Prenatal diagnosis of Krabbe disease using a fluorescent derivative of galactosylceramide

Rapid and Efficient Stable Gene Transfer to Mesenchymal Stromal Cells Using a Modified Foamy Virus Vector

Mesenchymal stromal cells (MSCs) hold great promise for regenerative medicine. Stable ex vivo gene transfer to MSCs could improve the outcome and scope of MSC therapy, but current vectors require multiple rounds of transduction, involve genotoxic viral promoters and/or the addition of cytotoxic cationic polymers in order to achieve efficient transduction. We describe a self-inactivating foamy virus vector (FVV), incorporating the simian macaque foamy virus envelope and using physiological promoters, which efficiently transduces murine MSCs (mMSCs) in a single-round. High and sustained expression of the transgene, whether GFP or the lysosomal enzyme, arylsulphatase A (ARSA), was achieved. Defining MSC characteristics (surface marker expression and differentiation potential), as well as long-term engraftment and distribution in the murine brain following intracerebroventricular delivery, are unaffected by FVV transduction. Similarly, greater than 95% of human MSCs (hMSCs) were stably transduced using the same vector, facilitating human application. This work describes the best stable gene transfer vector available for mMSCs and hMSCs.

Surface-modified protein microspheres capture amyloid-β and inhibit its aggregation and toxicity

The biocompatible and biodegradable properties of protein microspheres and the recent advances in their preparation have generated considerable interest of utilizing these core-shell structures for drug delivery and diagnostic applications. However, effective targeting of protein microspheres to desirable cells or loci still remains a challenge. Here, we describe for the first time a facile one-pot sonochemical approach for covalent modification of protein microspheres made from serum albumin; the surface of which is covalently decorated with a short recognition peptide to target amyloid-β (Aβ) as the main pathogenic protein in Alzheimer's disease (AD). The microspheres were characterized for their morphology, size, and entrapment efficacy by electron microscopy, dynamic light scattering and confocal microscopy. Fluorescence-activated cell-sorting analysis and Thioflavin-T binding assay demonstrated that the conjugated microspheres bind with high affinity and selectivity to Aβ, sequester it from the medium and reduce its aggregation. Upon incubation with Aβ, the microspheres induced formation of amorphous aggregates on their surface with no apparent fibrillar structure. Moreover, the microspheres directly reduced the Aβ-induced toxicity toward neuron like PC12 cells. The conjugated microspheres are smaller than unmodified microspheres and remained stable throughout the incubation under physiological conditions.

Specific Determination of β-Galactocerebrosidase Activity via Competitive Inhibition of β-Galactosidase

Background: The determination of cellular β-galactocerebrosidase activity is an established procedure to diagnose Krabbe disease and monitor the efficacy of gene/stem cell-based therapeutic approaches aimed at restoring defective enzymatic activity in patients or disease models. Current biochemical assays for β-galactocerebrosidase show high specificity but generally require large protein amounts from scanty sources such as hematopoietic or neural stem cells. We developed a novel assay based on the hypothesis that specific measurements of β-galactocerebrosidase activity can be performed following complete inhibition of β-galactosidase activity.

Methods: We performed the assay using 2–7.5 μg of sample proteins with the artificial fluorogenic substrate 4-methylumbelliferone-β-galactopyranoside (1.5 mmol/L) resuspended in 0.1/0.2 mol/L citrate/phosphate buffer, pH 4.0, and AgNO3. Reactions were incubated for 30 min at 37 °C. Fluorescence of liberated 4-methylumbelliferone was measured on a spectrofluorometer (λex 360 nm, λem 446 nm).

Results: AgNO3 was a competitive inhibitor of β-galactosidase [inhibition constant (Ki) = 0.12 μmol/L] and completely inhibited β-galactosidase activity when used at a concentration of 11 μmol/L. Under this condition, the β-galactocerebrosidase activity was preserved and could be specifically and accurately measured. The assay can detect β-galactocerebrosidase activity in as little as 2 μg cell protein extract or 7.5 μg tissue. Assay validation was performed using (a) brain tissues from wild-type and twitcher mice and (b) murine GALC−/− hematopoietic stem cells and neural precursor cells transduced by GALC-lentiviral vectors.

Conclusions: The procedure is straightforward, rapid, and reproducible. Within a clinical context, our method unequivocally discriminated cells from healthy subjects and Krabbe patients and is therefore suitable for diagnostic applications.

Microwave-assisted synthesis of near-infrared fluorescent sphingosine derivatives

Microwave-assisted synthesis of near-infrared fluorescent sphingosine derivatives is described, and the utility of the probes demonstrated by co-localization studies with visible wavelength fluorescent sphingosine derivatives.

