Michiel Voskuil

Stimulation of arteriogenesis; a new concept for the treatment of arterial occlusive disease

After birth two forms of vessel growth can be observed; angiogenesis and arteriogenesis. Angiogenesis refers to the formation of capillary networks. Arteriogenesis refers to the growth of preexistent collateral arterioles leading to formation of large conductance arteries that are well capable to compensate for the loss of function of occluded arteries. The process of arteriogenesis is initiated when shear stresses increase in the preexistent collateral pathways upon narrowing of a main artery. The increased shear stress leads to an upregulation of cell adhesion molecules for circulating monocytes, which accumulate subsequently around the proliferating arteries and provide the several required cytokines and growth factors. Several strategies are currently tested for their potential to stimulate the process of arteriogenesis. These strategies focus either at shear stress, at direct stimulation of endothelial and smooth muscle cell growth or at the monocytic pathway and promising results were obtained from experimental studies. However, some important questions remain to be answered before arteriogenesis can be brought from bench to bedside.

Physiological Basis and Long-Term Clinical Outcome of Discordance Between Fractional Flow Reserve and Coronary Flow Velocity Reserve in Coronary Stenoses of Intermediate Severity

Background—Discordance between fractional flow reserve (FFR) and coronary flow velocity reserve (CFVR) may reflect important coronary pathophysiology but usually remains unnoticed in clinical practice. We evaluated the physiological basis and clinical outcome associated with FFR/CFVR discordance. Methods and Results—We studied 157 intermediate coronary stenoses in 157 patients, evaluated by FFR and CFVR between April 1997 and September 2006 in which revascularization was deferred. Long-term follow-up was performed to document the occurrence of major adverse cardiac events: cardiac death, myocardial infarction, or target vessel revascularization. Discordance between FFR and CFVR occurred in 31% and 37% of stenoses at the 0.75, and 0.80 FFR cut-off value, respectively, and was characterized by microvascular resistances during basal and hyperemic conditions. Follow-up duration amounted to 11.7 years (Q1–Q3, 9.9–13.3 years). Compared with concordant normal results of FFR and CFVR, a normal FFR with an abnormal CFVR was associated with significantly increased major adverse cardiac events rate throughout 10 years of follow-up, regardless of the FFR cut-off applied. In contrast, an abnormal FFR with a normal CFVR was associated with equivalent clinical outcome compared with concordant normal results: ⩽3 years when FFR <0.75 was depicted abnormal and throughout 10 years of follow-up when FFR ⩽0.80 was depicted abnormal. Conclusions—Discordance of CFVR with FFR originates from the involvement of the coronary microvasculature. Importantly, the risk for major adverse cardiac events associated with FFR/CFVR discordance is mainly attributable to stenoses where CFVR is abnormal. This emphasizes the requirement of intracoronary flow assessment in addition to coronary pressure for optimal risk stratification in stable coronary artery disease.

Arteriogenesis Proceeds via ICAM-1/Mac-1- Mediated Mechanisms

Monocyte adhesion to shear stress–activated endothelium stands as an important initial step during arteriogenesis (collateral artery growth). Using multiple approaches, we tested the hypothesis that monocyte adhesion via intercellular adhesion molecule-1 (ICAM-1) and selectin interactions is essential for adaptive arteriogenesis. Forty-eight New Zealand White rabbits received either solvent, monocyte chemoattractant protein-1 (MCP-1) alone, MCP-1 plus ICAM-mab, or MCP-1 plus an IgG2a isotype control via osmotic minipumps. After 7 days, collateral conductance was evaluated: solvent 4.01 (mL/min per 100 mm Hg), MCP-1 plus ICAM-mab 8.04 (versus solvent P =NS), and MCP-1 alone 33.11 (versus solvent P <0.05). Furthermore, the right femoral arteries of ICAM-1−/−, Mac-1−/− and mice having defective selectin interactions (FT4/7−/−) as well as their corresponding controls were ligated. One week later, perfusion ratios were determined by the use of fluorescent microspheres. FT4/7−/− mice did not show any significant difference in perfusion restoration whereas ICAM-1−/− and Mac-1−/− mice had a significant reduction in arteriogenesis as compared with matching controls (FT4/7-WT 37±9%, FT4/7−/− 32±3%, P =0.31; C57BL/6J 59±9%, ICAM-1−/− 36±8%, P <0.05; Mac-1−/− 42±3%, P <0.05). ICAM-1/Mac-1–mediated monocyte adhesion to the endothelium of collateral arteries is an essential step for arteriogenesis, whereas this process can proceed via selectin interaction independent mechanisms. Furthermore, in vivo treatment with monoclonal antibodies against ICAM-1 totally abolishes the stimulatory effect of MCP-1 on collateral artery growth, suggesting that the mechanism of the MCP-1–induced arteriogenesis proceeds via the localization of monocytes rather than the action of the MCP-1 molecule itself.

