Aluminium chelator (transferrin) reverses biochemical deficiency in Alzheimer brain preparations

Neurotoxic effects of dietary aluminium

Neurochemical responses to chronic oral aluminium administration have been studied in rats. Aluminium (0.3%) was added to drinking water of adult rats for four weeks or longer and weanling rats were given aluminium for eight weeks. Selective cognitive impairment was demonstrated in the adult rats. Aluminium inhibited calcium flux and phosphoinositide metabolism, one product of which (inositol 1,4,5-trisphosphate) modulates intracellular calcium levels. In weanling rats aluminium decreased the in vivo concentration of inositol 1,4,5-trisphosphate in the hippocampus. An increase in cyclic AMP concentrations by 30-70% in various brain regions in adult and weanling rats was found. Aluminium enhanced agonist-stimulated but not basal cyclic AMP production in vitro. It was postulated that aluminium inhibits the GTPase activity of the stimulatory G protein, Gs, leading to prolonged activation of Gs after receptor stimulation and increased cyclic AMP production. Aluminium treatment also increased the phosphorylation of microtubule-associated protein 2 (MAP-2) and the 200 kDa neurofilament protein (NF-H) but several other phosphoproteins were unaffected. Concentrations of seven structural proteins--MAP-2, tau, NF-H, NF-M (150 kDa), NF-L (68 kDa), tubulin and spectrin--were measured in rat brain regions by immunoblot methods. MAP-2 was most consistently decreased. These studies show that chronic oral aluminium administration to rats has significant neurochemical consequences. Three sites of action are implicated: altered calcium homeostasis, enhanced cyclic AMP production, and changes in cytoskeletal protein phosphorylation states and concentrations.

Aluminum chelation: chemistry, clinical, and experimental studies and the search for alternatives to desferrioxamine

This review focuses on aluminum (Al) chelation, its chemistry and biology. The toxicology and biology of Al in mammalian organisms are briefly reviewed to introduce the problems associated with excessive Al exposure and accumulation and the challenges facing an effective Al chelator. The basics of Al chelation chemistry are considered to help the reader understand the Al chelation chemical literature. The chemical properties of Al enable prediction of effective functional groups for Al chelation. A compilation of distribution coefficients between octanol and aqueous phases (Do/a) for chelators and their complexes with Al shows the effect of complexation on lipophilicity. A compilation of stability constants for Al.chelator complexes illustrates the role of oxygen in ligands that form stable complexes. The history of clinical Al chelation therapy is reviewed, with emphasis on desferrioxamine (DFO), which has been extensively used since 1980. The beneficial and adverse effects and limitations of DFO use in end-stage renal-diseased patients, in patients with neurodegenerative disorders, including Alzheimer's disease, and in animal models of Al intoxication are presented. The methods to evaluate potential Al chelators in vitro, in vivo, and using computer modeling are discussed. The Al chelation literature is reviewed by the chemical class of chelators, including fluoride, carboxylic acids, amino acids, catechols, polyamino carboxylic acids, phenyl carboxylic acids, the hydroxypyridinones, and hydroxamic acids.

The cellular toxicity of aluminium

Aluminium is a serious environmental toxicant and is inimical to biota. Omnipresent, it is linked with a number of disorders in man including Alzheimer's disease, Parkinson's dementia and osteomalacia. Evidence supporting aluminium as an aetiological agent in such disorders is not conclusive and suffers principally from a lack of consensus with respect to aluminium's toxic mode of action. Obligatory to the elucidation of toxic mechanisms is an understanding of the biological availability of aluminium. This describes the fate of and response to aluminium in any biological system and is thus an important influence of the toxicity of aluminium. A general theme in much aluminium toxicity is an accelerated cell death. Herein mechanisms are described to account for cell death from both acute and chronic aluminium challenges. Aluminium associations with both extracellular surfaces and intracellular ligands are implicated. The cellular response to aluminium is found to be biphasic having both stimulatory and inhibitory components. In either case the disruption of second messenger systems is observed and GTPase cycles are potential target sites. Specific ligands for aluminium at these sites are unknown though are likely to be proteins upon which oxygen-based functional groups are orientated to give exceptionally strong binding with the free aluminium ion.

Aluminum toxicity and Alzheimer's disease. Is there a connection?

Similarities between Alzheimer's disease and aluminum toxicity have led to the suggestion that a causal relationship may exist. However, the two disorders differ in many respects. The author reviews the evidence concerning the relationship between aluminum toxicity and Alzheimer's disease and answers the question, is there a connection?

Disturbance of cerebral function by aluminium in haemodialysis patients without overt aluminium toxicity

The psychomotor function of 27 long-term haemodialysis patients with apparently normal cerebral function, who had only mildly raised serum aluminium (mean 59 [SEM 9] micrograms/l), was measured by means of a computerised version of the symbol digit coding test. Compared with those of control subjects matched for age and the patients' estimated premorbid IQ, the patients' response times were significantly longer (2.51 [0.10] vs 1.88 [0.05] s). Abnormalities were also detected in five other computerised tests of psychomotor function. The mean activity of erythrocyte dihydropteridine reductase (DHPR), which is inhibited by aluminium, rose during 3 months' desferrioxamine treatment in most of the 15 patients so treated. Although there was no relation between baseline psychomotor function and either indices of cumulative aluminium exposure or erythrocyte DHPR activity, changes in DHPR induced by desferrioxamine correlated with changes in psychomotor performance (r = 0.62). The flash-stimulated visual evoked potential (measured in 10 patients) was delayed (133.4 [2.4] ms), although the pattern-stimulated visual evoked potential remained normal (101.8 [3.2] ms). The difference between the visual evoked potentials stimulated by flash and pattern was significantly greater in the patients than in the controls (31.6 [4.3] vs 19.4 [2.4] ms) and was significantly related to the symbol digit coding response times and to the oral aluminium intake. The results suggest that much more rigorous exclusion of aluminium from the dialysate and diet of dialysis patients is necessary.