Several studies have implicated oxidative stress as one of the important mechanisms of toxic effects of lead (Pb). In the present study we tested the beneficial effects of calcium (Ca2+) and zinc (Zn2+) in protecting the Pb-induced oxidative stress in the brains of developing and adult mice. Mice were lactationally exposed to 0.2% Pb and supplemented with either calcium (Ca2+) or zinc (Zn2+) and the mitochondrial antioxidant enzymes [superoxide dismutase (SOD), xanthine oxidase (XO) and catalase (CAT)] and lipid peroxidation (LP) were analyzed in cortex, hippocampus, cerebellum and medulla of brains excised on postnatal day (PND) 14, 21, 28 and 3 months. The levels of free radicals were measured using direct Electron Paramagnetic Resonance (EPR) spectroscopy. Exposure to Pb resulted a significant decrease in the activities of SOD, XO and CAT while the LP levels were significantly increased in different brain regions. Evaluation of EPR signals and g-values showed abundant accumulation of free radicals in different regions of the brain following Pb exposure. Interestingly the supplementation with Ca2+ or Zn2+ reversed the Pb-induced effects on antioxidant enzymes, LP and free radical formation; however Zn2+ supplementation appeared to be more protective. These findings strongly support that zinc and calcium supplementation significantly protect the Pb-induced oxidative stress, a major contributing factor to neurotoxicity.

Hypercholesterolemia increases levels of β-amyloid (Aβ), a peptide that accumulates in Alzheimer's disease brains. Because cholesterol in the blood does not cross the blood brain barrier (BBB), the link between circulating cholesterol and Aβ accumulation is not understood. In contrast to cholesterol, the oxidized cholesterol metabolite 27-hydroxycholestrol can cross the BBB, potentially increasing Aβ levels. However, the mechanisms by which cholesterol or 27-hydroxycholesterol regulate Aβ levels are not known. The insulin-like growth factor-1 (IGF-1) regulates the glycogensynthase kinase-3α (GSK-3α) and the insulin degrading enzyme (IDE). While GSK-3α increases Aβ production, IDE is a major Aβ-degrading enzyme. We report here that feeding rabbits with a cholesterol-enriched diet increases Aβ levels in the hippocampus, an effect that is associated with reduced IGF-1 levels. 27-hydroxycholestrol also increases Aβ and reduces IGF-1 levels in organotypic hippocampal slices from adult rabbits. We suggest that hypercholesterolemia-induced Aβ accumulation may be mediated by 27-hydroxycholesterol, involving IGF-1 signaling.

Rats were lactationally exposed to low- (0.2%) and high-level (1%) lead (Pb) from postnatal day 1 (PND1) through PND21 through the drinking water of the mother. The levels of catecholamines, epinephrine, norepinephrine and dopamine and the activity of the enzyme monoamine oxidase (MAO) were determined in the cerebellum, hippocampus and cerebral cortex in young (1-month-old) and adult (3-month-old) rats. Pb-exposure decreased the activity of mitochondrial MAO in all the brain regions in a dose-dependent manner. The synaptosomal catecholamines (epinephrine, norepinephrine and dopamine), however, increased with low level (0.2%) Pb-exposure and significantly decreased with high level (1%) Pb-exposure in both the age groups. In general, the young rats seem to be more vulnerable to Pb-neurotoxicity. These data suggest that Pb-exposure perturbs the aminergic system in the cerebral cortex, cerebellum and hippocampus and may contribute to the cognitive and behavioural impairments observed in Pb-exposed rats.

Accumulation of β-amyloid (Aβ) peptide in the brain is a major hallmark of Alzheimer’s disease (AD). Hypercholesterolemia is a risk factor for AD and has been shown by laboratory studies to cause Aβ accumulation. Aβ levels in the brain are governed by its generation from amyloid precursor protein by β-secretase (BACE1), degradation by the insulin degrading enzyme (IDE), clearance from the brain by the low density lipoprotein receptor-related protein (LRP-1), and transport from circulation into the brain by receptor for advanced glycation end products (RAGE). However, the mechanisms by which hypercholesterolemia causes Aβ accumulation in the brain and contributes to the pathogenesis of AD are still to be determined. In the present study, we determined the extent to which hypercholesterolemia-induced Aβ accumulation is associated with alterations in BACE1, IDE, LRP-1, and RAGE expression levels. We show that hypercholesterolemia increases Aβ production, an effect that is associated with increased levels of BACE1 and RAGE and reduced levels of IDE and LRP-1. These results suggest that reducing Aβ accumulation in the brain may require strategies that combine reduction of generation and transport of Aβ in addition to acceleration of degradation and clearance of this peptide.

Since alterations in monoamines and monoamine oxidase (MAO) have been postulated to play a role in toxic effects of lead (Pb) on the central nervous system, we have examined the protective effects of calcium (Ca 2+ ) and zinc (Zn 2+ ) supplementation on Pb-induced perturbations in the levels of monoamines and the activity of MAO. Swiss albino mice were lactationally exposed to low (0.2%) and high (1%) levels of Pb-acetate via drinking water of the mother. Pb-exposure commenced on postnatal day (PND) 1, continued up to PND 21 and stopped at weaning. Ca 2+ or Zn 2+ (0.02% in 0.2% Pb-water or 0.1% in 1% Pb-water) was supplemented separately to the mother up to PND 21. The levels of monoamines (epinephrine, norepinephrine, dopamine and serotonin) and the activity of MAO in the brain regions such as hippocampus, cortex, cerebellum and medulla of young (1 month old) and adult (3 month old) mice were determined in the synaptosomal fractions. The synaptosomal monoamines though increased with low level (0.2%) Pb-exposure, significantly decreased with high level (1%) Pb-exposure in all the brain regions in both the age groups. In general, the young mice seem to be more vulnerable to Pb-neurotoxicity. Ca 2+ or Zn 2+ supplementation significantly reversed the Pb-induced perturbations both in the levels of monoamines and in the activity of MAO. However, the recovery in monoamine levels and MAO activity was more pronounced with Ca 2+ supplementation as compared to Zn 2+ . These results provide evidence that dietary Ca 2+ and/or Zn 2+ provide protection against Pb-induced neurotoxic effects.