Enzymes that hydrolyze adenine nucleotides in platelets from breast cancer patients

Effects of clopidogrel bisulfate on B16-F10 cells and tumor development in a murine model of melanoma

Metastatic melanoma is a very aggressive skin cancer. Platelets are constituents of the tumor microenvironment and, when activated, contribute to cancer progression, especially metastasis and inflammation. P2Y12 is an adenosine diphosphate receptor that triggers platelet activation. Inhibition of P2Y12 by clopidogrel bisulfate (CB) decreases platelet activation, which is also controlled by the extracellular concentration and the metabolism of purines by purinergic enzymes. We evaluated the effects of CB on the viability and proliferation of cultured B16-F10 cells. We also used a metastatic melanoma model with C57BL-6 mice to evaluate cancer development and purine metabolism modulation in platelets. B16-F10 cells were administered intraperitoneally to the mice. Two days later, the animals underwent a 12-day treatment with CB (30 mg/kg by gavage). We have found that CB reduced cell viability and proliferation in B16-F10 culture in 72 h at concentrations above 30 µm. In vivo, CB decreased tumor nodule counts and lactate dehydrogenase levels and increased platelet purine metabolism. Our results showed that CB has significant effects on melanoma progression.

AMP hydrolysis reduction in blood plasma of breast cancer elderly patients after different treatments

Adenine nucleotides are important signaling molecules that mediate biological functions in many conditions, including cancer. The enzymes CD39 and CD73 produce adenosine in the extracellular milieu that has a very important role in tumor development. This study aimed to evaluate nucleotide hydrolysis in the plasma blood of breast cancer elderly patients. In this prospective cohort study, we investigated the ectonucleotidases activity in breast cancer elderly patients, at the moment of diagnosis and after treatment. Control group consisted of elderly women without cancer diagnostic. The nucleotide hydrolysis assay was performed by the malachite green method and used ATP, ADP, or AMP as substrates. Paired t test or Wilcoxon rank-sum test was used. Our data showed that breast cancer patients presented high levels of ATP and AMP hydrolyses when compared to control group at the moment of diagnosis. When analyzing the differences between the samples at the time of diagnostic and 6 months after treatment, we observed a significant reduction on CD73 activity after all treatments used: surgery, chemotherapy, radiotherapy, or hormone therapy. The results with APCP, a specific CD73 inhibitor, showed that the AMP hydrolysis was inhibited in all conditions evaluated. We observed a diminished ADPase activity in the patients without metastasis when compared to metastatic breast cancer patients. The results showed that AMP hydrolysis was reduced in the blood plasma of breast cancer elderly patients after different treatments. This study strengthens the potential role of CD73 enzyme as a biomarker for breast cancer treatment response.

Ectophosphatase activity in the triple-negative breast cancer cell line MDA-MB-231

Breast cancer is one of the most common cancers in the female population worldwide, and its development is thought to be associated with genetic mutations that lead to uncontrolled and accelerated growth of breast cells. This abnormal behavior requires extra energy, and indeed, tumor cells display a rewired energy metabolism compared to normal breast cells. Inorganic phosphate (Pi) is a glycolytic substrate of glyceraldehyde-3-phosphate dehydrogenase and has an important role in cancer cell proliferation. For cells to obtain Pi, ectoenzymes in the plasma membrane with their catalytic site facing the extracellular environment can hydrolyze phosphorylated molecules, and this is an initial and possibly limiting step for the uptake of Pi by carriers that behave as adjuvants in the process of energy harvesting and thus partially contributes to tumor energy requirements. In this study, the activity of an ectophosphatase in MDA-MB-231 cells was biochemically characterized, and the results showed that the activity of this enzyme was higher in the acidic pH range and that the enzyme had a K_m  = 4.5 ± 0.5 mM para-nitrophenylphosphate and a V_max  = 2280 ± 158 nM × h^-1  × mg protein^-1 . In addition, classical acid phosphatase inhibitors, including sodium orthovanadate, decreased enzymatic activity. Sodium orthovanadate was able to inhibit ectophosphatase activity while also inhibiting cell proliferation, adhesion, and migration, which are important processes in tumor progression, especially in metastatic breast cancer MDA-MB-231 cells that have higher ectophosphatase activity than MCF-7 and MCF-10 breast cells.

