Strong protective effect of the APOL1 p.N264K variant against G2-associated focal segmental glomerulosclerosis and kidney disease

African Americans have a significantly higher risk of developing chronic kidney disease, especially focal segmental glomerulosclerosis -, than European Americans. Two coding variants (G1 and G2) in the APOL1 gene play a major role in this disparity. While 13% of African Americans carry the high-risk recessive genotypes, only a fraction of these individuals develops FSGS or kidney failure, indicating the involvement of additional disease modifiers. Here, we show that the presence of the APOL1 p.N264K missense variant, when co-inherited with the G2 APOL1 risk allele, substantially reduces the penetrance of the G1G2 and G2G2 high-risk genotypes by rendering these genotypes low-risk. These results align with prior functional evidence showing that the p.N264K variant reduces the toxicity of the APOL1 high-risk alleles. These findings have important implications for our understanding of the mechanisms of APOL1-associated nephropathy, as well as for the clinical management of individuals with high-risk genotypes that include the G2 allele.

Cross-sectional analysis of racial differences in hydration and neighborhood deprivation in young adults

BACKGROUND

Inadequate hydration is associated with cardiovascular and kidney disease morbidity and all-cause mortality. Compared with White individuals, Black individuals exhibit a higher prevalence of inadequate hydration, which may contribute to racial health disparities. However, the underlying reasons for these differences in hydration remain unclear.

OBJECTIVE

This cross-sectional study aimed to investigate whether neighborhood deprivation contributes to racial differences in hydration status.

METHODS

We assessed 24 Black and 30 White college students, measuring 24-hour urine osmolality, urine flow rate, urine specific gravity, and plasma copeptin concentration. Participants recorded their food and fluid intake for 3 d to assess total water intake from food and beverages. Neighborhood socioeconomic deprivation was measured using a tract-level Area Deprivation Index.

RESULTS

Black participants exhibited higher urine osmolality (640 [314] compared with 440 [283] mOsm/kg H2O, respectively, P = 0.006) and lower urine flow rate (1.06 [0.65] compared with 1.71 [0.89] ml/min, respectively, P = 0.009) compared with White participants, indicating greater hypohydration among Black participants. Black participants reported lower total water intake from food and beverages than White participants (2.3 ± 0.7 compared with 3.5 ± 1.1 L/day, respectively, P < 0.01). Black participants exhibited higher copeptin than White participants (6.3 [3.1] compared with 4.5 [2.3] pmol/L, P = 0.046), and urine osmolality mediated 67% of the difference (P = 0.027). Black participants reported greater cumulative exposure to neighborhood deprivation during childhood (ages 0-18 y). Furthermore, neighborhood deprivation during childhood was associated with urine specific gravity (P = 0.031) and total water intake from food and beverages (P = 0.042) but did not mediate the racial differences in these measures.

CONCLUSION

Our data suggest that compared with White young adults, Black young adults are hypohydrated and exhibit higher plasma copeptin concentration, and that greater neighborhood deprivation is associated with chronic underhydration irrespective of race. This trial was registered at clinicaltrials.gov as NCT04576338.

Associations of FGF23 with 10-Year Change in eGFR and UACR and with Incident CKD in the CARDIA Cohort

Key Points

FGF23 has a nonlinear positive association with incident CKD among healthy, middle-aged adults. The relationship between FGF23 and incident CKD was only significant among participants with cFGF23 levels in the highest quartile. FGF23 is not associated with 10-year change in eGFR or 10-year change in UACR among healthy, middle-aged adults.

Background

The relationship of fibroblast growth factor 23 (FGF23) with incident CKD has been examined in older but not younger populations.

Methods

Linear regression models were used to examine the associations of c-terminal FGF23 (cFGF23) and intact FGF23 (iFGF23) with 10-year change (1995–96 to 2005–06) in eGFR and urine albumin-to-creatinine ratio (UACR) in the Coronary Artery Risk Development in Young Adults cohort. Cox proportional hazard models were used to assess the association of cFGF23 with incident CKD, defined as eGFR <60 ml/min per 1.73 m2 or UACR ≥30 mg/g. Multivariable models were adjusted for age, sex, race, education, field center, physical activity, body mass index, diabetes, smoking, and systolic BP.

Results

Among 2511 participants, the mean age was 45±3.6 years; mean eGFR was 96.5±14.0 ml/min per 1.73 m2; and median UACR was 4.3 (interquartile range, 3.0–6.7) mg/g. Most (62.6%) participants were nonsmokers; the prevalence of diabetes was low (6.6%); and median values for 10-year changes in eGFR and UACR were modest (−5.50 ml/min per 1.73 m2 and 0.70 mg/g, respectively). No consistent associations between cFGF23 and 10-year change in eGFR and UACR were observed. During a median follow-up of 9.98 years, incident CKD developed in 258 participants. There was a nonlinear association of cFGF23 with incident CKD, and relative to the lowest quartile of cFGF23, a significant relationship was detected only among participants in the highest quartile (hazard ratio, 1.58; 95% confidence interval, 1.09 to 2.27). Similar findings were observed for iFGF23.

Conclusion

Among middle-aged adults in the Coronary Artery Risk Development in Young Adults cohort, median eGFR and UACR changes were modest and cFGF23 and iFGF23 were not consistently associated with 10-year change in eGFR or UACR. A nonlinear relationship was observed between cFGF23 and incident CKD, with individuals with highest cFGF23 levels being at risk of developing CKD.

Strong protective effect of the APOL1 p.N264K variant against G2-associated focal segmental glomerulosclerosis and kidney disease

Black Americans have a significantly higher risk of developing chronic kidney disease (CKD), especially focal segmental glomerulosclerosis (FSGS), than European Americans. Two coding variants (G1 and G2) in the APOL1 gene play a major role in this disparity. While 13% of Black Americans carry the high-risk recessive genotypes, only a fraction of these individuals develops FSGS or kidney failure, indicating the involvement of additional disease modifiers. Here, we show that the presence of the APOL1 p.N264K missense variant, when co-inherited with the G2 APOL1 risk allele, substantially reduces the penetrance of the G1G2 and G2G2 high-risk genotypes by rendering these genotypes low-risk. These results align with prior functional evidence showing that the p.N264K variant reduces the toxicity of the APOL1 high-risk alleles. These findings have important implications for our understanding of the mechanisms of APOL1 -associated nephropathy, as well as for the clinical management of individuals with high-risk genotypes that include the G2 allele.

Iron-Deficiency Anemia in CKD: A Narrative Review for the Kidney Care Team

Anemia is a common complication of chronic kidney disease (CKD) and is associated with increased mortality and reduced health-related quality of life. Anemia is characterized by a decrease in hemoglobin, the iron-rich protein that the body uses for oxygen transport. Iron is required to produce hemoglobin, and disruptions in the iron homeostasis can lead to iron-deficiency anemia. Management of anemia in individuals with CKD is typically performed by a team of physicians, nurse practitioners, physician assistants, or registered nurses. Throughout the care continuum, the management can be enhanced by multidisciplinary care, and individuals with CKD can benefit from the involvement of other specialties, with dietitians/nutritionists playing an important role. However, a key area of unmet clinical need is how to assess and address iron-deficiency anemia. This review aims to provide an overview of iron-deficiency anemia in CKD and how this may be diagnosed and managed by the entire kidney care team, such as describing the mechanisms underlying iron homeostasis, the complications of iron-deficiency anemia, and the current challenges associated with its diagnosis and treatment in CKD. Opportunities for each multidisciplinary team member to add value to the care of individuals with CKD and iron-deficiency anemia are also described.

The damaging duo: Obesity and excess dietary salt contribute to hypertension and cardiovascular disease

Hypertension is a primary risk factor for cardiovascular disease. Cardiovascular disease is the leading cause of death among adults worldwide. In this review, we focus on two of the most critical public health challenges that contribute to hypertension-obesity and excess dietary sodium from salt (i.e., sodium chloride). While the independent effects of these factors have been studied extensively, the interplay of obesity and excess salt overconsumption is not well understood. Here, we discuss both the independent and combined effects of excess obesity and dietary salt given their contributions to vascular dysfunction, autonomic cardiovascular dysregulation, kidney dysfunction, and insulin resistance. We discuss the role of ultra-processed foods-accounting for nearly 60% of energy intake in America-as a major contributor to both obesity and salt overconsumption. We highlight the influence of obesity on elevated blood pressure in the presence of a high-salt diet (i.e., salt sensitivity). Throughout the review, we highlight critical gaps in knowledge that should be filled to inform us of the prevention, management, treatment, and mitigation strategies for addressing these public health challenges.

Lipoprotein(a) and the Risk for Recurrent Atherosclerotic Cardiovascular Events Among Adults With CKD: The Chronic Renal Insufficiency Cohort (CRIC) Study

Rationale & Objective

Many adults with chronic kidney disease (CKD) and atherosclerotic cardiovascular disease (ASCVD) have high lipoprotein(a) levels. It is unclear whether high lipoprotein(a) levels confer an increased risk for recurrent ASCVD events in this population. We estimated the risk for recurrent ASCVD events associated with lipoprotein(a) in adults with CKD and prevalent ASCVD.

Study Design

Observational cohort study.

Setting & Participants

We included 1,439 adults with CKD and prevalent ASCVD not on dialysis enrolled in the Chronic Renal Insufficiency Cohort study between 2003 and 2008.

Exposure

Baseline lipoprotein(a) mass concentration, measured using a latex-enhanced immunoturbidimetric assay.

Outcomes

Recurrent ASCVD events (primary outcome), kidney failure, and death (exploratory outcomes) through 2019.

Analytical Approach

We used Cox proportional-hazards regression models to estimate adjusted HR (aHRs) and 95% CIs.

Results

Among participants included in the current analysis (mean age 61.6 years, median lipoprotein(a) 29.4 mg/dL [25th-75th percentiles 9.9-70.9 mg/dL]), 641 had a recurrent ASCVD event, 510 developed kidney failure, and 845 died over a median follow-up of 6.6 years. The aHR for ASCVD events associated with 1 standard deviation (SD) higher log-transformed lipoprotein(a) was 1.04 (95% CI, 0.95-1.15). In subgroup analyses, 1 SD higher log-lipoprotein(a) was associated with an increased risk for ASCVD events in participants without diabetes (aHR, 1.23; 95% CI, 1.02-1.48), but there was no evidence of an association among those with diabetes (aHR, 0.99; 95% CI, 0.88-1.10, P comparing aHRs = 0.031). The aHR associated with 1 SD higher log-lipoprotein(a) in the overall study population was 1.16 (95% CI, 1.04-1.28) for kidney failure and 1.02 (95% CI, 0.94-1.11) for death.

Limitations

Lipoprotein(a) was not available in molar concentration.

Conclusions

Lipoprotein(a) was not associated with the risk for recurrent ASCVD events in adults with CKD, although it was associated with a risk for kidney failure.

