Chelation therapy for childhood lead poisoning. The changing scene in the 1990s

Retained bullets and lead toxicity: a systematic review

INTRODUCTION

Lead toxicity secondary to retained bullet(s) (RB) after a penetrating gunshot wound is a rare but likely underdiagnosed condition, given the substantial number of firearm injuries in the United States. There is currently no consensus on the indications for surveillance, chelation, or surgical intervention.

OBJECTIVE

The purpose of our review is to summarize the literature on systemic lead toxicity secondary to RBs to help guide clinicians in the management of these patients.

METHODOLOGY

The primary literature search was conducted in Medline (PubMed), EMBASE, Cochrane, and CENTRAL using the following MESH terms: "chelation" and "lead poisoning" or "lead toxicity" or "lead" and "bullet" or "missile" or "gunshot", or "bullet".

RESULTS

The search identified 1,082 articles. After exclusions, a total of 142 articles were included in our final review, the majority of which were case reports. Several factors appear to increase the risk of developing lead toxicity including the location of the RB, the presence of a fracture or recent trauma, number of fragments, hypermetabolic states, and bullet retention duration. Particularly, RBs located within a body fluid compartment like an intra-articular space appear to be at a substantially higher risk of developing lead toxicity. Even though patients with lead toxicity from RBs will have similar symptoms to patients with lead toxicity from other sources, the diagnosis of lead poisoning may occur months or years after a gunshot wound. Symptomatic patients with high blood lead levels (BLLs) tended to improve with a combination of chelation and surgical removal of RBs.

CONCLUSIONS

We suggest surveillance with serial BLLs should be performed. Patients with intra-articular RBs appear to be at increased risk of lead toxicity and if possible, early surgical removal of the RBs is warranted, especially given that signs of toxicity are vague, and patients may not have access to follow-up. Long-term chelation should not be used as a surgical alternative and management should be multidisciplinary.

Dietary intake of magnesium-l-threonate alleviates memory deficits induced by developmental lead exposure in rats

Elevation of brain magnesium enhances cognitive capacity.

Neuroprotective effects of xanthone derivative of Garcinia mangostana against lead-induced acetylcholinesterase dysfunction and cognitive impairment

Lead poisoning is a common environmental toxicity and low level of lead exposure is responsible for neurobehavioral or intelligence defects. This study was designed to investigate the protective effect of a xanthone derivative of Garcinia mangostana against lead-induced acetycholinesterase (AChE) dysfunction and cognitive impairment in mice. ICR mice were exposed to lead acetate (Pb) in drinking water (1%) with or without xanthone co-administration (100 and 200mg/kgBW/day) for 38days. Xanthone possesses a high phenolic content, which is positive correlation with its antioxidant activity (R(2)=0.98). The IC50 of xanthone on scavenging free radical activities, hydroxyl radical, superoxide radical, hydrogen peroxide and nitric oxide in cell-free system were 0.48±0.08, 1.88±0.09, 2.20±0.03 and 0.98±0.40mg/mL, respectively. We found that Pb induced AChE dysfunction and memory deficit in a dose dependent manner, indicated by in vitro and in vivo studies. However, xanthone significantly restored AChE activity in the blood and brains of mice and prevented Pb-induced neurobehavioral defect indicators with Forced Swimming and Morris water maze tests. Xanthone treatment improved all indicators compared to the Pb-treated group. In conclusion, xanthone alleviates Pb-induced neurotoxicity, in part, by suppression of oxidative damage and reversing AChE activity with a reduction in learning deficit and memory loss.

Protective effect of Thunbergia laurifolia (Linn.) on lead induced acetylcholinesterase dysfunction and cognitive impairment in mice

Thunbergia laurifolia (linn., TL), a natural phenolic compound, has been reported to have many benefits and medicinal properties. The current study ascertains the total phenolic content present in TL aqueous leaf extract and also examines the antioxidant ability of the extract in preserving acetylcholinesterase (AChE) activity of mice exposed to lead in vivo and in vitro model. Mice were given lead acetate (Pb) in drinking water (1 g/L) together with TL 100 and 200 mg/kg/day. The result showed that Pb induced AChE dysfunction in both in vitro and in vivo studies. TL significantly prevented Pb induced neurotoxicity in a dose-dependent manner which was indicated by comparatively better performance of TL treated mice in Morris Water Maze Swimming Test and increased AChE activity in the tissue sample collected from the brains of these mice. TL also exhibited the greatest amount of phenolic content, which has a significant positive correlation with its antioxidant capacity (P < 0.05). Taken together, these data suggested that the total phenolic compounds in TL could exhibit antioxidant and in part neuroprotective properties. It may play a potential treatment strategy for Pb contamination.

