Defects in degradation of blood group A and B glycosphingolipids in Schindler and Fabry diseases

Abstract

Skin fibroblast cultures from patients with inherited lysosomal enzymopathies, ␣ -N -acetylgalactosaminidase ( ␣ -NAGA) and ␣ -galactosidase A deficiencies (Schindler and Fabry disease, respectively), and from normal controls were used to study in situ degradation of blood group A and B glycosphingolipids. Glycosphingolipids A-6-2 (Gal N AcCer, globotetraosylceramide) were tritium labeled in their ceramide moiety and used as natural substrates. The degradation rate of glycolipid A-6-2 was very low in fibroblasts of all the ␣ -NAGA-deficient patients (less than 7% of controls), despite very heterogeneous clinical pictures, ruling out different residual enzyme activities as an explanation for the clinical heterogeneity. Strongly elevated urinary excretion of blood group A glycolipids was detected in one patient with blood group A, secretor status (five times higher than upper limit of controls), in support of the notion that blood group A-active glycolipids may contribute as storage compounds in blood group A patients. When glycolipid B-6-2 was fed to ␣ -galactosidase A-deficient cells, the degradation rate was surprisingly high (50% of controls), while that of globotriaosylceramide was reduced to less than 15% of control average, presumably reflecting differences in the lysosomal enzymology of polar glycolipids versus less-polar ones.Relatively

Blood group A glycosphingolipid accumulation in the hair of patients with α-N-acetylgalactosaminidase deficiency

“…Our findings imply that blood group A-GSL is constitutively degraded by a-NAGA in normal hair but accumulates in the hair of Kanzaki disease patients. This is consistent with recent reports that lysosomal a-NAGA acts on the a-Nacetylgalactosamine terminal of oligosaccharide chains on glycoproteins (Michalski and Klein, 1999) and on the a-N-acetylgalactosamine terminal of blood group A-GSL (Asfaw et al, 1998(Asfaw et al, , 2002. GSL accumulation in the tissues of patients with a-NAGA deficiency has not been demonstrated directly.…”

Acid sphingomyelinase deficiency. Phenotype variability with prevalence of intermediate phenotype in a series of twenty‐five Czech and Slovak patients. A multi‐approach study

“…In contrast to NP ¢broblasts, the capacity of lysosomal enzymes in normal cells usually greatly exceeds substrate in£ux. This implies that the control values are generally underestimated, as was observed in similar experiments testing degradation capacity of di¡erent glycohydrolases in mutant and normal cells (Asfaw et al 2002). This e¡ect is more obvious in longer chase experiments.…”

“…Such minor values and small di¡er-ences in residual activity are insigni¢cant and are generally observed in loading experiments (Asfaw et al 2002). On the other hand, patients 22 and 25 may have an unusually high capacity for SM hydrolysis, re£ecting their clinical status (Table 7).…”

“…Pre-incubation in the lipoprotein-free medium enhances expression of LDL-receptors and promotes apoB/E-receptor-mediated pathway of substrate cellular transportation, thus providing fast and speci¢c lysosomal targeting of SM. This is a similar strategy to substrate application in liposomal form with integrated apolipoprotein E (Asfaw et al 1998(Asfaw et al , 2002.…”

Tandem Mass Spectrometry of Sphingolipids: Application in Metabolic Studies and Diagnosis of Inherited Disorders of Sphingolipid Metabolism

“…The experiments conducted with stable isotope-labeled substrates and tandem mass spectrometry facilitated a more accurate quantification analysis of the lipids, and the results were better correlated with the clinical and biochemical phenotypes of the samples. The procedure used to prepare the cellular lipids for tandem mass spectrometry analysis was simple and relatively rapid; unlike radioisotope assays, it did not require separation during the pre-analytical phase (Asfaw, et al, 2002;. However, experiments with radiolabeled glycolipid substrates indicate the entire metabolic pattern (Fig 10A) and can thus make it possible to identify relevant metabolites to be further analyzed via tandem mass spectrometry.…”