Effect of Minoxidil on Trabecular Outflow via the Paracellular Pathway

PURPOSE: To investigate the pathway and effects of minoxidil on trabecular outflow in cultured human trabecular meshwork (TM) cells. METHODS: After exposing primarily cultured TM cells to 0, 10, 50, or 100 µM minoxidil sulfate (MS), trabecular outflow was assessed by measuring TM cell monolayer permeability to carboxyfluorescein and transepithelial electrical resistance. To assess the pathway of permeability changes, caveolin-1, occludin, and claudin-5 levels were measured via western blot. Generation of reactive oxygen species (ROS) was measured using the dichlorofluorescein diacetate assay. To assess the involvement of nitric oxide (NO) in minoxidil-induced permeability increase, the degrees of endothelial nitric oxide synthase mRNA expression and NO production were measured with reverse transcription polymerase chain reaction and Griess assays, respectively. Permeability was also measured with co-exposure to 50 µM N-acetyl cysteine. RESULTS: MS significantly increased TM cell monolayer permeability (p < 0.05) and decreased transepithelial electrical resistance (p < 0.05). MS decreased the degree of endothelial nitric oxide synthase mRNA expression but did not affect NO production. MS decreased occludin and claudin-5 levels but did not affect caveolin-1 level. MS at 100 µM increased the generation of ROS, and MS-induced permeability increase was attenuated after co-exposure to 50 µM N-acetyl cysteine. CONCLUSIONS: Minoxidil may preferentially increase trabecular permeability via a paracellular pathway by downregulation of tight junction proteins. This minoxidil-induced permeability through the TM may be mediated by generation of ROS.