Bilirubin Reduces the Uptake of Estrogen Precursors and the Followed Synthesis of Estradiol in Human Placental Syncytiotrophoblasts via Inhibition and Downregulation of Organic Anion Transporter 4.

Estrogen biosynthesis in human placental trophoblasts requires the human organic anion transporter 4 (hOAT4)-mediated uptake of fetal derived precursors such as dehydroepiandrosterone-3-sulfate (DHEAS) and 16α-hydroxy-DHEA-S (16α-OH-DHEAS). Scant information is available concerning the contribution of fetal metabolites on the impact of placental estrogen precursor transport and the followed estrogen synthesis. This study substantiated the roles of bilirubin as well as bile acids (taurochenodeoxycholic acid, taurocholic acid, glycochenodeoxycholic acid, chenodeoxycholic acid) on the inhibition of hOAT4-mediated uptake of probe substrate 6-carboxylfluorescein and DHEAS in stably transfected hOAT4-Chinese hamster ovary cells, with the IC50 of 1.53 and 0.98 µM on 6-carboxylfluorescein and DHEAS, respectively, for bilirubin, and 90.2, 129, 16.4, and 12.3 µM on 6-CF for taurochenodeoxycholic acid, glycochenodeoxycholic acid, taurocholic acid, and chenodeoxycholic acid. Bilirubin (2.5-10 µM) concentration-dependently inhibited the accumulation of estradiol precursor DHEAS in human choriocarcinoma JEG-3 cells (reduced by 60% at 10 µM) and primary human trophoblast cells (reduced by 80% at 10 µM). Further study confirmed that bilirubin (0.625-2.5 µM) concentration-dependently reduced the synthesis and secretion of estradiol in primary human trophoblast cells, among which 2.5 µM of bilirubin reduced the synthesis of estradiol by 30% and secretion by 35%. In addition, immunostaining and Western blot results revealed a distinct downregulation of hOAT4 protein expression in primary human trophoblast cells pretreated with 2.5 µM of bilirubin. In conclusion, this study demonstrated that bilirubin reduced the uptake of estrogen precursors and the followed synthesis of estradiol in human placenta via inhibition and downregulation of organic anion transporter 4. SIGNIFICANCE STATEMENT: Fetal metabolites, especially bilirubin, were first identified with significant inhibitory effects on the hOAT4-mediated uptake of estrogen precursor DHEAS in hOAT4-CHO, JEG-3 and PHTCs. Bilirubin concentration-dependently suppressed the estradiol synthesis and secretion in PHTCs treated with DHEAS, which was synchronized with the decline of hOAT4 protein expression. Additionally, those identified bile acids exhibited a weaker inhibitory effect on the secretion of estradiol.

Determination of intracellular anlotinib, osimertinib, afatinib and gefitinib accumulations in human brain microvascular endothelial cells by liquid chromatography/tandem mass spectrometry.

RATIONALE: Brain metastases are a common complication in patients with non-small-cell lung cancer (NSCLC). Anlotinib hydrochloride is a novel multi-target tyrosine kinase inhibitor (TKI) exhibiting a superior overall response rate for brain metastases from NSCLC. The penetrability of anlotinib and three generations of epidermal growth factor receptor (EGFR) TKIs (osimertinib, afatinib and gefitinib) into brain microvascular endothelial cells (HBMECs) was compared. METHODS: A sensitive quantification method for the four TKIs was developed using liquid chromatography coupled to tandem mass spectrometry (LC/MS/MS). Anlotinib and the three EGFR TKIs were separated on an ACQUITY BEH C18 column after a direct protein precipitation, and then analyzed using electrospray ionization in positive ion mode. The linearity, accuracy, precision, limit of quantification, specificity and stability were assessed. RESULTS: The four analytes could be efficiently quantified in a single run of 3.8 min. The validation parameters of all analytes satisfy the acceptance criteria of bioanalytical method guidelines. The calibration range was 0.2-200 ng mL-1 for anlotinib and gefitinib, 1-500 ng mL-1 for osimertinib and 1-200 ng mL-1 for afatinib. The penetration of anlotinib across HBMECs was comparable with that of afatinib and gefitinib but less than that of osimertinib. CONCLUSIONS: A sensitive LC/MS/MS method to simultaneously measure anlotinib, osimertinib, afatinib and gefitinib in cell extracts was successfully validated and applied to determine their uptake inside HBMECs, which could pave the way for future research on the role of anlotinib in NSCLC brain metastases.

