Combining a synthetic spermicide with a natural trichomonacide for safe, prophylactic contraception

Abstract

Study question: Can a specifically acting synthetic spermicide (DSE-37) be combined with a natural microbicide (saponins) for safe, prophylactic contraception? Summary answer: A 1:1 (w/w) combination of DSE-37 and Sapindus saponins can target sperm and Trichomonas vaginalis very precisely without any noticeable off-target effects on somatic cells at effective concentrations. What is known already: Broad-spectrum vaginal agents like nonoxynol-9 (N-9) and cellulose sulfate failed clinically as microbicides due to non-specific off-target effects, whereas agents that specifically targeted retroviruses have shown promise in clinical trials. DSE-37 and Sapindus saponins respectively target human sperm and Trichomonas vaginalis very specifically, in vitro. Study design: A comprehensive study of efficacy and safety was undertaken using in vitro (human) and in vivo (rabbit) models. The 1:1 combination of DSE-37 and Sapindus saponins was based on the in vitro spermicidal and anti-Trichomonal activities of the two components. N-9, the spermicide in clinical use, served as reference control. Free sperm thiols were fluorescently glinted to reveal difference in targets of the test agents. Materials, methods: On/off-target effects were evaluated in vitro against human sperm, Trichomonas vaginalis, HeLa, Vk2/E6E7, End1/E6E7 and Lactobacillus jensenii, using standard assays of drug susceptibility, cell-viability, flow cytometric assessment of cell apoptosis and qPCR for expression of pro-inflammatory cytokine mRNAs. Spermicidal effect was also recorded live. In vivo contraceptive efficacy (pregnancy/fertility rates) and safety (vaginal histopathology and in situ immune-labeling of inflammation markers VCAM-1, E-selectin and NFkB) were evaluated in rabbits. Free thiols on sperm (target of DSE-37) were fluorescently visualized using a commercial kit. Main results and the role of chance: A 0.003% drug ‘combination’ containing 0.0015% each of DSE-37 and Sapindus saponins in physiological saline irreversibly immobilized 100% human sperm in ~30 seconds and eliminated 100% Trichomonas vaginalis in 24 hours, without causing any detectable toxicity to human cervical (HeLa) cells and Lactobacilli in 24-48 hours, in vitro. Nonoxynol-9 at 0.003% exhibited lower microbicidal activity against Trichomonas but failed completely in spermicidal assays while causing severe toxicity to HeLa cells and Lactobacilli in 12-24 hours. The ‘combination’ completely prevented pregnancy in rabbits at a vaginal dose of 20 mg (1% in K-Y Jelly), while application of 5% ‘combination’ in K-Y Jelly for 4 consecutive days caused negligible alterations in epithelial lining of rabbit vagina with minor changes in levels of inflammation markers. N-9 at 20 mg vaginal dose prevented pregnancy in 33% animals and a 4-day repeat application of 2% N-9 gel caused severe local toxicity to vaginal epithelium with molecular expression of acute inflammation. Limitations, reasons for caution: Number of animals used for in vivo efficacy study was limited by the approval of the animal ethics committee. Wider implications of the findings: Anti-Trichomonal contraceptives with specifically acting synthetic component and clinically-proven-safe natural component may define a new concept in empowering women to control their fertility and reproductive health. Study funding/competing interest(s): The study was funded by CSIR-Network Project ‘PROGRAM’ (BSC0101) and partly by the Ministry of Health and Family Welfare, Government of India (GAP0001). The funding agencies did not play any role in this study and none of the authors had any competing interest(s).