Inhibition of spermatogonial differentiation by testosterone

Ascorbic acid attenuates gasoline-induced testicular toxicity, sperm quality deterioration, and testosterone imbalance in rats

The present study evaluated the protective effect of ascorbic acid (ASCB) against gasoline fumes (PET) induced testicular oxidative stress, sperm toxicity, and testosterone imbalance in Wistar rats. Twenty-four (24) male albino rats (75 ± 16 g) were randomized into three experimental groups (N = 8). The control group: received normal saline, PET group: exposed to PET 6 h daily by inhalation in an exposure chamber and PET + 200 mg ASCB/kg body weight group: exposed to PET 6 h daily by inhalation and administered ASCB per os. Treatment of ASCB and PET exposure was done thrice and five times weekly for a period of 10 weeks respectively. ASCB co-treatment prevented PET-induced increases in the oxidative stress markers (glutathione, glutathione S-transferase, superoxide dismutase, catalase, hydrogen peroxide generation, nitric oxide, and lipid peroxidation) and serum testosterone concentration (p < .05). Sperm quality was low and those with damaged heads and tails increased alongside histological injuries in the PET-exposed rats, which were also minimized with ASCB administration. ASCB protected against PET-induced oxidative stress, sperm, and testis damage in rats.

The long noncoding RNA CIRBIL is a regulator of steroidogenesis in mice

Infertility affects roughly 8-12 % of couples worldwide, and in above 50 % of couples, male factors are the primary or contributing cause. Many long noncoding RNAs (lncRNAs) are detected in the testis, but their functions are not well understood. CIRBIL was 862 nucleotides in length and was found to be localized mostly in the cytosol of Leydig cell, a small portion was positioned inside the seminiferous tubules. Loss of CIRBIL in mice resulted in male subfertility, characterized by smaller testis and increased germ cell apoptosis. Deletion of CIRBIL significant decreased the number of sperm and impaired the integrity of sperm head and tail. In CIRBIL KO mice, testosterone levels in serum and expression of testosterone biosynthesis genes (STAR and 3β-HSD) were both reduced. Gene Ontology (GO) term and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway were primarily enriched in steroid synthesis process in CIRBIL-binding proteins. Protein-protein (PPI) interaction networks revealed that both cis- and trans-regulated target genes of CIRBIL were associated with testosterone synthesis. Collectively, our results strongly suggest that CIRBIL is a regulator of steroid hormone synthesis.

Allogeneic offspring produced by induction of PD-L1 in spermatogonial stem cells via self-renewal stimulation

The testis is an immune-privileged organ. It is considered that the testis somatic microenvironment is responsible for immune suppression. However, immunological properties of spermatogonial stem cells (SSCs) have remained unknown. Here, we report the birth of allogeneic offspring by enhanced expression of immunosuppressive PD-L1 in SSCs. In vitro supplementation of GDNF and FGF2 increased expression of PD-L1 in SSCs. Cultured SSCs maintained allogeneic spermatogenesis that persisted for >1 year. However, depletion or gene editing of Pd-l1 family genes in SSCs prevented allogeneic spermatogenesis, which suggested that germ cells are responsible for suppression of the allogeneic response. PD-L1 was induced by activation of the MAPK14-BCL6B pathway, which drives self-renewal by reactive oxygen species (ROS) generation. By contrast, reduced ROS or Mapk14 deficiency downregulated PD-L1. Allogeneic offspring were born after SSC transplantation into congenitally infertile and chemically castrated mice. Thus, SSCs have unique immunological properties, which make allogeneic recipients into "surrogate fathers."

Integrated biomarker response to assess the effects of pesticide residues on Nile Tilapia in aquatic ecosystems contaminated by cotton-field effluents

An in-situ study combined with an integrated biomarker response was used to evaluate the impact of agricultural effluents in the physiological responses of Nile tilapia reared in cages and enclosures of water reservoirs in North Benin. Fish were distributed in fish farming systems at two sites: Songhai located outside the cotton basin and Batran located in the most productive commune. They were sampled for blood and organs before (BST), during (DST) and after (AST) pesticide treatment. Pesticide residues were analysed in water, sediments and fish muscles. Several biomarkers were investigated related to the immune (peroxidase, lysozyme and complement activities, superoxide anion production) and reproductive (sex steroids and vitellogenin levels) responses as well as neurotoxicity (cholinesterase activity) and tissue alterations. Biomarkers were assessed and analysed via the integrated biomarker response (IBR). The results showed that Batran water reservoir was a more harmful ecosystem for fish than Songhai one, especially by depressing some immune and reproductive functions in relation to a higher-level of pesticide contamination. They also demonstrated that the contact of fish to sediments in enclosures aggravated the pesticide burden on fish. Therefore, using males as bioindicators would improve the sensitivity of the used biomarkers since males seemed more affected than females especially due to pesticide estrogenic induction impacting their reproductive system.

Low concentrations of glyphosate alone affect the pubertal male rat meiotic step: An in vitro study

Glyphosate is the most used herbicide in the world. Controversial studies exist on its effect on the male reproductive system. We used the validated BioAlter® model to test the effects of low concentrations of Glyphosate. Pubertal rat seminiferous tubules were treated with Glyphosate 50 nM, 500 nM, 5 μM or 50 μM over a 3-week culture period. The Trans-Epithelial Electrical Resistance was not modified by any of the concentrations. The decrease of Clusterin mRNAs suggested that glyphosate would target the integrity of Sertoli cells. The decrease of the numbers of germ cells from day 14 onward highlighted the chronic effect of glyphosate at 50 nM, 500 nM or 5 μM. No consistent effect of glyphosate was observed on the numbers of spermatogonia or on their specific mRNA levels. However, those low concentrations of glyphosate targeted young spermatocytes and middle to late pachytene spermatocytes resulting in a decrease of the numbers of round spermatids, the direct precursors of spermatozoa. This study underlines that the effect of a toxicant should be also studied at low doses and during the establishment of the blood-testis barrier.

Cylindrospermopsin directly disrupts spermatogenesis in isolated male zebrafish testis

Cylindrospermopsin (CYN) is a cytotoxin, and its documented effects in mammals include damage to several organs. CYN also has hormone-disrupting properties, including estrogenic activity, progesterone production inhibition, and apoptosis induction. While CYN has been reported to exert reproductive toxicity in mice, little is known about its effect on fish reproductive function. Using ex vivo organ culture, we investigated the direct action of CYN on the male reproductive system. Isolated zebrafish testis was exposed to 250, 500, and 1000 µg/L CYN for 24 h and 7 d, followed by histo-morphological analysis. The results demonstrate that exposure to CYN led to a decrease in cell types from all three phases of spermatogenesis in zebrafish testis. There were also significant changes in fshr, lhr, and igf3 transcript levels, as well as testosterone secretion following exposure to CYN. In summary, this study provides novel information on the adverse effects of CYN on testicular spermatogenesis and male reproduction in zebrafish. These results provide a framework for a better understanding of CYN toxicity and the mechanism underlying the adverse action of CYN on male reproduction in fish.

