The role and regulation of nitric oxide and oxidative stress in cardiometabolic disease : focus on preeclampsia

Abstract

Cardiovascular (CVD) and metabolic diseases account for significant morbidity and mortality. Over the last decades, despite significant research and clinical effort, their global prevalence is estimated to further increase. This trend is similarly observed in the pregnant population, which increases the risk of cardiometabolic complications of pregnancy, such as preeclampsia (PE), which in turn, predisposes both the mother and offspring to increased future cardiovascular and metabolic risk. Disruption of the delicate balance between nitric oxide (NO) and reactive oxygen species (ROS) leads to a vicious pathogenic cycle which results in oxidative stress and systemic vascular dysfunction, key features of numerous CVD and metabolic diseases. In the vasculature, NO is predominantly synthesised via endothelial nitric oxide synthase (eNOS), although the nitrate-nitrite-NO pathway can serve as an additional source. The latter can be stimulated by dietary inorganic nitrate, found in leafy green vegetables and beetroot.

The present thesis aimed to further explore the role of NO deficiency and oxidative stress in the pathogenesis of cardiometabolic disease, with focus on PE. We sought to dissect the mechanisms underlying the beneficial metabolic effects of dietary nitrate, investigate the role and mechanisms underlying erythrocrine function on endothelial homeostasis, assess the feasibility of conducting a clinical dietary nitrate intervention RCT in PE women and finally, examine how monocyte-derived factors perpetuate endothelial oxidative stress in PE.

In study I, models of diet-induced metabolic syndrome and liver steatosis demonstrated a novel therapeutic role of dietary nitrate, mediated via modulation of AMPK signalling and NADPH oxidase-derived oxidative stress. In studies II, III, and IV, ex vivo incubations of red blood cells (RBCs) and healthy murine aortas were utilised to specifically evaluate functional RBCendothelial interactions. In study II, a lack of RBC eNOS induced endothelial dysfunction (ED), in part mediated via vascular arginase, elevated endothelial oxidative stress, and reduced NO bioavailability. In studies III and IV, RBCs isolated from PE patients, but not healthy pregnant women, induced ED, mediated via elevated arginase activity, reduced NO bioavailability, and elevated oxidative stress, in a contact-dependent manner. Study IV demonstrated that short term (7-day) dietary nitrate supplementation was well accepted and not associated with any adverse events. No significant differences in blood pressure changes were observed. Beneficial nitrate-independent effects on RBC-endothelial communication were observed ex vivo. In Study V an in vitro approach demonstrated that peripheral blood mononuclear cells (PBMCs) isolated from PE women increase oxidative stress and reduce NO bioavailability in the endothelium, which was prevented by antioxidant treatment (Silibinin).

The balance between NO bioavailability and oxidative stress governs endothelial homeostasis. Beneficially targeting this delicate balance can be achieved via dietary inorganic nitrate, which holds safe, therapeutic promise for cardiometabolic disease. The RBC is a central player in mediating this balance in the vascular microenvironment, dysregulated erythrocrine function results in ED. Further investigation regarding RBC-endothelial signalling may provide insight into previously discarded therapeutic approaches for cardiometabolic diseases.