Nanomaterials have shown immense potential across various fields, but their interaction with biological systems raises concerns about genotoxicity. The assessment of DNA damage, chromosomal aberrations, and mutagenic potential is critical to understanding the risks associated with nanomaterial exposure. Several well-established assays, including the comet assay, micronucleus test, and analysis of oxidative DNA adducts, provide mechanistic insights into how nanomaterials induce genetic alterations.

The comet assay, or single-cell gel electrophoresis, is a sensitive method for detecting DNA strand breaks caused by nanomaterials. When cells are exposed to certain nanoparticles, such as metal oxides or carbon-based materials, the assay reveals increased tail moment and tail intensity, indicating DNA fragmentation. For instance, titanium dioxide nanoparticles have been shown to generate reactive oxygen species (ROS), leading to oxidative DNA damage detectable via the comet assay. Similarly, silver nanoparticles induce dose-dependent DNA strand breaks in human lymphocytes, with higher concentrations correlating with greater damage. The mechanism often involves ROS generation, which attacks the phosphodiester backbone of DNA, resulting in single- or double-strand breaks.

Chromosomal aberrations are another critical endpoint in nanomaterial genotoxicity studies. The micronucleus test is widely used to assess chromosomal damage and mitotic abnormalities. This test detects micronuclei formed from acentric chromosome fragments or whole chromosomes lagging during cell division. Studies on cerium oxide nanoparticles demonstrate an increase in micronucleus frequency in mammalian cells, suggesting clastogenic or aneugenic effects. Similarly, multi-walled carbon nanotubes have been observed to disrupt spindle formation during mitosis, leading to chromosomal missegregation. The underlying mechanisms often involve interference with the mitotic apparatus or direct interaction with DNA, resulting in structural or numerical chromosomal aberrations.

Oxidative DNA adducts serve as biomarkers for nanomaterial-induced genotoxicity. Many nanomaterials, particularly transition metal-based nanoparticles, catalyze Fenton-like reactions, producing hydroxyl radicals that modify DNA bases. Common oxidative lesions include 8-oxo-2'-deoxyguanosine (8-oxodG), which is a well-studied marker of oxidative stress. For example, iron oxide nanoparticles have been shown to elevate 8-oxodG levels in exposed cells, indicating oxidative DNA base modifications. The formation of these adducts can lead to mispairing during DNA replication, increasing the risk of mutations. Additionally, some nanomaterials interfere with DNA repair enzymes, exacerbating the persistence of oxidative lesions.

The mechanisms of nanomaterial-induced DNA damage are multifaceted. One primary pathway involves ROS generation, which is influenced by the material’s surface chemistry, size, and composition. Smaller nanoparticles often exhibit higher reactivity due to their increased surface area-to-volume ratio, leading to greater ROS production. Surface coatings can also modulate toxicity; for instance, polyethylene glycol-functionalized gold nanoparticles show reduced ROS generation compared to uncoated counterparts. Another mechanism is direct physical interaction between nanoparticles and DNA. Certain cationic nanoparticles, such as those with amine surface groups, can bind electrostatically to the negatively charged DNA backbone, causing condensation or strand breaks.

Nanomaterials may also interfere with cellular repair processes. Some studies report that exposure to nanoparticles downregulates key DNA repair proteins, such as OGG1 (an enzyme responsible for excising 8-oxodG) or XRCC1 (involved in base excision repair). This suppression compromises the cell’s ability to correct oxidative lesions, increasing genomic instability. Additionally, nanoparticles can induce inflammation, leading to secondary genotoxic effects. For example, long, rigid carbon nanotubes have been shown to trigger chronic inflammatory responses, which in turn promote ROS production and DNA damage in surrounding tissues.

The relationship between nanoparticle properties and genotoxicity is complex. Shape, surface charge, and dissolution rate all play roles in determining biological impact. High-aspect-ratio nanomaterials, such as certain metal nanowires, have been associated with frustrated phagocytosis and prolonged inflammatory responses, indirectly contributing to DNA damage. Similarly, soluble nanoparticles like zinc oxide can release ions that directly interact with DNA or disrupt zinc-finger proteins involved in DNA repair.

While in vitro studies provide valuable mechanistic insights, in vivo models are essential for understanding systemic genotoxicity. Rodent studies have shown that certain nanoparticles, when inhaled or ingested, can translocate to secondary organs, including the liver and bone marrow, where they induce DNA damage. For example, silica nanoparticles administered via inhalation have been detected in the bloodstream and subsequently in the liver, where they increase oxidative DNA adducts. These findings highlight the importance of considering biodistribution when evaluating nanomaterial risks.

In summary, nanomaterials can induce DNA damage, chromosomal aberrations, and mutagenesis through multiple mechanisms, including ROS generation, direct DNA interaction, and interference with repair pathways. The comet assay, micronucleus test, and oxidative adduct analysis are indispensable tools for assessing these effects. Understanding the relationship between nanomaterial properties and genotoxicity is crucial for developing safer designs while harnessing their technological potential. Future research should focus on elucidating long-term genomic consequences and developing strategies to mitigate adverse effects without compromising functionality.