Quantification of Cellular Acid Sphingomyelinase and Galactocerebroside β-Galactosidase Activities by Electrospray Ionization Mass Spectrometry

Background: Diagnosis of Niemann-Pick (A and B) and Krabbe diseases is achieved by measurement of the lysosomal enzymes acid sphingomyelinase (ASM) and galactocerebroside β-galactosidase (GCG), respectively. Conventional assays use radiolabeled or fluorescent substrates and do not allow simultaneous determination of two or more enzymes in the sample.

Methods: We developed a sensitive and specific method to assay ASM and GCG in skin fibroblast homogenates using biotinylated substrate conjugates. The products were purified by bioaffinity capture on streptavidin-agarose beads and, following release, were analyzed by electrospray ionization mass spectrometry. Quantification was achieved using stable-isotope-labeled internal standards that were chemically identical to the products of the enzymatic reactions.

Results: The method demonstrated excellent linearity of ASM and GCG enzymatic product formation with the amount of cellular protein and incubation time. The range of ASM activities in fibroblast lysates from six healthy patients was 39–70 nmol · mg−1 · h−1 compared with 3.7–5.1 nmol · mg−1 · h−1 in cell lysates from two patients affected with Niemann-Pick A disease. The GCG activities toward the corresponding substrate conjugate were 4.0–6.8 nmol · mg−1 · h−1 in cell lysates from healthy patients compared with 0.1–0.2 nmol · mg−1 · h−1 in cell lysates from two patients affected with Krabbe disease. The amounts of substrate conjugates needed per analysis were 15 nmol (14 μg) for both ASM and GCG.

Conclusions: Electrospray mass spectrometry combined with the use of biotinylated substrate conjugates and bioaffinity purification represents a new approach for the diagnosis of lysosomal storage diseases as demonstrated for Niemann-Pick A and Krabbe diseases. No radioactive substrates are used, and the method uses a single instrumental platform to determine both ASM and GCG in one cell sample.

Lead exposure affects levels of galactolipid metabolic enzymes in the developing rat brain

Lead poisoning is known to cause myelin defects. Galactolipids are the major lipid components of myelin and myelin-competent oligodendrocytes. The present study examines the cellular activity of enzymes involved in the galactolipid pathway, tissue concentrations of galactolipids, and the cellular activity of 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNPase) in rat pups exposed to lead in utero and subsequently through maternal milk from exposed mothers and in drinking water following weaning. Pups from control and lead-treated groups (500 or 2000 ppm lead in the drinking water) were euthanized by decapitation on postnatal day 7, 14, 21, 35, or 56. Lead decreased levels of galactolipids and the oligodendrocyte marker CNPase in the brain to a similar degree. The ratios of galactocerebrosides/sulfatides and nonhydroxy fatty acid/hydroxy fatty acid forms of the galactolipids were not altered by lead treatment. In contrast, the activities of the galactolipid metabolic enzymes were reduced to a degree significantly greater than that of CNPase or galactolipids. These results are consistent with previously obtained data indicating that in vitro cultured oligodendroglial progenitor cells are a target for Pb toxicity. Chronic Pb exposure may impact on brain development by impairing timely myelin production due to perturbation of the early developmental commitment of oligodendroglial progenitors. It is further suggested that perturbation of the galactolipid pathway during the developmental maturation of oligodendrocytes may represent a contributing mechanism for Pb-induced neurotoxicity.

Electron microscopic finding of eccrine sweat gland epithelial cells in a patient with Krabbe disease

A 13 month old boy was found to have severely reduced beta-galactocerebrosidase activity suggesting infantile Krabbe disease. Clinically, the patient showed a progressive neurological deterioration with white-matter disease on radiological study. Axillary skin biopsy was performed to support the diagnosis. On electron microscopy, needle-like inclusions, which are the typical finding seen in the cytoplasm of astrocytes and Schwann cells in the classic infantile form, were present in eccrine sweat gland epithelial cells. This method is useful for diagnosis when nerve biopsy and biochemical analysis are not readily available.

Fluorescence-based diagnosis of lipid storage diseases by analysis of the culture medium of skin fibroblasts

Glycosphingolipids, labeled with the fluorescent probe lissamine rhodamine were administered to skin fibroblasts in culture and were hydrolyzed in the intact cells to the corresponding lissamine rhodamine ceramide (N-acylsphingosine). This fluorescent ceramide was converted in the intact cells to the corresponding sphingomyelin which was secreted into the culture medium. In comparison, ceramide is not formed in cells derived from patients with lipid storage diseases, because of deficiencies in lysosomal glycolipid hydrolases. Consequently, fluorescent sphingomyelin was absent from the culture medium or present in considerably reduced quantities. This provided a procedure for diagnosing lipidoses, by analyzing the lissamine rhodamine sphingomyelin content in the culture medium, while maintaining the cells intact.

