Association of urinary calcium excretion with serum calcium and vitamin D levels.

BACKGROUND AND OBJECTIVES: Population-based data on urinary calcium excretion are scarce. The association of serum calcium and circulating levels of vitamin D [25(OH)D2 or D3] with urinary calcium excretion in men and women from a population-based study was explored. DESIGN, SETTINGS, PARTICIPANTS, & MEASUREMENTS: Multivariable linear regression was used to explore factors associated with square root-transformed 24-hour urinary calcium excretion (milligrams per 24 hours) taken as the dependent variable with a focus on month-specific vitamin D tertiles and serum calcium in the Swiss Survey on Salt Study. RESULTS: In total, 624 men and 669 women were studied with mean ages of 49.2 and 47.0 years, respectively (age range=15-95 years). Mean urinary calcium excretion was higher in men than in women (183.05 versus 144.60 mg/24 h; P<0.001). In adjusted models, the association (95% confidence interval) of square root urinary calcium excretion with protein-corrected serum calcium was 1.78 (95% confidence interval, 1.21 to 2.34) mg/24 h per milligram per deciliter in women and 0.59 (95% confidence interval, -0.11 to 1.29) mg/24 h per milligram per deciliter in men. Men in the third 25(OH)D3 tertile had higher square root urinary calcium excretion than men in the first tertile (0.99; 95% confidence interval, 0.36 to 1.63 mg/24 h per nanogram per milliliter), and the corresponding association was 0.32 (95% confidence interval, -0.22 to 0.85) mg/24 h per nanogram per milliliter in women. These sex differences were more marked under conditions of high urinary sodium or urea excretions. CONCLUSIONS: There was a positive association of serum calcium with urinary calcium excretion in women but not men. Vitamin 25(OH)D3 was associated with urinary calcium excretion in men but not women. These results suggest important sex differences in the hormonal and dietary control of urinary calcium excretion.

Mechanism of urinary calcium regulation by urinary magnesium and pH.

Urinary magnesium and pH are known to modulate urinary calcium excretion, but the mechanisms underlying these relationships are unknown. In this study, the data from 17 clinical trials in which urinary magnesium and pH were pharmacologically manipulated were analyzed, and it was found that the change in urinary calcium excretion is directly proportional to the change in magnesium excretion and inversely proportional to the change in urine pH; a regression equation was generated to relate these variables (R(2) = 0.58). For further exploration of these relationships, intravenous calcium chloride, magnesium chloride, or vehicle was administered to rats. Magnesium infusion significantly increased urinary calcium excretion (normalized to urinary creatinine), but calcium infusion did not affect magnesium excretion. Parathyroidectomy did not prevent this magnesium-induced hypercalciuria. The effect of magnesium loading on calciuria was still observed after treatment with furosemide, which disrupts calcium and magnesium absorption in the thick ascending limb, suggesting that the effect may be mediated by the distal nephron. The calcium channel TRPV5, normally present in the distal tubule, was expressed in Xenopus oocytes. Calcium uptake by TRPV5 was directly inhibited by magnesium and low pH. In summary, these data are compatible with the hypothesis that urinary magnesium directly inhibits renal calcium absorption, which can be negated by high luminal pH, and that this regulation likely takes place in the distal tubule.

Association of calcemia and serum vitamin D with 24H-urinary calcium excretion in a swiss population-based study

Background: Elevated urinary calcium excretion is associated with reduced bone mineral density. Population-based data on urinary calcium excretion are scarce. We explored the association of serum calcium and circulating levels of vitamin D (including 25(OH)D2 and 25(OH)D3) with urinary calcium excretion in men and women in a population-based study. Methods: We used data from the "Swiss Survey on Salt" conducted between 2010 and 2012 and including people aged 15 years and over. Twenty-four hour urine collection, blood analysis, clinical examination and anthropometric measures were collected in 11 centres from the 3 linguistic regions of Switzerland. Vitamin D was measured centrally using liquid chromatography - tandem mass spectrometry. Hypercalciuria was defined as urinary calcium excretion >0.1 mmol/kg/24h. Multivariable linear regression was used to explore factors associated with 24-hour urinary calcium excretion (mmol/24h) squared root transformed, taken as the dependant variable. Vitamin D was divided into monthspecific tertiles with the first tertile having the lowest value and the third tertile having the highest value. Results: The 669 men and 624 women had mean (SD) age of 49.2 (18.1) and 47 (17.9) years and a prevalence of hypercalciuria of 8.9% and 8.0%, respectively. In adjusted models, the association of urinary calcium excretion with protein-corrected serum calcium was (β coefficient } standard error, according to urinary calcium squared root transformed) 1.125 } 0.184 mmol/L per square-root (mmol/24h) (P<0.001) in women and 0.374 } 0.224 (P=0.096) in men. Men in the third month-specific vitamin D tertile had higher urinary calcium excretion than men in the first tertile (0.170 } 0.05 nmol/L per mmol/24h, P=0.001) and the corresponding association was 0.048 } 0.043, P= 0.272 in women. Conclusion: About one in eleven person has hypercalciuria in the Swiss population. The positive association of serum calcium with urinary calcium excretion was steeper in women than in men, independently of menopausal status. Circulating vitamin D was associated positively with urinary calcium excretion only in men. The reasons underlying the observed sex differences in the hormonal control of urinary calcium excretion need to be explored in further studies.

