Early life exposure to N-nitrosamine drives genotoxicity, mutagenesis, and tumorigenesis in DNA repair-deficient mice

N-Nitrosodimethylamine (NDMA) is a probable human carcinogen found in contaminated pharmaceuticals and drinking water, yet the impact of age on NDMA susceptibility remains poorly understood. Using DNA repair-deficient (Aag-/-;Mgmt-/-) and wild-type mice, we systematically compare the effects of NDMA exposure in juveniles and adults. Juvenile Aag-/-;Mgmt-/- mice are profoundly more vulnerable, exhibiting persistent DNA damage, inflammation, and mutations that lead to liver pathology and tumorigenesis, particularly in males. Adults, by comparison, are resistant to NDMA. Wild-type mice show similar, attenuated trends. NDMA-induced DNA adduct levels are comparable across age groups, implicating proliferation-dependent responses to adducts, rather than adduct formation, as the primary driver of age-related risk. Supporting this mechanism, triiodothyronine-stimulated cell proliferation in adults partially recapitulates juvenile sensitivity, linking cell division to NDMA genotoxicity. Our findings identify developmental stage, sex, and DNA repair capacity as key modifiers of NDMA-induced carcinogenesis, with potential implications for environmental risk assessment and regulatory policy.