Aluminum alters NMDA receptor 1A and 2A/B expression on neonatal hippocampal neurons in rats

Effects of simultaneous versus post exposure epigallocatechin-3-gallate treatment on aluminum induced neurotoxicity in rat hippocampus: A multi-approach study

Chronic aluminium(Al) exposure can affect the antioxidant and glutaminergic systems through N-methyl-D-aspartate receptors (NMDAR). This study was aimed to investigate the neurotoxic effect of Al through different mechanisms in rat hippocampus and to evaluate the protective role of epigallocatechin gallate (EGCG), a well-known antioxidant, with simultaneous administration of Al,as well as post-treatment after Al exposure.For this purpose, aluminum chloride(AlCl₃) was administered simultaneously with two different EGCG doses for 8 weeks as the first part of the study.In the second part of the study, after 4 weeks of AlCl₃ pre-administration, two different EGCG doses were also administered during four additional weeks as post-treatment.Al administration led to oxidative stress and increased acetylcholinesterase levels.NMDAR subunit mRNA expressions were down-regulated by Al, which was apparent in NMDAR1/2B subunits.Simultaneous EGCG treatment has shown a better neuroprotective effect in terms of these mechanisms and represents novel approach for the prevention of neurodegenerative diseases likely to be induced by Al.

The association between blood lymphocyte NMDAR, group I mGluRs and cognitive function changes in occupationally aluminum-exposed workers and verification in rats

BACKGROUND

Many studies have shown that occupational aluminum (Al) exposure could affect the cognitive functions of workers and cause mild cognitive impairment (MCI). Glutamate receptors (GluRs) play an important role in learning and memory functions.

METHODS

352 workers in a large Al production enterprise were investigated in this research. MMSE, CDT, DST, VFT, FOM were used to evaluate the cognitive functions of workers. Plasma Al levels as exposure indices were measured by Graphite Furnace Atomic Absorption Method (GFAAS). The expression of GluRs was measured by ELISA. Cognitive function comprehensive scores were obtained through factor analysis. Then a rat model of chronic AlCl₃ exposure was established. The detection method of Al levels and protein expression were the same as mentioned-above.

RESULTS

Compared with the Q1 group, the DST, VFT, and comprehensive cognitive function scores of the Q4 group were lower(P < 0.05). For every 1μg/L increase in plasma Al concentration, the risk of cognitive impairment increases 1.051 times (95 %CI:1.031,1.072). Both NMDAR1 and NMDAR2A protein expression level of Q1 group were higher than those of Q2, Q3, Q4 group (all P < 0.05). The mediating effect ratio of NMDAR1 between plasma Al levels and cognitive function comprehensive scores was a1*b1/c=11.30 %, and the mediating effect ratio of NMDAR2A was |a2*b2/c|=21.77 %. Compared with control group, the escape latency of rats in the high Al dose group was longer day by day (P < 0.05). With the increase of Al dose, the relative expression of NMDAR1, NMDAR2A, NMDAR2B, GluR1 and mGluR5 in cerebral cortex and lymphocytes of rats were decreased (P < 0.05). The result of correlation analysis on NMDAR1 protein expression between brain cortex and lymphocyte showed that the correlation coefficient is r = 0.646(P < 0.05).

CONCLUSION

Taking together the results from both Al exposed workers and animal, there is a certain correlation between NMDAR1 protein contents of brain cortex and peripheral lymphocytes. We propose that lymphocyte NMDAR1 could be considered as a peripheral potential marker of cognitive impairment for further observation.

Regulation of mGluR1 on the Expression of PKC and NMDAR in Aluminum-Exposed PC12 Cells

Aluminum demonstrates clear neurotoxicity and can cause Alzheimer's disease (AD)-like symptoms, including cognitive impairment. One toxic effect of aluminum is a decrease in synaptic plasticity, but the specific mechanism remains unclear. In this study, PC12 cells were treated with Al(mal)₃ to construct a toxic cell model. (S)-3,5-Dihydroxyphenylglycine (DHPG), α-methyl-4-carboxyphenylglycine (MCPG), and mGluR1-siRNA were used to interfere with the expression of metabotropic glutamate receptor subtype 1 (mGluR1). Polymerase chain reaction and western blotting were used to investigate the expression of mGluR1, protein kinase C (PKC), and N-methyl-D-aspartate receptor (NMDAR) subunits. ELISA was used to detect PKC enzyme activity. In PC12 cells, mRNA and protein expressions of PKC and NMDAR subunits were inhibited by Al(mal)₃. Aluminum may further regulate the expression of NMDAR1 and NMDAR2B through mGluR1 to regulate PKC enzyme activity, thereby affecting learning and memory functions. Furthermore, the results implied that the mGluR1-PKC-NMDAR signaling pathway may predominately involve positive regulation. These findings provide new targets for studying the neurotoxic mechanism of aluminum.

