Recombinant mouse PAP has pH-dependent ectonucleotidase activity and acts through A(1)-adenosine receptors to mediate antinociception

dECM based dusal-responsive vascular graft with enzyme-controlled adenine release for long-term patency

Rapid occlusion is the culprit leading to implantation failure of biological blood vessels. Although adenosine is a clinical-proven drug to overcome the problem, its short half-life and turbulent burst-release limit its direct application. Thus, a pH/temperature dual-responsive blood vessel possessed controllable long-term adenosine secretion was constructed based on acellular matrix via compact crosslinking by oxidized chondroitin sulfate (OCSA) and functionalized with apyrase and acid phosphatase. These enzymes, as adenosine micro-generators, controlled the adenosine release amount by "real-time-responding" to acidity and temperature of vascular inflammation sites. Additionally, the macrophage phenotype was switched from M1 to M2, and related factors expression proved that adenosine release was effectively regulated with the severity of inflammation. What's more, the ultra-structure for degradation resisting and endothelialization accelerating was also preserved by their "double-crosslinking". Therefore, this work suggested a new feasible strategy providing a bright future of long-term patency for transplanted blood vessels.

Structural insights into a new substrate binding mode of a histidine acid phosphatase from Legionella pneumophila

MapA is a histidine acid phosphatase (HAP) from Legionella pneumophila that catalyzes the hydroxylation of a phosphoryl group from phosphomonoesters by an active-site histidine. Several structures of HAPs, including MapA, in complex with the inhibitor tartrate have been solved and the substrate binding tunnel identified; however, the substrate recognition mechanism remains unknown. To gain insight into the mechanism of substrate recognition, the crystal structures of apo-MapA and the MapA^D281A mutant in complex with 5'-AMP were solved at 2.2 and 2.6 Å resolution, respectively. The structure of the MapA^D281A/5'-AMP complex reveals that the 5'-AMP fits fully into the substrate binding tunnel, with the 2'-hydroxyl group of the ribose moiety stabilized by Glu201 and the adenine moiety sandwiched between His205 and Phe237. This is the second structure of a HAP/AMP complex solved with 5'-AMP binding in a unique manner in the active site. The structure presents a new substrate recognition mechanism of HAPs.

Purinergic Signaling in Endometriosis-Associated Pain

Endometriosis is an estrogen-dependent gynecological disease, with an associated chronic inflammatory component, characterized by the presence of endometrial tissue outside the uterine cavity. Its predominant symptom is pain, a condition notably altering the quality of life of women with the disease. This review is intended to exhaustively gather current knowledge on purinergic signaling in endometriosis-associated pain. Altered extracellular ATP hydrolysis, due to changes in ectonucleotidase activity, has been reported in endometriosis; the resulting accumulation of ATP in the endometriotic microenvironment points to sustained activation of nucleotide receptors (P2 receptors) capable of generating a persistent pain message. P2X3 receptor, expressed in sensory neurons, mediates nociceptive, neuropathic, and inflammatory pain, and is enrolled in endometriosis-related pain. Pharmacological inhibition of P2X3 receptor is under evaluation as a pain relief treatment for women with endometriosis. The role of other ATP receptors is also discussed here, e.g., P2X4 and P2X7 receptors, which are involved in inflammatory cell–nerve and microglia–nerve crosstalk, and therefore in inflammatory and neuropathic pain. Adenosine receptors (P1 receptors), by contrast, mainly play antinociceptive and anti-inflammatory roles. Purinome-targeted drugs, including nucleotide receptors and metabolizing enzymes, are potential non-hormonal therapeutic tools for the pharmacological management of endometriosis-related pain.

Structural and functional characterization of engineered bifunctional fusion proteins of CD39 and CD73 ectonucleotidases

Extracellular diphosphate and triphosphate nucleotides are released from activated or injured cells to trigger vascular and immune P₂ purinergic receptors, provoking inflammation and vascular thrombosis. These metabokines are scavenged by ectonucleoside triphosphate diphosphohydrolase-1 (E-NTPDase1 or CD39). Further degradation of the monophosphate nucleoside end products occurs by surface ecto-5'-nucleotidase (NMPase) or CD73. These ectoenzymatic processes work in tandem to promote adenosinergic responses, which are immunosuppressive and antithrombotic. These homeostatic ectoenzymatic mechanisms are lost in the setting of oxidative stress, which exacerbates inflammatory processes. We have engineered bifunctional enzymes made up from ectodomains (ECDs) of CD39 and CD73 within a single polypeptide. Human alkaline phosphatase-ectodomain (ALP-ECD) and human acid phosphatase-ectodomain (HAP-ECD) fusion proteins were also generated, characterized, and compared with these CD39-ECD, CD73-ECD, and bifunctional fusion proteins. Through the application of colorimetrical functional assays and high-performance liquid chromatography kinetic assays, we demonstrate that the bifunctional ectoenzymes express high levels of CD39-like NTPDase activity and CD73-like NMPase activity. Chimeric CD39-CD73-ECD proteins were superior in converting triphosphate and diphosphate nucleotides into nucleosides when compared with ALP-ECD and HAP-ECD. We also note a pH sensitivity difference between the bifunctional fusion proteins and parental fusions, as well as ectoenzymatic property distinctions. Intriguingly, these innovative reagents decreased platelet activation to exogenous agonists in vitro. We propose that these chimeric fusion proteins could serve as therapeutic agents in inflammatory diseases, acting to scavenge proinflammatory ATP and also generate anti-inflammatory adenosine.

