and the vessels will grow toward each other. Take away the barrier and the vessels will fuse.

"I think, for me, the beauty and the wonder in the life sciences is taking a small cell which then grows into a big thing," Bein says.

Pathologist Radu Stan, M.D., is also fascinated with how cells work, especially in angiogenesis. "What I do is I look at how molecules go from the blood to the tissues and vice versa—in normal tissues and in clinically significant settings, such as inflammation and tumors," he says. He's investigating the endothelial structures—particularly the openings known as caveolae, transendothelial channels, fenestrae, and vesiculo-vacuolar organelles—that are involved in vascular permeability. He also discovered PV-1, a protein that is upregulated in acute and chronic myocarditis.

Stan is a willing collaborator with the other researchers and often shares his knowledge of cell biology techniques, such as purification protocols and fractionation. "We have collaborations in which I have them set up experiments by which they could pursue their molecules—everybody has a favorite molecule," he says conspiratorially. "This goes both ways. I'm doing experiments that I was discussing with Nick Shworak. He helped me figure out something. That's how things work."

While the basic research on genes, molecules, and cells is important, there comes a point where the scientists have to see what's going on in living bodies. Ebo de Muinck, M.D., runs the Angiogenesis Center's preclinical research labs and is developing imaging techniques that will make it possible to see angiogenesis in live animals. He uses methods like echocardiography, Doppler technology, magnetic resonance imaging, electroparamagnetic resonance imaging, and 3-D imaging.

The preclinical labs rely on mice and other small mammals for thir research. Karen Moodie, D.V.M., a veterinarian and a member of the preclinical lab team, makes sure that precautions are taken to guard against pain and suffering in the animals used for research.

Top: Kiflai Bein, second from the left, gets input from other researchers on the progress of his lab's work. Above Right: Arie Horowitz. Above Left: Radu Stan, left, and Mike Simons.

Mice are useful research models because they are very similar genetically to humans. Scientists can breed "knock-out" strains of mice to see whether blood-vessel growth is affected when certain genes or proteins are missing. But mice are small, their hearts beat 600 times a minute (compared to human hearts, which beat only about 70 times a minute), and blood moves through mice so quickly that it's difficult for imaging agents to illuminate their vessels unless very rapid scanners are used. That's because the blood vessels in mice are too small for the iodine-containing contrast agents used in humans to work. Zhenwu Zhuang, M.D., is trying to develop contrast agents that are safe and effective to use in small animals.

Meanwhile, de Muinck's lab is exploring ways to stimulate new blood-vessel growth in mice. The researchers first create a blockage by tying off part of a blood vessel in a hind leg or the heart. New vessels begin to grow in the border between the infarcted and the healthy tissue. The researchers can identify the new growth by way of targeting peptides that stick to molecules expressed only on actively growing blood vessels. De Muinck explains that he plans to "use nanoparticles that are decorated with these targeting peptides to deliver drugs to these new blood vessels, so we can stimulate their growth. [Later] we can come back again with targeted nanoparticles—but this time the particles

carry an imaging molecule—so we can measure the extent to which we have increased the number of new blood vessels."

He points out that such imaging nanoparticles could also be useful in detecting new blood vessels in tumors. Of course, angiogenesis-stimulating drugs would only be tested on patients for whom cancer has been ruled out.

Justin Pearlman, M.D., the director of Dartmouth's Advanced Imaging Center, also shares his expertise with the Angiogenesis Research Center. Animals that need to be imaged are placed in a microinsert, which is a tube that goes inside the larger tubes of MRI or CT scanners. Dartmouth is one of the few medical centers anywhere that does angiogenesis imaging. "There are other places doing perfusion-sensitive imaging," a technique that is also done at DHMC, says Pearlman.

Nationwide, there are approximately 175 active angiogenesis clinical trials—testing angiogenic as well as anti-angiogenic agents—according to the NIH's ClinicalTrials.gov Web site. At least 15 of those trials are being conducted at Dartmouth—five by investigators affiliated with the Angiogenesis Research Center and at least 10 by cancer researchers.

Just as plant roots grow toward water, laboratory-bred blood vessels grow toward other vessels in response to chemical signals, explains Kiflai Bein.

One of the Dartmouth trials involves testing the blood of people with coronary artery disease to determine if there are genetic differences between people who have a natural ability to grow new blood vessels and those who don't. "Some patients are very efficient at making their own collateral arteries so are able, in the presence of narrowing of their coronary arteries, to open up new blood vessels that are really arteries that perfuse the ischemic territories," says de Muinck. "We already are noticing some differences between the genes that are switched on in the white blood cells from the patients with collateral, versus the white blood cells from the patients without collateral."