Intercellular exchange of lysosomal enzymes: enzyme assays in single human fibroblasts after co-cultivation

Quantitative cytochemical analysis of (single) cultured cells

Human fibroblasts or amniotic fluid cells can be cultivated in special dishes with a bottom of thin transparent plastic foil. After quick freezing and freeze-drying small groups of cultured cells or single cells can be isolated by dissecting small pieces of plastic foil under the stereomicroscope. These can be incubated in (sub)microlitre volumes of substrate and the absorbance, fluorescence or radioactivity can be measured and expressed per cell. When absorbance is measured with a microscope spectrophotometer in 1-10 microliter, microcuvettes, the minimum amount of coloured product that can be determined is of the order of 10(-11) moles. Incubation under paraffin oil in 0.05 microliter of substrate, followed by fluorescence measurements in 1-5 microliter with a microscope fluorometer, allows down to 10(-14) mol of methylumbelliferone, which is the end-product in many analyses of lysosomal enzymes, to be detected. (Re)cycling procedures have an even greater sensitivity (10(-15)-10(-19)mol) but they are more complicated and limited to NAD(P)(H)-dependent reactions. Several radiometric procedures have also been adapted for the analysis of small numbers of cultured cells but most of them still require 10(4)-10(5) human fibroblasts. These microtechniques allow rapid prenatal diagnosis of at least 20 different genetic metabolic diseases to be made within 7-14 days after amniocentesis at the 14th-16th week of pregnancy. Enzyme assays on single cultured cells have also enabled complementation studies to be done on heterokaryons after hybridization of different types of mutant fibroblasts, as well as investigations of the intercellular exchange of lysosomal enzymes between normal and mutant cells.

Assessment of lysosomal function by quantitative histochemical and cytochemical methods

Quantitative histochemistry and cytochemistry enables a direct link to be made between metabolic functions such as the activity of lysosomal enzymes and the morphology of a tissue or a type of cell. Several approaches exist such as microchemistry based on (bio)chemical analysis of a single cell or a small piece of tissue dissected from a freeze-dried section. This technique has been routinely used for prenatal diagnosis of inherited enzyme defects and especially of lysosomal storage diseases. Other approaches are cytofluorometry or cytophotometry, which are based on the principle that a fluorescent or coloured final reaction product is precipitated at the site of the enzyme. The amount of final reaction product is analysed per cell or per unit volume of tissue using either a microscope cytofluorometer or flow cytometer for fluorescence measurements or an image analysing system or scanning and integrating cytophotometer for absorbance measurements. In principle, fluorescence methods are to be preferred over chromogenic methods because they are more sensitive and enable multiparameter analysis. However, only a limited number of fluorogenic methods are at hand that give a final reaction product which is sufficiently water-insoluble to guarantee good localisation. The best results have been obtained with methods based on naphthol AS-TR derivatives and with methods for the demonstration of protease activity using methoxynaphthylamine derivatives as substrates and 5'-nitrosalicylaldehyde as coupling reagent. Chromogenic methods are far better with respect to localisation properties and, therefore, most commonly used for quantitative histochemical analysis of lysosomal enzyme activities.(ABSTRACT TRUNCATED AT 250 WORDS)

The expression of hex A and hex B isozymes of hexosaminidase in parental and experimental human fibroblast cells and their components

The expression of the two major isozyme forms of hexosaminidase (EC 3.2.1.30), hexosaminidase A and hexosaminidase B, has been examined. The parental cells and/or cellular components of parental cells are individually fused using inactivated Sendai virus with the aid of a micromanipulator. The progeny cells produced from such hybrids are subjected to a microenzymatic assay which allows measurements at the single cell level. The lysosomal-deficient cells used in this study are Tay-Sachs and Sandhoff fibroblasts, and the normal cells used are WI-38 (fetal lung fibroblasts), amniotic fluid cells (GM 473), and JASD3 (normal human foreskin). The results show that the ratio of cell components which are fused to form the experimental cell affects the percentage of hexosaminidase A expressed in the progeny cells. Furthermore, our results imply the presence of a "factor" in the Sandhoff cell's cytoplasm which, together with the Tay-Sachs nucleus, is necessary for hexosaminidase A expression in the experimental cell's progeny.

