Damage from a traumatic brain injury can continue well after the initial impact due to decreased blood flow and secondary harm to nerve cells. Two researchers are taking a closer look at these injury-related changes in the brain’s small blood vessels to learn how they occur and how to stop them.

 “Following traumatic brain injury, there is a disturbance in the microcirculation, in addition to neuronal damage. The vessels contract and dilate abnormally at different time points, which leads to disturbed supply of blood and, in general, oxygen to the brain,” explained Theodor Petrov, MD, PhD, assistant professor of anatomy and cell biology. That decrease in oxygen and other vital metabolites, such as glucose, can result in additional neuronal loss. He and José Rafols, PhD, professor of anatomy and cell biology, recently received a $1 million, three-year grant from the National Institutes of Health to study the problem.

In particular, they are interested in substances produced by some of the cells that make up the walls of these blood vessels. “These specific cells, called endothelial cells, produce active substances that lead to abnormal constriction or abnormal dilation. We are studying these substances and have focused on two molecules that have a significant effect on microvascular contractility,” Dr. Petrov said.

The two substances are nitric oxide (NO) and endothelin-1.

Dr. Rafols explained that blood flow in the brain is unique in that the nervous system doesn’t control it directly. Instead, NO and endothelin-1 play against each other to determine the diameter of the blood vessels and adjust flow. Nitric oxide is a powerful vasodilator that causes the vessels to open wider, allowing more blood to flow through them. Endothelin-1 is the opposite. It is one of the most effective vasoconstrictors in the entire body. Brain injury upsets the normal balance between the two and disrupts blood flow.

Drs. Petrov and Rafols are investigating the molecular and cellular mechanisms responsible for the production of the two substances, as well as the genes that regulate their production. For the latter, they are developing so-called anti-sense oligoprobes to help them ultimately seek out the genetic instructions (the messenger RNA) that tell the cell how to make the two substances. Once they learn enough about the chain of events from messenger RNA to protein synthesis, Dr. Petrov said, “We propose to genetically manipulate the system to reduce the abnormal upregulation of the genes that encode for these two molecules.” In other words, the cells wouldn’t be able to make abnormal amounts of NO and endothelin-1, because they would no longer have access to those genetic instructions. “This is called a genetic therapeutic approach,” Dr. Petrov said.

The two researchers also plan to learn more about the receptors that react with endothelin-1, and about an injury-induced enzyme that may be important in NO overproduction. One of the ways to assess NO, a diffusable gas, is to study the expression of the three enzymes that regulate its synthesis. These enzymes are called NOS, or nitric oxide synthases. Healthy organisms only express two of the three enzymes, with the third – named inducible NOS, or iNOS – occurring only after a brain injury. Their research will target this enzyme.

“The problem with NOS is that it can also generate large amounts of nitric oxide and produce toxic effects to brain cells,” Dr. Rafols said. “So if nitric oxide is upregulated excessively, it ultimately will damage the nerve cells.”

Through these different research paths, Dr. Rafols said their work will provide important insights into the control of microcirculation in the brain both normally and following traumatic brain injury, and hopefully offer new therapies for brain-injury patients.