Off-target effects of the lysosomal acid lipase inhibitors Lalistat-1 and Lalistat-2 on neutral lipid hydrolases

Objectives: Lysosomal acid lipase (LAL) is the key enzyme, which degrades neutral lipids at an acidic pH in lysosomes. The role of LAL in various cellular processes has mostly been studied in LAL-knockout mice, which share phenotypical characteristics with humans suffering from LAL deficiency. In vitro, the cell-specific functions of LAL have been commonly investigated by using the LAL inhibitors Lalistat-1 and Lalistat-2.Methods: We performed lipid hydrolase activity assays and serine hydrolase-specific activity-based labeling combined with quantitative proteomics to investigate potential off-target effects of Lalistat-1 and -2.Results: Pharmacological LAL inhibition but not genetic loss of LAL impairs isoproterenol-stimulated lipolysis as well as neutral triglyceride and cholesteryl ester hydrolase activities. Apart from LAL, Lalistat-1 and -2 also inhibit major cytosolic lipid hydrolases responsible for lipid degradation in primary cells at neutral pH through off-target effects. Their binding to the active center of the enzymes leads to a decrease in neutral lipid hydrolase activities in cells overexpressing the respective enzymes.Conclusions: Our findings are critically important since they demonstrate that commonly used concentrations of these inhibitors are not suitable to investigate the role of LAL-specific lipolysis in lysosomal function, signaling pathways, and autophagy. The interpretation of their effects on lipid metabolism should be taken with caution and the applied inhibitor concentrations in cell culture studies should not exceed 1 mM.(c) 2022 The Author(s). Published by Elsevier GmbH. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Automated summary

Our findings demonstrate that Lalistat-1 and Lalistat-2 not only inhibit the action of LAL, but also suppress the activity of cytosolic lipid hydrolases responsible for lysosomal function. This has critical implications for understanding the role of LAL in lysosomal function, signaling pathways, and autophagy.