Designed Chemical Intervention with Thiols for Prophylactic Contraception

• Published in: PloS one Vol. 8; no. 6; p. e67365
• Main Authors: Sharma, Monika, Kumar, Lokesh, Jain, Ashish, Verma, Vikas, Sharma, Vikas, Kushwaha, Bhavana, Lal, Nand, Kumar, Lalit, Rawat, Tara, Dwivedi, Anil K, Maikhuri, Jagdamba P, Sharma, Vishnu L, Gupta, Gopal
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 27.06.2013; Public Library of Science (PLoS)
• Subjects: Acquired immune deficiency syndrome; AIDS; Alkylation; Animals; Biology; Birth control; Carbon; Chemical interference; Chemistry; Contraception; Contraception - methods; Contraceptive Agents - pharmacology; Drug Design; Drugs; Endocrinology; Enzymes; Female; Fertility; Gene expression; Hexokinase; HIV; Human immunodeficiency virus; Humans; Interference; Male; Medicine; Metabolism; Metronidazole; Microbicides; Motility; Nonoxynol; Parasitic diseases; Pathogens; pH effects; Polyethylene glycol; Pregnancy; Protective coatings; Pyrrolidine; Rabbits; Sexually transmitted diseases; Somatic cells; Sperm; Spermatocidal Agents - pharmacology; Spermatozoa - drug effects; STD; Sulfhydryl Compounds - pharmacology; Surfactants; Thiols; Trichomonas; Trichomonas Infections - drug therapy; Trichomonas Infections - microbiology; Trichomonas vaginalis; Trichomonas vaginalis - drug effects; Vagina; Vagina - drug effects; Vagina - microbiology
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0067365

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.