Arylamines suppress their own activation and that of nitroarenes in V79 Chinese hamster cells by competing for acetyltransferases.

The effect of 2-aminofluorene (2-AF) on the toxicity of 2-aminoanthracene (2-AA) and 1,6-dinitropyrene (1,6-DNP) was studied in N-acetyltransferase-proficient V79-NHr1A2 cells genetically engineered for the expression of cytochrome P4501A2, and in wild-type V79-NH cells. 2-AA inhibited the growth of V79-NHr1A2 cells and induced the formation of micronuclei at concentrations of 0.1 to 1.0 microM, but was virtually without toxic effects at a concentration of 10 microM. Addition of 2-AF protected against the cytotoxic and genotoxic effects elicited by low concentrations of 2-AA. Half-maximum protection was observed at 0.2 to 0.5 microM 2-AF. The arylamine also prevented the cytotoxicity caused by 1,6-DNP in V79-NH cells and completely suppressed the formation of 1-acetylamino-6-nitropyrene from 1,6-DNP in these cells. The results indicate that arylamines and related N-hydroxyarylamines are substrates for the same acetyltransferase in V79-NH cells. In consequence, arylamines are capable of suppressing the activation of their proximate cytotoxic and genotoxic products in these cells and, presumably, in vivo.

Effect of cadmium and copper on monoamine oxidase type A and B in brain and liver mitochondria.

The effect of cadmium and copper on monoamine oxidase type A and B in mitochondrial preparations from brain and liver was determined in vitro. The results showed a dose-related inhibition of the enzyme. Both the A and B forms of the enzyme were similarly inhibited by the presence of either cadmium or copper. Copper has been shown to be a 7-8 times more potent inhibitor of monoamine oxidase than cadmium. The data suggest that the intracellular concentration of unbound copper (13 mumol/l) or cadmium (100 mumol/l) may inhibit monoamine oxidase in brain and liver by 50%.

Metabolism and cytotoxicity of benzo(a)pyrene in the human lung tumour cell line NCI-H322.

1. The human lung tumour cells NCI-H322 metabolized benzo(a)pyrene (BP) at a rate of 160 pmol/10(6) cells/h for at least 8 h. About 30% of the total metabolites were water-soluble, 30% of which were conjugates with glutathione. The water-soluble fraction also contained BP sulphates but no BP glucuronides. 2. The cytotoxic potency of BP and its metabolites, 3-hydroxybenzo(a)pyrene (3-OH-BP) and (+/-) anti-7,8-dihydroxy-7,8-dihydrobenzo(a)pyrene (7,8-diol-BP), differed by an order of magnitude with the ranking 7,8-diol-BP greater than BP greater than 3-OH-BP. The cytotoxicity of BP was not detected at the end of a 24 h treatment period but became increasingly apparent at later times. In contrast, the cytotoxicity of 3-OH-BP was observed immediately after the treatment period and did not increase greatly thereafter. 7,8-Diol-BP caused both 'immediate' and 'late' effects. 3. The time course and concentration dependence suggested that the cytotoxicity of BP in NCI-H322 cells was not attributable to the formation of 3-OH-BP, but more likely resulted from the formation of other products such as 7,8-diol-BP.

Glutathione depletion suppresses conjugation of benzo[a]pyrene metabolites and (+/-)-trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene metabolites with glutathione but does not affect their binding to DNA in C3H/10T1/2 mouse fibroblasts.

The study was aimed at determining the role of glutathione (GSH) conjugation in the binding of reactive benzo[a]pyrene (BaP) species to DNA of C3H/10T1/2 cells. In order to suppress GSH conjugation cells were depleted of GSH by treatment with buthionine sulfoximine for 18 h and 1-chloro-2,4-dinitrobenzene for 1 h prior to incubation with radiolabelled substrates. Under these conditions GSH levels decreased to less than 1% of the control value. C3H/10T1/2 cells produced GSH conjugates with 7,8-dihydroxy-9,10-oxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BaPDE) comprising 6% of the total metabolites formed from BaP or (+/-)-trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene (BaP-7,8-diol). In GSH-depleted cells formation of GSH conjugates with metabolic products of BaP or BaP-7,8-diol was suppressed to 1% of total metabolites during an 8-h incubation period. Metabolic activation of BaP and BaP-7,8-diol by C3H/10T1/2 cells resulted in the formation of DNA adducts which largely consisted of BaPDE:deoxyguanosine. Depletion of GSH altered neither the degree of DNA binding nor the pattern of DNA adducts to any significant extent. When C3H/10T1/2 cells were co-incubated with microsomes from liver of 3-methylcholanthrene-treated rats for 1 h in order to activate BaP or BaP-7,8-diol extracellularly, the same pattern of GSH conjugates and DNA adducts was generated as by intracellular metabolism of the polycyclic hydrocarbons. No GSH conjugates were detected following co-incubation of microsomes with GSH-depleted C3H/10T1/2 cells. The formation of DNA adducts again remained unaffected by the suppression of conjugation. C3H/10T1/2 cells are apparently capable of conjugating BaPDE with GSH but are not capable of trapping by GSH conjugation those BaPDE moieties which bind to DNA. The results are compatible with the notion that BaPDE is partially contained in a cellular compartment--presumably the lipid environment of membranes--where it is inaccessible to GSH transferases of C3H/10T1/2 cells.

Glutathione conjugation protects some, but not all, cell lines against DNA binding of benzo[alpha]pyrene metabolites.

Three major types of cell lines were distinguished according to their capacity for glutathione (GSH) conjugation of extracellularly generated benzo[alpha]pyrene (BaP) metabolites, and the level of DNA binding of such metabolites. (i) Cells, e.g. HepG2, which conjugate BaP metabolites only very poorly with GSH and are highly susceptible to DNA binding. The number of DNA adducts in these cells (approximately 10 pmol/mg DNA) is taken to be the maximum DNA binding in 'unprotected' cells. (ii) Cells, e.g. V79 and NCI-H322, which efficiently conjugate BaP metabolites with GSH but, like HepG2 cells, are 'unprotected' as indicted by maximum DNA binding. (iii) Cells, e.g. 2sFou and H4IIEC3/G-, which are positive for GSH conjugation and exhibit only very little DNA binding. When GSH conjugation in these apparently 'protected' cells is suppressed by depletion of GSH, the level of DNA binding increases to that found in 'unprotected' lines. GSH depletion does not substantially affect DNA binding in 'unprotected' cells. The results show that, although GSH conjugation is capable of suppressing DNA binding of reactive BaP metabolites in some cell types, it fails to protect against DNA binding in others. It is possible that the reactive species are compartmentalized and certain cell types are protected, because they are able to specifically trap those BaP metabolites which bind to DNA.