The molecular mechanisms utilised by mesenchymal stem cells in migration to acute myocardial infarction

Heart damage caused by acute myocardial infarction (AMI) is a leading cause of death and disability in Australia. Novel therapies are still required for the treatment of this condition due to the poor reparative ability of the heart. As such, cellular therapies that assist in the recovery of heart muscle are of great current interest. Culture expanded mesenchymal stem cells (MSC) represent a stem and progenitor cell population that has been shown to promote tissue recovery in pre-clinical studies of AMI. For MSC-based therapies in the clinic, an intravenous route of administration would ideally be used due to the low cost, ease of delivery and relative safety. The study of MSC migration is therefore clinically relevant for a minimally invasive cell therapy to promote regeneration of damaged tissue. C57BL/6, UBI-GFP-BL/6 and CD44-/-/GFP+/+ mice were utilised to investigate mMSC migration. To assist in murine models of MSC migration, a novel method was used for the isolation of murine MSC (mMSC). These mMSC were then expanded in culture and putative mMSC were positive for Sca-1, CD90.2, and CD44 and were negative for CD45 and CD11b. Furthermore, mMSC from C57BL/6 and UBI-GFP-BL/6 mice were shown to differentiate into cells of the mesodermal lineage. Cells from CD44-/-/GFP+/+ mice were positive for Sca-1 and CD90.2, and negative for CD44, CD45 and CD11b however, these cells were unable to differentiate into adipocytes and chondrocytes and express lineage specific genes, PLIN and ACAN. Analysis of mMSC chemokine receptor (CR) expression showed that although mMSC do express chemokine receptors, (including those specific for chemokines released after AMI), these were low or undetectable by mRNA. However, protein expression could be detected, which was predominantly cytoplasmic. It was further shown that in both healthy (unperturbed) and inflamed tissues, mMSC had very little specific migration and engraftment after intravenous injection. To determine if poor mMSC migration was due to the inability of mMSC to respond to chemotactic stimuli, chemokine expression in bone marrow, skin injury and hearts (healthy and after AMI) was analysed at various time points by quantitative real-time PCR (qRT PCR). Many chemokines were up-regulated after skin biopsy and AMI, but the highest acute levels were found for CXCL12 and CCL7. Due to their high expression in infarcted hearts, the chemokines CXCL12 and CCL7 were tested for their effect on mMSC migration. Despite CR expression at both protein and mRNA levels, migration in response to CXCL12 and CCL7 was low in mMSC cultured on Nunclon plastic. A novel tissue culture plastic technology (UpCellTM) was then used that allowed gentle non-enzymatic dissociation of mMSC, thus preserving surface expression of the CRs. Despite this the in vitro data indicated that CXCL12 fails to induce significant migration ability of mMSC, while CCL7 induces significant, but low-level migration. We speculated this may be because of low levels of surface expression of chemokine receptors. In a strategy to increase cell surface expression of mMSC chemokine receptors and enhance their in vitro and in vivo migration capacity, mMSC were pre-treated with pro-inflammatory cytokines. Increased levels of both mRNA and surface protein expression were found for CRs by pre-treating mMSC with pro-inflammatory cytokines including TNF-á, IFN-ã, IL-1á and IL-6. Furthermore, the chemotactic response of mMSC to CXCL12 and CCL7 was significantly higher with these pretreated cells. Finally, the effectiveness of this type of cell manipulation was demonstrated in vivo, where mMSC pre-treated with TNF-á and IFN-ã showed significantly increased migration in skin injury and AMI models. Therefore this thesis has demonstrated, using in vitro and in vivo models, the potential for prior manipulation of MSC as a possible means for increasing the utility of intravenously delivery for MSC-based cellular therapies.

Comparative effectiveness of population interventions to improve access to reperfusion for ST-segment–elevation myocardial infarction in Australia

