Renal control of calcium, phosphate, and magnesium homeostasis

A synthetic review: natural history of amniote reproductive modes in light of comparative evolutionary genomics

There is a current lack of consensus on whether the ancestral parity mode was oviparity (egg-laying) or viviparity (live-birth) in amniotes and particularly in squamates (snakes, lizards, and amphisbaenids). How transitions between parity modes occur at the genomic level has primary importance for how science conceptualises the origin of amniotes, and highly variable parity modes in Squamata. Synthesising literature from medicine, poultry science, reproductive biology, and evolutionary biology, I review the genomics and physiology of five broad processes (here termed the 'Main Five') expected to change during transitions between parity modes: eggshell formation, embryonic retention, placentation, calcium transport, and maternal-fetal immune dynamics. Throughout, I offer alternative perspectives and testable hypotheses regarding proximate causes of parity mode evolution in amniotes and squamates. If viviparity did evolve early in the history of lepidosaurs, I offer the nucleation site hypothesis as a proximate explanation. The framework of this hypothesis can be extended to amniotes to infer their ancestral state. I also provide a mechanism and hypothesis on how squamates may transition from viviparity to oviparity and make predictions about the directionality of transitions in three species. After considering evidence for differing perspectives on amniote origins, I offer a framework that unifies (i) the extended embryonic retention model and (ii) the traditional model which describes the amniote egg as an adaptation to the terrestrial environment. Additionally, this review contextualises the origin of amniotes and parity mode evolution within Medawar's paradigm. Medawar posited that pregnancy could be supported by immunosuppression, inertness, evasion, or immunological barriers. I demonstrate that this does not support gestation or gravidity across most amniotes but may be an adequate paradigm to explain how the first amniote tolerated internal fertilization and delayed egg deposition. In this context, the eggshell can be thought of as an immunological barrier. If serving as a barrier underpins the origin of the amniote eggshell, there should be evidence that oviparous gravidity can be met with a lack of immunological responses in utero. Rare examples of two species that differentially express very few genes during gravidity, suggestive of an absent immunological reaction to oviparous gravidity, are two skinks Lampropholis guichenoti and Lerista bougainvillii. These species may serve as good models for the original amniote egg. Overall, this review grounds itself in the historical literature while offering a modern perspective on the origin of amniotes. I encourage the scientific community to utilise this review as a resource in evolutionary and comparative genomics studies, embrace the complexity of the system, and thoughtfully consider the frameworks proposed.

Functional dynamics of G protein-coupled receptors reveal new routes for drug discovery

G protein-coupled receptors (GPCRs) are the largest human membrane protein family that transduce extracellular signals into cellular responses. They are major pharmacological targets, with approximately 26% of marketed drugs targeting GPCRs, primarily at their orthosteric binding site. Despite their prominence, predicting the pharmacological effects of novel GPCR-targeting drugs remains challenging due to the complex functional dynamics of these receptors. Recent advances in X-ray crystallography, cryo-electron microscopy, spectroscopic techniques and molecular simulations have enhanced our understanding of receptor conformational dynamics and ligand interactions with GPCRs. These developments have revealed novel ligand-binding modes, mechanisms of action and druggable pockets. In this Review, we highlight such aspects for recently discovered small-molecule drugs and drug candidates targeting GPCRs, focusing on three categories: allosteric modulators, biased ligands, and bivalent and bitopic compounds. Although studies so far have largely been retrospective, integrating structural data on ligand-induced receptor functional dynamics into the drug discovery pipeline has the potential to guide the identification of drug candidates with specific abilities to modulate GPCR interactions with intracellular effector proteins such as G proteins and β-arrestins, enabling more tailored selectivity and efficacy profiles.

Increased magnesium intake does not mitigate MAFLD risk associated with magnesium deficiency

Serum magnesium cannot accurately assess magnesium deficiency. The association between magnesium deficiency and metabolic dysfunction-associated fatty liver disease (MAFLD) remains unclear. Selecting 3,377 participants in the United States, we assessed the degree of magnesium deficiency in the population using magnesium depletion score (MDS). Multinomial logistic regression assessed the association between magnesium deficiency and MAFLD. Subgroup analyses assessed the association between dietary magnesium intake and MAFLD under different magnesium deficiency statuses. Structural equation modeling (SEM) revealed mediation effects. Magnesium deficiency was associated with MAFLD (ORseverevs.none: 1.69, 95%CI: 1.16-2.46; p for trend < 0.001). Magnesium intake was negatively associated with MAFLD only in the subgroup without magnesium deficiency (p for trend < 0.01). Inflammation, oxidative stress, and aging significantly mediated the association between MDS and MAFLD (all p < 0.05). In American adults, magnesium deficiency assessed by MDS might be a risk factor for MAFLD, with inflammation, oxidative stress, and aging potentially being key mechanisms. Simply increasing magnesium intake would not mitigate MAFLD risk associated with magnesium deficiency. Correcting magnesium deficiency might prevent MAFLD.

Natural variation of magnesium stable isotopes in human kidney stones

Kidney stones, as typical biominerals produced within the human body, pose a significant threat to human health, affecting over 12% of the global population. However, the exact mechanisms underlying their formation are not fully understood. Recent metal isotopic analysis provides a new way to study the roles of metal cations in biological processes within organisms. Here, we report the Mg isotope ratios of human kidney stones for the first time. The total range of measured values for δ26Mg in kidney stones is 1.05‰, from -1.12‰ to -0.07‰. Our data exhibit a significant 24Mg enrichment compared with the values calculated from density functional theory. We suggest that the Mg-isotopic fractionations in vivo are linked to active Mg transport mediated by proteins during intestinal absorption and preferential renal reabsorption of ionized Mg2+ via tight junctional proteins. Our results indicate that the inhibitory effect of Mg on kidney stones is related to the kink-blocking mechanism, and the incorporation of hydrated Mg lessens the extent of inhibition and the magnitude of isotope discrimination. We show that metal isotopes provide new insights into the underlying biological processes and human health.

Blood Pressure Stability and Plasma Aldosterone Reduction: The Effects of a Sodium and Bicarbonate-Rich Water - A Randomized Controlled Intervention Study

Objective: Hypertension is a recognized risk factor for cardiovascular disease (CVD), and dietary sodium intake has been linked to its development. However, mineral water high in bicarbonate and sodium does not appear to have adverse effects on blood pressure.This study examines the effects of consuming a mineral water high in bicarbonate and sodium (HBS) compared to a low bicarbonate and sodium (LBS) mineral water on blood pressure and related factors.Methods: A randomized controlled intervention was conducted with 94 healthy participants, consuming 1,500 - 2,000 mL daily of either mineral water high in bicarbonate and sodium (HBS water, n = 49) or low in bicarbonate and sodium (LBS water, n = 45). Blood pressure, anthropometrics, and urinary calcium and sodium excretion were assessed at baseline and after 28 days. 3-day food protocols were assessed to evaluate possible dietary changes.Results: Blood pressure changes did not differ between the groups. Both normotensive and hypertensive subjects showed similar changes in systolic blood pressure (SBP), diastolic blood pressure (DBP), and mean arterial pressure (MAP) in response to the different test waters. Serum aldosterone decreased significantly in both groups, with a greater reduction in the HBS group. Urinary calcium excretion significantly decreased (p = 0.002) and sodium excretion increased in the HBS group. Multiple linear regression analyses indicated no association between urinary sodium excretion and systolic blood pressure increase in the HBS group (B = 0.046, p = 0.170). Changes in urinary sodium excretion did not correlate with changes in serum aldosterone in the same group (r=-0.146, p = 0.350).Conclusions: The study revealed no significant differences in blood pressure changes between individuals consuming HBS water and LBS water. Notably, the additional sodium intake from the test water was effectively excreted.Trial registration: This trial was registered in the German Clinical Trials Register (DRKS00025341, https://drks.de/search/en).

Dairy and Exercise for Bone Health: Evidence from Randomized Controlled Trials and Recommendations for Future Research

PURPOSE OF REVIEW

To examine evidence from randomized controlled trials (RCTs) on how modifiable factors such as exercise and nutrition, with a focus on dairy products, play a role in improving bone health across the lifespan.

RECENT FINDINGS

Meta-analyses of RCTs demonstrate the advantages of consuming dairy products to improve bone mineral density/content (BMD/BMC) and markers of bone metabolism and turnover (BTMs). Eighteen RCTs were conducted investigating the combined effects of dairy and exercise, with most indicating a benefit in youth and adult populations. Results were less conclusive in older adults, perhaps due to altered requirements for dairy/nutrients and exercise with increased age.   RCTs demonstrate that dairy product consumption alone benefits bone health and can enhance the effects of exercise on bone. This may help improve skeletal growth and development in adolescence and prevent osteoporosis with increased age. Future RCTs should account for habitual nutrient intakes, and dairy dosage, timing, and matrix effects.

