Next-generation risk assessment (NGRA) has emerged as a promising alternative to non-animal studies owing to the increasing demand for the risk assessment of inhaled toxicants. In this study, NGRA was used to assess the inhalation risks of two biocides commonly used as humidifier disinfectants: polyhexamethylene guanidine phosphate (PHMG-p) and chloromethylisothiazolinone/methylisothiazolinone (CMIT/MIT). Human bronchial epithelial cell transcriptomic data were processed based on adverse outcome pathways and used to establish transcriptome-based points of departure (tPODs) for each biocide. tPOD values were 0.00500-0.0510 μg/cm² and 0.0342-0.0544 μg/cm² for PHMG-p and CMIT/MIT, respectively. tPODs may provide predictive power comparable to that of traditional animal-based PODs (aPODs). The tPOD-based NGRA determined that both PHMG-p and CMIT/MIT present a high inhalation risk. Moreover, the identified PHMG-p posed a higher risk than CMIT/MIT, and children were identified as more susceptible population compared to adults. This finding is consistent with observations from actual exposure events. Our findings suggest that NGRA with transcriptomics offers a reliable approach for risk assessment of specific humidifier disinfectant biocides, while acknowledging the limitations of current models and in vitro systems, particularly regarding uncertainties in pharmacokinetics (PK) and pharmacodynamics (PD).

OBJECTIVES: Exposure to humidifier disinfectants has been linked to respiratory diseases, including interstitial lung disease, asthma, and pneumonia. Consequently, numerous toxicological studies have explored respiratory damage as both a necessary and sufficient condition for these diseases. We systematically reviewed and integrated evidence from toxicological studies by applying the evidence integration method established in previous research to confirm the biological plausibility of the association between exposure and disease.METHODS: We conducted a literature search focusing on polyhexamethylene guanidine phosphate (PHMG) and chloromethylisothiazolinone/methylisothiazolinone (CMIT/MIT), the primary ingredients in humidifier disinfectants. We selected relevant studies based on their quality and the population, exposure, comparator, outcome (PECO) statements. These studies were categorized into three lines of evidence: hazard information, animal studies, and mechanistic studies. Based on a systematic review, we integrated the evidence to develop an aggregate exposure pathway–adverse outcome pathway (AEP-AOP) model for respiratory damage. The reliability and relevance of our findings were assessed by comparing them with the hypothesized pathogenic mechanisms of respiratory diseases.RESULTS: By integrating toxicological evidence for each component of the AEP-AOP framework for PHMG and CMIT/MIT, we developed an AEP-AOP model that elucidates how disinfectants released from humidifiers expose target sites, triggering molecular initiating events and key events that ultimately lead to respiratory damage. This model exhibits high reliability and relevance to the pathogenesis of respiratory diseases.CONCLUSIONS: The AEP-AOP model developed in this study provides strong evidence, based on evidence-based toxicology, that exposure to humidifier disinfectants causes respiratory diseases. This model demonstrates the pathways leading to respiratory damage, a hallmark of these conditions.

Sphagnum palustre (a moss) has been traditionally used in Korea for the cure of several diseases such as cardiac pain and stroke. In this research, the inhibitory effect of S. palustre on aromatase (cytochrome P450 19, CYP19) activity was studied. [1β-3H] androstenedione was used as a substrate and incubated with S. palustre extract and recombinant human CYP19 in the presence of NADPH. S. palustre extract inhibited aromatase in a concentration-dependent manner (IC50 value: 36.4 ± 8.1 µg/mL). To elucidate the major compounds responsible for the aromatase inhibitory effects of S. palustre extract, nine compounds were isolated from the extract and tested for their inhibition of aromatase activity. Compounds 1, 6, and 7 displayed aromatase inhibition, while the inhibition by the other compounds was negligible.Video ClipAromatase enzyme activity: 4 min 16 sec

Cigarette smoking is associated with carcinogenesis owing to the mutagenic and genotoxic effects of cigarette smoke. The aim of this study was to evaluate the mutagenic and genotoxic effects of Korean cigarettes using in vitro assays. We selected 2 types of cigarettes (TL and TW) as benchmark Korean cigarettes for this study, because they represent the greatest level of nicotine and tar contents among Korean cigarettes. Mutagenic potency was expressed as the number of revertants per μg of cigarette smoke condensate (CSC) total particulate matter whereas genotoxic potency was expressed as a concentration-dependent induction factor. The CSC was prepared by the International Organization for Standardization 3308 smoking method. CHO-K1 cells were used in vitro micronucleus (MNvit) and comet assays. Two strains of Salmonella typhimurium (Salmonella enterica subsp.enterica; TA98 and TA1537) were employed in Ames tests. All CSCs showed mutagenicity in the TA98 and TA1537 strains. In addition, DNA damage and micronuclei formation were observed in the comet and MNvit assays owing to CSC exposure. The CSC from the 3R4F Kentucky reference (3R4F) cigarette produced the most severe mutagenic and genotoxic potencies, followed by the CSC from the TL cigarette, whereas the CSC from the TW cigarette produced the least severe mutagenic and genotoxic potencies. The results of this study suggest that the mutagenic and genotoxic potencies of the TL and TW cigarettes were weaker than those of the 3R4F cigarette. Further study on standardized concepts of toxic equivalents for cigarettes needs to be conducted for more extensive use of in vitro tests.

The widespread use of disinfectants, particularly during the coronavirus disease (COVID-19) pandemic, has significantly increased human exposure to biocides, raising concerns about their potential health risks, especially when inhaled. Benzalkonium chloride (BKC), a quaternary ammonium compound commonly used as a disinfectant and preservative, is a notable example because it is frequently used in household products and medical settings. Despite its broad usage, limited research has been conducted on the respiratory and systemic toxicities of BKC. Here, we conducted a research review of the literature on the respiratory toxicity of BKC. This research review suggests that, while current studies imply that BKC may induce respiratory diseases, the evidence remains insufficient. We employed an aerosol exposure model using primary bronchial epithelial cells to simulate inhalation exposure to BKC in humans. Transcriptomic analysis was performed to identify differentially expressed genes (DEGs) associated with toxicological pathways, including endoplasmic reticulum (ER) stress, apoptosis, mitochondrial dysfunction, and epithelial-mesenchymal transition (EMT). The results were integrated with gene-disease association databases to explore the links between BKC exposure and respiratory diseases such as asthma, chronic obstructive pulmonary disease (COPD), and pulmonary fibrosis. Our study also examined the systemic effects of BKC by analysing the secreted proteins, suggesting possible cardiovascular implications. These findings highlight the need for further research on the health impacts of BKC, particularly its long-term effects, and underscore the importance of regulating its use to minimise the potential health risks associated with exposure via inhalation.

Lung-on-a-chip (LOC) conditions were established to assess acute inhalation toxicity. Cell viability from reference chemicals was analyzed using ROC curves to classify UN GHS categories and evaluate the predictive capacity of the test.