Naked mole-rats have distinctive cardiometabolic and genetic adaptations to their underground low-oxygen lifestyles.

The naked mole-rat Heterocephalus glaber is a eusocial mammal exhibiting extreme longevity (37-year lifespan), extraordinary resistance to hypoxia and absence of cardiovascular disease. To identify the mechanisms behind these exceptional traits, metabolomics and RNAseq of cardiac tissue from naked mole-rats was compared to other African mole-rat genera (Cape, Cape dune, Common, Natal, Mahali, Highveld and Damaraland mole-rats) and evolutionarily divergent mammals (Hottentot golden mole and C57/BL6 mouse). We identify metabolic and genetic adaptations unique to naked mole-rats including elevated glycogen, thus enabling glycolytic ATP generation during cardiac ischemia. Elevated normoxic expression of HIF-1α is observed while downstream hypoxia responsive-genes are down-regulated, suggesting adaptation to low oxygen environments. Naked mole-rat hearts show reduced succinate levels during ischemia compared to C57/BL6 mouse and negligible tissue damage following ischemia-reperfusion injury. These evolutionary traits reflect adaptation to a unique hypoxic and eusocial lifestyle that collectively may contribute to their longevity and health span.

Determinants of COVID-19 immunisation uptake in a country with high mortality and a low vaccination rate.

BACKGROUND: Research concerned with attitudes towards COVID-19 vaccination in upper middle-income countries such as Bosnia and Herzegovina (B&H) is scarce. Currently, B&H has the lowest number of fully vaccinated adults in Europe, and the highest cumulative number of COVID-19 deaths and SARS-CoV-2 infected individuals. The aim of our study was to examine the factors associated with COVID-19 vaccination status in B&H. METHODS: An online survey among 1304 B&H adults was conducted in October 2021 evaluating vaccine acceptance, together with socio-demographic variables, attitudes and beliefs related to COVID-19 vaccination. RESULTS: The results from a binary logistic regression indicate that those who believed that the COVID-19 vaccine was effective were 45 times more likely to be vaccinated compared to those who did not. We also show that those who had received childhood immunisations were 41 times more likely to be vaccinated against COVID-19 compared to those who had never been previously immunised. Other significant factors were related to respondents' trust in government institutions and healthcare policymakers as well as trust in public healthcare workers. CONCLUSION: We suggest that future vaccination campaigns should be aimed at educating the public regarding the importance and safety of vaccines, together with strengthening trust in the public health system.

Diagnostic and prognostic biomarkers reflective of cardiac remodelling in diabetes mellitus: A scoping review.

AIMS: The aim of this scoping review is to evaluate the current biomarkers used in the assessment of adverse cardiac remodelling in people with diabetes mellitus (DM) and in the diagnosis and prognosis of subsequent cardiovascular disease. We aim to discuss the biomarkers' pathophysiological roles as a reflection of the cardiac remodelling mechanisms in the presence of DM. METHODS: We performed the literature search to include studies from 2003 to 2021 using the following databases: MEDLINE, Scopus, Web of Science, PubMed, and Cochrane library. Articles that met our inclusion criteria were screened and appraised before being included in this review. The PRISMA guidelines for Scoping Reviews were followed. RESULTS: Our literature search identified a total of 43 eligible articles, which were included in this scoping review. We identified 15 different biomarkers, each described by at least two studies, that were used to determine signs of cardiac remodelling in cardiovascular disease (CVD) and people with DM. NT-proBNP was identified as the most frequently employed biomarker in this context; however, we also identified emerging biomarkers including hs-CRP, hs-cTnT, and Galectin-3. CONCLUSION: There is a complex relationship between DM and cardiovascular health, where more research is needed. Current biomarkers reflective of adverse cardiac remodelling in DM are often used to diagnose other CVDs, such as NT-proBNP for heart failure. Hence there is a need for identification of specific biomarkers that can detect early signs of cardiac remodelling in the presence of DM. Further research into these biomarkers and mechanisms can deepen our understanding of their role in DM-associated CVD and lead to better preventative therapies.

Fasting increases susceptibility to acute myocardial ischaemia/reperfusion injury through a sirtuin-3 mediated increase in fatty acid oxidation.

