Methodology of the quantitative cytochemical analysis of single or small numbers of cultured cells

Metachromatic leukodystrophy genotypes in The Netherlands reveal novel pathogenic ARSA variants in non-Caucasian patients

Metachromatic leukodystrophy (MLD) is an autosomal recessively inherited sulfatide storage disease caused by deficient activity of the lysosomal enzyme arylsulfatase A (ASA). Genetic analysis of the ARSA gene is important in MLD diagnosis and screening of family members. In addition, more information on genotype prevalence will help interpreting MLD population differences between countries. In this study, we identified 31 different ARSA variants in the patient cohort (n = 67) of the Dutch expertise center for MLD. The most frequently found variant, c.1283C > T, p.(Pro428Leu), was present in 43 (64%) patients and resulted in a high prevalence of the juvenile MLD type (58%) in The Netherlands. Furthermore, we observed in five out of six patients with a non-Caucasian ethnic background previously unreported pathogenic ARSA variants. In total, we report ten novel variants including four missense, two nonsense, and two frameshift variants and one in-frame indel, which were all predicted to be disease causing in silico. In addition, one silent variant was found, c.1200C > T, that most likely resulted in erroneous exonic splicing, including partial skipping of exon 7. The c.1200C > T variant was inherited in cis with the pseudodeficiency allele c.1055A > G, p.(Asn352Ser) + ∗96A > G. With this study we provide a genetic base of the unique MLD phenotype distribution in The Netherlands. In addition, our study demonstrated the importance of genetic analysis in MLD diagnosis and the increased likelihood of unreported, pathogenic ARSA variants in patients with non-Caucasian ethnic backgrounds.

Prenatal Diagnosis of Lysosomal Storage Disorders Using Chorionic Villi

Prenatal enzymatic diagnosis for an array of lysosomal storage disorders (LSDs) can be performed accurately, provided that a confirmed diagnosis by biochemical/molecular study in the index case is available and a strict defined protocol, specific to each individual disorder is followed. The present chapter describes the protocols for reliable and accurate prenatal enzymatic diagnoses by fluorometric and spectrophotometric methods of lysosomal storage disorders: Gaucher, Fabry, Pompe, Niemann Pick A/B, Tay Sach, Sandhoff, GM1, Mucoplysaccharidoses, Wolman, Krabbe, Metachromatic leukodystrophy, and Batten diseases using uncultured chorionic villi samples. The biological reference intervals for enzyme levels in normal and affected fetuses are given for interpretation of prenatal results. It is imperative to establish normal reference interval in each laboratory to take into account the local environment, technical variations, and different ethnicities. Besides, enzyme activity in the fetus should be represented as percentage of the mean activity of enzyme of normal fetuses. The pitfalls and challenges in prenatal diagnosis as well as technical problems in performing enzyme assays are also discussed to help the reader in standardization and performing the assays for correct diagnosis.

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)

First-trimester diagnosis of Lesch-Nyhan syndrome

Chorionic villi were sampled at 8-9 weeks' gestation in four women whose fetuses were at risk for Lesch-Nyhan syndrome. Radiochemical assay of hypoxanthine phosphoribosyl transferase activity and fetal sexing (in two fetuses by means of a Y chromosome specific cDNA probe) showed that three fetuses were affected. The biochemical findings were confirmed after therapeutic abortion in two cases and spontaneous abortion in the third. Chorion biopsy and ultramicroscale enzymology may be a suitable alternative to recombinant-DNA-based methods for first-trimester diagnosis in selected diseases where the abnormal gene product is an enzyme expressed in the chorion by the 8th week of pregnancy.

An automatic pulsed laser microfluorometer with high spatial and temporal resolution

The paper describes an automatic pulsed laser microfluorometer with high spatial and temporal resolution, developed in our laboratories. The instrument consists of: (i) a nitrogen-laser-pumped dye-laser for the excitation of the fluorescence, (ii) a microscope with additional optics to focus the excitation beam on the sample and to collect the fluorescence, (iii) filters or monochromators to select the output wavelength, (iv) a fast photomultiplier tube to detect the signal, and (v) a dual time-scale microprocessor-controlled signal averager for the acquisition and processing of the signal. Examples are given that show the potential of the time-resolved fluorescence microscopy in studying, quantitatively and qualitatively, the properties of fluorescent molecules.

Microenzymatic assays for lysosomal enzymes in primary amniotic fluid cell cultures

A study of three lysosomal enzymes (hexosaminidase, beta-galactosidase and alpha-galactosidase) in normal primary amniotic fluid cell cultures using a microenzymatic assay is presented. No difference in enzyme activity was found between primary and amniotic cell cultures in passage number one. A progressive change in the proportions of hexosaminidase A and hexosaminidase B with time was demonstrated in culture. The feasibility of this procedure for the early prenatal diagnosis of disorders due to lysosomal enzyme deficiency is discussed.

