Clinical trial of gossypol as a male contraceptive drug. Part II. Hypokalemia study

A trifunctional contraceptive gel enhances the safety and quality of sexual intercourse

Current contraceptive methods come with a number of drawbacks, including low efficacy, in the case of commercial contraceptive gels, and a reduction in the quality of sexual intercourse, in the case of condoms. Adding pharmacologically-active agents to contraceptive gels holds the potential to improve sexual experience, and hardbor safety and hygiene. In this study, we fabricated a Carbomer-based contraceptive gel consisting of three agents: tenofovir, gossypol acetate, and nitroglycerin (TGN), with pH adjusted to 4.5 (to be compatible with the vagina). In vitro, the gossypol component of the contraceptive gel proved to be a significantly effective spermicide. When the concentration of gossypol acetate was 10 mg/ml, the spermicidal ability reached 100% after 30s. In addition, tenofovir in the gel significantly inhibited lentiviral transfection efficiency in cell-containing media. In 6 pairs of rats, the gel successfully prevented all females from conceiving after successful mating. Moreover, increased sexual frequency and enhanced erection, which were promoted by the nitroglycerin in the components, were observed in male rats that had the gel applied to their penises. This novel TGN contraceptive gel yielded a higher contraceptive success rate than that of the commercial contraceptive gel (Contragel®). In addition, it has the added benefits to prevent sexually transmitted diseases and improve male libido and erection function during sexual intercourse. Combining three FDA-approved and marketed agents together, our trifunctional TGN gel has a great potential for further translation and commercialization.

Update on Novel Hormonal and Nonhormonal Male Contraceptive Development

BACKGROUND

The advent of new methods of male contraception would increase contraceptive options for men and women and advance male contraceptive agency. Pharmaceutical R&D for male contraception has been dormant since the 1990s. The Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) has supported a contraceptive development program since 1969 and supports most ongoing hormonal male contraceptive development. Nonhormonal methods are in earlier stages of development.

CONTENT

Several hormonal male contraceptive agents have entered clinical trials. Novel single agent products being evaluated include dimethandrolone undecanoate, 11β-methyl-nortestosterone dodecylcarbonate, and 7α-methyl-19-nortestosterone. A contraceptive efficacy trial of Nestorone®/testosterone gel is underway. Potential nonhormonal methods are at preclinical stages of development. Many nonhormonal male contraceptive targets that affect sperm production, sperm function, or sperm transport have been identified.

SUMMARY

NICHD supports development of reversible male contraceptive agents. Other organizations such as the World Health Organization, the Population Council, and the Male Contraception Initiative are pursuing male contraceptive development, but industry involvement remains limited.

Emerging approaches to male contraception

Despite significant interests in contraception by men, effective methods of male contraception are limited to vasectomy and condoms. Recently, there have been several promising advances in male contraceptive research. This review will update readers on recent research in both hormonal and nonhormonal approaches to male contraception. Hormonal approaches to male contraception have been stymied by adverse effects, formulations requiring injections or implants, a 5% to10% nonresponse rate, as well as poor understanding of user acceptability. In the last several years, research has focused on novel, orally bioavailable androgens such as dimethandrolone undecanoate and 11β-methyl-19-nor-testosterone. Additionally, combinations of a topical testosterone gel combined with a gel containing segesterone acetate, a potent progestin, have shown promise in clinical trials recently. Simultaneously, significant preclinical progress has been made in several approaches to nonhormonal male contraceptives, including compounds that inhibit sperm motility such as eppin, compounds that inhibit retinoic acid binding or biosynthesis, and reversible approaches to obstruction of the vas deferens. It is imperative for these areas of research to continue making strides so that there is a gamut of contraceptive options for couples to choose from. Some of these approaches will hopefully reach clinical utility soon, greatly improving contraceptive choice for couples.

