- Lipoprotein-X
Lipoprotein-X (Lp-X) is an abnormal
low density lipoprotein found incholestasis .Structure
Lipoprotein-X is a lamellar particle of 30 to 70 nm in diameter as revealed by electron microscopy. It is characterized by its high content of
phospholipids (66% by weight) and unesterifiedcholesterol (22%), and its low content ofprotein (6%), cholesterol esters (3%), andtriglycerides (3%). The protein component is dominated by albumin, located in the core, and byapolipoprotein C, located on the surface of the particle. Using zonal ultracentrifugation, lipoprotein-X can be divided into three distinct populations: Lp-X1, Lp-X2, and Lp-X3, differing in density and apolipoprotein composition.Pathogenesis
The pathogenesis of lipoprotein-X in cholestasis is not totally resolved. Normally, the
liver excretes lipoprotein complexes into the bile showing phospholipid and unesterified cholesterol concentrations similar to Lipoprotein-X. The in vitro incubation of thesebile lipoproteins with serum or albumin leads to the appearance of Lp-X–like particles. These findings suggest that the reflux ofbile into the plasma compartment causes the formation of lipoprotein-X incholestasis as a result of a physicochemical, nonmetabolic process. On the other hand, lipoprotein-X particles found in familial LCAT deficiency are identical to those in cholestasis regarding ultrastructure and biochemical composition. It has been supposed that reduced LCAT activities, common in patients with hepatocellular disease, cause, alone or in combination with other factors, the formation of Lipoprotein-X in cholestasis. Lipoprotein-X is mainly removed by the reticuloendothelial system of the liver and thespleen , as shown by studies using radioactively labeled lipoprotein-X in rats. Other organs, such as thekidney , also actively clear Lipoprotein-X from the plasma.Literature
*Seidel D, Alaupovic P, Furman RH. A lipoprotein characterizing obstructive jaundice. I. Method for quantitative separation and identification of lipoproteins in jaundiced subjects. J Clin Invest. 1969 Jul;48(7):1211-23. [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=4978447&query_hl=4&itool=pubmed_docsum PubMed abstract]
* Seidel D, Alaupovic P, Furman RH, McConathy WJ. A lipoprotein characterizing obstructive jaundice. II. Isolation and partial characterization of the protein moieties of low density lipoproteins. J Clin Invest. 1970 Dec;49(12):2396-407. [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=5480863&query_hl=4&itool=pubmed_docsum PubMed abstract]
*Sörös P, Böttcher J, Maschek H, Selberg O, Müller MJ. Lipoprotein-X in patients with cirrhosis: its relationship to cholestasis and hypercholesterolemia. Hepatology. 1998 Nov;28(5):1199-205. [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=9794902&query_hl=2&itool=pubmed_DocSum PubMed abstract]
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