Deficiency of monogalactosyl diglycerid beta-B-galactosidase activity in krabbe's disease

Expression of Ripk1 and DAM genes correlates with severity and progression of Krabbe disease

Krabbe disease, an inherited leukodystrophy, is a sphingolipidosis caused by deficiency of β-galactocerebrosidase: it is characterized by myelin loss, and pathological activation of macrophage/microglia and astrocytes. To define driving pathogenic factors, we explored the expression repertoire of candidate neuroinflammatory genes: upregulation of receptor interacting protein kinase 1 (Ripk1) and disease-associated microglia (DAM) genes, including Cst7 and Ch25h, correlated with severity of Krabbe disease genetically modelled in the twitcher mouse. Upregulation of Ripk1 in Iba1/Mac2-positive microglia/macrophage associated with the pathognomic hypertrophic/globoid phenotype of this disease. Widespread accumulation of ubiquitinin1 in white and grey matter co-localised with p62. In Sandhoff disease, another sphingolipid disorder, neuroinflammation, accumulation of p62 and increased Ripk1 expression was observed. The upregulated DAM genes and macrophage/microglia expression of Ripk1 in the authentic model of Krabbe disease strongly resemble those reported in Alzheimer disease associating with disturbed autophagosomal/lysosomal homeostasis. Activation of this shared molecular repertoire, suggests the potential for therapeutic interdiction at a common activation step, irrespective of proximal causation. To clarify the role of Ripk1 in the pathogenesis of Krabbe disease, we first explored the contribution of its kinase function, by intercrossing twitcher and the K45A kinase-dead Ripk1 mouse and breeding to homozygosity. Genetic ablation of Ripk1 kinase activity neither altered the neuropathological features nor the survival of twitcher mice. We conclude that Ripk1 kinase-dependent inflammatory and degenerative capabilities play no instrumental role in Krabbe disease; however, putative kinase-independent functions of Ripk1 remain formally to be explored in its molecular pathogenesis.

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.

Galactocerebrosidase from human urine: purification and partial characterization

Galactocerebrosidase (GALC, EC 3.2.1.46) was purified from human urine by a series of hydrophobic affinity column chromatography steps. The activity was enriched 176,000-fold from concentrated urine by only four columns, including octyl Sepharose, hydroxylapatite, butyl Sepharose and ethyl-agarose. The overall recovery was about 20% but only low amounts were obtained due to its low abundance. The estimated final specific activities of several batches were between 1 and 2 mmol/h per mg protein. The final purified fractions were essentially free of other lysosomal enzyme activities. The most pure fractions showed a series of bands between 50 and 53 kDa on sodium dodecylsulfate-polyacrylamide gel electrophoresis which were determined to have identical N-terminal amino acid sequence. In addition, gel filtration of partially purified GALC after disassociation showed one peak of activity estimated to have a molecular mass near 50 kDa. GALC was also purified from human brain and human placenta using the same methods demonstrating the usefulness of this procedure in obtaining GALC from solid human tissues. In addition to the bands migrating near 50 kDa from urine, there were also bands at 80 kDa and 30 kDa in some preparations. By N-terminal sequencing and the use of antipeptide antibodies, the 80 kDa band was demonstrated to have the same N-terminal amino acids as the 50-53 kDa bands. The 30 kDa band had a unique sequence. The relationship between the different molecular weight species remains to be determined. The purification of GALC and the securing of amino acid sequence information will aid in the cloning of the GALC gene. This enzyme is deficient in human patients with Krabbe disease and several animal species.

2,3-di-O-tetradecyl-1-O-(beta-D-glucopyranosyl)-sn-glycerol is a substrate for human glucocerebrosidase

