Therapeutic potential for transient inhibition of adenosine deaminase in systemic inflammatory response syndrome

Ganoderma lucidum polysaccharide peptide alleviates hyperuricemia by regulating adenosine deaminase and urate transporters

Hyperuricemia (HUA) affects human health and is involved in the pathogenesis of common chronic diseases. Previous studies showed that Ganoderma lucidum extract lowered HUA in animals. However, the active ingredient and pharmacological mechanism of Ganoderma lucidum extract in the improvement of HUA are unknown. The purpose of this study was to determine the anti-HUA efficacy and related mechanism of Ganoderma lucidum polysaccharide peptide (GLPP) using a potassium oxonate (PO)-induced mouse model and an adenosine-induced cell model. The experimental results showed that blood uric acid (UA) was decreased up to 40.6% by GLPP in HUA mice in a dose-dependent manner. Additionally, GLPP significantly reduced UA production by inhibiting the hepatic and blood adenosine deaminase (ADA) activity and increased UA excretion by decreasing the expression of glucose transporter 9 (GLUT9) and increasing the expression of organic anion transporter 1 (OAT1) in kidney. The adenosine-induced cell model showed that the inhibitory effect of GLPP on ADA activity may be the main reason for the alleviation of HUA by GLPP. Furthermore, PO-induced renal histopathological damage was also alleviated by GLPP in a dose-dependent manner. The experimental results in this study indicated that GLPP exerted anti-HUA effects via regulating the UA production and excretion, suggesting that GLPP could be developed into a therapeutic agent for HUA.

Inhibition of adenosine deaminase activity reverses resistance to the cytotoxic effect of high adenosine levels in cervical cancer cells

Adenosine (ADO) generation in the tumor microenvironment (TME) plays important roles in the promotion of tumor growth, invasion, and metastasis and in suppression of the antitumor immune response. Recently, adenosine deaminase (ADA) activity in the TME has been proposed to be a compensatory mechanism against toxic accumulation of ADO in cancerous tissues. In the present study, the expression and functional activity of ADA in cervical cancer (CeCa) tumor cells were analyzed: C33A (HPV-), CaSki (HPV + ), and HeLa (HPV + ) cells. CeCa tumor cells, as well as activated T lymphocytes (ATLs), which were used as a positive control, showed different ADA contents in the membrane and intracellularly and a strong ability to convert ADO into inosine (INO). Treatment of tumor cells with EHNA, a specific ADA inhibitor, decreased the viability of CeCa tumor cells in a dose-dependent manner. In C33A (EHNA half maximal inhibitory concentration (IC₅₀) = 374 μM), CaSki (EHNA IC₅₀ = 273.6 μM), and HeLa (EHNA IC₅₀ = 252.2 μM) cells, EHNA strongly reversed the resistance of tumor cells to the cytotoxic effect of high concentrations of ADO; 38.82 ± 3.1%, 47.18 ± 4.7%, and 71.63 ± 6.9% of the cells were apoptotic, and 40 ± 4.8%, 52 ± 5.3% and 70 ± 6.8% of the cells had mitochondrial membrane damage, respectively. In ATLs (EHNA IC₅₀ = 391.8 μM) treated with EHNA, 32.4 ± 4.4% were apoptotic, and 32 ± 4.3% had mitochondrial membrane damage. These results suggest that the presence and activity of ADA in CeCa tumor cells can provide protection against the cytotoxic effect of high ADO contents in the TME. Therefore, the inhibition of ADA could be a strategy for the treatment of CeCa.

Serum adenosine deaminase levels are associated with diabetic kidney disease in type 2 diabetic patients

The aim of the present study was to evaluate the association between adenosine deaminase (ADA) levels and diabetic kidney disease (DKD) in patients with type 2 diabetes (T2D). In this study, patients with T2D who had been screened for DKD were recruited. Patients with an estimated glomerular filtration rate (eGFR) < 60 mL/min/1.73 m2 or a urinary albumin-to-creatinine ratio (UACR) ≥ 30 mg/g for 3 months were identified as having DKD. The prevalence of DKD was 13.3%, and the range of serum ADA levels was 4-37 U/L. Serum ADA levels were positively associated with cystatin C levels and UACR (r = 0.295 and r = 0.302, respectively, both P < 0.05) and negatively associated with eGFR (r = -0.342, P < 0.05). The proportion of participants with DKD increased significantly from 3.8% in the first tertile (T1) to 13.6% in the second tertile (T2) and 25.9% in the third tertile (T3) of ADA (P for trend < 0.001). After adjusting for clinical risk factors for DKD via multiple logistic regression, the corresponding odds ratios (ORs) of DKD for the participants in T2 and T3 vs those in T1 of ADA were 5.123 (1.282-20.474) and 10.098 (1.660-61.431), respectively. Receiver operating characteristic (ROC) analysis revealed that the optimal cutoff value of ADA to indicate DKD was 10 U/L. Its corresponding sensitivity and specificity were 75.5 and 56.4%, respectively. Our results demonstrated that serum ADA levels were closely associated with DKD and partly reflect the risk of DKD in patients with T2D.