Increased cytokines production and oxidative stress are related with purinergic signaling and cell survival in post-thyroidectomy hypothyroidism

Thyroid hormones have essential roles in regulation of cellular functions, including the immune system. The purinergic signaling, activated through extracellular nucleotides and nucleosides has also strong implications in immune response regulation. Hypothyroidism may involve effects on the immune and purinergic systems. In view of that, we evaluated cytokines levels, their relation with the expression of purinergic enzymes and the effects of this condition on immune system cells from patients with post-thyroidectomy hypothyroidism. Increased IL6, IL10, IL17 and TNF-α levels as well as an increase in CD73 expression in lymphocytes were observed in patients' blood. Moreover, augmented myeloperoxidase activity, lipid peroxidation and thiolgroup production were observed in post-thyroidectomy hypothyroidism. In addition, proliferation and cell death of lymphocytes were enhanced when exposed to patients' serum. This study demonstrates that hypothyroidism is related to changes in the purinergic system, increased cytokines production and oxidative stress, which interfere in the cell life and signaling.

Beyond PD-1/PD-L1 Inhibition: What the Future Holds for Breast Cancer Immunotherapy

Cancer immunotherapy has altered the management of human malignancies, improving outcomes in an expanding list of diseases. Breast cancer - presumably due to its perceived low immunogenicity - is a late addition to this list. Furthermore, most of the focus has been on the triple negative subtype because of its higher tumor mutational load and lymphocyte-enriched stroma, although emerging data show promise on the other breast cancer subtypes as well. To this point the clinical use of immunotherapy is limited to the inhibition of two immune checkpoints, Programmed Cell Death Protein 1 (PD-1) and Cytotoxic T-lymphocyte-associated Protein 4 (CTLA-4). Consistent with the complexity of the regulation of the tumor - host interactions and their lack of reliance on a single regulatory pathway, combinatory approaches have shown improved efficacy albeit at the cost of increased toxicity. Beyond those two checkpoints though, a large number of co-stimulatory or co-inhibitory molecules play major roles on tumor evasion from immunosurveillance. These molecules likely represent future targets of immunotherapy provided that the promise shown in early data is translated into improved patient survival in randomized trials. The biological role, prognostic and predictive implications regarding breast cancer and early clinical efforts on exploiting these immune-related therapeutic targets are herein reviewed.

The signaling effects of ATP on melanoma-like skin cancer

Melanoma is a type of skin cancer originated by the malignant transformation of melanocytes. Increasing incidence and mortality require efforts focused on studies and research about this cancer. Its microenvironment is rich in extracellular ATP, but there are no studies evaluating the ectonucleotidases and ATP effects on tumor-derived melanoma cells with known amounts of ATP. This way, the objective of this work was to evaluate the purinergic signaling in the pathophysiology of in vivo melanoma and the in vitro effects of ATP signaling. We found increased and effective extracellular ATP hydrolysis in platelets and a significant decrease of extracellular ATP levels and adenosine hydrolysis. In addition, we cultured PBMCs of melanoma patients and used ATP salt with specific concentrations to evaluate its signaling effects. The enzymatic activity analysis revealed that even with higher ATP doses cells metabolize adenine nucleotides less efficiently, and present low ATP, ADP and AMP hydrolytic activity in CM compared to CT cells. In summary, we showed for the first time important data about the purinergic signaling in the pathophysiology of melanoma and ATP signaling exercising immunosuppressive effects. Therefore, as already shown for other tumors, the purinergic signaling should be considered a potential target for melanoma management and treatment and could offer novel therapeutic prospects.

