Background: Heart Rate Variability (HRV) as a research outcome has the potential for misclassification due to its inability to account for changes in the heart rate. HRV can be parsed into Acceleration Capacity (AC) and Deceleration Capacity (DC) which address these limitations. Objectives: To investigate the associations between AC and DC with short-term and long-term metal PM2.5 exposures; and examine if these associations are mediated by inflammation. Methods: A panel of 45-50 male welders, mean age 39-40 years, had continuous PM2.5 exposure during typical welding work shifts for 4-6 hours repeated 2-5 times over sampling periods in 2010-2012. We also obtained continuous recordings of digital electrocardiograms (ECG) over their work shift using Holter monitors during the same time; and analyzed blood samples before and after each welding shift for potential mediators of inflammation. In our first analysis, we used linear mixed models to assess the association between hourly PM2.5 exposure and each of simultaneously measured hourly AC and DC, controlling for covariates. Then, mediation analysis was done using linear mixed models to assess the associations between shift PM2.5 exposure, potential mediator levels, and AC and DC, controlling for relevant covariates in order to deduce the direct and indirect effects (via the mediator) of PM2.5 on AC and DC. In our final analysis, we used linear regression to assess the association between CEI PM2.5 exposure and each of current AC and DC, controlling for confounders. Results: Negative exposure-response associations were found for AC and DC with increased PM2.5 both in the short-term and long-term exposure after adjusting for covariates. In our mediation models, the proportion of the total effect of PM2.5 on AC or DC (indirect effect) mediated through IL-6 on AC was at best 4%. Conclusions: There are sustained acute and chronic effects of metal particulates on AC and DC even after exposure has ceased. These findings suggest that there may be more pathways that sustain response following exposure other than a direct effect of metal particulates on AC and DC. Furthermore, there may be complex mediating pathways involving interleukin 6. / Environmental Health

Current prevention recommendations for ovarian cancer are limited, and the underlying etiology is not fully elucidated. The associations of common modifiable factors, such as psychosocial and lifestyle factors, with ovarian cancer risk need to be more fully evaluated. Thus, I examined the association of ovarian cancer with depression, physical activity, hypertension, and antihypertensive medication use among participants from two prospective cohort studies: the Nurses' Health Study and Nurses' Health Study II. Cox proportional hazards models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for these associations. Depression was associated with about 30% increased risk of ovarian cancer (HR = 1.30, 95% CI 1.05-1.60). Higher risk was also observed among women with persistent positive depression status than women intermittently positive or persistently negative for depression. Contrary to the hypothesis that physical activity may lower ovarian cancer risk, we observed that both low and high physical activity was associated with a modest increase in ovarian cancer risk (HR for ≥27 [approximately equivalent to 1 hr/day of brisk walking] versus 3-9 MET-hrs/week = 1.26, 95% CI 1.02, 1.55; HR for <3 versus 3-9 MET-hrs/week = 1.19, 95% CI 0.94, 1.52). However, these associations were only restricted to premenopausal physical activity, and postmenopausal activity was not associated with ovarian cancer risk. While hypertension was not associated with risk (HR = 1.03, 95% CI 0.87, 1.21), use of thiazide diuretics was associated with an increased risk of ovarian cancer (HR = 1.35, 95% CI 1.04, 1.74), and use of calcium channel blockers was associated with a suggestively lower risk (HR = 0.73, 95% CI 0.53, 1.01). Our results need to be confirmed by other studies, but suggest that these common modifiable factors may have a moderate impact on ovarian cancer risk. This represents an opportunity to broaden our understanding of ovarian cancer etiology and potentially improve prevention strategies for ovarian cancer. / Epidemiology

Mitochondria are membrane-bound organelles found in the cytoplasm of almost all eukaryotic cells. Their main functions include energy metabolism, free radical production, calcium homeostasis and apoptosis. Located closely to the source of reactive oxidative stress (ROS) production, Mitochondrial DNA (mtDNA) is extremely susceptible to oxidative damage due to its absence of protective histones, the lack of introns and a scarcity of the efficient DNA repair mechanisms. Associations between leukocyte mtDNA copy number (mtCN) and various oxidative stress related health outcomes have been demonstrated in multiple prospective studies. MtCN has also been suggested to be a contributor to many cancer types. These pieces of evidence suggest that mtCN in leukocytes may serve as a candidate biomarker for oxidative stress related general health outcomes. In this work, we determined associations between mtCN and skin cancer as well as lung cancer risk by case-control studies nested within the Nurses’ Health Study (NHS) and the Health Professional Follow-Up Study (HPFS). Furthermore, we examined relationships between various oxidative stress generating factors (age, smoking, physical activity, body anthropometric indices, weight change and alcohol consumption) and mtCN among women using controls from the previous two studies. Relative mtCN in peripheral blood leukocytes (PBL) was measured by quantitative PCR (qPCR)-based assay and covariates were collected by biannually updated questionnaires. Our results indicate that obesity and weight gain are associated with lower mtCN. Moreover, mtCN may be more sensitive to obesity, while telomere length reflects aging better. In terms of cancer risks, women with low mtCN are more likely to develop skin cancer and the increased melanoma risk associated with low mtCN is more apparent among women with low constitutional risk or high UV exposure history. Although mtCN was not significantly associated with lung cancer risk, current smokers might be more susceptible for the disease when mtCN first starts to decrease. / Epidemiology

