Differences in postprandial concentrations of very—low-density lipoprotein and chylomicron remnants between normotriglyceridemic and hypertriglyceridemic men with and without coronary heart disease

Abstract

It has been suggested that the postprandial elevation of plasma triglycerides is more closely linked to coronary heart disease (CHD) than the fasting triglyceride level. However, the postprandial situation is complex, as hepatogenous triglyceride-rich lipoprotein (TRL) particles (apolipoprotein [apo]B-100 and very—low-density lipoprotein [VLDL]) are mixed in the blood with apoB-48—containing lipoproteins secreted from the intestine. To analyze the relative proportion of liver-derived and intestinal apoB-containing TRL in subjects with and without CHD, we performed standardized oral fat-loading tests in young survivors of myocardial infarction, a large proportion of whom are hypertriglyceridemic (HTG), as well as sex- and population-matched healthy control subjects. A special effort was made to recruit healthy HTG subjects as controls for the HTG patients. Fasting plasma triglycerides (3.74 ± 1.35 v 3.01 ± 0.83, NS), low-density lipoprotein (LDL) cholesterol, and VLDL lipids, and apoB-100 and apoB-48 content at Svedberg flotation rate (Sf) 60–400, Sf 20–60, and Sf 12–20 did not differ between HTG patients (n = 10) and HTG controls (n = 14). Normotriglyceridemic (NTG) patients (n = 15) had higher fasting plasma triglycerides (1.44 ± 0.39 v 0.98 ± 0.33 mmol/L, P < .05) and LDL cholesterol (4.07 ± 0.71 v 3.43 ± 0.64, P < .05) than NTG controls (n = 34). The triglyceride elevation was accounted for by a higher level of small VLDL (apoB-100 in the Sf 20–60 fraction, 52 ± 17 v 29 ± 20 mg/L, P < .05). HTG patients responded with clearly elevated plasma triglycerides in the late postprandial phase, ie, 7, 8, and 9 hours after fat intake. Essentially, this was explained by a retention of large VLDL particles, since HTG patients exhibited no major differences in apoB-48 concentrations in the Sf > 400, Sf 60–400, and Sf 20–60 fractions but showed marked differences in the level of apoB-100 at Sf 60–400 (large VLDL) 9 hours after fat intake when compared with HTG controls (101 ± 13 v 57 ± 5 mg/L, P < .01). NTG patients were characterized by a more rapid increase of large VLDL in the early postprandial state, ie, 3 hours after fat intake, with a mean increase from baseline to 3 hours of 24.1 ± 6.7 mg/L for NTG patients and 11.8 ± 2.0 mg/L for controls ( P < .05). ApoB-48 levels were also slightly higher, but all TRL parameters returned to baseline within 9 hours after fat intake. In conclusion, elevated triglyceride levels in the postprandial state in CHD patients are explained to a large extent by the accumulation of endogenous TRL. This suggests that the postprandial dyslipidemia encountered in CHD is more dependent on a failure of regulation of endogenous TRL versus the exogenous TRL species.