Accumulation of galactosylsphingosine (psychosine) in the twitcher mouse: determination by HPLC

The Effect of Donepezil Hydrochloride in the Twitcher Mouse Model of Krabbe Disease

Krabbe disease (KD) is a rare demyelinating disorder characterized by demyelination caused by mutations in the GALC gene, resulting in toxic accumulation of psychosine. Psychosine has been identified as detrimental to oligodendrocytes, leading to demyelination through diverse hypothesized pathways. Reducing demyelination is essential to maintain neurological function in KD; however, therapeutic interventions are currently limited. Acetylcholinesterase inhibitors (AChEi) are commonly used for symptomatic management of Alzheimer's Disease and are suggested to have potential disease-modifying effects, including regulating myelin state. In particular, donepezil, an AChEi, has demonstrated promising effects in cellular and animal models, including promotion of the expression of myelin-related genes and reduction of glial cell reactivity. This drug also acts as an agonist for sigma-1 receptors (Sig-1R), which are implicated in demyelination diseases. In the context of drug repurposing, here, we demonstrate that administration of donepezil has protective effects in the twitcher mouse model of KD. We provide data showing that donepezil preserves myelin and reduces glial cell reactivity in the brains of twitcher mice. Moreover, donepezil also improves behavioral phenotypes and increases lifespan in twitcher animals. These findings suggest that donepezil, with its dual activity as an AChE inhibitor and Sig-1R agonist, may hold promise as a therapeutic candidate for demyelinating diseases, including KD.

Perinatal loss of galactosylceramidase in both oligodendrocytes and microglia is crucial for the pathogenesis of Krabbe disease in mice

Lysosomal galactosylceramidase (GALC) is expressed in all brain cells, including oligodendrocytes (OLs), microglia, and astrocytes, although the cell-specific function of GALC is largely unknown. Mutations in GALC cause Krabbe disease (KD), a fatal neurological lysosomal disorder that usually affects infants. To study how Galc ablation in each glial cell type contributes to Krabbe pathogenesis, we used conditional Galc-floxed mice. Here, we found that OL-specific Galc conditional knockout (CKO) in mice results in a phenotype that includes wasting, psychosine accumulation, and neuroinflammation. Microglia- or astrocyte-specific Galc deletion alone in mice did not show specific phenotypes. Interestingly, mice with CKO of Galc from both OLs and microglia have a more severe neuroinflammation with an increase in globoid cell accumulation than OL-specific CKO alone. Moreover, the enhanced phenotype occurred without additional accumulation of psychosine. Further studies revealed that Galc knockout (Galc-KO) microglia cocultured with Galc-KO OLs elicits globoid cell formation and the overexpression of osteopontin and monocyte chemoattractant protein-1, both proteins that are known to recruit immune cells and promote engulfment of debris and damaged cells. We conclude that OLs are the primary cells that initiate KD with an elevated psychosine level and microglia are required for the progression of neuroinflammation in a psychosine-independent manner.

Chromatographic Separation and Quantitation of Sphingolipids from the Central Nervous System or Any Other Biological Tissue

Chromatographic separation and purification of an individual lipid to homogeneity have long been introduced. Using this concept, a more precise method has been developed to identify and characterize the sphingolipid composition(s) using a small amount (30 mg) of biological sample. Sphingolipids (lipids containing sphingosine or dihydrosphingosine) are well-known regulators of the central nervous system development and play a critical role in neurodegenerative diseases. Introducing a silicic acid column chromatography, sphingolipid components have been separated to individual fractions such as ceramide, glucosyl/galactosylceramide, other neutral and acidic glycosphingolipids, including (dihydro)sphingosine and psychosine; as well as phospholipids from which individual components are quantified employing a single or combination of other advanced chromatography procedures such as thin-layer chromatography, gas chromatography-mass spectrometry, and high-performance liquid chromatography-mass spectrometry.

Diverse Biological Functions of Sphingolipids in the CNS: Ceramide and Sphingosine Regulate Myelination in Developing Brain but Stimulate Demyelination during Pathogenesis of Multiple Sclerosis

Sphingolipids are enriched in the Central Nervous System (CNS) and display multiple biological functions. They participate in tissue development, cell recognition and adhesion, and act as receptors for toxins. During myelination, a variety of interactive molecules such as myelin basic protein, myelin associated glycoprotein, phospholipids, cholesterol, sphingolipids, etc., participate in a complex fashion. Precise roles of some sphingolipids in myelination still remain unexplored. Our investigation delineated participation of several sphingolipids in myelination during rat brain development as well as in human brain demyelination during pathogenesis of Multiple Sclerosis (MS). These sphingolipids included Ceramide (Cer)/dihydroceramide (dhCer), Sphingosine (Sph)/dihydrosphingosine (dhSph), and glucosyl/galactosylceramide (glc/galCer) as we detected these by column chromatography, high performance thin-layer chromatography, gas chromatography-mass spectrometry, and high-performance liquid chromatography. Cer/dhCer level rises during rat brain development starting at Embryonic stage (E) until postnatal day (P21), then gradually falls until the maturity (P30 and onwards), and remains steady maintaining a constant ratio (4–4.5:1) throughout the brain development. GlcCer is the initial Monoglycosylceramide (MGC) that appears at early Postnatal stage (P8) and then GalCer appears at P10 with an increasing trend until P21 and its concentration remains unaltered. Sph and dhSph profiles show a similar trend with an initial peak at P10 and then a comparatively smaller peak at P21 maintaining a ratio of (2–2.5:1) of Sph:dhSph. The profiles of all these sphingolipids, specifically at P21, clearly indicate their importance during rat brain development but somewhat unspecified roles in myelination. While Cer has been reported to involve in neurodegenerative diseases such as Alzheimer’s disease and Parkinson’s disease, Sph being a potent inhibitor of protein kinase C has recently been implicated in CNS demyelination due to MS. Inflammatory cytokines stimulate Sph elevation in MS brains and lead to demyelination due to oligodendrocyte death as we examined by using human oligodendroglioma culture. In conclusions, sphingolipids are essential for brain development but they have deleterious effects in demyelinating diseases such as MS.

A microglial hypothesis of globoid cell leukodystrophy pathology

Globoid cell leukodystrophy (GLD), also known as Krabbe's disease, is a fatal demyelinating disease accompanied by the formation of giant, multinucleated cells called globoid cells. Previously believed to be a byproduct of inflammation, these cells can be found early in disease before evidence of any damage. The precise mechanism by which these globoid cells cause oligodendrocyte dysfunction is not completely understood, nor is their cell type defined. This Review outlines the idea that microglial cells are transformed into an unknown and undefined novel M3 phenotype in GLD, which is cytotoxic to oligodendrocytes, leading to disease progression. © 2016 Wiley Periodicals, Inc.

Substrate reduction therapy for Krabbe's disease

Krabbe's disease (KD) is a lysosomal storage disorder in which galactosylceramide, a major glycosphingolipid of myelin, and psychosine (galactose-sphingosine) cannot be adequately metabolized because of a deficiency in galactosylceramidase. Substrate reduction therapy (SRT) has been tested in preclinical studies. The premise of SRT is to reduce the synthesis of substrates that are not adequately digested so that the substrate burden is lowered, resulting in less accumulation of unmetabolized material. SRT is used for Gaucher's disease, in which inhibitors of the terminal biosynthetic step are used. Unfortunately, an inhibitor for the final step of galactosylceramide biosynthesis, i.e., UDP glycosyltransferase 8 (a.k.a. UDP-galactose ceramide galactosyltransferase), has not been found. Approaches that inhibit an earlier biosynthetic step or that lessen the substrate burden by other means, such as genetic manipulations, have been tested in the twitcher mouse model of KD. Either as a stand-alone therapy or in combination with other approaches, SRT slowed the disease course, indicating that this approach has potential therapeutic value. For instance, in individuals with adult-onset disease, SRT theoretically could lessen the production of substrates so that residual enzymatic activity could adequately manage the lower substrate burden. In more severe forms of disease, SRT theoretically could be part of a combination therapy. However, SRT has the potential to impair normal function by reducing the synthesis of galactosylceramide to levels that impede myelin function, or SRT could have other deleterious effects. Thus, multiple issues need to be resolved before this approach is ready for testing in humans. © 2016 Wiley Periodicals, Inc.

