Cholesterol unesterified, determination

Assays for the determination of cholesterol in routine clinical laboratories include cholesterol esterase and thus quantify total cholesterol (i.e., unesterified and es-terified cholesterol). However, specific assays are also available that lack cholesterol esterase and hence allow the determination of unesterified or free cholesterol. The difference between total and unesterified cholesterol gives the concentration of cholesterol esters. 

In order to determine the mechanism of this enhanced utilization of droplet cholesterol, the effect of SCPj on individual steps of the sterol transfer process and of mitochondrial utilization was tested. The ability of pure SCPj to bind unesterified cholesterol from lipid droplets was determined by incubation of lipid droplets with SCPj for 20 min at 37 C, followed by subsequent analysis of the levels of isotopic cholesterol remaining with the reisolated lipid droplets and that bound to SCPj in the droplet-free subnatant fraction. There was a linear increase in the amount of subnatant radioactivity with increasing amounts of SCPj added to the lipid droplets... 

Because the risk for atherosclerotic disease is directly proportional to the plasma levels of LDL cholesterol and inversely proportional to those of HDL cholesterol, a major public health goal has been to lower LDL and raise HDL cholesterol levels. The most successful drug Interventions to date have been aimed at reducing plasma LDL. The steady-state levels of plasma LDL are determined by the relative rates of LDL formation and LDL removal or clearance. LDL receptors, especially those expressed In the liver, play a major role in clearing LDL from the plasma. The liver Is key In cholesterol regulation not only because It Is the site of about 70 percent of the body s LDL receptors, but also because it is the site where unesterified cholesterol and Its bile acid... 

The functional role of plasma HDL has not been determined. This lipoprotein is known to exchange unesterified cholesterol and phospholipids with LDL (Gould et al., 1955 Eder, 1957) and red cells (Ashworth and Green, 1964). It is possible that the HDL protein acts as one of the rate-limiting factors in these processes. 

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