Lieske, John C.

This retrospective analysis investigated plasma oxalate (POx) as a potential predictor of end-stage kidney disease (ESKD) among primary hyperoxaluria (PH) patients. PH patients with type 1, 2, and 3, age 2 or older, were identified in the Rare Kidney Stone Consortium (RKSC) PH Registry. Since POx increased with falling estimated glomerular filtration rate (eGFR), patients were stratified by chronic kidney disease (CKD) subgroups (stages 1, 2, 3a, and 3b). POx values were categorized into quartiles for analysis. Hazard ratios (HRs) and 95% confidence intervals (95% CIs) for risk of ESKD were estimated using the Cox proportional hazards model with a time-dependent covariate. There were 118 patients in the CKD1 group (nine ESKD events during follow-up), 135 in the CKD 2 (29 events), 72 in CKD3a (34 events), and 45 patients in CKD 3b (31 events). During follow-up, POx Q4 was a significant predictor of ESKD compared to Q1 across CKD2 (HR 14.2, 95% CI 1.8–115), 3a (HR 13.7, 95% CI 3.0–62), and 3b stages (HR 5.2, 95% CI 1.1–25), p < 0.05 for all. Within each POx quartile, the ESKD rate was higher in Q4 compared to Q1–Q3. In conclusion, among patients with PH, higher POx concentration was a risk factor for ESKD, particularly in advanced CKD stages.

Anoctamins typically function as Ca 2+ activated Cl − channels (CaCC) or as specific, phospholipid scramblases. GWAS of miniature schnauzers (>40% with recurrent calcium oxalate (CaOx) kidney stones) revealed a risk locus including an anoctamin 4 (ANO4) variant. ANO4 in mammals was initially reported as a phosphatidylserine (PS) scramblase. Urinary extracellular vesicles (EV) show decreased ANO4 protein in human stone formers. However, in Drosophila renal structures (Malpighian tubules, MTs), subdued (the ANO4‐homolog), functions as both a CaCC and scramblase. Since subdued also functions to defend against gram‐negative bacteria, it was knocked down to determine whether CaOx crystals were altered by bacterial infection. Subdued was knockdown (KD) in MT principle cells by crossing Uro:Gal4 flies with UAS: subdued ‐RNAi flies. F1‐flies were evaluated using CaOx crystallization in dissected MTs as well as after 4d NaOx feeding protocols. To evaluate infection, uropathic E. coli (UPEC):eGFP were fed to flies or added to NaOx solution before an overnight time‐lapse. Interestingly, the canine ANO4 variant has a 0.01 allele variant frequency at a residue conserved in humans, canines and Drosophila . Rapid crystallization experiments show that MTs with subdued‐KD have fewer CaOx crystals than control MTs. However, prolonged NaOx feeding assays showed that subdued‐KD in MTs produces enlarged CaOx crystals. These feeding assays also showed an unexpected phenotype: crystal clustering and matting structures (e.g., bacterial biofilms). These structures have similar patterning to human kidney stones [Sivaguru et al., PMID: 30213974]. Following a four day feeding of NaOx, when UPEC + NaOx is introduced overnight ( ex vivo ), a three hour bacterial event occurs, causing crystals to more tightly pack. Finally, when UPEC is introduced during a rapid crystallization experiment, the bacteria heavily localize in subdued‐KD MT lumens while control MTs have little eGFP‐fluorescence. Thus, UPEC facilitates CaOx crystal aggregates in subdued‐KD MTs while the nature of this interaction is unknown. In human kidney, ANO4 localizes in thick ascending limb (NKCC2 + ), while in murine kidney localizes more proximal in the Loop of Henle (UMOD + ). As mice are resistant to CaOx stones, these slight location differences may reveal altered TAL function by ANO4. This Drosophila avatar indicates that subdued (ANO4) normally limits CaOx crystal aggregation and limits UPEC growth. As an apparent pathogenic amino acid is conserved in mammals and flies; subdued’ s role in fly bacterial infection suggests an additional ANO4 role in human kidney stone formation. These results indicate that examining antibacterial treatments with UPEC infection may allow an antibiotic approach to more efficiently eliminate kidney stones. Future experiments determine what functional aspect of subdued alters CaOx crystallization. Moreover, this simple kidney stone avatar‐the fly – continues to provide new and mechanistic insights to CaOx stone formation. Support or Funding Information Support: Oxalosis & Hyperoxaluria Foundation, R25‐DK101405, Mayo Foundation Drosophila MT (Uro:Gal4 x UAS‐ subdued ‐RNAi) viewed with (A) DIC for CaOx birefringence, (B) fluorescence to visualize UPEC:eGFP and (C) merged to show coincidence of UPEC with CaOx crystals. The red line indicates the length of the CaOx/UPEC mass. This is not observed in control MTs. Figure 1