Characterization of 6-hexadecanoylamino-4-methylumbelliferyl-beta-D- galactopyranoside as fluorogenic substrate of galactocerebrosidase for the diagnosis of Krabbe disease

6-Hexadecanoylamino-4-methylumbelliferyl-beta-D-galactopyranoside (HMGal) has been shown to be a specific fluorogenic substrate of galactocerebrosidase and to facilitate the simple enzymatic diagnosis of Krabbe disease in human patients and in twitcher mice. HMGal hydrolysis at pH 4.5 is optimally stimulated by sodium taurocholate (0.25%) and oleic acid (0.05%) with a Km of 0.150, 0.04 and 0.03 mM, respectively for control mouse kidney, human fibroblasts and leukocytes. In control samples, the specific activity (nmol/mg prot./h) for HMGal is higher than for the natural substrate, galactocerebroside, and is severely deficient in the twitcher mouse and in patients with Krabbe disease. Comparative investigation of galactocerebrosidase activity in fibroblasts, leukocytes and brain with radioactive and fluorogenic substrates reveals a good agreement between the results of the two methods. Galactocerebroside (Gal-Cer) is a competitive inhibitor of HMGal hydrolysis in mouse kidney homogenates while GM1-ganglioside has no inhibitory effect in the same assay system. The sensitivity and specificity of this fluorogenic substrate for galactocerebrosidase provides a simple and rapid method for the diagnosis of Krabbe disease, and for the purification of this enzyme from normal tissues.

Rapid kidney changes resulting from glycosphingolipid depletion by treatment with a glucosyltransferase inhibitor

The ceramide analog, D-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol, inhibits the glucosylation of ceramide and thus, by virtue of the normal catabolism of the higher glucosphingolipids, leads to a general depletion of cellular glucolipids. In a previous study with chronic administration of this inhibitor in mice, it was found that the kidneys and liver, particularly the former, grew more poorly than the organs of control mice. This study shows that the inhibitor produces rapid decreases in glucolipid concentration in kidney which are maintained for at least 5 days without noticeable harm. The changes were enhanced by inclusion of L-cycloserine in the injection scheme. Cycloserine blocks ketosphinganine synthase and thus slows the synthesis of all sphingolipids. However, sphingomyelin levels did not drop significantly in this study. The glucosyltransferase inhibitor also produced a small decrease in kidney beta-D-glucuronidase and distinct increases in the levels of glucocerebrosidase, galactocerebrosidase and sphingomyelinase. It also produced a small but distinct decrease in the level of glucosyltransferase, after a delay of a few hours, possibly because the inhibitor was metabolized to a covalently inactivating product. Comparison with kidney, liver and brain showed that the kidney was more sensitive to the action of the morpholino inhibitor.

Synthesis and characterization of NBD-PS: a fluorescent analog of cerebroside arylsulfatase A deficiency disorders

N-[7-Nitrobenz-2-oxa-1,3-diazol-4-yl]psychosine sulfate (NBD-PS), a fluorescent analog of cerebroside sulfate (CS), was synthesized and tested as an alternative to the radiolabeled forms of CS used for assaying arylsulfatase A (ASA) in its physiological role as a cerebroside sulfate sulfohydrolase. NBD-PS simulates the natural substrate for ASA. Protocols have been developed for its use in differentiating low enzyme activities in diagnostic samples. Hydrolysis of NBD-PS is specific for ASA and optimal assay parameters were identical to those determined for CS. Differentiations between each of the major phenotypes for ASA activity were possible in the set of samples tested. One particular advantage was the ability to discriminate between individuals exhibiting arylsulfatase A pseudodeficiency and the truly deficient individuals with metachromatic leukodystrophy. Differential diagnosis was possible with fibroblast extracts by an assay that is more sensitive than procedures employing radioisotopes. Reaction products may be analyzed quantitatively by HPLC, or semiquantitatively with TLC. NBD-PS provides a simpler, safer, and more cost-effective means of performing natural substrate enzyme assays for ASA. Phenotyping with the fluorescence assay is an effective alternative to the laborious radioactive CS preparations and tissue culture loading studies that have previously been necessary.

Krabbe disease: increased incidence in a highly inbred community

Krabbe disease (globoid cell leukodystrophy) was found with very high incidence (6/1,000 live births) in a large Druze kindred in Israel. The clinical data on 12 of the affected children demonstrated clinical variability even though these children are homozygous for the same mutation by descent from a common ancestor.