Left Ventricular Systolic Dysfunction in NBCe1-B/C-Knockout Mice.

Congenital proximal renal tubular acidosis (pRTA) is a rare systemic disease caused by mutations in the SLC4A4 gene that encodes the electrogenic sodium bicarbonate cotransporter, NBCe1. The major NBCe1 protein variants are designated NBCe1-A, NBCe1-B, and NBCe1-C. NBCe1-A expression is kidney-specific, NBCe1-B is broadly expressed and is the only NBCe1 variant expressed in the heart, and NBCe1-C is a splice variant of NBCe1-B that is expressed in the brain. No cardiac manifestations have been reported from patients with pRTA, but studies in adult rats with virally induced reduction in cardiac NBCe1-B expression indicate that NBCe1-B loss leads to cardiac hypertrophy and prolonged QT intervals in rodents. NBCe1-null mice die shortly after weaning, so the consequence of congenital, global NBCe1 loss on the heart is unknown. To circumvent this issue, we characterized the cardiac function of NBCe1-B/C-null (KOb/c) mice that survive up to 2 months of age and which, due to the uninterrupted expression of NBCe1-A, do not exhibit the confounding acidemia of the globally null mice. In contrast to the viral knockdown model, cardiac hypertrophy was not present in KOb/c mice as assessed by heart-weight-to-body-weight ratios and cardiomyocyte cross-sectional area. However, echocardiographic analysis revealed reduced left ventricular ejection fraction, and intraventricular pressure-volume measurements demonstrated reduced load-independent contractility. We also observed increased QT length variation in KOb/c mice. Finally, using the calcium indicator Fura-2 AM, we observed a significant reduction in the amplitude of Ca2+ transients in paced KOb/c cardiomyocytes. These data indicate that congenital, global absence of NBCe1-B/C leads to impaired cardiac contractility and increased QT length variation in juvenile mice. It remains to be determined whether the cardiac phenotype in KOb/c mice is influenced by the absence of NBCe1-B/C from neuronal and endocrine tissues.

Widespread intracoronary allogeneic cardiosphere-derived cell therapy with and without cyclosporine in reperfused myocardial infarction.

Allogeneic cardiosphere-derived cell (CDC) therapy has been demonstrated to improve myocardial function when administered to reperfused myocardial infarcts. We previously pretreated animals with low-dose cyclosporine immunosuppression to limit allogeneic CDC rejection, but whether it is necessary and, if so, can be initiated at the time of reperfusion remains uncertain. Closed-chest swine (n = 29 animals) were subjected to a 90-min left anterior descending (LAD) coronary artery occlusion. Using a three-way blinded design, we randomized two groups to receive global intracoronary infusions of 20 × 106 CDCs 30 min after reperfusion. A third control group was treated with saline. One CDC group received cyclosporine 10 min before reperfusion (2.5 mg/kg iv and 100 mg/day po), whereas the other groups received placebos. After 1 mo, neither chronic infarct size relative to area at risk (saline control, 46.2 ± 4.0%; CDCs, 46.4 ± 2.1%; and CDCs + cyclosporine, 49.2 ± 3.1%; P = 0.79) nor ejection fraction (saline control, 51 ± 2%; CDCs, 51 ± 2%; and CDC + cyclosporine, 48 ± 2%; P = 0.42) were different among treatment groups. Multiple histological measures of cellular remodeling, myocyte proliferation, and apoptosis were also not different among treatment groups. In contrast to previous studies, we were unable to reproduce the cardioprotective effects demonstrated by allogeneic CDCs without cyclosporine. Furthermore, initiation of intravenous cyclosporine at the time of reperfusion followed by oral therapy was not sufficient to elicit the functional improvement observed in studies where cyclosporine was started 72 h before CDC therapy. This suggests that oral cyclosporine pretreatment may be necessary to effect cardiac repair with allogeneic CDCs.NEW & NOTEWORTHY In a three-way blinded, randomized design, we determined whether allogeneic CDCs administered at reperfusion improved myocardial function and whether intravenous cyclosporine enhanced their efficacy. In contrast to prior studies using oral cyclosporine, CDCs with or without intravenous cyclosporine had no effect on function or infarct size. This indicates that CDCs may be most efficacious for treating chronic LV dysfunction where cyclosporine can be initiated at least 72 h before cell therapy.

