The effects of aluminum loading on selected tissue calcium and magnesium concentrations in rats

Effects of aluminum exposure on bone mineral density, mineral, and trace elements in rats

The purpose of the study was to investigate the effects of aluminum (Al) exposure on bone mineral elements, trace elements, and bone mineral density (BMD) in rats. One hundred Wistar rats were divided randomly into two groups. Experimental rats were given drinking water containing aluminum chloride (AlCl(3), 430 mg Al(3+)/L), whereas control rats were given distilled water for up to 150 days. Ten rats were sacrificed in each group every 30 days. The levels of Al, calcium (Ca), phosphorus (P), magnesium (Mg), zinc (Zn), iron (Fe), copper (Cu), manganese (Mn), selenium (Se), boron (B), and strontium (Sr) in bone and the BMD of femur were measured. Al-treated rats showed lower deposition of Ca, P, and Mg compared with control rats. Levels of trace elements (Zn, Fe, Cu, Mn, Se, B, and Sr) were significantly lower in the Al-treated group than in the control group from day 60, and the BMD of the femur metaphysis in the Al-treated group was significantly lower than in the control group on days 120 and 150. These findings indicate that long-term Al exposure reduces the levels of mineral and trace elements in bone. As a result, bone loss was induced (particularly in cancellous bone).

Effects of low-molecular-weight aluminum complexes on brain tissue calcium homeostasis

The in vitro effects of low-molecular-weight aluminum complexes (citrate, lactate, and ATP complex) on the Ca2+ uptake and aluminum-induced lipid peroxidation of brain tissue show that the modification of the calcium homeostasis is determined by the nature of the ligand and that there is no correlation between the aluminum-induced lipid peroxidation and the Ca2+ uptake. The same characteristics have been shown by a similar study performed with Ehrlich carcinoma cells. The electrophoretic analyses of the aluminum lactate-albumin and aluminum lactate-ATP interactions indicate an aluminum transfer from the lactate to the albumin and ATP ligands. The increased Ca2+ uptake when ATP is present in the incubation medium with aluminum citrate and aluminum lactate corroborates the suggested mediator role of ATP in cellular calcium homeostasis modification induced by iron.

Element variations in pregnant and nonpregnant female rats orally intoxicated by aluminum lactate

Pregnant or nonpregnant female rats were orally intoxicated by aluminum lactate (400 mg Al/kg/d) from d 0-19 of gestation to determine the treatment's influence on element variations in the females and their fetuses. The aluminum levels of plasma, liver, spleen, and kidneys were significantly higher in treated pregnant rats than non-pregnant female rats. Differences of P, Ca, Cu, Zn, or Mg levels were observed among the four groups of female rats in the tissues and plasma. The aluminum content of the 20-d-old fetuses did not significantly differ between the treated and control groups. On the contrary, calcium and magnesium levels in the whole fetuses from treated or nontreated dams are significantly different.

Hematological effects of aluminum on living organisms

1. Aluminum has been of great interest for many researchers over a number of years; its biochemical and physiological role is not yet fully clear. There are few papers describing the hematological consequences of its excess in living organisms and most of their data are cited in this paper. 2. Aluminum reduced the deformability of erythrocytes, and such cells are rather frequently retained in the reticuloendothelial system of the spleen and eliminated faster from the blood stream. 3. Aluminum produces peroxidative changes in the erythrocytes membrane, leading to hemolysis. Therefore, the depressed erythrocyte count in animals intoxicated with aluminum may be the consequence of both the hemolytic action of aluminum and the shortened time of survival of erythrocytes. 4. It was demonstrated that aluminum inhibits heme biosynthesis in vitro. This problem requires, however, further studies and observation. 5. Changes occurring under the influence of Al3+ on the leukocyte system of animals suggest the influence of this element on the resistance of the organism, but the mechanism of the action of Al3+ still requires elucidation. 6. Cell metabolism including blood cells may be affected by aluminum in many ways, the more so as the element may combine in vitro with amino acids, peptides, proteins, enzymes, substrates, cofactors, nucleotides and carbohydrates. Aluminum stimulates NADPH oxidation and takes part in the process of free radical formation.

Tissue distribution and urinary excretion of essential elements in rats orally exposed to aluminum chloride

The purpose of this study was to determine disorders in the metabolism of the essential elements (Ca, Fe, Cu, and Zn) in some tissues of rats, as well as to detect the dynamics of urinary excretion of these metals after oral administration of 20 mgAl/kg every day for 8 wk. The elements were determined in brain, kidneys, blood, and urine of the animals in 1st, 2nd, 3rd, 4th, and 8th wk after the exposure to AlCl3. After the 1st wk of aluminium administration, we observed increase of Ca and a decrease of Fe in blood. In brain Ca, Fe, and Cu concentrations were significantly higher in Al-treated rats than in controls after 8-wk exposure. The concentration changes of the essential metals in the tissue were accompanied by increase of the Ca, Fe, and Zn urinary excretion. We assume that the increase in urinary excretion of Ca and the decrease of Fe in the blood may be sensitive indicators of oral aluminium administration.

