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1.  The Peroxisomal Proliferator-Activated Receptor (PPAR) α Agonist, Fenofibrate, Prevents Fractionated Whole-Brain Irradiation-Induced Cognitive Impairment 
Radiation research  2014;181(1):33-44.
We hypothesized that dietary administration of the peroxisomal proliferator-activated receptor α agonist, fenofibrate, to young adult male rats would prevent the fractionated whole-brain irradiation (fWBI)-induced reduction in cognitive function and neurogenesis and prevent the fWBI-induced increase in the total number of activated microglia. Eighty 12–14-week-old young adult male Fischer 344 × Brown Norway rats received either: (1) sham irradiation, (2) 40 Gy of fWBI delivered as two 5 Gy fractions/week for 4 weeks, (3) sham irradiation + dietary fenofibrate (0.2% w/w) starting 7 days prior to irradiation, or (4) fWBI + fenofibrate. Cognitive function was measured 26–29 weeks after irradiation using: (1) the perirhinal cortex (PRh)-dependent novel object recognition task; (2) the hippocampal-dependent standard Morris water maze (MWM) task; (3) the hippocampal-dependent delayed match-to-place version of the MWM task; and (4) a cue strategy preference version of the MWM to distinguish hippocampal from striatal task performance. Neurogenesis was assessed 29 weeks after fWBI in the granular cell layer and subgranular zone of the dentate gyrus using a doublecortin antibody. Microglial activation was assessed using an ED1 antibody in the dentate gyrus and hilus of the hippocampus. A significant impairment in perirhinal cortex-dependent cognitive function was measured after fWBI. In contrast, fWBI failed to alter hippocampal-dependent cognitive function, despite a significant reduction in hippocampal neurogenesis. Continuous administration of fenofibrate prevented the fWBI-induced reduction in perirhinal cortex-dependent cognitive function, but did not prevent the radiation-induced reduction in neurogenesis or the radiation-induced increase in activated microglia. These data suggest that fenofibrate may be a promising therapeutic for the prevention of some modalities of radiation-induced cognitive impairment in brain cancer patients.
PMCID: PMC4144193  PMID: 24397438
The annals of applied statistics  2014;8(2):1232-1255.
Gene/pathway-based methods are drawing significant attention due to their usefulness in detecting rare and common variants that affect disease susceptibility. The biological mechanism of drug responses indicates that a gene-based analysis has even greater potential in pharmacogenetics. Motivated by a study from the Vitamin Intervention for Stroke Prevention (VISP) trial, we develop a gene-trait similarity regression for survival analysis to assess the effect of a gene or pathway on time-to-event outcomes. The similarity regression has a general framework that covers a range of survival models, such as the proportional hazards model and the proportional odds model. The inference procedure developed under the proportional hazards model is robust against model misspecification. We derive the equivalence between the similarity survival regression and a random effects model, which further unifies the current variance-component based methods. We demonstrate the effectiveness of the proposed method through simulation studies. In addition, we apply the method to the VISP trial data to identify the genes that exhibit an association with the risk of a recurrent stroke. TCN2 gene was found to be associated with the recurrent stroke risk in the low-dose arm. This gene may impact recurrent stroke risk in response to cofactor therapy.
PMCID: PMC4091797  PMID: 25018788
association study; gene/pathway; pharmacogenetics; similarity regression; survival data; proportional odds model; proportional hazard model
3.  Prediction of mortality using a multi-bed vascular calcification score in the Diabetes Heart Study 
Cardiovascular Diabetology  2014;13(1):160.
Vascular calcified plaque, a measure of subclinical cardiovascular disease (CVD), is unlikely to be limited to a single vascular bed in patients with multiple risk factors. Consideration of vascular calcified plaque as a global phenomenon may allow for a more accurate assessment of the CVD burden. The aim of this study was to examine the utility of a combined vascular calcified plaque score in the prediction of mortality.
Vascular calcified plaque scores from the coronary, carotid, and abdominal aortic vascular beds and a derived multi-bed score were examined for associations with all-cause and CVD-mortality in 699 European-American type 2 diabetes (T2D) affected individuals from the Diabetes Heart Study. The ability of calcified plaque to improve prediction beyond Framingham risk factors was assessed.
Over 8.4 ± 2.3 years (mean ± standard deviation) of follow-up, 156 (22.3%) participants were deceased, 74 (10.6%) from CVD causes. All calcified plaque scores were significantly associated with all-cause (HR: 1.4-1.8; p < 1x10−5) and CVD-mortality (HR: 1.5-1.9; p < 1×10−4) following adjustment for Framingham risk factors. Associations were strongest for coronary calcified plaque. Improvement in prediction of outcome beyond Framingham risk factors was greatest using coronary calcified plaque for all-cause mortality (AUC: 0.720 to 0.757, p = 0.004) and the multi-bed score for CVD mortality (AUC: 0.731 to 0.767, p = 0.008).
Although coronary calcified plaque and the multi-bed score were the strongest predictors of all-cause mortality and CVD-mortality respectively in this T2D-affected sample, carotid and abdominal aortic calcified plaque scores also significantly improved prediction of outcome beyond traditional risk factors and should not be discounted as risk stratification tools.
Electronic supplementary material
The online version of this article (doi:10.1186/s12933-014-0160-5) contains supplementary material, which is available to authorized users.