Downregulation of glucose-6-phosphatase expression contributes to fluoxetine-induced hepatic steatosis.

Fluoxetine is a first-line selective serotonin reuptake inhibitor widely applied for the treatment of depression; however, it induces abnormal hepatic lipid metabolism. Considering decreased expression or function of glucose-6-phosphatase (G6Pase), a key enzyme in gluconeogenesis, or the upregulation of fatty acid uptake, causes hepatic lipid accumulation. The aim of this study was to elucidate whether G6Pase regulation and fatty acid uptake alteration contribute to fluoxetine-induced abnormal hepatic lipid metabolism. Our study revealed that 8-week oral administration of fluoxetine dose-dependently increased hepatic triglyceride, causing hepatic steatosis. Concomitantly, the expression of G6Pase in mouse livers and primary mouse hepatocytes (PMHs) was downregulated in a concentration-dependent manner. Furthermore, fluoxetine increased the concentrations of glucose-6-phosphate (G6Pase substrate) and acetyl CoA (the substrate for de novo lipogenesis) in mouse livers. Additionally, fluoxetine also induced lipid accumulation and downregulated G6Pase expression in HepG2 cells. However, the uptake of green fluorescent fatty acid (BODIPY™ FL C16) in PMHs was not changed after fluoxetine treatment, indicating that fluoxetine-induced hepatic steatosis was not associated with fatty acid uptake alteration. In conclusion, fluoxetine downregulated hepatic G6Pase expression, subsequently enhanced the transformation of glucose to lipid, and ultimately resulted in hepatic steatosis, but with no impact on fatty acid uptake.

Multiple Drug Transporters Contribute to the Placental Transfer of Emtricitabine.

Emtricitabine (FTC) is a first-line antiviral drug recommended for the treatment of AIDS during pregnancy. We hypothesized that transporters located in the placenta contribute to FTC transfer across the blood-placenta barrier. BeWo cells, cell models with stable or transient expression of transporter genes, primary human trophoblast cells (PHTCs), and small interfering RNAs (siRNAs) were applied to demonstrate which transporters were involved. FTC accumulation in BeWo cells was reduced markedly by inhibitors of equilibrative nucleoside transporters (ENTs), concentrative nucleoside transporters (CNTs), organic cation transporters (OCTs), and organic cation/carnitine transporter 1 (OCTN1) and increased by inhibitors of breast cancer resistance protein (BCRP) and multidrug resistance-associated proteins (MRPs). ENT1, CNT1, OCTN1, MRP1/2/3, and BCRP, but not ENT2, CNT3, OCTN2, or multidrug resistance protein 1 (MDR1), were found to transport FTC. FTC accumulation in PHTCs was decreased significantly by inhibitors of ENTs and OCTN1. These results suggest that ENT1, CNT1, and OCTN1 probably contribute to FTC uptake from maternal circulation to trophoblasts and that ENT1, CNT1, and MRP1 are likely involved in FTC transport between trophoblasts and fetal blood, whereas BCRP and MRP1/2/3 facilitate FTC transport from trophoblasts to maternal circulation. Coexistence of tenofovir or efavirenz with FTC in the cell medium did not influence FTC accumulation in BeWo cells or PHTCs.

Downregulation of PDZK1 by TGF-ß1 promotes renal fibrosis via inducing epithelial-mesenchymal transition of renal tubular cells.

