Irisin, the hormone of physical activity

Harvard scientists discover a key substance in the healthy effects of sport and search for a drug that mimics its activity | Used as a drug, it could improve the treatment of diabetes and obesity

A newly discovered hormone released during physical activity helps you burn calories efficiently even after you've finished exercising. The hormone clarifies why physical activity improves the health of people with diabetes or obesity and, given as a drug, could improve the treatment of these patients. The researchers who have discovered it, from Harvard Medical School (USA), have created a company that will develop a drug from the hormone.

The Harvard team had shown in previous research that when you engage in physical activity, muscle cells produce a protein called PGC1-alpha. This protein has several positive effects on the muscles themselves. However, exercising is not only healthy for the muscles, but for the whole body. It remained to discover what are the mechanisms by which physical activity improves metabolism beyond the muscles.

«There was a feeling, in this scientific field, that exercise speaks to various tissues in the body. "The question was how?" said Bruce Spiegelman, director of the research, in a statement released by Harvard Medical School.

In an elegant series of experiments presented yesterday in the journal Nature, Spiegelman's team has shown that a hitherto unknown hormone is secreted from the PGC1-alpha protein. This hormone reaches the white fat cells (or bad fat, since its excess is harmful to health) through the blood and helps them to become brown fat (or good fat, since it is beneficial).

So striking is the effect of this hormone that its discoverers have called it irisin, in reference to the Greek goddess Iris, the messenger of the gods. Irisin is presented as the hormone that carries a health message from muscle to fat.

In experiments with mice, Harvard researchers have found that physical activity raises the level of irisin in the body. They have also found that when obese mice are injected with irisin, their metabolism becomes more efficient, so they burn more calories even if they continue to eat as much and move as little as before; therefore, irisin could be effective for the treatment of obesity. Equally important, the mice injected with irisin had improved control of their blood sugar level; therefore, irisin could also be effective for the treatment of diabetes.

These results "open a very interesting and hopeful panorama," said yesterday Anna Nuvials, director of the diabetes and obesity laboratory at the Idibaps research institute at the Hospital Clínic. "We have run out of medications to help these patients lose weight and we are all waiting for something new." But Nuvials warned that we must wait to see how research progresses to know if irisin can become a useful drug for people.

For now, Harvard researchers have observed that physically active people have higher levels of irisin than sedentary people. And that "mouse irisin and human irisin are 100% identical," as they write in Nature. But it remains to be seen if the benefits observed in mice are repeated in people and if the hormone, administered as a drug, has acceptable side effects.

The pharmaceutical company Ember Therapeutics, founded by Bruce Spiegelman himself, has begun development of a drug based on irisin. Based on the researcher's calculations, clinical trials in people could start within two years.

In future experiments, Spiegelman plans to also study which types of physical activity produce a more pronounced increase in irisin in healthy people.