Journal of Lipid Research, Vol 23, 92-96, Copyright © 1982 by Lipid Research, Inc.
Measurement of receptor-independent lipoprotein catabolism using 1,2 cyclohexanedione-modified low density lipoprotein
HR Slater, CJ Packard and J Shepherd
The utility of 1,2 cyclohexanedione-modified low density lipoprotein
(CHD-LDL) as a marker for the measurement of receptor independent LDL
catabolism has been assessed by examining its metabolic properties in
cultured human fibroblasts and in rabbits. Cell culture studies showed that
the inhibition of high affinity membrane receptor binding produced by the
modification could be partially reversed by prolonged incubation of the
CHD-LDL at 37 degrees C. Pre-exposure of the complex to alkaline pH (pH
10.5) prevented this and yielded a product that was apparently stable.
Despite its regained ability to bind to the fibroblast receptor,
125I-labeled CHD-LDL incubated at 37 degrees C for 24 hr either in vivo or
in vitro was removed from rabbit plasma in the same manner as freshly
prepared 131I-labeled CHD-LDL and as 131I-labeled CHD- LDL that had been
treated at pH 10.5. However, its plasma clearance was significantly faster
than that of reductively methylated LDL. We believe that this may result
from differential catabolism of these modified lipoproteins rather than
from susceptibility of the CHD-LDL to receptor-directed catabolism.
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