Risk Factors for Incident CKD in Black and White Americans: The REGARDS Study

RATIONALE & OBJECTIVE

Little information exists on the incidence of and risk factors for chronic kidney disease (CKD) in contemporary US cohorts and whether risk factors differ by race, sex, or region in the United States.

STUDY DESIGN

Observational cohort study.

SETTING & PARTICIPANTS

4,198 Black and 7,799 White participants aged at least 45 years, recruited from 2003 through 2007 across the continental United States, with baseline estimated glomerular filtration rate (eGFR)>60mL/min/1.73m2 and eGFR assessed again approximately 9 years later.

EXPOSURES

Age, sex, race (Black or White), region ("stroke belt" or other), education, income, systolic blood pressure, body mass index, diabetes, coronary heart disease, hyperlipidemia, smoking, and albuminuria.

OUTCOMES

(1) eGFR change and (2) incident CKD defined as eGFR<60mL/min/1.73m2 and≥40% decrease from baseline or kidney failure.

ANALYTICAL APPROACH

Linear regression and modified Poisson regression were used to determine the association of risk factors with eGFR change and incident CKD overall and stratified by race, sex, and region.

RESULTS

Mean age of participants was 63±8 (SD) years, 54% were female, and 35% were Black. After 9.4±1.0 years of follow-up, CKD developed in 9%. In an age-, sex-, and race-adjusted model, Black race (β =-0.13; P<0.001) was associated with higher risk of eGFR change, but this was attenuated in the fully adjusted model (β=0.02; P=0.5). Stroke belt residence was independently associated with eGFR change (β =-0.10; P<0.001) and incident CKD (relative risk, 1.14 [95% CI, 1.01-1.30]). Albuminuria was more strongly associated with eGFR change (β of-0.26 vs-0.17; P=0.01 for interaction) in Black compared with White participants. Results were similar for incident CKD.

LIMITATIONS

Persons of Hispanic ethnicity were excluded; unknown duration and/or severity of risk factors.

CONCLUSIONS

Established CKD risk factors accounted for higher risk of incident CKD in Black versus White individuals. Albuminuria was a stronger risk factor for eGFR decrease and incident CKD in Black compared with White individuals. Living in the US stroke belt is a novel risk factor for CKD.

Associations of Urine Biomarkers of Kidney Tubule Health With Incident Hypertension and Longitudinal Blood Pressure Change in Middle-Aged Adults: The CARDIA Study

BACKGROUND

Urine biomarkers of kidney tubule injury associate with incident hypertension in older adults with comorbidities, but less is known about these associations in younger adults.

METHODS

In 1170 participants of the CARDIA study (Coronary Artery Risk Development in Young Adults; mean age, 45 years; 40% Black people; 56% women) without hypertension, cardiovascular disease, or kidney disease at baseline, we examined associations of urine MCP-1 (monocyte chemoattractant protein-1), α1m (alpha-1-microglobulin), KIM-1 (kidney injury molecule-1), EGF (epidermal growth factor), IL (interleukin)-18, YKL-40 (chitinase-3-like protein 1), and UMOD (uromodulin) with incident hypertension (onset of systolic blood pressure [BP] ≥130 mm Hg or diastolic BP ≥80 mm Hg or initiation of hypertension medications) and longitudinal BP change in models adjusted for hypertension risk factors, estimated glomerular filtration rate, and albuminuria.

RESULTS

After a median 9.9 (interquartile range, 5.9-10.2) years, 376 participants developed incident hypertension. In demographic-adjusted analyses, higher tertiles of EGF associated with lower risk of incident hypertension in both Black and White participants. After multivariable adjustment, the risk of incident hypertension remained lower in tertile 2 (hazard ratio, 0.70 [95% CI, 0.50-0.97]) and tertile 3 (hazard ratio, 0.58 [0.39-0.85]) of EGF versus tertile 1. In fully adjusted models, participants in EGF tertile 3 had smaller 10-year increases in systolic (-3.4 [95% CI, -6.1 to -0.7] mm Hg) and diastolic BP (-2.6 [95% CI, -4.6 to -0.6] mm Hg) than tertile 1. Other biomarkers showed inconsistent associations with incident hypertension and BP change.

CONCLUSIONS

In middle-aged adults without hypertension, cardiovascular disease, or kidney disease, higher urine EGF associated with lower risk of incident hypertension and lower 10-year BP elevations.

Dietary Patterns, Apolipoprotein L1 Risk Genotypes, and CKD Outcomes Among Black Adults in the Reasons for Geographic and Racial Differences in Stroke (REGARDS) Cohort Study

Rationale & Objective

Dietary factors may impact inflammation and interferon production, which could influence phenotypic expression of Apolipoprotein1 (APOL1) genotypes. We investigated whether associations of dietary patterns with kidney outcomes differed by APOL1 genotypes.

Study Design

Prospective cohort.

Settings & Participants

5,640 Black participants in the Reasons for Geographic and Racial Differences in Stroke (REGARDS).

Exposures

Five dietary patterns derived from food frequency questionnaires: Convenience foods, Southern, Sweets and Fats, Plant-based, and Alcohol/Salads.

Outcomes

Incident chronic kidney disease (CKD), CKD progression, and kidney failure. Incident CKD was defined as a change in estimated glomerular filtration rate (eGFR) to <60 mL/min/1.73 m2 accompanied by a ≥25% decline from baseline eGFR or development of kidney failure among those with baseline eGFR ≥60 mL/1.73 m2 body surface area. CKD progression was defined as a composite of 40% reduction in eGFR from baseline or development of kidney failure in the subset of participants who had serum creatinine levels at baseline and completed a second in-home visit/follow-up visit.

Analytical Approach

We examined associations of dietary pattern quartiles with incident CKD (n=4,188), CKD progression (n=5,640), and kidney failure (n=5,640). We tested for statistical interaction between dietary patterns and APOL1 genotypes for CKD outcomes and explored stratified analyses by APOL1 genotypes.

Results

Among 5,640 Black REGARDS participants, mean age was 64 years (standard deviation = 9), 35% were male, and 682 (12.1%) had high-risk APOL1 genotypes. Highest versus lowest quartiles (Q4 vs Q1) of Southern dietary pattern were associated with higher adjusted odds of CKD progression (OR, 1.28; 95% CI, 1.01-1.63) but not incident CKD (OR, 0.92; 95% CI, 0.74-1.14) or kidney failure (HR, 1.48; 95% CI, 0.90-2.44). No other dietary patterns showed significant associations with CKD. There were no statistically significant interactions between APOL1 genotypes and dietary patterns. Stratified analysis showed no consistent associations across genotypes, although Q3 and Q4 versus Q1 of Plant-based and Southern patterns were associated with lower odds of CKD progression among APOL1 high- but not low-risk genotypes.

Limitations

Included overlapping dietary patterns based on a single time point and multiple testing.

Conclusions

In Black REGARDS participants, Southern dietary pattern was associated with increased risk of CKD progression. Analyses stratified by APOL1 genotypes suggest associations may differ by genetic background, but these findings require confirmation in other cohorts.

Association of Uremic Solutes With Cardiovascular Death in Diabetic Kidney Disease

RATIONALE & OBJECTIVE

Cardiovascular disease (CVD) is a major cause of mortality among people with diabetic kidney disease (DKD). The pathophysiology is inadequately explained by traditional CVD risk factors. The uremic solutes trimethylamine-N-oxide (TMAO) and asymmetric and symmetric dimethylarginine (ADMA, SDMA) have been linked to CVD in kidney failure with replacement therapy (KFRT), but data are limited in populations with diabetes and less severe kidney disease.

STUDY DESIGN

Observational cohort.

SETTINGS & PARTICIPANTS

Random subcohort of 555 REGARDS (Reasons for Geographic and Racial Differences in Stroke) study participants with diabetes and estimated glomerular filtration rate (eGFR) <60 mL/min/1.73 m2 at study entry.

EXPOSURE

ADMA, SDMA, and TMAO assayed by liquid chromatography-mass spectrometry in plasma and urine.

OUTCOME

Cardiovascular mortality (primary outcome); all-cause mortality and incident KFRT (secondary outcomes).

ANALYTICAL APPROACH

Plasma concentrations and ratios of urine to plasma concentrations of ADMA, SDMA, and TMAO were tested for association with outcomes. Adjusted Cox regression models were fitted and hazard ratios of outcomes calculated per standard deviation and per doubling, and as interquartile comparisons.

RESULTS

The mean baseline eGFR was 44 mL/min/1.73 m2. Cardiovascular death, overall mortality, and KFRT occurred in 120, 285, and 89 participants, respectively, during a mean 6.2 years of follow-up. Higher plasma ADMA and SDMA (HRs of 1.20 and 1.28 per 1-SD greater concentration), and lower ratios of urine to plasma concentrations of ADMA, SDMA, and TMAO (HRs per halving of 1.53, 1.69, and 1.38) were associated with cardiovascular mortality. Higher plasma concentrations of ADMA, SDMA, and TMAO (HRs of 1.31, 1.42, and 1.13 per 1-SD greater concentration) and lower urine to plasma ratios of ADMA, SDMA, and TMAO (HRs per halving of 1.34, 1.37, and 1.26) were associated with all-cause mortality. Higher plasma ADMA and SDMA were associated with incident KFRT by categorical comparisons (HRs of 2.75 and 2.96, comparing quartile 4 to quartile 1), but not in continuous analyses.

LIMITATIONS

Single cohort, restricted to patients with diabetes and eGFR < 60 mL/min/1.73 m2, potential residual confounding by GFR, no dietary information.

CONCLUSIONS

Higher plasma concentrations and lower ratios of urine to plasma concentrations of uremic solutes were independently associated with cardiovascular and all-cause mortality in DKD. Associations of ratios of urine to plasma concentrations with mortality suggest a connection between renal uremic solute clearance and CVD pathogenesis.

SMOC2 gene interacts with APOL1 in the development of end-stage kidney disease: A genome-wide association study

Background

Some but not all African-Americans (AA) who carry APOL1 nephropathy risk variants (APOL1) develop kidney failure (end-stage kidney disease, ESKD). To identify genetic modifiers, we assessed gene-gene interactions in a large prospective cohort of the REasons for Geographic and Racial Differences in Stroke (REGARDS) study.

Methods

Genotypes from 8,074 AA participants were obtained from Illumina Infinium Multi-Ethnic AMR/AFR Extended BeadChip. We compared 388 incident ESKD cases with 7,686 non-ESKD controls, using a two-locus interaction approach. Logistic regression was used to examine the effect of APOL1 risk status (using recessive and additive models), single nucleotide polymorphism (SNP), and APOL1^*SNP interaction on incident ESKD, adjusting for age, sex, and ancestry. APOL1 ^*SNP interactions that met the threshold of 1.0 × 10^-5 were replicated in the Genetics of Hypertension Associated Treatment (GenHAT) study (626 ESKD cases and 6,165 controls). In a sensitivity analysis, models were additionally adjusted for diabetes status. We conducted additional replication in the BioVU study.

