Myocardial angiotensin II receptor expression and ischemia-reperfusion injury

Cardioprotective Mechanisms against Reperfusion Injury in Acute Myocardial Infarction: Targeting Angiotensin II Receptors

Ischemia/reperfusion injury is a process associated with cardiologic interventions, such as percutaneous coronary angioplasty after an acute myocardial infarction. Blood flow restoration causes a quick burst of reactive oxygen species (ROS), which generates multiple organelle damage, leading to the activation of cell death pathways. Therefore, the intervention contributes to a greater necrotic zone, thus increasing the risk of cardiovascular complications. A major cardiovascular ROS source in this setting is the activation of multiple NADPH oxidases, which could result via the occupancy of type 1 angiotensin II receptors (AT1R); hence, the renin angiotensin system (RAS) is associated with the generation of ROS during reperfusion. In addition, ROS can promote the expression of NF-κΒ, a proinflammatory transcription factor. Recent studies have described an intracellular RAS pathway that is associated with increased intramitochondrial ROS through the action of isoform NOX4 of NADPH oxidase, thereby contributing to mitochondrial dysfunction. On the other hand, the angiotensin II/ angiotensin type 2 receptor (Ang II/AT2R) axis exerts its effects by counter-modulating the action of AT1R, by activating endothelial nitric oxide synthase (eNOS) and stimulating cardioprotective pathways such as akt. The aim of this review is to discuss the possible use of AT1R blockers to hamper both the Ang II/AT1R axis and the associated ROS burst. Moreover; we suggest that AT1R antagonist drugs should act synergistically with other cardioprotective agents, such as ascorbic acid, N-acetylcysteine and deferoxamine, leading to an enhanced reduction in the reperfusion injury. This therapy is currently being tested in our laboratory and has shown promising outcomes in experimental studies.

Heart Failure and Cardiorenal Syndrome: A Narrative Review on Pathophysiology, Diagnostic and Therapeutic Regimens-From a Cardiologist's View

In cardiorenal syndrome (CRS), heart failure and renal failure are pathophysiologically closely intertwined by the reciprocal relationship between cardiac and renal injury. Type 1 CRS is most common and associated with acute heart failure. A preexistent chronic kidney disease (CKD) is common and contributes to acute kidney injury (AKI) in CRS type 1 patients (acute cardiorenal syndrome). The remaining CRS types are found in patients with chronic heart failure (type 2), acute and chronic kidney diseases (types 3 and 4), and systemic diseases that affect both the heart and the kidney (type 5). Establishing the diagnosis of CRS requires various tools based on the type of CRS, including non-invasive imaging modalities such as TTE, CT, and MRI, adjuvant volume measurement techniques, invasive hemodynamic monitoring, and biomarkers. Albuminuria and Cystatin C (CysC) are biomarkers of glomerular filtration and integrity in CRS and have a prognostic impact. Comprehensive "all-in-one" magnetic resonance imaging (MRI) approaches, including cardiac magnetic resonance imaging (CMR) combined with functional MRI of the kidneys and with brain MRI are proposed for CRS. Hospitalizations due to CRS and mortality are high. Timely diagnosis and initiation of effective adequate therapy, as well as multidisciplinary care, are pertinent for the improvement of quality of life and survival. In addition to the standard pharmacological heart failure medication, including SGLT2 inhibitors (SGLT2i), renal aspects must be strongly considered in the context of CRS, including control of the volume overload (diuretics) with special caution on diuretic resistance. Devices involved in the improvement of myocardial function (e.g., cardiac resynchronization treatment in left bundle branch block, mechanical circulatory support in advanced heart failure) have also shown beneficial effects on renal function.

Communication Between Cardiomyocytes and Fibroblasts During Cardiac Ischemia/Reperfusion and Remodeling: Roles of TGF-β, CTGF, the Renin Angiotensin Axis, and Non-coding RNA Molecules

Communication between cells is a foundational concept for understanding the physiology and pathology of biological systems. Paracrine/autocrine signaling, direct cell-to-cell interplay, and extracellular matrix interactions are three types of cell communication that regulate responses to different stimuli. In the heart, cardiomyocytes, fibroblasts, and endothelial cells interact to form the cardiac tissue. Under pathological conditions, such as myocardial infarction, humoral factors released by these cells may induce tissue damage or protection, depending on the type and concentration of molecules secreted. Cardiac remodeling is also mediated by the factors secreted by cardiomyocytes and fibroblasts that are involved in the extensive reciprocal interactions between these cells. Identifying the molecules and cellular signal pathways implicated in these processes will be crucial for creating effective tissue-preserving treatments during or after reperfusion. Numerous therapies to protect cardiac tissue from reperfusion-induced injury have been explored, and ample pre-clinical research has attempted to identify drugs or techniques to mitigate cardiac damage. However, despite great success in animal models, it has not been possible to completely translate these cardioprotective effects to human applications. This review provides a current summary of the principal molecules, pathways, and mechanisms underlying cardiomyocyte and cardiac fibroblast crosstalk during ischemia/reperfusion injury. We also discuss pre-clinical molecules proposed as treatments for myocardial infarction and provide a clinical perspective on these potential therapeutic agents.

