Apolipoprotein A1

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [2]

Synonyms and keywords: Apo A-1; Apo A-I; Apo A1; Apo AI; ApoA-1; ApoA-I; apolipoprotein A 1; apolipoprotein A I; apolipoprotein A-1; apolipoprotein A-I; apolipoprotein AI

Apolipoprotein A-I
PDB rendering based on 1av1.
Available structures
PDB Ortholog search: Template:Homologene2PDBe PDBe, Template:Homologene2uniprot RCSB
Identifiers
Symbols APOA1 ; MGC117399
External IDs Template:OMIM5 Template:MGI HomoloGene47900
RNA expression pattern
More reference expression data
Orthologs
Template:GNF Ortholog box
Species Human Mouse
Entrez n/a n/a
Ensembl n/a n/a
UniProt n/a n/a
RefSeq (mRNA) n/a n/a
RefSeq (protein) n/a n/a
Location (UCSC) n/a n/a
PubMed search n/a n/a

Overview

Apolipoprotein A1 is the major protein component of high density lipoprotein (HDL) in plasma. The protein promotes cholesterol efflux from tissues to the liver for excretion. It is a cofactor for lecithin cholesterolacyltransferase (LCAT) which is responsible for the formation of most plasma cholesteryl esters. ApoA-I was also isolated as a prostacyclin(PGI2) stabilizing factor, and thus may have an anticlotting effect.[1] Defects in the gene encoding it are associated with HDL deficiencies, including Tangier disease, and with systemic non-neuropathic amyloidosis.

Activity associated with high HDL-C and protection from heart disease

As a major component of the high density lipoprotein complex ("good cholesterol"), ApoA-I helps to clear cholesterol from arteries. Five of nine men found to carry a mutation (E164X) who were at least 35 years of age had developed premature coronary artery disease.[2] One of four mutants of ApoA-I is present in roughly 0.3% of the Japanese population, but is found 6% of those with low HDL cholesterol levels.

ApoA-I Milano is a naturally occurring mutant of ApoA-I, found in a family descended from a single couple of the 18th century. Described in 1980, it was the first known molecular abnormality of apolipoproteins.[3] Paradoxically, carriers of this mutation have very low HDL cholesterol levels, but no increase in the risk of heart disease. Biochemically, ApoA-I contains an extra cysteine bridge, causing it to exist as a homodimer or as a heterodimer with ApoA-II. However, the enhanced cardioprotective activity of this mutant (which likely depends on cholesterol efflux) cannot easily be replicated by other cysteine mutants.[4]

Recombinant Apo-I Milano dimers formulated into liposomes can reduce atheromas in animal models by up to 30%.[5] ApoA-I Milano has also been shown in small clinical trials to have a statistically significant[6] effect in reducing (reversing) plaque build-up on arterial walls. In human trials the reversal of plaque build-up was measured over the course of five weeks.[6][7]

APP018 (formerly D-4F), an 18-amino acid peptide (Ac-D-W-F-K-A-F-Y-D-K-V-A-E-K-F-K-E-A-F-NH2[8][9], using D-amino acids) that can be taken orally, was developed by Bruin Pharmaceuticals (a little-known company founded by Dr. Alan Fogelman, named after the UCLA Bruins[10][11]) and sold to Novartis for $200 million USD. The peptide and close variations thereof such as D-5F have been shown to elevate HDL-C and reduce atherosclerotic build-up in early animal data. The peptide has been tested with a variety of modifications, formulated with an excipient such as poly(lactide-co-glycolide) (PLG), and formed into ProLease[12] drug-polymer microspheres. If all continues to go well it is expected to reach the pharmacy shelf around 2013.[13]

Lately, two novel susceptibility haplotypes i.e. P2-S2-X1 and P1-S2-X1 have been discovered in ApoAI-CIII-AIV gene cluster on chromosme 11q23, who confer approximately threefold higher risk of coronary heart disease in normal [3] as well as non-insulin diabetes mellitus[4].

Role in other diseases

A G/A polymorphism in the promoter of the ApoA-I gene has been associated with the age at which patients presented with Alzheimer disease.[14] Protection from Alzheimer disease by ApoA1 may rely on a synergistic interaction with alpha-tocopherol[15].

Amyloid deposited in the knee following surgery consists largely of ApoA-I secreted from chondrocytes (cartilage cells).[16] A wide variety of amyloidosis symptoms are associated with rare ApoA-I mutants.

ApoA-I binds to lipopolysaccharide or endotoxin, and has a major role in the anti-endotoxin function of HDL.[17]

Lately, two novel susceptibility haplotypes i.e. P2-S2-X1 and P1-S2-X1 have been discovered in ApoAI-CIII-AIV gene cluster on chromosme 11q23, who confer approximately threefold higher risk of coronary heart disease in normal [5] as well as non-insulin diabetes mellitus[6].

