Mutagenicity of nitro compounds in Salmonella typhimurium in the presence of flavin mononucleotide in a preincubation assay

A series of nitro compounds (18 aromatic and one aliphatic) was evaluated using a modification of the standard Salmonella typhimurium mutagenicity assay. A preincubation protocol was used with flavin mononucleotide (FMN) incorporated into the assay mixture to facilitate nitro reduction. Several aromatic nitro compounds (m-nitroaniline, p-nitroaniline, 2,6-dinitrotoluene, 2,4-dinitrotoluene,2,3-dinitrotoluene,1,8-dinitronaphthalene), which were negative or only weakly mutagenic when tested in the standard plate incorporation assay, showed FMN-dependent mutagenic responses with this procedure. For some nitro compounds, the addition of FMN was not needed for the detection of mutagenicity in the modified protocol. Not all nitro compounds were positive using the preincubation procedure with FMN. The lack of mutagenicity, however, does not appear to be the result of the inability of the modified method to reduce nitro compounds, since it was found that reduction does occur under the assay conditions for the two nonmutagens evaluated for nitro reduction (nitrobenzene and p-nitrophenol). It is suggested that the modified protocol may be useful for evaluating the mutagenicity of many nitro compounds.     

Cyclopenta[cd]fluoranthene and its precursors in combustion exhausts: a survey of their bacterial mutagenic activity

Cyclopenta[cd]fluoranthene (1) and 3-ethynylfluoranthene (2) have both recently been identified in combustion exhausts. In this study, their mutagenic activities were compared to that of fluoranthene (3), one of the most abundant polycyclic aromatic hydrocarbons (PAHs) in combustion exhausts, in the Salmonella/microsome reversion assay (Ames assay) using S. typhimurium strain TA98. The mutagenicity of 1 was modest in comparison to other active cyclopenta PAHs. Unexpectedly, 2 was mutagenic both with and without exogenous metabolic activation (rat liver S9). Furthermore, cyclopenta[cd]fluoranthene-3,4-epoxide (6) was synthesized in order to evaluate its role as the ultimate mutagenic active form of 1. The epoxide 6 was a direct-acting mutagen. In addition, a pyrolysate containing a mixture of 1 (85%), 2 (2%), and 3 (13%) obtained by flash vacuum thermolysis of 3-(1-chloroethenyl)fluoranthene (2a) at 1,050 degrees C was also mutagenic, but a significant mutagenic response was detected only in the presence of S9 activation. The results of this study indicate that 1 and 2 can contribute to the mutagenic activity of combustion exhausts.     

Changes of the level of cytochrome P-450 and NADPH-cytochrome P-450 reductase in rats with hereditary degeneration of the retina

In animals with hereditary degeneration of the retina the level of cytochrome P-450 in the brain microsomal fraction is found to be higher than that in healthy animals. In rats with hereditary degeneration of the retina the activity of NADPH-cytochrome P-450 reductase is unchanged in all tissues examined except for the retina, where it is markedly higher than in healthy animals on postnatal day 90. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 117, N ^o 3, pp. 259–261, March, 1994     

Mutagenicity and toxicity of aflatoxin precursors

The Salmonella/microsome test and the chick embryo test were used to determine the mutagenicity and toxicity of five aflatoxin B₁ precursors. A definite pattern emerges: the nearer to B₁ an intermediate appears in the biosynthetic pathway, the more potent is its mutagenicity and toxicity.     

Cytochrome P-450 content and its induction in primary rat liver tumors

Laboratory for the Study of Carcinogens and Laboratory of the Mechanisms of Carcinogenesis, All-Union Oncologic Scientific Center, Academy of Medical Sciences of the USSR, Moscow. (Presented by Academician of the Academy of Medical Sciences of the USSR N. N. Trapeznikov.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 105, No. 2, pp. 198–200, February, 1988.     

