Sex differences in the formation and persistence of DNA adducts of 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) in CDF1 mice

Abstract

The potent food mutagen 2-amino-3-methylimidazo[4,5-f]-quinoline (IQ) is carcinogenic in the CDF1 mouse, affecting the liver, lungs and forestomach. Females are approximately twice as sensitive as males to liver tumor induction. Using 32P-postlabeling assays, the dose-response of IQ-DNA adduct formation was determined in various organs of male and female CDF1 mice after single p.o. doses of IQ. To determine the possible correlation between IQ-DNA adduct formation, persistence and tumorigenicity in target organs, young adult male and female CDF1 mice were treated with a single p.o. dose (50 mg/kg) of IQ, and IQ-DNA adducts were isolated and quantitated in liver, lungs, forestomach, small intestine and large intestine over a 24 day period. In the range of 5-50 mg IQ/kg, IQ-DNA adduct formation was related to dose in all organs examined (liver, lungs, stomach, small intestine, large intestine). Total adduct formation (expressed as relative adduct labeling, RAL) 24 h after administration was highest in the liver (6.4-6.9 x 10(-7)) with lower levels, in decreasing order, in the large intestine, small intestine (non-target organs), forestomach and lungs (target organs). In all cases the major adduct, comprising 68-79% of the total, co-chromatographed with standard N-(deoxyguanosin-8-yl)-IQ. Up to three additional IQ-specific adducts could be detected. Except in the liver, adduct levels 24 h after administration of IQ were 2- to 3-fold higher in females than in males. There was no preferential retention of any one of the four adducts 1-24 days after administration of IQ. Beyond day 4 after administration, total adducts in the liver of females were approximately 2-fold higher than those in males, and the rate of removal from female lung was approximately 2-fold faster than that from male lung during the 1-24 day time period. Both these findings correspond to the known sex differences in IQ-induced tumor incidences in these organs. The higher adduct levels in non-target organs (intestines) as compared to target organs (lungs and stomach), combined with the absence of differential persistence of any individual adduct indicates that, in addition to adduct formation and persistence, other factors contribute to the target organ specificity of IQ in CDF1 mice.

Dietary modulation of DNA adduct formation of the food mutagen 2-amino-3-methylimidazo[4,5-f]quinoline in the male Fischer 344 rat.

“…Adduct formation was dosedependent in all three organs ( Figures 2-4), and hepatic adduct levels measured 1 day after IQ administration to animals on either the AIN-76A diet or the regular chow diet were 8-to 11-fold higher than in the large intestine and 14-fold to more than 50-fold higher than in the small intestine (Figures 2-4). These data are in agreement with our previous findings (14).…”

“…The IQ-DNA adduct pattern obtained was similar in all three tissues ( Figure 1) and was identical to that observed earlier in similarly treated Fischer 344 rats (14). The pattern was independent of the diet and organs from vehicle-treated animals showed no IQ-related adducts (data not shown).…”

“…The animal was treated with a single oral dose of 50 mg IQ/kg using dimethyl sulfoxide-0.05 M sodium phosphate (1:4) as the vehicle (1 ml/animal). The adduct pattern is identical to that observed before (14), adduct 1 being the 3,[32P15-bisphosphate of N-(deoxyguanosin-8-yl)-IQ ( 11). 32P-Postlabeling assays were run under intensification conditions.…”

“…N-Hydroxy-IQ (N-OH-IQ) reacts with DNA in vitro to yield DNA adducts (8,9), but in the cell, various esterification reactions are thought to cause further enhancement of its reactivity (8,10). Using 32p-postlabeling methodology, we have isolated and quantitated specific IQ-DNA adducts formed in Salmonella after exposure of the bacteria to IQ in the presence of an activating system and in various organs of the Fischer 344 rat, CDF1 mouse, and cynomolgus monkey after administration of IQ in vivo (11)(12)(13)(14). In each case the adduct pattern was identical to that obtained after reaction of N-OH-IQ with calf thymus DNA and the major adduct (adduct 1) cochromatographed with synthetic standard N-(deoxyguanosin-8-yl)-IQ (11 and large intestine (C) of a male Fischer 344 rat maintained on a regular pelleted rodent chow diet.…”

“…IQ-DNA adducts were isolated by 32p-posdabeling, using the intensification version of the assay as described before (14). The extent of adduct formation was expressed as relative adduct labeling (RAL) values, which were calculated by dividing the counts per minute (cpm) per adduct by the sum of the cpm in the adduct and the normal nucleotides, making adjustments for dilution and aliquot factors.…”