Molecular and Therapeutic Insights of Alpha-Lipoic Acid as a Potential Molecule for Disease Prevention

Alpha-lipoic acid is an organic, sulfate-based compound produced by plants, humans, and animals. As a potent antioxidant and a natural dithiol compound, it performs a crucial role in mitochondrial bioenergetic reactions. A healthy human body, on the other hand, can synthesize enough α-lipoic acid to scavenge reactive oxygen species and increase endogenous antioxidants; however, the amount of α-lipoic acid inside the body decreases significantly with age, resulting in endothelial dysfunction. Molecular orbital energy and spin density analysis indicate that the sulfhydryl (-SH) group of molecules has the greatest electron donating activity, which would be responsible for the antioxidant potential and free radical scavenging activity. α-Lipoic acid acts as a chelating agent for metal ions, a quenching agent for reactive oxygen species, and a reducing agent for the oxidized form of glutathione and vitamins C and E. α-Lipoic acid enantiomers and its reduced form have antioxidant, cognitive, cardiovascular, detoxifying, anti-aging, dietary supplement, anti-cancer, neuroprotective, antimicrobial, and anti-inflammatory properties. α-Lipoic acid has cytotoxic and antiproliferative effects on several cancers, including polycystic ovarian syndrome. It also has usefulness in the context of female and male infertility. Although α-lipoic acid has numerous clinical applications, the majority of them stem from its antioxidant properties; however, its bioavailability in its pure form is low (approximately 30%). However, nanoformulations have shown promise in this regard. The proton affinity and electron donating activity, as a redox-active agent, would be responsible for the antioxidant potential and free radical scavenging activity of the molecule. This review discusses the most recent clinical data on α-lipoic acid in the prevention, management, and treatment of a variety of diseases, including coronavirus disease 2019. Based on current evidence, the preclinical and clinical potential of this molecule is discussed.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s43450-023-00370-1.

Microenvironment of the male and female reproductive tracts regulate sperm fertility: Impact of viscosity, pH, and osmolality

BACKGROUND

Terminally differentiated mammalian sperm are exposed to gradients of viscosity, pH, and osmolality both in the male and female reproductive tract during their perilous journey to quest the ovum. The complex physicochemical factors play an integral role in preparing sperm for the fertilization process.

OBJECTIVES

To elucidate the influence of the reproductive tract microenvironment especially viscosity, pH, and osmolality in regulating sperm functional and fertilization competence.

MATERIALS AND METHODS

The data used in this review were collected from the research papers and online databases focusing on the influence of viscosity, pH, and osmolality on sperm function.

DISCUSSION

The gradients of viscosity, pH, and osmolality exist across various segments of the male and female reproductive tract. The changes in the viscosity create a physical barrier, pH aid in capacitation and hyperactivation, and the osmotic stress selects a progressive sperm subpopulation for accomplishing fertilization. The sperm function tests are developed based on the concept that the male genotype is the major contributor to the reproductive outcome. However, recent studies demonstrate the significance of sperm genotype-environment interactions that are essentially contributing to reproductive success. Hence, it is imperative to assess the impact of physicochemical stresses and the adaptive ability of the terminally differentiated sperm, which in turn would improve the outcome of the assisted reproductive technologies and male fertility assessment.

CONCLUSION

Elucidating the influence of the reproductive tract microenvironment on sperm function provides newer insights into the procedures that need to be adopted for selecting fertile males for breeding, and ejaculates for the assisted reproductive technologies.

