Direct action of endocrine disrupting chemicals on human sperm

Effect of in vitro exposure of first-line antiretrovirals on healthy human spermatozoa on kinematics and motility

PURPOSE

Contemporary antiretroviral (ARV) medications are used by millions of men for HIV treatment worldwide. Limited data exist on their direct effect on sperm motility. This pilot study hypothesizes that in vitro exposure to ARVs will reduce sperm kinematic and motility parameter values.

METHODS

This laboratory-based experimental study analyzed sperm motility and kinematics after exposure to the ARVs Dolutegravir, Tenofovir, and Emtricitabine, individually and in combination. Each participant (n = 23) served as their experimental control. The Microptic SCA® Computer Assisted Sperm Analysis (CASA) system, Barcelona, Spain was used to generate quantitative data on sperm motility and the kinematics Straight-line velocity (VSL), Straightness index (STR), Linearity Index (LIN), Beat cross frequency (BCF), and the oscillation index (WOB).

RESULTS

VSL, STR, LIN, and WOB of the non-progressive (grade c) spermatozoa were significantly decreased after ARV treatment. BCF of the medium velocity progressive sperm population (grade b) was significantly increased 90 min after exposure in the Tenofovir arm, and a significant decrease in the proportion of grade b spermatozoa was recorded at 90 min in all the antiretroviral arms when compared to the control arm. No impaired sperm motility was observed within the first 30 min of exposure.

CONCLUSION

Pharmacovigilance is a healthcare emergency as the fast-changing world of newer drugs leaves clinicians vulnerable. They must prescribe drugs whose long-term somatic and germline adverse effects are not fully understood. Guidelines and drugs are changing faster than we can monitor for side effects. Despite Dolutegravir being the only mainstream integrase inhibitor first-line ARV in South Africa for five years, its replacement, Cabotegravir, is already being launched. More research in this field is required, especially for commonly prescribed drugs. This preliminary pilot study concludes that the current first-line ARVs used by HIV patients and HIV-negative patients on pre-exposure prophylaxis (PrEP) can alter sperm motility and kinematics. Further research with a larger sample size is warranted to quantify its impact on human fertility, addressing the limitations of this study, before a comprehensive conclusion of the effects of ARVs on human male fertility can be drawn. Of particular importance would be to study the impact of ARVs on reactive oxygen species levels in semen and sperm DNA fragmentation.

The major phytocannabinoids, delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD), affect the function of CatSper calcium channels in human sperm

STUDY QUESTION

Do the main psychoactive phytocannabinoid delta-9-tetrahydrocannabinol (THC) and its non-psychoactive analog cannabidiol (CBD) affect human sperm function?

SUMMARY ANSWER

THC and CBD affect the sperm-specific Ca2+ channel CatSper, suppress activation of the channel by progesterone (P4) and prostaglandin E1 (PGE1), and THC also alters human sperm function in vitro.

WHAT IS KNOWN ALREADY

Marijuana (Cannabis sativa) is one of the most commonly used recreational drugs worldwide. Although the effects of phytocannabinoids on semen parameters have been studied, there is no evidence of a direct impact of THC and CBD on human sperm.

STUDY DESIGN, SIZE, DURATION

We investigated the effects of the major psychoactive phytocannabinoid, THC, its non-psychoactive analog, CBD, and their major metabolites on Ca2+ influx via CatSper in human spermatozoa. THC and CBD were selected to further evaluate their action on P4-, PGE1-, and pH-induced activation of CatSper. The effects of THC and CBD on sperm motility, penetration into viscous media, and acrosome reaction (AR) were also assessed.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The effects of phytocannabinoids on CatSper activity were investigated on semen samples from healthy volunteers and men with homozygous deletion of the CATSPER2 gene using kinetic Ca2+ fluorimetry and patch-clamp recordings. Motility was assessed by computer-assisted sperm analysis (CASA). Sperm penetration into viscous media was assessed using a modified Kremer test. The AR was evaluated by flow cytometry using Pisum sativum agglutinin-stained spermatozoa.

MAIN RESULTS AND THE ROLE OF CHANCE

Both THC and CBD increased the intracellular calcium concentration with CBD inducing a greater increase compared to THC. These Ca2+ signals were abolished in men with homozygous deletion of the CATSPER2 gene demonstrating that they are mediated through CatSper. THC suppressed the P4- and the PGE1-induced Ca2+ increase with a half-maximal inhibitory concentration (IC50) of 1.88 ± 1.15 µM and 0.98 ± 1.10, respectively. CBD also suppressed the P4- and PGE1-induced Ca2+ signal with an IC50 of 2.47 ± 1.12 µM and 6.14 ± 1.08 µM, respectively. The P4 and PGE1 responses were also suppressed by THC and CBD metabolites, yet with greatly reduced potency and/or efficacy. THC and CBD were found to inhibit the Ca2+ influx evoked by intracellular alkalization via NH4Cl, with THC featuring a higher potency compared to CBD. In conclusion, THC and CBD inhibit both the ligand-dependent and -independent activation of CatSper in a dose-dependent manner. This indicates that these phytocannabinoids are genuine CatSper inhibitors rather than P4 and PGE1 antagonists. Finally, THC, but not CBD, impaired sperm hyperactivation and penetration into viscous media and induced a small increase in AR.

LIMITATIONS, REASONS FOR CAUTION

Future studies are needed to assess whether cannabis consumption can affect fertility since this study was in vitro.

WIDER IMPLICATIONS OF THE FINDINGS

The action of THC and CBD on CatSper in human sperm may interfere with the fertilization process, but the impact on fertility remains to be elucidated. THC inhibits the P4 and the PGE1 response more potently than CBD and most previously described CatSper inhibitors. THC can be used as a starting point for the development of non-hormonal contraceptives targeting CatSper.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the Swiss Center for Applied Human Toxicology (SCAHT), the Département de l'Instruction Publique (DIP) of the State of Geneva and the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation). The authors declare that no conflicts of interest have been identified that might affect the impartiality of the research reported.

TRIAL REGISTRATION NUMBER

N/A.

Dibutyl phthalate disrupts [Ca2+]i, reactive oxygen species, [pH]i, protein kinases and mitochondrial activity, impairing sperm function

To explore the mechanism of sperm dysfunction caused by dibutyl phthalate (DBP), the effects of DBP on intracellular [Ca2+] and [pH], reactive oxygen species (ROS), lipid peroxidation (LPO), mitochondrial permeability transition pore (mPTP) opening, mitochondrial membrane potential (MMP), adenosine triphosphate (ATP) levels, phosphorylation of protein kinase A (PKA) substrate proteins and phosphotyrosine (p-Tyr) proteins, sperm motility, spontaneous acrosome reaction, and tail bending were examined in mouse spermatozoa. At 100 µg/mL, DBP significantly increased tail bending and [Ca2+]i. Interestingly, DBP showed biphasic effects on [pH]i. DBP at 10-100 µg/mL significantly decreased sperm motility. Similarly, Ca2+ ionophore A23187 decreased [pH]i sperm motility, suggesting that DBP-induced excessive [Ca2+]i decreased sperm motility. DBP significantly increased ROS and LPO. DBP at 100 µg/mL significantly decreased mPTP closing, MMP, and ATP levels in spermatozoa, as did H2O2, indicative of ROS-mediated mitochondrial dysfunction caused by DBP. DBP as well as H2O2 increased p-Tyr sperm proteins and phosphorylated PKA substrate sperm proteins. DBP at 1-10 µg/mL significantly increased the spontaneous acrosome reaction, suggesting that DBP can activate sperm capacitation. Altogether, DBP showed a biphasic effect on intracellular signaling in spermatozoa. At concentrations relevant to seminal ortho-phthalate levels, DBP activates [pH]i, protein tyrosine kinases and PKA via physiological levels of ROS generation, potentiating sperm capacitation. DBP at high doses excessively raises [Ca2+]i and ROS and disrupts [pH]i, impairing the mitochondrial function, tail structural integrity, and sperm motility.