Association of urinary calcium excretion with serum calcium and vitamin D levels

Contexte de recherche Mon projet de thèse en médecine concerne l'exploration des facteurs associés à l'excrétion urinaire de calcium durant 24h dans une étude populationnelle suisse. Les données qui ont été utilisées sont issues d'une étude populationnelle connue sous le nom de « Swiss survey on Salt intake », qui a été effectuée entre janvier 2010 et mars 2012 et avait pour but principal d'investiguer la consommation de sel de la population suisse. L'étude a regroupé plusieurs centres d'investigations dans toute la Suisse (11 centres dans 9 cantons), dans trois langues nationales (français, allemand et italien) et concerne des participants âgés de plus de 15 ans. Cette étude avait l'avantage de collecter des données anthropométriques, sanguines, urinaires, de lister les traitements et de poser des questions sur le style de vie (alcool, activité physique, etc.). A notre connaissance, peu d'articles populationnels explorent les facteurs associés à l'excrétion urinaire de calcium durant 24h et notamment l'association de celle-ci avec le calcium corrigé sanguin et la 250H-vitamine D2*3 sanguin chez les hommes et les femmes. Méthodes Après exclusions des données manquantes, 1293 participants sur 1550 ont été retenus pour l'analyse statistique. Celle-ci a été effectuée grâce au logiciel Stata 12. Nous avons utilisé la régression linéaire multiple dont la variable dépendante était l'excrétion urinaire de calcium durant 24h en stratifiant les analyses par sexe (en raison des interactions statistiques significatives entre calcémie et sexe, et entre vitamine D et sexe). Les variables indépendantes comprenaient des variables en lien avec l'excrétion urinaire de calcium (vingt-quatre covariables au total) dont la 250H-vitamine D2+3 (avec la variabilité saisonnière) et la calcémie (calcium sérique corrigé par les protéines). Résultats D'importantes différences entre hommes et femmes ont été observées : une association positive entre l'excrétion urinaire de calcium durant 24h et la calcémie corrigée a été trouvée chez les femmes mais pas chez les hommes. En parallèle, nous relevons une association positive entre l'excrétion urinaire de calcium durant 24h et la 250H-vitamine D2+3 chez les hommes mais pas chez les femmes (liée essentiellement à la présence 250H-vitamine D3 en quantité bien plus importante que la 250H-vitamine D2). Nous soulevons deux hypothèses possibles pour expliquer ces importances différences hommes-femmes. La première hypothèse est l'influence des hormones sexuelles. La seconde hypothèse est la contribution des facteurs diététiques. De nouvelles analyses et de nouvelles études populationnelles sont nécessaires pour confirmer ou infirmer ces hypothèses. Perspectives Une prochaine étape sera d'explorer l'influence de l'excrétion urinaire de sodium, de potassium et d'urée sur les associations observées afin d'étudier une possible influence de l'alimentation sur ces résultats. Une autre étape consistera à doser les hormones sexuelles dans les échantillons de cette étude ou dans ceux d'une autre étude. La prévalence de l'hypercalciurie dans cette étude (9 % chez les hommes et 8.1% chez les femmes) est plus basse que dans d'anciennes études non-populationnelles. Il paraît important de mentionner qu'il existe peu de données sur les normes de calciurie dans la population générale et qu'il n'existe pas de consensus international claire concernant la définition de l'hypercalciurie. Cette prévalence élevée est notamment pertinente dans la cadre des néphrolithiasés, qui sont connues pour être plus fréquentes chez les hommes que chez les femmes. Enjeux Les différences hommes-femmes observées pourraient avoir des implications pour améliorer notre compréhension des mécanismes impliqués dans les lithiases urinaires et dans le risque cardiovasculaire associé ainsi que dans notre compréhension des mécanismes associés à l'ostéoporose.

