The Endothelium as a Driver of Liver Fibrosis and Regeneration

Liver fibrosis is a common feature of sustained liver injury and represents a major public health problem worldwide. Fibrosis is an active research field and discoveries in the last years have contributed to the development of new antifibrotic drugs, although none of them have been approved yet. Liver sinusoidal endothelial cells (LSEC) are highly specialized endothelial cells localized at the interface between the blood and other liver cell types. They lack a basement membrane and display open channels (fenestrae), making them exceptionally permeable. LSEC are the first cells affected by any kind of liver injury orchestrating the liver response to damage. LSEC govern the regenerative process initiation, but aberrant LSEC activation in chronic liver injury induces fibrosis. LSEC are also main players in fibrosis resolution. They maintain liver homeostasis and keep hepatic stellate cell and Kupffer cell quiescence. After sustained hepatic injury, they lose their phenotype and protective properties, promoting angiogenesis and vasoconstriction and contributing to inflammation and fibrosis. Therefore, improving LSEC phenotype is a promising strategy to prevent liver injury progression and complications. This review focuses on changes occurring in LSEC after liver injury and their consequences on fibrosis progression, liver regeneration, and resolution. Finally, a synopsis of the available strategies for LSEC-specific targeting is provided.Supported in part by the Instituto de Salud Carlos III (PI14/00182, PI17/00298 and PIE00027/15); FEDER “Una manera de hacer Europa”). Centro de Investigación Biomédica en Red de Enfermedades Hepáticas y Digestivas (CIBERehd) is funded by the Instituto de Salud Carlos III. EL is supported by an iPFIS grant from Instituto de Salud Carlos III (IFI17/00010). MR is supported by AGAUR-SGR2017-517 grant from Generalitat de Catalunya

Aging Influences Hepatic Microvascular Biology and Liver Fibrosis in Advanced Chronic Liver Disease.

Advanced chronic liver disease (aCLD) represents a major public health concern. aCLD is more prevalent and severe in the elderly, carrying a higher risk of decompensation. We aimed at understanding how aging may impact on the pathophysiology of aCLD in aged rats and humans and secondly, at evaluating simvastatin as a therapeutic option in aged animals. aCLD was induced in young (1 month) and old (16 months) rats. A subgroup of aCLD-old animals received simvastatin (5 mg/kg) or vehicle (PBS) for 15 days. Hepatic and systemic hemodynamic, liver cells phenotype and hepatic fibrosis were evaluated. Additionally, the gene expression signature of cirrhosis was evaluated in a cohort of young and aged cirrhotic patients. Aged animals developed a more severe form of aCLD. Portal hypertension and liver fibrosis were exacerbated as a consequence of profound deregulations in the phenotype of the main hepatic cells: hepatocytes presented more extensive cell-death and poorer function, LSEC were further capillarized, HSC over-activated and macrophage infiltration was significantly increased. The gene expression signature of cirrhosis significantly differed comparing young and aged patients, indicating alterations in sinusoidal-protective pathways and confirming the pre-clinical observations. Simvastatin administration for 15-day to aged cirrhotic rats improved the hepatic sinusoidal milieu, leading to significant amelioration in portal hypertension. This study provides evidence that aCLD pathobiology is different in aged individuals. As the median age of patients with aCLD is increasing, we propose a real-life pre-clinical model to develop more reliable therapeutic strategies. Simvastatin effects in this model further demonstrate its translational potential

Simvastatin Prevents Progression of Acute on Chronic Liver Failure in Rats With Cirrhosis and Portal Hypertension.

