Role of adenosine in immunomodulation: Review of the literature

Adenosine 5'-Triphosphate Metabolism in Red Blood Cells as a Potential Biomarker for Post-Exercise Hypotension and a Drug Target for Cardiovascular Protection

The importance of adenosine and ATP in regulating many biological functions has long been recognized, especially for their effects on the cardiovascular system, which may be used for management of hypertension and cardiometabolic diseases. In response to ischemia and cardiovascular injury, ATP is broken down to release adenosine. The effect of adenosine is very short lived because it is rapidly taken up by erythrocytes (RBCs), myocardial and endothelial cells, and also rapidly catabolized to oxypurine metabolites. Intracellular adenosine is phosphorylated back to adenine nucleotides via a salvage pathway. Extracellular and intracellular ATP is broken down rapidly to ADP and AMP, and finally to adenosine by 5′-nucleotidase. These metabolic events are known to occur in the myocardium, endothelium as well as in RBCs. Exercise has been shown to increase metabolism of ATP in RBCs, which may be an important mechanism for post-exercise hypotension and cardiovascular protection. The post-exercise effect was greater in hypertensive than in normotensive rats. The review summarizes current evidence in support of ATP metabolism in the RBC as a potential surrogate biomarker for cardiovascular protection and toxicities. It also discusses the opportunities, challenges, and obstacles of exploiting ATP metabolism in RBCs as a target for drug development and precision medicine.

NMR metabolic profiling of lipopolysaccharide-induced mice sepsis and the treatment effects of berberine

¹H NMR metabolomics to study lipopolysaccharide-induced mice sepsis and the treatment effects of berberine.

A Pilot Study to Assess Adenosine 5'-triphosphate Metabolism in Red Blood Cells as a Drug Target for Potential Cardiovascular Protection

OBJECTIVE

To study the effect of exercise preconditioning on adenosine 5'triphosphate (ATP) metabolism in red blood cells and cardiovascular protection against injury induced by isoproterenol in vivo.

METHODS

Male Sprague Dawley rats (SDR) were each exercised on a treadmill for 15 minutes at 10 m/min and 10% grade (n = 7) (LowEx), or 14 m/min and 22% grade (n = 8) (VigEx). Two hours after the exercise, each rat received a single dose of isoproterenol (30 mg/kg) by subcutaneous (sc) injection. Two separate groups of SDR were used as control: One received no exercise (n = 10) (NoEx) and the other received no exercise and no isoproterenol (n = 11) (NoIso). Serial blood samples were collected over 5 hours for measurement of ATP and its catabolites by a validated HPLC. Hemodynamic recording was collected continuously for the duration of the experiment. Data were analysed using ANOVA and t-tests and difference considered significant at p < 0.05.

RESULTS

Exercise pre-conditioning (both LowEx and VigEx) reduced mortality after isoproterenol from 50% to < 30% (p > 0.05). It attenuated the rebound in blood pressure significantly (p < 0.05 between NoEx vs VigEx), attenuated the increase of RBC adenosine 5'-monophosphate (AMP) concentrations induced by isoproterenol, and also decreased the breakdown of ATP to AMP in the RBC (p < 0.05 vs NoEx).

CONCLUSION

Exercise pre-conditioning decreased the blood pressure rebound and also breakdown of ATP in RBC after isoproterenol which may be exploited further as a drug target for cardiovascular protection and prevention.

Purinergic signalling and immune cells

This review article provides a historical perspective on the role of purinergic signalling in the regulation of various subsets of immune cells from early discoveries to current understanding. It is now recognised that adenosine 5'-triphosphate (ATP) and other nucleotides are released from cells following stress or injury. They can act on virtually all subsets of immune cells through a spectrum of P2X ligand-gated ion channels and G protein-coupled P2Y receptors. Furthermore, ATP is rapidly degraded into adenosine by ectonucleotidases such as CD39 and CD73, and adenosine exerts additional regulatory effects through its own receptors. The resulting effect ranges from stimulation to tolerance depending on the amount and time courses of nucleotides released, and the balance between ATP and adenosine. This review identifies the various receptors involved in the different subsets of immune cells and their effects on the function of these cells.

Granulomas of intestinal tuberculosis and Crohn's disease can be differentiated by CD73 cell surface marker expression: a pilot study

BACKGROUND

Intestinal tuberculosis (ITB) and Crohn's disease are similar granulomatous disorders. Granulomas are present in both and difficult to differentiate on histopathology alone. A recent study demonstrated recruitment of mesenchymal cells (MSCs) at the periphery of granulomas in lymph node tuberculosis which suppressed T cell responses. We hypothesized that granulomas of ITB would also recruit MSCs to evade host immune response.