Fasting increases susceptibility to acute myocardial ischaemia/reperfusion injury (IRI) but the mechanisms are unknown. Here, we investigate the role of the mitochondrial NAD+-dependent deacetylase, Sirtuin-3 (SIRT3), which has been shown to influence fatty acid oxidation and cardiac outcomes, as a potential mediator of this effect. Fasting was shown to shift metabolism from glucose towards fatty acid oxidation. This change in metabolic fuel substrate utilisation increased myocardial infarct size in wild-type (WT), but not SIRT3 heterozygous knock-out (KO) mice. Further analysis revealed SIRT3 KO mice were better adapted to starvation through an improved cardiac efficiency, thus protecting them from acute myocardial IRI. Mitochondria from SIRT3 KO mice were hyperacetylated compared to WT mice which may regulate key metabolic processes controlling glucose and fatty acid utilisation in the heart. Fasting and the associated metabolic switch to fatty acid respiration worsens outcomes in WT hearts, whilst hearts from SIRT3 KO mice are better adapted to oxidising fatty acids, thereby protecting them from acute myocardial IRI.

Artificial intelligence in cardiology: Hope for the future and power for the present.

Cardiovascular disease (CVD) is the principal cause of mortality and morbidity globally. With the pressures for improved care and translation of the latest medical advances and knowledge to an actionable plan, clinical decision-making for cardiologists is challenging. Artificial Intelligence (AI) is a field in computer science that studies the design of intelligent agents which take the best feasible action in a situation. It incorporates the use of computational algorithms which simulate and perform tasks that traditionally require human intelligence such as problem solving and learning. Whilst medicine is arguably the last to apply AI in its everyday routine, cardiology is at the forefront of AI revolution in the medical field. The development of AI methods for accurate prediction of CVD outcomes, non-invasive diagnosis of coronary artery disease (CAD), detection of malignant arrythmias through wearables, and diagnosis, treatment strategies and prediction of outcomes for heart failure (HF) patients, demonstrates the potential of AI in future cardiology. With the advancements of AI, Internet of Things (IoT) and the promotion of precision medicine, the future of cardiology will be heavily based on these innovative digital technologies. Despite this, ethical dilemmas regarding the implementation of AI technologies in real-world are still unaddressed.

Ischemia-Selective Cardioprotection by Malonate for Ischemia/Reperfusion Injury.

BACKGROUND: Inhibiting SDH (succinate dehydrogenase), with the competitive inhibitor malonate, has shown promise in ameliorating ischemia/reperfusion injury. However, key for translation to the clinic is understanding the mechanism of malonate entry into cells to enable inhibition of SDH, its mitochondrial target, as malonate itself poorly permeates cellular membranes. The possibility of malonate selectively entering the at-risk heart tissue on reperfusion, however, remains unexplored. METHODS: C57BL/6J mice, C2C12 and H9c2 myoblasts, and HeLa cells were used to elucidate the mechanism of selective malonate uptake into the ischemic heart upon reperfusion. Cells were treated with malonate while varying pH or together with transport inhibitors. Mouse hearts were either perfused ex vivo (Langendorff) or subjected to in vivo left anterior descending coronary artery ligation as models of ischemia/reperfusion injury. Succinate and malonate levels were assessed by liquid chromatography-tandem mass spectrometry LC-MS/MS, in vivo by mass spectrometry imaging, and infarct size by TTC (2,3,5-triphenyl-2H-tetrazolium chloride) staining. RESULTS: Malonate was robustly protective against cardiac ischemia/reperfusion injury, but only if administered at reperfusion and not when infused before ischemia. The extent of malonate uptake into the heart was proportional to the duration of ischemia. Malonate entry into cardiomyocytes in vivo and in vitro was dramatically increased at the low pH (≈6.5) associated with ischemia. This increased uptake of malonate was blocked by selective inhibition of MCT1 (monocarboxylate transporter 1). Reperfusion of the ischemic heart region with malonate led to selective SDH inhibition in the at-risk region. Acid-formulation greatly enhances the cardioprotective potency of malonate. CONCLUSIONS: Cardioprotection by malonate is dependent on its entry into cardiomyocytes. This is facilitated by the local decrease in pH that occurs during ischemia, leading to its selective uptake upon reperfusion into the at-risk tissue, via MCT1. Thus, malonate's preferential uptake in reperfused tissue means it is an at-risk tissue-selective drug that protects against cardiac ischemia/reperfusion injury.

