The Significance of Bile in the Biliopancreatic Limb on Metabolic Improvement After Duodenal-Jejunal Bypass

INTRODUCTION

Duodenal-jejunal bypass (DJB) is an experimental procedure in metabolic surgery that does not have a restrictive component. Changes in bile acid (BA) dynamics and intestinal microbiota are possibly related to metabolic improvement after DJB. Our previous studies involving obese diabetic rats showed the crucial role of the biliopancreatic limb (BPL) in metabolic improvement after DJB caused by BA reabsorption. We established a new DJB procedure to prevent bile from flowing into the BPL and aimed to elucidate the importance of bile in the BPL after DJB.

METHODS

Otsuka Long-Evans Tokushima Fatty rats with diabetes were divided into three groups: two DJB groups and a sham group (n = 11). Duodenal-jejunal anastomosis was performed proximal to the papilla of Vater in the DJB group (n = 11). However, the DJB-D group (n = 11) underwent a new procedure with duodenal-jejunal anastomosis distal to the papilla of Vater for preventing bile flow into the BPL.

RESULTS

Glucose metabolism improved and weight gain was suppressed in the DJB group, but not in the DJB-D and sham groups. Serum BA level and conjugated BA concentration were elevated in the DJB group. The gut microbiota was altered only in the DJB group; the abundance of Firmicutes and Bacteroidetes decreased and that of Actinobacteria increased. However, the DJB-D group exhibited no apparent change in the gut microbiota, similar to the sham group.

CONCLUSION

BAs are essential in the BPL for metabolic improvement after DJB; they can improve the gut microbiota in these processes.

Roles for Bile Acid Signaling and Nonsense-Mediated Ribonucleic Acid Decay in Small Bowel Resection-Associated Liver Injury

INTRODUCTION

Massive intestinal loss resulting in short bowel syndrome has been linked to intestinal failure associated liver disease. Efforts to elucidate the driving force behind the observed hepatic injury have identified inflammatory mediators, alterations in the microbiome, extent of structural and functional intestinal adaptation, and toxic shifts in the bile acid pool. In the present study, we posit that ileocecal resection interrupts the delivery of these hepatotoxic substances to the liver by physically disrupting the enterohepatic circulation, thereby shielding the liver from exposure to the aforementioned noxious stimuli.

METHODS

Mice underwent sham, 50% proximal, or 50% distal small bowel resection (SBR), with or without tauroursodeoxycolic acid supplementation. Enterohepatic signaling and nonsense-mediated ribonucleic acid (RNA) decay were evaluated and correlated with hepatic injury.

RESULTS

When compared to 50% proximal SBR, mice that underwent ileocecal resection exhibited reduced hepatic oxidative stress and exhibited a more physiological bile acid profile with increased de novo bile acid synthesis, enhanced colonic bile acid signaling, and reduced hepatic proliferation. Distal intestinal resection promoted an adaptive response including via the nonsense-mediated RNA decay pathway to satisfactorily process injurious messenger RNA and successfully maintain homeostasis. By contrast, this adaptive response was not observed in the proximal SBR group and hepatic injury persisted.

CONCLUSIONS

In summary, interruption of enterohepatic circulation via ileocecal resection abrogates the liver's exposure to toxic and inflammatory mediators while promoting physiological adaptations in bile acid metabolism and maintaining existing homeostatic pathways.

The interaction of bile acids and gut inflammation influences the pathogenesis of inflammatory bowel disease

Bile acids (BA) are amphipathic molecules originating from cholesterol in the liver and from microbiota-driven biotransformation in the colon. In the gut, BA play a key role in fat digestion and absorption and act as potent signaling molecules on the nuclear farnesoid X receptor (FXR) and membrane-associated G protein-coupled BA receptor-1 (GPBAR-1). BA are, therefore, involved in the maintenance of gut barrier integrity, gene expression, metabolic homeostasis, and microbiota profile and function. Disturbed BA homeostasis can activate pro-inflammatory pathways in the gut, while inflammatory bowel diseases (IBD) can induce gut dysbiosis and qualitative and/or quantitative changes of the BA pool. These factors contribute to impaired repair capacity of the mucosal barrier, due to chronic inflammation. A better understanding of BA-dependent mechanisms paves the way to innovative therapeutic tools by administering hydrophilic BA and FXR agonists and manipulating gut microbiota with probiotics and prebiotics. We discuss the translational value of pathophysiological and therapeutic evidence linking BA homeostasis to gut inflammation in IBD.

Interim results from an ongoing, open-label, single-arm trial of odevixibat in progressive familial intrahepatic cholestasis

Background & Aims

PEDFIC 2, an ongoing, open-label, 72-week study, evaluates odevixibat, an ileal bile acid transporter inhibitor, in patients with progressive familial intrahepatic cholestasis.

Methods

PEDFIC 2 enrolled and dosed 69 patients across two cohorts; all received odevixibat 120 μg/kg per day. Cohort 1 comprised children from PEDFIC 1, and cohort 2 comprised new patients (any age). We report data through 15 July 2020, with Week 24 of PEDFIC 2 the main time point analysed. This represents up to 48 weeks of cumulative exposure for patients treated with odevixibat from the 24-week PEDFIC 1 study (cohort 1A) and up to 24 weeks of treatment for those who initiated odevixibat in PEDFIC 2 (patients who received placebo in PEDFIC 1 [cohort 1B] or cohort 2 patients). Primary endpoints for this prespecified interim analysis were change from baseline to Weeks 22-24 in serum bile acids (sBAs) and proportion of positive pruritus assessments (≥1-point drop from PEDFIC 2 baseline in pruritus on a 0-4 scale or score ≤1) over the 24-week period. Safety monitoring included evaluating treatment-emergent adverse events (TEAEs).

Results

In cohort 1A, mean change from PEDFIC 1 baseline to Weeks 22-24 of PEDFIC 2 in sBAs was -201 μmol/L (p <0.0001). For cohort 1B and cohort 2, mean changes from odevixibat initiation to weeks 22-24 in sBAs were -144 and -104 μmol/L, respectively. The proportion of positive pruritus assessments in the first 24-week period of PEDFIC 2 was 33%, 56%, and 62% in cohorts 1A, 1B, and 2, respectively. Most TEAEs were mild or moderate. No drug-related serious TEAEs occurred.

Conclusions

Odevixibat in patients with progressive familial intrahepatic cholestasis was generally well tolerated and associated with sustained reductions in sBAs and pruritus.

Clinical Trials Registration

This study is registered at ClinicalTrials.gov (NCT03659916).

Impact and Implications

Disrupted bile flow is a hallmark feature of patients with progressive familial intrahepatic cholestasis and can result in build-up of bile constituents in the liver with spill over into the bloodstream; other effects that patients can experience include extremely itchy skin, and because not enough bile reaches the gut, patients can have problems digesting food, which may lead to poor growth. Odevixibat is an orally administered medication that shunts bile acids away from the liver. The current study, called PEDFIC 2, suggested that odevixibat can improve the problematic signs and symptoms of progressive familial intrahepatic cholestasis and was generally safe for patients.

A comprehensive perspective on the disposition, metabolism, and pharmacokinetics of representative multi-components of Dengzhan Shengmai in rats with chronic cerebral hypoperfusion after oral administration

ETHNOPHARMACOLOGICAL RELEVANCE

Dengzhan Shengmai capsule (DZSM), an evidence-based Chinese medicine comprising Erigeron breviscapus (Vaniot) Hand. -Mazz., Panax ginseng C.A.Mey., Ophiopogon japonicus (Thunb.) Ker Gawl., and Schisandra chinensis (Turcz.) Baill., exhibits an excellent efficacy in treating cardio- and cerebrovascular diseases. It contains caffeoyl compounds, flavonoids, saponins, and lignans as primary active components. However, so far, the characteristics of disposition, metabolism, and pharmacokinetics of its active components remain mostly unclear.

AIM OF STUDY

To elucidate disposition, metabolism, and pharmacokinetics of representative components of DZSM in rats with chronic cerebral hypoperfusion (CCH) by integrating ex vivo and in situ approaches.

MATERIALS AND METHODS

Exposure and distribution of absorbed prototypes and their metabolites were comprehensively investigated using sensitive LC-MS/MS and high-resolution LC-Q-TOF/MS. Pharmacokinetics of representative 16 components (12 prototypes and 4 metabolites) with different chemical categories, relatively high in vivo levels, wide tissue distribution, and reported neuroprotective activities were profiled. The ex vivo everted gut sac and in situ linked-rat models were adopted.

RESULTS

Representative 12 prototypes including 6 caffeoyl compounds (CA, 5-CQA, 3-CQA, 4-CQA, 1,3-CQA, and 3,4-CQA), 1 flavonoid (Scu), 2 saponins (Rd and Rg2), and 3 lignans (SchA, SchB, and SolA) presented characteristic absorption, disposition, and pharmacokinetics profiles in CCH rats. The caffeoyl compounds and flavonoid were well absorbed, exhibited wide distribution, and underwent extensive intestinal metabolism, such as methylation, isomerization, and sulfoconjugation. For CA, 5-CQA, Scu, and 4 related metabolites, the enterohepatic circulation was observed and resulted in bimodal or multimodal pharmacokinetic profiles. Saponins showed relatively low systemic exposure and limited distribution. The PPD-type ginsenoside Rd exhibited longer elimination half-life and systemic circulation than the PPT-type ginsenoside Rg2. No enterohepatic circulation was observed regarding saponins, suggesting that the multimodal pharmacokinetic profile of Rd could be due to its multi-site intestinal absorption. Lignans presented a low in vivo exposure and broad distribution. They were mainly transformed into hydroxylated metabolites. Corresponding to its bimodal pharmacokinetic profile, one metabolite of lignans completed the enterohepatic cycle.

