The International Agency for Research on Cancer (IARC) has classified processed/cured meats as Group 1 carcinogens (carcinogenic to humans), and grilled meats as Group 2A carcinogens (possibly carcinogenic to humans), largely implicated in colorectal cancer. Cooked meats contain several classes of carcinogens including heterocyclic aromatic amines (HAAs) and polycyclic aromatic hydrocarbons (PAHs) in grilled red meats, and N-nitroso compounds (NOCs) in processed meats. These compounds undergo bioactivation by enzymes to produce reactive species that form DNA adducts, which can lead to cancer. 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is the most mass-abundant HAA formed in high-temperature cooked meats, and is a colorectal and prostate carcinogen in rodents. The prototypical PAH is benzo[a]pyrene, a recognized human lung and possible gastrointestinal tract carcinogen. NOCs are formed during the curing process of meat. Secondary amines in meat products also may undergo nitrosation in the GI tract to form endogenous NOC. In addition, ingested heme has been proposed to catalyze the formation of lipid peroxidation products in the lower GI tract and contribute to colonic DNA damage. Whereas HAAs and PAHs lead to bulky DNA adducts formed with 2′-deoxyguanosine (dG), NOCs produce small alkylation products adducts such as O6-methyl-2′-deoxyguanosine and O6-carboxylmethyl-2′-deoxyguanosine. However, specific mass spectrometry-based methods have rarely been employed to screen for DNA adducts in human colorectum. Recently, our laboratory identified PhIP-DNA adducts in the prostate biopsy samples of cancer patients. Identification of mutation-prone DNA adducts of meat mutagens in colorectum would strengthen the epidemiology paradigms for a role of these chemicals in the etiology of colorectal cancer. We are developing methods to measure DNA adducts of these different classes carcinogens in human colorectum. DNA is isolated from fresh-frozen tumor adjacent colon tissue and matching formalin-fixed paraffin-embedded (FFPE) tissue. DNA is then digested with a cocktail of enzymes to produce individual non-modified nucleosides and chemically-modified nucleosides. The DNA adducts are enriched from non-modified nucleosides either by offline solid-phase extraction or online trapping before analysis via high-resolution nanoESI-UHPLC-MS/MS. The limit of quantification for these DNA lesions is 2 - 5 adducts in 109 DNA bases.

Screening for DNA adducts in human colon by high-resolution nano-ESI UHPLC/MSn

256th National Meeting (2018)

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