Quantitation and characterization of glucosylsphingosine in cerebrospinal fluid (CSF), plasma, and brain of monkey model with Gaucher disease

Treatment with conduritol-β-epoxide (CBE) in preclinical species is expected to be a powerful approach to generate animal models of Gaucher disease (GD) and Parkinson's disease associated with heterozygous mutations in Glucocerebrosidase (GBA-PD). However, it is not fully elucidated how quantitatively the change in glucosylsphingosine (GlcSph) levels in cerebrospinal fluid (CSF) correlates with that in the brain, which is expected to be clinically informative. Herein, we aimed to investigate the correlation with successfully quantified GlcSph in monkey CSF by developing highly sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods. The GlcSph in normal monkey CSF was 0.635 ± 0.177 pg/mL at baseline and increased by CBE treatment at 3 mg/kg daily for five days up to a moderate level, comparable to that in GD patients. The balance between GlcSph and galactosylsphingosine (GalSph) in the CSF matched that in the brain rather than plasma. In addition, GlcSph in the CSF was increased, accompanied by that in the brain at a dose of 3 mg/kg daily. These results indicate that GlcSph in the CSF is worth evaluating for concentration changes in the brain. Thus, this model can be useful for evaluating GBA-related diseases such as GD and GBA-PD.

Glucocerebrosidase haploinsufficiency in A53T α-synuclein mice impacts disease onset and course

Mutations in GBA1 encountered in Gaucher disease are a leading risk factor for Parkinson disease and associated Lewy body disorders. Many GBA1 mutation carriers, especially those with severe or null GBA1 alleles, have earlier and more progressive parkinsonism. To model the effect of partial glucocerebrosidase deficiency on neurological progression in vivo, mice with a human A53T α-synuclein (SNCA^A53T) transgene were crossed with heterozygous null gba mice (gba^+/-). Survival analysis of 84 mice showed that in gba^+/-//SNCA^A53T hemizygotes and homozygotes, the symptom onset was significantly earlier than in gba^+/+//SNCA^A53T mice (p-values 0.023-0.0030), with exacerbated disease progression (p-value <0.0001). Over-expression of SNCA^A53T had no effect on glucocerebrosidase levels or activity. Immunoblotting demonstrated that gba haploinsufficiency did not lead to increased levels of either monomeric SNCA or insoluble high molecular weight SNCA in this model. Immunohistochemical analyses demonstrated that the abundance and distribution of SNCA pathology was also unaltered by gba haploinsufficiency. Thus, while the underlying mechanism is not clear, this model shows that gba deficiency impacts the age of onset and disease duration in aged SNCA^A53T mice, providing a valuable resource to identify modifiers, pathways and possible moonlighting roles of glucocerebrosidase in Parkinson pathogenesis.

Measurement of psychosine in dried blood spots--a possible improvement to newborn screening programs for Krabbe disease

BACKGROUND

Newborn screening (NBS) for Krabbe disease (KD) in New York and Missouri is conducted by measuring galactocerebrosidase (GALC) activity using tandem mass spectrometry (MS/MS). These NBS efforts have shown that the incidence of KD is unexpectedly low (1:400,000) while many individuals (ca. 1:6000) with reduced GALC activity and genotypes of uncertain significance are detected and subjected to follow up testing. Psychosine (PSY) is a putative marker of KD progression and can be measured in dried blood spots (DBS). We sought to determine the role that PSY levels play in NBS for KD, follow up, and treatment monitoring.

METHODS

PSY was eluted from DBS with methanol containing N,N-dimethyl-D-erythro-sphingosine as internal standard (IS). Liquid chromatography-MS/MS was conducted over 17 minutes in the multiple reaction monitoring positive mode to follow the precursor to product species transitions for PSY and IS. Separation of the structural isomers PSY and glucosylsphingosine was accomplished by hydrophilic interaction liquid chromatography.