CONCLUSION

The disposition, metabolism, and pharmacokinetic profiles of representative active components of DZSM were comprehensively characterized and elucidated.

Development of a population pharmacokinetic model and optimal dosing regimen of leflunomide in Korean population

PURPOSE

Leflunomide is an immunosuppressive drug indicated for the treatment of rheumatoid arthritis (RA). While the pharmacokinetics (PK) of its active metabolite A771726 reportedly show large interindividual variability, no efficient dose individualization strategy is currently available. The goal of this work was to develop a population PK model for A771726 and propose an optimal individualized dosing strategy.

METHODS

A771726 plasma concentration data were collected from 50 healthy male volunteers participating in two leflunomide PK studies given a single oral dose of 40 mg. Concentrations were elevated in low body weight (WT) subjects and showed multiple peaks. Thus, A771726 PK modeling was conducted incorporating allometry scaling and enterohepatic circulation (EHC). For dose optimization, simulating a set of 1000 virtual subjects from the developed model and dividing the subjects into 5 groups with WT of 50, 60, 70, 80, 90 kg, respectively, the optimal dose was explored that achieves the drug concentration most similar to the target, which was defined as the concentration for the 70 kg subject treated with the current standard dosage regimen (the loading dose of 100 mg QD for 3 days, followed by the maintenance dose of 20 mg QD).

RESULTS

The data were best described by a two compartment model with first order absorption incorporating EHC with the bile released into the intestine. None of the covariates tested was found to be significant other than WT used in allometry. Simulation showed that the optimal loading dose increased by 15 mg for every 10 kg increment in WT while the optimal maintenance dose was 15 and 25 mg for 50 and 90 kg groups, respectively, and the same (= 20 mg) for the others. Large concentration differences from the target observed in low and high WT groups disappeared when optimal doses were given.

CONCLUSIONS

This work demonstrates the importance of a population PK model-based dose optimization approach in maintaining drug therapeutic concentrations in leflunomide treatment.

First evidence of neonicotinoid insecticides in human bile and associated hepatotoxicity risk

Neonicotinoids (NEOs) are widely applied in agricultural lands and are widespread in different environments, accelerating threats to ecosystems and human health. A number of in vitro/in vivo studies have reported adverse effects of NEOs on mammalian health, but the link between NEO exposure and toxic effects on human liver remains unclear. We randomly recruited 201 participants and quantified eight commercialized NEOs in bile. High frequency and concentration of detection indicate low degradation of human liver on NEOs. The main NEOs are nitenpyram and dinotefuran, which contribute to about 86% of the total residual levels of eight NEOs, due to the highest solubility in bile and are not degraded easily in liver. In contrast, imidacloprid and thiacloprid are major compounds in human blood, according to previous studies, suggesting that individual NEOs behave differently in blood and bile distribution. There was no statistical difference in NEO residues between cancer and non-cancer participants and among the different participant demographics (e.g., age, gender, and body mass index). The serum hematological parameters -bile acid, total bilirubin, cholesterol and alkaline phosphatase -were positively correlated with individual NEO concentrations, suggesting that NEO exposure affects liver metabolism and even enterohepatic circulation. The study first examined the NEO residues in human bile and provided new insights into their bioavailability and hepatoxicity risk.

Disruption of Enterohepatic Circulation of Bile Acids Ameliorates Small Bowel Resection Associated Hepatic Injury

BACKGROUND

Massive small bowel resection (SBR) is associated with liver injury and fibrosis. Efforts to elucidate the driving force behind hepatic injury have identified multiple factors, including the generation of toxic bile acid metabolites.

METHODS

Sham, 50% proximal, and 50% distal SBR were carried out in C57BL/6 mice to determine the effect of jejunal (proximal SBR) versus ileocecal resection (distal SBR) on bile acid metabolism and liver injury. Tissues were harvested at 2 and 10-week postoperative timepoints.

RESULTS

When compared with 50% proximal SBR, mice that underwent distal SBR exhibited less hepatic oxidative stress as verified by decreased mRNA expression of tumor necrosis factor-α (TNFα, p ≤ 0.0001), nicotinamide adenine dinucleotide phosphate oxidase (NOX, p ≤ 0.0001), and glutathione synthetase (GSS, p ≤ 0.05). Distal SBR mice also exhibited a more hydrophilic bile acid profile with reduced abundance of insoluble bile acids (cholic acid (CA), taurodeoxycholic acid (TCA), and taurolithocholic acid (TLCA)), and increased abundance of soluble bile acids (tauroursodeoxycholic acid (TUDCA)). In contrast with proximal SBR, ileocecal resection alters enterohepatic circulation leading to reduced oxidative stress and promotes physiological bile acid metabolism.

CONCLUSION

These findings challenge the notion that preservation of the ileocecal region is beneficial in patients with short bowel syndrome. Administration of selected bile acids may present potential therapy to mitigate resection-associated liver injury.

LEVEL OF EVIDENCE

III-Case-Control Study.

Novel nitroxide-bile acid conjugates inform substrate requirements for human bile acid transporters

Transport of bile acids within the enterohepatic circulation from the liver to the intestines via the gallbladder and back to the liver via the portal vein plays a critical role in bile acid regulation and homeostasis. Deficiency of fibroblast growth factor 19 (FGF19), a hormone whose role is to suppress de novo hepatic bile acid synthesis to maintain homeostatic levels, results in bile acid diarrhea (BAD). FGF19 also modulates gallbladder motility so that bile acids are concentrated in the gallbladder until postprandial contraction. To assess bile acid transport and diagnose ailments like BAD that are associated with altered bile acid synthesis and transport, we created bile acid conjugates with nitroxide radicals. Because nitroxides are paramagnetic and can promote proton relaxation, we reasoned that these paramagnetic conjugates should act as contrast agents in in vivo magnetic resonance imaging (MRI). We tested substrate capability by assessing the inhibitory potential of these novel agents against taurocholate uptake by the apical sodium dependent bile acid transporter (ASBT) and the Na⁺/taurocholate cotransporting polypeptide (NTCP). Surprisingly, neither the paramagnetic compounds CA-Px-1 and CA-Px-2, nor their reduced forms, CA-Px-1H and CA-Px-2H, inhibited hASBT- or hNTCP-mediated taurocholate uptake. Therefore, the new conjugates cannot serve as contrast agents for MRI in vivo. However, our findings identify important structural constraints of transportable bile acid conjugates and suggest potential modifications to overcome these limitations.

New insights into the bile acid-based regulatory mechanisms and therapeutic perspectives in alcohol-related liver disease

Cholestasis is a key causative factor in alcohol-related liver disease (ALD) and variable degrees of cholestasis occur in all stages of ALD. However, the pathogenetic mechanisms and biomarkers associated with cholestasis are not well characterized. Cholestatic disease is marked by the disruption of bile acids (BA) transport and homeostasis. Consequently, in both human and experimental ALD, the disease shows a direct correlation with an imbalance in BA equilibrium, which in turn may also affect the severity of the disease. Modulation of BA metabolism or signaling pathways is increasingly considered as a potential therapeutic strategy for ALD in humans. In this paper, we highlight the key advances made in the past two decades in characterizing the molecular regulatory mechanisms of BA synthesis, enterohepatic circulation, and BA homeostasis. We summarize recent insights into the nature of the linkage between BA dysregulation and ALD, including the abnormal expression of genes involved in BA metabolism, abnormal changes in receptors that regulate BA metabolism, and disturbance in the gut flora engaged in BA metabolism caused by alcohol consumption. Additionally, we provide novel perspectives on the changes in BAs in various stages of ALD. Finally, we propose potential pharmacological therapies for ALD targeting BA metabolism and signaling.

A simple and sensitive HPLC-FL method for bioanalysis of velpatasvir, a novel hepatitis C virus NS5A inhibitor, in rat plasma: Investigation of factors determining its oral bioavailability

Velpatasvir is a novel inhibitor of hepatitis C virus nonstructural protein 5A that received US Food and Drug Administration approval for the treatment of patients with chronic hepatitis C virus genotypes 1-6. In the present study, a sensitive bioanalytical method for velpatasvir was developed using high-performance liquid chromatography coupled with a fluorescence detector system, which was applied to elucidate the factors determining the oral bioavailability and disposition of velpatasvir. This method offered sufficient sensitivity, with a lower limit of quantification of 0.5 ng/mL, which is comparable to previously reported methods using liquid chromatography coupled with tandem mass spectrometry. Velpatasvir exhibited low oral bioavailability, moderate intestinal permeability, and significant biliary excretion in rats. It was also found to be significantly metabolized in the liver, with a low-to-moderate extraction ratio; however, its intestinal metabolism and enterohepatic circulation did not occur. Thus, our present results demonstrate that the oral bioavailability of velpatasvir is primarily dependent on gut absorption and hepatic first-pass metabolism. The fractions of velpatasvir dose unabsorbed from the gut and eliminated by the liver before reaching the systemic circulation following oral administration were estimated to be 32.8%-58.6% and 4.74%-30.54% of the oral dose, respectively. To our knowledge, this is the first systematic study to investigate the contributory roles of biopharmaceutical and pharmacokinetic factors on the oral bioavailability of velpatasvir, together with a new bioanalytical method for velpatasvir.

