Masters Degrees (Physiological Sciences)

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Browsing Masters Degrees (Physiological Sciences) by Author "Breedt, Emilene S."

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    An evaluation of trimetazidine as a therapeutic intervention in a newly established ex vivo mouse model of acute heart failure
    (Stellenbosch : Stellenbosch University, 2016-03) Breedt, Emilene S.; Essop, M. Faadiel; Lacerda, Lydia; Stellenbosch University. Faculty of Science. Dept. of Physiological Sciences.
    ENGLISH ABSTRACT: Introduction Acute heart failure (AHF) is the most common primary diagnosis for hospitalized heart diseases in Africa. Although Sub-Saharan women are more prone to suffer from de novo AHF at a much younger age, females have historically been underrepresented in biomedical research studies. As increased fatty acid oxidation (FAO) with heart failure triggers detrimental effects within the myocardium, we hypothesized trimetazidine (TMZ) (a partial FAO inhibitor) treatment will provide cardio protection to control and diabetic mouse hearts subjected to AHF. We further hypothesized that TMZ efficacy will be influenced by different phases of the estrous cycle. Aims 1) Establish an unique ex vivo AHF model using hearts isolated from db/db mice and their lean control littermates (db/+); 2) Evaluate whether FA-albumin filtering can replace the gold standard method of dialysis for perfusate preparation; 3) Assess whether we can identify the different phases namely proestrus, estrus (follicular phase), metestrus and diestrus (luteal phase) of the estrous cycle in the female mice; and 4) Evaluate TMZ as a therapeutic option in our ex vivo AHF model for normal and obese/diabetic mice, respectively, ascertain if there are sex-based differences, and determine whether the phases of the estrous cycle can influence cardio protection. Methods The Langendorff retrograde isolated heart perfusion system was employed to establish an ex vivo AHF model that consisted of three phases: Stabilization – Krebs-Henseleit buffer (10 mM glucose) at 100 cmH2O (25 minutes); Critical Acute Heart Failure (CAHF) – (2.5 mM glucose, 1.2 mM palmitic acid bound to 3% bovine serum albumin [BSA]) at 20 cmH2O (25 minutes); and Recovery Acute Heart Failure (RAHF) – (10 mM glucose, 1.2 mM palmitic acid bound to 3% BSA) at 100 cmH2O (25 minutes). 5 μM TMZ was administered in the perfusate at either the CAHF or RAHF phase for the full duration of the respective phase. The filter versus dialysis experiments were run for 30 minutes in Krebs-Henseleit buffer (10 mM glucose, 1.2 mM palmitic acid bound to 3% BSA). Phases of the estrous cycle were determined by vaginal smear cytology or “wet smears” and viewed under a light microscope. Enzyme-linked immunosorbent assays (ELISA) were utilized to measure serum hormonal levels while Western blotting was employed to assess protein expression levels. Results Our model mimicked de novo AHF in the switch from stabilization to CAHF and partial recovery in the switch from CAHF to RAHF. This study established that the dialysis method for FA-BSA preparations can be substituted by a simple filtering protocol. While vaginal smear cytology confirmed acyclicity of obese females (therefore lost follicular phase), lean females exhibited normal estrous cycle phases. Commercial ELISA kits were not adequately sensitive to detect hormonal fluctuations. All groups displayed a severe decrease in function during CAHF and recovery with RAHF (vs. CAHF). Lean and obese males benefited equally from TMZ treatment administered during the RAHF phase. The lean females in the two main phases of the estrous cycle (follicular and luteal) responded in distinct ways. Here lean follicular females were the only group to respond to TMZ treatment during the CAHF phase, while lean luteal females did not respond to therapy but rather displayed an inherent cardio protection that was lost with obesity. Obese luteal females also benefited from TMZ treatment during RAHF. No changes were observed in protein expression levels of 3-keotacyl-CoA thiolase (3-KAT) nor pyruvate dehydrogenase (PDH). Conclusion A novel ex vivo mouse AHF model has successfully been established and utilized the filtering method as opposed to the gold standard dialysis method. TMZ as a therapy for AHF showed great promise in improving functional recovery of mice subjected to the AHF protocol. Sex differences were present only in lean groups where the phases of the estrous cycle influenced therapy, while obesity only affected TMZ efficacy in females. The optimization of cardiac metabolism by TMZ emerges as a novel and worthy therapeutic option to investigate for the treatment of AHF in normal and diabetic patients (for both genders).