Disorders of calcium and magnesium balance: a physiology-based approach

The Association Between Dietary Magnesium Intake and Pulmonary Function: Recent Fndings from NHANES 2007-2012

This article aims to study the correlation between dietary magnesium intake and pulmonary function, utilizing data from the National Health and Nutrition Examination Survey (NHANES) database. This cross-sectional study examined representative samples of adults from the USA (n = 818; NHANES 2007-2012) to explore the correlation between magnesium intake and pulmonary function. We obtained the average magnesium intake over 2 days, as well as measured pulmonary function parameters, including forced expiratory volume in the first second (FEV1), forced vital capacity (FVC), FEV1/FVC, peak expiratory flow rate (PEF), and forced expiratory flow between 25 and 75% of FVC (FEF25-75%). Weighted multivariable linear regression was used to investigate the relationship between magnesium intake and pulmonary function. Additionally, subgroup analyses, interaction tests, and sensitivity analyses were conducted. Weighted multiple linear regression models revealed a significant positive correlation between magnesium and pulmonary function, even after adjusting for all included confounding variables. When we categorized magnesium intake into tertiles, we found that participants in the highest tertile of magnesium intake had significantly higher values for FVC (β: 898.54, 95%CI: 211.82-1585.25), FEV1 (β: 858.16, 95%CI: 212.41-1503.91), FEV1/FVC (β: 0.024, 95%CI: 0.004-0.044), PEF (β: 1324.52, 95%CI: 481.71-2167.33), and FEF25-75% (β: 831.39, 95%CI: 84.93-1577.84). Upon stratifying the data by age and sex, it was observed that this positive correlation was particularly pronounced among men aged 40-79. At the same time, the stability of the results was further confirmed by sensitivity analyses. This study suggested that dietary magnesium intake may improve pulmonary function.

Hypomagnesemia-Induced Seizures Post Severe Acute Kidney Injury

Acute kidney injury (AKI) is a common complication in children admitted to pediatric intensive care units. It is known to be associated with increased morbidity and mortality. Here, we report prolonged, transient, increased renal magnesium (Mg) wasting after severe acute kidney injury presenting with a generalized tonic-clonic seizure.

The Impact of Multispecies Probiotics on Calcium and Magnesium Status in Healthy Male Rats

Although probiotics have been discovered in numerous diseases in the last decade, there is little consensus on the relationship between probiotic properties and minerals balance and their distribution in the organism. This research aimed to evaluate the calcium (Ca) and magnesium (Mg) status in rats on a diet containing multispecies probiotics. Thirty male 10-week-old Wistar rats were selected and divided into three groups (n = 10 rats)—a group fed a standard diet (C), a group fed a low-dose of multispecies probiotics with 2.5 × 10⁹ CFU per day (LD), and a group fed high-dose of multispecies probiotics 1 × 10¹⁰ CFU per day (HD) for 6 weeks. The results revealed that HD intake significantly increased the Ca concentration in hair and Mg concentration in femur bones. A significant positive correlation was found between calcium and magnesium levels in hair. The Ca/Mg molar ratio was lower in testicles in the groups with probiotics. In conclusion, multispecies probiotics altered the Ca concentration in hair and Mg level in femur bone, and also changed the molar ratio of these elements in testicles in male rats.

Dietary magnesium restriction affects hematopoiesis and triggers neutrophilia by increasing STAT-3 expression and G-CSF production

BACKGROUND & AIMS

Magnesium (Mg²⁺) is able to modulate the differentiation and proliferation of cells. Mg²⁺ restriction can trigger neutrophilia, but the processes that result in this change have yet to be investigated and are not fully understood. Hematopoiesis is a complex process that is regulated by many factors, including cytokines and growth factors, and is strongly influenced by nutrient availability. In this context, our objective was to investigate the impact of the short-term restriction of dietary Mg²⁺ on bone marrow hematopoietic and peripheral blood cells, especially in processes related to granulocyte differentiation and proliferation.

METHODS

Male C57BL/6 mice were fed a Mg²⁺ restricted diet (50 mg Mg²⁺/kg diet) for 4 weeks. Cell blood count and bone marrow cell count were evaluated. Bone marrow cells were also characterized by flow cytometry. Gene expression and cytokine production were evaluated, and a colony-forming cell assay related to granulocyte differentiation and proliferation was performed.

