Protection Against Oxidative Stress-Induced Retinal Cell Death by Compounds Isolated From Ehretia asperula

Ehretia asperula (E asperula) is a well-known traditional medicinal plant in Vietnam with potent activity against a wide range of diseases, including hepatitis B and various cancers. Although E asperula has been used in traditional medicine, the efficacy of E asperula and its bioactive components on retinal degenerative diseases has not been fully evaluated. In present this study, we found that ethanolic extracts of E asperula increased cell viability in retinal precursor cells exposed to glutamate/BSO-induced excitotoxicity/oxidative stress. The major responsible bioactive compounds were rosmarinic acid and methylrosmarinic acid. First, 10 known compounds were isolated from E asperula leaves. Their chemical structures were determined using 1D and 2D nuclear magnetic resonance, and compared with published data. Using high-performance liquid chromatography, we determined the content of 4 compounds in E asperula extract: rosmarinic acid, lithospermic acid B, astragalin, and kaempferol 3-rutinoside. The most abundant of these compounds was lithospermic acid B. The protective effects of the pure compounds and ethanolic extracts against excitotoxicity and oxidative stress-induced retinal cell death were tested in R28 cells. Both 70% and 95% ethanolic extracts of E asperula increased cell viability in these conditions. Rosmarinic acid and methyl rosmarinic acid were more effective at protecting against retinal cell death and elevated reactive oxygen species in cells subjected to glutamate/BSO-induced excitotoxicity/oxidative stress. These findings suggested that E asperula could potentially be used to treat retinal degeneration.