Biomarkers as MEDiators of racial disparities in risk factors (BioMedioR): Rationale, study design, and statistical considerations

The association of leptin and incident hypertension in the reasons for geographic and racial differences in stroke (REGARDS) cohort

Leptin is an adipokine associated with obesity and with hypertension in animal models. Whether leptin is associated with hypertension independent of obesity is unclear. Relative to White adults, Black adults have higher circulating leptin concentration. As such, leptin may mediate some of the excess burden of incident hypertension among Black adults. REGARDS enrolled 30,239 adults aged ≥45 years from 48 US states in 2003-07. Baseline leptin was measured in a sex- and race-stratified sample of 4400 participants. Modified Poisson regression estimated relative risk (RR) of incident hypertension (new ≥140/≥90 mmHg threshold or use of antihypertensives) per SD of log-transformed leptin, stratified by obesity (BMI of 30 kg/m2). Inverse odds ratio weighting estimated the % mediation by leptin of the excess hypertension RR among Black relative to White participants. Among the 1821 participants without prevalent hypertension, 35% developed incident hypertension. Obesity modified the relationship between leptin and incident hypertension (P-interaction 0.006) such that higher leptin was associated with greater hypertension risk in the crude model among those with BMI < 30 kg/m2, but not those with BMI ≥ 30 kg/m2. This was fully attenuated when adjusting for anthropometric measures. In the crude model, Black adults had a 52% greater risk of incident hypertension. Leptin did not significantly mediate this disparity. In this national U.S. sample, leptin was associated with incident hypertension among non-obese but not obese adults. Future investigations should focus on the effect of weight modification on incident hypertension among non-obese adults with elevated leptin.

Factor VIII and Incident Hypertension in Black and White Adults: The REasons for Geographic and Racial Differences in Stroke (REGARDS) Cohort

BACKGROUND

Nearly half of all Americans have hypertension, and Black adults experience a disproportionate burden. Hypercoagulability may relate to hypertension risk, and higher levels of factor VIII increase thrombosis risk. Black adults have higher factor VIII and more hypertension than other groups. Whether higher factor VIII associates with incident hypertension is unknown.

METHODS

The Biomarkers as Mediators of Racial Disparities in Risk Factors (BioMedioR) study measured certain biomarkers in a sex-race stratified sample of 4,400 REGARDS participants who attended both visits. We included BioMedioR participants, excluding those with prevalent hypertension, missing factor VIII level, or covariates of interest. Modified Poisson regression estimated risk ratios (RR) for incident hypertension by higher log-transformed factor VIII level per SD (SD of log-transformed factor VIII, 0.33). Weighting was applied to take advantage of REGARDS sampling design.

RESULTS

Among the 1,814 participants included (55% female, 24% Black race), the median follow-up was 9.5 years and 35% (2,146/6,138) developed hypertension. Black participants had a higher median (IQR) factor VIII level (105.6%; 87.1%-126.9%) than White participants (95.6%; 79.8%-115.9%; P < 0.001). The age- and sex-adjusted Black-White hypertension RR was 1.45 (95% CI 1.28, 1.63). Higher factor VIII was not associated with more hypertension (final model RR 1.01; 95% CI 0.94, 1.07).

CONCLUSIONS

In a prospective study of Black and White adults without prevalent hypertension, factor VIII was not associated with greater hypertension risk.

Endothelial Dysfunction Biomarkers and CKD Incidence in the REGARDS Cohort

Introduction

Chronic kidney disease (CKD) is only partly caused by traditional risk factors. Endothelial dysfunction is common in CKD and may contribute to CKD incidence. We studied the association of circulating biomarkers reflecting endothelial dysfunction with incident CKD.

