Triphenyl phosphate induced reproductive toxicity through the JNK signaling pathway in Caenorhabditis elegans

Insights into the effects of aging on the combined toxicity of polystyrene nanoplastics and chlordane against Caenorhabditis elegans

Nanoplastics are emerging contaminants that may co-exist with organochlorine pesticides and adversely affect invertebrates in the environment. However, the impact of environmental aging on the combined toxicity of nanoplastics and organochlorine pesticides remains unclear. This study investigated the effects of aging on the combined toxicity of polystyrene nanoplastics (PS NPs) and chlordane against Caenorhabditis elegans. The results showed that photo-aging altered the physicochemical properties of PS NPs and promoted the combined toxicity of PS NPs and chlordane to nematodes by reducing survival rate, body length and enhancing germline apoptosis. Additionally, combined exposure of nematodes to aged PS NPs and chlordane significantly increased reactive oxygen species production and intestinal permeability, suggesting that aging enhances combined toxicity through oxidative stress and intestinal damage. Moreover, aging increased chlordane contents in nematodes without promoting PS NPs accumulation, potentially leading to increased combined toxicity of PS NPs and chlordane. Notably, aging significantly increased the accumulation of PS NPs in the posterior intestine of the nematode during co-exposure, which may be responsible for the most sensitive and highest degree of change in germline apoptosis. These observations emphasize the significance of accounting for environmental aging as well as the accumulation and distribution of nanoplastics in organisms when assessing the combined effects of nanoplastics and coexisting pollutants.

Adverse Effects of Aryl Organophosphate Esters on Reproduction

Aryl organophosphate esters (AOPEs) have been widely detected in environmental media and human samples, and increasing evidence shows that AOPEs induce adverse effects on reproductive health. This Review summarizes the exposure levels, reproductive toxicity data, and underlying mechanisms of three legacy AOPEs, including triphenyl phosphate (TPHP), 2-ethylhexyl diphenyl phosphate (EHDPP), and tricresyl phosphate (TCrP). Reproduction-related nuclear receptors (RrNRs) were concluded to play important roles in the reproductive toxicity induced by AOPEs, as all three typical AOPEs and their hydroxylated metabolites elicit binding affinity to RrNRs. We further investigated the RrNRs binding ability of the other 55 emerging AOPEs (eAOPEs) through molecular docking and found most eAOPEs (54/55) showed potential binding ability to RrNRs, especially to estrogen receptor α. This Review helped us to comprehensively understand the adverse effects of AOPEs on reproduction and predict the potential health risk of eAOPEs. AOPEs are easily metabolized in organisms, and their hydroxylated metabolites even show more potency to bind RrRNs. This Review also highlights the necessity to take the contribution of hydroxylated metabolites into account in future research.

Endocrine disruption of Triphenyl Phosphate via VIT-2 in Caenorhabditis elegans: A comparative analysis with estradiol and 4-hydroxytamoxifen

Triphenyl phosphate (TPHP) is widely used as a flame retardant and plasticizer in consumer products and is frequently detected in the environment. TPHP competitively binds to estrogen receptors, exhibiting both estrogenic and anti-estrogenic effects, leading to ongoing debate about its role. This study demonstrates that TPHP shows a higher affinity for the estrogen receptor NHR-14 in Caenorhabditis elegans (C. elegans) compared to the typical estrogen estradiol (E2) and the estrogen antagonist 4-hydroxytamoxifen (4-HT). The study also examines the production, distribution, and transport of the estrogen biomarker Vitellogenin family member 2 (VIT-2) following exposure to TPHP, E2, and 4-HT. Environmentally-relevant concentrations of TPHP significantly increased VIT-2 transcription and protein expression levels in C. elegans during early pregnancy, similar to the effects observed with E2. However, during peak pregnancy, TPHP exposure led to abnormal accumulation of VIT-2, primarily due to an increase in the Gibbs Free Energy of the VIT-2_RME-2 complex, which reduced their affinity and subsequently impaired the normal transport of VIT-2. These findings provide novel insights into the toxic mechanisms of TPHP in oviparous animals, highlighting its broader environmental impacts and emphasizing the urgency for further research and regulatory actions to mitigate its risks.