PMCID: PMC4266952  PMID: 25496604
Vascular calcified plaque; Mortality; Computed tomography; Type 2 diabetes
4.  Association Between Inflammatory Components and Physical Function in the Health, Aging, and Body Composition Study: A Principal Component Analysis Approach 
In older adults, studies demonstrate an inverse relationship between physical function and individual inflammatory biomarkers. Given that the inflammatory response is a complex system, a combination of biomarkers may increase the strength and consistency of these associations. This study uses principal component analysis to identify inflammatory “component(s)” and evaluates associations between the identified component(s) and measures of physical function.
Principal component analysis with a varimax rotation was used to identify two components from eight inflammatory biomarkers measured in 1,269 older persons. The study sample is a subset of the Health, Aging, and Body Composition study.
The two components explained 56% of the total variance in the data (34%, component 1 and 22%, component 2). Five markers (tumor necrosis factor-alpha [TNF-α], sTNFRI, sTNFRII, interleukin [IL]-6sR, IL-2sR) loaded highest on the first component (TNF-α related), whereas three markers (C-reactive protein [CRP], IL-6, plasminogen activator inhibitor-1) loaded highest on the second component (CRP related). After adjusting for age, sex, race, site, sampling indicator, total lean and fat mass, physical activity, smoking, and anti-inflammatory drug use, knee strength and a physical performance battery score were inversely related to the TNF-α-related component, but not to the CRP-related component (knee strength: β^TNFα = −2.71, p = .002; β^CRP = −0.88, p = .325; physical performance battery score: β^TNFα = −0.05, p < .001; β^CRP = −0.02, p = .171). Both components were positively associated with 400-m walk time, inversely associated with grip strength, and not associated with 20-m walking speed.
At least two inflammatory components can be identified in an older population, and these components have inconsistent associations with different aspects of physical performance.
PMCID: PMC2800809  PMID: 19228783
Inflammation; Physical function; Aging; Principal component analysis
5.  The PPARδ agonist, GW0742, inhibits neuroinflammation, but does not restore neurogenesis or prevent early delayed hippocampal-dependent cognitive impairment after whole-brain irradiation 
Brain tumor patients often develop cognitive impairment months to years after partial or fractionated whole-brain irradiation (fWBI). Studies suggest that neuroinflammation and decreased hippocampal neurogenesis contribute to the pathogenesis of radiation-induced brain injury. In this study, we determine if the peroxisomal proliferator-activated receptor (PPAR)δ agonist, GW0742, can prevent radiation-induced brain injury in C57Bl/6 wild-type (WT) and PPARδ knockout (KO) mice. Dietary GW0742 prevented the acute increase in IL-1β mRNA and ERK phosphorylation measured at 3 h after a single 10 Gy dose of WBI; it also prevented the increase in the number of activated hippocampal microglia 1 week after WBI. In contrast, dietary GW074 failed to prevent the radiation-induced decrease in hippocampal neurogenesis determined 2 months after WBI in WT mice, or mitigate their hippocampal-dependent spatial memory impairment measured 3 months after WBI using the Barnes maze task. PPARδ KO mice exhibited defects including decreased numbers of astrocytes in the dentate gyrus/hilus of the hippocampus and a failure to exhibit a radiation-induced increased in activated hippocampal microglia. Interestingly, the number of astrocytes in the dentate gyrus/hilus was reduced in WT mice, but not in PPARδ KO mice 2 months after WBI. These results demonstrate that, although dietary GW0742 prevents the increase in inflammatory markers and hippocampal microglial activation in WT mice after WBI, it does not restore hippocampal neurogenesis or prevent early delayed hippocampal-dependent cognitive impairment after WBI. Thus, the exact relationship between radiation-induced neuroinflammation, neurogenesis, and cognitive impairment remains elusive.
PMCID: PMC3884086  PMID: 23499837
(PPAR)δ agonists; C57Bl/6 wild-type mice; PPARδ KO mice; whole-brain irradiation; cognitive impairment; neuroinflammation; neurogenesis
6.  The influence of subclinical cardiovascular disease and related risk factors on cognition in type 2 diabetes mellitus: The DHS-Mind study 
We hypothesized that measures of coronary artery calcified plaque (CAC) collected at baseline from the Diabetes Heart Study (DHS) would explain associations between cognition and diabetes collected at follow-up approximately 7 years later. The DHS is a sibling study of cardiovascular disease (CVD) in a cohort with a high prevalence of type 2 diabetes (~80%). Associations between baseline CAC and cognitive performance were tested using generalized estimating equations and mixed effects models to adjust for familial relationships. Diabetes status was associated (p<0.05) with poorer performance on tests of verbal memory, processing speed, and semantic fluency adjusting for age, sex, education, and hypertension status. As hypothesized, including CAC in the statistical model attenuated this association. Additionally, CAC and fasting glucose predicted performance in tasks not associated with diabetes status in this study (Stroop Task, Phonemic Fluency). These results confirm work attributing the heterogeneity of cognitive outcomes in type 2 diabetes to subclinical risk factors that combine to affect different aspects of brain function. Importantly, these results imply that risk factor intervention should begin before comorbidities, particularly CVD, become clinically apparent.
