4-Hydroxynitrophenylacetic acid (RNS marker)

Marker of nitrosative stress caused by reactive nitrogen species (RNS). Raised values occur with mitochondrial damage, chronic inflammation and NO dysregulation.

What 4-hydroxynitrophenylacetic acid shows

4-Hydroxy-3-nitrophenylacetic acid is the nitrated form of 4-hydroxyphenylacetic acid, a breakdown product of the amino acid tyrosine that is largely produced by gut bacteria and from plant polyphenols. Reactive nitrogen compounds – above all peroxynitrite, which is formed from nitric oxide and superoxide, and nitrogen dioxide – attach a nitro group to the ring of this acid. At the same time it is an important breakdown product of free 3-nitrotyrosine, which is released when nitrated proteins are turned over. The acid is water-soluble and is excreted via the kidneys in urine; its content in urine therefore reflects how much nitration takes place in the body overall.

Low 4-hydroxynitrophenylacetic acid – what does it mean?

A low value shows that few nitrated tyrosine compounds are being formed: nitric oxide fulfils its tasks as a messenger, and superoxide dismutase neutralises superoxide before it reacts with NO to form peroxynitrite. Because the value also depends on how much precursor gut bacteria and tyrosine breakdown supply, it is considered in connection with other markers of oxidative and nitrosative stress.

High 4-hydroxynitrophenylacetic acid – what happens in the body?

A high value shows that more tyrosine structures are being nitrated in the body. Peroxynitrite and other reactive nitrogen compounds alter not only this small acid but also proteins, fats in membranes and DNA; enzymes of the respiratory chain with their iron-sulphur centres are particularly sensitive, so the mitochondria produce less ATP. At the same time NO is used up, which is then lacking for widening the blood vessels. Raised values occur when immune cells produce a lot of NO and superoxide during inflammation, with exposure to smoking or nitrogen oxides from the air, and when a lot of nitrite from food forms nitrating compounds in acidic gastric juice; an altered gut flora that supplies more precursor can also raise the value.

The interpretation is given in your report.