8-Oxoguanine


8-Oxoguanine is one of the most common DNA lesions resulting from reactive oxygen species modifying guanine, and can result in a mismatched pairing with adenine resulting in G to T and C to A substitutions in the genome. In humans, it is primarily repaired by DNA glycosylase OGG1. It can be caused by ionizing radiation, in connection with oxidative metabolism.
Image:8-oxoG forming Hoogsten base pair with dA.svg|thumb|left|8-oxoG in a Hoogsteen base pair with dA
Image:GC base pair jypx3.png|thumb|left|180px|For comparison here is a standard GC base pair with both bases in the anti configuration of the bond between base and sugar.

In body fluids

Increased concentrations of 8-oxoguanine in body fluids have been found to be associated with increased risk of mutagenesis and carcinogenesis.
Care must be taken in the assay of 8-oxoguanine due to the ease with which it can be oxidised during extraction and the assay procedure.

Cancer, aging, infertility

The role of the deoxyriboside form of 8-oxoguanine, 8-oxo-2'-deoxyguanosine in cancer and aging also applies to 8-oxoguanine. Oxoguanine glycosylase is employed in the removal of 8-oxoguanine from DNA by the process of base excision repair. As described in oxoguanine glycosylase, deficient expression of this enzyme causes 8-oxoguanine to accumulate in DNA. This accumulation may then lead upon replication of DNA to mutations including some that contribute to carcinogenesis. 8-oxoguanine is usually formed by the interaction of reactive oxygen species with the guanine base in DNA under conditions of oxidative stress; as noted in the article about them, such species may have a role in aging and male infertility, and 8-oxoguanine can be used to measure such stress.