Decreased Equilibrative Nucleoside Transporter 1 (ENT1) Activity Contributes to the High Extracellular Adenosine Levels in Mesenchymal Glioblastoma Stem-Like Cells

Glioblastoma multiforme is one of the most malignant types of cancer. This is mainly due to a cell subpopulation with an extremely aggressive potential, called glioblastoma stem-like cells (GSCs). These cells produce high levels of extracellular adenosine which has been associated with increased chemoresistance, migration, and invasion in glioblastoma. In this study, we attempted to elucidate the mechanisms that control extracellular adenosine levels in GSC subtypes. By using primary and U87MG-derived GSCs, we associated increased extracellular adenosine with the mesenchymal phenotype. [3H]-adenosine uptake occurred mainly through the equilibrative nucleoside transporters (ENTs) in GSCs, but mesenchymal GSCs have lower expression and ENT1-mediated uptake activity than proneural GSCs. By analyzing expression and enzymatic activity, we determined that ecto-5'-nucleotidase (CD73) is predominantly expressed in proneural GSCs, driving AMPase activity. While in mesenchymal GSCs, both CD73 and Prostatic Acid Phosphatase (PAP) contribute to the AMP (adenosine monophosphate) hydrolysis. We did not observe significant differences between the expression of proteins involved in the metabolization of adenosine among the GCSs subtypes. In conclusion, the lower expression and activity of the ENT1 transporter in mesenchymal GSCs contributes to the high level of extracellular adenosine that these GSCs present.

Downregulation of adenosine and adenosine A1 receptor contributes to neuropathic pain in resiniferatoxin neuropathy

This study demonstrates that functional prostatic acid phosphatase is required for maintaining the balance of cellular adenosine analgesia in systemic small-fiber neuropathy.

The neurochemical effects of adenosine signaling in small-fiber neuropathy leading to neuropathic pain are yet to be explored in a direct manner. This study examined this system at the level of ligand (through the ectonucleotidase activity of prostatic acid phosphatase [PAP]) and adenosine A1 receptors (A1Rs) in resiniferatoxin (RTX) neuropathy, a peripheral neurodegenerative disorder that specifically affects nociceptive nerves expressing transient receptor potential vanilloid type 1 (TRPV1). We conducted immunohistochemistry on dorsal root ganglion (DRG) neurons, high-performance liquid chromatography for functional assays, and pharmacological interventions to alter PAP and A1Rs in mice with RTX neuropathy. In DRG of RTX neuropathy, PAP(+) neurons were reduced compared with vehicle-treated mice (P = 0.002). Functionally, PAP ectonucleotidase activity was consequently reduced (ie, the content of adenosine in DRG, P = 0.012). PAP(+) neuronal density was correlated with the degree of mechanical allodynia, which was reversed by intrathecal (i.t.) lumbar puncture injection of recombinant PAP with a dose-dependent effect. Furthermore, A1Rs were downregulated (P = 0.002), and this downregulation was colocalized with the TRPV1 receptor (31.0% ± 2.8%). Mechanical allodynia was attenuated in a dose-dependent response by i.t. injection of the A1R ligand, adenosine; however, no analgesia was evident when an exogenous adenosine was blocked by A1R antagonist. This study demonstrated dual mechanisms of neuropathic pain in TRPV1-induced neuropathy, involving a reduced adenosine system at both the ligand (adenosine) and receptor (A1Rs) levels.

Treatment with methyl-β-cyclodextrin prevents mechanical allodynia in resiniferatoxin neuropathy in a mouse model

Specialized microdomains which have cholesterol-rich membrane regions contain transient receptor potential vanilloid subtype 1 (TRPV1) are involved in pain development. Our previous studies have demonstrated that the depletion of prostatic acid phosphatase (PAP) – a membrane-bound ectonucleotidase ­– and disordered adenosine signaling reduce the antinociceptive effect. The role of membrane integrity in the PAP-mediated antinociceptive effect in small-fiber neuropathy remains unclear, especially with respect to whether TRPV1 and PAP are colocalized in the same microdomain which is responsible for PAP-mediated antinociception. Immunohistochemistry was conducted on the dorsal root ganglion to identify the membrane compositions, and pharmacological interventions were conducted using methyl-β-cyclodextrin (MβC) – a membrane integrity disruptor that works by depleting cholesterol – in pure small-fiber neuropathy with resiniferatoxin (RTX). Immunohistochemical evidence indicated that TRPV1 and PAP were highly colocalized with flotillin 1 (66.7%±9.7%) and flotillin 2 (73.7%±6.0%), which reside in part in the microdomain. MβC mildly depleted PAP, which maintained the ability to hydrolyze phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2] and delayed the development of mechanical allodynia. MβC treatment had no role in thermal transduction and neuronal injury following RTX neuropathy. In summary, this study demonstrated the following: (1) membrane cholesterol depletion preserves PAP-mediated antinociception through PI(4,5)P2 hydrolysis and (2) pain hypersensitivity that develops after TRPV1(+) neuron depletion-mediated neurodegeneration following RTX neuropathy is attributable to the downregulation of PAP analgesic signaling.

Summary: The role and mechanism of cholesterol-rich membrane integrity in pain development for small-fiber neuropathy remains unclear. Depletion of membrane cholesterol contents preserves functional PAP profiles and the antinociceptive effect after RTX neuropathy.

Expression of Prostatic Acid Phosphatase in Rat Circumvallate Papillae

ATP and its metabolites are important for taste signaling in taste buds, and thus a clearance system for them would play critical roles in maintenance of gustatory function. A previous report revealed that mRNAs for ecto-5'-nucleotidase (NT5E) and prostatic acid phosphatase (PAP) were expressed by taste cells of taste buds, and NT5E-immunoreactivity was detected in taste cells. However, there was no information on PAP-immunoreactivity in taste buds. In this study, we examined the expression profile of PAP in rat taste buds. In the isolated rat taste buds, we detected expression of mRNA for PAP, but NT5E was not detected differing from the case of mouse ones (Dando et al., 2012, J Neuroscience). On immunohistochemical analysis, PAP-immunoreactivity was found predominantly in NTPDase2-positive type I and SNAP25-positive type III taste cells, while there were no apparent signals of it in PLC-β2-positive type II, α-gustducin-positive type II, AADC-positive type III and 5HT-positive type III ones. As for NT5E, we could not detect its immunoreactivity in rat taste buds, and co-localization of it with any taste cell markers, although mouse taste buds expressed NT5E as reported previously. These findings suggest that PAP expressed by type I and one of type III taste cells of rats may contribute to metabolic regulation of the extracellular levels of adenine nucleotides in the taste buds of circumvallate papillae, and the regulating mechanisms for adenine nucleotides in taste buds might be different between rats and mice.

