Involvement of pregnane X receptor in the suppression of carboxylesterases by metformin in vivo and in vitro, mediated by the activation of AMPK and JNK signaling pathway

Phenobarbital Induces SLC13A5 Expression through Activation of PXR but Not CAR in Human Primary Hepatocytes

Phenobarbital (PB), a widely used antiepileptic drug, is known to upregulate the expression of numerous drug-metabolizing enzymes and transporters in the liver primarily via activation of the constitutive androstane receptor (CAR, NR1I3). The solute carrier family 13 member 5 (SLC13A5), a sodium-coupled citrate transporter, plays an important role in intracellular citrate homeostasis that is associated with a number of metabolic syndromes and neurological disorders. Here, we show that PB markedly elevates the expression of SLC13A5 through a pregnane X receptor (PXR)-dependent but CAR-independent signaling pathway. In human primary hepatocytes, the mRNA and protein expression of SLC13A5 was robustly induced by PB treatment, while genetic knockdown or pharmacological inhibition of PXR significantly attenuated this induction. Utilizing genetically modified HepaRG cells, we found that PB induces SLC13A5 expression in both wild type and CAR-knockout HepaRG cells, whereas such induction was fully abolished in the PXR-knockout HepaRG cells. Mechanistically, we identified and functionally characterized three enhancer modules located upstream from the transcription start site or introns of the SLC13A5 gene that are associated with the regulation of PXR-mediated SLC13A5 induction. Moreover, metformin, a deactivator of PXR, dramatically suppressed PB-mediated induction of hepatic SLC13A5 as well as its activation of the SLC13A5 luciferase reporter activity via PXR. Collectively, these data reveal PB as a potent inducer of SLC13A5 through the activation of PXR but not CAR in human primary hepatocytes.

IL-6 downregulates hepatic carboxylesterases via NF-κB activation in dextran sulfate sodium-induced colitis

Ulcerative colitis (UC) is associated with increased levels of inflammatory factors, which is attributed to the abnormal expression and activity of enzymes and transporters in the liver, affecting drug disposition in vivo. This study aimed to examine the impact of intestinal inflammation on the expression of hepatic carboxylesterases (CESs) in a mouse model of dextran sulfate sodium (DSS)-induced colitis. Two major CESs isoforms, CES1 and CES2, were down-regulated, accompanied by decreases in hepatic microsomal metabolism of clopidogrel and irinotecan. Meanwhile, IL-6 levels significantly increased compared with other inflammatory factors in the livers of UC mice. In contrast, using IL-6 antibody simultaneously reversed the down-regulation of CES1, CES2, pregnane X receptor (PXR), and constitutive androstane receptor (CAR), as well as the nuclear translocation of NF-κB in the liver. We further confirmed that treatment with NF-κB inhibitor abolished IL-6-induced down-regulation of CES1, CES2, PXR, and CAR in vitro. Thus, it was concluded that IL-6 represses hepatic CESs via the NF-κB pathway in DSS-induced colitis. These findings indicate that caution should be exercised concerning the proper and safe use of therapeutic drugs in patients with UC.

Regulation of CAR and PXR Expression in Health and Disease

Pregnane X receptor (PXR, NR1I2) and constitutive androstane receptor (CAR, NR1I3) are members of the nuclear receptor superfamily that mainly act as ligand-activated transcription factors. Their functions have long been associated with the regulation of drug metabolism and disposition, and it is now well established that they are implicated in physiological and pathological conditions. Considerable efforts have been made to understand the regulation of their activity by their cognate ligand; however, additional regulatory mechanisms, among which the regulation of their expression, modulate their pleiotropic effects. This review summarizes the current knowledge on CAR and PXR expression during development and adult life; tissue distribution; spatial, temporal, and metabolic regulations; as well as in pathological situations, including chronic diseases and cancers. The expression of CAR and PXR is modulated by complex regulatory mechanisms that involve the interplay of transcription factors and also post-transcriptional and epigenetic modifications. Moreover, many environmental stimuli affect CAR and PXR expression through mechanisms that have not been elucidated.

Alterations in viability and CYP1A1 expression in SH SY5Y cell line by pollutants present in Madín Dam, Mexico

Currently one of the problems facing global development is the availability of water. Although water is abundant the planet only a small portion is for human use and consumption. The problem is exacerbated due to different factors, mainly: meteorological phenomena, the presence of contaminants in the water and the increase in the number of inhabitants. Potential effects of pollutants not only can affect freshwater biota but also can be implicated in cancer development and neurodegenerative diseases in humans. The study was conducted in the Madín Dam, a reservoir of economic importance for the geographical area in which it is located, as well as catering to the population of nearby areas, and is a place where recreational activities such as fishing and kayaking are carried out. The aim of this study was to identify the toxic effects that the pollutants present in the water of the Madín Dam can generate on a human cell line (SH SY5Y) evaluating the cell viability and the participation of the Aril Hydrocarbon Receptor (AhR) and Pregnane X receptor (PXR) through of the expression of the CYP1A1 and CYP3A4 (canonical genes). In one of the five sites analyzed, cell viability was up to 50%, in this site a decrease in the normal expression of CYP1A1 was observed (p < 0.05) and the CYP3A4 gene was not expressed in the cells SH SY5Y. These results show that the SH SY5Y cell line is a good biomarker for assessing the human toxicity of environmental pollutants and relating it to neurodegenerative diseases.

