The effects of psychological and oxidative stress on the temporal profile of stress proteins and antioxidant status during atherogenesis in Japanese quail

This thesis reports the results of four experimental studies which were designed to examine the effects of psychological stress on the interrelationships of heat shock proteins (HSP) and endogenous antioxidants during atherogenesis in an avian model, the atherosclerosissusceptible (SUS) Japanese quail. The first study examined the effect of psychological stress in quail fed a cholesterolsupplemented diet for four weeks. As expected, cholesterol-supplemented birds showed significant increases in plaque scores compared to birds fed a non-cholesterol-supplemented diet. The heterophil/lymphocyte ratio was increased in birds exposed to stress and in cholesterol-supplemented birds. Stress or cholesterol feeding alone increased HSP 70 in aortic and heart tissues, whereas lower HSP 70 levels were detected in cholesterol fed birds exposed to stress compared to non-stressed cholesterol fed birds. The stress protocol lowered aortic catalase and heart superoxide dismutase levels, and had little effect on enzymes of the glutathione (GSH) redox cycle. A functional decrease in the antioxidant capacity ofthe heart as measured by thiobarbituric-acid reactive substances (TBARS) was detected following stress alone or cholesterol supplementation. In the next longer-term study, I examined the effects of temporal stress during atherogenesis. There were no differences in plaque score between early stressed, recently stressed and non-stressed cholesterol-supplemented birds. Moreover, cholesterol-fed birds exposed to early stress had lower plasma cholesterol levels than cholesterol-fed birds exposed to recent stress or no stress, suggesting that stress may have preconditioned the birds during cholesterol feeding. In general, stressed cholesterol-fed birds had lower HSP 70 and heme oxygenase (HO-1) levels in their aortic and heart tissue compared to non-stressed cholesterolfed birds. Furthermore, cholesterol-supplementation alone also increased heart and aortic ferritin and catalytic iron levels, and increased generation of TBARS which is indicative of increased oxidative stress. In the third study, aortic endothelial cells from random bred wild-type strain (WILD) and SUS and atherosclerosis-resistant (RES) Japanese quail were isolated and characterized. GSH levels were higher in the SUS cells and lowest in RES cells, and glutathione reductase was higher in WILD cells than SUS and SUS cells. Subconfluent monolayers of RES cells had higher HO activity compared with SUS cells whereas HO activity levels were similar between strains at confluence. Catalytic iron levels were higher in SUS cells than WILD and RES cells. In the final study of this thesis, aortic endothelial cells were exposed to in-vitro oxidative challenge to further investigate the role of HO and glutathione in the RES and SUS strains. Overall, the RES cells exhibited higher HO activity and HO-1 protein and lower LDH release and T BARS levels compared with cells isolated from the SUS strain. In summary, while stress factors imposed did not alter the aortic plaque scores, some associations between and/or cholesterol feeding related to the development of atherosclerosis have been established. These studies provide evidence that some genetic factors in atherosclerosis are manifested at the level of endothelial cells, given the distinct differences in HO and antioxidant components from RES and SUS cells. Therefore, these studies could further characterize the association and possibly the interrelationship of psychological stress to oxidant-induced injury and the subsequent development of atherosclerosis. TABLE OF CONTENTS Abstract i i TABLE OF CONTENTS iv List of Tables viii List of Figures ix List of Abbreviations xii Acknowledgements xiii Chapter 1 1 Literature Review 1 Cardiovascular Disease 1 Antioxidants 2 Heat Shock Proteins 4 Heme oxygenase 6 HO-1 induction by oxidative stress 8 The potential roles of HO reaction products 5 Biliverdin and bilirubin 9 Carbon monoxide 10 Ferritin and iron 11 Genetic models of HO deficiency 14 Knock-out mice 14 Human HO-1 deficiency 14 The HO gene 15 HO and atherosclerosis 16 HO-1 is induced by oxidized LDL 16 Anti-atherogenic properties of HO-1 17 Conclusions 19 The atherosclerosis-resistant and -susceptible Japanase quail 20 CHAPTER 2 23 The effect of psychological stress on aortic plaque development in the atherosclerosissusceptible (SUS) Japanese quail 23 Preface 23 Introduction 23 Materials and Methods 25 Animal model 25 Experimental Diets 25 Experimental Design 26 Stress protocol 26 Determination of aortic plaque score 28 White blood cell differential counts 31 Sample preparation 31 Plasma cholesterol and triglyceride levels 32 Aortic cholesterol and triglyceride levels 33 HSP70 33