Hamster hepatocyte-mediated activation of procarcinogens to mutagens in the L5178Y/TK mutation assay

Eight procarcinogens including three nitrosamines, three polycyclic hydrocarbons, and two aromatic amines were tested for mutagenic potential at the thymidine kinase (TK) locus in L5178Y mouse lymphoma cells co-cultivated with viable hamster hepatocytes. All eight chemicals produced substantial mutagenic activity as indicated by increased trifluorothymidine resistance in L5178Y cells treated in the presence of hepatocytes. Mutagenic responses to benzo[a]pyrene, 3-methyl-cholanthrene, N-nitrosodiethylamine, and N-nitrosodipropylamine first increased, then plateaued within the range of mutagen concentrations tested, while consistent dose-dependent increases in mutant frequencies were observed following 2-aminoanthracene, 2-aminofluorene, or N-nitrosodimethylamine treatments. The relatively flat portions of the mutant frequency curves for benzo[a]pyrene and 3-methylcholanthrene coincided with maximum chemical solubility as obvious from visible or microscopically detectable precipitate. These hamster cells readily facilitated the metabolism of 1,2-benzanthracene to a detectable mutagen and were especially competent in the activation of the two aromatic amines. Thus, cultured hamster hepatocytes can activate a variety of chemical carcinogens including polycyclic hydrocarbons to mutagens in a whole cell-mediated in vitro assay using L5178Y/TK^+/? cells as the target organism.     

The mutagenicity of 5-azacytidine and other inhibitors of replicative DNA synthesis in the L5178Y mouse lymphoma cell

The mutagenic potential of the cytidine analog, 5-azacytidine (Aza Cyd), was tested at the thymidine kinase (TK) gene locus of L5178Y mouse lymphoma cells. 3-h exposure to as little as 20 ng/ml Aza Cyd yielded a substantial increase in TK-deficient L5178Y cells as measured by drug-induced resistance to trifluorothymidine (TFTres) 48 h later. This mutagenic effect was diminished up to 75% when Aza Cyd was tested in the presence of either enzymatically active or heat-denatured 9000 X g supernatant prepared from rat liver homogenate. The mutagenicity of Aza Cyd was also decreased in the presence of 1-5 X 10(-3) M thymidine and eliminated in the presence of greater than 1 X 10(-5) M cytidine. Two L5178Y TK-deficient cell lines had no selective survival advantage compared to TK-competent L5178Y cell stock when plated in soft-agar medium that contained Aza Cyd. Four other specific inhibitors of scheduled DNA synthesis in mammalian cells, deoxyadenosine, aphidicolin, 1-beta-D-arabinofuranosylcytosine, and hydroxyurea were also L5178Y/TK mutagens. These data along with other published results suggest that chemicals known to disrupt nucleotide biosynthesis, alter deoxyribonucleotide pools, or directly inhibit DNA polymerase can cause stable, heritable increases in TFT resistance through mechanisms dependent upon altered replicative DNA synthesis, yet not necessarily dependent upon DNA incorporation or the binding of these mutagenic agents to nuclear DNA.     

Mutagenicity towards Salmonella typhimurium of some known genotoxic agents, activated by isolated hepatocytes of monkey (Macaca fascicularis). Comparison with isolated human hepatocytes

This paper describes some striking differences between isolated human and monkey hepatocytes in their capacity to activate some known genotoxic agents into products mutagenic towards Salmonella typhimurium. Isolated monkey hepatocytes, in contrast to human hepatocytes, appeared to activate benzidine (BZ), N-acetylbenzidine (MABZ), N,N'-diacetylbenzidine (DABZ), 2-aminofluorene (2-AF) and 2-acetylaminofluorene (2-AAF) poorly. With monkey hepatocytes BZ was slightly more mutagenic than DABZ, whereas with human hepatocytes DABZ was more active than BZ. N-Nitrosodimethylamine (DMN) and N-nitrosodiethylamine (DEN) were also found to be poorly mutagenic when activated by monkey hepatocytes, unlike the human hepatocytes. However, the polycyclic arylhydrocarbons benzo[a]pyrene (B[a]P) and 7,12-dimethylbenzanthracene (7,12-DMBA) were highly active in the presence of monkey hepatocytes, unlike the human hepatocytes. A metabolic study showed that monkey liver preparations seem to possess a higher monooxygenase activity towards B[a]P than human liver preparations.     