AIM

The purpose of this study was to demonstrate MSC markers in granulomas of ITB and evaluate whether distribution of MSC markers could differentiate between granulomas of Crohn's and ITB.

METHODS

We initially retrospectively enrolled 17 patients with confirmed ITB (8) or Crohn's (9) with granulomas on histopathology. Tissues were evaluated by immunofluorescence for MSC markers CD29, CD90, CD73 and absence of haematopoietic markers CD31, CD34, CD45 and CD14. Double-staining was done to confirm presence of MSCs. Subsequently, 23 postoperative specimens of Crohn's (18) and ITB (5) were analyzed for validation.

RESULTS

Overall, 27 Crohn's and 13 ITB cases were assessed. CD29 and CD90 positive cells were noted around both ITB and Crohn's granulomas. MSC marker CD73 was expressed around the granulomas of ITB alone and was completely absent in the Crohn's. The subsequent assessment of granulomas in postoperative specimens of Crohn's and ITB also showed similar results.

CONCLUSION

Granulomas of ITB and Crohn's disease can be differentiated by CD73 MSC surface marker expression. The differential CD73 expression around ITB granuloma indicates that Mycobacterium tuberculosis evades host immunity by recruiting MSCs with CD73 expression. MSCs with increased CD73 expression could be the future for therapeutic intervention in Crohn's.

Ketamine and peripheral inflammation

The old anesthetic ketamine has demonstrated interactions with the inflammatory response. This review intends to qualify the nature and the mechanism underlying this interaction. For this purpose, preclinical data will be presented starting with the initial works, and then, the probable mechanisms will be discussed. A summary of the most relevant clinical data will be presented. In conclusion, ketamine appears as a unique "homeostatic regulator" of the acute inflammatory reaction and the stress-induced immune disturbances. This is of some interest at a moment when the short- and long-term deleterious consequences of inadequate inflammatory reactions are increasingly reported. Large-scale studies showing improved patient's outcome are, however, required before to definitively assert the clinical reality of this positive effect.

Effect of acute exercise on cardiovascular hemodynamic and red blood cell concentrations of purine nucleotides in hypertensive compared with normotensives rats

OBJECTIVE

The mechanisms of exercise-induced health benefits are complex and not fully understood. This study investigated the effects of exercise and hypertension on cardiovascular hemodynamic responses and red blood cell (RBC) concentrations of purine nucleotides using normotensive and hypertensive rat models in vivo.

METHODS

Sprague Dawley rats (SDRs) and spontaneously hypertensive rats (SHRs) were exercised on a treadmill for 15 min at a speed of 10 m/min and 5% grade. Blood samples were obtained from each rat before, during, and after exercise for measurement of adenosine 5'-triphosphate (ATP) and guanosine 5'-triphosphate (GTP) concentrations in RBCs by a validated high-performance liquid chromatography assay. They were returned to a restrainer after exercise, and hemodynamic recording collected continuously up to 6 h. Two separate groups (SDRs and SHRs) without exercise were used as controls. Biomarker data were compared between SDRs and SHRs using analysis of variance and t test and difference considered significant at p < 0.05.

RESULTS

The study has demonstrated for the first time a difference in the postexercise effect between SDRs and SHRs. The 15 min of exercise significantly increased systolic blood pressure (SBP) (129 ± 16 to 162 ± 26 mmHg) and heart rate (HR) (416 ± 29 to 491 ± 26 bpm) in SDRs (p < 0.05), but not in SHRs. The postexercise hemodynamic effects were more profound in SHRs. SBP and diastolic blood pressure (DBP) also fell significantly in the control group of SHRs (SBP 184 ± 14 to 152 ± 29 mmHg and DBP 149 ± 9 to 120 ± 14 mmHg, p < 0.05 for both) towards the end of the experiment but not in the SDR group. The RBC concentrations of ATP and GTP increased after exercise in both SDRs and SHRs which were significantly correlated with the postexercise hemodynamic effect (p < 0.05).

CONCLUSION

SHRs were more tolerant to increases in HR and SBP induced by exercise, and have more profound postexercise hemodynamic effects than SDRs. The hemodynamic effects were linked closely with RBC concentrations of ATP and GTP in both SDRs and SHRs.

