In vitro mutagenicity and cell-transformation screening of N-(2,3-epoxy-propyl)-phthalimide.

N-(2,3-Epoxy-propyl)-phthalimide (EPP) was tested for genetic activity in the Salmonella/microsome mutagenicity test. Concentration-dependent mutagenicity was demonstrated in S. typhimurium strains TA1535, TA1537 and TA100 with and without rat S9. It was inactive in strain TA1538, and active without rat S9 in TA98 at the high dose. EPP induced 6-thioguanine-resistant mutants of Chinese hamster ovary cells in the absence of an exogenous activating system. EPP produced dose-dependent enhancement of SA7 virus transformation of primary hamster-embryo cells, and transformed secondary hamster-embryo cells in a non-dose-related fashion. At a dose of 5 g/kg p.o. or i.m., EPP was inactive in the host-mediated assay using C57Bl/6XC3H mice and S. typhimurium strain TA1535. Murine testicular DNA synthesis was not inhibited by oral administration of EPP at 1000 mg/kg.     

Mutagenic and genotoxic effects of theophylline and theobromine in Salmonella assay and in vivo sister chromatid exchanges in bone marrow cells of mice.

The mutagenic and genotoxic effects of two methylxanthines, theophylline (TH) and theobromine (TB), were assessed in the Ames mutagenicity assay (in strains TA97a, TA100, TA102 and TA104) and in vivo sister chromatid exchanges (SCEs) in bone marrow cells of mice. These are the two most commonly used nervous system stimulators throughout the world. TH is used in the long-term treatment of asthma. Bacterial mutagenicity assay showed very weak mutagenic effects of both drugs in Salmonella strains TA102 and TA104 only in certain concentrations when S9 was added to it. No mutagenic effects were observed in any other strains used in this assay either with or without metabolic activation. But results of in vivo SCE assay indicate that these two drugs can induce significant SCE in bone marrow cells of mice.     

Genotoxicity assessment of new synthesized acridine derivative--3,6-diamino-10-methyl-9,10-dihydroacridine.

A new synthesized acridine derivative, 3,6-diamino-10-methyl-9, 10-dihydroacridine (AcrH), was tested for in vitro reverse mutations with Salmonella TA strains, chromosome aberrations and sister chromatid exchanges (SCE) in human lymphocytes, and for in vivo chromosome aberrations in bone marrow of mice. Using the classic plate incorporation method, mutagenicity of AcrH in bacterial cells (TA97a, TA98, TA100 and TA102) was observed in the experiments performed with, and without, rat liver S9 metabolic activation. The reverse mutation assay showed no difference in mutagenic activity between AcrH and acriflavine (Acr(+)) in the test with TA97. The results of in vitro chromosome aberrations assay revealed potential clastogenicity. The test using macroculture of human lymphocytes induced mainly chromatid gaps. The experiments with human lymphocytes revealed SCE-inducing effect of AcrH and Acr(+). In an in vivo study, AcrH given intraperitoneally to Balb/c mice did not cause any significant increase in the percentage of cells with aberrations compared to the negative control.     

Genotoxic activity of pulp mill effluent in Salmonella and Saccharomyces cerevisiae assays

An XAD-2 resin concentrate of chlorination-stage pulp mill effluent was found to induce mutations in Salmonella typhimurium strains TA1535, TA100 and TA98 but not in strains TA1537 or TA1538. The presence of either S9 mix, S9 mix without cofactors, or heat-inactivated S9 mix, reduced the mutagenic effects. Dose-related increases in gene conversion, mitotic recombination and aberrant colony formation in Saccharomyces cerevisiae strain D7 also were found.     

Evaluation of the genetic and embryotoxic effects of bis(tri-n-butyltin)oxide (TBTO), a broad-spectrum pesticide, in multiple in vivo and in vitro short-term tests

