Heparin and chondroitin sulfate inhibit adenine nucleotide hydrolysis in liver and kidney membrane enriched fractions

Analysis of Extracellular ATP Distribution in the Intervertebral Disc

Progressive loss of proteoglycans (PGs) is the major biochemical change during intervertebral disc (IVD) degeneration. Adenosine triphosphate (ATP) as the primary energy source is not only critical for cell survival but also serves as a building block in PG synthesis. Extracellular ATP can mediate a variety of physiological functions and was shown to promote extracellular matrix (ECM) production in the IVD. Therefore, the objective of this study was to develop a 3D finite element model to predict extracellular ATP distribution in the IVD and evaluate the impact of degeneration on extracellular ATP distribution. A novel 3D finite element model of the IVD was developed by incorporating experimental measurements of ATP metabolism and ATP-PG binding kinetics into the mechano-electrochemical mixture theory. The new model was validated by experimental data of porcine IVD, and then used to analyze the extracellular distribution of ATP in human IVDs. Extracellular ATP was shown to bind specifically with PGs in IVD ECM. It was found that annulus fibrosus cells hydrolyze ATP faster than that of nucleus pulposus (NP) cells whereas NP cells exhibited a higher ATP release. The distribution of extracellular ATP in a porcine model was consistent with experimental data in our previous study. The predictions from a human IVD model showed a high accumulation of extracellular ATP in the NP region, whereas the extracellular ATP level was reduced with tissue degeneration. This study provides an understanding of extracellular ATP metabolism and its potential biological influences on the IVD via purinergic signaling.

Sulfatase 2 Inhibition Sensitizes Triple-Negative Breast Cancer Cells to Chemotherapy Through Augmentation of Extracellular ATP

Background

Breast cancer is the leading cause of cancer-related death among women worldwide. Patients diagnosed with triple-negative breast cancer (TNBC) have limited therapeutic options that produce durable responses. Hence, a diagnosis of TNBC is associated with a poor prognosis compared to other types of breast cancer. As a result, there is a critical need for novel therapies that can deepen and prolong responses.We previously found that chemotherapy causes the release of extracellular adenosine triphosphate (eATP). Augmenting eATP release can boost the response of TNBC cells to chemotherapy and cause increased cell death. However, eATP concentrations are limited by several families of extracellular ATPases, which complicates the design of compounds that attenuate eATP degradation.In this study, we hypothesized that heparan sulfate (HS) would inhibit extracellular ATPases and accentuate chemotherapy-induced cytotoxicity in TNBC by augmenting eATP. HS can be desulfated by sulfatase 1 and 2; sulfatase 2 is consistently highly expressed in a variety of cancers including breast cancer, whereas sulfatase 1 is not. We hypothesized that the sulfatase 2 inhibitor OKN-007 would exacerbate chemotherapy-induced eATP release and TNBC cell death.

Methods

TNBC cell lines and nontumorigenic immortal mammary epithelial cells were treated with paclitaxel in the presence of heparan sodium sulfate and/or OKN-007; eATP content and cell viability were evaluated. In addition, protein and cell surface expression of sulfatases 1 and 2 were determined in all examined cell lines via ELISA, Western blot, and flow cytometry analyses.

Results

Sulfatase 2 was highly expressed in TNBC cell lines and human breast cancer samples but not in immortal mammary epithelial cells and much less so in normal human breast tissue and ductal carcinoma in situ samples. OKN-007 exacerbated chemotherapy-induced eATP release and chemotherapy-induced TNBC cell death. When combined with chemotherapy, OKN-007 attenuated cells with a cancer-initiating cell phenotype.

Conclusions

These results suggest that sulfatase 2 inhibitors in combination with chemotherapy attenuate the viability of TNBC cells more than chemotherapy alone by exacerbating eATP release. These effects, as well as their capacity to attenuate the cancer-initiating cell fraction, may translate into combination therapies for TNBC that induce deeper and more durable responses.

