The lifelong fallout of a concussive brain injury is well-documented. A blow to the head – whether it comes from an NFL tackle, a battlefield explosion, or a fall off a ladder – can cause brain damage responsible for a debilitating degree of memory loss, mood swings, seizures, and more.
And though the blunt instrument that inflicts such damage is typically known, the cellular mechanisms that inflict such trouble have so far remained a mystery.
Now, a biology student at Stanford and researchers at the National Institutes of Health have devised a method for observing the immediate effects of a mild traumatic brain injury (TBI) in real time in mice. The work has revealed how individual cells respond to the injury and has helped the researchers suggest a possible therapeutic approach for limiting brain damage in humans.
The bulk of direct research concerning the physiological effects of TBIs is conducted post mortem. Scientists dissect a deceased patient's tissue to learn the full extent of the injury and what types of brain cells were damaged or killed.
But very little is known about what happens at the cellular level in the first hours after an injury, which has hindered the development of therapies that could prevent such damage from occurring in the first place.
For the past several years, Theo Roth (pictured), a senior majoring in biology at Stanford, has spent his summers and other academic breaks working in Dorian McGavern's lab at the National Institute of Neurological Disorders and Stroke (NINDS), part of the National Institutes of Health. In that time, Roth and other members of McGavern's research group designed a model in which they could inflict a specific injury to a mouse's brain and use an intracranial microscope to image individual cells, starting at 5 minutes after the injury.
"We can actually see how all the cell populations there react dynamically," said Roth, the first author on the research paper. "Then, knowing what the cells do – how they change function and morphology – we could piece together what their roles are and how they interact, and then what types of interventions might be relevant."
Evidence in humans
The brain's first line of defense is called the meninges, a thin layer of tissue that wraps the brain and creates a nearly impermeable barrier to harmful molecules. At the direct site of the injury, however, Roth found that the meninges can become damaged, tearing blood vessels and causing hemorrhaging. As cells in the meninges and other nearby tissues die, their toxic innards – in particular, molecules called reactive oxygen species (ROS) – can leak through the meninges onto healthy brain cells.
The brain tries to plug the holes in the meninges, Roth said, by quickly mobilizing special cells called microglia toward the site of the injury, a reaction that had never been seen in living brains before this study. The patch isn't perfect, however, and some ROS and other potentially toxic molecules still leak through to the brain cells. Within 9 to 12 hours after the initial injury, brain cells begin to die.
These observations were very similar to analysis of human MRI scans conducted by study co-author Lawrence Latour, a scientist from NINDS and the Center for Neuroscience and Regenerative Medicine.
Latour examined 142 patients who had recently suffered a concussion but whose initial MRI scans had not revealed any physical damage to the brain tissue. Many of these patients were sent home from the hospital with the negative scans, but had since suffered headaches, memory loss, or other hallmark symptoms of a mild brain injury.
Latour injected the patients with a dye and conducted a follow-up MRI scan; in 49 percent of these patients, Latour and his colleagues saw the dye leaking through the meninges. This, the study authors said, indicates that a similar process involving the meninges, microglia, and oxidative agents can play a role in causing neurologic damage in humans.
This realization could lead to devising emergency therapies.
A roadmap for treatment
The researchers began searching for ways to prevent the damage caused when ROS pass through the meninges. They zeroed in on a natural antioxidant molecule found in human cells called glutathione that can chemically neutralize ROS molecules.
By applying glutathione directly on the mouse's skull moments after the injury, the scientists were able to reduce cell death by 67 percent. Even applying glutathione 3 hours after the injury had a positive effect, reducing cell death by 51 percent.
"This idea that we have a time window within which to work, potentially up to 3 hours, is exciting and may be clinically important," said McGavern, the senior author of the study.
Furthermore, because applying glutathione directly to the skull minimized the damage, drug delivery via a subcutaneous patch might work as well as more invasive procedures.
There are several steps before the technique could be attempted in humans. The long-term effects in mice need to be measured and it must be determined whether effective amounts of glutathione or other therapeutic drugs can pass through the human skull.
"The acute phase of a traumatic brain injury is thought to be untreatable," Roth said. "But this is a promising start."
Roth isn't sure of his role in the next steps of this research; he is currently applying to dual MD-PhD programs with a goal of eventually working in academic medicine, most likely therapeutic research.
"It was an incredible experience for me," Roth said. "I was able to work in a lab –with advanced equipment and techniques – that was willing to have an undergraduate come in and do advanced independent work."
Illustration: Stanford University.
Stanford University News Release (12/11/13)
Science Daily (12/11/13)
Abstract (Nature; (12/08/13))