Transmural variation in microvascular remodeling following percutaneous revascularization of a chronic coronary stenosis in swine.

Remodeling of the coronary microcirculation is known to occur distal to a chronic coronary stenosis, but the reversibility of these changes and their functional significance on maximum myocardial perfusion before and after revascularization is unknown. Accordingly, swine instrumented with a chronic silastic stenosis on the left anterior descending coronary artery to produce hibernating myocardium underwent percutaneous coronary intervention (PCI; n = 8) and were compared with animals with a persistent stenosis (n = 8), as well as sham controls (n = 6). Stenotic animals demonstrated an increased subendocardial arteriolar wall thickness-to-lumen ratio (37.8 ± 3.3 vs. 28.3 ± 1.3% in sham, P = 0.04), reduced lumen area per arteriole (597 ± 88 vs. 927 ± 113 µm2, P = 0.04), and a compensatory increase in arteriolar density (9.4 ± 1.0 vs. 5.3 ± 0.4 arterioles/mm2, P < 0.01). As a result, vasodilated flow immediately after PCI was similar to normally perfused remote regions (5.1 ± 1.0 vs. 4.8 ± 0.9 ml·min-1·g-1, P = 0.87). When assessed 1-mo after PCI, increases in wall thickness-to-lumen diameter (42.2 ± 3.3%) and reductions in lumen area per arteriole (638 ± 59 µm2) remained unchanged, but arteriolar density returned to normal (5.2 ± 0.5 arterioles/mm2). As a result, maximum subendocardial flow during adenosine declined and was lower than remote regions (2.6 ± 0.3 vs. 5.9 ± 1.1 ml·min-1·g-1, P = 0.01). There was no microvascular remodeling in subepicardial arterioles, and maximum perfusion remained unchanged. These data demonstrate that subendocardial microvascular remodeling occurs distal to a chronic epicardial stenosis. The regression of arteriolar density without increases in luminal area may precipitate stress-induced subendocardial ischemia in the absence of a physiologically significant stenosis.NEW & NOTEWORTHY Swine with a chronic coronary stenosis exhibit subendocardial microvascular remodeling distal to a critical stenosis characterized by an increase in arteriolar wall thickness and reduction in lumen area with a compensatory increase in arteriolar density. The present study is the first to demonstrate that subendocardial arteriolar density normalizes 1-mo after revascularization, but the lumen area of individual arterioles remains reduced. This leads to a reduction in maximal subendocardial perfusion at this time point despite initial normalization of vasodilator reserve after revascularization. This pattern of chronic microvascular structural remodeling could contribute to recurrent subendocardial ischemia in the absence of coronary restenosis during tachycardia and increases in myocardial oxygen demand.

Quantitative proteomic and phosphoproteomic profiling of ischemic myocardial stunning in swine.

Despite decades of research on the pathophysiology of myocardial stunning, protein changes and/or phosphorylation status underlying alterations in cardiac function/structure remain inadequately understood. Here, we utilized comprehensive and quantitative proteomic and phosphoproteomic approaches to explore molecular mechanisms of myocardial stunning in swine. The closed-chest swine (n = 5 pigs) were subjected to a 10-min left anterior descending coronary artery (LAD) occlusion producing regional myocardial stunning. Tissues from the ischemic LAD region and a remote nonischemic area of the left ventricle were collected 1 h after reperfusion. Ion current-based proteomics (IonStar) and quantitative phosphoproteomics were employed in parallel to identify alterations in protein level and site-specific phosphorylation changes. A novel swine heart protein database exhibiting high accuracy and low redundancy was developed here to facilitate comprehensive study. Further informatic investigations identified potential protein-protein interactions in stunned myocardium. In total, we quantified 2,099 protein groups and 4,699 phosphorylation sites with only 0.4% missing values. Proteomic analyses revealed downregulation of contractile function and extracellular matrix remodeling. Meanwhile, alterations in phosphorylation linked with contractile dysfunction and apoptotic cell death were uncovered. NetworKIN/STRING analysis predicted regulatory kinases responsible for altered phosphosites, such as protein kinase C-mediated phosphorylation of cardiac troponin I-S199 and CaMKII-mediated phosphorylation of phospholamban-T17. In summary, the ion current-based proteomics and phosphoproteomics reliably identified novel alterations in protein content and phosphorylation contributing to contractile dysfunction, extracellular matrix (ECM) damage, and programmed cell death in stunned myocardium, which corroborate well with our physiological observations. Moreover, this work developed a comprehensive database of the swine heart proteome, a highly valuable resource for future translational research in porcine models with cardiovascular diseases.NEW & NOTEWORTHY We first used ion current-based proteomics and phosphoproteomics to reliably identify novel alterations in protein expression and phosphorylation contributing to contractile dysfunction, extracellular matrix (ECM) damage, and programmed cell death in stunned myocardium and developed a comprehensive swine heart-specific proteome database, which provides a valuable resource for future research in porcine models of cardiovascular diseases.

