PFOA evokes extracellular Ca2+ influx and compromises progesterone-induced response in human sperm

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.

How Per- and Poly-Fluoroalkyl Substances Affect Gamete Viability and Fertilization Capability: Insights from the Literature

There has been emerging research linking per- and poly-fluoroalkyl substances (PFAS) to gamete viability and fertility. PFAS, prevalent in the environment and water supplies, undergo slow degradation due to their C-F bond and a long half-life (2.3-8.5 years). In females, PFAS inhibit the hypothalamic-pituitary-gonadal (HPG) axis, reducing follicle-stimulating hormone (FSH) and luteinizing hormone (LH) levels, leading to the inhibition of androgen and estradiol production. PFAS have been found to cause detrimental effects on egg quality through impairing folliculogenesis. In males, PFAS can impair sperm motility and morphology: two fundamental qualities of successful fertilization. PFAS exposure has been proven to inhibit testosterone production, sperm capacitation, and acrosomal reaction. After fertilization, the results of PFAS exposure to embryos have also been investigated, showing reduced development to the blastocyst stage. The aim of this review is to report the main findings in the literature on the impact of PFAS exposure to gamete competency and fertilization capability by highlighting key studies on both male and female fertility. We report that there is significant evidence demonstrating the negative impacts on fertility after PFAS exposure. At high doses, these environmentally abundant and widespread compounds can significantly affect human fertility.

Environmental pollutants and male infertility: Effects on CatSper

Infertility is a growing health concern among many couples worldwide. Men account for half of infertility cases. CatSper, a sperm-specific Ca2+ channel, is expressed on the cell membrane of mammalian sperm. CatSper plays an important role in male fertility because it facilitates the entry of Ca2+ necessary for the rapid change in sperm motility, thereby allowing it to navigate the hurdles of the female reproductive tract and successfully locate the egg. Many pollutants present in the environment have been shown to affect the functions of CatSper and sperm, which is a matter of capital importance to understanding and solving male infertility issues. Environmental pollutants can act as partial agonists or inhibitors of CatSper or exhibit a synergistic effect. In this article, we briefly describe the structure, functions, and regulatory mechanisms of CatSper, and discuss the body of literature covering the effects of environmental pollutants on CatSper.

Degradation and mechanism of PFOA by peroxymonosulfate activated by nitrogen-doped carbon foam-anchored nZVI in aqueous solutions

Perfluorooctanoic acid (PFOA) is an emerging pollutant that is non-biodegradable and presents severe environmental and human health risks. In this study, we present an effective and mild approach for PFOA degradation that involves the use of nitrogen-doped carbon foam anchored with nanoscale zero-valent iron (nZVI@NCF) to activate low concentration peroxymonosulfate (PMS) for the treatment. The nZVI@NCF/PMS system efficiently removed 84.4% of PFOA (2.4 μM). The active sites of nZVI@NCF including Fe0 (110) and graphitic nitrogen played crucial roles in the degradation. Electrochemical analyses and density functional theory calculations revealed that nZVI@NCF acted as an electronic donor, transferring electrons to both PMS and PFOA during the reaction. By further analyzing the electron paramagnetic resonance and byproducts, it was determined that electron transfer and singlet oxygen were responsible for PFOA degradation. Three degradation pathways involving decarboxylation and surface reduction of PFOA in the nZVI@NCF/PMS system were determined. Finding from this study indicate that nZVI@NCF/PMS systems are effective in degrading PFOA and thus present a promising persulfate-advanced oxidation process technology for PFAS treatment.

Perfluorooctanoic acid suppresses sperm functions via abnormal Protein Kinase B activation during capacitation

Perfluorooctanoic acid (PFOA) is a perfluorinated compound, a synthesized chemical, and has been used in several industrial products for more than 70 years. Although PFOA is known to exert toxic effects in normal cells, there is no detailed information on its reproductive toxicity and its effects on sperm functions related to protein kinase B (AKT). Therefore, this study was conducted to explore the effects of PFOA on sperm functions via AKT. Boar spermatozoa were incubated with different concentrations of PFOA (0, 0.1, 1, 10, and 100 μM) to induce capacitation. Sperm functions (sperm motility, motion kinematic parameters, capacitation status, cell viability, and intracellular ATP levels) were evaluated. In addition, the expression levels of AKT, phospho-AKT, phospho-PKA, and tyrosine phosphorylated proteins were evaluated by western blotting. Results showed significant decreases in sperm motility and motion kinematic parameters. PFOA treatment significant suppressed spermatozoa capacitation and intracellular ATP levels. Furthermore, it significantly decreased the levels of phospho-PKA and tyrosine phosphorylated proteins. The levels of AKT phosphorylation at Thr308 and Ser473 also significantly decreased. These findings suggest that PFOA diminishes sperm functions during capacitation and induces unnatural phosphorylation in AKT, leading to reproductive toxicity. Therefore, people should be aware of reproductive toxicity when using PFOA.