Methods

The Reasons for Geographical and Racial Differences in Stroke (REGARDS) study is a prospective cohort of 30,239 Black or White adults aged ≥45 years. Baseline levels of intercellular cellular adhesion molecule 1 (ICAM-1), vascular cellular adhesion molecule 1 (VCAM-1), factor VIII (FVIII), and E-selectin were measured in 3300 participants without baseline CKD or albuminuria who attended a second visit 9.4 years later. Kidney outcomes were incident CKD (estimated glomerular filtration rate [eGFR] <60 ml/min per 1.73 m2 and ≥40% decline or onset of new end-stage kidney disease), incident ≥30% eGFR decline, and incident albuminuria (albumin-to-creatinine ratio [ACR] ≥30 mg/g). Sequentially adjusted logistic regression models assessed the association of biomarkers with kidney outcomes.

Results

Median age of participants was 62 years, 49% were women, and 46% identified as Black. Of the participants, 228 (6.9%) developed CKD, 613 (18.9%) experienced ≥30% decline in eGFR, and 356 (11.4%) developed albuminuria. The adjusted odds ratios (ORs) for incident CKD per 1 SD increment biomarker was 1.12 for ICAM-1 (95% confidence interval [CI]: 1.02-1.22), 1.10 for VCAM-1 (95% CI: 1.01-1.20), 1.15 for FVIII (95% CI: 1.06-1.24), and 1.10 for E-selectin (95% CI: 1.01-1.20). Results were similar for incident ≥30% eGFR decline but not albuminuria, where only higher FVIII was positively associated.

Conclusion

Higher concentration of ICAM-1, VCAM-1, FVIII, and E-selectin were associated with incident CKD and ≥30% eGFR decline in a large cohort study. Higher FVIII was also associated with incident albuminuria.

Cytokines, C-Reactive Protein, and Risk of Incident Hypertension in the REGARDS Study

BACKGROUND

Hypertension is a highly prevalent cardiovascular disease risk factor that may be related to inflammation. Whether adverse levels of specific inflammatory cytokines relate to hypertension is unknown. The present study sought to determine whether higher levels of IL (interleukin)-1β, IL-6, TNF (tumor necrosis factor)-α, IFN (interferon)-γ, IL-17A, and CRP (C-reactive protein) are associated with a greater risk of incident hypertension.

METHODS

The REGARDS study (Reasons for Geographic and Racial Difference in Stroke) is a prospective cohort study that recruited 30 239 community-dwelling Black and White adults from the contiguous United States in 2003 to 2007 (visit 1), with follow-up 9 years later in 2013 to 2016 (visit 2). We included participants without prevalent hypertension who attended follow-up 9 years later and had available laboratory measures and covariates of interest. Poisson regression estimated the risk ratio of incident hypertension by level of inflammatory biomarkers.

RESULTS

Among 1866 included participants (mean [SD] aged of 62 [8] years, 25% Black participants, 55% women), 36% developed hypertension. In fully adjusted models comparing the third to first tertile of each biomarker, there was a greater risk of incident hypertension for higher IL-1β among White (1.24 [95% CI, 1.01-1.53]) but not Black participants (1.01 [95% CI, 0.83-1.23]) and higher TNF-α (1.20 [95% CI, 1.02-1.41]) and IFN-γ (1.22 [95% CI, 1.04-1.42]) among all participants. There was no increased risk with IL-6, IL-17A, or CRP.

CONCLUSIONS

Higher levels of IL-1β, TNF-α, and IFN-γ, representing distinct inflammatory pathways, are elevated in advance of hypertension development. Whether modifying these cytokines will reduce incident hypertension is unknown.

Proneurotensin/Neuromedin N and Risk of Incident CKD and Other Kidney Outcomes in Community-Living Individuals: The REGARDS Study

Rationale & Objective

Plasma proneurotensin/neuromedin N (pro-NT/NMN) is a precursor of neurotensin, a tridecapeptide linked with type 2 diabetes mellitus and other comorbid conditions associated with kidney disease. Whether pro-NT/NMN is directly associated with incident chronic kidney disease (CKD), and whether that association differs by race, is uncertain. We evaluated whether pro-NT/NMN levels were associated with increased risk of kidney outcomes.

Study Design

Prospective cohort.

Setting & Participants

Participants in Biomarker Mediators of Racial Disparities in Risk Factors, a nested cohort from the REasons for Geographic And Racial Differences in Stroke study, with available stored serum and urine samples from baseline and second visits for biomarker measurement.

