Glutathione metabolism in cultured Sertoli cells and spermatogenic cells from hamsters

In vitro study of doxorubicin-induced oxidative stress in spermatogonia and immature Sertoli cells

Pediatric chemotherapy treatments can impair long-term male fertility. Unfortunately, no fertility preservation solution is available for pre-pubertal boys. Studies suggest that doxorubicin, used against pediatric cancers, induces oxidative stress in the testis. However, the targeted testicular cell types remain unknown. The goal of this study was to determine whether doxorubicin can induce oxidative stress in rat spermatogonia (GC-6Spg) and immature Sertoli (Ser-W3) cell lines, and to assess their protection by antioxidants. Using the MTT assay, we have shown that doxorubicin induces a time- and dose-dependent cytotoxicity in these two cell lines, Ser-W3 being more sensitive than GC-6Spg. After 3 h of treatment, reactive oxygen species and nuclear 8-oxo-deoxyguanosine increase in Ser-W3, but not in GC-6Spg. Moreover, after 6 h of treatment, intracellular reduced glutathione levels decrease significantly in Ser-W3 cells. These results show that doxorubicin induces oxidative stress in the Ser-W3 cell line. However, a depletion in glutathione does not affect their survival, and supplementation only offers a weak protection after exposure to doxorubicin, suggesting that the glutathione system is not essential for Ser-W3 cell line's defense against doxorubicin. On the other hand, among four antioxidants selected from the literature, none reduces the cytotoxicity of doxorubicin in Ser-W3 cells. Together, our data suggest that oxidative stress may not be a major pathway for doxorubicin's cytotoxicity in GC-6Spg and Ser-W3 lines. This study provides new insights in the mechanisms by which chemotherapies affect the pre-pubertal testis, with the long-term goal to help improve the quality of life of pediatric cancer survivors.

Bisphenol A effect on glutathione synthesis and recycling in testicular Sertoli cells

BACKGROUND AND OBJECTIVE

Controversial effects of bisphenol A (BPA) have been reported on testicular function. These differences might reflect dissimilar exposure conditions. Dose responses to toxicants may be non-linear, e.g. U-shaped, with effects at low and at high levels of exposure and lower or inexistent effects at intermediate levels. Sertoli cells produce high levels of glutathione (GSH) as a cell defense mechanism. In this study, we addressed the question whether the exposure to different doses of BPA could influence Sertoli cell GSH synthesis and recycling.

MATERIALS AND METHODS

Primary Sertoli cell cultures were exposed to various doses of BPA (0.5 nM-100 μM). Cell viability was measured as an outcome of toxic effect. GSH cell content was determined to evaluate cell response to toxicant exposure. Glutamate-cysteine ligase catalytic (GCLC) and modulatory (GCLM) subunit expression were assessed to estimate GSH synthesis, and GSH reductase (GR) expression to estimate GSH recycling.

RESULTS

BPA 100 μM, but not lower doses, decreased cell viability. BPA 10 and 50 μM, but not lower doses, induced an increment in Sertoli cell GSH levels, due to a rapid upregulation of GCLC and GR and a slower upregulation of GCLM.

CONCLUSIONS

High doses of BPA are deleterious for Sertoli cells. Intermediate doses do not affect Sertoli cell viability and increase cell content of GSH owing to increased GSH synthesis and recycling enzyme expression. Lower doses of BPA are not capable of eliciting a cell defense response. These observations may explain a non-linear dose response of Sertoli cells to BPA.

FSH and bFGF stimulate the production of glutathione in cultured rat Sertoli cells

