Life-long sports engagement enhances adult erythrocyte adenylate energetics

Regular physical activity reduces age-related metabolic and functional decline. The energy stored in adenine nucleotides (ATP, ADP, and AMP) is essential to enable multiple vital functions of erythrocytes and body tissues. Our study aimed to predict the rate of age-related changes in erythrocyte adenylate energetics in athletes and untrained controls. The erythrocyte concentration of adenylates was measured in 68 elite endurance runners (EN, 20–81 years), 58 elite sprinters (SP, 21–90 years), and 62 untrained individuals (CO, 20–68 years). Resting concentrations of ATP, total adenine nucleotide pool, and ADP/AMP ratio were lowest in the CO group and highest in the SP group. The concentration of erythrocyte ADP and AMP was lowest in the EN group and highest in the CO group. In all studied groups, we found a significant increase in the concentration of most erythrocyte adenylate metabolites with age. For ADP and AMP, the trend was also significant but decreasing. Our study strongly suggests that lifelong sports and physical activity participation supports erythrocyte energetics preservation. Although the direction and the predicted rates of change are similar regardless of the training status, the concentrations of particular metabolites are more advantageous in highly trained athletes than in less active controls. Of the two analyzed types of physical training, sprint-oriented training seems to be more efficient in enhancing erythrocyte metabolism throughout adulthood and old age than endurance training.

The Complementary Roles of Chloroplast Cyclic Electron Transport and Mitochondrial Alternative Oxidase to Ensure Photosynthetic Performance

Chloroplasts use light energy and a linear electron transport (LET) pathway for the coupled generation of NADPH and ATP. It is widely accepted that the production ratio of ATP to NADPH is usually less than required to fulfill the energetic needs of the chloroplast. Left uncorrected, this would quickly result in an over-reduction of the stromal pyridine nucleotide pool (i.e., high NADPH/NADP+ ratio) and under-energization of the stromal adenine nucleotide pool (i.e., low ATP/ADP ratio). These imbalances could cause metabolic bottlenecks, as well as increased generation of damaging reactive oxygen species. Chloroplast cyclic electron transport (CET) and the chloroplast malate valve could each act to prevent stromal over-reduction, albeit in distinct ways. CET avoids the NADPH production associated with LET, while the malate valve consumes the NADPH associated with LET. CET could operate by one of two different pathways, depending upon the chloroplast ATP demand. The NADH dehydrogenase-like pathway yields a higher ATP return per electron flux than the pathway involving PROTON GRADIENT REGULATION5 (PGR5) and PGR5-LIKE PHOTOSYNTHETIC PHENOTYPE1 (PGRL1). Similarly, the malate valve could couple with one of two different mitochondrial electron transport pathways, depending upon the cytosolic ATP demand. The cytochrome pathway yields a higher ATP return per electron flux than the alternative oxidase (AOX) pathway. In both Arabidopsis thaliana and Chlamydomonas reinhardtii, PGR5/PGRL1 pathway mutants have increased amounts of AOX, suggesting complementary roles for these two lesser-ATP yielding mechanisms of preventing stromal over-reduction. These two pathways may become most relevant under environmental stress conditions that lower the ATP demands for carbon fixation and carbohydrate export.

Inhibition of xanthine oxidase ameliorates functional and metabolic impairment in type 2 diabetic hearts under pressure overload