Improving the immunosuppressive potential of articular chondroprogenitors in a three-dimensional culture setting

Cartilage repair in osteoarthritic patients remains a challenge. Identifying resident or donor stem/progenitor cell populations is crucial for augmenting the low intrinsic repair potential of hyaline cartilage. Furthermore, mediating the interaction between these cells and the local immunogenic environment is thought to be critical for long term repair and regeneration. In this study we propose articular cartilage progenitor/stem cells (CPSC) as a valid alternative to bone marrow-derived mesenchymal stem cells (BMMSC) for cartilage repair strategies after trauma. Similar to BMMSC, CPSC isolated from osteoarthritic patients express stem cell markers and have chondrogenic, osteogenic, and adipogenic differentiation ability. In an in vitro 2D setting, CPSC show higher expression of SPP1 and LEP, markers of osteogenic and adipogenic differentiation, respectively. CPSC also display a higher commitment toward chondrogenesis as demonstrated by a higher expression of ACAN. BMMSC and CPSC were cultured in vitro using a previously established collagen-chondroitin sulfate 3D scaffold. The scaffold mimics the cartilage niche, allowing both cell populations to maintain their stem cell features and improve their immunosuppressive potential, demonstrated by the inhibition of activated PBMC proliferation in a co-culture setting. As a result, this study suggests articular cartilage derived-CPSC can be used as a novel tool for cellular and acellular regenerative medicine approaches for osteoarthritis (OA). In addition, the benefit of utilizing a biomimetic acellular scaffold as an advanced 3D culture system to more accurately mimic the physiological environment is demonstrated.

Renal vasculature reactivity to agonist of P2X7 receptor is increased in streptozotocin-induced diabetes

BACKGROUND

Diabetic nephropathy is characterized by the dysfunction of renal microvasculature. The involvement of the P2X7 receptor, being a part of the purinergic system, is presumable in this process. The aim of our study was to investigate the P2X7 receptor-mediated renal microvasculature response and renal metabolism of extracellular adenine nucleotides in diabetic rats.

METHODS

Study was performed on streptozotocin-induced diabetic Wistar rats. The vascular response to BzATP, an agonist of the P2X7 receptor, was monitored based on the changes of cortical blood flow (CBF), glomerular filtration rate (GFR) and glomerular inulin space (GIS). The renal interstitial fluid (RIF) was probed by microdialysis technique and concentrations of ATP and adenosine were measured. Activity on NTDPase and 5'-nucleotidases was measured on renal membranes.

RESULTS

Diabetic kidneys were characterized by decreased ATP RIF and increased adenosine RIF concentrations with accompanied enhancement of NTDPase and 5'-nucleotidase activities. BzATP induced a more pronounced increase of CBF and decrease of GFR and GIS in diabetes rats. These effects were abolished by A438079, an antagonist of the P2X7 receptor.

CONCLUSIONS

It is possible that increased P2X7 receptor reactivity may be involved in the pathogenesis of diabetic nephropathy.

ATP promotes extracellular matrix biosynthesis of intervertebral disc cells

We have recently found a high accumulation of extracellular adenosine triphosphate (ATP) in the center of healthy porcine intervertebral discs (IVD). Since ATP is a powerful extracellular signaling molecule, extracellular ATP accumulation might regulate biological activities in the IVD. The objective of this study was therefore to investigate the effects of extracellular ATP on the extracellular matrix (ECM) biosynthesis of porcine IVD cells isolated from two distinct anatomical regions: the annulus fibrosus (AF) and nucleus pulposus (NP). ATP treatment significantly promotes ECM deposition and corresponding gene expression (aggrecan and type II collagen) by both cell types in three-dimensional agarose culture. A significant increase in ECM accumulation has been found in AF cells at a lower ATP treatment level (20 μM) compared with NP cells (100 μM), indicating that AF cells are more sensitive to extracellular ATP than NP cells. NP cells also exhibit higher ECM accumulation and intracellular ATP than AF cells under control and treatment conditions, suggesting that NP cells are intrinsically more metabolically active. Moreover, ATP treatment also augments the intracellular ATP level in NP and AF cells. Our findings suggest that extracellular ATP not only promotes ECM biosynthesis via a molecular pathway, but also increases energy supply to fuel that process.

