Race, Genetic Ancestry, and Estimating Kidney Function in CKD

BACKGROUND

The inclusion of race in equations to estimate the glomerular filtration rate (GFR) has become controversial. Alternative equations that can be used to achieve similar accuracy without the use of race are needed.

METHODS

In a large national study involving adults with chronic kidney disease, we conducted cross-sectional analyses of baseline data from 1248 participants for whom data, including the following, had been collected: race as reported by the participant, genetic ancestry markers, and the serum creatinine, serum cystatin C, and 24-hour urinary creatinine levels.

RESULTS

Using current formulations of GFR estimating equations, we found that in participants who identified as Black, a model that omitted race resulted in more underestimation of the GFR (median difference between measured and estimated GFR, 3.99 ml per minute per 1.73 m² of body-surface area; 95% confidence interval [CI], 2.17 to 5.62) and lower accuracy (percent of estimated GFR within 10% of measured GFR [P₁₀], 31%; 95% CI, 24 to 39) than models that included race (median difference, 1.11 ml per minute per 1.73 m²; 95% CI, -0.29 to 2.54; P₁₀, 42%; 95% CI, 34 to 50). The incorporation of genetic ancestry data instead of race resulted in similar estimates of the GFR (median difference, 1.33 ml per minute per 1.73 m²; 95% CI, -0.12 to 2.33; P₁₀, 42%; 95% CI, 34 to 50). The inclusion of non-GFR determinants of the serum creatinine level (e.g., body-composition metrics and urinary excretion of creatinine) that differed according to race reported by the participants and genetic ancestry did not eliminate the misclassification introduced by removing race (or ancestry) from serum creatinine-based GFR estimating equations. In contrast, the incorporation of race or ancestry was not necessary to achieve similarly statistically unbiased (median difference, 0.33 ml per minute per 1.73 m²; 95% CI, -1.43 to 1.92) and accurate (P₁₀, 41%; 95% CI, 34 to 49) estimates in Black participants when GFR was estimated with the use of cystatin C.

CONCLUSIONS

The use of the serum creatinine level to estimate the GFR without race (or genetic ancestry) introduced systematic misclassification that could not be eliminated even when numerous non-GFR determinants of the serum creatinine level were accounted for. The estimation of GFR with the use of cystatin C generated similar results while eliminating the negative consequences of the current race-based approaches. (Funded by the National Institute of Diabetes and Digestive and Kidney Diseases and others.).

A Healthy Beverage Score and Risk of Chronic Kidney Disease Progression, Incident Cardiovascular Disease, and All-Cause Mortality in the Chronic Renal Insufficiency Cohort

BACKGROUND

Beverages are a source of calories and other bioactive constituents but are an understudied aspect of the diet. Different beverages have varying effects on health outcomes.

OBJECTIVES

We created the Healthy Beverage Score (HBS) to characterize participants' beverage patterns and examined its association with chronic kidney disease (CKD) progression, incident cardiovascular disease (CVD), and all-cause mortality among individuals with CKD.

METHODS

We conducted a prospective analysis of 2283 adults aged 21-74 y with a baseline estimated glomerular filtration rate of 20-70 mL · min-1 · 1.73 m-2 from the Chronic Renal Insufficiency Cohort. Diet was assessed using a 124-item FFQ at visit 1 (2003-2008). The HBS, ranging from 7 to 28 possible points, consisted of 7 components, each scored from 1 to 4 based on rank distribution by quartile, except alcohol, which was based on sex-specific cutoffs. Participants were given more points for higher consumption of low-fat milk and of coffee/tea, for moderate alcohol, and for lower consumption of 100% fruit juice, whole-fat milk, artificially sweetened beverages, and sugar-sweetened beverages. CKD progression, incident CVD, and mortality were ascertained through January 2018. We conducted multivariable Cox proportional hazards models.

RESULTS

There were 815 cases of CKD progression, 285 cases of incident CVD, and 725 deaths over a maximum of 14 y of follow-up. Compared with participants in the lowest tertile of the HBS, participants in the highest tertile had a 25% lower likelihood of CKD progression (HR: 0.75; 95% CI: 0.63, 0.89; P-trend = 0.001) and a 17% lower likelihood of all-cause mortality (HR: 0.83; 95% CI: 0.69, 1.00; P-trend = 0.04) after adjusting for sociodemographic, clinical, and dietary factors. There was no significant trend for incident CVD.

CONCLUSIONS

Among individuals with CKD, a healthier beverage pattern was inversely associated with CKD progression and all-cause mortality. Beverage intake may be an important modifiable target in preventing adverse outcomes for individuals with CKD.

Hypotonic swelling-induced Ca(2+) release by an IP(3)-insensitive Ca(2+) store

Hypotonic swelling increases the intracellular Ca(2+) concentration ([Ca(2+)](i)) in vascular smooth muscle cells (VSMC). The source of this Ca(2+) is not clear. To study the source of increase in [Ca(2+)](i) in response to hypotonic swelling, we measured [Ca(2+)](i) in fura 2-loaded cultured VSMC (A7r5 cells). Hypotonic swelling produced a 40.7-nM increase in [Ca(2+)](i) that was not inhibited by EGTA but was inhibited by 1 microM thapsigargin. Prior depletion of inositol 1,4,5-trisphosphate (IP(3))-sensitive Ca(2+) stores with vasopressin did not inhibit the increase in [Ca(2+)](i) in response to hypotonic swelling. Exposure of (45)Ca(2+)-loaded intracellular stores to hypotonic swelling in permeabilized VSMC produced an increase in (45)Ca(2+) efflux, which was inhibited by 1 microM thapsigargin but not by 50 microg/ml heparin, 50 microM ruthenium red, or 25 microM thio-NADP. Thus hypotonic swelling of VSMC causes a release of Ca(2+) from the intracellular stores from a novel site distinct from the IP(3)-, ryanodine-, and nicotinic acid adenine dinucleotide phosphate-sensitive stores.