Exploring the effects and mechanisms of organophosphorus pesticide exposure and hearing loss

Organochlorine pesticides: occurrence, spatial distribution of residues, toxicity, and toxic mechanisms

Organochlorine pesticides (OCPs) are a class of synthetic, broad-spectrum insecticides that have been widely used for plant pest control over the last century. OCPs are persistent organic pollutants (POPs) with mutagenic, teratogenic, and carcinogenic properties. Although most OCPs are banned to use now, they are ubiquitous in the environment and food, and identified in the serum and urine of humans. Exposure to OCPs could affect the human nervous system, auditory system, and endocrine system, leading to neurodegenerative diseases, hearing loss, cancer, and other diseases. Further, the toxic mechanisms of OCPs are explored from oxidative stress, DNA damage, and inflammatory response. Overall, this review offers a comprehensive insight into the occurrence, spatial distribution of residues, toxicity, and toxic mechanisms of OCPs.

Protective effects of indole-3-propionic acid against TCP-induced hearing loss in mice by mitigating oxidative stress and promoting neutrophil recruitment

Sensorineural hearing loss (SNHL) poses a significant global health challenge with substantial socioeconomic and medical implications. The pathophysiology involves excessive reactive oxygen species (ROS) in the cochlea, inflammation, cellular apoptosis, etc. Tryptophan metabolite indole-3-propionic Acid (IPA), produced by gut microbiota, may offer therapeutic benefits by modulating inflammation, oxidative stress, and immune responses. However, the roles of IPA in protecting from treatment hearing loss in adult mice remain to be investigated. We previously validated that exposure to pesticide metabolite 3, 5, 6-Trichloro-2-pyridinol (TCP) caused hearing loss in mice. Herein, continuous administration of 40 mg/kg IPA for 21 days significantly attenuated the hearing threshold elevation in C57BL/6 mice exposed to 50 mg/kg TCP. IPA treatment reduced the loss of hair cells (HCs) and spiral ganglion neurons (SGNs), preserved nerve fibers, and reversed the damage to spiral ligaments (SL) and stria vascularis (SV). Similarly, IPA cotreatment decreased ROS accumulation in the cochlea and inhibited HC and SGN apoptosis. Transcriptomic analysis showed that IPA enhanced immune responses, particularly through neutrophil recruitment and the activation of regenerative signals like IFNγ. These findings underscore IPA's protective effects against TCP-induced hearing loss, highlighting the role of immune mechanisms in cochlear protection.

Molecular docking and molecular dynamics simulations revealed interaction mechanism of acetylcholinesterase with organophosphorus pesticides and their alternatives

Organophosphate pesticides (OPs) are widely used in agricultural fields and can inhibit the activity of human acetylcholinesterase (hAChE) by covalently binding to serine at the enzyme's active site. However, the molecular recognition mechanisms beyond their covalent binding remain unclear. This study employed molecular docking along with molecular dynamics simulations (MD) to investigate four representative OPs, Phosphamidon, Monocrotophos, Dichlorvos, and Trichlorfon, as well as two potential alternatives Magnolol (MAG) and Honokiol (HON), to understand the conformational change of hAChE and its molecular recognition mechanism. The results indicate that, in addition to these OPs, the selected substitutes also induce various changes in the internal structure of hAChE, especially interactions with key residues around Trp86, Tyr124, Tyr337, and His447. Energy calculations utilizing MM-GBSA and SIE methods further reveal the critical role of van der Waals interactions in hAChE's interaction with these OPs and their substitutes. It is worth noting that two potential pesticide alternatives MAG and HON differ in structure from OPs at the benzene ring and hydroxyl positions, resulting in their weaker binding energy with hAChE. Furthermore, the accuracy of simulation models was validated through in silico site-directed mutagenesis based on the key residues. By identifying dynamic structural changes and energy signatures, this study provides valuable information for finding safer alternatives to OPs.

Impact of pesticide exposure on auditory health: Mechanisms, efferent system disruption, and public health implications

