Kinetics of induction of DNA damage and lacZ gene mutations in stomach mucosa of mice treated with beta-propiolactone and N-methyl-N '-nitro-N-nitrosoguanidine, using single-cell gel electrophoresis and Muta (TM) Mouse models

beta-Propiolactone (BPL) and N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) ar e two direct alkylating agents that induce multiple genetic lesions and tum ors in the rodent stomach. We measured the kinetics of the induction of DNA damage by using the single-cell gel electrophoresis assay (SCGE) and the i nduction of gene mutations by using the Muta(TM)Mouse model in the glandula r stomach mucosa of mice exposed to a single oral administration of BPL or MNNG. The aims were to determine the optimal sampling time and to investiga te the cause-effect relationship between DNA damage and gene mutations. The induction of comets, evaluated in individual cells with the tail moment, w as analyzed 1, 2, 4, 24, and 72 hr after a single oral administration of 25 mg/kg BPL or 20 mg/kg MNNG. The effects of both compounds were most intens e at the earlier sampling times (1-2 hr), tailing off 4 hr after treatment and becoming undetectable at 72 hr. The lacZ mutant frequency (MF) was meas ured 3, 7, 14, 28, and 50 days after a single oral administration of 150 mg /kg BPL or 100 mg/kg MNNG, and 3 and 14 days after a single administration of 25 mg/kg BPL or 20 mg/kg MNNG. The MF was strongly enhanced at the highe st doses and all sampling times, the most marked effects being observed 14 days (11.1-fold) and 28 days (19.0-fold) after BPL and MNNG administration, respectively. At the lowest doses, only a small increase in MF (similar to 2.5- to 3.5-fold) was found at both sampling times. Primary DNA damage det ected with SCGE shortly after treatment (1-2 hr) was rapidly (3 days) trans formed into stable gene mutations that remained detectable for 50 days. The se results illustrate the ability and complementarity of the SCGE and Muta Mouse models to assess the genotoxicity of direct alkylating agents in the mouse gastric mucose in vivo. (C) 1999 Wiley-liss, Inc.