Lysosomal Re-acidification Prevents Lysosphingolipid-Induced Lysosomal Impairment and Cellular Toxicity

Neurodegenerative lysosomal storage disorders (LSDs) are severe and untreatable, and mechanisms underlying cellular dysfunction are poorly understood. We found that toxic lipids relevant to three different LSDs disrupt multiple lysosomal and other cellular functions. Unbiased drug discovery revealed several structurally distinct protective compounds, approved for other uses, that prevent lysosomal and cellular toxicities of these lipids. Toxic lipids and protective agents show unexpected convergence on control of lysosomal pH and re-acidification as a critical component of toxicity and protection. In twitcher mice (a model of Krabbe disease [KD]), a central nervous system (CNS)-penetrant protective agent rescued myelin and oligodendrocyte (OL) progenitors, improved motor behavior, and extended lifespan. Our studies reveal shared principles relevant to several LSDs, in which diverse cellular and biochemical disruptions appear to be secondary to disruption of lysosomal pH regulation by specific lipids. These studies also provide novel protective strategies that confer therapeutic benefits in a mouse model of a severe LSD.

Generation of a LacZ reporter transgenic mouse line for the stereological analysis of oligodendrocyte loss in galactosylceramidase deficiency

Krabbe's disease is a leukodystrophy resulting from deficiency of galactosylceramidase and the accumulation of galactosylsphingosine (psychosine) in the nervous system. Psychosine is believed to cause central demyelination by killing oligodendrocytes. Quantitative analysis of this process is lacking. To address this, we generated a new transgenic reporter twitcher line in which myelinating oligodendrocytes are genetically marked by the expression of LacZ under control of the myelin basic protein (MBP) promoter. MBP-LacZ-twitcher transgenic mice were used for unbiased stereological quantification of β-galactosidase+ oligodendrocytes in the spinal cord. As expected, we found decreased numbers of these cells in mutant cords, paralleling the severity of clinical disease. The decrease of oligodendrocytes does not correlate well with the increase of psychosine. The new MBP-LacZ-twitcher line will be a useful genetic tool for measuring changes in oligodendrocyte numbers in different regions of the mutant CNS and in preclinical trials of therapies to prevent demyelination. © 2016 Wiley Periodicals, Inc.

Glucosylsphingosine is a key biomarker of Gaucher disease

Gaucher disease (GD) involves the accumulation of glucosylceramide (GL1) and its deacylated lysolipid, glucosylsphingosine (lyso-GL1) which is implicated in mediating immune dysregulation and skeletal disease. The aim of our study was to assess plasma Lyso-GL1 as a biomarker of GD and its response to therapy. Plasma lyso-GL1 in 169 patients with GD type 1 (GD1) was measured by LC-MS/MS. Significant predictors of plasma LGL1 were assessed by Pearson's correlation coefficient, Wilcoxon Mann Whitney test and multiple linear regression. Propensity scores were used to match patients on treatment mode: Enzyme Replacement Therapy (ERT) vs. Eliglustat Tartrate SRT (ELI-SRT). Plasma Lyso-GL1 levels in healthy controls averaged 1.5 ng/ml (1.3-1.7; 95% CI). In untreated GD patients, the levels were massively elevated (180.9 ng/ml: 95% CI, 145.4-216.5) and imiglucerase ERT resulted in marked reduction (89 ng/ml: 95% CI, 69.2-129.4) (P < 0.001). Lyso-GL1 correlated with chitotriosidase (r = 0.59 P < 0.001), CCL18 (r = 0.62 P <0.001), hepatomegaly (r = 0.28 P < 0.001), splenomegaly (r = 0.27 P = 0.003), splenectomy (P = 0.01) and treatment mode (P < 0.001). By multiple linear regression, the strongest predictors of lyso-GL1 were age (P < 0.001), splenectomy (P = 0.02), Chitotriosidase (P < 0.001) and CCL18 levels (P = 0.001). After propensity score matching to obtain comparable groups of patients on ERT vs ELI-SRT, lyso-GL1 levels were lower among patients receiving ELI-SRT by 113 ng/ml (95% CI: 136-90.3 ng/ml P < 0.001). Plasma lyso-GL1 is a key biomarker of GD. ERT reduced lyso-GL1 levels. By propensity scoring, ELI-SRT resulted in greater reduction of lyso-GL1 than ERT. Am. J. Hematol. 91:1082-1089, 2016. © 2016 Wiley Periodicals, Inc.

Psychosine-triggered endomitosis is modulated by membrane sphingolipids through regulation of phosphoinositide 4,5-bisphosphate production at the cleavage furrow

Endomitosis is a special type of mitosis in which only cytokinesis-the final step of the cell division cycle-is defective, resulting in polyploid cells. Although endomitosis is biologically important, its regulatory aspects remain elusive. Psychosine, a lysogalactosylceramide, prevents proper cytokinesis when supplemented to proliferating cells. Cytokinetic inhibition by psychosine does not inhibit genome duplication. Consequently cells undergo multiple rounds of endomitotic cell cycles, resulting in the formation of giant multiploid cells. Here we successfully quantified psychosine-triggered multiploid cell formation, showing that membrane sphingolipids ratios modulate psychosine-triggered polyploidy in Namalwa cells. Among enzymes that experimentally remodel cellular sphingolipids, overexpression of glucosylceramide synthase to biosynthesize glycosylsphingolipids (GSLs) and neutral sphingomyelinase 2 to hydrolyze sphingomyelin (SM) additively enhanced psychosine-triggered multiploidy; almost all of the cells became polyploid. In the presence of psychosine, Namalwa cells showed attenuated cell surface SM clustering and suppression of phosphatidylinositol 4,5-bisphosphate production at the cleavage furrow, both important processes for cytokinesis. Depending on the sphingolipid balance between GSLs and SM, Namalwa cells could be effectively converted to viable multiploid cells with psychosine.

Transplantation of mouse embryonic stem cell-derived oligodendrocytes in the murine model of globoid cell leukodystrophy

INTRODUCTION

Globoid cell leukodystrophy (GLD) is a severe disorder of the central and peripheral nervous system caused by the absence of galactocerebrosidase (GALC) activity. Cell-based therapies are highly promising strategies for GLD. In this study, G-Olig2 mouse embryonic stem cells (ESCs) were induced into oligodendrocyte progenitor cells (OPCs) and were implanted into the brains of twitcher mice, an animal model of GLD, to explore the therapeutic potential of the cells.

METHODS

The G-Olig2 ESCs were induced into OPCs by using cytokines and a multi-step differentiation procedure. Oligodendrocyte markers were detected by reverse transcription-polymerase chain reaction (RT-PCR) and immunocytochemistry. The toxicity of psychosine to OPCs was determined by a cell proliferation assay kit. The GALC level of OPCs was also examined. OPCs were labeled with Dir and transplanted into the brains of twitcher mice. The transplanted cells were detected by in-Vivo Multispectral Imaging System and real-time PCR. The physiological effects of twitcher mice were assessed.

