Pregnancy represses induction of efflux transporters in livers of type I diabetic mice

Research advances in the role and pharmaceuticals of ATP-binding cassette transporters in autoimmune diseases

Autoimmune diseases are caused by the immune response of the body to its antigens, resulting in tissue damage. The pathogenesis of these diseases has not yet been elucidated. Most autoimmune diseases cannot be cured by effective drugs. The treatment strategy is to relieve the symptoms of the disease and balance the body's autoimmune function. The abnormal expression of ATP-binding cassette (ABC) transporters is directly related to the pathogenesis of autoimmune diseases and drug therapy resistance, which poses a great challenge for the drug therapy of autoimmune diseases. Therefore, this paper reviews the interplay between ABC transporters and the pathogenesis of autoimmune diseases to provide research progress and new ideas for the development of drugs in autoimmune diseases.

Sitosterolemia: Twenty Years of Discovery of the Function of ABCG5ABCG8

Sitosterolemia is a lipid disorder characterized by the accumulation of dietary xenosterols in plasma and tissues caused by mutations in either ABCG5 or ABCG8. ABCG5 ABCG8 encodes a pair of ABC half transporters that form a heterodimer (G5G8), which then traffics to the surface of hepatocytes and enterocytes and promotes the secretion of cholesterol and xenosterols into the bile and the intestinal lumen. We review the literature from the initial description of the disease, the discovery of its genetic basis, current therapy, and what has been learned from animal, cellular, and molecular investigations of the transporter in the twenty years since its discovery. The genomic era has revealed that there are far more carriers of loss of function mutations and likely pathogenic variants of ABCG5 ABCG8 than previously thought. The impact of these variants on G5G8 structure and activity are largely unknown. We propose a classification system for ABCG5 ABCG8 mutants based on previously published systems for diseases caused by defects in ABC transporters. This system establishes a framework for the comprehensive analysis of disease-associated variants and their impact on G5G8 structure-function.

Imbalance of Drug Transporter-CYP450s Interplay by Diabetes and Its Clinical Significance

The pharmacokinetics of a drug is dependent upon the coordinate work of influx transporters, enzymes and efflux transporters (i.e., transporter-enzyme interplay). The transporter-enzyme interplay may occur in liver, kidney and intestine. The influx transporters involving drug transport are organic anion transporting polypeptides (OATPs), peptide transporters (PepTs), organic anion transporters (OATs), monocarboxylate transporters (MCTs) and organic cation transporters (OCTs). The efflux transporters are P-glycoprotein (P-gp), multidrug/toxin extrusions (MATEs), multidrug resistance-associated proteins (MRPs) and breast cancer resistance protein (BCRP). The enzymes related to drug metabolism are mainly cytochrome P450 enzymes (CYP450s) and UDP-glucuronosyltransferases (UGTs). Accumulating evidence has demonstrated that diabetes alters the expression and functions of CYP450s and transporters in a different manner, disordering the transporter-enzyme interplay, in turn affecting the pharmacokinetics of some drugs. We aimed to focus on (1) the imbalance of transporter-CYP450 interplay in the liver, intestine and kidney due to altered expressions of influx transporters (OATPs, OCTs, OATs, PepTs and MCT6), efflux transporters (P-gp, BCRP and MRP2) and CYP450s (CYP3As, CYP1A2, CYP2E1 and CYP2Cs) under diabetic status; (2) the net contributions of these alterations in the expression and functions of transporters and CYP450s to drug disposition, therapeutic efficacy and drug toxicity; (3) application of a physiologically-based pharmacokinetic model in transporter-enzyme interplay.

Editor's Highlight: Farnesoid X Receptor Protects Against Low-Dose Carbon Tetrachloride-Induced Liver Injury Through the Taurocholate-JNK Pathway