EXPRESS: NGF-trkA signaling modulates the analgesic effects of prostatic acid phosphatase in resiniferatoxin-induced neuropathy

Background

Neuropathic pain in small-fiber neuropathy results from injury to and sensitization of nociceptors. Functional prostatic acid phosphatase (PAP) acts as an analgesic effector. However, the mechanism responsible for the modulation of PAP neuropathology, which leads to loss of the analgesic effect after small-fiber neuropathy, remains unclear.

Results

We used a resiniferatoxin (RTX)-induced small-fiber neuropathy model to examine whether functional PAP(+) neurons are essential to maintain the analgesic effect. PAP(+) neurons were categorized into small to medium neurons (25th–75th percentile: 17.1–23.7 µm); these neurons were slightly reduced by RTX (p = 0.0003). By contrast, RTX-induced activating transcription factor 3 (ATF3), an injury marker, in PAP(+) neurons (29.0% ± 5.6% vs. 0.2% ± 0.2%, p = 0.0043), indicating PAP neuropathology. Moreover, the high-affinity nerve growth factor (NGF) receptor (trkA) colocalized with PAP and showed similar profiles after RTX-induced neuropathy, and the PAP/trkA ratios correlated with the degree of mechanical allodynia (r = 0.62, p = 0.0062). The NGF inducer 4-methylcatechol (4MC) normalized the analgesic effects of PAP; specifically, it reversed the PAP and trkA profiles and relieved mechanical allodynia. Administering 2.5S NGF showed similar results to those of administering 4MC. This finding suggests that the analgesic effect of functional PAP is mediated by NGF-trkA signaling, which was confirmed by NGF neutralization.

Conclusions

This study revealed that functional PAP(+) neurons are essential for the analgesic effect, which is mediated by NGF-trkA signaling.

TNAP and Pain Control

Chronic pain is one of the most debilitating and expensive diseases, yet current therapies are often insufficient in bringing about long-term relief. Further, many treatments for chronic pain also carry significant side effects. The molecule adenosine has long been identified as a potent inhibitor of nociceptive circuits in the spinal cord; however, the widespread expression of adenosine receptors in many organ systems has limited its use as an analgesic. Recently several 5' ectonucleotidases, including tissue non-specific alkaline phosphatase (TNAP), have been characterized for their ability to generate endogenous adenosine in nociceptive circuitry of the dorsal spinal cord. These ectonucleotidases have the ability to hydrolyze the endogenous pronociceptive nucleotides like adenosine triphosphate (ATP) into the antinociceptive nucleoside adenosine. This chapter discusses the role of TNAP and other ectonucleotidases in nociceptive circuits, and their potential as future targets of new therapeutics to treat chronic pain.

Crystal structure and tartrate inhibition of Legionella pneumophila histidine acid phosphatase

Histidine acid phosphatases (HAPs) utilize a nucleophilic histidine residue to catalyze the transfer of a phosphoryl group from phosphomonoesters to water. HAPs function as protein phosphatases and pain suppressors in mammals, are essential for Giardia lamblia excystation, and contribute to virulence of the category A pathogen Francisella tularensis. Herein we report the first crystal structure and steady-state kinetics measurements of the HAP from Legionella pneumophila (LpHAP), also known as Legionella major acid phosphatase. The structure of LpHAP complexed with the inhibitor l(+)-tartrate was determined at 2.0 Å resolution. Kinetics assays show that l(+)-tartrate is a 50-fold more potent inhibitor of LpHAP than of other HAPs. Electrostatic potential calculations provide insight into the basis for the enhanced tartrate potency: the tartrate pocket of LpHAP is more positive than other HAPs because of the absence of an ion pair partner for the second Arg of the conserved RHGXRXP HAP signature sequence. The structure also reveals that LpHAP has an atypically expansive active site entrance and lacks the nucleotide substrate base clamp found in other HAPs. These features imply that nucleoside monophosphates may not be preferred substrates. Kinetics measurements confirm that AMP is a relatively inefficient in vitro substrate of LpHAP.

Extracellular acidosis impairs P2Y receptor-mediated Ca(2+) signalling and migration of microglia

Microglia are the resident macrophage and immune cell of the brain and are critically involved in combating disease and assaults on the brain. Virtually all brain pathologies are accompanied by acidosis of the interstitial fluid, meaning that microglia are exposed to an acidic environment. However, little is known about how extracellular acidosis impacts on microglial function. The activity of microglia is tightly controlled by 'on' and 'off' signals, the presence or absence of which results in generation of distinct phenotypes in microglia. Activation of G protein coupled purinergic (P2Y) receptors triggers a number of distinct behaviours in microglia, including activation, migration, and phagocytosis. Using pharmacological tools and fluorescence imaging of the murine cerebellar microglia cell line C8B4, we show that extracellular acidosis interferes with P2Y receptor-mediated Ca(2+) signalling in these cells. Distinct P2Y receptors give rise to signature intracellular Ca(2+) signals, and Ca(2+) release from stores and Ca(2+) influx are differentially affected by acidotic conditions: Ca(2+) release is virtually unaffected, whereas Ca(2+) influx, mediated at least in part by store-operated Ca(2+) channels, is profoundly inhibited. Furthermore, P2Y1 and P2Y6-mediated stimulation of migration is inhibited under conditions of extracellular acidosis, whereas basal migration independent of P2Y receptor activation is not. Taken together, our results demonstrate that an acidic microenvironment impacts on P2Y receptor-mediated Ca(2+) signalling, thereby influencing microglial responses and responsiveness to extracellular signals. This may result in altered behaviour of microglia under pathological conditions compared with microglial responses in healthy tissue.

