Photodynamic therapy effect on the ultrastructure of Trichomonas vaginalis trophozoites and their effectiveness in experimentally infected animals

Background Trichomonas vaginalis is an amitochondrial parasitic that causes human trichomoniasis, the most common non-viral sexually transmitted infection in the world. The therapy of choice is metronidazole (MTZ). Despite MTZ effectiveness, resistant cases are becoming more frequent. Another point to emphasize are the side effects that may result in treatment discontinuation, leading to further spread of infection and emergence of resistant strains. This scenario reveals the need to develop new therapeutic options. Photodynamic therapy (PDT) is an experimental treatment that involves the activation of photosensitive substances and the generation of cytotoxic oxygen species and free radicals to promote the selective destruction of target tissues. A previous study, from our group, identified an excellent in vitro PDT activity using methylene blue and light emitting diode against MTZ sensitive and resistant strains of T. vaginalis . The aim of this study was to evaluate the efficacy of PDT in vivo and clarify its high trichomonicidal potential by evaluating its action upon T. vaginalis trophozoites through transmission electron microscopy (TEM). Methodology Seven-week-old female Balb/c mice were infected intravaginally with T. vaginalis trophozoites. On the third day of infection, methylene blue was introduced into the vaginal canal of the animals, which then received 68.1 J / cm 2 of radiation for 35.6 sec. Control groups without infection and infected, treated with metronidazole were also included for comparison. Twenty-four hours after treatment the vaginal canal of the animals was scraped and the samples processed by the immunocytochemistry technique. After in vitro photodynamic treatment, T. vaginalis trophozoites were processed for TEM. Ultrathin sections were collected in 400-mesh copper grids, contrasted with 5% uranyl acetate and 3% lead citrate, in aqueous solutions for 20 and 5 min., respectively and observed in a Jeol JEM 230 transmission electron microscope. Results TEM showed morphological changes such as centripetal displacement of organelles, cannibalism, hydrogenosomal damage, intense cytoplasmic vacuolization, dilated endoplasmic reticulum cisternae and membrane discontinuity, in both resistant and sensitive strains, suggesting that trichomonicidal activity is mainly due to necrosis. PDT significantly reduced infection in animals treated with a single therapy session, compared to control groups, being statistically as efficient as MTZ. Conclusions Our results demonstrated high trichomonicidal activity of PDT with morphological alterations compatible with necrosis. Therefore these results indicate that PDT represents not only an alternative therapy for refractory trichomoniasis, but also routinely for this important neglected parasitic disease.