Translational fusion of two beta-subunits of human chorionic gonadotropin results in production of a novel antagonist of the hormone

The strategy of translationally fusing the alpha- and beta-subunits of human chorionic gonadotropin (hCG) into a single-chain molecule has been used to produce novel analogs of hCG. Previously we reported expression of a biologically active single-chain analog hCGalphabeta expressed using Pichia expression system. Using the same expression system, another analog, in which the alpha-subunit was replaced with the second beta-subunit, was expressed (hCGbetabeta) and purified. hCGbetabeta could bind to LH receptor with an affinity three times lower than that of hCG but failed to elicit any response. However, it could inhibit response to the hormone in vitro in a dose-dependent manner. Furthermore, it inhibited response to hCG in vivo indicating the antagonistic nature of the analog. However, it was unable to inhibit human FSH binding or response to human FSH, indicating the specificity of the effect. Characterization of hCGalphabeta and hCGbetabeta using immunological tools showed alterations in the conformation of some of the epitopes, whereas others were unaltered. Unlike hCG, hCGbetabeta interacts with two LH receptor molecules. These studies demonstrate that the presence of the second beta-subunit in the single-chain molecule generated a structure that can be recognized by the receptor. However, due to the absence of alpha-subunit, the molecule is unable to elicit response. The strategy of fusing two beta-subunits of glycoprotein hormones can be used to produce antagonists of these hormones.

Establishment of the need for oestrogen during implantation in non-human primates

Deprivation of oestrogen during post-ovulatory mated cycles in proven fertile female bonnet monkeys by tamoxifen, aromatase inhibitor or oestrogen antiserum resulted in inhibition of pregnancy establishment in all three groups of animals. However, more than 85% of the animals became pregnant within three exposures to proven fertile males in the control group. These results suggest the requirement for oestrogen in pregnancy establishment in primates. Based on this conclusion, it is suggested that use of a suitable and potent anti-oestrogenic compound can be exploited as an alternative approach to contraception.

Effect of chronic administration of 7alpha-methyl-19-nortestosterone on serum testosterone, number of spermatozoa and fertility in adult male bonnet monkeys (Macaca radiata)

Hormonal approaches to male contraception that are based on the suppression of LH secretion require androgen replacement treatment to maintain sexual behaviour and secondary sexual characteristics. Androgen supplementation not only involves large and frequent doses of testosterone esters but also results in undesirable effects on the prostate gland. In an attempt to avoid such problems, a synthetic androgen, 7alpha-methyl-19-nortestosterone (MENT), which is much more potent than testosterone, has been developed. In the present study, MENT was administered at different doses (25, 50, 100, 300 and 1000 microg day(-1)) either alone or in combination with oestradiol via Silastic implants for a specified period to adult male bonnet monkeys (Macaca radiata). Blood and semen samples were collected at specific intervals and analysed for serum testosterone and seminal parameters, respectively. The results of the present study clearly indicate that administration of MENT at all doses tested results in suppression of the nocturnal surge of testosterone (by day 3), as well as a decrease in the number of spermatozoa (by day 45). Co-administration of oestradiol resulted in a reduction in the dose of MENT required to suppress the nocturnal surge. None of the male bonnet monkeys treated with MENT were able to impregnate females, clearly demonstrating the efficacy of MENT in blocking fertility in male bonnet monkeys.

Immunobiology of a synthetic luteinizing hormone receptor peptide 21-41

Immunization of adult male rabbits with a synthetic luteinizing hormone-receptor peptide (LH-RP; representing amino-acids 21-41 of the extracellular domain of the rat LH receptor) resulted in production of high-titer antibodies capable of interacting with particulate and cell-based LH receptors. The antibody produced was able to inhibit binding of 125I-labeled human chorionic gonadotropin (hCG) to a particulate sheep luteal LH receptor preparation by 40%-50%. Maximal inhibitory activity was correlated with high antibody titer. Immunocytometry revealed that the antibody could directly bind to cells having LH receptors, such as rat granulosa and Leydig cells. The antibodies recognized a 77-kilodalton membrane protein in Western blots of mouse testicular extracts. Interaction of endogenous Leydig cell LH receptor with the LH-RP antibody resulted in both hormone agonist and antagonistic activities. The hormone-mimicking activity (increase in serum testosterone over control) was confined only to the early phase of immunization when the antibody titer was low. Blockade of LH receptor during the later part of immunization resulted in a significant reduction in serum testosterone over controls and inhibition of spermatogenesis. DNA flow cytometry showed that a specific and significant inhibition of meiosis (transformation of primary spermatocytes to round and elongated spermatids P < .01) and spermiogenesis (transformation of round spermatids to elongated spermatids P < .0001) occurred following blockade of LH function.

