In vivo analysis of intramuscular gene transfer in human subjects studied by on-line ultrasound imaging

The current study was designed to test the hypothesis that intramuscular (i.m.) injection of naked DNA leads to distribution of the injectate remote from the site of needle placement, a finding that might be expected to facilitate i.m. gene transfer. Transcutaneous ultrasound imaging was employed to monitor online the extent to which a solution of phVEGF165 was distributed among the skeletal musculature during 288 i.m. injections in 18 consecutive patients. In 237 (82.3%) of 288 muscle sites, the injection was performed into the distal calf muscle. In 51 (17.7%) of 288 muscle sites, injection was performed into the first and/or second interosseous muscles of the dorsal foot. Unperturbed muscle was recognized by a characteristic echogenic, stippled texture that was bounded by more intensely echogenic fascia. When i.m. gene transfer was performed into the calf muscles, the injectate was distributed along a longitudinal dimension of 3.59 +/- 0.79 cm (1.39-5.87 cm); the corresponding area of injectate measured by on-line planimetry was 1.83 +/- 0.51 cm2 (0.62-3.41 cm2). When i.m. gene transfer was performed into the interosseous muscles of the foot, the longitudinal extent of injectate distribution was 2.49 +/- 0.66 cm (1.61-3.91 cm), with a corresponding injectate area of 1.71 +/- 0.54 cm2 (0.51-2.86 cm2). These findings establish that a solution of plasmid DNA administered by direct i.m. injection into the skeletal muscles of the limb is distributed well beyond the site of needle entry. Thus, the use of multiple injections performed at different sites is likely to result in broad distribution of DNA injectate, a physical factor that may act to facilitate naked DNA and/or other gene transfer strategies.

Improvement in chronic ischemic neuropathy after intramuscular phVEGF165 gene transfer in patients with critical limb ischemia

OBJECTIVE

To investigate the effects of vascular endothelial growth factor gene therapy on ischemic neuropathy in patients with critical limb ischemia.

DESIGN

An open-label, dose-escalating trial. Patients with angiographically proven critical leg ischemia received injections of phVEGF(165) human plasmid in the muscles of the ischemic limb. Testing before treatment and at 3 and 6 months included (1) symptom severity score, (2) clinical examination score, and (3) electrophysiologic studies. Clinical and electrophysiologic examiners were masked to each other's findings.

SETTING

A tertiary care referral hospital and a major teaching affiliate of Tufts University School of Medicine, Boston, Mass.

RESULTS

Of 29 consecutive patients enrolled, 17 (19 limbs) completed the 6 months of study. Six patients had diabetes. Compared with baseline studies, treated patients had significant clinical improvements in the symptom score (P<.01), sensory examination score (P<.01), total examination score (P =.01), peroneal motor amplitude (P =.03), and quantitative vibration threshold (P =.04). Improvement in the vascular ankle-brachial index in treated legs (P<.01) corresponded to improvement in neuropathy in the same limb. Neurologic improvement was seen in 4 of 6 patients with diabetes who completed the study. No clinical, electrophysiologic, or vascular improvements were observed in untreated legs.

CONCLUSIONS

Ischemic neuropathy might be a reversible condition, and therapeutic angiogenesis might be an effective treatment. The presence of diabetes does not preclude a response to this therapy.

Vascular endothelial growth factor(165) gene transfer augments circulating endothelial progenitor cells in human subjects

Preclinical studies in animal models and early results of clinical trials in patients suggest that intramuscular injection of naked plasmid DNA encoding vascular endothelial growth factor (VEGF) can promote neovascularization of ischemic tissues. Such neovascularization has been attributed exclusively to sprout formation of endothelial cells derived from preexisting vessels. We investigated the hypothesis that VEGF gene transfer may also augment the population of circulating endothelial progenitor cells (EPCs). In patients with critical limb ischemia receiving VEGF gene transfer, gene expression was documented by a transient increase in plasma levels of VEGF. A culture assay documented a significant increase in EPCs (219%, P<0.001), whereas patients who received an empty vector had no change in circulating EPCs, as was the case for volunteers who received saline injections (VEGF versus empty vector, P<0.001; VEGF versus saline, P<0.005). Fluorescence-activated cell sorter analysis disclosed an overall increase of up to 30-fold in endothelial lineage markers KDR (VEGF receptor-2), VE-cadherin, CD34, alpha(v)beta(3), and E-selectin after VEGF gene transfer. Constitutive overexpression of VEGF in patients with limb ischemia augments the population of circulating EPCs. These findings support the notion that neovascularization of human ischemic tissues after angiogenic growth factor therapy is not limited to angiogenesis but involves circulating endothelial precursors that may home to ischemic foci and differentiate in situ through a process of vasculogenesis.