The relationship between adenosine deaminase and heart rate-corrected QT interval in type 2 diabetic patients

BACKGROUND

Prolonged heart rate-corrected QT (QTc) interval may reflect poor prognosis of patients with type 2 diabetes (T2D). Serum adenosine deaminase (ADA) levels are related to hyperglycemia, insulin resistance (IR) and inflammation, which may participate in diabetic complications. We investigated the association of serum ADA levels with prolonged QTc interval in a large-scale sample of patients with T2D.

METHODS

In this cross-sectional study, a total of 492 patients with T2D were recruited. Serum ADA levels were determined by venous blood during fasting. QTc interval was estimated from resting 12-lead ECGs, and prolonged QTc interval was defined as QTc > 440 ms.

RESULTS

In this study, the prevalence of prolonged QTc interval was 22.8%. Serum ADA levels were positively associated with QTc interval (r = 0.324, P < 0.0001). The proportion of participants with prolonged QTc interval increased significantly from 9.2% in the first tertile (T1) to 24.7% in the second tertile (T2) and 39.0% in the third tertile (T3) of ADA (P for trend < 0.001). After adjusting for other possible risk factors by multiple linear regression analysis, serum ADA level was still significantly associated with QTc interval (β = 0.217, t = 3.400, P < 0.01). Multivariate logistic regression analysis showed that female (OR 5.084, CI 2.379-10.864, P < 0.001), insulin-sensitizers treatment (OR 4.229, CI 1.290-13.860, P = 0.017) and ADA (OR 1.212, CI 1.094-1.343, P < 0.001) were independent contributors to prolonged QTc interval.

CONCLUSIONS

Serum ADA levels were independently associated with prolonged QTc interval in patients with T2D.

The protective effects of the Lactarius deliciosus and Agrocybe cylindracea mushrooms on histopathology of carbon tetrachloride induced oxidative stress in rats

We investigated the protective effects of L. deliciosus and A. cylindracea supplementation against carbon tetrachloride (CCI₄) induced oxidative stress by measuring levels of adenosine deaminase (ADA) and myeloperoxidase (MPO), and by observing histopathological changes in liver and kidney tissues of rats. We divided 36 rats into six groups: control, CCl₄, L. deliciosus, A. cylindracea, CCl₄ + L. deliciosus, and CCl₄ + A. cylindracea. We found that administration of CCI₄, A. cylindracea, and CCl₄ + A. cylindracea increased MPO and ADA levels. We observed severe hepato-renal degenerative and necrotic lesions in the CCI₄, A. cylindracea and CCl₄ + A. cylindracea groups. Severe lesions of the liver and kidney were not observed with A. cylindracea administration. CCI₄ induced hepato-renal lesions were ameliorated by L. deliciosus extract supplementation. L. deliciosus could be an important dietary antioxidant for preventing histologic lesions in liver and kidney due to CCI₄ induced oxidative stress in rats.

Time Series Gene Expression Profiles Analysis Identified Several Potential Biomarkers for Sepsis

Sepsis is a life-threatening disorder and leads to organ dysfunction and death. Therefore, searching for more alternative biomarkers is of great significance for sepsis assessment and surveillance. In our study, the gene expression profiles of 163 samples from healthy controls and septic patients were analyzed and 8 gene co-expression modules were identified by constructing weighted gene co-expression network. The blue and yellow modules showed close correlations with the phenotypic trait "days postsepsis." Besides, differentially expressed genes (DEGs) over time in septic patients were screened using Short Time-series Expression Miner (STEM) program. The intersection of genes in the blue and yellow modules and DEGs, which were significantly enriched in "HTLV-1 infection" pathway, was analyzed with protein-protein interaction network. The logistic regression model based on these eight mRNAs was constructed to determine the type of the sample reliably. Eight vital genes CECR1, ANXA2, ELANE, CTSG, AZU1, PRTN3, LYZ, and DEFA4 presented high scores and may be associated with sepsis, which provided candidate biomarkers for sepsis.

Adenosine deaminase inhibition

Adenosine deaminase is a critical enzyme in purine metabolism that regulates intra and extracellular adenosine concentrations by converting it to inosine. Adenosine is an important purine that regulates numerous physiological functions by interacting with its receptors. Adenosine and consequently adenosine deaminase can have pro or anti-inflammatory effects on tissues depending on how much time has passed from the start of the injury. In addition, an increase in adenosine deaminase activity has been reported for various diseases and the significant effect of deaminase inhibition on the clinical course of different diseases has been reported. However, the use of inhibitors is limited to only a few medical indications. Data on the increase of adenosine deaminase activity in different diseases and the impact of its inhibition in various cases have been collected and are discussed in this review. Overall, the evidence shows that many studies have been done to introduce inhibitors, however, in vivo studies have been much less than in vitro, and often have not been expanded for clinical use.