Alterations in sperm characteristics of follicle-stimulating hormone (FSH)-immunized men are similar to those of FSH-deprived infertile male bonnet monkeys

The quality of sperm ejaculated by bonnet monkeys and normal, healthy proven fertile volunteer men, both actively immunized with ovine follicle-stimulating hormone (oFSH), was examined at different times of study for chromatin packaging and acrosomal glycoprotein concentration by flow cytometry. Susceptibility of sperm nuclear DNA to dithiothreitol (DTT)-induced decondensation, as measured by ethidium bromide binding, was markedly high compared with values at day 0 in men and monkeys during periods when FSH antibody titer was high. Sperm chromatin structure assay yields alphat values, which is another index of chromatin packaging. Higher alphat values, signifying poor packaging, occurred in both species following immunization with heterologous pituitary FSH. The binding of fluorosceinated pisum sativum agglutinin (PSA-FITC) to acrosome of sperm of monkeys and men was significantly low, compared with values at day 0 (control) during periods when cross-reactive FSH antibody titer was high and endogenous FSH was not detectable. Blockade of FSH function in monkeys by active immunization with a recombinant oFSH receptor protein corresponding to a naturally occurring messenger RNA (mRNA) also resulted in production of sperm with similar defects in chromatin packaging and reduced acrosomal glycoprotein concentration. Thus, it appears that in monkeys and men, lack of FSH signaling results in production of sperm that exhibit defective chromatin packaging and reduction in acrosomal glycoprotein content. These characteristics are similar to that exhibited by sperm of some class of infertile men. Interestingly, these alterations in sperm quality occur well ahead of decreased sperm counts in the ejaculate.

Effect of long-term treatment with aromatase inhibitor on testicular function of adult male bonnet monkeys (M. radiata)

The role/need for estrogen in regulating testicular function of adult male bonnet monkeys (M. radiata) has been investigated by dosing orally a group of five normal males 2.5 mgs of CGP 47645, a long-acting nonsteroidal aromatase inhibitor (AI), once every 5 days for over 150 days. Such treatment resulted in a 10-fold increment in nocturnal serum testosterone (T) levels, which were sustained for 85 days of treatment, and a twofold increment in basal serum T levels was present throughout the 150 days of treatment. Analysis of ejaculated semen showed a marked reduction (approximately 90%) in sperm counts in four out of five monkeys between Days 55-85 of treatment. During this period, the motility score also was markedly reduced from a normal score of 3-5 to 0-2. Flow cytometric analysis of testicular germ cells obtained from biopsy tissue taken on Days 63 and 120 indicated a marked reduction only in elongating/elongated spermatid population (compared to Day 0 values), suggesting inhibition in spermiogenic process. Epididymal sperm maturation also seemed effected as sperm chromatin, on flow cytometric analysis for decondensability following exposure to 5 mM dithiotreitol, showed to be in a hypercondensed state. This study thus indicates that estrogen has an important role in providing normal testicular and sperm function in the primate.

Demonstration of complimentarity between monoclonal antibodies (MAbs) to human chorionic gonadotropin (hCG) and polyclonal antibodies to luteinizing hormone/hCG receptor (LH-R) and their use in better understanding hormone-receptor interaction

