The intrahepatic expression levels of bile acid transporters are inversely correlated with the histological progression of nonalcoholic fatty liver disease

A structural and mechanistic model for BSEP dysfunction in PFIC2 cholestatic disease

BSEP (ABCB11) transports bile salts across the canalicular membrane of hepatocytes, where they are incorporated into bile. Biallelic mutations in BSEP can cause Progressive Familial Intrahepatic Cholestasis Type 2 (PFIC2), a rare pediatric disease characterized by hepatic bile acid accumulation leading to hepatotoxicity and, ultimately, liver failure. The most frequently occurring PFIC2 disease-causing mutations are missense mutations, which often display a phenotype with decreased protein expression and impaired maturation and trafficking to the canalicular membrane. To characterize the mutational effects on protein thermodynamic stability, we carried out biophysical characterization of 13 distinct PFIC2-associated variants using in-cell thermal shift (CETSA) measurements. These experiments reveal a cluster of residues localized to the NBD2-ICL2 interface, which exhibit severe destabilization relative to wild-type BSEP. A high-resolution (2.8 Å) cryo-EM structure provides a framework for rationalizing the CETSA results, revealing a novel, NBD2-localized mechanism through which the most severe missense patient mutations drive cholestatic disease. These findings suggest potential strategies for identifying mechanism-based small molecule correctors to address BSEP trafficking defects and advance novel therapies for PFIC2 and other cholestatic diseases.

Inhibition of ATGL alleviates MASH via impaired PPARα signalling that favours hydrophilic bile acid composition in mice

BACKGROUND & AIMS

Adipose triglyceride lipase (ATGL) is an attractive therapeutic target in insulin resistance and metabolic dysfunction-associated steatotic liver disease (MASLD). This study investigated the effects of pharmacological ATGL inhibition on the development of metabolic dysfunction-associated steatohepatitis (MASH) and fibrosis in mice.

METHODS

Streptozotocin-injected male mice were fed a high-fat diet to induce MASH. Mice receiving the ATGL inhibitor atglistatin (ATGLi) were compared to controls using liver histology, lipidomics, metabolomics, 16s rRNA, and RNA sequencing. Human ileal organoids, HepG2 cells, and Caco2 cells treated with the human ATGL inhibitor NG-497, HepG2 ATGL knockdown cells, gel-shift, and luciferase assays were analysed for mechanistic insights. We validated the benefits of ATGLi on steatohepatitis and fibrosis in a low-methionine choline-deficient mouse model.

RESULTS

ATGLi improved serum liver enzymes, hepatic lipid content, and histological liver injury. Mechanistically, ATGLi attenuated PPARα signalling, favouring hydrophilic bile acid (BA) synthesis with increased Cyp7a1, Cyp27a1, Cyp2c70, and reduced Cyp8b1 expression. Additionally, reduced intestinal Cd36 and Abca1, along with increased Abcg5 expression, were consistent with reduced levels of hepatic triacylglycerol species containing polyunsaturated fatty acids, like linoleic acid, as well as reduced cholesterol levels in the liver and plasma. Similar changes in gene expression associated with PPARα signalling and intestinal lipid transport were observed in ileal organoids treated with NG-497. Furthermore, HepG2 ATGL knockdown cells revealed reduced expression of PPARα target genes and upregulation of genes involved in hydrophilic BA synthesis, consistent with reduced PPARα binding and luciferase activity in the presence of the ATGL inhibitors.

CONCLUSIONS

Inhibition of ATGL attenuates PPARα signalling, translating into hydrophilic BA composition, interfering with dietary lipid absorption, and improving metabolic disturbances. Validation with NG-497 opens a new therapeutic perspective for MASLD.

IMPACT AND IMPLICATIONS

Despite the recent approval of drugs novel mechanistic insights and pathophysiology-oriented therapeutic options for MASLD (metabolic dysfunction-associated steatotic liver disease) are still urgently needed. Herein, we show that pharmacological inhibition of ATGL, the key enzyme in lipid hydrolysis, using atglistatin (ATGLi), improves MASH (metabolic dysfunction-associated steatohepatitis), fibrosis, and key features of metabolic dysfunction in mouse models of MASH and liver fibrosis. Mechanistically, we demonstrated that attenuation of PPARα signalling in the liver and gut favours hydrophilic bile acid composition, ultimately interfering with dietary lipid absorption. One of the drawbacks of ATGLi is its lack of efficacy against human ATGL, thus limiting its clinical applicability. Against this backdrop, we could show that ATGL inhibition using the human inhibitor NG-497 in human primary ileum-derived organoids, Caco2 cells, and HepG2 cells translated into therapeutic mechanisms similar to ATGLi. Collectively, these findings reveal a possible new avenue for MASLD treatment.

The bile acid profile

As a large and structurally diverse family of small molecules, bile acids play a crucial role in regulating lipid, glucose, and energy metabolism. In the human body, bile acids share a similar chemical structure with many isomers, exhibit little difference in polarity, and possess various physiological activities. The types and contents of bile acids present in different diseases vary significantly. Therefore, comprehensive and accurate detection of the content of various types of bile acids in different biological samples can not only provide new insights into the pathogenesis of diseases but also facilitate the exploration of novel strategies for disease diagnosis, treatment, and prognosis. The detection of disease-induced changes in bile acid profiles has emerged as a prominent research focus in recent years. Concurrently, targeted metabolomics methods utilizing high-performance liquid chromatography-mass spectrometry (HPLC-MS) have progressively established themselves as the predominant technology for the separation and detection of bile acids. Bile acid profiles will increasingly play an important role in diagnosis and guidance in the future as the relationship between disease and changes in bile acid profiles becomes clearer. This highlights the growing diagnostic value of bile acid profiles and their potential to guide clinical decision-making. This review aims to explore the significance of bile acid profiles in clinical diagnosis from four perspectives: the synthesis and metabolism of bile acids, techniques for detecting bile acid profiles, changes in bile acid profiles associated with diseases, and the challenges and future prospects of applying bile acid profiles in clinical settings.

Metabolic disorders, inter-organ crosstalk, and inflammation in the progression of metabolic dysfunction-associated steatotic liver disease

Metabolic dysfunction-associated steatotic liver disease (MASLD) represents a global health concern, affecting over 30 % of adults. It is a principal driver in the development of cirrhosis and hepatocellular carcinoma. The complex pathogenesis of MASLD involves an excessive accumulation of lipids, subsequently disrupting lipid metabolism and prompting inflammation within the liver. This review synthesizes the recent research progress in understanding the mechanisms contributing to MASLD progression, with particular emphasis on metabolic disorders and interorgan crosstalk. We highlight the molecular mechanisms linked to these factors and explore their potential as novel targets for pharmacological intervention. The insights gleaned from this article have important implications for both the prevention and therapeutic management of MASLD.

Free fatty acids induce bile acids overproduction and oxidative damage of bovine hepatocytes via inhibiting FXR/SHP signaling

Hepatic oxidative injury induced by free fatty acids (FFA) and metabolic disorders of bile acids (BA) increase the risk of metabolic diseases in dairy cows during perinatal period. However, the effects of FFA on BA metabolism remained poorly understood. In present study, high concentrations of FFA caused cell impairment, oxidative stress and BA overproduction. FFA treatment increased the expression of BA synthesis-related genes [cholesterol 7a-hydroxylase (CYP7A1), hydroxy-delta-5-steroid dehydrogenase, 3 beta- and steroid delta-isomerase 7, sterol 12α-hydroxylase, sterol 27-hydroxylase and oxysterol 7α-hydroxylase], whereas reduced BA exportation gene (ATP binding cassette subfamily C member 1) and inhibited farnesoid X receptor/small heterodimer partner (FXR/SHP) pathway in bovine hepatocytes. Knockdown of nuclear receptor subfamily 1 group H member 4 (NR1H4) worsened FFA-caused oxidative damage and BA production, whereas overexpression NR1H4 ameliorated FFA-induced BA production and cell oxidative damage. Besides, reducing BA synthesis through knockdown of CYP7A1 can alleviate oxidative stress and hepatocytes impairment caused by FFA. In summary, these data demonstrated that regulation of FXR/SHP-mediated BA metabolism may be a promising target in improving hepatic oxidative injury of dairy cows during high levels of FFA challenges.