RESULTS

Pre-analytical and analytical factors were studied and revealed satisfactory results. PSY was also measured in DBS collected from controls (range: <8 nmol/L, N = 220), KD patients at various disease stages (range: 8-112, N = 26), and GALC mutation carriers (range: <15 nmol/L, N = 18).

CONCLUSIONS

PSY measurement in DBS could serve as a 2nd tier assay in NBS for KD, simplify and reduce the cost of follow up protocols, help determine disease progression, and be used to monitor KD patients following hematopoietic stem cell transplantation. However, additional chronological measurements of PSY in KD patients are required to confirm these possibilities.

CNS, lung, and lymph node involvement in Gaucher disease type 3 after 11 years of therapy: clinical, histopathologic, and biochemical findings

A Caucasian male with Gaucher disease type 3, treated with continuous enzyme therapy (ET) for 11 years, experienced progressive mesenteric and retroperitoneal lymphadenopathy, lung disease, and neurological involvement leading to death at an age of 12.5 years. Autopsy showed significant pathology of the brain, lymph nodes, and lungs. Liver and spleen glucosylceramide (GluCer) and glucosylsphingosine (GluS) levels were nearly normal and storage cells were cleared. Clusters of macrophages and very elevated GluCer and GluS levels were in the lungs, and brain parenchymal and perivascular regions. Compared to normal brain GluCer (GC 18:0), GluCer species with long fatty acid acyl chains were increased in the patient's brain. This profile was similar to that in the patient's lungs, suggesting that these lipids were present in brain perivascular macrophages. In the patient's brain, generalized astrogliosis, and enhanced LC3, ubiquitin, and Tau signals were identified in the regions surrounding macrophage clusters, indicating proinflammation, altered autophagy, and neurodegeneration. These findings highlight the altered phenotypes resulting from increased longevity due to ET, as well as those in poorly accessible compartments of brain and lung, which manifested progressive disease involvement despite ET.

Glucosylsphingosine is a highly sensitive and specific biomarker for primary diagnostic and follow-up monitoring in Gaucher disease in a non-Jewish, Caucasian cohort of Gaucher disease patients

Background

Gaucher disease (GD) is the most common lysosomal storage disorder (LSD). Based on a deficient β-glucocerebrosidase it leads to an accumulation of glucosylceramide. Standard diagnostic procedures include measurement of enzyme activity, genetic testing as well as analysis of chitotriosidase and CCL18/PARC as biomarkers. Even though chitotriosidase is the most well-established biomarker in GD, it is not specific for GD. Furthermore, it may be false negative in a significant percentage of GD patients due to mutation. Additionally, chitotriosidase reflects the changes in the course of the disease belatedly. This further enhances the need for a reliable biomarker, especially for the monitoring of the disease and the impact of potential treatments.

Methodology

Here, we evaluated the sensitivity and specificity of the previously reported biomarker Glucosylsphingosine with regard to different control groups (healthy control vs. GD carriers vs. other LSDs).

Findings

Only GD patients displayed elevated levels of Glucosylsphingosine higher than 12 ng/ml whereas the comparison controls groups revealed concentrations below the pathological cut-off, verifying the specificity of Glucosylsphingosine as a biomarker for GD. In addition, we evaluated the biomarker before and during enzyme replacement therapy (ERT) in 19 patients, demonstrating a decrease in Glucosylsphingosine over time with the most pronounced reduction within the first 6 months of ERT. Furthermore, our data reveals a correlation between the medical consequence of specific mutations and Glucosylsphingosine.

Interpretation

In summary, Glucosylsphingosine is a very promising, reliable and specific biomarker for GD.

