Serum Irisin May Predict Cardiovascular Events in Elderly Patients With Chronic Kidney Disease Stage 3-5.

OBJECTIVE: Irisin is a circulating myokine released from skeletal muscles after physical exercise. Irisin production decreases during the course of chronic kidney disease (CKD) as a potential consequence of sarcopenia and physical inactivity. METHODS: This observational study explored the relationship of serum irisin with cardiovascular outcome in 79 patients with stage 3-5 CKD. RESULTS: Serum irisin was significantly higher in healthy subjects (n = 20) than that in CKD patients (7 ± 2 vs. 3.1 ± 0.9 µg/mL; P = .0001) and was higher in patients with CKD stage 3 (3.2 ± 1 µg/mL) than in patients at stage 4 and 5 taken together (n = 36, 2.8 ± 0.7 µg/mL, P = .05). Patients in the lowest serum irisin tertile had lower serum 1,25(OH)2D levels (21 ± 11 pg/mL) than patients in the middle (30 ± 13 pg/mL; P = .005) and the highest tertile (27 ± 14 pg/mL; P = .047). Patients in the highest tertile had lower Kauppila score (10.6 ± 6.9) than patients in the middle (11.8 ± 5.5; P = .007) and the lowest tertile (6.9 ± 6.8; P = .043). Twenty patients suffered from cardiovascular events during a 3-year follow-up. A Cox regression model using age, body weight, presence of diabetes mellitus, gender, Kauppila calcification score, serum values of FGF23 (as logarithm), phosphate, sclerostin, albumin and cholesterol, estimated glomerular filtration rate, and serum irisin tertiles as covariates showed that patients in the highest tertile of serum irisin had a lower cardiovascular risk than patients in the middle tertile (B, 2.38; odds ratio, 10.8; 95% confidence interval, 1.65-58.13; P = .013) or in the lowest tertile (B, 1.61; odds ratio, 5; 95% confidence interval, 1.09-22.83; P = .038). CONCLUSIONS: These findings suggest that serum irisin may be a marker of cardiovascular outcome in patients with CKD.

Idiopathic calcium nephrolithiasis: a review of pathogenic mechanisms in the light of genetic studies.

BACKGROUND: Calcium nephrolithiasis is a multifactorial disease with a polygenic milieu. Association studies identified genetic polymorphisms potentially implicated in the pathogenesis of calcium nephrolithiasis. The present article reviews the mechanisms of calcium stone formation and the potential contribution of gene polymorphisms to lithogenic mechanisms. SUMMARY: Endoscopy observations suggested that precipitation of calcium-oxalate on the Randall's plaque at the papilla surface may cause idiopathic calcium-oxalate stones. The Randall's plaque is a hydroxyapatite deposit in the interstitium of the kidney medulla, which resembles a soft tissue calcification. Conversely, calcium-phosphate stones may develop from crystalline deposits located at the tip of the Bellini duct. Polymorphisms of eleven genes have been associated with stones in genome-wide association studies and replicated candidate-gene association studies: VDR, SLC34A1, SLC34A4, CLDN14, and CaSR genes coding for proteins regulating tubular phosphate and calcium reabsorption; CaSR, MGP, OPN, PLAU, and UMOD genes coding for proteins preventing calcium salt precipitation; AQP1 gene coding for a water channel in the proximal tubule. The renal activity of the last gene, DGKH, is unknown. Polymorphisms in these genes may predispose to calcium-oxalate and -phosphate stones by increasing the risk of calcium-phosphate precipitation in the tubular fluid. Key Messages: Genetic findings suggest that tubular fluid supersaturation with respect to calcium and phosphate predisposes to calcium-oxalate stones by triggering cellular mechanisms that lead to the Randall's plaque formation.

Different Efficacy of Burosumab on Physical Performance and Serum Phosphate in Adult Patients with X-Linked Hyphophosphatemic Rickets during the First Six-Month of Treatment.

