Metabolic consequences of ileal interruption of the enterohepatic circulation of bile acids

The enterohepatic circulation of bile acids comprises a tightly regulated process of hepatic bile acid secretion, intestinal reabsorption and transport back to the liver. Disruption of this process has significant consequences for both gastrointestinal, liver and whole-body homeostasis and therefore offers opportunities for therapeutic intervention. In this review we discuss the effects of (pharmacological) interruption of the enterohepatic circulation at different levels. Recently, several studies have been published on ileal interruption of the enterohepatic circulation of bile acids, targeting the apical-sodium dependent bile acid transporter (ASBT, SLC10A2), as therapy for various diseases. However, ambiguous results have been reported and in-depth mechanistic insights are lacking. Here we discuss these novel studies and review the current knowledge and literature on the consequences of ASBT inhibition and its potential effects on physiology and metabolism

Pegbelfermin (BMS-986036):an investigational PEGylated fibroblast growth factor 21 analogue for the treatment of nonalcoholic steatohepatitis

Introduction: Nonalcoholic fatty liver disease (NAFLD) is the most common liver disease worldwide and is strongly associated with obesity and insulin resistance. NAFLD refers to a spectrum of disorders ranging from asymptomatic hepatic steatosis (nonalcoholic fatty liver, NAFL) to nonalcoholic steatohepatitis (NASH), which increases the risk of developing more severe forms of liver disease such as progressive fibrosis, cirrhosis, and liver cancer. Currently, there are no food and drug administration (FDA) approved drugs to treat NASH. Pegbelfermin (BMS-986036) is a PEGylated fibroblast growth factor 21 (FGF21) analogue that is under investigation for the treatment of NASH. Areas covered: We reviewed the (pre)clinical pegbelfermin studies and compared these with other studies that assessed FGF21 and FGF21 analogues in the treatment of NASH. Expert opinion: With no FDA approved treatments available for NASH, there is an urgent need for novel therapies. Pegbelfermin is a systemic treatment with pleiotropic effects on various tissues. Short-term adverse effects are limited, but more research is required to study potential long-term safety issues. In a phase 2a trial, pegbelfermin has shown promising improvements in several NASH related outcomes. However, clinical trials demonstrating long-term benefits on hard outcomes such as liver histology, cirrhosis development, or survival are required for further validation

The Role of Lipophagy in the Development and Treatment of Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) or metabolic (dysfunction) associated liver disease (MAFLD), is, with a global prevalence of 25%, the most common liver disorder worldwide. NAFLD comprises a spectrum of liver disorders ranging from simple steatosis to steatohepatitis, fibrosis, cirrhosis and eventually end-stage liver disease. The cause of NAFLD is multifactorial with genetic susceptibility and an unhealthy lifestyle playing a crucial role in its development. Disrupted hepatic lipid homeostasis resulting in hepatic triglyceride accumulation is an hallmark of NAFLD. This disruption is commonly described based on four pathways concerning 1) increased fatty acid influx, 2) increased de novo lipogenesis, 3) reduced triglyceride secretion, and 4) reduced fatty acid oxidation. More recently, lipophagy has also emerged as pathway affecting NAFLD development and progression. Lipophagy is a form of autophagy (i.e. controlled autolysosomal degradation and recycling of cellular components), that controls the breakdown of lipid droplets in the liver. Here we address the role of hepatic lipid homeostasis in NAFLD and specifically review the current literature on lipophagy, describing its underlying mechanism, its role in pathophysiology and its potential as a therapeutic target

Regulation of Intestinal UDP-Glucuronosyltransferase 1A1 by the Farnesoid X Receptor Agonist Obeticholic Acid Is Controlled by Constitutive Androstane Receptor through Intestinal Maturation