Opposing Visual Impairments Induced by Structurally Similar Organophosphate Flame Retardants TPHP and CDP in Zebrafish Larvae

Vision is the primary sensory function for most animals and is also a sensitive toxic target of environmental pollutants. A new class of organophosphate flame retardants (OPFRs) termed emerging OPFRs (eOPFRs) with limited toxicological information is rapidly developed into the substitutes of traditional OPFRs. In this study, we investigated the visual toxicity of triphenyl phosphate (TPHP, one traditional OPFR) and cresyl diphenyl phosphate (CDP, one emerging OPFR) on zebrafish larvae at environmentally relevant concentrations (3 and 30 nM). After 5 days of exposure, an opposite toxicity was found between the two OPFRs, manifested in the light perception and the gene expressions of visual opsins. CDP caused a weak reaction to light and overall inhibition of opsin expression (0.7- to 0.8-fold) in the larvae, while TPHP tended to stimulate these events (1.2- to 2.4-fold). Besides, we identified a key transcription factor, tbx2a, that was significantly disrupted in both OPFRs' exposure. The differing ways in which both OPFRs bind to Tbx2a may be the reason behind their opposite effects. These findings provided new clues for the toxicological mechanisms of OPFRs and revisited the question regarding safe substitutes for those emerging contaminants.

Alanine Derived from Ruminococcus_E bovis Alleviates Energy Metabolic Disorders during the Peripartum Period by Providing Glucogenic Precursors

Peripartum dairy cows commonly experience energy metabolism disorders, which lead to passive culling of postpartum cows and a decrease in milk quality. By using ketosis peripartum dairy cows as a model, this study aims to elucidate the metabolic mechanism of peripartum cows and provide a novel way for managing energy metabolic disorders. From a cohort of 211 cows, we integrated multi-omics data (metagenomics, metabolomics, and transcriptomics) to identify key microbes and then utilized an in vitro rumen fermentation simulation system and ketogenic hepatic cells to validate the potential mechanisms and the effects of postbiotics derived from key microbes. Postpartum cows with metabolic disorders compensate for glucose deficiency through mobilizing muscle proteins, which leads to marked decreases in milk protein content. Concurrently, these cows experience rumen microbiota disturbance, with marked decreases in the concentrations of volatile fatty acids and microbial protein, and the deficiency of alanine (Ala) in microbial protein is correlated with the metabolic disorder phenotype. Metagenomic binning and in vitro fermentation assays reveal that Ruminococcus_E bovis (MAG 189) is enriched in amino acid biosynthesis functions and responsible for Ala synthesis. Furthermore, transcriptomic and metabolomic analyses of the liver in metabolic disorder cows also show impaired amino acid metabolism. Supplementation with Ala can alleviate ketogenesis in liver cell models by activating the gluconeogenesis pathway. This study reveals that Ruminococcus_E bovis is associated with host energy metabolism homeostasis by supplying glucogenic precursors to the liver and suggests the use of Ala as a method for the treatment of energy metabolism disorders in peripartum cows.

Detection and screening of organophosphate esters in infant formula from Shanghai, China: distribution characteristics and risk evaluation

