Decrease of glial fibrillary acidic protein in rat frontal cortex following aluminum treatment

Naproxen as a potential candidate for promoting rivastigmine anti-Alzheimer activity against aluminum chloride-prompted Alzheimer's-like disease in rats; neurogenesis and apoptosis modulation as a possible underlying mechanism

BACKGROUND AND AIM

Alzheimer's disease (AD) is one of the leading causes of dependence and disability among the elderly worldwide. The traditional anti-Alzheimer medication, rivastigmine, one of the cholinesterase inhibitors (ChEIs), fails to achieve a definitive cure. We tested the hypothesis that naproxen administration to the rivastigmine-treated aluminum chloride (AlCl3) Alzheimer's rat model could provide an additive neuroprotective effect compared to rivastigmine alone.

MATERIALS AND METHODS

The studied groups were control (Cont), AlCl₃ treated (Al), rivastigmine treated (RIVA), naproxen treated (Napro), and combined rivastigmine and naproxen treated (RIVA + Napro). Rats' memory, spatial learning, and cognitive behavior were assessed followed by evaluation of hippocampal acetylcholinesterase (AChE) activity. Hippocampal and cerebellar histopathology were thoroughly examined. Activated caspase-3 and the neuroepithelial stem cells marker; nestin expressions were immunohistochemically assayed.

RESULTS

AD rats displayed significantly impaired memory and cognitive function, augmented hippocampal AChE activity; massive neurodegeneration associated with enhanced astrogliosis, apoptosis, and impaired neurogenesis. Except for the enhancement of neurogenesis and suppression of apoptosis, the combination therapy had no additional neuroprotective benefit over rivastigmine-only therapy.

CONCLUSION

Naproxen's efficacy was established by its ability to function at the cellular level, improved neurogenesis, and decreased, apoptosis without having an additional mitigating impact on cognitive impairment in rivastigmine-treated AD rats.

Neuroprotective effects of eugenol against aluminiuminduced toxicity in the rat brain

Aluminium (Al) is a neurotoxic metal that contributes to the progression of several neurodegenerative diseases. The aim of the present study was to evaluate the protective effect of dietary eugenol supplementation against aluminium (Al)- induced cerebral damage in rats. Male Wistar rats were divided into four groups: normal controls, rats fed a diet containing 6,000 μg g-1 eugenol, rats intoxicated daily with aluminium chloride (84 mg kg-1 body weight) p. o. and fed either a basal diet or a eugenol-containing diet. Daily oral administration of Al for four consecutive weeks to rats significantly reduced brain total antioxidant status (TAS) (11.42±0.31 μmol g-1 tissue, p<0.001) with a subsequent significant enhancement of lipid peroxidation (MDA) (32.55±1.68 nmol g-1 tissue, p<0.002). In addition, Al enhanced brain acetylcholinesterase activity (AChE) (46.22±4.90 U mg-1 protein, p<0.001), tumour necrosis factor alpha (TNF-α) (118.72±11.32 pg mg-1 protein, p<0.001), and caspase 3 (Casp-3) (8.77±1.26 ng mg-1 protein, p<0.001) levels, and in contrast significantly suppressed brain-derived neurotrophic factor (BDNF) (82.74±14.53 pg mg-1 protein, p<0.002) and serotonin (5-HT) (1.54±0.12 ng mg-1 tissue, p<0.01) levels. Furthermore, decreased glial fibrillary acidic protein (GFAP) immunostaining was noticed in the striatum of Al-intoxicated rats, compared with untreated controls. On the other hand, co-administration of dietary eugenol with Al intoxication restored brain BDNF (108.76±2.64 pg mg-1 protein) and 5-HT (2.13±0.27 ng mg-1 tissue) to normal levels, enhanced brain TAS (13.43±0.24 μmol g-1 tissue, p<0.05), with a concomitant significant reduction in TNF-α (69.98±4.74 pg mg-1 protein) and Casp-3 (3.80±0.37 ng mg-1 protein) levels (p<0.001), as well as AChE activity (24.50±3.25 U mg-1 protein, p<0.001), and increased striatal GFAP immunoreactivity, compared with Al-treated rats. Histological findings of brain tissues verified biochemical data. In conclusion, eugenol holds potential as a neuroprotective agent through its hydrophobic, antioxidant, and anti-apoptotic properties, as well as its neurotrophic ability against Al-induced brain toxicity in rats.

