Alkaline phosphatase as a reporter of cancerous transformation

Enzyme-Activatable Near-Infrared Photosensitizer with High Enrichment in Tumor Cells Based on a Multi-Effect Design

Enzyme-activatable near-infrared (NIR) fluorescent probes and photosensitizers (PSs) have emerged as promising tools for molecular imaging and photodynamic therapy (PDT). However, in living organisms selective retention or even enrichment of these reagents after enzymatic activation at or near sites of interest remains a challenging task. Herein, we integrate non-covalent and covalent retention approaches to introduce a novel "1-to-3" multi-effect strategy-one enzymatic stimulus leads to three types of effects-for the design of an enzyme-activatable NIR probe or PS. Using this strategy, we have constructed an alkaline phosphatase (ALP)-activatable NIR fluorogenic probe and a NIR PS, which proved to be selectively activated by ALP to switch on NIR fluorescence or photosensitizing ability, respectively. Additionally, these reagents showed significant enrichment (over 2000-fold) in ALP-overexpressed tumor cells compared to the culture medium, accompanied by massive depletion of intracellular thiols, the major antioxidants in cells. The investigation of this ALP-activatable NIR PS in an in vivo PDT model resulted in complete suppression of HeLa tumors and full recovery of all tested mice. Encouragingly, even a single administration of this NIR PS was sufficient to completely suppress tumors in mice, demonstrating the high potential of this strategy in biomedical applications.

Alkaline phosphatase combined with γ-glutamyl transferase is an independent predictor of prognosis of hepatocellular carcinoma patients receiving programmed death-1 inhibitors

Background

Immunotherapy plays an increasingly critical role in the systemic treatment of HCC. This current study aimed to establish a novel prognostic predictor of Programmed death 1 (PD-1) inhibitor therapy in hepatocellular carcinoma (HCC) independent of Child-Pugh grade.

Methods

Our study screened patients with HCC who received PD-1 inhibitors at Tongji Hospital Affiliated to Tongji Medical College of Huazhong University of Science and Technology from January 2018 to December 2020. ALG grade was determined by the patient's serum ALP and GGT levels before the initiation of PD-1 inhibitors. The endpoints of our study were overall survival (OS) and progression free survival (PFS). Follow-up ended at May 31, 2022.

Results

Eighty- five patients (77 with Child-Pugh grade A, 8 with Child-Pugh grade B at baseline) were enrolled according to the inclusion criteria. Patients with Child-Pugh grade A achieved longer PFS and OS than those with Child-Pugh grade B. Patients with ALG grade 3 at baseline showed worse tumor response and poorer survival, and ALG grade could stratify patients with Child-Pugh grade A into subgroups with significantly different prognosis.

Conclusions

ALG grade, combining ALP and GGT, is a novel and readily available prognostic marker and the predictive effect of ALG grade on patient prognosis is independent of Child-Pugh grade.

Evaluation of Placental Alkaline Phosphatase Expression as A Potential Target of Solid Tumors Immunotherapy by Using Gene and Protein Expression Repositories

Placental alkaline phosphatase (PLAP) is a membrane enzyme mainly expressed in the placenta. PLAP is shown to be expressed in ovarian cancer (OV), however, there is little known about its expression in other cancers. Using gene and protein expression deposited data, we surveyed PLAP expression across malignant and normal human tissues to explore the potential of PLAP as an immunotherapy target. We detected more than two-fold increased PLAP expression in multiple solid tumors including ovarian cancer, testicular germ cell tumors (TGCT), and uterine corpus endometrial carcinoma (UCEC) compared with matched normal tissues. We also showed association of PLAP expression with high mortality pancreatic adenocarcinoma (PAAD). Altogether, our results suggest that PLAP can be a promising target for immunotherapy of multiple cancers, especially OV, TGCT, and UCEC.