Clinical applications of small molecule inhibitors of Pregnane X receptor

The canonical effect of Pregnane X Receptor (PXR, NR1I2) agonism includes enhanced hepatic uptake and a concomitant increase in the first-pass metabolism and efflux of drugs in mammalian liver and intestine. In patients undergoing combination therapy, PXR-mediated gene regulation represents the molecular basis of numerous food-drug, herb-drug, and drug-drug interactions. Moreover, PXR activation promotes chemotherapeutic resistance in certain malignancies. Additional research efforts suggest that sustained PXR activation exacerbates the development of fatty liver disease. Additional metabolic effects of PXR activation in liver are the inhibition of fatty acid oxidation and gluconeogenesis. The identification of non-toxic and selective PXR antagonists is therefore of current research interest. Inhibition of PXR should decrease adverse effects, improve therapeutic effectiveness, and advance clinical outcomes in patients with cancer, fatty liver, and diabetes. This review identifies small molecule PXR antagonists described to date, discusses possible molecular mechanisms of inhibition, and seeks to describe the likely biomedical consequences of the inhibition of this nuclear receptor superfamily member.

Role of c-Jun-N-Terminal Kinase in Pregnane X Receptor-Mediated Induction of Human Cytochrome P4503A4 In Vitro

Cytochrome P450 CYP3A4 is the most abundant drug-metabolizing enzyme and is responsible for the metabolism of ∼50% of clinically available drugs. Induction of CYP3A4 impacts the disposition of its substrates and leads to harmful clinical consequences, such as failure of therapy. To prevent such undesirable consequences, the molecular mechanisms of regulation of CYP3A4 need to be fully understood. CYP3A4 induction is regulated primarily by the xenobiotic nuclear receptor pregnane-X receptor (PXR). After ligand binding, PXR is translocated to the nucleus, where it binds to the CYP3A4 promoter and induces its gene expression. PXR function is modulated by phosphorylation(s) by multiple kinases. In this study, we determined the role of the c-Jun N-terminal kinase (JNK) in PXR-mediated induction of CYP3A4 enzyme in vitro. Human liver carcinoma cells (HepG2) were transfected with CYP3A4 luciferase and PXR plasmids, followed by treatment with JNK inhibitor (SP600125; SP) and PXR activators rifampicin (RIF) or hyperforin. Our results indicate that SP treatment significantly attenuated PXR-mediated induction of CYP3A4 reporter activity, as well as gene expression and enzyme activity. JNK knockdown by siRNA (targeting both JNK 1 and 2) also attenuated CYP3A4 induction by RIF. Interestingly, SP treatment attenuated JNK activation by RIF. Furthermore, treatment with RIF increased PXR nuclear levels and binding to the CYP3A4 promoter; SP attenuated these effects. This study shows that JNK is a novel mechanistic regulator of CYP3A4 induction by PXR.

Dexmedetomidine impairs P‑glycoprotein‑mediated efflux function in L02 cells via the adenosine 5'‑monophosphate‑activated protein kinase/nuclear factor‑κB pathway

Dexmedetomidine (DEX) a type of the anaesthetic that has been widely used in anaesthesia and intensive care. However, whether DEX affects the pharmacokinetics of drugs remains elusive. As hepatic P-glycoprotein (P-gp) serves a critical role in the disposition of drugs, the present study aimed to address whether P-gp function could be affected by DEX in vitro. In the present study, L02 cells (a normal human liver cell line) were exposed to DEX for 24 h and P-gp function was evaluated by the intracellular accumulation of Rhodamine 123. The results indicated that P-gp function was significantly impaired by DEX treatment and that the mRNA levels and protein levels of P-gp were downregulated in a dose- and time-dependent manner. Importantly, DEX-induced downregulation of P-gp was associated with adenosine 5′-monophosphate-activated protein kinase (AMPK) activation, as it was significantly attenuated by AMPK inhibition using dorsomorphin. Furthermore, the results revealed that changes in the subcellular localisation of nuclear factor (NF)-κB following AMPK activation were involved in the P-gp regulation in response to DEX treatment. Collectively, these results suggested that DEX impairs P-glycoprotein-mediated efflux function in L02 cells via the AMPK/NF-κB pathway, which provided direct evidence that the hepatic disposition of drugs may be affected by DEX through the downregulation of P-gp.