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MUCOSAL BIOLOGY

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

Takanari Nakano,^1,5 Ikuo Inoue,² David H. Alpers,³ Yasutada Akiba,^4,6 Shigehiro Katayama,² Rina Shinozaki,¹ Jonathan D. Kaunitz,^4,5 Susumu Ohshima,⁷ Masumi Akita,⁷ Seiichiro Takahashi,¹ Iwao Koyama,^,1 Makoto Matsushita,¹ and Tsugikazu Komoda¹

Departments of ¹Biochemistry, ²Diabetes and Endocrinology, and ⁷Morphological Science, Biomedical Research Center, Faculty of Medicine, Saitama Medical University, Saitama, Japan; ³Department of Medicine, Washington University School of Medicine, St. Louis, Missouri; ⁴Greater Los Angeles Veterans Affairs Healthcare System, Los Angeles, ⁵Department of Medicine, School of Medicine, University of California, Los Angeles, ⁶Brentwood Biomedical Research Institute, Los Angeles, California

Submitted 18 September 2008 ; accepted in final form 25 April 2009

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 enzyme-labeled fluorescence-97 as substrate. Four hours 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 4–6 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 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 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