DALLAS, March 31 -- A gene therapy approach to circumvent leg blood vessels obstructed by atherosclerosis that was reported last fall at the American Heart Association's Scientific Sessions has been successfully extended to a larger group of patients.
The research findings on this treatment, called therapeutic angiogenesis, are reported in today's Circulation: Journal of the American Heart Association.
The treatment, used to grow new blood vessels to bypass obstructions of blood flow in the legs of people with critical limb ischemia, was devised and is being evaluated by Jeffery Isner, M.D., at St. Elizabeth's Medical Center in Boston.
Critical limb ischemia occurs when the blood circulation in the individual's legs has become obstructed by atherosclerosis, the same disease process that creates the fat-filled plaques that clog coronary arteries, the blood vessels feeding the heart.
Isner, senior author of the Circulation paper, presented findings on the use of the gene for human vascular endothelial growth factor (VEGF) on eight patients with critical limb ischemia at the AHA conference last November. The paper reports on these eight patients.
Since submitting the paper, he has treated a total of 29 patients and in the process found two other unexpected results of the therapy.
Patients with premature atherosclerosis -- an inflammatory disease of the blood vessels of the legs which usually strikes young men -- respond well to the gene therapy. Isner says this finding is intriguing since these patients have generally been considered to be unresponsive to any therapy.
In addition, patients with sensory neuropathy -- acute loss of feeling in the feet -- have also benefited from the gene therapy. "This is surprising since a sensory neuropathy secondary to reduced blood flow to the feet, has traditionally been considered irreversible," says Isner, professor of medicine and pathology at Tufts University School of Medicine and chief of cardiovascular research at St. Elizabeth's Medical Center.
Isner's findings about premature atherosclerosis and sensory neuropathy are not specifically presented in the journal paper.
About two-thirds of the treatments for critical limb ischemia has been successful, according to Isner and he says that figure is "encouraging, since none of them had other treatment options." If the gene therapy had not been effective, the patients would have had their afflicted legs amputated. As research continues, Isner hopes to improve the success rate of gene therapy for people with critical limb ischemia.
Since submitting the paper to Circulation, Isner has been evaluating this gene therapy to grow blood vessels to bypass obstructed heart arteries. Two people have been treated.
"Both are doing fine, but both are still less than one month post-treatment so no follow-up tests have yet been done," says Isner. "I think all we can say is that the procedure itself has gone fine."
The effectiveness of the gene therapy was gauged by before and after clinical assessments which included diagnostic angiogram, which produces an image that shows blood flow in vessels; magnetic resonance angiography; measurement of the ankle-brachial pressure; and, if possible, exercise testing.
In the published study results, in eight of the 10 treated legs, improved blood flow was demonstrated by magnetic resonance imaging. Angiograms showed evidence of newly visible vessels in seven of the 10 treated limbs.
At follow-up examinations, one to six months after the last injection, blood pressure in the individuals' ankles had increased from 0.33 to 0.47 ankle index. "The blood pressure in the ankle and the arm should be equal," explains Isner.
The gene for this growth factor, which was derived from a human pituitary tumor, is being replicated in Isner's laboratory at St. Elizabeth's Medical Center, which funded the clinical trials of initial eight patients in the study.
For the injections, the gene was not attached to a virus or another "Trojan horse" medium to transport the DNA inside the cell. The "naked" DNA was administered twice, four weeks apart. A total dose of 4,000 micrograms of the "naked" DNA of what is known as the 165-amino-acid isoform of human vascular endothelial growth factor (phVEGF165) was injected directly into the muscles of the afflicted leg.
Doses of 500 micrograms each of VEGF pDNA were diluted in a sterile saline solution. In each patient, 2,000 micrograms of the growth factor were injected into the calf or thigh muscles of the diseased leg. During the course of the study, the volume of the injections was progressively increased from 0.75 milliliters in the first three treatments to 3 milliliters in the next six treatments to finally 5 milliliters in the last 11 treatments.
Four weeks after the first 2,000-microgram injection, a second 2,000-microgram injection was made, increasing the total amount of growth factor to 4,000 micrograms per patient.
Patients were followed up on a weekly basis within the first eight weeks after initiation of the treatment and at monthly intervals thereafter.
Co-authors are Iris Baumgartner, M.D.; Ann Pieczek, R.N.; Richard Blair, M.D.; Orit Manor Ph.D.; Marianne Kearney, B.S. and Kenneth Walsh, Ph.D.
Media advisory: Dr. Isner can be reached at (617) 789-2392. (Please do not publish telephone number.)