Expression of hepatic genes involved in bile acid metabolism in dairy cows with fatty liver

Bile acids are cholesterol-derived molecules that are primarily produced in the liver. In nonruminants with fatty liver, overproduction of bile acids is associated with liver injury. During the transition period, fatty liver is a metabolic disorder that can affect up to 50% of high-producing dairy cows. The purpose of this study was to provide a comprehensive evaluation on hepatic bile acid metabolism in dairy cows with fatty liver by assessing expression changes of genes involved in bile acid synthesis, export and uptake. The serum activities of aspartate aminotransferase, alanine aminotransferase and glutamate dehydrogenase and concentration of total bile acids were all greater, whereas serum concentration of total cholesterol was lower in cows with fatty liver than in healthy cows. Content of total bile acids was higher but total cholesterol was slightly lower in liver tissues from fatty liver cows than from healthy cows. The hepatic mRNA abundance of cholesterol 7a-hydroxylase (CYP7A1), hydroxy-delta-5-steroid dehydrogenase, 3 β- and steroid delta-isomerase 7 (HSD3B7) and sterol 12α-hydroxylase (CYP8B1), enzymes involved in the classic pathway of bile acid synthesis, was higher in fatty liver cows than in healthy cows. Compared with healthy cows, the hepatic mRNA abundance of alternative bile acid synthesis pathway-related genes sterol 27-hydroxylase (CYP27A1) and oxysterol 7α-hydroxylase (CYP7B1) did not differ in cows with fatty liver. The protein and mRNA abundance of bile acid transporter bile salt efflux pump (BSEP) were lower in the liver of dairy cow with fatty liver. Compared with healthy cows, the hepatic mRNA abundance of bile acid transporters solute carrier family 51 subunit α (SLC51A), ATP binding cassette subfamily C member 1 (ABCC1) and 3 (ABCC3) was greater in cows with fatty liver, whereas the solute carrier family 51 subunit β (SLC51B) did not differ. The expression of genes involved in bile acid uptake, including solute carrier family 10 member 1 (NTCP), solute carrier organic anion transporter family member 1A2 (SLCO1A2) and 2B1 (SLCO2B1) was upregulated in dairy cows with fatty liver. Furthermore, the hepatic protein and mRNA abundance of bile acid metabolism regulators farnesoid X receptor (FXR) and small heterodimer partner (SHP) were lower in cows with fatty liver than in healthy cows. Overall, these data suggest that inhibition of FXR signaling pathway may lead to the increased bile acid synthesis and uptake and decreased secretion of bile acids from hepatocytes to the bile, which elevates hepatic bile acids content in dairy cows with fatty liver. As the hepatotoxicity of bile acids has been demonstrated on nonruminant hepatocytes, it is likely that the liver injury is induced by increased hepatic bile acids content in dairy cows with fatty liver.

Inflammatory liver diseases and susceptibility to sepsis

Patients with inflammatory liver diseases, particularly alcohol-associated liver disease and metabolic dysfunction-associated fatty liver disease (MAFLD), have higher incidence of infections and mortality rate due to sepsis. The current focus in the development of drugs for MAFLD is the resolution of non-alcoholic steatohepatitis and prevention of progression to cirrhosis. In patients with cirrhosis or alcoholic hepatitis, sepsis is a major cause of death. As the metabolic center and a key immune tissue, liver is the guardian, modifier, and target of sepsis. Septic patients with liver dysfunction have the highest mortality rate compared with other organ dysfunctions. In addition to maintaining metabolic homeostasis, the liver produces and secretes hepatokines and acute phase proteins (APPs) essential in tissue protection, immunomodulation, and coagulation. Inflammatory liver diseases cause profound metabolic disorder and impairment of energy metabolism, liver regeneration, and production/secretion of APPs and hepatokines. Herein, the author reviews the roles of (1) disorders in the metabolism of glucose, fatty acids, ketone bodies, and amino acids as well as the clearance of ammonia and lactate in the pathogenesis of inflammatory liver diseases and sepsis; (2) cytokines/chemokines in inflammatory liver diseases and sepsis; (3) APPs and hepatokines in the protection against tissue injury and infections; and (4) major nuclear receptors/signaling pathways underlying the metabolic disorders and tissue injuries as well as the major drug targets for inflammatory liver diseases and sepsis. Approaches that focus on the liver dysfunction and regeneration will not only treat inflammatory liver diseases but also prevent the development of severe infections and sepsis.

Impact of non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH) on the expression and function of hepatobiliary transporters: A comprehensive mechanistic review

The liver plays a central role in the biotransformation and disposition of endogenous molecules and xenobiotics. In addition to drug-metabolizing enzymes, transporter proteins are key determinants of drug hepatic clearance. Hepatic transporters are transmembrane proteins that facilitate the movement of chemicals between sinusoidal blood and hepatocytes. Other drug transporters translocate molecules from hepatocytes into bile canaliculi for biliary excretion. The formers are known as basolateral, while the latter are known as canalicular transporters. Also, these transporters are classified into two super-families, the solute carrier transporter (SLC) and the adenosine triphosphate (ATP)-binding cassette (ABC) transporter. The expression and function of transporters involve complex regulatory mechanisms, which are contributing factors to interindividual variability in drug pharmacokinetics and disposition. A considerable number of liver diseases are known to alter the expression and function of drug transporters. Among them, non-alcoholic fatty liver disease (NAFLD) is a chronic condition with a rapidly increasing incidence worldwide. NAFLD, recently reclassified as metabolic dysfunction-associated steatotic liver disease (MASLD), is a disease continuum that includes steatosis with or without mild inflammation (NASH), and potentially neuroinflammatory pathology. NASH is additionally characterized by the presence of hepatocellular injury. During NAFLD and NASH, drug transporters exhibit altered expression and function, leading to altered drug pharmacokinetics and pharmacodynamics, thus increasing the risk of adverse drug reactions. The purpose of the present review is to provide comprehensive mechanistic information on the expression and function of hepatic transporters under fatty liver conditions and hence, the impact on the pharmacokinetic profiles of certain drugs from the available pre-clinical and clinical literature.

Alterations in zonal distribution and plasma membrane localization of hepatocyte bile acid transporters in patients with NAFLD

BACKGROUND

NAFLD is highly prevalent with limited treatment options. Bile acids (BAs) increase in the systemic circulation and liver during NAFLD progression. Changes in plasma membrane localization and zonal distribution of BA transporters can influence transport function and BA homeostasis. However, a thorough characterization of how NAFLD influences these factors is currently lacking. This study aimed to evaluate the impact of NAFLD and the accompanying histologic features on the functional capacity of key hepatocyte BA transporters across zonal regions in human liver biopsies.

METHODS

A novel machine learning image classification approach was used to quantify relative zonal abundance and plasma membrane localization of BA transporters (bile salt export pump [BSEP], sodium-taurocholate cotransporting polypeptide, organic anion transporting polypeptide [OATP] 1B1 and OATP1B3) in non-diseased (n = 10), NAFL (n = 9), and NASH (n = 11) liver biopsies. Based on these data, membrane-localized zonal abundance (MZA) measures were developed to estimate transporter functional capacity.

RESULTS

NAFLD diagnosis and histologic scoring were associated with changes in transporter membrane localization and zonation. Increased periportal BSEPMZA (mean proportional difference compared to non-diseased liver of 0.090) and decreased pericentral BSEPMZA (-0.065) were observed with NASH and also in biopsies with higher histologic scores. Compared to Non-diseased Liver, periportal OATP1B3MZA was increased in NAFL (0.041) and NASH (0.047). Grade 2 steatosis (mean proportional difference of 0.043 when compared to grade 0) and grade 1 lobular inflammation (0.043) were associated with increased periportal OATP1B3MZA.

CONCLUSIONS

These findings provide novel mechanistic insight into specific transporter alterations that impact BA homeostasis in NAFLD. Changes in BSEPMZA likely contribute to altered BA disposition and pericentral microcholestasis previously reported in some patients with NAFLD. BSEPMZA assessment could inform future development and optimization of NASH-related pharmacotherapies.

Physical exercise plays a role in rebalancing the bile acids of enterohepatic axis in non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is considered as one of the most common diseases of lipid metabolism disorders, which is closely related to bile acids disorders and gut microbiota disorders. Bile acids are synthesized from cholesterol in the liver, and processed by gut microbiota in intestinal tract, and participate in metabolic regulation through the enterohepatic circulation. Bile acids not only promote the consumption and absorption of intestinal fat but also play an important role in biological metabolic signaling network, affecting fat metabolism and glucose metabolism. Studies have demonstrated that exercise plays an important role in regulating the composition and function of bile acid pool in enterohepatic axis, which maintains the homeostasis of the enterohepatic circulation and the health of the host gut microbiota. Exercise has been recommended by several health guidelines as the first-line intervention for patients with NAFLD. Can exercise alter bile acids through the microbiota in the enterohepatic axis? If so, regulating bile acids through exercise may be a promising treatment strategy for NAFLD. However, the specific mechanisms underlying this potential connection are largely unknown. Therefore, in this review, we tried to review the relationship among NAFLD, physical exercise, bile acids, and gut microbiota through the existing data and literature, highlighting the role of physical exercise in rebalancing bile acid and microbial dysbiosis.

Microbial transformations of bile acids and their receptors in the regulation of metabolic dysfunction-associated steatotic liver disease

Bile acids (BAs) play important roles in the digestion of dietary fats and molecular signal transduction, and modulation of the BA composition usually affects the progression of metabolic diseases. While the liver produces primary BAs, the gut microbiota modifies these products into various forms that greatly increase their diversity and biological functions. Mechanistically, BAs can regulate their own metabolism and transport as well as other key aspects of metabolic processes via dedicated BA receptors. Disruption of BA transport and homeostasis leads to the progression of liver diseases, including metabolic dysfunction-associated steatotic liver disease (MASLD) and hepatocellular carcinoma (HCC). Here, we summarize the microbial transformations of BAs and their downstream signaling in the development of metabolic diseases and present new insights into novel therapeutic strategies targeting BA pathways that may contribute to these diseases.

