Abstract 9565: Impact of Hepatic GPAT1 or DGAT2 Deficiency on Plasma Lipids and MTP Inhibitor-Induced Elevation of Liver Triglycerides in Mice

Abstract

Purpose: Systemic microsomal triglyceride transfer protein (MTP) inhibitors induce beneficial changes in the serum lipid profile in animals and humans, including reduced total and LDL cholesterol (LDL-C) as well as VLDL triglyceride (TG). However, as a consequence of their mechanism of action, these agents also elevate intestinal and hepatic triglyceride levels. A treatment that ameliorates liver TG accumulation could conceivably prevent hepatotoxicity and provide a path forward for developing these compounds. As a proof of principle, we sought to induce hepatic deficiency of either of two key enzymes in the TG biosynthetic pathway - GPAT1 and DGAT2 - and measure the impact of their loss on liver TG accumulation induced by a MTP inhibitor in mice. Methods: A recombinant adeno-associated viral vector (AAV) was used to introduce shRNA directed against either GPAT1 or DGAT2 to the livers of B6[Tg(CETP)/LDLR tm1 ] F1 mice - a model with a serum lipid profile similar to humans. Stable isotope tracer techniques were employed to assess the degree to which de novo liver TG synthesis was compromised in these animals, thereby indicating in vivo target engagement. Once target engagement was confirmed, the animals were challenged with a MTP inhibitor and liver TG levels assessed ex vivo one week later. Impacts on the plasma lipid profile were also assessed. Results: At 42 days post AAV treatment, hepatic GPAT1 and DGAT2 mRNA levels were reduced by over 90% relative to controls by their respective AAV-shRNA vectors. Both treatments were associated with significant and distinct changes in the manner in which intravenously administered 13 C-oleic acid tracer was incorporated into various lipid species by the liver. Of the two treatments, only DGAT2 altered the overall plasma lipid profile, with significantly reduced plasma TG, Apolipoprotein B, and total, VLDL, LDL and HDL cholesterol. Both treatments significantly lowered liver TG levels, both alone and in response to a MTP inhibitor. In the case of DGAT2, the elevated liver TG induced by MTP inhibition was nearly abolished. Conclusion: These data provide proof of principle that inhibiting hepatic TG synthesis ameliorates liver TG accumulation in response to MTP inhibition.