Taurocholic acid, a primary 12α-hydroxylated bile acid, induces leakiness in the distal small intestine in rats

A high-fat diet increases 12α-hydroxylated (12αOH) bile acid (BA) secretion in rats, and secondary BAs are responsible for the leaky gut. This study aimed to examine the role of primary 12αOH BAs in gut barrier impairment in rats using dietary cholic acid (CA) supplementation (0.5 g/kg diet). The CA diet increased the 12αOH BAs concentrations in the small and large intestine, accompanied by gut barrier impairment. Based on the luminal 12αOH BAs concentrations, ex vivo gut leakiness was determined. Deoxycholic acid increased permeability in the large intestine, whereas taurocholic acid (TCA) increased the ileal permeability, but not jejunal permeability. A Rho kinase inhibitor attenuated TCA-induced ileal permeability. Administration of vancomycin, which abolishes secondary BAs, did not influence the gut leakiness induced by the CA diet. Changes in the gut permeation marker in the tail vein blood suggested the possibility that the CA-induced leakiness occurred in the small intestine. The CA diet enhanced the phosphorylation of myosin light chain 2 and reduced claudins expressions in rat ileal epithelia. Reductions in barrier function-related genes were observed in the ileum, but not in the colon of the CA-fed rats. Overall, the present study demonstrated the significance of TCA in proximal gut leakiness.

Impact of route-dependent phase-II gut metabolism and enterohepatic circulation on the bioavailability and systemic disposition of resveratrol in rats and humans: A comprehensive whole body physiologically-based pharmacokinetic modeling

Resveratrol, a natural polyphenolic phytoalexin, is a dietary supplement that improves the outcomes of metabolic, cardiovascular, and other age-related diseases due to its diverse pharmacological activities. Although there have been several preclinical and clinical investigations of resveratrol, the contributions of gut phase-II metabolism and enterohepatic circulation to the oral bioavailability and pharmacokinetics of resveratrol remain unclear. Furthermore, a physiologically-based pharmacokinetic (PBPK) model that accurately describes and predicts the systemic exposure profiles of resveratrol in clinical settings has not been developed. Experimental data were acquired from several perspectives, including in vitro protein binding and blood distribution, in vitro tissue S9 metabolism, in situ intestinal perfusion, and in vivo pharmacokinetics and excretion studies. Using these datasets, an in-house whole-body PBPK model incorporating route-dependent phase-II (glucuronidation and sulfation) gut metabolism and enterohepatic circulation processes was constructed and optimized for chemical-specific parameters. The developed PBPK model aligned with the observed systemic exposure profiles of resveratrol in single and multiple dosing regimens with an acceptable accuracy of 0.538-0.999-fold errors. Furthermore, the model simulations elucidated the substantial contribution of gut first-pass metabolism to the oral bioavailability of resveratrol and suggested differential effects of enterohepatic circulation on the systemic exposure of resveratrol between rats and humans. After partial modification and verification, our proposed PBPK model would be valuable to optimize dosage regimens and predict food-drug interactions with resveratrol-based natural products in various clinical scenarios.

Dietary raffinose ameliorates hepatic lipid accumulation induced by cholic acid via modulation of enterohepatic bile acid circulation in rats

Enterohepatic circulation of 12α-hydroxylated (12αOH) bile acid (BA) is enhanced depending on the energy intake in high-fat diet-fed rats. Such BA metabolism can be reproduced using a diet supplemented with cholic acid (CA), which also induces simple steatosis, without inflammation and fibrosis, accompanied by some other symptoms that are frequently observed in the condition of non-alcoholic fatty liver in rats. We investigated whether supplementation of the diet with raffinose (Raf) improves hepatic lipid accumulation induced by the CA-fed condition in rats. After acclimation to the AIN-93-based control diet, male Wistar rats were fed diets supplemented with a combination of Raf (30 g/kg diet) and/or CA (0·5 g/kg diet) for 4 weeks. Dietary Raf normalised hepatic TAG levels (two-way ANOVA P < 0·001 for CA, P = 0·02 for Raf and P = 0·004 for interaction) in the CA-supplemented diet-fed rats. Dietary Raf supplementation reduced hepatic 12αOH BA concentration (two-way ANOVA P < 0·001 for CA, P = 0·003 for Raf and P = 0·03 for interaction). The concentration of 12αOH BA was reduced in the aortic and portal plasma. Raf supplementation increased acetic acid concentration in the caecal contents (two-way ANOVA P = 0·001 as a main effect). Multiple regression analysis revealed that concentrations of aortic 12αOH BA and caecal acetic acid could serve as predictors of hepatic TAG concentration (R² = 0·55, P < 0·001). However, Raf did not decrease the secondary 12αOH BA concentration in the caecal contents as well as the transaminase activity in the CA diet-fed rats. These results imply that dietary Raf normalises hepatic lipid accumulation via suppression of enterohepatic 12αOH BA circulation.

Dihydroartemisinin improves hypercholesterolemia in ovariectomized mice via enhancing vectorial transport of cholesterol and bile acids from blood to bile

The increase of concentrations of total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) in the serum of postmenopausal women is the important risk factor of the high morbidity of cardiovascular diseases of old women worldwide. To test the anti-hypercholesterolemia function of dihydroartemisinin (DHA) in postmenopausal women, ovariectomized (OVX) mice were generated, and DHA were administrated to OVX mice for 4 weeks. The blood and liver tissues were collected for biochemical and histological tests respectively. The mRNA and protein expression levels of genes related to metabolism and transport of cholesterol, bile acid and fatty acid in the liver or ileum were checked through qPCR and western blot. DHA could significantly reduce the high concentrations of TC and LDL-C in the serum and the lipid accumulation in the liver of ovariectomized mice. The expression of ABCG5/8 was reduced in liver of OVX mice, and DHA could up-regulate the expression of them. Genes of transport proteins for bile salt transport from blood to bile, including Slc10a1, Slco1b2 and Abcb11, were also significantly up-regulated by DHA. DHA also down-regulated the expression of Slc10a2 in the ileum of OVX mice to reduce the absorption of bile salts. Genes required for fatty acid synthesis and uptake, such as Fasn and CD36, were reduced in the liver of OVX mice, and DHA administration could significantly up-regulate the expression of them. These results demonstrated that DHA could improve hypercholesterolemia in OVX mice through enhancing the vectorial transport of cholesterol and bile acid from blood to bile.

Scintigraphic patterns and analysis of their association with the diagnosis of bile acid malabsorption

OBJETIVE

To evaluate the enterohepatic circulation of 75-Selenium turoselecolic acid (⁷⁵Se-SeHCAT) during the first 3 h and its correlation with the abdominal retention at the 7th day (AR₇), as contribution to the clinical study of biliar acid malabsorption (BAM).

MATERIALS AND METHODS

38 patients with chronic diarrhea were retrospectively studied. Acquisition protocol included static abdominal images at 1st, 2nd and 3rd hour and the 7th day after oral administration of the radiopharmaceutical. Images of 1-3 h determined 5 patterns of enterohepatic circulation that, due to their location, were characterized as: 1) gallbladder 2-3 h, 2) gallbladder 3 h, 3) gallbladder-abdomen 2-3 h, 4) abdomen, 5) upper left abdomen. The association of these patterns with the AR₇ (Fisher, STATA) were investigated. Patients were classified as Non BAM (AR₇ > 15%), mild-BAM (AR₇ 15-10%), moderate-BAM (AR₇ 10-5%) or severe-BAM (AR₇ < 5%).

RESULTS

19 patients had an AR₇ diagnostic of BAM (7 mild-BAM, 5 moderate-BAM, 7 severe-BAM). The pattern "gallbladder at 2-3 h" was statistically associated with Non BAM (p 0,008), while "gallbladder-abdomen at 2-3 h" was correlated with having BAM (p 0,029).

CONCLUSION

Variations detected at the abdominal level in images during the first 3 h were associated with changes in intestinal absorption and the incorporation of the radiopharmaceutical into the pool of bile acids, so visual interpretation of the images at 2nd and 3rd hour could be useful in the final assessment of the study.

Scintigraphic patterns and análisis of its association with the diagnosis of bile acid malabsorption

OBJETIVE

To evaluate the enterohepatic circulation of 75-Selenium turoselecolic acid (75Se-SeHCAT) during the first 3 hours and its correlation with the abdominal retention at the 7th day (AR7), as contribution to the clinical study of biliar acid malabsorption (BAM).

MATERIALS AND METHODS

38 patients with chronic diarrhea were retrospectively studied. Acquisition protocol included static abdominal images at 1st, 2nd and 3rd hour and the 7th day after oral administration of the radiopharmaceutical. Images of 1 to 3 hours determined 5 patterns of enterohepatic circulation that, due to their location, were characterized as: 1) gallbladder 2-3 hours, 2) gallbladder 3 hours, 3) gallbladder-abdomen 2-3 hours, 4) abdomen, 5) upper left abdomen. The association of these patterns with the AR7 (Fisher, STATA) were investigated. Patients were classified as Non BAM (AR7>15%), mild-BAM (AR7: 15-10%), moderate-BAM (AR7: 10-5%) or severe-BAM (AR7<5%).

