Race/Ethnicity, Dietary Acid Load, and Risk of End-Stage Renal Disease among US Adults with Chronic Kidney Disease

The Role of Dietary Acid Load on Progression of Estimated Glomerular Filtration Rate Among Individuals Diagnosed With Chronic Kidney Disease

OBJECTIVE

Individuals with chronic kidney disease (CKD) are at an increased risk for developing metabolic acidosis. Metabolic acidosis has been shown to worsen kidney function and exacerbate systemic inflammation. Diets high in protein foods can exacerbate metabolic acidosis as protein foods tend to be more acidic, while fruits and vegetables are more alkalotic. The main objective of this systematic review was to determine if higher consumption of fruits and vegetables in adults with CKD stages 1-5 reduces the rate of decline of estimated glomerular filtration rate.

METHODS

Searches of Cumulated Index to Nursing and Allied Health Literature (CINAHL -Elton B. Stephens Company [EBSCO]), Cochrane Library (Wiley), Dissertation & Thesis Global (ProQuest), Embase (Elsevier), Medline (OVID), PubMed (National Library of Medicine), Scopus (Elsevier), and Web of Sciences (Clarivate) identified 1,451 articles published between January 2015 and June 2023.

RESULTS

After independent review, 7 total studies were included. Six of the studies found an association between dietary acid load and progression of CKD.

CONCLUSIONS

Dietary counseling focusing on decreasing dietary acid load may be beneficial for individuals with CKD.

AACC/NKF Guidance Document on Improving Equity in Chronic Kidney Disease Care

BACKGROUND

Kidney disease (KD) is an important health equity issue with Black, Hispanic, and socioeconomically disadvantaged individuals experiencing a disproportionate disease burden. Prior to 2021, the commonly used estimated glomerular filtration rate (eGFR) equations incorporated coefficients for Black race that conferred higher GFR estimates for Black individuals compared to non-Black individuals of the same sex, age, and blood creatinine concentration. With a recognition that race does not delineate distinct biological categories, a joint task force of the National Kidney Foundation and the American Society of Nephrology recommended the adoption of the CKD-EPI 2021 race-agnostic equations.

CONTENT

This document provides guidance on implementation of the CKD-EPI 2021 equations. It describes recommendations for KD biomarker testing, and opportunities for collaboration between clinical laboratories and providers to improve KD detection in high-risk populations. Further, the document provides guidance on the use of cystatin C, and eGFR reporting and interpretation in gender-diverse populations.

SUMMARY

Implementation of the CKD-EPI 2021 eGFR equations represents progress toward health equity in the management of KD. Ongoing efforts by multidisciplinary teams, including clinical laboratorians, should focus on improved disease detection in clinically and socially high-risk populations. Routine use of cystatin C is recommended to improve the accuracy of eGFR, particularly in patients whose blood creatinine concentrations are confounded by processes other than glomerular filtration. When managing gender-diverse individuals, eGFR should be calculated and reported with both male and female coefficients. Gender-diverse individuals can benefit from a more holistic management approach, particularly at important clinical decision points.

Lifestyle and chronic kidney disease: A machine learning modeling study

Background

Individual lifestyle varies in the real world, and the comparative efficacy of lifestyles to preserve renal function remains indeterminate. We aimed to systematically compare the effects of lifestyles on chronic kidney disease (CKD) incidence, and establish a lifestyle scoring system for CKD risk identification.

Methods

Using the data of the UK Biobank cohort, we included 470,778 participants who were free of CKD at the baseline. We harnessed the light gradient boosting machine algorithm to rank the importance of 37 lifestyle factors (such as dietary patterns, physical activity (PA), sleep, psychological health, smoking, and alcohol) on the risk of CKD. The lifestyle score was calculated by a combination of machine learning and the Cox proportional-hazards model. A CKD event was defined as an estimated glomerular filtration rate <60 ml/min/1.73 m², mortality and hospitalization due to chronic renal failure, and self-reported chronic renal failure, initiated renal replacement therapy.