Association between magnesium deficiency score and anemia in older Americans: A cross-sectional study

Some studies have indicated an association between serum magnesium and anemia, but these are primarily limited to research on serum magnesium. Few studies have explored the relationship between the bioavailability of magnesium and anemia. This study explores the association between the Magnesium Deficiency Score (MDS) and anemia among elderly Americans using data from the National Health and Nutrition Examination Survey (NHANES) 2009-2018. Anemia was defined based on World Health Organization criteria, and MDS was calculated considering factors such as the use of diuretics, proton-pump inhibitors, alcohol consumption, and renal function status. A total of 3383 individuals were included in our study. Results showed a positive correlation between MDS and anemia, with higher MDS levels associated with increased anemia prevalence. Subgroup analyses revealed that this association was consistent across different genders, poverty income ratio, and smoking populations, with a notably strong correlation in the non-Hispanic White group. The study suggests that improving the bioavailability of magnesium to reduce MDS may be a factor in preventing anemia in the elderly. This is the first study to explore the relationship between MDS and anemia in this population, highlighting the potential role of magnesium bioavailability in anemia prevention. Further prospective studies are needed to confirm these results and explore the underlying mechanisms.

Chronic Kidney Disease-associated Lung Injury Is Mediated by Phosphate-induced MAPK/AKT Signaling

Chronic kidney disease (CKD) is associated with systemic phosphate elevations, called hyperphosphatemia. Translational studies have shown that hyperphosphatemia contributes to CKD-associated inflammation and injury in various tissues, including the kidney, heart, liver, and parathyroid gland. Mechanisms underlying pathologic actions of elevated phosphate on cells are not well understood but seem to involve uptake of phosphate through sodium phosphate cotransporters and phosphate-induced signaling via FGFR1 (fibroblast growth factor receptor 1). Clinical studies indicate patients with CKD are more likely to develop inflammatory and restrictive lung diseases, such as fibrotic interstitial lung diseases, and here we aimed to determine whether hyperphosphatemia can cause lung injury. We found that a mouse model of CKD and hyperphosphatemia, induced by an adenine-rich diet, develops lung fibrosis and inflammation. Elevation of systemic phosphate concentration by administration of a high-phosphate diet in a mouse model of primary lung inflammation and fibrosis, induced by bleomycin, exacerbated lung injury in the absence of kidney damage. Our in vitro studies identified increases of proinflammatory cytokines in human lung fibroblasts exposed to phosphate elevations. Phosphate activated ERK 1/2 (extracellular signal-related kinase 1/2) and PKB/AKT (protein kinase B) signaling, and pharmacological inhibition of ERK, AKT, FGFR1, or sodium phosphate cotransporters prevented phosphate-induced proinflammatory cytokine upregulation. In addition, inhibition of FGFR1 or sodium phosphate cotransporters decreased the phosphate-induced activation of ERK and AKT. Our study suggests that phosphate can directly target lung fibroblasts and induce an inflammatory response and that hyperphosphatemia in CKD and non-CKD models contributes to lung injury. Phosphate-lowering strategies might protect from CKD-associated lung injury.

Revisiting voltage-coupled H+ secretion in the collecting duct

Experimental studies have shown that V-type ATPase-driven H+ secretion is dependent on transepithelial voltage. On this basis, the "voltage hypothesis" of urinary acidification by the collecting duct was derived. Accordingly, it has been supposed that the lumen-negative potential created by the reabsorption of Na+ via the epithelial Na+ channel (ENaC) enhances electrogenic H+ secretion via V-type H+-ATPase. This concept continues to be widely used to explain acid/base disorders. Importantly, however, a solid proof of principle for the voltage hypothesis in physiologically relevant situations has not been reached. Rather, it has been challenged by recent in vivo functional studies. In this review, we outline the arguments and experimental observations explaining why voltage-coupled H+ secretion in the collecting duct often appears poorly applicable for rationalizing changes in H+ secretion as a function of more or less ENaC function in the collecting duct.

Lipid-core nanocapsules containing simvastatin do not affect the biochemical and hematological indicators of toxicity in rats

Our research group previously studied the effectiveness of lipid-core nanocapsules (LNC) containing simvastatin (SV-LNC) in treating cognitive impairment in rats. While our results were promising, we needed to evaluate the potential toxicity of the nanoparticles themselves. This study aimed to compare the biochemical and hematological parameters of adult Wistar rats receiving LNC or SV-LNC to those receiving low doses of simvastatin crystals dispersed in a saline solution over 45 days. We discovered that LNC and SV-LNC, which are both nanometers in size with low polydispersity index, negative zeta potential, and high SV encapsulation efficacy, were not more toxic than SV crystals based on various biochemical markers of hepatic, pancreatic, renal, mineral, bony, alkaline phosphatase, glucose, and uric acid damage. Furthermore, LNC exhibited no toxicity for hematological parameters, including red and white blood cell counts. Based on this animal model of toxicological study, our findings suggest that long-term administration of LNC is a safe and promising nanocarrier.

Renal expression of calcium and phosphorus transporters: contrasting responses to dietary calcium and microbial phytase in broilers and growing pigs

Enhanced dietary Ca intake linearly increases intestinal Ca absorption in pigs, but not in broilers, suggesting potential differences in whole body Ca homeostasis. To determine the role of kidney in Ca homeostasis in these species, we varied in growing pigs in experiment (Exp) 1, the dietary Ca content 2·0 v. 9·6 g/kg and phytase 0 v. 500 FTU/kg, in broilers, in Exp 2 the dietary Ca/retainable P from 1·3 to 2·8 and phytase 0 v. 1000 FTU/kg, and in Exp 3 dietary Ca/P from 0·50 to 1·75. Increasing dietary Ca reduced renal mRNA expression of Ca-related transporters (TRPV5, TRPV6, CaBP-D28k and NCX1) and tight junctions (CLDN-12 and -16) in pigs, indicating Ca reabsorption was reduced to maintain Ca homeostasis. In broilers (Exp 2), high dietary Ca increased renal TRPV6, CaBP-D28k and CLDN-2 mRNA, indicating an increased capacity for Ca reabsorption. Moreover, the effect of dietary Ca was enhanced by inclusion of dietary phytase in pigs but reduced in broilers. Furthermore, increasing dietary Ca upregulated inorganic phosphate transporter 1 (PiT-1), while phytase downregulated xenotropic and polytropic retrovirus receptor 1 (XPR1) mRNA expression in pigs; in broilers, dietary Ca downregulated renal mRNA expression of Na-dependent phosphate transporter IIa (NaPi-IIa), PiT-1, PiT-2 and XPR1, while phytase downregulated NaPi-IIa but upregulated PiT-2 and XPR1 mRNA expression. In Exp 3, Ca/P effect on transporter mRNA expression was largely consistent with Exp 2. In conclusion of this study, together with previously measured data about Ca and P homeostasis, in pigs the kidneys play a more regulatory role in Ca homeostasis than in broilers where the intestine is more important for regulation.

Phosphate metabolism: its impact on disorders of mineral metabolism

Regulatory molecules typically work cooperatively to ensure the efficient functioning of hormonal systems. Examples include LH and FSH in reproductive biology, insulin and glucagon in glucose metabolism. Similarly, calcium and phosphorus are important regulators of skeletal homeostasis. In the circulation, these molecules are under the control of PTH, 1,25(OHD), and FGF23. In turn, these hormones depend upon a mutual and complex interplay among themselves. For example, alterations in calcium metabolism influence phosphorus homeostasis, as occurs in primary hyperparathyroidism (PHPT). Not as well recognized is the influence that abnormalities in phosphorus metabolism can have on calcium homeostasis. In this review, we call attention to the impact that abnormalities in phosphorus can have on calcium metabolism.

Ratios of calcium to citrate administration in blood transfusion for traumatic hemorrhage: A retrospective cohort study

BACKGROUND

Massive transfusion with citrated blood products causes hypocalcemia, which is associated with mortality. Recognition of this problem has led to increased calcium administration; however, the optimal dosing is still unknown.

STUDY DESIGN AND METHODS

This retrospective, single-center study included level 1 trauma patients in 2019 and 2020 who underwent an operation within 12 h of arrival and received a transfusion. Preoperative and intraoperative administrations were totaled to calculate the ratio of administered calcium to the number of blood transfusions for each patient. The citrate content of each blood component was estimated to calculate a second ratio, the ratio of administered calcium to administered citrate. Receiver Operating Characteristic (ROC) curves were performed on both ratios to determine the optimal cutoff values for predicting severe hypocalcemia (ionized calcium <0.9 mmol/L) and hypercalcemia (>1.35 mmol/L) at the end of the intraoperative period.

RESULTS

A total of 506 trauma activations were included, receiving a mean of 17.4 citrated blood products and 16.3 mmol of calcium (equivalent to 2400 mg of calcium chloride). No ratio was statistically significant in differentiating severely hypocalcemic patients from the rest. A calcium to blood ratio of 0.903 mmol of administered calcium per citrated blood product differentiated hypercalcemic patients from the rest.

DISCUSSION

Quantifying received calcium and citrated blood products was insufficient to predict severe hypocalcemia, suggesting other contributions to hypocalcemia. We demonstrated an upper-limit ratio for calcium administration in traumatic hemorrhage; however, further studies are required to determine what calcium dosing regimen results in the best outcomes.

