November 21, 1997 ... Toronto researchers have found that a gene critical for weight control does not contribute to diabetes as previously thought. Leptin is a weight-regulating hormone that is normally produced in the body's fat cells. Leptin administration induces weight loss, and the hormone is currently being tested in clinical trials as a weight-control drug in obese patients. The drug, however, is also known for inhibiting insulin secretion, a known risk factor for exacerbation of diabetes.
A research team led by Dr. Daniel Drucker, an endocrinologist at The Toronto Hospital and a member of the University of Toronto Banting and Best Diabetes Centre, has shown in animal studies that leptin improves insulin sensitivity and glucose control. The results, published today in the December issue of Diabetes, contrast previous studies which suggested leptin may, in fact, antagonize insulin action and indirectly contribute to diabetes. "Our study clearly shows that in spite of leptin's inhibitory regulation of insulin, the net effect of leptin treatment is to significantly lower blood glucose," Dr. Drucker says. "This is good news for people who may be candidates for leptin treatment and have diabetes. We have found that leptin treatment is, in fact, beneficial for patients with diabetes: leptin causes insulin to work more efficiently and the diabetes is improved."
In the study, mice with diabetes were treated with leptin for two weeks. Although leptin reduced levels of insulin in the mice, the glucose (blood sugar) levels were still significantly lower in the leptin-treated group. "The study shows that the net overall dominant effect of leptin in diabetes is to improve insulin sensitivity and insulin action," Dr. Drucker says.
Diabetes is best described as a disease of defective energy balance. The food we eat is largely broken down by our digestive system into sugar, fat and amino acids. The sugar circulates through the body as blood glucose which is needed for fuel and energy. To accomplish this, however, a hormone called insulin must be present. Insulin is produced in the pancreas. But in people with diabetes, the pancreas produces insufficient amounts or none at all, or the body's tissues may be resistant to insulin action. When this happens blood glucose rises and passes out of the body through urine. The body then turns to less efficient sources of energy and a catabolic state ensues.