Cholesterol Efflux Capacity of Apolipoprotein A-I Varies with the Extent of Differentiation and Foam Cell Formation of THP-1 Cells

Apolipoprotein A-I (apoA-I), the main protein component of high-density lipoprotein (HDL), has many protective functions against atherosclerosis, one of them being cholesterol effluxcapacity. Although cholesterol effluxcapacity measurement is suggested to be a key biomarker for evaluating the risk of development of atherosclerosis, the assay has not been optimized till date. This study aims at investigating the effect of different states of cells on the cholesterol effluxcapacity. We also studied the effect of apoA-I modification by homocysteine, a risk factor for atherosclerosis, on cholesterol effluxcapacity in different states of cells. The cholesterol effluxcapacity of apoA-I was greatly influenced by the extent of differentiation of THP-1 cells and attenuated by excessive foam cellformation. N-Homocysteinylated apoA-I indicated a lower cholesterol effluxcapacity than normal apoA-I in the optimized condition, whereas no significant difference was observed in the cholesterol effluxcapacity between apoA-I in the excessive cell differentiation or foam cellformation states. These results suggest that cholesterol effluxcapacity of apoA-I varies depending on the state of cells. Therefore, the cholesterol effluxassay should be performed using protocols optimized according to the objective of the experiment.