Evaluation of genotoxicity of N-nitrosodibenzylamine in Chinese hamster V79 cells and in Salmonella

Health concerns have arisen due to the formation of N-nitrosodibenzylamine (NDBzA; CAS No. 5336-53-8) in pork processed in a new type of rubber netting. In view of the potent carcinogenicity of related nitrosamines (e.g. N-nitroso-n-dibutylamine and N-nitrosodiethylamine), NDBzA was evaluated for genotoxicity in vitro in both Chinese hamster V79 cells and in Salmonella. In V79 cells, concentrations up to 25 micrograms/ml were tested with and without activation by rat or hamster hepatocytes. Significant elevation of SCE frequency was seen only at 25 micrograms/ml in the presence of uninduced hamster hepatocytes. Mutation to 6-thioguanine resistance was observed at 25 micrograms/ml, in the absence of hepatocytes and in the presence of induced (Aroclor 1254) or uninduced hamster hepatocytes, but not with rat hepatocytes. With uninduced rat hepatocytes, a small but significant (p less than 0.05) increase in the mutation frequency was seen with 10 micrograms/ml NDBzA. In the Salmonella assay, using a pre-incubation protocol and concentrations up to 1000 micrograms/ml, NDBzA was negative in strain TA98, and in TA100 with rat S9, but was positive at the highest dose in TA100 with hamster S9, and more strongly with Aroclor 1254-induced hamster S9. When activated by uninduced rat or hamster hepatocytes, as opposed to S9, NDBzA was negative with all tester strains. Hamster hepatocytes activated more than rat in the V79 studies, and hamster S9 was more strongly activating in the Salmonella assay. These results indicate that NDBzA is weakly mutagenic to both Salmonella and V79 cells.     

Mutagenic activation of 3-amino-1,4-dimethyl-5H-pyrido(4,3-b)indole(Trp-P-1) and 3-amino-1-methyl-5H-pyrido(4,3-b)indole (Trp-P-2) by primary cultures of adult rat hepatocytes: effect of Aroclor induction in vitro

The mutagenic activation of tryptophan pyrolysis products, Trp-P-1 and Trp-P-2, was studied in a Salmonella TA98/hepatocyte mutagenesis assay. Adult rat hepatocytes in primary culture were either untreated or induced by the addition of Aroclor 1254 (2 micrograms/ml) 18-20 h before the mutagenesis test which was performed at day 1 and at day 2 after the isolation of hepatocytes. The mutagenic activation of Trp-P-1 and Trp-P-2 was studied as a function of the time of incubation and of the concentration of chemical. Trp-P-1 and Trp-P-2 incubated for 20 min in the presence of untreated hepatocytes and bacteria gave rise to a weak number of revertants which doubled the level of spontaneous mutants. Aroclor-induced hepatocytes became highly competent in mutagenic activation of tryptophan pyrolysis products and the induction ratio reached 4.9 and 7.1 for Trp-P-1 and Trp-P-2, respectively, after 60 min of incubation, on day 2 of the experiment. It should be noted that the induction ratio was higher on day 2 than on day 1. When conditions were standardized, i.e. Aroclor-induced hepatocytes on day 2, final concentration of cellular protein about 1 mg/ml, 20 min of incubation, the Salmonella/hepatocyte assay produced a linear concentration-dependent mutagenic response for Trp-P-1 and Trp-P-2. By comparing the results obtained with Aroclor-induced hepatocytes and Aroclor-induced liver S9 fraction in the Salmonella test, it could be estimated that hepatocytes were 3 times less active than the S9 fraction with regard to mutagenic activation of both Trp-P-1 and Trp-P-2.     

Evaluation of diallate and triallate herbicides for genotoxic effects in a battery of in vitro and short-term in vivo tests

Commercial-grade preparations of two thiocarbamate herbicides, diallate and triallate, were evaluated for their mutagenic potential in a battery of short-term bioassays. All in vitro bioassays were performed with and without mammalian metabolic activation, and all such tests were repeated after an interval of at least 1 week. Diallate and triallate were tested in the Salmonella/microsome assay over dose ranges of 0.59 to 118.0 micrograms/plate and 6.37 to 1273 micrograms/plate, respectively. Both diallate and triallate gave positive results in S. typhimurium strains TA1535, TA98, and TA100 only in the presence of a rat-liver metabolic activation system. In Saccharomyces cerevisiae strain D7, diallate was tested at concentrations from 1.18 to 29.50 micrograms/ml, and triallate was tested at 0.955 to 9.548 micrograms/ml. Both diallate and triallate gave negative results for mitotic gene conversion, mitotic crossing-over, and reverse mutation. In the mouse lymphoma L5178Y TK+/- assay, diallate was tested at concentrations ranging from 1 to 72 micrograms/ml, and triallate was tested at 0.5 to 60 micrograms/ml. Both herbicides produced mutagenic responses in the mouse lymphoma assay in the presence of metabolic activation. In the Drosophila sex-linked recessive lethal test, flies were exposed to 0.0004% diallate and 0.001% triallate. In this assay, diallate was considered mutagenic, whereas triallate did not produce a detectable mutagenic response.     

