Serum sclerostin is associated with recurrent kidney stone formation independent of hypercalciuria

Background

Kidney stones are frequent in industrialized countries with a lifetime risk of 10 to 15%. A high percentage of individuals experience recurrence. Calcium-containing stones account for more than 80% of kidney stones. Diet, environmental factors, behavior, and genetic variants contribute to the development of kidney stones. Osteocytes excrete the 21 kDa glycoprotein sclerostin, which inhibits bone formation by osteoblasts. Animal data suggests that sclerostin might directly or indirectly regulate calcium excretion via the kidney. As hypercalciuria is one of the most relevant risk factors for kidney stones, sclerostin might possess pathogenic relevance in nephrolithiasis.

Methods

We performed a prospective cross-sectional observational controlled study in 150 recurrent kidney stone formers (rKSF) to analyse the association of sclerostin with known stone risk factors and important modulators of calcium-phosphate metabolism. Serum sclerostin levels were determined at the first visit. As controls, we used 388 non-stone formers from a large Swiss epidemiological cohort.

Results

Sclerostin was mildly increased in rKSF in comparison to controls. This finding was more pronounced in women compared to men. Logistic regression indicated an association of serum sclerostin with rKSF status. In hypercalciuric individuals, sclerostin levels were not different from normocalciuric patients. In Spearman correlation analysis we found a positive correlation between sclerostin, age, and BMI and a negative correlation with eGFR. There was a weak correlation with iPTH and intact FGF 23. In contrast, serum sclerostin levels were not associated with 25-OH Vitamin D3, 1,25-dihydroxy-Vitamin D3, urinary calcium and phosphate or other urinary lithogenic risk factors.

Conclusion

This is the first prospective controlled study investigating serum sclerostin in rKSF. Sclerostin levels were increased in rKSF independent of hypercalciuria and significantly associated with the status as rKSF. It appears that mechanisms other than hypercalciuria may be involved and thus further studies are required to elucidate underlying pathways.

The Impact of Moderate Hypophosphatemia on the Clinical Management of Primary Hyperparathyroidism

Background and objective The impact of moderate hypophosphatemia (hypoP) on primary hyperparathyroidism (PHPT) and its use as an independent surgical criterion has not been adequately evaluated in the literature. In light of this, we conducted this study to address the scarcity of data on this topic. Methods We conducted a retrospective evaluation of data related to 164 (133 females and 31 males) patients with PHPT who met the criteria for inclusion in the study. HypoP, which is indicated by phosphorus (P) levels lower than 2.5 mg/dL, was found in 78 (47.5%) patients, and moderate hypoP (1-1.99 mg/dL) was found in 25 patients (15.2%). Results PHPT severity was worse in hypoP patients than non-hypoP patients, as evidenced by higher levels of mean serum calcium (12.9 ±1.0 mg/dL vs. 11.1 ±0.3 mg/dL respectively, p<0.001), parathormone (PTH) [median (interquartile range, IQR): 455.3 (455.3) ng/L vs. 124.0 (84.0) ng/L respectively, p<0.001] and mean 24-hour urinary calcium (414.6 ±168.5 mg/day vs. 291.5 ±161.4 mg/day respectively, p=0.026) as well as lower levels of mean BMI (25.6 ±3.9 kg/m2 vs. 29.0 ±4.0 kg/m2 respectively, p=0.18) and mean 25-hydroxy vitamin D3 (13.8 ±7.3 µg/L vs. 18.2 ±7.8 µg/L respectively, p=0.001). Among the whole study population as well as among patients with Ca levels <1.0 mg/dL according to the upper limit of normal, P level was determined to be an independent factor affecting the indication for surgical treatment [β: -1.96,p=0.038, odds ratio (OR): 0.14, 95% confidence interval (CI): 0.02-0.89 and β: -2.3, p=0.034, OR: 0.10, 95% CI: 0.12-0.84 respectively]. Conclusion We found a strong correlation between moderate hypoP and the severity of the biochemical manifestations of PHPT. In asymptomatic PHPT patients, moderate hypoP was predictive of surgical indication, independent of age and level of hypercalcemia.

