Y. Chandrashekhar

Hypoxia-induced microRNA-424 expression in human endothelial cells regulates HIF-α isoforms and promotes angiogenesis

Adaptive changes to oxygen availability are critical for cell survival and tissue homeostasis. Prolonged oxygen deprivation due to reduced blood flow to cardiac or peripheral tissues can lead to myocardial infarction and peripheral vascular disease, respectively. Mammalian cells respond to hypoxia by modulating oxygen-sensing transducers that stabilize the transcription factor hypoxia-inducible factor 1α (HIF-1α), which transactivates genes governing angiogenesis and metabolic pathways. Oxygen-dependent changes in HIF-1α levels are regulated by proline hydroxylation and proteasomal degradation. Here we provide evidence for what we believe is a novel mechanism regulating HIF-1α levels in isolated human ECs during hypoxia. Hypoxia differentially increased microRNA-424 (miR-424) levels in ECs. miR-424 targeted cullin 2 (CUL2), a scaffolding protein critical to the assembly of the ubiquitin ligase system, thereby stabilizing HIF-α isoforms. Hypoxia-induced miR-424 was regulated by PU.1-dependent transactivation. PU.1 levels were increased in hypoxic endothelium by RUNX-1 and C/EBPα. Furthermore, miR-424 promoted angiogenesis in vitro and in mice, which was blocked by a specific morpholino. The rodent homolog of human miR-424, mu-miR-322, was significantly upregulated in parallel with HIF-1α in experimental models of ischemia. These results suggest that miR-322/424 plays an important physiological role in post-ischemic vascular remodeling and angiogenesis.

Pathogenesis of congestive state in chronic obstructive pulmonary disease. Studies of body water and sodium, renal function, hemodynamics, and plasma hormones during edema and after recovery.

BackgroundThe pathogenesis of salt and water accumulation in patients with chronic obstructive pulmonary disease is unclear and may differ from that in patients with congestive heart failure due to myocardial disease. This study was undertaken to investigate some of the mechanisms involved. Methods and ResultsHemodynamics, water and electrolyte spaces, renal function, and plasma hormone concentrations were measured in nine patients with edema due to chronic obstructive pulmonary disease and in six patients after recovery. Mean cardiac output (3.8±0.26 I/min·m2) was normal, but right atrial (11±1 mm Hg) and mean pulmonary arterial (41±3 mm Hg) pressures were increased. Mean pulmonary arterial wedge pressure (11±1 mm Hg) was normal. Pulmonary vascular resistance (8.6±1.3 mm Hg · min · m2/l) was increased, but systemic vascular resistance (19.3±1.3 mm Hg · min · m2/l) and mean arterial pressure (83±4 mm Hg) were low. All patients were hypoxemic (Pao2, 40±2 mm Hg) and hypercapnic (Paco2, 60±2 mmHg). There was a significant increase in total body water (+21%), extracellular volume (+45%), plasma volume (+45%), blood volume (+88%), and exchangeable sodium (+38.2%). Renal plasma flow was severely reduced (−63.2%), but glomerular filtration rate was only mildly decreased (−32%). Significant increases were seen in plasma norepinephrine (3.5-fold normal), renin activity (7.6-fold normal), vasopressin (twice normal), atrial natriuretic peptide (9.4-fold normal), growth hormone (10.7-fold normal), and cortisol (1.9-fold normal). After recovery, the Pao2 increased (50±3 mm Hg) and Paco2 fell (45±4 mm Hg), and the patients became free from edema. All the body compartments returned toward normal, although they did not entirely reach normal values. Renal plasma flow increased significantly, and glomerular filtration became normal. Right atrial and pulmonary arterial pressures and pulmonary vascular resistance decreased (p<0.01). Cardiac output decreased but not significantly. Blood pressure increased but not significantly. However, systemic vascular resistance increased significantly to a normal value. ConclusionsWe conclude that patients with edema due to chronic obstructive pulmonary disease have severe retention of salt and water, reduction in renal blood flow and glomerular filtration, and neurohormonal activation similar to that seen in patients with edema due to myocardial disease. However, unlike the latter, in chronic obstructive pulmonary disease cardiac output is normal, and systemic vascular resistance and arterial blood pressure are low. This probably is due to the vasodilator properties of hypercapnia. The consequent low arterial blood pressure may be the stimulus for the neurohormonal activation and retention of salt and water.

