Urine proteomic profiling in patients with nephrolithiasis and cystinuria

Immune-inflammatory process in nephrolithiasis: A bibliometric analysis (2000-2023)

The research on the mechanism of nephrolithiasis formation is of great importance due to the fact that the high incidence and recurrence rate of nephrolithiasis bring considerable economic burdens to patients and society. As an important component in the nephrolithiasis formation process, the immune-inflammatory process has been gradually valued by researchers in recent years. In this study, articles related to the immune-inflammatory process of nephrolithiasis published since 2000 were retrieved based on the Web of Science (WoS) database. Eventually, a total of 370 articles were selected for subsequent analyses. Besides, VOSviewer, CiteSpace, and Bibliometrix were employed to quantitatively analyze and visualize the data. The number of articles related to the immune-inflammatory process of nephrolithiasis has increased rapidly in the last five years. From the country level, most articles were contributed by China (n = 140) and the United States (n = 99) contributed the most documents. From the institution level, University of Florida (n = 36) and Nagoya City University (n = 21) had the most articles. From the journal level, Journal of Urology and Urolithiasis published the most articles in this field. Keywords mainly included inflammation, oxidative stress, calcium oxalate, osteopontin, and hyperoxaluria, which represented the research directions in this field. The most productive author was Khan SR (n = 33), whose articles obtained the highest number of citations (2086 times). These efforts may help researchers understand the current progress and status of research on the immune-inflammatory process of nephrolithiasis and identify future research hotspots and directions.

Bone mineral density assessment in patients with cystinuria

BACKGROUND

Cystinuria is a rare genetic disease characterized by impaired tubular transport of cystine. Clinical features of cystinuria mainly include nephrolithiasis and its complications, although cystinuric patients may present with other comorbidities. There are currently no data on bone features of patients with cystinuria. Our aim is to characterize bone mineral density (BMD) in cystinuria.

METHODS

Our study included adult cystinuric patients with estimated glomerular filtration rate (eGFR) ≥ 60 mL/min/1.73 m2 followed at 3 specialized outpatient clinics in Italy (Rome, Naples and Verona). Markers of bone turnover were analyzed in a centralized laboratory. Clinical, biochemical and dual-energy X-ray absorptiometry (DEXA) data were collected from September 2021 to December 2022. Linear regression models were used to evaluate statistically significant deviations from zero of Z-scores.

RESULTS

Twenty-seven patients were included in the study. Mean (SD) age was 37 (15) years, 41% were women. Mean estimated glomerular filtration rate was 99 mL/min/1.73 m2. Serum parameters associated with bone turnover (parathyroid hormone, FGF23, calcium and phosphate) were all in the normal range, with only 4 patients showing mild hypophosphatemia. Prevalence of low bone mineral density, defined as Z-score ≤  - 2 at any site, was 15%. Average Z-scores were negative across most sites.

CONCLUSIONS

Our study suggests that cystinuric patients have lower bone mineral density compared with individuals of the same sex and age, even when their kidney function is normal.

Effect of urine alkalization on urinary inflammatory markers in cystinuric patients

Background

Cystinuria is associated with a high prevalence of chronic kidney disease (CKD). We previously described a urinary inflammatory-protein signature (UIS), including 38 upregulated proteins, in cystinuric patients (Cys-patients), compared with healthy controls (HC). This UIS was higher in Cys-patients with CKD. In the present observational study, we aimed to investigate the UIS in Cys-patients without CKD and patients with calcium nephrolithiasis (Lith-patients), versus HC and the effect of urine alkalization on the UIS of Cys-patients.

Methods

UIS was evaluated by nano-liquid chromatography coupled to high-resolution mass spectrometry in adult HC, Lith-patients and non-treated Cys-patients with an estimated glomerular filtration rate >60 mL/min/1.73 m2, and after a 3-month conventional alkalizing treatment in Cys-patients.

Results

Twenty-one Cys-patients [12 men, median age (interquartile range) 30.0 (25.0-44.0) years], 12 Lith-patients [8 men, 46.2 (39.5-54.2) years] and 7 HC [2 men, 43.1 (31.0-53.9) years] were included. Among the 38 proteins upregulated in our previous work, 11 proteins were also upregulated in Cys-patients compared with HC in this study (5 circulating inflammatory proteins and 6 neutrophil-derived proteins). This UIS was also found in some Lith-patients. Using this UIS, we identified two subclusters of Cys-patients (5 with a very high/high UIS and 16 with a moderate/low UIS). In the Cys-patients with very high/high UIS, urine alkalization induced a significant decrease in urinary neutrophil-derived proteins.

Conclusion

A high UIS is present in some Cys-patients without CKD and decreases under alkalizing treatment. This UIS could be a prognostic marker to predict the evolution towards CKD in cystinuria.

