Is calcium oxalate nucleation in postprandial urine of males with idiopathic recurrent calcium urolithiasis related to calcium phosphate nucleation and the intensity of stone formation? Studies allowing insight into a possible role of urinary free citrate and protein

Sex-specific Stone-forming Phenotype in Mice During Hypercalciuria/Urine Alkalinization

Sex differences in kidney stone formation are well known. Females generally have slightly acidic blood and higher urine pH when compared with males, which makes them more vulnerable to calcium stone formation, yet the mechanism is still unclear. We aimed to examine the role of sex in stone formation during hypercalciuria and urine alkalinization through acetazolamide and calcium gluconate supplementation, respectively, for 4 weeks in wild-type (WT) and moderately hypercalciuric [TRPC3 knockout [KO](-/-)] male and female mice. Our goal was to develop calcium phosphate (CaP) and CaP+ calcium oxalate mixed stones in our animal model to understand the underlying sex-based mechanism of calcium nephrolithiasis. Our results from the analyses of mice urine, serum, and kidney tissues show that female mice (WT and KO) produce more urinary CaP crystals, higher [Ca2+], and pH in urine compared to their male counterparts. We identified a sex-based relationship of stone-forming phenotypes (types of stones) in our mice model following urine alkalization/calcium supplementation, and our findings suggest that female mice are more susceptible to CaP stones under those conditions. Calcification and fibrotic and inflammatory markers were elevated in treated female mice compared with their male counterparts, and more so in TRPC3 KO mice compared with their WT counterparts. Together these findings contribute to a mechanistic understanding of sex-influenced CaP and mixed stone formation that can be used as a basis for determining the factors in sex-related clinical studies.

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.

Melamine promotes calcium crystal formation in three-dimensional microfluidic device

Melamine, which induces proximal tubular (PT) cell damage has a greater nephrotoxic effect when combined with cyanuric and uric acids; however, it is unknown whether such effect can stimulate calcium phosphate (CaP)/calcium oxalate (CaOx) stone formation. Here, we show that melamine acts as an inducer of CaP, CaOx and CaP + CaOx (mixed) crystal formations in a time and concentration-dependent manner by stabilizing those crystals and further co-aggregating with melamine. To explore the physiological relevance of such melamine-augmented calcium crystal formation, we used 2-dimensional (2D) and 3D microfluidic (MF) device, embedded with PT cells, which also resembled the effect of melamine-stimulated CaP, CaOx and mixed crystal formation. Significantly, addition of preformed CaP and/or CaOx crystal in the presence of melamine, further potentiated those crystal formations in 3D MFs, which helped the growth and aggregation of mixed crystals. Our data show that the mechanism of such predisposition of stone formation could be largely due to co-crystallization between melamine and CaP/CaOx and pronounced effect on induction of stone-forming pathway activation in 3D MF. Taken together, melamine-induced CaP and/or CaOx crystal formation ex-vivo will help us in understanding the larger role of melamine as an environmental toxicant in producing the pathology in similar cellular microenvironments.

Comparative Analysis of Compositions between Calcium Phosphate Calculi and Urinary Crystallites in the Stone-Formers

The chemical composition of urinary crystallites of less than 1000 nm from 10 calcium phosphate (CaP) stone-formers were investigated and compared with that from healthy subjects using X-ray power diffraction, Fourier transform infrared spectroscopy and nanoparticle size analyzer. Although there were some calcium oxalate monohydrate (COM) crystals in CaP stones, the main components of crystallites in urine of CaP stone formers were uric acid (UA), CaP and COM, while that in healthy urine was mainly UA and a small amount of COM. That is, the CaP content in urinary crystallites of CaP stone-formers was significantly higher than that of controls. The particle size range of crystallites in lithogenic urine was 3~1000 nm and most of these crystallites were aggregated, but it was 30~500 nm in healthy subjects.

Biochemical determinants of severe lithogenic activity in patients with idiopathic calcium nephrolithiasis

OBJECTIVE

To analyze the biochemical alterations in plasma and the urine determinants of severe lithogenic activity in patients with idiopathic calcium nephrolithiasis.

METHODS

We performed a cross-sectional study of 120 patients divided into 2 groups: group 1, 60 patients without nephrolithiasis; and group 2, 60 patients with severe and/or recurrent calcium nephrolithiasis. In all patients, a study of renal function, calcium metabolism, and bone remodeling markers, and a study of the lithogenic factors were performed in urine after fasting and in 24-hour urine samples.