Systematic review of the impact of calcium channel blockers on sperm function

This study explores the effects of calcium channel blockers (CCBs) on sperm function, a critical aspect of male fertility. Male infertility, responsible for 30-50 % of infertility cases, often involves issues with sperm motility and capacitation, both of which are heavily influenced by calcium ions and specific ion channels like CatSper and voltage-dependent calcium channels (VDCCs). CCBs, which are commonly prescribed for cardiovascular conditions, inhibit these calcium channels, potentially disrupting sperm function. A comprehensive literature review showed varied results: some studies demonstrated that CCBs such as nifedipine reduce sperm motility and the acrosome reaction, causing reversible infertility, while others found no significant impact on fertilization rates in IVF treatments. Supporting these findings, animal studies indicated that CCBs impair spermatogenesis and sperm function without necessarily affecting hormonal levels. The research suggests that the impact of CCBs on male fertility might be reversible, emphasizing the need for more extensive in vivo studies to further understand these effects and their clinical significance for patients on CCB therapy.

Sperm Intracellular Calcium Evaluation

The evaluation of the intracellular calcium is essential in studying sperm capacitation and acrosome reaction, among other processes. Here, we describe the use of chlortetracycline (CTC) to study Ca2+ distribution in relation to the sperm capacitation state, and the evaluation of Ca2+ levels in spermatozoa using a low or a high-affinity Ca2+ dye (Rhod-5 N-AM and Fluo-4-AM, respectively) by flow cytometry. Rhod-5 N-AM staining method also allows the study of Ca2+ in subcellular compartments, whereas the changes in intracellular Ca2+ levels can be measured in spermatozoa loaded with Fluo-4-AM by plate reader fluorometry.

Assessing male reproductive toxicity of environmental pollutant di-ethylhexyl phthalate with network toxicology and molecular docking strategy

Environmental pollutants, especially endocrine-disrupting chemicals (EDCs) like di-ethylhexyl phthalate (DEHP), pose serious threats to human health, with DEHP widely implicated in male reproductive toxicity. However, the complex molecular interactions remain unknown. We employed a network toxicology approach combined with molecular docking analysis to identify potential targets and mechanisms of DEHP's toxic effects. Databases such as ChEMBL, STITCH, OMIM, and GeneCards were utilized to gather data, and Cytoscape software was used to construct protein-protein interaction networks. A total of 51 potential targets were identified, with eight core targets, including PTGS2, CASP3, and ESR1, highlighted for their roles in oxidative stress, apoptosis, and hormonal dysregulation. KEGG pathway enrichment analysis revealed significant associations with pathways in cancer, cytokine-mediated signaling, and the hypothalamic-pituitary-gonadal axis. Additionally, gene expression datasets from the Gene Expression Omnibus (GEO) database were analyzed to identify differentially expressed genes overlapped with DEHP targets in testicular diseases. Molecular docking results confirmed strong binding affinities between DEHP and the core target proteins, suggesting a robust interaction mechanism. This study underscores the need for further investigation into DEHP's toxic mechanisms and its combined effects with other environmental pollutants, paving the way for comprehensive risk assessments and the development of targeted intervention strategies.

Urinary benzophenone-3 concentrations and ovarian reserve in a cohort of subfertile women

OBJECTIVE

To evaluate the association between the urinary benzophenone-3 concentrations and measures of ovarian reserve (OR) among women in the Environment and Reproductive Health study seeking fertility treatment at Massachusetts General Hospital (MGH) in Boston, Massachusetts.

DESIGN

Prospective cohort study.

SETTING

MGH infertility clinic in Boston, Massachusetts.

PATIENT(S)

Women in the Environment and Reproductive Health cohort seeking fertility treatment.

INTERVENTION(S)

Women contributed spot urine samples prior to assessment of OR outcomes that were analyzed for benzophenone-3 concentrations.

MAIN OUTCOME MEASURE(S)

Antral follicle count (AFC) and day 3 follicle-stimulating hormone (FSH) levels were evaluated as part of standard infertility workups during unstimulated menstrual cycles. Quasi-Poisson and linear regression models were used to evaluate the association of the specific gravity-adjusted urinary benzophenone-3 concentrations with AFC and FSH, with adjustment for age and physical activity. In the secondary analyses, models were stratified by age.

RESULT(S)

This study included 142 women (mean age ± standard deviation, 36.1 ± 4.6 years; range, 22-45 years) enrolled between 2009 and 2017 with both urinary benzophenone-3 and AFC measurements and 57 women with benzophenone-3 and FSH measurements. Most women were White (78%) and highly educated (49% with a graduate degree). Women contributed a mean of 2.7 urine samples (range, 1-10), with 37% contributing ≥2 samples. Benzophenone-3 was detected in 98% of samples. The geometric mean specific gravity-corrected urinary benzophenone-3 concentration was 85.9 μg/L (geometric standard deviation, 6.2). There were no associations of benzophenone-3 with AFC and day 3 FSH in the full cohort. In stratified models, a 1-unit increase in the log geometric mean benzophenone-3 concentration was associated with a 0.91 (95% confidence interval, 0.86-0.97) times lower AFC among women aged ≤35 years and an increase in the FSH concentration of 0.73 (95% confidence interval, 0.12-1.34) IU/L among women aged >35 years.

CONCLUSION(S)

In the main models, urinary benzophenone-3 was not associated with OR. However, younger patients may be vulnerable to the potential effects of benzophenone-3 on AFC. Further research is warranted.

The sperm-specific K+ channel Slo3 is inhibited by albumin and steroids contained in reproductive fluids

To locate and fertilize the egg, sperm probe the varying microenvironment prevailing at different stages during their journey across the female genital tract. To this end, they are equipped with a unique repertoire of mostly sperm-specific proteins. In particular, the flagellar Ca2+ channel CatSper has come into focus as a polymodal sensor used by human sperm to register ligands released into the female genital tract. Here, we provide the first comprehensive study on the pharmacology of the sperm-specific human Slo3 channel, shedding light on its modulation by reproductive fluids and their constituents. We show that seminal fluid and contained prostaglandins and Zn2+ do not affect the channel, whereas human Slo3 is inhibited in a non-genomic fashion by diverse steroids as well as by albumin, which are released into the oviduct along with the egg. This indicates that not only CatSper but also Slo3 harbours promiscuous ligand-binding sites that can accommodate structurally diverse molecules, suggesting that Slo3 is involved in chemosensory signalling in human sperm.

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.

