title: Measurement of reverse cholesterol transport pathways in humans: in vivo rates of free cholesterol efflux, esterification, and excretion.
abstract: BACKGROUND
  Reverse cholesterol transport from peripheral tissues is considered the principal atheroprotective mechanism of high-density lipoprotein, but quantifying reverse cholesterol transport in humans in vivo remains a challenge. We describe here a method for measuring flux of cholesterol though 3 primary components of the reverse cholesterol transport pathway in vivo in humans: tissue free cholesterol (FC) efflux, esterification of FC in plasma, and fecal sterol excretion of plasma-derived FC.
  
  
  RESULTS
  A constant infusion of [2,3-(13)C(2)]-cholesterol was administered to healthy volunteers. Three-compartment SAAM II (Simulation, Analysis, and Modeling software; SAAM Institute, University of Washington, WA) fits were applied to plasma FC, red blood cell FC, and plasma cholesterol ester (13)C-enrichment profiles. Fecal sterol excretion of plasma-derived FC was quantified from fractional recovery of intravenous [2,3-(13)C(2)]-cholesterol in feces over 7 days. We examined the key assumptions of the method and evaluated the optimal clinical protocol and approach to data analysis and modeling. A total of 17 subjects from 2 study sites (n=12 from first site, age 21 to 75 years, 2 women; n=5 from second site, age 18 to 70 years, 2 women) were studied. Tissue FC efflux was 3.79±0.88 mg/kg per hour (mean ± standard deviation), or ≍8 g/d. Red blood cell-derived flux into plasma FC was 3.38±1.10 mg/kg per hour. Esterification of plasma FC was ≍28% of tissue FC efflux (1.10±0.38 mg/kg per hour). Recoveries were 7% and 12% of administered [2,3-(13)C(2)]-cholesterol in fecal bile acids and neutral sterols, respectively.
  
  
  CONCLUSIONS
  Three components of systemic reverse cholesterol transport can be quantified, allowing dissection of this important function of high-density lipoprotein in vivo. Effects of lipoproteins, genetic mutations, lifestyle changes, and drugs on these components can be assessed in humans. (J Am Heart Assoc. 2012;1:e001826 doi: 10.1161/JAHA.112.001826.).
authors.affiliation: KineMed, Inc,  Emeryville, CA (S.T., J.V., A.G., S.K., J.D., H.M., E.M., J.L., M.A.).
authors.forename: Scott
authors.initials: S
authors.lastname: Turner
authors.forename: Jason
authors.initials: J
authors.lastname: Voogt
authors.forename: Michael
authors.initials: M
authors.lastname: Davidson
authors.forename: Alex
authors.initials: A
authors.lastname: Glass
authors.forename: Salena
authors.initials: S
authors.lastname: Killion
authors.forename: Julie
authors.initials: J
authors.lastname: Decaris
authors.forename: Hussein
authors.initials: H
authors.lastname: Mohammed
authors.forename: Kaori
authors.initials: K
authors.lastname: Minehira
authors.forename: Drina
authors.initials: D
authors.lastname: Boban
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Murphy
authors.forename: Jayraz
authors.initials: J
authors.lastname: Luchoomun
authors.forename: Mohamad
authors.initials: M
authors.lastname: Awada
authors.forename: Richard
authors.initials: R
authors.lastname: Neese
authors.forename: Marc
authors.initials: M
authors.lastname: Hellerstein
keywords: cholesterol efflux; esterification; isotope labeling, stable; reverse cholesterol transport; sterol excretion