Mutagenicity of hydrogen peroxide in V79 Chinese hamster cells.

Hydrogen peroxide (H2O2) was investigated for its potential to induce gene mutations in V79 Chinese hamster cells. Exposure of 2-3 x 106 cells/100-mm dish to 0.5-4.0 mM H2O2 for 1 h resulted in a concentration-dependent increase in the frequency of 6-thioguanine-resistant clones. At 4 mM H2O2 the mutation frequency was increased about 6-fold above that in controls and survival of the cells was reduced by 50%. Cytotoxicity was markedly increased at lower cell densities. When only 100-200 cells/100-mm dish were exposed to H2O2 for 1 h, 50% were killed at an H2O2 concentration as low as 60 μM. The results show that mutagenicity of H2O2 in mammalian cells in vitro has escaped attention previously because the concentrations tested were too low, presumably because the likely toxicity of H2O2 to V79 cells treated at high cell densities was overestimated

Pyruvate and related α-ketoacids protect mammalian cells in culture against hydrogen peroxide-induced cytotoxicity.

Pyruvate efficiently protected V79 Chinese hamster cells against the lethal effects of hydrogen peroxide. Protection was also provided by other α-ketoacids, such as α-ketobutyrate, α-ketoglutarate and α-ketoadipate, although higher concentrations were required. The corresponding β-ketoacids had no effect. The results indicate that pyruvate and other α-ketoacids possess antioxidant activity in vitro and, probably, in vivo

Thiourea induces DNA repair synthesis in primary rat hepatocyte cultures and gene mutations in V79 Chinese hamster cells.

Thiourea was investigated for its capacity to cause DNA alterations in cultured mammalian cells. The induction of DNA repair in primary rat hepatocyte cultures and of gene mutations in V79 Chinese hamster cells were used as biological endpoints. In hepatocytes, thiourea elicited a linear increase in DNA repair replication in the concentration range tested (5-25 mM). In V79 cells, thiourea (10-40 mM) significantly increased the frequency of 8-azaguanine-resistant mutants. The present results show that thiourea is weakly, but definitely, genotoxic and mutagenic in cultured mammalian cells

Mutagenicity and cytotoxicity of 2-chlorobenzylidene malonitrile (CS) and metabolites in V79 Chinese hamster cells.

The genotoxicity of the sensory irritant 2-chlorobenzylidene malonitrile (CS) to V79 Chinese hamster cells was investigated using the induction of gene mutations, micronuclei and DNA repair synthesis as biological endpoints. CS efficiently induced micronuclei and mutants resistant to 6-thioguanine in these cells, but it did not elicit DNA repair synthesis. Induction of micronuclei and mutants showed very similar courses of concentration dependence, suggesting that both events were caused by the same mechanism. The hydrolysis products of CS, o-chlorobenzaldehyde and malononitrile dit not induce micronuclei and were much less cytotoxic than CS. The observation of heritable genetic changes in cells exposed to CS in the absence of detectable DNA damage suggests that the genetic effects of CS are not caused by an interaction of the compound or its hydrolysis products with DNA. It appears more likely that the mutagenic activity is the consequence of effects of CS on the mitotic apparatus of the cells causing chromosomal aneuploidy

Involvement of different pathways in the genotoxicity of nitropropanes in cultured mammalian cells.

The metabolic pathways leading to genotoxicity of nitropropanes in mammalian cells were investigated by measuring the effects of 2-nitropropane (2-NP) and 1-nitropropane (1-NP) on various cell lines characterized for their expression of cytochrome P450-dependent mono-oxygenases. Cells used were the rat hepatoma cell lines 2sFou, H4IIEC3/G- and C2Rev7, which express various forms of cytochrome P450-dependent mono-oxygenases, and V79 Chinese hamster cells which lack these enzyme activities. Induction of DNA repair synthesis, micronuclei and, where assessable, mutations to 6-thioguanine (TG) resistance served as indicators of genotoxic effects. 2-NP elicited a positive response at all endpoints measured in the hepatoma lines after pretreatment of the cells with dexamethasone, an inducer of various liver-specific cytochrome P450 forms. Genotoxicity was much weaker or not detectable in cells not pretreated with the inducer. 1-NP was not genotoxic in the hepatoma cells irrespective of whether the cells were pretreated or not. Neither isomers elicited DNA repair synthesis in V79 cells, but both isomers caused mutations to TG resistance, and 1-NP increased the number of micronucleated and multinucleated cells. The findings show that there are different pathways in mammalian cells by which nitropropanes can be converted to genotoxic products. Presumably the induction of liver tumours by 2-NP is linked to the metabolic pathway which is characterized by the formation of genotoxic metabolities from 2-NP but not 1-NP. This pathway appears to depend on the presence of liver-specific, dexamethasone-inducible, cytochrome P450 forms. The relevance of the genotoxic effects of the nitropropanes observed in V79 cells for the situation in vivo is open to question

Microsome- and hepatocyte-mediated mutagenicity of hydroxyurea and related aliphatic hydroxamic acids in V79 Chinese hamster cells.

The potential of N-hydroxyurea to induce gene mutations in V79 Chinese hamster cells was investigated. Upon metabolic activation by liver microsomes from phenobarbital-treated rats or by isolated rat hepatocytes co-cultured with the V79 cells, hydroxyurea caused a concentration-dependent increase in the frequency of HGPRT-deficient mutants. Hydroxyurea was not mutagenic in the absence of metabolic activation. Addition of catalase inhibited microsome-mediated mutagenicity, indicating that hydrogen peroxide was involved in the formation of the mutagenic DNA lesion. Acetohydroxamic acid and N-hydroxyurethane also induced hepatocyte-mediated mutagenicity, suggesting that the potential to elicit metabolism-dependent mutagenicity may be a common property of aliphatic hydroxamic acids

A possible mechanism for the in vitro activation of L-serine deaminase activity in Escherichia coli K12.

L-Serine deaminase is inactive in crude extracts of Escherichia coli K12, but can be activated by incubation with iron and dithiothreitol. This activation requires oxygen, and is inhibited by free radical scavengers and by diethylene triamine pentaacetic acid, which prevents Fe cycling. We suggest that in vitro activation of L-serine deaminase is catalyzed by an oxidant (perhaps hydroxyl radicals). Also, activation may be accompanied by a decrease in molecular weight and involve both a cleavage of the polypeptide chain and a reversible reduction of the molecule