The voltage-gated T-type Ca2+ channel is key to the sperm motility of Atlantic salmon (Salmo salar)

Ca²⁺ is a key element in the sperm activation process of Salmo salar. However, the molecular mechanisms by which this ion enters the sperm cell have been poorly studied. In this study, we examined, for the first time, the role of the voltage-gated T-type Ca²⁺ channel in the activation of sperm motility of Salmo salar. Using an in vitro inhibition assay, a significant decrease in total and progressive motility (P < 0.0001) was observed in Salmo salar sperm when they were treated with NNC-55-0396, a highly selective blocker. The in silico analysis showed that this blocker is docked with a strong affinity for the pore of the voltage-gated T-type calcium channel suggesting the blocking of Ca²⁺ ions. The results show that the T-type voltage-gated Ca²⁺ channel is key to sperm motility in Salmo salar.

The role of alkalinization-induced Ca2+ influx in sperm motility activation of a viviparous fish Redtail Splitfin (Xenotoca eiseni)

Mechanisms regulating sperm motility activation are generally known in oviparous fishes, but are poorly understood in viviparous species. The mechanism of osmotic-shock induced signaling for oviparous fishes is not suitable for viviparous fishes which activate sperm motility within an isotonic environment. In addition, the presence of sperm bundles in viviparous fishes further complicates study of sperm activation mechanisms. The goal of this study was to establish methodologies to detect intracellular Ca2+ signals from sperm cells within bundles, and to investigate the signaling mechanism of sperm activation of viviparous fish using Redtail Splitfin (Xenotoca eiseni) as a model. Motility was assessed by classification of bundle dissociation and computer-assisted sperm analysis, and intracellular Ca2+ was assessed using the fluorescent probe Fura-2 AM. Bundle dissociation and sperm motility increased with extracellular Ca2+ and pH levels. Intracellular Ca2+ signals were detected from sperm within bundles, and increased significantly with extracellular Ca2+ and pH levels. Major channel blockers known to inhibit Ca2+ influx (NiCl2, ruthenium red, GdCl3, SKF-96365, nimodipine, verapamil, methoxyverapamil, mibefradil, NNC 55-0396, ω-Conotoxin MVIIC, bepridil, and 2-APB) failed to inhibit Ca2+ influx, except for CdCl2, which partially inhibited the influx. We propose a novel mechanism for motility regulation of fish sperm: an alkaline environment in the female reproductive tract opens Ca2+ channels in the sperm plasma membrane without osmotic shock, and the Ca2+ influx functions as a second messenger to activate motor proteins controlling flagella movement.

Effects of temperature on sperm motility of burbot Lota lota: spontaneous activation and calcium dependency

Several factors regulating activation of spermatozoon motility in Eurasian burbot, Lota lota, including osmolality, calcium (Ca²⁺ ) ions, and temperature were investigated. Spermatozoon motility in Eurasian burbot, Lota lota was assessed at 4 and 30°C in seminal fluid, isotonic media (with and without Ca²⁺ ) and hypotonic media (with and without Ca²⁺ ). Spermatozoa were spontaneously activated in seminal fluid at 20°C and the maximum motility was recorded at 30°C, which is out of the spawning temperature range, indicating that no risk of activation occurs during routine semen handling in artificial insemination. Initiation of spermatozoon motility in L. lota is mediated by Ca²⁺ and sensitivity to Ca²⁺ is dependent on temperature.

Effects of cryopreservation on cAMP-dependent protein kinase and AMP-activated protein kinase in Atlantic salmon (Salmo salar) spermatozoa: Relation with post-thaw motility

Sperm motility in fish with external fertilization is critical for reproductive efficiency in aquaculture, especially in salmonids. Gamete preservation techniques, such as cryopreservation, however, reduce sperm motility and fertilizing capacity. Very few studies have addressed cryodamage from energetic and cell signalling approaches. In this study, cAMP-dependent protein kinase (PKA) and AMP-activated kinase (AMPK) activities were quantified in fresh and cryopreserved spermatozoa of Atlantic salmon (Salmo salar); and the relation with motility was analysed. Results indicate there was a decrease in membrane integrity and motility in post-thawed spermatozoa compared to fresh samples, however, there was about 30% of cells with intact plasma membrane but incapable of motility. The PKA and AMPK activities were less after cryopreservation, indicating that loss of motility may be related to alteration of these key enzymes. Furthermore, PKA and AMPK activities were positively correlated with each other and with motility; and inhibition decreased motility, indicating there is a functional relationship between PKA and AMPK. The PKA inhibition also decreased AMPK activity, but results from protein-protein docking analyses indicated AMPK activation directly by PKA is unlikely, thus an indirect mechanism may exist. There have been no previous reports of these kinase actions in fish spermatozoa, making these findings worthy of assessment when there are future studies being planned, and may serve as base knowledge for optimization of cryopreservation procedures and development of biotechnologies to improve reproduction efficiency in the aquaculture industry.

