AMP-deoxynojirimycin is a hydrophobic deoxynojirimycin derivative that has high potency and selectivity for non-lysosomal glucosylceramidase (NLGases). Its inhibitory activity is favored by its proximity to the cell surface and interaction with the plasma membrane (Overkleeft HS et al, 1998). Patients with Gaucher disease, a lysosomal storage disorder, are deficient of glucocerebrosidases that is required for intra-lysosomal glycosphingolipid catabolism. Thus, accumulation of glucosylceramide is observed in the macrophages of these patients. However, NLGase is not deficient in these Gaucher patients and therefore accumulation of glucosylceramide is not observed in other cell types.
Marinesco-Sjögren-like syndrome (MSS) is identified by autosomal recessive mutations in SIL1 nucleotide exchange factor. Haugarvoll et al identified a novel homozygous GBA2 mutation (a gene encoding for NLGases) in two MSS patients, who do not harbor SIL1 mutations. These patients presented with cerebellar ataxia, cataracts and mental retardation. Furthermore, an enzymatic assay was developed to assess the activity of GBA2 in these patients.
Investigated patients had raised levels of glucosylceramide in erythrocytes and plasma. This led to the study of the enzymatic activity of GBA2 in these individuals, using leukocytes. Substrate, 4-metylumbelliferon-β-glucopyranoside (4-MU-beta-glc), was added to a homogenate of isolated leukocytes. However, 4-MU-beta-glc is also a substrate for lysosomal and cytosolic glucosylceramidases (GBA1 and GBA2 respectively). Therefore, GBA2 was inhibited using AMP-deoxynojirimycin to assess its activity. The higher percentage of residual GBA2 activity in one of the patients, compared to controls, revealed loss of GBA2 activity in this patient.
For further details, please refer to the original paper: Haugarvoll et al (2017).