Two-step activation of valproic acid (VPA) by hepatic cytochrome P-450

There is now considerable evidence that the unsaturated metabolite of VPA, delta 4-VPA, may be responsible for VPA-induced hepatic injury. It is proposed that VPA is activated to a hepatotoxic species by a two-step cytochrome P-450-mediated mechanism consisting of 1) desaturation and 2) unknown activation, possibly by epoxide formation, involving one or more P-450 isozymes with subsequent covalent binding to cellular macromolecules. In vivo and in vitro experimental protocols are indicated for testing the proposed hypothesis.     

Mutagenicity testing in Salmonella typhimurium strains possessing both the his reversion and ara forward mutation systems and different levels of classical nitroreductase or O-acetyltransferase activities

The induction of forward mutations to L-arabinose resistance (Ara^R) and of reversions to histidine prototrophy (His⁺) can be quantitatively compared in Salmonella typhimurium BA strains. The BA bacteria carry the araD531 allele required for the Ara assay and a his auxotrophy (hisD3052 or hisG46) required for the His assay. In this study, 2 new sets of BA indicator strains have been constructed in order to combine the Ara forward and the His reverse mutation assays of S. typhimurium with deficiency, or overproduction, in either classical nitroreductase or O-acetyltransferase for mutagenicity testing of nitro-containing chemicals. Nine mutagens with different chemical structures were tested to compare the specific mutagenic sensitivities of the new constructions with those of the parental and of the conventional TA indicator bacteria. The Ara test, which responded with high sensitivity to all chemicals tested, revealed important differences between the standard tester strains TA98 and TA100 with respect to the activation of mutagens considered to be dependent on classical nitroreductase activity. Total correspondence was found between the specific mutagenic sensitivities of the defective and the overproducing bacteria in the genetic background of TA98 but not in that of TA100. In the genetic background of TA100, chemicals such as nitrofurantoin and nitrofurazone displayed 10-fold reduced mutagenicity to the “classical nitroreductase” defective strain without increasing mutagenicity to the corresponding overproducing bacteria. This discrepancy might be attributed to the greater nitroreduction capability of strain TA100 (68.12 nmole/min/mg protein) as compared to TA98 (24.42 nmole/min/mg protein), by assuming that nitrofurantoin and nitrofurazone are such good substrates for classical nitroreductase that the additional enzyme activity produced from the corresponding overexpressing plasmid when present in TA100 no longer affected their metabolic activation. We propose that the Ara forward mutation test carried out in the set of overproducing bacteria constructed in the genetic background of TA98 might play a role for routine testing of large number of samples. The isogenic defective strains could be used in cases of uncertain results with the corresponding overproducing bacteria. Finally, the reversion of the his alleles accompanying the Ara assay in the BA strains could play a role in assessing the presence of mixtures of chemicals with different mutagenic specificity in samples of environmental relevance such as urban air, foods, and water.     

The Inhibitory Activity of the Extracts of Popular Medicinal Herbs on CYP1A2, 2C9, 2C19 and 3A4 and the Implications for Herb-Drug Interaction

Background

Studies have suggested an increasing practice of concurrent herb-drug consumption. One of the major clinical risks of such concomitant herb-drug use is pharmacokinetic herb-drug interaction (HDI). This is brought about by the ability of phytochemicals to inhibit or induce the activity of metabolic enzymes. The aim of this study was to investigate the potential of the crude aqueous extracts of three popular medicinal herbs used in South Africa to inhibit major cytochrome P450 (CYP) enzymes.

Materials and Methods

The extracts of Bowiea volubilis, Spirostachys africana and Tulbaghia violacea were incubated with human liver microsomes (HLM) to monitor the phenacetin O-deethylation, diclofenac 4′-hydroxylation, S-mephenytoin 4′-hydroxylation and testosterone 6β-hydroxylation as respective probe reactions for CYP1A2, CYP2C9, CYP2C19 and CYP3A4. The inhibitory activity, where observed, was profiled against the extract concentration.