Monitoring of Urinary Calcium and Phosphorus Excretion in Preterm Infants - Comparison of two Methods

OBJECTIVES: Premature babies require supplementation with calcium and phosphorus to prevent metabolic bone disease of prematurity. To guide mineral supplementation, two methods of monitoring urinary excretion of calcium and phosphorus are used: urinary calcium or phosphorus concentration and calcium/creatinine or phosphorus/creatinine ratios. We compare these two methods in regards to their agreement on the need for mineral supplementation. METHODS: Retrospective chart review of 230 premature babies with birthweight <1500 g, undergoing screening of urinary spot samples from day 21 of life and fortnightly thereafter. Hypothetical cut-off values for urine calcium or phosphorus concentration (1 mmol/l) and urine calcium/creatinine ratio (0.5 mol/mol) or phosphorus/creatinine ratio (4 mol/mol) were applied to the sample results. The agreement on whether or not to supplement the respective minerals based on the results with the two methods was compared. Multivariate general linear models sought to identify patient characteristic to predict disagreeing results. RESULTS: 24.8% of cases disagreed on the indication for calcium supplementation, 8.8% for phosphorus. Total daily calcium intake was the only patient characteristic associated with discordant results. CONCLUSIONS: With the intention to supplement the respective mineral, comparison of urinary mineral concentration with mineral/creatinine ratio is moderate for Calcium and good for Phosphorus. The results do not allow to identify superiority of either method on the decision which babies require calcium and/or phosphorus supplements.

Calcium intake and metabolic bone disease after eight years of Roux-en-Y gastric bypass

Background Roux-en-Y gastric bypass (RYGBP) has been found to be the most efficient way to lose weight and maintain the weight loss in morbid obesity. However, with the formation of a new stomach and the modification of intestinal anatomy, there are significant changes on physiological properties of these organs that lead to nutrient deficiency, including calcium. The objectives of this study were to evaluate calcium intake, bone metabolism, and prevalence of metabolic bone disease in women subjected to RYGBP after 8 years. Methods Food frequency questionnaire and 3-day dietary recall, laboratory tests of bone metabolism and bone mineral density were accessed. Results Calcium intake was below the recommendation in all women. Serum PTH and alkaline phosphatase were elevated, whereas vitamin D and urinary calcium were significantly lower. Also, a higher prevalence of metabolic bone disease than the one expected for the normal population at the same age was noted. Conclusion These data suggest that metabolic bone disease could be a complication of this type of surgery.

Vitamin D Receptor and Calcium-Sensing Receptor Gene Polymorphisms in Hypercalciuric Stone-Forming Patients

Background/Aim: Some studies have identified an association of kidney stone formation with vitamin D receptor (VDR) or calcium-sensing receptor (CaSR) polymorphisms. We aimed to evaluate the association between these polymorphisms with urinary calcium excretion (uCa) in calcium-stone-forming patients. Methods: VDR polymorphism, detected by BsmI digestion, and 3 CaSR polymorphisms (G/T at codon 986, G/A at codon 990 and C/G at codon 1011), detected by direct sequencing, were evaluated in 100 hypercalciuric (HCa) and 101 normocalciuric (NCa) calcium-stone-forming patients. Results: The total allelic frequency of VDR polymorphism was: 16% BB, 49% Bb and 35% bb. The prevalence of bb genotype was significantly higher in the HCa when compared to the NCa group (43 vs. 27%). With respect to CaSR polymorphisms, 986S, 990G and 1011E variant alleles were detected, respectively, in 5, 4 and 3% of the whole sample and 5 CaSR haplotypes were identified: 94% ARQ (wildtype), 3% SRQ, 1.5% AGQ, 1.0% ARE and 0.5% AGE. No statistical differences have been observed between NCa and HCa with respect to these CaSR haplotypes. Conclusions: The present study suggested that bb homozygous for VDR polymorphism was overrepresented in hypercalciuric stone formers. Urinary calcium excretion was not associated with CaSR polymorphism in the present sample. Copyright (C) 2009 S. Karger AG, Basel

Genetics of calcium homeostasis in humans: continuum between monogenic diseases and continuous phenotypes