Starvation is associated with changes in the elemental composition of the pancreatic beta-cell

By using the proton microprobe technique we have investigated the elemental composition of both pancreatic beta-cells and exocrine pancreas from fed and 24 h or 48 h starved obese hyperglycemic mice. Among the 15 elements measured in the beta-cells both Ca and Fe increased while Mg and S decreased significantly after 24 h of starvation, the effects being more pronounced after 48 h. When animals were starved for 48 h there was a decrease in the contents of Cl, Rb and Cu, whereas that of Al and Mn increased with 152 and 55%, respectively. There was an initial decrease in Na after 24 h of starvation, which was followed by an increase after 48 h. This is in contrast to Cd, which first increased and then decreased to a value lower than that obtained in the fed animal. The content of K showed a small decrease and that of Pb showed an increase only in the 24 h starved group. In the beta-cells the contents of Zn and P did not change subsequent to starvation. In the exocrine pancreas Na, Cl and P decreased after 24 h of starvation and except for Na, the decrease was maintained when the starvation period was increased to 48 h. After 24 h there was a significant, though transient, increase in K, Mg and Rb. With regard to the contents of Zn, Cu and S there was a progressive decrease as the starvation continued. In contrast to the endocrine pancreas the content of Al in the exocrine pancreas did not change after 48 h of starvation. There was no change in islet insulin content subsequent to starvation. The extent to which the observed changes in beta-cell elemental composition is involved in the impaired insulin release associated with starvation, merits further investigations.

Developmental alterations in offspring of female rats orally intoxicated by aluminum lactate at different gestation periods

Pregnant rats were treated orally with aluminum lactate (400 mg Al/kg/day) during three periods of gestation to determine the treatment's influence on mortality, weight gain, neuromotor maturation, and learning abilities of their pups. No effect of treatment on litter size, mortality rate, and weight gain of pups was detected. In the negative geotaxis test, the scores of pups from females treated during the second and third weeks of gestation were diminished. In the locomotor coordination and the operant conditioning tests, significant differences in the comparison of controls vs. the three treated groups were found, indicating long-term effects of early intoxication upon the central nervous system.

Effects of parathyroidectomy on tissue calcium, phosphorus, magnesium, and copper concentrations in aluminum-loaded uremic rats

Rats were subjected to a two-stage 5/6 nephrectomy and treated with Al for 2 and 4 wk with a cumulative dose of 4.2 and 8.4 mg of Al, respectively. Other animals were parathyrectomized (PTx) and loaded with 8.4 mg of Al for 4 wk. Total Al, Ca, P, Mg, and Cu contents were analyzed in the liver, kidney, and bone by inductively coupled plasma atomic emission spectrometry (ICP-AES). The results showed that Al given to growing uremic rats significantly increased the content of Al in the liver, kidney, and bone. Moreover, Al treatment increased the liver and kidney Ca levels and decreased the Ca and P values in bone. Previous parathyroidectomy significantly reduced Al accumulation within organs and changes in the Ca and P levels in the bone, liver, and kidney. The result was not influenced by different degrees of renal failure.

Aluminum-induced neurotoxicity: alterations in membrane function at the blood-brain barrier

Aluminum is established as a neurotoxin, although the basis for its toxicity is unknown. It recently has been shown to alter the function of the blood-brain barrier (BBB), which regulates exchanges between the central nervous system (CNS) and peripheral circulation. The BBB owes its unique properties to the integrity of the cell membranes that comprise it. Aluminum affects some of the membrane-like functions of the BBB. It increases the rate of transmembrane diffusion and selectively changes saturable transport systems without disrupting the integrity of the membranes or altering CNS hemodynamics. Such alterations in the access to the brain of nutrients, hormones, toxins, and drugs could be the basis of CNS dysfunction. Aluminum is capable of altering membrane function at the BBB; many of its effects on the CNS as well as peripheral tissues can be explained by its actions as a membrane toxin.

Reduced intestinal calcium and dietary calcium intake, increased aluminum absorption, and tissue concentration in the rat

To test the influence of calcium (Ca) on aluminum (Al) absorption, Ca was withheld from or added (1mM) to the perfusate of the in situ rat gut. The rats had been maintained on Purina Rat Chow. Ca addition significantly decreased (to 70%) the rate of Al disappearance from the gut and decreased (to 55%) the area under the curve of Al appearance in portal blood. To test the influence of Ca deficiency on Al absorption, rats were maintained on a low-Ca (0.008%) or a Ca-replete (0.5%) diet for 1-4 wk. The in situ gut was prepared, and a perfusate containing approximately 1 microM Ca was used. The rate of Al disappearance from the gut of low-Ca diet rats was significantly faster than from the gut of rats maintained on the Ca-replete diet, averaging 156% of the latter. Al appearance in portal blood was significantly greater (averaging 38%) in rats maintained on the low-Ca diet than in controls. To determine if Ca deficiency influences Al tissue distribution independent of gastrointestinal Al absorption, rats maintained on a low-Ca or a Ca-replete diet received 20 ip Al injections over 1 mo. Rats eating the low-Ca diet demonstrated enhanced tissue Al accumulation in all tissues studied, except for muscle and cerebral cortex. These results demonstrate enhanced Al absorption and tissue retention in the presence of reduced intestinal Ca concentration and reduced Ca intake.

