Everett Hodge

Comparative Effects of Basic Fibroblast Growth Factor and Vascular Endothelial Growth Factor on Coronary Collateral Development and the Arterial Response to Injury

BACKGROUND We have shown that the angiogenic peptides basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF) enhance canine coronary collateral development when administered for > or = 4 weeks. bFGF, a pluripotent mitogen of mesodermally derived cells, could theoretically exacerbate neointimal smooth muscle cell hyperplasia, a fundamental component of atherosclerosis. VEGF, an endothelial cell-specific mitogen and vascular permeability factor, could have deleterious effects related to vascular hyperpermeability. The present investigation had two aims: (1) to ascertain whether brief (7-day) systemic arterial treatment with bFGF or VEGF would improve myocardial collateral perfusion and (2) to determine whether these peptides induce neointimal accumulation in vivo. METHODS AND RESULTS Dogs were subjected to ameroid-induced occlusion of the left circumflex coronary artery and randomized to bFGF 1.74 mg (n = 9), VEGF 0.72 mg (n = 9), or saline (n = 10) as a daily left atrial bolus (days 10 to 16). Additional dogs were randomized to VEGF 0.72 mg (n = 6) or saline (n = 5); however, treatment was delayed by 1 week. Coincident with the institution of treatment, all dogs underwent balloon denudation injury of the iliofemoral artery. bFGF markedly increased maximal collateral flow but did not exacerbate neointimal accumulation. VEGF had no discernible effect on maximal collateral flow, but it exacerbated neointimal thickening after vascular injury. CONCLUSIONS Short-term treatment with bFGF enhanced collateral development without increasing neointimal accumulation at sites of vascular injury. Although VEGF did not increase collateral development as administered in this study, it significantly exacerbated neointimal accumulation. These data provide support for the clinical investigation of bFGF in selected patients with ischemic heart disease.

Effects of Chronic Systemic Administration of Basic Fibroblast Growth Factor on Collateral Development in the Canine Heart

BACKGROUND Recently we reported that intracoronary administration of basic fibroblast growth factor (bFGF), a potent angiogenic peptide, increases collateral blood flow in dogs subjected to progressive left circumflex coronary artery (LCx) occlusion. The aim of the present study was to examine the effect of systemically administered bFGF on collateral blood flow and to assess its pharmacokinetics and potential side effects. METHODS AND RESULTS Forty-seven dogs were subjected to progressive ameroid-induced occlusion of the LCx, an intervention known to induce the development of collateral vessels. In phase I of the investigation, dogs were randomized to receive bFGF 1.74 mg/d (n = 10) or saline (n = 9) as a left atrial injection for 4 weeks. Relative collateral blood flow was assessed serially with radiolabeled microspheres in the conscious state during maximal coronary vasodilatation. Initiation of bFGF treatment was temporally associated with a marked acceleration of collateral development; however, collateral flow in control dogs improved toward the end of the study, approaching that of bFGF-treated dogs at the 38-day end point. Phase II of the investigation was a three-armed study of extended duration to determine whether bFGF caused a sustained increase in collateral function. Dogs were randomized to receive bFGF 1.74 mg/d for 9 weeks (n = 7), bFGF 1.74 mg/d for 5 weeks followed by placebo for 4 weeks (n = 11), or placebo for 9 weeks (n = 10). Relative and absolute collateral blood flow were assessed serially with microspheres during maximal coronary vasodilatation. Between the 10th and 17th days after ameroid placement, bFGF-treated dogs exhibited marked improvement in collateral flow such that maximal collateral conductance exceeded that of controls by 24% at the 5-week crossover point. Final collateral conductance was similar in dogs receiving bFGF for 5 and 9 weeks despite withdrawal of treatment in the former group. bFGF administration was associated with a 21% increase in final collateral conductance as well as a 49% increase in collateral zone vascular density. Prolonged bFGF administration was also associated with a decrease in arterial pressure, moderate thrombocytopenia, and moderate, reversible anemia. CONCLUSIONS Systemic administration of bFGF enhanced collateral conductance in dogs with progressive single-vessel coronary occlusion. The beneficial effect of bFGF occurred primarily between the 7th and 14th days of therapy, and regression of collateral development was not noted after withdrawal of treatment. The present investigation provides impetus to the concept that collateral development can be enhanced pharmacologically-specifically by bFGF-raising the possibility that such an intervention might eventually be applied clinically.

