Loss of organic anion transporting polypeptide 1a1 increases deoxycholic acid absorption in mice by increasing intestinal permeability

Gualou Xiebai Decoction ameliorates increased Caco-2 monolayer permeability induced by bile acids via tight junction regulation, oxidative stress suppression and apoptosis reduction

Gualou Xiebai Decoction (GXD), a classic prescription, is widely used to dealing with inflammatory diseases in China for thousands of years. Abnormal metabolic state of bile acids (BAs) is confirmed to cause intestinal epithelial barrier dysfunction. In preliminary work, we observed that GXD could decrease intestinal permeability in hyperlipidemia mice. The present study aimed to explore the protective effect of GXD on intestinal mucosa in vitro. Caco-2 cell monolayer permeability among different groups was determined by measuring the concentrations of FITC-dextran in the lower compartments and transepithelial electrical resistance (TEER). Meanwhile, mRNA and protein expressions of tight junctions (TJs) were investigated. Generation of intracellular reactive oxygen species (ROS) and the ratio of cell apoptosis induced by BAs were assessed by fluorescence probe and flow cytometry. GXD was shown to keep the cell monolayer in low permeable status, increase TEER and mRNA and protein expressions of occludin (Ocln) and zonula occluden 2 (ZO2) remarkably in cells challenged with cholic acid (CA), deoxycholic acid (DCA) and glycocholic acid (GCA). However, no significant effects were uncovered against the pathological effects of taurocholic acid (TCA). Meanwhile, generation of ROS and increased levels of apoptotic cells caused by CA, DCA and GCA were dramatically decreased by GXD, which were not observed on TCA. GXD could significantly attenuate intestinal barrier dysfunction induced by BAs via TJs regulation, oxidative stress suppression and cell apoptosis decrease, but such effects and behind mechanisms differed among different kinds of BAs.

Effect of Gender and Various Diets on Bile Acid Profile and Related Genes in Mice

Diet is an important factor for many diseases. Previous studies have demonstrated that several diets had remarkable effects on bile acid (BA) homeostasis, but no comprehensive information for both genders has been reported. Therefore, the current study characterized the nine most used laboratory animal diets fed to both genders of mice for a comparable evaluation of the topic. The results revealed that marked gender difference of BA homeostasis is ubiquitous in mice fed the various diets, and of the nine diets fed to mice, the atherogenic and calorie-restricted diets had the most marked effects on BA homeostasis, followed by the laboratory chow and essential fatty acid-deficient diets. More specifically, females had higher concentrations of total BAs in serum when fed six of the nine diets compared with male mice, and 26 of the 35 BA-related genes had marked gender difference in mice fed at least one diet. Although mice fed the calorie-restricted and atherogenic diets had increased BA, which was more pronounced in serum than liver, the intestinal farnesoid X nuclear receptor-fibroblast growth factor 15 axis changed in the opposite direction and resulted in different hepatic expression patterns of Cyp7a1 Compared with AIN-93M purified diet, higher hepatic expression of multidrug resistance-associated protein 3 was the only alteration in mice fed the laboratory chow diet. The other diets had little or no effect on BA concentrations in the liver and plasma or in the expression of BA-related genes. This study indicates that gender, the atherogenic diet, and the calorie-restricted diet have the most marked effects on BA homeostasis. SIGNIFICANCE STATEMENT: Previous evidence suggested that various diets have effect on bile acid (BA) homeostasis; however, it is not possible to directly compare these findings, as they are all from different studies. The current study was the first to systematically investigate the influence of the nine most used experimental mouse diets on BA homeostasis and potential mechanism in both genders of mice and indicates that gender, the atherogenic diet, and the calorie-restricted diet have the most marked effects on BA homeostasis, which will aid future investigations.

