Attenuation of HIV-specific T cell responses Among people with HIV on ART following dipyridamole treatment.

Twelve weeks of dipyridamole increased extracellular adenosine levels and decreased T cell activation in people with human immunodeficiency virus (HIV). In this analysis, we investigated the effect of dipyridamole on HIV-specific T cell responses. We compared changes in Gag- and Env-specific T cell responses using intracellular cytokine staining, following 12 wk of dipyridamole treatment vs placebo.

8-Aminoguanine and Its Actions on Renal Excretory Function.

Background: The endogenous purine 8-aminoguanine induces diuresis/natriuresis/glucosuria by inhibiting PNPase (purine nucleoside phosphorylase); however, mechanistic details are unknown.

Methods: Here, we further explored in rats 8-aminoguanine's effects on renal excretory function by combining studies using intravenous 8-aminoguanine, intrarenal artery infusions of PNPase substrates (inosine and guanosine), renal microdialysis, mass spectrometry, selective adenosine receptor ligands, adenosine receptor knockout rats, laser doppler blood flow analysis, cultured renal microvascular smooth muscle cells, HEK293 cells expressing A receptors and homogeneous time resolved fluorescence assay for adenylyl cyclase activity.

Results: Intravenous 8-aminoguanine caused diuresis/natriuresis/glucosuria and increased renal microdialysate levels of inosine and guanosine.

Biochemical pathways of 8-aminoguanine production in Sprague-Dawley and Dahl salt-sensitive rats.

Background: 8-Aminoguanine exerts natriuretic and antihypertensive activity. Whether and how "free" 8-aminoguanine exists in vivo is unclear. Because 8-nitroguanosine is naturally occurring, we tested the hypothesis that 8-aminoguanine can arise from: pathway 1, 8-nitroguanosine → 8-aminoguanosine → 8-aminoguanine; and pathway 2, 8-nitroguanosine → 8-nitroguanine → 8-aminoguanine.

Brief Report: Dipyridamole Decreases Gut Mucosal Regulatory T-Cell Frequencies Among People With HIV on Antiretroviral Therapy.

Background: We had previously conducted a double-blind, randomized placebo-controlled, partial cross-over trial showing that 12 weeks of dipyridamole decreased CD8 T-cell activation among treated HIV(+) individuals by increasing extracellular adenosine levels.

Methods: In this substudy, rectosigmoid biopsies were obtained from 18 participants (9 per arm), to determine whether 12 weeks of dipyridamole affects mucosal immune cells. Participants randomized to placebo were then switched to dipyridamole for 12 weeks while the treatment arm continued dipyridamole for another 12 weeks.

Author Correction: Simultaneous Inhibition of Glycolysis and Oxidative Phosphorylation Triggers a Multi-Fold Increase in Secretion of Exosomes: Possible Role of 2',3'-cAMP.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Purine Metabolites in Tumor-Derived Exosomes May Facilitate Immune Escape of Head and Neck Squamous Cell Carcinoma.

Body fluids of patients with head and neck squamous cell carcinoma (HNSCC) are enriched in exosomes that reflect properties of the tumor. The aim of this study was to determine whether purine metabolites are carried by exosomes and evaluate their role as potential contributors to tumor immune escape. The gene expression levels of the purine synthesis pathway were studied using the Cancer Genome Atlas (TCGA) Head and Neck Cancer database.

Adenosine receptors regulate exosome production.

Exosomes, small-sized extracellular vesicles, carry components of the purinergic pathway. The production by cells of exosomes carrying this pathway remains poorly understood. Here, we asked whether type 1, 2A, or 2B adenosine receptors (ARs, ARs, and ARs, respectively) expressed by producer cells are involved in regulating exosome production.

Tumor-derived exosomes promote angiogenesis via adenosine A receptor signaling.

Rationale: One hallmark of tumor-derived exosomes (TEX) is the promotion of cancer progression by stimulating angiogenesis. This study was performed to evaluate the role of adenosine receptors in TEX-induced angiogenesis.

Methods: TEX produced by UMSCC47 head and neck cancer cell line were isolated by mini size exclusion chromatography (mini-SEC).

Characterization of the N-etheno-bridge method to assess extracellular metabolism of adenine nucleotides: detection of a possible role for purine nucleoside phosphorylase in adenosine metabolism.

The goal of this study was to determine the validity of using N-etheno-bridged adenine nucleotides to evaluate ecto-nucleotidase activity. We observed that the metabolism of N-etheno-ATP versus ATP was quantitatively similar when incubated with recombinant CD39, ENTPD2, ENTPD3, or ENPP-1, and the quantitative metabolism of N-etheno-AMP versus AMP was similar when incubated with recombinant CD73. This suggests that ecto-nucleotidases process N-etheno-bridged adenine nucleotides similarly to endogenous adenine nucleotides.

