Effect of thrombin fragment (TP508) on myocardial ischemia-reperfusion injury in hypercholesterolemic pigs

Hyperlipidaemia and cardioprotection: Animal models for translational studies

Hyperlipidaemia is a well-established risk factor for cardiovascular diseases and therefore, many animal model have been developed to mimic the human abnormal elevation of blood lipid levels. In parallel, extensive research for the alleviation of ischaemia/reperfusion injury has revealed that hyperlipidaemia is a major co-morbidity that attenuates the cardioprotective effect of conditioning strategies (preconditioning, postconditioning and remote conditioning) and that of pharmacological interventions by interfering with cardioprotective signalling pathways. In the present review article, we summarize the existing data on animal models of hypercholesterolaemia (total, low density and HDL abnormalities) and hypertriglyceridaemia used in ischaemia/reperfusion injury and protection from it. We also provide recommendations on preclinical animal models to be used for translations of the cardioprotective strategies into clinical practice. LINKED ARTICLES: This article is part of a themed issue on Risk factors, comorbidities, and comedications in cardioprotection. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.23/issuetoc.

Cardioprotective effect of hyperkalemic cardioplegia in an aquaporin 7-deficient murine heart

BACKGROUND

Hyperkalemic cardioplegia using St. Thomas' Hospital solution No. 2 (STH2) is commonly used to protect the myocardium during surgery. Mice deficient in the myocyte channel aquaporin 7 (AQP7) show significantly reduced glycerol and ATP contents and develop obesity; however, the influence of AQP7 on cardioplegia effectiveness remains unclear.

METHODS

After determining the influence of ischemic duration on cardiac function, isolated hearts of male wild-type (WT) and AQP7-knockout (KO) mice (> 13 weeks old) were aerobically Langendorff-perfused with bicarbonate buffer, and randomly allocated to the control group (25 min of global ischemia) and STH2 group (5 min of STH2 infusion before 20 min of global ischemia, followed by 60 min of reperfusion).

RESULTS

Final recovery of left ventricular developed pressure (LVDP) of WT and AQP7-KO hearts in the control group was 24.5 ± 12.4% and 20.6 ± 8.4%, respectively, which were significantly lower than those of the STH2 group (96.4 ± 12.7% and 92.9 ± 27.6%). Troponin T levels of WT and AQP-KO hearts significantly decreased in the STH2 groups (142.9 ± 27.2 and 219.9 ± 197.3) compared to those of the control (1725.0 ± 768.6 and 1710 ± 819.9).

CONCLUSIONS

AQP7 was not involved in the protective efficacy of STH2 in this mouse model, suggesting its clinical utility even in complications of metabolic disease.

A novel experimental thrombotic myocardial infarction and primary angioplasty model in swine

AIMS

We sought to develop a reproducible animal model for acute myocardial infarction (AMI) in adult atherosclerosis-prone pigs.

METHODS AND RESULTS

A coil was placed in the right coronary artery or the left anterior descending artery in 26 downsized spontaneously hypercholesterolaemic pigs and left untreated until thrombotic occlusion. Then, we crossed the thrombotic occlusion with a guidewire, followed by predilatation, thrombus visualisation with optical coherence tomography (OCT) imaging and, finally, deployment of a stent and repeated OCT. After revascularisation, we calculated the index of microcirculatory resistance (IMR). After a feasibility phase (six animals), acute thrombotic occlusion was achieved in all 20 pigs. Eighteen animals were successfully revascularised and survived until sacrifice. Thrombus formation was confirmed by OCT, measurement of thrombin-antithrombin complexes and pathology examination. Myocardial necrosis was confirmed by troponin T elevation, myocardial staining and pathology examination. Distal thrombotic embolisation and microvascular obstruction were supported by increased IMR and pathology examination.

CONCLUSIONS

A porcine model of thrombotic occlusion AMI in miniaturised adult spontaneously atherosclerosis-prone pigs is feasible by percutaneous intracoronary placement of a coil. The reperfusion by angioplasty completed this model which mirrors human pathological conditions with myocardial infarction, necrosis and distal embolisation.

