Browsing by Author "Zhang, Junfeng"

This thesis assesses indoor fine particulate matter (PM2.5) levels in homes in Los Angeles County, California and identifies variables that might impact the effectiveness of High-Efficiency Particulate Air (HEPA) filters in reducing PM2.5 levels in residential settings. While research has confirmed that HEPA filters effectively reduce PM in controlled environments, additional research is needed to understand how well HEPA filters work in residential and commercial settings. For this study, twelve homes in Los Angeles County had either HEPA filters (n=6) or sham filters installed in their bedrooms and living rooms for six months. All twelve homes had indoor and outdoor air pollution sensors installed to monitor and report hourly PM2.5 levels. Results showed varying degrees of HEPA filter effectiveness in each home. One home experienced a reduction in the geometric mean PM2.5 from 6.99 (2.13) µg/m3 during the pre-filter period to 3.2 (2.2) µg/m3 during the filter period; four homes experienced reductions between 0.51 and 1.33 µg/m3; one home experienced a 0.09 µg/m3 increase. In homes with sham filters, all experienced increases in PM2.5 between 0.22 and 1.76 µg/m3. I identified temporal patterns in indoor and outdoor PM2.5 levels and investigated whether housing characteristics and behavior patterns influence the concentration of PM2.5 and the indoor/outdoor (I/O) ratio of particles. A relationship is seen between dramatic spikes in outdoor pollution during events such as the 4the of July and indoor PM2.5 levels. While this is a small study, results from this can be used to inform future study design and best practices for HEPA filter use.

Background - Multiple research studies have demonstrated consistent associations between particulate matter smaller than 2.5 µm in diameter (PM2.5) and relevant health endpoints of Type 2 Diabetes Mellitus (T2DM) and metabolic syndrome (MS). Patients with pre-diabetes symptoms constitute a significant population who not only have the risk of progressing to diabetes but also are susceptible to metabolic syndrome. Evidence suggests that response to acute PM2.5 exposure could be assessed by monitoring metabolic clinical indices.

Method – This Beijing panel study had a total of 114 subjects divided equally into two groups: pre-diabetic and healthy groups. Inter-group differences in clinical indices (blood pressure, fasting blood glucose) responding to pre-24 hours PM2.5 exposure were assessed using mixed-effects linear regression models.

Results – With a limited sample size and partial data available to the current analysis, this study reveals no significant association of PM2.5 with fasting blood glucose or blood pressure in both healthy and pre-diabetic populations.

Conclusions – Our data did not provide evidence that PM2.5 exposure has significant association with blood pressure or fasting blood glucose. Moreover, no significant response differences were observed existed between the pre-diabetic population and the healthy population.

It has been commonly accepted until recently that particulate matter (PM) is responsible for the cardiovascular toxicity of air pollution mixtures, while ozone (O3) mainly adversely affects respiratory health. However, there is increasing evidence that O3, independent of PM, is also associated with cardiovascular hospitalizations and mortality, even at levels below current regulatory standards. The mechanisms underlying these epidemiological associations between O3 and cardiovascular disease remain poorly understood. The goal of this dissertation research is to use human biomarker outcomes in real-world exposure scenarios to elucidate plausible mechanisms by which O3 affects cardiovascular health.

The findings of this dissertation research are primarily based on a single longitudinal cohort study designed to assess biomarker associations with time-activity-adjusted air pollutant exposures and with indoor air purification interventions, specifically different combinations of a high efficiency particulate air (HEPA) filter and a particle-removing and O3-producing electrostatic precipitator (ESP). Eighty-nine healthy participants living on a work campus in Changsha City, China were recruited for this study conducted from December 1st, 2014 - January 31st, 2015. The unique quasi-experimental setting of participants all living and working together on a work campus allowed for better characterization of air pollutant exposure effects due to minimal variation in potential confounders. At baseline, workers had a combination of an ESP and a HEPA in the central air handling units (AHUs) of their work and living spaces. During a five-week intervention period from December 6th, 2014 to January 13th, 2015, subjects were split into two groups, both of which had the ESPs turned off and one of which also had the HEPAs removed, and after this intervention original conditions were restored. Biomarkers indicative of inflammation and oxidative stress, arterial stiffness, myocardial function, blood pressure, thrombotic factors, and spirometry were measured at four sessions, one at baseline, two at two and four weeks into the intervention period, and one two weeks after restoring baseline conditions post-intervention. Indoor and outdoor O3 and PM of less than or equal to 2.5 µm in diameter (PM2.5), along with ambient co-pollutants NO2 and SO2, were monitored throughout the study period and combined with time-activity information and filtration conditions of each residence and office. These data were used to estimate 24-hour and 2-week combined indoor and outdoor average exposure concentrations, in addition to exposures in filtered and unfiltered environments.

