A sensitive cytochemical staining method for glucose-6-phosphate dehydrogenase activity in individual erythrocytes. I. Optimalization of the staining procedure

Glucose-6-phosphate dehydrogenase is dispensable for human erythroid cell differentiation in vitro

Glucose-6-phosphate dehydrogenase (G6PD) deficiency impairs cellular processes under oxidative stress. Individuals with severe G6PD deficiency still produce sufficient numbers of erythrocytes. Nevertheless, the G6PD independence of erythropoiesis remains questionable. This study elucidates the effects of G6PD deficiency on the generation of human erythrocytes. Peripheral blood-derived CD34-positive hematopoietic stem and progenitor cells (HSPCs) of human subjects with normal, moderate, and severe G6PD activities were cultured in two distinct phases: erythroid commitment and terminal differentiation. Regardless of G6PD deficiency, HSPCs were able to proliferate and differentiate into mature erythrocytes. There was no impairment in erythroid enucleation among the subjects with G6PD deficiency. To our knowledge, this study is the first report of effective erythropoiesis independent of G6PD deficiency. The evidence firmly indicates that the population with the G6PD variant could produce erythrocytes to an extent similar to that in healthy individuals.

Impairment of invasion and maturation and decreased selectivity of Plasmodium falciparum in G6PD Viangchan and Mahidol variants

Background

Protection against Plasmodium falciparum is observed in a population deficient in glucose-6-phosphate dehydrogenase (G6PD), particularly in African and Mediterranean regions. However, such protection remains unknown among G6PD-deficient individuals in Southeast Asia.

Methods

In this study, we assessed the invasion and maturation of P falciparum K1 in a culture of erythrocytes isolated from Thai subjects carrying Viangchan (871G > A) and Mahidol (487G > A).

Results

We found that the parasites lost their ability to invade hemizygous and homozygous G6PD-deficient erythrocytes of Viangchan and Mahidol variants in the second and third cycles of intraerythrocytic development. It is interesting to note that P falciparum parasites selectively grew in erythrocytes from hemi- and homozygous genotypes with normal G6PD activity. Moreover, externalization of phosphatidylserine upon P falciparum infection was significantly increased only in Viangchan hemizygous variant cells.

Conclusions

This study is the first to show that blockage of invasion in long-term culture and potentially enhanced removal of parasitized erythrocytes were observed for the first time in erythrocytes from Viangchan and Mahidol G6PD-deficient individuals.

Rapid quantitative assays for glucose-6-phosphate dehydrogenase (G6PD) and hemoglobin combined on a capillary-driven microfluidic chip

Rapid tests for glucose-6-phosphate dehydrogenase (G6PD) are extremely important for determining G6PD deficiency, a widespread metabolic disorder which triggers hemolytic anemia in response to primaquine and tafenoquine medication, the most effective drugs for the radical cure of malaria caused by Plasmodium parasites. Current point-of-care diagnostic devices for G6PD are either qualitative, do not normalize G6PD activity to the hemoglobin concentration, or are very expensive. In this work we developed a capillary-driven microfluidic chip to perform a quantitative G6PD test and a hemoglobin measurement within 2 minutes and using less than 2 μL of sample. We used a powerful microfluidic module to integrate and resuspend locally the reagents needed for the G6PD assay and controls. We also developed a theoretical model that successfully predicts the enzymatic reactions on-chip, guides on-chip reagent spotting and allows efficient integration of multiple assays in miniaturized formats with only a few nanograms of reagents.

Glucose-6-phosphate dehydrogenase deficiency

Glucose 6-phosphate dehydrogenase (G6PD) deficiency is 1 of the commonest human enzymopathies, caused by inherited mutations of the X-linked gene G6PD. G6PD deficiency makes red cells highly vulnerable to oxidative damage, and therefore susceptible to hemolysis. Over 200 G6PD mutations are known: approximately one-half are polymorphic and therefore common in various populations. Some 500 million persons with any of these mutations are mostly asymptomatic throughout their lifetime; however, any of them may develop acute and sometimes very severe hemolytic anemia when triggered by ingestion of fava beans, by any of a number of drugs (for example, primaquine, rasburicase), or, more rarely, by infection. Approximately one-half of the G6PD mutations are instead sporadic: rare patients with these mutations present with chronic nonspherocytic hemolytic anemia. Almost all G6PD mutations are missense mutations, causing amino acid replacements that entail deficiency of G6PD enzyme activity: they compromise the stability of the protein, the catalytic activity is decreased, or a combination of both mechanisms occurs. Thus, genotype-phenotype correlations have been reasonably well clarified in many cases. G6PD deficiency correlates remarkably, in its geographic distribution, with past/present malaria endemicity: indeed, it is a unique example of an X-linked human polymorphism balanced through protection of heterozygotes from malaria mortality. Acute hemolytic anemia can be managed effectively provided it is promptly diagnosed. Reliable diagnostic procedures are available, with point-of-care tests becoming increasingly important where primaquine and its recently introduced analog tafenoquine are required for the elimination of malaria.