RESULTS

Oligodendrocyte markers were expressed in OPCs, and 76%±5.76% of the OPCs were enhanced green fluorescent protein (eGFP)-positive, eGFP was driven by the Olig2 promoter. The effect of psychosine on cell viability indicated that OPCs were more resistant to psychosine toxicity. The GALC level of OPCs was 10.0±1.23 nmol/hour per mg protein, which was significantly higher than other cells. Dir-labeled OPCs were injected into the forebrain of post-natal day 10 twitcher mice. The transplanted OPCs were myelin basic protein (MBP)-positive and remained along the injection tract as observed by fluorescent microscopy. The level of the Dir fluorescent signal and eGFP mRNA significantly decreased at days 10 and 20 after injection, as indicated by in-Vivo Multispectral Imaging System and real-time PCR. Because of poor cell survival and limited migration ability, there was no significant improvement in brain GALC activity, MBP level, life span, body weight, and behavioral deficits of twitcher mice.

CONCLUSIONS

ESC-derived OPC transplantation was not sufficient to reverse the clinical course of GLD in twitcher mice.

Missense mutation in mouse GALC mimics human gene defect and offers new insights into Krabbe disease

Krabbe disease is a devastating pediatric leukodystrophy caused by mutations in the galactocerebrosidase (GALC) gene. A significant subset of the infantile form of the disease is due to missense mutations that result in aberrant protein production. The currently used mouse model, twitcher, has a nonsense mutation not found in Krabbe patients, although it is similar to the human 30 kb deletion in abrogating GALC expression. Here, we identify a spontaneous mutation in GALC, GALCtwi-5J, that precisely matches the E130K missense mutation in patients with infantile Krabbe disease. GALCtwi-5J homozygotes show loss of enzymatic activity despite normal levels of precursor protein, and manifest a more severe phenotype than twitcher, with half the life span. Although neuropathological hallmarks such as gliosis, globoid cells and psychosine accumulation are present throughout the nervous system, the CNS does not manifest significant demyelination. In contrast, the PNS is severely hypomyelinated and lacks large diameter axons, suggesting primary dysmyelination, rather than a demyelinating process. Our data indicate that early demise is due to mechanisms other than myelin loss and support an important role for neuroinflammation in Krabbe disease progression. Furthermore, our results argue against a causative relationship between psychosine accumulation, white matter loss and gliosis.

Peripheral neuropathy in the Twitcher mouse involves the activation of axonal caspase 3

Infantile Krabbe disease results in the accumulation of lipid-raft-associated galactosylsphingosine (psychosine), demyelination, neurodegeneration and premature death. Recently, axonopathy has been depicted as a contributing factor in the progression of neurodegeneration in the Twitcher mouse, a bona fide mouse model of Krabbe disease. Analysis of the temporal-expression profile of MBP (myelin basic protein) isoforms showed unexpected increases of the 14, 17 and 18.5 kDa isoforms in the sciatic nerve of 1-week-old Twitcher mice, suggesting an abnormal regulation of the myelination process during early postnatal life in this mutant. Our studies showed an elevated activation of the pro-apoptotic protease caspase 3 in sciatic nerves of 15- and 30-day-old Twitcher mice, in parallel with increasing demyelination. Interestingly, while active caspase 3 was clearly contained in peripheral axons at all ages, we found no evidence of caspase accumulation in the soma of corresponding mutant spinal cord motor neurons. Furthermore, active caspase 3 was found not only in unmyelinated axons, but also in myelinated axons of the mutant sciatic nerve. These results suggest that axonal caspase activation occurs before demyelination and following a dying-back pattern. Finally, we showed that psychosine was sufficient to activate caspase 3 in motor neuronal cells in vitro in the absence of myelinating glia. Taken together, these findings indicate that degenerating mechanisms actively and specifically mediate axonal dysfunction in Krabbe disease and support the idea that psychosine is a pathogenic sphingolipid sufficient to cause axonal defects independently of demyelination.

Sphingolipidomics: methods for the comprehensive analysis of sphingolipids

Sphingolipids comprise a highly diverse and complex class of molecules that serve as both structural components of cellular membranes and signaling molecules capable of eliciting apoptosis, differentiation, chemotaxis, and other responses in mammalian cells. Comprehensive or "sphingolipidomic" analyses (structure specific, quantitative analyses of all sphingolipids, or at least all members of a critical subset) are required in order to elucidate the role(s) of sphingolipids in a given biological context because so many of the sphingolipids in a biological system are inter-converted structurally and metabolically. Despite the experimental challenges posed by the diversity of sphingolipid-regulated cellular responses, the detection and quantitation of multiple sphingolipids in a single sample has been made possible by combining classical analytical separation techniques such as high-performance liquid chromatography (HPLC) with state-of-the-art tandem mass spectrometry (MS/MS) techniques. As part of the Lipid MAPS consortium an internal standard cocktail was developed that comprises the signaling metabolites (i.e. sphingoid bases, sphingoid base-1-phosphates, ceramides, and ceramide-1-phosphates) as well as more complex species such as mono- and di-hexosylceramides and sphingomyelin. Additionally, the number of species that can be analyzed is growing rapidly with the addition of fatty acyl Co-As, sulfatides, and other complex sphingolipids as more internal standards are becoming available. The resulting LC-MS/MS analyses are one of the most analytically rigorous technologies that can provide the necessary sensitivity, structural specificity, and quantitative precision with high-throughput for "sphingolipidomic" analyses in small sample quantities. This review summarizes historical and state-of-the-art analytical techniques used for the identification, structure determination, and quantitation of sphingolipids from free sphingoid bases through more complex sphingolipids such as sphingomyelins, lactosylceramides, and sulfatides including those intermediates currently considered sphingolipid "second messengers". Also discussed are some emerging techniques and other issues remaining to be resolved for the analysis of the full sphingolipidome.

Simultaneous quantification of glucosylceramide and galactosylceramide by normal-phase HPLC using O-phtalaldehyde derivatives prepared with sphingolipid ceramide N-deacylase

We report here a method of simultaneously quantifying glucosylceramide (GlcCer) and galactosylceramide (GalCer) by normal-phase HPLC using O-phtalaldehyde derivatives. Treatment with sphingolipid ceramide N-deacylase which converts the cerebrosides in the sample to their lyso-forms was followed by the quantitative labeling of free NH(2) groups of the lyso-cerebrosides with O-phtalaldehyde. Using this method, 14.1 pmol of GlcCer and 10.4 pmol of GalCer, and 108.1 pmol of GlcCer and 191.1 pmol of GalCer were detected in zebrafish embryos and RPMI 1864 cells, respectively, while 22.2 pmol of GlcCer but no GalCer was detected in CHOP cells using cell lysate containing 100 microg of protein. Linearity for the determination of each cerebroside was observed from 50 to 400 microg of protein under the conditions used, which corresponds to approximately 10(3) to 10(5) RPMI cells and 5 to 80 zebrafish embryos. The present method clearly revealed that the treatment of RPMI cells with a GlcCer synthase inhibitor P4 resulted in a marked decrease in GlcCer but not GalCer, concomitantly with a significant decrease in the GlcCer synthase activity. On the other hand, GlcCer but not GalCer increased 2-fold when an acid glucocerebrosidase inhibitor CBE was injected into zebrafish embryos. Interestingly, the treatment of CHOP cells with ciclosporin A increased GlcCer possibly due to the inhibition of LacCer synthase. A significant increase in levels of GlcCer in fibroblasts from patients with Gaucher disease was clearly shown by the method. The proposed method is useful for the determination of GlcCer and GalCer levels in various biological samples.