Migration of developing germ cells from the basal to the adluminal compartment of the seminiferous epithelium requires extensive tissue restructuring, resulting in the production of reactive oxygen species. Sertoli cells are involved in this process. Glutathione (GSH), produced by Sertoli cells, has an essential role in cell protection against oxidative stress. Intracellular GSH content is maintained by de novo synthesis, involving glutamate-cysteine ligase catalytic (GCLC) and modulatory (GCLM) subunits, and by recycling from oxidized GSH, catalysed by glutathione reductase (GR). To assess whether follicle-stimulating hormone (FSH) and basic fibroblast growth factor (bFGF) modulate GSH production in Sertoli cells by regulating the expression of GCLC, GCLM and/or GR, we performed in vitro studies using rat Sertoli cells in primary culture. FSH and bFGF stimulation increased Sertoli cell GSH levels after 24 h incubation. The simultaneous addition of FSH and bFGF did not produce any further effect. GCLM expression was upregulated by FSH and bFGF 6 h. At 24 h, only the FSH-mediated effect was still observed. FSH and bFGF also upregulated GR expression. In conclusion, our results show that FSH and bFGF increase GSH levels in Sertoli cells through stimulation of the de novo synthesis and recycling by upregulating GCLM and GR expression respectively. Therefore, protection of germ cells against oxidative stress seems to be regulated by hormones and germ cell-released growth factors capable of influencing the production of Sertoli cell GSH.

Glutathione peroxidase (GPX) activity in seminal plasma of healthy and infertile males

Human spermatozoa are more dependent on glutathione peroxidase/glutathione reductase (GPX/GR) system, via reduced glutathione (GSH), to inactivate reactive oxygen metabolites (ROMs) such as hydrogen peroxide and organic hydroperoxides. To demonstrate whether there is a substantial difference in GPX activity between normal and pathological seminal plasma, we decided to evaluate the activity of this enzyme in healthy subjects and infertile males with normal hormonal patterns. Our results demonstrate that in healthy subjects the seminal plasma contains a GPX activity that is about 10 times greater than the GPX activity detected in the seminal plasma of infertile males. By using specific antibodies against plasmatic GPX (GPX3), we also demonstrate that enzymatic activity, detected in the seminal plasma of both healthy and infertile males is GPX3. Therefore, the evaluation of GPX activity in human seminal plasma could be a new useful marker of gonadal function in men.

Oxidative stress, spermatogenesis and fertility

Reactive oxygen species production and glutathione depletion in mammalian male germ cells are physiological events that are requisite to the functional maturation and capacitation of spermatozoa. In relation to this oxidative stress, an oxidation of the bulk of protein sulfydryl groups takes place during the final phases of male germ cell maturation. The selenoenzyme phospholipid hydroperoxide glutathione peroxidase catalyzes this reaction, and accounts for both the assembly of the mid-piece of spermatozoa and chromatin condensation. This process highlights the role of H2O2 and selenium in spermatogenesis and provides a mechanism for coupling a 'physiologically controlled' oxidative stress to a specialized phenotypic function.

Human oviductal cells produce a factor(s) that maintains the motility of human spermatozoa in vitro

OBJECTIVE

To characterize in part the factor(s) in conditioned medium (CM) that maintains sperm motility after human oviductal cell culture.

DESIGN

Controlled, experimental, laboratory study.

SETTING

University-based gynecology unit.

PATIENT(S)

Fallopian tubes were obtained from patients who underwent tubal ligation or hysterectomy. Semen with normal sperm parameters was obtained from men who visited subfertility clinics.

INTERVENTION(S)

Spermatozoa were incubated with CM and their motility was evaluated by a computer-aided sperm analysis system.

MAIN OUTCOME MEASURE(S)

Curvilinear velocity, straight-line velocity, average path velocity, linearity, amplitude of lateral head displacement, beat cross-frequency, and percentage of spermatozoa that exhibited hyperactivation.

RESULT(S)

Compared with their baseline motility (0 hour), spermatozoa incubated with CM maintained various motility parameters for a longer period than did control spermatozoa. All the motility parameters of the CM-treated spermatozoa were higher than those of the control spermatozoa at the same time point. This effect of CM was dose-dependent and increased with the duration of incubation. The effect was stable at 56 degrees C but was not observed after 100 degrees C heat treatment. Trypsin, but not proteinase K, abolished the effect. A fraction with a molecular weight of <3 kd in the CM was responsible for the observed effect.

CONCLUSION(S)

Human oviductal cells produce a peptide(s) that maintains sperm motility.

