Dialysis encephalopathy: neuropathologic aspects

Aluminium in the Human Brain: Routes of Penetration, Toxicity, and Resulting Complications

Aluminium (Al) is the most ubiquitous metal in the Earth's crust. Even though its toxicity is well-documented, the role of Al in the pathogenesis of several neurological diseases remains debatable. To establish the basic framework for future studies, we review literature reports on Al toxicokinetics and its role in Alzheimer's disease (AD), autism spectrum disorder (ASD), alcohol use disorder (AUD), multiple sclerosis (MS), Parkinson's disease (PD), and dialysis encephalopathy (DE) from 1976 to 2022. Despite poor absorption via mucosa, the biggest amount of Al comes with food, drinking water, and inhalation. Vaccines introduce negligible amounts of Al, while the data on skin absorption (which might be linked with carcinogenesis) is limited and requires further investigation. In the above-mentioned diseases, the literature shows excessive Al accumulation in the central nervous system (AD, AUD, MS, PD, DE) and epidemiological links between greater Al exposition and their increased prevalence (AD, PD, DE). Moreover, the literature suggests that Al has the potential as a marker of disease (AD, PD) and beneficial results of Al chelator use (such as cognitive improvement in AD, AUD, MS, and DE cases).

Autopsy case of aluminum encephalopathy

We report the case of a 59-year-old female aluminum encephalopathy patient who had chronic renal failure and took 3.0 g hydroxy-aluminum gel per day for the control of serum phosphorus level during a 15-year period. Nine months before her death she developed disorientation, memory disturbance, emotional incontinence, general convulsions and consciousness disturbance. Neuropathologically, the brain showed nerve cell atrophy and mild loss with stromal spongiosis, proliferation of astrocytes and microglia in the cerebral cortex, basal ganglia and thalamus. Some nerve cells were stained immunohistochemically by phosphorylated neurofilament, but apparent neurofibrillary tangles were not observed. Aluminum was detected in the nerve cells of the cerebral cortex by X-ray microanalysis. Despite the long-term intake of aluminum, there were no neuropathological findings of Alzheimer's disease. The findings in our case suggested that aluminum alone might not develop Alzheimer's disease.

Subacute fatal aluminum encephalopathy after reconstructive otoneurosurgery: a case report

We report a 52-year-old woman who underwent otoneurosurgery to resect acoustic neurinoma. Bone reconstruction was performed with an aluminium (Al)-containing cement. Six weeks later the patient suffered from loss of consciousness, myoclonic jerks, and persistent grand mal seizures, clinical symptoms that resembled those of lethal dialysis encephalopathy of the 1960s and 1970s. She died 6 months later because of septic complications. Light- and electron-microscopic investigation of the central nervous system (CNS) showed pathognomonic Al-containing intracytoplasmic argyrophilic inclusions in choroid plexus epithelia, neurons, and cortical glia. These changes are characteristics of dialysis-associated encephalopathy (DAE), induced nowadays by long-term ingestion of Al-containing drugs (and with benign clinical courses). Atomic absorption spectrometry showed an increase of mean bulk Al concentration of the cortex and subcortex up to 9.3 microg/g (normal range <2 microg/g); laser microprobe showed the increase of Al in subcellular structures. This unique case again shows the extraordinary neurotoxicity of Al, which was, in our patient, initiated by an amount of about 30 mg Al and apparently caused by direct Al access to the brain parenchyma via a cerebrospinal fluid leakage.

Aluminum pretreatment impairs the ability of astrocytes to protect neurons from glutamate mediated toxicity

A number of laboratories have shown that astrocytes protect neurons from glutamate excitotoxicity. The experiments described in this paper were designed to address the question whether prior exposure of astrocytes to aluminum (in the form of aluminum citrate) interfered with the ability of astrocytes to protect neurons from glutamate excitotoxicity. Our culture paradigm consisted of highly enriched cultures of neurons and astrocytes grown on separate coverslips; this design enables one to subject either the neurons or the astrocytes to specific treatments and recombine the cells into the same petri dish simply by moving coverslips from dish to dish. We have confirmed findings of other laboratories that astrocytes could protect neurons from glutamate-induced death when glutamate (100 microM) is added to the culture medium. We have also demonstrated that prior treatment of astrocytes with 100 microM aluminum citrate impairs this ability of astrocytes to promote neuronal survival. No differences, however, were observed in the ability of control and aluminum-treated astrocytes to take up glutamate. These findings suggest that aluminum may cause astrocytes to: (i) secrete a factor that makes neurons more susceptible to glutamate-induced toxicity; (ii) secrete a neuronotoxic factor in the presence of glutamate; or (iii) reduce secretion of a factor that protects neurons from glutamate excitotoxicity.

