Interaction of L-ascorbic acid on the disposition of lead in rats

(Ascorb)ing Pb Neurotoxicity in the Developing Brain

Lead (Pb) neurotoxicity is a major concern, particularly in children. Developmental exposure to Pb can alter neurodevelopmental trajectory and has permanent neuropathological consequences, including an increased vulnerability to further stressors. Ascorbic acid is among most researched antioxidant nutrients and has a special role in maintaining redox homeostasis in physiological and physio-pathological brain states. Furthermore, because of its capacity to chelate metal ions, ascorbic acid may particularly serve as a potent therapeutic agent in Pb poisoning. The present review first discusses the major consequences of Pb exposure in children and then proceeds to present evidence from human and animal studies for ascorbic acid as an efficient ameliorative supplemental nutrient in Pb poisoning, with a particular focus on developmental Pb neurotoxicity. In doing so, it is hoped that there is a revitalization for further research on understanding the brain functions of this essential, safe, and readily available vitamin in physiological states, as well to justify and establish it as an effective neuroprotective and modulatory factor in the pathologies of the nervous system, including developmental neuropathologies.

Developmental lead (Pb)-induced deficits in redox and bioenergetic status of cerebellar synapses are ameliorated by ascorbate supplementation

Neurotoxicity induced by exposure to heavy metal lead (Pb) is a concern of utmost importance particularly for countries with industrial-based economies. The developing brain is especially sensitive to exposure to even minute quantities of Pb which can alter neurodevelopmental trajectory with irreversible effects on motor, emotive-social and cognitive attributes even into later adulthood. Chemical synapses form the major pathway of inter-neuronal communications and are prime candidates for higher order brain (motor, memory and behavior) functions and determine the resistance/susceptibility for neurological disorders, including neuropsychopathologies. The synaptic pathways and mechanisms underlying Pb-mediated alterations in neuronal signaling and plasticity are not completely understood. Employing a biochemically isolated synaptosomal fraction which is enriched in synaptic terminals and synaptic mitochondria, this study aimed to analyze the alterations in bioenergetic and redox/antioxidant status of cerebellar synapses induced by developmental exposure to Pb (0.2 %). Moreover, we test the efficacy of vitamin C (ascorbate; 500 mg/kg body weight), a neuroprotective and neuromodulatory antioxidant, in mitigation of Pb-induced neuronal deficits. Our results implicate redox and bioenergetic disruptions as an underlying feature of the synaptic dysfunction observed in developmental Pb neurotoxicity, potentially contributing to consequent deficits in motor, behavioral and psychological attributes of the organisms. In addition, we establish ascorbate as a key ingredient for therapeutic approach against Pb induced neurotoxicity, particularly for early-life exposures.

Exposure to mixtures of mercury, cadmium, lead, and arsenic alters the disposition of single metals in tissues of Wistar rats

Humans throughout the world are exposed regularly to mixtures of environmental toxicants. Four of the most common heavy metal toxicants in the environment are mercury (Hg), cadmium (Cd), lead (Pb), and arsenic (As). Numerous studies have assessed the effects and disposition of individual metals in organ systems; however, humans are usually exposed to mixtures of toxicants or metals rather than to a single toxicant. Therefore, the purpose of the current study was to test the hypothesis that exposure to a mixture of toxic heavy metals alters the disposition of single metals in target organs. Wistar rats (Rattus norvegicus) were exposed to Hg, Cd, Pb, or As as a single metal or as a mixture of metals. Rats were injected intravenously for three days, following which kidneys, liver, brain, and blood were harvested. Samples were analyzed for content of Hg, Cd, Pb, and As via inductively coupled plasma mass spectrometry. In general, exposure to a mixture of metals reduced accumulation of single metals in target organs. Interestingly, exposure to mixtures of metals with Pb and/or As increased the concentration of these metals specifically in the liver. The findings from this study indicate that exposure to mixtures of toxic heavy metals may alter significantly the distribution and accumulation of these metals in target organs and tissues.