Beneficial effects of theophylline infusions in surgical patients with intra-abdominal hypertension

BACKGROUND

Intra-abdominal hypertension (IAH) can cause high mortality. Recently, we found that IAH was associated with increased serum levels of adenosine and interleukin 10. Our present "hypothesis-generated study" was based on the above mentioned results.

MATERIALS AND METHODS

In this uncontrolled clinical trial, a total of 78 patients with IAH were enrolled representing a 13-20 mmHg range of intra-abdominal pressure (IAP). Patients requiring surgical abdominal decompression were excluded. Patients were treated with the following protocols: standard supportive therapy (ST, n = 38) or ST plus infusion with the adenosine receptor antagonist theophylline (T, n = 40). Over the 5-day measurement period, IAP was monitored continuously and serum adenosine concentration and other clinical and laboratory measurements were monitored daily. Mortality was followed for the first 30 days following the diagnosis of IAH.

RESULTS

Mortality of ST patients was 55%, which is compatible to other studies. Serum adenosine concentration was found to be directly proportional to IAP. Of the 40 patients receiving T treatment, survival was 100%. An increased survival related to theophylline infusion correlated with improving serum concentrations of IL-10, urea, and creatinine, as well as 24-h urine output, fluid balance, mean arterial pressure, and O(2)Sat.

CONCLUSIONS

Adenosine receptor antagonism with T following IAH diagnosis resulted in markedly reduced mortality in patients with moderated IAH (<20 mmHg). Theophylline-associated mortality reduction may be related to improved renal perfusion and improved MAP, presumably caused by adenosine receptor blockade. Because this study was not a randomized controlled study, these compelling observations require further multicentric clinical confirmation.

Exercise improves hemodynamic profiles and increases red blood cell concentrations of purine nucleotides in a rodent model

OBJECTIVE

To study the effect of exercise on hemodynamic profiles and red blood cell (RBC) concentrations of adenosine-5'-triphosphate (ATP).

METHODS

Male Sprague-Dawley (SD) rats (n = 9) were exercised on a treadmill for 15 min at a speed of 10 m/min with a 5% gradient after an hour settling down in a restrainer. Blood samples were collected via an indwelling carotid artery catheter using a 'Stopping Solution' from each rat before, during and after exercise. Hemodynamic recordings were collected continuously throughout the experiment. Concentrations of ATP and other purine nucleotides in the RBCs were determined by a validated high-performance liquid chromatography (HPLC) assay. A control group (n = 12) was treated the same way except without the exercise. Data between groups were analyzed by analysis of variance (ANOVA) and Student's t-test, and differences were considered significant when p < 0.05.

RESULTS

Exercise increased systolic blood pressure (SBP; 141±23 vs. 132±17 mmHg) and heart rate (HR; 420±33 vs. 397±41 bpm), but decreased diastolic blood pressure (DBP; 105±18 vs. 110±14 mmHg). This was followed by a postexercise condition when SBP, DBP, and HR were decreased for the remainder of the experiment. RBC concentrations of ATP and guanosine-5'-triphosphate (GTP) increased significantly during exercise and continued to increase for 5 hours postexercise (1.5±0.75 vs. 0.96 vs. 0.36 mM for ATP; and 0.14±0.061 vs. 0.058±0.030 mM) (p < 0.05).

CONCLUSION

Exercise increased RBC ATP concentrations in a rodent model, which was correlated with the decrease in BP and HR postexercise.

Increased serum adenosine and interleukin 10 levels as new laboratory markers of increased intra-abdominal pressure

BACKGROUND

Increased intra-abdominal pressure (IAP), intra-abdominal hypertension (IAH) and abdominal compartment syndrome (ACS) are severe complications of surgical interventions with a high rate of mortality. The technique of IAP measurement is accurate, precise, reproducible and cost-effective. However, laboratory measures for monitoring of IAH have not been defined. We investigated the linkage between the serum levels of adenosine and interleukin 10 (IL-10) with IAP.

METHODS

The sera of 25 surgical patients with IAP <12 mmHg and of 45 surgical patients with IAP >12 mmHg were tested. Serum adenosine concentration was measured by HPLC. Serum IL-1β, IL-2, IL-4, IL-10, TNFα, IFNγ and IL-10 were determined by enzyme linked immunosorbent assay (ELISA). CRP was measured by nephelometry.