Urinary concentrations of bisphenol A, parabens and benzophenone-type ultra violet light filters in relation to sperm DNA fragmentation in young men: A chemical mixtures approach

People are daily exposed to multiple endocrine disruptor compounds (EDCs) that may interfere with different molecular and cellular processes, promoting a potential estrogenic, androgenic, or anti-androgenic state. However, most epidemiological studies attempting to establish relationships between EDCs exposure and health effects are still considering individual compounds. A few studies have shown associations between exposure to individual non-persistent EDCs and sperm DNA fragmentation (SDF) in different male populations. Thus, the aim of this study was to investigate associations between combined exposure to non-persistent EDCs and SDF index in young men. A cross-sectional study was conducted with 158 healthy university students from Southeaster Spain. The participants provided spot urine and semen samples on the same day. The concentrations of urinary bisphenol A (BPA), benzophenones [2,4-dihydroxybenzophenone (BP-1); 2,2',4,4'-tetrahydroxybenzophenone (BP-2), 2-hydroxy-4-methoxybenzophenone (BP-3), 2,2'-dihydroxy-4-methoxybenzophenone (BP-8), 4-hydroxybenzophenone (4OHBP)], and parabens (methylparaben, ethylparaben, propylparaben, butylparaben) were measured by dispersive liquid-liquid microextraction and ultrahigh-performance liquid chromatography with tandem mass spectrometry detection. SDF was analysed using a Sperm Chromatin Dispersion test. Statistical analyses were carried out using Bayesian Kernel Machine Regression models to evaluate associations between combined exposure to these compounds and SDF index while adjusting by relevant covariates. The increase in urinary concentration of 4OHBP was found to be the most important contributor to the negative association between urinary EDCs concentrations and SDF index, being of -5.5 % [95 % CI: -10.7, -0.3] for those in percentile 50, and - 5.4 % [95 % CI: -10.8, -0.1] for those in percentile 75. No significant associations were observed between other EDCs and SDF index. Our findings show that urinary 4OHBP levels may be associated with a decrease in the SDF index. Nonetheless, the effects we observed were likely to be small and of uncertain clinical significance. Further research is needed to replicate our findings in other male populations.

Human fertilization in vivo and in vitro requires the CatSper channel to initiate sperm hyperactivation

The infertility of many couples rests on an enigmatic dysfunction of the man's sperm. To gain insight into the underlying pathomechanisms, we assessed the function of the sperm-specific multisubunit CatSper-channel complex in the sperm of almost 2,300 men undergoing a fertility workup, using a simple motility-based test. We identified a group of men with normal semen parameters but defective CatSper function. These men or couples failed to conceive naturally and upon medically assisted reproduction via intrauterine insemination and in vitro fertilization. Intracytoplasmic sperm injection (ICSI) was, ultimately, required to conceive a child. We revealed that the defective CatSper function was caused by variations in CATSPER genes. Moreover, we unveiled that CatSper-deficient human sperm were unable to undergo hyperactive motility and, therefore, failed to penetrate the egg coat. Thus, our study provides the experimental evidence that sperm hyperactivation is required for human fertilization, explaining the infertility of CatSper-deficient men and the need of ICSI for medically assisted reproduction. Finally, our study also revealed that defective CatSper function and ensuing failure to hyperactivate represents the most common cause of unexplained male infertility known thus far and that this sperm channelopathy can readily be diagnosed, enabling future evidence-based treatment of affected couples.

Ovarian follicular fluid levels of phthalates and benzophenones in relation to fertility outcomes

BACKGROUND

Many endocrine disrupting chemicals (EDCs), for instance phthalates and benzophenones, are associated with adverse fertility outcomes and semen quality parameters.

OBJECTIVE

To evaluate if concentrations of selected phthalate metabolites and benzophenones measured in follicular fluid are associated with fertility outcomes (i.e., reproductive hormones, antral follicle count, detected heartbeat at gestational week 7, and live birth) and, in a supplementary study, if measured concentrations of chemicals in follicular fluid can exert biological effects on human spermatozoa.

METHODS

Overall, 111 couples from a fertility clinic in Denmark contributed with 155 follicular fluid samples. Concentrations of 43 metabolites from 19 phthalates and phthalate substitutes and six benzophenones were measured in follicular fluid using liquid chromatography-tandem mass spectrometry. Multiple linear and logistic regression with an applied generalized estimating equation model allowing more than one measurement per woman assessed the association between follicular EDC levels and fertility outcomes. The assessment of biological effects of individual and mixtures of EDCs on human spermatozoa was conducted through a human sperm cell based Ca2+-fluorimetric assay.

RESULTS

Benzophenone-3 (BP-3) and seven metabolites of five phthalates were detectable in follicular fluid. Women with metabolites of dibutyl phthalate isomers in the highest tertiles had lower antral follicle count (MiBP: β = -5.35 [95 % CI: -9.06; -2.00], MnBP: β = -5.25 [95 % CI: -9.00; -2.00]) and lower odds for detecting a heartbeat at gestational week 7 (MiBP: OR = 0.35 [95 % CI: 0.14; 0.91], MnBP: OR = 0.39 [95 % CI: 0.13; 1.15]). Mixtures of the measured concentrations of BP-3 and the seven phthalate metabolites induced a small significant increase in the intracellular calcium ion concentration in human spermatozoa from healthy donors (n = 3).

DISCUSSION

Phthalate metabolites and BP-3 were detectable in follicular fluid and high concentrations of some phthalate metabolites were linked with lower chance of successful fertility treatment outcomes. Chemical mixture concentrations in follicular fluid induced a calcium response in human spermatozoa highlighting possible biological effects at physiologically relevant concentrations.

Xenobiotic Exposure and Migraine-Associated Signaling: A Multimethod Experimental Study Exploring Cellular Assays in Combination with Ex Vivo and In Vivo Mouse Models

BACKGROUND

Mechanisms for how environmental chemicals might influence pain has received little attention. Epidemiological studies suggest that environmental factors such as pollutants might play a role in migraine prevalence. Potential targets for pollutants are the transient receptor potential (TRP) channels ankyrin 1 (TRPA1) and vanilloid 1 (TRPV1), which on activation release pain-inducing neuropeptide calcitonin gene-related peptide (CGRP).

OBJECTIVE

In this study, we aimed to examine the hypothesis that environmental pollutants via TRP channel signaling and subsequent CGRP release trigger migraine signaling and pain.

METHODS

A calcium imaging-based screen of environmental chemicals was used to investigate activation of migraine pain-associated TRP channels TRPA1 and TRPV1. Based on this screen, whole-cell patch clamp and in silico docking were performed for the pesticide pentachlorophenol (PCP) as proof of concept. Subsequently, PCP-mediated release of CGRP and vasodilatory responses of cerebral arteries were investigated. Finally, we tested whether PCP could induce a TRPA1-dependent induction of cutaneous hypersensitivity in vivo in mice as a model of migraine-like pain.

RESULTS

A total of 16 out of the 52 screened environmental chemicals activated TRPA1 at 10 or 100 μ M . None of the investigated compounds activated TRPV1. Using PCP as a model of chemical interaction with TRPA1, in silico molecular modeling suggested that PCP is stabilized in a lipid-binding pocket of TRPA1 in comparison with TRPV1. In vitro, ex vivo, and in vivo experiments showed that PCP induced calcium influx in neurons and resulted in a TRPA1-dependent CGRP release from the brainstem and dilation of cerebral arteries. In a mouse model of migraine-like pain, PCP induced a TRPA1-dependent increased pain response (N total = 144 ).

DISCUSSION

Here we show that multiple environmental pollutants interact with the TRPA1-CGRP migraine pain pathway. The data provide valuable insights into how environmental chemicals can interact with neurobiology and provide a potential mechanism for putative increases in migraine prevalence over the last decades. https://doi.org/10.1289/EHP12413.

Effects of preconception exposure to phthalates on mouse sperm capacitation parameters

BACKGROUND

Phthalates have been linked to adverse male reproductive health, including poor sperm quality and embryo quality as well as a longer time to pregnancy (months of unprotected intercourse before conception occurs). The present study aimed to evaluate the effect of preconception exposure to two ubiquitous phthalate chemicals, di(2-ethylhexyl) phthalate (DEHP), di-n-butyl phthalate (DBP), and their mixture on sperm function, fertilization, and embryo development in mice.

