Hyperthermia sensitizes pigmented cells to laser damage without changing threshold damage temperature

Area of Science:

• Ophthalmology
• Biophysics
• Cell Biology

Background:

• Laser-induced thermal damage is a concern in ophthalmology.
• Retinal pigment epithelial (RPE) cells are crucial for retinal health.
• Understanding protective measures against thermal damage is vital.

Purpose of the Study:

• To investigate the protective efficacy of mild hyperthermia against laser-induced thermal damage in RPE cells.
• To determine how pigment granule location influences hyperthermia's protective or sensitizing effects.

Main Methods:

• Utilized an in vitro retinal model with artificially pigmented human RPE cells (hTERT-RPE1).
• Applied mild hyperthermia preconditioning (PC) followed by laser photothermal challenge (514 nm, 65 W/cm²).
• Assessed laser-induced cell damage using fluorescence indicator dyes, microthermography, and Raman microspectroscopy.

Main Results:

• Hyperthermia preconditioning altered laser-induced cell damage based on pigment granule location.
• Intracellular pigment granules during hyperthermia led to 94% damage, while extracellular led to 25% damage, compared to 44% in untreated cells.
• Microthermography showed hyperthermia did not change cell death threshold temperature, suggesting altered heat absorption/localization.
• Raman microspectroscopy revealed chemical changes in intracellular pigment granules post-hyperthermia.

Conclusions:

• Mild hyperthermia's effect on laser-induced RPE cell damage is location-dependent.
• Intracellular pigment granules undergo chemical modifications during hyperthermia, impacting heat absorption and dissipation.
• These findings suggest a novel mechanism for thermal protection/sensitization in RPE cells.