Transforming growth factor-beta 1 (TGF-ß1)-induced epithelial-mesenchymal transition (EMT) of renal tubular cells promotes renal fibrosis and the progression of chronic kidney disease (CKD). PDZ domain-containing 1 (PDZK1) is highly expressed in renal tubular epithelial cells; however, its role in TGF-ß1-induced EMT remains poorly understood. The present study showed that PDZK1 expression was extremely downregulated in fibrotic mouse kidneys and its negative correlation with TGF-ß1 expression and the degree of renal fibrosis. In addition, TGF-ß1 downregulated the mRNA expression of PDZK1 in a time- and concentration-dependent manner in vitro. The downregulation of PDZK1 exacerbated TGF-ß1-induced EMT upon oxidative stress, while the overexpression of PDZK1 had the converse effect. Subsequent investigations demonstrated that TGF-ß1 downregulated PDZK1 expression via p38 MAPK or PI3K/AKT signaling in vitro, but independently of ERK/JNK MAPK signaling. Meanwhile, inhibition of the p38/JNK MAPK or PI3K/AKT signaling using chemical inhibitors restored the PDZK1 expression, mitigated renal fibrosis, and elevated renal levels of endogenous antioxidants carnitine and ergothioneine in adenine-induced CKD mice. These findings provide the first evidence suggesting a negative correlation between PDZK1 and renal fibrosis, and identifying PDZK1 as a novel suppressor of renal fibrosis in CKD through ameliorating oxidant stress.

Effects and mechanisms of Polygonati Rhizoma polysaccharide on potassium oxonate and hypoxanthine-induced hyperuricemia in mice.

Hyperuricemia, a prevalent metabolic disturbance intricately linked to gout and chronic kidney disease (CKD), may be relieved by traditional Chinese medicine Polygonati Rhizoma. It is derived from the rhizomes of Polygonatum sibiricum, Polygonatum kingianum, and Polygonatum cyrtonema, which are rich in polysaccharides and are effective hyperuricemia alleviators. This study investigated the potential of Polygonatum sibiricum polysaccharide (PSP) in managing hyperuricemia. PSP (125, 250, and 500 mg/kg, i.g.) or allopurinol was administered to hyperuricemia mice treated with potassium oxonate and hypoxanthine for two weeks. PSP effectively decreased serum uric acid levels by inhibiting xanthine oxidase and adenosine deaminase activity and expression in the liver and modulating uric acid-related transporters (URAT1, OAT1, and OAT3) in the kidney. PSP lowered serum creatinine and blood urea nitrogen levels, alleviating hyperuricemia-induced renal tubular epithelial-mesenchymal fibrosis. In vitro, PSP promoted mitochondrial biogenesis via the PGC-1α/NRF1/TFAM pathway, suppressed reactive oxygen species production, and prevented cytochrome C and dynamin-related protein 1 dysregulation in HK-2 cells. Furthermore, PSPA (Mw 4.0 kDa) and PSPB (Mw 112.2 kDa) isolated from PSP exhibit different uric acid-lowering mechanisms. In conclusion, our findings highlight the therapeutic potential of PSP and its nephroprotective effects in hyperuricemia, thereby supporting its development as a therapeutic agent for hyperuricemia.

SLC15A3 plays a crucial role in pulmonary fibrosis by regulating macrophage oxidative stress.