Dialysis-associated encephalopathy: light and electron microscopic morphology and topography with evidence of aluminum by laser microprobe mass analysis

Recently we described silver-staining variants for the demonstration of beta/A4 amyloid and neurofibrillary tangles in senile dementia of Alzheimer type (SDAT). The same methods allowed, for the first time, the visualization of characteristic patterns and distinct morphological changes in human dialysis-associated encephalopathy. Light and electron microscopy demonstrated typical silver-stained inclusions in the cytoplasm of choroidal epithelium, glia and neurons. Performing laser microprobe mass analysis on en-bloc silver-stained semithin sections, evidence for significant amounts of aluminum was obtained within the lesions. Prominent aluminum-signals were obtained additionally in adjacent structures and nuclei of sections which were stained with toluidine-blue exclusively. Silver-stained paraffin sections of ten patients with a history of long-term hemodialysis were evaluated. The choroidal epithelium--obviously the most sensitive structure--showed black inclusions ranging from a few dots to a complete black staining of cells. Glial cells presented massive silver-stained deposits, which were restricted to the gray matter. Finally, neurons revealed numerous fine-granular black inclusions, scattered throughout the cytoplasm. Brain stem nuclei were primarily affected, but neurons within cortex, subcortical gray matter and spinal cord were also involved to various degrees; inclusions were not evident in the nucleus dentatus and the oliva inferior. Vessel-related deposits were found frequently. By electron microscopy the cytoplasm of neurons was filled either with large amounts of small electron-dense granules, or with lipofuscin granules, containing numerous irregular, non-membrane-bound inclusions. Massive electron-dense depositions were seen in the cytoplasm of choroidal epithelia and in proximity to nuclei of cortical astro- and oligodendroglia. The described neuronal changes and, in particular, alterations of choroidal epithelium and glia are completely different from characteristic plaques and tangles in SDAT.

Increased cerebral blood flow in anemic patients on long-term hemodialytic treatment

CBF was measured in 15 patients on chronic hemodialytic treatment. CBF was measured with xenon-133 inhalation using single photon emission tomography. In addition, computerized tomography (CT) and a neurological examination were done prior to hemodialysis. Mean CBF was 66.2 +/- 17.3 (SD) ml 100 g-1 min-1, which was significantly higher (t-test, p less than 0.05) than for an age-matched control group (54.7 +/- 10.2 ml 100 g-1 min-1). However, the hematocrit for the patients was considerably lower, 0.30 +/- 0.07, as compared to 0.43 +/- 0.03 in the controls. A significant negative correlation was observed between CBF and the hematocrit (y = -1.79x + 120.7, r = -0.71, p less than 0.01). Calculating CBF from this equation in the dialyzed patients using a hematocrit of 0.43 yielded a mean CBF value of 43.7 ml 100 g-1 min-1, i.e., 20% below the expected. Two patients showed a focal CBF decrease. CT showed central or cortical atrophy in five patients, and two had small hypodense lesions. The neurological examination revealed slight to moderate dementia in seven cases. Although mean CBF was found to be increased by 21% as compared to the control group, an even higher CBF level would have been expected to outweigh the decreased oxygen carrying capacity of the blood. The findings suggest a lowered metabolic demand of the brain tissue, probably due to subtle brain damage.

Aluminium intoxication in undialysed adults with chronic renal failure

The dialysis encephalopathy syndrome (DES) consists of altered mental status, communication difficulty, seizures and myoclonus. It has been attributed to elevated serum aluminium (A1) levels. Two undialysed patients with chronic renal failure who presented with the characteristic syndrome are reported. The first, a 48 year old female, had used A1 containing phosphate binders for two years. Her serum A1 level was 25.34 mumol/L. Despite treatment with desferoximine and dialysis, she died. Necropsy revealed elevated A1 levels in the cerebral cortex (19 mcg/gm) and spongioform change in the outer three cortical layers. The second patient, a 46 year old woman, had a serum A1 of 8.70 mumol/L. She had never taken A1 containing phosphate binders but had taken several grams/day of citrate for at least six months. Treatment with haemodialysis and discontinuation of the citrate produced a resolution of symptoms and return of the A1 level to normal. During two years of haemodialysis there has been no recurrence.

