HMGB1 impairs endothelium-dependent relaxation in diabetes through TLR4/eNOS pathway

Endothelium-dependent relaxation (EDR) is an initial key step leading to various vascular complications in patients with diabetes. However, the underlying mechanism of EDR impairment in diabetes is not fully understood. Present study defined the role of high-mobility group protein (HMGB1) in EDR related to diabetes. Serum level of HMGB1 was increased in diabetic patients and in db/db mice. Serum HMGB1 level was also positively correlated with HbA1c and negatively correlated with nitric oxide (NO) in diabetic patients. Results from wire myograph showed that recombinant HMGB1 (rHMGB1) was capable of impairing EDR of aortas from wild-type (WT) mice by an eNOS-dependent mechanism. Consistently, HMGB1 inhibitor glycyrrhizin acid (GA) decreased the serum level of HMGB1 and rescued EDR impairment partly in db/db mice. Furthermore, rHMGB1 mediated EDR impairment was abolished in aortas of TLR4^-/- mice. In addition, high-glucose-induced HMGB1 upregulation and secretion in endothelial cells. In conclusion, HMGB1 contributes to the EDR impairment through TLR4/eNOS pathway in the setting of diabetes. GA as the HMGB1 inhibitor could attenuate EDR impairment in an animal model of diabetes.