Biomarkers of Kidney Tubule Health, CKD Progression, and Acute Kidney Injury in SPRINT (Systolic Blood Pressure Intervention Trial) Participants

Urine Epidermal Growth Factor and Kidney Function Decline in Middle-Aged Adults

Rationale & Objective

The diagnosis and prognostication of chronic kidney disease (CKD) largely rely on glomerular measures that may not reflect tubular damage. We investigated the associations of urine kidney tubule biomarkers with estimated glomerular filtration rate (eGFR) change among middle-aged adults, when chronic diseases typically emerge.

Study Design

An observational cohort study.

Setting & Participants

A total of 1,145 participants of the Coronary Artery Risk Development in Young Adults (CARDIA) study without CKD, hypertension, or cardiovascular disease at the year 20 visit.

Exposures

Seven different biomarkers of tubular health: urine epidermal growth factor (EGF), alpha-1-microglobulin (α1m), interleukin-18, kidney injury molecule-1, monocyte chemoattractant protein-1, uromodulin, and chitinase-3-like protein 1.

Outcomes

Ten-year eGFR change and incident reduced eGFR (new onset of eGFR < 60 mL/min/1.73 m2).

Analytical Approach

We examined associations of tubular health biomarkers with 10-year eGFR change and incident reduced eGFR with linear mixed models and interval-censored proportional hazards regression models, respectively. Both minimally and fully adjusted models were controlled for urine creatinine levels.

Results

The mean age of participants was 44.8 ± 3.7 years, with 39% African American and 56% female. The average 10-year change in eGFR was -18.6 mL/min/1.73 m2 (95% CI, -19.4 to -17.8). In contrast to the other tubular biomarkers, which showed conflicting results, EGF demonstrated strong, consistent associations with both kidney outcomes. Each 1-standard deviation (SD) higher EGF was associated with a 2.37 mL/min/1.73 m2 (95% CI, 0.64-4.10) smaller 10-year decrease in eGFR and a 42% (95% CI, 4%-64%) lower risk of incident reduced eGFR in the fully adjusted model.

Limitations

Observational design, measurements of eGFR were done only at 5-year intervals during follow-up.

Conclusions

In middle-aged, community-dwelling adults without hypertension, cardiovascular disease or CKD, higher urine EGF concentrations are associated with slower eGFR decline, whereas other kidney tubule biomarkers lacked a consistent association with kidney function decline.

Clinical significance of amphiregulin in patients with chronic kidney disease

BACKGROUND

Amphiregulin (AREG) is a ligand of epidermal growth factor receptor (EGFR), which plays an important role in injury-induced kidney fibrosis. However, the clinical significance of serum soluble AREG in chronic kidney disease (CKD) is unclear. In this study, we elucidated the clinical significance of serum soluble AREG in CKD by analyzing the association of serum soluble AREG levels with renal function and other clinical parameters in patients with CKD.

METHODS

In total, 418 Japanese patients with CKD were enrolled, and serum samples were collected for the determination of soluble AREG and creatinine (Cr) levels, and other clinical parameters. Additionally, these parameters were evaluated after 2 and 3 years. Moreover, immunohistochemical assay was performed ate AREG expression in the kidney tissues of patients with CKD.

RESULTS

Soluble AREG levels were positively correlated with serum Cr (p < 0.0001). Notably, initial AREG levels were positively correlated with changes in renal function (ΔCr) after 2 (p < 0.0001) and 3 years (P = 0.048). Additionally, soluble AREG levels were significantly higher (p < 0.05) in patients with diabetic nephropathy or primary hypertension. Moreover, AREG was highly expressed in renal tubular cells in patients with advanced CKD, but only weakly expressed in patients with preserved renal function.

CONCLUSION

Serum soluble AREG levels were significantly correlated with renal function, and changes in renal function after 2 and 3 years, indicating that serum soluble AREG levels might serve as a biomarker of renal function and renal prognosis in CKD.

Fibrosis in Chronic Kidney Disease: Pathophysiology and Therapeutic Targets

Chronic kidney disease (CKD) is a slowly progressive condition characterized by decreased kidney function, tubular injury, oxidative stress, and inflammation. CKD is a leading global health burden that is asymptomatic in early stages but can ultimately cause kidney failure. Its etiology is complex and involves dysregulated signaling pathways that lead to fibrosis. Transforming growth factor (TGF)-β is a central mediator in promoting transdifferentiation of polarized renal tubular epithelial cells into mesenchymal cells, resulting in irreversible kidney injury. While current therapies are limited, the search for more effective diagnostic and treatment modalities is intensive. Although biopsy with histology is the most accurate method of diagnosis and staging, imaging techniques such as diffusion-weighted magnetic resonance imaging and shear wave elastography ultrasound are less invasive ways to stage fibrosis. Current therapies such as renin-angiotensin blockers, mineralocorticoid receptor antagonists, and sodium/glucose cotransporter 2 inhibitors aim to delay progression. Newer antifibrotic agents that suppress the downstream inflammatory mediators involved in the fibrotic process are in clinical trials, and potential therapeutic targets that interfere with TGF-β signaling are being explored. Small interfering RNAs and stem cell-based therapeutics are also being evaluated. Further research and clinical studies are necessary in order to avoid dialysis and kidney transplantation.