Background We recently reported that upregulated AMP deaminase (AMPD), via reduction in the tissue adenine nucleotide pool, contributes to exacerbation of diastolic dysfunction under pressure overload in OLETF, a rat model of obese type 2 diabetes (T2DM). Upregulated AMPD also possibly promotes xanthine oxidase (XO)-mediated ROS production, since AMPD deaminases AMP to IMP, which is further converted to inosine, providing substrates of XO, hypoxanthine and xanthine. Here, we examined the hypothesis that inhibition of XO ameliorates the pressure overload-induced diastolic dysfunction by suppression of ROS-mediated mitochondrial dysfunction and/or vascular dysfunction in T2DM rats. Methods and results Metabolomic analyses revealed that levels of xanthine and uric acid in the LV myocardium were significantly higher by 37% and 51%, respectively, in OLETF than in LETO, non-diabetic control rats, under the condition of phenylephrine-induced pressure overloading (200–230 mmHg). Myocardial XO activity in OLETF was 57.9% higher than that in LETO, which may be attributed to 31% higher level of inosine, a positive regulator of XO, in OLETF than in LETO. The activity of XO was significantly attenuated by administration of topiroxostat, an XO inhibitor at 0.5 mg/kg/day for 14 days. Pressure volume loop analyses showed that the pressure overloading resulted in significantly higher LVEDP in OLETF than in LETO (18.3±1.5 vs. 12.2±1.3 mmHg, p<0.05, n=7), though LVEDPs at baseline were comparable in OLETF and LETO (5.6±0.4 vs. 4.7±0.7 mmHg). Treatment with topiroxostat significantly suppressed the pressure overload-induced elevation of LVEDP in OLETF (18.3±1.5 vs. 11.3±1.1 mmHg, p<0.05) but not in LETO. Under the condition of pressure overloading, Ea/Ees, an index for ventricular-arterial coupling, was higher in OLETF than in LETO (2.3±0.3 vs. 1.6±0.3, p<0.05), and it was also improved by topiroxostat in OLETF (1.2±0.2, p<0.05). Myocardial ATP content was lower in OLETF than in LETO (2966±400 vs. 1818±171 nmol/g wet tissue, p<0.05), and treatment with topiroxostat significantly restored the ATP level (2629±307 nmol/g wet tissue). The LV myocardium of OLETF under pressure overload showed significantly higher level of malondialdehyde and 4-hydroxynonenal, an indicator of lipid peroxidation, than that of LETO. Measurement of oxygen consumption rate by Seahorse XFe96 Analyzer in mitochondria isolated from LV tissues revealed that state 3 respiration was significantly suppressed in OLETF by 43% compared to LETO, and it was restored by treatment with topiroxostat. Conclusion Both activity and substrates of XO are increased in T2DM hearts, in which upregulation of AMPD may play a role. Inhibition of XO ameliorates pressure overload-induced diastolic dysfunction and improves ventricular-arterial coupling in diabetic hearts, most likely through protection of mitochondrial function from ROS-mediated injury. Funding Acknowledgement Type of funding source: Public grant(s) – National budget only. Main funding source(s): Grant-in-aid for Scientific Research (#26461132, #17K09584) from the Japanese Society for the Promotion of Science

Mitochondrial antioxidant plastomitin alters the myocardial energy state and prevented the development of systolic dysfunction in doxorubicin-induced cardiomyopathy