RESULTS

19 patients had an AR7 diagnostic of BAM (7 mild-BAM, 5 moderate-BAM, 7 severe-BAM). The pattern "gallbladder at 2-3 hours" was statistically associated with Non BAM (p 0,008), while "gallbladder-abdomen at 2-3 hours" was correlated with having BAM (p 0,029).

CONCLUSION

Variations detected at the abdominal level in images during the first 3 hours were associated with changes in intestinal absorption and the incorporation of the radiopharmaceutical into the pool of bile acids, so visual interpretation of the images at 2nd and 3rd hour could be useful in the final assessment of the study.

The selective PPAR-delta agonist seladelpar reduces ethanol-induced liver disease by restoring gut barrier function and bile acid homeostasis in mice

Alcohol-associated liver disease is accompanied by dysregulation of bile acid metabolism and gut barrier dysfunction. Peroxisome proliferator-activated receptor-delta (PPARδ) agonists are key metabolic regulators and have anti-inflammatory properties. Here, we evaluated the effect of the selective PPAR-delta agonist seladelpar (MBX-8025) on gut barrier function and bile acid metabolism in a mouse model of ethanol-induced liver disease. Wild type C57BL/6 mice were fed LieberDeCarli diet containing 0%-36% ethanol (caloric) for 8 weeks followed by a single binge of ethanol (5 g/kg). Pair fed mice received an isocaloric liquid diet as control. MBX-8025 (10 mg/kg/d) or vehicle were added to the liquid diet during the entire feeding period (prevention), or during the last 4 weeks of Lieber DeCarli diet feeding (intervention). In both prevention and intervention trials, MBX-8025 protected mice from ethanol-induced liver disease, characterized by lower serum alanine aminotransferase (ALT) levels, hepatic triglycerides, and inflammation. Chronic ethanol intake disrupted bile acid metabolism by increasing the total bile acid pool and serum bile acids. MBX-8025 reduced serum total and secondary bile acids, and the total bile acid pool as compared with vehicle treatment in both prevention and intervention trials. MBX-8025 restored ethanol-induced gut dysbiosis and gut barrier dysfunction. Data from this study demonstrates that seladelpar prevents and treats ethanol-induced liver damage in mice by direct PPARδ agonism in both the liver and the intestine.

Enterohepatic circulation of bile acids and their emerging roles on glucolipid metabolism

Bile acids (BAs) are amphiphilic molecules with a nonpolar steroid carbon skeleton and a polar carboxylate side chain. Recently, BAs have aroused the attention of scholars due to their potential roles on metabolic diseases. As important endogenous ligands, BAs are wildly active in the enterohepatic circulation, during which microbiota play a significant role in promoting the hydrolysis and dehydroxylation of BAs. Besides, many pathways initiated by BAs including glucolipid metabolism and inflammation signaling pathways have been reported to regulate the host metabolism and maintain immune homeostasis. Herein, the characteristics on the enterohepatic circulation and metabolism of BAs are systematically summarized. Moreover, the regulation mechanism of the glucolipid metabolism by BAs is intensively discussed. Worthily, FXR and TGR5, which are involved in glucolipid metabolism, are the prime candidates for targeted therapies of chronic metabolic diseases such as diabetes and hypercholesterolemia.

Role of n-3 Fatty Acids on Bile Acid Metabolism and Transport in Dyslipidemia: A Review

Dietary n-3 fatty acids, especially of marine origin, eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3), have always been lauded for their profound effects on regulating the risk factors for major metabolic disorders. Yet, their consumption rate is poor compared to n-6 fatty acids [linoleic acid (18:2n-6)], which are predominantly consumed. Hence, the skewed n-6 to n-3 fatty acid ratio may have a bearing on the risk factors of various diseases, including dyslipidemia. Dyslipidemia and other lifestyle diseases associated with it, such as diabetes, obesity, hypertension, are a growing concern in both developed and developing countries. A common strategy for addressing dyslipidemia involves bile acid (BA) sequestration, to interrupt the enterohepatic circulation of BA, resulting in the modulation of lipid absorption in the intestine, thereby normalizing the levels of circulating lipids. The BA homeostasis is under the tight control of hepatic and enteric BA transporters. Many investigations have reported the effects of dietary constituents, including certain fatty acids on the reabsorption and transport of BA. However, a critical review of the effects of n-3 fatty acids on BA metabolism and transport is not available. The present review attempts to explore certain unmapped facets of the n-3 fatty acids on BA metabolism and transport in dyslipidemia, and their interplay with biological processes involving lipid rafts and gut microbiome.

ASBT(SLC10A2): A promising target for treatment of diseases and drug discovery

Bile acids has gradually become a new focus in various diseases, and ASBT as a transporter responsible for the reabsorption of ileal bile acids, is a key hinge associated to the bile acids-cholesterol balance and bile acids of enterohepatic circulation. The cumulative studies have also shown that ASBT is a promising target for treatment of liver, gallbladder, intestinal and metabolic diseases. This article briefly reviewed the process of bile acids enterohepatic circulation, as well as the regulations of ASBT expression, covering transcription factors, nuclear receptors and gut microbiota. In addition, the relationship between ASBT and various diseases were discussed in this paper. According to the structural classification of ASBT inhibitors, the research status of ASBT inhibitors and potential ASBT inhibitors of traditional Chinese medicine (such resveratrol, jatrorrhizine in Coptis chinensis) were summarized. This review provides a basis for the development of ASBT inhibitors and the treatment strategy of related diseases.

Bile acid transporter-mediated oral drug delivery

Bile acids are synthesized in the liver, stored in the gallbladder, and secreted into the duodenum at meals. Apical sodium-dependent bile acid transporter (ASBT), an ileal Na⁺-dependent transporter, plays the leading role of bile acid absorption into enterocytes, where bile acids are delivered to basolateral side by ileal bile acid binding protein (IBABP) and then released by organic solute transporter OSTα/β. The absorbed bile acids are delivered to the liver via portal vein. In this process called "enterohepatic recycling", only 5% of the bile acid pool (~3 g in human) is excreted in feces, indicating the large recycling capacity and high transport efficacy of ASBT-mediated absorption. Therefore, bile acid transporter-mediated oral drug delivery has been regarded as a feasible and potential strategy to improve the oral bioavailability. This review introduces the key factors in enterohepatic recycling, especially the mechanism of bile acid uptake by ASBT, and the development of bile acid-based oral drug delivery for ASBT-targeting, including bile acid-based prodrugs, bile acid/drug electrostatic complexation and bile acid-containing nanocarriers. Furthermore, the specific transport pathways of bile acid in enterocytes are described and the recent finding of lymphatic delivery of bile acid-containing nanocarriers is discussed.

Ileal bile acid transporter inhibition as an anticholestatic therapeutic target in biliary atresia and other cholestatic disorders

Biliary atresia is a rare cholestatic liver disease that presents in infants and rapidly advances to death in the absence of intervention. As a result of blockage or destruction of the biliary tract, bile acids accumulate and drive inflammation, fibrosis, and disease progression. The standard of care, Kasai portoenterostomy (KPE), is typically performed shortly after diagnosis (currently at ~ 2 months of age) and aims to restore bile flow and relieve cholestasis. Nevertheless, most patients continue to experience liver injury from accumulation of bile acids after KPE, since there are no known effective therapeutics that may enhance survival after KPE. Improving cholestasis via interruption of the enterohepatic circulation of bile acids may directly attenuate hepatic bile acid retention and reduce the risk of early organ failure. Directly addressing intrahepatic accretion of bile acids to avoid inherent bile acid toxicities provides an attractive and plausible therapeutic target for biliary atresia. This review explores the novel therapeutic concept of inhibiting the sole ileal bile acid transporter (IBAT), also known as ASBT (apical sodium-bile acid transporter, encoded by SLC10A2), as a means to reduce hepatic bile acid concentration after KPE. By reducing return of bile acids to the cholestatic liver, IBAT inhibitors may potentially lessen or delay liver damage associated with the hepatotoxicity and cholangiopathy of bile acid accumulation. The clinical programs of 2 IBAT inhibitors in development for the treatment of pediatric cholestatic liver diseases, maralixibat and odevixibat, are highlighted.

Gender differences in the bile acid profiles of APP/PS1 transgenic AD mice

Alzheimer's disease (AD) is a neurodegenerative disease and presents in the accumulation of amyloid and neurofibrillary tangle. The association between modulations of gut symbiotic microbes with neurological disease via bidirectional gut-brain axis has been well documented. Bile acid (BA) pools in the enterohepatic circulation could be valuable for probing complex biochemical interactions between host and their symbiotic microbiota. Herein we investigated the levels of 28 BAs in several compartments in enterohepatic circulation (including jejunal, ileum, cecum, colon and feces, plasma and liver tissue) by employing an APP/PS1 induced transgenic AD mouse model. We found that BA profiles in AD mice were gender specific. We observed decreased levels of taurine-conjugated primary BAs (TUDCA, TCA, T-α-MCA and T-β-MCA) and increased levels of secondary BA (iso-DCA) in plasma and liver extracts for female AD transgenic mice. In contrast, increased levels of TDCA in liver extracts and decreased levels of T-β-MCA in jejunal content were noted in male AD mice. These observations suggested that perturbations of BA profiles in AD mice displayed clear gender variations. Our study highlighted the roles of gut microbiota on neurodegenerative disease, which could be gender specific.

