Endothelin-B Receptors and Left Ventricular Dysfunction after Regional versus Global Ischaemia-Reperfusion in Rat Hearts

Background. Endothelin-1 (ET-1) is implicated in left ventricular dysfunction after ischaemia-reperfusion. ETA and ETB receptors mediate diverse actions, but it is unknown whether these actions depend on ischaemia type and duration. We investigated the role of ETB receptors after four ischaemia-reperfusion protocols in isolated rat hearts. Methods. Left ventricular haemodynamic variables were measured in the Langendorff-perfused model after 40-and 20-minute regional or global ischaemia, followed by 30-minute reperfusion. Wild-type (n = 39) and ETB-deficient (n = 41) rats were compared. Infarct size was measured using fluorescent microspheres after regional ischaemia-reperfusion. Results. Left ventricular dysfunction was more prominent in ETBdeficient rats, particularly after regional ischaemia. Infarct size was smaller (P = 0.006) in wild-type (31.5 ± 4.4%) than ETBdeficient (45.0 ± 7.3%) rats after 40 minutes of regional ischaemia-reperfusion. Although the recovery of left ventricular function was poorer after 40-minute ischaemia-reperfusion, end-diastolic pressure in ETB-deficient rats was higher after 20 than after 40 minutes of regional ischaemia-reperfusion. Conclusion. ETB receptors exert cytoprotective effects in the rat heart, mainly after regional ischaemia-reperfusion. Longer periods of ischaemia suppress the recovery of left ventricular function after reperfusion, but the role of ETB receptors may be more important during the early phases

The effect of growth factors and biomaterials on the left ventricle after myocardial infarction: an experimental study

