Calcium and Phosphate Hormones: Vitamin D, Parathyroid Hormone, and Fibroblast Growth Factor 23

Vitamin D3 suppresses Npt2c abundance and differentially modulates phosphate and calcium homeostasis in Npt2a knockout mice

Vitamin D3 is clinically used for the treatment of vitamin D3 deficiency or osteoporosis, partially because of its role in regulating phosphate (Pi) and calcium (Ca2+) homeostasis. The renal sodium-phosphate cotransporter 2a (Npt2a) plays an important role in Pi homeostasis; however, the role of vitamin D3 in hypophosphatemia has never been investigated. We administered vehicle or vitamin D3 to wild-type (WT) mice or hypophosphatemic Npt2a-/- mice. In contrast to WT mice, vitamin D3 treatment increased plasma Pi levels in Npt2a-/- mice, despite similar levels of reduced parathyroid hormone and increased fibroblast growth factor 23. Plasma Ca2+ was increased ~ twofold in both genotypes. Whereas WT mice were able to increase urinary Pi and Ca2+/creatinine ratios, in Npt2a-/- mice, Pi/creatinine was unchanged and Ca2+/creatinine drastically decreased, coinciding with the highest kidney Ca2+ content, highest plasma creatinine, and greatest amount of nephrocalcinosis. In Npt2a-/- mice, vitamin D3 treatment completely diminished Npt2c abundance, so that mice resembled Npt2a/c double knockout mice. Abundance of intestinal Npt2b and claudin-3 (tight junctions protein) were reduced in Npt2a-/- only, the latter might facilitate the increase in plasma Pi in Npt2a-/- mice. Npt2a might function as regulator between renal Ca2+ excretion and reabsorption in response to vitamin D3.

Calcium, Phosphorus and Magnesium Abnormalities Associated with COVID-19 Infection, and Beyond

The coronavirus disease (COVID-19) pandemic caused by the novel coronavirus SARS-CoV-2 has had a profound impact on global health, leading to a surge in research to better understand the pathophysiology of the disease. Among the various aspects under investigation, disruptions in mineral homeostasis have emerged as a critical area of interest. This review aims to provide an overview of the current evidence linking calcium, phosphorus and magnesium abnormalities with COVID-19 infection and explores the potential implications beyond the acute phase of the disease. Beyond the acute phase of COVID-19, evidence suggests a potential impact of these mineral abnormalities on long-term health outcomes. Persistent alterations in calcium, phosphorus and magnesium levels have been linked to increased cardiovascular risk, skeletal complications and metabolic disorders, warranting continuous monitoring and management in post-COVID-19 patients.

Evaluating the Arterial Stiffness as a Useful Tool in the Management of Obese Children

Childhood obesity speeds up the development of arterial stiffness and progressively increases the values of arterial pressure. The purpose of this study is to investigate the value of using pulse wave analysis (PWA) to measure arterial stiffness as a sign of vascular wall impairment in obese children. The research was focused on 60 subjects: 33 obese and 27 normal-weight. Ages ranged from 6 to 18 years old. PWA includes parameters such as pulse wave velocity (PWV), augmentation index (AIx), peripheral and central blood pressure (SBP, DBP, cSBP, cDBP), heart rate, and central pulse pressure (cPP). The device used was a Mobil-O-Graph. Blood parameters were taken from the subject's medical history, not older than 6 months. A high BMI and a large waist circumference are linked to a high PWV. The levels of LDL-c, triglycerides (TG), non-HDL-c, TG/HDL-c ratio, and total cholesterol-HDL-c ratio significantly correlate to PWV, SBP, and cSBP. Alanine aminotransferase is a reliable predictor of PWV, AIx, SBP, DBP, and cDBP, while aspartate aminotransferase is a significant predictor of AIx, mean arterial pressure (MAP), cSBP, and cPP. 25-OH-Vitamin D negatively correlates with PWV, SBP, and MAP and significantly predicts the MAP. Cortisol and TSH levels are not significant to arterial stiffness in obese children without specific comorbidities and neither is fasting glucose in obese children without impaired glucose tolerance. We conclude that PWA contributes valuable data regarding patients' vascular health and should be considered a reliable tool in the management of obese children.

Genetic Disorders of Calcium and Phosphorus Metabolism

In this review, we describe genetic mutations affecting metabolic pathways of calcium and phosphorus homeostasis. Calcium and phosphorus homeostasis has tight hormonal regulation by three major hormones: vitamin D, parathyroid hormone (PTH) and fibroblast growth factor 23 (FGF23). We describe the physiology and pathophysiology of disorders, their biochemical profile, clinical characteristics, diagnostics, and treatments.

