Effect of diuretics on renal tubular transport of calcium and magnesium

The magnesium depletion score is associated with increased likelihood of kidney stone disease among female adults

OBJECT

The association between magnesium depletion score (MDS) and kidney stone disease (KSD) remains unknown. This study was designed to investigate the association of MDS with KSD in adults.

METHODS

A total of 19,654 participants were enrolled from the National Health and Nutrition Examination Surveys (NHANES). The MDS was calculated by assessing four aspects, including alcohol assumption, renal function, and use of diuretics and proton pump inhibitor. Multivariable logistic regressions were performed to explore the associations between MDS and the prevalence of KSD. Linear correlations were conducted explore the relationship of testosterone with MDS.

RESULTS

In the multivariable logistic regressions with full adjustment for confounding variables, the odds ratio of MDS associating with KSD was 1.28 (95% CI: 1.04-1.58, P = 0.022) in total population, and 1.70 (95% CI: 1.16-2.50, P=0.007) in female participants. Besides, compared to the lowest MDS, the highest MDS was associated with a lower testosterone (β = -16.39, P=0.009) after full adjustment in non-menopause women.

CONCLUSION

This study highlighted a positive correlation of high MDS with KSD in female population, which may be associated low level of serum testosterone.

Population pharmacokinetics and dose optimization of magnesium sulfate in Chinese preeclampsia population

OBJECTIVE

To establish the population pharmacokinetics (PPK) of magnesium sulfate (MgSO4)in women with preeclampsia (PE), and to determine the key covariates having an effect in magnesium pharmacokinetics in Chinese PE.

METHODS

Pregnant women with PE prescribed MgSO4 were enrolled in this prospective study from April 2021 to April 2023. On the initial day of administration, the patients were administered a loading dose of 5 g in conjunction with 10 g of magnesium sulfate as a maintenance dose. On the second day, only the maintenance dose was administration, and maternal blood samples were taken at 0, 4, 5, and 12 h after the second day's 10 g maintenance dose. The software Phoenix was used to estimate PPK parameters of MgSO4, such as clearance (CL) and volume of distribution (V), and to model PPK models with patient demographic, clinical, and laboratory covariates.

RESULTS

A total of 199 blood samples were collected from 51 women with PE and PPK profiles were analyzed. The PPK of MgSO4 is consistent with to a one-compartment model. The base model adequately described the maternal serum magnesium concentrations after magnesium administration. The population parameter estimates were as follows: CL was 2.98 L/h, V was 25.07 L. The model predictions changed significantly with covariates (BMI, creatinine clearance, and furosemide). Furosemide statistically influences V. The creatinine clearance, BMI and furosemide jointly affects CL. Monte Carlo simulation results showed that a loading dose combined with a maintenance dose would need to be administered daily to achieve the therapeutic blood magnesium concentrations. For the non-furosemide group, the optimal dosing regimen was a 5 g loading dose combined with a 10 g maintenance dose of MgSO4. For the furosemide group, the optimal dosing regimen was a 2.5 g loading dose combined with a 10 g maintenance dose of MgSO4.

CONCLUSIONS

The magnesium PPK model was successfully developed and evaluated in Chinese preeclampsia population, and the dose optimization of MgSO4 was completed through Monte Carlo simulation.

How the kidney regulates magnesium: a modelling study

The kidneys are crucial for maintaining Mg2+ homeostasis. Along the proximal tubule and thick ascending limb, Mg2+ is reabsorbed paracellularly, while along the distal convoluted tubule (DCT), Mg2+ is reabsorbed transcellularly via transient receptor potential melastatin 6 (TRPM6). TRPM6 and other renal transporter expressions are regulated by sex hormones. To investigate renal Mg2 handling, we have developed sex-specific computational models of electrolyte transport along rat superficial nephron. Model simulations indicated that along the proximal tubule and thick ascending limb, Mg2+ and Na+ transport occur parallelly, but they are dissociated along the DCT. In addition, our models predicted higher paracellular Mg2+ permeability in females to attain similar cortical thick ascending limb fractional Mg2+ reabsorption in both sexes. Furthermore, DCT fractional Mg2+ reabsorption is higher in females than in males, allowing females to better fine-tune Mg2+ excretion. We validated our models by simulating the administration of three classes of diuretics. The model predicted significantly increased, marginally increased and significantly decreased Mg2+ excretions for loop, thiazide and K-sparing diuretics, respectively, aligning with experimental findings. The models can be used to conduct in silico studies on kidney adaptations to Mg2+ homeostasis alterations during conditions such as pregnancy, diabetes and chronic kidney disease.

Magnesium and Vascular Calcification in Chronic Kidney Disease: Current Insights

Magnesium (Mg) plays crucial roles in multiple essential biological processes. As the kidneys are the primary organ responsible for maintaining the blood concentration of Mg, people with chronic kidney disease (CKD) may develop disturbances in Mg. While both hyper- and hypomagnesemia may lead to adverse effects, the consequences associated with hypomagnesemia are often more severe and lasting. Importantly, observational studies have shown that CKD patients with hypomagnesemia have greater vascular calcification. Vascular calcification is accelerated and contributes to a high mortality rate in the CKD population. Both in vitro and animal studies have demonstrated that Mg protects against vascular calcification via several potential mechanisms, such as inhibiting the formation of both hydroxyapatite and pathogenic calciprotein particles as well as limiting osteogenic differentiation, a process in which vascular smooth muscle cells in the media layer of the arteries transform into bone-like cells. These preclinical findings have led to several important clinical trials that have investigated the effects of Mg supplementation on vascular calcification in people with CKD. Interestingly, two major clinical studies produced contradictory findings, resulting in a state of equipoise. This narrative review provides an overview of our current knowledge in the renal handling of Mg in health and CKD and the underlying mechanisms by which Mg may protect against vascular calcification. Lastly, we evaluate the strength of evidence from clinical studies on the efficacy of Mg supplementation and discuss future research directions.

Risk Factors of Cetuximab-Induced Hypomagnesemia and the Effect of Magnesium Prophylaxis in Patients with Head and Neck Cancer: A Retrospective Study

Hypomagnesemia is a characteristic adverse event of cetuximab in patients with head and neck cancer (HNC). However, there is limited information about its prevalence, risk factors, and preventive strategies. This study aimed to investigate the risk factors of hypomagnesemia and examine the preventive effects of prophylactic magnesium (Mg) administration. We initially investigated HNC patients treated with cetuximab between 2013 and 2019. Our institute started prophylactic Mg treatment (20-mEq Mg sulfate administration before cetuximab) in practice during this period. We retrospectively assess the preventive efficacy by comparing patients before and after its implementation. In total, 109 patients were included. In 60 patients without prophylaxis, all-grade and grade ≥2 hypomagnesemia at 3 months occurred in 61.7 and 15.0% of patients. The incidence of hypomagnesemia was not affected by regimens and concomitant medications. In 49 patients treated with prophylactic Mg treatment, there was no significant decrease in the cumulative incidence of hypomagnesemia. However, the preventive Mg treatment eliminated the need for additional Mg repletion to maintain Mg levels in patients treated with paclitaxel + cetuximab. A risk factor in patients without prophylaxis was a low Mg level at pre-treatment (≤2.0 mg/dL) (odds ratio: 6.03, 95% confidence interval: 1.78-20.4, p = 0.004), whereas that in patients with prophylaxis was the number of cetuximab doses (≥10) (odds ratio: 5.50, 95% confidence interval: 1.52-19.87, p = 0.009). In conclusion, a low pre-treatment Mg level was the only risk factor that could be avoided by prophylactic Mg administration. This preventive intervention is recommended for managing cetuximab-induced hypomagnesemia.

The Association between Magnesium Depletion Score and Hypertension in US Adults: Evidence from the National Health and Nutrition Examination Survey (2007-2018)

The magnesium depletion score (MDS) emerges as a new valuable predictor of the body's magnesium status index. This study aims to explore the link between MDS and hypertension (HTN) using the National Health and Nutrition Examination Survey (NHANES) data. A total of 9708 participants from NHANES (2007-2018) were enrolled to investigate MDS's connection with HTN. HTN was defined based on clinical guidelines. MDS classification (low, 0-1; middle, 2; high, 3-5) relied on alcohol consumption, diuretic use, proton-pump inhibitor (PPI) usage, and kidney disease. Multivariable logistic regression assessed MDS-HTN association. Subsequent analyses included interaction tests, subgroups, and sensitivity analysis. Each unit increase in MDS correlated with an 87% higher HTN risk (OR, 1.87; 95% CI, 1.64-2.13) after adjusting for confounders. High MDS participants exhibited significantly elevated HTN risk compared to low MDS counterparts (OR, 8.31; 95% CI, 4.81-14.36), with a significant trend across MDS groups (p < 0.001). Subgroup analyses supported a consistent positive correlation. Sensitivity analysis confirmed a robust association. The results indicated a positive correlation between MDS and the risk of developing HTN in US adults.