Pharmacodynamics of basic fibroblast growth factor: route of administration determines myocardial and systemic distribution

OBJECTIVE We have shown that basic fibroblast growth factor (bFGF/FGF-2) enhances myocardial collateral development in a canine model of progressive coronary occlusion when delivered via the left atrial or intracoronary routes; however, we have found intravenous bFGF ineffective in the same model. Data on the fate and efficacy of intravenous bFGF are limited. We hypothesized that first pass lung uptake might limit myocardial bFGF availability after intravenous injection. We postulated that delivery of bFGF through the distal port of a wedged Swan Ganz catheter might circumvent this problem by restricting exposure of bFGF to a limited number of pulmonary binding sites. This study evaluated differential regional uptake of 125I labeled bFGF following bolus intravenous, Swan Ganz, left atrial, intracoronary, and pericardial delivery. METHODS Mongrel dogs were used. Human recombinant bFGF, monoiodinated with 125I, was mixed with cold bFGF to a specific activity of 0.03 microCi/microgram. Approximately 100 micrograms/kg was injected per animal by the intravenous, left atrial, Swan Ganz, intracoronary, or pericardial route. Dogs were killed 15 min or 150 min later. The heart, lungs, liver, spleen, and kidneys were harvested and 125I activity was assessed. Immunohistochemical and pharmacokinetic studies were also performed. RESULTS Serum half life of bFGF was comparable after intracoronary, intravenous and left atrial delivery (50 min); however, there were significant differences with regard to pharmacodynamics. After intracoronary administration, 3-5% of the total bFGF dose was recovered from the heart, with the peptide immunolocalized to the extracellular matrix and vascular endothelium. In contrast, only 1.3% of the injected bFGF was localized to the heart after left atrial administration and 0.5% was recovered after intravenous or Swan Ganz delivery. Pericardial administration resulted in substantial cardiac bFGF delivery; 19% was present at 150 min. Myocardial uptake was similar with Swan Ganz and intravenous delivery, suggesting that the administered dose did not saturate available pulmonary binding sites. CONCLUSIONS These data predict efficacy of intracoronary, left atrial, and pericardial bFGF for myocardial angiogenesis, and a lack of efficacy after bolus intravenous and Swan Ganz administration.

Adenoviral-mediated gene transfer induces sustained pericardial VEGF expression in dogs: effect on myocardial angiogenesis.

OBJECTIVE Angiogenic peptides like VEGF (vascular endothelial growth factor) and bFGF (basic fibroblast growth factor) have entered clinical trials for coronary artery disease. Attempts are being made to devise clinically relevant means of delivery and to effect site-specific delivery of these peptides to the cardiac tissue, in order to limit systemic side-effects. We characterized the response of the pericardium to delivery of a replication-deficient adenovirus carrying the cDNA for AdCMV.VEGF165, and assessed the effect of pericardial VEGF165 on myocardial collateral development in a canine model of progressive coronary occlusion. METHODS Ameroid constrictors were placed on the proximal left circumflex coronary artery of mongrel dogs. Ten days later, 6 x 10(9) pfu AdCMV.VEGF165 (n = 9). AdRSV.beta-gal (n = 9), or saline (n = 7) were injected through an indwelling pericardial catheter. Transfection efficiency was assessed by X-gal staining. Pericardial and serum VEGF levels were measured serially by ELISA. Maximal myocardial collateral perfusion was quantified with radiolabeled or fluorescent microspheres 28 days after treatment. RESULTS In AdRSV.beta-gal-treated dogs, there was extensive beta-gal staining in the pericardium and epicardium, with minimal beta-gal staining in the mid-myocardium and endocardium. Pericardial delivery of AdCMV.VEGF165 resulted in sustained (8-14 day) pericardial transgene expression, with VEGF levels peaking 3 days after infection (> 200 ng/ml) and decreasing thereafter. There was no detectable increase in serum VEGF levels. Maximal collateral perfusion, a principal correlate of collateral development and angiogenesis, was equivalent in all groups. CONCLUSION Adenoviral-mediated gene transfer is capable of inducing sustained VEGF165 expression in the pericardium; however, locally targeted pericardial VEGF delivery failed to improve myocardial collateral perfusion in this model.

Effect of basic fibroblast growth factor on myocardial angiogenesis in dogs with mature collateral vessels.

OBJECTIVES We sought to evaluate the potential of basic fibroblast growth factor (bFGF) to enhance coronary collateral perfusion in dogs with chronic single-vessel coronary occlusion. A secondary goal was to examine whether the salutary effects of bFGF treatment, previously proved effective in the short term, would be maintained in the long term (6 months). BACKGROUND bFGF, an angiogenic growth factor, is currently the subject of a Phase I trial in patients with ischemic heart disease. It has been shown to promote collateral development in dogs with progressive coronary occlusion when given during the period of natural collateralization. The effect of bFGF on quiescent collateral vessels, a subject of significant clinical importance, is uncertain. METHODS Dogs were subjected to ameroid-induced occlusion of the left circumflex coronary artery and randomized to bFGF (1.74 mg/day for 7 days), a regimen previously proved effective, or to saline solution. Maximal collateral perfusion was assessed 6 months later, and the dogs were reassigned to a course of bFGF or saline solution. Collateral perfusion was reevaluated after the second treatment course. RESULTS At 6 months, collateral function was identical in the groups treated initially with bFGF and saline solution. The subsequent course of bFGF did not induce further collateralization. CONCLUSIONS Although we previously demonstrated the salutary effects of this bFGF regimen in the short term (5 weeks), collateral flow in control dogs reached parity with that of bFGF-treated dogs after 6 months. bFGF did not induce further collateralization in dogs with mature collateral vessels, underscoring the priming role of ischemia for bFGF-induced collateral development.