Adenosine and inosine increase cutaneous vasopermeability by activating A(3) receptors on mast cells

Functional variability of the adenosine A3 receptor (ADORA3) gene polymorphism in aspirin-induced urticaria

BACKGROUND

To improve understanding of aspirin hypersensitivity, this study focused on adenosine as a noncyclooxygenase target molecule of aspirin. Adenosine may affect the release of histamine from cutaneous mast cells through a mechanism mediated by the adenosine A3 receptor.

OBJECTIVES

To investigate the genetic contribution of adenosine A3 receptor gene (ADORA3) polymorphisms in the pathogenesis of aspirin-induced urticaria (AIU) in a case-control association study in a Korean population.

METHODS

A case-control association study was performed in 385 patients with AIU and 213 normal controls from a Korean population. The functional variability of genetic polymorphisms in the ADORA3 gene was analysed in in vitro studies that included a luciferase reporter assay and an electrophoretic mobility shift assay (EMSA), and ex vivo studies that included real-time polymerase chain reaction for mRNA expression in peripheral blood mononuclear cells and a histamine release assay.

RESULTS

A significant association of ADORA3 promoter polymorphism at -1050G/T was found with the phenotype of AIU. Patients with AIU showed higher frequency of the haplotype, ht1 (T(-1050) C(-564) ), compared with normal healthy controls. Moreover, ht1 (TC) was found to be a high-transcript haplotype by the luciferase activity assay, and a -564C allele-specific DNA binding protein was found by EMSA. Increased basophil histamine release was noted in subjects who had the high-transcript haplotype, ht1 (TC).

CONCLUSION

These results suggest that the high-transcript haplotype, ht1 (TC), of the ADORA3 gene may contribute to the development of cutaneous hyper-reactivity to aspirin, leading to the clinical presentation of AIU.

The pharmacological role of phosphatases (acid and alkaline phosphomonoesterases) in snake venoms related to release of purines - a multitoxin

Snake venom components, acting in concert in the prey, cause their immobilization and initiate digestion. To achieve this, several hydrolytic enzymes of snake venom have evolved to interfere in various physiological processes, which are well defined. However, hydrolytic enzymes such as phosphatases (acid and alkaline phosphomonoesterases) are less studied and their pharmacological role in venoms is not clearly defined. Also, they show overlapping substrate specificities and have other common biochemical properties causing uncertainty about their identity in venoms. The near-ubiquitous distribution of these enzymes in venoms, suggests a significant role for these enzymes in envenomation. It appears that these enzymes may play a central role in liberating purines (mainly adenosine) - a multitoxin and through the action of purines help in prey immobilization. However, apart from this, these enzymes could also possess other pharmacological activities as venom enzymes have been evolved to interfere in diverse physiological processes. This has not been verified by pharmacological studies using purified enzymes. Further research is needed to biologically characterize these enzymes in snake venoms, such that their role in venom is clearly established.

Systems parasitology: effects of Fasciola hepatica on the neurochemical profile in the rat brain

We characterize the integrated response of a rat host to the liver fluke Fasciola hepatica using a combination of ¹H nuclear magnetic resonance spectroscopic profiles (liver, kidney, intestine, brain, spleen, plasma, urine, feces) and multiplex cytokine markers of systemic inflammation. Multivariate mathematical models were built to describe the main features of the infection at the systems level. In addition to the expected modulation of hepatic choline and energy metabolism, we found significant perturbations of the nucleotide balance in the brain, together with increased plasma IL-13, suggesting a shift toward modulation of immune reactions to minimize inflammatory damage, which may favor the co-existence of the parasite in the host. Subsequent analysis of brain extracts from other trematode infection models (i.e. Schistosoma mansoni, and Echinostoma caproni) did not elicit a change in neural nucleotide levels, indicating that the neural effects of F. hepatica infection are specific. We propose that the topographically extended response to invasion of the host as characterized by the modulated global metabolic phenotype is stratified across several bio-organizational levels and reflects the direct manipulation of host–nucleotide balance.

Interactions between immunity and metabolism - contributions from the metabolic profiling of parasite-rodent models

A combined interdisciplinary research strategy is even more crucial in immunology than in many other biological sciences in order to comprehend the closely linked interactions between cell proliferation, molecular signalling and gene rearrangements. Because of the multi-dimensional nature of the immune system, an abundance of different experimental approaches has developed, with a main focus on cellular and molecular mechanisms. The role of metabolism in immunity has been underexplored so far, and yet researchers have made important contributions in describing associations of immune processes and metabolic pathways, such as the central role of the l-arginine pathway in macrophage activation or the immune regulatory functions of the nucleotides. Furthermore, metabolite supplement studies, including nutritional administration and labelled substrates, have opened up new means of manipulating immune mechanisms. Metabolic profiling has introduced a reproducible platform for systemic assessment of changes at the small-molecule level within a host organism, and specific metabolic fingerprints of several parasitic infections have been characterized by 1H NMR spectroscopy. The application of multivariate statistical methods to spectral data has facilitated recovery of biomarkers, such as increased acute phase protein signals, and enabled direct correlation to the relative cytokine levels, which encourages further application of metabolic profiling to explore immune regulatory systems.

An insight into the sialome of blood-feeding Nematocera

Within the Diptera and outside the suborder Brachycera, the blood-feeding habit occurred at least twice, producing the present day sand flies, and the Culicomorpha, including the mosquitoes (Culicidae), black flies (Simulidae), biting midges (Ceratopogonidae) and frog feeding flies (Corethrellidae). Alternatives to this scenario are also discussed. Successful blood-feeding requires adaptations to antagonize the vertebrate's mechanisms of blood clotting, platelet aggregation, vasoconstriction, pain and itching, which are triggered by tissue destruction and immune reactions to insect products. Saliva of these insects provides a complex pharmacological armamentarium to block these vertebrate reactions. With the advent of transcriptomics, the sialomes (from the Greek word sialo = saliva) of at least two species of each of these families have been studied (except for the frog feeders), allowing an insight into the diverse pathways leading to today's salivary composition within the Culicomorpha, having the sand flies as an outgroup. This review catalogs 1288 salivary proteins in 10 generic classes comprising over 150 different protein families, most of which we have no functional knowledge. These proteins and many sequence comparisons are displayed in a hyperlinked spreadsheet that hopefully will stimulate and facilitate the task of functional characterization of these proteins, and their possible use as novel pharmacological agents and epidemiological markers of insect vector exposure.

Adenosine receptors and vascular inflammation

Epidemiological studies have shown a positive correlation between poor lung function and respiratory disorders like asthma and the development of adverse cardiovascular events. Increased adenosine (AD) levels are associated with lung inflammation which could lead to altered vascular responses and systemic inflammation. There is relatively little known about the cardiovascular effects of adenosine in a model of allergy. We have shown that A(1) adenosine receptors (AR) are involved in altered vascular responses and vascular inflammation in allergic mice. Allergic A(1)wild-type mice showed altered vascular reactivity, increased airway responsiveness and systemic inflammation. Our data suggests that A(1) AR is pro-inflammatory systemically in this model of asthma. There are also reports of the A(2B) receptor having anti-inflammatory effects in vascular stress; however its role in allergy with respect to vascular effects has not been fully explored. In this review, we have focused on the role of adenosine receptors in allergic asthma and the cardiovascular system and possible mechanism(s) of action.

