Lack of effect of norfloxacin on hyperdynamic circulation in bile duct-ligated rats despite reduction of endothelial nitric oxide synthase function: result of unchanged vascular Rho-kinase?

Carbohydrate supplementation retains intestinal barrier and ameliorates bacterial translocation in an antibiotic-induced mouse model

Bacterial translocation (BT), with antibiotic use as an inducer, is associated with increased risk of developing multiple inflammatory disorders, and is closely associated with intestinal barrier integrity. Deacetylated konjac glucomannan (DKGM) and konjac oligo-glucomannan (KOGM) are two of the most widely used derivatives in the food industry. They are structurally and physiologically distinct from konjac glucomannan (KGM), and previous studies have confirmed their prebiotic effects. But whether they play a role in antibiotic-induced BT is unknown. Here, we applied an antibiotic cocktail (Abx) to a mouse model and investigated whether and how KGM and its derivatives function in BT and inflammation response amelioration during and after antibiotics, and which intervention plan is more effective. The results showed that KGM and its derivatives all inhibited BT. The colon tissue lesions caused by BT were largely alleviated, and short-chain fatty acid (SCFA) production was highly improved with the supplementation of carbohydrates. The prolonged intervention plan using KGM and its derivatives was more efficient than intervention only during the Abx administration period. Among the three dietary fibers, KGM behaved best, while DKGM and KOGM behaved equivalently. Additionally, KGM and its derivatives all reduced the inflammatory response accompanying BT, but DKGM may have a direct inhibitory efficacy in inflammation other than that through IL-10, unlike KGM or KOGM.

Beta-blockers in patients with liver cirrhosis: Pragmatism or perfection?

With increasing decompensation, hyperdynamic circulatory disturbance occurs in liver cirrhosis despite activation of vasoconstrictors. Here, the concept of a therapy with non-selective beta-blockers was established decades ago. They lower elevated portal pressure, protect against variceal hemorrhage, and may also have pleiotropic immunomodulatory effects. Recently, the beneficial effect of carvedilol, which blocks alpha and beta receptors, has been highlighted. Carvedilol leads to "biased-signaling" via recruitment of beta-arrestin. This effect and its consequences have not been sufficiently investigated in patients with liver cirrhosis. Also, a number of questions remain open regarding the expression of beta-receptors and its intracellular signaling and the respective consequences in the intra- and extrahepatic tissue compartments. Despite the undisputed role of non-selective beta-blockers in the treatment of liver cirrhosis, we still can improve the knowledge as to when and how beta-blockers should be used in which patients.

Current and investigational drugs in early clinical development for portal hypertension

Introduction

The development of portal hypertension leads to a majority of complications associated with chronic liver disease. Therefore, adequate treatment of portal hypertension is crucial in the management of such patients. Current treatment options are limited and consist mainly of medications that decrease the hyperdynamic circulation, such as non-selective beta blockers, and treatment of hypervolemia with diuretics. Despite these options, mortality rates have not improved over the last two decades. Newer, more effective treatment options are necessary to help improve survival and quality of life in these patients.

Areas covered

Multiple preclinical models and clinical studies have demonstrated potential efficacy of a variety of new treatment modalities. We introduce treatment options including the use of vasodilation promotors, vasoconstriction inhibitors, anticoagulants, antiangiogenics, and anti-inflammatory drugs. We examine the most recent studies for treatment options within these drug classes and offer insights as to which show the most promise in this field.

Methodology

Published studies that identified novel medical treatment options of portal hypertension were searched using PubMed (https://pubmed.ncbi.nlm.nih.gov/). Clinical trials listed in Clinicaltrials.gov were also searched with a focus on more recent and ongoing studies, including those with completed recruitment. Searching with key terms including "portal hypertension" as well as individually searching specific treatment medications that were listed in other publications was carried out. Finally, current societal guidelines and recent review articles relevant to the management of portal hypertension were evaluated, and listed references of interest were included.

Conclusion

Many ongoing early phase studies demonstrate promising results and may shape the field of portal hypertension management in future. As concrete results become available, larger RCTs will be required before making definitive conclusions regarding safety and efficacy and whether or not they can be incorporated into routine clinical practice. Statins, anticoagulants, and PDE inhibitors have been among the most studied and appear to be most promising.

