UC Irvine

PURPOSE: Brimonidine is a selective alpha-2 adrenergic agonist used to reduce intraocular pressure and it has been shown to have some neuroprotective effects. Hydroquinone (HQ) is a toxicant present in cigarette smoke, and other sources. In this study, we investigated the cyto-protective effects in vitro of Brimonidine on human retinal pigment epithelium cells (ARPE-19) and human retinal Müller cells (MIO-M1) that had been treated with HQ. METHODS: Cells were pretreated for 6 h with different doses of Brimonidine tartrate 0.1% (1/2×, 1×, 5×, 10×), followed by a 24-h exposure to 100 μM of HQ, while the Brimonidine was still present. Assays were used to measure cell viability, mitochondrial membrane potential (ΔΨm), reactive oxygen species (ROS) production, and lactate dehydrogenase (LDH) release. RESULTS: Brimonidine increased the cell viability at all concentrations studied in both cell lines studied. ΔΨm also improved at all Brimonidine doses in ARPE-19 cells and in the 5× and 10× dosages MIO-M1 cells. The ROS levels decreased at 1×, 5×, and 10× doses of Brimonidine in ARPE-19 but only at 10× on MIO-M1 cells. The 10×-Brimonidine ARPE-19 cells had decreased LDH release, but no LDH changes were observed on MIO-M1 cells. CONCLUSION: HQ-induced toxicity is mediated through mitochondrial damaging, oxidative stress-related and necrosis-related pathways; Brimonidine significantly prevented the mitochondrial damaging and oxidative stress-related effects but had little effect on blocking the necrosis component of HQ-toxicity. Brimonidine protective effects differ between the different retinal cell types and high concentrations of Brimonidine (10×) have minimal damaging effects on human retinal cells.