Pharmacological targeting of steroid regeneration by 11βHSD1 after myocardial infarction improves functional outcome in a translational pig model

Myocardial infarction (MI) affects more than a 100,00 people annually in the UK. Although 70% of patients survive, they often do so with damage to their myocardium that leads to the development of heart failure (HF). Despite improvements in drug therapy, HF prognosis remains poor, with approximately half of patients dying within 5 years of diagnosis. Glucocorticoids released from the adrenal gland immediately after MI are initially cardioprotective. However, prolonged and/or excessive exposure to glucocorticoid has a detrimental effect on infarct repair due to anti-angiogenic and anti-inflammatory effects. The regeneration of cortisol from its inactive form cortisone in target tissue by 11 betahydroxysteroid dehydrogenase type 1 (11βHSD1) is a major determinant of cortisol levels in target tissue. Genetic targeting of 11βHSD1 in mice enhanced angiogenesis in the infarct border after MI, prevented infarct expansion and consequently improved cardiac function. This thesis tested the hypothesis that intervention with a pharmacological inhibitor of 11βHSD1 after MI can improve cardiac function in a clinically relevant translational mini-pig model. MI was induced by temporary coronary artery occlusion followed by reperfusion in anaesthetised adult female Goettingen mini-pigs. All mini-pigs received aspirin and an antiarrhythmic drug prior to surgery. A control group (n=6) received no further treatment. The main study mini-pigs received a clinically relevant therapeutic ‘standard therapy’ regime including a statin, anti-platelet agent and ACE inhibitor (n=20). From 48h post-MI, the study mini-pigs additionally received either an oral 11βHSD1 inhibitor (11βHSD1i, n=11), or vehicle (n=9). At 48h and 28d post-MI, plasma was collected and magnetic resonance imaging (MRI) was conducted for detection of infarct size (retention of gadolinium, Gd) and cardiac functional and structural assessment. The animals were culled at 28d after MI and fixed and frozen myocardial tissue was collected for further analysis, including mass spectrometry imaging (MSI), histology, immunohistochemistry, genomic and proteomic analysis. The first aim was to confirm 11βHSD1i delivery and target engagement. 11βHSD1i was detected in the plasma of treated mini-pigs, and successful enzyme inhibition was reflected in higher plasma substrate (cortisone) levels compared to standard therapy treated mini-pigs. Matrix-assisted laser desorption/ionisation (MALDI)-MSI in myocardial slices detected 11βHSD1i at high intensity in the infarct area, compared to lower intensity in the remote myocardium. The second aim was to determine if there are any beneficial effects of 11βHSD1i administration after MI on cardiac function, structure and infarct size 28d after MI, on top of standard therapy. Injury resulted in temporary elevation of plasma troponin I and Gd retention in MRI. In contrast to the mouse MI model, neovascularisation was not observed in the mini-pig model in the infarct and infarct border zone. However, there was an increase in mature smooth muscle coated vessels in the infarct area compared to the remote myocardium. Although there was no difference in infarct size or angiogenesis in the infarct and border zone, inhibition with 11βHSD1i prevented deterioration of cardiac and ventricular dilation. Given the improvement in cardiac function and structural outcomes, the final aim of this thesis was to determine the effect of 11βHSD1i on wound repair in the infarcted heart. In both treatment groups, activated fibroblasts and CD163+ macrophages were still present in the infarct area at 28d post-MI showing ongoing repair. While there was no difference in macrophage density between groups, fibroblast activation protein area was higher in the 11βHSD1i-treated mini-pigs. Collagen gene expression and protein content in the infarct and border were similar in both groups. However, picrosirius red-polarised light microscopy revealed a higher percentage of thin collagen in the infarct of 11βHSD1i-treated mini-pigs, compared to standard therapy. This was in line with decreased expression of collagen processing genes and proteins including LOX, PCOLCE2 and FN1. Proteomic pathway analysis also identified extracellular matrix organisation among the top regulated pathways due to 11βHSD1i compared to standard therapy alone. In conclusion, the data reveal that pharmacological 11βHSD1i after MI improves cardiac function and reduces progression towards HF. This improvement is clinically relevant as it was tested in a translational ischemia/reperfusion MI model, where treatment was started after MI and on top of drugs typically prescribed for MI patients. In contrast to the mouse MI model, this outcome could not be attributed to enhancement of neovascularisation and prevention of infarct expansion. 11βHSD1i beneficial effects are likely secondary to its effect on extracellular matrix processing in the infarct and infarct border zone, in line with detection of the drug at higher intensity in the infarct zone. Given that 11βHSD1i drugs have already passed phase 2 clinical trials in diabetes and Alzheimer’s disease, the data presented in this thesis justifies their repurposing to prevent the development of HF after MI.