Pressure sensitive

2019-03-08 06:14:04

By Jonathan Knight in San Francisco A NEW gene therapy technique could boost the chances of heart bypass patients. Heart specialists in Massachusetts and California have used high pressure to force antisense DNA into the cells of blood vessels before they are implanted. The first human patients to have the DNA-treated implants are doing well. Surgeons bypass most blockages in the heart with a segment of vein taken from the patient’s leg. But within five years, a third of the grafts are blocked, because moving the vein switches on genes that cause abnormal cell growth and inflammation. “You’re asking a vein to work as an artery,” says Michael Mann of Brigham and Women’s Hospital in Boston, one of the authors of the study. Previous studies in rabbits have shown that knocking out these genes before implanting the vein can help the bypass resist atherosclerosis. In the rabbit study, the researchers used a virus to deliver antisense DNA that bound to transcripts of the problem genes, preventing their translation into proteins. But there are concerns about using viruses for gene therapy in humans. Inactivated viruses could mutate and become dangerous. Also, viruses are not very efficient at delivering the DNA to the smooth muscle cells of the vein. Now Mann and Victor Dzau, also at Brigham and Women’s Hospital, and their colleagues at Stanford University in Palo Alto have tried a new approach. They put short segments of human vein into a small plastic cylinder and added a solution of DNA fragments capable of binding to the interleukin-6 gene, one of the genes that causes inflammation. Then they briefly doubled the pressure by pumping more solution into the container. After allowing the vessels to recover, the researchers examined thin slices under the microscope. They found that the antisense DNA, labelled with a fluorescent dye, glowed in the nuclei of 90 per cent of the cells. They also confirmed that the procedure had blocked the interleukin-6 gene. Cultures of the vessels contained only a third of the normal amount of protein (Proceedings of the National Academy of Sciences, vol 96, p 6411). Mann thinks the pressure may allow the DNA to enter by altering the normal structure of the cell membrane. Getting DNA into tissues evenly, as Mann and Dzau have done, has been one of the major obstacles to successful cardiovascular gene therapy, says Keith March of Indiana University in Indianapolis: