Humans are exposed to a wide variety of chemicals from different sources, in both environmental and occupational settings. Numerous chemicals have been shown to exert endocrine disrupting properties, affecting normal function of the endocrine system. These are known as endocrine disrupting chemicals (EDCs). EDCs significantly impact public health by contributing to adverse health outcomes, including disrupted hormonal functions, impaired reproductive health, and metabolic diseases. Most of the epidemiological studies examining the adverse health effects of disrupted hormonal functions measure the levels of endogenous hormones and their carrier proteins and therefore may miss hormonal effects of EDCs. The endogenous hormones are traditionally measured by radioimmunoassay, enzyme-linked immunosorbent assay, and tandem mass spectrometry (MS/MS) and therefore lack any information on the biological effects of chemical exposure. As a result, novel methods that simultaneously capture both endogenous and exogenous chemicals modulating the hormone receptor signaling provide a better assessment of the combined effects of chemical exposure on hormonal functions. Herein, we show that the Chemical-Activated LUciferase gene eXpression (CALUX) assay is useful and can be used in epidemiologic research as an alternative method to measure total biological effects of chemical exposures on hormone receptor function. This dissertation aims to assess the effects of chemical exposure and other factors including race/ethnicity, alcohol consumption, and Indigenous American ancestry on hormone receptor bioactivities in human plasma/serum. Chapter 1 provides a review of the broadly relevant literature, including the endocrine system, functions of the hormone receptors, EDCs, factors modulating hormonal functions, and adverse health outcomes associated with EDC exposure. Chapter 2 focuses on a study that applied the estrogen receptor (ER)- and androgen receptor (AR)-mediated CALUX assays to measure serum estrogenic and androgenic bioactivities in workers occupationally exposed to trichloroethylene (TCE). This study not only provides evidence that occupational exposure to chemicals affects hormone receptor function, but it also is the first study to demonstrate that TCE is associated with elevated estrogenic bioactivity, which warrants further research on TCE and the estrogen related pathway. In Chapter 3, the CALUX assays were applied to assess the serum estrogenic, androgenic, and glucocorticogenic bioactivities in formaldehyde (FA) exposed workers. This study indicates that FA exposure does not affect hormone bioactivity measured in exposed workers. These TCE and FA human studies demonstrate the feasibility of CALUX assays on measuring hormone bioactivity in occupationally exposed subjects. Chapter 4 applies the CALUX assay to explore the influence of demographic and lifestyle factors on plasma glucocorticogenic bioactivity in a larger study of 503 women who participated as controls in the San Francisco Bay Area Breast Cancer Study. This study reports that race/ethnicity, alcohol intake and Indigenous American ancestry influence plasma glucocorticogenic bioactivity, which could explain observed disparities in disease outcomes. Finally, in Chapter 5, the main findings of this dissertation are summarized and future research is suggested.

The first genome-wide scans searching for follicular lymphoma (FL) risk factors revealed that a section of chromosome 6 powerfully impacts risk of this disease. Common genetic variants within the human leukocyte antigen (HLA) gene region were shown to be associated with an approximate doubling of individual disease odds. This dissertation aims to concurrently improve the resolution of, expand upon, clarify, and take the first steps in explaining these findings. Chapter 1 provides a review of the broadly relevant literature, including the epidemiology of FL and related lymphomas, the molecular immunology of FL, and the HLA gene region. Chapter 2 is a study making use of the highest possible resolution HLA genotyping methodology for its time, applied to an FL case-control study. This study not only increased our knowledge of known risk factors, it also was the first study to demonstrate an association of FL with variation at HLA-DPB1. Chapter 3 describes the method which will soon be used to localize to a single locus the associations which are ambiguously assigned to several genes. Using pilot data, this study demonstrate the feasibility of performing genetic ancestry matching and HLA imputations on historically stored samples. Chapter 4 uses data from several studies to identify two amino-acid positions, which may themselves explain a substantial portion of FL risk. The fact that these amino acid positions lie in the key peptide binding groove of HLA-DRB1 gives some evidence that peptide binding is the mechanism by which these HLA associations are impacting FL development. Finally, in Chapter 5 the peptide binding properties of HLA class II alleles are computationally investigated, examining potential environmental and internal proteomes likely to be encountered by HLA proteins. This approach reveals that certain alleles which impact FL risk are predicted to be exceptionally strong or weak at binding peptides, and several candidate antigens are mined from the data. Concluding in Chapter 6, the state of HLA-FL research is summarized, and future research is recommended.

