Aluminum alters calcium influx and efflux from bone in vitro

The suppressive effects of aluminum chloride on the osteoblasts function

Aluminum (Al) exposure impairs bone formation, and bone formation is mediated by the osteoblasts. But effects of Al on the osteoblasts function remain elusive. The osteoblasts were exposed to 0, 0.0252, 0.126, 0.252mg/mL AlCl₃·6H₂O for 24h. The osteoblasts viability, TGF-β₁, BMP-2, IGF-I and Cbfα1 mRNA expressions, and GSH-P_x and SOD activities, ROS concentration were determined. The osteoblasts ultrastructural features were also observed. The results showed that AlCl₃ suppressed the osteoblasts viability, TGF-β₁, BMP-2, IGF-I and Cbfα1 mRNA expressions, GSH-P_x and SOD activities, and elevated ROS concentration compared with the CG. The ultrastructural features of osteoblasts in the HG showed mitochondrial swelling, foam-like structure, uneven distribution of chromatin, incomplete cell membrane and cytoplasm spillover compared with the CG. It indicates that AlCl₃ inhibits osteoblasts viability, growth regulation factors mRNA expressions, anti-oxidative function, and damaged the osteoblasts histology structure, impairing the osteoblasts function.

Aluminum exposure and toxicity in neonates: a practical guide to halt aluminum overload in the prenatal and perinatal periods

BACKGROUND

During the last years, human newborns have been overexposed to biologically reactive aluminum, with possible relevant consequences on their future health and on their susceptibility to a variety of diseases. Children, newborns and particularly preterm neonates are at an increased risk of aluminum toxicity because of their relative immaturity.

DATA SOURCES

Based on recent original publications and classical data of the literatures, we reviewed the aluminum content in mother's food during the intrauterine life as well as in breast milk and infant formula during lactation. We also determined the possible role of aluminum in parenteral nutrition solutions, in adjuvants of vaccines and in pharmaceutical products. A special focus is placed on the relationship between aluminum overexposure and the insurgence of bone diseases.

RESULTS

Practical points of management and prevention are suggested. Aluminum sources that infants may receive during the first 6 months of life are presented. In the context of prevention of possible adverse effects of aluminum overload in fetal tissues during development, simple suggestions to pregnant women are described. Finally, practical points of management and prevention are suggested.

CONCLUSIONS

Pediatricians and neonatologists must be more concerned about aluminum content in all products our newborns are exposed to, starting from monitoring aluminum concentrations in milk- and soy-based formulas in which, on the basis of recent studies, there is still too much aluminum.

Metabolic Bone Disease After Chronic Antacid Administration in an Infant

OBJECTIVE

To describe a case of hypophosphatemia and metabolic bone disease (MBD) due to aluminum-containing antacids.

CASE SUMMARY

An 8-month-old white boy was brought to the emergency department due to irritability and pain with movement. Upon examination, the infant was irritable, unable to bear weight, had palpable clavicular bony lesions, point tenderness of the hips, and poor head control. The infant had lost several developmental milestones over the past 4 months (eg, ability to roll over) and had decreased appetite and minimal weight gain. Skeletal survey revealed multiple rib fractures, osteoporosis, and Ricketts. Hypophosphatemia (2.3 mg/dL; normal 3.2–6.3) and an elevated serum aluminum level (14 μg/L, normal 0–9) were noted. Past medical history was positive for gastroesophageal reflux. He had been started on ranitidine and aluminum hydroxide (1/2 teaspoonful per 6-ounce bottle) at 2 months of age. The infant's formula contained elevated aluminum levels. Further investigation showed that 1/2 tablespoonful instead of 1/2 teaspoonful of antacid had been added to each 6-ounce formula bottle for the prior 6 months; only 1 month of antacid therapy had been recommended. An objective causality assessment revealed a probable adverse drug event.

DISCUSSION

Phosphate-binding substances such as aluminum-containing antacids can bind large amounts of phosphorus, causing hypophosphatemia and MBD.