The Role of Serum Calcium Levels in Pediatric Dyslipidemia: Are There Any?

Background: No previous study explored the association between serum calcium levels and dyslipidemia in children. This study aimed to explore this relationship in children, based on a multicenter cross-sectional study population in China. Methods: Cross-sectional data was derived from the Pediatric Reference Intervals in China (PRINCE) study conducted between 2017 and 2018 involving 5,252 males and 5,427 females with a mean age of 10.0 ± 4.6 years. Multivariable logistic regression models were applied to calculate odds ratios (ORs), with 95% confidence intervals (CIs), for dyslipidemia of each serum calcium level and albumin-corrected calcium levels, which were sorted into quartiles. The restricted cubic spline model was fitted for the dose-response analysis. An L-shaped dose-response relation between calcium levels and the probability of dyslipidemia was found after the adjustment for multiple potential confounding factors, p for non-linear < 0.001. Results: Using the middle category of calcium level as the reference, multivariable-adjusted ORs and 95% CIs of the lowest and the highest quartile categories were 0.96 (0.82-1.12) and 1.29 (1.12-1.48), respectively, for total serum calcium levels and 1.06 (0.91-1.23) and 1.39 (1.21-1.60) for albumin-corrected calcium levels. Conclusions: Individuals with higher levels of serum calcium were associated with increased risk of dyslipidemia in a sample of a healthy Chinese pediatric population. The association between serum calcium levels and dyslipidemia needs to be examined prospectively in future studies.

Rickets in Children: An Update

Rickets refers to a deficient mineralization of the growth plate cartilage, predominantly affecting longer bones. Despite the fact that preventive measures are available, it is still a common disease worldwide; nutritional rickets, due to vitamin D deficiency or dietary calcium inadequate intake, remains the most common form. Medical history, physical examination, radiologic features and biochemical tests are essential for diagnosis. Although recent studies suggest hypophosphatemia as the leading alteration, rickets is classically divided into two categories: calcipenic rickets and phosphopenic rickets. Knowledge of this categorization and of respective clinical and laboratory features is essential for rapid diagnosis and correct management. The aim of this review is to analyze the epidemiological, pathogenetic, clinical, and therapeutic aspects of the different forms of rickets, describing the novelties on this “long-lived” disease.

Changes in duodenal and nephritic Ca and P absorption in hens during different egg-laying periods

Ca and P metabolic disorders during the egg-laying period can reduce egg production, impair eggshell quality, and even cause bone problems in hens; however, little is known regarding the capacity of duodenal and nephritic Ca and P absorption. Here, the levels of serum Ca and P metabolic indices and the expression of duodenal and renal Ca and P transporter genes were measured in hens at different egg-laying stages. The Ca, 25-(OH)-VD3, and 1,25-(OH)2-VD3 content increased during the peak (43 weeks of age) and late (72 weeks of age) egg-laying periods compared to that during the early (23 weeks of age) egg-laying period; however, there were no differences in Pi levels among the three egg-laying periods. Moreover, duodenal VDR and CaBP-D28k mRNA expression was markedly higher but NPt2b mRNA expression was markedly lower during the peak and late egg-laying periods than during the early egg-laying period. Furthermore, nephritic CaBP-D28k, PMCA1b, and FGFR1 mRNA expression was markedly higher but NPt2a and Cyp24a1 mRNA expression was markedly lower during the peak and late egg-laying periods than during the early egg-laying period. In conclusion, the present study indicated that the increased duodenal and nephritic Ca absorption during the peak and late egg-laying periods may be associated with the VD-VDR pathway, while the decreased P absorption despite relatively stable serum P levels in all three egg-laying stages may associated with osteolysis.

Acute Kidney Injury and Pediatric Bone Health

Acute kidney injury (AKI) has been associated with deleterious impacts on a variety of body systems. While AKI is often accompanied by dysregulation of mineral metabolism-including alterations in calcium, phosphate, vitamin D, parathyroid hormone, fibroblast growth factor 23, and klotho-its direct effects on the skeletal system of children and adolescents remain largely unexplored. In this review, the pathophysiology of dysregulated mineral metabolism in AKI and its potential effects on skeletal health are discussed, including data associating AKI with fracture risk.