA inhibitors. In search of the PKC isotype(s) underlying these differential effects of PKC in SMC, we identified eight isotypes expressed in human SMC. Only PKC-alpha, -beta I, -delta, and -epsilon were eliminated by downregulation, suggesting that one or more of these four enzymes facilitate the observed phorbol ester-dependent effects of PKC in SMC. In summary, we found that PKC activation enhances proliferation but inhibits migration of human vascular SMC. These differential effect of PKC on vascular cells appears to be mediated through PKC-alpha, -beta I, -delta, and/or -epsilon.

Cross-sectional pattern of collateral vessels in patients with superficial femoral artery occlusion

RATIONALE AND OBJECTIVES

The purpose of this study was to identify the cross-sectional location of collateral vessels in patients with peripheral vascular disease on three-dimensional magnetic resonance angiograms (3D MRAs) to suggest sites for intravascular or transcutaneous angiogenesis gene delivery in the lower extremity.

METHODS

The axial locations were measured and categorized by tissue compartments, as well as by radial coordinates with respect to the femur.

RESULTS

Collateral vessels in the thigh were identified in 24 of 93 consecutive patients who underwent peripheral 3D MRA. Ninety-one percent (99/109) of the observed collaterals were located near the adductor canal level of the thigh, with 78% (31/46) of these collaterals located in the fat in or surrounding the posterior muscle.

CONCLUSIONS

The majority of collateral vessels in the thigh are located in the fat or muscle within the posterior compartment near the femur at the level of the adductor canal.

Thrombolysis for native arterial occlusions of the lower extremities: clinical outcome and cost

INTRODUCTION

Intra-arterial thrombolysis is commonly used as the initial treatment of acute or subacute lower extremity ischemia.

METHODS

To evaluate the efficacy and cost of thrombolysis, we retrospectively analyzed 100 consecutive cases (87 patients) in which intra-arterial lysis (urokinase) was used as the initial treatment for native arterial lower extremity occlusive disease. The mean age of patients was 67 years, 57% of the patients were male, and preexisting peripheral vascular disease was present in 74%. Presenting symptoms were limb-threatening ischemia (53%) and claudication (47%). Acute symptoms (< 2 weeks' duration) were present in 48%.

RESULTS

The 30-day morbidity rate was 31%, and four patients died. Complications were significant bleeding (23%), ischemic stroke (1%), and renal failure with (2%) and without (2%) dialysis. Concomitant angioplasty was performed in 63%. Complete or significant lysis as demonstrated with angiography was achieved in 75% of iliac, 58% of femoropopliteal, and 41% of crural vessels (P <.001). Within 30 days of lysis, 9% of patients underwent major amputation and 20% surgical revascularization (in 3 patients the extent of revascularization was lessened by the lytic therapy). Amputation-free survival was 83% and 75% at 6 months and 2 years, respectively. Relief of ischemia (defined as relief of claudication or limb salvage without major surgical intervention) was achieved in only 70% and 43% of patients at 30 days and 2 years, respectively (Kaplan-Meier analysis; mean follow-up, 31 months). Patients with aortoiliac disease had significantly better outcomes than those with infrainguinal disease (P =.03). Duration or type of presenting symptoms did not predict outcome. The cost of the initial hospitalization per patient for thrombolysis was $18,490.

CONCLUSION

Thrombolysis can be as or more costly than surgery and is associated with a suboptimal outcome in a significant number of patients. These data lead us to caution against a uniform policy of initial thrombolysis for patients who present with lower extremity ischemia.

Contrast-enhanced peripheral MR angiography from the abdominal aorta to the pedal arteries: combined dynamic two-dimensional and bolus-chase three-dimensional acquisitions

Wang Y, Winchester PA, Khilnani NM, et al. Contrast-enhanced peripheral MR angiography from the abdominal aorta to the pedal arteries: Combined dynamic two-dimensional and bolus-chase three-dimensional acquisitions. Invest Radiol 2001;36:170-177.

RATIONALE AND OBJECTIVES

To obtain reliable contrast-enhanced peripheral MR angiography for imaging peripheral vascular disease from the abdominal aorta to the pedal arteries.

METHODS

A protocol consisting of contrast-enhanced, dynamic two-dimensional (2D) acquisition at the feet and calf and bolus-chase three-dimensional (3D) acquisition from the abdominal aorta to the calf was developed and applied in patients with peripheral vascular disease. The performance of this integrated protocol was assessed in 89 consecutive patients.

RESULTS

The bolus-chase 3D acquisition was of diagnostic quality in 100% of the acquisitions in the abdomen, 96% in the thigh, and 43% in the calf. The poor quality of the calf acquisitions was due to insufficient spatial resolution, poor arterial signal, and venous contamination. Diagnostic-quality images were obtained in 100% of the dynamic 2D acquisitions of the calf and 98% of the feet.

CONCLUSIONS

The combined dynamic 2D and bolus-chase 3D contrast-enhanced MR angiography technique provides diagnostic images of the entire lower extremity.

Anatomically tailored k-Space sampling for bolus-chase three-dimensional MR digital subtraction angiography

The purpose of this study was to evaluate a variable k-space sampling method for bolus-chase three-dimensional magnetic resonance digital subtraction angiography in the arterial system from the abdomen to the calf. Imaging time was minimized by tailoring the acquisition according to the vascular anatomy of the station. For images obtained in 30 patients, results with the modified protocol were compared to those with the previously published protocol. For all stations, significant improvement (P <.001) was found with the modified protocol.

Elevated Egr-1 in human atherosclerotic cells transcriptionally represses the transforming growth factor-beta type II receptor

Atherosclerotic lesions may progress due to a "failure to die" by vascular repair cells. Egr-1, a zinc finger transcription factor, is elevated more than 5-fold in human carotid lesions relative to the adjacent tunica media. Lesion cells in vitro also express 2-3-fold higher Egr-1 mRNA and protein levels but express much lower levels of the transforming growth factor-beta (TGF-beta) Type II receptor (TbetaR-2) and are functionally resistant to the antiproliferative effects of TGF-beta. Lesion cells fail to express a TbetaR-2 promoter/chloramphenicol acetyltransferase (CAT) construct but overexpress an Egr-1-inducible platelet-derived growth factor-A promoter/CAT construct. Transfection of Egr-1 cDNA represses TbetaR-2/CAT constructs but induces PDGF-A/CAT. Egr-1 transfection reduces the levels of TbetaR-2 and confers resistance to the antiproliferative effect of TGF-beta1. Egr-1 can interact directly with both the -143 Sp1 site and the positive regulatory element 2 (PRE2) (ERT/ets) region of the TbetaR-2 promoter. Thus, although activating a family of stress-responsive genes, Egr-1 also transcriptionally represses one of the major inhibitory pathways that restrains vascular repair.

