RESUMO
Protoporphyrin IX (PpIX) is a precursor of heme synthesis and is known to be an active photosensitizer and precursor of photosensitizers applied in photodynamic therapy (PDT) and photodynamic diagnostics (PDD). On irradiation with visible light, PpIX undergoes phototransformation, producing photoproducts which may also be phototoxic and increase its efficacy. The mechanism of PpIX phototransformation depends on environmental characteristics and can be different in vitro and in vivo. In this paper, we present a comparative study of the photoactivity of synthetic PpIX and PpIX extracted from the Harderian gland of ssp Rattus novergicus albinus rats, along with their photoproducts toward murine B16F-10 melanoma cells. It was observed that when irradiated with visible light the endogenous PpIX demonstrates photocytotoxicity ten times higher than the synthetic PpIX. The photoproduct of endogenous PpIX also possesses phototoxicity, though slightly lower than that of PpIX itself. The rate of cell internalization for both endogenous PpIX and its photoproduct was eightfold greater than that obtained for the synthetic porphyrin. This difference might result from a complexation of the native PpIX with some amphiphilic compounds during its synthesis within the Harderian glands, which facilitates the cell uptake of PpIX. Fluorescence microscopy images show that both endogenous and synthetic porphyrins are localized after uptake predominantly in the mitochondrial region of cells.