An overview on nucleases (DNase, RNase, and phosphodiesterase) in snake venoms

In this review, we have compiled the data on pharmacological activities associated with endogenous purine release related enzymes-nucleases (DNases, RNases, and phosphodiesterases). The results of studies on toxic effects of these enzymes, emphasizing the future directions in this field, are summarized. One of the major problems facing toxicologists is the identification and characterization of specific venom nucleases since they share similar substrate specificities and biochemical properties. In this review, we have attempted to clarify some of the discrepancies about these enzymes. Further, we have tried to correlate the existence of nuclease enzymes in relation to endogenous release of purines, a multitoxin, during snake envenomation, and we also discuss the possible actions of purines. We hope that this review will stimulate renewed interest among toxicologists to biologically characterize these enzymes and elucidate their role in envenomation.

Therapeutic potential of adenosine receptor antagonists and agonists

The adenosine receptors (A(1), A(2A), A(2B) and A(3)) are important and ubiquitous mediators of cellular signalling, which play vital roles in protecting tissues and organs from damage. Launched drugs include the adenosine receptor antagonists theophylline and doxofylline (both used as bronchodilators in respiratory disorders such as asthma), while several compounds are presently in clinical trials for a range of indications, including heart failure, Parkinson's disease, rheumatoid arthritis, cancer, pain and chronic obstructive pulmonary disease. A host of companies and institutions are addressing the huge potential for the development of selective adenosine receptor agonists and antagonists, so that it appears we are on the verge of a new wave of compounds approaching the market for many unmet medical needs. This review presents an analysis of the patenting activity in the area for 2006 and an interpretation and reflection on the developments that we can expect in the future.

Adenosine A(3) receptors regulate heart rate, motor activity and body temperature

AIM

To examine the phenotype of mice that lack the adenosine A(3) receptor (A(3)R).

METHODS

We examined the heart rate, body temperature and locomotion continuously by telemetry over several days. In addition, the effect of the adenosine analogue R-N(6)-phenylisopropyl-adenosine (R-PIA) was examined. We also examined heat production and food intake.

RESULTS

We found that the marked diurnal variation in activity, heart rate and body temperature, with markedly higher values at night than during day time, was reduced in the A(3)R knock-out mice. Surprisingly, the reduction in heart rate, activity and body temperature seen after injection of R-PIA in wild type mice was virtually eliminated in the A(3)R knock-out mice. The marked reduction in activity was associated with a decreased heat production, as expected. However, the A(3)R knock-out mice, surprisingly, had a higher food intake but no difference in body weight compared to wild type mice.

CONCLUSIONS

The mice lacking adenosine A(3) receptors exhibit a surprisingly clear phenotype with changes in diurnal rhythm and temperature regulation. Whether these effects are due to a physiological role of A(3) receptors in these processes or whether they represent a role in development remains to be elucidated.

Adenosine A(3) receptor stimulation induces protection of skeletal muscle from eccentric exercise-mediated injury

Effective therapy to reduce skeletal muscle injury associated with severe or eccentric exercise is needed. The purpose of this study was to determine whether adenosine receptor stimulation can mediate protection from eccentric exercise-induced muscle injury. Downhill treadmill exercise (-15 degrees ) was used to induce eccentric exercise-mediated skeletal muscle injury. Experiments were conducted in both normal wild-type (WT) mice and also in beta-sarcoglycan knockout dystrophic mice, animals that show an exaggerated muscle damage with the stress of exercise. In the vehicle-treated WT animals, eccentric exercise increased serum creatine kinase (CK) greater than 3-fold to 358.9 +/- 62.7 U/l (SE). This increase was totally abolished by stimulation of the A(3) receptor. In the dystrophic beta-sarcoglycan-null mice, eccentric exercise caused CK levels to reach 55,124 +/- 5,558 U/l. A(3) receptor stimulation in these animals reduced the CK response by nearly 50%. In the dystrophic mice at rest, 10% of the fibers were found to be damaged, as indicated by Evans blue dye staining. While this percentage was doubled after exercise, A(3) receptor stimulation eliminated this increase. Neither the A(1) receptor agonist 2-chloro-N(6)-cyclopentyladenosine (0.05 mg/kg) nor the A(2A) receptor agonist 2-p-(2-carboxyethyl)phenethylamino-5'-N-ethylcarboxamidoadenosine (0.07 mg/kg) protected skeletal muscle from eccentric exercise injury in WT or dystrophic mice. The protective effect of adenosine A(3) receptor stimulation was absent in mice, in which genes for phospholipase C beta2/beta3 (PLCbeta2/beta3) and beta-sarcoglycan were deleted. The present study elucidates a new protective role of the A(3) receptor and PLCbeta2/beta3 and points to a potentially effective therapeutic strategy for eccentric exercise-induced skeletal muscle injury.

Anti-adipogenesis by 6-thioinosine is mediated by downregulation of PPAR gamma through JNK-dependent upregulation of iNOS

Adipocyte dysfunction is associated with the development of obesity. This study shows that 6-thioinosine inhibits adipocyte differentiation. The mRNA levels of PPAR gamma and C/EBPalpha, but not C/EBPbeta and delta, were reduced by 6-thioinosine. Moreover, the mRNA levels of PPAR gamma target genes (LPL, CD36, aP2, and LXRalpha) were down-regulated by 6-thioinosine. We also demonstrated that 6-thioinosine inhibits the transactivation activity and the mRNA level of PPAR gamma. Additionally, attempts to elucidate a possible mechanism underlying the 6-thioinosine-mediated effects revealed that 6-thioinosine induced iNOS gene expression without impacting eNOS expression, and that this was mediated through activation of AP-1, especially, JNK. In addition, 6-thioinosine was found to operate upstream of MEKK-1 in JNK activation signaling. Taken together, these findings suggest that the inhibition of adipocyte differentiation by 6-thioinosine occurs primarily through the reduced expression of PPAR gamma, which is mediated by upregulation of iNOS via the activation of JNK.

Insulin potentiates FcepsilonRI-mediated signaling in mouse bone marrow-derived mast cells

Factors contained in physiological microenvironments in tissues where mast cells differentiate and reside may influence mast cell responsiveness and modify antigen-dependent activation. A possible direct or indirect role of mast cell responses in diabetes mellitus prompted us to study the impact of insulin treatment on antigen triggered signaling pathways downstream of FcepsilonRI in bone marrow-derived mouse mast cells (BMMCs). We found that insulin alone stimulates tyrosine phosphorylation of tyrosine kinases Lyn, Syk, Fyn, the adapter protein Gab2 (Grb2-associated binding protein 2), Akt and activates ERK, JNK and p38 kinase. Effect of insulin on FcepsilonRI signaling pathways was marked by enhanced phosphorylation of Lyn, Fyn, Gab2 and Akt. Furthermore, BMMC stimulated with antigen in the presence of insulin responded with enhanced protein kinase theta (PKCtheta) activity and increased JNK phosphorylation when compared to BMMC triggered with antigen alone. Functional studies reveal enhanced degranulation and altered cytoskeletal rearrangement when BMMCs were treated simultaneously with insulin and antigen. Our results suggest that insulin tunes antigen-mediated responses of mast cells.