Comparison of Spectrophotometry, Chromate Inhibition, and Cytofluorometry Versus Gene Sequencing for Detection of Heterozygously Glucose-6-Phosphate Dehydrogenase-Deficient Females

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most common enzyme deficiency worldwide. Detection of heterozygously deficient females can be difficult as residual activity in G6PD-sufficient red blood cells (RBCs) can mask deficiency. In this study, we compared accuracy of 4 methods for detection of G6PD deficiency in females. Blood samples from females more than 3 months of age were used for spectrophotometric measurement of G6PD activity and for determination of the percentage G6PD-negative RBCs by cytofluorometry. An additional sample from females suspected to have G6PD deficiency based on the spectrophotometric G6PD activity was used for measuring chromate inhibition and sequencing of the G6PD gene. Of 165 included females, 114 were suspected to have heterozygous deficiency. From 75 females, an extra sample was obtained. In this group, mutation analysis detected 27 heterozygously deficient females. The sensitivity of spectrophotometry, cytofluorometry, and chromate inhibition was calculated to be 0.52 (confidence interval [CI]: 0.32-0.71), 0.85 (CI: 0.66-0.96), and 0.96 (CI: 0.71-1.00, respectively, and the specificity was 1.00 (CI: 0.93-1.00), 0.88 (CI: 0.75-0.95), and 0.98 (CI: 0.89-1.00), respectively. Heterozygously G6PD-deficient females with a larger percentage of G6PD-sufficient RBCs are missed by routine methods measuring total G6PD activity. However, the majority of these females can be detected with both chromate inhibition and cytofluorometry.

In Situ Localization of Transketolase Activity in Epithelial Cells of Different Rat Tissues and Subcellularly in Liver Parenchymal Cells

Metabolic mapping of enzyme activities (enzyme histochemistry) is an important tool to understand (patho)physiological functions of enzymes. A new enzyme histochemical method has been developed to detect transketolase activity in situ in various rat tissues and its ultrastructural localization in individual cells. In situ detection of transketolase is important because this multifunctional enzyme has been related with diseases such as cancer, diabetes, Alzheimer's disease, and Wernicke-Korsakoff's syndrome. The proposed method is based on the tetrazolium salt method applied to unfixed cryostat sections in the presence of polyvinyl alcohol. The method appeared to be specific for transketolase activity when the proper control reaction is performed and showed a linear increase of the amount of final reaction product with incubation time. Transketolase activity was studied in liver, small intestine, trachea, tongue, kidney, adrenal gland, and eye. Activity was found in liver parenchyma, epithelium of small intestine, trachea, tongue, proximal tubules of kidney and cornea, and ganglion cells in medulla of adrenal gland. To demonstrate transketolase activity ultrastructurally in liver parenchymal cells, the cupper iron method was used. It was shown that transketolase activity was present in peroxisomes and at membranes of granular endoplasmic reticulum. This ultrastructural localization is similar to that of glucose-6-phosphate dehydrogenase activity, suggesting activity of the pentose phosphate pathway at these sites. It is concluded that the method developed for in situ localization of transketolase activity for light and electron microscopy is specific and allows further investigation of the role of transketolase in (proliferation of) cancer cells and other pathophysiological processes.

Maintaining Specimen Integrity for G6PD Screening by Cytofluorometric Assays

Cytochemical staining remains an efficient way of identifying females who are heterozygous for the X chromosome-linked glucose-6-phosphate dehydrogenase (G6PD) gene. G6PD is highly polymorphic with certain alleles resulting in low intracellular G6PD activity in red blood cells. Low intracellular G6PD activity is associated with a risk of severe hemolysis when exposed to an oxidative stress such as fava beans, certain drugs and infections. Heterozygous females express the enzyme from both X-chromosome alleles resulting in two red blood cell populations each with G6PD enzyme characteristics representative of each allele; for example, normal and deficient. Cytochemical staining is the only way to determine the relative representation of each allele in red blood cells, a feature that is critical when assessing the risk for severe hemolysis when exposed to an oxidant such as the anti-malarial drug primaquine. This letter discusses red blood cell integrity with respect to the cytofluorometric assays for G6PD activity. An approach to making this test more robust is suggested. The approach makes this test more reliable and extends its use to a broader range of blood specimens.

