1-Naphthol β-D-glucuronide formed intraluminally in rat small intestine mucosa and absorbed into the colon

doi:10.1016/S0024-3205(99)00403-8

Life Sciences

Volume 65, Issue 15, 3 September 1999, Pages 1579-1588

https://doi.org/10.1016/S0024-3205(99)00403-8 Get rights and content

Abstract

UDP-glucuronosyltransferase expressed in the rat intestinal epithelial cells is important as the first barrier against chemicals. The distribution of 1-naphthol and its glucuronide formed in rat intestine was estimated by using everted intestine. Roughly 60% of the 1-naphthol added to the mucosal fluid was absorbed into the mucosa of the small intestine and colon within 30 min. Approximately 66% of the 1-naphthol absorbed in the proximal intestine was secreted intraluminally as a glucuronide, and a minimal 9% was transported into the serosal fluid as a glucuronide. In the distal intestine, ~34% was secreted intraluminally and 30% was transported into the serosal fluid as a glucuronide. The greatest amount of the glucuronide (37% of the absorbed 1-naphthol) was transported into the serosal fluid, whereas a minimal 7% was secreted intraluminally in the colon. In marked contrast, the colon was found to transport 1-naphthol-glucuronide from the mucosal fluid into the serosal fluid at an approximately 8-fold higher rate than that of the small intestine. These results suggest that, in the small intestine, phenolic xenobiotics are mostly glucuronidated and secreted intraluminally and that the resulting glucuronide is absorbed and transported into the serosal side of the colon.

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This phenomenon has already been demonstrated in human head and neck squamous carcinoma cells [29] and in undifferentiated human colonic carcinoma cells [30], but never in differentiated human colonic epithelial cells. Other enzymes were for the first time identified by microarrays as potential targets of butyrate, one UDP-glucuronosyltransferase (UGT1A6) involved in colonic lumen compounds detoxification [31] class K glycosylphosphatidylinositol, (GPI) surface protein (PIGK) and (Dol-P-man flippase) SL15, both involved in GPI anchorage [32–34], and protein–N-glycanase (PNGase), which cleaves protein–N-glycan linkage. Real time PCR revealed that butyrate modulating effects reached statistical significance only for three enzymes: galectin-1, α2,3-sialyltransferase V, and Dol-P-man flippase.
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A full-length cDNA encoding a phenol UDP-glucuronosyltransferase was isolated by plaque hybridization, RT-PCR and 5′-RACE from a cDNA library prepared from the bovine liver. The deduced amino acid sequence (529 amino acid residues) has A signal sequence (23 amino acid residues) at the amino terminus and a transmembrane-anchoring domain (17 amino acid residues) at the carboxyl terminus. The encoded protein has a potential asparagine-linked glycosylation site (Asn291). The cloned cDNA was named bovUGT1A6 on the basis of the amino acid similarity. BovUGT1A6 cloned in the pAAH5 expression vector was transformed into Saccharomyces cerevisiea AH22 cells to obtain an active 54-kDa bovUGT1A6 enzyme. The expressed enzyme represented UDP-glucuronosyltransferase activities toward 1-naphthol and 4-methylumbelliferone, comfirming that the isolated cDNA is an isoform of bovine phenol UDP-glucuronosyltransferase. Microsomal UDP-glucuronosyltransferase activity toward 1-naphthol in the bovine kidney cortex was found to be higher than that in the liver and other organs, and mRNA of bovUGT1A6 was more strongly detected in the kidney on Northern blotting analysis. These results suggest that the bovine kidney, which strongly expresses bovUGT1A6, is a significant organ for xenobiotics glucuronidation.

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1-Naphthol β-D-glucuronide formed intraluminally in rat small intestine mucosa and absorbed into the colon

Abstract

Biochem. Pharmacol.

Toxicol. Appl. Pharmacol.

Gastroenterology

Biochem. Pharmacol.

Role of Extrahepatic Metabolism

Clin. Pharmacokint.

J. Pharmacol. Exp. Ther.

J. Biochem.

Eur. J. Biochem.

J. Biochem.

J. Biochem.