The influence of temperature on 5-aminolevulinic acid-based photodynamic reaction in keratinocytes in vitro.

Background/purpose: Based on the observation that increasing skin temperature could improve 5-aminolevulinic acid (ALA) penetration and accumulation of protoporphyrin IX (PpIX) in the ALA-based photodynamic therapy (PDT), this study was designed to investigate how temperature change varied the therapeutic effect of ALA-based PDT in vitro.

Methods: HaCat cells were cultured with or without ALA at various temperatures. ALA uptake and PpIX accumulation were analyzed before laser irradiation as the baseline. After irradiation, cell death and cytokine secretions in the media, including interleukin (IL)-1alpha, tumor necrosis factor (TNF)-alpha and basic fibroblast growth factor (bFGF) were assayed, and the morphological changes were recorded.

Results: With increasing temperature, the amount of ALA uptake, intracellular PpIX concentration and cell death increased in both the PDT and the non-PDT groups. Secretions of IL-1alpha, TNF-alpha and bFGF also increased and reached a peak around 44-47 degrees C and then declined at a higher temperature. This biphasic response might be due to protein thermolysis that occurs when cells reach beyond thermal tolerance.

Conclusions: Elevating temperature could augment photodynamic reactions to a certain extent, but adverse effects occurred when cells were overheated.