Postprandial exchange of apolipoprotein C-III between plasma lipoproteins

Three healthy male subjects were given a high fat meal after fasting for 12 h. Blood samples were drawn at hourly intervals over 6 h. The plasma triglyceride levels reached peak values within 3 to 6 h postprandially. Plasma cholesterol concentration, however, remained constant in the three subjects as well as in a fasting normal subject. Apolipoprotein C-III (apoC-III), a major apoprotein in triglyceride-rich lipoprotein particles and known to be exchangeable between plasma high density lipoproteins (HDL) and triglyceride-rich particles, was studied in regard to its net transfer between lipoproteins during meal absorption and postabsorptive lipolysis. ApoC-III levels in total plasma as quantitated by radioimmunoassay were stable regardless of the increase of plasma triglycerides. When triglyceride levels increased after a meal, apoC-III in the d. less than 1.063 lipoprotein fraction increased concomitantly, while apoC-III in HDL decreased. The converse was observed during lipolysis as plasma triglycerides fell. In any case, apoC-III levels in d. less than 1.063 lipoproteins were positively correlated with plasma triglycerides (r = 0.82, p less than 0.01) after the meal. The finding suggests that the apoC-III concentrations in HDL are very dynamic in vivo. ApoC-III can transfer from HDL to triglyceride-rich particles during meal absorption and can transfer from triglyceride-rich particles to HDL during postabsorptive lipolysis.