Two decades of abdominal aortic aneurysm repair: have we made any progress?

PURPOSE

Over the past 20 years, there have been numerous advances in our ability to detect and to treat abdominal aortic aneurysms (AAAs). We hypothesized that these advances would lead to (1) an increase in the rate of elective repair and a decrease in the incidence of ruptured AAA (rAAA) and (2) a decrease in operative deaths for both elective AAA (eAAA) and rAAA.

METHODS

To test these hypotheses, we investigated the incidence and outcomes of eAAA and rAAA surgery between 1979 and 1997, using the National Hospital Discharge Survey. This data set is a randomized, stratified sample representing discharges from the nation's acute care, nonfederally funded hospitals. Codes from the International Classification of Diseases, Ninth Revision were used to identify our study population.

RESULTS

Over the past 19 years, there has been no change in the incidence rate of eAAA repair (range, 44.1-77.9 per 100,000). Moreover, the incidence of rAAAs presenting to the nation's hospitals has not changed (range, 6.6-16.3 per 100,000). There has been no consistent improvement over time in operative deaths associated with either eAAA or rAAA repair (average rates over the study period: eAAA, 5.6%; rAAA, 45.7%). Significant predictors of death from eAAA in patients included an age older than 80 years, African American race, congestive heart failure (CHF), and diabetes (P<.0001 for all). Significant predictors of death from rAAA in patients included age older than 70 years, African American race, female sex, renal failure, and a hospital bed size more than 500 (P<.05 for all).

CONCLUSION

On a national level, over the past 19 years, our ability to identify and to treat patients with AAA has not improved. Advances in technology and critical care have not affected outcome. Regionalization of care, screening of high-risk populations, and endovascular repair are strategies that might allow further improvement in the outcome of patients with aneurysmal disease.

Is lower extremity revascularization worthwhile in patients with end-stage renal disease?

BACKGROUND

The purpose of this study was to review the results of lower extremity revascularization in patients with end-stage renal disease and to determine in these patients the functional benefit and cost of an aggressive approach to limb preservation.

METHODS

During a 5-year period at our institution, 33 bypass operations were performed on 31 limbs of 23 dialysis-dependent patients. Indications for revascularization were limited (18) or extensive (12) tissue loss or ischemia without tissue loss (3). Procedures included aortobifemoral bypass (1), femoropopliteal bypass (10), and femorotibial/pedal bypass (22). A digital or transmetatarsal amputation was performed in 57% of limbs.

RESULTS

The 30-day primary patency was 100%. Cumulative primary and secondary patency rates at 2 years were 65% and 79%, respectively. Limb salvage was 67% and 59% at 1 and 2 years, respectively. Patient survival was poor (47% at 2 years). Peritoneal dialysis was predictive of poor survival (P <.001). Four of 5 patients on peritoneal dialysis died within 3 months of intervention. Extensive tissue loss was predictive of a diminished rate of limb salvage (P =.027). Only 39% of limbs with extensive tissue loss were salvaged at 1 year compared with 78% and 100% of limbs with limited and no tissue loss, respectively. The average hospital cost was $44,308 per year of limb salvage.

CONCLUSIONS

Although revascularization of ischemic limbs in dialysis patients can be achieved with an excellent initial graft patency and reasonable limb salvage, patient survival is poor and costs are high. A selective approach to revascularization in these complicated patients may be indicated. For patients treated with peritoneal dialysis and for those with extensive tissue loss, primary amputation may be the preferred approach.

The cost-effectiveness of repairing ruptured abdominal aortic aneurysms

BACKGROUND

Although advances in technology have reduced the operative risk of elective abdominal aortic aneurysm (AAA) repair, the surgical repair of ruptured AAAs is associated with a much poorer prognosis and a higher cost. Accordingly, it has been suggested that patients with predictably high rates of morbidity and mortality from ruptured AAA may not benefit from surgical intervention.

METHODS AND RESULTS

A cost-effectiveness analysis was performed with the use of a Markov decision-analytic model to compute long-term survival in quality-adjusted life years and lifetime costs for a hypothetical cohort of patients with ruptured AAAs managed with either a strategy of open surgical repair or no intervention. Probability estimates for the various outcomes were based on a review of the literature. Average costs of (1) the immediate hospitalization ($28,356) and (2) complications resulting from the procedure were based on the average use of resources as reported in the literature and from a hospital's cost accounting system. Our measure of outcome was the incremental cost-effectiveness ratio. For our base-case analysis, the repair of ruptured AAAs was cost-effective with an incremental cost-effectiveness ratio of $10,754. (Society is usually willing to pay for interventions with cost-effectiveness ratios of less than $60,000; for example, the costeffectiveness ratios for coronary artery bypass grafting and dialysis are $9500 and $54,400, respectively.) In sensitivity analyses, the cost-effectiveness of repairing ruptured AAAs was influenced only by alterations in the operative mortality. If the operative mortality exceeded 88%, repair of ruptured AAAs was no longer cost-effective. As an independent variable, increasing age had no substantial impact on the cost-effectiveness, although it is reported to be associated with increased operative mortality. It was necessary that the patient's cost of the initial hospitalization for ruptured AAA exceed $195,000 before repairing ruptured AAAs was no longer cost-effective.

CONCLUSIONS

Our analysis suggests that despite the high cost and poor outcomes, the surgical repair of ruptured AAAs is still cost-effective when compared with no intervention. The cost of repairing ruptured AAAs falls within society's acceptable limits and therefore should not be a consideration in the management of patients with AAAs.

The effect of protein kinase C and its alpha subtype on human vascular smooth muscle cell proliferation, migration and fibronectin production

BACKGROUND

Vascular smooth muscle cell (SMC) migration, proliferation and extracellular matrix protein production are key steps in the formation of intimal hyperplasia, a process that leads to failure of vascular reconstructions. Protein kinase C (PKC) may be involved in all 3 cellular events. PKC consists of a family of 11 isotypes, 8 of which we have identified in human vascular SMCs. In this study we evaluate the role of PKCalpha as a second messenger for proliferation, migration and fibronectin production induced by human saphenous vein SMCs.

METHODS

DNA synthesis was evaluated by using (3)H-thymidine incorporation. Mitogen-activated protein kinase (MAP-K) activation was quantified by Western blotting with an antibody to its phosphorylated substrate, Elk-1. Chemotaxis was evaluated by using a microchemotaxis chamber. SMC fibronectin was measured by Western blotting. For all experiments, PKCalpha was blocked with a selective inhibitor, Gö6976.

