Effect of Different Irradiation Modes of Azulene-mediated Photodynamic Therapy on Singlet Oxygen and PGE2 Formation.

Azulene samples in ethanol/distilled water (1, 10 and 100 µm) were irradiated with a 638 nm red laser (0.5 watts, light-to-target distance 2 cm, energy density 4 or 40 J cm-2 ) by either continuous, fractionation or pulse mode. Singlet oxygen in the samples was measured using 10 µm 9,10-dimethyl anthracene (positive control 10 μm erythrosine) and relative fluorescence intensities were measured at 375/436 nm excitation/emission. Peripheral blood mononuclear cells (PBMCs, 1 × 105 cells/well) preincubated with 0.01 μg mL-1 rhTNF-α for 6 h were cultured with irradiated azulene samples in RPMI-1640 under standard conditions. PGE2 was quantified by rhPGE2 ELISA kit using a Varioscan® microplate reader at an excitation wavelength of 420 nm. Kruskal Wallis with Dunn`s test was performed at a significance level of P < 0.05. The highest singlet oxygen amount was found in 10 µm azulene samples irradiated at 40 J cm-2 under continuous mode (P = 0.001 when compared with 10 µm erythrosine). PGE2 expression in rhTNF-α-induced PBMCs was reduced to 45% of control by 1 µm azulene irradiated at 40 J cm-2 under fractionation mode. Fractionation mode with intermediate laser energy density in the presence of low concentration of azulene could increase singlet oxygen and tend to reduce PGE2 .