Combined endothelial and myocardial protection by endothelin antagonism enhances transplant allograft preservation

Sulforaphane Regulates eNOS Activation and NO Production via Src-Mediated PI3K/Akt Signaling in Human Endothelial EA.hy926 Cells

Sulforaphane (SFN) is a naturally occurring isothiocyanate that is abundant in many cruciferous vegetables, such as broccoli and cauliflower, and it has been observed to exert numerous biological activities. In the present study, we investigate the effect of SFN on eNOS, a key regulatory enzyme of vascular homeostasis and underlying intracellular pathways, in human endothelial EA.hy926 cells. The results indicate that SFN treatment significantly increases NO production and eNOS phosphorylation in a time- and dose-dependent fashion and also augments Akt phosphorylation in a time- and dose-dependent manner. Meanwhile, pretreatment with LY294002 (a specific PI3K inhibitor) suppresses the phosphorylation of eNOS and NO production. Furthermore, SFN time- and dose-dependently induces the phosphorylation of Src kinase, a further upstream regulator of PI3K, while PP2 pretreatment (a specific Src inhibitor) eliminates the increase in phosphorylated Akt, eNOS and the production of NO derived from eNOS. Overall, the present study uncovers a novel effect of SFN to stimulate eNOS activity in EA.hy926 cells by regulating NO bioavailability. These findings provide clear evidence that SFN regulates eNOS activity and NO bioavailability, suggesting a promising therapeutic candidate to prevent endothelial dysfunction, atherosclerosis and other cardiovascular diseases.

Prognostic Value of Biomarkers in Cardiac Allograft Vasculopathy following Heart Transplantation: A Literature Review

Cardiac allograft vasculopathy (CAV), also known as cardiac transplant vasculopathy, is a major determinant of long-term survival among cardiac transplantation recipients. Histologically, CAV is featured by diffuse, concentric thickening of the vascular wall, and primarily affects large and small epicardial coronary arteries, intramyocardial arteries, and veins. Owing to graft denervation, CAV typically follows an insidious course, and patients may not experience classic angina symptoms but instead present with progressive heart failure or ventricular arrhythmias. Recent studies on biomarkers have furthered the knowledge concerning the prediction and prognosis of CAV. Given its association with metabolic, thrombotic, inflammatory, and immunologic markers, CAV is likely to represent a complex multifactorial process that involves both immune-mediated and non-immune-mediated pathways. In order to identify the high-risk patients that would benefit from early intervention, future research is warranted to examine the usefulness of a biomarker panel in CAV risk stratification.

Recipient hypertonic saline infusion prevents cardiac allograft dysfunction

OBJECTIVE

Hypertonic saline (HTS) has potent immune and vascular effects. We assessed recipient pretreatment with HTS on allograft function in a porcine model of heart transplantation and hypothesized that HTS infusion would limit endothelial and left ventricular (LV) dysfunction following transplantation.

METHODS

Heart transplants were performed after 6 hours of cold ischemic storage. Recipient pigs were randomized to treatment with or without HTS (7.5% NaCl) before cardiopulmonary bypass (CPB). Using a myograft apparatus, coronary artery endothelial-dependent (Edep) and -independent (Eind) relaxation was assessed. LV performance was determined using pressure-volume loop analysis. Pulmonary interleukin (IL)-2, IL-6, and tumor necrosis factor (TNF)-α expression was measured.

RESULTS

Weaning from CPB and LV performance after transplantation were improved in HTS-treated animals. Successful weaning from CPB was greater in the HTS-treated hearts (8 of 8 vs 2 of 8; P < .05). Mean LV functional recovery was improved in the HTS-treated animals, as assessed by preload recruitable stroke work (65 ± 10% vs 27 ± 10%; P < .001) and end-systolic elastance (55 ± 7% vs 37 ± 4%; P < .001). Treatment with HTS resulted in improved Edep (mean maximum elastance [Emax], 56 ± 5% vs 37 ± 7%; P < .001) and Eind (mean Emax%, 77 ± 6% vs 52 ± 4%; P < .001) vasorelaxation compared with control. Pulmonary expression of IL-2, IL-6, and TNF-α increased following transplantation, whereas HTS therapy attenuated IL production (P < .001). Transplantation increased plasma TNF-α levels and LV TNF-α expression, whereas HTS prevented this up-regulation (P < .001).

