Epicardial gene therapy and laser revascularization

The role of periadventitial fat in atherosclerosis

CONTEXT

It has become increasingly evident that adipose tissue is a multifunctional organ that produces and secretes multiple paracrine and endocrine factors. Research into obesity, insulin resistance, and diabetes has identified a proinflammatory state associated with obesity. Substantial differences between subcutaneous and omental fat have been noted, including the fact that omental fat produces relatively more inflammatory cytokines. Periadventitial fat, as a specific adipose tissue subset, has been overlooked in the field of atherosclerosis despite its potential diagnostic and therapeutic implications.

OBJECTIVE

To review (1) evidence for the role of adventitial and periadventitial fat in vessel remodeling after injury, (2) the relationship between adventitial inflammation and atherosclerosis, (3) the association between periadventitial fat and plaque inflammation, and (4) the diagnostic and therapeutic implications of these roles and relationships for the progression of atherosclerosis.

DATA SOURCES

We present new data showing greater uptake of iron, administered in the form of superparamagnetic iron oxide, in the periadventitial fat of atherosclerotic mice than in control mice. In addition, macrophage density in the periadventitial fat of lipid-rich plaques is increased compared with fibrocalcific plaques.

CONCLUSIONS

There is a striking paucity of data on the relationship between the periadventitial fat of coronary arteries and atherosclerosis. Greater insight into this relationship might be instrumental in making strides into the pathophysiology, diagnosis, and treatment of coronary artery disease.

Enhanced neovasculature formation in ischemic myocardium following delivery of pleiotrophin plasmid in a biopolymer

Coronary heart disease is currently the leading killer in the western world. Therapeutic angiogenic agents are currently being examined for treatment of this disease. We have recently demonstrated the effective use of Pleiotrophin (PTN) as a therapeutic agent for treatment of ischemic myocardium. We have also shown that injection of the biopolymer fibrin glue preserves left ventricular geometry and prevents a deterioration of cardiac function following myocardial infarction. Due to the low transfection efficiency of naked plasmid injections, we examined the use of PTN plasmid and the biopolymer as a gene-activated matrix in the myocardium. In this study, we demonstrate that delivery of PTN plasmid in fibrin glue increases neovasculature formation compared to injection of the naked plasmid in saline.

Focal angiogenic therapy for myocardial ischemia

BACKGROUND

Therapeutic angiogenesis, which involves the administration of angiogenic cytokines to stimulate collateral formation and improve myocardial perfusion, is being tested as an alternative treatment for patients with medically intractable angina who are no longer candidates for conventional revascularization techniques.

METHODS

Administration of recombinant protein formulations for these growth factors and transfection of the DNA itself have proven effective in animal models. At present, transfection of the DNA (gene therapy) appears preferable in that a single administration achieves a prolonged but transient, localized exposure of the ischemic tissues to the angiogen. The important technical aspects of surgical gene therapy via a mini thoracotomy incision are described.

RESULTS

Four Phase I clinical trials of angiogenic therapy recently have been reported, two involving administration of the recombinant protein combined with coronary bypass and two involving gene therapy alone. These studies have shown that this approach is relatively safe; the early evidence of efficacy is encouraging. The largest study reported six-month follow-up on 30 patients who received plasmid DNA for vascular endothelial growth factor-165 (VEGF165) and documented improvement in angina, treadmill exercise tolerance, and myocardial perfusion in the majority of patients studied.

CONCLUSIONS

These preliminary results will need to be supported by randomized clinical trials in which angiogenic therapy alone is compared to standard medical therapy or a placebo. Catheter-based intramyocardial gene transfer and combined coronary arterial bypass grafting or transmyocardial laser revascularization plus gene therapy trials are also underway. If proven effective, angiogenic therapy may provide a relatively noninvasive modality for revascularization of ischemic myocardium not amenable to current techniques.