Direct quantitation of psychosine from alkaline-treated lipid extracts with a semi-synthetic internal standard

Psychosine is an important bioactive sphingolipid metabolite and plays an essential role in the pathogenesis of Krabbe's disease. Herein, we extended shotgun lipidomics for the characterization and quantitation of psychosine in alkaline-treated crude lipid extracts by using neutral loss scan of 180 amicro (i.e., galactose) in the positive-ion mode. Specifically, we semi-synthesized N,N-dimethyl psychosine and used it as an internal standard for quantitation of psychosine. After characterization of the fragmentation patterns of psychosine and the selected internal standard and optimization of the experimental conditions, we demonstrated that a broad linear dynamic range for the quantitation of psychosine and a limit of detection at a concentration of low fmol/microl were achieved using this approach. The developed method is generally simpler and more efficient than other previously reported methods. Multiple factors influencing quantitation of psychosine were extensively examined and/or discussed. The levels of psychosine in diabetic mouse nerve tissue samples were determined by the developed methodology. Collectively, the developed approach, as a new addition to the shotgun lipidomics technology, will be extremely useful for understanding the pathways/networks of sphingolipid metabolism and for exploring the important roles of psychosine in a variety of physiological and pathological conditions.

Simultaneous quantification of lyso-neutral glycosphingolipids and neutral glycosphingolipids by N-acetylation with [3H]acetic anhydride

We describe a new method that permits quantification in the pmol to nmol range of three lyso-neutral glycosphingolipids (lyso-n-GSLs), glucosylsphingosine (GlcSph), galactosylsphingosine (GalSph), and lactosylsphingosine, in the same sample as neutral glycosphingolipids (n-GSLs). Lyso-n-GSLs and n-GSLs are initially obtained from a crude lipid extract using Sephadex G25 chromatography, followed by their isolation in one fraction, which is devoid of other contaminating lipids, by aminopropyl solid-phase chromatography. Lyso-n-GSLs and n-GSLs are subsequently separated from one another by weak cation exchange chromatography. N-GSLs are then deacylated by strong alkaline hydrolysis, and the N-deacylated-GSLs and lyso-n-GSLs are subsequently N-acetylated using [3H]acetic anhydride. An optimal concentration of 5 mM acetic anhydride was established, which gave >95% N-acetylation. We demonstrate the usefulness of this technique by showing an approximately 40-fold increase of both GlcSph and glucosylceramide in brain tissue from a glucocerebrosidase-deficient mouse, as well as significant lactosylceramide accumulation. The application and optimization of this technique for lyso-n-GSLs and lyso-GSLs will permit their quantification in small amounts of biological tissues, particularly in the GSL storage diseases, such as Gaucher and Krabbe's disease, in which GlcSph and GalSph, respectively, accumulate.

Aminopropyl solid phase extraction and 2 D TLC of neutral glycosphingolipids and neutral lysoglycosphingolipids

Methods for isolation of neutral lysoglycosphingolipids (n-lyso-GSLs) such as glucosylsphingosine and galactosylsphingosine normally involve mild alkaline or acid hydrolysis followed by multiple chromatography steps, yielding relatively low recoveries of n-lyso-GSLs and neutral glycosphingolipids (n-GSLs). We now describe a new technique for isolating these compounds using one chromatography step, resulting in quantitative recovery of n-GSLs and n-lyso-GSLs. Lipids are extracted using a modified Folch procedure in which recovery is optimized by reextracting the Folch upper phase with water-saturated butanol. The extract is applied to an aminopropyl solid phase column from which both n-GSLs and n-lyso-GSLs elute in the same fraction. Separation is achieved using a new two-dimensional thin-layer chromatography procedure. The usefulness of this technique for biological samples was tested by examining Glc[4,5-(3)H]ceramide and Glc[4,5-(3)H]sphingosine accumulation in metabolically-labeled neurons treated with an inhibitor of lysosomal glucocerebrosidase. Accurate quantification of both lipids was obtained with Glc[4,5-(3)H]ceramide and Glc[4,5-(3)H]sphingosine accumulating at levels of 20 nmol/mg DNA and 40 pmol/mg DNA, respectively. This simple and rapid technique can therefore be used for the analysis of lyso-GSLs and GSLs in the same tissue, which may permit the determination of their metabolic pathways in normal and in pathological tissues, such as those taken from Gaucher and Krabbe's disease patients.

Delayed clinical and pathological signs in twitcher (globoid cell leukodystrophy) mice on a C57BL/6 x CAST/Ei background

Modifier genes may account for the phenotypic variability observed in the late-onset forms of globoid cell leukodystrophy (GCL) in humans. In order to begin a search for modifier genes, the effect of genetic background on the clinical and pathological manifestations of GCL was investigated in twitcher mice. Twitcher mice on a C57BL/6 x CAST/Ei background had an increased life span (61.4 +/- 2.5 vs 37.0 +/- 0.6 days), a delayed onset of tremor (24 vs 21 days), and a delayed decline in walking ability compared to C57BL/6 twitcher mice. Pathologically, C57BL/6 x CAST/Ei twitcher mice had fewer lectin-positive globoid cells, less gliosis, and a greater preservation of myelin compared to C57BL/6 twitcher mice under moribund conditions. Similar concentrations of psychosine, the toxic species that accumulates in GCL, were measured by tandem mass spectrometry between moribund C57BL/6 twitcher mice (286.5 pmol/mg protein), 40-day C57BL/6 x CAST/Ei twitcher mice (276.5 pmol/mg), and moribund C57BL/6 x CAST/Ei twitcher mice (247.0 pmol/mg), suggesting that the milder phenotype in CAST/Ei x C57BL/6 twitcher mice did not correlate with less psychosine. In summary, the introduction of modifier genes from the wild, inbred CAST/Ei strain had a phenotypic effect resulting in a significantly slower disease course.

Glucosylsphingosine accumulation in tissues from patients with Gaucher disease: correlation with phenotype and genotype

Gaucher disease, the inherited deficiency of lysosomal glucocerebrosidase, presents with a wide spectrum of clinical manifestations including neuronopathic and non-neuronopathic forms. While the lipid glucosylceramide is stored in both patients with Gaucher disease and in a null allele mouse model of Gaucher disease, elevated levels of a second potentially toxic substrate, glucosylsphingosine, are also found. Using high performance liquid chromatography, glucosylsphingosine levels were measured in tissues from patients with type 1, 2, and 3 Gaucher disease. Glucosylsphingosine was measured in 16 spleen samples (8 type 1; 4 type 2; and 4, type 3) and levels ranged from 54 to 728 ng/mg protein in the patients with type 1 disease, 133 to 1200 ng/mg protein in the patients with type 2, and 109 to 1298 ng/mg protein in the type 3 samples. The levels of splenic glucosylsphingosine bore no relation to the type of Gaucher disease, the age of the patient, the genotype, nor the clinical course. In the same patients, hepatic glucosylsphingosine levels were lower than in spleen. Glucosylsphingosine was also measured in brains from 13 patients (1 type 1; 8 type 2; and 4 type 3). While the glucosylsphingosine level in the brain from the type 1 patient, 1.0 ng/mg protein, was in the normal range, the levels in the type 3 samples ranged from 14 to 32 ng/mg protein, and in the type 2 samples from 24 to 437 ng/mg protein, with the highest values detected in two fetuses with hydrops fetalis. The elevated levels found in brains from patients with neuronopathic Gaucher disease support the hypothesis that glucosylsphingosine may contribute to the nervous system involvement in these patients.