To test the hypothesis that air pollutant exposures observed during this study would be associated with biomarker outcomes, associations between each exposure measure and biomarker were analyzed with single- and two-pollutant linear mixed models. The 24-hour mean O3 exposure concentrations during the study ranged from 1.4 to 19.4 ppb, corresponding with daily 8-hour maximum outdoor concentrations ranging from 3.6 to 60.5 ppb, with all but six days during the study period falling below the WHO 8-hour mean O3 guideline of 50 ppb6. Within this range, in models controlling for a second co-pollutant and other potential confounders, a 10 ppb increase in 24-hour O3 was associated with mean percent increases (95% CIs) of 36.3% (29.9%, 43.0%) in the platelet activation marker soluble P-selectin (sCD62P), 2.8% (0.6%, 5.1%) in diastolic blood pressure (DBP), and 18.1% (4.5%, 33.5%) and 31.0% (0.2%, 71.1%) in the pulmonary inflammation markers fractional exhaled nitric oxide (FeNO) and exhaled breath condensate nitrite and nitrate (EBCNN), respectively, as well as a -9.5% (-17.7%, -1.4%) decrease in arterial stiffness marker augmentation index (AI) and a -15.5% (-23.8%, -6.2%) decrease in the systemic oxidative stress marker urinary malondialdehyde (UMDA). A 10 ppb increase in 2-week O3 was associated with increases of 61.1% (37.8%, 88.2%) in sCD62P and 126.2% (12.1%, 356.2%) in EBCNN. In contrast, PM2.5, NO2, and SO2 exposure measures were variably and weakly associated with markers indicating increased arterial stiffness and endothelial cell dysfunction. Only the O3 associations with sCD62P are robust in two-pollutant models and multiple testing p-value correction. These results suggest that O3 exposure enhances cardiovascular disease risk through platelet activation and blood pressure increases at levels lower than those capable of affecting lung function.

To examine if the removal of HEPA filtration and ESP in the indoor air purification systems were associated with changes in biomarker outcomes, Bayesian hierarchical generalized ridge regression (GRR) models accounting for subject-specific intercept random effects were used to assess associations between categorical intervention variables while controlling for cumulative pollutant exposures in unfiltered microenvironments, namely outdoors and places other than the offices and dorms. The GRR models allowed for more stable maximized likelihood estimates when model predictors were highly correlated. When factoring in time-activity patterns, subjects without HEPA filtration had total 24-hour PM2.5 exposures on average 37.9 µg/m3 (88.3%) higher than subjects with HEPA filtration, and the removal of the ESPs resulted in a small average reduction of 2.2 ppb (a 32.8% decrease as compared to the overall mean 24-hour O3 exposure) in each subject’s total 24-hour O3 exposure. Despite this large change in PM2.5 exposure, no biomarkers were associated with HEPA removal in any models, but ESP removal was associated with decreases of -17.1% (-23.1%, -11.3%) in sCD62P, -3.6% (-5.5%, -1.4%) in systolic blood pressure (SBP), and -3.3% (-5.9%, -0.7%) in DBP. In addition, though subjects spent an average of 64.5% of their time in filtered locations during each two-week period between sampling visits, cumulative air pollutant exposure in unfiltered environments was associated with increased sCD62P for O3, increased FeNO for PM2.5, and increased EBC MDA and decreased subendocardial viability ratio (SEVR, a marker of myocardial oxygen supply and demand) for SO2. This study suggests that ESP use may result in O3-associated adverse health effects, biomarkers traditionally associated with PM exposure may not show a response weeks into an intervention, and time spent in environments filtered by particulate air filters, though perhaps not ESPs, should be maximized to avoid the health effects of cumulative high exposures in unfiltered locations.