RESULTS

Gö6976, at concentrations that allow selective inhibition of PKCalpha, inhibited platelet-derived growth factor-stimulated SMC proliferation and MAP-K activation by 30% to 40% and 30% to 60%, respectively. SMC chemotaxis was stimulated approximately 2-fold by the PKCalpha inhibitor. Neither basal nor transforming growth factor-betaI induced fibronectin production was affected by Gö6976.

CONCLUSIONS

Our data suggest that PKCalpha is a positive mediator of SMC proliferation and MAP-K activity, a negative regulator of migration and has no effect on SMC fibronectin production. These data suggest that modulating activities of specific PKC isotypes might be useful in both the study and control of intimal hyperplasia.

The effect of growth factors, cytokines, and extracellular matrix proteins on fibronectin production in human vascular smooth muscle cells

PURPOSE

Although 60% to 80% of the mature intimal hyperplastic plaque is composed of extracellular matrix (ECM) proteins, little is known about the factors that stimulate smooth muscle cells (SMCs) to produce these proteins. A major component of the ECM protein is fibronectin. Thus we studied fibronectin production and its response to various growth factors, cytokines, and other ECM proteins that are released at the time of vascular injury.

METHODS

Quiescent cultured human SMCs were stimulated for varying intervals with increasing concentrations of agonist. Fibronectin in the cell medium was assayed by immunoblotting with a fibronectin-specific antibody.

RESULTS

After 72 hours of stimulation, transforming growth factor-beta (10 ng/mL) had the most profound effect on fibronectin production (9.6- +/- 2.1-fold; P <.05), followed by epidermal growth factor (100 ng/mL; 5.0- +/- 0.1-fold; P <.05, for both). Surprisingly, the platelet-derived growth factors (AA, AB, and BB) and fibroblast growth factor did not stimulate fibronectin production. Among the matrix proteins studied, only collagen type I (20 microg/mL) stimulated fibronectin production (1.9- +/- 0.1-fold; P <.05), whereas collagen type IV and laminin had no effect. The contractile protein angiotensin II (100 ng/mL) was a weak stimulant of fibronectin (1.6- +/- 0.2-fold; P <.05). Time course studies of fibronectin production up to 72 hours revealed kinetics that varied with each agonist. Transforming growth factor-beta stimulated significant early production of fibronectin, whereas fibronectin production in response to epidermal growth factor and collagen type I was initially modest but increased with time. The effect of angiotensin II did not become evident until 72 hours.

CONCLUSION

Cytokines, growth factors, and matrix proteins have varying quantitative effects on ECM protein production by human vascular SMCs. Knowledge of the factors that influence ECM protein production may allow for the design of specific inhibitors that can prevent intimal hyperplasia.

Improving cost efficiency on a vascular surgery service

BACKGROUND

A vascular task force (VTF) consisting of two vascular surgeons and other key personnel was established to reduce costs and improve efficiency in the management of patients on a vascular surgery service.

METHODS

The VTF met monthly beginning in 1994 to study and implement changes in the management of patients with (1) abdominal vascular, (2), carotid endarterectomy (3) distal bypass, and (4) other vascular procedures, including amputations. Length of stay, and fixed and variable costs were assessed for change over time using Pearson correlation coefficients.

RESULTS

Improvements in efficiency (length of stay) and decreases in costs (fixed and variable costs) from fiscal year 1993 to fiscal year 1996 were significant for the total group of vascular patients (P </=0.001), with some intergroup differences. The major improvements were in the abdominal vascular and carotid endarterectomy groups, where length of stay and fixed and variable costs were reduced significantly (P </=0.01). Management of distal bypass and other vascular surgery patients showed less striking improvement.

CONCLUSION

Vascular surgeons in collaboration with other dedicated personnel involved in the care of vascular patients can improve efficiency and reduce costs. Advances were greatest in patients who required operations for carotid and abdominal vascular disorders and least for patients who required distal bypasses and other vascular procedures.

High-level expression of Egr-1 and Egr-1-inducible genes in mouse and human atherosclerosis

To understand the mRNA transcript profile in the human atherosclerotic lesion, RNA was prepared from the fibrous cap versus adjacent media of 13 patients undergoing carotid endarterectomy. cDNA expression arrays bearing 588 known genes indicated that lesions express unexpectedly high levels of the early growth response gene, Egr-1 (NGFI-A), a zinc-finger transcription factor that modulates a cluster of stress-responsive genes including PDGF and TGF-beta. Expression of Egr-1 was an average of 5-fold higher in the lesion than in the adjacent media, a result confirmed by RT-PCR, and many Egr-1-inducible genes were also strongly elevated in the lesion. Time-course analyses revealed that Egr-1 was not induced ex vivo. Immunocytochemistry indicated that Egr-1 was expressed prominently in the smooth muscle-actin positive cells, particularly in areas of macrophage infiltration, and in other cell types, including endothelial cells. Induction of atherosclerosis in LDL receptor-null mice by feeding them a high-fat diet resulted in a progressive increase in Egr-1 expression in the aorta. Thus, induction of Egr-1 by atherogenic factors may be a key step in coordinating the cellular events that result in vascular lesions.

Activation of integrin receptors is required for growth factor-induced smooth muscle cell dysfunction

PURPOSE

Growth factors and cytokines such as platelet-derived growth factor (PDGF), epidermal growth factor (EGF), basic fibroblast growth factor (bFGF), and transforming growth factor beta (TGF-beta) stimulate smooth muscle cell (SMC) proliferation and extracellular matrix (ECM) protein production by binding and activating their respective receptors. Recent investigations suggest that simultaneous activation of integrins, which are heterodimeric receptors for ECM, may also be required for growth factor and cytokine function. In this study, we tested the hypothesis that activation of two integrins, alpha v beta 3 and alpha 2 beta 1, both previously identified in vascular SMCs, is necessary for growth factor- and cytokine-induced vascular SMC dysfunction.

METHODS

DNA synthesis was measured after stimulation of SMCs derived from human saphenous vein with the growth factors PDGF-BB, EGF, and bFGF. SMC fibronectin (Fn) production was measured (by means of Western blotting) in SMCs stimulated for 72 hours with TGF-beta1 or EGF. Both endpoints were measured in the presence and absence of antibodies that block the function of the alpha v beta 3 and alpha 2 beta 1 integrins as well as the alpha2 and beta1 subunits.

RESULTS

The alpha v beta 3 integrin blocking antibody significantly inhibited PDGF-BB-, EGF-, and bFGF-induced SMC proliferation. The alpha v beta 3 integrin antibody also markedly inhibited TGF-1- and EGF-induced SMC Fn production. Neither the alpha 2 beta 1 integrin nor the alpha2 or the beta1 subunits inhibited either proliferation or matrix protein production in response to any of these agonists.