Comparison of quantitative and qualitative tests for glucose-6-phosphate dehydrogenase deficiency

A barrier to eliminating Plasmodium vivax malaria is inadequate treatment of infected patients. 8-Aminoquinoline–based drugs clear the parasite; however, people with glucose-6-phosphate dehydrogenase (G6PD) deficiency are at risk for hemolysis from these drugs. Understanding the performance of G6PD deficiency tests is critical for patient safety. Two quantitative assays and two qualitative tests were evaluated. The comparison of quantitative assays gave a Pearson correlation coefficient of 0.7585 with significant difference in mean G6PD activity, highlighting the need to adhere to a single reference assay. Both qualitative tests had high sensitivity and negative predictive value at a cutoff G6PD value of 40% of normal activity if interpreted conservatively and performed under laboratory conditions. The performance of both tests dropped at a cutoff level of 45%. Cytochemical staining of specimens confirmed that heterozygous females with > 50% G6PD-deficient cells can seem normal by phenotypic tests.

G6PD testing in support of treatment and elimination of malaria: recommendations for evaluation of G6PD tests

Malaria elimination will be possible only with serious attempts to address asymptomatic infection and chronic infection by both Plasmodium falciparum and Plasmodium vivax. Currently available drugs that can completely clear a human of P. vivax (known as "radical cure"), and that can reduce transmission of malaria parasites, are those in the 8-aminoquinoline drug family, such as primaquine. Unfortunately, people with glucose-6-phosphate dehydrogenase (G6PD) deficiency risk having severe adverse reactions if exposed to these drugs at certain doses. G6PD deficiency is the most common human enzyme defect, affecting approximately 400 million people worldwide.Scaling up radical cure regimens will require testing for G6PD deficiency, at two levels: 1) the individual level to ensure safe case management, and 2) the population level to understand the risk in the local population to guide Plasmodium vivax treatment policy. Several technical and operational knowledge gaps must be addressed to expand access to G6PD deficiency testing and to ensure that a patient's G6PD status is known before deciding to administer an 8-aminoquinoline-based drug.In this report from a stakeholder meeting held in Thailand on October 4 and 5, 2012, G6PD testing in support of radical cure is discussed in detail. The focus is on challenges to the development and evaluation of G6PD diagnostic tests, and on challenges related to the operational aspects of implementing G6PD testing in support of radical cure. The report also describes recommendations for evaluation of diagnostic tests for G6PD deficiency in support of radical cure.

Evaluation of the phenotypic test and genetic analysis in the detection of glucose-6-phosphate dehydrogenase deficiency

BACKGROUND

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is particularly prevalent in historically malaria-endemic countries. Although most individuals with G6PD deficiency are asymptomatic, deficiency can result in acute haemolytic anaemia after exposure to oxidative agents. A reliable test is necessary for diagnosing the deficiency to prevent an acute haemolytic crisis following, for example, anti-malarial treatment. The aim of this study was to investigate which method was the best predictor of this disorder.

METHODS

The present study investigated four G6PD activity detections (fluorescence spot (FS), methaemoglobin reduction (MR), biochemical and cytochemical test). These methods accompanied with mutation analysis of blood samples were taken from 295 apparently healthy individuals with unknown G6PD deficiency status.

RESULTS

Molecular characterization of 295 Thai adults revealed an overall prevalence of 14.2%. The G6PD Viangchan (871 G>A) was the most common (83.3%), followed by G6PD Mahidol (487G>A) (11.9%), and G6PD Union (1360 C>T) (4.8%). There were two cases of G6PD deficiency carrying the double mutations of Viangchan (871G > A)-Mahidol (487G > A) and Viangchan (871G > A)-Union (1360C > T). In comparison, the prevalence of G6PD deficiency was 6.1% by FS test and 7.1% by MR test. G6PD activity was 11 ± 2.5 IU/gHb in non-deficient females (mean ± SD), and 10.9 ± 0.6 IU/gHb in non-deficient males. The upper and lower limit cut-off points for partial and severe deficiency in adults were 5.7 IU/gHb (60% of the normal mean) and 0.95 IU/gHb (10% of the normal mean), respectively. All hemizygote, homozygote and double mutations were associated with severe enzyme deficiency (the residual enzyme activity <10% of the normal mean), whereas only 14.3% of the heterozygote mutations showed severe enzyme deficiency. Based on the cut-off value <5.7 IU/gHb, the quantitative G6PD assay diagnosed 83% of cases as G6PD-deficient. Using a cut-off number of negative cell >20% in the cytochemical assay to define G6PD deficiency, the prevalence of G6PD deficiency was closest to the molecular analysis (12.9% G6PD-deficient) compared to the others methods.

CONCLUSION

The cytochemical method is a significant predictor of this disease, while FS and MR test are recommended for the detection of severe G6PD deficiency in developing countries.