Ideally, clinical guidelines would be informed by well-designed randomized experiments. However, it is generally not possible to conduct a randomized trial for every clinically relevant decision. Decision makers therefore often have to rely on observational data. Guidelines that rely on observational data due to the absence of randomized trials benefit when the analysis mimics the analysis of a hypothetical target trial. This can be achieved by explicitly formulating the protocol of the target trial, and thoroughly discussing the feasibility of the conditions that must be met in order to validly emulate the target trial using observational data. In chapter one, we discuss the emulation of trials that compare the effects of different timing strategies, that is, strategies that vary the frequency of delivery of a medical intervention or procedures, and provide an application to surveillance for colorectal cancer. In chapter two, we discuss a study design that attempts to avoid bias by comparing initiators of the treatment of interest with initiators of an “active comparator” that is believed to be inactive for the outcome, in order to emulate a randomized trial that compares the treatment of interest with an inactive comparator. In chapter three, we describe a new method that combines randomized trial data and external information to emulate a different target trial. We apply this method to a randomized trial of postmenopausal hormone therapy in order to emulate a trial of a joint intervention on hormone therapy and statin therapy.

Background: welders are often exposed to various types of metals from the welding fumes and they also have high risks of cardiac autonomic dysfunction. Knowing the hazardous components within metals mixture as well as understanding the potential underlying mechanisms is essential for environmental and occupational regulations. Objective: to identify metal components which are associated with cardiac autonomic responses, as measured by two novel markers -acceleration capacity (AC) and deceleration capacity (DC); to examine whether inflammation mediates effects of metals exposure on AC/DC changes; to identify epigenetic variants which are associated with AC/DC changes. Methods: we collected urine, blood and electrocardiogram (ECG) samples from 75 welders over six sampling occasions between June 2003 and June 2012. Urinary concentrations of 16 types of metals were determined. Blood serum samples were analyzed for inflammatory cytokines levels including CRP, IL-2, IL4, IL6 and IL8. AC and DC values were quantified from ECG recordings. Firstly, we used linear mixed-effects models with Lasso to identify hazardous metals that were significantly associated with AC or DC changes. We fitted the co-pollutants model with “selected” metals in the linear mixed model to estimate the exposure-response relationship. Then, we conducted a mediation analysis to examine whether inflammatory cytokines mediated the effects of metals exposure on AC or DC changes. We report both direct and indirect effects in single pollutant model as well as co-pollutants models. Finally, we conducted the epigenome-wide association study (EWAS) to identify epigenetic variants that were associated with AC or DC changes. Results: we observed negative associations between urinary mercury and chromium concentrations with both DC and AC changes. Indirect effects of metals exposure on AC or DC through inflammation pathway were not significant. We identified GPR133 gene at which methylation level changes were associated with DC values. Conclusion: metals exposures are associated with impaired cardiac autonomic functions. Our study did not provide evidence that these effects were mediated through inflammation pathway. However, DNA methylation of specific genes may be a potential pathway linking environmental and occupational pollutants exposure and alterations in cardiac autonomic responses.