PMCID: PMC3770734  PMID: 23659774
type 2 diabetes; cardiovascular disease; atherosclerosis; cognition
7.  Genetic Associations with Plasma B12, B6, and Folate Levels in an Ischemic Stroke Population from the Vitamin Intervention for Stroke Prevention (VISP) Trial 
Background: B vitamins play an important role in homocysteine metabolism, with vitamin deficiencies resulting in increased levels of homocysteine and increased risk for stroke. We performed a genome-wide association study (GWAS) in 2,100 stroke patients from the Vitamin Intervention for Stroke Prevention (VISP) trial, a clinical trial designed to determine whether the daily intake of high-dose folic acid, vitamins B6, and B12 reduce recurrent cerebral infarction.
Methods: Extensive quality control (QC) measures resulted in a total of 737,081 SNPs for analysis. Genome-wide association analyses for baseline quantitative measures of folate, Vitamins B12, and B6 were completed using linear regression approaches, implemented in PLINK.
Results: Six associations met or exceeded genome-wide significance (P ≤ 5 × 10−08). For baseline Vitamin B12, the strongest association was observed with a non-synonymous SNP (nsSNP) located in the CUBN gene (P = 1.76 × 10−13). Two additional CUBN intronic SNPs demonstrated strong associations with B12 (P = 2.92 × 10−10 and 4.11 × 10−10), while a second nsSNP, located in the TCN1 gene, also reached genome-wide significance (P = 5.14 × 10−11). For baseline measures of Vitamin B6, we identified genome-wide significant associations for SNPs at the ALPL locus (rs1697421; P = 7.06 × 10−10 and rs1780316; P = 2.25 × 10−08). In addition to the six genome-wide significant associations, nine SNPs (two for Vitamin B6, six for Vitamin B12, and one for folate measures) provided suggestive evidence for association (P ≤ 10−07).
Conclusion: Our GWAS study has identified six genome-wide significant associations, nine suggestive associations, and successfully replicated 5 of 16 SNPs previously reported to be associated with measures of B vitamins. The six genome-wide significant associations are located in gene regions that have shown previous associations with measures of B vitamins; however, four of the nine suggestive associations represent novel finding and warrant further investigation in additional populations.
PMCID: PMC4123605  PMID: 25147783
VISP; association; GWAS; one-carbon metabolism; B12; B6; folate
8.  The Effects of a Long-Term Physical Activity Intervention on Serum Uric Acid in Older Adults at Risk for Physical Disability 
Observational studies show a relationship between elevated serum uric acid (UA) and better physical performance and muscle function. The purpose of this paper was to determine whether regular participation in an exercise intervention, known to improve physical functioning, would result in increased serum UA. For this study, 424 older adults at risk for physical disability were randomized to participate in either a 12-mo moderate-intensity physical activity (PA) or a successful aging (SA) health education intervention. UA was measured at baseline, 6, and 12 mo (n = 368, 341, and 332, respectively). Baseline UA levels were 6.03 ± 1.52 mg/dl and 5.94 ± 1.55 mg/dl in the PA and SA groups, respectively. The adjusted mean UA at month 12 was 4.8% (0.24 mg/dl) higher in the PA compared with the SA group (p = .028). Compared with a health education intervention, a 1-yr PA intervention results in a modest increase in systemic concentration of UA in older adults at risk for mobility disability.
PMCID: PMC4120269  PMID: 23295313
exercise; aging; health education
9.  Association of SNPs in the UGT1A gene cluster with total bilirubin and mortality in the Diabetes Heart Study 
Atherosclerosis  2013;229(1):155-160.
A negative relationship between total bilirubin concentration (TBili) and CVD risk has been documented in a series of epidemiological studies. In addition, TBili is thought to be under strong genetic regulation via the UGT1A gene family, suggesting it may be a heritable CVD risk factor. However, few studies directly relate TBili-associated UGT1A variants to CVD severity or outcome. This study replicated the genetic association for TBili in the Diabetes Heart Study (DHS), and examined the relationships of TBili-associated SNPs with measures of subclinical CVD and mortality.
This investigation included 1220 self-described European American (EA) individuals from the DHS, a family-based study examining risk for macrovascular complications in type 2 diabetes (T2D). Genetic associations with TBili were examined using the Affymetrix Genome-wide Human SNP Array 5.0 and the Illumina Infinium Human Exome beadchip v1.0. Subsequent analyses assessed the relationships of the top TBili-associated SNPs with measures of vascular calcified plaque and mortality.
A genome-wide association study (GWAS) detected 18 SNPs within the UGT1A gene family associated with TBili at p<5×10-8. The top hit was rs887829 (p=8.67×10-20). There was no compelling evidence of association between the top TBili-associated SNPs and vascular calcified plaque (p=0.05-0.88). There was, however, evidence of association with all-cause mortality (p=0.0004-0.06), the top hit being rs2741034.
These findings support a potential role for UGT1A genetic variants in risk for mortality in T2D. Further quantification of the extent of CVD risk conferred by UGT1A gene family variants in a high risk cohort with T2D is still required.
PMCID: PMC3691283  PMID: 23642732
bilirubin; genetics; cardiovascular disease; vascular calcified plaque
10.  Identification of rare variants for hypertension with incorporation of linkage information 
BMC Proceedings  2014;8(Suppl 1):S109.
