Translatability of mRNA from brain of infant rabbits exposed chronically to aluminium

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.

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.

Aluminum effect on lipid peroxidation and on the activities of superoxide dismutase and catalase in the cerebral hemisphere and liver of young chicks

Aluminum was injected (i.p.) as aluminum sulphate (4, 40 and 100 mg/kg body weight, n = 5 per group) daily into day-old White Leghorn male chicks for 7, 15 and 30 days. Aluminum (Al) treatment (100 mg dose) to chicks over 7 and 30 days resulted in a decrease in activities of cytosolic total and CN(-)-sensitive superoxide dismutase (SOD) in the cerebral hemisphere (CH). In the 15-day treated group, activities of cytosolic total, CN(-)-sensitive and CN(-)-insensitive SOD of CH were decreased in response to all doses of Al. In the liver, activities of cytosolic total and CN(-)-sensitive SOD were decreased in response to all doses of Al treatment for 7 and 15 days. But 40 and 100 mg doses were effective in decreasing activities of the enzymes in the 30-day treated group. The catalase (CAT) activity of CH of chicks was inhibited by all doses of Al under treatment for 7 days, but was inhibited only in the case of the 100 mg dose when the duration of treatment was increased to 15 days. The inhibition was again observed in chicks treated for 30 days in response to 40 and 100 mg doses. CAT activity of liver of chicks was decreased in response to all doses of Al in the 7-day treated group and in response to 40 and 100 mg doses in the 15- and 30-day treated groups. Al treatment did not affect lipid peroxide levels of CH and liver of chicks. These results suggest that decrease in activities in SOD and CAT in CH and liver of the chicks after Al treatment constitutes one of the factors for the mechanism of tissue injury by Al.

Metal binding and ferritin immunoreactivity in a high molecular weight fraction from rat brain

A high molecular weight protein fraction (PI) from rat brain that exhibited heat- and acid-resistant properties like ferritin was characterized with respect to its reactivity with spleen ferritin antiserum, iron (Fe) content and Fe and aluminum (Al) binding. This fraction eluted on Sepharose 4B and Sepharose 6B columns with an apparent Mr of 2 100 000. A second Fe-rich fraction (PII) with an Mr of 500 000 showed lower anti-ferritin activity. The PI and PII fractions from liver, when prepared without the heat and acid steps, were similar to those found in brain. In both tissues, the PI fraction had a low Fe/ferritin ratio (0.28 +/- 0.08 microgram/microgram for brain and 0.22 +/- 0.05 microgram/microgram for liver). Similarly the PII fractions had high Fe/ferritin ratios (1.48 +/- 0.44 microgram/microgram for brain and 1.34 +/- 0.10 microgram/microgram for liver). Analysis of Fe binding to brain PI revealed one high affinity site (Kd = 157 +/- 30.0 X 10(-6) M; Bmax = 1.42 +/- 0.11 micromol Fe/mg protein) and one low affinity site (Kd = 890 +/- 100 X 10(-6) M; Bmax = 5.24 +/- 0.96 micromol Fe/mg protein). Removal of Fe from brain PI with 1% thioglycollic acid solution prior to Fe binding, increased binding affinity at both sites, while total binding remained unchanged. A1 bound to brain PI with high affinity (Kd = 59.7 +/- 13.6 X 10(-6) M; Bmax = 0.24 +/- 0.02 micromol A1/mg protein). These results demonstrate the presence of two ferritin-like, metal-binding (MB) proteins in rat brain.

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.

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.

Brain protein synthesis in rabbits following low level aluminium exposure

1. Infant rabbits received s.c.injections 3 times weekly of low doses of aluminium (A1) maltolate (0.5-1.5 mg Al/kg body wt) or aluminium lactate (8 mg Al/kg body wt) from 5 or 10 days of age to 14 or 22 days of age. 2. Brain was used to provide a cell-free protein synthesizing system and this system exhibited increased activity in preparations from Al-exposed infants. The mRNA fraction obtained from the brain polysomal RNA also was more active following Al exposure. 3. The synthesis of immunoprecipitable calmodulin was significantly elevated.