The prevention of left ventricular remodeling post-myocardial infarction constitutes an important therapeutic target. The present thesis evaluated a biomaterial-based therapeutic approach, aiming towards the prevention of infarct expansion and the improvement of left ventricular function. Using the in vivo rat model, we examined composite treatments based on various biodegradable materials, characterized by different properties.In the first part of the thesis, a biodegradable scaffold exerting biventricular mechanical restraint was compared with epicardial hydrogel application. In a total number of 230 Wistar rats (358±7g), implantation was performed with and without prior myocardial infarction, induced by permanent coronary artery ligation. Left ventricular pressure recordings evaluated diastolic filling after scaffold implantation. Degradation rates and inflammatory/foreign body response were studied at 3, 7 and 15 days post-ligation. Remodeling indices were evaluated by echocardiography 15 days post-ligation. Biodegrability was ~50% by 7 days and 100% by 15 days post-implantation for both materials. No differences were found in diastolic pressure. Inflammatory/foreign body response peaked at 3 days post-implant, with subsequent remission, but fibroblastic reaction was more pronounced after scaffold than after hydrogel implantation. Post-ligation, ejection fraction was higher in the scaffold (40.0±1.5%) or hydrogel groups (37.0±1.3%), compared to controls (30.6±1.9%). Wall tension index was lower with either biomaterial, but left ventricular end-diastolic diameter was shorter (p=0.044) and sphericity was attenuated (p=0.029) after scaffold, compared to hydrogel implantation. It can be concluded that both biomaterials showed favorable histological responses and attenuated remodeling, but epicardial restraint produced better results compared to hydrogel alone.In the second part of the thesis, hydrogel alginate-based biomaterials were evaluated, with or without the addition of growth hormone (GH). These biomaterials were compared with biventricular epicardial restraint, exerted by an alginate-based scaffold. Ten minutes after permanent coronary artery ligation, 48 Wistar rats (333±5gr) were randomized into (a) alginate intramyocardial injection with or (b) without GH, (c) biventricular restraint via an alginate-based scaffold, or (d) no treatment. Echocardiographic and histologic indices of left ventricular remodeling were examined 3 weeks post-infarction, followed by immunohistochemical evaluation of collagen-content and angiogenesis, as well as macrophage- and myofibroblast-count. Compared to controls, all three treatments displayed favorable effects, but alginate+GH consistently improved end-diastolic and end-systolic diameters, ventricular sphericity, wall tension index and infarct thickness. Similarly, microvascular density and myofibroblast-count in the infarct and peri-infarct areas were higher after alginate+GH, whereas macrophage-count and collagen-content did not differ between groups.Biomaterials represent a promising therapeutic strategy in the treatment of myocardial infarction. Further investigation is needed, aiming at further exploring the value of biomaterials as carriers of local delivery of drugs and/or cells. Myocardial tissue engineering has yet to overcome many challenges that will likely exploit its therapeutic effects on myocardial repair and regeneration.Η πρόληψη της αναδιαμόρφωσης της αριστερής κοιλίας αποτελεί σημαντικό θεραπευτικό στόχο μετά το έμφραγμα του μυοκαρδίου. Στην διδακτορική διατριβή, αξιολογήθηκε μία θεραπευτική παρέμβαση, με στόχο τη μερική αναγέννηση του κοιλιακού μυοκαρδίου μετά το έμφραγμα και τη βελτίωση της λειτουργικότητας της αριστερής κοιλίας, με την εμφύτευση βιο-αποδομήσιμων υλικών. Στο πρώτο μέρος, παρασκευάστηκε και αξιολογήθηκε, ένα βιοϋλικό πολυαιθυλενογλυκόλης σε δύο μορφές: αυτή του υδροπηκτώματος, εφαρμοζόμενο με επικαρδιακή επάλειψη και αυτή του σύνθετου ικριώματος εμφυτευόμενο στο επικάρδιο των δύο κοιλιών, για μηχανικό περιορισμό τους. Τυχαιοποιήθηκαν 230 φυσιολογικοί επίμυες τύπου Wistar, με και χωρίς έμφραγμα του μυοκαρδίου. Τα στάδια αποδόμησης και η αντίδραση ξένου σώματος μελετήθηκαν 3, 7 και 15 ημέρες μετά την πρόκληση του εμφράγματος και την εμφύτευση, ενώ οι δείκτες αναδιαμόρφωσης εκτιμήθηκαν υπερηχοκαρδιογραφικά στις 15 ημέρες. Και τα δύο βιοϋλικά αποδομήθηκαν κατά ~50% στις 7 και 100% στις 15 ημέρες, ενώ η αντίδραση ξένου σώματος ήταν μέγιστη την 3η ημέρα. Η ινοβλαστική αντίδραση ήταν πιο έντονη στην ομάδα του ικριώματος, συγκριτικά με εκείνη του υδροπηκτώματος. Στις εμφραγματικές ομάδες, το κλάσμα εξώθησης ήταν μεγαλύτερο στις ομάδες του ικριώματος (40.0±1.5%) και του υδροπηκτώματος (37.0±1.3%), συγκριτικά με την ομάδα ελέγχου (30.6±1.9%). Η τοιχωματική τάση ήταν μειωμένη και στις δυο ομάδες βιοϋλικών. Στην ομάδα του ικριώματος, η τελοδιαστολική διάμετρος της αριστερής κοιλίας ήταν μικρότερη (p=0.044), και ο δείκτης σφαιρικότητας μειωμένος (p=0.029), συγκριτικά με την ομάδα του υδροπηκτώματος. Συμπερασματικά, και τα δύο βιοϋλικά έδειξαν ευνοϊκή εικόνα ιστολογικής αντίδρασης και μείωσαν την αναδιαμόρφωση, αλλά ο επικαρδιακός μηχανικός περιορισμός, με το ικρίωμα βιοϋλικού είχε καλύτερα αποτελέσματα, συγκριτικά με την επικαρδιακή εφαρμογή του υδροπηκτώματος. Στο δεύτερο μέρος, χρησιμοποιήθηκαν δυο βιοϋλικά, με βάση το αλγινικό οξύ: σαν υδροπήκτωμα (με ή χωρίς πρόσδεση αυξητικής ορμόνης), καθώς και σαν σύνθετο ικρίωμα. Μετά την πρόκληση εμφράγματος, 48 επίμυες τυχαιοποιήθηκαν σε ομάδες: (α) ενδομυοκαρδιακή έγχυση αλγινικού υδροπηκτώματος με και (β) χωρίς αυξητική ορμόνη, (γ) αμφικοιλιακό περιορισμό της καρδιάς με αλγινικό ικρίωμα ή (δ) καμία παρέμβαση. Τρεις εβδομάδες μετά, έγιναν υπερηχοκαρδιογραφικές μετρήσεις και εκτιμήθηκαν ιστολογικές παράμετροι. Συγκριτικά με την ομάδα ελέγχου, και οι τρεις εφαρμογές είχαν ευεργετικά αποτελέσματα, αλλά η ομάδα (α) έδειξε καλύτερα αποτελέσματα στη διάμετρο της αριστερής κοιλίας (τελοδιαστολική και τελοσυστολική), στο δείκτη σφαιρικότητας, στην τοιχωματική τάση και στο πάχος του εμφραγματικού τοιχώματος. Ομοίως, η μικροαγγειακή πυκνότητα και η προσέλκυση μυοϊνοβλαστών στην εμφραγματική και περι-εμφραγματική περιοχή ήταν εντονότερες στην ομάδα (α). Συμπερασματικά, η ενδομυοκαρδιακή έγχυση αυξητικής ορμόνης προσδεδεμένης σε αλγινικό υδροπήκτωμα βελτιώνει την αγγειογένεση και μειώνει την αναδιαμόρφωση μετά το έμφραγμα του μυοκαρδίου, πιο αποτελεσματικά από ότι το αλγινικό υδροπήκτωμα μόνο ή σαν ικρίωμα.Η εφαρμογή των βιοϋλικών, ως φορείς φαρμακευτικών ουσιών ή/και διαφοροποιημένων ή μη κυττάρων, αποτελεί μία πολλά υποσχόμενη στρατηγική στη θεραπεία του εμφράγματος του μυοκαρδίου. Η ιστοτεχνολογία του μυοκαρδίου έχει ακόμη να απαντήσει σε πολλές προκλήσεις, προκειμένου να μεγιστοποιηθούν οι θεραπευτικές επιδράσεις στη μυοκαρδιακή αποκατάσταση και αναγέννηση