P2Y11 Agonism Prevents Hypoxia/Reoxygenation- and Angiotensin II-Induced Vascular Dysfunction and Intimal Hyperplasia Development

Vascular dysfunction in cardiovascular diseases includes vasomotor response impairments, endothelial cells (ECs) activation, and smooth muscle cells (SMCs) proliferation and migration to the intima. This results in intimal hyperplasia and vessel failure. We previously reported that activation of the P2Y11 receptor (P2Y11R) in human dendritic cells, cardiofibroblasts and cardiomyocytes was protective against hypoxia/reoxygenation (HR) lesions. In this study, we investigated the role of P2Y11R signaling in vascular dysfunction. P2Y11R activity was modulated using its pharmacological agonist NF546 and antagonist NF340. Rat aortic rings were exposed to angiotensin II (AngII) and evaluated for their vasomotor response. The P2Y11R agonist NF546 reduced AngII-induced vascular dysfunction by promoting EC-dependent vasorelaxation, through an increased nitric oxide (NO) bioavailability and reduced AngII-induced H₂O₂ release; these effects were prevented by the use of the P2Y11R antagonist NF340. Human vascular SMCs and ECs were subjected to AngII or H/R simulation in vitro. P2Y11R agonist modulated vasoactive factors in human ECs, that is, endothelial nitric oxide synthase (eNOS) and endothelin-1, reduced SMC proliferation and prevented the switch towards a synthetic phenotype. H/R and AngII increased ECs secretome-induced SMC proliferation, an effect prevented by P2Y11R activation. Thus, our data suggest that P2Y11R activation may protect blood vessels from HR-/AngII-induced injury and reduce vascular dysfunctions. These results open the way for new vasculoprotective interventions.

New insights into the non-hemostatic role of von Willebrand factor in endothelial protection

During exposure to ischemia-reperfusion (I/R) insult, angiotensin II (AngII)-induced endothelin-1 (ET-1) upregulation in endothelial cells progressively impairs nitric oxide (NO) bioavailability while increasing levels of superoxide anion (O₂^-) and leading to the onset of endothelial dysfunction. Moreover, the overexpression of ET-1 increases the endothelial and circulating levels of von Willebrand factor (vWF), a glycoprotein with a crucial role in arterial thrombus formation. Nowadays, the non-hemostatic role of endothelial vWF is emerging, although we do not yet know whether its increased expression is cause or consequence of endothelial dysfunction. Notably, the vWF blockade or depletion leads to endothelial protection in cultured cells, animal models of vascular injury, and patients as well. Despite the recent efforts to develop an effective pharmacological strategy, the onset of endothelial dysfunction is still difficult to prevent and remains closely related to adverse clinical outcome. Unraveling the non-hemostatic role of endothelial vWF in the onset of endothelial dysfunction could provide new avenues for protection against vascular injury mediated by AngII.

Angiotensin IV protects cardiac reperfusion injury by inhibiting apoptosis and inflammation via AT4R in rats

Angiotensin IV (Ang IV) is formed by aminopeptidase N from Ang III by removing the first N-terminal amino acid. Previously, we reported that Ang III has some cardioprotective effects against global ischemia in Langendorff heart. However, it is not clear whether Ang IV has cardioprotective effects. The aim of the present study was to evaluate the effect of Ang IV on myocardial ischemia-reperfusion (I/R) injury in rats. Before ischemia, male Sprague-Dawley rats received Ang IV (1mg/kg/day) for 3 days. Anesthetized rats were subjected to 45min of ischemia by ligation of left anterior descending coronary artery followed by reperfusion and then, sacrificed 1 day or 1 week after reperfusion. Plasma creatine kinase (CK) and lactate dehydrogenase (LDH) concentrations, and infarct size were measured. Quantitative analysis of apoptotic and inflammatory proteins in ventricles were performed using Western blotting. Pretreatment with Ang IV attenuated I/R-induced increases in plasma CK and LDH levels, and infarct size, which were blunted by Ang IV receptor (AT4R) antagonist and but not by antagonist for AT1R, AT2R, or Mas receptor. I/R increased Bax, caspase-3 and caspase-9 protein levels, and decreased Bcl-2 protein level in ventricles, which were blunted by Ang IV. I/R-induced increases in TNF-α, MMP-9, and VCAM-1 protein levels in ventricles were also blunted by Ang IV. Ang IV increased the phosphorylation of Akt and mTOR. These effects were attenuated by co-treatment with AT4R antagonist or inhibitors of downstream signaling pathway. Myocardial dysfunction after reperfusion was improved by Ang IV. These results suggest that Ang IV has cardioprotective effect against I/R injury by inhibiting apoptosis via AT4R and PI3K-Akt-mTOR pathway.

