Lipids are used as cellular building blocks and condensed energy stores and also act as signaling molecules. The glycerolipid/ fatty acid cycle, encompassing lipolysis and lipogenesis, generates many lipid signals. Reliable procedures are not available for measuring activities of several lipolytic enzymes for the purposes of drug screening, and this resulted in questionable selectivity of various known lipase inhibitors. We now describe simple assays for lipolytic enzymes, including adipose triglyceride lipase (ATGL), hormone sensitive lipase (HSL), sn-1-diacylglycerol lipase (DAGL), monoacylglycerol lipase, alpha/beta-hydrolase domain 6, and carboxylesterase 1 (CES1) using recombinant human and mouse enzymes either in cell extracts or using purified enzymes. We observed that many of the reported inhibitors lack specificity. Thus, Cay10499 (HSL inhibitor) and RHC20867 (DAGL inhibitor) also inhibit other lipases. Marked differences in the inhibitor sensitivities of human ATGL and HSL compared with the corresponding mouse enzymes was noticed. Thus, ATGListatin inhibited mouse ATGL but not human ATGL, and the HSL inhibitors WWL11 and Compound 13f were effective against mouse enzyme but much less potent against human enzyme. Many of these lipase inhibitors also inhibited human CES1. Results describe reliable assays for measuring lipase activities that are amenable for drug screening and also caution about the specificity of the many earlier described lipase inhibitors.
        
Title: Synthesis and structure-activity relationship for a novel class of potent and selective carbamate-based inhibitors of hormone selective lipase with acute in vivo antilipolytic effects Ebdrup S, Refsgaard HH, Fledelius C, Jacobsen P Ref: Journal of Medicinal Chemistry, 50:5449, 2007 : PubMed
Hormone-sensitive lipase (HSL) is an intracellular enzyme that has a central role in the regulation of fatty acid metabolism. The enzyme, therefore, is a potentially interesting pharmacological target for the treatment of insulin resistance and dyslipidemic disorders. Based on a high throughput screening, a carbamate based HSL inhibitor was identified and optimized into the selective HSL inhibitors 4-hydroxymethyl-piperidine-1-carboxylic acid 4-(5-trifluoromethylpyridin-2-yloxy)-phenyl ester (13f) and 4-hydroxy-piperidine-1-carboxylic acid 4-(5-trifluoromethylpyridin-2-yloxy)-phenyl ester (13g), with IC50 values of 110 and 500 nM, respectively. Both inhibitors were active in acute antilipolytic experiments in vivo and none of the inhibitors inhibited the cytochrome P450 (CYP) isoforms 2D6, 3A4, and 1A2.