Any guesses as to why leptin would work like insulin?
In the experiment reported in the new paper, Dr. Unger’s team injected genetically modified viruses that infected the rodents’ liver cells and turned them into leptin-producers.
In a matter of days, the wasting effects of excess glucagon stopped and blood sugar levels dropped near normal. After a few weeks, the leptin levels went down and the blood sugar levels went back up — but not nearly as high as for untreated mice. And the otherwise fatal high-glucagon symptoms never returned, even after almost a year.
A few scientists have thought that leptin was involved with the balance between insulin and glucagon and a few earlier experiments had used leptin along with insulin on rodents, but this is the first to show results without insulin, Dr. Unger said.
“Leptin seems to do everything that insulin does — and with a more prolonged effect,” Dr. Unger said.
Among the many questions left for researchers:
Will the leptin work without the potentially risky modified viruses? The next planned rodent experiment would use simple leptin injections.
Will the effects fade over time? Some of the rodents from the earlier tests are still alive and the researchers are watching.
Does the leptin control blood sugars enough to stave off the long-term effects of diabetes? If not, Dr. Unger says there are other possible adjunct treatments to consider.
But there are no promises that this work will ever produce practical treatments, Dr. Unger said. He’s been disappointed before. In the 1970s, he worked with another protein called somatostatin that seemed to offer a new treatment for diabetes, but the effect was too short-lived.
