The influence of high dietary aluminum on brain microtubule polymerization in mice

Aluminum promotes neuronal plasticity events in a mouse neuroblastoma cell line

The effects of aluminum(III) on microtubular meshwork have been investigated using cultured murine neuroblastoma cells grown in a medium containing aluminum lactate at defined metal concentrations (10-20 microM). A role of aluminum(III) in promoting neuronal plasticity events is suggested. These events including sprouting and neurite outgrowth are associated with an increased tyrosine-tubulin (Tyr-Tub) expression, which can be due to the enhanced needs of recently formed, highly dynamic microtubules typical of neuronal plasticity. After 48 and 72 h aluminum exposure, an upregulation of Tyr-Tub expression is detected and this is concentration-dependent. A high amount of Tyr-Tub is observed also in non-treated cells, although later than in aluminum-exposed cells. Thus, it is possible that aluminum(III) accelerates neuronal plasticity events, for which Tyr-Tub is confirmed to be a useful marker.

Acrylamide and carbon disulfide treatments increase the rate of rat brain tubulin polymerization

Acrylamide and carbon disulfide produce central-peripheral distal axonopathy in experimental animals and humans. The main feature of this disease is the focal swellings containing neurofilaments in distal axons, followed by nerve degeneration beyond these swellings. We studied the possible role of tubulin assembly kinetics in this disease. The rats were either administered acrylamide (50 mg/kg, ip, saline) or exposed to carbon disulfide (700 ppm, 9 h) via inhalation for 12 and 15 d, respectively. Tubulin, purified from both acrylamide-(10.37 +/- 0.3 vs 11.3 +/- 0.15) and carbon disulfide-treated (9.72 +/- 0.5 vs 11.18 +/- 0.25) rat brains showed increase in Vmax (OD/min x 10(3)) of its polymerization. However, only acrylamide treatment showed a decrease in time to Vmax, when brain supernatant was used for tubulin polymerization. In vitro addition of acrylamide (0.1-1 mM) to bovine brain tubulin also showed a decrease in time to Vmax (16-21%) of its polymerization. Carbon disulfide treatment of rats, on the other hand, showed a decrease in MAP-2 and an increase in a 120-kDa peptide concentration. The latter showed immunoreactivity with anti-MAP-2. The increase in the rate of tubulin polymerization by acrylamide and carbon disulfide treatment may alter the rate of transport of axonal constituents, including neurofilament, and contribute toward their accumulation in the focal swellings observed in this neuropathy.

Possible factors in the etiology of Alzheimer's disease

Inherited cases of Alzheimer's disease (AD) comprise only a very small proportion of the total. The remainder are of unknown etiopathogenesis, but they are very probably multifactorial in origin. This article describes studies on four possible factors: aluminum; viruses--in particular, herpes simplex type I virus (HSV1); defective DNA repair; and head trauma. Specific problems associated with aluminum, such as inadvertent contamination and its insolubility, have led to some controversy over its usage. Nonetheless, the effects of aluminum on animals and neuronal cells in culture have been studied intensively. Changes in protein structure and location in the cell are described, including the finding in this laboratory of a change in tau resembling that in AD neurofibrillary tangles, and also the lack of appreciable binding of aluminum to DNA. As for HSV1, there has previously been uncertainty about whether HSV1 DNA is present in human brain. Work in this laboratory using polymerase chain reaction has shown that HSV1 DNA is present in many normal aged brains and AD brains, but is absent in brains from younger people. Studies on DNA damage and repair in AD and normal cells are described, and finally, the possible involvement of head trauma is discussed.

Aluminum interaction with phosphoinositide-associated signal transduction

Concerning molecular and cellular mechanisms of aluminum toxicity, recent studies support the hypothesis that interactions of aluminum ions with elements of signal transduction pathways are apparently primary events in cells. In the case of the phosphoinositide-associated signalling pathway of neuroblastoma cells, guanine nucleotide-binding proteins (G proteins) and a phosphatidylinositol-4,5-diphosphate (PIP2)-specific phospholipase C are probable interaction sites for inhibitory actions of aluminum ions. Following interiorization of aluminum by the cell, metal interactions decrease the accumulation of inositol phosphates, especially that of inositol-1,4,5-triphosphate (IP3), concomitant with derangements of intracellular Ca2+ homeostasis. In the presence of high concentrations of Ca2+, formation of IP3 is also diminished in aluminum-pretreated cells, presumably involving a process not requiring Mg(2+)-dependent G proteins. At higher aluminum doses, metal-induced changes in the lipid milieu of the membrane-bound phospholipase may play a role. These types of primary interactions of aluminum ions with elements of cellular communication channels are probably crucial in the manifestation of the multifacetted aluminum toxicity syndrome. If present as a phosphate-like fluoro-aluminate, a stimulatory role of aluminum ions is displayed in G protein-coupled transmembrane signalling.