Rutin ameliorates perfluorooctanoic acid-induced testicular injury in mice by reducing oxidative stress and improving lipid metabolism

This study investigated the protective effect of rutin on reproductive and blood-testis barrier (BTB) damage induced by perfluorooctanoic acid (PFOA) exposure. In this study, male ICR mice were randomly divided into three groups, Ctrl group (ddH2O, 5 mL/kg), PFOA group (PFOA, 20 mg/kg/d, 5 mL/kg), PFOA + rutin group (PFOA, 20 mg/kg/d, 5 mL/kg; rutin, 20 mg/kg/d, 5 mL/kg). Mice were exposed to PFOA for 28 days by gavage once daily in the presence or absence of rutin. Histopathological observations demonstrated that rutin treatment during PFOA exposure can reduce structural damage to testis and epididymis such as atrophy of spermatogenic epithelium and stenosis of epididymal lumen, while increase in the number and layers of spermatogenic cells. Biochemical detection demonstrated that rutin can reduce 8-hydroxy-2'-desoxyguanosine (8-OHdG) concentration in the serum and testis tissues. Rutin can also ameliorate glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD) content, and reduce malondialdehyde (MDA) and total cholesterol (TC) content in testis tissues. Biotin tracking immunofluorescence and transmission electron microscopy demonstrated that rutin can ameliorate BTB structural damage during PFOA exposure. Rutin ameliorated the stress expression of tight junction proteins occludin and claudin-11. In conclusion, our findings suggested that rutin has a degree of protection in reproductive and BTB damage, which could put forward a new perspective on the application of rutin to prevent reproductive damage.

The Chemosensing Role of CatSper in Mammalian Sperm: An Updated Review

After sperm enter the female reproductive tract, the physicochemical and biochemical microenvironment undergoes significant changes. In particular, the large changes in various ions encountered by sperm may alter the physiology of sperm, ultimately compromising capacitation and fertilization. Thus, the rapid response to environmental variations is vital for sperm functions. For example, Calcium, the most crucial ion for sperm functions, enters into sperm via Ca2+ permeable ion channels. The cation channel of sperm (CatSper) is a sperm-specific, pH-sensitive, and Ca2+-permeable ion channel. It is responsible for the predominant Ca2+ entry in mammalian sperm and is involved in nearly every event of sperm to acquire fertilizing capability. In addition, CatSper also serves as a pivotal polymodal chemosensor in mammalian sperm by responding to multiple chemical cues. Physiological chemicals (such as progesterone, prostaglandins, β-defensins, and odorants) provoke Ca2+ entry into sperm by activating CatSper and thus triggering sperm functions. Additionally, synthetic and natural chemicals (such as medicines, endocrine disrupting chemicals, drugs of abuse, and antioxidants) affect sperm functions by regulating CatSper-dependent Ca2+ signaling. Therefore, understanding the interactions between CatSper and extracellular ligands sheds light on the mechanisms underlying male infertility and offers innovative diagnostic and treatment approaches. This underscores the importance of CatSper as a crucial regulatory target in male reproduction, linking sperm function with the extracellular environment. In conclusion, this review comprehensively summarizes the relevant studies describing the environmental factors that affect CatSper in humans and rodents.

Perfluorooctane sulfonate and perfluorooctanoic acid inhibit progesterone-responsive capacitation through cAMP/PKA signaling pathway and induce DNA damage in human sperm

Perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) are two persistent organic pollutants harmful to human health. They induce negative effects on male reproduction by influencing male hormones, spermatogenesis, and sperm quality. However, their effects and mechanisms on human sperm capacitation and fertilization remain unclear. Here, human sperm were incubated with different concentrations of PFOS or PFOA with progesterone during capacitation. Both PFOS and PFOA inhibited human sperm hyperactivation, sperm acrosome reaction, and protein tyrosine phosphorylation levels. PFOS and PFOA decreased intracellular Ca²⁺ concentration in the presence of progestrone, and subsequently decreased cAMP level, and PKA activity. PFOS and PFOA increased reactive oxygen species production and sperm DNA fragmentation duing the only 3h capacitation incubation. Conclusively, PFOA and PFOS may inhibit human sperm capacitation via the Ca²⁺-mediated cAMP/PKA signaling pathway in the presence of progesterone, and induce sperm DNA damage through increased oxidative stress, which is not conducive to fertilization.

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.