Mutagenicity and clastogenicity of adriamycin in L5178Y/TK(+/-)-3.7.2C mouse lymphoma cells

Adriamycin was found to be both mutagenic and clastogenic to L5178Y/TK(+/-)-3.7.2C mouse lymphoma cells. A dose of only 5 ng/ml (survival = 62% or 67%) gave an induced TK mutant frequency of 307 or 296 per 10(6) survivors in two separate experiments. This dose was also clastogenic, inducing 20 chromosome aberrations/100 cells analyzed. The majority of the mutants were small-colony mutants, indicating that adriamycin likely acts primarily by a clastogenic mechanism.     

The genotoxicity of lucidin,a natural component of Rubia tinctorum L., and lucidinethylether,a component of ethanolic Rubia extracts

The genotoxic activity of lucidin (1,3-dihydroxy-2-hydroxymethyl-9,10-anthraquinone), a natural component of Rubia tinctorum L., was tested in a battery of short-term tests. The compound was mutagenic in five Salmonella typhimurium strains without metabolic activation, but the mutagenicity was increased after addition of rat liver S9 mix. In V79 cells, lucidin was mutagenic at the hypoxanthine-guanine phosphoribosyl transferase gene locus and active at inducing DNA single-strand breaks and DNA protein cross-links as assayed by the alkaline elution method. Lucidin also induced DNA repair synthesis in primary rat hepatocytes and transformed C3HI M2-mouse fibroblasts in culture. We also investigated lucidinethylether, which is formed from lucidin by extraction of madder roots with boiling ethanol. This compound was also mutagenic in Salmonella, but only after addition of rat liver S9 mix. Lucidinethylether was weakly mutagenic to V79 cells which were cocultivated with rat hepatocytes. The compound did not induce DNA repair synthesis in hepatocytes from untreated rats, but positive results were obtained when hepatocytes from rats pretreated with phenobarbital were used. We conclude that lucidin and its derivatives are genotoxic.Abbreviations DMBA 7,12-dimethylbenz(a)anthracene - HA hydroxyanthraquinones - LUE lucidinethylether - PRH primary rat hepatocytes - UDS unscheduled DNA synthesis     

Mutation of V79 cells by N-dialkylnitrosamines after activation by hamster pancreas duct cells.

Pancreas duct epithelial cells (DEC), isolated from hamsters and cultured for up to 25 days, were able to metabolize N-nitrosobis(2-oxopropyl)amine (BOP) to species that were mutagenic in V79 cells. There was no decline in the nitrosamine-activating ability of DEC over the period of observation (25 d). DEC activated N-nitrosobis(2-hydroxypropyl)amine (BHP), N-nitrosodiethylamine (DEN), N-nitrosodimethylamine (DMN) and N-nitrosomethyl(2-oxopropyl)amine (MOP) and BOP in the same assay, although the mutation frequencies for BHP, DEN and DMN were barely different from that for the controls (4 +/- 1 mutants/10(6) cells). The mutation frequencies for a dose of 0.1 mM were BHP, 2 +/- 1; BOP, 113 +/- 7; DEN, 8 +/- 1; DMN, 5 +/- 2; and MOP, 18 +/- 3 (mutants/10(6) cells; means +/- SE). When hepatocytes were used the mutation frequencies were BHP, 3 +/- 1; BOP, 60 +/- 3; DEN, 8 +/- 2; DMN, 8 +/- 2; and MOP, 121 +/- 10. BOP was toxic to the DEC at doses above 0.1 mM. Experiments in which co-factors were omitted from the medium suggested that an isoform(s) of the cytochrome P-450 IIIA family was involved, directly or indirectly, in BOP activation.     

