Cigarette smoke extract-induced adipogenesis in Graves' orbital fibroblasts is inhibited by quercetin via reduction in oxidative stress

Cigarette smoking is known to aggravate Graves' orbitopathy (GO) severity by enhancing adipogenesis. We investigated the effect of quercetin, an antioxidant, on adipocyte differentiation induced by cigarette smoke extract (CSE) in primary cultured orbital fibroblasts (OFs) from GO patients. Freshly prepared CSE was added to the cells and H₂O₂ was used as a positive control. Intracellular reactive oxygen species (ROS) generation and adipogenesis were measured. The expressions of proteins peroxisome proliferator-activated receptor (PPAR) γ, CCAAT-enhancer-binding proteins (C/EBP) α and β, and heme oxygenase-1 (HO-1), an antioxidant enzyme, were examined during adipogenic differentiation. In result, CSE and H₂O₂ dose-dependently stimulated intracellular ROS production in normal and Graves' OFs. The effect of2%CSE was similar to that of 10 (μMH₂O₂; both concentrations were noncytotoxic and were used throughout the experiment. Quercetin pretreatment reduced the ROS generation stimulated by either CSE or H₂O₂ in preadipocyte OFs. CSE and H₂O₂ stimulated adipocyte differentiation in cultured OFs. The addition of quercetin (50 or 100mM) suppressed adipogenesis. Quercetin also suppressed ROS generation in differentiating OFs during adipogenesis stimulated by CSE and H₂O₂. Additionally, the expressions of PPARγ, C/EBPα, and C/EBPβ proteins were reduced in the quercetin-treated OFs. Quercetin also reduced the CSE- and H₂O₂-induced upregulation of ROS and HO-1 protein in differentiated OFs and preadipocyte OFs. As shown in this study, quercetin inhibited adipogenesis by reducing ROS in vitro, supporting the use of quercetin in the treatment of GO.