Factors influencing benzo[a]pyrene metabolism in human mammary epithelial cells in culture

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Abstract
We have examined the human mammary epithelial cell (HMEC) culture system developed in our laboratory for factors that might influence the metabolism of chemical carcinogens, specifically, the impact of interindividual variation and the effect of different culture conditions. Benzo[a]pyrene metabolism and DNA adduct formation in HMEC from 13 normal reduction mammoplasty specimens, from five non-tumorous mastectomy tissues and from eight primary carcinomas were investigated. The interindividual variation in formation of water and organosoluble metabolites was similar in all of the three categories of HMEC. A similar range of variation was found for DNA adduct formation among HMEC from reduction mammoplasty specimens. However, when the individual results of DNA adduct formation in the three categories were examined, HMEC from some specimens from non-tumorous mastectomy tissue and primary carcinomas had significantly increased DNA modification. We also measured the effects of BaP concentration, different culture media, the length of time in culture, the culture density, and the frequency of feeding on the conversion of tritiated BaP to various water and organosoluble metabolites. The BaP metabolite pattern by HMEC was generally stable in the face of these variables. However, suboptimal feeding regimens and lengthy passaging in culture reduced the capacity of the cells to metabolize BaP. The yield of BaP conjugates was reduced 10-fold with lengthy passaging in culture whereas the organosoluble metabolite yield was halved and DNA adduct formation was not affected. Increasing the concentration of BaP decreased the yield of water soluble metabolites relative to that of organosoluble, indicating differences in the capacity of the enzyme systems involved. The HMEC culture system offers several advantages for studies into the biochemical and molecular basis of chemical carcinogenesis in human epithelial cells: the large numbers of cells required can be easily generated; cells at all stages can be frozen for future experiments with no loss in activity; and a high capacity for carcinogen activation is retained during long-term culture.