RESULTS

Significant correlations of IAP were found only with serum levels of adenosine and IL-10. In the sera of patients with IAP >12 mmHg, the levels of both adenosine (1.61 versus 0.06 µM, p < 0.01) and IL-10 (63.23 versus 27.27 pg/ml, p < 0.01) were significantly higher than those in patients with IAP <12 mmHg. Moreover, significant correlations were found between individual patient IAP-adenosine values (r = 0.766, p < 0.001), IAP-IL-10 values (r = 0.792, p < 0.001) and adenosine-IL-10 values (r = 0.888, p < 0.001). A direct linear correlation between IAP-adenosine and IAP-10 values was only observed with IAP >15 (Grade II-IV).

CONCLUSION

We report associations between IAP and the serum adenosine and IL-10 levels providing new tools for the laboratory monitoring of IAH as well as further understanding of the pathomechanisms contributing to ACS.

Effect of Adenosine on the Growth of Human T-Lymphocyte Leukemia Cell Line MOLT-4

Adenosine has been observed to suppress the growth of MOLT-4 human leukemia cells in vitro. Changes in the cell cycle, especially increased percentage of cells in S phase, prolonged generation time, and induction of apoptosis at higher adenosine concentrations have been found to be responsible for the growth suppression. Dipyridamole, a drug inhibiting the cellular uptake of adenosine, reversed partially but significantly the adenosine-induced growth suppression. It follows from these results that the action of adenosine on the MOLT-4 cells comprises its cellular uptake and intracellular operation. These findings present new data on anticancer efficacy of adenosine.

Coronary artery disease: a study on the joint role of birth weight, adenosine deaminase, and gender

An inverse relationship between birth weight and coronary artery diseases is well documented but it remains unclear which exposure in early life might underlie such association. Recently it has been reported an association between adenosine deaminase genetic polymorphism and coronary artery diseases. Gender differences in the degree of this association have been also observed. These observations prompted us to study the possible joint effects of BW, ADA, and gender on the susceptibility to coronary artery diseases. 222 subjects admitted to hospital for nonfatal coronary artery diseases, and 762 healthy consecutive newborns were studied. ADA genotypes were determined by DNA analysis. A highly significant complex relationship has emerged among ADA, birth weight, and gender concerning their role on susceptibility to coronary artery diseases in adult life. Odds ratio analysis suggests that low birth weight is more important in females than in males. ADA^∗2 allele appears protective in males, while in females such effect is obscured by birth weight.

Immunomodulatory effect of Antrodia camphorata mycelia and culture filtrate

AIM OF THE STUDY

Antrodia camphorata, a precious folkloric medicinal mushroom, has been used to treat tumorigenic diseases in Taiwan. This study was to investigate the innate immunity augmentation effects of different fractions prepared from hot water extracts of submerged cultured Antrodia camphorata (AC).

MATERIALS AND METHODS

The cytokine induction potency of AC fraction in diluted peripheral blood culture was measured by ELISA. The effects of AC fraction on phagocytic activity and CD11b expression were measured by the ingestion of FITC-labeled Escherichia coli and by labeling with PE-labeled CD11b monoclonal antibody, respectively, using flow cytometry. The molecular mass of hot water-soluble polysaccharides and content of adenosine in AC fraction were determined by gel permeation chromatography (GPC) and HPLC, respectively.

RESULTS

The mycelia fraction, Fr. M II, and culture filtrate fractions, Fr. E II and Fr. E III, showed the strongest TNF-alpha and IL-6 induction effect as a function of their concentration. These fractions (20mug/ml) also showed marked activity in enhancing phagocytosis in human polymorphonuclear neutrophils (PMN) and monocytes. In parallel, the expression of CD11b, an early marker of PMN activation, was also up-regulated dose-dependently. Composition analysis suggested that immunomodulatory effect of mycelia is mainly attributed to the 10-20kDa polysaccharides and adenosine.

CONCLUSIONS

These results provide evidences that Antrodia camphorata can modulate innate immunity and may serve as an adjuvant for tumor treatment.

Purinergic regulation of neutrophil chemotaxis

Chemotaxis allows polymorphonuclear neutrophils (PMN) to rapidly reach infected and inflamed sites. However, excessive influx of PMN damages host tissues. Better knowledge of the mechanisms that control PMN chemotaxis may lead to improved treatments of inflammatory diseases. Recent findings suggest that ATP and adenosine are involved in PMN chemotaxis. Therefore, these purinergic signaling processes may be suitable targets for novel therapeutic approaches to ameliorate host tissue damage.

