Succimer and the reduction of tissue lead in juvenile monkeys

Succimer chelation does not produce lasting reductions of blood lead levels in a rodent model of retained lead fragments

Retained lead fragments from nonfatal firearm injuries pose a risk of lead poisoning. While chelation is well-established as a lead poisoning treatment, it remains unclear whether chelation mobilizes lead from embedded lead fragments. Here, we tested whether 1) DMSA/succimer or CaNa2EDTA increases mobilization of lead from fragments in vitro, and 2) succimer is efficacious in chelating fragment lead in vivo, using stable lead isotope tracer methods in a rodent model of embedded fragments. DMSA was > 10-times more effective than CaNa2EDTA in mobilizing fragment lead in vitro. In the rodent model, succimer chelation on day 1 produced the greatest blood lead reductions, and fragment lead was not mobilized into blood. However, with continued chelation and over 3-weeks post-chelation, blood lead levels rebounded with mobilization of lead from the fragments. These findings suggest prolonged chelation will increase fragment lead mobilization post-chelation, supporting the need for long-term surveillance in patients with retained fragments.

The management of embedded metal fragment patients and the role of chelation Therapy: A workshop of the Department of Veterans Affairs-Walter Reed National Medical Center

Exposure to retained metal fragments from war-related injuries can result in increased systemic metal concentrations, thereby posing potential health risks to target organs far from the site of injury. Given the large number of veterans who have retained fragments and the lack of clear guidance on how to medically manage these individuals, the Department of Veterans Affairs (VA) convened a meeting of chelation experts and clinicians who care for embedded fragment patients to discuss current practices and provide medical management guidance. Based on this group's clinical expertise and review of published literature, the evidence presented suggests that, at least in the case of lead fragments, short-term chelation therapy may be beneficial for embedded fragment patients experiencing acute symptoms associated with metal toxicity; however, in the absence of clinical symptoms or significantly elevated blood lead concentrations (greater than 80 µg/dL), chelation therapy may offer little to no benefit for individuals with retained fragments and pose greater risks due to remobilization of metals stored in bone and other soft tissues. The combination of periodic biomonitoring to assess metal body burden, longitudinal fragment imaging, and selective fragment removal when metal concentrations approach critical injury thresholds offers a more conservative management approach to caring for patients with embedded fragments.

Retained Lumbar Bullet: A Case Report of Chronic Lead Toxicity and Review of the Literature

BACKGROUND

Lead toxicity from retained bullet fragments is difficult to both predict and diagnose, but important to treat early, given the potential severity of disease. Blood lead levels > 25 μg/dL and 40 μg/dL are considered toxic in children and adults, respectively. Symptoms may range from nonspecific constitutional symptoms to seizures and coma. Chelation is the mainstay therapy for lead poisoning and levels to treat depend on patient age, blood lead levels, and the presence of symptoms. CASE 

REPORT

We present the case of a woman with symptoms of severe lead toxicity from 20-year-old retained bullet fragments. She had been seen by multiple providers for evaluation of each symptom, but a unifying diagnosis had not been found. After identifying this complication, she was treated appropriately and more serious complications were prevented. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: We present this case to increase awareness among emergency physicians of lead toxicity in patients with a seemingly unrelated constellation of symptoms and a history of a previous gunshot wound with retained bullet or bullet fragments.

Chemoprotective effect of monoisoamyl 2, 3-dimercaptosuccinate (MiADMS) on cytokines expression in cadmium chloride treated human lung cells

Cadmium is commercially profitable element, but it causes toxicity in humans and animals leading to diseases in various organs. The main route of cadmium exposure to humans is through inhalation. Lungs respond to insult through secretion of cytokines. In this study, the chemoprotective effect of monoisoamyl 2, 3-dimercaptosuccinate (MiADMS) was evaluated on viability and cytokines expression in CdCl2 treated human lung A549 cells by cytokine array. Cells were treated with 0, 50, 75, and 100 µM CdCl2 alone, 300 µM MiADMS alone, and co-treated with 300 µM MiADMS and 75 µM CdCl2 for 24 h. The viability was measured by crystal violet dye. The level of cytokines in the cells' lysate and cell culture medium was measured using Ray Biotech's Human Cytokine Array 6 in control cells, 75 µM CdCl2 alone and MiADMS co-treated cells. Array results were validated by ELISA kit. The CdCl2 caused a dose dependent decrease in cell viability, while MiADMS co-treatment resulted in a significant increase in viability of CdCl2 treated cells. Morphology of the cells treated with CdCl2 was destroyed, while MiADMS restored the lost shape in CdCl2 treated cells. In addition, the cells co-treated with MiADMS and CdCl2 showed modulation of cytokines expression in comparison to the CdCl2 alone treated cells. The ELISA results showed the similar pattern of cytokine expression as Human Cytokine Array and validated the array results. These results clearly show the chemoprotective effect of MiADMS and suggest that MiADMS can be used as antidote at moderate dose against CdCl2 toxicity.

