Effect of hyperapo B LDL on cholesterol esterification in THP-1 macrophages.
Hyperapobetalipoproteinemia (hyperapo B), a common disorder associated with coronary artery disease, is characterized by an increased number of small, dense, low density lipoprotein (LDL) particles. The cellular mechanisms responsible for early atherosclerosis in hyperapo B are unknown. We tested the hypothesis that hyperapo B LDL may be preferentially metabolized through an LDL receptor independent pathway promoting the accumulation of cellular cholesteryl ester (CE). THP-1 macrophages have little inducible LDL receptor activity after differentiation with phorbol esters and are, therefore, suitable for assessing non-LDL receptor mediated uptake of lipoproteins. LDL isolated from hyperapo B donors was found to have significantly lower total cholesterol to protein ratio (P = 0.03), higher average density (P = 0.0001) and smaller particle diameter (P = 0.016) compared with normal (control) LDL. LDL (250 micrograms lipoprotein-protein/ml) from normal (n = 11) and hyperapo B (n = 18) subjects were incubated for 24 h with THP-1 macrophages. The mean (S.D.) CE accumulation was 6.2 (3.6) for the normal and 6.4 (2.6) for the hyperapo B LDL (P = 0.84). CE accumulation in cells incubated with malondialdehyde modified (MDA) LDL, or without added lipoprotein, was 18.2 (2.0) and 0.6 (0.7), respectively. CE mass accumulation was significantly correlated with time (6-48 h) of incubation and concentration (100-500 micrograms/ml) of LDL protein (P < 0.05); no differences were observed between normal and hyperapo B LDL. Similarly, when the major LDL species was isolated by density gradient ultracentrifugation, mean (S.D.) CE was similar for the normal and hyperapo B LDL (8.7 (1.2) vs. 6.9 (1.5)). There were no differences in the mean (S.D.) incorporation of [14C]oleate into CE (nmol/mg cell protein per 6 h) in THP-1 macrophages incubated with normal or hyperapo B LDL (0.238 (0.045) vs. 0.211 (0.046)); results were comparable in human monocyte-derived (HMD) macrophages (0.298 (0.037) vs. 0.258 (0.022)). Also, mean (S.D.) cellular uptake and degradation (ng 125I/mg cell protein per h) in THP macrophages of normal and hyperapo B LDL were similar (uptake: 18 (14) vs. 12 (6.0); degradation: 58 (32) vs. 44 (8)). In summary: (1) hyperapo B LDL did not stimulate the accumulation of cellular CE via LDL receptor independent pathways in THP-1 macrophages, (2) normal and hyperapo B LDL stimulation of CE synthesis is similar in THP-1 and HMD macrophages and (3) no differences in cellular uptake and degradation of normal and hyperapo B LDL were observed in THP macrophages.
Kafonek
S D
SD
Department of Pediatrics, Johns Hopkins University School of Medicine, Baltimore, MD 21205.
Raikhel
I
I
Bachorik
P S
PS
Kwiterovich
P O
PO
D000328:Adult; D000368:Aged; D002460:Cell Line; D002784:Cholesterol / Q000378:metabolism*; D002788:Cholesterol Esters / Q000378:metabolism; D004951:Esterification; D005260:Female; D006801:Humans; D006951:Hyperlipoproteinemias / Q000378:metabolism; D008077:Lipoproteins, LDL / Q000378:metabolism; D008264:Macrophages / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D014280:Triglycerides / Q000378:metabolism; D014407:Tumor Cells, Cultured / Q000378:metabolism
D002788:Cholesterol Esters; D008077:Lipoproteins, LDL; D014280:Triglycerides; D002784:Cholesterol