Isolated Myocyte Contractile Function Is Normal in Postinfarct Remodeled Rat Heart With Systolic Dysfunction

BACKGROUND Postinfarction ventricular remodeling is associated with lengthening and contractile dysfunction of the remote noninfarcted myocardium. Mechanisms underlying this phenomenon remain unclear. METHODS AND RESULTS We studied serial changes in global left ventricular (LV) structure and function in infarcted (1, 2, 4, and 6 weeks after myocardial infarction) and sham-operated rat hearts and correlated them with structural and functional changes in myocytes isolated from the remote LV myocardium in the same hearts. Rats with myocardial infarction developed significant remodeling. The heart weight-to-body weight ratios were increased. LV volumes at filling pressure of 10 mm Hg were higher (305+/-28 versus 215+/-12 microL, P<.01). This was accompanied by global LV dysfunction (in vivo LV end-diastolic pressure, 4+/-1 versus 23+/-1.6 mm Hg; Langendorff LV developed pressure, 105+/-4 versus 62+/-9 mm Hg, P<.001 for both). Myocytes isolated from these hearts showed significant structural remodeling (LV myocytes, 24% longer and 15% wider; right ventricular myocytes, 38% longer and 31% wider, all P<.05). LV myocyte length correlated with changes in LV volume (r=.79) and function (LV developed pressure, r=-.81). However, LV myocytes from the same hearts showed normal contractile function and intracellular Ca2+ transients at baseline and during inotropic stimulation with increasing extracellular Ca2+ (1 to 6 mmol/L). The shortening-frequency relationship was also similar in myocytes from sham and myocardial infarction rats. CONCLUSIONS Postinfarct LV remodeling occurs predominantly by myocyte lengthening rather than by myocyte slippage. However, contractile function of the unloaded myocytes from the remote noninfarcted LV myocardium of the remodeled heart is normal. Therefore, myocyte contractile abnormalities may not contribute to global dysfunction of the remodeled heart. Reduced myocyte mass and nonmyocyte factors like increased wall stress, altered LV geometry, and changes in the myocardial interstitium may be more important in the genesis of postinfarct LV dysfunction in this model.

Why all the focus on cardiac imaging

Cardiovascular (CV) imaging has become the focus of numerous efforts on the part of public and private payers to constrain further growth in utilization of noninvasive services. The purpose of this brief report is to review the growth of CV imaging, detail recent changes in patterns of growth,

Endothelium-derived relaxing factor is important in mediating the high output state in chronic severe anemia

OBJECTIVES We evaluated the endothelial and vascular smooth muscle function in patients with chronic severe anemia to determine whether increased basal nitric oxide levels contribute to the systemic vasodilation and high cardiac output seen in these patients. BACKGROUND Patients with chronic severe anemia have a high output state due to a low systemic vascular resistance. However, the cause of the low vascular resistance is unclear. Because hemoglobin is a potent inhibitor of endothelium-derived relaxing factor, we postulated that in chronic severe anemia, low circulating hemoglobin results in reduced inhibition of endothelium-derived relaxing factor. The basal endothelium-derived relaxing factor activity therefore increases, and this contributes significantly to the low systemic vascular resistance and the hyperdynamic state seen in this condition. METHODS Hemodynamic variables and forearm blood flow (using plethysmography) were measured in eight patients with chronic severe anemia before (hematocrit 16 +/- 2% [mean +/- SD]) and within 24 h of red blood cell transfusion (n = 6, hematocrit 30 +/- 1%) and in six control subjects. The effect on baseline blood flow of blocking endothelium-derived relaxing factor activity with NG-monomethyl-L-arginine was investigated. In addition, the effects of both endothelium-dependent and endothelium-independent vasodilators on forearm blood flow were tested. RESULTS Baseline forearm blood flow was markedly increased in untreated patients (6.5 +/- 1.2 ml/min per 100 ml) compared with that in control subjects (2.8 +/- 0.7 ml/min per 100 ml, p < 0.0001, 95% confidence interval [CI] for difference -5 to -2.5). Red blood cell transfusion significantly reduced blood flow in the anemic patients to 3.5 +/- 1.1 ml/min per 100 ml (p < 0.001, 95% CI for difference -4.9 to -1.9), which was not significantly different from that in control subjects; increased systemic vascular resistance (796 +/- 141 to 1,230 +/- 151 dynes.s.cm-5, p < 0.001); and decreased cardiac output (4.9 +/- 0.6 to 3.5 +/- 0.5 liters/min per m2, p < 0.001). NG-monomethyl-L-arginine (16 mumol/min), a specific inhibitor of endothelium-derived relaxing factor, reduced forearm blood flow by an equal amount (p = 0.9, 95% CI for difference -0.7 to 0.8) in control subjects (0.98 +/- 0.39 ml/min) and treated patients (1.03 +/- 0.8 ml/min) but caused a threefold greater decrease in flow (2.9 +/- 0.9 ml/min) in untreated patients (p = 0.0003, 95% CI for difference between untreated patients and control subjects 1.1 to 2.7). These findings suggest increased basal endothelium-derived relaxing factor activity in patients with anemia. Stimulated forearm blood flows (both endothelium dependent and endothelium independent) were similar in all groups, confirming normal endothelial and smooth-muscle function. CONCLUSIONS These findings support the hypothesis that enhanced basal endothelium-derived relaxing factor activity makes an important contribution to the low systemic vascular resistance in chronic severe anemia.

