Lung Metabolism of Xenobiotic Compounds

Escherichia coli FPG and human OGG1 reduce DNA damage and cytotoxicity by BCNU in human lung cells

The pulmonary complications of 1,3-N,N'-bis(2-chloroethyl)-N-nitrosourea (BCNU) are among the most important dose-limiting factors of BCNU-containing cancer chemotherapeutic regimens. BCNU damages DNA of both cancer cells and normal cells. To increase the resistance of lung cells to BCNU, we employed gene transfer of Escherichia coli formamidopyrimidine-DNA glycosylase (FPG) and human 8-oxoguanine-DNA glycosylase (hOGG1) to A549 cells, a lung epithelial cell line, using a bicistronic retroviral vector, pSF91-RE, that encoded both FPG/hOGG1 and an enhanced green fluorescent protein. The transduced epithelial cells were sorted by flow cytometry, and expression of FPG/hOGG1 protein was determined by the level of FPG/hOGG1 RNA and enzyme activity. The single-cell gel electrophoresis (comet assay) measured DNA damage induced by BCNU. FPG/hOGG1-expressing A549 cells incubated with 40-500 microg/ml BCNU exhibited significantly less DNA damage than vector-transduced cells. In addition, FPG- and/or hOGG1-expressing cells incubated with 10-40 microg/ml BCNU showed at least a 25% increase in cell survival. Gene transfer of FPG/hOGG1 reduced BCNU-induced DNA damage and cytotoxicity of cultured lung cells and may suggest a new mechanism to reduce BCNU pulmonary toxicity.

Hypothesis: is lung disease after silicate inhalation caused by oxidant generation?

Inhaled silicate dusts may cause lung disease through their surface coordination of iron with subsequent oxidant generation via the Fenton reaction. Pneumoconiosis, irritant bronchitis, focal emphysema, and carcinoma may be produced by oxidants either directly through lipid peroxidation and protein inactivation, or indirectly by oxidant-mediated release of cytokines such as platelet-derived growth factor. The increased incidence of tuberculosis observed among silicate workers could be explained by accumulation of iron complexed by dust particles in the lung and made available to dormant mycobacteria as a virulence factor.