Toxic effects of polychlorinated biphenyls (Aroclor 1254) on human sperm motility

PCB126 impairs human sperm functions by affecting post-translational modifications and mitochondrial functions

Over the past few decades, there has been a consistent decline in semen quality across the globe, with environmental pollution being identified as the primary cause. Among the various contaminants present in the environment, persistent organic pollutants (POPs) have garnered significant attention due to their high toxicity, slow degradation, bio-accumulation, and long-range migration. PCBs, which include 210 congeners, are a crucial type of POPs that are known to have harmful effects on the environment and human health. Among the various PCB congeners, 3,3',4,4',5-pentachlorobiphenyl (PCB126) is a typical environmental endocrine-disrupting chemical that is widely distributed and has been associated with several health hazards. However, the impact and mechanism of PCB126 on human sperm function has not been fully elucidated. We aimed to investigate the effects of different concentrations of PCB126 (0.01, 0.1, 1, 10 μg/mL) on sperm motility, viability, hyperactivation, and acrosome reaction after incubation for different periods (1 and 2 h), delving deeper into the molecular mechanism of human sperm dysfunction caused by PCB126. First, we investigated the link between PCB126 treatment and the occurrence of protein modifications that are critical to sperm function regulation, such as tyrosine phosphorylation and lysine glutarylation. Second, we examined the potential impact of PCB126 on different parameters related to mitochondrial function, including reactive oxygen species, malondialdehyde levels, mitochondrial membrane potential, mitochondria respiration and adenosine triphosphate generation. Our findings indicate that exposure to environmental pollutants such as PCB126 in vitro may have a negative impact on human sperm functions by interfering with post-translational modifications and mitochondrial functions.

Quality of fresh and cryopreserved bovine sperm is reduced by BPA and BPF exposure

Bisphenol A (BPA) is an endocrine disrupting compound, used as the key monomer of polycarbonate plastics and epoxy resins. BPA has been detected in both humans and farm animals and has been correlated with decreased sperm counts and motility. BPS and BPF are structural analogs of BPA and are increasingly being used in manufacturing as BPA substitutes. In this study we aim to assess the direct outcomes of BPA, BPS and BPF exposure on bovine sperm parameters in vitro to elucidate how they affect sperm quality and fertilization potential, and to assess whether BPS and/or BPF are less harmful than BPA. Sperm from three or more bulls was obtained from either fresh samples or cryopreserved straws and exposed to 0.05 mg/mL of BPA, BPS and BPF in vitro. After 4h incubation, motility, capacitation, apoptosis/necrosis, and mitochondrial membrane potential levels were measured by CASA or computational flow cytometry. Results showed that BPA exposure significantly reduced both fresh and cryopreserved sperm motility, capacitation, viability and mitochondrial membrane potential levels. Furthermore, BPF significantly decreased motility, capacitation and mitochondrial membrane potential in cryopreserved sperm only. BPS did not have any significant effects on any of the parameters measured. Our results suggest that BPA is the most harmful to sperm, while BPF is toxic under certain conditions, and BPS seems to be the least detrimental. Overall, this study provides an understanding of how the ubiquitous environmental chemicals, bisphenols, may impact male fertility even after ejaculation.

Aroclor 1254 impairs sperm quality, fertilization ability, and embryo development of rainbow trout (Oncorhynchus mykiss)

The polychlorinated biphenyls (PCBs) in aquatic environment adversely affect non-target organisms, including fish. Especially, the male reproduction and next generation can be damaged through high exposure to these pollutants. Hence, the sperm cells were exposed to sublethal concentrations of Aroclor 1254 (0, 1, 5, 10, or 25 mg/l) for 4 h. The sperm quality parameters were analyzed by SCA (Sperm Class Analyzer). The fertility, eyeing, and hatching rates were determined as gamete markers. Lipid peroxidation (malondialdehyde-MDA), glutathione (GSH), and antioxidant enzymes [superoxide dismutase (SOD), glutathione peroxidase (GPx), and catalase (CAT)] were measured for determination of oxidative stress. Our results showed that Aroclor 1254 negatively affected the motility rate and duration, fertilization rate, embryogenesis, and hatching and also triggered antioxidant defense mechanisms at the highest concentration (25 mg L^-1). Furthermore, linear speed (VSL), linearity index (LIN), and amplitude lateral head (ALH) were significantly changed after exposure to 25 mg L^-1, and the lowest concentrations (1 and 10 mg L^-1) did not significantly affect the motility and fertilizing capacity. The embryogenesis and hatching were significantly affected by sperm exposure to 1, 10, and 25 mg L^-1 of Aroclor 1254. Consequently, Aroclor 1254 causes potential hazards in male germ cells, and the exposure of sperm cells to pollutants can adversely affect next generation of wild populations.