Rapid and selective generation of H2S within mitochondria protects against cardiac ischemia-reperfusion injury.

Mitochondria-targeted H2S donors are thought to protect against acute ischemia-reperfusion (IR) injury by releasing H2S that decreases oxidative damage. However, the rate of H2S release by current donors is too slow to be effective upon administration following reperfusion. To overcome this limitation here we develop a mitochondria-targeted agent, MitoPerSulf that very rapidly releases H2S within mitochondria. MitoPerSulf is quickly taken up by mitochondria, where it reacts with endogenous thiols to generate a persulfide intermediate that releases H2S. MitoPerSulf is acutely protective against cardiac IR injury in mice, due to the acute generation of H2S that inhibits respiration at cytochrome c oxidase thereby preventing mitochondrial superoxide production by lowering the membrane potential. Mitochondria-targeted agents that rapidly generate H2S are a new class of therapy for the acute treatment of IR injury.

Cardiac metabolic remodelling in chronic kidney disease.

Chronic kidney disease (CKD) affects millions of people globally and, for most patients, the risk of developing cardiovascular disease is higher than that of progression to kidney failure. Moreover, mortality owing to cardiovascular complications in patients with CKD is markedly higher than in matched individuals from the general population. This mortality was traditionally thought to be driven by coronary heart disease but >75% of patients with CKD have left ventricular hypertrophy, which contributes to mortality, particularly sudden cardiac death. The aetiology of cardiac complications in CKD is multifactorial. In addition to haemodynamic overload, uraemic toxin accumulation and altered ion homeostasis, which are known to underlie left ventricular hypertrophy in CKD and drive cardiac dysfunction, we examine the role of myocardial metabolic remodelling in CKD. Uraemic cardiomyopathy is characterized by myriad cardiac metabolic maladaptations, including altered mitochondrial function, changes in myocardial substrate utilization, altered metabolic transporter function and expression, and impaired insulin response and phosphoinositide-3 kinase-AKT signalling, which collectively lead to impaired cardiac energetics. Interestingly, none of the standard treatments used to treat CKD target the metabolism of the uraemic heart directly. An improved understanding of the cardiac metabolic perturbations that occur in CKD might allow the development of novel treatments for uraemic cardiomyopathy.

Loss of voltage-gated hydrogen channel 1 expression reveals heterogeneous metabolic adaptation to intracellular acidification by T cells.

Voltage-gated hydrogen channel 1 (Hvcn1) is a voltage-gated proton channel, which reduces cytosol acidification and facilitates the production of ROS. The increased expression of this channel in some cancers has led to proposing Hvcn1 antagonists as potential therapeutics. While its role in most leukocytes has been studied in depth, the function of Hvcn1 in T cells remains poorly defined. We show that Hvcn1 plays a nonredundant role in protecting naive T cells from intracellular acidification during priming. Despite sharing overall functional impairment in vivo and in vitro, Hvcn1-deficient CD4+ and CD8+ T cells display profound differences during the transition from naive to primed T cells, including in the preservation of T cell receptor (TCR) signaling, cellular division, and death. These selective features result, at least in part, from a substantially different metabolic response to intracellular acidification associated with priming. While Hvcn1-deficient naive CD4+ T cells reprogram to rescue the glycolytic pathway, naive CD8+ T cells, which express high levels of this channel in the mitochondria, respond by metabolically compensating mitochondrial dysfunction, at least in part via AMPK activation. These observations imply heterogeneity between adaptation of naive CD4+ and CD8+ T cells to intracellular acidification during activation.

Impact of reduced uterine perfusion pressure model of preeclampsia on metabolism of placenta, maternal and fetal hearts.

