Acyl ghrelin increases cardiac output while preserving right ventricular-pulmonary arterial coupling in heart failure.

AIM: Acyl ghrelin increases cardiac output (CO) in heart failure with reduced ejection fraction (HFrEF). This could impair the right ventricular-pulmonary arterial coupling (RVPAC), both through an increased venous return and right ventricular afterload. We aim to investigate if acyl ghrelin increases CO with or without worsening the right-sided haemodynamics in HFrEF assessed by RVPAC. METHODS AND RESULTS: The Karolinska Acyl ghrelin Trial was a randomized double-blind placebo-controlled trial of acyl ghrelin versus placebo (120-min intravenous infusion) in HFrEF. RVPAC was assessed echocardiographically at baseline and 120 min. ANOVA was used for difference in change between acyl ghrelin versus placebo, adjusted for baseline values. Of the 30 randomized patients, 22 had available RVPAC (acyl ghrelin n = 12, placebo n = 10). Despite a 15% increase in CO in the acyl ghrelin group (from 4.0 (3.5-4.6) to 4.6 (3.9-6.1) L/min, P = 0.003), RVPAC remained unchanged; 5.9 (5.3-7.6) to 6.3 (4.8-7.5) mm·(m/s)-1 , P = 0.372, while RVPAC was reduced in the placebo group, 5.2 (4.3-6.4) to 4.8 (4.2-5.8) mm·(m/s)-1 , P = 0.035. Comparing change between groups, CO increased in the acyl ghrelin group versus placebo (P = 0.036) while RVPAC and the right ventricular pressure gradient remained unchanged. CONCLUSION: Treatment with acyl ghrelin increases CO while preserving or even improving RVPAC in HFrEF, possibly due to increased contractility, reduced PVR and/or reduced left sided filling pressures. These potential effects strengthen the role of acyl ghrelin therapy in HFrEF with right ventricular failure.

Increased tetanic calcium in early fatigue of mammalian muscle fibers is accompanied by accelerated force development despite a decreased force.

During the initial phase of fatigue induced by repeated contractions in fast-twitch muscle fibers, tetanic force decreases despite increasing tetanic free cytosolic [Ca2+ ] ([Ca2+ ]cyt ). Here, we hypothesized that the increase in tetanic [Ca2+ ]cyt nevertheless has positive effects on force in early fatigue. Experiments on enzymatically isolated mouse flexor digitorum brevis (FDB) fibers showed that an increase in tetanic [Ca2+ ]cyt during ten 350 ms contractions required trains of electrical pulses to be elicited at short intervals (≤2 s) and at high frequencies (≥70 Hz). Mechanically dissected mouse FDB fibers showed greater decrease in tetanic force when the stimulation frequency during contractions was gradually reduced to prevent the increase in tetanic [Ca2+ ]cyt . Novel analyses of data from previous studies revealed an increased rate of force development in the tenth fatiguing contraction in mouse FDB fibers, as well as in rat FDB and human intercostal fibers. Mouse FDB fibers deficient in creatine kinase showed no increase in tetanic [Ca2+ ]cyt and slowed force development in the tenth contraction; after injection of creatine kinase to enable phosphocreatine breakdown, these fibers showed an increase in tetanic [Ca2+ ]cyt and accelerated force development. Mouse FDB fibers exposed to ten short contractions (43 ms) produced at short intervals (142 ms) showed increased tetanic [Ca2+ ]cyt accompanied by a marked (~16%) increase in the developed force. In conclusion, the increase in tetanic [Ca2+ ]cyt in early fatigue is accompanied by accelerated force development, which under some circumstances can counteract the decline in physical performance caused by the concomitant decrease in maximum force.

Pregnancy-Induced Hypertensive Disorder and Risks of Future Ischemic and Nonischemic Heart Failure.