Investigational drugs in early clinical development for portal hypertension

INTRODUCTION

Advanced chronic liver disease is considered a reversible condition after removal of the primary aetiological factor. This has led to a paradigm shift in which portal hypertension (PH) is a reversible complication of cirrhosis. The pharmacologic management of PH is centered on finding targets to modify the natural history of cirrhosis and PH.

AREAS COVERED

This paper offers an overview of the use of pharmacological strategies in early clinical development that modify PH. Papers included were selected from searching clinical trials sites and PubMed from the last 10 years.

EXPERT OPINION

A paradigm shift has generated a new concept of PH in cirrhosis as a reversible complication of a potentially curable disease. Decreasing portal pressure to prevent decompensation and further complications of cirrhosis that may lead liver transplantation or death is a goal. Therapeutic strategies also aspire achieve total or partial regression of fibrosis thus eliminating the need for treatment or screening of PH.

Targeting Gut–Liver Axis for Treatment of Liver Fibrosis and Portal Hypertension

Antifibrotic therapies for the treatment of liver fibrosis represent an unconquered area of drug development. The significant involvement of the gut microbiota as a driving force in a multitude of liver disease, be it pathogenesis or fibrotic progression, suggest that targeting the gut–liver axis, relevant signaling pathways, and/or manipulation of the gut’s commensal microbial composition and its metabolites may offer opportunities for biomarker discovery, novel therapies and personalized medicine development. Here, we review potential links between bacterial translocation and deficits of host-microbiome compartmentalization and liver fibrosis that occur in settings of advanced chronic liver disease. We discuss established and emerging therapeutic strategies, translated from our current knowledge of the gut–liver axis, targeted at restoring intestinal eubiosis, ameliorating hepatic fibrosis and rising portal hypertension that characterize and define the course of decompensated cirrhosis.

Bile Acids, Liver Cirrhosis, and Extrahepatic Vascular Dysfunction

The bile acid pool with its individual bile acids (BA) is modulated in the enterohepatic circulation by the liver as the primary site of synthesis, the motility of the gallbladder and of the intestinal tract, as well as by bacterial enzymes in the intestine. The nuclear receptor farnesoid X receptor (FXR) and Gpbar1 (TGR5) are important set screws in this process. Bile acids have a vasodilatory effect, at least according to in vitro studies. The present review examines the question of the extent to which the increase in bile acids in plasma could be responsible for the hyperdynamic circulatory disturbance of liver cirrhosis and whether modulation of the bile acid pool, for example, via administration of ursodeoxycholic acid (UDCA) or via modulation of the dysbiosis present in liver cirrhosis could influence the hemodynamic disorder of liver cirrhosis. According to our analysis, the evidence for this is limited. Long-term studies on this question are lacking.

Novel treatment options for portal hypertension

Portal hypertension is most frequently associated with cirrhosis and is a major driver for associated complications, such as variceal bleeding, ascites or hepatic encephalopathy. As such, clinically significant portal hypertension forms the prelude to decompensation and impacts significantly on the prognosis of patients with liver cirrhosis. At present, non-selective β-blockers, vasopressin analogues and somatostatin analogues are the mainstay of treatment but these strategies are far from satisfactory and only target splanchnic hyperemia. In contrast, safe and reliable strategies to reduce the increased intrahepatic resistance in cirrhotic patients still represent a pending issue. In recent years, several preclinical and clinical trials have focused on this latter component and other therapeutic avenues. In this review, we highlight novel data in this context and address potentially interesting therapeutic options for the future.

Novel Rat Model of Repetitive Portal Venous Embolization Mimicking Human Non-Cirrhotic Idiopathic Portal Hypertension

BACKGROUND

Non-cirrhotic idiopathic portal hypertension (NCIPH) is characterized by splenomegaly, anemia and portal hypertension, while liver function is preserved. However, no animal models have been established yet. This study assessed a rat model of NCIPH and characterized the hemodynamics, and compared it to human NCIPH.

METHODS

Portal pressure (PP) was measured invasively and coloured microspheres were injected in the ileocecal vein in rats. This procedure was performed weekly for 3 weeks (weekly embolization). Rats without and with single embolization served as controls. After four weeks (one week after last embolization), hemodynamics were investigated, hepatic fibrosis and accumulation of myofibroblasts were analysed. General characteristics, laboratory analyses and liver histology were collected in patients with NCIPH.

