Adenosine infusion increases plasma levels of VEGF in humans

The Exercise Preconditioning Effect on Cardiac Tissue Injury following Induction of Myocardial Infarction in Male Rats

Materials and Methods

Twenty-four male rats were divided into 4 groups including MI, Sham, HIIT, and HIIT+MI (N = 6). HIIT and HIIT+MI which underwent high-intensity interval training (HIIT) for 4 weeks (5 days a week). The training protocol included 10 intervals of 1-minute running, with 2 minutes rest between each interval. The training intensity was different every week according to the peak treadmill running speed (v peak) percentage of each rat. Isoproterenol injection was used to induce myocardial infarction (MI). Expressions of creatine kinase-MB (CK-MB), PGC-1α troponin-I, mitochondrial transcription factor A (TFAM), vascular endothelial growth factor (VEGF), and microRNA 126 (miR-126) genes were measured. The variables were measured using biochemical and RT-PCR methods. The significance level (P value≤0.05) was analyzed using ANOVA test.

Results

The results showed that 4 weeks of HIIT training led to a significant increase in PGC-1α, TFAm, and VEGF levels in the MI, HIIT, and HIIT+MI groups compared to the sham group (P = 0.001). HIIT exercises increased miR-126 in the different groups compared to the sham group; however, it was not significant.

Conclusion

The results obtained showed that HIIT exercise exerts cardio-protective effects to reduce cardiac tissue injury and necrosis against MI. These effects increase mitochondrial biogenesis and angiogenesis by inducing the increased expression of VEGF, TFAM, PGC-1α, and miR-126 genes in the heart tissue. Therefore, HIIT training, as a preconditioning program, was able to protect the cardiac tissue against MI.

Retinal Microvasculature in Schizophrenia

PURPOSE

Schizophrenia is associated with alterations in neural structure and function of the retina that are similar to changes seen in the retina and brain in multiple neurodegenerative disorders. Preliminary evidence suggests that retinal microvasculature may also be compromised in schizophrenia. The goal of this study was to determine, using optical coherence tomography angiography (OCTA), whether 1) schizophrenia is associated with alterations in retinal microvasculature density; and 2) microvasculature reductions are associated with retinal neural layer thinning and performance on a measure of verbal IQ.

PATIENTS AND METHODS

Twenty-eight outpatients with schizophrenia or schizoaffective disorder and 37 psychiatrically healthy control subjects completed OCT and OCTA exams, and the Wechsler Test of Adult Reading.

RESULTS

Schizophrenia patients were characterized by retinal microvasculature density reductions, and enlarged foveal avascular zones, in both eyes. These microvascular abnormalities were generally associated with thinning of retinal neural (macular and peripapillary nerve fiber layer) tissue (but the data were stronger for the left than the right eye) and lower scores on a proxy measure of verbal IQ. First- and later-episode patients did not differ significantly on OCTA findings.

CONCLUSION

The retinal microvasculature impairments seen in schizophrenia appear to be a biomarker of overall brain health, as is the case for multiple neurological conditions. Additional research is needed, however, to clarify contributions of social disadvantage and medical comorbidities to the findings.

Exosomes: Small EVs with Large Immunomodulatory Effect in Glioblastoma

Glioblastomas are among the most aggressive tumors, and with low survival rates. They are characterized by the ability to create a highly immunosuppressive tumor microenvironment. Exosomes, small extracellular vesicles (EVs), mediate intercellular communication in the tumor microenvironment by transporting various biomolecules (RNA, DNA, proteins, and lipids), therefore playing a prominent role in tumor proliferation, differentiation, metastasis, and resistance to chemotherapy or radiation. Exosomes are found in all body fluids and can cross the blood-brain barrier due to their nanoscale size. Recent studies have highlighted the multiple influences of tumor-derived exosomes on immune cells. Owing to their structural and functional properties, exosomes can be an important instrument for gaining a better molecular understanding of tumors. Furthermore, they qualify not only as diagnostic and prognostic markers, but also as tools in therapies specifically targeting aggressive tumor cells, like glioblastomas.

Effect of Age and Acute Exercise on Circulating Angioregulatory Factors

The balance of angiogenic factors, including vascular endothelial growth factor (VEGF), and angiostatic factors, like thrombospondin-1 (TSP-1) and endostatin, controls striated muscle angiogenic responses to exercise training. The effect of age on circulating levels of these factors following a bout of exercise is unclear. The authors hypothesized that older adults would have lower circulating VEGF but higher TSP-1 and endostatin after exercise compared with young adults. Ten young and nine older participants cycled for 45 min at 60% estimated HRmax. Serum [VEGF], [TSP-1], and [endostatin] obtained before (PREX), immediately after (POSTX0), and 3 hr after (POSTX3) exercise were analyzed. [VEGF] increased in older adults only from PREX to POSTX0 (p < .05). [TSP-1] increased in both age groups (p < .05). There was no effect of age or exercise on [endostatin]. In conclusion, immediately after exercise, both groups had a similar increase in [TSP-1], but [VEGF] increased in older adults only.

