Neurocognitive effects of aluminum

Derivation of Biomonitoring Equivalents for aluminium for the interpretation of population-level biomonitoring data

Aluminium is widely used in many consumer products, however the primary source of aluminium exposure to the Canadian general population is through food. Aluminium can cause neurotoxicity and reproductive toxicity at elevated exposure levels. Health-based exposure guidance values have been established for oral exposure to aluminium, including a Minimal Risk Level (MRL) by the Agency for Toxic Substances and Disease Registry (ATSDR), a Provincial Tolerable Weekly Intake (PTWI) by the Joint FAO/WHO Expert Committee on Food Additives (JECFA) and a Tolerable Weekly Intake (TWI) by the European Food Safety Authority (EFSA). Aluminium concentration in blood and urine can be used as a tool for exposure characterization in a population. A pharmacokinetic (PK) model was developed based on human dosing data to derive blood Biomonitoring Equivalents (BEs), whereas a mass balance approach was used to derive urine BEs for the above guidance values. The BEs for blood for daily intake consistent with the MRL, PTWI and TWI were 18, 16 and 8 μg/L, respectively. BEs for urine for the same guidance values were 137, 123 and 57 μg/L, respectively. The derived BEs may be useful in interpreting population-level biomonitoring data in a health risk context and thereby screening and prioritizing substances for human health risk assessment and risk management.

A Combination of Resveratrol and Curcumin is Effective Against Aluminum Chloride-Induced Neuroinflammation in Rats

BACKGROUND

Experimental studies have demonstrated that aluminum is an environmental toxin that induces neuroinflammation and the development of Alzheimer's disease.

OBJECTIVE

In this report, we investigated the beneficial effect of a combination of resveratrol and curcumin to reduce aluminum-induced neuroinflammation.

METHOD

We employed both an in vivo model of aluminum-induced neuroinflammation and an in vitro aluminum stimulated cultured PC-12 cells. Neuroinflammation in rats was assessed by measuring the expression of β-secretase, amyloid-β protein precursor, and γ-subunits (PS-1 and PS-2), along with the inflammatory COX-2, Il-1β, Il-1α, and TNF-α. Furthermore, we measured the expression profiles of neuro-protective Apurinic/apyrimidinic endonuclease 1 (APE1) protein and let-7c microRNA. In parallel, PC-12 cells were treated with 0.5 mM aluminum to induce a neuroinflammation-like state. In addition, curcumin effect, as a selective COX-2 expression inhibitor, was detected in a time course manner.

RESULTS

An overall significant attenuation of the inflammatory markers, as well as a decrease in the amyloidogenic mediators, was observed in resveratrol-curcumin treated rats. The therapeutic effect was also confirmed by transmission electron microscopic analysis of the brain cortexes. APE1 was significantly induced by resveratrol-curcumin combination. Both in vivo and in vitro studies indicated that Let-7c expression is significantly reduced after aluminum stimulation, an effect that was partially suppressed by co-addition of either resveratrol or curcumin and totally restored to the normal level by their combination.

CONCLUSIONS

The present study clearly indicates the synergistic and therapeutic effect of a  resveratrol-curcumin combination. We also show that both compounds exert beneficial effect either cooperatively or through differential molecular mechanisms in counteracting aluminum-induced neuroinflammation.

Protective effects of banana pectin against aluminum-induced cognitive impairment and aluminum accumulation in mice

To investigate the effect of pectin on absorption and bio-toxicity of aluminum, pectin extract (100 mg kg^-1 d^-1) from banana pulp was orally administrated to aluminum exposed mice (35 mg kg^-1 d^-1) for 6 weeks. Our result showed that body weight gain of the mice treated with aluminum plus banana pectin was 32.5% higher than that of mice exposed to aluminum alone after 6 weeks of the administration. In both the step-down inhibitory avoidance task and Morris water maze test, memory retention of aluminum-exposed mice was significantly improved by the pectin administration. Treatment with banana pectin effectively prevented absorption of aluminum from the gastrointestinal tract, total aluminum excretion of mice treated with banana pectin plus aluminum was 9.3% higher than that of mice exposed to aluminum alone on the 12th day. Aluminum level in serum, cerebrum, or cerebellum of mice treated with aluminum plus banana pectin was 30.8%, 17.5%, or 17.9% lower than that of mice exposed to aluminum alone on the 42nd day, respectively. In conclusion, banana pectin extract can effectively reduce aluminum toxicity in mice.

Multiple pharmacological activities of Caesalpinia crista against aluminium-induced neurodegeneration in rats: Relevance for Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia and mainly affects cognitive function of the aged populations. Aluminium, a neurotoxic metal, has been suggested as a contributing factor of AD. Caesalpinia crista is a medicinal plant known for its anti-microbial, anti-inflammatory and anti-oxidant properties. The present study was conducted in order to evaluate the neuroprotective effects of methanolic extracts of C. crista (MECC) on aluminium-induced neurodegeneration in rats. Co-administration with MECC significantly and dose dependently ameliorated the aluminium-dependent cognitive impairment, AChE hyperactivity and oxidative stress in the hippocampus and in the frontal cortex of rat brain. Moreover, MECC reduced the neuronal injury induced by aluminium as shown by the diminution of neuron loss and pyknosis in the CA1 and CA3 regions of the hippocampus. From this study, it is inferred that MECC protect against aluminium-induced behavioral alterations, cognitive function, oxidative stress and neuroinflammation in vivo. Therefore, this plant may serve as a source of natural products having multiple functions and could be utilized as an anti-AD preparation.

