Understanding formation processes of calcareous nephrolithiasis in renal interstitium and tubule lumen.

Kidney stone, one of the oldest known diseases, has plagued humans for centuries, consistently imposing a heavy burden on patients and healthcare systems worldwide due to their high incidence and recurrence rates. Advancements in endoscopy, imaging, genetics, molecular biology and bioinformatics have led to a deeper and more comprehensive understanding of the mechanism behind nephrolithiasis. Kidney stone formation is a complex, multi-step and long-term process involving the transformation of stone-forming salts from free ions into asymptomatic or symptomatic stones influenced by physical, chemical and biological factors. Among the various types of kidney stones observed in clinical practice, calcareous nephrolithiasis is currently the most common and exhibits the most intricate formation mechanism. Extensive research suggests that calcareous nephrolithiasis primarily originates from interstitial subepithelial calcified plaques and/or calcified blockages in the openings of collecting ducts. These calcified plaques and blockages eventually come into contact with urine in the renal pelvis, serving as a nidus for crystal formation and subsequent stone growth. Both pathways of stone formation share similar mechanisms, such as the drive of abnormal urine composition, involvement of oxidative stress and inflammation, and an imbalance of stone inhibitors and promoters. However, they also possess unique characteristics. Hence, this review aims to provide detailed description and present recent discoveries regarding the formation processes of calcareous nephrolithiasis from two distinct birthplaces: renal interstitium and tubule lumen.

Histone deacetylase 6 suppression of renal tubular epithelial cell promotes interstitial mineral deposition via alpha-tubulin acetylation.

Randall's plaque (RP) is derived from interstitial mineral deposition and is highly prevalent in renal calcium oxalate (CaOx) stone disease, which is predictive of recurrence. This study shows that histone deacetylase 6 (HDAC6) levels are suppressed in renal tubular epithelial cells in RP samples, in kidney tissues of hyperoxaluria rats, and in hyper-oxalate-treated or mineralized cultured renal tubular epithelial (MDCK) cells in vitro. Mineral deposition in MDCK cells was exacerbated by HDAC6 inhibition but alleviated by HDAC6 overexpression. Surprisingly, the expression of some osteogenic-associated proteins, were not increased along with the increasing of mineral deposition, and result of single-cell RNA sequencing of renal papillae samples revealed that epithelial cells possess lower calcific activity, suggesting that osteogenic-transdifferentiation may not have actually occurred in tubular epithelial cells despite mineral deposition. The initial mineral depositions facilitated by HDAC6 inhibitor were localized in extracellular dome rather than inside the cells, moreover, suppression of HDAC6 significantly increased the calcium content of co-cultured renal interstitial fibroblasts (NRK49F) and enhanced mineral deposition of indirectly co-cultured NRK49F cells, suggesting that HDAC6 may influence trans-MDCK monolayer secretion of mineral. Further experiments revealed that this regulatory role was partially alpha-tubulinLys40 acetylation dependent. Collectively, these results suggest that hyper-oxalate exposure led to HDAC6 suppression in renal tubular epithelial cells, which may contribute to interstitial mineral deposition by promoting alpha-tubulinLys40 acetylation. Therapeutic agents that influence HDAC6 activity may be beneficial in preventing RP and CaOx stone formation.

An overview of global research landscape in etiology of urolithiasis based on bibliometric analysis.

The high incidence, recurrence and treatment costs of urolithiasis have a serious impact on patients and society. For a long time, countless scholars have been working tirelessly on studies related to the etiology of urolithiasis. A comprehensive understanding of the current status will be beneficial to the development of this field. We collected all literature about the etiology of urolithiasis from 1990 to 2022 using the Web of Science (WoS) database. VOSviewer, Bibliometrix and CiteSpace software were used to quantitatively analyze and visualize the data as well. The query identified 3177 articles for final analysis, of which related to the etiology of urolithiasis. The annual number of publications related to urolithiasis research has steadily increased during the latest decade. United States (1106) and China (449) contributed the most publications. University of Chicago (92) and Indiana University (86) have the highest number of publications. Urolithiasis and Journal of Urology have published the most articles in the field. Coe FL is the most productive author (63 articles), whose articles have obtained the most citations in all (4141 times). The keyword, such as hypercalciuria, hyperoxaluria, citrate, oxidative stress, inflammation, Randall's plaque, are the most attractive targets for the researchers. Our review provides a global landscape of studies related to the etiology of urolithiasis, which can serve as a reference for future studies in this field.

