Effects of a National Cholesterol Education Program Step II Diet on apolipoprotein A-IV metabolism within triacylglycerol-rich lipoproteins and plasma

Background: Apolipoprotein (apo) A-IV is a major component of triacylglycer ol-rich lipoprotein (TRL) apolipoproteins. Objective: We investigated the effects of dietary saturated fat and cholest erol restriction on the metabolism of TRL and plasma apo A-IV. Design: We assessed TRL and plasma apo A-IV kinetics in 16 and 4 subjects, respectively, consuming an average US (baseline) diet for 6 wk and a Nation al Cholesterol Education Pro-ram Step II diet for 24 wk, respectively. At t he end of each diet period, all subjects received a primed, constant infusi on of deuterated leucine for 15 h with hourly feeding. Ratios of stable-iso tope tracer to tracee were measured by using gas chromatography-mass spectr ometry, and kinetic data were modeled by using SAAM II. Results: Mean apo A-IV concentrations during the isotope infusion period we re 6.9 +/-2.6 mg/L in TRL and 2.2 +/-3.2 mg/L in plasma with the baseline d iet; these values were 37.7% (P<0.001) and 19.4% (P<0.01) lower with the St ep II diet. Similar changes were observed in the fasting state between the 2 diets. The mean apo A-IV secretion rate decreased significantly from base line by 59.6% in TRLs and by 40.2% in plasma. Significant correlations were observed between TRL apo A-IV concentrations and the secretion rate (r=0.9 4, P<0.001) and between TRL apo A-IV pool size and TRL-cholesterol concentr ations (r = 0.48, P<0.01). Conclusions: Our data indicate that the National Cholesterol Education Prog ram Step II diet significantly decreases TRL and plasma apo A-IV concentrat ions compared with the average US diet and that this decrease is due to a d ecreased secretion rate.