Beneficial Effects of the Peroxisome Proliferator-Activated Receptor α/γ Agonist Aleglitazar on Progressive Hepatic and Splanchnic Abnormalities in Cirrhotic Rats with Portal Hypertension

Pathophysiology and therapeutic options for cirrhotic portal hypertension

Portal hypertension represents the primary non-neoplastic complication of liver cirrhosis and has life-threatening consequences, such as oesophageal variceal bleeding, ascites, and hepatic encephalopathy. Portal hypertension occurs due to increased resistance of the cirrhotic liver vasculature to portal blood flow and is further aggravated by the hyperdynamic circulatory syndrome. Existing knowledge indicates that the profibrogenic phenotype acquired by sinusoidal cells is the initial factor leading to increased hepatic vascular tone and fibrosis, which cause increased vascular resistance and portal hypertension. Data also suggest that the phenotype of hepatic cells could be further impaired due to the altered mechanical properties of the cirrhotic liver itself, creating a deleterious cycle that worsens portal hypertension in the advanced stages of liver disease. In this Review, we discuss recent discoveries in the pathophysiology and treatment of cirrhotic portal hypertension, a condition with few pharmacological treatment options.

Treating NASH by targeting peroxisome proliferator-activated receptors

The pathophysiology of non-alcoholic steatohepatitis (NASH) encompasses a complex set of intra- and extrahepatic driving mechanisms, involving numerous metabolic, inflammatory, vascular and fibrogenic pathways. The peroxisome proliferator-activated receptors (PPARs) α, β/δ and γ belong to the nuclear receptor family of ligand-activated transcription factors. Activated PPARs modulate target tissue transcriptomic profiles, enabling the body's adaptation to changing nutritional, metabolic and inflammatory environments. PPARs hence regulate several pathways involved in NASH pathogenesis. Whereas single PPAR agonists exert robust anti-NASH activity in several preclinical models, their clinical effects on histological endpoints of NASH resolution and fibrosis regression appear more modest. Simultaneous activation of several PPAR isotypes across different organs and within-organ cell types, resulting in pleiotropic actions, enhances the therapeutic potential of PPAR agonists as pharmacological agents for NASH and NASH-related hepatic and extrahepatic morbidity, with some compounds having already shown clinical efficacy on histological endpoints.

Emerging Therapeutic Targets for Portal Hypertension

Purpose of Review

Portal hypertension is responsible of the main complications of cirrhosis, which carries a high mortality. Recent treatments have improved prognosis, but this is still far from ideal. This paper reviews new potential therapeutic targets unveiled by advances of key pathophysiologic processes.

Recent Findings

Recent research highlighted the importance of suppressing etiologic factors and a safe lifestyle and outlined new mechanisms modulating portal pressure. These include intrahepatic abnormalities linked to inflammation, fibrogenesis, vascular occlusion, parenchymal extinction, and angiogenesis; impaired regeneration; increased hepatic vascular tone due to sinusoidal endothelial dysfunction with insufficient NO availability; and paracrine liver cell crosstalk. Moreover, pathways such as the gut-liver axis modulate splanchnic vasodilatation and systemic inflammation, exacerbate liver fibrosis, and are being targeted by therapy. We have summarized studies of new agents addressing these targets.

Summary

New agents, alone or in combination, allow acting in complementary mechanisms offering a more profound effect on portal hypertension while simultaneously limiting disease progression and favoring regression of fibrosis and of cirrhosis. Major changes in treatment paradigms are anticipated.

Improvement of non-invasive tests of liver steatosis and fibrosis as indicators for non-alcoholic fatty liver disease in type 2 diabetes mellitus patients with elevated cardiovascular risk profile using the PPAR-α/γ agonist aleglitazar

BACKGROUND

Peroxisome proliferator-activated receptor (PPAR) agonists may have favorable outcomes on non-alcoholic fatty liver disease. This study serves as proof of concept to evaluate whether dual PPAR-α/γ agonists improve non-invasive tests of liver steatosis and fibrosis.