In one study, a decrease in ApoA1 levels was detected in schizophrenia patients' CSF, brain and peripheral tissues.[18]

Factors affecting ApoA-I activity

ApoA-I production is decreased by Vitamin D, and increased by a drug that antagonizes it.[19]

Exercise or statin treatment may cause an increase in HDL-C levels by inducing ApoA-I production, but this depends on the G/A promoter polymorphism.[20]

References

  1. Yui Y, Aoyama T, Morishita H, Takahashi M, Takatsu Y, Kawai C (1988). "Serum prostacyclin stabilizing factor is identical to apolipoprotein A-I (Apo A-I). A novel function of Apo A-I". J. Clin. Invest. 82 (3): 803–7. PMID 3047170.
  2. Dastani Z, Dangoisse C, Boucher B, Desbiens K, Krimbou L, Dufour R, Hegele RA, Pajukanta P, Engert JC, Genest J, Marcil M (2006). "A novel nonsense apolipoprotein A-I mutation (apoA-I(E136X)) causes low HDL cholesterol in French Canadians". Atherosclerosis. 185 (1): 127–36. PMID 16023124.
  3. Franceschini G, Sirtori M, Gianfranceschi G, Sirtori CR (1981). "Relation between the HDL apoproteins and AI isoproteins in subjects with the AIMilano abnormality". Metab. Clin. Exp. 30 (5): 502–9. PMID 6785551.
  4. Zhu X, Wu G, Zeng W, Xue H, Chen B (2005). "Cysteine mutants of human apolipoprotein A-I: a study of secondary structural and functional properties". J. Lipid Res. 46 (6): 1303–11. PMID 15805548.
  5. Chiesa G, Sirtori CR (2003). "Apolipoprotein A-I(Milano): current perspectives". Curr. Opin. Lipidol. 14 (2): 159–63. PMID 12642784.
  6. 6.0 6.1 "Apo A1-Milano Trial: Where are we now?". Cleveland Clinic. Retrieved 2006-11-09.
  7. "Cedars-Sinai Heart Center - Apo A-1 Milano". Cedars-Sinai Heart Center. Retrieved 2006-11-09.
  8. Patent US 7,144,862 B2
  9. Patent WO2006 118805
  10. Matthew Herper, Forbes 07.11.05 "Novartis Enters 'Good Cholesterol' Battle."
  11. Fierce Biotech. "Bruin Pharmaceuticals."
  12. Bartus et al., 1998, Science 281:1161-2 [1]
  13. BioMarket Group AB, "Antidyslipidemics: market set for contraction as generics hit hard", October 4, 2006.
  14. Vollbach H, Heun R, Morris CM, Edwardson JA, McKeith IG, Jessen F, Schulz A, Maier W, Kölsch H (2005). "APOA1 polymorphism influences risk for early-onset nonfamiliar AD". Ann. Neurol. 58 (3): 436–41. PMID 16130094.
  15. Maezawa I, Jin LW, Woltjer RL, Maeda N, Martin GM, Montine TJ, Montine KS (2004). "Apolipoprotein E isoforms and apolipoprotein AI protect from amyloid precursor protein carboxy terminal fragment-associated cytotoxicity". J. Neurochem. 91 (6): 1312–21. PMID 15584908.
  16. Solomon A, Murphy CL, Kestler D, Coriu D, Weiss DT, Makovitzky J, Westermark P (2006). "Amyloid contained in the knee joint meniscus is formed from apolipoprotein A-I". Arthritis Rheum. 54 (11): 3545–50. PMID 17075859.
  17. Ma J, Liao XL, Lou B, Wu MP (2004). "Role of apolipoprotein A-I in protecting against endotoxin toxicity". Acta Biochim. Biophys. Sin. (Shanghai). 36 (6): 419–24. PMID 15188057.
  18. Huang JT, Wang L, Prabakaran S, Wengenroth M, Lockstone HE, Koethe D, Gerth CW, Gross S, Schreiber D, Lilley K, Wayland M, Oxley D, Leweke FM, Bahn S (2007). "Independent protein-profiling studies show a decrease in apolipoprotein A1 levels in schizophrenia CSF, brain and peripheral tissues". Mol Psychiatry. doi:10.1038/sj.mp.4002108. PMID 17938634.
  19. Wehmeier K, Beers A, Haas MJ, Wong NC, Steinmeyer A, Zugel U, Mooradian AD (2005). "Inhibition of apolipoprotein AI gene expression by 1, 25-dihydroxyvitamin D3". Biochim. Biophys. Acta. 1737 (1): 16–26. PMID 16236546.
  20. Lahoz C, Peña R, Mostaza JM, Jiménez J, Subirats E, Pintó X, Taboada M, López-Pastor A (2003). "Apo A-I promoter polymorphism influences basal HDL-cholesterol and its response to pravastatin therapy". Atherosclerosis. 168 (2): 289–95. PMID 12801612.


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