Enzyme reference materials: their place in diagnostic enzymology

The method-dependency of measurements of enzyme activity presents problems of interpretation and comparison. Enzyme calibration materials may provide results in agreed-upon units of catalytic concentration while allowing a choice of routine methods. However, this requires the calibrating and calibrated methods to be equally specific, close agreement in intermethod ratio to exist between the calibrator and target enzyme in serum, and absence of significant sample-dependent variation in the intermethod ratio.

Cloning, characterization, and expression of a cDNA encoding an inducible nitric oxide synthase from the human chondrocyte

Incubation of human articular chondrocytes with interleukin 1 beta results in the time-dependent expression of nitric oxide (NO) synthase. We report here the isolation of a cDNA clone which encodes a protein of 1153 amino acids with a molecular mass of 131,213 Da and a calculated isoelectric point of 7.9. CHO cells transfected with a plasmid harboring this cDNA clone expressed NO synthase activity that was inhibited by some L-arginine analogues. The deduced amino acid sequence of the human chondrocyte inducible NO synthase shows 51% identity and 68% similarity with the endothelial NO synthase and 54% identity and 70% similarity with the neuronal NO synthase. The similarity (88%) between the human chondrocyte NO synthase cDNA sequence and that reported for the murine macrophage suggests that the inducible class of enzyme is conserved between different cell types and across species.

A reference preparation of creatine kinase BB isoenzyme

Creatine kinase (CK; EC 2.7.3.2) catalytic activity in serum is widely measured in clinical chemistry practice and provides information for diagnosis and follow-up in many pathological conditions affecting heart, muscle, and brain. Depending on the organ involved, the predominant CK isoenzyme in serum varies. However, routine methods measure total CK catalytic activity, and standardized methods for doing so have been recommended by the International Federation of Clinical Chemistry and by several national scientific societies. Many commercial kits for those methods are now available. With use of a reference material for CK, commercial reagents can be compared with standardized methods, improving confidence in the results. Here we present a reference preparation of CK consisting of the BB isoenzyme purified from human placentae. We describe the procedure of purification and the properties of the lyophilized preparation of CK-BB, which has been certified by the Community Bureau of Reference of the Commission of the European Communities under the designation CRM 299. The preparation can be used to calibrate assays of the catalytic activity of CK-MM and CK-MB, as well as CK-BB.

Pre-exposure of murine macrophages to lipopolysaccharide inhibits the induction of nitric oxide synthase and reduces leishmanicidal activity

Murine macrophages produce nitric oxide (NO) from L-arginine on stimulation with lipopolysaccharide (LPS), alone or with interferon-gamma (IFN-gamma). The effect of incubation of macrophages with low concentrations of LPS on NO synthesis on subsequent stimulation was investigated, using a murine macrophage cell line, J774, and peritoneal macrophages from CBA mice. Cells which had been incubated with LPS produced significantly lower amounts of NO, and expressed lower levels of NO synthase activity, following stimulation with IFN-gamma and LPS, or with a high concentration of LPS. This effect was not reversed by tumor necrosis factor-alpha. The ability of CBA macrophages to kill the intracellular parasite Leishmania major was markedly reduced by pre-incubation with LPS. Reduced NO production by macrophages previously exposed to LPS is a manifestation of endotoxin tolerance, and may represent an important means of regulation of NO synthesis and thus a survival mechanism for intracellular parasites.

A method for the assay of phosphatidylinositol-specific phospholipase D activity in serum

A reproducible substrate for the assay of phosphatidylinositol-specific phospholipase D (PIPLD) can be prepared by extracting alkaline phosphatase from placental tissue with n-butanol under alkaline conditions. The alkaline phosphatase thus prepared retains its hydrophobic glycan phosphatidylinositol (GPI) anchor and aggregates into high M(r) forms. Incubation with serum hydrolyses the phosphate inositol linkage by PIPLD action, producing a less lipophilic, non-aggregated isoform of alkaline phosphatase. Three methods of measuring the amount of this isoform produced after a timed incubation with serum are described and compared: two types of phase partitioning systems, and electrophoresis and densitometry of the products after gradient-pore electrophoresis. All give comparable and reproducible measurements of PIPLD; however, the electrophoretic method is preferred for routine analysis.

