A Comparison of Lysosomal Enzymes Expression Levels in Peripheral Blood of Mild- and Severe-Alzheimer's Disease and MCI Patients: Implications for Regenerative Medicine Approaches

The association of lysosomal dysfunction and neurodegeneration has been documented in several neurodegenerative diseases, including Alzheimer's Disease (AD). Herein, we investigate the association of lysosomal enzymes with AD at different stages of progression of the disease (mild and severe) or with mild cognitive impairment (MCI). We conducted a screening of two classes of lysosomal enzymes: glycohydrolases (β-Hexosaminidase, β-Galctosidase, β-Galactosylcerebrosidase, β-Glucuronidase) and proteases (Cathepsins S, D, B, L) in peripheral blood samples (blood plasma and PBMCs) from mild AD, severe AD, MCI and healthy control subjects. We confirmed the lysosomal dysfunction in severe AD patients and added new findings enhancing the association of abnormal levels of specific lysosomal enzymes with the mild AD or severe AD, and highlighting the difference of AD from MCI. Herein, we showed for the first time the specific alteration of β-Galctosidase (Gal), β-Galactosylcerebrosidase (GALC) in MCI patients. It is notable that in above peripheral biological samples the lysosomes are more sensitive to AD cellular metabolic alteration when compared to levels of Aβ-peptide or Tau proteins, similar in both AD groups analyzed. Collectively, our findings support the role of lysosomal enzymes as potential peripheral molecules that vary with the progression of AD, and make them useful for monitoring regenerative medicine approaches for AD.

Pilot study of newborn screening for six lysosomal storage diseases using Tandem Mass Spectrometry

BACKGROUND

There is current expansion of newborn screening (NBS) programs to include lysosomal storage disorders because of the availability of treatments that produce an optimal clinical outcome when started early in life.

OBJECTIVE

To evaluate the performance of a multiplex-tandem mass spectrometry (MS/MS) enzymatic activity assay of 6 lysosomal enzymes in a NBS laboratory for the identification of newborns at risk for developing Pompe, Mucopolysaccharidosis-I (MPS-I), Fabry, Gaucher, Niemann Pick-A/B, and Krabbe diseases.

METHODS AND RESULTS

Enzyme activities (acid α-glucosidase (GAA), galactocerebrosidase (GALC), glucocerebrosidase (GBA), α-galactosidase A (GLA), α-iduronidase (IDUA) and sphingomyeline phosphodiesterase-1 (SMPD-1)) were measured on ~43,000 de-identified dried blood spot (DBS) punches, and screen positive samples were submitted for DNA sequencing to obtain genotype confirmation of disease risk. The 6-plex assay was efficiently performed in the Washington state NBS laboratory by a single laboratory technician at the bench using a single MS/MS instrument. The number of screen positive samples per 100,000 newborns were as follows: GAA (4.5), IDUA (13.6), GLA (18.2), SMPD1 (11.4), GBA (6.8), and GALC (25.0).

DISCUSSION

A 6-plex MS/MS assay for 6 lysosomal enzymes can be successfully performed in a NBS laboratory. The analytical ranges (enzyme-dependent assay response for the quality control HIGH sample divided by that for all enzyme-independent processes) for the 6-enzymes with the MS/MS is 5- to 15-fold higher than comparable fluorimetric assays using 4-methylumbelliferyl substrates. The rate of screen positive detection is consistently lower for the MS/MS assay compared to the fluorimetric assay using a digital microfluidics platform.

Does galactocerebrosidase activity predict Krabbe phenotype?

This study sought to determine whether galactocerebrosidase activity is predictive of Krabbe onset age, or of survival from onset when controlling for age at onset of signs. We analyzed data on 55 symptomatic patients from the Hunter James Kelly Research Institute's World-Wide Registry. They were tested for galactocerebrosidase activity at Jefferson Medical College (Philadelphia, PA), using survival models in a path model context. Higher galactocerebrosidase activity was predictive of later symptom onset times (P = 0.0011), but did not predict survival after symptom onset (P = 0.9064) when controlling for the logarithm of age at onset. No child with early infantile (aged 0-6 months) phenotype demonstrated galactocerebrosidase activity >0.1 nmol/hour/mg protein. Survival times within a given phenotype did not vary with galactocerebrosidase activity. Although low galactocerebrosidase activity does not predict phenotype, higher activity in the abnormal range (>0.1 nmol/hour/mg protein in this sample) was not identified in the early infantile variant. Galactocerebrosidase activity may be important to consider when predicting phenotype in the newborn screening population. Our findings provide empiric evidence that the upper end (0.15 nmol/hour/mg protein) of the high-risk galactocerebrosidase group in the New York State newborn screening program is conservatively appropriate.