BACKGROUND: Although adverse pregnancy outcomes are associated with an increased risk of cardiovascular disease, studies on timing and subtypes of heart failure after a hypertensive pregnancy are lacking. OBJECTIVES: The goal of this study was to assess the association between pregnancy-induced hypertensive disorder and risk of heart failure, according to ischemic and nonischemic subtypes, and the impact of disease characteristics and the timing of heart failure risks. METHODS: This was a population-based matched cohort study, comprising all primiparous women without a history of cardiovascular disease included in the Swedish Medical Birth Register between 1988 and 2019. Women with pregnancy-induced hypertensive disorder were matched with women with normotensive pregnancies. Through linkage with health care registers, all women were followed up for incident heart failure, classified as ischemic or nonischemic. RESULTS: In total, 79,334 women with pregnancy-induced hypertensive disorder were matched with 396,531 women with normotensive pregnancies. During a median follow-up of 13 years, rates of all heart failure subtypes were more common among women with pregnancy-induced hypertensive disorder. Compared with women with normotensive pregnancies, adjusted HRs (aHRs) with 95% CIs were as follows: heart failure overall, aHR: 1.70 (95% CI: 1.51-1.91); ischemic heart failure, aHR: 2.28 (95% CI: 1.74-2.98); and nonischemic heart failure, aHR: 1.60 (95% CI: 1.40-1.83). Disease characteristics indicating severe hypertensive disorder were associated with higher heart failure rates, and rates were highest within the first years after the hypertensive pregnancy but remained significantly increased thereafter. CONCLUSIONS: Pregnancy-induced hypertensive disorder is associated with an increased short-term and long-term risk of incident ischemic and nonischemic heart failure. Disease characteristics indicating more severe forms of pregnancy-induced hypertensive disorder amplify the heart failure risks.

Acyl ghrelin improves cardiac function in heart failure and increases fractional shortening in cardiomyocytes without calcium mobilization.

BACKGROUND AND AIMS: Ghrelin is an endogenous appetite-stimulating peptide hormone with potential cardiovascular benefits. Effects of acylated (activated) ghrelin were assessed in patients with heart failure and reduced ejection fraction (HFrEF) and in ex vivo mouse cardiomyocytes. METHODS AND RESULTS: In a randomized placebo-controlled double-blind trial, 31 patients with chronic HFrEF were randomized to synthetic human acyl ghrelin (0.1 µg/kg/min) or placebo intravenously over 120 min. The primary outcome was change in cardiac output (CO). Isolated mouse cardiomyocytes were treated with acyl ghrelin and fractional shortening and calcium transients were assessed. Acyl ghrelin but not placebo increased cardiac output (acyl ghrelin: 4.08 ± 1.15 to 5.23 ± 1.98 L/min; placebo: 4.26 ± 1.23 to 4.11 ± 1.99 L/min, P < 0.001). Acyl ghrelin caused a significant increase in stroke volume and nominal increases in left ventricular ejection fraction and segmental longitudinal strain and tricuspid annular plane systolic excursion. There were no effects on blood pressure, arrhythmias, or ischaemia. Heart rate decreased nominally (acyl ghrelin: 71 ± 11 to 67 ± 11 b.p.m.; placebo 69 ± 8 to 68 ± 10 b.p.m.). In cardiomyocytes, acyl ghrelin increased fractional shortening, did not affect cellular Ca2+ transients, and reduced troponin I phosphorylation. The increase in fractional shortening and reduction in troponin I phosphorylation was blocked by the acyl ghrelin antagonist D-Lys 3. CONCLUSION: In patients with HFrEF, acyl ghrelin increased cardiac output without causing hypotension, tachycardia, arrhythmia, or ischaemia. In isolated cardiomyocytes, acyl ghrelin increased contractility independently of preload and afterload and without Ca2+ mobilization, which may explain the lack of clinical side effects. Ghrelin treatment should be explored in additional randomized trials. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT05277415.

Associations between rheumatoid arthritis, incident heart failure, and left ventricular ejection fraction.