Extracellular inosine participates in tumor necrosis factor-alpha induced nitric oxide production in cultured Sertoli cells

Recent reports have described purinergic modulation of tumor necrosis factor-alpha (TNF-alpha) signaling in neutrophils and astrocytes. In Sertoli cells, both TNF-R1 and TNF-R2 TNF-alpha receptors are present and this cytokine modulates many functions of these cells related to the maintenance of spermatogenesis. Sertoli cells express distinct purinoreceptors and previous work has shown that these cells secrete extracellular nucleotides and their metabolites. In this work, we studied the possible role of extracellular purines in TNF-alpha signaling in cultured Sertoli cells. This cytokine increased inosine concentration from 30 min to 6 h, with no effect at 24 h. Both TNF-alpha and inosine increased nitrite accumulation and nitric oxide synthase activity. Erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA), an adenosine deaminase inhibitor, abolished the TNF-alpha induced inosine increase, nitrite accumulation and nitric oxide synthase activity. These results suggest that extracellular inosine acts as intermediary in TNF-alpha stimulated nitric oxide production in cultured Sertoli cells.

Stimulation of ANP secretion by 2-Cl-IB-MECA through A(3) receptor and CaMKII

Adenosine is a potent mediator of myocardial protection against hypertrophy via A(1) or A(3) receptors that may be partly related to atrial natriuretic peptide (ANP) release. However, little is known about the possible involvement of the A(3) receptor on ANP release. We studied the effects of the A(3) receptor on atrial functions and its modification in hypertrophied atria. A selective A(3) receptor agonist, 2-chloro-N(6)-(3-iodobenzyl) adenosine-5'-N-methyluronamide (2-CI-IB-MECA), was perfused into isolated, beating rat atria with and without receptor modifiers. 2-CI-IB-MECA dose-dependently increased the ANP secretion, which was blocked by the A(3) receptor antagonist, but the increased atrial contractility and decreased cAMP levels induced by 30muM 2-CI-IB-MECA were not affected. The 100muM 2-(1-hexylnyl)-N-methyladenosine (HEMADO) and N(6)-(3-iodobenzyl) adenosine-5'-N-methyluronamide (IB-MECA), A(3) receptor agonist, also stimulated the ANP secretion without positive inotropy. The potency for the stimulation of ANP secretion was 2-CI-IB-MECA>>IB-MECA=HEMADO. The inhibition of the ryanodine receptor or calcium/calmodulin-dependent kinase II (CaMKII) attenuated 2-CI-IB-MECA-induced ANP release, positive inotropy, and translocation of extracellular fluid. However, the inhibition of L-type Ca(2+) channels, sarcoplasmic reticulum Ca(2+)-reuptake, phospholipase C or inositol 1,4,5-triphosphate receptors did not affect these parameters. 2-CI-IB-MECA decreased cAMP level, which was blocked only with an inhibitor of CaMKII or adenylyl cyclase. These results suggest that 2-CI-IB-MECA increases the ANP secretion mainly via A(3) receptor activation and positive inotropy by intracellular Ca(2+) regulation via the ryanodine receptor and CaMKII.

Na-Tosyl-Phe chloromethyl ketone prevents granule movement and mast cell synergistic degranulation elicited by costimulation of antigen and adenosine

Adenosine has been shown to enhance mast cell degranulation when added together with an antigen. Such augmentation of mast cell activation is relevant to exacerbation of allergic asthma symptoms. Na-Tosyl-Phe chloromethyl ketone (TPCK) is a chymotrypsine-like chymase inhibitor, which has anti-inflammatory properties. In this study, we investigated the effects of TPCK on mast cell synergistic degranulation induced by antigen and adenosine. Here, we report that TPCK almost completely suppressed enhanced degranulation by inhibiting granule movement. Consistent with this, intraperitoneal administration of TPCK resulted in significant amelioration of passive cutaneous anaphylaxis in mice. Furthermore, we demonstrated that TPCK completely inhibited Thr308 phosphorylation of protein kinase B in mast cells stimulated with antigen and adenosine. These results provide a novel action of TPCK for the prevention of mast cell degranulation induced by antigen and adenosine.

Inosine and equilibrative nucleoside transporter 2 contribute to hypoxic preconditioning in the murine cardiomyocyte HL-1 cell line

The purine nucleoside adenosine is a physiologically important molecule in the heart. Brief exposure of cardiomyocytes to hypoxic challenge results in the production of extracellular adenosine, which then interacts with adenosine receptors to activate compensatory signaling pathways that lead to cellular resistance to subsequence hypoxic challenge. This phenomenon is known as preconditioning (PC), and, while adenosine is clearly involved, other components of the response are less well understood. Flux of nucleosides, such as adenosine and inosine, across cardiomyocyte membranes is dependent on equilibrative nucleoside transporters 1 and 2 (ENT1 and ENT2). We have previously shown in the murine cardiomyocyte HL-1 cell line that hypoxic challenge leads to an increase in intracellular adenosine, which exits the cell via ENT1 and preconditions via A1 and A3 adenosine receptor-dependent mechanisms. However, the role and contribution of inosine and ENT2 are unclear. In this study, we confirmed that ENT1 and ENT2 are both capable of transporting inosine. Moreover, we found that hypoxic challenge leads to a significant increase in levels of intracellular inosine, which exits the cell via both ENT1 and ENT2. Exogenously added inosine (5 μM) preconditions cardiomyocytes in an A1 adenosine receptor-dependent manner since preconditioning can be blocked by the A1 adenosine receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (1 μM) but not the A3 adenosine receptor antagonist MRS-1220 (200 nM). These data suggest that cardiomyocyte responses to hypoxic PC are more complex than previously thought, involving both adenosine and inosine and differing, but overlapping, contributions of the two ENT isoforms.

Adenosine induces airway hyperresponsiveness through activation of A3 receptors on mast cells

BACKGROUND

The mechanisms responsible for the development of airway hyperresponsiveness in asthma are poorly understood. Adenosine levels are high in the lungs of patients with asthma, but a role for adenosine in the development of this cardinal feature of asthma has not been previously reported.

OBJECTIVE

To determine the capacity of adenosine to induce airway hyperresponsiveness, and to investigate the mechanisms behind these effects of adenosine on airway physiology.

METHODS

Wild-type C57BL/6 mice were exposed to aerosolized adenosine analog adenosine-5' N-ethylcarboxamide (NECA), and subsequent hyperresponsiveness to methacholine was investigated by measuring airway mechanics after anesthesia and tracheostomy. Similar experiments were conducted with A(1)-deficient, A(3)-deficient, and mast cell-deficient mice, as well as with mast cell-deficient mice engrafted with wild-type (wt) or A(3)(-/-) mast cells. The effect of NECA on methacholine-induced tension development in ex vivo tracheal rings was also examined.

RESULTS

Exposure of wt mice to NECA resulted in the robust induction of airway hyperresponsiveness. NECA failed to induce hyperresponsiveness to methacholine in tracheal ring preps ex vivo, and NECA-induced airway hyperresponsiveness in vivo was not affected by the genetic inactivation of the A(1) adenosine receptor. In contrast, NECA-induced airway hyperresponsiveness was abolished in A(3) adenosine receptor-deficient mice and in mice deficient in mast cells. Reconstitution of mast cell-deficient mice with wt mast cells restored hyperresponsiveness, whereas reconstitution with A(3) receptor-deficient mast cells did not.

CONCLUSION

Adenosine induces airway hyperresponsiveness indirectly by activating A(3) receptors on mast cells.

