A Potential New Approach to Preventing Stroke Damage
A compound already used to treat severe sepsis could open up a whole new approach for treating stroke, the leading cause of long-term disability in the nation. The research, reported in the March issue of Nature Medicine, shows that a compound known as activated protein C or APC directly protects brain cells that normally die as a result of a stroke by curbing the cells' auto-destruct program.
The research, led by Berislav Zlokovic of the University of Rochester and John H. Griffin of The Scripps Research Institute (TSRI), opens up a new vista in a field where effective treatments are scant. While scientists have known some of the molecular players that contribute to stroke damage, studies with APC up to now have focused on other effects of the compound, such as its ability to stop the growth of blood clots and reduce inflammation. The new work is surprising because it points to an unsuspected ability of APC to directly prevent programmed cell death, which has quietly emerged over the past several years as the key to reducing the effects of stroke.
"This compound is working in a completely unexpected wayit gives us a new pathway to consider in assessing the damage done by stroke," says Zlokovic, who is director of the Frank P. Smith Laboratories for Neurological Surgery Research in addition to his position at the University of Rochester. "Since there is currently really only one effective treatment for stroke which reaches only a small percentage of patients, we're hopeful that this finding will spur further research that could help people who will otherwise have lifelong disability due to a brain attack."
The research was published online on Monday, February 3. The scientists showed that, in mice that had strokes, more than 65 percent of the brain cells that normally would die after a stroke survive because of APC. The compound reduced the neurological impact of stroke by 91 percent.
"Stroke is a huge problem," says Griffin, a biochemist and professor of molecular and experimental medicine at TSRI. "It's the third leading cause of death in this nation. The morbidity and sadness for people who survive strokes is overwhelming. If a new therapy could reduce the damage that a brain attack causes, that would be extremely valuable."
A stroke occurs when blood flow in the brain is interrupted, cutting off part of the brain from oxygen. Some brain damage happens immediately, but even when blood flow is restored, brain cells continue dying for hours or days. The initial shock from the lack of oxygen stuns brain cells; those that don't die immediately are plunged into a Hamlet-like "to be or not to be" drama, where cells decide whether they can survive or whether they're so damaged that they should kill themselves, in a process known as apoptosis, for the overall good of the body.
It's during this live-or-die drama after a stroke that APC inserts itself, the team shows in the Nature Medicine paper. APC dramatically decreases the cellular signals that convince brain cells to kill themselves after a stroke, and boosts the cellular signals that persuade the cells to survive. With APC, pro-suicide signals dwindle, and anti-suicide or anti-apoptosis signals increase.
With funding from the National Heart, Lung, and Blood Institute, Zlokovic and Griffin's team found that APC has a direct impact on a molecule known as p53, which is central to the downward spiral that envelops a cell which has been exposed to low-oxygen conditions. Normally in such cells, high levels of p53 are central to a biochemical cascade that results in compounds that literally chew up a cell's insides. The team discovered that APC works through two cellular receptors, EPCR and PAR-1, to cut the level of p53 in damaged cells by 75 percent and also boosts the proportion of other signals telling a cell to survive.
Currently there is one treatment available for stroke, a compound known as tPA (tissue plasminogen activator). TPA is useful for the 80 percent of strokes that involve a blood clot, but only if the patient is treated within a few hours. And tPA actually kills some brain cells. Someday physicians might be able to use a compound like APC to prevent damage for more than the few hours that tPA works, or even to minimize the brain damage that tPA itself causes.
"I'm cautiously optimistic that APC will prove to be extremely useful in treating ischemic stroke in patients," says Griffin. "These are very exciting results."
Griffin has had previous experience seeing such basic research on APC become clinically relevant. Twenty-five years ago, Griffin was one of the first scientists to purify protein C, contributing to a body of knowledge about the compound that led to its use to treat severe sepsis. Later he discovered two genetic disorders linked to a lack of APC, diseases that can now be treated because of his discoveries.
In addition to Zlokovic and Griffin, other authors of the recent Nature Medicine paper include Tong Cheng and Dong Liu of the University of Rochester, and Jose Fernandez of TSRI. Key materials for the experiments were provided by Francis Castellino and Elliot Rosen of the University of Notre Dame and Kenji Fukudome of Saga Medical School in Japan. Some experiments were done in collaboration with Socratech Laboratories, a Rochester start-up company founded by Zlokovic.
"Stroke is a huge problem. It's the third leading cause of death in this nation. The morbidity and sadness for people who survive strokes is overwhelming. If a new therapy could reduce the damage that a brain attack causes, that would be extremely valuable."
John H. Griffin