Nathan J Cherrington

PMID: 16260000;Abstract:

Multidrug resistance-associated proteins (Mrps) are ATP-dependent transporters which transport a wide variety of anionic and cationic compounds. The purpose of this study was to determine the tissue distribution of Mrp5 and 6 in male and female Sprague-Dawley rats in various tissues, and to investigate whether the expression is altered by cholestasis or administration of microsomal enzyme inducers (MEIs). These MEIs activate six different transcriptionally- mediated pathways, and their effects on Mrp5 and Mrp6 expression were determined. The effects of bile-duct ligation, a cholestasis model, on Mrp5 and 6 expression in male rats were quantified. Mrp5 had marked expression in adrenal gland, and moderate expression in cerebral cortex, cerebellum, and stomach. The MEIs polychlorinated biphenyl (PCB)126, phenobarbital, and PCB99 slightly repressed Mrp5, but no single class of receptor agonists induced or repressed Mrp5. Bile-duct ligation tended to increase Mrp5 expression, but was not statistically significant at a 3 day timepoint. Mrp6 expression was highest in intestine, liver, and kidney. Mrp6 was slightly repressed by phenobarbital, dexamethasone, and isoniazid, but no one class of receptor agonists induced or repressed Mrp6, and expression was also unchanged bile-duct ligation. In conclusion, Mrp5 in rats is most highly expressed in the adrenal gland, whereas Mrp6 is mainly expressed in excretory organs (liver, intestine, and kidney), suggesting markedly different functions. Hepatic mRNA levels of Mrp5 or Mrp6 do not seem to be coordinately regulated along with Phase I enzymes via receptor-mediated pathways, and are not part of the hepatoprotective upregulation of basolateral transporters that occurs during cholestasis. © 2005 Elsevier Inc. All rights reserved.

The transcription factor NFE2-related factor 2 (Nrf2) mediates detoxification and antioxidant gene transcription following electrophile exposure and oxidative stress. Mice deficient in Nrf2 (Nrf2-null) are highly susceptible to acetaminophen (APAP) hepatotoxicity and exhibit lower basal and inducible expression of cytoprotective genes, including NADPH quinone oxidoreductase 1 (Nqo1) and glutamate cysteine ligase (catalytic subunit, or Gclc). Administration of toxic APAP doses to C57BL/6J mice generates electrophilic stress and subsequently increases levels of hepatic Nqo1, Gclc and the efflux multidrug resistance-associated protein transporters 1-4 (Mrp1-4). It was hypothesized that induction of hepatic Mrp1-4 expression following APAP is Nrf2 dependent. Plasma and livers from wild-type (WT) and Nrf2-null mice were collected 4, 24 and 48 h after APAP. As expected, hepatotoxicity was greater in Nrf2-null compared to WT mice. Gene and protein expression of Mrp1-4 and the Nrf2 targets, Nqo1 and Gclc, was measured. Induction of Nqo1 and Gclc mRNA and protein after APAP was dependent on Nrf2 expression. Similarly, APAP treatment increased hepatic Mrp3 and Mrp4 mRNA and protein in WT, but not Nrf2-null mice. Mrp1 was induced in both genotypes after APAP, suggesting that elevated expression of this transporter was independent of Nrf2. Mrp2 was not induced in either genotype at the mRNA or protein levels. These results show that Nrf2 mediates induction of Mrp3 and Mrp4 after APAP but does not affect Mrp1 or Mrp2. Thus coordinated regulation of detoxification enzymes and transporters by Nrf2 during APAP hepatotoxicity is a mechanism by which hepatocytes may limit intracellular accumulation of potentially toxic chemicals.

