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Expression and localization of multidrug resistant protein mrp2 in rat small intestine
A D Mottino1, T Hoffman, L Jennes
1Graduate Center for Toxicology, University of Kentucky, Lexington 40536-0305, USA.
Abstract:
The expression of multidrug resistance-associated protein isoform 2 (mrp2), the ATP-dependent export pump that mediates the transport of glucuronic acid-, glutathione-, and sulfate-conjugated derivatives, was studied in rat small intestine. The small intestine was divided into nine equal segments, and mrp2 content was analyzed in homogenate and brush border membrane preparations by Western analysis. mrp2 protein was present mainly in brush border membrane of the proximal segments and gradually decreased from jejunum to the distal ileum. We also analyzed the content of mrp2 in three different populations of proximal enterocytes obtained from the upper and lower villus and the crypt regions. The export pump was mainly expressed in the villus cells and to a lesser degree in the crypt cells of the epithelium. Immunohistochemical analysis performed in duodenum, jejunum, and ileum confirmed in situ the Western blot findings. Analysis of mRNA encoding mrp2 in proximal and distal segments revealed a similar content in both regions, whereas distribution along the villus-crypt axis was similar to the protein gradient. Because conjugating enzymes are distributed similarly to mrp2, we conclude that they may act coordinately to contribute to first-pass metabolism of drugs and other xenobiotics in the proximal small intestine.
Insights
Multidrug resistance-associated protein 2 (MRP2) is concentrated in the proximal small intestine, particularly on villus cells. This localization suggests MRP2 plays a key role in drug metabolism in this region.
Area of Science:
- Pharmacology
- Gastroenterology
- Molecular Biology
Background:
- Multidrug resistance-associated protein 2 (MRP2) is an ATP-dependent export pump involved in transporting conjugated substances.
- Understanding MRP2 expression in the small intestine is crucial for comprehending drug disposition and xenobiotic metabolism.
Purpose of the Study:
- To investigate the expression and distribution of MRP2 in different segments and cell populations of the rat small intestine.
- To correlate MRP2 expression with potential roles in the first-pass metabolism of drugs and xenobiotics.
Main Methods:
- Western blot analysis of MRP2 protein in rat small intestine homogenates and brush border membrane preparations.
- Analysis of MRP2 content in enterocyte populations from villus and crypt regions.
- Immunohistochemical analysis of MRP2 expression in duodenal, jejunal, and ileal tissues.
- Quantitative analysis of MRP2 mRNA levels in proximal and distal small intestine segments.
Main Results:
- MRP2 protein was predominantly found in the brush border membrane of proximal small intestine segments, decreasing towards the distal ileum.
- MRP2 expression was highest in villus enterocytes and lower in crypt cells.
- mRNA distribution along the villus-crypt axis mirrored the protein gradient, while mRNA content was similar in proximal and distal segments.
- Immunohistochemistry confirmed the Western blot findings regarding MRP2 localization.
Conclusions:
- MRP2 exhibits a distinct segmental and cellular distribution within the rat small intestine, primarily in the proximal region and villus cells.
- The similar distribution of MRP2 and conjugating enzymes suggests a coordinated role in the first-pass metabolism of drugs and xenobiotics in the proximal small intestine.