Severe hypophosphatemia induced by excessive production of FGF23 in acute hepatitis: from bedside to bench

Background

Although hepatic production of FGF23 has been suggested in chronic settings, there are no data indicating hypophosphatemia resulting from acute hepatic FGF23 production. Based on two clinical observations of profound hypophosphatemia in the setting of acute hepatitis, our study investigates the hypothesis of acute FGF23 liver expression.

Methods

Retrospective analyses were conducted to estimate FGF23 liver expression both qualitatively (in situ hybridization) and quantitatively (relative FGF23 gene expression and protein production) on histological specimens of human and murine acute hepatitis livers, compared with controls of hepatic fibrosis or healthy liver.

Results

The index clinical case involves acute alcoholic hepatitis complicated by profound hypophosphatemia due to phosphate diabetes, revealing a major production of both FGF23 C-terminal fraction (cFGF23) and bio-intact form (iFGF23, 39 751 RU/mL, N: 21-91; and 228.6 pg/mL, N: 22.7-93.1, respectively). A second case of acute hepatitis related to erythrocytic protoporphyria also exhibited comparable abnormalities. In both cases, no other cause of renal phosphate wasting was identified, and the hydroelectrolytic disorders disappeared in parallel with normalization of the liver balance and FGF23 levels. Histological data of acute hepatitis compared with cirrhosis and healthy liver confirmed our hypothesis of hepatic FGF23 overproduction. Furthermore, mouse models showed a significant increase in FGF23 mRNA relative liver expression in acute hepatitis and a moderate increase in cirrhosis, compared with healthy liver (respectively 60.55 ± 16.75 and 3.70 ± 0.87 vs 1.00 ± 0.65, both P < .05). These findings were also confirmed at the protein level.

Conclusion

This translational study raises the hypothesis of renal phosphate wasting induced by excessive hepatic production of FGF23 in case of acute hepatitis.

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.

Dietary phosphorus and renal disease in cats: where are we?

PRACTICAL RELEVANCE

Phosphorus is an essential nutrient required for the normal function of every cell in the body and a deficiency in dietary phosphorus may lead to adverse effects. Conversely, high dietary phosphorus may cause kidney damage in otherwise healthy adult cats, particularly when provided in highly bioavailable forms and when the calcium-to-phosphorus ratio is low. For cats that have chronic kidney disease (CKD), phosphorus is the most important mineral in its pathogenesis and morbidity. As the disease progresses, elevated phosphorus may increase the risk of complications such as soft tissue mineralization, which can lead to a further decrease in renal function. Additionally, the hormones secreted in response to increased circulating phosphorus have harmful effects, such as bone resorption, and can cause cardiovascular pathology. Very low phosphorus diets can also be problematic in cats with early CKD, potentially leading to hypercalcemia.

CLINICAL CHALLENGES

There is currently a lack of maximum safety limits for dietary phosphorus in accepted nutritional guidelines in North American and Europe, which makes it difficult to assess the safety of some higher phosphorus cat foods. Additionally, information regarding phosphorus bioavailability is unknown for many diets and there are no commercially available tests. Similarly, there is no consensus regarding phosphorus requirement and recommended intake in cats with International Renal Interest Society stage 1-4 CKD despite there being targets for serum phosphorus.

AIMS

This review evaluates dietary phosphorus in healthy cats and cats with renal disease, and describes how newer research is informing evolving clinical approaches in feline nutrition.

AUDIENCE

The article is aimed at general practitioners, internal medicine specialists and veterinary nutritionists.

EVIDENCE BASE

Information provided in this article is drawn from the published literature.

Effects of the Interaction between Dietary Vitamin D3 and Vitamin K3 on Growth, Skeletal Anomalies, and Expression of Bone and Calcium Metabolism-Related Genes in Juvenile Gilthead Seabream (Sparus aurata)

The interaction between vitamin D and vitamin K is crucial for regulating bone metabolism and maintaining calcium homeostasis across diverse animal species due to their complementary roles in calcium metabolism and bone health. However, research on this interaction of vitamin D and K in fish, particularly Mediterranean species like gilthead seabream, is limited or not studied. This study aimed to understand the effects of different dietary combinations of vitamin D3 and K3 on juvenile gilthead seabream. Accordingly, seabream juveniles were fed with varying combinations of vitamin D3/vitamin K3 (mg/kg diet) for 3 months: (0.07/0.01), (0.20/0.58), (0.19/1.65), (0.51/0.74), (0.56/1.00). At the end of the trial, survival, growth, body morphology, serum calcitriol, and vertebral mineral composition remained unaffected by varying vitamin levels, while gene expression patterns related to bone formation, resorption, and calcium regulation in various tissues were significantly influenced by both vitamins and their interaction. Gilthead seabream juveniles fed the 0.07/0.01 mg/kg diet upregulated calcium-regulating genes in the gills, indicating an effort to enhance calcium absorption to compensate for dietary deficiencies. Conversely, an increase in vitamin D3 and K3 up to 0.19 and 1.65 mg/kg, respectively, upregulated bone formation, bone remodeling, and calcium homeostasis-related gene expression in vertebra and other tissues. On the contrary, a dietary increase in these vitamins up to 0.56 mg/kg vitamin D3 and 1.00 mg/kg vitamin K3 downregulated calcium metabolism-related genes in tissues, suggesting an adverse interaction resulting from elevated levels of these vitamins in the diet. Hence, sustaining an equilibrium in the dietary intake of vitamin D3 and vitamin K3, in an appropriately combined form, may potentially induce interactions between the vitamins, contributing to favorable effects on bone development and calcium regulation in gilthead seabream juveniles.

A Biodegradable Fiber Calcium Ion Sensor by Covalently Bonding Ionophores on Bioinert Nanoparticles

Implantable sensors, especially ion sensors, facilitate the progress of scientific research and personalized healthcare. However, the permanent retention of implants induces health risks after sensors fulfill their mission of chronic sensing. Biodegradation is highly anticipated; while; biodegradable chemical sensors are rare due to concerns about the leakage of harmful active molecules after degradation, such as ionophores. Here, a novel biodegradable fiber calcium ion sensor is introduced, wherein ionophores are covalently bonded with bioinert nanoparticles to replace the classical ion-selective membrane. The fiber sensor demonstrates comparable sensing performance to classical ion sensors and good flexibility. It can monitor the fluctuations of Ca2+ in a 4-day lifespan in vivo and biodegrade in 4 weeks. Benefiting from the stable bonding between ionophores and nanoparticles, the biodegradable sensor exhibits a good biocompatibility after degradation. Moreover, this approach of bonding active molecules on bioinert nanoparticles can serve as an effective methodology for minimizing health concerns about biodegradable chemical sensors.

Injection of luteinizing hormone or human chorionic gonadotropin increases calcium excretion and serum PTH in males

Animal and human studies have suggested that sex steroids have calciotropic actions, and it has been proposed that follicle-stimulating hormone (FSH) may exert direct effects on bone. Here, we demonstrate the expression of the receptor for Luteinizing hormone (LH) and human choriogonadotropin (hCG), LHCGR, in human kidney tissue, suggesting a potential influence on calcium homeostasis. To investigate the role of LHCGR agonist on calcium homeostasis in vivo, we conducted studies in male mice and human subjects. Male mice were treated with luteinizing hormone (LH), and human extrapolation was achieved by injecting 5000 IU hCG once to healthy men or men with hypergonadotropic or hypogonadotropic hypogonadism. In mice, LH treatment significantly increased urinary calcium excretion and induced a secondary increase in serum parathyroid hormone (PTH). Similarly, hCG treatment in healthy men led to a significant increase in urinary calcium excretion, serum PTH levels, and 1,25 (OH)2D3, while calcitonin, and albumin levels were reduced, possibly to avoid development of persistent hypocalcemia. Still, the rapid initial decline in ionized calcium coincided with a significant prolongation of the cardiac QTc-interval that normalized over time. The observed effects may be attributed to LH/hCG-receptor (LHCGR) activation, considering the presence of LHCGR expression in human kidney tissue, and the increase in sex steroids occurred several hours after the changes in calcium homeostasis. Our translational study shed light on the intricate relationship between gonadotropins, sex hormones and calcium, suggesting that LHCGR may be influencing calcium homeostasis directly or indirectly.

Paradoxes in magnesium transport in type 1 Bartter's syndrome and Gitelman's syndrome: a modeling analysis

Type 1 Bartter's syndrome and Gitelman's syndrome are characterized by mutations in two key renal Na+ transporters, Na-K-2Cl cotransporter (NKCC2) and Na-Cl cotransporter (NCC). Since these two transporters play an important role in regulating magnesium (Mg2+) and calcium (Ca2+) transport in the kidney, significant alterations in the transport of these two electrolytes are observed in type 1 Bartter's syndrome and Gitelman's syndrome. In this study, we used our sex-specific computational models of renal electrolyte transport in rats to understand the complex compensatory mechanisms, in terms of alterations in tubular dimensions and ion transporter activities, that lead to Mg2+ and Ca2+ preservation or wasting in these two genetic disorders. Given the sexual dimorphism in renal transporter patterns, we also assessed how the magnitude of these alterations may differ between males and females. Model simulations showed that in type 1 Bartter's syndrome, nephron adaptations prevent salt wasting and favor Mg2+ preservation but not Ca2+, whereas in Gitelman's syndrome, those adaptations favor Ca2+ preservation over Mg2+. In addition, our models predicted that the compensatory alterations in tubular dimensions and ion transporter activities are stronger in females than in males.NEW & NOTEWORTHY Although changes in Ca2+ excretion in type 1 Bartter's syndrome and Gitelman's syndrome are well understood, Mg2+ excretion displays an interesting paradox. This computational modeling study provides insights into how renal adaptations in these two disorders impact Ca2+ and Mg2+ transport along different nephron segments. Model simulations showed that nephron adaptations favor Mg2+ preservation over Ca2+ in Bartter's syndrome and Ca2+ preservation over Mg2+ in Gitelman's syndrome and are stronger in females than in males.

