Intranuclear aluminum accumulation in chronic animals with experimental neurofibrillary changes

Animal Model of Aluminum-Induced Alzheimer's Disease

Lack of a satisfactory animal model for Alzheimer's disease (AD) has limited the reach progress of the pathogenesis of the disease and of therapeutic agents aiming to important pathophysiological points. In this chapter, we analyzed the research status of animal model of aluminum-induced Alzheimer's disease. Compared with other animal models, Al-maltolate-treated aged rabbits is a more reliable and efficient system in sharing a common mechanism with the development of neurodegeneration in Alzheimer's disease.

The protective role of plant biophenols in mechanisms of Alzheimer's disease

Self-assembly of amyloid beta peptide (Aβ) into the neurotoxic oligomers followed by fibrillar aggregates is a defining characteristic of Alzheimer's disease (AD). Several lines of proposed hypotheses have suggested the mechanism of AD pathology, though the exact pathophysiological mechanism is not yet elucidated. The poor understanding of AD and multitude of adverse responses reported from the current synthetic drugs are the leading cause of failure in the drug development to treat or halt the progression of AD and mandate the search for safer and more efficient alternatives. A number of natural compounds have shown the ability to prevent the formation of the toxic oligomers and disrupt the aggregates, thus attracted much attention. Referable to the abundancy and multitude of pharmacological activities of the plant active constituents, biophenols that distinguish them from the other phytochemicals as a natural weapon against the neurodegenerative disorders. This review provides a critical assessment of the current literature on in vitro and in vivo mechanistic activities of biophenols associated with the prevention and treatment of AD. We have contended the need for more comprehensive approaches to evaluate the anti-AD activity of biophenols at various pathologic levels and to assess the current evidences. Consequently, we highlighted the various problems and challenges confronting the AD research, and offer recommendations for future research.

Targeting the progression of Parkinson's disease

By the time a patient first presents with symptoms of Parkinson's disease at the clinic, a significant proportion (50-70%) of the cells in the substantia nigra (SN) has already been destroyed. This degeneration progresses until, within a few years, most of the cells have died. Except for rare cases of familial PD, the initial trigger for cell loss is unknown. However, we do have some clues as to why the damage, once initiated, progresses unabated. It would represent a major advance in therapy to arrest cell loss at the stage when the patient first presents at the clinic. Current therapies for Parkinson's disease focus on relieving the motor symptoms of the disease, these unfortunately lose their effectiveness as the neurodegeneration and symptoms progress. Many experimental approaches are currently being investigated attempting to alter the progression of the disease. These range from replacement of the lost neurons to neuroprotective therapies; each of these will be briefly discussed in this review. The main thrust of this review is to explore the interactions between dopamine, alpha synuclein and redox-active metals. There is abundant evidence suggesting that destruction of SN cells occurs as a result of a self-propagating series of reactions involving dopamine, alpha synuclein and redox-active metals. A potent reducing agent, the neurotransmitter dopamine has a central role in this scheme, acting through redox metallo-chemistry to catalyze the formation of toxic oligomers of alpha-synuclein and neurotoxic metabolites including 6-hydroxydopamine. It has been hypothesized that these feed the cycle of neurodegeneration by generating further oxidative stress. The goal of dissecting and understanding the observed pathological changes is to identify therapeutic targets to mitigate the progression of this debilitating disease.

