Indian researchers have for the first time got proof for the association between cholesterol-lowering medications and depressive disorder in people on these drugs to prevent heart attack.

They discovered that cholesterol-lowering drug may have an effect on the activity of a brain chemical, which controls mood as well as behavior and thereby trigger nervousness and depression.

Cholesterol, a wax like substance, is the main offender in heart problem. Even though the human body requires it, a high level of serum cholesterol leads to blockage of coronary arteries thereby reducing circulation of blood to the heart muscles resulting in heart failure.

A class of drugs known as 'statins' that lower the cholesterol level -- by inhibiting a key enzyme responsible for its biosynthesis in the body - are the highest selling drugs in the global market and in clinical history with an estimated sale of 25 billion USD annually. They are extensively used as oral drugs to treat "hypercholesterolemia."

Although they are very effective in reducing cholesterol levels in humans, there is a growing concern that chronic use of statins causes depression and anxiety in patients.

Amitabha Chattopadhyay at the Centre for Cellular and Molecular Biology in Hyderabad said, "In the last few years, a number of publications in medical journals have reported apparent symptoms of anxiety and major depression in patients upon long-term statin administration."

Why should change in the level of a small greasy molecule in the body lead to changes in complex behavioral manifestations such as mood and anxiety has been a puzzle and there has been no molecular evidence to explain this till date.

However, a paper by Chattopadhyay's group just published in the journal Biochemistry sheds light into the association between use of statins and mood disorders. The researchers have shown that chronic cholesterol diminution by statins harms the function of the receptors for serotonin, a neurotransmitter in the brain that controls mood and behavior.

Chattopadhyay's group has earlier shown that maintaining normal cholesterol levels is vital for the function of cell membrane receptors for serotonin. Their newest researcher showed that cholesterol depletion in the brain affects the function of serotonin receptors leading to depression and anxiety.

The researchers presented that this in a test-tube experiment by researching the effect of statin on human serotonin receptors expressed in animal cells called "Chinese Hamster Ovary" cells.

Their results showed that long-term treatment with the drug caused significant changes in the structure and function of serotonin receptors. Adding cholesterol to cells treated with statin restored the function of the receptor to normal level. (With Inputs from Agencies)