Male reproductive toxicity involved in spermatogenesis induced by perfluorooctane sulfonate and perfluorooctanoic acid in Caenorhabditis elegans

Elucidating the degradation mechanisms of perfluorooctanoic acid and perfluorooctane sulfonate in various environmental matrices: a review of green degradation pathways

Given environmental persistence, potential for bioaccumulation, and toxicity of Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), the scientific community has increasingly focused on researching their toxicology and degradation methods. This paper presents a survey of recent research advances in the toxicological effects and degradation methods of PFOA and PFOS. Their adverse effects on the liver, nervous system, male reproductive system, genetics, and development are detailed. Additionally, the degradation techniques of PFOA and PFOS, including photochemical, photocatalytic, and electrochemical methods, are analyzed and compared, highlighted the potential of these technologies for environmental remediation. The biotransformation pathways and mechanisms of PFOA and PFOS involving microorganisms, plants, and enzymes are also presented. As the primary green degradation pathway for PFOA and PFOS, Biodegradation uses specific microorganisms, plants or enzymes to remove PFOA and PFOS from the environment through redox reactions, enzyme catalysis and other pathways. Currently, there has been a paucity of research conducted on the biodegradation of PFOA and PFOS. However, this degradation technology is promising owing to its specificity, cost-effectiveness, and ease of implementation. Furthermore, novel materials/methods for PFOA and PFOS degradation are presented in this paper. These novel materials/methods effectively improve the degradation efficiency of PFOA and PFOS and provide new ideas and tools for the degradation of PFOA and PFOS. This information can assist researchers in identifying flaws and gaps in the field, which can facilitate the formulation of innovative research ideas.

Reproductive toxicity of PFOA, PFOS and their substitutes: A review based on epidemiological and toxicological evidence

Per- and polyfluoroalkyl substances (PFAS) have already drawn a lot of attention for their accumulation and reproductive toxicity in organisms. Perfluorooctanoic acid (PFOA) and perfluorooctanoic sulfonate (PFOS), two representative PFAS, are toxic to humans and animals. Due to their widespread use in environmental media with multiple toxicities, PFOA and PFOS have been banned in numerous countries, and many substitutes have been produced to meet market requirements. Unfortunately, most alternatives to PFOA and PFOS have proven to be cumulative and highly toxic. Of the reported multiple organ toxicities, reproductive toxicity deserves special attention. It has been confirmed through epidemiological studies that PFOS and PFOA are not only associated with reduced testosterone levels in humans, but also with an association with damage to the integrity of the blood testicular barrier. In addition, for women, PFOA and PFOS are correlated with abnormal sex hormone levels, and increase the risk of infertility and abnormal menstrual cycle. Nevertheless, there is controversial evidence on the epidemiological relationship that exists between PFOA and PFOS as well as sperm quality and reproductive hormones, while the evidence from animal studies is relatively consistent. Based on the published papers, the potential toxicity mechanisms for PFOA, PFOS and their substitutes were reviewed. For males, PFOA and PFOS may produce reproductive toxicity in the following five ways: (1) Apoptosis and autophagy in spermatogenic cells; (2) Apoptosis and differentiation disorders of Leydig cells; (3) Oxidative stress in sperm and disturbance of Ca2+ channels in sperm membrane; (4) Degradation of delicate intercellular junctions between Sertoli cells; (5) Activation of brain nuclei and shift of hypothalamic metabolome. For females, PFOA and PFOS may produce reproductive toxicity in the following five ways: (1) Damage to oocytes through oxidative stress; (2) Inhibition of corpus luteum function; (3) Inhibition of steroid hormone synthesis; (4) Damage to follicles by affecting gap junction intercellular communication (GJIC); (5) Inhibition of placental function. Besides, PFAS substitutes show similar reproductive toxicity with PFOA and PFOS, and are even more toxic to the placenta. Finally, based on the existing knowledge, future developments and direction of efforts in this field are suggested.

