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8 International Journal of Photoenergy 2500 2000 1500 1000 800 600 400 200 ∗ ∗ ∗ ∗ 670nm light only (b) Cell toxicity 500 00 −500 0 1 2 3 4 Time point (hours) 670 nm light only LD only 670 nm light + LD (a) H2O2 production 5 Non-LD LD only 670nm light + LD Figure 6: (a) The effect of 9 J/cm2 of 670 nm light and light damage on H2 O2 production in 661 W photoreceptor cells is shown here where bars represent the percentage change of H2O2 production when compared to nonlight damaged cells. Light damage significantly increased H2O2 production in the cells directly after one hour of light exposure. H2O2 production steadily increased amongst light damaged cells, both treated and nontreated, with increasing time under bright light conditions (𝑛 = 3 for all groups; each run consisted of duplicate wells for each group; “∗” denotes significance using one-way ANOVA with Tukey’s post hoc test, 𝑃 < 0.05; error bars represent SEM). (b) There was an increase in cell toxicity in light damaged (LD) cells, both treated and nontreated, when compared to nonlight damaged cells. 670 nm light did not significantly decrease cell toxicity in control or light damaged conditions (𝑛 = 3 for all groups; each run consisted of duplicate wells for each group; “∗” denotes significance using one-way ANOVA with Tukey’s post hoc test, 𝑃 < 0.05; error bars represent SEM). also showed no change in ECAR when compared to light damage only cells. Nonlight damaged cells, both treated and nontreated, demonstrated an increase in ECAR readings when compared to light damaged cells, both treated and nontreated. 3.3. Effect of 670 nm Light on H2O2 Production. The produc- tion of H2O2 was measured as a time series throughout the 5-hour light damage paradigm we used for all of our in vitro experiments. H2O2 production increased by 1500% after one hour of light damage when compared to nonlight damaged cells (Figure 6(a)). This was followed by a steady increase with each hour in both treated and nontreated cells under the light damage paradigm. There was no significant difference in H2O2 production for nonlight damaged cells, regardless of 670 nm treatment or not. 3.4. Effect of 670 nm Light on Cell Toxicity. Cell toxicity and death were measured using a cell toxicity assay (Figure 6(b)). Cells on the plates that were light damaged had a significantly higher amount of cell death when compared to normal nonlight damaged cells. There were no significant differences in the amount of cell death between light damaged, 670 nm light treated cells and nondamaged, 670 nm light treated cells. 4. Discussion This study has generated three key novel findings on the action of 670nm in the light damaged model of retinal degeneration. First, our in vivo experiments suggest that lower doses of 670 nm light are protective against photorecep- tor death, while higher doses promote photoreceptor death. Second, in vivo experiments indicate that the protective efficacy of a specific dose of 670 nm light depends on the degree of retinal damage, such that high doses of 670 nm light may be damaging to a healthy retina but may be required to be protective against more severe or progressive retinal damage. Third, our in vitro experiments show an increase in spare respiratory capacity of 661 W cells treated with 670 nm light. 4.1. 670 nm Light Dose-Response. Previous studies have typi- cally used a single, often arbitrary dose of 670 nm light to test its efficacy in a simple damage paradigm [24, 26, 33–35]. In others, seemingly arbitrary treatment doses have varied with wavelength, tissue type, and the type of damage [21], leading to a difference in biological response. In this study we varied both the degree of damage and the dose of 670 nm light used to ameliorate that damage, in an attempt to demonstrate the importance of dosage in treatment with 670 nm red light. Our findings indicate that the lower doses of 670 nm light (9 J/cm2 and 18 J/cm2) protect photoreceptors from cell death in the low and medium intensity light damage paradigms (750 and 1000 lux). However, higher doses of 670 nm light either had no effect on photoreceptor death (36J/cm2) or induced additional death (90 J/cm2), in the low and moderate light damage paradigms (Figure 4). The capacity of 670 nm light alone to induce photoreceptor death was confirmed in Change from control (%) Number of positive labelled cellsPDF Image | 670 nm Light Therapy to Protect vs Photoreceptor Cell Death
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