RESULTS

Short-term dietary restriction of Mg²⁺ resulted in peripheral neutrophilia associated with an increased number of granulocytic precursors in the bone marrow. Additionally, Mg²⁺ restriction resulted in an increased number of granulocytic colonies formed in vitro. Moreover, the Mg²⁺ restricted group showed increased expression of CSF3 and CEBPα genes as well as increased production of G-CSF in association with increased expression of STAT3 protein.

CONCLUSION

Short-term dietary restriction of Mg²⁺ induces granulopoiesis by increasing G-CSF production and activating the CEBPα and STAT-3 pathways, resulting in neutrophilia in peripheral blood.

Hypomagnesemia in the Cancer Patient

Hypomagnesemia is a common medical problem that contributes to the morbidity and mortality of patients with cancer. This review summarizes magnesium physiology and highlights the mechanisms underlying magnesium disturbances due to cancer and cancer treatment. The causes of hypomagnesemia can be categorized according to the pathophysiologic mechanism: decreased intake, transcellular shift, gastrointestinal losses, and kidney losses. Patients with cancer are at risk for opportunistic infections, frequently experience cardiovascular complications, and often receive classes of medications that cause or exacerbate hypomagnesemia. Also, cancer-specific therapies are responsible for hypomagnesemia, including platinum-based chemotherapy, anti-EGF receptor mAbs, human EGF receptor-2 target inhibitors (HER2), and calcineurin inhibitors. Urinary indices, such as the fractional excretion of magnesium, can provide useful information about the etiology. The management of hypomagnesemia depends on the magnitude of hypomagnesemia and the underlying cause. We recommended checking serum magnesium at the beginning of treatment and as part of routine monitoring throughout cancer treatment. Opportunities exist for potential research and practice improvement, including further characterization of hypomagnesemia regarding the clinical effect on cancer outcomes, preventing hypomagnesemia in patients receiving high-risk anticancer agents, and developing effective therapeutic strategies.

General Aspects of Metal Ions as Signaling Agents in Health and Disease

This review focuses on the current knowledge on the involvement of metal ions in signaling processes within the cell, in both physiological and pathological conditions. The first section is devoted to the recent discoveries on magnesium and calcium-dependent signal transduction-the most recognized signaling agents among metals. The following sections then describe signaling pathways where zinc, copper, and iron play a key role. There are many systems in which changes in intra- and extra-cellular zinc and copper concentrations have been linked to important downstream events, especially in nervous signal transduction. Iron signaling is mostly related with its homeostasis. However, it is also involved in a recently discovered type of programmed cell death, ferroptosis. The important differences in metal ion signaling, and its disease-leading alterations, are also discussed.

Pharmacokinetics of magnesium and its effects on clinical variables following experimentally induced hypermagnesemia

The objectives of this study were to describe pharmacokinetic and pharmacodynamic changes as a result of a single intravenous administration of magnesium sulfate (MgSO₄ ) to healthy horses. MgSO₄ is a magnesium salt that has been used to calm horses in equestrian competition and is difficult to regulate because magnesium is an essential constituent of all mammals. Six healthy adult female horses were administered a single intravenous dose of MgSO₄ at 60 mg/kg of body weight over 5 min. Blood, urine, and cerebrospinal fluid (CSF) samples were collected, and cardiovascular parameters were monitored and echocardiograms performed at predetermined times. Noncompartmental pharmacokinetic analysis was applied to plasma concentrations of ionized magnesium (Mg²⁺ ). Objective data were analyzed using the Wilcoxon rank-sum test with p < .05 used as a determination for significance. Plasma concentrations of Mg²⁺ increased nearly fivefold, ionized calcium (Ca²⁺ ) decreased by nearly 10%, and the Ca²⁺ to Mg²⁺ ratio declined more than 3.5-fold and remained different than baseline until 24 hr (p < .05). Significant changes were seen with urinary fractional excretion of electrolytes, cardiovascular parameters, and echocardiographic measurements. No changes were detected in CSF electrolyte concentrations. The decrease in Ca²⁺ result of hypermagnesemia supports the interaction between these cations. Alterations detected in plasma electrolyte concentrations and urinary fractional excretion of electrolytes may serve as biomarkers for regulatory control for the nefarious administration of MgSO₄ .

Overweight & obese Australian adults and micronutrient deficiency

Background

Micronutrients have been implicated as an important factor in regulating various metabolic processes and thus playing a role in the aetiology of obesity. Many studies have been conducted worldwide that clearly show a direct link between obesity and micronutrient deficiencies. The aim of this study was to assess the nutritional status of overweight and obese Australian adults to see if there were any associations between BMI and serum micronutrient levels.

