HPLC fluorescence assay for measuring the activity of diacylglycerol lipases and the action of inhibitors thereof.

1,2-Diacylglycerol lipases (DAGLs) are the most important enzymes for the biosynthesis of the endocannabinoid 2-arachidonoylglycerol (2-AG), and their role in various pathophysiological conditions is currently under investigation. We synthesized a new 1,2-diacylglycerol substrate for these enzymes with a fluorogenic 4-(pyren-1-yl)butanoyl residue in sn-2 position. Using the fluorescent substrate, we measured DAGL activity in rat liver S9 fraction and brain microsomes. To this end, 2-acylglycerol release was directly determined via HPLC and fluorescence detection without further sample clean-up. The method was used to evaluate the action of several known DAGL inhibitors. These showed partly significant differences in their inhibitory effect on DAGLs in liver versus brain preparations. The method was verified by measuring the IC50 values for a subset of inhibitors by HPLC and single-quad MS detection using the deuterated natural DAGL substrate 1-stearoyl-2-arachidonoyl-sn-glycerol-d8. DAGL activity could also be measured with the new pyrene-labeled substrate by HPLC and UV instead of fluorescence detection, if larger quantities of the samples were injected into the HPLC system. Furthermore, using intact human sperm, we show that the substrate is also converted by DAGL enzymes in human cells.

HPLC fluorescence assay for measuring the activity of NAPE-PLD and the action of inhibitors affecting this enzyme.

N-Acyl phosphatidylethanolamine-hydrolyzing phospholipase D (NAPE-PLD) is the major enzyme for the biosynthesis of the endocannabinoid anandamide. The role of NAPE-PLD in various physiological and pathophysiological conditions is currently under investigation. For example, the enzyme might be involved in the control of neuronal activity, embryonic development and pregnancy, and prostate cancer. We synthesized a novel NAPE-PLD substrate with a fluorogenic pyrene substituent at the N-acyl residue as tool compound for studying this enzyme. As shown by HPLC with fluorescence detection, in rat brain microsomes the substrate was transformed into the expected pyrene-labeled N-acylethanolamine (NAE), but minor amounts of three by-products could also be detected. In the presence of pan-serine hydrolase and secretory phospholipase A2 inhibitors, the generation of these compounds, whose identity was verified using reference substances, was abolished. Based on these results, a method for determining the activity of NAPE-PLD was developed, validated, and applied to evaluate the action of known inhibitors of this enzyme. With human sperm, it was shown that the fluorescent substrate can also be used to study NAPE metabolism in intact cells.