Myocardial energy metabolism in ischemic preconditioning, role of adenosine catabolism

Brief episodes of ischemia and reperfusion render the myocardium more resistant to necrosis from a subsequent, otherwise lethal ischemic insult. This phenomenon is called ischemic preconditioning(IP). Today, much is known about the signalling pathways involved in IP; however, the details of the final steps leading to cardioprotection, remain elusive. Adenosine (a catabolite of ATP) plays a major role in the signalling pathways of IP. Following IP there is an unexplained discrepancy between an increased adenosine production (evidenced by increased 5’-nucleotidase activity) and the successively lower adenosine levels observed in the interstitial space. We propose that this discrepancy in adenosine production vs. availability may be due to an increased metabolic utilisation of adenosine by the IP myocardium. According to our hypothesis, IP induces/activates a metabolic pathway involving deamination of adenosine to inosine. Inosine is further catalysed (in presence of Pi) to hypoxanthine and ribose-1-phosphate. Ribose-1-phosphate can be converted to ribose-5-phosphate in a phosphoribomutase reaction. Ribose-5-phosphate is an intermediate of the hexose monophosphate pathway also operative under anaerobic conditions. Hence the ribose moiety of adenosine can be utilised to generate pyruvate and ultimately ATP (via lactate formation) n.b. without any initial ATP investment. Such cost-effective adenosine utilisation may at least partly explain the cardioprotective effect of IP. Objectives & Methods: In the current studies we investigated the role of adenosine metabolism according to the suggested metabolic pathway by addition of adenosine and inhibition of its metabolism during IP as well as by comparing tissue and interstitial levels of key energy-metabolites following different protocols of IP. Furthermore, we studied the importance of the IP protocol with regard to the number of ischemia and reperfusion cycles for the cardioprotective effect of IP. In addition, the validity of the microdialysis technique for experimental in vivo studies of myocardial energy metabolism was evaluated. For these purposes the microdialysis technique, tissue biopsies, and planimetric infarct size estimation in an open chest porcine heart-model was used. Results: Addition of adenosine via microdialysis probes enhanced the interstitial release of inosine, hypoxanthine and lactate in the myocardium of IP-subjects during prolonged ischemia. This finding did not occur in non-preconditioned subjects. Similar addition of deoxyadenosine a non-metabolizable adenosine receptor-agonist, did not evoke the same metabolic response. Purine nucleoside phosphorylase (PNP) is responsible for the conversion of inosine to hypoxanthine being a key enzyme in the above mentioned metabolic pathway. Inclusion of 8' aminoguanosine (a competitive inhibitor of PNP) decreased interstitial hypoxanthine release (as a token of PNP inhibition) and increased the release of taurine (marker of cellular injury) in the ischemic IP myocardium. Addition of inosine (a natural substrate of PNP) reverted these changes. Four IP cycles protected the heart more than one IP cycle as evidenced by morphometric and energy-metabolic data.Proportionally more hypoxanthine was found in the myocardium of IP subjects during prolonged ischemia. The ratio of tissue levels of inosine/hypoxanthine (used as an indicator of PNP activity) was significantly smaller in the IP groups. In addition, myocardial interstitial levels of energy-related metabolites (lactate, adenosine, inosine, and hypoxanthine) obtained by the microdialysis technique correlated with tissue biopsy levels of corresponding metabolites. Conclusions: IP activated a metabolic pathway favouring metabolism of exogenous adenosine to inosine, hypoxanthine and eventually lactate. Inhibition of adenosine metabolism following IP (via inhibition of PNP-activity resulted in enhanced cellular injury. PNP-activity is proportionally higher in IP-myocardium. Metabolic utilisation of adenosine in IP-myocardium (as outlined above) may represent a costeffective way to produce ATP and at least partly explain the cardioprotective effect of IP. IP protects the myocardium in a graded fashion. Furthermore, we confirmed the validity of the microdialysis technique (in the current setting) for studying dynamic changes of myocardial energy metabolism

Predicting mortality during long-term follow-up in pulmonary arterial hypertension

The European Society of Cardiology (ESC) and European Respiratory Society (ERS) guideline recommendation of comprehensive risk assessments, which classify patients with pulmonary arterial hypertension (PAH) as having low, intermediate or high mortality risk, has not been evaluated during long-term follow-up in a "real-life" clinical setting. We therefore aimed to investigate the utility of risk assessment in a clinical setting for up to 5 years post diagnosis. 386 patients with PAH from the Swedish PAH Registry were included. Risk group (low/intermediate/ high) and proportion of low-risk variables were investigated at 3-, 4- and 5-year follow-ups after time of diagnosis. In an exploratory analysis, survival rates of patients with low-intermediate or high-intermediate risk scores were compared. A low-risk profile was in multivariate Cox proportional hazards regressions found to be a strong, independent predictor of longer transplant-free survival (p&amp;lt;0.001) at the 3-, 4- and 5-year follow-ups. Also, for the 3-, 4- and 5-year follow-ups, survival rates significantly differed (p&amp;lt;0.001) between the three risk groups. Patients with a greater proportion of low-risk variables had better (p&amp;lt;0.001) survival rates. Patients with a high-intermediate risk score had worse survival rates (p&amp;lt;0.001) than those with a low-intermediate risk score. Results were similar when excluding patients with &amp;gt;= 3 risk factors for heart failure with preserved ejection fraction, atrial fibrillation and/or age &amp;gt;75 years at diagnosis. Our findings suggest that the ESC/ERS guideline strategy for comprehensive risk assessments in PAH is valid also during long-term follow-up in a "real-life" clinical setting.Funding Agencies|SPAHR; Actelion Pharmaceuticals Sweden AB; Bayer Health CareBayer AGBayer Healthcare Pharmaceuticals; Eli Lilly SwedenEli Lilly; GlaxoSmithKlineGlaxoSmithKline; NordInfu Care; PfizerPfizer; Swedish Association of Local Authorities and Regions</p