Effect of Intracoronary Metformin on Myocardial Infarct Size in Swine.

RATIONALE: Metformin has been demonstrated to decrease infarct size (IS) and prevent postinfarction left ventricular (LV) remodeling in rodents when given intravenously at the time of reperfusion. It remains unclear whether similar cardioprotection can be achieved in a large animal model. OBJECTIVE: The objective of this study was to determine whether intravascular infusion of metformin at the time of reperfusion reduces myocardial IS in a porcine model of acute myocardial infarction. METHODS AND RESULTS: In a blinded and randomized preclinical study, closed-chest swine (n=20) were subjected to a 60-minute left anterior descending coronary artery occlusion to produce myocardial infarction. Contrast-enhanced computed tomography was performed during left anterior descending coronary artery occlusion to assess the ischemic area-at-risk. Animals were randomized to receive either metformin or vehicle as an initial intravenous bolus (5 mg/kg) 8 minutes before reperfusion, followed by a 15-minute left coronary artery infusion (1 mg/kg per minute) commencing with the onset of reperfusion. Echocardiography and computed tomographic imaging of LV function were performed 1 week later, at which time the heart was removed for postmortem pathological analysis of area-at-risk and IS (triphenyltetrazolium chloride). Baseline variables including hemodynamics and LV function were similar between groups. Peak circulating metformin concentrations of 374±35 µmol/L were achieved 15 minutes after reperfusion. There was no difference between the area-at-risk as a percent of LV mass by computed tomography (vehicle: 20.7%±1.1% versus metformin: 19.7%±1.3%; P=0.59) or postmortem pathology (22.4%±1.2% versus 20.2%±1.2%; P=0.21). IS relative to area-at-risk averaged 44.5%±5.0% in vehicle-treated versus 38.2%±6.8% in metformin-treated animals ( P=0.46). There was no difference in global function 7 days after myocardial infarction as assessed by echocardiography or computed tomographic ejection fraction (56.2%±2.6% versus 56.3%±2.4%; P=0.98). CONCLUSIONS: In contrast to rodent hearts, postconditioning with high-dose metformin administered immediately before reperfusion does not reduce IS or improve LV function 7 days after myocardial infarction in swine. These results reinforce the importance of rigorously testing therapies in large animal models to facilitate clinical translation of novel cardioprotective therapies.

Nonocclusive multivessel intracoronary infusion of allogeneic cardiosphere-derived cells early after reperfusion prevents remote zone myocyte loss and improves global left ventricular function in swine with myocardial infarction.