Biochemical and computational insights of adenosine deaminase inhibition by Epigallocatechin gallate

Epigallocatechin gallate, a flavonoid from Camellia sinensis possess various pharmacological activities such as anticancer, antimicrobial and antioxidant etc. Adenosine deaminase, (ADA), is a key enzyme involved in the purine metabolism, the inhibitors of which is being considered as highly promising candidate for the development of anti-proliferative and anti-inflammatory drugs. In this work we studied adenosine deaminase inhibitory activity of epigallocatechin gallate by using biophysical and computational methods. The enzyme inhibition study result indicated that epigallocatechin gallate possess strong inhibitory activity on ADA. ITC study revealed the energetics of binding. Also the binding is confirmed by using fluorescence spectroscopy. The structural details of binding are obtained from molecular docking and MD simulation studies.

Computational and experimental validation of morin as adenosine deaminase inhibitor

Adenosine deaminase (ADA) is one of the major enzymes involved in purin metabolism, it has a significant role in cell growth and differentiation. Over-activity of ADA has been noticed in some pathology, like malignancy and inflammation and makes it an attractive target for the development of drugs for such diseases. In the present study, ADA inhibitory activity of morin, a bioactive flavonoid, was assessed through computational and biophysical methods. The enzyme kinetics data showed that morin is a competitive inhibitor of ADA. Binding energy calculated from ITC analysis was -7.11 kcal/mol. Interaction of morin with ADA was also studied using fluorescence quenching method. Molecular docking studies revealed the structural details of the interaction. Molecular dynamics study in explicit solvent was also conducted to assess the structural stability of protein ligand complex.

Adenosine Deaminase-2-Induced Hyperpermeability in Human Retinal Vascular Endothelial Cells Is Suppressed by MicroRNA-146b-3p

Purpose

We recently demonstrated that adenosine deaminase-2 (ADA2) contributes to diabetic retinopathy (DR) via up-regulating the production of inflammatory cytokines in macrophages. Also, microRNA (miR)-146b-3p has the ability to inhibit ADA2. The goal of this study was to investigate the potential role of ADA2 and therapeutic benefit of miR-146b-3p in retinal inflammation and endothelial barrier dysfunction during diabetes.

Methods

Adenosine deaminase-2 activity was determined by colorimetric method in diabetic human vitreous. Human monocyte cell line U937 was differentiated into macrophages and then treated with amadori glycated albumin (AGA), and conditioned medium (CM) was used to assess the changes in ADA2 activity and TNF-α and IL-6 levels by ELISA. Also, macrophages were transfected with miR-146b-3p before treatment with AGA. Permeability of human retinal endothelial cells (hRECs) was assessed by electric cell-substrate impedance sensing (ECIS) after treatment with macrophage CM. Zonula occludens (ZO)-1 was examined by immuno-fluorescence in hRECs. Leukocyte adhesion was assessed in hRECs by measuring myeloperoxidase (MPO) activity and intercellular adhesion molecule-1 (ICAM-1) expression.

Results

Adenosine deaminase-2 activity was significantly increased in diabetic human vitreous. ADA2 activity and TNF-α and IL-6 levels were significantly increased in human macrophages by AGA treatment. Amadori glycated albumin–treated macrophage CM significantly increased hREC permeability, disrupted ZO-1 pattern, and increased leukocyte adhesion to hRECs through up-regulating ICAM-1. All these changes were reversed by miR-146b-3p.

Conclusions

Adenosine deaminase-2 is implicated in breakdown of the blood–retinal barrier (BRB) in DR through macrophages-derived cytokines. Therefore, inhibition of ADA2 by miR-146b-3p might be a useful tool to preserve BRB function in DR.

Inhibitory activity of hibifolin on adenosine deaminase- experimental and molecular modeling study

Adenosine deaminase (ADA) is an enzyme involved in purine metabolism. ADA converts adenosine to inosine and liberates ammonia. Because of their critical role in the differentiation and maturation of cells, the regulation of ADA activity is considered as a potential therapeutic approach to prevent malignant and inflammatory disorders. In the present study, the inhibitory activity of a plant flavonoid, hibifolin on ADA is investigated using enzyme kinetic assay and isothermal titration calorimetry. The inhibitory constant of hibifolin was found to be 49.92μM±3.98 and the mode of binding was reversible. Isothermal titration calorimetry showed that the compound binds ADA with binding energy of -7.21Kcal/mol. The in silico modeling and docking studies showed that the bound ligand is stabilized by hydrogen bonds with active site residues of the enzyme. The study reveals that hibifolin can act as a potential inhibitor of ADA.

Acute-phase proteins, oxidative stress and enzyme activities of blood serum and peritoneal fluid in cattle with abomasal displacement

BACKGROUND

Blood serum and peritoneal fluid acute-phase proteins, oxidative stress indicators, and some enzymes could be used for evaluation of abomasal tissue damage because of displacement in displaced abomasum (DA) cases.

OBJECTIVES

The aim of this study was to investigate the concentrations of acute-phase proteins, oxidative stress indicators, and activities of enzymes in blood serum and peritoneal fluid in cattle with right displaced abomasum (RDA) and left displaced abomasum (LDA) and in healthy cows.

ANIMALS

A total of 60 Holstein Friesian cows in early lactation were used, 31 with left and 9 with right displaced abomasum without volvulus diagnosis and no other postpartum disease, and 20 healthy cows as a control.