Results

Two APOL1 risk alleles prevalence (recessive model) was similar in the REGARDS and GenHAT studies. Only one APOL1-SNP interaction, for rs7067944 on chromosome 10, ~10 KB from the PCAT5 gene met the genome-wide statistical threshold (P _interaction = 3.4 × 10^-8), but this interaction was not replicated in the GenHAT study. Among other relevant top findings (with P _interaction < 1.0 × 10^-5), a variant (rs2181251) near SMOC2 on chromosome six interacted with APOL1 risk status (additive) on ESKD outcomes (REGARDS study, P _interaction =5.3 × 10^-6) but the association was not replicated (GenHAT study, P _interaction = 0.07, BioVU study, P _interaction = 0.53). The association with the locus near SMOC2 persisted further in stratified analyses. Among those who inherited ≥1 alternate allele of rs2181251, APOL1 was associated with an increased risk of incident ESKD (OR [95%CI] = 2.27[1.53, 3.37]) but APOL1 was not associated with ESKD in the absence of the alternate allele (OR [95%CI] = 1.34[0.96, 1.85]) in the REGARDS study. The associations were consistent after adjusting for diabetes.

Conclusion

In a large genome-wide association study of AAs, a locus SMOC2 exhibited a significant interaction with the APOL1 locus. SMOC2 contributes to the progression of fibrosis after kidney injury and the interaction with APOL1 variants may contribute to an explanation for why only some APOLI high-risk individuals develop ESKD.

Association of Estimated GFR Calculated Using Race-Free Equations With Kidney Failure and Mortality by Black vs Non-Black Race

Importance

At a given estimated glomerular filtration rate (eGFR), individuals who are Black have higher rates of mortality and kidney failure with replacement therapy (KFRT) compared with those who are non-Black. Whether the recently adopted eGFR equations without race preserve racial differences in risk of mortality and KFRT at a given eGFR is unknown.

Objective

To assess whether eGFR equations with and without race and cystatin C document racial differences in risk of KFRT and mortality in populations including Black and non-Black participants.

Design, Setting, and Participants

Retrospective individual-level data analysis of 62 011 participants from 5 general population and 3 chronic kidney disease (CKD) US-based cohorts with serum creatinine, cystatin C, and follow-up for KFRT and mortality from 1988 to 2018.

Exposures

Chronic Kidney Disease Epidemiology Collaboration equation with serum creatinine (eGFRcr with and without race), cystatin C (eGFRcys without race), or both markers (eGFRcr-cys without race).

Main Outcomes and Measures

The prevalence of decreased eGFR at baseline and hazard ratios of KFRT and mortality in Black vs non-Black participants were calculated, adjusted for age and sex. Analyses were performed within each cohort and with random-effect meta-analyses of the models.

Results

Among 62 011 participants (20 773 Black and 41 238 non-Black; mean age, 63 years; 53% women), the prevalence ratio (95% CI; percent prevalences) of eGFR less than 60 mL/min/1.73 m2 comparing Black with non-Black participants was 0.98 (95% CI, 0.93-1.03; 11% vs 12%) for eGFRcr with race, 0.95 (95% CI, 0.91-0.98; 17% vs 18%) for eGFRcys, and 1.2 (95% CI, 1.2-1.3; 13% vs 11%) for eGFRcr-cys but was 1.8 (95% CI, 1.7-1.8; 15% vs 9%) for eGFRcr without race. During a mean follow-up of 13 years, 8% and 4% of Black and non-Black participants experienced KFRT and 34% and 39% died, respectively. Decreased eGFR was associated with significantly greater risk of both outcomes for all equations. At an eGFR of 60 mL/min/1.73 m2, the hazard ratios for KFRT comparing Black with non-Black participants were 2.8 (95% CI, 1.6-4.9) for eGFRcr with race, 3.0 (95% CI, 1.5-5.8) for eGFRcys, and 2.8 (95% CI, 1.4-5.4) for eGFRcr-cys vs 1.3 (95% CI, 0.8-2.1) for eGFRcr without race. The 5-year absolute risk differences for KFRT comparing Black with non-Black participants were 1.4% (95% CI, 0.2%-2.6%) for eGFRcr with race, 1.1% (95% CI, 0.2%-1.9%) for eGFRcys, and 1.3% (95% CI, 0%-2.6%) for eGFRcr-cys vs 0.37% (95% CI, -0.32% to 1.05%) for eGFRcr without race. Similar patterns were observed for mortality.

Conclusions and Relevance

In this retrospective analysis of 8 US cohorts including Black and non-Black individuals, the eGFR equation without race that included creatinine and cystatin C, but not the eGFR equation without race that included creatinine without cystatin C, demonstrated racial differences in the risk of KFRT and mortality throughout the range of eGFR. The eGFRcr-cys equation may be preferable to the eGFRcr equation without race for assessing racial differences in the risk of KFRT and mortality associated with low eGFR.

Associations of Plasma Biomarkers of Inflammation, Fibrosis, and Kidney Tubular Injury With Progression of Diabetic Kidney Disease: A Cohort Study

RATIONALE & OBJECTIVE

Most circulating biomarkers of chronic kidney disease (CKD) progression focus on factors reflecting glomerular filtration. Few biomarkers capture nonglomerular pathways of kidney injury or damage, which may be particularly informative in populations at high risk for CKD progression such as individuals with diabetes.

STUDY DESIGN

Cohort study.

SETTING & PARTICIPANTS

594 participants (mean age, 70 years; 53% women) of the Reasons for Geographic and Racial Differences in Stroke (REGARDS) study who had diabetes and an estimated glomerular filtration rate (eGFR)<60mL/min/1.73m² at baseline.

EXPOSURES

Plasma biomarkers of inflammation/fibrosis (TNFR1 and TNFR2, suPAR, MCP-1, YKL-40) and tubular injury (KIM-1) measured at the baseline visit.

OUTCOMES

Incident kidney failure with replacement therapy (KFRT).

ANALYTICAL APPROACH

Cox proportional hazards regression and least absolute shrinkage and selection operator regression adjusted for established risk factors for kidney function decline, baseline eGFR, and urinary albumin-creatinine ratio (UACR).

RESULTS

A total of 98 KFRT events were observed over a mean of 6.2±3.5 (standard deviation) years of follow-up. Plasma biomarkers were modestly associated with baseline eGFR (correlation coefficients ranging from-0.08 to-0.65) and UACR (0.14 to 0.56). In individual biomarker models adjusted for eGFR, UACR, and established risk factors, hazard ratios for incident KFRT per 2-fold higher biomarker concentrations were 1.52 (95% CI, 1.25-1.84) for plasma KIM-1, 1.54 (95% CI, 1.08-2.21) for TNFR1, 1.91 (95% CI, 1.16-3.14) for TNFR2, and 1.39 (95% CI, 1.05-1.84) for YKL-40. In least absolute shrinkage and selection operator regression models accounting for biomarkers in parallel, plasma KIM-1 and TNFR1 remained associated with incident KFRT.

LIMITATIONS

Single biomarker measurement, lack of follow-up eGFR assessments.

CONCLUSIONS

Individual plasma markers of inflammation/fibrosis (TNFR1, TNFR2, YKL-40) and tubular injury (KIM-1) were associated with risk of incident KFRT in adults with diabetes and an eGFR<60mL/min/1.73m² after adjustment for established risk factors.

Lung-kidney interactions and their role in chronic kidney disease-associated pulmonary diseases

Chronic illnesses rarely present in a vacuum, devoid of other complications, and chronic kidney disease is hardly an exception. Comorbidities associated with chronic kidney disease lead to faster disease progression, expedited dialysis dependency, and a higher mortality rate. Although chronic kidney disease is most commonly accompanied by cardiovascular diseases and diabetes, there is clear cross talk between the lungs and kidneys pH balance, phosphate metabolism, and immune system regulation. Our present understanding of the exact underlying mechanisms that contribute to chronic kidney disease-related pulmonary disease is poor. This review summarizes the current research on kidney-pulmonary interorgan cross talk in the context of chronic kidney disease, highlighting various acute and chronic pulmonary diseases that lead to further complications in patient care. Treatment options for patients presenting with chronic kidney disease and lung disease are explored by assessing activated molecular pathways and the body's compensatory response mechanisms following homeostatic imbalance. Understanding the link between the lungs and kidneys will potentially improve health outcomes for patients and guide healthcare professionals to better understand how and when to treat each of the pulmonary comorbidities that can present with chronic kidney disease.

High dietary salt intake increases urinary NGAL excretion and creatinine clearance in healthy young adults

In rodents and older patients with elevated blood pressure (BP), high dietary sodium increases excretion of biomarkers of kidney injury, but it is unclear whether this effect occurs in healthy young adults. The purpose of this study was to determine whether short-term high dietary salt increases urinary excretion of the kidney injury biomarkers neutrophil gelatinase-associated lipocalin (NGAL) and kidney injury molecule-1 (KIM-1) in healthy young adults. Twenty participants participated in a double-blind, placebo-controlled, randomized crossover study. For 10 days each, participants were asked to consume salt (3,900 mg sodium) or placebo capsules. We measured BP during each visit, obtained 24-h urine samples for measurements of electrolytes, NGAL, and KIM-1, and assessed creatinine clearance. Compared with placebo, salt loading increased daily urinary sodium excretion (placebo: 130.3 ± 62.4 mmol/24 h vs. salt: 287.2 ± 72.0 mmol/24 h, P < 0.01). There was no difference in mean arterial BP (placebo: 77 ± 7 mmHg vs. salt: 77 ± 6 mmHg, P = 0.83) between conditions. However, salt loading increased the urinary NGAL excretion rate (placebo: 59.8 ± 44.4 ng/min vs. salt: 80.8 ± 49.5 ng/min, P < 0.01) and increased creatinine clearance (placebo: 110.5 ± 32.9 mL/min vs. salt: 145.0 ± 24.9 mL/min, P < 0.01). Urinary KIM-1 excretion was not different between conditions. In conclusion, in healthy young adults 10 days of dietary salt loading increased creatinine clearance and increased urinary excretion of the kidney injury biomarker marker NGAL but not KIM-1.NEW & NOTEWORTHY In healthy young adults, 10 days of dietary salt loading increased creatinine clearance and increased urinary excretion of the kidney injury biomarker marker neutrophil gelatinase-associated lipocalin despite no change in resting blood pressure.

APOL1 Risk Variants Associated with Serum Albumin in a Population-Based Cohort Study

INTRODUCTION

The association of apolipoprotein L1 (APOL1) nephropathy risk variants (APOL1), unique to African-ancestry (African-American [AA]) populations, with systemic inflammation, a contributor to chronic kidney disease (CKD) and end-stage kidney disease (ESKD) is ill-defined. This study aimed to describe the role of inflammatory markers in the relationship between APOL1 and incident kidney outcomes using a prospective cohort study.