Coupling of renal sodium and calcium transport: a modeling analysis of transporter inhibition and sex differences

Ca2+ transport along the nephron occurs via specific transcellular and paracellular pathways and is coupled to the transport of other electrolytes. Notably, Na+ transport establishes an electrochemical gradient to drive Ca2+ reabsorption. Hence, alterations in renal Na+ handling, under pathophysiological conditions or pharmacological manipulations, can have major effects on Ca2+ transport. An important class of pharmacological agent is diuretics, which are commonly prescribed for the management of blood pressure and fluid balance. The pharmacological targets of diuretics generally directly facilitate Na+ transport but also indirectly affect renal Ca2+ handling. To better understand the underlying mechanisms, we developed a computational model of electrolyte transport along the superficial nephron in the kidney of a male and female rat. Sex differences in renal Ca2+ handling are represented. Model simulations predicted in the female rat nephron lower Ca2+ reabsorption in the proximal tubule and thick ascending limb, but higher reabsorption in the late distal convoluted tubule and connecting tubule, compared with the male nephron. The male rat kidney model yielded a higher urinary Ca2+ excretion than the female model, consistent with animal experiments. Model results indicated that along the proximal tubule and thick ascending limb, Ca2+ and Na+ transport occurred in parallel, but those processes were dissociated in the distal convoluted tubule. Additionally, we conducted simulations of inhibition of channels and transporters that play a major role in Na+ and Ca2+ transport. Simulation results revealed alterations in transepithelial Ca2+ transport, with differential effects among nephron segments and between the sexes.NEW & NOTEWORTHY The kidney plays an important role in the maintenance of whole body Ca2+ balance by regulating Ca2+ reabsorption and excretion. This computational modeling study provides insights into how Ca2+ transport along the nephron is coupled to Na+. Model results indicated that along the proximal tubule and thick ascending limb, Ca2+ and Na+ transport occur in parallel, but those processes were dissociated in the distal convoluted tubule. Simulations also revealed sex-specific responses to different pharmacological manipulations.

Claudin-19 localizes to the thick ascending limb where its expression is required for junctional claudin-16 localization

The kidney is critical for mineral homeostasis. Calcium and magnesium reabsorption in the renal thick ascending limb (TAL) involves claudin-16 (CLDN16) and claudin-19 (CLDN19) and pathogenic variants in either gene lead to familial hypomagnesemia with hypercalciuria and nephrocalcinosis (FHHNC) with severe calcium and magnesium wasting. While both CLDN16 and CLDN19 localize to the TAL, varying expression patterns in the renal tubule have been reported using different antibodies. We, therefore, studied the localization of CLDN19 in the kidneys of wild-type and Cldn19-deleted mice using three anti-CLDN19 antibodies and examined the role of Cldn19 deletion on CLDN16 and CLDN10 localization. We find that CLDN19 localizes to basolateral membrane domains of the medullary and cortical TAL but only to the tight junction of TALs in the outer stripe of outer medulla and cortex, where it colocalizes with CLDN16. Furthermore, in TALs from Cldn19-deleted mice, CLDN16 is expressed in basolateral membrane domains but not at the tight junction. In contrast, Cldn19 ablation does not change CLDN10 localization. These findings directly implicate CLDN19 in regulating permeability in the TAL by allowing junctional insertion of CLDN16 and may explain the shared renal phenotypic characteristics in FHHNC patients.

Severity of Hepatocyte Damage and Prognosis in Cirrhotic Patients Correlate with Hepatocyte Magnesium Depletion

We aimed to evaluate the magnesium content in human cirrhotic liver and its correlation with serum AST levels, expression of hepatocellular injury, and MELDNa prognostic score. In liver biopsies obtained at liver transplantation, we measured the magnesium content in liver tissue in 27 cirrhotic patients (CIRs) and 16 deceased donors with healthy liver (CTRLs) by atomic absorption spectrometry and within hepatocytes of 15 CIRs using synchrotron-based X-ray fluorescence microscopy. In 31 CIRs and 10 CTRLs, we evaluated the immunohistochemical expression in hepatocytes of the transient receptor potential melastatin 7 (TRPM7), a magnesium influx chanzyme also involved in inflammation. CIRs showed a lower hepatic magnesium content (117.2 (IQR 110.5-132.9) vs. 162.8 (IQR 155.9-169.8) μg/g; p < 0.001) and a higher percentage of TRPM7 positive hepatocytes (53.0 (IQR 36.8-62.0) vs. 20.7 (10.7-32.8)%; p < 0.001) than CTRLs. In CIRs, MELDNa and serum AST at transplant correlated: (a) inversely with the magnesium content both in liver tissue and hepatocytes; and (b) directly with the percentage of hepatocytes stained intensely for TRPM7. The latter also directly correlated with the worsening of MELDNa at transplant compared to waitlisting. Magnesium depletion and overexpression of its influx chanzyme TRPM7 in hepatocytes are associated with severity of hepatocyte injury and prognosis in cirrhosis. These data represent the pathophysiological basis for a possible beneficial effect of magnesium supplementation in cirrhotic patients.

A Delicate Balance: Challenges in the Management of Primary Hyperparathyroidism and Congestive Heart Failure

Primary hyperparathyroidism (PHPT) is an excessive parathyroid hormone (PTH) production disorder, causing increased calcium levels. Commonly, these cases are asymptomatic and detected incidentally on routine labs. These patients are usually conservatively managed and monitored periodically, including bone and kidney health evaluation. Medical management of severe hypercalcemia secondary to PHPT includes IV fluids, cinacalcet, bisphosphonates, and dialysis, while the surgical treatment is parathyroidectomy. Patients suffering from heart failure with reduced ejection fraction (HFrEF) on diuretics and PHPT require a delicate balance of their volume status to prevent exacerbation of either condition. In patients with these two comorbidities on the opposite ends of the volume spectrum, it can lead to challenges in managing these patients. We present a case of a woman with repeated hospitalizations due to poor volume status control.  An 82-year-old female with primary hyperparathyroidism (diagnosed 17 years ago), HFrEF due to non-ischemic cardiomyopathy, sick sinus syndrome with a pacemaker, and persistent atrial fibrillation presented to the emergency department with worsening bilateral lower limb swelling for several months. The remaining review of systems was largely negative. Her home medication regimen included carvedilol, losartan, and furosemide. Vitals were stable, and the physical exam revealed bilateral lower extremity pitting edema. Chest x-ray revealed cardiomegaly with mild pulmonary vascular congestion. Relevant labs were NT pro-BNP at 2190 pg/mL, calcium at 11.2 mg/dL, creatinine at 1.0 mg/dL, PTH at 143 pg/mL, and Vitamin D, 25-hydroxy at 48.6 ng/mL. The echocardiogram showed an ejection fraction (EF) of 39%, grade III diastolic dysfunction, severe pulmonary hypertension, and mitral and tricuspid regurgitation. The patient received IV diuretics and guideline-directed treatment for congestive heart failure exacerbation. She was managed conservatively for her hypercalcemia and advised to maintain hydration at home. Spironolactone and Dapagliflozin were added to her regimen, and the Furosemide dose was increased at discharge.  The patient was re-admitted three weeks later with fatigue and decreased fluid intake. Vitals were stable; however, the physical exam revealed dehydration. Pertinent labs were calcium at 13.4 mg/dL, potassium at 5.7 mmol/L, creatinine at 1.7 mg/dL (baseline 1.0), PTH at 204 pg/mL, and Vitamin D, 25-hydroxy at 54.1 ng/mL. Repeat ECHO showed an ejection fraction (EF) of 15%. She was started on gentle IV fluids to correct the hypercalcemia while preventing volume overload. Hypercalcemia and acute kidney injury improved with hydration. She was put on Cinacalcet 30 mg, and home medications were adjusted for better volume control at discharge. This case highlights the complications of balancing the volume status with primary hyperparathyroidism and CHF. Worsening HFrEF resulted in a higher diuretic requirement, thereby worsening her hypercalcemia. With emerging data on the correlation between PTH and cardiovascular risks, it is becoming necessary to assess the risks and benefits of conservative management in asymptomatic patients. Current research has also shown that various patient demographics and comorbidities prevent the surgical management of PHPT. Hence, in suitable candidates, parathyroidectomy must be considered early in patients with asymptomatic hyperparathyroidism.

