Extent and features of liver steatosis in vitro pave the way to endothelial dysfunction without physical cell-to-cell contact

Background and aims: Several chronic multifactorial diseases originate from energy unbalance between food intake and body energy expenditure, including non-alcoholic fatty liver disease (NAFLD), diabetes, and cardiovascular disorders. Vascular endothelium plays a central role in body homeostasis, and NAFLD is often associated with endothelial dysfunction (ED), the first step in atherosclerosis. Both sugars and fatty acids (FAs) are fuel sources for energy production, but their excess leads to liver steatosis which may trigger ED through a network of mechanisms which need to be clarified. Here, we investigated the crosstalk pathways between in vitro cultured steatotic hepatocytes (FaO) and endothelial cells (HECV) being mediated by soluble factors. Methods and results: We employed the conditioned medium approach to test how different extent and features of hepatic steatosis distinctively affect endothelium leading to ED. The steatogenic media collected from steatotic hepatocytes were characterized by high triglyceride content and led to lipid accumulation and fat-dependent dysfunction in HECV cells. We found a parallelism between (i) extent of hepatocyte steatosis and level of lipid accumulation in HECV cells; (ii) type of hepatocyte steatosis (with macro- or microvesicular LDs) and extent of oxidative stress, lipid peroxidation, nitric oxide release and expression of ED markers in HECV cells. Conclusions: The present findings seem to suggest that, in addition to triglycerides, other soluble mediators should be released by steatotic hepatocytes and may influence lipid accumulation and function of HECV cells. Further studies need to depict the exact profile of soluble factors involved in steatotic hepatocyte-endothelium crosstalk.