MATERIALS AND METHODS

DA diagnosis in dairy cows consisted of physical examination, laboratory, and specific DA tests. Acute-phase proteins, oxidative stress indicators, and enzyme activities were measured in blood serum and peritoneal fluid.

RESULTS

In the RDA group, serum haptoglobin (HPG), serum amyloid A (SAA), malondialdehyde (MDA), adenosine deaminase (ADA), myeleperoxidase (MPO), aspartate aminotransferase (AST), creatine kinase (CK, creatine kinase-MB (CK-MB), and gamma-glutamyl transferase (GGT) activity increased significantly, and serum HPG, MDA, ADA, and AST concentrations increased significantly in the LDA group (P < .05). Peritoneal fluid HPG, MDA, ADA, MPO, ALP, GGT, and LDH concentrations increased significantly, whereas NO concentrations reduced significantly in the RDA group, and HPG, MDA, ADA, and TP concentrations increased significantly, whereas concentrations of NO reduced significantly in the LDA group (P < .05).

CONCLUSIONS AND CLINICAL IMPORTANCE

There are acute-phase responses, oxidative stress, and abomasal tissue damage because of displacement in DA cases. Especially, HPG, MDA, ADA, and MPO concentrations can provide specific information to help in understanding these changes.

Effect of ghrelin on inflammatory response in lung contusion

The purpose of this study was to investigate the effects of ghrelin on inflammatory response and tissue damage following trauma-induced acute lung injury. Thirty male wistar albino rats (300-400 g) were randomly assigned into three groups: control group (n = 6), lung contusion plus saline (saline-treated, n = 12), and lung contusion plus ghrelin (ghrelin-treated, n = 12). Saline- or ghrelin-treated traumatic rats were sacrificed at two time points (24 and 72 hours) after lung contusion. Blood was collected for the analysis of serum adenosine deaminase (ADA). Tissue transforming growth factor-beta 1 (TGF-β1) and matrix metalloproteinase-2 (MMP-2) levels were measured by enzyme-linked immunosorbent assay and histopathological examination was performed on the lung tissue samples. Our results indicated that ghrelin significantly reduced morphologic damages. Serum ADA activities were significantly decreased after lung contusion and this decline started early with ghrelin treatment. TGF-β1 and MMP-2 levels in lung tissue were elevated at 72 hours after lung contusion and treatment with ghrelin significantly increased TGF-β1 level and reduced MMP-2 level. In conclusion, our study demonstrates that acute lung injury initiated proinflammatory responses and ghrelin administration showed an anti-inflammatory effect in lung contusion.

Adenosine Deaminase Isoenzymes in the Diagnosis and Monitoring of Rheumatoid Arthritis

The aim of this study was determination of the catalytic activities of adenosine deaminase (ADA), ADA1 and ADA2 isoenzymes in the serum of patients suffering from rheumatoid arthritis (RA) who were and were not treated with methotrexate (MTX), and identification of the possibilities of using these biochemical parameters in diagnosing and monitoring the treatment effects in RA. Catalytic activities of total ADA (tADA) and ADA2 in serum were determined by a spectrophotometric method. A statistically significant correlation was found between the total ADA and ADA1 values, as well as between tADA and ADA2 in the serum of all patients suffering from RA. Determination of ADA1 and ADA2 isoenzyme catalytic activities in the serum of patients who might be suffering from RA improves the diagnostic value of total ADA catalytic activity determination. ADA2 catalytic activity in serum can be a useful biochemical marker in diagnosing and monitoring RA. Decrease in ADA1 isoenzyme catalytic activities in the serum of patients suffering from RA who were treated with MTX can help in the observation of MTX therapy effects.

Sampling protein motion and solvent effect during ligand binding

An exhaustive description of the molecular recognition mechanism between a ligand and its biological target is of great value because it provides the opportunity for an exogenous control of the related process. Very often this aim can be pursued using high resolution structures of the complex in combination with inexpensive computational protocols such as docking algorithms. Unfortunately, in many other cases a number of factors, like protein flexibility or solvent effects, increase the degree of complexity of ligand/protein interaction and these standard techniques are no longer sufficient to describe the binding event. We have experienced and tested these limits in the present study in which we have developed and revealed the mechanism of binding of a new series of potent inhibitors of Adenosine Deaminase. We have first performed a large number of docking calculations, which unfortunately failed to yield reliable results due to the dynamical character of the enzyme and the complex role of the solvent. Thus, we have stepped up the computational strategy using a protocol based on metadynamics. Our approach has allowed dealing with protein motion and solvation during ligand binding and finally identifying the lowest energy binding modes of the most potent compound of the series, 4-decyl-pyrazolo[1,5-a]pyrimidin-7-one.

Adenosine deaminase activity in patients with Crohn's disease: distinction between active and nonactive disease

BACKGROUND

Crohn's disease (CD) is a common chronic inflammatory bowel disease. During the disease a cascade of immunologic events occur including mucosal influx of inflammatory cells like neutrophils. Adenosine deaminase (ADA) is important in inflammatory responses and serves as a marker of activated leukocytes.