Cognitive dysfunction associated with aluminum hydroxide-induced macrophagic myofasciitis: A reappraisal of neuropsychological profile

Patients with macrophagic myofasciitis (MMF) present with diffuse arthromyalgias, chronic fatigue, and cognitive disorder. Representative features of MMF-associated cognitive dysfunction include attentional dysfunction, dysexecutive syndrome, visual memory deficit and left ear extinction. Our study aims to reevaluate the neuropsychological profile of MMF. 105 unselected consecutive MMF patients were subjected to a neuropsychological battery of screen short term and long-term memory, executive functions, attentional abilities, instrumental functions and dichotic listening. From these results, patients were classified in four different groups: Subsymptomatic patients (n=41) with performance above pathological threshold (-1.65 SD) in all tests; Fronto-subcortical patients (n=31) who showed pathological results at executive functions and selective attention tests; Papezian patients (n=24) who showed pathological results in storage, recognition and consolidation functions for episodic verbal memory, in addition to fronto-subcortical dysfunction; and Extinction patients (n=9) who had a left ear extinction at dichotic listening test in association to fronto-subcortical and papezian dysfunction. In addition, inter-test analysis showed that patients with apparently normal cognitive functions (Subsymptomatic group) performed significantly worse to attention tests compared to others. In conclusion, our study shows that (i) most patients have specific cognitive deficits; (ii) all patients with cognitive deficit have impairment of executive functions and selective attention; (iii) patients without measurable cognitive deficits display significant weakness in attention; (iv) episodic memory impairment affects verbal, but not visual, memory; (v) none of the patients show an instrumental dysfunction.

γ-Aminobutyric acid (GABA) signalling in plants

The role of γ-aminobutyric acid (GABA) as a signal in animals has been documented for over 60 years. In contrast, evidence that GABA is a signal in plants has only emerged in the last 15 years, and it was not until last year that a mechanism by which this could occur was identified-a plant 'GABA receptor' that inhibits anion passage through the aluminium-activated malate transporter family of proteins (ALMTs). ALMTs are multigenic, expressed in different organs and present on different membranes. We propose GABA regulation of ALMT activity could function as a signal that modulates plant growth, development, and stress response. In this review, we compare and contrast the plant 'GABA receptor' with mammalian GABAA receptors in terms of their molecular identity, predicted topology, mode of action, and signalling roles. We also explore the implications of the discovery that GABA modulates anion flux in plants, its role in signal transduction for the regulation of plant physiology, and predict the possibility that there are other GABA interaction sites in the N termini of ALMT proteins through in silico evolutionary coupling analysis; we also explore the potential interactions between GABA and other signalling molecules.

Hesperidin and Silibinin Ameliorate Aluminum-Induced Neurotoxicity: Modulation of Antioxidants and Inflammatory Cytokines Level in Mice Hippocampus

Mounting evidence suggests that long-term aluminum exposure results in severe toxic effects, including neurobehavioral and neurochemical anomalies. The present study was performed to examine the neuroprotective potential of hesperidin and silibinin against aluminum chloride (AlCl3)-induced neurotoxicity in mice. AlCl3 (100 mg/kg/day) was injected daily through oral gavage for 42 days. Concomitantly, hesperidin (50 and 100 mg/kg/day, p.o.) and silibinin (100 and 200 mg/kg/day, p.o.) was administered for 42 days in different groups. The extent of cognitive impairment was assessed by Morris water maze and novel object recognition test on the 43rd day. Neurotoxicity was assessed by measuring oxido-nitrosative stress and proinflammatory cytokines in the hippocampus of mice. Six weeks treatment with AlCl3 caused cognitive impairment as indicated by an increase in the retention latency time and reduction in the percentage of recognition index. AlCl3-treated group showed oxido-nitrosative stress as indicated by increase in the level of lipid peroxidation, nitrite and depleted reduced glutathione, catalase activity in the hippocampus. Moreover, the chronic AlCl3 administration raised the proinflammatory cytokines (interleukin-1β and tumor necrosis factor-α) level and increased acetylcholinesterase activity and reduced the BDNF content in the hippocampus of AlCl3-treated animals. However, chronic treatment with hesperidin and silibinin at higher doses significantly ameliorated the AlCl3-induced cognitive impairment and hippocampal biochemical anomalies. The present study clearly indicated that hesperidin and silibinin exert neuroprotective effects against AlCl3-induced cognitive impairment and neurochemical changes. Amelioration of cognitive impairment may be attributed to the impediment of oxido-nitrosative stress and inflammation in the hippocampus.

Protective effect of apple (Ralls) polyphenol extract against aluminum-induced cognitive impairment and oxidative damage in rat

Aluminum (Al) has long been implicated in the pathogenesis of Alzheimer's disease (AD). Dietary polyphenols have been strongly associated with reduced risk of AD and the other nervous diseases. We aimed to evaluate the preventive effect of the apple polyphenol extract (APE) on Al-induced biotoxicity, in order to provide a new focus on the design of strategies to prevent AD and the other human diseases related to Al overload. Control, Al-treated (171.8 mg Al kg(-1)day(-1) 10 weeks), APE+Al (Al-treatment as previously plus 200 mg kg(-1)day(-1) 10 weeks), and group of APE per se were used. Al intake caused memory impairment, significant decrease of acetylcholinesterase, CK, SOD, CAT activity and the rate of ATP synthesis, increase the Al content, the level of malondialdehyde and β-amyloid 42. Administration of APE significantly improved memory retention, attenuated oxidative damage, acetylcholinesterase activity and Al level in Al treated rats. Furthermore, chlorogenic acid (ChA) was used for analyzing stability of polyphenols-Al(3+) complex. Log K1 was 10.51, and the mole ratio of Al(3+) to ligand was 1:1. We further found that the amounts of Al increased significantly in feces of the rats gavaged with AlCl3 plus ChA compared with AlCl3. Our finding has shown APE has neuroprotective effects against Al-induced biotoxicity. Chelating with Al and disturbing its absorption could account for the neuroprotective roles of dietary polyphenols against Al toxicity.

