title: Apolipoprotein A-I and A-II kinetic parameters as assessed by endogenous labeling with [(2)H(3)]leucine in middle-aged and elderly men and women.
abstract: The purpose of our study was to investigate high density lipoprotein (HDL) apolipoprotein (apo) A-I and apoA-II kinetics in a state of constant feeding after a primed-constant infusion of [5,5, 5-(2)H(3)]L-leucine in 32 normolipidemic older men and postmenopausal women (aged 41 to 79 years). ApoA-I and apoA-II were isolated from plasma HDL, and enrichment was determined by gas chromatography/mass spectrometry. The fractional secretion rate was obtained by using a monoexponential equation calculated with the SAAM II program (Department of Bioengineering, University of Washington, Seattle). Mean HDL cholesterol (HDL-C) and total triglyceride levels were 23% higher and 27% lower, respectively, in women than in men. Mean plasma apoA-I levels were 10% greater in women than in men, whereas mean apoA-II levels were similar. HDL size, estimated by gradient-sizing gels and by the HDL-C/apoA-I+apoA-II ratio, was significantly higher in women than in men. Mean apoA-I secretion rates (SRs) were similar in men and women (12.28+/-3.64 versus 11.96+/-2.92 mg/kg per day), whereas there was a trend toward a lower (-13%) apoA-I fractional catabolic rate (FCR) in women compared with men (0.199+/-0.037 versus 0. 225+/-0.062 pools per day, P=0.11). Mean apoA-II SRs (2.21+/-0.57 versus 2.27+/-0.91 mg/kg per day) and FCRs (0.179+/-0.034 versus 0. 181+/-0.068 pools per day) were similar in men and women. For the group as a whole, there was an inverse association between the HDL-C/apoA-I+apoA-II ratio and apoA-I FCR and between the ratio and triglyceride levels. Plasma levels of apoA-I and apoA-II were correlated with their respective SRs but not FCRs. These data suggest a major role for apoA-I and apoA-II SRs in regulating the plasma levels of these proteins, whereas apoA-I FCR might be an important factor contributing to the differences in apoA-I levels between men and postmenopausal women. Moreover, plasma triglyceride levels are important determinants of HDL size and apoA-I catabolism.
authors.affiliation: Lipid Metabolism Laboratory, Jean Mayer USDA Human Nutrition Research Center of Aging at Tufts University, Boston, MA 02111, USA.
authors.forename: W
authors.initials: W
authors.lastname: Velez-Carrasco
authors.forename: A H
authors.initials: AH
authors.lastname: Lichtenstein
authors.forename: Z
authors.initials: Z
authors.lastname: Li
authors.forename: G G
authors.initials: GG
authors.lastname: Dolnikowski
authors.forename: S
authors.initials: S
authors.lastname: Lamon-Fava
authors.forename: F K
authors.initials: FK
authors.lastname: Welty
authors.forename: E J
authors.initials: EJ
authors.lastname: Schaefer
mesh_terms: D000328:Adult; D000368:Aged; D016632:Apolipoprotein A-I / Q000493:pharmacokinetics*; D016633:Apolipoprotein A-II / Q000493:pharmacokinetics*; D008076:Cholesterol, HDL / Q000378:metabolism; D005260:Female; D006801:Humans; D007930:Leucine / Q000493:pharmacokinetics; D008297:Male; D008875:Middle Aged; D017698:Postmenopause; D012727:Sex Characteristics; D014316:Tritium
chemical_list: D016632:Apolipoprotein A-I; D016633:Apolipoprotein A-II; D008076:Cholesterol, HDL; D014316:Tritium; D007930:Leucine