TRANSCRIPTOMICS OF NATURAL AND SYNTHETIC VITAMIN D IN HUMAN HEPATOCYTE LIPOTOXICITY

Vitamin D (VD) has been used to prevent non-alcoholic fatty liver disease (NAFLD), a condition of lipotoxicity associated with a defective metabolism and function of this vitamin. Different forms of VD are available and can be used for this scope, but their effects on liver cell lipotoxicity remain unexplored. In this study we compared a natural formulation rich in VD2 (Shiitake Mushroom extract or SM-VD2) with a synthetic formulation containing pure VD3 (SV-VD3) and the bioactive metabolite 1,25(OH)₂-D3. These were investigated in chemoprevention mode in human HepaRG liver cells supplemented with oleic and palmitic acid to induce lipotoxicity. All the different forms of VD showed similar efficacy in reducing the levels of lipotoxicity and the changes that lipotoxicity induced on the cellular transcriptome. However, the three forms of VD generated different gene fingerprints suggesting diverse, even if functionally convergent, cytoprotective mechanisms. Main differences were 1) the number of differentially expressed genes (SV-VD3 > 1,25(OH)₂-D3 > SM-VD2), 2) their identity that demonstrated significant gene homology between SM-VD2 and 1,25(OH)₂-D3, and 3) the number and type of biological functions identified by Ingenuity Pathway Analysis as relevant to liver metabolism and cytoprotection annotations. Immunoblot confirmed a different response of VDR and other VDR-related proteins to natural and synthetic VD formulations, including FXR, PXR, PPARγ/PGC-1α, and CYP3A4 and CYP24A1. In conclusion, different responses of the cellular transcriptome drive the cytoprotective effect of natural and synthetic formulations of VD in the free fatty acid-induced lipotoxicity of human hepatocytes.

Wheat germ oil vitamin E cytoprotective effect and its nutrigenomics signature in human hepatocyte lipotoxicity

Wheat germ oil (WGO) is rich in α-tocopherol (vitamin E, VE), a vitamin that has long been suggested to exert hepatoprotective effects. In this study, this function of WGO-VE and its transcriptomics fingerprint were investigated in comparison with RRR-α-tocopherol and all-rac-α-tocopherol (nVE and sVE, respectively), in human liver cells treated with oleic acid (OA) to develop steatosis and lipotoxicity. Used in chemoprevention mode, all the VE formulations afforded significant reduction of the OA-induced steatosis and its consequent impact on lipotoxicity indicators, including ROS production and efflux (as H₂O₂), and apoptotic and necrotic cell death. A trend toward a better control of lipotoxicity was observed for WGO-VE and nVE compared to sVE. Gene microarray data demonstrated that these effects of VE formulations were associated with significantly different responses of the cellular transcriptome to compensate for the modifications of OA treatment, including the downregulation of cellular homeostasis genes and the induction of genes associated with defects of liver cell metabolism, fibrosis and inflammation, liver disease and cancer. Ingenuity Pathway Analysis data showed that WGO-VE modulated genes associated with liver carcinogenesis and steatosis, whereas nVE modulated genes involved in liver cell metabolism and viability biofunctions; sVE did not significantly modulate any gene dataset relevant to such biofunctions. In conclusion, WGO-VE prevents lipotoxicity in human liver cells modulating genes that differ from those affected by the natural or synthetic forms of pure VE. These differences can be captured by precision nutrition tools, reflecting the molecular complexity of this VE-rich extract and its potential in preventing specific cues of hepatocellular lipotoxicity.