Effect of low-density lipoprotein apheresis on kinetics of apolipoprotein B in heterozygous familial hypercholesterolemia

Food Intake Suppresses ApoB Secretion and Fractional Catabolic Rates in Humans

BACKGROUND

Humans spend much of the day in the postprandial state. However, most research and clinical guidelines on plasma lipids pertain to blood drawn after a 12-hour fast. We aimed to study the metabolic differences of apoB lipoproteins between the fasting and postprandial states.

METHODS

We investigated plasma apoB metabolism using stable isotope tracers in 12 adult volunteers under fasting and continuous postprandial conditions in a randomized crossover study. We determined the metabolism of apoB in multiple lipoprotein subfractions, including light and dense VLDLs (very-low-density lipoproteins), IDLs (intermediate-density lipoproteins), and light and dense LDLs (low-density lipoproteins) that do or do not contain apoE or apoC3.

RESULTS

A major feature of the postprandial state is 50% lower secretion rate of triglyceride-rich lipoproteins and concurrent slowdown of their catabolism in circulation, as shown by 34% to 55% lower rate constants for the metabolic pathways of conversion by lipolysis from larger to smaller lipoproteins and direct clearance of lipoproteins from the circulation. In addition, the secretion pattern of apoB lipoprotein phenotypes was shifted from particles containing apoE and apoC3 in the fasting state to those without either protein in the postprandial state.

CONCLUSIONS

Overall, during the fasting state, hepatic apoB lipoprotein metabolism is activated, characterized by increased production, transport, and clearance. After food intake, endogenous apoB lipoprotein metabolism is globally reduced as appropriate to balance dietary input to maintain the supply of energy to peripheral tissues.

Dietary monounsaturated fat activates metabolic pathways for triglyceride-rich lipoproteins that involve apolipoproteins E and C-III

BACKGROUND

Dietary monounsaturated fat (MUFA) and complex carbohydrates have different effects on triglyceride-rich lipoprotein (TRL) metabolism.

OBJECTIVE

We hypothesized that apolipoprotein (apo) E and apo C-III might be involved in these dietary effects because of their crucial role in TRL metabolism.

DESIGN

Twelve adults consumed, for 3 wk each, 2 isocaloric diets: first a carbohydrate-rich diet (48% complex carbohydrate, 8% MUFAs) and then a MUFA-rich diet (31% complex carbohydrate, 24% MUFAs) 12 mo later. The dietary composition of other macronutrients in the 2 diets was similar. Body weight was kept constant. Postprandial apo B kinetic studies using stable-isotope tracers were performed after each dietary intervention. Multiple VLDL, intermediate-density lipoprotein (IDL), and LDL fractions were prepared on the basis of apo E and apo C-III contents.

RESULTS

The MUFA diet increased by approximately 4-6-fold, the secretion of VLDLs and IDLs containing both apo E and apo C-III (E+CIII+) (P < 0.05). These are TRLs that mostly cleared from the circulation and are minor precursors of LDL. The MUFA diet also decreased by 60% (P < 0.05) the secretion of the TRLs without apo E or apo C-III (major precursors of LDL in plasma) and decreased their flux to LDLs. Total LDL flux did not change because the MUFA diet increased the flux to LDL from E-CIII+ TRLs, a process that requires the removal of apo C-III. In addition, the MUFA diet significantly increased the TRL fractional catabolic rate by 50% and doubled the percentage of TRLs that were cleared rather than being converted to LDLs.

CONCLUSION

MUFA intake activates synthetic and rapid catabolic pathways for TRL metabolism that involve apo E and apo C-III and suppresses the metabolism of more slowly metabolized VLDLs and IDLs, which do not contain these apolipoproteins.