Isoform-specific functions of phosphoinositide 3-kinases: p110 delta but not p110 gamma promotes optimal allergic responses in vivo

The leukocyte-enriched p110gamma and p110delta isoforms of PI3K have been shown to control in vitro degranulation of mast cells induced by cross-linking of the high affinity receptor of IgE (FcepsilonRI). However, the relative contribution of these PI3K isoforms in IgE-dependent allergic responses in vivo is controversial. A side-by-side comparative analysis of the role of p110gamma and p110delta in mast cell function, using genetic approaches and newly developed isoform-selective pharmacologic inhibitors, confirms that both PI3K isoforms play an important role in FcepsilonRI-activated mast cell degranulation in vitro. In vivo, however, only p110delta was found to be required for optimal IgE/Ag-dependent hypersensitivity responses in mice. These observations identify p110delta as a key therapeutic target among PI3K isoforms for allergy- and mast cell-related diseases.

Protective roles of adenosine A1, A2A, and A3 receptors in skeletal muscle ischemia and reperfusion injury

Although adenosine exerts cardio-and vasculoprotective effects, the roles and signaling mechanisms of different adenosine receptors in mediating skeletal muscle protection are not well understood. We used a mouse hindlimb ischemia-reperfusion model to delineate the function of three adenosine receptor subtypes. Adenosine A(3) receptor-selective agonist 2-chloro-N(6)-(3-iodobenzyl)adenosine-5'-N-methyluronamide (Cl-IBMECA; 0.07 mg/kg ip) reduced skeletal muscle injury with a significant decrease in both Evans blue dye staining (5.4 +/- 2.6%, n = 8 mice vs. vehicle-treated 28 +/- 6%, n = 7 mice, P < 0.05) and serum creatine kinase level (1,840 +/- 910 U/l, n = 13 vs. vehicle-treated 12,600 +/- 3,300 U/l, n = 14, P < 0.05), an effect that was selectively blocked by an A(3) receptor antagonist 3-ethyl-5-benzyl-2-methyl-6-phenyl-4-phenylethynyl-1,4-(+/-)-dihydropyridine-3,5-dicarboxylate (MRS-1191; 0.05 mg/kg). The adenosine A(1) receptor agonist 2-chloro-N(6)-cyclopentyladenosine (CCPA; 0.05 mg/kg) also exerted a cytoprotective effect, which was selectively blocked by the A(1) antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX; 0.2 mg/kg). The adenosine A(2A) receptor agonist 2-p-(2-carboxyethyl)phenethylamino-5'-N-ethylcarboxamidoadenosine (CGS-21680; 0.07 mg/kg)-induced decrease in skeletal muscle injury was selectively blocked by the A(2A) antagonist 2-(2-furanyl)-7-[3-(4-methoxyphenyl)propyl]-7H-pyrazolo[4,3-e] [1,2,4]triazolo[1,5-C]pyrimidin-5-amine (SCH-442416; 0.017 mg/kg). The protection induced by the A(3) receptor was abrogated in phospholipase C-beta2/beta3 null mice, but the protection mediated by the A(1) or A(2A) receptor remained unaffected in these animals. The adenosine A(3) receptor is a novel cytoprotective receptor that signals selectively via phospholipase C-beta and represents a new target for ameliorating skeletal muscle injury.

Identification and characterization of a salivary adenosine deaminase from the sand fly Phlebotomus duboscqi, the vector of Leishmania major in sub-Saharan Africa

Two transcripts coding for an adenosine deaminase (ADA) were identified by sequencing a Phlebotomus duboscqi salivary gland cDNA library. Adenosine deaminase was previously reported in the saliva of the sand fly Lutzomyia longipalpis but it was not present in the saliva of the sand flies Phlebotomus papatasi, P. argentipes, P. perniciosus and P. ariasi, suggesting that this enzyme is only present in the saliva of sand flies from the genus Lutzomyia. In the present work, we tested the hypothesis that the salivary gland transcript coding for ADA in Phlebotomus duboscqi, a sister species of Phlebotomus papatasi, produces an active salivary ADA. Salivary gland homogenates of P. duboscqi converted adenosine to inosine, suggesting the presence of ADA activity in the saliva of this species of sand fly; furthermore, this enzymatic activity was significantly reduced when using either salivary glands of recently blood-fed sand flies or punctured salivary glands, suggesting that this enzyme is secreted in the saliva of this insect. This enzymatic activity was absent from the saliva of P. papatasi. In contrast to other Phlebotomus sand flies, we did not find AMP or adenosine in P. duboscqi salivary glands as measured by HPLC-photodiode array. To confirm that the transcript coding for ADA was responsible for the activity observed in the saliva of this sand fly, we cloned this transcript into a prokaryotic expression vector and produced a soluble and active recombinant protein of approximately 60 kDa that was able to convert adenosine to inosine. Extracts of bacteria transformed with control plasmids did not show this activity. These results suggest that P. duboscqi transcripts coding for ADA are responsible for the activity detected in the salivary glands of this sand fly and that P. duboscqi acquired this activity independently from other Phlebotomus sand flies. This is another example of a gene recruitment event in salivary genes of blood-feeding arthropods that may be relevant for blood feeding and, because of the role of ADA in immunity, it may also play a role in parasite transmission.

Involvement of A1 adenosine receptors and neural pathways in adenosine-induced bronchoconstriction in mice

High levels of adenosine can be measured from the lungs of asthmatics, and it is well recognized that aerosolized 5'AMP, the precursor of adenosine, elicits robust bronchoconstriction in patients with this disease. Characterization of mice with elevated adenosine levels secondary to the loss of adenosine deaminase (ADA) expression, the primary metabolic enzyme for adenosine, further support a role for this ubiquitous mediator in the pathogenesis of asthma. To begin to identify pathways by which adenosine can alter airway tone, we examined adenosine-induced bronchoconstriction in four mouse lines, each lacking one of the receptors for this nucleoside. We show, using direct measures of airway mechanics, that adenosine can increase airway resistance and that this increase in resistance is mediated by binding the A(1) receptor. Further examination of this response using pharmacologically, surgically, and genetically manipulated mice supports a model in which adenosine-induced bronchoconstriction occurs indirectly through the activation of sensory neurons.

An insight into the sialome of the oriental rat flea, Xenopsylla cheopis (Rots)

BACKGROUND

The salivary glands of hematophagous animals contain a complex cocktail that interferes with the host hemostasis and inflammation pathways, thus increasing feeding success. Fleas represent a relatively recent group of insects that evolved hematophagy independently of other insect orders.

RESULTS

Analysis of the salivary transcriptome of the flea Xenopsylla cheopis, the vector of human plague, indicates that gene duplication events have led to a large expansion of a family of acidic phosphatases that are probably inactive, and to the expansion of the FS family of peptides that are unique to fleas. Several other unique polypeptides were also uncovered. Additionally, an apyrase-coding transcript of the CD39 family appears as the candidate for the salivary nucleotide hydrolysing activity in X.cheopis, the first time this family of proteins is found in any arthropod salivary transcriptome.

CONCLUSION

Analysis of the salivary transcriptome of the flea X. cheopis revealed the unique pathways taken in the evolution of the salivary cocktail of fleas. Gene duplication events appear as an important driving force in the creation of salivary cocktails of blood feeding arthropods, as was observed with ticks and mosquitoes. Only five other flea salivary sequences exist at this time at NCBI, all from the cat flea C. felis. This work accordingly represents the only relatively extensive sialome description of any flea species. Sialotranscriptomes of additional flea genera will reveal the extent that these novel polypeptide families are common throughout the Siphonaptera.