Activity of bromochlorodifluoromethane (BCF) in three mutation tests

The halocarbon BCF was tested in 3 assays to assess its mutagenicity and clastogenicity. It produced a positive response in Salmonella typhimurium strain TA1535 but was negative in TA1537, TA1538, TA98 and TA100. In an L5178Y mouse lymphoma microwell assay (TK locus), BCF was negative. BCF was administered at 5000 and 50 000 ppm in air for 6 h to groups of C57B1/6J mice of both sexes. Animals were killed at 24, 48 and 72 h after cessation of exposure and the incidence of bone marrow micronuclei per 1000 PCEs determined. There was no significant difference in the incidences of micronuclei between untreated animals and those exposed to either concentration of BCF at any of the sampling times. These results suggest that BCF is mutagenic in vitro in only one strain of Salmonella; in mammalian cells the compound induced no gene mutation in vitro nor clastogenic activity in vivo at doses that also produced clear evidence of toxicity.     

The mutagenic activity of selected compounds at the TK locus: rodent vs. human cells

The mutagenic (TFT resistance) and toxic responses of mouse lymphoma (MOLY) L5178Y cells and human lymphoblast (HULY) TK6 cells were compared for 13 chemicals. The mutagenic activities of 8 of the 13 chemicals (62%) examined in the HULY and MOLY assays are in agreement - the results being judged positive in both assays. However, a dramatic difference is observed when the two conditions of metabolic activation are considered separately; the overall concordance of 8/13 has been achieved by combining a 13/13 (100%) agreement in the absence of S9 with a 1/6 (17%) agreement in the presence of S9. In the absence of S9, the concentration ranges, lowest significant doses, and shapes of the concentration-response curves for both toxicity and mutagenicity were similar in spite of the differences in exposure times (4 h for MOLY, 20 for HULY) and expression times (2 days for MOLY, 3 days for HULY). The general agreement observed in the absence of S9 contrasted with the differences manifested in its presence. 6 compounds which were negative in the absence of S9 were tested in both the MOLY and HULY assays in the presence of S9. Of the 6 chemicals, only 1 was positive in both MOLY and HULY under the latter condition; 4 others were positive in MOLY and negative in HULY whereas 1 was positive in HULY and negative in MOLY.     

Genotoxicity of 6 oxime compounds in the salmonella/mammalian-microsome assay and mouse lymphoma TK +/- assay

To aid in the selection of chemical candidates for in vivo tests, the mutagenicity of 6 oxime compounds was evaluated in the Salmonella plate incorporation assay and mouse lymphoma L5178Y TK +/- assay. All of the oximes were mutagenic in the mouse lymphoma assay in the absence of exogenous metabolic activation. Acetaldehyde oxime was also mutagenic in the presence of S9 activation. In contrast to these results, a positive response was noted only for 2-(hydroxyimino)-N-phenyl-acetamide oxime in strain TA1535 in the absence of activation in the Salmonella/microsome test.     

Endogenous xenobiotic enzyme levels in mammalian cells.

The response of mammalian cell lines to chemicals depends, in part, on the exogenous activation system used for the induction of a biological response. This could be attributed to differences in the expression of enzymes involved in xenobiotic metabolism. We have measured the activities of benzo[a]pyrene hydroxylase, dimethylaminoazobenzene N-demethylase, catalase, superoxide dismutase, peroxidase and glutathione-S-transferase in human lymphoblast TK6, mouse lymphoma L5178Y, Chinese hamster ovary (CHO) and lung (V79) and mouse C3H10T1/2 cell lines as well as in primary hepatocytes and S9 preparations of liver from male F344 rats. Nitroreductase was also measured in some of these preparations. Human lymphoblast TK6 and mouse C3H10T1/2 cells had the capacity to metabolize dimethylaminoazobenzene and the latter cell line also metabolized benzo[a]pyrene, indicating the presence of constitutive mono-oxygenase activity. Cytochrome P450 could not be detected spectrophotometrically in the cell lines. Western blot analysis indicated that P450 from the P450IIA family is expressed in C3H10T1/2 cells. Reactivity was also observed with an antibody to P450IA2; however, the identity of this protein remains uncertain. Superoxide dismutase, catalase and peroxidase, which protect cells against oxygen radical damage, were found in all the cell lines and in rat hepatocytes and S9. The human lymphoblast TK6 cell line, however, had the least of each of these three enzymes. Glutathione-S-transferase activity was detected at varying levels in all cell types. Nitroreductase activity was high in S9 and Chinese hamster ovary cells and lower in mouse lymphoma and Chinese hamster V79 cells.     