Hypophosphatasia: A Unique Disorder of Bone Mineralization

Hypophosphatasia (HPP) is a rare genetic disease characterized by a decrease in the activity of tissue non-specific alkaline phosphatase (TNSALP). TNSALP is encoded by the ALPL gene, which is abundantly expressed in the skeleton, liver, kidney, and developing teeth. HPP exhibits high clinical variability largely due to the high allelic heterogeneity of the ALPL gene. HPP is characterized by multisystemic complications, although the most common clinical manifestations are those that occur in the skeleton, muscles, and teeth. These complications are mainly due to the accumulation of inorganic pyrophosphate (PPi) and pyridoxal-5′-phosphate (PLP). It has been observed that the prevalence of mild forms of the disease is more than 40 times the prevalence of severe forms. Patients with HPP present at least one mutation in the ALPL gene. However, it is known that there are other causes that lead to decreased alkaline phosphatase (ALP) levels without mutations in the ALPL gene. Although the phenotype can be correlated with the genotype in HPP, the prediction of the phenotype from the genotype cannot be made with complete certainty. The availability of a specific enzyme replacement therapy for HPP undoubtedly represents an advance in therapeutic strategy, especially in severe forms of the disease in pediatric patients.

Molecular Genetics of Hypophosphatasia and Phenotype-Genotype Correlations

Hypophosphatasia (HPP) is due to deficient activity of the tissue-nonspecific isoenzyme of alkaline phosphatase (TNAP). This enzyme cleaves extracellular substrates inorganic pyrophosphates (PPi), pyridoxal-5'-phosphate (PLP), phosphoethanolamine (PEA) and nucleotides, and probably other substrates not yet identified. During the last 15 years the role of TNAP in mineralization, and to a less degree in brain, has been investigated, providing hypotheses and explanations for both bone and neuronal HPP phenotypes. ALPL, the gene encoding TNAP, is subject to many mutations, mostly missense mutations. A few number of mutations are recurrently found and may be quite frequent in particular populations. This reflects founder effects. The great variety of mutations results in a great number of compound heterozygous genotypes and in highly variable clinical expressivity. A good correlation was observed between the severity of the disease and in vitro enzymatic activity of the mutant protein measured after site-directed mutagenesis. Many missense mutations found in severe hypophosphatasia produced a mutant protein that failed to reach the cell membrane , was accumulated in the cis-Golgi and was subsequently degraded in the proteasome. Missense mutations located in the catalytic site or in the homodimer interface were often shown by site-directed mutagenesis to have a dominant negative effect. Currently molecular diagnosis of HPP is based on the sequencing of the coding sequence of ALPL that allows detection of approximately 95 % of mutations in severe cases. In addition, other genes, especially genes encoding proteins involved in the regulation of extracellular PPi concentration, could modify the phenotype (modifier genes).

A human monoclonal antibody specific to placental alkaline phosphatase, a marker of ovarian cancer

Placental alkaline phosphatase (PLAP) is a promising ovarian cancer biomarker. Here, we describe the isolation, affinity-maturation and characterization of two fully human monoclonal antibodies (termed B10 and D9) able to bind to human PLAP with a dissociation constant (Kd) of 10 and 30 nM, respectively. The ability of B10 and D9 antibodies to recognize the native antigen was confirmed by Biacore analysis, FACS and immunofluorescence studies using ovarian cancer cell lines and freshly-frozen human tissues. A quantitative biodistribution study in nude mice revealed that the B10 antibody preferentially localizes to A431 tumors, following intravenous administration. Anti-PLAP antibodies may serve as a modular building blocks for the development of targeted therapeutic products, armed with cytotoxic drugs, radionuclides or cytokines as payloads.

