Adenosine triphosphate in human semen: a study on conditions for a bioluminescence assay**Supported by the Swedish Medical Research Council, Project no. B85-17X-05696-06A, and the World Health Organization Task Force on Infertility, Geneva, Switzerland

Energy Sources for Exosome Communication in a Cancer Microenvironment

Simple Summary

Exosomal communication in the tumor microenvironment plays a crucial role in cancer development, progression, and metastasis, and is achieved by either short-distance communication with neighboring cells or long-distance communication with distant organs. Nevertheless, how exosomes gain energy to establish such communication and the different sources of energy are unclear. Recently, a handful of studies have demonstrated the presence of mitochondria, adenosine triphosphate, and glycolytic enzymes, which may serve as potential energy sources for exosomes. This review clarifies how exosomes maintain their structural integrity and stability during their intracellular communication, and reviews evidence of their energy source.

Abstract

Exosomes are crucial extracellular vesicles (EVs) with a diameter of approximately 30–200 nm. They are released by most cell types in their extracellular milieu and carry various biomolecules, including proteins and nucleic acids. Exosomes are increasingly studied in various diseases, including cancer, due to their role in local and distant cell–cell communication in which they can promote tumor growth, cancer progression, and metastasis. Interestingly, a tremendous number of exosomes is released by malignant cancer cells, and these are then taken up by autologous and heterologous recipient stromal cells such as immune cells, cancer stem cells, and endothelial cells. All these events demand an enormous amount of energy and require that exosomes remain stable while having the capacity to reach distant sites and cross physical barriers. Nevertheless, there is a dearth of research pertaining to the energy sources of exosomes, and questions remain about how they maintain their motility in the tumor microenvironment (TME) and beyond. Moreover, exosomes can produce adenosine triphosphate (ATP), an important energy molecule required by all cells, and mitochondria have been identified as one of the exosomal cargoes. These findings strengthen the prospect of exosomal communication via transfer of mitochondria and the bioenergetics of target recipient cells. In the TME, the accumulation of ATP and lactate may facilitate the entry of exosomes into cancer cells to promote metastasis, as well as help to target cancer cells at the tumor site. This review highlights how exosomes obtain sufficient energy to thrive in the TME and communicate with distant physiological destinations.

Extracellular vesicles and energy metabolism

Glycolytic enzymes are among the most frequently identified proteins in proteomics of exosomes/extracellular vesicles. This review brings up the possibility that exosomes/extracellular vesicles during their life-time in bodily fluids power important energy-consuming functions by glycolytic conversion of glucose or fructose into ATP. It was seen that prostasomes (exosomes of the prostate) could produce ATP by glycolysis and that the produced ATP quickly was consumed by adjacent prostasomal ATPases. The glycolytic ATP production appeared to be coupled to self-sustaining energy requirements. It will also be discussed how a failure in this machinery (lowered activity of ATPases) with a resultant polluting leakage of extracellular ATP could affect cancer development.

Relationship between post-thaw adenosine triphosphate content, motility and viability in cryopreserved bovine semen applying two different preservation methods

Motility and energy level in sperm cells are tightly linked, but not totally understood. The aim of this study was to examine whether adenosine triphosphate (ATP) content as a sperm quality parameter for bull semen could give additional information together with viability and motility. The objective was therefore to examine the relationships between alterations in sperm ATP content, motility and viability in bovine semen samples immediately after thawing and following post-thaw incubation at physiological temperature. Two different cryopreservation methods were compared. Ejaculates from ten young bulls were split into two and cryopreserved using conventional procedure with Biladyl^® (B) extender and with SpermVital^® (SV) immobilization technology. From each sample, simultaneous analysis of ATP content, motility and viability was performed post-thaw (T0) and after incubation at physiological temperature for three hours (T3). Multivariate correlation analysis showed high correlation at T0 between ATP content and viability (p < 0.05), ATP and total motility (p < 0.05), as well as progressive motility and viability (p < 0.05). However, there was no significant correlation between progressive motility and ATP content at T3, neither for B nor SV semen. We conclude that both preservation method and post-thaw incubation at physiological temperature affect ATP level in bull sperm cells partly independent of motility and viability. The ATP level of bovine spermatozoa post-thaw is therefore implicated to give supplementary information of sperm quality.