Comparative steroidogenic effects of hexafluoropropylene oxide trimer acid (HFPO-TA) and perfluorooctanoic acid (PFOA): Regulation of histone modifications

As a widely used alternative to perfluorooctanoic acid (PFOA), hexafluoropropylene oxide trimer acid (HFPO-TA) has been detected in the environment and humans; however, little is known regarding its male reproductive toxicity. To compare the effects of HFPO-TA on steroid hormone synthesis with PFOA, we exposed Leydig cells (MLTC-1) to non-lethal doses (0.1, 1, and 10 μM) of PFOA and HFPO-TA for 48 h. It was found that the levels of steroid hormones, 17α-hydroxyprogesterone (OHP), androstenedione (ASD), and testosterone (T) were significantly increased in 1 and 10 μM of PFOA and HFPO-TA groups, with greater elevation being observed in the HFPO-TA groups than in the PFOA groups at 10 μM. We further showed that the two rate-limiting steroidogenic genes (Star and Cyp11a1) were up-regulated, while Hsd3b, Cyp17a1, and Hsd17b were down-regulated or unchanged after PFOA/HFPO-TA exposure. Moreover, PFOA exposure significantly up-regulated histone H3K4me1/3 and H3K9me1, while down-regulated H3K4me2 and H3K9me2/3 levels. By contrast, H3K4me2/3 and H3K9me2/3 were enhanced, while H3K4me1 and H3K9me1 were repressed after HFPO-TA treatment. It was further confirmed that H3K4me1/3 were increased and H3K9me2 was decreased in Star and Cyp11a1 promoters by PFOA, while HFPO-TA increased H3K4me2/3 and decreased H3K9me1 in the two gene promoters. Therefore, we propose that low levels of PFOA/HFPO-TA enhance the expression of Star and Cyp11a1 by regulating H3K4 and H3K9 methylation, thus stimulating the production of steroid hormones in MLTC-1 cells. Collectively, HFPO-TA exhibits stronger effects on steroidogenesis compared to PFOA, which may be ascribed to the distinct regulation of histone modifications. These data suggest that HFPO-TA does not appear to be a safer alternative to PFOA on the aspect of male reproductive toxicity.

Environmental toxicants and nephrotoxicity: Implications on mechanisms and therapeutic strategies

Kidneys are one of the most important organs in the human body. In addition to filtering 200 liters of fluid every 24 hours, the kidney also regulates acid-base balance, maintains electrolyte balance, and removes waste and toxicants from the body. Nephrotoxicity is the term used to describe the deterioration of kidney function caused by the harmful effects of medications and various types of environmental toxicants. Exposure to environmental toxicants is an inevitable side effect in the world's increasing industrialization and even more prevalent in underdeveloped nations. Growing data over the past few years has illuminated the probable connection between environmental toxicants and nephrotoxicity. Phthalates, microplastics, acrylamide and bisphenol A are environmental toxicants of particular concern, which are known to have nephrotoxic effects. Such toxicants may accumulate in the kidneys of humans after being consumed, inhaled, or come into contact with the skin. They can enter cells through endocytosis and accumulate in the cytoplasm. Small-sized nephrotoxicants can cause a variety of ailments including inflammation with increased production of pro-inflammatory cytokines, oxidative stress, mitochondrial dysfunction, autophagy, and apoptosis. This study uncovers the potential for new insights concerning the relationship between various environmental toxicants and kidney health. The objectives of this review is to establish information gaps, assess and identify the toxicity mechanisms of different nephrotoxicants, identify innovative pharmacological therapies that demonstrate promising therapeutic benefits/ relevance, and discuss the predictions for the future based on the analysis of the literature.

Sublethal perfluorooctanoic acid and perfluorooctanesulfonic acid delay C. elegans larval development and population growth but do not alter egg hatching

Perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) are polyfluoroalkyl substances (PFAS) used as surface coatings in manufacturing. Exposure to PFAS was shown to be correlated with infertility, low birth weight, and delayed aspects of pubertal development in mammals. Despite many correlational studies, there have been few direct investigations examining the link between PFAS exposure and early animal development. The aim of this study was to (1) examine the effects of PFOA on development and reproduction using the roundworm Caenorhabditis elegans, a model with a high predictive value for human reproductive toxicity and (2) compare observations to exposure to PFOS. PFAS exposure did not markedly alter egg hatching but delayed population growth, in part due to slower larval development. PFAS-exposed worms took longer to progress through larval stages to reach reproductive maturity, and this was not attributed to PFOA-induced toxicity to their food. Our results provide a robust benchmark for testing developmental and reproductive toxicity for other PFAS and PFAS-alternatives which continue to be used in manufacturing and released into the environment.

