Indole-3-Propionic Acid Protects Against Heart Failure With Preserved Ejection Fraction.

BACKGROUND: Heart failure with preserved ejection fraction (HFpEF) is a common but poorly understood form of heart failure, characterized by impaired diastolic function. It is highly heterogeneous with multiple comorbidities, including obesity and diabetes, making human studies difficult. METHODS: Metabolomic analyses in a mouse model of HFpEF showed that levels of indole-3-propionic acid (IPA), a metabolite produced by gut bacteria from tryptophan, were reduced in the plasma and heart tissue of HFpEF mice as compared with controls. We then examined the role of IPA in mouse models of HFpEF as well as 2 human HFpEF cohorts. RESULTS: The protective role and therapeutic effects of IPA were confirmed in mouse models of HFpEF using IPA dietary supplementation. IPA attenuated diastolic dysfunction, metabolic remodeling, oxidative stress, inflammation, gut microbiota dysbiosis, and intestinal epithelial barrier damage. In the heart, IPA suppressed the expression of NNMT (nicotinamide N-methyl transferase), restored nicotinamide, NAD+/NADH, and SIRT3 (sirtuin 3) levels. IPA mediates the protective effects on diastolic dysfunction, at least in part, by promoting the expression of SIRT3. SIRT3 regulation was mediated by IPA binding to the aryl hydrocarbon receptor, as Sirt3 knockdown diminished the effects of IPA on diastolic dysfunction in vivo. The role of the nicotinamide adenine dinucleotide circuit in HFpEF was further confirmed by nicotinamide supplementation, Nnmt knockdown, and Nnmt overexpression in vivo. IPA levels were significantly reduced in patients with HFpEF in 2 independent human cohorts, consistent with a protective function in humans, as well as mice. CONCLUSIONS: Our findings reveal that IPA protects against diastolic dysfunction in HFpEF by enhancing the nicotinamide adenine dinucleotide salvage pathway, suggesting the possibility of therapeutic management by either altering the gut microbiome composition or supplementing the diet with IPA.

The impact of coffee subtypes on incident cardiovascular disease, arrhythmias, and mortality: long-term outcomes from the UK Biobank.

AIMS: Epidemiological studies report the beneficial effects of habitual coffee consumption on incident arrhythmia, cardiovascular disease (CVD), and mortality. However, the impact of different coffee preparations on cardiovascular outcomes and survival is largely unknown. The aim of this study was to evaluate associations between coffee subtypes on incident outcomes, utilizing the UK Biobank. METHODS AND RESULTS: Coffee subtypes were defined as decaffeinated, ground, and instant, then divided into 0, <1, 1, 2-3, 4-5, and >5 cups/day, and compared with non-drinkers. Cardiovascular disease included coronary heart disease, cardiac failure, and ischaemic stroke. Cox regression modelling with hazard ratios (HRs) assessed associations with incident arrhythmia, CVD, and mortality. Outcomes were determined through ICD codes and death records. A total of 449 563 participants (median 58 years, 55.3% females) were followed over 12.5 ± 0.7 years. Ground and instant coffee consumption was associated with a significant reduction in arrhythmia at 1-5 cups/day but not for decaffeinated coffee. The lowest risk was 4-5 cups/day for ground coffee [HR 0.83, confidence interval (CI) 0.76-0.91, P < 0.0001] and 2-3 cups/day for instant coffee (HR 0.88, CI 0.85-0.92, P < 0.0001). All coffee subtypes were associated with a reduction in incident CVD (the lowest risk was 2-3 cups/day for decaffeinated, P = 0.0093; ground, P < 0.0001; and instant coffee, P < 0.0001) vs. non-drinkers. All-cause mortality was significantly reduced for all coffee subtypes, with the greatest risk reduction seen with 2-3 cups/day for decaffeinated (HR 0.86, CI 0.81-0.91, P < 0.0001); ground (HR 0.73, CI 0.69-0.78, P < 0.0001); and instant coffee (HR 0.89, CI 0.86-0.93, P < 0.0001). CONCLUSION: Decaffeinated, ground, and instant coffee, particularly at 2-3 cups/day, were associated with significant reductions in incident CVD and mortality. Ground and instant but not decaffeinated coffee was associated with reduced arrhythmia.