Toxicity assessment of 3-O-[6-deoxy-3-O-methyl-β-D-allopyranosyl-(1 → 4)-β-D-oleandropyranosyl]-17β-marsdenin isolated from Gongronema latifolium leaf on selected brain and kidney function indices in mice

The safety of bioactive compounds, especially those isolated from medicinal plants, is a major concern for health authorities, pharmaceutical industries, and the public. Of recent, anti-tumor pregnane glycosides were isolated from Gongronema latifolium leaf, of which the toxicity of one, 3-O-[6-deoxy-3-O-methyl-β-D-allopyranosyl-(1 → 4)-β-D-oleandropyranosyl]-17β-marsdenin (3DMAOM), has not been evaluated. This study, therefore, evaluated the effects of 3DMAOM on selected brain and kidney function indices in mice. Female Swiss albino mice were randomly administered 5% dimethyl sulphoxide and different doses of 3DMAOM (0.5, 1, 2, and 4 mg/kg body weight) for fourteen (14) days, and their blood, brains, and kidneys were collected for biochemical analysis. There was no significant alteration in the activities of alkaline phosphatase (ALP), acetylcholinesterase, creatine kinase, Na+/K+-ATPase, Ca2+/Mg2+-ATPase, and Mg2+-ATPase in the brain of the treated groups compared to control. Also, no significant changes in the activities of ALP, gamma-glutamyltransferase, Na+/K+-ATPase, Ca2+/Mg2+-ATPase, and Mg2+-ATPase in the kidney of the treated groups compared to control. The plasma concentrations of Na+, K+, Cl-, PO43-, creatinine, and urea of mice were not significantly altered at all doses of the 3DMAOM compared to controls. However, the plasma concentration of Ca2+ was significantly reduced (p < 0.05) at all doses of the 3DMAOM, and the plasma concentration of uric acid was significantly reduced (p < 0.05) at 2 mg/kg body weight of the 3DMAOM compared to controls. These findings suggest that 3DMAOM isolated from Gongronema latifolium leaf may not adversely affect brain function but may affect calcium ion homeostasis in subjects.

Urinary Phosphate and Subclinical Atherosclerosis: The AWHS Study

(1) Background: Atherosclerosis is a leading cause of vascular death worldwide. High urinary phosphate has recently been identified as a cardiovascular risk factor, but its role has not been fully established. The aim of this study was to investigate the association between urinary phosphate and subclinical atherosclerosis in the carotid, femoral as well as coronary territories; (2) Methods: We performed a cross-sectional analysis of a sample of 1169 middle-aged men, aged 50.9 years (SD 3.7), without previous cardiovascular disease, belonging to the Aragon Workers Health Study (AWHS). Urinary phosphate was analyzed in urine samples using the Fiske-Subbarow method. The presence of carotid plaque and femoral plaque was assessed by ultrasound and coronary artery calcium score (CACS) by computed tomography. Demographic, anthropometric and clinical data were collected at annual medical examinations. Logistic regression models were used to estimate the prevalence of adjusted atherosclerosis in the different vascular arteries; (3) Results: A significant inverse association was observed between urinary phosphate and subclinical atherosclerosis in the carotid [OR 95% CI 0.69 (0.49-0.99)] and coronary (CACS > 200) [OR 95% CI 0.46 (0.23-0.88)] arteries; however, no statistically significant association was found between urinary phosphate and the presence of atheroma plaques in the femoral territory [OR 1.02 (0.72-1.45)]; (4) Conclusions: In middle-aged men, a higher urinary phosphate concentration is associated with a lower prevalence of subclinical carotid and coronary atherosclerosis compared with those with a lower urinary phosphate concentration.

Impact of Lactobacillus acidophilus and Its Combination with Isoflavone Products on Calcium Status, Calcium Transporters, and Bone Metabolism Biomarkers in a Post-Menopausal Osteoporotic Rat Model

Osteoporosis in menopausal women requires alternatives to current medications, considering their adverse effects. In this context, probiotics and isoflavone products are promising dietary interventions. The objective of our study was to examine the impacts of Lactobacillus acidophilus and its combination with daidzein and tempeh on calcium status, calcium transporters, and bone metabolism biomarkers in a post-menopausal osteoporotic rat model. A total of 48 female Wistar rats were exposed to a two-stage experiment involving calcium deficit induction and subsequent dietary interventions across six groups. Calcium levels, the gene expression of TRPV5 and TRPV6 calcium transporters, bone histopathology, serum bone metabolism markers, and blood biochemistry were evaluated. The results revealed that, while decreasing serum calcium levels, the groups that received the probiotic L. acidophilus and isoflavone combination exhibited increased bone metabolism biomarkers and decreased calcium transporter expressions, akin to the effects of bisphosphonate. Additionally, significant improvements in bone histopathology were observed in these groups. However, the group receiving probiotic L. acidophilus alone did not exhibit significant changes in bone resorption biomarkers, calcium transporter expression, or various blood parameters. Meanwhile, the combination of probiotic L. acidophilus with tempeh positively influenced hematological parameters and reduced cholesterol and triglyceride levels, but it led to elevated blood glucose levels. Correlation analyses highlighted associations between serum calcium levels, calcium transporter expression, and bone metabolism biomarkers. In conclusion, our findings suggest that the daily consumption of probiotic L. acidophilus in combination with isoflavone products may improve bone health in ovariectomized rats, warranting further research to elucidate potential interactions with other nutrients.

Association of urinary calcium excretion with chronic kidney disease in patients with type 2 diabetes

PURPOSE

Herein, we investigated the correlation between urinary calcium excretion (UCaE) and chronic kidney disease (CKD) in patients with type 2 diabetes mellitus (T2DM).

METHODS

From August 2018 to January 2023, a total of 2031 T2DM patients providing 24-h urine samples were included in the final analyses. Patients were separated into four cohorts, based on the UCaE quartiles. We then analyzed renal functional indicators like estimated glomerular filtration rate (eGFR) and urinary albumin excretion (UAE) among the four groups. Lastly, we utilized multivariable logistic regression models to investigate the correlation between UCaE and CKD.

RESULTS

After adjusting for confounding factors, we observed a decreasing trend in CKD prevalence (36.3%, 13.0%, 7.5%, and 6.6%, respectively, P < 0.001) across the UCaE quartiles. Albuminuria (55.5% vs. 40.0%, 36.5%, 37.4%) and macroalbuminuria prevalence (20.0% vs. 9.3%, 5.2%, 5.7%) in the lowest quartile were markedly elevated, compared to the remaining three quartiles (P < 0.001). Meanwhile, the eGFR level (P < 0.001) showed a clearly increasing trend across the UCaE quartiles, and patients with moderate-to-severe decreases in eGFR levels (with cutoff limits at 30-59, 15-30, and < 15 mL/min/1.73m2) were mostly found in the lowest quartile (P < 0.001). Logistic regression analysis revealed that patients in the lowest quartile experienced an enhanced prevalence of CKD, relative to those in the highest quartile (odds ratio: 5.90, 95% confidence interval: 3.60-9.67, P < 0.001).

CONCLUSION

Decreased UCaE was independently associated with the CKD prevalence in T2DM patients.

Calcium signalling and transport in the kidney

The kidney plays a pivotal role in regulating calcium levels within the body. Approximately 98% of the filtered calcium is reabsorbed in the nephron, and this process is tightly controlled to maintain calcium homeostasis, which is required to facilitate optimal bone mineralization, preserve serum calcium levels within a narrow range, and support intracellular signalling mechanisms. The maintenance of these functions is attributed to a delicate balance achieved by various calcium channels, transporters, and calcium-binding proteins in renal cells. Perturbation of this balance due to deficiency or dysfunction of calcium channels and calcium-binding proteins can lead to severe complications. For example, polycystic kidney disease is linked to aberrant calcium transport and signalling. Furthermore, dysregulation of calcium levels can promote the formation of kidney stones. This Review provides an updated description of the key aspects of calcium handling in the kidney, focusing on the function of various calcium channels and the physiological stimuli that control these channels or are communicated through them. A discussion of the role of calcium as an intracellular second messenger and the pathophysiology of renal calcium dysregulation, as well as a summary of gaps in knowledge and future prospects, are also included.