Role of MCP-1 as an inflammatory biomarker in nephropathy

The Monocyte chemoattractant protein-1 (MCP-1), also referred to as chemokine ligand 2 (CCL2), belongs to the extensive chemokine family and serves as a crucial mediator of innate immunity and tissue inflammation. It has a notable impact on inflammatory conditions affecting the kidneys. Upon binding to its receptor, MCP-1 can induce lymphocytes and NK cells' homing, migration, activation, differentiation, and development while promoting monocytes' and macrophages' infiltration, thereby facilitating kidney disease-related inflammation. As a biomarker for kidney disease, MCP-1 has made notable advancements in primary kidney diseases such as crescentic glomerulonephritis, chronic glomerulonephritis, primary glomerulopathy, idiopathic proteinuria glomerulopathy, acute kidney injury; secondary kidney diseases like diabetic nephropathy and lupus nephritis; hereditary kidney diseases including autosomal dominant polycystic kidney disease and sickle cell kidney disease. MCP-1 not only predicts the occurrence, progression, prognosis of the disease but is also closely associated with the severity and stage of nephropathy. When renal tissue is stimulated or experiences significant damage, the expression of MCP-1 increases, demonstrating a direct correlation with the severity of renal injury.

Clusters of Body Fat and Nutritional Parameters are Strongly Associated with Diabetic Kidney Disease in Adults with Type 2 Diabetes

INTRODUCTION

Diabetic kidney disease (DKD) has become the leading cause of chronic kidney disease and end-stage renal failure in most developed and many developing countries. Strategies aimed at identifying potential modifiable risk factors for DKD are urgently needed. Here, we investigated the association between clusters of body fat and nutritional parameters with DKD in adults with type 2 diabetes mellitus (T2DM).

METHODS

This was a cross-sectional study of 184 participants with T2DM. Biochemical parameters including fasting blood glucose, hemoglobin A1c, hemoglobin, albumin, creatinine, and urinary albumin-to-creatinine ratio (UACR) were measured. The data for percentage of body fat mass (PBF), visceral fat area (VFA), phase angle at 50 kHz (PA50), and body cell mass (BCM) were obtained by bioelectrical impedance analysis (BIA). DKD was diagnosed by UACR and estimated glomerular filtration rate. Factor analysis was used for dimensionality reduction clustering among variables. The association of clusters with the presence of DKD was assessed using binary logistic regression analysis.

RESULTS

Factor analysis identified two clusters which were interpreted as a body fat cluster with positive loadings of VFA, body mass index, waist circumstance, and PBF and a nutritional parameters cluster with positive loadings of PA50, hemoglobin, BCM, and albumin. Participants were divided into the four groups based on the sex-specific cutoff value (median) of each cluster score calculated using the cluster weights and the original variable values. Only participants with high body fat and poor nutritional parameters (OR 3.43, 95% CI 1.25-9.42) were associated with increased odds of having DKD.

CONCLUSION

Body fat and nutritional parameters were strongly associated with and considerably contributed to the presence of DKD, suggesting that body fat and nutrition might be promising markers representing metabolic state in pathogenesis of DKD and clinical utility of BIA might provide valuable recommendations to patients with T2DM.

The urine-to-plasma urea concentration ratio is associated with eGFR and eGFR decline over time in a population cohort

BACKGROUND

Evaluation of renal function and of factors associated with its decline are important public health issues. Besides markers of glomerular function [e.g. glomerular filtration rate (GFR)], those of tubular functions are rarely evaluated. Urea, the most abundant urinary solute, is markedly concentrated in urine when compared with plasma. We explored the urine-to-plasma ratio of urea concentrations (U/P urea ratio) as a marker of tubular functions.

METHODS

We evaluated the relationship of the U/P urea ratio with eGFR at baseline in 1043 participants (48 ± 17 years) from the Swiss Kidney Project on Genes in Hypertension (SKIPOGH) population-based cohort, using mixed regression. In 898 participants, we assessed the relation between U/P urea ratio and renal function decline between two study waves 3 years apart. We studied U/P ratios for osmolarity, Na, K and uric acid for comparison.

RESULTS

In a transversal study at baseline, estimated GFR (eGFR) was positively associated with U/P-urea ratio [βscaled = 0.08, 95% CI (0.04; 0.13)] but not with the U/P ratio of osmolarity. Considering separately participants with renal function >90 or ≤90 mL/min × 1.73 m2, this association was observed only in those with reduced renal function. In the longitudinal study, eGFR declined at a mean rate of 1.2 mL/min per year. A significant association was observed between baseline U/P urea ratio and eGFR decline [βscaled = 0.08, 95% CI (0.01; 0.15)]. A lower baseline U/P urea ratio was associated with a greater eGFR decline.

CONCLUSION

This study provides evidence that the U/P urea ratio is an early marker of kidney function decline in the general adult population. Urea is easy to measure with well-standardized techniques and at low cost. Thus, the U/P urea ratio could become an easily available tubular marker for evaluating renal function decline.

Urine Uromodulin, Kidney Tubulointerstitial Fibrosis, and Furosemide Response

BACKGROUND

Interstitial fibrosis and tubular atrophy (IFTA) are common findings on biopsy in chronic kidney disease (CKD) and are strongly predictive of kidney failure. IFTA is poorly correlated with estimated glomerular filtration rate (eGFR) and albuminuria, the most common measures of kidney function. Thus, IFTA is prognostically important, yet its presence and severity are invisible to the clinician except when kidney biopsies are obtained.

OBJECTIVES

The objective of this study was to investigate (1) the cross-sectional association between urine uromodulin (uUMOD) and IFTA and (2) to determine whether uUMOD levels were associated with diuretic response after a furosemide stress test.

METHODS

We performed logistic regression to evaluate the association between uUMOD and fibrosis. We used linear regression models to assess the association of uUMOD with diuretic response.