Antioxidant systems in rat epididymal spermatozoa

Mammalian caput and cauda epididymidal spermatozoa exhibit diverse stages of maturation, and their plasma membrane shows diverse composition and stability levels, thus enabling these spermatozoa to undergo the acrosomal reaction after transit through the epididymis. As a result, the study of antiperoxidative mechanisms is quite relevant, since epididymal spermatozoa must be properly protected against agents such as reactive oxygen species, which can impair the complex maturation process. We considered activities of certain enzymes (glutathione peroxidase [GPx], phospholipid hydroperoxide glutathione peroxidase [PHGPx], glutathione reductase [GR], superoxide dismutase [SOD], and catalase [CAT]) and the vitamin E content in isolated rat caput and cauda epididymidal spermatozoa. The results indicate that caput epididymidal sperm have significantly greater PHGPx (3.5x), GPx (2.4x), and SOD (1.7x) activities, as well as a greater amount of vitamin E (3.8x). There were no detectable differences in the GR and CAT activities of caput and cauda epididymidal spermatozoa. The substantial drop in PHGPx activity during epididymal transit is discussed in relation to an additional function of this enzyme: the use of caput sperm protamines as a sulfhydryl substrate. In vitro peroxidation of the two sperm populations by the free radical generator (azo-initiator) 2,2'-azobis(2-amidinopropane) dihydrochloride revealed that only about 13% of the vitamin E content of the caput epididymidal spermatozoa was consumed, which contrasts with the greater consumption (about 70%) of the vitamin in cauda epididymidal spermatozoa. Selective inhibition of PHGPx, SOD, or CAT did not change this picture. The higher susceptibility of cauda epididymidal spermatozoa to radicals is discussed in relation to the diverse enzymatic activities, vitamin E content, and peroxidative response. These factors are correlated with the different stages of sperm cell maturation, which are characterized-from caput to cauda epididymidis-by progressive destabilization of the plasma and acrosomal membranes.

Rat testicular extracellular superoxide dismutase: its purification, cellular distribution, and regulation

Using multiple HPLC steps, we have identified and purified a 68-kDa polypeptide (as estimated by gel permeation HPLC) to apparent homogeneity, from primary Sertoli cell-enriched culture medium, that consisted of two monomers of 35 (alpha chain) and 33 kDa (ss chain) on SDS-polyacrylamide gel running under reducing conditions. Partial N-terminal amino acid sequence analysis of these two monomers revealed sequences of NH2-DXGESGVDLADRL (SODEX-alpha) and NH2-XXDTGESGVDLADXL (SODEX-ss), which are identical to rat extracellular superoxide dismutase (SODEX) with the exceptions that SODEX-alpha and SODEX-ss are missing, respectively, four (Trp-Thr-Met-Ser) and two (Trp-Thr) amino acids from their N-termini, compared to rat SODEX, suggesting that the cleavage sites of the SODEX gene in the testis are different from that of other organs. Studies by sequential use of reverse transcription and polymerase chain reaction (PCR) using two SODEX primers have demonstrated the expression of SODEX in the heart, brain, lung, kidney, epididymis, testis, Sertoli, and germ cells, with low expression in the liver and ovary and no expression in the uterus, spleen, or thymus. Nucleotide sequence analysis of this 447-base pair PCR product from Sertoli cells revealed that its sequence is equivalent to the sequence of previously published rat SODEX. During testicular maturation, the SODEX steady-state mRNA level increased significantly from 20 to 60 days of age and then declined at 90 days of age. Such an increase in the testicular SODEX expression during maturation is not likely a result of an up-regulation by germ cells, since germ cells isolated from either 20- or 60-day-old rats when cocultured with Sertoli cells failed to elicit an increase in SODEX expression in the cocultures. Using primary Sertoli cell cultures in vitro, it was found that Sertoli cell SODEX expression was stimulated by interleukin-1alpha but not by either interferon-gamma or basic fibroblast growth factor. These results illustrate that Sertoli cells as well as germ cells synthesize and/or secrete a testicular variant of SODEX that may provide essential clues to understanding superoxide radical-mediated damage in the gonad.