Multi‑omics‑based analysis of the regulatory mechanism of gypenosides on bile acids in hypercholesterolemic mice

Gynostemma pentaphyllum is a traditional medicine used by ethnic minorities in southwest China and gypenosides are currently recognized as essential components of the pharmacological substances of Gynostemma pentaphyllum, which are effective in regulating metabolic syndrome, especially in improving hepatic metabolic disorders. The present study randomly divided C57BL/6J male mice into the normal diet control group (ND), high-fat diet modeling group (HFD) and gypenosides group (GP). Liquid chromatography-mass spectrometry (UPLC-MS) was applied to quantify bile acids in the liver, bile and serum of mice in ND, HFD and GP groups. Liver proteins were extracted for trypsin hydrolysis and analyzed quantitatively using UPLC-MS + MS/MS (timsTOF Pro 2). Total mouse liver RNA was extracted from ND, HFD and GP groups respectively, cDNA sequencing libraries constructed and sequenced using BGISEQ-500 sequencing platform. The expression of key genes Fxr, Shp, Cyp7a1, Cyp8b1, and Abab11 was detected by RT-qPCR. The results showed that gypenosides accelerated free bile acid synthesis by promoting the expression of bile acid synthase CYP7A1 and CYP8B1 genes and proteins and accelerating the secretion of conjugated bile acids from the liver to the bile ducts. GP inhibited the bile acid transporters solute carrier organic anion transporter family member (SLCO) 1A1 and SLCO1A4, reducing the reabsorption of free bile acids and accelerating the excretion of free bile acids from the blood to the kidneys. It also promoted the metabolic enzyme CYP3A11, which accelerated the metabolism and clearance of bile acids, thus maintaining the balance of the bile acid internal environment.

Anthocyanin-Rich Butterfly Pea Flower Extract Ameliorating Low-Grade Inflammation in a High-Fat-Diet and Lipopolysaccharide-Induced Mouse Model

This study aimed to explore the enhancive effects of butterfly pea flower (BF) extracts on metabolic and immune homeostasis in a low-grade inflammation mouse model. The BF extract was found to contain mainly anthocyanins among other flavonoids. BF supplementation alleviated metabolic endotoxemia by lowering the plasma glucose, lipopolysaccharide (LPS), and tumor necrosis factor-α (TNF-α) levels and restored lipid metabolism and the balance between Treg and Th17 cells, thereby inhibiting the dysfunctional liver and abdominal white adipose tissues. BF extract increased the tight junction protein expression and reduced the expression of proinflammatory cytokines, therefore sustaining the colonic mucosa structure. Furthermore, BF extracts reshaped the gut microbiota structure characterized by significantly promoted SCFA-producing gut microbiota such as Akkermansia and Butyricicoccaceae. Additionally, BF extracts enhanced fecal primary bile acid (BA) levels and modulated bile acid signaling in the liver and ileum to facilitate BA synthesis for the restoration of lipid metabolism. In summary, anthocyanin-enriched BF extracts alleviated the profound negative dietary alterations and helped maintain the metabolic health by modulating the various aspects of the gut microenvironment and enhancing hepatic bile acid synthesis.

Lactobacillus fermentum MCC2760 abrogate high-fat induced perturbations in the enterohepatic circulation of bile acids in rats

AIM

This study in hyperlipidemic rats elucidated the effect of Lactobacillus fermentum MCC2760 on intestinal bile acid (BA) uptake, hepatic BA synthesis, and enterohepatic BA transporters.

MAIN METHODS

Diets rich in saturated fatty acids [coconut oil (CO)] and omega-6 fatty acids [sunflower oil (SFO)] at 25 g fat/100 g diet were fed to rats with or without MCC2760 (10⁹ cells/kg body weight). After 60 days of feeding, intestinal BA uptake and expression of Asbt, Osta/b mRNA and protein, and hepatic expression of Ntcp, Bsep, Cyp7a1, Fxr, Shp, Lrh-1, and Hnf4a mRNA were measured. Hepatic expression of HMG-CoA reductase protein and its activity and total BAs in serum, liver, and feces were assessed.

KEY FINDINGS

Hyperlipidaemic groups (HF-CO and HF-SFO) had: 1) increased intestinal BA uptake, Asbt and Osta/b mRNA expression, and ASBT staining 2) increased BA in serum, 3) decreased hepatic expression of Ntcp, Bsep, and Cyp7a1 mRNA, and NTCP staining 4) increased activity of HMG-CoA reductase, 5) increased hepatic expression of Fxr and Shp mRNA, 6) decreased hepatic expression of Lrh-1 and Hnf4a mRNA, and 7) decreased BA in Feces when compared to their respective controls (N-CO and N-SFO) and experimental groups (HF-CO + LF and HF-SFO + LF). Immunostaining revealed increased intestinal Asbt and hepatic Ntcp protein expression in the HF-CO and HF-SFO groups compared to control and experimental groups.

SIGNIFICANCE

Incorporating probiotics like MCC2760 abrogated hyperlipidemia-induced changes in the intestinal uptake, hepatic synthesis, and enterohepatic transporters of BA in rats. Probiotic MCC2760 can be used to modulate lipid metabolism in high-fat-induced hyperlipidemic conditions.

Myclobutanil-mediated alteration of liver-gut FXR signaling in mice

The effects of exposure to Myclobutanil, a triazole fungicide, on the development and progression of nonalcoholic fatty liver disease (NAFLD) are unclear, but activation of nuclear receptors (NRs) is a known mechanism of azole-induced liver toxicity. Farnesoid X receptor (FXR) is a NR and is highly expressed in the liver and intestine. Activation of FXR tightly regulates bile acid (BA), lipid and glucose homeostasis, and inflammation partly through the induction of fibroblast growth factor 15 (FGF15; human ortholog FGF19). FXR activation is downregulated during NAFLD and agonists are currently being explored as potential therapeutic strategy. In this study, we aimed to clarify the effects of Myclobutanil exposure on FXR activation and NAFLD development. Reporter assay showed Myclobutanil treatment, following FXR activation with potent FXR agonist (GW4064), resulted in a dose-dependent decrease of FXR activity. Furthermore, a 10-day study in male mice demonstrated that cotreatment with Myclobutanil led to an 80% reduction of GW4064-induced ileal expression of Fgf15. In a diet-induced NAFLD study, low-fat diet (LFD) fed mice administered myclobutanil displayed decreased FXR activity in the liver and ileum, while high-fat-high-sugar-diet (HFHSD) fed mice showed an increase in hepatic FXR activity and an induction of target genes regulated by constitutive androstane receptor and/or pregnane X receptor. Our work demonstrates Myclobutanil inhibits FXR activity and modulates FXR activity differentially in mice fed LFD or HFHSD. Our studies suggest the importance of understanding how Myclobutanil could contribute to BA dysregulation in disease states such as NAFLD.

Considerations for Physiologically Based Modeling in Liver Disease: From Nonalcoholic Fatty Liver (NAFL) to Nonalcoholic Steatohepatitis (NASH)

Nonalcoholic fatty liver disease (NAFLD), representing a clinical spectrum ranging from nonalcoholic fatty liver (NAFL) to nonalcoholic steatohepatitis (NASH), is rapidly evolving into a global pandemic. Patients with NAFLD are burdened with high rates of metabolic syndrome-related comorbidities resulting in polypharmacy. Therefore, it is crucial to gain a better understanding of NAFLD-mediated changes in drug disposition and efficacy/toxicity. Despite extensive clinical pharmacokinetic data in cirrhosis, current knowledge concerning pharmacokinetic alterations in NAFLD, particularly at different stages of disease progression, is relatively limited. In vitro-to-in vivo extrapolation coupled with physiologically based pharmacokinetic and pharmacodynamic (IVIVE-PBPK/PD) modeling offers a promising approach for optimizing pharmacologic predictions while refining and reducing clinical studies in this population. Use of IVIVE-PBPK to predict intra-organ drug concentrations at pharmacologically relevant sites of action is particularly advantageous when it can be linked to pharmacodynamic effects. Quantitative systems pharmacology/toxicology (QSP/QST) modeling can be used to translate pharmacokinetic and pharmacodynamic data from PBPK/PD models into clinically relevant predictions of drug response and toxicity. In this review, a detailed summary of NAFLD-mediated alterations in human physiology relevant to drug absorption, distribution, metabolism, and excretion (ADME) is provided. The application of literature-derived physiologic parameters and ADME-associated protein abundance data to inform virtual NAFLD population development and facilitate PBPK/PD, QSP, and QST predictions is discussed along with current limitations of these methodologies and knowledge gaps. The proposed methodologic framework offers great potential for meaningful prediction of pharmacological outcomes in patients with NAFLD and can inform both drug development and clinical practice for this population.