Genetic deletion of the kidney sodium/proton exchanger-3 (NHE3) does not alter calcium and phosphate balance due to compensatory responses

The sodium/proton exchanger-3 (NHE3) plays a major role in acid-base and extracellular volume regulation and is also implicated in calcium homeostasis. As calcium and phosphate balances are closely linked, we hypothesized that there was a functional link between kidney NHE3 activity, calcium, and phosphate balance. Therefore, we examined calcium and phosphate homeostasis in kidney tubule-specific NHE3 knockout mice (NHE3loxloxPax8 mice). Compared to controls, these knockout mice were normocalcemic with no significant difference in urinary calcium excretion or parathyroid hormone levels. Thiazide-induced hypocalciuria was less pronounced in the knockout mice, in line with impaired proximal tubule calcium transport. Knockout mice had greater furosemide-induced calciuresis and distal tubule calcium transport pathways were enhanced. Despite lower levels of the sodium/phosphate cotransporters (NaPi)-2a and -2c, knockout mice had normal plasma phosphate, sodium-dependent 32Phosphate uptake in proximal tubule membrane vesicles and urinary phosphate excretion. Intestinal phosphate uptake was unchanged. Low dietary phosphate reduced parathyroid hormone levels and increased NaPi-2a and -2c abundances in both genotypes, but NaPi-2c levels remained lower in the knockout mice. Gene expression profiling suggested proximal tubule remodeling in the knockout mice. Acutely, indirect NHE3 inhibition using the SGLT2 inhibitor empagliflozin did not affect urinary calcium and phosphate excretion. No differences in femoral bone density or architecture were detectable in the knockout mice. Thus, a role for kidney NHE3 in calcium homeostasis can be unraveled by diuretics, but NHE3 deletion in the kidneys has no major effects on overall calcium and phosphate homeostasis due, at least in part, to compensating mechanisms.

Tenapanor: A Phosphate Absorption Inhibitor for the Management of Hyperphosphatemia in Patients With Kidney Failure

Because of increased risks of cardiovascular disease and death, patients with hyperphosphatemia receiving maintenance dialysis are advised to limit phosphorus consumption and are prescribed phosphate binders in an effort to better control serum phosphate concentrations. Because of large pill size, pill burden, and tolerability issues, phosphate binder adherence is relatively poor. On ingestion, phosphate is absorbed from the intestine via transcellular or paracellular transport. Data show that inhibiting sodium-hydrogen exchanger 3 modulates paracellular phosphate absorption (the predominant pathway in humans). Tenapanor is a first-in-class, minimally absorbed, phosphate absorption inhibitor that selectively inhibits sodium-hydrogen exchanger 3, with a mechanism distinct from, and complementary to, that of phosphate binders. In phase 3 and postregistrational studies, tenapanor conferred statistically significant and clinically meaningful reductions in serum phosphate in patients receiving maintenance dialysis with hyperphosphatemia. Here, we review the available preclinical and clinical data on the effects of tenapanor on controlling intestinal phosphate absorption.

Case report: Near-fatal hypermagnesemia resulting from the use of Epsom salts in a patient with normal renal function

Hypermagnesemia commonly occurs in patients with renal dysfunction. Diagnosing hypermagnesemia represents a challenge due to its rarity and the absence of routine monitoring of magnesium levels. Furthermore, the lack of awareness among clinicians regarding this uncommon condition frequently leads to delayed diagnoses. Few patients survive with a serum magnesium level exceeding 7 mmol/L. This article presents a case study of near-fatal hypermagnesemia resulting from the oral administration of Epsom salts in a patient with normal renal function. A 60-year-old female presented to the gastroenterology department on Oct. 6, 2023, with a 3-day history of black stools. She underwent subtotal gastrectomy in 2005 and has a stable history of nephrotic syndrome. To investigate the cause of her bleeding, electronic gastroscopy and colonoscopy were scheduled for Oct. 11, 2023. She experienced a sudden loss of consciousness 30 min after the ingestion of Epsom salts. The attending physician suspected a severe magnesium poisoning. She was promptly administered calcium gluconate, underwent tracheal intubation with ambu bag ventilation, and received early continuous renal replacement therapy (CRRT). Swift diagnosis and CRRT contributed to a reduction in her serum magnesium levels from an initial 8.71 mmol/L to 1.35 mmol/L, leading to a remarkable improvement in the toxic symptoms associated with hypermagnesemia. Subsequently, she was managed in the gastroenterology department, with gastroscopy revealing bleeding from the gastrointestinal anastomotic ulcer. Following conservative treatments including acid suppression, stomach protection, and hemostasis, her symptoms improved, and she was successfully discharged. This study aims to alert clinicians to the possibility of hypermagnesemia in individuals with normal renal function. Physicians should exercise caution when prescribing Epsom salts to patients with underlying gastrointestinal conditions. If necessary, alternative drug therapies may be considered to mitigate the risk of hypermagnesemia. Timely intervention is pivotal in averting life-threatening complications linked to hypermagnesemia.

Stepwise developmental mimicry generates proximal-biased kidney organoids

The kidney maintains body fluid homeostasis by reabsorbing essential compounds and excreting waste. Proximal tubule cells, crucial for renal reabsorption of a range of sugars, ions, and amino acids, are highly susceptible to damage, leading to pathologies necessitating dialysis and kidney transplants. While human pluripotent stem cell-derived kidney organoids are used for modeling renal development, disease, and injury, the formation of proximal nephron cells in these 3D structures is incomplete. Here, we describe how to drive the development of proximal tubule precursors in kidney organoids by following a blueprint of in vivo human nephrogenesis. Transient manipulation of the PI3K signaling pathway activates Notch signaling in the early nephron and drives nephrons toward a proximal precursor state. These "proximal-biased" (PB) organoid nephrons proceed to generate proximal nephron precursor cells. Single-cell transcriptional analyses across the organoid nephron differentiation, comparing control and PB types, confirm the requirement of transient Notch signaling for proximal development. Indicative of functional maturity, PB organoids demonstrate dextran and albumin uptake, akin to in vivo proximal tubules. Moreover, PB organoids are highly sensitive to nephrotoxic agents, display an injury response, and drive expression of HAVCR1 / KIM1 , an early proximal-specific marker of kidney injury. Injured PB organoids show evidence of collapsed tubules, DNA damage, and upregulate the injury-response marker SOX9 . The PB organoid model therefore has functional relevance and potential for modeling mechanisms underpinning nephron injury. These advances improve the use of iPSC-derived kidney organoids as tools to understand developmental nephrology, model disease, test novel therapeutics, and for understanding human renal physiology.

Dietary magnesium supplementation in cats with chronic kidney disease: A prospective double-blind randomized controlled trial

BACKGROUND

Plasma total magnesium concentration (tMg) is a prognostic indicator in cats with chronic kidney disease (CKD), shorter survival time being associated with hypomagnesemia. Whether this risk factor is modifiable with dietary magnesium supplementation remains unexplored.

OBJECTIVES

Evaluate effects of a magnesium-enriched phosphate-restricted diet (PRD) on CKD-mineral bone disorder (CKD-MBD) variables.

ANIMALS

Sixty euthyroid client-owned cats with azotemic CKD, with 27 and 33 allocated to magnesium-enriched PRD or control PRD, respectively.

METHODS

Prospective double-blind, parallel-group randomized trial. Cats with CKD, stabilized on a PRD, without hypermagnesemia (tMg >2.43 mg/dL) or hypercalcemia (plasma ionized calcium concentration, (iCa) >6 mg/dL), were recruited. Both intention-to-treat and per-protocol (eating ≥50% of study diet) analyses were performed; effects of dietary magnesium supplementation on clinicopathological variables were evaluated using linear mixed effects models.

RESULTS

In the per-protocol analysis, tMg increased in cats consuming a magnesium-enriched PRD (β, 0.25 ± .07 mg/dL/month; P < .001). Five magnesium supplemented cats had tMg >2.92 mg/dL, but none experienced adverse effects. Rate of change in iCa differed between groups (P = .01), with decreasing and increasing trends observed in cats fed magnesium-enriched PRD and control PRD, respectively. Four control cats developed ionized hypercalcemia versus none in the magnesium supplemented group. Log-transformed plasma fibroblast growth factor-23 concentration (FGF23) increased significantly in controls (β, 0.14 ± .05 pg/mL/month; P = .01), but remained stable in the magnesium supplemented group (β, 0.05±.06 pg/mL/month; P =.37).

CONCLUSIONS AND CLINICAL IMPORTANCE

Magnesium-enriched PRD is a novel therapeutic strategy for managing feline CKD-MBD in cats, further stabilizing plasma FGF23 and preventing hypercalcemia.

The Fate of Phosphate: Assessing Dietary Intake and Urinary Excretion in Swedish Adolescents

Background

A high total phosphorus (P) intake has been proposed to promote endothelial dysfunction and atherosclerosis. A diet rich in foods containing P additives could contribute to an excessive intake, potentially reflected as increased concentration of P in urine.

Objectives

This study aimed to assess the intake of total dietary P, P additives, and its sources and examine their correlation with urinary P in a cross-sectional national study in Swedish adolescents.

Methods

We constructed a database of P additives and applied it to the foods consumed by 3099 participants in the representative school-based dietary survey Riksmaten Adolescents 2016-17. Intake of total dietary P and P additives were assessed using two 24-h recalls. Urinary P was analyzed in a subsample of 756 participants using inductively coupled plasma mass spectrometry. Spearman rank correlation (ρ) was used to assess the association between dietary P intake and urinary P excretion.