Exposure

Baseline log-transformed pro-NT/NMN.

Outcomes

Incident CKD, progressive estimated glomerular filtration rate (eGFR) decline, incident albuminuria, and incident kidney failure within median follow-up time of 9.4 years.

Analytical Approach

Logistic regression.

Results

Among 3,914 participants, the mean ± SD age was 64 ± 8 (SD) years, 48% were women, and 51% were Black. Median baseline eGFR was 90 (IQR, 77-102) mL/min/1.73 m2. Each SD higher of pro-NT/NMN was associated with 9% higher odds of progressive eGFR decline (OR, 1.09; 95% CI, 1.00-1.20). There was no association observed with incident CKD (OR, 1.10; 95% CI, 0.96-1.27), incident albuminuria (OR, 1.08; 95% CI, 0.96-1.22), or incident kidney failure (OR, 1.10; 95% CI, 0.83-1.46). There were no differences in results by race or sex.

Limitations

Single measurement of pro-NT/NMN and limited generalizability.

Conclusions

Higher pro-NT/NMN was associated with progressive eGFR decline but no other manifestations of kidney disease incidence.

Soluble CD14 and Incident Diabetes Risk: The REasons for Geographic and Racial Differences in Stroke (REGARDS) Study

Context

Soluble CD14 (sCD14) is an inflammation biomarker with higher concentrations in White than Black adults. Higher sCD14 is seen in insulin resistance and diabetes. There are limited data on the relationship between sCD14 and incident diabetes.

Objective

To determine the association of sCD14 with incident diabetes risk in a large biracial US cohort and evaluate whether relationships differ by race.

Design

This study included 3401 Black and White participants from the REasons for Geographic And Racial Differences in Stroke (REGARDS) study without baseline diabetes who completed baseline and follow-up in-home visits. Modified Poisson regression models estimated risk ratios (RR) of incident diabetes per 1-SD increment sCD14, with adjustment for risk factors. A sCD14-by-race interaction evaluated whether associations differed by race.

Results

There were 460 cases of incident diabetes over a mean 9.5 years of follow-up. The association of sCD14 with diabetes differed by race (P for interaction < .09). Stratifying by race, adjusting for age, sex, and region, higher sCD14 was associated with incident diabetes in White (RR: 1.15; 95% CI: 1.01, 1.33) but not Black participants (RR: 0.96; 95% CI: 0.86, 1.08). In models adjusted for clinical and sociodemographic diabetes risk factors, the association was attenuated among White participants (RR: 1.10; 95% CI: 0.95, 1.28) and remained null among Black participants (RR: 0.90; 95% CI: 0.80, 1.01).

Conclusion

sCD14 was associated with incident diabetes risk in White but not Black adults, but this association was explained by diabetes risk factors.

Interleukin-6, Diabetes, and Metabolic Syndrome in a Biracial Cohort: The Reasons for Geographic and Racial Differences in Stroke Cohort

OBJECTIVE

Black Americans have a greater risk of type 2 diabetes than White Americans. The proinflammatory cytokine interleukin-6 (IL-6) is implicated in diabetes pathogenesis, and IL-6 levels are higher in Black individuals. This study investigated associations of IL-6 with incident diabetes and metabolic syndrome in a biracial cohort.

RESEARCH DESIGN AND METHODS

The Reasons for Geographic and Racial Differences in Stroke (REGARDS) study enrolled 30,239 Black and White adults age ≥45 years in 2003-2007, with a follow-up ∼9.5 years later. Baseline plasma IL-6 was measured in 3,399 participants at risk of incident diabetes and 1,871 at risk of metabolic syndrome. Relative risk (RR) by IL-6 was estimated with modified Poisson regression for both groups.