Identification of the core genes in Randall's plaque of kidney stone and immune infiltration with WGCNA network.

Background: Randall's plaque is regarded as the precursor lesion of lithiasis. However, traditional bioinformatic analysis is limited and ignores the relationship with immune response. To investigate the underlying calculi formation mechanism, we introduced innovative algorithms to expand our understanding of kidney stone disease. Methods: We downloaded the GSE73680 series matrix from the Gene Expression Omnibus (GEO) related to CaOx formation and excluded one patient, GSE116860. In the RStudio (R version 4.1.1) platform, the differentially expressed genes (DEGs) were identified with the limma package for GO/KEGG/GSEA analysis in the clusterProfiler package. Furthermore, high-correlated gene co-expression modules were confirmed by the WGCNA package to establish a protein-protein interaction (PPI) network. Finally, the CaOx samples were processed by the CIBERSORT algorithm to anchor the key immune cells group and verified in the validation series matrix GSE117518. Results: The study identified 840 upregulated and 1065 downregulated genes. The GO/KEGG results revealed fiber-related or adhesion-related terms and several pathways in addition to various diseases identified from the DO analysis. Moreover, WGCNA selected highly correlated modules to construct a PPI network. Finally, 16 types of immune cells are thought to participate in urolithiasis pathology and are related to hub genes in the PPI network that are proven significant in the validation series matrix GSE117518. Conclusion: Randall's plaque may relate to genes DCN, LUM, and P4HA2 and M2 macrophages and resting mast immune cells. These findings could serve as potential biomarkers and provide new research directions.

Correlation between CT attenuation value of renal papilla and the occurrence and development of renal calculi / 现代泌尿外科杂志

【Objective】 To analyze the correlation between CT attenuation value of renal papilla and occurrence and development of renal calculi. 【Methods】 The clinical data of 100 patients with calcium oxalate stones treated during Aug.2020 and Jul.2022 were retrospectively analyzed, including 60 with primary stones, and 40 with recurrent stones. The 30 healthy volunteers were enrolled in the control group. CT attenuation value of renal papilla was measured with plain scan CT, and risk factors were identified with the receiver operating characteristic (ROC) curve. The correlation of CT attenuation value and 24 h urine metabolism was analyzed. 【Results】 The CT attenuation value of renal papilla was significantly higher in the primary group [34.92 (IQR: 3.84)] and recurrent group [43.00 (IQR: 8.74)] than in the control group [32.58 (IQR: 5.21)] (P<0.05). Compared with the primary group, the recurrent group had decreased citric acid level but increased calcium level in 24 h urine (P<0.05). The citrate ion and calcium ion were correlated with the CT attenuation value (P<0.05). 【Conclusion】 Patients with high renal papilla density have a high risk of stone formation and recurrence. Increased renal papilla density is a warning signal for the development of stones. The high calcium and low citric acid in 24 h urine have certain effects on the occurrence and development of urolithiasis. Intake of calcium should be limited and citric acid should be supplemented in patients with calcium oxalate stones.

[Endoscopic papillary abnormalities and urinary stone recognition (EPSR): How and why?] / Reconnaissance endoscopique des anomalies papillaires et des calculs urinaires (REPC) : comment et quel intérêt ?

INTRODUCTION: The purpose of this article is to present the endoscopic papillary abnormalities and stone recognition (EPSR) to state-certified nurses (IDE and IBODE) working in the operating room. METHODS: This article is based on a literature review and the author's experience concerning the endoscopic papillary abnormalities and stone recognition. RESULTS: Since the advent of minimally invasive surgery and the laser, stones are no longer sent as one piece to laboratories, but fragmented. This has made it more difficult for biologists to fully analyze the stones, because they have less morphological data than before. Therefore, endoscopic papillary abnormalities and stone recognition have positioned themselves as tools that can compensate for this loss of information. They play a pivotal role in the identification of the lithogenesis cause, and thus allow a recurrence risk reduction of stones. CONCLUSION: Endoscopic papillary abnormalities and stone recognition are recent tools that require learning. However, the benefit of their uses is proven and is necessary for a complete management of urolithiasis.