Idiopathic pulmonary fibrosis (IPF) is a fatal and irreversible disease with few effective treatments. Alveolar macrophages (AMs) are involved in the development of IPF from the initial stages due to direct exposure to air and respond to external oxidative damage (a major inducement of pulmonary fibrosis). Oxidative stress in AMs plays an indispensable role in promoting fibrosis development. The oligopeptide histidine transporter SLC15A3, mainly expressed on the lysosomal membrane of macrophages and highly expressed in the lung, has proved to be involved in innate immune and antiviral signaling pathways. In this study, we demonstrated that during bleomycin (BLM)- or radiation-induced pulmonary fibrosis, the recruitment of macrophages induced an increase of SLC15A3 in the lung, and the deficiency of SLC15A3 protected mice from pulmonary fibrosis and maintained the homeostasis of the pulmonary microenvironment. Mechanistically, deficiency of SLC15A3 resisted oxidative stress in macrophages, and SLC15A3 interacted with the scaffold protein p62 to regulate its expression and phosphorylation activation, thereby regulating p62-nuclear factor erythroid 2-related factor 2 (NRF2) antioxidant stress pathway protein, which is related to the production of reactive oxygen species (ROS). Overall, our data provided a novel mechanism for targeting SLC15A3 to regulate oxidative stress in macrophages, supporting the therapeutic potential of inhibiting or silencing SLC15A3 for the precautions and treatment of pulmonary fibrosis.

Unconjugated bilirubin promotes uric acid restoration by activating hepatic AMPK pathway.

Hyperuricemia and its development to gout have reached epidemic proportions. Systemic hyperuricemia is facilitated by elevated activity of xanthine oxidase (XO), the sole source of uric acid in mammals. Here, we aim to investigate the role of bilirubin in maintaining circulating uric acid homeostasis. We observed serum bilirubin concentrations were inversely correlated with uric acid levels in humans with new-onset hyperuricemia and advanced gout in a clinical cohort consisting of 891 participants. We confirmed that bilirubin biosynthesis impairment recapitulated traits of hyperuricemia symptoms, exemplified by raised circulating uric acid levels and accumulated hepatic XO, and exacerbated mouse hyperuricemia development. Bilirubin administration significantly decreased circulating uric acid levels in hyperuricemia-inducing (HUA) mice receiving potassium oxonate (a uricase inhibitor) or fed with a high fructose diet. Finally, we proved that bilirubin ameliorated mouse hyperuricemia by increasing hepatic autophagy, restoring antioxidant defense and normalizing mitochondrial function in a manner dependent on AMPK pathway. Hepatocyte-specific AMPKα knockdown via adeno-associated virus (AAV) 8-TBG-mediated gene delivery compromised the efficacy of bilirubin in HUA mice. Our study demonstrates the deficiency of bilirubin in hyperuricemia progression, and the protective effects exerted by bilirubin against mouse hyperuricemia development, which may potentiate clinical management of hyperuricemia.

Estradiol reduced 5-HT reuptake by downregulating the gene expression of Plasma Membrane Monoamine Transporter (PMAT, Slc29a4) through estrogen receptor ß and the MAPK/ERK signaling pathway.

Estrogen deficiency-induced female depression is closely related to 5-hydroxytriptamine (5-HT) deficiency. Estradiol (17ß-estradiol, E2) regulates the monoamine transporters and acts as an antidepressant by affecting 5-HT clearance through estrogen receptors and related signaling pathways at the genomic level, although the specific mechanisms require further exploration. The brain expresses higher levels of plasma membrane monoamine transporter (PMAT, involved in 5-HT reuptake of the uptake 2 system) than other uptake transporters. In this study, we found that estrogen-deficient ovariectomized (OVX) rats had high PMAT mRNA and protein expression levels in the hippocampus and estradiol significantly reduced these levels. Furthermore, estradiol inhibited PMAT expression and reduced 5-HT reuptake in neurons and astrocytes and estradiol regulated the PMAT expression mainly by affecting estrogen receptor ß (ERß) at the genomic level in astrocytes. Further experiments showed that estradiol also regulated PMAT expression through the MAPK/ERK signaling pathway and not through the PI3K/AKT signaling pathway. In conclusion, estradiol inhibited 5-HT reuptake by regulating PMAT expression at the genomic level through ERß and the MAPK/ERK signaling pathway, highlighting the importance of PMAT in the antidepressant effects of estradiol through 5-HT clearance reduction.

