Apigenin and Naringenin Increase Apoptosis and Decrease Proliferation via Transcriptional Regulation
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Previous studies have shown that apigenin and naringenin (flavonoids) suppress colon carcinogenesis by inducing apoptosis and suppressing proliferation in rats. The goal of this thesis was to test the hypothesis that apigenin and naringenin affect colonocyte proliferation and apoptosis by regulating expression of genes involved in microbial recognition (TLR-2, TLR-4), short chain fatty acid transport (MCT-1), cell cycle (p21), and apoptosis (Bax, Bcl-2, Fas, Noxa) as well as to determine if the mechanism of action was p53 dependent. Scraped mucosa was obtained from rats which received diets (0.02% naringenin, 0.1% apigenin, or basal) for 10 wks and were treated with AOM. YAMC and mp53 YAMC cells were treated with apigenin (0.1, 1, and 10 μM), naringenin (0.1, 1, 10, 25, and 50 μM), or estradiol (1 nM, positive control) for 96 h at non-permissive conditions. In vivo, apigenin suppressed MCT-1 (p<0.03), Bax (p=0.05), and Fas (p<0.05) expression compared to the control diet; and both flavonoids suppressed p21 (p<0.02) and TLR-4 (p<0.01) expression. Diet did not affect expression of Bcl-2 or TLR-2. 1 μM or greater apigenin or naringenin treatment exhibited dose-dependent decreases (p<0.005) in cell numbers compared to vehicle in YAMCs, while no differences were identified in the mp53 YAMCs except with the highest treatment concentrations (p< 0.0001). No differences in proliferation were observed with apigenin or naringenin in either cell line, except with 20 μM apigenin treatment (p< 0.0001). Apoptosis and gene expression data were inconclusive in vitro due to a lack of response in the positive control. Considering MCT-1 is a butyrate transporter and butyrate induces colonocyte p21 expression, the suppression of p21 expression may be a MCT-1 mediated effect. Reduction of MCT-1, p21, and TLR-4 expression by apigenin and naringenin suggests that these flavonoids may be able to reduce colon carcinogenesis through their influence on expression of genes involved in multiple pathways. The dose-dependent reduction in cell number induced by apigenin and naringenin is in part p53-mediated; however, the reduction in mp53 YAMC cells resulting from the greatest concentrations suggests alternate pathways can be induced. These reductions in cell number were not related to changes in proliferation.
Daniels, Wesley Danielle (2014). Apigenin and Naringenin Increase Apoptosis and Decrease Proliferation via Transcriptional Regulation. Master's thesis, Texas A & M University. Available electronically from