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Effect of Hepes on the fibroblast cerebroside sulfate loading test
Abstract:
The intact fibroblast cerebroside sulfate loading test is useful because sulfatide hydrolysis can be demonstrated in late onset MLD cell types with 1% or less of normal arylsulfatase A. In such cells, hydrolysis of sulfatide was inhibited when the loading test was carried out in growth media containing the organic ampholyte Hepes. Since Hepes did not affect uptake of sulfatide nor intracellular levels of arylsulfatase A, it was concluded that Hepes inhibited sulfatide hydrolysis by increasing lysosomal pH. The cerebroside sulfate loading test in the presence of Hepes should be useful as a probe for arylsulfatase A dysfunction in atypical MLD fibroblasts.
Insights
The fibroblast cerebroside sulfate loading test effectively demonstrates sulfatide hydrolysis in metachromatic leukodystrophy (MLD) cells. Hepes buffer inhibits this hydrolysis by increasing lysosomal pH, aiding in diagnosing arylsulfatase A dysfunction.
Area of Science:
- Biochemistry
- Cell Biology
- Lysosomal Storage Disorders
Background:
- Metachromatic leukodystrophy (MLD) is a lysosomal storage disorder caused by arylsulfatase A (ARSA) deficiency.
- Late-onset MLD (MIM 249900) presents with residual ARSA activity, complicating diagnosis.
- The intact fibroblast cerebroside sulfate loading test is a functional assay for ARSA activity.
Purpose of the Study:
- To evaluate the utility of the intact fibroblast cerebroside sulfate loading test in detecting ARSA dysfunction in atypical MLD.
- To investigate the effect of Hepes buffer on sulfatide hydrolysis in MLD fibroblasts.
Main Methods:
- Fibroblast cultures from late-onset MLD patients with low arylsulfatase A activity were used.
- Cells were loaded with cerebroside sulfate, and hydrolysis was measured with and without Hepes buffer.
- Sulfatide uptake and intracellular ARSA levels were assessed.
Main Results:
- Sulfatide hydrolysis was detectable in MLD fibroblasts with ≤1% of normal ARSA activity.
- Hepes buffer significantly inhibited sulfatide hydrolysis in these cells.
- Hepes did not alter sulfatide uptake or intracellular ARSA levels, indicating lysosomal pH modulation.
Conclusions:
- The intact fibroblast cerebroside sulfate loading test is a sensitive method for demonstrating sulfatide hydrolysis in MLD.
- Hepes buffer serves as a valuable tool to enhance the diagnostic specificity of this assay by inhibiting hydrolysis via lysosomal alkalinization.
- This Hepes-modified loading test is a promising probe for identifying arylsulfatase A dysfunction in atypical MLD fibroblasts.