Intracoronary cardiosphere-derived cells (icCDCs) infused into the infarct-related artery reduce scar volume but do not improve left ventricular (LV) ejection fraction (LVEF). We tested the hypothesis that this reflects the inability of regional delivery to prevent myocyte death or promote myocyte proliferation in viable myocardium remote from the infarct. Swine (n = 23) pretreated with oral cyclosporine (200 mg/day) underwent a 1-h left anterior descending coronary artery (LAD) occlusion, which reduced LVEF from 61.6 ± 1.0 to 45.3 ± 1.5% 30 min after reperfusion. At that time, animals received global infusion of allogeneic icCDCs (n = 8), regional infusion of icCDCs restricted to the LAD using the stop-flow technique (n = 8), or vehicle (n = 7). After 1 mo, global icCDCs increased LVEF from 44.8 ± 1.9 to 60.8 ± 3.8% (P < 0.05) with no significant change after LAD stop-flow icCDCs (44.8 ± 3.6 to 50.9 ± 3.1%) or vehicle (46.5 ± 2.5 to 47.7 ± 2.6%). In contrast, global icCDCs did not alter infarct volume (%LV mass) assessed at 2 days (11.2 ± 2.3 vs. 12.6 ± 2.3%), whereas it was reduced after LAD stop-flow icCDCs (7.1 ± 1.1%, P < 0.05). Histopathological analysis of remote myocardium after global icCDCs demonstrated a significant increase in myocyte proliferation (147 ± 32 vs. 14 ± 10 nuclei/106 myocytes, P < 0.05) and a reduction in myocyte apoptosis (15 ± 9 vs. 46 ± 10 nuclei/106 myocytes, P < 0.05) that increased myocyte nuclear density (1,264 ± 39 vs. 1,157 ± 33 nuclei/mm2, P < 0.05) and decreased myocyte diameter (13.2 ± 0.2 vs. 14.5 ± 0.3 µm, P < 0.05) compared with vehicle-treated controls. In contrast, remote zone changes after regional LAD icCDCs were no different from vehicle. These data indicate that changes in global LVEF after icCDCs are dependent upon preventing myocyte loss and hypertrophy in myocardium remote from the infarct. These arise from stimulating myocyte proliferation and reducing myocyte apoptosis indicating the importance of directing cell therapy to viable remote regions.NEW & NOTEWORTHY Administration of allogeneic cardiosphere-derived cells to the entire heart via global intracoronary infusion shortly after myocardial infarction favorably influenced left ventricular ejection fraction by preventing myocyte death and promoting myocyte proliferation in remote, noninfarcted myocardium in swine. In contrast, regional intracoronary cell infusion did not significantly affect remote zone myocyte remodeling. Global cell administration targeting viable myocardium remote from the infarct may be an effective approach to prevent adverse ventricular remodeling after myocardial infarction.

Comparative Efficacy of Intracoronary Allogeneic Mesenchymal Stem Cells and Cardiosphere-Derived Cells in Swine with Hibernating Myocardium.

RATIONALE: Allogeneic bone marrow-derived mesenchymal stem cells (MSCs) and cardiosphere-derived cells (CDCs) have each entered clinical trials, but a direct comparison of these cell types has not been performed in a large animal model of hibernating myocardium. OBJECTIVE: Using completely blinded methodology, we compared the efficacy of global intracoronary allogeneic MSCs (icMSCs, ≈35×10(6)) and CDCs (icCDCs, ≈35×10(6)) versus vehicle in cyclosporine-immunosuppressed swine with a chronic left anterior descending coronary artery stenosis (n=26). METHODS AND RESULTS: Studies began 3 months after instrumentation when wall thickening was reduced (left anterior descending coronary artery % wall thickening [mean±SD], 38±11% versus 83±26% in remote; P<0.01) and similar among groups. Four weeks after treatment, left anterior descending coronary artery % wall thickening increased similarly after icCDCs and icMSCs, whereas it remained depressed in vehicle-treated controls (icMSCs, 51±13%; icCDCs, 51±17%; vehicle, 34±3%, treatments P<0.05 versus vehicle). There was no change in myocardial perfusion. Both icMSCs and icCDCs increased left anterior descending coronary artery myocyte nuclear density (icMSCs, 1601±279 nuclei/mm(2); icCDCs, 1569±294 nuclei/mm(2); vehicle, 973±181 nuclei/mm(2); treatments P<0.05 versus vehicle) and reduced myocyte diameter (icMSCs, 16.4±1.5 µm; icCDCs, 16.8±1.2 µm; vehicle, 20.2±3.7 µm; treatments P<0.05 versus vehicle) to the same extent. Similar changes in myocyte nuclear density and diameter were observed in the remote region of cell-treated animals. Cell fate analysis using Y-chromosome fluorescent in situ hybridization demonstrated rare cells from sex-mismatched donors. CONCLUSIONS: Allogeneic icMSCs and icCDCs exhibit comparable therapeutic efficacy in a large animal model of hibernating myocardium. Both cell types produced equivalent increases in regional function and stimulated myocyte regeneration in ischemic and remote myocardium. The activation of endogenous myocyte proliferation and regression of myocyte cellular hypertrophy support a common mechanism of cardiac repair.