Energy metabolism of intervertebral disc under mechanical loading

Intervertebral disc (IVD) degeneration is closely associated with low back pain (LBP), which is a major health concern in the U.S. Cellular biosynthesis of extracellular matrix (ECM), which is important for maintaining tissue integrity and preventing tissue degeneration, is an energy demanding process. Due to impaired nutrient support in avascular IVD, adenosine triphosphate (ATP) supply could be a limiting factor for maintaining normal ECM synthesis. Therefore, the objective of this study was to investigate the energy metabolism in the annulus fibrosus (AF) and nucleus pulposus (NP) of porcine IVD under static and dynamic compressions. Under compression, pH decreased and the contents of lactate and ATP increased significantly in both AF and NP regions, suggesting that compression can promote ATP production via glycolysis and reduce pH by increasing lactate accumulation. A high level of extracellular ATP content was detected in the NP region and regulated by compressive loading. Since ATP can serve not only as an intra-cellular energy currency, but also as a regulator of a variety of cellular activities extracellularly through the purinergic signaling pathway, our findings suggest that compression-mediated ATP metabolism could be a novel mechanobiological pathway for regulating IVD metabolism.

Endotoxin-induced effects on nucleotide catabolism in mouse kidney

Extracellular adenosine 5'-triphosphate (ATP) acts as a proinflammatory mediator. Adenosine, the final product of ATP breakdown, is an anti-inflammatory compound, acting mainly on adenosine A(2A) receptors. Considering that the kidney is an organ strongly affected during systemic inflammatory responses and that ectonucleotidases are responsible for the control of extracellular nucleotide and nucleoside levels, we examined the endotoxin-induced effects on ectonucleotidases in kidney membranes of mice, and whether CGS-21680 hydrochloride (3-[4-[2-[[6-amino-9-[(2R,3R,4S,5S)-5-(ethylcarbamoyl)-3,4-dihydroxy-oxolan-2-yl]purin-2-yl]amino]ethyl]phenyl]propanoic acid), a selective adenosine A(2A) receptor agonist, antagonizes the lipopolysaccharide (LPS)-induced effects on nucleotide catabolism in kidney. Animals were injected intraperitoneally with 12 mg/kg LPS and/or 0.5mg/kg CGS-21680 or saline. Nucleotidase activities were determined in kidney membrane preparations and ATP metabolism was measured by high performance liquid chromatography (HPLC) assay. Analysis of ectonucleotidase expression was carried out by semi-quantitative semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR). Exposure to endotoxemia promoted an increase in ATP and p-Nitrophenyl thymidine 5'-monophosphate (p-Nph-5'-TMP) hydrolysis, and a decrease in adenosine 5'-monophosphate (AMP) hydrolysis. CGS-21680 treatment failed to reverse these changes. HPLC analysis indicated a decrease in extracellular ATP and adenosine levels in groups treated with LPS and LPS plus CGS-21680. The expression pattern of ectonucleotidases revealed an increase in Entpd3, Enpp2, and Enpp3 mRNA levels after LPS injection. These findings indicate that nucleotide and nucleoside availability in mouse kidney is altered at different stages of endotoxemia, in order to protect the integrity of this organ when exposed to systemic inflammation.

Manganese effects in the liver following subacute or subchronic manganese chloride exposure in rats

Manganese (Mn) toxicity is most often found in mining and welding industry workers. Accumulation of manganese in the brain can result in a syndrome similar to that of Parkinson's disease. Observations on former Mn-alloy workers suggested that residual effects could last for years after exposure. The objective of this study was to assess effects of Mn in the liver of rats following subacute or subchronic exposure and after recovery. Male Sprague-Dawley rats were exposed to manganese chloride (MnCl(2)) for 30 days, 90 days, or for 90 days followed by a 30-day post-exposure recovery period. Results showed that MnCl(2) exposure resulted in liver injury in rats and the extent of injury correlated positively with exposure time. The effect in mitochondria was stronger than in the membrane or nucleus. Most of the changes in these biomarkers recovered when manganese exposure ceased.