Aluminium accumulation in relation to senile plaque and neurofibrillary tangle formation in the brains of patients with renal failure

The effects of long-term exposure to aluminium on the development of Alzheimer-type neuropathological changes have been studied post-mortem in patients with chronic renal failure who did not have dialysis encephalopathy. Administration of aluminium-containing phosphate binding compounds appears to be a major factor in the accumulation of aluminium in the brain of dialysis patients. The mean serum aluminium concentrations determined during life and brain aluminium concentrations determined post-mortem correlated with both the duration and total amount of aluminium hydroxide administered to these patients. No correlation was found between the presence of bone aluminium and either the mean serum or brain aluminium concentration. Longitudinal monitoring of serum aluminium concentrations may provide a more reliable index than bone biopsy of brain aluminium concentrations in dialysis patients. Dynamic secondary ion mass spectrometry revealed focal accumulations of aluminium associated with cortical pyramidal neurones. The majority of patients also showed immunostaining in pyramidal neurones with an antibody to the N-terminal region of the beta/A4 amyloid precursor protein, while staining was absent in age-matched control cases. One-third of the patients exhibited beta/A4-positive amorphous senile plaques in the cerebral cortex. However, there was no clear correlation between either the presence and intensity of beta/A4 amyloid precursor immunostaining or the presence of senile plaques and the concentration of aluminium in the cerebral cortex. Cortical neurofibrillary tangles were not observed in any of the dialysis patients. These data suggest that it is unlikely that aluminium plays any major role in neurofibrillary tangle formation and that its putative role in senile plaque formation is likely to be only part of a complex cascade of changes.

Aluminum chloride stimulates the release of endogenous glutamate, taurine and adenosine from cultured rat cortical astrocytes

Primary astrocyte cultures derived from neonatal rat cerebral cortex were treated for 5 min with 0.5 mM or 5.0 mM AlCl3, and the incubation medium was analyzed by HPLC for the content of released glutamate (Glu), taurine (Tau), serine (Ser) and the nucleoside adenosine (Ade). At 0.5 mM, AlCl3 stimulated Tau release to about 170% of basal levels, but did not affect the release of the other compounds. Treatment with 5.0 mM AlCl3 enhanced the release of Tau, Glu and Ade, to 800%, 1000% and 250%, respectively, but decreased the release of Ser to 70% compared to basal levels. The enhanced release of these neuroactive compounds from astrocytes may contribute to changes in neural transmission known to accompany exposure to aluminum.

Comparison of the regional distribution of transferrin receptors and aluminium in the forebrain of chronic renal dialysis patients

Recent studies have emphasised the potential neurotoxicity of aluminium in dialysis encephalopathy and it has also been suggested that this element may have a role in the pathogenesis of Alzheimer's disease. Aluminium is known to be transported by the iron transport protein transferrin. In this study using receptor autoradiography we have demonstrated the presence of transferrin binding sites in the human forebrain and shown a pattern similar to that found in other species. Imaging secondary ion mass spectrometry has demonstrated the distribution of aluminium-containing cell-like profiles in the brains of chronic renal dialysis patients who have raised levels of brain aluminium (greater than 4 micrograms/g dry weight) and even in dialysis patients where the gross level of aluminium was within the normal range. The density of these profiles corresponded to the regions of high transferrin receptor density. In contrast, the distribution of iron in the brain showed an inverse correlation with transferrin receptor density with highest iron levels present in the globus pallidus, an area of low transferrin receptor density. These results suggest that the regional distribution of neuropathological changes seen in dialysis encephalopathy patients and also Alzheimer's disease may reflect the distribution of transferrin receptors. The discrepancy between iron distribution and transferrin receptor distribution suggests that further, as yet uncharacterized mechanisms, govern the distribution of brain iron.

Progressive aphasia without dementia: two cases with focal spongiform degeneration

Two patients with the syndrome of progressive aphasia without evidence of generalized dementia underwent postmortem neuropathological examinations. In both patients, characteristic changes of Alzheimer's disease, Pick's disease, or Creutzfeldt-Jakob disease were absent. Both patients showed a focal spongiform change involving primarily layer 2 of the left inferior frontal gyrus (and temporal cortex in Patient 1) and a mild astrocytosis in layer 2 and deeper cortical layers. This focal, spongiform cortical degeneration in patients with progressive aphasia does not appear to duplicate any known central nervous system degenerative disease.