Pathway and single gene analysis of Caco-2 cell differentiation by ascorbate-stabilized quercetin

The aim was to investigate mechanisms contributing to quercetin’s previously described effects on cell-proliferation and -differentiation, which contradicted its proposed anti-carcinogenic potency. In a 10-day experiment, 40 µM quercetin stabilized by 1mM ascorbate reduced Caco-2 differentiation up to 50% (P<0.001). Caco-2 RNA from days 5 and 10, hybridized on HG-U133A2.0 Affymetrix® GeneChips®, showed 1,743 affected genes on both days (P<0.01). All 14 Caco-2 differentiation-associated genes showed decreased expression (P<0.01), including intestinal alkaline phosphatase that was confirmed technically (qRT-PCR) and functionally (enzyme-activity). The 1,743 genes contributed to 27 affected pathways (P<0.05) categorized under 6 gene ontology (GO) processes, including apoptosis and cell-cycle. Genes within these GO-processes showed fold changes that suggest increased cell-survival and -proliferation. Furthermore, quercetin downregulated expression of genes involved in tumor-suppression and phase II metabolism, and upregulated oncogenes. Gene expression changes mediated by ascorbate-stabilized quercetin were concordant with those occurring in human colorectal carcinogenesis (≈ 80-90%), but were opposite to those previously described for Caco-2 cells exposed to quercetin in the absence of ascorbate (≈ 75-90%). In conclusion, gene expression among Caco-2 cells exposed to ascorbate-stabilized quercetin showed mechanisms contrary to what is expected for a cancer-preventive agent. Whether this unexpected in vitro effect is relevant in vivo, remains to be elucidated. Keywords: Colon cancer; Caco-2; quercetin; differentiation Caco-2 cells were harvested on days 5 and 10 post-confluency. Per day, fold changes were calculated as quercetin vs. control.