Revisiting the pathogenesis of rheumatic fever and carditis

Rheumatic fever is one of the most-neglected ailments, and its pathogenesis remains poorly understood. The major thrust of research has been directed towards cross-reactivity between streptococcal M protein and myocardial α-helical coiled-coil proteins. M protein has also been the focus of vaccine development. The characteristic pathological findings suggest that the primary site of rheumatic-fever-related damage is subendothelial and perivascular connective tissue matrix and overlying endothelium. Over the past 5 years, a streptococcal M protein N-terminus domain has been shown to bind to the CB3 region in collagen type IV. This binding seems to initiate an antibody response to the collagen and result in ground substance inflammation. These antibodies do not cross-react with M proteins, and we believe that no failure of immune system and, possibly, no molecular mimicry occur in rheumatic fever. This alternative hypothesis shares similarity with collagen involvement in both Goodpasture syndrome and Alport syndrome.

T1 Mapping in Characterizing Myocardial Disease: A Comprehensive Review

Cardiovascular magnetic resonance provides insights into myocardial structure and function noninvasively, with high diagnostic accuracy and without ionizing radiation. Myocardial tissue characterization in particular gives cardiovascular magnetic resonance a prime role among all the noninvasive cardiovascular investigations. Late gadolinium enhancement imaging is an established method for visualizing replacement scar, providing diagnostic and prognostic information in a variety of cardiac conditions. Late gadolinium enhancement, however, relies on the regional segregation of tissue characteristics to generate the imaging contrast. Thus, myocardial pathology that is diffuse in nature and affecting the myocardium in a rather uniform and global distribution is not well visualized with late gadolinium enhancement. Examples include diffuse myocardial inflammation, fibrosis, hypertrophy, and infiltration. T1 mapping is a novel technique allowing to diagnose these diffuse conditions by measurement of T1 values, which directly correspond to variation in intrinsic myocardial tissue properties. In addition to providing clinically meaningful indices, T1-mapping measurements also allow for an estimation of extracellular space by calculation of extracellular volume fraction. Multiple lines of evidence suggest a central role for T1 mapping in detection of diffuse myocardial disease in early disease stages and complements late gadolinium enhancement in visualization of the regional changes in common advanced myocardial disease. As a quantifiable measure, it may allow grading of disease activity, monitoring progress, and guiding treatment, potentially as a fast contrast-free clinical application. We present an overview of clinically relevant technical aspects of acquisition and processing, and the current state of art and evidence, supporting its clinical use.

Comparison of Risk Scores to Estimate Perioperative Mortality in Aortic Valve Replacement Surgery

BACKGROUND Transaortic valve implantation has recently been introduced as an alternative to aortic valve replacement (AVR) for high-risk patients with aortic stenosis. However, accurate assessment of surgical risk is critical for appropriate patient selection. We compared the accuracy of The Society of Thoracic Surgeons (STS) risk score, the European System for Cardiac Risk Evaluation (EuroSCORE), and the Veterans Administration (VA) risk score in predicting perioperative mortality after AVR. METHODS We included 537 consecutive patients who underwent AVR for severe aortic stenosis at the Minneapolis VA Medical Center between 1997 and 2008. Observed and predicted perioperative (30-day) mortality rates were compared. Hosmer-Lemeshow goodness-of-fit test and receiver operating characteristic curves were performed to assess the performance of the scores. RESULTS Perioperative mortality rate was 5.9% (n=32). Predicted mortality rates for the EuroSCORE, STS score, and VA score were 15.6%, 3.6%, and 6.7%, respectively (p=0.001). The EuroSCORE overestimated mortality in all patients, most notably among those with ejection fraction less than 35% (49% predicted versus 9% observed). The EuroSCORE had poor calibration (goodness-of-fit test p<0.008), whereas the STS and the VA scores were well calibrated. However, all three scores displayed good discrimination characteristics per the areas under the receiver operating characteristic curves: STS score 0.73 (95% confidence interval: 0.69 to 0.77); VA score 0.66 (95% confidence interval: 0.62 to 0.70); and EuroSCORE 0.68 (95% confidence interval: 0.64 to 0.72; p>0.05). CONCLUSIONS The EuroSCORE substantially overestimates perioperative mortality risk in AVR, particularly in patients with low ejection fraction. These data have implications when deciding the appropriate intervention (transaortic valve implantation versus AVR) for high-risk aortic stenosis patients.