Investigations on the role of leukotrienes in remote hind limb preconditioning-induced cardioprotection in rats

The cardioprotective effects of remote hind limb preconditioning (RIPC) are well established, but its mechanisms still remain to be explored. Therefore, the present study was aimed to explore the possible involvement of 5-lipoxygenase-derived leukotrienes in RIPC. The hind limb was tied by a pressure cuff and was subjected to four episodes of inflation and deflation (5min each) to induce remote hind-limb preconditioning. Thereafter, the hearts were isolated and were subjected to global ischemia (30min) followed by reperfusion (120min) on the Langendorff apparatus. The extent of myocardial injury was assessed by measuring lactate dehydrogenase (LDH) and creatine kinase (CK) levels in the coronary effluent; the infarct size using TTC staining, and the hemodynamic parameters including LVDP, dp/dtmax and dp/dtmin. RIPC significantly decreased ischemia and reperfusion-induced increase in LDH, CK release, infarct size and improved LVDP, dp/dtmax and dp/dtmin. Administration of montelukast, leukotriene receptor antagonist (10 and 20mg/kg) and zileuton, 5-lipoxygenase inhibitor, (2.5 and 5mg/kg) abolished RIPC-induced cardioprotection. It may be concluded that hind limb ischemia stimulates 5-lipoxygenase to release leukotrienes which may elicit cardioprotection by humoral or neurogenic pathway.

Oxidative activation of CaMKIIδ in acute myocardial ischemia/reperfusion injury: A role of angiotensin AT1 receptor-NOX2 signaling axis

During ischemia/reperfusion (IR), increased activation of angiotensin AT1 receptors recruits NADPH oxidase 2 (NOX2) which contributes to oxidative stress. It is unknown whether this stimulus can induce oxidative activation of Ca(2+)/calmodulin-dependent protein kinase IIδ (CaMKIIδ) leading into the aggravation of cardiac function and whether these effects can be prevented by angiotensin AT1 receptors blockade. Losartan, a selective AT1 blocker, was used. Its effects were compared with effects of KN-93, an inhibitor of CaMKIIδ. Global IR was induced in Langendorff-perfused rat hearts. Protein expression was evaluated by immunoblotting and lipoperoxidation was measured by TBARS assay. Losartan improved LVDP recovery by 25%; however, it did not reduce reperfusion arrhythmias. Oxidized CaMKIIδ (oxCaMKIIδ) was downregulated at the end of reperfusion compared to before ischemia and losartan did not change these levels. Phosphorylation of CaMKIIδ mirrored the pattern of changes in oxCaMKIIδ levels. Losartan did not prevent the higher lipoperoxidation due to IR and did not influence NOX2 expression. Inhibition of CaMKII ameliorated cardiac IR injury; however, this was not accompanied with changes in the levels of either active form of CaMKIIδ in comparison to the angiotensin AT1 receptor blockade. In spite of no changes of oxCaMKIIδ, increased cardiac recovery of either therapy was abolished when combined together. This study showed that oxidative activation of CaMKIIδ is not elevated at the end of R phase. NOX2-oxCAMKIIδ signaling is unlikely to be involved in cardioprotective action of angiotensin AT1 receptor blockade which is partially abolished by concomitant CaMKII inhibition.

Low birth weight activates the renin-angiotensin system, but limits cardiac angiogenesis in early postnatal life

Low birth weight (LBW) is associated with increased risk of adult cardiovascular disease and this association may be partly a consequence of early programming of the renin-angiotensin system (RAS). We investigated the effects of LBW on expression of molecules in the RAS and cardiac tissue remodeling. Left ventricular samples were collected from the hearts of 21 days old lambs that were born average birth weight (ABW) and LBW. Cardiac mRNA expression was quantified using real-time RT-PCR and protein expression was quantified using Western blotting. DNA methylation and histone acetylation were assessed by combined bisulfite restriction analysis and chromatin immunoprecipitation, respectively. There were increased plasma renin activity, angiotensin I (ANGI), and ANGII concentrations in LBW compared to ABW lambs at day 20. In LBW lambs, there was increased expression of cardiac ACE2 mRNA, decreased ANGII receptor type 1 (AT1R) protein, and acetylation of histone H3K9 of the AT1R promoter but no changes in AT1R mRNA expression and AT1R promoter DNA methylation. There was no difference in the abundance of proteins involved in autophagy or fibrosis. BIRC5 and VEGF mRNA expression was increased; however, the total length of the capillaries was decreased in the hearts of LBW lambs. Activation of the circulating and local cardiac RAS in neonatal LBW lambs may be expected to increase cardiac fibrosis, autophagy, and capillary length. However, we observed only a decrease in total capillary length, suggesting a dysregulation of the RAS in the heart of LBW lambs and this may have significant implications for heart health in later life.