Extracellular calcium participates in several key physiological functions, such as control of blood coagulation, bone calcification or muscle contraction. Calcium homeostasis in humans is regulated in part by genetic factors, as illustrated by rare monogenic diseases characterized by hypo or hypercalcaemia. Both serum calcium and urinary calcium excretion are heritable continuous traits in humans. Serum calcium levels are tightly regulated by two main hormonal systems, i.e. parathyroid hormone and vitamin D, which are themselves also influenced by genetic factors. Recent technological advances in molecular biology allow for the screening of the human genome at an unprecedented level of detail and using hypothesis-free approaches, such as genome-wide association studies (GWAS). GWAS identified novel loci for calcium-related phenotypes (i.e. serum calcium and 25-OH vitamin D) that shed new light on the biology of calcium in humans. The substantial overlap (i.e. CYP24A1, CASR, GATA3; CYP2R1) between genes involved in rare monogenic diseases and genes located within loci identified in GWAS suggests a genetic and phenotypic continuum between monogenic diseases of calcium homeostasis and slight disturbances of calcium homeostasis in the general population. Future studies using whole-exome and whole-genome sequencing will further advance our understanding of the genetic architecture of calcium homeostasis in humans. These findings will likely provide new insight into the complex mechanisms involved in calcium homeostasis and hopefully lead to novel preventive and therapeutic approaches. Keyword: calcium, monogenic, genome-wide association studies, genetics.

Dairy calcium supplementation in overweight or obese persons: its effect on markers of fat metabolism

BACKGROUND: Dairy calcium supplementation has been proposed to increase fat oxidation and to inhibit lipogenesis. OBJECTIVE: We aimed to investigate the effects of calcium supplementation on markers of fat metabolism. DESIGN: In a placebo-controlled, crossover experiment, 10 overweight or obese subjects who were low calcium consumers received 800 mg dairy Ca/d for 5 wk. After 4 wk, adipose tissue was taken for biopsy for analysis of gene expression. Respiratory exchange, glycerol turnover, and subcutaneous adipose tissue microdialysis were performed for 7 h after consumption of 400 mg Ca or placebo, and the ingestion of either randomized slow-release caffeine (SRC; 300 mg) or lactose (500 mg). One week later, the test was repeated with the SRC or lactose crossover. RESULTS: Calcium supplementation increased urinary calcium excretion by 16% (P = 0.017) but did not alter plasma parathyroid hormone or osteocalcin concentrations. Resting energy expenditure (59.9 +/- 3.0 or 59.6 +/- 3.3 kcal/h), fat oxidation (58.4 +/- 2.5 or 53.8 +/- 2.2 mg/min), plasma free fatty acid concentrations (0.63 +/- 0.02 or 0.62 +/- 0.03 mmol/L), and glycerol turnover (3.63 +/- 0.41 or 3.70 +/- 0.38 micromol . kg(-1) . min(-1)) were similar with or without calcium, respectively. SRC significantly increased free fatty acid concentrations, resting fat oxidation, and resting energy expenditure. During microdialysis, epinephrine increased dialysate glycerol concentrations by 250% without and 254% with calcium. Expression of 7 key metabolic genes in subcutaneous adipose tissue was not affected by calcium supplementation. CONCLUSION: Dairy calcium supplementation in overweight subjects with habitually low calcium intakes failed to alter fat metabolism and energy expenditure under resting conditions and during acute stimulation by caffeine or epinephrine

Effects of pioglitazone on renal calcium excretion.

Context: Glitazones increase fracture risk in long-term users and in postmenopausal women. Studies have demonstrated deleterious effects of glitazones on bone metabolism. Glitazones also have direct renal tubular effects increasing sodium reabsorption. We hypothesized that glitazones may also regulate renal calcium excretion. Design: In this double-blind, randomized, placebo-controlled, four-way, crossover study, we examined the effects of pioglitazone (45 mg/d for 6 wk) or placebo on renal calcium and phosphate excretion and PTH levels during different sodium intakes in 16 individuals (eight with type 2 diabetes and eight with essential hypertension). Results: Pioglitazone had no effect on corrected plasma calcium and phosphate levels but decreased significantly the alkaline phosphatase and PTH levels. Pioglitazone induced on average a 45% increase in urinary calcium excretion. The fractional excretion of calcium rose to the same extent, suggesting a glomerular filtration rate-independent effect. Sodium intake did not influence the calciuric effect of pioglitazone. Changes in diurnal and nocturnal calciuria were similar. There was no effect of pioglitazone on phosphate excretion. Conclusion: Pioglitazone decreases PTH levels and increases urinary calcium excretion, independently from changes in glomerular filtration rate and from the sodium load, suggesting an inhibitory effect of pioglitazone on the tubular reabsorption of calcium. These effects may contribute to the increased fracture risk with glitazone treatment.