Burosumab is a monoclonal anti-FGF23 antibody used to treat patients with X-linked hypophosphatemic rickets (XLH). Its effect on serum phosphate and physical performance was compared in patients during a 6-month treatment with burosumab. Eight adult patients with XHL were treated with burosumab (1 mg/kg s.c. every 28 days). In the first 6 months of treatment, calcium-phosphate metabolism variables were measured, and muscle performance (tested with chair and walking test) and quality of life (tested with fatigue, BPI-pain and BPI-life questionnaires) were estimated. A significant increase in serum phosphate was observed during the treatment. From the 16th week, serum phosphate became significantly lower than its value in the 4th week. No patients had serum phosphate below the normal range at the 10th week, but seven patients were hypophosphatemic in the 20th and 24th week. All patients improved the execution time of the chair test and walking test, which reached a plateau after the 12th week. BPI-pain and BPI-life scores significantly decreased from baseline to the 24th week. In conclusion, a six-month burosumab treatment may significantly improve the general condition and physical performance of adult patients with XLH; this improvement was more stable and more indicative of treatment efficacy than that of serum phosphate.

Physical and psychological sequelae at three months after acute illness in COVID-19 survivors.

BACKGROUND: Coronavirus disease 2019 (COVID-19) may leave behind an altered health status early after recovery. We evaluated the clinical status of COVID-19 survivors at three months after hospital discharge. METHODS: In this prospective observational cohort study, hospitalized patients aged ≥18 years, evaluated at one (M1) and three (M3) months post-discharge were enrolled. 251 patients (71.3% males, median [IQR] age 61.8 [53.5-70.7] years) were included. Median (IQR) time from discharge to M3 was 89 (79.5-101) days. Primary outcome was residual respiratory dysfunction (RRD), defined by tachypnea, moderate to very severe dyspnea, or peripheral oxygen saturation ≤95% on room air at M3. RESULTS: RRD was found in 30.4% of patients, with no significant difference compared with M1. Chronic obstructive pulmonary disease and length of stay were independent predictors of RRD at multivariable logistic regression (OR [95% CI]: 4.13 [1.17-16.88], P=0.033; OR [95% CI]: 1.02 [1.00-1.04], P=0.047, respectively). Obesity and C-reactive protein levels upon admission were additional predictors at regression tree analysis. Impaired quality of life (QoL) was reported by 53.2% of patients. Anxiety and insomnia were each present in 25.5% of patients, and PTSD in 22.4%. No difference was found between M1 and M3 in QoL, anxiety or PTSD. Insomnia decreased at M3. Current major psychiatric disorder as well as anxiety, insomnia and PSTD at M1 independently predicted PTSD at M3. CONCLUSIONS: Clinical damage may persist at three months after discharge in COVID-19 survivors. Post-recovery follow-up is an essential component of patient management.

Serum concentrations of free indoxyl and p-cresyl sulfate are associated with mineral metabolism variables and cardiovascular risk in hemodialysis patients.

BACKGROUND: Indoxyl sulfate (IS) and p-cresyl sulfate (PCS) are uremic toxins associated with cardiovascular outcome in CKD patients. The present work is an analysis of the association of serum free, total IS and PCS with cardiovascular events and calcium-phosphate metabolism variables in hemodialysis patients. METHODS: Serum levels of total and free IS and PCS were measured in 139 hemodialysis patients. Their relationship with calcium-phosphate metabolism variables were tested in an observational cohort study. In addition, their association with cardiovascular events was investigated during a 4-year follow-up. RESULTS: Patients in the highest tertile (T3) of serum free IS showed lower serum 1,25(OH)2D compared to patients in the middle (T2) and lowest tertile (T1); in addition to this, T3 patients showed lower serum irisin than T1 patients and lower serum PTH than all the other subjects (T1 + T2) combined. Serum PTH was also measured during the two years after the baseline measurement and was higher in patients in the T1 than in those in the T3 of serum free IS. Cox regression analysis showed that cardiovascular risk was lower in T1 patients than in those in the T3 of serum free PCS, both using a univariate (OR 2.55, 95% CI 1.2-5.43; p = 0.015) or multivariate model (OR 2.48, 95% CI 1.12-5.51; p = 0.003). CONCLUSIONS: Serum free IS may be associated with PTH and 1,25(OH)2D secretion, whereas free PCS may predict cardiovascular risk in hemodialysis patients.

Genetics and calcium nephrolithiasis.