High Adenosine Extracellular Levels Induce Glioblastoma Aggressive Traits Modulating the Mesenchymal Stromal Cell Secretome

Glioblastoma is an aggressive, fast-growing brain tumor influenced by the composition of the tumor microenvironment (TME) in which mesenchymal stromal cell (MSCs) play a pivotal role. Adenosine (ADO), a purinergic signal molecule, can reach up to high micromolar concentrations in TME. The activity of specific adenosine receptor subtypes on glioma cells has been widely explored, as have the effects of MSCs on tumor progression. However, the effects of high levels of ADO on glioma aggressive traits are still unclear as is its role in cancer cells-MSC cross-talk. Herein, we first studied the role of extracellular Adenosine (ADO) on isolated human U343MG cells as a glioblastoma cellular model, finding that at high concentrations it was able to prompt the gene expression of Snail and ZEB1, which regulate the epithelial-mesenchymal transition (EMT) process, even if a complete transition was not reached. These effects were mediated by the induction of ERK1/2 phosphorylation. Additionally, ADO affected isolated bone marrow derived MSCs (BM-MSCs) by modifying the pattern of secreted inflammatory cytokines. Then, the conditioned medium (CM) of BM-MSCs stimulated with ADO and a co-culture system were used to investigate the role of extracellular ADO in GBM-MSC cross-talk. The CM promoted the increase of glioma motility and induced a partial phenotypic change of glioblastoma cells. These effects were maintained when U343MG cells and BM-MSCs were co-cultured. In conclusion, ADO may affect glioma biology directly and through the modulation of the paracrine factors released by MSCs overall promoting a more aggressive phenotype. These results point out the importance to deeply investigate the role of extracellular soluble factors in the glioma cross-talk with other cell types of the TME to better understand its pathological mechanisms.

Role of exosome-associated adenosine in promoting angiogenesis

The role of exosomes in different physiological and pathological settings is an emerging field of great current interest. One hallmark of exosomes is the promotion of blood vessel formation. Exosomes of different cellular origin have been shown to be enriched in angiogenic proteins which directly promote angiogenesis. In addition, exosomes are also efficacious producers of adenosine and potentially encapsulate adenosine in their lumen. The adenosine content of exosomes has been linked to their immunosuppressive effects. In this communication, we consider the possibility that adenosine production by tumor cell-derived exosomes may represent a novel pathway for stimulation of angiogenesis in the tumor microenvironment.

Number of Circulating CD 73-Expressing Lymphocytes Correlates With Survival After Cardiac Arrest

Background

Patients resuscitated from cardiac arrest (CA) have highly variable neurological, circulatory, and systemic ischemia‐reperfusion injuries. After the initial hypoxic‐ischemic insult, a cascade of immune and inflammatory responses develops and is often fatal. The role of the immune response in pathophysiological characteristics and recovery is not well understood. We studied immune cell activity and its association with outcomes in a cohort of CA survivors.

Methods and Results

After informed consent, we collected blood samples at intervals over a week after resuscitation from CA. We examined the expression of CD39 and CD73 (alias 5′‐nucleotidase), production of tumor necrosis factor‐α, generation of reactive oxygen species, and secretion of vascular endothelial growth factor by circulating myeloid and lymphoid cells, in comparison to cells obtained from control subjects before coronary artery bypass grafting surgery. The number of circulating total and CD73‐expressing lymphocytes correlated with survival after CA. Incubation of immune cells, obtained from post‐CA subjects, with AMP, a substrate for CD73, resulted in inhibition of tumor necrosis factor‐α production and generation of reactive oxygen species. This effect was blocked by adenosine 5′‐(α, β‐methylene) diphosphate, a specific inhibitor of CD73 and ZM 241385, an A2 adenosine receptor antagonist. We also found that AMP‐dependent activation of CD73 induces production of vascular endothelial growth factor.

Conclusions

CD73‐expressing lymphocytes mediate cellular protection from inflammation after CA through inhibition of proinflammatory activation of myeloid cells and promotion of vascular endothelial growth factor secretion. The contribution of CD73 lymphocytes in the regulation of acute inflammation and tissue injury after CA warrants further study.