METHODS

APOL1 high-risk status under a recessive genetic model was studied in 10,605 AA adults aged ≥45 years from the Reasons for Geographic and Racial Differences in Stroke study. The primary variables of interest were inflammatory markers: C-reactive protein (mg/dL), white blood cell count (cells/mm3), and serum albumin (sALB) (mg/dL). High inflammation status was defined if at least one of these inflammatory markers exceeded clinical threshold. The association between APOL1 and biomarkers were assessed using regression models adjusting for age, sex, ancestry, hypertension, lipid medications, albumin-to-creatinine ratio, and estimated glomerular filtration rate (eGFR). Models were stratified by diabetes status. We identified incident ESKD using USRDS linkage, and we defined incident CKD as an eGFR <60 mL/min/1.73 m2 and ≥25% decline in the eGFR and normal baseline eGFR and tested for mediation of APOL1 and outcomes by biomarkers using the causal inference approach.

RESULTS

Among 7,151 participants with data available on all inflammation markers, 4,479 participants had ≥1 marker meeting the clinical threshold. APOL1 high-risk status was associated with lower adjusted odds of reduced sALB {odds ratio (OR) (95% confidence interval [CI]): 0.59 [0.36, 0.96])}, and this association was significant in people with diabetes (OR [95% CI]: 0.40 [0.18, 0.89]) but not in those without diabetes. There was no association of APOL1 high-risk status with other markers or high inflammation status. APOL1 was independently associated with ESKD (OR [95% CI] = 1.78 [1.28, 2.48]) and CKD (OR [95% CI] = 1.38 [1.00, 1.91]). On mediation analysis, the direct effect between APOL1 and ESKD strengthened after accounting for sALB, but the estimated mediated effect was not statistically significant (OR [95% CI]: 0.98 [0.92, 1.05], p = 0.58).

CONCLUSION

APOL1 high-risk variants were associated with sALB. However, sALB did not statistically mediate the association between APOL1 and incident ESKD.

Recent Advances in the Role of Diet in Bone and Mineral Disorders in Chronic Kidney Disease

PURPOSE OF REVIEW

Chronic kidney disease mineral and bone disease (CKD-MBD) is a common complication of kidney disease and is strongly influenced by diet. The purpose of this manuscript is to review recent advances in the role of diet in CKD-MBD over the last 5 years.

RECENT FINDINGS

Many of the recent studies examining the role of diet in CKD-MBD have focused on the adverse effects of high phosphorus consumption on bone health and metabolism. In general, the studies have shown that high phosphorus consumption worsens markers of bone and mineral metabolism but that eating a diet with a calcium to phosphorus ratio closer to 1:1 can attenuate some of these effects. Recent studies also showed that dietary counseling is efficacious for improving markers of CKD-MBD. High consumption of phosphorus aggravates CKD-MBD. Dietary counseling may ameliorate these effects, for example, by consuming diets with higher calcium to phosphorus ratios.

New Creatinine- and Cystatin C-Based Equations to Estimate GFR without Race

BACKGROUND

Current equations for estimated glomerular filtration rate (eGFR) that use serum creatinine or cystatin C incorporate age, sex, and race to estimate measured GFR. However, race in eGFR equations is a social and not a biologic construct.

METHODS

We developed new eGFR equations without race using data from two development data sets: 10 studies (8254 participants, 31.5% Black) for serum creatinine and 13 studies (5352 participants, 39.7% Black) for both serum creatinine and cystatin C. In a validation data set of 12 studies (4050 participants, 14.3% Black), we compared the accuracy of new eGFR equations to measured GFR. We projected the prevalence of chronic kidney disease (CKD) and GFR stages in a sample of U.S. adults, using current and new equations.

RESULTS

In the validation data set, the current creatinine equation that uses age, sex, and race overestimated measured GFR in Blacks (median, 3.7 ml per minute per 1.73 m² of body-surface area; 95% confidence interval [CI], 1.8 to 5.4) and to a lesser degree in non-Blacks (median, 0.5 ml per minute per 1.73 m²; 95% CI, 0.0 to 0.9). When the adjustment for Black race was omitted from the current eGFR equation, measured GFR in Blacks was underestimated (median, 7.1 ml per minute per 1.73 m²; 95% CI, 5.9 to 8.8). A new equation using age and sex and omitting race underestimated measured GFR in Blacks (median, 3.6 ml per minute per 1.73 m²; 95% CI, 1.8 to 5.5) and overestimated measured GFR in non-Blacks (median, 3.9 ml per minute per 1.73 m²; 95% CI, 3.4 to 4.4). For all equations, 85% or more of the eGFRs for Blacks and non-Blacks were within 30% of measured GFR. New creatinine-cystatin C equations without race were more accurate than new creatinine equations, with smaller differences between race groups. As compared with the current creatinine equation, the new creatinine equations, but not the new creatinine-cystatin C equations, increased population estimates of CKD prevalence among Blacks and yielded similar or lower prevalence among non-Blacks.

CONCLUSIONS

New eGFR equations that incorporate creatinine and cystatin C but omit race are more accurate and led to smaller differences between Black participants and non-Black participants than new equations without race with either creatinine or cystatin C alone. (Funded by the National Institute of Diabetes and Digestive and Kidney Diseases.).

Atherosclerotic Cardiovascular Disease Events in Adults With CKD Taking a Moderate- or High-Intensity Statin: The Chronic Renal Insufficiency Cohort (CRIC) Study

Rationale & Objective

The 2018 American Heart Association/American College of Cardiology (AHA/ACC) cholesterol guideline uses risk stratification to guide the decision to initiate nonstatin lipid-lowering medication among adults with atherosclerotic cardiovascular disease (CVD). We determined atherosclerotic CVD (ASCVD) event rates among adults with chronic kidney disease (CKD) taking statin therapy within 2018 AHA/ACC cholesterol guideline risk categories.

Study Design

Observational cohort study.

Setting & Participants

Adults with CKD not on dialysis in the Chronic Renal Insufficiency Cohort (CRIC) study who were taking a moderate/high-intensity statin 1 year after enrollment (baseline for the current analysis, n = 1,753).

Exposure

2018 AHA/ACC cholesterol guideline risk categories: without a history of ASCVD, a history of 1 major ASCVD event and multiple high-risk conditions, and a history of ≥2 major ASCVD events.

Outcome

Adjudicated ASCVD events after the year 1 study visit.

Analytical Approach

We calculated age-sex standardized rates for ASCVD events and age-sex adjusted hazard ratios for ASCVD events accounting for the competing risk of death.

Results

There were 394 ASCVD events over a median follow-up period of 8 years. The ASCVD event rates (with 95% CI) per 1,000 person-years among participants without a history of ASCVD, with a history of 1 major ASCVD event and multiple high-risk conditions, and with a history of ≥2 major ASCVD events were 21.7 (18.4-25.1), 45.0 (37.8-52.3), and 73.3 (53.3-93.4), respectively. Compared with participants without a history of ASCVD, the HR (95% CI) rates for ASCVD events among those with a history of 1 major ASCVD event and multiple high-risk conditions, and with a history of ≥2 major ASCVD events were 1.89 (1.52-2.36) and 2.50 (1.85-3.39), respectively.

Limitations

Data on whether participants were taking a maximally tolerated statin dosage were unavailable.

Conclusions

The 2018 AHA/ACC cholesterol guideline identifies adults with CKD who have very high ASCVD risk despite taking a moderate/high-intensity statin.

Soluble Klotho and Incident Hypertension

BACKGROUND AND OBJECTIVES

Hypertension is associated with significant morbidity and mortality despite effective antihypertensive therapies. Soluble klotho is a circulating protein that in preclinical studies is protective against the development of hypertension. There are limited studies of klotho and blood pressure in humans.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Within the Health, Aging, and Body Composition Study, a cohort of well-functioning older adults, soluble klotho was measured in serum. We evaluated the cross-sectional and longitudinal association between klotho and blood pressure, prevalent hypertension, incident hypertension, and BP trajectories. Analyses were adjusted for demographics, cardiovascular disease and kidney disease risk factors, and measures of mineral metabolism including calcium, phosphate, parathyroid hormone, 25(OH) vitamin D, and fibroblast growth factor 23.

RESULTS

The median klotho concentration was 630 pg/ml (478-816, 25th to 75th percentile). Within the cohort, 2093 (76%) of 2774 participants had prevalent hypertension and 476 (70%) of the remaining 681 developed incident hypertension. There was no association between klotho and prevalent hypertension or baseline systolic BP, but higher klotho was associated with higher baseline diastolic BP (fully adjusted β=0.92 mmHg, 95% confidence interval, 0.24 to 1.60 mmHg, higher per two-fold higher klotho). Higher baseline serum klotho levels were significantly associated with a lower rate of incident hypertension (fully adjusted hazard ratio, 0.80; 95% confidence interval, 0.69 to 0.93 for every two-fold higher klotho). Higher klotho was also associated with lower subsequent systolic BP and diastolic BP (-0.16, 95% confidence interval, -0.31 to -0.01, mmHg lower systolic BP per year and -0.10, 95% confidence interval, -0.18 to -0.02, mmHg lower diastolic BP per year, for each two-fold higher klotho).

CONCLUSIONS

Higher klotho is associated with higher baseline diastolic but not systolic BP, a lower risk of incident hypertension, and lower BP trajectories during follow-up.

Treatment of Iron Deficiency Anemia in CKD and End-Stage Kidney Disease

Iron deficiency is common in individuals with chronic kidney disease and plays a major role in the development of anemia. Oral and intravenous iron agents are both available to replete iron in patients with chronic kidney disease diagnosed with iron deficiency. The choice of which agent to use is most often dictated by goals of therapy, tolerability, convenience, and response to prior therapy. Diminished absorption of iron in the gastrointestinal tract and a high incidence of gastrointestinal adverse effects can reduce the efficacy of oral iron agents, necessitating the use of i.v. iron formulations to treat iron deficiency anemia, particularly in patients requiring kidney replacement therapy. Newer oral agents may help to overcome these limitations and help treat iron deficiency in those not requiring kidney replacement therapy. Recent studies have provided new evidence that more aggressive repletion of iron in patients with chronic kidney disease requiring kidney replacement therapy may provide benefits with respect to anemia management and hard clinical outcomes such as cardiovascular disease and survival.

