Aluminium in rat cerebellar primary cultures: glial cells and GABAergic neurones

Aluminum induced oxidative stress, astrogliosis and cell death in rat astrocytes, is prevented by curcumin

Aluminum (Al) is recognized potent neurotoxic metal, which causes oxidative stress leading to intracellular accumulation of reactive oxygen species (ROS) and neuronal cell death in various neurodegenerative diseases. Among several medicinal plants with beneficial effects on health, curcumin acts as a multi-functional drug with antioxidant activity. Thus, the purpose of the present study was to evaluate the protective effect of curcumin against aluminum induced-oxidative stress and astrocytes death, in vitro ad in vivo. Incubation of cultured rat astrocytes with two concentrations of Al (37 μM and 150 μM) for 1 h provoked a dose-dependent reduction of the number of living cells as evaluated by Fluorescein diacetate and lactate dehydrogenase assay. Al-treated cells exhibited a reduction of both superoxide dismutase (SOD) and catalase activities. Pretreatment of astrocytes with curcumin (81 μM) prevented Al-induced cell death. Regarding in vivo study, rats were exposed acutely during three consecutive days to three different doses of Al (25 mg/kg, 50 mg/kg and 100 mg/kg, i.p injection), together with curcumin treatment (30 mg/kg). For the chronic model, animals were exposed to Al (3 g/l) in drinking water from intrauterine age to 4 months ages, plus curcumin treatment (175 mg/kg). Data showed that both acute and chronic Al intoxication induced an obvious astrogliosis within motor cortex and hippocampus, while, such effects were restored by curcumin. We showed herein that Al was highly toxic, induced astrocytes death. Then, curcumin protected astrocytes against Al-toxicity. The cytoprotective potential of curcumin is initiated by stimulation of endogenous antioxidant system.

Aluminium-induced imbalance in oxidant and antioxidant determinants in brain regions of female rats: protection by centrophenoxine

The present study was carried out to investigate the potential of centrophenoxine in modulating aluminium-induced neurotoxicity. Female Sprague Dawley rats were administered aluminium chloride orally (40 mg/kg b.w./day) for a period of 8 weeks. At the end of respective treatment, various markers of oxidative stress were determined in four different regions of brain: cerebrum cerebellum, medulla oblongata, and hypothalamus. Lipid peroxidation assay was also carried out using standard techniques. Simultaneously, the centrophenoxine group (100 mg/kg b.w./day) for 6 weeks was also run long to understand the role in ameliorating oxidative damage. A significant decrease in the activities of superoxide dismutase and catalase was noticed in all the four regions, the most significant being in the hypothalamus (0.603 +/- .06) and cerebrum (0.038 +/- .01). Due to aluminium toxicity, peroxidation of lipids was also found to be elevated in cerebrum (0.424 +/- .03), cerebellum (0.341 +/- .03), hypothalamus (1.018 +/- .007), and medulla oblongata (0.304 +/- .05). However, posttreatment with centrophenoxine significantly elevated the superoxide and catalase activities in different regions. In addition, lipid peroxidation status of membranes was significantly reduced after centrophenoxine posttreatment to aluminium-exposed animals. Centrophenoxine has proved to be beneficial in combating the damage caused by aluminium toxicity. However, further research is needed to have a better understanding of the molecular basis of aluminium-induced oxidative damage. In addition, the different aspects of centrophenoxine need to be unmasked.

Does neurotransmission impairment accompany aluminium neurotoxicity?

Neurobehavioral disorders, except their most overt form, tend to lie beyond the reach of clinicians. Presently, the use of molecular data in the decision-making processes is limited. However, as details of the mechanisms of neurotoxic action of aluminium become clearer, a more complete picture of possible molecular targets of aluminium can be anticipated, which promises better prediction of the neurotoxicological potential of aluminium exposure. In practical terms, a critical analysis of current data on the effects of aluminium on neurotransmission can be of great benefit due to the rapidly expanding knowledge of the neurotoxicological potential of aluminium. This review concludes that impairment of neurotransmission is a strong predictor of outcome in neurobehavioral disorders. Key questions and challenges for future research into aluminium neurotoxicity are also identified.

The distribution of aluminum into and out of the brain

The extent, rate and possible mechanism(s) by which aluminum enters and is removed from the brain are presented. Introduction of Al into systemic circulation as Al.transferrin, the predominant Al species in plasma, resulted in about 7 x 10(-5) of the dose in the brain 1 day after injection. This brain Al entry could be mediated by transferrin-receptor-mediated endocytosis (TfR-ME). When Al.citrate, the predominant small molecular weight Al species in blood plasma, is introduced systemically, Al rapidly enters the brain. The rate of Al.citrate brain influx suggests a more rapid process than mediated by diffusion or TfR-ME. The question has been raised: "Is the brain a 'one-way sink' for aluminum?". Clinical observations are a basis for this suggestion. Rat brain 26Al concentrations decreased only slightly from 1 to 35 days after systemic 26Al injection, in the absence or presence of the aluminum chelator desferrioxamine, suggesting prolonged brain Al retention. However, studies of brain and blood extracellular Al at steady state, using microdialysis, suggest brain Al efflux exceeds influx, suggesting carrier-mediated brain Al efflux. The predominant brain extracellular fluid Al species is probably Al.citrate. The hypothesis that brain Al efflux, presumably of Al.citrate, is mediated by the monocarboxylate transporter was tested and supported. Although some Al that enters the brain is rapidly effluxed, it is suggested that a fraction enters brain compartments within 24 h from which it is only very slowly eliminated.