Proteomics in Inherited Metabolic Disorders

Inherited metabolic disorders (IMD) are rare medical conditions caused by genetic defects that interfere with the body's metabolism. The clinical phenotype is highly variable and can present at any age, although it more often manifests in childhood. The number of treatable IMDs has increased in recent years, making early diagnosis and a better understanding of the natural history of the disease more important than ever. In this review, we discuss the main challenges faced in applying proteomics to the study of IMDs, and the key advances achieved in this field using tandem mass spectrometry (MS/MS). This technology enables the analysis of large numbers of proteins in different body fluids (serum, plasma, urine, saliva, tears) with a single analysis of each sample, and can even be applied to dried samples. MS/MS has thus emerged as the tool of choice for proteome characterization and has provided new insights into many diseases and biological systems. In the last 10 years, sequential window acquisition of all theoretical fragmentation spectra mass spectrometry (SWATH-MS) has emerged as an accurate, high-resolution technique for the identification and quantification of proteins differentially expressed between healthy controls and IMD patients. Proteomics is a particularly promising approach to help obtain more information on rare genetic diseases, including identification of biomarkers to aid early diagnosis and better understanding of the underlying pathophysiology to guide the development of new therapies. Here, we summarize new and emerging proteomic technologies and discuss current uses and limitations of this approach to identify and quantify proteins. Moreover, we describe the use of proteomics to identify the mechanisms regulating complex IMD phenotypes; an area of research essential to better understand these rare disorders and many other human diseases.

Roles of heat-shock protein 90 and its four domains (N, LR, M and C) in calcium oxalate stone-forming processes

Human heat-shock protein 90 (HSP90) has four functional domains, including NH₂-terminal (N), charged linker region (LR), middle (M) and COOH-terminal (C) domains. In kidney stone disease (or nephrolithiasis/urolithiasis), HSP90 serves as a receptor for calcium oxalate monohydrate (COM), which is the most common crystal to form kidney stones. Nevertheless, roles of HSP90 and its four domains in kidney stone formation remained unclear and under-investigated. We thus examined and compared their effects on COM crystals during physical (crystallization, growth and aggregation) and biological (crystal–cell adhesion and crystal invasion through extracellular matrix (ECM)) pathogenic processes of kidney stone formation. The analyses revealed that full-length (FL) HSP90 obviously increased COM crystal size and abundance during crystallization and markedly promoted crystal growth, aggregation, adhesion onto renal cells and ECM invasion. Comparing among four individual domains, N and C domains exhibited the strongest promoting effects, whereas LR domain had the weakest promoting effects on COM crystals. In summary, our findings indicate that FL-HSP90 and its four domains (N, LR, M and C) promote COM crystallization, crystal growth, aggregation, adhesion onto renal cells and invasion through the ECM, all of which are the important physical and biological pathogenic processes of kidney stone formation.

Urinary proteomics for kidney dysfunction: insights and trends

Introduction: Kidney dysfunction poses a high burden on patients and health care systems. Early detection and accurate prediction of kidney disease progression remains a major challenge. Compared to existing clinical parameters, urinary proteomics has the potential to reveal molecular alterations within the kidney that may alter its function before the onset of clinical symptoms. Thus, urinary proteomics has greater prognostic potential for assessment of kidney dysfunction progression.Areas covered: Advances in urinary proteomics for major causes of kidney dysfunction are discussed. The application of urinary extracellular vesicles for studying kidney dysfunction are discussed. Technological advances in urinary proteomics are discussed. The literature was identified using a database search for titles containing 'proteom*' and 'urin*' and published within the past 5 years. Retrieved literature was manually filtered to retain kidney dysfunctions-related studies.Expert opinion: Despite major advances, diagnosis by urinary proteomics has not been fully applied in any clinical settings. This could be attributed to the complex nature of kidney diseases, in addition to the constraints on study power and feasibility of incorporating mass spectrometry techniques in daily routine analysis. Nevertheless, we are confident that advances in urinary proteomics will soon provide superior insights into kidney disease beyond existing clinical parameters.

Linking 24-h urines to clinical phenotypes: what alternatives does the future bring?

PURPOSE OF REVIEW

The 24-h urine test is recommended as part of the metabolic evaluation for patients with nephrolithiasis to guide preventive interventions. However, this test may be challenging to interpret and has limits in its predictive ability. In this review, we summarize and discuss the most recent research on the opportunities and challenges for utilizing urinary biomarkers for kidney stone prevention.

RECENT FINDINGS

Contemporary studies utilizing the 24-h urine test have improved our understanding of how to better administer testing and interpret test results. Beyond the standard panel of 24-h urine parameters, recent applications of proteomics and metabolomics have identified protein and metabolic profiles of stone formers. These profiles can be assayed in future studies as potential biomarkers for risk stratification and prediction. Broad collaborative efforts to create large datasets and biobanks from kidney stone formers will be invaluable for kidney stone research.

SUMMARY

Recent advances in our understanding of kidney stone risk have opened opportunities to improve metabolic testing for kidney stone formers. These strategies do not appear to be mutually exclusive of 24-h urine testing but instead complementary in their approach. Finally, large clinical datasets hold promise to be leveraged to identify new avenues for stone prevention.