RESULTS

Weekly embolization induced a hyperdynamic circulation, with increased PP. The mesenteric flow and hepatic hydroxyproline content was significantly higher in weekly embolized compared to single embolized rats (mesenteric flow +54.1%, hydroxyproline +41.7%). Mesenteric blood flow and shunt volumes increased, whereas splanchnic vascular resistance was decreased in the weekly embolization group. Fibrotic markers αSMA and Desmin were upregulated in weekly embolized rats.

DISCUSSION

This study establishes a model using repetitive embolization via portal veins, comparable with human NCIPH and may serve to test new therapies.

HSC-specific inhibition of Rho-kinase reduces portal pressure in cirrhotic rats without major systemic effects

BACKGROUND & AIMS

Rho-kinase activation mediates cell contraction and increases intrahepatic resistance and consequently portal pressure in liver cirrhosis. Systemic Rho-kinase inhibition decreases portal pressure in cirrhosis, but also arterial pressure. Thus, liver-specific Rho-kinase inhibition is needed. The delivery of Rho-kinase inhibitor to activated hepatic stellate cells reduces fibrosis. It might also relax these contractile cells and therewith decrease intrahepatic resistance. We tested this hypothesis by performing acute experiments in cirrhotic rats.

METHODS

Cirrhosis models were CCl(4)-intoxication and bile duct ligation. Three hours after injection of the Rho-kinase inhibitor (Y26732) coupled with a carrier (mannose-6-phosphate modified human serum albumin), which targets activated hepatic stellate cells, hemodynamics were analyzed by the colored microsphere technique and direct pressure measurements. The delivery site and effect of Rho-kinase inhibitor were investigated by immunohistochemical stainings, as well as Western blot. Experiments with Rho-kinase inhibitor coupled with unmodified human serum albumin served as untargeted control.

RESULTS

In both models of cirrhosis, the carrier coupled Rho-kinase inhibitor lowered the portal pressure and decreased the hepatic-portal resistance. Immunohistochemical desmin-staining showed the carrier in hepatic stellate cells. The targeted therapy decreased the expression of the phosphorylated substrate of Rho-kinase (moesin) and abolished myosin light chains phosphorylation in fibrotic septae (collagen-staining). The targeted Rho-kinase inhibitor showed no major extrahepatic effects. By contrast, the untargeted Rho-kinase inhibitor elicited severe systemic hypotension.

CONCLUSIONS

Activated hepatic stellate cells are crucially involved in portal hypertension in cirrhosis. Targeting of Rho-kinase in hepatic stellate cells not only decreased fibrosis, as previously shown, but also lowers portal pressure acutely without major systemic effects as demonstrated in this study.

Intestinal decontamination inhibits TLR4 dependent fibronectin-mediated cross-talk between stellate cells and endothelial cells in liver fibrosis in mice

BACKGROUND & AIMS

Liver fibrosis is associated with angiogenesis and leads to portal hypertension. Certain antibiotics reduce complications of liver failure in humans, however, the effects of antibiotics on the pathologic alterations of the disease are not fully understood. The aim of this study was to test whether the non-absorbable antibiotic rifaximin could attenuate fibrosis progression and portal hypertension in vivo, and explore potential mechanisms in vitro.

METHODS

The effect of rifaximin on portal pressure, fibrosis, and angiogenesis was examined in wild type and Toll-like receptor 4 (TLR4) mutant mice after bile duct ligation (BDL). In vitro studies were carried out to evaluate the effect of the bacterial product and TLR agonist lipopolysaccharide (LPS) on paracrine interactions between hepatic stellate cells (HSC) and liver endothelial cells (LEC) that lead to fibrosis and portal hypertension.

RESULTS

Portal pressure, fibrosis, and angiogenesis were significantly lower in BDL mice receiving rifaximin compared to BDL mice receiving vehicle. Studies in TLR4 mutant mice confirmed that the effect of rifaximin was dependent on LPS/TLR4 pathway. Fibronectin (FN) was increased in the BDL liver and was reduced by rifaximin administration and thus, was explored further in vitro as a potential mediator of paracrine interactions of HSC and LEC. In vitro, LPS promoted FN production from HSC. Furthermore, HSC-derived FN promoted LEC migration and angiogenesis.

CONCLUSIONS

These studies expand our understanding of the relationship of intestinal microbiota with fibrosis development by identifying FN as a TLR4 dependent mediator of the matrix and vascular changes that characterize cirrhosis.