Photodynamic therapy of Pythium insidiosum inactivation in vitro and in vivo study / Terapia fotodinâmica para inativação do Pythium insidiosum  - estudo in vitro e in vivo

Layla Pires

Photodynamic Therapy (PDT) is a therapy based on the interaction of photosensitizer and light, in the presence of oxygen, to induce cellular death. Under the incidence of light, at an appropriated wavelength, these chemical compounds produce reactive oxygen species which affects the biomolecules of the target-cells. Pythiosis is a lifethreatening emerging disease caused by a fungus-like organism called Pythium insidiosum. Since it is not a true fungus, this microorganism does not present ergosterol in its plasmatic membrane, and so, does not respond satisfactorily to most antifungal drugs. Extensive surgical debridements are required, such as limb amputation, however, reccurence frequently occurs. In this study the PDT effect was investigated in an in vitro model, experimental in vivo infection and naturally occurred equine pythiosis. Besides, pharmacokinetic assays with chlorine, porphyrin and methylene blue were also carried out. It was observed inhibition rates greater than 95% for chlorine, while porphyrin showed satisfactory inhibition and methylene blue was inefficient to inactivate the pathogen. Pharmacokinetics assays corroborate with obtained in vitro results and demonstrated a possible affinity between chlorine and oomicetes. After ten minutes of incubation, for both chlorine and clorin e6 solutions, it was observed that these compounds were concentrated in intracellular specific structures. For longer incubation times the distribution of these compounds was observed along the hyphae and cellular wall. Porphyrin has shown heterogeneous distribution on cell culture. This fact may explain hyphal growth observed after PDT with this photossensitizer. Methylene blue was present only in the cell surface and so, did not inhibit the pathogen. By observing the morphological structure of the pathogen after PDT with different incubation times, it was evident that PDT is more efficient when employing longer incubation times. Only methylene blue did not inactivate the pathogen in none of the evaluated protocols. Concerning experimental infection, it was observed that chlorine concentrates in lesion 4 hours after intravenous administration, while the same was not observed for porphyrin. High light doses and irradiances were necessary for treating the lesions. It was evaluated 21 rabbits with complete response around 95%. The treatment of naturally infected equines showed promising results. Four horses were treated with two PDT sessions. Treated regions of healing and recovery of motor function of the animals were observed. Once again, chlorins showed improved results when compared to the other photosensitizers. Besides, it was observed the relation between incubation time and tissue response correlated to those observed in the kinetics study. The protocol for treating pythiosis, probably will be based on chlorine incubation time greater than 1 hour, high light dose and irradiance, that the results of the present study demonstrate that PDT is a potential treatment option for pythiosis.

Photodynamic therapy of Pythium insidiosum inactivation in vitro and in vivo study / Terapia fotodinâmica para inativação do Pythium insidiosum - estudo in vitro e in vivo

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