title: Postprandial changes in apolipoprotein(a) concentration of triglyceride-rich lipoproteins can be reproduced by in vitro incubation: implications for underlying mechanism.
abstract: We investigated the reciprocal changes in apolipoprotein(a) concentration in the lipoprotein of d > 1.006 and the triglyceride-rich lipoprotein (TRL) fractions of plasma which occur in vivo following fat ingestion. Twenty fasting subjects were studied before and 4 h after a fat-rich meal. In 75% of cases, in vitro incubation of the postprandial (4-h) TRL with autologous fasting (0-h) lipoproteins of d > 1.006 resulted in further substantial (> 5% total) reciprocal changes in apo(a) concentration of the 2 fractions. The increase in re-isolated postprandial TRL apo(a) was 25.1% +/- 5.1% of the total apo(a), compared to the insignificant increase (0.1% +/- 0.1%) in re-isolated fasting TRL. Most of the further increase in 4-h TRL apo(a) (94% +/- 4%) could be achieved by incubation with the corresponding 4-h chylomicron fraction (CM) alone. The re-isolated 4-h TRL apo(a) concentration correlated positively with 4-h plasma TG concentration (r = 0.65, P < 0.01) and other indices of postprandial lipaemia. In vitro incubation of pooled serum lipoproteins of d > 1.006 with serial dilutions of nascent CM obtained from chylous ascitic fluid revealed that the reciprocal changes in apo(a) concentration exhibit a curvilinear relationship with the concentration of CM triglyceride which plateaued round 7 mmol/l in this instance. We conclude that the reciprocal changes in apo(a) concentration between TRL and lipoproteins of d > 1.006 which occur in the postprandial phase are quantitatively significant and largely represent a redistribution process rather than de novo synthesis because they can be reproduced by in vitro incubation.
authors.affiliation: Department of Clinical Biochemistry, Royal Prince Alfred Hospital, Sydney, NSW, Australia.
authors.forename: D R
authors.initials: DR
authors.lastname: Sullivan
authors.forename: C W
authors.initials: CW
authors.lastname: Lam
authors.forename: W
authors.initials: W
authors.lastname: Jessup
authors.forename: R T
authors.initials: RT
authors.lastname: Dean
authors.forename: W J
authors.initials: WJ
authors.lastname: Hensley
mesh_terms: D000328:Adult; D000368:Aged; D001054:Apolipoproteins A / Q000378:metabolism*; D004041:Dietary Fats / Q000008:administration & dosage*; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D008074:Lipoproteins / Q000097:blood*; D008297:Male; D008875:Middle Aged; D014280:Triglycerides / Q000097:blood*
chemical_list: D001054:Apolipoproteins A; D004041:Dietary Fats; D008074:Lipoproteins; D014280:Triglycerides