Hepatotoxicity is of major concern for humans exposed to industrial chemicals and drugs. Disruption of farnesoid X receptor (FXR), a master regulator of bile acid (BA) metabolism, enhanced the sensitivity to liver injury in mice after toxicant exposure, but the precise mechanism remains unclear. In this study, the interconnection between BA metabolism, FXR, and chemically induced hepatotoxicity was investigated using metabolomics, Fxr-null mice (Fxr-/-) and hepatocytes, and recombinant adenoviruses. A single low-dose intraperitoneal injection of carbon tetrachloride (CCl4), an inducer of acute hepatitis in mice, resulted in more severe hepatocyte damage and higher induction of pro-inflammatory mediators, such as chemokine (C-C motif) ligand 2 (Ccl2), in Fxr-/-. Serum metabolomics analysis revealed marked increases in circulating taurocholate (TCA) and tauro-β-muricholate (T-β-MCA) in these mice, and forced expression of bile salt export protein (BSEP) by recombinant adenovirus in Fxr-/- ameliorated CCl4-induced liver damage. Treatment of Fxr-null hepatocytes with TCA, but not T-β-MCA, significantly increased c-Jun-N-terminal kinase (JNK) activation and Ccl2 mRNA levels, and up-regulation of Ccl2 mRNA was attenuated by co-treatment with a JNK inhibitor SP600125, indicating that TCA directly amplifies hepatocyte inflammatory signaling mainly mediated by JNK under FXR-deficiency. Additionally, pretreatment with SP600125 or restoration of FXR expression in liver by use of recombinant adenovirus, attenuated CCl4-induced liver injury. Collectively, these results suggest that the TCA-JNK axis is likely associated with increased susceptibility to CCl4-induced acute liver injury in Fxr-/-, and provide clues to the mechanism by which FXR and its downstream gene targets, such as BSEP, protects against chemically induced hepatotoxicity.

Regulation of drug metabolism and toxicity by multiple factors of genetics, epigenetics, lncRNAs, gut microbiota, and diseases: a meeting report of the 21st International Symposium on Microsomes and Drug Oxidations (MDO)

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 21^st 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.

Regulation of Drug Disposition Gene Expression in Pregnant Mice with Car Receptor Activation

More than half of pregnant women use prescription medications in order to maintain both maternal and fetal health. The constitutive androstane receptor (Car) critically affects the disposition of chemicals by regulating the transcription of genes encoding metabolic enzymes and transporters. However, the effects of Car activation on chemical disposition during pregnancy are unclear. This study aims to determine the degree to which pregnancy alters the expression of drug metabolizing enzymes and transporters in response to the pharmacological activation of Car. To test this, pregnant C57BL/6 mice were administered IP doses of vehicle, or a potent Car agonist, TCPOBOP, on gestation days 14, 15 and 16. Hepatic mRNA and protein expression of Car target genes (phase I, II and transporters) were quantified on gestation day 17. Pregnancy-related changes, such as induction of Cyp2b10, Ugt1a1 and Sult1a1 and repression of Ugt1a6, Gsta1, Gsta2 and Mrp6, were observed. Interestingly, the induction of Cyp2b10, Gsta1, Gsta2 and Mrp2-4 mRNAs by TCPOBOP was attenuated in maternal livers suggesting that Car activation is impeded by the biochemical and/or physiological changes that occur during gestation. Taken together, these findings suggest that pregnancy and pharmacological activation of Car can differentially regulate the expression of drug metabolism and transport genes.

Nrf2 Regulates the Sensitivity of Mouse Keratinocytes to Nitrogen Mustard via Multidrug Resistance-Associated Protein 1 (Mrp1)

Sulfur mustard and nitrogen mustard (mechlorethamine, HN2) are potent vesicants developed as chemical warfare agents. These electrophilic, bifunctional alkylating agents cause skin injury, including inflammation, edema, and blistering. HN2 covalently modifies macromolecules such as DNA, RNA, and proteins or is scavenged by glutathione, forming adducts that can contribute to toxicity. Multidrug resistance-associated protein 1 (Mrp1/MRP1) is a transmembrane ATPase known to efflux glutathione-conjugated electrophiles. In the present studies, we examined the effects of modulating Mrp1-mediated transport activity on the sensitivity of primary and PAM212 mouse keratinocytes to HN2. Primary keratinocytes, and to a lesser extent, PAM212 cells, express Mrp1 mRNA and protein and possess Mrp1 functional activity, as measured by calcein efflux. Sulforaphane, an activator of Nrf2, increased Mrp1 mRNA, protein, and functional activity in primary keratinocytes and PAM212 cells and decreased their sensitivity to HN2-induced growth inhibition (IC(50) = 1.4 and 4.8 µM in primary keratinocytes and 1 and 13 µM in PAM212 cells, in the absence and presence of sulforaphane, respectively). The Mrp1 inhibitor, MK-571, reversed the effects of sulforaphane on HN2-induced growth inhibition in both primary keratinocytes and PAM212 cells. In primary keratinocytes from Nrf2(-/-) mice, sulforaphane had no impact on Mrp1 expression or activity, or on sensitivity to HN2, demonstrating that its effects depend on Nrf2. These data suggest that Mrp1-mediated efflux is important in regulating HN2-induced keratinocyte growth inhibition. Enhancing HN2 efflux from keratinocytes may represent a novel strategy for mitigating vesicant-induced cytotoxicity.