Anti-fertility and other actions of gossypol analogues

From a series of gossypol derivatives studied, we conclude that the carbonyl groups of gossypol are needed for inhibition of erythrocyte anion transport and the hydroxy groups affect but are not essential to that inhibition. In an in vitro mouse erythroleukemia cytocidal assay, the most active compounds were gossypol and apogossypol. The latter was not active in the inhibition of erythrocyte anion transport or in a spermicidal assay. Of the more simple structures related to gossypol, those that were active in the cytocidal and spermicidal assays were bi-aromatic, linked by a 1- and not a 4-carbon chain and had free phenolic hydroxyl groups. These results are included in a discussion of the specificity and mechanism of action of gossypol.

Interaction of gossypol with sperm macromolecules and enzymes

The interaction of gossypol with sperm macromolecules is an important process for the gossypol action. It is of our interests to study the nature of this interaction in order to understand the mechanism of action of gossypol. Our experimental results support the thesis that gossypol inhibits sperm motility by blocking ATP production and utilization. The drug acts on the mitochondria, suppressing oxygen consumption, inhibiting pyruvate dehydrogenase and ATPase activities and probably on the motility apparatus by blocking dynein ATPase activity and preventing protein phosphorylation. The nature of the chemical bond in the interaction of gossypol and macromolecules is through the Schiff base formation and by the hydrophobic and nucleophilic attraction.

Experiences with gossypol as a male pill

In 1981 to 1983 we performed a clinical study with gossypol involving 152 participants, and in 1983 to 1985 we conducted another study of 120 participants. The first study was aimed at confirming gossypol's antifertility efficacy and determining the existence of side effects. The objective of the latter study was to find out whether the addition of a potassium salt supplement or a potassium-sparing agent could alleviate the side effect of hypokalemia. In both studies, the participants took a gossypol pill, 20 mg/day for 60 to 75 days for loading, and 50 mg/wk for maintenance. All participants were followed up for a year. The antifertility efficacy was found to be more than 90%, and the chief side effect was lowered serum potassium. In our 1983 to 1985 study, we concluded that since neither potassium supplementation nor triamterene solved the problem, it is very likely that gossypol is a nephrotoxic agent. With 1 year of gossypol treatment, serum testosterone and serum luteinizing hormone showed no change, whereas serum follicle-stimulating hormone showed some elevation after 6 months. The Shanghai researchers found that in their gossypol users, plasma and urinary beta 2-microglobulin levels were elevated to a certain extent. However, 25 subjects in our 1983 to 1985 study showed no appreciable change. Our volunteers had stopped taking gossypol for more than 1 year. In 1986 we started a third study, which was aimed at finding the lowest antifertility dose to minimize possible renal toxicity.

Recent developments in immunocontraception

The possibility of controlling fertility by antibodies inactivating key reproductive hormones has been amply demonstrated by active and passive immunization in primates. Four birth control vaccines directed against human chorionic gonadotropin are currently in early clinical trials. The nature of these vaccines and the underlying principles are described, as are the available results from clinical studies. The alpha- and beta-subunits of human chorionic gonadotropin and the ovine gonadotropins have been cloned by recombinant deoxyribonucleic acid methods. A new breed of vaccines that combines the genes of gonadotropins linked to hepatitis B surface protein has been developed. The next generation of birth control vaccines is likely to be polyvalent and to have the ability to intercept fertility at more than one point. A number of monoclonal antibodies against human sperm have shown the presence of tissue-specific antigens and the possibility of preventing the fertilization of the egg. Inclusion of more than one carrier in the vaccine increases the percentage of high responders and accords immunoprophylactic benefits against more than one disease. Conjugates have also been developed to obtain high titers of antibodies against gonadotropin-releasing hormone with permissible adjuvants. This vaccine may have therapeutic applications in hormone-dependent cancers and precocious puberty.

Tripterygium wilfordii, a Chinese herb effective in male fertility regulation

A refined extract from the root xylem of Tripterygium wilfordii Hook. f. (the so-called multi-glycosides of the plant), available in the market as tablets for the long-term treatment of rheumatoid arthritis and various skin disorders, has recently been shown to possess a powerful antifertility effect in male rats and in men after oral administration at dose levels not showing apparent toxicity or side effects. Fertility appears to be reversible after cessation of treatment. Moreover, preliminary data indicated that the effective antifertility dose in men is only 1/3 of the recommended dose for the treatment of rheumatoid arthritis or skin diseases. This fact supports additional optimism that the side effects of this small dose will be much less as compared with those of the regular dose level. However, a large amount of further investigation is required before one can predict the future of the drug, which seems to hinge upon the successful isolation of the active principle(s) and the careful toxicological evaluation of the safety of the latter. The present paper is a review article summarizing the chemistry, the general pharmacology and the fertility regulatory effect of the plant.