Cryopreservation of glucose-6-phosphate dehydrogenase activity inside red blood cells: developing a specimen repository in support of development and evaluation of glucose-6-phosphate dehydrogenase deficiency tests

Background

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is a common human enzyme deficiency. It is characterized by abnormally low levels of G6PD activity. Individuals with G6PD deficiency are at risk of undergoing acute haemolysis when exposed to 8‒aminoquinoline-based drugs, such as primaquine. For this reason it is imperative to identify individuals with G6PD deficiency prior to administering these anti-malarial drugs. There is a need for the development and evaluation of point-of-care G6PD deficiency screening tests suitable for areas of the developing world where malarial treatments are frequently administered. The development and evaluation of new G6PD tests will be greatly assisted with the availability of specimen repositories.

Methods

Cryopreservation of erythrocytes was evaluated as a means to preserve G6PD activity. Blood specimens from 31 patients including ten specimens with normal G6PD activity, three with intermediate activity, and 18 with deficient activity were cryopreserved for up to six months.

Results

Good correlation in G6PD activity between fresh and cryopreserved specimens (R² = 0.95). The cryopreserved specimens show an overall small drop in mean G6PD activity of 0.23 U/g Hb (P=0.23). Cytochemical staining showed that intracellular G6PD activity distribution within the red blood cell populations is preserved during cryopreservation. Furthermore, the mosaic composition of red blood cells in heterozygous women is also preserved for six months or more. The fluorescent spot and the BinaxNOW qualitative tests for G6PD deficiency also showed high concordance in G6PD status determination between cryopreserved specimens and fresh specimens.

Conclusions

A methodology for establishing a specimen panel for evaluation of G6PD tests is described. The approach is similar to that used in several malaria research facilities for the cryopreservation of parasites in clinical specimens and axenic cultures. Specimens stored in this manner will aid both the development and evaluation of current and emerging G6PD tests. The availability of G6PD tests is a critical bottleneck to broader access to drugs that confer radical cure of Plasmodium vivax, a requirement for elimination of malaria.

Population screening for glucose-6-phosphate dehydrogenase deficiencies in Isabel Province, Solomon Islands, using a modified enzyme assay on filter paper dried bloodspots

Background

Glucose-6-phosphate dehydrogenase deficiency poses a significant impediment to primaquine use for the elimination of liver stage infection with Plasmodium vivax and for gametocyte clearance, because of the risk of life-threatening haemolytic anaemia that can occur in G6PD deficient patients. Although a range of methods for screening G6PD deficiency have been described, almost all require skilled personnel, expensive laboratory equipment, freshly collected blood, and are time consuming; factors that render them unsuitable for mass-screening purposes.

Methods

A published WST8/1-methoxy PMS method was adapted to assay G6PD activity in a 96-well format using dried blood spots, and used it to undertake population screening within a malaria survey undertaken in Isabel Province, Solomon Islands. The assay results were compared to a biochemical test and a recently marketed rapid diagnostic test.

Results

Comparative testing with biochemical and rapid diagnostic test indicated that results obtained by filter paper assay were accurate providing that blood spots were assayed within 5 days when stored at ambient temperature and 10 days when stored at 4 degrees. Screening of 8541 people from 41 villages in Isabel Province, Solomon Islands revealed the prevalence of G6PD deficiency as defined by enzyme activity < 30% of normal control was 20.3% and a prevalence of severe deficiency that would predispose to primaquine-induced hemolysis (WHO Class I-II) of 6.9%.

Conclusions

The assay enabled simple and quick semi-quantitative population screening in a malaria-endemic region. The study indicated a high prevalence of G6PD deficiency in Isabel Province and highlights the critical need to consider G6PD deficiency in the context of P. vivax malaria elimination strategies in Solomon Islands, particularly in light of the potential role of primaquine mass drug administration.

Glucose-6-phosphate dehydrogenase deficiency and malaria: cytochemical detection of heterozygous G6PD deficiency in women

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is a X-chromosomally transmitted disorder of the erythrocyte that affects 400 million people worldwide. Diagnosis of heterozygously-deficient women is complicated: as a result of lyonization, these women have a normal and a G6PD-deficient population of erythrocytes. The cytochemical assay is the only reliable assay to discriminate between heterozygously-deficient women and non-deficient women or homozygously-deficient women. G6PD deficiency is mainly found in areas where malaria is or has been endemic. In these areas, malaria is treated with drugs that can cause (severe) hemolysis in G6PD-deficient individuals. A cheap and reliable test is necessary for diagnosing the deficiency to prevent hemolytic disorders when treating malaria. In this review, it is concluded that the use of two different tests for diagnosing men and women is the ideal approach to detect G6PD deficiency. The fluorescent spot test is inexpensive and easy to perform but only reliable for discriminating hemizygous G6PD-deficient men from non-deficient men. For women, the cytochemical assay is recommended. However, this assay is more expensive and difficult to perform and should be simplified into a kit for use in developing countries.