Pioglitazone Ameliorates Neuron Loss in the Cortex after Aluminum-Treatment in Rats

The objective was evaluation of the effects of pioglitazone on medial prefrontal cortex (mPFC) of the rats exposed to aluminum (Al). Al induces structural changes in several brain regions, including mPFC. Pioglitazone is an agonist of peroxisomal proliferator activated receptor gamma. Male rats were randomly assigned to control, Al-treated (10 mg/kg/day), and Al + PIO-treated groups (Al+ 40 mg/kg/day). After 56 days, the right mPFCs were removed. Then, the volume of mPFC and its subdivisions, volume of vessels, and total number of neurons and glia were estimated using stereological methods. The results showed 13–38% decrease in the volume of the mPFC and its subdivisions, mainly in the infralimbic region (P < 0.02). Besides, the volume of the vessels reduced by 47% after Al-treatment (P < 0.02). The total number of the neurons and glial cells was also reduced (40% and 25%, resp.) in the Al-exposed rats in comparison to the control ones (P < 0.02). Treatment of the animals with Al + PIO ameliorated the neuron loss and no improvement was seen in other parameters (P < 0.02). It can be concluded that treatment of the rats with PIO could ameliorate the neuron loss in the mPFC of the Al-treated animals.

A novel insight on chronic AlCl3 neurotoxicity through IL-6 and GFAP expressions: modulating effect of functional food fenugreek seeds

OBJECTIVE

This study was designed to review the effect of chronic aluminium exposure on interleukin-6 (IL-6) secretion in the posterior brain and test the putative modulating effect of fenugreek seeds.

METHODS

Female Wistar rats were divided into four groups: control; AlCl3 during 5 months (500 mg/kg body weight, intragastric for 1 month then 1600 ppm via the drinking water); AlCl3 plus fenugreek seed powder (FSP) (5%) during the last 2 months and FSP alone.

RESULTS

Oral administration of aluminium chloride during 5 months caused hypoproduction of IL-6 together with a decrease in GFAP reactivity and an alteration of antioxidant status in the posterior brain. On the other hand, fenugreek seeds supplementation was able to enhance IL-6 expression, re-increase GFAP reactivity, and modulate the pro-oxidant-related effect.

DISCUSSION

In the context of recent researches, IL-6 hypoproduction in the posterior brain could be a novel mechanism of Al chronic toxicity with a direct effect on glial cells. Using FSP as a diet supplement could offer a neuroprotective effect against Al toxicity. This could be mediated by astroglial cells protection, antioxidant and immunomodulatory actions.

Hippocampal neuronal loss, decreased GFAP immunoreactivity and cognitive impairment following experimental intoxication of rats with aluminum citrate

Aluminum (Al) is a neurotoxic agent with deleterious actions on cognitive processes. Nevertheless, few studies have investigated the neuropathological effects underlying the Al-induced cognitive impairment. We have explored the effects of acute Al citrate intoxication on both hippocampal morphology and mnemonic processes in rodents. Adult male Wistar rats were intoxicated with a daily dose of Al citrate (320 mg/kg) during 4 days by gavage. Animals were perfused at 8 (G2), 17 (G3) and 31 days (G4) after intoxication. Control animals were treated with sodium citrate (G1). Animals were submitted to behavioral tests of open field and elevated T-maze. Immunohistochemistry was performed to label neurons (anti-NeuN) and astrocytes (anti-GFAP) in both CA1 and CA3 hippocampal regions. There was an increase in the locomotor activity in open field test for G2 in comparison to control group and other groups (ANOVA-Bonferroni, P<0.05). The elevated T-maze avoidance latency (AL) was higher in all intoxicated groups compared to control (P<0.05) in avoidance 1. These values remained elevated in avoidance 2 (P<0.05), but abruptly decreased in G2 and G3, but not in G1 and G4 animals in avoidance 3 (P<0.05). There were no significant differences for 1 and 2 escape latencies. There were intense neuronal loss and a progressive decrease in GFAP immunoreactivity in the hippocampus of intoxicated animals. The results suggest that Al citrate treatment induces deficits on learning and memory concomitant with neuronal loss and astrocyte impairment in the hippocampus of intoxicated rats.

