Validation of blood-based assays using dried blood spots for use in large population studies

Dried Blood Spots to Assess Cardiovascular-Kidney-Metabolic Health

Dried blood spot sampling offers a scalable strategy to close diagnostic gaps and improve global surveillance for cardiovascular-kidney-metabolic syndrome. However, assay performance and the extent of validity vary widely between biomarkers used in cardiovascular-kidney-metabolic health assessment under different settings and have not been well described. To fill this gap, we conducted a systematic search of the literature and a narrative synthesis through April 2024 and included reports with laboratory or field validation measuring biomarkers that can be used in cardiovascular-kidney-metabolic health assessment. We categorized assays into categories based on laboratory validation: excellent performance (r>0.95 with gold standard methods and coefficients of variation <5%), very good performance (r>0.90 and coefficients of variation <10%), reasonable performance (r>0.80 and coefficients of variation <15%), and poor performance (r<0.80 or coefficients of variation >15%). The extent of validation was determined by the total number of field validation studies with strong agreement. Hemoglobin A1c has strong laboratory and field validation and should be considered for expansion into clinical testing in low-resource settings. Traditional lipid biomarkers showed poor performance in field validation studies, but apoB (apolipoprotein B), creatinine, cystatin C, and NT-proBNP (N-terminal prohormone of brain natriuretic peptide) showed promising initial laboratory validation results and deserve greater attention in field validation studies. High-sensitivity C-reactive protein has strong laboratory and field validation but has limited clinical utility. Dried blood spot assays have been developed for biomarkers that offer mechanistic insights including inflammatory and vascular injury markers, fatty acids, malondialdehyde, asymmetric dimethylarginine, trimethylamine N-oxide, carnitines, and omics.

Overweight in mediating the association between depression and new-onset diabetes: A population-based research from Health and Retirement Study

BACKGROUND

Several studies have suggested a close link between depression, overweight, and new-onset diabetes, particularly among middle-aged and older populations; however, the causal associations remain poorly understood.

AIM

To investigate the role of overweight in mediating the association between depression and new-onset diabetes in middle-aged and older populations.

METHODS

Data of 9426 individuals aged ≥ 50 years from the 1998-2016 Health and Retirement Study database were analyzed. Weighted logistic regression was employed to obtain odds ratios (ORs) and 95% confidence intervals (95%CIs) for depression and new-onset diabetes in the middle-aged and older populations. Mediation analysis and the Sobel test were used to test the mediating effects of overweight between depression and the risk of new-onset diabetes.

RESULTS

New-onset diabetes was identified in 23.6% of the study population. Depression was significantly associated with new-onset diabetes (OR: 1.18, 95%CI: 1.03-1.35, P value: 0.014). Further adjustment for overweight attenuated the effect of depression on new-onset diabetes to 1.14 (95%CI: 1.00-1.30, P = 0.053), with a significant mediating effect (P of Sobel test = 0.003). The mediation analysis demonstrated that overweight accounted for 61% in depression for the risk of new-onset diabetes, with overweight having a partially mediating role in the depression-to-diabetes pathway.

CONCLUSION

New-onset diabetes was not necessarily a direct complication of depression; rather, depression led to behaviors that increase the risk of overweight and, consequently, new-onset diabetes.

Association of cystatin C kidney function measures with motoric cognitive risk syndrome: evidence from two cohort studies

BACKGROUND

This study aimed to examine the associations of cystatin C, cystatin C estimated glomerular filtration rate (eGFRcys), and the difference between eGFRs (eGFRdiff) using cystatin C and creatinine levels with incident motoric cognitive risk syndrome (MCR).

METHODS

We utilized data from two nationally representative cohort studies, the China Health and Retirement Longitudinal Study (CHARLS, 2011-2015) and the US Health and Retirement Study (HRS, 2010-2018). Baseline serum cystatin C and creatinine levels were measured, and eGFRcys and creatinine estimated GFR (eGFRcr) were calculated. MCR was defined as subjective cognitive complaints plus objectively measured slow gait speed. Multivariable logistic models were used to investigate the longitudinal associations between kidney function measurements and incident MCR.

RESULTS

In CHARLS (N = 2,085) and HRS (N = 1,240) cohorts, 7.4% and 7.2% developed MCR over follow-up. Each SD increment in serum cystatin C level was associated with elevated incident MCR odds, and an inverse association of eGFRcys with incident MCR was observed in both cohorts after multivariable adjustment and meta-analyses. The association between serum cystatin C and incident MCR remained significant even after adjusting for serum creatinine, suggesting that cystatin C is independently associated with MCR, regardless of kidney function levels. Additionally, each SD decrease in the absolute value of eGFRdiff was associated with lower odds of incident MCR among CHARLS participants.

CONCLUSIONS

Cystatin C and eGFRcys were correlated with an elevated MCR risk in two distinct populations. Specifically, eGFRdiff also related to incident MCR among Chinese older adults. Monitoring cystatin C-based kidney function could have significant clinical utility for identifying incident MCR risk, and represents a potential intervention target for healthier cognitive aging.

Racial and ethnic disparities in longitudinal trajectories of cardiovascular risk factors in U.S. middle-aged and older adults

BACKGROUND

Racial and ethnic disparities in cardiovascular disease (CVD) risk factors are well-documented. However, racial and ethnic differences in the longitudinal changes among multiple CVD risk factors are unknown.

METHODS

We used prospective cohort data of U.S. adults aged ≥50 in the 2006-2016 Health and Retirement Study. Group-based multi-trajectory models characterized age-related trajectories of systolic blood pressure ([BP] mmHg), non-HDL cholesterol (mg/dL), diabetes mellitus (DM), and smoking. Racial and ethnic differences in the multi-trajectory profiles were examined using multinomial logistic regression. Karlson-Holm-Breen methods were used to assess factors contributing to these associations.

RESULTS

Among 10,292 participants (median age: 61), approximately 32% had an overall favorable profile of CVD risk factors. Compared with non-Hispanic White adults, non-Hispanic Black adults were more likely to exhibit elevated systolic BP with high risks of DM (relative risk ratio [RRR] = 3.36; 95% CI, 2.69-4.21; P < .001) and with low risks of DM (RRR = 3.23; 95% CI, 2.38-4.38; P < .001). Non-Hispanic Black adults were also more likely to exhibit high rates of smoking with and without other co-occurring risk factors. Hispanic adults were most likely to exhibit high risks of DM with elevated systolic BP (RRR = 1.74; 95% CI, 1.28-2.38; P < .001) and without elevated systolic BP (RRR = 1.90; 95% CI, 1.50-2.40; P < .001). Education, income, and country-of-origin were significantly associated with the excess CVD risks observed among racial and ethnic minority groups.

CONCLUSIONS

Significant racial and ethnic disparities were observed in trajectories of CVD risk factors in U.S. adults. Social determinants largely contributed to these associations in non-Hispanic Black adults and Hispanic adults.

Age at diagnosis of diabetes, obesity, and the risk of dementia among adult patients with type 2 diabetes

BACKGROUND

While Type 2 Diabetes Mellitus (T2DM) prevalence is increasing among younger individuals, few studies have examined how age at T2DM diagnosis relates to dementia risk in diabetic populations. We aimed to investigate the association between age at T2DM diagnosis and subsequent dementia risk, and to determine whether obesity moderates this relationship.

METHODS

We conducted a prospective cohort study using data from the Health and Retirement Study (2002-2016) matched with its 2003 Diabetes Mail-Out Survey. The study included 1,213 dementia-free adults aged ≥50 with diagnosed T2DM. Primary exposures were age at T2DM diagnosis (categorized as <50, 50-59, 60-69, and ≥70 years) and obesity status (BMI ≥30 kg/m2). The outcome was incident dementia, assessed using the Telephone Interview for Cognitive Status. Cox proportional hazards models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs), adjusting for sociodemographic factors, health behaviors, health status, and diabetes medication use.

RESULTS

Over a median follow-up of 10 (interquartile range, 6-14) years, 216 (17.8%) participants developed dementia. Compared to participants diagnosed with T2DM at age ≥70 years, those diagnosed at younger ages had increased dementia risk: HR 1.70 (95% CI, 1.03-2.80) for 60-69 years, 1.72 (95% CI, 1.06-2.79) for 50-59 years, and 1.90 (95% CI, 1.14-3.18) for <50 years. Obesity significantly moderated this relationship, with obese individuals diagnosed with T2DM before age 50 showing the highest dementia risk (HR 3.05; 95% CI 1.23-7.56) compared to non-obese individuals diagnosed at ≥50 years.

CONCLUSIONS

Younger age at diagnosis of T2DM was significantly associated with a higher risk of dementia, particularly among individuals with obesity. Interventions specifically targeting obesity may be more effective in preventing dementia for adults with a younger onset of T2DM.

Elevated stress-responsive biomarkers are associated with HIV acquisition in young women in rural South Africa

OBJECTIVE

Biological markers of stress have been associated with HIV progression and pathogenesis but not with HIV incidence. We sought to determine if elevated stress-responsive biomarkers would be associated with incident HIV among adolescent girls and young women (AGYW).