Porcine Model of Hypertrophy-Independent Left Ventricular Stiffening via Repetitive Pressure Overload.

Diastolic dysfunction arising from alterations in myocardial structure and/or function is a central component of several cardiovascular disorders, including heart failure with preserved ejection fraction (HFpEF). Basic research aimed at understanding underlying mechanisms contributing to the development of diastolic dysfunction has generally centered upon models of left ventricular (LV) hypertrophy arising from persistent and severe elevations in myocardial afterload (e.g., aortic banding). Mechanisms of hypertrophy-independent diastolic dysfunction, on the other hand, have received less attention, even though overt anatomic LV hypertrophy is absent in many HFpEF patients. Here, we describe the development of a novel porcine model of repetitive pressure overload (RPO) in which chronic, intermittent exposure to transient episodes of hypertension produces an increase in LV stiffness, interstitial fibrosis, cardiomyocyte hypertrophy, and capillary rarefaction without significant changes in LV mass. This model offers important insight into how diastolic dysfunction and HFpEF may develop in the absence of comorbidities, sustained hypertension, or LV hypertrophy, while also providing a useful translational research tool for investigation of novel therapeutic approaches to restore myocardial compliance and improve diastolic function.

Stem cell stimulation of endogenous myocyte regeneration.

Cell-based therapy has emerged as a promising approach to combat the myocyte loss and cardiac remodelling that characterize the progression of left ventricular dysfunction to heart failure. Several clinical trials conducted over the past decade have shown that a variety of autologous bone-marrow- and peripheral-blood-derived stem and progenitor cell populations can be safely administered to patients with ischaemic heart disease and yield modest improvements in cardiac function. Concurrently, rapid progress has been made at the pre-clinical level to identify novel therapeutic cell populations, delineate the mechanisms underlying cell-mediated cardiac repair and optimize cell-based approaches for clinical use. The following review summarizes the progress that has been made in this rapidly evolving field over the past decade and examines how our current understanding of the mechanisms involved in successful cardiac regeneration should direct future investigation in this area. Particular emphasis is placed on discussion of the general hypothesis that the benefits of cell therapy primarily result from stimulation of endogenous cardiac repair processes that have only recently been identified in the adult mammalian heart, rather than direct differentiation of exogenous cells. Continued scientific investigation in this area will guide the optimization of cell-based approaches for myocardial regeneration, with the ultimate goal of clinical implementation and substantial improvement in our ability to restore cardiac function in ischaemic heart disease patients.

Galectin-3 Is Associated with Cardiac Fibrosis and an Increased Risk of Sudden Death.

BACKGROUND: Myocardial fibrosis is a common postmortem finding among individuals with Sudden Cardiac Death (SCD). Numerous in vivo and in vitro studies have shown that increased galectin-3 (gal3) expression into the myocardium is associated with higher incidence of fibrosis. Although elevated gal3 expression is linked with myocardial fibrosis, its role in predicting the risk of SCD is unknown. METHODS: We reviewed the clinical datasets and post-mortem examination of 221 subjects who had died suddenly. We examined myocardial pathology including the extent of cardiac hypertrophy, fibrosis, and the degree of coronary atherosclerosis in these subjects. In a select group of SCD subjects, we studied myocardial gal3 and periostin expression using immunohistochemistry. To further examine if a higher level of circulating gal3 can be detected preceding sudden death, we measured serum gal3 in a porcine model of subtotal coronary artery ligation which shows an increased tendency to develop lethal cardiac arrhythmias, including ventricular tachycardia or fibrillation. RESULTS: Of the total 1314 human subjects screened, 12.7% had SCD. Comparison of age-matched SCD with non-SCD subjects showed that SCD groups had excessive myocardial fibrosis involving both the left ventricular free wall and interventricular septum. In pigs with subtotal coronary artery ligation and SCD, we detected significantly elevated circulating gal3 levels approximately 10 days preceding the SCD event. Immunohistochemistry showed increased myocardial gal3 and periostin expression in pigs that died suddenly, compared to the controls. CONCLUSION: Our study shows that increased gal3 is associated with a higher risk of myocardial fibrosis and the risk of SCD. This supports the importance of larger translational studies to target gal3 to prevent cardiac fibrosis and attenuate the risk of SCD.