A new insight on Al-maltolate-treated aged rabbit as Alzheimer's animal model

Lack of an adequate animal model for Alzheimer's disease (AD) has limited an understanding of the pathogenesis of the disease and the development of therapeutic agents targeting key pathophysiological processes. There are undoubtedly few satisfactory animal models for exploring therapies targeting at amyloid beta (Abeta) secretion, deposition, aggregation, and probably the inflammatory response. However, an understanding of the complex events--tau, Abeta, oxidative stress, redox active iron, etc.--involved in the neuronal cell loss is still unclear due to the lack of a suitable animal model system. The use of neurotoxic agents particularly aluminum-organic complexes, especially Al-maltolate, expands the scope of AD research by providing new animal models exhibiting neurodegenerative processes relevant to AD neuropathology. Examination of different species of aged animals including the rapidly advancing transgenic mouse models revealed very limited AD-like pathology. Most other animal models have single event expression such as extracellular Abeta deposition, intraneuronal neurofilamentous aggregation of proteins akin to neurofibrillary tangles, oxidative stress or apoptosis. To date, there are no paradigms of any animal in which all the features of AD were evident. However, the intravenous injection of Al-maltolate into aged New zealand white rabbits results in conditions which mimics a number of neuropathological, biochemical and behavioral changes observed in AD. Such neurodegenerative effects include the formation of intraneuronal neurofilamentous aggregates that are tau positive, immunopositivity of Abeta, presence of redox active iron, oxidative stress and apoptosis, adds credence to the value of this animal model system. The use of this animal model should not be confused with the ongoing controversy regarding the possible role of Al in the neuropathogenesis, a debate which by no means has been concluded. Above all this animal model involving neuropathology induced by Al-maltolate provides a new information in understanding the mechanism of neurodegeneration.

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.

Impairment of motor coordination in mice after ingestion of aluminum chloride

The mechanisms of aluminum (Al) neurotoxicity is of increasing interest. Al compounds are known to produce neurological and behavioral abnormalities in some mammalian species. The present study was designed to determine the effects of Al chloride on the skilled motor performance in mice on the rota-rod treadmill. Al chloride, depending on the duration of treatment, produced an impairment of the motor coordination ability in mice.

Reversibility of neurofilamentous inclusion formation following repeated sublethal intracisternal inoculums of AlCl3 in New Zealand white rabbits

In this report, we describe the clinical, topographical and immunohistochemical characteristics of neurofilament (NF) inclusion formation induced by the intracisternal inoculation of young adult New Zealand white rabbits at 28-day intervals with 100 micrograms AlCl3 over the course of 267 days. The ability to recover following cessation of aluminum exposure has also been assessed. The extent of neurofilamentous inclusion formation was proportionate to the cumulative amount of AlCl3 inoculated and initially consisted of fusiform axonal distention in the ventral spinal cord at day 51 following the initial inoculum. Spinal motor neuron perikaryal inclusions and discrete axonal spheroids were observed at day 107 and supraspinal neurofilamentous pathology by day 156. Perikaryal inclusions were immunoreactive to antibodies recognizing both poorly phosphorylated (SMI 32) and more highly phosphorylated high molecular weight NF (NFH). In contrast, axonal spheroids were intensely immunoreactive at all stages with antibodies recognizing highly phosphorylated NFH and an age-dependent NFH phosphorylation state (SMI 34) with only faint SMI 32 immunoreactivity. Immunoreactivity to an antibody recognizing ubiquitin-protein conjugates did not appear until day 156, whereas inclusions were not immunoreactive to antibodies recognizing either phosphatase-dependent or -independent microtubule-associated protein tau at any stage. Upon withdrawal from further AlCl3 exposure after intervals of 51, 107 or 156 days following the initial inoculum, clinical recovery ensued in all rabbits. In all but the most severely affected rabbits, perikaryal neurofilamentous inclusions resolved. However, axonal spheroids continued to be prominent. These studies demonstrate that the repetitive intracisternal inoculation of AlCl3 in New Zealand white rabbits induces a reversible process of neurofilamentous inclusion formation that preferentially affects motor neurons, and in which recovery will occur in those inclusions containing an admixture of both poorly and highly phosphorylated NFH.