Effect of Diabetes Mellitus and Its Control on Myocardial Contractile Function in Rats

AIM: This work was done to study the effect of both types of diabetes mellitus (DM) on myocardial contractility in rats. Also, we investigated the role of treatment of DM with insulin and rosiglitazone (used as treatment for type 1 and type 2 DM respectively) in improvement of myocardial dysfunction in diabetic rats.METHODS: The study included 50 male Wistar albino rats, divided into 5 groups: control (group I), streptozotocin induced type 1 DM (group II), fructose induced type 2 DM (group III), insulin treated type 1 diabetic rats (group IV) and rosiglitazone treated type 2 diabetic rats (group V). At the end of the study, retro-orbital blood samples were withdrawn and blood glucose, plasma triglyceride (TG), total cholesterol (TC) and thyroid hormones levels were measured. Rats were then anesthetized and their hearts were excised and connected to Langendorff apparatus to perform mechanical cardiac performance tests including heart rate (HR), left ventricular developed pressure (LVDP) and maximum rate of pressure rise (+dp/dt).RESULTS: Data of the study showed that relative to control group, there was significant increase in blood glucose, plasma TG and TC levels while, thyroid hormones and myocardial performance parameters showed significant decrease in both type 1 and type 2 diabetic rats. Treatment of type 1 diabetic rats with insulin and type 2 with rosiglitazone resulted in significant decrease in blood glucose, plasma TG and TC levels associated with significant improvement in thyroid hormones and myocardial performance parameters. The results also showed that insulin treatment of type 1 was more effective in ameliorating all parameters than treatment of type 2 by rosiglitazone.CONCLUSION: We concluded that the induction of both types of diabetes resulted in decreased myocardial performance parameters. The  treatment of type 1 and type 2 diabetes by insulin and oral rosiglitazone respectively improved to a great extent the altered metabolism and  mechanical myocardial parameters, with more improving effect of  insulin in type 1 than rosiglitazone in type 2 DM.

Oxidative stress-mediated effects of angiotensin II in the cardiovascular system

Angiotensin II (Ang II), an endogenous peptide hormone, plays critical roles in the pathophysiological modulation of cardiovascular functions. Ang II is the principle effector of the renin-angiotensin system for maintaining homeostasis in the cardiovascular system, as well as a potent stimulator of NAD(P)H oxidase, which is the major source and primary trigger for reactive oxygen species (ROS) generation in various tissues. Recent accumulating evidence has demonstrated the importance of oxidative stress in Ang II-induced heart diseases. Here, we review the recent progress in the study on oxidative stress-mediated effects of Ang II in the cardiovascular system. In particular, the involvement of Ang II-induced ROS generation in arrhythmias, cell death/heart failure, ischemia/reperfusion injury, cardiac hypertrophy and hypertension are discussed. Ca²⁺/calmodulin-dependent protein kinase II is an important molecule linking Ang II, ROS and cardiovascular pathological conditions.

Highly purified human peripheral blood monocytes produce IL-6 but not TNFalpha in response to angiotensin II

HYPOTHESIS

Monocytes produce pro-inflammatory cytokines in response to Angiotensin II (AngII).

INTRODUCTION

AngII has been suggested by many to be pro-inflammatory and likely to contribute to the migration of leukocytes in patients with cardiovascular conditions.

MATERIALS AND METHODS

Monocytes were purified from peripheral blood mononuclear cells (PBMCs) by negative selection using antibodies conjugated to magnetic beads. Detection of CD14(+) and AT(1)R expression was achieved by double-labeling flow cytometry. Highly purified monocytes were then stimulated with AngII (6 and 24 h) to assess IL-6 and TNF-α transcript levels by qRT-PCR and protein secretion by ELISA.

RESULTS

Monocytes comprised 9.7 ± 2.0% of the PBMCs. Monocyte isolation by negative selection yielded a purity of up to 99.8%. We demonstrated AT(1)R expression on 9.5 ± 0.3% of highly purifed CD14(+)/CD16(-) monocytes. Stimulation of highly purified monocytes with AngII resulted in increased transcript levels of IL-6 at 6 h but not at 24 h, and increased secretion of IL-6 in a dose-dependent manner compared with controls (p <0.01). Conversely, there was no increase in TNF-α mRNA transcripts or protein secretion.

CONCLUSIONS

We provide evidence that a CD14(+)/CD16(-) subset of highly purified human monocytes express AT(1)R and respond to AngII exposure in vitro by producing IL-6 but not TNF-α.