Results

The mean (SD) intake of total P was 1538 (±667) mg/d. Food containing P additives were consumed by 92% of adolescents and the median (IQR) intake was 49 (22-97; range: 0.01-947) mg/d, corresponding to 5% (1%-6%; range: 0%-50%) of total P. The main contributing food to P additives was cola drinks, while the main contributing food group was sausage dishes. Total P intake was weakly correlated with urinary P (ρ = 0.12; P < 0.01) but not with intake of P additives.

Conclusions

Nearly, all participants consumed P additives, contributing to an average of 5% of total P intake but ranging up to 50%. The intake of total P, but not P additives, was weakly reflected in the urinary P. Access to more comprehensive information on P additives in foods would improve further evaluation of potential health consequences.

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.

Associations of Dietary Calcium and Phosphorus With Vascular and Valvular Calcification: The ARIC Study

Background

High dietary calcium and phosphorus may accelerate vascular calcification, but epidemiological data are inconsistent. Most of those studies assessed diet at one point and have not been systematically evaluated.

Objectives

The purpose of this study was to assess the associations of dietary calcium and phosphorus intakes in middle age with coronary artery and extra-coronary calcification at older age.

Methods

We studied 1,914 participants from the ARIC (Atherosclerosis Risk In Communities) study (mean age 80.5 years) without coronary heart disease who underwent chest computed tomography scans at visit 7 (2018-2019) and completed a 66-item food frequency questionnaire at 2 earlier visits (visit 1 [1987-1989] and visit 3 [1993-1995]). Dietary calcium and phosphorus intakes were averaged between these 2 visits. Calcification was quantified by the Agatston score in coronary artery, ascending aorta, descending aorta, aortic valve ring, aortic valve, and mitral valve.

Results

Dietary calcium intake was inversely associated with coronary artery and ascending aorta calcification, whereas the association was not significant for other measures of extra-coronary calcification. For example, the highest vs lowest quartile of calcium intake showed an adjusted OR of 0.66 (95% CI: 0.45-0.98) for coronary artery calcification (Agatston score ≥75th percentile). Dietary phosphorus intake demonstrated similar results, but the magnitude of the association was weaker than dietary calcium intake.

Conclusions

Dietary calcium and phosphorus intakes at middle age were not positively associated with vascular and valvular calcification at over 75 years old. Our findings did not support the link between a calcium or phosphorus-rich diet and vascular and valvular calcification.

Plasma levels and dietary intake of minerals in patients with type 2 diabetes and chronic kidney disease: A case-control study

BACKGROUND AND AIM

Diabetic kidney disease (DKD) is the primary cause of chronic kidney disease (CKD) worldwide. Altered mineral levels leading to adverse outcomes are widely reported in diabetes but limited in DKD, in the Indian scenario, hence this study was taken up to address this issue.

METHODS

A hospital-based case-control study was taken up with 54 healthy controls (C) and 140 subjects with type 2 diabetes wherein 74 subjects with diabetes and CKD formed the DKD group, and 66 subjects with diabetes but no CKD formed the diabetic no-chronic kidney disease (DNCKD) group. High-resolution inductively coupled plasma mass spectrometry was used to evaluate the blood levels of minerals (calcium (Ca), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), copper (Cu), zinc (Zn), and selenium (Se)), and a raw food-based food frequency questionnaire for dietary intakes. Estimated glomerular filtration rate (eGFR) was calculated using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation (mL/min/1.73 m2) and albuminuria. Spearman's rank correlation was used to evaluate the relationship between the categorical variables.

RESULTS

The median values of plasma Ca in the DKD group were significantly lower compared with the DNCKD and C groups (10.5 mg/dL vs. 11.0 mg/dL and 11.7 mg/dL, p<0.001). Furthermore, plasma Ca levels lowered with declining kidney function, as evidenced by the eGFR and albuminuria segregation. Dietary intake of minerals did not correlate with the corresponding plasma levels. However, in the DKD group, eGFR correlated positively with the plasma levels of Ca (r= 0.422, p=0.001), Cr (r= 0.351, p=0.008), Mn (r= 0.338, p=0.011), Fe (r= 0.403, p=0.002), Cu (r= 0.274, p=0.041) and negatively with Se (r= -0.486, p<0.001).

CONCLUSION

Plasma Ca levels are lower in the DKD group with a strong positive association with eGFR, indicating its role in predicting the onset and progression of kidney function decline.

Homeostasis in networks with multiple inputs

Homeostasis, also known as adaptation, refers to the ability of a system to counteract persistent external disturbances and tightly control the output of a key observable. Existing studies on homeostasis in network dynamics have mainly focused on 'perfect adaptation' in deterministic single-input single-output networks where the disturbances are scalar and affect the network dynamics via a pre-specified input node. In this paper we provide a full classification of all possible network topologies capable of generating infinitesimal homeostasis in arbitrarily large and complex multiple inputs networks. Working in the framework of 'infinitesimal homeostasis' allows us to make no assumption about how the components are interconnected and the functional form of the associated differential equations, apart from being compatible with the network architecture. Remarkably, we show that there are just three distinct 'mechanisms' that generate infinitesimal homeostasis. Each of these three mechanisms generates a rich class of well-defined network topologies-called homeostasis subnetworks. More importantly, we show that these classes of homeostasis subnetworks provides a topological basis for the classification of 'homeostasis types': the full set of all possible multiple inputs networks can be uniquely decomposed into these special homeostasis subnetworks. We illustrate our results with some simple abstract examples and a biologically realistic model for the co-regulation of calcium ( Ca ) and phosphate ( PO 4 ) in the rat. Furthermore, we identify a new phenomenon that occurs in the multiple input setting, that we call homeostasis mode interaction, in analogy with the well-known characteristic of multiparameter bifurcation theory.

Magnesium status modulating the effect of serum vitamin D levels on retinopathy: National Health and Nutrition Examination Survey 2005 to 2008

Aim

Magnesium levels may influence the effect of vitamin D levels on the body. This study aimed to assess the combined effect of magnesium status as reflected by magnesium depletion score (MDS) and vitamin D status on the risk of retinopathy.

Methods

This cross-sectional study included participants aged 40 years and older with complete information on vitamin D, MDS, and retinopathy assessment from the 2005-2008 National Health and Nutrition Examination Survey (NHANES). Logistic regression analysis was utilized to analyze the relationship of MDS and vitamin D with retinopathy and expressed as odds ratio (OR) and 95% confidence interval (CI).

Results

Of these 4,953 participants included, 602 (9.53%) participants had retinopathy. Serum vitamin D levels ≤30 nmol/L (vs. >30 nmol/L) (OR = 1.38, 95%CI: 1.05-1.81) and MDS >2 points (vs. ≤2 points) (OR = 1.47, 95%CI: 1.01-2.16) were associated with higher odds of retinopathy. There was an interaction between MDS and vitamin D on the increased odds of retinopathy (OR = 2.29, 95%CI: 1.12-4.68, P interaction = 0.025). In different MDS groups, serum vitamin D levels ≤30 nmol/L increased the odds of retinopathy only in the MDS >2 group (OR = 2.90, 95%CI: 1.16-7.24), but not in the MDS ≤2 group (p = 0.293). Subgroups analyses demonstrated that the interaction between MDS and serum vitamin D on retinopathy was observed in males (OR = 6.88, 95%CI: 1.41-33.66, P interaction = 0.019), people with diabetes (OR = 3.43, 95%CI: 1.78-6.63, P interaction < 0.001), and people with body mass index (BMI) ≥25 kg/m2 (OR = 2.46, 95%CI: 1.11-5.44, P interaction = 0.028).

Conclusion

Magnesium plays a moderating role in the relationship between serum vitamin D and retinopathy. The protective effect of vitamin D against retinopathy was primarily present among those with inadequate magnesium levels.

Tubular phosphate transport: a comparison between different methods of urine sample collection in FGF23-dependent hypophosphatemic syndromes

OBJECTIVES

Tubular maximum phosphate reabsorption per glomerular filtration rate (TmP/GFR) is used to evaluate renal phosphate reabsorption and it is a useful tool for the differential diagnosis of hypophosphatemic syndromes. TmP/GFR is typically calculated from fasting plasma and second morning void urine samples, obtained 2 h after the first void (TmP/GFR 2 h). The purpose of this study was to evaluate if TmP/GFR calculated from 24 h urine collection (TmP/GFR 24 h) can be used as an alternative for TmP/GFR 2 h in patients with urine phosphate wasting.

METHODS

We enrolled adult patients with X-linked hypophosphatemia (XLH) or tumor-induced osteomalacia (TIO). All patients underwent blood and urine sample collections, to calculate TmP/GFR 24 h and TmP/GFR 2 h.

