Photodynamic Therapy Using Toluidine Blue O (TBO) Dye as a Photosensitizer against Leishmania major

Background: Photodynamic therapy (PDT) is alternative treatment of cutaneous leishmaniasis (CL), and phenolthiazine dyes such as Toluidine Blue O (TBO) have the potential role in PDT and notably affect para-sites inactivation. This study aimed to evaluate the effectiveness of PDT by using TBO and a light-emitting diode (LED) in the treatment of zoonotic CL (ZCL). Methods: The study was conducted in Iran University of Medical Sciences, Tehran, Iran in 2018-2020. Dif-ferent concentration (7.8 μg/ mL up to 500 μg/ mL) of TBO as a photosensitizer and a 630 nm LED light as a source of light were used for antileishmanial activity against both forms of Leishmania major promastigotes and intracellular amastigotes. Effective concentration (EC50) and cell cytotoxicity (CC50) were calculated in both infected and non-infected J774.A1 macrophages, respectively. As well as inhibitory concentration (IC50) was quantified in L. major promastigotes for 2 h, 24 h, and 48 h after incubation using a MTT colorimetric assay. Results: TBO dye in combination with the PDT significantly decreases the L. major promastigotes and intra-cellular amastigotes viability when compared with TBO alone. Both TBO dye in combination with the PDT and TBO alone had no toxic effects on the mice macrophages; however, it significantly killed the entered par-asites inside the cells. Our results in the current study established satisfactory findings in clearing intracellular L. major parasites in in-vitro conditions. Conclusion: TBO dye in combination with the PDT can be considered as a harmless, effective and im-portantly perfect treatment against L. major, causative agent of ZCL, in an in-vitro situation without any nega-tive toxicity to the mice macrophages.