Effects of Carvedilol and Thyroid Hormones Co-administration on Apoptotic and Survival Proteins in the Heart After Acute Myocardial Infarction

Influence of carvedilol and thyroid hormones on inflammatory proteins and cardioprotective factor HIF-1α in the infarcted heart

Inflammatory pathways of Toll-like receptor 4 (TLR4) and NLRP3 inflammasome contribute to acute myocardial infarction (AMI) pathophysiology. The hypoxia-inducible factor 1α (HIF-1α), however, is a key transcription factor related to cardioprotection. This study aimed to compare the influence of carvedilol and thyroid hormones (TH) on inflammatory and HIF-1α proteins and on cardiac haemodynamics in the infarcted heart. Male Wistar rats were allocated into five groups: sham-operated group (SHAM), infarcted group (MI), infarcted treated with the carvedilol group (MI + C), infarcted treated with the TH group (MI + TH), and infarcted co-treated with the carvedilol and TH group (MI + C + TH). Haemodynamic analysis was assessed 15 days post-AMI. The left ventricle (LV) was collected for morphometric and Western blot analysis. The MI group presented LV systolic pressure reduction, LV end-diastolic pressure elevation, and contractility index decrease compared to the SHAM group. The MI + C, MI + TH, and MI + C + TH groups did not reveal such alterations compared to the SHAM group. The MI + TH and MI + C + TH groups presented reduced MyD88 and NLRP3 and increased HIF-1α levels. In conclusion, all treatments preserve the cardiac haemodynamic, and only TH, as isolated treatment or in co-treatment with carvedilol, was able to reduce MyD88 and NLRP3 and increase HIF-1α in the infarcted heart.

Cardioprotection by post-conditioning with exogenous triiodothyronine in isolated perfused rat hearts and isolated adult rat cardiomyocytes

Ischemic post-conditioning (iPoCo) by coronary re-occlusion/reperfusion during immediate reperfusion after prolonged myocardial ischemia reduces infarct size. Mechanical manipulation of culprit lesions, however, carries the risk of coronary microembolization which may obscure iPoCo's cardioprotection. Pharmacological post-conditioning with exogenous triiodothyronine (T3) could serve as an alternative conditioning strategy. Similar to iPoCo, T3 may activate cardioprotective prosurvival pathways. We aimed to study T3's impact on infarct size and its underlying signal transduction. Hearts were isolated from male Lewis rats (200-380 g), buffer-perfused and subjected to 30 min/120 min global zero-flow ischemia/reperfusion (I/R). In additional hearts, either iPoCo (2 × 30 s/30 s I/R) was performed or T3 (100-500 µg/L) infused at reperfusion. Infarct size was demarcated with triphenyl tetrazolium chloride staining and calculated as percent of ventricular mass. Infarct size was reduced with iPoCo to 16 ± 7% vs. 36 ± 4% with I/R only. The maximum infarct size reduction was observed with 300 µg/L T3 (14 ± 2%). T3 increased the phosphorylation of protein kinase B and mitogen extracellular-regulated-kinase 1/2, both key enzymes of the reperfusion injury salvage kinase (RISK) pathway. Pharmacological RISK blockade (RISK-BL) during reperfusion abrogated T3's cardioprotection (35 ± 10%). Adult ventricular cardiomyocytes were isolated from buffer-perfused rat hearts and exposed to 30 min/5 min hypoxia/reoxygenation (H/R); reoxygenation was initiated without or with T3, respectively, and without or with RISK-BL, respectively. Maximal preservation of viability was observed with 500 µg/L T3 after H/R (27 ± 4% of all cells vs. 5 ± 3% in time-matched controls). Again, RISK-BL abrogated protection (11 ± 3%). Mitochondria were isolated at early reperfusion from buffer-perfused rat hearts without or with iPoCo or 300 µg/L T3, respectively, at reperfusion. T3 improved mitochondrial function (i.e.: increased respiration, adenosine triphosphate production, calcium retention capacity, and decreased reactive oxygen species formation) to a similar extent as iPoCo. T3 at reperfusion reduces infarct size by activation of the RISK pathway. T3's protection is a cardiomyocyte phenomenon and targets mitochondria.