Guluronic acid disaccharide inhibits reactive oxygen species production and amyloid-β oligomer formation.

In general, Cu(II) is the critical factor in catalyzing reactive oxygen species (ROS) production and accelerating amyloid-β (Aβ) oligomer formation in Alzheimer's disease (AD). Natural chelating agents with good biocompatibility and appropriate binding affinity with Cu(II) have emerged as potential candidates for AD therapy. Herein, we tested the capability of guluronic acid disaccharide (Di-GA), a natural chelating agent with the moderate association affinity to Cu(II), in inhibiting ROS production and Aβ oligomer formation. The results showed that Di-GA was capable of chelating with Cu(II) and reducing ROS production, even in solutions containing Fe(II), Zn(II), and Aβ. In addition, Di-GA can also capture Cu(II) from Cu-Aβ complexes and decrease Aβ oligomer formation. The cellular results confirmed that Di-GA prevented SH-SY5Y cells from ROS and Aβ oligomer damage by reducing the injury of ROS and Aβ oligomers on cell membrane and decreasing their intracellular damage on mitochondria. Notably, the slightly higher efficiency of Di-GA in chelating with Cu(I) than Cu(II) can be benefit for its in vivo applications, as Cu(I) is not only the most active but also the special intermediate specie during ROS production process. All of these results proved that Di-GA could be a promising marine drug candidate in reducing copper-related ROS damage and Aβ oligomer toxicity associated with AD.