Lower-extremity edema associated with gene transfer of naked DNA encoding vascular endothelial growth factor

BACKGROUND

Vascular endothelial growth factor (VEGF) promotes angiogenesis and vascular permeability. The extent to which VEGF may cause tissue edema in humans has not been established.

OBJECTIVE

To evaluate patients undergoing VEGF gene transfer for evidence of lower-extremity edema.

DESIGN

Prospective consecutive case series.

SETTING

Hospital outpatient clinic.

PATIENTS

62 patients with critical limb ischemia and 28 patients with claudication.

INTERVENTION

Gene transfer of VEGF DNA.

MEASUREMENTS

Semiquantitative analysis of lower-extremity edema.

RESULTS

Lower-extremity edema was observed in 31 of 90 (34%) patients. Edema was less common in patients with claudication than in those with pain at rest (P = 0.016) or ischemic ulcers (P < 0.001), and it was less common in patients with pain at rest than in those with ischemic ulcers (P= 0.017). Treatment was typically limited to a brief course of oral diuretics.

CONCLUSIONS

Vascular endothelial growth factor may enhance vascular permeability in humans. At the doses of plasmid DNA used in this study, lower-extremity edema responded to oral diuretic therapy and did not seem to be associated with serious sequelae.

Constitutive expression of phVEGF165 after intramuscular gene transfer promotes collateral vessel development in patients with critical limb ischemia

BACKGROUND

Preclinical studies have indicated that angiogenic growth factors can stimulate the development of collateral arteries, a concept called "therapeutic angiogenesis." The objectives of this phase 1 clinical trial were (1) to document the safety and feasibility of intramuscular gene transfer by use of naked plasmid DNA encoding an endothelial cell mitogen and (2) to analyze potential therapeutic benefits in patients with critical limb ischemia.

METHODS AND RESULTS

Gene transfer was performed in 10 limbs of 9 patients with nonhealing ischemic ulcers (n=7/10) and/or rest pain (n=10/10) due to peripheral arterial disease. A total dose of 4000 microg of naked plasmid DNA encoding the 165-amino-acid isoform of human vascular endothelial growth factor (phVEGF165) was injected directly into the muscles of the ischemic limb. Gene expression was documented by a transient increase in serum levels of VEGF monitored by ELISA. The ankle-brachial index improved significantly (0.33+/-0.05 to 0.48+/-0.03, P=.02); newly visible collateral blood vessels were directly documented by contrast angiography in 7 limbs; and magnetic resonance angiography showed qualitative evidence of improved distal flow in 8 limbs. Ischemic ulcers healed or markedly improved in 4 of 7 limbs, including successful limb salvage in 3 patients recommended for below-knee amputation. Tissue specimens obtained from an amputee 10 weeks after gene therapy showed foci of proliferating endothelial cells by immunohistochemistry. PCR and Southern blot analyses indicated persistence of small amounts of plasmid DNA. Complications were limited to transient lower-extremity edema in 6 patients, consistent with VEGF enhancement of vascular permeability.

CONCLUSIONS

These findings may be cautiously interpreted to indicate that intramuscular injection of naked plasmid DNA achieves constitutive overexpression of VEGF sufficient to induce therapeutic angiogenesis in selected patients with critical limb ischemia.

Histopathology of in-stent restenosis in patients with peripheral artery disease

BACKGROUND

Clinical studies have suggested that smooth muscle cell (SMC) hyperplasia is the most likely cause of in-stent restenosis. However, pathological data regarding this issue are limited. Specifically, direct evidence of proliferative activity in tissues excised from stenotic stents has not been previously reported.