Is the Aluminum Hypothesis dead?

The Aluminum Hypothesis, the idea that aluminum exposure is involved in the etiology of Alzheimer disease, dates back to a 1965 demonstration that aluminum causes neurofibrillary tangles in the brains of rabbits. Initially the focus of intensive research, the Aluminum Hypothesis has gradually been abandoned by most researchers. Yet, despite this current indifference, the Aluminum Hypothesis continues to attract the attention of a small group of scientists and aluminum continues to be viewed with concern by some of the public. This review article discusses reasons that mainstream science has largely abandoned the Aluminum Hypothesis and explores a possible reason for some in the general public continuing to view aluminum with mistrust.

Distinctive clinical features in arthro-myalgic patients with and without aluminum hydroxyde-induced macrophagic myofasciitis: an exploratory study

Macrophagic myofasciitis (MMF) is a specific histological lesion assessing the persistence of vaccine-derived aluminum oxyhydroxide in muscle tissue, at a site of previous immunization. Long-lasting MMF is usually detected in patients with arthromyalgias, chronic fatigue, and stereotyped cognitive dysfunction. MMF diagnosis requires muscle biopsy, an invasive procedure not suitable for the routine investigation of all patients with musculoskeletal pain. To help decision making in routine practice, we designed a retrospective analysis of 130 consecutive arthro-myalgic patients, previously immunized with aluminum-containing vaccines, in whom deltoid muscle biopsy was performed for diagnostic purposes. According to biopsy results, the patients were ascribed to either the MMF or the non-MMF group. MMF was diagnosed in 32.3% of the patients. MMF and non-MMF groups were similar according to both the injected vaccines and the delay between vaccination and biopsy. MMF patients had less frequent fibromyalgia than non-MMF patients (≥11 fibromyalgic tender points in 16.6 vs 55.5%, p < 0.04), and more often abnormal evoked potentials suggestive of CNS demyelination (38.5 vs 5.7%, p < 0.01). Predictive bioclinical scores based on simple variables such as the number of fibromyalgic tender points, arthralgias, and spinal pain, had sensitivity ranging from 50 to 88.1% and specificity from 36.4 to 76.1%.

IN CONCLUSION

(i) most aluminum-containing vaccine receivers do not have long-lasting MMF in their muscle, but the prevalence of MMF among patients with arthromyalgia following immunization is substantial; (ii) patients with MMF have more CNS dysfunction and less fibromyalgic tender points than non-MMF patients; (iii) predictive scores may help to identify patients at high vs low risk of MMF.

Naringin protects memory impairment and mitochondrial oxidative damage against aluminum-induced neurotoxicity in rats

Aluminum has been indicated in neurodegenerative disorders and naringin, a bioflavonoid has been used to reduce neurotoxic effects of aluminum against aluminum chloride-induced rats. Therefore, present study has been designed to explore the possible role of naringin against aluminum-induced cognitive dysfunction and oxidative damage in rats. Aluminum (100 mg/kg) and naringin (40 and 80 mg/kg) drug treatment were administered orally for six weeks to male wistar rats. Various behavioral performance tasks, biochemical, mitochondrial oxidative parameters, and aluminum concentration in the brain were assessed. Aluminum chloride treatment significantly caused cognitive dysfunction and mitochondria oxidative damage as compared to vehicle treated control group. Besides, aluminum chloride treatment significantly increased acetyl cholinesterase activity and aluminum concentration in the brain as compared to sham. Chronic administration of naringin significantly improved cognitive performance and attenuated mitochondria oxidative damage, acetyl cholinesterase activity, and aluminum concentration in aluminum-treated rats as compared to control rats. Results of the study demonstrate neuroprotective potential of naringin against aluminum chloride-induced cognitive dysfunction and mitochondrial oxidative damage.

Neurocognitive effects in welders exposed to aluminium

Objectives:

Various authors who studied the effects of aluminium (Al) exposure on the neurocognitive system in the last 30 years have reached different and often contradictory conclusions. The aim of this study is to help clarify the effects that the metal causes on cognitive ability in a group of naval welders exposed to Al.

Methods:

The study was performed on a sample of 86 male Al welders in a shipyard in Messina. The average value of environmental Al, recorded in the workplace, was 19.5 mg/m3. The blood levels of Al, zinc, manganese, lead and chromium were monitored in all the subjects. The reagents used for the neuropsychic study were the Wechsler Memory Scale (WMS), the Colour Word Test or Stroop Test and the Test of Attention Matrixes. The results were compared with those obtained in a similar control group not exposed to Al and with an Al-b value of 6.93 g/l.

Results:

For all the mental reagents used, the reply is obtained in the sample of exposed subjects showed decreased cognitive response with regard to attention and memory performance. The comparison between the individual tests showed greater sensitivity of performance studied using the WMS and the Stroop Test compared with the Test of Attention Matrixes. The alterations encountered in the cognitive functions studied increased proportionally to time of exposure and quantity of metal absorbed.

Conclusion:

The study confirmed that occupational exposure to Al causes alteration in cognitive responses that are more evident in complex functions.

