Novel Urinary Biomarkers For Improved Prediction Of Progressive Egfr Loss In Early Chronic Kidney Disease Stages And In High Risk Individuals Without Chronic Kidney Disease

Assessment and Risk Prediction of Chronic Kidney Disease and Kidney Fibrosis Using Non-Invasive Biomarkers

Effective management of chronic kidney disease (CKD), a major health problem worldwide, requires accurate and timely diagnosis, prognosis of progression, assessment of therapeutic efficacy, and, ideally, prediction of drug response. Multiple biomarkers and algorithms for evaluating specific aspects of CKD have been proposed in the literature, many of which are based on a small number of samples. Based on the evidence presented in relevant studies, a comprehensive overview of the different biomarkers applicable for clinical implementation is lacking. This review aims to compile information on the non-invasive diagnostic, prognostic, and predictive biomarkers currently available for the management of CKD and provide guidance on the application of these biomarkers. We specifically focus on biomarkers that have demonstrated added value in prospective studies or those based on prospectively collected samples including at least 100 subjects. Published data demonstrate that several valid non-invasive biomarkers of potential value in the management of CKD are currently available.

Recent progress in mass spectrometry-based urinary proteomics

Serum or plasma is frequently utilized in biomedical research; however, its application is impeded by the requirement for invasive sample collection. The non-invasive nature of urine collection makes it an attractive alternative for disease characterization and biomarker discovery. Mass spectrometry-based protein profiling of urine has led to the discovery of several disease-associated biomarkers. Proteomic analysis of urine has not only been applied to disorders of the kidney and urinary bladder but also to conditions affecting distant organs because proteins excreted in the urine originate from multiple organs. This review provides a progress update on urinary proteomics carried out over the past decade. Studies summarized in this review have expanded the catalog of proteins detected in the urine in a variety of clinical conditions. The wide range of applications of urine analysis-from characterizing diseases to discovering predictive, diagnostic and prognostic markers-continues to drive investigations of the urinary proteome.

Urine MMP7 as a kidney injury biomarker

Matrix metalloproteinase 7 (MMP-7) is a secreted endopeptidase involved in the degradation of extracellular matrix components and the activation of cytokines and growth factors. The regulation of MMP-7 can be transcriptionally regulated by AP-1 or Wnt/β-catenin or post-translationally by proteolytic activation. MMP-7 expression is low or absent in the healthy kidney, but is significantly upregulated in kidney injury, including AKI and CKD. The function of MMP-7 in kidney disease may differ for CKD and AKI; it may have a profibrotic role in CKD and an anti-apoptotic and regenerative function in AKI. Additionally, the potential of MMP-7 as a biomarker has been studied in different kidney diseases, and the results are promising. Recently, combined unbiased kidney proteomics and transcriptomics approaches identified kidney MMP-7 as the protein having the strongest association with both fibrosis and eGFR and confirmed the predictive role of plasma MMP-7 levels for kidney function decline in over 11 000 individuals. Additionally, urinary MMP-7, combined with urinary cystatin C (CysC) and retinol binding protein (RBP) was reported to provide information on tubular injury in focal segmental glomerulosclerosis and minimal change disease. We now present an overview of research on MMP-7 expression and function in kidney diseases and discuss its potential as a biomarker of kidney diseases.

Dynamics of urine proteomics biomarker and disease progression in patients with IgA nephropathy

BACKGROUND

Immunoglobulin A nephropathy (IgAN) frequently leads to kidney failure. The urinary proteomics-based classifier IgAN237 may predict disease progression at the time of kidney biopsy. We studied whether IgAN237 also predicts progression later in the course of IgAN.

METHODS

Urine from patients with biopsy-proven IgAN was analyzed using capillary electrophoresis-mass spectrometry at baseline (IgAN237-1, n = 103) and at follow-up (IgAN237-2, n = 89). Patients were categorized as "non-progressors" (IgAN237 ≤0.38) and "progressors" (IgAN237 >0.38). Estimated glomerular filtration rate (eGFR) and urinary albumin-creatinine ratio slopes were calculated.

RESULTS

Median age at biopsy was 44 years, interval between biopsy and IgAN237-1 was 65 months and interval between IgAN237-1 and IgAN237-2 was 258 days (interquartile range 71-531). IgAN237-1 and IgAN237-2 values did not differ significantly and were correlated (rho = 0.44, P < .001). Twenty-eight percent and 26% of patients were progressors based on IgAN237-1 and IgAN237-2, respectively. IgAN237 inversely correlated with chronic eGFR slopes (rho = -0.278, P = .02 for score-1; rho = -0.409, P = .002 for score-2) and with ±180 days eGFR slopes (rho = -0.31, P = .009 and rho = -0.439, P = .001, respectively). The ±180 days eGFR slopes were worse for progressors than for non-progressors (median -5.98 versus -1.22 mL/min/1.73 m2 per year for IgAN237-1, P < .001; -3.02 vs 1.08 mL/min/1.73 m2 per year for IgAN237-2, P = .0047). In multiple regression analysis baseline progressor/non-progressor according to IgAN237 was an independent predictor of eGFR180days-slope (P = .001).

CONCLUSION

The urinary IgAN237 classifier represents a risk stratification tool in IgAN also later in the course of the dynamic disease. It may guide patient management in an individualized manner.

A set of urinary peptides can predict early renal damage in primary hypertension

OBJECTIVES

Renal diseases caused by primary hypertension (HTN) are often asymptomatic without sensitive markers for early diagnosis and prediction, easily progressing to severe and irreversible renal damage in patients with clinical manifestations. This study explored whether a set of urinary peptides could serve as a potential biomarker for early prediction of renal damage in HTN.

METHODS

Urinary peptides level of healthy individuals, HTN + normoalbuminuric and HTN + albuminuria patients were compared, and 22 baseline data including sex, age, renal function, hypertensive fundus lesions were collected. Patients diagnosed with HTN, albuminuria, and normal renal function were followed up. According to the follow-up results, the cut-off value of a set of urinary peptides in predicting hypertensive renal injury was calculated and analyzed in the high-risk and low-risk groups of HTN patients for its performance in detecting early hypertensive renal injury.

RESULTS

Among a sum of 319 participants, average urinary peptides level was significantly higher in patients with HTN than in normal individuals. A total of 147 HTN patients with normal albuminuria were followed up for a mean of 3.8 years. Thirty-five patients showed urinary albumin-to-creatinine ratio (uACR) at least 30 mg/g for three consecutive times. The receiver-operating characteristic (ROC) curve showed that the urinary peptides cut-off value for evaluating new-onset proteinuria in patients with HTN was 0.097. Based on this cut-off value, 39 and 108 patients were included in the high-risk and low-risk groups, respectively. Specifically, compared with patients in the low-risk group, those in the high-risk group showed significantly longer duration of HTN, higher proportions of hypertensive fundus lesions and at least 30 mg/g uACR, and higher levels of homocysteine (Hcy), cystatin C (CysC), beta-2 microglobulin (β2-MG), and uACR. 76.9% of high-risk patients had significantly higher new-onset proteinuria than the low-risk group. Correlation analysis demonstrated a positive correlation between urinary peptides and UACR ( r  = 0.494, P  < 0.001). The incidence of new-onset albuminuria was significantly higher in the high-risk group than in the low-risk group, as shown by Cox regression analysis. The areas under the curve of urinary peptides, Hcy, β2-MG and CysC were 0.925, 0.753, 0.796 and 0.769, respectively.

CONCLUSION

A set of urinary peptides is a predictor of new-onset proteinuria in patients with HTN, therefore, it can be used for diagnosing patients with early renal injury in patients with HTN, contributing to early prevention and treatment of hypertensive nephropathy.

