M<sub>1</sub>G (pyrimido[1,2-a]purin-10(3H)-one) is a heterocyclic compound which is a by-product of base excision repair (BER) of a specific type of DNA adduct called M<sub>1</sub>dG. The M<sub>1</sub>dG adduct in turn is formed by a condensation reaction between guanosine nucleotides in DNA and either malondialdehyde (propanedial) or acrolein. If not repaired, these adducts are mutagenic and carcinogenic.
Malondialdehyde is an end product of lipid peroxidation while acrolein is a result of DNA peroxidation.
M<sub>1</sub>dG is the major endogenous DNA adduct in humans. M<sub>1</sub>dG adducts have been detected in cell DNA in liver, leucocytes, pancreas and breast in concentrations of 1-120 per 10<sup>8</sup> nucleotides. Detection and quantification of M<sub>1</sub>dG adducts in the body as measured by free M<sub>1</sub>G is a tool for detecting DNA damage that may lead to cancer. Free M<sub>1</sub>G is also biomarker for oxidative stress.