Medicinal Chemistry
Emerging Roles of Purinergic Signaling in
Diabetes
Carmen Fotino, Ph.D.1*; Diego Dal Ben, Ph.D 2, Elena Adinolfi, Ph.D3*.
1Ferrara 12th January 2018
Running title: purinergic signaling and diabetes Abstract: 212 words
Manuscript: 4308 words
Tables: 0
Figures: 3
References: 116
Affiliations: 1 Diabetes and Metabolism Research Institute, City of Hope, Duarte, CA, USA 2 School of Pharmacy, Medicinal Chemistry Unit University of Camerino, Camerino, Italy, 3Department of Morphology, Surgery and Experimental Medicine, University of Ferrara, Ferrara Italy
*Please, address correspondence to: Elena Adinolfi: elena.adinolfi@unife.it Carmen Fotino: fotino.carmen@gmail.com These two authors equally contributed.
ABBREVIATIONS:
A1 A1 Adenosine Receptor A2A A2A Adenosine Receptor A2B A2B Adenosine Receptor A3 A3 Adenosine Receptor ADP: Adenosine Diphosphate AMP: Adenosine Monophosphate AR: Adenosine Receptor ATP: Adenosine 5′-Triphosphate BzATP: Benzoylbenzoyl ATP eATP: Extracellular ATP FFA: Free Fatty Acid HFD: High Fat Diet IL: Interleukin NF-κB: nuclear factor-κBP2XR: Ionotropic Purinergic Receptor P2YR: Metabotropic Purinergic Receptor TNF-α: Tumor Necrosis Factor-α
T1D: Type 1 Diabetes T2D: Type 2 Diabetes UDP: Uridine Diphosphate
ABSTRACT
Background: Purinergic signaling accounts for a complex network of receptors and extracellular enzymes
responsible for the generation, recognition and degradation of extracellular ATP and adenosine. The main actors of this system include P2X, P2Y and Adenosine Receptors, ectonucleotidases CD39 and CD73 and Adenosine Deaminase. The purinergic network recently emerged as a central player in several physiopathological conditions particularly those linked to immune system regulation including type 1 and type 2 diabetes.
Methods: Here we give an overview of recent findings linking purinergic signaling with diabetes
pathogenesis, including purines roles in altered glucose homeostasis, impaired metabolic control, and immune system-mediated pancreatic β cells destruction. We particularly focused our attention on established preclinical experimental models of diabetes development and therapy including NOD mice, streptozotocin-induced β islets degeneration, and islet transplantation.
Results: The summarized studies delineate a central role of purines, their receptors and degrading enzymes
in diabetes by demonstrating that manipulation of the purinergic axis at different levels can prevent or exacerbate the insurgency and evolution of both type 1 and type 2 diabetes.
Conclusions: The reported preclinical data and the availability of several effective compounds targeting the
different steps of the purinergic response strongly suggest that P2 and Adenosine Receptors or ecto-nucleotidases will be feasible therapeutic targets for the treatment of diabetes.
KEYWORDS:
Diabetes; Purinergic signaling; P2X; P2Y; Adenosine; Adenosine receptors; Adenosine Deaminase; beta cells; islets; metabolic syndrome; extracellular ATP; type 1 diabetes; type 2 diabetes; inflammation.
INTRODUCTION
Adenosine 5’-triphosphate (ATP, Figure 1), despite being the main energy currency of the cell, is also a known extracellular messenger triggering a complex range of physiopathological responses via interaction with its receptors or following degradation to adenosine (Figure 2) by ectonucleotidases. ATP is present at high concentration inside the cell (5-10 mM) while it is virtually absent in the extracellular milieu where it could be released following cell membrane damage but also via vesicular release, transporters or ion channels [1]. Once in the extracellular space, ATP is sensed by ionotropic (P2X) or metabotropic (P2Y) purinergic receptors, which are expressed by virtually whole cells [2]. Inotropic P2X receptors include seven ion channels, which, upon binding with their preferential ligand ATP, activate cellular influx of Na+
and Ca2+ and K+ efflux. Among the eight P2Y receptors ATP is the preferred ligand only for P2Y2 and P2Y11
while the natural agonists of the other proteins of the family include ADP, UTP, UDP or UDP-glucose [3, 4]. Extracellular ATP (eATP) was attributed an important role in inflammatory reactions including regulation of both innate and cell-mediated immune responses via activation of P2Y and P2X receptors [5, 6]. Besides interacting with P2 receptor eATP is also rapidly cleared by plasma membrane ectonucleotidases (E-NTPDases). Four plasma membrane-bound E-NTPDases with distinct localization and biological properties have been described (NTPDase 1, 2, 3 and 8). NTPDase1 (CD39) hydrolyzing ATP and ADP generates adenosine monophosphate (AMP) that is further hydrolyzed to adenosine by ecto-5’-nucleotidase (CD73) [7, 8]. Under specific physiopathological conditions, CD39 and CD73 expression may change. For instance, hypoxia upregulates both ectonucleotidases: CD39 through Sp1-dependent pathways [9] and CD73 through binding of hypoxia-inducible factor (HIF)-1α [10]. The activity of CD39 is reversible, while the activity of CD73 is virtually irreversible, representing an important step in the conversion of eATP into adenosine which is a potent immunosuppressive molecule. Once released or produced via ATP degradation, adenosine signals through four different subtypes of G protein-coupled receptors classified as A1, A2A, A2B and A3 [11, 12]. Activation of A1 and A3 Adenosine Receptors (ARs) decreases intracellular levels
of cAMP while stimulation of A2A and A2B causes an increase of cAMP levels. A1 and A2A are high-affinity
receptors, whereas the A2B and A3 receptors show lower adenosine affinity. The final key component of the
adenosine pathway is Adenosine Deaminase (ADA) that is present in two isoforms ADA1 and ADA2, catalyzing the irreversible deamination of adenosine into inosine. The result of ADA activity is depletion of adenosine in the local microenvironment, limiting its immunomodulatory effects.
Early reports linking purinergic signaling with diabetes [13-15] were further confirmed by a wealth of studies associating diabetes to the modulation of eATP levels and its degradation into adenosine [4, 16]. Diabetes is a growing worldwide disease that can be classified into two main groups: type 1 diabetes (T1D) and type 2 diabetes (T2D). T1D is the result of the progressive attack of the insulin-producing beta ( β) cells from the immune system [17]. The etiology of T1D remains elusive. It has been recognized that in genetically predisposed subjects loss of β cell function and mass results from an immune-mediated destruction.
T2D is characterized by insulin resistance/insulin sensitivity and β cell dysfunction. Unlike T1D, a chronic low-grade inflammation process plays a critical role in the pathogenesis of metabolic syndrome, obesity-induced insulin resistance and T2D [18]. In fact, macrophages together with other immune cells infiltrate
liver, muscle, pancreas and adipose tissue promoting a pro-inflammatory phenotype. Pro-inflammatory cytokines such as tumor necrosis factor (TNF)-α, interleukin (IL)-1β and IL-6, are increased in obese and T2D patients and these markers positively correlate with insulin resistance and features of the metabolic syndrome. In both types of diabetes hyperglycemia (high blood glucose levels) is the common feature that leads to long-term complications classified as microvascular (i.e. retinopathy, neuropathy and nephropathy) and macrovascular (i.e. cardiovascular disease) responsible for the morbidity and mortality associated with the disease. Reaching a stable metabolic control helps to delay or prevent diabetic complications and over the recent years many improvements have been reported thank to new drug delivery and monitoring devices. Here we will give an overview on the role of purinergic signaling in the pathogenesis of T1D and T2D, focusing on the pro-inflammatory versus the suppressive role of the different members of the purine system.
