lcz696 ADA catalyzes the deamination of adenosine and deoxya
ADA catalyzes the deamination of adenosine and deoxyadenosine into their respective inosine nucleoside (Cristalli et al., 2001). This conversion is an initial step in a series of reactions responsible for lymphocyte proliferation and differentiation. Moreover, ADA is considered an indicator of cellular immunity and fundamental for the differentiation of lymphocytes (Blake and Berman, 1982). In this study, the increased ADA activity observed in serum of SCA patients may lead to a decrease in extracellular adenosine levels and increase in extracellular inosine production. Increased adenosine levels play a functional role in promoting sickling, hemolysis and damage to multiple tissues in sickle cell disease through the induction of 2,3-DPG in lcz696 (Zhang et al., 2011). Production of 2,3-DPG occurs only in RBCs and decreases the oxygen binding affinity of hemoglobin (Sasaki and Chiba, 1983).
ADA may be a marker of inflammation during hypoxia and its expression is increased in SCA (Eltzschig et al., 2006). The elevated levels of adenosine in SCA patients observed in this study may be attributed to the increased AMPase activity and could compensate for the increased ADA activity observed in SCA. Our result follows similar trend with previous investigation in our laboratory where increased E-ADA activity was reported in lymphocytes and platelets of SCA patients (Castilhos et al., 2015, 2016), reinforcing the involvement and alterations of this membrane-bound and soluble NTPDase as well as ADA activities in the pathophysiology of SCA. This is also in agreement with the work of Silva-Pinto et al. (2014) that observed HU-treated patients displayed increased ADA activity, compared with untreated, indicating a novel mechanism of action of HU mediated by the reduction of adenosine levels and its effects on pathophysiological processes in SCA.
Adenosine level was observed to be regulated to the normal level in the serum of SCA patients. However, the results obtained for the HPLC analysis of other purine levels revealed that inosine was significantly decreased while hypoxanthine level was elevated in SCA. The reason for the alterations of these important purines (inosine and hypoxanthine) levels in SCA may not be categorically stated. The whole blood in humans including the red blood cell (RBC) contains purine nucleoside phosphorylase (PNP); an enzyme that converts inosine to hypoxanthine (Farthing et al., 2015). Although, the PNP activity has not been investigated in this study, we speculate that the increased PNP activity may probably have facilitated the rapid breakdown of inosine to hypoxanthine and the availability of hypoxanthine could play a pivotal role in reperfusion injury associated with SCA (Rao et al., 1990).
In addition to the increased NTPDase, 5′-nucleotidase and ADA activities in SCA patients, we performed an in vitro study to verify if treatment with folic acid and hydroxyurea could modify these enzyme activities in SCA patients. The preliminary results do not show that these drugs modify these activities. This may be adjudged that these activities are solely from the enzymes present on serum of SCA patients. The hypothesis of in vitro effects of the two drugs analyzed was to check whether the drugs could modify the activities of the enzymes in normal healthy individual. Hence, results from our study show that these drugs do not modify the activities of NTPDase, 5′-nucleotidase and ADA in vitro in healthy individuals. Although, we may not be able to categorically state the effect of the drugs on the activities of NTPDase, 5′-nucleotidase and ADA activities in SCA in vitro, however, we observed that there was a significant change in NTPDase, 5′-nucleotidase and ADA activities in vivo in SCA patients in comparison to the normal healthy subjects.
Conflict of interests
Acknowledgements We sincerely thank the sickle cell anemia patients who accepted to participate in the study, the Serviço de Hemato-Oncologia do Hospital Universitário de Santa Maria and Projeto Pilão – Presença Negra no Campo, Projeto “Educação e Saúde na Doença Falciforme” do Centro de Ciências da Saúde-Departamento de Saúde da Comunidade – UFSM for supplying some materials used for the experiment. This study was supported by the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Fundação de Amparo à Pesquisa do Rio Grande do Sul (FAPERGS), and Fundação Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), Brazil.