NONINVASIVE METHODS FOR MEASURING DNA ALKYLATION IN EXPERIMENTAL-ANIMALS AND HUMANS

Alkylpurines are liberated from alkylated DNA by glycosylase repair en zymes and, in most cases, excreted in urine without further metabolism . This phenomenon forms the basis of noninvasive methods to measure DN A alkylation in vivo. In the case of methyl adducts, such as 7-methylg uanine (7-MeGua), natural backgrounds exist due to RNA turnover. Howev er, deuterated (d3) methylating agents or precursors give rise to d3-7 -MeGua and d3-3-methyladenine (3-MeAde), which can be readily quantita ted using gas chromatography-mass spectrometry (GC-MS). A deuterated p robe drug, such as d6-aminopyrine, can be used to measure endogenous n itrosation levels in experimental animals. In contrast, for higher alk yl homologues of alkylpurines, natural backgrounds are low or nonexist ent and can he directly measured by GC-MS using stable isotope labeled internal standards. For example, increased levels of urinary 3-ethyla denine were observed in cigarette smokers. Due to recent advances in a nalytical methodology, notably immunoaffinity cleanup of urine, measur ements of excreted DNA adducts can be used in studies in human populat ions exposed to low levels of alkylating carcinogens.