These O3 associations with platelet activation and blood pressure are consistent with related results in some studies but not others, and so I hypothesized that age and sex may influence each individual’s response to O3 and account for some of this variability. I tested this hypothesis by assessing pollutant exposure by age or by sex interaction term estimates in association with biomarker outcomes in the GRR models. This statistical analysis was applied not only to the main study conducted in Changsha, but also to a subsequent study conducted in Shanghai with similar exposure and biomarker measurements that had younger study participants with more balanced sex ratio. In addition, the exposure and biomarker data between these two studies were pooled for an additional analysis checking the results from the individual study findings. In the main Changsha Study, significant age by pollutant exposure interaction terms were observed for the associations between 24-hour and 2-week O3 and sCD62P, 2-week O3 and SBP, and 2-week SO2 and PWV. In addition, the association between PWV and 2-week SO2 was significantly higher in men, and the association between PWV and 24h O3 was significantly higher in women, though the latter interaction term became nonsignificant in a sensitivity analysis assessing the independent interaction effect. No interaction terms were significant in the Shanghai Study analysis. In the pooled analysis, the 24-hour O3 exposure by age interaction term was significant for both sCD62P and SBP. Also, the pooled analysis showed that women had a significantly higher association between 24-hour O3 exposure and PWV as had been seen in the Changsha Study, but as in that case this association was not robust to the sensitivity analyses. These results indicate that older individuals are more susceptible to O3-associated effects on platelet activation and blood pressure, which is supported by literature examining age-associated changes in platelets and vascular tone.

Taken together these results and the findings in previous research examining cardiovascular pathophysiologic mechanisms, a coherent, plausible mechanistic pathway emerges. In this pathway, O3-associated reaction products in the airway lead to the propagation of signals that activate platelets, which in turn enhance blood pressure and induce a procoagulant state. The findings of this dissertation contribute to the mechanistic understanding of how O3 exposure affects cardiovascular health outcomes.

Background and Aims Exposure to air pollution has been associated with increased risks of cardiopulmonary diseases, cancer, and mortality. Simultaneously, greenspace has also documented to be protective of mortality. Oxidative stress may be an intermediate biomarker in these processes. There has been little investigation on the effects of residential greenness and air pollution on oxidative stress. There are two aims of this study: 1) To explore the association of personal and ambient air pollution exposure with urinary oxidative stress levels; 2) To investigate the association of quantified-contemporary greenness with urinary oxidative stress levels and the interaction between greenness and air pollution exposure in affecting oxidative stress levels, respectively.

Methods In an existing panel study named AIRLESS (Effects of AIR pollution on cardiopuLmonary disEaSe in urban and peri-urban reSidents in Beijing), 123 residents living in an urban district (Haidian district) and 128 residents in a peri-urban district (Pinggu) of Beijing participated in the study. All participants were non-smokers, ≥ 49 years of age, and included 110 men and 140 women. Personal and ambient exposures to air pollutants were assessed for each participant during winter 2016 and summer 2017, respectively. Each participant was instructed to carry a validated personal air monitor (PAM) to measure particulate matters (PM1, PM2.5, and PM10), nitrogen dioxide, carbon monoxide, and ozone concentrations at a high spatiotemporal resolution seven consecutive days in each sampling season. We calculated contemporaneous green space coverage level by the average daily satellite-derived Normalized Difference Vegetation Index (NDVI) in the zone with 500m*500m grids by Google Earth Engine (GEE) using the Moderate-resolution Imaging Spectroradiometer (MODIS) dataset from NASA (National Aeronautics and Space Administration). We used the coordinates of the ambient air pollution monitoring stations and monitoring dates to match the NDVI data. Multiple oxidative stress biomarkers were measured, including urinary free malondialdehyde (MDA), urinary total MDA, and urinary 8-hydroxydeoxyguanosine (8-OHdG). All biomarkers were normalized by urinary creatinine in statistical analyses. Due to the right skewness, all biomarkers data were ln-transformed in the aim-specific analyses. (1) The association of personal and ambient air pollution exposure with the percent change of urinary oxidative stress biomarkers was estimated using linear mixed-effects models and the distributed lag linear model was used to investigate daily air pollutants’ hysteresis effects on the percent change of urinary oxidative stress biomarkers. (2) The association between tertiary NDVI with urinary oxidative stress biomarkers was estimated using linear mixed-effects regression and subgroup analysis was used to test the robustness of the association between quantified NDVI with the mean percent change of oxidative stress biomarkers using the linear mixed-effects model in different groups. (3) To explore the interaction between greenness and air pollution in affecting oxidative stress by each of these exposure variables, stratified analyses were conducted to examine whether air pollution exposure modifies the effect of greenness and whether greenness modifies the effect of air pollution. Tertiles of NDVI, personal PM2.5 exposure, and personal ozone exposure were used in these analyses.