Effects of dietary L-carnitine on puberty indices in the young breeder rooster

The aim of current study was to investigate the effect of dietary L-Carnitine (LC) in immature roosters on reproductive hormones, lipid profile and testicular histology at the time of maturity. Eighteen 12-wk-old breeder roosters (Ross 308) of similar weights were randomly allocated into 3 dietary treatments (LC-0: basic diet, LC-250: basic diet + 250 mg LC/kg of diet, LC-500: basic diet + 500 mg of LC/kg of diet) in 6 replicates. The feeding program and photoperiod regimen were performed based on ROSS 308 management handbook. Dietary LC supplementation markedly improved testicle weight and testicle index (p < 0.05). Comb height was also affected by LC supplementation (p < 0.05). The testicle weight and index, comb height, and shank lengths improved linearly with increasing levels of dietary LC (p < 0.05). The LC-250 and LC-500 diets significantly improved the number of sertoli cells (NSC), height epithelium seminiferous tubules (HEST), seminiferous tubules diameter (STD), spermiogenesis index (SI) and tubular differentiation index (TDI) of rooster's testis tissue (p < 0.05). The number of seminiferous tubules (NST) was affected by of the amount of LC (p < 0.05). The roosters on the LC-250 mg/kg diet had longer HEST compared to roosters that received the LC-500 mg/kg diet (p < 0.05). Testicular histology parameters increased in a linear and quadratic manner in response to increasing levels of LC (p < 0.05). Dietary LC significantly increased (p < 0.05) plasma concentrations of testosterone, GnRH, LH, FSH and High-Density Lipoprotein (HDL), but reduced the plasma concentration of Low-Density Lipoprotein (LDL). However, no significant differences were observed between LC-250 and LC-500 groups in these parameters. Plasma testosterone, GnRH, LH, LDL and HDL were affected in a linear and quadratic manner in response to increasing levels of LC (p < 0.05). Similarly, FSH increased linearly with increasing dietary LC (p < 0.05). Thus, adding up to 250g of LC per kg of the rooster chicken can improve reproductive hormones, blood lipids and testicular histology parameters at the time of maturity.

The effectiveness of traditional Japanese medicine Goshajinkigan in irradiation-induced aspermatogenesis in mice

Background

Infertility and gonadal dysfunction are well known side-effects by cancer treatment in males. In particularly, chemotherapy and radiotherapy induced testicular damage, resulting in prolonged azoospermia. However, information regarding therapeutics to treat spermatogenesis disturbance after cancer treatment is scarce. Recently, we demonstrated that Goshajinkigan, a traditional Japanese medicine, can completely rescue severe busulfan-induced aspermatogenesis in mice. In this study, we aimed to detect the effects of Goshajinkigan on aspermatogenesis after irradiation.

Methods

This is animal research about the effects of traditional Japanese medicine on infertility after cancer treatment. C57BL/6 J male mice received total body irradiation (TBI: a single dose of 6Gy) at 4 weeks of age and after 60 days were reared a Goshajinkigan (TJ107)-containing or TJ107-free control diet from day 60 to day 120. Then, two untreated females were mated with a single male from each experimental group. On day 60, 120 and 150, respectively, the sets of testes and epididymis of the mice in each group after deep anesthetization were removed for histological and cytological examinations.

Results

Histological and histopathological data showed that 6Gy TBI treatment decreased the fertility rate (4/10) in the control diet group; in contrast, in the TJ107-diet group, the fertility rate was 10/10 (p < 0.05 vs. 6Gy group). Supplementation with TJ107 was found to rescue the disrupted inter-Sertoli tight junctions via the normalization of claudin11, occludin, and ZO-1 expression and reduce serum anti-germ cell autoantibodies.

Conclusions

These findings show the therapeutic effect on TBI-induced aspermatogenesis and the recovering disrupted gonadal functions by supplementation with TJ107.

Postnatal testis development in the collared peccary (Tayassu tajacu), with emphasis on spermatogonial stem cells markers and niche

Collared peccaries (Tayassu tajacu) present a unique testis cytoarchitecture, where Leydig cells (LC) are mainly located in cords around the seminiferous tubules (ST) lobes. This peculiar arrangement is very useful to better investigate and understand the role of LC in spermatogonial stem cells (SSCs) biology and niche. Recent studies from our laboratory using adult peccaries have shown that the undifferentiated type A spermatogonia (A_und or SSCs) are preferentially located in ST regions adjacent to the intertubular compartment without LC. Following these studies, our aims were to investigate the collared peccary postnatal testis development, from birth to adulthood, with emphasis on the establishment of LC cytoarchitecture and the SSCs niche. Our findings demonstrated that the unique LC cytoarchitecture is already present in the neonate peccary's testis, indicating that this arrangement is established during fetal development. Based on the most advanced germ cell type present at each time period evaluated, puberty (the first sperm release in the ST lumen) in this species was reached at around one year of age, being preceded by high levels of estradiol and testosterone and the end of Sertoli cell proliferation. Almost all gonocytes and SSCs expressed Nanos1, Nanos2 and GFRA1. The analysis of SSCs preferential location indicated that the establishment of SSCs niche is coincident with the occurrence of puberty. Taken together, our findings reinforced and extended the importance of the collared peccary as an animal model to investigate testis function in mammals, particularly the aspects related to testis organogenesis and the SSCs biology and niche.

Effects of Chemotherapy and Radiotherapy on Spermatogenesis: The Role of Testicular Immunology

Substantial improvements in cancer treatment have resulted in longer survival and increased quality of life in cancer survivors with minimized long-term toxicity. However, infertility and gonadal dysfunction continue to be recognized as adverse effects of anticancer therapy. In particular, alkylating agents and irradiation induce testicular damage that results in prolonged azoospermia. Although damage to and recovery of spermatogenesis after cancer treatment have been extensively studied, there is little information regarding the role of differences in testicular immunology in cancer treatment-induced male infertility. In this review, we briefly summarize available rodent and human data on immunological differences in chemotherapy or radiotherapy.

Leydig cells contribute to the inhibition of spermatogonial differentiation after irradiation of the rat

Irradiation with 6 Gy produces a complete block of spermatogonial differentiation in LBNF1 rats that would be permanent without treatment. Subsequent suppression of gonadotropins and testosterone (T) restores differentiation to the spermatocyte stage; however, this process requires 6 weeks. We evaluated the role of Leydig cells (LCs) in maintenance of the block in spermatogonial differentiation after exposure to radiation by specifically eliminating functional LCs with ethane dimethane sulfonate (EDS). EDS (but not another alkylating agent), given at 10 weeks after irradiation, induced spermatogonial differentiation in 24% of seminiferous tubules 2 weeks later. However, differentiation became blocked again at 4 weeks as LCs recovered. When EDS was followed by treatment with GnRH antagonist and flutamide, sustained spermatogonial differentiation was induced in >70% of tubules within 2 weeks. When EDS was followed by GnRH antagonist plus exogenous T, which also inhibits LC recovery but restores follicle stimulating hormone (FSH) levels, the spermatogonial differentiation was again rapid but transient. These results confirm that the factors that block spermatogonial differentiation are indirectly regulated by T, and probably FSH, and that adult and possibly immature LCs contribute to the production of such inhibitory factors. We tested whether insulin-like 3 (INSL3), a LC-produced protein whose expression correlated with the block in spermatogonial differentiation, was indeed responsible for the block by injecting synthetic INSL3 into the testes and knocking down its expression in vivo with siRNA. Neither treatment had any effect on spermatogonial differentiation. The Leydig cell products that contribute to the inhibition of spermatogonial differentiation in irradiated rats remain to be elucidated.