A classifier based on 273 urinary peptides predicts early renal damage in primary hypertension

OBJECTIVES

Renal diseases caused by primary hypertension (HTN) are often asymptomatic without sensitive markers for early diagnosis and prediction, easily progressing to severe and irreversible renal damage in patients with clinical manifestations. This study explored whether a classifier developed based on 273 urinary peptides (CKD273) could serve as a potential biomarker for early prediction of renal damage in HTN.

METHODS

Urinary CKD273 level of healthy individuals, HTN + normoalbuminuric and HTN + albuminuria patients were compared, and 22 baseline data including sex, age, renal function, and hypertensive fundus lesions were collected. Patients diagnosed with HTN, albuminuria, and normal renal function were followed up. According to the follow-up results, the cut-off value of CKD273 in predicting hypertensive renal injury was calculated and analyzed in the high-risk and low-risk groups of HTN patients for its performance in detecting early hypertensive renal injury.

RESULTS

Among a sum of 319 participants, average urinary CKD273 level was significantly higher in patients with HTN than in normal individuals. A total of 147 HTN patients with normal albuminuria were followed up for a mean of 3.8 years. Thirty-five patients showed urinary albumin-to-creatinine ratio (uACR) at least 30 mg/g for three consecutive times. The receiver-operating characteristic (ROC) curve showed that the urinary CKD273 cut-off value for evaluating new-onset proteinuria in patients with HTN was 0.097. Based on this cut-off value, 39 and 108 patients were included in the high-risk and low-risk groups, respectively. Specifically, compared with patients in the low-risk group, those in the high-risk group showed significantly longer duration of HTN, higher proportions of hypertensive fundus lesions and at least 30 mg/g uACR, and higher levels of homocysteine (Hcy), cystatin C (CysC), beta-2 microglobulin (β2-MG), and uACR. 76.9% of high-risk patients had significantly higher new-onset proteinuria than the low-risk group. Correlation analysis demonstrated a positive correlation between urinary CKD273 and UACR ( r  = 0.494, P  = 0.000). The incidence of new-onset albuminuria was significantly higher in the high-risk group than in the low-risk group, as shown by Cox regression analysis. The areas under the curve of CKD273, Hcy, β2-MG, and CysC were 0.925, 0.753, 0.796, and 0.769, respectively.

CONCLUSION

Urinary CKD273 is a predictor of new-onset proteinuria in patients with HTN, therefore, it can be used for diagnosing patients with early renal injury in patients with HTN, contributing to early prevention and treatment of hypertensive nephropathy.

Recent Advances in Urinary Peptide and Proteomic Biomarkers in Chronic Kidney Disease: A Systematic Review

Biomarker development, improvement, and clinical implementation in the context of kidney disease have been a central focus of biomedical research for decades. To this point, only serum creatinine and urinary albumin excretion are well-accepted biomarkers in kidney disease. With their known blind spot in the early stages of kidney impairment and their diagnostic limitations, there is a need for better and more specific biomarkers. With the rise in large-scale analyses of the thousands of peptides in serum or urine samples using mass spectrometry techniques, hopes for biomarker development are high. Advances in proteomic research have led to the discovery of an increasing amount of potential proteomic biomarkers and the identification of candidate biomarkers for clinical implementation in the context of kidney disease management. In this review that strictly follows the PRISMA guidelines, we focus on urinary peptide and especially peptidomic biomarkers emerging from recent research and underline the role of those with the highest potential for clinical implementation. The Web of Science database (all databases) was searched on 17 October 2022, using the search terms "marker *" OR biomarker * AND "renal disease" OR "kidney disease" AND "proteome *" OR "peptid *" AND "urin *". English, full-text, original articles on humans published within the last 5 years were included, which had been cited at least five times per year. Studies based on animal models, renal transplant studies, metabolite studies, studies on miRNA, and studies on exosomal vesicles were excluded, focusing on urinary peptide biomarkers. The described search led to the identification of 3668 articles and the application of inclusion and exclusion criteria, as well as abstract and consecutive full-text analyses of three independent authors to reach a final number of 62 studies for this manuscript. The 62 manuscripts encompassed eight established single peptide biomarkers and several proteomic classifiers, including CKD273 and IgAN237. This review provides a summary of the recent evidence on single peptide urinary biomarkers in CKD, while emphasizing the increasing role of proteomic biomarker research with new research on established and new proteomic biomarkers. Lessons learned from the last 5 years in this review might encourage future studies, hopefully resulting in the routine clinical applicability of new biomarkers.

Progression of chronic kidney disease among black patients attending a tertiary hospital in Johannesburg, South Africa

BACKGROUND

Chronic kidney disease (CKD) is a major public health issue worldwide and is an important contributor to the overall non-communicable disease burden. Chronic kidney disease is usually asymptomatic, and insidiously and silently progresses to advanced stages in resource limited settings.

METHODOLOGY

A prospective longitudinal study was carried out on black patients with CKD attending the kidney outpatient clinic at Charlotte Maxeke Johannesburg Academic Hospital (CMJAH) in South Africa, between September 2019 to March 2022. Demographic and clinical data were extracted from the ongoing continuous clinic records, as well as measurements of vital signs and interviews at baseline and at follow up. Patients provided urine and blood samples for laboratory investigations as standard of care at study entry (0) and at 24 months, and were followed up prospectively for two (2) years. Data were descriptively and inferentially entered into REDcap and analysed using STATA version 17, and multivariable logistic regression analysis was used to identify predictors of CKD progression.

RESULTS

A total of 312 patients were enrolled into the study, 297 (95.2%) patients completed the study, 10 (3.2%) patients were lost to follow and 5 (1.6%) patients died during the study period. The prevalence of CKD progression was 49.5%, while that of CKD remission was 33% and CKD regression was 17.5%. For patients with CKD progression the median age at baseline was 58 (46-67) years, the median eGFR was 37 (32-51) mL/min/1.73 m2, median urine protein creatinine ratio (uPCR) was 0.038 (0.016-0.82) g/mmol and the median haemoglobin (Hb) was 13.1 (11.7-14.4) g/dl; 95.2% had hypertension, 40.1% patients had diabetes mellitus and 39.5% had both hypertension and diabetes mellitus. Almost half (48.3%) of patients with CKD progression had severely increased proteinuria and 45.6% had anaemia. Variables associated with higher odds for CKD progression after multivariable logistic regression analysis were severely increased proteinuria (OR 32.3, 95% CI 2.8-368.6, P = 0.005), moderately increased proteinuria (OR 23.3, 95% CI 2.6-230.1, P = 0.007), hypocalcaemia (OR 3.8, 95% CI 1.0-14.8, P = 0.047), hyponatraemia (OR 4.5, 95% CI 0.8-23.6, P = 0.042), anaemia (OR 2.1, 95% CI 1.0-4.3, P = 0.048), diabetes mellitus (OR 1.8, 95% CI 0.9-3.6, P = 0.047), elevated HbA1c (OR 1.8, 95% CI 1.2-2.8, P = 0.007) and current smoking (OR 2.8, 95% CI 0.9-8.6, P = 0.049).

CONCLUSION

Our study identified a higher prevalence of CKD progression in a prospective longitudinal study of black patients with CKD compared with literature reports. CKD Progression was associated with proteinuria, diabetes mellitus, elevated HbA1c, anaemia, hypocalcaemia, hyponatraemia and current smoking in a cohort of black patients with CKD who had controlled hypertension and diabetes mellitus at baseline.

Clinical Risk Factors For Kidney Tubule Biomarker Abnormalities Among Hypertensive Adults With Reduced eGFR in the SPRINT Trial

BACKGROUND

Urine biomarkers of kidney tubule health may distinguish aspects of kidney damage that cannot be captured by current glomerular measures. Associations of clinical risk factors with specific kidney tubule biomarkers have not been evaluated in detail.