Longitudinal Visualization of Viable Cancer Cell Intratumoral Distribution in Mouse Models Using Oatp1a1-Enhanced Magnetic Resonance Imaging

OBJECTIVES

Multimodality reporter gene imaging provides valuable, noninvasive information on the fate of engineered cell populations. To complement magnetic resonance imaging (MRI) measures of tumor volume and 2-dimensional reporter-based optical measures of cell viability, reporter-based MRI may offer 3-dimensional information on the distribution of viable cancer cells in deep tissues.

MATERIALS AND METHODS

Here, we engineered human and murine triple-negative breast cancer cells with lentivirus encoding tdTomato and firefly luciferase for fluorescence imaging and bioluminescence imaging (BLI). A subset of these cells was additionally engineered with lentivirus encoding organic anion transporting polypeptide 1a1 (Oatp1a1) for MRI. Oatp1a1 operates by transporting gadolinium ethoxybenzyl diethylenetriamine pentaacetic acid (Gd-EOB-DTPA) into cells, and it concomitantly improves BLI substrate uptake. After orthotopic implantation of engineered cells expressing or not expressing Oatp1a1, longitudinal fluorescence imaging, BLI, and 3-Tesla MRI were performed.

RESULTS

Oatp1a1-expressing tumors displayed significantly increased BLI signals relative to control tumors at all time points (P < 0.05). On MRI, post-Gd-EOB-DTPA T1-weighted images of Oatp1a1-expressing tumors exhibited significantly increased contrast-to-noise ratios compared with control tumors and precontrast images (P < 0.05). At endpoint, tumors expressing Oatp1a1 displayed intratumoral MR signal heterogeneity not present at earlier time points. Pixel-based analysis of matched in vivo MR and ex vivo fluorescence microscopy images revealed a strong, positive correlation between MR intensity and tdTomato intensity for Oatp1a1-expressing tumors (P < 0.05), but not control tumors.

CONCLUSIONS

These results characterize Oatp1a1 as a sensitive, quantitative, positive contrast MRI reporter gene for 3-dimensional assessment of viable cancer cell intratumoral distribution and concomitant BLI enhancement. This multimodality reporter gene system can provide new insights into the influence of viable cancer cell intratumoral distribution on tumor progression and metastasis, as well as improved assessments of anticancer therapies.

β-Klotho deficiency shifts the gut-liver bile acid axis and induces hepatic alterations in mice

β-Klotho (encoded by Klb) is an obligate coreceptor, mediating both fibroblast growth factor (FGF)15 and FGF21 signaling. Klb^-/- mice are refractory to metabolic FGF15 and FGF21 action and exhibit derepressed (increased) bile acid (BA) synthesis. Here, we deeply phenotyped male Klb^-/- mice on a pure C57BL/6J genetic background, fed a chow diet focusing on metabolic aspects. This aims to better understand the physiological consequences of concomitant FGF15 and FGF21 signaling deficiency, in particular on the gut-liver axis. Klb^-/- mice present permanent growth restriction independent of adiposity and energy balance. Klb^-/- mice also exhibit few changes in carbohydrate metabolism, combining normal gluco-tolerance, insulin sensitivity, and fasting response with increased gluconeogenic capacity and decreased glycogen mobilization. Livers of Klb^-/- mice reveal pathologic features, including a proinflammatory status and initiation of fibrosis. These defects are associated to a massive shift in BA composition in the enterohepatic system and blood circulation featured by a large excess of microbiota-derived deoxycholic acid, classically known for its genotoxicity in the gastrointestinal tract. In conclusion, β-Klotho is a gatekeeper of hepatic integrity through direct action (mediating FGF21 anti-inflammatory signaling) and indirect mechanisms (mediating FGF15 signaling that maintains BA level and composition).