L-NAME-treatment alters ectonucleotidase activities in kidney membranes of rats

AIMS

To investigate the effect of N(omega)-Nitro-L-arginine methyl ester (l-NAME) treatment, known to induce a sustained elevation of blood pressure, on ectonucleotidase activities in kidney membranes of rats.

MAIN METHODS

L-NAME (30 mg/kg/day) was administered to Wistar rats for 14 days in the drinking water. Enzyme activities were determined colorimetrically and their gene expression patterns were analyzed by semi-quantitative RT-PCR. The metabolism of ATP and the accumulation of adenosine were evaluated by HPLC in kidney membranes from control and hypertensive rats. PKC phosphorylation state was investigated by Western blot.

KEY FINDINGS

We observed an increase in systolic blood pressure from 115+/-12 mmHg (control group) to 152+/-18 mmHg (l-NAME-treated group). Furthermore, the hydrolysis of ATP, ADP, AMP, and p-Nph-5'TMP was also increased (17%, 35%, 27%, 20%, respectively) as was the gene expression of NTPDase2, NTPDase3 and NPP3 in kidneys of hypertensive animals. Phospho-PKC was increased in hypertensive rats.

SIGNIFICANCE

The general increase in ATP hydrolysis and in ecto-5'-nucleotidase activity suggests a rise in renal adenosine levels and in renal autoregulatory responses in order to protect the kidney against the threat presented by hypertension.

Adenine nucleotide hydrolysis in patients with aseptic and bacterial meningitis

The meningitis is a disease with high mortality rates capable to cause neurologic sequelae. The adenosine (the final product of ATP hydrolysis by ectonucleotidases), have a recognized neuroprotective actions in the central nervous system (CNS) in pathological conditions. The aim of the present study was evaluate the adenine nucleotides hydrolysis for to verify one possible role of ATP, ADP and AMP hydrolysis in inflammatory process such as meningitis. The hydrolysis was verified in cerebrospinal fluid (CSF) from human patients with aseptic and bacterial meningitis. Our results showed that the ATP hydrolysis was reduced 12.28% (P < 0.05) in bacterial meningitis and 22% (P < 0.05) in aseptic meningitis. ADP and AMP hydrolysis increased 79.13% (P < 0.05) and 26.37% (P < 0.05) in bacterial meningitis, respectively, and 57.39% (P < 0.05) and 42.64% (P < 0.05) in aseptic meningitis, respectively. This may be an important protective mechanism in order to increase adenosine production.

ATP and ADP hydrolysis in the kidney and liver of fish, chickens and rats

We investigated NTPDase-like activity [ecto-nucleoside triphosphate diphosphohydrolases (E-NTPDases)] in liver and kidney membrane from silver catfish (Rhamdia quelen), chicken (Gallus gallus) and rat (Rattus norvegicus) under different conditions and in the presence of several inhibitors. The cation concentration required for maximal activity was 0.5, 1.5 and 2.0 mM for fish, chicken and rat liver, respectively (with ATP and ADP as substrates). The maximal activity in the kidney was observed at calcium concentrations of 0.5, 2.0, 1.5 mM (ATP) and 0.5, 1.5, 1.0 (ADP) for fish, chickens and rats, respectively. The results showed that the pH optimum for all animals and for the two tissues was close to 8.0. The temperature chosen was 25 degrees C for fish and 36 degrees C for chicken and rat preparations. Ouabain had no effect on the NTPDase-like activity of fish, chickens or rats. NTPDase activity was decreased in the presence of lanthanum in the chicken (ADP) and rat (ATP and ADP) liver. In the kidney, lanthanum inhibited fish ATP and rat ATP and ADP (0.2 mM) hydrolysis. N-ethylmaleimide (NEM) had an inhibitory effect on the kidney of all species at the concentration of 3.0 mM (ADP). Orthovanadate only inhibited fish membrane NTPDase; azide only inhibited the preparation at high concentrations (10 mM) and fluoride inhibited it at 10 mM (fish and chicken) and 5 mM (rat). Trifluoperazine (0.05-0.2 mM) and suramin (0.03-0.3 mM) inhibited NTPDase at all concentrations tested. These results suggest that NTPDase-like activity shows a different behavior among the vertebrate species and tissues studied. Additionally, we propose that NTPDase1 is the main enzyme present in this preparation.