Methods

Baseline serum micronutrient data of overweight and obese individuals with a body mass index (BMI) between 25 and 40 kg/m² and aged between 18 and 65 years was compared to the clinical micronutrient reference ranges for associations between BMI and micronutrient status.

Results

There were significant negative associations between BMI and serum vitamin D (p = 0.044), folate (p = 0.025), magnesium (p = 0.010) and potassium (p = 0.023).

Conclusions

Overweight and obesity appears to impact on the bioavailability and utilisation of micronutrients with absorption, excretion, storage/distribution (fat sequestering, tissue dispersion), metabolism (catabolic losses, possibly oxidative), increased physiologic requirements, and lower absolute total dietary intake being the current theory for observed differences. While vitamins D, folate, magnesium and potassium showed a negative relationship to BMI, other micronutrients did not. This may be explained by the fortification of certain processed foods, or the possibility of overweight and obese people eating more to satisfy their nutritional requirements.

Vitamin D deficiency is a potential risk factor for lipid Amphotericin B nephrotoxicity

Invasive fungal infections (IFI) is a worldwide serious health problem and Amphotericin B (AmB) has been considered the drug of choice for IFI treatment. Despite its efficacy, clinical use of AmB has been associated with renal toxicity. Some lines of evidence have shown that an extemporaneous lipid emulsion preparation of AmB (AmB/LE) was able to attenuate nephrotoxicity, presenting similar benefits at a lower cost. Studies have been demonstrating that hypovitaminosis D may hasten the progression of kidney disease and reflect on a worse prognosis in cases of drug-induced nephrotoxicity. In view of the high worldwide incidence of hypovitaminosis D, the aim of this study was to investigate whether vitamin D deficiency may induce AmB/LE-related nephrotoxicity. Wistar rats were divided into four groups: control, received a standard diet for 34 days; AmB/LE, received a standard diet for 34 days and AmB/LE (5 mg/kg/day) intraperitoneally in the last 4 days; VDD, received a vitamin D-free diet for 34 days; and VDD+AmB/LE, received a vitamin D-free diet for 34 days and AmB/LE as described. At the end of the protocol, animals were euthanized and blood, urine and renal tissue samples were collected in order to evaluate AmB/LE effects on renal function and morphology. Association of AmB/LE and vitamin D deficiency led to diminished glomerular filtration rate and increased tubular injury, evidenced by reduced renal protein expression of NaPi-IIa and TRPM6 leading to hyperphosphaturia / hypermagnesuria. VDD+AmB/LE rats also presented alterations in the PTH-Klotho-FGF-23 signaling axis, urinary concentrating defect and hypertension, probably due to an inappropriate activation of the renin-angiotensin-aldosterone system. Hence, it is important to monitor vitamin D levels in AmB/LE treated patients, since vitamin D deficiency induces AmB/LE nephrotoxicity.

Amphotericin B (AmB) is the treatment of choice for systemic fungal infections. Despite its efficacy, clinical use of AmB has been associated with renal toxicity. In an attempt to improve the therapeutic effect and to reduce adverse reactions, lipid formulations of AmB were developed. Among these formulations, an in-house lipid emulsion preparation of AmB (AmB/LE) is a lower cost alternative with similar benefits. Furthermore, vitamin D is an essential nutrient for the regulation of several physiological activities. Hence, vitamin D deficiency or insufficiency can contribute to the progression of diseases and increase the risk of chronic illnesses as well. Nowadays, VDD is a health problem worldwide and its prevalence in general population is high, including the sunny and industrialized countries, where vitamin D supplementation has been successfully implemented. Thus, it is essential to monitor vitamin D levels in both patients treated with conventional or lipid formulations of AmB in order to ensure a better prognosis in the development of renal diseases.

TRPV5 in renal tubular calcium handling and its potential relevance for nephrolithiasis