ABC transporters: human disease and pharmacotherapeutic potential

Adenosine triphosphate (ATP)-binding cassette (ABC) transporters are a 48-member superfamily of membrane proteins that actively transport a variety of biological substrates across lipid membranes. Their functional diversity defines an expansive involvement in myriad aspects of human biology. At least 21 ABC transporters underlie rare monogenic disorders, with even more implicated in the predisposition to and symptomology of common and complex diseases. Such broad (patho)physiological relevance places this class of proteins at the intersection of disease causation and therapeutic potential, underlining them as promising targets for drug discovery, as exemplified by the transformative CFTR (ABCC7) modulator therapies for cystic fibrosis. This review will explore the growing relevance of ABC transporters to human disease and their potential as small-molecule drug targets.

Changes in Disposition of Ezetimibe and Its Active Metabolites Induced by Impaired Hepatic Function: The Influence of Enzyme and Transporter Activities

Ezetimibe (EZE) is a selective cholesterol absorption inhibitor. Hepatic impairment significantly increases the systemic exposure of EZE and its main active phenolic glucuronide, EZE-Ph. Although changes in efflux transporter activity partly explain the changes in EZE-Ph pharmacokinetics, the causes of the changes to EZE and the effects of the administration route on EZE-Ph remain unclear. A carbon tetrachloride (CCl₄)-induced hepatic failure rat model was combined with in vitro experiments to explore altered EZE and EZE-Ph disposition caused by hepatic impairment. The plasma exposure of EZE and EZE-Ph increased by 11.1- and 4.4-fold in CCl₄-induced rats following an oral administration of 10 mg/kg EZE, and by 2.1- and 16.4-fold after an intravenous injection. The conversion of EZE to EZE-Ph decreased concentration-dependently in CCl₄-induced rat liver S9 fractions, but no change was observed in the intestinal metabolism. EZE-Ph was a substrate for multiple efflux and uptake transporters, unlike EZE. In contrast to efflux transporters, no difference was seen in the hepatic uptake of EZE-Ph between control and CCl₄-induced rats. However, bile acids that accumulated due to liver injury inhibited the uptake of EZE-Ph by organic anion transporting polypeptides (OATPs) (glycochenodeoxycholic acid and taurochenodeoxycholic acid had IC₅₀ values of 15.1 and 7.94 μM in OATP1B3-overexpressed cells). In conclusion, the increased plasma exposure of the parent drug EZE during hepatic dysfunction was attributed to decreased hepatic glucuronide conjugation, whereas the increased exposure of the metabolite EZE-Ph was mainly related to transporter activity, particularly the inhibitory effects of bile acids on OATPs after oral administration.

Linking Nonalcoholic Fatty Liver Disease and Brain Disease: Focusing on Bile Acid Signaling

A metabolic illness known as non-alcoholic fatty liver disease (NAFLD), affects more than one-quarter of the world's population. Bile acids (BAs), as detergents involved in lipid digestion, show an abnormal metabolism in patients with NAFLD. However, BAs can affect other organs as well, such as the brain, where it has a neuroprotective effect. According to a series of studies, brain disorders may be extrahepatic manifestations of NAFLD, such as depression, changes to the cerebrovascular system, and worsening cognitive ability. Consequently, we propose that NAFLD affects the development of brain disease, through the bile acid signaling pathway. Through direct or indirect channels, BAs can send messages to the brain. Some BAs may operate directly on the central Farnesoid X receptor (FXR) and the G protein bile acid-activated receptor 1 (GPBAR1) by overcoming the blood-brain barrier (BBB). Furthermore, glucagon-like peptide-1 (GLP-1) and the fibroblast growth factor (FGF) 19 are released from the intestine FXR and GPBAR1 receptors, upon activation, both of which send signals to the brain. Inflammatory, systemic metabolic disorders in the liver and brain are regulated by the bile acid-activated receptors FXR and GPBAR1, which are potential therapeutic targets. From a bile acid viewpoint, we examine the bile acid signaling changes in NAFLD and brain disease. We also recommend the development of dual GPBAR1/FXR ligands to reduce side effects and manage NAFLD and brain disease efficiently.

Bile acid metabolism and signaling, the microbiota, and metabolic disease

The diversity, composition, and function of the bacterial community inhabiting the human gastrointestinal tract contributes to host health through its role in producing energy or signaling molecules that regulate metabolic and immunologic functions. Bile acids are potent metabolic and immune signaling molecules synthesized from cholesterol in the liver and then transported to the intestine where they can undergo metabolism by gut bacteria. The combination of host- and microbiota-derived enzymatic activities contribute to the composition of the bile acid pool and thus there can be great diversity in bile acid composition that depends in part on the differences in the gut bacteria species. Bile acids can profoundly impact host metabolic and immunological functions by activating different bile acid receptors to regulate signaling pathways that control a broad range of complex symbiotic metabolic networks, including glucose, lipid, steroid and xenobiotic metabolism, and modulation of energy homeostasis. Disruption of bile acid signaling due to perturbation of the gut microbiota or dysregulation of the gut microbiota-host interaction is associated with the pathogenesis and progression of metabolic disorders. The metabolic and immunological roles of bile acids in human health have led to novel therapeutic approaches to manipulate the bile acid pool size, composition, and function by targeting one or multiple components of the microbiota-bile acid-bile acid receptor axis.

Identification of Shared Gene Signatures in Different Stages of Nonalcoholic Fatty Liver Disease Using Integrated Microarray Datasets

Background: Nonalcoholic fatty liver disease (NAFLD) is the most common type of chronic liver disease worldwide. Left untreated, it can be a risk factor for developing cirrhosis or hepatocellular carcinoma (HCC). Although experts have made many efforts to find the underlying mechanisms of NAFLD, they remain a mystery. Objectives: This study aimed to distinguish common gene signatures and pathways in the human liver during NAFLD progression through systems biology. Methods: In this study, the researchers selected three microarray datasets, GSE48452, GSE63067, and GSE89632, from the NCBI GEO database to explore differentially expressed genes (DEGs) among healthy controls, simple steatosis, and nonalcoholic steatohepatitis (NASH) patients. Furthermore, protein-protein interaction (PPI) networks and pathway enrichment analyses were used to detect common genes and biological pathways in different stages of NAFLD. Results: The current study included 45 healthy participants, 36 simple steatosis patients, and 46 NASH patients. Common genes for NAFLD progression were Chi3L1, ICAM1, MT1A, MT1H, ABCB11, ACOT1, CYP2C9, HSP90B1, and CPB2, which are involved in inflammation and oxidative stress pathways. Conclusions: The present study investigated the shared vital genes and pathways between different stages of NAFLD, which may facilitate understanding NAFLD mechanisms and identifying potential therapeutic targets in this disease.

Alisol B 23-acetate adjusts bile acid metabolisim via hepatic FXR-BSEP signaling activation to alleviate atherosclerosis

BACKGROUND

Postmenopausal women have a high incidence of atherosclerosis. Phytosterols have been shown to have cholesterol-lowering properties. Alisa B 23-acetate (AB23A) is a biologically active plant sterol isolated from Chinese herbal medicine Alisma. However, the atherosclerosis effect of AB23A after menopause and its possible mechanism have not been reported yet.

PURPOSE

To explore whether AB23A can prevent atherosclerosis by regulating farnesoid X receptor and subsequently increasing fecal bile acid and cholesterol excretion to reduce plasma cholesterol levels.

METHODS

Aortic samples from premenopausal and postmenopausal women with ascending aortic arteriosclerosis were analyzed, and bilateral ovariectomized (OVX) female LDLR^-/- mice and free fatty acid (FFA)-treated L02 cells were used to analyze the effect of AB23A supplementation therapy.

RESULTS

AB23A increased fecal cholesterol and bile acids (BAs) excretion dependent on activation of hepatic farnesoid X receptor (FXR) in ovariectomized mice. AB23A inhibited hepatic cholesterol 7α-hydroxylase (CYP7A1) and sterol 12α-hydroxylase (CYP8B1) via inducing small heterodimer partner (SHP) expression. On the other hand, AB23A increased the level of hepatic chenodeoxycholic acid (CDCA), and activated the hepatic BSEP signaling. The activation of hepatic FXR-BSEP signaling by AB23A in ovariectomized mice was accompanied by the reduction of liver cholesterol, hepatic lipolysis, and bile acids efflux, and reduced the damage of atherosclerosis. In vitro, AB23A fixed abnormal lipid metabolism in L02 cells and increased the expression of FXR, BSEP and SHP. Moreover, the inhibition and silencing of FXR canceled the regulation of BSEP by AB23A in L02 cells.

CONCLUSION

Our results shed light into the mechanisms behind the cholesterol-lowering of AB23A, and increasing FXR-BSEP signaling by AB23A may be a potential postmenopausal atherosclerosis therapy.

