Role of lysophosphatidylcholine in brush-border intestinal alkaline phosphatase release and restoration

Abstract

Intestinal alkaline phosphatase (IAP) is a brush-border membrane ectoenzyme (BBM-IAP) that is released into the lumen (L-IAP) after a high-fat diet. We examined the effects of oil feeding and the addition of mixed-lipid micelles on the formation of L-IAP in oil-fed rat intestine, Caco-2 cell monolayers, and mouse intestinal loops. We localized IAP in the duodenum of rats fed corn oil using fluorescence microscopy with enzymelabeled fluorescence-97 as substrate. Four hours after oil feeding, L-IAP increased ϳ10-fold accompanied by the loss of BBM-IAP, consistent with BBM-IAP release. Rat IAP isozyme mRNAs progressively increased 4 -6 h after oil feeding, followed by the increase of IAP activity in the subapical location at 6 h, consistent with the restoration of IAP protein. Postprandial lipid-micelle components, sodium taurocholate with or without oleic acid, mono-oleylglycerol, cholesterol, or lysophosphatidylcholine (lysoPC) were applied singly or as mixedlipid micelles to the apical surface of polarized Caco-2 cell monolayers. LysoPC increased L-IAP Ͼ10-fold over basal release. LysoPC released IAP into the apical medium more than other intestinal brush-border enzymes, 5Ј-nucleotidase, sucrase, aminopeptidase N, and lactase, without comparable lactate dehydrogenase release or cell injury. LysoPC increased human IAP mRNA levels by 1.5-fold in Caco-2 cells. Luminally applied lysoPC also increased release of IAP preferentially in mouse intestinal loops. These data show that lysoPC accelerates the formation of L-IAP from BBM-IAP, followed by enhanced IAP synthesis, suggesting the role that lysoPC might play in the turnover of brush-border proteins.Caco-2 cells; lipid absorption; small intestine; enzyme-labeled fluorescence-97 MAMMALIAN ALKALINE PHOSPHATASES (APs; orthophosphoric monoester phosphohydrolase, EC 3.1.3.1) are ectoenzymes anchored in the outer leaflet of the plasma membrane by glycosyl phosphatidylinositol (GPI) (15). Human intestine expresses one intestinal type of AP (IAP) encoded by the IAPI gene, whereas rats have two IAP isoenzymes, named IAP-I and IAP-II, which are encoded by the ALPi and ALPii genes, respectively (18). IAP expression is largely restricted to the gut, especially to the brush border of the enterocytes, and its expression and activity are highest in the duodenum (4).The nonhydrolytic functions of IAP still remain speculative. There has been emerging evidence for the functional role of IAP as a detoxifying enzyme for lipopolysaccharide (LPS) (3, 9). IAP activity is associated with the reduction of inflammatory conditions in the bowel (9): exposure of the intestinal wall to LPS induces IAP gene expression (3). IAP detoxifies LPS by removing its phosphate esters in vitro (30). IAP deficiency is associated with increased LPS toxicity in zebrafish and in Caco-2 cells (3, 9). In vivo, however, the localization of IAP and LPS is mismatched because IAP is expressed mostly in the upper small intestine, whereas the exposure of LPS produced by the microflora to the intestinal mucosa occurs in...

Glyceroglycolipids Affect Uptake of Carotenoids Solubilized in Mixed Micelles by Human Intestinal Caco‐2 Cells

“…Some amphiphilic substances such as lysoPtdCho [47][48][49], dodecylphosphocholine [50], and 2-alkoxy-3-alkylamidopropylphosphocholines [51] enhanced the absorption of hydrophilic agents such as dextran and mannitol by decreasing the integrity of the intercellular barrier formed by cell-to-cell/cell-matrix adhesion. The intestinal absorption of these hydrophilic agents was thought to be mediated by paracellular diffusion, which is the transport process across the intercellular barrier to the basolateral side.…”

Cellular function and molecular structure of ecto-nucleotidases

“…Furthermore, after ingestion of a high-fat diet, IAP in the intestinal luminal content increases by more than 10-fold. The process by which ingested fatty acids mediate the IAP release into the intestinal lumen involves production of lipoprotein particles secreted from the enterocytes [572].…”

Crucial role of alkaline sphingomyelinase in sphingomyelin digestion: a study on enzyme knockout mice

“…Because the decreased alkaline phosphatase activity in the mucosa was not associated with a similar decrease in the intestinal lumen, rather a small increase in the distal part of the small intestine, further studies should focus on the membrane binding, releasing, and translocation of the enzyme in alk-SMase KO mice. Of interest is a recent fi nding that lysophosphatidylcholine, also a substrate for alk-SMase ( 15 ), can stimulate alkaline phosphatase release in the intestinal tract ( 41 ). Whether the luminal levels of lysophosphatidylcholine are increased in the KO mice and thus enhance the release of alkaline phosphatase from the mucosa is of interest for investigation.…”