Central or peripheral delivery of an adenosine A1 receptor agonist improves mechanical allodynia in a mouse model of painful diabetic neuropathy

Diabetic peripheral neuropathy is a common complication of diabetes mellitus, and a significant proportion of individuals suffer debilitating pain that significantly affects their quality of life. Unfortunately, symptomatic treatment options have limited efficacy, and often carry significant risk of systemic adverse effects. Activation of the adenosine A1 receptor (A1R) by the analgesic small molecule adenosine has been shown to have antinociceptive benefits in models of inflammatory and neuropathic pain. The current study used a mouse model of painful diabetic neuropathy to determine the effect of diabetes on endogenous adenosine production, and if central or peripheral delivery of adenosine receptor agonists could alleviate signs of mechanical allodynia in diabetic mice. Diabetes was induced using streptozocin in male A/J mice. Mechanical withdrawal thresholds were measured weekly to characterize neuropathy phenotype. Hydrolysis of AMP into adenosine by ectonucleotidases was determined in the dorsal root ganglia (DRG) and spinal cord at 8 weeks post-induction of diabetes. AMP, adenosine and the specific A1R agonist, N(6)-cyclopentyladenosine (CPA), were administered both centrally (intrathecal) and peripherally (intraplantar) to determine the effect of activation of adenosine receptors on mechanical allodynia in diabetic mice. Eight weeks post-induction, diabetic mice displayed significantly decreased hydrolysis of extracellular AMP in the DRG; at this same time, diabetic mice displayed significantly decreased mechanical withdrawal thresholds compared to nondiabetic controls. Central delivery AMP, adenosine and CPA significantly improved mechanical withdrawal thresholds in diabetic mice. Surprisingly, peripheral delivery of CPA also improved mechanical allodynia in diabetic mice. This study provides new evidence that diabetes significantly affects endogenous AMP hydrolysis, suggesting that altered adenosine production could contribute to the development of painful diabetic neuropathy. Moreover, central and peripheral activation of A1R significantly improved mechanical sensitivity, warranting further investigation into this important antinociceptive pathway as a novel therapeutic option for the treatment of painful diabetic neuropathy.

Deletion of ENTPD3 does not impair nucleotide hydrolysis in primary somatosensory neurons or spinal cord

Ectonucleotidases are membrane-bound or secreted proteins that hydrolyze extracellular nucleotides.  Recently, we identified three ectonucleotidases that hydrolyze extracellular adenosine 5'-monophosphate (AMP) to adenosine in primary somatosensory neurons.  Currently, it is unclear which ectonucleotidases hydrolyze ATP and ADP in these neurons.  Ectonucleoside triphosphate diphosphohydrolases (ENTPDs) comprise a class of enzymes that dephosphorylate extracellular ATP and ADP.  Here, we found that ENTPD3 (also known as NTPDase3 or CD39L3) was located in nociceptive and non-nociceptive neurons of the dorsal root ganglion (DRG), in the dorsal horn of the spinal cord, and in free nerve endings in the skin.  To determine if ENTPD3 contributes directly to ATP and ADP hydrolysis in these tissues, we generated and characterized an Entpd3 knockout mouse.  This mouse lacks ENTPD3 protein in all tissues examined, including the DRG, spinal cord, skin, and bladder.  However, DRG and spinal cord tissues from Entpd3 (-/-) mice showed no reduction in histochemical staining when ATP, ADP, AMP, or UTP were used as substrates.  Additionally, using fast-scan cyclic voltammetry (FSCV), adenosine production was not impaired in the dorsal spinal cord of Entpd3 (-/-) mice when the substrate ADP was applied.  Further, Entpd3 (-/-) mice did not differ in nociceptive behaviors when compared to wild-type mice, although Entpd3 (-/-) mice showed a modest reduction in β-alanine-mediated itch.  Taken together, our data indicate that deletion of Entpd3 does not impair ATP or ADP hydrolysis in primary somatosensory neurons or in dorsal spinal cord.  Moreover, our data suggest there could be multiple ectonucleotidases that act redundantly to hydrolyze nucleotides in these regions of the nervous system.

Emerging roles of human prostatic Acid phosphatase

Prostate cancer is one of the most prevalent non-skin related cancers. It is the second leading cause of cancer deaths among males in most Western countries. If prostate cancer is diagnosed in its early stages, there is a higher probability that it will be completely cured. Prostatic acid phosphatase (PAP) is a non-specific phosphomonoesterase synthesized in prostate epithelial cells and its level proportionally increases with prostate cancer progression. PAP was the biochemical diagnostic mainstay for prostate cancer until the introduction of prostate-specific antigen (PSA) which improved the detection of early-stage prostate cancer and largely displaced PAP. Recently, however, there is a renewed interest in PAP because of its usefulness in prognosticating intermediate to high-risk prostate cancers and its success in the immunotherapy of prostate cancer. Although PAP is believed to be a key regulator of prostate cell growth, its exact role in normal prostate as well as detailed molecular mechanism of PAP regulation is still unclear. Here, many different aspects of PAP in prostate cancer are revisited and its emerging roles in other environment are discussed.

Acid evoked thermal hyperalgesia involves peripheral P2Y1 receptor mediated TRPV1 phosphorylation in a rodent model of thrombus induced ischemic pain

Background

We previously developed a thrombus-induced ischemic pain (TIIP) animal model, which was characterized by chronic bilateral mechanical allodynia without thermal hyperalgesia (TH). On the other hand we had shown that intraplantar injection of acidic saline facilitated ATP-induced pain, which did result in the induction of TH in normal rats. Because acidic pH and increased ATP are closely associated with ischemic conditions, this study is designed to: (1) examine whether acidic saline injection into the hind paw causes the development of TH in TIIP, but not control, animals; and (2) determine which peripheral mechanisms are involved in the development of this TH.

Results

Repeated intraplantar injection of pH 4.0 saline, but not pH 5.5 and 7.0 saline, for 3 days following TIIP surgery resulted in the development of TH. After pH 4.0 saline injections, protein levels of hypoxia inducible factor-1α (HIF-1α) and carbonic anhydrase II (CA II) were elevated in the plantar muscle indicating that acidic stimulation intensified ischemic insults with decreased tissue acidity. At the same time point, there were no changes in the expression of TRPV1 in hind paw skin, whereas a significant increase in TRPV1 phosphorylation (pTRPV1) was shown in acidic saline (pH 4.0) injected TIIP (AS-TIIP) animals. Moreover, intraplantar injection of chelerythrine (a PKC inhibitor) and AMG9810 (a TRPV1 antagonist) effectively alleviated the established TH. In order to investigate which proton- or ATP-sensing receptors contributed to the development of TH, amiloride (an ASICs blocker), AMG9810, TNP-ATP (a P2Xs antagonist) or MRS2179 (a P2Y1 antagonist) were pre-injected before the pH 4.0 saline. Only MRS2179 significantly prevented the induction of TH, and the increased pTRPV1 ratio was also blocked in MRS2179 injected animals.

