Ldlr−/− Mice Lacking PEMT Have Elevated Plasma Trimethylamine‐oxide Levels But Are Protected From High Fat Diet‐Induced Atherosclerosis.

Abstract

BackgroundPhosphatidylethanolamine N‐methyltransferase (PEMT) is a hepatic enzyme that converts phosphatidylethanolamine into phosphatidylcholine (PC) via three methylation reactions. The PEMT pathway makes 30% of the PC required in the liver and is the only de novo source of choline. PEMT deficient mice are protected against atherosclerosis when bred with either the Ldlr−/− and Apoe−/− mice. PEMT deficiency causes decreased VLDL secretion, plasma LDL levels and homocysteine, which are risk factors for atherosclerosis. Recently, choline supplementation was shown to enhance atherosclerosis in ApoE−/− mice and was dependent on the conversion of choline to trimethylamine (TMA) by the microbial flora in the gut, which was oxidized to trimethylamine N‐oxide (TMAO) by hepatic enzymes. In addition, plasma choline and TMAO have been associated with increased risk of CVD in multiple cohort studies. The purpose of this study was to examine the effects of dietary choline supplementation on plasma TMAO levels, and investigate whether choline supplementation eliminates the atheroprotective effect of PEMT deficiency in LDLR−/− miceMethodsWe performed two sets of experiments: In first experiment, 10–12 week old Pemt+/+/Ldlr−/− and Pemt−/−/Ldlr−/− mice were fed a chow diet for 12 weeks. In the second experiment, Pemt+/+/Ldlr−/− and Pemt−/−/Ldlr−/− mice were fed a 40% high‐fat/0.5% cholesterol diet (HFD) supplemented with either 3 or 10 g/kg choline for 12 weeks.ResultsPEMT+/+/Ldlr−/− and PEMT−/−/Ldlr−/− mice do not develop atherosclerosis on chow diet and there was no difference in plasma cholesterol between genotypes. When fed a HFD, PEMT−/−/Ldlr−/− mice are protected against atherosclerosis as compared to PEMT+/+/Ldlr−/− mice. Interestingly, choline supplementation did not increase atherosclerosis in the PEMT−/−/Ldlr−/− mice. Plasma cholesterol levels were reduced in PEMT−/−/Ldlr−/−, which did not increase on choline supplementation. Surprisingly, PEMT−/−/Ldlr−/− mice have elevated TMAO levels, which was reduced to control levels by choline supplementation. Furthermore, liver histology showed that PEMT−/−/Ldlr−/− mice developed fatty liver that was improved by choline supplementation.ConclusionCholine supplementation does not reverse the protection of PEMT−/−/Ldlr−/− mice against atherosclerosis. PEMT−/−/Ldlr−/− mice have high TMAO levels and fatty liver on HFD. Surprisingly, choline supplementation normalized TMAO levels and reduced the fatty liver. Therefore, plasma TMAO levels are not associated with atherosclerosis but may be associated with fatty liver disease.Support or Funding InformationFunding: ALMA, NSERC and CIHR