The immediate impact of semen diluent and rate of dilution on the sperm quality index, ATP utilization, gas exchange, and ionic balance of broiler breeder sperm

The sperm quality index (SQI) is a tool used to predict overall rooster semen quality, fertility, and hatchability. However, semen must be diluted before SQI analysis, and research has shown that the SQI is most predictive of fertility at lower semen dilutions. Therefore, the present study was undertaken to determine why the SQI is not as predictive of fertility at higher semen dilutions and whether semen diluent type alters the SQI, adenosine triphosphate (ATP) utilization, gas exchange, and ionic balance of broiler breeder sperm. Semen was diluted with saline, seminal plasma, or minimum essential medium (MEM) from 2- to 200-fold. The following parameters were measured for each diluent type at each dilution: SQI, ATP, Na+, Ca2+, K+, Cl-, CO2, and O2. To examine the rate of sperm motility, the SQI was expressed as SQI/million sperm per mL (SQI/sperm). There was an interaction between diluent type and dilution for the SQI, SQI/sperm, CO2 generated, O2 used, as well as Na+, Ca2+, and K+ internalization. For sperm diluted with saline, the SQI declined more rapidly with increasing dilution. However, SQI/sperm increased rapidly when semen was diluted with MEM or SP. Sperm diluted in SP used ATP with increasing dilution whereas sperm diluted with saline and MEM generated ATP. Neat semen contained no free O2; however, each diluent type contained abundant O2 resulting in more O2 available as semen was diluted. Sperm diluted in SP produced more CO2 and used more O2 than semen diluted in saline or MEM. For SQI/sperm, ATP and CO2 generated, as well as Na+ and Ca2+ internalization, differences between diluent types occurred when semen was diluted 50-fold and greater. In conclusion, it appears that sperm motility, ATP utilization, gas exchange, and ionic balance are altered by diluent type and rate of dilution. These alterations in semen quality are exacerbated at semen dilutions of 50-fold and greater yielding an SQI that is not indicative of sperm motility or fertility.

Glucose induces a Na(+),K(+)-ATPase-dependent transient hyperpolarization in human sperm. I. Induction of changes in plasma membrane potential by the proton ionophore CCCP

When human sperm was incubated in medium deprived of glucose, glucose restoration caused a transient hyperpolarization of the plasma membrane. This hyperpolarization was also induced by fructose but not by 2-deoxyglucose, a substrate that cannot be metabolized. The hyperpolarization was inhibited by NaF, a glycolysis inhibitor, but not by mitochondrial inhibitors (cyanide, rotenone and antimycin), suggesting that it depended on glycolysis. Furthermore, the hyperpolarization was still induced in medium containing a high concentration of KCl and was insensitive to the K(+) channel blocker TEA and the Cl(-) channel blocker niflumic acid, but it was blocked by ouabain. This suggested that upon glucose addition, there was an increase in the concentration of ATP, that in turns increased the Na(+),K(+)-ATPase activity. Since this pump is electrogenic (2K(+)/3Na(+)) the plasma membrane hyperpolarized. On the other hand, CCCP, a proton ionophore, inhibited the hyperpolarization induced by glucose. When CCCP was added to glucose-treated hyperpolarized sperm, it caused a depolarization that triggered a Ca(2+) influx sensitive to nickel, an inhibitor of voltage-dependent calcium channels. Moreover, CCCP caused hyperpolarization in sperm incubated in medium without calcium, a known condition that depolarizes sperm. This indicated that CCCP induced proton permeability in the plasma membrane that was able to change the membrane potential to a value corresponding to the E(H) and that was also able to clamp it, so that it prevented the hyperpolarization induced by glucose.

Viability and function of human sperm in electrolyte-free cold preservation

OBJECTIVE

To assess the viability and function of human sperm in electrolyte-free cold preservation.

DESIGN

Prospective comparative study.

SETTING

Andrology laboratory of our hospital.

PATIENT(S)

Ten semen samples obtained from patients attending our infertility clinic.

INTERVENTION(S)

Ejaculated sperm were washed using the electrolyte-free Percoll gradient and were then preserved in 0.33 M glucose solution, 0.16 M NaCl solution, 0.16 M KCl solution at 4 degrees C for 4 weeks. As a control, TEST (TES and Tris) yolk buffer (TYB) was added to the ejaculated semen and preserved at 4 degrees C.

MAIN OUTCOME MEASURE(S)

Sperm tail morphology, motility, viability (eosin-Y stain), and the concentration of adenosine triphosphate (ATP) were analyzed.