Reduced L/B/K alkaline phosphatase gene expression in renal cell carcinoma: plausible role in tumorigenesis

Renal cell carcinoma (RCC) is the most common kidney cancer in adults. Although several genes have been found to be involved in carcinogenesis of RCC, more great efforts are needed to identify new genes which are responsible for the process. Clear cell RCC, originates from proximal tubule cells, is the most common pathological type of RCC. Alkaline phosphatase (ALP) is a marker enzyme of brush border membrane of proximal tubular cells. Our previous studies showed a significant decreased activity of Liver/Bone/Kidney (L/B/K) alkaline phosphatase in RCC. In the present study, we explored the molecular basis of the decreased activity of ALP in RCC. Immunohistochemistry, immunofluorescence and flow cytometry analysis showed decreased ALP protein in RCC. Additionally, real time PCR documented significantly reduced ALP gene expression (P = 0.009). Moreover, RCC cell lines (ACHN and A498) transfected with full length L/B/K cDNA showed decreased migratory property as well as viability of these cells as compared with controls (P = 0.000). Further, L/B/K ALP cDNA transfected cells (ACHN and A498) showed significant increased apoptosis as compared to control (P = 0.000). These findings suggest the new role of ALP in cell viability and apoptosis and involvement in RCC tumorigenesis. However, further studies are needed to explore the exact molecular mechanism.

Cellular function and molecular structure of ecto-nucleotidases

Ecto-nucleotidases play a pivotal role in purinergic signal transmission. They hydrolyze extracellular nucleotides and thus can control their availability at purinergic P2 receptors. They generate extracellular nucleosides for cellular reuptake and salvage via nucleoside transporters of the plasma membrane. The extracellular adenosine formed acts as an agonist of purinergic P1 receptors. They also can produce and hydrolyze extracellular inorganic pyrophosphate that is of major relevance in the control of bone mineralization. This review discusses and compares four major groups of ecto-nucleotidases: the ecto-nucleoside triphosphate diphosphohydrolases, ecto-5'-nucleotidase, ecto-nucleotide pyrophosphatase/phosphodiesterases, and alkaline phosphatases. Only recently and based on crystal structures, detailed information regarding the spatial structures and catalytic mechanisms has become available for members of these four ecto-nucleotidase families. This permits detailed predictions of their catalytic mechanisms and a comparison between the individual enzyme groups. The review focuses on the principal biochemical, cell biological, catalytic, and structural properties of the enzymes and provides brief reference to tissue distribution, and physiological and pathophysiological functions.

Anti-proliferative effect of levamisole on human myeloma cell lines in vitro

Levamisole has been employed as an immunomodulatory agent in conjunction with 5-fluorouracil in the treatment of colon cancer relapse. At high doses, levamisole has been shown to have both anti-cancer and immunosuppressive activities. In vitro, levamisole has been shown to potentiate the anti-proliferative effect of 5-fluorouracil in several types of tumor cell lines; however, its mechanism of cytotoxic action and its molecular targets in cells remains to be elucidated. Here, the effect of levamisole on the proliferative response of the human multiple myeloma cell lines RPMI 8226 and U266B1 was studied in vitro. Treatment of both lines with varying concentrations of levamisole for 48 and 72 h in culture resulted in a significant inhibition of proliferation (unstimulated) in a dose-dependent manner, as assessed by an 3-[(4,5-dimethylthiazole-2-yl)-2,5-diphenyltetrazolium bromide dye assay. Furthermore, measurements of cell viability (using a trypan blue dye exclusion assay) clearly showed that the levamisole was cytotoxic. The preliminary evaluation of the mechanism of this cytotoxic effect revealed that this drug induced apoptosis in the myeloma cells, as evidenced by increases in the levels of DNA fragmentation, release of cytochrome c into the cytoplasm, and the activation of caspase-3 activity in the cells. The results of these studies strongly suggest that levamisole could be a potent anti-myeloma agent and might be considered in the treatment of multiple myeloma in the future.