Follicle-stimulating hormone enhances recovery from low-dose doxorubicin-induced spermatogenic disorders in mice

PURPOSE

We aimed to investigate the effects of FSH for promoting spermatogenesis in mice with low-dose doxorubicin-induced spermatogenesis impairment.

METHODS

Eight-wk-old male imprinting control region mice were divided into three groups. Groups D and F received 0.5 mg/kg of doxorubicin twice weekly for 5 weeks. Group C received saline instead of doxorubicin. After inducing spermatogenesis impairment, group D was treated daily with saline for 4 weeks. Group F was given 1 IU of recombinant human FSH daily for 4 weeks. Spermatogenesis recovery was evaluated based on the testis weight, sperm count, histological assessment, and mating. The percentage of sperm with unfragmented deoxyribonucleic acid (DNA) was analyzed by single-cell pulsed-field gel electrophoresis, and the serum FSH levels were measured.

RESULTS

The elevation of serum FSH advanced slowly. The testis weight, sperm count, percentage of seminiferous tubules with spermatogenesis, percentage of sperm with unfragmented DNA and pregnancy rate were significantly increased by the administration of FSH.

CONCLUSION

Our study findings indicated that the immediate administration of exogenous FSH can promote the recovery from impaired spermatogenesis induced by low-dose doxorubicin before endogenous FSH increases to the maximum level.

Regeneration of spermatogenesis in a mouse model of azoospermia by follicle-stimulating hormone and oestradiol

Busulfan is a chemotherapeutic drug that induces sterility, azoospermia and testicular atrophy. To induce degeneration of spermatogenesis, we used different amounts of busulfan. Adult male C57Bl/6 mice were treated with 15, 30 and 45 mg kg(-1) of busulfan. After 5 weeks, animals had daily injections of 7.5 IU human follicle-stimulating hormone (hFSH) and 12.5 μg kg(-1) oestradiol benzoate (EB), separately or simultaneously. After this time, the animals were killed and blood samples were taken through cardiac puncture. Testes were used for histopathology experiments, DNA flow cytometry and RNA extraction for expression of c-kit and cyclin B1 genes. EB unlike FSH has induced stimulatory effects on spermatogenesis, increased the level of serum testosterone 2-fold and caused a 2-fold increase in the number of haploid cells. The result showed that hFSH with EB multiplied EB stimulatory effects on spermatogenesis up to four times. Expression of c-kit and cyclin B1 genes increased in EB and hFSH+EB groups. These findings suggest that EB regulates spermatogonial stem cells via hFSH. hFSH with EB had synergistic effect on regeneration of spermatogenesis.

Protective Role of GnRH Antagonist on Chemotherapy-induced Spermatogenesis Disorder: A Morphological Study

PURPOSE

Anti cancer drugs is one of the most important chemotherapeutic factors which can influence spermatogenesis process and germinal epithelium. Since dividing cells are mainly affected by anticancer drugs, the aim of the present study is to investigate the preventive effect of GnRH antagonist on spermatogenic defect produced by anticancer drugs.

METHODS

In the present study thirty adult male mice aging 6-8 weeks were divided into 3 groups as: Control, Experimental 1 and Experimental 2. Experimental 1 group received Cisplatin for 5 days as 2.5 mg/kg intraperitoneally and Experimental 2 group received 0.25 mg/kg cetrorelix (GnRH antagonist) one week before cisplatin treatment and continued for 3 weeks. The mice in all groups were sacrificed 35 days after the last injection and testis specimens were fixed in boueins, formaldehyde fixative and 2.5% Glutaraldehide then prepared for light and electron microscopic examination.

RESULTS

Light microscopy (LM) study showed that the number of spermatogonial cells, thickness of germinal epithelium, was decreased in Experimental 1group. Electron microscopy revealed that in this group several intercellular spaces appeared between spermatogenic cells and secretory granules in interstitial cells was increased. There were several vacuolated mitochondria and destroyed organelles in spermatogonial cells but in Experimental 2 group condition was similar to control group.

CONCLUSION

These results indicate that the cetrorelix administration before cancer treatment may protect germinal epithelium against side effects of cisplatin.

Spermatogonial behavior in rats during radiation-induced arrest and recovery after hormone suppression

Ionizing radiation has been shown to arrest spermatogenesis despite the presence of surviving stem spermatogonia, by blocking their differentiation. This block is a result of damage to the somatic environment and is reversed when gonadotropins and testosterone are suppressed, but the mechanisms are still unknown. We examined spermatogonial differentiation and Sertoli cell factors that regulate spermatogonia after irradiation, during hormone suppression, and after hormone suppression combined with Leydig cell elimination with ethane dimethane sulfonate. These results showed that the numbers and cytoplasmic structure of Sertoli cells are unaffected by irradiation, only a few type A undifferentiated (Aund) spermatogonia and even fewer type A1 spermatogonia remained, and immunohistochemical analysis showed that Sertoli cells still produced KIT ligand (KITLG) and glial cell line-derived neurotrophic factor (GDNF). Some of these cells expressed KIT receptor, demonstrating that the failure of differentiation was not a result of the absence of the KIT system. Hormone suppression resulted in an increase in Aund spermatogonia within 3 days, a gradual increase in KIT-positive spermatogonia, and differentiation mainly to A3 spermatogonia after 2 weeks. KITL (KITLG) protein expression did not change after hormone suppression, indicating that it is not a factor in the stimulation. However, GDNF increased steadily after hormone suppression, which was unexpected since GDNF is supposed to promote stem spermatogonial self-renewal and not differentiation. We conclude that the primary cause of the block in spermatogonial development is not due to Sertoli cell factors such (KITL\GDNF) or the KIT receptor. As elimination of Leydig cells in addition to hormone suppression resulted in differentiation to the A3 stage within 1 week, Leydig cell factors were not necessary for spermatogonial differentiation.

Effect of genistein administration on the recovery of spermatogenesis in the busulfan-treated rat testis

Objective

Impairment of spermatogenesis has been identified as an inevitable side effect of cancer treatment. Although estrogen treatment stimulates spermatogenic recovery from the impaired spermatogenesis by suppressing the intra-testicular testosterone (ITT) level, side effects of estrogen are still major impediments to its clinical application in humans. Soybeans are rich in genistein, which is a phytoestrogen that binds to estrogen receptors and has an estrogenic effect. We investigated the effects of genistein administration on ITT levels, testis weight, and recovery of spermatogenesis in rats treated with a chemotherapeutic agent, busulfan.

Methods

Busulfan was administered intraperitoneally to rats, and then a GnRH agonist was injected subcutaneously into the back, or genistein was administered orally.

