Chemical that regulates circadian rhythm identified

Washington, Nov 8 : Scientists from University of Southern California have identified a chemical that appears to play a vital role in regulation of body's circadian rhythm.

The chemical is hydrogen peroxide (H2O2), the active ingredient in colour safe bleach. Produced in all animal cells, hydrogen peroxide may act as a signal for the active and resting phases of living things.

The study showed that hydrogen peroxide given to fruit flies has dramatic effects on their daily rhythms and activity levels.

'H2O2 might be functioning as a systemic signal by which rhythms are regulated within cells and between cells,' said lead author John Tower, associate professor in molecular and computational biology at the USC College of Letters, Arts and Sciences.

Most people are familiar with the concept of a circadian rhythm that governs sleeping and waking. But that is not the only circadian rhythm in the body.

Many organs and tissues within the body have their own independent circadian rhythms, and they also interact to coordinate their rhythms.

Mitochondria produce hydrogen peroxide as a by-product of oxygen combustion, making the chemical a candidate signal molecule.

'This is a logical way to connect rhythms to metabolism,' Tower said. 'We know a lot about how circadian rhythms are regulated within certain cells. However, we have very little information on what signals coordinate circadian rhythms and how these rhythms are linked between metabolism and behaviour.'

For the rhythms of even two cells to agree, some sort of signal has to pass between them.

Tower's research group set out to find the signal by probing the action of an enzyme in mitochondria that converts toxic by-products of the body's combustion process into hydrogen peroxide, itself a harmful but less toxic substance which other defenses later break down further.

Tower and his team had noticed that overexpression of the enzyme, known as superoxide dismutase (SOD), boosted the activity level of fruit flies and even increased the life span of certain genetically engineered strains.

Tower suspected that hydrogen peroxide was the key ingredient in SOD's action.

'Hydrogen peroxide is a great candidate for a signaling molecule that would be involved in rhythms and behaviors. It's the most stable and diffusible of the reactive oxygen species (by-products of combustion), but no one had demonstrated a role for it,' the expert added.

The study is published in the journal PLoS ONE.