The effect of onion exposure on gene expression profiles in intestinal Caco-2 cells

Background: Human intestinal tissue samples are barely accessible to study potential health benefits of nutritional compounds. Numbers of animals used in animal trials, however, need to be minimalized. Therefore, in this study we explored the applicability of an in vitro model, namely human intestinal Caco-2 cells, to study the effect of food compounds on (intestinal) health. In vitro digested yellow (YOd) and white onion extracts (WOd) were used as model food compounds and transcriptomics was applied to obtain more insight into their mode of actions in the intestinal cells. Methods: Caco-2 cells were incubated with in vitro digested onion extracts for 6 hours, total RNA was extracted and Affymterix Human Gene 1.1 ST arrays were used to analyze the gene expression profiles. To identify onion-induced gene expression profiles in Caco-2 cells, digested yellow onion and white onion samples were compared to a digest control samples. Results: We found that yellow onion (n=5586, p<0.05) had a more pronounced effect on gene expression than white onion (n=3688, p<0.05). However, a substantial number of genes (n=3281, p<0.05) were affected by both onion variants in the same direction. Pathway analyses revealed that mainly processes related to oxidative stress, and especially the Keap1-Nrf2 pathway, were affected by onions. Our data fit with previous in vivo studies showing that the beneficial effects of onions are mostly linked to their antioxidant properties. Conclusion: our data indicate that the in vitro Caco-2 intestinal model can be used to determine modes of action of nutritional compounds and can thereby reduce the number of animals used in conventional nutritional intervention studies. Microarray analysis was performed on 21-days differentiated Caco-2 cells incubated with digested white onion (WOd), digested yellow onion (YOd) and saline digest (Sd = control) for 6 hours. This experiment was performed three times, so three independent biological replicates per treatment were included in the microarray analysis.