DESIGN

We conducted a case-cohort study within the HIV Prevention Trials Network (HPTN) 068 study among 949 AGYW in South Africa. Cases were AGYW who tested HIV-positive during the eight-year follow-up. Unmatched controls were randomly selected from the HIV-negative population at enrollment.

METHODS

Dried blood spots from cases and controls were tested from enrollment (2011-2012) for C-reactive protein (CRP), herpes simplex virus type-1 (HSV-1) antibody titers, and cytomegalovirus (CMV) antibody titers. Cox proportional hazards models estimated the association between each biomarker and time to incident HIV.

RESULTS

Compared to AGYW with the lowest CRP levels, those with medium and high CRP levels had a higher hazard ratio (HR) of incident HIV [HR: 1.45, 95% confidence interval (CI): 0.95, 2.21; HR: 1.50, 95% CI: 0.98, 2.30, respectively], although not statistically significant. The relative hazard of incident HIV was also higher among AGYW who were CMV seropositive vs. seronegative (low antibodies HR: 2.18, 95% CI: 1.2, 3.87; medium HR: 2.25, 95% CI: 1.28, 3.95; high HR: 1.78, 95% CI: 0.99, 3.21). Those with the highest HSV-1 antibody levels experienced an increased hazard of HIV compared to those who were HSV-1 seronegative (HR: 1.58, 95% CI: 1.03, 2.44).

CONCLUSIONS

Biological stress may increase AGYW's susceptibility to HIV acquisition through changes in immune function, viral infection, and increased biological vulnerability to disease.

Hepatic WDR23 proteostasis mediates insulin homeostasis by regulating insulin-degrading enzyme capacity

Maintaining insulin homeostasis is critical for cellular and organismal metabolism. In the liver, insulin is degraded by the activity of the insulin-degrading enzyme (IDE). Here, we establish a hepatic regulatory axis for IDE through WDR23-proteostasis. Wdr23KO mice have increased IDE expression, reduced circulating insulin, and defective insulin responses. Genetically engineered human cell models lacking WDR23 also increase IDE expression and display dysregulated phosphorylation of insulin signaling cascade proteins, IRS-1, AKT2, MAPK, FoxO, and mTOR, similar to cells treated with insulin, which can be mitigated by chemical inhibition of IDE. Mechanistically, the cytoprotective transcription factor NRF2, a direct target of WDR23-Cul4 proteostasis, mediates the enhanced transcriptional expression of IDE when WDR23 is ablated. Moreover, an analysis of human genetic variation in WDR23 across a large naturally aging human cohort in the US Health and Retirement Study reveals a significant association of WDR23 with altered hemoglobin A1C (HbA1c) levels in older adults, supporting the use of WDR23 as a new molecular determinant of metabolic health in humans.

The mediating role of systemic inflammation and moderating role of racialization in disparities in incident dementia

BACKGROUND

Exposure to systemic racism is linked to increased dementia burden. To assess systemic inflammation as a potential pathway linking exposure to racism and dementia disparities, we investigated the mediating role of C-reactive protein (CRP), a systemic inflammation marker, and the moderating role of the racialization process in incident dementia.

METHODS

In the US Health and Retirement Study (n = 6,908), serum CRP was measured at baseline (2006, 2008 waves). Incident dementia was classified by cognitive tests over a six-year follow-up. Self-reported racialized categories were a proxy for exposure to the racialization process. We decomposed racialized disparities in dementia incidence (non-Hispanic Black and/or Hispanic vs. non-Hispanic white) into 1) the mediated effect of CRP, 2) the moderated portion attributable to the interaction between racialized group membership and CRP, and 3) the controlled direct effect (other pathways through which racism operates).

RESULTS

The 6-year cumulative incidence of dementia is 12%. Among minoritized participants (i.e., non-Hispanic Black and/or Hispanic), high CRP levels ( ≥ 75th percentile or 4.73μg/mL) are associated with 1.26 (95%CI: 0.98, 1.62) times greater risk of incident dementia than low CRP ( < 4.73μg/mL). Decomposition analysis comparing minoritized versus non-Hispanic white participants shows that the mediating effect of CRP accounts for 3% (95% CI: 0%, 6%) of the racial disparity, while the interaction effect between minoritized group status and high CRP accounts for 14% (95% CI: 1%, 27%) of the disparity. Findings are robust to potential violations of causal mediation assumptions.

CONCLUSIONS

Minoritized group membership modifies the relationship between systemic inflammation and incident dementia.

The reciprocal associations between social deficits, social engagement, and inflammation: Longitudinal evidence comparing venous blood samples and dried blood spots and mapping the modifying role of phenotypic and genotypic depression

BACKGROUND

Social psychoneuroimmunology suggests an interplay between social deficits (loneliness and isolation) and chronic inflammation, but the direction of these relationships remains unclear. We estimated the reciprocal associations of social deficits and social engagement with levels of C-reactive protein (CRP), compared the consistency of the findings depending on the biological sampling method used, and examined the modifying role of phenotypic and genotypic depression.

METHODS

We used longitudinal nationally representative data from the US (Health and Retirement Study, 3 waves, 2006-16) and England (English Longitudinal Study of Ageing, 4 waves, 2004-18). Loneliness, social isolation, and social engagement were self-reported. CRP was measured using dried blood spots (US) and venous blood samples (England). Cross-lagged panel models were fitted and tested interactions with phenotypic depression (above-threshold depressive symptom scores) and genotypic depression (polygenic score for major depressive disorder).

RESULTS

We included 15,066 participants (mean age = 66.1 years, SD = 9.8) in the US and 10,290 (66.9 years, SD = 10.5) in England. We found reciprocal associations between loneliness and CRP using dried blood spots and venous blood samples. Higher CRP predicted higher subsequent loneliness and higher loneliness predicted elevated CRP. Both phenotypic and genotypic depression modified this reciprocal association. There were also reciprocal associations for social engagement in venous blood samples: higher CRP predicted lower social engagement and greater social engagement predicted lower subsequent CRP. Associations between social isolation and CRP were inconsistent and unidirectional.

CONCLUSIONS

Loneliness may increase chronic inflammation, whereas social engagement may reduce inflammation. As these relationships were reciprocal, there may be a loop between inflammation, loneliness, and social engagement. This loop was stronger in those with depression or at high genetic risk for major depressive disorder. This relationship for loneliness was present in both blood sampling methods despite contrasting methods of CRP measurement, indicating that the finding is not attributable to measurement bias in biomarkers.

Parental Preconception Posttraumatic Stress Symptoms and Maternal Prenatal Inflammation Prospectively Predict Shorter Telomere Length in Children

OBJECTIVE

Parental trauma exposure and trauma-related distress can increase the risk of adverse health outcomes in offspring, but the pathways implicated in intergenerational transmission are not fully explicated. Accelerated biological aging may be one mechanism underlying less favorable health in trauma-exposed individuals and their offspring. This study examines the associations of preconception maternal and paternal posttraumatic stress disorder (PTSD) symptoms with child telomere length, and maternal prenatal C-reactive protein (CRP) as a biological mechanism.

METHODS

Mothers ( n = 127) and a subset of the fathers ( n = 84) reported on PTSD symptoms before conception. Mothers provided blood spots in the second and third trimesters that were assayed for CRP. At age 4 years, children provided buccal cells for measurement of telomere length. Models adjusted for parental age, socioeconomic status, maternal prepregnancy body mass index, child biological sex, and child age.

RESULTS

Mothers' PTSD symptoms were significantly associated with shorter child telomere length ( β = -0.22, SE = 0.10, p = .023). Fathers' PTSD symptoms were also inversely associated with child telomere length ( β = -0.21, SE = 0.11), although nonsignificant ( p = .065). There was no significant indirect effect of mothers' PTSD symptoms on child telomere length through CRP in pregnancy, but higher second-trimester CRP was significantly associated with shorter child telomere length ( β = -0.35, SE = 0.18, p = .048).

CONCLUSIONS

Maternal symptoms of PTSD before conception and second-trimester inflammation were associated with shorter telomere length in offspring in early childhood, independent of covariates. Findings indicate that intergenerational transmission of parental trauma may occur in part through accelerated biological aging processes and provide further evidence that prenatal proinflammatory processes program child telomere length.Open Science Framework Preregistration:https://osf.io/7c2d5/?view_only=cd0fb81f48db4b8f9c59fc8bb7b0ef97 .

A naturally occurring variant of SHLP2 is a protective factor in Parkinson's disease

Mitochondrial DNA single nucleotide polymorphisms (mtSNPs) have been associated with a reduced risk of developing Parkinson's disease (PD), yet the underlying mechanisms remain elusive. In this study, we investigate the functional role of a PD-associated mtSNP that impacts the mitochondrial-derived peptide (MDP) Small Humanin-like Peptide 2 (SHLP2). We identify m.2158 T > C, a mtSNP associated with reduced PD risk, within the small open reading frame encoding SHLP2. This mtSNP results in an alternative form of SHLP2 (lysine 4 replaced with arginine; K4R). Using targeted mass spectrometry, we detect specific tryptic fragments of SHLP2 in neuronal cells and demonstrate its binding to mitochondrial complex 1. Notably, we observe that the K4R variant, associated with reduced PD risk, exhibits increased stability compared to WT SHLP2. Additionally, both WT and K4R SHLP2 show enhanced protection against mitochondrial dysfunction in in vitro experiments and confer protection against a PD-inducing toxin, a mitochondrial complex 1 inhibitor, in a mouse model. This study sheds light on the functional consequences of the m.2158 T > C mtSNP on SHLP2 and provides insights into the potential mechanisms by which this mtSNP may reduce the risk of PD.