Preclinical evaluation of triiodothyronine nanoparticles as a novel therapeutic intervention for resuscitation from cardiac arrest.

BACKGROUND: Given emerging evidence of rapid non-genomic cytoprotective effects of triiodothyronine (T3), we evaluated the resuscitative efficacy of two nanoparticle formulations of T3 (T3np) designed to prolong cell membrane receptor-mediated signaling. METHODS: Swine (n = 40) were randomized to intravenous vehicle (empty np), EPI (0.015 mg/kg), T3np (0.125 mg/kg), or T3np loaded with phosphocreatine (T3np + PCr; 0.125 mg/kg) during CPR following 7-min cardiac arrest (n = 10/group). Hemodynamics and biomarkers of heart (cardiac troponin I; cTnI) and brain (neuron-specific enolase; NSE) injury were assessed for up to 4-hours post-ROSC, at which time the heart and brain were collected for post-mortem analysis. RESULTS: Compared with vehicle (4/10), the rate of ROSC was higher in swine receiving T3np (10/10; p < 0.01), T3np + PCr (8/10; p = 0.08) or EPI (10/10; p < 0.01) during CPR. Although time to ROSC and survival duration were comparable between groups, EPI was associated with a ∼2-fold higher post-ROSC concentration of cTnI vs T3np and T3np + PCr and the early post-ROSC rise in NSE and neuronal injury were attenuated in T3np-treated vs EPI-treated animals. Analysis of hippocampal ultrastructure revealed deterioration of mitochondrial integrity, reduced active zone length, and increased axonal vacuolization in EPI-treated animals vs controls. However, the frequency of these abnormalities was diminished in animals resuscitated with T3np. CONCLUSIONS: T3np achieved a ROSC rate and post-ROSC survival that was superior to vehicle and comparable to EPI. The attenuation of selected biomarkers of cardiac and neurologic injury at individual early post-ROSC timepoints in T3np-treated vs EPI-treated animals suggests that T3np administration during CPR may lead to more favorable outcomes in cardiac arrest.

Survivin regulates intracellular stiffness and extracellular matrix production in vascular smooth muscle cells.

Vascular dysfunction is a common cause of cardiovascular diseases characterized by the narrowing and stiffening of arteries, such as atherosclerosis, restenosis, and hypertension. Arterial narrowing results from the aberrant proliferation of vascular smooth muscle cells (VSMCs) and their increased synthesis and deposition of extracellular matrix (ECM) proteins. These, in turn, are modulated by arterial stiffness, but the mechanism for this is not fully understood. We found that survivin is an important regulator of stiffness-mediated ECM synthesis and intracellular stiffness in VSMCs. Whole-transcriptome analysis and cell culture experiments showed that survivin expression is upregulated in injured femoral arteries in mice and in human VSMCs cultured on stiff fibronectin-coated hydrogels. Suppressed expression of survivin in human VSMCs significantly decreased the stiffness-mediated expression of ECM components related to arterial stiffening, such as collagen-I, fibronectin, and lysyl oxidase. By contrast, expression of these ECM proteins was rescued by ectopic expression of survivin in human VSMCs cultured on soft hydrogels. Interestingly, atomic force microscopy analysis showed that suppressed or ectopic expression of survivin decreases or increases intracellular stiffness, respectively. Furthermore, we observed that inhibiting Rac and Rho reduces survivin expression, elucidating a mechanical pathway connecting intracellular tension, mediated by Rac and Rho, to survivin induction. Finally, we found that survivin inhibition decreases FAK phosphorylation, indicating that survivin-dependent intracellular tension feeds back to maintain signaling through FAK. These findings suggest a novel mechanism by which survivin potentially modulates arterial stiffness.

Effects of endothelin-1 on endothelial progenitor cell function.

