Novel disulphide esters of carbothioic acid as potent, non-detergent spermicides with low toxicity to Lactobacillus and HeLa cells in vitro

Mitochondria-Targeted Compounds to Assess and Improve Human Sperm Function

Significance: Currently 10%-15% of couples in reproductive age face infertility issues. More importantly, male factor contributes to 50% of these cases (either alone or in combination with female causes). Among various reasons, impaired sperm function is the main cause for male infertility. Furthermore, mitochondrial dysfunction and oxidative stress due to increased reactive oxygen species (ROS) production, particularly of mitochondrial origin, are believed to be the main contributors. Recent Advances: Mitochondrial dysfunction, particularly due to increased ROS production, has often been linked to impaired sperm function/quality. For decades, different methods and approaches have been developed to assess mitochondrial features that might correlate with sperm functionality. This connection is now completely accepted, with mitochondrial functionality assessment used more commonly as a readout of sperm functionality. More recently, mitochondria-targeted compounds are on the frontline for both assessment and therapeutic approaches. Critical Issues: In this review, we summarize the current methods for assessing key mitochondrial parameters known to reflect sperm quality as well as therapeutic strategies using mitochondria-targeted antioxidants aiming to improve sperm function in various situations, particularly after sperm cryopreservation. Future Directions: Although more systematic research is needed, mitochondria-targeted compounds definitely represent a promising tool to assess as well as to protect and improve sperm function. Antioxid. Redox Signal. 37, 451-480.

Comparative in vitro study on the local tolerance and efficacy of benzalkonium chloride, myristalkonium chloride and nonoxynol-9 as active principles in vaginal contraceptives

BACKGROUND

Spermicides have been identified as a potentially attractive alternative to hormonal contraceptives and/or intrauterine devices. Thus, this study aimed evaluating the efficacy and local tolerance of benzalkonium chloride (BKC) and myristalkonium chloride (MKC) contained in Pharmatex^® vaginal formulations and compare them with nonoxynol-9 (N-9), the most common active ingredient in topical vaginal contraceptives.

METHODS

Human normozoospermic samples were assessed for motility, viability, acrosome status and penetration ability after exposure to control, N-9 or different BKC and MKC doses for 0 and 10 minutes. Local tolerance on HeLa cells was evaluated by the Trypan-blue and MTT assays.

RESULTS

Exposure to BKC and MKC reduced acrosome integrity while promoting total immobilisation and complete loss of sperm viability (p < .001, n = 15). Both compounds also compromised sperm penetration ability upon exposure (p < .001, n = 15). N-9 induced the same outcomes (p < .001, n = 15); nevertheless, it was more toxic to HeLa cells than BKC and MKC (p < .05, n = 14).

CONCLUSIONS

BKC and MKC present strong in vitro spermicidal activity at lower doses than N-9 and were better tolerated after immediate exposure than N-9. Available Pharmatex^® galenic formulations were as effective as products based on N-9.

Tideglusib, a prospective alternative to nonoxynol-9 contraceptive

Objectives

We aimed to evaluate the antifertility activity and vaginal irritation effects of tideglusib in vivo using rabbit models and to evaluate the cytotoxical effects of tideglusib to sperm, vaginal cells and vaginal bacteria (L. acidophilus) in vitro.

Study design

We treated female rabbits with vaginal tideglusib 1 mM, nonoxynol-9 (N-9) or vehicle control (Poloxamer 407). In experiment 1, we sacrificed females (n = 6 each) after 10 days of daily administration and assessed vaginal histological changes using Eckstein irritation score. In experiment 2, females (n = 9 each) received estradiol benzoate to induce ovulation 24 h prior to vaginal treatment followed by introduction of a fertile male. These females underwent necropsy at the 21st day to assess pregnancy status. In experiment 3, we used an HTM-TOX IVOS sperm motility analyzer and scanning electron microscopy (SEM) to evaluate the effect of tideglusib on human sperm samples. In experiment 4, we evaluated the effect of tideglusib on lactobacillus and vaginal cell growth in vitro.

