Brain protein synthesis in rabbits following low level aluminium exposure

Hormetic Neurobehavioral effects of low dose toxic chemical mixtures in real-life risk simulation (RLRS) in rats

The current study aims to assess the long-term effects of very low dose exposures to a complex chemical mixture on motor performance and behavioural changes in rats. For twelve months (equivalent to thirty years in human terms), four groups of Sprague Dawley rats (five males and five females per group) were exposed to a thirteen chemical mixture (in drinking water) in doses of 0, 0.25, 1 and 5xADI/TDI (acceptable daily intake/tolerable daily intake) (mg/kg body weight/day). After twelve month exposure, the rats' motor performances were assessed by rotarod test, and their behavioural changes were assessed by open field exploratory test and elevated plus maze test. Exposure to the chemical mixture resulted in a statistically significant increase in the locomotor activity quantified by the number of crossings over external squares and in the spatial orientation activity quantified as the number of rearings in the lower dose group (0.25xADI/TDI) compared with the control group (p < 0.05). No significant changes were observed in the two higher dose groups (1xADI/TDI, 5xADI/TDI) compared with the control group. The administration of a very low doses of a cocktail of 13 chemicals led to a dose-dependent stimulation of the nervous system, rather than its inhibition.

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.

Effect of long-term exposure to aluminum on the acetylcholinesterase activity in the central nervous system and erythrocytes

Aluminum (Al), a neurotoxic agent, has been associated with Alzheimer's disease (AD), which is characterized by cholinergic dysfunction in the central nervous system. In this study, we evaluated the effect of long-term exposure to aluminum on acetylcholinesterase (AChE) activity in the central nervous system in different brain regions, in synaptosomes of the cerebral cortex and in erythrocytes. The animals were loaded by gavage with AlCl(3) 50 mg/kg/day, 5 days per week, totalizing 60 administrations. Rats were divided into four groups: (1) control (C); (2) 50 mg/kg of citrate solution (Ci); (3) 50 mg/kg of Al plus citrate (Al + Ci), and (4) 50 mg/kg of Al (Al). AChE activity in striatum was increased by 15% for Ci, 19% for Al + Ci and 30% for Al, when compared to control (P < 0.05). The activity in hypothalamus increased 23% for Ci, 26% for Al + Ci and 28% for Al, when compared to control (P < 0.05). AChE activity in cerebellum, hippocampus and cerebral cortex was decreased by 11%, 23% and 21% respectively, for Al, when compared to the respective controls (P < 0.05). AChE activity in synaptosomes was increased by 14% for Al, when compared to control (P < 0.05). Erythrocyte AChE activity was increased by 17% for Al + Ci and 11% for Al, when compared to control (P < 0.05). These results indicate that Al affects at the same way AChE activity in the central nervous system and erythrocyte. AChE activity in erythrocytes may be considered a marker of easy access of the central cholinergic status.

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.

Inorganics and hormesis

The article is a comprehensive review of the occurrence of hormetic dose-response relationships induced by inorganic agents, including toxic agents, of significant environmental and public health interest (e.g., arsenic, cadmium, lead, mercury, selenium, and zinc). Hormetic responses occurred in a wide range of biological models (i.e., plants, invertebrate and vertebrate animals) for a large and diverse array of endpoints. Particular attention was given to providing an assessment of the quantitative features of the dose-response relationships and underlying mechanisms that could account for the biphasic nature of the hormetic response. These findings indicate that hormetic responses commonly occur in appropriately designed experiments and are highly generalizeable with respect to biological model responses. The hormetic dose response should be seen as a reliable feature of the dose response for inorganic agents and will have an important impact on the estimated effects of such agents on environmental and human receptors.

Aluminium-induced biphasic effect

Increased bioavailability of aluminium has raised concerns about the toxic effect of aluminium. The cholinotoxic effect of aluminium is already well established. The biological response of an organism following exposure to a chemical may be biphasic. Although aluminium-induced biphasic change has been reported in diverse organ systems, the biphasic effect on cholinergic system has received less attention. In vitro and in vivo studies have demonstrated an aluminium-induced biphasic effect on the marker enzyme of cholinergic system, acetylcholinesterase. The biphasic effect of aluminium on the acetylcholinesterase enzyme activity may be due to the direct neurotoxic effect of the metal and the level of aluminium accumulated. Among various hypotheses, peroxidation-induced changes in the structure of membrane following aluminium accumulation seems to explain the biphasic effect of aluminium on acetylcholinesterase activity.