Examination of the emerging role of transporters in the assessment of nephrotoxicity.

INTRODUCTION: The kidney is vulnerable to various injuries based on its function in the elimination of many xenobiotics, endogenous substances and metabolites. Since transporters are critical for the renal elimination of those substances, it is urgent to understand the emerging role of transporters in nephrotoxicity. AREAS COVERED: This review summarizes the contribution of major renal transporters to nephrotoxicity induced by some drugs or toxins; addresses the role of transporter-mediated endogenous metabolic disturbances in nephrotoxicity; and discusses the advantages and disadvantages of in vitro models based on transporter expression and function. EXPERT OPINION: Due to the crucial role of transporters in the renal disposition of xenobiotics and endogenous substances, it is necessary to further elucidate their renal transport mechanisms and pay more attention to the underlying relationship between the transport of endogenous substances and nephrotoxicity. Considering the species differences in the expression and function of transporters, and the low expression of transporters in general cell models, in vitro humanized models, such as humanized 3D organoids, shows significant promise in nephrotoxicity prediction and mechanism study.

Upregulation of hepatic CD36 via glucocorticoid receptor activation contributes to dexamethasone-induced liver lipid metabolism disorder in mice.

Glucocorticoids such as dexamethasone (DEX) are widely prescribed to treat numerous conditions and diseases. However, glucocorticoid-induced liver lipid metabolism disorder, even nonalcoholic fatty liver disease, has caused extensive attention. Since fatty acid transporters such as CD36 and FATP play crucial roles in hepatic fatty acid uptake, this work examined their potential involvement in DEX-induced liver lipid accumulation. Chronic DEX administration (1-5 mg/kg/day over 28 days) induced hepatic lipid accumulation in mice. Fatty acid uptake in HepG2 cells and mouse primary hepatocytes was also stimulated after incubation with 0.5-2 µM DEX. Meanwhile, qPCR and western blotting demonstrated dose-dependent upregulation of CD36 expression by DEX in the mouse liver and in cultured hepatocytes. Glucocorticoid receptor (GR) inhibition with mifepristone (RU486) and siRNA-mediated GR knockdown attenuated lipid accumulation in hepatocytes by inhibiting DEX-induced CD36 upregulation, and direct binding of GR to the CD36 promoter was demonstrated by luciferase reporter and chromatin immunoprecipitation assays. These results indicate that DEX promotes free fatty acid uptake leading to hepatic steatosis by upregulating CD36 expression via activation of GR. Thus, strategies aimed at inhibiting GR/CD36 expression or activity might help prevent or reduce the onset and progression of hepatic lipid metabolism disorders induced by glucocorticoid drugs.

Proton pump inhibitor-induced risk of chronic kidney disease is associated with increase of indoxyl sulfate synthesis via inhibition of CYP2E1 protein degradation.

Proton pump inhibitors (PPIs) are widely used to treat acid-related disorders in the gastrointestinal tract; however, PPI use increases the risk of chronic kidney disease (CKD) through unclear mechanisms. Considering that PPIs disturb the gut microbiome balance, which is involved in the precursor of gut-derived uremic toxin accumulation, and that gut-derived uremic toxins aggravate CKD progression, the aim of this study is to elucidate whether PPIs affect gut-derived uremic toxin metabolism, including indoxyl sulfate (IS), p-cresyl sulfate, and trimethylamine-N-oxide, as a mechanism for causing CKD. The present study showed that 3 week-treatment of PPIs (omeprazole, lansoprazole, and pantoprazole at 30 mg/kg) in mice only increased IS plasma levels among the above three gut-derived uremic toxins. Additionally, lansoprazole increased IS plasma concentrations along with increased exposure dose (7.5-30 mg/kg) and duration (1-3 weeks). However, nephrotoxicity with mild changes in glomerular structure and signs of fibrosis were observed only in groups exposed to a 3-week treatment of PPIs (30 mg/kg). As the concentrations of indole (the precursor of IS from gut metabolism) in the colon were only increased in the pantoprazole-treated group, the mechanism of increased IS exposure remains unclear. Further studies revealed that PPIs (omeprazole and lansoprazole; but not pantoprazole) increased IS production from indole in primary mouse hepatocytes in a concentration-dependent manner. Additionally, the increased protein levels of hepatic CYP2E1 (the key enzyme mediating IS formation) due to suppressed degradation resulted in an increase in IS levels. Although omeprazole and lansoprazole significantly inhibited IS uptake in hOAT1/3 in vitro, 3 weeks of PPI treatment did not reduce IS renal excretion in mice. In conclusion, PPIs induced IS synthesis via increased hepatic CYP2E1 protein level, subsequently leading to increased IS exposure. These findings present a plausible biological mechanism to explain the association of PPI use with the increased risk of CKD.

