Heme oxygenase (HO) is a cytoprotective and antioxidant enzyme involved in the conversion of heme into biliverdin (subsequently converted to bilirubin) with the simultaneous release of CO and FeII. The activity and the expression of the inducible isoform HO-1 can be modulated by several factors such as heavy metals, metalloporphyrins, nitric oxide, hypoxia, UV radiation and heat. In experimental models of myocardial infarction (MI), overexpression of HO-1 before the ischemic event has been shown to greatly reduce the functional and structural damage in the myocardial tissue. However, although very promising, these data are not able to reproduce the actual clinical situation in which a pharmacological intervention to modulate the expression of HO-1 can only follow the ischemic event. Previous studies, performed in the laboratory in which I attended my internship thesis, have shown that even a post-infarctual pharmacological induction of HO-1 could be effective in reducing infarct size and ventricular remodeling in a rat model of permanent ligation of the left descendant anterior coronary artery (LAD). Aim of this thesis was to investigate some aspects of this study for understanding how, in spite of an irreversible loss of the myocardial tissue that is directly triggered by ischemia, the induction of HO-1 following MI initiation may reduce tissue damage associated with the processes occurring in the later stages of ischemia, and so attenuate the long-term ventricular modifications determining the progression towards heart failure. To this purpose, a study was carried out to analyze the time-course of the increase in the expression level and enzymatic activity of HO-1 following administration of its strong transcriptional inducer cobalt protoporphyrin IX (COPP). Moreover, the specificity of HO-1 induction in determining the beneficial effects observed was studied in a group of infarcted rats undergoing treatment with CoPP in combination with tin mesoporphyrin (SnMP), a potent inhibitor of HO activity. The experiments were performed in male Wistar rats, 10-12 weeks old, in which the chronic myocardial infarction was induced by permanent LAD ligation. Animals were divided into 3 treatment groups: saline (control-MI), CoPP (MI-CoPP) and CoPP + SnMP (MI-CoPP + SnMP). The treatments were administered intraperitoneally 10 minutes after the artery ligation, and thereafter once a week for an overall study period of 4 weeks to assess long-term effects. A group of rats subjected to the same surgical procedures except for the final ligation of the artery was used as control group for surgical stress ("sham" group). In addition, temporal activation of HO-1 was monitored in a group of animals at 8-48 hours following CoPP treatment, by Western blot analysis of cardiac protein expression, and quantification of HO enzymatic activity in microsomal fractions isolated from heart and liver tissue. The results demonstrated that CoPP induced a clear increase in HO-1 protein expression and HO enzymatic activity starting up from 16 hours after treatment. Moreover, the specific role of HO-1 induction in reducing long-term heart remodeling and functional alterations was confirmed by the abolition of the beneficial effects after administration of the inhibitor SnMP.
IL RUOLO DELL'EME OSSIGENASI-1 NELLA RIDUZIONE DEL DANNO CARDIACO A LUNGO TERMINE IN UN MODELLO DI INFARTO CRONICO NEL RATTO
2014
Abstract
Heme oxygenase (HO) is a cytoprotective and antioxidant enzyme involved in the conversion of heme into biliverdin (subsequently converted to bilirubin) with the simultaneous release of CO and FeII. The activity and the expression of the inducible isoform HO-1 can be modulated by several factors such as heavy metals, metalloporphyrins, nitric oxide, hypoxia, UV radiation and heat. In experimental models of myocardial infarction (MI), overexpression of HO-1 before the ischemic event has been shown to greatly reduce the functional and structural damage in the myocardial tissue. However, although very promising, these data are not able to reproduce the actual clinical situation in which a pharmacological intervention to modulate the expression of HO-1 can only follow the ischemic event. Previous studies, performed in the laboratory in which I attended my internship thesis, have shown that even a post-infarctual pharmacological induction of HO-1 could be effective in reducing infarct size and ventricular remodeling in a rat model of permanent ligation of the left descendant anterior coronary artery (LAD). Aim of this thesis was to investigate some aspects of this study for understanding how, in spite of an irreversible loss of the myocardial tissue that is directly triggered by ischemia, the induction of HO-1 following MI initiation may reduce tissue damage associated with the processes occurring in the later stages of ischemia, and so attenuate the long-term ventricular modifications determining the progression towards heart failure. To this purpose, a study was carried out to analyze the time-course of the increase in the expression level and enzymatic activity of HO-1 following administration of its strong transcriptional inducer cobalt protoporphyrin IX (COPP). Moreover, the specificity of HO-1 induction in determining the beneficial effects observed was studied in a group of infarcted rats undergoing treatment with CoPP in combination with tin mesoporphyrin (SnMP), a potent inhibitor of HO activity. The experiments were performed in male Wistar rats, 10-12 weeks old, in which the chronic myocardial infarction was induced by permanent LAD ligation. Animals were divided into 3 treatment groups: saline (control-MI), CoPP (MI-CoPP) and CoPP + SnMP (MI-CoPP + SnMP). The treatments were administered intraperitoneally 10 minutes after the artery ligation, and thereafter once a week for an overall study period of 4 weeks to assess long-term effects. A group of rats subjected to the same surgical procedures except for the final ligation of the artery was used as control group for surgical stress ("sham" group). In addition, temporal activation of HO-1 was monitored in a group of animals at 8-48 hours following CoPP treatment, by Western blot analysis of cardiac protein expression, and quantification of HO enzymatic activity in microsomal fractions isolated from heart and liver tissue. The results demonstrated that CoPP induced a clear increase in HO-1 protein expression and HO enzymatic activity starting up from 16 hours after treatment. Moreover, the specific role of HO-1 induction in reducing long-term heart remodeling and functional alterations was confirmed by the abolition of the beneficial effects after administration of the inhibitor SnMP.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
