The role and medical prospects of long non-coding RNAs in cardiovascular disease

Cardiovascular disease (CVD) has reached epidemic proportions and is a leading cause of death worldwide. One of the long-standing goals of scientists is to repair heart tissue damaged by various forms of CVD such as cardiac hypertrophy, dilated cardiomyopathy, myocardial infarction, heart fibrosis, and genetic and developmental heart defects such as heart valve deformities. Damaged or defective heart tissue has limited regenerative capacity and results in a loss of functioning myocardium. Advances in transcriptomic profiling technology have revealed that long noncoding RNA (lncRNA) is transcribed from what was once considered "junk DNA." It has since been discovered that lncRNAs play a critical role in the pathogenesis of various CVDs and in myocardial regeneration. This review will explore how lncRNAs impact various forms of CVD as well as those involved in cardiomyocyte regeneration. Further, we discuss the potential of lncRNAs as a therapeutic modality for treating CVD.

Risk factors for disease progression in low-teens normal-tension glaucoma

Background/Aims

To investigate the risk factors for disease progression of normal-tension glaucoma (NTG) with pretreatment intraocular pressure (IOP) in the low-teens.

Methods

One-hundred and two (102) eyes of 102 patients with NTG with pretreatment IOP≤12 mm Hg who had been followed up for more than 60 months were retrospectively enrolled. Patients were divided into progressor and non-progressor groups according to visual field (VF) progression as correlated with change of optic disc or retinal nerve fibre layer defect. Baseline demographic and clinical characteristics including diurnal IOP and 24 hours blood pressure (BP) were compared between the two groups. The Cox proportional hazards model was used to identify the risk factors for disease progression.

Results

Thirty-six patients (35.3%) were classified as progressors and 66 (64.7%) as non-progressors. Between the two groups, no significant differences were found in the follow-up periods (8.7±3.4 vs 7.7±3.2 years; p=0.138), baseline VF mean deviation (−4.50±5.65 vs −3.56±4.30 dB; p=0.348) or pretreatment IOP (11.34±1.21 vs 11.17±1.06 mm Hg; p=0.121). The multivariate Cox proportional hazards model indicated that greater diurnal IOP at baseline (HR=1.609; p=0.004), greater fluctuation of diastolic BP (DBP; HR=1.058; p=0.002) and presence of optic disc haemorrhage during follow-up (DH; HR=3.664; p=0.001) were risk factors for glaucoma progression.

Conclusion

In the low-teens NTG eyes, 35.3% showed glaucoma progression during the average 8.7 years of follow-up. Fluctuation of DBP and diurnal IOP as well as DH were significantly associated with greater probability of disease progression.

Targeting reperfusion injury in acute myocardial infarction: a review of reperfusion injury pharmacotherapy

INTRODUCTION

Acute myocardial infarction (AMI) (secondary to lethal ischemia-reperfusion [IR]) contributes to much of the mortality and morbidity from ischemic heart disease. Currently, the treatment for AMI is early reperfusion; however, this itself contributes to the final myocardial infarct size, in the form of what has been termed 'lethal reperfusion injury'. Over the last few decades, the discovery of the phenomena of ischemic preconditioning and postconditioning, as well as remote preconditioning and remote postconditioning, along with significant advances in our understanding of the cardioprotective pathways underlying these phenomena, have provided the possibility of successful mechanical and pharmacological interventions against reperfusion injury.

AREAS COVERED

This review summarizes the evidence from clinical trials evaluating pharmacological agents as adjuncts to standard reperfusion therapy for ST-elevation AMI.

EXPERT OPINION

Reperfusion injury pharmacotherapy has moved from bench to bedside, with clinical evaluation and ongoing clinical trials providing us with valuable insights into the shortcomings of current research in establishing successful treatments for reducing reperfusion injury. There is a need to address some key issues that may be leading to lack of translation of cardioprotection seen in basic models to the clinical setting. These issues are discussed in the Expert opinion section.

Twenty-four hour blood pressure pattern in patients with normal tension glaucoma in the habitual position

PURPOSE

To investigate the relationship between blood pressure (BP) parameters in the habitual position and glaucomatous damage at initial presentation in patients with untreated normal tension glaucoma (NTG).