Galactosylsphingosine (psychosine)-induced expression of cytokine-mediated inducible nitric oxide synthases via AP-1 and C/EBP: implications for Krabbe disease

Globoid cell leukodystrophy (Krabbe disease) is characterized by the accumulation of a toxic metabolite, psychosine (galactosylsphingosine), which is a substrate for the deficient enzyme (galactocerebroside beta-galactosidase). This study underscores the possible role of psychosine in the effect of inducible nitric oxide synthase (iNOS) -derived NO in the pathophysiology of this demyelinating disease. For the first time, we provide evidence of the expression of iNOS in CNS of Krabbe patient and show that the iNOS-expressing cells in the CNS were astrocytes. Psychosine potentiated the LPS-induced production of proinflammatory cytokines (IL-1beta, IL-6, and TNF-alpha) in primary rat astrocytes and regulated the cytokine-mediated production of NO in C6 glioma and primary rat astrocyte. Psychosine induced cytokine-mediated nuclear translocation of AP-1 and C/EBP by potentiating the expression of Fra-1 and C/EBP-delta proteins. This suggests that psychosine maintained or sustained the cytokine-primed expression of iNOS by further potentiating the nuclear translocation of AP-1 and C/EBP without modulating the cytokine-mediated transcription activity of NF-kappaB. This study hypothesizes that accumulated psychosine leads to production of cytokines and iNOS expression. The ensuing excessive production of NO and ONOO- may play a role in pathogenesis of Krabbe disease.

Identification of a molecular target of psychosine and its role in globoid cell formation

Globoid cell leukodystrophy (GLD) is characterized histopathologically by apoptosis of oligodendrocytes, progressive demyelination, and the existence of large, multinuclear (globoid) cells derived from perivascular microglia. The glycosphingolipid, psychosine (d-galactosyl-beta-1,1' sphingosine), accumulates to micromolar levels in GLD patients who lack the degradative enzyme galactosyl ceramidase. Here we document that an orphan G protein-coupled receptor, T cell death-associated gene 8, is a specific psychosine receptor. Treatment of cultured cells expressing this receptor with psychosine or structurally related glycosphingolipids results in the formation of globoid, multinuclear cells. Our discovery of a molecular target for psychosine suggests a mechanism for the globoid cell histology characteristic of GLD, provides a tool with which to explore the disjunction of mitosis and cytokinesis in cell cultures, and provides a platform for developing a medicinal chemistry for psychosine.

Responses to cyclic AMP is impaired in the twitcher Schwann cells in vitro

Twitcher (twi/twi) is a murine model of genetic demyelinating disease globoid cell leukodystrophy (GLD). Available data suggest that demyelination in GLD is caused by degeneration or dysfunction of myelin-forming cells resulting from an accumulation of psychosine, a toxic substrate of galactosylceramidase and a potent inhibitor of protein kinase C (PKC). We investigated proliferation and differentiation of twi/twi Schwann cells in response to forskolin, an adenylate cyclase activator. In twi/twi Schwann cells isolated at the postnatal day (P) 10 prior to the onset of demyelination, proliferation and an expression of the surface galactocerebroside (galC) in response to forskolin were similar to those of +/+ mice. However, in twi/twi Schwann cells isolated from demyelinating sciatic nerves at P20 or P30, fewer numbers of cells expressed surface galC compared to age matched control (+/+) Schwann cells. In all Schwann cells, surface galC expression was lost after 3 days in vitro (DIV). However, with an administration of 50 microM forskolin in the media containing 1% fetal bovine serum (FBS) on the 4 DIV, surface galC could be reexpressed in all +/+ and P10 twi/twi Schwann cells but not in P20 or P30 twi/twi cells. In the media containing 10% FBS, forskolin also stimulated proliferation of Schwann cells from P10 twi/twi, and P10 and P30+/+ mice but not those from P30 twi/twi mice. These results are consistent with a metabolic perturbation of twi/twi Schwann cells that may be reflecting cellular dysfunctions by inhibition of the PKC.

Quantitative analysis of free sphingoid bases in the brain and spinal cord tissues by high-performance liquid chromatography with a fluorescence detection

The o-phthaldialdehyde precolumn derivatives of psychosine, sphinganine and sphingosine extracted from brain and spinal cord tissues were determined by high-performance liquid chromatography-fluorescence detection. This method was developed with the purpose of detecting an endogenous amount of psychosine, sphingosine and sphinganine using small aliquots of brain tissues and spinal cord in rats. These sphingolipid bases were extracted in various ratios of chloroform-methanol and several pH values. Recovery of the method is about 81% in 12 ng/tube (final volume, 320 microl), 90-95% in 45 ng/tube of sphingosine and sphinganine within 2-12% relative standard deviation. Detection limits of these sphingoid bases were about 0.05 pmol/mg brain tissue. In the forebrain, brainstem and spinal cord of rats at three different ages of postnatal days (PND) 1, PND 13 and 6 months old, the endogenous concentrations of psychosine, sphingosine and sphinganine were determined. From these results, this method is suitable for the determination of sphingoid bases in small aliquot of brain and spinal cord tissues.

Psychosine blocks quisqualate-induced glutamate excitotoxicity in hippocampal CA sector neurons

Quisqualate is a potent specific agonist for Group 1 metabotropic glutamate receptors (mGluR's), that activate G protein-coupled phospholipase C (PLC) in a molecular signal-transduction mechanism that raises cytoplasmic Ca2+ and, when excessive, damages hippocampal neurons. Psychosine (beta-galactosylsphingosine), a cationic lysosphingolipid occurring naturally in nervous tissues, dose-dependently inhibited PLC activation induced by metabotropic alpha 1-adrenergic receptor signaling in cultured rat brain astrocytes in vitro. In the present study, we have tested neuroprotective efficacy of psychosine in vivo, in a rat model of glutamate excitotoxicity induced by intracerebroventricular (i.c.v.) administration of quisqualate. A sublethal i.c.v. dose of quisqualate caused episodes of prolonged akinesia and convulsions, and major damage to pyramidal neurons of the hippocampal CA1 and CA3 sector, but not to granule cell neurons of the dentate gyrus. Prior infusion of psychosine greatly attenuated quisqualate-induced behaviors, and fully prevented destruction by quisqualate of vulnerable hippocampal neurons. Psychosine may prove useful in prophylaxis of neurodegenerative disorders that arise from intensive hippocampal Group 1 mGluR stimulation.

Impairment of protein kinase C activity in twitcher Schwann cells in vitro

Twitcher (twi/twi) is a murine model of globoid cell leukodystrophy in humans caused by a genetic deficiency in activity of galactosylceramidase. Our previous study demonstrated that the rate of Schwann cell proliferation in twi/twi was considerably lower than that of the control (+/+) in vitro. We hypothesize that the lower mitotic rate in twi/twi results from the metabolic perturbation of Schawann cells caused by an accumulation of the toxic metabolite of galactosylceramidase, psychosine, a potent inhibitor of protein kinase C (PKC). Mouse Schwann cells are known to be stimulated to divide by growth factors in media containing fetal bovine serum. The stimulation by glial growth factor (GGF) or platelet-derived growth factor-BB (PDGF-BB) is though to be through the PKC pathway, but not by the basic fibroblast growth factor (bFGF) or transforming growth factor-beta (TGF-beta). Thus, we tested responses of twi/twi and +/+ Schwann cells to these growth factors. Schwann cells were isolated from the dorsal root ganglia at 30 days of age and the experiments were carried out at 21 days in vitro. In media containing PDGF-BB or bovine pituitary extract (BPE), the mitotic rate of twi/twi Schwann cells was 76% or 69% of the +/+ value, respectively, while significant differences were detected between twi/twi and +/+ in cultures containing TGF-beta or bFGF. When phorbol 12,13-dibutyrylate, a specific activator of PKC, was added to the media containing PDGF-BB or BPE, the mitotic rate of twi/twi Schwann cells improved up to 90% of +/+ cells. Staurosporine, an inhibitor of PKC. suppressed the proliferation of both twi/twi and +/+ Schwann cells. However, proliferation of twi/twi Schwann cells was suppressed by one-tenth of the concentration required for +/+ Schwann cells. These results are consistent with an accumulation of psychosine, an inhibitor of PKC, and suggest that the signal transduction system through PKC is impaired in the twi/twi Schwann cells.

