Purified prostaglandin synthase activates aromatic amines to derivatives that are mutagenic to Salmonella typhimurium.

Prostaglandin H synthase (PHS) is widely distributed in mammalian tissues and has the ability to oxidize a variety of mutagens and carcinogens. It may therefore play a key role in the metabolic activation of xenobiotics. The present study documents that highly purified PHS can be used in conjunction with 5-phenyl-4-pentenyl-1-hydroperoxide (PPHP), a relatively stable and non-mutagenic hydroperoxide substrate, for the metabolic activation of aromatic amines to mutagenic derivatives that can be detected in short-term Salmonella typhimurium mutagenesis assays. The PHS-based activation system alone was not mutagenic for these tester strains, nor were the test compounds significantly toxic for the bacteria over the concentration range tested. When used in conjunction with Salmonella strains TA98 and TA100 in a modified Ames assay, this system should prove useful for screening of a wide range of compounds for metabolic activation by this mammalian peroxidase. The potential broad utility of this purified PHS-dependent metabolic activation system was investigated by evaluating the activation of 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) and 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ), which are representative of a group of mutagenic and carcinogenic heterocyclic arylamines to which humans are exposed via their diet. Both IQ and MeIQ were activated by PHS to potent mutagens and confirm the utility of the PPHP/PHS system for the activation of premutagens. Whereas the extent of activation of aromatic amines by S9-based systems is significantly greater than for the PHS activation system described herein, PHS may play a significant role in target tissues in which it is present at significantly greater levels than P450 isoenzymes. Moreover, it is likely that the substrate specificity of PHS differs sufficiently from that of P450 isoenzymes so that PHS may activate some compounds that are not efficiently activated by mixed-function oxidase based systems.     

Uptake, metabolism and mutagenic activity of aromatic glycidyl compounds

Aromatic diglycidyl compounds are very active mutagens when assayed in in vitro tests. In vivo, however, resorcinol diglycidyl ether provided no evidence for the clastogenic activity, while diglycidylaniline exhibited definite mutagenic activity in the micronucleus test. Since the only difference between these two compounds lies in the binding mode of the glycidyl groups to the aromatic nucleus (i.e. ether oxygen vs. aminic nitrogen), this apparent discrepancy in mutagenic activity led to the question of the mechanisms involved in such an activity difference. Although no clear signs of differential uptake or excretion could be detected in mice, differences could be seen in the spectrum of urinary metabolites; while resorcinol diglycidyl ether seemed to become fully converted to the genetically inactive bis-diol compound, a sizeable proportion of diglycidylaniline was converted only to the diol-epoxide. In vitro investigations and enzyme kinetic measurements with postmitochondrial supernatant of rat or mouse liver homogenate (S-9) finally yielded the biochemical explanation for this behaviour, as they showed a very low affinity of the diol-epoxide metabolite of diglycidylaniline for the epoxide hydrolase, normally involved in the degradation of such compounds. The diol-epoxide obtained from resorcinol diglycidyl ether, on the other hand, has an affinity to the degradation enzyme similar to, or even higher than, the one measured with the parent substance.     

Comparison of the mutagenic specificity induced by four nitro-group-containing aromatic amines in Salmonella typhimurium his genes

Four nitrated aromatic amines (2-nitro-p-phenylenediamine [2NPD], 3-nitro-o-phenylenediamine [3NPD], 4-nitro-o-phenylenediamine [4NPD] and 4,4'-dinitro-2-biphenylamine [DNBA]) are direct-acting mutagens in Salmonella typhimurium strain TA100. These compounds were tested further using the Xenometrix strains of S. typhimurium: TA7001, TA7002, TA7003, TA7004, TA7005, and TA7006, with and without S9 mix in the plate incorporation assay. The direct-acting mutagenicity of 2NPD, 4NPD, and DNBA was detected with TA7002, TA7004 and TA7005. 2NPD and DNBA showed some activity in TA7006; DNBA also showed some activity in TA7003. Mutagenicity was generally decreased in these strains when S9 was added. 3NPD was mutagenic in TA7004 without S9 and in TA7005 with and without S9. These data suggest that 2NPD, 4NPD and DNBA induced TA-->AT and CG-->AT transversions as well as GC-->AT transitions in the his gene. 3NPD induced CG-->AT transversions and GC-->AT transitions. 2NPD and DNBA also induced a small portion of CG-->GC transversions.     

Analysis of mutagenic activity of airborne particulate matter, standard reference materials and reference compounds using base pair-specific Salmonella typhimurium tester strains

The mutagenicity profiles of organic extracts of airborne dust samples from Mannheim, Germany, and two standard reference materials (SRM) as well as eight compounds with different chemical properties were investigated using tester strains Salmonella typhimurium TA700x (Ames II Assay). Each strain of this series carries a unique missense mutation in the histidine operon and is reverted by only one specific base substitution out of six possible changes. Mutation patterns of eight compounds with different modes of genotoxic action reveal significant differences. Samples of airborne particulate matter (APM) from an industrialized town in Germany (Mannheim) were collected for five consecutive days once a month for 1 year using an automatic high-volume air sampler. Samples taken from Monday to Friday were Soxhlet-extracted and prepared according to standard methods. Although the threshold limit for the least active strains is not triggered by all samples, it can be concluded that mutation patterns of the samples do not vary between different seasons. Standard reference materials (SRMs) were prepared and tested using the same methods. SRMs and APM samples from Mannheim reveal similar mutagenicity profiles in TA700x strains. The comparison of the mutagenicity profiles of air dust extracts from Mannheim and the SRMs, respectively, with reference compounds investigated so far shows some similarities although the patterns do not fit perfectly. Mutagenicity profiles of TA700x-activity of nitro-aromatic compounds published so far are similar to those of APM collected in Mannheim, Germany, as well as to standard reference materials 1648 and 1649.     