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

OBJECTIVES

Aluminum is notorious as a neurotoxic metal. The aim of our study was to determine whether endoplasmic reticulum (ER) stress is involved in aluminum-induced apoptosis in astrocytes.

METHODS

Mitochondrial RNA (mRNA) was analyzed by reverse transcription (RT)-PCR following pulse exposure of aluminum glycinate to primary cultured astrocytes. Tunicamycin was used as a positive control.

RESULTS

Gene expression analysis revealed that Ire1β was up-regulated in astrocytes exposed to aluminum while Ire1α was up-regulated by tunicamycin. Exposure to aluminum glycinate, in contrast to tunicamycin, seemed to down-regulate mRNA expression of many genes, including the ER resident molecular chaperone BiP/Grp78 and Ca(2+)-binding chaperones (calnexin and calreticulin), as well as stanniocalcin 2 and OASIS. The down-regulation or non-activation of the molecular chaperons, whose expressions are known to be protective by increasing protein folding, may spell doom for the adaptive response. Exposure to aluminum did not have any significant effects on the expression of Bax and Bcl2 in astrocytes.

CONCLUSIONS

The results of this study demonstrate that aluminum may induce apoptosis in astrocytes via ER stress by impairing the protein-folding machinery.

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.

Immunoassay for glial fibrillary acidic protein: antigen recognition is affected by its phosphorylation state

Glial fibrillary acid protein (GFAP) is used commonly as a marker of astrogliosis and astrocyte activation in several situations involving brain injury. Its content may be measured by immunocytochemistry, immunoblotting or enzyme-linked immunosorbent assay (ELISA), usually employing commercial antibodies. Two major post-translational modifications in GFAP (phosphorylation and proteolysis) may alter the interpretation of results or for immunoassay standardization. This study using a non-sandwich ELISA aimed to investigate the putative changes in the immunorecognition due to the phosphorylated state of the antigen by a routinely used polyclonal anti-GFAP antibody from DAKO. Results involving in vitro phosphorylation of purified GFAP or biological samples (brain tissue, cell culture and cerebrospinal fluid) mediated by protein kinase dependent on cAMP indicate that GFAP phosphorylation improves the recognition by the used antibody. These results provide support to the understanding of fast changes in the GFAP-immunoreactivity and suggest that caution is necessary in the interpretation of results using this antibody, as well as indicate that the effect of post-translational modifications must be considered during the standardization of immunoassays with other antibodies.

Some aspects of astroglial functions and aluminum implications for neurodegeneration

The present decade had witnessed an unprecedented attention focused on glial cells as a result of their unusual physiological roles that are being unraveled. It is now known that, rather than being a mere supporter of neurons, astroglia are actively involved in their modulation. The aluminum hypothesis seems to have been laid to rest, probably due to contradictory epidemiological reports on it as a causative factor of neurodegenerative diseases. Surprisingly, newer scientific evidences continue to appear and recent findings have implicated astrocytes as the principal target of its toxic action. In view of the likely detrimental effects of the interaction between these two infamous partners in neuroscience on neurons and nervous system, we have reviewed some aspects of glia-neuron interaction and discussed the implications of aluminum-impaired astrocytic functions on neurodegeneration. Because sporadic causes still account for the majority of the neurodegenerative diseases of which Alzheimer's disease is the most prominent, it has been suggested that neurotoxicologists should not relent in screening for the environmental agents, such as aluminum, and that considerable attention should be given to glial cells in view of the likely implications of environmental toxicants on their never-imagined newly reported roles in the central nervous system (CNS).