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

A randomized controlled study was designed to evaluate the merit of whether ingesting potassium salt or potassium (K) blocking agent while using gossypol contraceptive drug could alleviate the symptom of hypokalemia. Results indicate that K salt supplementation did not reverse the gossypol-related hypokalemia and that the blocking agent triamterene did not prevent loss of or enhance the retention of serum K.

Clinical trial of gossypol as a male contraceptive drug. Part I. Efficacy study

The main objective of the research is to study the effectiveness and safety of gossypol as a male contraceptive drug. Using a double-blind, randomized, controlled study design, gossypol was found to be an effective male antifertility drug, with no adverse effects on libido nor appetite. In terms of serum potassium levels, there were no statistical differences between gossypol and placebo groups at the end of the loading phase. However, through the ensuing 12 months of maintenance phase, a statistically significant trend toward reduced serum potassium level was evident.

Endocrine approaches to male fertility control

As in the female, gametogenesis in the male is under the control of luteinizing hormone (LH) and follicle stimulating hormone (FSH). Their suppression should inhibit spermatogenesis. If a non-androgenic substance is used to suppress gonadotrophins, androgens must be supplemented to maintain virility, potency and metabolic processes. To avoid administration of several substances, testosterone and its esters were used to develop a male antifertility agent. Although azoospermia can be induced in a high proportion of men with administration of testosterone esters alone, this effect is not uniform. Even frequent injections with testosterone enanthate at weekly intervals fail to inhibit spermatogenesis in all participants. Combinations of gestagenic compounds with testosterone esters show a somewhat better effect, but again azoospermia is only achieved in around 50% of participants. LHRH analogues, although considered by many to offer a realistic potential for male fertility regulation, have not been proven to be successful for this purpose so far. Animal studies in monkeys and preliminary clinical trials demonstrate that agonistic analogues of LHRH have to be given continuously by pump or implant to achieve a pronounced effect on spermatogenesis. But even under these provisions, results in clinical trials have been worse than effects achieved with testosterone/gestagen combinations. Whether new antagonistic compounds offer a better potential awaits clinical trials. Studies in non-human primates demonstrate that testosterone by itself can maintain and initiate spermatogenesis. Based on these findings one could postulate an attenuating effect of high serum androgen levels after supplementation with available testosterone esters. Trials of alternative androgenic substances with slow-release characteristics and without high serum levels after single injections, like 19-nortestosterone hexyloxyphenylpropionate (19NT-HPP), tend to support this theory. With slow-release testosterone preparations under development by the WHO and more advanced delivery systems for LHRH analogues it is not unreasonable to speculate that an effective endocrine antifertility agent for the male will become available.

Influence of testosterone substitution on sperm suppression by LHRH agonists

To investigate the effect of LHRH (GnRH) agonists on sperm suppression, we studied the effect of a depot preparation of D-Trp6 LHRH in 10 normal men for 30 weeks. In addition, to determine the role of androgenic substitution on sperm suppression, the volunteers were divided into two groups: group 1 (n = 5) received a low dose T substitution (125 mg of T enanthate every month), while group 2 (n = 5) received a normal T substitution (120 mg of T undecanoate every day). Four men became azoospermic in group 1 and none in group 2. Moreover, administration of additional T injections in 1 volunteer of group 1 resulted in the reappearance of spermatozoa in the ejaculate. Return to the low dose therapy produced azoospermia. These results suggest that testosterone supplementation supports spermatogenesis.

Spermicidal effect in vitro by the active principle of garlic

The in vitro spermicidal effect of Allitridum, an active principle of garlic, was investigated. The data showed that sperm motility was inhibited with various concentrations of Allitridum at different intervals ranging from 20 seconds-200 minutes as compared to control. An obvious immobilization of spermatozoa occurred at 7.5 mg/ml of Allitridum. The effects on sperm motility appeared to be dose-dependent.

Effects of gossypol on human and monkey sperm motility in vitro

The effects of gossypol acetic acid on human and monkey sperm motility in vitro were studied by using multiexposure photography technique. Human and monkey spermatozoa were inhibited by gossypol to different degrees. Monkey sperm were absolutely immotile within 15 min after 50 microM of gossypol was added, but motility of human spermatozoa was not completely suppressed by gossypol even at the highest concentration used and longest duration of exposure.