P2X, P2Y and T1D
ATP affects insulin secretion by intracellular mechanisms and activating extracellular P2 receptors on the cell surface of the pancreatic β cell [19] and this effect is dependent on blood glucose concentrations [20, 21] (Figure 3). Indeed, expression of P2X and P2Y receptors were found in human islets, in mouse and rat β cells and pancreas [22-27]. In the rat insulinoma (INS-1) cell line the activation of P2X3 receptor caused a decrease in insulin secretion regardless of glucose concentrations [28]. Notably, in human islets, ATP co-released with insulin from β cells stimulate P2X3 receptors resulting in increased intracellular Ca2+
concentrations and amplification of insulin release [26]. These findings suggest a positive autocrine signal mediated by ATP for insulin release in human β cells. Moreover, it has been shown that activation of P2Y receptors may have a role in the regulation of insulin secretion. Activation of the P2Y4 receptor was shown to stimulate insulin secretion independently of blood glucose levels [28]. On the contrary, under high glucose levels, insulin release was inhibited upon stimulation of P2Y1 and P2Y6 [29]. Interestingly, other studies showed that activation of P2Y1 and P2Y6 receptors stimulate insulin secretion when glucose levels are low [30].
Transplantation of pancreatic islets is an appealing therapeutic option for the restoration and preservation of β cell function in patients with unstable T1D [31, 32]. Involvement of the ATP/P2X system in T cell activation and Th1/Th17 polarization has been demonstrated in a mouse model of islet transplantation [33, 34] (Figure 3). Higher mRNA expression of P2X1 was observed in syngeneic and allogeneic islets graf whereas P2X7 expression was significantly higher specifically in the allogeneic graf [35]. In vivo treatment with oxidized ATP (oATP, Figure 1), an inhibitor of P2X7, in a model of islets allotransplantation was able to promote long-term graf survival and this was associated with a Th1 reduction and reduced CD4+ T effector and Th17 cells [35]. Moreover, expression of P2X7within CD4+ T cell appeared to be upregulated in
peripheral blood mononuclear cells (PBMC) from T1D and long-term islet-transplanted patients, suggesting a link between activation of the immune system and expression of P2X7 [35-37]. Importantly, ATP released from activated T cells acts as a proliferative autocrine signal through P2X7 receptor [38-40]. Inhibition of this pathway by using oATP in vitro resulted in decreased levels of IL-2 and lower T cell proliferation and associated in vivo with reduced T cell-mediated inflammation in T1D mouse models [38, 41].
Streptozotocin (STZ)-induced T1D in rodents has been very helpful in understanding the pathogenic mechanism of diabetes [42]. In a recent study, it was observed that P2X7-/- mice treated for 5 consecutive
days with STZ were resistant to T1D development presenting lower blood glucose levels compared to WT mice [43]. In the pancreas of those mice, proinflammatory cytokines such as IL-1β and IFN-γ were not increased. Furthermore, a reduction in immune cell infiltration was observed in the pancreatic lymph nodes of P2X7-/- mice [43]. Accordingly, treatment in vivo with a P2X7 antagonist prevented STZ-induced
diabetes suggesting that P2X7 could be a good pharmacological target for the prevention or treatment of T1D. The role of purinergic receptors has been also explored in the non-obese diabetic (NOD) mouse that has been considered a valuable surrogate in vivo ‘preclinical’ model of T1D [44, 45]. In this model, a T cell-based autoimmune process results in the progressive destruction of pancreatic islets in 60-80% of the females and 20-30% of the males starting afer 12 weeks of age [44]. A study from Coutinho-Silva R. and collaborators analyzed the expression of P2X7 receptors in the pancreatic islets and spleen of the NOD mouse using flow cytometry [46]. In non-diabetic NOD mice, the expression of P2X7 receptors was observed in glucagon-producing alpha (α) cells at the periphery of the islets. In prediabetic NOD mice (12 weeks of age) a migration of P2X7+ cells was observed from the periphery to the center of the islets and in
34 weeks old NOD mice P2X7+ cells and α cells were no longer expressed in the islets [46]. Stimulation of
P2X7 receptor in NOD lymphocyte mice results in shedding of the lymphocyte homing receptor CD62L and MHC class I [47]. In any case, genetic ablation of the P2X7 in the NOD did not alter T1D incidence either male or female mice [48]. Recently, in the NOD mouse model, two P2Y receptors (P2Y2 and P2Y6) were found to be present in previously defined insulin-dependent diabetes (Idd) regions [49]. In addition, analysis of the presence of single nucleotide polymorphisms (SNPs) for P2X and P2Y receptors in NOD mice displayed different polymorphism in the UTR regions, in exons and in the intron regions [49]. Nevertheless, more studies in the NOD mouse model as well as in humans will help to elucidate the role of purinergic receptors in the pathophysiology of T1D.
P2X, P2Y and T2D
The P2X7 receptor is possibly the best-known component of the purinergic system which is involved in immune reactions, mainly due to its role in the maturation and secretion of IL-1β [50, 51]. IL-1β expression and release were shown to be increased in islets of T2D subjects [52] and it is known its contribution to the development of the disease. Blockade of IL-1β by the synthetic interleukin-1 receptor antagonist (IL-1Ra) showed improvement in glucose levels and β cell function as well as reduced inflammation in individuals with T2D [53-57]. An interesting study by Glas et al., showed that islets exposed in vitro to elevated glucose, palmitic acid or BzATP (a P2X agonist, Figure 1) levels for 30 min resulted in increased expression of P2X7 and induced IL-1Ra and insulin secretion [58]. This is not surprising as together with IL1-β maturation and release P2X7 was also shown to be involved in the consequent production of IL-1Ra [59]. Accordingly, in WT mice fed a high-fat diet (HFD) serum levels of IL-1β and IL-1Ra were unchanged, instead P2X7-/- mice showed significantly lower levels of both IL-1β and IL-1Ra during 16 weeks follow up
correlating with changes in β cell mass [58]. The β cells of human pancreatic sections from obese non-diabetic patients showed high levels of P2X7 while the expression was barely detectable in pancreatic sections from diabetic subjects [58]. Moreover, P2X7-/- mice fed with HFD exhibited hyperglycemia,
hyperinsulinemia and impaired β cell function associated with increased β cell apoptosis when compared to wild-type (WT) mice [58]. These results suggest that P2X7 may be involved in the compensatory mechanism of β cell to increase insulin demand. However, when analyzing the role of P2X7 in T2D we should not underestimate the pro-inflammatory role of the receptor, which was indeed implicated in renal phlogosis consequent to HFD intake via activation of the NLRP3 inflammasome axis [60]. Evidence of reduced renal inflammation and functional alterations was retrieved in P2X7-/- mice, while the kidneys of
T2D subjects with documented renal disease showed increased P2X7 and inflammasome expression [60]. Accordingly, in T2D patients P2X7 was involved in the increase of inflammatory mediators such as C-reactive protein, TNF-α, and IL-1β accompanied by a decrease in IL-10 [61]. Furthermore, patients with deficient metabolic control together with elevated circulating low-density lipoprotein (LDL) show an increased P2X7 expression in macrophage, T, and B cells [62]. Therefore, current literature is far to be conclusive on the role exerted by P2X7 in T2D etiopathology and further studies will be required to fully explore the potential of the receptor as a therapeutic target for this condition.
Recent genetic studies have identified an association between gene variants of the purinergic signaling and T2D risk. P2rx3, P2rx4 and P2rx5 gene variants located in intronic regions were found to be significantly associated with increased diabetes risk and higher fasting glucose levels. Also, P2RY1 gene polymorphisms
were associated with glucose homeostasis [63] and a previous study with P2RY1-null mice demonstrate
impaired glucose homeostasis associated with increased insulin release [64]. However, further investigations will be required to strengthen the role of P2 receptors as possible T2D biomarkers.
CD39/CD73 and T1D
Expression of CD39 has been demonstrated in human β cells (Figure 3) [65] and its inhibition (i.e., using the antagonist ARL 67156, Figure 1) caused an increase in insulin secretion from islet cells under low glucose concentrations [26] suggesting that ATP released by human islet is degraded by active ectonucleotidases. In fact, exogenously added CD39 does not show a reduction in insulin secretion in low glucose [26]. On the contrary, CD73 was found to be expressed only in rat islet cells [66] but absent in human and mouse endocrine cells. However, CD73 is largely expressed on leukocytes and plays an important role in leukocyte trafficking.