BACKGROUND: Circulating endothelial progenitor cells (EPCs) contribute to vascular endothelial repair. Endothelin (ET)-1 is associated with endothelial damage and atherogenesis. The experimental aim of this study was to determine, in vitro, the effects of ET-1 on the ability of EPCs to form colonies, migrate, release angiogenic growth factors and resist apoptosis. METHODS: Peripheral blood samples were collected from 10 healthy adult humans. Cells with phenotypic EPC characteristics were isolated and EPC colony-forming capacity (CFU assay), migratory activity (Boyden chamber), release of angiogenic growth factors (enzyme immunoassay) and apoptosis (TUNEL assay) were determined in the absence and presence of ET-1 (100 pmol). RESULTS: EPC colony-forming units (42±12 vs. 39±11), migratory capacity (910±146 vs. 936±148 AU) and release of vascular endothelial growth factor (202.8±68.1 vs. 204.8±69.8 pg/mL) and granulocyte-colony stimulating factor (1294.4±378.3 vs. 1136.1±310.3 pg/mL) were not significantly affected by ET-1. EPCs treated with ET-1 demonstrated a 20% increase (p<0.05) in cellular apoptosis. The proapoptotic effect of ET-1 was abolished with ET receptor blockade as well as with apocynin, a nicotinamide adenine dinucleotide phosphate (NADPH) inhibitor. CONCLUSIONS: These results indicate that ET-1 does not affect EPC colony formation, migratory capacity or angiogenic growth factor release, but does increase EPC susceptibility to apoptosis through an NADPH-dependent mechanism. Increased EPC apoptosis may contribute to the proatherogenic effects of ET-1.

Enhanced endothelin-1 system activity with overweight and obesity.

Endothelin (ET)-1-mediated vasoconstrictor tone contributes to the development and progression of several adiposity-related conditions, including hypertension and atherosclerotic vascular disease. The aims of the present study were to determine 1) whether endogenous ET-1 vasoconstrictor activity is elevated in overweight and obese adults, and, if so, 2) whether increased ET-1-mediated vasoconstriction contributes to the adiposity-related impairment in endothelium-dependent vasodilation. Seventy-nine adults were studied: 34 normal weight [body mass index (BMI) < 25 kg/m(2)], 22 overweight (BMI ≥ 25 and < 30 kg/m(2)), and 23 obese (BMI ≥ 30 kg/m(2)). Forearm blood flow (FBF) responses to intra-arterial infusion of ET-1 (5 pmol/min for 20 min) and selective ET-1 receptor blockade (BQ-123, 100 nmol/min for 60 min) were determined. In a subset of the study population, FBF responses to ACh (4.0, 8.0, and 16.0 µg·100 ml tissue(-1)·min(-1)) were measured in the absence and presence of selective ET-1 receptor blockade. The vasoconstrictor response to ET-1 was significantly blunted in overweight and obese adults (∼ 70%) compared with normal weight adults. Selective ET-1 receptor blockade elicited a significant vasodilator response (∼ 20%) in overweight and obese adults but did not alter FBF in normal weight adults. Coinfusion of BQ-123 did not affect FBF responses to ACh in normal weight adults but resulted in an ∼ 20% increase (P < 0.05) in ACh-induced vasodilation in overweight and obese adults. These results demonstrate that overweight and obesity are associated with enhanced ET-1-mediated vasoconstriction that contributes to endothelial vasodilator dysfunction and may play a role in the increased prevalence of hypertension with increased adiposity.

Aging is associated with a proapoptotic endothelial progenitor cell phenotype.

The aim of this study was to determine if aging is associated with enhanced endothelial progenitor cell (EPC) sensitivity to apoptosis. Cells with phenotypic EPC characteristics were isolated from healthy, nonobese young (age 25 ± 1 years) and older (61 ± 1 years) men. Intracellular active caspase-3 concentrations in response to staurosporine stimulation were approximately 35% higher (p < 0.05) in EPCs from older (3.15 ± 0.29 pg/ml) compared with young (2.33 ± 0.24 pg/ml) men. Protein expression of Akt, p70 S6-kinase and Bcl-2 was markedly lower (approx. 35, 75 and 60%, respectively, all p < 0.05) in EPCs from older compared with young men, whereas there were no age-related differences in either 14-3-3ε or Bax expression. Additionally, EPC telomerase activity was 57% lower (p < 0.05) in older (0.18 ± 0.11 AU) versus young (0.43 ± 0.11 AU) men. These results indicate that aging is associated with a proapoptotic EPC phenotype characterized by decreased expression of key antiapoptotic proteins associated with the PI-3-kinase signaling pathway and reduced telomerase activity. These age-related changes likely contribute, in part, to the diminished ability of EPCs to resist an apoptotic stimulus in older men. Increased susceptibility to apoptosis may contribute to the numerical and functional impairments observed in EPCs with aging.

