The use of rat urine extracted on XAD-2 resin and assayed in a microsuspension-modified Ames test as an in vivo indicator of genotoxic exposure.

The measurement of urinary mutagenicity is a non-invasive monitoring tool which often reflects an animal's recent exposure to genotoxic agents. Although studies in man are indispensable for monitoring industrial and/or environmental exposure to genotoxins, a sensitive laboratory animal model is necessary for mechanistic studies on the role of specific chemical exposure in altering urinary mutagenicity. The objective of this study was to enhance the sensitivity of the methodology used for detecting urinary mutagenicity in rats by using XAD-2 resin to extract and concentrate the urine and a microsuspension-modified Ames test to quantify mutagenicity. The polycyclic aromatic hydrocarbon benzo[a]pyrene (BP) and the aromatic amine 2-acetylaminofluorene (AAF) were used as test compounds. Under the conditions of our study, AAF administered to rats by gavage at doses of 1 mg/kg or higher induced a dose-dependent increase in urine mutagenicity. The greatest mutagenic response was seen when S9 was present during the microsuspension-modified Ames test and beta-glucuronidase (BG) was not included. Similarly, BP administered to rats by gavage at doses of 10 mg/kg or higher induced a dose-dependent increase in urinary mutagenicity. The relative importance of BG and S9 were quite different with BP than with AAF. With BP, mutagenicity was greatest when both S9 and BG were present during the microsuspension-modified Ames test, and least with S9 and without BG. In both AAF- and BP-treated animals, extraction of the urine on XAD-2 resin markedly enhanced the mutagenic response compared to neat urine, but partitioning of the XAD-2 eluate into methylene chloride always diminished the mutagenicity of the urine extract. The results demonstrate the sensitivity and reproducibility of rodent urinary mutagenicity assays when XAD-2 resin is used to extract and concentrate the urine and a microsuspension-modified Ames test is used to quantify mutagenicity. This sensitive method should facilitate mechanistic studies on the roles of specific environmental agents in affecting urinary mutagenicity and, in addition, may be used during acute, subchronic and chronic rodent bioassays as a non-invasive in vivo indicator of genotoxic exposure.

Persistence of benzo[a]pyrene and 7,8-dihydro-7,8-dihydroxybenzo[a] pyrene in Fischer 344 rats: time distribution of total metabolites in blood, urine and feces.

A comparison of the rates of elimination of [3H]benzo[a] pyrene (BaP) and 7,8-dihydro-7,8-diol-[3H]benzo[a]pyrene (BPD), after subcutaneous injection into Fischer 344 rats, shows they are both eliminated at about the same rates and with the same pattern over at least 7 days post-exposure. The end-rate of combined urinary and fecal excretion was approximately 40 nmol/day. About 20% of the injected BaP and approximately 3% of the injected BPD remained at the site of injection for at least 9 days. The remainder was distributed throughout the animal. If the rate of excretion continued at the observed steady-state rates, the BaP and BPD could persist for up to 40 days for each milligram of injected substance. The concentration of excretion products were highest during day 1 and day 2 following exposure, decreased exponentially to a concentration of approximately 0.5 microM (mixed metabolites) by day 5 following exposure, and then continued to be excreted at that rate. Feces contained the highest total amounts of radioactivity, which were approximately 2- to 4-fold higher than the amounts in urine and approximately 15- to 50-fold higher than in total blood. The conversion of organic 3H to 3H2O during the experimental period indicates that whole-body phenol(quinone) formation was significant for BaP metabolism, but was much less for BPD metabolism. When BaP was injected, both blood and urine contained water-soluble, volatile tritium counts (3H2O). Injection of BPD resulted in volatile 3H2O in urine but not in blood. The persistence of BaP and BPD metabolites in skin, blood, urine and feces compartments indicates there is a substantial reservoir of the chemical(s) that could be used to replenish repaired or discarded DNA adducts.

Studies on the chromatographic fractionation of metabolites of benzo[a]pyrene in faeces and urine from germfree and conventional rats.

Rats, germfree and conventional, were dosed with 14C-labelled benzo[a]pyrene. Faeces and urine were collected. Metabolites in faeces were effectively extracted with a new method using a combination of solvents and solid sorbents. Metabolites in urine were extracted with octadecylsilane-bonded silica. The metabolites were fractionated into groups by chromatography on a cation exchanger (SP-LH-20 or SP-Sephadex C-25) and an anion exchanger (TEAP-LH-20). Some of the groups were further purified by column chromatography and analysed by HPLC and TLC. The analyses show a complex pattern of metabolism. A large part of the metabolites (9-24% depending on animal type and route of excretion) had amphoteric properties, e.g. like glutathione and cysteine conjugates. The abundance of conjugates sensitive to beta-glucuronidase and sulphatase was low. The relative amount of acidic conjugates in faeces was much higher in the germfree than in the conventional rats indicating the influence of the intestinal flora on the metabolism. The results support the view that the mercapturic acid pathway is a quantitatively important metabolic route for benzo[a]pyrene in rats. The methods of extraction and group fractionation were designed to be generally applicable to the analysis of lipophilic xenobiotics and their metabolites.