Tissue engineering for post-myocardial infarction ventricular remodeling

Myocardial tissue engineering involves the design of biomaterial scaffolds, aiming at regenerating necrotic myocardium after myocardial infarction. Biomaterials provide mechanical support to the infarct area and they can be used as vehicles for sustained and controlled local administration of cells and growth factors. Although promising results have been reported in experimental studies, many issues need to be addressed before human use.© 2011 Bentham Science Publishers Ltd

Transforming growth factor-β inhibition and endothelin receptor blockade in rats with monocrotaline-induced pulmonary hypertension

Transforming growth factor-β (TGF-β) inhibition is an investigational therapy for pulmonary arterial hypertension with promising results in experimental studies. The present work compared this approach with endothelin-receptor blockade and evaluated the effects of combined administration. Pulmonary arterial hypertension was induced by single monocrotaline injection (60 mg/kg) in 75 Wistar rats and 15 rats served as controls. Intervention groups consisted of treatment with an antibody against TGF-β-ligand, bosentan, both or none, initiated four weeks after monocrotaline injection. Right ventricular systolic pressure, pulmonary vascular remodeling, and exercise tolerance were evaluated eight weeks after monocrotaline injection. Either treatment, alone or in combination, lowered mortality. Comparable efficacy was found in the three treatment groups in terms of right ventricular systolic pressure (~45% decrease) and hypertrophy (~30% decrease), as well as exercise capacity. The three treatment groups equally ameliorated pulmonary vascular remodeling, evidenced by decreased vessel-wall thickness (in vessels 50-200 μm) and a smaller number of pre-capillary arterioles (< 50 μm) with a muscularized media. Treatment either with an antibody against TGF-β or with endothelin receptor blockade are equally effective in experimental pulmonary hypertension. Their combination provides no added benefit, indicating common mechanisms of action. © 2012, Taylor and Francis Inc. All rights reserved

Endothelin-B receptors and left ventricular dysfunction after regional versus global ischaemia-reperfusion in rat hearts

Background. Endothelin-1 (ET-1) is implicated in left ventricular dysfunction after ischaemia-reperfusion. ETA and ETB receptors mediate diverse actions, but it is unknown whether these actions depend on ischaemia type and duration. We investigated the role of ETB receptors after four ischaemia-reperfusion protocols in isolated rat hearts. Methods. Left ventricular haemodynamic variables were measured in the Langendorff-perfused model after 40- and 20-minute regional or global ischaemia, followed by 30-minute reperfusion. Wild-type (n = 39) and ETB-deficient (n = 41) rats were compared. Infarct size was measured using fluorescent microspheres after regional ischaemia-reperfusion. Results. Left ventricular dysfunction was more prominent in ETB-deficient rats, particularly after regional ischaemia. Infarct size was smaller (P = 0.006) in wild-type (31.5 ± 4.4%) than ETB-deficient (45.0 ± 7.3%) rats after 40 minutes of regional ischaemia-reperfusion. Although the recovery of left ventricular function was poorer after 40-minute ischaemia-reperfusion, end-diastolic pressure in ETB-deficient rats was higher after 20 than after 40 minutes of regional ischaemia-reperfusion. Conclusion. ETB receptors exert cytoprotective effects in the rat heart, mainly after regional ischaemia-reperfusion. Longer periods of ischaemia suppress the recovery of left ventricular function after reperfusion, but the role of ETB receptors may be more important during the early phases. © 2012 Sofia-Iris Bibli et al