Murine model of genetic demyelinating disease: the twitcher mouse

Twitcher mouse is an authentic murine model of human genetic demyelinating disease, globoid cell leukodystrophy (GLD), or Krabbe disease. Since its discovery at the Jackson Laboratory (Bar Harbor, ME) this model has been used extensively for the morphological, biochemical-enzymatic studies to clarify pathogenesis and also for therapeutic manipulation of genetic demyelinating disease in humans. As a result of these studies, now we know that (1) GLD is caused by a deficiency of lysosomal enzyme galactosylceramidase, and a toxic metabolite, psychosine, accumulates in the tissue, including the nervous system, damaging myelin forming cells and resulting in secondary demyelination; (2) morphological features of demyelination and associated cellular reactions in demyelination in this mutant are similar to those seen in autoimmune or toxic demyelination; and (3) with enzyme supplementation provided by bone marrow transplantation, remyelination occurs to some extent in demyelinated fibers in both central and peripheral nervous systems of twitcher mouse.

The twitcher mouse: a model for Krabbe disease and for experimental therapies

The twitcher is a naturally-occurring mouse mutant caused by an abnormality in the gene coded for galactosylceramidase. It is therefore genetically equivalent to human globoid cell leukodystrophy (Krabbe disease). Affected mice develop clinical symptoms at the onset of the active myelination period and, if untreated, die by 35 +/- days. The pathology is very similar to that in human disease. Toxicity of galactosylsphingosine (psychosine) that accumulates abnormally in the nervous system is considered to be primarily responsible for the pathogenesis. Transplantation of bone marrow cells from normal donors is partially effective and triples the life span of affected mice to 100 +/- days with evidence of remyelination in the CNS. The mutation responsible for the twitcher mutant has recently been identified. It is expected that this model will be useful for basic studies on treatment of this group of genetic disorders affecting the brain through transgenic and/or gene therapy approaches.

Pathological and biochemical studies of fetal Krabbe disease

Morphological and biochemical analysis of tissue from a 21-week-old fetus with Krabbe disease was performed. Galactosylceramidase activity was virtually absent in cultured amniotic cells obtained during the pregnancy of this fetus. The prenatal diagnosis was confirmed by enzymatic analysis of fetal cultured skin fibroblasts and by enzyme analysis of fetal brain, kidney and liver. The galactocerebroside content of brain and spinal cord of the affected fetus was essentially identical to that observed in an age-matched control fetus. Accumulation of galactosylsphingosine was found in all tissues examined from the fetus with Krabbe disease. The highest galactosylsphingosine level was detected in spinal cord of the affected fetus: it was 40 times the concentration observed in controls. The occurrence of inclusion bodies were limited to spinal cord of the fetus with Krabbe disease. These data verify that the pathological and biochemical findings of Krabbe disease are present during the second trimester of pregnancy.

Spacio-temporal progression of demyelination in twitcher mouse: with clinico-pathological correlation

The twitcher (twi/twi) is an authentic murine model of human globoid cell leukodystrophy (GLD), caused by a deficiency of galactosylceramidase. Similar to human GLD, the twitcher shows progressive deterioration of neurological function and its neuropathology is characterized by a collection of periodic acid-Schift stain (PAS)-positive macrophages in the areas of demyelination. However, there are some differences in the clinico-pathological aspects between human and murine GLD. We investigated the spacio-temporal progression of neuropathology in the twitcher from postnatal day (PND) 10 to 45. No clinical symptoms or neuropathological changes were apparent in twi/twi until PND 15. Generally, infiltration of macrophages, concomitant with myelin degeneration, was recognized in the cerebellar white matter and the brain stem after PND 20, then in cerebral white matter after PND 25, and in cerebral and cerebellar gray matter after PND 30. The demyelination was very severe in the radix of the 8th and the 5th cranial nerves. The neurological symptoms such as tremor, spasticity and cranial nerve dysfunction were well correlated with the progression of pathological changes. Demyelination progressed in an orderly fashion such that myelin degeneration began 10 to 20 days after the commencement of myelination in any of the given nerve fiber tracts. This suggests that there are no significant differences in the metabolism of galactocerebroside in the myelin and myelin-forming cells in individual nerve fiber tracts throughout the murine brain. Over-expression of glial fibrillary acidic protein was already present before the initiation of obvious demyelination.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuropathology of twitcher mice: examination by histochemistry, immunohistochemistry, lectin histochemistry and Fourier transform infrared microspectroscopy

The twitcher mouse is an authentic animal model of globoid cell leukodystrophy, which is a genetic disease that affects the lysosomal enzyme galactocerebroside beta-galactosidase. This enzyme deficiency causes one of its substrates, galactosylsphingosine (psychosine), to accumulate in myelin-forming cells, which eventually results in their death. In the central nervous system, the death of oligodendrocytes is thought to cause a series of secondary pathological changes. In this study, several techniques were utilized to examine the neuropathology of two different brain regions in the twitcher mouse--the hindbrain and the cerebrum. Neuropathological changes were as follows: (1) demyelination was detected in the hindbrain but not in the cerebrum, (2) a high density of periodic acid-Schiff-positive cells were detected in the hindbrain and to a lesser extent in the cerebrum, (3) astrocyte gliosis was pronounced in both the hindbrain and cerebrum, and (4) macrophages were abundant in both the hindbrain and the cerebrum. We found that Periodic acid-Schiff-positive cells, astrocyte gliosis and macrophage infiltration were present in white and gray matter regions of the cerebrum, while they were generally absent from the granule and molecular layers of the cerebellum. In addition to these studies, we utilized the technique of Fourier transform infrared (FT-IR) microspectroscopy to identify the in situ distribution of psychosine in the brains of twitcher mice. Evidence was obtained that indicates a large accumulation of psychosine in the hindbrain, and to a lesser extent in the white matter of the cerebrum in the twitcher mouse, but not the normal mouse. There was no evidence for the accumulation of psychosine in the molecular layer of the cerebellum from the twitcher or normal mouse. Our conclusions are as follows: (1) pathology is more advanced in the hindbrain compared to the cerebrum, which is likely due to the hindbrain becoming myelinated prior to the cerebrum, (2) demyelination is not necessary for the development of secondary pathological changes, (3) pathology is not limited to white matter in the cerebrum, (4) pathology is not present in all brain regions, i.e. the granule and molecular layers of the cerebellum are devoid of pathological changes, and (5) psychosine accumulates in both the cerebrum and hindbrain, but not in the molecular layer of the cerebellum in the twitcher mouse. This study demonstrates that FT-IR microspectroscopy can be used to correlate chemical changes to histopathological changes in brains from twitcher mice, which suggests that FT-IR microspectroscopy may be a useful tool for studies examining other brain diseases.