Beneficial effect of sesame oil on heavy metal toxicity

Heavy metals become toxic when they are not metabolized by the body and accumulate in the soft tissue. Chelation therapy is mainly for the management of heavy metal-induced toxicity; however, it usually causes adverse effects or completely blocks the vital function of the particular metal chelated. Much attention has been paid to the development of chelating agents from natural sources to counteract lead- and iron-induced hepatic and renal damage. Sesame oil (a natural edible oil) and sesamol (an active antioxidant) are potently beneficial for treating lead- and iron-induced hepatic and renal toxicity and have no adverse effects. Sesame oil and sesamol significantly inhibit iron-induced lipid peroxidation by inhibiting the xanthine oxidase, nitric oxide, superoxide anion, and hydroxyl radical generation. In addition, sesame oil is a potent inhibitor of proinflammatory mediators, and it attenuates lead-induced hepatic damage by inhibiting nitric oxide, tumor necrosis factor-α, and interleukin-1β levels. Because metal chelating therapy is associated with adverse effects, treating heavy metal toxicity in addition with sesame oil and sesamol may be better alternatives. This review deals with the possible use and beneficial effects of sesame oil and sesamol during heavy metal toxicity treatment.

The effect of sodium selenite on lead induced cognitive dysfunction

The effect of lead (Pb) on spatial memory and hippocampal long-term potentiation (LTP) as a key risk factor has been widely recognized and the oxidative damage has been proposed as a possible mechanism of lead neurotoxicity. Selenium (Se) is a nutritionally essential trace element with known antioxidant potential. In this study we investigated the effect and the underlying mechanisms of Se supplementary on Pb induced cognition and synaptic plasticity impairment. Lactating Sprague-Dawley rats (SD rats) were randomly divided to four groups: 0ppm lead acetate (Pb); 0ppm Pb and 0.2ppm sodium selenite (Se); 100ppm Pb; 100ppm Pb and 0.2ppm Se. Lactating rats were treated with or without Pb and/or Se throughout lactation until weaning. The levels of hippocampal LTP, the spatial memory, the apoptosis of hippocampal neurons, the levels of lactate dehydrogenase (LDH) release, and the serum level of superoxide dismutase (SOD) and malondialdehyde (MDA) were assayed. It had been observed that in Pb group the spatial memory, the induce level of LTP, the serum SOD level decreased, the LDH release level, the neurons apoptosis level, the serum MDA level increased, while in the Se supplements groups, the spatial memory, the induce level of LTP increased significantly. Compared with the Pb group, Se supplements shown down regulated the level of LDH, the neurons apoptosis and the serum MDA, and up regulated the level of serum SOD. We could draw the conclusion that Se supplements could alleviate toxic effect of lead on hippocampal LTP and spatial memory. The treated with selenium around 0.2ppm may protect against spatial memory dysfunction induced by lead exposure.

Locomotor damage and brain oxidative stress induced by lead exposure are attenuated by gallic acid treatment

We investigated the antioxidant potential of gallic acid (GA), a natural compound found in vegetal sources, on the motor and oxidative damages induced by lead. Rats exposed to lead (50 mg/kg, i.p., once a day, 5 days) were treated with GA (13.5mg/kg, p.o.) or EDTA (110 mg/kg, i.p.) daily, for 3 days. Lead exposure decreased the locomotor and exploratory activities, reduced blood ALA-D activity, and increased brain catalase (CAT) activity without altering other antioxidant defenses. Brain oxidative stress (OS) estimated by lipid peroxidation (TBARS) and protein carbonyl were increased by lead. GA reversed the motor behavior parameters, the ALA-D activity, as well as the markers of OS changed by lead exposure. CAT activity remained high, possibly as a compensatory mechanism to eliminate hydroperoxides during lead poisoning. EDTA, a conventional chelating agent, was not beneficial on the lead-induced motor behavior and oxidative damages. Both GA (less) and EDTA (more) reduced the lead accumulation in brain tissue. Negative correlations were observed between the behavioral parameters and lipid peroxidation and the lead levels in brain tissue. In conclusion, GA may be an adjuvant in lead exposure, mainly by its antioxidant properties against the motor and oxidative damages resulting from such poisoning.