Dried blood spot based biomarkers in the Health and Retirement Study: 2006 to 2016

INTRODUCTION

The Health and Retirement Study (HRS) has collected biomarker data over multiple waves. Such data can help improve our understanding of health changes in individuals and the causal pathways related to health. There are, however, technical challenges to using the HRS dried blood spots (DBS) biomarker data due to changes over time in assay protocols, platforms, and laboratories. We provide technical and summary information on biological indicators collected as part of the HRS from 2006 to 2016 that should be helpful to users of the data.

METHODS

We describe the opportunities and challenges provided by the HRS DBS data as well as insights provided by the data. The HRS collected DBS from its nationally representative sample of respondents 51 years of age or older from 2006 to 2016. DBS-based biomarkers were collected from half the sample in 2006, 2010, and 2014, and from the other half of the sample in 2008, 2012, and 2016. These DBS specimens were used to assay total and HDL cholesterol, glycosylated hemoglobin, C-reactive protein, and cystatin C from 2006 to 2016, and Interleukin 6 was added in 2014/2016. Samples included approximately 6000 individuals at each wave, and completion rates ranged from 81% to 90%. HRS transformed DBS values into venous blood equivalents to make them more comparable to those of the whole blood-based assays collected in most other studies and to facilitate longitudinal analysis.

RESULTS

Distribution of changes over time by age shows that total cholesterol levels decreased for each age, while HbA1c levels increased. Cystatin C shows a clear age gradient, but a number of other markers do not. Non-Hispanic Black persons and Hispanic respondents have a higher incidence of risk levels of each biomarker except for CRP among non-Hispanic Black older persons.

CONCLUSION

These public-use DBS data provide analysis opportunities that can be used to improve our understanding of health change with age in both populations and among individuals.

Achieving routine application of dried blood spots for erythropoietin receptor agonist analysis in doping control: low-volume single-spot detection at minimum required performance level

Background: Erythropoietin receptor agonists (ERAs) are substances prohibited in sports and currently monitored in urine and blood. There is a great interest in new matrices like dried blood spots (DBSs). Method: A direct method for the detection of ERAs in DBSs using one single spot of 25 μl has been optimized and validated. Results: Limits of detection close or equal to those required by the World Anti-Doping Agency for serum/plasma samples were achieved, using a volume 20-times lower. All analytes were stable for at least 90 days at room temperature. Conclusion: Method performance was comparable to the requirements established for blood samples and, thus, monitoring of ERAs is reliable in DBSs in the context of doping control.

A randomised study of nurse collected venous blood and self-collected dried blood spots for the assessment of cardiovascular risk factors in the Understanding Society Innovation Panel

Dried blood spot (DBS) sample collection has been suggested as a less invasive, cheaper and more convenient alternative to venepuncture, which requires trained personnel, making it a potentially viable approach for self-collection of blood on a large scale. We examine whether participants in a longitudinal survey were willing to provide a DBS sample in different interview settings, and how resulting cardiovascular risk biomarkers compared with those from venous blood to calculate clinical risk. Participants of the Understanding Society Innovation Panel, a representative sample of UK households, were randomly assigned to three modes of interview. Most participants (84%) were interviewed in their allocated mode. Participants (n = 2162) were interviewed by a nurse who collected both a blood sample by venepuncture and a DBS card ('nurse collection') or participants were seen by an interviewer or took part in the survey online to self-collect a DBS card ('self-collection'). All DBS cards were returned in the post after the sample had dried. Lipids (total cholesterol, HDL-cholesterol, triglycerides), HbA1c and C-reactive protein were measured in venous and DBS samples and equivalence was calculated. The resultant values were used to confirm equivalent prevalence of risk of cardiovascular disease in each type of blood sample by mode of participation. Of participants interviewed by a nurse 69% consented to venous blood sample and 74% to a DBS sample, while in the self-collection modes, 35% consented to DBS collection. Demographic characteristics of participants in self-collection mode was not different to those in nurse collection mode. The percentage of participants with clinically raised biomarkers did not significantly differ between type of blood collection (for example, 62% had high cholesterol (> 5 mmol/l) measured by venepuncture and 67% had high cholesterol within the self-collected DBS sample (p = 0.13)). While self-collected DBS sampling had a lower response rate to DBS collected by a nurse, participation did not vary by key demographic characteristics. This study demonstrates that DBS collection is a feasible method of sample collection that can provide acceptable measures of clinically relevant biomarkers, enabling the calculation of population levels of cardiovascular disease risk.

Sense of purpose in life and allostatic load in two longitudinal cohorts

OBJECTIVE

Sense of purpose in life has been linked with better physical health, longevity, and reduced risk for disability and dementia, but the mechanisms linking sense of purpose with diverse health outcomes are unclear. Sense of purpose may promote better physiological regulation in response to stressors and health challenges, leading to lower allostatic load and disease risk over time. The current study examined the association between sense of purpose in life and allostatic load over time in adults over age 50.

METHODS

Data from the nationally representative US Health and Retirement Study (HRS) and English Longitudinal Study of Ageing (ELSA) were used to examine associations between sense of purpose and allostatic load across 8 and 12 years of follow-up, respectively. Blood-based and anthropometric biomarkers were collected at four-year intervals and used to compute allostatic load scores based on clinical cut-off values representing low, moderate, and high risk.

RESULTS

Population-weighted multilevel models revealed that sense of purpose in life was associated with lower overall levels of allostatic load in HRS, but not in ELSA after adjusting for relevant covariates. Sense of purpose in life did not predict rate of change in allostatic load in either sample.

CONCLUSIONS

The present investigation supports sense of purpose predicting preserved differentiation of allostatic regulation, with more purposeful individuals demonstrating consistently lower allostatic load over time. Persistent differences in allostatic burden may account for divergent health trajectories between individuals low and high in sense of purpose.

Decomposing interaction and mediating effects of race/ethnicity and circulating blood levels of cystatin C on cognitive status in the United States health and retirement study

Background and objectives

Elevated circulating cystatin C is associated with cognitive impairment in non-Hispanic Whites, but its role in racial disparities in dementia is understudied. In a nationally representative sample of older non-Hispanic White, non-Hispanic Black, and Hispanic adults in the United States, we use mediation-interaction analysis to understand how racial disparities in the cystatin C physiological pathway may contribute to racial disparities in prevalent dementia.

Methods

In a pooled cross-sectional sample of the Health and Retirement Study (n = 9,923), we employed Poisson regression to estimate prevalence ratios and to test the relationship between elevated cystatin C (>1.24 vs. ≤1.24 mg/L) and impaired cognition, adjusted for demographics, behavioral risk factors, other biomarkers, and chronic conditions. Self-reported racialized social categories were a proxy measure for exposure to racism. We calculated additive interaction measures and conducted four-way mediation-interaction decomposition analysis to test the moderating effect of race/ethnicity and mediating effect of cystatin C on the racial disparity.

Results

Overall, elevated cystatin C was associated with dementia (prevalence ratio [PR] = 1.2; 95% CI: 1.0, 1.5). Among non-Hispanic Black relative to non-Hispanic White participants, the relative excess risk due to interaction was 0.7 (95% CI: -0.1, 2.4), the attributable proportion was 0.1 (95% CI: -0.2, 0.4), and the synergy index was 1.1 (95% CI: 0.8, 1.8) in a fully adjusted model. Elevated cystatin C was estimated to account for 2% (95% CI: -0, 4%) for the racial disparity in prevalent dementia, and the interaction accounted for 8% (95% CI: -5, 22%). Analyses for Hispanic relative to non-white participants suggested moderation by race/ethnicity, but not mediation.

Discussion

Elevated cystatin C was associated with dementia prevalence. Our mediation-interaction decomposition analysis suggested that the effect of elevated cystatin C on the racial disparity might be moderated by race/ethnicity, which indicates that the racialization process affects not only the distribution of circulating cystatin C across minoritized racial groups, but also the strength of association between the biomarker and dementia prevalence. These results provide evidence that cystatin C is associated with adverse brain health and this effect is larger than expected for individuals racialized as minorities had they been racialized and treated as non-Hispanic White.

The Mediating Role of Systemic Inflammation and Moderating Role of Race/Ethnicity in Racialized Disparities in Incident Dementia: A Decomposition Analysis

Background

Exposure to systemic racism is linked to increased dementia burden. To assess systemic inflammation as a potential pathway linking exposure to racism and dementia disparities, we investigated the mediating role of C-reactive protein (CRP), a systemic inflammation marker, and the moderating role of race/ethnicity on racialized disparities in incident dementia.

Methods

In the US Health and Retirement Study (n=5,143), serum CRP was measured at baseline (2006, 2008 waves). Incident dementia was classified by cognitive tests over a six-year follow-up. Self-reported racialized categories were a proxy for exposure to the racialization process. We decomposed racialized disparities in dementia incidence (non-Hispanic Black and/or Hispanic vs. non-Hispanic White) into 1) the mediated effect of CRP, 2) the moderated portion attributable to the interaction between racialized group membership and CRP, and 3) the controlled direct effect (other pathways through which racism operates).

