Multiplex Mass Spectrometry for Enzymatic Activities Screening of Lysosomal Storage Diseases

Abstract

Lysosomal storage diseases (LSDs) are a group of rare and inherited disorders of lysosome function and they are classified into more than 50 types (e.g., mucopolysaccharidoses, neuronal ceroid lipofuscinoses, Fabry’s Disease; Pompe Disease, etc.). The majority of LSDs result from defective lysosomal enzyme activity leading to accumulation of endogenous macromolecules in the lysosome causing severe disease symptoms and finally death. For some LSDs, treatment is available in the form of enzyme replacement therapy with good results if the therapy is started as soon as possible, making the diagnosis of crucial importance. State of art now in LSDs diagnostic employs in first stage, enzymatic determinations by fluorimetry or by mass spectrometry (in few cases).In this report, we describe a highly specific and sensitive diagnostics on dry blood spots (DBSs) for (i) molecular determinations of LSDs, particularly mucopolysaccharidoses (MPSs) and neuronal ceroid lipofuscinoses (NCLs), by simultaneous fluorimetric and mass spectrometric analysis using new types of substrate derivatives based on different alkyl‐umbelliferone; (ii) clinical diagnostics of LSDs by multiplex‐MS‐MRM analysis using new type of substrate derivatives and (iii) clinical validation of the new developed methods using DBS samples for patients with established LSDs. We have developed a high‐throughput single and multiplexing assay for rare diseases (e.g. MPS 1, MPS 2, MPS 6, NCL 2, NCL 10, Fabry Disease, etc.) in DBSs. A common substrate for the fluorimetric measurement of a lysosomal enzyme activity is a molecule with 2 different parts which are bound covalently: a group recognized by the target enzyme (e.g. sugar, lipid) and 4‐umbelliferone and the product resulted after the enzymatic reaction is always 4‐methyl umbelliferone. In our tests, the enzymatic activity levels in DBSs were determinate by fluorimetry or multiple reactions monitoring mass spectrometry in the presence of an internal standard showing a good statistical correlation in singles assays. Moreover, we developed duplex and triplex assays for the diagnosis of different LSDs from the muccopolysacharidoses family using modified substrates based on different coumarin derivates obtained through Pechman condensation. The new umbelliferone derivatives were synthesize by substituting groups in position 4 and 7 of the alpha‐ coumarin molecule with others e.g. 4‐ ethyl‐ umbelliferone, 4‐propyl‐umbelliferone, etc.In conclusion, by quantification of umbelliferone derivatives as products of enzymatic reactions either by fluorimetry or mass spectrometry, the newly proposed substrates can be easily use for clinical diagnosis of several LSDs.