Genomic analysis may one day be a primary diagnostic tool for physicians deciding on a course of treatment for trauma and other critically ill patients in the intensive care unit (ICU), according to a new study by a national collaboration of more than 70 physicians and scientists.
The researchers showed that state-of-the-art techniques for rapidly analyzing changes in activity of all human genes will likely produce useful insights into the health of critically ill patients. The findings, which are available online and will be published in the March 29 issue of the Proceedings of the National Academy of Sciences, make it possible for physicians to begin answering important questions about critical care through genomic analysis.
"It's a very exciting time because our field has experienced such frustration with some of these questions, many of which have important ramifications for how we treat patients," says J. Perren Cobb, M.D., the paper's lead author and associate professor of surgery and of genetics at Washington University School of Medicine in St. Louis.
Nearly 5 million people are admitted to U.S. ICUs every year, and preliminary 2003 National Centers for Disease Control statistics cite accidental injuries and trauma as the fifth leading cause of death for that year. However, despite significant advances in organ support technology, physicians' ability to predict whether or not a given patient will respond to a specific course of treatment has been poor. To address these and other questions, countries such as Canada and Germany have established networks for research in critical care.
The new study, conducted by Cobb and his colleagues in the Inflammation and Host Response to Injury Large Scale Collaboration Program, is a significant step toward establishing such a U.S. research network.
Scientists tested two aspects of applying genomic technology in the ICU: Could the technology detect significant differences in the activity levels of genes in critically ill patients versus healthy patients? And could they establish testing procedures that would prevent local differences in ICUs and research laboratories across the United States from introducing noise or bias into the results?
"We wanted to make sure that we could consistently get the same results from an analysis regardless of where the sample was gathered," Cobb explains.
Researchers applied DNA microarrays, a genomic analysis technology, to blood samples and skeletal muscle from 34 severely injured patients and 23 healthy individuals. Critically ill patients were studied at the University of Washington, Seattle and the University of Rochester. Healthy patients were studied at Washington University at the University of Florida, the University of Rochester, and the Robert Wood Johnson Medical School of the University of Medicine and Dentistry of New Jersey.
Scientists identified key aspects of microarray testing procedures that were vital to obtaining results that could be reproduced regardless of where the studies were conducted, an essential criterion for rigorous science. The protocols they established also move researchers closer to being able to enroll large number of patients in longitudinal studies.
They also showed that genetic analysis technology has achieved levels of sensitivity and resolution sufficient to "see" dramatic changes in gene activity levels that take place in cells in the critically ill. Such changes in gene activity can, for example, reprogram white blood cells, immune system cells that circulate in the bloodstream. This reprogramming alters the relative populations of the different types of white blood cells and the genes they express. One white blood cell, the neutrophil, normally makes up 40 to 60 percent of circulating white blood cells but rises to comprise 80 to 90 percent after critical injury. The new approach will allow the investigators for the first time to monitor neutrophil gene activity genome-wide in injured patients.
In the new era of genetically based critical care research, one focus will be developing a better understanding of how these cells and other factors control inflammatory responses to severe injury.
"It has been clear for approximately two decades that critical injury can trigger the release of immune factors that cause massive inflammation, and this can sometimes overwhelm the body's ability to cope," Cobb says. "We have produced a great deal of insight into how those inflammatory responses are generated, and we've tried a number of strategies to block or weaken them, but so far we've had relatively little success."
As scientists' picture of how multiple genes interact to produce inflammatory responses becomes more complete, they may be able to develop more effective ways to dampen those responses and save lives.