The genetic and embryotoxic effects of bis(tri-n-butyltin)oxide (TBTO) were evaluated in multiple in vivo and in vitro short-term tests preparatory to its potential wide use as a molluscicide in control of schistosomiasis. When tested in the rec assay in Bacillus subtilis, TBTO was not mutagenic and it did not induce reverse mutations in Klebsiella pneumoniae. Neither in the presence nor in the absecne of rat liver activation system did TBTO produce point mutations in Salmonella typhimurium strains TA1530, TA1535, TA1538, TA97, TA98 or TA100. TBTO was matagenic in strain TA100 in a fluctuation test, but only in the presence of rat liver S9 (Aroclor-induced). TBTO did not induce gene mutations in the yeast Schizosaccharomyces pombe, mitotic gene conversions in the yeast Saccharomyces cerevisiae, nor sister-chromatid exchange in Chinese hamster ovary cells in the presence or absence of rat or mouse liver S9. In the latter cells, structural chromosomal aberrations, endoreduplicated and polyploid cells were induced. TBTO did not induce gene mutations in V79 Chinese hamster cells (to 8-azaguanine-, ouabain- or 6-thioguanine-resistance) in the presence of a rat liver postmitochondrial fraction or in cell (hamster embryo cells and human and mouse epidermal keratinocyte)-mediated assays. In mouse lymphoma cells, TBTO did not induce 6-thioguanine- or BUdR-resistant mutations. As many tumour promoters inhibit metabolic cooperation between V79 Chinese hamster 6-thioguanine-resistant/-sensitive cells, TBTO was tested but showed no such activity. TBTO was examined for the induction of recessive lethal mutations in adult Berlin K male Drosophila melanogaster, either by feeding or by injection. Doses of 0.37 or 0.74 mM did not increase the number of X-linked recessive lethal mutations. An increased number of micronuclei was observed in the polychromatic erythrocytes of male BALB/c mice 48 h after a single oral dose of TBTO (60 mg/kg bw), while a lower dose (30 mg/kg bw) was ineffective. Neither of the two doses had induced micronuclei 30 h after treatment. The reproductive toxicity of TBTO was studied in NMRI mice. In a 10-day toxicity study, the LD50 and LD10 were 74 and 34 mg/kg bw, respectively. An increased frequency of cleft palates was seen in the fetuses of mice (compared with controls, 0.7%) treated orally during pregnancy with 11.7 mg/kg TBTO (7%), 23.4 mg/kg (24%) or 35 mg/kg (48%).(ABSTRACT TRUNCATED AT 400 WORDS)     

Genotoxic evaluation of extracts from Aplysina fulva, a Brazilian marine sponge

A range of biologically active secondary metabolites with pharmacological application has been reported to occur in marine sponges. The present study was undertaken to provide a set of data on the safety of a hydro-alcoholic extract (ALE) and an aqueous fraction (AQE) from Aplysina fulva Pallas, 1766 (Aplysinidae, Verongida, Porifera). Salmonella typhimurium strains TA97, TA98, TA100 and TA102, Escherichia coli strains PQ65, OG40, OG100, PQ35 and PQ37 and Balb/c 3T3 mouse fibroblasts were used to detect induction of DNA lesions by ALE and AQE. Assays used for these analyses were a bacterial (reverse) mutation assay (Ames test), the SOS-chromotest and the comet assay. Both extracts presented identical infrared 2-oxazolidone spectra. ALE treatment induced a higher frequency of type-4 comets, indicative of increasing DNA migration, in the alkaline comet assay. ALE also induced a weak genotoxic effect, as expressed by the induction factor (IF) values in the test with E. coli strain PQ35 (IF=1.5) and by cytotoxic effects in strains PQ35, PQ65 and PQ37. Positive SOS induction (IF=1.7) was detected in strain PQ37 treated with diluted AQE. No genotoxic effects were observed in strains PQ35, PQ65, OG40 and OG 100 after treatment with AQE dilutions. Using the bacterial (reverse) mutation test and survival assays with or without S9 mix, after 60min of pre-incubation, we observed for strain TA97 treated with ALE a weak mutagenic response (MI=2.2), while cytotoxic effects were seen for strains TA98, TA100 and TA102. AQE did not show mutagenic activity in any of the strains tested, but a weak cytotoxic effect was noted in strain TA102. Our data suggest that both ALE and AQE from A. fulva induce DNA breaks leading to cytotoxicity and mutagenicity under the conditions used.     

Mutagenicity study of fried sausages in Salmonella, Drosophila and mammalian cells in vitro and in vivo

The basic extract of pan-fried sausages was studied for mutagenic potential in seven test systems. Mutagenic activity was high in the standard Ames assay in the Salmonella typhimurium strains TA1538 and TA98 in presence of S9 mix. In vivo, in the intrasanguine host-mediated assay with strain TA98 on Aroclor-pretreated mice, the mutagenic activity of the extract was low. A borderline activity was seen in the SCE assay in vitro with V79 Chinese hamster cells in presence of S9 mix. No significant mutagenic action was found in the gene-mutation assay for thioguanine resistance with V79 cells, the Drosophila sex-linked recessive lethal test, the micronucleus test and the mammalian spot test.     