CD4+ regulatory T cells (Tregs) are important for the maintenance of immune homeostasis and a low
number of these cells has been reported in NOD mice [67] and human patients with T1D [68]. CD39 is expressed on both murine [7, 69] and human [70] CD4+ Tregs and is necessary for the suppressive activity
of these cells while CD73 is expressed on CD4+ Tregs in mice but absent in humans [7, 71]. In mice, Tregs
use both CD39 and CD73 to degrade ATP converting it in adenosine to exert suppression of other T cells [7, 69]. Furthermore, overexpression of CD39 in C57BL/6 mice causes protection from multiple low dose streptozotocin (MLDS)-induced diabetes, while CD39-/- mice have faster and higher rates of diabetes in this
model [72]. Instead, CD73-/- mice are resistant to MLDS-induced diabetes, probably as a consequence of
impaired leukocyte trafficking [73]. Recently, in children with T1D, it has been shown a lower mean fluorescence intensity (MFI) of Treg cells (CD4+CD25hi) compared to healthy controls with low expression of
CD39/CD73 and T2D
Expression of CD39+ and CD39+CD19+ cells was shown to be increased in PBMC of T2D patients with
impaired metabolic control compared to healthy controls paralleled by an increase of CD39 enzyme activity [62]. Importantly, a significant correlation between the percentage of CD39+ cells or CD39+CD19+
cells and fasting plasma glucose levels and the percentage of HbA1c was observed. In addition, IL-17 levels were found to be low in the serum of T2D patients compared to controls. These data indicate a role for CD39+ cells in regulating inflammation in T2D patients [62]. In a cohort of African Americans subjects, a
common CD39 two SNPs haplotype was associated with an increased risk for end-stage renal disease (ESRD) secondary to T2D [75].
Analysis of the CD39 and CD73 activities in platelets from T2D and T2D/hypertensive patients showed a significant increase when compared to healthy controls. Probably, such alterations are involved in compensatory physiological responses to these diseases and are related to important mechanisms of thromboregulation [76].
In a recent study, increased expression of CD39+ cells followed by a decreased proportion of CD73+ cells
within CD4+ T cells was found in patients with T2D and obesity compared to the control group. A positive
correlation between CD39 expression and body mass index (BMI) and age was also observed, while CD73 negatively correlates with different parameters such as BMI, HbA1c, cholesterol, and triglycerides suggesting a possible role for CD39 and CD73 in the inflammation observed in patients with T2D [77]. Furthermore, Cortez-Espinoza N et al., showed in T2D patients a lower percentage of CD39+ Treg cells
negatively correlating with weight and BMI [78]. At the same time, they showed lower levels of CD4+IL-17+
cells in obese T2D patients and a positive correlation of those cells with glucose and HbA1c. CD39 expression was observed in a subpopulation of Th17 cells that correlate with glucose and HbA1c suggesting that CD39 may be involved in modulating the effector capacity of Th17 cells [78].
Adenosine, Adenosine receptors and T1D
AR mRNAs were found to be expressed in mouse pancreatic islets as well as in rodent insulinoma cell lines (rat INS-1 and mouse β-TC6 cells) indicating an involvement of adenosine in the regulation of β-cell function. Activation of A1 receptor-induced inhibition of insulin release in INS-1 cells and in mouse and rat
pancreatic islets [79]. In addition, it was shown that adenosine increased insulin secretion by islets in the presence of normal (5.5 mM) or high levels of glucose (20 mM). Under high glucose concentrations, insulin secretion was blocked by pretreating the islets with an A2A antagonist but not by A2B and A3 antagonists
while this effect was potentiated using an A1 antagonist [80]. Adenosine has an important role in regulating
β cell proliferation and survival [80, 81]. In fact, β-TC6 cells treated with the A3 receptor agonist
Cl-IB-MECA, (Figure 2) markedly reduced proliferation [80] and this effect was in part antagonized by pre-treating cells with the selective A3 receptor antagonist VUF5574 (Figure 3) [80].
It has been shown that adenosine and its receptors are involved in regulating the interactions between β cells and immune cells in T1D. Recent data indicate that conditions of stress, such as treatment with MLDS in C57BL/6 mice, is associated with decreased islet mRNA expression of A1 that is paralleled by an increase
lymphocyte co-cultures and to improve engrafment of marginal islet mass in diabetic recipients [82]. A key involvement for A2B has been described in organ ischemia-reperfusion injury that is ameliorated by
agonistic treatment [83]; however, this has not been yet confirmed in islet cells. Treatment with the nonselective AR agonist NECA (Figure 2) ameliorates diabetes development in both MLDS model in CD1 mice and in cyclophosphamide-induced T1D in NOD mice [84]. While individually administered selective agonists of A1, A2A and A3 ARs (CCPA, CGS21680, and IBMECA, respectively, Figure 2) did not show
protection, NECA ameliorated MLDS-induced hyperglycemia in both wild-type and A2A-/- mice, and its
effects were reverted by A2B receptor antagonist MRS 1754 (Figure 2) [84].
In islets from C57BL/6 mice overexpressing CD39, which are protected from MLDS-induced diabetes, basal mRNA expression of A2B was constitutively higher when compared to WT controls and it does not change
following MLDS [72]. Progressive decrease in mRNA expression of Adora1 paralleled by increased expression of Adora2a have been described in NOD mouse islets obtained by laser capture microscopy (LCM) at 12 and 20 weeks of age, when compared to the congenic, non-diabetes prone NOD.B10 strain [85]. Expression of A1 was detected by immunofluorescence in sections of NOD and human pancreata and
co-localized primarily with α cells and few β cells, but disappeared with the progression of T1D in NOD mice (i.e., 20 weeks of age), and in high risk (namely, autoantibody-positive, AA+) and human subjects with
T1D on pancreatic specimens obtained from the nPOD (Network for Pancreatic Organ Donors with Diabetes) [85, 86].
Adenosine, Adenosine receptors and T2D
Many studies have linked adenosine signaling with the regulation of glucose homeostasis and the pathophysiology of T2D [16, 87, 88]. In T2D, an important role is played by adipose tissue and its dysfunction consisting of impaired storage of triglyceride, increased lipolysis and increased levels of circulating free fatty acids (FFAs) may cause secondary insulin resistance in other tissues such as skeletal muscle and liver [89]. In the visceral fat of WT and A2B-/- mice fed on HFD for 16 weeks an increased
expression of A2B AR was observed and this was related to the development of features of metabolic
syndrome and T2D [90]. In addition, adipose tissue obtained from HFD-treated A2B-/- mice had higher levels
of tumor necrosis factor (TNF)-α and monocyte chemotactic protein-1 (MCP-1) than control mice. In patients with obesity A2B receptor expression in subcutaneous fat positively associated with BMI and
insulin receptor substrate 2 (IRS-2) mRNA expression, which suggests that this AR subtype is involved in adipose tissue metabolism in humans [90].
Classically activated macrophages have a proinflammatory action and contribute to the pathogenesis of obesity-induced insulin resistance while alternatively activated macrophages are less inflammatory and protect against insulin resistance [91]. In vitro studies have shown a stimulatory effect of A2B receptor on
alternative macrophage activation [92, 93]. Furthermore, knockout mice for the A2B receptor have
decreased levels of markers of alternatively activated macrophages in the stromal vascular fraction of adipose tissue [92]. Figler RA et al., showed an increase in IL-6 production in macrophages and endothelial cells (ECs) of diabetic mice when A2B receptor was activated and a significant association between SNPs in
the A2B receptor and markers of inflammation such as IL-6 and CRP was observed in patients with T2D [94].
A very recent study showed mRNA expression of AR in sorted macrophages F4/80+ from isolated islets, with Adora1 being highly expressed (10.5 fold) in the F4/80- population, in addition to P2X (P2rx4, P2rx7) and P2Y (P2ry2, P2ry6, P2ry14) receptors [95].
Adenosine released from fat cells may play an opposing role in the regulation of adipocyte function [96]. In fact, it has been shown in a murine osteoblast precursor cell line (7F2) that A1 AR agonist-induced
adipocyte differentiation and this was confirmed by increased mRNA expression of adipocyte markers. By contrast, stimulation of A2B ARs inhibited adipogenesis and stimulated the differentiation of these cells
toward an osteoblastic phenotype [97]. Transgenic mice overexpressing A1 AR in the adipose tissue showed
lower levels of FFAs and did not develop insulin resistance [98]. Pancreas perfusion in A1-/-mice showed an
increase in the second phase of insulin secretion indicating that those receptors are involved in the regulation of pancreatic islets function [99].
