Not just bleach: Hydrogen peroxide may tell time for living cells

PLoS ONE study finds possible timekeeping roles for the common chemical made naturally by the body

If a circadian rhythm is like an orchestra – the united expression of the rhythms of millions of cells – a common chemical may serve as the conductor, or at least as the baton.

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

A study published in the journal PLoS ONE shows 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.

Tower's study suggests a link between metabolism – the production of energy by mitochondria, often described as the energy factories inside cells – and an animal's daily 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 behavior."

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.