MATERIALS AND METHODS

Adult male C57BL/6J mice aged 8-9 weeks were exposed to di(2-ethylhexyl) phthalate, di-n-butyl phthalate, or their mixture (di-n-butyl phthalate + di(2-ethylhexyl) phthalate) at 2.5 mg/kg/day or vehicle for 40 days (equivalent to one spermatogenic cycle) via surgically implanted osmotic pumps. Caudal epididymal spermatozoa were extracted and analyzed for motility using computer-assisted sperm analyses. Sperm phosphorylation of protein kinase A substrates and tyrosine phosphorylation, markers of early and late capacitation events, respectively, were analyzed by Western blots. In vitro fertilization was used to evaluate the sperm fertilizing capacity.

RESULTS

While the study did not reveal any significant differences in sperm motility and fertilization potential, abnormal sperm morphology was observed in all phthalate exposures, particularly in the phthalate mixture group. In addition, the study revealed significant differences in sperm concentration between control and exposed groups. Moreover, protein phosphorylation of protein kinase A substrates was decreased in the di(2-ethylhexyl) phthalate and mixture exposure groups, while no significant changes in protein tyrosine phosphorylation were observed in any of the groups. Assessment of the reproductive functionality did not reveal significant effects on in vitro fertilization and early embryo development rates but showed wide variability in the phthalate mixture group.

CONCLUSION

Our findings suggest that preconception phthalate exposure affects sperm numbers and phosphorylation of protein kinase A substrates involved in capacitation. Future research is warranted to examine the associations between phthalate exposure and capacitation in human spermatozoa.

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.

The action of physiological and synthetic steroids on the calcium channel CatSper in human sperm

The sperm-specific channel CatSper (cation channel of sperm) controls the intracellular Ca2+ concentration ([Ca2+]i) and plays an essential role in sperm function. It is mainly activated by the steroid progesterone (P4) but is also promiscuously activated by a wide range of synthetic and physiological compounds. These compounds include diverse steroids whose action on the channel is so far still controversial. To investigate the effect of these compounds on CatSper and sperm function, we developed a high-throughput screening (HTS) assay to measure changes in [Ca2+]i in human sperm and screened 1,280 approved and off-patent drugs including 90 steroids from the Prestwick chemical library. More than half of the steroids tested (53%) induced an increase in [Ca2+]i and reduced the P4-induced Ca2+ influx in human sperm in a dose-dependent manner. Ten of the most potent steroids (activating and P4-inhibiting) were selected for a detailed analysis of their action on CatSper and their ability to act on sperm acrosome reaction (AR) and penetration in viscous media. We found that these steroids show an inhibitory effect on P4 but not on prostaglandin E1-induced CatSper activation, suggesting that they compete for the same binding site as P4. Pregnenolone, dydrogesterone, epiandrosterone, nandrolone, and dehydroepiandrosterone acetate (DHEA) were found to activate CatSper at physiologically relevant concentrations within the nanomolar range. Like P4, most tested steroids did not significantly affect the AR while stanozolol and estropipate slightly increased sperm penetration into viscous medium. Furthermore, using a hybrid approach integrating pharmacophore analysis and statistical modelling, we were able to screen in silico for steroids that can activate the channel and define the physicochemical and structural properties required for a steroid to exhibit agonist activity against CatSper. Overall, our results indicate that not only physiological but also synthetic steroids can modulate the activity of CatSper with varying potency and if bound to CatSper prior to P4, could impair the timely CatSper activation necessary for proper fertilization to occur.

CatSper Calcium Channels: 20 Years On

The flagellar-specific Ca2+ channel CatSper is the predominant Ca2+ entry site in mammalian sperm. CatSper-mediated Ca2+ signaling affects nearly every event that regulates sperm to acquire fertilizing capability. In this review, we summarize some of the main findings from 20 years of CatSper research and highlight recent progress and prospects.

Synthesis and Functional Characterization of Novel RU1968-Derived CatSper Inhibitors with Reduced Stereochemical Complexity

The sperm-specific Ca2+ channel CatSper (cation channel of sperm) controls the intracellular Ca2+ concentration and, thereby, the swimming behavior of sperm from many species. The steroidal ethylenediamine RU1968 (1) represents a well-characterized, potent, and fairly selective cross-species inhibitor of CatSper. Due to its two additional centers of chirality in the amine-bearing side chain, RU1968 is a mixture of diastereomeric pairs of enantiomers and, thus, difficult to synthesize. This has hampered the use of this commercially not available inhibitor as a powerful tool for research. Here, simplifying both structure and synthesis, we introduced novel stereochemically less complex and enantiomerically pure aminomethyl RU1968 analogues lacking the C-21 CH3 moiety. Starting from (+)-estrone, a five-step synthesis was developed comprising a Wittig reaction as the key step, leading to a diastereomerically pure 17β-configured aldehyde. Subsequent reductive amination yielded diastereomerically and enantiomerically pure amines. Compared to RU1968, the novel ethylenediamine 2d and homologous trimethylenediamine derivative 2e inhibited CatSper with similar and even twofold enhanced potency, respectively. Considering that these aminomethyl analogues are enantiomerically pure and much easier to synthesize than RU1968, we envisage their common use in future studies investigating the physiology of CatSper in sperm.

Organic food consumption and fecundability in a preconception cohort study of Danish couples trying to conceive

BACKGROUND

Little is known about potential health effects of eating organic food in relation to reproduction.

OBJECTIVE

We examined associations between organic food consumption and fecundability.

METHODS

Data were derived from a preconception cohort study of Danish couples trying to conceive (SnartForaeldre.dk, SF). Participants completed a baseline questionnaire on socio-demographics, anthropometrics and lifestyle and a validated food-frequency questionnaire, which included questions on proportions of organic food consumed within six food groups. Participants were followed up with bimonthly questionnaires for up to 12 months or until pregnancy. Analyses were restricted to 2061 participants attempting pregnancy for ≤6 cycles at enrollment and 1303 with <3 cycles. Fecundability ratios (FRs) and 95% confidence intervals (CI) were estimated by proportional probabilities regression models adjusted for potential confounders including age, lifestyle and socioeconomic factors. Associations were examined for vegetables, fruits, cereals, dairy products, eggs and meat, separately, and for the overall pattern of organic food consumption (organic sum score).

RESULTS

The final analytic sample comprised 2069 participants. In the full cohort, organic food consumption was not meaningfully associated with fecundability. Among participants <3 cycles of pregnancy attempt at study entry (n = 1303), the FR was 1.11 (95% CI 0.93, 1.33) for the category 'less than half', for 'more than half' the FR was 1.17 (95% CI 0.99, 1.38) and for 'almost everything' the FR was 1.12 (95% CI 0.97, 1.28).

CONCLUSION

Higher consumption of organic foods was not meaningfully associated with fecundability, although slightly greater fecundability was seen among participants with <3 cycles of pregnancy attempt time.

Impact of environmental phthalate on human health and their bioremediation strategies using fungal cell factory- A review

Phthalates are utilized as plasticizers in plastic products to enhance their durability, transparency, and elasticity. However, phthalates are not covalently bonded to the polymer matrix of the phthalate-containing products and can be gradually released into the environment through biogeochemical processes. Hence, phthalates are now pervasive in our environment, including our food. Reports suggested that phthalates exposure to the mammalian systems is linked to various health consequences. It has become vital to develop highly efficient strategies to reduce phthalates from the environment. In this context, the utilization of fungi for phthalate bioremediation (mycoremediation) is advantageous due to their highly effective enzyme secretory system. Extracellular and intracellular enzymes of fungi are believed to break down the phthalates by ester hydrolysis to produce phthalic acid and alcohol, and subsequent digestion of the benzene rings of phthalic acid and their metabolites. The present review scrutinizes and highlights the knowledge gap in phthalate prevalence, exposure to mammals, and associated human health challenges. Furthermore, discusses the role of fungi and their secretory enzymes in the biodegradation of phthalates and gives a perspective to better describe and tackle this continuous threat.