Effects of dietary aluminum excess and manganese deficiency on neurobehavioral endpoints in adult mice

Studies in mice have suggested that both dietary Al excess and dietary Mn deficiency promote oxidative tissue damage. To determine if these factors can interact to produce functional nervous system damage, female mice (N = 10-12 per group) were fed diets with control or low Mn (35 or 3 micrograms Mn/g diet) and/or control or high Al (25 or 1000 micrograms Al/g diet, Al as Al lactate) content for a 90-day period. No overt signs of neurotoxicity were observed in any group. Excess Al produced a threefold Al accumulation in both liver and brain, a slight acceleration of growth, decreased motor activity, decreased grip strength, and decreased startle responsiveness. Manganese deprivation led to liver, brain, and femur Mn depletion and reduced liver MnSOD activity but no neurobehavioral changes. No interactive effects between Al excess and Mn deficiency were observed. Neither Al excess nor Mn deficiency altered brain or liver lipid peroxidation measures. This study suggests that (1) subchronic dietary Al at doses of 1000 micrograms Al/g diet produces elevated brain Al and altered neurobehavioral indices in adult mice; (2) brain lipid peroxidation is not altered by this treatment; (3) dietary Mn deficiency does not influence Al neurotoxicity in adult mice.

Developmental toxicity evaluation of oral aluminum in rats: influence of citrate

To evaluate the influence of citrate on the potential developmental toxicity of high doses of aluminum (133 mg/kg/day), three groups of pregnant Sprague-Dawley rats were given by gavage aluminum hydroxide (384 mg/kg/day), aluminum citrate (1064 mg/kg/day), or aluminum hydroxide (384 mg/kg/day) concurrent with citric acid (62 mg/kg/day) on gestational days 6 through 15. Control animals received distilled water. At termination on gestation day 20, live fetuses were examined for external, visceral, and skeletal alterations. There were no significant differences between controls and Al-treated rats on pre- or postimplantation loss, number of live fetuses per litter, or sex ratio. Fetal body weight was significantly reduced in the group treated with Al(OH)3 and citric acid. Although no increases in the incidence of malformations were observed, the incidence of skeletal variations was significantly increased in the group given Al(OH)3 concurrent with citric acid. In summary, although the administration of citric acid did not modify the lack of embryotoxicity and teratogenicity of Al(OH)3 in rats, some signs of maternal toxicity and fetotoxicity could be observed in this group.

Effects of aluminum on brain lipid peroxidation

Excessive dietary aluminum (Al) has been proposed to be a factor contributing to several neurological disorders in humans. Six 8-week-old female Swiss Webster mice were fed for 10 weeks purified diets containing 100 (control, 100 Al), 500 (500 Al) or 1000 (1000 Al) micrograms Al/g diet. Brain and liver lipid peroxidation was determined by evaluating the production of 2-thiobarbituric acid reactive substances (TBARS) in brain and liver homogenates in the presence or absence of 50 microM ferrous iron. TBARS production in the absence of iron in brain homogenates from mice fed the 1000 Al diet was higher (30%) than that in the 100 Al control group (3.1 vs. 2.4 nmol TBARS/mg protein). The addition of ferrous iron increased TBARS production in brain homogenates from all 3 dietary groups. The iron-induced TBARS production was 26% higher in the 1000 Al brain homogenates than in the 100 Al group (4.9 vs. 3.9 nmol TBARS/mg protein). Brain TBARS production in the presence and absence of iron was similar between the 100 and 500 Al groups. TBARS production in liver homogenates measured either with or without iron was similar for the 3 groups. These results show that, in mice, dietary Al intoxication leads to increased brain TBARS production, suggesting that enhanced lipid peroxidation may be one possible mechanism underlying the neurological damage associated with increased tissue Al.