Results

The total irritation score of tideglusib vs. N-9 was 3.4 ± 2.07 vs. 7.8 ± 3.82, p <.05. The pregnancy rate of tideglusib, N-9 and control group was 11.1%, 0% and 88.9%, respectively. Tideglusib exhibited a dose-dependent spermostatic/spermicidal activity, and the minimum effective concentrations of tideglusib and N-9 were 8.724 ± 3.047 μM and 219.75 ± 41.78 μM, respectively. SEM and transmission electron microscopy revealed acrosomal membrane impairments caused by tideglusib. Tideglusib was much less toxic to vaginal cells and L. acidophilus than N-9 in vitro.

Conclusions

Evaluation using rabbit models indicated that tideglusib is a prospective spermicidal contraceptive with low vaginal irritation effects.

Implications

Tideglusib or tideglusib analogues may be a contraceptive with perspective to replace N-9. It is possible for a spermicide to balance spermicidal activity and vaginal/cervical irritation effects very well.

Innovative Disulfide Esters of Dithiocarbamic Acid as Women-Controlled Contraceptive Microbicides: A Bioisosterism Approach

In an ongoing effort to discover an effective, topical, dual-function, non-surfactant contraceptive vaginal microbicide, a novel series of 2,2'-disulfanediylbis(3-(substituted-1-yl)propane-2,1-diyl) disubstituted-1-carbodithioates were designed by using a bioisosterism approach. Thirty-three compounds were synthesized, and interestingly, most demonstrated multiple activities: they were found to be spermicidal at a minimal effective concentration of 1-0.001 %, trichomonacidal against drug-susceptible and resistant Trichomonas strains at minimal inhibitory concentration (MIC) ranges of 10.81-377.64 and 10.81-754.14 μM, respectively, and fungicidal at MIC 7.93-86.50 μM. These compounds were also found to be non-cytotoxic to human cervical (HeLa) epithelial cells and vaginal microflora (Lactobacilli) in vitro. The most promising compound, 2,2'-disulfanediylbis(3-(pyrrolidin-1-yl)propane-2,1-diyl)dipyrrolidine-1-carbodithioate (5), exhibited spermicidal activity 15-fold higher than that of the marketed spermicide Nonoxynol-9 (N-9) and also demonstrated microbicidal potency. To identify common structural features required for spermicidal activity, a 3D-QSAR analysis was carried out, as well as in vivo efficacy studies and fluorescent labeling studies to determine the biological targets of compound 5.

A unique dithiocarbamate chemistry during design & synthesis of novel sperm-immobilizing agents

Unusual loss of CS₂ observed in benzyl substituted dithiocarbamates during synthesis of double edged spermicides which acted through sulfhydryl binding.

Designed Chemical Intervention with Thiols for Prophylactic Contraception

Unlike somatic cells, sperm have several-fold more available-thiols that are susceptible to redox-active agents. The present study explains the mechanism behind the instant sperm-immobilizing and trichomonacidal activities of pyrrolidinium pyrrolidine-1-carbodithioate (PPC), a novel thiol agent rationally created for prophylactic contraception by minor chemical modifications of some known thiol drugs. PPC, and its three derivatives (with potential active-site blocked by alkylation), were synthesized and evaluated against live human sperm and metronidazole-susceptible and resistant Trichomonas vaginalis, in vitro. Sperm hexokinase activity was evaluated by coupled enzyme assay. PPC irreversibly immobilized 100% human sperm in ∼30 seconds and totally eliminated Trichomonas vaginalis more efficiently than nonoxynol-9 and metronidazole. It significantly inhibited (P<0.001) thiol-sensitive sperm hexokinase. However, the molecule completely lost all its biological activities once its thiol group was blocked by alkylation. PPC was subsequently formulated into a mucoadhesive vaginal film using GRaS excipients and evaluated for spermicidal and microbicidal activities (in vitro), and contraceptive efficacy in rabbits. PPC remained fully active in quick-dissolving, mucoadhesive vaginal-film formulation, and these PPC-films significantly reduced pregnancy and fertility rates in rabbits. The films released ∼90% of PPC in simulated vaginal fluid (pH 4.2) at 37°C in 5 minutes, in vitro. We have thus discovered a common target (reactive thiols) on chiefly-anaerobic, redox-sensitive cells like sperm and Trichomonas, which is susceptible to designed chemical interference for prophylactic contraception. The active thiol in PPC inactivates sperm and Trichomonas via interference with crucial sulfhydryl-disulfide based reactions, e.g. hexokinase activation in human sperm. In comparison to non-specific surfactant action of OTC spermicide nonoxynol-9, the action of thiol-active PPC is apparently much more specific, potent and safe. PPC presents a proof-of-concept for prophylactic contraception via manipulation of thiols in vagina for selective targeting of sperm and Trichomonas, and qualifies as a promising lead for the development of dually protective vaginal-contraceptive.

