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Blue Light Differentially Modulates Cell Survival and Growth

¹ Department of Oral Rehabilitation, Medical College of Georgia School of Dentistry, Augusta, GA 30912-1260; and
² University of Geneva School of Dental Medicine, Geneva, Switzerland;

View larger version (34K): [in a new window]   Figure 1. Blue light differentially altered survival and growth of cells. Succinate dehydrogenase (SDH) activity (estimating cell survival and growth, MTT method, expressed as optical density [OD] of solubilized formazan @ 560 nm) was measured at 24-hour intervals for 72 hrs after exposure to QTH (2 min, 60 J/cm2) and PAC (30 sec, 60 J/cm2) light sources (Table). Cells were fibroblastic (Balb/c 3T3-mouse lung, HGF-human gingival, WI-38-human lung) or epithelial (MCF-7-human breast carcinoma, OSC-2-human oral squamous cell carcinoma, NHEK-normal human foreskin) in origin. Cells were plated at 12,500 cells/cm2 24 hrs prior to light exposure at time zero. Both suppression (Balb/c, OSC-2, MCF-7) and stimulation (WI-38, NHEK) of cell growth were observed. Error bars indicate standard deviations, and asterisks (*) indicate SDH activity statistically different from no-light control within each time period (ANOVA, Tukey, = 0.05, n = 3).

View larger version (44K): [in a new window]   Figure 2. Effect of blue light on cellular succinate dehydrogenase activity correlated with population doubling time of cells. Cells were fibroblasts (Balb/c 3T3-mouse lung, HGF-human gingival, WI-38-human lung) or epithelial (MCF-7-human breast carcinoma, OSC-2-human oral squamous cell carcinoma, NHEK-normal human foreskin). Correlation (least-squares method, linear model) of population doubling time of cells vs. succinate dehydrogenase (SDH) activity (MTT method) as a percentage of no-light controls, 72 hrs after exposure to either the plasma-arc curing (A, PAC, 2 min, 60 J/cm2), quartz-tungsten halogen (B, QTH, 10 sec, 5 J/cm2), or laser (C, Laser, 30 sec, 60 J/cm2) light sources (Table). In each case (A,B, and C), the slope of the fitted line was significantly different from zero (p < 0.05). The strongest correlation between the SDH effect and doubling time was with the PAC source (C). The laser induced significant (D, 40–50%, p < 0.05, ANOVA, Tukey, n = 3) stimulation of SDH activity of WI-38 and HGF at 72 hrs and some stimulation of NHEK (30%, not significant). Error bars in D indicate standard deviations.

View larger version (86K): [in a new window]   Figure 3. Blue light suppressed mitochondrial activity in Balb/c 3T3 fibroblasts. Balb/c fibroblasts were chosen for further study because they were most sensitive to blue light (Figs. 1, 2). Photomicrographs (A, B, C, and D, 50x, bar = 500 µm) of cells (fixed with 4% formalin) 72 hrs post-exposure to blue light from QTH (B, 2 min, 60 J/cm2), PAC (C, 30 sec, 60 J/cm2), or Laser (D, 10 sec, 5 J/cm2) sources (Table). No-light controls are shown in A. Presence of the blue formazan dye is indicative of active mitochondrial succinate dehydrogenase (SDH). Cells in the no-light controls (A) show high levels of formazan, whereas light-exposed cells (B,C,D) show little or no formazan, indicating inactive SDH. TEM (E,F) of identically treated (fixed and processed as described in METHODS) cells 6 hrs post-QTH exposure show evidence of degenerating mitochondria (DM, in panel F) vs. normal mitochondria (M) in no-light controls in panel E. Light-exposed mitochondria in F show loss of inner mitochondrial membrane structure and a dark staining of the outer membrane. TEM micrographs courtesy of Dr. Franklin Tay, University of Hong Kong.