Formalin-fixed paraffin-embedded tissue as a source for quantitation of carcinogen DNA adducts: aristolochic acid as a prototype carcinogen

Abstract

DNA adducts are a measure of internal exposure to genotoxicants. However, the measurement of DNA adducts in molecular epidemiology studies often is precluded by the lack of fresh tissue. In contrast, formalin-fixed paraffin-embedded (FFPE) tissues frequently are accessible, although technical challenges remain in retrieval of high quality DNA suitable for biomonitoring of adducts. Aristolochic acids (AA) are human carcinogens found in Aristolochia plants, some of which have been used in the preparation of traditional Chinese herbal medicines. We previously established a method to measure DNA adducts of AA in FFPE tissue. In this study, we examine additional features of formalin fixation that could impact the quantity and quality of DNA and report on the recovery of AA-DNA adducts in mice exposed to AA. The yield of DNA isolated from tissues fixed with formalin decreased over 1 week; however, the levels of AA-DNA adducts were similar to those in fresh frozen tissue. Moreover, DNA from FFPE tissue served as a template for PCR amplification, yielding sequence data of comparable quality to DNA obtained from fresh frozen tissue. The estimates of AA-DNA adducts measured in freshly frozen tissue and matching FFPE tissue blocks of human kidney stored for 9 years showed good concordance. Thus, DNA isolated from FFPE tissues may be used to biomonitor DNA adducts and to amplify genes used for mutational analysis, providing clues regarding the origin of human cancers for which an environmental cause is suspected.