April 1, 2009

Enzyme acts as molecular depression switch

U.S. researchers say they've identified, for the first time, an enzyme that is essential to the onset of depressive symptoms caused by chronic inflammation.

The University of Illinois scientists identified the enzyme IDO (indoleamine 2,3 dioxygenase) as a molecular switch that induces depressive symptoms in some cases.

Physicians have long known patients with chronic inflammation, such as coronary heart disease or rheumatoid arthritis, are more likely than others to become depressed, the researchers said, and some pro-inflammatory drugs are also known to induce symptoms of depression in a significant number of patients.

In the new study, mice were exposed to Bacille Calmette-Guerin, a tuberculosis vaccine that produces low-grade, chronic inflammation in mice, the researchers said. The mice exposed to BCG display the normal symptoms of illness, but after those symptoms fade the mice continue to exhibit depressive-like behaviors that can be reversed with anti-depressants.

Professors Keith Kelley and Robert Dantzer, who led the study, said the finding highlights IDO as a potential target for development of new antidepressant drugs.

The study is detailed in the Journal of Immunology.