Simultaneous Inhibition of Glycolysis and Oxidative Phosphorylation Triggers a Multi-Fold Increase in Secretion of Exosomes: Possible Role of 2'3'-cAMP.

Exosome secretion by cells is a complex, poorly understood process. Studies of exosomes would be facilitated by a method for increasing their production and release. Here, we present a method for stimulating the secretion of exosomes.

DPP4 Inhibition, NPY, PYY, SDF-1, and a Hypertensive Genetic Background Conspire to Augment Cell Proliferation and Collagen Production: Effects That Are Abolished by Low Concentrations of 2-Methoxyestradiol.

By reducing their metabolism, dipeptidyl peptidase 4 inhibition (DPP4I) enhances the effects of numerous peptides including neuropeptide Y (NPY), peptide YY (PYY), and SDF-1 Studies show that separately NPY, PYY and SDF-1 stimulate proliferation of, and collagen production by, cardiac fibroblasts (CFs), preglomerular vascular smooth muscle cells (PGVSMCs), and glomerular mesangial cells (GMCs), particularly in cells isolated from genetically hypertensive rats. Whether certain combinations of these factors, in the absence or presence of DPP4I, are more profibrotic than others is unknown. Here we contrasted 24 different combinations of conditions (DPP4I, hypertensive genotype and physiologic levels [3 nM] of NPY, PYY, or SDF-1) on proliferation of, and [H]-proline incorporation by, CFs, PGVSMCs, and GMCs.

A Randomized, Placebo-Controlled, Pilot Clinical Trial of Dipyridamole to Decrease Human Immunodeficiency Virus-Associated Chronic Inflammation.

Background: Adenosine is a potent immunoregulatory nucleoside produced during inflammatory states to limit tissue damage. We hypothesized that dipyridamole, which inhibits cellular adenosine uptake, could raise the extracellular adenosine concentration and dampen chronic inflammation associated with human immunodeficiency virus (HIV) type 1.

Methods: Virally suppressed participants receiving antiretroviral therapy were randomized 1:1 for 12 weeks of dipyridamole (100 mg 4 times a day) versus placebo capsules.

Extracellular Ubiquitin(1-76) and Ubiquitin(1-74) Regulate Cardiac Fibroblast Proliferation.

SDF-1α (stromal cell-derived factor-1α) is a CXCR4-receptor agonist and DPP4 (dipeptidyl peptidase 4) substrate. SDF-1α, particularly when combined with sitagliptin to block the metabolism of SDF-1α by DPP4, stimulates proliferation of cardiac fibroblasts via the CXCR4 receptor; this effect is greater in cells from spontaneously hypertensive rats versus Wistar-Kyoto normotensive rats. Emerging evidence indicates that ubiquitin(1-76) exists in plasma and is a potent CXCR4-receptor agonist.

Adenosine Receptors Influence Hypertension in Dahl Salt-Sensitive Rats: Dependence on Receptor Subtype, Salt Diet, and Sex.

The influence of adenosine receptors on blood pressure in salt-sensitive hypertension is unknown. Here, we examined the effects of salt diets on arterial blood pressures (radiotelemetry) in female and male Dahl salt-sensitive wild-type versus female and male Dahl salt-sensitive A, A, or A receptor knockouts (AKOs, AKOs, and AKOs, respectively). At baseline, all rats were on a 0.

8-Aminoguanosine and 8-Aminoguanine Exert Diuretic, Natriuretic, Glucosuric, and Antihypertensive Activity.

In vivo, guanine moieties in DNA, RNA, guanine nucleotides, or guanosine or guanine per se can undergo nitration (for example, by peroxynitrite) or hydroxylation (for example, by superoxide anion) on position 8 of the purine ring. Subsequent catabolism of these modified biomolecules leads to the production of a diverse group of 8-nitro, 8-amino, and 8-hydroxy guanosine and guanine compounds. Indeed, studies suggest the in vivo existence of 8-nitroguanosine, 8-nitroguanine, 8-aminoguanosine, 8-aminoguanine, 8-hydroxyguanosine, 8-hydroxy-2'-deoxyguanosine, and 8-hydroxyguanine.

2-Methoxyestradiol, an endogenous 17β-estradiol metabolite, inhibits microglial proliferation and activation via an estrogen receptor-independent mechanism.

