Ligong Chen

DNA methylation in repetitive elements and post-traumatic stress disorder: a case-control study of US military service members.

AIM We investigated serum DNA methylation patterns in genomic repetitive elements, LINE-1 and Alu, for post-traumatic stress disorder (PTSD) cases and controls who were US military service members recently deployed to Afghanistan or Iraq. METHODS Cases (n = 75) had a postdeployment diagnosis of PTSD. Controls (n = 75) were randomly selected service members with no postdeployment PTSD diagnosis. Pre- and post-deployment sera were accessed, DNA was extracted and DNA methylation (percentage 5-methyl cytosine) was quantified via pyrosequencing. Conditional and unconditional logistic regressions were used to compare: cases post- to pre-deployment; controls post- to pre-deployment; cases to controls predeployment; cases to controls postdeployment. RESULTS LINE-1 was hypermethylated in controls post- versus pre-deployment (odds ratio [OR]: 1.33; 95% CI: 1.06-1.65) and hypomethylated in cases versus controls postdeployment (OR: 0.82; 95% CI: 0.67-1.01). Alu was hypermethylated for cases versus controls predeployment (OR: 1.46; 95% CI: 1.08-1.97). CONCLUSION Patterns of hypermethylation of LINE-1 in controls postdeployment and of Alu in cases postdeployment are intriguing and may suggest resilience or vulnerability factors.

PTSD and DNA Methylation in Select Immune Function Gene Promoter Regions: A Repeated Measures Case-Control Study of U.S. Military Service Members.

Background: The underlying molecular mechanisms of PTSD are largely unknown. Distinct expression signatures for PTSD have been found, in particular for immune activation transcripts. DNA methylation may be significant in the pathophysiology of PTSD, since the process is intrinsically linked to gene expression. We evaluated temporal changes in DNA methylation in select promoter regions of immune system-related genes in U.S. military service members with a PTSD diagnosis, pre- and post-diagnosis, and in controls. Methods: Cases (n = 75) had a post-deployment diagnosis of PTSD in their medical record. Controls (n = 75) were randomly selected service members with no PTSD diagnosis. DNA was extracted from pre- and post-deployment sera. DNA methylation (%5-mC) was quantified at specific CpG sites in promoter regions of insulin-like growth factor 2 (IGF2), long non-coding RNA transcript H19, interleukin-8 (IL8), IL16, and IL18 via pyrosequencing. We used multivariate analysis of variance and generalized linear models to calculate adjusted means (adjusted for age, gender, and race) to make temporal comparisons of %5-mC for cases (pre- to post-deployment) versus controls (pre- to post-deployment). Results: There were significant differences in the change of %5-mC pre- to post-deployment between cases and controls for H19 (cases: +0.57%, controls: −1.97%; p = 0.04) and IL18 (cases: +1.39%, controls: −3.83%; p = 0.01). For H19 the difference was driven by a significant reduction in %5-mC among controls; for IL18 the difference was driven by both a reduction in %5-mC among controls and an increase in %5-mC among cases. Stratified analyses revealed more pronounced differences in the adjusted means of pre-post H19 and IL18 methylation differences for cases versus controls among older service members, males, service members of white race, and those with shorter deployments (6–12 months). Conclusion: In the study of deployed personnel, those who did not develop PTSD had reduced %5-mC levels of H19 and IL18 after deployment, while those who did develop PTSD had increased levels of IL18. Additionally, pre-deployment the people who later became cases had lower levels of IL18 %5-mC compared with controls. These findings are preliminary and should be investigated in larger studies.

