title: Designed Chemical Intervention with Thiols for Prophylactic Contraception.
abstract: 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.
authors.affiliation: Division of Endocrinology, CSIR-Central Drug Research Institute, Lucknow, India.
authors.forename: Monika
authors.initials: M
authors.lastname: Sharma
authors.forename: Lokesh
authors.initials: L
authors.lastname: Kumar
authors.forename: Ashish
authors.initials: A
authors.lastname: Jain
authors.forename: Vikas
authors.initials: V
authors.lastname: Verma
authors.forename: Vikas
authors.initials: V
authors.lastname: Sharma
authors.forename: Bhavana
authors.initials: B
authors.lastname: Kushwaha
authors.forename: Nand
authors.initials: N
authors.lastname: Lal
authors.forename: Lalit
authors.initials: L
authors.lastname: Kumar
authors.forename: Tara
authors.initials: T
authors.lastname: Rawat
authors.forename: Anil K
authors.initials: AK
authors.lastname: Dwivedi
authors.forename: Jagdamba P
authors.initials: JP
authors.lastname: Maikhuri
authors.forename: Vishnu L
authors.initials: VL
authors.lastname: Sharma
authors.forename: Gopal
authors.initials: G
authors.lastname: Gupta
mesh_terms: D000818:Animals; D003267:Contraception / Q000379:methods; D003270:Contraceptive Agents / Q000494:pharmacology*; D015195:Drug Design; D005260:Female; D006801:Humans; D008297:Male; D011247:Pregnancy; D011817:Rabbits; D013089:Spermatocidal Agents / Q000494:pharmacology*; D013094:Spermatozoa / Q000187:drug effects*; D013438:Sulfhydryl Compounds / Q000494:pharmacology*; D014245:Trichomonas Infections / Q000188:drug therapy / Q000382:microbiology; D014246:Trichomonas vaginalis / Q000187:drug effects*; D014621:Vagina / Q000187:drug effects* / Q000382:microbiology
chemical_list: D003270:Contraceptive Agents; D013089:Spermatocidal Agents; D013438:Sulfhydryl Compounds