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Human cell mutagenicity of mono- and dinitropyrenes in metabolically competent MCL-5 cells
W F Busby1, B W Penman, C L Crespi
1Center for Environmental Health Sciences, Massachusetts Institute of Technology, Cambridge 02139.
Abstract:
Nitropyrenes are ubiquitous environmental pollutants that may pose a human health hazard because some are highly potent mutagens and carcinogens. The mutagenicity (trifluorothymidine resistance at the thymidine kinase locus) of 1-, 2-, and 4-nitropyrene (1-, 2-, and 4-NP), 1,3-, 1,6-, and 1,8-dinitropyrene (1,3-, 1,6-, and 1,8-DNP), and pyrene was assessed in a quantitative forward mutation assay using a metabolically competent line (MCL-5) of human B-lymphoblastoid cells. These cells contain endogenous cytochrome P450 activity (CYP1A1) and two plasmids that express cDNAs for four additional P450s (CYP1A2, CYP2A6, CYP2E1, CYP3A4) and microsomal epoxide hydrolase found in human liver. The major finding is that 2-NP and 1,3-DNP, both potent bacterial mutagens, were nonmutagenic in this assay. The following mutagenic potency series, expressed as the minimum detectable mutagen concentration (MDMC) in nmol/ml, was obtained: 1,6-DNP (0.8), 1,8-DNP (1.5), 4-NP (3.1), 1-NP (9.1), 2-NP (> 81), 1,3-DNP (> 86), pyrene (> 494). There was over an 11-fold difference between the most potent (1.6-DNP) and the least potent (1-NP) mutagen. 1,6-DNP was approximately twice as mutagenic as 1,8-DNP, which was almost twice as mutagenic as 4-NP, which, in turn was nearly three times as potent as 1-NP. This is the first report on the testing of 2-NP and 4-NP for mutagenicity in mammalian cell cultures. The human cell mutagenicity of these compounds was discussed in terms of potency series of nitropyrenes obtained from animal carcinogenicity experiments and other mammalian cell mutagenicity assays.
Insights
Nitropyrenes are environmental pollutants. While some nitropyrenes are potent mutagens in bacteria, 2-nitropyrene and 1,3-dinitropyrene showed no mutagenicity in human cells, unlike other tested nitropyrenes.
Area of Science:
- Environmental Science
- Toxicology
- Genetics
Background:
- Nitropyrenes are widespread environmental pollutants.
- Some nitropyrenes are known mutagens and carcinogens, posing human health risks.
- Assessing mutagenicity in human cells is crucial for risk evaluation.
Purpose of the Study:
- To evaluate the mutagenicity of various nitropyrenes and pyrene in a human cell line.
- To compare the mutagenic potency of different nitropyrenes in a metabolically competent human cell system.
- To investigate the differential mutagenicity of nitropyrenes between bacterial and human cell assays.
Main Methods:
- Utilized a quantitative forward mutation assay in a metabolically competent human B-lymphoblastoid cell line (MCL-5).
- MCL-5 cells possess endogenous and expressed cytochrome P450s and epoxide hydrolase for metabolic activation.
- Assayed 1-, 2-, 4-nitropyrene, 1,3-, 1,6-, 1,8-dinitropyrene, and pyrene for mutagenicity.
Main Results:
- 1,6-Dinitropyrene (0.8 nmol/ml) and 1,8-dinitropyrene (1.5 nmol/ml) were the most potent mutagens.
- 4-Nitropyrene (3.1 nmol/ml) and 1-nitropyrene (9.1 nmol/ml) also exhibited mutagenicity.
- 2-Nitropyrene (> 81 nmol/ml) and 1,3-dinitropyrene (> 86 nmol/ml) were nonmutagenic in this human cell assay, despite bacterial mutagenicity.
Conclusions:
- Mutagenic potency varies significantly among nitropyrenes in human cells.
- The human cell mutagenicity profile differs from bacterial assays, highlighting the importance of mammalian cell testing.
- 2-Nitropyrene and 1,3-dinitropyrene may pose a lower mutagenic risk in humans than previously suggested by bacterial data.