We conducted linkage analysis using the genome-wide association study data on chromosome 3, and then assessed association between hypertension and rare variants of genes located in the regions showing evidence of linkage. The rare variants were collapsed if their minor allele frequencies were less than or equal to the thresholds: 0.01, 0.03, or 0.05. In the collapsing process, they were either unweighted or weighted by the nonparametric linkage log of odds scores in 2 different schemes: exponential weighting and cumulative weighting. Logistic regression models using the generalized estimating equations approach were used to assess association between the collapsed rare variants and hypertension adjusting for age and gender. Evidence of association from the weighted and unweighted collapsing schemes with minor allele frequencies ≤0.01, after accounting for multiple testing, was found for genes DOCK3 (p = 0.0090), ARMC8 (p = 1.29E-5), KCNAB1 (p = 5.8E-4), and MYRIP (p = 5.79E-6). DOCK3 and MYRIP are newly discovered. Incorporating linkage scores as weights was found to help identify rare causal variants with a large effect size.
PMCID: PMC4144469  PMID: 25519312
11.  The Role of Metabolic Syndrome, Adiposity, and Inflammation in Physical Performance in the Health ABC Study 
Metabolic syndrome (MetS) and functional limitation have been linked, but whether and how specific components of MetS and associated factors, such as inflammation, drive this relationship is unknown.
Data are from 2,822 men and women, aged 70–79 years, participating in the Health, Aging, and Body Composition (Health ABC) study and followed for 5 years. Presence of MetS at baseline was defined according to the National Cholesterol Education Program Adult Treatment Panel III guidelines. Interleukin-6, C-reactive protein, and body fat mass were measured at baseline. Measures of physical performance, including 400-m walk time, 20-m walking speed, and the Health ABC physical performance battery (PPB) were obtained at baseline and examination years 2, 4, and 6.
A total of 1,036 (37%) individuals met criteria for MetS. MetS was associated with poorer physical performance at baseline. Effect estimates between MetS and gait speed, and components of the Health ABC PPB (standing balance and repeated sit-to-stand performance) were modestly attenuated after adjustment for inflammation. All associations were attenuated to nonsignificance after adding total body fat mass to the model. Longitudinal analyses yielded similar results. Individual MetS component analysis revealed that abdominal obesity explained the largest fraction of the variation in physical performance.
Although inflammatory biomarkers partially accounted for the relationship between MetS and aspects of physical performance, overall findings implicate adiposity as the primary factor explaining poorer physical performance in older adults with MetS.
PMCID: PMC3623483  PMID: 23109678
Metabolic syndrome; Physical function; Inflammation; Obesity.
12.  Usefulness of Biventricular Volume as a Predictor of Mortality in Patients with Diabetes Mellitus (From the Diabetes Heart Study) 
The American journal of cardiology  2013;111(8):1152-1158.
Individuals with type 2 diabetes mellitus (DM) are at increased risk of cardiovascular disease (CVD) and mortality. Beyond traditional CVD risk factors, novel measures reflecting additional aspects of disease pathophysiology, such as biventricular volume (BiVV), may be useful for risk stratification. This study examined the relationship between BiVV and risk for mortality in European Americans with type 2 DM from the Diabetes Heart Study. BiVV was calculated from 771 non-contrast computed tomography scans performed to image coronary artery calcified plaque (CAC). Relationships between BiVV and traditional CVD risk factors were examined. Cox proportional hazards regression was performed to determine risk for mortality (all-cause and CVD-mortality) associated with increasing BiVV. Area under the curve analysis was used to assess BiVV utility in risk prediction models. During 8.4 ± 2.4 years (mean ± SD) of follow-up, 23% of the sample were deceased. In unadjusted analyses, BiVV was significantly associated with increasing body mass index, height, CAC, history of hypertension and prior myocardial infarction (p<0.0001–0.012). BiVV was significantly associated with all-cause (HR: 2.45; CI: 1.06–5.67; p=0.036) and CVD-mortality (HR: 4.36; CI: 1.36–14.03; p=0.014) in models adjusted for other known CVD risk factors. Area under the curve increased from 0.76 to 0.78 (p=0.04) and 0.74 to 0.77 (p=0.02) for all-cause and CVD-mortality on inclusion of BiVV. In conclusion, in the absence of echocardiography or other noninvasive imaging modalities to assess ventricular volumes, or when such methods are contra-indicated, BiVV from computed tomography may be considered as a tool for stratification of high-risk individuals, such as those with type 2 DM.
PMCID: PMC3618594  PMID: 23351459
cardiovascular disease; heart size; diabetes; risk-prediction
13.  Genome-Wide Meta-Analysis of Homocysteine and Methionine Metabolism Identifies Five One Carbon Metabolism Loci and a Novel Association of ALDH1L1 with Ischemic Stroke 
PLoS Genetics  2014;10(3):e1004214.
