"The originator of the entire process is hydrogen peroxide, which we also know as a bleaching agent," explains Professor Heinz Decker of the Institute of Biophysics at Mainz University. "With advancing age, hydrogen peroxide builds up in larger amounts in the hair follicle and ultimately inhibits the synthesis of the colour pigment melanin."
Hydrogen peroxide - or H2O2 by its chemical formula - is a by-product of metabolism, and as such it is generated in small amounts throughout the human body, consequently also in hair follicles. With increasing age, the quantity builds up, because the human body can no longer keep up neutralising the hydrogen peroxide using the enzyme catalyse, which breaks down hydrogen peroxide into its two components water and oxygen. In their work, the scientists showed that in aging cells this enzyme is still present but in very limited concentration.
This has dramatic consequences. Hydrogen peroxide attacks the enzyme tyrosinase by oxidising an amino acid, methionine, at the active site. As a consequence, this key enzyme, which normally starts the synthesising pathway of the colouring pigment melanin, does not function anymore. Oxidation by hydrogen peroxide not only interferes with the production of melanin, but also inhibits other enzymes that are needed for the repair of damaged proteins. As a result, a cascade of events is set off, at the end of which stands the gradual loss of pigments in the entire hair from its root to its tip.
With this research work, the scientists from Mainz and Bradford not only solved - on a molecular level - the age-old riddle of why hair turns gray in old age, but also have pointed out approaches for future therapy of vitiligo, a skin pigment disorder. For melanin is not only the pigment in hair, but it is also responsible for colour in skin and eyes.
MEDICA.de; Source: Johannes Gutenberg-Universität Mainz