The use of methyl-β-cyclodextrin to solubilize cholesterol prior to coating onto a C18 stationary phase

Cholesterol Assay Based on Recombinant Cholesterol Oxidase, ABTS, and Horseradish Peroxidase

Cholesterol determination by cholesterol oxidase reaction is a fast, convenient, and highly specific approach with widespread use in clinical diagnostics. Routinely, endpoint measurements with 4-aminophenazone or 4-aminoantipyrine as chromogens and sodium cholate, surfactants, or alcohols as solubilizing agents are used. Here we describe a novel kinetic method to determine cholesterol in 0.05-0.75 mM range in neutral or acidic buffers by use of recombinant cholesterol oxidase from Nocardioides simplex in a coupled reaction with horseradish peroxidase, ABTS as a chromogen, and methyl-β-cyclodextrin as a solubilizing agent.

Mechanism of hepatic targeting via oral administration of DSPE-PEG-cholic acid-modified nanoliposomes

In oral administration, gastrointestinal physiological environment, gastrointestinal epithelial cell membranes, and blood circulation are typical biological barriers to hepatic delivery of ligand-modified nanoparticle drug delivery systems. To elucidate the mechanism of oral hepatic targeting of cholic acid receptor-mediated nanoliposomes (LPs) (distearoyl phosphatidylethanolamine–polyethylene glycol–cholic acid-modified LPs, CA-LPs), evaluations were performed on colon cancer Caco-2 cell monolayers, liver cancer HepG2 cells, and a rat intestinal perfusion model. CA-LPs, ~100 nm in diameter, exhibited sustained-release behavior and had the greatest stability in rat gastrointestinal fluid and serum for both size and entrapment efficiency. CA-LPs demonstrated highest transport across Caco-2 cells and highest cellular uptake by HepG2 cells. The enhanced endocytosis of CA-LPs was found to be mediated by Na⁺/taurocholate cotransporting polypeptide and involved the caveolin-mediated endocytosis pathway. Further, we used fluorescence resonance energy transfer (FRET) technology to show that the CA-LPs maintained their structural integrity in part during the transport across the Caco-2 cell monolayer and uptake by HepG2 cells.