Results

The 6-year cumulative incidence of dementia was 15.5%. Among minoritized participants (i.e., non-Hispanic Black and/or Hispanic), high CRP levels (> 75th percentile or 4.57mcg/mL) was associated with 1.27 (95%CI: 1.01,1.59) times greater risk of incident dementia than low CRP (<4.57mcg/mL). Decomposition analysis comparing minoritized versus non-Hispanic White participants showed that the mediating effect of CRP accounted for 2% (95% CI: 0%, 6%) of the racial disparity, while the interaction effect between minoritized group status and high CRP accounted for 12% (95% CI: 2%, 22%) of the disparity. Findings were robust to potential violations of causal mediation assumptions.

Conclusions

Systemic inflammation mediates racialized disparities in incident dementia.

Home monitoring of haemoglobin A1c in diabetes: A systematic review and narrative synthesis on accuracy, reliability and patient acceptability

AIM

In the UK people with diabetes who do not attend annual review appointments often have higher haemoglobin A_1c (HbA_1c ) levels. We aim to determine the acceptability of self-collected posted capillary blood samples, and if they produce accurate and reliable HbA_1c results.

METHODS

We include adult studies comparing capillary blood to venous blood for measuring HbA_1c . We exclude methods not suitable for postage. Electronic databases of MEDLINE, Embase, CINAHL, Web of Science, Google Scholar and OpenGrey were searched from inception to September 2021, as well as relevant conference abstracts. Two reviewers performed study selection, data extraction and risk of bias assessment independently. Narrative synthesis was performed.

RESULTS

Our search retrieved 3747 records. Following de-duplication and screening 30 articles were included. The mean difference (MD) and limits of agreement (LoA) between capillary and venous HbA_1c were smaller and narrower respectively when micro/capillary tubes (micro/cap) were used for capillary blood storage compared to dried blood spots (capDBS) (micro/cap MD range -0.4 to 1.4 mmol/mol vs. capDBS MD range -4.3 to 7.2 mmol/mol, micro/cap LoA width 2.4 to 6 mmol/mol vs. capDBS LoA width 11.7 to 16.8 mmol/mol). After using self-collection kits, 83%-96% of participants reported satisfaction, 87%-99% found it easy and 69%-94% reported they would use it again.

CONCLUSION

Microtubes/capillary tubes look promising as a method of self-collecting and posting capillary blood samples for the measurement of HbA_1c based on the accuracy and reliability findings presented. DBS samples demonstrated comparatively poorer accuracy. Data on acceptability were limited and further research is needed.

The Mediating Role of Systemic Inflammation and Moderating Role of Race/Ethnicity in Racialized Disparities in Incident Dementia: A Decomposition Analysis

Background

Exposure to systemic racism is linked to increased dementia burden. To assess systemic inflammation as a potential pathway linking exposure to racism and dementia disparities, we investigated the mediating role of C-reactive protein (CRP), a systemic inflammation marker, and the moderating role of race/ethnicity on racialized disparities in incident dementia.

Methods

In the US Health and Retirement Study (n=5,143), serum CRP was measured at baseline (2006, 2008 waves). Incident dementia was classified by cognitive tests over a six-year follow-up. Self-reported racialized categories were a proxy for exposure to the racialization process. We decomposed racialized disparities in dementia incidence (non-Hispanic Black and/or Hispanic vs. non-Hispanic White) into 1) the mediated effect of CRP, 2) the moderated portion attributable to the interaction between racialized group membership and CRP, and 3) the controlled direct effect (other pathways through which racism operates).

Results

The 6-year cumulative incidence of dementia was 15.5%. Among minoritized participants (i.e., non-Hispanic Black and/or Hispanic), high CRP levels (> 75th percentile or 4.57μg/mL) was associated with 1.27 (95%CI: 1.01,1.59) times greater risk of incident dementia than low CRP (≤4.57μg/mL). Decomposition analysis comparing minoritized versus non-Hispanic White participants showed that the mediating effect of CRP accounted for 2% (95% CI: 0%, 6%) of the racial disparity, while the interaction effect between minoritized group status and high CRP accounted for 12% (95% CI: 2%, 22%) of the disparity. Findings were robust to potential violations of causal mediation assumptions.

Conclusions

Systemic inflammation mediates racialized disparities in incident dementia.

Postal methods for monitoring HbA1c in diabetes mellitus: a protocol for systematic review

BACKGROUND

Worldwide there are an estimated 463 million people with diabetes. In the UK people with diabetes are offered annual review, which includes monitoring of haemoglobin A1c (HbA1c). This can identify people with diabetes who are not meeting their glycaemic targets, enabling early intervention. Those who do not attend these reviews often have poorer health outcomes. During the COVID-19 pandemic, there was a 77% reduction in monitoring of HbA1c in the UK.

AIM

It is hypothesised that people with diabetes could take finger-prick samples at home for measurement of HbA1c. This study will examine the agreement and correlation of capillary HbA1c values compared with a venous reference standard. It will explore reliability and repeatability of capillary HbA1c testing methods, as well as the direction of effect of storage variables. The study will also explore patient acceptability and safety. It will look at capillary blood methods that would be suitable for posting.

DESIGN & SETTING

A systematic review will be undertaken.

METHOD

The core terms of 'Diabetes', 'HbA1c' and 'Capillary sampling' will be used to search MEDLINE, Embase, Cumulative Index to Nursing and Allied Health Literature (CINAHL), Web of Science Core Collection, Google Scholar, OpenGrey, and other grey literature, from database inception until 2021. Risk of bias will be assessed using the 'COSMIN Risk of Bias tool to assess the quality of studies on reliability and measurement error'.

CONCLUSION

A narrative synthesis will be produced to explore whether there are viable postal alternatives to venous sampling, as well as exploring acceptability and safety of patient self-collection.

Effects of spot size on biomarker levels of field-collected dried blood spots: A new algorithm for exact dried blood spot size measurement

OBJECTIVES

The quality of blood values analyzed from survey-collected dried blood spot (DBS) samples is affected by fieldwork conditions, particularly spot size. We offer an image-based algorithm that accurately measures the area of field-collected DBS and we investigate the impact of spot size on the analyzed blood marker values.

METHODS

SHARE, a pan-European study, collected 24 000 DBS samples in 12 countries in its sixth wave. Our new algorithm uses photographs of the DBS samples to calculate the number of pixels of the blood-covered area to measure the spot sizes accurately. We ran regression models to examine the association of spot size and seven DBS analytes. We then compared the application of our new spot-size measures to common spot-size estimation.

RESULTS

Using automated spot-size measurement, we found that spot size has a significant effect on all markers. Smaller spots are associated with lower measured levels, except for HbA1c, for which we observe a negative effect. Our precisely measured spot sizes explain substantially more variance of DBS analytes compared to commonly used spot-size estimation.

CONCLUSION

The new algorithm accurately measures the size of field-collected DBS in an automated way. This methodology can be applied to surveys even with very large numbers of observations. The measured spot sizes improve the accuracy of conversion formulae that translate blood marker values derived from DBS into venous blood values. The significance of the spot-size effects on biomarkers in DBS should also incentivize the improvement of fieldwork training and monitoring.

C-Reactive Protein, Subjective Aging, and Incident Cardiovascular Disease: A Mediation Model

OBJECTIVES

Negative self-perceptions of aging (SPA) and an older subjective age are associated with a greater likelihood of cardiovascular disease. We predicted that C-reactive protein (CRP), a marker of stress-related inflammation, would mediate this relation.

METHOD

Data from up to 6 602 participants ages 50-101 in the Health and Retirement Study (2008-2018) were analyzed using logistic regressions with mediation. Subjective aging was assessed in 2008 or 2010, CRP was assessed 2 years later, and diagnosis of heart disease or stroke was assessed in the years from CRP measurement to 2018.

RESULTS

Significant indirect effects occurred in all models, indicating that negative SPA and older subjective age are associated with a greater likelihood of heart disease and stroke through elevated levels of the inflammatory marker CRP.

DISCUSSION

These findings suggest that psychological factors such as subjective aging impact cardiovascular health through physiological mechanisms, specifically markers of inflammation.

Estimated Pulse Wave Velocity and All-Cause Mortality: Findings From the Health and Retirement Study

Background and Objectives

The gold standard method for the assessment of vascular aging is carotid-femoral pulse wave velocity (cfPWV). cfPWV can be estimated from 2 commonly assessed clinical variables-age and blood pressure. This analysis uses data from the Health and Retirement Study to examine the relationship between estimated pulse wave velocity (ePWV) and mortality among 9,293 middle age and older adults.

Research Design and Methods

Cox proportional hazard models were used to predict mortality occurring over a 10- to 12-year period. Controls were included for sociodemographic characteristics (age, gender, race, ethnicity, wealth, income, and education), health status (history of cardiovascular disease [CVD], diabetes, and stroke and related medication use), health behaviors (smoking, physical activity, and body mass index), and CVD-related biomarkers (systolic and diastolic blood pressure, C-reactive protein, cystatin c, hemoglobin A1c, total cholesterol, and high-density lipoprotein cholesterol).

