Oxidative stress (OS) in non-alcoholic fatty liver disease (NAFLD) promotes liver injury and inflammation. Treatment with vitamin E (α-tocopherol, αT), a lipid-soluble antioxidant, improves liver injury but also decreases steatosis, thought to be upstream of OS, through an unknown mechanism. To elucidate the mechanism, we combined a mechanistic human trial interrogating pathways of intrahepatic triglyceride (IHTG) accumulation and in vitro experiments. 50% of NAFLD patients (n = 20) treated with αT (200–800 IU/d) for 24 weeks had a ≥ 25% relative decrease in IHTG by magnetic resonance spectroscopy. Paired liver biopsies at baseline and week 4 of treatment revealed a decrease in markers of hepatic de novo lipogenesis (DNL) that strongly predicted week 24 response. In vitro, using HepG2 cells and primary human hepatocytes, αT inhibited glucose-induced DNL by decreasing SREBP-1 processing and lipogenic gene expression. This mechanism is dependent on the antioxidant capacity of αT, as redox-silenced methoxy-αT is unable to inhibit DNL in vitro . OS by itself was sufficient to increase S2P expression in vitro , and S2P is upregulated in NAFLD livers. In summary, we utilized αT to demonstrate a vicious cycle in which NAFLD generates OS, which feeds back to augment DNL and increases steatosis. Clinicaltrials.gov : NCT01792115.

BaCKgRoUND aND aIMS: 17-Beta hydroxysteroid dehydrogenase 13 (HSD17B13) is genetically associated with human nonalcoholic fatty liver disease (NAFLD). Inactivating mutations in HSD17B13 protect humans from NAFLDassociated and alcohol-associated liver injury, fibrosis, cirrhosis, and hepatocellular carcinoma, leading to clinical trials of anti-HSD17B13 therapeutic agents in humans. We aimed to study the in vivo function of HSD17B13 using a mouse model. appRoaCH aND ReSUltS: Single-cell RNA-sequencing and quantitative RT-PCR data revealed that hepatocytes are the main HSD17B13-expressing cells in mice and humans. We compared Hsd17b13 whole-body knockout (KO) mice and wild-type (WT) littermate controls fed regular chow (RC), a high-fat diet (HFD), a Western diet (WD), or the National Institute on Alcohol Abuse and Alcoholism model of alcohol exposure. HFD and WD induced significant weight gain, hepatic steatosis, and inflammation. However, there was no difference between genotypes with regard to body weight, liver weight, hepatic triglycerides (TG), histological inflammatory scores, expression of inflammation-related and fibrosis-related genes, and hepatic retinoid levels. Compared to WT, KO mice on the HFD had hepatic enrichment of most cholesterol esters, monoglycerides, and certain sphingolipid species. Extended feeding with the WD for 10 months led to extensive liver injury, fibrosis, and hepatocellular carcinoma, with no difference between genotypes. Under alcohol exposure, KO and WT mice showed similar hepatic TG and liver enzyme levels. Interestingly, chow-fed KO mice showed significantly higher body and liver weights compared to WT mice, while KO mice on obesogenic diets had a shift toward larger lipid droplets.

Study approval. All experiments with mice were approved by the Ethics Review Committee for Animal Experimentation of the Graduate School of Biomedical Sciences, Hiroshima University (A18-64). All experiments with human samples were approved under NTUH-REC 201812063RINC and OHSRP 18-NIDDK-00585.