Biochemical and cytochemical evaluation of heterozygote individuals with glucose-6-phosphate dehydrogenase deficiency

The aim of this study was to diagnose heterozygous glucose-6-phosphate dehydrogenase (G6PD) deficient females by an inexpensive cytochemical G6PD staining method that is easy to perform, allowing diagnosis of G6PD deficiency without cumbersome genetic analysis. Three subject groups were included in the study. The first group consisted of 15 hemizygous deficient males. The second and the third group were composed of 15 heterozygous deficient females and 15 healthy individuals, respectively. Biochemical determination and cytochemical staining of G6PD activity were performed in samples of all subjects. Results obtained with the cytochemical staining method correlated significantly with the biochemical data (p < 0.001), but a only 51-68% of the erythrocytes were stained positively in females with normal biochemical G6PD activity despite their having a G6PD-deficient child. This observation clearly indicates that these individuals are heterozygously deficient. These findings show that the cytochemical staining method to detect G6PD activity in erythrocytes is reliable, sensitive and specific and is superior to the biochemical method. Therefore, this method can be used routinely to detect heterozygous G6PD deficiency.

Improved localization of glucose-6-phosphate dehydrogenase activity in cells with 5-cyano-2,3-ditolyl-tetrazolium chloride as fluorescent redox dye reveals its cell cycle-dependent regulation

Since the introduction of cyano-ditolyl-tetrazolium chloride (CTC), a tetrazolium salt that gives rise to a fluorescent formazan after reduction, it has been applied to quantify activity of dehydrogenases in individual cells using flow cytometry. Confocal laser scanning microscopy (CLSM) showed that the fluorescent formazan was exclusively localized at the surface of individual cells and not at intracellular sites of enzyme activity. In the present study, the technique has been optimized to localize activity of glucose-6-phosphate dehydrogenase (G6PD) intracellularly in individual cells. Activity was demonstrated in cultured fibrosarcoma cells in different stages of the cell cycle. Cells were incubated for the detection of G6PD activity using a medium containing 6% (w/v) polyvinyl alcohol, 5 mM CTC, magnesium chloride, sodium azide, the electron carrier methoxyphenazine methosulphate, NADP, and glucose-6-phosphate. Before incubation, cells were permeabilized with 0.025% glutaraldehyde. Fluorescent formazan was localized exclusively in the cytoplasm of fibrosarcoma cells. The amount of fluorescent formazan in cells increased linearly with incubation time when measured with flow cytometry and CLSM. When combining the Hoechst staining for DNA with the CTC method for the demonstration of G6PD activity, flow cytometry showed that G6PD activity of cells in S phase and G2/M phase is 27 +/- 4% and 43 +/- 4% higher, respectively, than that of cells in G1 phase. CLSM revealed that cells in all phases of mitosis as well as during apoptosis contained considerably lower G6PD activity than cells in interphase. It is concluded that posttranslational regulation of G6PD is responsible for this cell cycle-dependent activity.

Ultrastructural localization of xanthine oxidoreductase activity in isolated rat liver cells

Xanthine oxidoreductase (XOR) can exist in a dehydrogenase form (XD) and an oxidase form (XO). The D-form uses NAD as cofactor and the O-form uses oxygen as second substrate and produces oxygen radicals. Both enzymes have a high affinity for hypoxanthine and xanthine as substrate and produce uric acid, a potent antioxidant. In the present study, XOR activity was demonstrated with the ferricyanide method in permeabilized isolated rat liver cells at the electron microscopical level. Moreover, ultrastructural localization of XO activity in these cells was studied with the cerium salt method. Activity of both XOR and XO was found in matrix and core of peroxisomes of rat liver parenchymal cells. Only XOR activity was present as well in the cytoplasm of rat liver parenchymal cells. In Kupffer cells and sinusoidal endothelial cells, XOR activity was demonstrated in vesicles and occasionally on granular endoplasmic reticulum. XO activity was not found in Kupffer cells and sinusoidal endothelial cells. The presence of uric acid oxidase activity in matrix and core of peroxisomes as was found previously suggests further breakdown of purines to allantoin in peroxisomes. It is suggested that the major function of XOR activity in the cytoplasm of rat liver parenchymal cells and in sinusoidal cells is not the production of oxygen radicals, but rather the production of uric acid which can act as a potent antioxidant.