Gastric floating tablet improves the bioavailability and reduces the hypokalemia effect of gossypol in vivo

Gossypol (Gos) is a natural polyphenolic compound that has shown a number of valuable biological properties such as antifertility, antioxidation, and antitumor activities. However, the clinical application of Gos has been hindered by its notable adverse effects such as hypokalemia, hemolytic anemia, and so on. Using sustained-release dosage form provides a hopeful solution to this problem. In this study, a gastric floating tablet for sustained-release of Gos (Gos-GFT) was developed using polyvinylpyrrolidone, hydroxypropyl methyl cellulose, ethyl cellulose, lactose, sodium bicarbonate, and magnesium stearate. Gos-GFT had an average weight of around 200 mg with a drug content percentage of around 13.66%. The physicochemical properties of Gos-GFT satisfied the pharmacopoeial requirements for tablets. Gos-GFT was able to float in an acidic medium and had a sustained drug release for over 12 h. In vivo studies showed that the relative bioavailability of Gos-GFT, as compared with Gos powders, was larger than that of a non-gastric floating tablet which was a dosage form used for comparison with Gos-GFT. Furthermore, compared with the Gos powders and the non-gastric floating Gos tablets, Gos-GFT could prolong the in vivo action time of Gos, and significantly relieve hypokalemia which is a major adverse effect of Gos. These properties made Gos-GFT a promising Gos preparation that warrants further investigation for more extensive clinical applications of this natural compound.

Development of Novel Male Contraceptives

Unintended pregnancy is surprisingly common, accounting for 40-50% of pregnancies worldwide. Contraception is the most effective means of preventing unintended pregnancy. Seventy percent of all contraceptives are used by women; however, some women are unable to use contraceptives due to health conditions or side effects. Many men wish to take a more active role family planning, but currently have only two effective male contraceptive options, condoms and vasectomy. Therefore, work to develop novel male contraceptives analogous to popular female methods, such as daily pills or long-acting shots and implants, is underway. This paper will briefly discuss the pros and cons of condoms and vasectomies, and then review the research into novel methods of male contraception.

Male Contraceptive Development: Update on Novel Hormonal and Nonhormonal Methods

BACKGROUND

Development of new methods of male contraception would address an unmet need for men to control their fertility and could increase contraceptive options for women. Pharmaceutical research and development for male contraception was active in the 1990s but has been virtually abandoned. The Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) has supported a contraceptive development program since 1969 and supports the majority of hormonal male contraceptive development. Nonhormonal methods are also in development but are at earlier stages.

CONTENT

Several hormonal male contraceptive agents have entered clinical trials. Single-agent products being evaluated include dimethandrolone undecanoate, 11β-methyl-nortestosterone dodecyl carbonate, and 7α-methyl-19-nortestosterone. A contraceptive efficacy trial of Nestorone^® gel and testosterone gel in a single application will begin in 2018. Potential nonhormonal methods are at preclinical stages of development. Many nonhormonal male contraceptive targets that affect either sperm production or sperm function have been identified. Targeted pathways include the retinoic acid pathway, bromodomain and extraterminal proteins, and pathways for Sertoli cell-germ cell adhesion or sperm motility. Druggable targets include CatSper, the sperm Na+/K+-exchanger, TSSK, HIPK4, EPPIN, and ADAMs family proteins. Development of a procedure to reversibly block the vas deferens (initially developed in India in the 1980s) is undergoing early stage research in the US under the trade name Vasalgel™.

SUMMARY

NICHD has supported the development of reversible male contraceptive agents. Other organizations such as the World Health Organization and the Population Council are pursuing male contraceptive development, but industry involvement remains dormant.