Possible factors in the etiology of Alzheimer's disease

Inherited cases of Alzheimer's disease (AD) comprise only a very small proportion of the total. The remainder are of unknown etiopathogenesis, but they are very probably multifactorial in origin. This article describes studies on four possible factors: aluminum; viruses--in particular, herpes simplex type I virus (HSV1); defective DNA repair; and head trauma. Specific problems associated with aluminum, such as inadvertent contamination and its insolubility, have led to some controversy over its usage. Nonetheless, the effects of aluminum on animals and neuronal cells in culture have been studied intensively. Changes in protein structure and location in the cell are described, including the finding in this laboratory of a change in tau resembling that in AD neurofibrillary tangles, and also the lack of appreciable binding of aluminum to DNA. As for HSV1, there has previously been uncertainty about whether HSV1 DNA is present in human brain. Work in this laboratory using polymerase chain reaction has shown that HSV1 DNA is present in many normal aged brains and AD brains, but is absent in brains from younger people. Studies on DNA damage and repair in AD and normal cells are described, and finally, the possible involvement of head trauma is discussed.

Aluminum neurotoxicity: an experimental approach to the induction of neurofilamentous inclusions

Acute or chronic aluminum neurotoxicity experiments in the rabbit suggest that aluminum can induce phosphorylation of neurofilamentous proteins. This may result in abnormal resistance to degradation or transport of neurofilament protein and so to the accumulation of neurofilaments in abnormal cells. The possible importance of this process in ALS is considered in relation to the neurofilamentous abnormalities characteristic of intraneuronal inclusions in ALS and in other neurodegenerative disorders.

Enhanced neurite growth in cultured neuroblastoma cells exposed to aluminum

Patients with aluminum-induced encephalopathy syndromes have been shown to have a high level of aluminum concentration in the brain. In the present study, the effects of aluminum were studied in mouse neuroblastoma cells (N-2A) grown in medium supplemented with aluminum (100 microM). It was found that aluminum enhanced neurite growth within 2 days of exposure. The mean total length of neurites in the control after 14 days in culture was 29.8 +/- 4.7 microns, whereas the neurite length of cells pre-exposed to aluminum for 2 days and then maintained in normal media for an additional 12 days was 56.4 +/- 8.9 microns. Further, the duration of exposure did not significantly promote a greater neurite response. The neurite length of cells exposed to aluminum for 14 days (60.7 +/- 9.6 microns) was not statistically different from that of cells exposed to aluminum for 2 days. Using morin stain, intracellular aluminum was detected within 24 h of exposure in the majority of aluminum-exposed cells. Intracellular aluminum did not disappear from those cells even after they were grown for 12 days in control medium. Our finding suggests that a brief exposure (2 days) to low level aluminum (100 microM) is sufficient to cause long-lasting effects on the morphology of neuroblastoma cells in culture. Such neurite behavior associated with aluminum exposure may suggest a morphological basis for the dementia seen in aluminum encephalopathy.

Chronic aluminum-induced motor neuron degeneration: clinical, neuropathological and molecular biological aspects

The monthly intracisternal inoculation of young adult New Zealand white rabbits with low-dose (100 micrograms) aluminum chloride induces aggregates of phosphorylated neurofilament that mimics the intraneuronal inclusions of amyotrophic lateral sclerosis. The chronic progressive myelopathy and topographically-specific motor neuron degeneration that occurs in the absence of suppressions of neurofilament messenger RNA levels in this model contrasts with the acute fulminant encephalomyelopathy and nonspecific gene suppressions that occur subsequent to high-dose (1000 micrograms) aluminum chloride inoculations. Further analysis of this unique model of chronic motor system degeneration can be expected to provide additional insights into the pathogenesis of amyotrophic lateral sclerosis.

Immunohistochemical study of microtubule-associated protein 2 and ubiquitin in chronically aluminum-intoxicated rabbit brain

Experimental neurofibrillary change was produced in rabbit brain by daily subcutaneous aluminum tartrate injection for 40 days. The production of experimental neurofibrillary changes was confirmed by immunostaining with antibodies against neurofilament triplet proteins and the brain tissue was studied immunohistochemically with antibodies against microtubule-associated protein (MAP) 2 and ubiquitin. The hippocampal neurons of the chronically aluminum-intoxicated rabbit brain showed diminished staining of dendrites by anti-MAP2 antibody. The length of anti-MAP2-positive dendrites in hippocampus was significantly shorter than that of the control brain. In the cortex somata of a subset of pyramidal neurons were intensively stained by anti-MAP2 antibody, while the MAP2 immunoreactivity of distal dendrites was diminished. The immunostaining by anti-ubiquitin antibody revealed the positive staining of the neurons bearing experimental neurofibrillary changes in the lower brain stem nuclei. It is speculated that MAP2 dislocation and ubiquitination are accompanying phenomena of the production of experimental neurofibrillary changes in chronically aluminum-intoxicated rabbit brains.