Neutrophils as sources of extracellular nucleotides: functional consequences at the vascular interface

Nucleotide signaling is currently an area of intense investigation. Extracellular adenosine triphosphate (ATP) liberated during hypoxia or inflammation can either signal directly to purinergic receptors or, after phosphohydrolytic metabolism, can activate surface adenosine receptors. Given the association of polymorphonuclear leukocytes (PMNs) with adenine nucleotide/nucleoside signaling in the inflammatory milieu, it was recently demonstrated that PMNs actively release ATP via a connexin 43 hemichannel-dependent mechanism. Here, we review the mechanisms of ATP release and subsequent functional implications of ATP metabolism at the interface between PMN and vascular endothelial cells during inflammation and in hypoxia.

Oral administration of submerged cultivated Grifola frondosa enhances phagocytic activity in normal mice

Grifola frondosa fruiting body (Maitake) has been used as a dietary supplement due to its antitumour and immunomodulatory properties. The aim of this study was to evaluate the immunomodulatory effects of orally administered submerged cultivated G. frondosa mixture, including both mycelium and culture broth, in a healthy murine model. Composition analyses showed that submerged cultivated G. frondosa mixture contained only 32.48% carbohydrate, which was less than half of fruiting bodies. The content of adenosine, a potential immunomodulatory agent in medicinal mushrooms, was 2.8 mg g(-1). After feeding 8-week-old female BALB/cByJ mice with AIN-93G diet containing 0% (C), 1% (G1), 3% (G3) or 5% (G5) (wt/wt) G. frondosa mixture for 31 days, neither body weight nor the outward appearance of organs showed any significant difference among different diet groups. Splenocyte subpopulation, mitogen-activated cytokine release and splenic NK activity were not affected by G. frondosa administration, either. On the other hand, the phagocytic activity was enhanced in leucocytes of groups G3 and G5, without exerting detectable levels of serum proinflammatory cytokines. These results suggested that oral administration of submerged cultivated G. frondosa mixture may enhance host innate immunity against foreign pathogens without eliciting adverse inflammatory response.

Role of extracellular nucleotide phosphohydrolysis in intestinal ischemia-reperfusion injury

Extracellular adenosine has been implicated as an innate antiinflammatory metabolite, particularly during conditions of limited oxygen availability such as ischemia. Because extracellular adenosine generation is primarily produced via phosphohydrolysis from its precursor molecule adenosine-monophosphate (AMP) through the enzyme ecto-5'-nucleotidase (CD73), we examined the contribution of CD73-dependent adenosine production in modulation of intestinal ischemia-reperfusion (IR) injury. Following transcriptional and translational profiling of intestinal tissue that revealed a prominent induction of murine CD73, we next determined the role of CD73 in protection against intestinal IR injury. Interestingly, pharmacological inhibition or targeted gene deletion of CD73 significantly enhanced not only local intestinal injury, but also secondary organ injury, following IR as measured by intestinal and lung myeloperoxidase, aspartate and alanine aminotransferase, interleukin (IL) -1, IL-6, and histological injury. To confirm the role of CD73 in intestinal adenosine production, we measured adenosine tissue levels and found that they were increased with IR injury. In contrast, CD73-deficient (cd73(-/-)) mice had lower adenosine levels at baseline and no increase with IR injury. Finally, reconstitution of cd73(-/-) mice or treatment of wild-type mice with soluble 5'-nucleotidase was associated with significantly lower levels of injury. These data reveal a previously unrecognized role of CD73 in attenuating intestinal IR-mediated injury.

HPLC assay with UV detection for determination of RBC purine nucleotide concentrations and application for biomarker study in vivo

ATP and other purine nucleotides are important biomarkers for ischemia and may have considerable potential as targets for management of ischemic heart disease and stroke. The main objective of the study is to develop a rapid HPLC assay, which has adequate sensitivity and specificity for measuring concentrations of ATP, ADP, AMP, GTP, GDP and GMP in erythrocytes (RBC). The assays used ion-pair chromatography coupled with ultraviolet detection at 254 nm to separate and detect the purine nucleotides. Using 50-100 microL of RBC lysate as blank biologic matrix, the assay was linear from 100 to 2000 microg/mL for ATP and ADP, and 20-400 microg/mL for AMP, GTP, and GDP with coefficients of determination (r(2)) >0.99. GDP and GMP were not measurable in the study because of low concentrations and interference from endogenous materials, respectively. The intra-assay and inter-assay variations over a period of 1 year were less than 10% and 20%, respectively for most of the nucleotides. The assay was successfully applied to two pilot biomarker studies to measure RBC concentrations of the purine nucleotides in rats under restraining and exercise conditions. Preliminary results showed that the RBC concentrations of ATP and GTP were higher in the spontaneously hypertensive rats (SHR) compared to the Sprague-Dawley (SD) rats, and that exercise increased RBC concentrations of ATP in rats treated with the calcium channel blocker diltiazem.