Hypophosphatasia

Hypophosphatasia is a rare inherited disorder characterized by defective bone and tooth mineralization, and deficiency of serum and bone alkaline phosphatase activity. The frequency of the disease has been estimated to be one in 100 000 for severe forms, but mild forms of hypophosphatasia may be more common. The symptoms are highly variable in their clinical expression, which ranges from stillbirth without mineralized bone to early tooth loss without bone symptoms. The transmission of severe forms is autosomal recessive, while milder forms may be transmitted as dominant or recessive autosomal traits. The diagnosis is based on serum alkaline phosphatase assay and molecular analysis of the liver/bone/kidney alkaline phosphatase gene (ALPL). Currently, there is no treatment for the disease. Over the past 10 years, great progress has been made in understanding the structure of tissue non-specific alkaline phosphatase, its function in bone mineralization, and the effect of ALPL mutations responsible for hypophosphatasia.

Effects of Magnesium Ions on Thermal Inactivation of Alkaline Phosphatase

The effect of Mg2+ on the thermal inactivation and unfolding of calf intestinal alkaline phosphatase has been studied at different temperatures and Mg2+ concentrations. Increasing the Mg2+ concentration in the denatured system significantly enhanced the inactivation and unfolding of the enzyme during thermal inactivation. The analysis of the kinetic course of substrate reaction during thermal inactivation showed that at 47 degrees C the increased free Mg2+ concentration caused the inactivation rate to increase. Increasing the temperature strengthened the effect of Mg2+ on the thermal inactivation. Control experiment showed that this is not due to salt effect. The time course of fluorescence emission spectra showed that the emission maximum for Mg2+-containing system was always higher than that of Mg2+-free system, and the higher temperature enhanced this difference. In addition, Mg2+ also enhanced the unfolding rate of the enzyme at 47 degrees C. The potential biological significance of these results are discussed.

Alkaline phosphatase retained in HepG2 hepatocarcinoma cells vs. alkaline phosphatase released to culture medium: difference of aberrant glycosylation

Liver tissue is the source of 90% of serum alkaline phosphatase (AP). The serum levels and structures of tumor marker proteins change under many disease conditions as well as cancer. The study was aimed at determining the type of alkaline phosphatase (AP) present in HepG2 hepatocellular carcinoma cell line. Alkaline phosphatase rich extracts of healthy human liver, HepG2 hepatocarcinoma cells, as well as the condition medium of HepG2 cells were prepared by extraction with 40% n-butanol and 30-50% acetone precipitation, and subjected to various chromatographic procedures. Lectin affinity chromatography of the samples with concanavalin A-Sepharose 4B showed considerable differences in the elution patterns. Non-denaturing polyacrylamide gel electrophoresis of the culture medium yielded a relatively slow migrating band of activity that coincided with none of the three bands of activity produced by the normal liver extract, nor with the bands of the cell pellet extract. Inhibition patterns were established by measuring the enzyme activities in the presence of varying concentrations of L-phenylalanine, L-leucine, L-homoarginine, and levamisole. The APs from the cell line were neuraminidase sensitive. According to the results the main AP produced and released to the medium by HepG2 cell line is an aberrantly glycosylated tissue non-specific AP. In addition, the differences between the cell-pellet AP and the culture medium AP seemed to stem from different sugar moieties in their structures.

The 1.9 A crystal structure of heat-labile shrimp alkaline phosphatase

Alkaline phosphatases are non-specific phosphomonoesterases that are distributed widely in species ranging from bacteria to man. This study has concentrated on the tissue-nonspecific alkaline phosphatase from arctic shrimps (shrimp alkaline phosphatase, SAP). Originating from a cold-active species, SAP is thermolabile and is used widely in vitro, e.g. to dephosphorylate DNA or dNTPs, since it can be inactivated by a short rise in temperature. Since alkaline phosphatases are zinc-containing enzymes, a multiwavelength anomalous dispersion (MAD) experiment was performed on the zinc K edge, which led to the determination of the structure to a resolution of 1.9 A. Anomalous data clearly showed the presence of a zinc triad in the active site, whereas alkaline phosphatases usually contain two zinc and one magnesium ion per monomer. SAP shares the core, an extended beta-sheet flanked by alpha-helices, and a metal triad with the currently known alkaline phosphatase structures (Escherichia coli structures and a human placental structure). Although SAP lacks some features specific for the mammalian enzyme, their backbones are very similar and may therefore be typical for other higher organisms. Furthermore, SAP possesses a striking feature that the other structures lack: surface potential representations show that the enzyme's net charge of -80 is distributed such that the surface is predominantly negatively charged, except for the positively charged active site. The negatively charged substrate must therefore be directed strongly towards the active site. It is generally accepted that optimization of the electrostatics is one of the characteristics related to cold-adaptation. SAP demonstrates this principle very clearly.