MATERIALS AND METHODS

In this study, we investigated the activity of total ADA (tADA) and its isoenzymes, ADA1 and ADA2, in serum and neutrophils derived from 20 active patients with CD, 20 patients in remission, as well as in 15 healthy controls.

RESULTS

Patients with active disease had significantly (P<0.001) higher levels of tADA in serum (22.9±4.9 U/l) than patients in remission or healthy controls (14.0±3.4 U/l and 13.2±2.4 U/l respectively). ADA2, the main isoenzyme in the serum was higher in active patients by 60% as compared with patients in remission and healthy controls (19.7±1.9 U/l, 12.3±1.2 U/l, and 12.2±0.9 U/l respectively). We did not find a significant difference in these parameters between healthy controls and stable patients. There was a positive correlation (R=0.516) between tADA activity and C-reactive protein levels in patients with CD. Enhanced activity in tADA was also detected in neutrophils that were obtained from all patients with CD as compared with healthy controls (15.3±2.9 U/g, 14.1±2.3 U/g, and 9.4±2.9 U/g protein, respectively). This is mainly due to a significant increment (up to 51%) in ADA1 activity, the main isoenzyme in the neutrophils (84% out of the tADA). The cause of this increment remains to be elucidated.

CONCLUSION

The results obtained in this study demonstrated elevated levels of tADA and ADA2 in patients with active disease. As the patient improves and becomes clinically stable these levels decrease, approaching normal values. tADA and ADA2 can be used as markers of inflammation, and provide a supportive indicator of CD activity.

The blockade of adenosine deaminase ameliorates chronic experimental colitis through the recruitment of adenosine A2A and A3 receptors

Adenosine modulates immune/inflammatory reactions. This study investigates the expression of adenosine deaminase in the inflamed colon, the effects of adenosine deaminase inhibitors on established colitis, and the recruitment of adenosine receptors by endogenous adenosine after adenosine deaminase blockade. Adenosine deaminase expression was determined by Western blot. The effects of 4-amino-2-(2-hydroxy-1-decyl)pyrazole[3,4-d]pyrimidine (APP; a novel adenosine deaminase inhibitor), erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA; a reference adenosine deaminase inhibitor), dexamethasone, and selective adenosine receptor antagonists were tested in rats with 2,4-dinitrobenzenesulfonic acid-induced colitis. Systemic (food intake, body and spleen weight) and colonic [macroscopic/microscopic damage, tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and malondialdehyde (MDA)] inflammatory parameters were assessed. Test drugs were administered intraperitoneally for 6 days, starting at day 5 from colitis induction. Adenosine deaminase was detected in normal colon, and its expression was increased in inflamed tissues. Colitis was associated with decreased food intake and body weight, augmented spleen weight, and increased levels of colonic TNF-α, IL-6, and MDA. APP or EHNA, but not dexamethasone, improved food intake and body weight. APP, EHNA, and dexamethasone counteracted the increments of spleen weight, ameliorated macroscopic and microscopic indexes of inflammation, and reduced TNF-α, IL-6, and MDA levels. The beneficial effects of APP and EHNA on inflammatory parameters were prevented by the pharmacological blockade of A(2A) or A(3) receptors, but not A(1) or A(2B). The present results show that: 1) bowel inflammation is associated with an enhanced adenosine deaminase expression; and 2) the anti-inflammatory actions of adenosine deaminase inhibitors against chronic established colitis depend on the sparing of endogenous adenosine, leading to enhanced A(2A) and A(3) receptor activation.

The adenosine deaminase inhibitor erythro-9-[2-hydroxyl-3-nonyl]-adenine decreases intestinal permeability and protects against experimental sepsis: a prospective, randomised laboratory investigation

INTRODUCTION

The treatment of septic conditions in critically ill patients is still one of medicine's major challenges. Cyclic nucleotides, adenosine and its receptors play a pivotal role in the regulation of inflammatory responses and in limiting inflammatory tissue destruction. The aim of this study was to verify the hypothesis that adenosine deaminase-1 and cyclic guanosine monophosphate-stimulated phosphodiesterase inhibition by erythro-9-[2-hydroxyl-3-nonyl]-adenine could be beneficial in experimental endotoxicosis/sepsis.

METHOD

We used two established animal models for endotoxicosis and sepsis. Twenty-four male Wistar rats that had been given intravenous endotoxin (Escherichia coli lipopolysaccharide) were treated with either erythro-9-[2-hydroxyl-3-nonyl]-adenine infusion or 0.9% saline during a study length of 120 minutes. Sepsis in 84 female C57BL/6 mice was induced by caecal ligation and puncture. Animals were treated with repeated erythro-9-[2-hydroxyl-3-nonyl]-adenine injections after 0, 12 and 24 hours or 4, 12 and 24 hours for delayed treatment.