Results

The weight of the testes was significantly reduced by the treatment with busulfan. The testis weight was partially restored after busulfan treatment by additional treatment with either the GnRH agonist or genistein. Busulfan also induced atrophy of a high percentage of the seminiferous tubules, but this percentage was decreased by additional treatment with either the GnRH agonist or genistein. Treatment with genistein was effective at suppressing and maintaining ITT levels comparable to that in the GnRH agonist group.

Conclusion

Genistein effectively suppressed ITT levels and stimulated the recovery of spermatogenesis in rats treated with a chemotherapeutic drug. This suggests that genistein may be a substitute for estrogens, for helping humans to recover fertility after cancer therapy without the risk of side effects.

Coordination of spermatogenic processes in the testis: lessons from cystic spermatogenesis

A common observation in the vertebrate testis is that new germ cell clones enter spermatogenesis proper before previously formed clones have completed their development. The extent to which the developmental advance of any given germ cell clone in any phase of spermatogenesis is dependent on that of neighboring clones and/or on the coordinating influence of associated Sertoli cells in the immediate vicinity or of others further away remains unclear. This review presents an overall synthesis of findings in an ancient vertebrate, the spiny dogfish shark and shows that, even at this phyletic level, the developmental advance of a given germ cell clone is the outcome of various processes emanating from its spatiotemporal relationship with (1) its own complement of Sertoli cells in the anatomically distinct spermatocyst and (2) Sertoli cells associated with other germ cell clones that lie upstream or downstream in the spermatogenic progression and that secrete, among others, androgen and estrogen destined for target sites upstream. Analysis of the protracted spermatogenic cycle shows the coordination in space and time of spermatogenic and steroidogenic events. Furthermore, the natural withdrawal of pituitary gonadotropin support in the dogfish causes a distinct and highly ordered gradient of apoptosis among the spermatogonial generations; this in turn is a major contributing factor to the cyclic nature of sperm production observed in this lower vertebrate. Because of the simplicity of their testicular organization, their cystic spermatogenesis and their phylogenetic position, cartilaginous fishes constitute a valid vertebrate reference system for comparative analysis with higher vertebrates.

Gonadotropin-Releasing Hormone Antagonist (Cetrorelix) Therapy Fails to Protect Nonhuman Primates (Macaca arctoides) From Radiation-Induced Spermatogenic Failure

Treatment of men of reproductive age with radiation or alkylating agents often produces prolonged azoospermia. We previously demonstrated that suppression of testosterone (T) with gonadotropin-releasing hormone (GnRH) analogs restored spermatogenesis following atrophy induced by radiation or chemotherapy in rats. This study tested whether GnRH antagonist therapy could reverse radiation-induced testicular injury in primates with a similar protocol. Adult male stump-tailed macaques were given either 6.7 Gy radiation to the testis alone, 6.7 Gy radiation combined with GnRH-antagonist treatment starting on the day of exposure, or daily injections of the GnRH antagonist Cetrorelix for 3 months alone and were monitored for 18 months. Cetrorelix alone produced a 20-40-week fully reversible suppression of serum T, but although spermatogenic recovery was incomplete, 40%-90% of tubules contained differentiating germ cells. Following radiation alone, testis volumes were reduced to approximately 28% and sperm counts to less than 1% of pretreatment values. A biopsy at 18 months after radiation showed that only 3.0% of seminiferous tubule cross sections had germ cells. In irradiated animals that received GnRH antagonist, testis volumes were reduced to 18% of pretreatment volume, and at 18 months, only 1.9% of seminiferous tubule cross sections contained germ cells. Inhibin B values were reduced to 10% and 3% of pretreatment levels in the radiation-only and the radiation plus GnRH antagonist groups, respectively. Species differences exist in the testicular response to radiation, GnRH antagonist therapy, or both, so that rescue protocols that were successful in rodents might not work in primates.

Rat models of post-irradiation recovery of spermatogenesis: interstrain differences

Recently, we reported large differences between rat strains in spermatogenesis recovery at 10 weeks after 5-Gy irradiation suggesting that there are interstrain as well as interspecies differences in testicular radiation response. To determine whether these interstrain differences in sensitivity might be a result of the particular dose and time-point chosen, we performed dose-response and time-course studies on sensitive Brown-Norway (BN) and more resistant spontaneously hypertensive rats (SHR) and Sprague-Dawley (SD) rats. Type A spermatogonia were observed in atrophic tubules at 10 weeks after irradiation in all strains indicating that tubular atrophy was caused by a block in their differentiation, but the doses to produce the block ranged from 4.0 Gy in BN to 10 Gy in SD rats. Although the numbers of type A spermatogonial were unaffected at doses below 6 Gy, higher doses reduced their number, indicating that stem cell killing also contributed to the failure of recovery. After 10 weeks, there was no further recovery and even a decline in spermatogonial differentiation in BN rats, but in SHR rats, sperm production returned to control levels by 20 weeks after 5.0 Gy and, after 7.5 Gy, differentiation resumed in 60% of tubules by 30 weeks. Suppression of testosterone and gonadotropins after irradiation restored production of differentiated cells in nearly all tubules in BN rats and in all tubules in SHR rats. Thus, the differences in recovery of spermatogenesis between strains were a result of both quantitative differences in their sensitivities to a radiation-induced, hormone-dependent block of spermatogonial differentiation and qualitative interstrain differences in the progression of post-irradiation recovery. The progression of recovery in SHR rats was similar to the prolonged delays in recovery of human spermatogenesis after cytotoxic agent exposure and thus may be a system for investigating a phenomenon also observed in men.

Endosulfan and flutamide impair testicular development in the juvenile Asian catfish, Clarias batrachus

Endosulfan and flutamide, a widely used pesticide and a prostate cancer/infertility drug, respectively, have an increased risk of causing endocrine disruption if they reach water bodies. Though many studies are available on neurotoxicity/bioaccumulation of endosulfan and receptor antagonism of flutamide, only little is known about their impact on testicular steroidogenesis at molecular level. Sex steroids play an important role in sex differentiation of lower vertebrates including fishes. Hence, a small change in their levels caused by endocrine disruptors affects the gonadal development of aquatic vertebrates significantly. The aim of this study was to evaluate the effects of endosulfan and flutamide on testis-related transcription factor and steroidogenic enzyme genes with a comparison on the levels of androgens during critical period of catfish testicular development. We also analyzed the correlation between the above-mentioned genes and catfish gonadotropin-releasing hormone (cfGnRH)-tryptophan hydroxylase2 (tph2). The Asian catfish, Clarias batrachus males at 50 days post hatch (dph) were exposed to very low dose of endosulfan (2.5 μg/L) and flutamide (33 μg/L), alone and in combination for 50 days. The doses used in this study were far less than those used in the previous studies of flutamide and reported levels of endosulfan in surface water and sediments. Sampling was done at end of the treatments (100 dph) to perform testicular germ cell count (histology), measurements of testosterone (T) and 11-ketotestosterone (11-KT) by enzyme immunoassay and transcript quantification by quantitative real-time PCR. In general, treatments decreased the expression of several genes including testis-related transcription factors (dmrt1, sox9a and wt1), steroidogenic enzymes (11β-hsd2, 17β-hsd12 and P450c17), steroidogenic acute regulatory protein and orphan nuclear receptors (nr2c1 and Ad4BP/SF-1). In contrast, the transcripts of cfGnRH and tph2 were elevated in the brain of all treated groups with maximum elevation in the endosulfan group. However, combination of endosulfan and flutamide (E+F) treatment showed minor antagonism in a few results of transcript quantification. Levels of T and 11-KT were elevated after flutamide and E+F treatments while no change was seen in the endosulfan group signifying the effect of flutamide as an androgen receptor antagonist. All the treatments modulated testis growth by decreasing the progression of differentiation of spermatogonia to spermatocytes. Based on these results, we suggest that the exposure to endosulfan and flutamide, even at low doses, impairs testicular development either directly or indirectly at the level of brain.