BACKGROUND: Rheumatoid arthritis (RA) is an independent risk factor for heart failure (HF). Yet, the association between RA and left ventricular ejection fraction (LVEF) in incident HF is not well studied, nor are outcomes of HF in RA by LVEF. METHODS: We identified incident HF patients between 2003 and 2018 through the Swedish Heart Failure Registry, enriched with data from national health registers. Using logistic regression, associations between a prior diagnosis of RA and LVEF among HF patients and vs age, sex, and geographical area matched general population controls without HF were assessed. Additionally, associations between HF with vs without a prior diagnosis of RA, by LVEF, and outcomes up to 5 years after HF diagnosis were investigated using Cox regression. LVEF was primarily dichotomized at 40% and secondarily categorized as <40%, 40% to 49%, and ≥50%. Covariates included demographics and cardiovascular comorbidities. RESULTS: Among 20,916 incident HF patients, 331 (1.6%) had RA vs 1,047/103,501 (1.0%) of HF-free controls. The odds ratio (OR) for RA was 1.4 (95% CI: 1.1-1.8) in LVEF<40% vs HF-free controls and 1.6 (95% CI: 1.3-2.0) in LVEF≥40% vs HF-free controls. Among HF patients, RA was more common in HF with LVEF ≥40% (1.9%) vs LVEF<40% (1.3%), corresponding to OR 1.4 (95% CI: 1.1-1.7). No associations between RA and cardiovascular outcomes were observed across LVEF. An association between RA and all-cause mortality was observed only for patients with LVEF<40% (hazard ratio: 1.4; 95% CI: 1.1-1.8). CONCLUSIONS: RA was independently associated with incident HF, particularly HF with LVEF≥40%. RA did not associate with cardiovascular outcomes following HF diagnosis but was associated with increased risk of all-cause mortality in HF with LVEF<40%.

Citrullination is linked to reduced Ca2+ sensitivity in hearts of a murine model of rheumatoid arthritis.

AIMS: Cardiac contractile dysfunction is prevalent in rheumatoid arthritis (RA), with an increased risk for heart failure. A hallmark of RA has increased levels of peptidyl arginine deaminases (PAD) that convert arginine to citrulline leading to ubiquitous citrullination, including in the heart. We aimed to investigate whether PAD-dependent citrullination in the heart was linked to contractile function in a mouse model of RA during the acute inflammatory phase. METHODS: We used hearts from the collagen-induced arthritis (CIA) mice, with overt arthritis, and control mice to analyze cardiomyocyte Ca2+ handling and fractional shortening, the force-Ca2+ relationship in isolated myofibrils, the levels of PAD, protein post-translational modifications, and Ca2+ handling protein. Then, we used an in vitro model to investigate the role of TNF-α in the PAD-mediated citrullination of proteins in cardiomyocytes. RESULTS: Cardiomyocytes from CIA mice displayed larger Ca2+ transients than controls, whereas cell shortening was similar in the two groups. Myofibrils from CIA hearts required higher [Ca2+ ] to reach 50% of maximum shortening, ie Ca2+ sensitivity was lower. This was associated with increased PAD2 expression and α-actin citrullination. TNF-α increased PAD-mediated citrullination which was blocked by pre-treatment with the PAD inhibitor 2-chloroacetamide. CONCLUSION: Using a mouse RA model we found evidence of impaired cardiac contractile function linked to reduced Ca2+ sensitivity, increased expression of PAD2, and citrullination of α-actin, which was triggered by TNF-α. This provides molecular and physiological evidence for acquired cardiomyopathy and a potential mechanism for RA-associated heart failure.

Improved skeletal muscle fatigue resistance in experimental autoimmune myositis mice following high-intensity interval training.

BACKGROUND: Muscle weakness and decreased fatigue resistance are key manifestations of systemic autoimmune myopathies (SAMs). We here examined whether high-intensity interval training (HIIT) improves fatigue resistance in the skeletal muscle of experimental autoimmune myositis (EAM) mice, a widely used animal model for SAM. METHODS: Female BALB/c mice were randomly assigned to control (CNT) or EAM groups (n = 28 in each group). EAM was induced by immunization with three injections of myosin emulsified in complete Freund's adjuvant. The plantar flexor (PF) muscles of mice with EAM were exposed to either an acute bout or 4 weeks of HIIT (a total of 14 sessions). RESULTS: The fatigue resistance of PF muscles was lower in the EAM than in the CNT group (P < 0.05). These changes were associated with decreased activities of citrate synthase and cytochrome c oxidase and increased expression levels of the endoplasmic reticulum stress proteins (glucose-regulated protein 78 and 94, and PKR-like ER kinase) (P < 0.05). HIIT restored all these alterations and increased the peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) and the mitochondrial electron transport chain complexes (I, III, and IV) in the muscles of EAM mice (P < 0.05). CONCLUSIONS: HIIT improves fatigue resistance in a SAM mouse model, and this can be explained by the restoration of mitochondria oxidative capacity via inhibition of the ER stress pathway and PGC-1α-mediated mitochondrial biogenesis.

Myositis-specific autoantibodies and QTc changes by ECG in idiopathic inflammatory myopathies.