Effects of Polychlorinated Biphenyls on Animal Reproductive Systems and Epigenetic Modifications

Polychlorinated biphenyls (PCBs) are a group of highly toxic endocrine-disrupting chemicals comprising 209 homologs. PCBs are extensively found in the environment and can induce typical estrogenic and profound, long-lasting effects on animals. In this article, the introduction of PCB residues into the environment and the pathways of PCB enrichment in animals are described. PCBs are widely deposited and eventually accumulate in human tissues and body fluids through biomagnification. PCBs can significantly decrease animal fertility and interfere with endocrine processes, leading to the development of various diseases and even cancer. The effects of PCBs on the reproductive systems of animals can also be passed to their offspring, indicating that PCBs may affect the epigenetic modification process. There is currently no treatment to effectively inhibit the toxicity of PCBs in organisms; therefore, the severity of PCB toxicity needs to be widely recognized.

Effect of exposure to 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and polychlorinated biphenyls (PCBs) on mitochondrial DNA (mtDNA) copy number in rats

Mitochondria are intracellular organelles responsible for biological oxidation and energy production. These organelles are susceptible to damage from oxidative stress and compensate for damage by increasing the number of copies of their own genome, mitochondrial DNA (mtDNA). Cancer and environmental exposure to some pollutants have also been associated with altered mtDNA copy number. Since exposures to polychlorinated biphenyls (PCBs) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) have been shown to increase oxidative stress, we hypothesize that mtDNA copy number will be altered with exposure to these compounds. mtDNA copy number was measured in DNA from archived frozen liver and lung specimens from the National Toxicology Program (NTP) study of female Harlan Sprague Dawley rats exposed to TCDD (3, 10, or 100 ng/kg/day), dioxin-like (DL) PCB 126 (10, 100, or 1000 ng/kg/day), non-DL PCB 153 (10, 100, or 1000 μg/kg/day), and PCB 126 + PCB 153 (10 ng/kg/day + 10 μg/kg/day, 100 ng/kg/day + 100 μg/kg/day, or 1000 ng/kg/day + 1000 μg/kg/day, respectively) for 13 and 52 weeks. An increase in mtDNA copy number was observed in the liver and lung of rats exposed to TCDD and the lung of rats exposed to the mixture of PCB 126 and PCB 153. A statistically significant positive dose-dependent trend was also observed in the lung of rats exposed to PCB 126 and a mixture of PCB 153 and PCB 126, although in neither case was the control copy number significantly exceeded at any dose level. These exposures produced a range of pathological responses in these organs in the two-year NTP studies. Conversely, there was a significant decrease or no change in mtDNA copy number in the liver and lung of rats exposed to non-DL PCB 153. This is consistent with a general lack of PCB 153 mediated liver or lung injury in the NTP study, with the exception of liver hypertrophy. Together, the results suggest that an increase in mtDNA copy number may serve as a sensitive, early biomarker of mitochondrial injury and oxidative stress that contributes to the development of the toxicity of dioxin-like compounds.

