The Measurement of High-Density Lipoprotein Mediated Cholesterol Efflux from Macrophage Cells by Liquid Chromatography Tandem Mass Spectrometry

Abstract

Background: Studies have shown a negative association between macrophage cholesterol efflux and atherosclerotic cardiovascular diseases (CVD). However, the current methods for measuring cholesterol efflux require a radioactive tracer and involve a variety of cell treatments, making the measurement of macrophage cholesterol efflux impractical for use in clinical laboratories. In this study, we developed a non-radioactive and precise LC/MS/MS method for the measurement of high-density lipoprotein (HDL) mediated cholesterol efflux from J774 macrophages. Methods: J774 cells were seeded on 12-well plates at a density of 1.5×10⁵ cells/ml in H-DMEM medium, and when the cells were approximately 80% confluent, they were incubated with H-DMEM medium containing 2% FBS, 0.5 μg/ml ACAT inhibitor Sandoz 58-035, and 20 μg/ml [3,4-¹³C]cholesterol for 6 h. After washing and equilibrating the cells, HDL samples were added at a final concentration of 7% and incubated for 8 h. The cells were lysed, and [3,4-¹³C]cholesterol and cholesterol were measured by LC/MS/MS. Cholesterol efflux was expressed as the percent decrease of cell [3,4-¹³C]cholesterol mass during the incubation. Results: When incubated with [3,4-¹³C]cholesterol enriched J774 cells, HDL mediated higher cell cholesterol efflux than influx compared to serum and isolated LDL; therefore, HDL was used as the extracellular acceptor. The results from healthy volunteers showed that the rate of cholesterol efflux was negatively correlated with weight, BMI, blood pressure, and FER_HDL and positively correlated with HDL-C, HDL2-C, and apoAI levels. Conclusions: A LC/MS/MS method for the measurement of HDL mediated cholesterol efflux from macrophage cells has been established. This method is non-radioactive, precise and reliable and is potentially useful for the assessment of HDL function and cardiovascular disease risks.