Aluminium exposure from parenteral nutrition in preterm infants and later health outcomes during childhood and adolescence

Aluminium is the most common metallic element, but has no known biological role. It accumulates in the body when protective gastrointestinal mechanisms are bypassed, renal function is impaired, or exposure is high – all of which apply frequently to preterm infants. Recognised clinical manifestations of aluminium toxicity include dementia, anaemia and bone disease. Parenteral nutrition (PN) solutions are liable to contamination with aluminium, particularly from acidic solutions in glass vials, notably calcium gluconate. When fed parenterally, infants retain >75% of the aluminium, with high serum, urine and tissue levels. Later health effects of neonatal intravenous aluminium exposure were investigated in a randomised trial comparing standard PN solutions with solutions specially sourced for low aluminium content. Preterm infants exposed for >10 d to standard solutions had impaired neurologic development at 18 months. At 13–15 years, subjects randomised to standard PN had lower lumbar spine bone mass; and, in non-randomised analyses, those with neonatal aluminium intake above the median had lower hip bone mass. Given the sizeable number of infants undergoing intensive care and still exposed to aluminium via PN, these findings have contemporary relevance. Until recently, little progress had been made on reducing aluminium exposure, and meeting Food and Drug Administration recommendations (<5 μg/kg per d) has been impossible in patients <50 kg using available products. Recent advice from the UK Medicines and Healthcare regulatory Authority that calcium gluconate in small volume glass containers should not be used for repeated treatment in children <18 years, including preparation of PN, is an important step towards addressing this problem.

Memory deficit in mice administered aluminum-maltolate complex

Recently, aluminum (Al) has been identified as one of the environmental factors responsible for cause certain nerve degeneration diseases, particularly, Alzheimer's disease (AD). However, the relationship between Al and AD is controversial. We previously examined whether Al induced neurotoxin in the brain of mice when aluminum-maltolate complex (ALM) was administered daily for 120 days. Our results revealed that Al accumulated in the brain induced oxidative stress, and the nerve degeneration was detected in the brain of the ALM-treated group. On the basis of these results, we have tried to examine whether the incorporated Al affects memory in mice with regard to an indicator of spatial memory deficits depending on the chemical forms of Al, namely, as an ion (AlCl3) and in the form of a complex (ALM). We administered saline, AlCl3, and ALM at a concentration of 40 micromol Al/kg body weight to mice by daily ip injections for 60 days. We assessed spatial memory by a water maze task and determined the Al levels in the brain of the mice by the neutron activation analysis method. Spatial memory deficit as an indicator of the swimming time was related to Al accumulation in the brain of mice; the chemical form of the Al compound was important in order to exhibit the memory deficit in mice; the uptake of Al is higher in mice when it is administered in a complex form than in an ionic form.

Protective effect of Ginkgo biloba leaf extract on learning and memory deficit induced by aluminum in model rats

OBJECTIVE

To examine the protective effect of Ginkgo biloba leaf extract (GbE) on learning and memory deficit induced by aluminum chloride (AlCl(3)), and explore its mechanisms.

METHODS

The rat models with learning and memory deficit were induced by administering via gastrogavage and drinking of AlCl(3) solution. And the model rats were treated with GbE at the dose of 50, 100, 200 mg/kg every day for 2 months accompanied with drinking of AlCl(3) solution, respectively. Their abilities of spatial learning and memory were tested by Morris water maze, and the acetylcholinesterase (AChE) activity in serum was assayed with chemical method, the AChE expression in hippocampus was observed by immunohistochemistry assay, and then quantitative analysis was done by BI 2000 image analysis system.

RESULTS

Learning and memory deficit of rats could be induced by AlCl(3) solution (P < 0.01), and AChE expressions in rats hippocampus were increased (P < 0.01); GbE ameliorated learning and memory deficit and reduced AChE expression in rats hippocampus in a dose-dependent manner, while GbE significantly increased serum AChE activity at the dose of 200 mg/kg each day (P < 0.05).

CONCLUSION

GbE can ameliorate learning and memory deficit induced by AlCl(3), which may be due to its inhibition of the AChE expression in hippocampus.

Acetylcholinesterase activation and enhanced lipid peroxidation after long-term exposure to low levels of aluminum on different mouse brain regions

Aluminum (Al), oxidative stress and impaired cholinergic functions have all been related to Alzheimer's disease (AD). The present study evaluates the effect of aluminum on acetylcholinesterase (AChE) and lipid peroxidation in the mouse brain. Mice were loaded by gavage with Al 0.1 mmol/kg/day 5 days per week during 12 weeks. The mice were divided into four groups: (1) control; (2) 10 mg/mL of citrate solution; (3) 0.1 mmol/kg of Al solution; (4) 0.1 mmol/kg of Al plus 10 mg/mL of citrate solution. AChE activity was determined in the hippocampus, striatum, cortex, hypothalamus and cerebellum and lipid peroxidation was determined in the hippocampus, striatum and cortex. An increase of AChE activity was observed in the fourth group (Al + Ci) in the hippocampus (36%), striatum (54%), cortex (44%) and hypothalamus (22%) (p<0.01). The third group (Al) presented a decrease of AChE activity in the hypothalamus (20%) and an enhancement in the striatum (27%). Lipid peroxidation, measured by TBARS (thiobarbituric acid reactive substances), was elevated in the hippocampus and cerebral cortex when compared with the control (p < 0.01). The effect of aluminum on AChE activity may be due to a direct neurotoxic effect of the metal or perhaps a disarrangement of the plasmatic membrane caused by increased lipid peroxidation.

Aluminum decreases the glutathione regeneration by the inhibition of NADP-isocitrate dehydrogenase in mitochondria

Effect of aluminum on the NADPH supply and glutathione regeneration in mitochondria was analyzed. Reduced glutathione acted as a principal scavenger of reactive oxygen species in mitochondria. Aluminum inhibited the regeneration of glutathione from the oxidized form, and the effect was due to the inhibition of NADP-isocitrate dehydrogenase the only enzyme supplying NADPH in mitochondria. In cytosol, aluminum inhibited the glutathione regeneration dependent on NADPH supply by malic enzyme and NADP-isocitrate dehydrogenase, but did not affect the glucose 6-phosphate dehydrogenase dependent glutathione formation. Aluminum can cause oxidative damage on cellular biological processes by inhibiting glutathione regeneration through the inhibition of NADPH supply in mitochondria, but only a little inhibitory effect on the glutathione generation in cytosol.