Glucocerebrosidase, the lysosomal enzyme that is deficient in patients with Gaucher's disease, hydrolyses non-physiological aryl beta-D-glucosides and glucocerebroside, its substrate in vivo. We document that 2,3,-di-O-tetradecyl-1-O-(beta-D-glucopyranosyl)-sn-glycerol (2,3,-di-14:0-beta-Glc-DAG) inhibits human placental glucocerebrosidase activity in vitro (Ki 0.18 mM), and the nature of inhibition is typical of a mixed-type pattern. Furthermore, 2,3-di-14:0-beta-Glc-DAG was shown to be an excellent substrate for the lysosomal beta-glucosidase (Km 0.15 mM; Vmax. 19.8 units/mg) when compared with the natural substrate glucocerebroside (Km 0.080 mM; Vmax. 10.4 units/mg). The observations that (i) glucocerebrosidase-catalysed hydrolysis of 2,3-di-14:0-beta-Glc-DAG is inhibited by conduritol B epoxide and glucosylsphingosine, and (ii) spleen and brain extracts from patients with Gaucher's disease are unable to hydrolyse 2,3-di-14:O-beta-Glc-DAG demonstrate that the same active site on the enzyme is responsible for catalysing the hydrolysis of 4-methylumbelliferyl beta-D-glucopyranoside, glucocerebroside and 2,3-di-14:O-beta-Glc-DAG. With the aid of computer modelling we have established that the oxygen atoms in 2,3-DAG-Glc at the C-1, C-4*, C-5* (the ring oxygen in glucose) and C-2 positions correspond topologically to the oxygens at C-1, C-4* and C-5* and the nitrogen atom attached to C-2 respectively in glucocerebroside (* signifies a carbon atom in glucose); furthermore, all of the distances with respect to overlap of corresponding heteroatoms range from 0.02 A to 0.77 A (0.002-0.077 nm). A root-mean-square deviation of 0.31 A (0.031 nm) was obtained when the energy-minimized structures of 2,3-di-14:O-beta-Glc-DAG and glucocerebroside were compared using the latter four heteroatom co-ordinates.

A case of Krabbe's leukodystrophy without globoid cells

Krabbe's globoid cell leukodystrophy is a rare hereditary progressive neurological disease of infants, in which there is deficient activity of galactosylceramide beta-galactosidase. The pathological hallmark is the presence of multinucleated globoid cells in the white matter associated with severe myelin depletion and gliosis. We report a second case where galactosylceramide beta-galactosidase deficiency was proven but no globoid cells were found in the brain. Symptoms began within the first 10 months of life and a deficiency of galactosylceramide beta-galactosidase activity was demonstrated in peripheral blood leukocytes and skin fibroblasts. The child survived till 8 yrs 7 mths. The reason for the absence of globoid cells is not clear but may be related to different effects of the gene mutation on the four substrates or possibly the interaction of sphingolipid activator protein-2.

Galactosylceramide and galactosylsphingosine loading studies in cultured skin fibroblasts in human and murine globoid cell leukodystrophy

Cell level studies of 3H-galactosylceramide(GalCer) and 3H-galactosyl sphingosine (GalSph) have been carried out in cultured skin fibroblasts from human and murine globoid cell leukodystrophy (GLD). GalCer loading studies disclosed that the hydrolysis rates of GalCer in human control and GLD were 72% and 45%, respectively, and those from the murine control and GLD cells were 77% and 21%, respectively, on the 5th day of culture. On the other hand, GalSph loading studies showed that the hydrolysis rate of GalSph in the human control and GLD were 40% and 10%, respectively, and those from murine control and GLD cells were 38% and 10% on the 12th day of culture. These data suggest that both GalCer and GalSph degradations were impaired in cell level in human and murine GLD. Furthermore, when radioactive 3H-GalSph was loaded into cultured fibroblasts from murine and human GLD, 3H-GalCer band was formed via GalSph. These data strongly suggest that GalCer could be synthesized through the GalSph route as a minor pathway at least in cultured skin fibroblasts, although the major pathway to synthesize GalCer should be via ceramide.

Effect of bone marrow transplantation on enzyme levels and clinical course in the neurologically affected twitcher mouse

The effect of allogeneic bone marrow transplantation (BMT) was investigated in the neurologically affected twitcher mouse, a model for human Krabbe's disease. Twitcher mice have a hereditary deficiency of the lysosomal enzyme galactosylceramidase, which causes growth delay, tremor, and paralysis of the hind legs. Death occurs at 30-40 d of age. After BMT galactosylceramidase activity increased to donor levels in hemopoietic organs. In lung, heart, and liver, galactosylceramidase activity rose to levels intermediate between those of twitcher and normal mice. Increased galactosylceramidase activity in liver parenchymal cells indicated uptake of the donor enzyme by recipient cells of nonhemopoietic origin. Enzyme activity also increased in kidney tissue. BMT resulted in a gradual increase in galactosylceramidase activity in the central nervous system to 15% of normal donor levels. A 5-6-fold increase in galactosylceramidase activity was found in the peripheral nervous system. This increase in enzyme activity was accompanied by a partial alleviation of neurological symptoms. In particular, paralysis of the hind legs was prevented by BMT. BMT led to a modest restoration of growth and prolonged survival. In several cases, the mice survived for more than 100 d, but eventually all animals died with severe neurological disease.

