DALLAS — A longtime diabetes researcher at University of Texas Southwestern Medical School is setting up human tests for a new treatment he says might have fewer side effects than standard insulin therapy.

Dr. Roger Unger, chairman of diabetes research at the school, is quick to warn a novel method that worked in mice with Type 1 diabetes may not help people.

“You can’t make any claims until the tests have been done,” he said.

The tests using leptin, a natural hormone produced by fat cells, would build on results of experiments performed by Unger’s research team and published Monday in a major scientific journal, Proceedings of the National Academy of Sciences

The paper, titled “Leptin monotherapy in insulin dependent type 1 diabetes,” describes studies done on diabetic mice. The journal cites the new paper as “reporting findings of exceptional interest.”

The new work is a follow-up to a paper published in 2008 by Unger’s team that reported about diabetic mice and rats that were genetically modified to produce extra leptin and thrived without insulin. The 2008 paper was the research equivalent of a talking dog — startling even to experts, whether or not it said anything practical.

Genetic modification is not an option for humans, so Unger’s team next tried treating mice using a technique well-known to people with diabetes: leptin injections delivered by a pump. Not only did the leptin-treated mice thrive, Unger said, but they did so without some of the side effects familiar to people using insulin.

“I think (this) paper is much bigger, because the last one was just academic,” said Unger, 85, who has been researching diabetes for more than 50 years. “This is a translatable paper into something that might be useful for people. The other was not.”

Unger’s team has been ready to start testing leptin on people for almost a year, he said. The hospital is prepared, they have an ample supply of potential volunteers, and they’ve lined up funding. What’s holding the process up, Unger said, is getting the manufacturers of leptin to set up the logistics to guarantee the supply.

“We thought it would happen six months ago,” he said. “And it hasn’t happened yet.”

Why is his claim about leptin such a surprise? Since 1921, when researchers first linked what is now known as Type 1 diabetes to a lack of insulin, doctors have assumed the only successful treatment replaced insulin, usually through multiple daily injections. Insulin is used by more than a million Type 1 diabetics in the United States.

Unger and other diabetes experts agree leptin is a long way from becoming a practical treatment. Dr. Barbara Kahn, a diabetes expert at Harvard Medical School and chief of endocrinology at Beth Israel Deaconess Medical Center, was asked to co-author a commentary to run with Unger’s new paper.

Among the challenges Kahn says leptin therapy might face:

• Mice snack frequently on slow-digesting food. People eat meals a few times a day. Leptin levels that kept blood sugar stable in mice may not be able to handle the rapid ups and downs in blood sugar created by the human eating pattern.

• The mice used in the tests had a shortage of leptin. Most Type 1 diabetics have normal leptin levels. The amount of additional leptin needed to control blood sugar in people may induce significant side effects that are more damaging than those associated with insulin.

• Extra leptin could make it harder for a Type 1 diabetic to be aware of the dangerous condition of low blood sugar — and make it harder to return low blood sugar to normal levels.