Background: Cholesterol ester storage disease (CESD) and Wolman Disease (WD) are due to deficiency of lysosomal acid lipase (LAL). A new method is described for the measurement of LAL in dried blood spots (DBS) using Lalistat 2 an inhibitor of LAL.
Methods: LAL activity in DBS extracts was measured using the substrate 4-methylumbelliferyl palmitate. LAL activity was determined by measuring total lipase activity and lipase activity in the presence of Lalistat 2. The specificity of Lalistat 2 was investigated using human recombinant LAL (hrLAL) and human pancreatic lipase (hPL).
Results: Lalistat 2 inhibited hrLAL with 1% residual activity at 1 μM inhibitor but had no effect on hPL up to 10 μM. LAL activity in DBS samples obtained from normal controls (n=140) was 0.50-2.30 nmol/punch/h and in patients with CESD was <0.03 nmol/punch/h (n=11). Activity in carriers showed intermediate activity: 0.15-0.40 nmol/punch/h (n=15).
Conclusions: Measurement of LAL using DBS is made difficult by the presence of other lipases in whole blood. Lalistat 2 is a specific inhibitor of LAL which allows the determination of LAL in DBS. Results show the method differentiates clearly between normal controls, carriers and affected cases.
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