Efficient Removal of Perfluorinated Chemicals from Contaminated Water Sources Using Magnetic Fluorinated Polymer Sorbents

Efficient removal of per- and polyfluoroalkyl substances (PFAS) from contaminated waters is urgently needed to safeguard public and environmental health. In this work, novel magnetic fluorinated polymer sorbents were designed to allow efficient capture of PFAS and fast magnetic recovery of the sorbed material. The new sorbent has superior PFAS removal efficiency compared with the commercially available activated carbon and ion-exchange resins. The removal of the ammonium salt of hexafluoropropylene oxide dimer acid (GenX) reaches >99 % within 30 s, and the estimated sorption capacity was 219 mg g-1 based on the Langmuir model. Robust and efficient regeneration of the magnetic polymer sorbent was confirmed by the repeated sorption and desorption of GenX over four cycles. The sorption of multiple PFAS in two real contaminated water matrices at an environmentally relevant concentration (1 ppb) shows >95 % removal for the majority of PFAS tested in this study.

Perfluorooctanoic acid exposure in vivo perturbs mitochondrial metabolic during oocyte maturation

Perfluorooctanoic acid (PFOA), a member of a group of polyfluorinated and perfluorinated alkyl substances (PFAS), is associated with adverse pregnancy outcomes in mammals. However, the effects of in vivo exposure to PFOA on the female reproductive system and the underlying mechanisms remain unclear. In our study, we constructed a mouse model to investigate whether low-dose PFOA (1 mg/kg/day) or high-dose PFOA (5 mg/kg/day) affect meiosis maturation of oocytes and the potential mechanisms that may be associated with oocyte maturation disorder. Our results indicate that low-dose and high-dose PFOA can lead to impaired oocyte maturation, which is manifested by decreased rate of embryonic foam rupture and first polar body extrusion. Moreover, PFOA exposure harmed the mitochondrial metabolic, resulting in low levels of ATP contents, high reactive oxygen species, aberrant mitochondrial membrane potential. In addition, the proportion of DNA damage marker γ-H2AX was also significantly increased in PFOA exposure oocytes. These changes lead to abnormal arrangements of the spindle and chromosomes during oocyte maturation. In conclusion, our results for the first time illustrated that exposure to PFOA in vivo in female mice impaired the meiosis maturation of oocytes, which provided a basis for studying the mechanism of PFOA reproductive toxicity in female mammals.

Analysis of reproductive damage in earthworms (Amynthas corticis) exposed to cypermethrin

Cypermethrin contamination was a potential threat to soil organisms. In the present work, reproductive damage in earthworms (Amynthas corticis) exposed to cypermethrin was investigated. It was found that earthworms could absorb and accumulate residual cypermethrin in soil, and also earthworm activities helped accelerate the degradation of cypermethrin in soil. The accumulation of cypermethrin in earthworms induced sperm damage, and cypermethrin not only caused the imbalance of calcium homeostasis in earthworm sperm cells by inhibiting earthworm sperm Ca²⁺-ATP and Ca²⁺-Mg²⁺-ATP enzyme activities but also caused barriers in acrosome reaction. It also affected sperm energy supply of earthworms by inhibiting the activity of Na⁺-K⁺-ATPase and Mg²⁺-ATPase of earthworm sperm. Meanwhile, the inhibition of acrosome enzyme activity of earthworm sperm by cypermethrin led to hinder fertilization and reduced cocoon production of earthworms, and the damage of cypermethrin to sperm of earthworm was a significant cause of its reproductive toxicity. The results of the evaluation of IBR index showed that reproductive toxicity of cypermethrin to earthworms reduced with the increasing time. The decreased reproductive toxicity of cypermethrin to earthworms at the later stage of exposure (42-56 d) might be due to a combination of reduced absorption of cypermethrin in soil by earthworms, decreased accumulation of cypermethrin in the body, and improved sperm capacitation.

In vitro investigation of endocrine disrupting effects of pesticides on Ca2+-signaling in human sperm cells through actions on the sperm-specific and steroid-activated CatSper Ca2+-channel

BACKGROUND

Ca²⁺-signaling controls sperm cell functions necessary for successful fertilization. Multiple endocrine disrupting chemicals have been found to interfere with normal Ca²⁺-signaling in human sperm cells through an activation of the sperm-specific CatSper Ca²⁺-channel, which is vital for normal male fertility.

OBJECTIVES

We investigated 53 pesticides for their ability to interfere with CatSper mediated Ca²⁺-signaling and function in human sperm cells.

METHODS

Effects of the pesticides on Ca²⁺-signaling in human sperm cells were evaluated using a Ca²⁺-fluorometric assay. Effects via CatSper were assessed using the specific CatSper inhibitor RU1968. Effects on human sperm function and viability were assessed using an image cytometry-based acrosome reaction assay and the modified Kremer's sperm-mucus penetration assay.