The role of arginine vasopressin and its receptors in the normal and failing rat heart

OBJECTIVE To evaluate the role of arginine vasopressin (AVP) in the normal and post-myocardial infarction (post-MI) hearts, and to investigate whether chronic AVP receptor antagonism can attenuate post-infarct ventricular remodeling. BACKGROUND A number of neurohormones, like norepinephrine and angiotensin II, have detrimental effects in heart failure (HF) and inhibiting them is beneficial. AVP shares some important properties with these hormones and is activated in HF. However, its role in the syndrome of HF, especially the effect of AVP inhibition, is largely undefined. METHODS AND RESULTS Effects of AVP-V1a and AVP-V2 receptor stimulation on normal rat cardiomyocyte contractile function, intracellular calcium [Ca2+]i, inositol 3 phosphate (IP3) generation and cell survival were studied. In post-MI rats, AVP receptor function was assessed in cardiomyocytes as well as isolated working hearts. AVP receptor total number (ligand binding) and mRNA levels (RT-PCR) were measured in myocytes. Finally, the effects of chronic AVP-V1a blockade were assessed in post-MI rats using echo and morphometry to measure ventricular remodeling. Normal cardiomyocytes showed a dose-dependent increase in myocyte contractile function, [Ca2+]i, and IP3 generation in response to AVP-V1a receptor stimulation. AVP-V2 agonists had no effect. Cells from MI hearts showed reduced inotropic response to AVP-V1a stimulation. Myocyte AVP-V1a receptor number and receptor mRNA were decreased. Prolonged exposure to AVP reduced cellular viability. However, chronic AVP-V1a blockade did not attenuate structural remodeling or improve function in post-MI hearts. CONCLUSIONS Isolated adult rat cardiomyocytes bear AVP-V1a receptors that mediate inotropic effects through the IP3 pathway. These receptors are functionally and numerically downregulated in the post-MI remodeled hearts. Despite evidence that AVP is cytotoxic to cells, chronic AVP-V1a receptor blockade does not attenuate post-MI ventricular remodeling in this model. Thus, AVP may not play a major role in the structural progression of HF.

Association of Coronary Stenosis and Plaque Morphology With Fractional Flow Reserve and Outcomes

IMPORTANCE Obstructive coronary lesions with reduced luminal dimensions may result in abnormal regional myocardial blood flow as assessed by stress-induced myocardial perfusion imaging or a significant fall in distal perfusion pressure with hyperemia-induced vasodilatation (fractional flow reserve [FFR] ≤0.80). An abnormal FFR has been demonstrated to identify high-risk lesions benefitting from percutaneous coronary intervention while safely allowing revascularization to be deferred in low-risk lesions, resulting in a decrease in the number of revascularization procedures as well as substantially reduced death and myocardial infarction. While FFR identifies hemodynamically significant lesions likely to produce ischemia-related symptoms, it remains less clear as to why it might predict the risk of acute coronary syndromes, which are usually due to plaque rupture and coronary thrombosis. OBSERVATIONS Although the atherosclerotic plaques with large necrotic cores (independent of the degree of luminal stenosis) are known to be associated with vulnerability to rupture and acute coronary syndromes, emerging evidence also suggests that they may induce greater rates of ischemia and reduced FFR compared with non-lipid-rich plaques also independent of the degree of luminal narrowing. It is proposed that the presence of large necrotic cores within the neointima may be associated with the inability of the vessel to dilate and may predispose to ischemia and abnormal FFR. CONCLUSIONS AND RELEVANCE Having a normal FFR requires unimpaired vasoregulatory ability and significant luminal stenosis. Therefore, FFR should identify lesions that are unlikely to possess large necrotic core, rendering them safe for treatment with medical therapy alone. Further studies are warranted to determine whether revascularization decisions in patients with stable coronary artery disease could be improved by assessment of both plaque composition and ischemia.