CONCLUSION

The alpha v beta 3 integrin is required for growth factor- and cytokine-induced SMC proliferation and FN production, whereas alpha 2 beta 1 is not. Since activation of alpha v beta 3 is required for the activity of at least four distinct growth factors and cytokines, inhibition of this integrin might be used as a therapeutic tool for the prevention of intimal hyperplasia.

Is carotid endarterectomy cost-effective in symptomatic patients with moderate (50% to 69%) stenosis?

OBJECTIVE

Recently published data from the North American Carotid Endarterectomy Trial revealed a benefit for carotid endarterectomy (CEA) in symptomatic patients with moderate (50% to 69%) carotid stenosis. This benefit was significant but small (absolute stroke risk reduction at 5 years, 6.5%; 22.2% vs 15.7%), and thus, the authors of this study were tentative in the recommendation of operation for these patients. To better elucidate whether CEA in symptomatic patients with moderate carotid stenosis is a proper allocation of societal resources, we examined the cost-effectiveness of this intervention.

METHODS

A decision-analytic Markov process model was constructed to determine the cost-effectiveness of CEA versus medical treatment for a hypothetical cohort of 66-year-old patients with moderate carotid stenosis. This model allowed the comparison of not only the immediate hospitalization but also the lifetime costs and benefits of these two strategies. Our measure of outcome was the cost-effectiveness ratio (CER), defined as the incremental lifetime cost per quality-adjusted life year saved. We assumed an operative stroke and death rate of 6.6% and a declining risk of ipsilateral stroke after the ischemic event with medical treatment (first year, 9.3%; second year, 4%; subsequent years, 3%). The hospitalization cost of CEA ($6,420) and the annual costs of major stroke ($26,880), minor stroke ($798), and aspirin therapy ($63) were estimated from a hospital cost accounting system and the literature.

RESULTS

CEA for moderate carotid stenosis increased the survival rate by 0.13 quality-adjusted life years as compared with medical treatment at an additional lifetime cost of $580. Thus, CEA was cost-effective with a CER of $4,462. Society is usually willing to pay for interventions with CERs of less than $60,000 (eg, CERs for coronary artery bypass grafting at $9,100 and for dialysis at $53,000). CEA was not cost-effective if the perioperative risk was greater than 11.3%, if the ipsilateral stroke rate associated with medical treatment at 1 year was reduced to 4.3%, if the age of the patient exceeded 83 years, or if the cost of CEA exceeded $13,200.

CONCLUSION

CEA in patients with symptomatic moderate carotid stenosis of 50% to 69% is cost-effective. Perioperative risk of stroke or death, medical and surgical stroke risk, cost of CEA, and age are important determinants of the cost-effectiveness of this intervention.

The role of mitogen-activated protein kinase and protein kinase C in fibronectin production in human vascular smooth muscle cells

BACKGROUND

After evaluating various growth factors, cytokines, and extracellular matrix (ECM) proteins, we found that the most potent agonists of smooth muscle cell (SMC) fibronectin (Fn) production were transforming growth factor-beta (TGF-beta) and epidermal growth factor (EGF). To determine the possible signaling pathways involved in the production of this matrix protein, we investigated the role of the intracellular proteins, protein kinase C (PKC) and mitogen-activated protein kinase (MAP-K), in TGF-beta- and EGF-induced human vascular SMC Fn production.

MATERIALS AND METHODS

After stimulation of human SMCs with TGF-beta (10 ng/ml) and EGF (100 ng/ml), Fn in the cell medium was assayed by immunoblotting using a specific antibody. PKC was activated by brief stimulation of SMC with phorbol 12,13-dibutyrate (PDBu) and inhibited by downregulation with PDBu or the inhibitor, GF109203X. MAP-K was inhibited with PD098059.

RESULTS

PKC activation increased basal and synergistically enhanced TGF-beta- and EGF-induced Fn production. However, inhibition of PKC by downregulation and GF109203X did not diminish Fn production by TGF-beta and EGF. Surprisingly, these two methods of inhibition slightly increased basal and agonist-induced Fn production. The MAP-K kinase inhibitor, PD098059, produced an almost complete inhibition of EGF and a partial inhibition of TGF-beta-induced Fn production.

CONCLUSIONS

Activation of PKC stimulates Fn production; however, neither TGF-beta nor EGF produce Fn through a PKC-dependent pathway. EGF and TGF-beta both stimulate Fn production at least in part through the intracellular signaling protein MAP-K. Understanding the signaling pathways involved in extracellular matrix protein production will allow the design of specific inhibitors of intimal hyperplasia.

The cost-effectiveness of endovascular repair versus open surgical repair of abdominal aortic aneurysms: A decision analysis model

PURPOSE

Endovascular repair (EVR) is a less-invasive method for the treatment of abdominal aortic aneurysms (AAAs) as compared with open surgical repair (OSR). The potential benefits of EVR include increased patient acceptance, less resource utilization, and cost savings. This study was designed to determine whether the EVR of AAAs is a cost-effective alternative to OSR.

METHODS

A cost-effectiveness analysis was performed using a Markov decision analysis model to compute long-term survival rates in quality-adjusted life years and lifetime costs for a hypothetical cohort of patients who underwent either OSR or EVR. Probability estimates of the different outcomes of the two alternative strategies were made on the basis of a review of the literature. The average costs of (1) the immediate hospitalization ($16,016 for OSR, $20,083 for EVR), (2) the complications that resulted from each procedure, (3) the subsequent interventions, and (4) the surveillance protocol were determined on the basis of average resource utilization as reported in the literature and from our hospital's cost accounting system. Our measure of outcome was the cost-effectiveness ratio.

RESULTS

For our base-case analysis (70-year-old men with 5-cm AAAs), EVR was cost-effective with a cost-effectiveness ratio of $22,826-society usually is willing to pay for interventions with cost-effectiveness ratios of less than $60,000 (eg, cost-effectiveness ratios for coronary artery bypass grafting and dialysis are $9500 and $54,400, respectively). This conclusion did not vary significantly with increases in procedural costs for EVR (ie, if the cost of the endograft increased from $8000 to $12,000, EVR remained cost-effective with a cost-effectiveness ratio of $32,881). The cost-effectiveness of EVR was critically dependent on EVR producing a large reduction in the combined mortality and long-term morbidity rate (stroke, dialysis-dependent renal failure, major amputation, myocardial infarction) as compared with OSR (ie, a reduction in the combined mortality and long-term morbidity rate of OSR from 9.1% to 4.7% made EVR no longer cost-effective).