The role of nitric oxide in myocardial repair and remodeling

Nitric oxide (NO) plays a crucial role in many aspects of the pathophysiology of heart failure. NO is a double-edged sword; NO inhibits ischemia/reperfusion (I/R) injury, represses inflammation, and prevents left ventricular (LV) remodeling, whereas excess NO and co-existence of reactive oxygen species (ROS) with NO are injurious. The failing heart is exposed to not only oxidative stress by a plethora of humoral factors and inflammatory cells but also nitrosative stress. Activation of nitric oxide synthase (NOS) of any isoforms, [i.e., endothelial NOS (eNOS), inducible NOS (iNOS), and neuronal NOS (nNOS)], concomitant with oxidative stress results in NOS uncoupling, leading to further oxidative/nitrosative stress. Indiscriminate removal of oxidative stress is not an effective means to prevent this detrimental process, because oxidative stress is necessary for an adaptive mechanism for cell survival against noxious stimuli. Therefore, removal of ROS in a site-specific manner or inhibition of the source of injurious ROS without affecting redox-sensitive survival signal transduction pathways represents a promising approach to elicit the beneficial effect of NO. Recent emerging pharmacological tools and regular exercise inhibit ROS generation in the proximity of NOSs, thereby increasing bioavailable NO and exerting cardioprotection against I/R injury and LV remodeling.

Renin Angiotensin system as a regulator of cell volume. Implications to myocardial ischemia

It is known that long lasting changes in cell volume are incompatible with cellular functions. In the present review, I discussed the role of cell volume on gene expression and protein synthesis as well as the importance of the renin angiotensin system on the regulation of cell volume in the failing heart. Moreover, the relationship between mechanical stretch, cell volume and the renin angiotensin system as well some translational studies are also described and their relevance to the prevention or reduction of cardiac damage during myocardial ischemia is emphasized.

Ischemic preconditioning: from molecular mechanisms to therapeutic opportunities

Ischemia/reperfusion (I/R) injury is a major contributory factor to cardiac dysfunction and infarct size that determines patient prognosis after acute myocardial infarction. Considerable interest exists in harnessing the heart's endogenous capacity to resist I/R injury, known as ischemic preconditioning (IPC). The IPC research has contributed to uncovering the pathophysiology of I/R injury on a molecular and cellular basis and to invent potential therapeutic means to combat such damage. However, the translation of basic research findings learned from IPC into clinical practice has often been inadequate because the majority of basic research findings have stemmed from young and healthy animals. Few if any successful implementations of IPC have occurred in the diseased hearts that are the primary target of viable therapies activating cardioprotective mechanisms to limit cardiac dysfunction and infarct size. Therefore, the first purpose of this review is to facilitate understanding of pathophysiology of I/R injury and the mechanisms of cardioprotection afforded by IPC in the normal heart. Then I focus on the problems and opportunities for successful bench-to-bedside translation of IPC in the diseased hearts.

Dose and time-dependent apoptotic effects by angiotensin II infusion on left ventricular cardiomyocytes

OBJECTIVE

To gain insight into the regulation of cardiac apoptosis we studied the dose-response and time-course effects of angiotensin II (Ang II) infusion on ventricular cardiomyocyte apoptosis and on the expression of Bax and Bcl-2 genes and proteins.

STUDY DESIGN AND METHODS

In the dose-response study, Ang II was infused subcutaneously at doses of 100, 200, 400, 800 and 1200 ng/kg per min for 14 days. In the time-course study, rats infused with Ang II at doses of 200 and 400 ng/kg per min were followed for 7 and 14 days. The cardiomyocyte apoptotic density was assessed by DNA end labelling (terminal deoxynucleotide nick-end labelling; TUNEL). Gene and protein expression of Bcl-2 and Bax were evaluated by reverse transcriptase-polymerase chain reaction and by Western blots.

RESULTS

Systolic blood pressure and left ventricular mass were increased in a dose-dependent manner in Ang II-infused rats. A statistically significant increase in the rate of cardiac apoptosis and pro-apoptotic changes of Bcl-2 and Bax gene and protein expression was observed when high doses of Ang II (800-1200 ng/kg per min) were infused. A positive correlation of apoptotic density with Bax and a negative correlation with Bcl-2 and Bcl-2/Bax ratio were found. Cardiac apoptosis was greatly influenced by the timing of Ang II infusion. Losartan-treated Ang II-infused rats exhibited normalized systolic blood pressure, left ventricular weight, apoptosis, and Bax and Bcl-2 levels.

CONCLUSIONS

Our results are consistent with the pathophysiological role of Ang II in induction of cardiac apoptosis, and explain the cardioprotective effect of Ang II receptor antagonists.