Nephrolithiasis or renal stone disease is an increasingly common problem, and its relatively high recurrence rate demands better treatment options. The majority of patients with nephrolithiasis have stones that contain calcium (Ca²⁺), which develop upon "supersaturation" of the urine with insoluble Ca²⁺ salts; hence processes that influence the delivery and renal handling of Ca²⁺ may influence stone formation. Idiopathic hypercalciuria is indeed frequently observed in patients with kidney stones that contain Ca²⁺. Genetic screens of nephrolithiasis determinants have identified an increasing number of gene candidates, most of which are involved in renal Ca²⁺ handling. This review provides an outline of the current knowledge regarding genetics of nephrolithiasis and will mainly focus on the epithelial Ca²⁺ channel transient receptor potential vanilloid 5 (TRPV5), an important player in Ca²⁺ homeostasis. Being a member of the TRP family of ion channels, TRPV5 is currently part of a revolution in structural biology. Recent technological breakthroughs in the cryo-electron microscopy field, combined with improvements in biochemical sample preparation, have resulted in high-resolution 3-dimensional structural models of integral membrane proteins, including TRPV5. These models currently are being used to explore the proteins' structure-function relationship, elucidate the molecular mechanisms of channel regulation, and study the putative effects of disease variants. Combined with other multidisciplinary approaches, this approach may open an avenue toward better understanding of the pathophysiological mechanisms involved in hypercalciuria and stone formation, and ultimately it may facilitate prevention of stone recurrence through the development of effective drugs.

Parathyroid glands: the normal development, anatomy and histological structure

Parathyroid glands (PG) are endocrine glands, which are the most important humoral regulators of calcium and phosphorus metabolism in the body. They were first described by an Englishman Richard Owen in 1849. Most of patients have four PG – upper and lower. In 13% of cases there are more than four PG. The glands arise as diverticula from the endoderm of the third and fourth branchial pouches between the fifth and twelfth week of gestation. The IV branchial pouch forms the upper gland, and III pouch forms the inferior gland. The parathyroid hormone production has been demonstrated as early as 83/7 weeks gestational age. The formation, migration, differentiation and functioning of the PGs are determined by a number of genes and changes in them could lead to disfunction in these processes. The ectopic of PG is possible when migration violation (up to 22% of cases). The most common location of the ectopic PG is parenchyma of the thymus and thyroid gland. Each PG is richly vascularized and it is surrounded by a thin connective tissue. In adults, there are two types of parenchymal cells: the chief cells (active and inactive forms) and the oxyphil cells. During the life, the ratio of types of parenchymal cells and their activity have been changing, as well as the characteristics of the stroma.

Medical Hypoparathyroidism

Hypoparathyroidism is a metabolic disorder characterized by hypocalcemia, hyperphosphatemia, and inadequate levels of or function of parathyroid hormone (PTH). The authors review the nonsurgical or medical causes of hypoparathyroidism. The most common of the nonsurgical causes is autoimmune destruction of the parathyroid. Magnesium deficiency or excess can cause a functional hypoparathyroidism. Genetic conditions result in hypoparathyroidism as part of a syndrome or in isolation. Pseudohypoparathyroidism reflects a resistance to PTH. Infiltrative, metastatic, radiation destruction, mineral deposition, or idiopathic are uncommon causes of hypoparathyroidism. This article reviews the causes of hypoparathyroidism and an approach to the evaluation of this condition.

Extreme hypomagnesemia: characteristics of 119 consecutive inpatients

Extreme hypomagnesemia (hypoMg) can be encountered in many situations, but little data currently exist. Our aim is to describe the epidemiological, clinical, etiological characteristics, and the biological abnormalities of consecutive inpatients with extreme hypomagnesemia. In our observational monocentric study, between 1st July 2000 and April 2015, all inpatients with extreme hypomagnesemia, defined by at least one plasma magnesium concentration (P_Mg) below 0.3 mmol/L, were included. Demographic, clinical, biological characteristics and the drugs prescribed before the qualifying P_Mg measurement were retrospectively collected. 41,069 patients had at least one P_Mg assessment. The prevalence of extreme hypomagnesemia is 0.3% (119 inpatients). The median age is 70 years, 52% are women. The patients were mainly hospitalized in intensive care (n = 37, 31.1%), oncology (n = 21, 17.6%), gastroenterology (n = 18, 15.1%) and internal medicine (n = 16, 13.4%) departments. One hundred patients (84%) had a medical history of gastrointestinal disease (39% with bowel resections, 24% with stoma), and 50 (42%) had a cancer history. The drugs most commonly prescribed (known to induce hypoMg) are proton pump inhibitors (PPI) (n = 77, 70%), immunosuppressive regimens (n = 25, 22.5%), platinum salt-based chemotherapies (n = 19, 17.1%), and diuretics (n = 22, 19.8%). The suspected causes of hypomagnesemia are often multiple, but drugs (46%, including PPI in 19%) and chronic gastrointestinal disorders (37%) are prominent. Associated electrolyte disturbances include hypocalcemia (77%) and mild hypokalemia (51%). The 1-month mortality from all causes is 16%. Extreme hypomagnesemia is rare in inpatients, and is frequently associated with severe hypocalcemia. Digestive disorders and drugs are the main contributory causes.