Aluminum chloride induces neuroinflammation, loss of neuronal dendritic spine and cognition impairment in developing rat

Aluminum (Al) is present in the daily life of humans, and the incidence of Al contamination increased in recent years. Long-term excessive Al intake induces neuroinflammation and cognition impairment. Neuroinflammation alter density of dendritic spine, which, in turn, influence cognition function. However, it is unknown whether increased neuroinflammation is associated with altered density of dendritic spine in Al-treated rats. In the present study, AlCl3 was orally administrated to rat at 50, 150 and 450 mg/kg for 90d. We examined the effects of AlCl3 on the cognition function, density of dendritic spine in hippocampus of CA1 and DG region and the mRNA levels of IL-1β, IL-6, TNF-α, MHC II, CX3CL1 and BNDF in developing rat. These results showed exposure to AlCl3 lead to increased mRNA levels of IL-1β, IL-6, TNF-α and MCH II, decreased mRNA levels of CX3CL1 and BDNF, decreased density of dendritic spine and impaired learning and memory in developing rat. Our results suggest AlCl3 can induce neuroinflammation that may result in loss of spine, and thereby leads to learning and memory deficits.

A modified technique for culturing primary fetal rat cortical neurons

The study explored a modified primary culture system for fetal rat cortical neurons. Day E18 embryos from pregnant Sprague Dawley rats were microdissected under a stereoscope. To minimize enzymatic damage to the cultured neurons, we applied a sequential digestion protocol using papain and Dnase I. The resulting sifted cell suspension was seeded at a density of 50,000 cells per cm² onto 0.1 mg/mL L-PLL-covered vessels. After a four-hour incubation in high-glucose Dulbecco's Modified Eagle's Medium (HG-DMEM) to allow the neurons to adhere, the media was changed to neurobasal medium that was refreshed by changing half of the volume after three days followed by a complete medium change every week. The cells displayed progressively robust neurite extension, and nonneuronal-like cells could barely be detected by five days in vitro (DIV); cell growth was still substantial at 14 DIV. Neurons were identified by β-tubulin III immunofluorescence, and neuronal purity within the cultures was assessed at over 95% by both flow cytometry and by dark-field counting of β-tubulin III-positive cells. These results suggest that the protocol was successful and that the high purity of neurons in this system could be used as the basis for generating various cell models of neurological disease.

Aluminum overload increases oxidative stress in four functional brain areas of neonatal rats

BACKGROUND

Higher aluminum (Al) content in infant formula and its effects on neonatal brain development are a cause for concern. This study aimed to evaluate the distribution and concentration of Al in neonatal rat brain following Al treatment, and oxidative stress in brain tissues induced by Al overload.

METHODS

Postnatal day 3 (PND 3) rat pups (n =46) received intraperitoneal injection of aluminum chloride (AlCl3), at dosages of 0, 7, and 35 mg/kg body wt (control, low Al (LA), and high Al (HA), respectively), over 14 d.

RESULTS

Aluminum concentrations were significantly higher in the hippocampus (751.0 ± 225.8 ng/g v.s. 294.9 ± 180.8 ng/g; p < 0.05), diencephalon (79.6 ± 20.7 ng/g v.s. 20.4 ± 9.6 ng/g; p < 0.05), and cerebellum (144.8 ± 36.2 ng/g v.s. 83.1 ± 15.2 ng/g; p < 0.05) in the HA group compared to the control. The hippocampus, diencephalon, cerebellum, and brain stem of HA animals displayed significantly higher levels of lipid peroxidative products (TBARS) than the same regions in the controls. However, the average superoxide dismutase (SOD) activities in the cerebral cortex, hippocampus, cerebellum, and brain stem were lower in the HA group compared to the control. The HA animals demonstrated increased catalase activity in the diencephalon, and increased glutathione peroxidase (GPx) activity in the cerebral cortex, hippocampus, cerebellum, and brain stem, compared to controls.

CONCLUSION

Aluminum overload increases oxidative stress (H2O2) in the hippocampus, diencephalon, cerebellum, and brain stem in neonatal rats.