Progressive dysfunction of twitcher Schwann cells is evaluated better in vitro than in vivo

The twitcher mutant (twi/twi) is an authentic murine model of globoid cell leukodystrophy, a genetic demyelinating disorder, where normally formed myelin degenerates due to a metabolic perturbation of myelin forming cells. We investigated the rate of Schwann cell proliferation in vivo and in vitro using thymidine autoradiography to evaluate cellular function of homozygous twitcher (twi/twi), and heterozygous (+/twi) and normal littermate (+/+) mice. At day 10 prior to onset of demyelination in twi/twi, the thymidine uptake by Schwann cells from sciatic nerves was similar regardless of genotype. In +/twi or +/+, the rate of proliferation in sciatic nerves sharply declined after day 10 and remained low at day 20 and thereafter. In contrast, in twi/twi nerve, in which myelin degeneration became progressively severe after day 10, Schwann cell proliferation persisted. Reflecting the in vivo status of Schwann cells as described by Clemence et al., thymidine uptake in vitro by Schwann cells from older twi/twi mice was transiently higher for the first 24 h in culture. When the rate of proliferation was determined for Schwann cells 1 to 8 days in vitro (DIV), twi/twi Schwann cells proliferated generally less than that of +/twi or +/+ and the rate progressively declined with age. The results of this study suggest that progressive dysfunction of twi/twi Schwann cells is better demonstrated in vitro than in vivo. We suggest that in vitro kinetic studies would provide useful methodology to evaluate the Schwann cell function in genetic or hereditary neuropathies in humans, in which intrinsic Schwann cell dysfunction is suspected as cause of demyelination and contribute to the understanding of their pathogenesis.

Progressive impairment of Schwann cell proliferation in vitro in murine globoid cell leukodystrophy (twitcher)

In an attempt to elucidate possible functional derangement in Schwann cells in globoid cell leukodystrophy (GLD), we investigated the proliferative capacity in vitro of Schwann cells from the twitcher (twi/twi), a murine model of human GLD, with thymidine autoradiography and cell counts. Regardless of genotype, Schwann cell numbers increased faster and initial thymidine incorporation was higher in suckling than in adult mice. Compared with cells from heterozygous (+/twi) or normal (+/+) mice, however, proliferative capacity of Schwann cells from twi/twi was depressed in both sucklings and adults. Reflecting in vivo activation secondary to demyelination, the number of labeled Schwann cells was transiently higher during the first 24 h in adult twi/twi cultures but the rate of proliferation declined thereafter and remained low during an 8 day period in culture. Our study demonstrates that proliferative capacity of twi/twi Schwann cells was impaired in vitro, possibly as a consequence of metabolic perturbation by a deficiency of galactosylceramidase.

Accumulation of lysosphingolipids in tissues from patients with GM1 and GM2 gangliosidoses

By using a sensitive method, we assayed lysocompounds of gangliosides and asialogangliosides in tissues from four patients with GM2 gangliosidosis (one with Sandhoff disease and three with Tay-Sachs disease) and from three patients with GM1 gangliosidosis [one with infantile type (fetus), one with late-infantile, and one with adult type]. In the brain and spinal cord of all the patients except for an adult GM1 gangliosidosis patient, abnormal accumulation of the lipids was observed, though the concentration in the fetal tissue was low. In GM2 gangliosidosis, the amounts of lyso GM2 ganglioside accumulated in the brain were similar among the patient with Sandhoff disease and the patients with Tay-Sachs disease, whereas the concentration of asialo lyso GM2 ganglioside in the brain was higher in the former patient than in the latter patients. By comparing the sphingoid bases of neutral sphingolipids, gangliosides, and lysosphingolipids, it was suggested that lysosphingolipids in the diseased tissue are synthesized by sequential glycosylation from free sphingoid bases, but not by deacylation of the sphingolipids. Because lysosphingolipids are known to be cytotoxic, the abnormally accumulated lysophingolipids may well be the pathogenetic agent for the neuronal degeneration in gangliosidoses.

Novel procedure for measuring psychosine derivatives by an HPLC method

We developed a sensitive and simple method to determine galactosylsphingosine and glucosylsphingosine as a 4-fluoro-7-nitrobenzofurazan autofluorescent compound, using HPLC equipped with a Showdex sugar column. Amounts of galactosylsphingosine were successfully measured in the picomole range. This novel procedure is more stable and simpler than the previous method using o-phthalaldehyde. It was applied to tissues from the twitcher mouse, an animal model of human globoid cell leukodystrophy. The amount of galactosylsphingosine was 34-102 micrograms/kg of wet tissues in control cerebrum and cerebellum, whereas in twitcher mice the range was 2,251-4,228 micrograms/kg of wet tissues. The psychosine concentration was also increased in the liver and kidney of twitcher mice, respectively, 1,513 micrograms and 1,106 micrograms/kg of wet tissue (normal liver, 125 micrograms; normal kidney, 74 micrograms/kg of wet tissue). This novel procedure is useful for the pathochemical evaluation of lysosphingolipids in various sphingolipidoses as well as in other neuropathological and cellular conditions.

A sensitive assay of lysogangliosides using high-performance liquid chromatography

Lysogangliosides, LGM1, LGM2 and LGM3, each carrying a single sphingoid base (i.e., C18:1, C18:0, C20:1, C20:0), were prepared and a sensitive assay method of these lipids using HPLC was developed. The method involves fluorescence derivatization of the free amino group of the molecule with o-phthalaldehyde, separation of the molecular species of each lysoganglioside using reversed-phase HPLC and assay on the basis of a known amount of one of the lysogangliosides, as the internal standard. Using this method, lysoganglioside can be accurately assayed in the range of 5-1000 pmol. For assay of the lipid in the tissue, crude isolation procedures including extraction of lipids, Folch's partition and DEAE-Sepharose and AG 1-X2 column chromatographies were required before the fluorescence derivatization. In the normal human and the bovine cerebral cortex, 0.4-2.0 pmol/mg protein of LGM1 containing C18:1 and C20:1 sphingosine residues were detected. In the frontal cortex from a patient with Sandhoff disease, an abnormal accumulation (55-78 pmol/mg protein) of LGM2 was noted. Among various molecular species, LGM2 containing C18:1 was the most abundant.

Abnormality in cultured oligodendrocytes and Schwann cells isolated from the twitcher mouse

Oligodendrocytes and Schwann cells were isolated from the brain and dorsal root ganglia of the twitcher mouse, a murine model of Krabbe's disease (globoid cell leukodystrophy), and grown in tissue culture. Oligodendrocytes were cultured for up to 22 d in vitro and were immunostained with a galactocerebroside antibody, a specific marker for oligodendrocytes. The control oligodendrocytes developed well-branched processes and membrane sheets, whereas the twitcher oligodendrocyte had wirelike processes with no membrane expansion and progressive degeneration. Schwann cells from the twitcher could not extend their processes as long as normal counterparts. The amounts of psychosine in the enriched population of oligodendrocytes and Schwann cells from the twitcher mouse are about 50-fold and 70-fold higher, respectively, than those in the control cells. These data suggest that psychosine may play an important role in the progression of abnormal features of oligodendroglial membrane formation and in the absence of process elongation in Schwann cells in the twitcher mutant.

