Extracellular ATP hydrolysis in Caco-2 human intestinal cell line

Extracellular nucleotides and nucleosides activate signaling pathways that play major roles in the physiology and pathophysiology of the gastrointestinal tract. Ectonucleotidases hydrolyze extracellular nucleotides and thus regulate ligand exposure to purinergic receptors. In this study, we investigated the expression, localization and activities of ectonucleotidases using Caco-2 cells, a model of human intestinal epithelial cells. In addition, by studying ATP release and the rates of extracellular ATP (eATP) hydrolysis, we analyzed the contribution of these processes to the regulation of eATP in these cells. Results show that Caco-2 cells regulate the metabolism of eATP and by-products by ecto-nucleoside triphosphate diphosphohydrolase-1 and -2, a neutral ecto-phosphatase and ecto-5'-nucleotidase. All these ectoenzymes were kinetically characterized using intact cells, and their presence confirmed by denatured and native gels, western blot and cytoimmunofluorescence techniques. In addition, regulation of eATP was studied by monitoring the dynamic balance between intracellular ATP release and ectoATPase activity. Following mechanical and hypotonic stimuli, Caco-2 cells triggered a strong but transient release of intracellular ATP, with almost no energy cost, leading to a steep increase of eATP concentration, which was later reduced by ectoATPase activity. A data-driven algorithm allowed quantifying and predicting the rates of ATP release and ATP consumption contributing to the dynamic accumulation of ATP at the cell surface.

Immortalization of Mesenchymal Stromal Cells by TERT Affects Adenosine Metabolism and Impairs their Immunosuppressive Capacity

Mesenchymal stromal cells (MSCs) are promising candidates for cell-based therapies, mainly due to their unique biological properties such as multipotency, self-renewal and trophic/immunomodulatory effects. However, clinical use has proven complex due to limitations such as high variability of MSCs preparations and high number of cells required for therapies. These challenges could be circumvented with cell immortalization through genetic manipulation, and although many studies show that such approaches are safe, little is known about changes in other biological properties and functions of MSCs. In this study, we evaluated the impact of MSCs immortalization with the TERT gene on the purinergic system, which has emerged as a key modulator in a wide variety of pathophysiological conditions. After cell immortalization, MSCs-TERT displayed similar immunophenotypic profile and differentiation potential to primary MSCs. However, analysis of gene and protein expression exposed important alterations in the purinergic signaling of in vitro cultured MSCs-TERT. Immortalized cells upregulated the CD39/NTPDase1 enzyme and downregulated CD73/NT5E and adenosine deaminase (ADA), which had a direct impact on their nucleotide/nucleoside metabolism profile. Despite these alterations, adenosine did not accumulate in the extracellular space, due to increased uptake. MSCs-TERT cells presented an impaired in vitro immunosuppressive potential, as observed in an assay of co-culture with lymphocytes. Therefore, our data suggest that MSCs-TERT have altered expression of key enzymes of the extracellular nucleotides/nucleoside control, which altered key characteristics of these cells and can potentially change their therapeutic effects in tissue engineering in regenerative medicine.

The expression of NTPDase1 and -2 of Leishmania infantum chagasi in bacterial and mammalian cells: Comparative expression, refolding and nucleotidase characterization

Visceral Leishmaniasis (VL) represents an important global health problem in several warm countries around the world. The main targets in this study are the two nucleoside triphosphate diphosphohydrolases (NTPDases) from Leishmania infantum chagasi that are the main etiologic agent of VL in the New World. These enzymes, called LicNTPDase1 and -2, are homologous to members 5 and 6 of the mammalian E-NTPDase/CD39 superfamily of enzymes. These enzymes hydrolyze nucleotides and accordingly can participate in the purine salvage pathways and in the modulation of purinergic signaling through the extracellular nucleotide-dependent host immune responses. They can therefore affect adhesion and infection of host cells and the parasite virulence. To further characterize these enzymes, in this work, we expressed LicNTPDase1 and -2 in the classical bacterial system Escherichia coli and mammalian cell system COS-7 cells. Our data demonstrate that changes in refolding after expression in bacteria can increase the activity of recombinant (r) rLicNTPDase2 up to 20 times but has no significant effect on rLicNTPDase1. Meanwhile, the expression in COS-7 led to a significant increase in activity for rLicNTPDase1.

17β-Estradiol upregulates ecto-5'-nucleotidase (CD73) in hippocampal synaptosomes of female rats through action mediated by estrogen receptor-α and -β

17β-Estradiol (E2) crucially affects several processes in the hippocampus of both sexes. E2 acts upon estradiol receptors ERα and ERβ, influencing target gene expression and/or modulates intracellular signaling cascades. Another potent modulator of hippocampal function is nucleoside adenosine, the final product of ectonucleotidase cascade, enzymes which hydrolyze extracellular ATP to adenosine. The last and rate-limiting step of the hydrolysis is catalyzed by membrane-bound ecto-5'-nucleotidase (eN). Previous findings obtained on adenosine metabolism in brain suggest that eN may be modulated by ovarian steroids. Therefore, the present study reports that the activity and protein abundance of membrane-bound eN fluctuates across the estrus cycle in the hippocampal synaptosomes of female rats. Further, we analyzed the role of E2 and its intracellular receptors on the expression of eN in ovariectomized females. We found that E2 upregulated eN activity and protein abundance in the hippocampal synaptosomes. Application of nonspecific ER antagonist, ICI 182,780 and selective ERα and ERβ agonists, PPT and DPN, respectively, demonstrated the involvement of both receptor subtypes in observed actions. Selective ERα receptor agonist, PPT, induced upregulation of both the protein level and activity of eN, while application of selective ERβ receptor agonist, DPN, increased only the activity of eN. In both cases, E2 entered into the intracellular compartment and activated ER(s), which was demonstrated by membrane impermeable E2-BSA conjugate. Together these results imply that E2-induced effects on connectivity and functional properties of the hippocampal synapses may be in part mediated through observed effect on eN.

Attenuated allergic airway inflammation in Cd39 null mice

BACKGROUND

Extracellular Adenosine-5'-Triphosphate (ATP) is known to accumulate in the lung, following allergen challenge, and contributes via activation of purinergic receptors on dendritic cells (DC), to the development of allergic airway inflammation (AAI). Extracellular ATP levels in the airways are normally tightly regulated by CD39. This ectonucleotidase is highly expressed by DC purified from skin (Langerhans cells) and bone marrow, and has been shown to modulate DC adaptive/haptenic immune responses. In this study, we have evaluated the impact of Cd39 deletion and associated perturbation of purinergic signaling in AAI.

METHODS

Standard ovalbumin (OVA)-alum and house dust mite (HDM) bone marrow-derived DC (BMDC)-dependent models of AAI were used to study effects of Cd39. Migration assays, time lapse microscopy, and T-cell priming assays were further used to determine functional relevance of Cd39 expression on BMDC in the setting of immune and Th2-mediated responses in these models.

RESULTS

Cd39(-/-) mice exhibited marked increases in BALF ATP levels but paradoxically exhibited limited AAI in both OVA-alum and HDM models. These pathophysiological abnormalities were associated with decreased myeloid DC activation and chemotaxis toward ATP, and were linked to purinergic receptor desensitization responses. Further, Cd39(-/-) DCs exhibited limited capacity to both prime Th2 responses and form stable immune synaptic interactions with OVA-transgenic naïve T cells.

