Sex differences in atherosclerosis and exercise effects

This thesis aimed to investigate the sex differences in atherosclerosis, in particular how the proteome and pathophysiology differs. In addition, we sought to investigate the potential benefit of an exercise programme, in reducing CVD risks, using a randomised controlled trial including postmenopausal women.

Sex differences in atherosclerosis were first investigated via proteomic analysis of human carotid endarterectomy samples. Initially, five intraplaque biopsies were taken from distinct atheroma regions, including; internal control, fatty streak, plaque shoulder, plaque centre, and fibrous cap. Protein extracts from these biopsies were subjected to analysis by mass spectrometry. The novel sampling method was successful in reducing the effect of plaque heterogeneity, a limitation in previous proteomic studies of atherosclerosis, and a number of previously unreported proteins were identified in human carotid atheroma. In addition to this, with the inclusion of multivariate statistical modelling, it was found that 43 proteins significantly discriminated the carotid atheroma between men and women. These proteins were grouped by function, and it was found that atheroma from men was associated with the increased abundance of inflammatory response proteins, including phospholipase-A2 membrane associated and lysozyme C, and atheroma from women was associated with increased abundance of blood coagulation, complement activation, and transport proteins, notably including; antithrombin-III, coagulation factor XII, and afamin. In addition, differences were also ii observed in the abundance of iron metabolism related proteins. These sex differences were further expanded upon from a pathophysiological perspective. Immunohistochemistry stainings of ferritin and transferrin receptor 1 were found significantly increased in the atheroma from men. Moreover, the levels of plasma haemoglobin were also significantly increased in men and were associated with the development of more vulnerable and severe plaque types. The more vulnerable and severe plaque types were also associated with significantly greater macrophage infiltration. In summary, these results are indicative of men developing atheroma with greater inflammation that are more vulnerable, due to increased iron and inflammatory proteins and macrophage infiltration, whereas atheroma from women develop with less inflammation and a more stable phenotype.

The randomised controlled clinical trial aimed at investigating the effects of resistance training (RT), over a 15-week period, in postmenopausal women. Plasma samples were obtained at week-0 and week-15 of the study period, and analyses were performed primarily using a series of immunoassays. Results showed that women participating in RT, with good compliance, were associated with significant decreases in plasma levels of ferritin, lipids, and inflammatory adipokines. These results suggest that the use of regular RT may be a beneficial intervention in reducing the levels of body iron, lipids, and inflammation, all of which are risk factors for the development of CVD. However, validation studies are required in a larger cohort of postmenopausal women, in addition to the inclusion or complementary studies in middle-aged men.

In summary, the works included in this thesis further expand on the current knowledge of sex differences in atherosclerosis, and also provides information on the potential of an exercise intervention to beneficially reduces the effects of known risk factors of CVD.