We have earlier reported that polyclonal antisera raised in rabbits to a luteinizing hormone/chorionic gonadotropin receptor (LH-R) purified from sheep luteal tissue has antibodies exhibiting hormone agonistic and antagonistic activities. Western blot analysis showed this antibody (LHR-anti IgG) to be highly specific to sheep luteal LH receptor (LH-R) (Jeyakumar and Moudgal, 1991). Using this, along with a battery of mouse monoclonal antibodies (MAbs) to hCG, an attempt has been made to better understand the interaction of LH/hCG with its receptor. Of the eight hCG MAbs screened, three (B14/B7, B52/18 and A7/G4) were specific to the beta-subunit; while a second set of three (G10/F7, H9/E9 and B52/21) were specific to the alpha-subunit. Two additional MAbs (B52/28 and F9/G8) did not recognize individual subunits, but bound like the rest intact hCG. Both 125I hCG and 125I anti LHR-IgG bound specifically to ovine luteal membrane LH-R. Assuming that a certain degree of similarity should exist between hCG and LHR-anti IgG, different hCG MAbs were tested for their ability to block the binding of either 125I hCG or 125I LHR-anti IgG to sheep luteal LH-R. It appears that hCG and LH-R share a minimum of four sites that are complementary to each other and these are recognized by the hCG MAbs B14/B7, G10/F7, A7/G4, and H9/E9. Whereas two of the MAbs B14/B7 and G10/F7 blocked the binding of both 125I labeled hCG and LHR-anti IgG to the receptor, MAbs A7/G4 and H9/E9 only inhibited the binding of 125I LHR-anti IgG to the LH-R. Although individually B14/B7 and G10/F7 blocked the binding of 125I LHR-anti IgG to LH-R to a maximum extent of 43%, together they inhibited binding by as much as 80%. The ability of B14/B7 to inhibit binding of 125I LHR-anti IgG to the receptor was also significantly increased by the addition of A7/G4. Finally, by demonstrating direct binding of the immobilized hCG MAbs B14/B7, G10/F7, A7/G4, and H9/E9 to LHR-anti IgG, we have been able to establish that the receptor binding sites of hCG and LHR-anti IgG are complementary and that a set of four sites are recognizable by the hCG MAbs. From the degree of interaction, it appears that two sites recognized by MAbs B14/B7 and G10/F7 (representing a site each in the beta- and alpha-subunit of hCG) have a prominent role in the interaction of hCG with its receptor. Thus, this study has provided us with an opportunity to investigate the interaction of LH/hCG with its receptor by an indirect approach of monitoring the binding of their respective antibodies with each other.

Effect of chronic administration of Tamoxifen on fertility in male bonnet monkeys (Macaca radiata)

Administration of Tamoxifen via the Alzet pump at a rate of 50 micrograms hr-1 for 90 days in the adult male bonnet monkeys Macaca radiata had no effect on the serum testosterone concentration determined at 10 AM and 10 PM as well as total sperm count determined at 15-day intervals over a period of 260 days. However, a significant reduction in sperm motility was observed beyond 90 days up until the 225th day. Breeding studies conducted from day 90 to 260 revealed that these males were infertile.

Electroejaculation and seminal parameters in bonnet monkeys (Macaca radiata)

In the present study, our experience in the collection of semen from adult bonnet monkeys and some of the characteristics of semen are reported. Semen samples were collected by penile stimulation every 15 days over a period of 3 years. The penile method of ejaculation was more consistent with an increased volume of semen. A distinct sesonality in the sperm count of the bonnet monkey was observed. Sperm counts were high during the months of August to October and started declining from November onwards. The sperm counts were significantly (P < 0.05) higher during the mid and post-monsoon (July to November) periods than the pre- and early monsoon (March to June) periods.

Use of norethisterone and estradiol in mini doses as a contraceptive in the male. Efficacy studies in the adult male bonnet monkey (Macaca radiata)

Administration of norethisterone (NET) or NET + estradiol benzoate using an Alzet minipump or as once-a-month intramuscular injection of their depot forms, NET-enanthate (NET-EN) and estradiol valerate (E-val), resulted in azoospermia in all monkeys (n = 13) within 60 to 150 days of treatment. Although addition of depot form of testosterone (T, 20 mg/month) to the regimen restored the behavioral response typical of a normal male, it did not reverse the azoospermic state. Serum T (heightened nocturnal) levels were significantly reduced (> 85%, p < 0.001) in all the treated groups. Evidence for blockade in spermatogenesis following treatment was obtained by DNA flow cytometry. Following withdrawal of treatment, the T level was restored to normalcy within 15 days but 120 days more were required for the animals to exhibit normal sperm counts. In conclusion, the efficacy of once-a-month injection of relatively low doses of NET-EN + E-Val to bring about azoospermia in monkeys, in a relatively short time, has been demonstrated. As the results are uniform and reproducible, it appears desirable that this steroid regimen be tested in man for its contraceptive efficacy.