Results

During a median of the 11-year follow-up, 13,555 participants developed the CKD event. Bread, walking time, moderate activity, and vigorous activity ranked as the top four risk factors of CKD. A healthy lifestyle mainly consisted of whole grain bread, walking, moderate physical activity, oat cereal, and muesli, which have scored 12, 12, 10, 7, and 7, respectively. An unhealthy lifestyle mainly included white bread, tea >4 cups/day, biscuit cereal, low drink temperature, and processed meat, which have scored −12, −9, −7, −4, and −3, respectively. In restricted cubic spline regression analysis, a higher lifestyle score was associated with a lower risk of CKD event (p for linear relation < 0.001). Compared to participants with the lifestyle score < 0, participants scoring 0–20, 20–40, 40–60, and >60 exhibited 25, 42, 55, and 70% lower risk of CKD event, respectively. The C-statistic of the age-adjusted lifestyle score for predicting CKD events was 0.710 (0.703–0.718).

Conclusion

A lifestyle scoring system for CKD prevention was established. Based on the system, individuals could flexibly choose healthy lifestyles and avoid unhealthy lifestyles to prevent CKD.

Health inequities and the inappropriate use of race in nephrology

Chronic kidney disease is an important clinical condition beset with racial and ethnic disparities that are associated with social inequities. Many medical schools and health centres across the USA have raised concerns about the use of race - a socio-political construct that mediates the effect of structural racism - as a fixed, measurable biological variable in the assessment of kidney disease. We discuss the role of race and racism in medicine and outline many of the concerns that have been raised by the medical and social justice communities regarding the use of race in estimated glomerular filtration rate equations, including its relationship with structural racism and racial inequities. Although race can be used to identify populations who experience racism and subsequent differential treatment, ignoring the biological and social heterogeneity within any racial group and inferring innate individual-level attributes is methodologically flawed. Therefore, although more accurate measures for estimating kidney function are under investigation, we support the use of biomarkers for determining estimated glomerular filtration rate without adjustments for race. Clinicians have a duty to recognize and elucidate the nuances of racism and its effects on health and disease. Otherwise, we risk perpetuating historical racist concepts in medicine that exacerbate health inequities and impact marginalized patient populations.

Racial disparities in preemptive waitlisting and deceased donor kidney transplantation: Ethics and solutions

Kidney transplantation prior to dialysis, known as "preemptive transplant," enables patients to live longer and avoid the substantial quality of life burdens due to chronic dialysis. Deceased donor kidneys are a public resource that ought to provide health benefits equitably. Unfortunately, White, better educated, and privately insured patients enjoy disproportionate access to preemptive transplantation using deceased donor kidneys. This problem has persisted for decades and is exacerbated by the first-come, first-served approach to kidney allocation for predialysis patients. In this Personal Viewpoint, we describe the diverse barriers to preemptive waitlisting and kidney transplant. The analysis focuses on healthcare system features that particularly disadvantage Black patients, such as the waitlisting eligibility criterion of a single glomerular filtration rate or creatinine clearance ≤20 ml/min, and neglect of wide variation in the rate of progression to end-stage kidney disease (ESKD) in allocating preemptive transplants. We propose initiatives to improve equity including: (1) standardization of waitlisting eligibility criteria related to kidney function; (2) aggressive education for clinicians about early transplant referral; (3) innovations in electronic medical record capabilities; and (4) rapid status 7 listing by centers. If those initiatives fail, the transplant field should consider eliminating preemptive waitlisting and transplantation with deceased donor kidneys.

The therapeutic importance of acid-base balance

Baking soda and vinegar have been used as home remedies for generations and today we are only a mouse-click away from claims that baking soda, lemon juice, and apple cider vinegar are miracles cures for everything from cancer to COVID-19. Despite these specious claims, the therapeutic value of controlling acid-base balance is indisputable and is the basis of Food and Drug Administration-approved treatments for constipation, epilepsy, metabolic acidosis, and peptic ulcers. In this narrative review, we present evidence in support of the current and potential therapeutic value of countering local and systemic acid-base imbalances, several of which do in fact involve the administration of baking soda (sodium bicarbonate). Furthermore, we discuss the side effects of pharmaceuticals on acid-base balance as well as the influence of acid-base status on the pharmacokinetic properties of drugs. Our review considers all major organ systems as well as information relevant to several clinical specialties such as anesthesiology, infectious disease, oncology, dentistry, and surgery.

