Recently, a research team led by Barbara B. Kahn, MD, head of the diabetes division at Beth Israel Deaconess Medical Center, showed that rising RBP4 levels predict insulin resistance. Insulin resistance is an early sign of type 2 diabetes and rising heart disease risk.
Another major risk factor for diabetes and heart disease is deep belly fat. Doctors call this accumulation of fat around the organs of the abdomen "visceral adiposity." Could belly fat explain the link between RBP4 and diabetes/heart disease risk?
To find out, Kahn's team joined forces with researchers Matthias Blüher, MD, and colleagues at the University of Leipzig, Germany. They obtained deep belly fat samples from 196 German patients undergoing abdominal surgery. Sixty-six study participants were lean and 130 were obese.
- There was 60 times more RBP4 gene activity in the belly fat of obese patients than in the belly fat of lean patients.
- Blood levels of RBP4 were two to three times higher in obese patients than in lean patients.
- Regardless of whether a patient was lean or obese, higher blood levels of RBP4 meant more deep belly fat and more insulin resistance.
"This suggests a potential role for RBP4 as a convenient marker not only for type 2 diabetes but also for [heart disease] risk," the researchers conclude in the July issue of the journal Cell Metabolism.
The body uses RBP4 -- retinol (vitamin A)-binding-protein 4 -- to carry vitamin A in the blood. In a news release, Kahn says it's not yet clear whether these newly discovered roles for RBP4 are due to vitamin A or to the protein itself.
In earlier studies, Kahn and colleagues showed that RBP4 causes insulin resistance in mice. If it works the same way in people, it might be the target of new diabetes drugs. Interestingly, a cancer drug called fenretinide reduces RBP4 levels. In obese mice, this drug improves insulin sensitivity and blood sugar tolerance.
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