A molecular mechanism of aluminium-induced Alzheimer's disease?

An abundance of research has continued to link aluminium (Al) with Alzheimer's disease (AD) (Strong et al., J. Toxicol. Environ. Health 48 (1996) 599; Savory et al., J. Toxicol. Environ. Health 48 (1996) 615). Animals loaded with Al develop both symptoms and brain lesions that are similar to those found in AD. However, these animal models of Al intoxication are not representative of human exposure to Al. They have not addressed the significance of a truly chronic exposure to Al. If Al is a cause of AD it is effective at the level of our everyday exposure to the metal and AD will be one possible outcome of the life-long presence of a low, though burgeoning, brain Al burden. Individual susceptibility to AD will be as much to do with differences in brain physiology as with changes in our everyday exposure to the metal. There will be a chemical response and indeed biochemical/physiological response in the brain to Al. The question is whether brain Al homeostasis could impact upon brain function. In reviewing the recent literature covering the neurotoxicity of Al and, in particular, of the known and probable mechanisms involved in brain Al homeostasis I have identified a mechanism through which a truly chronic exposure to Al would bring about subtle and persistent changes in neurotransmission which, in time, could instigate the cascade of events known collectively as AD. This mechanism involves the potentiation of the activities of neurotransmitters by the action of Al-ATP at adenosine 5'-triphosphate (ATP) receptors in the brain.

Chronic exposure to aluminium impairs the glutamate-nitric oxide-cyclic GMP pathway in the rat in vivo

Aluminium is neurotoxic and is considered a possible etiologic factor in Alzheimer's disease, dialysis syndrome and other neurological disorders. The molecular mechanism of aluminium-induced impairment of neurological functions remains unclear. We showed that aluminium impairs the glutamate-nitric oxide-cGMP pathway in cultured neurons. The aim of this work was to assess by in vivo brain microdialysis whether chronic administration of aluminium in the drinking water (2.5% aluminium sulfate) also impairs the glutamate-nitric oxide-cGMP pathway in the cerebellum of rats in vivo. Chronic exposure to aluminium reduced NMDA-induced increase of extracellular cGMP by ca 50%. The increase in extracellular cGMP induced by the nitric oxide generating agent S-nitroso-N-acetylpenicillamine was higher (240%) in rats treated with aluminium than in controls. Immunoblotting experiments showed that aluminium reduced the cerebellar content of calmodulin and nitric oxide synthase by 34 and 15%, respectively. Basal activity of soluble guanylate cyclase was decreased by 66% in aluminium-treated rats, while the activity after stimulation with S-nitroso-N-acetylpenicillamine was similar to controls. Basal cGMP in the cerebellar extracellular space was decreased by 50% in aluminium-treated rats. These results indicate that chronic exposure to aluminium reduces the basal activity of guanylate cyclase and impairs the glutamate-nitric oxide-cGMP pathway in the animal in vivo.

CXC chemokines interleukin-8 (IL-8) and growth-related gene product alpha (GROalpha) modulate Purkinje neuron activity in mouse cerebellum

We give here evidence that Purkinje neurons (PNs) of mouse cerebellar slices studied with patch clamp technique combined with laser confocal microscopy, respond to human IL-8 and GROalpha by (i) a cytosolic Ca2+ transient compatible with inositol (1,4,5) trisphosphate (InsP3) formation; (ii) an enhancement of the neurotransmitter release; and (iii) an impairment of the long-term depression of synaptic strength (LTD). It was also found the expression of IL-8 receptor type 2 in PN and granule cells by immunofluorescence, immunoblotting and RT-PCR analysis. Considered together these findings suggest that IL-8 and GROalpha may play a neuromodulatory role on mouse cerebellum.

High sensitivity quantitative analysis of cobalt uptake in rat cerebellar granule cells with and without excitatory amino acids

We quantified the effect of the excitatory amino acids kainate and glutamate on the uptake of cobalt in primary rat cerebellar granule neurons, by using inductively coupled plasma-atomic emission spectroscopy (ICP-AES). We quantitatively demonstrated that Co2+ uptake, although enhanced by glutamate and kainate also takes place in the absence of excitatory amino acids. We also found that cobalt uptake is not significantly altered by the presence of glutamate receptor competitive or noncompetitive antagonists, indicating that cobalt uptake in granule neurons does not require glutamate receptor stimulation. Our results suggest, therefore, that Co2+ may enter the cell by passive diffusion through the plasma membrane.