CONCLUSIONS

Recipient HTS pretreatment preserves allograft vasomotor and LV function, and HTS therapy limits CPB-induced injury. HTS may be a novel recipient intervention to prevent graft dysfunction.

Donor simvastatin treatment and cardiac allograft ischemia/reperfusion injury

Ischemia/reperfusion injury of a transplanted heart may result in serious early and late adverse effects such as primary graft dysfunction, increased allograft immunogenicity, and initiation of fibroproliferative cascades that compromise the survival of the recipient. Microvascular dysfunction has a central role in ischemia/reperfusion injury through increased vascular permeability, leukocyte adhesion and extravasation, thrombosis, vasoconstriction, and the no-reflow phenomenon. Here we review the involvement of microvascular endothelial cells and their surrounding pericytes in ischemia/reperfusion injury, and the pleiotropic, cholesterol-independent effects of statins on microvascular dysfunction. In addition, we delineate how the rapid vasculoprotective effects of statins could be used to protect cardiac allografts against ischemia/reperfusion injury by administering statins to the organ donor before graft removal and transplantation.

Visfatin activates eNOS via Akt and MAP kinases and improves endothelial cell function and angiogenesis in vitro and in vivo: translational implications for atherosclerosis

Improving endothelial nitric oxide synthase (eNOS) bioactivity and endothelial function is important to limit native, vein graft, and transplant atherosclerosis. Visfatin, a NAD biosynthetic enzyme, regulates the activity of the cellular survival factor, Sirt1. We hypothesized that visfatin may improve eNOS expression, endothelial function, and postnatal angiogenesis. In human umbilical vein (HUVEC) and coronary artery endothelial cells, we evaluated the effects of recombinant human visfatin on eNOS protein and transcript expression and mRNA stability, in the presence and absence of visfatin RNA silencing. We also assessed visfatin-induced protein kinase B (Akt) activation and its association with src-tyrosine kinases, phosphorylation of Ser(1177) within eNOS in the presence and absence of phosphatidylinositol 3-kinase (PI 3-kinase) inhibition with LY-294002, and evaluated the contributory role of extracellular signal-regulated kinase 1/2. Finally, we determined the impact of visfatin on HUVEC migration, proliferation, inflammation-induced permeability, and in vivo angiogenesis. Visfatin (100 ng/ml) upregulated and stabilized eNOS mRNA and increased the production of nitric oxide and cGMP. Visfatin-treated HUVEC demonstrated greater proliferation, migration, and capillary-like tube formation but less tumor necrosis factor-alpha-induced permeability; these effects were decreased in visfatin gene-silenced cells. Visfatin increased total Akt and Ser(473)-phospho-Akt expression with concomitant rises in eNOS phosphorylation at Ser(1177); these effects were blocked by LY-2940002. Studies with PP2 showed that the nonreceptor tyrosine kinase, src, is an upstream stimulator of the PI 3-kinase-Akt pathway. Visfatin also activated mitogen-activated protein (MAP) kinase through PI 3-kinase, and mitogen/extracellular signal-regulated kinase inhibition attenuated visfatin-elicited Akt and eNOS phosphorylation. Visfatin-filled Matrigel implants showed an elevated number of infiltrating vessels, and visfatin treatment produced significant recovery of limb perfusion following hindlimb ischemia. These results indicate a novel effect of visfatin to stimulate eNOS expression and function in endothelial cells, via a common upstream, src-mediated signaling cascade, which leads to activation of Akt and MAP kinases. Visfatin represents a translational target to limit endothelial dysfunction, native, vein graft and transplant atherosclerosis, and improve postnatal angiogenesis.