The future of male contraception: a fertile ground

The continued and rapid expansion of the Earth’s population mandates the need for safe and effective measures of contraception. While a plethora of options exist for women, methods of contraception for the male partner are limited to condoms and vasectomy. The sequela of this discrepancy has led to the family planning burden falling disproportionately on the female partner. For the past several decades, extensive research has been undertaken exploring the feasibility of hormonal male contraception. This proposed method of contraception has focused on suppressing spermatogenesis by exploiting the hypothalamic-pituitary-gonadal (HPG) axis. Beginning with proof of concept studies in the early nineties, administration of testosterone in healthy male subjects has been shown to be an efficacious method of inducing sterility. Owing to ethnic differences in spermatogenesis suppression and the comparatively low rate of azoospermia in Caucasian men with androgen-only regimens, investigators have explored the addition of progestins to further enhance the efficacy of hormonal contraception. Though studies have revealed promise with androgen-progestin regimens, the lack of long-term studies has precluded the development of a marketable product. Recently, more research has been directed towards identifying non-hormonal alternatives to male contraception. These non-hormonal options have ranged from the development of devices facilitating reversible occlusion of the vas deferens lumen to medications disrupting various pathways in the process of spermatogenesis. Underlying the development of hormonal and non-hormonal strategies is the shared enthusiasm men and women have towards these male directed methods. The willingness of couples to pursue these alternatives combined with the global need to reduce the psychological and socioeconomic implications of unintended pregnancy ensures that research will continue to bring this goal to fruition.

Phenolic Profiling and Evaluation of Contraceptive Effect of the Ethanolic Extract of Salsola imbricata Forssk. in Male Albino Rats

Reported researches dealing with either composition or bioactivity of Salsola imbricata are limited. This study was conducted aiming to investigate the phenolic composition of the plant and evaluate its efficacy as male contraceptive. Polyphenols, namely, phenolic acids and flavonoids, were qualitatively and quantitatively analysed by RP-HPLC in the hydrolysed methanol extract using two different wavelengths, 280 and 330 nm. The efficiency of different solvents in extracting the plant phenolics was assessed via spectrophotometric determination of the total phenolic and flavonoid contents. Acute toxicity study was carried out on the ethanolic extract to ascertain its safety prior to biological evaluation. The contraceptive effect was assessed, in male rats, by oral administration of the extract at two doses (250 and 500 mg/kg b. wt.), over a period of 65 days. HPLC analyses allowed the identification and quantification of a total of 13 and 8 components in the hydrolysed-methanol extract; the overall phenolic composition was dominated by quercitrin (12.692%) followed by coumaric acid (4.251%). Prolonged oral administration of the ethanolic extract caused slight reduction in the testis weight only. A significant decrease in the sperm count was observed (P < 0.01) in the two treated groups while significant decrease in the epididymal sperm motility was only observed in the high dose group. Morphological abnormalities were observed in sperms of treated animals. No distinct change in serum FSH, LH, and testosterone concentration was recorded. The histopathological findings supported to a high extent these results. The male contraceptive activity of Salsola imbricata could be ascribed to its phenolic components, especially quercitrin.

Male contraception: history and development

Although the twentieth century has seen great strides in the development of female contraception, not a single new agent has been introduced as an approved method for common use for male contraception. Condoms (considered uncomfortable by some) and vasectomy (a permanent invasive procedure) are the only options provided to men, leaving an undue burden on women to bear contraceptive responsibility. Significant developments have, however, been made with regard to hormonal and nonhormonal contraception, and minor, reversible, procedural contraception. This article reviews the currently available, soon to be available, and theoretically possible methods of male contraception.

Male contraception

Contraception is an accepted route for the control of population explosion in the world. Traditionally hormonal contraceptive methods have focused on women. Male contraception by means of hormonal and non hormonal methods is an attractive alternative. Hormonal methods of contraception using testosterone have shown good results. Non hormonal reversible methods of male contraception like reversible inhibition of sperm under guidanceare very promising. In this article we have reviewed the current available options for male contraception.

La contraception masculine « verte »: mythe ou réalité ?

Le refus des solutions « chimiques », souvent jugées suspectes, mène un nombre croissant de contemporains à rechercher une alternative naturelle chaque fois qu’elle existe. Le domaine médical — et en particulier celui qui concerne la reproduction — échappe d’autant moins à cette aspiration qu’il s’y trouve des bases historiques multimillénaires. Il a également des justifications économiques dans tous les pays où l’accès aux médicaments est problématique, sinon illusoire. La contraception masculine n’est pas oubliée dans ce contexte; en particulier dans les pays émergents où la natalité élevée pose un problème de société. Des principes actifs extraits de plantes ont fait — et font encore-l’objet de recherches très circonstanciées. Il existe de bonnes raisons de penser que des solutions existent dans ce registre. Des tests menés in vivo chez l’animal (surtout), mais aussi in vitro sur des spermatozoïdes isolés concluent à l’existence d’effets centraux, périphériques ou spermicides significatifs. Les vertus thérapeutiques souvent multiples des plantes concernées mènent toutefois à rester vigilants pour ne pas associer, en cas d’utilisation systémique, un effet secondaire indésirable à l’effet contraceptif recherché.