Sperm motility in fishes: (III) diversity of regulatory signals from membrane to the axoneme

Fish spermatozoa acquire potential for motility in the sperm duct where they are immotile. Osmolality of the seminal plasma is a key factor to maintain spermatozoa in the quiescent state in either freshwater or marine fishes. However, potassium (K⁺) ions prevent spermatozoa motility in salmonid and sturgeon fishes, while CO₂ inhibits spermatozoa motility in flatfishes. Once, spermatozoa are released at spawning, their motility is initiated in hypo-osmotic and hyper-osmotic environments in freshwater and marine fishes, respectively. Some substances produced by the testes (a progestin), or released from oocytes (peptides) induce spermatozoa hypermotility in some marine fishes including the Atlantic croaker and Pacific herrings, respectively. Duration of spermatozoa motility is short, lasting for a few seconds to few minutes in most fishes due to rapid depletion of energy required for the beating of the motility apparatus called axoneme. In the osmotic-activated spermatozoa, K⁺ and water effluxes occur in freshwater and marine fishes, respectively, which trigger spermatozoa motility signaling. In general, initiation of axonemal beating is associated with an increase in intracellular calcium (Ca²⁺) ions in spermatozoa of both freshwater and marine fishes and a post- or pre-increase in intracellular pH, while cyclic adenosine monophosphate (cAMP) remains unchanged. However, axonemal beating is cAMP-dependent in demembranated spermatozoa of salmonid and sturgeon fishes. Calcium from extracellular environment or intracellular stores supply required Ca²⁺ concentration for axonemal beating. Several axonemal proteins have been so far identified in fishes that are activated by Ca²⁺ and cAMP, directly or mediated by protein kinase C and protein kinase A, respectively. The present study reviews differences and similarities in complex regulatory signals controlling spermatozoa motility initiation in fishes, and notes physiological mechanisms that await elucidation.

Culex pipiens sperm motility is initiated by a trypsin-like protease from male accessory glands

In most animals, sperm are stored in a quiescent state in the male reproductive tract and only initiate motility when released into either the female reproductive tract, or, in the case of broadcast spawners, the external environment. Male accessory gland secretions transferred into the female reproductive tract may provide factors that modulate sperm viability and storage, or aid in sperm competition, as well as activate sperm motility. In several insects, serine proteases have been implicated in activating sperm motility. Our previous studies have shown that, in Culex quinquefasciatus, either a male accessory gland extract or purified trypsin is sufficient to initiate sperm motility in vitro. The objective of this study was to identify and characterize trypsin-like enzymes produced in the Culex male accessory glands. Mass spectrometry was used to analyze accessory gland proteins and this preliminary proteomic analysis identified 4 trypsin-like proteases (trypsin, trypsin4, and two trypsin7 isoforms). When measured with the chromogenic trypsin substrate N_a -benzoyl-L-arginine-ethyl-ester-hydrochloride (BAEE), trypsin-like protease activity in the accessory glands was robust, with a pH optimum of 8. The pH range for the Culex trypsin activity was substantially narrower than a mammalian homologue (porcine pancreatic trypsin). A soybean trypsin inhibitor (SBTI) -agarose affinity column was used to independently identify trypsin-like accessory gland proteins. Several proteins were enriched in the eluate, as detected by silver staining of SDS-PAGE gels. Taken together, these data demonstrate the presence of trypsin-like activity and several trypsin-like proteins in the Culex male accessory glands.

