Glycyrrhizin protects IGFBP-3 knockout mice from retinal damage.

We previously reported that insulin-like growth factor binding protein 3 (IGFBP-3) knockout (KO) mice have neuronal and vascular damage to the retina. We also reported that glycyrrhizin, a high mobility growth factor binding protein 1 (HMGB1) inhibitor, is protective to the diabetic retina. In this study, we investigated whether glycyrrhizin could reduce neuronal and vascular damage in the IGFBP-3 KO mouse retina. We used measurements of retinal thickness, cell number in the ganglion cell layer, degenerate capillaries, reactive oxygen species (ROS) and protein levels of HMGB1, tumor necrosis factor alpha (TNFα), interleukin-1-beta (IL-1β) and sirtuin 1 (SIRT1) to determine whether glycyrrhizin could protect the retina. Data show that glycyrrhizin in the drinking water was effective in reducing neuronal damage at 2 months and vascular damage at 6 months. Glycyrrhizin reduced ROS levels at 6 months, and reduced levels of HMGB1, TNFα, and IL-1β at both 2 and 6 months. Taken together, the data suggest that glycyrrhizin is protective to the retina of IGFBP-3 KO mice through anti-inflammatory mechanisms.