Disaster-related exposures and health effects among US Coast Guard responders to Hurricanes Katrina and Rita: a cross-sectional study

Objective: Disaster responders work among poorly characterized physical and psychological hazards with little understood regarding health consequences of their work. Methods: A survey administered to 2834 US Coast Guard responders to Hurricanes Katrina and Rita provided data on exposures and health effects. Prevalence odds ratios (PORs) evaluated associations between baseline characteristics, missions, exposures, and health effects. Results: Most frequent exposures were animal/insect vector (n = 1309; 46%) and floodwater (n = 817; 29%). Most frequent health effects were sunburn (n = 1119; 39%) and heat stress (n = 810; 30%). Significant positive associations were for mold exposure and sinus infection (POR = 10.39); carbon monoxide and confusion (POR = 6.27); lack of sleep and slips, trips, falls (POR = 3.34) and depression (POR = 3.01); being a Gulf-state responder and depression (POR = 3.22). Conclusions: Increasing protection for disaster responders requires provisions for adequate sleep, personal protective equipment, and access to medical and psychological support.

Global DNA methylation and tumor suppressor gene promoter methylation and gastric cancer risk in an Omani Arab population

AIM We carried out a case-control study in an Omani Arab population to investigate the association between gastric cancer and peripheral blood leukocyte DNA methylation in LINE-1 and in the tumor suppressor genes CDH1, p16, TP53 and RUNX3. MATERIALS & METHODS We quantified methylation (%5-mC) in DNA extracted from peripheral blood leukocytes via pyrosequencing. We calculated odds ratios (ORs) and 95% CIs using logistic regression. RESULTS We found patterns of global hypomethylation (LINE-1: OR(continuous) = 0.59; 95% CI: 0.42-0.82) and TP53 promoter hypomethylation (OR(continuous) = 0.64; 95% CI: 0.16-0.85) for cases versus controls; p16 promoter region hypomethylation was not statistically significant. Evaluating LINE-1, TP53 and p16 jointly yielded a more pronounced negative association with gastric cancer (OR: 0.24; 95% CI: 0.09-0.66). Age was a significant effect modifier. We found no differences by tumor grade, stage or histology. CONCLUSION We found a pattern of global hypomethylation and promoter region hypomethylation of TP53 and p16 in cases versus controls for this population of Omani Arabs.

High pesticide exposure events and DNA methylation among pesticide applicators in the agricultural health study

Pesticide exposure has been associated with acute and chronic adverse health effects. DNA methylation (DNAm) may mediate these effects. We evaluated the association between experiencing unusually high pesticide exposure events (HPEEs) and DNAm among pesticide applicators in the Agricultural Health Study (AHS), a prospective study of applicators from Iowa and North Carolina. DNA was extracted from whole blood from male AHS pesticide applicators (n = 695). Questionnaire data were used to ascertain the occurrence of HPEEs over the participants lifetime. Pyrosequencing was used to quantify DNAm in CDH1, GSTp1, and MGMT promoters, and in the repetitive element, LINE‐1. Linear and robust regression analyses evaluated adjusted associations between HPEE and DNAm. Ever having an HPEE (n = 142; 24%) was associated with elevated DNAm in the GSTp1 promoter at CpG7 (chr11:67,351,134; P < 0.01) and for the mean across the CpGs measured in the GSTp1 promoter (P < 0.01). In stratified analyses, elevated GSTP1 promoter DNAm associated with HPEE was more pronounced among applicators >59 years and those with plasma folate levels ≤16.56 ng/mL (p‐interaction <0.01); HPEE was associated with reduced MGMT promoter DNAm at CpG2 (chr10:131,265,803; P = 0.03), CpG3 (chr10:131,265,810; P = 0.05), and the mean across CpGs measured in the MGMT promoter (P = 0.03) among applicators >59 years and reduced LINE‐1 DNAm (P = 0.05) among applicators with ≤16.56 ng/mL plasma folate. Non‐specific HPEEs may contribute to increased DNAm in GSTp1, and in some groups, reduced DNAm in MGMT and LINE‐1. The impacts of these alterations on disease development are unclear, but elevated GSTp1 promoter DNAm and subsequent gene inactivation has been consistently associated with prostate cancer. Environ. Mol. Mutagen. 58:19–29, 2017.