Preeclampsia is a cardiovascular pregnancy complication characterised by new onset hypertension and organ damage or intrauterine growth restriction. It is one of the leading causes of maternal and fetal mortality in pregnancy globally. Short of pre-term delivery of the fetus and placenta, treatment options are limited. Consequently, preeclampsia leads to increased cardiovascular disease risk in both mothers and offspring later in life. Here we aim to examine the impact of the reduced uterine perfusion pressure (RUPP) rat model of preeclampsia on the maternal cardiovascular system, placental and fetal heart metabolism. The surgical RUPP model was induced in pregnant rats by applying silver clips around the aorta and uterine arteries on gestational day 14, resulting in ~ 40% uterine blood flow reduction. The experiment was terminated on gestational day 19 and metabolomic profile of placentae, maternal and fetal hearts analysed using high-resolution 1H NMR spectroscopy. Impairment of uterine perfusion in RUPP rats caused placental and cardiac hypoxia and a series of metabolic adaptations: altered energetics, carbohydrate, lipid and amino acid metabolism of placentae and maternal hearts. Comparatively, the fetal metabolic phenotype was mildly affected. Nevertheless, long-term effects of these changes in both mothers and the offspring should be investigated further in the future.

Senescence and Type 2 Diabetic Cardiomyopathy: How Young Can You Die of Old Age?

Inflammation is well understood to be a physiological process of ageing however it also underlies many chronic diseases, including conditions without an obvious pathogenic inflammatory element. Recent findings have unequivocally identified type 2 diabetes (T2D) as a chronic inflammatory disease characterized by inflammation and immune senescence. Immunosenescence is a hallmark of the prolonged low-grade systemic inflammation, in particular associated with metabolic syndrome and can be a cause as well as a consequence of T2D. Diabetes is a risk factor for cardiovascular mortality and remodelling and with particular changes to myocardial structure, function, metabolism and energetics collectively resulting in diabetic cardiomyopathy. Both cardiomyocytes and immune cells undergo metabolic remodelling in T2D and as a result become trapped in a vicious cycle of lost metabolic flexibility, thus losing their key adaptive mechanisms to dynamic changes in O2 and nutrient availability. Immunosenescence driven by metabolic stress may be both the cause and key contributing factor to cardiac dysfunction in diabetic cardiomyopathy by inducing metabolic perturbations that can lead to impaired energetics, a strong predictor of cardiac mortality. Here we review our current understanding of the cross-talk between inflammaging and cardiomyocytes in T2D cardiomyopathy. We discuss potential mechanisms of metabolic convergence between cell types which, we hypothesize, might tip the balance between resolution of the inflammation versus adverse cardiac metabolic remodelling in T2D cardiomyopathy. A better understanding of the multiple biological paradigms leading to T2D cardiomyopathy including the immunosenescence associated with inflammaging will provide a powerful target for successful therapeutic interventions.

Nectar-feeding bats and birds show parallel molecular adaptations in sugar metabolism enzymes.

In most vertebrates, the demand for glucose as the primary substrate for cellular respiration is met by the breakdown of complex carbohydrates, or energy is obtained by protein and lipid catabolism. In contrast, a few bat and bird species have convergently evolved to subsist on nectar, a sugar-rich mixture of glucose, fructose, and sucrose.1-4 How these nectar-feeders have adapted to cope with life-long high sugar intake while avoiding the onset of metabolic syndrome and diabetes5-7 is not understood. We analyzed gene sequences obtained from 127 taxa, including 22 nectar-feeding bat and bird genera that collectively encompass four independent origins of nectarivory. We show these divergent taxa have undergone pervasive molecular adaptation in sugar catabolism pathways, including parallel selection in key glycolytic and fructolytic enzymes. We also uncover convergent amino acid substitutions in the otherwise evolutionarily conserved aldolase B (ALDOB), which catalyzes rate-limiting steps in fructolysis and glycolysis, and the mitochondrial gatekeeper pyruvate dehydrogenase (PDH), which links glycolysis and the tricarboxylic acid cycle. Metabolomic profile and enzyme functional assays are consistent with increased respiratory flux in nectar-feeding bats and help explain how these taxa can both sustain hovering flight and efficiently clear simple sugars. Taken together, our results indicate that nectar-feeding bats and birds have undergone metabolic adaptations that have enabled them to exploit a unique energy-rich dietary niche among vertebrates.

