Mechanistic insight of the photodynamic effect induced by tri- and tetra-cationic porphyrins on Candida albicanscells

Abstract

The photodynamic mechanism of action induced by 5-(4-trifluorophenyl)-10,15,20-tris(4-N,N,N-trimethylammoniumphenyl)porphyrin (TFAP³⁺), 5,10,15,20-tetrakis(4-N,N,N-trimethylammoniumphenyl)porphyrin (TMAP⁴⁺) and 5,10,15,20-tetrakis(4-N-methylpyridyl)porphyrin (TMPyP⁴⁺) was investigated on Candida albicanscells. These cationic porphyrins are effective photosensitizers, producing a ∼5 log decrease of cell survival when the cultures are incubated with 5 μM photosensitizer and irradiated for 30 min with visible light. Studies under anoxic conditions indicated that oxygen is necessary for the mechanism of action of photodynamic inactivation of this yeast. Furthermore, photoinactivation of C. albicanscells was negligible in the presence of 100 mM azide ion, whereas the photocytotoxicity induced by these porphyrins increased in D₂O. In contrast, the addition of 100 mM mannitol produced a negligible effect on the cellular phototoxicity. On the other hand, in vitro direct observation of singlet molecular oxygen, O₂(¹Δ_g) phosphorescence at 1270 nm was analyzed using C. albicans in D₂O. A shorter lifetime of O₂(¹Δ_g) was found in yeast cellular suspensions. These cationic porphyrins bind strongly to C. albicanscells and the O₂(¹Δ_g) generated inside the cells is rapidly quenched by the biomolecules of the cellular microenvironment. Therefore, the results indicate that these cationic porphyrins appear to act as photosensitizers mainly via the intermediacy of O₂(¹Δ_g).