Pesticide exposure has been linked to adverse effects on auditory health, impacting both peripheral and central auditory systems. Studies suggest that organophosphate, carbamate, organochlorine, and pyrethroid pesticides disrupt auditory processing through oxidative stress, neuroinflammation, and interference with cholinergic signaling. These disruptions may compromise sensory hair cells, spiral ganglion neurons, and auditory pathways, impairing precise signal transmission. The auditory efferent system, responsible for cochlear protection and auditory signal modulation, appears particularly susceptible to pesticide-induced alterations. This system relies on cholinergic transmission to regulate cochlear amplification and selective attention, functions that may be disrupted by pesticide exposure. Evidence from epidemiological and experimental studies highlights the potential for long-term auditory dysfunction in populations exposed to pesticides, with agricultural workers and their families facing elevated risks due to prolonged contact with agrochemicals. This review integrates findings on pesticide exposure and its implications for auditory health, discussing potential peripheral and central ototoxicity pathways. The cumulative effects of chronic exposure are emphasized, including the gradual degradation of auditory processing capabilities. Additionally, the need for targeted interventions, such as audiological monitoring and enhanced safety protocols, is addressed. Further research is critical to elucidate the mechanisms underlying pesticide-induced auditory damage and identify protective strategies. Such investigations can inform evidence-based policies to mitigate the public health impact of pesticide exposure while maintaining agricultural productivity. A multidisciplinary approach is essential to safeguard auditory health in vulnerable populations exposed to these environmental hazards.

Environmental ototoxicants: an update

Approximately 5 years ago, we proposed the establishment of a new category of ototoxicants: environmental ototoxicants, in addition to the recognized categories of occupational and drug-related ototoxicants. Since the publication of our review, the scientific literature has confirmed the potential for hearing impairment (HI) caused by the general population's exposure to various chemicals. However, the extent of this exposure's contribution to the global incidence of hearing loss (HL) has yet to be estimated. Due to the growing health, financial, and social challenges related to HL in the general population, we have reviewed the literature on HL in individuals exposed to environmental chemicals. Additionally, we have broadened the list of environmental ototoxicants to include several previously recognized as occupational ototoxicants. These substances include the following: organophosphate insecticides (OPIs), organochlorine pesticides (OCPs): hexachlorocyclohexane (HCH), dieldrin, dichlorodiphenyldichloroethylene (DDE), and hexachlorobenzene (HCB); pyrethroids, bisphenol A (BPA), benzophenone-3 (BP-3), triclosan (TCS), parabens (PBs), per- and polyfluorinated compounds (PFCs), metals and trace elements (such as cadmium (Cd), lead (Pb), manganese (Mn), iron (Fe), mercury (Hg), selenium (Se), barium (Ba), and arsenic (As)), polycyclic aromatic hydrocarbons (PAHs), volatile organic compounds (VOCs), styrene. Additionally, we have included alcohol, which is widely consumed and known for its ototoxic effects.

Factors affecting the quality of postoperative rehabilitation in children with cochlear implants based on the theory of knowledge, attitude and practice

OBJECTIVES

This study aimed to examine factors that influence postoperative rehabilitation outcomes in children with cochlear implants, using a knowledge-attitude-practice (KAP) framework.

DESIGN

A total of 683 children with cochlear implants participated in this study. Hearing and speech assessments were conducted through face-to-face and/or telephone interviews, while parents' or guardians' KAP were assessed following detailed instructions provided beforehand. Responses were recorded meticulously.

SETTING

Data were collected through a convenience sampling method at a children's hospital.

PARTICIPANTS

Out of 840 questionnaires distributed, 683 completed questionnaires were retained for analysis after excluding responses with missing data.

RESULTS

Parents' average KAP score was 8.03 (SD = 3.13). Household income and education levels directly influenced KAP scores, while certain child characteristics were significantly associated with higher scores on the Infant-Toddler Meaningful Auditory Integration Scale (IT-MAIS). Children who were outgoing (32.29 points), had used a cochlear implant for more than 3 years (32.78 points), and had surgery funded by state support (32.14 points) demonstrated higher MAIS scores. Factors such as personality, monthly family income, surgery funding and parents' beliefs significantly affected rehabilitation outcomes among children.

CONCLUSION

Parental knowledge about deafness, trust in cochlear implant procedures and healthcare providers, and parental behaviours during the treatment and rehabilitation process have a direct impact on children's health outcomes. Enhancing parents' KAP levels is critical to improve rehabilitation outcomes for children with cochlear implants.

Organophosphorus Pesticides Management Strategies: Prohibition and Restriction Multi-Category Multi-Class Models, Environmental Transformation Risks, and Special Attention List

Organophosphorus pesticides (OPs) have become one of the most widely used pesticides in Chinese agriculture; however, methods to identify potential restrictions on OPs molecules are lacking. Therefore, this study retrieved the OPs restriction list and constructed eight multi-class, multi-category machine learning models for OPs restrictions. Among these, the random forest (RF) model demonstrated excellent predictive performance, as it was successfully validated and applied. Potential environmental transformation products of OPs were obtained using EAWAG-BBD software, while toxicity indicators for the parent OPs and their transformation products were predicted with ADMETlab 3.0 software. This study found that unrestricted OPs, such as phorate, parathion, and chlorpyrifos, exhibited a high probability of toxicity. Additionally, the environmental transformation products of OPs posed similar comprehensive toxicity risks as the parent compounds. A special attention list for OPs was created based on the toxicity risks of unrestricted parent OPs and their transformation products, using standard deviation classification. Phorate and parathion were identified as OPs requiring special attention. This paper aims to provide an effective method for identifying the potential restriction levels of OPs and to propose an evaluation system that comprehensively considers the health risk, thereby supporting the improvement and optimization of management and usage strategies for OPs.