CONCLUSIONS

We report this case to increase awareness of the risk of hypophosphatemia and MBD (likely aluminum related) with use of over-the-counter aluminum-containing antacids in pediatrics, as well as the hazards of prescribing doses in “spoonful” units.

Initial in vitro interaction of osteoblasts with nano-porous alumina

In the present study we have used a characterised primary human cell culture model to investigate cellular interactions with nano-porous alumina. This material, prepared by anodisation, is being developed as a coating on titanium alloy implants. The structure of the alumina, as determined by X-ray diffraction and transmission electron microscopy, was amorphous. When studying cell/material interactions we used both biochemical and morphological parameters. Cell viability, proliferation and phenotype were assessed by measurement of redox reactions in the cells, cellular DNA, tritiated thymidine ([3H]-TdR) incorporation and alkaline phosphatase (ALP) production. Results showed a normal osteoblastic growth pattern with increasing cell numbers during the first 2 weeks. A peak in cell proliferation was seen on day 3, after which cell growth decreased, followed by an increase in ALP production, thus indicating that the osteoblastic phenotype was retained on the alumina. Cell adhesion was observed, the osteoblast-like cells having a flattened morphology with filipodia attached to the pores of the material. SDS-PAGE and western blot measurements showed that the nano-porous alumina was able to adsorb fibronectin. Trace amounts of aluminium ions were measured in the surrounding medium, but no adverse effect on cell activity was observed.

Adynamic bone and chronic renal failure: an overview

Renal osteodystrophy may present with a wide spectrum of bone lesions, ranging from high bone turnover to low bone turnover. Decreased serum calcium and 1,25-dihydroxy vitamin D synthesis and retention of phosphate are involved in the pathogenesis of high bone turnover. However, several factors may influence the evolution of this disorder. The use of different therapeutic approaches (such as calcium supplements, phosphate binders, vitamin D metabolites, etc.), the type of treatment (either hemodialysis or continuous ambulatory peritoneal dialysis), and also the changes in the type of patients to whom we are offering dialysis (more diabetics and older patients are currently included in dialysis programs) may have introduced changes modifying the form of presentation of the bone metabolic disorders. As a result, recent studies reported a greater prevalence of adynamic forms of renal osteodystrophy. Patients with adynamic bone (with or without aluminum) would have more difficulties in handling and buffering calcium loads; consequently, they would have a higher risk of extraosseous calcifications.

Role of exchanged ions in the integration of ionomeric (glass polyalkenoate) bone substitutes

Ionomeric (glass polyalkenoate) implants are synthetic materials which can be used for repairing bone defects. It has been suggested that ions are leached from these implants during healing and that they influence cellular activity in the surrounding tissues. Morphological, immunohistochemical and microanalytical techniques were used to compare the osteogenic capacity of implants which eluted aluminium ions with implants which did not elute aluminium ions. The extracellular matrix molecules fibronectin and tenascin were located upon the surface of both implanted materials. Thick seams of lamellar bone were apposed to implants containing labile aluminium ions, but the bone was poorly mineralized. At the same time, transient increases were apparent in osteoblast activity on periosteal and endosteal surfaces and in chondrocyte activity in the growth plate and articular cartilages. In contrast, small amounts of mineralized lamellar bone were apposed to substituted implants (without aluminium) and the growth plate and articular cartilages remained normal in thickness and morphology. These results suggest that exchanged ions can influence the amount and quality of bone apposed to the implant. They also suggest that the effect of the ions depends upon their concentration and the state of differentiation of osteogenic cells.

Distribution of aluminum in different brain regions and body organs of rat

In the present study, an attempt has been made to investigate the distribution of aluminum in different regions of brain and body organs of male albino rats, following subacute and acute aluminum exposure. Aluminum was observed to accumulate in all regions of the brain with maximum accumulation in the hippocampus. Subcellular distribution of aluminum indicated that there was maximum localization in the nucleus followed by cytosolic, microsomal, and mitochondrial deposition. Elution profile of cytosolic proteins on G-75 Sephadex column revealed a substantial amount of aluminum bound to high-mol-wt protein fraction. Aluminum was also seen to compartmentalize in almost all the tissues of the body to varying extents, and the highest accumulation was in the spleen.

