Adenosine deaminase activity in patients with the intestinal type of gastric carcinoma

Adenosine, Schizophrenia and Cancer: Does the Purinergic System Offer a Pathway to Treatment?

For over a century, a complex relationship between schizophrenia diagnosis and development of many cancers has been observed. Findings from epidemiological studies are mixed, with reports of increased, reduced, or no difference in cancer incidence in schizophrenia patients. However, as risk factors for cancer, including elevated smoking rates and substance abuse, are commonly associated with this patient population, it is surprising that cancer incidence is not higher. Various factors may account for the proposed reduction in cancer incidence rates including pathophysiological changes associated with disease. Perturbations of the adenosine system are hypothesized to contribute to the neurobiology of schizophrenia. Conversely, hyperfunction of the adenosine system is found in the tumor microenvironment in cancer and targeting the adenosine system therapeutically is a promising area of research in this disease. We outline the current biochemical and pharmacological evidence for hypofunction of the adenosine system in schizophrenia, and the role of increased adenosine metabolism in the tumor microenvironment. In the context of the relatively limited literature on this patient population, we discuss whether hypofunction of this system in schizophrenia, may counteract the immunosuppressive role of adenosine in the tumor microenvironment. We also highlight the importance of studies examining the adenosine system in this subset of patients for the potential insight they may offer into these complex disorders.

Purine-Metabolising Enzymes and Apoptosis in Cancer

The enzymes of both de novo and salvage pathways for purine nucleotide synthesis are regulated to meet the demand of nucleic acid precursors during proliferation. Among them, the salvage pathway enzymes seem to play the key role in replenishing the purine pool in dividing and tumour cells that require a greater amount of nucleotides. An imbalance in the purine pools is fundamental not only for preventing cell proliferation, but also, in many cases, to promote apoptosis. It is known that tumour cells harbour several mutations that might lead to defective apoptosis-inducing pathways, and this is probably at the basis of the initial expansion of the population of neoplastic cells. Therefore, knowledge of the molecular mechanisms that lead to apoptosis of tumoural cells is key to predicting the possible success of a drug treatment and planning more effective and focused therapies. In this review, we describe how the modulation of enzymes involved in purine metabolism in tumour cells may affect the apoptotic programme. The enzymes discussed are: ectosolic and cytosolic 5'-nucleotidases, purine nucleoside phosphorylase, adenosine deaminase, hypoxanthine-guanine phosphoribosyltransferase, and inosine-5'-monophosphate dehydrogenase, as well as recently described enzymes particularly expressed in tumour cells, such as deoxynucleoside triphosphate triphosphohydrolase and 7,8-dihydro-8-oxoguanine triphosphatase.

Ectonucleotide pyrophosphatase/phosphodiesterase (E-NPP) and adenosine deaminase (ADA) activities in prostate cancer patients: influence of Gleason score, treatment and bone metastasis

The relation between adenine nucleotides and cancer has already been described in literature. Considering that the enzymes ectonucleotide pyrophosphatase/phosphodiesterase (E-NPP) and adenosine deaminase (ADA) act together to control nucleotide levels, we aimed to investigate the role of these enzymes in prostate cancer (PCa). E-NPP and ADA activities were determined in serum and platelets of PCa patients and controls. We also verified the influence of the Gleason score, bone metastasis and treatment in the enzyme activities. Platelets and serum E-NPP activity increased, whereas ADA activity in serum decreased in PCa patients. In addition, Gleason score, metastasis and treatment influenced E-NPP and ADA activities. We may propose that E-NPP and ADA are involved in the development of PCa. Moreover, E-NPP and ADA activities are modified in PCa patients with distinct Gleason score, with bone metastasis, as well as in patients under treatment.

Diagnostic value of adenosine deaminase activity in benign and malignant breast tumors

BACKGROUND AND AIMS

The present study was carried out to evaluate the activity of adenosine deaminase (ADA) and its isoenzymes ADA1 and ADA2 activities as a diagnostic tool in patients with benign and malignant breast disease.