Establishment of a quantitative, qualitative, and high-throughput analysis of sulfatides from small amounts of sera by matrix-assisted laser desorption ionization-time of flight mass spectrometry

Based on our previous measurements of sulfatides, we further developed a quantitative, qualitative, and high-throughput analytical method for serum sulfatides as forms of lysosulfatides by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). Using 0.1N NaOH in 90% MeOH for saponification instead of absolute MeOH, as previously used, we succeeded in eliminating the formation of lysosulfatide artifacts, facilitating much more sensitive detection. The use of MonoTip C18 allowed quantitation of serum sulfatides from 100 50-mul serum specimens within 1 working day. Purification of lysosulfatides with MonoTip C18 also gave rise to clear MALDI-TOF MS spectra, allowing overall analysis of sphingoid molecular species of sulfatides in serum. The composition was as follows: d18:1 (61.3+/-2.8%), d18:2 (13.3+/-1.7%), t18:0 (11.8+/-1.5%), d18:0 (7.6+/-0.8%), d20:0 (3.0+/-1.2%), t20:0 (2.3+/-0.8%), and d20:1 (1.6+/-0.5%). This is also the first detailed report on sphingoid molecular species of sulfatides in human serum. We believe that this method is suitable for daily clinical analysis of sulfatides in various clinical samples such as blood, urine, cerebrospinal fluid, and specimens from biopsies.

Hematopoietic Cell Transplantation Ameliorates Clinical Phenotype and Progression of the CNS Pathology in the Mouse Model of Late Onset Krabbe Disease

Krabbe disease is a genetic demyelinating disease caused by a deficiency of galactosylceramidase. The majority of cases are of infantile onset with rapid clinical course. A rare late onset form with milder clinical symptoms also exists. The latter form has been reported to respond well to the bone marrow transplantation (BMT) therapy. We tested whether the BMT could be an effective therapy for the mouse model of the late onset form, saposin-A-/- (SAP-A-/-) mice. We used green fluorescent protein transgenic mice as the donors. Chimeric SAP-A-/- mice that received BMT showed very little evidence of neurologic symptoms. At postnatal day 190 when severe demyelination was evident in naive SAP-A-/- mice, demyelination was virtually absent in the brain of chimeric SAP-A-/- mice. Presence of residual enzyme activity, at the time of rapid myelination in SAP-A-/- mice, appears to limit initial inflammatory responses and macrophage infiltration, thereby preventing progression of demyelination in the CNS in SAP-A-/- mice. In contrast, the peripheral nerves showed features of hypertrophic neuropathy with hypomyelination and onion bulb formation, suggesting that there are different cellular responses to the BMT in the CNS and PNS.

Enzyme replacement therapy results in substantial improvements in early clinical phenotype in a mouse model of globoid cell leukodystrophy

Globoid cell leukodystrophy (GLD) or Krabbe disease is a devastating, degenerative neurological disorder caused by mutations in the galactosylceramidase (GALC) gene that severely affect enzyme activity. Currently, treatment options for this disorder are very limited. Enzyme replacement therapy (ERT) has been shown to be effective in lysosomal storage disorders with predominantly peripheral manifestations such as type I Gaucher's and Fabry's disease. Little however is known about the possible benefit of ERT in GLD, which has a substantial central nervous system component. In this study, we examined the effect of peripheral GALC injections in the twitcher mouse model of the disease. Although we were unable to block the precipitous decline that normally occurs just before death, we did observe significant early improvements in motor performance, a substantial attenuation in the initial failure to thrive, and an increase in life span. Immunohistochemical and activity analyses demonstrated GALC uptake in multiple tissues, including the brain. This was associated with a decrease in the abnormal accumulation of the GALC substrate psychosine, which is thought to play a pivotal role in disease pathology. These results indicate that peripheral ERT is likely to be beneficial in GLD.

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.

Sphingolipid profile in the CNS of the twitcher (globoid cell leukodystrophy) mouse: a lipidomics approach