Calcium nephrolithiasis is one of the most prevalent uronephrologic disorders in the western countries. Studies in families and twins evidenced a genetic predisposition to calcium nephrolithiasis. Family-based or case-control studies of single-candidate genes evidenced the possible involvement of calcium-sensing receptor (CASR), vitamin D receptor (VDR), and osteopontin (OPN) gene polymorphisms in stone formation. The only high-throughput genome-wide association study identified claudin 14 (CLDN14) gene as a possible major gene of nephrolithiasis. Specific phenotypes were related with these genes: CASR gene in normocitraturic patients, VDR gene in hypocitraturic patients with severe clinical course, and CLDN14 gene in hypercalciuric patients. The pathogenetic weight of these genes remains unclear, but an alteration of their expression may occur in stone formers. Technological skills, accurate clinical examination, and a detailed phenotype description are the basis to get new insight about the genetic basis of nephrolithiasis.

Calcium-sensing receptor and calcium kidney stones.

Calcium nephrolithiasis may be considered as a complex disease having multiple pathogenetic mechanisms and characterized by various clinical manifestations. Both genetic and environmental factors may increase susceptibility to calcium stones; therefore, it is crucial to characterize the patient phenotype to distinguish homogeneous groups of stone formers. Family and twin studies have shown that the stone transmission pattern is not mendelian, but complex and polygenic. In these studies, heritability of calcium stones was calculated around 50%Calcium-sensing receptor (CaSR) is mostly expressed in the parathyroid glands and in renal tubules. It regulates the PTH secretion according to the serum calcium concentration. In the kidney, it modulates electrolyte and water excretion regulating the function of different tubular segments. In particular, CaSR reduces passive and active calcium reabsorption in distal tubules, increases phosphate reabsorption in proximal tubules and stimulates proton and water excretion in collecting ducts. Therefore, it is a candidate gene for calcium nephrolithiasis.In a case-control study we found an association between the normocitraturic stone formers and two SNPs of CaSR, located near the promoters region (rs7652589 and rs1501899). This result was replicated in patients with primary hyperparathyroidism, comparing patients with or without kidney stones. Bioinformatic analysis suggested that the minor alleles at these polymorphisms were able to modify the binding sites of specific transcription factors and, consequently, CaSR expression.Our studies suggest that CaSR is one of the candidate genes explaining individual predisposition to calcium nephrolithiasis. Stone formation may be favored by an altered CaSR expression in kidney medulla involving the normal balance among calcium, phosphate, protons and water excretion.

[Hyperparathyroidism as a cardiovascular risk factor in chronic kidney disease: an update from a biological-cellular perspective]. / L'iperparatiroidismo come fattore di rischio cardiovascolare nell'insufficienza renale: un update dal punto di vista biologico-cellulare.

Cardiovascular complications are the main cause of death in patients with chronic kidney disease (CKD). Among these complications, calcific arteriosclerosis and myocardial hypertrophy are the main predictors of cardiovascular morbidity and mortality. Epidemiological studies have shown their association with hyperparathyroidism, which has therefore been included among the non-traditional cardiovascular risk factors. Studies in laboratory animals have shown that PTH administration may induce calcific arteriosclerosis and myocardial hypertrophy. The former develops independently of hyperphosphatemia, but its mechanisms remain unknown. The latter is characterized by increased thickness of the myocardial fibers and especially the fibrous interstitium; its development is influenced by protein kinase C activation and the subsequent increase in cytosolic calcium as well as activation of intracellular signaling pathways inducing protein synthesis and proliferation. Different from these findings, in other studies PTH infusion was able to produce vasodilatation and to favor myocardial cell contraction and regeneration. These effects depend on protein kinase A activation. PTH may produce different and sometimes contradictory functional effects in the arteries and myocardium that are probably related to different experimental or clinical conditions. In patients with CKD and hyperparathyroidism, PTH may be considered a uremic toxin exerting its effects mainly by increasing cellular calcium. Thus, hyperparathyroidism is confirmed to be a target for the conservative therapy of CKD.

Role of blood pressure dysregulation on kidney and mortality outcomes in COVID-19. Kidney, blood pressure and mortality in SARS-CoV-2 infection.