Inhibitor profiles of alkaline phosphatases in bovine preattachment embryos and adult tissues

The alkaline phosphatases are a small family of isozymes. Bovine preattachment embryos transcribe mRNA for two tissue-specific alkaline phosphatases (TSAP2 and TSAP3) beginning at the 4- and 8-cell stages. Whereas no mRNA has been detected in oocytes, there is maternally inherited alkaline phosphatase activity. It is not known which isozyme(s) is responsible for the maternal activity or when TSAP2 and TSAP3 form functional protein. No antibodies are available that recognize the relevant bovine alkaline phosphatases. Therefore, sensitivity to heat and chemical inhibition was used to separate the different isozymes. By screening tissues, it was determined that the bovine tissue-nonspecific alkaline phosphatase (TNAP) is inactivated by low temperatures (65C) and low concentrations of levamisole (<1 mM), whereas bovine tissue-specific isozymes require higher temperatures (90C) and levamisole concentrations (>5 mM). Inhibition by L-homoarginine and L-phenylalanine was less informative. Cumulus cells transcribe two isozymes and the pattern of inhibition suggested heterodimer formation. Inhibition of alkaline phosphatase in bovine embryos before the 8-cell stage indicated the presence of only TNAP. At the 16-cell stage the pattern was consistent with TNAP plus TSAP2 or -3 activity, and in morulae and blastocysts the pattern indicated that the maternal TNAP is fully supplanted by TSAP2 or TSAP3.

Primary structure of cold-adapted alkaline phosphatase from a Vibrio sp. as deduced from the nucleotide gene sequence

Alkaline phosphatases (AP) are widely distributed in nature, and generally have a dimeric structure. However, there are indications that either monomeric or multimeric bacterial forms may exist. This paper describes the gene sequence of a psychrophilic marine Vibrio AP, previously shown to be particularly heat labile. The kinetic properties were also indicative of cold adaptation. The amino acid sequence of the Vibrio G15-21 AP reveals that the residues involved in the catalytic mechanism, including those ligating the metal ions, have precedence in other characterized APs. Compared with Escherichia coli AP, the two zinc binding sites are identical, whereas the metal binding site, normally occupied by magnesium, is not. Asp-153 and Lys-328 of E. coli AP are His-153 and Trp-328 in Vibrio AP. Two additional stretches of amino acids not present in E. coli AP are found inserted close to the active site of the Vibrio AP. The smaller insert could be accommodated within a dimeric structure, assuming a tertiary structure similar to E. coli AP. In contrast the longer insert would most likely protrude into the interface area, thus preventing dimer formation. This is the first primary structure of a putative monomeric AP, with indications as to the basis for a monomeric existence. Proximity of the large insert loop to the active site may indicate a surrogate role for the second monomer, and may also shape the catalytic as well as stability characteristics of this enzyme.