Hydrolysis of ATP, ADP, and AMP is increased in blood plasma of prostate cancer patients

Prostate cancer is among the major malignancies that affect men around the world. Adenine nucleotides are important signaling molecules that mediate innumerous biological functions in pathophysiological conditions, including cancer. These molecules are degraded by several ectoenzymes named ectonucleotidases that produce adenosine in the extracellular medium. Some of these ecto-enzymes can be found in soluble in the blood stream. Thus, the present study aimed to evaluate the hydrolysis of adenine nucleotides (ATP, ADP, and AMP) in the plasma blood of patients with prostate cancer. Peripheral blood samples were collected, and questionnaires were filled based on the clinical data of the medical records. The nucleotide hydrolysis was performed by Malachite Green method using ATP, ADP, and AMP as substrates. Plasma from prostate cancer patients presented an elevated hydrolysis of all nucleotides evaluated when compared to healthy individuals. NTPDase inhibitor (ARL67156) and the alkaline phosphatase inhibitor (levamisole) did not alter ATP hydrolysis. However, AMP hydrolysis was reduced by the CD73 inhibitor, APCP, and by levamisole, suggesting the action of a soluble form of CD73 and alkaline phosphatase. On microvesicles, it was observed that there was a low expression and activity of CD39 and almost absent of CD73. The correlation of ATP, ADP, and AMP hydrolysis with clinic pathological data demonstrated that patients who received radiotherapy showed a higher AMP hydrolysis than those who did not, and patients with lower clinical stage (CS-IIA) presented an elevated ATP hydrolysis when compared to those with more advanced clinical stages (CS-IIB and CS-III). Patients of all clinical stages presented an elevated AMPase activity. Therefore, we can suggest that the nucleotide hydrolysis might be attributed to soluble ecto-enzymes present in the plasma, which, in a coordinate manner, produce adenosine in the blood stream, favoring prostate cancer progression.

High levels of extracellular ATP lead to chronic inflammatory response in melanoma patients

Skin cancer represents a serious public health problem and melanoma is considered the most significant due to its high metastasis capacity. Evasion mechanisms are the main characteristic of these tumor cells to escape of immune response. Extracellular nucleotides and nucleosides play an important role in inflammatory and immune responses. In this study, we analyzed the expression and activity of purinergic system enzymes in platelets and lymphocytes, ATP levels quantification, as well the level of pro and anti-inflammatory interleukins in the serum of 23 patients with surgical melanoma removal (CM group) and 23 control subjects (CT group). Results showed a decrease in ATP, ADP, and AMP hydrolysis and an increase in ATP levels quantification in CM group. The pro-inflammatory cytokines were elevated in CM group when compared to CT group. These results suggest an inflammatory process, even after surgical removal, due to elevated extracellular ATP levels. Besides, CM group displayed an increase in IL-10 levels and an increased in ADA activity in platelets and lymphocytes. Once adenosine and IL-10 are anti-inflammatory molecules, these results indicate a down-regulation of immune system front to malignant process. The alteration in nucleotide and nucleoside hydrolysis reinforces the purinergic systems role in this cancer. Therefore, even after surgical removal, the purinergic system can develop a chronic inflammatory micro-environment that can influence directly on relapse or metastasis.

Urinary Biomarkers of Whole Grain Wheat Intake Identified by Non-targeted and Targeted Metabolomics Approaches

Mounting evidence suggests that whole grain (WG) intake plays an important role in chronic disease prevention. However, numerous human studies have failed to produce clear-cut conclusions on this topic. Here, a combination of non-targeted and targeted metabolomics approaches, together with kinetic studies, was used to investigate biomarkers of WG wheat intake and further explore the diet-disease associations. Via these integrated approaches, forty-one compounds were identified as the most discriminating endogenous metabolites after WG versus refined grain (RG) wheat bread consumption. The corresponding biological assessment of these endogenous changes suggests that, in contrast to RG consumption, WG wheat consumption may facilitate antioxidant defense systems and moderate the risk factors of cancer, cardiovascular diseases, and other chronic diseases. A panel of urinary markers consisting of seven alkylresorcinol metabolites and five benzoxazinoid derivatives as specific biomarkers, as well as five phenolic acid derivatives, was also established to cover multiple time points and longer time periods for correctly and objectively monitoring WG wheat intake. Through these findings, we have established a comprehensive biomarker pool to better assess WG wheat consumption, and to monitor the endogenous changes that are linked to health effects of WG wheat consumption.