Early risk prediction in idiopathic versus connective tissue disease-associated pulmonary arterial hypertension : call for a refined assessment

Despite systematic screening and improved treatment strategies, the prognosis remains worse in patients with connective tissue disease-associated pulmonary arterial hypertension (CTD-PAH) compared to patients with idiopathic/hereditary pulmonary arterial hypertension (IPAH). We aimed to investigate differences in clinical characteristics, outcome and performance of the European Society of Cardiology (ESC)/ European Respiratory Society (ERS) risk stratification tool in these patient groups. This retrospective analysis included incident patients with CTD-PAH (n=197, of which 64 had interstitial lung disease, ILD) or IPAH (n=305) enrolled in the Swedish PAH Register (SPAHR) 2008-2019. Patients were classified as low, intermediate or high risk at baseline, according to the "SPAHR-equation". One-year survival, stratified by type of PAH, was investigated by Cox proportional regression. At baseline, CTD-PAH patients had lower diffusing capacity for carbon monoxide and lower haemoglobin but, at the same time, lower N-terminal prohormone-brain natriuretic peptide, longer 6 min walk distance, better haemodynamics and more often a low-risk profile. No difference in age, World Health Organisation functional class (WHO-FC) or renal function between groups was found. One-year survival rates were 75, 82 and 83% in patients with CTD-PAH with ILD, CTD-PAH without ILD and IPAH, respectively. The 1-year mortality rates for low-, intermediate- and high-risk groups in the whole cohort were 0, 18 and 34% (p&amp;lt;0.001), respectively. Corresponding percentages for CTD-PAH with ILD, CTD-PAH without ILD and IPAH patients were: 0, 26, 67% (p=0.008); 0, 19, 39% (p=0.004); and 0, 16, 29% (p=0.001), respectively. The ESC/ERS risk assessment tool accurately identified low-risk patients but underestimated the 1-year mortality rate of CTD-PAH and IPAH patients assessed as having intermediate risk at diagnosis.Funding Agencies|Swedish Research CouncilSwedish Research CouncilEuropean Commission; Medical Faculty of Lund University; Swedish Rheumatism Association, King Gustaf V 80-year Fund; Osterlund Foundation; Kock Foundation; EULAR Orphan Disease Programme</p

Risk stratification in chronic thromboembolic pulmonary hypertension predicts survival

To investigate if the pulmonary arterial hypertension (PAH) risk assessment tool presented in the 2015 ESC/ERS guidelines is valid for patients with chronic thromboembolic pulmonary hypertension (CTEPH) when taking pulmonary endarterectomy (PEA) into account. Design. Incident CTEPH patients registered in the Swedish PAH Registry (SPAHR) between 2008 and 2016 were included. Risk stratification performed at baseline and follow-up classified the patients as low-, intermediate-, or high-risk using the proposed ESC/ERS risk algorithm. Results. There were 250 CTEPH patients with median age (interquartile range) 70 (14) years, and 53% were male. Thirty-two percent underwent PEA within 5 (6) months. In a multivariable model adjusting for age, sex, and pharmacological treatment, patients with intermediate-risk or high-risk profiles at baseline displayed an increased mortality risk (Hazard Ratio [95% confidence interval]: 1.64 [0.69-3.90] and 5.39 [2.13-13.59], respectively) compared to those with a low-risk profile, whereas PEA was associated with better survival (0.38 [0.18-0.82]). Similar impact of risk profile and PEA was seen at follow-up. Conclusion. The ESC/ERS risk assessment tool identifies CTEPH patients with reduced survival. Furthermore, PEA improves survival markedly independently of risk group and age. Take home message: The ESC/ERS risk stratification for PAH predicts survival also in CTEPH patients, even when taking PEA into account.Funding agencies: Financial support was provided by an unrestricted research grant from the Swedish Society for Pulmonary Hypertension to A.S; ActelionPharmaceuticals Sweden AB, Bayer Health Care; Eli Lilly Sweden; GlaxoSmithKline AB,; Nordic Infu Care; Pfizer AB. Since 2011, SPAHR is a national quality registry and the Swedish Association of Local Authorities and Regions give financial support. The financial supporters had no role in data collection, analysis or interpretationand no right in disapproving the manuscript.</p