Identification of polycyclic aromatic compounds in mutagenic emissions from steel casting

Workers in ferrous foundries show increased risk of lung cancer. In the steel casting process hot metal is poured into sand moulds solidified with organic binders, producing a plume of smoke containing a variety of organic compounds and showing strong mutagenicity in the Salmonella/S9 assay. We have collected the emissions produced when steel is poured into an experimental sand mould solidified with oil, clay and cereal, a widely used binder system. The organic constituents of these emissions have been fractionated by preparative reverse-phase high performance liquid chromatography (HPLC) and mutagenic fractions have been analysed by capillary column gas chromatography/mass spectrometry (GC/MS). Of the 65 compounds for which mass spectra are reported, 54 have been tentatively identified as alkyl derivatives of polycyclic aromatic compounds. Many compounds of this class are known to be carcinogenic and mutagenic. In addition, several unsubstituted polycyclic aromatic hydrocarbons, including the carcinogenic benz[a]anthracene and benzo[a]pyrene, were found to be present.     

Pitfalls in immunocytochemistry with special reference to the specificity problems in the localization of neuropeptides

In this review, the different types of specificity in immunocytochemistry (ICC) are discussed. Some examples of misinterpretations on the basis of ICC results are given. A strategy is proposed to assess the specificity of antisera and to test them again after purification.     

Fungal flora of Egyptian baladi bread with special reference to the mutagenic effects of their toxic metabolites

The fungal flora of wheat flour and baladi bread in upper Egypt were investigated. Most of the isolated fungal species belong to the genus Aspergillus. The presence of non heat resistant fungi of the both flat surfaces of baladi bread, came from contamination after baking and from improper handling at homes. Among the heat resistant fungi, A. fumigatus and A. niger, were recorded to inhabit the spongy crumb although the high temperature of baking process which reached approximately 100 ° C in the center of the bread.The mutagenic effects of the fungal metabolites of the extract of mouldy bread was investigated. Several kinds of aberrations were observed in all stages of mitotic division. The most interesting effect of these fungal metabolites were the induction of tripolar and quadripolar spindle. Multinucleate and polyploid cells were also observed under relatively high concentrations. It was noticed that at either higher concentrations or lower concentrations with long exposure, damaged cells were observed. The hazards involved through the consumption of individuals to such mouldy bread, is accumulation of possible deleterious effects from both long and short term exposure to these toxic metabolites.     

Biotransformation of various substituted aromatic compounds to chiral dihydrodihydroxy derivatives

The biotransformation of four different classes of aromatic compounds by the Escherichia coli strain DH5alpha(pTCB 144), which contained the chlorobenzene dioxygenase (CDO) from Pseudomonas sp. strain P51, was examined. CDO oxidized biphenyl as well as monochlorobiphenyls to the corresponding cis-2,3-dihydro-2,3-dihydroxy derivatives, whereby oxidation occurred on the unsubstituted ring. No higher substituted biphenyls were oxidized. The absolute configurations of several monosubstituted cis-benzene dihydrodiols formed by CDO were determined. All had an S configuration at the carbon atom in meta position to the substituent on the benzene nucleus. With one exception, the enantiomeric excess of several 1,4-disubstituted cis-benzene dihydrodiols formed by CDO was higher than that of the products formed by two toluene dioxygenases. Naphthalene was oxidized to enantiomerically pure (+)-cis-(1R,2S)-dihydroxy-1,2-dihydronaphthalene. All absolute configurations were identical to those of the products formed by toluene dioxygenases of Pseudomonas putida UV4 and P. putida F39/D. The formation rate of (+)-cis-(1R,2S)-dihydroxy-1,2-dihydronaphthalene was significantly higher (about 45 to 200%) than those of several monosubstituted cis-benzene dihydrodiols and more than four times higher than the formation rate of cis-benzene dihydrodiol. A new gas chromatographic method was developed to determine the enantiomeric excess of the oxidation products.     

In vitro metabolic activation of ethidium bromide and other phenanthridinium compounds: mutagenic activity in Salmonella typhimurium.

The induction of mutation by a variety of mutagens has been measured utilizing the hypoxanthine-guanine phosphoribosyl transferase (HGPRT) locus in Chinese hamster ovary (CHO) cells (CHO/HGPRT) system). These mutagens include physical agents such as UV light and X-rays, and chemicals such as alkylating agents, ICR-191, and metallic compounds. This system can also be modified for study of the mutagenicity of promutagens such as dimethylnitrosamine (DMN) which require biotransformation for mutagenic action, either through the addition of a rat liver microsomal activation preparation or through a host-mediated activation step using Balb/c athymic mice.