Purinergic signalling and cancer

Receptors for extracellular nucleotides are widely expressed by mammalian cells. They mediate a large array of responses ranging from growth stimulation to apoptosis, from chemotaxis to cell differentiation and from nociception to cytokine release, as well as neurotransmission. Pharma industry is involved in the development and clinical testing of drugs selectively targeting the different P1 nucleoside and P2 nucleotide receptor subtypes. As described in detail in the present review, P2 receptors are expressed by all tumours, in some cases to a very high level. Activation or inhibition of selected P2 receptor subtypes brings about cancer cell death or growth inhibition. The field has been largely neglected by current research in oncology, yet the evidence presented in this review, most of which is based on in vitro studies, although with a limited amount from in vivo experiments and human studies, warrants further efforts to explore the therapeutic potential of purinoceptor targeting in cancer.

Role of the purinergic system in patients with cervical intraepithelial neoplasia and uterine cancer

INTRODUCTION

Cervical cancer remains the second leading cause of death among women. Intraepithelial neoplasias and uterine invasive cancer are frequently associated with disturbances in coagulation and changes in the concentrations of adenine nucleotides. This work intended to analyze changes in extracellular adenine nucleotide hydrolysis and blood platelet aggregation in patients diagnosed for cervical intraepithelial neoplasia in different stages as well as uterine invasive cancer.

PATIENTS AND METHODS

NTPDase, E-NPP, 5'-nucleotidase, total ADA and its isoforms (ADA1 and ADA2), as well as the platelet aggregation from patients with different stages of cervical intraepithelial neoplasia (NICs I, NIC II, NIC III) and uterine invasive cancer were verified.

RESULTS

Neither ATP hydrolysis nor E-NPP activity was changed by the neoplasia stage. On the other hand, ADP and AMP hydrolysis as well as ADA activity were enhanced in NIC I group. AMP hydrolysis was also increased in the cancer group. ADA 1 was the ADA isoform found in platelets from both control and patient groups.

CONCLUSION

Our results showed for the first time that NTPDase, 5'-nucleotidase, E-NPP and ADA are not sensible regarding the grade of neoplasia development, since no significant difference was found between the groups studied. Only ADP hydrolysis and ADA activity showed a significant enhancement in NIC I group related to the other stages possibly as a result of the beginning of the neoplasic transformation. This increase could be reflecting a body's reaction against the probable high adenosine levels. We propose for the first time that the ADA isoform present in platelets is ADA 1.

Activities of adenine nucleotide and nucleoside degradation enzymes in platelets of rats infected by Trypanosoma evansi

Nucleotide and nucleoside-degrading enzymes, such as nucleoside triphosphate diphosphohydrose (NTPDase), 5'-nucleotidase and adenosine deaminase (ADA) are present in the surface membranes of platelets, involved in clotting disturbances of Trypanosoma evansi-infected animals. Thus, this study was aimed at evaluating the activities of these enzymes in platelets of rats experimentally infected with T. evansi. Animals were divided into four groups, according to the level of parasitemia. Blood samples were collected on days 3 (group A: at the beginning of parasitemia), 5 (group B: high parasitemia) and 15 (group C: chronic infection), post-infection. Group D (control group) was composed of non-infected animals for platelet count, separation and enzymatic assays. Animals from groups A and B showed marked thrombocytopenia, but platelet count was not affected in chronically infected rats. NTPDase, 5'-nucleotidase and ADA activities decreased (p<0.05) in platelets from rats of groups A and B, when compared to the control group. In group C, only NTPDase and 5'-nucleoside activities decreased (p<0.001). The correlations between platelet count and nucleotide/nucleoside hydrolysis were positive and statistically significant (p<0.05) in groups A and B. Platelet aggregation was decreased in all infected groups, in comparison to the control group (p<0.05). It is concluded that the alterations observed in the activities of NTPDase, 5'-nucleotidase and ADA in platelets of T. evansi-infected animals might be related to thrombocytopenia, that by reducing the number of platelets, there was less release of ATP and ADP. Another possibility being suggested is that changes have occurred in the membrane of these cells, decreasing the expression of these enzymes in the cell membrane.