Fibroblast Growth Factor 23 and Incident Cardiovascular Disease and Mortality in Middle-Aged Adults

Background Higher circulating fibroblast growth factor 23 (FGF23) associates with greater risk of cardiovascular disease (CVD) and mortality in older adults. The association of FGF23 with cardiovascular outcomes in younger populations has been incompletely explored. Methods and Results We measured C-terminal FGF23 (cFGF23) and intact FGF23 (iFGF23) in 3151 middle-aged adults (mean age, 45±4) who participated in the year 20 examination of the CARDIA (Coronary Artery Risk Development in Young Adults) study. We used separate Cox proportional hazards models to examine the associations of cFGF23 and iFGF23 with incident CVD and mortality, adjusting models sequentially for sociodemographic, clinical, and laboratory factors. A total of 157 incident CVD events and 135 deaths occurred over a median 7.6 years of follow-up (interquartile range, 4.1-9.9). In fully adjusted models, there were no statistically significant associations of FGF23 with incident CVD events (hazard ratio per doubling of cFGF23: 1.14, 95%CI 0.97,1.34; iFGF23: 0.76, 95%CI 0.57,1.02) or all-cause mortality (hazard ratio per doubling of cFGF23, 1.17; 95% CI, 1.00-1.38; iFGF23, 0.86; 95% CI, 0.64-1.17). In analyses stratified by CVD subtypes, higher cFGF23 was associated with greater risk of heart failure hospitalization (hazard ratio per doubling of cFGF23, 1.52; 95% CI, 1.18-1.96) but not coronary heart disease or stroke, whereas iFGF23 was not associated with CVD subtypes in any model. Conclusions In middle-aged adults with few comorbidities, higher cFGF23 and iFGF23 were not independently associated with greater risk of CVD events or death. Higher cFGF23 was independently associated with greater risk of heart failure hospitalization.

State-of-the-Art Management of Hyperphosphatemia in Patients With CKD: An NKF-KDOQI Controversies Perspective

Phosphate binders are among the most common medications prescribed to patients with kidney failure receiving dialysis and are often used in advanced chronic kidney disease (CKD). In patients with CKD glomerular filtration rate category 3a (G3a) or worse, including those with kidney failure who are receiving dialysis, clinical practice guidelines suggest "lowering elevated phosphate levels towards the normal range" with possible strategies including dietary phosphate restriction or use of binders. Additionally, guidelines suggest restricting the use of oral elemental calcium often contained in phosphate binders. Nutrition guidelines in CKD suggest<800-1,000mg of calcium daily, whereas CKD bone and mineral disorder guidelines do not provide clear targets, but<1,500mg in maintenance dialysis patients has been previously recommended. Many different classes of phosphate binders are now available and clinical trials have not definitively demonstrated the superiority of any class of phosphate binders over another with regard to clinical outcomes. Use of phosphate binders contributes substantially to patients' pill burden and out-of-pocket costs, and many have side effects. This has led to uncertainty regarding the use and best choice of phosphate binders for patients with CKD or kidney failure. In this controversies perspective, we discuss the evidence base around binder use in CKD and kidney failure with a focus on comparisons of available binders.

Fibroblast growth factor 23 and cognitive impairment: The health, aging, and body composition study

BACKGROUND

Concentrations of fibroblast growth factor 23 (FGF-23), a hormone that regulates phosphorus and vitamin D metabolism, increase as kidney function declines. Excess fibroblast growth factor 23 may impact brain function through promotion of vascular disease or through direct effects on neuronal tissue.

METHODS

In the Healthy Aging and Body Composition Study, a longitudinal observational cohort of well-functioning older adults, intact serum FGF-23 was assayed in 2,738 individuals. Cognitive function was assessed at baseline and longitudinally at years 3, 5, and 8 by administration of the Modified Mini Mental State Examination (3MSE), a test of global cognitive function, and the Digit Symbol Substitution Test (DSST), a test primarily of executive function. The associations between FGF-23 and baseline cognitive function and incident cognitive impairment were evaluated using logistic and Poisson regression respectively, and were adjusted for demographics, baseline estimated glomerular filtration rate (eGFR), urine albumin/creatinine ratio, comorbidity, and other measures of mineral metabolism including soluble klotho.

RESULTS

The mean (SD) age was 74(3) years, with 51% female, and 39% black. The median (25th, 75th) FGF-23 concentration was 47 pg/mL (37, 60). Three hundred ninety-two individuals had prevalent cognitive impairment by the 3MSE and 461 by the DSST. There was no observed association between FGF-23 and baseline cognitive function for either cognitive test. There were 277 persons with incident cognitive impairment by 3MSE, and 333 persons with incident cognitive impairment by DSST. In fully adjusted models, each two-fold higher concentration of baseline FGF-23 was not associated with incident cognitive impairment by the 3MSE (IRR = 1.02[0.88, 1.19] fully adjusted model) or by the DSST (IRR = 0.98 [0.84, 1.15]. We saw no difference when analyses were stratified by eGFR greater than or less than 60 ml/min/1.73m2.

CONCLUSION

Intact FGF-23 was not associated with baseline cognitive function or incident cognitive impairment in this cohort well-functioning older adults.

Association of FGF23 with Incident Sepsis in Community-Dwelling Adults: A Cohort Study

BACKGROUND

Fibroblast growth factor 23 (FGF23) is a hormone that regulates vitamin D activity. Higher circulating FGF23 concentrations have been associated with an increased risk of infection-related hospitalization, but the association of FGF23 with risk of sepsis remains unclear.

METHODS

We examined the association of FGF23 with incident sepsis events in the Reasons for Geographic and Racial Differences in Stroke (REGARDS) study, a national longitudinal cohort of black and white adults ≥45 years of age. Using a case-cohort design, we measured baseline FGF23 in 703 sepsis cases and in 991 participants randomly selected from the REGARDS cohort. We defined sepsis as the presence of a serious infection plus two or more Systemic Inflammatory Response Syndrome criteria. We identified first sepsis hospitalizations during 2003-2012 by adjudicated medical record review. Cox proportional hazards models were used to examine associations of FGF23 with incident sepsis, adjusting for age, sex, race, income, education, smoking, body mass index, physical activity, chronic pulmonary disease, eGFR, urine albumin-creatinine ratio, and high-sensitivity C-reactive protein. We also examined whether associations differed by age, race, sex, and CKD by testing interaction terms.

RESULTS

Higher FG23 concentrations were associated with greater risk of sepsis (hazard ratio [HR] per doubling of FGF23, 1.37; 95% CI, 1.22 to 1.54) in models adjusted for sociodemographic and clinical variables. After further adjusting for eGFR, urine albumin-creatinine ratio, and high-sensitivity C-reactive protein, the association was attenuated and no longer statistically significant (HR per doubling, 1.01; 95% CI, 0.85 to 1.21). The results did not statistically differ by strata of age, sex, race, or CKD.

CONCLUSIONS

In community-dwelling adults, higher FGF23 concentrations were not independently associated with higher risk of sepsis.

Association of Urine Albumin Excretion With Incident Heart Failure Hospitalization in Community-Dwelling Adults

OBJECTIVES

This study examined the association between urinary albumin excretion and incident heart failure (HF) hospitalization.

BACKGROUND

Excess urinary albumin excretion is more strongly associated with incident stroke and coronary heart disease risk in black than in white individuals. Whether similar associations extend to HF is unclear.

METHODS

This study examined the associations between the urinary albumin-to-creatinine ratio (ACR) and incident hospitalization for HF overall in 24,433 REGARDS (Reasons for Geographic and Racial Differences in Stroke) study participants free of suspected HF at baseline; findings were stratified by race and HF subtype (preserved vs. reduced ejection fraction). Models were adjusted for sociodemographic, clinical, and laboratory variables including estimated glomerular filtration rate, and multiple imputation was used to account for missing covariate data.

RESULTS

After a median follow-up of 9.2 years, 881 incident HF events (332 preserved ejection fraction, 447 reduced ejection fraction, 102 unspecified) were observed. Compared to the lowest ACR category (<10 mg/g), the risk of incident HF increased with increasing ACR categories (10 to 29 mg/g hazard ratio [HR]: 1.49; 95% confidence interval [CI]: 1.26 to 1.78; 30 to 300 mg/g HR: 2.32; 95% CI: 1.93 to 2.78; >300 mg/g HR: 4.42; 95% CI: 3.36 to 5.83) in the fully adjusted model. Results did not differ by race. The magnitude of the association between ACR and HF with preserved ejection fraction was greater than with HF with reduced ejection fraction (HR comparing highest vs. lowest ACR category: 6.20; 95% CI: 4.15 to 9.26 vs. HR: 4.37; 95% CI: 3.00 to 6.25, respectively; p = 0.05).

CONCLUSIONS

Higher ACR was associated with greater risk of incident HF hospitalization in community-dwelling black and white adults.

Effect of Ferric Citrate versus Ferrous Sulfate on Iron and Phosphate Parameters in Patients with Iron Deficiency and CKD: A Randomized Trial

BACKGROUND AND OBJECTIVES

Ferric citrate is an oral medication approved for treatment of iron deficiency anemia in patients with CKD not requiring dialysis. The relative efficacy of ferric citrate versus ferrous sulfate in treating iron deficiency in patients with CKD is unclear.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We randomized 60 adults with moderate to severe CKD (eGFR 15-45 ml/min per 1.73 m2) and iron deficiency (transferrin saturation [TSAT] ≤30% and ferritin ≤300 ng/ml) to ferric citrate (2 g three times a day with meals, n=30) or ferrous sulfate (325 mg three times a day, n=30) for 12 weeks. Primary outcomes were change in TSAT and ferritin from baseline to 12 weeks. Secondary outcomes were change in hemoglobin, fibroblast growth factor 23 (FGF23), and hepcidin.

RESULTS

Baseline characteristics were well balanced between study arms. There was a greater increase in TSAT (between-group difference in mean change, 8%; 95% confidence interval [95% CI], 1 to 15; P=0.02) and ferritin (between-group difference in mean change, 37 ng/ml; 95% CI, 10 to 64; P=0.009) from baseline to 12 weeks in participants randomized to ferric citrate as compared with ferrous sulfate. Similarly, as compared with ferrous sulfate, treatment with ferric citrate resulted in a greater increase in hepcidin from baseline to 12 weeks (between-group difference, 69 pg/ml; 95% CI, 8 to 130). There were no between-group differences in mean change for hemoglobin (0.3 g/dl; 95% CI, -0.2 to 0.8), intact FGF23 (-29 pg/ml; 95% CI, -59 to 0.1), or C-terminal FGF23 (61 RU/ml; 95% CI, -181 to 58). The incidence of adverse events did not differ between treatment arms.

CONCLUSIONS

As compared with ferrous sulfate, treatment with ferric citrate for 12 weeks resulted in a greater mean increase in TSAT and ferritin concentrations in individuals with moderate to severe CKD and iron deficiency.

CLINICAL TRIAL REGISTRY NAME AND REGISTRATION NUMBER

Impact of Ferric Citrate vs Ferrous Sulfate on Iron Parameters and Hemoglobin in Individuals With Moderate to Severe Chronic Kidney Disease (CKD) With Iron Deficiency, NCT02888171.

Plasma 25-Hydroxyvitamin D and the Longitudinal Risk of Sepsis in the REGARDS Cohort

BACKGROUND

Low baseline plasma 25-hydroxyvitamin D (25(OH)D) is associated with increased risk of acute respiratory infections, but its association with long-term risk of sepsis remains unclear.

METHODS

We performed a case-cohort analysis of participants selected from the Reasons for Geographic and Racial Differences in Stroke (REGARDS) study, a US cohort of 30239 adults aged ≥45 years. We measured baseline plasma 25(OH)D in 711 sepsis cases and in 992 participants randomly selected from the REGARDS cohort. We captured sepsis events by screening records with International Classification of Disease methods and then adjudicating clinical charts for significant, suspected infection and severe inflammatory response syndrome criteria on presentation.