Efficacy of oral agar in management of indirect hyperbilirubinemia in full-term neonates

Aim: This prospective randomized case control study aimed to investigate effect of oral agar administration in reducing total serum bilirubin (TSB) levels in full-term neonates with jaundice in comparison with control.Materials and methods: One hundred sixty full-term neonates were enrolled with TSB 10-19 mg/dl at first week of age from Assiut University Children's Hospital. Neonates were divided according to TSB into outpatient group (n = 100) (TSB 10-15 mg/dl) and admitted group (n = 60) (TSB > 15-19 mg/dl). Outpatients group were subdivided into agar group received oral agar and control group received placebo. Admitted group were subdivided into agar group received oral agar plus phototherapy combination and control group received phototherapy alone. Neonates in the agar supplementation received oral agar 600 mg/kg/day dissolved in 10 ml distilled water twice daily till TSB decreased to 7 mg/dl. Daily weight, stool frequency and side effects of treatment were observed for each group. TSB was determined pretreatment then serially every 48 h until TSB level reaching ≤7 mg/dl.Results: Agar fed was effective in lowering TSB in neonates with TSB 10-15 mg/dl. TSB percentage changes were not significantly lower in agar-fed newborn with TSB >15-19 mg/dl compared with control groups after 24 h and 7 days. Age fed shortened the time required to decrease TSB and increased stooling frequency.Conclusions: Oral agar supplemented feeding at 600 mg/kg/day is safe for full-term neonates and useful in decreasing TSB and phototherapy duration. The efficacy of phototherapy in decreasing TSB level in neonatal hyperbilirubinemia can be augmented with oral agar usage.

Correlation between 12α-hydroxylated bile acids and insulin secretion during glucose tolerance tests in rats fed a high-fat and high-sucrose diet

Background

Previously, we found a significant relationship in a rat study between energy intake and bile acid (BA) metabolism especially 12α-hydroxylated (12αOH) BAs. The present study was designed to reveal relationships among BA metabolism, glucose tolerance, and cecal organic acids in rats fed a high-fat and high-sucrose diet (HFS) by using multivariate and multiple regression analyses in two types of glucose tolerance tests (GTTs).

Methods

Male WKAH/HkmSlc rats were fed with a control or a HFS for 13 weeks. Oral glucose tolerance test (OGTT) and intraperitoneal glucose tolerance test (IPGTT) were performed at week 9 and 11, respectively. BAs were analyzed by using ultra high-performance liquid chromatography-mass spectrometry. Organic acid concentrations in cecal contents were analyzed by using ultra high-performance liquid chromatography with post-column pH buffered electric conductivity method.

Results

A positive correlation of aortic 12αOH BA concentration was observed with energy intake and visceral adipose tissue weight. We found that an increase of 12αOH BAs in enterohepatic circulation, intestinal contents and feces in the HFS-fed rats compared to those in control rats regardless of no significant increase of total BA concentration in the feces in the test period. Fecal 12αOH BA concentration was positively correlated with maximal insulin level in OGTT and area under curve of insulin in IPGTT. There was a positive correlation between aortic 12αOH BAs concentration and changes in plasma glucose level in both OGTT and IPGTT. In contrast, a decrease in the concentration of organic acids was observed in the cecal contents of the HFS-fed rats. Multiple linear regression analysis in the IPGTT revealed that the concentrations of aortic 12αOH BA and cecal acetic acid were the predictors of insulin secretion. Moreover, there was a positive correlation between concentration of portal 12αOH BAs and change in insulin concentration of peripheral blood in the IPGTT.

Conclusion

The distribution analysis of BA compositions accompanied by GTTs revealed a close relationship between 12αOH BA metabolism and insulin secretion in GTTs in rats.

The gut microbiome: an orchestrator of xenobiotic metabolism

Microbes inhabiting the intestinal tract of humans represent a site for xenobiotic metabolism. The gut microbiome, the collection of microorganisms in the gastrointestinal tract, can alter the metabolic outcome of pharmaceuticals, environmental toxicants, and heavy metals, thereby changing their pharmacokinetics. Direct chemical modification of xenobiotics by the gut microbiome, either through the intestinal tract or re-entering the gut via enterohepatic circulation, can lead to increased metabolism or bioactivation, depending on the enzymatic activity within the microbial niche. Unique enzymes encoded within the microbiome include those that reverse the modifications imparted by host detoxification pathways. Additionally, the microbiome can limit xenobiotic absorption in the small intestine by increasing the expression of cell-cell adhesion proteins, supporting the protective mucosal layer, and/or directly sequestering chemicals. Lastly, host gene expression is regulated by the microbiome, including CYP450s, multi-drug resistance proteins, and the transcription factors that regulate them. While the microbiome affects the host and pharmacokinetics of the xenobiotic, xenobiotics can also influence the viability and metabolism of the microbiome. Our understanding of the complex interconnectedness between host, microbiome, and metabolism will advance with new modeling systems, technology development and refinement, and mechanistic studies focused on the contribution of human and microbial metabolism.

Pharmacokinetics and enterohepatic circulation of jervine, an antitumor steroidal alkaloid from Veratrum nigrum in rats

Jervine, a novel steroidal alkaloid from Veratrum nigrum L., exhibits both antitumor effect and potential toxicity. The aim of study was to characterize the pharmacokinetic behaviors and enterohepatic circulation of jervine in rats. A rapid and simple ultra-high performance liquid chromatography-tandem mass spectrometric method was developed and validated for quantification of jervine and alpinetin (internal standard) in rat plasma. After extraction from rat plasma by a simple protein-precipitation method, the analyte was separated on a C₁₈ column (2.1 mm × 50 mm, 1.7 μm) using water with 0.1% formic acid and acetonitrile as the mobile phase delivered at a flow rate of 0.4 mL/min. Jervine and alpinetin were determined in the positive mode with multiple reaction monitoring (MRM) of the ion transitions at m/z 426.3 → 108.8 and m/z 271.0 → 166.9, respectively. Molecular docking method was used to investigate the binding of jervine to p-glycoprotein and dehydroepiandrosterone sulfotransferase. The method was well validated within acceptance limits including specificity, matrix effect, recovery, precision, accuracy, and stability, and was successfully applied to the pharmacokinetic study of jervine after oral and intravenous administration to rats. Jervine presented a small volume of distribution, fast absorption, high oral bioavailability, and enterohepatic circulation. The enterohepatic circulation was first observed in veratrum alkaloids, and was further investigated by molecular docking studies, which was related to the binding of jervine to p-glycoprotein and dehydroepiandrosterone sulfotransferase. The pharmacokinetic properties and enterohepatic circulation of jervine in rats provided a significant basis for the drug-drug interaction and toxicity study in the future.

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It is the first pharmacokinetic and bioavailability study of jervine in rats.

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A simple protein precipitation was used for pretreatment and the LLOQ was 0.25 ng/mL.

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The enterohepatic circulation was first observed in veratrum alkaloids.

Determination of sulfamonomethoxine in tilapia (Oreochromis niloticus × Oreochromis mossambicus) by liquid chromatography-tandem mass spectrometry and its application pharmacokinetics study

A precise and reliable analytical method to measure trace levels of sulfamonomethoxine (SMM) and N⁴-acetyl metabolite in tilapia samples using liquid chromatography-tandem mass spectrometry was developed. Optimized chromatographic separation was performed on C18 reversed-phase columns using gradient elution with methanol and 5 mmol/L of an ammonium acetate aqueous solution (adjusted to pH 3.5 using formic acid). This study investigated the pharmacokinetic properties and tissue distribution of SMM and its major metabolite N⁴-acetyl sulfamonomethoxine (AC-SMM) in tilapia after a single dose of 100 mg kg⁻¹ body weight of orally administered SMM. Blood and tissues were collected between 0.5 and 192 h with 14 total sampling time points. SMM was rapidly absorbed, and extensively distributed in the bile and liver through systemic circulation. Enterohepatic circulation of SMM was observed in the tilapia body. Acetylation percentages were 45% (blood), 90% (liver), 62% (kidney), 98% (bile), and 52% (muscle). High concentrations of AC-SMM accumulated in the tilapia bile. At 192 h, AC-SMM concentration in the bile remained at 4710 μg kg⁻¹. The k_e value of AC-SMM (0.015 h⁻¹) in the blood was lower than that of SMM (0.032 h⁻¹). This study demonstrated effective residue monitoring and determined the pharmacokinetic properties of SMM and AC-SMM in tilapia.

A 19F magnetic resonance imaging-based diagnostic test for bile acid diarrhea

In up to 50% of people diagnosed with a common ailment, diarrhea-predominant irritable bowel syndrome, diarrhea results from excess spillage of bile acids into the colon-data emerging over the past decade identified deficient release of a gut hormone, fibroblast growth factor 19 (FGF19), and a consequent lack of feedback suppression of bile acid synthesis as the most common cause. ⁷⁵Selenium homotaurocholic acid (SeHCAT) testing, considered the most sensitive and specific means of identifying individuals with bile acid diarrhea, is unavailable in many countries, including the United States. Other than SeHCAT, tests to diagnose bile acid diarrhea are cumbersome, non-specific, or insufficiently validated; clinicians commonly rely on a therapeutic trial of bile acid binders. Here, we review bile acid synthesis and transport, the pathogenesis of bile acid diarrhea, the reasons clinicians frequently overlook this disorder, including the limitations of currently available tests, and our efforts to develop a novel ¹⁹F magnetic resonance imaging (MRI)-based diagnostic approach. We created ¹⁹F-labeled bile acid analogues whose in vitro and in vivo transport mimics that of naturally occurring bile acids. Using dual ¹H/¹⁹F MRI of the gallbladders of live mice fed ¹⁹F-labeled bile acid analogues, we were able to differentiate wild-type mice from strains deficient in intestinal expression of a key bile acid transporter, the apical sodium-dependent bile acid transporter (ASBT), or FGF15, the mouse homologue of FGF19. In addition to reviewing our development of ¹⁹F-labeled bile acid analogue-MRI to diagnose bile acid diarrhea, we discuss challenges to its clinical implementation. A major limitation is the paucity of clinical MRI facilities equipped with the appropriate coil and software needed to detect ¹⁹F signals.

