Scientists have stumbled upon a drug that may prevent heat stroke for people prone to the deadly condition. Ironically, it's the same drug flaunted three years ago as the "couch potato pill" for its ability to build muscle and increase endurance in mice that never break a sweat.
The study appears today (Jan. 8) in the journal Nature Medicine.
As with the 2008 couch potato study, the researchers have only tested the drug, abbreviated as AICAR, in mice. However, the drug was 100-percent effective in preventing death in these mice genetically engineered to be susceptible to heat stroke. Thus, the finding has implications for anyone exposed to heat or with abnormal heat sensitivity, the researchers said.
Heat stroke is caused by prolonged exposure to temperatures over 100 degrees Fahrenheit (37.8 degrees Celsius), and it is common among the elderly and athletes. Many U.S. soldiers in Iraq and Afghanistan suffered from heat stroke brought on by high temperatures and heavy gear.
Some people have a genetic disorder called malignant hyperthermia that places them at high risk for heat stroke, even without the heat. The disorder is associated with a mutation in the RYR1 gene, which causes uncontrolled muscle contractions and increases in body temperature, typically induced by certain drugs such as general anesthesia.
Researchers led by Susan Hamilton at Baylor College of Medicine in Houston studied the effects of the drug AICAR on mice with this RYR1 mutation. When these mice exercise in a hot room, they suffer the hallmarks of malignant hyperthermia and die.
Hamilton's group was inspired by the 2008 AICAR study, published in the journal Cell, which demonstrated how AICAR slowed muscle fatigue and increased muscle endurance. They wondered whether AICAR could control the muscle contractions typical of the RYR1 mutation, but in this case triggered by heat not anesthesia.
Sure enough, AICAR prevented an otherwise sure death in all the mice exposed to heat, even those mice given AICAR just 10 minutes before exercising.
While RYR1 mutations only account for a small percentage of heat stroke cases in the general human population, AICAR might offer broad protection, said Robert Dirksen, a study author at the University of Rochester Medical Center in Rochester, N.Y.
"We think the fundamental process that occurs during heat stroke in individuals with RYR1 mutations is likely to be similar to what happens ... by exposure to even greater temperatures or a longer time" in people without the mutation, Dirksen said. "Our study takes an important first step towards developing a new drug therapy that may be part of the standard treatment regimen for heat stroke."
Although promising, much more research is needed on AICAR and heat stroke, the scientists said, noting that the "couch potato" pill for humans has not come to fruition.