A new method for measuring cholesterol efflux capacity uses stable isotope-labeled, not radioactive-labeled, cholesterol

• Main Authors: Tomo Shimizu, Osamu Miyazaki, Takeo Iwamoto, Tomoyuki Usui, Ryo Sato, Chika Hiraishi, Hiroshi Yoshida
• Format: Article
• Language: English
• Published: Elsevier 2019-11-01
• Series: Journal of Lipid Research
• Subjects: apolipoprotein; reverse cholesterol transport; high density lipoprotein; mass spectrometry; stable isotope tracers; [d7]cholesterol
• Online Access: http://www.sciencedirect.com/science/article/pii/S002222752032294X

The incidence of cardiovascular events correlates inversely with cholesterol efflux capacity (CEC) more than with HDL-cholesterol level. The measurement of CEC is used to qualify cardiovascular disease risk and is conventionally performed with radioisotope (RI)-labeled cholesterol. Here, we established a CEC measurement technique using stable isotope-labeled cholesterol as an alternative, and we compared the new method with RI and fluorescence (boron dipyrromethene difluoride-cholesterol) methods in cells and in patient serum. We incubated J774 cells labeled with [d7]cholesterol ([d7]C) with patient serum depleted of apoB, and [d7]C extracted from the culture medium was quantified by liquid chromatography/quadrupole time-of-flight mass spectrometry. [d7]C efflux increased with greater apoB-depleted serum concentration and longer incubation time. The assay coefficient of variation (CV) of five consecutive measurements of three sets of samples ranged from 7.3% to 9.5%, and the interassay CV determined by measuring three samples four times ranged from 4.1% to 8.5%, both indicating good precision. We then measured CEC levels of 41 outpatients with serum HDL-cholesterol levels between 36 and 94 mg/dl (mean: 61.7 ± 18.0 mg/dl); in the presence of cAMP, we observed a significant, positive correlation between CEC levels determined with the stable isotope and RI methods that was stronger than the correlation between measurements obtained by the fluorescence and RI methods (r = 0.73, P < 0.0001 vs. r = 0.55, P < 0.001). Therefore, our stable isotope method can be considered useful as a non-RI method and thus deserves evaluation in future clinical studies.