CONCLUSIONS

Cd39-deficient DCs exhibit limited capacity to induce Th2 immunity in a DC-driven model of AAI in vivo. Our data demonstrate a role of CD39 and perturbed purinergic signaling in models of AAI.

Role of ecto-NTPDases on UDP-sensitive P2Y(6) receptor activation during osteogenic differentiation of primary bone marrow stromal cells from postmenopausal women

This study aimed at investigating the expression and function of uracil nucleotide-sensitive receptors (P2Y(2), P2Y(4), and P2Y(6)) on osteogenic differentiation of human bone marrow stromal cells (BMSCs) in culture. Bone marrow specimens were obtained from postmenopausal female patients (68 ± 5 years old, n = 18) undergoing total hip arthroplasty. UTP and UDP (100 µM) facilitated osteogenic differentiation of the cells measured as increases in alkaline phosphatase (ALP) activity, without affecting cell proliferation. Uracil nucleotides concentration-dependently increased [Ca(2+)](i) in BMSCs; their effects became less evident with time (7 > 21 days) of the cells in culture. Selective activation of P2Y(6) receptors with the stable UDP analog, PSB 0474, mimicked the effects of both UTP and UDP, whereas UTPγS was devoid of effect. Selective blockade of P2Y(6) receptors with MRS 2578 prevented [Ca(2+)](i) rises and osteogenic differentiation caused by UDP at all culture time points. BMSCs are immunoreactive against P2Y(2), P2Y(4), and P2Y(6) receptors. While the expression of P2Y(6) receptors remained fairly constant (7∼21 days), P2Y(2) and P2Y(4) became evident only in less proliferative and more differentiated cultures (7 < 21 days). The rate of extracellular UTP and UDP inactivation was higher in less proliferative and more differentiated cell populations. Immunoreactivity against NTPDase1, -2, and -3 rises as cells differentiate (7 < 21 days). Data show that uracil nucleotides are important regulators of osteogenic cells differentiation predominantly through the activation of UDP-sensitive P2Y(6) receptors coupled to increases in [Ca(2+)](i) . Endogenous actions of uracil nucleotides may be balanced through specific NTPDases determining whether osteoblast progenitors are driven into proliferation or differentiation.

Expression of ecto-ATPase NTPDase2 in human dental pulp

Dental pulpal nerve fibers express ionotropic adenosine triphosphate (ATP) receptors, suggesting that ATP signaling participates in the process of dental nociception. In this study, we investigated if the principal enzymes responsible for extracellular ATP hydrolysis, namely, nucleoside triphosphate diphosphohydrolases (NTPDases), are present in human dental pulp. Immunohistochemical and immunofluorescence experiments showed that NTPDase2 was predominantly expressed in pulpal nerve bundles, Raschkow's nerve plexus, and in the odontoblast layer. NTPDase2 was expressed in pulpal Schwann cells, with processes accompanying the nerve fibers and projecting into the odontoblast layer. Odontoblasts expressed the gap junction protein, connexin43, which can form transmembrane hemichannels for ATP release. NTPDase2 was localized close to connexin43 within the odontoblast layer. These findings provide evidence for the existence of an apparatus for ATP release and degradation in human dental pulp, consistent with the involvement of ATP signaling in the process of dentin sensitivity and dental pain.

Nucleoside triphosphate diphosphohydrolases role in the pathophysiology of cognitive impairment induced by seizure in early age

Studies have shown that seizures in young animals lead to later cognitive deficits. There is evidence that long-term potentiation (LTP) and long-term depression (LTD) might contribute to the neural basis for learning and memory mechanism and might be modulated by ATP and/or its dephosphorylated product adenosine produced by a cascade of cell-surface transmembrane enzymes, such as E-NTPDases (ecto-nucleoside triphosphate diphosphohydrolases) and ecto-5'-nucleotidase. Thus, we have investigated if hippocampal ecto-nucleotidase activities are altered at different time periods after one episode of seizure induced by kainic acid (KA) in 7 days old rats. We also have evaluated if 90 day-old rats previously submitted to seizure induced by KA at 7 days of age presented cognitive impairment in Y-maze behavior task. Our results have shown memory impairment of adult rats (Postnatal day 90) previously submitted to one single seizure episode in neonatal period (Postnatal day 7), which is accompanied by an increased ATP hydrolysis in hippocampal synaptosomes. The metabolism of ATP evaluated by HPLC confirmed that ATP hydrolysis was faster in adult rats treated with KA in neonatal period than in controls. Surprisingly, the mRNA and protein levels as seen by PCR and Western blot, respectively, were not altered by the KA administration in early age. Since we have found an augmented hydrolysis of ATP and this nucleotide seems to be important to LTP induction, we could assume that impairment of memory and learning observed in adult rats which have experienced a convulsive episode in postnatal period may be a consequence of the increased ATP hydrolysis. These findings correlate the purinergic signaling to the cognitive deficits induced by neonatal seizures and contribute to a better understanding about the mechanisms of seizure-induced memory dysfunction.

Changes in expression and activity levels of ecto-5'-nucleotidase/CD73 along the mouse female estrous cycle

AIM

Extracellular ATP and its hydrolysis product adenosine modulate various reproductive functions such as those requiring contraction, hormone synthesis and maintenance of fluid composition. Moreover, adenosine is a key molecule for sperm capacitation. Extracellular nucleotide and nucleoside levels are affected by cell surface ectonucleotidases, amongst which the ectonucleoside triphosphate diphosphohydrolase (E-NTPDase) family is the most abundant and effective to hydrolyse ATP and ADP to AMP. In the female reproductive tract three members of this family have been recently identified: NTPDase1, NTPDase2 and NTPDase3 (Histochem. Cell Biol.131, 2009, 615). The purpose of the present study was to characterize in this system the expression profile of ecto-5'-nucleotidase (CD73), the enzyme generating adenosine from AMP.

METHODS

Immunological techniques and in situ enzymatic assays were used to characterize the ecto-5'-nucleotidase expression in the mouse female reproductive tract along the four stages of the estrous cycle, that were determined by vaginal smear examination.

RESULTS

Ecto-5'-nucleotidase was abundantly detected in the corpora lutea of the ovaries, as well as in several epithelia, such as that of oviducts, uterus and endometrial glands. Marked changes in endometrial ecto-5'-nucleotidase expression and activity along the estrous cycle are described, these being maximum at estrus phase, coinciding with optimal female sexual receptivity.

CONCLUSION

The adenosine generated thereby, besides other functions, might contribute to sperm capacitation, thus significantly influencing fertility.

Specificity of the ecto-ATPase inhibitor ARL 67156 on human and mouse ectonucleotidases

BACKGROUND AND PURPOSE

ARL 67156, 6-N,N-Diethyl-D-beta-gamma-dibromomethylene adenosine triphosphate, originally named FPL 67156, is the only commercially available inhibitor of ecto-ATPases. Since the first report on this molecule, various ectonucleotidases responsible for the hydrolysis of ATP at the cell surface have been cloned and characterized. In this work, we identified the ectonucleotidases inhibited by ARL 67156.