17β-Estradiol inhibits angiotensin II-induced collagen synthesis of cultured rat cardiac fibroblasts via modulating angiotensin II receptors

Circulating endogenous estrogen is considered to be cardiovascular protective, but the underlying mechanisms remain obscure. The cardiac fibroblasts, the most abundant cell type present in the heart, are responsible for the deposition of extracellular matrix. Angiotensin II has been known to stimulate cardiac collagen gene expression. The present study was designed to investigate the effect of 17beta-estradiol on the angiotensin II-induced proliferation and collagen synthesis in cultured cardiac fibroblasts by using real-time polymerase chain reaction (PCR), Western blot and 3-[4,5-dimethylthiazol-2-yl]-2, 5-diphenyl-tetrazolium bromide proliferation assay. Angiotensin II increased the cell proliferation and synthesis of collagen types I and III. Angiotensin II up-regulated the gene expression of the angiotensin AT(1) receptor and down-regulated the gene expression of the angiotensin AT(2) receptor in cardiac fibroblasts. The effects of angiotensin II was abolished by the angiotensin AT(1) receptor antagonist, losartan, but not by the angiotensin AT(2) receptor antagonist, PD 123319. 17beta-estradiol prevented increases in proliferation and attenuated the collagen synthesis in response to angiotensin II. The increased AT(1) receptor mRNA levels and decreased AT(2) receptor mRNA levels were partially reversed by 17beta-estradiol treatment. In conclusion, the down-regulation of angiotensin AT(1) receptor expression and function is likely to be an important mechanism accounting for the inhibitory effect of 17beta-estradiol on angiotensin II-stimulated proliferation and collagen synthesis in cardiac fibroblasts. This effect may confer at least in part the cardiac protective action of 17beta-estradiol under pathological conditions with increased activity of the rennin-angiotensin system.

Cardioprotective effects of rosiglitazone are associated with selective overexpression of type 2 angiotensin receptors and inhibition of p42/44 MAPK

Current evidence points to renin-angiotensin system as a key mediator in ischemia-reperfusion injury. Rosiglitazone, a peroxisome proliferator-activated receptor-gamma (PPAR-gamma) ligand, has recently been shown to confer cardioprotection against ischemia-reperfusion in animal models. We sought to examine the expression of ANG II receptors during PPAR-gamma-mediated cardioprotection. Male Sprague-Dawley rats (nondiabetic) were fed either regular rat chow (control diet group, n = 9) or rosiglitazone-rich diet (rosiglitazone-rich diet group, n = 9) and were subjected to 1 h of myocardial ischemia followed by 1 h of reperfusion. A third group of rats had only thoracotomy and pericardiotomy and served as a sham control group (n = 9). Hemodynamics, infarct size, and expression of ANG II type 1 and type 2 receptors (AT1 and AT2) were measured in all groups. There was a 58% reduction of infarct size in the rosiglitazone-rich diet group (P < 0.01 vs. control diet group). Increased myocardial expression of AT(1) receptors in the ischemic-reperfused myocardium was attenuated in the rosiglitazone-rich diet group (P < 0.05 vs. control diet group). Importantly, myocardial AT2 mRNA and protein expression were significantly increased (by >100-fold) in the rosiglitazone-rich diet group (P < 0.05). These changes were accompanied by inhibition of p42/44 MAPK in the rosiglitazone-rich diet group, while the Akt1 expression, believed to mediate insulin sensitization, remained similar in all three groups. The cardioprotective effects of rosiglitazone against myocardial ischemia-reperfusion injury are independent of its insulin-sensitizing properties and are associated with significant overexpression of AT2 receptors along with inhibition of p42/44 MAPK.

The new face of bispecific antibodies: targeting cancer and much more

The term magic bullet was first coined by bacteriologist Paul Ehrlich in the late 1800s to describe a chemical with the ability to specifically target microorganisms while sparing normal host cells. His concept was later expanded to include treatments for cancer, but it is only in recent decades, with development and improvements in monoclonal antibody (mAb) technology, that the full therapeutic implications of "magic bullet" strategies have been realized. Expanding on the success of mAb-targeting, linking the specificity of two mAbs into a single agent, called a bispecific antibody (BiAb), allows for targeting of a therapeutic biological agent or cell to specific tissue antigens. Classically, BiAbs have been used for several decades to redirect cytotoxic T cells or other effector cells to kill tumor cells. Here, we review preclinical models and ongoing phase I clinical trials in which arming polyclonally activated T cells with BiAbs may provide anti-tumor activity without dose-limiting toxicities. Additionally, we review findings from this novel strategy that merges magic bullet technology with hematopoietic stem cells to repair injured myocardium. Arming stem cells with BiAbs directed at injury-associated antigens enhances specific homing and engraftment to myocardial infarctions and may significantly improve cardiac function, strongly suggesting new paradigms for BiAb-targeting applications in tissue repair.

Virtual reality of stem cell transplantation to repair injured myocardium

The search for the fountain of youth continues into the 21st century with hopes that embryonic or hematopoietic stem cells (SC) will repair injured tissues in the heart, lungs, pancreas, muscles, nerves, liver, or skin. This commentary focuses on the potential of SC for inducing cardiac regeneration after myocardial injury, the barriers to SC treatment that need to be overcome for ensuring successful cardiac repair, and the experimental approaches that can be applied to the problem.