Dihydroflavonoids as Bioactive Components of Penthorum chinense, a Miao Ethnomedicine, against NAFLD through Bile Acid Metabolism Pathway

Penthorum chinense Pursh. is a traditional herbal medicine of Miao, and its extracts (PCPE) have been used for treatment of liver diseases in the clinic including nonalcoholic fatty liver disease (NAFLD). However, the active components and pharmacological mechanisms of PCPE for treating NAFLD remain unclear. This study aimed to explore potential mechanisms of action through network pharmacology, molecular docking combined with experimental in vitro. A total of five dihydroflavonoids (1-5) with the same parent nucleus of pinocembrin (PCB) from PCPE, were selected as bioactive ingredients and 109 potential targets related to NAFLD were obtained from public databases and literature mining. The core targets related to the bile secretion signaling were selected based on PPI network and KEGG enrichment analysis for exploring the mechanism of PCPE against NAFLD. Molecular docking results showed good interaction between the core targets in bile secretion signaling pathway and the five compounds predicted to be bioactive. With the strong binding activity to retinoid X receptor-alpha (RXRA) and farnesoid X receptor (FXR) protein, pinocembrin-7-O-β-D-glucoside (PCBG, the highest content in PCPE) and its metabolite PCB, could significantly increase the expression of RXRA, FXR and bile salt export pump (BSEP) in L02 cells, and significantly decrease the expression of cholesterol 7α-hydroxylase (CYP7A1) at mRNA and protein levels. This study provided favorable evidence for mechanism of the main dihydroflavonoids of PCPE against NAFLD, and presented a paradigm for the study of ethnomedicine.

Bile acid coordinates microbiota homeostasis and systemic immunometabolism in cardiometabolic diseases

Cardiometabolic disease (CMD), characterized with metabolic disorder triggered cardiovascular events, is a leading cause of death and disability. Metabolic disorders trigger chronic low-grade inflammation, and actually, a new concept of metaflammation has been proposed to define the state of metabolism connected with immunological adaptations. Amongst the continuously increased list of systemic metabolites in regulation of immune system, bile acids (BAs) represent a distinct class of metabolites implicated in the whole process of CMD development because of its multifaceted roles in shaping systemic immunometabolism. BAs can directly modulate the immune system by either boosting or inhibiting inflammatory responses via diverse mechanisms. Moreover, BAs are key determinants in maintaining the dynamic communication between the host and microbiota. Importantly, BAs via targeting Farnesoid X receptor (FXR) and diverse other nuclear receptors play key roles in regulating metabolic homeostasis of lipids, glucose, and amino acids. Moreover, BAs axis per se is susceptible to inflammatory and metabolic intervention, and thereby BAs axis may constitute a reciprocal regulatory loop in metaflammation. We thus propose that BAs axis represents a core coordinator in integrating systemic immunometabolism implicated in the process of CMD. We provide an updated summary and an intensive discussion about how BAs shape both the innate and adaptive immune system, and how BAs axis function as a core coordinator in integrating metabolic disorder to chronic inflammation in conditions of CMD.

Liver damage promotes pro-inflammatory T-cell responses against apolipoprotein B-100

OBJECTIVES

Liver-derived apolipoprotein B-100 (ApoB100) is an autoantigen that is recognized by atherogenic CD4⁺ T cells in cardiovascular disease (CVD). CVD is a major mortality risk for patients with chronic inflammatory liver diseases. However, the impact of liver damage for ApoB100-specific T-cell responses is unknown.

METHODS

We identified ApoB100-specific T cells in blood from healthy controls, nonalcoholic fatty liver disease (NAFLD) patients, and CVD patients by activation-induced marker expression and analyzed their differentiation pattern in correlation to the lipid profile and liver damage parameters in a cross-sectional study. To assess the induction of extrahepatic ApoB100-specific T cells upon transient liver damage in vivo, we performed hydrodynamic tail vein injections with diphtheria toxin A (DTA)-encoding plasmid in human ApoB100-transgenic mice.

RESULTS

Utilizing immunodominant ApoB100-derived peptides, we found increased ApoB100-specific T-cell populations in NAFLD and CVD patients compared to healthy controls. In a peptide-specific manner, ApoB100 reactivity in healthy controls was accompanied by expression of the regulatory T (Treg)-cell transcription factor FOXP3. In contrast, FOXP3 expression decreased, whereas expression of pro-inflammatory cytokine interleukin (IL)-17A increased in ApoB100-specific T cells from NAFLD and CVD patients. Dyslipidemia and liver damage parameters in blood correlated with reduced FOXP3 expression and elevated IL-17A production in ApoB100-specific T-cell populations, respectively. Moreover, DTA-mediated transient liver damage in human ApoB100-transgenic mice accumulated IL-17a-expressing ApoB100-specific T cells in the periphery.

CONCLUSION

Our results show that liver damage promotes pro-inflammatory ApoB100-specific T-cell populations, thereby providing a cellular mechanism for the increased CVD risk in liver disease patients.

Reversal of NAFLD After VSG Is Independent of Weight-Loss but RYGB Offers More Efficacy When Maintained on a High-Fat Diet

PURPOSE

Bariatric surgery is emerging as an effective treatment for obesity and the metabolic syndrome. Recently, we demonstrated that Roux-en-Y gastric bypass (RYGB), but not vertical sleeve gastrectomy (VSG), resulted in improvements to white adipose physiology and enhanced brown adipose functioning. Since beneficial alterations to liver health are also expected after bariatric surgery, comparing the post-operative effects of RYGB and VSG on liver physiology is essential to their application in the treatment of non-alcoholic fatty liver disease (NAFLD).

MATERIALS AND METHODS

The effects of RYGB and VSG on liver physiology were compared using diet induced mouse model of obesity. High-fat diet (HFD) was administered for 12 weeks after surgery and alterations to liver physiology were assessed.

RESULTS

Both RYGB and VSG showed decreased liver weight as well as reductions to hepatic cholesterol and triglyceride levels. There were demonstrable improvements to NAFLD activity score (NAS) and fibrosis stage scoring after both surgeries. In RYGB, these beneficial changes to liver function resulted from the downregulation of pro-fibrotic and upregulation anti-fibrotic genes, as well as increased fatty acid oxidation and bile acid flux. For VSG, though similar alterations were observed, they were less potent. However, VSG did significantly downregulate pro-fibrotic genes and showed increased glycogen content paralleled by decreased glycogenolysis which may have contributed to the resolution of NAFLD.

CONCLUSION

RYGB and VSG improve liver physiology and function, but RYGB is more efficacious. Resolutions of NAFLD in RYGB and VSG are achieved through different processes, independent of weight loss.

Strategies to Diagnose Nonalcoholic Steatohepatitis: A Novel Approach to Take Advantage of Pharmacokinetic Alterations

Nonalcoholic steatohepatitis (NASH) is the progressive form of nonalcoholic fatty liver disease (NAFLD) and is diagnosed by a liver biopsy. Because of the invasiveness of a biopsy, the majority of patients with NASH are undiagnosed. Additionally, the prevalence of NAFLD and NASH creates the need for a simple screening method to differentiate patients with NAFLD versus NASH. Noninvasive strategies for diagnosing NAFLD versus NASH have been developed, typically relying on imaging techniques and endogenous biomarker panels. However, each technique has limitations, and none can accurately predict the associated functional impairment of drug metabolism and disposition. The function of several drug-metabolizing enzymes and drug transporters has been described in NASH that impacts drug pharmacokinetics. The aim of this review is to give an overview of the existing noninvasive strategies to diagnose NASH and to propose a novel strategy based on altered pharmacokinetics using an exogenous biomarker whose disposition and elimination pathways are directly impacted by disease progression. Altered disposition of safe and relatively inert exogenous compounds may provide the sensitivity and specificity needed to differentiate patients with NAFLD and NASH to facilitate a direct indication of hepatic impairment on drug metabolism and prevent subsequent adverse drug reactions. SIGNIFICANCE STATEMENT: This review provides an overview of the main noninvasive techniques (imaging and panels of biomarkers) used to diagnose NAFLD and NASH along with a biopsy. Pharmacokinetic changes have been identified in NASH, and this review proposes a new approach to predict NASH and the related risk of adverse drug reactions based on the assessment of drug elimination disruption using exogenous biomarkers.

Review article: therapeutic aspects of bile acid signalling in the gut-liver axis

BACKGROUND

Bile acids are important endocrine modulators of intestinal and hepatic signalling cascades orchestrating critical pathophysiological processes in various liver diseases. Increasing knowledge on bile acid signalling has stimulated the development of synthetic ligands of nuclear bile acid receptors and other bile acid analogues.

AIM

This review summarises important aspects of bile acid-mediated crosstalk between the gut and the liver ("gut-liver axis") as well as recent findings from experimental and clinical studies.

METHODS

We performed a literature review on bile acid signalling, and therapeutic applications in chronic liver disease.