Study of pathogenesis in twitcher mouse, an enzymatically authentic model of Krabbe's disease

The twitcher mouse was investigated by examining in vivo synthesis of galactosylceramide (Galcer) and galactosylsphingosine (Galsph) in a sciatic nerve culture, and in vitro enzymic activities for synthesis of Galcer and Galsph in the spinal cord from normal and affected mice. For the in vivo study, the sciatic nerve was incubated for 24 h in medium containing [3H]galactose, or [3H]-sphingosine-labeled Galcer or Galsph. With [3H]galactose, reduced synthesis of Galcer was found as early as 1 week of age and synthesis decreased to about 15% of normal value at 4 weeks. Increased Galsph was detected after 7 days of feeding with galactose. In a study of [3H]sphingosine-labeled Galcer and Galsph feeding, Galcer did not induce Galsph synthesis in either normal or affected mice, and synthesis of Galcer from Galsph was found only in normal mice, suggesting that Galcer was synthesized from sphingosine after hydrolysis of Galsph. In vitro, the activities of UDP-galactose: ceramide galactosyltransferase and UDP-galactose: sphingosine galactosyltransferase were reduced to less than 50% of control after 2 weeks of age in affected mice. We conclude that (1) decreased Galcer was due to impaired synthesis of Galcer, (2) Galsph was synthesized from galactose and not from deacylation of Galcer, and (3) Galsph accumulation was due not to increased synthesis but to decreased hydrolysis.

Lysosulfatide (sulfogalactosylsphingosine) accumulation in tissues from patients with metachromatic leukodystrophy

We describe here a sensitive assay method for lysosulfatide (sulfogalactosylsphingosine) in human tissues using HPLC. The method involves extraction of lipids, saponification, isolation using a C18 Sep-Pak column, derivatization with o-phthalaldehyde, and detection of the fluorescent lysosulfatide using HPLC. In control subjects, a small amount of lysosulfatide was detected in the cerebral white matter (9-35 pmol/mg of protein), spinal cord (35 pmol/mg of protein), sciatic nerve (14 pmol/mg of protein), and kidney (approximately 2 pmol/mg of protein) but not in the cerebral gray matter and liver. A marked accumulation of the lipid was noted in tissues from six patients with metachromatic leukodystrophy (MLD). The concentration of lysosulfatide was high in the cerebral white matter, spinal cord, and sciatic nerve (223-1,172 pmol/mg of protein). Even in the cerebral gray matter, kidney, and liver, where lysosulfatide was hardly detected in the control sample, a considerable amount (3-45 pmol/mg of protein) accumulated in MLD patients. The concentration and distribution pattern of lysosulfatide were similar to those of galactosylsphingosine (psychosine) accumulated in patients with Krabbe disease. Therefore, the accumulation of lysosulfatide may explain the demyelination in patients with MLD, as is the case with Krabbe disease.

Accumulation of galactosylsphingosine (psychosine) does not interfere with phosphorylation and methylation of myelin basic protein in the twitcher mouse

In attempts to elucidate mechanisms of demyelination in the twitcher mouse (Twi), phosphorylation and methylation of myelin basic protein (MBP) were examined in the brainstem and spinal cord of this species. Phosphorylation of MBP in isolated myelin by an endogenous kinase and an exogenous [32P]ATP was not impaired and protein kinase C activity in the brain cytosol was not reduced. When the methylation of an arginine residue of MBP was examined in slices of the brainstem and spinal cord, using [3H]methionine as a donor of the methyl groups, no difference was found between Twi and the controls. Radioactivity of the [3H] methionine residue of MBP of Twi was also similar to that of the controls. Thus, accumulation of psychosine in Twi does not interfere with the activity of endogenous kinase, methylation of MBP, and the synthesis and transport of MBP into myelin membrane.

Biochemical pathogenesis of demyelination in globoid cell leukodystrophy (Krabbe's disease): the effects of psychosine upon oligodendroglial cell culture

The effects of psychosine on the metabolism of myelin associated glycolipids such as galactocerebroside and sulfatide in mouse brain cell cultures were investigated in order to clarify the mechanism of demyelination in globoid cell leukodystrophy (Krabbe's disease). The incorporation of 3H-galactose into cerebroside and sulfatide was studied in the presence of psychosine (1-3 micrograms/ml medium). These data indicated that psychosine inhibited the incorporation of 3H-galactose into cerebroside and sulfatide not in astroglial cell culture but in oligodendroglial cell culture. Oligodendrocytes produce myelin in the central nervous system, and cerebroside and sulfatide are major components of myelin. These results suggest that psychosine influences the lipid metabolisms of myelin and subsequently leads to the demyelination in Krabbe's disease.

Biochemical and morphological studies of dorsal root ganglion and its cultured cells from twitcher mouse (murine globoid cell leukodystrophy)

The biochemical pathogenesis of globoid cell leukodystrophy (GLD) (Krabbe disease) was investigated in vitro using the cultured neural cells obtained from dorsal root ganglion (DRG) of twitcher mouse (murine Krabbe disease). Electron microscopic examination of twitcher DRG of 30 days old showed the demyelination and abnormal inclusion bodies, whereas mitochondrial structure appeared to be intact. Cultured neural cells from control mice were well proliferated to form the network processes, while those from twitcher were decreased in cell numbers and showed the vacuolation of cell body, degeneration of processes, and finally died after three weeks. There was no apparent difference of lipid composition between control and twitcher DRG, and the galactocerebroside levels from control were similar to those of twitcher. However, marked accumulation of psychosine was found in the 30-day-old-twitcher DRG. The level of psychosine from twitcher DRG was elevated approximately 70 to 80-fold compared with those of control. These data suggest that neural cells from twitcher mice degenerative with age also in vitro and accumulation of psychosine in twitcher DRG may play an important role for the demyelination in GLD.

Metabolism of free sphingoid bases in murine tissues and in cultured human fibroblasts

Metabolism of free sphingoid bases present in normal tissues [Kobayashi, T., Mitsuo, K. & Goto, I. (1988) Eur. J. Biochem. 172, 747-752] was examined in mouse tissues and in human cultured fibroblasts. Subcellular fractionation studies of the mouse liver revealed most of free sphingoid bases to be in the membrane fractions. Fibroblasts from patients with Farber's disease contained concentrations of free sphingoid bases similar to those seen in the normal fibroblasts. When L-cycloserine, a potent inhibitor of the first reaction of sphingoid base synthesis, was added to the culture medium, the concentration of free sphingoid bases in fibroblasts decreased, dose-dependently. Thus, most of the free sphingoid bases in the tissue probably do not derive from the degradation of sphingolipids but are newly synthesized. Free sphingoid bases in microsomes from the brainstem and spinal cord were acylated or glycosylated when incubated with acyl-CoA or UDP-glycoside. However, the reaction for the synthesis of ceramide was much greater and more rapid than that of glycosylsphingosine synthesis. In liver microsomes, ceramide synthesis from endogenous free sphingoid bases was observed but synthesis of glycosylsphingosine was not evident. Therefore, the main pathway of metabolism of free sphingoid bases is presumably acylation (to ceramide) but not glycosylation (to lysoglycosphingolipid).

The twitcher mouse: attenuated processes of Schwann cells in unmyelinated fibers

Morphological alterations occurring in Schwann cells of unmyelinated fibers (unmyelinated Schwann cells) were investigated in the sciatic nerve of the twicher mouse, a murine model of human globoid cell leukodystrophy. After postnatal day 10, the number of Schwann cell-axon units gradually increased and the number of unmyelinated axons per unit progressively decreased in the twitcher mouse. However, the total number of unmyelinated axons showed no significant differences between twitcher and normal mice. Thus, these alterations of unmyelinated Schwann cells in the twitcher mouse suggest that attenuated branching of cellular processes develops at an early stage and progresses together with progression of demyelination in this mutant.