Conclusion

Collectively these data show that maintenance of an acidic environment in the ischemic hind paw of TIIP rats results in the phosphorylation of TRPV1 receptors via a PKC-dependent pathway, which leads to the development of TH mimicking what occurs in chronic ischemic patients with severe acidosis. More importantly, peripheral P2Y1 receptors play a pivotal role in this process, suggesting a novel peripheral mechanism underlying the development of TH in these patients.

Survival of methicillin-resistant Staphylococcus aureus during thermal processing of frankfurters, summer sausage, and ham

Infections from antibiotic-resistant bacteria are a major concern for human health professionals around the world. Methicillin-resistant Staphylococcus aureus (MRSA) is just one of the resistant organisms of concern. MRSA prevalence has also been recently reported in retail meat products at rates higher than originally thought. Although the risk of contracting an infection from handling contaminated meat products is thought to be low, very little is known about this organism from a food safety perspective. The objective of this study was to determine the survival of MRSA during thermal processing of frankfurters, summer sausage, and boneless ham. Frankfurters, summer sausage, and boneless ham were manufactured using formulations and processing procedures developed at the Iowa State University meat laboratory. Thermal processing resulted in a significant log reduction (p<0.05) for boneless ham, summer sausage, and frankfurters when compared to uncooked, positive controls for each of the three processed meat products. All products were thermally processed to an internal temperature of 70°C and promptly cooled to 7.2°C. Boneless ham showed the highest log reduction (7.28 logs) from cooking, followed by summer sausage (6.75 logs) and frankfurters (5.53 logs). The results of this study indicate that thermal processing of ham, summer sausage, and frankfurters to 70°C is sufficient to reduce the risk of MRSA as a potential food safety hazard.

Tissue-nonspecific alkaline phosphatase acts redundantly with PAP and NT5E to generate adenosine in the dorsal spinal cord

Prostatic acid phosphatase (PAP) and ecto-5'-nucleotidase (NT5E) hydrolyze extracellular AMP to adenosine in dorsal root ganglia (DRG) neurons and in the dorsal spinal cord. Previously, we found that adenosine production was reduced, but not eliminated, in Pap⁻/⁻/Nt5e⁻/⁻ double knock-out (dKO) mice, suggesting that a third AMP ectonucleotidase was present in these tissues. Here, we found that tissue-nonspecific alkaline phosphatase (TNAP, encoded by the Alpl gene) is expressed and functional in DRG neurons and spinal neurons. Using a cell-based assay, we found that TNAP rapidly hydrolyzed extracellular AMP and activated adenosine receptors. This activity was eliminated by MLS-0038949, a selective pharmacological inhibitor of TNAP. In addition, MLS-0038949 eliminated AMP hydrolysis in DRG and spinal lamina II of dKO mice. Using fast-scan-cyclic voltammetry, we found that adenosine was rapidly produced from AMP in spinal cord slices from dKO mice, but virtually no adenosine was produced in spinal cord slices from dKO mice treated with MLS-0038949. Last, we found that AMP inhibited excitatory neurotransmission via adenosine A1 receptor activation in spinal cord slices from wild-type, Pap⁻/⁻, Nt5e⁻/⁻, and dKO mice, but failed to inhibit neurotransmission in slices from dKO mice treated with MLS-0038949. These data suggest that triple elimination of TNAP, PAP, and NT5E is required to block AMP hydrolysis to adenosine in DRG neurons and dorsal spinal cord. Moreover, our data reveal that TNAP, PAP, and NT5E are the main AMP ectonucleotidases in primary somatosensory neurons and regulate physiology by metabolizing extracellular purine nucleotides.

High-throughput screen identifies cyclic nucleotide analogs that inhibit prostatic acid phosphatase

The secretory and transmembrane isoforms of prostatic acid phosphatase (PAP) can dephosphorylate extracellular adenosine 5'-monophosphate (AMP) to adenosine, classifying PAP as an ectonucleotidase. Currently, there are no compounds that inhibit PAP in living cells. To identify small-molecule modulators of PAP, we used a 1536-well-based quantitative high-throughput fluorogenic assay to screen the Library of Pharmacologically Active Compounds (LOPAC(1280)) arrayed as eight-concentration dilution series. This fluorogenic assay used difluoro-4-methylumbelliferyl phosphate as substrate and collected data in kinetic mode. Candidate hits were subsequently tested in an orthogonal absorbance-based biochemical assay that used AMP as substrate. From these initial screens, three inhibitors of secretory human (h) and mouse (m)PAP were identified: 8-(4-chlorophenylthio) cAMP (pCPT-cAMP), calmidazolium chloride, and nalidixic acid. These compounds did not inhibit recombinant alkaline phosphatase. Of these compounds, only pCPT-cAMP and a related cyclic nucleotide analog (8-[4-chlorophenylthio] cGMP; pCPT-cGMP) inhibited the ectonucleotidase activity of transmembrane PAP in a cell-based assay. These cyclic nucleotides are structurally similar to AMP but cannot be hydrolyzed by PAP. In summary, we identified two cyclic nucleotide analogs that inhibit secretory and transmembrane PAP in vitro and in live cells.

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.

Orally active adenosine A(1) receptor agonists with antinociceptive effects in mice

Adenosine A(1) receptor (A(1)AR) agonists have antinociceptive effects in multiple preclinical models of acute and chronic pain. Although numerous A(1)AR agonists have been developed, clinical applications of these agents have been hampered by their cardiovascular side effects. Herein we report a series of novel A(1)AR agonists, some of which are structurally related to adenosine 5'-monophosphate (5'-AMP), a naturally occurring nucleotide that itself activates A(1)AR. These novel compounds potently activate A(1)AR in several orthogonal in vitro assays and are subtype selective for A(1)AR over A(2A)AR, A(2B)AR, and A(3)AR. Among them, UNC32A (3a) is orally active and has dose-dependent antinociceptive effects in wild-type mice. The antinociceptive effects of 3a were completely abolished in A(1)AR knockout mice, revealing a strict dependence on A(1)AR for activity. The apparent lack of cardiovascular side effects when administered orally and high affinity (K(i) of 36 nM for the human A(1)AR) make this compound potentially suitable as a therapeutic.