Results

Extracts of Bowiea volubilis inhibited the metabolic activity of CYP1A2 and CYP3A4 with IC₅₀ values of 92.3 ± 5.5 µg/mL and 8.1 ± 0.6 µg/mL respectively. Similar observation with Spirostachys africana showed inhibitory activity against CYP1A2 and CYP3A4 with respective IC₅₀ values of 14.3 ± 0.6 µg/mL and 47.4 ± 2.4 µg/mL. Tulbaghia violacea demonstrated relatively weak inhibitory activity against CYP1A2 (767.4 ± 10.8 µg/mL) and CYP2C9 (921 ± 15.3 µg/mL).

Conclusion

The results suggest the potential for HDI between the herbs and the substrates of the affected enzymes, if sufficient in vivo concentration is attained.     

Mutagenicity tests of fabric-finishing agents in salmonella typhimurium: Fiber-reactive wool dyes and cotton flame retardants

Thirty-nine fabric-finishing agents were tested for mutagenic activity in Salmonella typhimurium. Twenty-four fiber-reactive wool dyes and three acid dyes (not fiber-reactive) were screened by spot tests in strains TA100, TA98, TA1535, and TA1537. Among these dyes, seven bromoacrylamide dyes and one vinyl sulfone dye were mutagenic. Additionally, one of the three acid dyes was mutagenic in spot tests. The mutagenicity of the acid dye was due to an impurity or breakdown product rather than to the dye itself; the origin of the activities of the other dyes is unknown. No mutagenicity was observed among five chlorotriazine or four sulfonyl-ethane sulfonic acid dyes. Eight phosphorus-containing flame retardants (phosphonium, phosphine, phosphine oxide, and phosphonic acid derivatives) and methyl-N-methylolcarbamate, which is employed to obtain a flame-retardant finish on cotton, were tested for mutagenicity in strains TA100, TA98, TA1535, and TA1537, using quantitative incorporation assays. All were nonmutagenic. Two of three bromoalkyl-substituted triazine flame retardants were mutagenic in strains TA100 and TA1535. It is unknown whether this activity is due to impurities or to the parent compound. The flame retardants tested were either in actual commercial use or in experimental development for potential commercial processes. These results indicate the need for early testing of potential fabric-finishing agents and processes.     

Comparative analysis of family 1 cytochrome P-450 mRNA expression in human intestinal adenocarcinoma and intact portion of the intestine

The expression of mRNA of proteins involved in the transformations of cytostatics (cytochrome P-450 1A1 and 1B1 isoforms) and genes encoding proteins participating in their regulation (Ah receptor, AHRR and ARNT) in intestinal tumors and intact portions of the intestine were studied. The expression of cytochrome P-450 1A1 increased in poorly differentiated tumors in comparison with its expression in intact portions of the intestine (tumor/intact tissue=1.65). The expression of cytochrome P-450 1B1 was higher in well-differentiated tumors (tumor/intact tissue=1.62). The possibility of practical use of high expression of cytochrome P-450 isoforms in tumors in comparison with intact intestinal tissue is discussed. Translated from Byulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 146, No. 8, pp. 217–220, August, 2008     

Mutagenicity of (R) and (S) styrene 7,8-oxide and the intermediary mercapturic acid metabolites formed from styrene 7,8-oxide

We have tested the two enantiomers of styrene 7,8-oxide and various thioether metabolites of racemic styrene 7,8-oxide for their direct mutagenicity in Salmonella typhimurium TA100. The mutagenicity data suggests that the (R) enantiomer is more mutagenic than the (S) enantiomer, with the racemic mixture intermediate between the two. The thioether metabolites were not mutagenic. The difference in the mutagenicities of enantiomers probably resulted from a stereoselective process in the Salmonella tester strain. At the present time it is not clear whether the rate-limiting reaction is the interaction of the enantiomers with DNA or some other cellular component.