Phytosterols and phytosterolemia: gene-diet interactions

Abstract

Phytosterol intake is recommended as an adjunctive therapy for hypercholesterolemia, and plant sterols/stanols can reduce cholesterol absorption at the intestinal lumen through the Niemann-Pick C1 Like 1 (NPC1L1) transporter pathway by competitive solubilization in mixed micelles. Phytosterol absorption is of less magnitude than cholesterol and is preferably secreted in the intestinal lumen by ABCG5/G8 transporters. Therefore, plasma levels of plant sterols/stanols are negligible compared with cholesterol, under an ordinary diet. The mechanisms of cholesterol and plant sterols absorption and the whole-body pool of sterols are discussed in this chapter. There is controversy about treatment with statins inducing further increase in plasma non-cholesterol sterols raising concerns about the safety of supplementation of plant sterols to such drugs. In addition, increase in plant sterols has also been reported upon consumption of plant sterol-enriched foods, regardless of other treatments. Rare mutations on ABCG5/G8 transporters affecting cholesterol/non-cholesterol extrusion, causing sitosterolemia with xanthomas and premature atheroslerotic disease are now known, and cholesterol/plant sterols absorption inhibitor, ezetimibe, emerges as the drug that reduces phytosterolemia and promotes xanthoma regression. On the other hand, common polymorphisms affecting the NPC1L1 transporter can interfere with the action of ezetimibe. Gene-diet interactions participate in this intricate network modulating the expression of genetic variants on specific phenotypes and can also affect the individual response to the hypolipidemic treatment. These very interesting aspects promoted a great deal of research in the field.

Keywords: Cardiovascular disease; Ezetimibe; Gene–diet interaction; Phytosterolemia; Plant sterols; Statins.

Figures

Fig. 1

Representation of chemical structures of cholesterol, plant sterols, and stanols. Stanols lack the ∆5 double bond in the B-ring. Saturation of sterols gives rise to stanols

Fig. 2

Representation of cholesterol and non-cholesterol sterol intestinal absorption and extrusion. ABCG5/G8 = adenosine triphosphate (ATP)-binding cassette (ABC) transporter family (ABCG5 and ABCG8); ACAT2 = acyl-cholesterol acyl transferase; ApoB48 = apolipoprotein B48; LXRα = liver X receptor α; MTP = microsomal triglyceride transfer protein; NPC1L1 = Niemann-Pick C1 Like 1 protein