Induction of macrophage parasiticidal activity by Staphylococcus aureus and exotoxins through the nitric oxide synthesis pathway

Murine peritoneal macrophages stimulated in vitro with killed Gram-positive bacteria Staphylococcus aureus or its membrane components in the presence of interferon-gamma (IFN-gamma) expressed high levels of nitric oxide (NO) synthase and produced large amounts of NO in a dose-dependent manner. This is not due to the contamination by Gram-negative endotoxin because the stimulatory activity was not affected by the addition of polymyxin B. The expression of the NO synthase and the synthesis of NO by macrophages stimulated with toxic shock syndrome toxin-1 (TSST), lipoteichoic acid (LTA) or killed whole S. aureus together with IFN-gamma was inhibited by the glucocorticoid, dexamethasone or by the specific inhibitor of NO synthesis, L-N-iminoethyl-ornithine (L-NIO). The exotoxins together with IFN-gamma also activated macrophages to kill the intracellular parasite Leishmania major. The leishmanicidal activity was completely inhibited by L-NIO.

Recombinant migration inhibitory factor induces nitric oxide synthase in murine macrophages

A recombinant form of migration inhibitory factor (MIF) obtained from COS-1 cells transfected with a cDNA library from a human T cell hybridoma is able to activate, in a dose-dependent manner, murine macrophages to express nitric oxide (NO) synthase and to produce high levels of NO in vitro. The time course of the induction of NO synthase is similar to that produced by the IFN-gamma. Enzyme activity peaks at 24 h and is undetectable by 72 h. MIF can synergize with IFN-gamma in the induction of NO synthesis, and the induction of NO synthase by both MIF and IFN-gamma is sensitive to inhibition by dexamethasone. However, unlike IFN-gamma-induced NO generation, MIF is sufficient for the induction of the enzyme, does not synergize with LPS, and is highly sensitive to inhibition by transforming growth factor.

Recombinant migration inhibitory factor induces nitric oxide synthase in murine macrophages

A recombinant form of migration inhibitory factor (MIF) obtained from COS-1 cells transfected with a cDNA library from a human T cell hybridoma is able to activate, in a dose-dependent manner, murine macrophages to express nitric oxide (NO) synthase and to produce high levels of NO in vitro. The time course of the induction of NO synthase is similar to that produced by the IFN-gamma. Enzyme activity peaks at 24 h and is undetectable by 72 h. MIF can synergize with IFN-gamma in the induction of NO synthesis, and the induction of NO synthase by both MIF and IFN-gamma is sensitive to inhibition by dexamethasone. However, unlike IFN-gamma-induced NO generation, MIF is sufficient for the induction of the enzyme, does not synergize with LPS, and is highly sensitive to inhibition by transforming growth factor.

Phase partitioning detects differences between phospholipase-released forms of alkaline phosphatase--a GPI-linked protein

A number of enzymes are known to release alkaline phosphatase and other glycan phosphatidylinositol-anchored proteins from membrane surfaces. We describe a novel approach to detect and measure these activities by partitioning in aqueous phase systems. The procedures avoid the complications of micelle-formation involving hydrophobic molecules that may arise with detergent-based partition systems and can clearly distinguish between inositol-specific phospholipase C and D activities.