Endothelin receptor antagonism by tezosentan attenuates lung injury induced by aortic ischemia-reperfusion

Tezosentan is a novel dual endothelin receptor antagonist. The purpose of this study was to examine the effect of tezosentan on lung injury induced by abdominal aortic ischemia-reperfusion (IR) in rats. Thirty-two Wistar-albino rats were randomized into four groups (eight per group) as follows: control group (sham laparotomy), aortic IR group (120 min ischemia and 120 min reperfusion), aortic IR + tezosentan group (a bolus intravenous injection of 10 mg/kg tezosentan before ischemia plus continuous intravenous infusion of 1 mg/kg/hr tezosentan during 120 min ischemia and 120 min reperfusion), and control + tezosentan. Blood and lung tissue samples were obtained for biochemical analysis. Protein concentrations in bronchoalveolar lavage fluid and lung wet/dry weight ratios were measured. A histological evaluation was also done. Aortic IR significantly increased (p < 0.05 vs. control group) and tezosentan significantly decreased (p < 0.05 vs. aortic IR group) the plasma level of tumor necrosis factor-alpha; lung tissue levels of malondialdehyde, catalase, and myleperoxidase; and protein concentration in bronchoalveolar lavage fluid and lung wet/dry weight ratio. Histological evaluation showed that tezosentan attenuated the morphological changes associated with lung injury. The results of this study indicate that tezosentan attenuates lung injury induced by aortic IR in rats. We propose that this protective effect of tezosentan is due to (1) reduced systemic inflammatory response, (2) reduced oxidative stress and lipid peroxidation in lung tissue, (3) reduced pulmonary microvascular leakage, and (4) inhibition of leukocyte infiltration into lung tissue.

Mitochondria-targeted cytoprotective peptides for ischemia-reperfusion injury

It is now recognized that oxidative injury and mitochondrial dysfunction are responsible for many clinical disorders with unmet needs, including ischemia-reperfusion injury, neurodegeneration, and diabetes. Mitochondrial dysfunction can lead to cell death by apoptosis or necrosis. As mitochondria are the major source of intracellular reactive oxygen species (ROS), and mitochondria are also the primary target for ROS, the ideal drug therapy needs to be targeted to mitochondria. A number of approaches have been used for targeted delivery of therapeutic agents to mitochondria. This review will focus on a novel class of cell-permeable small peptides (Szeto-Schiller peptides) that selectively partition to the inner mitochondrial membrane and possess intrinsic mitoprotective properties. Studies with isolated mitochondrial preparations and cell cultures show that these SS peptides can scavenge ROS, reduce mitochondrial ROS production, and inhibit mitochondrial permeability transition. They are very potent in preventing apoptosis and necrosis induced by oxidative stress or inhibition of the mitochondrial electron transport chain. These peptides have demonstrated excellent efficacy in animal models of ischemia-reperfusion, neurodegeneration, and renal fibrosis, and they are remarkably free of toxicity. The pharmacology of the SS peptides in models of ischemia-reperfusion will be the focus of this review.

Mechanisms of ET-1-induced endothelial dysfunction

There is now increasing evidence that endothelial dysfunction is an early event in the pathophysiology of cardiovascular diseases and can be corrected with certain therapies such as angiotensin converting enzyme inhibitors angiotensin type I receptor antagonists and stains independently of blood pressure lowering effects. Restoring endothelial function appears to be a crucial target since endothelial dysfunction predicts cardiovascular events in various situations such as coronary artery disease peripheral artery disease, or hypertension and in patients undergoing vascular surgery. Preclinical and clinical data strongly support that endothelin receptor antagonists belong to this restricted class of pharmacological agents able to act on the endothelium, and offer a potential therapeutic approach for numerous diseases associated with endothelial dysfunction. The purpose of this review will be therefore, 1) to propose mechanisms by which ET-1 can cause endothelial dysfunction; 2) to provide an overview of pathological situations associated with endothelial dysfunction related to ET-1; and 3) to assemble evidence on efficacy of endothelin receptor antagonists for improvement of endothelial function.

Endothelin-1 accentuates the proatherosclerotic effects associated with C-reactive protein

OBJECTIVES

The proinflammatory marker C-reactive protein has been demonstrated to play a role in the development of atherosclerosis. Endothelin-1 and nitric oxide homeostasis is crucial for normal vasomotor function, limiting inflammatory activation and maintaining a nonthrombogenic endothelial surface. In addition to its vasoactive properties, endothelin-1 is also an inflammatory cytokine. We have previously demonstrated that C-reactive protein impairs endothelial cell nitric oxide production. Protein kinase C, an important signal transducer within the cell, is involved in several cellular responses to external stimuli. We therefore sought to determine whether endothelin-1 exposure modulates C-reactive protein's effects on nitric oxide production via protein kinase C.