Organophosphate esters (OPEs) have raised great concerns in recent years. However, information regarding their occurrence in infant formula remains limited. Thus, thirty-two OPEs were measured in infant formula sold in Shanghai, China in 2023. The results showed that OPE occurrence in infant formula was widespread. The median concentrations of organophosphate diesters, organophosphate triesters, and total OPEs were 2.28, 5.20, and 8.63 ng/g, respectively. Tris(2-chloroisopropyl) phosphate (TCPP) showed the highest median concentration (1.95 ng/g), followed by triethyl phosphate, bis(1-chloro-2-propyl) phosphate (BCPP), tri-isobutyl phosphate, and triphenyl phosphate (0.532-0.581 ng/g). The dominant chloro-OPEs (TCPP and BCPP) were regional-specific. Compared to corresponding triesters, the diester concentrations were often lower, except for bis(2-butoxyethyl) phosphate and tributoxyethyl phosphate. Additionally, five novel OPEs with phenyl groups were identified, showing high detection frequencies and comparable concentrations to TCPP. Raw materials and food processing methods might affect individual OPEs. The estimated daily intakes (EDIs) ranged from 62.3 to 355 ng/kg bw/day. The highest EDI occurred in infants of 0-6 months of age but posed no obvious health risk for infants and toddlers. Further studies are still needed to evaluate the possible health implications arising from the novel OPEs and their metabolites, as well as the potentially synergistic effects.

Cresyl diphenyl phosphate (a novel organophosphate ester) induces hepatic steatosis by directly binding to liver X receptor α: From molecule action to risk assessment

Cresyl diphenyl phosphate (CDP), a novel organophosphate ester (OPE), has been increasingly detected in various environmental and human samples. However, its toxicity, mechanisms, and health risks remain largely unknown. In this work, we investigated CDP-induced hepatic steatosis through Liver X Receptor α (LXRα) pathway across the molecular interactions, signaling pathways, cell functions, animal effects, and population risks, and compared them to triphenyl phosphate (TPHP) and tricresyl phosphate (TCRP). Receptor binding results showed that all three OPEs bound to LXRα directly in the order of TCRP > CDP > TPHP. Docking results suggested that the three aryl groups played an essential role in the binding of these chemicals to LXRα. They also activated LXRα-mediated lipogenesis pathway and promoted lipid accumulation in HepG2 cells. The intracellular concentration and LXRα-bound concentration of the chemicals in HepG2 cells followed a consistent order of CDP > TCRP > TPHP. In mice, exposure to CDP activated LXRα-mediated de novo lipogenesis pathway, leading to hepatic steatosis. Risk assessment results suggested that few populations (5.38 %) face a LXRα-mediated hepatic steatosis risk from CDP exposure. Collectively, our results demonstrate that CDP could bind to LXRα, activate the subsequent de novo lipogenesis pathway, inducing hepatic steatosis, and increasing adverse health risks.

An ingenious chemiluminescence sensing strategy for recalcitrant triphenyl phosphate based on oxidant-free UV-activated MIL-100(Fe) gel system

BACKGROUND

Organophosphate flame retardants (OPFRs) are notorious emerging contaminants threatening the environment and human health. Triphenyl phosphate (TPHP), which has an extremely serious biotoxicity, is a typical harmful OPFR. Due to its wide use, TPHP has been discovered in various environmental mediums. Moreover, it is pretty recalcitrant to the removal process, resulting in the need for a technique to understand it better. Hence, accurate and quick discrimination of TPHP in the environment is critical to further evaluate its potential effect on ecosystems and human health.

RESULTS

An ingenious oxidant-free chemiluminescence (CL) sensor based on the oxidant-free UV/MIL-100(Fe) gel system was established for TPHP detection. The oxidation of luminol in the UV-activated MIL-100(Fe) gel has resulted in remarkable CL emission, which is contributed by reactive oxygen species (ROS) generated by it. Notably, the CL intensity was inhibited significantly after introducing TPHP. An investigation into the mechanism underlying the effect of CL suppression demonstrated that TPHP competed with luminol to consume ROS from UV-activated MIL-100(Fe) gel, contributing to CL inhibition. The subsequent sensing performance experiments demonstrated the advantages of environmentally friendly, economic efficiency, user-friendly operation, rapid determination, potential for compact size, high selectivity, and sensitivity. Additionally, these investigations confirmed the low limit of detection (210 ng L-1) and wide linear range (10-1000 μg L-1).

