Submitted on September 18, 2008
Revised on March 17, 2009
Accepted on April 25, 2009
Role of lysophosphatidylcholine in brush border intestinal alkaline phosphatase release and restoration
Takanari Nakano1*, Ikuo Inoue2, David H. Alpers3, Yasutada Akiba4, Shigehiro Katayama, Rina Shinozaki, Jonathan D. Kaunitz5, Susumu Ohshima, Masumi Akita, Seiichiro Takahashi, Iwao Koyama2, Makoto Matsushita, and Tsugikazu Komoda6
1 CURE/UCLA & BBRI
2 Saitama Medical University
3 University of Washington School of Medicine
4 CURE/UCLA, VAGLAHS, BBRI
5 VAGLAHS
6 Saitama Medical School
* To whom correspondence should be addressed. E-mail: nk.takanari{at}gmail.com.
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 ELF-97 as substrate. Four hrs after oil feeding, L-IAP increased ~ 10-fold accompanied by the loss of BBM-IAP, consistent with BBM-IAP release. Rat IAP isozyme mRNAs progressively increased 4 to 6 hrs after oil feeding, followed by the increase of IAP activity in the sub-apical location at 6 hrs, consistent with the restoration of IAP protein. Post-prandial lipid micelle components, sodium taurocholate with or without oleic acid, monooleylglycerol, cholesterol, or lysophosphatidylcholine (lysoPC) were applied singly or as mixed-lipid micelles to the apical surface of polarized Caco-2 cell monolayers. LysoPC increased L-IAP > 10-fold over basal release. LysoPC released IAP into the apical medium more than other intestinal brush border enzymes, 5'-nucleotidase, sucrase, aminopeptidase N and lactase, without comparable LDH 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.