RESULTS

Among 52 participants, the mean age was 42 ± 16 years, 48% were women, 23% had diabetes, and the median eGFR was 56 mL/min/1.73 m2. The mean uUMOD concentration was 5.1 (8.4) μg/mL. Each halving of uUMOD was associated with 1.74 higher odds (95% CI: 1.10, 2.75) of grade 2 or 3 fibrosis. However, this association was no longer significant after adjusting for baseline eGFR and albuminuria. Each halving of uUMOD was associated with a decreased response to furosemide. This association was also no longer significant after adjusting for baseline eGFR and albuminuria.

CONCLUSION

In a population of individuals with a wide range of kidney function undergoing clinically indicated kidney biopsies, we did not find an association between uUMOD and interstitial fibrosis or response to loop diuretics after adjusting for eGFR and albuminuria.

Ambulatory urine biomarkers associations with acute kidney injury and hospitalization in people with HIV

BACKGROUND

People with HIV (PWH) generally have worse ambulatory levels of kidney injury biomarkers and excess risk of acute kidney injury (AKI) compared to persons without HIV. We evaluated whether ambulatory measures of subclinical kidney injury among PWH are associated with subsequent AKI.

METHODS

In the Predictors of Acute Renal Injury Study (PARIS), which enrolled 468 PWH from April 2016 to August 2019, we measured 10 urine biomarkers of kidney health (albumin, a1m, b2M, NGAL, IL18, KIM-1, EGF, UMOD, MCP-1, YKL40) at baseline and annually during follow-up. Using multivariable Cox regression models, we evaluated baseline and time-updated biomarker associations with the primary outcome of AKI (≥0.3 mg/dl or ≥1.5-times increase in serum creatinine from baseline) and secondary outcome of all-cause hospitalization.

RESULTS

At baseline, the mean age was 53 years old, and 45% self-identified as female. In time-updated models adjusting for sociodemographic factors, comorbidities, albuminuria, estimated glomerular filtration rate, and HIV-associated factors, higher KIM-1 [hazard ratio (HR) = 1.30 per twofold higher; 95% confidence interval (CI) 1.03-1.63] and NGAL concentrations (HR = 1.24, 95% CI 1.06-1.44) were associated with higher risk of hospitalized AKI. Additionally, in multivariable, time-updated models, higher levels of KIM-1 (HR = 1.19, 95% CI 1.00, 1.41), NGAL (HR = 1.13, 95% CI 1.01-1.26), and MCP-1 (HR = 1.20, 95% CI 1.00, 1.45) were associated with higher risk of hospitalization.

CONCLUSIONS

Urine biomarkers of kidney tubular injury, such as KIM-1 and NGAL, are strongly associated with AKI among PWH, and may hold potential for risk stratification of future AKI.

Kidney urinary biomarkers in patients with branched-chain amino acid and cobalamin metabolism defects

There is a clinical need for early detection of chronic kidney disease (CKD) in patients with organic acidurias. We measured kidney markers in a longitudinal study over 5 years in 40 patients with methylmalonic aciduria (Mut0 ), propionic aciduria (PA), cobalamin A (CblA), and cobalamin C (CblC) deficiencies. Neutrophil gelatinase-associated lipocalin (NGAL), calprotectin (CLP), kidney injury molecule-1 (KIM-1), dickkopf-3 (DKK-3), albumin and beta-2-microglobulin (B2MG) in urine, as well as cystatin C (CysC) in serum were quantified. In Mut0 patients, mean concentrations of B2MG, KIM-1, and DKK-3 were elevated compared with healthy controls, all markers indicative of proximal tubule damage. In PA patients, mean B2MG, albumin, and CLP were elevated, indicating signs of proximal tubule and glomerulus damage and inflammation. In CblC patients, mean B2MG, NGAL, and CLP were increased, and considered as markers for proximal and distal tubule damage and inflammation. B2MG, was elevated in all three diseases, and correlated with DKK-3 in Mut0 /CblA and with eGFR(CysC) and KIM-1 in PA patients, respectively. None of the markers were elevated in CblA patients. Significant deterioration of kidney function, as determined by steady increase in CysC concentrations was noted in seven patients within the observation period. None of the investigated biomarker profiles showed a clear increase or added value for early detection. In conclusion, we identified disease-specific biomarker profiles for inflammation, tubular, and proximal damage in the urine of Mut0 , PA, and CblC patients. Whether these biomarkers can be used for early detection of CKD requires further investigation, as significant kidney function deterioration was observed in only a few patients.

External Validation of a Urinary Biomarker Risk Score for the Prediction of Steroid Responsiveness in Adults With Nephrotic Syndrome

Introduction

In idiopathic nephrotic syndrome, response to corticosteroids remains the best indicator of prognosis. Noninvasive markers to predict a patient's response to steroids would allow improved prognostication and a more personalized approach to management. We have previously derived a urinary biomarker risk score which can differentiate steroid sensitive nephrotic syndrome (SSNS) from steroid resistant nephrotic syndrome (SRNS) in children. The goal of this study was to validate this previously derived biomarker risk score in a cohort of steroid-naïve adult patients, to determine whether the panel could be used to predict steroid responsiveness at the time of initial diagnosis.

Methods

In this external validation study, clinical data, and urinary specimens (obtained before initiation of steroid treatment) from adult patients were used in the Nephrotic Syndrome Study Network (NEPTUNE) cohort. A panel of 5 previously identified and validated urinary biomarkers, including neutrophil gelatinase-associated lipocalin (NGAL), vitamin D binding protein (VDBP), Fetuin-A (FetA), Transthyretin (TTR), and alpha-1 acid glycoprotein 2 (AGP2) was measured. A summary risk score for steroid resistance was calculated based on biomarker concentrations. Receiver operating characteristic curves were created for each log-transformed biomarker concentration and for the individual and combined biomarker risk score.