A scanning microinterferometer with correction of errors caused by overlapping 'ghost' images

An experimental setup has been built to correct the errors caused by overlapping 'ghost' images when scanning and integrating measurements are carried out with the Jamin-Libedef interference microscope. First a reference field with the object, producing the 'ghost' image, is scanned and the values of the optical path difference (OPD) of each point in the reference field are stored in a computer. Subsequently, the OPD of the object to be measured is calculated for each point by adding the measuring result to the average OPD of five points, located around the corresponding point in the reference field. The applicability of the setup has been tested by measurements with Sepharose beads, Hela cells and the Zeiss microinterference refractometer. The difference between measurements on the same object with and without overlapping 'ghost' image was about 10%. The reproducibility was tested by repeated measurements on the same cell whereby a standard deviation of 1.1% was found.

Separation of acid and neutral alpha-glucosidase isoenzymes from fetal and adult tissues, cultivated fibroblasts and amniotic fluid cells by DEAE-cellulose and sephadex G-100 column chromatography

Isoenzymes of alpha-glucosidases (EC 3.2.1.20) from various human organs and body fluids from fetuses and adults were separated by DEAE-cellulose column chromatography and gel filtration using Sephadex G-100. A minicolumn (0.35 X 2.5 cm) was used for the DEAE-cellulose column chromatography of extracts from tissues as well as cultivated cells of skin fibroblasts and amniotic fluid. The enzyme activity in the eluates was measured by the use of a methylumbelliferyl derivative as substrate and a very sensitive Microscope fluorimeter. In most tissue samples alpha-glucosidase was eluted mainly as a single peak when monitored at acid pH and as two peaks when the activity was measured at neutral pH in both columns. Another small peak representing alpha-glucosidase was found in fresh extracts of cultured cells on DEAE-cellulose columns. Neutral alpha-glucosidase especially in fibroblasts was extremely sensitive to storage at -20 degrees C. DEAE-cellulose column chromatography of plasma and amniotic fluid showed similar elution patterns of alpha-glucosidase. Differences were noticed in the elution pattern of urine from infants and adults. The tissue distribution and the different characteristics of the enzyme in samples of various origins and ages were discussed.

A rapid and simple microfractionation method for the analysis of hexosaminidase A and B activities in small numbers of cultured (amniotic fluid) cells

A simple and rapid microfractionation procedure is described which enables the separate analysis of hexosaminidase A and B activities in as little as a few hundred to a thousand cultured human cells. 25 microliter cell homogenate is added to a pellet of DEAE-cellulose and 50 microliter 0.1 M NaCl in buffer. After centrifugation the hex B and I forms are measured in the supernatant, whereas hex A is determined by direct incubation of the DEAE pellet with methylumbelliferyl substrate. The reliability and reproducibility of the method is compared with that of heat inactivation and column chromatography. The application of the procedure is illustrated by analyses of fibroblasts and cultured amniotic fluid cells from pregnancies at risk for Tay-Sachs disease and by serum assays for the diagnosis and heterozygote testing of this disease.

[Microchemical investigation of alpha D-glucosidases using 4-methylumnelliferyl- and 2-naphthyl-alpha-d-glucoside (author's transl)]

In crude homogenates prepared from freeze-dried cryostate sections of various rat organs the Km and Vmax of acid and neutral alpha-glucosidase as well as the effect of the pH, substrate and enzyme concentration and the incubation time on the activity were determined fluorometrically with 4-methylumbelliferyl- and 2-naphthyl alpha-d-glucoside as substrates. On the basis of the biochemical data 2 assays were developed for the microchemical measurement of both alpha-glucosidases in groups of epithelial cells isolated from freeze dried cryostate sections of the epididymis, jejunum, ilium, liver and kidney of suckling and adult rats. The rate of hydrolysis of 2-naphthyl and 4-methylumbelliferyl alpha-d-glucoside differs moderately. However, due to the higher sensitivity of 4-methylumbelliferone the methylumbelliferyl derivative is preferable especially for the evaluation of alpha-d-glucosidases in cells with low enzyme activity.