METHODS

Endothelial cells were incubated with C-reactive protein (200 microg), endothelin-1 (100 nM), C-reactive protein + endothelin-1, or phosphate-buffered saline solution (control) for 24 hours. After exposure, endothelial nitric oxide synthase expression was determined in addition to total nitric oxide production and protein kinase C translocation and activity.

RESULTS

Endothelial nitric oxide synthase protein expression was reduced following incubation with C-reactive protein and endothelin-1 treatment compared with baseline by 40% and 45%, respectively (P = .04); however, no additive effects were seen with coincubation. C-reactive protein produced a 47% decrease in nitric oxide production compared with control. Coincubation with endothelin-1 resulted in a synergistic 70% reduction in nitric oxide production (P = .001). C-reactive protein exposure inhibited translocation of protein kinase C lambda compared with control (P = .01). Furthermore, coincubation of C-reactive protein with endothelin-1 led to a synergistic inhibition of protein kinase C lambda translocation (P = .01). C-reactive protein exposure reduced protein kinase C activity by 40% compared with control (P = .02), although coincubation with endothelin-1 had a synergistic reduction in activity (P = .02).

CONCLUSIONS

Our results indicate that endothelin-1 exposure accentuated C-reactive protein's impairment of endothelial nitric oxide production via synergistic inhibition of protein kinase C lambda translocation and activity. Our investigations suggest that endothelin-1 inhibition and protein kinase C stimulation may provide a novel therapeutic strategy to improve vascular nitric oxide homeostasis and mitigate the proatherosclerotic effects of C-reactive protein.

Use of diffusion tensor imaging to predict myocardial viability after warm global ischemia: possible avenue for use of non-beating donor hearts

BACKGROUND

The assessment of myocardial viability after global warm ischemia (WI) but before reperfusion is challenging. We hypothesized that fractional anisotropy (FA), a magnetic resonance imaging (MRI) parameter of water diffusion that characterizes cellular integrity within tissues, provides a rapid and useful method for evaluating the viability of hearts after WI.

METHODS

Dog hearts were exposed to 60 minutes of WI after exanguination, explanted and preserved in a cold, non-beating state for 6 hours, using continuous perfusion (CP) or static cold storage (CS). Toward the end of preservation, a global FA assessment, acquired using MRI, was compared with analyses obtained from myocardial biopsies that included adenosine triphosphate (ATP), endothelin-1 (ET-1) and caspase-3 levels, light microscopy and tetrazolium staining. Functional recovery was analyzed after restoration of blood flow on a non-working Langendorff preparation.

RESULTS

FA measured at the end of CP showed strong correlations with all parameters of functional recovery (developed pressure, R = 0.60; dP/dt, R = 0.96; -dP/dt, R = 0.96). Although FA also correlated with tissue levels of ATP, ET-1 and caspase-3 (R = 0.77, -0.84, -0.64), recovery of myocardial function did not correlate with these markers or any other conventional analyses of myocardial injury (troponin I, changes on light microscopy or tetrazolium staining).

CONCLUSIONS

FA, an MRI-based parameter that indicates cellular integrity, was found to reflect better myocardial ATP stores, less induction of ET-1 and caspase-3 and improved functional recovery of hearts after global WI. As a clinically applicable tool capable of rapidly differentiating reversible from lethal injury, diffusion tensor imaging may prove useful in the eventual adoption of non-beating donor hearts for transplantation.

Heart Preservation Using Continuous Ex Vivo Perfusion Improves Viability and Functional Recovery

BACKGROUND

Cold static storage (CS) is a proven preservation method for heart transplantion, yet early postoperative graft dysfunction remains prevalent, so continuous perfusion (CP) during ex vivo transport may improve viability and function of heart grafts.

METHODS AND RESULTS

Canine hearts underwent CP (n=9) or CS (n=9) for 6 h while intramyocardial pH was continuously monitored. Biopsies were assayed for ATP, caspase-3, malondialdehyde (MDA), and endothelin-1 (ET-1) levels at baseline, after preservation (t1), and after 1 h of blood reperfusion on a Langendorff model (t2). Functional recovery was determined at t2 by +dP/dt, -dP/dt, developed pressure, peak pressure and end-diastolic pressure. CP resulted in higher tissue pH and ATP stores and reduced caspase-3, MDA and ET-1 levels compared with CS at both t1 and t2. Post reperfusion recovery was significantly greater in CP vs CS for all myocardial functional parameters except end-diastolic pressure. Weight gain was significantly increased in CP vs CS at t1, but not at t2.