BACKGROUND: In February 2020 the corona virus disease 2019 (COVID-19) infection started spreading throughout Italy, hitting the Lombardy region very hard. Despite the high diffusion, only a subset of patients developed severe COVID-19: around 25% of them developed acute kidney injury (AKI) and one-third of them died. Elderly patients and patients with high comorbidities were identified as being at higher risk of severe COVID-19. METHODS: Our prospective observational cohort study includes 392 consecutive patients hospitalized for COVID-19 in Milan (median age 67 years, 75% male). We evaluated the relationship between blood pressure at presentation, presence of AKI at Emergency Department admission and during hospitalization, and total in-hospital mortality (24%). RESULTS: Although 58% of our study patients reported a history of hypertension (HYP) (86% on treatment), 30% presented with low blood pressure levels. Only 5.5% were diagnosed with AKI on admission; 75% of hypertensive patients discontinued therapy during hospitalization (only 20% were on treatment at discharge). Gender and hypertension were strongly associated with AKI at admission (odds ratio 11). Blood pressure was inversely correlated with increased risk of AKI upon admission, regardless of the severity of respiratory distress. Age over 65, history of hypertension, and severity of respiratory distress were the main predictors of AKI, which developed in 34.7% of cases during hospitalization. AKI was associated with increased in-hospital mortality. Hypertension and low blood pressure at presentation were the main predictors of in-hospital mortality, together with age over 65, baseline pulmonary involvement, and severity of illness. CONCLUSIONS: In patients hospitalized for COVID-19, hypertension and low blood pressure at presentation are important risk factors for AKI and mortality. Early reduction of antihypertensive therapy may improve outcomes in patients with SARS-CoV-2 infection.

Calcium kidney stones are associated with a haplotype of the calcium-sensing receptor gene regulatory region.

BACKGROUND: Calcium-sensing receptor gene (CaSR) is a candidate to explain susceptibility to calcium kidney stones. Thus, we studied CaSR gene single-nucleotide polymorphisms (SNPs) and haplotypes associated with stones. METHODS: Four hundred and sixty-three calcium stone formers and 213 healthy controls were genotyped for 21 SNPs mapping the whole CaSR gene. CaSR gene structure was studied. SNPs and haplotypes were analysed for association with stones. RESULTS: Three haplotype blocks were identified in the CaSR gene. The first block was characterized by six SNPs and included gene promoters. The rs7652589 and rs1501899 SNPs and the CATTCA haplotype of the first block were significantly more frequent in normocitraturic calcium kidney stone formers than controls. The risk of stones was increased in normocitraturic homozygous patients and heterozygotes for the CATTCA haplotype. The rate of stones was higher in stone formers with the CATTCA haplotype. In a three-generation family, calcium stones were associated with the CATTCA haplotype. The bioinformatic analysis identified a new site for the octamer-binding transcription factor 1 in the presence of the variant alleles at the rs7652589 and rs1501899 SNPs. This transcription factor may downregulate the transcription of vitamin D-dependent genes and the CaSR expression. Conclusion. SNPs and CATTCA haplotype of the CaSR gene first block is associated with kidney stones in normocitraturic patients.

[Comparative study of the short-term effect of mineral water on calcium metabolism]. / Studio comparativo dell'effetto a breve termine di due acque minerali sul metabolismo del calcio.

Mineral water may be a useful means to achieve optimal dietary calcium intake, but the effect of different mineral waters on calcium metabolism is unknown. We therefore evaluated calcium excretion in 24-hour urine in 10 healthy individuals (5 women and 5 men) after two weeks of drinking at least 1500 mL/day of mineral water with a low electrolyte content or 1500 mL/day of mineral water rich in calcium and bicarbonate but with a different sodium content. The low-sodium water Sangemini was one of these two mineral waters. Calcium excretion did not significantly increase after intake of the Sangemini mineral water in comparison with the baseline period of low-electrolyte mineral water intake. Conversely, the calcium excretion increased significantly after intake of the second mineral water. The plasma concentration of C-terminal telopeptide of type I collagen and the urinary phosphate excretion decreased after intake of the second mineral water in comparison with the baseline period, whereas they did not decrease after intake of Sangemini water. Therefore, phosphate excretion was higher after drinking Sangemini water than the other studied mineral water. Drinking Sangemini water may have a slight effect on calcium excretion and may not inhibit bone turnover in the short term. The lesser effect of Sangemini water on calcium excretion could be useful in the treatment of osteoporosis.