RESULT(S)

The number of sperm with normal tail form and the motility of sperm preserved in glucose solution (electrolyte-free cold preservation) were significantly (P < 0.01) higher for 4 weeks than those of sperm preserved in the other three media. The sperm viability in glucose solution was 75.5%, 65.4%, and 51.3%, after 1, 2, and 4 weeks, respectively. The ATP concentration after 1, 2, and 4 weeks remained 64.2%, 53.0%, and 4.3% of the prestorage value, respectively, in the sperm stored in glucose solution.

CONCLUSION(S)

The morphology, motility, viability, and ATP concentration of sperm in electrolyte-free cold preservation were substantially better than those in NaCl solution, KCl solution, or TYB for 2 weeks.

Sperm motility and ATP content in seminal hyperviscosity

Objective spermatic motility (Hamilton Thorne Research), the rapid progressive spermatozoa (grade A) recovery after swim-up, and the spermatozoa ATP content (bioluminescence) were studied in normoviscous and hyperviscous asthenospermic samples. The amplitude of lateral head displacement (ALH) was significantly lower in hyperviscous semen (normal: 4.6 +/- 0.7 microns [n = 20], high: 3.5 +/- 1.2 microns [n = 16]; p < .05). The grade A recovery percentage after swim-up was significantly higher in semens with high consistency (normal: 71.0 +/- 38.0 [n = 14], high: 181.3 +/- 108.9 [n = 6]; p < .05). The ATP content per living spermatozoa was in the normal consistency group 449.4 +/- 65.1 pmol per million living spermatozoa (n = 29) and in the high consistency batch 605.1 +/- 242.8 (n = 9), p < .05. In asthenospermia, the spermatozoa from hyperviscous samples have minor ALH values, better response to swim-up, and high ATP content than those from normoviscous ejaculates.

Stimulation of movement and acrosome reaction of human spermatozoa by PC12 liposomes encapsulating ATP

The effect of co-incubating human spermatozoa with 8 mmol/L dilauroylphosphatidylcholine (PC12) liposomes containing 6 mmol/L adenosine 5'-triphosphate (LATP) was assessed by CASA and compared to that obtained with blank PC12 liposomes (LB). The aim of this study was to investigate if such treatments can improve sperm movement and sustain sperm motility over time. Significant and similar increases in straight-line velocity and linearity of sperm movement in B2 capacitating medium (both p < 0.01) were obtained with LB and LATP treatments (final concentration: 0.38 mmol/L PC12 and 0.5 mmol/L ATP) while in Tyrode's medium supplemented with 10 mg/mL BSA, these movement parameters were increased significantly only in sperm aliquots treated with LATP. Furthermore, after incubation for 0.5 h in Tyrode's, a bioluminescence assay of intracellular ATP indicated no significant change in ATP concentration for LATP-treated spermatozoa while the ATP content of control and LB-treated spermatozoa decreased significantly during the same period (both p < 0.05). The effect of liposomes on the acrosome reaction was also investigated jointly with CASA. These experiments were performed by fluorescence microscopy, using PSA-FITC and the supravital stain Hoechst 33258. After a precapacitation period of 3 h in BWW medium the spermatozoa were incubated for 1 h with LATP, LB, LB+free ATP and free ATP alone (final concentration 0.5 mmol/L ATP). Under these conditions the percentage of acrosome-reacted spermatozoa was increased similarly after LATP and LB treatments compared to control (respectively from 4.9 to 12%, p < 0.01 and 4.9 to 11.3%, p < 0.05) but the percentage of true acrosome-reacted spermatozoa, and the values for all movement characteristics (except percentage motility) were increased significantly only with LATP treatment. The results indicate the potential of PC12 vesicles for introducing highly hydrophilic compounds into spermatozoa, as well as for modulating membrane structures and functions required for fertilization.

Sperm adenosine triphosphate concentrations before and after freezing as a marker of cryolysis

Frozen semen samples are generally used today for artificial insemination and in vitro fertilization (IVF) and have various advantages above freshly produced semen. A disadvantage is that substances may leak out of the sperm if the membrane is damaged during freezing. In this study sperm ATP concentration was determined before freezing and after thawing and correlated with fertilization in an IVF program. After freezing and thawing the average sperm motility decreased significantly (p < or = .0001). Sperm ATP concentration was also significantly lower after freezing and thawing (p = .0004). Sperm ATP concentration after thawing did not correlated with fertilization. ATP concentration was a good marker of cryolysis but not of fertilization.

