Julien Fromonot

Increased Gut Redox and Depletion of Anaerobic and Methanogenic Prokaryotes in Severe Acute Malnutrition

Severe acute malnutrition (SAM) is associated with inadequate diet, low levels of plasma antioxidants and gut microbiota alterations. The link between gut redox and microbial alterations, however, remains unexplored. By sequencing the gut microbiomes of 79 children of varying nutritional status from three centers in Senegal and Niger, we found a dramatic depletion of obligate anaerobes in malnutrition. This was confirmed in an individual patient data meta-analysis including 107 cases and 77 controls from 5 different African and Asian countries. Specifically, several species of the Bacteroidaceae, Eubacteriaceae, Lachnospiraceae and Ruminococceae families were consistently depleted while Enterococcus faecalis, Escherichia coli and Staphylococcus aureus were consistently enriched. Further analyses on our samples revealed increased fecal redox potential, decreased total bacterial number and dramatic Methanobrevibacter smithii depletion. Indeed, M. smithii was detected in more than half of the controls but in none of the cases. No causality was demonstrated but, based on our results, we propose a unifying theory linking microbiota specificity, lacking anaerobes and archaea, to low antioxidant nutrients, and lower food conversion.

NF-κB enhances hypoxia-driven T-cell immunosuppression via upregulation of adenosine A2A receptors

Hypoxia affects inflammation by modulating T-cell activation via the adenosinergic system. We supposed that, in turn, inflammation influences cell hypoxic behavior and that stimulation of T-cells in inflammatory conditions involves the concerted action of the nuclear factor κB (NF-κB) and the related hypoxia-inducible factor 1α (HIF-1α) on the adenosinergic system. We addressed this hypothesis by monitoring both transcription factors and four adenosinergic signaling parameters - namely adenosine, adenosine deaminase (ADA), adenosine A2A receptor (A2AR) and cAMP - in T-cells stimulated using phorbol myristate acetate and phytohemagglutinin and submitted to hypoxic conditions which were mimicked using CoCl2 treatment. We found that cell viability was more altered in stimulated than in resting cells under hypoxia. Detailed analysis showed that: i) NF-κB activation remained at basal level in resting hypoxic cells but greatly increased following stimulation, stimulated hypoxic cells exhibiting the higher level; ii) HIF-1α production induced by hypoxia was boosted via NF-κB activation in stimulated cells whereas hypoxia increased HIF-1α production in resting cells without further activating NF-κB; iii) A2AR expression and cAMP production increased in stimulated hypoxic cells whereas adenosine level remained unchanged due to ADA regulation; and iv) the presence of H2S, an endogenous signaling molecule in inflammation, reversed the effect of stimulation on cell viability by down-regulating the activity of transcription factors and adenosinergic immunosuppression. We also found that: i) the specific A2AR agonist CGS-21680 increased the suppressive effect of hypoxia on stimulated T-cells, the antagonist ZM-241385 exhibiting the opposite effect; and ii) Rolipram, a selective inhibitor of cAMP-specific phosphodiesterase 4, and 8-Br-cAMP, a cAMP analog which preferentially activates cAMP-dependent protein kinase A (PKA), increased T-cell immunosuppression whereas H-89, a potent and selective inhibitor of cAMP-dependent PKA, restored cell viability. Together, these data indicate that inflammation enhances T-cell sensitivity to hypoxia via NF-κB activation. This process upregulates A2AR expression and enhances cAMP production and PKA activation, resulting in adenosinergic T-cell immunosuppression that can be modulated via H2S.

Ticagrelor Improves Peripheral Arterial Function in Acute Coronary Syndrome Patients: Relationship With Adenosine Plasma Level.

Ticagrelor, a P2Y12 receptor antagonist, significantly reduces the incidence of major cardiovascular events in acute coronary syndrome (ACS) compared with standard treatment with clopidogrel (1). It has been suggested that this benefit effect may be accounted for by its pleiotropic properties via a purinergic mechanism. Indeed, ticagrelor increases the endogenous adenosine plasma level (APL) via red blood cell uptake inhibition in primary ACS patients compared with clopidogrel (2). However, the link between these “pleiotropic” properties and the improvement in microvascular dysfunction (MiD) remains poorly investigated. This study aimed to determine whether the increase in APL achieved with ticagrelor might improve endothelial dysfunction in primary ACS patients.