Enhanced mast cell activation in mice deficient in the A2b adenosine receptor

Antigen-mediated cross-linking of IgE bound to mast cells via the high affinity receptor for IgE triggers a signaling cascade that results in the release of intracellular calcium stores, followed by an influx of extracellular calcium. The collective increase in intracellular calcium is critical to the release of the granular contents of the mast cell, which include the mediators of acute anaphylaxis. We show that the sensitivity of the mast cell to antigen-mediated degranulation through this pathway can be dramatically influenced by the A2b adenosine receptor. Loss of this G_s-coupled receptor on mouse bone marrow–derived mast cells results in decreased basal levels of cyclic AMP and an excessive influx of extracellular calcium through store-operated calcium channels following antigen activation. Mice lacking the A2b receptor display increased sensitivity to IgE-mediated anaphylaxis. Collectively, these findings show that the A2b adenosine receptor functions as a critical regulator of signaling pathways within the mast cell, which act in concert to limit the magnitude of mast cell responsiveness when antigen is encountered.

The A2B adenosine receptor protects against inflammation and excessive vascular adhesion

Adenosine has been described as playing a role in the control of inflammation, but it has not been certain which of its receptors mediate this effect. Here, we generated an A2B adenosine receptor-knockout/reporter gene-knock-in (A2BAR-knockout/reporter gene-knock-in) mouse model and showed receptor gene expression in the vasculature and macrophages, the ablation of which causes low-grade inflammation compared with age-, sex-, and strain-matched control mice. Augmentation of proinflammatory cytokines, such as TNF-alpha, and a consequent downregulation of IkappaB-alpha are the underlying mechanisms for an observed upregulation of adhesion molecules in the vasculature of these A2BAR-null mice. Intriguingly, leukocyte adhesion to the vasculature is significantly increased in the A2BAR-knockout mice. Exposure to an endotoxin results in augmented proinflammatory cytokine levels in A2BAR-null mice compared with control mice. Bone marrow transplantations indicated that bone marrow (and to a lesser extent vascular) A2BARs regulate these processes. Hence, we identify the A2BAR as a new critical regulator of inflammation and vascular adhesion primarily via signals from hematopoietic cells to the vasculature, focusing attention on the receptor as a therapeutic target.

Adenosine metabolism and murine strain-specific IL-4-induced inflammation, emphysema, and fibrosis

To define the factors that control the tissue effects of IL-4, we compared the effects of Tg IL-4 in Balb/c and C57BL/6 mice. In the former, IL-4 caused modest eosinophilic inflammation and mild airway fibrosis and did not shorten survival. In C57BL/6 mice, IL-4 caused profound eosinophilic inflammation, airway fibrosis, emphysematous alveolar destruction, and premature death. These differences could not be accounted for by changes in Th2 or Th1 cytokines, receptor components, STAT6 activation, MMPs, or cathepsins. In contrast, in C57BL/6 mice, alveolar remodeling was associated with decreased levels of tissue inhibitors of metalloproteinase 2, -3, and -4 and alpha1-antitrypsin, and fibrosis was associated with increased levels of total and bioactive TGF-beta1. Impressive differences in adenosine metabolism were also appreciated, with increased tissue adenosine levels and A(1), A(2B), and A(3) adenosine receptor expression and decreased adenosine deaminase (ADA) activity in C57BL/6 animals. Treatment with ADA also reduced the inflammation, fibrosis, and emphysematous destruction and improved the survival of C57BL/6 Tg animals. These studies demonstrate that genetic influences control IL-4 effector pathways in the murine lung. They also demonstrate that IL-4 has different effects on adenosine metabolism in Balb/c and C57BL/6 mice and that these differences contribute to the different responses that IL-4 induces in these inbred animals.

A3 adenosine receptor activation decreases mortality and renal and hepatic injury in murine septic peritonitis

The role of A3 adenosine receptors (ARs) in sepsis and inflammation is controversial. In this study, we determined the effects of A3AR modulation on mortality and hepatic and renal dysfunction in a murine model of sepsis. To induce sepsis, congenic A3AR knockout mice (A3AR KO) and wild-type control (A3AR WT) mice were subjected to cecal ligation and double puncture (CLP). A3AR KO mice had significantly worse 7-day survival compared with A3AR WT mice. A3AR KO mice also demonstrated significantly higher elevations in plasma creatinine, alanine aminotransferase, aspartate aminotransferase, keratinocyte-derived chemokine, and TNF-alpha 24 h after induction of sepsis compared with A3AR WT mice. Renal cortices from septic A3AR KO mice exhibited increased mRNA encoding proinflammatory cytokines and enhanced nuclear translocation of NF-kB compared with samples from A3AR WT mice. A3AR WT mice treated with N6-(3-iodobenzyl)ADO-5'N-methyluronamide (IB-MECA; a selective A3AR agonist) or 3-ethyl-5-benzyl-2-methyl-4-phenylethynyl-6-phenyl-1,4-(+/-)-dihydropyridine-3,5-dicarboxylate (MRS-1191; a selective A3AR antagonist) had improved or worsened 7-day survival after induction of sepsis, respectively. Moreover, A3AR WT mice treated with IB-MECA or MRS-1191 showed acutely improved or worsened, respectively, renal and hepatic function following CLP. IB-MECA significantly reduced mortality in mice lacking the A1AR or A2aAR but not the A3AR, demonstrating specificity of IB-MECA in activating A3ARs and mediating protection against sepsis-induced mortality. We conclude that endogenous or exogenous A3AR activation confers significant protection from murine septic peritonitis primarily by attenuating the hyperacute inflammatory response in sepsis.

Inosine released after hypoxia activates hepatic glucose liberation through A3 adenosine receptors

Inosine, an endogenous nucleoside, has recently been shown to exert potent effects on the immune, neural, and cardiovascular systems. This work addresses modulation of intermediary metabolism by inosine through adenosine receptors (ARs) in isolated rat hepatocytes. We conducted an in silico search in the GenBank and complete genomic sequence databases for additional adenosine/inosine receptors and for a feasible physiological role of inosine in homeostasis. Inosine stimulated glycogenolysis (approximately 40%, EC50 4.2 x 10(-9) M), gluconeogenesis (approximately 40%, EC50 7.8 x 10(-9) M), and ureagenesis (approximately 130%, EC50 7.0 x 10(-8) M) compared with basal values; these effects were blunted by the selective A3 AR antagonist 9-chloro-2-(2-furanyl)-5-[(phenylacetyl)amino][1,2,4]-triazolo[1,5-c]quinazoline (MRS 1220) but not by selective A1, A2A, and A2B AR antagonists. In addition, MRS 1220 antagonized inosine-induced transient increase (40%) in cytosolic Ca2+ and enhanced (90%) glycogen phosphorylase activity. Inosine-induced Ca2+ mobilization was desensitized by adenosine; in a reciprocal manner, inosine desensitized adenosine action. Inosine decreased the cAMP pool in hepatocytes when A1, A2A, and A2B AR were blocked by a mixture of selective antagonists. Inosine-promoted metabolic changes were unrelated to cAMP decrease but were Ca2+ dependent because they were absent in hepatocytes incubated in EGTA- or BAPTA-AM-supplemented Ca2+-free medium. After in silico analysis, no additional cognate adenosine/inosine receptors were found in human, mouse, and rat. In both perfused rat liver and isolated hepatocytes, hypoxia/reoxygenation produced an increase in inosine, adenosine, and glucose release; these actions were quantitatively greater in perfused rat liver than in isolated cells. Moreover, all of these effects were impaired by the antagonist MRS 1220. On the basis of results obtained, known higher extracellular inosine levels under ischemic conditions, and inosine's higher sensitivity for stimulating hepatic gluconeogenesis, it is suggested that, after tissular ischemia, inosine contributes to the maintenance of homeostasis by releasing glucose from the liver through stimulation of A3 ARs.