PAPupuncture has localized and long-lasting antinociceptive effects in mouse models of acute and chronic pain

Acupuncture has been used for millennia to treat pain, although its efficacy and duration of action is limited. Acupuncture also has brief (1–2 h) antinociceptive effects in mice and these effects are dependent on localized adenosine A₁ receptor (A₁R) activation. Intriguingly, adenosine 5’-monophosphate (AMP) is basally elevated near acupuncture points. This finding suggested that it might be possible to inhibit nociception for a longer period of time by injecting prostatic acid phosphatase (PAP, ACPP) into acupuncture points. PAP is an ectonucleotidase that dephosphorylates extracellular AMP to adenosine, has a long half-life in vivo and is endogenously found in muscle tissue surrounding acupuncture points. Here, we found that injection of PAP into the popliteal fossa—a space behind the knee that encompasses the Weizhong acupuncture point—had dose- and A₁R-dependent antinociceptive effects in mouse models of acute and chronic pain. These inhibitory effects lasted up to six days following a single injection, much longer than the hour-long inhibition provided by acupuncture. Antinociception could be transiently boosted with additional substrate (AMP) or transiently blocked with an A₁R antagonist or an inhibitor of phospholipase C. This novel therapeutic approach—which we term “PAPupuncture”—locally inhibits pain for an extended period of time (100x acupuncture), exploits a molecular mechanism that is common to acupuncture, yet does not require acupuncture needle stimulation.

Secretion and N-linked glycosylation are required for prostatic acid phosphatase catalytic and antinociceptive activity

Secretory human prostatic acid phosphatase (hPAP) is glycosylated at three asparagine residues (N62, N188, N301) and has potent antinociceptive effects when administered to mice. Currently, it is unknown if these N-linked residues are required for hPAP protein stability and activity in vitro or in animal models of chronic pain. Here, we expressed wild-type hPAP and a series of Asn to Gln point mutations in the yeast Pichia pastoris X33 then analyzed protein levels and enzyme activity in cell lysates and in conditioned media. Pichia secreted wild-type recombinant (r)-hPAP into the media (6-7 mg protein/L). This protein was as active as native hPAP in biochemical assays and in mouse models of inflammatory pain and neuropathic pain. In contrast, the N62Q and N188Q single mutants and the N62Q, N188Q double mutant were expressed at lower levels and were less active than wild-type r-hPAP. The purified N62Q, N188Q double mutant protein was also 1.9 fold less active in vivo. The N301Q mutant was not expressed, suggesting a critical role for this residue in protein stability. To explicitly test the importance of secretion, a construct lacking the signal peptide of hPAP was expressed in Pichia and assayed. This "cellular" construct was not expressed at levels detectable by western blotting. Taken together, these data indicate that secretion and post-translational carbohydrate modifications are required for PAP protein stability and catalytic activity. Moreover, our findings indicate that recombinant hPAP can be produced in Pichia--a yeast strain that is used to generate biologics for therapeutic purposes.

PAP and NT5E inhibit nociceptive neurotransmission by rapidly hydrolyzing nucleotides to adenosine

Background

Prostatic acid phosphatase (PAP) and ecto-5'-nucleotidase (NT5E, CD73) produce extracellular adenosine from the nucleotide AMP in spinal nociceptive (pain-sensing) circuits; however, it is currently unknown if these are the main ectonucleotidases that generate adenosine or how rapidly they generate adenosine.

Results

We found that AMP hydrolysis, when measured histochemically, was nearly abolished in dorsal root ganglia (DRG) neurons and lamina II of spinal cord from Pap/Nt5e double knockout (dKO) mice. Likewise, the antinociceptive effects of AMP, when combined with nucleoside transport inhibitors (dipyridamole or 5-iodotubericidin), were reduced by 80-100% in dKO mice. In addition, we used fast scan cyclic voltammetry (FSCV) to measure adenosine production at subsecond resolution within lamina II. Adenosine was maximally produced within seconds from AMP in wild-type (WT) mice but production was reduced >50% in dKO mice, indicating PAP and NT5E rapidly generate adenosine in lamina II. Unexpectedly, we also detected spontaneous low frequency adenosine transients in lamina II with FSCV. Adenosine transients were of short duration (<2 s) and were reduced (>60%) in frequency in Pap^-/-, Nt5e^-/- and dKO mice, suggesting these ectonucleotidases rapidly hydrolyze endogenously released nucleotides to adenosine. Field potential recordings in lamina II and behavioral studies indicate that adenosine made by these enzymes acts through the adenosine A₁ receptor to inhibit excitatory neurotransmission and nociception.

Conclusions

Collectively, our experiments indicate that PAP and NT5E are the main ectonucleotidases that generate adenosine in nociceptive circuits and indicate these enzymes transform pulsatile or sustained nucleotide release into an inhibitory adenosinergic signal.

Impact of ectoenzymes on p2 and p1 receptor signaling

P2 receptors that are activated by extracellular nucleotides (e.g., ATP, ADP, UTP, UDP, Ap(n)A) and P1 receptors activated by adenosine control a diversity of biological processes. The activation of these receptors is tightly regulated by ectoenzymes that metabolize their ligands. This review presents these enzymes as well as their roles in the regulation of P2 and P1 receptor activation. We focus specifically on the role of ectoenzymes in processes of our interest, that is, inflammation, vascular tone, and neurotransmission. An update on the development of ectonucleotidase inhibitors is also presented.