Results We found positive associations of CO and ozone personal exposure, respectively, with percent change of the three oxidative stress biomarkers. The association tended to be significant only in the ozone model with the percent change of 8-OHdG [8.69% 95%CI: (2.98,14.39), p-value=0.004]. However, in the models of ambient air pollution, some non-significantly negative associations were observed. Consistent positive associations of ambient lag 1- and 2- day CO exposure with the percent change in levels of each of the three oxidative stress biomarkers were weakly persisted. However, the positive associations remained significant between CO exposure and total MDA (p value=0.033) only in lag2-day. In the analyses of greenness as the exposure variable, we observed that individuals who lived in greener areas tended to have lower levels of oxidative stress. Participants in the highest NDVI tertile (0.36-0.83) had significantly lower free and total MDA levels, mean and (95%CI) by -20.21% (-37.84%, -1.30%) and -17.77% (-32.89%, -2.16%), respectively, compared to the lowest NDVI tertile (0.11-0.25) (p-value =0.028). In the urban area, we found significant negative associations of NDVI with free MDA (p-=0.003), total MDA (p =0.005), and 8-OHdG (p=0.022), but not in the peri-urban area. In the modification (interaction) analyses, we observed negative estimates of quantified NDVI associated with each of the three biomarkers in the low personal ozone exposure group (Ozone≤18.7 ppb). We also observed negative estimates of quantified NDVI associated with free and total MDA in the low PM2.5 exposure group (PM2.5≤32μg/m3). In addition, we observed significant effects of personal ozone exposure on 8-OHdG [17.77 95%CI: (8.04, 27.56), p value=0.010]; personal CO exposure on free MDA [12.48 95%CI: (3.15, 21.85), p value=0.012 and total MDA [9.06 95%CI: (1.28, 16.64), p value=0.021] only in participants falling in the lowest NDVI tertile; and the positive associations were no longer significant in participants with higher tertiary NDVI.

Conclusion The protective effects of greenness on oxidative stress, especially in urban residents, elucidates the importance of green space in the urban built environment. Additionally, the adverse effects of air pollution exposure on oxidative stress indicates the noteworthiness of personal protection against air pollution exposure in urban residents.

The World Health Organization (WHO) estimated that 92% of the world’s population lived in areas with outdoor air pollution levels exceeding the WHO guidelines in 2014. Although the ultimate solution is to control emission sources, exposure reduction strategies at the individual level can address more immediate needs. As people typically spend approximately 80% of their time indoors, improvement of indoor air quality, such as using air filtration technologies, may lead to reduced total exposure. However, evidence is limited to support the effectiveness of air filtration in bringing beneficial health effects to the users. The goal of this dissertation research is to evaluate the health impact of indoor air filtration in healthy adults and asthmatic children using two randomized, double-blind, crossover trials (Aim 1 and Aim 2). Utilizing data from these two trials and other data, this dissertation also addresses two methodological questions. Aim 3 examines the relationship between free and total malondialdehyde, a biomarker of oxidative stress commonly used in air pollution research, in various types of human specimens. Aim 4 evaluates the relationship between the subjective evaluation of asthma control by childhood asthma control test (C-ACT) and objective indicators of lung pathophysiology using longitudinal measurements.