Adenosine receptors as therapeutic targets

Adenosine receptors are major targets of caffeine, the most commonly consumed drug in the world. There is growing evidence that they could also be promising therapeutic targets in a wide range of conditions, including cerebral and cardiac ischaemic diseases, sleep disorders, immune and inflammatory disorders and cancer. After more than three decades of medicinal chemistry research, a considerable number of selective agonists and antagonists of adenosine receptors have been discovered, and some have been clinically evaluated, although none has yet received regulatory approval. However, recent advances in the understanding of the roles of the various adenosine receptor subtypes, and in the development of selective and potent ligands, as discussed in this review, have brought the goal of therapeutic application of adenosine receptor modulators considerably closer.

Gestational diabetes and the adenosine/L-arginine/nitric oxide (ALANO) pathway in human umbilical vein endothelium

Altered endothelial cell function is a key factor associated with vascular disorders and is critical in the fetal growth and development. Pregnancies affected by diseases such as gestational diabetes are associated with human umbilical vein endothelial dysfunction, a finding that has been associated with a high incidence of vascular complications during the adult life. Limited information is available addressing cellular mechanisms associated with altered human umbilical vein endothelial function in gestational diabetes. One of the key signalling pathways associated with altered vascular physiology is the synthesis of the vasodilator nitric oxide (NO) from the cationic amino acid L-arginine by the endothelium (i.e. the endothelial L-arginine/NO pathway). The activity of this signalling pathway is modulated by D-glucose, adenosine, insulin, and ATP, among other molecules, and is upregulated (transcriptional, post-transcriptional and post-translational levels) in gestational diabetes. This review focuses on the cellular and molecular mechanisms involved with elevated adenosine levels in fetal umbilical vein blood and the endothelial L-arginine/NO pathway activity in gestational diabetes. We suggest that a lower capacity of adenosine transport by the fetal endothelium in gestational diabetes leads to extracellular accumulation of this nucleoside and its higher bio-availability activates endothelial P1 type purinoceptors. A functional association between A2a purinoceptor subtype signalling and the activity of the l-arginine transport mediated by human cationic amino acid transporters and endothelial NO synthase activity (i.e. 'ALANO pathway') is proposed, revealing in part the mechanisms that account for human umbilical vein endothelial cell dysfunction programmed through the development of the fetus in gestational diabetes.

Effects of follicle-stimulating hormone and vitamin A upon purinergic secretion by rat Sertoli cells

Follicle-stimulating hormone (FSH) and vitamin A (retinol) are two of the main regulators of the male reproductive system. Recently, it has been described that extracellular purines can affect some important reproductive-related functions in Sertoli cells and germinative cells, by activating specific purinergic receptors. In this work, we report that both FSH and retinol are able to induce changes in the levels of extracellular purines of cultured rat Sertoli cells. FSH induced an increase in adenosine, mainly caused by enhanced ecto-ATPase activity, while retinol increased xanthine and hypoxanthine levels, and decreased uric acid concentration by an unknown mechanism. These data indicate that purinergic signaling may be involved in the control and/or regulation of some of the reproductive-related actions of these hormones.

Mechanisms of adenosine-induced cytotoxicity and their clinical and physiological implications

Extracellular ATP (ATPo) and adenosine are cytotoxic to several cancer cell lines, suggesting their potential use for anticancer therapy. Adenosine causes cytotoxicity, either when added exogenously or when generated from ATPo hydrolysis, via mechanisms which are not mutually exclusive and which involve, adenosine receptor activation, pyrimidine starvation and/or increases in intracellular S-adenosylhomocysteine: S-adenosylmethionine ratio. Given that adenosine also appears to protect against cytotoxicity via mechanisms including immunity against damage by oxygen free radicals, an understanding of the contribution of adenosine to ATPo-induced cytotoxicity is thus crucial, when considering any potential therapeutic use for these compounds. However, such an understanding has been largely hindered by the fact that many studies have not focused enough on the possibility that both ATPo and adenosine may mediate cytotoxicity in the same system. Such studies can benefit from use a range of ATPo concentrations when assessing the contribution of adenosine to ATPo-induced cytotoxicity. Whilst future molecular and pharmacological studies are needed to establish the nature of the cytotoxic adenosine receptor, it is possible that more than just one adenosine receptor type is involved and that the cytotoxic receptor(s) type is more likely to have a low affinity for adenosine. Activation of the adenosine receptor(s) would thus lead to cytotoxicity only at relatively high adenosine concentrations, while lower adenosine concentrations mediate non-cytotoxic physiological effects.

Partially adenosine deaminase-deficient mice develop pulmonary fibrosis in association with adenosine elevations

Adenosine, a signaling nucleoside, exhibits tissue-protective and tissue-destructive effects. Adenosine levels in tissues are controlled in part by the enzyme adenosine deaminase (ADA). ADA-deficient mice accumulate adenosine levels in multiple tissues, including the lung, where adenosine contributes to the development of pulmonary inflammation and chronic airway remodeling. The present study describes the development of pulmonary fibrosis in mice that have been genetically engineered to possess partial ADA enzyme activity and, thus, accumulate adenosine over a prolonged period of time. These partially ADA-deficient mice live for up to 5 mo and die from apparent respiratory distress. Detailed investigations of the lung histopathology of partially ADA-deficient mice revealed progressive pulmonary fibrosis marked by an increase in the number of pulmonary myofibroblasts and an increase in collagen deposition. In addition, in regions of the distal airways that did not exhibit fibrosis, an increase in the number of large foamy macrophages and a substantial enlargement of the alveolar air spaces suggest emphysemic changes. Furthermore, important proinflammatory and profibrotic signaling pathways, including IL-13 and transforming growth factor-beta1, were activated. Increases in tissue fibrosis were also seen in the liver and kidneys of these mice. These changes occurred in association with pronounced elevations of lung adenosine concentrations and alterations in lung adenosine receptor levels, supporting the hypothesis that elevation of endogenous adenosine is a proinflammatory and profibrotic signal in this model.

Adenosine-dependent pulmonary fibrosis in adenosine deaminase-deficient mice

Pulmonary fibrosis is a common feature of numerous lung disorders, including interstitial lung diseases, asthma, and chronic obstructive pulmonary disease. Despite the prevalence of pulmonary fibrosis, the molecular mechanisms governing inflammatory and fibroproliferative aspects of the disorder are not clear. Adenosine is a purine-signaling nucleoside that is generated in excess during cellular stress and damage. This signaling molecule has been implicated in the regulation of features of chronic lung disease; however, the impact of adenosine on pulmonary fibrosis is not well understood. The goal of this study was to explore the impact of endogenous adenosine elevations on pulmonary fibrosis. To accomplish this, adenosine deaminase (ADA)-deficient mice were treated with various levels of ADA enzyme replacement therapy to regulate endogenous adenosine levels in the lung. Maintaining ADA-deficient mice on low dosages of ADA enzyme therapy led to chronic elevations in lung adenosine levels that were associated with pulmonary inflammation, expression of profibrotic molecules, collagen deposition, and extreme alteration in airway structure. These features could be blocked by preventing elevations in lung adenosine. Furthermore, lowering lung adenosine levels after the establishment of pulmonary fibrosis resulted in a resolution of fibrosis. These findings demonstrate that chronic adenosine elevations are associated with pulmonary fibrosis in ADA-deficient mice and suggest that the adenosine functions as a profibrotic signal in the lung.

