(The New York Times News Service) -- A drug used to treat psoriasis may also relieve the depression and fatigue associated with the condition, researchers report.

And it may one day offer a new avenue of treatment for depression itself, the scientists say.

Etanercept, which goes under the brand name Enbrel, works by blocking a protein called tumor necrosis factor-alpha, which is produced by the body and promotes inflammation. High concentrations of TNF-alpha have also been linked to major depression, the researchers says.

"When people get a cold, infections, psoriasis, arthritis, they tend to feel bad and have low energy, they want to sleep more, they are moody and depressed," says lead researcher Dr. Ranga Krishnan, chairman of Duke University's department of psychiatry. "It has been shown that this is due to the elevation of cytokines such as TNF-alpha," he adds.

The question that Krishnan and his colleagues wanted to answer was whether blocking TNF-alpha could improve the symptoms of depression and fatigue.

To test the theory, Krishnan's team assigned 618 psoriasis patients to receive injections of 50 milligrams of etanercept twice a week for 12 weeks, or a placebo. After this period, the patients were all given etanercept for an additional 84 weeks.

The researchers found that after 12 weeks, 47 percent of the patients receiving etanercept had a 75 percent or greater improvement in their psoriasis, compared with 5 percent of those receiving a placebo.

In addition, patients receiving etanercept had a significant improvement in guilt, irritability, interest, appearance, work, sleep and sexual symptoms, compared with those receiving a placebo.

Patients receiving the drug also showed lower levels of fatigue.

Improvement was strongly related to the improvements in joint and skin pain caused by psoriasis, the researchers report.

The researchers noted that the improvement in depression was not correlated with improvement in symptoms. However, the study was not designed to detect the effect of etanercept on primary depression.

The study findings were published Wednesday in an early online edition of The Lancet.

People shouldn't consider getting TNF-alpha injections to fight depression based on this study, Krishnan says. "The next question is, if we treat people with depression without psoriasis, would it be a benefit," he says. "If it does, it opens up a whole new avenue of treating depression."

One expert thinks that relieving the symptoms of psoriasis is the reason that patients felt less depressed and less tired.

"There has been some data that the drug gives an increased feeling of well-being," says Dr. Jeffrey M. Weinberg, director of the clinical research center in the department of dermatology at St. Luke's-Roosevelt Hospital Center, in New York City. "But I think any therapy that improves psoriasis is going to improve depression and fatigue."

Weinberg adds that he doesn't think his psoriasis patients are depressed at the start of therapy. "But my patients are very happy when they are doing better," he says. "Not only can we improve the disease, but the disease also has a social-psycho impact, and successful therapy can positively impact that."

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