Photodynamic effect of Soranjidiol on intracellular amastigotes of Leishmania braziliensis

Abstract

The study of new treatments on the amastigote form (A) of Leishmania is important, since these multiply within macrophages (M), spreading the infection within humans. Soranjidiol (Sor) is a compound (genus Heterophyllaea) that possesses photosensitizing properties. The effect of Sor on M from the J774.A1 cell line, infected with A from L. braziliensis and using white LED, was studied.

2x10⁵ M/well were coinfected with a 1:10 MOI of promastigotes. After 24 h, the following tests were added to the microplate, protected from light (n=3): negative control (CN, only with PBS), Amphotericin B 0.5 µM (Anf), and Sor at 5 and 10 µM (non-cytotoxic Sor concentrations for M). For the irradiation conditions (n=3), the following were included: CN (CN-L) and Sor at 5 and 10 µM (Sor-5L and Sor-10L). After 10 min (pre-irradiation time), they were irradiated with LED (dose: 11 J/cm2) for 15 min. At the end, the solutions were replaced by RPMI medium, incubating them for 72 h. We performed Giemsa staining to determine the infection rate (IT): number of intracellular A/M infected multiplied by the percentage of infection. For the comparison of the treatments, a two-way ANOVA and the Bonferroni post hoc test were performed.

The RT after treatment with Sor in the dark and at both concentrations did not present significant differences with respect to CN (509.1 ± 33.5). Sor-5L photoactivation reduced RT (354.6 ± 47.6) by 27% compared to CN-L (486.3 ± 8.8, p<0.05) and was similar to that obtained with Anf (347.5 ± 38.6). For Sor-10L, a greater reduction in IT was obtained (184.9 ± 67.0, p<0.0001), which represents 62% less compared to CN-L.

In conclusion, treatment with Sor and white LED significantly reduced IT in a dose-dependent manner. These results agree with those obtained in previous trials on L. amazonensis, which motivates us to continue with the study of Sor and/or the implementation of a combination therapy with Anf, in order to achieve an effective and accessible treatment for cutaneous leishmaniasis.