8-OHdG: the pathway in the body

This page shows the biochemical pathway behind the laboratory value 8-OHdG (8-hydroxy-2'-deoxyguanosine): which stations follow one another, which enzymes carry out each step and which cofactors they use. Every statement has a source. The page describes general textbook knowledge and says nothing about any individual person.

In brief

8-OHdG is a fragment of the DNA base guanine that has been oxidised by oxygen radicals. Cells cut such building blocks out of DNA or remove them from the nucleotide pool; the fragments pass into the urine.

The pathway step by step

1. Oxygen → Superoxide Respiratory chain When oxygen picks up a single electron, superoxide forms – a radical, meaning a molecule with an unpaired electron. Source 1
2. Superoxide → Hydrogen peroxide SOD1, SOD2 · Manganese, Copper and zinc The superoxide dismutases convert two superoxide molecules into hydrogen peroxide and oxygen. SOD2 works in the mitochondrion with manganese, SOD1 in the cytoplasm with copper and zinc. Source 2
3. Hydrogen peroxide → Water Catalase, GPx · Glutathione, Selenium Catalase and glutathione peroxidase break hydrogen peroxide down into water. Glutathione peroxidase carries selenium in its active site. Source 2
4. Hydrogen peroxide → Hydroxyl radical Fenton reaction · Iron (Fe²⁺) When hydrogen peroxide meets ferrous iron, the hydroxyl radical forms. It reacts at once with whichever molecule lies closest. This route is called the Fenton reaction. Source 3
5. Hydroxyl radical → 8-oxo-dG in DNA Of the four building blocks of DNA, guanine is the most easily oxidised. It becomes 8-oxo-dG, an altered base that the cell recognises as damage. Source 4
6. 8-oxo-dGTP → 8-oxo-dGMP MTH1 (NUDT1) The enzyme MTH1 removes two phosphate groups from the oxidised building block. It then no longer fits into DNA and has left the pool. Source 5
7. 8-oxo-dGMP → 8-OHdG Nucleotidase A nucleotidase removes the last phosphate group. What remains is the nucleoside 8-OHdG, which the cell does not convert any further. Source 5, 4
8. 8-OHdG → In urine Both fragments pass into the blood and are excreted via the kidneys. How much comes from the DNA strand and how much from the pool of building blocks has not been fully resolved. Source 4, 5
9. 8-oxoguanine → In urine via blood and kidney Both fragments pass into the blood and are excreted via the kidneys. How much comes from the DNA strand and how much from the pool of building blocks has not been fully resolved. Source 4, 5

Cofactors in this pathway

• Selenium — Component of glutathione peroxidase, which breaks hydrogen peroxide down to water Source 2In the ORY catalogue as a laboratory value: Selen
• Glutathione — Supplies glutathione peroxidase with the electrons used to break down peroxides Source 2In the ORY catalogue as a laboratory value: Glutathion (GSH)
• Manganese — Metal at the centre of SOD2, which converts superoxide in the mitochondrion Source 2
• Copper — Metal at the centre of SOD1, which converts superoxide in the cytosol Source 2In the ORY catalogue as a laboratory value: Kupfer (Cu)
• Zinc — Second metal of SOD1; holds the structure of the enzyme Source 2In the ORY catalogue as a laboratory value: Zink
• Iron — Haem iron of catalase; free Fe²⁺ forms hydroxyl radicals in the Fenton reaction Source 2, 3In the ORY catalogue as a laboratory value: Eisen
• Vitamin C — Water-soluble antioxidant that intercepts radicals by donating electrons Source 2In the ORY catalogue as a laboratory value: Vitamin C (Ascorbinsäure)

Sources

1. Murphy MP. How mitochondria produce reactive oxygen species. Biochem J 2009 · PubMed 19061483
2. Jomova K, Alomar SY, Alwasel SH et al. Several lines of antioxidant defense against oxidative stress: antioxidant enzymes, nanomaterials with multiple enzyme-mimicking activities, and low-molecular-weight antioxidants. Arch Toxicol 2024 · PubMed 38483584
3. Wardman P, Candeias LP. Fenton chemistry: an introduction. Radiat Res 1996 · PubMed 8619017
4. Cooke MS, Olinski R, Loft S. Measurement and meaning of oxidatively modified DNA lesions in urine. Cancer Epidemiol Biomarkers Prev 2008 · PubMed 18199707
5. Nakabeppu Y, Ohta E, Abolhassani N. MTH1 as a nucleotide pool sanitizing enzyme: Friend or foe? Free Radic Biol Med 2017 · PubMed 27833032

Related pathways

• Glutathione — hydrogen peroxide
• Selenium — hydrogen peroxide
• Copper — Glutathion (GSH), Zink
• Vitamin C — Selen, Glutathion (GSH)
• Borrelia — Selen, Zink

As of 2026-09-16. Draft written by Claude to schema v2; sources checked in PubMed; expert review pending
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