Effects of vitamin E against aluminum neurotoxicity in rats

The present study examined the protective effects of vitamin E against aluminum-induced neurotoxicity in rats. Wistar rats were given daily aluminum via their drinking water containing 1600 mg/liter aluminum chloride for six weeks. Aluminum induced a significant increase in lipid peroxidation (LPO) in hippocampus and frontal cortex. Furthermore, aluminum caused marked elevation in the levels of the glial markers (glial fibrillary acidic protein (GFAP) and S100B) and proinflammatory cytokines (TNF-alpha and IL-1beta) in both brain areas. Vitamin E treatment reduced the contents of glial markers and cytokines and the levels of LPO. In conclusion, this study demonstrates that vitamin E ameliorates glial activation and reduces release of proinflammatory cytokines induced by aluminum.

Gene vaccination to bias the immune response to amyloid-beta peptide as therapy for Alzheimer disease

BACKGROUND

The amyloid-beta (Abeta) peptide has a central role in the neurodegeneration of Alzheimer disease (AD). Immunization of AD transgenic mice with Abeta(1-42) (Abeta(42)) peptide reduces both the spatial memory impairments and AD-like neuropathologic changes in these mice. Therapeutic immunization with Abeta in patients with AD was shown to be effective in reducing Abeta deposition, but studies were discontinued owing to the development of an autoimmune, cell-mediated meningoencephalitis. We hypothesized that gene vaccination could be used to generate an immune response to Abeta(42) that produced antibody response but avoided an adverse cell-mediated immune effect.

OBJECTIVE

To develop an effective genetic immunization approach for treatment and prevention of AD without causing an autoimmune, cell-mediated meningoencephalitis.

METHODS

Mice were vaccinated with a plasmid that encodes Abeta(42), administered by gene gun. The immune response of the mice to Abeta(42) was monitored by measurement of (1) antibody levels by enzyme-linked immunosorbent assay (ELISA) and Western blot and (2) Abeta(42)-specific T-cell response as measured by interferon-gamma enzyme-linked immunospot (ELISPOT) assay.

RESULTS

Gene-gun delivery of the mouse Abeta(42) dimer gene induced significant humoral immune responses in BALB/c wild-type mice after 3 vaccinations in 10-day intervals. All 3 mice in the treated group showed significant humoral immune responses. The ELISPOT assay for interferon-gamma release with mouse Abeta(42) peptide and Abeta(9-18) showed no evident cytotoxic T-lymphocyte response. We further tested the responses of wild-type BALB/c mice to the monomer Abeta(42) gene vaccine. Western blot evaluation showed both human and mouse Abeta monomer gene vaccine elicited detectable humoral immune responses. We also introduced the human Abeta(42) monomer gene vaccine into AD double transgenic mice APPswe/PSEN1(A246E). Mice were vaccinated with plasmids that encode Abeta(1-42) and Abeta(1-16), or with plasmid without the Abeta gene. Treated mice showed significant humoral immune responses as demonstrated by ELISA and by Western blot. These mice also showed no significant cellular immune response as tested by ELISPOT. One of the treated mice was killed at 7 months of age for histological observations, and scattered amyloid plaques were noted in all layers of the cerebral cortex and in the hippocampus in both Abeta(42)- and control-vaccinated mice. No definite difference was discerned between the experimental and control animals.

CONCLUSIONS

Gene-gun-administered genetic immunization with the Abeta(42) gene in wild-type BALB/c and AD transgenic mice can effectively elicit humoral immune responses without a significant T-cell-mediated immune response to the Abeta peptide. This immunotherapeutic approach could provide an alternative active immunization method for therapy and prevention of AD.

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

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.