Genotoxicity of nitrosated ranitidine

The genotoxicity of ranitidine, widely used in the therapy of peptic ulcers, and of nitrosated ranitidine was examined in test systems with the bacteria Salmonella typhimurium for gene mutations, and with the yeast Saccharomyces cerevisiae D7 for reverse mutations and gene conversion. Under the experimental conditions applied, ranitidine was negative in both systems, while the product obtained by nitrosation in vitro was mutagenic for Salmonella strains TA100 and TA98 with and without metabolic activation. The largest increase of his+ revertants, 3 times greater than the control, was obtained in strain TA100 in the absence of S9 fraction. Nitrosated ranitidine was also recombinogenic for the yeast S. cerevisiae.     

Host-mediated mutagenicity experiments with benzo[a]pyrene and two of its metabolites

Benzo[a]pyrene (BP) and two of its major metabolites, the ultimate mutagen BP-4,5-oxide and the proximate mutagen trans-7,8-dihydro-7,8-dihydroxybenzo[a]pyrene (BP-7,8-diol) were investigated for mutagenicity in Salmonella typhimurium TA1538, TA98 and TA100 using an intrasanguineous host-mediated assay. BP and BP-4,5-oxide were not mutagenic under any experimental conditions. BP-7,8-diol was inactive with the strain TA1538 but was mutagenic with the strains TA98 and TA100. The effect was potentiated by pretreatment of the host mice with the cytochrome P-450 inducer 5,6-benzoflavone. We conclude: (i) one of the reasons for the observed insensitivity of the intrasanguineous host-mediated assay towards BP is that BP-4,5-oxide, which contributes to the microsome-mediated mutagenicity of BP, is inactive in the host-mediated assay; (ii) the finding that BP-7,8-diol is mutagenic in the host-mediated assay demonstrates that the lack of mutagenicity of BP is not intrinsic; (iii) the potentiated mutagenicity after treatment of the hosts with 5,6-benzoflavone suggests that cytochrome P-450 is more important in the activation of BP-7,8-diol in this system than other enzymes (e.g. prostaglandin synthase) that can also activate this compound in vitro.     

Evaluation of the mutagenic potential of endosulfan using the Salmonella/mammalian microsome assay

The mutagenic potential of endosulfan, a polychlorinated insecticide, was assessed using the highly sensitive Salmonella tester strains TA97(a), TA98, TA100 and TA102. It exhibited a toxic effect at dose levels of 50 micrograms/plate and higher. Plate incorporation studies did not show mutagenic response with any of the tester strains used. A modification of the assay using a preincubation procedure showed mutagenic activity with and without metabolic activation with TA97(a) only. Increased toxicity was observed after addition of phenobarbital-induced S9 mix.     

Cycloheximide genotoxicity in in vitro and in vivo test systems

The aim of this study was to investigate if there was any genotoxic effect produced by the antibiotic cycloheximide, widely used as a fungicide in agriculture as well as in everyday laboratory practice. The battery of test systems included the bacterium Salmonella typhimurium (strains TA98 and TA100), the yeast Saccharomyces cerevisiae (D7), Allium cepa somatic cells and mouse bone marrow cells. This combination of test systems enabled us to establish possible effects caused by cycloheximide at different levels of the genome and to indicate a possible mechanism of action. The results obtained in experiments showed that cycloheximide did not induce frameshift or base-pair substitution mutations in S. typhimurium regardless of metabolic activation. In S. cerevisiae cycloheximide had only toxic effects but no increase of mitotic gene conversion was noticed under the conditions of the experiment. However, in A. cepa somatic cells as well as in mouse bone marrow cells cycloheximide showed its activity causing different genetic damages, e.g., chromosome breaks, mitotic disturbances and nuclear abnormalities.     