Biphasic effect of aluminium on cholinergic enzyme of rat brain

The cholinotoxic effect of aluminium has been widely reported. In vitro aluminium has a biphasic effect on acetylcholinesterase activity. The present study analyses its in vivo effect in brain regions. Rats were exposed to aluminium chloride by the oral route at a dose of 320 mg/kg body weight for shorter (4 and 14 days) and longer (60 days) duration. Acetylcholinesterase activity in olfactory bulb, striatum and hypothalamus brain regions increased after 4 and 14 days and decreased after 60 days of aluminium exposure. Aluminium level in the brain regions studied increased significantly. No significant change in body weight of rats exposed to aluminium was found. The biphasic change in acetylcholinesterase activity may be due to slow accumulation of aluminium in the brain regions and its effect on the enzyme.

Brain mRNA from infants of aluminium-exposed lactating rabbits

The neurotoxicity of aluminium (Al) involves bundling of neurofilaments, increased chromatin binding and decreased protein synthesis in Al injected rabbits. Thus, using an amphipathic Al ligand, maltol, experiments were carried out to examine whether or not administration of Al to lactating mother rabbits reduces brain protein synthesis in their offspring. Lactating mother rabbits received s.c. injections 3 times weekly of aluminium (Al) maltolate (1 mg Al/kg body wt) or an equivalent weight of maltol, for 4 weeks post-partum. Polysome preparations were obtained from the brain of their infants in order to assess mRNA translation in cell-free protein synthesizing systems. The brain polysomes showed a statistically significant reduction in the incorporation of [14C]leucine into protein. The poly (A)+ and poly (A)- fractions obtained from these polysomes showed reductions of 44% or more in the incorporation of [35S]methionine into protein. A variety of products separated by SDS-polyacrylamide gel electrophoresis all exhibited decreased labelling. These experiments suggest that infant rabbits exposed to a highly neurotoxic form of Al in milk exhibit changes in brain protein synthesis which resemble those in infants injected directly with Al.

The cellular toxicity of aluminium

Aluminium is a serious environmental toxicant and is inimical to biota. Omnipresent, it is linked with a number of disorders in man including Alzheimer's disease, Parkinson's dementia and osteomalacia. Evidence supporting aluminium as an aetiological agent in such disorders is not conclusive and suffers principally from a lack of consensus with respect to aluminium's toxic mode of action. Obligatory to the elucidation of toxic mechanisms is an understanding of the biological availability of aluminium. This describes the fate of and response to aluminium in any biological system and is thus an important influence of the toxicity of aluminium. A general theme in much aluminium toxicity is an accelerated cell death. Herein mechanisms are described to account for cell death from both acute and chronic aluminium challenges. Aluminium associations with both extracellular surfaces and intracellular ligands are implicated. The cellular response to aluminium is found to be biphasic having both stimulatory and inhibitory components. In either case the disruption of second messenger systems is observed and GTPase cycles are potential target sites. Specific ligands for aluminium at these sites are unknown though are likely to be proteins upon which oxygen-based functional groups are orientated to give exceptionally strong binding with the free aluminium ion.

Some effects of aluminium on rat brain protein synthesis

1. Infant rats and rabbits received intraperitonal aluminium (Al) chloride (5, 10 or 20 mg Al/kg body weight) every third day from one to four weeks of age. 2. When the polysomal fraction was tested in a protein synthesizing system, a significant increase in the incorporation of [14C] leucine, [14C] phenylalanine, or [35S] methionine into proteins in vitro was observed at the higher doses in rats but not rabbits. 3. The incorporation of [35S]methionine into brain ferritin was measured using polysomal mRNA or mRNA "stored" in the ribonucleoprotein (RNP) particle fraction. 4. The results suggest that Al exposure causes the mobilization of ferritin mRNA from the latter fraction to the polysomal fraction for increased ferritin synthesis.