Al(3+)-mediated changes in membrane physical properties participate in the inhibition of polyphosphoinositide hydrolysis

We investigated the possible involvement of Al(3+)-induced alterations in membrane physical properties in Al(3+)-mediated inhibition of polyphosphoinositide (PPI) hydrolysis by the enzyme phosphatidylinositol-specific phospholipase C (PI-PLC). Liposomes composed of brain phosphatidylcholine (PC) or of PC and a mixture of brain PPI (PC:PPI) were incubated in the presence of Al(3+) (1-100 microM). We evaluated: (1) the amount of membrane-bound Al(3+), (2) the effects of Al(3+) on key membrane physical properties (surface potential, lipid fluidity, and lipid arrangement), and (3) the hydrolysis of PPI. Al(3+) binding to PC:PPI (60:40 mol/mol) liposomes was 1.3 times higher than to PC:PPI (90:10 mol/mol) liposomes and did not change after treatment with Triton X-100. Al(3+) increased membrane surface potential, promoted the loss of membrane fluidity, and caused lateral phase separation in PC:PPI liposomes. Phosphatidylinositol and phosphatidylinositol monophosphate hydrolysis in the presence of PI-PLC was not affected by Al(3+), but a significant and concentration-dependent inhibition of PIP(2) hydrolysis was observed, an effect that was prevented by previous bilayer disruption with Triton X-100. The obtained results support the hypothesis that Al(3+) binding to liposomes promotes the formation of rigid clusters enriched in PPI, restricting the accessibility of the enzyme to the substrate and subsequently inhibiting PIP(2) hydrolysis by PI-PLC.

Aluminum accumulation and membrane fluidity alteration in synaptosomes isolated from rat brain cortex following aluminum ingestion: effect of cholesterol

In the present work, we studied the effect of cholesterol/phospholipid (CH/PL) molar ratio on aluminum accumulation and aluminum-induced alteration of membrane fluidity in rat brain cortex synaptosomes. We observed that sub-acute (daily supply of 1.00 g of AlCl(3) during 10 days) and chronic (daily supply of 0.03 g of AlCl(3) during 4 months) exposure to dietary aluminum leads to a synaptosomal aluminum enrichment of 45 and 59%, respectively. During chronic exposure to AlCl(3), the enhancement of aluminum content was prevented by administration of colestipol (0.31 g/day), which decreased the synaptosomal membrane CH/PL molar ratio (nmol/nmol) from 1.2 to 0.4. Fluorescence anisotropy analysis, using 1,6-diphenyl-1,3,5-hexatriene (DPH) and 1-(4-(trimethylamino)phenyl)-6-phenylhexa-1,3,5-triene (TMA-DPH), showed that after treatment with colestipol a decrease in membrane order occurs at the level of hydrophilic lipid-water surface and deeper hydrophobic region of the synaptosomal membrane. When the rats were exposed to aluminum, it was observed a significant enhancement of membrane fluidity, which was more pronounced at the level of the membrane hydrophilic regions. Meanwhile, when chronic exposure to dietary AlCl(3) was accompanied by treatment with colestipol, the aluminum-induced decrease in membrane order was negligible when compared to TMA-DPH and DPH anisotropy values measured upon colestipol treatment. In contrast, in vitro incubation of synaptosomes (isolated from control rats) with AlCl(3) induced a concentration-dependent rigidification of this more hydrophilic membrane region. The opposite action of aluminum on synaptosomal membrane fluidity, during in vivo and in vitro experiments, appears to be explained by alteration of synaptosomal CH/PL molar ratio, since a significant reduction (approximately 80%) of this parameter occurs during in vivo exposure to aluminum. In conclusion, during in vivo exposure to aluminum, fluidification of hydrophilic regions and reduction of CH/PL molar ratio of presynaptic membranes accompany the accumulation of this cation, which appear to restrict aluminum retention in brain cortex nerve terminals.

Aluminum: impacts and disease

Aluminum is the most widely distributed metal in the environment and is extensively used in modern daily life. Aluminum enters into the body from the environment and from diet and medication. However, there is no known physiological role for aluminum within the body and hence this metal may produce adverse physiological effects. The impact of aluminum on neural tissues is well reported but studies on extraneural tissues are not well summarized. In this review, the impacts of aluminum on humans and its impact on major physiological systems are summarized and discussed. The neuropathologies associated with high brain aluminum levels, including structural, biochemical, and neurobehavioral changes, have been summarized. In addition, the impact of aluminum on the musculoskeletal system, respiratory system, cardiovascular system, hepatobiliary system, endocrine system, urinary system, and reproductive system are discussed.

Aluminium toxicity in the rat brain: histochemical and immunocytochemical evidence

Although the neurotoxic actions of aluminium (Al) have been well documented, its contribution to neurodegenerative diseases such as Alzheimer's disease remains controversial. In the present study, we applied histochemical techniques to identify changes induced by intracerebroventricular Al injections (5.4 microg in 5.5 microl, daily over a period of 5 successive days) in the adult rat brain after survival periods of either 1 or 6 weeks. For both Al- and saline-infused controls, no major signs of gross histological changes were evident in cresyl violet-stained sections. Al (as indicated by the fluorescent Morin staining) was concentrated in white matter of the medial striatum, corpus callosum, and cingulate bundle. Immunoreactivity of astrocytes and phagocytic microglia based on glial fibrillary acidic protein and ED1 markers, respectively, revealed a greater inflammatory response in Al-injected animals compared to controls. Damage of the cingulate bundle in Al-treated animals led to a severe anterograde degeneration of cholinergic terminals in cortex and hippocampus, as indicated by acetylcholinesterase labelling. Our data suggest that the enhancement of inflammation and the interference with cholinergic projections may be the modes of action through which Al may cause learning and memory deficits, and contribute to pathological processes in Alzheimer's disease.

