Postnatal Expression and Induction by Pregnenolone-16α-Carbonitrile of the Organic Anion-Transporting Polypeptide 2 in Rat Liver

Abstract

ABSTRACT:Newborn rats are more sensitive to the toxic effects of cardiac glycosides than are adult rats. This is associated with a decreased ability to remove cardiac glycosides from blood into the liver. Pregnenolone-16␣-carbonitrile (PCN), a prototypical rodent CYP3A inducer and pregnane-X-receptor (PXR) ligand, stimulates the hepatic clearance of cardiac glycosides in newborn rats, which results in decreased toxicity of the cardiac glycosides. The mechanism responsible for this phenomenon is not clear; however, if elucidated, it would help in understanding and preventing potential drug-drug interactions. The recently cloned rat organic anion-transporting polypeptide 2 (oatp2) (Slc21a5) is a sinusoidal hepatic uptake transporter, with very high affinities for cardiac glycosides, and thus it was hypothesized that rat oatp2 increases during postnatal development and is inducible by PCN. In the present study, livers were removed from Sprague-Dawley rats from postnatal days (pnd) 0 to 45, in 5-day increments; as well as from pnd 10 to 90, in 10-day increments, after PCN (75 mg/kg i.p., for 4 days) or corn oil (vehicle for PCN) treatment. The protein and mRNA levels of rat oatp2 were determined by Western blot analysis and branched DNA signal amplification technique, respectively. Expression of rat oatp2 protein and mRNA increased gradually during postnatal development. PCN treatment increased liver to body weight ratio in both genders, and dramatically accelerated the maturation of hepatic oatp2 protein and mRNA levels. In summary, rat oatp2 undergoes age-dependent and chemical regulation during postnatal development, and is a potential target for drugdrug and age-drug interactions.Compared with adult rats, newborn rats are more sensitive to the toxicity elicited by cardiac glycosides, such as ouabain and digoxin (Klaassen, 1972(Klaassen, , 1973. This is associated with the decreased ability of the liver in newborn rats to remove cardiac glycosides from the blood, thereby causing greater toxicity in newborn rats (Klaassen, 1972). The mechanism of toxicity has been further characterized by showing that the rodent CYP3A inducer pregnenolone-16␣-carbonitrile (PCN 2 ) increases hepatic clearance of cardiac glycosides in newborns, thus reducing cardiac glycoside toxicity (Klaassen, 1974a,b). The kinetics of ouabain uptake in isolated hepatocytes from rats at various ages demonstrates that V max increases with age, suggesting an increase in uptake transporter(s). Although there is no statistical difference in the K m of ouabain uptake in hepatocytes during development, the K m tended to be higher in the young rats, suggesting the involvement of two transporting systems (Stacey and Klaassen, 1979).Further understanding of the hepatic uptake of cardiac glycosides was made possible by the recent advances in the cloning of the rat organic anion-transporting polypeptide 2 (oatp2) (Slc21a5) (Noe et al., 1997). Rat oatp2 is expressed in the hepatic sinusoidal membrane (Noe et al., 1997;Abe et al., 1998Abe et al., , 1999Gao et...

Endocrine Regulation of Gender-Divergent Mouse Organic Anion-Transporting Polypeptide (Oatp) Expression

“…In rats, no gender differences in hepatic Oatp1a4 mRNA expression exist (Li et al, 2002), but conflicting data have been reported regarding hepatic Oatp1a4 protein expression. Guo et al (2002a) showed hepatic Oatp1a4 protein expression is higher in females than males, whereas Rost et al (2005) reported that hepatic Oatp1a4 protein expression is higher in males than females. In mice, Oatp1a4 is higher in female than male mouse livers (Cheng et al, 2005a).…”

Tissue Distribution and Ontogeny of Mouse Organic Anion Transporting Polypeptides (Oatps)

“…In both rats and mice, Oatp1a1 is highly expressed in liver and kidney (Li et al, 2002), Oatp1a4 in liver and brain (Noé et al, 1997;Guo et al, 2002a), Oatp1a6 in kidney (Ogura et al, 2000;Choudhuri et al, 2001), Oatp1b2 in liver (Li et al, 2002), Oatp1c1 in brain (Sugiyama et al, 2003), Oatp4a1 in placenta (Leazer and Klaassen, 2003), and Oatp6b1 and 6c1 in testes (Suzuki et al, 2003). The high expression of Oatp1a5 in mouse testes has not been reported FIG.…”

BRAIN CYCLOSPORIN A LEVELS ARE DETERMINED BY ONTOGENIC REGULATION OFMDR1AEXPRESSION

“…Similarly, adult females maintained higher levels of P-gp expression in the kidney and liver as compared with males. This pattern of expression is not restricted to the mdr1a transporter since similar gender-dependent expression of the oatp2 transporter mRNA or protein occurs in rat or mouse liver during maturation (Guo et al, 2002;Cheng et al, 2005). A previous study reported that mdr1a mRNA expression in rat liver and kidney increased minimally (2-to 3-fold) during maturation (Rosati et al, 2003).…”