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Short description about cholesterol
Cholesterol is a sterol that constitutes the third most abundant lipids of the cell membranes. If you are wondering about the first and second most common membrane lipids then here is the answer. Phospholipids are the most abundant membrane lipids while the second most abundant membrane lipids are the glycolipids.
Cholesterol can be esterified (cholesteryl ester) and free cholesterol (non-esterified cholesterol). It is the free cholesterol that is mostly found in the cell membrane where it maintains the fluidity of the lipid bilayer. However, distribution of the cholesterol greatly varies among the various cell membranes.
Previously, various biochemical tests were used to measure the total cholesterol residues in the cell membranes and according to those biochemical tests, about 80-90% free cholesterols are found in the detergent-resistant fractions of the plasma membranes (DRMs). But, now a day, researchers have developed cholesterol analogs that can be used as fluorescent probes to localize and study the dynamics of the intracellular free cholesterols.
Fluorescent cholesterol analogs
The fluorescent probes are made up of cholesterols, some examples of which are as follows; dehydroergosterol, filipin, 22-NBD-cholesterol, 25-NBD-cholesterol, and BODIPY-cholesterol. Among these fluorescent probe cholesterol analogs, 22-NBD-cholesterol and 25-NBD-cholesterol are most commonly used. However, using these fluorescent probes, fluorescence microscopic examination shows that the exogenous NBD-cholesterols are hardly present in the cell membrane.
Therefore, to analyze the location and measure the dynamics of the free cholesterols on the plasma membrane, researchers developed a new fluorescent probe for the cholesterol on the cell membrane. They synthesized 3β-amino-5-cholestene, a fluorescent probe that they used to make new fluorescent probe-labeled cholesterol analog, 2-[3-dimethylamino-6-dimethylazaniumlidenexanthen-9-yl]-5-[2-[(5-cholestene-3β-yl) carbamoyl]ethylcarbamoyl]benzoate (R-Chol).