EXPERIMENTAL APPROACH

The effect of ARL 67156 on recombinant NTPDase1, 2, 3 & 8 (mouse and human), NPP1, NPP3 and ecto-5'-nucleotidase (human) have been evaluated. The inhibition of the activity of NTPDases (using the following substrates: ATP, ADP, UTP), NPPs (pnp-TMP, Ap(3)A) and ecto-5'-nucleotidase (AMP) was measured by colorimetric or HPLC assays.

KEY RESULTS

ARL 67156 was a weak competitive inhibitor of human NTPDase1, NTPDase3 and NPP1 with K(i) of 11+/-3, 18+/-4 and 12+/-3 microM, respectively. At concentrations used in the literature (50-100 microM), ARL 67156 partially but significantly inhibited the mouse and human forms of these enzymes. NTPDase2, NTPDase8, NPP3 and ecto-5'-nucleotidase activities were less affected. Importantly, ARL 67156 was not hydrolysed by either human NTPDase1, 2, 3, 8, NPP1 or NPP3.

CONCLUSIONS AND IMPLICATIONS

In cell environments where NTPDase1, NTPDase3, NPP1 or mouse NTPDase8 are present, ARL 67156 would prolong the effect of endogenously released ATP on P2 receptors. However, it does not block any ectonucleotidases efficiently when high concentrations of substrates are present, such as in biochemical, pharmacological or P2X(7) assays. In addition, ARL 67156 is not an effective inhibitor of NTPDase2, human NTPDase8, NPP3 and ecto-5'-nucleotidase.

Nucleoside triphosphate diphosphohydrolase-2 (NTPDase2/CD39L1) is the dominant ectonucleotidase expressed by rat astrocytes

Inflammatory and degenerative pathophysiological processes within the CNS are important causes of human disease. Astrocytes appear to modulate these reactions and are a major source of inflammatory mediators, e.g. extracellular adenine nucleotides, in nervous tissues. Actions following extracellular nucleotides binding to type 2 purinergic receptors are regulated by ectonucleotidases, including members of the CD39/ecto-nucleoside triphosphate diphosphohydrolase family. The ectonucleotidases of astrocytes expressed by rat brain rapidly convert extracellular ATP to ADP, ultimately to AMP. RT-PCR, immunocytochemistry as well as Western blotting analysis demonstrated expression of multiple ecto-nucleoside triphosphate diphosphohydrolase family members at both the mRNA and protein level. By quantitative real-time PCR, we identified Entpd2 (CD39L1) as the dominant Entpd gene expressed by rat hippocampal, cortical and cerebellar astrocytes. These data in combination with the elevated ecto-ATPase activity observed in these brain regions, suggest that NTPDase2, an ecto-enzyme that preferentially hydrolyzes ATP, is the major ecto-nucleoside triphosphate diphosphohydrolase expressed by rat astrocytes. NTPDase2 may modulate inflammatory reactions within the CNS and could represent a useful therapeutic target in human disease.

Noise exposure induces up-regulation of ecto-nucleoside triphosphate diphosphohydrolases 1 and 2 in rat cochlea

Extracellular ATP acting via P2 receptors in the inner ear initiates a variety of signaling pathways that may be involved in noise-induced cochlear injury. Nucleoside triphosphate diphosphohydrolase (NTPDase)1/CD39 and NTPDase2/CD39L1 are key elements for regulation of extracellular nucleotide concentrations and P2 receptor signaling in the cochlea. This study characterized the effect of noise exposure on regulation of NTPDase1 and NTPDase2 expression in the cochlea using a combination of real-time RT-PCR, immunohistochemistry and functional studies. Adult Wistar rats were exposed to broad band noise at 90 dB and 110 dB sound pressure level (SPL) for 72 h. Exposure to 90 dB SPL induced a small and temporary change of auditory thresholds (temporary threshold shift), while exposure to 110 dB SPL induced a robust and permanent change of auditory thresholds (permanent threshold shift). NTPDase1 and NTPDase2 mRNA transcripts were upregulated in the cochlea exposed to 110 dB SPL, while mild noise (90 dB SPL) altered only NTPDase1 mRNA expression levels. Changes in NTPDases expression did not correlate with levels of circulating corticosterone, implying that the up-regulation of NTPDases expression was not stress-related. Semi-quantitative immunohistochemistry in the cochlea exposed to 110 dB SPL localized the increased NTPDase1 and NTPDase2 immunostaining in the stria vascularis and up-regulation of NTPDase2 in the intraganglionic spiral bundle. In contrast, NTPDase1 was down-regulated in the cell bodies of the spiral ganglion neurones. Distribution of NTPDases was not altered in the cochlea exposed to 90 dB SPL. Functional studies revealed increased ectonucleotidase activities in the cochlea after exposure to 110 dB SPL, consistent with up-regulation of NTPDases. The changes in NTPDases expression may reflect adaptive response of cochlear tissues to limit ATP signaling during noise exposure.

Disordered cellular migration and angiogenesis in cd39-null mice

BACKGROUND

Nucleoside triphosphate diphosphohydrolase-1 (NTPDase1)/CD39 is the major ectonucleotidase of endothelial cells and monocytes and catalyzes phosphohydrolysis of extracellular nucleoside diphosphates (NDP) and triphosphates (NTP, eg, ATP and UTP). Deletion of cd39 causes perturbations in the hydrolysis of NTP and NDP in the vasculature. Activation of P2 receptors appears to influence endothelial cell chemotactic and mitogenic responses in vitro. Therefore, aberrant regulation of nucleotide P2 receptors may influence angiogenesis in cd39-null mice. Methods and Results- In control mice, implanted Matrigel plugs containing growth factors were rapidly populated by monocyte/macrophages, endothelial cells, and pericytes, with the development of new vessels over days. In cd39-null mice, migrating cells were completely confined to the tissue-Matrigel interface in a clearly stratified manner. Absolute failure of new vessel ingrowth was consistently observed in the mutant mice. Linked to these findings, chemotaxis of cd39-null monocyte/macrophages to nucleotides was impaired in vitro. This abnormality was associated with desensitization of nucleotide receptor P2Y-mediated signaling pathways.

CONCLUSIONS

Our findings demonstrate a role for NTPDase1 and phosphohydrolysis of extracellular nucleotides in the regulation of the cellular infiltration and new vessel growth in a model of angiogenesis.

Targeting platelet aggregation: CD39 gene transfer augments nucleoside triphosphate diphosphohydrolase activity in injured rabbit arteries

BACKGROUND

CD39, the major endothelial nucleoside triphosphate diphosphohydrolase (NTPDase), plays an important role in local thromboregulation. We hypothesized that balloon injury (BI) leads to an acute reduction in arterial NTPDase activity that could be restored by a targeted gene delivery strategy.