Differences in radiation sensitivity of recovery of spermatogenesis between rat strains

Previous studies with Lewis/Brown-Norway (BN) F1 hybrid rats indicated that spermatogenesis was much more sensitive to ionizing radiation than in the widely studied outbred Sprague Dawley stock, suggesting that there were genetically based differences; however, the relative sensitivities of various inbred strains had not been established. As a first step to defining the genes responsible for these differences, we compared the sensitivities of seven rat strains to radiation damage of spermatogenesis. Recovery of spermatogenesis was examined 10 weeks after 5-Gy irradiation of seven strains (BN, Lewis, Long-Evans, Wistar Kyoto, spontaneously hypertensive [SHR], Fischer 344, and Sprague Dawley). The percentages of tubules containing differentiated cells and testicular sperm counts showed that BN and Lewis were most sensitive to radiation (< 2% of tubules recovered, < 2 × 10(5) late spermatids per testis), Long-Evans, Wistar Kyoto, Fischer, and SHR were more resistant, and Sprague Dawley was the most resistant (98% of tubules recovered, 2 × 10(7) late spermatids per testis). Although increases in intratesticular testosterone levels and interstitial fluid volume after irradiation had been suggested as factors inhibiting recovery of spermatogenesis, neither appeared to correlate with the radiation sensitivity of spermatogenesis in these strains. In all strains, the atrophic tubules without differentiated germ cells nevertheless showed the presence of type A spermatogonia, indicating that their differentiation was blocked. Thus, we conclude that the differences in radiation sensitivity of recovery of spermatogenesis between rat strains of different genetic backgrounds can be accounted for by differences in the extent of the radiation-induced block of spermatogonial differentiation.

Proliferation and apoptosis in aged and photoregressed mammalian seminiferous epithelium, with particular attention to rodents and humans

Imbalances in the proliferation and apoptosis processes are involved in numerous epithelial alterations. In the seminiferous epithelium, normal spermatogenesis is regulated by spermatogonia proliferation and germ cell apoptosis, and both processes are involved in diverse pathological alterations of the seminiferous epithelium. Other physiological phenomena including aging and short photoperiod, in which apoptosis and proliferation seem to play important roles, cause testicular changes. Aging is accompanied by diminished proliferation and increased apoptosis, the latter occurring in specific states of the seminiferous cycle and considered the cause of epithelium involution. However, there is no clear evidence concerning whether proliferation decreases in the spermatogonia themselves or is due to an alteration in the cell microenvironment that surrounds them. As regards the factors that regulate the process, the data are scant, but it is considered that the diminution of c-kit expression in the spermatagonia, together with the diminution in antiapoptotic factors (Bcl-x(L))) of the intrinsic molecular pathway of apoptosis play a part in epithelial regression. A short photoperiod, especially in rodents, produces a gradual involution of the seminiferous epithelium, which is related with increased apoptosis during the regression phase and a diminution of apoptosis during recrudescence. Proliferative activity varies, especially during the total regression phase, when it usually increases in the undifferentiated spermatogonia. In other species showing seasonal reproduction, however, decreased proliferation is considered the main factor in the regression of the seminiferous epithelium. Little is known about how both phenomena are regulated, although data in rodents suggest that both the intrinsic and extrinsic pathways of apoptosis contribute to the increase in this process. In conclusion, regression of the seminiferous epithelium in physiological situations, as in many pathological situations, is a result of alterations in equilibrium between the proliferation and apoptosis of germinal cell types. However, both physiological phenomena showed important differences as regard proliferation/apoptosis and their regulation pathways, probably as a result of their irreversible or reversible character.

Hormonal suppression restores fertility in irradiated mice from both endogenous and donor-derived stem spermatogonia

Irradiation interrupts spermatogenesis and causes prolonged sterility in male mammals. Hormonal suppression treatment with gonadotropin-releasing hormone (GnRH) analogues has restored spermatogenesis in irradiated rats, but similar attempts were unsuccessful in irradiated mice, monkeys, and humans. In this study, we tested a stronger hormonal suppression regimen (the GnRH antagonist, acyline, and plus flutamide) for efficacy both in restoring endogenous spermatogenesis and in enhancing colonization of transplanted stem spermatogonia in mouse testes irradiated with a total doses between 10.5 and 13.5 Gy. A 4-week hormonal suppression treatment, given immediately after irradiation, increased endogenous spermatogenic recovery 1.5-fold, and 11-week hormonal suppression produced twofold increases compared with sham-treated irradiated controls. Furthermore, 10-week hormonal suppression restored fertility from endogenous surviving spermatogonial stem cells in 90% of 10.5-Gy irradiated mice, whereas only 10% were fertile without hormonal suppression. Four- and 11-week hormonal suppression also enhanced spermatogenic development from transplanted stem spermatogonia in irradiated recipient mice, by 3.1- and 4.8-fold, respectively, compared with those not given hormonal treatment. Moreover, the 10-week hormonal suppression regimen, but not a sham treatment, restored fertility of some 13.5-Gy irradiated recipient mice from donor-derived spermatogonial stem cells. This is the first report of hormonal suppression inducing recovery of endogenous spermatogenesis and fertility in a mouse model treated with anticancer agents. The combination of spermatogonial transplantation with hormonal suppression should be investigated as a treatment to restore fertility in young men after cytotoxic cancer therapy.

Androgen action via testicular peritubular myoid cells is essential for male fertility

Androgens are essential for normal spermatogenesis and male fertility, but how androgens exert this effect remains uncertain. Androgen receptors (ARs) are expressed in several testicular cell types, but continuing uncertainty exists over which cell type mediates androgen control of spermatogenesis. Androgen signaling via Sertoli cells (SCs) is essential for complete spermatogenesis, but the role for androgen signaling via peritubular myoid (PTM) cells is contentious. To address this controversy, we generated PTM-specific AR-knockout (PTM-ARKO) mice in which gross reproductive development was normal, but all PTM-ARKO males were azoospermic and infertile. Testis weight was reduced beyond puberty, and in adulthood there was an 86% reduction in germ cells, compared with wild-type littermates. These changes were not explained by any deficits in testosterone, luteinizing hormone, or follicle-stimulating hormone concentrations. SC function was impaired in PTM-ARKO males, indicated by reduced seminiferous tubule fluid production and reduced expression of some androgen-dependent SC genes. Androgen action via PTM cells is therefore essential for normal testis function, spermatogenesis, and fertility in males. This study also provides the first direct evidence for the importance of androgen-driven stromal-epithelial interactions underpinning the regulation of spermatogenesis; PTM-ARKO mice will enable identification of the new molecular pathways involved.