UDP-glucuronosyltransferase (UGT) 1A1 is the only transferase capable of conjugating serum bilirubin. However, temporal delay in the development of the UGT1A1 gene leads to an accumulation of serum bilirubin in newborn children. Neonatal humanized UGT1 (hUGT1) mice, which accumulate severe levels of total serum bilirubin (TSB), were treated by oral gavage with obeticholic acid (OCA), a potent FXR agonist. OCA treatment led to dramatic reduction in TSB levels. Analysis of UGT1A1 expression confirmed that OCA induced intestinal and not hepatic UGT1A1. Interestingly, Cyp2b10, a target gene of the nuclear receptor CAR, was also induced by OCA in intestinal tissue. In neonatal hUGT1/Car(-/-) mice, OCA was unable to induce CYP2B10 and UGT1A1, confirming that CAR and not FXR is involved in the induction of intestinal UGT1A1. However, OCA did induce FXR target genes, such as Shp, in both intestines and liver with induction of Fgf15 in intestinal tissue. Circulating FGF15 activates hepatic FXR and, together with hepatic Shp, blocks Cyp7a1 and Cyp7b1 gene expression, key enzymes in bile acid metabolism. Importantly, the administration of OCA in neonatal hUGT1 mice accelerates intestinal epithelial cell maturation, which directly impacts on induction of the UGT1A1 gene and the reduction in TSB levels. Accelerated intestinal maturation is directly controlled by CAR, since induction of enterocyte marker genes sucrase-isomaitase, alkaline phosphatase 3, and keratin 20 by OCA does not occur in hUGT1/Car(-/-) mice. Thus, new findings link an important role for CAR in intestinal UGT1A1 induction and its role in the intestinal maturation pathway. SIGNIFICANCE STATEMENT Obeticholic acid (OCA) activates FXR target genes in both liver and intestinal tissues while inducing intestinal UGT1A1, which leads to the elimination of serum bilirubin in humanized UGT1 mice. However, the induction of intestinal UGT1A1 and the elimination of bilirubin by OCA is driven entirely by activation of intestinal CAR and not FXR. The elimination of serum bilirubin is based on a CARdependent mechanism that facilitates the acceleration of intestinal epithelium cell differentiation, an event that underlies the induction of intestinal UGT1A1

Senescent cells in the development of cardiometabolic disease

Purpose of review Senescent cells have recently been identified as key players in the development of metabolic dysfunction. In this review, we will highlight recent developments in this field and discuss the concept of targeting these cells to prevent or treat cardiometabolic diseases. Recent findings Evidence is accumulating that cellular senescence contributes to adipose tissue dysfunction, presumably through induction of low-grade inflammation and inhibition of adipogenic differentiation leading to insulin resistance and dyslipidaemia. Senescent cells modulate their surroundings through their bioactive secretome and only a relatively small number of senescent cells is sufficient to cause persistent physical dysfunction even in young mice. Proof-of-principle studies showed that selective elimination of senescent cells can prevent or delay the development of cardiometabolic diseases in mice. Summary The metabolic consequences of senescent cell accumulation in various tissues are now unravelling and point to new therapeutic opportunities for the treatment of cardiometabolic diseases

Induction of fecal cholesterol excretion is not effective for the treatment of hyperbilirubinemia in Gunn rats