Results

The urine biomarker risk score predicted development of steroid resistance, with optimal sensitivity and specificity of 0.74, and area under the receiver operating characteristic curve (AUC) of 0.79 using both absolute and creatinine-corrected concentrations.

Conclusion

This study validates the previously derived urinary biomarker risk score to predict steroid resistance in adult patients with nephrotic syndrome at initial diagnosis.

Impaired Renal Function and Major Cardiovascular Events in Young Adults

BACKGROUND

Cardiovascular (CV) disease in young adults (aged 18-39 years) is on the rise. Whether subclinical reductions in kidney function (ie, estimated glomerular filtration rate [eGFR] above the current threshold for chronic kidney disease but below age-expected values) are associated with elevated CV risk is unknown.

OBJECTIVES

The goal of this study was to examine age-specific associations of subclinical eGFR reductions in young adults with major adverse cardiovascular events (MACEs) and MACE plus heart failure (MACE+).

METHODS

A retrospective cohort study of 8.7 million individuals (3.6 million aged 18-39 years) was constructed using linked provincial health care data sets from Ontario, Canada (January 2008-March 2021). Cox models were used to examine the association of categorized eGFR (50-120 mL/min/1.73 m2) with MACE (first of CV mortality, acute coronary syndrome, and ischemic stroke) and MACE+, stratified according to age (18-39, 40-49, and 50-65 years).

RESULTS

In the study cohort (mean age 41.3 years; mean eGFR 104.2 mL/min/1.73 m2; median follow-up 9.2 years), a stepwise increase in the relative risk of MACE and MACE+ was observed as early as eGFR <80 mL/min/1.73 m2 in young adults (eg, for MACE, at eGFR 70-79 mL/min/1.73 m2, ages 18-30 years: 2.37 events per 1,000 person years [HR: 1.31; 95% CI: 1.27-1.40]; ages 40-49 years: 6.26 events per 1,000 person years [HR: 1.09; 95% CI: 1.06-1.12]; ages 50-65 years: 14.9 events per 1,000 person years [HR: 1.07; 95% CI: 1.05-1.08]). Results persisted for each MACE component and in additional analyses (stratifying according to past CV disease, accounting for albuminuria at index, and using repeated eGFR measures).

CONCLUSIONS

In young adults, eGFR below age-expected values were associated with an elevated risk for MACE and MACE+, warranting age-appropriate risk stratification, proactive monitoring, and timely intervention.

Markers of Kidney Tubule Dysfunction and Major Adverse Kidney Events

BACKGROUND

Serum creatinine and albuminuria are primary markers of glomerular function and injury, respectively. Tubular secretion, acid-base homeostasis, protein reabsorption, among other tubular functions, are largely ignored. This mini-review aimed to discuss how two tubular functions, secretion, and acid-base homeostasis are associated with major adverse kidney events (MAKEs).

SUMMARY

Proximal tubular secretion is an essential function that allows the elimination of endogenous substances and drugs. Recently discovered endogenous markers in urine and plasma allow a noninvasive way of assessing tubular secretion markers. Several studies have found an association between these markers and a higher risk of chronic kidney disease (CKD) progression and mortality. In a study we recently performed among patients with CKD and at risk of cardiovascular events, lower tubular secretion was associated with an increased risk of acute kidney injury and metabolic acidosis, independent of baseline eGFR and albuminuria. The kidney tubules also play a crucial role in acid-base homeostasis. Although the standard clinical assessment of acidosis consists of measuring serum bicarbonate, urinary ammonium excretion decreases before over metabolic acidosis. Urinary ammonium excretion is associated with CKD progression, a higher risk of kidney failure, and an increased mortality risk, independent of baseline eGFR and albuminuria.

KEY MESSAGES

Novel biomarkers of kidney tubular health consistently associate with MAKEs, above and beyond baseline eGFR, albuminuria, and other CKD risk factors. Tubular markers may provide new opportunities to improve kidney prognosis, drug dosing, and monitoring for adverse events.

Combining robust urine biomarkers to assess chronic kidney disease progression

BACKGROUND

Urinary biomarkers may improve the prediction of chronic kidney disease (CKD) progression. Yet, data reporting the applicability of most commercial biomarker assays to the detection of their target analyte in urine together with an evaluation of their predictive performance are scarce.

METHODS

30 commercial assays (ELISA) were tested for their ability to quantify the target analyte in urine using strict (FDA-approved) validation criteria. In an exploratory analysis, LASSO (Least Absolute Shrinkage and Selection Operator) logistic regression analysis was used to identify potentially complementary biomarkers predicting fast CKD progression, determined as the ⁵¹CrEDTA clearance-based measured glomerular filtration rate (mGFR) decline (>10% per year) in a subsample of 229 CKD patients (mean age, 61 years; 66% men; baseline mGFR, 38 mL/min) from the NephroTest prospective cohort.

FINDINGS

Among the 30 assays, directed against 24 candidate biomarkers, encompassing different pathophysiological mechanisms of CKD progression, 16 assays fulfilled the FDA-approved criteria. LASSO logistic regressions identified a combination of five biomarkers including CCL2, EGF, KIM1, NGAL, and TGF-α that improved the prediction of fast mGFR decline compared to the kidney failure risk equation variables alone: age, gender, mGFR, and albuminuria. Mean area under the curves (AUC) estimated from 100 re-samples was higher in the model with than without these biomarkers, 0.722 (95% confidence interval 0.652-0.795) vs. 0.682 (0.614-0.748), respectively. Fully-adjusted odds-ratios (95% confidence interval) for fast progression were 1.87 (1.22, 2.98), 1.86 (1.23, 2.89), 0.43 (0.25, 0.70), 1.10 (0.71, 1.83), 0.55 (0.33, 0.89), and 2.99 (1.89, 5.01) for albumin, CCL2, EGF, KIM1, NGAL, and TGF-α, respectively.

