The Time-Course of Antioxidant Irisin Activity: Role of the Nrf2/HO-1/HMGB1 Axis

The production of free radicals is one of the basic mechanisms giving rise to the antimicrobial activity of macrophages; however, excessive accumulation of reactive oxygen species (ROS) can lead to cell damage, cell death, and release of the highly proinflammatory alarmin high-mobility group box 1 (HMGB1). This study aimed to evaluate the kinetics of antioxidant properties of the adipomyokine irisin administered shortly before or after macrophage activation to assess its effect on the nuclear factor erythroid 2-related factor 2 (Nrf2)/heme oxygenase-1 (HO-1)/HMGB1 pathway. The studies were performed on RAW 264.7 mouse macrophages treated with irisin (0, 25, and 50 nM) 2 h before or after lipopolysaccharide (LPS) stimulation. The effectiveness of respiratory burst and the expression of key factors of the antioxidant pathway, such as HO-1, Nrf2, superoxide dismutase 1 (SOD-1), SOD-2, glutathione peroxidase (GPx), catalase-9 (Cat-9), and HMGB1, were assessed. Irisin (50 nM) effectively reduced the free-radical production by macrophages. Furthermore, in both models, irisin altered the kinetics of expression of key factors of the downstream Nrf2/HO-1/HMGB1 pathway, leading to the increased production of Nrf2 and HO-1 and significantly reduced expression and release of HMGB1. In conclusion, irisin is a modulator of the Nrf2/HO-1/HMGB1 pathway and shows antioxidative and anti-inflammatory effects when administered both before and shortly after the activation of inflammatory mechanisms in mouse macrophages.