The fibrin-derived peptide Bbeta15-42 is cardioprotective in a pig model of myocardial ischemia-reperfusion injury

OBJECTIVE

The fibrin-derived peptide Bbeta15-42 has been shown to reduce infarct size in rodent models of ischemia-reperfusion injury. To increase its potential for translation into the clinic, we studied the effects of Bbeta15-42 in pigs, whose coronary anatomy is similar to that of humans. In addition, we evaluated the pharmacokinetics and safety of Bbeta15-42 in several species, including humans.

DESIGN

Animal study and phase I trial.

SETTING

University hospital and contract research laboratories.

SUBJECTS

Pigs/healthy volunteers.

INTERVENTIONS

Male farm-bred Landrace pigs were subjected to 1 hr of left anterior descending coronary artery occlusion followed by 3 hrs of reperfusion. At the time of reperfusion, Bbeta15-42 (2.4 mg/kg, n = 6) or random peptide (control; 2.4 mg/kg, n = 6) was administered as an intravenous bolus. As a positive control, pigs were subjected to ischemic preconditioning (n = 6). Cardiac damage and hemodynamics were recorded. Biodistribution and pharmacokinetics of Bbeta15-42 were determined in rats and dogs. In a phase I trial involving 30 male healthy volunteers, pharmacokinetics and safety were tested in a randomized, double-blinded, placebo-controlled, parallel-group, single ascending dose study.

MEASUREMENTS AND MAIN RESULTS

Bbeta15-42 and ischemic preconditioning significantly reduced myocardial infarct size and troponin I levels. Bbeta15-42 also reduces interleukin-6 levels, underlining its anti-inflammatory properties. Furthermore, in humans, the pharmacokinetics of the peptide Bbeta15-42 were comparable to those of animals, and no serious adverse effects were observed.

CONCLUSIONS

Bbeta15-42 elicits cardioprotection in pigs and is clinically safe in phase I testing of humans. This study confirms the new concept of a pathogenic role of fibrin derivatives in myocardial reperfusion injury, which can be inhibited by peptide Bbeta15-42.

Intestinal ischemia-reperfusion injury alters purinergic receptor expression in clinically relevant extraintestinal organs

BACKGROUND

Intestinal ischemia-reperfusion (IIR) injury is known to initiate the systemic inflammatory response syndrome, which often progresses to multiple organ failure. We investigated changes in purinoceptor expression in clinically relevant extra-intestinal organs following IIR injury.

MATERIALS AND METHODS

Anesthetized adult male BalbC mice were randomized to sham laparotomy (control, n = 5), or 15 min of superior mesenteric artery occlusion. Experimental ischemia was followed by a period of reperfusion [1 min (n = 6) or 1 h (n = 6)]. Mice were then sacrificed and lung, kidney, and intestinal tissues were harvested. Following RNA extraction, purinoceptor mRNA expression for P2Y2, A3, P2X7, A2b, P2Y4, and P2Y6 was analyzed using real-time RT-PCR.

RESULTS

Significant differences in purinoceptor expression were observed in the lungs and kidneys of mice exposed to IIR injury when compared to controls. Pulmonary P2Y2 receptor expression was increased in the 1 h IIR group when compared to control, while pulmonary A3 receptor expression was incrementally elevated following IIR injury. In the kidney, P2Y2 receptor expression was increased in the 1 h IIR group compared to both 1 min IIR and control, and A3 receptor expression was decreased in the 1 h IIR group compared to the 1 min IIR group. No significant changes were observed in the intestinal purinoceptor profiles.

CONCLUSION

Purinoceptor expression is altered in the murine lung and kidney, but not intestine following experimental IIR injury. These findings may implicate extracellular nucleotides and purinoceptors as possible mediators of the extra-intestinal organ dysfunction associated with IIR injury.

ADA*2 Allele of the Adenosine Deaminase Gene May Protect against Coronary Artery Disease

BACKGROUND/AIMS

The common G22A polymorphism in the adenosine deaminase (ADA) gene leads to substitution Asp8Asn. The lower activity of the enzyme encoded by A22 (ADA*2) allele may increase tissue concentrations of adenosine, a potent cardioprotective agent. In a case-control study, we investigated the association between ADA polymorphism and coronary artery disease (CAD).