Development of male contraceptive vaccine--a perspective

This paper reviews the recent advances that have occurred in the area of development of a male contraceptive vaccine. The vaccine candidates considered for review are hormone/hormone receptor-based proteins including luteinizing hormone-releasing hormone (LHRH)/LH, follicle stimulating hormone (FSH), as well as LH and FSH receptor proteins. The review also highlights the advances in our basic understanding of gonadotrophin action which have led to development of these vaccines. Focus is mainly on studies in the non-human primate which may be directly relevant to projected studies in the human. The data indicate that the vaccines are well tolerated by the primate (including the human based on limited data) and do not give rise to any known toxic symptoms or immediate health hazards. The response to the immunogen has been uniform and it may be possible to increase antibody titres as well as prolong the immune response by adding acceptable immune stimulators to the adjuvant cocktail and developing better immunization schedules or immunogen delivery systems. Contraceptive vaccines for the male are a feasible proposition and attention should now be focussed on evaluating carefully the bioefficacy of antibodies raised to recombinant ovine FSHbeta or FSH receptor protein fragments in both human and non-human primates. The advantage of the FSH/FSH receptor over the LHRH/LH-based vaccine lies in the fact that the former does not require an exogenous testosterone supplement to maintain accessory gland function, libido etc. The LHRH/LH-based vaccine results in azoospermia, while the FSH vaccine causes the production of low numbers of poor quality spermatozoa which are incapable of impregnating cycling females.

Immunization of male bonnet monkeys (M. radiata) with a recombinant FSH receptor preparation affects testicular function and fertility

Immunization of proven fertile adult male monkeys (n=3) with a recombinant FSH receptor protein preparation (oFSHR-P) (representing amino acids 1-134 of the extracellular domain of the receptor Mr approximately 15KDa) resulted in production of receptor blocking antibodies. The ability of the antibody to bind a particulate FSH receptor preparation and receptors in intact granulosa cells was markedly (by 30-80%) inhibited by FSH. Serum T levels and LH receptor function following immunization remained unchanged. The immunized monkeys showed a 50% reduction (p<0.001) in transformation of spermatogonia(2C) to primary spermatocytes (4C) as determined by flow cytometry and the 4C:2C ratio showed a correlative change (R 0.81, p<0.0007) with reduction in fertility index (sperm counts X motility score). Breeding studies indicated that monkeys became infertile between 242-368 days of immunization when the fertility index was in the range of 123+/-76 to 354+/-42 (compared to a value of 1602+/-384 on day 0). As the effects observed are near identical to that seen following immunization with FSH it is suggestive that oFSHR-P can substitute for FSH in the development of a contraceptive vaccine.

Effect of estrogen deprivation on the reproductive physiology of male and female primates

The availability of CGS 16949A, CGS 20267 and CGP 47645, a series of aromatase inhibitors (AIs) having high specific activity and specificity, made possible this study wherein the need for estrogen (E) for regulating (a) follicular maturation/ovulation, luteal function and pregnancy establishment, and (b) testicular function of the bonnet monkey (Macaca radiata) has been examined. Generally these compounds, used in the range of 500 microg to 2.5 mg/day did not inhibit follicular maturation although they did reduce E levels. Although low doses had no effect on ovulation it appears that relatively high doses of CGS 20267 and CGP 47645 could be inhibiting it. Three oral doses of letrozole (CGS 20267, each dose of 2 mg) during the follicular phase resulted in the formation of multiple follicles in cycling females, and these could be ovulated by exogenous hCG (1000 IU) treatment. Although administration of AI during the early luteal phase had no effect on progesterone (P) production, it prevented pregnancy establishment. Whereas AI administration in the female had no significant effect on luteinizing hormone (LH) and follicle stimulating hormone (FSH) levels (except at high drug dosages), it significantly increased serum testosterone (T) levels in the male. Sustained high levels of T (30-50 ng/ml) could be maintained for 100 days by administering 2.5 mg of CGP 47465 orally once in 5 days. Blockade of E synthesis in the male led to the disruption of testicular germ cell transformation, which in turn resulted in a significant reduction in sperm production. These studies with aromatase inhibitors in the monkey suggest that these compounds have a potential for use as fertility regulating agents in both the male and female primate.