RESULTS

We observed greater values for phosphorus in group 1 than in group 2 (P=.03). Also, we found greater values for intact parathyroid hormone (P=.01), osteocalcin (P=.000), and β-crosslaps (P=.000) in group 2 than in group 1. In the 24-hour urine samples, significant differences were found between groups 1 and 2 in calciuria (11.7 vs 17.4 mg/dL; P=.000), citraturia (50.6 vs 33.5 mg/dL; P=.002), calcium/creatinine quotient (0.14 vs 0.20; P=.001), calcium/citrate quotient (0.05 vs 0.13; P=.04), and calcium/creatinine quotient after fasting (0.09 vs 0.16; P=.000).

CONCLUSION

We consider the determinants of severe and/or recurrent calcium lithiasis to be hypercalciuria and hypocitraturia and a calcium/citrate quotient>0.06. As risk markers we can consider phosphatemia<2.9 mg/dL, phosphate/chlorine quotient>35, alkaline phosphatase>80 U/L, intact parathyroid hormone>60 pg/mL, osteocalcin>16 ng/mL, β-crosslaps>0.400 ng/mL, and β-crosslaps/osteocalcin quotient>0.028.

Idiopathic Recurrent Calcium Urolithiasis (IRCU): pathophysiology evaluated in light of oxidative metabolism, without and with variation of several biomarkers in fasting urine and plasma--a comparison of stone-free and -bearing male patients, emphasizing mineral, acid-base, blood pressure and protein status

BACKGROUND

IRCU is traditionally considered as life?style disease (associations with, among others, overweight, obesity, hypertension, type-2 diabetes), arising from excess, in 24 h urine, of calcium (Ca) salts (calcium oxalate (CaOx), calcium phosphate (CaPi)), supersaturation of, and crystallization in, tubular fluid and urine, causing crystal-induced epithelial cell damage, proteinuria, crystal aggregation and uroliths.

METHODS

Another picture emerges from the present uncontrolled study of 154 male adult IRCU patients (75 stone-bearing (SB) and 79 age-matched stone-free (SF)), in whom stone-forming and other parameters in fasting urine and plasma were contrasted with five biomarkers (see footnote) of oxidative metabolism (OM), without and with variation of markers.

RESULTS

1) In SB vs. SF unstratified OM biomarkers were statistically unchanged, but the majority of patients was overweight; despite, in SB vs. SF urine pH, total and non-albumin protein concentration were elevated, fractional urinary uric acid excretion and blood bicarbonate decreased, whereas urine volume, sodium, supersaturation with CaOx and CaPi (as hydroxyapatite) were unchanged; 2) upon variation of OM markers (strata below and above median) numerous stone parameters differed significantly, among others urine volume, total protein, Ca/Pi ratio, pH, sodium, potassium, plasma Ca/Pi ratio and parathyroid hormone, blood pressure, renal excretion of non-albumin protein and other substances; 3) a significant shift from SF to SB patients occurred with increase of urine pH, decrease of blood bicarbonate, and increase of diastolic blood pressure, whereas increase of plasma uric acid impacted only marginally; 4) in both SF and SB patients a strong curvilinear relationship links a rise of urine Ca/Pi to urine Ca/Pi divided by plasma Ca/Pi, but in SB urine Ca/Pi failed to correlate significantly with urine hydroxyapatite supersaturation; 5) also in SB, plasma Ca/Pi and urinary nitrate were negatively correlated, whereas in SF plasma Ca/Pi ratio, PTH and body mass index correlated positively; 6) multivariate regression analysis revealed that PTH, body mass index and nitrate together could explain 22 (p = 0.002) and only 7 (p = 0.06) per cent of variation of plasma Ca/Pi in SF and SB, respectively.

CONCLUSIONS

In IRCU a) numerous constituents of fasting urine, plasma, blood and blood pressure change in response to variation of OM biomarkers, suggesting involvement of OM imbalance as factor in functional deterioration of tissue; b) in the majority of patients a positive exponential relationship links urine Ca/Pi to urine Ca/Pi divided by plasma Ca/Pi, presumably to accumulate Ca outside tubular lumen, thereby minimizing intratubular and urinary Ca salt crystallization; c) alteration of interactions of low urine nitrate, PTH and Ca/Pi in plasma may be of importance in formation of new Ca stone and co-regulation of dynamics of blood vasculature; d) overweight, combined with OM-modified renal interstitial environment appears to facilitate these processes, carrying the risk that CaPi mineral develops within or/and close to blood vessel tissue, and spreads towards urothelium. - For future research focussing on IRCU pathogenesis studies are recommended on the role of affluent lifestyle mediated renal ischemia, mild hypertensive nephropathy, rise of uric acid precursor oxypurines and uricemia, clarifying also why loss of significance of interrelationships of OM biomarkers with traditional Ca stone risk factors is characteristic for SB patients.

