Simplified analysis of lipoprotein lipase activity: Evaluation of lipasemic activity of low molecular weight heparin in rats

A simple, rapid, and sensitive fluorescence-based method to assess triacylglycerol hydrolase activity

Lipases constitute an important class of water-soluble enzymes that catalyze the hydrolysis of hydrophobic triacylglycerol (TAG). Their enzymatic activity is typically measured using multistep procedures involving isolation and quantification of the hydrolyzed products. We report here a new fluorescence method to measure lipase activity in real time that does not require the separation of substrates from products. We developed this method using adipose triglyceride lipase (ATGL) and lipoprotein lipase (LpL) as model lipases. We first incubated a source of ATGL or LpL with substrate vesicles containing nitrobenzoxadiazole (NBD)-labeled TAG, then measured increases in NBD fluorescence, and calculated enzyme activities. Incorporation of NBD-TAG into phosphatidylcholine (PC) vesicles resulted in some hydrolysis; however, incorporation of phosphatidylinositol into these NBD-TAG/PC vesicles and increasing the ratio of NBD-TAG to PC greatly enhanced substrate hydrolysis. This assay was also useful in measuring the activity of pancreatic lipase and hormone-sensitive lipase. Next, we tested several small-molecule lipase inhibitors and found that orlistat inhibits all lipases, indicating that it is a pan-lipase inhibitor. In short, we describe a simple, rapid, fluorescence-based triacylglycerol hydrolysis assay to assess four major TAG hydrolases: intracellular ATGL and hormone-sensitive lipase, LpL localized at the extracellular endothelium, and pancreatic lipase present in the intestinal lumen. The major advantages of this method are its speed, simplicity, and elimination of product isolation. This assay is potentially applicable to a wide range of lipases, is amenable to high-throughput screening to discover novel modulators of triacylglycerol hydrolases, and can be used for diagnostic purposes.

Simple impedimetric sensor for rapid lipase activity quantification

A simple and rapid impedimetric sensor applicable for industrial lipase activity quantification was developed and characterized. It is based on the lipase catalyzed degradation by hydrolysis of a thin nanocomposite substrate sensitive layer deposited on a PCB stick electrode usable as disposable or regenerable. The sensitive layer degradation rate was evaluated by the impedance changes registration along time resulting from its thickness diminution applying a small amplitude AC voltage with a constant frequency. The AC current phase shift variations along the time caused by the impedance changes were registered as s sensor response. The sensor was characterized in terms of linear quantification range, LOD, precision and quantification time. The response time was found to be from 80 to 6 s for the linear concentration range from 0.99x10^-2 to 1.68 U.S.P. U mL^-1 with relative errors from 3.75% to 1.24% respectively and a LOD of 8x10^-3 U.S.P. U mL^-1. Finally, lipase spiked whey samples taken from milk industry were quantified and the results were validated by a titrimetric method revealing a good agreement (relative error less than 4.5%).

Hydroxyl-proton hydrogen bonding in the heparin oligosaccharide Arixtra in aqueous solution

Heparin is best known for its anticoagulant activity, which is mediated by the binding of a specific pentasaccharide sequence to the protease inhibitor antithrombin-III (AT-III). Although heparin oligosaccharides are thought to be flexible in aqueous solution, the recent discovery of a hydrogen bond between the sulfamate (NHSO3(-)) proton and the adjacent 3-O-sulfo group of the 3,6-O-sulfated N-sulfoglucosamine residue of the Arixtra (fondaparinux sodium) pentasaccharide demonstrates that definable elements of local structure are accessed. Molecular dynamics simulations of Arixtra suggest the presence of additional hydrogen bonds involving the C3-OH groups of the glucuronic acid and 2-O-sulfo-iduronic acid residues. NMR measurements of temperature coefficients, chemical shift differences, and solvent exchange rate constants provide experimental confirmation of these hydrogen bonds. We note that the extraction of rate constants from cross-peak buildup curves in 2D exchange spectroscopy is complicated by the presence of radiation damping in aqueous solution. A straightforward model is presented that explicitly takes into account the effects of radiation damping on the water proton relaxation and is sufficiently robust to provide an accurate measure of the proton exchange rate between the analyte hydroxyl protons and water.