CONCLUSION

Despite the high cost of new technology and the need for close postoperative surveillance, EVR is a cost-effective alternative for the repair of AAAs. However, the cost-effectiveness of this new technology is critically dependent on its potential to reduce morbidity and mortality rates as compared with OSR. EVR may not be cost-effective in medical centers where OSR can be performed with low risk.

Is thrombolysis of lower extremity acute arterial occlusion cost-effective?

BACKGROUND

The TOPAS (thrombolysis or peripheral artery surgery) trial randomized 544 patients with acute lower extremity ischemia to either surgery or thrombolysis. Although statistically equivalent 1-year morbidities and mortalities were demonstrated, the comparative cost-effectiveness of these two interventions has not been explored.

MATERIALS AND METHODS

We constructed a Markov decision-analytic model to determine the cost-effectiveness of thrombolysis relative to surgery for a hypothetical cohort of patients with acute lower extremity arterial occlusion. Our measure of outcome was the cost-effectiveness ratio (CER), defined as the incremental lifetime cost per quality-adjusted life year gained. Estimates of 1-year outcomes were based on the TOPAS trial: mortality (lysis, 20%; surgery, 17%), amputation (lysis, 15%; surgery, 13%), the number of additional interventions required following the initial procedure (lysis, 544; surgery, 439). Procedural costs were estimated from the cost accounting system at the New York Presbyterian Hospital as well as from the literature.

RESULTS

Operative intervention for acute lower extremity arterial occlusion extended life and was less costly compared to thrombolysis. The projected life expectancy for patients who underwent initial surgery was 5.04 years versus 4.75 years for initial thrombolysis. The lifetime costs were $57,429 for surgery versus $dollar;76,326 for thrombolysis. In performing sensitivity analyses, a threshold CER of $60,000 was considered what society would pay for accepted medical interventions. Thrombolysis became cost-effective if the 1-year mortality rate for lysis was lowered from 20 to 10.7%, if the amputation rate for lysis diminished from 15 to 3.9%, or if the 1-year cost of lysis could be reduced to a level below $13,000.

CONCLUSIONS

Initial surgery provides the most efficient and economical utilization of resources for acute lower extremity arterial occlusion. The high cost of thrombolysis is related to the expense of the lytic agents, the need for subsequent interventions in patients treated with initial lysis, and the long-term costs of amputation in patients who fail lytic therapy.

Risk factors and their role in the diseases of the arterial wall

The leading cause of death and disability in developed nations is atherosclerosis. Multiple risk factors, including hyperlipidemia, cigarette smoking, diabetes mellitus, and hypertension, predispose to the development of atherosclerosis. The mechanisms by which these risk factors exacerbate atherosclerosis involve the potentiation of endothelial and smooth muscle cell dysfunction as well as disturbances in coagulation. These mechanisms are discussed in detail in this chapter. Understanding the pathophysiology of how risk factors accelerate the progression of atherosclerosis will aid the clinician in attempts to treat the atherosclerotic patient.

Is routine duplex ultrasound surveillance after carotid endarterectomy cost-effective?

BACKGROUND

Although duplex ultrasound surveillance of patients after carotid endarterectomy (CEA) is routinely performed, the use of this policy has been questioned. We evaluated the cost-effectiveness of this strategy.

METHODS

Using a decision-analytic Markov model that depicts the natural history of patients after CEA, we compared a strategy of duplex ultrasound surveillance to a strategy of no surveillance. Probability estimates were derived from the literature and costs were obtained from the hospital's cost accounting system. Sensitivity analyses were performed to test the robustness and stability of our base-case conclusion to variations in the underlying assumptions.

RESULTS

Using baseline estimates we determined that duplex ultrasound surveillance after CEA reduced the incidence of stroke; however, this required significant additional expense, which resulted in an incremental cost-effectiveness ratio of $126,950. This ratio could decrease to a more acceptable level (less than $100,000) if a subset of patients could be identified whose rate of progression to greater than 80% stenosis exceeded 6% per year or whose stroke rate associated with uncorrected asymptomatic stenosis exceeded 2.6% per year. Also, the cost-effectiveness ratio was reduced to less than $100,000 if patients were younger than 55 years old at the time of initial CEA or if the cost of CEA could be reduced to less than $7,000.

CONCLUSIONS

Duplex ultrasound surveillance after CEA is associated with an unfavorable cost-effectiveness ratio. However, this strategy may be cost-effective in younger patients or in those patients who have a more progressive form of disease.

The impact of Clostridium difficile on a surgical service: a prospective study of 374 patients

OBJECTIVE

To evaluate the epidemiology of Clostridium difficile colitis (CDC) in a subset of patients admitted specifically to a surgical service.

SUMMARY BACKGROUND DATA

CDC is an increasingly prevalent nosocomial infection that can prolong hospitalization and adversely affect patient outcome. Although this disease has been investigated extensively in patients admitted to medical services, the incidence and risk factors for the development of this disease in patients admitted to a surgical service have not been studied.

METHODS

Over a 5-month period, 374 patients admitted to the general, vascular, thoracic, and urologic surgery services were monitored for the development of symptomatic CDC (defined as >3 bowel movements per 24 hours and a positive cytotoxin assay or culture).

RESULTS

Twenty-one patients developed CDC (incidence, 5.6%). Factors that independently predisposed to infection included admission from a skilled care facility, use of the antibiotic cefoxitin, and an operative procedure for bowel obstruction. Other factors associated with CDC included colectomy, treatment with any antibiotic, nasogastric tube suction, advanced age, and prior antibiotic treatment. Abdominal pain and fever were also more common in patients with CDC. Morbidity included prolonged hospitalization in all patients and urgent colectomy in one.

CONCLUSIONS

CDC frequently affects surgical patients, producing morbidity ranging from mild diarrhea to life-threatening illness. A variety of factors, many of which are associated with intestinal stasis, predispose to the development of CDC.

Smooth muscle cell migration and proliferation are mediated by distinct phases of activation of the intracellular messenger mitogen-activated protein kinase

PURPOSE

Mitogen-activated protein kinase (MAPK) is a ubiquitous signaling protein that has been associated with cellular proliferation; however, its role in cellular migration has not been established. In this study, we investigate the role of MAPK in platelet-derived growth factor (PDGF)-induced migration and proliferation of human vascular smooth muscle cells (SMCs).

METHODS

SMC migration was measured using a microchemotaxis assay (4 hours), and proliferation was assessed using 3H-thymidine uptake and cell counts. PD098059 was used as a specific noncompetitive inhibitor of MAPK activation.

