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Grayson A. Roumeliotis, Dov Kagain, Cindy M. Hutnik; Selective Laser Trabeculoplasty Promotes Phagocytosis In Cultured Trabecular Meshwork Cells. Invest. Ophthalmol. Vis. Sci. 2012;53(14):5958.
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© ARVO (1962-2015); The Authors (2016-present)
The mechanism by which selective laser trabeculoplasty (SLT) lowers intraocular pressure is still not known. In contrast to argon laser trabeculoplasty (ALT), there is no morphological change to the trabecular meshwork after SLT. Several authors have suggested that SLTs effect on intraocular pressure relies on an adaptive stress response resulting in a change in meshwork function. Phagocytosis of extracellular debris by trabecular meshwork cells is important for the maintenance of intraocular pressure. We hypothesized that a small amount of stress would promote phagocytosis in cultured human trabecular meshwork cells, and that SLT would have a similar effect.
Cultured primary cell cultures of human trabecular meshwork cells were used as a model of the in vivo trabecular meshwork. Cells were treated with tert-butyl hydroperoxide (t-BOOH) at 0.05mM, 0.1mM, 0.25mM, and 0.5mM concentrations for two hours. After treatment, cell viability was assessed using the MTT [3-(4,5- dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay. Phagocytic function was assessed using a novel application of the Vybrant™ phagocytosis assay. To assess the effect of SLT on these variables, cells were exposed to a 532-nm frequency doubled Q-switched: Nd: Yag laser (3-ns pulse with a 400 μm beam diameter). The proportion of the cell monolayer exposed to the laser was varied from 0-100% (0, 25%, 50%, 75%, 100%). Cell viability and phagocytosis were assessed four hours after laser treatment.
Treatment with 0.05mM, 0.1mM, 0.25mM t-BOOH resulted in 49% (SD= 8%, p<0.05, n=2), 37% (SD= 6%, p<0.05, n=2), 29% (SD=0.2%, p0.05, n= 2). SLT laser treatment did not affect cell viability (n=4), nor did it cause an observable morphologic change. However, SLT appears to stimulate phagocytosis. SLT laser treatment with 25, 50, 75 and 100% cell coverage resulted in increases of 34% (SD= 27%), 33% (SD= 40%), 15% (SD= 26%) , and 5% (SD= 9%) when compared to untreated control cells in three trials (n=3).
These data suggest that the trabecular meshwork exhibits a preconditioning response stress similar to other organ systems, wherein an early stress, here SLT or t-BOOH, elicits a response that protects against later stressors such as a phagocytic challenge. These findings have provided the basis for our ongoing work to elucidate the mechanism of SLTs effect on intraocular pressure.
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