METHODS

We performed a cross-sectional study in the Systolic Blood Pressure Intervention Trial among 2,436 participants with a baseline estimated glomerular filtration rate (eGFR) <60 ml/min/1.73 m2. Associations between demographic and clinical characteristics with urine biomarkers of kidney tubule health were evaluated using simultaneous multivariable linear regression of selected variables.

RESULTS

Each standard deviation higher age (9 years) was associated with 13% higher levels of chitinase-3-like protein-1 (YKL-40), indicating higher levels of tubulointerstitial inflammation and repair. Men had 31% higher levels of alpha-1 microglobulin and 16% higher levels of beta-2 microglobulin, reflecting worse tubule resorptive function. Black race was associated with significantly higher levels of neutrophil gelatinase-associated lipocalin (12%) and lower kidney injury molecule-1 (26%) and uromodulin (22%). Each standard deviation (SD) higher systolic blood pressure (SBP) (16 mmHg) was associated with 10% higher beta-2 microglobulin and 10% higher alpha-1 microglobulin, reflecting lower tubule resorptive function.

CONCLUSIONS

Clinical and demographic characteristics, such as race, sex, and elevated SBP, are associated with unique profiles of tubular damage, which could reflect under-recognized patterns of kidney tubule disease among persons with decreased eGFR.

Prevention of cardiorenal damage: importance of albuminuria

Chronic kidney disease (CKD) is projected to become a leading global cause of death by 2040, and its early detection is critical for effective and timely management. The current definition of CKD identifies only advanced stages, when kidney injury has already destroyed &gt;50% of functioning kidney mass as reflected by an estimated glomerular filtration rate &lt;60 mL/min/1.73 m2 or a urinary albumin/creatinine ratio &gt;six-fold higher than physiological levels (i.e. &gt; 30 mg/g). An elevated urinary albumin-excretion rate is a known early predictor of future cardiovascular events. There is thus a ‘blind spot’ in the detection of CKD, when kidney injury is present but is undetectable by current diagnostic criteria, and no intervention is made before renal and cardiovascular damage occurs. The present review discusses the CKD ‘blind spot’ concept and how it may facilitate a holistic approach to CKD and cardiovascular disease prevention and implement the call for albuminuria screening implicit in current guidelines. Cardiorenal risk associated with albuminuria in the high-normal range, novel genetic and biochemical markers of elevated cardiorenal risk, and the role of heart and kidney protective drugs evaluated in recent clinical trials are also discussed. As albuminuria is a major risk factor for cardiovascular and renal disease, starting from levels not yet considered in the definition of CKD, the implementation of opportunistic or systematic albuminuria screening and therapy, possibly complemented with novel early biomarkers, has the potential to improve cardiorenal outcomes and mitigate the dismal 2040 projections for CKD and related cardiovascular burden.

A universal predictive and mechanistic urinary peptide signature in acute kidney injury

BACKGROUND

The delayed diagnosis of acute kidney injury (AKI) episodes and the lack of specificity of current single AKI biomarkers hamper its management. Urinary peptidome analysis may help to identify early molecular changes in AKI and grasp its complexity to identify potential targetable molecular pathways.

METHODS

In derivation and validation cohorts totalizing 1170 major cardiac bypass surgery patients and in an external cohort of 1569 intensive care unit (ICU) patients, a peptide-based score predictive of AKI (7-day KDIGO classification) was developed, validated, and compared to the reference biomarker urinary NGAL and NephroCheck and clinical scores.

RESULTS

A set of 204 urinary peptides derived from 48 proteins related to hemolysis, inflammation, immune cells trafficking, innate immunity, and cell growth and survival was identified and validated for the early discrimination (&lt; 4 h) of patients according to their risk to develop AKI (OR 6.13 [3.96-9.59], p &lt; 0.001) outperforming reference biomarkers (urinary NGAL and [IGFBP7].[TIMP2] product) and clinical scores. In an external cohort of 1569 ICU patients, performances of the signature were similar (OR 5.92 [4.73-7.45], p &lt; 0.001), and it was also associated with the in-hospital mortality (OR 2.62 [2.05-3.38], p &lt; 0.001).

CONCLUSIONS

An overarching AKI physiopathology-driven urinary peptide signature shows significant promise for identifying, at an early stage, patients who will progress to AKI and thus to develop tailored treatments for this frequent and life-threatening condition. Performance of the urine peptide signature is as high as or higher than that of single biomarkers but adds mechanistic information that may help to discriminate sub-phenotypes of AKI offering new therapeutic avenues.

Urinary Protein Profiling for Potential Biomarkers of Chronic Kidney Disease: A Pilot Study

Proteinuria is a risk factor for chronic kidney disease (CKD) progression and associated complications. However, there is insufficient information on individual protein components in urine and the severity of CKD. We aimed to investigate urinary proteomics and its association with proteinuria and kidney function in early-stage CKD and in healthy individuals. A 24 h urine sample of 42 individuals (21-CKD and 21-healthy individuals) was used for mass spectrometry-based proteomics analysis. An exponentially modified protein abundance index (emPAI) was calculated for each protein. Data were analyzed by Mascot software using the SwissProt database and bioinformatics tools. Overall, 298 unique proteins were identified in the cohort; of them, 250 proteins belong to the control group with median (IQR) emPAI 39.1 (19−53) and 142 proteins belong to the CKD group with median (IQR) emPAI 67.8 (49−117). The level of 24 h proteinuria positively correlated with emPAI (r = 0.390, p = 0.011). The emPAI of some urinary proteomics had close positive (ALBU, ZA2G, IGKC) and negative (OSTP, CD59, UROM, KNG1, RNAS1, CD44, AMBP) correlations (r < 0.419, p < 0.001) with 24 h proteinuria levels. Additionally, a few proteins (VTDB, AACT, A1AG2, VTNC, and CD44) significantly correlated with kidney function. In this proteomics study, several urinary proteins correlated with proteinuria and kidney function. Pathway analysis identified subpathways potentially related to early proteinuric CKD, allowing the design of prospective studies that explore their response to therapy and their relationship to long-term outcomes.

Benchmarking CKD: incidence of CKD in a European country with low prevalence of chronic kidney disease and of kidney replacement therapy

Iceland was one of six European countries with an adjusted incidence of kidney replacement therapy (KRT) in 2018 lower than 100 per million persons (pmp), along with Estonia, Montenegro, Russia, Serbia and Finland. It was also one of 10 countries with an adjusted KRT prevalence <900 pmp. Furthermore, the prevalence of chronic kidney disease (CKD) in Iceland is up to 2.44-fold lower and the death rate from CKD up to 3.44-fold lower than in other countries with a low incidence of KRT, suggesting that the low KRT incidence actually reflects a low need for KRT rather than low uptake or availability of KRT. This identifies Iceland as a benchmark for countries trying to reduce KRT incidence. Iceland also represents one of the best genetically characterized populations in the world, facilitating studies on the influence of the genetic background versus environment and lifestyle on CKD. This issue of CKJ reports the incidence and risk factors for CKD in Icelandic adults. Diabetes, acute kidney injury, hypertension, cardiovascular disease, chronic lung disease, malignancy and major psychiatric illness were associated with an increased risk of incident CKD, as were obesity and sleep apnea in women. However, in 75% of incident CKD cases, CKD was first detected in category G3 or higher, emphasizing the need for new tools that allow an earlier diagnosis of CKD that precedes the loss of >50% of the functioning kidney mass and/or wider use of albuminuria as a screening tool. The European Society of Cardiology just recommended assessing albuminuria for routine cardiovascular risk workups for all.