SIGNIFICANCE

In this paper, a green, economical, and oxidant-free CL sensing strategy for TPHP has been established. It has the advantage of being rapid, having the potential for compact size, high selectivity, and sensitivity. This ingenious method has promising applications in real-time and online environmental monitoring, and it paves the way for the rapid and environmentally friendly identification of emerging contaminants that are structurally stable and recalcitrant to remove.

Integrated RNA sequencing and biochemical studies reveal endoplasmic reticulum stress and autophagy dysregulation contribute to Tri (2-Ethylhexyl) phosphate (TEHP)-induced cell injury in Sertoli cells

Tri (2-Ethylhexyl) phosphate (TEHP), widely used as a fire retardant and plasticizer, has been commonly found in the environment. Its potential health-related risks, especially reproductive toxicity, have aroused concern. However, the potential cellular mechanisms remain unexplored. In this study, we aimed to investigate the molecular mechanisms underlying TEHP-caused cell damage in Sertoli cells, which play a crucial role in supporting spermatogenesis. Our findings indicate that TEHP induces apoptosis in 15P-1 mouse Sertoli cells. Subsequently, we conducted RNA sequencing analyses, which suggested that ER stress, autophagy, and MAPK-related pathways may participate in TEHP-induced cytotoxicity. Furthermore, we demonstrated that TEHP triggers ER stress, activates p38 MAPK, and inhibits autophagy flux. Then, we showed that the inhibition of ER stress or p38 MAPK activation attenuates TEHP-induced apoptosis, while the inhibition of autophagy flux is responsible for TEHP-induced apoptosis. These results collectively reveal that TEHP induces ER stress, activates p38, and inhibits autophagy flux, ultimately leading to apoptosis in Sertoli cells. These shed light on the molecular mechanisms underlying TEHP-associated testicular toxicity.

Reproductive Toxicity and Multi/Transgenerational Effects of Emerging Pollutants on C. elegans

Emerging pollutants (EPs) are receiving increasing attention due to the threats they pose to the environment and human health. As EPs continue to emerge, risk assessment requires many model animals. Caenorhabditis elegans (C. elegans) has been an outstanding toxicological model organism due to its growth and development characteristics. Particularly, in studying the transgenerational influences of EPs, C. elegans has advantages in saving time and cost due to its short generation cycle. As infertility has become a major problem in human reproductive health, reproductive toxicities of EPs on contemporary nematodes and across generations of C. elegans were introduced in this review. Moreover, the underlying mechanisms involved in germ cell apoptosis, spermatogenesis, and epigenetic alteration were discussed. Future research opportunities and challenges are also discussed to expand our understanding of the reproductive influences of EPs.

Adipogenic Effects of Cresyl Diphenyl Phosphate (Triphenyl Phosphate Alternative) through Peroxisome Proliferator-Activated Receptor Gamma Pathway: A Comprehensive Study Integrating In Vitro, In Vivo, and In Silico from Molecule to Health Risk

Cresyl diphenyl phosphate (CDP), a novel organophosphate ester (OPE), has been detected in various environmental and human samples. However, there is very limited knowledge regarding its toxicity, mechanisms of action, and potential health risks. Using new alternative methods (NAMs), across the molecular interactions, signaling pathways, cell functions, animal effects, and population risks, we investigated the potential adipogenic effects and associated risks of CDP and legacy OPE triphenyl phosphate (TPHP) by acting on peroxisome proliferator-activated receptor gamma (PPARγ). Among the 19 screened OPEs, CDP bound to PPARγ with the highest binding potency, followed by TPHP. CDP activated PPARγ through fitting into the binding pocket with strong hydrophobicity and hydrogen bond interactions; CDP exhibited higher potency compared to TPHP. In 3T3-L1 cells, CDP enhanced the PPARγ-mediated adipogenesis activity, exhibiting greater potency than TPHP. The intracellular concentration and receptor-bound concentrations (RBC) of CDP were also higher than those of TPHP in both HEK293 cells and 3T3-L1 cells. In mice, exposure to CDP activated the PPARγ-mediated adipogenic pathway, leading to an increased white adipose tissue weight gain. Overall, CDP could bind to and activate PPARγ, thereby promoting preadipocyte differentiation and the development of white adipose tissue. Its potential obesogenic risks should be of high concern.