INTERPRETATION

This study provides a rigorous validation of multiple assays for relevant urinary biomarkers of CKD progression which combination may improve the prediction of CKD progression.

FUNDING

This work was supported by Institut National de la Santé et de la Recherche Médicale, Université de Paris, Assistance Publique Hôpitaux de Paris, Agence Nationale de la Recherche, MSDAVENIR, Pharma Research and Early Development Roche Laboratories (Basel, Switzerland), and Institut Roche de Recherche et Médecine Translationnelle (Paris, France).

Markers of Kidney Tubular Function Deteriorate While Those of Kidney Tubule Health Improve in Primary Aldosteronism After Targeted Treatments

Background Targeted treatment with mineralocorticoid receptor antagonists (MRAs) or adrenalectomy in patients with primary aldosteronism (PA) causes a decline in estimated glomerular filtration rate; however, the associated simultaneous changes in biomarkers of kidney tubule health still remain unclear. Methods and Results We matched 104 patients with newly diagnosed unilateral PA who underwent adrenalectomy with 104 patients with unilateral PA who were treated with MRAs, 104 patients with bilateral PA treated with MRAs, and 104 patients with essential hypertension who served as controls. Functional biomarkers were measured before the targeted treatment and 1 year after treatment, including serum markers of kidney function (cystatin C, creatinine), urinary markers of proximal renal tubular damage (L-FABP [liver-type fatty-acid binding protein], KIM-1 [kidney injury molecule-1]), serum markers of kidney tubular reserve and mineral metabolism (intact parathyroid hormone), and proteinuria. Compared with the patients with essential hypertension, the patients with PA had higher pretreatment serum intact parathyroid hormone and urinary creatinine-corrected parameters, including L-FABP, KIM-1, and albumin. The patients with essential hypertension and with PA had similar cystatin C levels. After treatment with MRAs or adrenalectomy of unilateral PA and MRAs of bilateral PA, the patients with PA had increased serum cystatin C and decreased urinary L-FABP/creatinine, KIM-1/creatinine, creatinine-based estimated glomerular filtration rate, intact parathyroid hormone, and proteinuria (all P<0.05). In multivariable regression models, a higher urinary L-FABP/creatinine ratio and older age were significantly correlated with the occurrence of kidney failure (estimated glomerular filtration rate dip ≥30%) in the patients with PA after targeted treatment. Conclusions Compared with the matched patients with essential hypertension, the incident patients with PA at diagnosis had higher levels of several biomarkers, including markers of kidney damage, tubular reserve/mineral metabolism, and proteinuria. Functional kidney failure in the patients with PA after treatment could be predicted by a higher baseline urinary L-FABP/creatinine ratio and older age. After targeted treatments in the patients with bilateral or unilateral PA, these biomarkers of kidney tubule health were restored, but creatinine-based estimated glomerular filtration rate declined, which may therefore reflect hemodynamic changes rather than intrinsic damage to kidney tubular cells.

An explorative study of inflammation-related proteins associated with kidney injury in male heat-stressed workers

Chronic kidney disease of non-traditional origin (CKDnt) and acute kidney injury (AKI) often affect heat-stressed Mesoamerican manual workers. Inflammation occurs concurrently with AKI in this population, but its role remains unknown. To explore links between inflammation and kidney injury in heat stress, we compared levels of inflammation-related proteins in cutters with and without increasing serum creatinine levels during sugarcane harvest. These sugarcane cutters have previously been identified to be repeatedly exposed to severe heat stress during the five month harvest season. A nested case-control study was conducted among male Nicaraguan sugarcane cutters in a CKDnt hotspot. Cases (n = 30) were defined as having an increase in creatinine of ≥0.3 mg/dL across the five-month harvest. Controls (n = 57) had stable creatinine levels. Ninety-two inflammation-related proteins in serum were measured before and after harvest using Proximity Extension Assays. Mixed linear regression was used to identify differences in protein concentrations between cases and controls before harvest, differential trends during harvest, and association between protein concentrations and the urine kidney injury markers Kidney Injury Molecule (KIM)-1, Monocyte Chemoattractant Protein (MCP)-1 and albumin. One protein, chemokine (C-C motif) ligand 23 (CCL23), was elevated among cases at pre-harvest. Changes in seven inflammation-related proteins (CCL19, CCL23, colony-stimulating factor 1 [CSF1], hepatocyte and fibroblast growth factors [HGF and FGF23], and tumor necrosis factor beta [TNFB] and TNF-related activation-induced cytokine [TRANCE]) were associated with case status and at least two out of three urine kidney injury markers (KIM-1, MCP-1 and albumin). Several of these have been implicated in myofibroblast activation, which likely is an important step in kidney interstitial fibrotic disease such as CKDnt. This study provides an initial exploration of immune system determinants of, and activation during, kidney injury experienced during prolonged heat stress.

APOC1 as a novel diagnostic biomarker for DN based on machine learning algorithms and experiment

INTRODUCTION

Diabetic nephropathy is the leading cause of end-stage renal disease, which imposes a huge economic burden on individuals and society, but effective and reliable diagnostic markers are still not available.