Collagen fibrils and cell nuclei are entrapped within Randall's plaques but not in CaOx matrix overgrowth: A microscopic inquiry into Randall's plaque stone pathogenesis.

Calcium oxalate (CaOx) stones can grow attached to the renal papillary calcification known as Randall's plaque. Although stone growth on Randall's plaque is a common phenomenon, this mechanism of stone formation is still poorly understood. The objective of this study was to investigate the microenvironment of mature Randall's plaque, explore its molecular composition and differentiate plaque from CaOx overgrowth using multimodal imaging on demineralized stone sections. Fluorescence imaging showed consistent differences in autofluorescence patterns between Randall's plaque and calcium oxalate overgrowth regions. Second harmonic generation imaging established the presence of collagen only in regions of decalcified Randall's plaque but not in regions of CaOx overgrowth matrix. Surprisingly, in these stone sections we observed cell nuclei with preserved morphology within regions of mature Randall's plaque. These conserved cells had variable expression of vimentin and CD45. The presence of nuclei in mature plaque indicates that mineralization is not necessarily associated with cell death. The markers identified suggest that some of the entrapped cells may be undergoing dedifferentiation or could emanate from a mesenchymal or immune origin. We propose that entrapped cells may play an important role in the growth and maintenance of Randall's plaque. Further characterization of these cells and thorough analyses of the mineralized stone forming renal papilla will be fundamental in understanding the pathogenesis of Randall's plaque and CaOx stone formation.

Macrophage Function in Calcium Oxalate Kidney Stone Formation: A Systematic Review of Literature.

Background: The global prevalence and recurrence rate of kidney stones is very high. Recent studies of Randall plaques and urinary components in vivo, and in vitro including gene manipulation, have attempted to reveal the pathogenesis of kidney stones. However, the evidence remains insufficient to facilitate the development of novel curative therapies. The involvement of renal and peripheral macrophages in inflammatory processes offers promise that might lead to the development of therapeutic targets. The present systematic literature review aimed to determine current consensus about the functions of macrophages in renal crystal development and suppression, and to synthesize evidence to provide a basis for future immunotherapy. Methods: We systematically reviewed the literature during February 2021 according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Articles investigating the relationship between macrophages and urolithiasis, particularly calcium oxalate (CaOx) stones, were extracted from PubMed, MEDLINE, Embase, and Scopus. Study subjects, languages, and publication dates were unrestricted. Two authors searched and screened the publications. Results: Although several studies have applied mixed modalities, we selected 10, 12, and seven (total, n = 29) of 380 articles that respectively described cultured cells, animal models, and human samples.The investigative trend has shifted to macrophage phenotypes and signaling pathways, including micro (m)-RNAs since the discovery of macrophage involvement in kidney stones in 1999. Earlier studies of mice-associated macrophages with the acceleration and suppression of renal crystal formation. Later studies found that pro-inflammatory M1- and anti-inflammatory M2-macrophages are involved. Studies of human-derived and other macrophages in vitro and ex vivo showed that M2-macrophages (stimulated by CSF-1, IL-4, and IL-13) can phagocytose CaOx crystals, which suppresses stone development. The signaling mechanisms that promote M2-like macrophage polarization toward CaOx nephrocalcinosis, include the NLRP3, PPARγ-miR-23-Irf1/Pknox1, miR-93-TLR4/IRF1, and miR-185-5p/CSF1 pathways.Proteomic findings have indicated that patients who form kidney stones mainly express M1-like macrophage-related proteins, which might be due to CaOx stimulation of the macrophage exosomal pathway. Conclusions: This systematic review provides an update regarding the current status of macrophage involvement in CaOx nephrolithiasis. Targeting M2-like macrophage function might offer a therapeutic strategy with which to prevent stones via crystal phagocytosis.