Globoid cell leukodystrophy (Krabbe disease) is caused by mutations in galactosylceramidase, a lysosomal enzyme that acts to digest galactosylceramide, a glycolipid concentrated in myelin, and psychosine (galactosylsphingosine). Globoid cell leukodystrophy has been identified in many species including humans and twitcher mice. Several studies on human tissue have examined the lipid profile in this disease by gas, liquid or thin layer chromatography. Electrospray ionization tandem mass spectrometry combined with reverse phase HPLC has become a powerful alternative strategy, used here to compare the sphingolipid profile of pons/medulla tissue from twitcher mice with control tissue. In this lipidomics LC-MS approach, we scanned for precursors of m/z 264 to obtain a semi-quantitative profile of ceramides and galactosylceramides. Sphingosine-1-phosphate, C18:0 ceramide, C22:0 ceramide and C24:0 ceramide levels were reduced in the pons/medulla of twitcher mice compared to levels in control mice at 31 and 35-37 days of age. The levels of C22:0 and C24:0 galactosylceramide were similar between twitcher and control specimens and there was a trend toward reduced levels of C24:1 galactosylceramide and C24:1 hydroxy-galactosylceramide in twitcher specimens. Psychosine, C 16:0 ceramide and C 18:0 galactosylceramide levels were increased in the CNS of twitcher mice compared to levels in control mice. These data indicate that there is a trend toward decreased levels of long chain fatty acids and increased levels of shorter chain fatty acids in galactosylceramides and ceramides from twitcher mice compared with control mice, and such changes may be due to demyelination characteristic of acute pathology.

Internal residue loss produced by rearrangement of a novel cationic glycosphingolipid, glyceroplasmalopsychosine, in collision-induced dissociation

A novel plasmal conjugate of galactosylsphingosine (psychosine), Gro1(3)-O-plasmal-O-6Galbeta-sphingosine (glyceroplasmalopsychosine), was analyzed by electrospray ionization and liquid secondary ion mass spectrometry with low- or high-energy collision-induced dissociation (CID). In the product ion spectra of the [M + H](+) ions, [M + H - glycerol](+) ions arising from the loss of a glycerol were predominant. Unexpectedly, CID of the [M + H - glycerol](+) ion produced an outstanding ion, [(M + H - glycerol) - Hex](+), which required the loss of the galactose from inside the molecule. This ion was greatly reduced in the spectra of N,N-dimethyl derivatives, indicating that the [(M + H - glycerol) - Hex](+) ion is formed from an intramolecular rearrangement with migration of the plasmal residue to the free amino group of sphingosine. It would be expected that the rearrangement occurs simultaneously with the elimination of glycerol or a rearranged [M + H](+) ion leads to the elimination of glycerol, to form a Schiff base-type [M + H - glycerol](+) ion, from which the terminal galactose could be removed by the normal mechanism of glycosidic cleavage. On the other hand, the [M + Na - glycerol](+) ion derived from the sodiated molecule did not produce an ion corresponding to the rearrangement reaction, possibly owing to a higher stability of the sodiated ions against conformational changes.

Quantification of galactosylsphingosine in the twitcher mouse using electrospray ionization-tandem mass spectrometry

Globoid cell leukodystrophy (Krabbe disease) is an autosomal recessive inherited neurodegenerative disorder caused by the deficiency of the lysosomal enzyme beta-galactosylceramidase. The pathogenesis of the disorder has been proposed to arise from the accumulation of the cytotoxic metabolite galactosylsphingosine (psychosine). The twitcher mouse is a naturally occurring murine model of globoid cell leukodystrophy. We have developed a rapid, sensitive, and specific mass spectrometric method for determining the galactosylsphingosine concentration in the tissues of twitcher mice. Galactosylsphingosine is extracted from the tissues in methanol, isolated using strong cation-exchange and C18 solid-phase extraction chromatography, and then directly analyzed using electrospray ionization-tandem mass spectrometry. A lactosylsphingosine internal standard has been employed for quantification. The assay demonstrated significant accumulation of galactosylsphingosine in the brain, spinal cord, and kidney of twitcher mice. It is anticipated that this method may be of use in the monitoring of experimental therapies for globoid cell leukodystrophy.

