Browsing by Author "Ogundipe, Temitope Richard"
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- ItemIdentification of potential biomarkers of cardiotoxicity induced by doxorubicin therapy in a tumour bearing model by targeting specific micro-RNAs(Stellenbosch : Stellenbosch University, 2021-03) Ogundipe, Temitope Richard; Sishi, Balindiwe J. N.; Stellenbosch University. Faculty of Science. Dept. of Physiological Sciences.ENGLISH ABSTRACT: Introduction: Anthracycline-induced cardiotoxicity, a major side effect of chemotherapeutic drugs such as doxorubicin (DOX), has been a priority within the field of cardio-oncology for a number of decades. While multiple approaches and strategies have been utilized to understand and rectify this enigmatic condition, very little translatable research success has been achieved. Paramount to the reasons for this lack of utilizable return is that research has largely focused on the acute form of this disease, which is reversible, in contrast to the chronic form which has no cure. The majority of the tried and tested interventions have prioritized the oxidative stress theory, and the experimental models that have been developed have omitted the potential contributory effect of tumours within this context. Since their discovery, the elucidation of the primary roles of microRNAs (miRNAs) in the pathogenesis of oncological and non-oncological diseases has received much attention. As such, the detection of the existence of cell-free miRNAs in circulation has motivated researchers to investigate the role of these small evolutionary conserved endogenous single-stranded, non-coding RNAs as prospective non-invasive biomarkers. Therefore, this study explored the expression profile of a few miRNAs that have been observed in other pathologies that have the potential to be of significance in this context, by using a clinically relevant model that takes into account the plausible effects of tumour presence and the known DOX concomitant consequences. Methods: Chronic DOX-induced cardiotoxicity was initiated through cumulative DOX injections (2.5 mg/kg/week) in 37 female Sprague-Dawley rats over the course of eight weeks. Prior to this, breast cancer mammary gland tumours were induced in these experimental animals through the injection of LA7 cells into the mammary fat pad following a carefully optimized protocol. Comparisons were carried out between groups that included a vehicle (control) (Hank’s balanced salt solution), tumour, DOX and a combination of the tumour and DOX-treatment. A week after the last DOX injection, animals were euthanized, blood was collected and the heart was excised for molecular and biochemical analysis. To detect early changes in miRNA profile expression, some animals were sacrificed after five weeks to represent early chronic modifications, whereas the rest of the experimental animals were sacrificed after nine weeks to represent late chronic adaptions. While miRNA manifestation was evaluated from plasma samples collected and assessed via quantitative PCR, the hallmarks of DOX-induced cardiotoxicity such as cardiac hypertrophy, fibrosis, oxidative stress and apoptosis were assessed via histological staining and western blotting techniques. Results and Discussion: Mammary tumours were successfully induced and reached a peak volume (2563.00 ± 478.20 mm3) after two weeks of LA7 cell inoculation. It was also evident from these results that DOX is an effective chemotherapeutic agent for breast cancer; as tumour growth was significantly lower (1523.00 ± 457.80 mm3, p< 0.01) at this time point when compared to the tumour only group. Whilst miR-208a was significantly down-regulated in all treatment groups when compared to the vehicle (control) after eight weeks, plasma miR-29b expression was substantially upregulated across all groups after eight weeks versus the four week time point. This study observed no noteworthy changes in miRNA-133a and 133b following eight weeks of treatment. Together, these results, in amalgamation with increased collagen deposition (306.90 ± 52.62%, p < 0.01) vs control (100.00 ± 6.35%), cleaved caspase-7 (844.10 ± 166.21%, p <0.05) vs control (100.00 ± 3.40%) and MLC-2v (406.90± 47.18%, p < 0.01) vs control (100.00 ± 3.12%), in the combination group, demonstrated that miR-208a exhibits potential as a non-invasive biomarker of late chronic myocardial toxicity linked to fibrosis, apoptosis and cardiac hypertrophy, respectively. miR-208a and miR-133a remain the only miRNAs in this context that may have the potential to be utilized as early chronic biomarkers of cardiotoxicity in the presence of a tumour, however further investigations are warranted.