METHODS

A hundred and seventy-one CAD patients from the north-western part of Poland and 200 consecutive newborns from the same population were genotyped by PCR-RFLP.

RESULTS

Twenty-five ADA*1/*2 heterozygotes (12.5%) and 2 ADA*2/*2 homozygotes (1%) were found in the control group, while only 10 *1/*2 heterozygotes (5.9%) and no *2/*2 homozygotes were found in the CAD group. Frequencies of ADA*2 carriers (5.9% vs. 13.5%, p = 0.015) and ADA*2 allele (2.9% vs. 7.3%, p = 0.0083) were lower in CAD patients than in controls. Among CAD patients, a significantly lower proportion of *2 allele carriers was treated with diuretics and ACE inhibitors when compared to *1/*1 wild-type homozygotes.

CONCLUSION

ADA*2 allele may decrease genetic susceptibility to CAD. ADA should be added to the list of candidate genes modifying the risk of cardiovascular diseases.

Physiological roles for ecto-5'-nucleotidase (CD73)

Nucleotides and nucleosides influence nearly every aspect of physiology and pathophysiology. Extracellular nucleotides are metabolized through regulated phosphohydrolysis by a series of ecto-nucleotidases. The formation of extracellular adenosine from adenosine 5’-monophosphate is accomplished primarily through ecto-5’-nucleotidase (CD73), a glycosyl phosphatidylinositol-linked membrane protein found on the surface of a variety of cell types. Recent in vivo studies implicating CD73 in a number of tissue protective mechanisms have provided new insight into its regulation and function and have generated considerable interest. Here, we review contributions of CD73 to cell and tissue stress responses, with a particular emphasis on physiologic responses to regulated CD73 expression and function, as well as new findings utilizing Cd73-deficient animals.

Pathophysiology and therapeutic potential of purinergic signaling

The concept of a purinergic signaling system, using purine nucleotides and nucleosides as extracellular messengers, was first proposed over 30 years ago. After a brief introduction and update of purinoceptor subtypes, this article focuses on the diverse pathophysiological roles of purines and pyrimidines as signaling molecules. These molecules mediate short-term (acute) signaling functions in neurotransmission, mechanosensory transduction, secretion and vasodilatation, and long-term (chronic) signaling functions in cell proliferation, differentiation, and death involved in development and regeneration. Plasticity of purinoceptor expression in pathological conditions is frequently observed, including an increase in the purinergic component of autonomic cotransmission. Recent advances in therapies using purinergic-related drugs in a wide range of pathological conditions will be addressed with speculation on future developments in the field.

Adenosine inhibits the release of interleukin-1beta in activated human peripheral mononuclear cells

The effects of adenosine and subtype-specific activators of adenosine receptors (A1, A2A, A2B and A3) were studied on the release of interleukin-1beta (IL-1beta) from peripheral mononuclear cells, monocytes and lymphocytes. In the cells activated by the protein kinase C specific phorbol ester (phorbol 12-myristate 13-acetate) and Ca(2+) ionophore (A23187) both adenosine and the subtype-specific receptor agonists, CPA (A1), CGS 21680 (A2A) and IB-MECA (A3) induced a concentration-dependent inhibition of IL-1beta release. The rank order of potency in the inhibition of IL-1beta release was CPA=CGS 21680>IB-MECA>adenosine>NECA (in the presence of A1, A2A and A3 receptor inhibitors). The inhibitory actions of CPA, CGS 21680 or IB-MECA were significantly reduced in the presence of DPCPX, ZM 243185 or MRS 1191 as subtype-specific antagonists on A1, A2A and A3 adenosine receptors, respectively. It can be concluded that adenosine inhibits the release of IL-1beta from the activated human peripheral mononuclear cells. In this process A1, A2A and A3 receptors are involved.

ACTIONS OF ADENOSINE AT ITS RECEPTORS IN THE CNS: Insights from Knockouts and Drugs

Adenosine and its receptors have been the topic of many recent reviews ( 1 – 26 ). These reviews provide a good summary of much of the relevant literature—including the older literature. We have, therefore, chosen to focus the present review on the insights gained from recent studies on genetically modified mice, particularly with respect to the function of adenosine receptors and their potential as therapeutic targets. The information gained from studies of drug effects is discussed in this context, and discrepancies between genetic and pharmacological results are highlighted.