Enzymes that hydrolyze adenine nucleotides in platelets and polymorphisms in the alpha2 gene of integrin alpha2beta1 in patients with von Willebrand disease

Von Willebrand disease (VWD) is one of the most common inherited bleeding diseases caused by a qualitative or quantitative deficiency of the von Willebrand factor (FvW). FvW is a multimeric glycoprotein synthesized by megakaryocytes and endothelial cells and it is present in the subendothelial matrix, blood plasma, platelets, and endothelium. This glycoprotein plays an important role in thrombus formation by initiating platelet adhesion to sites of injury as well as platelet aggregation. The aim of this study was to evaluate the activities of enzymes that hydrolyze adenine nucleotides in platelets, ristocetin-induced platelet aggregation (RIPA), and polymorphisms of the alpha2 gene of alpha2beta1 integrin from VWD patients. Platelet nucleoside triphosphate diphosphohydrolase (NTPDase), 5'-nucleotidase, and ecto-nucleotide pyrophosphatase/phosphodiesterase (E-NPP) activities were verified in 14 VWD patients. For RIPA determination, a final concentration of 1.25 mg/ml of ristocetin was used. Polymorphisms of the alpha2 gene were analyzed through PCR. Platelet NTPDase and E-NPP were decreased in VWD patients. 5'-Nucleotidase activity was not statistically significant between controls and VWD patients. RIPA was significantly reduced, with an allelic frequency of 78.57% for 807C in VWD patients. Our results indicated reduced platelet NTPDase and E-NPP activities which might be related to the low platelet adhesiveness. The prevalence of the 807C allele might account for the variability in bleeding in VWD.

Nucleotide degrading enzymes in platelets from uterine cervical neoplasia patients treated with conization or radiotherapy

BACKGROUND

Uterine cervical neoplasia is an important worldwide malignancy sometimes associated with thrombosis. Ectonucleotidases are membrane-bound enzymes which participate in thromboregulation by hydrolyzing adenine nucleotides in the extracellular medium. In this sense, we aimed to investigate their activity in patients with uterine cervical neoplasia.

METHODS

We evaluated NTPDase and 5'-nucleotidase activities from patients previously treated for uterine cervical neoplasia with either conization or radiotherapy (RTX). These patients were divided into four groups: two conization groups (I and II) and two RTX groups (III and IV), which were further divided based on the amount of time that had passed since the conclusion of their treatment, where groups I and III were extended-remission-period groups (patients with 1 to 5 years elapsed after the conclusion of treatment), and groups II and IV were recently treated patients (treated up to three months before).

RESULTS

For both conization and RTX groups, ATP and ADP hydrolysis decreased in the extended-remission groups when compared to the control and recently treated groups. On the other hand, AMP hydrolysis was decreased in all the treated groups (both conization and RTX) compared to the control. CD39 expression was decreased in extended-remission groups (I and III) when compared to the other groups.

CONCLUSIONS

NTPDase protects against platelet aggregation and 5'-nucleotidase is more involved in the control of adenosine formation.

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.

Effects in vitro of guanidinoacetate on adenine nucleotide hydrolysis and acetylcholinesterase activity in tissues from adult rats

Guanidinoacetate methyltransferase (GAMT) deficiency is a disorder of creatine metabolism characterized by low plasma creatine concentrations in combination with elevated guanidinoacetate (GAA) concentrations. The aim of this work was to investigate the in vitro effect of guanidinoacetate in NTPDase, 5'-nucleotidase and acetylcholinesterase activities in the synaptosomes, platelets and blood of rats. The results showed that in synaptosomes the NTPDase and 5'-nucleotidase activities were inhibited significantly in the presence of GAA at concentrations of 50, 100, 150 and 200 microM (P < 0.05). However, in platelets GAA at the same concentrations caused a significant increase in the activities of these two enzymes (P < 0.05). In relation to the acetylcholinesterase activity, GAA caused a significant inhibition in the activity of this enzyme in blood at concentrations of 150 and 200 microM (P < 0.05), but did not alter the acetylcholinesterase activity in synaptosomes from the cerebral cortex. Our results suggest that alterations caused by GAA in the activities of these enzymes may contribute to the understanding of the neurological dysfunction of GAMT-deficient patients.