Results

By 2018, 26.19% of the weighted analytic sample were reported as deceased. In the fully specified models that control for age, age-squared, systolic and diastolic blood pressure, sociodemographic variables, health status and behaviors, and biomarkers, ePWV was associated with a greater likelihood of mortality.

Discussion and Implications

An estimate of PWV derived from age and blood pressure is independently associated with an increased likelihood of death in a representative sample of middle age and older adults in the United States.

Women with lower systemic inflammation demonstrate steeper cognitive decline with age: Results from a large prospective, longitudinal sample

Background

Men and women experience large disparities in prevalence, detection, and clinical course of neurodegenerative diseases. Inflammation has been implicated in the pathogenesis of neurodegenerative diseases, yet there is a paucity of literature documenting sex differences in this phenomenon in prospective, longitudinal studies.

Methods

Participants were 4217 non-smoking individuals (62.2% female; aged 46–91 at enrollment) enrolled in the Health and Retirement Study who provided dried blood spots and completed a standardized assessment of cognitive function 3 times across 8 years. Inflammation was indexed using C-reactive protein (CRP).

Results

Higher CRP was associated with lower concurrent cognitive function, b = −0.13 (SE = 0.06), p < .05, but less decline in cognitive function over time, b = 0.02 (SE = 0.01), p < .05. Sex moderated the association between CRP and decline in total cognitive function, b = 0.02 (SE = 0.01), p < .05, such that the steepest declines in cognitive function were observed among women with the lowest CRP concentrations.

Conclusions

Women with lower systemic inflammation as measured by CRP may be at risk of going undetected for neurodegenerative disease, especially given their overall higher cognitive scores. This may perpetuate sex-related disparities in prevention and clinical course. Attention to the underlying biological mechanisms explaining the link between lower CRP and risk for cognitive decline for women and its potential clinical implications are needed.

•

Sex differences in links between inflammation and cognitive function are under-explored.

•

Higher CRP was associated with lower concurrent cognitive function, only in men.

•

Women with lower CRP showed the steepest declines in cognitive functioning.

Childhood adversity is associated with heightened inflammation after sleep loss

OBJECTIVES

To investigate whether childhood adversity exacerbates the relationship between sleep restriction and inflammation.

METHODS

Participants (N = 46) were randomly assigned to an experimental sleep restriction group (n = 25) or a night of typical sleep (n = 21). Participants provided a dried blood spot sample the morning before and after the experimental night.

RESULTS

A significant interaction emerged between childhood adversity and group assignment on C-reactive protein (CRP) after the experimental night (Beta = -0.02, SE = 0.01, P = .03, 95% CI: -0.05, -0.002). Sleep restriction resulted in an increase in CRP at high levels of childhood adversity (+1 SD; Effect = -0.57, SE = 0.15, P< .001; 95% CI: -0.87, -0.26) but not low levels of childhood adversity (Effect = -0.08, SE = 0.10, P = .40; 95% CI: -0.29, 0.12).

CONCLUSION

Childhood adversity may amplify the effect of sleep loss on markers of inflammation.

Longitudinal associations between C-reactive protein and cognitive performance in normative cognitive ageing and dementia

BACKGROUND

systemic inflammation appears to play an important role in the pathogenesis and expression of Alzheimer's disease and other dementias. Previous research has found that elevated levels of serum C-reactive protein (CRP) is associated with poorer cognitive functioning and increased risk for dementia. However, most studies are limited by single CRP measurements, which fail to capture long-term inflammatory exposures or dynamic changes in inflammation and cognition which may occur across repeated measurements.

METHODS

using data from 3,563 older adults aged 65-101 from the Health and Retirement Study, we examined bivariate changes in CRP and cognition measured repeatedly over a 10-year follow-up. Bivariate multilevel models estimated the effect of time-varying CRP on cognition among cognitively healthy older adults and in a subset of 427 participants who reported incident dementia onset during the follow-up period.

RESULTS

in cognitively healthy participants, CRP was associated with lower level of cognitive functioning, but not rate of change over time. This effect was significant in participants under 80 years of age (b = -0.09, standard error (SE) = 0.05, P = 0.04), but not in older participants. In participants with incident dementia, those with higher CRP experienced smaller rates of cognitive decline, leading up to dementia diagnosis.

CONCLUSIONS

elevated levels of CRP predict poorer cognition and increased dementia risk in cognitively healthy adults under the age of 80. Conversely, increased CRP may confer protective effects on cognition in the prodromal stage of dementia.

Elevated C-Reactive Protein in Alzheimer's Disease without Depression in Older Adults: Findings from the Health and Retirement Study

We examined the association between differential diagnoses of major stroke and probable Alzheimer's disease (AD) and Mixed AD on c-reactive protein (CRP) in older adults with and without depression. Secondary data analyses examined associations between blood-based measures of probable peripheral inflammation using CRP collected from dried blood spots in the Health and Retirement Study (HRS), a nationally representative sample of individuals aged 50 and older. A validated pattern recognition algorithm was utilized to identify cognitive decline indicative of probable AD, Mixed AD, and major stroke. Negative binomial regressions were utilized to model concentrations of serologic CRP. On average, participants (N=4,601) were 70 years old, female, and non-Hispanic white. Mixed AD participants had 0.26 mg/dL increase in CRP compared to unimpaired participants, controlling for demographics, health behaviors and comorbidities. Those with Mixed AD had 2.14 times increased odds of having high CRP (OR=2.14; [1.19-3.85]). In analyses stratified by depression, adults with Mixed AD and without depression had an additional 0.37 mg/dL increase in CRP (SE=0.06; p<0.001) compared to unimpaired adults. Those with AD without depression had an 0.20 mg/dL increase in CRP (SE=0.07; p<0.01). Age was not associated with increased CRP in non-depressed older adults. Depressed adults with major stroke had a -0.26 mg/dL decrease in CRP (SE=0.11; p=0.02), controlling for hypertension, alcoholic drinks/beverages per week and smoking status. Concentration modeling revealed that participants with major stroke, probable AD and probable mixed AD without depression had significantly higher CRP concentrations when compared to unimpaired older adults.

Household air pollution and blood markers of inflammation: A cross-sectional analysis

Household air pollution (HAP) from biomass stoves is a leading risk factor for cardiopulmonary outcomes; however, its toxicity pathways and relationship with inflammation markers are poorly understood. Among 180 adult women in rural Peru, we examined the cross-sectional exposure-response relationship between biomass HAP and markers of inflammation in blood using baseline measurements from a randomized trial. We measured markers of inflammation (CRP, IL-6, IL-10, IL-1β, and TNF-α) with dried blood spots, 48-h kitchen area concentrations and personal exposures to fine particulate matter (PM_2.5 ), black carbon (BC), and carbon monoxide (CO), and 48-h kitchen concentrations of nitrogen dioxide (NO₂ ) in a subset of 97 participants. We conducted an exposure-response analysis between quintiles of HAP levels and markers of inflammation. Markers of inflammation were more strongly associated with kitchen area concentrations of BC than PM_2.5 . As expected, kitchen area BC concentrations were positively associated with TNF-α (pro-inflammatory) concentrations and negatively associated with IL-10, an anti-inflammatory marker, controlling for confounders in single- and multi-pollutant models. However, contrary to expectations, kitchen area BC and NO₂ concentrations were negatively associated with IL-1β, a pro-inflammatory marker. No associations were identified for IL-6 or CRP, or for any marker in relation to personal exposures.

Dried blood spot collection, sample quality, and fieldwork conditions: Structural validations for conversion into standard values

OBJECTIVES

SHARE, a pan-European panel study in 27 European countries and Israel, has collected dried blood spot (DBS) samples from approximately 27 000 respondents in 13 countries. We aim to obtain factors to convert analyte values between DBS and venous blood samples (VBS) taking account of adverse fieldwork conditions such as small spot size, high temperature and humidity, short drying time and long shipment times.

METHODS

We obtained VBS and DBS from a set of 20 donors in a laboratory setting, and treated the DBS in a systematic and controlled fashion simulating SHARE fieldwork conditions. We used the 3420 outcomes to estimate from DBS analyte values the values that we would have obtained had it been feasible to collect and analyze the donors' venous blood samples.

RESULTS

The influence of field conditions and sample quality on DBS analyte values is significant and differs among assays. Varying spot size is the main challenge and affects all markers except HbA1c. Smaller spots lead to overly high measured levels. A missing desiccant is detrimental for all markers except CRP and tHb. The temperature to which the samples are exposed plays a significant role for HDL and CysC, while too brief a drying time affects CRP and CysC. Lab-based adjustment formulae only accounting for the differences between re-liquefied DBS and venous blood do not address these fieldwork conditions.

CONCLUSIONS

By simulating adverse fieldwork conditions in the lab, we were able to validate DBS collected under such conditions and established conversion formulae with high prediction accuracy.