Effects of aluminum on bone surface ion composition

Aluminum induces net calcium efflux from cultured bone. To determine whether aluminum alters the bone surface ion composition in a manner consistent with predominantly cell-mediated resorption, a combination of cell-mediated resorption and physicochemical dissolution or physicochemical dissolution alone, we utilized an analytic high-resolution scanning ion microprobe with secondary ion mass spectroscopy to determine the effects of aluminum on bone surface ion composition. We cultured neonatal mouse calvariae with or without aluminum (10(-7) M) for 24 h and determined the relative ion concentrations of 23Na, 27Al, 39K, and 40Ca on the bone surface and eroded subsurface. Control calvariae have a surface (depth approximately 6 nm) that is rich in Na and K compared with Ca(Na/Ca) = 24.4 + 1.4, mean + 95% confidence limit of counts per second of detected secondary ions, K+Ca = 13.2 + 0.9). Aluminum is incorporated into the bone and causes a depletion of surface Na and K relative to Ca (Na/Ca = 9.6 + 0.7, K/Ca = 4.9 + 0.4; each p < 0.001 versus control). After erosion (depth approximately 50 nm), control calvariae have more Na and K than Ca (Na/Ca = 16.0 + 0.1, K/Ca = 7.5 + 0.1); aluminum again depleted Na and K relative to Ca (Na/Ca = 4.1 + 0.1 K/Ca = 1.9 + 0.1; each p < 0.001 versus control). Aluminum produced a greater net efflux of Ca (362 +/- 53, mean +/- SE, nmol/bone/24 h) than control (60 +/- 30, p < 0.001). With aluminum, the fall in the ratios of both Na/Ca and K/Ca coupled with net Ca release from bone indicates that aluminium induces a greater efflux of Na and K than Ca from the bone surface and is consistent with an aluminum-induced removal of the bone surface. This alteration in surface ion concentration and calcium efflux is consistent with that observed when calcium is lost from bone through a combination of cell-mediated resorption and physicochemical dissolution.

Systematic assessment of bone resorption, collagen synthesis, and calcification in chick embryonic calvaria in vitro: effects of prostaglandin E2

A systematic method has been developed to assess bone resorption, matrix formation, and calcification in a single calvarial culture from 20-day-old chick embryos. The bones were prelabeled with 45Ca by an injection into the egg white before culture. In the last 2 h of incubation, the bones were further labeled with both 3H-proline and 3H-tetracycline. Bone resorption was assessed as 45Ca release into the medium. Collagen synthesis was measured by the incorporation of 3H-proline into collagenase-digestible protein (CDP). Since tetracycline has been commonly used as an in vivo marker for osteoid calcification, we assessed in vitro calcification as the uptake of 3H-tetracycline into bone. By using this method, we studied the effects of prostaglandin E2 (PGE2) and indomethacin, which inhibits biosynthesis of PGE2, on bone resorption and formation. The cultured bone synthesized approximately 300 ng of PGE2 during every 24 h of incubation, and indomethacin (10(-6) M) completely inhibited the synthesis. In indomethacin-treated cultures, % 45Ca release and the labeling of CDP were significantly reduced. These reductions were not seen when exogenous PGE2 (10(-9) M) comparable to its endogenous level was added along with the indomethacin. Furthermore, 10(-8) to 10(-5) M PGE2 increased % 45Ca release and the CDP labeling. In addition, the uptake of 3H-tetracycline into the cultured bone was also enhanced by PGE2. In devitalized calvaria, PGE2 had no effect on 3H-tetracycline uptake, suggesting that the stimulative effect on PGE2 was cell-mediated.(ABSTRACT TRUNCATED AT 250 WORDS)