Effects of pre- and postconditioning on arrhythmogenesis in the in vivo rat model

The antiarrhythmic potential of postconditioning in in vivo models remains poorly defined. We compared the effects of pre- and postconditioning on ventricular arrhythmogenesis against controls with and without reperfusion. Wistar rats (n = 40, 269 ± 3 g) subjected to ischemia (30 minutes)-reperfusion (24 hours) were assigned to the following groups: (1) preconditioning (2 cycles), (2) postconditioning (6 cycles), or (3) no intervention and were compared with (4) nonreperfused infarcts and (5) sham-operated animals. Infarct size was measured, and arrhythmogenesis was evaluated with continuous telemetric electrocardiographic recording, heart rate variability indices, and monophasic action potentials (MAPs). During a 24-hour observation period, no differences in mortality were observed. Reperfusion decreased infarct size and ameliorated sympathetic activation during the late reperfusion phase. Preconditioning decreased infarct size by a further 35% (P =.0017), but only a marginal decrease (by 18%, P =.075) was noted after postconditioning. Preconditioning decreased arrhythmias during ischemia and early reperfusion, whereas postconditioning almost abolished them during the entire reperfusion period. No differences were noted in MAPs or in the magnitude of sympathetic activation between the 2 interventions. Compared to postconditioning, preconditioning affords more powerful cytoprotection, but both interventions exert antiarrhythmic actions. In the latter, these are mainly evident during the ischemic phase and continue during early reperfusion. Postconditioning markedly decreases reperfusion arrhythmias during a prolonged observation period. The mechanisms underlying the antiarrhythmic effects of pre- and postconditioning are likely different but remain elusive. © The Author(s) 2013

Endothelin-B Receptors and Left Ventricular Dysfunction after Regional versus Global Ischaemia-Reperfusion in Rat Hearts

Background. Endothelin-1 (ET-1) is implicated in left ventricular dysfunction after ischaemia-reperfusion. ETA and ETB receptors mediate diverse actions, but it is unknown whether these actions depend on ischaemia type and duration. We investigated the role of ETB receptors after four ischaemia-reperfusion protocols in isolated rat hearts. Methods. Left ventricular haemodynamic variables were measured in the Langendorff-perfused model after 40- and 20-minute regional or global ischaemia, followed by 30-minute reperfusion. Wild-type (n=39) and ETB-deficient (n=41) rats were compared. Infarct size was measured using fluorescent microspheres after regional ischaemia-reperfusion. Results. Left ventricular dysfunction was more prominent in ETB-deficient rats, particularly after regional ischaemia. Infarct size was smaller (P=0.006) in wild-type (31.5±4.4%) than ETB-deficient (45.0±7.3%) rats after 40 minutes of regional ischaemia-reperfusion. Although the recovery of left ventricular function was poorer after 40-minute ischaemia-reperfusion, end-diastolic pressure in ETB-deficient rats was higher after 20 than after 40 minutes of regional ischaemia-reperfusion. Conclusion. ETB receptors exert cytoprotective effects in the rat heart, mainly after regional ischaemia-reperfusion. Longer periods of ischaemia suppress the recovery of left ventricular function after reperfusion, but the role of ETB receptors may be more important during the early phases

Attenuation of post-infarction remodeling in rats by sustained myocardial growth hormone administration