Up-regulation of hepatic CD36 by increased corticosterone/cortisol levels via GR leads to lipid accumulation in liver and hypertriglyceridaemia during pregnancy.

BACKGROUND AND PURPOSE: Plasma triglyceride (TG) levels increase as gestation proceeds, and abnormal elevation of TG increases the risk of pregnancy complications. The current study explored the mechanisms involved in hypertriglyceridaemia during pregnancy. EXPERIMENTAL APPROACH: Lipid profile and expression levels of key genes involved in liver TG metabolism in non-pregnant and pregnant mice were studied. The effects of pregnancy-related hormones on key genes and the underlying mechanisms were uncovered in vitro and in vivo. KEY RESULTS: Plasma and hepatic TG levels were elevated, while hepatic fatty acid translocase (FAT/CD36) was up-regulated in pregnant mice. Corticosterone and cortisol (endogenous glucocorticoids that are elevated during pregnancy), but not oestradiol or progesterone, significantly up-regulated CD36 in hepatocytes, and this was abolished after knockdown of the glucocorticoid receptor (GR) using a siRNA or in the presence of GR antagonists, RU486 and AL082D06. The luciferase reporter gene and chromatin immunoprecipitation assay further revealed that corticosterone/cortisol promoted the direct binding of GR to the CD36 promoter and up-regulated its transcription. Chronic corticosterone exposure induced liver lipid accumulation and increased plasma TG levels in mice, which were attenuated by RU486 via inhibition of the GR-CD36 pathway. CONCLUSIONS AND IMPLICATIONS: Increased corticosterone/cortisol induces liver lipid accumulation and hypertriglyceridaemia during pregnancy by accelerating fatty acid uptake into hepatocytes via activation of GR and its target gene, CD36. Our results may be useful for the prevention of severe hypertriglyceridaemia and associated pregnancy complications.

Gut inflammation exacerbates high-fat diet induced steatosis by suppressing VLDL-TG secretion through HNF4α pathway.

Nonalcoholic fatty liver disease (NAFLD) is increasingly identified in inflammatory bowel disease (IBD) patients with unclear etiology. In the current study we assessed the contribution of colonic inflammation to NAFLD development and the underlying mechanism in a mouse model for IBD. Our results showed that dextran sulfate sodium (DSS)-induced gut colitis directly led to hepatic inflammation, injury and further exacerbated hepatic steatosis caused by high fat diet (HF) feeding. The essential genes assessment, hepatic metabolic analysis and triglyceride-rich very low-density lipoprotein (VLDL-TG) secretion assays revealed a higher ß-oxidation of fatty acids (FAs) but impaired VLDL-TG secretion in liver of DSS-treated mice. Disruption of the intestinal barrier by DSS promoted liver inflammation, which strongly suppressed hepatic VLDL-TG secretion and further aggravated HF-induced VLDL-TG secretion impairment through down-regulation of apolipoprotein B (APOB), hence promoting the storage of triglycerides (TG) in the liver. Inflammation induced by mixed proinflammatory cytokines or LPS obviously inhibited the expression of microsomal triglyceride transfer protein (MTP) and APOB expression and subsequently increased TG content via the suppression of HNF4α in mouse primary hepatocytes. In addition, the downregulation of MTP and APOB by proinflammatory cytokines was also rescued through activating Hnf4α by cortisol. Altogether, our results demonstrated that chronic inflammation exacerbated hepatic steatosis by inhibiting the secreting of hepatic VLDL-TG through HNF4α pathway, suggesting that restoring hepatic VLDL-TG secretion may be a novel strategy for treatment of NAFLD in IBD.