Bioaccumulation and trophic transfer of perfluorinated alkyl substances (PFAS) in marine biota from the Belgian North Sea: Distribution and human health risk implications

Per- and polyfluorinated alkyl substances (PFAS) are highly persistent chemicals, which pose a potential risk for aquatic wildlife due to their bioaccumulative behaviour and toxicological effects. Although the distribution of PFAS in marine environments has been studied worldwide, little is known on the contamination of PFAS in the southern North Sea. In the present study, the bioaccumulation and trophic transfer of Perfluoroalkyl acids (PFAAs) was studied in liver and muscle tissue of seven fish species and in whole-body tissue of two crustacean species, collected at 10 sites in the Belgian North Sea. Furthermore, the human and ecological health risks were examined. Overall, perfluorooctane sulfonate (PFOS) was predominant in all matrices and other long-chain PFAS were frequently detected. Mean PFOS concentrations ranged from <LOQ to 107 ng/g (ww) in fish liver, from <LOQ to 24 ng/g ww in fish muscle and from 0.29 to 5.6 ng/g ww in crustaceans. Elevated perfluorotridecanoic acid (PFTrDA) concentrations were detected in fish liver from the estuarine and coastal region (<LOQ-116 ng/g ww), indicating a specific point source of this compound. Based on stable isotope analysis, no distinctive trophic transfer patterns of PFAS could be identified which implies that the bioconcentration of PFAS from the surrounding abiotic environment is most likely dominating over the biomagnification in the studied biota. The consumption of commercially important species such as the brown shrimp (Crangon crangon), plaice (Pleuronecta platessa), sole (Solea solea) and whiting (Merlangus merlangus) might pose potential health risks if it exceeds 17 g/day, 18 g/day, 26 g/day and 43 g/day respectively. Most PFOS measurements did not exceed the QS_biota,hh of 9.1 ng/g ww, however, the benchmark of 33 ng/g ww targeting the protection of wildlife from secondary poisoning was exceeded for 43% and 28% of the samples in plaice and sole.

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.

A chronic exposure to bisphenol A reduces sperm quality in goldfish associated with increases in kiss2, gpr54, and gnrh3 mRNA and circulatory LH levels at environmentally relevant concentrations

The bisphenol A (BPA)-disrupted reproductive functions have been demonstrated in male animals. In fish, it has been shown that environmentally relevant concentrations of BPA decrease sperm quality associated with inhibition of androgen biosynthesis. However, BPA effects on neuroendocrine regulation of reproduction to affect testicular functions are largely unknown. In the present study, reproductive functions of hypothalamus and pituitary were studied in mature male goldfish exposed to nominal 0.2, 2.0 and 20.0 μg/L BPA. At 90 d of exposure, sperm volume, velocity, and density and motility were decreased in goldfish exposed to 0.2, 2.0, and 20.0 μg/L BPA, respectively (p < 0.05). At 30 d of exposure, there were no significant changes in circulatory LH levels and mRNA transcripts of kiss1, Kiss2, gpr54, and gnrh3. At 90 d of exposure, circulatory LH levels showed trends toward increases in BPA exposed goldfish, which was significant in those exposed to 2.0 μg/L (P < 0.05). At this time, Kiss2, gpr54, and gnrh3 mRNA levels were increased in goldfish exposed to any concentrations of BPA (p < 0.05). This study shows that BPA-diminished sperm quality was accompanied by an increase in circulatory LH levels associated with increases in mRNA transcripts of upstream neuroendocrine regulators of reproduction in goldfish. Further, this is the first study to report circulatory levels of LH in fish exposed to BPA.

The Bisphenols Found in the Ejaculate of Men Does Not Pass through the Testes

Exposure to bisphenols is related to negative effects on male reproduction. The bisphenols exposure is associated with several modes of action including negative impact on the blood–testis barrier (BTB) in testes or direct effect on spermatozoa. Bisphenols have been detected in human seminal plasma, but the possible mechanism of seminal transfer of bisphenols is not clear. Some authors consider the transfer through the blood–testis barrier to be crucial. Therefore, in this work, we compared normozoospermic men and men after vasectomy who have interrupted vas deferens and their ejaculate does not contain testicular products. We measured the concentration of bisphenol A (BPA), bisphenol S (BPS) and bisphenol F (BPF) in the urine and seminal plasma of these men using liquid chromatography tandem mass spectrometry (LC/MSMS). We found that the ratio of urinary and seminal plasma content of bisphenols did not differ in normozoospermic men or men after vasectomy. From the obtained data, it can be concluded that the pathways of transport of bisphenols into seminal plasma are not primarily through the testicular tissue, but this pathway is applied similarly to other routes of transmission by a corresponding ejaculate volume ratio. To a much greater extent than through testicular tissue, bisphenols enter the seminal plasma mainly as part of the secretions of the accessory glands.

Heavy metal and metalloid - induced reproductive toxicity

Heavy metals and metalloid exposure are among the most common factors responsible for reproductive toxicity in human beings. Several studies have indicated that numerous metals and metalloids can display severe adverse properties on the human reproductive system. Metals like lead, silver, cadmium, uranium, vanadium, and mercury and metalloids like arsenic have been known to induce reproductive toxicity. Moderate to minute quantities of lead may affect several reproductive parameters and even affect semen quality. The ecological and industrial exposures to the various heavy metals and metalloids have disastrous effects on the reproductive system ensuing in infertility. This work emphasizes the mechanism and pathophysiology of the aforementioned heavy metals and metalloids in reproductive toxicity. Additionally, this work aims to cover the classical protective mechanisms of zinc, melatonin, chelation therapy, and other trending methods to prevent heavy metal-induced reproductive toxicity.

Compounds enhancing human sperm motility identified using a high-throughput phenotypic screening platform

STUDY QUESTION

Can a high-throughput screening (HTS) platform facilitate male fertility drug discovery?

SUMMARY ANSWER

An HTS platform identified a large number of compounds that enhanced sperm motility.

WHAT IS KNOWN ALREADY

Several efforts to find small molecules modulating sperm function have been performed but none have used high-throughput technology.

STUDY DESIGN, SIZE, DURATION

Healthy donor semen samples were used and samples were pooled (3-5 donors per pool). Primary screening was performed singly; dose-response screening was performed in duplicate (using independent donor pools).

PARTICIPANTS/MATERIALS, SETTING, METHODS

Spermatozoa isolated from healthy donors were prepared by density gradient centrifugation and incubated in 384-well plates with compounds (6.25 μM) to identify those compounds with enhancing effects on motility. Approximately 17 000 compounds from the libraries, ReFRAME, Prestwick, Tocris, LOPAC, CLOUD and MMV Pathogen Box, were screened. Dose-response experiments of screening hits were performed to confirm the enhancing effect on sperm motility. Experiments were performed in a university setting.

MAIN RESULTS AND THE ROLE OF CHANCE

From our primary single concentration screening, 105 compounds elicited an enhancing effect on sperm motility compared to dimethylsulphoxide-treated wells. Confirmed enhancing compounds were grouped based on their annotated targets/target classes. A major target class, phosphodiesterase inhibitors, were identified, in particular PDE10A inhibitors as well as number of compounds not previously known to enhance human sperm motility, such as those related to GABA signalling.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

Although this approach provides data about the activity of the compound, it is only a starting point. For example, further substantive experiments are necessary to provide a more comprehensive picture of each compound's activity, the effect on the kinetics of the cell populations and subpopulations, and their potential mechanisms of action. Compounds have been tested with prepared donor spermatozoa, incubated under non-capacitating conditions, and only incubated with compounds for a relatively short period of time. Therefore, the effect of compounds under different conditions, for example in whole semen, for longer incubation times, or using samples from patient groups, may be different and require further study. All experiments were performed in vitro.