Endocrine disrupting chemicals: Impacts on human fertility and fecundity during the peri-conception period

It is becoming increasingly difficult to avoid exposure to man-made endocrine disrupting chemicals (EDCs) and environmental toxicants. This escalating yet constant exposure is postulated to partially explain the concurrent decline in human fertility that has occurred over the last 50 years. Controversy however remains as to whether associations exist, with conflicting findings commonly reported for all major EDC classes. The primary aim of this extensive work was to identify and review strong peer-reviewed evidence regarding the effects of environmentally-relevant EDC concentrations on adult male and female fertility during the critical periconception period on reproductive hormone concentrations, gamete and embryo characteristics, as well as the time to pregnancy in the general population. Secondly, to ascertain whether individuals or couples diagnosed as sub-fertile exhibit higher EDC or toxicant concentrations. Lastly, to highlight where little or no data exists that prevents strong associations being identified. From the greater than 1480 known EDCs, substantial evidence supports a negative association between exposure to phthalates, PCBs, PBDEs, pyrethroids, organochloride pesticides and male fertility and fecundity. Only moderate evidence exists for a negative association between BPA, PCBs, organochloride pesticides and female fertility and fecundity. Overall fewer studies were reported in women than men, with knowledge gaps generally evident for both sexes for all the major EDC classes, as well as a paucity of female fertility studies following exposure to parabens, triclosans, dioxins, PFAS, organophosphates and pyrethroids. Generally, sub-fertile individuals or couples exhibit higher EDC concentrations, endorsing a positive association between EDC exposure and sub-fertility. This review also discusses confounding and limiting factors that hamper our understanding of EDC exposures on fertility and fecundity. Finally, it highlights future research areas, as well as government, industry and social awareness strategies required to mitigate the negative effects of EDC and environmental toxicant exposure on human fertility and fecundity.

Endocrine-disrupting chemicals alter the neuromolecular phenotype in F2 generation adult male rats

Endocrine-disrupting chemical (EDC) exposures to the fetus have long-lasting effects on health and disease in adulthood. Such EDC exposure to the F1 fetuses also reaches the germ cells that become the F2 generation. Previously, we demonstrated that adult social and communicative behaviors such as ultrasonic vocalizations and mating behaviors were altered by EDCs in F2 rats, especially males. In the current study, we used the brains of these F2 males to ascertain the underlying molecular changes in the hypothalamus related to these behavioral outcomes. Their progenitors were Sprague-Dawley rat dams, treated on pregnancy days 8 to 18 with one of three treatments: a polychlorinated biphenyl (PCB) mixture, Aroclor 1221, selected because it is weakly estrogenic; the anti-androgenic fungicide vinclozolin (VIN); or the vehicle, 6% dimethylsulfoxide in sesame oil (VEH). In adulthood, F1 male and female offspring were bred with untreated partners to generate paternal or maternal lineages of the F2 offspring, the subjects of molecular work. Quantitative real-time PCR was conducted in the medial preoptic area (POA) and the ventromedial nucleus (VMN) of the hypothalamus, selected for their roles in social and sexual behaviors. Of the genes assessed, steroid hormone receptors (estrogen receptor α, androgen receptor, progesterone receptor) but not dopamine receptors 1 and 2 or DNA methyltransferase 3a expression were altered, particularly in the VIN males. Several significant correlations between behavior and gene expression were also detected. These results suggest that preconceptional exposure of male rats to EDCs at the germ cell stage alters the neuromolecular phenotype in adulthood in a lineage-dependent manner.

Transgenerational Effects of Endocrine-Disrupting Chemicals on Male and Female Reproduction

Endocrine-disrupting chemicals are known to interfere with normal reproductive function and hormone signaling. Phthalates, bisphenol A, pesticides, and environmental contaminants such as polychlorinated biphenyls and dioxins are known endocrine-disrupting chemicals that have been shown to negatively affect both male and female reproduction. Exposure to these chemicals occurs on a daily basis owing to these compounds being found in plastics, personal care products, and pesticides. Recently, studies have shown that these chemicals may cause transgenerational effects on reproduction in both males and females. This is of concern because exposure to these chemicals prenatally or during adult life can negatively impact the reproductive health of future generations. This mini-review summarizes the endocrine-disrupting chemicals that humans are exposed to on a daily basis and what is known about the transgenerational effects that these chemicals may have on male and female reproduction.