Urinary saturation and nephrocalcinosis in preterm infants: effect of parenteral nutrition.

Urinary lithogenic and inhibitory factors were studied in 27 preterm infants; 16 had total parenteral nutrition (TPN) and 11 had breastmilk with an additional glucose-sodium chloride infusion. Urines were collected for 24 hours on day 2 (period A), day 3 (B), and once between days 4 and 10 (C). Urinary calcium oxalate saturation was calculated by the computer program EQUIL 2. Renal ultrasonography was performed every second week until discharge. The calcium/creatinine ratio increased in infants on TPN (A 0.91; C 1.68 mol/mol) and was significantly higher at period C than that in infants on breastmilk/infusion (A 0.52; C 0.36). The oxalate/creatinine ratio was persistently higher with TPN (203 mmol/mol) than with breastmilk/infusion (98; 137). The citrate/creatinine remained constant with TPN (0.44 mol/mol), whereas it increased significantly with breastmilk/infusion (0.26; 0.49). Calcium/citrate rose considerably with TPN, but decreased with breastmilk/infusion to a significantly lower level than with TPN. The urinary calcium oxalate saturation increased with TPN (2.4; 4.5) and decreased with breastmilk/infusion (2.1; 1.5) to a significantly lower value than with TPN. Nephrocalcinosis developed in two infants on TPN. Mean daily calcium intake was similar in both groups, whereas protein, sodium, and phosphorus intake were significantly higher on TPN. It is concluded that the increase in urinary calcium oxalate saturation observed with TPN is due to the combined effect of an increased urinary calcium excretion and higher urinary oxalate/creatinine and calcium/citrate ratios. The changes observed are likely to be caused by TPN itself, which differs in several respects from breastmilk feeding.