METHODS

Fifty-four eyes from 54 subjects diagnosed with NTG were consecutively enrolled. BP was measured with an automated ambulatory monitoring device in the habitual position during 24-hour in-hospitalization. Patients were classified into three groups: non-dippers, dippers, and over-dippers. corresponded to the degree of reduction in their nocturnal mean arterial pressure (MAP) compared with their diurnal MAP. Regression models were used to evaluate potential risk factors, including: age, pre-admission office intraocular pressure (IOP), central corneal thickness (CCT), and BP parameters. Functional outcome variables for glaucomatous damage included mean deviation (MD) and pattern standard deviation (PSD) on a Humphrey field analyzer (HFA). Anatomic outcome variables were TSNIT score (temporal, superior, nasal, inferior, and temporal) average, superior average, inferior average, and nerve fiber indicator (NFI) score on scanning laser polarimetry with variable corneal compensation (SLP-VCC; GDx-VCC).

RESULTS

Marked systolic blood pressure (SBP), diastolic blood pressure (DBP), and MAP fluctuation were noted in the over-dipper group (p<0.05). A linear regression analysis model revealed that nocturnal trough DBP and MAP, average nocturnal SBP, and MAP were all significantly associated with a decreased average TSNIT score and an increased NFI score.

CONCLUSIONS

Nocturnal BP reduction estimated in the habitual position was associated with structural damage in eyes with NTG. This finding may suggest systemic vascular etiology of NTG development associated with nocturnal BP reduction.

Evaluation of BM-573, a novel TXA2 synthase inhibitor and receptor antagonist, in a porcine model of myocardial ischemia-reperfusion

AIMS

To investigate whether BM-573 (N-tert-butyl-N'-[2-(4'-methylphenylamino)-5-nitro-benzenesulfonyl]urea), an original combined thromboxane A2 synthase inhibitor and receptor antagonist, prevents reperfusion injury in acutely ischemic pigs.

METHODS

Twelve animals were randomly divided in two groups: a control group (n = 6) intravenously infused with vehicle, and a BM-573-treated group (n = 6) infused with BM-573 (10 mg kg(-1) h(-1)). In both groups, the left anterior descending (LAD) coronary artery was occluded for 60 min and reperfused for 240 min. Either vehicle or BM-573 was infused 30 min before LAD occlusion and throughout the experiment. Platelet aggregation induced by arachidonic acid ex vivo measured was prevented by BM-573.

RESULTS

In both groups, LAD occlusion decreased cardiac output, ejection fraction, slope of stroke work--end-diastolic volume relationship, and induced end-systolic pressure-volume relationship (ESPVR) rightward shift, while left ventricular afterload increased. Ventriculo-arterial coupling and mechanical efficiency decreased. In both groups, reperfusion further decreased cardiac output and ejection fraction, while ESPVR displayed a further rightward shift. Ventriculo-arterial coupling and mechanical efficiency remained impaired. Area at risk, evidenced with Evans blue, was 33.2+/-3.4% of the LV mass (LVM) in both groups, and mean infarct size, revealed by triphenyltetrazolium chloride (TTC), was 27.3+/-2.6% of the LVM in the BM-573-treated group (NS). Histological examination and immunohistochemical identification of desmin revealed necrosis in the anteroseptal region similar in both groups, while myocardial ATP dosages and electron microscopy also showed that BM-573 had no cardioprotective effect.

CONCLUSIONS

These data suggest that BM-573 failed to prevent reperfusion injury in acutely ischemic pigs.

Substrate dependence of the postischemic cardiomyocyte recovery: Dissociation between functional, metabolic and injury markers

