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Biochemical and Molecular Actions of Nutrients

Quercetin Attenuates Nuclear Factor-B Activation and Nitric Oxide Production in Interleukin-1ß–Activated Rat Hepatocytes¹

Department of Physiology, University of León, 24071 León, Spain

²To whom correspondence should be addressed. E-mail: dfimtg{at}unileon.es.

We investigated whether different concentrations of the flavonoid quercetin ameliorate nitric oxide production and nuclear factor (NF)-B activation in interleukin (IL)-1ß–activated rat hepatocytes. Primary cultures of rat hepatocytes were treated with IL-1ß alone or with quercetin in concentrations ranging from 5 to 100 µmol/L. The generation of reactive oxygen species, assessed by flow cytometry using dichlorodihydrofluorescein diacetate, was significantly reduced, and the oxidized:reduced glutathione ratio decreased in cultures treated with 50 and 100 µmol/L of quercetin. Quercetin at 100 µmol/L significantly prevented the IL-1ß-induced release of nitrite into the culture medium. Western blot and reverse transcription-PCR analyses demonstrated that increased levels of inducible nitric oxide synthase (iNOS) protein and mRNA in hepatocytes stimulated by IL-1ß were prevented by 50 µmol/L and 100 µmol/L of quercetin. Electrophoretic mobility shift assay experiments and Western blots indicated that quercetin blocked the activation of NF-B and decreased the inhibitor B protein levels induced by IL-1ß. In summary, quercetin, a natural flavonol widely distributed in the human diet, inhibits NO production in IL-1ß–stimulated hepatocytes through the inhibition of iNOS expression. Although the mode of action remains to be clarified, our findings support the view that the mechanism of action is via inhibition of IL-1ß–induced NF-B activation.

KEY WORDS: • interleukin-1ß • nitric oxide • nuclear factor-B • quercetin • rat cultured hepatocytes

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