IVACAFTOR restores FGF19 regulated bile acid homeostasis in cystic fibrosis patients with an S1251N or a G551D gating mutation

OBJECTIVE

Disruption of the enterohepatic circulation of bile acids (BAs) is part of the gastrointestinal phenotype of cystic fibrosis (CF). Ivacaftor (VX-770), a cystic fibrosis transmembrane conductance regulator (CFTR) potentiator, improves pulmonary function in CF patients with class III gating mutations. We studied the effect of ivacaftor on the enterohepatic circulation by assessing markers of BA homeostasis and their changes in CF patients.

METHODS

In CF patients with an S1251N mutation (N = 16; age 9-35 years S125N study/NTR4873) or a G551D mutation (N = 101; age 10-24 years; GOAL study/ NCT01521338) we analyzed plasma fibroblast growth factor 19 (FGF19) and 7α-hydroxy-4-cholesten-3-one (C4) levels, surrogate markers for intestinal BA absorption and hepatic synthesis, respectively, before and after treatment with ivacaftor.

RESULTS

At baseline, median FGF19 was lower (52% and 53%, P < .001) and median C4 higher (350% and 364%, P < .001), respectively, for the S1251 N and G551D mutation patient groups compared to healthy controls. Treatment with ivacaftor significantly increased FGF19 and reduced C4 levels towards normalization in both cohorts but this did not correlate with CFTR function in other organs, as measured by sweat chloride levels or pulmonary function.

CONCLUSIONS

We demonstrate that patients with CFTR gating mutations display interruption of the enterohepatic circulation of BAs reflected by lower FGF19 and elevated C4 levels. Treatment with ivacaftor partially restored this disruption of BA homeostasis. The improvement did not correlate with established outcome measures of CF, suggesting involvement of modulating factors of CFTR correction in different organs.

Cholecystectomy and risk of metabolic syndrome

The gallbladder physiologically concentrates and stores bile during fasting and provides rhythmic bile secretion both during fasting and in the postprandial phase to solubilize dietary lipids and fat-soluble vitamins. Bile acids (BAs), major lipid components of bile, play a key role as signaling molecules in modulating gene expression related to cholesterol, BA, glucose and energy metabolism. Cholecystectomy is the most commonly performed surgical procedure worldwide in patients who develop symptoms and/or complications of cholelithiasis of any type. Cholecystectomy per se, however, might cause abnormal metabolic consequences, i.e., alterations in glucose, insulin (and insulin-resistance), lipid and lipoprotein levels, liver steatosis and the metabolic syndrome. Mechanisms are likely mediated by the abnormal transintestinal flow of BAs, producing metabolic signaling that acts without gallbladder rhythmic function and involves the BAs/farnesoid X receptor (FXR) and the BA/G protein-coupled BA receptor 1 (GPBAR-1) axes in the liver, intestine, brown adipose tissue and muscle. Alterations of intestinal microbiota leading to distorted homeostatic processes are also possible. According to this view, cholecystectomy, via BA-induced changes in the enterohepatic circulation, is a risk factor for the metabolic abnormalities and becomes another “fellow traveler” with, or another risk factor for the metabolic syndrome.

Animal models to study bile acid metabolism

The use of animal models, particularly genetically modified mice, continues to play a critical role in studying the relationship between bile acid metabolism and human liver disease. Over the past 20 years, these studies have been instrumental in elucidating the major pathways responsible for bile acid biosynthesis and enterohepatic cycling, and the molecular mechanisms regulating those pathways. This work also revealed bile acid differences between species, particularly in the composition, physicochemical properties, and signaling potential of the bile acid pool. These species differences may limit the ability to translate findings regarding bile acid-related disease processes from mice to humans. In this review, we focus primarily on mouse models and also briefly discuss dietary or surgical models commonly used to study the basic mechanisms underlying bile acid metabolism. Important phenotypic species differences in bile acid metabolism between mice and humans are highlighted.

N-(4-[18F]fluorobenzyl)cholylglycine, a novel tracer for PET of enterohepatic circulation of bile acids: Radiosynthesis and proof-of-concept studies in rats

INTRODUCTION

Enterohepatic circulation (EHC) of conjugated bile acids is an important physiological process crucial for regulation of intracellular concentrations of bile acids and their function as detergents and signal carriers. Only few bile acid-derived imaging agents have been synthesized and hitherto none have been evaluated for studies of EHC. We hypothesized that N-(4-[¹⁸F]fluorobenzyl)cholylglycine ([¹⁸F]FBCGly), a novel fluorine-18 labeled derivative of endogenous cholylglycine, would be a suitable tracer for PET of the EHC of conjugated bile acids, and we report here a radiosynthesis of [¹⁸F]FBCGly and a proof-of-concept study by PET/MR in rats.

METHODS

A radiosynthesis of [¹⁸F]FBCGly was developed based on reductive alkylation of glycine with 4-[¹⁸F]fluorobenzaldehyde followed by coupling to cholic acid. [¹⁸F]FBCGly was investigated in vivo by dynamic PET/MR in anesthetized rats; untreated or treated with cholyltaurine or rifampicin. Possible in vivo metabolites of [¹⁸F]FBCGly were investigated by analysis of blood and bile samples, and the stability of [¹⁸F]FBCGly towards enzymatic de-conjugation by Cholylglycine Hydrolase was tested in vitro.

RESULTS

[¹⁸F]FBCGly was produced with a radiochemical purity of 96% ± 1% and a non-decay corrected radiochemical yield of 1.0% ± 0.3% (mean ± SD; n = 12). PET/MR studies showed that i.v.-administrated [¹⁸F]FBCGly underwent EHC within 40-60 min with a rapid transhepatic transport from blood to bile. In untreated rats, the radioactivity concentration of [¹⁸F]FBCGly was approximately 15 times higher in bile than in liver tissue. Cholyltaurine and rifampicin inhibited the biliary secretion of [¹⁸F]FBCGly. No fluorine-18 metabolites of [¹⁸F]FBCGly were observed.

CONCLUSION

We have developed a radiosynthesis of a novel fluorine-18 labeled bile acid derivative, [¹⁸F]FBCGly, and shown by PET/MR that [¹⁸F]FBCGly undergoes continuous EHC in rats without metabolizing. This novel tracer may prove useful in PET studies on the effect of drugs or diseases on the EHC of conjugated bile acids.

Cholesterol and bile acid-mediated regulation of autophagy in fatty liver diseases and atherosclerosis

Liver is the major organ that regulates whole body cholesterol metabolism. Disrupted hepatic cholesterol homeostasis contributes to the pathogenesis of nonalcoholic steatohepatitis, dyslipidemia, atherosclerosis, and cardiovascular diseases. Hepatic bile acid synthesis is the major catabolic mechanism for cholesterol elimination from the body. Furthermore, bile acids are signaling molecules that regulate liver metabolism and inflammation. Autophagy is a highly-conserved lysosomal degradation mechanism, which plays an essential role in maintaining cellular integrity and energy homeostasis. In this review, we discuss emerging evidence linking hepatic cholesterol and bile acid metabolism to cellular autophagy activity in hepatocytes and macrophages, and how these interactions may be implicated in the pathogenesis and treatment of fatty liver disease and atherosclerosis.

"With a little help from my friends" - The role of microbiota in thyroid hormone metabolism and enterohepatic recycling

The gut microbiota is composed of over 1200 species of anaerobes and aerobes bacteria along with bacteriophages, viruses and fungal species. Increasing evidence indicates that the intestinal microbiota, beside digestive equilibrium, is also crucial for immunologic, hormonal and metabolic homeostasis. The intestinal microbiota interacts with distant organs by signals which may be part of the bacteria themselves or their metabolites. Dysbiosis has been observed in inflammatory or autoimmune disorders such as multiple sclerosis or type 1 diabetes as well as in obesity and type 2 diabetes. Functional thyroid disorders were associated with bacterial overgrowth and a different microbial composition. Although thyroid metabolism was apparently disregarded, the interference of microbiota on peripheral iodothyronine homeostasis is an intriguing issue. In this review we focused on the interactions of intestinal microbiota with thyroid-related micronutrients and with the metabolic steps of endogenous and exogenous iodothyronines.

Innovations and Improvements in Pharmacokinetic Models Based on Physiology

BACKGROUND

Accompanied by significant improvements of modeling techniques and computational methods in medical sciences, the last thirty years saw the flourishing of pharmacokinetic models for applications in the pharmacometric field. In particular, physiologically based pharmacokinetic (PBPK) models, grounded on a mechanistic foundation, have been applied to explore a multiplicity of aspects with possible applications in patient care and new drugs development, as in the case of siRNA therapies.