A mutation in the saposin A domain of the sphingolipid activator protein (prosaposin) gene results in a late-onset, chronic form of globoid cell leukodystrophy in the mouse

Sphingolipid activator proteins (saposins A, B, C and D) are small homologous glycoproteins derived from a common precursor protein (prosaposin) encoded by a single gene. They are required for in vivo degradation of sphingolipids with short carbohydrate chains. Six cysteines and one glycosylation site are strictly conserved in all four saposins. Total deficiency of all saposins and specific deficiency of saposin B or C are known among human patients. A mouse model of total saposin deficiency closely mimics the human disease. However, no specific saposin A or D deficiency is known. We introduced an amino acid substitution (C106F) into the saposin A domain by the Cre/loxP system which eliminated one of the three conserved disulfide bonds. Saposin A(-/-) mice developed slowly progressive hind leg paralysis with clinical onset at approximately 2.5 months and survival up to 5 months. Tremors and shaking, prominent in other myelin mutants, were not obvious until the terminal stage. Pathology and analytical biochemistry were qualitatively identical to, but generally much milder than, that seen in the typical infantile globoid cell leukodystrophy (GLD) in man (Krabbe disease) and in several other mammalian species, due to genetic deficiency of lysosomal galactosylceramidase (GALC) (EC 3.2.1.46). Thus, saposin A is indispensable for in vivo degradation of galactosylceramide by GALC. It should now be recognized that, in addition to GALC deficiency, genetic saposin A deficiency could also cause chronic GLD. Genetic saposin A deficiency might be anticipated among human patients with undiagnosed late-onset chronic leukodystrophy without GALC deficiency.

Intraventricular administration of recombinant adenovirus to neonatal twitcher mouse leads to clinicopathological improvements

Twitcher mouse is a murine model of human globoid cell leukodystrophy (Krabbe disease), which is characterized by a genetic deficiency in galactocerebrosidase (GALC) activity. The nervous system is affected early and severely by demyelination in the white matter. So far, there is no effective treatment for Krabbe disease except bone marrow transplantation (BMT). However, BMT has inherent limitations such as unavailability of donors and graft-versus-host disease. In this study, we injected recombinant adenovirus encoding GALC into the lateral ventricle of twitcher mice at postnatal day 0 (PND 0) and the therapeutic effects were evaluated. Our results showed slight, but significant improvements in motor functions, body weight and twitching and a prolonged life span. In brain, GALC activity was increased to 15% that of normal littermates and psychosine concentration was decreased to 55% that of untreated twitcher mice at PND 15. The number of PAS-positive globoid cells in brain stem was also reduced significantly at PND 35. In contrast, when adenoviruses were injected to the twitcher mice at PND 15, almost no improvements were observed. These results demonstrate that the timing of treatment may be of great importance in Krabbe disease.

Biochemistry and neuropathology of mice doubly deficient in synthesis and degradation of galactosylceramide

We have generated mice doubly deficient in both synthesis and degradation of galactosylceramide by cross-breeding twitcher mice and galactosylceramide synthase (UDP-galactose:ceramide galactosyltransferase, CGT) knockout mice. The prediction that the phenotype of the doubly deficient mice should be the same as the cgt -/- mice, since the degrading enzyme should not be necessary if the substrate is not synthesized, proved to be only partially correct. In early stages of the disease, the doubly deficient mice (galc -/-, cgt -/-) were essentially indistinguishable from the cgt -/- mice. However, the doubly deficient mice had a much shorter life span than cgt -/- mice. Both galactosylceramide and galactosylsphingosine (psychosine), were undetectable in the brain of the cgt -/- and the doubly deficient mice. The characteristic twitcher pathology was never seen in the galc -/-, cgt -/- mice. However, after 43 days, neuronal pathology was observed in the brainstem and spinal cord. This late neuronal pathology has not been seen in the CGT knockout mice but has been described in some long surviving bone marrow-transplanted twitcher mice. Furthermore, the motor segment of the trigeminal nerve of the galc -/-, cgt -/- mice showed severe degeneration not seen in either twitcher or CGT knockout mice. Thus, the galc -/-, cgt -/- mice, while primarily showing the cgt -/- phenotype as predicted, develop late pathology that is seen only in twitcher mouse and also a unique pathology in the trigeminal nerve. These observations indicate that the functional relationship between galactosylceramidase and galactosylceramide synthase is complex.