Early-life long-term ibuprofen exposure reduces reproductive capacity involved in spermatogenesis impairment and associated with the transcription factor DAF-5 in Caenorhabditis elegans

Pharmaceuticals and personal care products (PPCPs) are emerging environmental contaminants and have raised significant concern due to their potential adverse impact on the environment. Ibuprofen is one of the most extensively used non-steroidal anti-inflammatory drugs (NSAIDs) and is also considered an environmental contaminant. The negative impact of ibuprofen on non-target organisms has been documented; however, the molecular mechanisms behind its reproductive toxicity remain unclear. We investigated the impact of early-life long-term ibuprofen exposure on reproductive capacity and its involvement of spermiogenesis in the non-target model organism Caenorhabditis elegans. Hermaphrodites were exposed to various ibuprofen concentrations (0.1, 1, 10, and 100 mg/L), resulting in a dose-dependent inhibition of reproduction. In addition, the lowest observed adverse effect concentration (LOAEC) for ibuprofen exposure on the total brood size of C. elegans was 0.1 mg/L, a concentration that falls within the environmentally relevant range for ibuprofen. Outcross progeny assays revealed a significant 47% reduction in total brood size for larval males (him-5) exposed to ibuprofen, while females (fog-2) exhibited only a minor effect. We found that early-life long-term ibuprofen exposure impairs spermatogenesis. The number of mitotic cells significantly reduced by 31%. The rate of sperm malformation in exposed males was 63%, much higher than in unexposed males (11%). Additionally, the percentage of sperm activation decreased from 89% to 39% in ibuprofen-exposed worms. Mechanistic insights indicated that ibuprofen downregulated mRNA levels of genes related to spermatogenesis and DAF-7/TGF-β signaling. RNAi assays provided evidence for the crucial role of the transcription factor DAF-5 in mediating the spermatogenesis impairment by ibuprofen. Our study provides insight into the environmental impacts of pharmaceutical contaminants, such as ibuprofen, on both male and female reproductive systems to safeguard environmental health.

PFOS-induced dyslipidemia and impaired cholinergic neurotransmission in developing zebrafish: Insight into its mechanisms

Perfluorooctane sulfonate (PFOS) is a persistent organic pollutant that has been widely detected in the environment and is known to accumulate in organisms, including humans. The study investigated dose-dependent mortality, hatching rates, malformations, lipid accumulation, lipid metabolism alterations, and impacts on cholinergic neurotransmission. Increasing PFOS concentration led to higher mortality, hindered hatching, and caused concentration-dependent malformations, indicating severe abnormalities in developing zebrafish. The results also demonstrated that PFOS exposure led to a significant increase in total lipids, triglycerides, total cholesterol, and LDL in a concentration-dependent manner, while HDL cholesterol levels were significantly decreased. Additionally, PFOS exposure led to a significant decrease in glucose levels. The study identified TGs, TCHO, and glucose as the most sensitive biomarkers in assessing lipid metabolism alterations. The study also revealed altered expression of genes involved in lipid metabolism, including upregulation of fasn, acaca, and hmgcr and downregulation of ldlr, pparα, and abca1, as well as decreased lipoprotein lipase (LPL) and increased fatty acid synthase (FAS) activity,suggesting an impact on fatty acid synthesis, cholesterol uptake, and lipid transport. Additionally, PFOS exposure led to impaired cholinergic neurotransmission, evidenced by a concentration-dependent inhibition of acetylcholinesterase activity, altered gene expressions related to neural development and function, and reduced Na+/K+-ATPase activity. STRING network analysis highlighted two distinct gene clusters related to lipid metabolism and cholinergic neurotransmission, with potential interactions through the pparα-creb1 pathway. Overall, this study provide important insights into the potential health risks associated with PFOS exposure, including dyslipidemia, cardiovascular disease, impaired glucose metabolism, and neurotoxicity. Further research is needed to fully elucidate the underlying mechanisms and potential long-term effects of PFOS exposure.