Targeting A2 adenosine receptors in cancer

Tumor cells use various ways to evade anti-tumor immune responses. Adenosine, a potent immunosuppressive metabolite, is often found elevated in the extracellular tumor microenvironment. Therefore, targeting adenosine-generating enzymes (CD39 and CD73) or adenosine receptors has emerged as a novel means to stimulate anti-tumor immunity. In particular, the A2 (A2a and A2b) adenosine receptors exhibit similar immunosuppressive and pro-angiogenic functions, yet have distinct biological roles in cancer. In this review, we describe the common and distinct biological consequences of A2a and A2b adenosine receptor signaling in cancer. We discuss recent pre-clinical studies and summarize the different mechanisms-of-action of adenosine-targeting drugs. We also review the rationale for combining inhibitors of the adenosine pathway with other anticancer therapies such immune checkpoint inhibitors, tumor vaccines, chemotherapy and adoptive T cell therapy.

Adenosine receptors and caffeine in retinopathy of prematurity

Retinopathy of prematurity (ROP) is a major cause of childhood blindness in the world and is caused by oxygen-induced damage to the developing retinal vasculature, resulting in hyperoxia-induced vaso-obliteration and subsequent delayed retinal vascularization and hypoxia-induced pathological neovascularization driven by vascular endothelial growth factor (VEGF) signaling pathway in retina. Current anti-VEGF therapy has shown some effective in a clinical trial, but is associated with the unintended effects on delayed eye growth and retinal vasculature development of preterm infants. Notably, cellular responses to hypoxia are characterized by robust increases in extracellular adenosine production and the markedly induced adenosine receptors, which provide a novel target for preferential control of pathological angiogenesis without affecting normal vascular development. Here, we review the experimental evidence in support of adenosine receptor-based therapeutic strategy for ROP, including the aberrant adenosine signaling in oxygen-induced retinopathy and the role of three adenosine receptor subtypes (A₁R, A_2AR, A_2BR) in development and treatment of ROP using oxygen-induced retinopathy models. The clinical and initial animal evidence that implicate the therapeutic effect of caffeine (a non-selective adenosine receptor antagonist) in treatment of ROP are highlighted. Lastly, we discussed the translational potential as well therapeutic advantage of adenosine receptor- and caffeine-based therapy for ROR and possibly other proliferative retinopathy.

Polydeoxyribonucleotide, an Adenosine-A2A Receptor Agonist, Preserves Blood Testis Barrier from Cadmium-Induced Injury

Cadmium (Cd) impairs blood-testis barrier (BTB). Polydeoxyribonucleotide (PDRN), an adenosine A_2A agonist, has positive effects on male reproductive system. We investigated the effects of PDRN on the morphological and functional changes induced by Cd in mice testes. Adult Swiss mice were divided into four groups: controls administered with 0.9% NaCl (1 ml/kg, i.p., daily) or with PDRN (8 mg/kg, i.p. daily), animals challenged with Cd chloride (CdCl₂; 2 mg/kg, i.p, daily) and animals challenged with CdCl₂ (2 mg/kg, i.p., daily) and treated with PDRN (8 mg/kg, i.p., daily). Experiments lasted 14 days. Testes were processed for biochemical, structural, and ultrastructural evaluation and hormones were assayed in serum. CdCl₂ increased pERK 1/2 expression and Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH) levels; it decreased testosterone (TE) and inhibin-B levels and induced structural damages in extratubular compartment and in seminiferous epithelium, with ultrastructural features of BTB disruption. Many TUNEL-positive germ cells were present. CdCl₂ increased tubular TGF-β3 immunoreactivity and reduced claudin-11, occludin, and N-cadherin immunoreactivity. PDRN administration reduced pERK 1/2 expression, FSH, and LH levels; it increased TE and inhibin-B levels, ameliorated germinal epithelium changes and protected BTB ultrastructure. Few TUNEL-positive germ cells were present and the extratubular compartment was preserved. Furthermore, PDRN decreased TGF-β3 immunoreactivity and enhanced claudin-11, occludin, and N-cadherin immunoreactivity. We demonstrate a protective effect of PDRN on Cd-induced damages of BTB and suggest that PDRN may play an important role against Cd, particularly against its harmful effects on gametogenesis.