Lipids of nervous tissue: composition and metabolism

As indicated in the Introduction, the many significant developments in the recent past in our knowledge of the lipids of the nervous system have been collated in this article. That there is a sustained interest in this field is evident from the rather long bibliography which is itself selective. Obviously, it is not possible to summarize a review in which the chemistry, distribution and metabolism of a great variety of lipids have been discussed. However, from the progress of research, some general conclusions may be drawn. The period of discovery of new lipids in the nervous system appears to be over. All the major lipid components have been discovered and a great deal is now known about their structure and metabolism. Analytical data on the lipid composition of the CNS are available for a number of species and such data on the major areas of the brain are also at hand but information on the various subregions is meagre. Such investigations may yet provide clues to the role of lipids in brain function. Compared to CNS, information on PNS is less adequate. Further research on PNS would be worthwhile as it is amenable for experimental manipulation and complex mechanisms such as myelination can be investigated in this tissue. There are reports correlating lipid constituents with the increased complexity in the organization of the nervous system during evolution. This line of investigation may prove useful. The basic aim of research on the lipids of the nervous tissue is to unravel their functional significance. Most of the hydrophobic moieties of the nervous tissue lipids are comprised of very long chain, highly unsaturated and in some cases hydroxylated residues, and recent studies have shown that each lipid class contains characteristic molecular species. Their contribution to the properties of neural membranes such as excitability remains to be elucidated. Similarly, a large proportion of the phospholipid molecules in the myelin membrane are ethanolamine plasmalogens and their importance in this membrane is not known. It is firmly established that phosphatidylinositol and possibly polyphosphoinositides are involved with events at the synapse during impulse propagation, but their precise role in molecular terms is not clear. Gangliosides, with their structural complexity and amphipathic nature, have been implicated in a number of biological events which include cellular recognition and acting as adjuncts at receptor sites. More recently, growth promoting and neuritogenic functions have been ascribed to gangliosides. These interesting properties of gangliosides wIll undoubtedly attract greater attention in the future.(ABSTRACT TRUNCATED AT 400 WORDS)

Biochemical aspects of globoid and metachromatic leukodystrophies

Galactosylceramides and sulfogalactosylceramides are characteristic lipids of the myelin sheath. Two genetically determined leukodystrophies are caused by an inability to enzymically hydrolyze these glycolipids. Thus, a deficiency of galactocerebroside beta-galactosidase results in globoid cell leukodystrophy, whereas a reduced activity of arylsulfatase A is responsible for metachromatic leukodystrophy. Besides these disorders, deficiencies of arylsulfatases A, B, C, and other sulfatases have been shown in a distinct condition called "multiple sulfatase deficiency." All of these disorders are fatal and are characterized by marked demyelination and severe mental retardation. The cause of this demyelination is not known. However, cytotoxic galactosylsphingosine and sulfogalactosylsphingosine have been suggested as the agents responsible for this demyelination. Recent immunological studies have also shown that patients with globoid and metachromatic leukodystrophies contain a mutant galactocerebroside beta-galactosidase and arylsulfatase A, respectively. The mutant enzymes have different kinetic properties compared to the enzymes from normal subjects. However, they can cross-react with antibodies to these enzymes. Since partially purified preparations of galactocerebroside beta-galactosidase and homogeneous arylsulfatase A are now available, the possibility of enzyme replacement therapy in globoid and metachromatic leukodystrophies is discussed.