Oxidative stress and mitochondrial damage induced by a novel pesticide fluopimomide in Caenorhabditis elegans

Fluopimomide is a novel pesticide intensively used in agricultural pest control; however, its excessive use may have toxicological effects on non-target organisms. In this study, Caenorhabditis elegans was used to evaluate the toxic effects of fluopimomide and its possible mechanisms. The effects of fluopimomide on the growth, pharyngeal pumping, and antioxidant systems of C. elegans were determined. Furthermore, the gene expression levels associated with mitochondria in the nematodes were also investigated. Results indicated that fluopimomide at 0.2, 1.0, and 5.0 mg/L notably (p < 0.001) decreased body length, pharyngeal pumping, and body bends in the nematodes compared to the untreated control. Additionally, fluopimomide at 0.2, 1.0, and 5.0 mg/L notably (p < 0.05) increased the content of malondialdehyde by 3.30-, 21.24-, and 33.57-fold, respectively, while fluopimomide at 1.0 and 5.0 mg/L significantly (p < 0.001) increased the levels of reactive oxygen species (ROS) by 49.14% and 77.06% compared to the untreated control. In contrast, fluopimomide at 1.0 and 5.0 mg/L notably reduced the activities of target enzyme succinate dehydrogenase and at 5.0 mg/L reduced the activities of antioxidant enzyme superoxide dismutase. Further evidence revealed that fluopimomide at 1.0 and 5.0 mg/L significantly inhibited oxygen consumption and at 0.2, 1.0, and 5.0 mg/L significantly inhibited ATP level in comparison to the untreated control. The expression of genes related to the mitochondrial electron transport chain mev-1 and isp-1 was significantly downregulated. ROS levels in the mev-1 and isp-1 mutants after fluopimomide treatments did not change significantly compared with the untreated mutants, suggesting that mev-1 and isp-1 may play critical roles in the toxicity induced by fluopimomide. Overall, the results demonstrate that oxidative stress and mitochondrial damage may be involved in toxicity of fluopimomide in C. elegans.

Putative adverse outcome pathways of the male reproductive toxicity derived from toxicological studies of perfluoroalkyl acids

Adverse outcome pathway (AOP) as a conceptual framework is a powerful tool in the field of toxicology to connect seemingly discrete events at different levels of biological organizations into an organized pathway from molecular interactions to whole organism toxicity. Based on numerous toxicological studies, eight AOPs for reproductive toxicity have been endorsed by the Organization for Economic Co-operation and Development (OECD) Task Force on Hazard Assessment. We have conducted a literature survey on the mechanistic studies on male reproductive toxicity of perfluoroalkyl acids (PFAAs), a class of global environmental contaminants with high persistence, bioaccumulation and toxicity. Using the AOP development strategy, five new AOPs for male reproductive toxicity were proposed here, namely (1) changes in membrane permeability leading to reduced sperm motility, (2) disruption of mitochondrial function leading to sperm apoptosis, (3) decreased gonadotropin-releasing hormone (GnRH) expression in hypothalamus leading to reduced testosterone production in male rats, (4) activation of the p38 signaling pathway leading to disruption of BTB in mice, (5) inhibition of p-FAK-Tyr407 activity leading to the destruction of BTB. The molecular initiating events in the proposed AOPs are different from those in the endorsed AOPs, which are either receptor activation or enzyme inhibition. Although some of the AOPs are still incomplete, they can serve as a building block upon which full AOPs can be developed and applied to not only PFAAs but also other chemical toxicants with male reproductive toxicity.

Occurrence, source, ecological risk, and mitigation of phthalates (PAEs) in agricultural soils and the environment: A review

The widespread distribution of phthalates (PAEs) in agricultural soils is increasing drastically; however, the environmental occurrence and potential risk of PAEs in agricultural systems remain largely unreviewed. In this study, the occurrence, sources, ecotoxicity, exposure risks, and control measures of PAEs contaminants in agricultural soils are summarized, and it is concluded that PAEs have been widely detected and persist in the soil at concentrations ranging from a few μg/kg to tens of mg/kg, with spatial and vertical variations in China. Agrochemicals and atmospheric deposition have largely contributed to the elevated contamination status of PAEs in soils. In addition, PAEs cause multi-level hazards to soil organisms (survival, oxidative damage, genetic and molecular levels, etc.) and further disrupt the normal ecological functions of soil. The health hazards of PAEs to humans are mainly generated through dietary and non-dietary pathways, and children may be at a higher risk of exposure than adults. Improving the soil microenvironment and promoting biochemical reactions and metabolic processes of PAEs are the main mechanisms for mitigating contamination. Based on these reviews, this study provides a valuable framework for determining future study objectives to reveal environmental risks and reduce the resistance control of PAEs in agricultural soils.

