Hormone may be heart-healthy insulin substitute

Type 1 diabetics may soon have a more heart-friendly way to control blood sugar.

A new study in mice shows that leptin, a hormone produced by fat cells, lowers blood sugar as well as insulin does; but unlike insulin it does not increase cholesterol levels. The finding could quickly lead to improved treatment for type 1 diabetes, also known as juvenile diabetes.

Leptin and insulin worked equally well to lower blood sugar levels in diabetic mice, and using a combination of the two hormones allowed researchers to dramatically decrease the amount of insulin mice needed, Roger Unger of the University of Texas Southwestern Medical Center at Dallas and colleagues report in a paper to be published online this week in the Proceedings of the National Academy of Sciences.

The new results are “game-changing,” says Sanjoy Dutta, director of insulin research at the Juvenile Diabetes Research Foundation International in New York City.  “It’s a brilliant finding.”

Currently, diabetics must inject relatively high doses of insulin to control blood sugar. But extra insulin revs up production of lipids such as cholesterol, which can lead to cardiovascular disease, a common problem for people with diabetes.

Although mice treated with leptin alone fared just as well in the new study as animals on insulin alone, Dutta says human patients likely won’t be able to give up insulin altogether — at least not any time soon. Researchers would first have to show that leptin can safely replace insulin in people as it does in mice. In the meantime, using insulin and leptin together may reduce the heart and circulatory complications that accompany type 1 diabetes.

Leptin therapy may not be effective, though, for the more than 90 percent of diabetics in the United States who have type 2 diabetes, previously known as the adult-onset form. Many of these diabetics already have high leptin levels due to obesity, so researchers say it is not clear whether taking more leptin would treat that form of the disease.

“[Leptin therapy] should be viewed with cautious optimism, Dutta says. “Leptin is not a cure, and to say that we can do away with insulin would be blasphemous at this point.”

In an earlier study, Unger and his colleagues engineered adult mice with type 1 diabetes to make more leptin. The mice were essentially cured of their diabetes (SN Online 8/25/08). Now, the researchers show that injected leptin can substitute for insulin without requiring gene therapy.

Unger says his group hopes to begin human studies of leptin therapy in combination with insulin.