Changes in gene expression in somatic cells of rat testes resulting from hormonal modulation and radiation-induced germ cell depletion

Although gonadotropins and androgen are required for normal spermatogenesis and both testosterone and follicle-stimulating hormone (FSH) are responsible for the inhibition of spermatogonial differentiation that occurs in irradiated rats, it has been difficult to identify the specific genes involved. To study specific hormonally regulated changes in somatic cell gene expression in the testis that may be involved in these processes, without the complication of changing populations of germ cells, we used irradiated LBNF(1) rats, the testes of which contain almost exclusively somatic cells except for a few type A spermatogonia. Three different groups of these rats were treated with various combinations of gonadotropin-releasing hormone antagonist, an androgen receptor antagonist (flutamide), testosterone, and FSH, and we compared the gene expression levels 2 wk later to those of irradiated-only rats by microarray analysis. By dividing the gene expression patterns into three major patterns and 11 subpatterns, we successfully distinguished, in a single study, the genes that were specifically regulated by testosterone, by luteinizing hormone (LH), and by FSH from the large number of genes that were not hormonally regulated in the testis. We found that hormones produced more dramatic upregulation than downregulation of gene expression: Testosterone had the strongest upregulatory effect, LH had a modest but appreciable upregulatory effect, and FSH had a minor upregulatory effect. We also separately identified the somatic cell genes that were chronically upregulated by irradiation. Thus, the present study identified gene expression changes that may be responsible for hormonal action on somatic cells to support normal spermatogenesis and the hormone-mediated block in spermatogonial development after irradiation.

Male gonadal toxicity

Cancer treatment with chemotherapy or radiotherapy causes gonadal toxicity in male patients. The endpoint of most concern for future reproductive options is the induction of prolonged azoospermia, which may or may not be reversible. The immediate effects of therapy and its reversibility are most readily observed in post-pubertal patients, but the same antineoplastic regimens given to prepubertal males can induce permanent azoospermia. The probability of permanent azoospermia is related to the specific agents used and their doses. The most damaging are alkylating agents (particularly chlorambucil, procarbazine, cyclophosphamide, melphalan, and busulfan), cisplatin and radiation to the region of the testicles.

Donor Sertoli cells transplanted into irradiated rat testes stimulate partial recovery of endogenous spermatogenesis

Irradiation of rat testes leads to the failure to support differentiation of the surviving spermatogonia due to damage of the somatic environment. To determine the involvement of Sertoli cells in this somatic damage, we transplanted seminiferous tubule cells from normal immature GFP-transgenic rats into the testes of irradiated rats. The donor Sertoli cells colonized and developed in the host testes. In many seminiferous tubules, the donor Sertoli cells formed abnormal spherical structures in the lumen, but in some tubules they formed a normal-appearing epithelium, but with only isolated spermatogonia, on the basement membrane. When the donor cells were injected into the interstitial region of the testis, they formed tubule-like structures containing Sertoli cells and occasional isolated spermatogonia, both of donor origin. Surprisingly, in host tubules adjacent to these newly formed donor-cell tubules or adjacent to the endogenous tubules with abnormal donor Sertoli-cell structures, endogenous spermatogonia differentiated to the spermatocyte or even to spermatid stages. Around these newly donor cell-formed tubules and the host tubules with abnormal donor Sertoli-cell structures, many cells including macrophages, which perhaps represented chronic inflammation, accumulated in the interstitium. We conclude that the donor Sertoli cells that colonized the seminiferous tubules did not directly support recovery of spermatogenesis. Instead, the colonizing Sertoli cells acted indirectly on the interstitium to stimulate localized differentiation of endogenous spermatogonia.

In vitro culture and differentiation of buffalo (Bubalus bubalis) spermatogonia

The objective of this study was to develop a culture system which could support buffalo spermatogonia differentiation into spermatids in vitro. Testes from 3- to 5-month-old buffaloes were decapsulated and seminiferous tubules were enzymatically dissociated to recover spermatogonia and sertoli cells. The cells were cultured in modified Dulbecco modified Eagle medium supplemented with different concentrations of foetal bovine serum, retinol, testosterone for 2 months at 37 degrees C. Spermatogonia and sertoli cells were identified with an antibody against c-kit or GATA4, respectively. The viability of spermatogonia in the media supplemented with different concentrations of serum was all significantly higher (p < 0.05) compared with that in the medium without serum. A-paired or A-aligned spermatogonia and spermatogonial colonies (AP-positive) were observed after 7-10 days of culture and spermatid-like cells with a flagellum (6-8 microm) appeared after 30 days of culture. For cultured conditions, retinol could not significantly promote the formation of spermatid-like cells (p > 0.05), whereas supplementation of testosterone could significantly promote (p < 0.05) the formation of spermatid-like cells after 41 days of culture. The expression of the spermatid-specific marker gene (PRM2) was identified after 30 days of culture by RT-PCR. Yet, the transition protein 1 (TP1, a haploid makers) was not detected. Meanwhile, spermatids developed in vitro were also confirmed by Raman spectroscopy. These results suggest that buffalo spermatogonia could differentiate into spermatids in vitro based on the analysis of their morphology, PRM2 expression and Raman spectroscopy. Yet, the normality of the spermatid-like cells was not supported by TP1 expression.

Hormonal suppression for fertility preservation in males and females

Methods to restore fertility of men and women sterilized by medical treatments and environmental toxicant exposures are under investigation. Rendering spermatogenesis and ovarian follicular development kinetically quiescent by suppression of gonadotropins has been proposed to protect them from damage by cytotoxic therapy. Although the method fails to protect the fertility of male mice and monkeys, gonadotropin and testosterone suppression in rats before or after cytotoxic therapy do enhance the recovery of spermatogenesis. However, the mechanism involves not the induction of quiescence but rather the reversal, by suppression of testosterone, of a block in differentiation of surviving spermatogonia caused by damage to the somatic environment. In men, only one of eight clinical trials was successful in protecting or restoring spermatogenesis after cytotoxic therapy. In women, protection of primordial follicles in several species from damage by cytotoxic agents using GnRH analogs has been claimed; however, only two studies in mice appear convincing. The protection cannot involve the induction of quiescence in the already dormant primordial follicle but may involve direct effects of GnRH analogs or indirect effects of gonadotropin suppression on the whole ovary. Although numerous studies in female patients undergoing chemotherapy indicate that GnRH analogs might be protective of ovarian function, none of the studies showing protection were prospective randomized clinical trials and thus they are inconclusive. Considering interspecies differences and similarities in the gonadal sensitivity to cytotoxic agents and hormones, mechanistic studies are needed to identify the specific beneficial effects of hormonal suppression in select animal models that may be applicable to humans.