The progress of renal papillary calcium plaque lesions / 中华泌尿外科杂志

The formation mechanism of kidney stones is complex. It is generally recognized that abnormal urine conditions or renal tubular epithelial cell damage, together with other factors cause the formation of renal papillary subepithelial calcium plaques (Randall’s plaques) or stone crystals that block the renal tubules (Randall’s plugs), and then oversaturated crystals gathering on Randall's plaque or plug and forming stones. However, there are many pathophysiological changes and manifestations, such as renal papillary anchoring stones, renal papillary crypts, renal papillary tip erosion, and exogenous renal papilla Renal papillary lesions, which may be an early manifestations before the formation of kidney stones. The study of renal papillary calcium plaque is very important for the pathogenesis of kidney stones, as well as the prevention and treatment of patients with stones. By focusing on the development process of Randall plaque theory, the formation and transformation mechanism of Randall plaque, as well as the manifestations and clinical treatment of the above mentioned different types of renal papillary calcium plaque lesions, this article reviewed three aspects of stone formation, including Randall’s plaque, renal papillary lesions with stones, and renal papillary lesions related to stone.

Research advance in Randall plaque of kindey stone. / 肾结石Randallæ–‘å—ç ”ç©¶è¿›å±•.

Urinary calculi are characterized by high incidence and recurrence rate, which is a challenge in urology. The theory of Randall plaque is widely recognized by scholars. The mechanism of Randall plaque formation includes vascular calcification, osteogenic transformation and so on. However, it still lacks a unified theory for the Randall plaque formation. As an important type of non-coding RNA, long non-coding RNA (lncRNA) is closely related to the occurrence and progress of many diseases. The difference in lncRNA expression between the renal papillary tissues of non-calculous patients and the renal papillary tissues of Randall plaque in renal calculous patients suggests that lncRNA may be involved in the formation of Randall plaque. Pseudoxanthoma elasticum is a rare autosomal recessive hereditary disease, caused by a mutation in the ABCC6 gene. Patients with pseudoxanthoma elasticum have a high prevalence of calculi, and plaque formation is observed in the patient's kidney, which may suggest that mutation in the ABCC6 gene might be involved in the formation of Randall plaque.

Long non-coding RNA H19 promotes osteogenic differentiation of renal interstitial fibroblasts through Wnt-ß-catenin pathway.

Randall's plaque (RP) serves as a nidus on which idiopathic calcium oxalate stones form. Renal interstitial mineralization may be the cause underlying RP, and recent studies demonstrated the similarities between the interstitial mineralization and ectopic calcification. The present study aimed to investigate whether human renal interstitial fibroblasts (hRIFs) could form calcification under osteogenic conditions, and whether long non-coding RNA H19 participated in regulating osteogenic differentiation of hRIFs through Wnt-ß-catenin pathway. HRIFs were isolated and induced for osteogenic differentiation under osteogenic conditions. Runx2, OCN, alkaline phosphatase (ALP) activity, and the mineralized nodule formation were used to assess the osteogenic phenotype. Molecule expressions were determined by qRT-PCR, immunofluorescence staining, and western blot. The mineralized nodules were assessed by Alizarin red staining. Compared to the normal renal papillary tissue, Runx2, OCN, and H19 were significantly upregulated in RP. After hRIFs were induced with osteogenic medium, osteogenic markers (Runx2, OCN and ALP), ß-catenin and H19 were significantly upregulated, and the mineralized nodules are formed. Additionally, overexpression of H19 promoted the osteogenic phenotype of hRIFs and increased the expression of ß-catenin, whereas knock-down of H19 or XAV939 (inhibitor of Wnt-ß-catenin signaling pathway) significantly repressed the osteogenic phenotype of hRIFs and decreased the ß-catenin. Moreover, XAV939 was shown to abolish the osteogenic differentiation of hRIFs promoted by H19. The study demonstrated that ectopic calcification partly participated in the formation of RP, and H19 promoted osteogenic differentiation of hRIFs by activating Wnt-ß-catenin pathway, which shed new light on the molecular mechanism of the RP formation.

Relationship of endoscopic lesions of the renal papilla with type of renal stone and 24 h urine analysis.

