Nathan J Cherrington

PMID: 12695343;Abstract:

Messenger RNA levels of rat organic anion transporter 1 (Oat1; Slc22a6) and Oat2 (Slc22a7) in kidney and Oat3 (Slc22a8) in liver are gender-predominant. Oat1 and Oat3 are male-predominant, whereas Oat2 is female-predominant. Gonadectomized and hypophysectomized (HX) rats were studied to determine whether sex steroids and/or growth hormone (GH) are responsible for these gender-divergent patterns. GH was administered to HX rats by two daily injections (simulating male secretion) or continuous infusion (simulating female secretion). Oat1 mRNA levels, normally higher in male than female kidney, were lowered by gonadectomy and HX in male rats, but not in females. Additionally, GH injections or infusion did not alter Oat1 levels in HX rats. Oat2 mRNA levels, typically much higher in female than in male kidney, were unaffected by gonadectomy. However, HX dramatically decreased Oat2 in female kidney without altering male levels. GH administered by continuous infusion increased Oat2 in kidneys of both HX male and female rats, whereas injections had no affect. Gonadectomy reduced Oat3 mRNA levels in male livers without affecting levels in female livers. In contrast, HX decreased male and elevated female Oat3 mRNA. GH injections did not significantly change Oat3 mRNA levels in HX rats, but infusion decreased Oat3 mRNA in liver. In conclusion, androgens, but not GH, are responsible for the Oat1 mRNA gender difference in kidney; the female GH secretion pattern is responsible for the Oat2 mRNA gender difference in kidney; and both androgens and the female GH secretion pattern are responsible for the Oat3 mRNA gender difference in liver.

Garlic oil (GO) contains several linear sulfur compounds, including diallyl sulfide (DAS), diallyl disulfide (DADS), and diallyl trisulfide (DATS), that induce drug-metabolizing enzymes such as CYP2B and NAD(P)H quinone oxidoreductase 1 (NQO1). CYP2B and NQO1 are primarily regulated by constitutive androstane receptor (CAR) and nuclear factor E2-related factor 2 (Nrf2) transcription factors, respectively. The purpose of this study was to determine whether GO and its specific constituents induce these two enzymes via CAR and Nrf2 activation. Female Wistar-Kyoto (WKY) rats express little CAR protein and exhibit less induction of CYP2B1/2 than males. GO, DAS, and DADS, but not DATS, induced CYP2B1/2 mRNA levels to a greater extent in WKY males than in females, suggesting CAR activation. Conversely, DAS induced NQO1 levels equally in WKY males and females, indicating CAR-independent induction in rats. DAS, but not GO, DADS, or DATS, induced CYP2B10 mRNA levels 530-fold in wild-type (WT) mice, whereas this induction was attenuated in CAR(-/-) mice. DAS induced NQO1 in WT and CAR(-/-) mice equally, suggesting CAR-independent induction in mice. DAS induced NQO1 5-fold in WT mice, whereas induction was completely absent in Nrf2(-/-) mice, indicating DAS also activates Nrf2. DAS induction of CYP2B10 mRNA was independent of Nrf2 presence or absence. In in vivo transcription assays, DAS activated the human CYP2B6 promoter, and the antioxidant response element of the human NQO1 promoter, respectively. These studies indicate that GO constituents, particularly DAS, activate CAR and Nrf2 to induce drug-metabolizing enzymes.

PMID: 14570762;Abstract:

We previously demonstrated that multidrug resistance protein 3 (Mrp3/ABCC3) is induced in rat liver by phenobarbital (PB) and several other microsomal enzyme inducers that induce cytochrome P450 2B (CYP2B). CYP2B is induced by constitutive androstane receptor (CAR)-retinoid X receptor (RXR) heterodimer binding to a phenobarbital-responsive promoter element in the CYP2B promoter. Hepatic mRNA levels of CYP2B and Mrp3 were measured in three models of altered CAR activity to determine whether CAR is also involved in the induction of Mrp3. In Wistar Kyoto rats, where males express higher CAR protein levels than females, the induction of CYP2B1/2 was significantly higher in males than in females by PB, diallyl sulfide, and trans-stilbene oxide but not oltipraz. Mrp3 was induced by each of these treatments, but in contrast to CYP2B1/2, to a similar magnitude in males and females. In male hepatocyte-specific RXRα^-/- mice, CYP2B10 was not induced by diallyl sulfide or oltipraz but remained inducible by PB and trans-stilbene oxide after considering the decrease in basal CYP2B10 expression. Mrp3, however, was induced by PB, diallyl sulfide, trans-stilbene oxide and oltipraz in both wild-type and RXRα^-/- mice. Additionally, constitutive expression of Mrp3 was significantly reduced in RXRα^-/- mice. In CAR^-/- mice, the robust induction of CYP2B10 by PB was completely absent. However, Mrp3 was equally induced both in wild-type and CAR ^-/- mice by PB. These data clearly demonstrate that induction of hepatic Mrp3 by PB and other microsomal enzyme inducers is CAR-independent and implies a role for RXRα in the constitutive expression of Mrp3.

PMID: 15126247;Abstract:

The organic cation (OC) transporters OCT1 and OCT2 are suspected of mediating substrate entry from the blood into proximal tubule cells as the first step in renal secretion of OCs. We examined the contribution of each process in different rabbit renal proximal tubule (RPT) segments, taking advantage of the fact that rabbit orthologs of OCT1 and OCT2 can be distinguished by the high affinity of the former for tyramine (TYR) and of the latter for cimetidine (CIM). We verified that TEA uptake, for which both transporters share a similar affinity, is relatively constant in all three segments (apparent inhibitory constant of 33, 74, and 30 μM and maximal rate of mediated TEA uptake of 0.8, 1.0, and 1.2 pmol·mm^-1 in S1, S2, and S3. respectively). In the S1 segment, TYR was a more effective inhibitor of TEA uptake than CIM (IC50 values of 39 and 328 μM, respectively), implicating OCT1 as the predominant pathway for TEA transport. The opposite profiles were noted in the S2 segment (IC50 values of 302 and 20 μM for TYR and CIM, respectively) and S3 segment (IC50 values of 2,900 and 54 μM TYR and CIM, respectively), suggesting that OCT2 is the predominant TEA transporter in the later portion of RPT, TEA sufficient to saturate OCT1 and OCT2 blocked only 37% of mediated amantadine transport in the S2 segment, confirming the functional presence of at least one additional OC transporter (perhaps OCT3). These data indicate that renal OC transport involves the concerted activity of a suite of transport processes.

PMID: 21878559;PMCID: PMC3226375;Abstract:

Transporters located on the sinusoidal and canalicular membranes of hepatocytes regulate the efflux of drugs and metabolites into blood and bile, respectively. Changes in the expression or function of these transporters during liver disease may lead to a greater risk of adverse drug reactions. Nonalcoholic fatty liver disease (NAFLD) is a progressive condition encompassing the relatively benign steatosis and the more severe, inflammatory state of nonalcoholic steatohepatitis (NASH). Here, we present an analysis of the effect of NAFLD progression on the major ATP-binding cassette (ABC) efflux transport proteins ABCC1-6, ABCB1, and ABCG2. Human liver samples diagnosed as normal, steatotic, NASH (fatty), and NASH (not fatty) were analyzed. Increasing trends in mRNA expression of ABCC1, ABCC4-5, ABCB1, and ABCG2 were found with NAFLD progression, whereas protein levels of all transporters exhibited increasing trends with disease progression. Immunohistochemical staining of ABCC3, ABCB1, and ABCG2 revealed no alterations in cellular localization during NAFLD progression. ABCC2 staining revealed an alternative mechanism of regulation in NASH in which the transporter appears to be internalized away from the canalicular membrane. This correlated with a preferential shift in the molecular mass of ABCC2 from 200 to 180 kDa in NASH, which has been shown to be associated with a loss of glycosylation and internalization of the protein. These data demonstrate increased expression of multiple efflux transporters as well as altered cellular localization of ABCC2 in NASH, which may have profound effects on the ability of patients with NASH to eliminate drugs in an appropriate manner. Copyright © 2011 by The American Society for Pharmacology and Experimental Therapeutics.