Unravelling the Complex Relationship between Diet and Nephrolithiasis: The Role of Nutrigenomics and Nutrigenetics

Nephrolithiasis is an increasingly prevalent condition, especially in high income countries, and is associated with high morbidity. Extraordinary progress in genetics made the identification of genetic forms of nephrolithiasis possible. These genetic diseases are usually rare and do not account for the most common forms of nephrolithiasis that are the result of several factors such as environment, dietary habits, and predisposing genes. This knowledge has shaped what we classify as nephrolithiasis, a condition that is now recognized as systemic. How and to what extent all these factors interact with one another and end in kidney stone formation, growth, and recurrence is not completely understood. Two new research fields have recently been trying to give some answers: nutrigenomics and nutrigenetics. These fields have the aim of understanding the intricate diet/genome interface that influences gene expression regulation mainly through epigenetic mechanisms and results in specific medical conditions such as cancer, metabolic syndrome, and cardiovascular diseases. Epigenetics seems to play a crucial role and could represent the link between environmental factors, that we are constantly exposed to, and risk factors for nephrolithiasis. In this systematic review, we summarize all the available evidence of proven or hypothesized epigenetic mechanisms related to nephrolithiasis.

Urinary tetrahydroaldosterone is associated with circulating FGF23 in kidney stone formers

The spectrum of diseases with overactive renin–angiotensin–aldosterone system (RAS) or elevated circulating FGF23 overlaps, but the relationship between aldosterone and FGF23 remains unclarified. Here, we report that systemic RAS activation sensitively assessed by urinary tetrahydroaldosterone excretion is associated with circulating C-terminal FGF23. We performed a retrospective analysis in the Bern Kidney Stone Registry, a single-center observational cohort of kidney stone formers. Urinary excretion of the main aldosterone metabolite tetrahydroaldosterone was measured by gas chromatography–mass spectrometry. Plasma FGF23 concentrations were measured using a C-terminal assay. Regression models were calculated to assess the association of plasma FGF23 with 24 h urinary tetrahydroaldosterone excretion. We included 625 participants in the analysis. Mean age was 47 ± 14 years and 71% were male. Mean estimated GFR was 94 ml/min per 1.73 m². In unadjusted analyses, we found a positive association between plasma FGF23 and 24 h urinary tetrahydroaldosterone excretion (β: 0.0027; p = 4.2 × 10^–7). In multivariable regression models adjusting for age, sex, body mass index and GFR, this association remained robust (β: 0.0022; p = 2.1 × 10^–5). Mineralotropic hormones, 24 h urinary sodium and potassium excretion as surrogates for sodium and potassium intake or antihypertensive drugs did not affect this association. Our data reveal a robust association of RAS activity with circulating FGF23 levels in kidney stone formers. These findings are in line with previous studies in rodents and suggest a physiological link between RAS system activation and FGF23 secretion.

Predictors of Bone Mineral Density in Kidney Stone Formers

Introduction

Nephrolithiasis is associated with an increased fracture risk, but predictors of bone mineral density (BMD) in stone formers (SFs) remain poorly defined.

Methods

We conducted a retrospective analysis in the Bern Kidney Stone Registry (BKSR), an observational cohort of kidney SFs. Inclusion criteria were age ≥18 years and ≥1 past stone episode. Participants with non–calcium (Ca)-containing kidney stones, a history of primary hyperparathyroidism or antiresorptive or anabolic bone treatment were excluded. Multivariable linear regression analyses were used to assess the association of blood and 24-hours urine parameters and stone composition with BMD at the lumbar spine and femoral neck.

Results

In the analysis, 504 participants were included, mean age was 46 years, and 76% were male. In multivariable analyses, fasting (β: −0.031; P = 0.042), postload (β: −0.059; P = 0.0028) and Δ postload − fasting (β: −0.053; P = 0.0029) urine Ca-to-creatinine ratios after 1 week of a sodium- and Ca- restricted diet and Ca oxalate dihydrate stone content (β: −0.042; P = 0.011) were negatively associated with z scores at the lumbar spine. At the femoral neck, alkaline phosphatase (β: −0.035; P = 0.0034) and parathyroid hormone (PTH) (β: −0.035; P = 0.0026) were negatively associated with z scores, whereas 24-hours urine Ca (β: 0.033; P = 0.0085), magnesium (β: 0.043; P = 3.5 × 10⁻⁴), and potassium (β: 0.032; P = 0.012) correlated positively with z scores at the femoral neck.

Conclusion

Our study reveals distinct predictors of BMD in SFs. Commonly available clinical parameters, such as kidney stone composition results, can be used to identify SFs at risk for low BMD.