In a more recent study, it has been observed that T2D patients had an increased percentage of A2A+ cells
within CD8+, CD19+, and CD14+ cells compared to healthy control [77]. Cells activated in vitro with
Concanavalin A (ConA) and treated with a selective A2A agonist (GS21680) showed a decrease in the
proportion of apoptosis in CD8+ T cells and in total lymphocytes in T2D patients [77].
Although many studies have analyzed the role of A2B receptor demonstrating that activation of this
receptor could be a potential target for the treatment of T2D, the role of the A3 receptor is still unknown.
In conclusion, targeting A1 and A2B receptors may be considered as a treatment for obesity, but definitely
further studies are needed to provide a deeper understanding of the adenosine signaling in the pathophysiology of T2D.
Adenosine deaminase and T1D
Adenosine Deaminase (ADA) is present in two isoforms ADA1 and ADA2, expressed and catalyzing the irreversible deamination of adenosine into inosine. ADA1 has been described in myelomonocytic lineage cells. ADA2 is the predominant isoform present in the serum of normal subjects. ADA2 serum levels were shown to significantly increase in immune-mediated conditions, including in patients with T1D and T2D, when compared to healthy controls [100]. Inhibition of ADA with EHNA (Figure 2) was shown to improve the engrafment and survival of islet allografs in mice [101]. High levels of ADA are expressed in the dendritic cells from NOD mice [102]. Conversely, dendritic cells from a NOD.ADA-/- fail to efficiently trigger
autoimmune diabetes, suggesting the important role of ADA for dendritic cell-mediated T cell activation [102]. It remains to be determined whether high levels of ADA are constitutively expressed in diabetes-prone individuals, for instance on islet cells (particularly on the β cells) and/or on immune cell subsets. Elevated ADA activity in islet cells would result in faster degradation of adenosine, reducing its ability to modulate immunity in the local microenvironment. This aspect could be relevant to the physiopathology of T1D, possibly representing a susceptibility candidate marker. Interestingly, it has been recently reported that pre-diabetic NOD mice display an altered metabolic signature characterized by high plasma levels of
inosine starting at 5 weeks of age when compared to age-matched C57BL/6 mice [49]. Collectively, these observations suggest that ADA may play an important role in the development and amplification of islet immunity, which deserves further elucidations.
Adenosine Deaminase and T2D
Early studies showed that ADA is widely distributed in human tissues with the highest activity present in lymphoid and fat tissues, in the liver, heart and skeletal muscle [103-105]. ADA activity was shown to be increased in patients with T2D compared to controls [106, 107] and more recently, the activity of the ADA2 isoform in T2D patients with poor glycaemic control was found to be significantly higher when compared to patients with low values of HbA1c [108]. Moreover, serum ADA levels were found to be significantly higher in non-obese T2D subjects and a strong positive correlation with fasting plasma glucose was observed [109] suggesting an association between ADA and non-obese T2D subjects.
In T2D patients the activity of ADA2 directly correlates with HbA1C levels [100]. Following studies suggested that a low proportion of the ADA*2 allele was present in an Italian cohort of T2D subjects with a BMI of 25 kg/m2 while a high proportion was observed in subjects with a BMI higher than 34 kg/m2 [110].
Also, high acid phosphatase locus 1 (ACP1) activity/low ADA activity joint genotype positively associated with high glycaemic levels and with high BMI and low ACP1 activity/high ADA activity joint genotype positively associated with dyslipidemia [111]. Further mechanistic studies are required to better define the role of ADA in T2D.
Conclusions
Diabetes is an emerging global health problem still lacking an efficacious treatment. Increasing evidence appraised in this review strongly suggest a central role for purinergic signaling in the etiology of both β cells malfunction and immune/inflammatory reactions leading to diabetes development. Several drugs targeting purinergic signaling have been developed in time and some of them are currently in advanced stage clinical trials for different pathologies being generally well tolerated [50, 112-116] and making them easily available also for trials in selected cohorts of diabetic patients. Among purinergic receptors and transforming enzymes, CD39, CD73, P2X7, P2X3 and adenosine deaminase are possibly the best therapeutic candidates to target T1D while P2X7, A2B, and A1 emerge as druggable receptors for the cure of T2D.
Although further preclinical studies will be required to better understand the involvement of the purinergic system in the pathology, we strongly believe that the purinergic network including ligands, receptors and transforming enzymes will be a sure source of single or combined therapeutic options for the treatment of diabetes.
Conflict of Interests.
The Authors have no conflict of interests to disclose.
This work was supported by Institutional funds of the University of Ferrara.
Figure legends
Figure 1. P2X and CD39 ligands. Examples of P2X and CD39 ligands: ATP (adenosine-5'-triphosphate), oATP
(adenosine-5 -triphosphate-2 ,3 -dialdehyde),′ ′ ′ BzATP (2'(3')-O-(4-Benzoylbenzoyl)adenosine-5'-triphosphate), and ARL 67156 (6-N,N-Diethyl-β-γ-dibromomethyleneadenosine-5 -triphosphate).′
Figure 2. ARs and ADA ligands. Examples of ARs and ADA ligands: Adenosine, NECA (adenosine-5 -N-′
ethyluronamide), IB-MECA and Cl-IBMECA (N6-(3-iodobenzyl)-adenosine-5 -N-methyluronamide and 2-′ chloro-N6-(3-iodobenzyl)-adenosine-5 -N-methyluronamide, respectively), CCPA (2-chloro-N6-′ cyclopentyladenosine), CGS21680 (2-(4-(2-Carboxyethyl)phenethylaminoadenosine-5 -N-ethyluronamide)),′ VUF5574 (3-(2-methoxyphenyl)-1-(2-pyridin-3-yl-quinazolin-4-yl)urea), MRS 1754 (N-(4-cyanophenyl)-2-[4-(2,3,6,7-tetrahydro-2,6-dioxo-1,3-dipropyl-1H-purin-8-yl)phenoxy]-acetamide), and EHNA (erythro-9-(2-hydroxy-3-nonyl)adenine).
Figure 3. Role of Purinergic Signaling in pancreatic β cells. ATP secreted in the extracellular space through
P2X and P2Y receptors and hydrolyzed into Adenosine by CD39 and CD73 may contribute to the regulation of insulin secretion.
REFERENCE
[1] Di Virgilio, F.; Adinolfi, E., Extracellular purines, purinergic receptors and tumor growth. Oncogene, 2017,
36, (3), 293-303.
[2] Ralevic, V.; Burnstock, G., Receptors for purines and pyrimidines. Pharmacol Rev, 1998, 50, (3), 413-492. [3] Burnstock, G., Purine and pyrimidine receptors. Cell Mol Life Sci, 2007, 64, (12), 1471-1483.
[4] Burnstock, G.; Novak, I., Purinergic signalling and diabetes. Purinergic Signal, 2013, 9, (3), 307-324. [5] Idzko, M.; Ferrari, D.; Eltzschig, H.K., Nucleotide signalling during inflammation. Nature, 2014, 509, (7500), 310-317.
[6] Di Virgilio, F., P2X receptors and inflammation. Curr Med Chem, 2015, 22, (7), 866-877.
[7] Deaglio, S.; Dwyer, K.M.; Gao, W.; Friedman, D.; Usheva, A.; Erat, A.; Chen, J.F.; Enjyoji, K.; Linden, J.; Oukka, M.; Kuchroo, V.K.; Strom, T.B.; Robson, S.C., Adenosine generation catalyzed by CD39 and CD73 expressed on regulatory T cells mediates immune suppression. J Exp Med, 2007, 204, (6), 1257-1265.
[8] Clayton, A.; Al-Taei, S.; Webber, J.; Mason, M.D.; Tabi, Z., Cancer exosomes express CD39 and CD73, which suppress T cells through adenosine production. J Immunol, 2011, 187, (2), 676-683.
[9] Eltzschig, H.K.; Kohler, D.; Eckle, T.; Kong, T.; Robson, S.C.; Colgan, S.P., Central role of Sp1-regulated CD39 in hypoxia/ischemia protection. Blood, 2009, 113, (1), 224-232.