Glucagon-like peptide-1 receptor and sarcoglycan delta genetic variants can affect cardiovascular risk in chronic kidney disease patients under hemodialysis.

BACKGROUND: Chronic kidney disease (CKD) patients under hemodialysis show a higher risk of cardiovascular (CV) mortality and morbidity than the general population. This study aims to identify genetic markers that could explain the increased CV risk in hemodialysis. METHODS: A total of 245 CKD patients under hemodialysis were recruited and followed up for 5 years to record CV events. Genetic analysis was performed using single-nucleotide polymorphisms (SNPs) genotyping by Infinium Expanded Multi-Ethnic Genotyping Array (Illumina, San Diego, CA, USA) comparing patients with and without a history of CV events [161 cardiovascular diseases (CVDs) and 84 no CVDs]. The fixation index (Fst) measure was used to identify the most differentiated SNPs, and gene ontology analysis [Protein Analysis THrough Evolutionary Relationships (PANTHER) and Ingenuity Pathway Analysis (IPA)] was applied to define the biological/pathological roles of the associated SNPs. Partitioning tree analysis interrogated the genotype-phenotype relationship between discovered genetic variants and CV phenotypes. Cox regression analysis measured the effect of these SNPs on new CV events during the follow-up (FU). RESULTS: Fst analysis identified 3218 SNPs that were significantly different between CVD and no CVD. Gene ontology analysis identified two of these SNPs as involved in cardiovascular disease pathways (Ingenuity Pathway) and heart development (Panther) and belonging to 2 different genes: Glucagon-like peptide-1 receptor (GLP1R) and Sarcoglycan delta (SGCD). The phenotype-genotype analysis found a higher percentage of CVD patients carrying the GLP1R rs10305445 allele A (P = 0.03) and lower percentages of CVD patients carrying the SGCD rs145292439 allele A (P = 0.038). Moreover, SGCD rs145292439 was associated with higher levels of high-density lipoprotein (P = 0.015). Cox analysis confirmed the increased frequency of CV events during the 5-year FU in patients carrying GLP1R rs1035445 allele A but it did not show any significant association with SGCD rs145292439. CONCLUSIONS: This study identified GLP1R rs10305445 and SCGD rs145292439 as potential genetic markers that may explain the higher risk of CVD in hemodialysis patients.

A diagnostic-therapeutic pathway for patients with kidney stone disease: 2020 update / Percorso diagnostico-terapeutico per il paziente con calcolosi renale: update 2020

The natural history of urinary kidney stone disease includes the risk of relapses and can be associated with the risk of chronic kidney disease, bone and cardiovascular disease. For this reason, a wide clinical-metabolic assessment of the kidney stone patient is of great importance since the first presentation of the stone, to set an appropriate preventive treatment. The proposed diagnostic-therapeutic pathway includes a careful medical history, in order to highlight a secondary kidney stone disease and the main risk factors for kidney stones, chronic renal disease, or cardiovascular and bone disease; a metabolic evaluation on multiple levels, according to the severity of the disease, and the presence or absence of risk factors, and appropriate instrumental investigations. Thus, the information collected makes it possible to set a preventive treatment consisting of general rules and, if necessary, specific pharmacological or nutritional interventions. This paper has been prepared by the Italian Multidisciplinary Study Group for Kidney Stone Disease, and it is addressed to the several professional figures involved in the management of patients suffering from nephrolithiasis, from the emergency doctor to the general practitioner, urologist, nephrologist, radiologist, and dietician. A diagnostic-therapeutic pathway for patients with kidney stone disease was first published on this Journal in 2010. The present contribution aims at amending and updating the article published exactly ten years ago, to serve as an easy-to-use reference and to guide good clinical practice in this field.

Calcium-sensing receptor: evidence and hypothesis for its role in nephrolithiasis.