Heterogeneity of sperm density profiles following 16-week therapy with continuous infusion of high-dose LHRH analog plus testosterone

LHRH agonist analogs have been investigated as potential male contraceptives. It has been shown that the LHRH agonistic analog [D-Trp6,Pro9-NEt] LHRH (LHRHA) given to men in single doses up to 500 micrograms daily for up to 20 weeks with the coadministration of testosterone enanthate produces reversible oligozoospermia. Individual responses to the treatment, however, were variable. In this study, we gave the same analog to eight normal male volunteers as a continuous infusion of 500 micrograms daily for 16 weeks. Testosterone enanthate, 100 mg, was given by injection every second week. Six of the subjects became oligozoospermic but the other two retained sperm counts that were greater than 20 million/ml, although their treatment continued for 20 weeks. The reasons for this variability of response are not clear. Serum immunoreactive LH values increased during the infusion period whereas testosterone declined. FSH values fell during treatment in all subjects except the two non-responders. The acute pituitary response to LHRHA during the treatment or shortly thereafter (48 h) was completely abolished, and bioactive LH values were suppressed totally. FSH, LH, testosterone and sperm counts returned to normal in all subjects following discontinuation of LHRHA infusion. Continuous infusion of 500 micrograms of LHRHA daily for 16 weeks with 100 mg of testosterone enanthate every 2 weeks induced desensitization of the pituitary, loss of LH bioactivity, and decreases of FSH and testosterone. This mode of administration, however, did not improve sperm density results obtained earlier by single daily injections of the analog. Heterogeneity of sperm density profiles still persists for reasons that are not yet clear.

The effect of gossypol on fast axonal transport and microtubule assembly

Gossypol at micromolar concentrations (2 microM) was found to inhibit axonal transport and a microsomal ATPase activity in the frog sciatic nerve, although axonal microtubules and the neuronal content of AMP, ADP and ATP were not affected. At slightly higher concentrations (30-40 microM), gossypol also inhibited microtubule assembly and neuronal energy metabolism. Gossypol accumulated in the nerve and the results indicate that gossypol may act as a potent neurotoxin.

The inhibitory effect of some ionophores on human sperm motility

The inhibitory effect of five ionophores, namely, A23187, nonactin, nigericin, monensin and m-chlorocarbonyl cyanide phenylhydrazone, on human sperm motility were measured with a trans-membrane migration method. The concentrations of A23187 and nigericin that decreased sperm motility to 50% of control were 20 microM (10.5 mg/l) and 8 microM (5.8 mg/l), respectively. Because these two ionophores were more potent than previously reported membrane-active sperm-immobilizing agents, we propose that ionophores could be a new category of vaginal contraceptive if a pharmaceutical preparation that is safe to be administered in vivo can be developed.

Gonadotrophin-releasing hormone agonists for new approaches to contraception in man

Potent and long-acting stimulatory analogues to the hypothalamic gonadotrophin-releasing hormone (GnRH) were originally developed for profertility purposes. Paradoxically they proved to possess anti-fertility properties. Their anti-gonadal properties are at present being utilized for therapeutic purposes, e.g. contraception, treatment of central precocious puberty and sex steroid-dependent benign and malignant diseases of the reproductive organs, predominantly metastatic prostatic cancer. This review will be limited to the potential use of superactive GnRH agonists for contraception in women and men. Inhibit ion of ovulation by continuous GnRH agonist administration has been studied most extensively and will be dealt with in more detail. Other approaches to interfere with corpus luteum function (induction of in adequate luteal function, luteolysis or early abortion) have so far proved less successful. In males, complete azoospermia has not been consistently achieved by chronic high dose GnRH superagonist therapy alone. Testosterone supplementation is mandatory to avoid the unacceptable side effects associated with GnRH superagonist therapy, namely loss of libido and potency. Thus, to date, inhibition of ovulation by repeated intranasal GnRH agonist administration seems to have the greatest potential as a future contraceptive method. In long-term clinical trials, this new lead to birth control has already proved to provide safe, reliable and reversible contraception in women.

Clinical trial of 19-nortestosterone-hexoxyphenylpropionate (Anadur) for male fertility regulation

To test the effectiveness of 19-nortestosterone (19NT) as an antifertility agent, 12 normal men (age, 24.0 +/- 2.2 years) received 19NT-hexoxyphenylpropionate (19NT-HPP), 200 mg/week intramuscularly for 7 weeks. After this initial phase, two groups were formed that received injections at different intervals. Except for the 19NT serum levels, there was no difference in treatment effects between both groups. 19NT-HPP administration in general suppressed gonadotropins below detection limits, accompanied by testosterone levels well in the castrate range. At the end of the treatment phase, azoospermia or severe oligozoospermia (total sperm count less than 5 X 10(6)) was present in ten volunteers. No loss of libido or potency was reported. Administration of 19NT-HPP did not affect liver enzymes, creatinine, uric acid, serum electrolytes, or serum lipids. The presented data demonstrate that 19NT-HPP as a single entity given every 3 weeks can suppress sperm output in a high proportion of men and simultaneously maintain virility.