OBJECTIVES: The aim of this study was to investigate cardiac involvement detected by ECG in patients with idiopathic inflammatory myopathies (IIMs) and to evaluate possible associations between the autoantibody profile and ECG changes in these patients. METHODS: In a Scandinavian cross-sectional study, patients were included from two Danish centres and one Swedish centre. Resting 12-lead ECG was investigated in 261 patients with IIM compared with 102 patients with systemic sclerosis (SSc) and 48 healthy controls (HCs). ECG changes were correlated to clinical manifestations and myositis-specific and myositis-associated autoantibodies (MSAs and MAAs, respectively). RESULTS: Patients with IIM had a longer mean corrected QT (QTc) duration and more frequently presented with prolonged QTc (≥450 ms; P = 0.038) compared with HCs. A longer QTc duration was recorded in SSc compared with IIM [433 ms (s.d. 23) vs 426 (24); P = 0.011], yet there was no significant difference in the fraction with prolonged QTc (SSc: 22%, IIM: 16%; P = 0.19). In multivariable regression analyses, anti-Mi2 (P = 0.01, P = 0.035) and anti-Pl-7 (P = 0.045, P = 0.014) were associated with QTc duration and prolonged QTc in IIM. Elevated CRP was associated with prolonged QTc (P = 0.041). CONCLUSION: The presence of QTc abnormalities was as common in patients with IIM as in patients with SSc, including prolonged QTc seen in almost one-fifth of the patients. Anti-Mi2, anti-Pl-7 and elevated CRP may serve as biomarkers for cardiac disease in IIM, but needs to be confirmed in a larger prospective study.

Mitochondrial NDUFA4L2 is a novel regulator of skeletal muscle mass and force.

The hypoxia-inducible nuclear-encoded mitochondrial protein NADH dehydrogenase (ubiquinone) 1 alpha subcomplex, 4-like 2 (NDUFA4L2) has been demonstrated to decrease oxidative phosphorylation and production of reactive oxygen species in neonatal cardiomyocytes, brain tissue and hypoxic domains of cancer cells. Prolonged local hypoxia can negatively affect skeletal muscle size and tissue oxidative capacity. Although skeletal muscle is a mitochondrial rich, oxygen sensitive tissue, the role of NDUFA4L2 in skeletal muscle has not previously been investigated. Here we ectopically expressed NDUFA4L2 in mouse skeletal muscles using adenovirus-mediated expression and in vivo electroporation. Moreover, femoral artery ligation (FAL) was used as a model of peripheral vascular disease to induce hind limb ischemia and muscle damage. Ectopic NDUFA4L2 expression resulted in reduced mitochondrial respiration and reactive oxygen species followed by lowered AMP, ADP, ATP, and NAD+ levels without affecting the overall protein content of the mitochondrial electron transport chain. Furthermore, ectopically expressed NDUFA4L2 caused a ~20% reduction in muscle mass that resulted in weaker muscles. The loss of muscle mass was associated with increased gene expression of atrogenes MurF1 and Mul1, and apoptotic genes caspase 3 and Bax. Finally, we showed that NDUFA4L2 was induced by FAL and that the Ndufa4l2 mRNA expression correlated with the reduced capacity of the muscle to generate force after the ischemic insult. These results show, for the first time, that mitochondrial NDUFA4L2 is a novel regulator of skeletal muscle mass and force. Specifically, induced NDUFA4L2 reduces mitochondrial activity leading to lower levels of important intramuscular metabolites, including adenine nucleotides and NAD+ , which are hallmarks of mitochondrial dysfunction and hence shows that dysfunctional mitochondrial activity may drive muscle wasting.

Larger improvements in fatigue resistance and mitochondrial function with high- than with low-intensity contractions during interval training of mouse skeletal muscle.