RESULTS

Coincubation of SMCs with PD098059 resulted in significant inhibition of PDGF-BB (5 ng/ml)-induced SMC chemotaxis and proliferation. The IC50 for both processes was approximately 10 mumol/L with complete inhibition at 50 mumol/L. Stimulation of SMCs with PDGF produced an early peak in MAPK activity followed by a plateau of activity that persisted for 24 hours. We hypothesized that variations in the temporal activation of MAPK might explain the action of this enzyme on these two disparate cellular events. By adding PD098059 at intervals after stimulation of SMCs with PDGF, we demonstrated an association between MAPK activity within the first 15 minutes and SMC migration, whereas MAPK activity between 1 and 4 hours was associated with SMC proliferation.

CONCLUSIONS

MAPK activity is essential for both SMC migration and proliferation, and distinct phases of enzyme activation are required to stimulate these two discrete cellular events. Inhibition of this signaling protein may prove to be a useful method for preventing intimal hyperplasia.

Activation of pp60c-src is necessary for human vascular smooth muscle cell migration

BACKGROUND

The most widely distributed nonreceptor tyrosine kinase is pp60c-src (src), yet the role of this intracellular signaling protein in cell migration has not been defined. Given that smooth muscle cell (SMC) migration is essential for the development of intimal hyperplasia, we investigated the importance of src in locomotion of human vascular SMC.

METHODS

SMC migration was evaluated using a microchemotaxis chamber assay and videomicroscopy. Src kinase activity was determined by measuring phosphorylation of a synthetic derivative of p34cdc2, a specific substrate for src. Blocking antibodies to src were introduced using a cytoplasmic microinjection technique.

RESULTS

Stimulation of SMC with platelet-derived growth factor (PDGF)-BB and AB resulted in an increase in src activation, whereas PDGF-AA did not consistently enhance src activity. These findings correlated with the ability of the PDGF isotypes to stimulate SMC chemotaxis; PDGF-BB and AB produced 7.4 +/- 0.3- and 5.3 +/- 0.5-fold increases in SMC chemotaxis, whereas PDGF-AA inhibited chemotaxis. SMC migration in response to PDGF-BB and serum was significantly inhibited by intracellular injection of a blocking antibody.

CONCLUSIONS

Our findings reveal an association between agonist-induced src activation and chemotaxis. Moreover, an antibody that inhibits src activation dramatically inhibits migration of individual SMC. We conclude that activation of src is necessary for SMC migration. Because of its importance in SMC migration, either molecular or pharmacologic inhibitors of src may be useful in the control of intimal hyperplasia.

Platelet-derived growth factor and extracellular matrix proteins provide a synergistic stimulus for human vascular smooth muscle cell migration

PURPOSE

Smooth muscle cell (SMC) migration contributes significantly to the hyperplastic response that follows arterial injury. In vitro studies have shown that a number of growth factors and extracellular matrix (ECM) proteins individually stimulate vascular SMC migration. However, after arterial injury, SMCs exist in a complex environment in which they are exposed to many of these proteins simultaneously. The response of SMCs to multiple simultaneous stimuli may differ significantly from their response to any single individual stimulus. In this study, we evaluated the chemotactic response of human vascular SMCs to various combinations of growth factors and ECM proteins.

METHODS

Human saphenous vein SMCs were used for all experiments. Using a 4-hour modified Boyden-chamber assay, we evaluated the effect on SMC chemotaxis of combinations of one of three growth factors (platelet-derived growth factor [PDGF]-AB, basic fibroblast growth factor [bFGF], or epidermal growth factor [EGF]), and one of four ECM proteins (fibronectin, laminin, or collagen type I or IV). A standard fluorimetric assay was used to assess changes in intracellular calcium ([Ca2+]i) in response to the various combinations of growth factors and ECM proteins.

RESULTS

A simple additive effect was seen between ECM proteins and bFGF or EGF. However, when SMCs were simultaneously exposed to PDGF and ECM proteins, we observed a synergistic increase in chemotaxis. This synergy was evident for all concentrations of collagen type I and IV but only with higher concentrations of fibronectin and laminin. We evaluated whether intracellular calcium may be the signaling pathway through which this synergistic effect is mediated. Although ECM proteins alone did not stimulate a rise in [Ca2+]i, ECM proteins enhanced the early peak in [Ca2+]i induced by PDGF.

CONCLUSION

These data show that PDGF acts synergistically with the ECM proteins to promote SMC migration; this effect appears to be specific for PDGF and was not observed with other growth factors. The mechanism responsible for this phenomenon may be a synergistic increase in [Ca2+]i in SMCs simultaneously exposed to both proteins.

The role of integrins in saphenous vein vascular smooth muscle cell migration

PURPOSE

Smooth muscle cell (SMC) migration is an essential feature of the intimal hyperplastic process that so frequently limits the patency of vascular reconstructions. The purpose of this investigation was to evaluate the effect of a series of integrins, or cell surface receptors that mediate cellular attachment, on platelet-derived growth factor (PDGF) and extracellular matrix (ECM) protein-induced migration of human SMCs.

METHODS

Immunofluorescence staining was used to search for various integrins and subunits on the surface of SMCs derived from human saphenous vein. Chemotaxis and haptotaxis of SMCs to various matrix proteins and PDGF were assayed using a 48-well microchemotaxis chamber in the presence or absence of antibodies that blocked the function of these integrins.

RESULTS

Several subunits (beta 1, alpha 2, alpha 5) and one integrin (alpha v beta 3) were identified in saphenous vein SMCs. The beta 1 integrin antibody inhibited chemotaxis to collagen I and IV, laminin, and PDGF. The alpha 2 integrin antibody inhibited collagen I and IV, and laminin-induced chemotaxis. The alpha 5 integrin antibody had no effect on SMC migration. The alpha v beta 3 integrin antibody inhibited chemotaxis to PDGF but not to the ECM proteins.

CONCLUSIONS

Integrins are necessary for SMC migration induced by PDGF and ECM proteins. The integrin or subunits responsible for facilitating migration varies with the stimulant. Agonists designed to inhibit integrin function might be used to suppress SMC migration and suppress the formation of intimal hyperplasia.