Manipulation of the gut microbiota by the use of prebiotic fibre does not override a genetic predisposition to heart failure.

Increasing evidence supports a role for the gut microbiota in the development of cardiovascular diseases such as hypertension and its progression to heart failure (HF). Dietary fibre has emerged as a modulator of the gut microbiota, resulting in the release of gut metabolites called short-chain fatty acids (SCFAs), such as acetate. We have shown previously that fibre or acetate can protect against hypertension and heart disease in certain models. HF is also commonly caused by genetic disorders. In this study we investigated whether the intake of fibre or direct supplementation with acetate could attenuate the development of HF in a genetic model of dilated cardiomyopathy (DCM) due to overexpression of the cardiac specific mammalian sterile 20-like kinase (Mst1). Seven-week-old male mice DCM mice and littermate controls (wild-type, C57BL/6) were fed a control diet (with or without supplementation with 200 mM magnesium acetate in drinking water), or a high fibre diet for 7 weeks. We obtained hemodynamic, morphological, flow cytometric and gene expression data. The gut microbiome was characterised by 16S rRNA amplicon sequencing. Fibre intake was associated with a significant shift in the gut microbiome irrespective of mouse genotype. However, neither fibre or supplementation with acetate were able to attenuate cardiac remodelling or cardiomyocyte apoptosis in Mst1 mice. Furthermore, fibre and acetate did not improve echocardiographic or hemodynamic parameters in DCM mice. These data suggest that although fibre modulates the gut microbiome, neither fibre nor acetate can override a strong genetic contribution to the development of heart failure in the Mst1 model.

The gut microbiota and blood pressure in experimental models.

PURPOSE OF REVIEW: To summarize evidence supporting that microorganisms colonizing our gastrointestinal tract, collectively known as the gut microbiota, are implicated in the development and maintenance of hypertension in experimental models. RECENT FINDINGS: The use of gnotobiotic (germ-free) mice has been essential for advancement in this area: they develop higher blood pressure (BP) if they receive faecal transplants from hypertensive patients compared to normotensive donors, and germ-free mice have a blunted response to angiotensin II. Experimental hypertension is consistently accompanied by changes in the composition of the gut microbiota. This is combined with a shift in microbial diversity and the deterioration of the gut epithelial barrier commonly referred to as gut dysbiosis. Restoration of normal gut biosis and microbiota alleviates and protects against the development of hypertension in both genetic and pharmacological models. This has been achieved by the use of antibiotics, faecal transplants between normotensive and hypertensive strains, and the use of prebiotics (i.e. food stuff that feeds the microbiota), probiotics (i.e. live bacteria) and gut metabolites (i.e. short-chain fatty acids). SUMMARY: Research into experimental hypertension supports that the gut microbiota contributes to the regulation of BP. Manipulation of the microbiota might represent a new tool to prevent hypertension.

High-Fiber Diet and Acetate Supplementation Change the Gut Microbiota and Prevent the Development of Hypertension and Heart Failure in Hypertensive Mice.

BACKGROUND: Dietary intake of fruit and vegetables is associated with lower incidence of hypertension, but the mechanisms involved have not been elucidated. Here, we evaluated the effect of a high-fiber diet and supplementation with the short-chain fatty acid acetate on the gut microbiota and the prevention of cardiovascular disease. METHODS: Gut microbiome, cardiorenal structure/function, and blood pressure were examined in sham and mineralocorticoid excess-treated mice with a control diet, high-fiber diet, or acetate supplementation. We also determined the renal and cardiac transcriptome of mice treated with the different diets. RESULTS: We found that high consumption of fiber modified the gut microbiota populations and increased the abundance of acetate-producing bacteria independently of mineralocorticoid excess. Both fiber and acetate decreased gut dysbiosis, measured by the ratio of Firmicutes to Bacteroidetes, and increased the prevalence of Bacteroides acidifaciens. Compared with mineralocorticoid-excess mice fed a control diet, both high-fiber diet and acetate supplementation significantly reduced systolic and diastolic blood pressures, cardiac fibrosis, and left ventricular hypertrophy. Acetate had similar effects and markedly reduced renal fibrosis. Transcriptome analyses showed that the protective effects of high fiber and acetate were accompanied by the downregulation of cardiac and renal Egr1, a master cardiovascular regulator involved in cardiac hypertrophy, cardiorenal fibrosis, and inflammation. We also observed the upregulation of a network of genes involved in circadian rhythm in both tissues and downregulation of the renin-angiotensin system in the kidney and mitogen-activated protein kinase signaling in the heart. CONCLUSIONS: A diet high in fiber led to changes in the gut microbiota that played a protective role in the development of cardiovascular disease. The favorable effects of fiber may be explained by the generation and distribution of one of the main metabolites of the gut microbiota, the short-chain fatty acid acetate. Acetate effected several molecular changes associated with improved cardiovascular health and function.