Prepubertal to adulthood exposure to low doses of glyphosate-based herbicide increases the expression of the Havcr1 (Kim1) biomarker and causes mild kidney alterations

Glyphosate is a nonselective and postemergent herbicide used to combat weeds in several crops, which raises concerns about risks to human health since residues are detected in urine, human milk, surface water and several types of food. Feces and urine are the major routes of elimination of glyphosate, making the kidney a sensitive target for the development of toxicity. In fact, farmers are at high risk of developing chronic kidney disease. In this sense, this study aims to investigate kidney function by measuring the serum levels of urea and creatinine, examining the histological morphology, and analyzing the mRNA expression of genes related to tubular transport of ions, urea and urates and the biomarker of kidney disease Kim1, and the levels of lead in the kidney in male Wistar rats orally exposed to low levels of glyphosate-based herbicide (GBH: 0, 0.5 or 5 mg/kg) from weaning to adult life by gavage. GBH0.5 showed reduced serum urea concentration, presence of tubulointerstitial swelling and mononuclear cell infiltration into the interstitium, increased gene expression of Kim1 and reduced gene expression of Slc14a1. GBH5 showed reduced serum urea and increased serum creatinine concentrations, tubulointerstitial swelling, interstitial fibrosis, and reduced expression of Trpm6 and Trpv5. Exposure to GBH did not affect the levels of Pb in the kidneys of animals. In conclusion, glyphosate at low doses may cause mild kidney damage. It is necessary to evaluate whether the long-term effects of this constant injury may contribute to the development of chronic kidney disease of uncertain etiology.

Furosemide rescues hypercalciuria in familial hypomagnesaemia with hypercalciuria and nephrocalcinosis model

AIM

Perturbed calcium homeostasis limits life expectancy in familial hypomagnesaemia with hypercalciuria and nephrocalcinosis (FHHNC). This rare disease occurs by loss-of-function mutations in CLDN16 or CLDN19 genes, causing impaired paracellular reabsorption of divalent cations along the cortical thick ascending limb (cTAL). Only partial compensation takes place in the ensuing late distal convoluted tubule, connecting tubule, and collecting duct, where the luminal transient receptor potential channel V5 (TRPV5), as well as basolateral plasma membrane calcium ATPase (PMCA) and sodium-potassium exchanger (NCX1) mediate transcellular Ca²⁺ reabsorption. The loop diuretic furosemide induces compensatory activation in these distal segments. Normally, furosemide enhances urinary calcium excretion via inhibition of the aforementioned cTAL. As Ca²⁺ reabsorption in the cTAL is already severely impaired in FHHNC patients, furosemide may alleviate hypercalciuria in this disease by activation of the distal transcellular Ca²⁺ transport proteins.

METHODS

Cldn16-deficient mice (Cldn16^-/- ) served as a FHHNC model. Wild-type (WT) and Cldn16^-/- mice were treated with furosemide (7 days of 40 mg/kg bw) or vehicle. We assessed renal electrolyte handling (metabolic cages) and key divalent transport proteins.

RESULTS

Cldn16^-/- mice show higher Ca²⁺ excretion than WT and compensatory stimulation of Cldn2, TRPV5, and NCX1 at baseline. Furosemide reduced hypercalciuria in Cldn16^-/- mice and enhanced TRPV5 and PMCA levels in Cldn16^-/- but not in WT mice.

CONCLUSIONS

Furosemide significantly reduces hypercalciuria, likely via upregulation of luminal and basolateral Ca²⁺ transport systems in the distal nephron and collecting duct in this model for FHHNC.

Molecular mechanisms, physiological roles, and therapeutic implications of ion fluxes in bone cells: Emphasis on the cation-Cl- cotransporters

Bone turnover diseases are exceptionally prevalent in human and come with a high burden on physical health. While these diseases are associated with a variety of risk factors and causes, they are all characterized by common denominators, that is, abnormalities in the function or number of osteoblasts, osteoclasts, and/or osteocytes. As such, much effort has been deployed in the recent years to understand the signaling mechanisms of bone cell proliferation and differentiation with the objectives of exploiting the intermediates involved as therapeutic preys. Ion transport systems at the external and in the intracellular membranes of osteoblasts and osteoclasts also play an important role in bone turnover by coordinating the movement of Ca²⁺ , PO₄ ^2- , and H⁺ ions in and out of the osseous matrix. Even if they sustain the terminal steps of osteoformation and osteoresorption, they have been the object of very little attention in the last several years. Members of the cation-Cl^- cotransporter (CCC) family are among the systems at work as they are expressed in bone cells, are known to affect the activity of Ca²⁺ -, PO₄ ^2- -, and H⁺ -dependent transport systems and have been linked to bone mass density variation in human. In this review, the roles played by the CCCs in bone remodeling will be discussed in light of recent developments and their potential relevance in the treatment of skeletal disorders.

[The short test with hydrochlorothiazide in differential diagnosis between primary normocalcemic and secondary hyperparathyroidism for inpatient treatment]

BACKGROUND

Differential diagnosis between the normocalcemic primary hyperparathyroidism (nPHPT) and secondary hyperparathyroidism (SHPT) due to hypercalciuria remains a challenge.

AIM

The aim of this study was to investigate the capability of short test with hydrochlorothiazide for the differential diagnosis of nPHPT and SHPT.

MATERIALS AND METHODS

A retrospective study was conducted with the participation of 28 patients who underwent a functional test with thiazide diuretics during hospitalization in the Department of parathyroid glands pathology and mineral disorders of the Endocrinology Research Centre, Russia. Parameters of mineral metabolism were evaluated before and 3-5 days after taking hydrochlorothiazide 50 mg/day.

RESULTS

According to baseline and dynamic biochemical evaluation patients were divided into 3 groups. Group 1 (n=21) included patients with confirmed PHPT, who reached hypercalcemia accompanying with an elevated level of iPTH (n=19) or an increased level of iPTH accompanying with normocalcemia (n=2). In group 1, baseline Caadj. was 2.48 mmol/l [2.47; 2.52], iPTH 107.5 pg/ml [86.8; 133.0], after short test - 2.63 mmol/l [2.59; 2.66] and 102.1 pg/ml [95,7; 124,1]. Group 2 included only one who was diagnosed with SHPT, a normal value of iPTH with concomitant normocalcemia was achieved after 4 days of hydrochlorothiazide therapy (baseline Caadj. 2.35 mmol/l, iPTH 74.5 pg/ml vs at 2.27 mmol/l and 50.7 pg/ml respectively). Patients with doubtful results of the test entered in group 3 (n=6), they did not achieve significant changes in the calcium and iPTH levels, so it was recommended to continue the test on an outpatient basis (baseline Caadj. 2.39 mmol/l [2.33;2.45], iPTH 97.0 pg/ml [83.1;117.0]); after short test - 2.47 mmol/l [2.42; 2.48] and 91.3 pg/ml [86.9; 124.0] respectively). Groups with PHPT and SHPT and doubtful results significantly differed from each other in Caadj (р=0.003, U-test, Bonferroni correction Р0=0.006), but not in iPTH, daily calciuria, eGFR, and phosphorus. There were no significant differences in the incidence of classical complications of PHPT.

CONCLUSION

The diagnosis of PHPT was confirmed in 21/28 patients 3-5 days after taking hydrochlorothiazide 50 mg/day. The obtained results are significant for the differential diagnosis in hospitalized patients with an unspecified genesis of hyperparathyroidism.

The kidney reabsorption-related Magnesium Depletion Score is associated with increased likelihood of abdominal aortic calcification among US adults

BACKGROUND

Kidney reabsorption has a vital role in magnesium homeostasis. This study aimed to determine the relationship between the kidney reabsorption-related magnesium depletion score (MDS) and abdominal aortic calcification (AAC).

METHODS

We obtained the data of 2640 individuals from the National Health and Nutrition Examination Survey (NHANES) database and analyzed the relationship between MDS and AAC scores. MDS is a scoring system developed to predict status of magnesium deficiency that fully considered the pathophysiological factors influencing the kidneys' reabsorption capability. AAC was quantified by the Kauppila score system based on dual-energy X-ray absorptiometry. We performed stratified analysis and multiple equation regression analysis. R and EmpowerStats were used for data analysis.