Structural evidence for a functional role of human tissue nonspecific alkaline phosphatase in bone mineralization

The human tissue nonspecific alkaline phosphatase (TNAP) is found in liver, kidney, and bone. Mutations in the TNAP gene can lead to Hypophosphatasia, a rare inborn disease that is characterized by defective bone mineralization. TNAP is 74% homologous to human placental alkaline phosphatase (PLAP) whose crystal structure has been recently determined at atomic resolution (Le Du, M. H., Stigbrand, T., Taussig, M. J., Ménez, A., and Stura, E. A. (2001) J. Biol. Chem, 276, 9158-9165). The degree of homology allowed us to build a reliable TNAP model to investigate the relationship between mutations associated with hypophosphatasia and their probable consequences on the activity or the structure of the enzyme. The mutations are clustered within five crucial regions, namely the active site and its vicinity, the active site valley, the homodimer interface, the crown domain, and the metal-binding site. The crown domain and the metal-binding domain are mammalian-specific and were observed for the first time in the PLAP structure. The crown domain contains a collagen binding loop. A synchrotron radiation x-ray fluorescence study confirms that the metal in the metal-binding site is a calcium ion. Several severe mutations in TNAP occur around this calcium site, suggesting that calcium may be of critical importance for the TNAP function. The presence of this extra metal-binding site gives new insights on the controversial role observed for calcium.

Crystal structure of alkaline phosphatase from human placenta at 1.8 A resolution. Implication for a substrate specificity

Human placental alkaline phosphatase (PLAP) is one of three tissue-specific human APs extensively studied because of its ectopic expression in tumors. The crystal structure, determined at 1.8-A resolution, reveals that during evolution, only the overall features of the enzyme have been conserved with respect to Escherichia coli. The surface is deeply mutated with 8% residues in common, and in the active site, only residues strictly necessary to perform the catalysis have been preserved. Additional structural elements aid an understanding of the allosteric property that is specific for the mammalian enzyme (Hoylaerts, M. F., Manes, T., and Millán, J. L. (1997) J. Biol. Chem. 272, 22781-22787). Allostery is probably favored by the quality of the dimer interface, by a long N-terminal alpha-helix from one monomer that embraces the other one, and similarly by the exchange of a residue from one monomer in the active site of the other. In the neighborhood of the catalytic serine, the orientation of Glu-429, a residue unique to PLAP, and the presence of a hydrophobic pocket close to the phosphate product, account for the specific uncompetitive inhibition of PLAP by l-amino acids, consistent with the acquisition of substrate specificity. The location of the active site at the bottom of a large valley flanked by an interfacial crown-shaped domain and a domain containing an extra metal ion on the other side suggest that the substrate of PLAP could be a specific phosphorylated protein.

Effect of synthetic lipids on apoptosis and expression of alkaline phosphatase in B-lymphocytes: influence on lipopolysaccharide action

Synthetic lipids were examined for their ability to mimic or to antagonize lipopolysaccharide (LPS) action in murine B-lymphocytes. Several recognized effects of LPS were analyzed: prevention of spontaneous apoptosis, expression of alkaline phosphatase (ALP) and stimulation of proliferation. Three synthetic lipids were used for that purpose: a lipopeptide (compound MTPP) which carries non-hydroxylated fatty acids, and is thus unrelated to LPS, and two glycolipids with hydroxylated fatty acids (compounds D2 and PPDm2-B), structurally related to the lipid A region of enterobacterial and Rhodopseudomonas LPS, respectively. We found that the ability of these lipids to induce LPS-like responses was not correlated with their structural analogy with LPS. Thus, the lipopeptide, MTPP, mimicked LPS in the three activities, whereas the glycolipid, D2, did not. In contrast, the ability of synthetic lipids to block LPS effects was correlated with their structural analogy with LPS. We thus observed that compound D2 selectively blocked LPS-induced ALP expression and that PPDm2-B selectively inhibited LPS-induced prevention of apoptosis. These synthetic lipids could therefore be useful for studying the LPS-mediated signals involved in B-cell activation and apoptosis.