Urine peptidome in combination with transcriptomics analysis highlights MMP7, MMP14 and PCSK5 for further investigation in chronic kidney disease

Chronic kidney disease (CKD) is characterized by the loss of kidney function. The molecular mechanisms underlying the development and progression of CKD are still not fully understood. Among others, the urinary peptidome has been extensively studied, with several urinary peptides effectively detecting disease progression. However, their link to proteolytic events has not been made yet. This study aimed to predict the proteases involved in the generation of CKD-associated urinary excreted peptides in a well-matched (for age, sex, lack of heart disease) case-control study. The urinary peptide profiles from CKD (n = 241) and controls (n = 240) were compared and statistically analyzed. The in-silico analysis of the involved proteases was performed using Proteasix and proteases activity was predicted based on the abundance changes of the associated peptides. Predictions were cross-correlated to transcriptomics datasets by using the Nephroseq database. Information on the respective protease inhibitors was also retrieved from the MEROPS database. Totally, 303 urinary peptides were significantly associated with CKD. Among the most frequently observed were fragments of collagen types I, II and III, uromodulin, albumin and beta-2-microglobulin. Proteasix predicted 16 proteases involved in their generation. Through investigating CKD-associated transcriptomics datasets, several proteases are highlighted including members of matrix metalloproteinases (MMP7, MMP14) and serine proteases (PCSK5); laying the foundation for further studies towards elucidating their role in CKD pathophysiology.

Urinary levels of pro-fibrotic transglutaminase 2 (TG2) may help predict progression of chronic kidney disease

Renal clinical chemistry only detects kidney dysfunction after considerable damage has occurred and is imperfect in predicting long term outcomes. Consequently, more sensitive markers of early damage and better predictors of progression are being urgently sought, to better support clinical decisions and support shorter clinical trials. Transglutaminase 2 (TG2) is strongly implicated in the fibrotic remodeling that drives chronic kidney disease (CKD). We hypothesized that urinary TG2 and its ε-(γ-glutamyl)-lysine crosslink product could be useful biomarkers of kidney fibrosis and progression. Animal models: a rat 4-month 5/6th subtotal nephrectomy model of CKD and a rat 8-month streptozotocin model of diabetic kidney disease had 24-hour collection of urine, made using a metabolic cage, at regular periods throughout disease development. Patients: Urine samples from patients with CKD (n = 290) and healthy volunteers (n = 33) were collected prospectively, and progression tracked for 3 years. An estimated glomerular filtration rate (eGFR) loss of 2-5 mL/min/year was considered progressive, with rapid progression defined as > 5 mL/min/year. Assays: TG2 was measured in human and rat urine samples by enzyme-linked immunosorbent assay (ELISA) and ε-(γ-glutamyl)-lysine by exhaustive proteolytic digestion and amino acid analysis. Urinary TG2 and ε-(γ-glutamyl)-lysine increased with the development of fibrosis in both animal model systems. Urinary TG2 was 41-fold higher in patients with CKD than HVs, with levels elevated 17-fold by CKD stage 2. The urinary TG2:creatinine ratio (UTCR) was 9 ng/mmol in HV compared with 114 ng/mmol in non-progressive CKD, 1244 ng/mmol in progressive CKD and 1898 ng/mmol in rapidly progressive CKD. Both urinary TG2 and ε-(γ-glutamyl)-lysine were significantly associated with speed of progression in univariate logistic regression models. In a multivariate model adjusted for urinary TG2, ε-(γ-glutamyl)-lysine, age, sex, urinary albumin:creatinine ratio (UACR), urinary protein:creatinine ratio (UPCR), and CKD stage, only TG2 remained statistically significant. Receiver operating characteristic (ROC) curve analysis determined an 86.4% accuracy of prediction of progression for UTCR compared with 73.5% for UACR. Urinary TG2 and ε-(γ-glutamyl)-lysine are increased in CKD. In this pilot investigation, UTCR was a better predictor of progression in patients with CKD than UACR. Larger studies are now warranted to fully evaluate UTCR value in predicting patient outcomes.

Evidence of chronic kidney injury in patients not meeting KDIGO criteria for CKD

Subjects not meeting KDIGO criteria for chronic kidney disease (CKD), i.e. normoalbuminuric (urinary albumin:creatinine ratio, UACR <30 mg/g) individuals with an estimated glomerular filtration rate >60 mL/min/1.73 m², are considered at no increased cardiovascular or kidney risk associated with kidney disease, but the incidence of subclinical atherosclerosis, cardiovascular events and CKD progression is already increased in the high-normal UACR range (10–30 mg/g). Earlier intervention in this subclinical pre-CKD stage may diminish cardiorenal risk. However, tools to predict albuminuria development and to identify those subjects who will benefit most from intervention are limited. Recent data have identified urine molecular changes within the normoalbuminuria condition, consisting of an altered urinary peptidome, proteome and metabolome, which represent subclinical organ damage and processes such as inflammation, oxidative stress, tricarboxylic acids cycle deregulation, impaired fatty acids β-oxidation or defective tubular reabsorption.

CKD: The burden of disease invisible to research funders

The uptake of the current concept of chronic kidney disease (CKD) by the public, physicians and health authorities is low. Physicians still mix up CKD with chronic kidney insufficiency or failure. In a recent manuscript, only 23% of participants in a cohort of persons with CKD had been diagnosed by their physicians as having CKD while 29% has a diagnosis of cancer and 82% had a diagnosis of hypertension. For the wider public and health authorities, CKD evokes kidney replacement therapy (KRT). In Spain, the prevalence of KRT is 0.13%. A prevalent view is that for those in whom kidneys fail, the problem is "solved" by dialysis or kidney transplantation. However, the main burden of CKD is accelerated aging and all-cause and cardiovascular premature death. CKD is the most prevalent risk factor for lethal COVID-19 and the factor that most increases the risk of death in COVID-19, after old age. Moreover, men and women undergoing KRT still have an annual mortality which is 10-100-fold higher than similar age peers, and life expectancy is shortened by around 40 years for young persons on dialysis and by 15 years for young persons with a functioning kidney graft. CKD is expected to become the fifth global cause of death by 2040 and the second cause of death in Spain before the end of the century, a time when 1 in 4 Spaniards will have CKD. However, by 2022, CKD will become the only top-15 global predicted cause of death that is not supported by a dedicated well-funded CIBER network research structure in Spain. Leading Spanish kidney researchers grouped in the kidney collaborative research network REDINREN have now applied for the RICORS call of collaborative research in Spain with the support of the Spanish Society of Nephrology, ALCER and ONT: RICORS2040 aims to prevent the dire predictions for the global 2040 burden of CKD from becoming true. However, only the highest level of research funding through the CIBER will allow to adequately address the issue before it is too late.

CKD: The burden of disease invisible to research funders

The uptake of the current concept of chronic kidney disease (CKD) by the public, physicians and health authorities is low. Physicians still mix up CKD with chronic kidney insufficiency or failure. In a recent manuscript, only 23% of participants in a cohort of persons with CKD had been diagnosed by their physicians as having CKD while 29% has a diagnosis of cancer and 82% had a diagnosis of hypertension. For the wider public and health authorities, CKD evokes kidney replacement therapy (KRT). In Spain, the prevalence of KRT is 0.13%. A prevalent view is that for those in whom kidneys fail, the problem is “solved” by dialysis or kidney transplantation. However, the main burden of CKD is accelerated aging and all-cause and cardiovascular premature death. CKD is the most prevalent risk factor for lethal COVID-19 and the factor that most increases the risk of death in COVID-19, after old age. Moreover, men and women undergoing KRT still have an annual mortality which is 10–100-fold higher than similar age peers, and life expectancy is shortened by around 40 years for young persons on dialysis and by 15 years for young persons with a functioning kidney graft. CKD is expected to become the fifth global cause of death by 2040 and the second cause of death in Spain before the end of the century, a time when 1 in 4 Spaniards will have CKD. However, by 2022, CKD will become the only top-15 global predicted cause of death that is not supported by a dedicated well-funded CIBER network research structure in Spain. Leading Spanish kidney researchers grouped in the kidney collaborative research network REDINREN have now applied for the RICORS call of collaborative research in Spain with the support of the Spanish Society of Nephrology, ALCER and ONT: RICORS2040 aims to prevent the dire predictions for the global 2040 burden of CKD from becoming true. However, only the highest level of research funding through the CIBER will allow to adequately address the issue before it is too late.