METHODS

This is a post-hoc analysis of a randomized, double-blind, placebo-controlled, multi-center trial comprising 7226 patients with type 2 diabetes mellitus and recent coronary artery disease randomized to receive aleglitazar, a PPAR-α/γ agonists, or placebo for two years. Main outcomes were change in non-invasive tests for liver steatosis and fibrosis: Liver Fat Score (LFS), Liver Accumulation Product (LAP), Fibrosis-4 (FIB-4), and NAFLD Fibrosis Score (NFS).

RESULTS

LFS, LAP and FIB-4 decreased upon treatment, whereas scores in the placebo group remained the same or increased (P<0.001). NFS responded differently but remained consistently lower than placebo. In the treatment group more participants shifted to a lower FIB-4 and NFS category, or improved in respect to the LAP cut-off values compared to the placebo group (P<0.001 for FIB-4 and LAP, P<0.004 for NFS). LFS had a low discriminative power in this study.

CONCLUSION

This post-hoc analysis showed improvement of non-invasive tests of liver steatosis and fibrosis after starting dual PPAR-α/γ agonist treatment, adding to the evidence that this pathway has potential in non-alcoholic fatty liver disease treatment.

Review article: vascular effects of PPARs in the context of NASH

BACKGROUND

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors known to regulate glucose and fatty acid metabolism, inflammation, endothelial function and fibrosis. PPAR isoforms have been extensively studied in metabolic diseases, including type 2 diabetes and cardiovascular diseases. Recent data extend the key role of PPARs to liver diseases coursing with vascular dysfunction, including nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH).

AIM

This review summarises and discusses the pathobiological role of PPARs in cardiovascular diseases with a special focus on their impact and therapeutic potential in NAFLD and NASH.

RESULTS AND CONCLUSIONS

PPARs may be attractive for the treatment of NASH due to their liver-specific effects but also because of their efficacy in improving cardiovascular outcomes, which may later impact liver disease. Assessment of cardiovascular disease in the context of NASH trials is, therefore, of the utmost importance, both from a safety and efficacy perspective.

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.

Portal hypertension in cirrhosis: Pathophysiological mechanisms and therapy

Portal hypertension, defined as increased pressure in the portal vein, develops as a consequence of increased intrahepatic vascular resistance due to the dysregulation of liver sinusoidal endothelial cells (LSECs) and hepatic stellate cells (HSCs), frequently arising from chronic liver diseases. Extrahepatic haemodynamic changes contribute to the aggravation of portal hypertension. The pathogenic complexity of portal hypertension and the unsuccessful translation of preclinical studies have impeded the development of effective therapeutics for patients with cirrhosis, while counteracting hepatic and extrahepatic mechanisms also pose a major obstacle to effective treatment. In this review article, we will discuss the following topics: i) cellular and molecular mechanisms of portal hypertension, focusing on dysregulation of LSECs, HSCs and hepatic microvascular thrombosis, as well as changes in the extrahepatic vasculature, since these are the major contributors to portal hypertension; ii) translational/clinical advances in our knowledge of portal hypertension; and iii) future directions.

The Agonists of Peroxisome Proliferator-Activated Receptor-γ for Liver Fibrosis

Liver fibrosis is a common link in the transformation of acute and chronic liver diseases to cirrhosis. It is of great clinical significance to study the factors associated with the induction of liver fibrosis and elucidate the method of reversal. Peroxisome proliferator-activated receptors (PPARs) are a class of nuclear transcription factors that can be activated by peroxisome proliferators. PPARs play an important role in fibrosis of various organs, especially the liver, by regulating downstream targeted pathways, such as TGF-β, MAPKs, and NF-κB p65. In recent years, the development and screening of PPAR-γ ligands have become a focus of research. The PPAR-γ ligands include synthetic hypolipidemic and antidiabetic drugs. In addition, microRNAs, lncRNAs, circRNAs and nano new drugs have attracted research interest. In this paper, the research progress of PPAR-γ in the pathogenesis and treatment of liver fibrosis was discussed based on the relevant literature in recent years.