RESULTS

Twenty patients (17 XLH and 3 TIO), aged 24-78 years, were included. All patients had low TmP/GFR 2 h (0.35 mmol/L, IQR 0.24-0.47 mmol/L) and TmP/GFR 24 h (0.31 mmol/L, IQR 0.22-0.43 mmol/L). The concordance correlation coefficient between TmP/GFR 2 h and TmP/GFR 24 h was 0.86 (95 % CI: 0.69-0.93), with a systematic bias of 0.05 mmol/L (95 % limits of agreement: -0.10 to 0.20). Furthermore, in 70 % (i.e., 14 patients out of 20) and 80 % (i.e., 16 patients out of 20) of cases the difference between TmP/GFR 2 h and TmP/GFR 24 h was within ±30 % and ±35 %, respectively.

CONCLUSIONS

Despite TmP/GFR 2 and 24 h show a relatively suboptimal agreement, the difference between the two parameters appears to be small and not clinically significant in the setting of adult patients with FGF23-dependent urine phosphate wasting and secondary hypophosphatemia.

Development of a kidney microphysiological system hardware platform for microgravity studies

Determining the physiological effects of microgravity on the human kidney is limited to relatively insensitive tests of biofluids (blood and urine) that do not return abnormal results until more than 50% of kidney function is lost. We have developed an "organ on chip" microphysiological model of the human kidney proximal tubule (PT-MPS) that can recapitulate many kidney functions and disease states and could play a critical role in determining mechanisms of early kidney dysfunction in microgravity. However, the ground-based PT-MPS system is incompatible with spaceflight as it requires a large pneumatic system coupled to a cell incubator for perfusion and intensive hand-on manipulation. Herein, we report the hardware engineering and performance of the Kidney Chip Perfusion Platform (KCPP), a small, advanced, semi-autonomous hardware platform to support kidney microphysiological model experiments in microgravity. The KCPP is composed of five components, the kidney MPS, the MPS housing and valve block, media cassettes, fixative cassettes, and the programable precision syringe pump. The system has been deployed twice to the ISSNL (aboard CRS-17 and CRS-22). From each set of ISSNL experiments and ground-based controls, we were able to recover PT-MPS effluent for biomarker analysis and RNA suitable for transcriptomics analysis demonstrating the usability and functionality of the KCPP.

Lipid Toxicity in the Cardiovascular-Kidney-Metabolic Syndrome (CKMS)

Recent studies of Cardiovascular-Kidney-Metabolic Syndrome (CKMS) indicate that elevated concentrations of derivatives of phospholipids (ceramide, sphingosine), oxidized LDL, and lipoproteins (a, b) are toxic to kidney and heart function. Energy production for renal proximal tubule resorption of critical fuels and electrolytes is required for homeostasis. Cardiac energy for ventricular contraction/relaxation is preferentially supplied by long chain fatty acids. Metabolism of long chain fatty acids is accomplished within the cardiomyocyte cytoplasm and mitochondria by means of the glycolytic, tricarboxylic acid, and electron transport cycles. Toxic lipids and excessive lipid concentrations may inhibit cardiac function. Cardiac contraction requires calcium movement from the sarcoplasmic reticulum from a high to a low concentration at relatively low energy cost. Cardiac relaxation involves calcium return to the sarcoplasmic reticulum from a lower to a higher concentration and requires more energy consumption. Diastolic cardiac dysfunction occurs when cardiomyocyte energy conversion is inadequate. Diastolic dysfunction from diminished ATP availability occurs in the presence of inadequate blood pressure, glycemia, or lipid control and may lead to heart failure. Similar disruption of renal proximal tubular resorption of fuels/electrolytes has been found to be associated with phospholipid (sphingolipid) accumulation. Elevated concentrations of tissue oxidized low-density lipoprotein cholesterols are associated with loss of filtration efficiency at the level of the renal glomerular podocyte. Macroscopically excessive deposits of epicardial and intra-nephric adipose are associated with vascular pathology, fibrosis, and inhibition of essential functions in both heart and kidney. Chronic triglyceride accumulation is associated with fibrosis of the liver, cardiac and renal structures. Successful liver, kidney, or cardiac allograft of these vital organs does not eliminate the risk of lipid toxicity. Lipid lowering therapy may assist in protecting vital organ function before and after allograft transplantation.

Dynamics of bone mineralization in primiparous sows as a function of dietary phosphorus and calcium during lactation

To maximize the efficiency of dietary P utilization in swine production, understanding the mechanisms of P utilization in lactating sows is relevant due to their high P requirement and the resulting high inorganic P intake. Gaining a better knowledge of the Ca and P quantities that can be mobilized from bones during lactation, and subsequently replenished during the following gestation, would enable the development of more accurate P requirements incorporating this process of bone dynamics. The objective was to measure the amount of body mineral reserves mobilized during lactation, depending on dietary digestible P and phytase addition and to measure the amount recovered during the following gestation. Body composition of 24 primiparous sows was measured by dual-energy x-ray absorptiometry 2, 14, 26, 70 and 110 days after farrowing. Four lactation diets were formulated to cover nutritional requirements, with the exception of Ca and digestible P: 100% (Lact100; 9.9 g Ca and 3.0 g digestible P/kg), 75% (Lact75), 50% without added phytase (Lact50) and 50% with added phytase (Lact50 + FTU). The gestation diet was formulated to cover the nutritional requirements of Ca and digestible P (8.2 g Ca and 2.6 g digestible P/kg). During the 26 days of lactation, each sow mobilized body mineral reserves. The mean amount of mobilized bone mineral content (BMC) was 664 g, representing 240 g Ca and 113 g P. At weaning, the BMC (g/kg of BW) of Lact50 sows tended to be lower than Lact100 sows (-12.8%, linear Ca and P effect × quadratic time effect) while the BMC of Lact50 + FTU sows remained similar to that of Lact100 sows. During the following gestation, BMC returned to similar values among treatments. Therefore, the sows fed Lact50 could recover from the higher bone mineral mobilization that occurred during lactation. The P excretion was reduced by 40 and 43% in sows fed Lact50 and Lact50 + FTU, respectively, relative to sows fed Lact100. In conclusion, the quantified changes in body composition during the lactation and following gestation of primiparous sows show that bone mineral reserves were mobilized and recovered and that its degree was dependent on the dietary P content and from phytase supplementation during lactation. In the future, considering this potential of the sows' bone mineralization dynamics within the factorial assessment of P requirement and considering the digestible P equivalency of microbial phytase could greatly limit the dietary use of inorganic phosphates and, thus, reduce P excretion.

Inherited non-FGF23-mediated phosphaturic disorders: A kidney-centric review

Phosphate is freely filtered by the glomerulus and reabsorbed exclusively in the proximal tubule by two key transporters, NaPiIIA and NaPiIIC, encoded by SLC34A1 and SLC34A3, respectively. Regulation of these transporters occurs primarily through the hormone FGF23 and, to a lesser degree, PTH. Consequently, inherited non-FGF23 mediated phosphaturic disorders are due to generalised proximal tubular dysfunction, loss-of-function variants in SLC34A1 or SLC34A3 or excess PTH signalling. The corresponding disorders are Renal Fanconi Syndrome, Infantile Hypercalcaemia type 2, Hereditary Hypophosphataemic Rickets with Hypercalciuria and Familial Hyperparathyroidism. Several inherited forms of Fanconi renotubular syndrome (FRTS) have also been described with the underlying genes encoding for GATM, EHHADH, HNF4A and NDUFAF6. Here, we will review their pathophysiology, clinical manifestations and the implications for treatment from a kidney-centric perspective, focussing on those disorders caused by dysfunction of renal phosphate transporters. Moreover, we will highlight specific genetic aspects, as the availability of large population genetic databases has raised doubts about some of the originally proposed gene-disease associations concerning phosphate transporters or their associated proteins.

Protective effect of chicory and/or artichoke leaves extracts on carbon tetrachloride and gamma-irradiation-induced chronic nephrotoxicity in rats

The prevalence of chronic kidney disease (CKD) is in progress that causes kidney failure, leading to global problems. This manuscript investigated the nephroprotective effects of chicory (CLE) and/or artichoke (ALE) leaves extracts on carbon tetrachloride (CCl4 ) and gamma-irradiation (Rad)-induced chronic nephrotoxicity in rats. Rats were divided into 10 groups (10 animals/group): group 1: control, groups 2-7 rats were treated with CLE, ALE, CLE/ALE, CCl4 , Rad, and CCl4 /Rad, respectively. Groups 8 to 10, rats were intoxicated with CCl4 /Rad, and treated with CLE, ALE, and CLE/ALE extracts, respectively, for 4 weeks. The data demonstrated that CCl4 administration or Rad exposure induced high levels of urea and creatinine, with low levels of total protein and albumin in the serum. However, high levels of malondialdehyde (MDA), nitric oxide (NO), hydrogen peroxide (H2 O2 ), some pro-inflammatory markers such as interleukins (IL-1β, IL-2, IL-6), TNF-α, NF-κB, the fibrotic marker; TGF-β1, calcium, and copper, low contents of reduced glutathione (GSH), iron, and zinc, and suppression of the antioxidant enzymes' activity, superoxide dismutase (SOD), and catalase (CAT) were observed. In addition, the Wnt and β-catenin protein expression ratios were up-regulated in the kidney tissues of the CCl4 , and Rad intoxicated animals. However, the combined treatment CCl4 /Rad augmented these measurements. On the other hand, CLE, ALE, and CLE/ALE treatments demonstrated nephroprotection in the kidney tissues of CCl4 /Rad intoxicated animals, in the order of CLE/ALE>ALE>CLE by ameliorating the investigated parameters. Kidney tissues' histopathological examinations confirmed these results. In conclusion, CLE and/or ALE demonstrated nephroprotection against CCl4 /Rad co-toxicity mediated by down-regulation of renal Wnt/β-catenin protein expressions.

