The Versatile Role of Uromodulin in Renal Homeostasis and Its Relevance in Chronic Kidney Disease

Comprehensive identification of stone-promoting proteins in the urine of kidney stone formers

Urinary proteins have crucial roles in modulating kidney stone formation. While stone-inhibiting urinary proteins are well characterized, stone-promoting urinary proteins are insufficiently explored. This knowledge gap limits our ability to fully comprehend the pathogenic mechanisms underlying nephrolithiasis and hampers the development of targeted therapeutic/preventive interventions. Therefore, we systematically identified stone-promoting proteins from the urine of 30 calcium oxalate (CaOx) nephrolithiatic patients (stone formers). Urinary proteins were fractionated by anion exchange and size-exclusion chromatography. A total of 15 protein fractions (SF1-SF15) were tested for their modulating activities on CaOx crystals by various assays compared with the control. The fractions with net CaOx-promoting activities were then identified by nanoLC-ESI-Qq-TOF MS/MS. From 15 fractions, 9 had net CaOx-promoting activities in all crystal assays. Among 3-99 proteins identified from these fractions, alpha-1acid glycoprotein 2, alpha-1-antitrypsin, apolipoprotein D, CD44 antigen, endosialin, fibrinogen alpha chain, interleukin-18-binding protein, kallikrein-1, retinol-binding protein 4, and titin have been found to increase in the urine of stone formers compared with controls, reinforcing their potential roles as CaOx stone promoters. This study offers the largest collection of CaOx stone-promoting proteins that will shed light on pathogenic mechanisms of nephrolithiasis and may allow further development of new drug targets to treat/prevent nephrolithiasis.

Biomarkers in Contrast-Induced Nephropathy: Advances in Early Detection, Risk Assessment, and Prevention Strategies

Contrast-induced nephropathy (CIN) represents a significant complication associated with the use of iodinated contrast media (ICM), especially in individuals with preexisting renal impairment. The pathophysiology of CIN encompasses oxidative stress, inflammation, endothelial dysfunction, and hemodynamic disturbances, resulting in acute kidney injury (AKI). Early detection is essential for effective management; however, conventional markers like serum creatinine (sCr) and estimated glomerular filtration rate (eGFR) exhibit limitations in sensitivity and timeliness. This review emphasizes the increasing significance of novel biomarkers in enhancing early detection and risk stratification of contrast-induced nephropathy (CIN). Recent advancements in artificial intelligence and computational analytics have improved the predictive capabilities of these biomarkers, enabling personalized risk assessment and precision medicine strategies. Additionally, we discuss mitigation strategies, including hydration protocols, pharmacological interventions, and procedural modifications, aimed at reducing CIN incidence. Incorporating biomarker-driven assessments into clinical decision-making can enhance patient management and outcomes. Future research must prioritize the standardization of biomarker assays, the validation of predictive models across diverse patient populations, and the exploration of novel therapeutic targets. Utilizing advancements in biomarkers and risk mitigation strategies allows clinicians to improve the safety of contrast-enhanced imaging and reduce the likelihood of renal injury.

Comparative assessment of the effects of dotinurad and febuxostat on the renal function in chronic kidney disease patients with hyperuricemia

Although hyperuricemia is associated with chronic kidney disease (CKD), the impact of uric acid (UA)-lowering drugs on CKD has been controversial. Previous investigations have primarily included xanthine oxidase inhibitors; therefore, research of dotinurad, a recently developed selective urate reabsorption inhibitor, is necessary. This retrospective study included 58 patients with CKD; of these, 29 newly initiated dotinurad and 29 initiated febuxostat. The effects of dotinurad and febuxostat on the serum UA, urinary UA-to-creatinine ratio (UUCR), and estimated glomerular filtration rate (eGFR) during 3 months were analyzed to compare their impacts on renal function. Dotinurad and febuxostat decreased serum UA (8.40 ± 1.11 to 6.50 ± 0.80 mg/dL [p < 0.001] and 8.91 ± 1.21 to 6.05 ± 1.28 mg/dL [p = < 0.001], respectively). The UUCR increased after dotinurad (0.35 ± 0.15 to 0.40 ± 0.21 g/gCr [p = 0.024]); however, it decreased after febuxostat (0.33 ± 0.12 to 0.21 ± 0.06 g/gCr [p = 0.002]). The eGFR improved after dotinurad (33.9 ± 15.2 to 36.2 ± 15.9 mL/min/1.73 m2 [p < 0.001]). No change was observed after febuxostat treatment (33.4 ± 19.6 to 34.1 ± 21.6 mL/min/1.73 m2). Renal function improved only with dotinurad, thus highlighting its renoprotective effects beyond the reduction of serum UA.

