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Tiny Bubbles in My Veins?

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WebMD Health News

June 6, 2000 -- It's not exactly what Don Ho envisioned when he sang "Tiny Bubbles": Floating tiny bubbles to the heart and other organs via the circulatory system, then using ultrasound technology to pop them once they reach their destination so they can deliver drug or gene therapy right to the targeted tissues.

Smaller than red blood cells -- so there is no risk of them blocking blood vessels -- the bubbles would be injected into a vein. Once they arrive at the desired location, they would be popped, or imploded, by ultrasound waves. This implosion would enable the drug or gene to enter the cells.

A researcher who has helped to develop the so-called microbubble technique, Evan Unger, MD, of the University of Arizona and president of ImaRx Therapeutics, presented his findings at an Acoustical Society of America meeting in Atlanta. Microbubbles already are being used for medical diagnosis, but not for therapy. In fact, Unger's company developed microbubble diagnostic tools that were subsequently sold to Du Pont. Now his firm, along with some others, is focusing on using the bubbles for treatments.

Unger tells WebMD the technique is a promising avenue to site-specific drug delivery or gene therapy. The basic idea is that by targeting the ultrasound onto a tumor, for example, the drug attacking the tumor can be much more concentrated.

And microbubbles aren't just for drugs. In a study in rats, published in Circulation: Journal of the American Heart Association, researchers used the technique to deliver genes to the heart.

"It is possible to use ultrasound-mediated microbubble destruction to deliver genes and other small [agents that are active in the body] directly to the heart," says study author Paul A. Grayburn, MD. "This method is noninvasive and could avoid the systemic side effects of medications that are administered by conventional methods, oral or IV."

Researchers also are studying delivery of genes using a virus, but this is problematic because the infection is delivered not only to the target organ but to other tissues as well. In hopes of achieving organ-specific gene delivery, Grayburn and colleagues introduced a test gene into microbubbles and injected them into the veins of laboratory rats. Then, using ultrasound, they burst the bubbles once they reached the heart. The virus then attached and expressed the gene into the heart muscle, without infecting surrounding tissues.

The heart is not the only organ that could benefit from this "tiny bubble" technology, Grayburn tells WebMD. "Theoretically, this technique could be used to treat any kind of disease in an organ or tissue that is accessible by ultrasound. It should work best for treatments that only require gene expression for a limited time period, because the body is very efficient at recognizing and eliminating foreign DNA," says Grayburn, a professor of internal medicine at the University of Texas Southwestern Medical Center in Dallas and chief of cardiology at Dallas VA Medical Center.

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