METHODS

Differentially expressed genes (DEGs) were characterized and functional enrichment analysis was performed in DN patients. Meanwhile, a weighted gene co-expression network (WGCNA) was also constructed. For further, algorithms Lasso and SVM-RFE were applied to screening the DN core secreted genes. Lastly, WB, IHC, IF, and Elias experiments were applied to demonstrate the hub gene expression in DN, and the research results were confirmed in mouse models and clinical specimens.

RESULTS

17 hub secretion genes were identified in this research by analyzing the DEGs, the important module genes in WGCNA, and the secretion genes. 6 hub secretory genes (APOC1, CCL21, INHBA, RNASE6, TGFBI, VEGFC) were obtained by Lasso and SVM-RFE algorithms. APOC1 was discovered to exhibit elevated expression in renal tissue of a DN mouse model, and APOC1 is probably a core secretory gene in DN. Clinical data demonstrate that APOC1 expression is associated significantly with proteinuria and GFR in DN patients. APOC1 expression in the serum of DN patients was 1.358±0.1292μg/ml, compared to 0.3683±0.08119μg/ml in the healthy population. APOC1 was significantly elevated in the sera of DN patients and the difference was statistical significant (P > 0.001). The ROC curve of APOC1 in DN gave an AUC = 92.5%, sensitivity = 95%, and specificity = 97% (P < 0.001).

CONCLUSIONS

Our research indicates that APOC1 might be a novel diagnostic biomarker for diabetic nephropathy for the first time and suggest that APOC1 may be available as a candidate intervention target for DN.

Novel pathogenic variants in CUBN uncouple proteinuria from renal function

BACKGROUND

Proteinuria is an unfavorable clinical condition highly associated with a risk of renal and cardiovascular disease in chronic kidney disease (CKD). However, whether all proteinuria forms are linked to renal impairment are still unclear. Cubilin is an endocytic receptor highly expressed in renal proximal tubules mediating uptake of albumin, transferrin and α1-microglobulin.

METHODS

Exome sequencing method initially identified candidate genes. With the application of exome sequencing combined with Sanger sequencing, we further focused on CUBN through bioinformatics analysis. The pathogenic effects of the potentially causative variants were verified utilizing complementary analysis of clinical data and systematic characterization of the variants' expression and function with clinical samples and in vitro experiments in HEK293T cell lines along with in vivo experiments in mice.

RESULTS

In this study, we identified four novel variants locating after the vitamin B12 (vitB12)-binding domain of Cubilin (encoded by CUBN, NM_001081.3: c.4397G > A (p.C1466Y), c.6796C > T (p.R2266X), c.6821 + 3A > G and c.5153_5154delCT (p.S1718X)) in two families. Moreover, the variants severely affected the expression and function of Cubilin in renal proximal tubules and caused albuminuria, increasing levels in urine transferrin and α1-microglobulin, but without progressive glomerular filtration barrier (GFB) impairment, vitB12 deficiencies or abnormal blood levels of HDL and albumin. Further mechanistic insights showed that the variants after the vitB12-binding domain of CUBN merely disrupted the association with Amnionless (AMN) that exhibited aberrant localization in cell cytoplasm rather than membrane.

CONCLUSIONS

Here, our findings suggested that different mutation types after the vitB12-binding domain of CUBN uncouple proteinuria from glomerular filtration barrier, that may be an unexpectedly common benign condition in humans and may not require any proteinuria-lowering treatment or renal biopsy.

Xenobiotics Delivered by Electronic Nicotine Delivery Systems: Potential Cellular and Molecular Mechanisms on the Pathogenesis of Chronic Kidney Disease

Chronic kidney disease (CKD) is characterized as sustained damage to the renal parenchyma, leading to impaired renal functions and gradually progressing to end-stage renal disease (ESRD). Diabetes mellitus (DM) and arterial hypertension (AH) are underlying diseases of CKD. Genetic background, lifestyle, and xenobiotic exposures can favor CKD onset and trigger its underlying diseases. Cigarette smoking (CS) is a known modified risk factor for CKD. Compounds from tobacco combustion act through multi-mediated mechanisms that impair renal function. Electronic nicotine delivery systems (ENDS) consumption, such as e-cigarettes and heated tobacco devices, is growing worldwide. ENDS release mainly nicotine, humectants, and flavorings, which generate several byproducts when heated, including volatile organic compounds and ultrafine particles. The toxicity assessment of these products is emerging in human and experimental studies, but data are yet incipient to achieve truthful conclusions about their safety. To build up the knowledge about the effect of currently employed ENDS on the pathogenesis of CKD, cellular and molecular mechanisms of ENDS xenobiotic on DM, AH, and kidney functions were reviewed. Unraveling the toxic mechanisms of action and endpoints of ENDS exposures will contribute to the risk assessment and implementation of proper health and regulatory interventions.

Endogenous markers of kidney function and renal drug clearance processes of filtration, secretion, and reabsorption

The kidneys are responsible for maintaining physiologic homeostasis. The kidneys clear a variety of drugs and other substances through passive (filtration) and active processes that utilize transport proteins. Renal clearance is comprised of the processes of glomerular filtration, tubular secretion, and tubular reabsorption. Endogenous biomarkers, such as creatinine and cystatin C, are routinely used to estimate renal clearance. Understanding the contributing components of renal function and clearance, through the use of biomarkers, is necessary in elucidating the renal pharmacology of drugs and other substances. While exogenous markers of kidney function have been known for decades, several complexities have limited their usage. Several endogenous markers are being evaluated and hold promise to elucidate the individual components of kidney function that represent filtration, secretion, and reabsorption.