RESULTS

In the study sample, the median age of participants was 65.0 years, 41% self-identified as black, and 45% were male. Mean plasma 25(OH)D concentration was 25.8 ng/mL; for 31% of participants, it was <20 ng/mL. The adjusted risk of community-acquired sepsis was higher for each lower category of baseline 25(OH)D. Specifically, in a Cox proportional hazards model adjusting for multiple potential confounders, when compared to a baseline 25(OH)D >33.6 ng/mL, lower 25(OH)D groups were associated with higher hazards of sepsis (16.5-22.4 ng/mL; hazard ratio [HR]; 3.21; 95% confidence interval [CI], 1.98 to 5.21 and <16.5 ng/mL; HR, 6.81, 95% CI, 3.95 to 11.73). Results did not materially differ in analyses stratified by race or age.

CONCLUSIONS

In the REGARDS cohort of community-dwelling US adults, low plasma 25(OH)D measured at a time of relative health was independently associated with increased risk of sepsis.

Fibroblast Growth Factor 23 and Blood Pressure in Older Adults: The Health, Aging, and Body Composition Study

FGF-23 (fibroblast growth factor 23) regulates phosphorus and vitamin D. Elevated FGF-23 is associated with incident hypertension in young- and middle-aged adults, but there is limited data in older adults. Serum FGF-23 was measured using an intact ELISA assay in 2496 participants of the Healthy Aging and Body Composition Study. The association between FGF-23 and prevalent hypertension (self-reported and confirmed by use of antihypertensive medications) and number of antihypertensive medications was determined. The associations between FGF-23 and incident hypertension, and diastolic and systolic blood pressure trajectories were evaluated over 10 years. Models were adjusted for demographics, estimated glomerular filtration rate and albuminuria, cardiovascular disease risk factors, and measures of mineral metabolism. The mean (SD) age was 75 (3) years, with 51% women, and 40% black participants. The prevalence of hypertension at baseline was 75% and the mean systolic and diastolic blood pressures were 134 (21) mm Hg and 70 (12) mm Hg, respectively. The majority of participants without hypertension at baseline developed incident hypertension (576 of 1109 or 52%). In adjusted models, each 2-fold higher FGF-23 was associated with prevalent baseline hypertension (odds ratio=1.46 [1.24-1.73]) and greater number of blood pressure medications (IRR=1.14 [1.08-1.21]) but not with baseline diastolic or systolic blood pressure. In fully adjusted longitudinal analyses, a 2-fold higher FGF-23 was associated with incident hypertension (hazard ratio=1.18 [1.03-1.36]) and worsening systolic blood pressures (β=0.24 [0.08-0.40] mm Hg per year increase), but not with diastolic blood pressures (β=0.04 [-0.04 to 0.12] mm Hg per year increase). Higher FGF-23 concentrations are associated with prevalent and incident hypertension as well as rising systolic blood pressures in community-living older adults.

Incidence and Implications of Atrial Fibrillation/Flutter in Hypertension: Insights From the SPRINT Trial

We evaluated the impact of intensive blood pressure control on the incidence of new-onset atrial fibrillation/flutter (AF) and the prognostic implications of preexisting and new-onset AF in SPRINT (Systolic Blood Pressure Intervention Trial) participants. New-onset AF was defined as occurrence of AF in 12-lead electrocardiograms after randomization in participants free of AF at baseline. Poisson regression modeling was used to calculate incident rates of new-onset AF. Multivariable-adjusted Cox proportional hazard models were used to evaluate the risk of adverse cardiovascular events (composite of myocardial infarction, non-myocardial infarction acute coronary syndrome, stroke, heart failure, or cardiovascular death). In 9327 participants, 8.45% had preexisting AF, and 1.65% had new-onset AF. The incidence of new-onset AF was 4.53 per 1000-person years, with similar rates in the standard and intensive treatment arms (4.95 versus 4.11 per 1000-person years; adjusted P=0.14). Participants with preexisting AF (adjusted hazard ratio, 1.83 [95% CI, 1.46-2.31]; P<0.001) and new-onset AF (adjusted hazard ratio, 2.45 [95% CI, 1.58-3.80]; P<0.001) had a greater risk for development of adverse cardiovascular events compared with those with no AF. Participants with preexisting AF who achieved blood pressure <120/80 mm Hg at 3 months continued have a poor prognosis (adjusted hazard ratio, 1.88 [95% CI, 1.32-2.70]; P=0.001) compared with those with no AF. Intensive blood pressure control does not diminish the incidence of new-onset AF in an older, high-risk, nondiabetic population. Both preexisting and new-onset AF have adverse prognostic implications. In participants with preexisting AF, residual cardiovascular risk is evident even with on-treatment blood pressure <120/80 mm Hg. Registration- URL: https://www.clinicaltrials.gov; Unique identifier: NCT01206062.

Chronic Kidney Disease Awareness and Longitudinal Health Outcomes: Results from the REasons for Geographic And Racial Differences in Stroke Study

BACKGROUND

The majority of people with chronic kidney disease (CKD) are unaware of their kidney disease. Assessing the clinical significance of increasing CKD awareness has critical public health and healthcare delivery implications. Whether CKD awareness among persons with CKD is associated with longitudinal health behaviors, disease management, and health outcomes is unknown.

METHODS

We analyzed data from participants with CKD in the REasons for Geographic And Racial Differences in Stroke study, a national, longitudinal, population-based cohort. Our predictor was participant CKD awareness. Outcomes were (1) health behaviors (smoking avoidance, exercise, and nonsteroidal anti-inflammatory drug use); (2) CKD management indicators (angiotensin-converting enzyme inhibitor or angiotensin receptor blocker use, statin use, systolic blood pressure, fasting blood glucose, and body mass index); (3) change in estimated glomerular filtration rate (eGFR) and urine albumin-to-creatinine ratio (UACR); and (4) health outcomes (incident end-stage kidney disease [ESKD], coronary heart disease [CHD], stroke, and death). Logistic and linear regressions were used to examine the association of baseline CKD awareness with outcomes of interest, adjusted for CKD stage and participant demographic and clinical factors.

RESULTS

Of 6,529 participants with baseline CKD, 285 (4.4%) were aware of their CKD. Among the 3,586 participants who survived until follow-up (median 9.5 years), baseline awareness was not associated with subsequent odds of health behaviors, CKD management indicators, or changes in eGFR and UACR in adjusted analyses. Baseline CKD awareness was associated with increased risk of ESKD (adjusted hazard ratio [aHR] 1.44; 95% CI 1.08-1.92) and death (aHR 1.18; 95% CI 1.00-1.39), but not with subsequent CHD or stroke, in adjusted models.

CONCLUSIONS

Individuals aware of their CKD were more likely to experience ESKD and death, suggesting that CKD awareness reflects disease severity. Most persons with CKD, including those that are high-risk, remain unaware of their CKD. There was no evidence of associations between baseline CKD awareness and longitudinal health behaviors, CKD management indicators, or eGFR decline and albuminuria.

Ambulatory Blood Pressure Phenotypes in Adults Taking Antihypertensive Medication with and without CKD

BACKGROUND AND OBJECTIVES

Recent guidelines recommend out-of-clinic BP measurements.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We compared the prevalence of BP phenotypes between 561 black patients, with and without CKD, taking antihypertensive medication who underwent ambulatory BP monitoring at baseline (between 2000 and 2004) in the Jackson Heart Study. CKD was defined as an albumin-to-creatinine ratio ≥30 mg/g or eGFR <60 ml/min per 1.73 m². Sustained controlled BP was defined by BP at goal both inside and outside of the clinic and sustained uncontrolled BP as BP above goal both inside and outside of the clinic. Masked uncontrolled hypertension was defined by controlled clinic-measured BP with uncontrolled out-of-clinic BP.

RESULTS

CKD was associated with a higher multivariable-adjusted prevalence ratio for uncontrolled versus controlled clinic BP (prevalence ratio, 1.44; 95% CI, 1.02 to 2.02) and sustained uncontrolled BP versus sustained controlled BP (prevalence ratio, 1.66; 95% CI, 1.16 to 2.36). There were no statistically significant differences in the prevalence of uncontrolled daytime or nighttime BP, nondipping BP, white-coat effect, and masked uncontrolled hypertension between participants with and without CKD after multivariable adjustment. After multivariable adjustment, reduced eGFR was associated with masked uncontrolled hypertension versus sustained controlled BP (prevalence ratio, 1.42; 95% CI, 1.00 to 2.00), whereas albuminuria was associated with uncontrolled clinic BP (prevalence ratio, 1.76; 95% CI, 1.20 to 2.60) and sustained uncontrolled BP versus sustained controlled BP (prevalence ratio, 2.02; 95% CI, 1.36 to 2.99).

CONCLUSIONS

The prevalence of BP phenotypes defined using ambulatory BP monitoring is high among adults with CKD taking antihypertensive medication.

Effects of phosphorus and calcium to phosphorus consumption ratio on mineral metabolism and cardiometabolic health

Phosphorus is a common additive used in food processing that is typically consumed in excess of the recommended daily allowance; however, our knowledge of its effects on health, in the context of normal renal function, is limited. Unlike phosphorus, calcium intake is generally less than recommended, and it has been hypothesized that the calcium to phosphorus ratio may be partly responsible for the proposed negative health consequences. Therefore, this study sought to determine the effects of increased phosphorus additive intake, in the context of high calcium consumption, on endocrine markers of mineral metabolism and cardiometabolic health. An outpatient feeding study was performed in which healthy adults were fed a run-in control diet for 2 weeks followed by a phosphorus additive enhanced diet with supplemental calcium to an approximate ratio of 1 (experimental diet) for 2 weeks. Blood and urine samples were collected, and participants had brachial flow-mediated dilatation measured, with analyses comparing follow-up measures to baseline. Two weeks of experimental diet increased serum fibroblast growth factor 23 concentrations but lowered body weight and serum leptin; however, other phosphorus responsive factors such as osteopontin and osteocalcin did not increase. A complementary study in male mice also demonstrated that the regulation of known dietary phosphorus responsive factors was mostly abrogated when dietary calcium was raised in parallel with phosphorus. In conclusion, the study identifies weight, leptin and insulin as responsive to dietary phosphorus and that certain aspects of the systemic phosphorus response are attenuated by a corresponding high calcium intake.

Racial Differences in the Associations Between Food Insecurity and Fibroblast Growth Factor 23 in the Coronary Artery Risk Development in Young Adults Study

OBJECTIVE

Food insecurity is associated with consumption of phosphate additive-laden processed food and beverage products, which could result in higher levels of fibroblast growth factor 23 (FGF23) to compensate for the increased dietary phosphate load. We sought to determine whether food insecurity is associated with higher levels of FGF23. We stratified analyses by race since differences may occur between food insecurity and diet quality across races.