CONCLUSIONS

Low-grade tissue acidosis and energy depletion occur during CS and are associated with oxidative injury and apoptosis during reperfusion. CP attenuates these biochemical and pathologic manifestations of tissue injury, together with improved myocardial recovery, despite mild, transient edema.

Treatment of allograft vasculopathy in heart transplantation

Cardiac allograft vasculopathy remains one of the main causes of morbidity and mortality after heart transplantation, although its impact is becoming somewhat smaller as prophylactic measures are implemented. Advances in the understanding of the molecular and cellular mechanisms involved in the genesis and development of cardiac allograft vasculopathy are opening ways for new diagnostic and therapeutic strategies. Successful prophylaxis of the early stages of the disease has been demonstrated with the use of newer immunosuppressive agents, such as sirolimus and everolimus, that will probably be included in future protocols. For most patients with established cardiac allograft vasculopathy, currently available revascularisation methods and retransplantation are not appropriate options. Antiproliferative agents could provide significant improvement in terms of symptom relief and prognosis, but their definite value must be proven in well-designed trials.

Elevated endothelin-1 levels impair nitric oxide homeostasis through a PKC-dependent pathway

BACKGROUND

Endothelin-1 (ET-1) plays an important role in the maintenance of vascular tone and pathological states such as ischemia/reperfusion (I/R) injury, coronary vasospasm, and cardiac allograft vasculopathy. We assessed the effects of elevated ET-1 levels as seen after I/R to determine if ET-1 modulates nitric oxide (NO) production via the translocation of specific protein kinase C (PKC) isoforms.

METHODS AND RESULTS

Human saphenous vein endothelial cells (HSVECs) (n=8) were incubated with ET-1 or phosphate-buffered saline (PBS) for 24 hours. NO production was determined in the supernatant by measuring nitrate/nitrite levels. Protein expression of endothelial nitric oxide synthase (eNOS), inducible NOS (iNOS), caveolin-1 and PKC were determined. Lastly, PKC translocation and activity were assessed after exposure to the drug of interest. HSVECs exposed to ET-1 displayed decreased NO production. PKC inhibition reduced NO production, whereas PKC activation increased production. NO production was maintained when HSVECs exposed to ET-1 were treated with the PKC agonist, PMA. eNOS protein expression was reduced after ET-1 treatment. PKC inhibition also downregulated eNOS protein expression, whereas PMA upregulated expression. ET-1 exposure led to a significant increase in PKCdelta and PKCalpha translocation compared with control, whereas translocation of PKClambda was inhibited. ET-1 exposure significantly reduced overall PKC activity compared with control.

CONCLUSIONS

Our study demonstrates that high levels of ET-1 impair endothelial NO production via an isoform-specific PKC-mediated inhibition of eNOS expression. ET-1 antagonism with bosentan stimulates translocation of PKClambda and leads to increased PKC activity and NO production. ET-1 antagonism may provide a novel therapeutic strategy to improve vascular homeostasis.

Cardiac allograft vasculopathy: The achilles’ heel of long-term survival after cardiac transplantation

Over the past 40 years, cardiac transplantation has evolved as the single best long-term option for eligible candidates with end-stage heart failure. Approximately 2000 transplants are performed annually in the United States, and with the institution of calcineurin-based immunotherapy, surveillance biopsies, and programmatic-based patient care, life expectancy at 1 and 12 years is 85% and 50%, respectively. Cardiac allograft vasculopathy (CAV) is the number one cause of death after the first year of transplantation. The incidence of CAV remains as high as 50% at 5 years, with life expectancy significantly abbreviated once it is recognized. Although current immunotherapy has reduced the likelihood of cellular rejection, it has not impacted CAV substantially. Better treatment of established risk factors and the advent of newer antiproliferative immunotherapy may hold promise in treating CAV. However, future therapies must address the multitude of mechanisms underlying CAV. This manuscript reviews the pathophysiology, clinical manifestations, screening, and diagnostic strategies for cardiac allograft vasculopathy while emphasizing current treatment paradigms designed to stave off or retard the progression of CAV.