β-Sitosterol Mitigates Apoptosis, Oxidative Stress and Inflammatory Response by Inactivating TLR4/NF-кB Pathway in Cell Models of Diabetic Nephropathy.

Abstract

Podocyte injury plays a pivotal role in the pathogenesis of diabetic nephropathy (DN), leading to proteinuria formation. β-Sitosterol is a natural compound with anti-inflammatory, anti-diabetic, nephroprotective and antioxidant properties. The studyaimed to explore whether and how β-Sitosterol protected podocytes against high glucose (HG)-induced inflammatory andoxidative injury. DN cell models were established by stimulating podocytes or renal tubular epithelial cells (HK-2) cells with 25 mM glucose. Cell viability and apoptosis were evaluated using cell counting kit-8 assays and flow cytometry analyses. Westernblotting was used to quantify protein levels of genes related to podocyte injury, HK-2 cell damage, inflammation, and TLR4/NF-кB pathway. Contents of oxidative stress biomarkers were evaluated by corresponding commercial kits while proinflammatorycytokine levels were determined by enzyme-linked immunosorbent assay. Immunofluorescence staining was performed todetect intracellular levels of reactive oxygen species (ROS) and Nrf2 nuclear translocation. Experimental results revealed that HG treatment induced podocyte dysfunction by impairing cell viability while accelerating theapoptosis, and the changes were reversed by β-sitosterol treatment. Moreover, β-sitosterol repressed HG-evoked oxidative stressby reducing ROS and malondialdehyde (MDA) levels while increasing activities of antioxidant enzymes. The reduction ofproinflammatory cytokines mediated by β-sitosterol in HG-stimulated podocytes suggested the anti-inflammatory role of β-sitosterol. Additionally, the activation of the TLR4/NF-кB signaling induced by HG was inhibited by β-sitosterol in podocytes.Inactivation of the TLR4 using TAK-242 enhanced the protective effects of β-sitosterol against HG-mediated oxidative stressand inflammation. Similarly, β-sitosterol also protected HK-2 cells from HG-induced oxidative stress, inflammation, andapoptosis. In summary, β-sitosterol exerts anti-inflammatory, anti-oxidative, and anti-apoptotic activities in HG-induced podocytes or HK-2 cells by inhibiting TLR4/NF-кB signaling.