Protein phosphorylation in spermatozoa motility of Acipenser ruthenus and Cyprinus carpio

Spermatozoa of externally fertilizing freshwater fish possess several different modes of motility activation. Spermatozoa of common carp (Cyprinus carpio L.) are activated by hypoosmolality, whereas spermatozoa of sterlet (Acipenser ruthenus) require Ca2+ and low concentration of K+ for motility activation. Intracellular signaling differs between these two species as well, particularly in terms of utilization of secondary messengers (cAMP and Ca2+), and kinase activities. The current study was performed in order to determine the importance of protein phosphorylation and protein kinases for activation of sperm motility in carp and sterlet. Treatment with kinase inhibitors indicates that protein kinases A and C (PKA and PKC) participate in spermatozoa motility of both species. Immunodetection of phospho-(Ser/Thr) PKA substrates shows that phosphorylated proteins are localized differently in spermatozoa of carp and sterlet. Strong phosphorylation of PKC substrate was observed in flagella of sterlet spermatozoa, whereas in carp sperm, PKC substrates were lightly phosphorylated in the midpiece and flagella. Motility activation induced either phosphorylation or dephosphorylation on serine, threonine and tyrosine residues of numerous proteins in carp and sterlet spermatozoa. Proteomic methods were used to identify proteins whose phosphorylation state changes upon the initiation of sperm motility. Numerous mitochondrial and glycolytic enzymes were identified in spermatozoa of both species, as well as axonemal proteins, heat shock proteins, septins and calcium-binding proteins. Our results contribute to an understanding of the roles of signaling molecules, protein kinases and protein phosphorylation in motility activation and regulation of two valuable fish species, C. carpio and A. ruthenus.

Effects of storage time on the motility, mortality and calcium levels of Atlantic salmon Salmo salar spermatozoa

This study estimates spermatozoa mortality, morphology, motility and intracellular calcium levels in Atlantic salmon Salmo salar milt after prolonged storage. Milt samples were preserved at 4° C for 25 days and then evaluated for mortality. Motility remained high for the first 3 days and the mortality was low during the first 5 days of storage. A decrease of >50% in calcium content was observed after 5 days of storage. When spermatozoa were activated, calcium levels increased >200% in relative fluorescence units (RFU); this rate of increase was lost when the samples were stored for extended periods of time and was only partially manifested in a zero calcium solution. The results suggest that in vitro storage of S. salar spermatozoa at 4° C for a period of 3 days preserves motility and limits mortality to levels similar to those of fresh spermatozoa. This method also maintains intracellular calcium storage critical for spermatozoa performance.

Regulation of hamster sperm hyperactivation by extracellular Na+

Mammalian sperm motility has to be hyperactivated to be fertilization-competent. Hyperactivation is regulated by extracellular environment. Osmolality of mammalian semen is higher than that in female reproductive tract; however, the effect of them on hyperactivation has not been investigated. So we investigated the effect of osmotic environment on hyperactivation using hamster spermatozoa at first. Increase in the osmolality of the media (∼370 mOsm) by increasing the concentration of NaCl (∼150 mmol/L) caused the delay of the expression of hyperactivation. When NaCl concentration varied in the same range (75–150 mmol/L) whereas the osmolality was fixed at 370 mOsm by adding mannitol, the delay of hyperactivation occurred dependent on NaCl concentration. Increase in NaCl concentration also caused suppression of curvilinear velocity, bend angle, and sliding velocity of the flagellum at the onset of incubation, suggesting that NaCl concentration affect both activation and hyperactivation in hamster spermatozoa. Hamster sperm intracellular Ca2+ concentration decreased as extracellular NaCl concentration increased, whereas membrane potential and intracellular pH were unaffected by extracellular NaCl concentration. SN-6 and SEA0400, inhibitors of Na+-Ca2+ exchanger (NCX), increased intracellular Ca2+ and accelerated hyperactivation in the presence of 150 mmol/L NaCl. Tyrosine phosphorylation on fibrous sheath proteins was unaffected by extracellular NaCl concentration. These results suggest that extracellular Na+ suppresses hamster sperm hyperactivation by reducing intracellular Ca2+ via an action of NCX in a tyrosine phosphorylation-independent manner. It seems that the removal of suppression by extracellular Na+ leads to the expression of hyperactivated motility.