Clioquinol and vitamin B12 (cobalamin) synergistically rescue the lead-induced impairments of synaptic plasticity in hippocampal dentate gyrus area of the anesthetized rats in vivo

Lead (Pb(2+)) exposure in development induces impairments of synaptic plasticity in the hippocampal dentate gyrus (DG) area of the anesthetized rats in vivo. The common chelating agents have many adverse effects and are incapable of alleviating lead-induced neurotoxicity. Recently, CQ, clioquinol (5-chloro-7-iodo-8-hydroxy-quinoline), which is a transition metal ion chelator and/or ionophore with low affinity for metal ions, has yielded some promising results in animal models and clinical trials related to dysfunctions of metal ions. In addition, CQ-associated side effects are believed to be overcome with vitamin B12 (VB12) supplementation. To determine whether CQ treatment could rescue impairments of synaptic plasticity induced by chronic Pb(2+) exposure, we investigated the input/output functions (I/Os), paired-pulse reactions (PPRs) and long-term potentiation (LTP) of different treatment groups in hippocampal DG area of the anesthetized rat in vivo by recording field potentials and measured hippocampal Pb(2+) concentrations of different treatment groups by PlasmaQuad 3 inductive coupled plasma mass spectroscopy. The results show: CQ alone does not rescue the lead-induced impairments of synaptic plasticity in hippocampal DG area of the anesthetized rats in vivo; VB12 alone partly rescues the lead-induced impairments of LTP; however the co-administration of CQ and VB12 totally rescues these impairments of synaptic plasticity and moreover, the effects of CQ and VB12 co-administration are specific to the lead-exposed animals.

The dual face of endogenous alpha-aminoketones: pro-oxidizing metabolic weapons

Amino metabolites with potential prooxidant properties, particularly alpha-aminocarbonyls, are the focus of this review. Among them we emphasize 5-aminolevulinic acid (a heme precursor formed from succinyl-CoA and glycine), aminoacetone (a threonine and glycine metabolite), and hexosamines and hexosimines, formed by Schiff condensation of hexoses with basic amino acid residues of proteins. All these metabolites were shown, in vitro, to undergo enolization and subsequent aerobic oxidation, yielding oxyradicals and highly cyto- and genotoxic alpha-oxoaldehydes. Their metabolic roles in health and disease are examined here and compared in humans and experimental animals, including rats, quail, and octopus. In the past two decades, we have concentrated on two endogenous alpha-aminoketones: (i) 5-aminolevulinic acid (ALA), accumulated in acquired (e.g., lead poisoning) and inborn (e.g., intermittent acute porphyria) porphyric disorders, and (ii) aminoacetone (AA), putatively overproduced in diabetes mellitus and cri-du-chat syndrome. ALA and AA have been implicated as contributing sources of oxyradicals and oxidative stress in these diseases. The end product of ALA oxidation, 4,5-dioxovaleric acid (DOVA), is able to alkylate DNA guanine moieties, promote protein cross-linking, and damage GABAergic receptors of rat brain synaptosome preparations. In turn, methylglyoxal (MG), the end product of AA oxidation, is also highly cytotoxic and able to release iron from ferritin and copper from ceruloplasmin, and to aggregate proteins. This review covers chemical and biochemical aspects of these alpha-aminoketones and their putative roles in the oxidative stress associated with porphyrias, tyrosinosis, diabetes, and cri-du-chat. In addition, we comment briefly on a side prooxidant behaviour of hexosamines, that are known to constitute building blocks of several glycoproteins and to be involved in Schiff base-mediated enzymatic reactions.

Can antioxidants be beneficial in the treatment of lead poisoning?

Recent studies have shown that lead causes oxidative stress by inducing the generation of reactive oxygen species, reducing the antioxidant defense system of cells via depleting glutathione, inhibiting sulfhydryl-dependent enzymes, interfering with some essential metals needed for antioxidant enzyme activities, and/or increasing susceptibility of cells to oxidative attack by altering the membrane integrity and fatty acid composition. Consequently, it is plausible that impaired oxidant/antioxidant balance can be partially responsible for the toxic effects of lead. Where enhanced oxidative stress contributes to lead-induced toxicity, restoration of a cell's antioxidant capacity appears to provide a partial remedy. Several studies are underway to determine the effect of antioxidant supplementation following lead exposure. Data suggest that antioxidants may play an important role in abating some hazards of lead. To explain the importance of using antioxidants in treating lead poisoning the following topics are addressed: (i) Oxidative damage caused by lead poisoning; (ii) conventional treatment of lead poisoning and its side effects; and (iii) possible protective effects of antioxidants in lead toxicity.