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Journal of Lipid Research, Vol. 47, 115-122, January 2006 Formation of high density lipoproteins containing both apolipoprotein A-I and A-II in the rabbit
* Lipid Research Group, The Heart Research Institute, Camperdown, Sydney, New South Wales 2050, Australia Published, JLR Papers in Press, October 12, 2005. 1 Present address of N. J. Hime: The Scripps Research Institute, Immunology Department, North Torrey Pines Road, La Jolla, CA 92037.
2 To whom correspondence should be addressed. e-mail: k.rye{at}hri.org.au Human plasma HDLs are classified on the basis of apolipoprotein composition into those that contain apolipoprotein A-I (apoA-I) without apoA-II [(A-I)HDL] and those containing apoA-I and apoA-II [(A-I/A-II)HDL]. ApoA-I enters the plasma as a component of discoidal particles, which are remodeled into spherical (A-I)HDL by LCAT. ApoA-II is secreted into the plasma either in the lipid-free form or as a component of discoidal high density lipoproteins containing apoA-II without apoA-I [(A-II)HDL]. As discoidal (A-II)HDL are poor substrates for LCAT, they are not converted into spherical (A-II)HDL. This study investigates the fate of apoA-II when it enters the plasma. Lipid-free apoA-II and apoA-II-containing discoidal reconstituted HDL [(A-II)rHDL] were injected intravenously into New Zealand White rabbits, a species that is deficient in apoA-II. In both cases, the apoA-II was rapidly and quantitatively incorporated into spherical (A-I)HDL to form spherical (A-I/A-II)HDL. These particles were comparable in size and composition to the (A-I/A-II)HDL in human plasma. Injection of lipid-free apoA-II and discoidal (A-II)rHDL was also accompanied by triglyceride enrichment of the endogenous (A-I)HDL and VLDL as well as the newly formed (A-I/A-II)HDL. We conclude that, irrespective of the form in which apoA-II enters the plasma, it is rapidly incorporated into spherical HDLs that also contain apoA-I to form (A-I/A-II)HDL.
Supplementary key words high density lipoproteins containing apolipoprotein A-I without apolipoprotein A-II high density lipoprotein formation triglyceride-enriched high density lipoproteins Abbreviations: apoA-I, apolipoprotein A-I; (A-I)HDL, high density lipoproteins containing apolipoprotein A-I without apolipoprotein A-II; (A-I/A-II)HDL, high density lipoproteins containing apolipoprotein A-I and apolipoprotein A-II; (A-II)HDL, high density lipoproteins containing apolipoprotein A-II without apolipoprotein A-I; rHDL, reconstituted high density lipoprotein
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