Control of sturgeon sperm motility: Antagonism between K+ ions concentration and osmolality

Spermatozoa are stored in a quiescent state in the male reproductive tract and motility is induced in response to various environmental stimuli, such as change of osmolality (general case) and a decrease of extracellular K+ in fish from Acipenseridae family. This study was aimed to investigate the relationship between osmolality and extracellular K+ concentration in controlling sperm motility in sturgeon. Pre-incubation of sturgeon sperm for 5s in hypertonic solutions of glycerol, NaCl, or sucrose (each of 335 mOsm/kg osmolality) prepares sturgeon spermatozoa to become fully motile in presence of high concentration of K+ ions (15 mM), which has previously been demonstrated to fully repress motility. Furthermore, presence of 0.5mM KCl during the high osmolality pre-incubation exposure completely prevented subsequent spermatozoa activation in a K+-rich media. Manipulating the transport of K+ ions by the presence of K+ ionophore (valinomycin), it was concluded that once an efflux of K+ ions, the precursor of sturgeon sperm motility activation, is taking place, spermatozoa then become insensitive to a large extracellular K+ concentration.

Role of calcium on the initiation of sperm motility in the European eel

Sperm from European eel males treated with hCGrec was washed in a calcium free extender, and sperm motility was activated both in the presence (seawater, SW) and in the absence of calcium (NaCl+EDTA), and treated with calcium inhibitors or modulators. The sperm motility parameters were evaluated by a computer-assisted sperm analysis (CASA) system, and changes in the [Ca(2+)]i fluorescence (and in [Na(+)]i in some cases) were evaluated by flow cytometry. After sperm motility was activated in a medium containing Ca(2+) (seawater, SW) the intracellular fluorescence emitted by Ca(2+) increased 4-6-fold compared to the levels in quiescent sperm. However, while sperm activation in a Ca-free media (NaCl+EDTA) resulted in a percentage of motility similar to seawater, the [Ca(2+)]i levels did not increase at all. This result strongly suggests that increasing [Ca(2+)]i is not a pre-requisite for the induction of sperm motility in European eel sperm. Several sperm velocities (VCL, VSL, VAP) decreased when sperm was activated in the Ca-free activator, thus supporting the theory that Ca(2+) has a modulatory effect on sperm motility. The results indicate that a calcium/sodium exchanger (NCX) which is inhibited by bepridil and a calcium calmodulin kinase (inhibited by W-7), are involved in the sperm motility of the European eel. Our results indicate that the increase in [Ca(2+)]i concentrations during sperm activation is due to an influx from the external medium, but, unlike in most other species, it does not appear to be necessary for the activation of motility in European eel sperm.