Twitcher mice with only a single active galactosylceramide synthase gene exhibit clearly detectable but therapeutically minor phenotypic improvements

Cross-breeding of mouse mutants, each defective in either synthesis (CGT knockout) or degradation (twitcher) of galactosylceramide, generates hybrids with a genotype of galc -/-, cgt +/-, in addition to doubly deficient mice. They are ideally suited to test the potential usefulness of limiting synthesis of the substrate as a treatment of genetic disorders due to degradative enzyme defects. The rate of accretion of galactosylceramide in the brain of CGT knockout carrier mice (cgt +/-) is approximately two-thirds of the normal, suggesting a gene-level compensation for the reduced gene dosage. Phenotype of twitcher mice with a single dose of normal cgt gene was indeed milder with statistical significance, albeit only slightly. Compared among 10 paired littermates, the difference in the life span was 7+/-3.9 days (S.D.) and the difference in the maximum attained body weight was 1.9+/-1.2 g (S.D.). Neuropathologists were able to distinguish blindly galc -/-, cgt +/- mice from galc -/-, cgt +/+ mice. The brain psychosine level in galc -/-, cgt +/- mice was also approximately two-thirds of the galc -/-, cgt +/+ mice. These observations indicate that reduction of galactosylceramide synthesis to two-thirds of the normal level results in minor but clearly detectable phenotypic improvements. Because of the detrimental consequences of drastic reduction in galactosylceramide synthesis that may be required for pragmatically meaningful improvements, this approach by itself is unlikely to be useful as the sole treatment but may be helpful as a supplement to other therapies.

Genetic galactocerebrosidase deficiency (globoid cell leukodystrophy, Krabbe disease) in rhesus monkeys (Macaca mulatta)

Globoid cell leukodystrophy, or Krabbe disease, is a severe disorder of the peripheral and central nervous system myelin caused by deficient galactocerebrosidase (GALC) activity. This autosomal recessive disease affects humans and animals including dogs, mice, and rhesus monkeys. Cloning of the human and animal GALC genes opened opportunities for therapeutic trials using animal models. We describe the clinical, pathologic, and biochemical features of the affected rhesus monkey. Affected monkeys had very low GALC activity and a two base pair deletion in both copies of the GALC gene. Clinical signs of tremors, hypertonia, and incoordination led to humane euthanasia by 5 months of age. At necropsy, peripheral nerves were enlarged. Microscopically, the cerebral, cerebellar, and spinal cord white matter was infiltrated with periodic acid-Schiff-positive multinucleated globoid cells, and there was a striking lack of myelin. Peripheral nerve fibers were decreased in number and separated by Alcian blue- and safranin O-positive material. Myelin sheaths were greatly diminished. Lipid analysis of brains of 12-day-old and 158-day-old affected monkeys revealed a great excess of psychosine in white matter. The rhesus monkey model will be especially useful for exploring treatment options, including prenatal bone marrow transplantation and various approaches to gene therapy.

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.

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.

Infantile and fetal globoid cell leukodystrophy: analysis of galactosylceramide and galactosylsphingosine

Galactosylceramide and galactosylsphingosine (psychosine) were assayed in tissues from infants and fetuses with globoid cell leukodystrophy (GLD). Galactosylceramide concentrations were not increased in nervous tissues or other organs. Using a sensitive assay method, we found galactosylsphingosine accumulations in GLD tissues, both infantile and fetal, which suggests that GLD is a generalized galactosylsphingosine storage disease. High galactosylsphingosine levels were observed in the brain, spinal cord, and sciatic nerve of infants with GLD and in the spinal cord of a fetus with GLD, where lesions characteristic to GLD were noted. In tissues without morphological changes, such as somatic organs and the brain in fetal GLD, galactosylsphingosine concentrations were low. These results suggest that a close relationship exists between galactosylsphingosine accumulation and the pathogenesis of GLD. The finding that galactosylsphingosine, but not galactosylceramide, accumulates in the tissue of GLD can be explained by our previous observation that galactosylceramide, but not galactosylsphingosine, is readily hydrolyzed by an intact galactosylceramidase II, which is genetically distinct from galactosylceramidase I.

