Adenosine receptor modulation: potential implications in veterinary medicine

Pharmacological Tuning of Adenosine Signal Nuances Underlying Heart Failure With Preserved Ejection Fraction

Heart failure with preserved ejection fraction (HFpEF) roughly represents half of the cardiac failure events in developed countries. The proposed 'systemic microvascular paradigm' has been used to explain HFpHF presentation heterogeneity. The lack of effective treatments with few evidence-based therapeutic recommendations makes HFpEF one of the greatest unmet clinical necessities worldwide. The endogenous levels of the purine nucleoside, adenosine, increase significantly following cardiovascular events. Adenosine exerts cardioprotective, neuromodulatory, and immunosuppressive effects by activating plasma membrane-bound P1 receptors that are widely expressed in the cardiovascular system. Its proven benefits have been demonstrated in preclinical animal tests. Here, we provide a comprehensive and up-to-date critical review about the main therapeutic advantages of tuning adenosine signalling pathways in HFpEF, without discounting their side effects and how these can be seized.

Adjuvant drug-assisted bone healing: Part III - Further strategies for local and systemic modulation

In this third in a series of reviews on adjuvant drug-assisted bone healing, further approaches aiming at influencing the healing process are discussed. Local and systemic modulation of bone metabolism is pursued with use of a number of drugs with completely different indications, which are characterized by a pleiotropic spectrum of action. These include drugs used to treat lipid disorders (HMG-CoA reductase inhibitors), hypertension (ACE inhibitors), osteoporosis (bisphosphonates), cancer (proteasome inhibitors) and others. Potential applications to enhance bone healing are discussed.

Increased adenosine concentration in bronchoalveolar lavage fluid of horses with lower airway inflammation

Several reports have suggested a role for adenosine in the pathogenesis of chronic airway conditions and this has led to new therapeutic strategies to limit airway inflammation. In this study, detectable levels of adenosine in bronchoalveolar lavage (BAL) samples from 11 horses with non-infectious lower-airway inflammation and 14 healthy controls are reported, with significantly higher values in horses with airway inflammation. Although these increased levels did not correlate with changes in neutrophil percentage in BAL, a positive association between adenosine levels and signs of lower airway inflammation (clinical score) was observed. These novel findings support the hypothesis that adenosine may contribute to bronchoconstriction and also act as a pro-inflammatory mediator in the bronchoalveolar milieu of horses with airway inflammation. Further investigation of this axis could lead to new approaches for the treatment of highly prevalent lower airway inflammatory conditions in the horse.

The effect of adenosine on pro-inflammatory cytokine production by porcine T cells

Adenosine is a well described anti-inflammatory modulator of immune responses. The aim of the present study was to describe the role of common adenosine agonist 5'-N-ethylcarboxamidoadenosine (NECA) in cytokine production by main porcine T cell subpopulations. TNF-α, IFN-γ, IL-2 and IL-10 were detected by multicolor flow cytometry together with cell surface markers CD3, CD4 and CD8. It was found that NECA inhibits (in a dose-dependent manner) production of pro-inflammatory TNF-α and Th1-associated cytokines IFN-γ, IL-2 in all concanavalin A-stimulated T cell subpopulations. Moreover, production of IL-10 was potentiated in all T cell subpopulations tested. These corresponded well with the fact that all T cell subsets expressed mRNA for adenosine receptor (AR) subtypes to comparable extents. Contrary to concanavalin A-stimulated cells, NECA had a moderate effect on PMA-stimulated T cells, suggesting that AR in pigs acts via signaling pathways not associated with protein-kinase C. Non-selective antagonist CGS15943 as well as allosteric modulator SCH202676 failed to reverse the effect of NECA in pigs. In conclusion, NECA has an anti-inflammatory effect on porcine T cell subpopulations.

Use of Propentofylline in Feline Bronchial Disease: Prospective, Randomized, Positive-Controlled Study

Propentofylline is a methylxanthine derivative with bronchodilating actions similar to those of theophylline. Nineteen cats with bronchial disease were enrolled in this study. All cats received a low dose of prednisolone; 10 of the cats additionally received propentofylline. Propentofylline-treated cats significantly improved in their auscultation scores, respiratory pattern scores, and radiological bronchial markings score over the observation period, and they coughed less and slept less at the end of the study. No significant changes were noted in the control group. This study provides evidence that a combination therapy with prednisolone and propentofylline in cats with bronchial disease might be superior over monotherapy with prednisolone.

Airway hyperresponsiveness to adenosine 5'-monophosphate in feline chronic inflammatory lower airway disease

Airway hyperresponsiveness is a key feature of human asthma and chronic bronchitis and response to the indirectly acting agonist adenosine 5'-monophosphate (AMP) is thought to reflect underlying airway inflammation. To examine whether airway responsiveness testing (ART) with AMP may be used to differentiate healthy cats from those with asthma (FA) and chronic bronchitis (CB), 24 cats (9 FA, 6 CB, 9 controls) underwent ART with AMP at concentrations of 0.1, 1, 10, 100 and 500mg/mL using barometric whole body plethysmography. The defined endpoint of ART, an increase in enhanced pause (Penh) exceeding 300% of the post-saline value (baseline), was reached in 9/15 patients (7 FA, 2 CB), but in none of the controls. Mean Penh (±SD) at baseline (BL) was 0.49±0.16 for cases, and 0.54±0.16 for controls, and was significantly increased after AMP challenge in clinical cases (2.62±2.20), but not in controls (0.63±0.30, P<0.05). After separating responder (R) and non-responder (NR) cases, a more pronounced difference after challenge was found (R: 3.96±1.84, NR: 0.6±0.21, P<0.001). The provocative concentration of the agonist that increased Penh to 300% of BL (PC Penh 300) in R cases was 52.98±48.04mg/mL AMP. Age had no influence on the responder status or PC Penh 300. It was concluded that AMP challenge may offer a new method for the identification of cats with lower inflammatory airway disease, and possibly for monitoring disease progression or response to therapy.

Recovery of respiratory activity after C2 hemisection (C2HS): involvement of adenosinergic mechanisms

Consequences of spinal cord injury (SCI) depend on the level and extent of injury. Cervical SCI often results in a compromised respiratory system. Primary treatment of SCI patients with respiratory insufficiency continues to be with mechanical ventilatory support. In an animal model of SCI, an upper cervical spinal cord hemisection paralyzes the hemidiaphragm ipsilateral to the side of injury. However, a latent respiratory motor pathway can be activated to restore respiratory function after injury. In this review, restoration of respiratory activity following systemic administration of theophylline, a respiratory stimulant will be discussed. Pharmacologically, theophylline is a non-specific adenosine receptor antagonist, a phosphodiesterase inhibitor and a bronchodilator. It has been used in the treatment of asthma and other respiratory-related diseases such as chronic obstructive pulmonary disease (COPD) and in treatment of apnea in premature infants. However, the clinical use of theophylline to improve respiration in SCI patients with respiratory deficits is a more recent approach. This review will focus on the use of theophylline to restore respiratory activity in an animal model of SCI. In this model, a C2 hemisection (C2HS) interrupts the major descending respiratory pathways and paralyzes the ipsilateral hemidiaphragm. The review also highlights involvement of central and peripheral adenosine receptors in functional restitution. Biochemical binding assays that highlight changes in adenosine receptors after chronic theophylline administration are discussed as they pertain to understanding adenosine receptor-mediation in functional recovery. Finally, the clinical application of theophylline in SCI patients with respiratory deficits in particular is discussed.