Defining the substrate that influences the most favourably the myocardial post-ischemic recovery is subject of debates, due to dissociation between functional and biochemical benefits. Hence, we studied the effects of either glucose or different fatty acids on the functional and metabolic recovery of post-ischemic cardiomyocytes in a substrate-free hypoxia model of simulated ischemia-reperfusion. Rat cardiomyocytes were submitted to a 2.5 h simulated ischemia followed by a 2 h reoxygenation without substrate (control), or with either glucose, octanoic acid, oleic acid, or elaidic acid. During simulated ischemia, electromechanical function gradually disappeared while the cellular viability and mitochondrial function declined. During control simulated reperfusion, cardiomyocytes recovered near normal function but a significant reduction in the action potential amplitude and rate persisted. The addition of glucose or oleic acid during simulated reperfusion promoted a faster, better and sustain functional recovery. Amongst the fatty acids, the functional recovery was slower with elaidic and octanoic acids as compared with oleic acid. The mitochondrial function was better improved during simulated reperfusion with glucose than with the tested fatty acids, among which elaidic acid was the less unfavourable. Paradoxically, the addition of whichever substrate during simulated reperfusion tended to worsen the cellular viability. Thus, cardiomyocytes recovery strongly relies on the characteristics of the substrate supplied at the onset of simulated reperfusion: glucidic or lipidic nature, chain-length, insaturation degree. Moreover, these data suggest that defining the appropriateness of a given substrate for the post-ischemic cardiomyocyte recovery is closely related to the functional and the biological endpoints in consideration.

Ventricular premature beat-driven intermittent restoration of coronary blood flow reduces the incidence of reperfusion-induced ventricular fibrillation in a cat model of regional ischemia

With a cat model of regional cardiac ischemia, we examined whether the incidence of reperfusion-induced ventricular fibrillation (VF) could be reduced by ventricular premature beat (VPB)-driven intermittent reperfusion. In addition, we assessed whether the effect of the intermittent reperfusion was comparable with that of ischemic preconditioning in suppressing the VF. Of 15 cats subjected to uninterrupted reperfusion after 20-minute occlusion of the left anterior descending coronary artery, 13 (86.70%) had VF, whereas only 1 (7.1%) of 14 cats subjected to the VPB-driven intermittent reperfusion had VF. This incidence of VF was significantly lower than that of the animal group subjected to uninterrupted reperfusion. However, it was not statistically different from that (3 of 15) of the group subjected to a 10-minute episode of the coronary artery occlusion before the 20-minute occlusion (i.e., "ischermic preconditioning"). Our results suggest that the VPB-driven intermittent reperfusion (i.e., "postconditioning") is very effective in preventing reperfusion-induced VF and as good as, if not better than, ischemic preconditioning.

Ischemic heart disease and antioxidants: mechanistic aspects of oxidative injury and its prevention

The disease state of myocardial ischemia results from a hypoperfusion-induced insufficiency of heart-muscle oxidative metabolism due to inadequate coronary circulation. Myocardial ischemia is an important, lifespan-limiting medical problem and a major economic health-care concern. Reperfusion, although avidly pursued in the clinic as essential to the ultimate survival of acutely ischemic heart muscle, may itself carry an injury component. Cardiac reperfusion injury appears to reflect, at least in part, an oxidant burden established upon reoxygenation of ischemic myocardium. Laboratory evidence demonstrates that oxidative stress to the heart-muscle cell (cardiomyocyte) can elicit the three known types of ischemia-reperfusion injury that directly affect the myocardium: arrhythmia, stunning, and infarction. The limited clinical occurrence of serious reperfusion arrhythmias has restricted the importance of antioxidants as antiarrhythmic agents against this form of myocardial ischemia-reperfusion damage. Despite the utmost clinical significance of lethal cardiomyocyte injury as a negative prognostic indicator for the ischemic heart-disease patient, inconsistent results of antioxidant interventions in reducing infarct size have somewhat tempered interest in antioxidant infarct trials. By contrast, the negative clinical consequences of stunning may indeed be preventable by utilizing antioxidants to help restore postischemic cardiac pump function. Several as yet unanswered questions remain regarding oxidative stress in the reperfused heart, its significance to cardiomyocyte damage, and its ability to elicit specific postischemic myocardial derangements. Targeted mechanistic studies are required to address these questions and to define the pathogenic role of oxidative stress (and, hence, the therapeutic potential of antioxidant intervention) in myocardial ischemia-reperfusion injury. The overall aim of current research in this area is to enable the cardiac surgeon/cardiologist to advance beyond the largely palliative drugs now available for management of the coronary heart-disease patient and attack directly the pathogenic determinants of heart-muscle ischemia-reperfusion injury. Optimal use of antioxidants may help address this important medical need.

