Translational Approach for the Study of Metabolic-Associated Fatty Liver Disease (MAFLD): A Wide Spectrum Disease

Metabolic-associated fatty liver disease (MAFLD), tightly associated with obesity, is a major cause of chronic liver disease worldwide. It encompasses a wide spectrum of conditions, ranging from simple steatosis (MAFL) to the more severe metabolic-associated steatohepatitis (MASH). At present, diagnosis still depends on liver biopsy, an invasive procedure with some risks for the patient. Furthermore, to date, there is no approved pharmacological treatment. Consequently, there is an urgent need to develop non-invasive diagnostic biomarkers and to identify new therapeutic targets for MAFLD. Further studies are also necessary to study the crosstalk of the liver with other organs to provide a more extensive view of its pathogenesis. In general, we aimed to fulfill the existing scientific gaps in terms of therapy, diagnosis, and pathophysiology of MAFLD using a translational approach. Therapy: Triterpenic acid and acteoside, the major components of APPLIVER and ACTEOS respectively, have been reported to exert hepatoprotective effects but the molecular mechanisms remain elusive, particularly in the MAFLD context. We assessed their effects in an in vitro model resembling the MAFLD-related pathophysiological mechanisms. ACTEOS reduced both the TNF-a and reactive oxygen species (ROS) production and, most importantly, attenuated collagen deposition elicited by the excess of free fatty acids (FFA) in the co-culture model. APPLIVER also showed inhibition of both TNF-a production and collagen deposition caused by FFA accumulation. The compounds in the absence of FFA did not induce any cellular effects. Diagnosis: Several reports indicate fibrosis as the strongest predictor of long-term clinical outcomes in MAFLD patients. We assessed the performance of plasma ficolin-2 (FCN-2) as a biomarker of fibrosis identified by an in silico discovery strategy. The plasma level of FCN-2 was inversely correlated with the stage of liver fibrosis, independently of steatosis, inflammation, and ballooning. Moreover, FCN-2 level decreased significantly in a stepwise fashion from minimal- (F0/F1) to moderate/advanced- fibrosis (F2-F3) and in cirrhotic subjects (F4). The diagnostic performance of FCN-2 in detecting F ≥ 2 was higher than other non-invasive fibrosis algorithms (APRI, FIB-4). The diagnostic accuracy improved when combined with AST to Platelet Ratio Index (APRI) score and high-density lipoprotein (HDL). Overall, FCN-2 plasma level can accurately discriminate liver fibrosis status (minimal vs. moderate/advanced), significantly improving fibrosis diagnostic algorithms. Pathophysiology: Through our simple in silico analysis, we identified omentin-1, a novel adipocytokine expressed by VAT, and we explored its role in obesity-related MAFLD. In clinical validation, the obese groups showed significantly lower VAT expression (mRNA and protein) and plasma level of omentin-1 as compared to the lean group. Interestingly, within the MASH group, fibrosis did not affect omentin-1 expression. Likewise, VAT of mice fed with a high-fat diet, showing histological signs of MASH, showed decreased omentin-1 (mRNA and protein) as compared to control diet mice. In vitro, omentin-1 addition on fat-laden human hepatocytes showed no effect on steatosis but significantly decreased TNF-a levels, ER stress, and oxidative stress. The same results were obtained using ex vivo VAT explants from obese subjects upon omentin-1 supplementation. In addition, omentin-1 reduced nuclear factor kappa B (NF-kB) mRNA expression in both in vitro and ex vivo studies. In VAT explants, D-glucose and insulin significantly reduced omentin-1 expression (mRNA and protein level). Altogether, our findings suggest that reduced levels of omentin-1 contribute to MAFLD development. Omentin-1 supplementation reduces inflammation, ER stress, and oxidative stress probably via inhibiting the NF-kB pathway and might also play a role in the regulation of glucose-insulin metabolism.