Genotoxicity assessment of ethylenediamine dinitrate (EDDN) and diethylenetriamine trinitrate (DETN)

Ethylenediamine dinitrate (EDDN) and diethylenetriamine trinitrate (DETN) are relatively insensitive explosive compounds that are being explored as safe alternatives to other more sensitive compounds. When used in combination with other high explosives they are an improvement and may provide additional safety during storage and use. The genetic toxicity of these compounds was evaluated to predict the potential adverse human health effects from exposure by using a standard genetic toxicity test battery which included: a gene mutation test in bacteria (Ames), an in vitro Chinese Hamster Ovary (CHO) cell chromosome aberration test and an in vivo mouse micronucleus test. The results of the Ames test showed that EDDN increased the mean number of revertants per plate with strain TA100, without activation, at 5000μg/plate compared to the solvent control, which indicated a positive result. No positive results were observed with the other tester strains with or without activation in Salmonella typhimurium strains TA98, TA1535, TA1537, and Escherichia coli strain WP2 uvrA. DETN was negative for all Salmonella tester strains and E. coli up to 5000μg/plate both with and without metabolic activation. The CHO cell chromosome aberration assay was performed using EDDN and DETN at concentrations up to 5000μg/mL. The results indicate that these compounds did not induce structural chromosomal aberrations at all tested concentrations in CHO cells, with or without metabolic activation. EDDN and DETN, when tested in vivo in the CD-1 mouse at doses up to 2000mg/kg, did not induce any significant increase in the number of micronuclei in bone marrow erythrocytes. These studies demonstrate that EDDN is mutagenic in one strain of Salmonella (TA100) but was negative in other strains, for in vitro induction of chromosomal aberrations in CHO cells, and for micronuclei in the in vivo mouse micronucleus assay. DETN was not genotoxic in all in vitro and in vivo tests. These results show the in vitro and in vivo genotoxicity potential of these chemicals.     

Genotoxic evaluation of extracts from Aplysina fulva, a Brazilian marine sponge

A range of biologically active secondary metabolites with pharmacological application has been reported to occur in marine sponges. The present study was undertaken to provide a set of data on the safety of a hydro-alcoholic extract (ALE) and an aqueous fraction (AQE) from Aplysina fulva Pallas, 1766 (Aplysinidae, Verongida, Porifera). Salmonella typhimurium strains TA97, TA98, TA100 and TA102, Escherichia coli strains PQ65, OG40, OG100, PQ35 and PQ37 and Balb/c 3T3 mouse fibroblasts were used to detect induction of DNA lesions by ALE and AQE. Assays used for these analyses were a bacterial (reverse) mutation assay (Ames test), the SOS-chromotest and the comet assay. Both extracts presented identical infrared 2-oxazolidone spectra. ALE treatment induced a higher frequency of type-4 comets, indicative of increasing DNA migration, in the alkaline comet assay. ALE also induced a weak genotoxic effect, as expressed by the induction factor (IF) values in the test with E. coli strain PQ35 (IF = 1.5) and by cytotoxic effects in strains PQ35, PQ65 and PQ37. Positive SOS induction (IF = 1.7) was detected in strain PQ37 treated with diluted AQE. No genotoxic effects were observed in strains PQ35, PQ65, OG40 and OG 100 after treatment with AQE dilutions. Using the bacterial (reverse) mutation test and survival assays with or without S9 mix, after 60 min of pre-incubation, we observed for strain TA97 treated with ALE a weak mutagenic response (MI = 2.2), while cytotoxic effects were seen for strains TA98, TA100 and TA102. AQE did not show mutagenic activity in any of the strains tested, but a weak cytotoxic effect was noted in strain TA102. Our data suggest that both ALE and AQE from A. fulva induce DNA breaks leading to cytotoxicity and mutagenicity under the conditions used.     

Screening of safrole, eugenol, their ninhydrin positive metabolites and selected secondary amines for potential mutagenicity.

The mutagenicity of safrole, eugenol, the secondary amines, with which they combine during metabolism, and the ninhydrin positive urinary metabolites of safrole and eugenol was tested. The panel of tests included the direct bacterial assay, a microsomal mutagenesis assay and a host-mediated assay. With the direct bacterial assay employing four mutant strains of Salmonella typhimurium (TA1530, TA1531, TA1532, TA1964), all the compounds gave negative results. In the microsomal mutagenesis assay, employing the same four mutant strains, safrole and safrole metabolite II were mutagenic with strains TA1530 and TA1532. Dimethylamine was also found to be a weak mutagen in the microsomal mutagenesis assay with strain TA1530. Safrole and safrole metabolite II were also mutagenic in the host-mediated assay with strains TA1950 and TA1952. Negative results were observed for safrole metabolites I and III, eugenol, eugenol metabolites I and II, piperidine, pipecolic acid, proline, and pyrrolidine in all three assay systems.     