Low glucose-6-phosphate dehydrogenase enzyme activity level at the time of hemolysis in a male neonate with the African type of deficiency

Glucose-6-phosphate dehydrogenase (G6PD) levels are not usually drawn in the evaluation of black neonates with hyperbilirubinemia because of the oft-stated opinion that the levels may be normal at the time of hemolysis and thus will be misleading. In fact, this opinion is not applicable to newborns as many studies have shown that deficiency in the conjugating ability of the liver, not hemolysis, is the main cause of neonatal jaundice associated with G6PD deficiency. We present a case report of a neonate with brisk hemolysis and hyperbilirubinemia in whom the G6PD level was abnormally low at the time of the hemolytic episode. DNA analysis showed him to have the A-(202A,376G) variant and, as well, the UGT1A1 promoter repeat polymorphism associated with Gilbert's disease. This case, as well as a review of the literature, indicates that enzyme levels are not normal in patients with G6PD A- who are undergoing hemolysis.

Quantitative cytochemical analysis of glucose-6-phosphate dehydrogenase activity in living isolated hepatocytes of European flounder for rapid analysis of xenobiotic effects

There is a great need for rapid but reliable assays to determine quantitatively effects of xenobiotics on biological systems in environmental research. Hepatocytes of European flounder are sensitive to low-dose toxic stress. Glucose-6-phosphate dehydrogenase (G6PDH) is the major source of NADPH in cells and is therefore of major importance for NADPH-dependent xenobiotic biotransformation and defense against toxic injury. These facts prompted us to develop a sensitive cytochemical method to detect G6PDH activity in living isolated flounder hepatocytes using the tetrazolium salt method. The intact plasma membrane did not appear to be a barrier for substrate, co-enzyme, and dye molecules because the intracellular enzyme reaction started immediately when incubation medium was added and could be monitored in real time per individual cell using image analysis. The reaction was effectively stopped for end point measurements by using 4% formaldehyde in 0.1 M phosphate buffer (pH 5.3). The final reaction product, formazan, was stable in hepatocytes for at least 12 days at 4C. This is the first time that a chromogenic histochemical assay is applied to living cells. This approach provides an easy tool for large-scale screening of xenobiotic metabolism and cellular stress defense.

Localization of glucose-6-phosphate dehydrogenase activity on ribosomes of granular endoplasmic reticulum, in peroxisomes and peripheral cytoplasm of rat liver parenchymal cells

Glucose-6-phosphate dehydrogenase activity has been localized ultrastructurally in fixed tissues. Activity was found in particular in association with ribosomes of granular endoplasmatic reticulum. Biochemical studies indicated that glucose-6-phosphate dehydrogenase activity is also present in the cytoplasm and in peroxisomes. Fixation may be held responsible for selective inactivation of part of glucose-6-phosphate dehydrogenase activity. In the present study, we applied the ferricyanide method for the demonstration of glucose-6-phosphate dehydrogenase activity in unfixed cryostat sections of rat liver in combination with the semipermeable membrane technique and in isolated rat liver parenchymal cells. Isolated liver parenchymal cells were permeabilized with 0.025% glutaraldehyde after NADP+ protection of the active site of glucose-6-phosphate dehydrogenase. This treatment resulted in only slight inactivation of glucose-6-phosphate dehydrogenase activity. The composition of the incubation medium was optimized on the basis of rapid light microscopical analysis of the formation of reddish-brown final reaction product in sections. With the optimized method, electron dense reaction product was observed in cryostat sections on granular endoplasmic reticulum, in mitochondria and at the cell border. However, the ultrastructural morphology was rather poor. In contrast, the morphology of incubated isolated cells was preserved much better. Electron dense precipitate was found on ribosomes of the granular endoplasmic reticulum, in peroxisomes and the cytoplasm, particularly at the periphery of cells. In conclusion, our ultrastructural study clearly demonstrates that it is essential to use mildly-fixed cells to allow detection of glucose-6-phosphate dehydrogenase activity in all cellular compartments where activity is present.

Enzyme activities of six different dehydrogenases in Ehrlich ascites cells measured by flow cytometry

Flow cytometric measurements of the activities of lactate dehydrogenase, glucose-6-phosphate dehydrogenase, isocitrate dehydrogenase, glycerol-3-phosphate dehydrogenase, succinate dehydrogenase and glutamate dehydrogenase in single Ehrlich ascites tumour cells are described using a tetrazolium salt/fluorescent formazan reaction. Applying cyano-ditolyl-tetrazolium chloride (CTC) as redox dye indicating enzyme reaction, and DAPI as a fluorochrome for nuclear DNA staining, the bivariate flow cytometric assay of enzyme activity and cell cycle analysis was established. Furthermore, adopting the calibration procedure reported formerly, consisting of biochemical determination and flow cytometry of the same sample performed parallelly, the enzyme activities were expressed in biochemical units. The dehydrogenase activities found in Ehrlich ascites cells were 97.5 fmol H2 per average positive cell during 5 min for lactate dehydrogenase, 69.0, 10.6, 25.3, 29.7, and 19.0 fmol H2 per average positive cell during 20 min for glucose-6-phosphate dehydrogenase, isocitrate dehydrogenase, glycerol-3-phosphate dehydrogenase, succinate dehydrogenase and glutamate dehydrogenase, respectively. This quantitative procedure can offer an alternative analytic tool for enzyme cytology.

