| Summary: | Systemic lupus erythematosus (SLE) carries a significantly enhanced risk of developing cardiovascular disease (CVD) and remains a leading cause of death in these patients, accounting for ~25% of all causes of mortality. Although there is clear evidence li nking accelerated atherosclerosis to SLE (and consequently an increase in cardiovascular events), another factor that may contribute to CVD related morbidity and mortality is reperfusion injury that occurs post - ischaemia. This is termed ischaemic / reperfu sion (I/R) injury and is a known important contributor to the size of the eventual infarct in the heart, which in animal studies has been shown to account for up to 40 - 50% of the final infarct size. Hydroxychloroquine (HCQ), originally an anti - malarial dr ug, is now used to treat autoimmune disorders, including SLE. HCQ has been shown to modulate inflammation in rheumatic diseases such as SLE and rheumatoid arthritis as well as have potential cardiovascular benefits in these patients. One of the keys aims o f this thesis was to explore the potential use of HCQ in reducing cardiac I/R injury. HCQ was found to be cardioprotective in an in vitro neonatal cardiomyocytes simulated I/R injury model as well as in an in vivo cardiac I/R injury model. This was found to be through an ERK - dependent mechanism which was blocked in the presence of the ERK inhibitor U0126 both in vitro and in vivo . Another relevant question addressed in this thesis was if I/R injury is enhanced in lupus. There is evidence from an autoimmune prone mouse model that lupus IgG are pathogenic in mesenteric I/R injury . However, no study as yet has investigated human lupus IgG in a heart model. IgG was purified from the serum of SLE patients (aPL +ve vs aP L – ve), antiphospholipid syndrome (APS) patients, juvenile onset SLE (JSLE) patients and healthy volunteers. The pre - treatment of neonatal rat cardiomyocytes with IgG from all 3 patient groups enhanced simulated I/R injury. However, the most pathogenic wer e those who were aPL positive. Interestingly, JSLE patients who were all aPL negative, enhanced I/R injury to similar levels as those who tested positive in the adult patient cohort. An enhanced p38 MAPK phosphorylation was observed in the presence of aPL positive IgG and this pathogenic effect was blocked in the presence of the p38 inhibitor SB23580. The results ob tained in this thesis have identified a potential role for HCQ in the cardiovascular field as a cardioprotective therapeutic in myocardial I/R injury. Additionally , IgG purified from patients with SLE , APS and JSLE have been shown to accelerate myocardial I/R injury.
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