Injections of a hormone naturally produced by fat cells can reduce the severity of diabetes and related disorders in mice, two teams of scientists report in the August issue of Nature Medicine. The findings also show that the hormone, called adiponectin, plays an active role in regulating blood sugar levels.
Nearly 16 million Americans, almost 6% of the population, have diabetes--an inability to control the blood levels of sugar called glucose. People with type 1 diabetes lack the hormone insulin, which helps cells absorb blood sugar. Insulin also keeps sugar balanced by preventing excess amounts from leaving storage areas in the body, such as the liver. In type 2 diabetes, insulin is present, but cells don't respond. This insulin "resistance," recent studies have shown, develops both in people who are obese and those with very little fat. Because fat tissues are the sole producers of adiponectin, researchers had proposed that the hormone may play a role in metabolism.
Probing the link between adiponectin deficiency and metabolic disorders like diabetes and obesity, researchers from the Albert Einstein College of Medicine in New York City injected adiponectin into wild-type mice, diabetic mice, and obese diabetic mice. The team found that the injections normalized the elevated blood levels of glucose in the mice. In addition, the researchers observed that adiponectin regulated the production of glucose by rat liver cells--suggesting that the hormone helps suppress the release of sugar stores.
Meanwhile, a team at the University of Tokyo also injected mice with adiponectin and saw the same reduction in insulin resistance. However, Takashi Kadowaki and colleagues found that they could completely reverse insulin resistance by injecting mice with both adiponectin and the hormone leptin (another protein produced by fat cells). The two papers "offer a glimpse at the possible physiological roles" for adiponectin, perhaps leading to treatments for both obesity and diabetes, says cell biologist Philipp Scherer, who led the Albert Einstein team.
"If correct, the data are very exciting," says cell biologist Alan Saltiel of the University of Michigan School of Medicine. Much remains to be learned, including the hotly debated mechanisms behind adiponectin's effect. But at least one genomics company, Genset of Paris, France, is already planning clinical trials of the hormone.