Sickle Cell Trait Prevalence Among U.S. Military Service Members: 1992–2012

BACKGROUND Population-based estimates of sickle cell trait (SCT) prevalence in the U.S. military across services and over time are lacking. METHODS SCT prevalence by service, race/ethnicity, and gender in 5-year time intervals was estimated using demographic, ambulatory, and hospital SCT encounter (International Classification of Diseases, 9th Revision, Clinical Modification 282.5) data for active duty, enlisted between 1992 and 2012 and limited SCT laboratory results. RESULTS Our study identified 15,081 SCT subjects. SCT prevalence varied significantly by race, year, gender, and service branch. SCT prevalence was highest for non-Hispanic blacks (5.02%; prevalence ratio = 56.33, confidence interval [CI] = 52.14-60.85; compared to non-Hispanic white) in 2005-2009 (0.40%; prevalence ratio = 10.04, CI = 9.21-10.94; compared to 1992-1994), for women (2.97%; prevalence ratio = 3.14, CI = 3.04-3.25; compared to men), and in the Navy (2.26%; prevalence ratio = 2.96, CI = 2.84-3.02; compared to Army). Among foreign born, Africans were more likely to be SCT+ (prevalence ratio = 1.68, CI = 1.39-2.04; compared to non-U.S. North American). CONCLUSION This study estimated the prevalence of SCT within U.S. military enlisted force and describes variability across services for race, time intervals, gender, and foreign-born region and will support investigation into the health effects of SCT in young adult populations.

Association Between Sickle Cell Trait With Selected Chronic Medical Conditions in U.S. Service Members

Introduction Sickle cell trait (SCT), the heterozygous carrier state for hemoglobin S, is present in an estimated 1.6% of all newborns and 7.3% in black individuals in the USA. SCT has long been considered a benign condition with anticipated normal life expectancy and no increased risk for chronic diseases. The medical literature is inconclusive on the potential association between SCT and chronic medical conditions (CMC) including chronic kidney disease, venous thromboembolism, and stroke. Studies addressing these questions are lacking particularly in non-Black young adults. Materials and Methods We conducted a retrospective cohort study among U.S. active duty, enlisted, service members who entered from 1992 to 2012 using existing Department of Defense (DoD Military Healthcare System databases). SCT positive subjects (1,323) were matched by demographic characteristics to SCT negative subjects (3,136) and followed through 2013 for CMC that included deep vein thrombosis, diabetes mellitus and hematologic, pulmonary, and renal conditions. Results The rate of developing any of the included CMC was higher for those with SCT (incidence rate ratio = 1.71 95% CI 1.61-1.81) compared with those who were SCT negative and their healthcare utilization rate for any of CMC studied was higher for SCT positive compared with negative individuals (URR = 2.45 95% CI 2.41-2.50), with the highest rate ratios observed for hematologic and renal conditions. SCT positive compared with negative individuals were more likely to have encounter diagnoses of sickle cell disease and diabetes Type II and were less likely to have encounter diagnoses of other hemoglobinopathies and diabetes type I. Conclusion SCT in these racially diverse, young adults increased both the incidence of and healthcare utilization for thromboembolism, diabetes mellitus type II, sickle cell disease, pulmonary, and chronic renal conditions. These findings suggest that clinicians treating young adults with SCT should exercise heightened surveillance for these CMC to ensure both early diagnosis and access to treatments.

The Association Between Sickle Cell Trait in U.S. Service Members with Deployment, Length of Service, and Mortality, 1992–2012

