Analytical in vitro approach for studying cyto- and genotoxic effects of particulate airborne material

In the field of inhalation toxicology, progress in the development of in vitro methods and efficient exposure strategies now offers the implementation of cellular-based systems. These can be used to analyze the hazardous potency of airborne substances like gases, particles, and complex mixtures (combustion products). In addition, the regulatory authorities require the integration of such approaches to reduce or replace animal experiments. Although the animal experiment currently still has to provide the last proof of the toxicological potency and classification of a certain compound, in vitro testing is gaining more and more importance in toxicological considerations. This paper gives a brief characterization of the CULTEX® Radial Flow System exposure device, which allows the exposure of cultivated cells as well as bacteria under reproducible and stable conditions for studying cellular and genotoxic effects after the exposure at the air-liquid or air-agar interface, respectively. A commercial bronchial epithelial cell line (16HBE14o-) as well as Salmonella typhimurium tester strains were exposed to smoke of different research and commercial available cigarettes. A dose-dependent reduction of cell viability was found in the case of 16HBE14o- cells; S. typhimurium responded with a dose-dependent induction of revertants. The promising results recommend the integration of cellular studies in the field of inhalation toxicology and their regulatory acceptance by advancing appropriate validation studies.

Mutagenicity studies of kojic acid

Kojic acid, a fungal metabolite produced by some species of Aspergillus and Penicillium, was found to induce sister chromatid exchanges and chromosomal aberrations in Chinese hamster ovary cells in the presence or absence of the rat liver S9 mix. Furthermore, this compound was demonstrated to induce mutations in Salmonella typhimurium strains TA98 and TA100 using both plate-incorporation and preincubation methods.

Mutagenicity of the C-nitroso analog of fenitrothion

The chemicals fenitrothion, nitroso fenitrothion, amino fenitrothion and 3-methyl-4-nitrophenol were tested for mutagenicity to Salmonella typhimurium strains TA98 and TA100, both in the presence and absence of rat liver S-9 mix. The strong mutagenicity of nitroso fenitrothion to both strains either in the presence or absence of S-9 mix contrasted with the observation that fenitrothion displayed no mutagenicity in these tester strains. The results suggest that the normal nitroreductases present in TA98 and TA100 cannot metabolize fenitrothion to a mutagenic metabolite. This inability of the tester strains to effect partial nitroreduction results in the failure of this screening system to predict the potential genotoxicity of this pesticide.

Characterization of water-soluble glucuronide and sulphate conjugates of aflatoxin B1. 1. Urinary excretion in monkey, rat and mouse

Water-soluble aflatoxin conjugates prepared from urine samples from rats, mice and rhesus monkeys dosed with [14C]aflatoxin B1 (AFB1) ip or iv were hydrolysed by enzymes (beta-glucuronidase and sulphatase), acid or a combination of both treatments. Different amounts of AFB1 and its metabolites were found in hydrolysates from different sources, indicating the presence of glucuronide, sulphate and possibly mercapturate conjugates of aflatoxins. In addition to aflatoxins M1, P1, Q1 and B2a, AFB1 was frequently identified in the products released from the hydrolysates. These water-soluble aflatoxin conjugates were not mutagenic to Salmonella typhimurium TA98 in the presence of rat-liver S-9 mix. However, chloroform extracts of the hydrolysates from beta-glucuronidase and sulphatase treatment showed mutagenic activity in these bacteria in the presence of S-9 mix. Although very low levels of AFB1 radioactivity were detected in the hydrolysates, the potent mutagenic activity of AFB1 contributed to the high numbers of revertant colonies. AFP1 was detected in urine samples from monkeys that were pretreated with phenobarbital before an iv dose of AFB1. No mutagenic activity was detected in the enzymatic hydrolysate of the sample from these monkeys. The results thus indicate that AFB1 can form glucuronide and/or sulphate conjugate(s) directly and be excreted in the urine.

Mutagenicity of azo dyes in the Salmonella/microsome assay using in vitro and in vivo activation

The mutagenicity of 6 azo dyes, including direct black 38 (DB38), direct black 19 (DB19), direct brown 95 (DB95), solvent yellow 3 (SY3), trypan blue (TPB), and food black 2 (FB2), was examined in the Salmonella/microsome assay. The effect of chemical azo reduction (dithionite) and in vivo metabolism on the mutagenicity of the dyes was also studied. In vivo azo-dye metabolites were isolated from the urine of rats intubated with dyes by XAD-2 column chromatography. Urinary metabolites from all the treated animals, except animals treated with FB2, induced frame-shift mutations in strains TA1538 and TA98 in the presence of liver S9 activation. The control urine did not increase the incidence of revertants in strains TA1538 and TA98. Thus, XAD-2 chromatography can be used to isolate genotoxic metabolites from the urine of animals intubated with azo dyes.

