Arylsulphatases in human brain: assay, some properties, and distribution

Ultra-performance liquid chromatography/tandem mass spectrometry for determination of sulfatides in dried blood spots from patients with metachromatic leukodystrophy

RATIONALE

Metachromatic leukodystrophy (MLD) is a genetic autosomal recessive disease caused by a deficiency in arylsulfatase A. Accumulated sulfatides can be detected in the urine and detection of sulfatiduria is a useful test for diagnosis and monitoring. To our knowledge, no studies have explored the accumulation of sulfatides in dried blood spots (DBSs). We developed an ultra-performance liquid chromatography/tandem mass spectrometry (UPLC/MS/MS) method for measuring sulfatides in DBSs from patients with MLD.

METHODS

DBSs were eluted with internal standard. After mixing and centrifugation, the organic layer was transferred to a 96-well microplate and dried, then resuspended in methanol/propanol solution. Samples were analyzed on an UPLC system. Total running time was 4 min. Quantification was achieved by multiple reaction monitoring using a tandem mass spectrometer. We evaluated the precision, linearity, and ion suppression of the method and analyzed sulfatide concentrations in DBS specimens from MLD patients (n = 9), pseudodeficiency (PD) patient (n = 1), obligate heterozygotes (OH) (n = 2) and normal controls (n = 124).

RESULTS

In negative-ion mode, sulfatides species subjected to collision-induced dissociation readily fragment to produce an intense ion at m/z 96.8 (HSO4(-)). The precisions of low and high concentration controls ranged from 5.4 to 19.9%. The sulfatides produced linear responses. Molecular species of sulfatides were barely detected in DBSs from normal individuals and the PD-OH group [mean (range), 0.07 (<0.05-0.34) and 0.13 (<0.05-0.22) µg/mL, respectively]. In contrast, the DBSs from MLD patients showed a marked increase in several molecular species of sulfatide [mean (range), 2.02 (1.18-3.89) µg/mL].

CONCLUSIONS

Simultaneous detection for sulfatides using UPLC/MS/MS can be successfully applied to DBS analysis. This method provides a fast and effective screening and monitoring tool for the diagnosis and treatment of MLD.

Expert recommendations for the laboratory diagnosis of MPS VI

Mucopolysaccharidosis VI (MPS VI) is a lysosomal storage disease caused by a deficiency of N-acetylgalactosamine 4-sulfatase (arylsulfatase B, ASB). This enzyme is required for the degradation of dermatan sulfate. In its absence, dermatan sulfate accumulates in cells and is excreted in large quantities in urine. Specific therapeutic intervention is available; however, accurate and timely diagnosis is crucial for maximal benefit. To better understand the current practices for diagnosis and to establish diagnostic guidelines, an international MPS VI laboratory diagnostics scientific summit was held in February of 2011 in Miami, Florida. The various steps in the diagnosis of MPS VI were discussed including urinary glycosaminoglycan (uGAG) analysis, enzyme activity analysis, and molecular analysis. The following conclusions were reached. Dilute urine samples pose a significant problem for uGAG analysis and MPS VI patients can be missed by quantitative uGAG testing alone as dermatan sulfate may not always be excreted in large quantities. Enzyme activity analysis is universally acknowledged as a key component of diagnosis; however, several caveats must be considered and the appropriate use of reference enzymes is essential. Molecular analysis supports enzyme activity test results and is essential for carrier testing, subsequent genetic counseling, and prenatal testing. Overall the expert panel recommends caution in the use of uGAG screening alone to rule out or confirm the diagnosis of MPS VI and acknowledges enzyme activity analysis as a critical component of diagnosis. Measurement of another sulfatase enzyme to exclude multiple sulfatase deficiency was recommended prior to the initiation of therapy. When feasible, the use of molecular testing as part of the diagnosis is encouraged. A diagnostic algorithm for MPS VI is provided.

A novel mass spectrometric assay for the cerebroside sulfate activator protein (saposin B) and arylsulfatase A

A mass spectrometric method is described for monitoring cerebrosides in the presence of excess concentrations of alkali metal salts. This method has been adapted for use in the assay of arylsulfatase A (ASA) and the cerebroside sulfate activator protein (CSAct or saposin B). Detection of the neutral glycosphingolipid cerebroside product was achieved via enhancement of ionization efficiency in the presence of lithium ions. Assay samples were extracted into the chloroform phase as for the existing assays, dried, and diluted in methanol-chloroform-containing lithium chloride. Samples were analyzed by electrospray ionization mass spectrometry with a triple quadrupole mass spectrometer in the multiple reaction monitoring tandem mass spectrometric mode. The assay has been used to demonstrate several previously unknown or ambiguous aspects of the coupled ASA/CSAct reaction, including an absolute in vitro preference for CSAct over the other saposins (A, C, and D) and a preference for the non-hydroxylated species of the sulfatide substrate over the corresponding hydroxylated species. The modified assay for the coupled ASA/CSAct reaction could find applicability in settings in which the assay could not be performed previously because of the need for radiolabeled substrate, which is now not required.