Distribution of ecto-nucleotidases in mouse sensory circuits suggests roles for nucleoside triphosphate diphosphohydrolase-3 in nociception and mechanoreception

Nucleotide-activated P2X channels and P2Y metabotropic receptors participate in nociceptive signaling. Agonist availability is regulated by nucleoside triphosphate diphosphohydrolase-1 (NTPDase1), -2, -3, and -8, a family of enzymes that hydrolyze extracellular ATP to generate ADP (a P2Y agonist) and AMP. They provide a major source of extracellular AMP, the substrate for adenosine production by ecto-5'-nucleotidase (NT5E), and thereby regulate adenosine (P1) receptor signaling. NTPDases vary in their efficiency of tri- and diphosphate hydrolysis; therefore, which family members are expressed impacts nucleotide availability and half-life. This study employed enzyme activity histochemistry to examine the distribution of ATPase activity and immunohistochemistry for NTPDase1, 2, 3, and 8 in dorsal root ganglion (DRG) and spinal cord. Nucleotidase activity was robust in spinal dorsal horn, confirming that nociceptive pathways are a major site of nucleotide transmission. In DRG, extensive staining revealed ATPase activity in a subset of neurons and in non-neuronal cells. mRNA for NTPDase1-3, but not NTPDase8, was detected in lumbar DRG and spinal cord. Immunoreactivity for NTPDase3 closely matched the distribution of ATPase activity, labeling DRG central projections in the dorsal root and superficial dorsal horn, as well as intrinsic spinal neurons concentrated in lamina II. In DRG, NTPDase3 co-localized with markers of nociceptors and with NT5E. In addition, labeling of a subset of larger-diameter neurons in DRG was consistent with intense staining of Meissner corpuscle afferents in glabrous skin. Merkel cells and terminal Schwann cells of hair follicle afferents were also labeled, but the axons themselves were negative. We propose that NTPDase3 is a key regulator of nociceptive signaling that also makes an unexpected contribution to innocuous tactile sensation.

Pain-relieving prospects for adenosine receptors and ectonucleotidases

Adenosine receptor agonists have potent antinociceptive effects in diverse preclinical models of chronic pain. By contrast, the efficacy of adenosine and adenosine receptor agonists in treating pain in humans is unclear. Two ectonucleotidases that generate adenosine in nociceptive neurons were recently identified. When injected spinally, these enzymes have long-lasting adenosine A(1) receptor-dependent antinociceptive effects in inflammatory and neuropathic pain models. Furthermore, recent findings indicate that spinal adenosine A(2A) receptor activation can enduringly inhibit neuropathic pain symptoms. Collectively, these studies suggest the possibility of treating chronic pain in humans by targeting specific adenosine receptor subtypes in anatomically defined regions with agonists or with ectonucleotidases that generate adenosine.

Structural and functional analysis of human prostatic acid phosphatase

Prostatic acid phosphatase (PAP) is the most abundant phosphatase in human prostate tissue/secretions. It is a clinically important protein for its relevance as a biomarker of prostate carcinoma. Furthermore, it has a potential role in fertilization. We describe here most of the features of PAP including gene regulation, gene/protein structure, functions, its role in tumor progression and evolutionary features. PAP has phosphatase activity and is an extensively studied biomarker of prostate cancer. The major action of PAP is to dephosphorylate macromolecules with the help of catalytic residues (His(12) and Asp(258)) that are located in the cleft between two domains. This article will be of great interest to all those scientists who are working in the area of prostate pathophysiology.

Prostatic acid phosphatase reduces thermal sensitivity and chronic pain sensitization by depleting phosphatidylinositol 4,5-bisphosphate

Prostatic acid phosphatase (PAP) is expressed in nociceptive dorsal root ganglion (DRG) neurons, functions as an ectonucleotidase, and generates adenosine extracellularly. Here, we found that PAP inhibits noxious thermal sensitivity and sensitization that is associated with chronic pain through sustained activation of the adenosine A(1) receptor (A(1)R) and phospholipase C-mediated depletion of phosphatidylinositol 4,5-bisphosphate (PIP(2)). In mice, intrathecal injection of PAP reduced PIP(2) levels in DRGs, inhibited thermosensation through TRPV1, and enduringly reduced thermal hyperalgesia and mechanical allodynia caused by inflammation, nerve injury, and pronociceptive receptor activation. This included inhibitory effects on lysophosphatidic acid, purinergic (ATP), bradykinin, and protease-activated (thrombin) receptors. Conversely, PIP(2) levels were significantly elevated in DRGs from Pap(-/-) mice, and this correlated with enhanced thermal hyperalgesia and mechanical allodynia in Pap(-/-) mice. To directly test the importance of PIP(2) in nociception, we intrathecally injected PIP(2) into mice. This transiently (2 h) elevated PIP(2) levels in lumbar DRGs and transiently (2 h) enhanced thermosensation. Additionally, thermal hyperalgesia and mechanical allodynia were enduringly enhanced when PIP(2) levels were elevated coincident with injury/pronociceptive receptor stimulation. Nociceptive sensitization was not affected if PIP(2) levels were elevated in the absence of ongoing pronociceptive receptor stimulation. Together, our data suggest that PIP(2) levels in DRGs directly influence thermosensation and the magnitude of nociceptive sensitization. Moreover, our data suggest there is an underlying "phosphoinositide tone" that can be manipulated by an adenosine-generating ectonucleotidase. This tone regulates how effectively acute nociceptive insults promote the transition to chronic pain.

Recombinant ecto-5'-nucleotidase (CD73) has long lasting antinociceptive effects that are dependent on adenosine A1 receptor activation

BACKGROUND

Ecto-5'-nucleotidase (NT5E, also known as CD73) hydrolyzes extracellular adenosine 5'-monophosphate (AMP) to adenosine in nociceptive circuits. Since adenosine has antinociceptive effects in rodents and humans, we hypothesized that NT5E, an enzyme that generates adenosine, might also have antinociceptive effects in vivo.

RESULTS

To test this hypothesis, we purified a soluble version of mouse NT5E (mNT5E) using the baculovirus expression system. Recombinant mNT5E hydrolyzed AMP in biochemical assays and was inhibited by alpha,beta-methylene-adenosine 5'-diphosphate (alpha,beta-me-ADP; IC50 = 0.43 microM), a selective inhibitor of NT5E. mNT5E exhibited a dose-dependent thermal antinociceptive effect that lasted for two days when injected intrathecally in wild-type mice. In addition, mNT5E had thermal antihyperalgesic and mechanical antiallodynic effects that lasted for two days in the complete Freund's adjuvant (CFA) model of inflammatory pain and the spared nerve injury (SNI) model of neuropathic pain. In contrast, mNT5E had no antinociceptive effects when injected intrathecally into adenosine A1 receptor (A1R, Adora1) knockout mice.

CONCLUSION

Our data indicate that the long lasting antinociceptive effects of mNT5E are due to hydrolysis of AMP followed by activation of A1R. Moreover, our data suggest recombinant NT5E could be used to treat chronic pain and to study many other physiological processes that are regulated by NT5E.