Background Improving timely access to reperfusion is a major goal of ST-segment–elevation myocardial infarction care. We sought to compare the population impact of interventions proposed to improve timely access to reperfusion therapy in Australia. Methods and Results Australian hospitals, population, and road network data were integrated using Geographical Information Systems. Hospitals were classified into those that provided primary percutaneous coronary intervention (PPCI) or fibrinolysis. Population impact of interventions proposed to improve timely access to reperfusion (PPCI, fibrinolysis, or both) were modeled and compared. Timely access to reperfusion was defined as the proportion of the population capable of reaching a fibrinolysis facility ≤60 minutes or a PPCI facility ≤120 minutes from emergency medical services activation. The majority (93.2%) of the Australian population has timely access to reperfusion, mainly (53%) through fibrinolysis. Only 40.2% of the population had timely access to PPCI, and access to PPCI services is particularly limited in regional and nonexistent in remote areas. Optimizing the emergency medical services’ response or increasing PPCI services resulted in marginal improvement in timely access (1.8% and 3.7%, respectively). Direct transport to PPCI facilities and interhospital transfer for PPCI improves timely access to PPCI for 19.4% and 23.5% of the population, respectively. Prehospital fibrinolysis markedly improved access to timely reperfusion in regional and remote Australia. Conclusions Significant gaps in timely provision of reperfusion remain in Australia. Systematic implementation of changes in service delivery has potential to improve timely access to PPCI for a majority of the population and improve access to fibrinolysis to those living in regional and remote areas.

Predictors of physical and mental health-related quality of life outcomes among myocardial infarction patients

Background Health-related quality of life (HRQoL) is an important outcome for patients diagnosed with coronary heart disease. This report describes predictors of physical and mental HRQoL at six months post-hospitalisation for myocardial infarction. Methods Participants were myocardial infarction patients (n=430) admitted to two tertiary referral centres in Brisbane, Australia who completed a six month coronary heart disease secondary prevention trial (ProActive Heart). Outcome variables were HRQoL (Short Form-36) at six months, including a physical and mental summary score. Baseline predictors included demographics and clinical variables, health behaviours, and psychosocial variables. Stepwise forward multiple linear regression analyses were used to identify significant independent predictors of six month HRQoL. Results Physical HRQoL was lower in participants who: were older (p<0.001); were unemployed (p=0.03); had lower baseline physical and mental HRQoL scores (p<0.001); had lower confidence levels in meeting sufficient physical activity recommendations (p<0.001); had no intention to be physically active in the next six months (p<0.001); and were more sedentary (p=0.001). Mental HRQoL was lower in participants who: were younger (p=0.01); had lower baseline mental HRQoL (p<0.001); were more sedentary (p=0.01) were depressed (p<0.001); and had lower social support (p=0.001). Conclusions This study has clinical implications as identification of indicators of lower physical and mental HRQoL outcomes for myocardial infarction patients allows for targeted counselling or coronary heart disease secondary prevention efforts. Trial registration Australian Clinical Trials Registry, Australian New Zealand Clinical Trials Registry, CTRN12607000595415. Keywords: Myocardial infarction; Secondary prevention; Cardiac rehabilitation; Telephone-delivered; Health-related quality of life; Health coaching; Tele-health

A comparative analysis of risk stratification tools for emergency department patients with chest pain

Background: Appropriate disposition of emergency department (ED) patients with chest pain is dependent on clinical evaluation of risk. A number of chest pain risk stratification tools have been proposed. The aim of this study was to compare the predictive performance for major adverse cardiac events (MACE) using risk assessment tools from the National Heart Foundation of Australia (HFA), the Goldman risk score and the Thrombolysis in Myocardial Infarction risk score (TIMI RS). Methods: This prospective observational study evaluated ED patients aged ≥30 years with non-traumatic chest pain for which no definitive non-ischemic cause was found. Data collected included demographic and clinical information, investigation findings and occurrence of MACE by 30 days. The outcome of interest was the comparative predictive performance of the risk tools for MACE at 30 days, as analyzed by receiver operator curves (ROC). Results: Two hundred eighty-one patients were studied; the rate of MACE was 14.1%. Area under the curve (AUC) of the HFA, TIMI RS and Goldman tools for the endpoint of MACE was 0.54, 0.71 and 0.67, respectively, with the difference between the tools in predictive ability for MACE being highly significant [chi2 (3) = 67.21, N = 276, p < 0.0001]. Conclusion: The TIMI RS and Goldman tools performed better than the HFA in this undifferentiated ED chest pain population, but selection of cutoffs balancing sensitivity and specificity was problematic. There is an urgent need for validated risk stratification tools specific for the ED chest pain population.