Characterization of NTPDase (NTPDase1; ecto-apyrase; ecto-diphosphohydrolase; CD39; EC 3.6.1.5) activity in human lymphocytes

Human lymphocytes contain NTPDase (NTPDase-1; ecto-apyrase; ecto-diphosphohydrolase; CD39; EC 3.6.1.5), a cation-dependent enzyme that hydrolyzes ATP and ADP and also other di- and triphosphate nucleosides, acting at an optimum pH of 8.0. A significant inhibition of ATP and ADP hydrolysis (P<0.05) was observed in the presence of 20 mM sodium azide. NTPDase inhibitors, 20 mM sodium fluoride, 0.2 mM trifluoperazine and 0.3 mM suramin, significantly decreased ATP and ADP hydrolysis (P<0.05) and ADP hydrolysis was only inhibited by 0.5 mM orthovanadate (P<0.05). ATP and ADP hydrolysis was not inhibited in the presence of 0.01 mM Ap5A (P1,P5-di(adenosine-5')pentaphosphate), 0.1 mM ouabain, 1 mM levamisole, 2 microg/mL oligomycin, 0.1 mM N-ethylmaleimide (NEM), or 5 mM sodium azide. With respect to kinetic behavior, apparent K(m) values of 77.6+/-10.2 and 106.8+/-21.0 microM, and V(max) values of 68.9+/-8.1 and 99.4+/-8.5 (mean+/-S.E., n=3) nmol Pi/min/mg protein were obtained for ATP and ADP, respectively. A Chevilard plot demonstrated that only one enzymatic site is responsible for the hydrolysis of ATP and ADP. The presence of CD39 was determined by flow cytometry, showing a low density of 2.72+/-0.24% (mean+/-S.E.; n=30) in human peripheral lymphocytes. The study of NTPDase activity in human lymphocytes may be important to determine the immune response status against infectious agents related to ATP and ADP hydrolysis.

NTPDase and 5'-nucleotidase activities in rats with alloxan-induced diabetes

Diabetes is associated with a hypercoagulable state. In this study, we investigated the potential effects of alloxan-induced diabetes on the activities of the enzymes NTPDase (E.C. 3.6.1.5, apyrase, ATP diphosphohydrolase, ecto/CD39) and 5'-nucleotidase (E.C. 3.1.3.5, CD73) that can control the levels of ADP and adenosine, two substances that regulates platelet aggregation. In the alloxan-treated rats, NTPDase activity was significantly increased by 88 and 35% with ATP as substrate and by 156 and 58% with ADP as substrate in platelets and synaptosomes, respectively (P< 0.05). AMP hydrolysis was increased by 142% (platelets) and 70% (synaptosomes) in diabetic rats compared to control. These results demonstrate that alloxan-induced diabetes interferes with ATP, ADP, and AMP hydrolysis in platelets and synaptosomes. Taken together, these results may indicate that in diabetic rats both NTPDase and 5'-nuleotidase from the central nervous system (CNS) and platelets respond similarly with increased activity. Thus, we speculate that platelets could be used as a potential peripheral marker of central alterations in NTPDase and 5'-nucleotidase activities in diabetes.