[10] Synnestvedt, K.; Furuta, G.T.; Comerford, K.M.; Louis, N.; Karhausen, J.; Eltzschig, H.K.; Hansen, K.R.; Thompson, L.F.; Colgan, S.P., Ecto-5'-nucleotidase (CD73) regulation by hypoxia-inducible factor-1 mediates permeability changes in intestinal epithelia. J Clin Invest, 2002, 110, (7), 993-1002.
[11] Fredholm, B.B.; AP, I.J.; Jacobson, K.A.; Klotz, K.N.; Linden, J., International Union of Pharmacology. XXV. Nomenclature and classification of adenosine receptors. Pharmacol Rev, 2001, 53, (4), 527-552.
[12] Fredholm, B.B.; AP, I.J.; Jacobson, K.A.; Linden, J.; Muller, C.E., International Union of Basic and Clinical Pharmacology. LXXXI. Nomenclature and classification of adenosine receptors--an update. Pharmacol Rev, 2011, 63, (1), 1-34.
[13] Mikhail, T.H.; Awadallah, R., The effect of ATP and certain trace elements on the induction of experimental diabetes. Z Ernahrungswiss, 1977, 16, (3), 176-183.
[14] Tahani, H.M., The purinergic nerve hypothesis and insulin secretion. Z Ernahrungswiss, 1979, 18, (2), 128-138.
[15] Tang, J.; Pugh, W.; Polonsky, K.S.; Zhang, H., Preservation of insulin secretory responses to P2 purinoceptor agonists in Zucker diabetic fatty rats. Am J Physiol, 1996, 270, (3 Pt 1), E504-512.
[16] Antonioli, L.; Blandizzi, C.; Csoka, B.; Pacher, P.; Hasko, G., Adenosine signalling in diabetes mellitus--pathophysiology and therapeutic considerations. Nat Rev Endocrinol, 2015, 11, (4), 228-241.
[17] Atkinson, M.A.; Eisenbarth, G.S., Type 1 diabetes: new perspectives on disease pathogenesis and treatment.
Lancet, 2001, 358, (9277), 221-229.
[18] Esser, N.; Legrand-Poels, S.; Piette, J.; Scheen, A.J.; Paquot, N., Inflammation as a link between obesity, metabolic syndrome and type 2 diabetes. Diabetes Res Clin Pract, 2014, 105, (2), 141-150.
[19] Wang, C.; Geng, B.; Cui, Q.; Guan, Y.; Yang, J., Intracellular and extracellular adenosine triphosphate in regulation of insulin secretion from pancreatic beta cells (beta). J Diabetes, 2014, 6, (2), 113-119.
[20] Squires, P.E.; James, R.F.; London, N.J.; Dunne, M.J., ATP-induced intracellular Ca2+ signals in isolated human insulin-secreting cells. Pflugers Arch, 1994, 427, (1-2), 181-183.
[21] Petit, P.; Lajoix, A.D.; Gross, R., P2 purinergic signalling in the pancreatic beta-cell: control of insulin secretion and pharmacology. Eur J Pharm Sci, 2009, 37, (2), 67-75.
[22] Richards-Williams, C.; Contreras, J.L.; Berecek, K.H.; Schwiebert, E.M., Extracellular ATP and zinc are co-secreted with insulin and activate multiple P2X purinergic receptor channels expressed by islet beta-cells to potentiate insulin secretion. Purinergic Signal, 2008, 4, (4), 393-405.
[23] Coutinho-Silva, R.; Parsons, M.; Robson, T.; Burnstock, G., Changes in expression of P2 receptors in rat and mouse pancreas during development and ageing. Cell Tissue Res, 2001, 306, (3), 373-383.
[24] Coutinho-Silva, R.; Parsons, M.; Robson, T.; Lincoln, J.; Burnstock, G., P2X and P2Y purinoceptor expression in pancreas from streptozotocin-diabetic rats. Mol Cell Endocrinol, 2003, 204, (1-2), 141-154.
[25] Petit, P.; Manteghetti, M.; Puech, R.; Loubatieres-Mariani, M.M., ATP and phosphate-modified adenine nucleotide analogues. Effects on insulin secretion and calcium uptake. Biochem Pharmacol, 1987, 36, (3), 377-380. [26] Jacques-Silva, M.C.; Correa-Medina, M.; Cabrera, O.; Rodriguez-Diaz, R.; Makeeva, N.; Fachado, A.; Diez, J.; Berman, D.M.; Kenyon, N.S.; Ricordi, C.; Pileggi, A.; Molano, R.D.; Berggren, P.O.; Caicedo, A., ATP-gated P2X3 receptors constitute a positive autocrine signal for insulin release in the human pancreatic beta cell. Proc Natl
Acad Sci U S A, 2010, 107, (14), 6465-6470.
[27] Silva, A.M.; Rodrigues, R.J.; Tome, A.R.; Cunha, R.A.; Misler, S.; Rosario, L.M.; Santos, R.M., Electrophysiological and immunocytochemical evidence for P2X purinergic receptors in pancreatic beta cells.
Pancreas, 2008, 36, (3), 279-283.
[28] Santini, E.; Cuccato, S.; Madec, S.; Chimenti, D.; Ferrannini, E.; Solini, A., Extracellular adenosine 5'-triphosphate modulates insulin secretion via functionally active purinergic receptors of X and Y subtype.
Endocrinology, 2009, 150, (6), 2596-2602.
[29] Ohtani, M.; Suzuki, J.; Jacobson, K.A.; Oka, T., Evidence for the possible involvement of the P2Y(6) receptor in Ca (2+) mobilization and insulin secretion in mouse pancreatic islets. Purinergic Signal, 2008, 4, (4), 365-375.
[30] Parandeh, F.; Abaraviciene, S.M.; Amisten, S.; Erlinge, D.; Salehi, A., Uridine diphosphate (UDP) stimulates insulin secretion by activation of P2Y6 receptors. Biochem Biophys Res Commun, 2008, 370, (3), 499-503.
[31] Mineo, D.; Pileggi, A.; Alejandro, R.; Ricordi, C., Point: steady progress and current challenges in clinical islet transplantation. Diabetes Care, 2009, 32, (8), 1563-1569.
[32] Piemonti, L.; Pileggi, A. In Endotext. De Groot, L.J.; Chrousos, G.; Dungan, K.; Feingold, K.R.; Grossman, A.; Hershman, J.M.; Koch, C.; Korbonits, M.; McLachlan, R.; New, M.; Purnell, J.; Rebar, R.; Singer, F.; Vinik, A., Eds.: South Dartmouth (MA), 2000.
[33] Atarashi, K.; Nishimura, J.; Shima, T.; Umesaki, Y.; Yamamoto, M.; Onoue, M.; Yagita, H.; Ishii, N.; Evans, R.; Honda, K.; Takeda, K., ATP drives lamina propria T(H)17 cell differentiation. Nature, 2008, 455, (7214), 808-812. [34] Ferrari, D.; Pizzirani, C.; Adinolfi, E.; Lemoli, R.M.; Curti, A.; Idzko, M.; Panther, E.; Di Virgilio, F., The P2X7 receptor: a key player in IL-1 processing and release. J Immunol, 2006, 176, (7), 3877-3883.
[35] Vergani, A.; Fotino, C.; D'Addio, F.; Tezza, S.; Podetta, M.; Gatti, F.; Chin, M.; Bassi, R.; Molano, R.D.; Corradi, D.; Gatti, R.; Ferrero, M.E.; Secchi, A.; Grassi, F.; Ricordi, C.; Sayegh, M.H.; Maffi, P.; Pileggi, A.; Fiorina, P., Effect of the purinergic inhibitor oxidized ATP in a model of islet allograft rejection. Diabetes, 2013, 62, (5), 1665-1675.
[36] Vergani, A.; Tezza, S.; Fotino, C.; Visner, G.; Pileggi, A.; Chandraker, A.; Fiorina, P., The purinergic system in allotransplantation. Am J Transplant, 2014, 14, (3), 507-514.
[37] Fotino, C.; Vergani, A.; Fiorina, P.; Pileggi, A., P2X receptors and diabetes. Curr Med Chem, 2015, 22, (7), 891-901.
[38] Schenk, U.; Westendorf, A.M.; Radaelli, E.; Casati, A.; Ferro, M.; Fumagalli, M.; Verderio, C.; Buer, J.; Scanziani, E.; Grassi, F., Purinergic control of T cell activation by ATP released through pannexin-1 hemichannels.