Background Unconjugated hyperbilirubinemia, a feature of neonatal jaundice or Crigler-Najjar syndrome, can lead to neurotoxicity and even death. We previously demonstrated that unconjugated bilirubin (UCB) can be eliminated via transintestinal excretion in Gunn rats, a model of unconjugated hyperbilirubinemia, and that this is stimulated by enhancing fecal fatty acid excretion. Since transintestinal excretion also occurs for cholesterol (TICE), we hypothesized that increasing fecal cholesterol excretion and/or TICE could also enhance fecal UCB disposal and subsequently lower plasma UCB concentrations. Methods To determine whether increasing fecal cholesterol excretion could ameliorate unconjugated hyperbilirubinemia, we treated hyperbilirubinemic Gunn rats with ezetimibe (EZE), an intestinal cholesterol absorption inhibitor, and/or a liver X receptor (LXR) and farnesoid X receptor (FXR) agonist (T0901317 (T09) and obeticholic acid (OCA), respectively), known to stimulate TICE. Results We found that EZE treatment alone or in combination with T09 or OCA increased fecal cholesterol disposal but did not lower plasma UCB levels. Conclusions These findings do not support a link between the regulation of transintestinal excretion of cholesterol and bilirubin. Furthermore, induction of fecal cholesterol excretion is not a potential therapy for unconjugated hyperbilirubinemia. Impact Increasing fecal cholesterol excretion is not effective to treat unconjugated hyperbilirubinemia. This is the first time a potential relation between transintestinal excretion of cholesterol and unconjugated bilirubin is investigated. Transintestinal excretion of cholesterol and unconjugated bilirubin do not seem to be quantitatively linked. Unlike intestinal fatty acids, cholesterol cannot "capture" unconjugated bilirubin to increase its excretion. These results add to our understanding of ways to improve and factors regulating unconjugated bilirubin disposal in hyperbilirubinemic conditions

Efficient reabsorption of transintestinally excreted cholesterol is a strong determinant for cholesterol disposal in mice[S]

Transintestinal cholesterol excretion (TICE) is a major route for eliminating cholesterol from the body and a potential therapeutic target for hypercholesterolemia. The underlying mechanism, however, is largely unclear, and its contribution to cholesterol disposal from the body is obscured by the counteracting process of intestinal cholesterol reabsorption. To determine the quantity of TICE independent from its reabsorption, we studied two models of decreased intestinal cholesterol absorption. Cholesterol absorption was inhibited either by ezetimibe or, indirectly, by the genetic inactivation of the intestinal apical sodium-dependent bile acid transporter (ASBT; SLC10A2). Both ezetimibe treatment and Asbt inactivation virtually abrogated fractional cholesterol absorption (from 46% to 4% and 6%, respectively). In both models, fecal neutral sterol excretion and net intestinal cholesterol balance were considerably higher than in control mice (5- and 7-fold, respectively), suggesting that, under physiological conditions, TICE is largely reabsorbed. In addition, the net intestinal cholesterol balance was increased to a similar extent but was not further increased when the models were combined, suggesting that the effect on cholesterol reabsorption was already maximal under either condition alone. On the basis of these findings, we hypothesize that the inhibition of cholesterol (re)absorption combined with stimulating TICE will be most effective in increasing cholesterol disposal

Identification of the fructose transporter GLUT5 (SLC2A5) as a novel target of nuclear receptor LXR

Fructose has become a major constituent of our modern diet and is implicated as an underlying cause in the development of metabolic diseases. The fructose transporter GLUT5 (SLC2A5) is required for intestinal fructose absorption. GLUT5 expression is induced in the intestine and skeletal muscle of type 2 diabetes (T2D) patients and in certain cancers that are dependent on fructose metabolism, indicating that modulation of GLUT5 levels could have potential in the treatment of these diseases. Using an unbiased screen for transcriptional control of the human GLUT5 promoter we identified a strong and specific regulation by liver X receptor alpha (LXR alpha, NR1H3). Using promoter truncations and site-directed mutagenesis we identified a functional LXR response element (LXRE) in the human GLUT5 promoter, located at -385 bp relative to the transcriptional start site (TSS). Finally, mice treated with LXR agonist T0901317 showed an increase in Glut5 mRNA and protein levels in duodenum and adipose tissue, underscoring the in vivo relevance of its regulation by LXR. Together, our findings show that LXR alpha regulates GLUT5 in mice and humans. As a ligand-activated transcription factor, LXR alpha might provide novel pharmacologic strategies for the selective modulation of GLUT5 activity in the treatment of metabolic disease as well as cancer.</p