Exogenous aluminum accumulates in the lysosomes of cultured rat cortical neurons

In order to study the intracellular localization of aluminum, 0.01% AlCl3 was added to rat cerebral organotypic cultures following 14 days incubation in a standard medium. The cultures were maintained in the aluminum (Al)-containing medium for 1 or 3 days. Subsequently, electron probe X-ray micro-analysis (EPXMA), was used to localize aluminum in the neurons. The Al was found in the cells as early as after 1 day of AlCl3 exposure. The Al was detected exclusively in the neuronal lysosomes, in 66% (1 day exposure) and 97% (3 days) of the measured lysosomes. This localization was confirmed by laser microprobe mass analysis (LAMMA) measurements. Our results demonstrate an Al localization in the neurons, exposed to exogenous Al, different from that in the brains of patients with Alzheimer's disease.

Aluminum produces age related behavioral toxicity in the rabbit

Two- to 3.4-year-old, retired breeder, rabbits received repeated aluminum (Al) lactate or sodium (Na) lactate injections. All six rabbits receiving twenty 400 mumol Al/kg SC injections died, demonstrating much higher mortality than previously seen in younger rabbits. Subsequent rabbits receiving Al were dosed with 200 mumole/kg injections. Aluminum injections inhibited body weight gain. Renal function, as measured by creatinine clearance, in these rabbits was inferior to younger rabbits, perhaps contributing to the Al induced toxicity. Renal function decreased during Al injections suggesting a nephrotoxic effect of Al. Rabbits were tested for their ability to acquire, retain and extinguish a classically conditioned reflex, nictitating membrane extension. Rabbits which received Al acquired and retained the conditioned response less well than Na lactate injected rabbits. Impaired acquisition was evidenced by lower percent conditioned responses, more trials to 1 to 10 consecutive conditioned responses and longer conditioned response latencies. Aluminum injections produced significant elevations in tissue Al concentration in frontal gray and hippocampal brain as well as most peripheral tissues studied. Aluminum induced behavioral toxicity is greater in adult and aged rabbits than in young rabbits. Aged rabbits are more susceptible to Al induced mortality than adult or young rabbits.

Neuronal gene expression in aluminum myelopathy

1. Aluminum administration to susceptible animal species results in neurofilament accumulation in neuronal perikarya and proximal axons. Pathogenetic studies in vivo have shown that aluminum rapidly associates with neuronal chromatin. Whether the effect of aluminum on DNA components plays a role in the production of the neurofibrillary lesion remains unclear. 2. In this study we used Northern analysis and in situ hybridization to evaluate mRNA levels of specific neuronal and glial components in the rabbit spinal cord at various times following aluminum administration. 3. Our results show that (a) all neuronal mRNAs evaluated (neurofilament triplet components, neuronal-specific enolase, and amyloid precursor protein) are markedly decreased, with no decrease in glial fibrillary acidic protein; (b) the effect on neuronal gene expression occurs early and concurrently with the development of the neurofibrillary lesion and reverses rapidly after a single dose of aluminum; and (c) there is a direct correlation between the severity of the neurofibrillary lesion and the decrease in neuronal mRNA levels. 4. We interpret our results to mean that the accumulation of neurofilaments in this model is not due to a selective effect on neurofilament gene expression but may be due to an inhibition of genes coding for components involved in processing of neurofilament proteins.