BACKGROUND: Our purpose was to study the relationship of the 3 different types of endoscopic calcifications of the renal papilla (Randall's plaque, intratubular calcification, papillary crater) with the type of stone and urine analysis. METHODS: This prospective study examined 41 patients (age range: 18 to 80 years) who received retrograde intrarenal surgery (RIRS) for renal lithiasis (mean stone size: 15.3 ± 7.2 mm). The renal papilla injuries were endoscopically classified as Randall's plaque, intratubular calcification, or papillary crater. Calculi were classified as uric acid, calcium oxalate monohydrate (COM; papillary and cavity), calcium oxalate dihydrate (COD), or calcium phosphate (CP). A 24 h urine analysis of calcium, oxalate, citrate, phosphate, and pH was performed in all patients. The relationship of each type of papillary injury with type of stone and urine chemistry was determined. Fisher's exact test and Student's t-test were used to determine the significance of relationships, and a p value below 0.05 was considered significant. RESULTS: The most common injury was tubular calcification (78%), followed by Randall's plaque (58%), and papillary crater (39%). There was no significant relationship of Randall's plaque with type of stone. However, endoscopic intratubular calcification (p = 0.025) and papillary crater (p = 0.041) were more common in patients with COD and CP stones. There were also significant relationships of papillary crater with hypercalciuria (p = 0.036) and hyperoxaluria (p = 0.024), and of Randall's plaque with hypocitraturia (p = 0.005). CONCLUSIONS: There are certain specific relationships between the different types of papillary calcifications that were endoscopically detected with stone chemistry and urine analysis. COD and CP stones were associated with endoscopic tubular calcifications and papillary craters. Hypercalciuria was associated with tubular calcification, and hypocitraturia was associated with Randall's plaque.

Fatty acid-binding protein 4 downregulation drives calcification in the development of kidney stone disease.

Nephrolithiasis is a significant source of morbidity, and its incidence has increased significantly over the last decades. This rise has been attributed to concurrent increasing rates of obesity, associated with a 3-time risk of developing NL. To date, the mechanism by which obesity is linked to stone formation has not been elucidated. We aimed to utilize a transcriptomics approach to discover the missing link between these two epidemic diseases. We investigated gene expression profiling of nephrolithiasis patients by two RNA-sequencing approaches: comparison between renal papilla tissue with and without the presence of calcified Randall's plaques (RP), and comparison between the papilla, medulla, and cortex regions from within a single recurrent stone forming kidney. Results were overlaid between differently expressed genes found in the patient cohort and in the severely lithogenic kidney to identify common genes. Overlay of these two RNA-sequencing datasets demonstrated there is impairment of lipid metabolism in renal papilla tissue containing RP linked to downregulation of fatty acid binding protein (FABP) 4. Immunohistochemistry of human kidney specimens and microarray analysis of renal tissue from a nephrolithiasis mouse model confirmed that FABP4 downregulation is associated with renal stone formation. In a FABP4 knockout mouse model, FABP4 deficiency resulted in development of both renal and urinary crystals. Our study revealed that FABP4 plays an important, previously unrecognized role in kidney stone formation, providing a feasible mechanism to explain the link between nephrolithiasis and metabolic syndrome.

Osteogenic Differentiation of Renal Interstitial Fibroblasts Promoted by lncRNA MALAT1 May Partially Contribute to Randall's Plaque Formation.

BACKGROUND: The current belief is that Randall's plaques (RP) constitute a nidus for the formation of idiopathic calcium oxalate stones, but the upstream events in RP formation remain unclear. The present study aimed to investigate whether RP formation shares similarities with biomineralization and to illustrate the potential role played by the lncRNA MALAT1 in osteogenic differentiation of human renal interstitial fibroblasts (hRIFs). MATERIALS AND METHODS: Biomineralization and MALAT1 expression were assessed in RP, and hRIFs were isolated and induced under osteogenic conditions for further experiments. The transcription initiation and termination sites in MALAT1 were identified by 5' and 3' RACE. RNA immunoprecipitation assays and luciferase assays were used to validate the interactions among MALAT1, Runx2 and miRNAs. RESULTS: Upregulated expression of osteogenic markers and MALAT1 was observed in RP and hRIFs induced with osteogenic medium. Biomineralization in RP and calcium phosphate (CaP) deposits in induced hRIFs were further verified by electron microscopy. Furthermore, overexpression of MALAT1 promoted the osteogenic phenotype of hRIFs, while treatment with a miR-320a-5p mimic and knockdown of Runx2 significantly suppressed the osteogenic phenotype. Further analysis showed that MALAT1 functioned as a competing endogenous RNA to sponge miR-320a-5p, leading to upregulation of Runx2 and thus promoting osteogenic differentiation of hRIFs. CONCLUSION: Ectopic calcification and MALAT1 partially contributed to the formation of RP, in which MALAT1 might promote Runx2 expression to regulate osteogenic differentiation of hRIFs by sponging miRNA-320a-5p. The current study sheds new light on the lncRNA-directed mechanism of RP formation via a process driven by osteogenic-like cells.