RESULTS

Intestinal and hepatic bile acid signalling pathways maintain bile acid homeostasis. Perturbations of bile acid-mediated gut-liver crosstalk dysregulate transcriptional networks involved in inflammation, fibrosis and endothelial dysfunction. Bile acids induce enterohepatic feedback signalling by the release of intestinal hormones, and regulate enterohepatic circulation. Importantly, bile acid signalling plays a central role in maintaining intestinal barrier integrity and antibacterial defense, which is particularly relevant in cirrhosis, where bacterial translocation has a profound impact on disease progression. The nuclear bile acid farnesoid X receptor (FXR) is a central intersection in bile acid signalling and has emerged as a relevant therapeutic target.

CONCLUSIONS

Experimental evidence suggests that bile acid signalling improves the intestinal barrier and protects against bacterial translocation in cirrhosis. FXR agonists have displayed efficacy for the treatment of cholestatic and metabolic liver disease in randomised controlled clinical trials. However, similar effects remain to be shown in advanced liver disease, particularly in patients with decompensated cirrhosis.

Artichoke leaf extract supplementation lowers hepatic oxidative stress and inflammation and increases multidrug resistance-associated protein 2 in mice fed a high-fat and high-cholesterol diet

Artichoke (Cynara scolymus) leaf extract (ALE) contains many phytonutrients that may have antioxidant and anti-inflammation activities against many diseases including liver damage. To investigate the protective effects of ALE on high-fat and high-cholesterol (HFHC) diet-induced steatohepatitis and liver damage in mice, twenty-four female mice were fed an HFHC diet without or with 0.5% and 1% ALE supplementation for 6 weeks. The antioxidant and anti-inflammation activities and histological changes in the liver after ALE treatment were evaluated. The results show that ALE treatment reduced the HFHC diet-induced elevation of liver damage, as indicated by an increased alanine aminotransferase activity in plasma and perivenular inflammatory infiltrates in the liver. In addition, ALE ameliorated HFHC diet-induced depletion of hepatic glutathione (GSH) and elevations of plasma total cholesterol, triglyceride and hepatic triglyceride. ALE suppressed HFHC diet-induced accumulation of cholesterol precursors, including squalene and desmosterol in the liver. Higher hepatic GSH contents and activities of GSH-related enzymes were observed after ALE treatment. Higher expressions of nuclear factor erythroid 2-related factor 2 and heme oxygenase-1 (HO-1) were induced by the HFHC diet; however, ALE treatment reduced HO-1 expression. The NOD-like receptor protein 3, caspase-1, and interleukin-1β protein and mRNA levels were reduced in the liver by ALE. A higher multidrug resistance-associated protein 2 expression in the liver was found after ALE treatment. These results suggest that ALE may ameliorate oxidative stress, inflammation and lipid metabolism disorder in HFHC diet-induced steatohepatitis and liver damage.

Abnormal Metabolism in the Progression of Nonalcoholic Fatty Liver Disease to Hepatocellular Carcinoma: Mechanistic Insights to Chemoprevention

Nonalcoholic fatty liver disease (NAFLD) is on the rise and becoming a major contributor to the development of hepatocellular carcinoma (HCC). Reasons for this include the rise in obesity and metabolic syndrome in contrast to the marked advances in prevention and treatment strategies of viral HCC. These shifts are expected to rapidly propel this trend even further in the coming decades, with NAFLD on course to become the leading etiology of end-stage liver disease and HCC. No Food and Drug Administration (FDA)-approved medications are currently available for the treatment of NAFLD, and advances are desperately needed. Numerous medications with varying mechanisms of action targeting liver steatosis and fibrosis are being investigated including peroxisome proliferator-activated receptor (PPAR) agonists and farnesoid X receptor (FXR) agonists. Additionally, drugs targeting components of metabolic syndrome, such as antihyperglycemics, have been found to affect NAFLD progression and are now being considered in the treatment of these patients. As NAFLD drug discovery continues, special attention should be given to their relationship to HCC. Several mechanisms in the pathogenesis of NAFLD have been implicated in hepatocarcinogenesis, and therapies aimed at NAFLD may additionally harbor independent antitumorigenic potential. This approach may provide novel prevention and treatment strategies.

Dynamics of the enterohepatic circulation of bile acids in healthy humans

Regulation of bile acid metabolism is normally discussed as the regulation of bile acid synthesis, which serves to compensate for intestinal loss in order to maintain a constant pool size. After a meal, bile acids start cycling in the enterohepatic circulation. Farnesoid X receptor-dependent ileal and hepatic processes lead to negative feedback inhibition of bile acid synthesis. When the intestinal bile acid flux decreases, the inhibition of synthesis is released. The degree of inhibition of synthesis and the mechanism and degree of activation are still unknown. Moreover, in humans, a biphasic diurnal expression pattern of bile acid synthesis has been documented, indicating maximal synthesis around 3 PM and 9 PM. Quantitative data on the hourly synthesis schedule as compensation for intestinal loss are lacking. In this review, we describe the classical view on bile acid metabolism and present alternative concepts that are based on the overlooked feature that bile acids transit through the enterohepatic circulation very rapidly. A daily profile of the cycling and total bile acid pool sizes and potential controlled and uncontrolled mechanisms for synthesis are predicted. It remains to be elucidated by which mechanism clock genes interact with the Farnesoid X receptor-controlled regulation of bile acid synthesis. This mechanism could become an attractive target to enhance bile acid synthesis at night, when cholesterol synthesis is high, thus lowering serum LDL-cholesterol.

Abnormal metabolic processes involved in the pathogenesis of non-alcoholic fatty liver disease (Review)

Non-alcoholic fatty liver disease (NAFLD) is one of the most common chronic liver diseases and can lead to liver cirrhosis or liver cancer in severe cases. In recent years, the incidence of NAFLD has increased substantially. The trend has continued to increase and has become a key point of concern for health systems. NAFLD is often associated with metabolic abnormalities caused by increased visceral obesity, including insulin resistance, diabetes mellitus, hypertension, dyslipidemia, atherosclerosis and systemic microinflammation. Therefore, the pathophysiological mechanisms of NAFLD must be clarified to develop new drug treatment strategies. Recently, researchers have conducted numerous studies on the pathogenesis of NAFLD and have identified various important regulatory factors and potential molecular mechanisms, providing new targets and a theoretical basis for the treatment of NAFLD. However, the pathogenesis of NAFLD is extremely complex and involves the interrelationship and influence of multiple organs and systems. Therefore, the condition must be explored further. In the present review, the abnormal metabolic process, including glucose, lipid, amino acid, bile acid and iron metabolism are reviewed. It was concluded that NAFLD is associated with an imbalanced metabolic network that involves glucose, lipids, amino acids, bile acids and iron, and lipid metabolism is the core metabolic process. The current study aimed to provide evidence and hypotheses for research and clinical treatment of NAFLD.

Heterozygous knockout of Bile salt export pump ameliorates liver steatosis in mice fed a high-fat diet

The incidence of nonalcoholic steatohepatitis (NASH) is increasing worldwide, including in Asian countries. We reported that the hepatic expression of bile salt export pump (BSEP) was downregulated in patients with NASH, suggesting that BSEP is involved in the pathogenesis of NASH. To identify the underlying mechanism, we analyzed Bsep heterozygous knock-out (Bsep^+/- mice) and wild-type (WT) C57BL/6J mice fed a high-fat diet (HFD) (32.0% animal fat) or normal diet. We examined histological changes, levels of hepatic lipids and hepatic bile acids, and expression of genes related to bile acid and cholesterol metabolism. HFD-fed Bsep^+/- mice exhibited milder hepatic steatosis and less weight gain, compared to HFD-fed WT mice. The concentrations of total bile acid, triglycerides, and cholesterols were reduced in the liver of HFD-fed Bsep^+/- mice. Regarding hepatic bile acid metabolism, the expression levels of Farnesoid X receptor (Fxr) and Multidrug resistance-associated protein 2 were significantly upregulated in HFD-fed Bsep^+/- mice, compared to HFD-fed WT mice. Furthermore, several alterations were observed in upstream cholesterol metabolism in the liver. The expression levels of bile acid metabolism-related genes were also altered in the intestine of HFD-fed Bsep^+/- mice. In conclusion, HFD-fed Bsep^+/- mice exhibited significant alterations of the expression levels of genes related to bile acid and lipid metabolism in both the liver and ileum, resulting in alleviated steatosis and less weight gain. These results suggest the importance of BSEP for maintenance of bile acid and cholesterol metabolism. Further investigations of the involvement of BSEP in the pathogenesis of NASH will provide greater insight and facilitate the development of novel therapeutic modalities.