Inhibition of dinitropyrene mutagenicity in vitro and in vivo using Salmonella typhimurium and the intrasanguinous host-mediated assay

Dinitropyrenes (DNP), present in polluted air, are potent direct-acting mutagens in Salmonella typhimurium TA98. This mutagenicity is markedly reduced in the presence of rat-liver S9 or microsomes. This has now been confirmed using mouse hepatic fractions. Since most in vitro test systems do not adequately simulate conditions encountered in the intact animal, we have investigated dinitropyrene mutagenicity to Salmonella in the host-mediated assay. 1,8-Dinitropyrene (1,8-DNP) given p.o. to BALB/c mice induced a weak mutagenic effect in S. typhimurium TA98 recovered from the liver 1 h after i.v. administration (optimum time). Over the entire dose range tested no toxicity to bacterial cells was detected. Mutation induction in vivo was dose-related with maximum response at 1 mg DNP/kg body weight. This optimum dose, however, was non-mutagenic to strains TA98/1,8-DNP6 (O-transacetylase-deficient) or TA98NR/1,8-DNP6 (nitroreductase- and O-transacetylase-deficient). 1,3-Dinitropyrene and 1,6-dinitropyrene were weakly mutagenic to TA98 at doses similar to 1,8-DNP. Studies with [14C]1,8-DNP showed that 1 h after oral dosing (1 mg/kg), over 100 ng of 1,8-DNP equivalents were present in the liver (= 0.73% dose). However, only about 5.5 ng were present in the bacterial pellet, suggesting that hepatic components in vivo, as in vitro, bind to DNP, thus interfering with its interaction with Salmonella.     

Mutagenicity testing of condensates of smoke from titanium dioxide/hexachloroethane and zinc/hexachloroethane pyrotechnic mixtures

Condensates of smoke from titanium dioxide/hexachloroethane and zinc/hexachloroethane pyrotechnic mixtures were investigated for their potential to produce genetic damage in the tester strains TA98, TA100, TA1535 and TA1537 of Salmonella typhimurium and in the mouse bone marrow micronucleus assay. Both smoke condensates contained several chlorinated hydrocarbons among which tetrachloroethylene, hexachloroethane, hexachlorobutadiene and hexachlorobenzene were identified by GC/MS. Condensate of smoke from titanium dioxide/hexachloroethane showed a dose-related positive response in the Salmonella assay with strains TA98 and TA100 in the absence of metabolic activation from rat liver S9 fraction. Both smoke condensates were negative in the micronucleus assay but produced a small but significant depression of erythropoietic activity. The results indicate that smoke condensate from titanium dioxide/hexachloroethane mixtures contains unidentified compound(s) that may be considered mutagenic in the Salmonella assay.     

Butylated hydroxyanisole, butylated hydroxytoluene and tert.-butylhydroquinone are not mutagenic in the Salmonella/microsome assay using new tester strains

The phenolic antioxidants butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT) and tert.-butylhydroquinone (TBHQ) were reassessed for mutagenic activity using the recently developed Salmonella tester strains TA97, TA102 and TA104, and in addition TA100. None of the phenolic antioxidants showed mutagenic activity, either with or without metabolic activation. At doses of 100 micrograms/plate and higher all 3 phenolic antioxidants exhibited toxic effects. A modification of the assay using the preincubation procedure with strain TA104 did not affect mutation frequencies. Combinations of BHA and BHT, tested to detect possible synergistic effects, did not exert mutagenic activity.     

Mutagenicity studies on fenitrothion in bacteria and mammalian cells

The mutagenicity of fenitrothion was determined in strains of Salmonella typhimurium and Escherichia coli. Fenitrothion was found to be non-mutagenic in Salmonella typhimurium strains of TA98, TA1535 and TA1537 and in Escherichia coli WP2uvrA both with and without S9 mix, while weak mutagenicity was observed only in Salmonella typhimurium TA100 and enhanced by the addition of S9 mix. The mutagenicity observed in the TA100 strain was not expressed in a nitroreductase-deficient strain, TA100 NR, and decreased in a transacetylase-deficient strain, TA100 1,8-DNP6. The mutagenicity of fenitrothion was also examined by a gene mutation assay using the gene for hypoxanthine-guanine phosphoribosyltransferase (hgprt) in V79 Chinese hamster lung cells. Fenitrothion did not induce any increment of 6-thioguanine-resistant mutant cells at doses ranging from 0.01 to 0.3 mM regardless of the presence or absence of S9 mix. These results suggest that reduction of fenitrothion by a bacterial nitroreductase of TA100 to an active form is essential for the expression of the mutagenicity of fenitrothion in TA100 and that a bacterial transacetylase of TA100 also has an important role in the process of mutagenic activation.     