Interval training (IT) results in improved fatigue resistance in skeletal muscle mainly due to an increased aerobic capacity, which involves increased muscle mitochondrial content and/or improved mitochondrial function. We hypothesized that IT with high-intensity contractions is more effective in increasing mitochondrial function, and hence fatigue resistance, than low-intensity contractions. To study this hypothesis without interference from differences in muscle fiber recruitment obliged to occur during voluntary contractions, IT was performed with in situ supramaximal electrical stimulation where all muscle fibers are recruited. We compared the effect of IT with repeated low-intensity (20 Hz stimulation, IT20) and high-intensity (100 Hz stimulation, IT100) contractions on fatigue resistance and mitochondrial content and function in mouse plantar flexor muscles. Muscles were stimulated every other day for 4 weeks. The averaged peak torque during IT bouts was 4.2-fold higher with IT100 than with IT20. Both stimulation protocols markedly improved in situ fatigue resistance, although the improvement was larger with IT100. The citrate synthase activity, a biomarker of mitochondrial content, was similarly increased with IT20 and IT100. Conversely, increased expression of mitochondrial respiratory chain (MRC) complexes I, III, and IV was only observed with IT100 and this was accompanied by increases in MRC supercomplex formation and pyruvate-malate-driven state 3 respiration in isolated mitochondria. In conclusion, the IT-induced increase in fatigue resistance is larger with high-intensity than with low-intensity contractions and this is linked to improved mitochondrial function due to increased expression of MRC complexes and assembly of MRC supercomplexes.

Vitamin C and E Treatment Blocks Changes in Kynurenine Metabolism Triggered by Three Weeks of Sprint Interval Training in Recreationally Active Elderly Humans.

The kynurenine pathway (KP) is gaining attention in several clinical fields. Recent studies show that physical exercise offers a therapeutic way to improve ratios of neurotoxic to neuroprotective KP metabolites. Antioxidant supplementation can blunt beneficial responses to physical exercise. We here studied the effects of endurance training in the form of sprint interval training (SIT; three sessions of 4-6 × 30 s cycling sprints per week for three weeks) in elderly (~65 years) men exposed to either placebo (n = 9) or the antioxidants vitamin C (1 g/day) and E (235 mg/day) (n = 11). Blood samples and muscle biopsies were taken under resting conditions in association with the first (untrained state) and last (trained state) SIT sessions. In the placebo group, the blood plasma level of the neurotoxic quinolinic acid was lower (~30%) and the neuroprotective kynurenic acid to quinolinic acid ratio was higher (~50%) in the trained than in the untrained state. Moreover, muscle biopsies showed a training-induced increase in kynurenine aminotransferase (KAT) III in the placebo group. All these training effects were absent in the vitamin-treated group. In conclusion, KP metabolism was shifted towards neuroprotection after three weeks of SIT in elderly men and this shift was blocked by antioxidant treatment.

Mechanistic and Therapeutic Implications of Extracellular Vesicles as a Potential Link Between Covid-19 and Cardiovascular Disease Manifestations.

Extracellular vesicles (EVs), which are cell released double layered membrane particles, have been found in every circulating body fluid, and provide a tool for conveying diverse information between cells, influencing both physiological and pathological conditions. Viruses can hijack the EVs secretory pathway to exit infected cells and use EVs endocytic routes to enter uninfected cells, suggesting that EVs and viruses can share common cell entry and biogenesis mechanisms. SARS-CoV-2 is responsible of the coronavirus disease 2019 (Covid-19), which may be accompanied by severe multi-organ manifestations. EVs may contribute to virus spreading via transfer of virus docking receptors such as CD9 and ACE2. Covid-19 is known to affect the renin angiotensin system (RAS), and could promote secretion of harmful EVs. In this scenario EVs might be linked to cardiovascular manifestations of the Covid-19 disease through unbalance in RAS. In contrast EVs derived from mesenchymal stem cells or cardiosphere derived cells, may promote cardiovascular function due to their beneficial effect on angiogenesis, fibrosis, contractility and immuno-modulation. In this article we assessed the potential impact of EVs in cardiovascular manifestations of Covid-19 and highlight potential strategies to control the extracellular signaling for future therapies.

Loss of α-actinin-3 during human evolution provides superior cold resilience and muscle heat generation.

The protein α-actinin-3 expressed in fast-twitch skeletal muscle fiber is absent in 1.5 billion people worldwide due to homozygosity for a nonsense polymorphism in ACTN3 (R577X). The prevalence of the 577X allele increased as modern humans moved to colder climates, suggesting a link between α-actinin-3 deficiency and improved cold tolerance. Here, we show that humans lacking α-actinin-3 (XX) are superior in maintaining core body temperature during cold-water immersion due to changes in skeletal muscle thermogenesis. Muscles of XX individuals displayed a shift toward more slow-twitch isoforms of myosin heavy chain (MyHC) and sarcoplasmic reticulum (SR) proteins, accompanied by altered neuronal muscle activation resulting in increased tone rather than overt shivering. Experiments on Actn3 knockout mice showed no alterations in brown adipose tissue (BAT) properties that could explain the improved cold tolerance in XX individuals. Thus, this study provides a mechanism for the positive selection of the ACTN3 X-allele in cold climates and supports a key thermogenic role of skeletal muscle during cold exposure in humans.