Specific determination of germ cell alkaline phosphatase for early diagnosis and monitoring of seminoma: performance and limitations of different analytical techniques

Two-dimensional electrophoresis, ion-exchange chromatography and immunoassay were evaluated in order to improve the diagnostic specificity of the germ cell specific isoenzyme of alkaline phosphatase (GCAP) for the detection of seminoma. Assessment of GCAP is hampered by its structural heterogeneity and low serum concentration. The structural heterogeneity of GCAP from seminoma tissue could be clearly visualized by two-dimensional electrophoresis. We inferred that it depended on allelic amino acid substitutions, varying sialylation and differential cleavage of the membrane anchor. The allelic variability of GCAP affects the accuracy of immunological measurements. However, immunoassay was found to be the only technique sensitive enough to assess GCAP in serum. The elevated GCAP levels in 15% of healthy blood donors were shown to be correlated with smoking. Further studies clarifying how to interpret the values measured in smokers are prerequisite for the introduction of GCAP as a serum marker for seminoma. In the future, GCAP might be utilized for the detection of carcinoma in situ (CIS) cells in ejaculate. Assessment of the enhanced expression of cellular GCAP by CIS cells exfoliated into ejaculate could be a means for noninvasive, early diagnosis that presumably will not be hampered by the patient's smoking habits.

Expression of alkaline phosphatase by a B-cell hybridoma and its modulation during cell growth and apoptosis

The 7TD1 B-cell hybridoma was found to spontaneously express alkaline phosphatase (ALP), an enzyme which is produced by splenic B lymphocytes once optimally activated. Determination of ALP levels during cell growth and departure to apoptosis showed fluctuations. Following a temporary increase within the first 24 h, enzyme expression was maintained at high levels during the early proliferation stage, and then declined from 3 to 4 days in mid-exponential phase to basal levels at day 6 when living cells were no longer detectable and the apoptotic process was completed. The protein synthesis inhibitor, cycloheximide (1 microg/ml), decreased ALP production while stimulating a strong apoptosis of 7TD1 cells, within 4 h. Aphidicolin (1 microg/ml) maintained ALP production and provoked a release of ALP activity into the surrounding medium; it also induced apoptosis, but with a 24 h delay. Quantification of apoptosis and ALP expression by flow cytometry, after simultaneous staining of DNA with Hoechst 33342 and ALP with naphthol AS-TR phosphate/Fast Red RC fluorescent reagent, revealed cell cycle modulation of ALP expression, its activity increasing as 7TD1 cells progressed from G1 phase into S and G2/M phases of the cell cycle in control as well as in drug-treated cells. Kinetics of drug-induced apoptosis and higher expression of ALP associated preferentially with active cell growth during the prevention stage of apoptosis suggested a possible link between cellular ALP expression and cell survival.

Separation of the two most closely related isoenzymes of alkaline phosphatase by two-dimensional electrophoresis

Seminoma is the most frequent testicular germ cell tumor. While effective curative treatment of the disease is available today, there is to date no tumor marker suited for the diagnosis and follow-up. Several authors have suggested that the germ-cell-specific isoenzyme of alkaline phosphatase (GCAP) might be valuable for this purpose. GCAP shows 98% sequence homology with the placental isoenzyme of alkaline phosphatase (PLAP). Both display a high degree of phenotypic heterogeneity. Until now all attempts to raise an antibody reacting specifically with GCAP have failed. Consequently there is no immunological assay that allows the measurement of GCAP in the presence of PLAP. Two-dimensional electrophoresis with a sigmoid immobilized pH-gradient of 3-10 for the first dimension makes it possible to differentiate clearly between these two closely related isoenzymes. Additionally, it resolves their many phenotypic variants. This is of special interest, since malignant transformation affects the glycosylation patterns of many glycoproteins. For the detection of GCAP and PLAP in two-dimensional electrophoresis it is essential to purify the raw tissue extracts thoroughly. A chromatographic method suited for this purpose is presented.

