Alkylating Agents as Genotoxins: Mechanisms, Health Risks, and Analytical Gaps

The carcinogenic risks of cigarette smoking are extensively documented and well-known, with polycyclic aromatic hydrocarbons (PAHs), nitrosamines, and tar identified as notable damaging contributors. However, a subset of cigarette smoke components known as alkylating agents, such as acrolein and formaldehyde, also exert genotoxic effects through direct mechanisms, distinct from PAH and nitrosamines. Alkylating agents do not require metabolic activation to form DNA adducts, and some alkylating agents, such as formaldehyde, form DNA crosslinks instead. The lack of metabolic activation allows them to pose a more direct mutagenic risk in human tissue, potentially leading to carcinogenesis. This review examines the molecular mechanisms by which these alkylating agents damage DNA, evaluates the assays currently used to quantify this damage, and identifies the key methodological shortcomings that limit cross-study comparability and clinical validity. Evidence from controlled exposure studies, using MMS and DMS as model alkylating agents, shows that they induce N7-methylguanine and O6-methylguanine adducts, with downstream repair involving pathways such as homologous recombination (HR) in eukaryotic models. Formaldehyde produces DNA-protein crosslinks at endogenously relevant concentrations. The comet assay remains a widely used DNA damage quantification tool, but suffers from inter-laboratory variability. Notably, many published studies use unrealistic compound concentrations and single-agent studies that fail to resemble the complex mixture toxicity of actual cigarette smoke. Direct-acting alkylating agents represent a less studied but mechanistically significant contributor to the harmful implications of cigarette smoke. Standardisation of assay methodology, adoption of physiologically relevant dosing, and mixture-based experimental designs are urgently needed. A prospective experimental protocol using Saccharomyces cerevisiae as a model organism is also proposed.