Discrepancy Between Stone and Tissue Mineral Type in Patients with Idiopathic Uric Acid Stones.

Objectives: To describe the papillary pathology found in uric acid (UA) stone formers, and to investigate the mineral form of tissue deposits. Materials and Methods: We studied eight UA stone formers treated with percutaneous nephrolithotomy. Papillae were imaged intraoperatively using digital endoscopy, and cortical and papillary biopsies were taken. Biopsies were analyzed by light microscopy, micro-CT, and microinfrared spectroscopy. Results: As expected, urine pH was generally low. UA supersaturation exceeded one in all but one case, compatible with the stone material. By intraoperative imaging, the renal papillae displayed a heterogeneous mixture of plaque and plugging, ranging from normal to severe. All patients had mineral in ducts of Bellini and inner medullary collecting ducts, mainly apatite with lesser amounts of urate and/or calcium oxalate in some specimens. Papillary and cortical interstitial tissue injury was modest despite the tubule plugging. No instance was found of a stone growing attached to either plaque or plugs. Conclusions: UA stone formers resemble those with ileostomy in having rather low urine pH while forming tubule plugs that contain crystals that can only form at pH values above those of their bulk urine. This discrepancy between tissue mineral deposits and stone type suggests that local tubular pH exceeds that of the bulk urine, perhaps because of localized tubule injury. The manner in which UA stones form and the discordance between tubule crystals and stone type remain open research questions.

Research advance in Randall plaque of kindey stone / 中南大学学报(医学版)

Urinary calculi are characterized by high incidence and recurrence rate, which is a challenge in urology. The theory of Randall plaque is widely recognized by scholars. The mechanism of Randall plaque formation includes vascular calcification, osteogenic transformation and so on. However, it still lacks a unified theory for the Randall plaque formation. As an important type of non-coding RNA, long non-coding RNA (lncRNA) is closely related to the occurrence and progress of many diseases. The difference in lncRNA expression between the renal papillary tissues of non-calculous patients and the renal papillary tissues of Randall plaque in renal calculous patients suggests that lncRNA may be involved in the formation of Randall plaque. Pseudoxanthoma elasticum is a rare autosomal recessive hereditary disease, caused by a mutation in the ABCC6 gene. Patients with pseudoxanthoma elasticum have a high prevalence of calculi, and plaque formation is observed in the patient's kidney, which may suggest that mutation in the ABCC6 gene might be involved in the formation of Randall plaque.

Pseudoxanthoma Elasticum, Kidney Stones and Pyrophosphate: From a Rare Disease to Urolithiasis and Vascular Calcifications.

Pseudoxanthoma elasticum is a rare disease mainly due to ABCC6 gene mutations and characterized by ectopic biomineralization and fragmentation of elastic fibers resulting in skin, cardiovascular and retinal calcifications. It has been recently described that pyrophosphate (a calcification inhibitor) deficiency could be the main cause of ectopic calcifications in this disease and in other genetic disorders associated to mutations of ENPP1 or CD73. Patients affected by Pseudoxanthoma Elasticum seem also prone to develop kidney stones originating from papillary calcifications named Randall's plaque, and to a lesser extent may be affected by nephrocalcinosis. In this narrative review, we summarize some recent discoveries relative to the pathophysiology of this mendelian disease responsible for both cardiovascular and renal papillary calcifications, and we discuss the potential implications of pyrophosphate deficiency as a promoter of vascular calcifications in kidney stone formers and in patients affected by chronic kidney disease.

Urinary extracellular vesicle-associated MCP-1 and NGAL derived from specific nephron segments differ between calcium oxalate stone formers and controls.