H2O2-induced oxidative injury in rat cardiac myocytes is not potentiated by 1,1,1-trichloroethane, carbon tetrachloride, or halothane

Free radical-induced oxidative stress has been linked to ischemia-reperfusion injury of the myocardium. The .OH radical is considered the most damaging radical and can be increased in cells by treatment in vitro with H2O2. The purpose of the present study was to determine if aliphatic halocarbons enhance H2O2-induced oxidative injury in isolated cardiac myocytes from neonatal rats. Oxidative damage was assessed by measuring release of thiobarbituric acid-reactive substances (TBARS) from lipid peroxidation, loss of lactate dehydrogenase (LDH) through damaged sarcolemmal membranes, and alterations in intracellular calcium ([Ca2+]i) transients in electrically stimulated (1 Hz, 10 ms, 60 V) myocytes. H2O2 increased TBARS release and LDH leakage in a concentration-dependent (20-200 microM) manner. Continuous suffusion with H2O2 first altered the configuration of [Ca2+]i transients, then eliminated them, and finally caused [Ca2+]i overload (basal [Ca2+]i exceeded peak systolic [Ca2+]i of control). The time to [Ca2+]i overload was inversely associated with concentration, and the shortest time to overload was obtained with 100 microM H2O2. A 1-h preincubation of myocytes with the iron chelator deferoxamine inhibited all effects of H2O2. 1,1,1-Trichloroethane, carbon tetrachloride, or halothane at 1 mM significantly and reversibly reduced [Ca2+]i transients but did not influence TBARS release or LDH leakage. Simultaneous exposure of myocytes to H2O2 and halocarbons did not affect the myocyte response to H2O2 exposure. Results indicate that the three halocarbons tested do not enhance H2O2-induced oxidative injury in isolated cardiac myocytes.

Reperfusion in acute myocardial infarction: effect of timing and modulating factors in experimental models

Timely reperfusion of ischemic myocardium in experimental animals halts the advancing transmural "wavefront" of ischemic cell death and thereby limits myocardial infarct size by limiting its transmural extent. The time window of opportunity for such salvage in most experimental models of regional ischemia is the first 3 hours. The number of myocytes that can be salvaged by reperfusion decreases exponentially during this period, such that at 3 hours, reperfusion limits infarct size by only about 10%. The rate of lethal ischemic cell injury and therefore the amount of myocardium that can be salvaged by reperfusion after a particular duration of ischemia is dependent both on the degree of blood flow deficit and the rate of ischemic metabolism. In experimental animal models, several interventions, including hypothermia, calcium antagonists, and "ischemic preconditioning," have been shown to reduce the rate of ischemic metabolism and to limit myocardial infarct size when assessed after a defined period of ischemia and reperfusion. Hypothetically, interventions that could prevent additional myocyte necrosis caused by some deleterious aspects of reperfusion ("lethal reperfusion injury") also could serve as valuable adjunctive therapy. However, studies of therapies designed to prevent lethal reperfusion injury have produced conflicting results. Thus, the concept that lethal reperfusion injury occurs remains controversial. Experimental evidence indicates that reperfusion accelerates both the initial inflammatory response and later process of infarct repair. Late reperfusion of infarcts in dogs, which does not limit myocardial infarct size, appears to accelerate the replacement of necrotic myocardium by scar without altering the size of the final scar.

High arrythmogenesis during early reperfusion of ischaemic myocardium: participation of oxygen free radicals

The early period of reperfusion of ischaemic myocardium leads to a high incidence of severe tachyarrhythmias including ventricular fibrillation (VF), accompanied by a sudden transitional dysfunction. Oxygen free radicals (OFR) have been identified as one of the principal factors responsible for reperfusion-induced events. However, direct evidence for participation of OFR in the arrhythmogenic mechanisms upon reperfusion is still lacking. In the present study, in isolated Langendorff-perfused rat hearts subjected to 30 min global ischaemia, the onset of reperfusion induced 100% incidence of both ventricular tachycardia (VT) and VF with their gradual cessation during 5 min of reperfusion. Generation of H2O2 in the myocardium in the first minutes of reperfusion was demonstrated by means of cerium cytochemistry. There was an increased density of cerium perhydroxide precipitate distributed throughout the myocytes and endothelial cells, confirmed by X-ray microanalysis. The mechanism of the arrhythmogenic effect of OFR may involve the inhibition of the sarcolemmal Na+/K+ ATPase activity, as was revealed by subjecting the isolated sarcolemmal fraction of rat heart to the action of an oxy-radical generating system (H2O2 + FeSO4).