Bile Acid Uptake Transporters as Targets for Therapy

Bile acids are potent signaling molecules that regulate glucose, lipid and energy homeostasis predominantly via the bile acid receptors farnesoid X receptor (FXR) and transmembrane G protein-coupled receptor 5 (TGR5). The sodium taurocholate cotransporting polypeptide (NTCP) and the apical sodium dependent bile acid transporter (ASBT) ensure an effective circulation of (conjugated) bile acids. The modulation of these transport proteins affects bile acid localization, dynamics and signaling. The NTCP-specific pharmacological inhibitor myrcludex B inhibits hepatic uptake of conjugated bile acids. Multiple ASBT-inhibitors are already in clinical trials to inhibit intestinal bile acid uptake. Here, we discuss current insights into the consequences of targeting bile acid uptake transporters on systemic and intestinal bile acid dynamics and discuss the possible therapeutic applications that evolve as a result.

Sweroside ameliorates α-naphthylisothiocyanate-induced cholestatic liver injury in mice by regulating bile acids and suppressing pro-inflammatory responses

AIM

Sweroside is an iridoid glycoside with diverse biological activities. In the present study we investigated the effects of sweroside on α-naphthylisothiocyanate (ANIT)-induced cholestatic liver injury in mice.

METHODS

Mice received sweroside (120 mg·kg(-1)·d(-1), ig) or a positive control INT-747 (12 mg·kg(-1)·d(-1), ig) for 5 d, and ANIT (75 mg/kg, ig) was administered on d 3. The mice were euthanized on d 5, and serum biochemical markers, hepatic bile acids and histological changes were analyzed. Hepatic expression of genes related to pro-inflammatory mediators and bile acid metabolism was also assessed. Primary mouse hepatocytes were exposed to a reconstituted mixture of hepatic bile acids, which were markedly elevated in the ANIT-treated mice, and the cell viability and expression of genes related to pro-inflammatory mediators were examined.

RESULTS

Administration of sweroside or INT-747 effectively ameliorated ANIT-induced cholestatic liver injury in mice, as evidenced by significantly reduced serum biochemical markers and attenuated pathological changes in liver tissues. Furthermore, administration of sweroside or INT-747 significantly decreased ANIT-induced elevation of individual hepatic bile acids, such as β-MCA, CA, and TCA, which were related to its effects on the expression of genes responsible for bile acid synthesis and transport as well as pro-inflammatory responses. Treatment of mouse hepatocytes with the reconstituted bile acid mixture induced significant pro-inflammatory responses without affecting the cell viability.

CONCLUSION

Sweroside attenuates ANIT-induced cholestatic liver injury in mice by restoring bile acid synthesis and transport to their normal levels, as well as suppressing pro-inflammatory responses.

Importance of Large Intestine in Regulating Bile Acids and Glucagon-Like Peptide-1 in Germ-Free Mice

It is known that 1) elevated serum bile acids (BAs) are associated with decreased body weight, 2) elevated glucagon-like peptide-1 (GLP-1) levels can decrease body weight, and 3) germ-free (GF) mice are resistant to diet-induced obesity. The purpose of this study was to test the hypothesis that a lack of intestinal microbiota results in more BAs in the body, resulting in increased BA-mediated transmembrane G protein-coupled receptor 5 (TGR5) signaling and increased serum GLP-1 as a mechanism of resistance of GF mice to diet-induced obesity. GF mice had 2- to 4-fold increased total BAs in the serum, liver, bile, and ileum. Fecal excretion of BAs was 63% less in GF mice. GF mice had decreased secondary BAs and increased taurine-conjugated BAs, as anticipated. Surprisingly, there was an increase in non-12α-OH BAs, namely, β-muricholic acid, ursodeoxycholic acid (UDCA), and their taurine conjugates, in GF mice. Further, in vitro experiments confirmed that UDCA is a primary BA in mice. There were minimal changes in the mRNA of farnesoid X receptor target genes in the ileum (Fibroblast growth factor 15, small heterodimer protein, and ileal bile acid-binding protein), in the liver (small heterodimer protein, liver receptor homolog-1, and cytochrome P450 7a1), and BA transporters (apical sodium dependent bile acid transporter, organic solute transporter α, and organic solute transporter β) in the ileum of GF mice. Surprisingly, there were marked increases in BA transporters in the large intestine. Increased GLP-1 levels and gallbladder size were observed in GF mice, suggesting activation of TGR5 signaling. In summary, the GF condition results in increased expression of BA transporters in the colon, resulting in 1) an increase in total BA concentrations in tissues, 2) a change in BA composition to favor an increase in non-12α-OH BAs, and 3) activation of TGR5 signaling with increased gallbladder size and GLP-1.