RESULTS

28 of 53 pesticides were found to induce Ca²⁺-signals in human sperm cells at 10 µM. The majority of these 28 active pesticides induced Ca²⁺-signals through CatSper and interfered with subsequent Ca²⁺-signals induced by the two endogenous CatSper ligands progesterone and prostaglandin E₁. Multiple active pesticides were found to affect Ca²⁺-mediated sperm functions and viability at 10 µM. Low nM dose mixtures of the active pesticides alone or in combination with other environmental chemicals were found to significantly induce Ca²⁺-signals and inhibit Ca²⁺-signals induced subsequently by progesterone and prostaglandin E₁.

CONCLUSIONS

Our results show that pesticides, both alone and in low nM dose mixtures, interfere with normal Ca²⁺-signaling in human sperm cells in vitro in low nM concentrations. Biomonitoring of the active pesticides in relevant matrices such as blood and reproductive fluids is very limited and the effects of real time human pesticide exposure on human sperm cells and fertility thus remains largely unknown. To which extent human pesticide exposure affects the chances of a successful fertilization in humans in vivo needs further research.

The role of dissolved organic matter during Per- and Polyfluorinated Substance (PFAS) adsorption, degradation, and plant uptake: A review

The negative effects of polyfluoroalkyl substances (PFAS) on the environment and health have recently attracted much attention. This article reviews the influence of soil- and water-derived dissolved organic matter (DOM) on the environmental fate of PFAS. In addition to being co-adsorped with PFAS to increase the adsorption capacity, DOM competes with PFAS for adsorption sites on the surface of the material, thereby reducing the removal rate of PFAS or increasing water solubility, which facilitates desorption of PFAS in the soil. It can quench some active species and inhibit the degradation of PFAS. In contrast, before DOM in water self-degrades, DOM has a greater promoting effect on the degradation of PFAS because DOM can complex with iron, iodine, among others, and act as an electron shuttle to enhance electron transfer. In soil aggregates, DOM can prevent microorganisms from being poisoned by direct exposure to PFAS. In addition, DOM increases the desorption of PFAS in plant root soil, affecting its bioavailability. In general, DOM plays a bidirectional role in adsorption, degradation, and plant uptake of PFAS, which depends on the types and functional groups of DOM. It is necessary to enhance the positive role of DOM in reducing the environmental risks posed by PFAS. In future, attention should be paid to the DOM-induced reduction of PFAS and development of a green and efficient continuous defluorination technology.

Endocrine disruptor chemicals. A review of their effects on male reproduction and antioxidants as a strategy to counter it

Endocrine disruptor chemicals are exogenous molecules that generate adverse effects on human health by destabilizing the homeostasis of endocrine system and affecting directly human reproductive system by inhibiting or activating oestrogenic or androgenic receptors. Endocrine disruptor chemicals generate transgenerational epigenetic problems, besides being associated with male infertility. Epidemiological data indicate that the increase in reproductive problems in males in the last 50 years is correlated with the increase of endocrine disrupting chemicals in the environment, being associated with a decrease in semen quality and direct effects on spermatozoa, such as alterations in motility, viability and acrosomal reaction, due to the generation of oxidative stress, and have also been postulated as a possible cause of testicular dysgenesis syndrome. Diverse antioxidants, such as C and E vitamins, N-acetylcysteine, selenium and natural vegetable extracts, are among the alternatives under study to counter the effects of endocrine disruptor chemicals. In some cases, the usage of them has given positive results and the opposite in others. In this review, we summarize the recent information about the effects of endocrine disruptor chemicals on male reproduction, on sperm cells, and the results of studies that have tested antioxidants as a strategy to diminish their harmful effects.

Steroidal Antagonists of Progesterone- and Prostaglandin E1-Induced Activation of the Cation Channel of Sperm

The cation channel of sperm (CatSper) is the principal entry point for calcium in human spermatozoa and its proper function is essential for successful fertilization. As CatSper is potently activated by progesterone, we evaluated a range of steroids to define the structure-activity relationships for channel activation and found that CatSper is activated by a broad range of steroids with diverse structural modifications. By testing steroids that failed to elicit calcium influx as inhibitors of channel activation, we discovered that medroxyprogesterone acetate, levonorgestrel, and aldosterone inhibited calcium influx produced by progesterone, prostaglandin E₁, and the fungal natural product l-sirenin, but these steroidal inhibitors failed to prevent calcium influx in response to elevated K⁺ and pH. In contrast to these steroid antagonists, we demonstrated for the first time that the T-type calcium channel blocker ML218 acts similarly to mibefradil, blocking CatSper channels activated by both ligands and alkalinization/depolarization. These T-type calcium channel blockers produced an insurmountable blockade of CatSper, whereas the three steroids produced antagonism that was surmountable by increasing concentrations of each activator, indicating that the steroids selectively antagonize ligand-induced activation of CatSper rather than blocking channel function. Both the channel blockers and the steroid antagonists markedly reduced hyperactivated motility of human sperm assessed by computer-aided sperm analysis, consistent with inhibition of CatSper activation. Unlike the channel blockers mibefradil and ML218, which reduced total and progressive motility, medroxyprogesterone acetate, levonorgestrel, and aldosterone had little effect on these motility parameters, indicating that these steroids are selective inhibitors of hyperactivated sperm motility. SIGNIFICANCE STATEMENT: The steroids medroxyprogesterone acetate, levonorgestrel, and aldosterone selectively antagonize progesterone- and prostaglandin E₁-induced calcium influx through the CatSper cation channel in human sperm. In contrast to T-type calcium channel blockers that prevent all modes of CatSper activation, these steroid CatSper antagonists preferentially reduce hyperactivated sperm motility, which is required for fertilization. The discovery of competitive antagonists of ligand-induced CatSper activation provides starting points for future discovery of male contraceptive agents acting by this unique mechanism.