The scientific basis for chelation: animal studies and lead chelation

This presentation summarizes several of the rodent and non-human studies that we have conducted to help inform the efficacy and clinical utility of succimer (meso-2,3-dimercaptosuccincinic acid) chelation treatment. We address the following questions: (1) What is the extent of body lead, and in particular brain lead reduction with chelation, and do reductions in blood lead accurately reflect reductions in brain lead? (2) Can succimer treatment alleviate the neurobehavioral impacts of lead poisoning? And (3) does succimer treatment, in the absence of lead poisoning, produce neurobehavioral deficits? Results from our studies in juvenile primates show that succimer treatment is effective at accelerating the elimination of lead from the body, but chelation was only marginally better than the complete cessation of lead exposure alone. Studies in lead-exposed adult primates treated with a single 19-day course of succimer showed that chelation did not measurably reduce brain lead levels compared to vehicle-treated controls. A follow-up study in rodents that underwent one or two 21-day courses of succimer treatment showed that chelation significantly reduced brain lead levels, and that two courses of succimer were significantly more efficacious at reducing brain lead levels than one. In both the primate and rodent studies, reductions in blood lead levels were a relatively poor predictor of reductions in brain lead levels. Our studies in rodents demonstrated that it is possible for succimer chelation therapy to alleviate certain types of lead-induced behavioral/cognitive dysfunction, suggesting that if a succimer treatment protocol that produced a substantial reduction of brain lead levels could be identified for humans, a functional benefit might be derived. Finally, we also found that succimer treatment produced lasting adverse neurobehavioral effects when administered to non-lead-exposed rodents, highlighting the potential risks of administering succimer or other metal-chelating agents to children who do not have elevated tissue lead levels. It is of significant concern that this type of therapy has been advocated for treating autism.

Stable lead isotopes in environmental health with emphasis on human investigations

There has been widespread use of stable lead isotopes in the earth sciences for more than 40 years focussed on the origin and age of rocks and minerals with lesser application in environmental investigations where the emphasis has been directed typically to the source of lead in environmental media such as air, water and soils. In contrast, the number of environmental health investigations focussed on humans (and primates) is limited in spite of the demonstrated utility of the approach in pioneering studies in the early 1970's. This paper reviews the status of lead isotopes in human investigations especially over the past 2 decades, the period over which most activity has taken place. Following a brief introduction to the method, examples are provided illustrating the use of lead isotopes in a wide spectrum of activities including sources and pathways of lead in diverse environments from urban to mining communities, various applications associated with pregnancy, the contribution of bone lead to blood lead including in the elderly, the half-life of lead in blood, and lead in bones and other media. A brief outline of critical research on non-human primates is also given. The lead isotope method is a powerful technique for tracing lead and could be employed more widely in human investigations.

Response of lead-induced oxidative stress and alterations in biogenic amines in different rat brain regions to combined administration of DMSA and MiADMSA

The present study was planned to investigate if combined administration of meso-2,3-dimercaptosuccinic acid (DMSA) and monoisoamyl DMSA (MiADMSA) could achieve better recovery in the altered biochemical parameters suggestive of brain oxidative stress and depletion of lead from blood and brain following acute lead exposure. Male Wistar rats were exposed to lead nitrate (50 mg/kg, i.p., once daily for 5 days) followed by treatment with the above chelating agents using two different doses of 25 or 50 mg/kg (orally) either alone and in combination once daily for five consecutive days. Lead exposure resulted in the significant inhibition of delta-aminolevulinic acid dehydratase activity and depletion of glutathione (GSH) in blood. These changes were accompanied by significant reduction in blood hemoglobin, RBC levels and superoxide dismutase and catalase activities. Significant increase in blood reactive oxygen species (ROS) and thiobarbituric acid reactive substances (TBARS) levels were noted. We observed marked increase in brain ROS level while GSH/oxidized glutathione ratio showed significant decrease accompanied by a significant increase in blood and brain lead concentration. The levels of norepinephrine, dopamine and serotonin in different brain regions were also altered on lead exposure. Co-administration of DMSA and MiADMSA particularly at the lower dose was most effective in the recovery of lead-induced changes in the hematological variables and oxidative stress and resulted in more pronounced depletion of lead from blood and brain compared to monotherapy with these chelators. On the other hand, combined administration of MiADMSA (50 mg/kg) in combination with DMSA (25 mg/kg each) had additional beneficial effect over the individual effect of chelating agent in the recovery of altered levels of brain biogenic amines. The study suggests that administration of MiADMSA is generally a better lead chelator than DMSA while combined administration of DMSA and MiADMSA might be a better treatment option compared to monotherapy at least in the removal of lead from the target tissues.