Non-communicable diseases (NCDs), including type 2 diabetes (T2D) and breast cancer, account for a vast majority of deaths worldwide. The incidence rates of these morbidities vary widely among different ethnic groups with racial minorities disproportionately affected by these chronic pathologies. Known risk factors among those afflicted with T2D and breast cancer include genetic markers, diet, obesity, and other lifestyle factors. However, these risk factors cannot fully explain the observed incidence rates across different ethnic populations. For migrant populations whose environment is often altered throughout their lifetime, environmental factors play a significant role in the development of chronic diseases. For this reason, approaches that are aimed at identifying non-genetic factors are necessary. This dissertation makes use of an exposome approach known as the receptorome. This methodology was used to investigate differences in hormone receptor activity and their association to breast cancer and T2D in migrant populations. The introduction in Chapter 1 provides an overview of the exposome approach highlighting the role of steroid hormones and environmental mimics in the development of two chronic diseases that disproportionately affect migrant populations. Chapter 2 investigates the association between estrogenic activity and nativity, genetic ancestry, and lifestyle factors among Mexican women. Chapter 3 is an extension of the previous chapter, providing further evidence that ancestry and other breast cancer risk factors may be associated with mechanisms linked through the endocrine system. This study demonstrates the importance of endogenous and exogenous estrogens among different racial/ethnic groups and their potential role in breast cancer incidence rates. Chapter 4 examines hormone receptor activity and the association to T2D and persistent organic pollutants in South Indian Asians and European Whites living in London. Lastly, Chapter 5 summarizes all findings and elucidates a secondary technique, known as metabolomics, to aid in the identification of novel environmental risk factors affecting the incidence rates of NCDs in migrant groups.

The prevalence of type 2 diabetes (T2D) has nearly doubled since 1980. T2D is characterized by hyperglycemia, insulin resistance, and long-term complications. Poor nutrition, sedentary lifestyle, and obesity, are among the strongest risk factors for the development of this metabolic disease. Environmental pollutants however, also have the potential to alter glucose homeostasis and lead to the development of T2D. Arsenic is one of these chemicals, with epidemiologic studies worldwide supporting this association. The precise mechanism of action by which arsenic exhibits its diabetogenic effects however, remains unclear. Since the late 2000s, select heat-producing adipose depots have been identified and shown to be intricately involved in glucose metabolism. Brown and beige adipocytes are important regulators of energy expenditure and both lipid and glucose homeostasis. This dissertation aims to identify whether arsenic increases the risk of T2D development among obese individuals, and identify its effects on thermogenic adipocytes involved in glucose metabolism and energy expenditure. Chapter 1 is a state-of-the-science review of the disruptive effects of arsenic exposure on glucose homeostasis, with an emphasis on findings from experimental studies. Chapter 2 is a cross-sectional analysis of a unique arsenic exposed population in Northern Chile. This chapter examines the effects of arsenic exposure on T2D development, and evaluates whether arsenic and obesity may act synergistically to increase T2D risk. While proposed pathways for arsenic’s role in T2D include alterations in pancreatic β-cell function and insulin secretion, these findings are reported only at high arsenic exposure concentrations. Therefore, further investigation to elucidate arsenic’s diabetogenic molecular targets in mammalian models is required at relevant public health concentrations. Chapter 3 examines the effects of chronic low-dose arsenic exposure on thermogenesis and recruitable beige adipocytes involved in key metabolic pathways in vivo. Chapter 4 informs current statistical methodologies for indirect calorimetry analysis by implementing longitudinal data analysis techniques and randomization-based inference to better capture how environmental chemical exposures alter energy expenditure over time. Lastly, Chapter 5 summarizes the current state of arsenic research within the context of metabolic biology, and highlights how interdisciplinary research has the potential to inform current environmental standards and public health interventions.