Managing Dosage Adjustments in Pseudo-Hypocreatinemia: Insights from Vancomycin-Induced Nephrotoxicity in a Sarcopenic Patient

Adjusting the dosage of renal excretory drugs according to the patient's renal function is essential. Vancomycin necessitates such adjustments due to its potential to cause nephrotoxicity when administered in excess. Creatinine-based equations for assessing the glomerular filtration rate, such as the Cockcroft-Gault and Modification of Diet in Renal Disease equations, are often used for dosage adjustments. However, vancomycin-induced nephrotoxicity sometimes occurs in critically ill patients, even in those with a normal estimated glomerular filtration rate. This case involved a 64-year-old male with cholangitis who developed vancomycin-induced nephrotoxicity. The patient was sarcopenic and had multiple risk factors that predisposed him to drug-induced nephrotoxicity. Moreover, creatinine-based equations may lead to the overestimation of glomerular filtration rate and subsequent vancomycin overdose. This case underscores the need for careful interpretation of creatinine-based assessments. We propose strategies to optimize medication dosing, particularly in patients with sarcopenia, to mitigate such risks.

Relationship Between Serum Uromodulin as a Marker of Kidney Damage and Metabolic Status in Patients with Chronic Kidney Disease of Non-Diabetic Etiology

Chronic kidney disease (CKD) is often associated with dyslipidemia, marked by lipid abnormalities that can worsen kidney function and increase cardiovascular risk. A promising biomarker for evaluating kidney function and metabolic status in chronic kidney disease (CKD) is serum uromodulin (sUmod). This study sought to further investigate the relationship between sUmod levels and metabolic status in non-diabetic CKD patients. A sensitive ELISA method was used to determine sUmod levels in 90 adults with obstructive nephropathy and 30 healthy controls. Kidney function was assessed using the measured glomerular filtration rate (mGFR) through renal clearance of 99mTc-diethylenetriamine penta-acetic acid, along with cystatin C levels. Additionally, glycemic and lipid statuses were evaluated. sUmod concentrations showed a significant association with High-density lipoprotein (HDL) levels. Furthermore, CKD patients with lower sUmod levels had significantly lower Apolipoprotein A-I (Apo A-I) values compared to the control group. Significant predictors of lower sUmod concentrations identified in this study were higher glycemia (B = -15.939; p = 0.003) and lower HDL cholesterol levels (B = 20.588; p = 0.019). We conclude that, in addition to being significantly reduced in CKD patients, sUmod is a potential predictor of metabolic syndrome (MS) in this population. Lower sUmod concentrations, independent of mGFR, predict lower HDL cholesterol levels and higher glycemia values.

Zinc deficiency induces hypertension by paradoxically amplifying salt sensitivity under high salt intake in mice

BACKGROUND

Hypertension is one of the major etiologies that cause chronic kidney disease (CKD) and can exacerbate kidney dysfunction. Zinc is an essential trace element playing a role in blood pressure regulation, and zinc deficiency, a common comorbidity in patients with CKD, can cause hypertension. However, the precise mechanism underlying zinc deficiency-induced hypertension is unknown. Sodium (Na+) retention due to inappropriate Na+ reabsorption in the renal tubule is the principal pathophysiology of hypertension. Therefore, this study aimed to investigate the association between zinc deficiency and salt sensitivity.

METHODS

Adult mice were fed a zinc-adequate (ZnA) or zinc-deficient (ZnD) diet combined with/without high salt in drinking water (HS) for 4 weeks (n = 6 each). Changes in blood pressure, urinary sodium excretion, and the expressions of the proximal tubular Na+ transporter, Na+/H+ exchanger 3 (NHE3), which mostly contributes to filtered Na+ reabsorption and the downstream Na+-Cl- transporter (NCC) were analyzed.

RESULTS

Urinary Na+ excretion significantly increased in ZnD mice, indicating that zinc deficiency causes natriuresis. NHE3 expressions were significantly suppressed, whereas NCC was upregulated in ZnD mice. Interestingly, the combination of high salt and ZnD diet (HS-ZnD) reversed the urinary Na+ loss. The NCC remained activated and NHE3 expressions paradoxically increased in HS-ZnD mice compared with those fed the combination of high salt and ZnA diet. In addition, blood pressure significantly increased only in HS-ZnD mice.

CONCLUSION

The combination of zinc deficiency and high salt causes hypertension. Zinc is associated with salt-sensitivity, potentially through NHE3 and NCC regulation.

The role of uromodulin in cardiovascular disease: a review

Uromodulin, also referred to as Tamm Horsfall protein (THP), is a renal protein exclusively synthesized by the kidneys and represents the predominant urinary protein under normal physiological conditions. It assumes a pivotal role within the renal system, contributing not only to ion transport and immune modulation but also serving as a critical factor in the prevention of urinary tract infections and kidney stone formation. Emerging evidence indicates that uromodulin may serve as a potential biomarker extending beyond renal function. Recent clinical investigations and Mendelian randomization studies have unveiled a discernible association between urinary regulatory protein levels and cardiovascular events and mortality. This review primarily delineates the intricate relationship between uromodulin and cardiovascular disease, elucidates its predictive utility as a novel biomarker for cardiovascular events, and delves into its involvement in various physiological and pathophysiological facets of the cardiovascular system, incorporating recent advancements in corresponding genetics.