Sci Signal, 2008, 1, (39), ra6.
[39] Baricordi, O.R.; Ferrari, D.; Melchiorri, L.; Chiozzi, P.; Hanau, S.; Chiari, E.; Rubini, M.; Di Virgilio, F., An ATP-activated channel is involved in mitogenic stimulation of human T lymphocytes. Blood, 1996, 87, (2), 682-690.
[40] Adinolfi, E.; Callegari, M.G.; Cirillo, M.; Pinton, P.; Giorgi, C.; Cavagna, D.; Rizzuto, R.; Di Virgilio, F., Expression of the P2X7 receptor increases the Ca2+ content of the endoplasmic reticulum, activates NFATc1, and protects from apoptosis. J Biol Chem, 2009, 284, (15), 10120-10128.
[41] Lang, P.A.; Merkler, D.; Funkner, P.; Shaabani, N.; Meryk, A.; Krings, C.; Barthuber, C.; Recher, M.; Bruck, W.; Haussinger, D.; Ohashi, P.S.; Lang, K.S., Oxidized ATP inhibits T-cell-mediated autoimmunity. Eur J Immunol, 2010, 40, (9), 2401-2408.
[42] Wu, J.; Yan, L.J., Streptozotocin-induced type 1 diabetes in rodents as a model for studying mitochondrial mechanisms of diabetic beta cell glucotoxicity. Diabetes Metab Syndr Obes, 2015, 8, 181-188.
[43] Vieira, F.S.; Nanini, H.F.; Takiya, C.M.; Coutinho-Silva, R., P2X7 receptor knockout prevents streptozotocin-induced type 1 diabetes in mice. Mol Cell Endocrinol, 2016, 419, 148-157.
[44] Anderson, M.S.; Bluestone, J.A., The NOD mouse: a model of immune dysregulation. Annu Rev Immunol, 2005, 23, 447-485.
[45] Atkinson, M.A.; Leiter, E.H., The NOD mouse model of type 1 diabetes: as good as it gets? Nat Med, 1999,
5, (6), 601-604.
[46] Coutinho-Silva, R.; Robson, T.; Beales, P.E.; Burnstock, G., Changes in expression of P2X7 receptors in NOD mouse pancreas during the development of diabetes. Autoimmunity, 2007, 40, (2), 108-116.
[47] Elliott, J.I.; Higgins, C.F., Major histocompatibility complex class I shedding and programmed cell death stimulated through the proinflammatory P2X7 receptor: a candidate susceptibility gene for NOD diabetes. Diabetes, 2004, 53, (8), 2012-2017.
[48] Chen, Y.G.; Scheuplein, F.; Driver, J.P.; Hewes, A.A.; Reifsnyder, P.C.; Leiter, E.H.; Serreze, D.V., Testing the role of P2X7 receptors in the development of type 1 diabetes in nonobese diabetic mice. J Immunol, 2011, 186, (7), 4278-4284.
[49] Madsen, R.; Banday, V.S.; Moritz, T.; Trygg, J.; Lejon, K., Altered metabolic signature in pre-diabetic NOD mice. PLoS One, 2012, 7, (4), e35445.
[50] De Marchi, E.; Orioli, E.; Dal Ben, D.; Adinolfi, E., P2X7 Receptor as a Therapeutic Target. Adv Protein
Chem Struct Biol, 2016, 104, 39-79.
[51] Orioli, E.; De Marchi, E.; Giuliani, A.L.; Adinolfi, E., P2X7 receptor orchestrates multiple signalling pathways triggering inflammation, autophagy and metabolic/trophic responses. Curr Med Chem, 2017.
[52] Maedler, K.; Sergeev, P.; Ris, F.; Oberholzer, J.; Joller-Jemelka, H.I.; Spinas, G.A.; Kaiser, N.; Halban, P.A.; Donath, M.Y., Glucose-induced beta cell production of IL-1beta contributes to glucotoxicity in human pancreatic islets. J Clin Invest, 2002, 110, (6), 851-860.
[53] van Poppel, P.C.; van Asseldonk, E.J.; Holst, J.J.; Vilsboll, T.; Netea, M.G.; Tack, C.J., The interleukin-1 receptor antagonist anakinra improves first-phase insulin secretion and insulinogenic index in subjects with impaired glucose tolerance. Diabetes Obes Metab, 2014, 16, (12), 1269-1273.
[54] Larsen, C.M.; Faulenbach, M.; Vaag, A.; Volund, A.; Ehses, J.A.; Seifert, B.; Mandrup-Poulsen, T.; Donath, M.Y., Interleukin-1-receptor antagonist in type 2 diabetes mellitus. N Engl J Med, 2007, 356, (15), 1517-1526. [55] Cavelti-Weder, C.; Babians-Brunner, A.; Keller, C.; Stahel, M.A.; Kurz-Levin, M.; Zayed, H.; Solinger, A.M.; Mandrup-Poulsen, T.; Dinarello, C.A.; Donath, M.Y., Effects of gevokizumab on glycemia and inflammatory markers in type 2 diabetes. Diabetes Care, 2012, 35, (8), 1654-1662.
[56] Sloan-Lancaster, J.; Abu-Raddad, E.; Polzer, J.; Miller, J.W.; Scherer, J.C.; De Gaetano, A.; Berg, J.K.; Landschulz, W.H., Double-blind, randomized study evaluating the glycemic and anti-inflammatory effects of
subcutaneous LY2189102, a neutralizing IL-1beta antibody, in patients with type 2 diabetes. Diabetes Care, 2013, 36, (8), 2239-2246.
[57] Sauter, N.S.; Schulthess, F.T.; Galasso, R.; Castellani, L.W.; Maedler, K., The antiinflammatory cytokine interleukin-1 receptor antagonist protects from high-fat diet-induced hyperglycemia. Endocrinology, 2008, 149, (5), 2208-2218.
[58] Glas, R.; Sauter, N.S.; Schulthess, F.T.; Shu, L.; Oberholzer, J.; Maedler, K., Purinergic P2X7 receptors regulate secretion of interleukin-1 receptor antagonist and beta cell function and survival. Diabetologia, 2009, 52, (8), 1579-1588.
[59] Wilson, H.L.; Francis, S.E.; Dower, S.K.; Crossman, D.C., Secretion of intracellular IL-1 receptor antagonist (type 1) is dependent on P2X7 receptor activation. J Immunol, 2004, 173, (2), 1202-1208.
[60] Solini, A.; Menini, S.; Rossi, C.; Ricci, C.; Santini, E.; Blasetti Fantauzzi, C.; Iacobini, C.; Pugliese, G., The purinergic 2X7 receptor participates in renal inflammation and injury induced by high-fat diet: possible role of NLRP3 inflammasome activation. J Pathol, 2013, 231, (3), 342-353.
[61] Wu, H.; Nie, Y.; Xiong, H.; Liu, S.; Li, G.; Huang, A.; Guo, L.; Wang, S.; Xue, Y.; Wu, B.; Peng, L.; Song, M.; Li, G.; Liang, S., P2X7 Receptor Expression in Peripheral Blood Monocytes Is Correlated With Plasma C-Reactive Protein and Cytokine Levels in Patients With Type 2 Diabetes Mellitus: a Preliminary Report. Inflammation, 2015, 38, (6), 2076-2081.
[62] Garcia-Hernandez, M.H.; Portales-Cervantes, L.; Cortez-Espinosa, N.; Vargas-Morales, J.M.; Fritche Salazar, J.F.; Rivera-Lopez, E.; Rodriguez-Rivera, J.G.; Quezada-Calvillo, R.; Portales-Perez, D.P., Expression and function of P2X(7) receptor and CD39/Entpd1 in patients with type 2 diabetes and their association with biochemical parameters.
Cell Immunol, 2011, 269, (2), 135-143.
[63] Todd, J.N.; Poon, W.; Lyssenko, V.; Groop, L.; Nichols, B.; Wilmot, M.; Robson, S.; Enjyoji, K.; Herman, M.A.; Hu, C.; Zhang, R.; Jia, W.; Ma, R.; Florez, J.C.; Friedman, D.J., Variation in glucose homeostasis traits associated with P2RX7 polymorphisms in mice and humans. J Clin Endocrinol Metab, 2015, 100, (5), E688-696. [64] Leon, C.; Freund, M.; Latchoumanin, O.; Farret, A.; Petit, P.; Cazenave, J.P.; Gachet, C., The P2Y(1) receptor is involved in the maintenance of glucose homeostasis and in insulin secretion in mice. Purinergic Signal, 2005, 1, (2), 145-151.