RESULTS

A total of 2640 participants were included with the mean AAC score of 1.47 ± 0.07. Participants in higher MDS tended to have higher AAC scores (MDS scored 0: 0.75 (0.56, 0.93), MDS scored 1: 1.02 (0.84, 1.21), MDS scored 2: 2.34 (1.80, 2.87), MDS scored 3: 3.19 (2.46, 3.92), MDS ≥ 4: 4.99 (3.49, 6.49)). Compared with those in the lowest MDS scored 0, the highest subgroup (MDS ≥ 4) was associated with a higher AAC score (β = 4.24, 95% CI: 2.78-5.70, p < 0.001), and the association was not altered (β = 1.81, 95% CI: 0.54-3.09, p = 0.002) after adjusting for numerous covariates. Subgroup analyses showed that stronger associations between MDS and AAC score were detected in adults with lower levels of magnesium intake and older (all p for interaction < 0.05).

CONCLUSIONS

The MDS is a promising tool for identifying individuals with magnesium deficiency status who may benefit from dietary magnesium supplementation to reduce the risks of AAC.

The p.Pro482Ala Variant in the CNNM2 Gene Causes Severe Hypomagnesemia Amenable to Treatment with Spironolactone

Renal hypomagnesemia syndromes involving CNNM2 protein pathogenic variants are associated with variable degrees of neurocognitive dysfunction and hypomagnesemia. Here, we report a family with a novel CNNM2 p.Pro482Ala variant, presenting with overt hypomagnesemia and mild neurological involvement (autosomal dominant renal hypomagnesemia 6, HOMG6, MIM# 613882). Using a bioinformatics approach, we showed that the p.Pro482Ala amino acid substitution causes a 3D conformational change in CNNM2 structure in the cystathionin beta synthase (CBS) domain and the carboxy-terminal protein segment. A novel finding was that aldosterone inhibition with spironolactone helped to alleviate hypomagnesemia and symptoms in the proband.

Association of Total Calcium With Serum Uric Acid Levels Among United States Adolescents Aged 12-19 Years: A Cross-Sectional Study

Aims

Evidence of a link between total calcium (CA) and serum uric acid (SUA) is absent in adolescents. Thus, this study aimed to determine the relationship between total CA levels and SUA levels in United States adolescents.

Methods

A cross-sectional study analyzed a sample composed of 8,309 United States adolescents aged 12–19 years from the National Health and Nutrition Examination Survey database (1999–2006 survey cycle). Multivariable linear regression analyses and multivariable logistic regression analyses were used to assess the correlation of total CA with SUA levels and hyperuricemia. Furthermore, the dose-response relationship of total CA and SUA levels was analyzed using smooth curve fitting (penalized spline method).

Results

According to multivariable linear regression analysis, every 1 mg/dL increase in total CA level is associated with a 0.33 mg/dL (β = 0.33, 95% CI: 0.27–0.40, p < 0.001) increase in SUA. Multivariable logistic regression analyses showed that every 0.1 mg/dL increase in total CA level is linked with an 8% increased risk of hyperuricemia (OR = 1.08, 95% CI: 1.06–1.10, p < 0.001). The analyses of smooth curve fitting revealed that total CA levels were linearly correlated with SUA levels (P_{non–linearity} = 0.152). The results were highly stable in all subgroups. The interaction analysis results presented that race/ethnicity had an interactive role in associating total CA with SUA levels.

Conclusions

In United States adolescents, total CA levels were linearly and positively correlated with SUA levels.

Gentamicin Inhibits Ca2+ Channel TRPV5 and Induces Calciuresis Independent of the Calcium-Sensing Receptor-Claudin-14 Pathway

BACKGROUND

Treatment with the aminoglycoside antibiotic gentamicin can be associated with severe adverse effects, including renal Ca²⁺ wasting. The underlying mechanism is unknown but it has been proposed to involve activation of the Ca²⁺-sensing receptor (CaSR) in the thick ascending limb, which would increase expression of claudin-14 (CLDN14) and limit Ca²⁺ reabsorption. However, no direct evidence for this hypothesis has been presented.

METHODS

We studied the effect of gentamicin in vivo using mouse models with impaired Ca²⁺ reabsorption in the proximal tubule and the thick ascending limb. We used a Cldn14 promoter luciferase reporter assay to study CaSR activation and investigated the effect of gentamicin on activity of the distal nephron Ca²⁺ channel transient receptor potential vanilloid 5 (TRPV5), as determined by patch clamp in HEK293 cells.

RESULTS

Gentamicin increased urinary Ca²⁺ excretion in wild-type mice after acute and chronic administration. This calciuretic effect was unaltered in mice with genetic CaSR overactivation and was present in furosemide-treated animals, whereas the calciuretic effect in Cldn14^-/- mice and mice with impaired proximal tubular Ca²⁺ reabsorption (claudin-2 [CLDN2]-deficient Cldn2^-/- mice) was equivalent to that of wild-type mice. In vitro, gentamicin failed to activate the CaSR. In contrast, patch clamp analysis revealed that gentamicin strongly inhibited rabbit and human TRPV5 activity and chronic gentamicin administration downregulated distal nephron Ca²⁺ transporters.

CONCLUSIONS

Gentamicin does not cause hypercalciuria via activation of the CaSR-CLDN14 pathway or by interfering with proximal tubular CLDN2-dependent Ca²⁺ reabsorption. Instead, gentamicin blocks distal Ca²⁺ reabsorption by direct inhibition of the Ca²⁺ channel TRPV5. These findings offer new insights into Ca²⁺ wasting in patients treated with gentamicin.

The Extraglycemic Effect of SGLT-2is on Mineral and Bone Metabolism and Bone Fracture

Type 2 diabetes mellitus (T2DM) is a risk factor for osteoporosis. The effects of T2DM and anti-diabetic agents on bone and mineral metabolism have been observed. Sodium-glucose co-transporter 2 inhibitors (SGLT-2is) promote urinary glucose excretion, reduce blood glucose level, and improve the cardiovascular and diabetic nephropathy outcomes. In this review, we focused on the extraglycemic effect and physiological regulation of SGLT-2is on bone and mineral metabolism. SGLT-2is affect the bone turnover, microarchitecture, and bone strength indirectly. Clinical evidence of a meta-analysis showed that SGLT-2is might not increase the risk of bone fracture. The effect of SGLT-2is on bone fracture is controversial, and further investigation from a real-world study is needed. Based on its significant benefit on cardiovascular and chronic kidney disease (CKD) outcomes, SGLT-2is are an outstanding choice. Bone mineral density (BMD) and fracture risk evaluation should be considered for patients with a high risk of bone fracture.

The Effects of Osteoporotic and Non-osteoporotic Medications on Fracture Risk and Bone Mineral Density

Osteoporosis is a highly prevalent bone disease affecting more than 37.5 million individuals in the European Union (EU) and the  United States of America (USA). It is characterized by low bone mineral density (BMD), impaired bone quality, and loss of structural and biomechanical properties, resulting in reduced bone strength. An increase in morbidity and mortality is seen in patients with osteoporosis, caused by the approximately 3.5 million new osteoporotic fractures occurring every year in the EU. Currently, different medications are available for the treatment of osteoporosis, including anti-resorptive and osteoanabolic medications. Bisphosphonates, which belong to the anti-resorptive medications, are the standard treatment for osteoporosis based on their positive effects on bone, long-term experience, and low costs. However, not only medications used for the treatment of osteoporosis can affect bone: several other medications are suggested to have an effect on bone as well, especially on fracture risk and BMD. Knowledge about the positive and negative effects of different medications on both fracture risk and BMD is important, as it can contribute to an improvement in osteoporosis prevention and treatment in general, and, even more importantly, to the individual's health. In this review, we therefore discuss the effects of both osteoporotic and non-osteoporotic medications on fracture risk and BMD. In addition, we discuss the underlying mechanisms of action.

Mechanisms Underlying Calcium Nephrolithiasis

Nephrolithiasis is a worldwide problem with increasing prevalence, enormous costs, and significant morbidity. Calcium-containing kidney stones are by far the most common kidney stones encountered in clinical practice. Consequently, hypercalciuria is the greatest risk factor for kidney stone formation. Hypercalciuria can result from enhanced intestinal absorption, increased bone resorption, or altered renal tubular transport. Kidney stone formation is complex and driven by high concentrations of calcium-oxalate or calcium-phosphate in the urine. After discussing the mechanism mediating renal calcium salt precipitation, we review recent discoveries in renal tubular calcium transport from the proximal tubule, thick ascending limb, and distal convolution. Furthermore, we address how calcium is absorbed from the intestine and mobilized from bone. The effect of acidosis on bone calcium resorption and urinary calcium excretion is also considered. Although recent discoveries provide insight into these processes, much remains to be understood in order to provide improved therapies for hypercalciuria and prevent kidney stone formation. Expected final online publication date for the Annual Review of Physiology, Volume 84 is February 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Disorders of Divalent Ions (Magnesium, Calcium, and Phosphorous) in Patients With Cancer

Disorders of the divalent ions (magnesium, calcium, and phosphorous) are frequently encountered in patients with cancer. Of these, hypomagnesemia, hypocalcemia, hypercalcemia, and hypophosphatemia are seen most commonly. These electrolyte disturbances may be related to the underlying malignancy or due to side effects of anticancer therapy. When caused by a paraneoplastic process, these abnormalities may portend a poor prognosis. Importantly, the development of severe electrolyte derangements may be associated with symptoms that negatively impact quality of life, preclude the administration of critical chemotherapeutic agents, or lead to life-threatening complications that require hospitalization and emergent treatment. In accordance, prompt recognition and treatment of these disorders is key to improving outcomes in patients living with cancer. This review will discuss selected derangements of the divalent ions seen in this population, with a focus on paraneoplastic and therapy-associated etiologies.