Developmental lead (Pb)-induced deficits in hippocampal protein translation at the synapses are ameliorated by ascorbate supplementation

BACKGROUND

Lead (Pb) is a persistent environmental neurotoxin and its exposure even in minute quantities has been known to induce neuronal defects. The immature brain is singularly sensitive to Pb neurotoxicity, and its exposure during development has permanent detrimental effects on the brain developmental trajectory and neuronal signaling and plasticity, culminating into compromises in the cognitive and behavioral attributes which persists even later in adulthood. Several molecular pathways have been implicated in the Pb-mediated disruption of neuronal signaling, including elevated oxidative stress, alterations in neurotransmitter biology, and mitochondrial dysfunction. Nevertheless, the neuronal targets and biochemical pathways underlying these Pb-mediated alterations in synaptic development and function have not been completely deduced. In this respect, recent studies have shown that synaptic signaling and its maintenance and plasticity are critically dependent on localized de novo protein translation at the synaptic terminals.

MATERIALS AND METHODS

The present study hence aimed to assess the alterations in the synapse-specific translation induced by developmental Pb exposure. To this end, in vitro protein translation rate was analyzed in the hippocampal synaptoneurosomal fractions of rat pups pre- and postnatally exposed to Pb using a puromycin incorporation assay. Moreover, we evaluated the therapeutic effects of ascorbic acid supplementation against Pb-induced deficits in synapse-localized protein translation.

RESULTS

We observed a significant loss in the rates of de novo protein translation in synaptoneurosomes of Pb-exposed pups compared to age-matched control pups. Interestingly, ascorbate supplementation lead to an appreciable recovery in Pb-induced translational deficits. Moreover, the deficit in activity-dependent synaptic protein translation was found to correlate significantly with the increase in the blood Pb levels.

CONCLUSION

Dysregulation of synapse-localized de novo protein translation is a potentially critical determinant of Pb-induced synaptic dysfunction and the consequent deficits in behavioral, social, and psychological attributes of the organisms. In addition, our study establishes ascorbate supplementation as a key ameliorative agent against Pb-induced neurotoxicity.

Dietary compounds as modulators of metals and metalloids toxicity

A large part of the population is exposed to metals and metalloids through the diet. Most of the in vivo studies on its toxicokinetics and toxicity are conducted by means of exposure through drinking water or by intragastric or intraperitoneal administration of aqueous standards, and therefore they do not consider the effect of the food matrix on the exposure. Numerous studies show that some components of the diet can modulate the toxicity of these food contaminants, reducing their effect on a systemic level. Part of this protective role may be due to a reduction of intestinal absorption and subsequent tissue accumulation of the toxic element, although it may also be a consequence of their ability to counteract the toxicity directly by their antioxidant and/or anti-inflammatory activity, among other factors. The present review provides a compilation of existing information about the effect that certain components of the diet have on the toxicokinetics and toxicity of the metals and metalloids of greatest toxicological importance that are present in food (arsenic, cadmium, lead, and mercury), and of their most toxic chemical species.

Protective Role of Tinospora cordifolia against Lead-induced Hepatotoxicity

The importance of Tinospora cordifolia stem and leaves extract was investigated for its possible hepatoprotective effect in Swiss albino male mice against lead nitrate induced toxicity. Oral administration of plant extracts prevented the occurrence of lead nitrate induced liver damage. The decreased level of tissue enzymes, i.e., superoxide dismutase (SOD), catalase (CAT) and increased level of aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), and acid phosphatase (ACP) were observed in mice treated with lead. Administration of aqueous stem extract (400 mg/kg body weight, orally) and aqueous leaves extract (400 mg/kg body weight, orally) along with the lead nitrate (5 mg/kg body weight, i.p. for 30 days) increased the activities of SOD and CAT and decreased the levels of AST, ALT, ALP, and ACP enzymes in mice. These biochemical observations were supplemented by histopathology/histological examinations of liver section. Results of this study revealed that plant extract could afford protection against lead-induced hepatic damage.

Ascorbic Acid Supplementation Does Not Improve Efficacy of meso -Dimercaptosuccinic Acid Treatment in Lead-Exposed Suckling Rats

It was suggested that ascorbic acid as a natural chelating agent can influence lead toxicokinetics and improve chelating properties of dimercaptosuccinic acid (DMSA) in adult rats. In this paper potential benefits of ascorbic acid supplementation, alone or combined with DMSA, in decreasing lead retention in suckling rats were evaluated. Such data in young mammals are not available. L-Ascorbic acid (daily dose 650 mg/kg b.wt.) and/or DMSA (daily dose 91 mg/kg b.wt.) were administered orally to suckling Wistar rats either during ongoing 8-day oral lead exposure (as acetate; daily dose 2 mg lead/kg b.wt.) or after 3-day lead exposure (total dose 12 mg lead/kg b.wt.). Lead concentrations were analysed in the carcass (skeleton), liver, kidneys and brain by atomic absorption spectrometry. By ascorbic acid supplementation lead retention was not reduced under either lead exposure condition. Lead concentration was even increased in the carcass. Treatment with DMSA under both exposure conditions significantly reduced lead in all analysed tissues. Combined treatment with ascorbic acid and DMSA during ongoing lead exposure was substantially less effective than DMSA treatment alone, and did not affect DMSA efficacy when administered after lead exposure. It was concluded that ascorbic acid administered either during or after lead exposure in suckling rats has no beneficial effect on either lead retention or DMSA chelation effectiveness.