METHODS

Recombinant adenoviral vectors containing human CD39 (Ad-CD39) or beta-galactosidase (Ad-LacZ) were used. Endothelial (ECs) and smooth muscle cells (SMCs) were infected in vitro and NTPDase activity measured. New Zealand white rabbits (N = 28) underwent bilateral iliofemoral artery balloon injury, followed by incubation with Ad-CD39, Ad-LacZ, or vehicle. Explanted vessels were analyzed for NTPDase activity and localization of CD39 expression by immunohistochemistry. Deposition of fluorescent-labeled platelets was studied 3 days after injury and vector treatment.

RESULTS

In vitro, Ad-CD39 infection resulted in a greater than 40-fold increase in adenosine diphosphatase activity in ECs and a 3-fold increase in SMCs. In vivo, CD39 transgene expression localized to the luminal aspect of Ad-CD39--treated vessels. BI resulted in an acute reduction in vessel wall NTPDase activity (P <.05). Ad-CD39 augmented NTPDase activity when compared with vehicle or Ad-LacZ (P <.05). Platelet deposition on the injured arterial surface was modest and not different between Ad-CD39-- and Ad-LacZ--treated vessels.

CONCLUSIONS

BI decreases native NTPDase activity, which can be augmented by adenovirus-mediated gene transfer of CD39. Further studies are required to determine whether targeted delivery of CD39 could convey thromboprotective properties to an injured vessel.

P2Y(6) nucleotide receptor mediates monocyte interleukin-8 production in response to UDP or lipopolysaccharide

Extracellular nucleotides are autocrine and paracrine cellular mediators that signal through P2 nucleotide receptors. Monocytic cells express several P2Y receptors but the role of these G protein-coupled receptors in monocytes is not known. Here, we present evidence that P2Y(6) regulates chemokine production and release in monocytes. We find that UDP, a selective P2Y(6) agonist, stimulates interleukin (IL)-8 release in human THP-1 monocytic cells whereas other nucleotides are relatively inactive. P2 receptor antagonists or P2Y(6) antisense oligonucleotides inhibit IL-8 release induced by UDP. Furthermore, UDP specifically activated IL-8 production in astrocytoma 1321N1 cells transfected with human P2Y(6). Since lipopolysaccharide has been suggested to activate P2 receptors via nucleotide release, we tested whether IL-8 production stimulated by lipopolysaccharide might result from P2Y(6) activation. P2 antagonists or apyrase, an enzyme which hydrolyzes nucleotides including UDP, inhibit IL-8 production induced by lipopolysaccharide but not by other stimuli. Furthermore, IL-8 gene expression activated by lipopolysaccharide is enhanced by P2Y(6) overexpression and inhibited by P2Y(6) antisense oligonucleotides. Thus, UDP activates IL-8 production via P2Y(6) in monocytic cells. Furthermore, lipopolysaccharide mediates IL-8 production at least in part by autocrine P2Y(6) activation. These findings indicate a novel role for P2Y(6) in innate immune defenses.

The C-terminal cysteine-rich region dictates specific catalytic properties in chimeras of the ectonucleotidases NTPDase1 and NTPDase2

Ecto-nucleoside triphosphate diphosphohydrolases (E-NTPDases) comprise a novel family of ectonucleotidases that are important in the hydrolysis of extracellular nucleotides. The related NTPDase1 (ecto-apyrase) and NTPDase2 (ecto-ATPase) share a common membrane topography with a transmembrane domain at both the N- and C-terminus, an extensive extracellular loop with five 'apyrase conserved regions' (ACR1 to ACR5), and a cysteine-rich C-terminal region. Whereas NTPDase1 expressed in CHO cells hydrolyzes ATP and ADP equivalently, NTPDase2 has a high preference for the hydrolysis of ATP over ADP. In addition recombinant NTPDase1 hydrolyzes ATP to AMP with the formation of only minor amounts of free ADP. In contrast, ADP appears as the major free product when ATP is hydrolyzed by NTPDase2. In order to determine molecular domains responsible for these differences in catalytic properties, chimeric cDNAs were constructed in which N-terminal sequences of increasing length of NTPDase1 were substituted by the corresponding sequences of NTPDase2 and vice versa. The turnover points were contained within ACR1 to ACR5. Chimeric cDNAs were expressed in CHO cells and surface expression was verified by immunocytochemistry. ATP and ADP hydrolysis rates and ADP and AMP product formation were determined using HPLC. Amino-acid residues between ACR3 and ACR5 and in particular the cysteine-rich region between ACR4 and ACR5 conferred a phenotype to the chimeric enzymes that corresponded to the respective wild-type enzyme. Protein structure rather than the conserved ACRs may be of major relevance for determining differences in the catalytic properties between the related wild-type enzymes.

Assignment of ecto-nucleoside triphosphate diphosphohydrolase-1/cd39 expression to microglia and vasculature of the brain

Extracellular nucleotides are ubiquitous extracellular mediators that interact with and activate nucleotide type 2 (P2) receptors. These receptors initiate a wide variety of signalling pathways that appear important for functional associations between neurons and glial cells and for the regulation of blood flow, haemostatic and inflammatory reactions in the brain. Ectonucleotidases are extracellular nucleotide-metabolizing enzymes that modulate P2 receptor-mediated signalling by the regulated hydrolysis of these agonists. A considerable number of ectoenzyme species with partially overlapping substrate and tissue distributions have been described. Major candidates for expression in the brain are members of the ecto-nucleoside triphosphate diphosphohydrolase (E-NTPDase or CD39) family. The production of cd39-/- mice and specific reagents have enabled us to analyse the specific cellular distribution of NTPDase1 (CD39), the prototype member of the enzyme family, in the mouse brain. Using monospecific antibodies and enzyme histochemical staining, we have identified NTPDase1 as a major ectonucleotidase associated with both microglia and the endothelial and smooth muscle cells of the vasculature. NTPDase1 is not expressed by neurons and astrocytes. Additional unidentified ectonucleotidase functional activity is observed at lower levels throughout the brain parenchyma. NTPDase1 may regulate P2 receptor-mediated functions of microglia as well as influence nucleotide signalling between neurons or astrocytes that are associated with multiple microglial ramifications. The expression of NTPDase1 by cerebrovascular endothelial and smooth muscle cells also suggests involvement in the regulation of blood flow and thrombogenesis.

Distribution, cloning, and characterization of porcine nucleoside triphosphate diphosphohydrolase-1

In this study, we have investigated the distribution of the enzyme nucleoside triphosphate diphosphohydrolase-1 (NTPDase1; EC 3.6.1.5) in a subset of pig tissues by biochemical activity and Western blotting with antibodies against porcine NTPDase1. The highest expression of this enzyme was found in vascular endothelium, smooth muscle, spleen and lung. The complete cDNA of NTPDase1 from aorta endothelial cells was sequenced using primer walking. The protein consists of 510 amino acids, with a calculated molecular mass of 57 756 Da. The amino-acid sequence indicated seven putative N-glycosylation sites and one potential intracellular cGMP- and cAMP-dependent protein kinase phosphorylation site. As expected, the protein has a very high homology to other known mammalian ATPDases and CD39 molecules, and includes all five apyrase conserved regions. Expression of the complete cDNA in COS-7 cells confirmed that NTPDase1 codes for a transmembrane glycoprotein with ecto-ATPase and ecto-ADPase activities. Two proteolytic products of NTPDase1, with molecular mass of 54 and 27 kDa, respectively, were consistently present in proteins from transfected COS-7 cells and in particulate fractions from different tissues. A trypsin cleavage site, giving rise to these two cleavage products, was identified. In order to remain enzymatically active, the two cleavage products have to interact by non-covalent interactions.