Arsenic (As) is a well established cause of cancer in humans, and increasing evidence indicates that As has deleterious effects on the immune system that are not directly related to carcinogenesis. However, the mechanisms of As toxicity remain poorly understood. Our laboratory previously reported decreased urinary levels of human beta-defensin-1 (HBD1) peptides in As-exposed individuals from two cross-sectional studies based in Nevada and Chile, and confirmed in vitro that As exposure suppressed HBD1 mRNA expression which is encoded by the DEFB1 gene. DEFB1 is constitutively expressed in epithelial tissues, plays a role in both the innate and adaptive branches of the immune system, and is implicated in anti-tumor immunity. Therefore, the objectives of this dissertation are to review the immunotoxicological effects of As, characterize the effects of As on DEFB1 gene and protein expression in relevant in vitro model systems, investigate the molecular mechanisms mediating these effects, and explore the influence of other metals on HBD1 levels.

A comprehensive review of the literature on the immune-related effects associated with As exposure in humans, animals and in vitro models reveals that chronic exposure to As can severely impair various aspects of immune function and consequently result in elevated risk of infections and chronic diseases. However, further investigation is needed to better understand the relationship between As exposure and the development of disease, and several recommendations are discussed to help bridge the gaps in knowledge.

The current research investigated the effects of As exposure on DEFB1 in cells derived from target tissues of toxicity using immortalized non-tumorigenic human HOK-16B keratinocytes and HK-2 kidney epithelial cells. DEFB1 mRNA levels were more abundant in HK-2 cells than in HOK-16B cells, and were suppressed by exposure to arsenite (As^III) or monomethylarsonous acid (MMA^III), the postulated more toxic metabolite. The suppressive effect of AsIII and MMA^III treatments on DEFB1 transcript levels continued for several passages after removal of As. HBD1 peptide levels were significantly reduced following exposure to As^III, but were not affected by treatment with lead, cadmium or chromium, suggesting that decreased HBD1 may be a specific response to As. Finally, As^III treatment was found to suppress DEFB1 promoter activity, indicating that the inhibition of DEFB1 mRNA by As is likely due to transcriptional down-regulation. Taken together, the research presented here provides evidence that our previous findings of decreased urinary HBD1 levels are likely due to a direct effect of As on the kidney, and suggest a novel mechanism by which As exposure may promote cancer development.

This dissertation summarizes the known in vivo and in vitro effects of As on the immune system, characterizes the effects of As on DEFB1 using relevant cell culture models, and establishes DEFB1 as a potentially relevant biomarker of response to As. Future studies should address the role of DEFB1 inhibition in As immunotoxicity and carcinogenicity.

The prevalence of type II diabetes (T2D) is escalating worldwide, yet incidence rates differ dramatically between ethnic groups. Some known risk factors of T2D include diet, exercise, and genetic inheritability, yet these factors alone cannot fully explain the differences observed between populations. Better approaches are needed to identify other non-genetic factors, such as toxic chemical exposures, that are related to T2D, particularly in highly-susceptible populations. The exposome is a relatively new concept used to investigate causes of disease due to endogenous and exogenous exposures. This dissertation aims to use semi-targeted exposomics to examine biomarkers of exposure and disease that are associated with T2D. Chapter 1, the introduction, discusses the broader objectives of exposomics, including ideal comparison populations for identifying underlying causes of chronic disease. In the case of T2D, Asian Indians are a population of great interest, with a 3-4-fold higher risk of T2D than European white counterparts. Chapter 2 examines blood concentrations of environmental pollutants in small volumes of plasma in Asian Indian immigrants and a low-risk comparison group, European whites. This study is the first to investigate associations between persistent organic pollutants and T2D in Asian Indians. Chapter 3 describes a method to measure sources of variability in a potential biomarker of T2D, microRNA (miRNA). This study demonstrates the importance of empirically measuring technical and biological sources of variability and using simulations to inform power calculations for new biomarkers of interest. Chapter 4 takes lessons learned from Chapter 3 and applies them to a case-control study on plasma miRNA in Asian Indians. In the concluding Chapter 5, the current state of research on T2D as it relates to blood biomarkers of environmental exposures and disease are described for Asian Indians and other highly susceptible groups.