Mutagenicity and clastogenicity of proflavin in L5178Y/TK +/- -3.7.2.C cells

We evaluated the ability of proflavin to induce specific-locus mutations at the heterozygous thymidine kinase (tk) locus of L5178Y/TK +/- -3.7.2C mouse lymphoma cells, which appears to permit the recovery of mutants due to single-gene and chromosomal mutations. Proflavin was highly mutagenic at the tk locus, producing 724-965 TK mutants/10(6) survivors (background = 56-85/10(6); survival = 29-32%). Most of the mutants were small colonies, which suggested that proflavin may induce chromosomal mutations. The potent clastogenicity of proflavin was confirmed by cytogenetic analysis for chromosomal aberrations. At the highest dose analyzed (1.5 micrograms/ml), proflavin produced 82 aberrations/100 metaphaes (background = 2/100). The large-colony TK mutant frequency produced by proflavin (48-109/10(6) survivors; background = 23/10(6); survival = 57-61%) was similar to published HPRT mutant frequencies produces by proflavin in L5178Y and CHO cells (50-100/10(6) survivors; background = 2-50/10(6); survival = 50-62%). These results lead to the conclusion that proflavin is a potent clastogen and induces a high frequency of small-colony TK mutants; however, it induces a low frequency of HPRT mutants and a low frequency of large-colony TK mutants.     

Inhibitory effect of organic solvents on the mutagenicity of N-nitrosodialkylamines in Salmonella

The influence of organic solvents on the mutagenicity of 11 N-nitrosamines was examined in Salmonella typhimurium TA100 using the Ames's liquid incubation assay in the presence of rat-liver S9. The mutagenic activities of N-nitrosodimethylamine, N-nitrosodiethylamine, 6 oxidative derivatives of N-nitrosopropylamine and N-nitroso-2,6-dimethylmorpholine were considerably decreased by addition of dimethyl sulfoxide, dimethyl formamide, acetone, 95% ethanol or acetonitrile, which are recommended for use as solvents in the assay by Ames's group, to the incubation mixture. The mutagenic activities of N-nitrosodipropylamine and N-nitrosodibutylamine, which are barely soluble in water, were also suppressed by increasing concentrations of dimethyl sulfoxide. These organic solvents did not appear to exert their influence by desmutagenic and antimutagenic actions. In contrast, the recoveries of unmetabolized carcinogens from preincubation mixtures and from agar plates were significantly higher in the presence of organic solvents than in their absence. The results indicate that the inhibitory effect is a result of interference with the process of metabolic activation by liver S9.     

The mutagenic potency of 4 agents at the thymidine kinase locus in mouse lymphoma L5178Y cells in vitro: effects of exposure time

Mutagenic potency at the thymidine kinase (TK) locus in mouse lymphoma L5178Y cells (expressed as induced trifluorothymidine (TFT)-resistant mutants/total dose) was assessed for 4 agents (ethyl methanesulphonate (EMS), benzidine, 1,8-dinitropyrene (1,8-DNP) and ICRF 159) using short (3-4 h) and long (21-24 h) exposure times. The mutagenic potency of EMS was found to be essentially independent of concentration and exposure time when tested over a cytotoxic range consistent with routine testing procedures. Similar results were obtained with benzidine but for both 1,8-DNP and ICRF 159 mutagenic potency was found to be highly dependent on the concentration and exposure time. 1,8-DNP failed to induce any significant increases in mutant frequency when tested at concentrations up to 5 micrograms/ml using short exposure times, whereas the compound was active at concentrations as low as 0.1 microgram/ml when the exposure period was extended to 21 h. Under the latter conditions, however, the molar potency of 1,8-DNP was found to be inversely related to concentration over a range extending from 0.1 to 5 micrograms/ml. ICRF 159 induced increases in the frequency of TFT-resistant mutants using short or long exposure times. When a short exposure time was used, however, the mutagenic potency of the antitumour agent decreased with increasing concentration between 1 and 500 micrograms/ml. Although possible explanations can be offered to account for these observations the results illustrate potential problems which may arise in this system when comparing mutagenic potency values for a range of compounds with a view to assessing relative risk.     

Urethane and N-nitrosodiethylamine are mutagenic for the Syrian hamster fetus

Urethane and N-nitrosodiethylamine are soluble environmental carcinogens that initiate tumors transplacentally, but have a mixed history of effectiveness in mutagenesis assays in vitro or in vivo with adult rodents. To test for their transplacental mutagenicity, Syrian hamster fetuses at 12 days in gestation were exposed transplacentally to urethane or N-nitrosodiethylamine at 0.5 or 1.0 mM/kg. The fetal cells were isolated on day 13 of gestation and tested for diphtheria toxin resistance as a mutation marker. Both compounds were significantly mutagenic, at both doses, causing 6- to 20-fold increases in mutations compared with controls. Compared with N-nitrosodiethylamine, urethane was somewhat more effective as a mutagen with a more marked dose-response. These results are consistent with mutagenesis as part of the mechanism of transplacental carcinogenicity of urethane and N-nitrosodiethylamine.     

