Role of Glycyrrhizin in the Reduction of Inflammation in Diabetic Kidney Disease

BACKGROUND: Diabetic kidney disease (DKD) is one of the most debilitating complications of type 2 diabetes. Recent evidence suggests chronic inflammation to be one of the causal factors of DKD. The mechanisms entailed are not completely elucidated except that a variety of cytokines play a major role in this process. High mobility group box 1 (HMGB1) is a pro-inflammatory toll-like receptor-4 (TLR4)-binding cytokine that is involved in inflammation-associated gene expression. This investigation was designed to assess the involvement of HMGB1, TLR-4, and nuclear factor (NF)-κB in the development of DKD and to evaluate that whether blocking HMGB1 by its natural inhibitor Glycyrrhizin (GLC) can reduce the progression of the disease. METHODS: Studies were carried out in 8-10-weeks old Zucker diabetic fatty (ZDF) and lean, age- and gender-matched rats. At 10 weeks of age, ZDF rats as compared to controls, showed hyperglycemia, without proteinuria. After 8-10 weeks of the development of diabetes, ZDF animals that showed proteinuria were treated with GLC for 4 weeks. In addition, normal rat kidney (NRK-52E) cells with epithelial-like morphology were comparatively treated with GLC under hyperglycemic condition in vitro. RESULTS: Substantial increase in the expression of HMGB1, TLR4, and NF-κB in vivo and in vitro under hyperglycemic conditions was observed as compared to normoglycemic conditions. The overexpression of HMGB1, TLR4, NF-κB, and glomerular injury marker nestin was significantly ameliorated by GLC administration. CONCLUSION: Our findings suggest that hyperglycemia-induced HMGB1 activation in ZDF rats may contribute to the progression of DKD.