Reversible intracellular ATP changes in intact rat spermatozoa and effects on flagellar sperm movement

The initiation of motility and modification of energy metabolism of rat caudal epididymal spermatozoa can be induced by dilution in a saline medium. We have investigated in these cells the relationships between the energy reserve (sperm ATP content measured by bioluminescence) and flagellar movement (high speed videomicrography, 200 frames/sec). A steady state was observed in sperm ATP content, progressive velocity (Vp) and flagellar beat frequency (F) with sperm dilution in a medium with glucose, lactate, pyruvate and acetate substrates after 30 minutes of incubation. Without these substrates, changes in metabolic pathways occurred immediately and initially disturbed the relationship between ATP levels and F, suggesting differences in motility initiation when energy is from an endogenous origin via mitochondrial oxidative phosphorylation. This "energy crisis" was reversed by the addition of substrates to the medium. The three-dimensional flagellar movement observed in the presence of substrates quickly became two-dimensional in their absence. The flagellar beat envelope became more splayed, the mean amplitude of lateral head displacement increased and F decreased. The resulting high flagellar beat efficiency can be compared to that observed during hyperactivation which is a physiological event related to a fall in intracellular ATP level. In both media, the displacement of the flagellum in relation to the wave axis varied sinusoidally. The sine period increased with time when the spermatozoa were incubated in the medium without substrates. These results suggest a gradual slowing-down of the velocity of wave formation in the proximal part of the flagellum.

Adenosine triphosphate (ATP) in human spermatozoa

The seminal adenosine triphosphate (ATP) content was determined by bioluminescence after treatment with trichloroacetic acid (TCA) in 81 semen samples 1.5 h after ejaculation obtained from men attending our fertility clinic, and selected to contain either 20% or less spermatozoa with good progressive motility (n = 22), or 60% or more spermatozoa with good progressive motility (n = 59) (Study I), and in 18 semen samples from fertile men 30 min and 3.5 h after ejaculation (Study II). The latter samples were divided into 2 equally large groups according to sperm motility. In Study I the mean sperm ATP concentration was significantly higher in the semen samples with bad motility (0.63 nmol per living spermatozoa x 10(-6)) than in semen samples with good motility (0.39 nmol per living spermatozoa x 10(-6); P less than 0.01). In Study II the ATP concentration per living spermatozoa was also lower in the group with the best motility in comparison with the spermatozoa with lower motility (P less than 0.01), both 30 min and 3.5 h after ejaculation. During the 3-5 h incubation the sperm ATP concentration decreased by 21% (P less than 0.01) in the former group of samples but remained unchanged in the latter group. The results indicate that, in semen samples with highly motile spermatozoa, the consumption of ATP is higher than in semen samples with impaired sperm motility. It is therefore essential that the time between ejaculation and ATP measurement is as short as possible to obtain comparable results. Repeated ATP measurements in combination with an analysis of the number of living spermatozoa, may provide further information on the fertilizing capacity of spermatozoa.

Effects of pH on the reactivation of human spermatozoa demembranated with Triton X-100

The aim of this work was to study the role of different parameters involved in the motility of human spermatozoa. Human spermatozoa were totally demembranated with 0.05% Triton X-100, and the demembranation was checked using electron microscopy. We have shown that, with a concentration of ATP-Mg lower than 2 mM, a pH effect was observed with a dose-dependent motility reactivation at pH 7.1, with 14% +/- 2.0% motile cells at 1 mM ATP-Mg and a straight line velocity (VSL) of 12.0 +/- 1.4 microns/sec. However, at pH 7.8, more than 65% of the spermatozoa were reactivated with as low as 0.02 mM ATP-Mg and 77.8% +/- 2.5% of them were motile at 1 mM ATP-Mg and had a VSL of 23.4 +/- 3.9 microns/sec. The depletion of free calcium by the addition of 0.5 mM EGTA in the reactivation medium (RM) improved the percentage of motile cells and the VSL most markedly at low ATP-Mg and low pH. If no MgSO4 was added in RM, cells were not motile at pH 7.8, but 30-40% reactivated at pH 7.1. If 5 mM Ca2+ was added to the RM, up to 88% of the cells became reactivated at both pHs, but the beat frequencies were very low, suggesting different mechanisms of reactivation when Mg2+ or when Ca2+ is present in the RM.