Activation of mutagens by hepatocytes and liver 9000 X g supernatant from human origin in the Salmonella typhimurium mutagenicity assay. Comparison with rat liver preparations

The mutagenicity of 10 known genotoxic compounds, of several chemical classes, was measured in Salmonella typhimurium mutagenicity assays comprising isolated human hepatocytes or human liver 9000 X g supernatant (S9) from 4 different individuals, as activating system. The mutagenic activity of several compounds as determined with the Salmonella/hepatocyte suspension assay showed obvious differences when compared with the values obtained in the Salmonella/S9 plate assay. For instance, the mutagenic activity of BZ, DMN and DEN appeared to be much higher in the hepatocyte assay than in the S9 assay. However, 2-AF and 2-AAF were activated more effectively into mutagens in the S9 assay than in the hepatocyte assay. 2-AF was slightly more mutagenic than 2-AAF in the hepatocyte assay, whereas it was far more mutagenic than 2-AAF in the S9 assay. DMN was found more mutagenic than DEN in the hepatocyte assay, whereas in the S9 assay DEN appeared to be slightly more mutagenic. Furthermore, great interindividual differences in the metabolic activation of certain compounds, e.g. BZ and DMN, were observed in the hepatocyte suspension assay, whereas these variations were less evident in the S9 plate assay. Comparison of the mutagenicity data obtained with the human liver preparations, with those obtained with rat liver preparations, showed great interspecies differences in the capacity to activate certain chemicals into mutagens. The use of human liver preparations, in particular isolated human hepatocytes, may be of great value in studies on inter- and intraspecies variations in metabolic activation of genotoxic agents.     

Metabolic activation capabilities of S9 and hepatocytes from uninduced rats to convert carcinogenic N-nitrosamines to mutagens

6 carcinogenic nitrosamines were studied in Salmonella typhimurium TA1535 after activation by S9 and by hepatocytes. All nitrosamines were activated by S9 from induced rats, regardless of their organotropy. The hepatocarcinogenic nitrosamines (N-nitrosodimethylamine, NDMA; N-nitrosodiethylamine, NDEA; N-nitrosomorpholine, NM and N-nitrosodibutylamine, NDBA) were activated to mutagens by S9 and by hepatocytes both derived from noninduced rat livers, NDMA and NM inducing more his+ revertants in the presence of hepatocytes. The oesophageal carcinogenic nitrosamine N-nitrosomethylbenzylamine (NMBeA) and bladder organotrophic N-nitroso(4-hydroxybutyl)butylamine(NBBOH) were neither converted by liver preparations of uninduced rats into mutagenic intermediates nor by hepatocytes. This study indicates that isolated cells derived from untreated animals may be better suited to study liver specific activation in vitro than disrupted subcellular metabolizing systems from induced animals.     

Mutagenicity towards Salmonella typhimurium of some known genotoxic agents,activated by isolated hepatocytes of monkey (Macaca fascicularis): Comparison with isolated human hepatocytes

This paper describes some striking differences between isolated human and monkey hepatocytes in their capacity to activate some known genotoxic agents into products mutagenic towards Salmonella typhimurium.Isolated monkey hepatocytes, in contrast to human hepatocytes, appeared to activate benzidine (BZ), N-acetylbenzidine (MABZ), N,N′-diacetylbenzidine (DABZ), 2-aminofluorene (2-AF) and 2-acetylaminofluorene (2-AAF) poorly. With monkey hepatocytes BZ was slightly more mutagenic than DABZ, whereas with human hepatocytes DABZ was more active than BZ. N-Nitrosodimethylamine (DMN) and N-nitrosodiethylamine (DEN) were also found to be poorly mutagenic when activated by monkey hepatocytes, unlike the human hepatocytes. However, the polycyclic arylhydrocarbons benzo[a]pyrene (B[a]P) and 7,12-dimethylbenzanthracene (7,12-DMBA) were highly active in the presence of monkey hepatocytes, unlike the human hepatocytes. A metabolic study showed that monkey liver preparations seem to possess a higher monooxygenase activity towards B[a]P than human liver preparations.