Purification, characterization, and localization of an ATP diphosphohydrolase in porcine kidney

Membranes of pig kidney cortex tissue were solubilized in the presence of Triton X-100. Partial purification of ATP diphosphohydrolase (ATPDase) was achieved by successive chromatography on concanavalin A-Sepharose, Q-Sepharose Fast Flow, and 5'-AMP-Sepharose 4B. Monoclonal antibodies against ATPDase were generated. Further purification of the ATPDase was obtained by immunoaffinity chromatography with these monoclonal antibodies. NH(2)-terminal amino acid sequencing of the 78-kDa protein showed a sequence very homologous to mammalian CD39. The protein is highly glycosylated, with a nominal molecular mass of approximately 57 kDa. The purified enzyme hydrolyzed di- and triphosphates of adenosine, guanosine, cytidine, uridine, inosine, and thymidine, but AMP and diadenosine polyphosphates could not serve as substrates. All enzyme activities were dependent on divalent cations and were partially inhibited by 10 mM sodium azide. The distribution of the enzyme in pig kidney cortex was examined immunohistochemically. The enzyme was found to be present in blood vessel walls of glomerular and peritubular capillaries.

Identification, characterization, and immunolocalization of a nucleoside triphosphate diphosphohydrolase in pig liver

Different isoforms of nucleoside triphosphate diphosphohydrolases (NTPDases; EC 3.6.1.5), also identified as ATP diphosphohydrolases, have been previously described in mammalian tissues. We report here the biochemical characterization of NTPDases in the pig liver. Optimum pH of catalysis is more acidic for this enzyme than for NTPDases (neutral or alkaline pH) found in other mammalian tissues. It is less sensitive to bile salts than the bovine spleen NTPDase. Calculated Km values for ATP and ADP (31 and 21 microM, respectively) are slightly higher than those reported for the latter enzyme. Electrophoretograms of these enzymes also show different migration patterns. Western blots with Ringo, an antibody that recognizes the different isoforms of mammalian NTPDases, show a small but reproducible difference in estimated molecular masses (75 kDa for liver vs 78 kDa for spleen NTPDase). A second antibody, generated against a different sequence of NTPDase I, does not recognize the liver enzyme, thereby indicating some differences in primary structure. Immunolocalization produced a strong signal on hepatocytes, epithelial cells of the bile duct system, and vascular cells. Immunoreactivity was variable among hepatocytes of different lobules and among hepatocytes within a given lobule. In general, those located in the perilobular zone were more reactive than those located in the central zone and in the periphery of the centrolobular vein.

Identification and characterization of a novel hepatic canalicular ATP diphosphohydrolase

We have identified and characterized a novel ATP diphosphohydrolase (ATPDase) with features of E-type ATPases from porcine liver. Immunoblotting with a specific monoclonal antibody to this ectoenzyme revealed high expression in liver with lesser amounts in kidney and duodenum. This ATPDase was localized by immunohistochemistry to the bile canalicular domain of hepatocytes and to the luminal side of the renal ductular epithelium. In contrast, ATPDase/cd39 was detected in vascular endothelium and smooth muscle in these organs. We purified the putative ATPDase from liver by immunoaffinity techniques and obtained a heavily glycosylated protein with a molecular mass estimated at 75 kDa. This enzyme hydrolyzed all tri- and diphosphonucleosides but not AMP or diadenosine polyphosphates. There was an absolute requirement for divalent cations (Ca(2+) > Mg(2+)). Biochemical activity was unaffected by sodium azide or other inhibitors of ATPases. Kinetic parameters derived from purified preparations of hepatic ATPDase indicated V(max) of 8.5 units/mg of protein with apparent K(m) of 100 microM for both ATP or ADP as substrates. NH(2)-terminal amino acid sequencing revealed near 50% identity with rat liver lysosomal (Ca(2+)-Mg(2+))-ATPase. The different biochemical properties and localization of the hepatic ATPDase suggest pathophysiological functions that are distinct from the vascular ATPDase/cd39.

Palmitoylation targets CD39/endothelial ATP diphosphohydrolase to caveolae

Ectonucleotidases influence purinergic receptor function by the hydrolysis of extracellular nucleotides. CD39 is an integral membrane protein that is a prototype member of the nucleoside 5'-triphosphate diphosphohydrolase family. The native CD39 protein has two intracytoplasmic and two transmembrane domains. There is a large extracellular domain that undergoes extensive glycosylation and can be post-translationally modified by limited proteolysis. We have identified a potential thioester linkage site for S-acylation within the N-terminal region of CD39 and demonstrate that this region undergoes palmitoylation in a constitutive manner. The covalent lipid modification of this region of the protein appears to be important both in plasma membrane association and in targeting CD39 to caveolae. These specialized plasmalemmal domains are enriched in G protein-coupled receptors and appear to integrate cellular activation events. We suggest that palmitoylation could modulate the function of CD39 in regulating cellular signal transduction pathways.

Analysis of CD39/ATP diphosphohydrolase (ATPDase) expression in endothelial cells, platelets and leukocytes

Purinergic signaling may influence hemostasis, inflammatory responses and apoptosis. Therefore, hydrolysis of extracellular ATP and ADP by the ATP diphosphohydrolase (ATPDase) could regulate these processes. We have previously demonstrated the identity between the vascular ATPDase and CD39. Here we show that levels of CD39 expression correlate with ATPDase activity in human endothelial cells (EC), platelets and selected monocyte, NK, and megakaryocyte cell lines. Western blotting revealed one to three isoforms of CD39/ATPDase: mobility variations of major protein resulted from post-translational modifications. Northern blotting and primer extension indicated two major mRNA transcripts and one transcription start point, respectively. In addition, mRNAs specific for purinergic P2 receptors were detected in all of the investigated cells, suggesting that the coexpressed CD39/ATPDase may regulate purinergic signaling. Thrombotic and inflammatory responses may be modulated by the expression of CD39/ATPDase.

Modulation of nucleoside [correction of nucleotide] triphosphate diphosphohydrolase-1 (NTPDase-1)cd39 in xenograft rejection

BACKGROUND

There is increasing evidence showing that extracellular nucleosides [corrected] may be important mediators of vascular inflammation. Nucleoside [corrected] triphosphate diphosphohydrolase-1 (NTPDase-1, identical to CD39), the major vascular endothelial ectonucleotidase, is responsible for the hydrolysis of both extracellular ATP and ADP in the blood plasma to AMP. Studies were therefore conducted to evaluate the role of vascular NTPDase-1/cd39 in modulating platelet activation and vascular injury in cardiac xenografts.

MATERIALS AND METHODS

Cardiac xenografts from both wild-type and cd39 knockout mice (C57BL/6 x 129 Svj) were transplanted into Lewis rats. Alterations in cd39 mRNA transcripts and NTPDase activity expression were evaluated in wild-type grafts in untreated rats and then following complement depletion and immunosuppression. Rejection responses were studied with both mutant and wild-type grafts in the following models: presensitization with or without complement depletion, complement depletion alone, and with chronic immunosuppression to induce long-term graft survival.