Cardio-protective effects of combined l-arginine and insulin: Mechanism and therapeutic actions in myocardial ischemia-reperfusion injury.

Reduced nitric oxide (NO) bioavailability plays a central role in the pathogenesis of myocardial ischemia-reperfusion injury (I-R), and reduced l-arginine transport via cationic amino acid transporter-1 is a key contributor to the reduced NO levels. Insulin can increase NO levels by increasing the transport of its substrate l-arginine but insulin alone exerts minimal cardiac protection in I-R. We hypothesized that combined insulin and l-arginine may provide cardioprotective effects in the setting of myocardial I-R. The effect of supplemental insulin, l-arginine and the combination was examined in cardiomyocytes exposed to hypoxia/reoxygenation and in isolated perfused mouse hearts undergoing ischemia/reperfusion. When compared to controls, cardiomyocytes treated upon reoxygenation with 1nM insulin+1mM l-arginine exhibited significant (all P<0.05) improvements in NO generation and mitochondrial membrane potential, with a concomitant fall in reactive oxygen species production and LDH release. Insulin also increased l-arginine uptake following hypoxia-reoxygenation (P<0.05; n=4-6). In langendorff perfused isolated mouse hearts, combined l-arginine-insulin treatment upon reperfusion significantly (all P<0.05; n=9-11) improved recovery of left ventricular developed pressure, rate pressure product and end diastolic pressure following ischemia, independent of any changes in post-ischemic coronary flow, together with significantly lower LDH release. The observed improvements were greater than l-arginine or insulin treatment alone. In isolated cardiomyocytes (n=3-5), 1nM insulin caused cationic amino acid transporter-1 to redistribute to the cellular membrane from the cytosol and the effects of insulin on l-arginine uptake were partially dependent on the PI3K/Akt pathway. l-arginine-insulin treatment may be a novel strategy to ameliorate I-R injury.

Atrial electrical and structural remodeling associated with longstanding pulmonary hypertension and right ventricular hypertrophy in humans.

INTRODUCTION: Pulmonary hypertension (PH) is common to a range of cardiopulmonary conditions and is associated with atrial arrhythmias. However, little is known of the isolated atrial effects of PH and right atrial dilatation (RA) in humans. To avoid the confounding effects of PH-associated disease states, we performed detailed electrophysiological (EP) and electroanatomic (EA) mapping of the RA in patients with idiopathic PH. METHODS AND RESULTS: Eight PH patients (mean pulmonary arterial [PA] pressure 39.0 ± 15.8 mmHg) and 16 age-matched controls (mean PA pressure 11.5 ± 4.1 mmHg, P < 0.0001) were studied. Corrected sinus node recovery times (cSNRT), atrial effective refractory periods (ERPs), conduction delay at the crista terminalis (CT), and inducibility of atrial fibrillation (AF) were evaluated. EA mapping (pacing cycle length 600 and 300 milliseconds) was performed to determine RA global and regional voltage, conduction velocities, atrial activation times, fractionated electrograms and double potentials. Patients with PH demonstrated a prolongation in cSNRT without significant change in atrial ERP and an increase in AF inducibility. PH was associated with lower tissue voltage (1.8 ± 0.4 mV in PH vs 2.2 ± 0.4 mV in controls, P = 0.02), increased low voltage areas (13.7 ± 8.2% in PH vs 6.2 ± 3.7% in controls, P < 0.01) and the presence of electrically silent areas. Conduction velocities were slower (global 67.3 ± 5.6 cm/s vs 92.8 ± 4.0 cm/s, P < 0.001) and fractionated electrograms and double potentials were more prevalent (14.7 ± 4.4% vs 6.3 ± 4.1, P < 0.01) in PH compared with controls, respectively. CONCLUSION: Idiopathic PH is associated with RA remodeling characterized by: generalized conduction slowing with marked regional abnormalities; reduced tissue voltage; and regions of electrical silence. These changes provide important insights into the isolated effects of PH fundamental to a range of clinical conditions associated with AF.