Coordinated Action of Aquaporins Regulates Sperm Motility in a Marine Teleost

In marine teleosts, such as the gilthead seabream, several aquaporin paralogs are known to be expressed during the hyperosmotic induction of spermatozoon motility in seawater. Here, we used immunological inhibition of channel function to investigate the physiological roles of Aqp1aa, Aqp1ab, and Aqp7 during seabream sperm activation. Double immunofluorescence microscopy of SW-activated sperm showed that Aqp1aa and Aqp7 were respectively distributed along the flagellum and the head, whereas Aqp1ab accumulated in the head and in discrete areas toward the anterior tail. Inhibition of Aqp1aa reduced the rise of intracellular Ca(2+), which is independent of external Ca(2+) and normally occurs upon activation, and strongly inhibited sperm motility. Impaired Aqp1aa function also prevented the intracellular trafficking of Aqp8b to the mitochondrion, where it acts as a peroxiporin allowing H2O2 efflux and ATP production during activation. However, restoring the Ca(2+) levels with a Ca(2+) ionophore in spermatozoa with immunosuppressed Aqp1aa function fully rescued mitochondrial Aqp8b accumulation and sperm motility. In contrast, exposure of sperm to Aqp1ab and Aqp7 antibodies did not affect motility during the initial phase of activation, but latently compromised the trajectory and the pattern of movement. These data reveal the coordinated action of spatially segregated aquaporins during sperm motility activation in a marine teleost, where flagellar-localized Aqp1aa plays a dual Ca(2+)-dependent role controlling the initiation of sperm motility and the activation of mitochondrial detoxification mechanisms, while Aqp1ab and Aqp7 in the head and anterior tail direct the motion pattern.

Randomized, triple-blind, placebo-controlled clinical trial examining the effects of alpha-lipoic acid supplement on the spermatogram and seminal oxidative stress in infertile men

OBJECTIVE

To evaluate effects of supplementation with alpha-lipoic acid (ALA) on the spermatogram and seminal oxidative stress biomarkers.

DESIGN

Randomized, triple-blind, placebo-controlled clinical trial.

SETTING

Infertility clinic.

PATIENT(S)

Infertile men.

INTERVENTION(S)

ALA (600 mg) or placebo for 12 weeks.

MAIN OUTCOME MEASURE(S)

Semen analysis, anthropometric, dietary, and physical activity assessments, total antioxidant capacity, and malondialdehyde.

RESULT(S)

At the end of study, the total sperm count, sperm concentration, and motility in the intervention group were significantly higher than in the control group. In the ALA group, the total sperm count, sperm concentration, and motility levels were also significantly increased at the end of study compared with baseline values. However, there were no significant differences in ejaculate volume, normal morphology percentage, and live sperm between groups. ALA supplementation also resulted in a significant improvement in seminal levels of total antioxidant capacity (TAC) and malondialdehyde compared with the placebo.

CONCLUSION(S)

According to the results, medical therapy of asthenoteratospermia with ALA supplement could improve quality of semen parameters. However, further investigation is suggested in this regard.

CLINICAL TRIAL REGISTRATION NUMBER

IRCT2013111010181N3.

Water contaminated with Didymosphenia geminata generates changes in Salmo salar spermatozoa activation times

Didimosphenia geminata ("didymo"), has become a powerful and devastating river plague in Chile. A system was developed in D. geminata channels with the purpose evaluating the effects of water polluted with didymo on the activation of Atlantic salmon (Salmo salar) spermatozoa. Results indicate that semen, when activated with uncontaminated river water had an average time of 60±21s. When using Powermilt, (a commercial activator), times of 240±21s are achieved, while rivers contaminated with D. geminata achieve a motility time of 30±12s. Interestingly enough, the kinetic parameters of VSL, VCL and VAP showed no significant changes under all of the conditions. Furthermore, the presence of D. geminata reduces activation time of the samples as the cells age, indicating increased effects in spermatozoa that are conserved for more than 5 days. D. geminata has antioxidant content, represented by polyphenols; 200ppm of polyphenol were obtained in this study per 10g of microalgae. Spermatozoa exposed to these extracts showed a reduction in mobility time in a dose dependent manner, showing an IC50 of 15ppm. The results suggest an effect on spermatozoa activation, possibly due to the release of polyphenols present in contaminated rivers, facilitating the alteration of sperm motility times, without affecting the viability or kinetics of the cells. These findings have important implications for current policy regarding the control of the algae. Current control measures focus on the number of visible species, and not on the compounds that they release, which this study shows, also have a problematic effect on salmon production.