Idiopathic recurrent calcium urolithiasis (IRCU): variation of fasting urinary protein is a window to pathophysiology or simple consequence of renal stones in situ? A tripartite study in male patients providing insight into oxidative metabolism as possible driving force towards alteration of urine composition, calcium salt crystallization and stone formation

Background

In IRCU it is uncertain whether variation of urinary protein, especially non-albumin protein (NAlb-P), is due to the presence of stones or reflects alteration of oxidative metabolism.

Aims

To validate in a tripartite cross-sectional study of 187 ambulatory male patients, undergoing a standardized laboratory programme, whether stones impact on N-Alb-P or the state of oxidative metabolism interferes with IRCU pathophysiology.

Methods

In part 1 the strata low and high of fasting urinary excretion rate per 2 h of N-Alb-P, malonedialdehyde, hypoxanthine, xanthine, pH and other urine components were compared, and association with renal stones in situ evaluated; in part 2 the co-variation of oxidatively modulated environment, fasting urinary pH, calcium (Ca) salt crystallization risk and the number of patients with stones in situ was examined; in part 3, the nucleation of Ca oxalate and Ca phosphate was tested in undiluted postprandial urine of patients and related to the state of oxidative metabolism.

Results

In part 1, N-Alb-P excretion > 4.3 mg was associated with increase of blood pressure, excretion of total protein, hypoxanthine (a marker of tissue hypoxia), malonedialdehyde (a marker of lipid peroxidation), sodium, magnesium, citrate, uric acid, volume, pH, and increase of renal fractional excretion of both NAlb-P and uric acid; when stones were present, urinary pH was elevated but other parameters were unaffected. Significant predictors of N-Alb-P excretion were malonedialdehyde, fractional N-Alb-P and hypoxanthine. In part 2, urine pH > 6.14 was associated with unchanged blood pressure and plasma vasopressin, increase of blood pH, urinary volume, malonedialde hyde, fractional excretion of N-Alb-P, uric acid, Ca phosphate, but not Ca oxalate, supersaturation; this spectrum was accompanied by decrease of concentration of urinary total and free magnesium, total and complexed citrate, plasma uric acid (in humans the major circulating antioxidant) and insulin; the number of stone-bearing patients was increased. Significant predictors of urine pH were body mass index, plasma insulin and uric acid (negative), and urinary xanthine (positive). In part 3 low plasma uric acid, not high urinary malonedialdehyde or high ratio malonedialdehyde/uric acid was significantly associated with diminished Ca but not oxalate tolerance, with the first nucleating crystal type being mostly Ca phosphate (hydroxyapatite), in the rest Ca oxalate dihydrate; uricemia correlated marginally positively (p = 0.055) with Ca tolerance of urine, stronger with blood pressure and insulin, and negatively with urinary xanthine, fractional N-Alb-P, volume, sodium.

Conclusions

In IRCU 1) not renal stones in situ, but disturbed oxidative metabolism apparently modulates nephron functionality, ending up in higher renal NAlb-P release, urinary volume, sodium and pH of fasting urine; 2) etiologically unknown decline of uricemia may represent antioxidant deficiency and cause a risk of hydroxyapatite crystallization and stone formation in a weakly acidic or alkaline inhibitor-deficient and NAlb-P-rich milieu; 3) several observations, linking oxidative and systemic metabolism, are compatible with Ca stone initiation beyond tubules.

Urinary phosphorus rather than urinary calcium possibly increases renal stone formation in a sample of Asian Indian, male stone-formers

The contribution of dietary Ca and P in renal stone formation is debated. Thus, the main objective was to investigate if there were any differences in the dietary, serum and urine values of Ca and P in stone formers (SF) compared with healthy controls (HC). The secondary aim was to analyse if dietary, serum and urine Ca and P correlated. The study enrolled ten patients with renal stones admitted for stone removal and ten healthy controls. Their dietary macronutrients, Ca and P intakes were calculated from 2-d dietary records. On the second day of dietary record 24-h urine was collected and on the third day morning a 5 ml blood sample was collected. Biochemical analyses were conducted for serum and urine Ca, P and uric acid with qualitative renal stone analysis. All the dietary intakes and urine P were significantly higher (P < 0·05) in SF than in HC. Correlation results showed that in SF dietary Ca correlated to serum and urine Ca. No such correlations were seen for P. Additionally, in SF urine Ca correlated to dietary proteins and fats but not to carbohydrates. None of the biochemical values lay outside the normal range of values. The study suggests urine P rather than urine Ca to be probably at work in the formation of renal stones. Limitation of protein intake with normal Ca intakes could provide a suitable measure to avoid renal stone formation.