RESULTS

Incident diabetes occurred in 14% and metabolic syndrome in 20%; both rates rose across IL-6 quartiles. There was a three-way interaction of IL-6, race, and central adiposity for incident diabetes (P = 8 × 10-5). In Black participants with and without central adiposity, RRs were 2.02 (95% CI 1.00-4.07) and 1.66 (1.00-2.75) for the fourth compared with first IL-6 quartile, respectively. The corresponding RRs were 1.73 (0.92-3.26) and 2.34 (1.17-4.66) in White participants. The pattern was similar for IL-6 and metabolic syndrome.

CONCLUSIONS

Although IL-6 was higher in Black than in White participants and those with central adiposity, the association of IL-6 with diabetes risk was statistically significant only among White participants without central adiposity. The association with metabolic syndrome risk was similarly stronger in low-risk groups. The results support the concept of interventions to lower inflammation in diabetes prevention, but to reduce race disparities, better biomarkers are needed.

Plasma proenkephalin A and incident chronic kidney disease and albuminuria in the REasons for Geographic And Racial Differences in Stroke (REGARDS) cohort

BACKGROUND

Plasma proenkephalin A (PENK-A) is a precursor of active enkephalins. Higher blood concentrations have been associated with estimated glomerular filtration rate (eGFR) decline in European populations. Due to the significant disparity in incident chronic kidney disease (CKD) between White and Black people, we evaluated the association of PENK-A with incident CKD and other kidney outcomes among a biracial cohort in the U.S.

METHODS

In a nested cohort of 4,400 participants among the REasons for Geographic And Racial Differences in Stroke, we determined the association between baseline PENK-A concentration and incident CKD using the creatinine-cystatin C CKD-EPI 2021 equation without race coefficient, significant eGFR decline, and incident albuminuria between baseline and a follow-up visit 9.4 years later. We tested for race and sex interactions. We used inverse probability sampling weights to account for the sampling design.

RESULTS

At baseline, mean (SD) age was 64 (8) years, 49% were women, and 52% were Black participants. 8.5% developed CKD, 21% experienced ≥ 30% decline in eGFR and 18% developed albuminuria. There was no association between PENK-A and incident CKD and no difference by race or sex. However, higher PENK-A was associated with increased odds of progressive eGFR decline (OR: 1.12; 95% CI 1.00, 1.25). Higher PENK-A concentration was strongly associated with incident albuminuria among patients without diabetes mellitus (OR: 1.29; 95% CI 1.09, 1.53).

CONCLUSION

While PENK-A was not associated with incident CKD, its associations with progression of CKD and incident albuminuria, among patients without diabetes, suggest that it might be a useful tool in the evaluation of kidney disease among White and Black patients.

D-dimer and the risk of hypertension: The REasons for Geographic And Racial Differences in Stroke Cohort Study

Background

Reasons for increased risk of hypertension in Black compared with White people are only partly understood. D-dimer, a thrombo-inflammatory marker higher in Black individuals, is also higher in people with hypertension. However, the impact of D-dimer on racial disparities in risk of incident hypertension has not been studied.

Objectives

To assess whether D-dimer is associated with the risk of incident hypertension, whether the association between D-dimer and the risk of incident hypertension differs by race, and whether the biology reflected by D-dimer explains racial disparities in the risk of incident hypertension.

Methods

This study included 1867 participants in the REasons for Geographic And Racial Differences in Stroke cohort study without baseline hypertension and with a second visit 9.4 years after baseline. Risk ratios of incident hypertension by baseline D-dimer level were estimated, a D-dimer-by-race interaction was tested, and the mediating effect of D-dimer (which represents underlying biological processes) on the association of race and hypertension risk was assessed.

Results

The risk of incident hypertension was 47% higher in persons in the top quartile than in those in the bottom quartile of D-dimer (risk ratio [RR]: 1.47; 95% CI: 1.23-1.76). The association was partly attenuated after adjusting for sociodemographic and adiposity-related risk factors (RR: 1.22; 95% CI: 1.02-1.47). The association of D-dimer and hypertension did not differ by race, and D-dimer did not attenuate the racial difference in the risk of incident hypertension.

Conclusion

D-dimer concentration reflects pathophysiology related to the development of hypertension. Specific mechanisms require further study and may involve adiposity.