Physiological and transcriptomic changes of zebrafish (Danio rerio) in response to Isopropylate Triphenyl Phosphate (IPPP) exposure

Isopropylate Triphenyl Phosphate (IPPP), a novel organophosphorus flame retardant, has become a widespread environmental pollutant. However, the toxic effects and mechanisms of IPPP remain unclear. In this study, we evaluated the neurodevelopmental toxicity effects of IPPP on zebrafish embryonic development, neurobehavior, and physiological and transcriptomic changes. The results showed that IPPP induced adverse developments such as low survival rates and hatching rates, decreased body length and eye distance, and also led to increased heart rates and embryonic malformation rates. The developmental defects mainly included typical pericardial edema, eye deformities, and a reduction in the number of newborn neurons. Mitochondrial energy metabolism disorders and apoptosis of cardiomyocytes may be responsible for heart malformation. Behavioral results showed that IPPP caused abnormal changes in swimming speed, total swimming distance and trajectory, and showed a low-dose effect. In addition, the decreased activity of neurotransmitters such as acetylcholinesterase (AchE) and dopamine (DA), and the changes in genes related to the central nervous system (CNS) and metabolism pathway may be the causes of neurodevelopmental toxicity of IPPP. Meanwhile, IPPP induced oxidative stress and apoptosis, and changed the ATPase activity of zebrafish larvae by altering nuclear factor erythroid2-related factor 2 (Nrf2) and mitochondrial signaling pathways, respectively. Transcriptome sequencing results indicated that Cytochrome P450 and drug metabolism, Energy metabolism-related pathways, Glutathione metabolism, Retinoid acid (RA) and REDOX signaling pathways were significantly enriched, and most of the genes in these pathways were up-regulated after IPPP treatment, which may be new targets for IPPP-induced neurodevelopment. In summary, the results of this study provide an important reference for a comprehensive assessment of the toxic effects and health risks of the new pollutant IPPP.

Testosterone Mediates Reproductive Toxicity in Caenorhabditis elegans by Affecting Sex Determination in Germ Cells through nhr-69/mpk-1/fog-1/3

Testosterone (T), an environmental androgen, significantly disrupts endocrine systems in wildlife and ecosystems. Despite growing concern over its high levels in aquatic environments, the reproductive toxicity of testosterone and its mechanisms are not well understood. In this study, we investigated the reproductive toxicity and mechanisms of testosterone using Caenorhabditis elegans (C. elegans) and assessed its ecological toxicity through the benchmark dose (BMD) method. Our results indicate that T concentrations exceeding 0.01 μg/L significantly reduce the brood size, decrease germ cell counts, and prolong the generation time in C. elegans as T concentrations increase. Furthermore, to elucidate the specific mechanisms, we analyzed the expression of nhr-69, mpk-1, and other genes involved in sex determination. These findings suggest that the nhr-69-mediated reproductive toxicity of T primarily affects sperm formation and the offspring number by influencing its downstream targets, mpk-1 and fog-1/3, which are critical in the germ cell sex-determining pathway. Additionally, this study determined that the 10% lower boundary of the baseline dose (BMDL10) is 1.160 ng/L, offering a more protective reference dose for the ecological risk assessment of T. The present study suggests that nhr-69 mediates the reproductive toxicity of T by influencing mpk-1 and fog-1/3, critical genes at the end of the germ cell sex-determining pathway, thereby providing a basis for establishing reproductive toxicity thresholds for T.