Diacylglycerol kinase epsilon protects against renal ischemia/reperfusion injury in mice through Krüppel-like factor 15/klotho pathway

Although recent studies have indicated that mutations in the gene encoding diacylglycerol kinase epsilon (DGKE) result in some proteinuria related hereditary kidney diseases, the DGKE expression pattern in the kidney and its contribution to acute kidney injury (AKI) remain unknown. Therefore, the present study was designed to detect the role of DGKE in mice with AKI. DGKE expression was time-dependently altered in the kidneys of mice with renal ischemia/reperfusion injury (IRI). Compared with wild-type (WT) mice, DGKE- overexpressing mice (Rosa26-Dgke^+/+) exhibited protective effects against renal IRI, including reduced serum creatinine, blood urea concentration, tubular cell death and inflammatory responses as well as improved morphological injuries. Consistently, in vitro, DGKE overexpression in human renal proximal tubule (HK-2) cells also protected against oxygen-glucose deprivation (OGD)/reoxygenation-induced cell death. Mechanistically, DGKE regulated Klotho expression, at least partly via the transcription factor Krüppel-like factor (KLF) 15. Moreover, a significant reduction in DGKE was also found in kidneys from patients with ischemia-associated acute tubular necrosis (ATN). Collectively, our studies demonstrate that DGKE protects against AKI in mice at least partly through KLF15/Klotho signaling pathway, indicating that DGKE may present an innovative therapeutic strategy for treating patients with AKI.

1,25-dihydroxyvitamin D as Predictor of Renal Worsening Function in Chronic Kidney Disease. Results From the PASCaL-1,25D Study

Background

Heterogeneous progression of chronic kidney disease (CKD) toward dialysis advocates improving in renal care management. Diagnosis and staging of CKD relies on estimated glomerular filtration rate (eGFR) and albuminuria. Tubular biomarkers emerged as new predictors of worsening renal function (WRF), due to partial inaccuracy of eGFR and existing WRF in non-proteinuric patients. Active vitamin D is synthesized in renal tubules and participates to mineral adaptation in CKD. Circulating 1,25-dihydroxyvitamin D [1,25(OH)₂D] was poorly investigated as a biomarker of endocrine tubular function and predictor of WRF.

Objective

Investigate capability of 1,25(OH)₂D to predict parathormone (PTH) increase and WRF in CKD stage 3-4.

Methods

PASCaL-1,25D was an observational, prospective, monocentric study. Primary outcomes were absolute and 20% increase in PTH, and WRF defined as 20% reduction in eGFR or dialysis initiation at 6 months.

Results

Seventy-one patients completed follow up. Absolute increase in PTH (1-84) was independently predicted by lower 1,25(OH)₂D levels (p = 0.0134). No association was detected between 1,25(OH)₂D and iPTH increase. Higher 1,25(OH)₂D was associated with reduced risk of WRF at univariate analysis [OR 0.89 (95% CI 0.86-0.93), p = 0.006]. The 1,25(OH)₂D/PTH (1-84) ratio was associated with non-significant 84% risk reduction for WRF [OR 0.16 (95% CI 0.06-0.41), p = 0.05]. Low 1,25(OH)₂D reached 100% sensitivity in predicting WRF in CKD stage 3 (AUC 9.909, p < 0.0001) and non-elderly patients (AUC 0.883, p < 0.0001). Machine learning models retained 1,25(OH)₂D/PTH (1-84) as relevant predictor of WRF together with eGFR and albuminuria. Age influenced interaction between renal and mineral biomarkers.

Conclusion

1,25(OH)₂D deserves attention as biomarker of tubular health, and sensible predictor of WRF on the short run among non-elderly patients affected by stage 3 CKD. The 1,25(OH)₂D/PTH (1-84) ratio may represent a composite biomarker of tubular reserve/endocrine response to the transition from adaptive to maladaptive equilibrium in CKD-MBD.

Urinary IL-18 is associated with arterial stiffness in patients with type 2 diabetes

OBJECTIVE

Diabetic kidney disease (DKD) has been shown to be associated with an excess risk of cardiovascular death. Inflammation has been considered central to type 2 diabetes (T2D) pathophysiology, and inflammation markers have been linked to cardiovascular disease. The serum and urinary IL-18 levels were significantly elevated in patients with T2D; however, whether interleukin 18 (IL-18) are associated with the severity of arterial stiffness remains to be determined. This study examined the relationship of IL-18 levels with pulse wave velocity (PWV) as a reflector for arterial stiffness in patients with T2D.

METHODS

A total of 180 participants with T2D who had undergone PWV examination were enrolled. Serum and urinary IL-18 levels were measured using sandwich enzyme linked immunosorbent assay (ELISA) kits. Arterial stiffness was determined by carotid-femoral PWV (cf-PWV) and carotid-radial PWV (cr-PWV).

RESULTS

The urinary IL-18 levels correlated positively with cf-PWV in patients with T2D with DKD (r = 0.418, p < 0.001); however, we found no significant correlation between urinary IL-18 and cf-PWV in diabetic subjects without DKD. In addition, we found no significant correlation between urinary IL-18 and cr-PWV in participants with T2D with or without DKD. Moreover, the association remained significant when controlling for arterial stiffness risk factors, urinary albumin-to-creatinine ratio and estimated glomerular filtration rate. cf-PWV was greater in the higher group of urinary IL-18 than in the lower group. Nevertheless, we found no significant correlation between serum IL-18 and cf-PWV in participants with T2D.

CONCLUSION

The urinary IL-18 levels appear to be associated with greater cf-PWV, suggesting the link between urinary IL-18 and arterial stiffness in patients with T2D.