Phthalate Metabolites Were Related to the Risk of High-Frequency Hearing Loss: A Cross-Sectional Study of National Health and Nutrition Examination Survey

Background

Phthalate metabolites are pervasive in the environment and linked to various health issues. This study aimed to investigate the relationship between phthalate metabolites and hearing loss.

Methods

We conducted a cross-sectional study with 1713 participants based on the National Health and Nutrition Examination Survey 2015-2018. Participants were defined as speech-frequency hearing loss (SFHL) or high-frequency hearing loss (HFHL). We analyzed the baseline characteristics of participants and assessed the detection rates of phthalate metabolites in samples. Phthalate metabolites with detection rates of >85% were enrolled. Then, restricted cubic spline and multivariable logistic regression analyses were conducted to explore the association of phthalate metabolites with hearing loss. Multi-model analysis was employed to select an optimal predictive model for HFHL based on phthalate metabolites and clinical factors.

Results

Among participants, 24.518% had SFHL and 41.998% had HFHL, associated with older age, higher BMI, male, non-Hispanic white, lower physical activity levels, higher exposure to work noise, hypertension, and diabetes. Monobenzyl phthalate (MBZP) showed a positive linear association with both SFHL and HFHL. Multivariable logistic regression revealed MBZP as a significant risk factor for HFHL (odds ratio=1.339, 95% confidence interval, 1.053-1.707). According to the area under curve (AUC) values, the logistic regression model had the best diagnostic performance of HFHL, with the highest AUC values of 0.865 in the test set. In the model, gender, diabetes, and MBZP were the top predictors of HFHL.

Conclusion

The study identified a significant association between MBZP exposure and HFHL, highlighting the need to reduce phthalate exposure.

Pesticide metabolite 3, 5, 6-trichloro-2-pyridinol causes massive damage to the cochlea resulting in hearing loss in adult mice

Pesticides are a group of extensively used man-made chemicals with high toxicity and strong residues, which are closely related to hearing health. Pesticide metabolite 3, 5, 6-Trichloro-2-pyridinol (TCP) exposure leads to neurotoxicity and auditory cell toxicity. However, whether TCP causes damage to hearing in adult mice is not clear. In this study, adult male C57BL/6 mice continuously exposed to TCP for 21 days showed a dose-dependent elevation of hearing threshold. Outer hair cells and spiral neuron cells were lost in a dose-dependent manner. Type I and V of spiral ligament were severely shrunk and stria vascularis were thinned in mice after 50 and 150 mg/kg TCP exposure. Similarly, ROS levels in the cochlea were significantly increased whereas the activities of anti-oxidation enzymes were decreased after TCP exposure. The expression level of Na+/K+ ATPase was decreased, resulting in cochlear potential disruption. Levels of inflammatory factors (TNF-α and IL-1β), γ-H2AX, and pro-apoptotic-related factors (Bax and cleaved-Caspase 3) were elevated, respectively. These results suggest that TCP can cause oxidative stress, inflammation, and imbalance of cochlear potential in the cochlea, induce cochlear DNA damage and apoptosis, and cause cochlear morphological changes, eventually leading to impaired hearing function.

Association between the systemic immune-inflammation index and hearing loss: A cross-sectional study of NHANES 2005 to 2018