N,N'-Dithiobisphthalimide, a disulfide aromatic compound, is a potent spermicide agent in humans

Several studies have shown that users of vaginal preparations containing nonoxynol-9 (N-9) are at a high risk for sexually transmitted diseases, including HIV. Therefore, there is a great interest in identifying compounds that can specifically inhibit sperm without damaging the vaginal lining, possess a powerful spermicide activity, and can be used in contraceptive vaginal preparations to replace N-9. In this work, we studied the spermostatic and/or spermicidal activity of five non-detergent, disulfide compounds on human sperm, HeLa cells, and Lactobacillus acidophilus. The motility and viability of human sperm in semen and culture medium was evaluated after treatment with different concentrations of the disulfide compounds (2.5 - 100 µM). In addition, we evaluated the cytotoxic effect on HeLa cells and L. acidophilus. We identified compound 101, N,N'-dithiobisphthalimide (No. CAS 7764-30-9), as the most effective molecule. It has a half maximal effective concentration (EC(50)) of 8 µM and a minimum effective concentration (defined as the concentration that immobilizes 100 percent of the sperm in 20 sec) of 24 µM. At these concentrations, compound 101 does not affect the viability of the sperm, HeLa cells, or L. acidophilus. Our results indicate that dithiobisphthalimide has a potent spermostatic, irreversible effect with no toxic effects on HeLa cells and L. acidophilus.

Novel trichomonacidal spermicides

Metronidazole, the U.S. Food and Drug Administration-approved drug against trichomoniasis, is nonspermicidal and thus cannot offer pregnancy protection when used vaginally. Furthermore, increasing resistance of Trichomonas vaginalis to 5-nitro-imidazoles is a cause for serious concern. On the other hand, the vaginal spermicide nonoxynol-9 (N-9) does not protect against sexually transmitted diseases and HIV in clinical situations but may in fact increase their incidence due to its nonspecific, surfactant action. We therefore designed dually active, nonsurfactant molecules that were capable of killing Trichomonas vaginalis (both metronidazole-susceptible and -resistant strains) and irreversibly inactivating 100% human sperm at doses that were noncytotoxic to human cervical epithelial (HeLa) cells and vaginal microflora (lactobacilli) in vitro. Anaerobic energy metabolism, cell motility, and defense against reactive oxygen species, which are key to survival of both sperm and Trichomonas in the host after intravaginal inoculation, depend crucially on availability of free thiols. Consequently, molecules were designed with carbodithioic acid moiety as the major pharmacophore, and chemical variations were incorporated to provide high excess of reactive thiols for interacting with accessible thiols on sperm and Trichomonas. We report here the in vitro activities, structure-activity relationships, and safety profiles of these spermicidal antitrichomonas agents, the most promising of which was more effective than N-9 (the OTC spermicide) in inactivating human sperm and more efficacious than metronidazole in killing Trichomonas vaginalis (including metronidazole-resistant strain). It also significantly reduced the available free thiols on human sperm and inhibited the cytoadherence of Trichomonas on HeLa cells. Experimentally in vitro, the new compounds appeared to be safer than N-9 for vaginal use.

Potent spermicidal effect of oleanolic acid 3-beta-D-glucuronide, an active principle isolated from the plant Sesbania sesban Merrill

BACKGROUND

The spermicidal activity of oleanolic acid 3-β-D-glucuronide (OAG), an active principle isolated from root extracts of Sesbania sesban, was evaluated.

