Sulforaphane attenuates HMGB1-mediated activation of inflammatory pathways in the liver of diabetic mice and suppresses ferroptosis

Abstract

The activation of inflammation is closely associated with ferroptosis and vice versa. Recently, we have demonstrated the involvement of ferroptosis, a newly defined form of iron-dependent cell death, in diabetes-induced liver pathology. We also found that sulforaphane (SFN), a natural isothiocyanate from cruciferous vegetables, prevents diabetes-induced hepatic ferroptosis by activating the Nrf2 signaling axis. Since ferroptosis and inflammation jointly fulfill physiological and pathological functions, in this study we investigated whether the anti-inflammatory effect of SFN is reflected in the modulation of high mobility group box 1 (HMGB1)-related activation of the inflammatory cascade in the liver of diabetic mice and how it is related to the extent of ferroptosis. HMGB1 is a damage-associated molecular pattern molecule that is released by ferroptotic cells, among others. Extracellular HMGB1 is a potent activator of well-characterized inflammation-related pathways, including JAK-STAT, NF-κB, and mitogen-activated protein kinase (MAPK), whose activities are associated with ferroptosis.For this purpose, male C57BL/6 mice in which diabetes was induced with streptozotocin (40 mg/kg/5 consecutive days) were treated with SFN (2.5 mg/kg/day from day 1 to 42). Blood glucose levels were measured once a week during the trial. On day 43, the liver was isolated and prepared for Western immunoblotting and ELISA tests. SFN was found to improve serum levels of glucose, ALT and triglycerides in diabetic mice and to enhance the diabetes-induced decrease in liver expression of GPX4, a hallmark of ferroptosis events. This improvement was partly due to the SFN-induced decrease in the increased expression of HMGB1 and its downstream pro-inflammatory activities related to the activation of MAPKs, NF-кB p65 and JAK1/STAT3 signaling pathways. SFN prevented diabetes- induced phosphorylation of p38 and extracellular signal-regulated kinases (ERKs), NF-κB 65 and STAT3 phosphorylation, and phosphorylation of protein kinase B (Akt), a key mediator of cell survival. The results obtained suggest that interfering with HMGB1 signaling pathways through SFN may enable effective intervention in diabetes by exerting therapeutic effects on inflammatory status and cell death such as ferroptosis.