Sex Hormone-Binding Globulin (SHBG) Modulates Inflammatory and Oxidative Stress Responses in Equine Immune Cells: Implications for Equine Metabolic Syndrome

Background : Sex hormone-binding globulin (SHBG) is a plasma glycoprotein mainly recognized for its role in regulating sex steroid bioavailability. However, recent studies indicate SHBG's involvement in a variety of biological processes, including those related to the immune system. In this study, the immunomodulatory effects of SHBG on lipopolysaccharide (LPS)-stimulated equine peripheral blood mononuclear cells (PBMCs) and macrophages were examined. Methods : Equine peripheral blood mononuclear cells (PBMCs) and macrophages were stimulated with LPS to induce an acute inflammatory response and subsequently treated with 50 nM SHBG. The anti-inflammatory activity of SHBG was assessed by analyzing the secretion of inflammatory mediators, the activation of regulatory T cells (Tregs), the proportion of M2 macrophages, and markers of oxidative and nitrosative stress. In addition, the therapeutic potential of SHBG was evaluated ex vivo using equine subcutaneous adipose tissue explants. Results : SHBG markedly reduced the secretion of pro-inflammatory cytokines and chemokines (IL-1β, IL-6, TNF-α, MCP-1), while enhancing the release of anti-inflammatory mediators including IL-10. It also promoted regulatory T cell (Treg) activation within the total PBMCs population, thereby contributing to an immunosuppressive environment. In macrophages, SHBG shifted the phenotype from pro-inflammatory M1 toward anti-inflammatory M2 subtype, facilitating the resolution of inflammation. Furthermore, SHBG mitigated oxidative and nitrosative stress by lowering reactive oxygen species (ROS) and nitric oxide (NO) levels and enhancing antioxidant enzymes activity, thus restoring redox balance. Importantly, conditioned media from SHBG-treated PBMCs reduced the pro-inflammatory impact of PBMC-derived mediators on subcutaneous adipose tissue (SAT) explants, as shown by the decreased IL-6 and IL-1β tissue expression compared with media from LPS-stimulated PBMCs. Conclusion : Collectively, these findings identify SHBG as a novel regulator of immune homeostasis, capable of attenuating inflammation and oxidative stress at multiple levels.