Myocardial and systemic iron depletion in heart failure implications for anemia accompanying heart failure.

OBJECTIVES: This study sought to determine the potential pathophysiological link between anemia and disease severity, and adverse outcome in heart failure (HF). BACKGROUND: Anemia frequently accompanies advanced HF; however, the pathophysiological mechanism responsible for the association between anemia and more severe HF remains uncertain. We hypothesized that a depletion of myocardial iron content may provide the biological link. METHODS: Complementary clinical and basic studies were performed. Hemodynamic, biochemical, and echocardiographic investigations were performed in 9 healthy controls and 25 patients with advanced HF (left ventricular ejection fraction: 23 ± 10%). Tissue iron content and type 1 transferrin receptor (Tfr1) expression were assessed in human myocardial tissue, and the regulation of Tfr1 expression was studied in isolated cardiomyocytes. RESULTS: HF patients displayed evidence of iron deficiency as measured by lower serum iron (p < 0.05) and transferrin saturation (TFS) (p < 0.05). When subclassified according to the presence of anemia, TFS was lower in anemic compared with nonanemic HF patients, whereas TFS in nonanemic HF patients was intermediate. In association, myocardial iron content was reduced in HF versus non-HF samples (0.49 ± 0.07 µg/g vs. 0.58 ± 0.09 µg/g, p < 0.05), and there was a significant reduction (p < 0.05) in the myocardial mRNA expression of Tfr1, which plays a key role in cellular iron transport. In the context of HF, catecholamines and aldosterone both down-regulated Tfr1 expression in isolated cardiomyocytes. CONCLUSIONS: This study suggests the presence of iron depletion in the failing human heart, providing a potential link for the association between anemia and adverse prognosis in HF.

Reduced L-arginine transport contributes to the pathogenesis of myocardial ischemia-reperfusion injury.

Myocardial injury due to ischemia-reperfusion (I-R) damage remains a major clinical challenge. Its pathogenesis is complex including endothelial dysfunction and heightened oxidative stress although the key driving mechanism remains uncertain. In this study we tested the hypothesis that the I-R process induces a state of insufficient L-arginine availability for NO biosynthesis, and that this is pivotal in the development of myocardial I-R damage. In neonatal rat ventricular cardiomyocytes (NVCM), hypoxia-reoxygenation significantly decreased L-arginine uptake and NO production (42 +/- 2% and 71 +/- 4%, respectively, both P < 0.01), maximal after 2 h reoxygenation. In parallel, mitochondrial membrane potential significantly decreased and ROS production increased (both P < 0.01). NVCMs infected with adenovirus expressing the L-arginine transporter, CAT1, and NVCMs supplemented with L-arginine both exhibited significant (all P < 0.05) improvements in NO generation and mitochondrial membrane potentials, with a concomitant significant fall in ROS production and lactate dehydrogenase release during hypoxia-reoxygenation. In contrast, L-arginine deprived NVCM had significantly worsened responses to hypoxia-reoxygenation. In isolated perfused mouse hearts, L-arginine infusion during reperfusion significantly improved left ventricular function after I-R. These improved contractile responses were not dependent on coronary flow but were associated with a significant decrease in nitrotyrosine formation and increases in phosphorylation of both Akt and troponin I. Collectively, these data strongly implicate reduced L-arginine availability as a key factor in the pathogenesis of I-R injury. Increasing L-arginine availability via increased CAT1 expression or by supplementation improves myocardial responses to I-R. Restoration of L-arginine availability may therefore be a valuable strategy to ameliorate I-R injury.