BACKGROUND & AIMS Cirrhosis and its clinical consequences can be aggravated by bacterial infections, ultimately leading to the development of acute on chronic liver failure (ACLF), characterized by acute decompensation, organ failure, and high mortality within 28 days. Little is known about cellular and molecular mechanisms of ACLF in patients with cirrhosis, so no therapeutic options are available. We developed a sepsis-associated preclinical model of ACLF to facilitate studies of pathogenesis and evaluate the protective effects of simvastatin. METHODS Male Wistar rats inhaled CCl until they developed cirrhosis (at 10 weeks) or cirrhosis with ascites (at 15-16 weeks). Male Sprague-Dawley rats received bile-duct ligation for 28 days or intraperitoneal thioacetamide for 10 weeks to induce cirrhosis. After induction of cirrhosis, some rats received a single injection of lipopolysaccharide (LPS) to induce ACLF; some were given simvastatin or vehicle (control) 4 hours or 24 hours before induction of ACLF. We collected data on changes in hepatic and systemic hemodynamics, hepatic microvascular phenotype and function, and survival times. Liver tissues and plasma were collected and analyzed by immunoblots, quantitative polymerase chain reaction, immuno(fluoro)histochemistry and immunoassays. RESULTS Administration of LPS aggravated portal hypertension in rats with cirrhosis by increasing the severity of intrahepatic microvascular dysfunction, exacerbating hepatic inflammation, increasing oxidative stress, and recruiting hepatic stellate cells and neutrophils. Rats with cirrhosis given LPS had significantly shorter survival times than rats with cirrhosis given the control. Simvastatin prevented most of ACLF-derived complications and increased survival times. Simvastatin appeared to increase hepatic sinusoidal function and reduce portal hypertension and markers of inflammation and oxidation. The drug significantly reduced levels of transaminases, total bilirubin, and ammonia, as well as LPS-mediated activation of hepatic stellate cells in liver tissues of rats with cirrhosis. CONCLUSIONS In studies of rats with cirrhosis, we found administration of LPS to promote development of ACLF, aggravating the complications of chronic liver disease and decreasing survival times. Simvastatin reduced LPS-induced inflammation and liver damage in rats with ACLF, supporting its use in treatment of patients with advanced chronic liver disease

Mitochondria-targeted antioxidant mitoquinone deactivates human and rat hepatic stellate cells and reduces portal hypertension in cirrhotic rats.

BACKGROUND & AIMS: In cirrhosis, activated hepatic stellate cells (HSC) play a major role in increasing intrahepatic vascular resistance and developing portal hypertension. We have shown that cirrhotic livers have increased reactive oxygen species (ROS), and that antioxidant therapy decreases portal pressure. Considering that mitochondria produce many of these ROS, our aim was to assess the effects of the oral mitochondria-targeted antioxidant mitoquinone on hepatic oxidative stress, HSC phenotype, liver fibrosis and portal hypertension. METHODS: Ex vivo: Hepatic stellate cells phenotype was analysed in human precision-cut liver slices in response to mitoquinone or vehicle. In vitro: Mitochondrial oxidative stress was analysed in different cell type of livers from control and cirrhotic rats. HSC phenotype, proliferation and viability were assessed in LX2, and in primary human and rat HSC treated with mitoquinone or vehicle. In vivo: CCl4 - and thioacetamide-cirrhotic rats were treated with mitoquinone (5 mg/kg/day) or the vehicle compound, DecylTPP, for 2 weeks, followed by measurement of oxidative stress, systemic and hepatic haemodynamic, liver fibrosis, HSC phenotype and liver inflammation. RESULTS: Mitoquinone deactivated human and rat HSC, decreased their proliferation but with no effects on viability. In CCl4 -cirrhotic rats, mitoquinone decreased hepatic oxidative stress, improved HSC phenotype, reduced intrahepatic vascular resistance and diminished liver fibrosis. These effects were associated with a significant reduction in portal pressure without changes in arterial pressure. These results were further confirmed in the thioacetamide-cirrhotic model. CONCLUSION: We propose mitochondria-targeted antioxidants as a novel treatment approach against portal hypertension and cirrhosis

Spermidine Supplementation Protects the Liver Endothelium from Liver Damage in Mice

Chronic liver diseases are multifactorial and the need to develop effective therapies is high. Recent studies have shown the potential of ameliorating liver disease progression through protection of the liver endothelium. Polyamine spermidine (SPD) is a caloric restriction mimetic with autophagy-enhancing properties capable of prolonging lifespan and with a proven beneficial effect in cardiovascular disease in mice and humans. We evaluated the use of dietary supplementation with SPD in two models of liver disease (CCl4 and CDAAH diet). We analyzed the effect of SPD on endothelial dysfunction in vitro and in vivo. C57BL/6J mice were supplemented with SPD in the drinking water prior and concomitantly with CCl4 and CDAAH treatments. Endothelial autophagy deficient (Atg7endo) mice were also evaluated. Liver tissue was used to evaluate the impact of SPD prophylaxis on liver damage, endothelial dysfunction, oxidative stress, mitochondrial status, inflammation and liver fibrosis. SPD improved the endothelial response to oxidative injury in vitro and improved the liver endothelial phenotype and protected against liver injury in vivo. SPD reduced the overall liver oxidative stress and improved mitochondrial fitness. The absence of benefits in the Atg7endo mice suggests an autophagy-dependent effect of SPD. This study suggests SPD diet supplementation in early phases of disease protects the liver endothelium from oxidative stress and may be an attractive approach to modify the chronic liver disease course and halt fibrosis progression