Potential of gene therapy for myocardial ischemia

PURPOSE OF REVIEW

Gene therapy-based treatment for myocardial ischemia is envisioned to involve multiple approaches.

RECENT FINDINGS

We discuss the various approaches and viral vectors available for this emerging field of cardioprotection by gene-based therapy. The prevention of arterial occlusion by the inhibition of clot formation or even atherosclerotic disease process is one approach. Another is the treatment of ischemia with genes that limit cardiac injury due to hypoxia. The molecular pathways that lead to cell damage and death are not yet fully understood. Thus, strides in the understanding of the disease process must be made.

SUMMARY

In spite of the lack of precise knowledge, delivery of certain genes has shown promise, and the development of various gene delivery techniques to the heart has shown progress.

Clinical relevance of angiotensin-converting enzyme gene polymorphisms to predict risk of mechanical ventilation after coronary artery bypass graft surgery

OBJECTIVE

Prolonged mechanical ventilation is a significant complication after coronary artery bypass graft surgery. Angiotensin-converting enzyme mediates ischemia-reperfusion injury, which is an important mechanism of postcoronary artery bypass graft complications. An insertion/deletion polymorphism within the angiotensin-converting enzyme gene is associated with variable concentrations of angiotensin-converting enzyme. Whether this polymorphism is associated with prolonged mechanical ventilation is not known. The primary objective was to determine whether the insertion/deletion angiotensin-converting enzyme gene polymorphism is associated with prolonged mechanical ventilation. The release of inflammatory mediators and risk of prolonged mechanical ventilation are higher after conventional coronary artery bypass graft compared with off-pump coronary artery bypass graft. Therefore, we examined the risk of prolonged mechanical ventilation for angiotensin-converting enzyme genotypes in patients undergoing conventional coronary artery bypass graft and off-pump coronary artery bypass graft separately. Tumor necrosis factor down-regulates angiotensin-converting enzyme concentrations, and functional polymorphisms within the tumor necrosis factor gene have been associated previously with prolonged mechanical ventilation. Therefore, we examined interactions between these polymorphisms.

DESIGN

Prospective observational cohort study.

SETTING

Tertiary care center.

SUBJECTS

Patients who underwent coronary artery bypass graft (with or without valve replacement surgery).

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

We measured angiotensin-converting enzyme genotype and time to extubate. Patients with the DD and DI genotypes were at higher risk of prolonged mechanical ventilation compared with those with the II genotypes (hazard ratio = 2.2 and 1.6, respectively, p =.0005). Interactions were seen between the angiotensin-converting enzyme genotypes with surgical technique and with tumor necrosis factor-308/lymphotoxin + 250 GG haplotype for prolonged mechanical ventilation (p =.078 and.0003, respectively). The association was stronger for those undergoing conventional coronary artery bypass graft, whereas neither angiotensin-converting enzyme genotype conferred higher risk to those undergoing off-pump coronary artery bypass graft.

CONCLUSIONS

Angiotensin-converting enzyme gene polymorphisms are associated with respiratory complications postcardiopulmonary bypass. The increased risk associated with genotype may be amenable to alternative surgical technique or pharmacologic manipulation.

Effect of AT(1) receptor blockade on cardiac apoptosis in angiotensin II-induced hypertension

Angiotensin II (ANG II) via AT(1) receptors induces apoptosis in cardiomyocytes in vitro. We tested the hypothesis that in vivo AT(1) receptor stimulation is accompanied by cardiac apoptosis and attempted to elucidate the molecular mechanisms involved in the death signaling pathway. Male Sprague-Dawley rats received ANG II (120 ng x kg(-1) x min(-1) sc) for 7 days with or without the AT(1) receptor antagonist losartan (10 mg x kg(-1) x day(-1) orally). Cardiac function was assessed by echocardiography. Apoptosis in the heart was detected and quantified by in situ TdT-mediated dUTP nick-end labeling (TUNEL) and radiolabeled DNA laddering. Expression of bax, bcl-2, caspase 3, and AT(1) and AT(2) receptors was examined by Western blot analysis. Activity of caspase 3 was also measured by a fluorometric immunosorbent enzyme assay. Tail cuff systolic blood pressure was elevated (P < 0.01, n = 6) in ANG II-infused rats (173 +/- 3 mmHg) versus controls (111 +/- 2 mmHg) and reduced by losartan (134 +/- 4 mmHg). Cardiac function was essentially unchanged in ANG II-infused rats. Increased internucleosomal DNA cleavage by TUNEL assay and radiolabeled DNA laddering showed results compatible with enhanced cardiomyocyte apoptosis in the hearts of ANG-II infused rats. The bax-to-bcl-2 ratio, expression of the active form of caspase 3 (17 kDa), and activity of caspase 3 in the hearts of the ANG II group increased more than twofold above controls. Protein expression of AT(1) and AT(2) receptors was significantly increased in ANG II-infused rats compared with control rats. Losartan-treated ANG II-infused rats exhibited normalized apoptosis, bax, caspase 3 activity, and AT(1) receptors. ANG II stimulation of AT(1) receptors in the heart in vivo is associated with an increased rate of apoptosis without major hemodynamic consequences. Bax and caspase 3 are involved in the apoptotic signaling pathway in this experimental paradigm.