Peptidomics and Capillary Electrophoresis

Peptides play a crucial role in many vitally important functions of living organisms. The goal of peptidomics is the identification of the "peptidome," the whole peptide content of a cell, organ, tissue, body fluid, or organism. In peptidomic or proteomic studies, capillary electrophoresis (CE) is an alternative technique for liquid chromatography. It is a highly efficient and fast separation method requiring extremely low amounts of sample. In peptidomic approaches, CE is commonly combined with mass spectrometric (MS) detection. Most often, CE is coupled with electrospray ionization MS and less frequently with matrix-assisted laser desorption/ionization MS. CE-MS has been employed in numerous studies dealing with determination of peptide biomarkers in different body fluids for various diseases, or in food peptidomic research for the analysis and identification of peptides with special biological activities. In addition to the above topics, sample preparation techniques commonly applied in peptidomics before CE separation and possibilities for peptide identification and quantification by CE-MS or CE-MS/MS methods are discussed in this chapter.

Associations between urinary cysteine-rich protein 61 excretion and kidney function decline in outpatients with chronic kidney disease: a prospective cohort study in Taiwan

OBJECTIVES

To examine whether urinary excretion of cysteine-rich protein 61 (Cyr61), an acknowledged proinflammatory factor in kidney pathologies, increases in chronic kidney disease (CKD) and is associated with subsequent rapid kidney function decline.

DESIGN

An observational cohort study.

SETTING

In the nephrology outpatient clinics of a tertiary hospital in Taiwan.

PARTICIPANTS

We enrolled 138 adult CKD outpatients (n=12, 32, 18, 18, 29 and 29 in stages 1, 2, 3a, 3b, 4 and 5 CKD, respectively) between February and October 2014 and followed them for 1 year. Their mean age was 60.46±13.16 years, and 51 (37%) of them were women.

PRIMARY OUTCOME MEASURES

Urinary Cyr61 levels were measured by ELISA. Rapid kidney function decline was defined as an estimated glomerular filtration rate (eGFR) decline rate ≥ 4 mL/min/1.73 m²/year or developing end-stage renal disease during subsequent 3-month or 1-year follow-up period. Models were adjusted for demographic and clinical variables.

RESULTS

The urine Cyr61-to-creatinine ratio (UCyr61CR) increased significantly in patients with stage 4 or 5 CKD. Multivariable linear regression analysis showed that log(UCyr61CR) was positively correlated with log(urine protein-to-creatinine ratio) (p<0.001) but negatively correlated with baseline eGFR (p<0.001) and hypertension (p=0.007). Complete serum creatinine data during the follow-up were available for 112 patients (81.2%). Among them, multivariable logistic regression identified log(UCyr61CR) was independently associated with rapid kidney function decline (adjusted OR 2.29, 95% CI 1.27 to 4.15) during the subsequent 3 months. UCyr61CR improved the discriminative performance of clinical models to predict 3-month rapid kidney function decline. In contrast, log(UCyr61CR) was not associated with rapid eGFR decline during the entire 1-year follow-up.

CONCLUSIONS

Elevated urinary Cyr61 excretion is associated with rapid short-term kidney function deterioration in patients with CKD. Measuring urinary Cyr61 excretion is clinically valuable for monitoring disease trajectory and may guide treatment planning.

RICORS2040: the need for collaborative research in chronic kidney disease

Chronic kidney disease (CKD) is a silent and poorly known killer. The current concept of CKD is relatively young and uptake by the public, physicians and health authorities is not widespread. Physicians still confuse CKD with chronic kidney insufficiency or failure. For the wider public and health authorities, CKD evokes kidney replacement therapy (KRT). In Spain, the prevalence of KRT is 0.13%. Thus health authorities may consider CKD a non-issue: very few persons eventually need KRT and, for those in whom kidneys fail, the problem is ‘solved’ by dialysis or kidney transplantation. However, KRT is the tip of the iceberg in the burden of CKD. The main burden of CKD is accelerated ageing and premature death. The cut-off points for kidney function and kidney damage indexes that define CKD also mark an increased risk for all-cause premature death. CKD is the most prevalent risk factor for lethal coronavirus disease 2019 (COVID-19) and the factor that most increases the risk of death in COVID-19, after old age. Men and women undergoing KRT still have an annual mortality that is 10- to 100-fold higher than similar-age peers, and life expectancy is shortened by ~40 years for young persons on dialysis and by 15 years for young persons with a functioning kidney graft. CKD is expected to become the fifth greatest global cause of death by 2040 and the second greatest cause of death in Spain before the end of the century, a time when one in four Spaniards will have CKD. However, by 2022, CKD will become the only top-15 global predicted cause of death that is not supported by a dedicated well-funded Centres for Biomedical Research (CIBER) network structure in Spain. Realizing the underestimation of the CKD burden of disease by health authorities, the Decade of the Kidney initiative for 2020–2030 was launched by the American Association of Kidney Patients and the European Kidney Health Alliance. Leading Spanish kidney researchers grouped in the kidney collaborative research network Red de Investigación Renal have now applied for the Redes de Investigación Cooperativa Orientadas a Resultados en Salud (RICORS) call for collaborative research in Spain with the support of the Spanish Society of Nephrology, Federación Nacional de Asociaciones para la Lucha Contra las Enfermedades del Riñón and ONT: RICORS2040 aims to prevent the dire predictions for the global 2040 burden of CKD from becoming true.

Current applications of capillary electrophoresis-mass spectrometry for the analysis of biologically important analytes in urine (2017 to mid-2021): A review

Capillary electrophoresis coupled online with mass detection is a modern tool for analyzing wide ranges of compounds in complex samples, including urine. Capillary electrophoresis with mass spectrometry allows the separation and identification of various analytes spanning from small ions to high molecular weight protein complexes. Similarly to the much more common liquid chromatography‐mass spectrometry techniques, the capillary electrophoresis separation reduces the complexity of the mixture of analytes entering the mass spectrometer resulting in reduced ion suppression and a more straightforward interpretation of the mass spectrometry data. This review summarizes capillary electrophoresis with mass spectrometry studies published between the years 2017 and 2021, aiming at the determination of various compounds excreted in urine. The properties of the urine, including its diagnostical and analytical features and chemical composition, are also discussed including general protocols for the urine sample preparation. The mechanism of the electrophoretic separation and the instrumentation for capillary electrophoresis with mass spectrometry coupling is also included. This review shows the potential of the capillary electrophoresis with mass spectrometry technique for the analyses of different kinds of analytes in a complex biological matrix. The discussed applications are divided into two main groups (capillary electrophoresis with mass spectrometry for the determination of drugs and drugs of abuse in urine and capillary electrophoresis with mass spectrometry for the studies of urinary metabolome).

Milestones of Precision Medicine: An Innovative, Multidisciplinary Overview

Although the concept of precision medicine, in which healthcare is tailored to the molecular and clinical characteristics of each individual, is not new, its implementation in clinical practice has been heterogenous. In some medical specialties, precision medicine has gone from being just a promise to a reality that achieves better patient outcomes. This is a fact if we consider, for example, the great advances made in the genetic diagnosis and subsequent treatment of countless hereditary diseases, such as cystic fibrosis, which have improved the life expectancy of many of the affected children. In the field of oncology, the development of targeted therapies has prolonged the survival of patients with breast, lung, colorectal, melanoma, and hematological malignancies. In other disciplines, clinical milestones are perhaps less well known, but no less important. The current challenge is to expand and generalize the use of technologies that are central to precision medicine, such as massively parallel sequencing, to improve the management (prevention and treatment) of complex conditions such as cardiovascular, kidney, or autoimmune diseases. This process requires investment in specialized expertise, multidisciplinary collaboration, and the nationwide organization of genetic laboratories for diagnosis of specific diseases.