Enzyme cytochemistry of unfixed leukocytes and bone marrow cells using polyvinyl alcohol for the diagnosis of leukemia

Cytochemical methods for the demonstration of enzyme activities in blood and bone marrow cells were systematically improved by the addition of an inert polymer, polyvinyl alcohol (PVA), to the incubation medium and by using optimized reaction media. The methods investigated were tetrazolium salt methods for lactate, glucose-6-phosphate, succinate and glutamate dehydrogenase, the indoxyl-tetrazolium salt method for alkaline phosphatase, the diaminobenzidine method for peroxidase, and diazonium salt methods for chloroacetate esterase, beta-glucosaminidase, beta-glucuronidase, acid phosphatase, and dipeptidylpeptidase II and IV. PVA in the media preserved the morphology of cells very well and prevented leakage of large molecules such as enzymes from the cells. Therefore, fixation or long periods of air-drying prior to incubation leading to substantial loss of enzyme activity could be avoided. A brief period of drying (2 min at 37 degrees C) of the cell preparations just before the incubation was sufficient for making the cells permeable. Localization of enzyme activities was very precise and precipitation of the final reaction product was confined to sites which are known to contain the enzyme under study (granules, mitochondria, lysosomes). These advantages advocate the use of PVA in haematological enzyme cytochemistry and especially for diagnosis of leukemia.

Comparison between the chromate inhibition test and a cytochemical method for the determination of glucose-6-phosphate dehydrogenase deficiency in erythrocytes

The sensitivity and specificity of the chromate inhibition test for the determination of glucose-6-phosphate dehydrogenase (G6PD) deficiency in erythrocytes were compared with a cytochemical staining method. Fifty blood samples were used in a double blind study. The samples were selected from 600 blood samples on the basis of two biochemical criteria, viz. either G6PD activity less than 4.8 IU/g Hb as analysed spectrophotometrically and/or G6PD activity less than glutathione reductase (GSSG-R) activity. The cytochemical assay was taken as reference because it has been proved to be sensitive and specific for the detection of heterozygous and homo/hemizygous forms of deficiency. Cytochemically, one hemizygously deficient patient, 19 heterozygotes and 30 normals were detected. When applying the chromate inhibition test a somewhat different result was obtained with the same samples: one of the 30 normals was classified as heterozygously deficient (3% false positives) and 5 of the 19 heterozygously deficient patients were classified as normal (26% false negatives). It is concluded that the chromate inhibition test is a more sensitive biochemical test than the fluorescence spot test or spectrophotometric assays. However, it is less reliable than the cytochemical test for the detection of heterozygously G6PD deficient patients.

Detection of glucose-6-phosphate dehydrogenase deficiency in erythrocytes: a spectrophotometric assay and a fluorescent spot test compared with a cytochemical method

The results of a quantitative spectrophotometric enzyme assay, a fluorescent spot test and a cytochemical assay for glucose-6-phosphate dehydrogenase deficiency were compared systematically. The high sensitivity of the spectrophotometric assay and the fluorescent spot test in the detection of severely deficient individuals was confirmed. For the detection of heterozygote females, however both tests were unreliable; the sensitivities of the fluorescent spot test and the spectrophotometric assay being 32% and 11% respectively. Specificities for both tests were high (99%). Introduction of the ratio of glucose-6-phosphate dehydrogenase and pyruvate kinase (G-6-PD/PK ratio) activities increased the sensitivity of the spectrophotometric assay to nearly 100%. It is concluded that the fluorescent spot test should be used for the diagnosis of G-6-PD deficiency in developing countries; whereas if spectrophotometric enzyme assays are available, the G-6-PD/PK ratio should always be performed. In cases where the ratio is less than 0.70, cytochemical analysis is indicated.