17β-Estradiol (estradiol) inhibits microglia proliferation. 2-Methoxyestradiol (2-ME) is an endogenous metabolite of estradiol with little affinity for estrogen receptors (ERs). We hypothesize that 2-ME inhibits microglial proliferation and activation and contributes to estradiol's inhibitory effects on microglia.

Adenosine Attenuates Human Coronary Artery Smooth Muscle Cell Proliferation by Inhibiting Multiple Signaling Pathways That Converge on Cyclin D.

The goal of this study was to determine whether and how adenosine affects the proliferation of human coronary artery smooth muscle cells (HCASMCs). In HCASMCs, 2-chloroadenosine (stable adenosine analogue), but not N(6)-cyclopentyladenosine, CGS21680, or N(6)-(3-iodobenzyl)-adenosine-5'-N-methyluronamide, inhibited HCASMC proliferation (A2B receptor profile). 2-Chloroadenosine increased cAMP, reduced phosphorylation (activation) of ERK and Akt (protein kinases known to increase cyclin D expression and activity, respectively), and reduced levels of cyclin D1 (cyclin that promotes cell-cycle progression in G1).

NPY1-36 and PYY1-36 activate cardiac fibroblasts: an effect enhanced by genetic hypertension and inhibition of dipeptidyl peptidase 4.

Cardiac sympathetic nerves release neuropeptide Y (NPY)1-36, and peptide YY (PYY)1-36 is a circulating peptide; therefore, these PP-fold peptides could affect cardiac fibroblasts (CFs). We examined the effects of NPY1-36 and PYY1-36 on the proliferation of and collagen production ([(3)H]proline incorporation) by CFs isolated from Wistar-Kyoto (WKY) normotensive rats and spontaneously hypertensive rats (SHRs). Experiments were performed with and without sitagliptin, an inhibitor of dipeptidyl peptidase 4 [DPP4; an ectoenzyme that metabolizes NPY1-36 and PYY1-36 (Y1 receptor agonists) to NPY3-36 and PYY3-36 (inactive at Y1 receptors), respectively].

Critical Role for the Adenosine Pathway in Controlling Simian Immunodeficiency Virus-Related Immune Activation and Inflammation in Gut Mucosal Tissues.

Unlabelled: The role of the adenosine (ADO) pathway in human immunodeficiency virus type 1/simian immunodeficiency virus (HIV-1/SIV) infection remains unclear. We compared SIVsab-induced changes of markers related to ADO production (CD39 and CD73) and breakdown (CD26 and adenosine deaminase) on T cells from blood, lymph nodes, and intestine collected from pigtailed macaques (PTMs) and African green monkeys (AGMs) that experience different SIVsab infection outcomes. We also measured ADO and inosine (INO) levels in tissues by mass spectrometry.

2',3'-cAMP, 3'-AMP, 2'-AMP and adenosine inhibit TNF-α and CXCL10 production from activated primary murine microglia via A2A receptors.

Background: Some cells, tissues and organs release 2',3'-cAMP (a positional isomer of 3',5'-cAMP) and convert extracellular 2',3'-cAMP to 2'-AMP plus 3'-AMP and convert these AMPs to adenosine (called the extracellular 2',3'-cAMP-adenosine pathway). Recent studies show that microglia have an extracellular 2',3'-cAMP-adenosine pathway. The goal of the present study was to investigate whether the extracellular 2',3'-cAMP-adenosine pathway could have functional consequences on the production of cytokines/chemokines by activated microglia.

Effect of dipeptidyl peptidase 4 inhibition on arterial blood pressure is context dependent.

Unlabelled: Because the effects of dipeptidyl peptidase 4 (DPP4) inhibitors on blood pressure are controversial, we examined the long-term effects of sitagliptin (80 mg/kg per day) on blood pressure (radiotelemetry) in spontaneously hypertensive rats (SHR), Wistar-Kyoto rats, and Zucker Diabetic-Sprague Dawley rats (metabolic syndrome model). In SHR, chronic (3 weeks) sitagliptin significantly increased systolic, mean, and diastolic blood pressures by 10.3, 9.

Guanosine regulates adenosine levels in the kidney.

In cell culture, extracellular guanosine increases extracellular adenosine by attenuating the disposition of extracellular adenosine (American Journal of Physiology - Cell Physiology 304: C406-C421, 2013). The goal of this investigation was to determine whether this "guanosine-adenosine mechanism" is operative in an intact organ. Twenty-seven isolated, perfused mouse kidneys were subjected to metabolic poisons (iodoacetate plus 2,4-dinitrophenol) to cause energy depletion and thereby stimulate renal adenosine production.