No worry that this secret will leak.

Mosquito bites, arthritic joints, and broken ankles cause swelling, in part, because plasma leaks from abnormally porous blood vessels. Angiopoietin-1 (Ang1), a recently discovered protein that enhances blood vessel growth, also appears to protect blood vessels from leaking.

Gavin Thurston of the University of California, San Francisco and his colleagues genetically engineered mice to express higher-than-normal amounts of Ang1 or another protein, vascular endothelial growth factor (VEGF), which also promotes blood vessel growth. They then measured leakiness of blood vessels by injecting the mice with blue dye and rubbing their ears with mustard oil, which stimulates nearby blood vessels to leak.

Normal mouse ears showed bluing around the edges, indicating that a little dye had leaked, Thurston says. Ears of mice that the researchers genetically manipulated to produce extra VEGF turned completely blue, he reports in the Dec. 24, 1999 SCIENCE. Mice that made both extra Ang1 and VEGF showed slightly blue ears, while the Ang1 mouse ears stayed white.

"We are trying to figure out how Ang1 works," says Thurston. Several groups are examining whether VEGF can restore blood flow to areas where it has been blocked (SN: 11/28/98, p. 346). Thurston suggests that Ang1 might prevent leaking of the new vessels that VEGF promotes. The next step is to see whether Ang1 can reduce plasma leakage in animals that haven't been genetically altered. Such research could lead to treatments for human diseases in which swelling plays a role, such as arthritis and asthma, says Thurston.