Formaldehyde is a widely used but highly reactive and toxic chemical. The International Agency for Research on Cancer classifies formaldehyde as a Group 1 carcinogen, based on nasopharyngeal cancer and leukemia studies. However, the correlation between formaldehyde exposure and leukemia incidence is a controversial issue. To understand the association between formaldehyde exposure and leukemia, we explored biological networks based on formaldehyde-related genes retrieved from public and commercial databases. Through the literature-based network approach, we summarized qualitative associations between formaldehyde exposure and leukemia. Our results indicate that oxidative stress-mediated genetic changes induced by formaldehyde could disturb the hematopoietic system, possibly leading to leukemia. Furthermore, we suggested major genes that are thought to be affected by formaldehyde exposure and associated with leukemia development. Our suggestions can be used to complement experimental data for understanding and identifying the leukemogenic mechanism of formaldehyde.

As industry develops in modern society, many chemicals are being used. The safety of chemicals is an important issue because humans are constantly exposed to chemicals throughout their daily life. Through a risk assessment, the hazardous human effects of chemicals can be identified. Recently, the adverse outcome pathway (AOP) framework has been used to predict the adverse effects of chemicals. As a conceptual framework for organizing existing biological knowledge, the AOP consists of a molecular initiating event, key events, and an adverse outcome. These independent elements represent biological responses and are connected by key event relationships. This AOP framework provides intuitive hazard identification that can be helpful for carcinogenic risk assessment of chemicals. In this review, we introduce the application of the AOP framework to risk assessment for predicting carcinogenicity of chemicals and illustrate the utility of this approach for cancer prevention.

Background: Ultraviolet B (UVB) radiation is a major cause of skin photodamage, including the damage associated with photodermatoses, aging, and cancer. Although many studies have shown that red light has photoprotective effects on skin, the mechanisms underlying these effects are still poorly understood. Objective: The aim of this study was to identify the photoprotective effects of visible red light against UVB-induced skin damage in normal human dermal fibroblast cells using a transcriptomic approach. Methods: Next-generation sequencing-based transcriptomic analyses were used to profile transcriptomic alterations and identify genes that are differentially expressed by visible red light and by UVB exposure. To understand the biological networks among identified genes, a literature-based biological pathway analysis was performed. Quantitative real-time polymerase chain reaction assays were used for mRNAlevel validation of selected key genes. Results: We observed that visible red light contributes to skin cell protection against UVB by modulating gene expression that enhances the adaptive response to redox and inflammatory balancing and by upregulating genes involved in DNA excision repair processes. We also identified that several key genes in the red light-induced biological network were differentially regulated. Conclusions: Visible red light enhanced the UVB-protective effects in normal human skin cells via the transcriptomic modulation of genes involved in cell-protective processes. Our findings from this nextgeneration sequencing analysis may lead to a better understanding of the cytoprotective effects of visible red light and provide direction for further molecular or mechanistic studies.

Based on epidemiological studies, an International Agency for Research on Cancer Working Group determined that strong inorganic acid mists containing sulfuric acid are carcinogenic to human even though, sulfuric acid, per se, is not. Accumulative studies indicate that there is a link between chronic occupational exposure to sulfuric acid mists and an increased risk of laryngeal cancer. Unintended, acute exposure to sulfuric acid mists can cause corrosive damage to target tissues depending on the route of exposure. This review compares the toxicity and carcinogenicity of sulfuric acid mists compared to other strong inorganic acid mists. It also examines the routes and duration of exposure (short-term, prolonged, and long-term). In vivo evidence does not support or refute the carcinogenicity of sulfuric inorganic mists even though its co-carcinogenic or promoting potential has been considered. On the basis of existing evidence on sulfuric acid mist toxicity, we suggested a putative adverse outcome pathway (AOP) relevant to carcinogenicity caused by mists containing sulfuric acid. A possible key factor involved in sulfuric acid mist carcinogenesis is the genotoxic effects of low pH since it can increase instability in chromosomes and DNA. A putative AOP for sulfuric acid mist carcinogenicity would help generate better risk assessments and more accurate predictions regarding the risk of developing cancer due to prolonged exposure. Establishing an AOP would also be useful for future studies examining the carcinogenicity of other strong inorganic mists.

Formaldehyde is a colorless, pungent, highly reactive, and toxic environmental pollutant used in various industries and products. Inhaled formaldehyde is a human and animal carcinogen that causes genotoxicity, such as reactive oxygen species formation and DNA damage. This study aimed to identify the toxic effects of inhaled formaldehyde through an integrated toxicogenomic approach utilizing database information. Microarray datasets (GSE7002 and GSE23179) were collected from the Gene Expression Omnibus database, and differentially expressed genes were identified. The network analyses led to the construction of the respiratory system-related biological network associated with formaldehyde exposure, and six upregulated hub genes (AREG, CXCL2, HMOX1, PLAUR, PTGS2, and TIMP1) were identified. The expression levels of these genes were verified via qRT-PCR in 3D reconstructed human airway tissues exposed to aerosolized formaldehyde. Furthermore, NRARP was newly found as a potential gene associated with the respiratory and carcinogenic effects of formaldehyde by comparison with human in vivo and in vitro formaldehyde-exposure data. This study improves the understanding of the toxic mechanism of formaldehyde and suggests a more applicable analytic pipeline for predicting the toxic effects of inhaled toxicants.

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