Резюме Цель исследования. Настоящая работа предпринята с целью изучения влияния митохондриального антиоксиданта пластомитина (ПМ, препарат SkQ1) на энергетическое состояние и функцию сердца крыс с кардиомиопатией, вызванной введением доксорубицина (Докс). Материалы и методы. Использовали крыс-самцов Вистар, которым вводили подкожно Докс (2 мг/кг/нед.) в течение 5 недель (группа Докс). Животным группы Докс+ПМ наряду с доксорубицином 5 недель подкожно вводили ПМ в дозе 0,32 мг/кг ежедневно. Контрольной группе животных в течение 5 недель вводили такой же объем физиологического раствора. Перед началом введения препаратов и через 8 недель у всех крыс была выполнена эхокардиография (ЭхоКГ) левого желудочка (ЛЖ). Дополнительно у части животных была изучена сократительная функция ЛЖ при помощи PV-катетера. Содержание адениннуклеотидов (АТФ, АДФ и АМФ), фосфокреатина (ФКр), креатина (Кр) и лактата в безбелковых экстрактах сердец определяли энзиматическими методами. Дыхание митохондрий в скинированных сапонином волокнах ЛЖ определяли полярографическим методом. Результаты. В конце исследования у животных группы Докс фракция выброса и фракция укорочения были достоверно снижены, а диастолический объём ЛЖ уменьшен по сравнению с этими показателями в контрольной группе. В группе Докс+ПМ фракция выброса, фракция укорочения, индекс сократимости миокарда, максимальная скорость развития давления и работа сердца были выше, чем в группе Докс и недостоверно отличались от величин в контроле. Эти изменения сочетались с достоверным увеличением содержания общего фонда адениннуклеотидов и креатина в сердце животных группы Докс+ПМ по сравнению с этими показателями у животных, получавших только Докс. Показатели скорости дыхания митохондрий в волокнах ЛЖ, выделенных из сердец животных группы Докс+ПМ, были выше, чем в группе Докс. Заключение. Применение ПМ предотвращало развитие систолической дисфункции у животных, получавших Докс. Это было связано с улучшением окислительного фосфорилирования и сохранением фонда адениннуклеотидов в сердце Summary Aim. This study was designed to explore effects of the mitochondrial antioxidant plastomitin (PM) on the energy state and heart function of rats with cardiomyopathy induced by doxorubicin (Dox) administration. Material and methods. Male Wistar rats were injected subcutaneously with Dox (2 mg / kg / weekly) for 5 weeks (Dox group). Animals of the Dox + PM group were subcutaneously injected with PM for 5 weeks at a dose of 0.32 mg/kg daily along with Dox. The control group of animals was injected for 5 weeks with the same volume of saline. Before the administration of drugs and after 8 weeks of the study, all rats were underwented echocardiography of the left ventricle (LV). Additionally, the LV contractile function was studied using a PV catheter in some animals. The contents of adenine nucleotides (ATP, ADP and AMP), phosphocreatine (PCr), creatine (Cr) and lactate in protein-free extracts of hearts were determined by enzymatic methods. Mitochondrial respiration in saponin-skinned LV fibers was determined using the polarographic method. Results. At the end of the study, in animals of Dox group, the ejection fraction, fractional shortening and LV diastolic volume were significantly reduced in comparison with these indices in the control group. In Dox + PM group, the ejection fraction, fractional shortening, myocardial contractility index, maximum rate of pressure development and heart work were significantly higher than in Dox group and did not differ from the control values. These functional alterations were combined with a significant increase in the content of myocardial adenine nucleotide pool and creatine in animals of Dox + PM group compared with these parameters in animals treated with Dox alone.The rate of mitochondrial respiration in LV fibers isolated from the hearts of animals of Dox + PM group was higher than in Dox group. Conclusion. Treatment with PM prevented the development of LV systolic dysfunction in animals received Dox. This beneficial effect was due to an improvement in oxidative phosphorylation and preservation of myocardial adenine nucleotide pool.

The mechanisms of cardiac protection using a synthetic agonist of galanin receptors during chronic administration of doxorubicin

The use of the anticancer drug doxorubicin (Dox) is limited by its cardiotoxic effect. The aim of this work was to study the effect of a new synthetic agonist of the galanin receptor GalR1-3 [Ala14, His15]-galanine (215) (G) on the metabolism, antioxidant enzyme activity, and cardiac function in rats with cardiomyopathy (CM) caused by chronic administration of Dox. Coadministration of peptide G and Dox significantly increased the fractional shortening (FS) and ejection fraction (EF) by an average of 30 4% compared with the indices in the Dox group. The reduced severity of cardiac dysfunction under the action of G was accompanied by a 2.5-fold decrease in the activity of creatine kinase-MB (CK-MB) in blood plasma. The protective mechanism of the action of peptide G is caused by a reduced lipid peroxidation (LP) that is due to the increased activity of Cu,Zn superoxide dismutase (Cu,Zn-SOD) and glutathione peroxidase (GSH-Px) in the damaged heart. Administration of peptide G significantly increased the adenine nucleotide pool (AH), ATP content, and the levels of phosphocreatine (PCr) and total creatine (Cr) in the damaged myocardium. It also reduced lactate accumulation relative to its content in the Dox group. The better energy supply of cardiomyocytes after treatment with peptide G prevented the accumulation of cytotoxic ammonia and disruption in the metabolism of the key myocardial amino acids (glutamic acid (Glu), aspartic acid (Asp), and alanine (Ala)). Peptide G significantly improved the morphological parameters of the heart in rats treated with Dox. The results show promise in using peptide G to efficiently correct functional, morphological, and metabolic damage to the heart caused by anthracycline chemotherapy.

The Pancreatic β-Cell: A Bioenergetic Perspective

The pancreatic β-cell secretes insulin in response to elevated plasma glucose. This review applies an external bioenergetic critique to the central processes of glucose-stimulated insulin secretion, including glycolytic and mitochondrial metabolism, the cytosolic adenine nucleotide pool, and its interaction with plasma membrane ion channels. The control mechanisms responsible for the unique responsiveness of the cell to glucose availability are discussed from bioenergetic and metabolic control standpoints. The concept of coupling factor facilitation of secretion is critiqued, and an attempt is made to unravel the bioenergetic basis of the oscillatory mechanisms controlling secretion. The need to consider the physiological constraints operating in the intact cell is emphasized throughout. The aim is to provide a coherent pathway through an extensive, complex, and sometimes bewildering literature, particularly for those unfamiliar with the field.