Understanding the Pathophysiology and Challenges of Development of Medical Countermeasures for Radiation-Induced Vascular/Endothelial Cell Injuries: Report of a NIAID Workshop, August 20, 2015

After the events of September 11, 2001, a decade of research on the development of medical countermeasures (MCMs) to treat victims of a radiological incident has yielded two FDA-approved agents to mitigate acute radiation syndrome. These licensed agents specifically target the mitigation of radiation-induced neutropenia and infection potential, while the ramifications of the exposure event in a public health emergency incident could include the entire body, causing additional acute and/or delayed organ/tissue injuries. Anecdotal data as well as recent findings from both radiation accident survivors and animal experiments implicate radiation-induced injury or dysfunction of the vascular endothelium leading to tissue and organ injuries. There are significant gaps in our understanding of the disease processes and progression, as well as the optimum approaches to develop medical countermeasures to mitigate radiation vascular injury. To address this issue, the Radiation and Nuclear Countermeasures Program of the National Institute of Allergy and Infectious Diseases (NIAID) organized a one-day workshop to examine the current state of the science in radiation-induced vascular injuries and organ dysfunction, the natural history of the pathophysiology and the product development maturity of potential medical countermeasures to treat these injuries. Meeting presentations were followed by a NIAID-led open discussion among academic investigators, industry researchers and government agency representatives. This article provides a summary of these presentations and subsequent discussion from the workshop.

Nuclear Countermeasure Activity of TP508 Linked to Restoration of Endothelial Function and Acceleration of DNA Repair

There is increasing evidence that radiation-induced damage to endothelial cells and loss of endothelial function may contribute to both acute radiation syndromes and long-term effects of whole-body nuclear irradiation. Therefore, several drugs are being developed to mitigate the effects of nuclear radiation, most of these drugs will target and protect or regenerate leukocytes and platelets. Our laboratory has demonstrated that TP508, a 23-amino acid thrombin peptide, activates endothelial cells and stem cells to revascularize and regenerate tissues. We now show that TP508 can mitigate radiation-induced damage to endothelial cells in vitro and in vivo. Our in vitro results demonstrate that human endothelial cells irradiation attenuates nitric oxide (NO) signaling, disrupts tube formation and induces DNA double-strand breaks (DSB). TP508 treatment reverses radiation effects on NO signaling, restores tube formation and accelerates the repair of radiation-induced DSB. The radiation-mitigating effects of TP508 on endothelial cells were also seen in CD-1 mice where systemic injection of TP508 stimulated endothelial cell sprouting from aortic explants after 8 Gy irradiation. Systemic doses of TP508 that mitigated radiation-induced endothelial cell damage, also significantly increased survival of CD-1 mice when injected 24 h after 8.5 Gy exposure. These data suggest that increased survival observed with TP508 treatment may be due to its effects on vascular and microvascular endothelial cells. Our study supports the usage of a regenerative drug such as TP508 to activate endothelial cells as a countermeasure for mitigating the effects of nuclear radiation.

Systemic administration of thrombin peptide TP508 enhances VEGF-stimulated angiogenesis and attenuates effects of chronic hypoxia

Revascularization of chronic wounds and ischemic tissue is attenuated by endothelial dysfunction and the inability of angiogenic factors to stimulate angiogenesis. We recently showed that TP508, a nonproteolytic thrombin peptide, increases perfusion and NO-dependent vasodilation in hearts with chronic ischemia and stimulates NO production by endothelial cells. In this study, we investigated systemic in vivo effects of TP508 on VEGF-stimulated angiogenesis in vitro using aortic explants in normoxic and hypoxic conditions. Mice were injected with saline or TP508 and 24 h later aortas were removed and cultured to quantify endothelial sprouting. TP508 injection increased endothelial sprouting and potentiated the in vitro response to VEGF. Exposure of control explants to hypoxia inhibited basal and VEGF-stimulated endothelial cell sprouting. This effect of hypoxia was significantly prevented by TP508 injection. Thus, TP508 systemic administration increases responsiveness of aortic endothelial cells to VEGF and diminishes the effect of chronic hypoxia on endothelial cell sprouting. Studies using human endothelial cells in culture suggest that protective effects of TP508 during hypoxia may involve stimulation of endothelial cell NO production. These data suggest potential clinical benefit of using a combination of systemic TP508 and local VEGF as a therapy for revascularization of ischemic tissue.

