American scientists identified a substance in blood as a biomarker for depression and pointed to a new class of antidepressants that could be freer of side effects and faster-acting than those in current use.
People with depression have low blood levels of acetyl-L-carnitine (LAC), a nutritional supplement that is being sold in drugstores, according to a study published on Monday in the Proceedings of the National Academy of Sciences.
Those with severe or treatment-resistant depression, or whose bouts of depression began earlier in life, have particularly low blood levels of the substance, according to the study.
Natalie Rasgon, a professor of psychiatry and behavioral sciences at Stanford University School of Medicine, described the findings as "an exciting addition to our understanding of the mechanisms of depressive illness."
Also, the study showed that oral or intravenous administration of LAC reversed the animals' symptoms and restored their normal behavior.
In Rasgon's study in collaboration with researchers from the Rockefeller University, the animals responded to LAC supplementation within a few days while current antidepressants typically take two to four weeks to kick in, both in animal experiments and among patients.
The animal studies suggested that LAC, a crucial mediator of fat metabolism and energy production throughout the body, played a special role in the brain, where it worked at least in part by preventing the excessive firing of excitatory nerve cells in brain regions called the hippocampus and frontal cortex.
The new study recruited 71 men and women who had been diagnosed with depression. Twenty-eight of them were judged to have moderate depression, and 43 had severe depression.
In comparing their blood samples with those of 45 healthy people, the depressed patients' LAC blood levels were found to be substantially lower.
Additional analysis revealed that patients with very low LAC exhibited more severe depression and were more likely to develop depression early in life.
The researchers also found that decreased LAC was associated with having a history of childhood trauma and treatment-resistant depression, particularly in women.
However, Rasgon cautioned against rushing to the store to pick up a bottle of LAC and self-medicating for depression.
"We've identified an important new biomarker of major depression disorder. We didn't test whether supplementing with that substance could actually improve patients' symptoms," said Rasgon. "This is the first step toward developing that knowledge, which will require large-scale, carefully controlled clinical trials."