Role of liver sinusoidal endothelial cells in liver diseases

Liver sinusoidal endothelial cells (LSECs) form the wall of the hepatic sinusoids. Unlike other capillaries, they lack an organized basement membrane and have cytoplasm that is penetrated by open fenestrae, making the hepatic microvascular endothelium discontinuous. LSECs have essential roles in the maintenance of hepatic homeostasis, including regulation of the vascular tone, inflammation and thrombosis, and they are essential for control of the hepatic immune response. On a background of acute or chronic liver injury, LSECs modify their phenotype and negatively affect neighbouring cells and liver disease pathophysiology. This Review describes the main functions and phenotypic dysregulations of LSECs in liver diseases, specifically in the context of acute injury (ischaemia-reperfusion injury, drug-induced liver injury and bacterial and viral infection), chronic liver disease (metabolism-associated liver disease, alcoholic steatohepatitis and chronic hepatotoxic injury) and hepatocellular carcinoma, and provides a comprehensive update of the role of LSECs as therapeutic targets for liver disease. Finally, we discuss the open questions in the field of LSEC pathobiology and future avenues of research.

Pan-PPAR agonist lanifibranor improves portal hypertension and hepatic fibrosis in experimental advanced chronic liver disease

BACKGROUND & AIMS

In advanced chronic liver disease (ACLD), deregulated hepatic necroinflammatory processes play a key role in the development of liver microvascular dysfunction, fibrogenesis, and increased hepatic vascular tone, resulting in progression of ACLD and portal hypertension. Given the current lack of an effective treatment, we aimed to characterise the effects of the pan-peroxisome proliferator-activated receptor (pan-PPAR) agonist lanifibranor in 2 preclinical models of ACLD, as well as in liver cells from patients with ACLD.

METHODS

Cirrhotic rats (thioacetamide or common bile duct ligation; TAA or cBDL) randomly received lanifibranor (100 mg/kg/day, po) or vehicle for 14 days (n = 12/group). PPAR expression, systemic and hepatic haemodynamics, presence of ascites, liver sinusoidal endothelial cell (LSEC) phenotype, hepatic stellate cell (HSC) activation, serum transaminases and albumin, hepatic macrophage infiltration, cytokine expression, and liver fibrosis were determined. Hepatic cells were isolated from the livers of patients with cirrhosis and their phenotype was evaluated after treatment with either lanifibranor or vehicle.

RESULTS

TAA-cirrhotic rats receiving lanifibranor showed significantly lower portal pressure compared with vehicle-treated animals (-15%; p = 0.003) without decreasing portal blood flow, indicating improved hepatic vascular resistance. Moreover, lanifibranor-treated TAA-rats showed decreased ascites, improved LSEC and HSC phenotypes, ameliorated hepatic microvascular function, reduced hepatic inflammation, and significant fibrosis regression (-32%; p = 0.020). These findings were confirmed in the cBDL rat model as well as in human liver cells from patients with cirrhosis, which exhibited phenotypic improvement upon treatment with lanifibranor.

CONCLUSIONS

Lanifibranor ameliorates fibrosis and portal hypertension in preclinical models of decompensated cirrhosis. Promising results in human hepatic cells further support its clinical evaluation for the treatment of ACLD.

LAY SUMMARY

Advanced chronic liver disease (ACLD) constitutes a serious public health issue for which safe and effective treatments are lacking. This study shows that lanifibranor improves portal hypertension and liver fibrosis, 2 key elements of the pathophysiology of ACLD, in preclinical models of the disease. Evaluation of lanifibranor in liver cells from patients with ACLD further supports its beneficial effects.

Liver sinusoidal endothelial cells are implicated in multiple fibrotic mechanisms

Chronic liver diseases are attributed to liver injury. Development of fibrosis from chronic liver diseases is a dynamic process that involves multiple molecular and cellular processes. As the first to be impacted by injury, liver sinusoidal endothelial cells (LSECs) are involved in the pathogenesis of liver diseases caused by a variety of etiologies. Moreover, capillarization of LSECs has been recognized as an important event in the development of chronic liver diseases and fibrosis. Studies have reported that various cytokines (such as vascular endothelial growth factor, transforming growth factor-β), and pathways (such as hedgehog, and Notch), as well as epigenetic and metabolic factors are involved in the development of LSEC-mediated liver fibrosis. This review describes the complexity and plasticity of LSECs in fibrotic liver diseases from several perspectives, including the cross-talk between LSECs and other intra-hepatic cells. Moreover, it summarizes the mechanisms of several kinds of LSECs-targeting anti-fibrosis chemicals, and provides a theoretical basis for future studies.