11β-Hydroxysteroid dehydrogenase-1 is involved in bile acid homeostasis by modulating fatty acid transport protein-5 in the liver of mice

11β-Hydroxysteroid dehydrogenase-1 (11β-HSD1) plays a key role in glucocorticoid receptor (GR) activation. Besides, it metabolizes some oxysterols and bile acids (BAs). The GR regulates BA homeostasis; however, the impact of impaired 11β-HSD1 activity remained unknown. We profiled plasma and liver BAs in liver-specific and global 11β-HSD1-deficient mice. 11β-HSD1-deficiency resulted in elevated circulating unconjugated BAs, an effect more pronounced in global than liver-specific knockout mice. Gene expression analyses revealed decreased expression of the BA-CoA ligase Fatp5, suggesting impaired BA amidation. Reduced organic anion-transporting polypeptide-1A1 (Oatp1a1) and enhanced organic solute-transporter-β (Ostb) mRNA expression were observed in livers from global 11β-HSD1-deficient mice. The impact of 11β-HSD1-deficiency on BA homeostasis seems to be GR-independent because intrahepatic corticosterone and GR target gene expression were not substantially decreased in livers from global knockout mice. Moreover, Fatp5 expression in livers from hepatocyte-specific GR knockout mice was unchanged. The results revealed a role for 11β-HSD1 in BA homeostasis.

Intestinal CYP3A4 protects against lithocholic acid-induced hepatotoxicity in intestine-specific VDR-deficient mice

Vitamin D receptor (VDR) mediates vitamin D signaling involved in bone metabolism, cellular growth and differentiation, cardiovascular function, and bile acid regulation. Mice with an intestine-specific disruption of VDR (Vdr(ΔIEpC)) have abnormal body size, colon structure, and imbalance of bile acid metabolism. Lithocholic acid (LCA), a secondary bile acid that activates VDR, is among the most toxic of the bile acids that when overaccumulated in the liver causes hepatotoxicity. Because cytochrome P450 3A4 (CYP3A4) is a target gene of VDR-involved bile acid metabolism, the role of CYP3A4 in VDR biology and bile acid metabolism was investigated. The CYP3A4 gene was inserted into Vdr(ΔIEpC) mice to produce the Vdr(ΔIEpC)/3A4 line. LCA was administered to control, transgenic-CYP3A4, Vdr(ΔIEpC), and Vdr(ΔIEpC)/3A4 mice, and hepatic toxicity and bile acid levels in the liver, intestine, bile, and urine were measured. VDR deficiency in the intestine of the Vdr(ΔIEpC) mice exacerbates LCA-induced hepatotoxicity manifested by increased necrosis and inflammation, due in part to over-accumulation of hepatic bile acids including taurocholic acid and taurodeoxycholic acid. Intestinal expression of CYP3A4 in the Vdr(ΔIEpC)/3A4 mouse line reduces LCA-induced hepatotoxicity through elevation of LCA metabolism and detoxification, and suppression of bile acid transporter expression in the small intestine. This study reveals that intestinal CYP3A4 protects against LCA hepatotoxicity.