METHOD

This article summarizes the features we recently introduced in PBPK modeling within a threeyear research project funded by Italian Research Ministry. Four major points are detailed: (i) the mathematical formulation of the model, which allows modulating its complexity as a function of the administration route and active principle; (ii) a dedicated parameter of the PBPK model quantifies the drugprotein binding, which affects the active principle distribution; (iii) the gall bladder compartment and the bile enterohepatic circulation process; (iv) the coupling of the pharmacokinetic and pharmacodynamic models to produce an overall understanding of the drug effects on mammalian body.

RESULTS

The proposed model is applied to two separate endovenous (remifentanil) and oral (sorafenib) drug administrations. The resulting PBPK simulations are consistent with the literature experimental data. Blood concentration predictability is confirmed in multiple reference subjects. Furthermore, in case of sorafenib administration in mice, it is possible to evaluate the drug concentration in the liver and reproduce the effects of the enterohepatic circulation. Finally, a preliminary application of the coupling of the pharmacokinetic/pharmacodynamic models is presented and discussed.

The role of bile acids in nonalcoholic fatty liver disease and nonalcoholic steatohepatitis

Nonalcoholic fatty liver disease is growing in prevalence worldwide. It is marked by the presence of macrosteatosis on liver histology but is often clinically asymptomatic. However, it can progress into nonalcoholic steatohepatitis which is a more severe form of liver disease characterized by inflammation and fibrosis. Further progression leads to cirrhosis, which predisposes patients to hepatocellular carcinoma or liver failure. The mechanism by which simple steatosis progresses to steatohepatitis is not entirely clear. However, multiple pathways have been proposed. A common link amongst many of these pathways is disruption of the homeostasis of bile acids. Other than aiding in the absorption of lipids and lipid-soluble vitamins, bile acids act as ligands. For example, they bind to farnesoid X receptor, which is critically involved in many of the pathways responsible for maintaining bile acid, glucose, and lipid homeostasis. Alterations to these pathways can lead to dysregulation of energy balance and increased inflammation and fibrosis. Repeated insults over time may be the key to development of steatohepatitis. For this reason, current drug therapies target aspects of these pathways to try to reduce and halt inflammation and fibrosis. This review will focus on the role of bile acids in these various pathways and how changes in these pathways may result in steatohepatitis. While there is no approved pharmaceutical treatment for either hepatic steatosis or steatohepatitis, this review will also touch upon the multitude of potential therapies.

Preformulation investigation and challenges; salt formation, salt disproportionation and hepatic recirculation

A compound, which is a selective peroxisome proliferator activated receptor (PPAR) agonist, was investigated. The aim of the presented studies was to evaluate the potential of the further development of the compound. Fundamental physicochemical properties and stability of the compound were characterized in solution by liquid chromatography and NMR and in solid-state by various techniques. The drug itself is a lipophilic acid with tendency to form aggregates in solution. The neutral form was only obtained in amorphous form with a glass-transition temperature of approximately 0°C. The intrinsic solubility at room temperature was determined to 0.03mg/mL. Chemical stability studies of the compound in aqueous solutions showed good stability for at least two weeks at room temperature, except at pH1, where a slight degradation was already observed after one day. The chemical stability in the amorphous solid-state was investigated during a period of three months. At 25°C/60% relative humidity (RH) and 40°C/75% RH no significant degradation was observed. At 80°C, however, some degradation was observed after four weeks and approximately 3% after three months. In an accelerated photostability study, degradation of approximately 4% was observed. Attempts to identify a crystalline form of the neutral compound were unsuccessful, however, salt formation with tert-butylamine, resulted in crystalline material. Results from stability tests of the presented crystalline salt form indicated improved chemical stability at conditions whereas the amorphous neutral form degraded. However, the salt form of the drug dissociated under certain conditions. The drug was administered both per oral and intravenously, as amorphous nanoparticles, to conscious dogs. Plasma profiles showed curves with secondary absorption peaks, indicating hepatic recirculation following both administration routes. A similar behavior was observed in rats after oral administration of a pH-adjusted solution. The observed double peaks in plasma exposure and the dissociation tendency of the salt form, were properties that contributed to make further development of the candidate drug challenging. Options for development of solid dosage forms of both amorphous and crystalline material of the compound are discussed.

Role of Saccharomyces boulardii in Reduction of Neonatal Hyperbilirubinemia

INTRODUCTION

Probiotics are known to reduce the severity of hyperbilirubinemia.

AIM

This study was done to evaluate the effect of probiotic on neonatal hyperbilirubinemia in term neonates.

MATERIALS AND METHODS

A total of 181 healthy term neonates after birth were divided into a control group (n=95) and a treatment group (n=86) randomly and treated with placebo and probiotic (Saccharomyces boulardii) respectively. A total of two doses were given orally in the first two consecutive days. The serum bilirubin levels were detected on day three of life. Babies were exclusively breastfed, clinical outcome was recorded. Comparison between groups was made by the non-parametric Mann-Whitney test. Analysis of Variance (ANOVA) was used to assess the quantitative variables. A p-value of <0.05 using a two-tailed test was taken as being of significance for all statistical tests.

RESULTS

On day 3, mean total serum bilirubin in control group among patient who has not developed clinical jaundice is 6.5mg% and in the treatment group is 5mg%. In patient with clinical jaundice, it is 13.6mg% in control group and 10.7mg% in the treatment group. The p-value was found to be <0.05 which is statistically significant. No obvious adverse reactions noted in either group.

CONCLUSION

Probiotics lowered the serum bilirubin level of healthy neonate with jaundice safely and significantly without any adverse reaction.

The effects of Chuanxiong on the pharmacokinetics of warfarin in rats after biliary drainage

ETHNOPHARMACOLOGICAL RELEVANCE

Chuanxiong Rhizoma (rhizomes of Ligusticum chuanxiong Hort), known as Chuanxiong in Chinese, has been used for treating cardiovascular diseases for centuries. Chuanxiong is a classical activating blood circulation herb in the treatment of thromboembolism heart diseases. Warfarin often combines with herbal prescriptions containing Chuanxiong in China.

AIM OF THE STUDY

The herb-drug interaction involving enterohepatic circulation process remains unclear. This study aimed to elucidate the effects of Chuanxiong Rhizoma on the pharmacokinetics of warfarin in rats after biliary drainage.

MATERIALS AND METHODS

Thirty-two rats were randomly divided into four groups: WN (healthy rats after the gastric-administration of 0.5mg/kg warfarin sodium), WO (a rat model of biliary drainage after the gastric-administration of 0.5mg/kg warfarin sodium), WCN (healthy rats after the gastric-administration of 0.5mg/kg warfarin sodium and 10g/kg Chuanxiong decoction), and WCO (a rat model of biliary drainage after the gastric-administration of 0.5mg/kg warfarin sodium and 10g/kg Chuanxiong decoction). The levels of warfarin and internal standard were quantified by LC-MS/MS. Comparisons between groups were performed according to the main pharmacokinetic parameters calculated by the DAS 2.1.1 software.

RESULTS

The established LC-MS/MS method was specific, precise and rapid. The pharmacokinetic parameters showed a significant difference between the WN and WO groups. There were significant differences in the area under the curve (AUC_0-t), peak concentration (C_max), total plasma clearance (CLz/F) and mean residence time (MRT_0-t) between the WCO and WCN groups; the AUC_0-t of warfarin in the WCN group was 2.42 times than that of the WN group (p<0.01); the WCO group displayed a decreased to 61.6% in the C_max compared the WO group (p<0.01).

CONCLUSION

Biliary drainage significantly influenced the disposition of warfarin, and Chuanxiong significantly affected the warfarin disposition in rat plasma.

Gut microbiota inhibit Asbt-dependent intestinal bile acid reabsorption via Gata4

BACKGROUND & AIMS

Regulation of bile acid homeostasis in mammals is a complex process regulated via extensive cross-talk between liver, intestine and intestinal microbiota. Here we studied the effects of gut microbiota on bile acid homeostasis in mice.

METHODS

Bile acid homeostasis was assessed in four mouse models. Germfree mice, conventionally-raised mice, Asbt-KO mice and intestinal-specific Gata4-iKO mice were treated with antibiotics (bacitracin, neomycin and vancomycin; 100 mg/kg) for five days and subsequently compared with untreated mice.

RESULTS

Attenuation of the bacterial flora by antibiotics strongly reduced fecal excretion and synthesis of bile acids, but increased the expression of the bile acid synthesis enzyme CYP7A1. Similar effects were seen in germfree mice. Intestinal bile acid absorption was increased and accompanied by increases in plasma bile acid levels, biliary bile acid secretion and enterohepatic cycling of bile acids. In the absence of microbiota, the expression of the intestinal bile salt transporter Asbt was strongly increased in the ileum and was also expressed in more proximal parts of the small intestine. Most of the effects of antibiotic treatment on bile acid homeostasis could be prevented by genetic inactivation of either Asbt or the transcription factor Gata4.

CONCLUSIONS

Attenuation of gut microbiota alters Gata4-controlled expression of Asbt, increasing absorption and decreasing synthesis of bile acids. Our data support the concept that under physiological conditions microbiota stimulate Gata4, which suppresses Asbt expression, limiting the expression of this transporter to the terminal ileum. Our studies expand current knowledge on the bacterial control of bile acid homeostasis.