An Acidic Environment Induces APOL1-Associated Mitochondrial Fragmentation

BACKGROUND

Apolipoprotein L1 gene (APOL1) G1 and G2 kidney-risk variants (KRVs) cause CKD in African Americans, inducing mitochondrial dysfunction. Modifying factors are required, because a minority of individuals with APOL1 high-risk genotypes develop nephropathy. Given that APOL1 function is pH-sensitive and the pH of the kidney interstitium is <7, we hypothesized the acidic kidney interstitium may facilitate APOL1 KRV-induced mitochondrial dysfunction.

METHODS

Human embryonic kidney (HEK293) cells conditionally expressing empty vector (EV), APOL1-reference G0, and G1 or G2 KRVs were incubated in media pH 6.8 or 7.4 for 4, 6, or 8 h. Genotype-specific pH effects on mitochondrial length (µm) were assessed using confocal microscopy in live cells and Fiji derivative of ImageJ software with MiNA plug-in. Lower mitochondrial length indicated fragmentation and early dysfunction.

RESULTS

After 6 h doxycycline (Dox) induction in pH 6.8 media, G2-expressing cells had shorter mitochondria (6.54 ± 0.40) than cells expressing EV (7.65 ± 0.72, p = 0.02) or G0 (7.46 ± 0.31, p = 0.003). After 8 h Dox induction in pH 6.8 media, both G1- (6.21 ± 0.26) and G2-expressing cells had shorter mitochondria (6.46 ± 0.34) than cells expressing EV (7.13 ± 0.32, p = 0.002 and p = 0.008, respectively) or G0 (7.22 ± 0.45, p = 0.003 and p = 0.01, respectively). Mitochondrial length in cells incubated in pH 7.4 media were comparable after 8 h Dox induction regardless of genotype. APOL1 mRNA expression and cell viability were comparable regardless of pH or genotype after 8 h Dox induction.

CONCLUSION

Acidic pH facilitates early mitochondrial dysfunction induced by APOL1 G1 and G2 KRVs in HEK293 cells. We propose that the acidic kidney interstitium may play a role in APOL1-mediated mitochondrial pathophysiology and nephropathy.

Plant-based diets to manage the risks and complications of chronic kidney disease

Traditional dietary recommendations for patients with chronic kidney disease (CKD) focus on the quantity of nutrients consumed. Without appropriate dietary counselling, these restrictions can result in a low intake of fruits and vegetables and a lack of diversity in the diet. Plant nutrients and plant-based diets could have beneficial effects in patients with CKD: increased fibre intake shifts the gut microbiota towards reduced production of uraemic toxins; plant fats, particularly olive oil, have anti-atherogenic effects; plant anions might mitigate metabolic acidosis and slow CKD progression; and as plant phosphorus has a lower bioavailability than animal phosphorus, plant-based diets might enable better control of hyperphosphataemia. Current evidence suggests that promoting the adoption of plant-based diets has few risks but potential benefits for the primary prevention of CKD, as well as for delaying progression in patients with CKD G3-5. These diets might also help to manage and prevent some of the symptoms and metabolic complications of CKD. We suggest that restriction of plant foods as a strategy to prevent hyperkalaemia or undernutrition should be individualized to avoid depriving patients with CKD of these potential beneficial effects of plant-based diets. However, research is needed to address knowledge gaps, particularly regarding the relevance and extent of diet-induced hyperkalaemia in patients undergoing dialysis.

Ethnic minority disparities in progression and mortality of pre-dialysis chronic kidney disease: a systematic scoping review

Background

There are a growing number of studies on ethnic differences in progression and mortality for pre-dialysis chronic kidney disease (CKD), but this literature has yet to be synthesised, particularly for studies on mortality.

Methods

This scoping review synthesized existing literature on ethnic differences in progression and mortality for adults with pre-dialysis CKD, explored factors contributing to these differences, and identified gaps in the literature. A comprehensive search strategy using search terms for ethnicity and CKD was taken to identify potentially relevant studies. Nine databases were searched from 1992 to June 2017, with an updated search in February 2020.