Interleukin-4 transgenic mice of resistant background are susceptible to Leishmania major infection

The outcome of cutaneous leishmaniasis is dependent on the balance of Th1 and Th2 cells. In the murine model, Th1 cells are host-protective whereas the Th2 cells are disease-promoting. However, the in vivo role of interleukin-4 (IL-4), a signature product of Th2 cells, is uncertain. We compared the course of Leishmania major infection in the genetically resistant 129/Sv mice and the mutant 129/Sv mice transgenic for the murine IL-4 gene under the control of the immunoglobulin heavy chain enhancer and promoter. We report here that in contrast to their wild-type parents, the IL-4 transgenic mice are susceptible to L. major infection. This is associated with the development of inexorably progressive lesions and parasite loads. Spleen cells from infected transgenic mice produced significantly higher levels of IL-4 but lower amounts of interferon-gamma when stimulated in vitro with leishmanial antigens compared to those from infected normal 129/Sv mice. Furthermore, sera from the infected transgenic mice contained higher levels of IL-4 and IgE than the sera of infected normal 129/Sv mice. These results, therefore, establish in a new animal model that IL-4 promotes disease development in murine cutaneous leishmaniasis.

Perspectives in Alkaline Phosphatase Research

Gene cloning and site-directed mutagenesis have had a profound effect on alkaline phosphatase research. Four distinct structural genes encoding placental, intestinal, and tissue-nonspecific isoenzymes have been cloned, sequenced, and mapped to human chromosomes. Differences in properties between the respective gene products are due to variations in primary structure involving only one, or a few, key amino acid residues. Recognition that alkaline phosphatase belongs to the category of molecules that are localized to cell membranes through a COOH-terminal glycan-phosphatidylinositol anchor provides a basis for understanding the generation of isoforms observed in plasma in disease. Isoforms produced by differential cleavage or preservation of the glycan-phosphatidylinositol anchor may offer new correlations with disease that are of diagnostic value. However, a more important contribution of alkaline phosphatase research to clinical chemistry may prove to be an increased understanding of disease processes at the molecular level.

Perspectives in alkaline phosphatase research

Gene cloning and site-directed mutagenesis have had a profound effect on alkaline phosphatase research. Four distinct structural genes encoding placental, intestinal, and tissue-nonspecific isoenzymes have been cloned, sequenced, and mapped to human chromosomes. Differences in properties between the respective gene products are due to variations in primary structure involving only one, or a few, key amino acid residues. Recognition that alkaline phosphatase belongs to the category of molecules that are localized to cell membranes through a COOH-terminal glycan-phosphatidylinositol anchor provides a basis for understanding the generation of isoforms observed in plasma in disease. Isoforms produced by differential cleavage or preservation of the glycan-phosphatidylinositol anchor may offer new correlations with disease that are of diagnostic value. However, a more important contribution of alkaline phosphatase research to clinical chemistry may prove to be an increased understanding of disease processes at the molecular level.

Changes in enzyme expression related to differentiation and regulatory factors: the acid phosphatase of osteoclasts and other macrophages

Human tartrate-resistant Type 5 acid phosphatase is a unique isoenzyme encoded by a gene located on chromosome 19. It is a member of a widely-distributed and structurally highly-conserved group of iron-containing proteins. It is normally expressed in certain tissue macrophages, notably osteoclasts and alveolar macrophages, but is virtually absent from the precursor monocytes. Factors which enhance or inhibit expression of this specific isoenzyme can be studied in monocytes and osteoclasts cultured in vitro. This provides opportunities to develop the use of Type 5 acid phosphatase as a reporter of pathophysiological events and an essential, though not sufficient, role in bone resorption by osteoclasts has been established by such studies.

A reference preparation of human prostatic acid phosphatase: purification, characterization and field trials

Acid phosphatase has been prepared in an apparently pure state by affinity chromatography from human prostatic tissue. When dissolved in an acidic albumin solution, lyophilized and stored at -20 degrees C for up to 2 years, no time-dependent loss of catalytic activity was detectable in the reconstituted material. Accelerated degradation tests also predicted complete stability. A preliminary distribution of the lyophilized preparation to 143 laboratories confirmed its robustness and demonstrated its potential usefulness as a calibrant to unify the results of different methods of measuring acid phosphatase activity.