Antioxidant system in rat testicular cells

The activity of the enzymes involved in the antioxidant defence--superoxide dismutase (SOD), glutathione peroxidase (GPx), reductase (GR), S-transferase (GST)--as well as the glutathione (GSH) levels were measured in different rat testicular cell populations. A differential distribution of these components among testicular cell types was clearly observed. Sertoli and peritubular cells had elevated SOD and GSH-dependent enzyme activities associated with a high GSH content. Compared with the somatic cells, pachytene spermatocytes (PS) and round spermatids (RS) presented a different antioxidant system characterized by higher SOD activity and GSH content associated with very low GSH-dependent enzyme activity. Spermatozoa exhibited the same enzymatic system as PS and RS but were devoid of GSH. Interstitial tissue displayed high GSH content, moderate SOD and GSH-related enzyme activity except for GPx which was very elevated. It is concluded that the different categories of testicular cells probably display a highly variable susceptibility to oxidative stress.

Epithelial cell coculture and the induction of sperm capacitation

OBJECTIVE

To investigate the influence of cultured human oviductal epithelial cells on the movement characteristics of human spermatozoa.

DESIGN

Human spermatozoa were cultured with monolayers of human epithelial or Vero cells or conditioned media derived from these cell types. The viability and movement characteristics of the cells was subsequently analyzed at 4, 24, and 48 hours.

SETTING

University hospital and Medical Research Council laboratories.

PATIENTS, PARTICIPANTS

Volunteer donors.

MAIN OUTCOME MEASURES

Movement characteristics of human spermatozoa.

RESULTS

The presence of both Vero and oviductal epithelial cells, but not conditioned media, had a general promoting effect on sperm survival, significantly enhancing sperm viability and motility for up to 48 hours of culture. In addition, the presence of oviductal epithelial cells had a specific, significant stimulatory effect on sperm capacitation, enhancing the incidence of hyperactivated motility after 4, 24, and 48 hours of culture. Significantly, this effect was not observed with cocultures containing Vero cells.

CONCLUSIONS

The coincubation of human spermatozoa with human oviductal epithelial cells provides a convenient system for the induction and analysis of sperm capacitation.

Induction and repair of DNA single-strand breaks and DNA base damage at different cellular stages of spermatogenesis of the hamster upon in vitro exposure to ionizing radiation

Alkaline elution has been used for quantitative detection of DNA damage caused by ionizing radiation in unlabeled somatic and germ cells. Both the induction and subsequent repair have been studied for two classes of DNA damage, viz. single-strand breaks (SSB), and base damage (BD) recognized by the gamma-endonuclease activity in a cell-free extract of Micrococcus luteus bacteria. The high sensitivity of the assay permitted the measurement of induction and repair of SSB and BD after in vitro exposure of hamster germ cells in different cellular stages of spermatogenesis (spermatocytes, round and elongated spermatids), and of bone-marrow cells, to biologically relevant doses (0-8 Gy) of 60Co gamma-rays. A dose-dependent increase was observed for both types of lesions, which was similar for most cell types. The elongated spermatids, however, showed a lower induction frequency of SSB (and perhaps BD). Spermatocytes, round spermatids and bone-marrow cells had normal, fast repair of the SSB when compared with the repair reported for cultured rodent cells and human lymphocytes. In contrast, the elongated spermatids showed hardly any SSB repair. The initial rate of repair of BD in spermatocytes and bone-marrow cells was in the same range as that for SSB, but only 60-70% of the initial BD was repaired within 1 h, whereas after that period no SSB were detectable. The round spermatids hardly repaired any BD within the first hour after irradiation, but after 7 h only a few BD could be detected. In elongated spermatids repair of BD could not be measured due to a high background level of this type of damage.