Results

8059 articles were identified and screened. Fifty-five studies (2 systematic review, 7 non-systematic reviews, and 46 individual studies) were included in this review. Most were US studies and compared African-American/Afro-Caribbean and Caucasian populations, and fewer studies assessed outcomes for Hispanics and Asians. Most studies reported higher risk of CKD progression in Afro-Caribbean/African-Americans, Hispanics, and Asians, lower risk of mortality for Asians, and mixed findings on risk of mortality for Afro-Caribbean/African-Americans and Hispanics, compared to Caucasians. Biological factors such as hypertension, diabetes, and cardiovascular disease contributed to increased risk of progression for ethnic minorities but did not increase risk of mortality in these groups.

Conclusions

Higher rates of renal replacement therapy among ethnic minorities may be partly due to increased risk of progression and reduced mortality in these groups. The review identifies gaps in the literature and highlights a need for a more structured approach by researchers that would allow higher confidence in single studies and better harmonization of data across studies to advance our understanding of CKD progression and mortality.

Epithelial-fibroblast cross talk aggravates the impact of the nephrotoxin ochratoxin A

BACKGROUND

Chronic nephropathies result from different pathogenic agents, including nutritional factors triggering vicious pathophysiological cycles. Ochratoxin A (OTA) is a globally occurring nephrotoxic mycotoxin detectable in a variety of foodstuff and suspected to cause tubulointerstitial damage. The underlying mechanisms are not sufficiently understood, compromising risk assessment. Because crosstalk of proximal tubule cells with fibroblasts is crucial for tubulointerstitial damage, we investigated the effects of OTA in co-culture of these two cell types.

METHODS

Rat renal proximal tubule cells (NRK-52E) and renal fibroblasts (NRK-49F) were exposed to nanomolar OTA concentrations under mono- and/or co-culture conditions for up to 48 h. We determined the impact on inflammation-, EMT- and fibrosis-associated proteins as well as microRNAs by western blot or qPCR, respectively. Alterations in cell morphology were quantitatively assessed. The roles of miRs, COX-2 and ERK1/2 in OTA-induced effects were investigated by specific inhibition.

FINDINGS

Only under co-culture condition, OTA caused an increase of vimentin, fibronectin and miR-21 and a decrease of collagen III, E-cadherin, COX-2 and WISP1 mRNA abundance in NRK-52E cells. In NRK-49F cells, OTA induced an increase of N-cadherin, COX-2, WISP1 in co-culture only. The OTA-induced increase of fibronectin in NRK-52E cells was prevented by simultaneous inhibition of miR-21 and -200a, COX-2 or ERK1/2. The OTA-induced increase of COX-2 in NRK-49F cells was prevented by inhibition of miR-21 and -200a or ERK1/2.

INTERPRETATION

Our results show that the complete nephropathic potential of nanomolar OTA, leading to EMT, is unveiled when cellular crosstalk is possible. In monoculture, the nephropathic potential is underestimated.

RESEARCH IN CONTEXT

Chronic nephropathies are a severe health burden and the result of different pathogenic mechanisms, including nutritional factors that trigger vicious pathophysiological cycles. Ochratoxin A (OTA) is a ubiquitous, globally occurring nephrotoxic mycotoxin detectable in a variety of foodstuff and suspected to cause tubulointerstitial damage. Because underlying pathomechanisms are unclear, risk assessment is problematic. Crosstalk of proximal tubule cells (the main target of OTA) with fibroblasts is crucial for the development of tubulointerstitial damage. We show that during co-culture of proximal tubule cells and fibroblasts, OTA-induced effects (e.g. epithelial-mesenchymal transition (EMT)) change significantly as compared to monoculture. Our results show that the complete nephropathic potential of OTA is unveiled when cellular crosstalk is possible. In monoculture, the nephropathic potential of OTA is underestimated.

APOL1, Acid Load, and CKD Progression

INTRODUCTION

High dietary acid load and metabolic acidosis are associated with an accelerated decline in kidney function and may contribute to the observed heterogeneity in end-stage renal disease (ESRD) risk according to APOL1 genotype. Our objective was to examine the associations of metabolic acidosis and dietary acid load with kidney disease progression, according to APOL1 genotype, among individuals with chronic kidney disease (CKD).

METHODS

We studied 1048 African American participants in the Chronic Renal Insufficiency Cohort. Metabolic acidosis was defined as blood levels of serum bicarbonate less than 22 mEq/L, and dietary acid load was quantified by potential renal acid load (PRAL) using data from the Diet Health Questionnaire. APOL1 status was defined as having 2 risk variants, consisting of either possible combination of the G1 and G2 risk alleles. We tested associations of APOL1 and dietary and metabolic acidosis with CKD progression, defined as time to ESRD or 50% decline in eGFR.