Effect of hyperoxic and hyperbaric conditions on the adenosinergic pathway and CD26 expression in rat

The nucleoside adenosine acts on the nervous and cardiovascular systems via the A2A receptor (A2AR). In response to oxygen level in tissues, adenosine plasma concentration is regulated in particular via its synthesis by CD73 and via its degradation by adenosine deaminase (ADA). The cell-surface endopeptidase CD26 controls the concentration of vasoactive and antioxidant peptides and hence regulates the oxygen supply to tissues and oxidative stress response. Although overexpression of adenosine, CD73, ADA, A2AR, and CD26 in response to hypoxia is well documented, the effects of hyperoxic and hyperbaric conditions on these elements deserve further consideration. Rats and a murine Chem-3 cell line that expresses A2AR were exposed to 0.21 bar O2, 0.79 bar N2 (terrestrial conditions; normoxia); 1 bar O2 (hyperoxia); 2 bar O2 (hyperbaric hyperoxia); 0.21 bar O2, 1.79 bar N2 (hyperbaria). Adenosine plasma concentration, CD73, ADA, A2AR expression, and CD26 activity were addressed in vivo, and cAMP production was addressed in cellulo. For in vivo conditions, 1) hyperoxia decreased adenosine plasma level and T cell surface CD26 activity, whereas it increased CD73 expression and ADA level; 2) hyperbaric hyperoxia tended to amplify the trend; and 3) hyperbaria alone lacked significant influence on these parameters. In the brain and in cellulo, 1) hyperoxia decreased A2AR expression; 2) hyperbaric hyperoxia amplified the trend; and 3) hyperbaria alone exhibited the strongest effect. We found a similar pattern regarding both A2AR mRNA synthesis in the brain and cAMP production in Chem-3 cells. Thus a high oxygen level tended to downregulate the adenosinergic pathway and CD26 activity. Hyperbaria alone affected only A2AR expression and cAMP production. We discuss how such mechanisms triggered by hyperoxygenation can limit, through vasoconstriction, the oxygen supply to tissues and the production of reactive oxygen species.

A2A adenosine receptor function in patients with vasovagal syncope

AIMS Adenosine is a possible mediator in vasovagal syncope (VVS) via the activation of its receptors. High expression of adenosine A2A receptors (A2AR) has been reported in VVS. The function of these over-expressed receptors in this population has never been evaluated. METHODS AND RESULTS We used Adonis, a specific-made antibody with A2AR agonist properties, to evaluate binding parameters (i.e. dissociation constant KD) and cAMP production (i.e. EC50) by peripheral blood mononuclear cells of 16 VVS patients. Eight healthy volunteers served as controls. A2AR expression was higher in patients than controls; mean: 11.5 ± 1.2 vs. 7.7 ± 0.8 AU, P = 0.04. Also, KD values were higher in patients than controls: 2.1 ± 0.02 × 10(-7) vs. 5 ± 1 × 10(-8) M, P < 0.01 In controls, KD values were lower than EC50 (5 ± 1.7 × 10(-8) vs. 2.8 ± 0.4 10(-7) M, P < 0.01), but in patients, KD values did not differ from EC50: 2. ± 0.2 × 10(-7) vs. 2.5 ± 0.4 × 10(-7) M, P > 0.05. However, four patients had lower EC50 (3.5 ± 0.3 × 10(-8) M) than KD (2.9 ± 1.2 × 10(-7) M; KD/EC50 = 9.6), suggesting the presence of spare receptors. CONCLUSION The function of A2AR of patients with VVS was preserved since their stimulation by Adonis led to cAMP production with an EC50 comparable with those in controls. However, their affinity was lower than those of controls. Our results suggest that A2AR are implicated in the physiopathology of VVS.

Ischemia-modified albumin and adenosine plasma concentrations are associated with severe systemic inflammatory response syndrome after cardiopulmonary bypass

PURPOSE Severe systemic inflammatory response syndrome (SIRS) occurring after cardiopulmonary bypass (CPB) is a common cause of mortality during cardiac surgery. These syndromes are characterized by vasoplegia and ischemia-reperfusion phenomenom. Adenosine is a strong endogenous vasodilating agent, which may be involved in blood pressure failure during CPB induced by severe SIRS. Ischemia-modified albumin (IMA) is considered as a sensitive marker of tissue ischemia. We examined whether the IMA or adenosine plasma concentrations (APCs) change during a severe SIRS-induced blood pressure failure during CPB. MATERIALS AND METHODS Plasma concentration and IMA (median [range]) were measured before, during, and after surgery in 86 patients who underwent coronary revascularization under CBP and were correlated to postoperative clinical course. RESULTS Preoperative APC values (1.45 [0.52-2.11] μmol L(-1) vs 0.36 [0.12-0.66] μmol L(-1)) and IMA (144 [91-198] IU mL(-1) vs 109 [61-183] U mL(-1)) were significantly increased in patients presenting postoperative severe SIRS. Mean durations of mechanical ventilation, stay in the intensive care unit, and requirement of vasoactive drugs were significantly higher in patients with higher APC and IMA, but APC was the best predictive marker a postoperative severe. CONCLUSIONS Adenosine plasma concentration and IMA concentration are associated with postoperative severe SIRS after CPB.