RESULTS

NTPDase biochemical activity in wild-type xenografts rapidly decreased after transplantation but soon rebounded with graft survival. Elevated levels of cd39 mRNA with associated increases in NTPDase activity were observed in all long-term surviving wild-type grafts. Hyperacute xenograft rejection times were comparable in wild-type and mutant grafts but cd39-deficient grafts were subject to more rapid rejection and exhibited pronounced vascular injury in complement-depleted, presensitized rats. The cd39-deficient grafts in immunosuppressed recipients were subject to increased intravascular platelet sequestration and fibrin deposition; this resulted in focal myocardial infarction in long-term surviving mutant xenografts.

CONCLUSIONS

Augmentation of NTPDase-1 activity may be an important adaptive response for graft survival. Our results suggest that NTPDase-1/cd39 influences pathways of vascular injury in cardiac xenografts.

Identification and immunolocalization of two isoforms of ATP-diphosphohydrolase (ATPDase) in the pig immune system

The occurrence of a variety of purine receptors in the immune system indicates that extracellular purines play important functional roles. Extracellular purine concentrations are, in great part, determined by ectonucleotidases, namely, the ATP diphosphohydrolase, also identified as CD39, a lymphocyte cell surface marker. The latter enzyme converts triphospho- and diphosphonucleosides to nucleoside monophosphates. In this study, high levels of ATPase and ADPase activities have been found in homogenates of the different pig lymphoid organs. Specific activities decreased in the following order: spleen > bone marrow > thymus > lymph glands. The parallel decrease in ATPase and ADPase activities, in the presence of sodium azide, indicated that an ATP diphosphohydrolase (ATPDase) was responsible for these activities. Particulate fractions, prepared from the different lymphoid organs by ultracentrifugation on a sucrose cushion, showed about a 10-fold enrichment of ATPDase activity. Identity of ATPDase was confirmed by electrophoretograms of the particulate fractions and Western immunoblots, with an antibody that recognizes ATPDases from different sources. Two isoforms of ATPDase were found (I and II), corresponding to molecular masses of 78,000 and 54,000, respectively, as estimated by SDS-PAGE. Immunohistochemical localization was carried out on these different organs: In spleen, reaction was found in both white and red pulps. A particularly intense reaction was put in evidence in nervous fibers of this organ. Immunolocalization also showed positive reactions with tonsilar lymphoid structures, diffuse lymphoid tissues, and nodules associated with stomach, duodenum, jejunum, and ileum. In addition, our observations establish the presence of ATPDase in lymphocytes and macrophages of the pig immune system.

Suppression of ATP diphosphohydrolase/CD39 in human vascular endothelial cells

Vascular ATP diphosphohydrolase/CD39 is an endothelial cell membrane protein with both ecto-ATPase and ecto-ADPase activities. Suppression of constitutive CD39 expression may result in elevated concentrations of ATP and ADP at the vascular interface that could predispose to thrombosis and inflammation. To study the effects of suppression of CD39 synthesis, stable 25-base antisense chimeric oligonucleotides targeting sequences at the 5' region of CD39 were designed. Transfection of these stable oligomers into cultured human endothelial cells resulted in dramatic decreases in levels of CD39 mRNA transcripts. Following transfection with antisense oligonucleotides, total ADPase activity fell from 26.0 +/- 3.1 in control cultures to 9.5 +/- 3.4 nmol of P(i) min(-1) (mg of protein)(-1) (p < 0.005); suppression of CD39 protein expression was also observed by Western blotting. Decreases in ATP diphosphohydrolase activity were associated with increases in concentrations of extracellular purine nucleotides released following stimulation of endothelial cells. Rates of initial hydrolysis of extracellular ATP released from purinergic agonist-stimulated endothelial cells decreased from 17.9 +/- 5.0 to 4.8 +/- 0.5 pmol min(-1) per 10(6) cells (p < 0.005) in antisense transfected cells. Therefore, CD39 regulates extracellular ATP concentrations and may be an important modulator of purinergic receptor activity in vascular endothelial cells.

Targeted disruption of cd39/ATP diphosphohydrolase results in disordered hemostasis and thromboregulation

CD39, or vascular adenosine triphosphate diphosphohydrolase, has been considered an important inhibitor of platelet activation. Unexpectedly, cd39-deficient mice had prolonged bleeding times with minimally perturbed coagulation parameters. Platelet interactions with injured mesenteric vasculature were considerably reduced in vivo and purified mutant platelets failed to aggregate to standard agonists in vitro. This platelet hypofunction was reversible and associated with purinergic type P2Y1 receptor desensitization. In keeping with deficient vascular protective mechanisms, fibrin deposition was found at multiple organ sites in cd39-deficient mice and in transplanted cardiac grafts. Our data indicate a dual role for adenosine triphosphate diphosphohydrolase in modulating hemostasis and thrombotic reactions.

Structural elements and limited proteolysis of CD39 influence ATP diphosphohydrolase activity

CD39, the mammalian ATP diphosphohydrolase (ATPDase), is thought to contain two transmembrane domains and five "apyrase conserved regions" (ACR) within a large extracellular region. To study the structure of this ectoenzyme, human CD39 was modified by directed mutations within these ACRs or by sequential deletions at both termini. ATPDase activity was well preserved with FLAG tagging, followed by the removal of either of the demonstrated C- or N-transmembrane regions. However, deletions within ACR-1 (aa 54-61) or -4 (aa 212-220), as well as truncation mutants that included ACR-1, -4, or -5 (aa 447-454), resulted in substantive loss of biochemical activity. Intact ACR-1, -4, and -5 within CD39 are therefore required for maintenance of biochemical activity. Native and mutant forms of CD39 lacking TMR were observed to undergo multimerization, associated with the formation of intermolecular disulfide bonds. Limited tryptic cleavage of intact CD39 resulted in two noncovalently membrane-associated fragments (56 and 27 kDa) that substantially augmented ATPDase activity. Glycosylation variation accounted for minor heterogeneity in native and mutant forms of CD39 but did not influence ATPDase function. Enzymatic activity of ATPDase may be influenced by certain posttranslational modifications that are relevant to vascular inflammation.

Demonstration and immunolocalization of ATP diphosphohydrolase in the pig digestive system

Two isoforms of ATP diphosphohydrolase (ATPDase; EC 3.6.1.5) have been previously characterized, purified, and identified. This enzyme is an ectonucleotidase that catalyzes the sequential release of gamma- and beta-phosphate groups of triphospho- and diphosphonucleosides. One of its putative roles is to modulate the extracellular concentrations of purines in different physiological systems. The purpose of this study was to define, identify, and localize these two isoforms of ATPDase in the pig digestive system. ATPDase activity was measured in pig stomach, duodenum, pancreas, and parotid gland. Enzyme assays, electrophoretograms, and Western blots with a polyclonal antibody that recognizes both isoforms demonstrate the presence of ATPDase in these organs. Immunolocalization showed intense reactions with gastric glands (parietal and chief cells), intestine (columnar epithelial cells), parotid gland, and pancreas. Smooth muscle cells all along the digestive tract were also highly reactive. Considering the variety of purinoceptors associated with the digestive system, the ATPDase is strategically positioned to modulate purine-mediated actions such as electrolyte secretion, glandular secretion, smooth muscle contraction, and blood flow.

