Development of a cardiac patch for the regeneration of infarcted hearts

  • Anna Galluzzo

Student thesis: Doctoral Thesis

Abstract

The inflammation that occurs after cardiac ischemia/reperfusion leads to high levels of oxidative stress, which produces deleterious effects that ultimately limit regeneration of the myocardium. This stress response can be prolonged, thereby affecting various stages of cardiac repair remodelling. Efforts to control such remodelling and stimulate cardiac tissue regeneration have therefore included the use of antioxidant or anti-inflammatory drug strategies. To date, such approaches have involved delivery of the drugs orally or by injection. The use of a scaffold that can be placed onto the heart immediately following surgery would allow sustained delivery of high concentrations of drug in situ, directly targeting the affected area. Moreover, implantation of such a material has the potential to encourage cell infiltration into the matrix, thereby promoting regeneration. The ultimate aim of this project was to develop a cardiac scaffold loaded with a drug with antioxidant and anti-inflammatory activity. Pyruvate is a well characterised anti-inflammatory and antioxidant drug. It has been added to cardioplegia by some surgical groups for its potential cardioprotective effects, although the therapeutic value of sustained delivery of this drug into the myocardium following cardiac surgery has not been investigated. Ethyl Pyruvate (EP) is a more stable form of this drug and was therefore the drug selected for investigation in the present study. Various alginate scaffolds were developed as drug delivery vehicles, with EP release characterised in vitro. Alginate gels prepared with (1-2%) low viscosity high guluronate alginate and crosslinked with 1:1 (0.6-1%) calcium chloride solution provided sustained release of about 2,000 - 3,000 µM of EP over 28-days period, characterised by an initial burst of about 85% of EP released in the first week, and the remaining EP was released over the following weeks.Since it is likely that an optimal scaffold for cardiac regeneration will have a porous structure with interconnected pores to allow cell infiltration and proliferation, a series of macro-porous alginate scaffolds were developed. Different methods were used to prepare the scaffolds and thus different EP release profiles were obtained. Overall, the scaffolds prepared with 1% low viscosity high guluronate alginate and double crosslinked with 1:1 (0.4-1%) calcium gluconate solution and 0.2 M calcium chloride bath and prepared with one cycle of free-drying (method 6) released about 5,000- 5,500 µg over 28 days (with 88-98% drug loading efficiency), the highest compared to the other formulations. The potential therapeutic benefits of such EP release were then investigated in vitro. When primary rat cardiac fibroblast cells were exposed to hydrogen peroxide (150 μM) in the presence of EP (1,000 - 20,000 μM), EP improved cell viability as measured by alamarBlue assay. Moreover, at (1,000 - 10,000 μM), EP significantly increased cell viability compared to the control. In contrast, EP had no protective effect on the cells that had been previously exposed to H2O2 (150 μM) for 24 hours. Alginate macro-porous scaffolds (prepared using method 6), which showed high porosity, the best EP release profiles and the highest EP loading efficiency, were then tested in a cardiac fibroblasts culture and cell viability was measured by Neutral Red assay after 5 days. In order to improve cell attachment in the scaffolds prepared in this study, Arginine-Glycine-Aspartic acid modified RGD alginate was also used to prepared the scaffolds for the cardiac fibroblast study. Cells seeded onto the RGD- Alginate + EP scaffolds presented higher cell viability compared to the scaffolds without EP, demonstrating that the cells benefit from the structure of the scaffold, as well as from the presence of EP. This
Date of Award22 Feb 2019
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsUniversity of Strathclyde
SupervisorChristopher McCormick (Supervisor) & Terry Gourlay (Supervisor)

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