Eccentric Resistance Training Ameliorates Muscle Weakness in a Mouse Model of Idiopathic Inflammatory Myopathies.

OBJECTIVE: High-force eccentric contractions (ECCs) have traditionally been excluded from rehabilitation programs that include patients with idiopathic inflammatory myopathies (IIMs) due to unverified fear of causing muscle damage and inflammation. In an IIM animal model that used mice with experimental autoimmune myositis (EAM), we undertook this study to investigate whether ECC training can safely and effectively be used to counteract muscle weakness in IIM. METHODS: EAM was induced in BALB/c mice by immunization with 3 injections of myosin emulsified in Freund's complete adjuvant. Controls (n = 12) and mice with EAM (n = 12) were exposed to either an acute bout of 100 ECCs or 4 weeks of ECC training (20 ECCs every other day). To induce ECCs, plantar flexor muscles were electrically stimulated while the ankle was forcibly dorsiflexed. RESULTS: Less cell damage, as assessed by Evans blue dye uptake, was observed in the muscles of mice with EAM, compared to controls, after an acute bout of 100 ECCs (P < 0.05). Maximum Ca2+ -activated force was decreased in skinned gastrocnemius muscle fibers from mice with EAM, and this was accompanied by increased expression of endoplasmic reticulum (ER) stress proteins, including Gsp78 and Gsp94 (P < 0.05). ECC training prevented the decrease in force and the increase in ER stress proteins and also enhanced the expression and myofibrillar binding of small heat-shock proteins (HSPs) (P < 0.05), which can stabilize myofibrillar structure and function. CONCLUSION: ECC training protected against the reduction in myofibrillar force-generating capacity in an IIM mouse model, and this occurred via inhibition of ER stress responses and small HSP-mediated myofibrillar stabilization.

Quantification of Plasma Kynurenine Metabolites Following One Bout of Sprint Interval Exercise.

The kynurenine pathway of tryptophan degradation produces several neuroactive metabolites suggested to be involved in a wide variety of diseases and disorders, however, technical challenges in reliably detecting these metabolites hampers cross-comparisons. The main objective of this study was to develop an accurate, robust and precise bioanalytical method for simultaneous quantification of ten plasma kynurenine metabolites. As a secondary aim, we applied this method on blood samples taken from healthy subjects conducting 1 session of sprint interval exercise (SIE). It is well accepted that physical exercise is associated with health benefits and reduces risks of psychiatric illness, diabetes, cancer and cardiovascular disease, but also influences the peripheral and central concentrations of kynurenines. In line with this, we found that in healthy old adults (n = 10; mean age 64 years), levels of kynurenine increased 1 hour (P = .03) after SIE, while kynurenic acid (KYNA) concentrations were elevated after 24 hours (P = .02). In contrast, no significant changes after exercise were seen in young adults (n = 10; mean age 24 years). In conclusion, the described method performs well in reliably detecting all the analyzed metabolites in plasma samples. Furthermore, we also detected an age-dependent effect on the degree by which a single intense training session affects kynurenine metabolite levels.

Vitamin C and E Treatment Blunts Sprint Interval Training-Induced Changes in Inflammatory Mediator-, Calcium-, and Mitochondria-Related Signaling in Recreationally Active Elderly Humans.