Enhancement of migration by protein kinase Calpha and inhibition of proliferation and cell cycle progression by protein kinase Cdelta in capillary endothelial cells

Activation of protein kinase C (PKC) induces angiogenesis, migration, and proliferation of endothelial cells (EC), but can also prevent growth factor-induced EC proliferation. To determine whether these disparate effects are mediated by substrates of individual PKC isoenzymes, PKCalpha and PKCdelta were overexpressed in rat microvascular EC. Basal and stimulated migration were enhanced in PKCalpha EC compared with either PKCdelta or control EC. Serum-induced growth of PKCdelta EC was decreased, while that of PKCalpha cells was similar to control EC. Phorbol ester markedly inhibited PKCdelta EC growth but enhanced growth of PKCalpha and control EC. To determine possible causes for this altered proliferation, the effect of PKCdelta on adhesion, mitogen-activated protein kinase activity, and cell cycle progression was measured. Adherence of PKCdelta EC to vitronectin was significantly enhanced. Serum-induced extracellular signal-regulated kinase-2 activity was increased equally in both PKCalpha and PKCdelta EC above that of control, while extracellular signal-regulated kinase-1 activity was similar in all EC. Cell cycle analysis suggested that PKCdelta EC entered S phase inappropriately and were delayed in passage through S phase. Thus, PKCalpha may mediate some proangiogenic effects of PKC activation; conversely, PKCdelta may direct antiangiogenic aspects of overall PKC activation, including slowing of the cell cycle progression.

Duplex ultrasound criteria for the identification of carotid stenosis should be laboratory specific

BACKGROUND AND PURPOSE

Published criteria for the determination of carotid stenosis have been widely applied by vascular laboratories. We compared two vascular laboratories and their duplex ultrasound (DU) machines in terms of their overall diagnostic performance and the optimal criteria to identify patients who have a 70% to 99% stenosis of the internal carotid artery.

METHODS

Measurements of stenosis by DU and angiography were compared for 123 carotid arteries (60 arteries, laboratory A; 63 arteries, laboratory B). Receiver operating characteristic (ROC) curves were created, and the areas under the ROC curves and the optimal criteria for determining a 70% to 99% stenosis were compared. Multiple regression analysis was used to measure the effect of laboratory on the relationship between angiographic stenosis and DU velocity parameters.

RESULTS

Areas under the ROC curves were similar for both laboratories (0.89 to 0.90, laboratory A; 0.90 to 0.92, laboratory B). However, the optimal criterion for the identification of a 70% to 99% carotid stenosis was different for each laboratory. For most velocity parameters, based on regression analyses, the predicted percent angiographic stenosis for laboratory A was significantly greater than that for laboratory B. In addition, performance differed between the laboratories when established criteria from the literature were applied.

CONCLUSIONS

Two vascular laboratories with similar diagnostic accuracy by ROC analysis have markedly different "optimal" DU criteria. For a given angiographic stenosis, velocities in one laboratory were consistently greater than those in the other laboratory. Laboratory-specific criteria rather than published criteria should be used to identify patients with internal carotid artery stenoses.

Is carotid endarterectomy cost-effective? An analysis of symptomatic and asymptomatic patients

BACKGROUND

The North American Symptomatic Carotid Endarterectomy Trial (NASCET) and the Asymptomatic Carotid Atherosclerosis Study (ACAS) showed significant risk reductions for carotid endarterectomy (CE) but did not consider the cost-effectiveness of CE.

METHODS AND RESULTS

We developed Markov models based on NASCET and ACAS to simulate hypothetical cohorts of patients with carotid stenosis and calculated quality-adjusted life expectancies and direct medical costs for those receiving either CE or medical therapy. For symptomatic patients, we used a surgical stroke risk of 5.8%, a 2-year stroke risk of 27.6% for medical patients, and a post-30-day surgical risk reduction of 87% for ipsilateral strokes. For symptom-free patients, we used a surgical stroke risk of 1.7%, a 5-year stroke risk of 17.5% for medical patients, and a post-30-day surgical risk reduction of 74% for ipsilateral strokes. Cost and quality-of-life estimates were estimated from the literature. The incremental cost-effectiveness ratio of CE versus medical therapy was $4100 and $52700 per quality-adjusted life year (QALY) gained for symptomatic and symptom-free patients, respectively. Incremental cost effectiveness ratios were < $50000/QALY gained for symptomatic patients for wide variations in baseline assumptions. For asymptomatic patients, the incremental cost-effectiveness ratio was $100900/QALY gained if the perioperative risk was 4%, $36400/QALY gained if the risk of untreated patients was doubled, and $13500/QALY gained if the cost of CE was halved.

CONCLUSIONS

Performance of CE is associated with favorable incremental cost-effectiveness ratios compared with other accepted medical interventions; however, the analysis for symptom-free patients was sensitive to a number of parameters.

Differential effects of platelet-derived growth factor isotypes on human smooth muscle cell proliferation and migration are mediated by distinct signaling pathways

BACKGROUND

Platelet-derived growth factor (PDGF) is a potent mitogen and chemoattractant for vascular smooth muscle cells (SMCs). Three isotypes of PDGF (BB, AB, and AA) have been identified; each of these isotypes may have differing effects on the behaviour of vascular SMCs. In this study we evaluated the influence of PDGF isotypes on proliferation and migration of human venous SMCs and explored the signaling pathways through which these effects are mediated.

METHODS

Proliferation was measured by a 72-hour assay of cell number, and migration was evaluated by a 4-hour microchemotaxis assay. The effects of PDGF isotypes on the activities of the signaling proteins mitogen-activated protein kinase (MAP-K), p 125 focal adhesion kinase (p125FAK), and tensin were measured by immunoprecipitation of these proteins and subsequent phosphorylation on myelin basic protein (in MAP-K) and Western blotting with antiphosphotyrosine (in tensin and p125FAK).

RESULTS

All three isotypes stimulated SMC proliferation (PDGF-BB > AB > AA). PDGF-BB and -AB, but not -AA, stimulated chemotaxis. All three isotypes activated MAP-K with an intensity that corresponded to their proliferative effects. PDGF-BB and -AB tyrosine phosphorylated tensin and p125FAK, whereas PDGF-AA had no effect on either of these proteins.

CONCLUSIONS

For human vascular SMCs the physiologic effects and the signaling pathways that mediate these effects are specific for each of the three PDGF isotypes. These data also suggest an association between MAP-K and SMC proliferation and between the proteins, p125FAK and tensin, and migration.

Extracellular matrix proteins are potent agonists of human smooth muscle cell migration

PURPOSE

Extracellular matrix proteins can stimulate smooth muscle cell (SMC) migration by three distinct mechanisms: chemokinesis (nondirected migration in the presence of soluble protein), chemotaxis (directed migration toward soluble protein), and haptotaxis (directed migration toward insoluble, substrate-bound protein). This study investigates the effects of four prevalent extracellular matrix proteins (collagen types I and IV, fibronectin, and laminin), and platelet-derived growth factor (PDGF) on haptotaxis, chemotaxis, and chemokinesis of human SMCs. The role of large guanosine triphosphate-binding proteins (G-proteins) in the signaling mediating these effects is also evaluated.