Mendelian Randomization of Dyslipidemia on Cognitive Impairment Among Older Americans

Background: Altered lipid metabolism may be a risk factor for dementia, and blood cholesterol level has a strong genetic component. We tested the hypothesis that dyslipidemia (either low levels of high-density lipoprotein cholesterol (HDL-C) or high total cholesterol) is associated with cognitive status and domains, and assessed causality using genetic predisposition to dyslipidemia as an instrumental variable. Methods: Using data from European and African genetic ancestry participants in the Health and Retirement Study, we selected observations at the first non-missing biomarker assessment (waves 2006-2012). Cognition domains were assessed using episodic memory, mental status, and vocabulary tests. Overall cognitive status was categorized in three levels (normal, cognitive impairment non-dementia, dementia). Based on 2018 clinical guidelines, we compared low HDL-C or high total cholesterol to normal levels. Polygenic scores for dyslipidemia were used as instrumental variables in a Mendelian randomization framework. Multivariable logistic regressions and Wald-type ratio estimators were used to examine associations. Results: Among European ancestry participants (n = 8,781), at risk HDL-C levels were associated with higher odds of cognitive impairment (OR = 1.20, 95% CI: 1.03, 1.40) and worse episodic memory, specifically. Using cumulative genetic risk for HDL-C levels as a valid instrumental variable, a significant causal estimate was observed between at risk low HDL-C levels and higher odds of dementia (OR = 2.15, 95% CI: 1.16, 3.99). No significant associations were observed between total cholesterol levels and cognitive status. No significant associations were observed in the African ancestry sample (n = 2,101). Conclusion: Our study demonstrates low blood HDL-C is a potential causal risk factor for impaired cognition during aging in non-Hispanic whites of European ancestry. Dyslipidemia can be modified by changing diets, health behaviors, and therapeutic strategies, which can improve cognitive aging. Studies on low density lipoprotein cholesterol, the timing of cholesterol effects on cognition, and larger studies in non-European ancestries are needed.

Historical Loss: Implications for Health of American Indians in the Blackfeet Community

BACKGROUND

Historical loss in American Indians (AIs) is believed to contribute to high incidence of mental health disorders, yet less is known about the associations between historical loss and physical health.

PURPOSE

To investigate whether frequency of thought about historical loss predicts risk factors for chronic physical health conditions in an AI community.

METHODS

Using Community Based Participatory research (CBPR) and Ecological Momentary Assessment (EMA), we measured frequency of thoughts about historical loss in 100 AI adults residing on the Blackfeet reservation. Participants completed a 1-week monitoring period, during which ambulatory blood pressure and daily levels of psychological stress were measured. At the end of the week, we collected a dried blood spot sample for measurement of C-reactive protein (CRP).

RESULTS

In hierarchical linear regression models controlling for demographics and relevant covariates, greater frequency of thoughts about historical loss predicted higher average daily psychological stress (B = .55, t = 6.47, p < .001, ΔR2 = .30) and higher levels of CRP (B = .33, t = 3.93, p < .001, ΔR2 = .10). Using linear mixed modeling with relevant covariates, we found that greater thoughts about historical loss were associated with higher systolic ambulatory blood pressure (B = .32, 95% CI = .22-.42, t = 6.48, p < .001, ΔR2 = .25; Fig. 1c) and greater diastolic ambulatory blood pressure (B = .19, 95% CI = .11-.27, t = 4.73, p < .001, ΔR2 = .19).

CONCLUSIONS

The data suggest that frequency of thought about historical loss may contribute to increased subclinical risk for cardiovascular disease in the Blackfeet community.

Neighborhood Characteristics and Inflammation among Older Black Americans: The Moderating Effects of Hopelessness and Pessimism

BACKGROUND

Research documents the adverse health effects of systemic inflammation. Overall, older Black Americans tend to have higher inflammation than older non-Hispanic white adults. Given that inflammation is related to a range of chronic health problems that disproportionately affect Blacks compared to whites, this racial disparity in inflammation may contribute to racial disparities in particular chronic health problems. Thus, a better understanding of its determinants in the older Black population is of critical importance. This analysis examined the association between neighborhood characteristics and inflammation in a national sample of older non-Hispanic Black Americans. An additional aim of this study was to determine whether hopelessness and pessimism moderates the association between neighborhood characteristics and inflammation.

METHODS

A sample of older non-Hispanic Black Americans aged 60+ were drawn from the Health and Retirement Study (N=1,004). Neighborhood characteristics included neighborhood physical disadvantage and neighborhood social cohesion. Inflammation was assessed by C-reactive protein (CRP).

RESULTS

The analyses indicated that neighborhood physical disadvantage and social cohesion were not associated with CRP. Hopelessness and pessimism moderated the association between neighborhood physical disadvantage and CRP.

CONCLUSIONS

Knowledge regarding the role of hopelessness and pessimism as moderator in the neighborhood-inflammation association can inform cognitive-behavioral interventions targeted at changes in cognition patterns.

Evaluation of 92 cardiovascular proteins in dried blood spots collected under field-conditions: Off-the-shelf affinity-based multiplexed assays work well, allowing for simplified sample collection

Workplace-collected blood spots deposited on filter paper were analysed with multiplexed affinity-based protein assays and found to be suitable for proteomics analysis. The protein extension assay (PEA) was used to characterize 92 proteins using 1.2 mm punches in repeated samples collected from 20 workers. Overall, 97.8% of the samples and 91.3% of the analysed proteins passed quality control. Both within and between spot correlations using six replicates from the same individual were above 0.99, suggesting that comparable levels are obtained from multiple punches from the same spot and from consecutive spots. Protein levels from dried blood and wet serum from the same individuals were compared and the majority of the analysed proteins were found to be significantly correlated. These results open up for simplified sample collection of blood in field conditions for proteomic analysis, but also highlight that not all proteins can be robustly measured from dried whole blood.

Early Signs of Gut Microbiome Aging: Biomarkers of Inflammation, Metabolism, and Macromolecular Damage in Young Adulthood

Emerging links between gut microbiota and diseases of aging point to possible shared immune, metabolic, and cellular damage mechanisms, operating long before diseases manifest. We conducted 16S rRNA sequencing of fecal samples collected from a subsample (n = 668) of Add Health Wave V, a nationally representative longitudinal study of adults aged 32-42. An overlapping subsample (n = 345) included whole-blood RNA-seq. We examined associations between fecal taxonomic abundances and dried blood spot-based markers of lipid and glucose homeostasis and C-reactive protein (measured in Wave IV), as well as gene expression markers of inflammation, cellular damage, immune cell composition, and transcriptomic age (measured in Wave V), using Bayesian hierarchical models adjusted for potential confounders. We additionally estimated a co-abundance network between inflammation-related genes and bacterial taxa using penalized Gaussian graphical models. Strong and consistent microbiota associations emerged for HbA1c, glucose, C-reactive protein, and principal components of genes upregulated in inflammation, DNA repair, and reactive oxygen species, with Streptococcus infantis, Pseudomonas spp., and Peptoniphilus as major players for each. This pattern was largely echoed (though attenuated) for immunological cell composition gene sets, and only Serratia varied meaningfully by transcriptomic age. Network co-abundance indicated relationships between Prevotella sp., Bacteroides sp., and Ruminococcus sp. and gut immune/metabolic regulatory activity, and Ruminococcus sp, Dialister, and Butyrivibrio crossotus with balance between Th1 and Th2 inflammation. In conclusion, many common associations between microbiota and major physiologic aging mechanisms are evident in early-mid adulthood and suggest avenues for early detection and prevention of accelerated aging.

Measurement of mitochondrial DNA copy number in dried blood spots: A pilot study

BACKGROUND

We evaluated the feasibility of mitochondrial DNA (mtDNA) copy number measurement in dried blood spots (DBS), its comparability with measurement in whole blood samples, and stability of mtDNA copy number from DBS over time.

METHODS

Women in this pilot study were participants in the Sister Study, a large prospective cohort. Sister Study participants provided a whole blood sample and DBS at enrollment. A second DBS sample was collected 5-10 years later from a subcohort of women with and without an incident breast cancer diagnosis between collections. Among 54 women (27 with breast cancer, 27 without) we measured mtDNA copy number from whole blood at enrollment and from DBS at both time points.

RESULTS

The average age at enrollment was 58.7 years (range:50-69). Values of mtDNA copy number measured in whole blood samples and DBS from enrollment were moderately correlated (Spearman R = 0.45; p = 0.005). Stability of mtDNA copy number in DBS from the two time points was moderate overall (ICC = 0.50) and similar between women with (ICC = 0.50) and without (ICC = 0.51) a breast cancer diagnosis between the two collections.

CONCLUSIONS

Our results suggest that measurement of mtDNA copy number in DBS is feasible and may be a valid alternative to measurement in whole blood samples.

Optimism, pessimism, and health biomarkers in older couples

OBJECTIVE

Studies have demonstrated the importance of optimism in predicting perceived general health. However, the handful of studies focusing on cardiovascular biomarkers show inconsistent effects. Additionally, no study examined whether spousal levels of optimism and pessimism affect an individual's biological markers of cardiovascular health. Thus, our objectives were to examine whether partners' optimism and pessimism affect individual biological markers, differentiating between between-dyad associations and within-dyad predictive processes.