Introduction Sickle cell trait (SCT) affects an estimated 5.02% of non-Hispanic blacks, 1.08% of Hispanics, and 0.1% of Whites in the U.S. military. Policies for SCT screening and occupational restrictions vary by service. Population-based studies of SCT with quantification of military-relevant outcomes are lacking. Methods The study design was a retrospective cohort of 15,081 SCT-positive versus 60,320 SCT-negative U.S. active duty personnel enlisted from 1992 to 2012 and followed through 2013. Military-relevant outcome included number and days of deployment, length of service, and cause of death. Results SCT-positive versus SCT-negative service members experienced more deployments (p < 0.01) and longer number of days deployed for all services, especially the Army (p < 0.001). The median length of service was longer for SCT-positive service members stratified by service and by gender (p < 0.05). The adjusted risk of length of service greater than 5 yr by SCT status was 1.37 (95% confidence interval 1.31-1.43) with greater than a three-fold higher risk in the Navy and Air Force compared with the Army. Crude mortality rate was not significantly different by SCT status, although deaths due to suicide, self-directed violence, and other non-specific causes were more common in SCT-positive service members. Conclusion We found that SCT-positive service members deployed more frequently, for greater lengths of time, and remained in service longer. No significant difference in crude mortality ratio was discovered. Additional research on military-relevant outcomes and a cost-effectiveness analysis of SCT screening practices are needed to inform evidence-based SCT enlistment policies.

Risk of Exertional Heat Illnesses Associated with Sickle Cell Trait in U.S. Military

Introduction A number of studies have found an association between sickle cell trait (SCT) and exertional heat illnesses (EHIs) including heat stroke, a potentially fatal condition. The strength of this association varied across studies, limiting the ability to quantify potential benefits of SCT-screening policies for competitive athletics and military service members. We determined the relative rate and attributable risk of developing EHI associated with being SCT positive and the EHI health care utilization. Methods We conducted a retrospective cohort study among U.S. enlisted, active duty service members during 1992-2012 from the Department of Defense Military Healthcare System databases. All 15,081 SCT-positive individuals and a sample of 60,320 from those considered SCT negative were followed through 2013 for EHI outcomes ranging from mild heat illness to heat stroke. Results The adjusted hazard ratio for EHI in SCT-positive compared with SCT-negative individuals was 1.24 (95% confidence interval 1.06, 1.45). Risk factors for EHI included age over 30 yr at enlistment, female gender, Marine Corps, combat occupations, and enlistment between April and June. An estimated 216 Department of Defense enlistees (95% confidence interval: 147, 370) would need to be screened to identify and potentially prevent one case of EHI. The attributable risk of EHI due to SCT was 33% (95% confidence interval 19, 45%). Conclusion Our findings suggest that SCT screening will identify approximately a third of SCT individuals at risk for EHI, but does not provide definitive evidence for universal compared with selective (e.g., occupational based) in military enlistees. A cost-effectiveness analysis is needed for policy makers to assess the overall value of universal SCT screening to prevent morbidity and mortality in both the military and the collegiate athletic populations.

Pesticide use and LINE-1 methylation among male private pesticide applicators in the Agricultural Health Study

Cancer risk may be associated with DNA methylation (DNAm) levels in Long Interspersed Nucleotide Element 1 (LINE-1), a surrogate for global DNAm. Exposure to certain pesticides may increase risk of particular cancers, perhaps mediated in part through global DNAm alterations. To date, human data on pesticide exposure and global DNAm alterations are limited. The goal of this study was to evaluate alterations of LINE-1 DNAm by pesticides in a variety of classes. Data from 596 cancer-free male participants enrolled in the Agricultural Health Study (AHS) were used to examine associations between use of 57 pesticides and LINE-1 DNAm measured via Pyrosequencing in peripheral blood leucocytes. Participants provided information on pesticide use at three contacts between 1993 and 2010. Associations of ever/never pesticide use and lifetime days of application (years of use × days per year) and LINE-1 DNAm level were assessed using linear regression, adjusting for potential confounders (race, age at blood draw, and frequency of drinking alcohol) and other moderately correlated pesticides. After adjustment, ever application of 10 pesticides was positively associated and ever application of eight pesticides was negatively associated with LINE-1 DNAm. In dose-response analyses, increases in five pesticides (imazethapyr, fenthion, EPTC, butylate, and heptachlor) were associated with increasing LINE-1 DNAm (ptrend < 0.05) and increases in three pesticides (carbaryl, chlordane, and paraquat) were associated with decreasing LINE-1 DNAm (ptrend < 0.05). This study provides some mechanistic insight into the pesticide-cancer relationship, which may be mediated in part by epigenetics.