Effects of elevating temperature on photodynamic reaction in laryngeal squamous carcinoma cells induced by delta-aminolevulinic acid

Abstract

To investigate effect of temperature on delta-aminolevulinic acid (ALA) induced photodynamic reaction in laryngeal squamous carcinoma cells. Human laryngeal squamous carcinoma cells of the line Hep-2 cells were co-cultured with 2 mmol/L ALA (Group A) or without ALA (Group B) at the culturing temperature 19 - 46 degrees C. Three hours later cellular protoporphyrin IX (PpIX) level was determined by high performance liquid chromatography with fluorescent detection. Laser scanning confocal microscopy was used to observe the fluorescent strength in the Hep-2 cells. The ratio of cell death (including necrosis and apoptosis) was detected with flow cytometer before and after photodynamic reaction. In Group A the PpIX level at the temperature of 19 degrees C was (0.25 +/- 0.06) microg/L, and raised to (1.07 +/- 0.11) microg/L at 46 degrees C. There was no cellular PpIX detected in Group B at any temperature. Before laser radiation the cell death ratios of both groups were the same at the temperature 19 - 37 degrees C, and at the temperature 37 - 46 degrees C. After laser radiation the cell death ratio of Group A raised from 31.11% to 98.92% as the temperature went up steadily, but the results of Group B showed the same curve as before laser radiation. At any same temperatures the cell death ratios of Group A were all significantly higher than those of Group B (all P < 0.05), and as the temperature was elevated the difference between the 2 groups raised from 28.99% to 59.26%. Moderate higher temperature enhances the PpIX production and photodynamic reaction in human laryngeal squamous carcinoma induced by ALA in vitro.