Mesenchymal stem cells ameliorate renal fibrosis by galectin-3/Akt/GSK3β/Snail signaling pathway in adenine-induced nephropathy rat

BACKGROUND

Tubulointerstitial fibrosis (TIF) is one of the main pathological features of various progressive renal damages and chronic kidney diseases. Mesenchymal stromal cells (MSCs) have been verified with significant improvement in the therapy of fibrosis diseases, but the mechanism is still unclear. We attempted to explore the new mechanism and therapeutic target of MSCs against renal fibrosis based on renal proteomics.

METHODS

TIF model was induced by adenine gavage. Bone marrow-derived MSCs was injected by tail vein after modeling. Renal function and fibrosis related parameters were assessed by Masson, Sirius red, immunohistochemistry, and western blot. Renal proteomics was analyzed using iTRAQ-based mass spectrometry. Further possible mechanism was explored by transfected galectin-3 gene for knockdown (Gal-3 KD) and overexpression (Gal-3 OE) in HK-2 cells with lentiviral vector.

RESULTS

MSCs treatment clearly decreased the expression of α-SMA, collagen type I, II, III, TGF-β1, Kim-1, p-Smad2/3, IL-6, IL-1β, and TNFα compared with model rats, while p38 MAPK increased. Proteomics showed that only 40 proteins exhibited significant differences (30 upregulated, 10 downregulated) compared MSCs group with the model group. Galectin-3 was downregulated significantly in renal tissues and TGF-β1-induced rat tubular epithelial cells and interstitial fibroblasts, consistent with the iTRAQ results. Gal-3 KD notably inhibited the expression of p-Akt, p-GSK3β and snail in TGF-β1-induced HK-2 cells fibrosis. On the contrary, Gal-3 OE obviously increased the expression of p-Akt, p-GSK3β and snail.

CONCLUSION

The mechanism of MSCs anti-renal fibrosis was probably mediated by galectin-3/Akt/GSK3β/Snail signaling pathway. Galectin-3 may be a valuable target for treating renal fibrosis.

Urinary Growth Differentiation Factor-15 (GDF15) levels as a biomarker of adverse outcomes and biopsy findings in chronic kidney disease

BACKGROUND

Growth Differentiation Factor-15 (GDF15) is a member of the TGF-β superfamily. Increased serum GDF15 has been associated with increased risk of chronic kidney disease (CKD) progression. However, no prior studies have addressed the significance of urinary GDF15 in adult CKD.

METHODS

We measured serum and urinary GDF15 in a prospective cohort of 84 patients who underwent kidney biopsy and assessed their association with outcomes (survival, kidney replacement therapy) during a follow-up of 29 ± 17 months.

RESULTS

There was a statistically significant correlation between serum and urine GDF15 values. However, while serum GDF15 values increased with decreasing glomerular filtration rate, urinary GDF15 did not. Immunohistochemistry located kidney GDF15 expression mainly in tubular cells, and kidney GDF15 staining correlated with urinary GDF15 values. Urine GDF15 was significantly higher in patients with a histologic diagnosis of diabetic nephropathy than in diabetic patients without diabetic nephropathy. This was not the case for serum GDF15. Both serum and urine GDF15 were negatively associated with patient survival in multivariate models. However, when both urine and serum GDF15 were present in the model, lower urine GDF15 predicted patient survival [B coefficient (SEM) - 0.395 (0.182) p 0.03], and higher urine GDF15 predicted a composite of mortality or kidney replacement therapy [0.191 (0.06) p 0.002], while serum GDF15 was not predictive. Decision tree analysis yielded similar results. The area under the curve (AUC) of the receiver operating curve (ROC) for urine GDF15 as a predictor of mortality was 0.95 (95% CI 0.89-1.00, p < 0.001).

CONCLUSIONS

In conclusion, urinary GDF15 is associated with kidney histology patterns, mortality and the need for renal replacement therapy (RRT) in CKD patients who underwent a kidney biopsy.

Understanding glomerular diseases through proteomics

INTRODUCTION

Chronic kidney disease is avery common and complex chronic disease. Uncovering the pathological patterns of CKD on the molecular level of bio-fluids and tissue appears to be both vital and promising for a more favorable outcome. We reviewed recently discovered proteomics biomarkers for CKD to provide new insight into disease pathology.

AREAS COVERED

We review the application of proteome analysis in the context of CKD with various etiologies within the last 5 years. Proteins and peptides associated with CKD as derived from multiple sources (urine, blood and tissue) are reported along with their various biological pathways.

EXPERT OPINION

A systematic and theoretical comprehension of the CKD pathology is essential for its successful management. The underlying complexity of the disease further requires specific conditions for reliable and interpretable results. In this context, clinical proteomics has resulted in first encouraging findings in CKD. A more complete understanding of the biological pathways related to the disease, based on the scope of a holistic proteomic approach, could improve substantially the management of CKD, especially when in conjunction with the current trend of personalized medicine.

Rational selection of a biomarker panel targeting unmet clinical needs in kidney injury

The pipeline of biomarker translation from bench to bedside is challenging and limited biomarkers have been adopted to routine clinical care. Ideally, biomarker research and development should be driven by unmet clinical needs in health care. To guide researchers, clinical chemists and clinicians in their biomarker research, the European Federation of Clinical Chemistry and Laboratory Medicine (EFLM) has developed a structured questionnaire in which the clinical gaps in current clinical pathways are identified and desirable performance specifications are predefined. In kidney injury, the high prevalence of the syndrome acute kidney injury (AKI) in the hospital setting has a significant impact on morbidity, patient survival and health care costs, but the use of biomarkers indicating early kidney injury in daily patient care remains limited. Routinely, medical labs measure serum creatinine, which is a functional biomarker, insensitive for detecting early kidney damage and cannot distinguish between renal and prerenal AKI. The perceived unmet clinical needs in kidney injury were identified through the EFLM questionnaire. Nephrologists within our tertiary care hospital emphasized that biomarkers are needed for (1) early diagnosis of in-hospital AKI after a medical insult and in critically ill patients, (2) risk stratification for kidney injury prior to a scheduled (elective) intervention, (3) kidney injury monitoring in patients scheduled to receive nephrotoxic medication and after kidney transplantation and (4) differentiation between prerenal AKI and structural kidney damage. The biomarker search and selection strategy resulted in a rational selection of an eleven-protein urinary panel for kidney injury that target these clinical needs. To assess the clinical utility of the proposed biomarker panel in kidney injury, a multiplexed LC-MS test is now in development for the intended translational research.

Value of Urine Peptides in Assessing Kidney and Cardiovascular Disease

Urinary peptides gained significant attention as potential biomarkers especially in the context of kidney and cardiovascular disease. In this manuscript the recent literature since 2015 on urinary peptide investigation in human kidney and cardiovascular disease is reviewed. The technology most commonly used in this context is capillary electrophoresis coupled mass spectrometry, in part owed to the large database available and the well-defined dataspace. Several studies based on over 1000 subjects are reported in the recent past, especially examining CKD273, a classifier for assessment of chronic kidney disease based on 273 urine peptides. Interestingly, the most abundant urinary peptides are generally collagen fragments, which may have gone undetected for some time as they are typically modified via proline hydroxylation. The data available suggest that urinary peptides specifically depict inflammation and fibrosis, and may serve as a non-invasive tool to assess fibrosis, which appears to be a key driver in kidney and cardiovascular disease. The recent successful completion of the first urinary peptide guided intervention trial, PRIORITY, is expected to further spur clinical application of urinary peptidomics, aiming especially at early detection of chronic diseases, prediction of progression, and prognosis of drug response.

