Considering the need to find spermicidal agents that are more effective in protecting against pregnancy as well as STDs, and are also less toxic, in this study we evaluated the spermicidal and anti-Trichomonas activity of WE and BE extracts, as well as the SP of Sapindus saponaria and its effect on Lactobacillus acidophilus, a common member of the vaginal microbiota.
S. saponaria is popularly known as “sabão-de-macaco”, “saboeiro”, “saboneteiro”, “fruta de sabão” and “sabão-de-soldado”  and is found in South and Central America, from forests to “cerrado”, a vast tropical savanna ecoregion. In Brazil, it is found from Para State to Rio Grande do Sul State [7, 23]. This plant has shown antimicrobial [8, 9] and antifungal activities, and no toxicity to HeLa cervical cells [11, 12].
In the present experiments, WE, BE and SP of S. saponaria were effective for total sperm immobilization (not viability) at MEC of 2.5 (gram %) for extracts and 1.25 (gram %) for SP. At MEC, 100% of spermatozoa showed positive red staining with eosin and negative hypo-osmotic swelling after treatment, indicating complete membrane damage and death. This result is similar to S. mukorossi, which is the best-known species of the genus Sapindus and is traditionally used in eastern medicine as a spermicide . S. mukorossi shows spermicidal activity , which is attributed to the presence of saponins [5, 25, 26]. Similarly, saponins of other plants have been used in contraceptive formulations, either as foaming agents or as spermicidal substances [27, 28].
The spermicidal local contraceptives incorporating microbicidal activity can play a significant role in controlling STDs . T. vaginalis causes trichomoniasis, which is the most prevalent non-viral human urogenital pathogen . In this study, the compounds inhibited two different strains of Trichomonas vaginalis. They were effective against the CS strain (MIC = 0.156 mg/mL for WE and BE, and 0.078 mg/mL for SP) and against the ATCC strain (MIC = 0.312, 0.156 and 0.078 mg/mL for WE, BE and SP, respectively), and the active anti-Trichomonas concentrations were lower than its effective spermicidal concentration. This accord with observations on saponins from S. mukorossi, which exhibit anti-Trichomonas activity at a 10-fold lower concentration than the effective spermicide against human spermatozoa . T. vaginalis is inhibited by saponins obtained from other plants [30, 31], showing that the anti-Trichomonas effect could also be related to the presence of saponins.
L. acidophilus is a important organism in the vaginal microbiota, and is responsible for maintaining acidic pH, preventing the growth of potential pathogens [32, 33]. The ideal spermicidal agent should preserve the healthier vaginal microflora through retention of Lactobacillus. In vitro studies have shown that N-9 is detrimental to Lactobacillus species [14–16], showing that its use could contribute for increase the incidence of STDs [34–36]. The present study showed that the WE, BE or SP of S. saponaria did not alter the growth of L. acidophilus colonies, showing that is not toxic to the common vaginal microbiota. This accord with the observations of Ojha et al.  who concluded that the saponins are far less toxic compared to N-9.
We acknowledge that in vivo studies are needed to completely confirm our results. One of the great challenges of research on the physiopathogenesis of diseases is to match the experimental conditions in vitro as much as possible to those in vivo, which are often much more complex . However, researchers recognize that these experiments do provide an approximation to in vivo conditions [37–39].