Role of glutathione in the maturation and fertilization of pig oocytes in vitro

The present study examined, by treatment of buthionine sulfoximine (BSO), which is a specific inhibitor of glutathione (GSH) synthesis, the role of GSH in the maturation and fertilization of pig oocytes in vitro. Follicular oocytes collected from prepubertal gilts at a local slaughterhouse were cultured for 36 h in Waymouth MB 752/1 with or without BSO (1 mM), fertilized in vitro, and assessed for GSH concentration (before insemination), maturation, and fertilization. The addition of BSO to maturation medium immediately after culture (Group I), 12 h after culture (Group II), or 24 h after culture (Group III) significantly decreased the GSH concentration in pig oocytes compared with the control (P < 0.01), whereas the rate of cumulus mass expansion at 36 h of culture and the rates of nuclear maturation and sperm penetration following in vitro insemination did not differ. However, the rate of pig oocytes having condensed sperm heads was significantly lower and the rate of male pronucleus formation of pig oocytes was significantly higher in oocytes matured in the control and Group III than in oocytes matured in Groups I and II (P < 0.01). In experiment 2, when BSO was added to maturation media 15, 18, 21, or 24 h after culture, the rate of pig oocytes having condensed sperm heads was significantly lower and the rate of male pronucleus formation of pig oocytes was significantly higher in oocytes matured in the medium supplemented with BSO at 21 or 24 h of culture than in oocytes matured in other groups (P < 0.05 or P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

DNA cell cycle distribution and glutathione (GSH) content according to circadian stage in bone marrow of cancer patients

DNA cell cycle distribution and glutathione (GSH) content in bone marrow were measured both at daytime and midnight over single 24 h periods in 15 cancer patients. Between patients the S-phase demonstrated a difference from lowest to highest value of 700%, whereas the corresponding difference for the G2/M-phase was nearly 900%. The mean GSH content measured in the bone marrow at the two timepoints was 2.24 +/- 0.21 nmol mg-1 protein, range 0.91-4.19 nmol mg-1 protein. A statistically significant higher fraction of cells in S-phase and G2/M-phase was found at daytime as compared to midnight when excluding the four patients with an abnormal circadian variation in cortisol. No significant temporal variation in total bone marrow GSH content was found, although a weak correlation between S-phase and GSH content was demonstrated (r = 0.42; P less than 0.05). This correlation was strengthened when not including the six patients with an abnormal cortisol pattern (4) and bone marrow infiltration (2) (r = 0.66; P = 0.005). Cells in S-phase demonstrated a positive correlation with cells in G2/M-phase (r = 0.64; P less than 0.0001). A negative correlation was found between GSH content and age (r = 0.53; P less than 0.005). Finally, a statistically significant positive correlation was demonstrated between cortisol and both S-phase and G2/M-phase (r = 0.57; P less than 0.001 and r = 0.38; P less than 0.05, respectively). The present study suggests a possibility of optimising cancer therapy and use of hematopoietic growth factors by determining individual average values and circadian stage dependent variation in bone marrow DNA cell cycle distribution. Furthermore, GSH content in bone marrow may predict this tissue's sensitivity to cytotoxic agents.

Comparative aspects of spermatogenic cell metabolism and Sertoli cell function in Xenopus laevis and mammals

Due to the relative dearth of data regarding somatic cell-germ cell interactions in the testes of non-mammalian chordates, functional homologies between Sertoli cells from diverse organisms have been difficult to assess. However, recent developments in non-mammalian testis cell and organ culture techniques have provided experimental approaches to compare Sertoli cell-germ cell interactions in different vertebrates. Data from in vitro analyses of Sertoli cell-germ cell interactions are presented to suggest that Sertoli cells from rodents and the frog Xenopus laevis have similarities in supporting energy metabolism and glutathione metabolism in spermatogenic cells. Comparative in vitro analyses of Sertoli cell functions should provide further insights into the evolution of cell-cell interactions in the testes.

Immunochemical detection of DNA damage induction and repair at different cellular stages of spermatogenesis of the hamster after in vitro or in vivo exposure to ionizing radiation

An immunochemical method has been used to detect quantitatively DNA damage caused by ionizing radiation in germ cells. With this method, DNA strand breaks as well as lesions converted into breaks in alkaline medium are measured as a function of controlled partial unwinding of the DNA, a time-dependent process starting at each breakage site, followed by the determination of the relative amount of single-stranded regions by use of a single-strand specific monoclonal antibody. With this method the induction and repair of DNA damage in different cellular stages of spermatogenesis (spermatocytes, round and elongated spermatids) of the hamster were investigated. Germ cells were irradiated in vitro with 60Co-gamma-rays, at doses between 0 and 5 Gy. A linear dose-response relationship was observed. Spermatocytes and round spermatids had normal, fast repair of the lesions when compared with the repair of these sites in cultured V79 or CHO cells and human lymphocytes. The elongated spermatids, however, showed hardly any repair. Similar results were obtained after the in vivo gamma-irradiation of hamsters with doses of 0. 4, and 8 Gy and subsequent isolation of germ cells. The damage was still detectable in the elongated spermatids at 24 h after exposure. The results of the experiments show substantial differences in repair capacity between different stages of germ cell development. Because DNA is the major target for mutation induction, this assay may be useful for assessment of the genetic risk of exposure of male germ cells to ionizing radiation, in relation to the stage of development.