Free sphingoid bases in normal murine tissues

Free sphingoid bases, which have been considered not to occur naturally, were detected in murine tissues by derivatization with o-phthalaldehyde and the use of high-performance liquid chromatography. The concentrations were 10-30 pmol/mg tissue. The lung contained the largest amounts of sphingoid bases. In the molecular species of sphingoid bases, the most abundant was C18-sphingenine followed by C18-sphinganine, 4-hydroxysphinganine and C20-sphingenine, in that order. The central nervous tissues contained relatively high amounts of C20-sphingenine and there was a high concentration of 4-hydroxysphinganine in the kidney. In addition, galactosylsphingenine was detected simultaneously in the spinal cord and sciatic nerve. Sphingoid bases were purified from normal murine lungs using lipid-extraction, cation-exchange and silicic acid column chromatographies, alkaline saponification and preparative thin-layer chromatography. In the purified sphingoid bases, erythro-C18-sphingenine and erythro-C18-sphinganine were identified using thin-layer chromatography, high-performance liquid chromatography and fast-atom-bombardment mass spectrometry. Free sphingoid bases occurring in normal tissues may be metabolic intermediates required for the synthesis or be products of degradation of the sphingolipids and function to regulate cellular metabolism.

Simultaneous determination of psychosine and cerebrosides

A new method was developed for the simultaneous determination of psychosine and cerebrosides in tissues. Total lipids extracted from the tissues were treated with [3H]acetic anhydride in toluene-methanol. Known amounts of nonradioactive N-acetylpsychosine were added to the reaction product and then subjected to mild alkaline methanolysis. After the product was washed, it was fractionated by silica gel column chromatography and the fraction containing glycolipids was benzoylated. The benzoylated product was finally fractionated on TLC. The amounts of benzoylated derivatives of nonhydroxy- and hydroxycerebrosides and N-acetylpsychosine were determined using a scanning densitometer. The amounts of psychosine in tissues were calculated from the radioactivity in the spot of N-acetylpsychosine and the recovery of added carrier N-acetylpsychosine. This method allowed us to determine 5 to 1000 pmol of psychosine and 1 to 20 nmol of cerebrosides in peripheral nerves and other tissues of the twitcher mouse as well as transfected Schwann cells derived from the sciatic nerves.

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

We developed a sensitive and simple procedure for determination of galactosylsphingosine (psychosine), using HPLC. The method involved extraction of lipids, separation by cation-exchange and C18 reverse-phase columns, and derivatization with o-phthalaldehyde. The fluorescent galactosylsphingosine was detected by HPLC. The amount of galactosylsphingosine was accurately assayed by simultaneous determination of glucosylsphingosine, as the internal standard. The detection limit was 0.5 ng/assay tube, and the quantitative range of the method was up to 750 ng. This procedure was applied to tissue from the twitcher mouse, an animal model of human globoid cell leukodystrophy, as well as tissue from normal and carrier mice. In the latter mice, a small amount of galactosylsphingosine was detected in the spinal cord (21.6-37.2 ng/100 mg wet weight) but not in the cerebrum and sciatic nerve. Marked accumulation of galactosylsphingosine was noted in the nervous tissues of the twitcher strain, even on postnatal day 4. The concentration of galactosylsphingosine was greater in the peripheral than in central nervous tissues. The spinal cord and brainstem contained more galactosylsphingosine than did the cerebrum and cerebellum. The concentration increased with age from 764 ng/100 mg in the sciatic nerve at 4 days to 5,910 ng/100 mg at 37 days. These data correlate well with the pathological changes; tissues containing higher concentrations of galactosylsphingosine show earlier and more severe pathological changes than those containing lower concentrations, thereby indicating the close link of galactosylsphingosine to the pathogenesis of the twitcher mouse.

