P XVI A.5 - P XVI A.5 Comparison of the O-alkyl adduct formation and the mutagenicity induced by...

between a rat model and humans for the proven human carcinogen aflatoxinBI (AFBI) and for a potential human carcinogen, the food mutagen 2-amino­3,8-dimethylimidazo[4,5-t]quinoxaline (MeIQx). Our studies with 14CAFB1(dose administered = 15 nglkg or 250 g equivalents of UK peanut butter)shaw a reduced formation of DNA adducts in human colon compared withthe rat (humans = 3 adductsl1012 nucleotides; Fischer rat = 37.4 adductsl1012

nucleotides) but a higher level of AFB,-albumin adducts (humans = 0.62 pgAFB)/mg serum albumin; Fisher rat = 0.15 pg AFB,/mg serum albumin.In contrast at body equivalent doses of MelQx (300 nglkg), higher levelsof DNA adducts were formed in human colon compared with the rat model(26 adductsl1012 nucleotides for humans and 17.1 adductsllOI2 nucleotidesfor the rat). These preliminary studies show the power of AMS to providehuman biomarker data and hence provide more accurate models for assessinghuman risk. AMS has the potential to measure genotoxin levels ID humangerm cells, particularly in patients undergoing cancer chemotherapy as wellas investigating the bioactivation of many identified and suspected humancarcinogens.

Ip XVI A.31 Formation of alkyI- and hydroxyl-guanine ad ductsIn DNA and mutation Induction caused by N­nltrosodlalkylamlne plus UVA

Sakae Arirnoto-Kobayashi", Keiko Kaji l , Gavain M.A. Sweetman", Peter B.Farrner'', Hikoya Hayatsu'. I Faculty ofPharmaceutical Sciences, OkayamaUniversity, Tsushima, Okayama700, Japan;1MRC Toxicology Unit, HodgkinBuilding, Leicester University, LancasterRoad, Leicester; LEI 9HN, UK

Previously we showed that when a mixture of N-nitrosodialkylamine and E.coli in saline was irradiated with UVA, mutagenesis of bacteria took place:there was no requirement for metabolic activation. When 06-alkylguanine­DNA alkyltransferase-deficient strains of E. coli and S. typhimurium wereused, the mutation levels of both N-nitrosodimethylamine (NDMA) + UVAand N-nitrosodiethylamine (NOEA) + UVA became remarkably higher thanthose observed with proficient strains. We treated calf thymus DNA withNOMA plus UVA and measured the 06-methylguanine (06-meG) and N7­methylguanine levels. The 06-meG level was increased as functions ofirradiation time and the amount of NOMA. The 8-oxodG/dG in DNA treatedwith NDMAINDEA plus UVA increased up to 40-70 fold over that ofthe untreated control. We have studied the spectrum of mutation causedby NDMA and NDEA with UVA (320-400 om) using standard tester strainsfor identifying types of mutations. Induced mutations by NDMA plus UVAwere the transition, GC to AT, and transversions, GC to CG, GC to TA, andAT to TA. NDEA plus UVA induced mainly the GC to CG transversion.The GC to AT transition may be caused by the formation of 06-meG andthe GC to TA transversion by 8-oxoG. The SOS mutagenesis may accountfor the elevated GC to CG and AT to TA transversions. We conclude thatboth alkylation and oxidation must be involved in mutations induced byNDMAINOEA plus UVA.

Keyword(s): N-Nitrosodialkylamine; UVA; DNA damage

Ip XVI A.41 Comparison of 0 6 alkylguanlne-DNA alkyltrans­ferase activity In Inbred mice after N-nltrosodlethylamlnetreatment

Victor Oreffo", Rajinder Singh', Peter Farmer". I MRC Toxicology Unit, P.O. Box /38, LeicesterLEI 9HN, UK

Inter-strain susceptibility to the NDEA induced lung tumours may in partdepend on differences in the formation and repair of06 alkylguanine adductswithin target lung tissues. A study to assess the relative risk of mutagenicdamage from the alkylating agent NDEA by measuring alkyltransferase (AT)enzyme activity was carried out. Three strains of mice that differ in theirsusceptibility to lung tumourigenesis (SWR high, Balblc intermediate andC57BU6J low), were treated with a single intraperitoneal dose of 15 mglkgofNDEA in saline. AT activity was determined in mouse lung (target tissue)after 2 h, 5 h, 10 h, 24 h, 3 days and 7 days and in liver (non target tissue) after2 h, 5 h, and 3 days. AT activity was low in the lung and appeared unchanged

S-XVI: DNA adducts and human cancers SI55

after NDEA exposure. Liver contained high levels of AT. AT activity wasdepleted by approximately 70% of control values in liver 2 h after NDEAexposure but resumed to normal control levels when measured after threedays. Whilst susceptibility of mouse lung to NDEA induced tumours maybe attributable in part to lower levels of AT activity, no apparent differencestn AT activity between strains was observed by this assay in lung or livertissue.

Keyword(s): Lung; N-Nitrosodiethylamine; Alkyltransferase

Ip XVI A.51 Comparison of the O-alkyl adduct formation andthe mutagenicity Induced by NDMA and NDEA InDrosophila

Yuki Goto", Tomoko Matsuda', Kazuo Ito1, Num-hoh Huh2, JiirgenThornale", Manfred F. Rajewsky', Hikoya Hayatsu', Tomoe Negishi". I Fac.ofPharm. Sci.. Okayama Uniu, Okayama 700, Japan;1Fac. ofMed., ToyamaMedicaland Pharmaceutical Uniu, Toyama 930-10, Japan;JInstituteofCellBiology, Uniu ofEssen MedicalSchool, D-45122Essen, Germany

Previously we reported that the mutagenicity of N -nitrosodimethylamine(NDMA) tn the Drosophila wing spot test is Io-fold stronger than that ofN-nitrosodiethylamine (NDEA). To investigate the reason for this difference,the amount of alkylated bases in Drosophila DNA were measured. 3rd instarlarvae were fed NDMAINDEA. A part of the treated larvae were grown toadult flies to score the mutant spots on their wings. From the rest of thelarvae, DNA was isolated. The DNA was digested to deoxyribonucleosidesand analyzed by HPLC. The amounts of alkyldeoxyribonucleosides weremeasured with radioimmunoassay using each monochronal antibody. Theextents of 0 6-methylguanine, 0 6-ethylguamne and d -ethylthymine forma­tion paralleled the somatic cell mutation. At the same dose of NDMA andNDEA, the value d -alkyldeoxyguancsine/Iu'' deoxyguanosine was similar:feeding 20 umol NDMA for 3 hr, it was 4.0, and it was 18.5 with the 6hr feeding. With NDEA, It was 5.4 (3 hr) and 14.6 (6 hr). The mutationfrequencies (spots/wing) were very different: with NDMA it was 3.5 (3 hr)and 15 (6 hr), and with NDEA it was 0.8 (3 hr) and 0.9 (6 hr). Similarresults were obtained for the formation of d -alkylthymidine. These resultssuggest that, in Drosophila, an O-methylation of guanine and thymine ismore mutagenic than an O-ethylation.

Keyword(s): Nitrosamine; Drosophila somatic cell mutation; O-Alkyl ad­ducts