The twitcher mouse: an ultrastructural study on the oligodendroglia

Morphological alterations of oligodendroglia were investigated in the spinal cord of the twitcher mouse, an authentic murine model of human globoid cell leukodystrophy (GLD) from day 5 to day 45 postnatal (p.n.). Typical inclusions were seen in the perikarya as well as the processes of oligodendroglia after day 10 with increasing frequency. The majority of the inclusions was non-crystalloid but rather needle-like or slender tubular in appearance. Ultrastructural features of cellular degeneration became first noticeable on days 25-30 in the oligodendroglial cytoplasm. These consisted of an increased number of microtubules and/or smooth cisterns, dispersed ribosomes, alteration of endoplasmic reticulum forming stacked lamellae or whorls, vesiculation or vacuolation of cytoplasm. The number of degenerating oligodendroglia increased in the older twitcher mice, so did the degenerating myelin sheath. However, even on day 45, when globoid cells became conspicuous in subpial and perivascular regions, many oligodendroglia and myelin sheaths were still well preserved. These observations suggested that oligodendroglial degeneration resulted in the degeneration of myelin sheaths but globoid cells appeared even before morphological evidence of myelin degeneration, presumably in response to the biochemical alterations resulted from the deficiency of galactosylceramidase.

A protein activator of galactosylceramide beta-galactosidase

A heat-stable protein was isolated from the spleen of a patient with Gaucher's disease. This protein will activate glucosylceramide beta-glucosidase activity (Ho, M.W. and O'Brien, J.S. (1971) Proc. Natl. Acad. Sci. U.S.A. 68, 2810-2813). When the specificity of this activator was tested using other enzymes and substrates, it was found to activate galactosylceramide beta-galactosidase activity and sphingomyelinase but not GM1 beta-galactosidase or sulfatide sulfatase. The ability to stimulate galactosylceramide beta-galactosidase was optimum at pH 4.6 in the presence of pure phosphatidylserine or other acidic lipids such as sulfatide and phosphatidylinositol. The partially purified activator protein could stimulate galactosylceramide beta-galactosidase activity in brain, liver, leukocytes and cultured fibroblasts. It was not able to stimulate the activity of this enzyme in tissue samples from patients with Krabbe's disease, demonstrating that it was acting on galactosylceramide beta-galactosidase and not GM1 beta-galactosidase. It was slowly denatured by treatment with Pronase, reaching 16% of starting levels after 24 h at 50 degrees C. Attempts to separate the abilities of this activator preparation to stimulate several lysosomal hydrolases by column chromatography were not successful.

The effects of psychosine upon growth of human skin fibroblasts from patients with globoid cell leukodystrophy

[3H]Thymidine incorporation into cultured skin fibroblasts from patients with globoid cell leukodystrophy (GLD) and from control individuals was utilized to monitor the effects of psychosine (galactosylsphingosine) upon cell replication. The concentration of psychosine necessary to inhibit 50% (ID50) of the growth of cultured skin fibroblasts was approximately 15 microgram/ml for both normal and GLD fibroblasts deficient in the enzyme galactosylceramide beta-galactosidase. Growth inhibition curves for GLD and for control fibroblasts were comparable after 3 days and after 7 days exposure to the glycolipid, so that accumulation of psychosine was not a critical factor affecting toxicity. Galactosylceramide, the major substrate for the enzyme galactosylceramide beta-galactosidase, did not inhibit [3H]thymidine incorporation into either normal or GLD fibroblasts at the concentration tested, in contrast to the highly toxic effects of psychosine at similar concentrations. The comparable inhibitory levels of psychosine in control cells and in GLD fibroblasts which are deficient in ability to hydrolyze this glycolipid suggest that the toxicity of psychosine is nonspecific. Therefore, these results are not consistent with the concept that globoid cell leukodystrophy is primarily a psychosine lipidosis.