Globoid cell leukodystrophy (Krabbe disease): normal umbilical cord blood galactocerebrosidase activity and polymorphic mutations

Globoid cell leukodystrophy is an inherited metabolic disorder of the central nervous system caused by deficiency of the lysosomal enzyme galactocerebrosidase. Haematopoietic stem cell transplantation is the only available effective treatment. The engraftment from normal donors provides competent cells able to correct the metabolic defect. Umbilical cord blood cells have proved to significantly decrease complications and improve engraftment rate compared to adult marrow cells in haematopoietic stem cell transplantation. Umbilical cord blood cells must be of sufficient activity to provide central nervous system recovery after engraftment is obtained. Galactocerebrosidase activity is known to be affected by two polymorphic alleles found at nucleotides 502 and 1637 of the cDNA for this gene. This enzyme activity and the polymorphic alleles noted above were analysed in 83 random samples of umbilical cord blood. The activity, assayed with the fluorogenic substrate 6-hexadecanoylamino-4-methylumbelliferyl-beta-galactopyranoside, in those with neither polymorphic allele was 4.6 +/- 1.7 units (nmol/h per mg protein). This optimal choice of cord blood was found in only 24% of specimens. Homozygotes for 1637T > C with activity of only 1.5 +/- 0.4 units represented 16% of the samples. Those heterozygous for 1637T > C with slightly better activity (2.3 +/- 0.7 units) represented 52% of the samples. Choice of umbilical cord blood for haematopoietic stem cell transplantation, therefore, requires consideration not only of cell quantity and HLA compatibility but also selection for normal alleles to obtain maximal enzymatic activity for central nervous system correction.

Measurements from normal umbilical cord blood of four lysosomal enzymatic activities: alpha-L-iduronidase (Hurler), galactocerebrosidase (globoid cell leukodystrophy), arylsulfatase A (metachromatic leukodystrophy), arylsulfatase B (Maroteaux-Lamy)

Umbilical cord blood (UCB) has received increasing attention as a source of unrelated hematopoietic stem cells for transplantation. Lysosomal diseases have been effectively treated and normal enzymatic activity has occurred subsequent to engraftment using UCB. The use of donor cells with normal amounts of enzyme, rather than those from carriers whose level may be 50% or less, is an obvious goal. The frequency of such heterozygotes varies from 1:10 to 1:140 or lower depending upon the disease at issue. We assayed the levels of lysosomal enzymes in normal UCB in random samples as well as those used for transplantation. We measured the following enzymatic activities: alpha-l-iduronidase (Hurler), galactocerebrosidase (globoid cell leuko- dystrophy) and arylsulfatase A (metachromatic leukodystrophy). For the latter, levels of activity in UCB are comparable to those found in adult blood. In the case of arylsulfatase B (Maroteaux-Lamy) a level lower than adult level was found. An informed choice by the transplanting physician based on the activity of the relevant enzyme in the UCB donor will provide a better opportunity for an improved prognosis for more complete correction of the recipient's primary disease. Bone Marrow Transplantation (2000) 25, 541-544.

Late onset globoid cell leukodystrophy (Krabbe's disease)--Swedish case with 15 years of follow-up

We describe a male patient with late onset globoid cell leukodystrophy (GLD) (Krabbe's disease) still alive at 24 years of age, with a well preserved intellectual and communicative capacity, in contrast to visual failure and severe central pyramidal and extrapyramidal motor disability with spasticity, dystonia, ataxia and peripheral neuropathy. Visual dysfunction began at 4 years of age, limping and balance problems at 8 years and epilepsy at 14 years of age. Neuroimaging at 15 years of age revealed white matter lesions, and nerve conduction velocity examinations showed a slowly developing polyneuropathy. Galactosylceramidase activity was reduced in leukocytes to 0.07 mu kat/kg protein compared with 0.02 (SD 0.01) mu kat/kg protein in infantile GLD.