METHODS

Total ADA, ADA1, and ADA2 activities of serum and tumor were analyzed using 58 subjects including 20 patients with benign breast disease (BBD), 34 patients with primary breast cancer, and 20 patients as normal control subjects.

RESULTS

The mean values for total ADA and ADA2 activities in the serum and tumor of BBD were significantly higher than those of healthy controls (p <0.01). Furthermore, the mean values for total ADA and ADA2 activities of patients with breast cancer were significantly higher than those of the benign group (p <0.005) and healthy subjects (p <0.0001).

CONCLUSIONS

Based on the present results, it is concluded that the assessment of total ADA and ADA2 activities may be used as a reliable test for differential diagnosis of benign and malignant breast disease.

Adenosine deaminase activity in the serum and malignant tumors of breast cancer: the assessment of isoenzyme ADA1 and ADA2 activities

OBJECTIVE

The potential relationship between adenosine deaminase activity and cancer progression was examined by investigating the activity of total ADA and its isoenzymes in serum and simultaneously in the cancerous tissue of each patient with breast cancer.

METHODS

Total ADA and its isoenzymes were measured using the Giusti method. ADA2 activity was measured in the presence of a specific ADA1 inhibitor, EHNA.

RESULTS

Our results indicated that ADA2 and total ADA activities were higher in serum and malignant tissues than those of corresponding controls (P < 0.05). Tumor ADA2 and total ADA activities were significantly (P < 0.05) correlated with lymph node involvement, histological grade and tumor size, whereas their levels in serum were significantly (P < 0.05) correlated with menopausal status and patient age.

CONCLUSION

Although serum and tumor total ADA activity and its ADA2 isoenzyme were both found to be increased, distinct correlation patterns were observed with some of the prognostic factors. It can be speculated that increased ADA and isoenzyme activities in serum originated from sources other than the breast tumors.

Activities of adenosine deaminase and 5'-nucleotidase in cancerous and noncancerous human colorectal tissues

In order to characterize human colorectal cancer, much attention has been paid to enzyme studies. However, little is known about the correlation between the levels of key enzymes of purine nucleotide pathway and some clinical and biological indicators of tumor invasiveness and aggressiveness. Adenosine deaminase (ADA) and 5'-nucleotidase (5'-NT) were measured in cancerous and cancer-free adjacent large bowel tissues from 38 patients with colorectal carcinoma. We have analyzed the relationship between the enzyme levels and some clinical and pathological parameters. The enzymes' activities were markedly higher in primary tumors than in corresponding normal mucosae. The ADA level in tumor tissue was significantly correlated with lymph node metastasis, histologic type, tumor location, and patient's age, whereas the 5'-NT level showed a significant correlation with tumor grade and tumor location. ADA activity in tumor tissues was significantly higher in patients whose clinical course remained stable than in those with recurrent diseases. The purine metabolism and salvage pathway activity of purine nucleotides are accelerated in the cancerous human colorectal tissue. Although our findings suggest that these enzymes' activities are most likely related to the same histomorphological architecture of the tumor, the authors believe that long-term follow-up studies are needed to evaluate the prognostic value of purine enzymes for colorectal cancer.

Tumor-promoting functions of adenosine

Tumor growth is a multifactorial process that, in addition to mutations leading to dysregulated expression of oncogenes and tumor suppressive genes, requires specific conditions that provide a supportive physiological environment at the primary and metastatic sites of the disease. Adenosine is one of the factors potentially contributing to tumor growth that thus far has not received adequate attention, despite evidence for a broad range of cytoprotective, growth-promoting, and immunosuppressive activities. Adenosine accumulates in solid tumors at high concentrations, and has been shown to stimulate tumor growth and angiogenesis and to inhibit cytokine synthesis, adhesion of immune cells to the endothelial wall, and the function of T-cells, macrophages, and natural killer cells. However, the mechanisms whereby adenosine accumulates in cancer and the specific effects that result from this accumulation are not well understood. This article surveys the available evidence that supports an important role of adenosine in cancer.