[The stability of freeze-drying lysosomal enzymes]

Enzyme assays for the diagnosis of lysosomal storage diseases have been underway in China only in a few laboratories, and the specimens for enzyme assay must not be inactivated by environmental factors. To solve the problem, the stability of freeze-drying lysosomal enzymes was tested.

Three pools for samples were set up: control leucocytes pool and plasma pool(40 individuals in each pool), control fibroblasts pool( 3 cell lines). 4 groups of different dispositions of samples were designed for the pools:(1)pellets or plasma directly stored at -80 degrees C as routine(non-freeze-drying group or N);(2)after freeze-drying, pellets or plasma immediately stored at -80 degrees C (0 week or 0W); (3) after freeze-drying, pellets or plasma stayed at room temperature for 1 week(simulated mail) then stored at -80 degrees C (1 week or 1W);(4) the same with 1W but 3 weeks at room temperature(3 weeks or 3W). Microassay for enzyme activity was employed: 20 enzymes in leucocytes pool, 14 enzymes in fibroblasts pool and 7 in plasma pool.

Enzyme activities among 4 groups in each sample pool were compared. Single factor analysis of variance (F test) showed no significance of differences (P>0.05) among 4 groups in leucocytes and fibroblasts pool, but highly significant differences (P<0.01) among 4 groups in plasma pool. "t test" showed no significance of differences (P> 0.05) between N and 3W in leucocytes and also fibroblasts pool, but very significant differences (P<0.01) between N and 3W in plasma pool.

The results suggest that freeze-drying samples from leucocytes and fibro- blasts can provide a stable resource for enzyme assay and be simple for transportation of the diagnostic samples. Though freeze-drying is not appropriate for the plasma samples, it is still applicable for wide use since only a few kinds of lysosomal enzyme being indicated to use plasma for enzyme assay.