With global industrialization and urbanization, the extensive spread of environmental contaminants endangers ecosystems and human health and is a leading cause of sickness and death (Chowdhury et al. 2023; Fuller et al. 2022; Mou et al. 2023). Cell biology methodologies provide a scientific foundation for analyzing and forecasting contaminant risk in environmental toxicology research. Cell damage assessment is an important component of cell biology methods, which, in addition to being important in disease diagnosis and monitoring (Burton and Stolzing 2018; Kamisawa et al. 2015; Maria and Davidson 2020) and drug development and safety assessment (Fucikova et al. 2020; Ingber 2022; Weaver et al. 2020), is also important in assessing the toxicity of environmental pollutants. Park and Choi discovered that cytotoxicity, genotoxicity, and ecotoxicity tests may accurately assess the possible impacts of environmental contaminants on human health and ecosystems (Park and Choi 2007). Rubio et al. found that polystyrene nanoparticles (PSNPs) induce oxidative stress and genetic damage in various human hematopoietic cell lines. The result underscores the importance of conducting cellular damage assays to assess the biological impacts of pollutants, including microplastics accurately (Rubio et al. 2020). According to Santos et al., the cytotoxicity and genotoxicity of chlorinated disinfection by-products of 1,3-diphenyl guanidine (DPG) confirmed the usefulness of cellular damage assays in the toxicity assessment of environmental pollutants (Marques dos Santos et al. 2022). These findings imply that cellular damage assays not only aid in the rapid screening and identification of harmful compounds but also provide valuable information for understanding the mechanism of action of pollutants.
The most frequent methods for determining the level of cell damage fall into three categories: cell viability assays, biochemical index tests, and morphological observations. Cell viability assays are important for assessing cell survival and function. Kamiloglu et al. discussed a variety of cell viability assays in detail, including staining exclusion (e.g., Taipan blue staining), colorimetric assays (e.g., MTT and MTS assays), fluorescence (e.g., resazurin and 5-CFDA-AM assays), luminescence (e.g., ATP assay), and flow cytometry. (e.g., membrane asymmetry and permeability measurements) (Kamiloglu et al. 2020). Changes in cell viability can directly reflect a cell's response to external stimuli and provide useful information about the level of cellular damage.
Biochemical index assays evaluate various biomarkers and are typically used to estimate cellular damage. Apoptosis tests are an essential part of this category, and the presence of apoptosis is typically determined using methods such as Annexin V-FITC labeling. Apoptosis markers include the production or activation of certain proteins such as cysteinyl asparaginases (Caspases) (Sahoo et al. 2023), cytochrome C (Morse et al. 2024), Bcl-2 family proteins (Czabotar and Garcia-Saez 2023), and p53 (Liu and Gu 2022), which can indicate whether a cell is undergoing programmed death. Furthermore, biochemical index testing relies heavily on the detection of oxidative stress indicators. Oxidative stress is a major cause of cellular injury, defined as the breakdown of the equilibrium between oxidants and antioxidants in cells in response to damaging stimuli from the internal and external environments, resulting in cell and tissue damage (Sinha et al. 2015). This imbalance could be induced by metabolic processes, exposure to toxic chemicals, or a weakened antioxidant system (Gu et al. 2020; Hodjat et al. 2015; Zheng et al. 2020). The state of cells under oxidative stress can be determined by measuring intracellular levels of antioxidants (e.g., glutathione GSH) and oxidation products (e.g., malondialdehyde MDA). Changes in these biomarkers can indicate the severity of cellular damage caused by environmental toxins.
Morphological observation assesses cell damage by directly examining changes in cell morphology under a microscope. If there are evident changes in the morphology of the cells following stimulation, such as cell swelling, cell membrane crumpling, and so on, this intuitive information can assist researchers in making a preliminary assessment of the degree of damage. The advantage is that it is intuitive and non-invasive, and morphological changes are typically one of the first responses to hazardous stimuli. Images can reveal changes in cell morphology, making them a valuable tool for analyzing cell damage. Soltanian-Zadeh et al. created an automated approach for segmenting retinal ganglion cells using adaptive optics OCT images that use poorly supervised deep learning. This method increases the accuracy and efficiency of cell damage assessment (Soltanian-Zadeh et al. 2021). Rendeiro et al. used high-parameter imaging mass spectrometry to study the effect of SARS-CoV-2 infection on lung pathology, demonstrating the disordered structure of infected and injured lungs as well as the widespread dispersion of immune infiltrates (Rendeiro et al. 2021). This research demonstrated that processing and analyzing cellular pictures can extract damage-related morphological characteristics, which can then be used to measure and quantify cellular damage.
In our investigation, we discovered that microscopic images of normal and stimulated injured cells had different grey scale distributions, indicating a change in brightness between them. Based on this observation, we suggest a novel hypothesis: picture brightness can measure the degree of cellular damage, and a grey-scale frequency analysis approach can be created to assess the degree of cellular damage.