The stability and aggregation properties of human liver acid beta-D-galactosidase

1. A method is described for following continuously the action of beta-galactosidase on 4-methylumbelliferyl beta-D-galactoside at pH 4.5, in which 4-methylumbelliferone production is measured at fluorescence excitation and emission wavelengths of 324 and 444nm respectively. 2. Initial-rate studies show that the presence of salt activates beta-galactosidase up to 100 mM, but is inhibitory above that concentration. The enzyme is very unstable at 37 degrees C and low ionic strength, but stability increases with ionic strength. 3. The stability of the enzyme at 37 degrees C decreases markedly with rising pH in the range 5.9--8.0. 4. Gel-filtration patterns demonstrate that there is a marked tendency to polymerization with increasing ionic strength. The gel-filtration pattern shows decreasing amounts of dimer with increasing pH. 5. The correlation between activity, stability and molecular form of beta-galactosidase is discussed. It is suggested that the dimeric form of the enzyme is the most stable and active form. The implications of this finding for the assay of beta-galactosidase under physiological conditions for prenatal diagnosis are discussed. 6. Evidence for the possible occurrence of a 36 000-mol.wt. from of beta-galactosidase is presented. 7. A computer program for the calculation of initial rates has been deposited as Supplementary Publication SUP 50114 (4 pages) at the British Library Lending Division, Boston Spa, Wetherby, West Yorkshire LS23 7BQ, U.K., from whom copies can be obtained on the terms indicated in Biochem. J. (1981) 193, 5.

Ozone sensitivity in aging WI-38 cells based on acid phosphatase content

Young [16-19 population doubling level (PDL)] and senescing (50-53 PDL) WI-38 cell populations were exposed to 1 ppm ozone for 2 hr and the resultant extracellular and intracellular acid phosphatase concentration was measured. Dose-response curves were also determined for surviving populations of young and old cells after a 1 hr ozone exposure ranging in concentration from 0 to 1.00 ppm. Senescing cells released 8 times more acid phosphatase per million cells than the young cells. Both old and young cells showed a clear dose-response to the 1 hr ozone gradient exposure. However, the older cells demonstrated a consistent 17% average lower survival rate than the young cells. The higher acid hydrolase level in older WI-38 cells is probably related to the lower survival rate observed in the older cells in vitro.

Clinical and biochemical abnormalities in porcine GM2-gangliosidosis

Progressive clinical changes of GM2-gangliosidosis in a herd of inbred Yorkshire swine were reduced postnatal growth rate; incoordination, usually evident at 3 months of age; numerous, gray-white spots scattered through the retina; prominent, dark blue cytoplasmic granules in many neutrophils; and an increased frequency of azurophilic granules in lymphocytes. There was less N-acetyl-β-D-hexosaminidase in tissue homogenates from affected than from normal pigs, but there was more in serum from affected pigs than in serum from either carrier or normal pigs. The serum enzyme assay was a reliable test to distinguish carrier pigs from normal pigs; carrier pigs had moderate enzyme activity, and normal pigs had the lowest enzyme activity. The frequency of affected and carrier pigs in this herd suggested that porcine GM2-gangliosidosis is a familial disease transmitted as an autosomal recessive trait. Cerebral cortical ganglioside was about two times higher than normal in the stillborn and newborn affected pigs and three to four times higher than normal in the 140- to 167-day-old moribund affected pigs. The major cerebral cortical gangliosides in control pigs were GT1, GD1b, GD1a, and GM1, with only trace amounts of GM2-ganglioside. GM2-ganglioside was as much as 58% of the total gangliosides in the brains of moribund affected pigs. The clinical and biochemical features of porcine GM2-gangliosidosis closely resembled those of the juvenile (type AB) form of the disease in man.

Lysosomal enzyme activities in different types of amniotic fluid cells measured by microchemical methods, combined with interference microscopy

In primary amniotic fluid cultures, four distinct types of cells were characterized as epithelioid (E I and E II), fibroblast-like (F), And large cells, Small numbers (1-200) of freeze-dried cells were isolated from colonies of each cell type and analyzed for the activity of three lysosomal enzymes: beta-N-acetylglucosaminidase, beta-galactosidase, and alpha-glucosidase. When expressed per cell, the activities for each of the enzymes were not significantly different among the small types of cells (EI, EII, and F). However, 5 to 10-fold higher enzyme activities were found in the large cells. The dry mass of individual large cells, as measured by microinterferometry, was also 5 to 10 times higher than that of the smaller cell types. When expressed per unit of dry mass, the enzyme activities tested, appeared to be independent of the type of amniotic fluid cell. The significance of this observation for the rapid prenatal diagnosis of metabolic diseases is discussed.

Autoradiographic detection of mucopolysaccharide accumulation in single fibroblasts

A method is described for localizing acid mucopolysaccharides autoradiographically in cultured cells. Normal fibroblasts and fibroblasts, from patients suffering from Mucopolysaccharidosis II disease (MPS II), were cultured for six days in the presence of 35SO4 and one day in unlabelled medium. The cultured cells were transferred to plastic film dish and, after settling, they were rapidly quenched, freeze-dried, fixed in osmium tetroxide vapour and embedded in Epon. Grain counting after autoradiography in 2 mum sections revealed a significant difference (P greater than 0.001) in 35SO4 incorporation in the perinuclear cytoplasm of MPS II cells and control cells grown under the same conditions. Autoradiography was also performed after mixing MPS II cells and control fibroblasts in a ratio 1:1-8 prior to freezing and the same ratio was found between labelled and unlabelled fibroblasts. These results demonstrate the feasibility of the present autoradiographic technique for the detection of the acid mucopolysaccharide storage at the single cell level.