Effects of perfluorooctane sulfonate (PFOS) on cognitive behavior and autophagy of male mice

Perfluorooctane sulfonate (PFOS), an emerging environmental pollutant, is reported to cause neurotoxicity in animals and humans, but its underlying mechanisms are still unclear. We used in vivo models to investigate the effects of PFOS on cognition-related behaviors and related mechanisms. After 45 days of intragastric administration of PFOS (2 mg/kg or 8 mg/kg) in 7-week-old C57BL/6 mice, muscle strength, cognitive function and anxiety-like behavior were evaluated by a series of behavioral tests. The underling mechanisms of PFOS on impaired behaviors were evaluated by HE/Nissl staining, electron microscopy observation and western blot analysis. The results indicated that PFOS-exposed mice exhibited significant cognitive impairment, anxiety, neuronal degeneration and the abnormities of synaptic ultrastructure in the cortex and hippocampus. Western blot analysis indicated that PFOS exposure increased microtubule-associated protein light chain 3 (LC3) and decreased p62 protein levels, which may be associated with activation of autophagy leading to neuron damage. In summary, our results suggest that chronic exposure to PFOS adversely affects cognitive-related behavior in mice. These findings provide new mechanistic insights into PFOS-induced neurotoxicity.

Toxic effects of per- and polyfluoroalkyl substances on sperm: Epidemiological and experimental evidence

As emerging organic contaminants, per- and polyfluoroalkyl substances (PFASs) have aroused worldwide concern due to their environmental persistence, ubiquitous presence, bioaccumulation, and potential toxicity. It has been demonstrated that PFASs can accumulate in human body and cause multiple adverse health outcomes. Notably, PFASs have been detected in the semen of human, posing a potential hazard to male fecundity. This article reviews the evidence about the toxic effects of exposure to PFASs on male reproduction, focusing on the sperm quality. Epidemiological studies showed that PFASs, such as perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS), were adversely associated with the semen parameters in humans, including sperm count, morphology and motility. Experimental results also confirmed that PFAS exposure led to testicular and epididymal damage, therefore impairing spermatogenesis and sperm quality. The mechanisms of reproductive toxicity of PFASs may be involved in blood-testosterone barrier destruction, testicular apoptosis, testosterone synthesis disorder, and membrane lipid composition alteration, oxidative stress and Ca²⁺ influx in sperm. In conclusion, this review highlighted the potential threat of exposure to PFASs to human spermatozoa.

DNA methylation 6 mA and histone methylation involved in multi-/trans-generational reproductive effects in Caenorhabditis elegans induced by Atrazine

Atrazine (ATR), a widely used triazine herbicide, is an environmental endocrine disruptor that can cause health problems. However, whether there are multi/trans-generational reproductive impacts of ATR have not been studied. Therefore, in this study, Caenorhabditis elegans was used as a preferable model organism to identify the multi/trans-generational reproductive toxicity of ATR. Only parental C.elegans (P0) were exposed to different concentrations (0.0004-40 mg/L) for 48 h and the subsequent offspring (F1-F5) were grown under ATR-free conditions and ATR conditions.The results showed that ATR exposure during P0 decreased fecundity, including a reduction in fertilized eggs, oocytes, and ovulation rate, delayed gonadal development, and decreased the relative area of gonad arm and germ cell number. Furthermore, continuous ATR exposure (P0-F5) causes a significant increase in reproductive toxicity in subsequent generations, although no significant toxicity occurred in the P0 generation after exposure to environmental-related concentrations, suggesting that ATR exposure might have cumulative effects. Likewise, parental exposure to ATR caused transgenerational toxicity impairments. Interestingly, only reproductive toxicity, not development toxicity, was transmitted to several generations (F1-F4), and the F2 generation showed the most notable changes. QRT-PCR results showed that genes expression related to DNA methylation 6 mA (damt-1, nmad-1) and histone H3 methylation (mes-4, met-2, set-25, set-2, and utx-1) can also be passed on to offspring. The function of H3K4 and H3K9 methylation were explored by using loss-of-function mutants for set-2, set-25, and met-2. Transmissible reproductive toxicity was absent in met-2(n4256), set-2(ok952), and set-25(n5021) mutants, which suggests that the histone methyltransferases H3K4 and H3K9 activity are indispensable for the transgenerational effect of ATR. Finally, the downstream genes of DNA methylation and histone H3 methylation were determined. ATR upregulated the expression of ZC317.7, hsp-6, and hsp-60. Mitochondrial stress in parental generation dependent transcription 6 mA modifiers may establish these epigenetic marks in progeny.