Increased bile acids in enterohepatic circulation by short-term calorie restriction in male mice

Previous studies showed glucose and insulin signaling can regulate bile acid (BA) metabolism during fasting or feeding. However, limited knowledge is available on the effect of calorie restriction (CR), a well-known anti-aging intervention, on BA homeostasis. To address this, the present study utilized a "dose-response" model of CR, where male C57BL/6 mice were fed 0, 15, 30, or 40% CR diets for one month, followed by BA profiling in various compartments of the enterohepatic circulation by UPLC-MS/MS technique. This study showed that 40% CR increased the BA pool size (162%) as well as total BAs in serum, gallbladder, and small intestinal contents. In addition, CR "dose-dependently" increased the concentrations of tauro-cholic acid (TCA) and many secondary BAs (produced by intestinal bacteria) in serum, such as tauro-deoxycholic acid (TDCA), DCA, lithocholic acid, ω-muricholic acid (ωMCA), and hyodeoxycholic acid. Notably, 40% CR increased TDCA by over 1000% (serum, liver, and gallbladder). Interestingly, 40% CR increased the proportion of 12α-hydroxylated BAs (CA and DCA), which correlated with improved glucose tolerance and lipid parameters. The CR-induced increase in BAs correlated with increased expression of BA-synthetic (Cyp7a1) and conjugating enzymes (BAL), and the ileal BA-binding protein (Ibabp). These results suggest that CR increases BAs in male mice possibly through orchestrated increases in BA synthesis and conjugation in liver as well as intracellular transport in ileum.

Organic anion-transporting polypeptide 1a4 (Oatp1a4) is important for secondary bile acid metabolism

Organic anion transporting polypeptides (human: OATPs; rodent: Oatps) were thought to have important functions in bile acid (BA) transport. Oatp1a1, 1a4, and 1b2 are the three major Oatp1 family members in rodent liver. Our previous studies have characterized the BA homeostasis in Oatp1a1-null and Oatp1b2-null mice. The present study investigated the physiological role of Oatp1a4 in BA homeostasis by using Oatp1a4-null mice. Oatp1a4 expression is female-predominant in livers of mice, and thereby it was expected that female Oatp1a4-null mice will have more prominent changes than males. Interestingly, the present study demonstrated that female Oatp1a4-null mice had no significant alterations in BA concentrations in serum or liver, though they had increased mRNA of hepatic BA efflux transporters (Mrp4 and Ostα/β) and ileal BA transporters (Asbt and Ostα/β). In contrast, male Oatp1a4-null mice showed significantly altered BA homeostasis, including increased concentrations of deoxycholic acid (DCA) in serum, liver and intestinal contents. After feeding a DCA-supplemented diet, male but not female Oatp1a4-null mice had higher concentrations of DCA in serum and livers than their WT controls. This suggested that Oatp1a4 is important for intestinal absorption of secondary BAs in male mice. Furthermore, loss of Oatp1a4 function did not decrease BA accumulation in serum or livers of bile-duct-ligated mice, suggesting that Oatp1a4 is not likely a BA uptake transporter. In summary, the present study for the first time demonstrates that Oatp1a4 does not appear to mediate the hepatic uptake of BAs, but plays an important male-predominant role in secondary BA metabolism in mice.

Influence of the functional polymorphisms in the organic anion transporting polypeptide 1B1 in the susceptibility to colorectal cancer

Colorectal cancer is an important cause of death throughout the world, and its etiology involves the interaction of genetic and environmental factors. Transporter proteins are important in protecting organs from xenobiotics or toxins. Organic anion-transporting polypeptide 1B1 (OATP1B1) plays role in hepatic uptake and clearance of albumin-bound amphipathic organic compounds, including endogen substances, drugs, or xenobiotics. The SLCO1B1 gene expressing OATP1B1 is highly polymorphic. Up to now, SLCO1BI variants were the focus of several investigations on drug pharmacokinetics and cancer susceptibility. However, no information has been available on association between SLCO1B1 and colorectal cancer risk. Therefore, the study aims to investigate the relationship between colorectal cancer and the functional common variants of SLCO1B1 (388 A>G, -11187 G>A, 521 T>C) and to estimate the prevalence of these variants in the Turkish population. To that end, the distributions of the variants were determined in 100 patients with colorectal cancer and 150 healthy volunteers. SLCO1B1 521 T>C was statistically significantly associated with colorectal cancer risk (odds ratio [OR]=2.66; 95% confidence interval [CI]=1.31-5.41; p=0.0057). In haplotype-based analysis, SLCO1B1 haplotype G(388)-T(11187)-T(521) might be associated with the development of colorectal cancer (OR=4.26; 95% CI=1.62-11.16; p=0.002). We believe that the findings may be beneficial to the development of efficacious preventive strategies and therapies for colorectal cancer.