In Aim 1 of this dissertation, a double-blinded, randomized, crossover study was conducted to examine the cardiorespiratory health effect of a sporadic, overnight use of indoor air filtration. Seventy healthy non-smoking adults were recruited from the medical and nursing students who were living in the same dormitory building in a suburb of Shanghai, China. The participants were aged 19 to 26 years old and included 41 (59%) females. Each participant received a true and a sham indoor air filtration session in a randomized sequence. Participants and research staff that performed health assessments were blinded to this sequence until the end of the study. Each filtration session was approximately 13 hours long. True and sham filtration sessions were separated by a two-week “washout” interval. During the study period, outdoor PM2.5 concentrations ranged from 18.6 to 106.9 µg/m3, which overlapped with levels measured in Western Europe and North America. Compared to sham filtration, true filtration on average decreased indoor PM2.5 concentration by 72.4% to 10.0 µg/m3 and particle number concentration by 59.2% to 2316/cm3. For lung function measured immediately after the end of filtration, true filtration significantly lowered airway impedance at 5 Hz (Z5) by 7.1% [95% CI: 2.4%, 11.9%], airway resistance at 5 Hz (R5) by 7.4% [95% CI: 2.4%, 12.5%], and small airway resistance (R5-R20) by 20.3% [95% CI: 0.1%, 40.5%], reflecting improved airway mechanics especially for the small airways. However, no significant improvements for spirometric indicators of lung function (FEV1, FVC) were observed. True filtration also significantly lowered von Willebrand factor (VWF) by 26.9% [95% CI: 7.3%, 46.4%] 24 hours after the end of filtration, indicating reduced risk for thrombosis. Stratified analysis in male and female participants showed that true filtration significantly decreased pulse pressure by 3.3% [95% CI: 0.8%, 7.4%] in females, and significantly reduced VWF by 42.4% [95% CI: 17.4%, 67.4%] and interleukin-6 by 22.6% [95% CI: 0.4%, 44.9%] in males. Effect modification analyses indicated that filtration effects in male and female participants were not significantly different. These findings suggest that a single overnight residential air filtration, capable of reducing indoor particle concentrations substantially, can lead to improved airway mechanics and reduced thrombosis risk.

Air pollution exposure is a well-established risk factor for asthma exacerbation. In individuals with asthma, indoor air filtration has only been evaluated for allergen removal in areas with low outdoor levels of PM2.5. As asthmatic individuals may be responsive to short-term changes in air pollution levels, it is not clear whether the exposures occurring outside the home environment can override the potential health benefits of residential indoor air filtration. In Aim 2 of this dissertation, I investigated the respiratory impact of residential indoor air filtration in asthmatic children living with moderate levels of outdoor PM2.5. This double-blind, randomized crossover trial recruited 43 participants (40% females) aged 5 to 13 with mild or moderate asthma. From February to April 2017, each participant used a true filtration device and a sham filtration device, respectively in their bedrooms for two weeks. A two-week washout period separated the two sessions. During the study, the average PM2.5 concentrations for outdoor, indoor with sham filtration, and indoor with true filtration were 56.5 µg/m3, 34.1µg/m3, and 14.8 µg/m3, respectively. Compared to sham filtration, on average, true filtration reduced indoor PM2.5 concentrations by 53.3%. Concomitantly, true filtration significantly decreased fractional exhaled oxide (FeNO) by 5.1 [95% CI: 0.5, 9.6] ppb, airway impedance at 5Hz (Z5) by 14.7% [3.7%, 25.8%], respiratory resistance at 5Hz (R5) by 22.4% [9.6%, 35.2%], and small airway resistance (R5-R20) by 40.6% [10.2,% 70.9%]. Peak expiratory flow (PEF) measurements were made twice daily throughout each two-week intervention session. PEF values during true filtration were 1.5% [0.7%, 2.4%] higher than the measurements during sham filtration. True filtration also introduced a non-significant increase on FEF25-75 by 5.80% [-4.09%, 15.68%]. Stratified analyses show that the participants with blood eosinophil count ≤ 500/mm3, compared to those with blood eosinophil count > 500/mm3, had a 24.3% greater increase of FEF25-75 by true filtration; and that the participants allergic to dust mite had smaller improvements in small airway resistance (R5 and R5-R20). These findings suggest that a two-week long intervention of indoor air filtration, capable of significantly reducing indoor PM2.5 concentrations, can lead to reduced respiratory inflammation, improved lung function (PEF) and airway mechanics in asthmatic children.