Effects of 1 alpha,25- and 24R,25-dihydroxyvitamin D3 on aluminum-induced rickets in growing uremic rats

Rats were subjected to a two-stage subtotal nephrectomy or sham operation, and treated with aluminum (Al) or both aluminum and vitamin D3 metabolites for 5 weeks with a cumulative dose of 13.6 mg aluminum. Animals were injected with 3H-thymidine and 3H-proline. The following analyses were performed: quantitative histology of tibial metaphyses and cytomorphometric electron microscopy of osteoclasts, quantitative (ICP-spectroscopy) and qualitative determination (histochemical staining) of aluminum within organs, and serum biochemistry (Ca, P, Mg, vitamin D3 metabolites, alkaline phosphatase, urea). The following new facts of the aluminum-related bone disease became evident: (a) Application of aluminum to growing uremic rats induced rickets, whose major epiphyseal growth plate changes were 1 alpha,25(OH)2D3-dependent. Addition of 1 alpha,25(OH)2D3 prevented the formation of rachitic metaphysis, but failed to prevent osteoid accumulation on epiphyseal and metaphyseal trabecular surfaces. Moreover, calcitriol produced hyperosteoidosis and osteosclerosis in the same rats. Aluminum did not alter the function of osteoblasts, while osteoclasts seemed inactivated. (b) The development of rickets was associated with suppressed serum levels of 1,25(OH)2D3, reduced phosphorus level and the high content of aluminum in the bone, kidney, and liver. The addition of 24R,25(OH)2D3 markedly exaggerated the reduction of serum levels of calcitriol. We suggested that aluminum induces rickets in growing uremic rats, which consists of two components: vitamin D refractory osteomalacia and 1 alpha,25(OH)2D3-dependent epiphyseal growth plate changes.

Voltage gating in VDAC is markedly inhibited by micromolar quantities of aluminum

The mitochondrial outer membrane contains voltage-gated channels called VDAC that are responsible for the flux of metabolic substrates and metal ions across this membrane. The addition of micromolar quantities of aluminum chloride to phospholipid membranes containing VDAC channels greatly inhibits the voltage dependence of the channels' permeability. The channels remain in their high conducting (open) state even at high membrane potentials. An analysis of the change in the voltage-dependence parameters revealed that the steepness of the voltage dependence decreased while the voltage needed to close half the channels increased. The energy difference between the open and closed states in the absence of an applied potential did not change. Therefore, the results are consistent with aluminum neutralizing the voltage sensor of the channel. pH shift experiments showed that positively charged aluminum species in solution were not involved. The active form was identified as being either (or both) the aluminum hydroxide or the tetrahydroxoaluminate form. Both of these could reasonably be expected to neutralize a positively charged voltage sensor. Aluminum had no detectable effect on either single-channel conductance or selectivity, indicating that the sensor is probably not located in the channel proper and is distinct from the selectivity filter.

Aluminum impairs glucose utilization and cholinergic activity in rat brain in vitro

The effects of AlCl3 on the production of 14CO2 from [U-14C]glucose and high affinity choline transport in rat brain synaptosomes, and on carbachol-stimulated hydrolysis of phosphoinositides in cortical slices were studied. In buffer containing either high K+ (50 mM) or low K+ (4.9 mM), 1 mM AlCl3 significantly depressed the synaptosomal production of 14CO2 from [U-14C]glucose to 54% and 44% of control rates, respectively. At a concentration of 0.1 mM, AlCl3 depressed the evolution of 14CO2 from [U-14C]glucose from synaptosomes incubated in the high K+ buffer, but did not significantly change 14CO2 production from synaptosomes in the low K+ buffer. Aluminum chloride also inhibited high affinity choline transport in synaptosomes prepared from rat cortex and from hippocampus with an IC50 of approximately 0.5 mM. In brain slices the carbachol-stimulated hydrolysis of phosphoinositides was inhibited by AlCl3 in a dose-dependent manner. One millimolar, 0.5 mM and 0.1 mM AlCl3 inhibited the carbachol-stimulated release of inositol phosphates by 75%, 44% and 33%, respectively. These same concentrations of AlCl3 inhibited the incorporation of [3H]inositol into phospholipids. This inhibitory effect was not dose-dependent as all 3 concentrations of AlCl3 inhibited phospholipid labelling to the same extent (27-37%). These results are discussed in relation to the in vivo neurotoxicity of aluminum.