The beneficial effect of hormone replacement treatment (HRT) on osteoporosis and menopausal symptoms has been well documented in randomised trials, but the impact of oestrogen-mediated metabolic changes on the risk of ischaemic heart disease (IHD) is still debated. Randomised studies have shown that HRT increases levels of high-density lipoprotein cholesterol while causing a reduction in the levels of low-density lipoprotein cholesterol, serum fibrinogen, plasminogen activator inhibitor and homocysteine. In addition, HRT increases insulin sensitivity in both normoglycaemic and diabetic women, Unlike oral contraceptives, HRT has not been associated with an increase in arterial blood pressure, whereas a small increase in the risk of breast cancer and of venous thromboembolism appears to occur with both treatments. Interestingly, some data suggest that oestrogen preparations may have different effects on lipids. For instance, the beneficial effect on cholesterol metabolism observed with oral conjugated oestrogen does not occur with transdermal oestradiol, suggesting that the first-pass effect through the portal circulation may be necessary to achieve the full metabolic effect of oestrogen treatment. Nevertheless, although a wealth of observational studies show that HRT is associated with a significant reduction in morbidity and mortality from IHD, the only randomised data available to date do not support these findings in postmenopausal women with established coronary artery disease.
Although the initiation, development, and maintenance of atrial fibrillation (AF) have been linked to alterations in myocyte redox state, the field lacks a complete understanding of the impact these changes may have on cellular signalling, atrial electrophysiology, and disease progression. Recent studies demonstrate spatiotemporal changes in reactive oxygen species production shortly after the induction of AF in animal models with an uncoupling of nitric oxide synthase activity ensuing in the presence of long-standing persistent AF, ultimately leading to a major shift in nitroso–redox balance. However, it remains unclear which radical or non-radical species are primarily involved in the underlying mechanisms of AF or which proteins are targeted for redox modification. In most instances, only free radical oxygen species have been assessed; yet evidence from the redox signalling field suggests that non-radical species are more likely to regulate cellular processes. A wider appreciation for the distinction of these species and how both species may be involved in the development and maintenance of AF could impact treatment strategies. In this review, we summarize how redox second-messenger systems are regulated and discuss the recent evidence for alterations in redox regulation in the atrial myocardium in the presence of AF, while identifying some critical missing links. We also examine studies looking at antioxidants for the prevention and treatment of AF and propose alternative redox targets that may serve as superior therapeutic options for the treatment of AF.
We are in the midst of a digital revolution in health care, although the application of new and useful technology in routine clinical practice is variable. The Characterizing Atrial fibrillation by Translating its Causes into Health Modifiers in the Elderly (CATCH ME) Consortium, in collaboration with the European Society of Cardiology (ESC), has funded the creation of two applications (apps) in atrial fibrillation (AF) for use in smartphones and tablets. The patient app aims to enhance patient education, improve communication between patients and health care professionals, and encourage active patient involvement in the management of their condition. The health care professional app is designed as an interactive management tool incorporating the new ESC Practice Guidelines on AF and supported by the European Heart Rhythm Association (EHRA), with the aim of improving best practice approaches for the care of patients with AF. Both stand-alone apps are now freely available for Android and iOS devices though the Google Play, Amazon, and Apple stores. In this article, we outline the rationale for the design and implementation of these apps. Our objective is to demonstrate the value of integrating novel digital technology into clinical practice, with the potential for patient engagement, optimization of pharmacological and interventional therapy in AF, and ultimately to improve patient outcomes.
Gene deletion of the neuronal nitric oxide synthase (nNOS) is associated with impaired relaxation and increased contraction both in vivo and in isolated left ventricular (LV) myocytes. Our recent work has shown that a reduction in protein kinase A-dependent phosphorylation of phospholamban, secondary to increased protein phosphatase (PP) activity, is responsible for the slower (Ca2+)i decay and myocyte relaxation that result from disrupting nNOS. The aim of the present study was to investigate the intracellular signalling underlying the nNOS-dependent regulation of myocardial contraction.
Methods and Results
Cell shortening was significantly increased in LV myocytes isolated from nNOS−/− mice and in wild type myocytes (nNOS+/+) after acute nNOS inhibition with L-VNIO (100 μmol/L) both under field-stimulation (3 Hz, 35°C) and in voltage-clamped conditions (from −70 to +20 mV, 25 ms, 35°C). Changes in myofilament Ca2+ sensitivity did not contribute to the increase in contraction in nNOS-/− since the size of tetanic contraction (at 20 Hz) relative to the rise of (Ca2+)i in the presence of thapsigargin did not differ between groups. In contrast, the L-type Ca2+ current density (ICa) was significantly greater after nNOS inhibition/gene deletion. Inhibition of soluble guanylate cyclase with ODQ (10 μmol/l) or PKG with RP-8-Br-cGMP (100 μmol/l) increased cell shortening in wild type but not in nNOS−/− LV myocytes, indicating that cGMP-mediated regulation of cardiac function downstream of NO is abolished in the absence of nNOS. Intracellular perfusion of the PKA inhibitor PKI (1 μmol/l) significantly reduced contraction only in nNOS−/− myocytes, whereas PP2A inhibition with okadaic acid (OA, 10 nmol/l) increased cell shortening in nNOS+/+ LV myocytes but not in nNOS−/−. Interestingly, OA (10 nmol/l) increased ICa only in nNOS+/+ LV myocytes thereby abolished the difference in ICa between nNOS+/+ and nNOS−/−. Phophorylation of ICa (assessed using Pro-Q Diamond phosphoprotein gel staining with ICaα1.2 immunoprecipitation lysates) was significantly increased in nNOS−/− LV myocardium comparing to nNOS+/+. Inhibition of PP1 by intracellular dialysis of inhibitor-2 (500 nM) did not affect myocyte contraction in either group.