With a grain of salt: Sodium elevation and metabolic remodelling in heart failure.

Elevated intracellular Na (Nai) and metabolic impairment are interrelated pathophysiological features of the failing heart (HF). There have been a number of studies showing that myocardial sodium elevation subtly affects mitochondrial function. During contraction, mitochondrial calcium (Camito) stimulates a variety of TCA cycle enzymes, thereby providing reducing equivalents to maintain ATP supply. Nai elevation has been shown to impact Camito; however, whether metabolic remodelling in HF is caused by increased Nai has only been recently demonstrated. This novel insight may help to elucidate the contribution of metabolic remodelling in the pathophysiology of HF, the lack of efficacy of current HF therapies and a rationale for the development of future metabolism-targeting treatments. Here we review the relationship between Na pump inhibition, elevated Nai, and altered metabolic profile in the context of HF and their link to metabolic (in)flexibility and mitochondrial reprogramming.

Structural basis for a complex I mutation that blocks pathological ROS production.

Mitochondrial complex I is central to the pathological reactive oxygen species (ROS) production that underlies cardiac ischemia-reperfusion (IR) injury. ND6-P25L mice are homoplasmic for a disease-causing mtDNA point mutation encoding the P25L substitution in the ND6 subunit of complex I. The cryo-EM structure of ND6-P25L complex I revealed subtle structural changes that facilitate rapid conversion to the "deactive" state, usually formed only after prolonged inactivity. Despite its tendency to adopt the "deactive" state, the mutant complex is fully active for NADH oxidation, but cannot generate ROS by reverse electron transfer (RET). ND6-P25L mitochondria function normally, except for their lack of RET ROS production, and ND6-P25L mice are protected against cardiac IR injury in vivo. Thus, this single point mutation in complex I, which does not affect oxidative phosphorylation but renders the complex unable to catalyse RET, demonstrates the pathological role of ROS production by RET during IR injury.

Mechanism of succinate efflux upon reperfusion of the ischaemic heart.

AIMS: Succinate accumulates several-fold in the ischaemic heart and is then rapidly oxidized upon reperfusion, contributing to reactive oxygen species production by mitochondria. In addition, a significant amount of the accumulated succinate is released from the heart into the circulation at reperfusion, potentially activating the G-protein-coupled succinate receptor (SUCNR1). However, the factors that determine the proportion of succinate oxidation or release, and the mechanism of this release, are not known. METHODS AND RESULTS: To address these questions, we assessed the fate of accumulated succinate upon reperfusion of anoxic cardiomyocytes, and of the ischaemic heart both ex vivo and in vivo. The release of accumulated succinate was selective and was enhanced by acidification of the intracellular milieu. Furthermore, pharmacological inhibition, or haploinsufficiency of the monocarboxylate transporter 1 (MCT1) significantly decreased succinate efflux from the reperfused heart. CONCLUSION: Succinate release upon reperfusion of the ischaemic heart is mediated by MCT1 and is facilitated by the acidification of the myocardium during ischaemia. These findings will allow the signalling interaction between succinate released from reperfused ischaemic myocardium and SUCNR1 to be explored.

Intracellular sodium elevation reprograms cardiac metabolism.

Intracellular Na elevation in the heart is a hallmark of pathologies where both acute and chronic metabolic remodelling occurs. Here, we assess whether acute (75 µM ouabain 100 nM blebbistatin) or chronic myocardial Nai load (PLM3SA mouse) are causally linked to metabolic remodelling and whether the failing heart shares a common Na-mediated metabolic 'fingerprint'. Control (PLMWT), transgenic (PLM3SA), ouabain-treated and hypertrophied Langendorff-perfused mouse hearts are studied by 23Na, 31P, 13C NMR followed by 1H-NMR metabolomic profiling. Elevated Nai leads to common adaptive metabolic alterations preceding energetic impairment: a switch from fatty acid to carbohydrate metabolism and changes in steady-state metabolite concentrations (glycolytic, anaplerotic, Krebs cycle intermediates). Inhibition of mitochondrial Na/Ca exchanger by CGP37157 ameliorates the metabolic changes. In silico modelling indicates altered metabolic fluxes (Krebs cycle, fatty acid, carbohydrate, amino acid metabolism). Prevention of Nai overload or inhibition of Na/Camito may be a new approach to ameliorate metabolic dysregulation in heart failure.

