Normalization genes for quantitative RT-PCR in differentiated Caco-2 cells used for food exposure studies.

Exposure of food products to small-intestinal-like Caco-2 cells, combined with a gene expression based response analysis can be a valuable tool to classify potential bioactive effects of food homogenates. In order to study changes in gene expression upon food exposure, a robust set of stably expressed genes is required for normalization. Here we present a set of reference genes suitable for RT-qPCR that has been validated for exposure studies with the intestinal-like Caco-2 cell line. This study identified ribosomal phosphoprotein P0 (RPLP0) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) as best reference genes. The set can be extended with β-2-microglobulin (B2M), splicing factor 3A, subunit 1 (SF3A1), and mitochondrial ribosomal protein L19 (MRPL19). Food homogenates did provoke responses in the Caco-2 cells, as was demonstrated by changed expression of NAD(P)H Quinone dehydrogenase 1 (NQO1), Claudin 4 (CLDN4), Nitric Oxide Synthase 2 (NOS2), and ATP-binding cassette, subfamily B, member 1 (ABCB1) in the same experiment. Results indicate that: i) natural food homogenates can exert effects in Caco-2 cells, and ii) stability in expression of the reference genes is not due to a lack of response of the Caco-2 cells.