Characterization of site-specific N-glycosylation signatures of isolated uromodulin from human urine

Uromodulin (Umod, Tamm-Horsfall protein) is the most abundant urinary N-glycoprotein produced exclusively by the kidney. It can form filaments to antagonize the adhesion of uropathogens. However, the site-specific N-glycosylation signatures of Umod in healthy individuals and patients with IgA nephropathy (IgAN) remain poorly understood due to the lack of suitable isolation and analytical methods. In this study, we first presented a simple and fast method based on diatomaceous earth adsorption to isolate Umod. These isolated glycoproteins were digested by trypsin and/or Glu-C. Intact N-glycopeptides with or without HILIC enrichment were analyzed using our developed EThcD-sceHCD-MS/MS. Based on the optimized workflow, we identified a total of 780 unique intact N-glycopeptides (7 N-glycosites and 152 N-glycan compositions) from healthy individuals. As anticipated, these glycosites exhibited glycoform heterogeneity. Almost all N-glycosites were modified completely by the complex type, except for one N-glycosite (N275), which was nearly entirely occupied by the high-mannose type for mediating Umod's antiadhesive activity. Then, we compared the N-glycosylation of Umod between healthy controls (n = 9) and IgAN patients (n = 9). The N-glycosylation of Umod in IgAN patients will drastically decrease and be lost. Finally, we profiled the most comprehensive site-specific N-glycosylation map of Umod and revealed its alterations in IgAN patients. Our method provides a high-throughput workflow for characterizing the N-glycosylation of Umod, which can aid in understanding its roles in physiology and pathology, as well as serving as a potential diagnostic tool for evolution of renal tubular function.

Renal tubular acidosis without interstitial nephritis in Sjögren's syndrome: a case report and review of the literature

BACKGROUND

Renal tubular acidosis is the principal clinical feature associated with tubulointerstitial nephritis in patients with primary Sjögren's syndrome. Renal tubular dysfunction due to interstitial nephritis has been considered the underlying pathophysiology connecting renal tubular acidosis and primary Sjögren's syndrome. However, the detailed mechanisms underlying the pathophysiology of renal tubular acidosis in primary Sjögren's syndrome is not fully understood.

CASE PRESENTATION

A 30-year-old woman was admitted with complaints of weakness in the extremities. The patient was hospitalized thirteen years earlier for similar issues and was diagnosed with hypokalemic paralysis due to distal renal tubular acidosis with primary Sjögren's syndrome. This diagnosis was based on a positive Schirmer's test. Besides, anti-Sjögren's syndrome-related antigen A was also detected. Laboratory tests indicated distal RTA; however, a renal biopsy showed no obvious interstitial nephritis. Laboratory tests conducted during the second admission indicated distal renal tubular acidosis. Therefore, a renal biopsy was performed again, which revealed interstitial nephritis. Histological analysis of acid-base transporters revealed the absence of vacuolar type H+-ATPases in the collecting duct. The vacuolar type H+-ATPase was also absent in the past renal biopsy, suggesting that the alteration in acid-base transporters is independent of interstitial nephritis.

CONCLUSIONS

This case study demonstrates that vacuolar-type H+-ATPases are associated with distal renal tubular acidosis, and distal renal tubular acidosis precedes interstitial nephritis in patients with primary Sjögren's syndrome.

Five-Aminolevulinic Acid (5-ALA) Induces Heme Oxygenase-1 and Ameliorates Palmitic Acid-Induced Endoplasmic Reticulum Stress in Renal Tubules

Steatosis, or ectopic lipid deposition, is the fundamental pathophysiology of non-alcoholic steatohepatitis and chronic kidney disease. Steatosis in the renal tubule causes endoplasmic reticulum (ER) stress, leading to kidney injury. Thus, ER stress could be a therapeutic target in steatonephropathy. Five-aminolevulinic acid (5-ALA) is a natural product that induces heme oxygenase (HO)-1, which acts as an antioxidant. This study aimed to investigate the therapeutic potential of 5-ALA in lipotoxicity-induced ER stress in human primary renal proximal tubule epithelial cells. Cells were stimulated with palmitic acid (PA) to induce ER stress. Cellular apoptotic signals and expression of genes involved in the ER stress cascade and heme biosynthesis pathway were analyzed. The expression of glucose-regulated protein 78 (GRP78), a master regulator of ER stress, increased significantly, followed by increased cellular apoptosis. Administration of 5-ALA induced a remarkable increase in HO-1 expression, thus ameliorating PA-induced GRP78 expression and apoptotic signals. BTB and CNC homology 1 (BACH1), a transcriptional repressor of HO-1, was significantly downregulated by 5-ALA treatment. HO-1 induction attenuates PA-induced renal tubular injury by suppressing ER stress. This study demonstrates the therapeutic potential of 5-ALA against lipotoxicity through redox pathway.