A case report of pseudohypoaldosteronism type II with a homozygous KLHL3 variant accompanied by hyperthyroidism

BACKGROUND

Pseudohypoaldosteronism type II (PHAII), also called Gordon syndrome, is a rare hereditary disease caused by variants in the WNK1, WNK4, KLHL3 and CUL3 genes. The combination of PHAII with hyperthyroidism and secondary hyperparathyroidism has not been reported previously.

CASE PRESENTATION

A 54-year-old female with recently diagnosed Graves' disease presented hyperkalemia, hypertension, hypercalciuria, elevated levels of parathyroid hormone (PTH) and normal renal function. PHAII was established based on the finding of a homozygous variant (c.328 A > G, T110A) in the KLHL3 gene. Low-dose thiazide diuretics normalized her potassium, calcium and PTH.

CONCLUSIONS

PHAII caused by a KLHL3 variant can affect adults later in life. This diagnosis should be considered in patients with hypertension, consistent hyperkalemia, and normal eGFR and can be corrected by thiazides. The patient also had hyperthyroidism and secondary hyperparathyroidism. The latter was also corrected by thiazide treatment. The hyperthyroidism was assumed to be unrelated to PHAII.

Cardiovascular Risk in Patients with Primary Hyperparathyroidism

Primary hyperparathyroidism (PHPT) is one of the most common endocrine disorders characterized by parathyroid hormone (PTH)-dependent hypercalcemia. Cardinal features include low trauma fractures, nephrolithiasis, and chronic kidney disease. Several experimental studies established that parathyroid hormone exerts actions on the cardiovascular (CV) system, including vasodilatation and positive inotropic and chronotropic effects. Observational studies, especially in severe cases, report a higher prevalence of hypertension, diabetes mellitus, lipid abnormalities, endothelial dysfunction, arrhythmias, and left ventricular hypertrophy in patients with PHPT, while the risk of CV events seems to be increased in severe cases. However, the effect of surgery is inconsistent on CV abnormalities and, more importantly, on CV disease (CVD) events, especially in mild cases. In the current review, we describe the available evidence linking PHPT and CVD, as well as the effect of surgical management and pharmacological treatment on CVD manifestations in patients with PHPT. Based on the current evidence, CVD is not considered an indication for surgery.

Soluble α-klotho anchors TRPV5 to the distal tubular cell membrane independent of FGFR1 by binding TRPV5 and galectin-1 simultaneously

Hypercalciuria is one of the early manifestations of diabetic nephropathy (DN). This is partially due to a decrease in the expression of renal transient receptor potential vanilloid type 5 (TRPV5), which is responsible for renal Ca²⁺ reabsorption. Soluble klotho has been previously determined to increase TRPV5 by cleaving sialic acid, causing TRPV5 to bind to membrane protein galectin-1. However, a recent study showed that soluble klotho binds to α2-3-sialyllactose, where sialic acid is located, on TRPV5, rather than cleave it. Here, we report that soluble klotho tethers TRPV5 on the membrane by binding both TRPV5 and galectin-1, thereby protecting membrane TRPV5 from diabetes-induced endocytosis. In the present study, we injected recombinant soluble α-klotho protein (rKL) into db/db and db/m mice for 8 wk and collected urine and kidneys. We administered rKL, AZD4547 [fibroblast growth factor (FGF) receptor type 1 inhibitor], and OTX008 (galectin-1 inhibitor) to cultured mouse distal tubular cells with or without 30 mM high-glucose (HG) exposure. db/db mice showed increased renal Ca²⁺ excretion and decreased renal TRPV5 expression. rKL treatment reversed this change. In vitro, TRPV5 expression in distal tubular cells decreased under HG conditions, and rKL successfully upregulated TRPV5 with or without FGF23. Also, immunofluorescence showed colocalization of klotho, TRPV5, and galectin-1 in distal tubule cells, suggesting that klotho binds to both TRPV5 and galectin-1. Moreover, when both FGF receptor type 1 and galectin-1 were inhibited, rKL failed to increase TRPV5 under HG conditions. Our results indicate that soluble klotho prevents TRPV5 from degradation and subsequent diabetes-induced endocytosis by anchoring TRPV5 through binding with both TRPV5 and galectin-1.NEW & NOTEWORTHY Soluble α-klotho anchors transient receptor potential vanilloid type 5 (TRPV5) on the apical membrane of the distal tubule by binding both TRPV5 and a membrane-abundant protein, galectin-1. This newly discovered mechanism works even when fibroblast growth factor (FGF)23 signaling is inhibited by treatment with FGF receptor type 1 inhibitor. Therefore, we identified how soluble α-klotho increases TRPV5 without FGF23. We confirmed this mechanism by observing that soluble α-klotho fails to enhance TRPV5 when both FGF receptor type 1 and galectin-1 are inhibited.

Nutritional and health factors affecting the bioavailability of calcium: a narrative review

Calcium is responsible for the effectiveness of various processes, and its supply in the diet is necessary for the normal function of the human body. Apart from being an important component of the skeleton, calcium also helps maintain the structure of cell organelles and regulates intracellular and extracellular fluid homeostasis. This review presents the nutritional and health factors that affect the bioavailability of calcium. Physiological conditions and factors such as pregnancy, infancy, menopause, old age, hormones, growth factors associated with calcium metabolism, diseases limiting its absorption, and intestinal microbiota are distinguished among endogenous factors. Although the calcium supply in the body is genetically conditioned and specific to each person, its qualitative and quantitative composition can be modified by external factors. The exogenous factors include dietary modifications with particular nutrients and pharmacological treatment. Adequate calcium levels increase bone protection and prevent osteoporosis, a disease involving low mineral bone mass.

[The use of diuretics in chronic heart failure. Position paper of the Russian Heart Failure Society]

The document focuses on key issues of diuretic therapy in CHF from the standpoint of current views on the pathogenesis of edema syndrome, its diagnosis, and characteristics of using diuretics in various clinical situations.

Calcium Transport in the Kidney and Disease Processes

Calcium is a key ion involved in cardiac and skeletal muscle contractility, nerve function, and skeletal structure. Global calcium balance is affected by parathyroid hormone and vitamin D, and calcium is shuttled between the extracellular space and the bone matrix compartment dynamically. The kidney plays an important role in whole-body calcium balance. Abnormalities in the kidney transport proteins alter the renal excretion of calcium. Various hormonal and regulatory pathways have evolved that regulate the renal handling of calcium to maintain the serum calcium within defined limits despite dynamic changes in dietary calcium intake. Dysregulation of renal calcium transport can occur pharmacologically, hormonally, and via genetic mutations in key proteins in various nephron segments resulting in several disease processes. This review focuses on the regulation transport of calcium in the nephron. Genetic diseases affecting the renal handling of calcium that can potentially lead to changes in the serum calcium concentration are reviewed.

AQP2 as a target of lycopene protects against atrazine-induced renal ionic homeostasis disturbance

Atrazine (ATR), a ubiquitous environmental contaminant in water and soil, causes environmental nephrosis. To reveal the toxic effect of ATR on the kidney and the potential chemical nephroprotective effect of lycopene (LYC), Kun-Ming mice of specific pathogen-free (SPF) grade were treated with LYC (5 mg kg-1) and/or ATR (50 mg kg-1 or 200 mg kg-1) for 21 days. The degree of renal injury was evaluated by measuring the ion concentration, ATPase activities and the mRNA expressions/levels of associated ATPase subunits. In addition, the expression of renal aquaporins (AQPs) was analyzed. The results showed that the renal tubular epithelial cells of ATR-exposed mice were swollen, the glomeruli were significantly atrophied, and the ion concentrations were obviously changed. The activity of Na+-K+-ATPase and the transcription of its subunits were downregulated. The activity of Ca2+-Mg2+-ATPase and the transcription of its subunits were upregulated. The expression of AQPs, especially the critical AQP2, was affected. Notably, ATR-induced nephrotoxicity was significantly improved by LYC supplementation. Therefore, LYC could protect the kidney against ATR-induced nephrotoxicity via maintaining ionic homeostasis, reversing the changes in ATPase activity and controlling the expression of AQPs on the cell membrane. These results suggested that AQP2 was a target of LYC and protected against ATR-induced renal ionic homeostasis disturbance.