Direct Evidence for Tumor Necrosis Factor-α Signaling in Arteriogenesis

Background—Arteriogenesis serves as an efficient mechanism for flow restoration after arterial occlusion. This process is associated with inflammatory mediators such as tumor necrosis factor-&agr; (TNF-&agr;), although their role in arteriogenesis remains unclear. We hypothesized that arteriogenesis is reduced in mice lacking functional TNF-&agr; or p55 receptor. To test this hypothesis, we developed a novel microsphere-based murine model of hindlimb perfusion measurement. Methods and Results—Unilateral femoral arteries of nude (n=9), TNF-&agr;−/− (n=9), TNF-&agr; receptor p55−/− (n=8), and p75−/− (n=8) mice as well as their appropriate genetic background controls were occluded. The nude mice underwent laser Doppler hindlimb flux measurements preoperatively, postoperatively, and after 7 days. Seven days after ligation, all animals underwent tissue perfusion determinations using fluorescent microspheres. Laser Doppler findings confirmed acute decrease in flux with falsely normal values after 1 week. Microsphere results from control mice showed perfusion restoration to values ≈50% of normal within 7 days. TNF-&agr;−/− mice demonstrated a significant reduction (45.1%) in collateral artery perfusion compared with controls (TNF-&agr;−/− 22.4±5.1% versus B6x129 49.7±9.3%;P <0.01). p55−/− mice exhibited an almost identical 45.8% reduction in collateral artery formation (p55−/− 28.3±4.3% versus C57BL/6J 61.8±9.1%;P <0.01), whereas p75−/− mice were equivalent to controls (p75−/− 54.5±5.5%;P =0.13). Conclusions—Microsphere techniques in mice offer a tool for the molecular dissection of arteriogenesis mechanisms. These results suggest that TNF-&agr; positively modulates arteriogenesis probably via signaling through its p55 receptor.

START Trial: a pilot study on STimulation of ARTeriogenesis using subcutaneous application of granulocyte-macrophage colony-stimulating factor as a new treatment for peripheral vascular disease.

Background—Granulocyte-macrophage colony-stimulating factor (GM-CSF) was recently shown to increase collateral flow index in patients with coronary artery disease. Experimental models showed beneficial effects of GM-CSF on collateral artery growth in the peripheral circulation. Thus, in the present study, we evaluated the effects of GM-CSF in patients with peripheral artery disease. Methods and Results—A double-blinded, randomized, placebo-controlled study was performed in 40 patients with moderate or severe intermittent claudication. Patients were treated with placebo or subcutaneously applied GM-CSF (10 &mgr;g/kg) for a period of 14 days (total of 7 injections). GM-CSF treatment led to a strong increase in total white blood cell count and C-reactive protein. Monocyte fraction initially increased but thereafter decreased significantly as compared with baseline. Both the placebo group and the treatment group showed a significant increase in walking distance at day 14 (placebo: 127±67 versus 184±87 meters, P=0.03, GM-CSF: 126±66 versus 189±141 meters, P=0.04) and at day 90. Change in walking time, the primary end point of the study, was not different between groups. No change in ankle-brachial index was found on GM-CSF treatment at day 14 or at day 90. Laser Doppler flowmetry measurements showed a significant decrease in microcirculatory flow reserve in the control group (P=0.03) and no change in the GM-CSF group. Conclusions—The present study does not support the use of GM-CSF for treatment of patients with moderate or severe intermittent claudication. Issues that need to be addressed are dosing, the selection of patients, and potential differences between GM-CSF effects in the coronary and the peripheral circulation.

Local Monocyte Chemoattractant Protein-1 Therapy Increases Collateral Artery Formation in Apolipoprotein E–Deficient Mice but Induces Systemic Monocytic CD11b Expression, Neointimal Formation, and Plaque Progression

