Apolipoprotein E (Apo E)

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Chapter One
Apolipoprotein E (Apo E)


Human plasma has five different types of apolipoproteins (A, B, C, D, and E) and some of them are further categorized into subtypes (Eichner et al., 2002), (Anthopoulos et al., 2010).

Apolipoprotein (Apo E) is a member of apolipoprotien gene family that was discovered in the 1970s and they are classified to three isoforms encoded by the E2, E3, E4 allele that were further subdivide into subforms giving six common isoforms of Apo E (Meigs et al., 2000), (Eichner et al., 2002), (Volcik et al., 2006), (Anoop et al., 2010).
Apolipoprotein gene polymorphism has different effects on lipid metabolism and it is associated with certain lipid transport disorders and hence it can play a role in different
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Synthesize of APO E:

It is produced primarily in the liver, but other organs and tissues also synthesize apo E, including brain, spleen, kidneys, gonads, adrenals and macrophages and its synthesis is regulated by interaction between hormonal and dietary factors (Leiva et al., 2005), (Anoop et al., 2010), (Ehara et al., 2012).
The liver plays a vital role in cholesterol homeostasis through the LDL receptors and Apo E receptors (Anoop et al., 2010).
The roles of Apo E that is synthesized in the immune system and the nervous system on lipid and lipoprotein metabolism are not well understood (Eichner et al., 2002), (Anthopoulos et al., 2010).

Function of APO E on lipid metabolism in human body:

Apo E play a role in lipid metabolism through maintaining the structural integrity of lipoproteins, serving as cofactors in enzymatic reactions, and acting as ligands for lipoprotein receptors (Eichner et al., 2002), (Chaudhary et al.,
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Apo E2 allele act by delaying catabolism of lipoproteins that contain Apo E causing cholesterol of exogenous origin and periphery to enter the liver through Apo E mediated uptake then compensatory upregulation of LDL receptors occur resulting in enhanced uptake of LDL and additionally there is delay in the conversion of intermediate density lipids (IDL) to LDL all that causes decrease in level of total cholesterol and LDL level while Apo E4 show opposite so it associated with hypercholesterolemia (Anoop et al., 2010).
Apo E also play a role in atherosclerotic process through binding to heparin and heparin like glycosaminoglycan present in the matrix of arterial walls so it cause muscle cell proliferation and migration in the intima (Anoop et al., 2010).
Measurement of apo e:
Studies are mainly concerned with laboratory test that detects Apo E polymorphism and less frequently Apo E protein concentrations in plasma or other biologic fluids (Eichner et al.,
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