METHODS AND RESULTS

Tissue specimens were retrieved by directional atherectomy from 10 patients in whom in-stent restenosis complicated percutaneous revascularization of peripheral artery disease. Analysis of cellular composition was performed quantitatively after cell-specific immunostaining. For specimens preserved in methanol (7 of 10), cellular proliferation was evaluated by use of antibodies to proliferating cell nuclear antigen (PCNA), cyclin E, and cdk2. TUNEL staining for apoptosis was performed on 8 paraformaldehyde-preserved specimens. Each of the 10 specimens contained extensive foci of hypercellularity composed predominantly of SMCs (mean+/-SEM, 59.3+/-3.0%). Evidence of ongoing proliferative activity was documented in all 7 methanol-preserved specimens: 24.6+/-2.3% of SMCs were PCNA-positive, 24.8+/-3.1% were cyclin E-positive, and 22.5+/-2.2% were cdk2-positive. Apoptotic cells were detected in all 8 specimens that had been appropriately preserved to permit DNA nick-end labeling. Macrophages and leukocytes were identified in each of the 10 specimens but accounted for a proportionately smaller number of cells (14.5+/-1.9% and 9.5+/-1.4%, respectively). Organized thrombus was observed in 6 of the 10 specimens.

CONCLUSIONS

These findings support the notion that in-stent restenosis results from SMC hyperplasia and suggest that adjunctive therapies designed to inhibit SMC proliferation may further enhance the utility of endovascular stents.

Restenosis of endovascular stents from stent compression

OBJECTIVES

We sought to determine the basis for restenosis within superficial femoral arteries (SFAs) and hemodialysis conduits treated with balloon-expandable stents.

BACKGROUND

Use of stents within coronary and peripheral vessels continues to increase exponentially. The mechanism of restenosis within stents placed at various vascular sites is not well understood. In particular, the implications of deploying a balloon-expandable stent in a compressible site are not well understood.

METHODS

After the serendipitous detection of stent deformation during intravascular ultrasound (IVUS) examination of a restenosed dialysis fistula, we evaluated a consecutive series of patients with stents placed in compressible vascular sites, including the SFA (six patients) and hemodialysis fistulae (five patients). Clinical, angiographic and IVUS examinations were performed to evaluate mechanisms of restenosis.

RESULTS

Stent compression was identified as the principal cause of restenosis in all dialysis conduits and SFAs. Stent deformity was not reliably identified by angiography; however, IVUS identified compression of two forms: eccentric deformation, implicating two-point compressive force, and complete circumferential encroachment of stent struts around the catheter, suggesting multidirectional compressive force. Despite redilation, secondary restenosis resulting from recurrent compression recurred in most sites.

CONCLUSIONS

Restenosis within balloon-expandable endovascular stents may occur as a result of stent compression, a phenomenon readily detected by IVUS, but often not by angiography. These findings have significant implications for the use of balloon-expandable stents within vascular sites subject to extrinsic compression, such as hemodialysis conduits, the adductor canal segment of the SFA and carotid arteries.

Elevated levels of basic fibroblast growth factor in patients with limb ischemia

Basic fibroblast growth factor (bFGF), a prototypic member of a family of heparin-binding growth factors, is angiogenic both in vitro and in vivo. Increased levels and activity of bFGF have been documented in a variety of diseases, including tumors. We sought to determine whether bFGF might be similarly elevated in patients with clinical evidence of limb ischemia. Serum was obtained at the time of percutaneous revascularization from patients with symptomatic peripheral vascular disease (46 procedures were performed on 40 patients). An enzyme-linked immunoassay specific for bFGF was used (limit of detection, 1 pg/ml; range in normal subjects, 0 to 5 pg/ml). Among the 40 patients (28 men, 12 women, mean age 70 years) studied, elevated circulating bFGF (> or = 10 pg/ml) was detected in 36 samples (78%); levels ranged from 10 to 310 pg/ml (mean +/- SEM = 62 +/- 12). In 16 (89%) of 18 patients with both rest pain and nonhealing ischemic ulcers, serum bFGF levels were elevated up to 30 times normal values. In conclusion, circulating levels of bFGF are elevated in patients with vascular insufficiency and may reflect a physiologic response to limb ischemia.

