In experiments with mice, RBP4 decreases insulin sensitivity of muscle and liver tissue, which is considered a precursor to diabetes, Chun said.
"It is still not clear whether RBP4 regulates insulin sensitivity by controlling retinoic acid metabolism or by directly acting on muscle or liver cells," Chun said. "The drug Fenretinide, which is shown to lower RBP4 levels, has been already used as a chemotherapeutic agent for cancer. The side effects of the drug, however, need to be carefully weighed against its possible benefit for metabolic diseases."
In another report published in the same issue of the journal, a research team led by Bruce Spiegelman of the Dana-Farber Cancer Institute in Boston identified a gene called PRDM16 that regulates the production of so-called "brown fat" in mice. Brown fat is a type of fat that actually generates heat and counters obesity caused by overeating.
"Brown fat is present in mice and in human infants, where it keeps them warm by dissipating food energy as heat, instead of storing it as 'white' fat," Spiegelman said in a prepared statement. "Human adults don't have much brown fat, but there is some, and from a therapeutic perspective, the question is whether that pathway can be reactivated."
The researchers hope their discovery will lead to new ways of treating obesity in humans.
For more information on risks for heart disease, visit the American Heart Association.
SOURCES: Barbara B. Kahn, M.D., chief, Division of Endocrinology, Diabetes and Metabolism, Beth Israel Deaconess Medical Center; Tae-Hwa Chun, M.D., Ph.D., Department of Internal Medicine, Metabolism, Endocrinology and Diabetes, University of Michigan, Ann Arbor; July 10, 2007, news release, Dana-Farber Cancer Institute; July 2007 Cell Metabolism