Comparison of high sensitivity troponin T and I assays in the diagnosis of non-ST elevation acute myocardial infarction in emergency patients with chest pain

Objectives: Concentrations of troponin measured with high sensitivity troponin assays are raised in a number of emergency department (ED) patients; however many are not diagnosed with acute myocardial infarction (AMI). Clinical comparisons between the early use (2 h after presentation) of high sensitivity cardiac troponin T (hs-cTnT) and I (hs-cTnI) assays for the diagnosis of AMI have not been reported. Design and methods: Early (0 h and 2 h) hs-cTnT and hs-cTnI assay results in 1571 ED patients with potential acute coronary syndrome (ACS) without ST elevation on electrocardiograph (ECG) were evaluated. The primary outcome was diagnosis of index MI adjudicated by cardiologists using the local cTnI assay results taken ≥6 h after presentation, ECGs and clinical information. Stored samples were later analysed with hs-cTnT and hs-cTnI assays. Results: The ROC analysis for AMI (204 patients; 13.0%) for hs-cTnT and hs-cTnI after 2 h was 0.95 (95% CI: 0.94–0.97) and 0.98 (95% CI: 0.97–0.99) respectively. The sensitivity, specificity, PLR, and NLR of hs-cTnT and hs-cTnI for AMI after 2 h were 94.1% (95% CI: 90.0–96.6) and 95.6% (95% CI: 91.8–97.7), 79.0% (95% CI: 76.8–81.1) and 92.5% (95% CI: 90.9–93.7), 4.48 (95% CI: 4.02–5.00) and 12.86 (95% CI: 10.51–15.31), and 0.07 (95% CI: 0.04–0.13) and 0.05 (95% CI:0.03–0.09) respectively. Conclusions: Exclusion of AMI 2 h after presentation in emergency patients with possible ACS can be achieved using hs-cTnT or hs-cTnI assays. Significant differences in specificity of these assays are relevant and if using the hs-cTnT assay, further clinical assessment in a larger proportion of patients would be required.

Telephone-delivered health coaching improves anxiety outcomes after myocardial infarction: The 'ProActive Heart' trial

Background: Recently, we found a telephone-delivered secondary prevention programme using health coaching (‘ProActive Heart’) to be effective in improving a range of key behavioural outcomes for myocardial infarction (MI) patients. What remains unclear, however, is the extent to which these treatment effects translate to important psychological outcomes such as depression and anxiety outcomes, an issue of clinical significance due to the substantial proportion of MI patients who experience depression and anxiety. The objective of the study was to investigate, as a secondary hypothesis of a larger trial, the effects of a telephone-delivered health coaching programme on depression and anxiety outcomes of MI patients. Design: Two-arm, parallel-group, randomized, controlled design with six-months outcomes. Methods: Patients admitted to one of two tertiary hospitals in Brisbane, Australia following MI were assessed for eligibility. Four hundred and thirty patients were recruited and randomly assigned to usual care or an intervention group comprising up to 10 telephone-delivered ‘health coaching’ sessions (ProActive Heart). Regression analysis compared Hospital Anxiety and Depression Scale scores of completing participants at six months (intervention: n = 141 versus usual care: n = 156). Results: The intervention yielded reductions in anxiety at follow-up (mean difference = −0.7, 95% confidence interval=−1.4,−0.02) compared with usual care. A similar pattern was observed in mean depression scores but was not statistically significant. Conclusions: The ProActive Heart programme effectively improves anxiety outcomes of patients following myocardial infarction. If combined with psychological-specific treatment, this programme could impact anxiety of greater intensity in a clinically meaningful way.

A preliminary investigation into adrenal responsiveness and outcomes in patients with cardiogenic shock after acute myocardial infarction