Plasma adenosine release is associated with bradycardia and transient loss of consciousness during experimental breath-hold diving

Plasma adenosine release is associated with bradycardia and transient loss of consciousness during experimental breath-hold diving Fabrice Joulia , Mathieu Coulange , Frederic Lemaitre , Guillaume Costalat , Frederic Franceschi , Vlad Gariboldi , Laetitia Nee , Julien Fromonot , Laurie Bruzzese , Gilles Gravier , Nathalie Kipson , Yves Jammes , Alain Boussuges , Michele Brignole , Jean Claude Deharo , Regis Guieu a,g,⁎

Plasma Ultrasensitive Cardiac Troponin During Long-Term Follow-up of Heart Transplant Recipients

BACKGROUND Plasma troponin is a risk factor for cardiac events in various populations. We evaluated the determinants and predictive value of plasma cardiac troponin I (cTnI) during the long-term follow-up of heart transplantation. METHODS AND RESULTS We prospectively measured cTnI in 100 heart transplant recipients, 13.0 ± 6.0 years after transplantation, during a routine visit including echocardiography and laboratory measurements. The patients were followed for 21.3 ± 4.9 months after this troponin measurement. cTnI ≥0.006 μg/L (detection threshold) was found in 37 of these 100 patients. Plasma troponin significantly increased with the presence and severity of coronary lesions detected by means of coronary angiography and was significantly associated with age, left ventricular mass, history of post-transplantation heart failure, body mass index, and plasma creatinine. Of 37 patients with cTnI ≥0.006 μg/L, 13 had a cardiac event during follow-up compared with 2 of 63 patients with cTnI <0.006 μg/L (P < .0001). The relation between cTnI and cardiac events remained significant in multivariate analysis. CONCLUSIONS cTnI is frequently detectable during long-term follow-up after heart transplantation and is associated with chronic graft rejection and renal failure. A detectable cTnI may help identify heart transplant recipients at high risk of cardiac events.

High homocysteine levels prevent via H2S the CoCl2-induced alteration of lymphocyte viability

High homocysteine (HCy) levels are associated with lymphocyte‐mediated inflammatory responses that are sometimes in turn related to hypoxia. Because adenosine is a potent lymphocyte suppressor produced in hypoxic conditions and shares metabolic pathways with HCy, we addressed the influence of high HCy levels on the hypoxia‐induced, adenosine‐mediated, alteration of lymphocyte viability. We treated mitogen‐stimulated human lymphocytes isolated from healthy individuals and the human lymphoma T‐cell line CEM with cobalt chloride (CoCl2)to reproduce hypoxia. We found that CoCl2‐altered cell viability was dose‐dependently reversed using HCy. In turn, the HCy effect was inhibited using DL‐propargylglycine, a specific inhibitor of the hydrogen sulphide (H2S)‐synthesizing enzyme cystathionine‐γ‐lyase involved in HCy catabolism. We then addressed the intracellular metabolic pathway of adenosine and HCy, and the role of the adenosine A2A receptor (A2AR). We observed that: (i) hypoxic conditions lowered the intracellular concentration of HCy by increasing adenosine production, which resulted in high A2AR expression and 3′, 5′‐cyclic adenosine monophosphate production; (ii) increasing intracellular HCy concentration reversed the hypoxia‐induced adenosinergic signalling despite high adenosine concentration by promoting both S‐adenosylhomocysteine and H2S production; (iii) DL‐propargylglycine that inhibits H2S production abolished the HCy effect. Together, these data suggest that high HCy levels prevent, via H2S production and the resulting down‐regulation of A2AR expression, the hypoxia‐induced adenosinergic alteration of lymphocyte viability. We point out the relevance of these mechanisms in the pathophysiology of cardiovascular diseases.

Pleiotropic effects of ticagrelor: Myth or reality?

In the PLATO study, ticagrelor, a direct-acting and reversible P2Y12 adenosine diphosphate receptor blocker, slightly but significantly reduced the incidence of cardiovascular and total mortality compared with clopidogrel [1]. The accuracy of the PLATO mortality data has been questioned by some authors [2]. In an adjusted indirect meta-analysis comparing prasugrel with ticagrelor for acute coronary syndromes (ACS), prasugrel and ticagrelor