title: Formation and persistence of N7- and O6-methyl-guanine in DNA of chick embryo brain cells in ovo following administration of N-nitroso-N-methylurea.
abstract: Previously, O6-methyl-guanine-DNA alkyltransferase (AT) of the chicken embryo has been investigated in vitro. In the present studies, the effect of in vivo (in ovo) treatment with methylnitrosourea (MNU) was examined at a developmental stage of 15 days and doses of 1.25-20 mg/egg, yielding about 1-16 mmol MNU/kg embryo weight. At intervals of 1-24 h, DNA of the brain was prepared. N7-methylguanine and O6-methylguanine were quantified by combining a rapid method of DNA isolation, high-pressure-liquid-chromatography (HPLC) and electrochemical detection of the guanine-alkyl adducts. In parallel, the AT activity of brain homogenates was determined. Within the range of the detection limits (N7-methylguanine: 16 nM, O6-methylguanine: 2.5 nM), no repair of the guanine adducts, being about 500 nmol O6-methyl- and 1800 nmol N7-methyl-adducts per mmol guanine 1 h following administration of 10 mg MNU/egg, was evident. The rather low acute toxicity of MNU in the chicken embryo at the 15th day of development DL50/24 h being > 4 mg MNU/embryo, argues, therefore, for an additional repair mechanism, e.g. cell replacement repair.
authors.affiliation: Institut für Pharmakologie, Toxikologie und Pharmazie, Tierärztliche Fakultät, Universität München, Deutschland.
authors.forename: S
authors.initials: S
authors.lastname: Schleifer
authors.forename: K
authors.initials: K
authors.lastname: Tempel
mesh_terms: D000818:Animals; D001921:Brain / Q000166:cytology* / Q000187:drug effects / Q000196:embryology*; D001923:Brain Chemistry; D002642:Chick Embryo; D002851:Chromatography, High Pressure Liquid / Q000379:methods / Q000662:veterinary; D004247:DNA / Q000032:analysis / Q000737:chemistry* / Q000378:metabolism; D018736:DNA Adducts / Q000032:analysis; D004305:Dose-Response Relationship, Drug; D004563:Electrochemistry / Q000379:methods; D006147:Guanine / Q000031:analogs & derivatives* / Q000032:analysis / Q000378:metabolism; D008770:Methylnitrosourea / Q000494:pharmacology*; D008780:Methyltransferases / Q000032:analysis* / Q000378:metabolism*; D019853:O(6)-Methylguanine-DNA Methyltransferase; D013997:Time Factors
chemical_list: D018736:DNA Adducts; D006147:Guanine; C008450:7-methylguanine; D008770:Methylnitrosourea; D004247:DNA; C008449:O-(6)-methylguanine; D008780:Methyltransferases; D019853:O(6)-Methylguanine-DNA Methyltransferase