Purpose The authors previously reported that quercetin significantly inhibits interleukin (IL)-1β-induced increases of proinflammatory cytokines in cultured primary orbital fibroblasts from Graves' orbitopathy (GO). This study investigated the inhibitory effect of quercetin on inflammation in cultured whole orbital tissue.

Methods Orbital fat tissues from GO and normal samples were cultured with or without non-toxic concentrations of quercetin. Lactate dehydrogenase (LDH) release was used to identify non-toxic concentrations of quercetin. IL-6, IL-8, IL-1α, IL-1β and tumour necrosis factor alpha (TNFα) proteins were measured in tissue culture supernatants by ELISA, and gene transcript levels were determined using quantitative PCR, expressed as relative fold changes of threshold cycle value relative to the control group.

Results The maximal non-cytotoxic treatment of quercetin was 100 μM for 72 h, based on the considerably low LDH release with these conditions. IL-1β, IL-6 and TNFα protein levels corrected for tissue weight were significantly higher in supernatants of GO samples than normal controls (p<0.05). Quercetin reduced IL-6, IL-8 and TNFα protein production in supernatants of all GO samples (n=4) in a dose-dependent manner; however, only the reduction in IL-6 was statistically significant (p<0.05). Quercetin had a significant suppression of tissue IL-6, IL-8, IL-1β and TNFα mRNA expression in cultured orbital tissues from three GO samples relative to untreated control tissue (p<0.05).

Conclusions Inhibition of proinflammatory cytokines by the natural product quercetin in both primary orbital fibroblasts and tissue culture provides the basis for its potential use as an anti-inflammatory agent in the treatment of GO.