METHODS

Human saphenous vein SMCs were used in all migration studies. Chemokinesis, chemotaxis, and haptotaxis to each of the matrix proteins were measured and compared with PDGF through the use of a 48-well microchemotaxis chamber. The role of G-proteins in matrix-induced SMC migration was studied with the modulators of G-protein function, cholera and pertussis toxins.

RESULTS

For all matrix proteins the relative strength of the various stimuli for migration was haptotaxis > chemotaxis > chemokinesis (p < 0.05). For all three stimuli collagen I and IV produced the most significant migration followed by fibronectin > PDGF-AB > laminin (p < 0.05). Pertussis toxin completely inhibited chemotaxis and partially inhibited haptotaxis by laminin but did not affect migration by other matrix proteins, whereas cholera toxin abolished migration in response to all four matrix proteins.

CONCLUSION

Matrix proteins, with the exception of laminin, provide a more significant stimulus for SMC locomotion than does the prototypical agonist, PDGF-AB. Of the three mechanisms by which migration can be stimulated, haptotaxis elicits the most profound effect. The importance of G-proteins as second messengers for migration varies with each matrix protein and with the mechanism of stimulation.

Role of protein kinase C in attachment, spreading, and migration of human endothelial cells

Attachment, spreading, and migration of vascular endothelial cells (EC) are necessary for angiogenesis, reendothelialization of an injured artery, or seeding of a prosthetic graft. However, little is known about the signaling pathways that mediate these effects. Protein kinase C (PKC) is a ubiquitous intracellular messenger which we have previously shown to be necessary for EC proliferation (Kent et al., 1995, Circ. Res. 77, 231-238). In this study, we investigate whether activation of PKC is necessary for EC attachment, spreading, and migration. Using human umbilical vein EC, we found that direct activation of PKC with the phorbol ester phorbol 12-myristate-13-acetate enhanced all three processes. Inhibition of PKC by the selective agent, chelerythrine, markedly diminished the ability of EC to attach, spread, and migrate. Depletion of intracellular PKC by downregulation (prolonged exposure of EC to phorbol ester) reduced EC attachment and migration; however, downregulation had no effect on endothelial spreading. PKC is a family of isotypes, each of which may control specific cellular functions. By Western blotting, we identified PKC alpha, beta, delta, epsilon, eta, theta, and zeta isotypes in human EC. Downregulation led to a significant reduction in the quantity of PKC alpha and epsilon. These data demonstrate that activation of PKC is both necessary and sufficient for attachment, spreading, and migration of human EC. An isotype of PKC that is susceptible to downregulation (either alpha and/or epsilon) is at least partially responsible for attachment and migration. Pharmacological activation of PKC may be used as a method to enhance reendothelialization.

Sequential helical CT angiography of aortoiliac disease

OBJECTIVE

The purpose of this work was to study aortoiliac disease with sequential helical CT angiography.

SUBJECTS AND METHODS

Sequential helical CT angiography combines two successive helical sets for data acquisition obtained during two successive bolus injections of IV contrast material and two breath-holds. Twenty-eight patients with aneurysm and 11 with occlusive disease had CT angiography. Of those 39 patients, 18 also had conventional catheter angiography. For each of the 39 patients, a CT angiogram of three segments of the aorta and 13 arteries was assessed, including the suprarenal, juxtarenal, and infrarenal aorta; celiac axis; superior and inferior mesenteric arteries; and pairs of renal, common iliac, hypogastric, external iliac, and common femoral arteries. In 18 patients undergoing both CT and conventional angiography, the appearance of these vessels was graded as occlusive (grade 0), severely stenotic (grade 1), moderately stenotic (grade 2), mildly stenotic (grade 3), normal (grade 4), ectatic (grade 5), and aneurysmal (grade 6).

RESULTS

Of the 624 arteries expected to be opacified in 39 patients, 585 (94%) were actually imaged with CT angiography. In the 18 patients who had both CT angiography and catheter angiography, the two studies were in complete agreement in 243 (90%) of 269 arteries. In 13 vessels (5%), CT angiography produced an image that was one grade higher-and in 11 vessels (4%), one grade lower-than conventional angiography. In two vessels, a two-grade difference was noted. The independent readings matched on the 0-6 scale in 95% of the evaluations. An additional 5% of the readings differed by one unit. Compared with conventional angiography, CT angiography of clinically significant (> or = 85%) narrowing (grades 0 and 1) and aneurysm (grade 6) yielded sensitivity of 93%, specificity of 96%, and accuracy of 95%.

CONCLUSION

Sequential helical CT angiography of the abdomen can provide sufficient vascular detail to allow evaluation of expanded vascular territories. The technique can allow accurate assessment of both stenotic and aneurysmal disease of the aorta and the iliac arteries.

Mid-term and long-term results with directional atherectomy of vein graft stenoses

PURPOSE

The purpose of this study was to evaluate the outcomes of our 6-year experience with directional atherectomy used for treatment of stenoses in infrainguinal vein grafts.

METHODS

From March 1988 to April 1994, 52 directional atherectomy procedures were undertaken in 42 patients to treat 67 stenoses in 44 vein grafts. Follow-up consisted of periodic physical examinations and graft surveillance; ankle/brachial indexes, pulse volume recordings, and color-flow duplex ultrasonography. Follow-up angiography (n = 18) was performed for recurrent symptoms, reproducible drop in ankle/brachial index of greater than 0.15, a twofold to threefold focal increase in peak systolic velocity, or incidentally during evaluation of the opposite leg.

RESULTS

Forty-nine of 52 (94%) procedures were technically successful. In two the residual diameter stenosis was greater than 30%, and in one atherectomy could not be performed. Complications were minor in six (11%) and major in three (6%): two acute graft occlusions and one delayed pseudoaneurysm at the atherectomy site. There were no deaths at 30 days. With a mean follow-up of 21 +/- 18 months, 36 of 44 grafts (82%) remained patent without restenosis; 6 others were patent but considered "failed"--5 (11%) with restenosis, 1 with a pseudoaneurysm; and 2 grafts (5%) occluded. Clinically 33 of 44 extremities (75%) were asymptomatic during follow-up. Claudication improved in five, recurred in three, and was unchanged in one. There was one below-knee amputation. Life-table analysis including all 52 procedures reveals cumulative primary atherectomy patency rates for the 44 grafts of 82%, 78%, and 78%, respectively, at 1, 2, and 3 years after atherectomy, and 86%, 83%, and 83% for the 67 individual stenoses treated.

CONCLUSIONS

Directional atherectomy of vein graft stenoses has high technical and clinical success rates, acceptably low morbidity rates, and offers better sustained patency rates than balloon angioplasty. Its long-term patency rate seems to approach that of surgical vein patch angioplasty.