[Azoindoxyl methods for the investigation of hydrolases. II. Biochemical and histochemical studies of acid beta-galactosidase (author's transl)]

The determination of various reaction constants yields the following assay for the photometric evaluation of acid beta-galactosidase (measurement of the azoindoxyl dye at 540 nm after extraction with dimethylformamide or -acetamide): 1.5 mM 5-Br-4-Cl-3-indolyl-beta-D-galactoside (1 mg dissolved in 0.05 ml dimethylformamide) and 0.01-0.015 ml hexazotized p-rosaniline/ml in 0.1 M citric acid-phosphate buffer, pH 4. By means of this procedure it becomes evident that the activity of the enzyme differs considerably in various rat organs; NaCl does not influence acid beta-galactosidase. -- Similar results were obtained with the indigogenic method; indigo can be dissolved and measured photometrically as the azoindoxyl dye. The enzyme is suppressed by high concentrations of hexazotized p-roaniline to 50%; low concentrations do not inhibit; the same is true for ferricyanide-ferrocyanide employed in the indigogenic media. -- The effect of glutar- and formaldehyde on acid beta-galactosidase cannot be investigated with the azoindoxyl reaction since the azoindoxyl dye partially withstands extraction from fixed blocks of tissue. On the basis of the biochemical findings the azoindoxyl technique can be recommended for the histochemical demonstration of acid beta-galactosidase: 7.5 mg (1.5 mM) 5-Br-4-Cl-3-indolyl-beta-D-galactoside (dissolved in 0.25 ml dimethylformamide) and 0.05-0.15 ml hexazonium-p-rosaniline in 10 ml 0.1 M citric acid-phosphate buffer, pH 4. After incubation the sections can be treated with osmium tetroxide followed by dehydration and mounting in resins or can be mounted without prior osmification of the azoindoxyl dye in glycerin jelly. The osmium chelate resists treatment with organic solvents; the stability of the chelate depends on the concentration of hexazotized p-rosaniline. After fixation in glutaraldehyde or in a mixture of form- and glutaraldehyde acid beta-galactosidase can be exactly localized in the lysosomes of many rat organs. In comparison with the indigogenic, the metal precipitation and the simultaneous azocoupling reactions for the in situ detection of acid beta-galactosidase the azoindoxyl procedure is superior if fixed material is used; it is equivalent or inferior in connection with membrane technique. The biochemical azoindoxyl assay represents a useful method for combined qualitative and quantitative studies of acid beta-galactosidase.

Cytofluorometric quantification of the activity and reaction kinetics of acid phosphatase

This paper describes how fluorogenic substrates derived from naphthol AS can be used for the microscopic demonstration and cytofluorometric quantification of the activity and reaction kinetics of acid phosphatase in single living cells. A special study has been made of acid naphthol AS-BI phosphatase. However, the method can be extended to other hydrolytic enzymes. The method is sensitive and accurate because: quantification of very low enzyme activity is possible; the reaction kinetics can be evaluated with a good degree of precision inasmuch as the initial reaction velocity is derived over short times; there is an absence of distributional error; and the errors due to extra-cellular diffusion of the hydrolysed substrate, to photodecomposition, and to autofluorescence can be contained within very narrow limits. The procedures for determining enzyme activity and reaction kinetics, and the instrumental characteristics and devices required for carrying out these measurements, are described. Some possible applications are indicated.

Rapid prenatal diagnosis of GM1-gangliosidosis using microchemical methods

Prenatal diagnoses were established in 3 pregnancies at risk for GM1-gangliosidosis at 9, 10, and 12 days after amniocentesis. Beta-galactosidase activities in cultured amniotic fluid cells were determined by microchemical assays in cell homogenates and in isolated groups of 10--30 freeze-dried cells. The latter method requires only a few hundred cells growing in one or more clones and will usually allow a diagnosis within 9--12 days after amniocentesis.

Prenatal diagnosis of genetic disorders

Three hundred and fifty pregnancies were monitored by transabdominal amniocentesis in the fourteenth to sixteenth week of gestation followed by karyotyping or biochemica assays of cultured amniotic fluid cells and analysis of alpha-fetoprotein in the amniotic fluid supernatant. The pregnancy was interrupted in 36 cases (10%) either becasue of a fetal abnormality or the presence of a male fetus in pregnancies at risk for an X-linked disease. Four chromosomal aberrations were found in 87 pregnancies tested because of advanced maternal age. In 101 pregnancies with a recurrence risk of Down's syndrome, 2 fetuses with an abnormal karyotype were detected. In 11 cases, in which 1 parent was a carrier of a balanced translocation, 2 unbalanced fetal karyotypes were found. Fetal chromosome studies in 43 pregancies at risk for an X-linked disease indicated the presence of a male fetus in 21 cases. Prenatal diagnosis of 11 different metabolic diseases was performed in a total of 34 cases. Microchemical techniques were used to allow completion of the diagnosis of seven different enzyme deficiencies within 9 to 22 days after amniocentesis. Alpha-fetoprotein assay in the amniotic fluid supernatant of 47 pregnancies at risk for an open neural tube defect resulted in the detection of 3 anencephalic fetuses during the second half of pregnancy. The safety and reliability of amniocentesis and the possible effects on the outcome of pregnancy are evaluated. Prenatal diagnosis offers a promising alternative for parents who are at risk of having a child with a genetic disease which can be detected in amniotic fluid or in cultured amniotic fluid cells.