Arylsulfatase A and beta-galactosidase activities in leukocytes and lymphocytes from normal and psychiatric subjects. Effects of blood-processing delay and interleukin-2 stimulation

Arylsulfatase A (ASA) and cerebroside-beta-galactosidase activities in leukocytes serve as a diagnostic tool for determining the presence of metachromatic leukodystrophy and globoid cell leukodystrophy, respectively. It has not been demonstrated whether a delay in blood processing and the presence of mixed cell types in different proportions in leukocytes affect the activities of the two enzymes in these cells. We have in the present study determined the specific activity in leukocytes and lymphocytes (T-cells) prepared from blood samples processed immediately after, 4, and 24 h after collection. In order to determine whether the enzyme activities in lymphocytes reflect expression of genetic trait, and not environmental or "state" influence, the activities of the two enzymes in interleukin 2-stimulated T-cells and resting T-cells were compared. A delay of up to 24 h in blood processing did not significantly change the specific activities of the two enzymes in both leukocytes and lymphocytes. The specific activity of ASA and beta-galactosidase in lymphocytes was 1.4-1.8 times that in leukocytes. The activities of the two enzymes in interleukin 2-stimulated T-cells did not differ from those in resting T-cells. These results indicate that blood-processing delay had no significant effects on ASA and beta-galactosidase activity. The data further indicate that the ASA and beta-galactosidase activity in interleukin 2-stimulated T-cells was not significantly different from resting lymphocytes from either normal or psychiatric subjects exposed to various medications. The activity levels in lymphocytes from psychiatric subjects thus reflect expression of genetic trait, rather than environmental or state influence.

Purification and characterization of galactocerebrosidase from human lymphocytes

Galactocerebrosidase was purified about 22,600-fold using several hydrophobic column and gel filtration steps with a 4.8% recovery, from human lymphocytes. Its specific activity was 1.54 x 10(5) nmol/h/mg with tritium-labeled galactocerebroside as the substrate in the taurocholate system. The optimal pH for galactocerebroside was 4.2 in the taurocholate system and 4.6 in the cholate system. The Km values for galactocerebroside were 5 microM in the taurocholate system and 25 microM in the cholate system. The molecular weight of the purified enzyme was estimated to be 90 kDa by sodium dodecylsulfate polyacrylamide gel electrophoresis and gel filtration. However, 70, 50, 40, and 30 kDa bands were also recognized on SDS-PAGE. The N-terminal amino acid sequences of the 70 kDa molecule and the three 50 kDa molecules were the same as that of the 90 kDa molecule. The N-terminal amino acid sequences of the 40 and 30 kDa molecules were unique. A monoclonal antibody raised against the purified enzyme effectively immunoprecipitated galactocerebrosidase activity, and an affinity column prepared with this monoclonal antibody bound the 90 and 50 kDa proteins. These results suggest that this enzyme is probably processed from the 90 kDa protein.

Thalamic and basal ganglia hyperdensities--a CT marker for globoid cell leukodystrophy?

Globoid cell leukodystrophy (Krabbe's disease) is a rare autosomal recessive lipidosis, with signs restricted to the nervous system, and is caused by deficiency of the lysosomal hydrolase galactocerebroside beta-galactosidase (galactocerebrosidase). In recent years there have been reports of neurological variants, where age of onset and manifestations differed from the classical form. In other cases, specific CT findings, mainly hyperdensities, have been seen. We report a case of late-infantile Krabbe's disease where thalamic and basal ganglia hyperdensities have been seen on CT scan. We also stress that clinicians should be aware of the possibility of Krabbe's disease in infants who display progressive encephalopathy and these CT findings.

[Comparison of spectrophotometric and fluorimetric methods of determination of galactocerebroside-beta-D-galactosidase in leukocytes]

A procedure was developed for estimation of galactocerebroside beta-D-galactosidase activity in leukocytes using a new fluorogenic compound 6-hexadecanoylamino-4-methylum-belliferyl-beta-D-galactop yra noside (HMGal) as a substrate. Some patterns of the fluorometric procedure were compared with corresponding parameters of the spectrophotometric method in which a chromogenic substrate HNGal was used. Sensitivity of the fluorometric procedure with HMGal as a substrate was increased 100-fold as compared with the spectrophotometric method. At the same time, the fluorometric procedure enabled to reduce considerably the incubation period and the cell protein content per an assay. High sensitivity and reproducibility of the procedure with HMGal as a substrate allowed to carry out biochemical diagnosis of Krabbe disease in leukocytes.