Role of CLOCK and circadian rhythms in calcium homeostasis

Le maintien d'une concentration sanguine constante de calcium est d'une importance cruciale et trois organes participent à la balance calcique normale : les reins, les intestins et les os. La concentration plasmatique de calcium est strictement régulée par l'hormone parathyroïdienne (PTH) et par la vitamine D. Des variations circadiennes de la PTH, de la vitamine D ainsi que du calcium plasmatique ont été décrites précédemment chez l'humain ainsi que chez le rat. Ces rythmes de PTH dans le sérum sont importants pour la régulation du remodelage de l'os. En effet, il a été montré chez les souris C57BL/6J que des injections de PTH une fois par jour mènent à une augmentation de la densité minérale de l'os alors que l'infusion en continu de PTH est associée à une diminution de cette densité. La vitamine D joue également un rôle fondamental dans la physiologie osseuse, car un déficit en vitamine D peut conduire à une ostéomalacie. Cependant la fonction des oscillations de vitamine D au niveau de l'homéostasie osseuse reste inconnue. L'horloge circadienne est un système interne de contrôle biologique du temps générant des rythmes de 24 heures dans l'expression des gènes, ainsi que dans la physiologie et le comportement. Ce contrôle s'opère par des boucles rétroactives positives et négatives de l'expression de gènes circadiens tels que CLOCK, BMAL1, CRY1 et 2 ou PERI et 2. Dans ce travail, nous avons émis l'hypothèse que l'homéostasie calcique est sous le contrôle de l'horloge circadienne. Dans un premier temps, nous avons montré chez les souris C57BL/6J des variations journalières des concentrations de calcium, de PTH et de vitamine D dans le sang, ainsi que de calcium dans les urines. Nous avons également démontré des changements au niveau de l'expression rénale des gènes importants dans l'homéostasie du calcium, tant au niveau de l'ARN messager que des protéines. Ensuite, pour analyser le rôle du système de l'horloge circadienne dans l'homéostasie du calcium, nous avons étudié des souris dans lesquelles a été supprimé le gène CLOCK crucial pour la fonction de l'horloge et nous avons comparé ces souris à des souris de type sauvage de même portée. Les souris CLOCK-I- étaient hypercalciuriques à chaque moment de la journée. Cependant le rythme circadien de l'excrétion de calcium était préservé. Le taux de calcium plasmatique ne différait pas entre les génotypes, mais les souris CLOCK -/- ne montraient pas de variations journalières de ce paramètre. Une perte du rythme journalier était également observée pour les niveaux de vitamine D, perte qui pourrait être une cause de l'altération de la micro-architecture osseuse révélée chez les souris CLOCK-/-. En effet, ces souris montrent une diminution du nombre de trabécules, de leur volume ainsi que de leur surface, ce qui suggère la présence d'ostéoporose. Nous avons également trouvé que le rythme de l'expression de l'ARN messager de CYP27B1 était aboli dans les reins des souris CLOCK -/-, ce qui peut expliquer l'altération du rythme de la vitamine D. Les taux sanguins de PTH étaient comparables entre les souris CLOCK -/- et de type sauvage. Dans les reins, une augmentation de l'expression de l'ARN messager de TRPV5 et NCX1 a été constatée, ce qui suggérerait une augmentation de la réabsorption de calcium dans le tubule convoluté distal et dans le tubule connecteur. Dans les intestins, la réabsorption calcique était diminuée, chez les souris CLOCK-I-, fait confirmé par une diminution des niveaux d'ARN messager de TRPV6 et PMCAL. En résumé, la suppression du gène CLOCK chez les souris a conduit à une hypercalciurie, une altération du rythme des taux plasmatiques de calcium et de vitamine D et à une détérioration de l'architecture osseuse. Pour conclure, ces résultats montrent que l'horloge circadienne est essentielle à l'homéostasie calcique ainsi qu'à la physiologie des os. - L'ostéoporose affecte environ 22 millions de femmes et 5.5 millions d'hommes en Europe, réduisant significativement leur qualité de vie et a causé 3.5 millions de nouvelles fractures en 2010. Les dépenses totales liées à ces fractures ont atteint 37 milliards d'euro et ce coût devrait augmenter de 25% d'ici à 2025. Le nombre de nouvelles fractures dues à l'ostéoporose à travers le monde est estimé à environ 1000 par heure. Parmi les causes de l'ostéoporose, le déficit én calcium et/ou en vitamine D joue un rôle important, mais il existe également des causes génétiques ou liées à des facteurs comme les hormones sexuelles (estrogènes, testostérone), l'âge, le tabac, le poids corporel, certains médicaments,... La vie est rythmique : ceci est dû à l'alternance naturelle du jour et de la nuit et de ses effets sur le corps. La prise alimentaire, par exemple, est un processus qui a lieu pendant la phase active, qui est prévisible (il se produit toujours au même moment) et qui peut être anticipé par le corps. Pour cela, une horloge interne est présente dans chaque cellule du corps et est synchronisée par la lumière du jour, entre autres stimuli. Cette horloge indique la phase du jour et régule l'expression de gènes impliqués dans les différents processus qui nécessitent une anticipation. Pendant mon travail de thèse, je me suis demandé si des îythmes circadiens (c'est-à-dire d'une durée d'environ 24 heures et indépendants des stimuli externes) étaient observables'pour les gènes régulant les flux de calcium dans le corps et si l'interruption de ces rythmes pouvait mener à des altérations de la qualité de l'os. J'ai d'abord travaillé avec des souris normales et j'ai pu montrer la présence de rythmes au niveau du calcium sanguin et urinaire, mais également au niveau des hormones et gènes qui contrôlent le métabolisme du calcium dans le corps, comme la vitamine D et l'hormone parathyroidienne. De manière intéressante, j'ai observé que la plupart de ces gènes ont un rythme synchronisé. J'ai ensuite utilisé un modèle de souris dans lequel l'horloge interne a été génétiquement invalidée et j'ai montré que ces souris présentent une augmentation de leur excrétion urinaire de calcium et un rythme circadien altéré de la vitamine D dans le sang. Ces souris absorbent aussi moins bien le calcium intestinal et présentent une ostéoporose marquée. Ce travail montre donc que l'horloge interne est nécessaire pour établir un rythme circadiens de certains facteurs influant les flux de calcium dans l'organisme, comme la vitamine D, et que la perturbation de ces rythmes mène à une dérégulation du métabolisme osseux. Ainsi, la perturbation de l'horloge interne peut causer une ostéoporose et une hypercalciurie qui pourraient aboutir à la formation de fractures et de calculs rénaux. L'extrapolation de ces observations chez l'homme ou à des changements plus subtiles des rythmes circadiens, comme le décalage horaire, restent à montrer. Cette recherche a démontré que les rythmes circadiens des mécanismes de régulation des flux de calcium dans l'organisme sont essentiels au maintien d'un squelette normal et suggère que les perturbations des rythmes circadiens pourraient être une nouvelle cause de l'ostéoporose. - Maintaining constant calcium concentration in the plasma is of a crucial importance and three organs participate in normal calcium balance - kidney, gut and bone. Plasma calcium concentration is strictly regulated by parathyroid hormone (PTH) and vitamin D. Circadian variations of PTH, vitamin D and plasma calcium were previously described in humans, as well as in rats. Rhythms in serum PTH are important for balanced bone remodelling. Indeed in C57BL/6J mice, PTH injection once per day leads to an increase in bone mineral density (BMD), whilst continuous infusion is associated with decreased BMD. Vitamin D also plays a crucial role in bone physiology, since the deficiency in vitamin D can lead to rickets/osteomalacia. However, the role of vitamin D rhythms in bone homeostasis remains unknown. The circadian clock is an. internal time-keeping system generating rhythms in gene expression with 24h periodicity, in physiology and in behaviour. It is operated by positive- and negative-feedback loops of circadian genes, such as CLOCK, BMAL1, CRY1 and 2 or PERI and 2. In this work, we hypothesized, that calcium homeostasis is under the control of the circadian clock. First, we showed daily variations in urinary calcium and serum calcium, PTH and l,25(OH)2 vitamin D, together with renal mRNA and protein levels of genes involved in calcium homeostasis in C57BL/6J mice. Second, and to investigate the role of the circadian clock system in calcium handling, we studied mice lacking the gene CLOCK crucial for fonction of the clock system and compared them to the WT littermates. CLOCK-/- mice were hypercalciuric at all timepoints of the day. However, the circadian rhythm of calcium excretion was preserved. Serum calcium levels did not differ between the genotypes, but CLOCK-/- mice did not exhibit daily variation for this parameter. Loss of rhythm was observed also for serum l,25(OH)2 vitamin D levels, which may be one of the causes of altered bone microarchitecture that was revealed in CLOCK-/- mice. They displayed increased trabecular separation and decreased trabecular number, trabecular bone volume and trabecular bone surface, suggestive of osteoporosis. We found that the rhythm of the mRNA expression of CYP27B1 was abolished in the kidney of CLOCK-/- mice, which could induce the altered rhythm of l,25(OH)2 vitamin. Serum PTH levels were comparable between CLOCK-/- and WT mice. In the kidney, increased mRNA expression of TRPV5 and NCX1 suggests increased calcium reabsorption in the distal convoluted and connecting tubule. In the gut, intestinal calcium absorption was decreased in CLOCK¬/- mice, confirmed by decreased mRNA levels of TRPV6 and PMCA1. In summary, deletion of the CLOCK gene in mice conducts to hypercalciuria, alteration of the rhythm in serum calcium and l,25(OH)2D levels, and impainnent of their bone microarchitecture. In conclusion, these data show that the circadian clock system is essential in calcium homeostasis and bone physiology.