By sequencing autozygous human populations, we identified a healthy adult woman with lifelong complete knockout of HAO1 (expected ~1 in 30 million outbred people). HAO1 (glycolate oxidase) silencing is the mechanism of lumasiran, an investigational RNA interference therapeutic for primary hyperoxaluria type 1. Her plasma glycolate levels were 12 times, and urinary glycolate 6 times, the upper limit of normal observed in healthy reference individuals (n = 67). Plasma metabolomics and lipidomics (1871 biochemicals) revealed 18 markedly elevated biochemicals (>5 sd outliers versus n = 25 controls) suggesting additional HAO1 effects. Comparison with lumasiran preclinical and clinical trial data suggested she has <2% residual glycolate oxidase activity. Cell line p.Leu333SerfsTer4 expression showed markedly reduced HAO1 protein levels and cellular protein mis-localisation. In this woman, lifelong HAO1 knockout is safe and without clinical phenotype, de-risking a therapeutic approach and informing therapeutic mechanisms. Unlocking evidence from the diversity of human genetic variation can facilitate drug development.

Patients with primary hyperoxaluria experience kidney stones from a young age and can develop progressive oxalate nephropathy. Progression to kidney failure often develops over a number of years, and is associated with systemic oxalosis, intensive dialysis, and often combined kidney and liver transplantation. There are no therapies approved by the Food and Drug Association. Thus, the Kidney Health Initiative, in partnership with the Oxalosis and Hyperoxaluria Foundation, initiated a project to identify end points for clinical trials. A workgroup of physicians, scientists, patients with primary hyperoxaluria, industry, and United States regulators critically examined the published literature for clinical outcomes and potential surrogate end points that could be used to evaluate new treatments. Kidney stones, change in eGFR, urine oxalate, and plasma oxalate were the strongest candidate end points. Kidney stones affect how patients with primary hyperoxaluria feel and function, but standards for measurement and monitoring are lacking. Primary hyperoxaluria registry data suggest that eGFR decline in most patients is gradual, but can be unpredictable. Epidemiologic data show a strong relationship between urine oxalate and long-term kidney function loss. Urine oxalate is reasonably likely to predict clinical benefit, due to its causal role in stone formation and kidney damage in CKD stages 1–3a, and plasma oxalate is likely associated with risk of systemic oxalosis in CKD 3b–5. Change in slope of eGFR could be considered the equivalent of a clinically meaningful end point in support of traditional approval. A substantial change in urine oxalate as a surrogate end point could support traditional approval in patients with primary hyperoxaluria type 1 and CKD stages 1–3a. A substantial change in markedly elevated plasma oxalate could support accelerated approval in patients with primary hyperoxaluria and CKD stages 3b–5. Primary hyperoxaluria type 1 accounts for the preponderance of available data, thus heavily influences the conclusions. Addressing gaps in data will further facilitate testing of promising new treatments, accelerating improved outcomes for patients with primary hyperoxaluria.