Dysfunction of organic anion transporting polypeptide 1a1 alters intestinal bacteria and bile acid metabolism in mice

Organic anion transporting polypeptide 1a1 (Oatp1a1) is predominantly expressed in liver and is able to transport bile acids (BAs) in vitro. Male Oatp1a1-null mice have increased concentrations of taurodeoxycholic acid (TDCA), a secondary BA generated by intestinal bacteria, in both serum and livers. Therefore, in the present study, BA concentrations and intestinal bacteria in wild-type (WT) and Oatp1a1-null mice were quantified to investigate whether the increase of secondary BAs in Oatp1a1-null mice is due to alterations in intestinal bacteria. The data demonstrate that Oatp1a1-null mice : (1) have similar bile flow and BA concentrations in bile as WT mice; (2) have a markedly different BA composition in the intestinal contents, with a decrease in conjugated BAs and an increase in unconjugated BAs; (3) have BAs in the feces that are more deconjugated, desulfated, 7-dehydroxylated, 3-epimerized, and oxidized, but less 7-epimerized; (4) have 10-fold more bacteria in the small intestine, and 2-fold more bacteria in the large intestine which is majorly due to a 200% increase in Bacteroides and a 30% reduction in Firmicutes; and (5) have a different urinary excretion of bacteria-related metabolites than WT mice. In conclusion, the present study for the first time established that lack of a liver transporter (Oatp1a1) markedly alters the intestinal environment in mice, namely the bacteria composition.

Organic anion transporting polypeptide 1a1 null mice are sensitive to cholestatic liver injury

Organic anion transporting polypeptide 1a1 (Oatp1a1) is predominantly expressed in livers of mice and is thought to transport bile acids (BAs) from blood into liver. Because Oatp1a1 expression is markedly decreased in mice after bile duct ligation (BDL). We hypothesized that Oatp1a1-null mice would be protected against liver injury during BDL-induced cholestasis due largely to reduced hepatic uptake of BAs. To evaluate this hypothesis, BDL surgeries were performed in both male wild-type (WT) and Oatp1a1-null mice. At 24 h after BDL, Oatp1a1-null mice showed higher serum alanine aminotransferase levels and more severe liver injury than WT mice, and all Oatp1a1-null mice died within 4 days after BDL, whereas all WT mice survived. At 24 h after BDL, surprisingly Oatp1a1-null mice had higher total BA concentrations in livers than WT mice, suggesting that loss of Oatp1a1 did not prevent BA accumulation in the liver. In addition, secondary BAs dramatically increased in serum of Oatp1a1-null BDL mice but not in WT BDL mice. Oatp1a1-null BDL mice had similar basolateral BA uptake (Na(+)-taurocholate cotransporting polypeptide and Oatp1b2) and BA-efflux (multidrug resistance-associated protein [Mrp]-3, Mrp4, and organic solute transporter α/β) transporters, as well as BA-synthetic enzyme (Cyp7a1) in livers as WT BDL mice. Hepatic expression of small heterodimer partner Cyp3a11, Cyp4a14, and Nqo1, which are target genes of farnesoid X receptor, pregnane X receptor, peroxisome proliferator-activated receptor alpha, and NF-E2-related factor 2, respectively, were increased in WT BDL mice but not in Oatp1a1-null BDL mice. These results demonstrate that loss of Oatp1a1 function exacerbates cholestatic liver injury in mice and suggest that Oatp1a1 plays a unique role in liver adaptive responses to obstructive cholestasis.