Paracrine factors in tubuloglomerular feedback: adenosine, ATP, and nitric oxide

The tubuloglomerular feedback response, the change in afferent arteriolar tone caused by a change in NaCl concentration at the macula densa, is likely initiated by the generation of a vasoactive mediator within the confines of the juxtaglomerular apparatus. Substantial progress has been made in identifying the nature of this mediator and the factors that modulate its effect on vascular tone. In support of earlier studies using P1 purinergic antagonists, the application of the knockout technique has shown that adenosine 1 receptors are absolutely required for eliciting TGF responses. The background level of angiotensin II appears to be an important cofactor determining the efficiency of A1AR-induced vasoconstriction, probably through a synergistic interaction at the level of the G protein-dependent transduction mechanism. The source of the adenosine is still unclear, but it is conceivable that adenosine is generated extracellularly from released ATP through a cascade of ecto-nucleotidases. There is also evidence that ATP may activate P2 receptors in preglomerular vessels, which may contribute to autoregulation of renal vascular resistance. Nitric oxide (NO), generated by the neuronal isoform of nitric oxide synthase in macula densa cells, reduces the constrictor effect of adenosine, but the regulation of NO release and its exact role in states of TGF-induced hyperfiltration are still unclear.

In vitro effects of L-arginine and guanidino compounds on NTPDase1 and 5'-nucleotidase activities from rat brain synaptosomes

Tissue accumulation of arginine (Arg), N-acetylarginine (NA), argininic acid (AA) and homoarginine (HA) occurs in hyperargininemia, an inborn error of the urea cycle. In the present study, we investigated the in vitro effects of Arg, NA, AA and HA on NTPDase1 and 5'-nucleotidase activities from synaptosomal cerebral cortex of rats. The results showed that Arg enhances NTPDase1 activity at the high concentrations tested (1.5 and 3.0mM) for both the ATP and ADP nucleotides. Activation was also observed with other guanidino compounds tested: NA, AA and HA activated ATP and ADP hydrolysis in all experiments at the concentration of 25 microM. Besides this, NA and AA activated ATP hydrolysis at a lower concentration (1 microM). In another set of experiments, we verified the effect of Arg on purified apyrase at pH 8.0 and 6.5 and observed an increase in the enzyme activity at all Arg concentrations tested (0.01-3.0mM). In contrast, Arg and the other guanidino compounds tested did not alter 5'-nucleotidase activity. These results suggest that changes in nucleotide hydrolysis may be involved in the brain dysfunction caused by hyperargininemia amongst other potential pathophysiological mechanisms involved in this condition.

Enzymes that hydrolyze adenine nucleotides in diabetes and associated pathologies

The activities of the enzymes NTPDase (E.C. 3.6.1.5, apyrase, ATP diphosphohydrolase, ecto-CD39) and 5'-nucleotidase (E.C. 3.1.3.5, CD73) were analyzed in platelets of type 2 diabetic, hypertensive and type 2 diabetic/hypertensive patients. The results showed an increase in platelet NTPDase activity in type 2 diabetic (34% and 72%), hypertensive (32% and 70%) and type 2 diabetic/hypertensive patients (30% and 55%) when compared to control (P<.01) with ATP and ADP as substrate, respectively. 5'-Nucleotidase activity was elevated in the hypertensive (60%) and type 2 diabetic/hypertensive (53%) groups when compared to the control and type 2 diabetic group (P<.01). No differences in sensitivity to inhibitors was detected between the platelets of controls and type 2 diabetic/hypertensive patients. No effects on the enzyme activities were observed when pharmacological doses of propranolol, captopril, furosemide, chlorpropamide, acetylsalicylic acid and glibenclamide were administered. Furthermore, changes in platelet adhesiveness and reactivity were found in all groups tested. In conclusion, we may postulate that NTPDase and 5'-nucleotidase from platelets are altered in patients with type 2 diabetes and hypertension. Probably, such alterations are involved in compensatory physiological responses in these diseases and are related to other important mechanisms of thromboregulation.