Circulating homocysteine levels (tHcy), a product of the folate one carbon metabolism pathway (FOCM) through the demethylation of methionine, are heritable and are associated with an increased risk of common diseases such as stroke, cardiovascular disease (CVD), cancer and dementia. The FOCM is the sole source of de novo methyl group synthesis, impacting many biological and epigenetic pathways. However, the genetic determinants of elevated tHcy (hyperhomocysteinemia), dysregulation of methionine metabolism and the underlying biological processes remain unclear. We conducted independent genome-wide association studies and a meta-analysis of methionine metabolism, characterized by post-methionine load test tHcy, in 2,710 participants from the Framingham Heart Study (FHS) and 2,100 participants from the Vitamin Intervention for Stroke Prevention (VISP) clinical trial, and then examined the association of the identified loci with incident stroke in FHS. Five genes in the FOCM pathway (GNMT [p = 1.60×10−63], CBS [p = 3.15×10−26], CPS1 [p = 9.10×10−13], ALDH1L1 [p = 7.3×10−13] and PSPH [p = 1.17×10−16]) were strongly associated with the difference between pre- and post-methionine load test tHcy levels (ΔPOST). Of these, one variant in the ALDH1L1 locus, rs2364368, was associated with incident ischemic stroke. Promoter analyses reveal genetic and epigenetic differences that may explain a direct effect on GNMT transcription and a downstream affect on methionine metabolism. Additionally, a genetic-score consisting of the five significant loci explains 13% of the variance of ΔPOST in FHS and 6% of the variance in VISP. Association between variants in FOCM genes with ΔPOST suggest novel mechanisms that lead to differences in methionine metabolism, and possibly the epigenome, impacting disease risk. These data emphasize the importance of a concerted effort to understand regulators of one carbon metabolism as potential therapeutic targets.
Author Summary
Elevated homocysteine (tHcy) is strongly associated with risk for common disorders such as stroke, cardiovascular disease and Alzheimer disease. Lowering tHcy levels has proven to have variable success in reducing clinical risk, so the question remains, “Are we correctly targeting these disorders by lowering tHcy?” Understanding folate one-carbon metabolism pathway (FOCM) genetic variation will aid us in developing new targets for therapy. The FOCM is essential in regulation of the epigenome, which controls genes in ways beyond nucleotide sequence. We present data generated from stroke-only and general populations where we identify strong association of genetic risk factors for variation in one-carbon metabolism function, characterized by the post-methionine load test. We show that GNMT harbors genetic and epigenetic differences that influence gene function, which may have downstream effects on the epigenome of the cell, affecting disease risk. We developed a genetic risk score that predicts post-methionine load homocysteine levels that may be useful in clinic. Finally, we identified a novel association between ischemic stroke and ALDH1L1, which emphasizes the clinical importance of this work. Our results highlight the importance of a concerted effort to target the FOCM (beyond tHcy) and parallel pathways in future pharmacogenetic work using the genetic variation we describe here.
PMCID: PMC3961178  PMID: 24651765
15.  Potential Impact of Adding Genetic Markers to Clinical Parameters in Predicting Prostate Biopsy Outcomes in Men Following an Initial Negative Biopsy: Findings from the REDUCE Trial 
European urology  2012;62(6):953-961.
Several germline single nucleotide polymorphisms (SNPs) have been consistently associated with prostate cancer (PCa) risk.
To determine whether there is an improvement in PCa risk prediction by adding these SNPs to existing predictors of PCa.
Design, setting, and participants
Subjects included men in the placebo arm of the randomized Reduction by Dutasteride of Prostate Cancer Events (REDUCE) trial in whom germline DNA was available. All men had an initial negative prostate biopsy and underwent study-mandated biopsies at 2 yr and 4 yr. Predictive performance of baseline clinical parameters and/or a genetic score based on 33 established PCa risk-associated SNPs was evaluated.
Outcome measurements and statistical analysis
Area under the receiver operating characteristic curves (AUC) were used to compare different models with different predictors. Net reclassification improvement (NRI) and decision curve analysis (DCA) were used to assess changes in risk prediction by adding genetic markers.
Results and limitations
Among 1654 men, genetic score was a significant predictor of positive biopsy, even after adjusting for known clinical variables and family history (p = 3.41 × 10−8). The AUC for the genetic score exceeded that of any other PCa predictor at 0.59. Adding the genetic score to the best clinical model improved the AUC from 0.62 to 0.66 (p < 0.001), reclassified PCa risk in 33% of men (NRI: 0.10; p = 0.002), resulted in higher net benefit from DCA, and decreased the number of biopsies needed to detect the same number of PCa instances. The benefit of adding the genetic score was greatest among men at intermediate risk (25th percentile to 75th percentile). Similar results were found for high-grade (Gleason score ≥7) PCa. A major limitation of this study was its focus on white patients only.
Adding genetic markers to current clinical parameters may improve PCa risk prediction. The improvement is modest but may be helpful for better determining the need for repeat prostate biopsy. The clinical impact of these results requires further study.
PMCID: PMC3568765  PMID: 22652152
Prostate cancer; Genetics; AUC; Detection rate; Reclassification; SNPs; Prospective study; Clinical trial
16.  Alzheimer's Disease Risk Assessment Using Large-Scale Machine Learning Methods 
PLoS ONE  2013;8(11):e77949.
The goal of this work is to introduce new metrics to assess risk of Alzheimer's disease (AD) which we call AD Pattern Similarity (AD-PS) scores. These metrics are the conditional probabilities modeled by large-scale regularized logistic regression. The AD-PS scores derived from structural MRI and cognitive test data were tested across different situations using data from the Alzheimer's Disease Neuroimaging Initiative (ADNI) study. The scores were computed across groups of participants stratified by cognitive status, age and functional status. Cox proportional hazards regression was used to evaluate associations with the distribution of conversion times from mild cognitive impairment to AD. The performances of classifiers developed using data from different types of brain tissue were systematically characterized across cognitive status groups. We also explored the performance of anatomical and cognitive-anatomical composite scores generated by combining the outputs of classifiers developed using different types of data. In addition, we provide the AD-PS scores performance relative to other metrics used in the field including the Spatial Pattern of Abnormalities for Recognition of Early AD (SPARE-AD) index and total hippocampal volume for the variables examined.
