Skeletal and cardiovascular consequences of a positive calcium balance during hemodialysis / Consequências esqueléticas e cardiovasculares de um balanço positivo de cálcio durante a hemodiálise

Abstract Patients on hemodialysis are exposed to calcium via the dialysate at least three times a week. Changes in serum calcium vary according to calcium mass transfer during dialysis, which is dependent on the gradient between serum and dialysate calcium concentration (d[Ca]) and the skeleton turnover status that alters the ability of bone to incorporate calcium. Although underappreciated, the d[Ca] can potentially cause positive calcium balance that leads to systemic organ damage, including associations with mortality, myocardial dysfunction, hemodynamic tolerability, vascular calcification, and arrhythmias. The pathophysiology of these adverse effects includes serum calcium changes, parathyroid hormone suppression, and vascular calcification through indirect and direct effects. Some organs are more susceptible to alterations in calcium homeostasis. In this review, we discuss the existing data and potential mechanisms linking the d[Ca] to calcium balance with consequent dysfunction of the skeleton, myocardium, and arteries.

Resumo Pacientes em hemodiálise são expostos ao cálcio, por meio do dialisato, pelo menos três vezes por semana. As alterações no cálcio sérico variam de acordo com a transferência de massa de cálcio durante a diálise, que é dependente do gradiente entre a concentração de cálcio no plasma e no dialisato (d [Ca]) e o estado de renovação do esqueleto que altera a capacidade do osso de incorporar cálcio. Embora subestimado, o d [Ca] pode potencialmente causar balanço positivo de cálcio que leva a danos em órgãos sistêmicos, incluindo associações com mortalidade, disfunção miocárdica, tolerabilidade hemodinâmica, calcificação vascular e arritmias. A fisiopatologia desses efeitos adversos inclui alterações do cálcio sérico, supressão do hormônio da paratireóide e calcificação vascular por meio de efeitos diretos e indiretos. Alguns órgãos são mais suscetíveis a alterações na homeostase do cálcio. Nesta revisão, discutimos os dados existentes e os mecanismos potenciais que ligam o d [Ca] ao equilíbrio do cálcio com a consequente disfunção no esqueleto, miocárdio e artérias.

Transplacental transport of fluoride, calcium and magnesium.

Background: In fluorosis endemic area, the amount of fluoride transferred to the fetus is significant in determining the early onset of fluorosis. The role played by placenta in transporting fluoride and other ions which are present in high concentrations in the local drinking water is studied. Aims & Objectives: The aim of the present study is to decipher the role of placenta in transport of fluoride to the fetus and to analyze the placental binding & distribution of fluoride, calcium and magnesium within the placenta. Materials & Methods: 200 healthy pregnant women aged between 17- 28 yrs were inducted in the study. All the women had a normal & uneventful delivery. The maternal blood, cord blood & placenta were collected immediately after delivery. The placenta was divided into 3 parts- the maternal side, fetal side & the peripheral. Separate tissue extracts were prepared from each site and analyzed. Fluoride, calcium and magnesium were quantified from the samples. Results: The average drinking water fluoride was 1.64±0.49ppm and ground water fluoride was 10.94±2.09ppm. Fluoride concentration of placenta on the maternal side was 1.62±0.787 ppm and in the periphery it was2.54±1.54 ppm (p<0.001) while that of the fetal side of placenta was1.41±0.776 ppm. Maternal and cord blood fluoride levels were1.21±0.79ppm and 0.45±0.304 ppm respectively (p<0.001). The concentrations of calcium in the maternal blood and cord blood were 9.67±1.53mg% and 9.89±1.89 mg% respectively (P<0. 5). The levels of calcium in the placenta were 8.79±1.36 mg%, 9.68±1.69 mg%, 13.87±3.32 mg% respectively on the maternal surface, fetal surface and periphery (p<0.001). The magnesium concentration on the peripheral part of placenta was twofold higher than that of the maternal serum and cord serum (p<0.001) indicating a significant accumulation of magnesium on the peripheral parts of the placenta. However, the differences in the magnesium concentrations of the placenta on the maternal and fetal surfaces with that of the maternal and cord blood sera were found to be insignificant. Conclusion: The results show that, Fluoride, Calcium and Magnesium accumulate in placenta, with the highest concentration being in the marginal part. The placenta therefore acts as a barrier to the transport of fluoride ions and protects against early fluorosis.

Advances of mechanical stimulation induced calcium response and transfer in osteoblasts / 医用生物力学

Calcium is not only the important signaling molecule within and between bone cells, but also the primary component of extracellular matrix in bone. It has been demonstrated during the past over 100 years that mechanical stimulations can regulate the molecular signal transduction and intercellular communication in bone cells as well as the bone mineralization and resorption at tissue level, but further more researches are still needed to give insight into the mechanism of mechanical stimulation-induced bone remodeling. This paper will summarize the related works on the following aspects: (1) the primary experimental approaches for studying mechanical stimulation induced calcium response and transfer in osteoblasts, (2) the calcium sources and mechanism of calcium response in osteoblasts, (3) the intercellular calcium transfer pathways and (4) characteristic parameters of calcium response and transfer in osteoblasts. Finally, several potential research directions in this field are presented in the paper.