Independent and combined effects of diethylhexyl phthalate and polychlorinated biphenyl 153 on sperm quality in the human and dog

A temporal decline in human and dog sperm quality is thought to reflect a common environmental aetiology. This may reflect direct effects of seminal chemicals on sperm function and quality. Here we report the effects of diethylhexyl phthalate (DEHP) and polychlorinated biphenyl 153 (PCB153) on DNA fragmentation and motility in human and dog sperm. Human and dog semen was collected from registered donors (n = 9) and from stud dogs (n = 11) and incubated with PCB153 and DEHP, independently and combined, at 0x, 2x, 10x and 100x dog testis concentrations. A total of 16 treatments reflected a 4 × 4 factorial experimental design. Although exposure to DEHP and/or PCB153 alone increased DNA fragmentation and decreased motility, the scale of dose-related effects varied with the presence and relative concentrations of each chemical (DEHP.PCB interaction for: DNA fragmentation; human p < 0.001, dog p < 0.001; Motility; human p < 0.001, dog p < 0.05). In both human and dog sperm, progressive motility negatively correlated with DNA fragmentation regardless of chemical presence (Human: P < 0.0001, r = −0.36; dog P < 0.0001, r = −0.29). We conclude that DEHP and PCB153, at known tissue concentrations, induce similar effects on human and dog sperm supporting the contention of the dog as a sentinel species for human exposure.

Elucidation of endocrine-disrupting polychlorinated biphenyls binding potency with steroidogenic genes: Integration of in silico methods and ensemble docking approaches

A myriad of polychlorinated biphenyls (PCBs) may have potential to reproductive axis and endocrine disruptions. PCBs mostly breach the cholesterol biotransformation in mitochondria through interfering with steroidogenic genes and lead to adverse consequences in steroidogenesis; however, studies are scanty. In this examination, the combinations of quantitative structure-activity relationship (QSAR) modeling and ensemble docking approaches was performed to envisage structural properties of PCBs that influence the developmental toxicity, estrogen receptor-mediated impacts, and to provide a better comprehension of binding levels between PCBs, steroidogenic acute regulatory protein (StAR) and cholesterol side-chain cleavage enzyme (CYP11A1). Prognostic QSAR models were illustrated with good robustness and predictive ability. Models provide extensive data on applicability domain and similarities between PCBs and training set compounds was used to implement for clustering and classification of toxic PCBs by employing Self-Organizing Maps. Docking and interaction profiles interpretations provided various insights into the structural features of PCBs that influence the cholesterol binding to StAR and CYP11A1 domains. The non-polar, atomic π - stacking and halogen bonds of PCBs with novel hotspots residues of StAR and CYP11A1 was indicated subtle conformational changes that barrier to cholesterol binding and/or locks to cholesterol ejection from Ω1-loop of StAR, and inhibits cholesterol to pregnenolone biosynthesis by CYP11A1; thus, these are probably revealed as block-cluster mechanisms. These outcomes are potential to be useful to predict developmental toxicity, endocrine disruption potencies and anti-steroidogenic activities of other environmental pollutants and provided sorted pinpoints for further evaluation of interaction mechanisms of PCBs with other sterodogenic genes.

Environmental Toxins and Male Fertility

PURPOSE OF REVIEW

Global industrialization has increased population exposure to environmental toxins. A global decline in sperm quality over the last few decades raises questions about the adverse impact of environmental toxins on male reproductive health.

RECENT FINDINGS

Multiple animal- and human-based studies on exposure to environmental toxins suggest a negative impact on semen quality, in terms of sperm concentration, motility, and/or morphology. These toxins may exert estrogenic and/or anti-androgenic effects, which in turn alter the hypothalamic-pituitary-gonadal axis (HPGA), induce sperm DNA damage, or cause sperm epigenetic changes. This chapter will discuss the most recent literature about the most common environmental toxins and their impact on spermatogenesis and its consequences on male fertility. Understanding the presence and underlying mechanism of these toxins will help us preserve the integrity of the male reproduction system and formulate better regulations against their indiscriminate use.