Regulation of salmonid fish sperm motility by osmotic shock-induced water influx across the plasma membrane

The motility of salmonid fish sperm is initiated by a decrease in the extracellular K(+) concentration. However, our previous studies revealed that salmonid fish sperm motility could be initiated in the presence of an inhibitory concentration of K(+) by drastic osmotic shock induced by suspension in a hypertonic glycerol solution and subsequent dilution in a hypotonic solution (glycerol-treatment). In the present study, we examined if an osmotic shock-induced water influx is involved in the regulation of salmonid fish sperm motility. HgCl2, a common inhibitor of aquaporins (AQPs), decreased the duration of salmonid fish sperm motility. Dilution of sperm cells in a hypotonic solution increased the cellular volume, whereas HgCl2 inhibited such an increase in cellular volume. Furthermore, the expression of AQP 1a and 10 in rainbow trout testes was confirmed. In contrast, HgCl2 did not affect glycerol-treated sperm motility, indicating that AQPs are not involved in glycerol-treated sperm motility. We also explored the possibility of aquaporin-independent water influx in glycerol-treated sperm by assessing the sperm membrane permeability using propidium iodide. The plasma membrane of glycerol-treated sperm was considerably permeabilized. The cellular volume was decreased in a hypertonic glycerol solution and increased upon subsequent hypoosmotic shock, indicating an AQP-independent water flux across the plasma membrane upon glycerol-treatment. Taken together, these results showed that water influx across the plasma membrane via AQP is crucial for the maintenance of salmonid fish sperm motility under normal conditions, whereas water influx by osmotic shock-induced membrane permeation is critical for the initiation of glycerol-treated sperm motility.

The role of Ca(2+) and Na (+) membrane transport in brook trout (Salvelinus fontinalis) spermatozoa motility

The role of environmental ion composition and osmolality in Ca(2+) signaled activation was assessed in spermatozoa of brook trout Salvelinus fontinalis. Milt from ten mature males was obtained by abdominal massage. Spermatozoa motility was evaluated in 0, 100, and 300 mOsm/kg NaCl or sucrose solutions, buffered by 10 mM Tris-HCl pH 8.5. For investigation of spermatozoa reaction to external Ca(2+) concentration, 2 mM ethylene glycol tetraacetic acid (EGTA) was added to the activation media as a calcium ions chelator. For investigation of the effect of external Na(+) concentration in conditions of low external Ca(2+), 100 µM amiloride was added to the EGTA-containing solutions as a Na(+) transport blocker. Low motility was observed in sucrose (Na(+) free) solutions containing 2 mM EGTA but not in Na(+) solutions containing 2 mM EGTA. Addition of amiloride led to significantly increased motility (P < 0.05) compared with sucrose (Na(+) free) solutions containing 2 mM EGTA. We conclude that Na(+) transport in Ca(2+)-free solutions plays a regulatory role in brook trout spermatozoa activation. The influence of competitive Na(+) and Ca(2+) transport on the control of spermatozoa activation requires further study with respect to its application for improvement of artificial activation and storage media.

Exposure to environmentally relevant concentrations of genistein during activation does not affect sperm motility in the fighting fish Betta splendens

Sperm collected from male fighting fish Betta splendens were activated in control water, water containing the ion-channel blocker gadolinium (a putative positive control), or water containing the isoflavone phytoestrogen genistein to determine the effects of acute genistein exposure on male reproductive function. Computer-assisted sperm analysis was used to quantify the proportion of sperm that were motile and the swimming velocity of those sperm. The highest concentration of gadolinium (100 μM) tested was effective at reducing sperm motility and velocity, but neither concentration of genistein tested (3.7 nM or 3.7 μM) significantly affected these sperm parameters. Our findings suggest that acute exposure to waterborne phytoestrogens during activation does not reduce the motility of fish sperm.