Mucolipidosis I: studies of sialidase activity and a prenatal diagnosis

The characteristics of the sialidase (N-acetyl-alpha-neuraminidase) of human leukocytes, fibroblasts and amniotic fluid cell cultures were determined with a radioactive assay method utilizing neuramin-[3H]lactitol as the enzyme substrate. Fibroblast cultures from patients with the inherited sialidase deficiency diseases including mucolipidosis I, sialidosis I and sialidosis II, juvenile type have less than 10% of normal sialidase activity using either this substrate, 2-(3'-methoxyphenyl)-N-acetyl-alpha-neuraminic acid, or 2'-(4-methylumbelliferyl)-N-acetyl-alpha-neuraminic acid. The total sialic acid content of fibroblasts and leukocytes from mucolipidosis I and sialidosis I patients is greatly elevated; this parameter is useful in establishing a diagnosis of sialidase deficiency. The sialic acid content of sialidosis II, juvenile type, with coexistent sialidase and beta-galactosidase deficiencies, is only slightly elevated above normal levels. A patient with mucolipidosis I has 16% of normal neuramin-[3H]lactitol sialidase activity in his peripheral leukocytes. His parents were clearly distinguished from the normal range using leukocyte enzyme levels and a maternal aunt was identified as a possible carrier. The presence of this enzyme in amniotic fluid cell cultures, both fibroblastic and mixed cell type, makes possible the prenatal detection of these diseases. A pregnancy from a family at risk for having a child with mucolipidosis I was monitored by amniocentesis and subsequent sialidase measurement of the amniotic fluid cell cultures.

Fetal Krabbe leukodystrophy. A morphologic study of two cases

Two new cases of Krabbe disease were diagnosed prenatally in a family with two previous affected children. The activity of galactosylceramide-beta-galactosidase was virtually absent in cultured amniotic cells. The prenatal diagnosis was confirmed enzymatically in cultured fibroblasts, brain, and visceral organs. Light and electron microscopy studies in both fetuses, 20 and 23 weeks of gestational age respectively, revealed the presence of typical globoid cells in the white matter of the spinal cord. Specific inclusions were also found in the brain stem and in peripheral nerves of the second fetus. A comparison with other Krabbe disease fetuses described in the literature contributes to the consensus that abnormal morphological findings can be expected in particular in the most actively myelinating areas of the nervous system. Although most of the cells containing the specific inclusions are probably non-glial in nature, some of them could represent myelination glia.

Specificity of galactosylceramidase activation by phosphatidylserine

Bovine brain phosphatidylserine effectively activates human brain galactosylceramidase (Hanada, E. and Suzuki, K. (1979) Biochim. Biophys. Acta 575, 410-420). Its effect on the other beta-galactosidase (Gm1-ganglioside beta-galactosidase) in human tissues, genetically distinct from galactosylceramidase, was examined. When partially purified human brain beta-galactosidase preparations, pure with respect to each other, were used as the enzyme source and when lactosylceramide, a common glycosphingolipid substrate for both beta-galactosidases, was used as the substrate, phosphatidylserine activated only hydrolysis of lactosylceramide by galactosylceramidase but not by GM1-ganglioside beta-galactosidase. With either galactosylceramide or lactosylceramide as substrate, and with phosphatidylserine as the activator, diagnosis of globoid cell leukodystrophy was possible using whole homogenates of cultured fibroblasts. Since 80-90% of lactosylceramide-cleaving activity in normal fibroblasts is due to GM1-ganglioside beta-galactosidase and since fibroblasts of globoid cell leukodystrophy patients are genetically deficient in galactosylceramidase but normal in GM1-ganglioside beta-galactosidase, these rsults are also consistent with specific activation of galactosylceramidase by phosphatidylserine.

The interrelations between high- and low-molecular weight forms of normal and mutant (Krabbe-disease) galactocerebrosidase

Galactocerebrosidase (beta-d-galactosyl-N-acylsphingosine galactohydrolase; EC 3.2.1.46) activity of brain and liver preparations from normal individuals and patients with Krabbe disease (globoid-cell leukodystrophy) have been separated by gel filtration into four different molecular-weight forms. The apparent mol.wts. were 760000+/-34000 and 121000+/-10000 for the high- and low-molecular-weight forms (peaks I and IV respectively) and 499000+/-22000 (mean+/-s.d.) and 256000+/-12000 for the intermediate forms (peaks II and III respectively). On examination by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis, the high- and low-molecular-weight forms revealed a single protein band with a similar mobility corresponding to a mol.wt. of about 125000. Antigenic identity was demonstrated between the various molecular-weight forms of the normal and the mutant galactocerebrosidases by using antisera against either the high- or the low-molecular-weight enzymes. The high-molecular-weight form of galactocerebrosidase was found to possess higher specific activity toward natural substrates when compared with the low-molecular-weight form. It is suggested that the high-molecular-weight enzyme is the active form in vivo and an aggregation process that proceeds from a monomer (mol.wt. approx. 125000) to a dimer (mol.wt. approx. 250000) and from the dimer to either a tetramer (mol.wt. approx. 500000) or a hexamer (mol.wt. approx. 750000) takes place in normal as well as in Krabbe-disease tissues.