RESULTS

In endotoxaemic rats, intestinal production of hypoxanthine increased from 9.8 +/- 90.2 micromol/l at baseline to 411.4 +/- 124.6 micromol/l and uric acid formation increased from 1.5 +/- 2.3 mmol/l to 13.1 +/- 2.7 mmol/l after 120 minutes. In endotoxaemic animals treated with erythro-9-[2-hydroxyl-3-nonyl]-adenine, we found no elevation of adenosine metabolites. The lactulose/L-rhamnose ratio (14.3 versus 4.2 in control animals; p = 2.5 x 10(-7)) reflects a highly permeable small intestine and through the application of erythro-9-[2-hydroxyl-3-nonyl]-adenine, intestinal permeability could be re-established. The lipopolysaccharide animals had decreased L-rhamnose/3-O-methyl-D-glucose urine excretion ratios. Erythro-9-[2-hydroxyl-3-nonyl]-adenine reduced this effect. The mucosa damage score of the septic animals was higher compared with control and therapy animals (p < 0.05). Septic shock induction by caecal ligation and puncture resulted in a 160-hour survival rate of about 25%. In contrast, direct adenosine deaminase-1 inhibition resulted in a survival rate of about 75% (p = 0.0018). A protective effect was still present when erythro-9-[2-hydroxyl-3-nonyl]-adenine treatment was delayed for four hours (55%, p = 0.029).

CONCLUSIONS

We present further evidence of the beneficial effects achieved by administering erythro-9-[2-hydroxyl-3-nonyl]-adenine, an adenosine deaminase-1 and cyclic guanosine monophosphate-stimulated phosphodiesterase inhibitor, in an endotoxicosis and sepsis animal model. This suggests a potential therapeutic option in the treatment of septic conditions.

Regional haemodynamic responses to adenosine receptor activation vary across time following lipopolysaccharide treatment in conscious rats

BACKGROUND AND PURPOSE

Studies using adenosine receptor antagonists have shown that adenosine-mediated vasodilatations play an important role in the maintenance of regional perfusion during sepsis, but it is unclear whether vascular sensitivity to adenosine is affected. Here, we assessed regional haemodynamic responses to adenosine agonists and antagonists in normal and lipopolysaccharide (LPS)-treated rats to investigate a possible role for adenosine in the haemodynamic sequelae.

EXPERIMENTAL APPROACH

Male Sprague-Dawley rats were chronically instrumented with pulsed Doppler flow probes to measure regional haemodynamic responses to adenosine-receptor agonists (adenosine, 2-choloro-N6-cyclopentyladenosine (CCPA)) and antagonists (8-phenyltheophylline (8-PT), 8-cyclopentyl-1,3-dipropylxanthine (DPCPX)), at selected time points in control and LPS-treated rats.

KEY RESULTS

The responses to 8-PT were consistent with endogenous adenosine causing bradycardia, and renal and hindquarters vasodilatation in control rats, whereas in LPS-treated rats, there was evidence for endogenous adenosine causing renal (at 1.5 h) and hindquarters (at 6 h) vasoconstriction. In control animals, exogenous adenosine caused hypotension, tachycardia and widespread vasodilatation, whereas in LPS-treated rats, the adenosine-induced renal (at 1.5 h) and hindquarters (at 6 h) vasodilatations were abolished. As enhanced A1 receptor-mediated vasoconstriction could explain the results in LPS-treated rats, vascular responsiveness to a selective A1-receptor agonist (CCPA) or antagonist (DPCPX) was assessed. There was no evidence for enhanced vasoconstrictor responsiveness to CCPA in LPS-treated rats, but DPCPX caused renal vasodilatation, consistent with endogenous adenosine mediating renal vasoconstriction under these conditions.

CONCLUSIONS AND IMPLICATIONS

The results show changes in adenosine receptor-mediated cardiovascular effects in endotoxaemia that may have implications for the use of adenosine-based therapies in sepsis.

Therapeutic benefit of pentostatin in severe IL-10-/- colitis

BACKGROUND

Pentostatin, an adenosine deaminase (ADA) inhibitor, is a purine antimetabolite used for the treatment of leukemias. ADA inhibition blunts expansion of proliferating lymphocytes and increases adenosine release, a potent anti-inflammatory molecule. Human inflammatory bowel disease (IBD) is driven by expansion of effector T cells (T(eff)) that overwhelm reulatory T cells (T(reg)) and propagate innate immune reponses. Here we study the therapeutic benefits of ADA inhibition to impair T(eff) cell expansion and reduce inflammatory cytokine release in IL-10-deficient (IL-10-/-) mice.

METHODS

Colitis was induced in IL-10-/- mice by administering piroxicam for two weeks. Mice were treated with daily pentostatin or phosphate-buffered saline for 1 week and effects on tissue inflammation, lymphocyte numbers and cytokine production examined.

RESULTS

Pentostatin reduced inflammation by >50% and nearly normalized serum amyloid A levels. Lymphocyte expansions in the colon and mesenteric lymph node (MLN) (3.5-fold and >5-fold respectively) dropped by >50-90%. Pro-inflammatory factors in the colon and MLN (IL-1beta, IFN-gamma, IL-6, CXCL10, TNF) dropped whereas FoxP3 and TGF-beta were unchanged. Reductions in cytokine production from equivalent numbers of T cells from pentostatin-treated mice after in vitro (36h) or in vivo (3h) activation suggested anti-inflammatory effects of pentostatin independent of lymphodepletion contributed to its therapeutic benefit. Analysis of mucosal lymphocyte subsets suggested pentostatin reduced numbers of effector CD4+ CD69+ T cells, while sparing CD4+ CD62L+ T cells.

