High Mobility Group Box1 Inhibitor Glycyrrhizic Acid Attenuates Kidney Injury in Streptozotocin-Induced Diabetic Rats.

BACKGROUND/AIMS: High mobility group box 1 (HMGB1) is an important mediator of the inflammatory response. It has been implicated in the pathogenesis of autoimmune diseases, atherosclerosis, and obesity. However, the effects of HMGB1 on diabetic nephropathy remain unclear. Here, we investigated the potential roles and mechanisms of an HMGB1 inhibitor, glycyrrhizic acid (GA), in renal injury with the streptozotocin (STZ)-induced rat model.

METHODS: The diabetic rat was generated by intraperitoneal injection of STZ and then treated with the HMGB1 inhibitor GA or saline for 8 weeks. Rats were randomly divided into three groups: the normal control and saline group (Control), the diabetic rats with saline group (Diabetic) and the diabetic rats plus GA group (Diabetic+GA). Peripheral blood was obtained for measurements of blood glucose, TNF-a, IL-6 and IL-1β. The mRNA levels of proinflammatory cytokines (TNF-a, IL-6 and IL-1β), chemokines (MCP-1), intercellular adhesion molecules (ICAM-1) and TGF-β1 in the kidneys were evaluated by quantitative real-time PCR. The protein levels of phosphorylated(p) and total(t) p38 MAPK, JNK, ERK, and NF-κB were measured by western blot.

RESULTS: We found that diabetic rats showed obvious renal lesions, an elevated urinary albumin/creatinine ratio (UACR) and increased expression levels of TGF-β1 and Col-IV in the kidneys, accompanied by significantly enhanced expression levels of HMGB1, receptor for advanced glycation end products (RAGE) and toll-like receptor 4 (TLR-4) in the kidney tissue. Furthermore, the GA treatment significantly reduced the UAC levels, ameliorated renal injury, and decreased the TNF-α, 1L-6, IL-1β, MCP-1, ICAM-1, TGF-β1 and Col-IV levels. Importantly, the expression levels of HMGBI, RAGE and TLR4 in the kidney tissues of the diabetic rats were also inhibited by the GA treatment. Furthermore, the GA treatment significantly reduced the phosphorylation levels of ERK and p38 MAPK and suppressed NF-κB translocation from the cytoplasm to the nucleus.

CONCLUSION: Our findings indicate that the HMGB1 inhibitor GA may improve renal injury and inflammatory responses in diabetic rats by regulating RAGE/TLR4-related ERK and p38 MAPK/NF-κB activation.