NTPDase and 5'-nucleotidase activities in platelets of human pregnants with a normal or high risk for thrombosis

The nucleotide degrading enzymes, ectonucleotidases, present on the platelet surface of human pregnant with a normal (without complications) or high risk for thrombosis (hypertension and gestational diabetes) were studied. NTPDase (E.C. 3.6.1.5, CD39) and 5'-nucleotidase (E.C. 3.1.3.5, CD73) activities of four patient groups, non-pregnant (NP, n = 18), pregnant without complications (P, n = 25), pregnant with hypertension (HP, n = 15) and pregnant with gestational diabetes mellitus (GDP, n = 10), were analyzed. Increased NTPDase activities were observed in the groups P (37.0%, S.D. = 2.03 and 34.0%, S.D. = 3.19), HP (40.0%, S.D. = 3.32 and 56.0%, S.D. = 3.25) and GDP (23.0%, S.D. = 2.30 and 42.0%, S.D. = 2.26) in comparison to the control group NP (p < 0.01, S.D. = 1.92 and S.D. = 2.48) when ATP and ADP were used as substrate, respectively. AMP was used as substrate to determine the 5'-nucleotidase activities, which showed to be elevated in the groups P (45.0%, S.D. = 1.73), HP (54.0%, S.D. = 2.64) and GDP (68.0%, S.D. = 1.69) when compared to the control group NP (p < 0.01, S.D. = 1.26). However, no statistically significant differences were observed between the groups P, HP and GDP. As a consequence, the enhanced ATP, ADP and AMP hydrolysis was ascribed to the pregnancy itself, independent of a normal or high risk for thrombosis. The enhanced NTPDase and 5'-nucleotidase activities in platelets suggest that these enzymes are involved in the thromboregulation process in the pregnancy.

Previous treatment with ebselen and vitamin E alters adenine nucleotide hydrolysis in platelets from adult rats experimentally demyelinated with ethidium bromide

Many aspects of the relationship between the demyelinating pathology and platelet function need to be elucidated. Thus, the activity of NTPDase and 5'-nucleotidase enzymes was analyzed in platelets from rats demyelinated with ethidium bromide (EB) and previously treated with ebselen (Ebs) and vitamin E (Vit. E). The animals were divided into four groups: for ebselen, the groups were: I-control (saline), II-(saline and Ebs), III-(EB) and IV-(EB and Ebs); and for vitamin E, the groups were: I - control (saline), II-(saline and Vit. E), III-(EB) and IV-(EB and Vit. E). After 3 and 21 days, the blood was collected and the platelets were separated for enzymatic assays. For the treatment with Ebs, the NTPDase activity for ATP substrate was significantly lower in groups II, III and IV (p < 0.05) after 3 days, while after 21 days, a reduction was observed in group III (p < 0.05). ADP hydrolysis was reduced in group II (p < 0.05) and increased in group IV (p < 0.05) after 3 days, while after 21 days there was an increase in group IV (p < 0.05). In the treatment with Vit. E, ATP hydrolysis was lower in groups II, III and IV (p < 0.05) after 3 and 21 days. ADP hydrolysis was increased in group II (p < 0.05) after 3 days, and in group IV (p < 0.05) after 21 days. However, 5'-nucleotidase activity was not altered by the treatments. These findings demonstrate that NTPDase activity in platelets is diminished in demyelinating events and the treatments with Ebs and Vit. E modulated adenine nucleotide hydrolysis.