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.

Role of adenosine in airway inflammation in an allergic mouse model of asthma

In the present study, we examined dynamic changes in cellular profile of bronchoalveolar lavage (BAL) fluid after adenosine challenge in ragweed sensitized and challenged mice. Mice systemically sensitized and airway challenged with ragweed showed marked airway inflammation manifesting increased eosinophils, lymphocytes, neutrophils and activated macrophages in BAL. Adenosine challenge further enhanced influx of inflammatory cells into BAL, notably neutrophils from 1 to 72 h and eosinophils from 1 to 48 h time-points (p<0.05), which sharply rose at 6-h time-point following adenosine challenge. Greater infiltration of lymphocytes into BAL was observed at 1 and 72 h and macrophages from 6 to 72 h (p<0.05) after adenosine challenge. Accordingly, markers of eosinophils, neutrophils and mast cells were analyzed at 6-h time-point after adenosine challenge. Adenosine challenge significantly increased the levels of eosinophil peroxidase, neutrophil myeloperoxidase and beta-hexosaminidase in BAL. There were more significant effects of adenosine challenge on the degranulation of mast cells in the lung than that in blood. The chemoattractant, eotaxin, was detected in BAL, which increased after adenosine challenge. Theophylline, a non-specific adenosine receptor antagonist, prevented adenosine-enhanced infiltration of inflammatory cells and their respective markers. Our findings suggest that adenosine plays an important role in airway inflammation in an allergic mouse model.

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.

Adenosine in the venoms from viperinae snakes of the genus Bitis: Identification and quantitation using LC/MS and CE/MS

Snake venoms are rich sources of toxic proteins and small molecules. This study was directed at molecules of molecular mass below 1 kDa. Thirty different venoms, of either neurotoxic or haemorrhagic type, were fractionated using size-exclusion chromatography. Only venoms of the Puff adder (Bitis arietans), Gaboon viper (Bitis gabonica), and Rhinoceros viper (Bitis nasicornis) exhibited large absorbance peaks at lambda(280 nm) in the total volume range of the chromatographic column indicating the presence of abundant low molecular mass material. Analysis of fractions containing this material using both HPLC and capillary electrophoresis interfaced with electrospray ion-trap mass spectrometry unequivocally established that the bioactive nucleoside, adenosine, was the major component. The concentrations of adenosine found (Puff adder--97.7 x 10(-6) mol L(-1); Gaboon viper--28.0 x 10(-6) mol L(-1); and Rhinoceros viper-56.8 x 10(-6) mol L(-1)) were above those required to activate all known sub-types of adenosine receptors. Adenosine may thus act at the site of envenomation causing local vasodilatation and may play a role in the subsequent systemic hypotension observed.

Mast cells as "tunable" effector and immunoregulatory cells: recent advances

This review focuses on recent progress in our understanding of how mast cells can contribute to the initiation, development, expression, and regulation of acquired immune responses, both those associated with IgE and those that are apparently expressed independently of this class of Ig. We emphasize findings derived from in vivo studies in mice, particularly those employing genetic approaches to influence mast cell numbers and/or to alter or delete components of pathways that can regulate mast cell development, signaling, or function. We advance the hypothesis that mast cells not only can function as proinflammatory effector cells and drivers of tissue remodeling in established acquired immune responses, but also may contribute to the initiation and regulation of such responses. That is, we propose that mast cells can also function as immunoregulatory cells. Finally, we show that the notion that mast cells have primarily two functional configurations, off (or resting) or on (or activated for extensive mediator release), markedly oversimplifies reality. Instead, we propose that mast cells are "tunable," by both genetic and environmental factors, such that, depending on the circumstances, the cell can be positioned phenotypically to express a wide spectrum of variation in the types, kinetics, and/or magnitude of its secretory functions.

Extracellular inosine modulates ERK 1/2 and p38 phosphorylation in cultured Sertoli cells: possible participation in TNF-alpha modulation of ERK 1/2

Extracellular ATP and adenosine modulation of MAPKs is well described in different cells types, but few studies have addressed the effects of extracellular inosine on these kinases. Previous results showed that hydrogen peroxide and TNF-alpha increase extracellular inosine concentration in cultured Sertoli cells and this nucleoside protects Sertoli cells against hydrogen peroxide induced damage and participates in TNF-alpha induced nitric oxide production. In view of the fact that MAPKs are key mediators of the cellular response to a large variety of stimuli, we investigated the effect of extracellular inosine on the phosphorylation of ERK 1/2 and p38 MAPKs in cultured Sertoli cells. The involvement of this nucleoside in the activation of ERK 1/2 by TNF-alpha was also investigated. Inosine and the selective A1 adenosine receptor agonist R-PIA increases the phosphorylation of ERK 1/2 and p38, and this was blocked by the selective A1 adenosine receptors antagonists, CPT and DPCPX. These antagonists also inhibited TNF-alpha increase in the phosphorylation of ERK 1/2. TNF-alpha also rapidly augmented extracellular inosine concentration in cultured Sertoli cells. These results show that extracellular inosine modulates ERK 1/2 and p38 in cultured Sertoli cells, possible trough A1 adenosine receptor activation. This nucleoside also participates in TNF-alpha modulation of ERK 1/2.

A3 adenosine receptor-mediated protection of the ischemic heart

The A3 adenosine receptor (A3AR) is attributed with multiple beneficial actions in ischemic-reperfused myocardium, including modulation of oncotic and apoptotic cell death and enhancement of contractile function. Additionally, the A3AR may attenuate vascular dysfunction and improve long-term outcome from myocardial insult (modulating hypertrophy and angiogenesis). Available evidence indicates that this receptor sub-type is minimally activated by endogenous adenosine during ischemia (A3AR antagonists exerting no effects on ischemic outcome), and is thus amenable to activation with exogenous agonists. Protected phenotypes arise with both pre- and post-ischemic treatment with A3AR agonists, and transient A3AR agonism also triggers early and delayed preconditioned states. The molecular basis for the varied protective actions of the A3AR remains poorly defined, and may well vary between species (e.g. rodent vs. human) and protective responses (e.g. acute vs. delayed protection). Nonetheless, A3ARs may be more promising as therapeutic "anti-ischemic" targets compared with other adenosine receptor subtypes, since A3AR agonists elicit fewer and less significant side-effects. This review addresses current knowledge and controversy regarding the protective actions (and associated signaling) of A3ARs in ischemic-reperfused heart.

Taxonomic distribution and quantitative analysis of free purine and pyrimidine nucleosides in snake venoms

The nucleoside content of 32 elapid and viperid venoms was examined. Free purines, principally adenosine (ADO), inosine (INO), and guanosine (GUA), comprised as much as 8.7% of the solid components of some venoms. Thus, purines are far more abundant in some venoms than many proteinaceous toxins. Hypoxanthine (HYP) was found in about half of elapid and viperine venoms, in which it is a relatively minor constituent (<60 microg/g). Adenosine monophosphate (AMP) was tentatively identified in only three elapid and two viperid venoms. The pyrimidines, uridine (URI) and cytidine (CYT), were also found in most elapid and viperine venoms. In most of these, the amount of uridine was substantially greater than that of cytidine. Thymidine (THY) was not found in any venom, indicating that DNA from disintegration of glandular cells is not the source of venom nucleosides. In contrast to elapid and viperine venoms, most crotaline venoms are devoid of free nucleosides. Elapid and viperine venoms also contained other minor, low molecular weight constituents that could not be positively identified. Some had spectra identical to those of adenosine, nicotinamide adenine dinucleotide (NAD), inosine, xanthosine (XAN), and guanosine, while others had unique spectra. There is no apparent correlation between quantities of venom nucleosides and literature values for the three dominant venom enzymes that release endogenous nucleosides, 5'-nucleotidase (5NUC), phosphodiesterase (PDE), and alkaline phosphomonoesterase (PME).

