Alpha-Pinene and Tannic Acid Inhibit Trichomonas vaginalis Protozoan Cells by Inducing Apoptosis

Background: Trichomoniasis is one of the most common sexually transmitted infections worldwide. The growing concern of drug resistance of this infection has cautioned the need for new drug development. We evaluated the potential antiproliferative and apoptotic effect of α-pinene and tannic acid (TA) on Trichomonas vaginalis cells. In addition, the cytotoxicity of agents on Vero cells was investigated. Methods:  Trichomonas cells were axenically cultured in TYI-S-33 medium. In vitro antiproliferative activity of α-pinene, TA, and metronidazole was investigated against Trichomonas cells. The assays were carried out in triplicate using microtiter plate and trypan blue staining method. Annexin V/PI staining with flow cytometry was used to evaluate apoptosis induction. In addition, the cytotoxic effect was measured by MTT assay. Results: α-Pinene and TA exhibited significant inhibition of the Trichomonas cells and the lowest IC50 values were 22.9 µg/ml and 140 µg/ml at 48 hours’ incubation, respectively. The CC50 was found at 116 μg/ml for α-pinene and 473 μg/ml for TA, after 48 hours of treatment. The flow cytometry study demonstrated that the natural compounds induced apoptosis in Trichomonas cells. After 24 hours of treatment, the induction of apoptosis was 5.2% - 36.6% at concentrations of 3.9 - 62.5 μg/ml for α-pinene and TA induced-apoptosis was 6.1% - 53.8% at concentrations of 125-2000 μg/ml. Conclusion: Although the results show the antiproliferative and apoptotic effect of α-pinene and TA on Trichomonas cells, in vivo studies are needed to further clarify the effects of these compounds.