Adenosine A2B receptor stimulates angiogenesis by inducing VEGF and eNOS in human microvascular endothelial cells

Angiogenesis is critical to wound repair due to its role in providing oxygen and nutrients that are required to support the growth and function of reparative cells in damaged tissues. Adenosine receptors are claimed to be of paramount importance in driving wound angiogenesis by inducing VEGF. However, the underlying mechanisms for the regulation of adenosine receptors in VEGF as well as eNOS remain poorly understood. In the present study, we found that adenosine and the non-selective adenosine receptor agonists (NECA) induced tube formation in HMEC-1 in a dose-dependent manner. Adenosine or NECA (10 µmol/L) significantly augmented the number and length of the segments in comparison with the control. Simultaneously, VEGF and eNOS were significantly upregulated following the administration of 10 µmol/L NECA, while they were suppressed after A2B AR genetic silencing and pharmacological inhibition by MRS1754. In addition, VEGF expression and eNOS bioavailability elimination significantly reduced the formation of capillary-like structures. Furthermore, the activation of A2B AR by NECA significantly increased the intracellular cAMP levels and concomitant CREB phosphorylation, eventually leading to the production of VEGF in HMEC-1. However, the activated PKA-CREB pathway seemed to be invalidated in the induction of eNOS. Moreover, we found that the elicited PI3K/AKT signaling in response to the induction of NECA assisted in regulating eNOS but failed to impact on VEGF generation. In conclusion, the A2B AR activation-driven angiogenesis via cAMP-PKA-CREB mediated VEGF production and PI3K/AKT-dependent upregulation of eNOS in HMEC-1.

The presence of adenosine A2a receptor in thyrocytes and its involvement in Graves' IgG-induced VEGF expression

Goitrogenesis in Graves' disease (GD) has been attributed to anti-TSH receptor antibody stimulation. Recently, a role for adenosine A2a receptor (A2aR) in goiter formation was reported in the thyroglobulin-A2aR transgenic mice. However, it is unclear whether A2aR is expressed in the thyroid and whether it is associated with the pathogenesis of goiter in GD. Here, we confirmed the expression of A2aR in FRTL-5 cells, primary normal human thyrocytes (both sexes were used without regard to sex), and thyroid tissue (both sexes were used without regard to sex) by PCR, Western blotting, immunohistochemistry, and immunofluorescence. After treatments with A2aR-specific agonist 2-p-(2-Carboxyethyl)phenethylamino-5'-N-ethylcarboxamidoadenosine or GD IgG, the mRNA and protein levels of vascular endothelial growth factor (VEGF), a growth factor related to goitrogenesis, were evaluated along with upstream signaling pathways. A2aR activation and GD IgG promoted the expression of VEGF in thyrocytes, which was accompanied by the activation of cAMP/protein kinase A/phosphorylated-cAMP-response element-binding protein, peroxisome proliferator-activated receptor γ coactivator-1α, and hypoxia-inducible factor-1α. The changes induced by GD IgG were partially abrogated by A2aR small interfering RNA and an A2aR antagonist. These results were supported by data on the goiter samples from the thyrotropin receptor adenovirus-induced GD mouse model (female). These data demonstrate that GD IgG could up-regulate the VEGF expression through A2aR, indicating a potential mechanism for goitrogenesis in GD.

Comparison of the effects of adenosine, inosine, and their combination as an adjunct to reperfusion in the treatment of acute myocardial infarction

Adenosine and inosine are both key intracellular energy substrates for nucleotide synthesis by salvage pathways, especially during ischemic stress conditions. Additionally they both possess cell protective and cell repair properties. The objective of this study is to detect potential advantages of the combination of adenosine and inosine versus each drug alone, in terms of ventricular function, infarct size reduction and angiogenesis. Myocardial ischemia was created in rodents and treated with adenosine, inosine or their combination. Results of experiments showed that the combination of both drugs significantly reduced infarct size and improved myocardial angiogenesis and ventricular function. The two compounds, while chemically similar, use different intracellular pathways, allowing for complementary biological activities without overlapping. The drug combination at specific 1 : 5 adenosine : inosine dose ratio demonstrated positive cardiologic effects, deserving further evaluation as an adjunct to reperfusion techniques during and after acute coronary syndrome. The association of adenosine and inosine may contribute to reduce myocardial infarction morbidity and mortality rates.