PURPOSE: This study investigated the significance of baseline cortisol levels and adrenal response to corticotropin in shocked patients after acute myocardial infarction (AMI). METHODS: A short corticotropin stimulation test was performed in 35 patients with cardiogenic shock after AMI by intravenously injecting of 250 μg of tetracosactrin (Synacthen). Blood samples were obtained at baseline (T0) before and at 30 (T30) and 60 (T60) minutes after the test to determine plasma total cortisol (TC) and free cortisol concentrations. The main outcome measure was in-hospital mortality and its association with T0 TC and maximum response to corticotropin (maximum difference [Δ max] in cortisol levels between T0 and the highest value between T30 and T60). RESULTS: The in-hospital mortality was 37%, and the median time to death was 4 days (interquartile range, 3-9 days). There was some evidence of an increased mortality in patients with T0 TC concentrations greater than 34 μg/dL (P=.07). Maximum difference by itself was not an independent predictor of death. Patients with a T0 TC 34 μg/dL or less and Δ max greater than 9 μg/dL appeared to have the most favorable survival (91%) when compared with the other 2 groups: T0 34 μg/dL or less and Δ max 9 μg/dL or less or T0 34 μg/dL or higher and Δ max greater than 9 μg/dL (75%; P=.8) and T0 greater than 34 μg/dL and Δ max 9 μg/dL or less (60%; P=.02). Corticosteroid therapy was associated with an increased mortality (P=.03). There was a strong correlation between plasma TC and free cortisol (r=0.85). CONCLUSIONS: A high baseline plasma TC was associated with a trend toward increased mortality in patients with cardiogenic shock post-AMI. Patients with lower baseline TC, but with an inducible adrenal response, appeared to have a survival benefit. A prognostic system based on basal TC and Δ max similar to that described in septic shock appears feasible in this cohort. Corticosteroid therapy was associated with adverse outcomes. These findings require further validation in larger studies.

Acute myocardial infarction: The spouse's experience

Given the marked changes in length of hospital stay and the number of CAB procedures being performed, it is essential that health professionals are aware of the potential impact these changes could have on the spouses of patients who have undergone CAB surgery. Results from numerous quantitative studies suggest that spouses of patients undergoing CAB surgery experience both physical and emotional stress before and after their partners surgery. While such studies have contributed to our understanding, they fail to capture the qualitative experience of what it is like to be a spouse of a partner who has undergone CAB surgery, specifically in the context of changes in the length of hospital stay. The objective of this study was to describe the experience of spouses of patients who had recently undergone CAB surgery. This study utilised a qualitative methodology and was guided by Husserl's phenomenological approach. Data was obtained from four participants by in depth open ended interviews. This study has implications for all health professionals involved in the care of patients and their families undergoing CAB surgery. If health professionals are to provide holistic care, they need to understand more fully the qualitative experience of spouses of critically ill patients. The purpose of this study was to describe the experience of spouses whose partner's had suffered an acute myocardial infarction (MI). The study was guided by a phenomenological approach. This qualitative type of study is new to nursing inquiry, therefore this investigation creates links with understanding the notion of psychosocial nursing processes with the leading cause of death in Australia. Literature concerning the spouses of myocardial infarction patients has predominantly employed quantitative methods, as such results have centred on structured data collection, and categorised outcomes. Such methods have failed to capture the insight of what it is like to be a spouse of a patient who has had an MI. In-depth interviews were conducted with three participants (2 females and 1 male) about their experiences. The major findings of the study were categorised under the headings of uncertainty, emotional turmoil, support information and lifestyle change. Conclusions suggest that spouses are neglected by health professionals and they require as much psychosocial support as their partner in terms of cardiac discharge planning. Spouses need to be granted special consideration, as they progress through a grieving and readjustment process in coming to terms with: (1) the need to support and care for their partner, (2) changes in their roles and (3) adjustments to their current lifestyles.

Myoblast Sheet Transplantation for Treatment of Heart Failure after Myocardial Infarction

Heart failure is a common, severe, and progressive condition associated with high mortality and morbidity. Because of population-aging in the coming decades, heart failure is estimated to reach epidemic proportions. Current medical and surgical treatments have reduced mortality, but the prognosis for patients has remained poor. Transplantation of skeletal myoblasts has raised hope of regenerating the failing heart and compensating for lost cardiac contractile tissue. In the present work, we studied epicardial transplantation of tissue-engineered myoblast sheets for treatment of heart failure. We employed a rat model of myocardial infarction-induced acute and chronic heart failure by left anterior descending coronary artery ligation. We then transplanted myoblast sheets genetically modified to resist cell death after transplantation by expressing antiapoptotic gene bcl2. In addition, we evaluated the regenerative capacity of myoblast sheets expressing the cardioprotective cytokine hepatocyte growth factor in a rat chronic heart failure model. Furthermore, we utilized in vitro cardiomyocyte and endothelial cell culture models as well as microarray gene expression analysis to elucidate molecular mechanisms mediating the therapeutic effects of myoblast sheet transplantation. Our results demonstrate that Bcl2-expression prolonged myoblast sheet survival in rat hearts after transplantation and induced secretion of cardioprotective, proangiogenic cytokines. After acute myocardial infarction, these sheets attenuated left ventricular dysfunction and myocardial damage, and they induced therapeutic angiogenesis. In the chronic heart failure model, inhibition of graft apoptosis by Bcl-2 improved cardiac function, supported survival of cardiomyocytes in the infarcted area, and induced angiogenesis in a vascular endothelial growth factor receptor 1- and 2-dependent mechanism. Hepatocyte growth factor-secreting myoblast sheets further enhanced the angiogenic efficacy of myoblast sheet therapy. Moreover, myoblast-secreted paracrine factors protected cardiomyocytes against oxidative stress in an epidermal growth factor receptor- and c-Met dependent manner. This protection was associated with induction of antioxidative genes and activation of the unfolded protein response. Our results provide evidence that inhibiting myoblast sheet apoptosis can enhance the sheets efficacy for treating heart failure after acute and chronic myocardial infarction. Furthermore, we show that myoblast sheets can serve as vehicles for delivery of growth factors, and induce therapeutic angiogenesis in the chronically ischemic heart. Finally, myoblasts induce, in a paracine manner, a cardiomyocyte-protective response against oxidative stress. Our study elucidates novel mechanisms of myoblast transplantation therapy, and suggests effective means to improve this therapy for the benefit of the heart failure patient.