Effects of Al(3+) and related metals on membrane phase state and hydration: correlation with lipid oxidation

The aim of the present study was to further understand how changes in membrane organization can lead to higher rates of lipid oxidation. We previously demonstrated that Al(3+), Sc(3+), Ga(3+), Be(2+), Y(3+), and La(3+) promote lipid packing and lateral phase separation. Using the probe Laurdan, we evaluated in liposomes if the higher rigidity of the membrane caused by Al(3+) can alter membrane phase state and/or hydration, and the relation of this effect to Al(3+)-stimulated lipid oxidation. In liposomes of dimyristoyl phosphatidylcholine and dimyristoyl phosphatidylserine, Al(3+) (10-100 microM) induced phase coexistence and displacement of T(m). In contrast, in liposomes of brain phosphatidylcholine and brain phosphatidylserine, Al(3+) (10-200 microM) did not affect membrane phase state but increased Laurdan generalized polarization (GP = -0. 04 and 0.09 in the absence and presence of 200 microM Al(3+), respectively). Sc(3+), Ga(3+), Be(2+), Y(3+), and La(3+) also increased GP values, with an effect equivalent to a decrease in membrane temperature between 10 and 20 degrees C. GP values in the presence of the cations were significantly correlated (r(2) = 0.98, P < 0.001) with their capacity to stimulate Fe(2+)-initiated lipid oxidation. Metal-promoted membrane dehydration did not correlate with ability to enhance lipid oxidation, indicating that dehydration of the phospholipid polar headgroup is not a mechanism involved in cation-mediated enhancement of Fe(2+)-initiated lipid oxidation. Results indicate that changes in membrane phospholipid phase state favoring the displacement to gel state can facilitate the propagation of lipid oxidation.

Selective modulation of GABAA receptors by aluminum

Aluminum has been implicated in several neurodegenerative conditions including Alzheimer's disease. Because the mammalian olfactory system has an unusual capacity for the uptake and transneuronal spread of inhaled substances such as aluminum, whole cell recording techniques were used to examine the actions of aluminum on basic membrane properties and amino acid receptors on rat olfactory bulb mitral/tufted (M/T) neurons in culture. Aluminum had little direct effects on M/T neurons. Aluminum (100 microM) did not evoke a membrane current or alter action-potential shape or duration. Aluminum also had no marked effects on the family of voltage-gated membrane currents evoked by a series of 10-mV, 50-ms depolarizing steps. However, aluminum dramatically potentiated the current evoked by 30 microM gamma-aminobutyric acid (GABA) at concentrations <100 microM. Conversely, higher concentrations of aluminum blocked the GABA-evoked current. The effects of aluminum on GABA-evoked currents were not voltage dependent. Aluminum (100 microM) equally potentiated both inward currents at -30 mV and outward currents at + 30 mV. At 300 microM, aluminum blocked both inward and outward currents to a similar extent. In some neurons, aluminum only blocked the current and potentiation was not observed. The biphasic action of aluminum on GABA-evoked currents suggests separate binding sites: a high-affinity potentiating site and a low-affinity inhibiting site. Despite its effects on GABA-evoked currents, aluminum did not alter membrane currents evoked by glutamate, N-methyl-D-aspartate, kainate, or glycine. Aluminum also did not reduce spontaneous excitatory synaptic activity, suggesting little, if any, effect on glutamate release. Although a causal role for aluminum in Alzheimer's disease and other neuropathological conditions remains controversial, it is clear that elevated aluminum concentrations in the brain are associated with a variety of cognitive impairments. The present results indicate that aluminum can alter the function of GABAA receptors and may suggest that aluminum can contribute to cognitive impairment through disruption of inhibitory circuits.

Alzheimer's disease risk factors as related to cerebral blood flow: additional evidence

In a previous report, Alzheimer's disease risk factors, including alcohol abuse, depression, Down's syndrome, cerebral glucose metabolism defect, head trauma, old age, Parkinson's disease, sleep disturbance, and underactivity, were shown to have an association with reduced cerebral blood flow. In this report an attempt is made to strengthen a hypothesis that reduced cerebral blood flow may be a required cofactor in the cause of Alzheimer's disease with examples of additional putative risks, including aluminum, ApoE 4 alleles, estrogen deficiency, family history of dementia, low education-attainment, olfactory deficit, and underactivity coupled with gender, considered to have a relationship or potential relationship with reduced cerebral blood flow. Factors, believed to ameliorate Alzheimer's disease, associated with improved or stabilized cerebral blood flow are tabulated. A tentative cerebral blood flow nomogram is shown as a potential model to possibly help predict Alzheimer's disease susceptibility.

Estimation of premorbid intelligence in Spanish people with the Word Accentuation Test and its application to the diagnosis of dementia

The Word Accentuation Test assesses the accentuation of 30 infrequent Spanish words written without the accentuation mark and is an easy-to-use tool for estimating premorbid intelligence of Spanish-speaking people. Its intraobserver (0.97) and interobserver (0.93) reliabilities and its correlation with the Wechsler Adult Intelligence Scale (.837) and Raven's Progressive Matrices (.655) are high, offering a good prediction of general intelligence. It is resistant to mental deterioration; 20 demented and 40 controls matched by sex, age, and education obtained similar scores. The discrepancies between current and predicted scores in Raven's scale can diagnose mild-moderate dementia with 0.79 accuracy (sensitivity, 0.78; specificity, 0.82).