A Paradigm to Discover Biomarkers Associated With Chronic Kidney Disease Progression

Biomarker discovery in the field of risk prediction in chronic kidney disease (CKD) embraces the prospect of improving our ability to risk stratify future adverse outcomes and thereby guide patient care in a new era of personalised medicine. However, many studies that report biomarkers predictive of CKD progression share a key methodological limitation: failure to characterise patients' renal progression precisely. This weakens any observable association between a biomarker and an outcome poorly defined by a patient's change in renal function over time. In this commentary, we discuss the need for a better approach in this research arena and describe a compelling strategy that has the advantage of offering robust and meaningful biomarker exploration relevant to CKD progression.

Development of a Biomarker Panel to Distinguish Risk of Progressive Chronic Kidney Disease

Chronic kidney disease (CKD) patients typically progress to kidney failure, but the rate of progression differs per patient or may not occur at all. Current CKD screening methods are sub-optimal at predicting progressive kidney function decline. This investigation develops a model for predicting progressive CKD based on a panel of biomarkers representing the pathophysiological processes of CKD, kidney function, and common CKD comorbidities. Two patient cohorts are utilised: The CKD Queensland Registry (n = 418), termed the Biomarker Discovery cohort; and the CKD Biobank (n = 62), termed the Predictive Model cohort. Progression status is assigned with a composite outcome of a ≥30% decline in eGFR from baseline, initiation of dialysis, or kidney transplantation. Baseline biomarker measurements are compared between progressive and non-progressive patients via logistic regression. In the Biomarker Discovery cohort, 13 biomarkers differed significantly between progressive and non-progressive patients, while 10 differed in the Predictive Model cohort. From this, a predictive model, based on a biomarker panel of serum creatinine, osteopontin, tryptase, urea, and eGFR, was calculated via linear discriminant analysis. This model has an accuracy of 84.3% when predicting future progressive CKD at baseline, greater than eGFR (66.1%), sCr (67.7%), albuminuria (53.2%), or albumin-creatinine ratio (53.2%).

Hypertensive nephropathy: a major roadblock hindering the advance of precision nephrology

In the 2017 Annual Report of the ERA-EDTA Registry, hypertension continues to be the second or third most common cause of renal replacement therapy (RRT) in Europe, tied with glomerulonephritis. There is, however, one little issue: hypertension-induced end-stage renal disease (ESRD) might not exist at all as currently understood, that is, as hypertensive nephrosclerosis. In this regard, the incidence of RRT due to hypertensive nephropathy is related to the incidence of other causes of ESRD but not to the burden of hypertension per country. The current definition of hypertensive nephropathy is non-specific, outdated and only allows a delayed diagnosis by exclusion. It is not helpful that 80% of chronic kidney disease patients develop hypertension and kidney biopsy has no findings specific for hypertensive nephropathy. There is an urgent need to redefine the concept of hypertensive nephropathy with a clear and comprehensive set of criteria that at least should indicate how other nephropathies, including familial nephropathies, should be excluded. Correct causality assessment and aetiology-based therapy is a key to the progress of nephrology and it should no longer be accepted that ‘hypertensive nephropathy’ serves to disguise a suboptimal diagnostic workup. A diagnosis of nephropathy of unknown cause would be more honest when the full range of alternative aetiological diagnoses is not explored.

Optimizing the timing of nephrology referral for patients with diabetic kidney disease

Age-standardized rates of diabetes mellitus (DM)-related complications, such as acute myocardial infarction, stroke or amputations, have decreased in recent years, but this was not associated with a clear reduction of the incidence of advanced chronic kidney disease (CKD) requiring renal replacement therapy. The early detection of diabetic kidney disease (DKD) is a key to reduce complications, morbidity and mortality. Consensus documents and clinical practice guidelines recommend referral of DM patients to nephrology when the estimated glomerular filtration rate falls below 30 mL/min/1.73 m² or when albuminuria exceeds 300 mg/g urinary creatinine. Conceptually, it strikes as odd that patients with CKD are referred to the specialist caring for the prevention and treatment of CKD only when >70% of the functioning kidney mass has been lost. The increasing global health burden of CKD, driven in large part by DKD, the suboptimal impact of routine care on DKD outcomes as compared with other DM complications, the realization that successful therapy of CKD requires early diagnosis and intervention, the advances in earlier diagnosis of kidney injury and the recent availability of antidiabetic drugs with a renal mechanism of action and lack of hypoglycaemia risk, which additionally are cardio- and nephroprotective, all point towards a paradigm shift in the care for DM patients in which they should be referred earlier to nephrology as part of a coordinated and integrated care approach.

Differential Urinary Proteome Analysis for Predicting Prognosis in Type 2 Diabetes Patients with and without Renal Dysfunction

Renal dysfunction, a major complication of type 2 diabetes, can be predicted from estimated glomerular filtration rate (eGFR) and protein markers such as albumin concentration. Urinary protein biomarkers may be used to monitor or predict patient status. Urine samples were selected from patients enrolled in the retrospective diabetic kidney disease (DKD) study, including 35 with good and 19 with poor prognosis. After removal of albumin and immunoglobulin, the remaining proteins were reduced, alkylated, digested, and analyzed qualitatively and quantitatively with a nano LC-MS platform. Each protein was identified, and its concentration normalized to that of creatinine. A prognostic model of DKD was formulated based on the adjusted quantities of each protein in the two groups. Of 1296 proteins identified in the 54 urine samples, 66 were differentially abundant in the two groups (area under the curve (AUC): p-value < 0.05), but none showed significantly better performance than albumin. To improve the predictive power by multivariate analysis, five proteins (ACP2, CTSA, GM2A, MUC1, and SPARCL1) were selected as significant by an AUC-based random forest method. The application of two classifiers—support vector machine and random forest—showed that the multivariate model performed better than univariate analysis of mucin-1 (AUC: 0.935 vs. 0.791) and albumin (AUC: 1.0 vs. 0.722). The urinary proteome can reflect kidney function directly and can predict the prognosis of patients with chronic kidney dysfunction. Classification based on five urinary proteins may better predict the prognosis of DKD patients than urinary albumin concentration or eGFR.

Analytical techniques for multiplex analysis of protein biomarkers

INTRODUCTION

The importance of biomarkers for pharmaceutical drug development and clinical diagnostics is more significant than ever in the current shift toward personalized medicine. Biomarkers have taken a central position either as companion markers to support drug development and patient selection, or as indicators aiming to detect the earliest perturbations indicative of disease, minimizing therapeutic intervention or even enabling disease reversal. Protein biomarkers are of particular interest given their central role in biochemical pathways. Hence, capabilities to analyze multiple protein biomarkers in one assay are highly interesting for biomedical research.

AREAS COVERED

We here review multiple methods that are suitable for robust, high throughput, standardized, and affordable analysis of protein biomarkers in a multiplex format. We describe innovative developments in immunoassays, the vanguard of methods in clinical laboratories, and mass spectrometry, increasingly implemented for protein biomarker analysis. Moreover, emerging techniques are discussed with potentially improved protein capture, separation, and detection that will further boost multiplex analyses.

EXPERT COMMENTARY

The development of clinically applied multiplex protein biomarker assays is essential as multi-protein signatures provide more comprehensive information about biological systems than single biomarkers, leading to improved insights in mechanisms of disease, diagnostics, and the effect of personalized medicine.