Taming the neutrophil: calcium clearance and influx mechanisms as novel targets for pharmacological control

Neutrophils are relatively insensitive to the anti-inflammatory actions of conventional chemotherapeutic agents, including corticosteroids, emphasizing the requirement for novel pharmacological strategies to control the potentially harmful proinflammatory activities of these cells. In the case of commonly-occurring inflammatory diseases of the airways, the neutrophil is the primary mediator of inflammation in conditions such as chronic obstructive pulmonary disease, cystic fibrosis, acute respiratory distress syndrome, bronchiectasis and non-eosinophilic bronchial asthma. Recent insights into the mechanisms utilized by neutrophils to restore Ca(2+) homeostasis following activation with Ca(2+)-mobilizing, proinflammatory stimuli have facilitated the identification of novel targets for anti-inflammatory chemotherapy in these cells. The most amenable of these from a chemotherapeutic perspective, is the cyclic AMP-dependent protein kinase-modulated endomembrane Ca(2+)-ATPase which promotes clearance of the cation from the cytosol of activated neutrophils. Second generation type 4 phosphodiesterase inhibitors and adenosine receptor agonists operative at the level of subtype A2A adenosine receptors, which are currently undergoing clinical and preclinical assessment respectively, hold promise as pharmacologic modulators during the restoration of Ca(2+) homeostasis. If this promise is realized, it may result in novel chemotherapeutic strategies for the control of hyperacute and chronic inflammatory conditions in which neutrophils are primary offenders. Alternative, potential future targets include the Na(+), Ca(2+)-exchanger and store-operated Ca(2+) channels, which cooperate in the refilling of intracellular Ca(2+) stores.

Dynamic purine signaling and metabolism during neutrophil-endothelial interactions

During episodes of hypoxia and inflammation, polymorphonuclear leukocytes (PMN) move into underlying tissues by initially passing between endothelial cells that line the inner surface of blood vessels (transendothelial migration, TEM). TEM creates the potential for disturbances in vascular barrier and concomitant loss of extravascular fluid and resultant edema. Recent studies have demonstrated a crucial role for nucleotide metabolism and nucleoside signaling during inflammation. These studies have implicated multiple adenine nucleotides as endogenous tissue protective mechanisms invivo. Here, we review the functional components of vascular barrier, identify strategies for increasing nucleotide generation and nucleoside signaling, and discuss potential therapeutic targets to regulate the vascular barrier during inflammation.

Potential value of adenosine 5'-triphosphate (ATP) and adenosine in anaesthesia and intensive care medicine

Extracellular adenosine and adenosine triphosphate (ATP) are involved in biological processes including neurotransmission, muscle contraction, cardiac function, platelet function, vasodilatation, signal transduction and secretion in a variety of cell types. They are released from the cytoplasm of several cell types and interact with specific purinergic receptors which are present on the surface of many cells. This review summarizes the evidence on the potential value and applicability of ATP (not restricted to ATP-MgCl(2)) and adenosine in the field of anaesthesia and intensive care medicine. It focuses, in particular, on evidence and roles in treatment of acute and chronic pain and in sepsis. Based on the evidence from animal and clinical studies performed during the last 20 years, ATP could provide a valuable addition to the therapeutic options in anaesthesia and intensive care medicine. It may have particular roles in pain management, modulation of haemodynamics and treatment of shock.

Endogenous adenosine produced during hypoxia attenuates neutrophil accumulation: coordination by extracellular nucleotide metabolism

Hypoxia is a well-documented inflammatory stimulus and results in tissue polymorphonuclear leukocyte (PMN) accumulation. Likewise, increased tissue adenosine levels are commonly associated with hypoxia, and given the anti-inflammatory properties of adenosine, we hypothesized that adenosine production via adenine nucleotide metabolism at the vascular surface triggers an endogenous anti-inflammatory response during hypoxia. Initial in vitro studies indicated that endogenously generated adenosine, through activation of PMN adenosine A(2A) and A(2B) receptors, functions as an antiadhesive signal for PMN binding to microvascular endothelia. Intravascular nucleotides released by inflammatory cells undergo phosphohydrolysis via hypoxia-induced CD39 ectoapyrase (CD39 converts adenosine triphosphate/adenosine diphosphate [ATP/ADP] to adenosine monophosphate [AMP]) and CD73 ecto-5'-nucleotidase (CD73 converts AMP to adenosine). Extensions of our in vitro findings using cd39- and cd73-null animals revealed that extracellular adenosine produced through adenine nucleotide metabolism during hypoxia is a potent anti-inflammatory signal for PMNs in vivo. These findings identify CD39 and CD73 as critical control points for endogenous adenosine generation and implicate this pathway as an innate mechanism to attenuate excessive tissue PMN accumulation.