Peroxisome proliferator-activated receptors in the pathogenesis and therapies of liver fibrosis

Liver fibrosis is a dynamic wound-healing process associated with the deposition of extracellular matrix produced by myofibroblasts. HSCs activation, inflammation, oxidative stress, steatosis and aging play critical roles in the progression of liver fibrosis, which is correlated with the regulation of the peroxisome proliferator-activated receptor (PPAR) pathway. As nuclear receptors, PPARs reduce inflammatory response, regulate lipid metabolism, and inhibit fibrogenesis in the liver associated with aging. Thus, PPAR ligands have been investigated as possible therapeutic agents. Mounting evidence indicated that some PPAR agonists could reverse steatohepatitis and liver fibrosis. Consequently, targeting PPARs might be a promising and novel therapeutic option against liver fibrosis. This review summarizes recent studies on the role of PPARs on the pathogenesis and treatment of liver fibrosis.

A randomised, double-blind, placebo-controlled, multi-centre, dose-range, proof-of-concept, 24-week treatment study of lanifibranor in adult subjects with non-alcoholic steatohepatitis: Design of the NATIVE study

Background Non-alcoholic steatohepatitis (NASH), a multifactorial disease, can progress to hepatic fibrosis and cirrhosis. The Peroxysomal Proliferator-Activated Receptors, PPARα, β/δ and γ, play a central role in the regulation of glucose and lipid metabolism and of the inflammatory and fibrogenic pathways in liver and in other organs that all contribute to NASH pathogenesis. Lanifibranor (IVA337), a panPPAR agonist, by acting on these three different PPAR isotypes, combines pharmacological effects that could address the different components of the disease as demonstrated in preclinical models. Objectives NATIVE study (EudraCT: 2016-001979-70, NCT: NCT03008070) aims to assess the safety and the efficacy of a 24-week treatment with lanifibranor (800 and 1200 mg/day) in adult non-cirrhotic NASH patients. The primary efficacy endpoint is a 2-point reduction in the activity part of the Steatosis Activity Fibrosis (SAF) histological score (combining inflammation and ballooning) without worsening of fibrosis. Design NATIVE is a Phase 2b randomised, placebo-controlled, double-blind, parallel-assignment, dose-range study. Eligible adult patients with a confirmed histological diagnosis of NASH should have a SAF Activity score of 3 or 4 (>2) and a SAF Steatosis score ≥ 1. There is no specific criterion related to the fibrosis score except that patients with cirrhosis (F4) were excluded. Summary This study will evaluate the efficacy of a 24-week treatment of NASH with lanifibranor based on histological evaluations (SAF score) by biopsy. The number of responders according to the SAF Activity score-based definition from baseline to 24 weeks will be compared between groups and serves as primary endpoint.

Endothelin-1 in portal hypertension: The intricate role of hepatic stellate cells

IMPACT STATEMENT

Portal hypertension is pathologically defined as increase of portal venous pressure, mainly due to chronic liver diseases such as fibrosis and cirrhosis. In fibrotic liver, activated hepatic stellate cells increase their contraction in response to endothelin-1 (ET-1) via autocrine and paracrine stimulation from liver sinusoidal endothelial cells and injured hepatocytes. Clinical studies are limited with ET receptor antagonists in cirrhotic patients with portal hypertension. Hence, studies are needed to find molecules that block ET-1 synthesis. Accumulation of extracellular matrix proteins in the perisinusoidal space, tissue contraction, and alteration in blood flow are prominent during portal hypertension. Therefore, novel matrix modulators should be tested experimentally as well as in clinical studies. Specifically, tumor necrosis factor-α, transforming growth factor-β1, Wnt, Notch, rho-associated protein kinase 1 signaling antagonists, and peroxisome proliferator-activated receptor α and γ, interferon-γ and sirtuin 1 agonists should be tested elaborately against cirrhosis patients with portal hypertension.