Effects of bendroflumethiazide on bone mineral density; results from the BONATHIAD randomized double-blind placebo-controlled cohort study

Purpose

Thiazide diuretics (TD) may play a role in preventing osteoporosis. The objective was to investigate the effects of bendroflumethiazide in combination with bisphosphonates on bone mineral density, selected blood parameters, blood pressure, pulse, and muscle function.

Methods

Double-blinded, randomized, placebo-controlled interventional study in postmenopausal osteoporotic women over the age of 50 years consisting of four arms: 1) 24 weeks with bendroflumethiazide +24 weeks of washout, 2) 24 weeks with placebo +24 weeks of washout, 3) 48 weeks with bendroflumethiazide, or 4) 48 weeks with placebo. At inclusion, participants were on oral bisphosphonates. Intervention consisted of either bendroflumethiazide or placebo. Dual energy X-ray absorptiometry (DXA), vertebral fracture assessment (VFA), quantitative CT (QCT) and selected blood parameters were acquired at baseline and at 48 weeks and Timed-Up-and-Go, handgrip strength, blood pressure, pulse and balance additionally at 24 weeks.

Results

139 postmenopausal Caucasian women over 50 years were randomized (mean age 64.7 years (SEM 0.6, range 51–79)). 109 (78%) completed the study. No difference in the effect of bendroflumethiazide on DXA, VFA, QCT, biochemistry or muscle function were found between the treatment arms.

Conclusion

Bendroflumethiazide for 24- or 48 weeks in combination with bisphosphonates does not improve bone mineral density, selected blood parameters or muscle function compared to placebo combined with bisphosphonates. Studies with longer treatment periods and more patients are needed to further characterize the effects of bendroflumethiazide on bone and subpopulations that might benefit from the treatment.

The impact of thiazide diuretics on bone mineral density and the trabecular bone score: the Rotterdam Study

The decreased risk of osteoporotic fractures in thiazide diuretics (TD) users is possibly not only caused by an increase in bone mineral density (BMD), but by an increase in other determinants of bone strength as well, such as the trabecular bone score (TBS). To test this hypothesis, we studied the association between TD use and both lumbar spine BMD (LS-BMD) and lumbar spine TBS (LS-TBS) cross-sectionally in 6096 participants from the Rotterdam Study, as well as the association between TD use and bone turnover estimated by serum osteocalcin levels. We found that past and current use of TD were associated with an increase of LS-BMD (β = 0.021 g/cm² (95% CI: 0.006;0.036) and β = 0.016 g/cm² (95% CI: 0.002;0.031), respectively). Use of ≥1 defined daily dose (DDD) (β = 0.028, 95% CI: 0.010;0.046; p for trend within DDD of use <0.001) and use of >365 days (β = 0.033, 95% CI: 0.014;0.052; p for trend within duration of use <0.001) were positively associated with LS-BMD. No significant association between TD use and LS-TBS was observed. Mean serum osteocalcin levels were significantly different between users and non-users of TD (20.2 ng/ml (SD 8.3) and 22.5 ng/ml (SD 17.0), respectively, p < 0.001). Furthermore, linear regression analysis showed that the use of TD was associated with a 3.2 ng/l (95% CI: -4.4.; -2.0) lower serum osteocalcin level compared to non-use of TD, when adjusted for Rotterdam Study cohort, age, and sex. Our results may implicate that the decreased fracture risk in TD users is explained by increased bone mass rather than by improved bone microarchitecture. Alternatively, changes in bone microarchitecture might not be detected through TBS and more sophisticated techniques are possibly needed to study a potential effect of TD on bone microarchitecture.

Cisplatin Decreases ENaC Activity Contributing to Renal Salt Wasting Syndrome

Cisplatin (CDDP) is an important anticancer drug. A common side effect of CDDP is renal salt and water-wasting syndrome (RSWS). The origin of RSWS is obscure. Emerging evidence, though, suggests that broad inhibition of sodium transport proteins by CDDP may result in decreases in tubular reabsorption, causing increases in sodium and water excretion. In this sense, CDDP would be acting like a diuretic. The effect of CDDP on the epithelial Na⁺ channel (ENaC), which is the final arbiter fine-tuning renal Na⁺ excretion, is unknown. We test here whether CDDP affects ENaC to promote renal salt and water excretion. The effects of CDDP and benzamil (BZM), a blocker of ENaC, on excretion of a sodium load were quantified. Similar to BZM, CDDP facilitated renal Na⁺ excretion. To directly quantify the effects on ENaC, principal cells in split-open tubules were patch clamped. CDDP, at doses comparable to those used for chemotherapy (1.5 µM), significantly decreased ENaC activity in native tubules. To further elaborate on this mechanism, the dose-dependent effects of CDDP on mouse ENaC (mENaC) heterologously expressed in Chinese Hamster Ovary (CHO) cells were tested using patch clamping. As in native tubules, CDDP significantly decreased the activity of mENaC expressed in CHO cells. Dose–response curves and competition with amiloride identified CDDP as a weak inhibitor of ENaC (apparent IC₅₀ = 1 µM) that competes with amiloride for inhibition of the channel, weakening the inhibitory actions of the latter. Such observations are consistent with CDDP being a partial modulator of ENaC, which possibly has a binding site that overlaps with that of amiloride. These findings are consistent with inhibition of ENaC by CDDP contributing to the RSWS caused by this important chemotherapy drug.

Furosemide administration results in a transient alteration in calcium balance in mature horses

Previous research documented that furosemide negatively impacted calcium balance for 3 days but did not determine when calcium balance returned to baseline. This study hypothesized that furosemide's impact on calcium would return to control values before 7 days post-administration. Ten mature geldings were assigned to either control (CON, n = 5) or treatment (FUR, n = 5) for the first of two 8-day total collections in crossover design. Treatment horses received one administration of furosemide (1 mg/kg, IV). A 10% sample of pooled faeces and urine from each day was kept. Calcium concentrations in hay, faeces and urine were determined by an atomic absorption spectrophotometer. Data were analysed using mixed-model-repeated measures ANOVA to determine influence of day and treatment. For urine output, FUR urinated twice as much during the 24 hr after administration than CON (p < .001). Horses in FUR excreted more urinary calcium 24-hr post-administration as compared to CON (9.3 ± 1.0 and 4.2 ± 1.0 g, respectively; p < .001). Calcium balance in FUR was more negative on day 1 than day 3 (p < .05). Faecal calcium concentrations remained the same from day 1 to day 7 in CON (6.3 ± 1.3 and 5.5 ± 1.3 g/kg, respectively; p > .10) but were lower in FUR on day 7 as compared to day 1 (4.8 ± 1.3 and 7.3 ± 1.3 g/kg, respectively; p < .001), indicating a potential mechanism to restore calcium balance. These findings corroborate previous studies on furosemide and calcium balance and provide evidence for a possible mechanism to recover net calcium losses after furosemide administration. Since calcium balance returns to baseline in 3 days and previous results have examined frequent, long-term use, furosemide may not negatively impact bone mineral content even if used over long periods.

Claudins in Renal Physiology and Pathology

Claudins are integral proteins expressed at the tight junctions of epithelial and endothelial cells. In the mammalian kidney, every tubular segment express a specific set of claudins that give to that segment unique properties regarding permeability and selectivity of the paracellular pathway. So far, 3 claudins (10b, 16 and 19) have been causally traced to rare human syndromes: variants of CLDN10b cause HELIX syndrome and variants of CLDN16 or CLDN19 cause familial hypomagnesemia with hypercalciuria and nephrocalcinosis. The review summarizes our current knowledge on the physiology of mammalian tight junctions and paracellular ion transport, as well as on the role of the 3 above-mentioned claudins in health and disease. Claudin 14, although not having been causally linked to any rare renal disease, is also considered, because available evidence suggests that it may interact with claudin 16. Some single-nucleotide polymorphisms of CLDN14 are associated with urinary calcium excretion and/or kidney stones. For each claudin considered, the pattern of expression, the function and the human syndrome caused by pathogenic variants are described.