Aluminum-induced neurofibrillary degeneration affects a subset of neurons in rabbit cerebral cortex, basal forebrain and upper brainstem

Neurofibrillary tangles in Alzheimer's disease show a predilection for cortical pyramidal and subcortical projection neurons. The antigenic composition, neuronal specificity and distribution of aluminum-induced neurofibrillary degeneration were examined in regions of rabbit brain analogous to those that develop neurofibrillary tangles in Alzheimer's disease. Neurofibrillary degeneration was induced by intraventricular instillation of aluminum chloride. In aluminum-treated rabbits, intensely immunoreactive filamentous aggregates were seen in affected neuronal perikarya after staining with an antiphosphorylated neurofilament antibody (SMI 31), while in controls immunoreactivity was confined to axon-like elements. Monoclonal antibodies against Microtubule-associated protein 2 and tau, which stain human neurofibrillary tangles, did not stain aluminum-induced neurofibrillary degeneration. Pyramidal neurons exhibiting neurofibrillary degeneration formed a discrete linear pattern in layers III and V of cortex. Cortical somatostatin and nicotinamide adenine dinucleotide phosphate diaphorase-reactive neurons identified in double-stained sections were unaffected. Large perikarya in the vicinity of the globus pallidus, some of which contained acetylcholinesterase, were frequently SMI 31-immunoreactive. Among the cell groups affected in the upper brainstem were the nucleus raphe dorsalis and locus coeruleus. These findings show that aluminum-induced neurofibrillary degeneration differs antigenically from neurofibrillary tangles in Alzheimer's disease. Nevertheless, many neuronal subsets that are particularly susceptible to Alzheimer's disease, including cortical pyramidal neurons, basal forebrain cholinergic neurons and upper brainstem catecholaminergic neurons, are also affected by aluminum-induced neurofibrillary degeneration.

Neurochemical characteristics of aluminum-induced neurofibrillary degeneration in rabbits

Aluminum-induced neurofibrillary degeneration in rabbits is known to affect particular populations of neurons. The neurotransmitter alterations which accompany aluminum neurofibrillary degeneration were examined in order to assess how closely they mimic those of Alzheimer's disease. There was a significant reduction in choline acetyltransferase activity in entorhinal cortex and hippocampus as well as significant reductions in cortical concentrations of serotonin and norepinephrine in the aluminum-treated rabbits. Significant reductions in glutamate, aspartate and taurine were found in frontoparietal and posterior parietal cortex. Concentrations of GABA were unchanged in cerebral cortex. Both substance P and cholecystokinin immunoreactivity were significantly reduced in entorhinal cortex but there were no significant changes in somatostatin, neuropeptide Y and vasoactive intestinal polypeptide. The five neuropeptides were unaffected in striatum, thalamus, cerebellum and brainstem. Neurochemical changes were found in the regions with the most neurofibrillary degeneration while regions with little or no neurofibrillary degeneration were unaffected. The reductions in choline acetyltransferase activity, serotinin and noradrenaline suggest that some neuronal populations preferentially affected in Alzheimer's disease are also affected by aluminum-induced neurofibrillary degeneration; however, the cortical somatostatin deficit which is a feature of Alzheimer's disease is not replicated in the aluminum model.

Aluminum neurotoxicity: altered expression of cytoskeletal genes

To better understand perturbations of the neuronal cytoskeleton that occur in several mammalian disorders, we have focused on an animal model in which neurofibrillary pathology follows the administration of aluminum salts. In susceptible species, the injection of aluminum produces accumulations of neurofilaments (NFs) in cell bodies and proximal axons of certain populations of neurons. Mechanisms involved in the production of these abnormalities are unclear; in particular, the role of gene expression in the genesis of this type of neurofibrillary pathology has not been examined. In this study of aluminum-intoxicated rabbits, the expression of genes coding for several cytoskeletal proteins was studied in the spinal cord and dorsal root ganglia (DRG)--tissues with and without neurofibrillary pathology, respectively. In aluminum-treated rabbits, in situ hybridization using a cDNA probe demonstrated the presence of mRNA coding for the 68-kDa NF (NF-L) protein in spinal cord motor neurons with NF accumulations as well in unaffected neurons. On Northern blots, the expression of genes coding for the NF-L protein and tubulin was reduced by approximately 3.5-fold and 3-fold, respectively, in spinal cords of aluminum-intoxicated rabbits as compared to controls. On blots, levels of actin mRNA were not significantly different in spinal cords of aluminum-treated rabbits as compared to controls, but there was a trend for a slight reduction. In DRG of intoxicated animals, the expression of genes coding for these cytoskeletal proteins was not altered.