Preservation of microvascular barrier function requires CD31 receptor-induced metabolic reprogramming.

Endothelial barrier (EB) breaching is a frequent event during inflammation, and it is followed by the rapid recovery of microvascular integrity. The molecular mechanisms of EB recovery are poorly understood. Triggering of MHC molecules by migrating T-cells is a minimal signal capable of inducing endothelial contraction and transient microvascular leakage. Using this model, we show that EB recovery requires a CD31 receptor-induced, robust glycolytic response sustaining junction re-annealing. Mechanistically, this response involves src-homology phosphatase activation leading to Akt-mediated nuclear exclusion of FoxO1 and concomitant ß-catenin translocation to the nucleus, collectively leading to cMyc transcription. CD31 signals also sustain mitochondrial respiration, however this pathway does not contribute to junction remodeling. We further show that pathologic microvascular leakage in CD31-deficient mice can be corrected by enhancing the glycolytic flux via pharmacological Akt or AMPK activation, thus providing a molecular platform for the therapeutic control of EB response.

Vascular KATP channels protect from cardiac dysfunction and preserve cardiac metabolism during endotoxemia.

KATP channels in the vasculature composed of Kir6.1 regulate vascular tone and may contribute to the pathogenesis of endotoxemia. We used mice with cell-specific deletion of Kir6.1 in smooth muscle (smKO) and endothelium (eKO) to investigate this question. We found that smKO mice had a significant survival disadvantage compared with their littermate controls when treated with a sub-lethal dose of lipopolysaccharide (LPS). All cohorts of mice became hypotensive following bacterial LPS administration; however, mean arterial pressure in WT mice recovered to normal levels, whereas smKO struggled to overcome LPS-induced hypotension. In vivo and ex vivo investigations revealed pronounced cardiac dysfunction in LPS-treated smKO, but not in eKO mice. Similar results were observed in a cecal slurry injection model. Metabolomic profiling of hearts revealed significantly reduced levels of metabolites involved in redox/energetics, TCA cycle, lipid/fatty acid and amino acid metabolism. Vascular smooth muscle-localised KATP channels have a critical role in the response to systemic infection by normalising cardiac function and haemodynamics through metabolic homeostasis. KEY MESSAGES: • Mice lacking vascular KATP channels are more susceptible to death from infection. • Absence of smooth muscle KATP channels depresses cardiac function during infection. • Cardiac dysfunction is accompanied by profound changes in cellular metabolites. • Findings from this study suggest a protective role for vascular KATP channels in response to systemic infection.

Cardiac metabolomic profile of the naked mole-rat-glycogen to the rescue.

The African naked mole-rat (Heterocephalus glaber) is unique among mammals, displaying extreme longevity, resistance to cardiovascular disease and an ability to survive long periods of extreme hypoxia. The metabolic adaptations required for resistance to hypoxia are hotly debated and a recent report provides evidence that they are able to switch from glucose to fructose driven glycolysis in the brain. However, other systemic alterations in their metabolism are largely unknown. In the current study, a semi-targeted high resolution 1H magnetic resonance spectroscopy (MRS) metabolomics investigation was performed on cardiac tissue from the naked mole-rat (NMR) and wild-type C57/BL6 mice to better understand these adaptations. A range of metabolic differences was observed in the NMR including increased lactate, consistent with enhanced rates of glycolysis previously reported, increased glutathione, suggesting increased resistance to oxidative stress and decreased succinate/fumarate ratio suggesting reduced oxidative phosphorylation and ROS production. Surprisingly, the most significant difference was an elevation of glycogen stores and glucose-1-phosphate resulting from glycogen turnover, that were completely absent in the mouse heart and above the levels found in the mouse liver. Thus, we identified a range of metabolic adaptations in the NMR heart that are relevant to their ability to survive extreme environmental pressures and metabolic stress. Our study underscores the plasticity of energetic pathways and the need for compensatory strategies to adapt in response to the physiological and pathological stress including ageing and ischaemic heart pathologies.