Purification, characterization, and localization of two ATP diphosphohydrolase isoforms in bovine heart

Two ATP diphosphohydrolase (ATPDase) isoforms have been purified from the bovine heart ventricle. The purification procedure includes the following steps: differential centrifugation, sucrose cushion centrifugation, solubilization with Triton X-100, DEAE agarose ion exchange, and Affi-Gel blue-Sepharose and concanavalin A (con A)-Sepharose chromatographies. The purified enzyme has an optimum pH of catalysis of 7.5 and requires Ca2+ or Mg2+. The apparent Michaelis constant of the enzyme, with ADP as the substrate, is 29 microM, and the apparent maximal velocity is 1.6 mumol.min-1.mg protein-1. Substrate specificity, heat-inactivation curves, and copurification of adenosinetriphosphatase (ATPase) and adenosinediphosphatase (ADPase) activities confirmed the identity of the purified enzyme as an ATPDase. In addition, polyacrylamide gel electrophoresis, under nondenaturing conditions, showed identical migration patterns for the protein involved in ATPase and ADPase activities. Western blot analysis, with an antibody that specifically recognizes the NH2-terminal sequence of pig pancreas ATPDase and specifically reacts with bovine and human ATPDases, showed cross-reactivity with the purified ATPDase isoforms from the bovine heart. Immunocytochemical localization in the ventricle produced strong reactions with the plasma membrane of Purkinje fiber cells and the majority of myocardial cells. Immunoreactivity was variable, producing a mosaic-like aspect. As expected, smooth muscle cells and endothelial cells of coronary vessels were highly reactive. This ectoenzyme could play a protective role against the potentially deleterious effects of extracellular ATP. In tandem with 5'-nucleotidase, it produces adenosine, a powerful vasodilator, especially in hypoxic or ischemic conditions that favor the release of ATP.

Purification and immunohistochemical localization of the ATP diphosphohydrolase in bovine lungs

We have recently described different isoforms of mammalian ATP diphosphohydrolase (ATPDase; EC 3.6.1.5). In the present study, we purified the lung ATPDase by column chromatographies followed by polyacrylamide gel electrophoresis under nondenaturing conditions. The active polypeptide that has a molecular mass of 78 kDa was identified by affinity labeling to the ATP analog 5'-p-fluorosulfonylbenzoyladenosine (FSBA), followed by detection on Western blot with an antibody specific for FSBA. N-glycosidase F treatment shifted the molecular mass of the 78-kDa polypeptide down to 54 kDa, indicating that the enzyme bears approximately 6-12 NH2-linked oligosaccharide chains. A polyclonal antibody raised against the pancreas ATPDase, which specifically recognized the 78-kDa glycoprotein on Western blot, was used to carry out an immunological survey of the enzyme distribution in bovine lungs. Immunoreactivity was detected on airway epithelia from the trachea down to alveolar cells, airway and vascular smooth muscle cells, submucous glands, chondrocytes, leucocytes, as well as endothelial and mesothelial cells. Such a wide distribution suggests that the ATPDase may affect a variety of physiological effects mediated by extracellular nucleotides, such as airway smooth muscle tone, surfactant secretion, platelet aggregation, and inflammation.

Purification of the blood vessel ATP diphosphohydrolase, identification and localisation by immunological techniques

ATP diphosphohydrolase (ATPDase) or apyrase (EC 3.6.1.5), an enzyme that hydrolyses the gamma and beta phosphate residues of triphospho- and diphosphonucleosides, has been purified from the bovine aorta media. A particulate fraction was isolated by differential, and sucrose cushion centrifugations, producing a 33-fold enrichment in ADPase activity. Solubilization of the enzyme from the particulate fraction with Triton X-100 caused a partial loss of activity. The solubilized enzyme was purified by DEAE-agarose, Affi-Gel blue and Concanavalin A column chromatographies yielding an additional 138-fold enrichment of the enzyme. The enzyme preparation was further purified by PAGE under non-denaturing conditions, followed by its detection on the gel. The active band was cut out and separated by SDS/PAGE. Overstaining with silver nitrate revealed a single band corresponding to a molecular mass of 78000. Presence of an ATP binding site on the latter protein was demonstrated by labelling with 5'-p-fluorosulfonylbenzoyladenosine (FSBA), an analogue of ATP, followed by its detection by a Western blot technique. Labelling specificity was demonstrated by competition experiments with Ca-ATP and Ca-ADP. An antiserum directed against the N-terminal sequence of the pig pancreas ATPDase (54 kDa) cross-reacted with the bovine aorta ATPDase at 78 kDa. Digestion of the ATPDase with N-glycosidase F caused a marked shift of the molecular mass, thereby showing multiple N-oligosaccharide chains. Immunohistochemical localisation confirmed the presence of ATPDase on both endothelial and smooth muscle cells.

Identification and characterization of CD39/vascular ATP diphosphohydrolase

Vascular ATP diphosphohydrolase (ATPDase) is a plasma membrane-bound enzyme that hydrolyses extracellular ATP and ADP to AMP. Analysis of amino acid sequences available from various mammalian and avian ATPDases revealed their close homology with CD39, a putative B-cell activation marker. We, therefore, isolated CD39 cDNA from human endothelial cells and expressed this in COS-7 cells. CD39 was found to have both immunological identity to, and functional characteristics of, the vascular ATPDase. We also demonstrated that ATPDase could inhibit platelet aggregation in response to ADP, collagen, and thrombin, and that this activity in transfected COS-7 cells was lost following exposure to oxidative stress. ATPDase mRNA was present in human placenta, lung, skeletal muscle, kidney, and heart and was not detected in brain. Multiple RNA bands were detected with the CD39 cDNA probe that most probably represent different splicing products. Finally, we identified an unique conserved motif, DLGGASTQ, that could be crucial for nucleotide binding, activity, and/or structure of ATPDase. Because ATPDase activity is lost with endothelial cell activation, overexpression of the functional enzyme, or a truncated mutant thereof, may prevent platelet activation associated with vascular inflammation.