Myocardial ischemia-reperfusion injury, antioxidant enzyme systems, and selenium: a review.

Coronary heart disease (CHD) remains the greatest killer in the Western world, and although the death rate from CHD has been falling, the current increased prevalence of major risk factors including obesity and diabetes, suggests it is likely that CHD incidence will increase over the next 20 years. In conjunction with preventive strategies, major advances in the treatment of acute coronary syndromes and myocardial infarction have occurred over the past 20 years. In particular the ability to rapidly restore blood flow to the myocardium during heart attack, using interventional cardiologic or thrombolytic approaches has been a major step forward. Nevertheless, while 'reperfusion' is a major therapeutic aim, the process of ischemia followed by reperfusion is often followed by the activation of an injurious cascade. While the pathogenesis of ischemia-reperfusion is not completely understood, there is considerable evidence implicating reactive oxygen species (ROS) as an initial cause of the injury. ROS formed during oxidative stress can initiate lipid peroxidation, oxidize proteins to inactive states and cause DNA strand breaks, all potentially damaging to normal cellular function. ROS have been shown to be generated following routine clinical procedures such as coronary bypass surgery and thrombolysis, due to the unavoidable episode of ischemia-reperfusion. Furthermore, they have been associated with poor cardiac recovery post-ischemia, with recent studies supporting a role for them in infarction, necrosis, apoptosis, arrhythmogenesis and endothelial dysfunction following ischemia-reperfusion. In normal physiological condition, ROS production is usually homeostatically controlled by endogenous free radical scavengers such as superoxide dismutase, catalase, and the glutathione peroxidase and thioredoxin reductase systems. Accordingly, targeting the generation of ROS with various antioxidants has been shown to reduce injury following oxidative stress, and improve recovery from ischemia-reperfusion injury. This review summarises the role of myocardial antioxidant enzymes in ischemia-reperfusion injury, particularly the glutathione peroxidase (GPX) and the thioredoxin reductase (TxnRed) systems. GPX and TxnRed are selenocysteine dependent enzymes, and their activity is known to be dependent upon an adequate supply of dietary selenium. Moreover, various studies suggest that the supply of selenium as a cofactor also regulates gene expression of these selenoproteins. As such, dietary selenium supplementation may provide a safe and convenient method for increasing antioxidant protection in aged individuals, particularly those at risk of ischemic heart disease, or in those undergoing clinical procedures involving transient periods of myocardial hypoxia.

Adverse effects of cigarette smoke on NO bioavailability: role of arginine metabolism and oxidative stress.

Endothelial dysfunction is a hallmark of cardiovascular disease, and the l-arginine:NO pathway plays a critical role in determining endothelial function. Recent studies suggest that smoking, a well-recognized risk factor for vascular disease, may interfere with l-arginine and NO metabolism; however, this remains poorly characterized. Accordingly, we performed a series of complementary in vivo and in vitro studies to elucidate the mechanism by which cigarette smoke adversely affects endothelial function. In current smokers, plasma levels of asymmetrical dimethyl-arginine (ADMA) were 80% higher (P = 0.01) than nonsmokers, whereas citrulline (17%; P < 0.05) and N-hydroxy-l-arginine (34%; P < 0.05) were significantly lower. Exposure to 10% cigarette smoke extract (CSE) significantly affected endothelial arginine metabolism with reductions in the intracellular content of citrulline (81%), N-hydroxy-l-arginine (57%), and arginine (23%), while increasing ADMA (129%). CSE significantly inhibited (38%) arginine uptake in conjunction with a 34% reduction in expression of the arginine transporter, CAT1. In conjunction with these studies, CSE significantly reduced the activity of eNOS and NO production by endothelial cells, while stimulating the production of reactive oxygen species. In conclusion, cigarette smoke adversely affects the endothelial l-arginine NO synthase pathway, resulting in reducing NO production and elevated oxidative stress. In conjunction, exposure to cigarette smoke increases ADMA concentration, the latter being a risk factor for cardiovascular disease.