Open-label extension of a randomized trial investigating safety and efficacy of rhPTH(1-84) in hypoparathyroidism

Hypoparathyroidism (HypoPT) is a rare disease, often inadequately controlled by conventional treatment. PARALLAX was a mandatory post-marketing trial assessing pharmacokinetics and pharmacodynamics of different dosing regimens of recombinant human parathyroid hormone 1-84 (rhPTH[1-84]) for treating HypoPT. The present study (NCT03364738) was a phase 4, 1-yr open-label extension of PARALLAX. Patients received only 2 doses of rhPTH(1-84) in PARALLAX and were considered treatment-naive at the start of the current study. rhPTH(1-84) was initiated at 50 μg once daily, with doses adjusted based on albumin-corrected serum calcium levels. Albumin-corrected serum calcium (primary outcome measure), health-related quality of life (HRQoL), adverse events, and healthcare resource utilization (HCRU) were assessed. The mean age of the 22 patients included was 50.0 yr; 81.8% were women, and 90.9% were White. By the end of treatment (EOT), 95.5% of patients had albumin-corrected serum calcium values in the protocol-defined range of 1.88 mmol/L to the upper limit of normal. Serum phosphorus was within the healthy range, and albumin-corrected serum calcium-phosphorus product was below the upper healthy limit throughout, while mean 24-h urine calcium excretion decreased from baseline to EOT. Mean supplemental doses of calcium and active vitamin D were reduced from baseline to EOT (2402-855 mg/d and 0.8-0.2 μg/d, respectively). Mean serum bone turnover markers, bone-specific alkaline phosphatase, osteocalcin, procollagen type I N-terminal propeptide, and type I collagen C-telopeptide increased 2-5 fold from baseline to EOT. The HCRU, disease-related symptoms and impact on HRQoL improved numerically between baseline and EOT. Nine patients (40.9%) experienced treatment-related adverse events; no deaths were reported. Treatment with rhPTH(1-84) once daily for 1 yr improved HRQoL, maintained eucalcemia in 95% of patients, normalized serum phosphorus, and decreased urine calcium excretion. The effects observed on urine calcium and the safety profile are consistent with previous findings.

Clinical trial identifier

NCT03364738.

Cardiovascular Consequences of Uremic Metabolites: an Overview of the Involved Signaling Pathways

The crosstalk of the heart with distant organs such as the lung, liver, gut, and kidney has been intensively approached lately. The kidney is involved in (1) the production of systemic relevant products, such as renin, as part of the most essential vasoregulatory system of the human body, and (2) in the clearance of metabolites with systemic and organ effects. Metabolic residue accumulation during kidney dysfunction is known to determine cardiovascular pathologies such as endothelial activation/dysfunction, atherosclerosis, cardiomyocyte apoptosis, cardiac fibrosis, and vascular and valvular calcification, leading to hypertension, arrhythmias, myocardial infarction, and cardiomyopathies. However, this review offers an overview of the uremic metabolites and details their signaling pathways involved in cardiorenal syndrome and the development of heart failure. A holistic view of the metabolites, but more importantly, an exhaustive crosstalk of their known signaling pathways, is important for depicting new therapeutic strategies in the cardiovascular field.

Oral Release Kinetics, Biodistribution, and Excretion of Dopants from Barium-Containing Bioactive Glass in Rats

Background: Inorganic biomaterials are biologically active and are used as implants and drug delivery system. They have therapeutically active elements present in their framework that are released in the physiological milieu. Release of these dopants above the supraphysiological limit may produce adverse effects and physicochemical interactions with the loaded drugs. Therefore, this necessitates evaluating the in vivo release kinetics, biodistribution, and excretion profiles of dopants from barium-doped bioglass (BaBG) that has potential anti-inflammatory, antiulcer, and regenerative properties. Methods: In vitro leaching of Ca, Si, and Ba from BaBG was analyzed in simulated body fluid. Release kinetics post single-dose oral administration (1, 5, and 10 mg/kg) was performed in rats. Blood was collected at different time points, and pharmacokinetic parameters of released elements were calculated. The routes of excretion and biodistribution in major organs were evaluated using ICP-MS. Results: Elements were released after the oral administration of BaBG into the plasma. They showed dose-dependent release kinetics and mean residence time. Cmax was observed at 24 h for all elements, followed by a downhill fall. There was also a dose-dependent increase in the volume of distribution, and the clearance of dopants was mostly through feces. Ba and Si were biodistributed significantly in the liver, spleen, and kidneys. However, by the end of day 7, there was a leveling-off effect observed for all elements. Conclusion: All of the dopants exhibited a dose-dependent increase in release kinetics and biodistribution in vital organs. This study will help in dose optimization and understanding of various physicochemical and pharmacokinetic interactions when BaBG is used for future pharmacological studies.

The Effects of Acid on Calcium and Phosphate Metabolism

A variety of changes in mineral metabolism aiming to restore acid-base balance occur in acid loading and metabolic acidosis. Phosphate plays a key role in defense against metabolic acidosis, both as an intracellular and extracellular buffer, as well as in the renal excretion of excess acid in the form of urinary titratable acid. The skeleton acts as an extracellular buffer in states of metabolic acidosis, as the bone matrix demineralizes, leading to bone apatite dissolution and the release of phosphate, calcium, carbonate, and citrate into the circulation. The renal handling of calcium, phosphate and citrate is also affected, with resultant hypercalciuria, hyperphosphaturia and hypocitraturia.

Calcium, Phosphorus, and Vitamin D Levels in a Series of Cystic Fibrosis Patients: A Cross-Sectional Study

Cystic fibrosis (CF) is a monogenic disease with different types of mutations that mainly affect the respiratory-digestive system. Calcium (Ca), phosphorus (P), and vitamin D (Vit-D) are essential nutrients for maintaining adequate growth and development, as well as key components in crucial metabolic pathways. Proper diagnosis, treatment, and response are decisive components of precision medicine. Therefore, we conducted a cross-sectional study to evaluate Ca, P, and Vit-D levels along with health and nutritional indicators, regarding their non-skeletal functions, in a series of CF patients. Anthropometric and clinical evaluation, biochemical analysis, dietary survey, and respiratory and pancreatic status were performed. Even though the results showed that all patients had normal dietary and serum Ca levels, 47% of patients had deficient Vit-D intake, 53% of patients had hypovitaminosis D, 35% had insufficient Vit-D levels, 18% had hypophosphatemia, 76% had elevated alkaline phosphate levels, 29% had hypercalciuria, and 65% had hyperphosphaturia. There were no significant differences between homozygous and compound heterozygous patients. Ca, P, and Vit-D levels were associated with body mass index; body composition; physical activity; diet; growth hormones; and the immune, liver, and kidney systems. We suggest a periodically evaluation of Ca and P losses.

Evaluation of various blood biomarkers associated with the outcomes of patients with COVID‑19 treated in intensive care units

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and the resulting coronavirus disease 2019 (COVID-19) represented a global public health crisis and the most significant pandemic in modern times. Transmission characteristics, and the lack of effective antiviral treatment protocol and protective vaccines, pushed healthcare systems, particularly intensive care units (ICUs), to their limits and led to extreme quarantine measures to control the pandemic. It was evident from an early stage that patient stratification approaches needed to be developed to better predict disease progression. In the present study, the predictive value of clinical and blood biomarkers for the outcomes of patients with COVID-19 hospitalized in the ICU were investigated, taking age and sex into consideration. The present study analyzed blood samples from 3,050 patients with COVID-19 hospitalized in the ICU. The analysis revealed that the levels of procalcitonin, N-terminal pro-B-type natriuretic peptide, D-dimer, ferritin, liver enzymes, C-reactive protein and lactate dehydrogenase were increased and were associated with disease progression, resulting in a prolonged hospitalization period and severe COVID-19 related complications. Additionally, significant age and sex disparities among these biomarkers were documented and discussed in specific cases. On the whole, the results of the present study suggest a potential association of the demographic characteristics and blood biomarkers with prolonged hospitalization in the ICU and the mortality of patients with COVID-19.

Nephrocalcinosis in Neonates

Nephrocalcinosis occurs in as many as 40% of preterm neonates. Many causes and contributors predispose neonates to develop nephrocalcinosis, including metabolic, genetic, and iatrogenic factors. Because nephrocalcinosis can be a manifestation of an underlying genetic disorder, neonates with nephrocalcinosis must undergo an evaluation to identify and address contributors, to prevent further renal calcium deposition that can potentially lead to renal dysfunction. In this article, we review the epidemiology, pathogenesis, diagnosis, and evaluation of nephrocalcinosis in neonates. We also summarize the natural history of nephrocalcinosis of prematurity as well as the management of this condition.