The use of galactosylceramides with uniform fatty acids as substrates in the diagnosis and carrier detection of Krabbe disease

Cerebroside-beta-galactosidase (galactosylceramidase EC 3.2.1.4.6) activity was studied using galactosylceramides of uniform fatty acid composition. The highest activity and the best discrimination between patients with Krabbe disease and controls were found with N-nervonoylgalactosylsphingosine (C 24: 1-cerebroside). As a general rule cerebrosides with a monoenoic fatty acid gave higher activity and better discrimination than the corresponding cerebroside with a saturated fatty acid, the differences being largest for the cerebrosides with the longest fatty acids. In two methods the C 24: 1 cerebroside was used as substrate in the assay of the cerebroside-beta-galactosidase activity in leukocytes from 12 Krabbe patients, 14 parents and 22 controls. In a third method lactosylceramide prepared from mammalian brain gangliosides was used as substrate. With all three methods the residual activity in the leukocytes of the Krabbe patients did not exceed 5%, there was no tendency for overlap between the activities of the patients and those of the obligate carriers, and the values of half the carriers fell within the range for the controls.

Spectrophotometric and fluorimetric assays of galactocerebrosidase activity, their use in the diagnosis of Krabbe's disease

Derivatives of galactocerebroside were prepared containing coloured (w-2,4,6-trinitrophenylaminolauric acid) or fluorescent (11-(9-anthroyloxy) undecanoic acid) fatty acid moieties.. These cerebrosides were used as substrates for galactocerebrosidase activity. By overcoming problems associated with the radioactively labelled substrates normally used, yet retaining good enzyme-substrate specificity, these derivatives provided useful and reliable alternative substrates for galactocerebrosidase activity. Enzyme activities in whole extracts of brain, liver, fibroblasts and cultured amniotic fluid cells were compared, using as substrates the novel cerebrosides as well as [3H]galactocerebroside. Good correlation of activities was obtained. In extracts derived from patients with Krabbe's disease marked deficiency of galactocerebrosidase activity was observed with each substrate, whereas extracts from heterozygous carriers exhibited a partial reduction in enzyme activity. The results show that these coloured and fluorescent galactocerebrosides may be used with confidence in the diagnosis and carrier detection of Krabbe's disease.

The two human lactosylceramidases and their respective enzyme activity deficiency diseases: inhibition studies using p-nitrophenyl-beta-D-galactoside

Total lactosyl ceramide beta-galactosidase (LC) activity from normal and pathologic human leukocytes and tissues was subdivided into LC I (EC 3.2.1.46) and LC II (EC 3.2.1.23) activity by means of specific inhibition of LC II with 5 mM p-nitrophenyl-beta-D-galactoside (Ki = 1.5 mM). In globoid-cell leudodystrophy, inhibition of total LC was nearly complete (only LC II is active), whereas in GM1-gangliosidosis Type 1, very little inhibition was found (only LC I is actict). Total LC activity was not significantly low in either of the diseases, which have different genetic origins. The ratio of LC I to LC II activity may display remarkable genetic variation in normal probands.

A rapid method for the estimation of beta-galactocerebrosidase, beta-glucocerebrosidase and sphingomyelinase activities in leukocytes

A method for the assay of leukocyte beta-galactocerebrosidase, beta-glucocerebrosidase and sphingomyelinase activities has been developed, based on the separation of the tritiated sphingolipid substrates from their corresponding radioactive hydrophobic product (ceramide) by thin-layer chromatography on Silica gel H coated microscope slides. For the determination of beta-galactocerebrosidase and beta-glucocerebrosidase activities the silica gel is impregnanted with sodium tetraborate. Each chromatogram is easily divided into two distinct zones and the radioactivity content of each is determined by liquid scintillation counting. The technique described, is rapid, less costly than conventional methods and provides an accurate assessment of sphingolipid hydrolase activity. It is suggested that it should be of considerable value in those areas which require the rapid analysis of large numbers of samples, such as in screening for the sphingolipidoses or for enzyme purification studies.

Globoid cell leukodystrophy: the first case with antemortem diagnosis in Japan

A Japanese boy was diagnosed as globoid cell leukodystrophy on the basis of a marked decrease in the galactocerebroside beta-galactosidase activity in the leukocytes and the serum when one year and two months old. At autopsy when 1 year and 10 months, microscopic findings were characteristic for those of globoid cell leukodystrophy. Galactocerebroside beta-galactosidase activities of leukocytes and sera of his father and mother were found to be half those of control subjects, thus it suggested the parents being heterozygotes of the disease.