Ionized magnesium and calcium concentration and their ratio in equine plasma samples as determined by a regulatory laboratory compared to a clinical reference laboratory

Magnesium sulfate (MgSO₄ ) was administered to calm competition horses. We evaluated the impact of regulatory requirements for the handling of blood samples on plasma ionized magnesium (iMg), ionized calcium (iCa), the iMg to iCa ratio, and pH. We hypothesized that iCa, iMg. and iMg/iCa would be similar among storage and collection methods. Four blood samples were collected from each of 50 horses on the same day: Group 1 - collection in a heparinized syringe and processed within hours in a clinical laboratory; Group 2 - collection into a plasma separator tube (PST) centrifuged just prior to analysis, and plasma processed as in (1); Group 3 - collection into a PST, refrigerated, shipped via overnight carrier to the United States Equestrian Federation (USEF) Equine Drug Testing and Research laboratory, centrifuged just prior to analysis, and plasma processed; and Group 4 - as in Group 3, but stored frozen at -80°C for 90 days, thawed, and plasma processed as in Group 3. Results for iMg/iCa are unit-less, adjusted iMg for potential influence of plasma protein and iCa, and highly correlated with iMg pH (r = -.933; P < 0.01). Samples processed immediately in a clinical reference laboratory had the greatest iMg/iCa. Both iMg/iCa and pH predictably decreased after freezing (P < 0.001). These data suggest that the iMg/iCa mirrors alterations in iMg regardless of storage and collection methods. This understanding can facilitate the development of a regulatory threshold for the control of the nefarious use of magnesium sulfate in competing horses, and an understanding of potential changes to iMg/iCa with storage of B samples.

Childhood Sustained Hypercalcemia: A Diagnostic Challenge

OBJECTIVE

This study aimed to call attention to hypercalcemia, a rare finding in children which carries the potential of leading to serious complications without proper intervention.

METHODS

Diagnosis, treatment, and clinical course of children with sustained hypercalcemia admitted between the years 2006-2016 were reviewed. Group 1 [parathyroid hormone (PTH)-dependent] consisted of patients with high/unsuppressed PTH levels and group 2 (PTH-independent) included cases with normal/suppressed PTH levels.

RESULTS

Twenty patients (11 male, 9 female) with a median age of 6.25 (0.03-17.88) years were evaluated. Symptoms were mostly related with the gastrointestinal system, while six patients (30%) were asymptomatic. Physical examination findings were diverse, non-specific, and normal in four patients (20%). Median time of diagnosis was 45 (2-720) days. Patients were divided into group 1 (n=7) and group 2 (n=13). Most frequent etiologies were primary hyperparathyroidism (n=5), idiopathic infantile hypercalcemia (IIH) (n=5), and malignancy (n=4). A moderate positive correlation was noted between serum calcium and creatinine levels (r=0.53, p=0.02). Nephrocalcinosis was the most common complication (n=9) (45%). Treatment was not implemented in 2 patients with mild hypercalcemia, while other patients received medical treatment ± surgery. Treatment-resistant patients were cases of malignancies and neonatal severe hyperparathyroidism. Long-term follow-up displayed resistant hypercalciuria in three infants diagnosed as IIH.

CONCLUSION

Many patients with childhood hypercalcemia are asymptomatic or exhibit a non-specific and heterogeneous clinical presentation, resulting in delayed diagnosis. Mild cases may not be recognized, while symptoms may be missed in the presence of accompanying illnesses. Nevertheless, serious complications may only be avoided with prompt diagnosis and intervention.

A Case of Renal Tubular Acidosis with Sjogren's Syndrome Showing Paradoxical Block of PTH Due to Severe Hypomagnesemia

Distal renal tubular acidosis (RTA) manifests either as Complete/Classical form or Incomplete/Latent Form. Distal RTA causes normal anion gap metabolic acidosis and hypokalemia. Interstitial Nephritis is the most frequent renal manifestation of Sjogren's, which presents as Distal RTA in 25-40% of patients with Sjogren's syndrome. Magnesium deficiency is frequently associated with hypokalemia. Although serum calcium is the main physiological control for the secretion of parathyroid hormone (PTH) by the parathyroid, serum magnesium can also exert similar effects. While low levels of magnesium stimulate the secretion of PTH, very low serum concentrations tend to induce a paradoxical block of PTH release by activation of the alpha-subunits of heterotrimeric G-proteins. This mimicks the activation of calcium sensing receptor leading to inhibition of PTH secretion. Here we describe the case history of a 35-year-old lady who presented to our hospital with severe hypokalemia due to distal RTA and perhaps had a paradoxical block of PTH secretion in the setting of severe hypomagnesemia.