NTPDase and 5'-nucleotidase activities in physiological and disease conditions: new perspectives for human health

Extracellular nucleotides and nucleosides act as signaling molecules involved in a wide spectrum of biological effects. Their levels are controlled by a complex cell surface-located group of enzymes called ectonucleotidases. There are four major families of ectonucleotidases, nucleoside triphosphate diphosphohydrolases (NTPDases/CD39), ectonucleotide pyrophosphatase/phosphodiesterases (E-NPPs), alkaline phosphatases and ecto-5'-nucleotidase. In the last few years, substantial progress has been made toward the molecular identification of members of the ectonucleotidase families and their enzyme structures and functions. In this review, there is an emphasis on the involvement of NTPDase and 5'-nucleotidase activities in disease processes in several tissues and cell types. Brief background information is given about the general characteristics of these enzymes, followed by a discussion of their roles in thromboregulatory events in diabetes, hypertension, hypercholesterolemia and cancer, as well as in pathological conditions where platelets are less responsive, such as in chronic renal failure. In addition, immunomodulation and cell-cell interactions involving these enzymes are considered, as well as ATP and ADP hydrolysis under different clinical conditions related with alterations in the immune system, such as acute lymphoblastic leukemia (ALL), B-chronic lymphocytic leukemia (B-CLL) and infections associated with human immunodeficiency virus (HIV). Finally, changes in ATP, ADP and AMP hydrolysis induced by inborn errors of metabolism, seizures and epilepsy are discussed in order to highlight the importance of these enzymes in the control of neuronal activity in pathological conditions. Despite advances made toward understanding the molecular structure of ectonucleotidases, much more investigation will be necessary to entirely grasp their role in physiological and pathological conditions.

Activities of enzymes that hydrolyze adenine nucleotides in platelets from rats experimentally demyelinated with ethidium bromide and treated with interferon-beta

The activities of the enzymes NTPDase (EC 3.6.1.5, apyrase, CD39) and 5'-nucleotidase (EC 3.1.3.5, CD73) were analyzed in platelets from rats submitted to demyelination by ethidium bromide (EB) and treated with interferon beta (IFN-beta). The following groups were studied: I - control (saline), II - (saline and IFN-beta), III - (EB) and IV - (EB and IFN-beta). After 7, 15 and 30 days, the animals (n=7) were sacrificed and the platelets were separated by the method of Lunkes et al. [Lunkes, G., Lunkes D., Morsch, V., Mazzanti, C., Morsch, A., Miron, V., Schetinger, M.R.C., 2004. NTPDase and 5'-nucleotidase in rats alloxan- induced diabetes. Diabetes Research and Clinical Practice 65, 1-6]. NTPDase activity for ATP and ADP substrates was significantly lower in groups II and III after seven days, when compared to control (p<0.001). At fifteen days, ATP hydrolysis was significantly lower in group III and IV and higher in group II (p<0.001), while there was an activation of ADP hydrolysis in group II (p<0.001), when compared with the control. 5'-nucleotidase activity was significantly higher in group IV (p<0.001) after seven days, and lower in the groups III and IV (p<0.001) after fifteen days in relation to the control. No significant differences were observed in NTPDase and 5'-nucleotidase activities after thirty days. In conclusion, our study demonstrated that the hydrolysis of adenine nucleotides is modified in platelets of rats demyelinated and treated with IFN-beta.

HIV infection is associated with increased NTPDase activity that correlates with CD39-positive lymphocytes

Infection with the human immunodeficiency virus (HIV) results in alterations in immune cells such as an increase or decrease of cytokine secretion and immunodeficiency. HIV causes a state of chronic cellular activation that can induce apoptosis in lymphocyte T-helpers, making the patient susceptive to opportunistic infections. The biochemical mechanisms involved in this immune response to HIV have been researched. Here, we have shown for the first time that ATP and ADP hydrolysis are essential for the immune response to HIV. Our results clearly indicate an increase of NTPDase-1 (EC 3.6.1.5) activity in lymphocytes of HIV-positive patients, confirmed by an enhanced CD39 expression on its surface. These results suggest that NTPDase-1 may be important to keep an adequate balance between the generation and consumption of ATP and to preserve cellular integrity and immune response to the HIV infection.