Background: Fine particulate matter (PM2.5) pollution is a major risk factor for cardiovascular diseases. Identifying modifiable factors and preventative strategies to mitigate the cardiovascular effect of PM2.5 is essential to aid the development of personalized intervention. Method: Chapter one and two were based on a crossover human intervention trial using B vitamin supplementation (2.5 mg/d folic acid, 50 mg/d vitamin B6, and 1 mg/d vitamin B12). Ten volunteer received three two-hour controlled exposure experiments to medical air or PM2.5 (250μg/m3), in pre-determined order. Chapter three utilized the Normative Aging Study, a longitudinal cohort study with 573 elderly men. We used electrocardiogram to measure resting heart rate (HR) and heart rate variability (HRV), hematology analyzer to determine white blood cell (WBC) counts, and Infinium HumanMethylation450 BeadChip to measure DNA methylation in peripheral CD4+ T helper (Th) cells (pre-, post-, 24-hr post-exposure). Blood TLR2 methylation was analyzed using pyrosequencing. Daily flavonoid and methyl nutrients intakes were assessed through the Food Frequency Questionnaire. Results: Compared to medical air, PM2.5 exposure was associated with 3.8 beat/min (95% CI, 0.3, 7.4; P=0.04) higher resting HR, 57.5% (95% CI, 2.5%, 81.5%; P=0.04) lower low-frequency (LF) power, and altered DNA methylation landscape, following exposure. PM2.5 exposure was associated with 11.5% (95% CI, 0.3%, 24.0%; P=0.04) higher total WBC count and 12.9% (95% CI, 4.4%, 22.1%; P=0.005) higher lymphocyte count, at 24-hour post-exposure. These effects of PM2.5 were abrogated with B vitamins supplement. In the Normative Aging Study, every 10 µg/m3 increase in 48-hour PM2.5 moving average was associated with 7.74% (95%CI: -1.21%, 15.90%; P=0.09), 7.46% (95%CI: 0.99%, 13.50%; P=0.02), 14.18% (95%CI, 1.14%, 25.49%; P=0.03), and 12.94% (95%CI, -2.36%, 25.96%; P=0.09) reductions in root mean square of successive differences (rMSSD), standard deviation of normal-to-normal intervals (SDNN), LF power, and high-frequency (HF) power, respectively. Higher TLR2 methylation exacerbated the rMSSD, SDNN, LF, and HF reductions associated with heightened PM2.5 (Pinteraction=0.006, 0.03, 0.05, 0.04, respectively). Every interquartile-range increase in flavonoid intake was associated with 5.09% reduction in mean TLR2 methylation (95%CI, 0.12%, 10.06%; P=0.05) and counteracted the effects of PM2.5 on LF (Pinteraction=0.05). Conclusions: Ambient PM2.5 exposure peak has unfavorable effect on cardiac autonomic function, the immune system, and the epigenome – which, can be counteracted by B vitamins supplementation. In addition, the epigenetic regulation of TLR2-related immunity may determine vulnerability of older individuals when confronted with air pollution peaks.

Despite important achievements of Environmental Epidemiology in identifying major environmental health problems in recent years, little is known about the underlying biological mechanisms that link environmental exposures to certain outcomes. Recent discovery of extracellular vesicles (EVs) as a novel mechanism of cellular communication has opened new avenues for non-invasive access to subclinical molecular signals, which might help exposing such mechanisms. In this work, we evaluate the potential of microRNAs, molecular signals that are contained in EVs circulating in the blood, as biomarkers in two very important environmental health problems: (a) the causal association between air pollution and cardiovascular disease and (b) the association between prenatal lead exposure and impaired fetal growth. For this work, we used cutting-edge and high-throughput methods to isolate EVs from the blood of study participants, and profile their content in microRNAs (evmiRNAs). We further incorporated a broad array of sophisticated statistical methods to (a) determine the association of ambient particulate matter of <2.5μm diameter (PM2.5) and evmiRNAs (Chapter 1), (b) determine the association between prenatal lead exposure and fetal growth (Chapter 2), and (c) evaluate the potential of evmiRNAs as early biomarkers of fetal growth impairment (Chapter 3). The findings from Chapter 1 showed positive associations between long-term exposure to PM2.5 and levels of evmiRNAs in the blood circulation of older individuals, several of which were found to be enriched in biological pathways related to cardiovascular disease. Results from Chapter 2 showed a negative association between prenatal exposure to lead and birthweight-for-gestational age (BWGA), and revealed that the magnitude of the association is much bigger in the lower percentiles of the BWGA distribution. Finally, the findings from Chapter 3 suggested that levels of evmiRNAs provide a very promising opportunity for the development of minimally-invasive biomarkers to detect and monitor impaired fetal growth early in pregnancy. This work demonstrates the tremendous potential of evmiRNAs in the field of Environmental Epidemiology. EVs and their content provide an unprecedented, yet easily accessible source of molecular signals that can help us better understand the biological mechanisms involved in linking environmental exposures to certain outcomes.