Globoid cell leucodystrophy in polled Dorset sheep

Globoid cell leucodystrophy (Krabbe's disease) was diagnosed in two Polled Dorset sheep from a stud farm. Clinical signs were hind limb incoordination progressing to tetraplegia. Histologic changes in white matter of the brain were myelin destruction, loss of oligodendroglia, astrogliosis and accumulation of distinctive periodic acid-Schiff (PAS)-positive globoid cells. The activities of galactocerebroside beta-galactosidase, the lysosmal enzyme specifically deficient in globoid leucodystrophy, and of three other glycosidase enzymes were compared in brain tissue of one affected and six unaffected sheep. Activities of the three nonspecific glycosidases were similar in all seven brains. Galactocerebrosidase activity was similar in the six control sheep, but in the affected brain was less than 6% of the control mean.

A comparison of the properties and bile salt specificities of galactosylceramide and lactosyl ceramide beta-galactosidase activities in human leucocytes and fibroblasts

The properties and bile salt specificities of galactosylceramide and lactosylceramide beta-galactosidase activities (GC and LC-beta-galactosidases) of human leucocytes and fibroblasts were compared. A number of differences were observed. Under the standard assay conditions the former activity was more sensitive to Zn2+ and Triton-X100. Glycocholate and cholate were more active stimulators of the GC-beta-galactosidase than the more frequently used taurocholate which was the most effective stimulator of LC-beta-galactosidase activity. It is postulated that some of the apparent differences in the properties of GC- and LC-beta-galactosidase activities may be attributed to the different micellar properties of the lipid substrates. Experiments with fibroblasts from patients with Krabbe's disease confirmed an almost total absence of GC-beta-galactosidase whichever bile acid was employed. Residual LC-beta-galactosidase activity detected in these cells was much higher ranging from 13% of the lowest measured value when measured with taurocholate to approximately normal values with glycocholate. Fibroblasts obtained from patients with GM1-gangliosidosis displayed close to normal GC and LC-beta-galactosidase activity under our experimental conditions. The data suggest that diagnoses of Krabbe's disease should be performed with galactosylceramide rather than lactosylceramide as substrate.

Human brain cerebroside beta-galactosidase: deficiency of transgalactosidic activity in Krabbe's disease

Under experimental conditions optimal for the assay of D-galactosyl-N-acylsphingosine galactohydrolase (EC 3.2.1.46) activity, homogenates of neurologically normal human brain tissue could transfer galactose from galactosyl ceramide (gal-cer), lactosyl ceramide (lac-cer), 4-methylumbelliferyl-beta-galactoside (4-MU-gal), or p-nitrophenyl-beta-galactoside (PNP-gal) to [1-14C]oleoyl sphingosine, but homogenates of brain tissue from patients with Krabbe's disease lacked this ability. The rate of hydrolysis of ganglioside GM1 and, to a lesser extent, of PNP-gal by homogenates of Krabbe's brain tissue was also decreased. Activity of PNP-beta-galactosidase in normal brain tissue, like that of cerebroside beta-galactosidase from the same source, was considerably more heat-stable than the activity of either 4-MU-beta-galactosidase or the predominant GM1 beta-D-galactosidase (EC 3.2.1.23). Lac-cer and GM1, as well as 4-MU-gal and PNP-gal, were competitive inhibitors of human-brain cerebroside beta-galactosidase. These findings confirm the ability of mammalian cerebroside beta-galactosidase to catalyze a transgalactosylation reaction and provide additional information on the substrate specificity of human brain cerebroside beta-galactosidase.