WIDER IMPLICATIONS OF THE FINDINGS

This phenotypic screening assay identified a large number of compounds that increased sperm motility. In addition to furthering our understanding of human sperm function, for example identifying new avenues for discovery, we highlight potential compounds as promising start-point for a medicinal chemistry programme for potential enhancement of male fertility. Moreover, with disclosure of the results of screening, we present a substantial resource to inform further work in the field.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by the Bill and Melinda Gates Foundation, Scottish Funding Council and Scottish Universities Life Science Alliance. C.L.R.B. is Editor for RBMO. C.L.R.B. receives funding from Chief Scientists Office (Scotland), ESHRE and Genus PLC, consulting fees from Exscientia and lecture fees from Cooper Surgical and Ferring. S.M.d.S. is an Associate Editor of Human Reproduction, and an Associate Editor of Reproduction and Fertility. S.M.d.S. receives funding from Cooper Surgical and British Dietetic Society. No other authors declared a COI.

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.

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.

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.

A Review on Environmental Contaminants-Related Fertility Threat in Male Fishes: Effects and Possible Mechanisms of Action Learned from Wildlife and Laboratory Studies

Increasing global rates of diminished fertility in males has been suggested to be associated with exposure to environmental contaminants (ECs). The aquatic environments are the final repository of ECs. As the reproductive system is conserved in vertebrates, studies on the effects of ECs on fertility endpoints in fishes provide us with valuable information to establish biomarkers in risk assessment of ECs, and to understand the ECs-related fertility threat. The aim of the present review was to evaluate associations between ECs and fertility determinants to better understand ECs-related male fertility threat in male fishes. Wildlife studies show that the reproductive system has been affected in fishes sampled from the polluted aquatic environment. The laboratory studies show the potency of ECs including natural and synthetic hormones, alkylphenols, bisphenols, plasticizers, pesticides, pharmaceutical, alkylating, and organotin agents to affect fertility determinants, resulting in diminished fertility at environmentally relevant concentrations. Both wildlife and laboratory studies reveal that ECs adverse effects on male fertility are associated with a decrease in sperm production, damage to sperm morphology, alternations in sperm genome, and decrease in sperm motility kinetics. The efficiency of ECs to affect sperm quality and male fertility highly depends on the concentration of the contaminants and the duration of exposure. Our review highlights that the number of contaminants examined over fertility tests are much lower than the number of contaminants detected in our environment. The ECs effects on fertility are largely unknown when fishes are exposed to the contaminants at early developmental stages. The review suggests the urgent need to examine ECs effects on male fertility when a fish is exposed at different developmental stages in a single or combination protocol. The ECs effects on the sperm genome are largely unknown to understand ECs-related inheritance of reproductive disorders transmitted to the progeny. To elucidate modes of action of ECs on sperm motility, it is needed to study functional morphology of the motility apparatus and to investigate ECs-disrupted motility signaling.

[Environmental endocrine disruptors and fertility]

Endocrine disruptor chemicals (EDCs) are ubiquitous contaminants in the environment, wildlife, and humans. During the last 20 years, several epidemiological, clinical and experimental studies have demonstrated the role of EDCs on the reduction of male and female fertility. The concept of foetal origins of adult disease is particularly topical in the field of reproduction. Moreover, exposure to EDCs during pregnancy has been shown to influence epigenetic programming of endocrine signalling and other important physiological pathways, and provided the basis for multi- and transgenerational transmission of adult diseases. However, the large panel of EDCs simultaneously present in the air, sol and water makes the quantification of human exposition still a challenge. Gas chromatography coupled with mass spectrometry, the measurement of total plasmatic hormonal bioactivity on stably transfected cell lines as well as the EDC analysis in hair samples are useful methods of evaluation. More recently, microRNAs analysis offers a new perspective in the comprehension of the mechanisms behind the modulation of cellular response to foetal or post-natal exposure to EDCs. They will help researchers and clinicians in identifying EDCs exposition markers and new therapeutic approaches in the future.

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.

Physiologically detectable bisphenol A impairs human sperm functions by reducing protein-tyrosine phosphorylation

BACKGROUND

Bisphenol A (BPA), a widely used plastic monomer and plasticizer, is detectable in blood, urine and semen of a healthy people, with concentrations ranging from 0.1 nM to 10 nM. It has been shown that in vitro exposure of BPA as low as 0.001 nM could significantly inhibited mouse sperm motility and acrosome reaction. However, it is still unclear whether BPA at those physiologically detectable concentration affects human sperm.

METHODS

The effects of different concentrations of BPA (0, 10^-3, 10^-2, 10^-1, 10, 10³ nM) on sperm functions were examined, including human sperm viability, kinematic parameters, hyperactivation and capacitation.

RESULTS

BPA caused a remarkable decline in human sperm viability, motility and progressive motility, hyperactivation, capacitation and progesterone-induced acrosome reaction. Mechanism studies showed that BPA could suppress the protein tyrosine phosphorylation level of human sperm, but had no effect on sperm calcium signaling.

CONCLUSIONS

Physiologically detectable concentrations of BPA may impair human sperm functions via suppressing protein tyrosine phosphorylation of human sperm, implying that environmental pollution of BPA might be a factor contributing to male infertility.

Association of exposure to residential greenness with semen quality: A retrospective longitudinal study of sperm donation volunteers in Guangdong province, China

BACKGROUND

Exposure to residential greenness has been associated with benefits on certain reproductive health outcomes. However, its potential benefits on semen quality remain unknown.

OBJECTIVES

To quantitatively explore the association between exposure to residential greenness and semen quality.

METHODS

We investigated 9142 sperm donation volunteers who underwent 38,682 semen examinations at Guangdong provincial human sperm bank in China during 2016-2019. Exposure to residential greenness was assessed using mean daily Normalized Difference Vegetation Index (NDVI) at each subject's residential address with a 400 m buffer during 0-90 days before each semen collection. Multivariate linear mixed models and linear regression models were used to assess the association between exposure to residential greenness and semen quality.

RESULTS

An interquartile range increase in exposure to residential greenness was significantly associated with a 0.034 (95% confidence interval [CI]: 0.005, 0.063) ml, 4.06 (95% CI: 0.76, 7.37) × 10⁶, and 0.32% (95% CI: 0.22%, 0.41%) increase in semen volume, total sperm number, and normal forms, respectively; similar trends were observed across quartiles of exposure to residential greenness (all p-values for liner trend <0.05 except for semen volume). The association of greenness exposure with semen volume and total sperm number was stronger in subjects 18-25 years, while the association with normal forms was stronger in subjects 26 years or older. The association for sperm concentration, total sperm number, and normal forms were stronger in cool season, while the association for semen volume was stronger in warm season.

CONCLUSION

We found that exposure to residential greenness was significantly associated with higher semen quality. Further studies are warranted to determine the causality of the association and its underlying mechanisms.