Calcium-sensing receptor (CaSR) is a plasma-membrane G protein-coupled receptor activated by extracellular calcium and expressed in kidney tubular cells. It inhibits calcium reabsorption in the ascending limb and distal convoluted tubule when stimulated by the increase of serum calcium levels; therefore, these tubular segments are enabled by CaSR to play a substantial role in the regulation of serum calcium levels. In addition, CaSR increases water and proton excretion in the collecting duct and promotes phosphate reabsorption and citrate excretion in the proximal tubule. These CaSR activities form a network in which they are integrated to protect the kidney against the negative effects of high calcium concentrations and calcium precipitates in urine. Therefore, the CaSR gene has been considered as a candidate to explain calcium nephrolithiasis. Epidemiological studies observed that calcium nephrolithiasis was associated with polymorphisms of the CaSR gene regulatory region, rs6776158, located within the promoter-1, rs1501899 located in the intron 1, and rs7652589 in the 5'-untranslated region. These polymorphisms were found to reduce the transcriptional activity of promoter-1. Activating rs1042636 polymorphism located in exon 7 was associated with calcium nephrolithiasis and hypercalciuria. Genetic polymorphisms decreasing CaSR expression could predispose individuals to stones because they may impair CaSR protective effects against precipitation of calcium phosphate and oxalate. Activating polymorphisms rs1042636 could predispose to calcium stones by increasing calcium excretion. These findings suggest that CaSR may play a complex role in lithogenesis through different pathways having different relevance under different clinical conditions.

Update on the genetics of nephrolithiasis.

Genetic studies of calcium kidney stones evidenced the possible involvement of calcium-sensing receptor gene, vitamin D receptor gene and bicarbonate-sensitive adenylate cyclase gene, but it is uncertain which specific polymorphisms could be responsible. Thus, further studies are required to better assess the involvement of these or other genes and the interactions between different genes and between genes and environment. In addition to research in humans, the study of different strains of knock-out mice let us include the gene of phosphate reabsorption carrier NPT2, caveolin-1, protein NHERF-1, osteopontin and Tamm-Horsfall protein among the possible determinants. Further steps in the knowledge of calcium stone causes may be done using the instruments that the modern biotechnology and bioinformatics have made available to the researchers.

Claudin-14 Gene Polymorphisms and Urine Calcium Excretion.

BACKGROUND AND OBJECTIVES: Claudin-16 and -19 are proteins forming pores for the paracellular reabsorption of divalent cations in the ascending limb of Henle loop; conversely, claudin-14 decreases ion permeability of these pores. Single-nucleotide polymorphisms in gene coding for claudin-14 were associated with kidney stones and calcium excretion. This study aimed to explore the association of claudin-14, claudin-16, and claudin-19 single-nucleotide polymorphisms with calcium excretion. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: We performed a retrospective observational study of 393 patients with hypertension who were naïve to antihypertensive drugs, in whom we measured 24-hour urine calcium excretion; history of kidney stones was ascertained by interview; 370 of these patients underwent an intravenous 0.9% sodium chloride infusion (2 L in 2 hours) to evaluate the response of calcium excretion in three different 2-hour urine samples collected before, during, and after saline infusion. Genotypes of claudin-14, claudin-16, and claudin-19 were obtained from data of a previous genome-wide association study in the same patients. RESULTS: Thirty-one single-nucleotide polymorphisms of the 3' region of the claudin-14 gene were significantly associated with 24-hour calcium excretion and calcium excretion after saline infusion. The most significant associated single-nucleotide polymorphism was rs219755 (24-hour calcium excretion in GG, 225±124 mg/24 hours; 24-hour calcium excretion in GA, 194±100 mg/24 hours; 24-hour calcium excretion in AA, 124±73 mg/24 hours; P<0.001; calcium excretion during saline infusion in GG, 30±21 mg/2 hours; calcium excretion during saline infusion in GA, 29±18 mg/2 hours; calcium excretion during saline infusion in AA, 17±11 mg/2 hours; P=0.03). No significant associations were found among claudin-16 and claudin-19 single-nucleotide polymorphisms and calcium excretion and between claudin-14, claudin-16, and claudin-19 single-nucleotide polymorphisms and stones. Bioinformatic analysis showed that one single-nucleotide polymorphism at claudin-14 among those associated with calcium excretion may potentially influence splicing of transcript. CONCLUSIONS: Claudin-14 genotype at the 3' region is associated with calcium excretion in 24-hour urine and after the calciuretic stimulus of saline infusion.

Arachidonic acid influences intracellular calcium handling in human osteoblasts.

