Induction of the intestinal membrane transporters ABCA1 and ABCG8 by 27-hydroxycholesterol through a redox mechanism

Abstract

Graphical abstract Redox-induction of expression and synthesis of ATP binding cassette transporters in CaCo-2 cells by externally added 27-hydroxycholesterol. 27OHC: 27-hydroxycholesterol; NOX: NADPH oxidase; ROS: reactive oxygen species; ABCA1: ATP binding cassette A1; ABCG8: ATP binding cassette G8; DPI: diphenylene iodonium. Abstract Objective We tested the effect of 27-hydroxycholesterol (27OHC) on the expression and synthesis of two membrane transporters involved in sterols extrusion from the intestinal epithelium into the gut lumen: ATP-binding cassette A1 (ABCA1) and G8 (ABCG8). Special attention was given to ABCG8, a key player in the intestinal cell discharge of plant sterols. Methods Differentiated CaCo-2 intestinal cells were supplemented with 27OHC, and added to the cell incubation medium at a final concentration of 1 or 5 µM. These 27OHC externally added amounts were proven to reach intracellular oxysterol levels within the range of those normally recovered in the human peripheral blood. Results An up-regulation of the ABCA1 and ABCG8 mRNAs was observed in the CaCo-2 cells supplemented with 27OHC. Moreover, both 1 µM and 5 µM 27OHC induced a net, and steady, statistically significant, increase of both ABCA1 and ABCG8 protein levels. Of interest, the cellular pre-treatment with diphenylene iodonium, a selective inhibitor of NADPH oxidase, i.e. a major intracellular source of reactive oxygen species, fully inhibited the 27OHC enhancement of both ABCA1 and ABCG8 protein synthesis. Conclusion This in vitro study shows for the first time that the addition of 27OHC to intestinal epithelial cells up-regulates ABCG8, the transporter discharging plant sterols into the gut lumen, besides confirming to induce ABCA1 as well. Importantly, the 27OHC-dependent up-regulation of the two transporters appears to involve a redox mechanism rather than the canonical liver-X-receptors-dependent pathway. Significance statement The 27OHC introduced with the diet might modulate the plant sterol extrusion in the gut, in parallel with that of cholesterol.