Effects of aluminium on the mineral metabolism of rats in relation to age

The present study was conducted to assess in rats the effects of chronic aluminium (Al) exposure on calcium (Ca), magnesium (Mg), manganese (Mn), copper (Cu), zinc (Zn) and iron (Fe) accumulation and urinary excretion in relation to the age of the animals. Male young (21 day old), adult (8 months), and old (16 months) rats were orally exposed to 0, 50, or 100 mg Al/kg/day for a period of 6.5 months. Urinary levels of essential elements were determined after 3 and 6.5 months of exposure, whereas tissue Ca, Mg, Mn, Cu, Zn and Fe concentrations were examined after 6.5 months of Al administration. A number of age-related changes in tissue accumulation and urinary excretion of essential elements following chronic exposure to Al were found. Concentrations of essential elements in most tissues of young Al-exposed rats were generally lower than those of adult and old rats. The highest levels of essential elements were found in old animals. Liver, testes and spleen were the tissues that showed the most remarkable increases in relation to the levels found in those tissues of young rats. Adult rats showed a pattern comparable to that of old animals for mineral metabolism in brain, whereas in bone and testes the pattern of accumulation was closer to that of young rats. While the urinary levels of Ca were generally reduced in the Al-exposed groups, no Al-associated changes were noted for Mg, Mn, Cu and Zn. In turn, after 6.5 months of Al administration Fe excretion was increased in Al-treated adult and old rats. The results of this study suggest that early stages of life cycle should be of special concern for Al-induced changes in the metabolism of essential elements.

The effect of social learning on a conditioned avoidance response of rats treated prenatally with aluminum lactate

Aluminum (Al) has been proven to be a behavioral teratogenic agent in a number of experimental studies. Prenatal exposures to Al lactate have been shown to cause cognitive deficits in a variety of species. The present experiment was carried out on SPRD rat pups treated prenatally with Al lactate to determine whether observational conditioning (social learning) would reverse the impairment in learning described previously following such treatment. A conditioned avoidance response was used as an observational learning task. The results provide evidence that Al-treated pups are capable of social learning (i.e., the performance of the avoidance response improved as a result that Al-treated learning); however, the response latency of the avoidance response was not different in these animals from those that were not exposed to such facilitation, suggesting that additional factors are involved in the effects of prenatal aluminum intoxication on cognitive processes.

Alzheimer's disease risk factors as related to cerebral blood flow

Inconsistencies within results of case-control studies on Alzheimer's disease risk factors led to a search of the literature for a potential cofactor. Reduced cerebral blood flow was selected and literature was surveyed for evidence of a cerebral blood flow linkage with the more than 40 putative risks. Alcohol abuse, depression, head trauma, underactivity, old age, sleep disturbance, glucose utilization, Down's syndrome, and Parkinson's disease are risk factors where an association with reduced cerebral blood flow is documented. Studies were cited showing that improved cerebral blood flow is associated with factors thought to be helpful in Alzheimer's disease, such as education or occupational attainment, exercise, headache, smoking, and arthritis/anti-inflammatory drugs to the extent that aspirin is used. Sugar consumption is identified as a potential risk factor with glucose management in Alzheimer's disease also shown to involve reduced cerebral blood flow. An hypothesis is developed showing how compromised regional cerebral blood flow could fit as a cofactor for genetic, autoimmune, and neurotoxic aspects of Alzheimer's disease.

Trace elements in drinking water coolers collected from primary schools, Riyadh, Saudi Arabia

A simple method for the spectrochemical analysis of water samples by inductively coupled plasma spectrometry is described. Samples from drinking water coolers in 32 schools in Riyadh were collected at a specific time during a typical school day and analyzed for aluminum (Al), beryllium (Be), cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), nickel (Ni), silicon (Si), strontium (Sr), vanadium (V), and zinc (Zn) to ascertain the water quality. The analysis of drinking water showed high concentrations of metals and in some cases exceeded the guideline limits recommended by EEC and WHO.

Age-related effects of aluminum ingestion on brain aluminum accumulation and behavior in rats

Both aluminum and aging have been associated with neurobehavioral changes in mammals. This study assessed in young (21 day old), adult (8 months), and old rats (16 months) the effects of prolonged aluminum ingestion on open-field activity and passive-avoidance conditioning. Aluminum was administered in drinking water as aluminum nitrate at doses of 0, 50, and 100 mg Al/kg/day over a 6.5 month period. There were no aluminum effects on the horizontal and vertical activity in an open-field, or in passive-avoidance learning in any group. On the other hand, measurement of aluminum concentrations in a number of brain regions indicated that the olfactory bulb and the rhachidical bulb were the regions with the highest aluminum levels, while the cortex and the thalamus were the cerebral regions showing the lowest aluminum content. For most brain regions analyzed the highest aluminum concentrations were found in young rats, which would indicate that early stages of the life cycle must be considered for enhanced brain aluminum accumulation.

Effects of aluminum on neuronal signal transduction: mechanisms underlying disruption of phosphoinositide hydrolysis

1. Aluminum is neurotoxic in humans and animals and alters formation of inositol phosphate (IP) second messengers following in vivo or in vitro exposure. 2. Several components of the IP signalling system including G-proteins, phosphatidylinositol-specific phospholipase C (PI-PLC), protein kinase C (PKC) and Ca2+ homeostasis are susceptible to inhibition/disruption by aluminum compounds. 3. Recent evidence suggests that, despite its effects on other components, competitive inhibition by aluminum of phosphatidylinositol 4,5-bisphosphate (PIP2) hydrolysis by PI-PLC underlies its effects on agonist-stimulated IP generation.

