Continuous wave He-Ne laser exposures (Intensity = 35 mW/cm², λ=632.8nm, Fluence range: 1J/cm² to 50 J/cm²) on non-confluent and fully confluent human malignant glioblastoma cells was found to increase the cellular production levels of H₂O₂. Modulations in the cellular metabolic activity were detected (through the MTS assay) three days after the laser irradiation. The metabolic activity was found to be dependent on the laser fluence for both cell growth conditions. Furthermore, three days after the laser exposure, the potential laser induced "bystander" effect was tested through the transfer of growth media from laser irradiated cells onto non-irradiated cells. After two additional days of incubation (5 days post exposure), the non-laser irradiated cells grown under the non-confluent condition were found to have a significant increase in their metabolic activities, whereas minimal to null response was found for the fully confluent condition. For cells grown under the non-confluent conditions, modulations in the metabolic activities in the non-irradiated cells were found to be laser fluence dependent from the initial laser exposed cells treatment conditions. The results herein support the hypothesis of an important role for light enhanced cellular H₂O₂ generation to yield bio-modulatory effects locally and at a distance. The classical "bi-phasic" modulation response of cells to light irradiation is hypothesized to depend upon the quantity of light enhanced H₂O₂ molecules generated from the mitochondria and the number of cells which interact with the H₂O₂ molecules.

Date Published: 18 February 2009
PDF: 12 pages
Proc. SPIE 7165, Mechanisms for Low-Light Therapy IV, 716508 (18 February 2009); doi: 10.1117/12.813409

Published in SPIE Proceedings Vol. 7165:
Mechanisms for Low-Light Therapy IV
Michael R. Hamblin; Ronald W. Waynant; Juanita Anders, Editor(s)