Contraction-induced secretion of VEGF from skeletal muscle cells is mediated by adenosine

The role of adenosine and contraction for secretion of vascular endothelial growth factor (VEGF) in skeletal muscle was investigated in human subjects and rat primary skeletal muscle cells. Microdialysis probes were inserted in the thigh muscle of seven male subjects, and dialysate was collected at rest, during infusion of adenosine, and during knee extensor exercise. The dialysate was analyzed for content of VEGF protein and adenosine. The mechanism of VEGF secretion from muscle cells in culture was examined in resting and electrostimulated cells and in response to the adenosine analog NECA and the adenosine A2A receptor specific analog CGS-21680. Adenosine receptors A1, A2A, and A2B were blocked with DPCPX, ZM-241385, and enprofylline, respectively. cAMP-dependent protein kinase A (PKA) and mitogen-activated protein kinase (MAPK) were inhibited by H-89 and PD-98509, respectively. The human experiment showed that adenosine infusion enhanced ( P < 0.05) the interstitial concentration of VEGF protein approximately fourfold above baseline. Exercise increased ( P < 0.05) the interstitial VEGF concentration approximately sixfold above rest in parallel with an approximately threefold increase in adenosine concentration. In accordance, in cultured muscle cells, NECA and contraction caused secretion of VEGF ( P < 0.05). The contraction-induced secretion of VEGF was abolished by the A2B antagonist enprofylline and by inhibition of PKA or MAPK. The results demonstrate that adenosine causes secretion of VEGF from human skeletal muscle cells and that the contraction-induced secretion of VEGF protein is partially mediated via adenosine acting on A2B adenosine receptors. Moreover, the contraction-induced secretion of VEGF protein from muscle is dependent on both PKA and MAPK activation, but only the MAPK pathway appears to be adenosine dependent, revealing involvement of additional pathways in VEGF secretion.

Genetic inactivation of the adenosine A2A receptor attenuates pathologic but not developmental angiogenesis in the mouse retina

PURPOSE

The adenosine A(2A) receptor (A(2A)R) modulates normal vascularization and pathologic angiogenesis in many tissues and may contribute to the pathogenesis of retinopathy of prematurity (ROP) characterized by abnormal retinal vascularization in surviving premature infants. Here, the authors studied the effects of the genetic inactivation of A(2A)R on normal retinal vascularization and the development of pathologic angiogenesis in oxygen-induced retinopathy (OIR), an animal model of ROP.

METHODS

After exposure to 75% oxygen for 5 days (postnatal day [P] 7-P12) and subsequently to room air for the next 9 days (P13-P21), we evaluated retinal vascular morphology by ADPase staining in retinal whole mounts, retinal neovascularization response by histochemistry in serial retinal sections, and retinal VEGF gene expression by real-time PCR analysis in A(2A)R knockout (KO) mice and their wild-type (WT) littermates.

RESULTS

At P17, A(2A)R KO mice displayed attenuated OIR compared with WT littermates, as evidenced by reduced vaso-obliteration and areas of nonperfusion in the center of the retina, reduced pathologic angiogenesis as evident by decreased non-ganglion cells and neovascular nuclei, and inhibited hypoxia-induced retinal VEGF gene expression. Notably, the attenuation of pathologic angiogenesis by A(2A)R inactivation was selective for OIR because it did not affect normal retinal vascularization during postnatal development.

CONCLUSIONS

These findings provide the first evidence that A(2A)R is critical for the development of OIR and suggest a novel therapeutic approach of A(2A)R inactivation for ROP by selectively targeting pathologic but not developmental angiogenesis in the retina.

Adenosine receptor agonists for promotion of dermal wound healing

Wound healing is a dynamic and complex process that involves a well-coordinated, highly regulated series of events including inflammation, tissue formation, revascularization and tissue remodeling. However, this orderly sequence is impaired in certain pathophysiological conditions such as diabetes mellitus, venous insufficiency, chronic glucocorticoid use, aging and malnutrition. Together with proper wound care, promotion of the healing process is the primary objective in the management of chronic poorly healing wounds. Recent studies have demonstrated that A(2A) adenosine receptor agonists promote wound healing in normal and diabetic animals and one such agonist, Sonedenoson, is currently being evaluated as a prospective new therapy of diabetic foot ulcers. We will review the mechanisms by which adenosine receptor activation affects the function of the cells and tissues that participate in wound healing, emphasizing the potential beneficial impact of adenosine receptor agonists in diabetic impaired healing.

Adenosine in burn blister fluid

BACKGROUND

Burn wound blister fluid is known to sustain suppressive effects on various components of the immune system. Damaged tissues cause an increase of adenosine concentrations. Since adenosine is a potent anti-inflammatory agent we hypothesized that burn blister fluid contains high concentrations of this nucleoside.

METHODS

Burn blister fluid was drawn from eleven patients who suffered a second degree burn injury. Adenosine concentrations were determined using high performance liquid chromatography (HPLC).

RESULTS

Elevated adenosine levels were detected in 6 of the 11 patients (54.5%), with an overall mean of 1.13+/-0.52 mM.

CONCLUSIONS

This is the first documented data showing increased concentrations of adenosine in burn blister fluid.