METHODS

Three waves of the Health and Retirement Study collected in 2006, 2010, and 2014 were used to test actor and partner effects of optimism and pessimism on C-reactive protein (CRP) and high-density lipoprotein. Multilevel longitudinal actor-partner models were used to examine the contribution of a partner's optimism and pessimism to each biomarker, adjusting for respondent's age, sex, depression, body mass index, daily activity levels, and a summary score of respondent's doctor-diagnosed chronic conditions.

RESULTS

Partners' pessimism and optimism levels were moderately associated. Results for within-person effects were all non-significant, both within and across waves. Associations at the between-person level were also non-significant, with the exception of a positive association between husbands' pessimism and their own CRP, and husbands' optimism and their wives' CRP.

CONCLUSIONS

Results suggest that optimism and pessimism may not play a pertinent role in within variability of biomarkers of cardiovascular diseases and have a minor role in predicting to between-person variability of biomarkers of cardiovascular diseases.

Dried blood spots: Effects of less than optimal collection, shipping time, heat, and humidity

OBJECTIVES

This study investigates how factors related to collection, storage, transport time, and environmental conditions affect the quality and accuracy of analyses of dried blood spot (DBS) samples.

METHODS

Data come from the 2016 Health and Retirement Study (HRS) DBS laboratory reports and the HRS merged with the National Climatic Data Center (NCDC) Global Historical Climate Network Daily (NCDC GHCN-Daily) and the NCDC Local Climatological Data, by zip code. We ran regression models to examine the associations between assay values based on DBS for five analytes (total cholesterol, high-density lipoprotein (HDL) cholesterol, glycosylated hemoglobin (HbA1c), C-reactive protein (CRP), and cystatin C) and the characteristics of DBS cards and drops, shipping time, and temperature, and humidity at the time of collection.

RESULTS

We found cholesterol measures to be sensitive to many factors including small spots, shipping time, high temperature and humidity. Small spots in DBS cards are related to lower values across all analytes. Longer DBS transit time before freezing is associated with lower values of total and HDL cholesterol and cystatin C. Results were similar whether or not venous blood sample values were included in equations.

CONCLUSIONS

Small spots, long shipping time, and exposure to high temperature and humidity need to be avoided if possible. Quality of spots and cards and information on shipping time and conditions should be coded with the data to make adjustments in values when necessary. The different results across analytes indicate that results cannot be generalized to all DBS assays.

Combining lipidomics and machine learning to measure clinical lipids in dried blood spots

INTRODUCTION

Blood-based sample collection is a challenge, and dried blood spots (DBS) represent an attractive alternative. However, for DBSs to be an alternative to venous blood it is important that these samples are able to deliver comparable associations with clinical outcomes. To explore this we looked to see if lipid profile data could be used to predict the concentration of triglyceride, HDL, LDL and total cholesterol in DBSs using markers identified in plasma.

OBJECTIVES

To determine if DBSs can be used as an alternative to venous blood in both research and clinical settings, and to determine if machine learning could predict 'clinical lipid' concentration from lipid profile data.

METHODS

Lipid profiles were generated from plasma (n = 777) and DBS (n = 835) samples. Random forest was applied to identify and validate panels of lipid markers in plasma, which were translated into the DBS cohort to provide robust measures of the four 'clinical lipids'.

RESULTS

In plasma samples panels of lipid markers were identified that could predict the concentration of the 'clinical lipids' with correlations between estimated and measured triglyceride, HDL, LDL and total cholesterol of 0.920, 0.743, 0.580 and 0.424 respectively. When translated into DBS samples, correlations of 0.836, 0.591, 0.561 and 0.569 were achieved for triglyceride, HDL, LDL and total cholesterol.

CONCLUSION

DBSs represent an alternative to venous blood, however further work is required to improve the combined lipidomics and machine learning approach to develop it for use in health monitoring.

Subjective Age and Cystatin C Among Older Adults

OBJECTIVE

Cystatin C (CysC) is a marker of kidney function that is relevant for the health and cognition of older adults. Little is known about the link between psychological factors and CysC. Therefore, the present study examined whether subjective age is related to CysC level and changes in CysC over time.

METHOD

Participants were 5,066 individuals drawn from the Health and Retirement Study aged from 50 to 107 years (60% women, mean age = 69.36 years, SD = 9.54). They provided data on subjective age, demographic covariates, and CysC at baseline. CysC was assessed again 4 years later.

RESULTS

Analysis revealed that an older subjective age was related to higher level of CysC at baseline and to an increase in CysC over 4 years, controlling for demographic factors. An older subjective age was also related to higher risk of exceeding the clinical threshold of CysC at baseline and 4 years later. Additional analysis revealed that disease burden, depressive symptoms, physical inactivity, and BMI partly mediated these associations.

CONCLUSION

The present study provides new evidence on the role of subjective age as a psychological factor associated with individuals' risk of kidney dysfunction, an association beyond chronological age.

Self-reported Instances of Major Discrimination, Race/Ethnicity, and Inflammation Among Older Adults: Evidence From the Health and Retirement Study

BACKGROUND

This study examines the relationship between self-reported instances of major discrimination and inflammation among older adults, and explores whether this relationship varies in accordance with race/ethnicity. We hypothesized that self-reported instances of major discrimination would be associated with higher levels of high-risk inflammation and that this relationship would be stronger for racial/ethnic minorities than whites.

METHODS

Data from the 2006/2008 Health and Retirement Study, an ongoing biennial nationally representative sample of older adults in the United States, were used to collect measures of self-reported instances of major discrimination and high-risk C-reactive protein (CRP), which was assayed from blood samples. Modified Poisson regression with robust standard errors was applied to estimate the prevalence ratios of self-reported instances of major discrimination, as it relates to high-risk CRP (CRP ≥ 22 kg/m2), and test whether this relationship varies by race/ethnicity.

RESULTS

Respondents who experienced any instances of major discrimination had a higher likelihood of high-risk CRP (prevalence ratio [PR]: 1.14, 95% confidence interval [CI] = 1.07-1.22) than those who did not report experiencing any instances of major discrimination. This association was independent of differences in newly diagnosed health conditions and socioeconomic status. The relationship between any self-reported instance of major discrimination and high-risk CRP was weaker for blacks than whites (PR: 0.81, 95% CI = 0.69-0.95).

CONCLUSIONS

Our study confirms that self-reported instances of major lifetime discrimination is a psychosocial factor that is adversely associated with high-risk CRP among older adults; this association is especially pronounced among older whites. Future studies among this population are required to examine whether the relationship between self-reported instances of major discrimination and high-risk CRP changes over time.

Perceived neighborhood social cohesion and cardiometabolic risk: a gene × environment study

People living in socially cohesive neighborhoods generally have better health. We extend this research by evaluating the hypothesis that perceived neighborhood cohesion may influence health by attenuating genetic liability for cardiometabolic risk factors. Using data from the Health and Retirement Study (n = 6615; mean age 69.7), we conducted a gene × environment interaction study hypothesizing that perceived neighborhood cohesion would attenuate the link between polygenic scores for waist-to-hip ratio (WHR) and body mass index and a measure of multisystem cardiometabolic risk (systolic and diastolic blood pressure, heart rate, A1c, C-reactive protein, and total and high-density lipoprotein cholesterol). In support of the hypothesis, results indicated that among people perceiving low neighborhood cohesion, higher WHR polygenic scores were associated with greater cardiometabolic risk. In contrast, the genetic-cardiometabolic risk link was much attenuated among those living in neighborhoods perceived as socially cohesive. Our results support community-level interventions to enhance the social cohesiveness of individuals' neighborhoods which may provide health benefits by reducing the risks associated with known genetic risk factors.

Socio-economic inequalities in C-reactive protein levels: Evidence from longitudinal studies in England and Indonesia

OBJECTIVE

The levels of health enjoyed by individuals vary according to socio-economic status, and inflammation has been proposed as one pathway through which socio-economic status influences health in high-income countries. However, little is known regarding the social determinants of inflammation in low- and middle-income countries. This study investigated the association between socio-economic status and C-reactive protein (CRP) in England and Indonesia.

METHODS

This study used data from 4923 respondents aged 50+ in the English Longitudinal Study of Ageing and from 1812 respondents from the Indonesian Family Life Survey at baseline. The sources of information on individuals' education attainment, wealth, CRP and other covariates were ELSA Waves 2, 4 and 6, and IFLS Waves 4 and 5. Linear mixed models were performed to identify the longitudinal relationships between socio-economic status and CRP, and joint models were used to deal with bias in longitudinal ageing surveys due to attrition.

RESULTS

Respondents with high school education (β = -0.036, p < 0.01) or college degree or higher (β = -0.127, p < 0.01) in England had lower CRP levels. Being wealthy is correlated with lower CRP levels in England (middle: β = -0.073, p < 0.01; wealthiest: β = -0.133, p < 0.01). Being wealthy and having higher education were related with higher level of CRP in Indonesia. However, those significant relationships vanished when health behaviour and health status were included in the analysis.

CONCLUSIONS

The relationships between socio-economic status and CRP proved to be different in England and Indonesia. Encouraging healthy lifestyles among older adults with low socio-economic status may be the main focus of efforts toward healthy ageing in England and other developed countries. However, in Indonesia and other developing countries, attention is also required to older adults in wealthier socio-economic groups.