Background: Lifestyle changed in Kuwait with the rapid development and economic expansion and the Americanization of the Kuwaiti market. Fast food and sedentary lifestyle became very prevalent. Environmental exposures such as passive tobacco smoke and extreme temperatures are common in Kuwait where the prevalence of chronic conditions is increasing. We describe a Kuwait based pregnancy-birth cohort and examine the associations between perinatal exposures and the risk of chronic disease. Methods: We recruited women from antenatal clinics in Kuwait and administered baseline questionnaires then followed the women postnatally. We examined maternal and lifestyle risk factors of gestational diabetes mellitus (GDM). We examined the association between passive tobacco smoke exposure and gestational diabetes, and finally we examined the association between preterm delivery with heat and humidity in Kuwait Results: We successfully enrolled 2,478 women and followed 2,254 to delivery. Overall, frequencies of stillbirth, preterm birth, and small for gestational age were comparable to other developed countries. The incidence of self-reported gestational diabetes was within the expected range worldwide. After past GDM history, pre-pregnancy obesity was the strongest maternal risk factor associated with GDM. We observed patterns suggestive of a positive association between home passive tobacco smoke exposure and GDM among primiparous women. Finally, high relative humidity but not temperature was associated with an increased risk of preterm delivery. Conclusions: We successfully established a large pregnancy birth cohort in Kuwait. There are several social and environmental challenges in Kuwait that may increase the risk of chronic disease such as diabetes, which is already very prevalent in Kuwait. Our results should be replicated and the results used to inform interventions to reduce the rates of chronic disease in Kuwait.

Epidemiological studies have examined the association between PM2.5 mass and mortality, but there remains uncertainty about the relative importance of species. PM2.5 contains various species, such as organic carbon, elemental carbon, and metals. Determining the differential toxicity of PM2.5 species and identifying species with greatest toxicity is of great importance to emission-control strategies and regulations. In the dissertation thesis, effects of PM2.5 species on health outcomes on different levels were estimated. The first study examined the association between PM2.5 species and mortality on approximately 4.5 million deaths for all causes, cardiovascular diseases, myocardial infarction, stroke, and respiratory diseases in 75 U.S. cities for 2000-2006, using city-season specific Poisson regression and multivariate meta-regression controlled for infiltration. Since cardiovascular diseases are leading causes of death within U.S. population, the second study aimed to determine which PM2.5 species are associated with blood pressure, an indicator of cardiovascular health, in a longitudinal cohort. Linear mixed-effects models with the adaptive LASSO penalty were applied to longitudinal data from 718 elderly men in the Veterans Affairs Normative Aging Study (NAS), 1999-2010. Species considered included 8 metals (Fe, K, Al, Ni, V, Cu, Zn, and Na) and 3 non-metals (S, Si, and Se). At last, the relationship between long-term exposure to PM2.5 species and epigenome-wide DNA methylation at 484 613 CpG probes in the longitudinal NAS cohort that included 646 subjects were investigated to explore the potential biological mechanisms on the epigenetic level in study 3. The studies have showed an increased risk of mortality and blood pressure associated with PM2.5, which varied with species, and differential DNA methylation linked to long-term exposure to particular components of PM2.5. In conclusion, mass alone might not be sufficient to evaluate the health effects of particles. Understanding the toxicity of particle components is crucial to public health.

Purpose: This dissertation addressed a gap in homelessness literature by examining mortality outcomes of an unsheltered cohort and by applying criteria developed at the Boston Health Care for the Homeless Program (BHCHP) to predict mortality. Methods: A 10-year prospective study was conducted with 445 unique unsheltered individuals. Data were collected during encounters with BHCHP’s Street Team clinicians, an integrated program providing care to homeless adults living outside. Decedent data were matched to the Massachusetts Department of Public Health death occurrence files. Analyses included describing the cohort and the high-risk criteria, calculating age-standardized all-cause and cause-specific mortality rates and age-stratified rate ratios using two comparison groups: the Massachusetts population and a general homeless cohort, and conducting survival analysis. The same methods were used when the high-risk for mortality was applied and the cohort was divided into a high-risk group and non-high-risk group. Results: During the study, 134 deaths occurred. The average age of death was 53 years old. The cohort was largely white and men. Blacks had a lower rate of death compared to whites. The all-cause mortality rate that was almost 10 times higher than the Massachusetts population and nearly three times higher than the general homeless cohort. The most common causes of death were noncommunicable diseases and causes attributable to substance use. Survival analysis showed low probabilities of survival and high rates of mortality for older age groups, men, and whites. Similar patterns of mortality outcomes were seen when the high-risk for mortality criteria were applied. The high-risk group had higher mortality rates than the non-high-risk group; both groups had higher mortality rates for comparisons to Massachusetts and for most comparisons to the general homeless cohort. Survival analysis showed lower probabilities of survival and higher rate of death for the high-risk group. Conclusions: Deaths occurred prematurely and the leading causes of death were common causes see in the general population. The high-risk for mortality criteria predicted an increased mortality rate. The results were seen despite near-universal access to insurance and care. Future studies are warranted to further understand these health disparities and the social determinants for the unsheltered population.