Summary and Conclusion
Abolition of cGMP-mediated signalling together with increased PKA-mediated phosphorylation of L-type Ca2+ channels secondary to a local reduction in PP2A activity account for the increased myocardial contraction observed in the presence of nNOS disruption. Taken together with our aforementioned findings on the mechanisms underlying impaired relaxation in nNOS−/− mice, these data suggest that nNOS-derived NO regulates the activity of subcellular pools of PPs, and by doing so it directs PKA mediated phosphorylation to specific protein targets in the cardiomyocyte.
Creatine buffers cellular adenosine triphosphate (ATP) via the creatine kinase reaction. Creatine levels are reduced in heart failure, but their contribution to pathophysiology is unclear. Arginine:glycine amidinotransferase (AGAT) in the kidney catalyses both the first step in creatine biosynthesis as well as homoarginine (HA) synthesis. AGAT-/- mice fed a creatine-free diet have a whole body creatine-deficiency. We hypothesized that AGAT-/- mice would develop cardiac dysfunction and rescue by dietary creatine would imply causality.Withdrawal of dietary creatine in AGAT-/- mice provided an estimate of myocardial creatine efflux of ∼2.7%/day; however, in vivo cardiac function was maintained despite low levels of myocardial creatine. Using AGAT-/- mice naïve to dietary creatine we confirmed absence of phosphocreatine in the heart, but crucially, ATP levels were unchanged. Potential compensatory adaptations were absent, AMPK was not activated and respiration in isolated mitochondria was normal. AGAT-/- mice had rescuable changes in body water and organ weights suggesting a role for creatine as a compatible osmolyte. Creatine-naïve AGAT-/- mice had haemodynamic impairment with low LV systolic pressure and reduced inotropy, lusitropy, and contractile reserve. Creatine supplementation only corrected systolic pressure despite normalization of myocardial creatine. AGAT-/- mice had low plasma HA and supplementation completely rescued all other haemodynamic parameters. Contractile dysfunction in AGAT-/- was confirmed in Langendorff perfused hearts and in creatine-replete isolated cardiomyocytes, indicating that HA is necessary for normal cardiac function.Our findings argue against low myocardial creatine per se as a major contributor to cardiac dysfunction. Conversely, we show that HA deficiency can impair cardiac function, which may explain why low HA is an independent risk factor for multiple cardiovascular diseases.
In the presence of diabetes (DM), myocardial glucose uptake and glycolysis are impaired and the heart rapidly adapts to use exclusively fatty acids (FA) for ATP generation. This maladaptation is believed to play a key role in the development of a cardiomyopathy over time. Here, we show that stimulating myocardial nitric oxide synthase (NOS) activity is sufficient to alleviate myocardial metabolic inflexibility, improve energy metabolism and prevent LV dysfunction in DM by increasing myocardial insulin-independent glucose transport.
Methods
Myocardial-specific overexpression of GTP cyclohydrolase I (mGCH1) was used to increase both tetrahydrobiopterin (BH4) and NOS activity in cardiomyocytes. Diabetes mellitus (DM) was induced by multiple low-dose streptozotocin injections (vs sham). PCr/ATP ratio was measured in perfused hearts using 31P-MRS, glucose transport estimated by deoxy-glucose uptake, and oxygen consumption rate (OCR) of intact cardiomyocytes using a phosphorescent probe.
Results
As expected, sham-injected mGCH1 transgenic hearts had higher BH4 levels and constitutive NOS activity compared with WT. 12 weeks after DM induction, LV dysfunction developed in WT mice but not in mGCH1 mice, in the absence of changes in myocardial BH4 content and NOS activity in either group. WT diabetic hearts had a lower PCr/ATP ratio (1.32±0.1 vs 1.73±0.1, p<0.05, n=11 per group) and mitochondrial creatine kinase (CK) activity (1.56±0.1 AU vs 1.98±0.1 AU, p<0.005, n=10 per group) when compared with non-diabetic WT mice, consistent with impaired cardiac energetics. By contrast, PCr/ATP and CK activity were preserved in diabetic mGCH1 hearts in the absence of differences in myocardial mitochondrial content. Myocardial GCH1 overexpression was associated with a higher protein levels of the insulin-independent glucose transporter, GLUT-1 (p<0.05, n=12 per group), but no changes in GLUT-4 protein. Myocardial glucose transport was 40% higher in LV myocytes from mGCH1 diabetic mice when compared with WT diabetic mice. This was accompanied by increased myocardial glucose oxidation, as determined by OCR. Pre-incubation of myocytes with inhibitors of NOS-PKG signalling (L-NAME, 1 mmol/L or Rp8pCPT PET cGMP 10 µmol/L) or GLUT-1 (STF-31, 10 µmol/L,) abolished all differences between mGCH and WT diabetic hearts.
Conclusions
Our study reveals that a myocardial increase in BH4 and NOS activity is sufficient to maintain a favourable substrate utilisation and preserve cardiac mitochondrial function in the presence of DM. This work provides new insight into the potential metabolic triggers of diabetic cardiomyopathy and suggests exciting new targets for BH4-based therapeutics.
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