DESIGN AND METHODS

The longitudinal community-based Coronary Artery Risk Development in Young Adults Study recruited from 4 US centers: Birmingham, AL; Chicago, IL; Minneapolis, MN; and Oakland, CA, during the cohort inception in 1985/1986. This analysis included 3,421 black and white participants from Coronary Artery Risk Development in Young Adults follow-up years 20, 25, and 30 who were enrolled in the study between the ages of 18 and 30 years. Econometric fixed effects models stratified by race that adjust by design for all time-invariant covariates were used to model the longitudinal association of food insecurity, defined as the self-reported ability to afford desired quantity and quality of food. The main outcome of interest was changing to the highest quartile of plasma FGF-23 concentrations.

RESULTS

During follow-up, 29% of blacks and 14% of whites experienced change in food security. Developing food insecurity was associated with a 1.48 greater odds of increasing to the highest quartile of FGF23 (95% confidence interval 1.02-2.15) among blacks; however, there was no significant longitudinal association among whites (odds ratio = 1.14, 95% confidence interval 0.67-1.95).

CONCLUSIONS

Among blacks, food insecurity was associated with an increase in levels of FGF23. Although phosphate consumption was presumed to mediate the association between food insecurity and FGF23 levels, we were unable to directly test this pathway.

APOL1 Nephropathy Risk Alleles and Mortality in African American Adults: A Cohort Study

RATIONALE & OBJECTIVE

APOL1 nephropathy risk alleles are associated with the development of chronic kidney disease (CKD) in African Americans. Although CKD is an established risk factor for mortality, associations of APOL1 risk alleles with mortality are uncertain.

STUDY DESIGN

Prospective cohort.

SETTINGS & PARTICIPANTS

10,380 African American and 17,485 white American participants in the Reasons for Geographic and Racial Differences in Stroke (REGARDS) Study.

EXPOSURES

APOL1 nephropathy risk alleles.

OUTCOMES

All-cause and cause-specific mortality.

ANALYTICAL APPROACH

Cox proportional hazards models were used to examine the association of APOL1 high-risk genotypes (2 risk alleles) versus APOL1 low-risk genotypes (0/1 risk allele) with all-cause and cause-specific mortality in African Americans and examine the risk for all-cause mortality in African Americans with high-risk genotypes versus African Americans with low-risk genotypes and white Americans.

RESULTS

APOL1 high-risk participants were younger and had a higher prevalence of albuminuria than low-risk participants. There was no statistically significant association of APOL1 high- versus low-risk genotypes with all-cause mortality in models adjusted for sociodemographic variables, comorbid conditions, and kidney function (HR, 0.88; 95% CI, 0.77-1.01). After further adjustment for genetic ancestry in a subset with available data, a statistically significant association emerged (HR, 0.81; 95% CI, 0.69-0.96). Associations differed by CKD status (Pinteraction=0.04), with African Americans with high-risk genotypes having lower risk for mortality than those with low-risk genotypes in fully adjusted models (HR, 0.78; 95% CI, 0.62-0.99) among those with CKD, but not those without CKD (HR, 0.84; 95% CI, 0.66-1.05). Compared with white Americans, African Americans with high-risk genotypes had a similar rate of mortality, whereas African Americans with low-risk genotypes had a higher rate of mortality (HR, 1.07; 95% CI, 1.00-1.14) in fully adjusted models.

LIMITATIONS

Lack of follow-up measures of kidney function.

CONCLUSIONS

African Americans with high-risk APOL1 genotypes had lower mortality than those with low-risk genotypes in multivariable-adjusted models including genetic ancestry.

APOL1 Nephropathy Risk Alleles and Risk of Sepsis in Blacks

BACKGROUND AND OBJECTIVES

apo L1 (APOL1) nephropathy risk alleles are associated with CKD in blacks. Although APOL1 has innate immune functions, little is known about the association of APOL1 genotypes with risk of infectious outcomes, such as sepsis. The objective of this study was to examine the associations of APOL1 nephropathy risk alleles with risk of sepsis in black adults.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We assessed the association of APOL1 risk alleles with incident sepsis in 10,366 black participants of the Reasons for Geographic and Racial Differences in Stroke study enrolled between 2003 and 2007 with follow-up through December 31, 2012. In Cox models adjusted for demographics, comorbid conditions, and principal components ancestry, we examined the association of APOL1 risk alleles with incident sepsis using recessive (comparing zero or one versus two risk alleles), dominant (zero versus one or two risk alleles), and additive genetic models. We also examined models stratified by diabetes and CKD status.

RESULTS

A total of 1320 (13%) participants had two APOL1 risk alleles, 4719 (46%) had one risk allele, and 4327 (42%) participants had zero risk alleles. A total of 306 sepsis events occurred over a median 6.5 years (interquartile range, 4.5-8.1). There were no statistically significant associations of APOL1 genotype with sepsis risk under recessive genetic models. APOL1 genotypes were associated with sepsis risk under dominant (hazard ratio, 1.55; 95% confidence interval, 1.13 to 2.11) and additive (hazard ratio per variant allele copy, 1.25; 95% confidence interval, 1.02 to 1.53) genetic models adjusted for covariates and ancestry. These associations did not vary by diabetes or CKD status (P _interaction>0.10 for both).

CONCLUSIONS

In community-dwelling black adults, carriage of APOL1 nephropathy risk alleles are common and associated with higher risk of sepsis.

Association of 25-hydroxyvitamin D with incident coronary heart disease in the Reasons for Geographic and Racial Differences in Stroke (REGARDS) study

BACKGROUND

Low circulating 25-hydroxyvitamin D (25[OH]D) has been associated with increased risk of coronary heart disease (CHD), but whether this association differs by race is unclear.

METHODS

We examined the association of 25[OH]D with incident CHD in the Reasons for Geographic and Racial Differences in Stroke (REGARDS) study, a prospective cohort study of black and white adults ≥45 years of age enrolled between 2003 and 2007 with follow-up through December 31, 2011. Using a case-cohort design, we measured 25[OH]D in 829 participants who developed incident CHD (cases) and in 813 participants without CHD randomly selected from the REGARDS cohort (comparison subcohort). Cox proportional hazards models were used to examine associations of 25[OH]D with incident CHD adjusting for established CHD risk factors in the study sample overall and stratified by race.

RESULTS

In the fully adjusted model, lower quintiles of 25[OH]D were associated with a greater risk of incident CHD (25[OH]D > 33.6 ng/mL reference; 25[OH]D > 27.1-33.6 ng/mL, hazard ratio [HR] 2.79, 95% CI 1.64-4.76; 25[OH]D > 22.4-27.1 ng/mL, HR 2.77, 95% CI 1.57-4.89; 25[OH]D > 16.5-22.4 ng/mL, HR 5.52, 95% CI 3.21-9.50; 25[OH]D ≤ 16.5 ng/mL, HR 7.46, 95% CI 4.19-13.25). The results were similar when 25[OH]D was examined on a continuous scale (HR per 10-ng/mL decrement in 25[OH]D 2.04, 95% CI 1.65-2.52). The results did not statistically differ by race whether 25[OH]D was examined as a categorical or continuous variable (P_interaction > .10).

CONCLUSIONS

Lower plasma 25(OH)D concentrations were associated with higher risk of incident CHD. In contrast to prior studies, these associations did not differ by race.

Racial Differences in Plasma Levels of N-Terminal Pro-B-Type Natriuretic Peptide and Outcomes: The Reasons for Geographic and Racial Differences in Stroke (REGARDS) Study

Importance

Recent studies have suggested that the natriuretic peptide system may be endogenously suppressed in black individuals who are free of prevalent cardiovascular disease. Whether natriuretic peptide levels contribute to racial disparities in clinical outcomes is unknown.

Objective

To examine racial differences in N-terminal pro-B-type natriuretic peptide (NTproBNP) levels and their association with all-cause mortality and cause-specific mortality in the Reasons for Geographic and Racial Differences in Stroke (REGARDS) study.

Design, Setting, and Participants

Baseline NTproBNP levels were measured in a randomly selected sample of 4415 REGARDS study participants. Those with prevalent cardiovascular disease and renal dysfunction were excluded. From July 1, 2003, to September 12, 2007, among the remaining 1998 individuals, racial differences in NTproBNP levels were estimated, and the percentage difference in NTproBNP levels by race was meta-analyzed and compared with published results on participants free of prevalent cardiovascular disease from the Dallas Heart Study and Atherosclerosis Risk in Communities study, using random effects modeling. The association of NTproBNP levels, race, all-cause mortality, and cause-specific mortality in the REGARDS study was studied using appropriate modeling techniques. Data analysis was conducted from July 1, 2003, to March 31, 2016.

Main Outcomes and Measures

Racial differences in NTproBNP levels and association with all-cause mortality and cause-specific mortality.

Results

Among the 1998 participants studied (972 women and 1026 men; median age, 63 years [interquartile range, 54-72 years]), median NTproBNP levels in black individuals were significantly lower than those in white individuals (46 pg/mL [interquartile range, 23-91] vs 60 pg/mL [interquartile range, 33-106]; P < .001). With multivariable adjustment, NTproBNP levels were up to 27% lower in black individuals as compared with white individuals (β, -0.32; 95% CI, -0.40 to -0.24; P < .001) in the REGARDS study. In meta-analysis of the 3 cohorts, NTproBNP levels were 35% lower in black individuals than white individuals. Among the REGARDS study participants, for every 1-SD higher log NTproBNP, there was a 31% increased risk of death in the multivariable-adjusted model (hazard ratio, 1.31; 95% CI, 1.11-1.54). This increase was driven primarily by association of NTproBNP with cardiovascular mortality (hazard ratio, 1.69; 95% CI, 1.19-2.41). No interaction between race and NTproBNP levels was observed with all-cause mortality and cause-specific mortality.

Conclusions and Relevance

Plasma NTproBNP levels are significantly lower in black individuals as compared with white individuals in the REGARDS study and in pooled results from the REGARDS study, Dallas Heart Study, and Atherosclerosis Risk in Communities study. Higher NTproBNP levels were associated with higher incidence of all-cause mortality and cardiovascular mortality in healthy black and white individuals, and this association did not differ by race.

Association of Fibroblast Growth Factor 23 With Risk of Incident Coronary Heart Disease in Community-Living Adults

Importance

Higher circulating fibroblast growth factor 23 (FGF23) concentrations are associated with cardiovascular disease events linked to heart failure, but associations of FGF23 with coronary heart disease (CHD) have been less consistent.

Objective

To determine the association of plasma FGF23 concentrations with incident CHD and whether this association differs by race, sex, or chronic kidney disease status.