The radiation-induced block in spermatogonial differentiation is due to damage to the somatic environment, not the germ cells

Radiation and chemotherapeutic drugs cause permanent sterility in male rats, not by killing most of the spermatogonial stem cells, but by blocking their differentiation in a testosterone-dependent manner. However, it is not known whether radiation induces this block by altering the germ or the somatic cells. To address this question, we transplanted populations of rat testicular cells containing stem spermatogonia and expressing the green fluorescent protein (GFP) transgene into various hosts. Transplantation of the stem spermatogonia from irradiated adult rats into the testes of irradiated nude mice, which do not show the differentiation block of their own spermatogonia, permitted differentiation of the rat spermatogonia into spermatozoa. Conversely transplantation of spermatogonial stem cells from untreated prepubertal rats into irradiated rat testes showed that the donor spermatogonia were able to colonize along the basement membrane of the seminiferous tubules but could not differentiate. Finally, suppression of testosterone in the recipient irradiated rats allowed the differentiation of the transplanted spermatogonia. These results conclusively show that the defect caused by radiation in the rat testes that results in the block of spermatogonial differentiation is due to injury to the somatic compartment. We also observed colonization of tubules by transplanted Sertoli cells from immature rats. The present results suggest that transplantation of spermatogonia, harvested from prepubertal testes to adult testes that have been exposed to cytotoxic therapy might be limited by the somatic damage and may require hormonal treatments or transplantation of somatic elements to restore the ability of the tissue to support spermatogenesis.

Spermatogonial differentiation in juvenile spermatogonial depletion (jsd) mice with androgen receptor or follicle-stimulating hormone mutations

The jsd mice experience a single wave of spermatogenesis, followed by an arrest of spermatogenesis because of a block in spermatogonial differentiation. Previous pharmacological and surgical studies have indicated that testosterone (T) and low scrotal temperatures but not FSH block spermatogonial differentiation in jsd mice. We sought to test these observations by genetic approaches by producing male jsd mutant mice with either defective androgen receptor (AR, Tfm mutation) or a deficiency of FSH (fshb(-/-)). In adult jsd-Tfm double-mutant mice, the tubule differentiation index was 95% compared with 14% in jsd littermates, suggesting that general ablation of AR function restored spermatogonial differentiation in jsd mice. The results indicated that this enhancement of differentiation was primarily a result of elevation of temperature caused by the cryptorchid position of the testis in jsd-Tfm double-mutant mice, which resulted from the lack of AR in the gubernaculum. The low levels of T were not a factor in the release of the spermatogonial differentiation block in the jsd-Tfm mice, but we were unable to determine whether inactivation of AR in the adult jsd testis had a direct effect on the restoration of spermatogonial differentiation because the elevated temperature bypassed the T-induced block in spermatogonial differentiation. Although spermatogonia were indeed present in adult jsd-fshb double-mutant mice and were capable of differentiation after androgen deprivation, these mice had a tubule differentiation index of 0%, ruling out the possibility that endogenous FSH inhibited spermatogonial differentiation in jsd mice. The results are consistent in support of the hypothesis that inhibition of spermatogonial differentiation in jsd mice is a result of T acting through the AR only at scrotal temperatures.

Both testosterone and follicle-stimulating hormone independently inhibit spermatogonial differentiation in irradiated rats

Simultaneous suppression of both testosterone and FSH with GnRH antagonists (GnRH-ant) reverses the radiation-induced block in spermatogonial differentiation in F1 hybrids of Lewis and Brown-Norway rats. Although addition of exogenous testosterone restores the block, it also raises FSH, and hence it had not been possible to conclusively determine which hormone was inhibiting spermatogonial differentiation. In the present study, we establish the relative roles of testosterone and FSH in this inhibition using three different approaches. The first approach involved the treatment of irradiated rats, in which differentiation was stimulated by GnRH-ant plus flutamide, with FSH for 2 wk; the FSH reduced the percentage of tubules that were differentiated (TDI) by about 2-fold, indicating that FSH does have an inhibitory role. The second approach involved treatment of irradiated, hypophysectomized rats with exogenous testosterone for 10 wk; testosterone also reduced the TDI, demonstrating that testosterone had a definite inhibitory effect, independent of pituitary hormones. Furthermore, in this protocol we showed that TDI in the hypophysectomized testosterone-treated group, which had higher intratesticular testosterone levels but lacked FSH, was slightly higher than the TDI in a GnRH-antagonist-testosterone-treated group of irradiated rats, which had normal physiological levels of FSH; this result supports a role for endogenous FSH in suppressing spermatogonial differentiation in the latter group. The third approach involved injection of an active anti-FSH antibody for 10 d in untreated, GnRH-ant plus flutamide-treated, or GnRH-ant plus testosterone-treated irradiated rats. This was not sufficient to increase the TDI. However, flutamide given in a similar treatment schedule did increase the TDI in GnRH-ant plus testosterone-treated rats. We conclude that both testosterone and FSH individually inhibit spermatogonial differentiation after irradiation, but testosterone is a more highly potent inhibitor than is FSH.

Effects of medroxyprogesterone and estradiol on the recovery of spermatogenesis in irradiated rats

Suppression of intratesticular testosterone (ITT) levels is required for spermatogenic recovery in rats after irradiation, but maintenance of peripheral testosterone (T) levels is important for many male functions. Considering the preservation of peripheral T while suppressing ITT, we tested the effects of a combination of a progestin, medroxyprogesterone acetate (MPA), plus T on spermatogenic recovery after irradiation, and compared its effects to those of T alone or T combined with estradiol (E2). Rats were given testicular irradiation (6 Gy) and treated during wk 3-7 after irradiation with MPA + T, or the individual steroids with or without GnRH antagonist (GnRH-ant), or GnRH-ant alone, or T + E2. Whereas GnRH-ant alone stimulated differentiation in 55% of tubules 13 wk after irradiation compared with 0% in irradiated-only rats, the addition of MPA reduced the percentage of tubules showing differentiation to 18%. However, T or MPA alone or the combination of the two induced germ cell differentiation in only 2-4% of tubules. In contrast, E2 stimulated differentiation in 88% of tubules, and T combined with E2 still resulted in differentiation in 30% of tubules. Although both MPA and E2 suppressed ITT levels to approximately 2% of control (2 ng/g testis), MPA was a less effective stimulator of spermatogenic recovery than E2 or GnRH-ant alone. MPA's function as a weak androgen was likely responsible for inhibiting spermatogenic recovery, as was the case for all other tested androgens. Thus, for clinical protection or restoration of spermatogenesis after radiation or chemotherapy by suppressing T production, MPA, at least in the doses used in the present study, is suboptimal. The combination of an estrogen with T appears to be most effective for stimulating such recovery.

