Protective Effects Of Personal Care And Consumer Product Chemical Substances On Age-related Hearing Loss: Studies On Human And Animal Models

Part I The association between hearing threshold and urinary personal care and consumer product metabolites in middle-aged and elderly people from the USABackground and Objective: Age-related hearing loss is a progressive sensorineural hearing loss that can significantly impact the quality of life and economic well-being of middle-aged and elderly individuals.Currently,cochlear implants are the only available treatment option for age-related hearing loss,underscoring the importance of preventative measures for age-related hearing loss.Benzophenone-3,bisphenol A,triclosan,methylparaben,propylparaben,2,5-dichlorophenol and 2,4-dichlorophenol are common chemical additives found in personal care and consumer products such as soap,shower gel,toothpaste and cosmetics.These substances are considered common environmental pollutants and have been widely reported to contribute to the development of various diseases in humans.However,despite their widespread exposure,no studies have yet investigated their relationship with age-related hearing loss.This study aims to investigate the association between these chemicals and hearing thresholds in middle-aged and elderly people and provide new insights for preventing age-related hearing loss.Method: The original data for this study was derived from middle-aged and elderly participants aged 45 and over who took part in the National Health and Nutrition Examination Survey between 2007 and 2016 and had complete pure-tone audiometry data and urinary personal care and consumer product metabolites data.We excluded participants with abnormal otoscopy or tympanometry peak values less than or equal to 0.3 m L.We also adjusted for potential confounding factors in all statistical models.We first used weighted linear regression models and restricted cubic spline regression models to analyze the effects of individual chemical exposure on the high-frequency or low-frequency hearing thresholds,using FDR-adjusted P-values based on the effective number of tests.Considering the correlation between these seven personal care product chemicals,we also used Bayesian kernel machine regression to analyze their joint effects on the high-frequency or low-frequency hearing thresholds.We also used unsupervised clustering methods to explore the exposure patterns of seven personal care product chemicals in middle-aged and elderly people,dividing the sample population into different exposure groups,and showing the least squares geometric means of high-frequency and low-frequency hearing thresholds in different groups.We also performed multiple sensitivity analyses to determine the robustness of our results.Results:In weighted linear regression,we found that only the antibacterial agent triclosan had a significant protective effect on high-frequency hearing thresholds in middle-aged and elderly people(β value(95%CI):-0.018(-0.034,-0.0029),P.adj=0.005).In restricted cubic spline regression,we found significant nonlinear associations between high-frequency hearing thresholds and the preservatives or antibacterial agents 2,4-dichlorophenol(P.adj=0.039),2,5-dichlorophenol(P.adj=0.039),and triclosan(P.adj=0.02).The association between 2,4-dichlorophenol and high-frequency hearing thresholds was approximately inverted ‘U’-shaped,with high-frequency hearing thresholds first increasing and then decreasing with increasing 2,4-dichlorophenol exposure,and the magnitude of the decrease was greater than that of the increase;while high-frequency hearing thresholds first slightly increased and then sharply decreased with increasing 2,5-dichlorophenol exposure;high-frequency hearing thresholds showed a downward trend with increasing triclosan exposure,but the curve was steeper in the first half and flatter in the second half.Using Bayesian kernel machine regression,we discovered that the combinedexposure to seven personal care product chemicals had a protective effect on hearing among middle-aged and elderly individuals,with a more pronounced effect on high-frequency thresholds.In addition,the dose-response relationships between individual chemicals and hearing thresholds shown by Bayesian kernel machine regression were generally consistent with those of restricted cubic spline regression.Only substances classified as preservatives demonstrated a protective effect on hearing among middle-aged and elderly individuals.Unsupervised clustering clustered the sample population into four clusters.Based on the different chemical exposure characteristics,we considered cluster 1 as a high exposure group for parabens;cluster 4 as a high exposure cluster for triclosan;cluster 2 as a high exposure group for dichlorophenols;cluster 3 as a low exposure group for personal care product chemicals.We then calculated the least squares geometric means of hearing thresholds for different clusters based on weighted linear regression.We found that compared with cluster 3,only the high exposure cluster for triclosan had the most obvious protective effect on high-frequency hearing(P=0.00258).In multiple sensitivity analyses,our results remained consistent.Conclusion: Through this part of the study,we found that antibacterial or bacteriostatic agents,represented by triclosan,in personal care products had a protective effect on high-frequency hearing thresholds in middle-aged and elderly people,which contradicted the previous reports of various toxic side effects of triclosan.In addition,due to the nature of cross-sectional studies,we could not completely rule out the possibility of reverse causality.Part II The protective effect of triclosan on age-related hearing loss: validation in animal modelsBackground and Objective: In the first part of the study,we observed for the first time in the population that preservatives or antibacterial agents,represented by triclosan,in personal care product chemicals had a significant protective effect on high-frequency hearing thresholds in middle-aged and elderly people,but this contradicted the previous reports of toxic side effects of triclosan.This protection needs further longitudinal studies to verify.Since triclosan is commonly used in toothpaste and mouthwash,recent studies have shown that adding a certain concentration of triclosan to the drinking water of mice can approximate the exposure pattern of triclosan in the