Purpose: Cystinuria is a genetic disorder with both autosomal recessive and incompletely dominant inheritance. The disorder disrupts cystine and other dibasic amino acid transport in proximal tubules of the kidney, resulting in recurrent kidney stone formation. Currently, there are no consensus guidelines on evaluation and management of this disease. This article represents the consensus of the author panel and will provide clinicians with a stepwise framework for evaluation and clinical management of patients with cystinuria based on evidence in the existing literature. Materials and Methods: A search of MEDLINE ® /PubMed ® and Cochrane databases was performed using the following key words: “cystine nephrolithiasis,” “cystinuria,” “penicillamine, cystine,” and “tiopronin, cystine.” In total, as of May 2018, these searches yielded 2335 articles, which were then evaluated for their relevance to the topic of evaluation and management of cystinuria. Evidence was evaluated by the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) system. Results: Twenty-five articles on the topic of cystinuria or cystine nephrolithiasis were deemed suitable for inclusion in this study. The literature supports a logical evaluation process and step-wise treatment approach beginning with conservative measures: fluid intake and dietary modification. If stone formation recurs, proceed to pharmacotherapeutic options by first alkalinizing the urine and then using cystine-binding thiol drugs. Conclusions: The proposed clinical pathways provide a framework for efficient evaluation and treatment of patients with cystinuria, which should improve overall outcomes of this rare, but highly recurrent, form of nephrolithiasis.

Kidney stones are a common urologic condition with a high amount of recurrence. Recurrence depends on a multitude of factors the incidence of precursors to kidney stones, plugs, and plaques. One method of characterising the stone precursors is endoscopic assessment, though it is manual and time‐consuming. Deep learning has become a popular technique for semantic segmentation because of the high accuracy that has been demonstrated. The present Letter examined the efficacy of deep learning to segment the renal papilla, plaque, and plugs. A U‐Net model with ResNet‐34 encoder was tested; the Letter examined dropout (to avoid overtraining) and two different loss functions (to address the class imbalance problem. The models were then trained in 1666 images and tested on 185 images. The Jaccard‐cross‐entropy loss function was more effective than the focal loss function. The model with the dropout rate 0.4 was found to be more effective due to its generalisability. The model was largely successful at delineating the papilla. The model was able to correctly detect the plaques and plugs; however, small plaques were challenging. Deep learning was found to be applicable for segmentation of an endoscopic image for the papilla, plaque, and plug, with room for improvement.

AbstractThis review examines calcium and phosphate transport in the kidney through the lens of the rare X‐linked genetic disorder Dent disease. Dent disease type 1 (DD1) is caused by mutations in the CLCN5 gene encoding ClC‐5, a Cl−/H+ antiporter localized to early endosomes of the proximal tubule (PT). Phenotypic features commonly include low molecular weight proteinuria (LMWP), hypercalciuria, focal global sclerosis and chronic kidney disease; calcium nephrolithiasis, nephrocalcinosis and hypophosphatemic rickets are less commonly observed. Although it is not surprising that abnormal endosomal function and recycling in the PT could result in LMWP, it is less clear how ClC‐5 dysfunction disturbs calcium and phosphate metabolism. It is known that the majority of calcium and phosphate transport occurs in PT cells, and PT endocytosis is essential for calcium and phosphorus reabsorption in this nephron segment. Evidence from ClC‐5 KO models suggests that ClC‐5 mediates parathormone endocytosis from tubular fluid. In addition, ClC‐5 dysfunction alters expression of the sodium/proton exchanger NHE3 on the PT apical surface thus altering transcellular sodium movement and hence paracellular calcium reabsorption. A potential role for NHE3 dysfunction in the DD1 phenotype has never been investigated, either in DD models or in patients with DD1, even though patients with DD1 exhibit renal sodium and potassium wasting, especially when exposed to even a low dose of thiazide diuretic. Thus, insights from the rare disease DD1 may inform possible underlying mechanisms for the phenotype of hypercalciuria and idiopathic calcium stones.

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.