Hepatic galactosylceramide in globoid cell leukodystrophy (Krabbe's disease)

Ceramides and other bioactive sphingolipid backbones in health and disease: lipidomic analysis, metabolism and roles in membrane structure, dynamics, signaling and autophagy

Sphingolipids are comprised of a backbone sphingoid base that may be phosphorylated, acylated, glycosylated, bridged to various headgroups through phosphodiester linkages, or otherwise modified. Organisms usually contain large numbers of sphingolipid subspecies and knowledge about the types and amounts is imperative because they influence membrane structure, interactions with the extracellular matrix and neighboring cells, vesicular traffic and the formation of specialized structures such as phagosomes and autophagosomes, as well as participate in intracellular and extracellular signaling. Fortunately, "sphingolipidomic" analysis is becoming feasible (at least for important subsets such as all of the backbone "signaling" subspecies: ceramides, ceramide 1-phosphates, sphingoid bases, sphingoid base 1-phosphates, inter alia) using mass spectrometry, and these profiles are revealing many surprises, such as that under certain conditions cells contain significant amounts of "unusual" species: N-mono-, di-, and tri-methyl-sphingoid bases (including N,N-dimethylsphingosine); 3-ketodihydroceramides; N-acetyl-sphingoid bases (C2-ceramides); and dihydroceramides, in the latter case, in very high proportions when cells are treated with the anticancer drug fenretinide (4-hydroxyphenylretinamide). The elevation of DHceramides by fenretinide is befuddling because the 4,5-trans-double bond of ceramide has been thought to be required for biological activity; however, DHceramides induce autophagy and may be important in the regulation of this important cellular process. The complexity of the sphingolipidome is hard to imagine, but one hopes that, when partnered with other systems biology approaches, the causes and consequences of the complexity will explain how these intriguing compounds are involved in almost every aspect of cell behavior and the malfunctions of many diseases.

Eccrine gland involvement in Krabbe's disease

Lysosomal storage inclusions were observed in skin eccrine gland secretory and myoepithelial cells in three cases of Krabbe's disease. In addition to storage there were numerous degenerative changes, occasionally resulting in cell necrosis. These findings suggest a generalized nature of the storage process in this lysosomal enzymopathy and point to high galactocerebroside turnover in eccrine gland epithelium. This knowledge may be of value in the biopsy diagnosis of Krabbe's disease.

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.

Genetic galactosylceramidase deficiency (globoid cell leukodystrophy, Krabbe disease) in different mammalian species

Globoid cell leukodystrophy (Krabbe disease) in man is a rare genetic disorder caused by deficiency of galactosylceramidase activity. Clinical and pathological manifestations are almost exclusively confined to the nervous system, particularly to the white matter and the peripheral nerve. The disease also occurs in four other mammalian species: dog, cat, sheep and mouse. Except for the feline disease, for which enzymatic information is lacking, these animal models are genetically equivalent to the human disease. The clinical and pathological features are fundamentally similar in all species, as might be expected from the same underlying genetic defect. Nevertheless, significant species differences are observed in the clinical course, severity of pathological alterations, and analytical biochemistry. These genetically "authentic" animal models provide an invaluable tool for studies of the rare human genetic disorder. Results of studies already done and the future potentials are discussed.

Abnormal accumulation of galactosylceramide in the kidney of twitcher mouse

The kidney tissue of the twitcher mice, a neurological mutant caused by a genetic deficiency of galactosylceramidase, contains enormously increased amounts, up to 50 times normal, of galactosylceramide. The finding is in sharp contrast with those in the enzymatically equivalent human disease, globoid cell leukodystrophy (Krabbe disease), in which no specific abnormal accumulation of galactosylceramide occurs despite the same genetic block in the catabolic pathway. This indicates that the same genetic defect can result in entirely different consequences in different species. Caution must be exercised even when "authentic animal models" are utilized for studies of human diseases.

Glycosylceramide synthesis in the developing spinal cord and kidney of the twitcher mouse, an enzymatically authentic model of human Krabbe disease

UDP-galactose:ceramide galactosyltransferase activity was assayed in the spinal cord and kidney of the recently discovered neurological mutant, the twitcher mouse, which is an enzymatically authentic model of human globoid cell leukodystrophy (Krabbe disease). The activity in the spinal cord was essentially normal during the early myelination period up to 15 days. There was a slight reduction at 20 days. At 25 and 33 days, the galactosyltransferase activity was drastically reduced compared to controls. In contrast, the galactosyltransferase activity in the kidney of twitcher mice remained normal throughout the developmental stages examined. Activity of the control enzyme UDP-glucose:ceramide glucosyltransferase was always normal in both the spinal cord and kidney. Thus, reduction of galactosylceramide synthesis occurs in the CNS secondarily to the pathological alteration of the oligodendroglia. No such reduction occurs in the kidney, at least for the last step of galactosylceramide synthesis. Reduced synthesis as the result of metabolic regulation in the presence of the catabolic block is therefore unlikely to be the cause of the lack of abnormal accumulation of galactosylceramide in the kidney of patients with globoid cell leukodystrophy.