Glutathione deficiency produced by inhibition of its synthesis, and its reversal; applications in research and therapy

Glutathione, which is synthesized within cells, is a component of a pathway that uses NADPH to provide cells with their reducing milieu. This is essential for (a) maintenance of the thiols of proteins (and other compounds) and of antioxidants (e.g. ascorbate, alpha-tocopherol), (b) reduction of ribonucleotides to form the deoxyribonucleotide precursors of DNA, and (c) protection against oxidative damage, free radical damage, and other types of toxicity. Glutathione interacts with a wide variety of drugs. Despite its many and varied cellular functions, it is possible to achieve therapeutically useful modulations of glutathione metabolism. This article emphasizes an approach in which the synthesis of glutathione is selectively inhibited in vivo leading to glutathione deficiency. This is achieved through use of transition-state inactivators of gamma-glutamylcysteine synthetase, the enzyme that catalyzes the first and rate-limiting step of glutathione synthesis. The effects of marked glutathione deficiency, thus produced in the absence of applied stress, include cellular damage associated with severe mitochondrial degeneration in a number of tissues. Such glutathione deficiency is not prevented or reversed by giving glutathione. The cellular utilization of GSH involves its extracellular degradation, uptake of products, and intracellular synthesis of GSH. This is a normal pathway by which cysteine moieties are taken up by cells. Glutathione deficiency induced by inhibition of its synthesis may be prevented or reversed by administration of glutathione esters which, in contrast to glutathione, are readily transported into cells and hydrolyzed to form glutathione intracellularly. Research derived from this model has led to several potentially useful therapeutic approaches, one of which is currently in clinical trial. Thus, certain tumors, including those that exhibit resistance to several drugs and to radiation, are sensitized to these modalities by selective inhibition of glutathione synthesis. An alternative interpretation is suggested which is based on the concept that some resistant tumors have high capacity for glutathione synthesis and that such increased capacity may be as significant or more significant in promoting the resistance of some tumors than the cellular levels of glutathione. Therapeutic approaches are proposed in which normal cells may be selectively protected against toxic antitumor agents and radiation by cysteine- and glutathione-delivery compounds. Current studies suggest that research on other modulations of glutathione metabolism and transport would be of interest.

Glutathione-dependent defence mechanisms in isolated round spermatids from the rat

The different mechanisms for glutathione-dependent inactivation of a number of oxidizing compounds and other xenobiotics were studied using isolated round spermatids from rats. For the estimation of cellular GSH a flow cytometric assay was used. The cells were exposed to the oxidizing compounds cumene hydroperoxide and diamide, to study the activity of the GSH redox cycle. Incubation of the isolated cells with these compounds showed that the cells had a limited capacity to withstand the oxidative stress associated with their inactivation. The GSH level of the spermatids was maintained during 18 h of incubation in the presence of low concentrations of cumene hydroperoxide and diamide, whereas spermatids exposed to higher concentrations showed a loss of both GSH and ATP. No partial loss of GSH from individual cells was observed. Diethyl maleate and 1,2-epoxy-p-(nitrophenoxy)propane (ENPP) were used to study the effect of glutathione S-transferase-catalysed GSH conjugation on the GSH content of spermatids. Exposure of the cells to low concentrations of diethyl maleate and ENPP resulted in a decrease in GSH content. The flow cytometric analysis showed that this was a partial loss of GSH from all cells, rather than GSH depletion in a part of the cell population. This diminution of the cellular GSH pool, however, did not affect the ATP content and viability of the cells. The present results indicate that spermatids can utilize GSH-dependent defence mechanisms against a number of model compounds.