Thiazide Diuretics and the Incidence of Osteoporotic Fracture: A Systematic Review and Meta-Analysis of Cohort Studies

Background: Thiazide diuretics may improve bone mineral density. However, results are inconsistent for studies evaluating the association between thiazides and risk of osteoporotic fracture. We performed an updated meta-analysis of cohort studies to determine the association between thiazides use and fracture risk.

Methods: Relevant studies were identified via systematic search of PubMed and Embase. A random-effect model was used for meta-analysis. Subgroup analyses were performed to explore the potential influences of study characteristics on the outcome.

Results: Seventeen cohort studies with 3,537,504 participants were included. The pooled results showed that use of thiazide diuretics at baseline did not significantly affect the risk of overall osteoporotic fracture incidence as compared with controls (risk ratio [RR]: 0.96, 95% confidence interval [CI]: 0.83 to 1.09, p = 0.51) with significant heterogeneity (p for Cochrane’s Q test < 0.001, I² = 90%). Results of subgroup analyses indicated that general status of the participants may be an important determinant for the association between thiazide diuretics and subsequent risk of osteoporotic fracture. Use of thiazide diuretics was associated with significantly reduced risk of fracture in patients with acute status including new-onset stroke or spinal cord injury (RR: 0.70, 95% CI: 0.57 to 0.86, p < 0.001), but not in those with good conditions such as community-dwelling population or hypertensive patients (p for subgroup difference = 0.02).

Conclusions: Use of thiazide diuretics is not associated with significantly affected risk of overall osteoporotic fracture. However, the association may be different according to the general status of the participants.

Dent disease: A window into calcium and phosphate transport

This review examines calcium and phosphate transport in the kidney through the lens of the rare X-linked genetic disorder Dent disease. Dent disease type 1 (DD1) is caused by mutations in the CLCN5 gene encoding ClC-5, a Cl^- /H⁺ antiporter localized to early endosomes of the proximal tubule (PT). Phenotypic features commonly include low molecular weight proteinuria (LMWP), hypercalciuria, focal global sclerosis and chronic kidney disease; calcium nephrolithiasis, nephrocalcinosis and hypophosphatemic rickets are less commonly observed. Although it is not surprising that abnormal endosomal function and recycling in the PT could result in LMWP, it is less clear how ClC-5 dysfunction disturbs calcium and phosphate metabolism. It is known that the majority of calcium and phosphate transport occurs in PT cells, and PT endocytosis is essential for calcium and phosphorus reabsorption in this nephron segment. Evidence from ClC-5 KO models suggests that ClC-5 mediates parathormone endocytosis from tubular fluid. In addition, ClC-5 dysfunction alters expression of the sodium/proton exchanger NHE3 on the PT apical surface thus altering transcellular sodium movement and hence paracellular calcium reabsorption. A potential role for NHE3 dysfunction in the DD1 phenotype has never been investigated, either in DD models or in patients with DD1, even though patients with DD1 exhibit renal sodium and potassium wasting, especially when exposed to even a low dose of thiazide diuretic. Thus, insights from the rare disease DD1 may inform possible underlying mechanisms for the phenotype of hypercalciuria and idiopathic calcium stones.

Pharmacological Npt2a Inhibition Causes Phosphaturia and Reduces Plasma Phosphate in Mice with Normal and Reduced Kidney Function

BACKGROUND

The kidneys play an important role in phosphate homeostasis. Patients with CKD develop hyperphosphatemia in the later stages of the disease. Currently, treatment options are limited to dietary phosphate restriction and oral phosphate binders. The sodium-phosphate cotransporter Npt2a, which mediates a large proportion of phosphate reabsorption in the kidney, might be a good therapeutic target for new medications for hyperphosphatemia.

METHODS

The authors assessed the effects of the first orally bioavailable Npt2a inhibitor (Npt2a-I) PF-06869206 in normal mice and mice that had undergone subtotal nephrectomy (5/6 Nx), a mouse model of CKD. Dose-response relationships of sodium, chloride, potassium, phosphate, and calcium excretion were assessed in response to the Npt2a inhibitor in both groups of mice. Expression and localization of Npt2a/c and levels of plasma phosphate, calcium, parathyroid hormone (PTH) and fibroblast growth factor 23 (FGF-23) were studied up to 24-hours after Npt2a-I treatment.

RESULTS

In normal mice, Npt2a inhibition caused a dose-dependent increase in urinary phosphate (ED₅₀ approximately 21 mg/kg), calcium, sodium and chloride excretion. In contrast, urinary potassium excretion, flow rate and urinary pH were not affected dose dependently. Plasma phosphate and PTH significantly decreased after 3 hours, with both returning to near baseline levels after 24 hours. Similar effects were observed in the mouse model of CKD but were reduced in magnitude.

CONCLUSIONS

Npt2a inhibition causes a dose-dependent increase in phosphate, sodium and chloride excretion associated with reductions in plasma phosphate and PTH levels in normal mice and in a CKD mouse model.

K+-Cl- cotransporter 1 (KCC1): a housekeeping membrane protein that plays key supplemental roles in hematopoietic and cancer cells

During the 1970s, a Na+-independent, ouabain-insensitive, N-ethylmaleimide-stimulated K+-Cl- cotransport mechanism was identified in red blood cells for the first time and in a variety of cell types afterward. During and just after the mid-1990s, three closely related isoforms were shown to account for this mechanism. They were termed K+-Cl- cotransporter 1 (KCC1), KCC3, and KCC4 according to the nomenclature of Gillen et al. (1996) who had been the first research group to uncover the molecular identity of a KCC, that is, of KCC1 in rabbit kidney. Since then, KCC1 has been found to be the most widely distributed KCC isoform and considered to act as a housekeeping membrane protein. It has perhaps received less attention than the other isoforms for this reason, but as will be discussed in the following review, there is probably more to KCC1 than meets the eye. In particular, the so-called housekeeping gene also appears to play crucial and specific roles in normal as well as pathological hematopoietic and in cancer cells.

Valproic Acid Inhibits NA-K-2CL Cotransporter RNA Expression in Male But Not in Female Rat Thymocytes

Objective

The NKCC1 is a recognized tumorigenesis marker as it is important for tumor cell proliferation, differentiation, apoptosis, and tumor progression. The study aim was to investigate the effect of sodium valproate (VPA) on thymus NKCC1 RNA expression.

Material and Methods

Wistar rats, age 4 to 5 weeks, were investigated in the control and VPA-treated male and female gonad-intact and castrated groups. The treatment duration with VPA 300 mg/kg/d was 4 weeks. Rat thymus was weighted; its lobe was taken for the expression of NKCC1 RNA determined by the real-time polymerase chain reaction method.

Results

The RNA expression of the Slc12a2 gene was found to be significantly higher in the gonad-intact male control compared with the gonad-intact female control (P = .04). There was a gender-related VPA treatment effect on NKCC1 RNA expression in thymus: The Slc12a2 gene RNA expression level was found to be decreased in VPA-treated gonad-intact males (P = .015), and no significant VPA effects were found in the castrated males and in the gonad-intact and castrated females compared with the respective controls (P > .05).

Conclusions

The study showed a gender-related difference in the NKCC1 RNA expression in rat thymus. The VPA decreases the NKCC1 expression in the thymus only in gonad-intact male rats. The NKCC1 RNA expression downregulation by VPA could be important for further VPA pharmacological studies in oncology.

Deregulated renal magnesium transport during lipopolysaccharide-induced acute kidney injury in mice

Magnesium (Mg²⁺) abnormalities during sepsis have been reported, but the underlying mechanisms during acute inflammation are poorly understood. We hypothesized that a decrease in GFR and/or changes in transporters or channels for Mg²⁺ could be responsible for the observed Mg²⁺ abnormalities. Therefore, we studied the metabolism of Mg²⁺ in a murine model of endotoxemia. LPS-induced hypermagnesemia was paralleled by a decrease in creatinine clearance and an increase in the fractional excretion of Mg²⁺. In agreement with an altered renal Mg²⁺ handling, endotoxemia decreased the renal expression of claudin (Cldn) 10b, Cldn16, Cldn19, parvalbumin, and of the solute carrier family (Slc) 41a3. Further, LPS increased the renal expression of Cldn14 and Slc41a1. The renal expression of the transient receptor potential melastin (Trpm) 6, Trpm7, and of cyclin M (Cnnm) 2 was unaltered in response to LPS. In vitro studies support a direct effect on the expression of Cldn10b, Cldn14, Cldn16, and Cldn19. Further, endotoxemia increased the fractional excretion of sodium, which was paralleled by a decrease of important renal sodium transporters. In the large intestine, the expression of Trpm7 was increased in response to LPS, whereas the expression of Trpm6 was decreased. Cnnm4 mRNA levels were unchanged in the large intestine. Further, Cldn12 and Na⁺-H⁺ exchanger 3 (Slc9a3) expressions were decreased in the small intestine in response to LPS. Our findings indicate that endotoxemia is associated with hypermagnesemia and a disturbed Mg²⁺ handling. It seems likely that LPS-induced hypermagnesemia is due to the decrease in renal function in response to LPS.

