Washington, Mar 12 : Researchers from the University of Illinois at Chicago College of Medicine have found a biomarker for depression that could lead to a quick lab test to identify patients suffering from the blues.
According to the researchers, the discovery could also help in determining whether a particular antidepressant is making headway against the problem.
"This test could serve to predict the efficacy of antidepressant therapy quickly, within four to five days, sparing patients the agony of waiting a month or more to find out if they are on the correct therapeutic regimen," said Mark Rasenick, UIC distinguished university professor of physiology and biophysics and psychiatry.
Rasenick said that the discovery could help millions of people who suffer from undiagnosed depression or receive unsuccessful treatment.
"We discovered that in depressed individuals a signaling protein is located in specific areas of the cell membrane called lipid rafts," he said.
The protein, called Gs alpha, activates adenylyl cyclase, a link in signal transduction, and is responsible for the action of neurotransmitters such as serotonin.
"These 'rafts' are thick, viscous, almost gluey areas, that either facilitate or impede communication between membrane molecules," Rasenick said.
"When Gs alpha is caught in these lipid raft domains, its ability to couple with and activate adenylyl cyclase is markedly reduced. Antidepressants help to move the Gs alpha out of these rafts and facilitate the action of certain neurotransmitters," he added.
In previous studies, Rasenick and his colleagues, as well as others, haave shown that Gs alpha changed its location in response to antidepressants, moving out of the lipid rafts to areas of the membrane that allow more efficient communication among membrane components responsible for neurotransmitter action.
In addition, antidepressant and antipsychotic drugs have been shown to concentrate in these lipid rafts.
"This new study shows that in depressed humans, Gs alpha protein is confined in lipid rafts, where it's less likely to mediate the action of neurotransmitters, and that antidepressants have the opposite effect," Rasenick said.
"In simple language -- we may be able to tell you if you are depressed and more importantly, whether you are responding to the chosen antidepressant therapy," he added.
According to the researchers, the new study might also provide an explanation to why antidepressants take so long to work and why chemically dissimilar compounds have similar effects.
For the study, brain samples of depressed people who had committed suicide were compared with controls that never had psychiatric disorders.
Rasenick and colleagues found that while the total amount of Gs alpha was the same in the depressed and non-depressed, the depressed have a greater proportion of Gs alpha confined to lipid rafts. The localization of other G proteins was not different.
The researchers have started further studies to confirm and expand these findings. The study is published in the March 12 issue of the Journal of Neuroscience.