[65] Kittel, A.; Garrido, M.; Varga, G., Localization of NTPDase1/CD39 in normal and transformed human pancreas. J Histochem Cytochem, 2002, 50, (4), 549-556.
[66] Lavoie, E.G.; Fausther, M.; Kauffenstein, G.; Kukulski, F.; Kunzli, B.M.; Friess, H.; Sevigny, J., Identification of the ectonucleotidases expressed in mouse, rat, and human Langerhans islets: potential role of NTPDase3 in insulin secretion. Am J Physiol Endocrinol Metab, 2010, 299, (4), E647-656.
[67] Green, E.A.; Choi, Y.; Flavell, R.A., Pancreatic lymph node-derived CD4(+)CD25(+) Treg cells: highly potent regulators of diabetes that require TRANCE-RANK signals. Immunity, 2002, 16, (2), 183-191.
[68] Kukreja, A.; Cost, G.; Marker, J.; Zhang, C.; Sun, Z.; Lin-Su, K.; Ten, S.; Sanz, M.; Exley, M.; Wilson, B.; Porcelli, S.; Maclaren, N., Multiple immuno-regulatory defects in type-1 diabetes. J Clin Invest, 2002, 109, (1), 131-140.
[69] Borsellino, G.; Kleinewietfeld, M.; Di Mitri, D.; Sternjak, A.; Diamantini, A.; Giometto, R.; Hopner, S.; Centonze, D.; Bernardi, G.; Dell'Acqua, M.L.; Rossini, P.M.; Battistini, L.; Rotzschke, O.; Falk, K., Expression of
ectonucleotidase CD39 by Foxp3+ Treg cells: hydrolysis of extracellular ATP and immune suppression. Blood, 2007,
110, (4), 1225-1232.
[70] Dwyer, K.M.; Hanidziar, D.; Putheti, P.; Hill, P.A.; Pommey, S.; McRae, J.L.; Winterhalter, A.; Doherty, G.; Deaglio, S.; Koulmanda, M.; Gao, W.; Robson, S.C.; Strom, T.B., Expression of CD39 by human peripheral blood CD4+ CD25+ T cells denotes a regulatory memory phenotype. Am J Transplant, 2010, 10, (11), 2410-2420. [71] Kobie, J.J.; Shah, P.R.; Yang, L.; Rebhahn, J.A.; Fowell, D.J.; Mosmann, T.R., T regulatory and primed uncommitted CD4 T cells express CD73, which suppresses effector CD4 T cells by converting 5'-adenosine monophosphate to adenosine. J Immunol, 2006, 177, (10), 6780-6786.
[72] Chia, J.S.; McRae, J.L.; Thomas, H.E.; Fynch, S.; Elkerbout, L.; Hill, P.; Murray-Segal, L.; Robson, S.C.; Chen, J.F.; d'Apice, A.J.; Cowan, P.J.; Dwyer, K.M., The protective effects of CD39 overexpression in multiple low-dose streptozotocin-induced diabetes in mice. Diabetes, 2013, 62, (6), 2026-2035.
[73] Chia, J.S.; McRae, J.L.; Cowan, P.J.; Dwyer, K.M., The CD39-adenosinergic axis in the pathogenesis of immune and nonimmune diabetes. J Biomed Biotechnol, 2012, 2012, 320495.
[74] Akesson, K.; Tompa, A.; Ryden, A.; Faresjo, M., Low expression of CD39(+) /CD45RA(+) on regulatory T cells (Treg ) cells in type 1 diabetic children in contrast to high expression of CD101(+) /CD129(+) on Treg cells in children with coeliac disease. Clin Exp Immunol, 2015, 180, (1), 70-82.
[75] Friedman, D.J.; Talbert, M.E.; Bowden, D.W.; Freedman, B.I.; Mukanya, Y.; Enjyoji, K.; Robson, S.C., Functional ENTPD1 polymorphisms in African Americans with diabetes and end-stage renal disease. Diabetes, 2009,
58, (4), 999-1006.
[76] Lunkes, G.I.; Lunkes, D.; Stefanello, F.; Morsch, A.; Morsch, V.M.; Mazzanti, C.M.; Schetinger, M.R., Enzymes that hydrolyze adenine nucleotides in diabetes and associated pathologies. Thromb Res, 2003, 109, (4), 189-194.
[77] Guzman-Flores, J.M.; Cortez-Espinosa, N.; Cortes-Garcia, J.D.; Vargas-Morales, J.M.; Catano-Canizalez, Y.G.; Rodriguez-Rivera, J.G.; Portales-Perez, D.P., Expression of CD73 and A2A receptors in cells from subjects with obesity and type 2 diabetes mellitus. Immunobiology, 2015, 220, (8), 976-984.
[78] Cortez-Espinosa, N.; Cortes-Garcia, J.D.; Martinez-Leija, E.; Rodriguez-Rivera, J.G.; Barajas-Lopez, C.; Gonzalez-Amaro, R.; Portales-Perez, D.P., CD39 expression on Treg and Th17 cells is associated with metabolic factors in patients with type 2 diabetes. Hum Immunol, 2015, 76, (9), 622-630.
[79] Verspohl, E.J.; Johannwille, B.; Waheed, A.; Neye, H., Effect of purinergic agonists and antagonists on insulin secretion from INS-1 cells (insulinoma cell line) and rat pancreatic islets. Can J Physiol Pharmacol, 2002, 80, (6), 562-568.
[80] Ohtani, M.; Oka, T.; Ohura, K., Possible involvement of A(2)A and A(3) receptors in modulation of insulin secretion and beta-cell survival in mouse pancreatic islets. Gen Comp Endocrinol, 2013, 187, 86-94.
[81] Annes, J.P.; Ryu, J.H.; Lam, K.; Carolan, P.J.; Utz, K.; Hollister-Lock, J.; Arvanites, A.C.; Rubin, L.L.; Weir, G.; Melton, D.A., Adenosine kinase inhibition selectively promotes rodent and porcine islet beta-cell replication. Proc
Natl Acad Sci U S A, 2012, 109, (10), 3915-3920.
[82] Chhabra, P.; Wang, K.; Zeng, Q.; Jecmenica, M.; Langman, L.; Linden, J.; Ketchum, R.J.; Brayman, K.L., Adenosine A(2A) agonist administration improves islet transplant outcome: Evidence for the role of innate immunity in islet graft rejection. Cell Transplant, 2010, 19, (5), 597-612.
[83] Zimmerman, M.A.; Grenz, A.; Tak, E.; Kaplan, M.; Ridyard, D.; Brodsky, K.S.; Mandell, M.S.; Kam, I.; Eltzschig, H.K., Signaling through hepatocellular A2B adenosine receptors dampens ischemia and reperfusion injury of the liver. Proc Natl Acad Sci U S A, 2013, 110, (29), 12012-12017.
[84] Nemeth, Z.H.; Bleich, D.; Csoka, B.; Pacher, P.; Mabley, J.G.; Himer, L.; Vizi, E.S.; Deitch, E.A.; Szabo, C.; Cronstein, B.N.; Hasko, G., Adenosine receptor activation ameliorates type 1 diabetes. FASEB J, 2007, 21, (10), 2379-2388.
[85] Yip, L.; Taylor, C.; Whiting, C.C.; Fathman, C.G., Diminished adenosine A1 receptor expression in pancreatic alpha-cells may contribute to the pathology of type 1 diabetes. Diabetes, 2013, 62, (12), 4208-4219. [86] Campbell-Thompson, M.; Wasserfall, C.; Kaddis, J.; Albanese-O'Neill, A.; Staeva, T.; Nierras, C.; Moraski, J.; Rowe, P.; Gianani, R.; Eisenbarth, G.; Crawford, J.; Schatz, D.; Pugliese, A.; Atkinson, M., Network for Pancreatic Organ Donors with Diabetes (nPOD): developing a tissue biobank for type 1 diabetes. Diabetes Metab Res Rev, 2012,
28, (7), 608-617.