The mouse juvenile spermatogonial depletion (jsd) phenotype is due to a mutation in the X-derived retrogene, mUtp14b

The recessive juvenile spermatogonial depletion (jsd) mutation results in a single wave of spermatogenesis, followed by failure of type A spermatogonia to differentiate, resulting in adult male sterility. We have identified a jsd-specific rearrangement in the mouse homologue of the Saccharomyces cerevisiae gene UTP14, termed mUtp14b. Confirmation that mUtp14b underlies the jsd phenotype was obtained by transgenic bacterial artificial chromosome (BAC) rescue. We also identified a homologous gene on the Mus musculus X chromosome (MMUX) (mUtp14a) that is the strict homologue of the yeast gene, from which the intronless mUtp14b has been derived by retrotransposition. Expression analysis showed that mUtp14b is predominantly expressed in the germ line of the testis from zygotene through round spermatids, whereas mUtp14a, although well expressed in all somatic tissues, could be detected only in the germ line in round spermatids. In yeast, depletion of the UTP proteins impedes production of 18S rRNA, leading to cell death. We propose that the retroposed autosomal copy mUtp14b, having acquired a testis-specific expression pattern, could have provided a mechanism for increasing the efficiency and/or numbers of germ cells produced by meeting the need for more 18S rRNA and protein. Such a mechanism would be of obvious reproductive advantage and be strongly selected for in evolution. Consistent with this hypothesis is the finding of a similar X-autosome retroposition of UTP14 in human which seems to have arisen independently of that in rodents. In jsd homozygotes, which lack a functional copy of Utp14b, insufficient production of rRNA quickly leads to a cessation of spermatogenesis.

The Ability of a Gonadotropin-Releasing Hormone Antagonist, Acyline, to Prevent Irreversible Infertility Induced by the Indenopyridine, CDB-4022, in Adult Male Rats: The Role of Testosterone1

Intratesticular testosterone (ITT) is known to play a critical role in the maintenance of spermatogenesis. We have used acyline, a GnRH antagonist, to suppress testosterone (T) production, and acyline and T implants to study the prevention of irreversible infertility induced by CDB-4022. Vehicle or acyline was administered to proven fertile male rats (n = 5/group) at a dose (210 microg/day) that completely suppressed (P < 0.05) T production, as measured by serum T, and testicular function, either before, concurrent with, or after vehicle or a single oral dose of 2.5 mg CDB-4022/kg (Week 0). Vehicle-treated males remained fertile, whereas acyline-treated males exhibited transitory infertility. CDB-4022 alone caused irreversible infertility in all males. Importantly, CDB-4022-treated males recovered fertility when acyline was started before CDB-4022 (Weeks -4 to 0; Weeks -4-9), but not when acyline was administered concurrently with or after CDB-4022 (Weeks 0-9; Weeks 10-19). At the end of this study (Week 34), testes weights, spermatid head counts (SHC), and tubule differentiation indices (TDI) were suppressed (P < 0.05) in infertile CDB-4022-treated males, but in rats that recovered fertility, these parameters were similar (P > 0.05) to those in vehicle-treated males. In addition, serum inhibin B and epididymal androgen-binding protein levels were nondetectable in infertile CDB-4022-treated rats. To test whether suppression of ITT was critical for prevention of CDB-4022-induced infertility, proven fertile rats (n = 7-8/group) received vehicle, acyline alone, or acyline and a T implant for 4 wk before CDB-4022 (Week 0). The T implant increased ITT in acyline-treated rats. Although ITT was lower (P < 0.05) in the T-implanted males than in untreated rats, it was sufficient to sustain spermiogenesis. Serum rFSH levels were also elevated in rats treated with acyline + T as compared with acyline alone during the treatment interval, but rFSH was still lower than in vehicle-treated rats. Rats in all treatment groups were rendered infertile initially, but the acyline + CDB-4022-treated rats recovered fertility by Week 10. In contrast, rats treated with CDB-4022 alone or acyline + T + CDB-4022 remained infertile until at least Week 16. Testes weights, SHC, and TDI were within normal ranges for acyline + CDB-4022-treated rats, but were decreased (P < 0.05) in CDB-4022- or acyline + T + CDB-4022-treated rats. Serum inhibin B levels were nondetectable by Week 1 in males rendered irreversibly infertile by CDB-4022; levels increased transiently and returned to baseline in rats protected by acyline pretreatment. These data indicate that pretreatment with acyline was able to prevent irreversible infertility in CDB-4022-treated rats, whereas posttreatment with acyline did not promote spermatogonial differentiation, as has been observed by others in rats that received GnRH analogs and various other testicular toxicants. Suppression of ITT and possibly rFSH by acyline appeared to be crucial in preventing irreversible infertility induced by CDB-4022. In this regard, our results are similar to those of investigators who have studied other testicular toxicants. Continued development of CDB-4022 as a potential male contraceptive will depend largely on its safety profile and whether its antispermatogenic activity is reversible in primates.

The low gonadotropin-independent constitutive production of testicular testosterone is sufficient to maintain spermatogenesis

Spermatogenesis is thought to critically depend on the high intratesticular testosterone (T) levels induced by gonadotropic hormones. Strategies for hormonal male contraception are based on disruption of this regulatory mechanism through blockage of gonadotropin secretion. Although exogenous T or T plus progestin treatments efficiently block gonadotropin secretion and suppress testicular T production, only approximately 60% of treated Caucasian men reach contraceptive azoospermia. We now report that in luteinizing hormone receptor knockout mice, qualitatively full spermatogenesis, up to elongated spermatids of late stages 13-16, is achieved at the age of 12 months, despite absent luteinizing hormone action and very low intratesticular T (2% of control level). However, postmeiotic spermiogenesis was blocked by the antiandrogen flutamide, indicating a crucial role of the residual low testicular T level in this process. The persistent follicle-stimulating hormone action in luteinizing hormone receptor knockout mice apparently stimulates spermatogenesis up to postmeiotic round spermatids, as observed in gonadotropin-deficient rodent models on follicle-stimulating hormone supplementation. The finding that spermatogenesis is possible without a luteinizing hormone-stimulated high level of intratesticular T contradicts the current dogma. Extrapolated to humans, it may indicate that only total abolition of testicular androgen action will result in consistent azoospermia, which is necessary for effective male contraception.

Suppression of testosterone stimulates recovery of spermatogenesis after cancer treatment

It is important to develop methods to prevent or reverse the infertility caused by chemotherapy or radiation therapy for cancer in men. Radiation and some chemotherapeutic agents kill spermatogonial stem cells, but we have shown that these cells survive in rats, although they are unable to differentiate. There is evidence that this phenomenon also occurs in men. The block to spermatogonial differentiation in rats is caused by some unknown change, either in the spermatogonia or the somatic elements of the testis, such that testosterone inhibits spermatogonial differentiation. In the rat, the spermatogenesis and fertility lost following treatment with radiation or some chemotherapeutic agents can be restored by suppressing testosterone with gonadotropin releasing hormone (GnRH) agonists or antagonists, either before or after the cytotoxic insult. The applicability of this procedure to humans is still unknown. Some anticancer regimens may kill all the stem cells, in which case the only option would be spermatogonial transplantation. However, in some cases stem cells survive and there is one report of stimulation of recovery of spermatogenesis with hormonal treatment. Clinical trials should focus on treating patients with hormones during or soon after anticancer treatment. The hormone regimen should involve suppression of testosterone production with minimum androgen supplementation used to improve the diminished libido.