Mutagen content of wines contaminated with common yeasts

Wines exhibiting a microbial haze were collected and their microbial contents identified. Contaminant yeast species were cultured in grape musts under controlled conditions and extracts of the resultant wines were assayed for mutagen content using four strains of Salmonella in the Ames Salmonella/microsome/faecalase system. The wine extracts exhibited some toxicity to Salmonella but no mutagen content. It would appear that mutagen content is more a function of the grape species and must preparation than of microbial metabolism during fermentation.

Mutagenicity of some monoaromatic hydroxamic acids

The mutagenicity of some monoaromatic hydroxamic acids was tested in the presence and absence of rat liver S-9 with Salmonella typhimurium tester strains TA98 and TA100. Of the five N-(chlorophenyl)-substituted hydroxamic acids and seven N-arylformohydroxamic acids tested, 2 of the first and 4 of the latter series were mutagenic to both strains upon metabolic activation. None of the four N-acetyl-type hydroxamic acids was mutagenic to either strain, even upon activation. Because some of the N-acetyl-derived hydroxamic acids were inactive, whereas the same aromatic nucleus possessing a formyl group displayed significant activity, a consideration of the nature of the aryl group in hydroxamic acid mutagenicity is important.

Mutagen content of table wines made from various grape species and hybrid cultivars

The mutagen content of wines produced from the European Vitis vinifera grapes was compared with that of wines produced from hybrids of V. vinifera and species indigenous to North America. Mutagens were extracted on an XAD-2 Amberlite resin column and activated with S-9 and/or faecalase in the Salmonella/microsomal mutagen assay. All white wines had insignificant mutagen levels. The only red wine to produce statistically significant reversion frequencies was that made from the Concord grape. The mutagens were shown to be extracted from the grape skins during fermentation.

Suppressive effects of chemicals in mixture on the Salmonella plate test response in the absence of apparent toxicity

There are chemicals that affect the number of his+ revertant colonies of Salmonella in the plate test at doses that are apparently nontoxic, but may be causing nonlethal, toxic effects. When mixed with mutagens, these chemicals reduce the numbers of his+ revertant colonies on the plate with no accompanying visible toxic effect on the background lawn. Some of these plates are indistinguishable from spontaneous control plates, leading to the possibility that the mutagens under test would be evaluated as nonmutagenic, or that the mutagenic response would be underestimated. The reduction in mutagen-induced revertant colonies in most cases is equivalent to the reduction in spontaneous revertants in the absence of mutagen. A spot test that permits a rapid screen of chemicals for inhibitory effects has been developed; a plate incorporation assay is used to confirm the effect. Toxic effects can be seen in the background lawns of plates examined at magnifications of 100X or greater.

The effect of culture conditions and toxicity on the Ames Salmonella/microsome agar incorporation mutagenicity assay

Various methods were used to reconstruct an environment similar to a chemically bactericidal or bacteriostatic effect in the Ames mutagenicity assay in order to determine whether a false-positive result could occur. Neither population reduction, sonication, nor increased histidine produced an increase of spurious revertant colonies.

Microbial mutagenicity of selected hydrazines

Selected hydrazines and related compounds were examined for their mutagenic activity in S. typhimurium strains TA1535 and TA1537. These in vitro assays were conducted with and without metabolic activation by Aroclor-induced rat-liver enzymes. Relatively high levels of mutagenicity were observed with phenylhydrazine X HCl, methylhydrazine, N'-acetyl-4-(hydroxymethyl)phenylhydrazine, and 4-(hydroxymethyl)benzenediazonium tetrafluoroborate, the stabilized salt of a carcinogenic metabolite of agaritine; only low levels of mutagenicity were observed with other compounds, although most are strong carcinogens. Several of the compounds were highly toxic to the bacteria, and detection of mutagenicity was enhanced by calculating the increase in mutagenic activity on the basis of the surviving fractions of bacteria.

