HMGB1 SUPPRESSION CONFERS NEUROPROTECTION AGAINST STROKE IN DIABETIC RATS

Diabetes is a principal risk factor for stroke, and results in poorer neurological outcome after stroke. High mobility group box-1 (HMGB1) was recently reported to mediate an increased inflammatory response through receptors for advanced glycation end products (RAGE) and Toll-like receptors (TLR). In this study, we investigated how blocking HMGB1, using glycyrrhizin, may reduce inflammation following ischemic stroke in a diabetic model. The effect of glycyrrhizin on non-stroke diabetic rats was assessed, following diabetes induction by streptozotocin. This was followed with the analysis of glucose, HMGB1 and cytokines levels. We then sought to determine the impact of HMGB1 suppression with glycyrrhizin after a stroke using transient occlusion of the middle cerebral artery. Infarct volume, HMGB1 levels, expression of TLR and RAGE and their subcellular pathways were measured. Results: In the non-stroke state, glycyrrhizin did not reduce glucose levels in diabetic rats, but significantly reduced HMGB1 and interleukin (IL)-1 beta levels. Furthermore, glycyrrhizin decreased the infarct volume after focal cerebral ischemia in diabetic rats (140 +/- 79 mm(3) versus 224 +/- 68 mm(3); p=0.03). HMGB1 secretion from the ischemic brain and expression of TLR2, TLR4 and RAGE were reduced after glycyrrhizin treatment. Intracellular signaling pathways related to HMGB1 receptors, such as NF-kappa B, ERK, and Akt, were reduced after HMGB1 inhibition using glycyrrhizin. Discussion: Our results indicate that HMGB1 suppression by glycyrrhizin reduces the inflammatory response in diabetes with or without stroke. We conclude that HMGB1 may be a good candidate to target for the inhibition of the inflammatory response after stroke.