Accumulation of aluminum by primary cultured astrocytes from aluminum amino acid complex and its apoptotic effect

Abstract

Aluminum salts or doses that are unlikely in the human system have been employed in toxicity studies and much attention had been focused on the secondary target (neurons) of its toxicity rather than the primary target (astroglia). In order to address these issues, we have investigated the uptake and apoptotic effects of aluminum amino acid complex on primary cultured astrocytes because these are fundamental in understanding the mechanism of aluminum neurotoxicity. Aluminum solubilized by various amino acids was differentially internalized by astrocytes (glycine>serine>>glutamine>>glutamate), but aluminum was not internalized from citrate complex following 24 h of exposure. Inhibition of glutamine synthetase, by methionine sulfoximine (MSO), enhanced the uptake of aluminum from various amino acid complexes within 8 h except from glutamine complex. Blockade of selective GLT-1 (EAAT2) and GlyT1, as well as nonspecific transporters, did not inhibit or had no effect on uptake of aluminum in complex with the corresponding amino acids. Ouabain also failed to inhibit uptake of aluminum complexed with glycine. Pulse exposure to aluminum glycinate in the absence or presence of MSO caused apoptosis in over 25% of primary cultured astrocytes, and apoptotic features such as chromatin condensation and fragmentation became evident as early as 3 days of culture in normal medium. Lower doses (as low as 0.0125 mM) also caused apoptosis. The present findings demonstrate that aluminum solubilized by amino acids, particularly glycine, could serve as better candidate for neurotoxicity studies. Citrate may be a chelator of aluminum rather than a candidate for its cellular uptake. Amino acid transporters may not participate in the uptake of aluminum solubilized by their substrates. Another pathway of aluminum internalization may be implicated in addition to passive diffusion but may not require energy in form of Na+/K+-ATPase. Impaired astrocyes' metabolism can aggravate their accumulation of aluminum and aluminum can compromise astrocytes via apoptosis. Thus, loss of astrocytic regulatory and supportive roles in the central nervous system (CNS) may be responsible for neurodegeneration observed in Alzheimer's disease.

Gene expression in primary cultured astrocytes affected by aluminum: alteration of chaperons involved in protein folding

“…Nevertheless, over-expression of Ire1a and Ire1b can activate a reporter gene that harbors an ER stress-response element (ERSE) in a manner that requires the endoribonuclease activity of Ire1 [43]. Thus, the up-regulation of Ire1b by aluminum glycinate in our study under an exposure regimen similar to that previously reported in a study reporting morphological evidence of apoptosis [24] demonstrates the involvement of ER stress. Therefore, Ire1a may not be essential for the transcriptional induction of several wellcharacterized UPR target genes [45], and Ire1a and Ire1b may be differentially induced, depending on the stimulus and/or tissue.…”

“…In some experiments, concentrations lower or higher than 0.1 mM were employed to assess concentration-dependent effects. Previous morphological studies on apoptosis did not find any adverse effects on cell viability/proliferation among cells exposed to test compounds at concentrations similar to those employed in our study [24].…”

“…Primary cultures of cortical astrocytes were prepared from 5-to 7-day-old mice as previously described [24]. Briefly, the cells were grown in D-MEM/F12 or D-MEM during the experimental period (cat.…”

“…Nevertheless, several recent findings have implicated astrocytes as the principal target of the toxic action of aluminum [19][20][21][22] and that aluminum can cause astrocyte death via apoptosis [23][24][25]. However, these reports only showed morphological evidence of apoptosis, and the molecular mechanisms by which aluminum causes astrocyte death are yet to be unraveled.…”

Assessment of Alum (Aluminium Sulphate) Treated SurfaceRunoff as Irrigation Water on the Growth and Development of Zea mays L

“…In addition, root cells show sensitivity to Al 3+ toxicity by a reduction in lateral root size [24]; [3]. This reduction in the activity of the root cells may be due to reduction in both new cell formation and cell elongation in the extension region of the root [25].…”