Reaction rate studies of glucose-6-phosphate dehydrogenase activity in sections of rat liver using four tetrazolium salts

The reaction rate of glucose-6-phosphate dehydrogenase activity in liver sections from fed and starved rats has been monitored by the continuous measurement at 37 degrees C of the reaction product as it is formed using scanning and integrating microdensitometry. Control media lacked either substrate or both substrate and coenzyme. All reactions were nonlinear; however, subtraction of either of the controls from the test response produced linearity. Differing responses in sections of livers from fed and fasted rats indicate that the appropriate control medium for use in the assay of this dehydrogenase is one lacking both substrate and coenzyme rather than a medium containing coenzyme. The reaction rate was the same with each of the final acceptors. Problems with the diffusion of the formazan of BPST and with the failure to precipitate the formazan of Neotetrazolium make Tetranitro BT and Nitro BT the tetrazolium salts of choice in quantitative dehydrogenase assays.

A sensitive cytochemical staining method for glucose-6-phosphate dehydrogenase activity in individual erythrocytes. II. Further improvements of the staining procedure and some observations with glucose-6-phosphate dehydrogenase deficiency

A cytochemical method for staining glucose-6-phosphate dehydrogenase (G6PD) activity in individual erythrocytes as reported previously has been optimized further by the incorporation of a number of technical improvements. Analysis of the enzyme content in erythrocytes of normal individuals as well as patients suffering from G6PD deficiency in the homozygous and heterozygous forms allows these three categories to be easily distinguished. Considerable formazan production occurs in most erythrocytes of a healthy person and only a small percentage of the cells appeared to be negative. Two cell populations of almost equal size could be discerned in heterozygotes for G6PD deficiency, one completely negative, the other with a variable amount of formazan per cell. Homozygous deficiency leads to a population of negative cells with a few positive ones after staining. It is concluded that a reliable method has been found for analysis of G6PD deficiency in erythrocytes at the single cell level.

Diffusion during dehydrogenase reactions: the effects of intermediate electron acceptors

A hamster cheek pouch model has been used to study the diffusion of reactants from the epithelium into adjacent muscle and connective tissue during the histochemical demonstration of glucose-6-phosphate dehydrogenase activity. The effects of the addition of intermediate electron acceptors to the incubation medium varied considerably from one acceptor to another, but were independent of the grade of polyvinyl alcohol incorporated into the medium. Menadione was the least effective intermediate both in transferring reducing equivalents from the primary dehydrogenase to Neotetrazolium chloride and in preventing diffusion. Phenazine methosulphate, Methylene Blue and Thionin were more efficient intermediates. Nevertheless, considerable diffusion occurred in the presence of Phenazine methosulphate, although very little diffusion was detectable with either of the thiazine dyes. It is suggested that these differences are related to different modes and sites of action of the carriers.

Cytophotometry of glucose-6-phosphate dehydrogenase activity in individual cells

With the aid of thin films of polyacrylamide gel containing purified glucose-6-phosphate dehydrogenase subjected to cytochemical procedures for the enzyme using tetranitro blue tetrazolium, arbitrary units of integrated absorbance obtained with a Barr & Stroud GN5 cytophotometer were converted into units of enzyme activity. This conversion enabled cytochemical data to be compared directly with biochemical values. The conversion was applied to the cytochemical estimation of glucose-6-phosphate dehydrogenase activity in isolated rat hepatocytes, mouse oocytes, rabbit thymocytes, human granulocytes and human fibroblasts. Several control procedures were performed to confirm the admissibility of this conversion, such as: the estimation of the absorption characteristics of the formazans of tetranitro blue tetrazolium both in solution and precipitated in biological specimens; the linearity of the relationship between the increase of absorbance and incubation time; and the effect of different incubation conditions on the amount of specific formazan production.

Enzyme cytochemical staining of individual cells with the use of a polyacrylamide carrier. Studies on the synthetizing reaction technique, the indigogenic method, the metal salt method, the post-azo-coupling technique, and the tetrazolium salt technique

A recently developed method for the (quantitative) demonstration of glucose-6-phosphate dehydrogenase activity in individual cells with the use of a polyacrylamide carrier has been extended for other enzyme cytochemical techniques. Isolated hepatocytes have been incorporated in the matrix of a thin transparent polyacrylamide gel prior to incubation in a cytochemical medium. The techniques which have been applied are the synthetizing reaction technique for glycogen phosphorylase, the indigogenic method for nonspecific esterase, the metal salt method for glucose-6-phosphatase, the post-azo-coupling technique for acid phosphatase, and the tetrazolium salt technique for succinate and lactate dehydrogenase activities. In all cases a few major problems which occur in the cytochemistry on single cells seem to be solved. The morphology is very well preserved, the final reaction product seems to be precipitated at the expected site of enzyme activity and the coloured end-product is highly specific for the enzyme activity to be studied, as has been demonstrated well with control experiments. The conclusion is reached, therefore, that this relatively simple device can be used routinely for the optimalization of enzyme cytochemistry of single cells.