Gene expression analysis of membrane transport proteins in normal and lipopolysaccharide-inflamed rat dental pulp.

INTRODUCTION: Membrane transport proteins (transporters) play a crucial role in the transmembrane uptake and/or efflux of various compounds such as inorganic ions, endogenous bioactive substances such as prostaglandins (PGs), and drugs such as nonsteroidal anti-inflammatory drugs. This study aimed to analyze mRNA expression of selected transporters related to drug disposition and PG transport in normal and lipopolysaccharide (LPS)-inflamed rat incisor pulp. METHODS: Pulp tissues were subjected to reverse transcription-polymerase chain reaction (PCR) detection for transporter isoforms belonging to organic anion transporting polypeptide (Oatp), organic anion transporter (Oat), organic cation transporter (Oct), multidrug resistance-associated protein (Mrp), and multidrug resistance protein (Mdr) families. The levels of mRNA expression for PG transporters (Oatp1a5, Oatp1b2, Oatp2a1, Oatp2b1, and Oatp3a1) were compared in normal and LPS-inflamed pulps by using real-time PCR. RESULTS: The pulp tissue expressed mRNAs for various transporters belonging to the Oatp, Oat, Oct, Mrp, and Mdr families. LPS inflammation caused significant up-regulation of Oatp2a1 (P < .01) and significant down-regulation of Oatp1a5, Oatp2b1 (P < .01), and Oatp3a1 (P < .05). CONCLUSIONS: Rat incisor dental pulp expressed mRNAs for various transporter isoforms. The levels of mRNA expression for PG transporters were significantly up-regulated or down-regulated in LPS-inflamed dental pulp.

Elevated systemic elimination of cimetidine in rats with acute biliary obstruction: the role of renal organic cation transporter OCT2.

Renal tubular secretion of cationic drugs is dominated by two classes of organic cation transporters, OCT2/SLC22A2 and MATE1/SLC47A1, localized to the basolateral and brush-border membranes of the renal tubular epithelial cells, respectively. However, little is known about the expression and function of these transporters in acute cholestasis. Systemic clearance of cimetidine was significantly higher in rats with bile duct ligation (BDL) for 24 hours than in sham-operated rats, with no significant changes in the volume of distribution between the groups. In addition, net tubular secretory clearance of cimetidine was significantly higher in the BDL rats compared with the sham rats, with no significant changes in the glomerular filtration rate. Moreover, the renal tissue-to-plasma concentration ratio of cimetidine was elevated in BDL rats, although the renal tissue-to-urine clearance ratio of cimetidine was not different between the two groups. The expression level of basolateral organic cation transporter rOCT2 protein in the kidney cortex was markedly higher in BDL rats than that in the sham rats, but that of H+/organic cation antiporter rMATE1 protein in the brush-border membranes was not significantly different between the two groups. These results demonstrate that the renal tubular secretion of cimetidine was increased by acute cholestasis, and this increase was attributable to elevated expression levels of rOCT2 but not of rMATE1 in the rat.

The ontogeny of drug metabolizing enzymes and transporters in the rat.

Knowledge of the ontogeny of the various systems involved in distribution and elimination of drugs is important for adequate interpretation of the findings during safety studies in juvenile animals. The present study was designed to collect information on plasma concentrations of total protein and albumin, enzyme activity and mRNA expression of cytochrome P450 isoenzymes (CYP1A1/2, CYP2B1/2, CYP2E1, CYP3A1/2, and CYP4A1), carboxylesterase and thyroxin glucuronidation (T4-GT) activity in liver microsomes, and mRNA expression of transporters (Mdr1a/b, Mrp1-3 and 6, Bsep and Bcrp, Oct1-2, Oat1-3 and Oatp1a4) in liver, kidney and brain tissue during development in Sprague-Dawley rats. Enzyme activities were determined by measuring the metabolism of marker substrates; expression of mRNAs was assessed using RTq-PCR. There were considerable differences in the ontogeny of the individual cytochrome P450 isoenzymes. In addition, ontogeny patterns of enzyme activity did not always parallel ontogeny patterns of mRNA expression. Ontogeny of the transporters depended on the transporter and the organ studied. Changes in mRNA expression of the various transporters during development are likely to result in altered elimination and/or tissue distribution of substrates, with concomitant changes in hepatic metabolism, renal excretion and passage through the blood-brain barrier. Consideration of the ontogeny of metabolizing enzymes and transporters may improve the design and interpretation of results of toxicity studies in juvenile animals.