A review of responses of terrestrial organisms to perfluorinated compounds

Perfluorinated compounds (PFCs) are a class of persistent organic pollutants with widespread distribution in the environment. Since the soil environment has become a significant sink for PFCs, the toxicological assessment about their potential effects on terrestrial organisms is necessary. This review compiles the toxicity researches of regular and emerging PFCs on classical terrestrial biota i.e. microorganisms, earthworms, and plants. In the soil environment, the bioavailability of PFCs much depends on their adsorption in soil, which is affected by soil properties and PFCs structure. By the exploration of bacterial community richness and structure, the gene expression, the influences of PFCs on soil microorganisms were revealed; while the plants and earthworms manifested the PFCs disruption not only through macroscopic indicators, but also from molecular and metabolite responses. Basically, the addition of PFCs would accelerate the production of reactive oxygen species (ROS) in terrestrial organisms, while the excessive ROS could not be eliminated by the defense system causing oxidative damage. Nowadays, the PFCs toxic mechanisms discussed are limited to a single strain, Escherichia coli; thus, the complexity of the soil environment demands further in-depth researches. This review warrants studies focus on more potential quantitative toxicity indicators, more explicit elaboration on toxicity influencing factors, and environmentally relevant concentrations to obtain a more integrated picture of PFCs toxicity on terrestrial biota.

Overview of the Mechanisms of Action of Selected Bisphenols and Perfluoroalkyl Chemicals on the Male Reproductive Axes

Male fertility has been deteriorating worldwide for considerable time, with the greatest deterioration recorded mainly in the United States, Europe countries, and Australia. That is, especially in countries where an abundance of chemicals called endocrine disruptors has repeatedly been reported, both in the environment and in human matrices. Human exposure to persistent and non-persistent chemicals is ubiquitous and associated with endocrine-disrupting effects. This group of endocrine disrupting chemicals (EDC) can act as agonists or antagonists of hormone receptors and can thus significantly affect a number of physiological processes. It can even negatively affect human reproduction with an impact on the development of gonads and gametogenesis, fertilization, and the subsequent development of embryos. The negative effects of endocrine disruptors on sperm gametogenesis and male fertility in general have been investigated and repeatedly demonstrated in experimental and epidemiological studies. Male reproduction is affected by endocrine disruptors via their effect on testicular development, impact on estrogen and androgen receptors, potential epigenetic effect, production of reactive oxygen species or direct effect on spermatozoa and other cells of testicular tissue. Emerging scientific evidence suggests that the increasing incidence of male infertility is associated with the exposure to persistent and non-persistent endocrine-disrupting chemicals such as bisphenols and perfluoroalkyl chemicals (PFAS). These chemicals may impact men’s fertility through various mechanisms. This study provides an overview of the mechanisms of action common to persistent (PFAS) and nonpersistent (bisphenols) EDC on male fertility.

The antidepressant Sertraline inhibits CatSper Ca2+ channels in human sperm

STUDY QUESTION

Do selective serotonin reuptake inhibitor (SSRI) antidepressants affect the function of human sperm?

SUMMARY ANSWER

The SSRI antidepressant Sertraline (e.g. Zoloft) inhibits the sperm-specific Ca²⁺ channel CatSper and affects human sperm function in vitro.

WHAT IS KNOWN ALREADY

In human sperm, CatSper translates changes of the chemical microenvironment into changes of the intracellular Ca²⁺ concentration ([Ca²⁺]_i) and swimming behavior. CatSper is promiscuously activated by oviductal ligands, but also by synthetic chemicals that might disturb the fertilization process. It is well known that SSRIs have off-target actions on Ca²⁺, Na⁺ and K⁺ channels in somatic cells. Whether SSRIs affect the activity of CatSper is, however, unknown.