Oxidative stress is a core mechanism involved in the cardiorespiratory effects of air pollution. Malondialdehyde (MDA) is a well-established marker of oxidative stress. However, most of its use in existing studies were conducted by researchers in clinical medicine and epidemiology, who were unaware that MDA is present in both unconjugated and conjugated forms. Aim 3 of this dissertation examined the relationship between free MDA (unconjugated MDA) and total MDA (the sum of both unconjugated and conjugated MDA) in various types of human biospecimens. Using bio-banked samples from multiple studies, free MDA and total MDA were measured simultaneously in nasal fluid (N=158), saliva (N=158), exhaled breath condensate (N=40), serum (N=232), and urine samples (N=429). MDA quantification was performed using an HPLC-fluorescence method with high sensitivity and specificity. Due to the right-skewed distribution of free MDA and total MDA, natural-log transformation was performed before subsequent statistical analyses. The relationship between the natural log of free and total MDA was evaluated by R2 of simple linear regression. T-test was used for comparisons of means between two groups. One-way analysis of variance was used in combination with Tukey’s test to compare the natural log of the ratio of free MDA to total MDA across various types of biospecimens. For exhaled breath condensate, serum, urine, nasal fluid and saliva samples, the R2 between free and total MDA were 0.61, 0.22, 0.59, 0.47 and 0.06, respectively; the medians of the free MDA to total MDA ratio were 48.1%, 17.4%, 9.8%, 5.1% and 3.0%, respectively. The free MDA to total MDA ratio in EBC > serum > urine > nasal fluid > saliva (P<0.001 for pairwise comparisons). These findings indicate that, for exhaled breath condensate and urine samples, using either free or total MDA can provide information regarding the level of oxidative stress; however, that is not the case for serum, nasal fluid, and saliva, given the low correlations between free and total MDA. For these types of biospecimens, future research is needed to examine which form of MDA better reflects oxidative stress, in a mechanistic fashion. Given these findings, free MDA in urine samples was measured in the Aim 1 study.

The Childhood Asthma Control Test (C-ACT) is a validated questionnaire that provides a subjective evaluation of asthma control using collective inputs from children and their caregivers. Cross-sectional studies have identified cut-points for discerning different degrees of asthma control. However, few studies have examined whether changes in the C-ACT score are reflective of changes in airway pathophysiology in longitudinal measurements from the same individuals. In Aim 4 of this dissertation, I utilized data from four clinical visits originally conducted for Aim 2. The clinical visits were scheduled bi-weekly over a period of six weeks. Thirty-seven children aged 5 to 10 with mild or moderate asthma (43% female) took the C-ACT. The scores were 24.4 ± 2.4 (mean ± standard deviation) and ranged from 16 to 27. Linear mixed-effects models were used to examine the association between C-ACT and clinical measurements from the same participants. As a change of two points in the C-ACT score is considered as the minimal clinically important difference, I reported the change in biomarkers associated with a two-point decrease in C-ACT score. Results showed that a two-point decrease was significantly associated with a 1.7% [95% CI: 0.1%, 3.3%] decrease in FEV1, a 1.6% [0.5%, 2.8%] decrease in FVC, and a 3.8% [0.0%, 7.6%] increase in airway resistance at 5 Hz (R5). For PEF measurements conducted within two weeks before the C-ACT, a two-point decrease in C-ACT score was significantly associated with a 17.3% [95%CI: 6.8%, 27.8%] increase in the coefficient of variation, while no significant association was observed with the average PEF value (P=0.12). In contrast, within-participant measurements showed no significant associations of C-ACT with respiratory inflammation (FeNO) or any of the small airway function and mechanics parameters (FEF25-75, FEF25-75, R5-R20, X5, and Fres). When examining individual questions of the C-ACT, none of the questions answered by the caregiver were significantly associated with indicators of lung function and respiratory inflammation. In contrast, three out of the four questions answered by the child demonstrated significant or marginally significant associations with FEV1, FVC, FEF25-75, R5, and R20. This suggests that in spite of the relatively young age of the participants, their perception of disease control provides important information for asthma control assessment. Overall, the findings in Aim 4 indicate that subjective evaluation of asthma control using the C-ACT was associated with objective measurements of airway obstruction, airway restriction, respiratory resistance and the variation of airflow limitations in longitudinal measurements. However, the C-ACT is not reflective of changes in respiratory inflammation and small airway mechanics, indicating that its use should be complementary to but not a substitute for these measurements.

