Species and sex-dependent toxicokinetics of 1-bromopropane: the role of hepatic cytochrome P450 oxidation and glutathione (GSH)

Association of 1-bromopropane exposure with asthma prevalence: A Korean National Health and Nutritional Examination Survey (2020-2021)-based study1

Exposure to 1-bromopropane (1-BP) is an emerging environmental and health concern due to its increasing environmental prevalence. Although the health effects of 1-BP exposure have been under-recognized, current evidence suggests the possibility of adverse pulmonary health effects due to 1-BP exposure. However, the association between 1-BP exposure and asthma prevalence remains unclear. Thus, we aimed to examine the association between 1-BP exposure and asthma prevalence in the general population. Using nationally representative data, we explored the potential impacts of indoor air quality (IAQ)-related behavioral factors on the level of 1-BP exposure. This study included 1,506 adults from the 2020-2021 Korea National Health and Nutrition Examination Survey. The prevalence of asthma was based on self-reported physician-diagnosed asthma. Urinary N-acetyl-S-(n-propyl)-L-cysteine (BPMA) levels were measured as a biomarker of 1-BP exposure, using high-performance liquid chromatography-mass spectrometry. Multiple logistic regression models were performed to investigate the associations between urinary BPMA metabolite and asthma prevalence after adjusting for potential confounders. Log-linear multiple regression models were used to examine the association between IAQ-related behavior and urinary BPMA concentration. Forty-seven individuals with asthma and 1,459 without asthma were included. Individuals in the highest quartile of urinary BPMA concentration had a 2.9 times higher risk of asthma than those in the lowest quartile (odds ratio [OR]: 2.85, 95% confidence interval [CI]: 1.02-7.98). The combination of natural and mechanical ventilation was associated with a reduced urinary BPMA concentration. Our findings suggest that 1-BP exposure is associated with the prevalence of asthma in adults and revealed higher urinary levels of BPMA in our study population compared to those in other countries. Given the emerging importance of IAQ, actively managing and modifying behavioral patterns to reduce 1-BP exposure in indoor environments could substantially attenuate the risk of asthma-related to 1-BP exposure.

Allyl Sulfide Counteracts 1-Bromopropane-Induced Neurotoxicity by Inhibiting Neuroinflammation and Oxidative Stress

Chronic exposure to 1-bromopropane (1-BP), an alternative to ozone-depleting solvents, produces potential neurotoxicity in occupational populations. However, no therapeutic strategy is available currently. Accumulating evidence suggests that cytochrome P4502E1 (CYP2E1) is critical for the active metabolism of 1-BP. The purpose of this study is aimed to test whether inhibition of CYP2E1 by allyl sulfide, a specific inhibitor of CYP2E1, could be able to protect against 1-BP-induced neurotoxicity. Male Wistar rats were intoxicated with 1-BP for 9 continuous weeks with or without allyl sulfide pretreatment. Results clearly demonstrated that 1-BP exposure induced decrease in NeuN+ cells and increase in cleaved caspase-3 expression and TUNEL+ cells in motor cortex of rats, which was significantly ameliorated by allyl sulfide. Allyl sulfide treatment also recovered the motor performance of rats treated with 1-BP. Mechanistically, allyl sulfide-inhibited 1-BP-induced expression of CYP2E1 in microglia, which was associated with suppression of microglial activation and M1 polarization in motor cortex of rats. Reduced oxidative stress was also observed in rats treated with combined allyl sulfide and 1-BP compared with 1-BP alone group. Furthermore, we found that allyl sulfide abrogated 1-BP-induced activation of Nuclear factor(NF)-κB and GSH/Thioredoxin/ASK1 pathways, the key factor for the maintenance of M1 microglial inflammatory response and oxidative stress-related neuronal apoptosis, respectively. Thus, our results showed that allyl sulfide exerted neuroprotective effects in combating 1-BP-induced neurotoxicity through inhibition of neuroinflammation and oxidative stress. Blocking CYP2E1 activity by allyl sulfide might be a promising avenue for the treatment of neurotoxicity elicited by 1-BP and other related neurotoxicants.

Physiologically based pharmacokinetic modeling for 1-bromopropane in F344 rats using gas uptake inhalation experiments

1-Bromopropane (1-BP) was introduced into the workplace as an alternative to ozone-depleting solvents and increasingly used in manufacturing industry. The potential exposure to 1-BP and the current reports of adverse effects associated with occupational exposure to high levels of 1-BP have increased the need to understand the mechanism of 1-BP toxicity in animal models as a mean of understanding risk in workers. Physiologically based pharmacokinetic (PBPK) model for 1-BP has been developed to examine 2 metabolic pathway assumptions for gas-uptake inhalation study. Based on previous gas-uptake experiments in the Fischer 344 rat, the PBPK model was developed by simulating the 1-BP concentration in a closed chamber. In the model, we tested the hypothesis that metabolism responsibilities were shared by the p450 CYP2E1 and glutathione (GSH) conjugation. The results showed that 2 metabolic pathways adequately simulated 1-BP closed chamber concentration. Furthermore, the above model was tested by simulating the gas-uptake data of the female rats pretreated with 1-aminobenzotrizole, a general P450 suicide inhibitor, or d,l-buthionine (S,R)-sulfoximine, an inhibitor of GSH synthesis, prior to exposure to 800 ppm 1-BP. The comparative investigation on the metabolic pathway of 1-BP through the PBPK modeling in both sexes provides critical information for understanding the role of p450 and GSH in the metabolism of 1-BP and eventually helps to quantitatively extrapolate current animal studies to human.