Effects of 10 T static magnetic field on the function of sperms and their offspring in Caenorhabditis elegans

With the wide application of static magnetic fields (SMFs), the risk of living organisms exposed to man-made magnetic fields that the intensity is much higher than geomagnetic field has gradually increased. Reproductive system is highly sensitive to environmental stress; however, the influence of high SMFs on reproduction system is still largely unknown. Here we explored the biological responses of SMFs exposure at an intensity of 10 T on the sperms and their offspring in him-5 male mutants of Caenorhabditis elegans (C. elegans). The size of unactivated sperms was deceased by 10 T SMF exposure, instead of the morphology. Exposure to 10 T SMF significantly altered the function of sperms in him-5 worms including the activation of sperms and the non-transferred ratio of sperms. In addition, the brood size assay revealed that 10 T SMF exposure eventually diminished the reproductive capacity of him-5 male worms. The lifespan of outcrossed offspring from exposed him-5 male mutants and unexposed fog-2 female mutants was decreased by 10 T SMF in a time dependent manner. Together, our findings provide novel information regarding the adverse effects of high SMFs on the sperms of C. elegans and their offspring, which can improve our understanding of the fundamental aspects of high SMFs on biological system.

Study on toxicity effects of environmental pollutants based on metabolomics: A review

In the past few decades, the toxic effects of environmental pollutants on non-target organisms have received more and more attention. As a new omics technology, metabolomics can clarify the metabolic homeostasis of the organism at the overall level by studying the changes in the relative contents of endogenous metabolites in the organism. Recently, a large number of studies have used metabolomics technology to study the toxic effects of environmental pollutants on organisms. In this review, we reviewed the analysis processes and data processes of metabolomics and its application in the study of the toxic effects of environmental pollutants including heavy metals, pesticides, polychlorinated biphenyls, polycyclic aromatic hydrocarbons, polybrominated diphenyl ethers and microplastics. In addition, we emphasized that the combination of metabolomics and other omics technologies will help to explore the toxic mechanism of environmental pollutants and provide new research ideas for the toxicological evaluation of environmental pollutants.

Signaling Proteins That Regulate Spermatogenesis Are the Emerging Target of Toxicant-Induced Male Reproductive Dysfunction

There is emerging evidence that environmental toxicants, in particular endocrine disrupting chemicals (EDCs) such as cadmium and perfluorooctanesulfonate (PFOS), induce Sertoli cell and testis injury, thereby perturbing spermatogenesis in humans, rodents and also widelife. Recent studies have shown that cadmium (e.g., cadmium chloride, CdCl₂) and PFOS exert their disruptive effects through putative signaling proteins and signaling cascade similar to other pharmaceuticals, such as the non-hormonal male contraceptive drug adjudin. More important, these signaling proteins were also shown to be involved in modulating testis function based on studies in rodents. Collectively, these findings suggest that toxicants are using similar mechanisms that used to support spermatogenesis under physiological conditions to perturb Sertoli and testis function. These observations are physiologically significant, since a manipulation on the expression of these signaling proteins can possibly be used to manage the toxicant-induced male reproductive dysfunction. In this review, we highlight some of these findings and critically evaluate the possibility of using this approach to manage toxicant-induced defects in spermatrogenesis based on recent studies in animal models.