Mutagenicity of anthraquinone and hydroxylated anthraquinones in the Ames/Salmonella microsome system

The mutagenicity of anthracene, anthraquinone, and four structurally similar compounds of each was evaluated in the Ames/Salmonella microsome assay. Anthraquinone was shown to be mutagenic for strains TA1537, TA1538, and TA98 in the absence of rat liver homogenate. The four anthraquinone derivatives tested were mutagenic for TA1537 exclusively. None of the anthracenes exhibited mutagenic activity.

Multivariate statistical methods in toxicology. III. Specifying joint toxic interaction using multiple regression analysis

Multiple regression is widely employed to study the contribution of components to the toxicologic effect of a mixture. Here, use is made of the fact that data obtained from standard curves of substances and from their mixtures are separable in regression analysis. Thus, under an assumption of additivity of responses, regression coefficients obtained for components in mixtures alone should be the same as for the individual substances. A t-test is developed such that nonsignificant t values support additivity, negative significant values support antagonism, and positive significant values support synergism. The results are applied to data on the mutagenicity of binary mixtures of azaserine, 4-nitroquinoline N-oxide, and 9-aminoacridine in TA 100 in the Ames assay.

Mutagenicity in Salmonella typhimurium and structure-activity relationships of wastewater components emanating from the manufacture of trinitrotoluene

The mutagenicity of 36 polynitroaromatic compounds was investigated with five strains of Salmonella typhimurium. Isomeric trinitrotoluenes (TNT), with the exception of 2,4,6-TNT and 2,3,4-TNT, exhibit mutagenicity independently of nitroreductase enzymes, but isomeric aminodinitrotoluenes (ADNT) and isomeric dinitrotoluenes (DNT) need nitroreductase to induce mutation. Within groups of isomeric TNTs, DNTs, and ADNTs, mutagenic response was enhanced by a para orientation of nitro groups. The mutagenic response of isomeric DNTs was found to correlate with the compound's ability to undergo charge-transfer complexation with reductive enzymes, whereas further complexation (such as a Janovsky complex) appears to be required for inducing mutation in dinitrobenzenes. These results indicate that polynitroaromatic compounds in TNT wastewaters possess a significant potential for biologic activity.

Evaluating statistical analyses and reproducibility of microbial mutagenicity assays

The NCI/NTP has completed the first phase of a 4-laboratory study on the reproducibility of testing chemicals for mutagenicity in the Salmonella/microsome assay. This paper is a report of the statistical analysis of some of that data. This analysis involved (1) identifying and removing spurious data; (2) determining the adequacy of the remaining data in making a decision on the mutagenicity of the test chemical; (3) performing the statistical tests; and (4) interpreting the results. Using this procedure, 7 approaches were used to determine the mutagenicity of a test. These approaches were the (1) 2-fold rule, (20 modified 2-fold rule, (3) one-way analysis of variance (homogeneity test), (4) test for linear trend, (5) combination of 3 and 4, (6) 97.5th percentile threshold rule and (7) confidence interval threshold rule. The conclusions drawn by each rule were compared to the microbiologists' interpretation, and the results of these comparisons were presented. In addition, the strengths and weakness of each rule were discussed. The reproducibility of the assay in this study was examined, and a discussion of the significance of these results was presented.

A rapid and simple scheme for confirmation of Salmonella tester strain phenotype

A simple scheme has been developed for confirming the phenotype of the standard set of Salmonella typhimurium tester strains. This scheme employs a series of filter paper discs impregnated with diagnostic mutagens or bacterial toxins. Up to 6 diagnostic discs can be placed on a petri dish to test a single Salmonella strain. The Salmonellae are distinguished by their responses to ampicillin, crystal violet, nitrofuratoin, 9-aminoacridine, 4-nitro-o-phenylenediamine and sodium azide.

The mutagenic and SOS-inducing potential of the soluble organic fraction collected from diesel particulate emissions

Studies involving the Ames Salmonella mutagenicity test and the Bacillus subtilis comptest have demonstrated that the soluble organic fraction of diesel particulate is potentially mutagenic and DNA damaging. The soluble organic fraction was extracted from exhaust particulate samples collected from four different diesel engines operated at specified conditions. For each fraction collected, an increase in the concentration of the organic material resulted in a subsequent increase in the number of histidine prototrophs obtained when this material was added to the histidine auxotrophic strains that comprise the Ames Salmonella test. Specifically, the number of induced revertants, for strains TA98 and TA100, ranged from less than one revertant per microgram of sample to 29 revertants per microgram of sample. The ability of these organic fractions to induce bacterial SOS functions also was determined by exposing competent cultures of Bacillus subtilis strain RUB827 to increasing concentrations of these extracts. With varying efficiencies, these samples were positive in their ability to induce the SOS system of B subtilis. Significantly, the toxicity of these mutagenic and DNA damaging samples never resulted in more than 95% killing, even for the highest concentrations tested in the Salmonella and B subtilis assay.