Presoaking dried blood spot with water improves efficiency for small-molecule analysis

The current method of extracting small molecules from dried blood spots (DBSs) and liquid blood is similar. However, owing to their different physical characteristics, a modification of the extraction process for DBS is required. We propose a modified method involving presoaking in water that results in better extraction efficiency for small-molecule analysis than the conventional protein precipitation method. Using blood and DBSs from eight subjects, the similarities, recovery rates and extraction efficiencies of both methods were compared. Quantitative analysis showed that seven and six out of ten conditions for the modified method group exhibited almost 100% recovery and extraction efficiency rates, respectively, compared with the conventional method group. Taken together, the results suggest that a presoaking step is needed for efficient DBS analysis.

Risk factors for nutrition-related chronic disease among adults in Indonesia

OBJECTIVE

To conduct a secondary data analysis detailing the associations between sociodemographic and behavioral factors and nutrition-related chronic disease.

METHODS

These analyses utilized 2014 data from the Indonesian Family Life Survey, a home-based survey that collected socioeconomic, dietary intake, physical activity, and biological data among adults. We explored four outcomes in relation to sociodemographic and behavioral determinants: 1) hypertension, 2) elevated high-sensitivity c-reactive protein (hs-CRP), and 3) central obesity, as these are critical metabolic determinants in the progression to cardiovascular disease, and 4) type 2 diabetes. Hypertension was defined as systolic blood pressure ≥140 mm or diastolic blood pressure ≥ 90mm or current use of antihypertensive medication. Elevated hs-CRP was defined as hs-CRP >3 mg/dL. Central obesity was defined as waist circumference ≥ 90 cm if male and waist circumference ≥ 80 cm if female, which are specific to South Asia. Type 2 diabetes was defined as glycated hemoglobin ≥ 6.5%. We employed separate gender-stratified multivariate logistic regression models to test the associations between sociodemographic and behavioral determinants and each nutrition-related chronic disease outcome. All analyses employed sampling weights, which account for the survey design.

RESULTS

In 2014, about 30% of adults were hypertensive and one-fifth had elevated hs-CRP. Approximately 70% of women had central obesity and 11.6% of women and 8.9% of men had diabetes. Older-age was consistently associated with nutrition-related chronic disease and being overweight was associated with hypertension, elevated hs-CRP, and type 2 diabetes. Regularly consuming instant noodles (women) and soda (men) were associated with elevated hs-CRP and soda consumption was associated with central obesity among men.

CONCLUSIONS

Large segments of the adult population in Indonesia now have or are at risk for non-communicable disease. Our analyses provide preliminary empirical evidence that interventions that target healthful food intake (e.g. reduce the intake of ultra-processed foods) should be considered and that the reduction of overweight is critical for preventing chronic diseases in Indonesia.

Field Test and Validation of the Multiplier Measles, Mumps, Rubella, and Varicella-Zoster Multiplexed Assay System in the Democratic Republic of the Congo by Using Dried Blood Spots

Here we describe baseline validation studies and field performance of a research-use-only chemiluminescent multiplex serology panel for measles, mumps, rubella, and varicella-zoster virus used with dried blood spots in support of the 2013-2014 Democratic Republic of the Congo Demographic and Health Survey. Characterization of the panel using U.S. FDA-cleared commercial kits shows good concordance for measles, mumps, rubella, and varicella-zoster with average sensitivity across assays of 94.9% and an average specificity of 91.4%. As expected, performance versus available standards validated for plaque-reduction assays does not provide a 1:1 correspondence with international units and yet demonstrates excellent linearity (average Hill's slope = 1.02) and ∼4 logs of dynamic range. In addition, for the four assays, the multiplexed format allowed for inclusion of three positive and two negative controls for each sample. A prototype Dynex Multiplier chemiluminescent automated immunoassay instrument with a charge-coupled device camera provided a rugged and robust processing and data acquisition platform. Performance of a multiplex instrument for serological testing in a substantially resource-limited environment shows excellent reproducibility, minimal cross-reactivity, and a clear discrimination between specific assays and should be considered a viable option for future serosurveys.IMPORTANCE The critical evaluation of immunization programs is key to identifying areas of suboptimal vaccination coverage, monitoring activities, and aiding development of public health policy. For evaluation of vaccine effectiveness, direct antibody binding assay methods, including enzyme immunoassay, enzyme-linked fluorescence assays, and indirect immunofluorescence assay, are most commonly used for detection of IgG antibodies. However, despite their well-demonstrated, reliable performance, they can be labor-intensive and time-consuming and require separate assays for each individual marker. This necessitates increased sample volumes, processing time, and personnel, which may limit assessment to a few key targets in resource-limited settings, that is, low- and middle-income locations where funding for public health or general infrastructure that directly impacts public health is restricted, limiting access to equipment, infrastructure, and trained personnel. One solution is a multiplexed immunoassay, which allows for the detection of multiple analytes in a single reaction for increased efficiency and rapid surveillance of infectious diseases in limited-resource settings. Thus, the scope of the project precluded a full validation, and here we present abbreviated validation studies demonstrating adequate sensitivity, specificity, and reproducibility.

Psychosocial stress and C-reactive protein from mid-adolescence to young adulthood

OBJECTIVE

Cardiovascular disease (CVD) is one of the most prevalent chronic conditions and leading causes of death. Although CVD clinically manifests in adulthood, underlying processes of CVD begin in the earlier decades of life. Inflammation has been shown to play a key role, but relatively little is understood about how inflammation changes over time among young individuals. Additionally, how psychosocial factors like stress may influence changes in inflammation earlier in the lifespan is not entirely clear. Thus, the current three-wave longitudinal study examined the developmental trajectory of CRP, a marker of systemic inflammation, over a 4-year period from mid-adolescence into young adulthood. Between- and within-person differences in stress in relation to changes in CRP were also examined.

METHOD

A sample of 350 individuals was recruited during mid-adolescence and participated in 1 to 3 assessments, 2 years apart. At each assessment, participants provided dried blood spots for the assessment of CRP and reported on recent major life events, perceived stress, and daily interpersonal stress.

RESULTS

Multilevel modeling indicated that CRP increased with age, and within-person increases in perceived stress, but not life events or daily stress, were associated with higher CRP. Between-person differences in average levels of stress from mid-adolescence into young adulthood were not associated with changes in CRP.

CONCLUSION

These findings suggest that the link between stress and systemic inflammation between mid-adolescence and young adulthood may be most affected by contemporaneous experiences of perceived stress. There was little evidence to suggest that CRP trajectories varied by between-person differences in overall average levels of perceived stress, life events, and daily stress. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Change in Cardiometabolic Risk Among Blacks, Whites, and Hispanics: Findings From the Health and Retirement Study

Background

Blacks experience greater multisystem physiological dysregulation, or cumulative biological risk, which is associated with poor cardiometabolic health and mortality. In this study, we assess race differences in change in risk over 4 years among older whites, blacks, and Hispanics.

Method

We examined race differences in 4-year change in individual biomarkers and a cumulative measure of risk-cardiometabolic risk (CMR)-using data for each respondent from two waves of the Health and Retirement Study's biomarker assessment (n = 5,512). CMR is a count of high-risk cardiovascular and metabolic biomarkers. We estimated mean CMR at baseline and follow-up by race/ethnicity, and used logistic regression to determine whether race differences exist in 4-year transitions between high- and low-risk states for individual biomarkers.

Results

Blacks had higher baseline CMR than whites and Hispanics and experienced an increase in risk over 4 years; conversely, CMR decreased among whites and Hispanics. Blacks were more likely to develop high-risk pulse pressure and high-risk hemoglobin A1c, which contributed to increases in CMR. Whites and Hispanics were more likely to become low-risk on C-reactive protein and high-density lipoprotein cholesterol which contributed to declines in CMR. Race differences in transitions between risk states remained after controlling for social, behavioral, and health care-related factors. However, the racial patterning of these differences was influenced by disease diagnosis and medication use.

Conclusions

We show that the cardiometabolic health of older blacks worsens as they age both absolutely and relative to that of whites and Hispanics because of poor blood pressure control and diabetes prevention.

Perceived neighborhood social cohesion and cardiometabolic risk: a gene × environment study

People living in socially cohesive neighborhoods generally have better health. We extend this research by evaluating the hypothesis that perceived neighborhood cohesion may influence health by attenuating genetic liability for cardiometabolic risk factors. Using data from the Health and Retirement Study (n = 6,615; mean age 69.7), we conducted a gene × environment interaction study hypothesizing that perceived neighborhood cohesion would attenuate the link between polygenic scores for waist-to-hip ratio (WHR) and body mass index and a measure of multisystem cardiometabolic risk (systolic blood pressure [SBP] and diastolic blood pressure [DBP], heart rate, A1c, C-reactive protein, and total and high-density lipoprotein cholesterol). In support of the hypothesis, results indicated that among people perceiving low neighborhood cohesion, higher WHR polygenic scores were associated with greater cardiometabolic risk. In contrast, the genetic-cardiometabolic risk link was much attenuated among those living in neighborhoods perceived as socially cohesive. Our results support community-level interventions to enhance the social cohesiveness of individuals' neighborhoods which may provide health benefits by reducing the risks associated with known genetic risk factors.