Abstract— Monocyte chemoattractant protein-1 (MCP-1) stimulates the formation of a collateral circulation on arterial occlusion. The present study served to determine whether these proarteriogenic properties of MCP-1 are preserved in hyperlipidemic apolipoprotein E–deficient (apoE−/−) mice and whether it affects the systemic development of atherosclerosis. A total of 78 apoE−/− mice were treated with local infusion of low-dose MCP-1 (1 &mgr;g/kg per week), high-dose MCP-1 (10 &mgr;g/kg per week), or PBS as a control after unilateral ligation of the femoral artery. Collateral hindlimb flow, measured with fluorescent microspheres, significantly increased on a 1-week high-dose MCP-1 treatment (PBS 22.6±7.2%, MCP-1 31.3±10.3%;P <0.05). These effects were still present 2 months after the treatment (PBS 44.3±4.6%, MCP-1 56.5±10.4%;P <0.001). The increase in collateral flow was accompanied by an increase in the number of perivascular monocytes/macrophages on MCP-1 treatment. However, systemic CD11b expression by monocytes also increased, as did monocyte adhesion at the aortic endothelium and neointimal formation (intima/media ratio, 0.097±0.011 [PBS] versus 0.257±0.022 [MCP-1];P <0.0001). Moreover, Sudan IV staining revealed an increase in aortic atherosclerotic plaque surface (24.3±5.2% [PBS] versus 38.2±9.5% [MCP-1];P <0.01). Finally, a significant decrease in the percentage of smooth muscle cells was found in plaques (15.0±5.2% [PBS] versus 5.8±2.3% [MCP-1];P <0.001). In conclusion, local infusion of MCP-1 significantly increases collateral flow on femoral artery ligation in apoE−/− mice up to 2 months after the treatment. However, the local treatment did not preclude systemic effects on atherogenesis, leading to increased atherosclerotic plaque formation and changes in cellular content of plaques.

Influence of Percutaneous Coronary Intervention on Coronary Microvascular Resistance Index

Background—Coronary microvascular resistance during maximal hyperemia is generally assumed to be unaffected by percutaneous coronary interventions (PCIs). We assessed a velocity-based index of hyperemic microvascular resistance (h-MRv) by using prototypes of a novel, dual-sensor (Doppler velocity and pressure)–equipped guidewire before and after PCI to test this hypothesis. Methods and Results—Aortic pressure, flow velocity (h-v), and pressure (h-Pd) distal to 24 coronary lesions were measured simultaneously during maximal hyperemia induced by intracoronary adenosine. Measurements were obtained in the reference vessel before PCI and in the target vessel before and after PCI, stenting, and ultrasound-guided, upsized stenting. h-Pd increased from 57.9±17.0 to 85.5±15.6 mm Hg, and h-MRv (ie, h-Pd/h-v) decreased from 2.74±1.40 to 1.58±0.61 mm Hg · cm−1 · s after stenting (both P<0.001). The reduction in h-MRv accounted for 34% of the decrease in total coronary resistance achieved by PCI. h-MRv of the target vessel after PCI was lower than that of the corresponding reference vessel despite a higher h-Pd in the reference vessel (P<0.01). Post-PCI baseline MRv was correlated with baseline Pd before PCI (P<0.01). Conclusions—PCI-induced restoration of Pd resulted in a reduction of h-MRv in accordance with the pressure dependence of h-MRv. The decrease in h-MRv to a level below that of the corresponding reference vessel in the immediate post-PCI period and a lowered baseline MRv suggest microvascular remodeling induced by long-term exposure to a low-pressure environment.

Effects of local MCP-1 protein therapy on the development of the collateral circulation and atherosclerosis in Watanabe hyperlipidemic rabbits

OBJECTIVE The objective of our study was to quantify the arteriogenic potency of Monocyte Chemoattractant Protein-1 (MCP-1) under hyperlipidemic conditions. Additionally, we aimed to determine the effects of locally applied MCP-1 on systemic serum lipid levels as well as on atherosclerosis. METHODS A total of sixty-four Watanabe rabbits was treated with either low dose MCP-1 (1 microg/kg/week), high dose MCP-1 (3.3 microg/kg/week) or PBS as a control substance. Substances were applied directly into the collateral circulation via an osmotic minipump with the catheter placed in the proximal stump of the ligated femoral artery. Either 1 week or 6 months after initiation of the treatment X-ray angiography was performed as well as measurements of collateral conductance using fluorescent microspheres. The extent of atherosclerosis was quantified in whole aortas using Sudan IV staining. RESULTS One week after ligation of the femoral artery a significant increase in collateral conductance was observed in animals treated with high dose MCP-1 (control: 2.2+/-0.8 ml/min/100 mmHg vs. MCP-1 high dose: 8.9+/-2.0 ml/min/100 mmHg, P<0.05). Six months after femoral artery ligation no differences were found between the treated and the control group (PBS; 44.9+/-11.6 ml/min/100 mmHg, MCP-1; 47.8+/-11.5 ml/min/100 mmHg, P=NS). No influence was found on serum lipids or on the development of atherosclerosis in the present model. CONCLUSION MCP-1 accelerates arteriogenesis upon femoral artery ligation under hyperlipidemic conditions. Six months after treatment these pro-arteriogenic effects of MCP-1 can no longer be observed. The present data do not show an effect of local MCP-1 treatment on serum lipids or on atherosclerosis. It should be noted however that a high standard deviation was observed for the data on atherosclerotic surface area, necessitating additional experiments in a different model of atherosclerosis.