Antifertility effects of Oldenlandia affinis in male rats - a preliminary study

Antifertility effects of an aqueous leaf extract of Oldenlandia affinis on male rats were investigated. The extract was administered intraperitoneally in sexually mature male rats at a dose of 24 mg/rat (n=8) for a total of eight injections over a 4 week period. There was a decrease in testis weights but all other accessory sex organs and vital organ weights were not affected by treatment with O. affinis extract. Testis histology revealed fewer spermatozoa or azoospermic seminiferous tubules in treated animals compared to controls with no change in neither tubule thickness nor Sertoli cell structure. O. affinis treatment caused a 17% decrease in sperm motility but there was no change in cauda epididymal sperm counts. However, serum testosterone levels decreased significantly (P<0.05) in the experimental group (602.4 ± 57 ng/dL) compared to controls (808.9 ± 55 ng/dL). These preliminary results show that the aqueous leaf extract of O. affinis suppresses fertility parameters in male rats.

Advances in male contraception

Despite significant advances in contraceptive options for women over the last 50 yr, world population continues to grow rapidly. Scientists and activists alike point to the devastating environmental impacts that population pressures have caused, including global warming from the developed world and hunger and disease in less developed areas. Moreover, almost half of all pregnancies are still unwanted or unplanned. Clearly, there is a need for expanded, reversible, contraceptive options. Multicultural surveys demonstrate the willingness of men to participate in contraception and their female partners to trust them to do so. Notwithstanding their paucity of options, male methods including vasectomy and condoms account for almost one third of contraceptive use in the United States and other countries. Recent international clinical research efforts have demonstrated high efficacy rates (90-95%) for hormonally based male contraceptives. Current barriers to expanded use include limited delivery methods and perceived regulatory obstacles, which stymie introduction to the marketplace. However, advances in oral and injectable androgen delivery are cause for optimism that these hurdles may be overcome. Nonhormonal methods, such as compounds that target sperm motility, are attractive in their theoretical promise of specificity for the reproductive tract. Gene and protein array technologies continue to identify potential targets for this approach. Such nonhormonal agents will likely reach clinical trials in the near future. Great strides have been made in understanding male reproductive physiology; the combined efforts of scientists, clinicians, industry and governmental funding agencies could make an effective, reversible, male contraceptive an option for family planning over the next decade.

Nonhormonal drugs for contraception in men: a systematic review

Nonhormonal drugs for contraception in men may have advantages over hormonal methods. The nonhormonal methods can have more rapid onset and less interference with androgen-dependent functions. This systematic review summarizes the clinical studies evaluating nonhormonal drugs administered to men for contraception. Relevant clinical results were found for gossypol, which is derived from the cotton plant, and for extracts of Tripterygium, a plant used in Chinese traditional medicine. Randomized, controlled trials were available on the efficacy of gossypol and on the effect of gossypol on potassium levels. Gossypol had problems with low efficacy and toxicity. For Tripterygium, 2 observational studies described men who were treated for rheumatoid arthritis. Although sperm density was lower among those taking Tripterygium, later reports indicated some toxicity. Nonclinical research continues on isolates of Tripterygium. No clinical studies for contraception in men were found for nonhormonal vaccines or neem, which is also a plant used for medicinal purposes. Clinical trials studied injecting styrene maleic anhydride into the vas deferens, but no comparative data were provided. At this time, no safe and effective nonhormonal drug is available for contraception in men.

TARGET AUDIENCE

Obstetricians & Gynecologists, Family Physicians.