Analysis of galactosylsphingosine (psychosine) in the brain

A sensitive and specific analytical procedure has been developed for determination of galactosylsphingosine (psychosine) in the brain. The method takes advantage of two unusual properties of psychosine--the strong positive charge and the reactivity of the free amino group. It involves lipid extraction, separation from other lipids on a cation-exchange column (AG-50W), elimination of the last trace of galactosylceramide by silicic acid chromatography, dansylation of psychosine, Florisil and DEAE-Sephadex chromatography, and finally, fluorescent densitometry of dansylated psychosine separated by thin-layer chromatography. The detection limit is 5-10 ng/100 mg brain tissue when the standard procedure is followed exactly. Reliable determination can be made for 50 ng/100 mg or higher in the presence of 200,000-fold excess of other lipids and in the presence of 40,000-fold excess of galactosylceramide. The sensitivity can be increased fivefold by using a larger aliquot for the final determination. This analytical procedure has been successfully applied to demonstrate abnormal accumulation of psychosine in the brain in human, canine, and murine genetic galactosylceramidase deficiencies (globoid cell leukodystrophy).

Progressive accumulation of toxic metabolite in a genetic leukodystrophy

Progressive accumulation of a cytotoxic metabolite, galactosylsphingosine (psychosine), was found in the brain of the twitcher mouse, a mutant caused by genetic deficiency of galactosylceramidase. Similar abnormal accumulation was also found in the brain of the genetic galactosylceramidase deficiency disease in the dog and in human patients (globoid cell leukodystrophy or Krabbe disease). Galactosylphingosine was absent in the brains of normal and heterozygous mice. The finding provides support for the psychosine hypothesis as the biochemical pathogenetic mechanism of globoid cell leukodystrophy. Analogous mechanisms may be important in the pathogenesis of other genetic lysosomal diseases.

Krabbe disease: a galactosylsphingosine (psychosine) lipidosis

The primary genetic defect underlying Krabbe disease or globoid cell leukodystrophy is considered to be a deficiency of galactosylceramide-beta-galactosidase. In the present study of the brains from 18 patients who had died from Krabbe disease at 7-37 months of age, the concentration of galactosylceramide of cerebral and cerebellar white matter was severely reduced to 10-20% of that in age-matched controls. The lowest values were found in the most long-standing cases. Lactosylceramide was reduced to about 50% of normal, while globotriaosylceramide, blobotetraosylceramide and III3-alpha-fucosylneolactotetraosylceramide were increased 10 to 100-fold. Two glycosphingolipids, which have never before been isolated from normal human brains were now isolated and characterized: galactosylsphingosine (psychosine) and galactosyl beta 1 leads to 4 galactosylceramide. We were unable to identify galactosylsphingosine in normal human brains with certainty. We estimate its concentration in the cerebral white matter in Krabbe disease to be increased at least 100-fold (higher than normal). Psychosine was isolated also from the cerebral cortex in Psychosine was isolated also from the cerebral cortex in Krabbe disease after derivatization to the N-acetyl form. Its concentration there was 1 nmol/g tissue compared with 6-10 nmol/g in the white matter. All the neutral glycosphingolipids were isolated and their structure proved by the quantitative determination of their components, degradation by acid and specific glycohydrolases and permethylation and gas-liquid chromatographic-mass spectrometric assay of the methylated sugars. The paradoxical findings of a severely reduced concentration of galactosylceramide and a primary deficiency of cerebroside-beta-galactosidase can be explained by the present finding of the accumulation of galactosylsphingosine in the brains from patients who had died from Krabbe disease. The enzyme has a broad specificity and it normally also degrades galactosylsphingosine. Because of competitive inhibition by the accumulated galactosylceramide its lysosomal hydrolysis will be blocked. The concentration of psychosine will steadily increase and reach toxic levels and kill the oligodendroglial cells. This results in an arrest of the galactosylceramide biosynthesis. Therefore, we feel that galactosylsphingosine and not galactosylceramide is the primary storage substance in the brain in Krabbe disease that the disease is a psychosine lipidosis.