Soluble Angiopoietin Receptor Tie-2 In Patients With Acute Myocardial Infarction And Its Detection By Optical Protein-Chip

The Tie-2 receptor has been shown to play a role in angiogenesis in atherosclerosis. The conventional method assaying the level of soluble Tie-2 (sTie-2) was ELISA. However, this method has some disadvantages. The aims of this research are to establish a more simple detection method, the optical protein-chip based on imaging ellipsomtry (OPC-IE) applying to Tie-2 assay. The sTie-2 biosensor surface on silicon wafer was prepared first, and then serum levels of sTie-2 in 38 patients with AMI were measured on admission (day 1), day 2, day 3 and day 7 after onset of chest pain and 41 healthy controls by ELISA and OPC-IE in parallel. Median level of sTie-2 increased significantly in the AMI patients when compared with the controls. Statistics showed there was a significant correlation in sTie-2 results between the two methods (r=0.923, P0.01). The result of this study showed that the level of sTie-2 increased in AMI, and OPC-IE assay was a fast, reliable, and convenient technique to measure sTie-2 in serum.

Mesenchymal stem cell therapy for the treatment of myocardial infarction

Mesenchymal stem cells (MSCs) are currently under investigation as repair agents in the preservation of cardiac function following myocardial infarction (MI). However concerns have emerged regarding the safety of acute intracoronary (IC) MSC delivery specifically related to mortality, micro-infarction and microvascular flow restriction post cell therapy in animal models. This thesis aimed to firstly identify an optimal dose of MSC that could be tolerated when delivered via the coronary artery in a porcine model of acute MI (AMI). Initial dosing studies identified 25x106 MSC to be a safe MSC cell dose, however, angiographic observations from these studies recognised that on delivery of MSC there was a significant adverse decrease in distal blood flow within the artery. This observation along with additional supportive data in the literature (published during the course of this thesis) suggested MSC may be contributing to such adverse events through the propagation of thrombosis. Therefore further studies aimed to investigate the innate prothrombotic activity of MSC. Expression of the initiator of the coagulation cascade initiator tissue factor (TF) on MSC was detected in high levels on the surface of these cells. MSC-derived TF antigen was catalytically active, capable of supporting thrombin generation in vitro and enhancing platelet-driven thrombus deposition on collagen under flow. Infusion of MSC via IC route was associated with a decreased coronary flow reserve when delivered but not when coadministered with an antithrombin agent heparin. Heparin also reduced MSC-associated in situ thrombosis incorporating platelets and VWF in the microvasculature. Heparin-assisted MSC delivery reduced acute apoptosis and significantly improved infarct size, left ventricular ejection fraction, LV volumes, wall motion and scar formation at 6 weeks post AMI. In addition, this thesis investigated the paracrine factors secreted by MSC, in particular focusing on the effect on cardiac repair of a novel MSC-paracrine factor SPARCL1. In summary this work provides new insight into the mechanism by which MSC may be deleterious when delivered by an IC route and a means of abrogating this effect. Moreover we present new data on the MSC secretome with elucidation of the challenges encountered using a single paracrine factor cardiac repair strategy.