Thermal injury by laser pulses: protection by heat shock despite failure to induce heat-shock response.

Pulsed lasers produce a variety of therapeutically useful effects in tissues by thermal mechanisms. In contrast with conventional hyperthermia, pulsed lasers rapidly induce extremely high temperatures confined to small areas within the tissues. It is not established, however, how cellular damage and repair responses differ between conventional and pulsed laser-induced hyperthermia. We have addressed this question by examining the induction of cellular heat-shock proteins (HSPs) and protection by heat-shock response against pulsed laser vs conventional hyperthermia. Cultured human dermal fibroblasts at confluency were exposed to single microsecond, 10.6-microns-wavelength pulses from a pulsed CO2 laser at radiant exposures between 0 and 1.3 J/cm2. Cell monolayers were directly exposed after removal of overlying medium. Positive control for the ability of the cells to synthesize of HSPs was obtained by heating the cells for 20 min in a water bath at 45 degrees C or 47 degrees C. The cultures were then labeled with L-[35S] methionine (Met), and proteins analyzed by sodium dodecyl sulfate polyacrylamide and two-dimensional gel electrophoresis 2 hr after exposure. The morphological alterations induced by laser or heat were similar under phase contrast microscopy. Conventional heating induced a heat-shock response, with the appearance of HSPs 2 hours after heating. In contrast, synthesis of HSPs could not be detected following laser irradiation, even at exposures decreasing both cell viability and incorporation of [35S] Met into cellular protein. Pre-exposure of cells to temperatures which induced synthesis of HSPs, however, significantly decreased cell death induced by subsequent laser irradiation.(ABSTRACT TRUNCATED AT 250 WORDS)