PMCID: PMC3826736  PMID: 24250789
17.  A Comparison of Bayesian and Frequentist Approaches to Incorporating External Information for the Prediction of Prostate Cancer Risk 
Genetic epidemiology  2012;36(1):71-83.
We present the most comprehensive comparison to date of the predictive benefit of genetics in addition to currently used clinical variables, using genotype data for 33 single-nucleotide polymorphisms (SNPs) in 1,547 Caucasian men from the placebo arm of the REduction by DUtasteride of prostate Cancer Events (REDUCE®) trial. Moreover, we conducted a detailed comparison of three techniques for incorporating genetics into clinical risk prediction. The first method was a standard logistic regression model, which included separate terms for the clinical covariates and for each of the genetic markers. This approach ignores a substantial amount of external information concerning effect sizes for these Genome Wide Association Study (GWAS)-replicated SNPs. The second and third methods investigated two possible approaches to incorporating meta-analysed external SNP effect estimates – one via a weighted PCa ‘risk’ score based solely on the meta analysis estimates, and the other incorporating both the current and prior data via informative priors in a Bayesian logistic regression model. All methods demonstrated a slight improvement in predictive performance upon incorporation of genetics. The two methods that incorporated external information showed the greatest receiver-operating-characteristic AUCs increase from 0.61 to 0.64. The value of our methods comparison is likely to lie in observations of performance similarities, rather than difference, between three approaches of very different resource requirements. The two methods that included external information performed best, but only marginally despite substantial differences in complexity.
PMCID: PMC3791431  PMID: 22890972
prostate cancer; genetic clinical risk prediction; genetic scores; Bayesian logistic regression; predictive assessment
18.  Total and Abdominal Adiposity Are Associated With Inflammation in Older Adults Using a Factor Analysis Approach 
Obesity-related increases in multiple inflammatory markers may contribute to the persistent subclinical inflammation common with advancing age. However, it is unclear if a specific combination of markers reflects the underlying inflammatory state. We used factor analysis to identify inflammatory factor(s) and examine their associations with adiposity in older adults at risk for disability.
Adiponectin, CRP, IL-1ra, IL-1sRII, IL-2sRα, IL-6, IL-6sR, IL-8, IL-15, sTNFRI, sTNFRII, and TNF-α were measured in 179 participants from the Lifestyle Interventions and Independence for Elders Pilot (Mean ± SD age 77 ± 4 years, 76% white, 70% women). Body mass index, waist circumference, and total fat mass were assessed by anthropometry and dual-energy x-ray absorptiometry.
IL-2sRα, sTNFRI, and sTNFRII loaded highest on the first factor (factor 1). CRP, IL-1ra, and IL-6 loaded highest on the second factor (factor 2). Factor 2, but not factor 1, was positively associated with 1-SD increments in waist circumference (β = 0.160 ± 0.057, p = .005), body mass index (β = 0.132 ± 0.053, p = .01), and total fat mass (β = 0.126 ± 0.053, p = .02) after adjusting for age, gender, race/ethnicity, site, smoking, anti-inflammatory medications, comorbidity index, health-related quality of life, and physical function. These associations remained significant after further adjustment for grip strength, but only waist circumference remained associated with inflammation after adjusting for total lean mass. There were no significant interactions between adiposity and muscle mass or strength for either factor.
Greater total and abdominal adiposity are associated with higher levels of an inflammatory factor related to CRP, IL-1ra, and IL-6 in older adults, which may provide a clinically useful measure of inflammation in this population.
PMCID: PMC3437966  PMID: 22451470
Aging; Adiposity; Inflammation; Muscle impairment; Factor analysis
19.  Using graded response model for the prediction of prostate cancer risk 
Human genetics  2012;131(8):1327-1336.
Disease risk-associated single nucleotide polymorphisms (SNPs) identified from genome-wide association studies (GWAS) have the potential to be used for disease risk prediction. An important feature of these risk-associated SNPs is their weak individual effect but stronger cumulative effect on disease risk. To date, a stable summary estimate of the joint effect of genetic variants on disease risk prediction is not available. In this study, we propose to use the graded response model (GRM), which is based on the item response theory, for estimating the individual risk that is associated with a set of SNPs. We compare the GRM with a recently proposed risk prediction model called cumulative relative risk (CRR). Thirty-three prostate cancer risk-associated SNPs were originally discovered in GWAS by December 2009. These SNPs were used to evaluate the performance of GRM and CRR for predicting prostate cancer risk in three GWAS populations, including populations from Sweden, Johns Hopkins Hospital, and the National Cancer Institute Cancer Genetic Markers of Susceptibility study. Computational results show that the risk prediction estimates of GRM, compared to CRR, are less biased and more stable.
PMCID: PMC3734950  PMID: 22461065
20.  Chronic Administration of the Angiotensin-Converting Enzyme Inhibitor, Ramipril, Prevents Fractionated Whole-Brain Irradiation-Induced Perirhinal Cortex-Dependent Cognitive Impairment 
Radiation research  2012;178(1):46-56.