STUDY DESIGN, SIZE, DURATION

We studied the action of the seven drugs belonging to the most commonly prescribed class of antidepressants, SSRIs, on resting [Ca²⁺]_i and Ca²⁺ influx via CatSper in human sperm. The SSRI Sertraline was selected for in-depth analysis of its action on steroid-, prostaglandin-, pH- and voltage-activation of human CatSper. Moreover, the action of Sertraline on sperm acrosomal exocytosis and penetration into viscous media was evaluated.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The activity of CatSper was investigated in sperm of healthy volunteers, using kinetic Ca²⁺ fluorimetry and patch-clamp recordings. Acrosomal exocytosis was investigated using Pisum sativum agglutinin and image cytometry. Sperm penetration in viscous media was evaluated using the Kremer test.

MAIN RESULTS AND THE ROLE OF CHANCE

Several SSRIs affected [Ca²⁺]_i and attenuated ligand-induced Ca²⁺ influx via CatSper. In particular, the SSRI Sertraline almost completely suppressed Ca²⁺ influx via CatSper. Remarkably, the drug was about four-fold more potent to suppress prostaglandin- versus steroid-induced Ca²⁺ influx. Sertraline also suppressed alkaline- and voltage-activation of CatSper, indicating that the drug directly inhibits the channel. Finally, Sertraline impaired ligand-induced acrosome reaction and sperm penetration into viscous media.

LIMITATIONS, REASONS FOR CAUTION

This is an in vitro study. Future studies have to assess the physiological relevance in vivo.

WIDER IMPLICATIONS OF THE FINDINGS

The off-target action of Sertraline on CatSper in human sperm might impair the fertilization process. In a research setting, Sertraline may be used to selectively inhibit prostaglandin-induced Ca²⁺ influx.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the Swiss Centre for Applied Human Toxicology (SCAHT), the Département de l’Instruction Publique of the State of Geneva, the German Research Foundation (CRU326), the Interdisciplinary Center for Clinical Research, Münster (IZKF; Str/014/21), the Innovation Fund Denmark (grant numbers 14-2013-4) and the EDMaRC research grant from the Kirsten and Freddy Johansen’s Foundation. The authors declare that no conflict of interest could be perceived as prejudicing the impartiality of the research reported.

TRIAL REGISTRATION NUMBER

NA.

Revisiting the action of steroids and triterpenoids on the human sperm Ca2+ channel CatSper

The sperm-specific Ca2+ channel CatSper (cation channel of sperm) is vital for male fertility. Contradictory findings have been published on the regulation of human CatSper by the endogenous steroids estradiol, testosterone and hydrocortisone, as well as the plant triterpenoids, lupeol and pristimerin. The aim of this study was to elucidate this controversy by investigating the action of these steroids and plant triterpenoids on human CatSper using population-based Ca2+-fluorimetric measurements, the specific CatSper-inhibitor RU1968 and a functional test assessing the CatSper-dependent penetration of human sperm cells into methylcellulose. Estradiol, testosterone and hydrocortisone were found to induce Ca2+-signals in human sperm cells with EC50 values in the lower μM range. By employing the specific CatSper-inhibitor RU1968, all three steroids were shown to induce Ca2+-signals through an action on CatSper, similar to progesterone. The steroids were found to dose-dependently inhibit subsequent progesterone-induced Ca2+-signals with IC50 values in the lower μM range. Additionally, the three steroids were found to significantly increase the penetration of human sperm cells into methylcellulose, similar to the effect of progesterone. The two plant triterpenoids, lupeol and pristimerin, were unable to inhibit progesterone-induced Ca2+-signals, whereas the CatSper-inhibitor RU1968 strongly inhibited progesterone-induced Ca2+-signals. In conclusion, this study supports the claim that the steroids estradiol, testosterone and hydrocortisone act agonistically on CatSper in human sperm cells, thereby mimicking the effect of progesterone, and that lupeol and pristimerin do not act as inhibitors of human CatSper.

Male reproductive toxicity of perfluorooctanoate (PFOA): Rodent studies

Perfluorooctanoic acid (PFOA) is an artificial organic substance widely used for decades, which seriously threatens human health. This study aimed to identify human-relevant correlates between PFOA exposure and the male rodent reproductive system. We performed a systematic literature review of the relevant literature of PubMed, Cochrane Library databases, Web of Science and Embase from the establishment to April 2020. Studies included the effects of PFOA on the reproductive system of male rodents. The meta-analysis was performed on the basis of the following points: level of testosterone and estradiol in serum, development of reproductive organs, pathological changes of reproduction organs and parameters of semen. A series of 16 studies was enrolled in this study. The standard mean difference (SMD) for PFOA-related reproductive toxicity was summarised as -0.39 (95% confidence interval [CI]: 0.71, -0.07). The lower serum testosterone levels, decreased absolute testicular and epididymal weights, higher serum estradiol levels, elevated relative testicular and seminal vesicle weights and increased incidence of Leydig cell adenoma and percentage of abnormal sperm were observed in the exposed group compared with the control group. However, no statistical difference was found in the day of preputial separation of pups and percentage of motile sperm. In conclusion, PFOA exposure heightens the reproductive system damage in male rodents. However, many studies included in the review did not identify mechanisms by which PFOA induces changes to the male reproductive system, which is an area for additional study.