Prevention of left ventricular remodeling is an important therapeutic target post-myocardial infarction. Experimentally, treatment with growth hormone (GH) is beneficial, but sustained local administration has not been thoroughly investigated. We studied 58 rats (322 ± 4 g). GH was administered via a biomaterial-scaffold, following in vitro and in vivo evaluation of degradation and drug-release curves. Treatment consisted of intra-myocardial injection of saline or alginate-hydrogel, with or without GH, 10 min after permanent coronary artery ligation. Echocardiographic and histologic remodeling-indices were examined 3 weeks post-ligation, followed by immunohistochemical evaluation of angiogenesis, collagen, macrophages and myofibroblasts. GH-release completed at 3 days and alginate-degradation at ∼7 days. Alginate + GH consistently improved left ventricular end-diastolic and end-systolic diameters, ventricular sphericity, wall tension index and infarct-thickness. Microvascular-density and myofibroblast-count in the infarct and peri-infarct areas were higher after alginate + GH. Macrophage-count and collagen-content did not differ between groups. Early, sustained GH-administration enhances angiogenesis and myofibroblast-activation and ameliorates post-infarction remodeling. © 2015 Taylor and Francis

Short-term ventricular restraint attenuates post-infarction remodeling in rats

Background/objectives: Left ventricular restraint attenuates post-infarction remodeling, but may be associated with unfavorable long-term histological response. We hypothesized that beneficial effects can be obtained with short-term restraint during the early post-infarction period; for this purpose, we evaluated a biodegradable scaffold in the in vivo rat model and compared it with epicardial hydrogel application. Methods: A total of 230 Wistar rats (358 ± 7 g) were studied. Implantation was performed with and without prior myocardial infarction, induced by permanent coronary artery ligation. Diastolic filling was evaluated by left ventricular pressure recordings after scaffold implantation. Degradation rates and inflammatory/foreign body response were studied at 3, 7 and 15 days post-ligation. Remodeling indices were evaluated by echocardiography 15 days post-ligation. Results: No differences were found in diastolic pressure. Biodegradability was ~ 50% by 7 days and 100% by 15 days for both materials. Likewise, inflammatory/foreign body response peaked at 3 days post-implant, with subsequent remission, but fibroblastic reaction was more pronounced after scaffold than after hydrogel implantation. Post-ligation, ejection fraction was higher in the scaffold (40.0 ± 1.5%) or hydrogel groups (37.0 ± 1.3%), compared to controls (30.6 ± 1.9%). Wall tension index was lower with either biomaterial, but left ventricular end-diastolic diameter was shorter (p = 0.044) and sphericity was attenuated (p = 0.029) after scaffold, compared to hydrogel implantation. Conclusions: Both biomaterials showed a favorable histological response and attenuated remodeling, but epicardial restraint produced better results compared to hydrogel alone. The latter approach merits further investigation due to the ease of implantation. © 2012 Elsevier Ireland Ltd

Short-term ventricular restraint attenuates post-infarction remodeling in rats

Background/objectives: Left ventricular restraint attenuates post-infarction remodeling, but may be associated with unfavorable long-term histological response. We hypothesized that beneficial effects can be obtained with short-term restraint during the early post-infarction period; for this purpose, we evaluated a biodegradable scaffold in the in vivo rat model and compared it with epicardial hydrogel application. Methods: A total of 230 Wistar rats (358 ± 7 g) were studied. Implantation was performed with and without prior myocardial infarction, induced by permanent coronary artery ligation. Diastolic filling was evaluated by left ventricular pressure recordings after scaffold implantation. Degradation rates and inflammatory/foreign body response were studied at 3, 7 and 15 days post-ligation. Remodeling indices were evaluated by echocardiography 15 days post-ligation. Results: No differences were found in diastolic pressure. Biodegradability was ~ 50% by 7 days and 100% by 15 days for both materials. Likewise, inflammatory/foreign body response peaked at 3 days post-implant, with subsequent remission, but fibroblastic reaction was more pronounced after scaffold than after hydrogel implantation. Post-ligation, ejection fraction was higher in the scaffold (40.0 ± 1.5%) or hydrogel groups (37.0 ± 1.3%), compared to controls (30.6 ± 1.9%). Wall tension index was lower with either biomaterial, but left ventricular end-diastolic diameter was shorter (p = 0.044) and sphericity was attenuated (p = 0.029) after scaffold, compared to hydrogel implantation. Conclusions: Both biomaterials showed a favorable histological response and attenuated remodeling, but epicardial restraint produced better results compared to hydrogel alone. The latter approach merits further investigation due to the ease of implantation. © 2012 Elsevier Ireland Ltd