Hydrolysis of P2-purinoceptor agonists by a purified ectonucleotidase from the bovine aorta, the ATP-diphosphohydrolase

Pharmacologists are becoming more and more aware of the possibility that certain ATP analogues currently used to classify the P2-purinoceptors are dephosphorylated by ectonucleotidases. In this study, we provide evidence that in the vascular system, these purine analogues are hydrolysed by an ATP-diphosphohydrolase (ATPDase). This enzyme is known as the major plasma membrane nucleotidase of endothelial and smooth muscle cells, and is believed to dephosphorylate extracellular triphospho- and diphosphonucleosides. Assays were conducted with a purified ATPDase from smooth muscle cells of bovine aorta. At a concentration of 250 microM, adenosine 5'-(alpha,beta-methylene) triphosphonate (alpha,beta-metATP), adenosine 5'-(beta,gamma-methylene) triphosphonate (beta,gamma-metATP), adenosine 5'-(alpha,beta-methylene) disphosphonate (alpha,beta-metADP), adenylyl 5'-(beta,gamma-imido) diphosphonate (beta,gamma-imidoATP) and adenosine 5'-O-(2-thiodiphosphate) (ADP beta S) all resisted dephosphorylation, whereas 2-chloroadenosine triphosphate (2-chloroATP), 2-methylthioadenosine triphosphate (2-MeSATP) and 8-bromoadenosine triphosphate (8-bromo-ATP) were hydrolysed at 99, 63, and 20% of the rate of ATP hydrolysis, respectively. All the non-hydrolysable analogues tested, except alpha,beta-metADP, competed with ATP and ADP for the ATPDase catalytic site, reducing their hydrolysis by 35-50%. Apparent Km values for ATP and ADP were estimated at 14.1 and 12.0 microM, respectively, whereas apparent Km and Ki values for the purine analogues ranged from 12 to 28 microM. These results strongly support the view that (1) the ATPDase is expected to reduce substantially the P2-response induced by ATP, ADP, and some hydrolysable agonists; and (2) by competing with the hydrolysis of endogenously released ATP and ADP, non-hydrolysable analogues could alter the amplitude or direction of the cellular response induced by these natural substrates.

Purification of pancreas type-I ATP diphosphohydrolase and identification by affinity labelling with the 5'-p-fluorosulphonylbenzoyladenosine ATP analogue

The enzyme recently identified as type-I ATP diphosphohydrolase (ATPDase; EC 3.6.1.5) has been purified from the zymogen granule membrane of pig pancreas. After solubilization with Triton X-100 and chromatographies on ion-exchange and Affi-Gel Blue columns an approximate 3500-fold purification was obtained. The enzyme preparation with a specific activity of 45 units/mg of protein was much further purified by PAGE under non-denaturing conditions. The active band localized on the gel contained two proteins after SDS/PAGE and silver staining, corresponding to apparent molecular masses of 56 and 54 kDa. The identity of the ATPDase was confirmed by an affinity labelling technique with 5'-p-fluorosulphonylbenzoyladenosine (FSBA) as an ATP analogue. The latter was detected by a Western blot technique. A strong reaction was observed with the band corresponding to 54 kDa. N-terminal sequence analysis revealed that the 56 kDa protein has significant similarities (50-72%) with lipases, whereas the 54 kDa enzyme has no significant similarity with any known proteins. N-glycosidase F treatment confirmed the glycoprotein nature of the enzyme and suggested that the enzyme bears several N-glycosylation sites. Comparisons of molecular masses and biochemical properties show that this ATPDase is different from other reported mammalian ATPDases.

The effects of nutritional quality and frequency of consumption of sugary foods on dental caries increment

This study investigates the association of dietary quality with dental caries increment of 11-year-old children. A 3-day dietary record including one weekend day was completed by the subjects and their parents. The nutritional quality was evaluated using a quality index based on the eating frequency of foods recommended in food guides and divided into 8 levels. The frequency of consumption of sugary foods, liquid and solid, at and between meals was also calculated. Two oral examinations 20 months apart were made in 1983-85; each time, the quality of oral hygiene was determined by using the simplified oral hygiene was determined by using the simplified oral hygiene index of Greene and Vermillon. the dental caries increment between the two examinations was evaluated using the DMFS index. When the subjects were distributed into 3 groups according to their nutritional quality index, the mean dental caries increment had a tendency to decrease as the nutritional quality increased for the total sample as well as for boys and girls considered separately; however, the analysis of variance did not reveal any differences of statistical significance. No association was established for children in this study between frequency of consumption of sugary foods and caries increment. No association was observed between nutritional quality and oral hygiene nor between the mother's education and the children's frequency of consumption of sugary foods. Thus, in our study, children with the highest dental caries increment are not necessarily the ones having a diet of poor nutritional quality nor the ones consuming sugary foods more frequently.

Influence of diet on plasma steroids and sex hormone-binding globulin levels in adult men

Several experimental studies have suggested that diet can alter the production and metabolism of steroids in men. The purpose of this study was to determine the levels of unconjugated steroids and steroid glucuronides as well as sex hormone-binding globulin (SHBG) among normal adult men who were either omnivorous or vegetarians. The participants were white volunteers ranging from 25-35 years of age and the blood samples were taken between 0900 h and 1000 h and between 1600 h and 1700 h for two consecutive days. No significant statistical change was found in plasma dehydroepiandrosterone, dehydroepiandrosterone sulfate, testosterone, dihydrotestosterone and estradiol levels. Vegetarian group showed a higher levels of sex hormone-binding globulin (SHBG) while the free androgen index (FAI; calculated by the ratio testosterone/SHBG) was lower in this group. Although the concentrations of androsterone glucuronide were higher in vegetarian group, the vegetarians had a 25-50% lower level of androstane-3 alpha, 17 beta-diol glucuronide and androstane-3 beta,17 beta-diol glucuronide. Our data further indicate that both, androstane-3 alpha,17 beta-diol glucuronide and androstane-3 beta,17 beta-diol glucuronide concentrations are significantly correlated with SHBG levels and with the FAI values. The increases in androstane-3 alpha,17 beta-diol glucuronide and androstane-3 beta,17 beta-diol glucuronide levels in the omnivorous group are probably a consequence of the elevation of the FAI. Our data suggest that in a vegetarian group, less testosterone is available for androgenic action.

[Frequency of food consumption in children. Weekdays versus weekends]

The accurate assessment of nutritional quality or of food eating frequency in epidemiologic studies depends among other things on the internal validity of the method. The purpose of this study was to compare the mean food eating frequencies at meals and between-meals of 20 specific food items obtained from a two-weekday-diet record to those obtained from one weekend-day. A three-day-diet record including a weekend-day was completed by 549 eleven-year old children with the help of their parents. For each pair of food frequencies observed, a Student t test was performed. The results showed that when comparing the means for two weekdays to one weekend-day, significant differences (p less than 0.05) were observed for soft drinks, pastries, milk and vegetables. Also fruit juices, whole grain cereals, fresh fruits, milk, green and yellow vegetables were eaten significantly less at meals during the weekend-day. Between-meal eating is generally more salted or more sweetened during the weekend-day. Foods generally considered to be more nutritious are eaten less during the weekend-day. The differences in food frequencies obtained showed the need of including one weekend-day in a three-day-diet record to avoid the overestimation of food consumption and of the quality of the diet.

Multiple regression analysis of dental status and related food behaviour of French Canadian adolescents

Variables included in a theoretical model of the caries process have been studied in an adolescent population. Four multiple regression analyses were performed to uncover significant explanatory factors for: DMF(T) index, plaque index, frequency of sweets consumption between meals and frequency of sweets consumption at meals. Each analysis produced a significant R2 explaining respectively 29%, 15%, 74% and 62% of the variance. The results demonstrated the contribution of the different factors included in the proposed model. They suggested that plaque index was by far the most significant factor of the DMF(T) index. Sweets consumption was a significant determinant of caries experience independent of any relation to plaque index. Adolescent girls, even with less plaque accumulation, had a higher caries index than boys of the same age. Parent's education was related to dental status of children at time of adolescence.