LEARNING OBJECTIVES

After completion of this article, the reader should be able to state that the number of studies concerning the use of nonhormonal drugs for male contraception are very limited, point out that the two nonhormonal drugs used to a small degree have varying results and serious side effects, and recall that there are limited clinical studies on use of vas deferens injections and vaccines in humans.

Male contraception

The provision of safe, effective contraception has been revolutionized in the past 40 yr following the development of synthetic steroids and the demonstration that administration of combinations of sex steroids can be used to suppress ovulation and, subsequently, other reproductive functions. This review addresses the current standing of male contraception, long the poor relation in family planning but currently enjoying a resurgence in both scientific and political interest as it is recognized that men have a larger role to play in the regulation of fertility, whether seen in geopolitical or individual terms. Condoms and vasectomy continue to be popular at particular phases of the reproductive lifespan and in certain cultures. Although not perfect contraceptives, condoms have the additional advantage of offering protection from sexually transmitted infection. The hormonal approach may have acquired the critical mass needed to make the transition from academic research to pharmaceutical development. Greatly increased understanding of male reproductive function, partly stimulated by interest in ageing and the potential benefits of androgen replacement, is opening up other avenues for investigation taking advantage of nonhormonal regulatory pathways specific to spermatogenesis and the reproductive tract.

Gossypol: reasons for its failure to be accepted as a safe, reversible male antifertility drug

Following clinical trials conducted in China in the 1970s, gossypol was proposed as a drug for male contraceptive use. This review summarizes the extensive investigations on formal animal toxicology and on the recovery of fertility in men after stopping gossypol treatment which led to the decision by the Special Programme of Research, Development and Research Training in Human Reproduction (HRP) at the World Health Organization (WHO), that gossypol would not be acceptable as an antifertility drug. It is concluded that the assessment of gossypol reinforces the mandatory requirement that future contraceptive drugs must be developed by the established routes of appropriate animal toxicology and phased clinical studies.

Haematological and serum biochemical changes in the rat due to protein malnutrition and gossypol-ethanol interactions

The effects of protein malnutrition on haematological and serum biochemical values were evaluated in gossypol-treated rats which were simultaneously fed with ethanol. Gossypol caused anaemia, leucopenia and thrombocytopenia in malnourished animals, suggesting a depression of bone marrow activity. Gossypol also caused a significant elevation of serum alkaline phosphatase and alanine aminotransferase activities and increases in the concentrations of Mg++ and Ca++ with reduced albumin, regardless of the nutritional status. These changes were more severe with malnutrition. Ethanol alone caused a thrombocytopenia but no other significant haematological changes. However, it appeared to cause derangement of lipid and protein metabolism as reflected in serum cholesterol and urea. The toxic effects seen in gossypol-treated rats were significantly reduced in animals simultaneously given ethanol. As the livers of gossypol-treated rats were significantly heavier than in these animals, it seems possible that ethanol consumption enhances the ability of the liver to metabolize gossypol, thereby reducing its accumulation and consequently its toxicity. However, further studies are needed to determine the mechanisms responsible.

Genetic toxicity studies of gossypol

Gossypol, a polyphenolic compound extracted from cotton plants, shows promise for use as a male contraceptive, as well as a treatment for gynecological disorders, cancer, and certain microbial diseases. Before gossypol can be considered safe for widespread human use, particularly by healthy people of childbearing age, its effect on normal genetic processes should be understood. Characterization of gossypol's genotoxic potential has not been approached systematically, although numerous clinical and laboratory studies have addressed issues relating to genetic effects of gossypol. This review summarizes results of relevant studies and offers recommendations for the emphasis of future efforts to understand gossypol's genotoxicity potential. Evidence suggesting that gossypol has any genotoxic effects in mammals under normal physiologic conditions so far is weak, at best. However, several unresolved issues that are important for establishing long-term genetic safety of gossypol were uncovered by this analysis. These include the need for a better understanding of the significance of weak increases in SCE frequency seen in a number of laboratory exposure studies, and more definitive, comprehensive animal tumor bioassay data.