Chymase inhibition reduces infarction and matrix metalloproteinase-9 activation and attenuates inflammation and fibrosis after acute myocardial ischemia/reperfusion

Chymase is activated after acute myocardial ischemia/reperfusion (AMI-R) and is associated with an early activation of matrix metalloproteinase-9 (MMP-9), which increases infarct size after experimental AMI, and late fibrosis. We assessed the effect of chymase inhibition on myocardial protection and early signs of fibrosis after AMI-R. Fourteen pigs underwent AMI-R and received intravenously either vehicle (V; n = 7) or chymase inhibitor (CM; n = 7). Separately, rat myocardial fibroblast was incubated with vehicle (n = 4), low-dose chymase (n = 4), high-dose chymase (n = 4), or high-dose chymase plus chymase inhibitor (n = 4). Infarct size (V, 41 ± 5; CM, 24 ± 5; P < 0.01) and serum troponin T (P = 0.03) at the end of reperfusion were significantly reduced in CM. Chymase activity in both the area at risk (AAR) (P = 0.01) and nonischemic area (P = 0.02) was significantly lower in CM. Myocardial levels of pro, cleaved, and cleaved/pro-MMP-9 in the AAR were significantly lower in CM than V (P < 0.01, < 0.01, and = 0.02, respectively), whereas phospho-endothelial nitric-oxide synthase (eNOS) (P < 0.01) and total eNOS (P = 0.03) were significantly higher in CM. Apoptotic cells (P = 0.05), neutrophils (P < 0.05), and MMP-9-colocalizing mast cells (P < 0.05) in the AAR were significantly reduced in CM. Interleukin-18 (P < 0.05) and intercellular adhesion molecule-1 (P < 0.05) mRNA levels were significantly lower in CM. In cultured cardiac fibrosis, Ki-67-positive cells were significantly higher in the high-dose chymase groups (P < 0.03). This study demonstrates that chymase inhibition plays crucial roles in myocardial protection related to MMP-9, inflammatory markers, and the eNOS pathway. It may also attenuate fibrosis induced by activated chymase after AMI-R.

Possible participation of endothelial cell apoptosis of coronary microvessels in the genesis of Takotsubo cardiomyopathy

BACKGROUND

Takotsubo cardiomyopathy (TCM) is characterized by systolic ballooning of the left ventricular apex. It is triggered by emotional or physical stress, but the exact mechanism through which stress leads to TCM is not known.

HYPOTHESIS

Coronary microvessel apoptosis is the missing link between stress and TCM.

METHODS

In 8 female patients with TCM, plasma catecholamines, Thrombolysis in Myocardial Infarction (TIMI) coronary flow grade and myocardial perfusion grade, and apoptosis of the coronary microvessels in the biopsied myocardial specimen by terminal deoxynucleotidyl transferase-mediated nick end-labeling (TUNEL) were examined.

RESULTS

Plasma epinephrine and norepinephrine were increased to 663 +/- 445 and 875 +/- 812 pg/mL (mean +/- SD), respectively. Acetylcholine-induced delayed myocardial perfusion through the ballooning apical segment without flow disturbance in the epicardial coronary arteries (indicating microvessel spasm) and focal myocardial necrosis were observed in all subjects. Apical ballooning disappeared and myocardial perfusion delay was not inducible 1 month later. The number of vessels having apoptotic endothelial cells/10 vessels in arterioles, venules, and capillaries at initial biopsy and repeat biopsy 1 month later were 8.3 +/- 1.4 vs 0.4 +/- 1.1, P < 0.0001; 6.8 +/- 1.8 vs 0.3 +/- 0.7, P < 0.0001; and 7.9 +/- 1.0 vs 0.5 +/- 0.9, P < 0.0001, respectively.

CONCLUSIONS

Left ventricular apical ballooning in TCM was considered to be caused by coronary microvessel spasm due to catecholamine-induced endothelial cell apoptosis and myocardial stunning after release of microvessel spasm. Endothelial cell apoptosis of coronary microvessel is therefore considered to be the missing link between stress and TCM.

Effect of thrombin fragment (TP508) on myocardial ischemia reperfusion injury in a model of type 1 diabetes mellitus

BACKGROUND

We investigated the efficacy of novel thrombin fragment TP508 on ischemia-reperfusion injury using a porcine model of type 1 diabetes mellitus.