[87] Andersson, O., Role of adenosine signalling and metabolism in beta-cell regeneration. Exp Cell Res, 2014,
321, (1), 3-10.
[88] Koupenova, M.; Ravid, K., Adenosine, adenosine receptors and their role in glucose homeostasis and lipid metabolism. J Cell Physiol, 2013.
[89] Guilherme, A.; Virbasius, J.V.; Puri, V.; Czech, M.P., Adipocyte dysfunctions linking obesity to insulin resistance and type 2 diabetes. Nat Rev Mol Cell Biol, 2008, 9, (5), 367-377.
[90] Johnston-Cox, H.; Koupenova, M.; Yang, D.; Corkey, B.; Gokce, N.; Farb, M.G.; LeBrasseur, N.; Ravid, K., The A2b adenosine receptor modulates glucose homeostasis and obesity. PLoS One, 2012, 7, (7), e40584.
[91] Chawla, A.; Nguyen, K.D.; Goh, Y.P., Macrophage-mediated inflammation in metabolic disease. Nat Rev
Immunol, 2011, 11, (11), 738-749.
[92] Csoka, B.; Koscso, B.; Toro, G.; Kokai, E.; Virag, L.; Nemeth, Z.H.; Pacher, P.; Bai, P.; Hasko, G., A2B adenosine receptors prevent insulin resistance by inhibiting adipose tissue inflammation via maintaining alternative macrophage activation. Diabetes, 2014, 63, (3), 850-866.
[93] Csoka, B.; Selmeczy, Z.; Koscso, B.; Nemeth, Z.H.; Pacher, P.; Murray, P.J.; Kepka-Lenhart, D.; Morris, S.M., Jr.; Gause, W.C.; Leibovich, S.J.; Hasko, G., Adenosine promotes alternative macrophage activation via A2A and A2B receptors. FASEB J, 2012, 26, (1), 376-386.
[94] Figler, R.A.; Wang, G.; Srinivasan, S.; Jung, D.Y.; Zhang, Z.; Pankow, J.S.; Ravid, K.; Fredholm, B.; Hedrick, C.C.; Rich, S.S.; Kim, J.K.; LaNoue, K.F.; Linden, J., Links between insulin resistance, adenosine A2B receptors, and inflammatory markers in mice and humans. Diabetes, 2011, 60, (2), 669-679.
[95] Weitz, J.R.; Makhmutova, M.; Almaca, J.; Stertmann, J.; Aamodt, K.; Brissova, M.; Speier, S.; Rodriguez-Diaz, R.; Caicedo, A., Mouse pancreatic islet macrophages use locally released ATP to monitor beta cell activity.
Diabetologia, 2018, 61, (1), 182-192.
[96] Eisenstein, A.; Ravid, K., G protein-coupled receptors and adipogenesis: a focus on adenosine receptors. J
Cell Physiol, 2014, 229, (4), 414-421.
[97] Gharibi, B.; Abraham, A.A.; Ham, J.; Evans, B.A., Contrasting effects of A1 and A2b adenosine receptors on adipogenesis. Int J Obes (Lond), 2012, 36, (3), 397-406.
[98] Dong, Q.; Ginsberg, H.N.; Erlanger, B.F., Overexpression of the A1 adenosine receptor in adipose tissue protects mice from obesity-related insulin resistance. Diabetes Obes Metab, 2001, 3, (5), 360-366.
[99] Johansson, S.M.; Salehi, A.; Sandstrom, M.E.; Westerblad, H.; Lundquist, I.; Carlsson, P.O.; Fredholm, B.B.; Katz, A., A1 receptor deficiency causes increased insulin and glucagon secretion in mice. Biochem Pharmacol, 2007,
74, (11), 1628-1635.
[100] Hoshino, T.; Yamada, K.; Masuoka, K.; Tsuboi, I.; Itoh, K.; Nonaka, K.; Oizumi, K., Elevated adenosine deaminase activity in the serum of patients with diabetes mellitus. Diabetes Res Clin Pract, 1994, 25, (2), 97-102. [101] Lum, C.T.; Sutherland, D.E.; Payne, W.D.; Gorecki, P.; Matas, A.J.; Najarian, J.S., Prolongation of mouse and rat pancreatic islet cell allografts by adenosine deaminase inhibitors and adenine arabinoside. J Surg Res, 1980,
28, (1), 44-48.
[102] Ghaemi Oskouie, F.; Shameli, A.; Yang, A.; Desrosiers, M.D.; Mucsi, A.D.; Blackburn, M.R.; Yang, Y.; Santamaria, P.; Shi, Y., High levels of adenosine deaminase on dendritic cells promote autoreactive T cell activation and diabetes in nonobese diabetic mice. J Immunol, 2011, 186, (12), 6798-6806.
[103] Ratech, H.; Hirschhorn, R., Serum adenosine deaminase in normals and in a patient with adenosine deaminase deficient-severe combined immunodeficiency. Clin Chim Acta, 1981, 115, (3), 341-347.
[104] Niedzwicki, J.G.; Abernethy, D.R., Structure-activity relationship of ligands of human plasma adenosine deaminase2. Biochem Pharmacol, 1991, 41, (11), 1615-1624.
[105] Van der Weyden, M.B.; Kelley, W.N., Human adenosine deaminase. Distribution and properties. J Biol
Chem, 1976, 251, (18), 5448-5456.
[106] Kurtul, N.; Pence, S.; Akarsu, E.; Kocoglu, H.; Aksoy, Y.; Aksoy, H., Adenosine deaminase activity in the serum of type 2 diabetic patients. Acta Medica (Hradec Kralove), 2004, 47, (1), 33-35.
[107] Lee, J.G.; Kang, D.G.; Yu, J.R.; Kim, Y.; Kim, J.; Koh, G.; Lee, D., Changes in Adenosine Deaminase Activity in Patients with Type 2 Diabetes Mellitus and Effect of DPP-4 Inhibitor Treatment on ADA Activity.
Diabetes Metab J, 2011, 35, (2), 149-158.
[108] Larijani, B.; Heshmat, R.; Ebrahimi-Rad, M.; Khatami, S.; Valadbeigi, S.; Saghiri, R., Diagnostic Value of Adenosine Deaminase and Its Isoforms in Type II Diabetes Mellitus. Enzyme Res, 2016, 2016, 9526593.
[109] Khemka, V.K.; Bagchi, D.; Ghosh, A.; Sen, O.; Bir, A.; Chakrabarti, S.; Banerjee, A., Raised serum adenosine deaminase level in nonobese type 2 diabetes mellitus. ScientificWorldJournal, 2013, 2013, 404320. [110] Bottini, E.; Gloria-Bottini, F., Adenosine deaminase and body mass index in non-insulin-dependent diabetes mellitus. Metabolism, 1999, 48, (8), 949-951.
[111] Bottini, N.; Gloria-Bottini, F.; Borgiani, P.; Antonacci, E.; Lucarelli, P.; Bottini, E., Type 2 diabetes and the genetics of signal transduction: a study of interaction between adenosine deaminase and acid phosphatase locus 1 polymorphisms. Metabolism, 2004, 53, (8), 995-1001.
[112] Lambertucci, C.; Dal Ben, D.; Buccioni, M.; Marucci, G.; Thomas, A.; Volpini, R., Medicinal chemistry of P2X receptors: agonists and orthosteric antagonists. Curr Med Chem, 2015, 22, (7), 915-928.
[113] DalBen, D.; Adinolfi, E., Editorial: Purinergic P2X receptors: physiological and pathological roles and potential as therapeutic targets. Curr Med Chem, 2015, 22, (7), 782.
[114] Sarvaria, A.; Topp, Z.; Saven, A., Current Therapy and New Directions in the Treatment of Hairy Cell Leukemia: A Review. JAMA Oncol, 2016, 2, (1), 123-129.
[115] Ochoa-Cortes, F.; Linan-Rico, A.; Jacobson, K.A.; Christofi, F.L., Potential for developing purinergic drugs for gastrointestinal diseases. Inflamm Bowel Dis, 2014, 20, (7), 1259-1287.
[116] Jacobson, K.A.; Muller, C.E., Medicinal chemistry of adenosine, P2Y and P2X receptors.
