Chemical Exposures, DNA Methylation and Whole Blood DNA Damage in Pet Golden Retrievers

Canine multicentric lymphoma (CL) is a common and typically fatal cancer among dogs. Although certain breeds have a higher incidence of CL, its environmental risk factors remain uncertain. Exposures to herbicides and volatile organic compounds (VOCs) associate with non-Hodgkin lymphoma in people. These exposures also correlate with measurable in vivo DNA strand breaks in dogs, even at estimated systemic concentrations that do not reach genotoxic thresholds. Herbicides and VOCs can also exert genotoxicity through differential DNA methylation. We therefore hypothesised that higher chemical exposures would be associated with differential global and gene-specific methylation in the blood of pet golden retrievers, and that differential gene-specific methylation would be further associated with measured DNA strand breaks and oxidised DNA damage. We performed Oxford Nanopore sequencing in 24 of 60 dogs from a recent case-control study within the Golden Retriever Lifetime Study cohort, selected based on the highest and lowest quintiles of estimated aggregate herbicide and VOC exposures. Contrary to our initial hypothesis, higher estimated chemical exposures were associated with relatively lower promoter methylation of antioxidant genes (median 0.335 versus 0.374; p = 0.007) and 8-oxoguanine DNA repair genes (median 0.254 versus 0.294; p = 0.007). This pattern could represent a compensatory response to chemical exposures rather than a driver of DNA damage. Follow-up studies are needed to determine whether these modest promoter methylation differences correspond to biologically meaningful increases in gene expression, antioxidant status and DNA repair capacity.