Insights of Worsening Renal Function in Type 1 Cardiorenal Syndrome: From the Pathogenesis, Biomarkers to Treatment

Type-1 cardiorenal syndrome refers to acute kidney injury induced by acute worsening cardiac function. Worsening renal function is a strong and independent predictive factor for poor prognosis. Currently, several problems of the type-1 cardiorenal syndrome have not been fully elucidated. The pathogenesis mechanism of renal dysfunction is unclear. Besides, the diagnostic efficiency, sensitivity, and specificity of the existing biomarkers are doubtful. Furthermore, the renal safety of the therapeutic strategies for acute heart failure (AHF) is still ambiguous. Based on these issues, we systematically summarized and depicted the research actualities and predicaments of the pathogenesis, diagnostic markers, and therapeutic strategies of worsening renal function in type-1 cardiorenal syndrome.

Effects of renal function on the urinary excretion and serum concentration of uric acid in patients with chronic kidney disease treated with febuxostat

BACKGROUND

Febuxostat is recommended for patients with chronic kidney disease (CKD) associated with hyperuricemia to lower the serum uric acid (sUA) concentration. However, it remains uncertain how this drug affects correlations between several laboratory parameters regarding glomerular filtration and renal tubular reabsorption of uric acid.

METHODS

We enrolled 148 patients with CKD with hyperuricemia. Of them, 122 were treated with febuxostat, and 26 were treated without it. Clinical and laboratory parameters were recorded to calculate the estimated glomerular filtration rate (eGFR), fractional excretion of uric acid (FEUA), and the estimated 24-h urinary excretion of uric acid (eEUA). We retrospectively examined the correlations between those parameters to compare the patients treated with febuxostat to those without it.

RESULTS

A significant inverse correlation between eGFR and FEUA was demonstrated in both patients treated with febuxostat and those without it. In patients treated with febuxostat, a significant inverse correlation was demonstrated between eGFR and sUA, whereas no significant correlation was demonstrated in those without it. There was a significant positive correlation between FEUA and eEUA in patients treated with febuxostat, whereas no significant correlation was revealed in those without it.

CONCLUSIONS

FEUA increased as eGFR declined in our study population. Febuxostat changed the correlation patterns between the clinical laboratory parameters. An additional administration of uricosuric agents would be helpful for further sUA lowering by increasing both FEUA and eEUA in patients treated with febuxostat.

Glomerular endothelial cell senescence drives age-related kidney disease through PAI-1

The mechanisms underlying the development of glomerular lesions during aging are largely unknown. It has been suggested that senescence might play a role, but the pathophysiological link between senescence and lesion development remains unexplained. Here, we uncovered an unexpected role for glomerular endothelial cells during aging. In fact, we discovered a detrimental cross-talk between senescent endothelial cells and podocytes, through PAI-1. In vivo, selective inactivation of PAI-1 in endothelial cells protected glomeruli from lesion development and podocyte loss in aged mice. In vitro, blocking PAI-1 in supernatants from senescent endothelial cells prevented podocyte apoptosis. Consistently, depletion of senescent cells prevented podocyte loss in old p16 INK-ATTAC transgenic mice. Importantly, these experimental findings are relevant to humans. We showed that glomerular PAI-1 expression was predictive of poor outcomes in transplanted kidneys from elderly donors. In addition, we observed that in elderly patients, urinary PAI-1 was associated with age-related chronic kidney disease. Altogether, these results uncover a novel mechanism of kidney disease and identify PAI-1 as a promising biomarker of kidney dysfunction in allografts from elderly donors.

Expanded Haemodialysis as a Current Strategy to Remove Uremic Toxins

Chronic kidney disease (CKD) is characterized by the retention of solutes named uremic toxins, which strongly associate with high morbidity and mortality. Mounting evidence suggests that targeting uremic toxins and/or their pathways may decrease the risk of cardiovascular disease in CKD patients. Dialysis therapies have been developed to improve removal of uremic toxins. Advances in our understanding of uremic retention solutes as well as improvements in dialysis membranes and techniques (HDx, Expanded Hemodialysis) will offer the opportunity to ameliorate clinical symptoms and outcomes, facilitate personalized and targeted dialysis treatment, and improve quality of life, morbidity and mortality.

Serum fibroblast growth factor 23 for early detection of acute kidney injury in critical illness

BACKGROUND

Serum fibroblast growth factor 23 (FGF23) is associated with acute kidney injury (AKI) and mortality in patients with critical illnesses. However, the accurate predictive performance of FGF23 on AKI remains inconclusive.

METHODS

Meta-analysis was performed using data sources including PubMed, Web of Science, EMBASE, and Cochrane (until June 1, 2021). Cohort or observational studies including patients with AKI and serum FGF23 level as the index test were included. The primary outcome was the AKI detective accuracy. This study has been registered in PROSPERO (CRD42021249930).

RESULTS

Eleven studies with 1946 patients in seven countries were included. Across all settings, the sensitivity and specificity for serum FGF23 levels to predict AKI were 82% (95% CI, 66-91%) and 77% (95% CI, 67-85%), respectively. The diagnostic odds ratio of FGF23 was 15.51 (95% CI, 4.89-49.19), with the pooled positive likelihood ratio of 3.62 (95% CI, 2.25-5.83) and a negative likelihood ratio of 0.23 (95% CI, 0.11-0.50). The area under the receiver operating characteristic curve to detect AKI was 0.86 (95% CI, 0.82-0.88). C-terminal FGF23 had a better performance than intact FGF23.

CONCLUSIONS

Plasma FGF23 is a valuable biomarker for incident AKI in critically ill patients. Comparisons of FGF23 with other biomarkers in AKI still need more studies to prove.