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Paraquat (PQ) is an agrochemical known to cause pulmonary fibrosis. PQ-induced collagen deposition in the lung is thought to require enzymatic formation of PQ radicals, but the specific enzymes responsible for this bioactivation event in vivo have not been identified. We tested the hypothesis that lung P450 oxidoreductase (POR or CPR) is important in PQ-induced lung fibrosis in mice. A lung-Cpr-null mouse model was utilized, which undergoes doxycycline-induced, Cre recombinase-mediated deletion of the Por gene specifically in airway Club cells and alveolar type 2 cells in the lung. The lungs of lung-Cpr-null mice and their wild-type littermates were collected on day 15 after a single intraperitoneal injection of saline (control) or PQ (20 mg/kg). Lung tissue sections were stained with picrosirius red for detection of collagen fibrils. Fibrotic lung areas were found to be significantly smaller (1.6-fold for males and 1.4-fold for females) in PQ-treated lung-Cpr-null mice than in sex- and treatment-matched wild-type mice. The levels of collagen in lung tissue homogenate were also lower (1.4-2.3-fold; p < 0.05) in PQ-treated lung-Cpr-null mice compared to PQ-treated wild-type mice. In contrast, plasma PQ toxicokinetic profiles were not different between sex-matched wild-type and lung-Cpr-null mice. Taken together, these results indicate that lung POR plays an important role in PQ-induced pulmonary fibrosis.

Variations in drug metabolism may alter drug efficacy and cause toxicity; better understanding of the mechanisms and risks shall help to practice precision medicine. At the 21st International Symposium on Microsomes and Drug Oxidations held in Davis, California, USA, in October 2-6, 2016, a number of speakers reported some new findings and ongoing studies on the regulation mechanisms behind variable drug metabolism and toxicity, and discussed potential implications to personalized medications. A considerably insightful overview was provided on genetic and epigenetic regulation of gene expression involved in drug absorption, distribution, metabolism, and excretion (ADME) and drug response. Altered drug metabolism and disposition as well as molecular mechanisms among diseased and special populations were presented. In addition, the roles of gut microbiota in drug metabolism and toxicology as well as long non-coding RNAs in liver functions and diseases were discussed. These findings may offer new insights into improved understanding of ADME regulatory mechanisms and advance drug metabolism research.

During acetaminophen (APAP) hepatotoxicity, increased expression of multidrug resistance-associated proteins 2, 3, and 4 (Mrp2-4) occurs. Mrp4 is the most significantly upregulated transporter in mouse liver following APAP treatment. Although the expression profiles of liver transporters following APAP hepatotoxicity are well characterized, the regulatory mechanisms contributing to these changes remain unknown. We hypothesized that Kupffer cell-derived mediators participate in the regulation of hepatic transporters during APAP toxicity. To investigate this, C57BL/6J mice were pretreated with clodronate liposomes (0.1 ml iv) to deplete Kupffer cells and then challenged with APAP (500 mg/kg ip). Liver injury was assessed by plasma alanine aminotransferase and hepatic transporter protein expression was determined by Western blot and immunohistochemistry. Depletion of Kupffer cells by liposomal clodronate increased susceptibility to APAP hepatotoxicity. Although increased expression of several efflux transporters was observed after APAP exposure, only Mrp4 was found to be differentially regulated following Kupffer cell depletion. At 48 and 72 h after APAP dosing, Mrp4 levels were increased by 10- and 33-fold, respectively, in mice receiving empty liposomes. Immunohistochemistry revealed Mrp4 staining confined to centrilobular hepatocytes. Remarkably, Kupffer cell depletion completely prevented Mrp4 induction by APAP. Elevated plasma levels of TNF-[alpha] and IL-1[beta] were also prevented by Kupffer cell depletion. These findings show that Kupffer cells protect the liver from APAP toxicity and that Kupffer cell mediators released in response to APAP are likely responsible for the induction of Mrp4. multidrug resistance protein; hepatotoxicity; macrophage; transporter; cytokine; Abcc4