Aluminum and Alzheimer's disease: perspectives for a cytoskeletal mechanism

A considerable volume of literature has accumulated concerning the association of aluminum with Alzheimer's disease. The pathogenic mechanisms resulting in Alzheimer's disease remain unknown, but recent investigations have focused on cytoskeletal abnormalities as perhaps the key lesion in Alzheimer's disease and related neurological disorders. The diversity of neuronal functions that are dependent on cytoskeletal integrity suggests that subtle effects on polymerization, assembly, transcription, or processing of cytoskeletal elements may have significant and far-reaching neurological effects. That aluminum may participate in the development of neuropathological lesions characteristic of Alzheimer's disease is suggested by evidence that aluminum is a potent cytoskeletal toxin, produces cognitive deficits in laboratory animals, and can be detected within abnormal neurons isolated from brain tissue from Alzheimer's disease patients. In this review, a critical look will be taken at the enigmatic role aluminum has played in Alzheimer's disease research, the possibility of its pathogenicity, and its use as a tool for the investigation of cytoskeletal changes that may result in the biochemical and, ultimately, clinical manifestations of Alzheimer's disease.

Total and poly(A) RNA yields during an aluminum encephalopathy in rabbit brains

The yields of total and poly(A) RNA were examined in rabbit forebrains during an experimentally induced aluminum encephalopathy. Rabbits (35 day old) were injected intracranially with 13 mumole Al lactate and sacrificed 1, 3, 7, 10, or 12 days later. IRNA yields (total RNA minus transfer RNA) were not significantly altered during the encephalopathy. Poly(A) RNA yields, assayed by oligo(dT)-cellulose fractionation and by a [3H]poly(U) hybridization assay on IRNA, were increased significantly by the end of the asymptomatic stage of the encephalopathy (7 days post-Al injection). The increase in messenger RNA population may represent either a compensatory response to cell damage induced by aluminum or the accumulation of messenger RNA for proteins directly related to the expression of aluminum toxicity.

Dendritic alterations in chronic animals with experimental neurofibrillary changes

Dendritic changes were quantitated in the cerebral cortex and subiculum of rabbits injected with aluminum tartrate for 90 days (5 days/week) at 100, 200, and 300 days after the last injection of aluminum. Both apical and basal dendrites of the cerebral cortex and subiculum responded similarly to aluminum tartrate. The dendrites were fewer and shorter in the animals examined at 200 and 300 days postinjection of aluminum tartrate. Such dendritic changes were more prominent at longer postinjection times and in dendrites that were more peripheral from the cell body. Aluminum-induced changes in apical dendrites were more prominent in the subiculum than in the cerebral cortex. Aluminum-induced changes in basal dendrites, however, were more prominent in the cerebral cortex than in the subiculum. The results suggest a time delay between the initial accumulation of neurofibrillary changes and the subsequent loss of peripheral dendritic branches, which appears to be long-lasting.

Synaptic density in chronic animals with experimental neurofibrillary changes

Synaptic density was quantitated in the cerebral cortex and subiculum of rabbits with experimental neurofibrillary changes. Animals were subjected to subcutaneous injection of aluminum tartrate for 90 days, and synapses stained with ethanolic phosphotungstic acid were analyzed in animals killed 100, 200, or 300 days postinjection with aluminum tartrate. A significant difference was found in synaptic density between animals injected with aluminum tartrate and their age-matched controls. This difference was a result of a low synaptic density present in animals killed 200 or 300 days postinjection of aluminum tartrate. In contrast, animals killed 100 days postinjection revealed the same synaptic density as their control. The data suggest that the synaptic depopulation associated with experimental neurofibrillary changes is a gradual process, and such changes are demonstrable only long after the initial appearance of neurofibrillary changes.