population,which provides a condition for further verifying the protective effect of triclosan on age-related hearing loss in mouse models.In this part of the study,we used the C57BL/6J mouse model to verify the protective effect of triclosan on age-related hearing loss and rule out reverse causality.Method:Twenty-four 3-month-old male C57BL/6J mice were randomly divided into four groups,six in each group,namely control group(10ml dimethyl sulfoxide added to drinking water),treatment 1 group(TCS1 group,drink 1ppm triclosan solution),treatment 2 group(TCS2 group,drink 10 ppm triclosan solution)and treatment 3 group(TCS3 group,drink 80 ppm triclosan solution).At the ages of 3,6 and 9 months,ABR thresholds of 16 k Hz,12 k Hz,8k Hz and 4k Hz frequencies were recorded.Statistical analysis was performed using R(version 4.0.4),and P<0.05 was considered statistically significant.Kruskal-Wallis test was used to determine whether the difference in ABR thresholds among groups was statistically significant.If the overall difference among groups was statistically significant,Wilcoxon rank sum test was used to determine the statistical significance of pairwise comparisons among groups.Results: At baseline,ABR threshold at all frequencies was roughly normal in the control group,TCS1 group,TCS2 group and TCS3 group,with no statistically significant differences.At 6 months of age,we observed a trend towards reduced hearing thresholds at 16 k Hz,12 k Hz and 8k Hz in the TCS2 group compared to the control group.In addition,we noted a trend towards increased differences in hearing thresholds between the TCS3 group and the TCS2 group.However,Kruskal-Wallis tests revealed no statistically significant differences in hearing thresholds between groups.At 9 months of age,overall differences in hearing thresholds at 16 k Hz and 12 k Hz were statistically significant across the four treatment groups.Pairwise comparisons between groups revealed that only the TCS2 group had significantly lower hearing thresholds compared to the control group.Conclusion: We have preliminarily validated the protective effect of triclosan on age-related hearing loss in a mouse model.As triclosan is primarily exposed orally as an antibacterial agent,we speculate that it may exert an indirect protective effect on hearing through the oral microbiome.However,this remains to be further validated.Part III: The Relationship between Urinary Triclosan Concentration,Oral Health Status,and Hearing Threshold in Middle-aged and Elderly People: Mediation Effect AnalysisBackground and Objective: In previous studies,we found that preservatives or antibacterial agents,represented by triclosan in personal care product chemicals,may have a protective effect on age-related hearing loss.We also verified the protective effect of triclosan on the age-related hearing loss in animal models,thus basically ruling out the possibility of reverse causality.However,previous population and cell experiments have shown that triclosan,as an antibacterial agent added to toothpaste and mouthwash,has many adverse effects on human health,which is contradictory to the protective effect of triclosan on age-related hearing loss that we observed.Therefore,we hypothesize that triclosan may exert a protective effect on hearing by regulating the oral microbiome and promoting oral health.If this hypothesis is correct,there may be evidence in middle-aged and elderly populations that triclosan exerts a protective effect on hearing through the intermediate factor of promoting oral health status.This study aims to use a mediation effect model to verify whether the protective effect of triclosan on age-related hearing loss overlaps with the mechanism by which triclosan promotes oral health status.Method: This study analyzed the sociodemographic,lifestyle,hearing measurement,urinary trichloroacetic acid metabolite concentration,and oral health survey questionnaire data of 655 middle-aged and elderly people aged 45 and over in the National Health and Nutrition Examination Survey from 2011 to 2015.We first used a weighted linear regression model adjusted for all covariates to calculate whether the difference in hearing thresholds between populations with different oral health status was significant.Then we used a logistic regression model to analyze the effect of quartile concentrations of triclosan on oral health status.Finally,we established a mediation effect model to explore whether triclosan can protect hearing by promotingoral health status.Results: We first calculated the weighted least squares geometric mean of hearing thresholds for different oral health statuses using a weighted linear regression model after adjusting for all covariates.We found that compared to populations with general/poor oral health,populations with good oral health had better high-frequency hearing.The high-frequency hearing threshold of populations with good oral health status was about 5d B lower than that of populations with general/poor oral health status,and the difference was statistically significant(P=0.0095).We used logistic regression to verify whether triclosan could promote oral health status in the samples we included.Consistent with previous research results,in this study,we also found that triclosan has a significant protective effect on oral health.Compared to the first quartile of triclosan,the remaining three quartiles all had a lower risk of poor oral health status.After stratifying by oral health status,we found that although triclosan still had a trend of producing a protective effect on high-frequency hearing in populations with general/poor oral health,the difference was no longer statistically significant.However,in participants with good oral health status,the protective effect of triclosan on high-frequency hearing was still significant.After discovering a significant relationship between urinary triclosan concentration,oral health status and high-frequency hearing threshold in middle-aged and elderly people,we used a mediation effect model to find that triclosan could play a role in protecting hearing by promoting oral health(the proportion of mediation pathways is 20%,P<10-16).Conclusion: The protective effect of triclosan on age-related hearing loss overlaps mechanistically with the role of triclosan in regulating oral microbiota to promote oral health status.There may be an ‘oral microbiota-inner ear’ axis in the human body similar to the ‘gut microbiota-brain’ axis.