Various disease models have been shown to alter hepatic drug-metabolizing enzyme (DME) and transporter expression and to induce cholestasis through altered enzyme and transporter expression. Previously, we detailed the regulation of hepatic DMEs during infectious colitis caused by Citrobacter rodentium infection. We hypothesized that this infection would also modulate hepatic drug transporter expression and key genes of bile acid (BA) synthesis and transport. Mice lacking Toll-like receptor 4 (TLR4), interleukin-6 (IL-6), or interferon-gamma (IFNγ) and appropriate wild-type animals were orally infected with C. rodentium and sacrificed 7 days later. In two wild-type strains, drug transporter mRNA expression was significantly decreased by infection for Slc22a4, Slco1a1, Slco1a4, Slco2b1, and Abcc6, whereas the downregulation of Abcc2, Abcc3, and Abcc4 were strain-dependent. In contrast, mRNA expressions of Slco3a1 and Abcb1b were increased in a strain-dependent manner. Expression of Abcb11, Slc10a1, the two major hepatic BA transporters, and Cyp7a1, the rate-limiting enzyme of BA synthesis, was also significantly decreased in infected animals. None of the above effects were caused by bacterial lipopolysaccharide, since they still occurred in the absence of functional TLR4. The downregulation of Slc22a4 and Cyp7a1 was absent in IFNγ-null mice, and the downregulation of Slco1a1 was abrogated in IL-6-null mice, indicating in vivo roles for these cytokines in transporter regulation. These data indicate that C. rodentium infection modulates hepatic drug processing through alteration of transporter expression as well as DMEs. Furthermore, this infection downregulates important genes of BA synthesis and transport and may increase the risk for cholestasis.

PMID: 18640236;PMCID: PMC2570650;Abstract:

The goal of this study was to identify alterations in mRNA and protein expression of various xenobiotic transport proteins in mouse kidney during cisplatin-induced acute renal failure. For this purpose, male C57BL/6J mice received a single dose of cisplatin (18 mg/kg, i.p.) or vehicle. Four days later, tissues were collected for assessment of plasma BUN, histopathological analysis of renal lesions, and mRNA and Western blot analysis of renal transporters including organic anion and cation transporters (Oat, Oct), organic anion transporting polypeptides (Oatp), multidrug resistance-associated proteins (Mrp), multidrug resistance proteins (Mdr), breast cancer resistance protein (Bcrp) and multidrug and toxin extrusion proteins (Mate). Cisplatin treatment caused necrosis of renal proximal tubules along with elevated plasma BUN and renal kidney injury molecule-1 mRNA expression. Cisplatin-induced renal injury increased mRNA and protein levels of the efflux transporters Mrp2, Mrp4, Mrp5, Mdr1a and Mdr1b. Uptake transporters Oatp2a1 and Oatp2b1 mRNA were also up-regulated following cisplatin. By contrast, expression of Oat1, Oat2, Oct2 and Oatp1a1 mRNA was reduced in cisplatin-treated mice. Expression of several uptake and efflux transporters was unchanged in cisplatin-treated mice. Apical staining of Mrp2 and Mrp4 proteins was enhanced in proximal tubules from cisplatin-treated mice. Collectively, these expression patterns suggest coordinated regulation of uptake and efflux pathways during cisplatin-induced renal injury. Reduced expression of basolateral and apical uptake transporters along with enhanced transcription of export transporters likely represents an adaptation to lower intracellular accumulation of chemicals, prevent their reabsorption and enhance urinary clearance. © 2008 Elsevier Ireland Ltd. All rights reserved.

PMID: 23462698;PMCID: PMC3629807;Abstract:

Unsafe use of alcohol results in approximately 2.5 million deaths worldwide, with cirrhosis contributing to 16.6% of reported deaths. Serum insulin levels are often elevated in alcoholism and may result in diabetes, which is why alcoholic liver disease and diabetes often are present together. Because there is a sizable population with these diseases alone or in combination, the purpose of this study was to determine whether transporter expression in human liver is affected by alcoholic cirrhosis, diabetes, and alcoholic cirrhosis coexisting with diabetes. Transporters aid in hepatobiliary excretion of many drugs and toxic chemicals and can be determinants of drug-induced liver injury. Drug transporter expression and transcription factor-relative mRNA and protein expression in normal, diabetic, cirrhotic, and cirrhosis with diabetes human livers were quantified. Cirrhosis significantly increased ABCC4, 5, ABCG2, and solute carrier organic anion (SLCO) 2B1 mRNA expression and decreased SLCO1B3 mRNA expression in the liver. ABCC1, 3-5, and ABCG2 protein expression was also upregulated by alcoholic cirrhosis. ABCC3-5 and ABCG2 protein expression was also upregulated in diabetic cirrhosis. Cirrhosis increased nuclear factor E2-related factor 2 mRNA expression, whereas it decreased pregnane-X-receptor and farnesoid-X-receptor mRNA expression in comparison with normal livers. Hierarchical cluster analysis indicated that expressions of ABCC2, 3, and 6; SLCO1B1 and 1B3; and ABCC4 and 5 were more closely related in the livers from this cohort. Overall, alcoholic cirrhosis altered transporter expression in human liver. © 2013 by The American Society for Pharmacology and Experimental Therapeutics.