ABSTRACT: Using mice deficient in hepatic cytochrome-P450 oxidoreductase (POR), which disables the liver cytochrome P450 system, the metabolism and biological response of the anti-carcinogenic flavonoid, quercetin, was examined. Profiling circulating metabolites revealed similar profiles over 72 h in wild type (WT) and POR-null (KO) mice, showing that hepatic P450 and reduced biliary secretion do not affect quercetin metabolism. Transcriptional profiling at 24 h revealed that 2-3 fold more genes responded significantly to quercetin in WT compared to KO in the jejunum, ileum, colon, and liver, suggesting that hepatic P450s mediate many of the biological effects of quercetin, such as immune function, estrogen receptor signaling and lipid, glutathione, purine, and amino acid metabolism, even though quercetin metabolism is not modified. The functional interpretation of expression data in response to quercetin (single dose of 7 mg/animal) revealed a molecular relationship between the liver and jejunum. In WT animals, amino acid and sterol metabolism were predominantly modulated in the liver, fatty acid metabolism response was shared between the liver and jejunum, and glutathione metabolism was modulated in the small intestine. In contrast, KO animals do not regulate amino acid metabolism in the liver or small intestine, they share the control of fatty acid metabolism between the liver and jejunum, and regulation of sterol metabolism is shifted from the liver to the jejunum and that of glutathione metabolism from the jejunum to the liver. This demonstrates that the quercetin-mediated regulation of these biological functions in extrahepatic tissues is dependent on the functionality of the liver POR. In conclusion, using a systems biology approach to explore the contribution of hepatic phase I detoxification on quercetin metabolism demonstrated the resiliency and adaptive capacity of a biological organism in dealing with a bioactive nutrient when faced with a tissue-specific molecular dysfunction. Experiment Overall Design: All animals were adapted to the RM3 (E) 801710 Soya-free powdered diet (B. S & S. [Scotland] Ltd, UK) over a period of 14 days. Quercetin was added separately to the semi-purified diets at a concentration of 6200 ppm (0.62 %; 6.2 g per kg). 65 male cytochrome P450 reductase null (KO) mice and 65 wild type (WT) C57BL/6 mice were reared, all aged between 6-8 weeks. Animals were housed 3 per cage, where both temperature and relative humidity were maintained within a range of 19-23oC and 40-70%, respectively. Twelve-hour periods of light were cycled with twelve-hour periods of darkness. Experiment Overall Design: For each strain of mouse, the following experimental design was used: a control group (25 mice) receiving powdered RM3 diet ad libitum and a group (25 mice) receiving a âhigh doseâ of quercetin (7 mg / mouse). The experimental diet was administered on day 15, following a 14-day adaptation period to the RM3 diet. Animals were sacrificed after 24 h. Experiment Overall Design: RNA samples destined for microarray analysis were only accepted and pooled into three groups if no aberrant signs of degradation (e.g. multiple peaks) were observed. The comprehensive gene expression profiles of the liver, jejunum, ileum, and colon were analyzed. In all cases, except those listed, RNA from 3 mice was pooled to form sample 1, another 3 mice to form sample 2, etc. Thus, 9 mice were used for the four experimental groups: wild-type, wild-type+quercetin, POR-null, POR-null+quercetin.