The flame retardant triphenyl phosphate alters the epigenome of embryonic cells in an aquatic in vitro model

Triphenyl phosphate (TPhP) is an organophosphate flame retardant and plasticizer that is added to a wide variety of consumer and industrial products. It is also a ubiquitous environmental pollutant. Exposure to TPhP has been shown to alter gene expression in metabolic and estrogenic signaling pathways in in vitro and in vivo models of a variety of species, and as such, is considered to be an endocrine disrupting chemical. Exposure to endocrine disrupting chemicals is increasingly being associated with changes to the epigenome, especially during embryonic development. The aim of this study was to evaluate whether TPhP exposure in aquatic ecosystems has the ability to alter the epigenome in two immortal cell lines derived from trout (Oncorhynchus mykiss). This study assessed whether 24 h exposure to TPhP resulted in changes to histone modification and DNA methylation profiles in steelhead trout embryonic cells and rainbow trout gill epithelial cells. Results show that several epigenetic modifications on histone H3 and DNA methylation are altered in the embryonic cells following TPhP exposure, but not in the gill epithelial cells. Specifically, histone H3 acetylation, histone H3 mono-methylation and global DNA methylation were found to be reduced. The alterations of these epigenetic modification profiles in the embryonic cells suggest that exposure to TPhP during fetal development may alter gene expression in the developing embryo, likely in metabolic and estrogenic pathways. The impacts to the epigenome determined in this study may even carry multigenerational detrimental effects on human and ecosystem health, which requires further investigation.

Triphenyl phosphate interferes with the synthesis of steroid hormones through the PPARγ/CD36 pathway in human trophoblast JEG-3 cells

Triphenyl phosphate (TPhP), a chemical commonly found in human placenta and breast milk, has been shown to disturb the endocrine system. Our previous study confirmed that TPhP could accumulate in the placenta and interference with placental lipid metabolism and steroid hormone synthesis, as well as induce endoplasmic reticulum (ER) stress through PPARγ in human placental trophoblast JEG-3 cells. However, the molecular mechanism underlying this disruption remains unknown. Our study aimed to identify the role of the PPARγ/CD36 pathway in TPhP-induced steroid hormone disruption. We found that TPhP increased lipid accumulation, total cholesterol, low- and high-density protein cholesterol, progesterone, estradiol, glucocorticoid, and aldosterone levels, and genes related to steroid hormones synthesis, including 3βHSD1, 17βHSD1, CYP11A, CYP19, and CYP21. These effects were largely blocked by co-exposure with either a PPARγ antagonist GW9662 or knockdown of CD36 using siRNA (siCD36). Furthermore, an ER stress inhibitor 4-PBA attenuated the effect of TPhP on progesterone and glucocorticoid levels, and siCD36 reduced ER stress-related protein levels induced by TPhP, including BiP, PERK, and CHOP. These findings suggest that ER stress may also play a role in the disruption of steroid hormone synthesis by TPhP. As our study has shed light on the PPARγ/CD36 pathway's involvement in the disturbance of steroid hormone biosynthesis by TPhP in the JEG-3 cells, further investigations of the potential impacts on the placental function and following birth outcome are warranted.

Organophosphorus Flame Retardant TPP-Induced Human Corneal Epithelial Cell Apoptosis through Caspase-Dependent Mitochondrial Pathway

A widely used organophosphate flame retardant (OPFR), triphenyl phosphate (TPP), is frequently detected in various environmental media and humans. However, there is little known on the human corneal epithelium of health risk when exposed to TPP. In this study, human normal corneal epithelial cells (HCECs) were used to investigate the cell viability, morphology, apoptosis, and mitochondrial membrane potential after they were exposed to TPP, as well as their underlying molecular mechanisms. We found that TPP decreased cell viability in a concentration-dependent manner, with a half maximal inhibitory concentration (IC50) of 220 μM. Furthermore, TPP significantly induced HCEC apoptosis, decreased mitochondrial membrane potential in a dose-dependent manner, and changed the mRNA levels of the apoptosis biomarker genes (Cyt c, Caspase-9, Caspase-3, Bcl-2, and Bax). The results showed that TPP induced cytotoxicity in HCECs, eventually leading to apoptosis and changes in mitochondrial membrane potential. In addition, the caspase-dependent mitochondrial pathways may be involved in TPP-induced HCEC apoptosis. This study provides a reference for the human corneal toxicity of TPP, indicating that the risks of OPFR to human health cannot be ignored.