Role of calcium oscillations in sperm physiology

Intracellular Ca²⁺ is a key regulator of cell signaling and sperm are not the exception. Cells often use cytoplasmic Ca²⁺ concentration ([Ca²⁺]_i) oscillations as a means to decodify external and internal information. [Ca²⁺]_i oscillations faster than those usually found in other cells and correlated with flagellar beat were the first to be described in sperm in 1993 by Susan Suarez, in the boar. More than 20 years passed before similar [Ca²⁺]_i oscillations were documented in human sperm, simultaneously examining their flagellar beat in three dimensions by Corkidi et al. 2017. On the other hand, 10 years after the discovery of the fast boar [Ca²⁺]_i oscillations, slower ones triggered by compounds from the egg external envelope were found to regulate cell motility and chemotaxis in sperm from marine organisms. Today it is known that sperm display fast and slow spontaneous and agonist triggered [Ca²⁺]_i oscillations. In mammalian sperm these Ca²⁺ transients may act like a multifaceted tool that regulates fundamental functions such as motility and acrosome reaction. This review covers the main sperm species and experimental conditions where [Ca²⁺]_i oscillations have been described and discusses what is known about the transporters involved, their regulation and the physiological purpose of these oscillations. There is a lot to be learned regarding the origin, regulation and physiological relevance of these Ca²⁺ oscillations.

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.

The Action of Reproductive Fluids and Contained Steroids, Prostaglandins, and Zn2+ on CatSper Ca2+ Channels in Human Sperm

The sperm-specific Ca²⁺ channel CatSper registers chemical cues that assist human sperm to fertilize the egg. Prime examples are progesterone and prostaglandin E₁ that activate CatSper without involving classical nuclear and G protein-coupled receptors, respectively. Here, we study the action of seminal and follicular fluid as well of the contained individual prostaglandins and steroids on the intracellular Ca²⁺ concentration of sperm from donors and CATSPER2-deficient patients that lack functional CatSper channels. We show that any of the reproductive steroids and prostaglandins evokes a rapid Ca²⁺ increase that invariably rests on Ca²⁺ influx via CatSper. The hormones compete for the same steroid- and prostaglandin-binding site to activate the channel, respectively. Analysis of the hormones’ structure–activity relationship highlights their unique pharmacology in sperm and the chemical features determining their effective properties. Finally, we show that Zn²⁺ suppresses the action of steroids and prostaglandins on CatSper, which might prevent premature prostaglandin activation of CatSper in the ejaculate, aiding sperm to escape from the ejaculate into the female genital tract. Altogether, our findings reinforce that human CatSper serves as a promiscuous chemosensor that enables sperm to probe the varying hormonal microenvironment prevailing at different stages during their journey across the female genital tract.

[Ca2+]i oscillations in human sperm are triggered in the flagellum by membrane potential-sensitive activity of CatSper

STUDY QUESTION

How are progesterone (P4)-induced repetitive intracellular Ca2+ concentration ([Ca2+]i) signals (oscillations) in human sperm generated?

SUMMARY ANSWER

P4-induced [Ca2+]i oscillations are generated in the flagellum by membrane potential (Vm)-sensitive Ca2+-influx through CatSper channels.

WHAT IS KNOWN ALREADY

A subset of human sperm display [Ca2+]i oscillations that regulate flagellar beating and acrosome reaction. Although pharmacological manipulations indicate involvement of stored Ca2+ in these oscillations, influx of extracellular Ca2+ is also required.

STUDY DESIGN, SIZE, DURATION

This was a laboratory study that used >20 sperm donors and involved more than 100 separate experiments and analysis of more than 1000 individual cells over a period of 2 years.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Semen donors and patients were recruited in accordance with local ethics approval from Birmingham University and Tayside ethics committees. [Ca2+]i responses and Vm of individual cells were examined by fluorescence imaging and whole-cell current clamp.

MAIN RESULTS AND THE ROLE OF CHANCE

P4-induced [Ca2+]i oscillations originated in the flagellum, spreading to the neck and head (latency of 1-2 s). K+-ionophore valinomycin (1 µM) was used to investigate the role of membrane potential (Vm). Direct assessment by whole-cell current-clamp confirmed that Vm in valinomycin-exposed cells was determined primarily by K+ equilibrium potential (EK) and was rapidly 'reset' upon manipulation of [K+]o. Pre-treatment of sperm with valinomycin ([K+]o = 5.4 mM) had no effect on the P4-induced [Ca2+] transient (P = 0.95; eight experiments), but application of valinomycin to P4-pretreated sperm suppressed activity in 82% of oscillating cells (n = 257; P = 5 × 10-55 compared to control) and significantly reduced both the amplitude and frequency of persisting oscillations (P = 0.0001). Upon valinomycin washout, oscillations re-started in most cells. When valinomycin was applied in saline with elevated [K+], the inhibitory effect of valinomycin was reduced and was dependent on EK (P = 10-25). Amplitude and frequency of [Ca2+]i oscillations that persisted in the presence of valinomycin showed similar sensitivity to EK (P < 0.01). The CatSper inhibitor RU1968 (4.8 and 11 µM) caused immediate and reversible arrest of activity in 36% and 96% of oscillating cells, respectively (P < 10-10). Quinidine (300 µM) which blocks the sperm K+ current (IKsper) completely, inhibited [Ca2+]i oscillations.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

This was an in-vitro study and caution must be taken when extrapolating these results to in-vivo regulation of sperm.

WIDER IMPLICATIONS OF THE FINDINGS

[Ca2+]i oscillations in human sperm are functionally important and their absence is associated with failed fertilisation at IVF. The data reported here provide new understanding of the mechanisms that underlie the regulation and generation (or failure) of these oscillations.

STUDY FUNDING/COMPETING INTEREST(S)

E.T.-N. was in receipt of a postgraduate scholarship from the CAPES Foundation (Ministry of Education, Brazil). E.M-M received travel funds from the Programa de Apoyo a los Estudios de Posgrado (Maestria y Doctorado en Ciencias Bioquimicas-Universidad Autonoma de Mexico). SGB and CLRB are recipients of a Chief Scientist Office (NHS Scotland) grant TCS/17/28. The authors have no conflicts of interest.

Phthalates in Albumin from Human Serum: Implications for Assisted Reproductive Technology

Albumin, a vital protein in cell culture systems, is derived from whole blood or blood products. The culture of human gametes and developing embryos for assisted reproduction (ART) uses albumin of human origin. Human serum albumin (HSA) is derived from expired blood obtained from blood banks. This blood has been stored in polyvinyl chloride bags made clear and flexible with di-2-ethylhexyl phthalate (DEHP). But DEHP can leach from the bags into stored blood and co-fractionate with HSA during albumin isolation. DEHP and its metabolite mono-ethylhexyl phthalate (MEHP), are known endocrine disruptors that are reported to have negative effects when directly supplemented in media for IVF using gametes from a variety of animals. Therefore, the contamination of ART media with DEHP and MEHP through HSA supplementation may have effects on the outcomes of ART procedures. While the embryology laboratory is strictly monitored to prevent a wide variety of contamination, phthalate contamination of HSA has not been broadly examined. This review outlines the function of HSA in ART procedures and the production of HSA from whole blood. Finally, the review highlights the effects of acute phthalate exposures on gametes during in vitro procedures.

UV filters in matched seminal fluid-, urine-, and serum samples from young men

Recent in vitro studies have shown that some chemical UV filters mimic the effect of progesterone in the activation of the CatSper Ca2⁺ channel in human spermatozoa. However, so far, the extent of exposure of human spermatozoa to chemical UV filters via the presence of these chemicals in seminal fluid has been unknown. Here, we present levels of UV filters measured in human seminal fluid and comparisons to levels measured in concurrently collected urine and serum samples. In total nine UV filters were analysed by TurboFlow-LC-MS/MS in paired urine, serum, and seminal fluid samples from 300 young Danish men from the general population; each man collected one of each sample type within 1 h. The samples were collected during February-December 2013 and only six of the men reported having used sunscreen during the 48 h preceding the sample collection. Four of the examined UV filters could be detected in seminal fluid samples at levels above LOD in more than 10% of the samples. Benzophenone (BP), benzophenone-1 (BP-1), and benzophenone-3 (BP-3) were most frequently detected in, respectively, 18%, 19%, and 27% of the seminal fluid samples albeit at levels one to two orders of magnitude lower than the levels observed in urine. 4-methyl-benzophenone (4-MBP) was detectable in 11% of the seminal fluid samples while in <5% of the urine samples. Overall 45% of the men had at least one of the UV filters present in their seminal fluid at detectable levels. For BP-1 and BP-3 individual levels in urine and seminal fluid were significantly correlated, while this was not evident for BP nor 4-MBP. In conclusion, chemical UV filters are present in men's seminal fluid; some of which can activate the human sperm-specific CatSper Ca²⁺ channel and thereby potentially interfere with the fertilisation process.