RESULTS

During a median follow-up period of 7 years, 379 participants had an incident CKD progression event (6.4 events per 100 person-years). After full adjustment, among participants with 2 APOL1 variants, the analysis failed to detect an association between metabolic acidosis or dietary acid load and CKD progression (hazard ratio [HR], 1.03; 95% confidence interval [CI], 0.96-1.11 per 1 mEq/L higher serum bicarbonate and an HR, 1.03; 95% CI, 0.92-1.15 per 10 mEq/L higher PRAL). Similar associations were noted among participants without the APOL1 high-risk genotype.

CONCLUSION

In a population at high risk of developing ESRD, metabolic acidosis and dietary acid load were not associated with CKD progression.

Sociodemographic and Kidney Disease Correlates of Nutrient Intakes Among Urban African Americans With Uncontrolled Hypertension

OBJECTIVE

The objective of this study was to determine the association between sociodemographic factors and intakes of 4 nutrients and associations between intakes and markers of kidney disease to identify opportunities to improve outcomes among clinically high-risk African Americans.

DESIGN AND METHODS

We conducted a cross-sectional study of baseline data from the Achieving Blood Pressure Control Together study, a randomized controlled trial of 159 African Americans (117 females) with uncontrolled hypertension in Baltimore MD. To determine the association between sociodemographic factors and nutrient intakes, we constructed linear and logistic regression models. Using logistic regression, we determined the association between below-median nutrient intakes and kidney disease. Our outcomes of interest were daily intakes of vitamin C, magnesium, dietary fiber, and potassium as estimated by the Block Fruit-Vegetable-Fiber Screener and kidney disease defined as estimated glomerular filtration rate <60 mL/min per 1.73 m2 or urinary albumin-to-creatinine ratio >=30 mg/g.

SETTING AND SUBJECTS

Baseline data from the Achieving Blood Pressure Control Together study, a randomized controlled trial of 159 African Americans (117 females) with uncontrolled hypertension, were obtained.

METHODS

To determine the association between sociodemographic factors and nutrient intakes, we constructed linear and logistic regression models. Using logistic regression, we determined the association between below-median nutrient intakes and kidney disease.

MAIN OUTCOME MEASURES

Our outcomes of interest were daily intakes of vitamin C, magnesium, dietary fiber, and potassium as estimated by the Block Fruit-Vegetable-Fiber Screener and kidney disease defined as estimated glomerular filtration rate <60 mL/min per 1.73 m² or urinary albumin-to-creatinine ratio ≥30 mg/g.

RESULTS

Overall, compared to Institute of Medicine recommendations, participants had lower intakes of magnesium, fiber, and potassium but higher vitamin C intakes. For females, sociodemographic factors that significantly associated with lower intake of the 4 nutrients were older age, obesity, lower health numeracy, and lesser educational attainment. For males, none of the sociodemographic factors were significantly associated with nutrient intakes. Below-median intake was significantly associated with albumin-to-creatinine ratio ≥30 (adjusted odds ratio [95% confidence interval]: 3.4 [1.5, 7.8] for vitamin C; 3.6 [1.6, 8.4] for magnesium; 2.9 [1.3, 6.5] for fiber; 3.6 [1.6, 8.4] for potassium), but not with estimated glomerular filtration rate <60.

CONCLUSION

African Americans with uncontrolled hypertension may have low intakes of important nutrients, which could increase their risk of chronic kidney disease. Tailored dietary interventions for African Americans at high risk for chronic kidney disease may be warranted.

Age-related Disease: A Revolution is Coming, Part 2-Dietary Acid Load, Hypertension, and Cardiovascular Disease

We are starting to develop the analytical tools to examine damage to our DNA and screen for the presence of clonal hematopoiesis of indeterminate potential. This type of technology will soon support the personalization of approaches to both the prevention and treatment of age-related diseases, which have historically been characterized as beyond our control. We are at the start of an era that will one day be looked upon as the age of precision personalized lifestyle health care. This article is the second in a series in which I will be examining new tools and research that I believe is paving the path forward and leading to exciting times ahead.