Pregnancy Impacts Entecavir Pharmacokinetics but Does Not Alter Its Renal Excretion.

Entecavir (ETV) is a first-line antiviral drug against the hepatitis B virus. This study was designed to investigate whether ETV pharmacokinetics changes during pregnancy and the underlying mechanism. The results showed that ETV exposure in plasma was higher in pregnant rats than in nonpregnant rats, whereas the exposure after delivery was recovered to that in nonpregnant rats. Because 70% of orally dosed ETV is eliminated by kidney, the effects of estradiol (E2) and progesterone (P4), 2 important hormones during pregnancy, on ETV-related renal transporters were investigated. Our results revealed that the activities of the ETV-related renal transporters hOAT1, hOAT3, hMATE1, and hMATE2-K were clearly inhibited by E2 and P4, resulting in reduced ETV accumulation in transporter-transfected cell models. However, the cumulative urinary excretion of ETV in pregnant rats exhibited no significant difference compared to nonpregnant rats, although the endogenous creatinine clearance in pregnant rats was 1.5-fold that of nonpregnant rats. In conclusion, ETV plasma exposure is increased during pregnancy, but ETV renal excretion displays no significant alteration. This may be because, during pregnancy, increased glomerular ETV filtration compensated for the decrease in renal tubular ETV secretion that occurs by E2- and P4-mediated inhibition of related transporters.

Roles of organic anion transporter 2 and equilibrative nucleoside transporter 1 in hepatic disposition and antiviral activity of entecavir during non-pregnancy and pregnancy.

BACKGROUND AND PURPOSE: Entecavir (ETV), a first-line antiviral drug against hepatitis B virus (HBV), has the possibility to be used to prevent mother-to-child transmission. The aim of present study was to clarify the mechanism of ETV uptake into hepatocytes and evaluate the alteration of ETV's hepatic distribution during pregnancy. EXPERIMENTAL APPROACH: The roles of equilibrative nucleotide transporter (ENT) 1 and organic anion transporter (OAT) 2 in ETV accumulation and anti-HBV efficacy were studied in human ENT1 or OAT2 overexpressed cell models and HepG2.2.15 cells, respectively; meanwhile, the liver-to-plasma ETV concentration ratios in non-pregnant and pregnant mice were measured to evaluate the effect of pregnancy on ETV hepatic distribution. KEY RESULTS: ETV was shown to be a substrate of ENT1 and OAT2. An ENT1 inhibitor significantly decreased the efficacy of ETV in HepG2.2.15 cells, while overexpression of OAT2 increased susceptibility of HBV to ETV. The liver-to-plasma ETV concentration ratios in pregnant mice were sharply reduced; whereas, the absolute concentration of ETV in the liver did not obviously alter in pregnancy. Although oestradiol and progesterone showed a concentration-dependent inhibition on ETV accumulation both in hepatic cell lines and in primary human hepatocytes, a physiologically relevant concentration of oestradiol and progesterone did not affect antiviral activity of ETV. CONCLUSIONS AND IMPLICATIONS: OAT2 and ENT1 are the main transporters involved in the hepatic uptake and anti-HBV efficacy of ETV. The concentration of ETV in the liver was not obviously altered during pregnancy, which indicates that dosage adjustment in pregnancy is not necessary.