Effects of the environmental endocrine disruptors di-2-ethylhexyl phthalate and mono-2-ethylhexyl phthalate on human sperm function in vitro

Di-2-ethylhexyl phthalate (DEHP), a plastic-derived, endocrine-disrupting chemical, has been shown to exhibit male reproductive toxicity. However, its effects on human mature spermatozoa are largely unknown. In this study we investigated the invitro effects of DEHP and mono-2-ethylhexyl phthalate (MEHP; the main metabolite of DEHP) on sperm function and the mechanisms involved. Human spermatozoa were exposed to phthalates invitro at the doses that cover the concentrations detected in human semen: 20nM-8 μM DEHP, 1nM-20 μM MEHP or a mixture of 20nM-8 μM DEHP and 1nM-20 μM MEHP. DEHP and MEHP, alone or in combination, had no effect on the viability, membrane integrity, motility, homeostasis of reactive oxygen species or mitochondrial activity of human spermatozoa. Interestingly, 1nM-20 μM MEHP and combinations of 20nM-8 μM DEHP and 1nM-20 μM MEHP enhanced penetration ability, hyperactivation and the spontaneous acrosome reaction of human spermatozoa, and increased intracellular free Ca2+ concentrations ([Ca2+]i) and tyrosine phosphorylation, two key signalling pathways that regulate sperm function. The findings of this study suggest that invitro exposure to MEHP metabolised from DEHP affects human sperm function by inducing increases in sperm [Ca2+]i and tyrosine phosphorylation, which adds to our understanding of the effects of DEHP on male reproduction.

Precursors of polychlorinated dibenzo-p-dioxins and dibenzofurans in Arctic and Antarctic marine sediments: Environmental concern in the face of climate change

Polychlorinated dibenzo-p-dioxins, dibenzofurans (PCDD/F) and their precursors - pentachlorophenol (PCP) and triclosan (TCS), constitute a group of persistent, highly toxic multimedia pollutants, being easily transported via atmosphere over long distances, thus particularly threatening to the polar areas. The global fate of PCDD/Fs is temperature-dependent, and their transfer and immobilization at the Poles are described by the grasshopper effect and the cold trap phenomenon. The aim of this interdisciplinary study was to perform a preliminary assessment of the present state of pollution of Arctic and Antarctic marine sediments by PCP and TCS along with determination of PCDD/Fs contamination by immunoassay. Sediments from 20 stations were collected during two polar expeditions (2013-2016). The study area covered Hornsund Fjord and the southwest coast of Wedel-Jarlsberg Land (Arctic) - Skodde Bay, Nottingham Bay, Isbjørnhamna Bay and Admiralty Bay (Antarctica) - Suszczewski Cove, Halfmoon Cove and Herve Cove. The studied contaminants were quantified in 60% of the collected sediments, with almost half exceeding the environmentally safe levels according European regulations and worldwide literature. The determined levels of PCP, TCS and PCDD/F in Arctic and Antarctic sediments were to be comparable to those reported in the southern Baltic Sea located in the intense industrialized mid-latitudes. Maximum concentrations were observed in the vicinity of retreating, marine terminating glaciers. This observation confirms reemission of POPs into the global cycle with respect to the worldwide ocean warming. The results of this study should gain attention of the international and regional environmental agencies as well as the main chlorine production decision makers.

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.

Sperm ion channels and transporters in male fertility and infertility

Mammalian sperm cells must respond to cues originating from along the female reproductive tract and from the layers of the egg in order to complete their fertilization journey. Dynamic regulation of ion signalling is, therefore, essential for sperm cells to adapt to their constantly changing environment. Over the past 15 years, direct electrophysiological recordings together with genetically modified mouse models and human genetics have confirmed the importance of ion channels, including the principal Ca²⁺-selective plasma membrane ion channel CatSper, for sperm activity. Sperm ion channels and membrane receptors are attractive targets for both the development of contraceptives and infertility treatment drugs. Furthermore, in this era of assisted reproductive technologies, understanding the signalling processes implicated in defective sperm function, particularly those arising from genetic abnormalities, is of the utmost importance not only for the development of infertility treatments but also to assess the overall health of a patient and his children. Future studies to improve reproductive health care and overall health care as a function of the ability to reproduce should include identification and analyses of gene variants that underlie human infertility and research into fertility-related molecules.

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.

Effects and Mechanisms of Phthalates' Action on Reproductive Processes and Reproductive Health: A Literature Review

The production of plastic products, which requires phthalate plasticizers, has resulted in the problems for human health, especially that of reproductive health. Phthalate exposure can induce reproductive disorders at various regulatory levels. The aim of this review was to compile the evidence concerning the association between phthalates and reproductive diseases, phthalates-induced reproductive disorders, and their possible endocrine and intracellular mechanisms. Phthalates may induce alterations in puberty, the development of testicular dysgenesis syndrome, cancer, and fertility disorders in both males and females. At the hormonal level, phthalates can modify the release of hypothalamic, pituitary, and peripheral hormones. At the intracellular level, phthalates can interfere with nuclear receptors, membrane receptors, intracellular signaling pathways, and modulate gene expression associated with reproduction. To understand and to treat the adverse effects of phthalates on human health, it is essential to expand the current knowledge concerning their mechanism of action in the organism.

The Ca2+ channel CatSper is not activated by cAMP/PKA signaling but directly affected by chemicals used to probe the action of cAMP and PKA

The sperm-specific Ca²⁺ channel CatSper (cation channel of sperm) controls the influx of Ca²⁺ into the flagellum and, thereby, the swimming behavior of sperm. A hallmark of human CatSper is its polymodal activation by membrane voltage, intracellular pH, and oviductal hormones. Whether CatSper is also activated by signaling pathways involving an increase of cAMP and ensuing activation of PKA is, however, a matter of controversy. To shed light on this question, we used kinetic ion-sensitive fluorometry, patch-clamp recordings, and optochemistry to study transmembrane Ca²⁺ flux and membrane currents in human sperm from healthy donors and from patients that lack functional CatSper channels. We found that human CatSper is neither activated by intracellular cAMP directly nor indirectly by the cAMP/PKA-signaling pathway. Instead, we show that nonphysiological concentrations of cAMP and membrane-permeable cAMP analogs used to mimic the action of intracellular cAMP activate human CatSper from the outside via a hitherto-unknown extracellular binding site. Finally, we demonstrate that the effects of common PKA inhibitors on human CatSper rest predominantly, if not exclusively, on off-target drug actions on CatSper itself rather than on inhibition of PKA. We conclude that the concept of an intracellular cAMP/PKA-activation of CatSper is primarily based on unspecific effects of chemical probes used to interfere with cAMP signaling. Altogether, our findings solve several controversial issues and reveal a novel ligand-binding site controlling the activity of CatSper, which has important bearings on future studies of cAMP and Ca²⁺ signaling in sperm.