Bioaccumulation of water soluble aluminium chloride in the hippocampus after transdermal uptake in mice

Normally, only very small amounts of ingested aluminium are absorbed and accumulated. Despite the percutaneous absorption of many drugs and chemicals, the skin has not been considered as a possible site at which aluminium could enter the body. Application of low aqueous concentrations of aluminium chloride (A1C1(3), 6H20) (0.025-0.1 micrograms/cm2) to healthy shaved Swiss mouse skin for 130 days led to a significant increase in urine, serum and whole brain aluminium, especially in the hippocampus, compared to control animals. This percutaneous uptake and accumulation of aluminium in the brain was greater than that caused by dietary exposure to 2.3 micrograms per day in feed and water. In vitro studies demonstrated the passage of aluminium through viable mouse skin. This study shows for the first time that aluminium is absorbed through the skin of mice in vivo and this contributes to a greater body burden than does oral uptake.

Bioavailability of labile aluminium in acidic drinking water: a study in the rat

The bioavailability of labile Al (Allab; Al3+, and monomeric hydroxo and sulfato complexes) in drinking water was studied in the rat. The hypothesis was that Allab in drinking water is more available for absorption in the gastro-intestinal tract than Al complexed in the rat feed. Male Sprague-Dawley rats were exposed to 4 mg Al/litre in acidic drinking water (pH 4-5) and 5 mg Al/kg in the feed for 10 wk. The Al intake of these rats was about twice that in a control group of rats that received Al only in the feed. Both a theoretical speciation calculation and a speciation analysis of the water in a flow injection system showed that more than 98% of the Al in the water was present as Allab. However, intake of this water did not result in increased levels of Al in the bone, liver or brain tissue of the rats. Al speciation in a simulated rat stomach indicated that Allab in drinking water is rapidly complexed by feed constituents as the water enters the acidic milieu of the stomach, resulting in a very low concentration of Allab. The concentration of dissolved Al was also low in comparison to the added amount of labile Al. The possibility of complex formation between Allab and feed components in the gastro-intestinal tract should be taken into account in further studies of the bioavailability of drinking water Al in experimental animals and in humans.

Aluminum toxicity in rat hippocampal neurons

A brief exposure of dissociated hippocampal culture to aluminum (AlCl3, 60 min) is toxic to neurons. The aluminum toxicity is independent of calcium or glutamate receptor activation. However, at a high concentration (1 mM), aluminum seems to have a protective effect.

Mechanisms underlying AlCl3 inhibition of agonist-stimulated inositol phosphate accumulation. Role of calcium, G-proteins, phospholipase C and protein kinase C

Possible mechanisms of AlCl3-induced inhibition of agonist-stimulated inositol phosphate (IP) accumulation were investigated using rat brain cortex slices, synaptosomes or homogenates. Under conditions in which AlCl3 inhibits carbachol (CARB)-stimulated IP accumulation (Gp-mediated), AlCl3 did not affect CARB (100 microM)-induced decreases (Gi-mediated) in 30 microM forskolin-stimulated cAMP accumulation, suggesting that AlCl3 may be specific for Gp-mediated signal transduction. To determine whether AlCl3 interfered with Gp function and/or phosphatidylinositol-specific phospholipase C (PiPLC) activity, effects of AlCl3 on CARB- and Ca(2+)-stimulated IP accumulation were examined in cortical synaptosomes. AlCl3 (500 microM) decreased CARB (1 mM)- and Ca2+ (20 microM ionomycin)-stimulated IP accumulation to 77 and 75% of control, respectively, suggesting that AlCl3 may not directly affect Gp activity, but does inhibit PiPLC activity. In cortical homogenates, AlCl3 (10-500 microM) inhibited hydrolysis of [3H]phosphatidylinositol 4,5-bisphosphate (PIP2) by PiPLC in a concentration-dependent manner with an estimated IC50 of 100 microM. The effects of AlCl3 on modulation of IP accumulation by extracellular Ca2+ and PKC were also examined as potential mechanisms. Decreasing the extracellular Ca2+ concentration ([Ca2+]e) from 1.0 to 0.1 mM decreased CARB-stimulated IP accumulation in slices. AlCl3 (500 microM) decreased significantly 1 mM CARB-stimulated IP accumulation in 1.0 and 0.1 mM Ca2+ solutions; however, the effect of AlCl3 on IP accumulation did not depend on [Ca2+]e. In cortical slices, inhibition of 1 mM CARB-stimulated IP accumulation by 500 microM AlCl3 was not altered by the PKC activator phorbol 12,13-dibutyrate (PdBu, 1 microM), or the PKC inhibitor H-7 (10 microM), suggesting that AlCl3 does not interfere with IP accumulation by activation of PKC. Other studies found that AlCl3 (10-100 microM) inhibited PKC activity in a concentration-dependent manner in both cytosolic and membrane fractions of cortical homogenates with an estimated IC50 of 60 microM. These results support the hypothesis that AlCl3 inhibition of agonist-stimulated IP accumulation may be mediated by inhibition of PiPLC activity, rather than disruption of G-protein function or modulation of the IP signalling system by Ca2+ or PKC.

Is aluminium an etiologic contributor to alcoholic amnesia and dementia?

Neurotoxicity from excess brain exposure to aluminium (Al) is well-documented, from both clinical observations and animal experiments, to impair learning, memory and cognition. The etiology of the cognitive impairment in chronic abusers of ethanol--alcoholic amnesia or dementia--is not known, but it is likely to be multifactorial. We hypothesize that a slowly-progressive accumulation of Al in the brain, so as to reach functionally-toxic levels, may be one such factor. This could occur because of an increased permeability of intestinal mucosa to entry of Al, arising from sustained exposure of the gastrointestinal tract to alcoholic beverages, plus a trend for more frequent ingestion of antacids based on Al salts for treating gastritis or ulcers caused by such exposure. If this be true, use of Al-containing medications, as well as all avoidable exposures to Al, should be contra-indicated for chronic heavy drinkers.