Quercetin is a dietary flavonoid showing in vitro a wide range of pharmacologic proprieties, including antioxidant, anti-microbial, anti-inflammatory and anti-proliferative activity. It has been identified as a modulator of proteasome activity, though its inhibitory or activating profile seems to depend to its concentration. At higher, micromolar, levels quercetin acts as an inhibitor of chymotrypsin-like activity whereas at lower doses it has been shown to behave as a proteasome activator that can influence cellular lifespan, survival and viability of HFL-1 primary human fibroblasts.
In contrast to the development of 20S proteasome inhibitors, drug-like molecules that can activate or enhance proteasome activity are rare and not well characterised, despite their potential therapeutic benefits for treating specific diseases in which an increase in proteasome activity is thought to be beneficial