An electroneutral organic cation (OC)/proton exchanger in the apical membrane of proximal tubules mediates the final step of renal OC excretion. Two members of the multidrug and toxin extrusion family, MATE1 and MATE2-K, were recently identified in human and rodent kidney and proposed to be the molecular basis of renal OC/[H.sup.+] exchange. To take advantage of the comparative value of the large database on the kinetic and selectivity characteristics of OC/[H.sup.+] exchange that exists for rabbit kidney, we cloned rbMATE1 and rbMATE2-K. The rabbit homologs have 75% (MATE1) and 74% (MATE2-K) amino acid identity to their human counterparts (and 51% identity with each other), rbMATE1 and rbMATE2-K exhibited [H.sup.+] gradient-dependent uptake and efflux of tetraethylammonium (TEA) when expressed in Chinese hamster ovary cells. Both transporters displayed similar affinities for selected compounds [[IC.sub.50] values within 2-fold for TEA, l-methyl-4-phenylpyridinium, and quinidine] and very different affinities for others ([IC.sub.50] values differing by 8- to 80-fold for choline and cimetidine, respectively). These results indicate that rbMATE1 and rbMATE2-K are multispecific OC/[H.sup.+] exchangers with similar, but distinct, functional characteristics. Overall, the selectivity of MATE 1 and MATE2-K correlated closely with that observed in rabbit renal brush-border membrane vesicles. organic cation; transport; tetraethylammonium; proximal tubule; kidney doi:10.1152/ajprenal.00102.2007

Cholestatic hepatitis is frequently found in Niemann-Pick C (NPC) disease. We studied the influence of diet and the low density lipoprotein receptor (LDLR, Ldlr in mice, known to be the source of most of the stored cholesterol) on liver disease in the mouse model of NPC. [Npc1.sup.-/-] mice of both sexes, with or without the Ldlr knockout, were fed a 18% fat, 1% cholesterol ('high-fat') diet and were evaluated by chemical and histological methods. Bile acid transporters [multidrug resistance protein (Mrps) 1-5; Ntcp, Bsep, and OatP1, 2, and 4] were quantitated by real-time RT-PCR. Many mice died prematurely (within 6 wk) with hepatomegaly. Histopathology showed an increase in macrophage and hepatocyte lipids independent of Ldlr genotype. Non-zone-dependent diffuse fibrosis was found in the surviving mice. Serum alanine aminotransferase was elevated in [Npc1.sup.-/-] mice on the regular diet and frequently became markedly elevated with the high-fat diet. Serum cholesterol was increased in the controls but not the [Npc1.sup.-/-] mice on the high-fat diet; it was massively increased in the [Ldlr.sup.-/-] mice. Esterified cholesterol was greatly increased by the high-fat diet, independent of Ldlr genotype. 7-Glutamyltransferase was also elevated in [Npc.sup.1-/-] mice, more so on the high-fat diet. Mrps 1-5 were elevated in [Npc1.sup.-/-] liver and became more elevated with the high-fat diet; Ntcp, Bsep, and OatP2 were elevated in [Npc1.sup.-/-] liver and were suppressed by the high-fat diet. In conclusion, [Npc1.sup.-/-] mice on a high-fat diet provide an animal model of NPC cholestatic hepatitis and indicate a role for altered bile acid transport in its pathogenesis. Niemann-Pick C; low density lipoprotein receptor knockout; neonatal cholestasis; bile acid transporters; non-zone-dependent fibrosis

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 [micro]M and maximal rate of mediated TEA uptake of 0.8, 1.0, and 1.2 pmol*[mm.sup.-1]*[min.sup.-1] in S1, S2, and S3, respectively). In the S1 segment, TYR was a more effective inhibitor of TEA uptake than CIM (I[C.sub.50] values of 39 and 328 [micro]M, respectively), implicating OCT1 as the predominant pathway for TEA transport. The opposite profiles were noted in the S2 segment (I[C.sub.50] values of 302 and 20 [micro]M for TYR and CIM, respectively) and S3 segment (I[C.sub.50] values of 2,900 and 54 [micro]M for 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. organic cation; cimetidine; kidney; organic cation transporter 1; organic cation transporter 2; tetraethylammonium