Per- and Polyfluoroalkyl Substance Toxicity and Human Health Review: Current State of Knowledge and Strategies for Informing Future Research

Reports of environmental and human health impacts of per- and polyfluoroalkyl substances (PFAS) have greatly increased in the peer-reviewed literature. The goals of the present review are to assess the state of the science regarding toxicological effects of PFAS and to develop strategies for advancing knowledge on the health effects of this large family of chemicals. Currently, much of the toxicity data available for PFAS are for a handful of chemicals, primarily legacy PFAS such as perfluorooctanoic acid and perfluorooctane sulfonate. Epidemiological studies have revealed associations between exposure to specific PFAS and a variety of health effects, including altered immune and thyroid function, liver disease, lipid and insulin dysregulation, kidney disease, adverse reproductive and developmental outcomes, and cancer. Concordance with experimental animal data exists for many of these effects. However, information on modes of action and adverse outcome pathways must be expanded, and profound differences in PFAS toxicokinetic properties must be considered in understanding differences in responses between the sexes and among species and life stages. With many health effects noted for a relatively few example compounds and hundreds of other PFAS in commerce lacking toxicity data, more contemporary and high-throughput approaches such as read-across, molecular dynamics, and protein modeling are proposed to accelerate the development of toxicity information on emerging and legacy PFAS, individually and as mixtures. In addition, an appropriate degree of precaution, given what is already known from the PFAS examples noted, may be needed to protect human health. Environ Toxicol Chem 2021;40:606-630. © 2020 SETAC.

Perfluorooctanoic acid induces cytotoxicity in spermatogonial GC-1 cells

Perfluorooctane acid (PFOA), a typical perfluorinated chemical, has been suggested to interfere with male reproductive function. In this study, mouse spermatogonial GC-1 cells were in vitro treated with PFOA (250, 500 or 750 μM) for 24 h to investigate the cytotoxicity of PFOA and its underlying mechanisms. Our results indicated that exposure to intermediate and high doses of PFOA suppressed the viability of GC-1 cells in a concentration-dependent manner. Furthermore, PFOA treatment markedly enhanced the generation of reactive oxygen species and malondialdehyde, with diminished activity of superoxide dismutase. Particularly, PFOA exposure evoked a decline in mitochondrial membrane potential and ATP production. Furthermore, the apoptotic index and caspase-3 activity were significantly elevated after treatment with PFOA. In addition, PFOA incubation caused an increase in LC3B-II/LC3B-I ratio. Meanwhile, PFOA resulted in an excessive accumulation of autophagosomes in the cytoplasm. Taken together, exposure to PFOA can elicit cytotoxicity to spermatogonial GC-1 cells in vitro, which may be link to the mitochondrial oxidative damage and induction of apoptosis and autophagy.

CatSper: The complex main gate of calcium entry in mammalian spermatozoa

Calcium ions (Ca²⁺) are involved in nearly every aspect of cellular life. They are one of the most abundant elements in mammals and play a vital role in physiological and biochemical processes acting mainly as intracellular messengers. In spermatozoa, several key functions are regulated by cytoplasmic Ca²⁺ concentration such as sperm capacitation, chemotaxis, hyperactive motility, and acrosome reaction. The sperm-specific ion channel CatSper is the principal calcium channel in sperm mediating the calcium influx into the sperm flagellum and acting as an essential modulator of downstream mechanisms involved in fertilization. This review aims to provide insights into the structure, localization, and function of the mammalian CatSper channel, primarily human and mice. The activation of CatSper by progesterone and prostaglandins, as well as the ligand-independent regulation of the channel by a change in the membrane voltage and intracellular pH are going to be addressed. Finally, major questions, challenges, and perspectives are discussed.

Pentachlorophenol inhibits CatSper function to compromise progesterone's action on human sperm

Pentachlorophenol (PCP), a highly toxic contaminant of chlorophenols, is common in a variety of environments and presents serious risks to animal and human health. However, the reproductive toxicity and potential actions of PCP have not been investigated thoroughly, especially in humans. Here, human spermatozoa were used to evaluate the effect of PCP on cell function and to explore the underlying mechanisms. PCP had no substantive effects on sperm viability or motility, nor on the ability to penetrate viscous medium, sperm hyperactivation or spontaneous acrosome reactions. However, PCP significantly inhibited these properties induced by progesterone (P4). Consistent with the functional observations, although PCP itself did not affect the basal intracellular Ca²⁺ concentrations and CatSper current, PCP dose-dependently inhibited increases of intracellular Ca²⁺ concentrations caused by P4. In addition, the activation of CatSper induced by P4 was largely suppressed by PCP. This is the first report showing that PCP may serves as an antagonist of the P4 membrane receptor to interfere with Ca²⁺ signaling by compromising the action of P4 on regulating sperm function. These findings suggest that the reproductive toxicity of PCP should also be a matter of concern as a mammalian health risk.