We hypothesized that chronic administration of the angiotensin-converting enzyme inhibitor, ramipril, to young adult male rats would prevent/ameliorate fractionated whole-brain irradiation-induced perirhinal cortex-dependent cognitive impairment. Eighty 12–14-week-old young adult male Fischer 344 rats received either: (1) sham irradiation, (2) 40 Gy of fractionated whole-brain irradiation delivered as two 5 Gy fractions/week for 4 weeks, (3) sham irradiation plus continuous administration of 15 mg/L of ramipril in the drinking water starting 3 days before irradiation, or (4) fractionated whole-brain irradiation plus ramipril. Cognitive function was assessed using a perirhinal cortex-dependent version of the novel object recognition task 26 weeks after irradiation. Microglial activation was determined in the perirhinal cortex and the dentate gyrus of the hippocampus 28 weeks after irradiation using the ED1 antibody. Neurogenesis was assessed in the granular cell layer and subgranular zones of the dentate gyrus using a doublecortin antibody. Fractionated whole-brain irradiation led to: (1) a significant impairment in perirhinal cortex-dependent cognitive function, (2) a significant increase in activated microglia in the dentate gyrus but not in the perirhinal cortex, and (3) a significant decrease in neurogenesis. Continuous administration of ramipril before, during, and after irradiation prevented the fractionated whole-brain irradiation-induced changes in perirhinal cortex-dependent cognitive function, as well as in microglial activation in the dentate gyrus. Thus, as hypothesized, continuous administration of the angiotensin-converting enzyme inhibitor, ramipril, can prevent the fractionated whole-brain irradiation-induced impairment in perirhinal cortex-dependent cognitive function.
PMCID: PMC3422865  PMID: 22687052
21.  Impact of HDL genetic risk scores on coronary artery calcified plaque and mortality in individuals with type 2 diabetes from the Diabetes Heart Study 
Patients with type 2 diabetes (T2D) are at elevated risk for cardiovascular disease (CVD) events and mortality. Recent studies have assessed the impact of genetic variants affecting high-density lipoprotein cholesterol (HDL) concentrations on CVD risk in the general population. This study examined the utility of HDL-associated single nucleotide polymorphisms (SNPs) for CVD risk prediction in European Americans with T2D enrolled in the Diabetes Heart Study (DHS).
Genetic risk scores (GRS) of HDL-associated SNPs were constructed and evaluated for potential associations with mortality and with coronary artery calcified atherosclerotic plaque (CAC), a measure of subclinical CVD strongly associated with CVD events and mortality. Two sets of SNPs were used to construct GRS; while all SNPs were selected primarily for their impacts on HDL, one set of SNPs had pleiotropic effects on other lipid parameters, while the other set lacked effects on low-density lipoprotein cholesterol (LDL) or triglyceride concentrations.
The GRS were specifically associated with HDL concentrations (4.90 × 10-7 < p < 0.02) in models adjusted for age, sex, and body mass index (BMI), but were not associated with LDL or triglycerides. Cox proportional hazards regression analysis suggested the HDL-associated GRS had no impact on risk of CVD-mortality (0.48 < p < 0.99) in models adjusted for other known CVD risk factors. However, associations between several of the GRS and CAC were observed (3.85 × 10-4 < p < 0.03) in models adjusted for other known CVD risk factors.
The GRS analyzed in this study provide a tool for assessment of HDL-associated SNPs and their impact on CVD risk in T2D. The observed associations between several of the GRS and CAC suggest a potential role for HDL-associated SNPs on subclinical CVD risk in patients with T2D.
PMCID: PMC3695806  PMID: 23799899
High-density lipoprotein cholesterol; Type 2 diabetes; Coronary artery calcified plaque; Mortality; Genetic risk score
22.  PPARδ prevents radiation-induced proinflammatory responses in microglia via transrepression of NF-κB and inhibition of the PKCα/MEK1/2/ERK1/2/AP-1 pathway 
Free radical biology & medicine  2012;52(9):1734-1743.
Partial or whole-brain irradiation is often required to treat both primary and metastatic brain cancer. Radiation-induced normal tissue injury, including progressive cognitive impairment, however, can significantly affect the well-being of the approximately 200,000 patients who receive these treatments each year in the US. Although the exact mechanisms underlying radiation-induced late effects remain unclear, oxidative stress and inflammation are thought to play a critical role. Microglia are key mediators of neuroinflammation. Peroxisomal proliferator-activated receptor (PPAR)δ has been shown to be a potent regulator of anti-inflammatory responses. Thus, we hypothesized that PPARδ activation would modulate the radiation-induced inflammatory response in microglia. Incubating BV-2 murine microglial cells with the PPARδ agonist, L-165041, prevented the radiation-induced increase in: i) intracellular reactive oxygen species generation, ii) Cox-2 and MCP-1 expression, and iii) IL-1β and TNF-α message levels. This occured, in part, through PPARδ-mediated modulation of stress activated kinases and proinflammatory transcription factors. PPARδ inhibited NF-κB via transrepression by physically interacting with the p65 subunit, and prevented activation of the PKCα/MEK1/2/ERK1/2/AP-1 pathway by inhibiting the radiation-induced increase in intracellular reactive oxygen species generation. These data support the hypothesis that PPARδ activation can modulate radiation-induced oxidative stress and inflammatory responses in microglia.