Renal ischemia-reperfusion injury impairs renal calcium, magnesium, and phosphate handling in mice

Fibroblast growth factor 23 (FGF23) levels are elevated in patients with acute kidney injury (AKI). The consequences on renal Ca²⁺, Mg²⁺, and P_i regulatory mechanisms are unknown. We hypothesized that renal ischemia-reperfusion (I/R) injury alters the expression of important renal Ca²⁺, Mg²⁺, and P_i transport proteins. I/R injury was induced in male C57BL/6 mice by clamping both renal arteries for 27 min. Mice were investigated 18 h later. The mRNA and protein levels of renal Ca²⁺, Mg²⁺, and P_i transport proteins were measured by RT-qPCR and western blot analysis. I/R injury-induced hyperphosphatemia and hypermagnesemia were paralleled by a decrease in glomerular filtration rate and an increase in the fractional excretion of Ca²⁺, Mg²⁺, and P_i. I/R injury affected the fibroblast growth factor 23 (FGF23)-klotho-vitamin D axis by increasing plasma levels of FGF23 and downregulation of renal klotho expression. Plasma levels of PTH and 1,25-dihydroxyvitamin D₃ were unchanged. Further, downregulation of key genes for paracellular reabsorption of Ca²⁺ and Mg²⁺ (claudin (Cldn)2, Cldn10b, Cldn16, Cldn19) and for active transcellular transport of Ca²⁺, Mg²⁺, and P_i (calbindin-D_28K, Ncx1, Pmca4, Cnnm2, Trpm7, NaP_i-2a, and NaP_i-2c) was observed. However, renal expression of Trpv5 and Trpv6 was increased. In vitro studies support a direct effect of proinflammatory cytokines on the mRNA expression of Cldn16, Cldn19, and Trpv6. Our findings indicate that renal I/R injury increases FGF23 blood levels independent of PTH and 1,25-dihydroxyvitamin D₃. This increase is associated with hypermagnesemia, hyperphosphatemia, and increased or decreased expression of specific renal Ca²⁺, Mg²⁺, and P_i transporters, respectively.

Drug use is associated with lower plasma magnesium levels in geriatric outpatients; possible clinical relevance

BACKGROUND

Hypomagnesemia has been associated with diabetes, cardiovascular disease, and other disorders. Drug use has been suggested as one of the risk factors for low magnesium (Mg) levels. In the elderly population, prone to polypharmacy and inadequate Mg intake, hypomagnesemia might be relevant. Therefore, we aimed to investigate associations between drug use and plasma Mg.

METHODS

Cross-sectional data of 343 Dutch geriatric outpatients were analysed by Cox and linear regression, while adjusting for covariates. Drug groups were coded according to the Anatomical Therapeutic Chemical classification system; use was compared to non-use. Hypomagnesemia was defined as plasma Mg < 0.75 mmol/l and <0.70 mmol/l.

RESULTS

Prevalence of hypomagnesemia was 22.2% (Mg < 0.75 mmol/l) or 12.2% (Mg < 0.70 mmol/l); 67.6% of the patients used ≥5 medications (polypharmacy). The number of different drugs used was inversely linearly associated with Mg level (beta -0.01; p < 0.01). Fully adjusted Cox regression showed significant associations of polypharmacy with hypomagnesemia (Mg < 0.75 mmol/l) (prevalence ratio (PR) 1.81; 95%CI 1.08-3.14), proton pump inhibitors (PR 1.80; 95%CI 1.20-2.72), and metformin (PR 2.34; 95%CI 1.56-3.50). Moreover, stratified analyses pointed towards associations with calcium supplements (PR 2.26; 95%CI 1.20-4.26), insulins (PR 3.88; 95%CI 2.19-6.86), vitamin K antagonists (PR 2.01; 95%CI 1.05-3.85), statins (PR 2.44; 95%CI 1.31-4.56), and bisphosphonates (PR 2.97; 95%CI 1.65-5.36) in patients <80 years; selective beta blockers (PR 2.01; 95%CI 1.19-3.40) if BMI <27.0 kg/m²; and adrenergic inhalants in male users (PR 3.62; 95%CI 1.73-7.56). Linear regression supported these associations.

CONCLUSION

As polypharmacy and several medications are associated with hypomagnesemia, Mg merits more attention, particularly in diabetes, cardiovascular disease, and in side-effects of proton pump inhibitors and calcium supplements.

Hypoparathyroidism and the Kidney

Hypocalcemia and hyperphosphatemia are the pathognomonic biochemical features of hypoparathyroidism, and result directly from lack of parathyroid hormone (PTH) action on the kidney. In the absence of PTH action, the renal mechanisms transporting calcium and phosphate reabsorption deregulate, resulting in hypocalcemia and hyperphosphatemia. Circulating calcium negatively regulates PTH secretion. Hypocalcemia causes neuromuscular disturbances ranging from epilepsy and tetany to mild paresthesia. Circulating phosphate concentration does not directly regulate PTH secretion. Hyperphosphatemia is subclinical, but chronically promotes ectopic mineralization disease. Vitamin D-thiazide treatment leads to ectopic mineralization and renal damage. PTH treatment has the potential for fewer side effects.

Sodium Dichloroacetate Pharmacological Effect as Related to Na-K-2Cl Cotransporter Inhibition in Rats

The study objective was to investigate a possible sodium dichloroacetate (DCA) pharmacological mechanism causing an increase in diuresis in rats. The aim was to define characteristics of 24-hour urinary Na⁺, K⁺, Cl^-, Ca²⁺, and Mg²⁺ excretion in Wistar male rats and to evaluate effect of a single-dose DCA and repeated DCA dosage on diuresis. Six control and 6 DCA-treated male rats aged 5 to weeks after a single DCA dose and repeated dosage were tested. The single DCA dose treatment caused a significantly higher 24-hour diuresis when compared to control (P < .05), and it was related to increased Cl^-, Na⁺, and K⁺ urine excretion and a significant increase in Ca²⁺ and Mg²⁺ excretion (P < .05); after the repeated 4-week DCA dosage, the diuresis was not increased, but the excretion of the Na⁺, Cl^-, Ca²⁺, and Mg²⁺ ions was significantly higher. Kidney immunohistochemistry has revealed that DCA continuous treatment results in an increase in the size of Henle loop thick ascending limb epithelial cells (P < .001). The study results show a significantly reduced RNA expression of Na-K-2Cl co-transporter (NKCC1) in thymus of 4-week DCA-treated rats (P < .03). The study data have indicated a possible mechanism of such pharmacological effect to be NKCC inhibition.

A model of calcium transport and regulation in the proximal tubule

The objective of this study was to examine theoretically how Ca²⁺ reabsorption in the proximal tubule (PT) is modulated by Na⁺ and water fluxes, parathyroid hormone (PTH), Na⁺-glucose cotransporter (SGLT2) inhibitors, and acetazolamide. We expanded a previously published mathematical model of water and solute transport in the rat PT (Layton AT, Vallon V, Edwards A. Am J Physiol Renal Physiol 308: F1343–F1357, 2015) that did not include Ca²⁺. Our results indicate that Ca²⁺ reabsorption in the PT is primarily driven by the transepithelial Ca²⁺ concentration gradient that stems from water reabsorption, which is itself coupled to Na⁺ reabsorption. Simulated variations in permeability or transporter activity elicit opposite changes in paracellular and transcellular Ca²⁺ fluxes, whereas a simulated decrease in filtration rate lowers both fluxes. The model predicts that PTH-mediated inhibition of the apical Na⁺/H⁺ exchanger NHE3 reduces Na⁺ and Ca²⁺ transport to a similar extent. It also suggests that acetazolamide- and SGLT2 inhibitor-induced calciuria at least partly stems from reduced Ca²⁺ reabsorption in the PT. In addition, backleak of phosphate (PO₄) across tight junctions is predicted to reduce net PO₄ reabsorption by ~20% under normal conditions. When transcellular PO₄ transport is substantially reduced by PTH, paracellular PO₄ flux is reversed and contributes significantly to PO₄ reabsorption. Furthermore, PTH is predicted to exert an indirect impact on PO₄ reabsorption via its inhibitory action on NHE3. This model thus provides greater insight into the mechanisms that modulate Ca²⁺ and PO₄ reabsorption in the PT.