CONCLUSIONS

Pentostatin dosages that avoid severe lymphocyte depletion effectively treat colitis by impairing T(eff) cell expansion and reducing pro-inflammatory cytokine production while preserving regulatory T(reg) populations and function.

Role of pulmonary adenosine during hypoxia: extracellular generation, signaling and metabolism by surface adenosine deaminase/CD26

Numerous parallels exist between limited oxygen availability (hypoxia) and acute inflammation. The lungs in particular are prone to acute inflammation during hypoxia, resulting in pulmonary edema, vascular leakage and neutrophil infiltration. The innate response elicited by hypoxia is associated with increased extracellular adenosine effects. Although studies on acute pulmonary hypoxia show a protective role of extracellular adenosine by attenuating pulmonary edema and excessive inflammation, chronic elevation of pulmonary adenosine may be detrimental. Adenosine deaminase (ADA)-deficient mice, for example, develop signs of chronic pulmonary injury in association with highly elevated levels of adenosine. Thus, the authors hypothesized the existence of hypoxia-elicited clearance mechanisms to offset deleterious influences of chronically elevated adenosine. Such studies indicated a second response to hypoxia characterized by pulmonary induction of ADA and CD26. In fact, hypoxia-inducible ADA is enzymatically active and tethered on the outside of the membrane via CD26 to form a complex capable of degrading extracellular adenosine to inosine. This paper reviews metabolic and transcriptional changes of extracellular adenosine generation, signaling and degradation during acute and prolonged pulmonary hypoxia.

THE EXTRACELLULAR CARDIAC PURINE METABOLOME IN SEPSIS

The total cardiac purine metabolome includes all of the adenine and guanine nucleoside and nucleosides and related molecules involved throughout the intracellular and extracellular compartments and various cell types in the heart. In considering purines as molecules involved in autocrine and paracrine communication, effective interstitial concentrations of the nucleoside adenosine, or purine metabolites, are of greatest interest. These molecules arise from the complex interactions between cardiac-specific cell types, including fibroblasts and myocytes, and noncardiac cells, such as tissue-resident macrophages and other immune cells that have vascular access. In the interstitial environment, adenosine can regulate vascular resistance, contractile function, and immunochemical interactions. The breakdown of purines can produce reactive oxygen species that also influence autocrine and paracrine interactions. A central enzyme in this paradigm, adenosine deaminase, is a pivotal molecule in regulating the balance between pro-inflammatory and anti-inflammatory signaling cascades. A new role for adenosine deaminase as an allosteric regulator of relevant membrane proteins has yet to be explored in the heart.

Endothelial catabolism of extracellular adenosine during hypoxia: the role of surface adenosine deaminase and CD26

Extracellular levels of adenosine increase during hypoxia. While acute increases in adenosine are important to counterbalance excessive inflammation or vascular leakage, chronically elevated adenosine levels may be toxic. Thus, we reasoned that clearance mechanisms might exist to offset deleterious influences of chronically elevated adenosine. Guided by microarray results revealing induction of endothelial adenosine deaminase (ADA) mRNA in hypoxia, we used in vitro and in vivo models of adenosine signaling, confirming induction of ADA protein and activity. Further studies in human endothelia revealed that ADA-complexing protein CD26 is coordinately induced by hypoxia, effectively localizing ADA activity at the endothelial cell surface. Moreover, ADA surface binding was effectively blocked with glycoprotein 120 (gp120) treatment, a protein known to specifically compete for ADA-CD26 binding. Functional studies of murine hypoxia revealed inhibition of ADA with deoxycoformycin (dCF) enhances protective responses mediated by adenosine (vascular leak and neutrophil accumulation). Analysis of plasma ADA activity in pediatric patients with chronic hypoxia undergoing cardiac surgery demonstrated a 4.1 +/- 0.6-fold increase in plasma ADA activity compared with controls. Taken together, these results reveal induction of ADA as innate metabolic adaptation to chronically elevated adenosine levels during hypoxia. In contrast, during acute hypoxia associated with vascular leakage and excessive inflammation, ADA inhibition may serve as therapeutic strategy.

Role of endogenous adenosine as a predictive marker of vasoplegia during cardiopulmonary bypass and postoperative severe systemic inflammatory response

OBJECTIVE

Systemic inflammatory response (SIRS) and severe SIRS (SIRS with organ dysfunction) occurring after cardiopulmonary bypass (CPB) are common causes of morbidity and mortality among cardiac surgical patients. These syndromes are often preceded by a profound vasodilation, characterized by vasoplegia occurring during surgery. Many substances have been implicated in their pathophysiology. Adenosine is a strong endogenous vasodilating agent released by endothelial cells and myocytes under metabolic stress and may be involved in blood pressure failure during CPB induced by severe SIRS.

DESIGN

A prospective comparative observational study.

SETTING

The operating room and intensive care unit of a tertiary care university hospital.

