HDL derived from the different phases of conjugated diene formation reduces membrane fluidity and contributes to a decrease in free cholesterol efflux from human THP-1 macrophages.
Oxidized HDL (ox-HDL) has been reported to reduce free cholesterol efflux from cells. In this study we investigate the effect of different stages of ox-HDL on macrophage membrane fluidity and its effect on free cholesterol efflux from macrophages as a cell function influenced by ox-HDL. HDL was oxidized by means of conjugated diene production using copper as a prooxidant. Fluidity of HDL and human THP-1 macrophage membranes was evaluated by changes in fluorescence anisotropy (r) by DPH probe where lower (r) values give higher fluidity. We found that ox-HDL derived from the propagation phase (PP-HDL) and the decomposition phase (DP-HDL) became less fluid ((r): 0.263+/-0.001, 0.279+/-0.002, respectively) than HDL from the lag phase (LP-HDL) and native HDL (nat-HDL) ((r): 0.206+/-0.001) (P<0.05). Macrophages incubated with PP-HDL and DP-HDL had less fluid membranes ((r): 0.231+/-0.001, 0.243+/-0.002, respectively) than those incubated with LP-HDL and nat-HDL ((r): 0.223+/-0.001) (P<0.05). Consequently, fluidity was reduced not only in ox-HDL but also in the cell membranes exposed to ox-HDL. A significant negative correlation was observed between macrophage membrane fluorescence anisotropy (r) and free cholesterol efflux from these cells (-0.876; P<0.05). Thus, lower membrane fluidity was associated with lower free cholesterol efflux from cells. In conclusion, the increase in the HDL oxidation process leads to a lost of macrophage membrane fluidity that could contribute to an explanation of the reduction of free cholesterol efflux from cells by ox-HDL.
D001693:Biological Transport, Active; D002460:Cell Line; D002784:Cholesterol / Q000378:metabolism*; D005454:Fluorescence Polarization; D006801:Humans; D008075:Lipoproteins, HDL / Q000737:chemistry* / Q000378:metabolism* / Q000494:pharmacology; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism*; D008560:Membrane Fluidity / Q000187:drug effects / Q000502:physiology*; D015394:Molecular Structure; D010084:Oxidation-Reduction
D008075:Lipoproteins, HDL; D002784:Cholesterol