Pharmacologic Regulation of the Renin—Angiotensin System: Physiologic and Pathologic Effects

Objective:

To review the physiologic and pathologic roles of the renin-angiotensin system in maintaining blood pressure, glomerular filtration rate, and myocardial tissue growth. The pharmacologic regulations of the pathologic effects of the renin-angiotensin system are emphasized, with a comparison between angiotensin-converting enzyme (ACE) inhibitors and angiotensin1receptor (AT1) antagonists.

Data Sources:

English-language basic science, clinical studies, and review articles were identified using MEDLINE, IOWA, and a manual search from January 1966 through September 1999. References were also obtained from the reference section of relevant published articles.

Study Selection and Data Extraction:

All articles identified were evaluated for possible inclusion in this review. Evaluative and comparative data from basic science and controlled clinical studies were reviewed.

Data Synthesis:

The renin-angiotensin system has a plethora of physiologic and pathologic roles in the regulation of blood pressure, renal function, and cell growth. The cellular mechanisms involved in eliciting the responses to the renin-angiotensin system are discussed in detail, with an emphasis on the pharmacologic regulation of the cellular responses. The role of angiotensin II in maintaining blood pressure, glomerular filtration rate, and in regulating myocardial cell growth secondary to myocardial infarction or as a complication of congestive heart failure are all reviewed. The ACE inhibitors and AT1antagonists have comparable pharmacologic effects that can influence their therapeutic application. The ACE inhibitors and AT, antagonists are compared regarding clinically and experimentally observed differences that may affect their therapeutic application.

Conclusions:

The physiologic and pathologic roles of the renin-angiotensin system make the ACE inhibitors and AT1antagonists ideal candidates in treating many conditions. Presently, few studies have been conducted that directly compare ACE inhibitors and AT, antagonists. An understanding of the basic underlying pharmacologic principles is essential when attempting to apply the scientific and clinical information of the ACE inhibitors and AT1antagonists with the intention of extrapolating to therapeutic utility.

Gallium-desferrioxamine protects the cat retina against injury after ischemia and reperfusion

This study sought to determine whether gallium-desferrioxamine (Ga/DFO) can curb free radical formation and mitigate biochemical and electrophysiological parameters of injury in the cat retina subjected to ischemia followed by reperfusion. For the biochemical studies, cat eyes were subjected to 90 min of retinal ischemia followed by 5 min of reperfusion, and enucleation of one eye of each cat was used to measure retinal reperfusion injury. Before enucleation of fellow eyes, 2.5 mg/kg Ga/DFO was injected intravenously 5 min before reperfusion. The flux of hydroxyl radicals, as measured directly by conversion of salicylate to 2,3- and 2,5-dihydroxybenzoic acid (2,3- and 2,5-DHBA), was significantly lower in Ga/DFO-treated eyes. The mean normalized level of 2,3-DHBA (considered a specific marker of hydroxyl radicals) was 3.5 times higher in untreated eyes. Ga/DFO caused a significant reduction, by 2.56-fold, in lipid peroxidation, as reflected by levels of malondialdehyde. Ascorbic acid, a natural antioxidant present in the retina, is severely depleted in untreated eyes. In contrast, in Ga/DFO-treated eyes, levels were 10 times higher than the control. Energy charge was 2.38 times higher in treated eyes. Levels of purine catabolites (hypoxanthine, xanthine, and uric acid) that reflect excessive metabolism of purine nucleotides were approximately twice higher in untreated retinas. Electroretionographic studies, performed on a different subset of animals, substantiated the biochemical results. In Ga/DFO-treated eyes the amplitude of the mixed cone-rod response b-wave (as compared with fellow nonischemic eyes) fully recovered within 24 h after ischemia (b-wave ratio 1.04 +/- 0.09, [mean +/- SEM]) whereas ischemic/reperfused and nontreated eyes recovered to only 0.33 +/- 0. 05. The results show that severe biochemical and functional retinal injury occurs in cat eyes subjected to ischemia and reperfusion. These severe changes were significantly reduced by a single administration of Ga/DFO just before reperfusion. We hypothesize that the protection afforded by Ga/DFO is due to a combined effect of "Push-Pull" mechanisms interfering with transition metal-dependent and free radical-mediated injurious processes.