The effect of arachidonic acid (AA) on intracellular Ca(2+) concentration ([Ca(2+)]i) in human osteoblasts MG63 was studied. AA caused a concentration-dependent increase in [Ca(2+)]i, mainly due to inward Ca(2+) transport from extracellular environment. Moreover, AA in Ca(2+) -free medium produced a small, transient increase of [Ca(2+)]i, indicating that AA may also trigger Ca(2+) release from intracellular stores. Because the [Ca(2+)]i response to AA was inhibited by the cyclooxygenase (COX) inhibitor indomethacin, we tested the effect of prostaglandins (PGs), products of COX pathway. PGs E1 and E2 caused an increase in [Ca(2+)]i, which, however, was far lower than that obtained with AA. The [Ca(2+)]i response to AA was not inhibited by nifedipine, suggesting that AA did not activate a voltage-dependent Ca(2+) channel. Our results indicate that AA could modulate [Ca(2+)]i in MG63 human osteoblasts, where it may influence Ca(2+) transport across both plasma and endoplasmic membranes. Furthermore, they suggest that osteoblast activity may be modulated by AA.

Vitamin D retains an important role in the pathogenesis and management of secondary hyperparathyroidism in chronic renal failure.

Chronic kidney disease (CKD) causes alterations in mineral metabolism inducing the development of secondary hyperparathyroidism (HPT) and renal osteodystrophy. Recently, it has been suggested that these alterations play an important role in determining extraskeletal calcification and thus cardiovascular morbidity and mortality among CKD patients. An impaired 1 alfa -hydroxylation of 25-hydroxycholecalciferol (25(OH)D3) to 1,25-dihydroxycholecalciferol (1,25(OH)2 D3) with decreased circulating 1,25(OH)2 D3 levels is commonly observed in patients with creatinine clearance below 70 ml/min. The reduction in 1,25(OH)2 D3 production triggers the up-regulation of parathyroid hormone (PTH) synthesis, through a decreased suppression on PTH gene transcription and a decreased intestinal calcium absorption. A reduced expression of vitamin D receptor (VDR) and a less efficient binding of the complex 1,25(OH)2 D3 -VDR to specific DNA segments account for the resistance to 1,25(OH)2 D3 in target cells. Thus, absolute and relative 1,25(OH)2 D3 deficiency is one of the causes of secondary HPT in patients with CKD, together with phosphate retention and skeletal resistance to PTH. Consistently with these pathophysiological mechanisms, the therapeutic use of 1,25(OH)2 D3 still represents a milestone for the treatment of secondary HPT and renal osteodystrophy, even though hypercalcemia and hyperphosphatemia are common adverse events and may increase the risk of cardiovascular calcifications. To reduce the impact of such adverse effects while retaining anti-PTH activity, 1,25(OH)2 D3 analogues with lower calcemic effects have been synthesized and are now available for clinical use.

Autosomal dominant hypocalcemia with mild type 5 Bartter syndrome.

Type 5 Bartter syndrome has been recently defined as a Bartter syndrome due to the most activating mutations of the calcium-sensing receptor (CaSR). It has been attributed to the inhibition exerted by CaSR activity on sodium transport in the thick ascending limb of the loop of Henle (TALH). Two monozygotic twin sisters (T1 and T2) with autosomal dominant hypocalcemia (ADH) due to a nonconservative activating CaSR mutation in the extracellular domain (K29E) were studied. They developed a Bartter-like syndrome characterized by a mild phenotype: hypokalemia occurred only at the age of 22 years; it was corrected with small doses of oral potassium in one twin, while the other twin needed no potassium supplements to maintain borderline levels of plasma potassium; alkalosis was absent; plasma renin and aldosterone production were not markedly activated. Furthermore, the natriuretic response to furosemide, a inhibitor of sodium reabsorption in the TALH, was conserved in both twins. The K29E mutation was previously reported as one of the most activating mutations of the CaSR gene leading to a very marked increase in CaSR sensitivity to calcium ions. These findings confirm that Bartter syndrome is typically associated with ADH provided that the underlying mutation of CaSR is able to produce a conspicuous gain of function. However, the phenotype of type 5 Bartter syndrome may manifest with variable severity, not directly related with the in vitro potency of the CaSR activating mutation.