Abstract
The study aimed to 1] develop a method which completely separated hepatic (VLDL1, VLDL2) and intestinal (chylomicron, CM) lipoproteins and 2] use the method to measure triacylglycerol (TAG) kinetics in these lipoproteins in the fed and fasting state in healthy subjects using intravenous (2)H5-glycerol as the tracer. An immunoaffinity method which completely separated hepatic and intestinal particles using sequential binding to three antibodies to apolipoprotein B100 (apoB100) was established and validated. Six healthy volunteers were studied in a fasted and continuous feeding study (study 1). Five additional healthy volunteers were studied in a continuous feeding study which included an oral (13)C3-glycerol tripalmitin tracer (study 2). In both studies an intravenous bolus of (2)H5-glycerol was administered to label TAG in hepatic and intestinal lipoproteins. In both feeding studies there was sufficient incorporation of the glycerol tracer into the exogenous lipoproteins to enable isotopic enrichment to be measured. In study 2 the oral tracer enrichment in VLDL1 was <5% of CM enrichment, 150 minutes after tracer administration demonstrating negligible contamination of VLDL1 with apoB48. Western blotting showed no detectable apoB100 in CMs. VLDL1 and VLDL2 TAG fractional catabolic rate (FCR) did not differ between feeding and fasting (study 1). There was no difference between CM and VLDL1 TAG FCR in both fed studies. In fed study 2, 47% of the total TAG production rate (CM+VLDL1) was from CM. This methodology may be a useful tool for understanding the abnormalities in postprandial TAG kinetics in metabolic syndrome and type 2 diabetes.