Use of rat/hamster S-9 mixture in the Ames mutagenicity assay

Based on the findings of Nagao et al [1978] that phenacetin is negative in the standard Ames test with Aroclor induced rat S-9 and positive with hamster S-9, the test was performed with a mixture of rat/hamster S-9. Phenacetin was mutagenic with the mixture. The activity of the mixture was compared to the rat S-9 alone with low concentrations of 2-aminoanthracene (a strong promutagen for Salmonella typhimurium TA 1535, TA 100, TA 1537, and TA 98), nitrosopiperidine (a weak promutagen), and 1,2 epoxybutane (a weak, direct-acting mutagen). Except for an increased mutagenic activation by the mixture with nitrosopiperidine the mixture was comparable to the rat S-9 alone, indicating that replacing rat S-9 with a rat/hamster S9 mixture in the standard Ames test could increase the sensitivity of the test without interfering with rat S-9 activity.

Microbiological studies investigation mutagenicity of deep frying fat fractions and some of their components

In this study, the Salmonella/microsome mutagenicity test according to Ames et al. (Mutation Res. 31:347, 1975) was performed in order to detect possible mutagenicity of oxidized deep frying fat fractions. Furthermore, the mono-, di-, tri- and tetrahydroxyoctadecanoic acids and the hydroperoxide of linoleic acid were investigated as model test substances. The Ames assay was carried out with and without metabolic activation including preincubation and liquid culture procedures as described by Mitchell (Mutation Res. 54:1, 1978). The results show no mutagenic effects for the oxidized fractions of deep frying fats nor for the model test substances. At higher concentrations, however, limited test reliability resulted from direct toxic effects on bacterial growth.

Mutagenicity of islandicin and chrysophanol in the Salmonella/microsome system

Chrysophanol and islandicin, two anthraquinones which are structurally related to emodin, were found to be frame-shift mutagens for Salmonella typhimurium strain TA 1537 after metabolic activation.

Mutagenicity of melanin from human red hair

The Salmonella typhimurium histidine reversion test of Ames et al. was used to demonstrate the pheomelanin, the red-brown polymeric pigment produced in human skin and hair, becomes mutagenic after exposure to long wave-length UV-light; a finding consistent with the UV-induced somatic mutation hypothesis for the origin of freckles and the high susceptibility of redheads and blonds to sunlight-induced skin cancers.

A comparison of the ability of frog and rat S-9 to activate promutagens in the Ames test

A mutagenesis assay employing the frog, Rana pipiens, is currently under development [McKinnell et al, 1979]. A question that must be answered is whether the frog is metabolically capable of activating a large number of promutagens. The Ames assay offers a simple means of comparing the metabolism of mutagens by different animal species. The Ames response obtained with frog-liver S-9 was compared to the response with rat-liver S-9, using the following compounds: Benzo(a)pyrene, 7,12-dimethylbenz(a)anthracene, 2-amino-fluorene, azobenzene, Sudan II, dibutylnitrosamine, hydrazine sulfate, hydroxyethylhydrazine, cyclophosphamide, 1,2-dichloroethane, tris(2,3 dibromopropyl)phosphate, diallate, quinoline, quercetin, aflatoxin B 1, emodin, and safrole. Of these compounds, activation by rat S-9 was observed for all except hydrazine sulfate and safrole. All except Sudan II, 1,2-dichloroethane, quinoline, and safrole gave positive Ames responses with frog S-9. In general, the responses with frog S-9 were quantitatively lower than those obtained with Aroclor-induced rat S-9; however, the optimum procedure for frog-liver induction has not been determined. The response to dichloroethane is very sensitive to the amount of activating enzyme present; it might be positive with optimally induced frog S-9. Thus, only two of the 15 compounds positive with rat S-9 were definitely missed when tested with frog S-9. We feel that the frog assay appears to be promising from the standpoint of false-negatives.