Vitamin A Absorption, Storage and Mobilization.
It is well established that chylomicron remnant (dietary) vitamin A is taken up from the circulation by hepatocytes, but more than 80 % of the vitamin A in the liver is stored in hepatic stellate cells (HSC). It presently is not known how vitamin A is transferred from hepatocytes to HSCs for storage. Since retinol-binding protein 4 (RBP4), a protein that is required for mobilizing stored vitamin A, is synthesized solely by hepatocytes and not HSCs, it similarly is not known how vitamin A is transferred from HSCs to hepatocytes. Although it has long been thought that RBP4 is absolutely essential for delivering vitamin A to tissues, recent research has proven that this notion is incorrect since total RBP4-deficiency is not lethal. In addition to RBP4, vitamin A is also found in the circulation bound to lipoproteins and as retinoic acid bound to albumin. It is not known how these different circulating pools of vitamin A contribute to the vitamin A needs of different tissues. In our view, better insight into these three issues is required to better understand vitamin A absorption, storage and mobilization. Here, we provide an up to date synthesis of current knowledge regarding the intestinal uptake of dietary vitamin A, the storage of vitamin A within the liver, and the mobilization of hepatic vitamin A stores, and summarize areas where our understanding of these processes is incomplete.
Department of Medicine, College of Physicians and Surgeons, Columbia University, 650 W 168th St., New York, NY, 10032, USA. wsb2@columbia.edu.
William S
WS
Blaner
Department of Medicine, College of Physicians and Surgeons, Columbia University, 650 W 168th St., New York, NY, 10032, USA.
Yang
Y
Li
Department of Medicine, College of Physicians and Surgeons, Columbia University, 650 W 168th St., New York, NY, 10032, USA.
Pierre-Jacques
PJ
Brun
Department of Medicine, College of Physicians and Surgeons, Columbia University, 650 W 168th St., New York, NY, 10032, USA.
Jason J
JJ
Yuen
Department of Medicine, College of Physicians and Surgeons, Columbia University, 650 W 168th St., New York, NY, 10032, USA.
Seung-Ah
SA
Lee
Department of Medicine, College of Physicians and Surgeons, Columbia University, 650 W 168th St., New York, NY, 10032, USA.
Robin D
RD
Clugston
D000273:Adipose Tissue / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D002338:Carotenoids / Q000378:metabolism; D002914:Chylomicrons / Q000378:metabolism; D005544:Forecasting; D055166:Hepatic Stellate Cells / Q000378:metabolism; D022781:Hepatocytes / Q000378:metabolism; D006801:Humans; D007408:Intestinal Absorption; D008074:Lipoproteins / Q000378:metabolism; D008099:Liver / Q000378:metabolism*; D008954:Models, Biological; D054839:Retinol-Binding Proteins, Plasma / Q000378:metabolism; D012709:Serum Albumin / Q000378:metabolism; D014801:Vitamin A / Q000378:metabolism*; D014802:Vitamin A Deficiency / Q000378:metabolism
D002914:Chylomicrons; D008074:Lipoproteins; D054839:Retinol-Binding Proteins, Plasma; D012709:Serum Albumin; D014801:Vitamin A; D002338:Carotenoids
Adipose tissue; Chylomicrons; Hepatic stellate cells; RBP4; Retinoid; Retinyl ester storage; Vitamin A