A high-pressure solution can significantly improve the delivery of therapeutic DNA into cells without the need for virus carriers. The discovery, reported in tomorrow Proceedings of the National Academy of Sciences , could help improve the chances of success of cardiovascular transplants and other operations.
A type of gene therapy called antisense therapy, designed to interfere with the expression of certain unwanted genes. the base by base, scientists build a short strand of DNA that exactly matches a portion of the gene's DNA sequence. Inside a cell, the antisense sequence binds to and inactivates the gene messenger RNA that normally direct the cellular machinery to produce the corresponding protein. Cardiologists, among them surgeon Michael Mann and colleagues at Harvard Medical School in Boston, showed that the use of antisense DNA to block the genes associated with graft rejection and disease can significantly improve the success surgery in laboratory animals. The challenge was to develop a way to circumvent the immune system and cell defenses and deliver foreign DNA to good cells.
A preferred technique for delivering foreign DNA into cells is to use a modified virus as the messenger. Mann and his team have a different approach. They removed over 100 rat hearts and filled the cavities of the heart and blood vessels with a saline solution containing an antisense sequence designed to block a gene for an inflammatory protein. After bathing the heart for 30 minutes at pressures up to 2 atmospheres, they transplanted hearts again in rats. Three days later, they found that half the nuclei of cardiac cells had taken the antisense DNA. Delivery rates with other techniques, including modified viruses have rarely exceeded 30%.
When researchers have tried this high pressure perfusion technique on the veins of the human legs, 0% of cell nuclei took antisense DNA, and production of inflammatory proteins dropped. Researchers still do not why the method works, but it may simply involve more effective dissemination and, perhaps, the changes induced by the pressure in the cell and nuclear membranes.
The results impress experts gene therapy. "I think it's great," says Gary Nabel, director of the National Institutes Vaccine Research Center of Health, who worked on cardiovascular gene therapy. The technique is particularly interesting, he says, because "it can be simplified and put into practice in the operating room," where surgeons could manipulate transplanted tissue as needed. Nabel also believes that high-pressure solutions could be adapted for use in gene therapies that provide replacement genes to cells, possibly without removing the body tissues.
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