A case of hypercalcemia with double pathology

Hypercalcemia has many causes including primary hyperparathyroidism, malignancy, and other rare etiologies. In most of the cases, hypercalcemia is secondary to one etiology. In this case, we are reporting hypercalcemia with two causes. The initial workup showed primary hyperparathyroidism due to parathyroid adenoma. But because all features were not fully explained by primary hyperparathyroidism, further work-up revealed multiple myeloma. This case represents coexistence of two different diseases, which was rarely reported in the literature previously. Usually, the co-diagnosis was made subsequently after failure to correct hypercalcemia. In our case, both diagnoses were established at the same time of the patient’s presentation as of high suspicion. Establishing the diagnosis early will aid in the initiation of treatment in a timely fashion.

Low magnesium diet alters distribution of macroelements and trace elements in tissues and organs of female rats

The aim of the present study was to assess whether dietary magnesium deficiency can alter distribution of macroelements and trace elements in different organs and tissues. Experiments were carried out on 12 adult female Wistar rats, which were fed either a diet with low Mg content (≤20mgkg^-1 of diet) (LMgD) or a diet with daily recommended Mg content (≈500mgkg^-1) as control group (CG) for 70 days. On the 70th day of the experiment heart, aorta, femoral skeletal muscle, forebrain, cerebellum, pituitary gland, thyroid gland, ovaries, uterus, liver, kidneys, and spleen were taken for analysis of mineral content. Concentrations of Fe and Ca were measured by inductively coupled plasma-atomic emission spectrometry, and levels of Na, K, Mg, Co, Cu, Zn, Ni, Se, I were determined by inductively coupled plasma mass spectrometry. On the 70th day, LMgD led to significant reduction of Mg level in red blood cells, plasma, aorta, uterus and thyroid gland compared to CG as well as resulted in significant decrease of Mg/Ca ratio in kidneys, spleen and ovaries. Contrary to this, an increase of Mg/Ca ratio was found in cerebellum of LMgD group. Significant decrease of K concentration was shown in aorta of LMgD animals compared to CG whereas myocardial K concentration was increased in LMgD group. Na level was two-fold higher in skeletal muscles of rats that received LMgD in comparison to CG (p=0.006). Increased concentrations of Fe in ovaries and uterus were found in LMgD. Mg restriction did not affect Zn concentration in any of tasted tissues. Se level was higher in spleen and lower in uterus of LMgD animals compared to CG. MgD was accompanied by increased level of Co in skeletal muscles and decreased its level in kidneys and uterus. LMgD feeding was associated with decreased concentrations of Ni in heart, thyroid gland, spleen, uterus and Co in heart, aorta, liver, kidneys, spleen and ovaries. The changes of Mg, K, Co content were accompanied by dramatic (10-fold) decrease of I concentration in aorta of LMgD animals. LMgD causes decrease of I content in ovaries and increase of I level in uterus vs CG. Thus, distribution of macroelements (Ca, Na, K) was weakly affected by Mg restriction that led to the most evident alterations of Co and Ni tissue levels. Moreover, mineral balance of uterus seems to be the most susceptible to low Mg intake. Hypomagnesaemia resulted in significant changes of 5 studied trace elements (Fe, Se, Cu, Ni and Co).

Calcium Homeostasis in Health and in Kidney Disease

Calcium is an important ion in cell signaling, hormone regulation, and bone health. Its regulation is complex and intimately connected to that of phosphate homeostasis. Both ions are maintained at appropriate levels to maintain the extracellular to intracellular gradients, allow for mineralization of bone, and to prevent extra skeletal and urinary calcification. The homeostasis involves the target organs intestine, parathyroid glands, kidney, and bone. Multiple hormones converge to regulate the extracellular calcium level: parathyroid hormone, vitamin D (principally 25(OH)D or 1,25(OH)2D), fibroblast growth factor 23, and α-klotho. Fine regulation of calcium homeostasis occurs in the thick ascending limb and collecting tubule segments via actions of the calcium sensing receptor and several channels/transporters. The kidney participates in homeostatic loops with bone, intestine, and parathyroid glands. Initially in the course of progressive kidney disease, the homeostatic response maintains serum levels of calcium and phosphorus in the desired range, and maintains neutral balance. However, once the kidneys are no longer able to appropriately respond to hormones and excrete calcium and phosphate, positive balance ensues leading to adverse cardiac and skeletal abnormalities. © 2016 American Physiological Society. Compr Physiol 6:1781-1800, 2016.