Circulating levels of tartrate-resistant acid phosphatase in macrophage-activated lung disease

Tartrate-resistant acid phosphatase (TrACP) is abundant in alveolar macrophages, suggesting that these cells might contribute to the activity of this isoenzyme in sera of patients with conditions characterized by activation of alveolar macrophages. TrACP was therefore measured in patients with pulmonary sarcoidosis and cryptogenic fibrosing alveolitis and compared with values in controls. Since osteoclasts are known to be the main source of TrACP in serum several indices of bone-turnover were also measured: serum bone-specific alkaline phosphatase and urine hydroxyproline:creatinine ratios. Patients with Paget's disease of bone constituted a reference group presenting increased bone turnover. TrACP was not significantly higher in the lung-disease groups than in controls, although there was a strong positive correlation with angiotensin-converting enzyme in pulmonary sarcoidosis. As expected, TrACP activity was elevated together with the other indices of bone turnover in Paget's disease. It is unlikely that TrACP from alveolar macrophages contributes significantly to serum acid phosphatase activity in lung disease.

Regulation and expression of type V (tartrate-resistant) acid phosphatase in human mononuclear phagocytes

Human type V (tartrate-resistant) acid phosphatase belongs to a unique group of iron-binding proteins that includes uteroferrin and other purple phosphatases. The enzyme is normally restricted to osteoclasts and certain phagocytic cells but its rôle is unknown. We show that phosphatase mRNA is abundant in cells of monohistiocytic phenotype and that enzyme expression in cultured human monocyte-derived macrophages is depressed by gamma-interferon and bacterial lipopolysaccharide, agents that promote functional differentiation in these cells. In contrast, phorbol ester, which stimulates intracellular calcium-mediated events, greatly enhances type V phosphatase expression and mRNA abundance. Lymphokine and phorbol ester-modulated expression of type V acid phosphatase expression thus represents a model system for investigating proliferative responses that are specific to cells of the mononuclear macrophage system.

Intracellular regulation of enzyme secretion from rat osteoclasts and evidence for a functional role in bone resorption

1. Osteoclasts are known to secrete acid phosphatase, an iron-containing phosphohydrolase. We have investigated (a) the possibility that acid phosphatase has a functional role in bone resorption and (b) the factors controlling enzyme secretion from isolated rat osteoclasts. 2. Osteoclasts were freshly disaggregated from neonatal rat long bones and dispersed at low densities on devitalized cortical bone slices or on plastic substrate. The levels of acid phosphatase in culture medium were measured spectrophotometrically using 4-nitrophenyl phosphate as hydrolysable substrate. The total plan area of bone resorbed was quantified by scanning electron microscopy in combination with image processing and analysis. 3. Ninety-three per cent of the total enzyme activity detected in the supernatant exposed to bone-osteoclast preparations was resistant to inhibition by D-tartaric acid and was bound to an antibody known to be highly specific for the osteoclast-derived isoenzyme, showing that it originated from osteoclasts. 4. A diminution in the level of supernatant enzyme activity achieved by incubating bone-osteoclast preparations with an antiserum specifically binding the osteoclast isoenzyme, or with a non-competitive inhibitor, molybdate or with competitive inhibitors, disphosphonates, led to a marked reduction of osteoclastic bone resorption. 5. The rate of the enzyme released into the culture supernatant, whether from resorbing (cultured on bone) or non-resorbing (cultured on plastic) osteoclasts declined gradually over 22 h, but that from the former was significantly depressed within the first 30 min of incubation. The supernatant enzyme concentration increased linearly up to 3 h; the levels released from resorbing osteoclasts remained consistently lower than those from non-resorbing cells. 6. Exposure of osteoclasts for 18 h to elevated [Ca2+]o levels produced a concentration-dependent inhibition of supernatant acid phosphatase levels. In the presence of 20 mM [Ca2+]o enzyme secretion from resorbing osteoclasts was significantly lower than that from non-resorbing cells. 7. Exposure of bone-osteoclast preparations to pertussis toxin produced no significant change of acid phosphatase release, while cholera toxin, dibutyryl cyclic AMP and forskolin produced a marked elevation of enzyme secretion. Ionomycin was found to inhibit enzyme release and this was less marked when osteoclasts were incubated on plastic substrate.(ABSTRACT TRUNCATED AT 400 WORDS)