Impaired L-arginine transport and endothelial function in hypertensive and genetically predisposed normotensive subjects.

BACKGROUND: Impaired endothelium-dependent NO-mediated vasodilation is a key feature of essential hypertension and may precede the increase in blood pressure. We investigated whether transport of the NO precursor L-arginine is related to decreased endothelial function. METHODS AND RESULTS: Radiotracer kinetics ([3H]L-arginine) were used to measure forearm and peripheral blood mononuclear cell arginine uptake in hypertensive subjects (n=12) and in 2 groups of healthy volunteers with (n=15) and without (n=15) a family history of hypertension. In conjunction, forearm blood flow responses to acetylcholine and sodium nitroprusside were measured before and after a supplemental intra-arterial infusion of L-arginine. In vivo and in vitro measures of L-arginine transport were substantially reduced in the essential hypertension and positive family history groups compared with the negative family history group; however, no difference was detected in peripheral blood mononuclear cell mRNA or protein expression levels for the cationic amino acid transporter CAT-1. Plasma concentrations of L-arginine and N(G),N(G')-dimethylarginine (ADMA) did not differ between groups. L-arginine supplementation improved the response to acetylcholine only in subjects with essential hypertension and positive family history. CONCLUSIONS: Similar to their hypertensive counterparts, normotensive individuals at high risk for the development of hypertension are characterized by impaired L-arginine transport, which may represent the link between a defective L-arginine/NO pathway and the onset of essential hypertension. The observed transport defect is not due to apparent alterations in CAT-1 expression or elevated endogenous ADMA.

beta-Adrenoceptor-mediated, nitric-oxide-dependent vasodilatation is abnormal in early hypertension: restoration by L-arginine.

BACKGROUND: It is unknown whether beta-adrenoceptor-mediated vasodilatation is altered in early hypertension and whether it can be modulated by L-arginine. METHODS AND DESIGN: We measured changes in forearm blood flow by plethysmography in response to acetylcholine (9 and 37 microg/min), sodium nitroprusside (200 and 800 ng/min) and the beta-receptor agonist, isoproterenol (50 and 200 ng/min) in 12 patients with essential hypertension (group EH) and in healthy volunteers with (group PFH; n = 14) and without (group NFH; n = 14) a family history of essential hypertension, before and during concomitant infusion of L-arginine (10 micromol/min). In five individuals from each group, infusion of acetylcholine and isoproterenol was repeated during the concurrent blockade of nitric oxide synthesis by N-monomethyl-L-arginine (L-NMMA; 4 micromol/min). RESULTS: The response to acetylcholine was reduced in groups EH and PFH compared with group NFH (both P < 0.05), whereas the vasodilator effects of isoproterenol and sodium nitroprusside were similar in all three groups. Acetylcholine- and isoproterenol-induced vasodilatation did not change during infusion of the nitric oxide precursor, L-arginine, in group NFH, but were significantly enhanced by L-arginine in groups PFH and EH [forearm blood flow before and after isoproterenol 200 ng/min: group PFH 11.8 +/- 1.02 and 13.3 +/- 1.08 ml/min, respectively (P < 0.05); group EH: 11.3 +/- 1.57 and 14.9 +/- 1.91 ml/min, respectively (P < 0.01)]. Co-infusion of L-NMMA blunted the response to acetylcholine and isoproterenol in group NFH (P < 0.05), but did not significantly modify vasodilatation in groups PFH and EH. CONCLUSIONS: Although beta-adrenergic vasodilatation seemed to be unaltered in early hypertension, L-arginine enhanced the response to isoproterenol, whereas concomitant inhibition of nitric oxide synthase by L-NMMA had no significant effect. These findings suggest that the nitric oxide component of isoproterenol-mediated vasodilatation is impaired in early hypertension and possibly compensated by increased beta-adrenoceptor responsiveness of smooth muscle cells. In this setting, supplementation of the nitric oxide precursor, L-arginine, enhances the vasodilator response to beta-adrenergic stimulation.