MondoA senses adenine nucleotides: transcriptional induction of thioredoxin-interacting protein

The MondoA–Mlx transcription complex plays a pivotal role in glucose homoeostasis by activating target gene expression in response to G6P (glucose 6-phosphate), the first reaction intermediate in glycolysis. TXNIP (thioredoxin-interacting protein) is a direct and glucose-responsive target of MondoA that triggers a negative-feedback loop by restricting glucose uptake when G6P levels increase. We show in the present study that TXNIP expression is also activated by AICAR (5-amino-4-imidazolecarboxamide ribofuranoside) and adenosine. Using pharmacological inhibitors and genetic knockdowns of purine metabolic enzymes, we establish that TXNIP induction by AICAR and adenosine requires their cellular uptake and metabolism to adenine nucleotides. AICAR induction of TXNIP depended on MondoA, but was independent of AMPK (AMP-activated protein kinase) activation and calcium. The findings of the present study have two important implications. First, in addition to activating AMPK, AICAR may have AMPK-independent effects on gene expression by regulating MondoA–Mlx activity following its flux into the adenine nucleotide pool. Secondly, MondoA–Mlx complexes sense elevated levels of G6P and adenine nucleotides to trigger a TXNIP-dependent feedback inhibition of glycolysis. We propose that this mechanism serves as a checkpoint to restore metabolic homoeostasis.

The influence of inhibiting no formation on metabolic recovery of ischemic rat heart by apelin-12

Apelin 12 (A-12) was synthesized by the automatic solid phase method with use of Fmoc 1H-NMR spectroscopy and mass spectrometry. Effects of apelin-12 (a peptide comprised of 12 aminoacids, A-12) on recovery of energy metabolism and cardiac function were studied in isolated working rat hearts perfused with Krebs buffer (KB) containing 11 mM glucose that were subjected to global ischemia and reperfusion. A short-term infusion of μM 140 A-12 in KB prior to ischemia enhanced myocardial ATP, the total adenine nucleotide pool (ΣAN=ATP+ADP+AMP) and the energy charge of cardiomyocites ((ATP+0.5ADP)/ΣAN) at the end of reperfusion compared with control (KB infusion) and reduced lactate content and lactate/pyruvate ratio in reperfused myocardium to the initial values. This effect was accompanied by improved recovery of coronary flow and cardiac function. Coadministration of 140 μM A-12 and 100 μM L-NAME (the nonspecific NOS inhibitor) profoundly attenuated the peptide influence on metabolic and functional recovery of reperfused hearts. The results indicate involvement of NO, formed under the peptide action, in mechanisms of cardioprotection that are tightly associated with recovery of energy metabolism in postischemic heart.

Experimentally observed phenomena on cardiac energetics in heart failure emerge from simulations of cardiac metabolism

The failing heart is hypothesized to suffer from energy supply inadequate for supporting normal cardiac function. We analyzed data from a canine left ventricular hypertrophy model to determine how the energy state evolves because of changes in key metabolic pools. Our findings—confirmed by in vivo 31P-magnetic resonance spectroscopy—indicate that the transition between the clinically observed early compensatory phase and heart failure and the critical point at which the transition occurs are emergent properties of cardiac energy metabolism. Specifically, analysis reveals a phenomenon in which low and moderate reductions in metabolite pools have no major negative impact on oxidative capacity, whereas reductions beyond a critical tipping point lead to a severely compromised energy state. The transition point corresponds to reductions in the total adenine nucleotide pool (TAN) of ≈30%, corresponding to the reduction observed in humans in heart failure [Ingwall JS, Weiss RG (2004) Is the failing heart energy starved? On using chemical energy to support cardiac function. Circ Res 95(2):135–145]. At given values of TAN and the total exchangeable phosphate pool during hypertrophic remodeling, the creatine pool attains a value that is associated with optimal ATP hydrolysis potential. Thus, both increases and decreases to the creatine pool are predicted to result in diminished energetic state unless accompanied by appropriate simultaneous changes in the other pools.