Type 5 acid phosphatase. Sequence, expression and chromosomal localization of a differentiation-associated protein of the human macrophage

The purple acid phosphatases and uteroferrin belong to a diverse multifunctional class of binuclear iron-containing proteins that includes haemerythrin and ribonucleotide reductase. In the pig, uteroferrin has been implicated in the delivery of iron to the foetus, but the role of the related human type 5 acid phosphatase that is principally found in resident tissue macrophages is not yet clear. To define further the function of this metalloenzyme, we have isolated and sequenced a cDNA clone for type 5 acid phosphatase and investigated expression of its gene in human tissues. The phosphatase clone contains an open reading frame of 975 bp and encodes a protein of 325 amino acids, including a signal peptide of 19 residues and two potential sites for N-glycosylation. The type 5 acid phosphatase gene mapped to the short arm of human chromosome 19 and was found to have a restriction fragment length polymorphism on digestion with XbaI. Expression of phosphatase mRNA was restricted to mononuclear phagocytes and the enzyme was induced greater than 20-fold on transformation of normal human monocytes to macrophages by culture in serum-supplemented medium. Type 5 acid phosphatase thus represents a tightly regulated system for the study of molecular events in the differentiation programme of the normal macrophage.

Inhibition of osteoclastic acid phosphatase abolishes bone resorption

Osteoclastic acid phosphatase is a member of a widely-distributed class of iron-containing proteins with acid phosphatase activity. Antibodies raised against one member of this class cross-react with other members from the same or different species, but not with acid phosphatase isoenzymes of different types. When antibodies to one such protein, porcine uteroferrin, are added to medium in which rat osteoclasts are incubated on devitalised cortical bone, both bone resorption and acid phosphatase activity are markedly inhibited. Furthermore, addition of molybdate (an inhibitor of this class of acid phosphatases) also inhibits both bone resorption and enzyme activity. These observations strongly suggest a functional role for osteoclastic acid phosphatase in bone resorption.

An immunoassay of human band 5 ("tartrate-resistant") acid phosphatase that involves the use of anti-porcine uteroferrin antibodies

We describe an immunoassay for human band-5 acid phosphatase in which antibodies to porcine uteroferrin, immobilized on Sepharose particles, are used. Band-5 acid phosphatase is the tartrate-resistant isoenzyme normally expressed in tissue macrophages such as osteoclasts and alveolar macrophages. The immunoassay is similar in reproducibility and sensitivity to assays based on inhibition by d-tartrate. However, compared with the latter, the greater specificity of the immunoassay makes it markedly less susceptible to errors arising from the presence of non-band-5 acid phosphatases, e.g., from prostate.

An immunoassay of human band 5 ("tartrate-resistant") acid phosphatase that involves the use of anti-porcine uteroferrin antibodies

We describe an immunoassay for human band-5 acid phosphatase in which antibodies to porcine uteroferrin, immobilized on Sepharose particles, are used. Band-5 acid phosphatase is the tartrate-resistant isoenzyme normally expressed in tissue macrophages such as osteoclasts and alveolar macrophages. The immunoassay is similar in reproducibility and sensitivity to assays based on inhibition by d-tartrate. However, compared with the latter, the greater specificity of the immunoassay makes it markedly less susceptible to errors arising from the presence of non-band-5 acid phosphatases, e.g., from prostate.