Ecto-5'-nucleotidase (CD73) inhibits nociception by hydrolyzing AMP to adenosine in nociceptive circuits

Ecto-5'-nucleotidase (NT5E, CD73) is a membrane-anchored protein that hydrolyzes extracellular adenosine 5'-monophosphate (AMP) to adenosine in diverse tissues but has not been directly studied in nociceptive neurons. We found that NT5E was located on peptidergic and nonpeptidergic nociceptive neurons in dorsal root ganglia (DRG) and on axon terminals in lamina II (the substantia gelatinosa) of spinal cord. NT5E was also located on epidermal keratinocytes, cells of the dermis, and on nociceptive axon terminals in the epidermis. Following nerve injury, NT5E protein and AMP histochemical staining were coordinately reduced in lamina II. In addition, AMP hydrolytic activity was reduced in DRG neurons and spinal cord of Nt5e(-/-) mice. The antinociceptive effects of AMP, when combined with the adenosine kinase inhibitor 5-iodotubericidin, were reduced by approximately 50% in Nt5e(-/-) mice and were eliminated in Adenosine A(1) receptor (A(1)R, Adora1) knock-out mice. Additionally, Nt5e(-/-) mice displayed enhanced sensitivity in the tail immersion assay, in the complete Freund's adjuvant model of inflammatory pain and in the spared nerve injury model of neuropathic pain. Collectively, our data indicate that the ectonucleotidase NT5E regulates nociception by hydrolyzing AMP to adenosine in nociceptive circuits and represents a new molecular target for the treatment of chronic pain. Moreover, our data suggest NT5E is well localized to regulate nucleotide signaling between skin cells and sensory axons.

Prostatic acid phosphatase is expressed in peptidergic and nonpeptidergic nociceptive neurons of mice and rats

Thiamine monophosphatase (TMPase, also known as Fluoride-resistant acid phosphatase or FRAP) is a classic histochemical marker of small- to medium-diameter dorsal root ganglia (DRG) neurons and has primarily been studied in the rat. Previously, we found that TMPase was molecularly identical to Prostatic acid phosphatase (PAP) using mice. In addition, PAP was expressed in a majority of nonpeptidergic, isolectin B4-binding (IB4⁺) nociceptive neurons and a subset of peptidergic, calcitonin gene-related peptide-containing (CGRP⁺) nociceptive neurons. At the time, we were unable to determine if PAP was present in rat DRG neurons because the antibody we used did not cross-react with PAP in rat tissues. In our present study, we generated a chicken polyclonal antibody against the secretory isoform of mouse PAP. This antibody detects mouse, rat and human PAP protein on western blots. Additionally, this antibody detects PAP in mouse and rat small- to medium-diameter DRG neurons and axon terminals in lamina II of spinal cord. In the rat, 92.5% of all PAP⁺ cells bind the nonpeptidergic marker IB4 and 31.8% of all PAP⁺ cells contain the peptidergic marker CGRP. Although PAP is found in peptidergic and nonpeptidergic neurons of mice and rats, the percentage of PAP⁺ neurons that express these markers differs between species. Moreover, PAP⁺ axon terminals in the rat partially overlap with Protein kinase Cγ (PKCγ⁺) interneurons in dorsal spinal cord whereas PAP⁺ axon terminals in the mouse terminate dorsal to PKCγ⁺ interneurons. Collectively, our studies highlight similarities and differences in PAP localization within nociceptive neurons of mice and rats.

Crystal Structures of the histidine acid phosphatase from Francisella tularensis provide insight into substrate recognition

Histidine acid phosphatases catalyze the transfer of a phosphoryl group from phosphomonoesters to water at acidic pH using an active-site histidine. The histidine acid phosphatase from the category A pathogen Francisella tularensis (FtHAP) has been implicated in intramacrophage survival and virulence, motivating interest in understanding the structure and mechanism of this enzyme. Here, we report a structure-based study of ligand recognition by FtHAP. The 1.70-A-resolution structure of FtHAP complexed with the competitive inhibitor l(+)-tartrate was solved using single-wavelength anomalous diffraction phasing. Structures of the ligand-free enzyme and the complex with inorganic phosphate were determined at resolutions of 1.85 and 1.70 A, respectively. The structure of the Asp261Ala mutant enzyme complexed with the substrate 3'-AMP was determined at 1.50 A resolution to gain insight into substrate recognition. FtHAP exhibits a two-domain fold similar to that of human prostatic acid phosphatase, consisting of an alpha/beta core domain and a smaller domain that caps the core domain. The structures show that the core domain supplies the phosphoryl binding site, catalytic histidine (His17), and an aspartic acid residue (Asp261) that protonates the leaving group, while the cap domain contributes residues that enforce substrate preference. FtHAP and human prostatic acid phosphatase differ in the orientation of the crucial first helix of the cap domain, implying differences in the substrate preferences of the two enzymes. 3'-AMP binds in one end of a 15-A-long tunnel, with the adenine clamped between Phe23 and Tyr135, and the ribose 2'-hydroxyl interacting with Gln132. The importance of the clamp is confirmed with site-directed mutagenesis; mutation of Phe23 and Tyr135 individually to Ala increases K(m) by factors of 7 and 10, respectively. The structural data are consistent with a role for FtHAP in scavenging phosphate from small molecules present in host macrophage cells.

A high throughput assay to identify small molecule modulators of prostatic acid phosphatase

Prostatic acid phosphatase (PAP) is expressed in nociceptive neurons and functions as an ectonucleotidase. Injection of the secretory isoform of PAP has potent antinociceptive effects in mouse models of chronic pain. These data suggested that a small molecule activator of PAP may have utility as a novel therapeutic for chronic pain, while inhibitors could be used to acutely inhibit PAP in vitro and in vivo. To identify small molecule modulators of PAP activity, we validated a high throughput, fluorescence-based biochemical assay and then used this assay to screen a compound library. We decreased the frequency of false positive activators by subtracting compound fluorescence from the final assay fluorescence. This approach significantly reduced the number of false positive activators found in the screen. While no activators were confirmed, seven novel inhibitors of PAP were identified. Our results suggest this high throughput assay could be used to identify small molecule modulators of PAP activity.