Control of anion and fluid secretion by apical P2-purinoceptors in the rat epididymis

1. Exogenous adenosine triphosphate (ATP) stimulated the short circuit current (SCC) in primary monolayer cultures of rat epididymal cells when added to the apical but not to the basolateral side of the monolayers. Half-maximal stimulation was achieved at 5 x 10(-8) M ATP. 2. The increase in SCC induced by ATP was dependent on the presence of extracellular Cl in the bathing solutions. 3. The effects of other adenosine derivatives, and purine and pyrimidine nucleotides were studied. Their orders of potency in stimulating SCC were: ATP greater than adenosine diphosphate much greater than adenosine monophosphate, adenosine, and ATP greater than inosine triphosphate greater than guanosine triphosphate greater than cytidine triphosphate. These results indicate that ATP interacts with a P2-purinoceptor at the apical membrane of the epididymal cells. 4. The SCC response to ATP was not blocked by 8-phenyltheophylline, a P1-purinoceptor antagonist or by propranolol. Although pretreatment of the cultures with piroxicam abolished the SCC response to bradykinin, it did not affect the response to ATP. This indicates that the SCC response to ATP was not mediated by an increase in the synthesis of prostaglandins. 5. Serosal to mucosal Cl flux (Js-m Cl) and net water flux were measured in the luminally perfused rat epididymis in vivo. ATP (1 microM) added to the luminal perfusion solution caused an increase in Js-m Cl and net water secretion by the epididymal duct. 6. Since spermatozoa contain a high concentration of ATP, it is proposed that ATP released from spermatozoa may affect anion and fluid secretion by the epididymis. The control of secretion via the apical purinoceptors offers a means by which spermatozoa regulate the fluidity of their own environment.

Clinical and biochemical applications of luciferases and luciferins

Recent advances in the analytical applications of bacterial and firefly luciferases and firefly luciferin are reviewed. Luciferases have been used in soluble and immobilized/co-immobilized forms in assays for a variety of enzymes, substrates, and cofactors. The firefly luciferase reaction forms the basis of rapid microbiological tests which have found application in susceptibility testing, detection of bacteriuria, activated sludge analysis, and food testing. Rapid microbiological assays are also possible using bacteriophages containing the lux genes from Virbrio harveyi. Both the firefly and the bacterial luciferase reaction have been applied in immunoassay and DNA probe assays and the firefly luciferin phosphate substrate for alkaline phosphatase labels has proven particularly successful.

The effects of oral administration of prostaglandin E2 on the human ejaculate

A single 1 mg dose of prostaglandin (PG) E2 was given orally to 19 men. Ejaculates were obtained 90 minutes and 24 and 48 hours thereafter. Before treatment, each man delivered another three semen samples with the same time intervals as during the study period. PGE2 was also administered to seven men during naproxen treatment and ejaculates were sampled as above. PGE2 did not influence the 90 minutes' posttreatment ejaculates, but after 24 hours there was a significant (P less than 0.05) decrease in sperm counts as compared to the control samples. The change in sperm count was suggested to be due to an effect of PG on the contractile elements in the deferent duct. Sperm motility, viability, and morphology as well as semen volume and adenosine triphosphate (ATP) content remained unchanged. The total semen PGE content was increased 24 hours after treatment from 169 micrograms/ejaculate to 213 micrograms/ejaculate (P = 0.02). In the combined PGE2/naproxen treatment the PGE levels were significantly (P less than 0.05) elevated in the ejaculate 48 hours after treatment. The increase may indicate an increased de novo synthesis of prostaglandins. Based on the results from the analysis of the composition of the 19-hydroxy PGF-isomers with and without naproxen treatment, it is speculated that oral PGE2 influences the cyclo-oxygenase activity.

Effect of prostaglandins on human sperm function in vitro and seminal adenosine triphosphate content

The aim of the present study was to evaluate the effect of addition of physiologic amounts of different prostaglandins normally present in semen, on sperm motility, on sperm penetration capacity in cervical mucus in vitro, and on the adenosine triphosphate (ATP) concentration in semen. Semen samples were obtained from volunteers who were attending the fertility outpatient clinic. Sperm motility was measured on a video recorder with a built-in timer, sperm penetration by the Kremer test, and ATP by bioluminescence assay. The addition of 19-hydroxy prostaglandin (PG) E to ejaculates positively stimulated sperm motility and sperm penetration capacity. The opposite effect was observed with 19-hydroxy PGF. PGE1, PGE2, and PGF2 alpha had no effect on either parameter, while PGF1 alpha reduced the sperm motility. The addition of 19-hydroxy PGE to ejaculates increased and the addition of 19-hydroxy PGF reduced semen concentrations of ATP. However, only the last-mentioned effect was statistically significant (P less than 0.05). It is suggested that, in particular, 19-hydroxy PGE and 19-hydroxy PGF are important regulators of sperm motility and that the effect may be mediated via effects on the ATP content in the spermatozoa.