Sprint interval training (SIT) has emerged as a time-efficient training regimen for young individuals. Here, we studied whether SIT is effective also in elderly individuals and whether the training response was affected by treatment with the antioxidants vitamin C and E. Recreationally active elderly (mean age 65) men received either vitamin C (1 g/day) and vitamin E (235 mg/day) or placebo. Training consisted of nine SIT sessions (three sessions/week for three weeks of 4-6 repetitions of 30-s all-out cycling sprints) interposed by 4 min rest. Vastus lateralis muscle biopsies were taken before, 1 h after, and 24 h after the first and last SIT sessions. At the end of the three weeks of training, SIT-induced changes in relative mRNA expression of reactive oxygen/nitrogen species (ROS)- and mitochondria-related proteins, inflammatory mediators, and the sarcoplasmic reticulum Ca2+ channel, the ryanodine receptor 1 (RyR1), were blunted in the vitamin treated group. Western blots frequently showed a major (>50%) decrease in the full-length expression of RyR1 24 h after SIT sessions; in the trained state, vitamin treatment seemed to provide protection against this severe RyR1 modification. Power at exhaustion during an incremental cycling test was increased by ~5% at the end of the training period, whereas maximal oxygen uptake remained unchanged; vitamin treatment did not affect these measures. In conclusion, treatment with the antioxidants vitamin C and E blunts SIT-induced cellular signaling in skeletal muscle of elderly individuals, while the present training regimen was too short or too intense for the changes in signaling to be translated into a clear-cut change in physical performance.

Head-to-head comparison of inorganic nitrate and metformin in a mouse model of cardiometabolic disease.

BACKGROUND/PURPOSE: Unhealthy dietary habits contribute to the increasing incidence of metabolic syndrome and type 2 diabetes (T2D), which is accompanied by oxidative stress, compromised nitric oxide (NO) bioavailability and increased cardiovascular risk. Apart from lifestyle changes, biguanides such as metformin are the first-line pharmacological treatment for T2D. Favourable cardiometabolic effects have been demonstrated following dietary nitrate supplementation to boost the nitrate-nitrite-NO pathway. Here we aim to compare the therapeutic value of inorganic nitrate and metformin alone and their combination in a model of cardiometabolic disease. EXPERIMENTAL APPROACH: Mice were fed control or high fat diet (HFD) for 7 weeks in combination with the NO synthase (NOS) inhibitor l-NAME to induce metabolic syndrome. Simultaneously, the mice were treated with vehicle, inorganic nitrate, metformin or a combination of nitrate and metformin in (drinking water). Cardiometabolic functions were assessed in vivo and tissues were collected/processed for analyses. KEY RESULTS: HFD + L-NAME was associated with cardiometabolic dysfunction, compared with controls, as evident from elevated blood pressure, endothelial dysfunction, impaired insulin sensitivity and compromised glucose clearance as well as liver steatosis. Both nitrate and metformin improved insulin/glucose homeostasis, whereas only nitrate had favourable effects on cardiovascular function and steatosis. Mechanistically, metformin and nitrate improved AMPK signalling, whereas only nitrate attenuated oxidative stress. Combination of nitrate and metformin reduced HbA1c and trended to further increase AMPK activation. CONCLUSION/IMPLICATIONS: Nitrate and metformin had equipotent metabolic effects, while nitrate was superior regarding protection against cardiovascular dysfunction and liver steatosis. If reproduced in future clinical trials, these findings may have implications for novel nutrition-based strategies against metabolic syndrome, T2D and associated complications.

Three weeks of sprint interval training improved high-intensity cycling performance and limited ryanodine receptor modifications in recreationally active human subjects.

PURPOSE: Mechanisms underlying the efficacy of sprint interval training (SIT) remain to be understood. We previously reported that an acute bout of SIT disrupts the integrity of the sarcoplasmic reticulum (SR) Ca2+ release channel, the ryanodine receptor 1 (RyR1), in recreationally active human subjects. We here hypothesize that in addition to improving the exercise performance of recreationally active humans, a period of repeated SIT sessions would make the RyR1 protein less vulnerable and accelerate recovery of contractile function after a SIT session. METHODS: Eight recreationally active males participated in a 3-week SIT program consisting of nine sessions of four-six 30-s all-out cycling bouts with 4 min of rest between bouts. RESULTS: Total work performed during a SIT session and maximal power (Wmax) reached during an incremental cycling test were both increased by ~ 7.5% at the end of the training period (P < 0.05). Western blots performed on vastus lateralis muscle biopsies taken before, 1 h, 24 h and 72 h after SIT sessions in the untrained and trained state showed some protection against SIT-induced reduction of full-length RyR1 protein expression in the trained state. SIT-induced knee extensor force deficits were similar in the untrained and trained states, with a major reduction in voluntary and electrically evoked forces immediately and 1 h after SIT (P < 0.05), and recovery after 24 h. CONCLUSIONS: Three weeks of SIT improves exercise performance and provides some protection against RyR1 modification, whereas it does not accelerate recovery of contractile function.