PATIENTS

Adenosine plasma levels (mean+/-sd; APLs) were measured before (baseline), during, and immediately after surgery in 35 patients who underwent aortic valve replacement involving CPB. APLs were correlated to operative and postoperative clinical courses.

MEASUREMENTS AND MAIN RESULTS

APLs were significantly higher in seven patients with vasoplegia and postoperative severe SIRS (1.6 micromol.L [0.2-2.6] vs. 0.4 micromol.L [0.1-1.0]) at baseline and during surgery. The duration of mechanical ventilation and stay in the intensive care unit were significantly longer for patients with higher APLs. Mean arterial pressure was inversely correlated with mean arterial APLs (Pearson's correlation coefficient: R=-0.66; p<.001).

CONCLUSIONS

High APLs were found in patients with operative vasoplegia and postoperative severe SIRS occurring after cardiopulmonary bypass. This suggests that adenosine release is involved in vasoplegia that occurs during the systemic inflammatory response to cardiac surgery. Further studies are needed to clarify the association between cytokine production and adenosine release in severe SIRS following cardiac surgery.

Macrophages are a source of extracellular adenosine deaminase-2 during inflammatory responses

Serum activity of the adenosine deaminase (ADA) isozyme, ADA2, has been reported to be elevated during various disease states. Macrophages have been suggested as the cellular source of extracellular ADA activity because they are one of the only cell types in which intracellular ADA2 activity has been measured, but extracellular secretion has never been demonstrated. Rat primary peritoneal macrophages (PPMs) and peripheral blood monocytes (PBMs) were harvested and incubated for 18 h in RPMI supplemented with horse serum. PPM and PBM lysates were assayed for intracellular ADA activity (ammonia production). In vitro and in vivo extracellular ADA activities were measured in media and rat serum, respectively. Activity of ADA1 was confirmed by selective inhibition with erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA). ADA2 activity was inhibited by 2'-deoxycoformcin only, and was increased at a low pH (6.5). Activity of both ADA isozymes was found in PPMs and PBMs, and their media. In a separate group of rats, peritonitis was induced by ip insertion of 400 mg/kg caecal slurry. PPMs were harvested 24 h later and incubated for 18 h. In PPMs from rats with peritonitis both isozymes were elevated by a similar proportion. In contrast, media from these PPMs had a lower ADA1 and a higher ADA2 activity compared to PPMs from nonseptic rats. This resulted in a greater proportion of ADA2 in media. The isozyme proportions in serum from septic rats more closely resembled that of the PPM media. The response of PBM was small relative to that of PPM. These results suggest that macrophages are a significant source of extracellular ADA isozymes, the activity of which increases during an inflammatory response. Because extracellular isozymes profiles differ from cellular concentrations, the data also suggest differential release of each isozyme from PPMs.

Treatment with N-acetylcysteine plus deferoxamine protects rats against oxidative stress and improves survival in sepsis*

OBJECTIVE

Oxidative stress plays an important role in the development of multiple organ failure and septic shock. Here we have evaluated the effects of a combination of antioxidants (N-acetylcysteine plus deferoxamine) in a murine model of polymicrobial sepsis induced by cecal ligation and puncture (CLP).

DESIGN

Prospective, randomized, controlled experiment.

SETTING

Animal basic science laboratory.

SUBJECTS

Male Wistar rats, weighing 300-350 g.

INTERVENTIONS

Rats subjected to CLP were treated with either N-acetylcysteine (20 mg/kg, 3 hrs, 6 hrs, 12 hrs, 18 hrs, and 24 hrs after CLP, subcutaneously) plus deferoxamine (20 mg/kg, 3 hrs and 24 hrs after CLP, subcutaneously) or vehicle with or without "basic support" (saline at 50 mL/kg immediately and 12 hrs after CLP plus ceftriaxone at 30 mg/kg and clindamycin 25 mg/kg every 6 hrs).

MEASUREMENTS AND MAIN RESULTS

After 12 hrs, tissue myeloperoxidase (indicator of neutrophil infiltration), thiobarbituric acid reactive species (as a marker of oxidative stress), catalase and superoxide dismutase activities (antioxidant enzymes), and mitochondrial superoxide production (index of uncoupling of electron transfer chain) were measured in major organs involved in septic response. Rats treated with antioxidants had significantly lower myeloperoxidase activity and thiobarbituric acid reactive species formation in all organs studied. Mitochondrial superoxide production was significantly reduced by antioxidant treatment. Furthermore, antioxidants significantly improved the balance between catalase and superoxide dismutase activities. Survival in untreated septic rats was 10%. Survival increased to 40% with fluids and antibiotics. In rats treated only with N-acetylcysteine plus deferoxamine, survival was also significantly improved (47%) in a manner similar to basic support. Survival increased to 66% with basic support with N-acetylcysteine plus deferoxamine.

CONCLUSIONS

Our data provide the first experimental demonstration that N-acetylcysteine plus deferoxamine reduces the consequences of septic shock induced by CLP in the rat, by decreasing oxidative stress and limiting neutrophil infiltration and mitochondrial dysfunction, thereby improving survival.