METHODS AND RESULTS

Alloxan-induced diabetic male Yucatan swine underwent 60 minutes of mid-left anterior descending coronary artery occlusion, followed by 120 minutes of reperfusion. Fifty minutes into ischemia, animals received either placebo (DM; n=8) or TP508 as a bolus of 1 mg/kg followed by infusion at 2.5 mg/kg per hour (DMT; n=8). Hemodynamic parameters and myocardial function were monitored. Monastryl blue/triphenyl tetrazolium chloride staining was used to assess sizes of the areas at risk and infarction. Coronary microvascular reactivity was measured and expression of cell survival and proapoptotic proteins quantified. Preoperative serum glucose values were similar between groups (309±57 mg/dL in DM versus 318±67 mg/dL in DMT; P=0.92). Infarct size was smaller in the TP508-treated group (5.3±1.9% in DMT versus 19.4±5.6% in DM; P=0.03). There was no statistically significant difference in global or regional left ventricular function between groups. Endothelium-dependent microvessel relaxation was moderately improved in the DMT group (P=0.09), whereas endothelium-independent relaxation was similar between groups. The expression of cell survival proteins Akt, phospho-p38, and mammalian target of rapamycin was higher in the areas at risk of DMT animals compared with DM animals (P<0.05), and expressions of proapoptotic glycogen synthase kinase 3β and caspase 3 were lower in the DMT group (P<0.05).

CONCLUSIONS

This study demonstrates that, in type 1 diabetic swine, TP508 reduces infarct size after ischemia-reperfusion. Thus, TP508 may offer a novel approach in cardioprotection from ischemia-reperfusion injury in diabetic patients.

RGD-dependent binding of TP508 to integrin alphavbeta3 mediates cell adhesion and induction of nitric oxide

TP508, a 23-amino acid RGD-containing synthetic peptide representing residues 508 to 530 of human prothrombin, mitigates the effects of endothelial dysfunction in ischaemic reperfusion injury. The objective of this study was to investigate whether TP508 binds to members of the integrin family of transmembrane receptors leading to nitric oxide synthesis. Immobilised TP508 supported adhesion of endothelial cells and alphavbeta3-expressing human embryonic kidney cells in a dose- and RGD-dependent manner. Soluble TP508 also inhibited cell adhesion to immobilised fibrinogen. The involvement of alphavbeta3 was verified with function-blocking antibodies and surface plasmon resonance studies. Adhesion of the cells to immobilised TP508 resulted in an induction of phosphorylated FAK and ERK1/2. In endothelial cells, TP508 treatment resulted in an induction of nitric oxide that could be inhibited by LM609, an alphavbeta3-specific, function-blocking monoclonal antibody. Finally, TP508 treatment of isolated rat aorta segments enhanced carbachol-induced vasorelaxation. These results suggest that TP508 elicits a potentially therapeutic effect through an RGD-dependent interaction with integrin alphavbeta3.

Effect of dimerized thrombin fragment TP508 on acute myocardial ischemia reperfusion injury in hypercholesterolemic swine

The thrombin-related peptide TP508 is a 23-amino acid monomer that represents a portion of the receptor binding domain in the thrombin molecule. TP508 is also known to readily convert to a dimer in an aqueous environment. In this study the dimeric form of TP508 was investigated in a porcine model of acute myocardial ischemia reperfusion injury (and compared with its monomer). Twenty-four hypercholesterolemic pigs underwent 60 min of mid-left anterior descending coronary artery occlusion followed by 120 min of reperfusion and received either vehicle (n = 6), TP508 monomer (n = 6), or two different doses of dimer (n = 6). Infarct size was significantly reduced in the monomer and two dimer groups compared with vehicle. Improvement in both endothelium-dependent and -independent coronary microvascular relaxations was also observed in treated groups. In addition, the expression of 27-kDa heat shock protein, alphaB-crystalline, and phosphorylated B-cell lymphoma 2 (Ser70) in the ischemic area at risk were higher in treated groups than in vehicle, whereas the expression of cleaved poly-ADP ribose polymerase was lower in treated groups. Finally, there were fewer apoptotic cells in treated groups than in vehicle. This study suggests that TP508 dimer provides a myocardial-protective effect on acute ischemia reperfusion injury in hypercholesterolemic swine, similar to TP508 monomer, by up-regulating cell survival pathways or down-regulating apoptotic pathways.