Noninvasive predictors of fibrosis in NASH with and without cirrhosis, just as good as histology (and hepatic venous pressure gradient?)

Portal Hypertension in Nonalcoholic Fatty Liver Disease: Challenges and Paradigms

Portal hypertension in cirrhosis is defined as an increase in the portal pressure gradient (PPG) between the portal and hepatic veins and is traditionally estimated by the hepatic venous pressure gradient (HVPG), which is the difference in pressure between the free-floating and wedged positions of a balloon catheter in the hepatic vein. By convention, HVPG≥10 mmHg indicates clinically significant portal hypertension, which is associated with adverse clinical outcomes. Nonalcoholic fatty liver disease (NAFLD) is a common disorder with a heterogeneous clinical course, which includes the development of portal hypertension. There is increasing evidence that portal hypertension in NAFLD deserves special considerations. First, elevated PPG often precedes fibrosis in NAFLD, suggesting a bidirectional relationship between these pathological processes. Second, HVPG underestimates PPG in NAFLD, suggesting that portal hypertension is more prevalent in this condition than currently believed. Third, cellular mechanoresponses generated early in the pathogenesis of NAFLD provide a mechanistic explanation for the pressure-fibrosis paradigm. Finally, a better understanding of liver mechanobiology in NAFLD may aid in the development of novel pharmaceutical targets for prevention and management of this disease.

Mechanotransduction in the pathogenesis of non-alcoholic fatty liver disease

Mechanobiology is a domain of interdisciplinary research that aims to explore the impact of physical force, applied externally or internally, on cell and tissue function, including development, growth, and differentiation. Mechanotransduction is a term that describes how cells sense physical forces (such as compression, stretch, and shear stress), convert them into biochemical signals, and mount adaptive responses integrated by the nucleus. There is accumulating evidence that mechanical forces extensively inform the biological behaviour of liver cells in health and disease. Recent research has elucidated many cellular and molecular mechanisms involved in this process including the pleiotropic control and diverse effects of the paralogous transcription co-activators YAP/TAZ, which play a prominent role in mechanotransduction. The liver sinusoids represent a unique microenvironment in which cells are exposed to mechanical cues originating in the cytoskeleton and at interfaces with adjacent cells, the extracellular matrix, and vascular or interstitial fluids. In non-alcoholic fatty liver disease (NAFLD), hepatocellular lipid accumulation and ballooning, activation of inflammatory responses, dysfunction of liver sinusoidal endothelial cells, and transdifferentiation of hepatic stellate cells into a pro-contractile and pro-fibrotic phenotype have been associated with aberrant cycles of mechanosensing and mechanoresponses. The downstream consequences of disrupted mechanical homeostasis likely contribute to the progression of NAFLD and promote the development of portal hypertension, cirrhosis, and hepatocellular carcinoma. Identification of molecular targets involved in pathogenic mechanotransduction will allow for the development of novel strategies to prevent the progression of liver disease in NAFLD.

Overlooked subclinical portal hypertension in non-cirrhotic NAFLD: Is it real and how to measure it?

Clinical and experimental advances related to the detection, magnitude and pathobiology of subclinical portal hypertension in non-alcoholic fatty liver disease (NAFLD), primarily observed in the presence of non-alcoholic steatohepatitis (NASH), prompt us to revisit current disease paradigms. Hepatic venous pressure gradient (HVPG) has been reported to underestimate portal pressure in NASH-related cirrhosis, while inaccuracy is more likely in non-cirrhotic livers, indicating a potential need for new and preferably non-invasive methods of measurement. Although clinically significant portal hypertension (HVPG ≥10 mmHg) retains its prognostic significance in NASH, subclinical portal hypertension (HVPG 6.0-9.5 mmHg) has been repeatedly detected in patients with NAFLD in the absence of cirrhosis or even significant fibrosis whereas the impact of these findings on disease outcomes remains unclear. Mechanocrine signalling pathways in various types of liver cell reveal a molecular basis for the adverse effects of subclinical portal hypertension and suggest a bidirectional relationship between portal pressure and fibrosis. These findings may guide efforts to improve risk assessment and identify novel therapeutic targets in NAFLD.

Report on the AASLD/EASL joint workshop on clinical trial endpoints in NAFLD

Non-alcoholic fatty liver disease (NAFLD) is a global public health concern. Its natural history, the development of non-alcoholic steatohepatitis (NASH) and fibrosis, is highly variable, prone to endogenous (e.g., genetics, microbiota) and exogenous (e.g., nutrition, alcohol, physical activity) disease modifiers, and can fluctuate over time. The complexity of its pathophysiology is reflected by the multitude of pharmacological targets in development. NASH clinical trials have provided valuable insight that is applicable to future trial design. Endpoints for NASH have evolved over the past decade and will continue to be refined. Currently accepted endpoints for conditional approval include resolution of NASH without worsening of fibrosis and/or improvement in fibrosis without worsening of NASH by standardized evaluation of paired liver histology. In pediatric NASH, practical obstacles, pubertal hormonal changes, and stringent safety requirements mandate adaptations in trial design. In adult patients with NASH-related cirrhosis, decrease in portal pressure as well as clinical events (e.g. decompensation, hepatocellular carcinoma, transplantation, death) are more prevalent and thereby are viable primary endpoints for clinical trials. Consideration of the natural fluctuation of disease, the clinical implication of the chosen primary endpoint, and factors that may affect placebo response will facilitate an accurate determination of efficacy of emerging therapeutics for NASH. Conclusion: The June 2018 American Association for the Study of Liver Diseases and European Association for the Study of the Liver joint workshop on NAFLD endpoints summarized important findings from ongoing and completed trials, defined the scientific evidence supporting distinct endpoints, and provided guidance for future trial design.

Report on the AASLD/EASL Joint Workshop on Clinical Trial Endpoints in NAFLD

Nonalcoholic fatty liver disease (NAFLD) is a global public health concern. Its natural history, the development of nonalcoholic steatohepatitis (NASH) and fibrosis, is highly variable, prone to endogenous (e.g., genetics, microbiota) and exogenous (e.g., nutrition, alcohol, physical activity) disease modifiers, and can fluctuate over time. The complexity of its pathophysiology is reflected by the multitude of pharmacological targets in development. NASH clinical trials have provided valuable insight that is applicable to future trial design. Endpoints for NASH have evolved over the past decade and will continue to be refined. Currently accepted endpoints for conditional approval include resolution of NASH without worsening of fibrosis and/or improvement in fibrosis without worsening of NASH by standardized evaluation of paired liver histology. In pediatric NASH, practical obstacles, pubertal hormonal changes, and stringent safety requirements mandate adaptations in trial design. In adult patients with NASH-related cirrhosis, clinical events (e.g. decompensation, hepatocellular carcinoma, transplantation, death) are more prevalent and thereby are viable primary endpoints. Consideration of the natural fluctuation of disease, the clinical implication of the chosen primary endpoint, and factors that may affect placebo response will facilitate an accurate determination of efficacy of emerging therapeutics for NASH. Conclusion: The June 2018 American Association for the Study of Liver Diseases and European Association for the Study of the Liver joint workshop on NAFLD endpoints summarized important findings from ongoing and completed trials, defined the scientific evidence supporting distinct endpoints, and provided guidance for future trial design.