Adenosine Deaminase Deficiency: Metabolic Basis of Immune Deficiency and Pulmonary Inflammation

Genetic deficiencies in the purine catabolic enzyme adenosine deaminase (ADA) in humans results primarily in a severe lymphopenia and immunodeficiency that can lead to the death of affected individuals early in life. The metabolic basis of the immunodeficiency is likely related to the sensitivity of lymphocytes to the accumulation of the ADA substrates adenosine and 2'-deoxyadenosine. Investigations using ADA-deficient mice have provided compelling evidence to support the hypothesis that T and B cells are sensitive to increased concentrations of 2'-deoxyadenosine that kill cells through mechanisms that involve the accumulation of dATP and the induction of apoptosis. In addition to effects on the developing immune system, ADA-deficient humans exhibit phenotypes in other physiological systems including the renal, neural, skeletal, and pulmonary systems. ADA-deficient mice develop similar abnormalities that are dependent on the accumulation of adenosine and 2'-deoxyadenosine. Detailed analysis of the pulmonary insufficiency seen in ADA-deficient mice suggests that the accumulation of adenosine in the lung can directly access cellular signaling pathways that lead to the development and exacerbation of chronic lung disease. The ability of adenosine to regulate aspects of chronic lung disease is likely mediated by specific interactions with adenosine receptor subtypes on key regulatory cells. Thus, the examination of ADA deficiency has identified the importance of purinergic signaling during lymphoid development and in the regulation of aspects of chronic lung disease.

Involvement of mast cells in adenosine-mediated bronchoconstriction and inflammation in an allergic mouse model

In allergen-induced asthma, activation of lung mast cells leads to bronchial constriction, increased mucus secretion, and an increase in the localization of inflammatory cells to the airways. The purpose of this study was to explore the role of mast cells in adenosine-mediated airway reactivity and inflammation using the mast cell degranulating agent, compound 48/80 (C48/80). Mice were sensitized and challenged with ragweed (or 0.9% saline) followed by C48/80 administration twice a day in increasing doses for 5 days. Dose-responsiveness to the nonspecific adenosine receptor agonist 5'-N-ethylcarboxamidoadenosine (NECA) was established, and lung lavage was performed 24 h later for cell differential analysis to evaluate inflammation. At a dose of 375 microg/ml (aerosolized NECA), C48/80 pretreatment resulted in a significant attenuation in airway reactivity when compared with sensitized control mice (330.07 versus 581.57%, respectively). Lung lavage from the C48/80 treated mice showed a decrease in eosinophils (17.7 versus 60.9%, respectively) and an increase in macrophages when compared with the sensitized control group (76.4 versus 30.8%, respectively). These results support the conclusion that mast cell degranulation plays an important role in adenosine receptor-mediated airway hyperresponsiveness and inflammation.

Mutant G-protein-coupled receptors as a cause of human diseases

G-protein-coupled receptors (GPCR) are involved in directly and indirectly controlling an extraordinary variety of physiological functions. Their key roles in cellular communication have made them the target for more than 60% of all currently prescribed drugs. Mutations in GPCR can cause acquired and inherited diseases such as retinitis pigmentosa (RP), hypo- and hyperthyroidism, nephrogenic diabetes insipidus, several fertility disorders, and even carcinomas. To date, over 600 inactivating and almost 100 activating mutations in GPCR have been identified which are responsible for more than 30 different human diseases. The number of human disorders is expected to increase given the fact that over 160 GPCR have been targeted in mice. Herein, we summarize the current knowledge relevant to understanding the molecular basis of GPCR function, with primary emphasis on the mechanisms underlying GPCR malfunction responsible for different human diseases.

Essential role for the p110delta phosphoinositide 3-kinase in the allergic response

Inflammatory substances released by mast cells induce and maintain the allergic response. Mast cell differentiation and activation are regulated, respectively, by stem cell factor (SCF; also known as Kit ligand) and by allergen in complex with allergen-specific immunoglobulin E (IgE). Activated SCF receptors and high-affinity receptors for IgE (FcvarepsilonRI) engage phosphoinositide 3-kinases (PI(3)Ks) to generate intracellular lipid second messenger signals. Here, we report that genetic or pharmacological inactivation of the p110delta isoform of PI(3)K in mast cells leads to defective SCF-mediated in vitro proliferation, adhesion and migration, and to impaired allergen-IgE-induced degranulation and cytokine release. Inactivation of p110delta protects mice against anaphylactic allergic responses. These results identify p110delta as a new target for therapeutic intervention in allergy and mast-cell-related pathologies.

Extracellular inosine is modulated by H2O2 and protects sertoli cells against lipoperoxidation and cellular injury

Extracellular purines are involved in the regulation of a wide range of physiological processes, including cytoprotection, ischemic preconditioning, and cell death. These actions are usually mediated via triggering of membrane purinergic receptors, which may activate antioxidant enzymes, conferring cytoprotection. Recently, it was demonstrated that the oxidative stress induced by cisplatin up-regulated A1 receptor expression in rat testes, suggesting an involvement of purinergic signaling in the response of testicular cells to oxidant injury. In this article, we report the effect of hydrogen peroxide on purinergic agonist release by cultured Sertoli cells. Extracellular inosine levels are strongly increased in the presence of H2O2, suggesting an involvement of this nucleoside on Sertoli cells response to oxidant treatment. Inosine was observed to decrease H2O2-induced lipoperoxidaton and cellular injury, and it also preserved cellular ATP content during H2O2 exposure. These effects were abolished in the presence of nucleoside uptake inhibitors, indicating that nucleoside internalisation is essential for its action in preventing cell damage.

A3 adenosine receptor signaling contributes to airway inflammation and mucus production in adenosine deaminase-deficient mice

Adenosine signaling has been implicated in chronic lung diseases such as asthma and chronic obstructive pulmonary disease; however, the specific roles of the various adenosine receptors in processes central to these disorders are not well understood. In this study, we have investigated the role(s) of the A(3) adenosine receptor in adenosine-dependent pulmonary inflammation observed in adenosine deaminase (ADA)-deficient mice. The A(3) receptor (A(3)R) was found to be expressed in eosinophils and mucus-producing cells in the airways of ADA-deficient mice. Treatment of ADA-deficient mice with MRS 1523, a selective A(3)R antagonist, prevented airway eosinophilia and mucus production. Similar findings were seen in the lungs of ADA/A(3) double knockout mice. Although eosinophils were decreased in the airways of ADA-deficient mice following antagonism or removal of the A(3)R, elevations in circulating and lung interstitial eosinophils persisted, suggesting signaling through the A(3)R is needed for the migration of eosinophils into the airways. These findings identify an important role for the A(3)R in regulating lung eosinophilia and mucus production in an environment of elevated adenosine.