Waveform generation is controlled by phosphorylation and swimming direction is controlled by Ca2+ in sperm from the mosquito Culex quinquefasciatus

Most animal sperm are quiescent in the male reproductive tract and become activated after mixing with accessory secretions from the male and/or female reproductive tract. Sperm from the mosquito Culex quinquefasciatus initiate flagellar motility after mixing with male accessory gland components, and the sperm flagellum displays three distinct motility patterns over time: a low amplitude, a long wavelength form (Wave A), a double waveform consisting of two superimposed waveforms over the length of the flagellum (Wave B), and finally, a single helical waveform that propels the sperm at high velocity (Wave C). This flagellar behavior is replicated by treating quiescent sperm with trypsin. When exposed to either broad spectrum or tyrosine kinase inhibitors, sperm activated by accessory gland secretions exhibited motility through Wave B but were unable to progress to Wave C. The MEK1/2 inhibitor UO126 and the ERK1/2 inhibitor FR180204 each blocked the transition from Wave B to Wave C, indicating a role for MAPK activity in the control of waveform and, accordingly, progressive movement. Furthermore, a MAPK substrate antibody stained the flagellum of activated sperm. In the absence of extracellular Ca(2+), a small fraction of sperm swam backwards, whereas most could not be activated by either accessory glands or trypsin and were immotile. However, the phosphatase inhibitor okadaic acid in the absence of extracellular Ca(2+) induced all sperm to swim backwards with a flagellar waveform similar to Wave A. These results indicate that flagellar waveform generation and direction of motility are controlled by protein phosphorylation and Ca(2+) levels, respectively.

Thermosensitive ion channel TRPV1 is endogenously expressed in the sperm of a fresh water teleost fish (Labeo rohita) and regulates sperm motility

Sperm cells exhibit extremely high sensitivity in response to slight changes in temperature, osmotic pressure and/or presence of various chemical stimuli. In most cases throughout the evolution, these physico-chemical stimuli trigger Ca (2+)-signaling and subsequently alter structure, cellular function, motility and survival of the sperm cells. Few reports have recently demonstrated the presence of Transient Receptor Potential (TRP) channels in the sperm cells from higher eukaryotes, mainly from higher mammals. In this work, we have explored if the sperm cells from lower vertebrates can also have thermo-sensitive TRP channels. In this paper, we demonstrate the endogenous presence of one specific thermo-sensitive ion channel, namely Transient Receptor Potential Vanilloid family member sub type 1 (TRPV1) in the sperm cells collected from fresh water teleost fish, Labeo rohita. By using western blot analysis, fluorescence assisted cell sorting (FACS) and confocal microscopy; we confirm the presence of this non-selective cation channel. Activation of TRPV1 by an endogenous activator NADA significantly increases the quality as well as the duration of fish sperm movement. The sperm cell specific expression of TRPV1 matches well with our in silico sequence analysis. The results demonstrate that TRPV1 gene is conserved in various fishes, ranging from 1-3 in copy number, and it originated by fish-specific duplication events within the last 320 million years (MY). To the best of our knowledge, this is the first report demonstrating the presence of any thermo-sensitive TRP channels in the sperm cells of early vertebrates as well as of aquatic animals, which undergo external fertilization in fresh water. This observation may have implications in the aquaculture, breeding of several fresh water and marine fish species and cryopreservation of fish sperms.

The Combinatorial Nature of Osmosensing in Fishes

Organisms exposed to altered salinity must be able to perceive osmolality change because metabolism has evolved to function optimally at specific intracellular ionic strength and composition. Such osmosensing comprises a complex physiological process involving many elements at organismal and cellular levels of organization. Input from numerous osmosensors is integrated to encode magnitude, direction, and ionic basis of osmolality change. This combinatorial nature of osmosensing is discussed with emphasis on fishes.