The relationship between systemic inflammation and hearing loss (HL) remains unclear. To investigate the association between the systemic immune-inflammation index (SII) and objective HL, this study was performed. Participants from the National Health and Nutrition Examination Survey (NHANES) spanning from 2005 to 2018 were analyzed. Two types of hearing loss were investigated: speech-frequency hearing loss (SFHL) and high-frequency hearing loss (HFHL). The SII score was constructed using the levels of peripheral neutrophil (N), lymphocyte (L), and platelet (P), and was defined as P multiplied by N/L (in units of 109/L). Weighted multivariable logistic regression and subgroup analysis were used to examine the relationship between HL and high-SII group (≥330 × 109/L). A total of 6428 participants were included in the study. This study found that the high-SII group was positively associated with a higher risk of HL (OR: 1.29, 95% CI: 1.05-1.57, P < .05) and HFHL (OR: 1.24, 95% CI: 1.05-1.46, P < .05), but not significant for SFHL (OR: 1.13, 95% CI: 0.94-1.37, P > .05). Subgroup analysis showed that this association was similar in different age groups. Finally, sensitivity analysis confirmed the robustness of the association. In the full model, increasing SII index per SD was associated with HL (OR: 1.17, 95% CI: 1.09-1.26, P < .001) and HFHL (OR: 1.13, 95% CI: 1.06-1.21, P < .001). The significance of SFHL was not detected with the increasing SII index (OR: 1.13, 95% CI: 0.94-1.37, P > .05). SII score was associated with HL and HFHL in the general adult population of the United States, but was not significantly correlated with SFHL.

Which Environmental Pollutants Are Toxic to Our Ears?-Evidence of the Ototoxicity of Common Substances

Ototoxicity refers to the adverse effects of substances on auditory or vestibular functions. This study examines the evidence of ototoxicity's association with exposure to common environmental pollutants, as documented in toxicological profiles by the Agency for Toxic Substances and Disease Registry. Our aim was to evaluate whether the evidence supports modifying the charting of ototoxic effects in the summary tables of these toxicological profiles and providing a guide for scientists to access these data. Health outcomes of interest included hearing loss, vestibular effects, cochlear lesions, tonal alterations, cellular damage, and ototoxicity-related outcomes (neurological, nephrotoxic, hepatic, and developmental effects). We obtained ototoxicity information for 62 substances. Hearing-related effects were reported, along with neurological effects. Overall, 26 profiles reported strong evidence of ototoxicity, including 13 substances previously designated as ototoxic by other health and safety agencies. Commonly studied outcomes included hearing loss, damage to ear anatomy, and auditory dysfunction. Vestibular dysfunction and tinnitus are rarely studied. Our findings highlight the lack of conclusive evidence of ototoxic properties for many substances, especially for pesticides and herbicides. This review supports charting the evidence of ototoxicity separately in toxicological profiles' summary tables. Improving the communication of ototoxicity-related health effects might impact their recognition and prompt further research. A stronger evidence base could support improved prevention efforts in terms of serious health outcomes.

Association between organophosphorus insecticides exposure and osteoarthritis in patients with arteriosclerotic cardiovascular disease

BACKGROUND

Organic phosphorus insecticides (OPPs) are a class of environmental pollutants widely used worldwide with potential human health risks. We aimed to assess the association between exposure to OPPs and osteoarthritis (OA) particularly in participants with atherosclerotic cardiovascular disease (ASCVD).

METHODS

Participants' information was obtained from data in the National Health and Nutrition Examination (NHANES). Weighted logistic regression models were utilized to detect associations between OPPs metabolites and OA. Restricted cubic spline plots (RCS) were drawn to visualize the dose-response relationship between each metabolite and OA prevalence. Weighted quantile sum (WQS) regression and Bayesian kernel-machine regression (BKMR), were applied to investigate the joint effect of mixtures of OPPs on OA.

RESULTS

A total of 6871 samples were included in our study, no significant associations between OPPs exposure and OA incidence were found in whole population. However, in a subset of 475 individuals with ASCVD, significant associations between DMP (odds ratio [OR] as a continuous variable = 1.22, 95% confidence interval [CI]: 1.07,1.28), DEP ((odds ratio [OR] of the highest tertile compared to the lowest = 2.43, 95% confidence interval [CI]: 1.21,4.86), and OA were observed. DMP and DEP showed an increasing dose-response relationship to the prevalence of OA, while DMTP, DETP, DMDTP and DEDTP showed a nonlinear relationship. Multi-contamination modeling revealed a 1.34-fold (95% confidence intervals:0.80, 2.26) higher prevalence of OA in participants with high co-exposure to OPPs compared to those with low co-exposure, with a preponderant weighting (0.87) for the dimethyl dialkyl phosphate metabolites (DMAPs). The BKMR also showed that co-exposure of mixed OPPs was associated with an increased prevalence of OA, with DMP showing a significant dose-response relationship.

CONCLUSION

High levels of urine dialkyl phosphate metabolites (DAP) of multiple OPPs are associated with an increased prevalence of OA in patients with ASCVD, suggesting the need to prevent exposure to OPPs in ASCVD patients to avoid triggering OA and further avoid the occurrence of cardiovascular events caused by OA.