Breeding of bonnet monkeys (Macaca radiata) in captivity

The results of studies on the breeding of South Indian bonnet monkeys (macaca radiata) over 20 years at our institution are presented. The menstrual cycle and hormonal changes were similar to those reported for Macaca mulatta. It was noted that summer amenorrhoea could be eliminated by housing the monkeys in rooms supplied with humidified air. Although a fertility index (proportion of animals becoming pregnant within three exposures to a proven fertile male) of 60 to 65% was achieved by random breeding, an index of 80 to 85% was achieved by controlled breeding (prior monitoring of serum estradiol-17 beta concentration on days 7, 8, 9, and 10).

Changes in testicular function following specific deprivation of LH in the adult male rabbit

Sexually mature male rabbits actively immunized against highly purified ovine LH (oLH) were used as a model system to study the effects of endogenous LH deprivation (and therefore testosterone) on spermatogenesis as well as pituitary FSH secretion. Immunization against oLH generated antibody titres capable of cross-reacting and neutralizing rabbit LH and this resulted in a significant reduction (P < 0.01) in serum testosterone levels by 2-4 weeks of immunization. A significant increase in circulating FSH concentration (from a basal level of approximately 1 ng to 60-100 ng/ml; P < 0.01) was observed within 4-6 weeks of immunization, perhaps a consequence of the negative feedback effect of the lack of testosterone. The effect of LH deprivation on spermatogenesis assessed by DNA flow cytometry and histological analyses of testicular biopsy tissue revealed that lack of testosterone primarily results in a rapid reduction and complete absence of round (1C) and elongated (HC) spermatids. The immediate effect of LH/testosterone deprivation thus appears to be at the step of meiotic transformation of primary spermatocytes (4C) to 1C. A significant reduction (> 80%; P < 0.01) in the 4C population and a relative accumulation (> 90%; P < 0.01) in spermatogonia (2C) was also observed, suggesting a need for testosterone during the transformation of 2C to 4C. In all but one of the rabbits, both qualitative and quantitative recovery in spermatogenesis occurred during the recovery phase, even at a time when only a marginal increase in serum testosterone (compared with the preimmunization) levels was observed as a result of a rapid decline in the cross-reactive antibody titres. These results clearly show that LH/testosterone deprivation in addition to primarily affecting the meiotic step also regulates the conversion of 2C to 4C during spermatogenesis.

Chronic suppression of testicular function by constant infusion of gonadotropin-releasing hormone agonist and testosterone supplementation in the bonnet monkey (Macaca radiata)

OBJECTIVE

To study the efficacy of long-term buserelin acetate infusion to desensitize pituitary and block testicular function in adult male monkeys (Macaca radiata).

ANIMALS

Proven fertile male monkeys exhibiting normal testicular function.

PROTOCOL

Each of the control (n = 5) and experimental monkeys (n = 10) received a fresh miniosmotic pump every 21 days, whereas pumps in controls delivered vehicle of experimentals released 50 micrograms buserelin acetate every 24 hours. On day 170 (renewed every 60 days) a silastic capsule containing crystalline testosterone (T) was implanted in the experimental monkeys. At the end of 3 years, treatment was stopped, and recovery of testicular function and fertility monitored.

RESULTS

(1) Treatment resulted in marked reduction of nocturnal but not basal serum T; (2) the pituitary remained desensitized to buserelin acetate throughout the 3-year period; (3) animals were largely azoospermic with occasional oligospermia exhibited by two monkeys; and (4) withdrawal of treatment restored testicular function, with 70% of animals regaining fertility.

CONCLUSION

Long-term infertility (but restorable) can be induced in male monkeys by constant infusion of buserelin acetate and T.