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.

Background Overgrowth of calcium oxalate on Randall's plaque is a mechanism of stone formation among idiopathic calcium oxalate stone-formers (ICSFs). It is less clear how stones form when there is little or no plaque.Design, setting, participants, & measurements Participants were a consecutive cohort of ICSFs who underwent percutaneous nephroscopic papillary mapping in the kidney or kidneys containing symptomatic stones and a papillary tip biopsy from a representative calyx during a stone removal procedure between 2009 and 2013. The distribution of Randall's plaque coverage was analyzed and used to divide ICSFs into those with a high ($5%; mean, 10.5%; n=10) versus low (,5%; mean, 1.5%; n=32) amount of plaque coverage per papilla. Demographic and laboratory features were compared between these two groups.Results Low-plaque stone formers tended to be obese (50% versus 10%; P=0.03) and have a history of urinary tract infection (34% versus 0%; P=0.04). They were less likely to have multiple prior stone events (22% versus 80%; P=0.002) and had a lower mean 24-hour urine calcium excretion (187686 mg versus 291699 mg; P,0.01). Morphologically, stones from patients with low amounts of plaque lacked a calcium phosphate core by microcomputed tomography. Papillary biopsies from low plaque stone-formers revealed less interstitial and basement membrane punctate crystallization.Conclusions These findings suggest that other pathways independent of Randall's plaque may contribute to stone pathogenesis among a subgroup of ICSFs who harbor low amounts of plaque.

Background and objectives Kidney stones and their risk factors aggregate in families, yet few studies have systematically estimated heritabilities and genetic correlations of the numerous urinary traits associated with risk of kidney stones.Design, setting, participants, & measurements Twenty-four-hour urine samples were collected from the Genetic Epidemiology Network of Arteriopathy cohort of families in Rochester, Minnesota, to measure urinary determinants of supersaturation. Diet was assessed using the Viocare food frequency questionnaire. Heritabilities and genetic correlations among the urinary traits were estimated using variance components methods.Results Samples were available from 811 individuals (344 men, 467 women; mean age 6669 years). Age, sex, and weight were significantly correlated with the majority of urinary traits. Many urine excretions (calcium, magnesium, citrate excretion) had strong evidence for heritability (P,0.01) both before and after adjusting for the identified covariates. Among significantly heritable urinary traits, genetic factors explained 20%-36% of interindividual variation after adjustment for covariates. Urinary calcium excretion was significantly genetically correlated with urinary magnesium and with urinary citrate excretion (P,0.05). Although eGFR influenced many urinary traits, controlling for eGFR did not greatly affect estimated heritabilities.Conclusions Evidence from this cohort suggests a strong heritable component to many urinary nephrolithiasis risk factors. Further study of genetic influences on urinary traits relevant for kidney stone pathogenesis is warranted.Clin J Am Soc Nephrol 9: 943-950, 2014.

Alkaline phosphatase (ALP) is an enzyme critical for physiological and pathological biomineralization. Experiments were designed to determine if ALP participates in formation of calcifying nanometer-sized particles (NPs) in vitro. Filtered homogenates of human calcified carotid artery, aorta and kidney stones were inoculated into cell culture medium containing 10% fetal bovine serum in the absence or presence of inhibitors of ALP or pyrophosphate. Calcific NP biofilm developed within one week after inoculation and their development was reduced by pyrophosphate and inhibitors of ALP. ALP protein and enzymatic activity were detected in washed NPs whether calcified or decalcified. Therefore, ALP activity is required for formation of calcifying NPs in vitro, as has previously been implicated during pathological calcification in vivo.

Background Kidney stones and their risk factors aggregate in families, yet few studies have estimated the heritability of known risk factors. Objective Estimate the heritability of dietary risk factors for kidney stones. Methods Dietary intakes were assessed using the Viocare Food Frequency Questionnaire in sibships enrolled in the Rochester, MN cohort of the Genetic Epidemiology Network of Arteriopathy. Measures of urinary supersaturation were determined using 24 hr urine samples. Heritabilities and genetic correlations were estimated using variance components methods. Results Samples were available from 620 individuals (262 men, 358 women, mean (SD) age 65(9) years). Dietary intakes of protein, sucrose, and calcium had strong evidence for heritability (p<0.01) after adjustment for age, sex, height and weight. Among the significantly heritable dietary intakes (p<0.05), genetic factors explained 22-50% of the inter-individual variation. Significant genetic correlations were observed among dietary protein, dietary sucrose, and dietary calcium intakes (p<0.001). Conclusions Evidence from this relatively large cohort suggests a strong heritable component to dietary intakes of protein, sucrose and calcium that contributes to nephrolithiasis risk. Further efforts to understand the interplay of genetic and environmental risk factors in kidney stone pathogenesis are warranted.