Increased serum bile acid concentration following low-dose chronic administration of thioacetamide in rats, as evidenced by metabolomic analysis

A liquid chromatography/time-of-flight mass spectrometry (LC/TOF-MS)-based metabolomics approach was employed to identify endogenous metabolites as potential biomarkers for thioacetamide (TAA)-induced liver injury. TAA (10 and 30mg/kg), a well-known hepatotoxic agent, was administered daily to male Sprague-Dawley (SD) rats for 28days. We then conducted untargeted analyses of endogenous serum and liver metabolites. Partial least squares discriminant analysis (PLS-DA) was performed on serum and liver samples to evaluate metabolites associated with TAA-induced perturbation. TAA administration resulted in altered levels of bile acids, acyl carnitines, and phospholipids in serum and in the liver. We subsequently demonstrated and confirmed the occurrence of compromised bile acid homeostasis. TAA treatment significantly increased serum levels of conjugated bile acids in a dose-dependent manner, which correlated well with toxicity. However, hepatic levels of these metabolites were not substantially changed. Gene expression profiling showed that the hepatic mRNA levels of Ntcp, Bsep, and Oatp1b2 were significantly suppressed, whereas those of basolateral Mrp3 and Mrp4 were increased. Decreased levels of Ntcp, Oatp1b2, and Ostα proteins in the liver were confirmed by western blot analysis. These results suggest that serum bile acids might be increased due to the inhibition of bile acid enterohepatic circulation rather than increased endogenous bile acid synthesis. Moreover, serum bile acids are a good indicator of TAA-induced hepatotoxicity.

Abnormal olanzapine toxicokinetic profiles--population pharmacokinetic analysis

CONTEXT

Olanzapine is widely used in the treatment of schizophrenia and it is becoming more frequently responsible for overdoses. Standard pharmacokinetic models do not fit to the toxic concentration data.

OBJECTIVE

The aim of present study is to investigate the reasons for an abnormal olanzapine plasma concentration time curve in the range of toxic concentrations. Two hypotheses were verified: entering the enterohepatic cycle, and drug deposition and its desorption from activated charcoal used for gastrointestinal decontamination.

MATERIALS AND METHODS

One-hundred thirty-five plasma concentration data from 21 patients hospitalized for acute olanzapine poisoning were analyzed with the use of the population pharmacokinetic approach. A non-linear mixed-effects modeling approach with Monolix 4.3.1 was employed.

RESULTS

A model assuming gallbladder emptying at irregular intervals was developed. Also, a model that describes desorption of olanzapine from the charcoal surface, in which the dose is divided into two absorbed fractions, was constructed. The analysis has found gastrointestinal decontamination and previous olanzapine treatment, as the significant covariates for toxicokinetic parameters of olanzapine.

CONCLUSION

Our study provides interesting models for investigation of toxic concentration of olanzapine, which may also be used as the basis for further model development for other drugs as well. The investigated population was not large enough to reliably confirm any of the proposed models. It would be well worth continuing this study with more substantial data. Also, any additional information about olanzapine metabolite concentration could be vital.

Propofol-related urine discoloration in a patient with fatal atypical intracerebral hemorrhage treated with hypothermia

Introduction

Mild therapeutic hypothermia is an increasingly recognised treatment option to reduce perihemorrhagic edema in severe intracerebral hemorrhage.

Case description

We report the case of a 77-year old woman with atypical intracerebral hemorrhage that was treated with mild hypothermia in addition to osmotic therapy. The patient’s urine subsequently showed a green discoloration. Urine discoloration was completely reversible upon discontinuation of propofol.

Discussion and evaluation

Propofol-related urine discoloration may have been provoked by hypothermia. Due to the benign nature of this side effect, propofol should be stopped and gastrointestinal function should be supported.

Conclusion

More studies are needed to show a causal role of hypothermia and related decreased enzymatic function.

The lipid flippase heterodimer ATP8B1-CDC50A is essential for surface expression of the apical sodium-dependent bile acid transporter (SLC10A2/ASBT) in intestinal Caco-2 cells

Deficiency of the phospholipid flippase ATPase, aminophospholipid transporter, class I, type 8B, member 1 (ATP8B1) causes progressive familial intrahepatic cholestasis type 1 (PFIC1) and benign recurrent intrahepatic cholestasis type 1 (BRIC1). Apart from cholestasis, many patients also suffer from diarrhea of yet unknown etiology. Here we have studied the hypothesis that intestinal ATP8B1 deficiency results in bile salt malabsorption as a possible cause of PFIC1/BRIC1 diarrhea. Bile salt transport was studied in ATP8B1-depleted intestinal Caco-2 cells. Apical membrane localization was studied by a biotinylation approach. Fecal bile salt and electrolyte contents were analyzed in stool samples of PFIC1 patients, of whom some had undergone biliary diversion or liver transplantation. Bile salt uptake by the apical sodium-dependent bile salt transporter solute carrier family 10 (sodium/bile acid cotransporter), member 2 (SLC10A2) was strongly impaired in ATP8B1-depleted Caco-2 cells. The reduced SLC10A2 activity coincided with strongly reduced apical membrane localization, which was caused by impaired apical membrane insertion of SLC10A2. Moreover, we show that endogenous ATP8B1 exists in a functional heterodimer with transmembrane protein 30A (CDC50A) in Caco-2 cells. Analyses of stool samples of post-transplant PFIC1 patients demonstrated that bile salt content was not changed, whereas sodium and chloride concentrations were elevated and potassium levels were decreased. The ATP8B1-CDC50A heterodimer is essential for the apical localization of SLC10A2 in Caco-2 cells. Diarrhea in PFIC1/BRIC1 patients has a secretory origin to which SLC10A2 deficiency may contribute. This results in elevated luminal bile salt concentrations and consequent enhanced electrolyte secretion and/or reduced electrolyte resorption.

Effect of various antibiotics on modulation of intestinal microbiota and bile acid profile in mice

Antibiotic treatments have been used to modulate intestinal bacteria and investigate the role of intestinal bacteria on bile acid (BA) homeostasis. However, knowledge on which intestinal bacteria and bile acids are modified by antibiotics is limited. In the present study, mice were administered various antibiotics, 47 of the most abundant bacterial species in intestine, as well as individual BAs in plasma, liver, and intestine were quantified. Compared to the two antibiotic combinations (vancomycin+imipenem and cephalothin+neomycin), the three single antibiotics (metronidazole, ciprofloxacin and aztreonam) have less effect on intestinal bacterial profiles, and thus on host BA profiles and mRNA expression of genes that are important for BA homeostasis. The two antibiotic combinations decreased the ratio of Firmicutes to Bacteroidetes in intestine, as well as most secondary BAs in serum, liver and intestine. Additionally, the two antibiotic combinations significantly increased mRNA of the hepatic BA uptake transporters (Ntcp and Oatp1b2) and canalicular BA efflux transporters (Bsep and Mrp2), but decreased mRNA of the hepatic BA synthetic enzyme Cyp8b1, suggesting an elevated enterohepatic circulation of BAs. Interestingly, the two antibiotic combinations tended to have opposite effect on the mRNAs of most intestinal genes, which tended to be inhibited by vancomycin+imipenem but stimulated by cephalothin+neomycin. To conclude, the present study clearly shows that various antibiotics have distinct effects on modulating intestinal bacteria and host BA metabolism.

In vivo disposition and metabolism of madecassoside, a major bioactive constituent in Centella asiatica (L.) Urb

ETHNOPHARMACOLOGICAL RELEVANCE

Centella asiatica (L.) Urb. herb is frequently used in traditional Chinese medicine for many indications, such as traumatic injuries, keloid and scar. Madecassoside is the main active ingredient of this herb drug with higher content than other triterpenoid constituents. Understandings of pharmacokinetic profiles of madecassoside should be beneficial for its development as a therapeutic agent.

MATERIALS AND METHODS

Sprague-Dawley rats were intravenously and orally administered madecassoside (100 mg/kg), respectively. Plasma, heart, liver, spleen, lung, kidney, brain, bile, urine and feces were collected at the designed time points. Madecassoside concentrations in biological samples were determined by a sensitive and well-validated liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS) method. A liquid chromatography coupled with time-of-flight mass spectrometry (LC-TOF-MS) method was established to identify its major metabolites in feces. To further pursue the disposition characteristics of madecassoside in rats, the involvement of the hepatobiliary efflux transporters in biliary elimination were studied by combination with digoxin (P-glycoprotein inhibitor) or probenecid (multidrug resistance-associated protein inhibitor). A linked-rat model was also used to assess the role of enterohepatic circulation in the pharmacokinetics of madecassoside.

RESULTS

After a single oral dosing, madecassoside was widely distributed in heart, liver, spleen, lung and kidney of rats, and the levels of madecassoside in liver and kidney were relatively higher than other organs. The excretions of madecassoside in bile, urine and feces were 7.16% (0-12 h), 0.25% (0-72 h) and 24.68% (0-72 h), respectively. The findings suggested that madecassoside might excrete mainly by metabolites. The combination with either digoxin or probenecid significantly attenuated the excretion of madecassoside as parent from bile, indicating that P-glycoprotein and multidrug resistance-associated protein might contribute to the hepatobiliary elimination of madecassoside. The presence of enterohepatic circulation, as implied by double-humped profiles in plasma and tissue concentration-time curves, was confirmed by a linked-rat model. Furthermore, three metabolities of madecassoside were indentified in rat feces and the possible metabolic pathways were proposed.

CONCLUSIONS

These findings provide valuable information regarding in vivo process of madecassoside, and help us to recognize the efficacy and safety of madecassoside itself, the relevant herbs or herbal preparations.