Human intestinal alkaline phosphatase-binding IgG in patients with severe bacterial infections

Patterns of alkaline phosphatase (AP)-binding proteins were observed in the alkaline pH range of 6.5-9.5 upon isoelectric focusing and blotting of serum from patients with inflammatory diseases. After isolation using affinity chromatography on protein A or immunoaffinity chromatography on AP coupled to cyanogen bromide (CNBr)-activated Sepharose, the AP-binding protein was identified as IgG on Western blots and in ELISA using human IgG-specific antibodies. It was shown that this IgG binds to AP from both calf (bovine) and human intestine. However, it binds neither to the human liver-bone-kidney (LBK) isoform nor to bacterial AP. Moderate reaction was observed with human placental AP. Comparing patients with various diagnoses (n = 284), AP-binding antibodies were mainly found in severe bacterial infections. They were not detected in serum from healthy blood donors (n = 300). The presence of AP-binding IgG was independent of the infected organ and the bacterial species causing infection. This antibody may be useful for discriminating bacterial from viral infection and for indicating severe bacterial inflammation.

Interpretation and clinical significance of alkaline phosphatase isoenzyme patterns

Alkaline phosphatase (ALP, EC 3.1.3.1) is a membrane-bound metalloenzyme that consists of a group of true isoenzymes, all glycoproteins, encoded for by at least four different gene loci: tissue-nonspecific, intestinal, placental, and germ-cell ALP. Through posttranslational modifications of the tissue-nonspecific gene, for example, through differences in carbohydrate composition, bone and liver ALP are formed. Nowadays, most commercially available methods for separating or measuring ALP isoenzymes are easy to perform and sensitive and allow for reproducible and quantitative results. As more isoenzymes and isoforms have been characterized, confusion has arisen due to the many different names they were given. For the sake of simplicity and because of structural analogies, we propose an alternative nomenclature for the ALP isoenzymes and isoforms based on their structural characteristics: soluble, dimeric (Sol), anchor-bearing (Anch), and membrane-bound (Mem) liver, bone, intestinal, and placental ALP. Together with lipoprotein-bound liver ALP and immunoglobulin-bound ALP, these names largely fit the many forms of ALP one can encounter in human serum and tissues. The clinically relevant isoenzymes are sol-liver, Mem-liver, lipoprotein-bound liver, and Sol-intestinal ALP in liver diseases, and Sol-bone and Anch-bone ALP in bone diseases. Many different isoenzyme patterns can be found in malignancies and renal diseases. This test provides the clinician with valuable information for diagnostic purposes as well as for follow-up of patients and monitoring of treatment. However, ALP isoenzyme determination will only provide clinically useful information if the patterns are correctly interpreted. In this respect, care should be taken to use the proper reference ranges, taking into account the age and sex of the patient. A normal total ALP activity does not rule out the presence of an abnormal isoenzyme pattern, particularly in children. Separating ALP into its isoenzymes adds considerable value to the mere assay of total ALP activity.

Cloning and expression of the bovine intestinal alkaline phosphatase gene: biochemical characterization of the recombinant enzyme

A complete genomic clone and a full-length cDNA coding for bovine intestinal alkaline phosphatase have been isolated and sequenced. The gene (5.4 kb) contains 11 exons separated by ten small introns at positions identical to those other members of the eukaryotic tissue-specific alkaline phosphatase family. In addition, 1.5 kb of upstream sequences contain putative regulatory elements showing sequence similarity to human and mouse intestinal alkaline phosphatase promoter sequences. To achieve recombinant bovine intestinal alkaline phosphatase expression, the coding region of the gene was subcloned into the pcDNA I eukaryotic expression vector and transfected into Chinese hamster ovary cells. Recombinant bovine intestinal alkaline phosphatase displays enzymatic properties comparable with those of purified native bovine intestinal alkaline phosphatase, a slightly increased thermal stability and, upon desialylation, it shows a homogeneous behaviour in agarose gel electrophoresis and isoelectric focusing. The availability of the recombinant bovine intestinal alkaline phosphatase and the elucidation of its primary sequence will help to accelerate our efforts to obtain the first crystallographic model of a eukaryotic alkaline phosphatase molecule.