The mutagenicity and DNA-damaging activity of cyclic aliphatic sulfuric acid esters.

The cyclic aliphatic sulfuric acid esters 1,2-ethylene sulfate (ESF), 1,3-propylene sulfate (PSF) and 1,3-butylene sulfate (BSF) have been tested for their mutagenic and DNA-damaging activity. Mutagenicity of the compounds was established with his-auxotrophic indicator strains of Salmonella typhimurium using the in vitro plate test and the host-mediated assay technique with mice as host animals. The DNA-damaging activity was tested in a repair test with Proteus mirabilis mutants defective in DNA repair.In the repair test with a set of P. mirabilis strains (PG713 hcr^?rec^?: PG273 hcr⁺rec⁺) PSF and BSF showed a preferential growth inhibition of the repair-defective strain suggesting DNA-damaging activity of these chemicals. No such activity was found for ESF using the same concentrations of 5 and 15 μmol/plate.All cyclic sulfates revert the tester strain TA1535 of S. typhimurium in vitro indicating their ability to induce base substitutions. Compared with the reference compounds dimethyl sulfate (DMS), diethyl sulfate (DES), 1,3-propane sulfone (PPS) and 1,4-butane sulfone (BTS) the mutagenic activity in the plate test can be described as follows: PPS > PSF > BSF > BTS > ESF > DES > DMS.Dose-response studies in the host-mediated assay with tester strain TA1950 of S. typhimurium as genetic indicator system revealed a linear dosedependency of mutagenic activity. For PPS and PSF the lowest effective dose (LED) has been established as 10 μmol/kg. The LED for BSF and BTS was 50 μmol/kg, DMS and DES were mutagenic in doses of 2500 μmol/kg, while ESF was only weakly mutagenic with a LED of 5000 μmol/kg.The dose-response studies in the host-mediated assay and the results obtained in the in vitro spot test demonstrate similarities in the mutagenic action of the cyclic sulfates PSF and BSF and the respective sulfones, while the stronger alkylating compound ESF was a weak mutagen both in vitro and in vivo.     

Genetic toxicity of the benzene metabolite trans, trans-muconaldehyde in mammalian and bacterial cells

Previous studies in our laboratory identified trans,trans-muconaldehyde (MUC), a six-carbon diene dialdehyde, as a microsomal metabolite of benzene. This ring-opened metabolite of benzene was also shown to be hematotoxic in mice in a manner similar to benzene. To further explore the role of MUC in relation to benzene toxicity, a number of test systems were utilized to determine its genotoxic potential. In B6C3F1 mice, MUC induced a highly significant increase in sister-chromatid exchange (SCE), the lowest effective dose being 3 mg/kg, but failed to induce any micronuclei (MN). In Chinese hamster ovary (CHO) cells, MUC at concentrations up to 0.8 micrograms/ml was negative in the hypoxanthine-guanine phosphoribosyl transferase (HGPRT) assay. Dose-related increases in the percentage of cells with MN were observed in CHO cells treated with 0.4-0.8 micrograms/ml MUC. MUC did not-cause unscheduled DNA synthesis in rat primary hepatocytes. Treatment of Salmonella typhimurium TA97 with MUC induced a low level of mutations at concentrations ranging from 10 to 70 micrograms/ml with or without S9 activation. MUC was inactive in strains TA1535, TA100, TA1538 and TA98. In CHO cells and rat primary hepatocytes, MUC was cytotoxic at 0.4 and 4.0 micrograms/ml, respectively. Concentrations of 100 micrograms/plate MUC were toxic for bacterial cells. The present findings indicate that MUC is nonmutagenic or minimally mutagenic in bacterial and mammalian in vitro systems. In mammalian cells, MUC is highly cytotoxic and genotoxic.