Edible Seaweed, Eisenia bicyclis, Protects Retinal Ganglion Cells Death Caused by Oxidative Stress

The purpose of the present study was to determine whether edible seaweed, Eisenia bicyclis, is effective in blunting the negative influence of N-methyl-d-aspartate (NMDA) on rat retinas and of oxidative stress-induced transformed retinal ganglion cell (RGC-5 cell line) death. The ethanol extract of E. bicyclis (EEEB) significantly attenuated the negative insult of l-buthionine-(S,R)-sulfoximine plus glutamate on RGC-5 cells. Treatment of the RGC-5 cells with EEEB reduced the reactive oxygen species and recovered the reduced glutathione level caused by various radical species such as H2O2, OH center dot, or O-2 center dot(-). Moreover, EEEB inhibited lipid peroxidation on rat brain homogenates caused by sodium nitroprusside. Applying NMDA to the retina affected the thickness of the inner plexiform layer (IPL) and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) produced a positive effect on ganglion cells. Importantly, EEEB protected the thinning of IPL and increased TUNEL positive cells in the ganglion cell layer (GCL). Five phlorotannin derivatives were isolated using chromatographic methods and liquid chromatography-mass spectroscopy analysis which has been known as an antioxidant. In conclusion, EEEB has a neuroprotective effect in vitro and in vivo. Furthermore, the major constituents of this extract, phlorotannins, could possibly be active compounds due to their antioxidative potency.