22 - Vitamin E (RRR-α-tocopherol) decreases hepatic de novo lipogenesis

Abstract

Non-alcoholic fatty liver disease (NAFLD) is becoming a major hepatic disease in the Western world. The hallmark feature of NAFLD is steatosis, the accumulation of hepatic triacylglycerol (TG), which results from the disruption of metabolic pathways, one of which is de novo lipogenesis (DNL). RRR-α-tocopherol (αT) can reduce steatosis in animals and NAFLD patients through a yet-unknown mechanism. We aimed to identify the mechanism by which αT decreases liver TG and whether its antioxidant (AO) effect is required for this effect. HepG2 cells cultivated under high glucose medium (25 mmol/L) had a 19% increase in lipid accumulation and 2-fold increase in expression of fatty acid synthase (FASN), a key enzyme in DNL, which were reversed by αT to control levels in a dose dependent manner (25-100 µmol/L, 48h). Similarly, 100 µmol/L of αT decreased incorporation of 14C glucose into lipids by 24%. We confirmed this effect in vivo in plasma samples from NAFLD patients (n=21), obtained before and after 4 weeks of αT supplementation (NCT01792115). Liver TG, measured by 1H-magnetic resonance spectroscopy, decreased in 55% of the patients. The lipogenic index, the ratio of C16:0/C18:2n6 in VLDL, reflects hepatic DNL. Patients with reduction in liver TG after 4 weeks of αT also had a significant reduction in the lipogenic index compared to non-responders (p=0.01). To address if αT reduces DNL through its AO function we synthesized methoxy-αT (m-αT), a lipid-soluble αT derivate lacking the AO function and compared it to αT, trolox (water-soluble αT analogue with AO capacity), and probucol (lipid-soluble AO). In our lipogenic HepG2 model, αT, m-αT, trolox and probucol decreased lipid content by max. 18, 0, 0 and 13%, respectively. Thus, our data indicates that αT reduces hepatic DNL in vitro and in vivo through a mechanism that is likely dependent on its antioxidative activity in the lipid compartment.