The pharmacokinetics of mycophenolic acid in rats with orotic acid induced nonalcoholic fatty liver disease

Post-transplantation nonalcoholic fatty liver disease (NAFLD) is common in liver transplant recipients. Changes in the expression levels and activities of drug-metabolizing enzymes and drug transporters have been reported in patients with NAFLD and relevant rodent models. Here, we evaluated whether the pharmacokinetics of mycophenolic acid (MPA), an immunosuppressant, would be altered in rats with NAFLD. NAFLD was induced by feeding a diet containing 1% (w/w) orotic acid for 20 days. The extent of hepatic glucuronidation of MPA to a major metabolite, mycophenolic acid-7-O-glucuronide (MPAG), did not differ between rats with NAFLD and controls. The expression levels of hepatic multidrug resistance-associated protein 2, responsible for biliary excretion of MPAG, were comparable in rats with NAFLD and controls; the biliary excretion of MPAG was also similar in the two groups. Compared with control rats, rats with NAFLD did not exhibit significant changes in the areas under the plasma concentration – time curves of MPA or MPAG after intravenous (5 mg/kg) or oral (10 mg/kg) administration of MPA. However, delayed oral absorption of MPA was observed in rats with NAFLD compared with controls; the MPA and MPAG peak plasma concentrations fell significantly and the times to achieve them were prolonged following oral administration of MPA.

Hepatic FATP5 expression is associated with histological progression and loss of hepatic fat in NAFLD patients

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH) are characterized by the accumulation of excess hepatic fat. However, in the progression from NASH to cirrhosis, hepatic fat is often lost. Our aim was to elucidate the mechanism underlying hepatic fat loss during NASH progression.

METHODS

Liver biopsies were performed at The University of Tokyo Hospital between November 2011 and March 2016 on 146 patients with NAFLD and 14 patients with cryptogenic cirrhosis who were not being treated with any diabetes or dyslipidemia drugs. Among them, 70 patients underwent liver biopsy after an overnight fast, and 90 patients were biopsied 5 h after an oral glucose tolerance test. Expression differences in genes encoding several fatty acid metabolism-related factors were examined and correlated with hepatic histological changes based on NAFLD activity scores. Prospective patient follow-up continued until June 2018.

RESULTS

The level of fatty acid transport protein 5 (FATP5), which is associated with free fatty acid intake, was significantly and inversely correlated with features of histological progression, including ballooning and fibrosis. This was confirmed by immunohistochemical analysis. Transcript levels of genes encoding fatty acid metabolism-related proteins were comparable between NASH with severe fibrosis and cryptogenic cirrhosis. Furthermore, a prospective cohort study demonstrated that low FATP5 expression was the most significant risk factor for hepatic fat loss.

CONCLUSIONS

Decreased hepatic FATP5 expression in NAFLD is linked to histological progression, and may be associated with hepatic fat loss during NASH progression to cirrhosis.

PAR2 controls cholesterol homeostasis and lipid metabolism in nonalcoholic fatty liver disease

OBJECTIVE

Increases in hepatic and plasma cholesterol occur in patients with nonalcoholic fatty liver disease (NAFLD), although the reason for this is not well understood. We investigated whether Protease-Activated Receptor 2 (PAR2) plays a role in cholesterol and lipid homeostasis in NAFLD.

METHODS

Human liver biopsies (n = 108) were quantified for PAR2 expression from NAFLD cases randomly selected and stratified by liver fibrosis stage, the primary predictor for clinical outcomes, while controlling for age, gender, and BMI between fibrosis groups. Demographic data and laboratory studies on plasma samples were obtained within 6 months of liver biopsy. Wild-type and PAR2-KO (C57BL/6 F2rl1-/-) mice were fed either normal or high fat diet for 16 weeks and plasma and liver assayed for lipids and soluble metabolites.

RESULTS

Severity of NAFLD and plasma cholesterol levels significantly correlated with hepatocyte PAR2 expression in NAFLD patients. Conversely, PAR2 deficiency in mice resulted in reduced expression of key hepatic genes involved in cholesterol synthesis, a 50% drop in plasma and total liver cholesterol, and induced a reverse cholesterol transport system that culminated in 25% higher fecal bile acid output. PAR2-deficient mice exhibited enhanced fatty acid β-oxidation with a ketogenic shift and an unexpected increase in liver glycogenesis. Mechanistic studies identified Gi-Jnk1/2 as key downstream effectors of protease-activated PAR2 in the regulation of lipid and cholesterol homeostasis in liver.

CONCLUSIONS

These data indicate that PAR2 may be a new target for the suppression of plasma cholesterol and hepatic fat accumulation in NAFLD and related metabolic conditions.

Why Bile Acids Are So Important in Non-Alcoholic Fatty Liver Disease (NAFLD) Progression

Non-alcoholic fatty liver disease (NAFLD) is a complex disease, affecting not just the liver, but also all other organs in the body. Despite an increasing amount of people worldwide developing NAFLD and having it progress to non-alcoholic steatohepatitis (NASH) and potentially cirrhosis, there is still no approved therapy. Therefore, huge efforts are being made to find and develop a successful treatment. One of the special interests is understanding the liver-gut axis and especially the role of bile acids in the progression of NAFLD. Farnesoid X receptor (FXR)-agonists have been approved und used in other liver diseases, such as primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC), and have shown signs of being able to decrease inflammation and potentially steatosis. This review will mainly focus on targets/ligands that play an important role in bile acid metabolism and give an overview of ongoing clinical as well as pre-clinical trials. With the complexity of the issue, we did not aim at giving a complete review, rather highlighting important targets and potential treatments that could be approved for NAFLD/NASH treatment within the next few years.

iPla2β Deficiency Suppresses Hepatic ER UPR, Fxr, and Phospholipids in Mice Fed with MCD Diet, Resulting in Exacerbated Hepatic Bile Acids and Biliary Cell Proliferation

Background: Group VIA calcium-independent phospholipase A2 (iPla2β) regulates homeostasis and remodeling of phospholipids (PL). We previously showed that iPla2β^-/- mice fed with a methionine-choline-deficient diet (MCD) exhibited exaggerated liver fibrosis. As iPla2β is located in the endoplasmic reticulum (ER), we investigated the mechanisms for this by focusing on hepatic ER unfolded protein response (UPR), ER PL, and enterohepatic bile acids (BA). Methods: Female WT (wild-type) and iPla2β^-/- mice were fed with chow or MCD for 5 weeks. PL and BA profiles were measured by liquid chromatography-mass spectrometry. Gene expression analyses were performed. Results: MCD feeding of WT mice caused a decrease of ER PL subclasses, which were further decreased by iPla2β deficiency. This deficiency alone or combined with MCD downregulated the expression of liver ER UPR proteins and farnesoid X-activated receptor. The downregulation under MCD was concomitant with an elevation of BA in the liver and peripheral blood and an increase of biliary epithelial cell proliferation measured by cytokeratin 19. Conclusion: iPla2β deficiency combined with MCD severely disturbed ER PL composition and caused inactivation of UPR, leading to downregulated Fxr, exacerbated BA, and ductular proliferation. Our study provides insights into iPla2β inactivation for injury susceptibility under normal conditions and liver fibrosis and cholangiopathies during MCD feeding.

Noninvasive diagnostic criteria for nonalcoholic steatohepatitis based on gene expression levels in peripheral blood mononuclear cells

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) consists of nonalcoholic fatty liver (NAFL) and nonalcoholic steatohepatitis (NASH); the latter progresses to liver cirrhosis and hepatocellular carcinoma. Discriminating NASH from NAFL typically involves liver biopsy. The mechanism of NASH progression is unclear but may involve immunological pathways. In this study, we examined expression levels of cytokine- and chemokine-encoding genes in peripheral blood mononuclear cells (PBMCs) from NAFLD patients and established immunological criteria for discriminating NASH from NAFL.

METHODS

PBMCs were obtained from 54 patients diagnosed histologically with NAFLD (NAFL, 18; NASH, 36). mRNA was extracted from PBMCs, and expression levels of cytokine- and chemokine-encoding genes were determined by quantitative real-time PCR. Statistical analysis was performed by nonparametric test.

RESULTS

Expression levels of interferon (IFN)γ, interleukin (IL)2, IL15, C-C-motif chemokine ligand (CCL)2, IL10, and C-X-C-motif chemokine ligand (CXCL)11 were significantly upregulated in NASH patients compared with NAFL patients. Moreover, their expression levels were positively correlated with the degree of ballooning of hepatocytes but not of steatosis or lobular inflammation. We focused on those encoding IL10, IFNγ, and CCL2, and developed a scoring system to discriminate NASH from NAFL. The discriminatory power of the criteria was validated in an independent cohort.

CONCLUSIONS

Expression levels of the cytokine- and chemokine-encoding genes in PBMCs were positively correlated with ballooning, suggesting their utility for the diagnosis of NASH. The data indicate that peripheral as well as intrahepatic immunity is involved in the progression of NASH. Our findings afford new insight into immunological mechanisms of NASH and will facilitate its noninvasive diagnosis.

A Network Involving Gut Microbiota, Circulating Bile Acids, and Hepatic Metabolism Genes That Protects Against Non-Alcoholic Fatty Liver Disease

SCOPE

Gut microbiota contributes to non-alcoholic fatty liver disease (NAFLD) pathogenesis by multiple mechanisms not yet completely understood. Novel differential features between germ-free mice (GFm) transplanted with protective or non-protective cecal microbiota against NAFLD are investigated.

