Validity of lymphoid cell line for enzymatic studies of GM2-gangliosidosis variant 0 (Sandhoff disease).

A lymphoid cell line established by Epstein-Barr virus (EBV)-transformation of peripheral blood B-lymphocytes from a patient with Sandhoff disease showed a severe deficiency of beta-N-acetylhexosaminidase activity (residual activity around 10% of that in lymphoid cell lines from normals or other lipidotic patients). This residual beta-N-acetylhexosaminidase was completely heat-labile in contrast to that of normals. The molecular forms of residual beta-N-acetylhexosaminidase from Sandhoff lymphoid cell line were separated by Con A-sepharose and electrofocusing. Their properties and electrofocusing profiles were compared to those from Sandhoff fibroblasts and from fetal brain: this comparison permitted to identify the residual molecular forms with Hex S and Hex C. The microheterogeneity of Hex S and Hex C, demonstrated by electrofocusing, was discussed. 2-Acetamido-2-deoxy-D-galactonolactone (GalNAcLone) showed a strong inhibitory effect on lysosomal Hex A, B and S, but only a very slight effect on Hex C. Studies of the inhibition type (competitive on Hex A, B and S and mixed on Hex C) gave some informations about the enzymatic site. Elsewhere, differences in affinity of GalNAcLone for the various isoenzymes could be utilized to define optimal assay conditions for specifically determining Hex C (standard assay containing 400 mumol/l of GalNAcLone). These results demonstrated that EBV-transformed lymphoid cell lines represent an accurate model system for enzymatic studies of Sandhoff disease.