Endothelin-1 vasoconstriction and the age-related decline in endothelium-dependent vasodilatation in men.

ET (endothelin)-1, a potent vasoconstrictor peptide released by the endothelium, plays an important role in vasomotor regulation and has been linked to diminished endothelial vasodilator capacity in several pathologies associated with human aging, including hypertension, Type 2 diabetes and coronary artery disease. However, it is currently unknown whether the decline in endothelial vasodilatation with advancing age is due to elevated ET-1 vasoconstrictor activity. Accordingly, we tested the hypothesis that the age-related impairment in ACh (acetylcholine)-mediated endothelium-dependent vasodilatation is due, at least in part, to increased ET-1-mediated vasoconstrictor tone. FBF (forearm blood flow) responses to ACh, SNP (sodium nitroprusside) and BQ-123 (ET(A) receptor blocker) were determined in 14 young (age, 25 ± 1 years) and 14 older (age, 61 ± 2 years) healthy non-obese men. Additionally, FBF responses to ACh were determined in the presence of ETA blockade. Vasodilatation to ACh was lower (approx. 25%; P<0.05) in the older men (from 4.9 ± 0.2 to 13.9 ± 0.9 ml·100 ml(-1) of tissue·min(-1)) compared with the young men (4.6 ± 0.3 to 17.2 ± 1.0 ml·100 ml(-1) of tissue·min(-1)). There were no differences in FBF responses to SNP between the young (4.8 ± 0.3 to 18.5 ± 0.3 ml·100 ml(-1) of tissue·min(-1)) and older (5.1 ± 0.3 to 17.3 ± 0.8 ml·100 ml(-1) of tissue·min(-1)) men. In the young men, resting FBF was not significantly altered by BQ-123, whereas, in the older men, FBF increased approx. 25% in response to BQ-123 infusion (P<0.05). Co-infusion of ACh with BQ-123 resulted in an approx. 20% increase in the ACh-induced vasodilatation in older men compared with saline. In contrast, FBF responses to ACh were not significantly altered by ET(A) blockade in the young men. In conclusion, these results demonstrate that ET-1 vasoconstrictor activity contributes, at least in part, to diminished endothelium-dependent vasodilatation in older men.

CD31+ T cells, endothelial function and cardiovascular risk.

Deficits in endothelial cell repair mechanisms are thought to contribute to the aetiology of endothelial dysfunction and, subsequently, cardiovascular disease (CVD). CD31(+) T cells or so-called "angiogenic T cells" are a newly defined T cell subset that exhibit favourable vascular qualities and show a strong negative relation with atherosclerotic disease severity. Despite growing evidence that CD31(+) T cells are important for vascular homeostasis, it is currently unknown if CD31(+) T cell number and function are related to endothelial function and CVD risk in healthy adults. To address this question, we studied 24 healthy adult men (ages: 21-70). Endothelial function was assessed by the forearm blood flow (FBF) response to intra-arterial infusion of acetylcholine (ACh) and CVD risk was estimated by Framingham Risk Score (FRS). CD31(+) T cell number was determined by fluorescence-activated cell sorting. Magnetic-activated cell sorting was used to isolate CD31(+) T cells for Boyden chamber migration. No relation was observed between CD31(+) T cell number and FBF response to ACh or FRS. However, CD31(+) T cell migration to stromal cell-derived factor (SDF)-1α and vascular endothelial growth factor (VEGF) was positively correlated with FBF response to ACh (r = 0.43 for SDF-1α; r = 0.38 for VEGF; both P<0.05) and inversely related to FRS (r = -0.53 for SDF-1α; r = -0.48 for VEGF; both P<0.05). These findings demonstrate that CD31(+) T cell function, but not number, is associated with in vivo endothelial function and CVD risk in healthy adult men.