The photodegradation behavior of two indium phthalocyanines and its influence on the photohaemolysis of human red blood cells

It is known phthalocyanines suffer photobleaching1 and that much more the photosensitizer is photobleached, the greater is the intensity of photobiological damage2. O-InTBPPc or M-InTTBPPc was encapsulated into PLGA-PEG nanoparticles and the photobleaching of each free and encapsulated compound and its influence on the photohaemolysis were evaluated. Relative absorbance (AR) measurement was performed in DMF and PBS solution using a spectrophotometer. The free M-InTTBPPc was photobleached faster than It was the free O-InTBPPc in organic solvent when the laser power was increased from 1 to 22 mW since the AR was decreased from 0.54 to 0.10, while the value for the free O-InTBPPc was decreased from 0.89 to 0.24. The free O-InTBPPc was 1.9x more photobleached in PBS solution than was the free M-InTTBPPc, but the encapsulated O-InTBPPc was 2.7x lesser photobleached than was the encapsulated M-InTTBPPc. It was not observed a photodegradation dependence with the increase of the free O-InTBPPc concentration (2-15 μmol/L) as It was for the free M-InTTBPPc in organic solvent, probably due to a higher aggregate state of the M-InTTBPPc. Both free and encapsulated compounds were photobleached in the PBS solution with a little concentration dependence. The higher tendency of the encapsulated M-InTTBPPc to suffer photobleaching reduced its efficiency to cause photohaemolysis (lower than 9%) while the encapsulated O-InTBPPc caused a photohaemolysis around 70%. The free O-InTBPPc was also more efficiency than it was the free MInTTBPPc to photohemolyze the HRBC. We thank CNPq, FAPES and IFES for financial support.