Effects of gossypol acetate on pituitary-adrenal axis in male albino rats

Histopathological effects of gossypol acetate (GA) on pituitary-adrenal axis in male Wistar rats were investigated. Sexually mature rats of proven fertility were administered orally with 10 and 25 mg/kg for 4 and 5 weeks, respectively. In both experimental groups, corticotrophs (ACTH cells) of anterior pituitary showed progressive regression. At the 10 mg low-dose treatment for 4 weeks, no significant changes were observed in all the zones of the adrenal gland, while at the same dose for 5 weeks of treatment, cells of zona glomerulosa showed hypertrophy and degranulation as compared to that of control. Cells of zona fasciculata and reticularis showed no significant changes. In the medulla, the thickly granulated cells were degranulated and reduced in number. At the 25 mg treatment, the cells of the zona fasciculata showed hypertrophy and degranulation. The possible mechanism of action of GA is discussed.

Relationship between hormone profiles and the restoration of spermatogenesis in men treated with gossypol

Gossypol acetic acid was administered orally to 35 male volunteers at a dose of 20 mg once a day for 52-70 days in the loading phase and twice a week for 22 months in the maintenance phase. Sperm counts and the serum concentrations of LH, FSH, prolactin, testosterone and oestradiol were monitored regularly during treatment and for a follow-up period of 12 months. At around 90 days after treatment, all treated participants approached or attained azoospermia and remained at this level throughout the maintenance phase. By the end of the follow-up phase, eight treated men were still azoospermic, while sperm counts in the other 27 men were restored to normal levels. The only hormone that changed significantly during and after the treatment was FSH. From the 6th month of the treatment to the end of the follow-up phase, serum concentrations of FSH in the eight participants that reached irreversible azoospermia were significantly higher than in the other 27 men or in controls. It is suggested that monitoring of FSH levels might be of diagnostic use for identifying those participants with irreversible azoospermia during gossypol treatment.

Effects of gossypol on the motility of mammalian sperm

The effects of the male contraceptive gossypol on the motility of mammalian spermatozoa are reviewed. The role of sperm motility in the processes of fertilization and the effect of the drug on these processes determine its effectiveness as a contraceptive. The promising male contraceptive potential of gossypol is discussed in the context of the serious adverse effects of the agent.

Gossypol as a toxicant in livestock

Many cases of gossypol toxicity have been misdiagnosed. The long-held belief that gossypol toxicity did not occur in ruminants has been a major hurdle to overcome. Field necropsies in which pulmonary congestion and edema were attributed to shipping-fever pneumonia, failure to examine the heart either grossly or microscopically, failure to believe that 200 ppm free gossypol could kill a calf, failure to believe that any age of sheep could suffer gossypol toxicity, and failure to believe that just because you fed the same thing last year, it will not cause a problem this year, all were factors in causing the misdiagnosis of this toxicity. Gossypol toxicity cases diagnosed will increase each year because of increased awareness among veterinarians. Continued research will help to increase our understanding of this multifactored toxin and, possibly, devise ways to detoxify it before it is utilized in a feed. Until then, it will have to be considered because it will continue to be present as a potential toxicant in the feed.

Inactivation of human immunodeficiency virus in vitro by gossypol

Gossypol, a polyphenolic aldehyde extracted from cottonseed, is a male anti-fertility agent which has been reported to have anti-viral activity. In this paper we report that gossypol inactivates human immunodeficiency virus (HIV) in an in vitro system. Following exposure of cell-free incubates of HIV to 100 uM gossypol, ultracentrifugation and inoculation of the washed pellet onto H9 cells, there is no evidence of elevated reverse transcriptase activity over 21 days. Treatment with lower concentrations of gossypol reduces the peak and lengthens the time to maximal reverse transcriptase activity compared with control cultures. These observations suggest that gossypol could be used as a vaginal spermicidal/virucidal agent. The mechanism of the in vitro anti-viral action as well as the effect of orally administered gossypol on the infectivity of semen of HIV-seropositive men warrant further study.