Clinical evidence of angiogenesis after arterial gene transfer of phVEGF165 in patient with ischaemic limb

BACKGROUND

Preclinical findings suggest that intra-arterial gene transfer of a plasmid which encodes for vascular endothelial growth factor (VEGF) can improve blood supply to the ischaemic limb. We have used the method in a patient.

METHODS

Our patient was the eighth in a dose-ranging series. She was aged 71 with an ischaemic right leg. We administered 2,000 micrograms human plasmid phVEGF165 that was applied to the hydrogel polymer coating of an angioplasty balloon. By inflating the balloon, plasmid DNA was transferred to the distal popliteal artery.

FINDINGS

Digital subtraction angiography 4 weeks after gene therapy showed an increase in collateral vessels at the knee, mid-tibial, and ankle levels, which persisted at a 12-week view. Intra-arterial doppler-flow studies showed increased resting and maximum flows (by 82% and 72%, respectively). Three spider angiomas developed on the right foot/ankle about a week after gene transfer; one lesion was excised and revealed proliferative endothelium, the other two regressed. The patient developed oedema in her right leg, which was treated successfully.

INTERPRETATION

Administration of endothelial cell mitogens promotes angiogenesis in patients with limb ischaemia.

Arterial gene transfer for therapeutic angiogenesis in patients with peripheral artery disease

The age-adjusted prevalence of peripheral arterial disease (PAD) in the U.S. population has been estimated to approach 12%. The clinical consequences of occlusive peripheral arterial disease (PAD) include pain on walking (claudication), pain at rest, and loss of tissue integrity in the distal limbs; the latter may ultimately lead to amputation of a portion of the lower extremity. Surgical bypass techniques and percutaneous catheter-based interventions may be used to successfully revascularize the limbs of certain patients with PAD. In many patients, however, the anatomic extent and distribution of arterial occlusion is too severe to permit relief of pain and/or healing of ischemic ulcers. No effective medical therapy is available for the treatment of such patients. The purpose of this clinical protocol is to document the safety of therapeutic angiogenesis achieved in this case by percutaneous catheter-based delivery of the gene encoding vascular endothelial growth factor (VEGF) in patients with PAD; and, as secondary objectives, investigate the bioactivity of this strategy to relieve rest pain and heal ischemic ulcers of the lower extremities. The rationale for this human protocol is based upon preclinical studies performed in a rabbit model of hindlimb ischemia. These studies are described in detail below and in the manuscripts enclosed in the Appendix to this proposal. In brief, a single intra-arterial bolus of VEGF recombinant human protein, delivered percutaneously to the ischemic limb via an intravascular catheter, resulted in angiographic, hemodynamic, physiologic, and histologic evidence of augmented collateral artery development. Subsequently, similar results were achieved using an angioplasty catheter with a hydrogel-coated balloon to deliver 400 micrograms of a plasmid containing the cDNA for VEGF to the internal iliac artery in the same animal model. Accordingly, we propose to administer arterial gene (VEGF) therapy to patients with rest pain and/or ischemic leg ulcers considered not to be candidates for conventional revascularization techniques. The dose of plasmid to be administered will be progressively escalated beginning with 500 micrograms for the first four patients, 1000 micrograms for the following six patients, 2000 micrograms for the third group of six patients, and 400 micrograms for the fourth group of six patients.

Focal compensatory enlargement of human arteries in response to progressive atherosclerosis. In vivo documentation using intravascular ultrasound

BACKGROUND

Previous postmortem studies have demonstrated compensatory enlargement of atherosclerotic arteries in animal models and patients. Conclusions regarding these changes were drawn based on a comparison of the dimensions of diseased arteries in one group of subjects with the dimensions of normal arteries in another group. This method admits potential confounding variables, such as demographics and other disease states, which might also have an impact on arterial size.