First Results of the DEB-AMI (Drug Eluting Balloon in Acute ST-Segment Elevation Myocardial Infarction) Trial A Multicenter Randomized Comparison of Drug-Eluting Balloon Plus Bare-Metal Stent Versus Bare-Metal Stent Versus Drug-Eluting Stent in Primary Percutaneous Coronary Intervention With 6-Month Angiographic, Intravascular, Functional, and Clinical Outcomes

OBJECTIVES The goal of this study was to compare angiographic, intravascular imaging, and functional parameters, as well as the clinical outcomes of patients treated with drug-eluting balloon (DEB) plus bare-metal stent (BMS) versus BMS versus drug-eluting stent (DES) for ST-segment elevated acute myocardial infarction (STEMI). BACKGROUND Concerns remain regarding the long-term safety of DES in STEMI. DEB could provide an attractive alternative in order to achieve potentially similar effectiveness but limiting the long-term hazards related to late-acquired stent malapposition and thus stent thrombosis. METHODS In this randomized, international, 2-center, single-blinded, 3-arm study, STEMI patients were randomly assigned to group A: BMS; group B: DEB plus BMS; or group C: DES after successful thrombus aspiration. The primary endpoint was 6-month angiographic in-stent late-luminal loss. Secondary endpoints were in-stent binary restenosis, major adverse cardiac events (MACE: cardiac death, myocardial infarction, target vessel revascularization). In a subgroup of patients, stent (mal)apposition (by optical coherence tomography) and endothelial function (by acetylcholine infusion) was assessed. RESULTS Overall, 150 patients were randomized. Procedural success was achieved in 96.7%. In groups A, B, and C, respectively, late-luminal loss was 0.74 ± 0.57 mm, 0.64 ± 0.56 mm, and 0.21 ± 0.32 mm (p < 0.01); binary restenosis was 26.2%, 28.6%, and 4.7% (p = 0.01); and MACE rates were 23.5%, 20.0%, and 4.1% (p = 0.02), respectively. The median percentage [25th to 75th interquartile range] of uncovered and malapposed stent struts per lesion was 0 [0 to 0.35], 2.84 [0 to 6.63], and 5.21 [3.25 to 14.5] (p < 0.01). Significant paradoxical vasoconstriction was seen in groups B and C. CONCLUSIONS In STEMI patients, DEB followed by BMS implantation failed to show angiographic superiority to BMS only. Angiographic results of DES were superior to both BMS and DEB. Moreover, DEB before implantation induced more uncovered and malapposed stent struts than BMS, but less than after DES. (Drug-Eluting Balloon in Acute Myocardial Infarction [DEB-AMI]; NCT00856765).

Diagnostic Accuracy of Combined Intracoronary Pressure and Flow Velocity Information During Baseline Conditions Adenosine-Free Assessment of Functional Coronary Lesion Severity

Background— The assessment of functional coronary lesion severity using intracoronary physiological parameters such as coronary flow velocity reserve and the more widely used fractional flow reserve relies critically on the establishment of maximal hyperemia. We evaluated the diagnostic accuracy of the stenosis resistance index during nonhyperemic conditions, baseline stenosis resistance index, compared with established hyperemic intracoronary hemodynamic parameters, because achievement of hyperemia can be cumbersome in daily clinical practice. Methods and Results— A total of 228 patients, including 299 lesions (mean stenosis diameter 55%±11%), underwent myocardial perfusion scintigraphy for documentation of reversible perfusion defects. Distal coronary pressure and flow velocity were assessed with sensor-equipped guidewires during baseline and maximal hyperemia, induced by an intracoronary bolus of adenosine (20–40 µg). We determined stenosis resistance (SR) during baseline and hyperemic conditions as well as fractional flow reserve and coronary flow velocity reserve. The discriminative value for myocardial ischemia on myocardial perfusion scintigraphy of all parameters was compared using receiver-operating-characteristic curves. Baseline SR showed good agreement with myocardial perfusion scintigraphy. The diagnostic performance of baseline SR (area under the curve, 0.77; 95% CI, 0.71–0.83) was as accurate as fractional flow reserve and coronary flow velocity reserve (area under the curve, 0.77; 95% CI, 0.71–0.83 and area under the curve, 0.75; 95% CI, 0.68–0.81 respectively; P>0.05 compared with baseline SR for both). However, hyperemic SR, combining both pressure and flow velocity information during hyperemia, was superior to all other parameters (area under the curve, 0.81; 95% CI, 0.76–0.87; P<0.05 compared with all other parameters). Conclusions— Combined pressure and flow velocity measurements during baseline conditions may provide a useful tool for functional lesion severity assessment without the need for potent vasodilators.