AbstractIt is widely accepted that the pathophysiologic pathways linking air pollution exposure and adverse health effects are via the augmentation of oxidative stress and inflammation in the respiratory tract and the circulatory system. Melatonin is a potent antioxidant and anti-inflammatory molecule and may thereby affect individuals’ biological responses to air pollution exposure. This dissertation aims to investigate the role of melatonin in pathophysiological responses to air pollution exposure. In Aim 1 of this dissertation research, a method was developed to simultaneously measure urinary concentrations of 6-sulfatoxymelatonin (aMT6s) and 8-hydroxy-2'-deoxyguanosine (8-OHdG). As a major metabolite of melatonin excreted in the urine, aMT6s has been widely used as a surrogate of circulating melatonin. Urinary 8-OHdG, a stable product of DNA oxidative damage, has been used as an oxidative stress biomarker. This new method is expected to have important applications in biomedical and environmental health studies involving the oxidative stress pathophysiological pathway. In Aim 2 of this dissertation research, the role of melatonin in oxidative stress responses to air pollution exposure was examined. Stored urine samples collected from 159 healthy adults, and their personal air pollution exposure data were used. These urine samples were analyzed for aMT6s and 8-OHdG; and statistical analyses were conducted to examine the relationships among aMT6s, 8-OHdG and another previously measured urinary oxidative stress biomarker, malondialdehyde (MDA), and pollutant exposures. The results of this analysis suggest the need for controlling for aMT6s as a confounder in using urinary 8-OHdG and MDA as biomarkers of oxidative stress related to short-term air pollution exposure. In Aim 3 of this dissertation research, the role of melatonin in inflammatory responses to air pollution exposure was examined. Blood inflammatory cytokines and urinary aMT6s were measured in 53 healthy adults three times within 2 consecutive months. Personal air pollution exposure was calculated prior to biospecimen collections. The study found that concentrations of proinflammatory cytokines were significantly and negatively associated with O3 exposures averaged over the preceding 12 hours while significantly but positively associated with O3 exposures averaged over the preceding 2 weeks. These findings suggest that exposure to O3 for different time durations may affect systemic inflammatory responses in different ways. In addition, the study found that pro-inflammatory responses to O3 exposure in the preceding 2 weeks may partly result from the depletion of endogenous melatonin by O3. In Aim 4 of this dissertation research, the role of melatonin in pathophysiologic and oxidative stress responses to air pollution exposure in asthmatic children was examined. Urine, nasal fluid, and pulmonary physiology data were obtained from 43 asthmatic children four times with a 2-week interval between the consecutive clinic visits. At each visit, pulmonary physiology indicators, comprised of airway mechanics, lung function, airway inflammation, and asthma symptom scores were measured. Stored urine samples were analyzed for aMT6s, 8-OHdG, and MDA; stored nasal fluid samples were analyzed for MDA. Personal exposures to PM2.5 and O3 prior to a health outcome measurement were calculated. Three major analyses were conducted in the Aim 4 study. First, the associations of personal air pollutant exposures with the indicators of pulmonary physiology were examined. The results show that daily changes in personal exposure to PM2.5 were associated with significantly increased small airway resistance, total airway resistance, and airway inflammation (fractional exhaled nitric oxide, FeNO). The findings suggest the importance of reducing personal exposure to PM2.5 as part of the asthma management plan to improve airflow limitation. Second, statistical analyses were conducted to examine the relationships among personal pollutant exposures, nasal fluid MDA, urinary 8-OHdG, urinary MDA, FeNO, and asthma symptom scores. The results showed that increased personal exposures to PM2.5 and O3 exposure were both associated with increased nasal MDA concentrations and worsened asthma symptom scores. Increased nasal MDA concentration was associated with decreased asthma symptom scores indicating worsening of asthma symptoms. These findings support that MDA in the nasal fluid may serve as a useful biomarker for monitoring asthma status, especially in relation to PM2.5 and O3 exposure, two known risk factors of asthma exacerbation. Third, statistical analyses were conducted to investigate the relationship of urinary aMT6s with personal air pollutant exposures, biomarkers of oxidative stress, and indicators of pulmonary physiology. The results showed that increasing urinary MDA or 8-OHdG concentration and personal exposures to PM2.5 and O3 were associated with increased urinary aMT6s concentrations in asthmatic children. We also found that increased concentration of urinary aMT6s was associated with improved pulmonary inflammation and airway resilience. The results suggest a potential biological mechanism that increased systemic oxidative stress may stimulate the excretion of melatonin as a defense mechanism to alleviate the adverse effects of air pollution exposure. In summary, the findings from this dissertation research support that endogenously generated melatonin can modulate oxidative, inflammatory, and physiological responses to air pollution exposure in a beneficial way. This dissertation research supports the need for future trials to assess the efficacy or effectiveness of using melatonin supplementation to mitigate the adverse health effects of air pollution exposure at the individual level. This is particularly important for susceptible populations living in highly polluted areas (e.g., developing countries and regions subject to frequent wildfires), people with melatonin deficiency, and those using dirty household fuels.