Photodynamic antimicrobial chemotherapy (PACT) using phenothiazine derivatives as photosensitizers against Leishmania braziliensis

Abstract

Cutaneous and mucocutaneous leishmaniasis are diseases characterized by skin or mucosal manifestations. In the new world, Leishmania braziliensis is the main etiological agent of cutaneous leishmaniasis, condition that may evolve to the mucocutaneous form. The therapeutic arsenal routinely employed to treat infected patients is unsatisfactory, especially for pentavalent antimonials, treatment recommended by the WHO, as they are often highly toxic, poorly tolerated and of variable effectiveness. This work aimed to evaluate in vitro the effectiveness of photodynamic antimicrobial chemotherapy as a new approach for the treatment of leishmaniasis. A laser (λ = 660 nm, 40 mW, 4.2 J/cm2 , and 8.4 J/cm2 , CW) associated to phenothiazine's derivatives (5 and 10 µg/ml, toluidine blue O, methylene blue, or phenothiazine) on the promastigote forms of L. braziliensis in a single session. Samples were removed and analyzed in a hemocytometer 72 hours after PACT and viability of the parasites was assessed in quadruplicates. An important decrease in the number of viable parasites on all treated groups in comparison to their controls was observed as all tested compounds lead to significant parasite lethality being the highest lethality achieved with 10 µg/ml of TBO. No lethality was observed on groups treated with laser or with any of the compounds separately. TBO presented higher parasite lethality in comparison to MB with impressive reduction from 1 hour to 5 minutes of pre-incubation time.