Alkaline mineral water lowers bone resorption even in calcium sufficiency: alkaline mineral water and bone metabolism.

BACKGROUND: Dietary acid charge enhances bone loss. Bicarbonate or alkali diet decreases bone resorption in humans. We compared the effect of an alkaline mineral water, rich in bicarbonate, with that of an acid one, rich in calcium only, on bone markers, in young women with a normal calcium intake. METHODS: This study compared water A (per litre: 520 mg Ca, 291 mg HCO(3)(-), 1160 mg SO(4)(-), Potential Renal Acid load (PRAL) +9.2 mEq) with water B (per litre: 547 mg Ca, 2172 mg HCO(3)(-), 9 mg SO(4)(-), PRAL -11.2 mEq). 30 female dieticians aged 26.3 yrs (SD 7.3) were randomized into two groups, followed an identical weighed, balanced diet (965 mg Ca) and drank 1.5 l/d of the assigned water. Changes in blood and urine electrolytes, C-telopeptides (CTX), urinary pH and bicarbonate, and serum PTH were measured after 2 and 4 weeks. RESULTS: The two groups were not different at baseline, and showed a similar increase in urinary calcium excretion. Urinary pH and bicarbonate excretion increased with water B, but not with water A. PTH (p=0.022) and S-CTX (p=0.023) decreased with water B but not with water A. CONCLUSION: In calcium sufficiency, the acid calcium-rich water had no effect on bone resorption, while the alkaline water rich in bicarbonate led to a significant decrease of PTH and of S-CTX.