Cerebrospinal Fluid S100B Increases Reversibly in Neonates of Methyl Mercury-Intoxicated Pregnant Rats

Methylmercury (MeHg), an organic methylated form of mercury, is one of the most hazardous environmental pollutants. MeHg is a potent neurotoxin, particularly during brain development. Neurotoxicity-induced by MeHg in prenatal age can cause mental disorders, cerebral palsy and seizures. We investigated cerebrospinal fluid (CSF) and brain tissue contents of S100B, a calcium binding protein produced and secreted by astrocytes, which has trophic and toxic activity on neurons depending on concentration. Pregnant rats were exposed to MeHg (5 mg/kg per day, on the 12th, 13th and 14th days of pregnancy). CSF and brain tissue (hippocampus, cerebral cortex and cerebellum) were obtained from neonate rats on 1, 15 and 30 days postnatal. MeHg accumulation was measured in brain tissue after birth and on the 30th postnatal day. An increase of CSF S100B was observed on the 15th, but not on the 30th postnatal day. Hippocampal tissue demonstrated increased S100B (and reduction in glial fibrillary acidic protein) immediately after birth, but not later. No changes in the S100B content were observed in cerebellum and cerebral cortex. No changes were observed in the spatial learning of these rats at adult age. These specific and reversible changes in the hippocampus could be related to the cognitive and epileptic disorders attributed to MeHg. Our results further indicate the glial involvement in the MeHg-induced neurotoxicity. The increment of CSF S100B in neonates exposed to MeHg reinforces the view that increased S100B is related to damage in the nervous system and that S100B could be a marker for MeHg-neurotoxicity. Although the cellular mechanism related to MeHg-induced increase in S100B content in CSF remains unknown, our results suggest the use of S100B as a peripheral marker of brain damage induced by MeHg.

Perinatal exposure to aluminum alters neuronal nitric oxide synthase expression in the frontal cortex of rat offspring

Disturbance of the neuronal nitric oxide signaling pathway by chronic exposure to aluminum (Al) in drinking water may be a causal factor of neurological disorders in offspring. In order to investigate the relationship between Al administration and expression of neuronal nitric oxide synthase (nNOS), the numbers and distribution patterns of nNOS-immunoreactive neurons were examined in the frontal cortex of offspring after exposure to 0, 5, and 10 mM of Al in drinking water during prenatal and neonatal periods. At the bregma 0.20 level, the number of nNOS-positive neurons was significantly increased (10%) and decreased (17%) following exposure to 5 and 10 mM of Al in drinking water, respectively. The change was more severe in the upper layer than in deep layer of the cortex. In contrast, at the bregma -2.80 level, the number and distribution pattern was not significantly changed following exposure to Al. These data suggest that Al toxicity may be mediated through disturbances to the nitric oxide signaling pathway and exhibits a biphasic effect, especially in the frontal area of the cortex. In addition, the results suggest that impaired expression of nNOS plays an important role in the development of neurological syndrome caused by an exposure to Al during the early developmental stage.

Response of regional brain glutamate transaminases of rat to aluminum in protein malnutrition

BACKGROUND

The mechanism of aluminum-induced neurotoxicity is not clear. The involvement of glutamate in the aluminium-induced neurocomplications has been suggested. Brain glutamate levels also found to be altered in protein malnutrition. Alterations in glutamate levels as well as glutamate-alpha-decarboxylase in different regions of rat brain has been reported in response to aluminum exposure. Thus the study of glutamate metabolising enzymes in different brain regions of rats maintained on either normal or restricted protein diet may be of importance for understanding the neurotoxicity properties of aluminium.

RESULTS

Dietary protein restrictions does not have an significant impact on regional aluminum content of the brain. The interaction of aluminum intoxication and protein restriction is significant in the thalamic area and the midbrain-hippocampal region in cases of glutamate oxaloacetate transaminase. In the case of glutamate pyruvate transaminase, this interaction is significant only in thalamic area.

CONCLUSION

The metabolism of amino acids, as indicated by activities of specific transaminases, of brain is altered in response to aluminum exposure. These alterations are region specific and are dependent on dietary protein intake or manipulation of the brain amino acid homeostasis.