HNF1B-associated clinical phenotypes: the kidney and beyond

Mutations in HNF1B, the gene encoding hepatocyte nuclear factor 1β are the most commonly identified genetic cause of renal malformations. HNF1B was first identified as a disease gene for diabetes (MODY5) in 1997, and its involvement in renal disease was subsequently noted through clinical observations in pedigrees affected by MODY5. Since then, a whole spectrum of associated phenotypes have been reported, including genital malformations, autism, epilepsy, gout, hypomagnesaemia, primary hyperparathyroidism, liver and intestinal abnormalities and a rare form of kidney cancer. The most commonly identified mutation, in approximately 50 % of patients, is an entire gene deletion occurring in the context of a 17q12 chromosomal microdeletion that also includes several other genes. Some of the associated phenotypes, especially the neurologic ones, appear to occur only in the context of this microdeletion and thus may not be directly linked to HNF1B. Here we review the spectrum of associated phenotypes and discuss potential implications for clinical management.

Calcium Extrusion Pump PMCA4: A New Player in Renal Calcium Handling?

Calcium (Ca²⁺) is vital for multiple processes in the body, and maintenance of the electrolyte concentration is required for everyday physiological function. In the kidney, and more specifically, in the late distal convoluted tubule and connecting tubule, the fine-tuning of Ca²⁺ reabsorption from the pro-urine takes place. Here, Ca²⁺ enters the epithelial cell via the transient receptor potential vanilloid receptor type 5 (TRPV5) channel, diffuses to the basolateral side bound to calbindin-D_28k and is extruded to the blood compartment via the Na⁺/Ca²⁺ exchanger 1 (NCX1) and the plasma membrane Ca²⁺ ATPase (PMCA). Traditionally, PMCA1 was considered to be the primary Ca²⁺ pump in this process. However, in recent studies TRPV5-expressing tubules were shown to highly express PMCA4. Therefore, PMCA4 may have a predominant role in renal Ca²⁺ handling. This study aimed to elucidate the role of PMCA4 in Ca²⁺ homeostasis by characterizing the Ca²⁺ balance, and renal and duodenal Ca²⁺-related gene expression in PMCA4 knockout mice. The daily water intake of PMCA4 knockout mice was significantly lower compared to wild type littermates. There was no significant difference in serum Ca²⁺ level or urinary Ca²⁺ excretion between groups. In addition, renal and duodenal mRNA expression levels of Ca²⁺-related genes, including TRPV5, TRPV6, calbindin-D_28k, calbindin-D_9k, NCX1 and PMCA1 were similar in wild type and knockout mice. Serum FGF23 levels were significantly increased in PMCA4 knockout mice. In conclusion, PMCA4 has no discernible role in normal renal Ca²⁺ handling as no urinary Ca²⁺ wasting was observed. Further investigation of the exact role of PMCA4 in the distal convoluted tubule and connecting tubule is required.

Hypomagnesemia Induced by Long-Term Treatment with Proton-Pump Inhibitors

In 2006, hypomagnesemia was first described as a complication of proton-pump inhibitors. To address this issue, we systematically reviewed the literature. Hypomagnesemia, mostly associated with hypocalcemic hypoparathyroidism and hypokalemia, was reported in 64 individuals on long-term proton-pump inhibitors. Hypomagnesemia recurred following replacement of one proton-pump inhibitor with another but not with a histamine type-2 receptor antagonist. The association between proton-pump inhibitors and magnesium metabolism was addressed in 14 case-control, cross-sectional studies. An association was found in 11 of them: 6 reports found that the use of proton-pump inhibitors is associated per se with a tendency towards hypomagnesemia, 2 found that this tendency is more pronounced in patients concurrently treated with diuretics, carboplatin, or cisplatin, and 2 found a relevant tendency to hypomagnesemia in patients with poor renal function. Finally, findings likely reflecting decreased intestinal magnesium uptake were observed on treatment with proton-pump inhibitors. Three studies did not disclose any relationship between magnesium metabolism and treatment with histamine type-2 receptor antagonists. In conclusion, proton-pump inhibitors may cause hypomagnesemia. In these cases, switching to a histamine type-2 receptor antagonist is advised.

