Association between in-utero exposure to diesel exhaust and N-acetyl-cysteine supplementation in hyperlipidemic pregnant mice and development of atherosclerosis at multiple vascular sites in the offspring

Thesis (Master's)--University of Washington, 2016-06

Association between in-utero exposure to diesel exhaust and N-acetyl-cysteine supplementation in hyperlipidemic pregnant mice and development of atherosclerosis at multiple vascular sites in the offspring Background: Ischemic heart disease (IHD) is the single largest cause of death worldwide, accounting for about 17.3 million annual deaths. In addition to the traditional risk factors for IHD, recent evidence points towards the role of environmental factors such as diesel exhaust (DE) emissions in the pathogenesis of the disease. Chemically, DE consists of a mixture of toxic gases and diesel particulate matter (DPM). Several mechanisms have been proposed for the toxicity of DPM in the body, such as its ability to cause oxidative stress, impair immunity, stimulate an inflammatory response and cause thromboischemic changes. Furthermore, there is ongoing research that supports the association between impaired in-utero growth and the pathogenesis of adult onset diseases including coronary heart disease. This study was designed to evaluate the effect of in-utero exposure to diesel exhaust in the development of atherosclerosis in the offspring later in life, with a focus on the histological changes. Methodology: In this study, pregnant hyperlipidemic apolipoproteinE (apoE -/-) deficient mice were randomized into one of four exposure groups: 1) Diesel exhaust and N-acetyl cysteine (NAC), referred to as DN 2) diesel exhaust and control water, referred to as DC 3) filtered air and NAC and, referred to as FN 4) filtered air and control water, referred to as FC. The exposures were restricted to the prenatal period and were discontinued after birth. The offspring born to these dams were nurtured in a controlled environment until they were 16 weeks of age, at which point they were sacrificed. Various tissue specimens were isolated, including the innominate arteries (IA) which were examined microscopically for the presence of atherosclerotic lesions and vascular remodeling. In specific, the atherosclerotic lesion areas and medial expansion areas were quantified and differences between the study groups were statistically analyzed. Results: Offspring born to diesel plus NAC (DN) dams exhibited the larger mean IA atherosclerotic lesion areas and medial thickening. The prevalence of peri-vascular adipose tissue (PVAT) in the DE exposed groups combined (diesel plus control water [DC] and diesel plus NAC [DN]) was 1.49 times (95% CI 1.02-1.54) that of the prevalence of PVAT in the filtered air groups (filtered air control [FC] and filtered air plus NAC [FN]). First litter pups recorded a significantly higher prevalence (p=0.011) of PVAT than their second litter counterparts. No correlation was seen between lesion development in the IA versus lesion development in the aortic sinus for a given group. Lastly, there was an increase in cumulative mortality between the 12th and 16th week for the DC group compared to the other groups. Conclusion: The results of this study suggest that in-utero DE exposure and NAC supplementation is associated with PVAT, but is largely not associated with vascular remodeling and atherosclerotic progression. More research is needed to further understand the inflammatory response to environmental toxins and the role of protective agents in the disease process.