DIFFERENTIAL EXPRESSION OF TRANSPORTERS IN THE INTESTINE AND ITS APPLICATION TO REGULATION OF THE DRUG ABSORPTION

Abstract

The present study was aimed to quantify the expression of mRNA of drugt ransporters, including PepT1, mrp2 and mdr1a in the small intestine and to examine the correlations between the expression and the transport activity. Variation in expression levels of transporters along the proximal-distal axis of the intestine was examined. Small intestine of starved and fed rats were removed and divided in eight segments and total RNAs isolated. In fed rats, yield of total RNA was constant among each segment, while the increase was observed in the upper part of small intestine of starved rats. Complementary DNA was prepared by reverse transcription of total RNA of each segment and real-time PCR was performed to quantify mRNA expression of various drug transporters. Expression of PepT1 mRNA was lower in upper segment than that in lower segment. In starved rats, PepT1 expression was increased significantly in the middle part of the intestine. As for mrp2, the expression was higher in upper segment and lower in lower segment and the increase in the expression by the starvation was observed in each segment of the intestine. The mdr1a expression was increased gradually along the proximal-distal axis of the small intestine and there was no difference between starved and fed rats. The actual number of PepT1 mRNA expressed in each segment was approximately 10-fold greater than that of mrp2 or mdrla. The intestinal absorption of cefadroxil (CDX) in each segment at pH6.0 was measured using Ussing chamber. Permeability coefficient of CDX was higher in the ileum and lower in the duodenum. In the starved rat, permeability coefficient of CDX in jejunum was significantly increased compared to fed rats. There was good correlation between PepT1 mRNA expression level and permeability coefficient of CDX under both fed and starved conditions. It is suggested that change in physiological and/or pharmacological state of the intestinal tissue may affect the expression and function of various transporters and thereby altars disposition of drugs.