Activation of human brain galactosylceramidase by phosphatidylserine

Assays of sphingolipid hydrolases in vitro generally require bile salts or other detergents. A few 'activator proteins' have been reported that can partially replace the detergents in the assay mixture. We report here that phosphatidylserine from bovine brain is a relatively specific activator of human brain galactosylceramidase in the absence of sodium taurocholate (phosphatidylserine system). Activity similar to that obtained with the conventional assay system containing taurocholate and oleic acid (taurocholate system) could be obtained. Other lipids tested generally gave less than 10% of the taurocholate system activity, but sulfatide could activate human brain galactosylceramidase to 20--30% of the taurocholate system. The properties of the reaction in the phosphatidylserine system were examined with human brain whole homogenate, crude soluble post-concanavalin A preparations, and partially purified preparations as the enzyme source and compared with those obtained with the taurocholate system. The pH optimum shifted from 4.2 in the taurocholate system to 4.7 in the phosphatidylserine system. The phosphatidylserine system was superior in the linearity of the reaction with respect to the enzyme protein. Reasonably linear Lineweaver-Burk plots could be obtained. The Km values for the phosphatidylserine system were greater than those for the taurocholate system. The effect of phosphatidylserine was not additive to that of taurocholate. Additional phosphatidylserine to the taurocholate system was either without effect at lower concentrations or inhibitory at higher concentrations. The assays of galactosylceramidase with phosphatidylserine and without taurocholate do not necessarily provide pragmatic advantages but offer a potentially useful system with which to study the mechanism of in vivo degradation of the membrane-bound glycosphingolipid.

Basic findings and current developments in sphingolipidoses

Sphingolipidoses are caused by recessively inherited deficiencies of lysosomal hydrolases. The clinical backgrounds of and current biochemical and genetic approaches to the different forms and variants of gangliosidoses, trihexosylceramidosis (Fabry's disease), galactosylceramidosis (Krabbe's disease), sulfatidoses (metachromatic leukodystrophies), glucosylceramidosis (Gaucher's disease), sphingomyelinoses (Niemann-Pick disease) and ceramidosis (Farber's disease) are presented.

Globoid cell leukodystrophy (Krabbe's disease). Metabolic studies with cultured fibroblasts

Metabolism of tritium-labelled galactosylceramide and lactosylceramide added to the culture medium was examined in cultured skin fibroblasts from 4 patients with globoid cell leukodystrophy (GLD) and 4 control individuals. The uptake of [3H]galactosylceramide and [3H]lactosylceramide by the fibroblasts continued actively at least up to 3 days. Approximately 30--40% of the galactosylceramide, which had been taken up, was released subsequently from the cells in a 4-day period, whereas only 10% of lactosylceramide was released during the same period. The GLD fibroblasts showed no abnormality in the kinetics of the uptake and in the release of these glycosphingolipids which are natural substrates of the beta-galactosidase genetically deficient in the disorder. This finding differs from that reported for fibroblasts from patients with metachromatic leukodystrophy, which showed abnormal accumulation and retention of sulfatide added to the culture media. However, degradation of added galactosylceramide to [3H]galactose by the GLD fibroblasts was only 25% of the control cells, while lactosylceramide was degraded at 70% of the normal rate. These findings are consistent with the known substrate specificities of the two acidic beta-galactosidases in human tissues; galactosylceramide is hydrolyzed almost exclusively by galactosylceramidase, while lactosylceramide can be hydrolyzed by both galactosylceramidase and GM1-ganglioside beta-galactosidase.

Canine globoid cell leukodystrophy. Part 1. Further ultrastructural study of the typical lesion

The ultrastructural changes of typical lesions in canine globoid cell leukodystrophy (GLD) have been studied. The globoid cells were located in the cerebral parenchyma as well as in the perivascular Virchow--Robin space. Features suggestive of a passage of the globoid cells from the cerebral parenchyma to the Virchow--Robin space were also observed through the interruptions in the basal lamina. The globoid cells had numerous thin pseudopods and contained various cytoplasmic inclusions which have been described previously. Detailed studies of these inclusions suggest that they represented aggregates of filamentous or linear sub-unit structures. Typical oligodendroglial cells were found on only a few occasions. Both globoid cells and oligodendroglia contained myelin debris, dense bodies and honey-comb like inclusions composed of numerous small myelin figures. In a few instances, crystalline polygonal inclusions identical to those found in the globoid cells, were found in the cytoplasm of the cells which were, with reasonable certainty, identifiable as oligodendroglia. In less affected areas where myelin was still present, degenerating oligodendroglia, with or without recognizable inclusions, were frequently encountered. Astrocytes and endothelial cells contained concentric lamellar inclusions and dense bodies but did not contain the tubular inclusions as seen in globoid cells. The possible significance of the ultrastructural features in regard to the pathogenesis of the GLD have been discussed.