STUDY DESIGN

Under the Sander-Cramer test criteria, the sperm-immobilizing activity of OAG was studied using highly motile rat sperm. Sperm mortality and membrane integrity were assessed by supravital staining, hypo-osmotic swelling (HOS), transmission electron microscopy (TEM) and sperm membrane lipid peroxidation (LPO). In vitro microbicidal potential and hemolytic index of OAG were examined in Lactobacillus culture and rat red blood corpuscles (RBCs), respectively. Post-intravaginal OAG application, the in vivo contraceptive efficacy was evaluated in rats. Ames test determined the carcinogenic potential of OAG.

RESULTS

The minimum effective concentration (MEC) of OAG was 50 mcg/mL. More than 97% of the OAG-treated sperm lost their HOS responsiveness in a dose-dependent manner. TEM and LPO revealed that OAG affected the sperm membrane integrity. OAG declined fertility to zero, was nonmutagenic and was not harmful to lactobacillus.

CONCLUSION

OAG has significant spermicidal activity that may be explored further.

Functional attenuation of human sperm by novel, non-surfactant spermicides: precise targeting of membrane physiology without affecting structure

BACKGROUND

We have attempted to identify structural, physiological and other targets on human sperm vulnerable to the spermicidal action of two novel series of non-detergent molecules, reported to irreversibly immobilize human sperm in <30 s, apparently without disrupting plasma membrane.

METHODS

Three sperm samples were studied. Scanning and transmission electron microscopy were used to assess structural aberrations of sperm membrane; plasma membrane potential and intracellular pH measurements (fluorometric) were used to detect changes in sperm physiology; reactive oxygen species (ROS, fluorometric) and superoxide dismutase activity (colorimetric) were indicators of oxidative stress; and sperm dynein ATPase activity demonstrated alterations in motor energy potential, in response to spermicide treatment. Post-ejaculation tyrosine phosphorylation of human sperm proteins (immunoblotting) was a marker for functional integrity.

RESULTS

Disulfide esters of carbothioic acid (DSE compounds) caused complete sperm attenuation at > or =0.002% concentration with hyper-polarization of sperm membrane potential (P < 0.001), intracellular alkalinization (P < 0.01), ROS generation (P < 0.05) and no apparent effect on sperm (n = 150) membrane structure. Isoxazolecarbaldehyde compounds required > or =0.03% for spermicidal action and caused disrupted outer acrosomal membrane structure, depolarization of membrane potential (P < 0.001), intracellular acidification (P < 0.01) and ROS generation (P < 0.01). Detergent [nonoxynol-9 (N-9)] action was sustainable at > or =0.05% and involved complete breakdown of structural and physiological membrane integrity with ROS generation (P < 0.001). All spermicides caused functional attenuation of sperm without inhibiting motor energetics. Unlike N-9, DSE-37 (vaginal dose, 200 microg) completely inhibited pregnancy in rats and vaginal epithelium was unchanged (24 h,10 mg).

CONCLUSIONS

The study reveals a unique mechanism of action for DSE spermicides. DSE-37 holds promise as a safe vaginal contraceptive. CDRI Communication No. 7545.

Synthesis of disulfide esters of dialkylaminocarbothioic acid as potent, non-detergent spermicidal agents

S,S'-[disulfanediylbis(dialkylaminopropane-2,1-diyl)]bis- (dialkylaminothiocarbamate) (14-31) were prepared and evaluated for the spermicidal activity and antifungal activity. Dialkyldithiocarbamates (1-5) were reacted with epichlorohydrin to give 1-dialkylaminocarbothioic acid S-[(2,3-epithio)propyl]ester (7-11), these on further reaction with a secondary amine gave S,S'-[disulfanediylbis(dialkylaminopropane-2,1-diyl)]bis- (dialkylaminothiocarbamate) (14-31). Some of these compounds (16, 19-21, 23, 30, 31) were found to be very potent spermicidal agents with marginal antifungal activity. Two compounds (20, 21) were 25 times more active than nonoxynol-9 (N-9), the spermicide currently in the market.