Progesterone, spermatozoa and reproduction: An updated review

The rapid effects of steroids on spermatozoa have been demonstrated for the first time more than three decades ago. Progesterone (P), which is present throughout the female genital tract with peaks of levels in the cumulus matrix surrounding the oocyte, has been shown to stimulate several sperm functions in vitro, including capacitation, hyperactivation, chemotaxis and acrosome reaction (AR). Besides an increase of intracellular calcium, P has been shown to activate other sperm signalling pathways including tyrosine phosphorylation of several sperm proteins. All these effects are mediated by extra-nuclear pathways likely involving interaction with molecules present on the sperm surface. In particular, the increase in intracellular calcium ([Ca²⁺]_i) in spermatozoa from human and several other mammalian species is mediated by the sperm specific calcium channel CatSper, whose expression and function are required for sperm hyperactive motility. P-mediated CatSper activation is indeed involved in promoting sperm hyperactivation, but the involvement of this channel in other P-stimulated sperm functions, such as AR and chemotaxis, is less clear and further studies are required to disclose all the involved pathways. In human spermatozoa, responsiveness to P in terms of [Ca²⁺]_i increase and AR is highly related to sperm fertilizing ability in vitro, suggesting that the steroid is a physiological inducer of AR during in vitro fertilization. In view of their physiological relevance, P-stimulated sperm functions are currently investigated to develop new tools to select highly performant spermatozoa for assisted reproduction.

Endocrine Disruptors in Water and Their Effects on the Reproductive System

Anthropogenic contaminants in water can impose risks to reproductive health. Most of these compounds are known to be endocrine disrupting chemicals (EDCs). EDCs can impact the endocrine system and subsequently impair the development and fertility of non-human animals and humans. The source of chemical contamination in water is diverse, originating from byproducts formed during water disinfection processes, release from industry and livestock activity, or therapeutic drugs released into sewage. This review discusses the occurrence of EDCs in water such as disinfection byproducts, fluorinated compounds, bisphenol A, phthalates, pesticides, and estrogens, and it outlines their adverse reproductive effects in non-human animals and humans.

Bisphenol A Diglycidyl Ether (BADGE) and Bisphenol Analogs, but Not Bisphenol A (BPA), Activate the CatSper Ca2+ Channel in Human Sperm

Aim: Evidence suggests that bisphenol A diglycidyl ether (BADGE), bisphenol A (BPA), and BPA analogs can interfere with human male fertility. However, the effect directly on human sperm function is not known. The CatSper Ca²⁺ channel in human sperm controls important sperm functions and is necessary for normal male fertility. Environmental chemicals have been shown to activate CatSper and thereby affect Ca²⁺ signaling in human sperm. BPA has previously been investigated for effects on Ca²⁺ signaling human sperm, whereas the effects of other BPA analogs are currently unknown. The aim of this study is thus to characterize the effect of BADGE, BPA, and the eight analogs BPG, BPAF, BPC, BPB, BPBP, BPE, BPF, BPS on Ca²⁺ signaling, and CatSper in human sperm. Methods: Direct effects of the bisphenols on Ca²⁺ signaling in human sperm cells were evaluated using a Ca²⁺ fluorimetric assay measuring changes in intracellular Ca²⁺. Effects via CatSper were assessed using the specific CatSper inhibitor RU1968. Effects on human sperm function was assessed using an image cytometry-based acrosome reaction assay and the modified Kremer's sperm-mucus penetration assay. Results: At 10 μM the bisphenols BPG, BPAF, BPC, BADGE, BPB, and BPBP induced Ca²⁺ signals in human sperm cells, whereas BPE, BPF, BPS, and BPA had no effect. The efficacy of the chemicals at 10 μM is BPG > BPAF > BPC > BADGE > BPB > BPBP. Dose-response relations of BPG, BPAF, BPC, BADGE, BPB, and BPBP yielded EC50-values in the nM-μM range. The induced Ca²⁺ signals were almost completely abolished using the CatSper inhibitor RU1968, indicating an effect of the bisphenols on CatSper. All bisphenols, except BPBP, were found to dose-dependently inhibit progesterone-induced Ca²⁺ signals, with BPG and BPAF displaying inhibition even in low μM doses. BPG and BPAF were shown to affect human sperm function in a progesterone-like manner. Conclusion: Our results show that the bisphenols BPG, BPAF, BPC, BADGE, BPB, and BPBP can affect Ca²⁺ signaling in human sperm cells through activation of CatSper. This could potentially disrupt human sperm function by interfering with normal CatSper-signaling and thus be a contributing factor in human infertility, either alone or in mixtures with other chemicals.