PMCID: PMC3341532  PMID: 22387176
Ionizing radiation; PPARδ; radiation-induced brain injury; microglia; inflammation; NF-κB; PKCα/MEK1/2/ERK1/2/AP-1 pathway
23.  Genome-wide two-locus epistasis scans in prostate cancer using two European populations 
Human genetics  2012;131(7):1225-1234.
Approximately 40 single nucleotide polymorphisms (SNPs) that are associated with prostate cancer (PCa) risk have been identified through genome-wide association studies (GWAS). However, these GWAS-identified PCa risk-associated SNPs can explain only a small proportion of heritability (~13%) of PCa risk. Gene–gene interaction is speculated to be one of the major factors contributing to the so-called missing heritability. To evaluate the gene–gene interaction and PCa risk, we performed a two-stage genome-wide gene–gene interaction scan using a novel statistical approach named “Boolean Operation-based Screening and Testing”. In the first stage, we exhaustively evaluated all pairs of SNP–SNP interactions for ~500,000 SNPs in 1,176 PCa cases and 1,101 control subjects from the National Cancer Institute Cancer Genetic Markers of Susceptibility (CGEMS) study. No SNP–SNP interaction reached a genome-wide significant level of 4.4E–13. The second stage of the study involved evaluation of the top 1,325 pairs of SNP–SNP interactions (Pinteraction < 1.0E–08) implicated in CGEMS in another GWAS population of 1,964 PCa cases from the Johns Hopkins Hospital (JHH) and 3,172 control subjects from the Illumina iControl database. Sixteen pairs of SNP–SNP interactions were significant in the JHH population at a Pinteraction cutoff of 0.01. However, none of the 16 pairs of SNP–SNP interactions were significant after adjusting for multiple tests. The current study represents one of the first attempts to explore the high-dimensional etiology of PCa on a genome-wide scale. Our results suggested a list of SNP–SNP interactions that can be followed in other replication studies.
PMCID: PMC3634576  PMID: 22367438
24.  Glomerular filtration rate and albuminuria predict mortality independently from coronary artery calcified plaque in the Diabetes Heart Study 
Risk stratification in individuals with type 2 diabetes (T2D) remains an important priority in the management of associated morbidity and mortality, including from cardiovascular disease (CVD). The current investigation examined whether estimated glomerular filtration rate (eGFR) and urine albumin:creatinine ratio (UACR) were independent predictors of CVD-mortality in European Americans (EAs) with T2D after accounting for subclinical CVD.
The family-based Diabetes Heart Study (DHS) cohort (n=1,220) had baseline measures of serum creatinine, eGFR, UACR and coronary artery calcified plaque (CAC) assessed by non-contrast computed tomography scan. Cox proportional hazards regression was performed to determine risk for all-cause mortality and CVD-mortality associated with indices of kidney disease after accounting for traditional CVD risk factors and CAC as a measure of subclinical CVD.
Participants were followed for 8.2±2.6 years (mean±SD) during which time 247 (20.9%) were deceased, 107 (9.1%) from CVD. Univariate analyses revealed positive associations between serum creatinine (HR:1.56; 95% CI:1.37–1.80; p<0.0001) and UACR (1.59; 1.43–1.77; p>0.0001) and negative associations between serum albumin (0.74; 0.65–0.84; p<0.0001) and eGFR (0.66; 0.58–0.76; p<0.0001) with all-cause mortality. Associations remained significant after adjustment for traditional CVD risk factors, as well as for CAC. Similar trends were noted when predicting risk for CVD-mortality.
The DHS reveals that kidney function and albuminuria are independent risk factors for all-cause mortality and CVD-mortality in EAs with T2D, even after accounting for CAC.
PMCID: PMC3637614  PMID: 23594619
Coronary artery calcified plaque; Mortality; Albuminuria; Type 2 diabetes; Risk prediction
25.  Angiotensin-Converting Enzyme Inhibitor Use by Older Adults Is Associated with Greater Functional Responses to Exercise 
To assess the association between angiotensin converting enzyme inhibitors (ACEis) and improvements in the physical function of older adults in response to chronic exercise training.
Secondary analysis of the Lifestyle Interventions and Independence for Elders Pilot (LIFE-P) study, a multisite randomized clinical trial to evaluate the effects of chronic exercise on the physical function of older adults at risk for mobility disability.
Four academic research centers within the United States.
Four hundred twenty-four individuals aged 70 to 89 with mild to moderate functional impairments categorized for this analysis as ACEi users, users of other antihypertensive drugs, or antihypertensive nonusers.
A 12-month intervention of structured physical activity (PA) or health education promoting successful aging (SA).
Change in walking speed during a 400-m test and performance on a battery of short-duration mobility tasks (Short Physical Performance Battery (SPPB)).
Physical activity significantly improved the adjusted walking speed of ACEi users (P < .001) but did not of nonusers. PA improved the adjusted SPPB score of ACEi users (P < .001) and of persons who used other antihypertensive drugs (P = .005) but not of antihypertensive nonusers (P = .91). The percentage of ACEi users deriving clinically significant benefit from exercise training for walking speed (30%) and SPPB score (48%) was dramatically higher than for nonusers (14% and 12%, respectively).
For older adults at risk for disability, exercise-derived improvements in physical function were greater for ACEi users than users of other antihypertensive drugs and antihypertensive nonusers.
PMCID: PMC3625953  PMID: 22726232
aging; exercise; physical function; LIFE Study; ACE inhibitors

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