Menstrual cycle-associated regulation of anabolic and catabolic enzymes causes luteal phase-characteristic expression of sulfatide in human endometrium

OBJECTIVE

Our purpose was to investigate the metabolic background of the expression of sulfoglycolipids in human endometrium during the luteal phase.

STUDY DESIGN

We investigated the expression of sulfoglycolipids by thin-layer chromatography immunostaining and the activities of galactosylceramide sulfotransferase and arylsulfatase A, which regulate the synthesis and degradation of sulfoglycolipid. In addition, arylsulfatase A messenger ribonucleic acid was studied by reverse transcriptase polymerase chain reaction.

RESULTS

Sulfoglycolipid expression showed a marked increase in the luteal phase but not in the follicular phase, whereas sialoglycolipids remained relatively constant. The increase of sulfoglycolipids was found to be due to 4.5-fold increased activation of sulfotransferase and a concurrent reduction of arylsulfatase A activity in the luteal phase. Arylsulfatase A messenger ribonucleic acid was detected in both phases and showed no significant changes.

CONCLUSIONS

These findings suggest that increased sulfoglycolipid expression in the luteal phase is due to the simultaneous regulation of sulfotransferase and arylsulfatase A, probably by sex steroid hormones.

Cellular localization of soluble and membrane-bound forms of arylsulfatase in rat brain

The cellular localization of the soluble and membrane-bound forms of the enzyme, arylsulfatase (ArS), in rat brain was investigated by measuring their activities in rat striatum after unilateral lesioning with the neurotoxin, kainic acid. Membrane-bound ArS (C form of ArS) activity was found to increase after lesioning and the increase paralleled that of the astroglial marker enzyme, glutamine synthetase. Total soluble ArS (A and B forms of ArS) was shown to decrease on day 2 after the kainic acid injection but rapidly increase thereafter. When the two soluble forms of arylsulfatase were measured separately, the activity associated with the A form was found to initially decrease followed by a rapid increase in activity, whereas the activity of the B form of the enzyme increased over the entire duration of the experiment. These data suggest that the ArS-C and B form of arylsulfatase predominate in proliferating astroglial cells, whereas the A form of arylsulfatase is present both in neuronal cell bodies and astroglia associated with the rat striatum.

Ascorbic acid sulfate sulfohydrolase (C2 sulfatase): the modulator of cellular levels of L-ascorbic acid in rainbow trout

The enzyme L-ascorbic acid 2-sulfate sulfohydrolase (C2 sulfatase) was purified from rainbow trout liver. The enzyme catalyzes the hydrolysis of L-ascorbic acid 2-sulfate and has a pH optimum at 6.0. It has a molecular weight of about 117,500 at pH 5.0 and is inhibited by a number of sulfhydryl blocking agents including L-ascorbic acid. C2 sulfatase activity was observed in most metabolic organs of rainbow trout. These findings suggest that the physiologic role of the enzyme is to maintain adequate cellular concentrations of L-ascorbic acid in the fish. The activity of the enzyme is controlled by L-ascorbic acid through feedback inhibition. Comparison of kinetic constants and inhibition patterns suggests that C2 sulfatase is structurally identical to human arylsulfatase A. However, unlike C2 sulfatase, human arylsulfatase A may not be involved in ascorbate metabolism. Its physiologic substrate is reported to be cerebroside-3-sulfate, not L-ascorbic acid 2-sulfate. A scheme is proposed to account for the functional divergence of these two structurally identical enzymes.

A sensitive fluorescence assay for the simultaneous and separate determination of arylsulphatases A and B

A sensitive fluorometric assay utilizing 4-methylumbelliferyl sulphate has been developed for the simultaneous determination of arylsulphatases A and B from leucocytes, based on the differential effect of silver ions on the two enzymes. The procedure allows discrimination between normal cases and those with metachromatic leucodystrophy.

Lysosomal enzymes in cerebral atrophy

In seven patients with cerebral atrophy due to pre-senile dementia and/or cerebrovascular disease, the activity of acid phosphatase in lumbar cerebrospinal fluid (CSF) was higher (p less than 0.05) than in six controls. The activity of arylsulphatase and beta-galactosidase in CSF was the same in the two groups. In the serum, the activities of acid phosphatase and arylsulphatase were the same in the two groups but the activity of beta-galactosidase was lower (p less than 0.02) in patients with cerebral atrophy.