Albuminuria Downregulation of the Anti-Aging Factor Klotho: The Missing Link Potentially Explaining the Association of Pathological Albuminuria with Premature Death

Ten percent of the adult population has chronic kidney disease (CKD), which is diagnosed when the glomerular filtration rate (GFR) is below 60 mL/min per 1.73 m² or when albuminuria is above 30 mg/day. The numerical thresholds were chosen because they are associated with an increased risk of CKD progression or premature death within a wider scenario of accelerated aging. Indeed, CKD is one of the fastest growing causes of death worldwide. A decreased GFR is associated with the accumulation of uraemic toxins that may promote tissue and organ damage. However, CKD may be diagnosed when the GFR is completely normal, as long as there is pathological albuminuria. A key unanswered question to stem the rise of CKD-associated deaths is whether the association between isolated albuminuria (when the GFR is normal) and premature death is causal. The recent demonstration that albuminuria per se directly suppresses the production of the anti-aging factor Klotho by kidney tubular cells may be one of the first steps to address the causality of the albuminuria-premature death-accelerated aging association. This hypothesis should be tested in interventional studies that should draw from translational science advances. Thus, the observation that albuminuria decreases Klotho production through epigenetic mechanisms implies that Klotho downregulation may persist after the correction of albuminuria, and innovative therapeutic approaches are needed to restore Klotho production. On the basis of recent literature, these may include manipulation of NF-kappaB regulators such as B cell lymphoma 3 protein (BCL-3), and epigenetic regulators such as histone deacetylases, or the repurposing of drugs such as pentoxifylline.

Klotho, the elusive kidney-derived anti-ageing factor

Chronic kidney disease (CKD) is one of the fastest growing causes of death worldwide. Only early diagnosis will allow prevention of both CKD progression and the negative impact of CKD on all-cause and cardiovascular mortality. Klotho is a protein produced by the kidneys that has anti-ageing and phosphaturic properties, preventing excess positive phosphate balance. There is evidence that Klotho downregulation is one of the earliest consequences of kidney injury. Thus the development of reliable assays to monitor Klotho levels may allow an early diagnosis of CKD and monitoring the impact of therapies aimed at preserving Klotho expression or at preventing CKD progression. However, the performance of Klotho assays has been suboptimal so far. In this issue of Clinical Kidney Journal, Neyra et al. explore methods to improve the reliability of Klotho assays.

Targeting the progression of chronic kidney disease

Chronic kidney disease (CKD) is a devastating condition that is reaching epidemic levels owing to the increasing prevalence of diabetes mellitus, hypertension and obesity, as well as ageing of the population. Regardless of the underlying aetiology, CKD is slowly progressive and leads to irreversible nephron loss, end-stage renal disease and/or premature death. Factors that contribute to CKD progression include parenchymal cell loss, chronic inflammation, fibrosis and reduced regenerative capacity of the kidney. Current therapies have limited effectiveness and only delay disease progression, underscoring the need to develop novel therapeutic approaches to either stop or reverse progression. Preclinical studies have identified several approaches that reduce fibrosis in experimental models, including targeting cytokines, transcription factors, developmental and signalling pathways and epigenetic modulators, particularly microRNAs. Some of these nephroprotective strategies are now being tested in clinical trials. Lessons learned from the failure of clinical studies of transforming growth factor β1 (TGFβ1) blockade underscore the need for alternative approaches to CKD therapy, as strategies that target a single pathogenic process may result in unexpected negative effects on simultaneously occurring processes. Additional promising avenues include preventing tubular cell injury and anti-fibrotic therapies that target activated myofibroblasts, the main collagen-producing cells.

Could IL-17A Be a Novel Therapeutic Target in Diabetic Nephropathy?

Chronic kidney disease has become a major medical issue in recent years due to its high prevalence worldwide, its association with premature mortality, and its social and economic implications. A number of patients gradually progress to end-stage renal disease (ESRD), requiring then dialysis and kidney transplantation. Currently, approximately 40% of patients with diabetes develop kidney disease, making it the most prevalent cause of ESRD. Thus, more effective therapies for diabetic nephropathy are needed. In preclinical studies of diabetes, anti-inflammatory therapeutic strategies have been used to protect the kidneys. Recent evidence supports that immune cells play an active role in the pathogenesis of diabetic nephropathy. Th17 immune cells and their effector cytokine IL-17A have recently emerged as promising targets in several clinical conditions, including renal diseases. Here, we review current knowledge regarding the involvement of Th17/IL-17A in the genesis of diabetic renal injury, as well as the rationale behind targeting IL-17A as an additional therapy in patients with diabetic nephropathy.

Urinary Peptidomic Biomarkers in Kidney Diseases

In order to effectively develop personalized medicine for kidney diseases we urgently need to develop highly accurate biomarkers for use in the clinic, since current biomarkers of kidney damage (changes in serum creatinine and/or urine albumin excretion) apply to a later stage of disease, lack accuracy, and are not connected with molecular pathophysiology. Analysis of urine peptide content (urinary peptidomics) has emerged as one of the most attractive areas in disease biomarker discovery. Urinary peptidome analysis allows the detection of short and long-term physiological or pathological changes occurring within the kidney. Urinary peptidomics has been applied extensively for several years now in renal patients, and may greatly improve kidney disease management by supporting earlier and more accurate detection, prognostic assessment, and prediction of response to treatment. It also promises better understanding of kidney disease pathophysiology, and has been proposed as a "liquid biopsy" to discriminate various types of renal disorders. Furthermore, proteins being the major drug targets, peptidome analysis may allow one to evaluate the effects of therapies at the protein signaling pathway level. We here review the most recent findings on urinary peptidomics in the setting of the most common kidney diseases.

Blood and urine biomarkers in chronic kidney disease: An update

INTRODUCTION

Chronic kidney disease (CKD) is a silent disease. Most CKD patients are unaware of their condition during the early stages of the disease which poses a challenge for healthcare professionals to institute treatment or start prevention. The trouble with the diagnosis of CKD is that in most parts of the world, it is still diagnosed based on measurements of serum creatinine and corresponding calculations of eGFR. There are controversies with the current staging system, especially in the methodology to diagnose and prognosticate CKD.

OBJECTIVE

The aim of this review is to examine studies that focused on the different types of samples which may serve as a good and promising biomarker for early diagnosis of CKD or to detect rapidly declining renal function among CKD patient.

METHOD

The review of international literature was made on paper and electronic databases Nature, PubMed, Springer Link and Science Direct. The Scopus index was used to verify the scientific relevance of the papers. Publications were selected based on the inclusion and exclusion criteria.

RESULT

63 publications were found to be compatible with the study objectives. Several biomarkers of interest with different sample types were taken for comparison.

CONCLUSION

Biomarkers from urine samples yield more significant outcome as compare to biomarkers from blood samples. But, validation and confirmation with a different type of study designed on a larger population is needed. More comparison studies on different types of samples are needed to further illuminate which biomarker is the better tool for the diagnosis and prognosis of CKD.

Proteomics for Clinical Assessment of Kidney Disease

Kidney disease is one of the fastest growing causes of death worldwide, disclosing an unmet clinical need for early diagnosis and optimized risk stratification that allows high risk patient selection for clinical trials and for more intensive nephroprotective interventions in the clinic. The current issue of PROTEOMICS-Clinical Applications contains four manuscripts that explore different aspects of clinical proteomics implementation in the context of acute kidney injury, chronic kidney disease and, more specifically, diabetic kidney disease, and kidney transplantation from a diagnostic and risk stratification point of view. Overall, the evidence discussed suggests that chronic kidney disease is an example where clinical proteomics has become a valuable tool ready for clinical implementation, expected to have a major impact in patient management.

The new Clinical Kidney Journal, 4 years later

The February 2015 issue of ckj started a new era with renewed efforts to be useful to the training and practicing nephrologists and a new focus on Clinical and Translational Nephrology. Four years later, it has become a truly global journal with contributors and readers from all over the world. The increase in quality of the published material has resulted in a nearly exponential growth of citations. Since 2016, ckj is listed in the new Emerging Sources Citation Index (ESCI) database from Clarivate Analytics and from January 2019 it will be listed in the full Science Citation Index. ckj will therefore receive its first official impact factor based upon 2018 citation to 2016 and 2017 articles. While no official impact factor was awarded for 2017, the estimated impact factors calculated from data available in Clarivate's Web of Science database rose to 2.987 in 2017, which would correspond to an estimated journal impact factor percentile of 72.4% in the Urology and Nephrology field.