Non-alcoholic fatty liver disease (NAFLD) affects one-third of the population worldwide, of which a substantial number of patients suffer from non-alcoholic steatohepatitis (NASH). NASH is a severe condition characterized by steatosis and concomitant liver inflammation and fibrosis, for which no drug is yet available. NAFLD is also generally conceived as the hepatic manifestation of the metabolic syndrome. Consequently, well-established drugs that are indicated for the treatment of type 2 diabetes and hyperlipidemia are thought to exert effects that alleviate the pathological features of NASH. One class of these drugs targets peroxisome proliferator-activated receptors (PPARs), which are nuclear receptors that play a regulatory role in lipid metabolism and inflammation. Therefore, PPARs are now also being investigated as potential anti-NASH druggable targets. In this paper, we review the mechanisms of action and physiological functions of PPARs and discuss the position of the different PPAR agonists in the therapeutic landscape of NASH. We particularly focus on the PPAR agonists currently under evaluation in clinical phase II and III trials. Preclinical strategies and how refinement and optimization may improve PPAR-targeted anti-NASH drug testing are also discussed. Finally, potential caveats related to PPAR agonism in anti-NASH therapy are stipulated.

Non-alcoholic steatohepatitis (NASH) is a chronic liver disease characterized by excessive triglyceride accumulation in the liver accompanied by inflammation, cell stress and apoptosis. It is the tipping point to the life-threatening stages of non-alcoholic fatty liver disease (NAFLD). Despite the high prevalence of NASH, up to five percent of the global population, there are currently no approved drugs to treat this disease. Animal models, mostly based on specific diets and genetic modifications, are often employed in anti-NASH drug development. However, due to interspecies differences and artificial pathogenic conditions, they do not represent the human situation accurately and are inadequate for testing the efficacy and safety of potential new drugs. Human-based in vitro models provide a more legitimate representation of the human NASH pathophysiology and can be used to investigate the dysregulation of cellular functions associated with the disease. Also in silico methodologies and pathway-based approaches using human datasets, may contribute to a more accurate representation of NASH, thereby facilitating the quest for new anti-NASH drugs. In this review, we describe the molecular components of NASH and how human-based tools can contribute to unraveling the pathogenesis of this disease and be used in anti-NASH drug development. We also propose a roadmap for the development and application of human-based approaches for future investigation of NASH.

The liver–heart axis potentially influences the risk of mortality in patients with heart failure. We aimed to identify the clinical utility of the fibrosis-4 (FIB-4) index in patients with heart failure for predicting mortality in the context of metabolic dysfunction-associated steatotic liver disease (MASLD). Patients with heart failure and a subsample of healthy participants were enrolled in the MyoVasc study (NCT04064450) and followed for nine years. Participants with excessive alcohol consumption were excluded. The Fatty Liver Index (FLI) and FIB-4 index were used to classify MASLD and hepatic fibrosis, respectively. Data were adjusted for potential confounders. The primary endpoint was all-cause mortality. 2726 participants, including 172 healthy individuals, were included in the study. The participants had a mean age of 64.4 ± 11.2 years and a median FIB-4 index of 1.59 (interquartile range [1.17; 2.17]). There were 532 deaths. The FIB-4 index was predictive for all-cause mortality (hazard ratio (HR) 1.341, 95% confidence interval (CI) [1.273; 1.412], p < 0.0001). The HRs and 95% CIs for the FIB-4 index in FLI categories were 1.597 [1.256; 2.031] (p = 0.00013, FLI <30), 1.802 [1.519; 2.138] (p < 0.0001, FLI 30–60), and 1.292 [1.215; 1.374] (p < 0.0001, FLI ≥60). The interaction term for the FIB-4 index with FLI ≥60 (reference FLI <30) was HR 0.774 [0.617; 0.972] (p = 0.027), indicating a smaller impact of the FIB-4 index in FLI ≥60 than in FLI <30 (HR 1.664 [1.333; 2.077], p < 0.0001). Multivariable linear regressions revealed relevant independent relationships between the FIB-4 index and N-terminal pro-B-type natriuretic peptide, systolic dysfunction, diastolic dysfunction and left ventricular hypertrophy in participants with a FLI below 60. In patients with heart failure, the FIB-4 index predicts all-cause mortality and relates to cardiac functional and structural changes, especially in those without MASLD. Johannes Gutenberg-University Mainz.