METHODS AND RESULTS

Gut microbiota composition, plasma, and fecal bile acids (BAs) and liver mRNAs are quantified in GFm recipients from four donor mice differing in NAFLD severity (control diet, high-fat diet [HFD]-responder, HFD-non-responder, and quercetin-supplemented HFD). Transplanted GFm are on control or HFD for 16-weeks. Multivariate analysis shows that GFm colonized with microbiota from HFD-non-responder and quercetin supplemented-HFD donors (protected against NAFLD) clusters together, whereas GFm colonized with microbiota from control and HFD-responder mice (non-protected against NAFLD) establishes another cluster. Protected phenotype is associated with increased gut Desulfovibrio and Oscillospira, reduced gut Bacteroides and Oribacterium, lower primary and higher secondary BAs in plasma and feces, induction of hepatic BA transporters, and repression of hepatic lipogenic and BA synthesis genes.

CONCLUSION

Protective gut microbiota associates with increased specific secondary BAs, which likely inhibit lipogenic pathways and enhance bile flow in the liver. This novel cross-talk between gut and liver, via plasma BAs, that promotes protection against NAFLD may have clinical and nutritional relevance.

Altered bile acid composition and disposition in a mouse model of non-alcoholic steatohepatitis

Non-alcoholic steatohepatitis (NASH) is a progressive inflammatory and fibrotic disease. However, the progression mechanism of NASH is not well understood. Bile acids are endogenous molecules that regulate cholesterol homeostasis, lipid solubilization in the intestinal lumen, and metabolic signaling via several receptors. In this study, we investigated the relationship between bile acid composition and NASH-associated fibrosis using a mouse model fed choline-deficient, L-amino-acid-defined, high-fat diet with 0.1% methionine (CDAHFD). C57BL/6 J mice fed CDAHFD developed NASH and fibrosis within few weeks. With the progress of NASH-associated liver fibrosis, altered bile acid composition was observed in the liver, bile, and peripheral plasma. Decreased mRNA levels of bile acid metabolizing enzymes such as Cyp7a1 and Baat were observed in contrast to increased Sult2a1 level in the liver. Increased mRNA levels of Ostβ and Abcc4 and decreased in mRNA levels of Bsep, Abcc2, Ntcp, and Oatp1b2, suggesting that bile acids efflux from hepatocytes into the peripheral plasma rather than into bile. In conclusion, the changes in bile acid metabolizing enzymes and transporters expression, resulting in increasing the total bile acid concentration in the plasma, signify a protection mechanism by the hepatocyte to reduce hepatotoxicity during disease progression to NASH but may promote liver fibrosis.

Disease-Associated Changes in Drug Transporters May Impact the Pharmacokinetics and/or Toxicity of Drugs: A White Paper From the International Transporter Consortium

Drug transporters are critically important for the absorption, distribution, metabolism, and excretion (ADME) of many drugs and endogenous compounds. Therefore, disruption of these pathways by inhibition, induction, genetic polymorphisms, or disease can have profound effects on overall physiology, drug pharmacokinetics, drug efficacy, and toxicity. This white paper provides a review of changes in transporter function associated with acute and chronic disease states, describes regulatory pathways affecting transporter expression, and identifies opportunities to advance the field.

Bile acid regulation: A novel therapeutic strategy in non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is characterized by excessive fat deposition in the liver in the absence of significant alcohol consumption. Dysregulated bile acid (BA) metabolism is an important indicator in the pathology of NAFLD, which could progress into more severe forms of liver injury. Lipid metabolism, immune environment and intestinal bacteria are all affected by dysregulated BA metabolism directly, but the mechanisms remain unclear. Several drug candidates that target BA metabolism, either used alone or in combination with other agents, are currently under development for treatment of NAFLD. Here, we summarize the relationship of dysregulated BA metabolism and NAFLD, discuss the effects and mechanisms of dysregulated BAs-induced lipid metabolism disorder. Challenges in developing novel treatments are also discussed.

Hepatic IRS1 and ß-catenin expression is associated with histological progression and overt diabetes emergence in NAFLD patients

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) is a risk factor for type 2 diabetes. Our aim was to investigate the relationship between NAFLD and impaired glucose metabolism in terms of insulin receptor substrate 1 and 2 (IRS1 and IRS2) expression in the liver.

METHODS

Liver biopsy was performed at the University of Tokyo Hospital between November 2011 and March 2016 on 146 patients with NAFLD who were not being treated with any diabetes or dyslipidemia drugs. Among them, 63 underwent liver biopsy after an overnight fast, and 83 at 5 h after an oral glucose tolerance test (OGTT). Differences in messenger RNA (mRNA) levels of several glucose metabolism-related factors were determined and correlated with hepatic histological changes assessed by NAFLD activity score. We prospectively followed up with the patients until May 2017.

RESULTS

Hepatic necroinflammation was significantly correlated with serum insulin levels and inversely correlated with IRS1 mRNA levels. In specimens obtained after an OGTT, hepatic necroinflammation and IRS1 expression correlated significantly with both peripheral and hepatic insulin resistance. We also found that hepatic β-catenin and glucokinase mRNA levels were elevated in patients undergoing liver biopsy after an OGTT, especially in those with less hepatic necroinflammation and a lower degree of fibrosis. A prospective cohort study showed that ballooning is the most significant risk factor for developing diabetes.

CONCLUSIONS

The decreased hepatic expression of IRS1 and β-catenin in NAFLD is linked to histological progression such as ballooning, and might lead to diabetes as a result of impaired glucose metabolism.

Asking the Right Questions With Animal Models: Methionine- and Choline-Deficient Model in Predicting Adverse Drug Reactions in Human NASH

In the past few decades, great conceptual and technological advances have been made in the field of toxicology, but animal model-based research still remains one of the most widely used and readily available tools for furthering our current knowledge. However, animal models are not perfect in predicting all systemic toxicity in humans. Extrapolating animal data to accurately predict human toxicities remains a challenge, and researchers are obligated to question the appropriateness of their chosen animal model. This paper provides an assessment of the utility of the methionine- and choline-deficient (MCD) diet fed animal model in reflecting human nonalcoholic steatohepatitis (NASH) and the potential risks of adverse drug reactions and toxicities that are associated with the disease. As a commonly used NASH model, the MCD model fails to exhibit most metabolic abnormalities in a similar manner to the human disease. The MCD model, on the other hand, closely resembles human NASH histology and reflects signatures of drug transporter alterations in humans. Due to the nature of the MCD model, it should be avoided in studies of NASH pathogenesis, metabolic parameter evaluation, and biomarker identification. But it can be used to accurately predict altered drug disposition due to NASH-associated transporter alterations.

Effect of Liver Disease on Hepatic Transporter Expression and Function

Liver disease can alter the disposition of xenobiotics and endogenous substances. Regulatory agencies such as the Food and Drug Administration and the European Medicines Evaluation Agency recommend, if possible, studying the effect of liver disease on drugs under development to guide specific dose recommendations in these patients. Although extensive research has been conducted to characterize the effect of liver disease on drug-metabolizing enzymes, emerging data have implicated that the expression and function of hepatobiliary transport proteins also are altered in liver disease. This review summarizes recent developments in the field, which may have implications for understanding altered disposition, safety, and efficacy of new and existing drugs. A brief review of liver physiology and hepatic transporter localization/function is provided. Then, the expression and function of hepatic transporters in cholestasis, hepatitis C infection, hepatocellular carcinoma, human immunodeficiency virus infection, nonalcoholic fatty liver disease and nonalcoholic steatohepatitis, and primary biliary cirrhosis are reviewed. In the absence of clinical data, nonclinical information in animal models is presented. This review aims to advance the understanding of altered expression and function of hepatic transporters in liver disease and the implications of such changes on drug disposition.

Bile acids and nonalcoholic fatty liver disease: Molecular insights and therapeutic perspectives

Nonalcoholic fatty liver disease (NAFLD) is a burgeoning health problem worldwide and an important risk factor for both hepatic and cardiometabolic mortality. The rapidly increasing prevalence of this disease and of its aggressive form nonalcoholic steatohepatitis (NASH) will require novel therapeutic approaches to prevent disease progression to advanced fibrosis or cirrhosis and cancer. In recent years, bile acids have emerged as relevant signaling molecules that act at both hepatic and extrahepatic tissues to regulate lipid and carbohydrate metabolic pathways as well as energy homeostasis. Activation or modulation of bile acid receptors, such as the farnesoid X receptor and TGR5, and transporters, such as the ileal apical sodium-dependent bile acid transporter, appear to affect both insulin sensitivity and NAFLD/NASH pathogenesis at multiple levels, and these approaches hold promise as novel therapies. In the present review, we summarize current available data on the relationships of bile acids to NAFLD and the potential for therapeutically targeting bile-acid-related pathways to address this growing world-wide disease. (Hepatology 2017;65:350-362).