Transfer of phospholipase A-resistant pyrene-dialkyl-glycerophosphocholine to plasma lipoproteins: differences between Lp[a] and LDL.
1-O-Hexadecyl-2-O-pyrenedecanyl-sn-glycero-3-phosphocholine, a non-hydrolyzable fluorescent diether analog of phosphatidylcholine (PC), was synthesized as a probe for studying phospholipid transfer to different lipoprotein classes with potential phospholipase activities. After incubation of total human plasma with the new probe at 37 degrees C for 4.5 h, a characteristic partition between the main lipoprotein fractions was observed. The fluorescent lipid was not degraded under these conditions and, therefore, served as a measure for choline glycerophospholipid distribution between plasma lipoproteins. In low density lipoprotein (LDL) and high density lipoprotein-3 (HDL3) the fluorescent PC analog showed only monomer fluorescence, whereas in Lp[a] and HDL2 monomer and excimer fluorescence were observed, indicating that the fluorescent phosphatidylcholine analog was incorporated into the respective lipoproteins to a different extent. According to the increased pyrene excimer fluorescence in Lp[a] compared with LDL the labeled phosphatidylcholine must be enriched and/or clustered in Lp[a]. Data from phospholipid and total fluorescence analyses are compatible with the assumption of higher label concentration in Lp[a]. On the other hand, transfer rates for serum protein-catalyzed lipid transport into isolated Lp[a] were slower as compared to LDL. It is suggested that slower lipid transfer to Lp[a] under these conditions is due to the decreased lipid mobility in the Lp[a] surface, whereas the higher extent of label partition into Lp[a] as observed in total plasma might be due to the higher affinity of apolipoproteins for phosphatidylcholine in Lp[a] (Sommer, A., et al. 1992. J. Biol. Chem. 267: 24217-24222). The use of a fluorescent dialkyl- instead of diacyl-glycerophosphocholine for transfer studies was mandatory, as we found that lipoproteins contained phospholipase A2 activity toward long-chain phosphatidylcholine. The lipoprotein-associated phospholipase A2 was three times more active in Lp[a] than in LDL. The degradation products formed by the phospholipase, fatty acids, and lyso-PC may add to the high atherogenic potential of Lp[a].
Gorges
R
R
Institut für Biochemie und Lebensmittelchemie, Technische Universität Graz, Austria.
Hofer
G
G
Sommer
A
A
Stütz
H
H
Grillhofer
H
H
Kostner
G M
GM
Paltauf
F
F
Hermetter
A
A
D001692:Biological Transport; D005456:Fluorescent Dyes; D005997:Glycerylphosphorylcholine / Q000378:metabolism*; D006801:Humans; D017270:Lipoprotein(a) / Q000378:metabolism*; D008077:Lipoproteins, LDL / Q000378:metabolism*; D010713:Phosphatidylcholines / Q000138:chemical synthesis / Q000378:metabolism*; D010741:Phospholipases A / Q000378:metabolism*; D054467:Phospholipases A2; D011721:Pyrenes / Q000138:chemical synthesis / Q000378:metabolism*
D005456:Fluorescent Dyes; D017270:Lipoprotein(a); D008077:Lipoproteins, LDL; D010713:Phosphatidylcholines; D011721:Pyrenes; D005997:Glycerylphosphorylcholine; D010741:Phospholipases A; D054467:Phospholipases A2