A lab test that could tell if a patient responds to antidepressants within a few days of starting therapy could soon be available, say US researchers.
The test would be based on measurement of a protein called Gs alpha, which acts as a biomarker for depression.
This protein is involved in the signalling processes responsible for the action of neurotransmitters such as serotonin, which play a key role in depression.
Previous research has shown that a proportion of Gs alpha proteins are caught up in lipid rafts within the cell membrane that hold it trapped and make it unable to act.
Research in rats has shown that administration of antidepressants frees the protein from these lipid rafts, facilitating neurotransmitter release.
Researchers measured the amount of the protein in lipid rafts in cells taken from the pre-frontal cortex and cerebellum of 16 people who had committed suicide. These were compared with cells taken from 16 people who had died with no history of psychiatric illness.
The controls and the suicide cases had the same overall amount of Gs alpha proteins in the cell membranes. However, a greater proportion of the protein was confined to lipid rafts in the depressed cases.
Lead researcher, Professor Mark Rasenick, an expert in physiology, biophysics and psychiatry at the University of Illinois at Chicago, said: 'This study shows that in depressed humans, Gs alpha protein is confined in lipid rafts, where it is less likely to mediate the action of neurotransmitters, and that antidepressants have the opposite effect.'
He added that you could test for depression by measuring the proportion of Gs alpha protein trapped in lipid rafts.
'With this test, we may be able to tell you if you are depressed and more importantly, whether you are responding to the chosen antidepressant therapy,' said Professor Rasenick.
'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.'
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