Substrate specificities of the two genetically distinct human brain beta-galactosidases

The two human brain beta-galactosidases were solubilized and fractionated by Sephadex G-200 gel filtration, free from each other. Substrate specificities of the two enzymes were examined for galactosylceramide, lactosyl-[N-stearoyl]ceramide, lactosyl-[N-lignoceroyl]ceramide, galactosyl-N-acetylgalactosaminyl-[N-stearoyl]ceramide, lactosyl-[N-lignoceroyl]ceramide, galactosyl-N-acetylgalactosaminyl-[N-acetylneuraminyl]galactosyl-glucosylceramide (GMI-ganglioside), galactosyl-N-acetylgalactosaminyl-galactosyl-glucosylceramide (asialo GM1-ganglioside), and 4-methylumbelliferyl beta-galactoside. Under appropriately optimized conditions, either of the two beta-galactosidases could hydrolyze all of the substrates, although with widely varying rates. Relative specific activities of galactosylceramide beta-galactosidase toward galactosylceramide, lactosyl-[N-steroyl]ceramide, lactosyl-[N-lignoceroyl]ceramide. GM1-ganglioside, asialo GM1-ganglioside, and 4-methylumbelliferyl beta-galactoside were 100, 510, 250, 39, 41 and 120, respectively. Relative specific activities of GM1-ganglioside beta-galactosidase toward the same series of the substrates were 0.3, 78, 19, 100, 150 and 240; However, the optimal assay conditions for any given natural substrate were sufficiently different for each beta-galactosidase so that diagnostic assays for the two genetic diseases due to beta-galactosidase deficiencies could be carried out in whole tissues. Since the relative distribution of the two enzymes vary greatly in different tissues, contributions by the two enzymes to degradation of the natural glycosphingolipids in vivo may well vary in different organs. These findings may have an important bearing on the biochemical pathogenesis of these genetic disorders.

Chemical pathology of krabbe's disease. IV. Studies of galactosylceramide and lactosylceramide BETA-galactosidases in brain, white blood cells and aminotic fluid cells

Galactosylceramide beta-galactosidase and lactosylceramide beta-galactosidase activities were investigated in normal human brain, leu-kocytes and amniotic fluid cells. The enzymatic assays were performed on brains from 11 patients with Krabbe's disease, on leukocytes from 16 patients and 18 obligate heterozygotes, and on amniotic fluid cells from 9 foetuses at risk. The brain enzyme was solubilized from a 900 g-100000 g pellet. With this enzyme preparation a profound deficiency of galactosylceramide beta-galactosidase activity in brain, approximately 1% of that in age-matched controls was shown. The lactosylceramide beta-galactosidase activity of brain was also strongly reduced, but not to the same extent as the other beta-galactosidase. Galactosylceramide beta-galactosidase activity in leukocytes from patients with Krabbe's disease was generally less than 5% of that in age-matched controls and there was no overlap between the patients and the obligate heterozygotes. Carrier detection by the leukocyte enzyme was, however, not possible because of considerable overlap between heterozygotes and normal controls. The lactosylceramide beta-galactosidase activity was only moderately reduced in leukocytes, but strongly reduced in cerebral tissue from patients with Krabbe's disease. The changes in the glycolipid pattern of cerebral tissue, recently described by us in patients with Krabbe's disease, offers an explanation to the serious glycolipid beta-galactosidase deficiency in CNS.

Lactosyl ceramidosis: normal activity for two lactosyl ceramide beta-galactosidases

Lactosyl ceramide beta-galactosidase activities in the fibroblasts from the previously described patient with so-called "lactosyl ceramidosis" were reexamined with the two recently developed assay methods which appear to measure two genetically distinct enzymes that can degrade this substrate. No deficiency of either of the lactosyl ceramide-cleaving enzymes was observed. In addition, sphingomyelinase activity was only one-sixth of normal, while all other enzymes examined were within the normal ranges.