Randall's plaque (RP; subepithelial calcification) appears to be an important precursor of kidney stone disease. However, RP cannot be noninvasively detected. The present study investigated candidate biomarkers associated with extracellular vesicles (EVs) in the urine of calcium stone formers (CSFs) with low (<5% papillary surface area) and high (≥5% papillary surface area) percentages of RP and a group of nonstone formers. RPs were quantitated via videotaping and image processing in consecutive CSFs undergoing percutaneous surgery for stone removal. Urinary EVs derived from cells of different nephron segments of CSFs (n = 64) and nonstone formers (n = 40) were quantified in biobanked cell-free urine by standardized and validated digital flow cytometer using fluorophore-conjugated antibodies. Overall, the number of EVs carrying surface monocyte chemoattractant protein (MCP)-1 and neutrophil gelatinase-associated lipocalin (NGAL) were significantly lower in CSFs compared with nonstone former controls (P < 0.05) but did not differ statistically between CSFs with low and high RPs. The number of EVs associated with osteopontin did not differ between any groups. Thus, EVs carrying MCP-1 and NGAL may directly or indirectly contribute to stone pathogenesis as evidenced by the lower of these populations of EVs in stone formers compared with nonstone formers. Validation of EV-associated MCP-1 and NGAL as noninvasive biomarkers of kidney stone pathogenesis in larger populations is warranted.

Renal Papillary Mapping and Quantification of Randall's Plaque in Pediatric Calcium Oxalate Stone Formers.

Introduction: Randall's plaque (RP) with attached stones is recognized as a primary mechanism for stone formation in adult calcium oxalate stone formers (CaOx SFs). The role of RP in pediatric stone pathogenesis is unknown, with no reported studies to date. The purpose of this study is to investigate renal papillary abnormalities and quantify RP in pediatric CaOx SFs. Methods: Eight pediatric CaOx SFs underwent ureteroscopy for symptomatic urolithiasis. The collecting system was mapped using a digital ureteroscope. Video for each patient was then reviewed using a retrograde pyelogram to confirm the location of each papilla. A single investigator (N.L.M.) reviewed the video to quantify RP. Each papilla was graded as having mild, moderate, or severe amount of RP. Patient history was recorded. Results: An average of nine papillae were mapped per patient. RP was present in 100% of patients and in 88.8% (64/72) of all papillae examined. When present, RP was uniformly distributed throughout the kidney without preferential distribution to a region or pole. The amount of RP on the papillae was graded as mild in 60%, moderate in 20.8%, and severe in 8.3%. The mean fractional RP coverage ranged from 0.39% to 9.34%. No correlation was found between the amount of plaque and age at first stone episode or number of prior stone episodes (p = 0.84). Attached stones were rare (1/8 patients). The two patients with severe RP had a small amount of calcium phosphate in their stone analysis. Conclusions: RP is common in pediatric CaOx SFs. Compared with adult CaOx SFs wherein up to 75% of stones are found attached to RP, attached stones were rare. The significance of these findings in the pathogenesis of pediatric stone formation remains unclear and will require longer term follow-up.

Helper T-cell signaling and inflammatory pathway lead to formation of calcium phosphate but not calcium oxalate stones on Randall's plaques.

OBJECTIVES: To elucidate the difference in the lithogenesis of calcium oxalate and calcium phosphate stones. METHODS: Renal papillary tissues were obtained from 23 idiopathic calcium oxalate and seven calcium phosphate stone patients who had undergone endoscopic lithotripsy. Samples were individually collected from two different regions in each patient: the papillary mucosa containing Randall's plaque and mucosa not containing Randall's plaque. A microarray analysis was carried out on those tissues to compare their gene expression patterns. Furthermore, a causal pathway analysis comparing their differences was carried out. RESULTS: Cluster analysis showed that gene expression profiles of calcium phosphate stone patients markedly differed from those of calcium oxalate stone patients. Disease and function analysis showed that Randall's plaque-containing tissues of calcium phosphate stone-forming patients had significantly higher movement and migration of mononuclear leukocytes, and lower tendency toward infection and lymph node formation than Randall's plaque-containing tissues of calcium oxalate stone formers. Additional pathway analysis showed increased immune cell signaling in calcium phosphate formers, such as the helper T cell 1 and 2 pathways, which was confirmed by their messenger ribonucleic acid expression. CONCLUSIONS: The present results show the upregulation of helper T-cell signaling pathways in Randall's plaque-containing papillae in calcium phosphate, but not in calcium oxalate stone formers. Thus, helper T-cell immune responses and the related inflammatory processes seem to lead to the formation of calcium phosphate stones on Randall's plaques.