Design, Setting, and Participants

We examined the association of FGF23 concentrations with incident CHD risk within the Reasons for Geographic and Racial Differences in Stroke study, a prospective cohort of black and white adults 45 years and older enrolled between January 2003 and October 2007 with follow-up through December 31, 2011. Using a case-cohort design, we measured FGF23 concentrations in 829 participants who developed incident CHD and in 812 participants randomly selected from the Reasons for Geographic and Racial Differences in Stroke study cohort (cohort random sample). To account for the stratified sampling design, the cohort random sample was weighted back to the original cohort overall (n = 22 127). Cox proportional hazards models were used to examine the association of FGF23 concentration with incident CHD, adjusting for CHD risk factors and kidney function. In prespecified analyses, we examined whether race, sex, or chronic kidney disease modified the association of FGF23 concentration with incident CHD.

Exposures

Plasma C-terminal FGF23 concentrations.

Main Outcomes and Measures

Investigator-adjudicated incident CHD events.

Results

Of the 22 127 participants in the weighted cohort random sample, 13 059 (58.9%) were female and 9435 (42.6%) were black, and the mean age was 64.3 (95% CI, 63.7-64.9) years. Greater age, lower estimated glomerular filtration rate, higher urine albumin to creatinine ratio, and female sex were associated with higher FGF23 concentration at baseline. In multivariable models adjusted for established CHD risk factors and kidney function, higher FGF23 concentrations were associated with greater risk of CHD (hazard ratio [HR] comparing fourth with first quartile, 2.15; 95% CI, 1.35-3.42). The magnitude and strength of these associations differed by sex. However, these differences were no longer observed when adjusting for hormone therapy in women (men: HR comparing fourth with first quartile, 2.40; 95% CI, 1.30-4.42; women: HR comparing fourth with first quartile, 2.34; 95% CI, 1.04-5.27) or when using sex-specific FGF23 quartiles (men: HR comparing fourth with first quartile, 2.65; 95% CI, 1.43-4.90; women: HR comparing fourth with first quartile, 2.26; 95% CI, 1.02-5.03).

Conclusions and Relevance

Higher FGF23 concentrations were associated with greater risk of CHD. Heterogeneity in the association by sex may be caused by differences in the distribution of plasma FGF23 concentrations or the use of hormone therapy in men vs women.

APOL1 Kidney Risk Variants and Cardiovascular Disease: An Individual Participant Data Meta-Analysis

BACKGROUND

Two coding variants in the apo L1 gene (APOL1) are strongly associated with kidney disease in blacks. Kidney disease itself increases the risk of cardiovascular disease, but whether these variants have an independent direct effect on the risk of cardiovascular disease is unclear. Previous studies have had inconsistent results.

METHODS

We conducted a two-stage individual participant data meta-analysis to assess the association of APOL1 kidney-risk variants with adjudicated cardiovascular disease events and death, independent of kidney measures. The analysis included 21,305 blacks from eight large cohorts.

RESULTS

Over 8.9±5.0 years of follow-up, 2076 incident cardiovascular disease events occurred in the 16,216 participants who did not have cardiovascular disease at study enrollment. In fully-adjusted analyses, individuals possessing two APOL1 kidney-risk variants had similar risk of incident cardiovascular disease (coronary heart disease, myocardial infarction, stroke and heart failure; hazard ratio 1.11, 95% confidence interval, 0.96 to 1.28) compared to individuals with zero or one kidney-risk variant. The risk of coronary heart disease, myocardial infarction, stroke and heart failure considered individually was also comparable by APOL1 genotype. APOL1 genotype was also not associated with death. There was no difference in adjusted associations by level of kidney function, age, diabetes status, or body-mass index.

CONCLUSIONS

In this large, two-stage individual participant data meta-analysis, APOL1 kidney-risk variants were not associated with incident cardiovascular disease or death independent of kidney measures.

APOL1 Nephropathy Risk Variants and Incident Cardiovascular Disease Events in Community-Dwelling Black Adults

BACKGROUND

APOL1 renal risk variants are strongly associated with chronic kidney disease in Black adults, but reported associations with cardiovascular disease (CVD) have been conflicting.

METHODS

We examined associations of APOL1 with incident coronary heart disease (n=323), ischemic stroke (n=331), and the composite CVD outcome (n=500) in 10 605 Black participants of the REGARDS study (Reasons for Geographic and Racial Differences in Stroke). Primary analyses compared individuals with APOL1 high-risk genotypes to APOL1 low-risk genotypes in Cox proportional hazards models adjusted for CVD risk factors and African ancestry.

RESULTS

APOL1 high-risk participants were younger and more likely to have albuminuria at baseline than APOL1 low-risk participants. The risk of incident stroke, coronary heart disease, or composite CVD end point did not significantly differ by APOL1 genotype status in multivariable models. The association of APOL1 genotype with incident composite CVD differed by diabetes mellitus status (P_interaction=0.004). In those without diabetes mellitus, APOL1 high-risk genotypes associated with greater risk of incident composite CVD (hazard ratio, 1.67; 95% confidence interval, 1.12-2.47) compared with those with APOL1 low-risk genotypes in multivariable adjusted models. This latter association was driven by ischemic strokes (hazard ratio, 2.32; 95% confidence interval, 1.33-4.07), in particular, those related to small vessel disease (hazard ratio, 5.10; 95% confidence interval, 1.55-16.56). There was no statistically significant association of APOL1 genotypes with incident CVD in subjects with diabetes mellitus. The APOL1 high-risk genotype was associated with higher stroke risk in individuals without but not those with chronic kidney disease in fully adjusted models.

CONCLUSIONS

APOL1 high-risk status is associated with CVD events in community-dwelling Black adults without diabetes mellitus.

Racial differences in the association of NT-proBNP with risk of incident heart failure in REGARDS

BACKGROUND

Black individuals have lower natriuretic peptide levels and greater risk of heart failure (HF) than white individuals. Higher N-terminal-pro-B-type natriuretic peptide (NT-proBNP) is associated with increased risk of incident HF, but little information is available in black individuals. We examined race-specific differences in 1) the association of NT-proBNP with incident HF and 2) the predictive ability of NT-proBNP for incident HF across body mass index (BMI) and estimated glomerular filtration rate (eGFR) categories.

METHODS

In a prospective case-cohort study, baseline NT-proBNP was measured among 687 participants with incident HF and 2,923 (weighted 20,075) non-case randomly selected participants. Multivariable Cox proportional hazard modeling was used to assess the objectives of our study. Global Wald Chi-square score estimated from multivariable Cox models was used to assess predictive ability of NT-proBNP across BMI and eGFR categories.

RESULTS

In the multivariable model, a doubling of NT-proBNP concentration was associated with greater risk of incident HF among white individuals [hazard ratio (HR): 1.73; 95% CI: 1.55-1.94] than black individuals (HR: 1.51; 95% CI: 1.34-1.70); Pinteraction by race = 0.024. Higher NT-proBNP was the strongest predictor of incident HF across all BMI and eGFR categories among white individuals. By contrast, among black individuals with obesity (BMI ≥ 30 kg/m2) or eGFR < 60 mL/min/1.73 m2, the predictive ability of NT-proBNP for incident HF was attenuated.

CONCLUSIONS

The magnitude of the association of higher NT-proBNP with incident HF risk was greater among white individuals than black individuals. The diminished ability of NT-proBNP to predict the risk of HF in black population with obesity or impaired kidney function highlights the need of further investigations.

Race-based demographic, anthropometric and clinical correlates of N-terminal-pro B-type natriuretic peptide

BACKGROUND

Population studies have shown that black race is a natriuretic peptide (NP) deficiency state. We sought to assess whether the effects of age, sex, body mass index (BMI) and estimated glomerular filtration rate (eGFR) on N-terminal-pro-B-type NP (NT-proBNP) levels differ in white and black individuals.

METHODS

The study population consisted of a stratified random cohort from the REasons for Geographic And Racial Differences in Stroke (REGARDS) study. The study outcomes were the effects of age, sex, BMI and eGFR on NT-proBNP levels independent of socioeconomic and cardiovascular disease factors. Multivariable regression analyses were used to assess the effects of age, sex, BMI and eGFR on NT-proBNP levels in blacks and whites.

RESULTS

Of the 27,679 participants in the weighted sample, 54.7% were females, 40.6% were black, and the median age was 64 years. Every 10-year higher age was associated with 38% [95% confidence interval (CI): 30%-45%] and 34% (95% CI: 22%-43%) higher NT-proBNP levels in whites and blacks, respectively. Female sex was associated with 31% (95% CI: 20%-43%) higher NT-proBNP levels in whites and 28% (95% CI: 15%-45%) higher in blacks. There was a significant linear inverse relationship between BMI and NT-proBNP in whites and a non-linear inverse relationship in blacks. Whites and blacks had a non-linear inverse relationship between eGFR and NT-proBNP. However, the non-linear relationship between NT-proBNP and eGFR differed by race (p = 0.01 for interaction).

CONCLUSIONS

The association of age and sex with NT-proBNP levels was similar in blacks and whites but the form of the BMI and eGFR relationship differed by race.

A PheWAS study of a large observational epidemiological cohort of African Americans from the REGARDS study

BACKGROUND

Cardiovascular disease, diabetes, and kidney disease are among the leading causes of death and disability worldwide. However, knowledge of genetic determinants of those diseases in African Americans remains limited.

RESULTS

In our study, associations between 4956 GWAS catalog reported SNPs and 67 traits were examined among 7726 African Americans from the REasons for Geographic and Racial Differences in Stroke (REGARDS) study, which is focused on identifying factors that increase stroke risk. The prevalent and incident phenotypes studied included inflammation, kidney traits, cardiovascular traits and cognition. Our results validated 29 known associations, of which eight associations were reported for the first time in African Americans.

CONCLUSION

Our cross-racial validation of GWAS findings provide additional evidence for the important roles of these loci in the disease process and may help identify genes especially important for future functional validation.

The Role of Vitamin D in CKD Stages 3 to 4: Report of a Scientific Workshop Sponsored by the National Kidney Foundation

Deficiency of 25-hydroxyvitamin D (25[OH]D) is common in patients with chronic kidney disease stages 3 and 4 and is associated with poor outcomes. However, the evaluation and management of vitamin D deficiency in nephrology remains controversial. This article reports on the proceedings from a "controversies conference" on vitamin D in chronic kidney disease that was sponsored by the National Kidney Foundation. The report outlines the deliberations of the 3 work groups that participated in the conference. Until newer measurement methods are widely used, the panel agreed that clinicians should classify 25(OH)D "adequacy" as concentrations > 20ng/mL without evidence of counter-regulatory hormone activity (ie, elevated parathyroid hormone). The panel also agreed that 25(OH)D concentrations < 15ng/mL should be treated irrespective of parathyroid hormone level. Patients with 25(OH)D concentrations between 15 and 20ng/mL may not require treatment if there is no evidence of counter-regulatory hormone activity. The panel agreed that nutritional vitamin D (cholecalciferol, ergocalciferol, or calcifediol) should be supplemented before giving activated vitamin D compounds. The compounds need further study evaluating important outcomes that observational studies have linked to low 25(OH)D levels, such as progression to end-stage kidney disease, infections, fracture rates, hospitalizations, and all-cause mortality. We urge further research funding in this field.