phytosterols Flashcards
phytosterols
plant-specific phytochemicals that are essential to plant cell membranes
can lower cholesterol
how do phytosterols affect cholesterol?
lowers cholesterol
1) competition of absorption into micelles: phytosterols are more hydrophobic than cholesterol
2) antagonist to SREBP proteins
3) LXR agonist (increase ABC/efflux, decrease NPC1L1/influx)
cholesterol transporters
NPC1L1, ABC, SR-B1
located in membrane of enterocytes and hepatocytes
NPC1L1
brush border membrane of enterocyte
cholesterol and phytosterol absorption
induced by SREBP-2, downregulated by LXR, cholesterol, phytosterol
ABC G5/G8 heterodimeric transporter
brush border of intestinal cells
secrete cholesterol back into intestinal lumen
ABC A1
cholesterol/phytosterol efflux to plasma HDL
(removing cholesterol from cells, package into HDL)
upregulated by LXR/RXR
SR-B1
in liver, removes cholesteryl esters from HDL
LXR
heterodimer with RXR, regulator of cholesterol homeostasis, prevent excess cholesterol accumulation in tissues
upregulates ABC / efflux
decrease influx (NPC1L1)
(phytosterols are an agonist to LXR)
SREBP-2
inhibited by phytosterols
SREBPs increase NPC1L1/cholesterol synthesis
(phytosterols are an antagonist to SREBP2)
What is a proposed mechanism by which phytosterols decrease cholesterol levels that does not involve any cholesterol transporter activity?
1) Antagonist to SREBP proteins
2) Competition into absorption of micelles - phytosterols more hydrophobic
Evidence suggests that phytosterols can decrease cholesterol levels by influencing the activity of cholesterol transporters. How do they accomplish this? Which cholesterol transporters are involved?
LXR-mediated targets
phytosterols have LXR agonist activity: NPC1L1 downregulated, ABC upregulated
SREBP antagonist