Withania somnifera root extract in the regulation of lead-induced oxidative damage in male mouse

The importance of Withania somnifera root extract in the regulation of lead toxicity with special reference to lipid peroxidative process has been investigated in liver and kidney tissues. While lead treatment (0.5 mg kg(-1)body wt. day(-1)for 20 days) enhanced hepatic and renal lipid peroxidation (LPO), administration of plant extract in the doses of 0.7 g kg(-1)and 1.4 g kg(-1)body wt. day(-1)along with equivalent doses of lead acetate for 20 days significantly decreased LPO and increased the activities of antioxidant enzymes, viz., superoxide dismutase (SOD) and catalase (CAT), thus retaining normal peroxidative status of the tissues. We suggest that the ameliorating role of root extract of W. somnifera in the lead intoxicated mice could be the result of its antiperoxidative action.

Does vitamin C intake protect against lead toxicity?

Although several animal studies suggest a protective relationship between blood lead concentrations and ascorbic acid, there are inconclusive results regarding the beneficial effect of ascorbic acid on lead concentrations in human studies. Data from the Third National Health and Nutrition Examination Survey examined the association between ascorbic acid and blood lead concentrations in 19,578 participants ages 6-90 years without a history of lead poisoning. Elevated blood lead concentrations were found in 0.4% of adults and 0.5% of youths. Serum ascorbic acid concentrations were inversely associated with the prevalence of elevated blood lead concentrations. However, there was no significant relationship between dietary ascorbic acid intake and blood lead concentrations. This study suggests that there may be a protective relationship between ascorbic acid and lead. Questions remain regarding the unique roles of dietary vitamin C versus supplemental vitamin C in explaining this relationship.

The effect of ascorbic acid supplementation on the blood lead levels of smokers

BACKGROUND

The study subjects were 75 adult men (20 to 30 years of age), who smoked one pack of cigarettes per day (minimum) and had no clinical signs of ascorbic acid deficiency or lead toxicity. None had a history of industrial exposure to lead, and the blood-lead levels were anticipated to be below 1.45 micromol/L, the minimum blood level associated with toxicity symptoms.

METHODS

The men were randomly assigned to three study groups of 25, and each group was provided a four-week supply of one level of daily ascorbic acid supplements (placebo, 200 mg or 1000 mg of ascorbic acid). We measured baseline and weekly serum and urine ascorbic-acid levels as well as blood and urine lead levels. The weekly group means and variations of the measured data were statistically compared by means of ANOVA and Pearson's correlation.

RESULTS

The serum ascorbic-acid levels of the groups receiving ascorbic acid increased significantly after one week (p< or =.001). There was no effect of placebo or 200 mg ascorbic-acid supplementation on the blood or urine lead levels. However, there was a 81% decrease in blood-lead levels in the 1000 mg ascorbic acid group after one week of supplementation (p< or =.001).

CONCLUSIONS

Daily supplementation with 1000 mg of ascorbic acid results in a significant decrease of blood-lead levels associated with the general population. Ascorbic acid supplementation may provide an economical and convenient method of reducing blood-lead levels, possibly by reducing the intestinal absorption of lead.

A physiological pharmacokinetic model describing the disposition of lead in the absence and presence of L-ascorbic acid in rats

The influence of L-ascorbic acid (As-Ac) on the multiple-tissue disposition of lead has been evaluated. Lead concentrations in femur, liver, kidney and plasma of rats were monitored over a 120h period after its intravenous bolus administration (1.0 mg/kg) in the absence and presence of As-Ac at steady state. The observed lead concentration-time data in different tissues of the rats, in the absence and presence of As-Ac, have been simulated using a physiological pharmacokinetic modelling technique. In both cases, the predicted lead concentrations in various tissues were in adequate agreement with the observed data. The model developed in the present investigation supports the previous finding that As-Ac may be useful as a prophylactic agent for lead poisoning.