Etiologic and therapeutic analysis in patients with hypokalemic nonperiodic paralysis

BACKGROUND

Hypokalemic nonperiodic paralysis represents a group of heterogeneous disorders with a large potassium (K(+)) deficit. Rapid diagnosis of curable causes with appropriate treatment is challenging to avoid the sequelae of hypokalemia. We prospectively analyzed the etiologies and therapeutic characteristics of hypokalemic nonperiodic paralysis.

METHODS

Over an 8-year period, patients with hypokalemic nonperiodic paralysis were enrolled by excluding those with hypokalemic periodic paralysis due to acute shift of K(+) into cells. Blood and spot urine samples were collected for the measurements of electrolytes, pH, and biochemistries. Intravenous potassium chloride (KCl) at a rate of 10-20 mmol/h was administered until muscle strength recovered.

RESULTS

We had identified 58 patients with hypokalemic nonperiodic paralysis from 208 consecutive patients with hypokalemic paralysis, and their average K(+) concentration was 1.8 ± 0.2 mmol/L. Among patients with low urinary K(+) excretion (n = 17), chronic alcoholism, remote diuretic use, and anorexia/bulimia nervosa were the most common causes. Among patients with high urinary K(+) excretion (n = 41) and metabolic acidosis, renal tubular acidosis and chronic toluene abuse were the main causes, while primary aldosteronism, Gitelman syndrome, and diuretics were the leading diagnoses with metabolic alkalosis. The average KCl dose needed to restore muscle strength was 3.8 ± 0.8 mmol/kg. Initial lower plasma K(+), volume depletion, and high urinary K(+) excretion were associated with higher recovery KCl dosage. During therapy, patients with paradoxical hypokalemia (n = 32) who required more KCl supplementation than patients without (4.1 ± 0.7 vs 3.4 ± 0.7 mmol/kg, P < 0.001) often exhibited significantly higher plasma renin activity and received a higher volume of normal saline before its appearance.

CONCLUSIONS

Understanding the common etiologies of hypokalemic nonperiodic paralysis may aid in early diagnosis. Patients with initial lower plasma K(+), renal K(+) wasting, and hypovolemia required higher recovery K(+) dosage. Paradoxical hypokalemia is prone to develop in hypovolemic patients even during K(+) supplementation with volume repletion.

Inherited disorders of calcium and phosphate metabolism

PURPOSE OF REVIEW

Inherited disorders of calcium and phosphate homeostasis have variable presentation and can cause significant morbidity. An understanding of the mode of inheritance and pathophysiology of these conditions will help in the diagnosis and early institution of therapy.

RECENT FINDINGS

Identification of genetic mutations in humans and animal models has advanced our understanding of many inherited disorders of calcium and phosphate regulation. Identification of mutations of calcium-sensing receptor has improved our understanding of hypocalcemic and hypercalcemic conditions. Mutations of Fgf23, Klotho and phosphate transporter genes have been identified to cause disorders of phosphate metabolism.

SUMMARY

Calcium and phosphate homeostasis is tightly regulated in a narrow range due to their vital role in many biological processes. Inherited disorders of calcium and phosphate metabolism though uncommon can have severe morbidity. Genetic counseling of the affected families is an important part of the follow-up of these patients.

The sodium chloride cotransporter SLC12A3: new roles in sodium, potassium, and blood pressure regulation

SLC12A3 encodes the thiazide-sensitive sodium chloride cotransporter (NCC), which is primarily expressed in the kidney, but also in intestine and bone. In the kidney, NCC is located in the apical plasma membrane of epithelial cells in the distal convoluted tubule. Although NCC reabsorbs only 5 to 10% of filtered sodium, it is important for the fine-tuning of renal sodium excretion in response to various hormonal and non-hormonal stimuli. Several new roles for NCC in the regulation of sodium, potassium, and blood pressure have been unraveled recently. For example, the recent discoveries that NCC is activated by angiotensin II but inhibited by dietary potassium shed light on how the kidney handles sodium during hypovolemia (high angiotensin II) and hyperkalemia. The additive effect of angiotensin II and aldosterone maximizes sodium reabsorption during hypovolemia, whereas the inhibitory effect of potassium on NCC increases delivery of sodium to the potassium-secreting portion of the nephron. In addition, great steps have been made in unraveling the molecular machinery that controls NCC. This complex network consists of kinases and ubiquitinases, including WNKs, SGK1, SPAK, Nedd4-2, Cullin-3, and Kelch-like 3. The pathophysiological significance of this network is illustrated by the fact that modification of each individual protein in the network changes NCC activity and results in salt-dependent hypotension or hypertension. This review aims to summarize these new insights in an integrated manner while identifying unanswered questions.