Quantitative assessment of mitochondrial morphology relevant for studies on cellular health and environmental toxicity

Mitochondria are essential organelles that play crucial roles in cellular energy metabolism, calcium signaling and apoptosis. Their importance in tissue homeostasis and stress responses, combined to their ability to transition between various structural and functional states, make them excellent organelles for monitoring cellular health. Quantitative assessment of mitochondrial morphology can therefore provide valuable insights into environmentally-induced cell damage. High-content screening (HCS) provides a powerful tool for analyzing organelles and cellular substructures. We developed a fully automated and miniaturized HCS wet-plus-dry pipeline (MITOMATICS) exploiting mitochondrial morphology as a marker for monitoring cellular health or damage. MITOMATICS uses an in-house, proprietary software (MitoRadar) to enable fast, exhaustive and cost-effective analysis of mitochondrial morphology and its inherent diversity in live cells. We applied our pipeline and big data analytics software to assess the mitotoxicity of selected chemicals, using the mitochondrial uncoupler CCCP as an internal control. Six different pesticides (inhibiting complexes I, II and III of the mitochondrial respiratory chain) were tested as individual compounds and five other pesticides present locally in Occitanie (Southern France) were assessed in combination to determine acute mitotoxicity. Our results show that the assayed pesticides exhibit specific signatures when used as single compounds or chemical mixtures and that they function synergistically to impact mitochondrial architecture. Study of environment-induced mitochondrial damage has the potential to open new fields in mechanistic toxicology, currently underexplored by regulatory toxicology and exposome research. Such exploration could inform health policy guidelines and foster pharmacological intervention, water, air and soil pollution control and food safety.

Noise-Related Hearing Disorder Among Vector Control Workers in Kuala Lumpur

Introduction Noise-related hearing disorder (NRHD) is the second most common sensorineural hearing loss, right after age-related hearing loss (presbycusis). It is the highest reported occupational disease and a major compensable occupational hazard in Malaysia. With the increase in dengue cases, the need for vector control workers to control the spread of dengue at the expense of being exposed to noisy fogging machines is critical. Methods This was a cross-sectional study of vector control workers conducted by a local authority in Kuala Lumpur. Participants were categorised as either vector control workers who were directly involved in fogging activities or those who were not. A self-administered questionnaire was used to collect sociodemographic, medical and occupational information. NRHD was confirmed by an audiogram test. Results This study found a high prevalence of NRHD among vector control workers exposed to fogging activity (occupational noise hazards), with 51.4% of them experiencing this condition. The predictors of NRHD include fogging status adjusted odds ratio (aOR) 1.94 (95% CI: 1.19 - 3.17), sex 18.28 (95% CI: 2.33 - 143.16) and age 2.03 (95% CI: 1.27 - 3.25). Conclusion The findings of this study imply that vector control workers are at risk of NRHD. The predictors of NRHD are fogging status, sex and age. These findings emphasise the major impact of occupational noise hazards on NRHD and emphasise the importance of addressing this issue to preserve employees' health; especially among male and older employees with chronic noise exposure.

3,5,6-Trichloro-2-pyridinol confirms ototoxicity in mouse cochlear organotypic cultures and induces cytotoxicity in HEI-OC1 cells

The metabolite of organophosphate pesticide chlorpyrifos (CPF), 3,5,6-Trichloro-2-pyridinol (TCP), is persistent and mobile toxic substance in soil and water environments, exhibiting cytotoxic, genotoxic, and neurotoxic properties. However, little is known about its effects on the peripheral auditory system. Herein, we investigated the effects of TCP exposure on mouse postnatal day 3 (P3) cochlear culture and an auditory cell line HEI-OC1 to elucidate the underlying molecular mechanisms of ototoxicity. The damage of TCP to outer hair cells (OHC) and support cells (SC) was observed in a dose and time-dependent manner. OHC and SC were a significant loss from basal to apical turn of the cochlea under exposure over 800 μM TCP for 96 h. As TCP concentrations increased, cell viability was reduced whereas reactive oxygen species (ROS) generation, apoptotic cells, and the extent of DNA damage were increased, accordingly. TCP-induced phosphorylation of the p38 and JNK MAPK are the downstream effectors of ROS. The antioxidant agent, N-acetylcysteine (NAC), could reverse TCP-mediated intracellular ROS generation, inhibit the expressive level of cleaved-caspase 3 and block phosphorylation of p38/JNK. Overall, this is the first demonstration of TCP damaging to peripheral sensory HCs and SC in organotypic cultures from the postnatal cochlea. Data also showed that TCP exposure induced oxidase stress, cell apoptosis and DNA damage in the HEI-OC1 cells. These findings serve as an important reference for assessing the risk of TCP exposure.