Impaired Hepatic Vitamin A Metabolism in NAFLD Mice Leading to Vitamin A Accumulation in Hepatocytes

BACKGROUND & AIMS: Systemic retinol (vitamin A) homeostasis is controlled by the liver, involving close collaboration between hepatocytes and hepatic stellate cells (HSCs). Genetic variants in retinol metabolism (PNPLA3 and HSD17B13) are associated with non-alcoholic fatty liver disease (NAFLD) and disease progression. Still, little mechanistic details are known about hepatic vitamin A metabolism in NAFLD, which may affect carbohydrate and lipid metabolism, inflammation, oxidative stress and the development of fibrosis and cancer, e.g. all risk factors of NAFLD. METHODS: Here, we analyzed vitamin A metabolism in 2 mouse models of NAFLD; mice fed a high-fat, high-cholesterol (HFC) diet and Leptin(ob) mutant (ob/ob) mice. RESULTS: Hepatic retinol and retinol binding protein 4 (RBP4) levels were significantly reduced in both mouse models of NAFLD. In contrast, hepatic retinyl palmitate levels (the vitamin A storage form) were significantly elevated in these mice. Transcriptome analysis revealed a hyperdynamic state of hepatic vitamin A metabolism, with enhanced retinol storage and metabolism (upregulated Lrat, Dgat1, Pnpla3, Raldh's and RAR/RXR-target genes) in fatty livers, in conjunction with induced hepatic inflammation (upregulated Cd68, Tnf alpha, Nos2, Il1 beta, 11-6) and fibrosis (upregulated Colla1, Acta2, Tgf beta, Timp1). Autofluorescence analyses revealed prominent vitamin A accumulation in hepatocytes rather than HSC in HFC-fed mice. Palmitic acid exposure increased Lrat mRNA levels in primary rat hepatocytes and promoted retinyl palmitate accumulation when co-treated with retinol, which was not detected for similarly-treated primary rat HSCs. CONCLUSION: NAFLD leads to cell type-specific rearrangements in retinol metabolism leading to vitamin A accumulation in hepatocytes. This may promote disease progression and/or affect therapeutic approaches targeting nuclear receptors

The chemotherapeutic drug doxorubicin does not exacerbate p16^Ink4a-positive senescent cell accumulation and cardiometabolic disease development in young adult female LDLR-deficient mice

Cancer survivors who received chemotherapy, such as the anthracycline doxorubicin (DOX), have an increased risk of developing complications later in life, including the development of chronic metabolic diseases. Although the etiology of this increased risk for late metabolic complications in cancer survivors is poorly understood, a causal role of therapy-induced senescent cells has been suggested. To study the role of cellular senescence in chemotherapy-induced metabolic complications, young adult female low-density lipoprotein receptor-deficient (Ldlr−/−)-p16-3MR mice, in which p16Ink4a-positive (p16Ink4a+) senescent cells can be genetically eliminated, were treated with four weekly injections of DOX (2.5 mg/kg) followed by a high-fat high-cholesterol diet for 12 weeks. While DOX treatment induced known short-term effects, such as reduction in body weight, gonadal fat mass, and adipose tissue inflammation, it was not associated with significant long-term effects on glucose homeostasis, hepatic steatosis, or atherosclerosis. We further found no evidence of DOX-induced accumulation of p16Ink4a+-senescent cells at 1 or 12 weeks after DOX treatment. Neither did we observe an effect of elimination of p16Ink4a+-senescent cells on the development of diet-induced cardiometabolic complications in DOX-treated mice. Other markers for senescence were generally also not affected except for an increase in p21 and Cxcl10 in gonadal white adipose tissue long-term after DOX treatment. Together, our study does not support a significant role for p16Ink4a+-senescent cells in the development of diet-induced cardiometabolic disease in young adult DOX-treated female Ldlr−/− mice. These findings illustrate the need of further studies to understand the link between cancer therapy and cardiometabolic disease development in cancer survivors.</p