Multigenerational effects and mutagenicity of three flame retardants on germ cells in Caenorhabditis elegans

Flame retardants (FRs) have raised public concerns because of their environmental persistence and negative impacts on human health. Recent evidence has revealed that many FRs exhibit reproductive toxicities and transgenerational impacts, whereas the toxic effects of FRs on germ cells remain barely explored. Here we investigated the multigenerational effects of three flame retardants (TBBPA, TCEP and TCPP) on germ cell development in Caenorhabditis elegans, and examined the germ cell mutagenicity of these FRs by using whole genome sequencing. Parental exposure to three FRs markedly increased germ cell apoptosis, and impeded oogenesis in F1-F6 offspring. In addition, the double-increased mutation frequencies observed in progeny genomes uncover the mutagenic actions of FRs on germ cells. Analysis of mutation spectra revealed that these FRs predominantly induced point mutations at A:T base pairs, whereas both small and large indels were almost unaffected. These results revealed the long-term effects of FRs on development and genomic stability of germ cells, which may pose risks to environmental organisms and human reproductive health. Taken together, our findings suggest that germ cell mutagenicity should be carefully examined for the environmental risk assessment of FRs and other emerging pollutants.

Triphenyl phosphate induced apoptosis of mice testicular Leydig cells and TM3 cells through ROS-mediated mitochondrial fusion inhibition

Triphenyl phosphate (TPHP) is a widely used organophosphate flame retardant and has biological toxicity. Previous studies showed TPHP can restrain testosterone biosynthesis in Leydig cells, while the underlying mechanisms remain unclear. In this study, C57BL/6J male mice were exposed to 0, 5, 50, and 200 mg/kg B.W. of TPHP for 30 d by oral, as well as TM3 cells were treated with 0, 50, 100, and 200 μM of TPHP for 24 h. Results showed that TPHP induced testes damage, including spermatogenesis disorders and testosterone synthesis inhibition. Meanwhile, TPHP can cause apoptosis in testicular Leydig cells and TM3 cells, as evidenced by the increased apoptosis rate and decreased Bcl-2/Bax ratio. Moreover, TPHP disrupted mitochondrial ultrastructure of testicular Leydig cells and TM3 cells, reduced healthy mitochondria content and depressed mitochondrial membrane potential of TM3 cells, as well as inhibited mitochondrial fusion proteins mitofusin 1 (Mfn1), mitofusin 2 (Mfn2), and optic atrophy 1 (Opa1) expression, without effect on mitochondrial fission proteins dynamin-related protein 1 (Drp1) and fission 1 (Fis1) in testicular tissue and/or TM3 cells. Then, the mitochondrial fusion promoter M1 was used to pre-treat TPHP-exposed TM3 cells to determine the roles of mitochondrial fusion inhibition in TPHP-induced Leydig cells apoptosis. The results showed M1 pretreatment alleviated the above changes and further mitigated TM3 cells apoptosis and testosterone levels decreased, indicating TPHP induced TM3 cells apoptosis by inhibited mitochondrial fusion. Intriguingly, the intervention experiment of N-acetylcysteine (NAC) showed that TPHP-induced mitochondrial fusion inhibition is ROS dependent, because inhibition of ROS overproduction alleviated mitochondrial fusion inhibition, and subsequently relieved TPHP-induced apoptosis in TM3 cells. In summary, above data revealed that apoptosis is a specific mechanism for TPHP-induced male reproductive toxicity, and that ROS-mediated mitochondrial fusion inhibition is responsible for Leydig cells apoptosis caused by TPHP.