Effect of Aegle marmelos on the growth of brushite crystals

Background

The urinary stone formation is a very common health problem due to the prolonged medication. Calcium Hydrogen Phosphate Dihydrate (CaHPO4.2H2O, CHPD and Brushite) is one of the major constituent of urinary stone crystals. The formation and deposition of brushite crystals is the central cause of recurrent kidney stone disease among the global population. The present study aims to investigate the effect of Aegle marmelos leaves on the growth of brushite crystals to explicate the inhibitory effect of urinary stones from a different point of view.

Methods

The CHPD crystals were grown by the Single Diffusion Gel growth technique. In order to inhibit the formation of urinary stones, CHPD crystals are grown in the laboratory in the pure form and by adding the prolonged medicine A. marmelos taken especially by diabetic patients. A comparative study of the pure and A. marmelos leaves added crystals has been carried out using the Growth factor, Powder X-ray diffraction, Microstructural parameters, FTIR and SEM-EDAX.

Results

Total mass of the grown crystals is found to decrease with increasing concentrations of leaf extract of the A. marmelos. On comparing with undoped, crystalline size of the A. marmelos doped samples is reduced. Disappearance of absorption band and peak shift in the FTIR shows the incorporation of functional groups of A. marmelos. The morphology changes of the treated crystals are assessed in SEM.

Conclusions

The result shows that herbal extracts prepared from A. marmelos have good inhibitory effect on the growth of the brushite urinary stone crystals considered.

Association of urinary sex steroid hormones with urinary calcium, oxalate and citrate excretion in kidney stone formers

BACKGROUND

Sex-specific differences in nephrolithiasis with respect to both distribution of prevalence and stone composition are widely described and may be influenced by sex hormones.

METHODS

We conducted a cross-sectional analysis of the relationship between 24-hour urinary sex hormone metabolites measured by gas chromatography-mass spectrometry with urinary calcium, oxalate and citrate excretion in a cohort of 628 kidney stone formers from a tertiary care hospital in Switzerland, taking demographic characteristics, kidney function and dietary factors into account.

RESULTS

We observed a positive association of urinary calcium with urinary testosterone and 17β-estradiol. Positive associations of urinary calcium with dehydroepiandrosterone, 5α-DH-testosterone, etiocholanolone, androsterone, and estriol were modified by net gastrointestinal alkali absorption or urinary sulfate excretion. As the only sex hormone, dehydroepiandrosterone was inversely associated with urinary oxalate excretion in adjusted analyses. Urinary citrate correlated positively with urinary testosterone. Associations of urinary citrate with urinary androsterone, 17β-estradiol and estriol were modified by urinary sulfate or sodium, or by sex.

CONCLUSIONS

Urinary androgens and estrogens are significantly associated with urinary calcium and citrate excretion, and associations are in part modified by diet. Our data furthermore reveal dehydroepiandrosterone as a novel factor associated with urinary oxalate excretion in humans.

Comparison of Supersaturation Outputs from Different Programs and Their Application in Testing Correspondence with Kidney Stone Composition

Introduction: Relative supersaturation (SS) for calcium oxalate (CaOx), calcium phosphate (CaP), and uric acid (UA) has been used for assessing urinary crystallization and estimated by programs, including EQUIL, Joint Expert Speciation System (JESS), and Lithorisk. We compared outputs from these programs and their correspondence with stone composition. Materials and Methods: SS of CaOx, CaP, and UA, using EQUIL, JESS, and Lithorisk were calculated from stone-forming patients. Pearson correlation coefficients were used to ascertain the correspondence between the outputs. Fractional regression models evaluated the relationship between SS and the percentage of each compound in the stones. Results: Two hundred eleven patients were included. Pearson correlation coefficients for CaOx (r ≥ 0.96), CaP (r ≥ 0.99), and UA SS (r ≥ 0.99) showed a high correspondence between all programs. We observed a significant correspondence between CaOx SS and the percentage of CaOx dihydrate in the stone (p < 0.001), as well as between the percentage of brushite and apatite and CaP SS. UA SS showed the strongest correspondence with the percentage of UA in the stones (p < 0.001). Conclusions: Good correlation between EQUIL, JESS, and Lithorisk was observed and good correspondence with stone composition. The magnitude of the association demonstrated by fractional regression models supports evidence for applying SS in clinical practice.