Urinary lithiasis and idiopathic hypercalciuria: the importance of dietary intake evaluation

PUSPOSE: To evaluate food intake of patients with urinary lithiasis and idiopathic hypercalciuria (IH). MATERIALS and METHODS: Between August 2007 and June 2008, 105 patients with lithiasis were distributed into 2 groups: Group 1 (n = 55) - patients with IH (urinary calcium excretion > 250 mg in women and 300 mg in men with normal serum calcium); Group 2 (n = 50) - normocalciuria (NC) patients . Inclusion criteria were: age over 18, normal renal function (creatinine clearance = 60 mL/min), absent proteinuria and negative urinary culture. Pregnant women, patients with some intestinal pathology, chronic diarrhea or using corticoids were excluded. The protocol of metabolic investigation was based on non-consecutive collection of two 24-hour samples for dosages of: calcium, sodium, uric acid, citrate, oxalate, magnesium and urinary volume. Food intake was evaluated through the quantitative method of Dietary Register of three days. RESULTS: Urinary excretion of calcium (433.33 ± 141.92 vs. 188.93 ± 53.09), sodium (280.08 ± 100.94 vs. 200.44.93 ± 65.81), uric acid (880.63 ± 281.50 vs. 646.74 ± 182.76) and magnesium (88.78 ± 37.53 vs. 64.34 ± 31.84) was significantly higher in the IH group in comparison to the NC group (p < 0.05). As regards the nutritional composition of food intake of IH and NC groups, there was no statistical significant difference in any nutrient evaluated. CONCLUSION: In our study, no difference was observed in the food intake of patients with urinary lithiasis and IH or NC.

Prevalence and densitometric characteristics of incomplete distal renal tubular acidosis in men with recurrent calcium nephrolithiasis

The aim of this study was to assess the prevalence of incomplete distal renal tubular acidosis (idRTA) in men with recurrent calcium nephrolithiasis and its potential impact on bone mineral density. We conducted a retrospective analysis of 150 consecutive, male idiopathic recurrent calcium stone formers (RCSFs), which had originally been referred to the tertiary care stone center of the University Hospital of Berne for further metabolic evaluation. All RCSFs had been maintained on a free-choice diet while collecting two 24-h urine samples and delivered second morning urine samples after 12 h fasting. Among 12 RCSFs with a fasting urine pH >5.8, a modified 3-day ammonium chloride loading test identified idRTA in 10 patients (urine pH >5.32, idRTA group). We matched to each idRTA subject 5 control subjects from the 150 RCSFs, primary by BMI and then by age, i.e., 50 patients, without any acidification defect (non-RTA group) for comparative biochemistry and dual energy X-ray absorptiometry (DEXA) analyses. The prevalence of primary idRTA among RCSFs was 6.7% (10/150). Patients with idRTA had significantly higher 2-h fasting and 24-h urine pH (2-h urine pH: 6.6 ± 0.4 vs. 5.2 ± 0.1, p = 0.001; 24-h urine pH: 6.1 ± 0.2 vs. 5.3 ± 0.3, p = 0.001), 24-h urinary calcium excretion (7.70 ± 1.75 vs. 5.69 ± 1.73 mmol/d, p = 0.02), but significantly lower 24-h urinary urea excretion (323 ± 53 vs. 399 ± 114 mmol/d, p = 0.01), urinary citrate levels (2.32 ± 0.82 vs. 3.01 ± 0.72 mmol/d, p = 0.04) and renal phosphate threshold normalized for the glomerular filtration rate (TmPO(4)/GFR: 0.66 ± 0.17 vs. 0.82 ± 0.21, p = 0.03) compared to non-RTA patients. No significant difference in bone mineral density (BMD) was found between idRTA and non-RTA patients for the lumbar spine (LS BMD (g/cm(2)): 1.046 ± 0.245 SD vs. 1.005 ± 0.119 SD, p = 0.42) or femoral neck (FN BMD (g/cm(2)): 0.830 ± 0.135 SD vs. 0.852 ± 0.127 SD). Thus, idRTA occurs in 1 in 15 male RCSFs and should be sought in all recurrent calcium nephrolithiasis patients. Bone mineral density, however, does not appear to be significantly affected by idRTA.