METHODS AND RESULTS

Using intravascular ultrasound, we studied a total of 62 paired, adjacent normal and diseased sites in the superficial femoral arteries of 20 patients undergoing peripheral vascular interventions. Morphological assessment was performed using a computer-based image analysis system. Measurements were made of the cross-sectional area of the arterial lumen, the atherosclerotic plaque, and the outer border of the artery. These dimensions were then compared to determine the effects of progressive atherosclerosis on arterial morphology. Luminal cross-sectional area decreased from 21.1 +/- 2.2 mm2 in normal segments to 16.7 +/- 0.8 mm2 (P = .0001) in adjacent atherosclerotic segments. Similarly, minimal luminal diameter decreased from 5.7 +/- 0.2 to 5.0 +/- 0.1 mm2, and maximal luminal diameter decreased from 6.2 +/- 0.2 to 5.7 +/- 0.2 mm2. At these same sites, total arterial area was 32.9 +/- 1.6 and 37.9 +/- 1.9 mm2 (P = .0001) in normal and diseased segments, respectively. Minimal and maximal arterial diameters demonstrated similar increases (7.3 +/- 0.2 to 7.7 +/- 0.2 mm2 [P = .0015] and 7.6 +/- 0.2 to 8.3 +/- 0.2 mm2 [P = .0001], respectively). Regression analysis disclosed correlation of the cross-sectional area of plaque to the total arterial area (R = .70, P = .0001).

CONCLUSIONS

Human arteries enlarge in response to progressive atherosclerosis. This compensatory mechanism results in an increase in arterial size that is proportionate to the cross-sectional area of plaque that has accumulated in the vessel. Intravascular ultrasound demonstrates that this process is focal compensatory enlargement at discrete sites of atherosclerotic narrowing immediately adjacent to more normal areas in which arterial size is smaller.

Combined physiologic and anatomic assessment of percutaneous revascularization using a Doppler guidewire and ultrasound catheter

Previous investigations have established the utility of intravascular ultrasound (IVUS) examination for the evaluation of arterial dimensions and qualitative changes following percutaneous revascularization. More recently, the feasibility of obtaining intravascular physiology findings before and/or after percutaneous revascularization by use of an intravascular Doppler Flowire (Cardiometrics) has been demonstrated. Accordingly, we investigated the feasibility of using this combined physiologic/anatomic approach to evaluate individuals undergoing percutaneous revascularization of stenotic or occluded coronary and peripheral arteries. A total of 76 patients were evaluated using the Flowire to guide an IVUS catheter. Revascularization of coronary and peripheral vascular stenoses and/or occlusions was achieved in these patients by balloon angioplasty, directional atherectomy, excimer laser angioplasty, and thrombolytic therapy, alone or in combination. Physiologic findings obtained with the Flowire reinforced conclusions regarding morphologic severity of candidate stenoses and anatomic adequacy of revascularization following IVUS examination. In certain ambiguous cases, information gained by one modality clarified information obtained with the other. Finally, one modality may also serve as an alternative when logistics preclude the serial use of both. The preliminary experience obtained in this feasibility trial confirmed that IVUS and the Flowire may be combined to assess both candidate lesions as well as postprocedural patency in patients undergoing percutaneous revascularization. The combination of anatomic and physiologic data available from IVUS and Flowire provides a far more sensitive and possibly more accurate analysis of the adequacy of revascularization than has been possible by angiography alone. The extent to which such a detailed investigation is required to optimize interventional therapy on a routine basis is the subject of subsequent investigations.

How does angioplasty work? Serial analysis of human iliac arteries using intravascular ultrasound

BACKGROUND

Previous studies regarding the mechanism by which balloon angioplasty increases luminal patency have generally used animal models or postmortem specimens from occasional fatal cases of angioplasty performed in human patients. In either case, conclusions regarding participatory mechanisms have relied exclusively on nonserial, postangioplasty histopathological examination.

