Effect of dietary triacylglycerol structure on lipoprotein metabolism: A comparison of the effects of dioleoylpalmitoylglycerol in which palmitate is esterified to the 2-or 1(3)-position of the glycerol

The effect on lipoprotein metabolism of diets enriched in different isomers of dioleoylpalmitoylglycerol was studied. One diet contained fat in which palmitate was esterified to the two outer positions of the glycerol (OOP) and the other in which it was esterified to the middle carbon (OPO). The lipid composition of chylomicrons was similar in rats fed either fat blend. However, triacylglycerol (TAG) in chylomicrons from OPO fed animals was relatively enriched in palmitic acid, at the expense of stearic, oleic and linoleic acids. Silver phase HPLC and 2-positional analysis clearly demonstrated that the identity of the fatty acid in the 2-position was similar in both dietary and chylomicron TAG. No significant differences could be seen in the in vitro hydrolysis of chylomicron TAG from animals fed the two fats labelled with [14C]palmitate. As expected, following hydrolysis, palmitate was released as free fatty acid from chylomicrons isolated from OOP-fed animals but within 2-monoacylglycerol from those fed OPO. The enrichment of chylomicrons with palmitate in animals fed O[14C]PO resulted in increased delivery of [14C]palmitate to the liver. In a further series of experiments Golden Syrian hamsters were fed diets containing the fat blends and either 0.005% or 0.12% (w/w) cholesterol, for 28 days. No differences in fasting plasma lipoprotein concentrations were seen in response to the dietary fats. We conclude that, while these isomeric triacylglycerols had transient effects on chylomicron metabolism, no significant longer term effects on plasma concentrations of endogenous lipoproteins could be found.