METHODS AND RESULTS

In the present study, intravascular ultrasound examination was performed before and after balloon angioplasty in 40 consecutive patients with iliac artery stenoses. The areas of the arterial wall, plaque, lumen, and areas resulting from angioplasty-induced plaque fractures were measured immediately after angioplasty in vivo and compared with findings recorded immediately before angioplasty. Angioplasty increased luminal cross-sectional area (CSA) from 11.5 +/- 0.6 mm2 before angioplasty to 25.4 +/- 1.2 mm2 after angioplasty (p = 0.0001). CSA of the portion of the postangioplasty neolumen contained within angioplasty-induced plaque fractures measured 10.0 +/- 0.8 mm2; the neolumen excluding the area contributed by these plaque fractures measured 15.4 +/- 0.8 mm2. Thus, the area contained within plaque fractures accounted for 10.0 mm2 (71.9%) of the 13.9-mm2 increase in luminal CSA after angioplasty. Analysis of CSA occupied by atherosclerotic plaque disclosed that plaque CSA decreased from 33.8 +/- 1.8 mm2 before angioplasty to 22.5 +/- 1.5 mm2 after angioplasty (p = 0.0001). Plaque CSA was thus reduced ("compressed") by 11.3 +/- 1.1 mm2. Total artery CSA increased ("stretched") slightly from 45.3 +/- 2.6 mm2 before angioplasty to 47.8 +/- 2.0 mm2 after angioplasty (p = 0.0025).

CONCLUSIONS

In vivo analysis of iliac stenoses by intravascular ultrasound immediately before and after angioplasty demonstrates that plaque fractures and "compression" of atherosclerotic plaque are the principal factors responsible for increased luminal patency resulting from balloon angioplasty. "Stretching" of the arterial wall provides an additional, but minor, contribution.

In vivo assessment of vascular pathology resulting from laser irradiation. Analysis of 23 patients studied by directional atherectomy immediately after laser angioplasty

BACKGROUND

The pathological consequences of cardiovascular laser irradiation have been studied extensively in vitro. Previous in vivo studies of laser-induced injury have included analyses of acute and/or chronic findings in experimental animals. Little information, however, is available regarding the acute effects of laser irradiation of human vascular tissues in vivo.

METHODS AND RESULTS

To determine the acute pathology resulting from laser irradiation of human vascular tissue in vivo, specimens retrieved from 23 patients by directional atherectomy immediately after laser angioplasty (19 peripheral and four coronary) were examined by light microscopy. Of the 23 patients, three (13.0%) were treated with a metal-capped ("hot-tip") fiber coupled to a continuous-wave neodymium:yttrium-aluminum-garnet (Nd:YAG) laser using up to 18 W power and 18-305 seconds of cumulative exposure time; in all three patients (100%), thermal injury, including frank charring several cell layers thick, was seen along the luminal borders of the atherectomy specimen. In eight of the 23 patients (34.5%), laser angioplasty was performed using a 250-microseconds holmium:YAG laser at fluences up to 2,300 mJ/mm2, a repetition rate of 5 Hz, and 25-200 seconds of cumulative exposure; in seven of eight patients (85.5%), the atherectomy specimen showed signs of vacuolar injury consisting of central and satellite Alcian-blue-negative vacuoles. In two patients (25.0%), there was a "smudged" or "shredded" edge, whereas in one patient, frank signs of thermal injury were observed. Finally, in 12 of the 23 patients (52.2%), laser angioplasty was performed using a 120-nsec excimer laser at fluences up to 60 mJ/mm2, a repetition rate of 25 Hz, and a cumulative exposure time of 21-315 seconds. Pathological findings among these 12 patients were limited to nine patients (75%) in whom a weakly basophilic, smudged, and/or shredded appearance approximately one cell layer thick was observed along the luminal border of the atherectomy specimen and two patients (16.7%) with small foci of vacuolar injury. None of the atherectomy specimens retrieved after excimer laser angioplasty disclosed signs of thermal injury.

CONCLUSIONS

These findings document that acute pathological alterations resulting from in vivo laser angioplasty are variable, depending on the laser source used, and are similar to that predicted by experimental studies performed previously in vitro. The prognostic implications of these varying pathological features remain to be clarified.