Reversal of lead-induced neuronal apoptosis by chelation treatment in rats: role of reactive oxygen species and intracellular Ca(2+)

Lead, a ubiquitous and potent neurotoxicant causes several neurophysiological and behavioral alterations. Toxic properties of lead have been attributed to its capability to mimic calcium and alter calcium homeostasis. In this study, we have addressed the following issues: 1) whether chelation therapy could circumvent the altered Ca(2+) homeostasis and prevent neuronal death in chronic lead-intoxicated rats, 2) whether chelation therapy could revert altered biochemical and behavioral changes, 3) whether combinational therapy using two different chelating agents was more advantageous over monotherapy in lead-treated rats, and 4) what could be the mechanism of neuronal apoptosis. Results indicated that lead caused a significant increase in reactive oxygen species, neuronal nitric-oxide synthetase, and intracellular free calcium levels along with altered behavioral abnormalities in locomotor activity, exploratory behavior, learning, and memory that were supported by changes in neurotransmitter levels. A fall in membrane potential, release of cytochrome c, and altered bcl(2)/bax ratio indicated mitochondrial-dependent apoptosis. Most of these alterations reverted toward normal level following combination therapy over monotherapy with calcium disodium EDTA (CaNa(2)EDTA) or monoisoamyl meso-2,3-dimercaptosuccinic acid (MiADMSA). It could be concluded from our present results that combined therapy with CaNa(2)EDTA and MiADMSA might be a better treatment protocol than monotherapy with these chelators in lead-induced neurological disorders. We for the first time report the role of Ca(2+) in regulating neurological dystrophy caused by chronic lead exposure in rats and its recovery with a two-course treatment regime of mono or combination therapy.

Succimer chelation normalizes reactivity to reward omission and errors in lead-exposed rats

This study evaluated the efficacy of a 3-week course of succimer treatment to alleviate behavioral deficits in rats exposed to lead (Pb) for the first 4 weeks of life. A 3 x 2 factorial design was used: three levels of lead exposure (No Pb, Moderate, and High Pb) and two levels of chelation (succimer or vehicle). Behavioral testing was conducted following chelation therapy, from 2 to 9 months of age; this report presents the results of two of the administered tasks: (1) a conditional olfactory discrimination task (baseline task), and (2) a conditional olfactory discrimination task with periodic reward omission on some correct trials (RO task). In the RO task, the performance disruption produced by committing an error on the previous trial was significantly greater for both unchelated lead-exposed groups than for controls. The High Pb rats were also more sensitive to reward omission than controls, providing converging evidence for impaired regulation of arousal or emotion. Importantly, succimer treatment was effective in normalizing the heightened reactivity of the lead-exposed animals to both errors and reward omission. In addition, non-lead-exposed rats that were treated with succimer tended to be more affected by a prior error than controls in their latency to respond on post-error trials. In sum, these findings provide new evidence that succimer chelation can significantly lessen the lasting neurobehavioral dysfunction produced by early lead exposure, but also suggest that there may be risks of administering the drug to individuals without elevated blood lead levels.

Succimer chelation improves learning, attention, and arousal regulation in lead-exposed rats but produces lasting cognitive impairment in the absence of lead exposure

BACKGROUND

There is growing pressure for clinicians to prescribe chelation therapy at only slightly elevated blood lead levels. However, very few studies have evaluated whether chelation improves cognitive outcomes in Pb-exposed children, or whether these agents have adverse effects that may affect brain development in the absence of Pb exposure.

OBJECTIVES

The present study was designed to answer these questions, using a rodent model of early childhood Pb exposure and treatment with succimer, a widely used chelating agent for the treatment of Pb poisoning.

RESULTS

Pb exposure produced lasting impairments in learning, attention, inhibitory control, and arousal regulation, paralleling the areas of dysfunction seen in Pb-exposed children. Succimer treatment of the Pb-exposed rats significantly improved learning, attention, and arousal regulation, although the efficacy of the treatment varied as a function of the Pb exposure level and the specific functional deficit. In contrast, succimer treatment of rats not previously exposed to Pb produced lasting and pervasive cognitive and affective dysfunction comparable in magnitude to that produced by the higher Pb exposure regimen.

CONCLUSIONS

These are the first data, to our knowledge, to show that treatment with any chelating agent can alleviate cognitive deficits due to Pb exposure. These findings suggest that it may be possible to identify a succimer treatment protocol that improves cognitive outcomes in Pb-exposed children. However, they also suggest that succimer treatment should be strongly discouraged for children who do not have elevated tissue levels of Pb or other heavy metals.

Low-level manganese exposure alters glutamate metabolism in GABAergic AF5 cells

Recent studies have suggested that the globus pallidus may be a particularly sensitive target of manganese (Mn), however, in vitro studies of the effects of Mn on GABAergic neurons have been restricted by the lack of a cell model expressing GABAergic properties. Here, we investigated the effects of low-level Mn treatment on cellular GABA and glutamate metabolism using the newly characterized AF5 rat neural-derived cell line, which displays GABAergic properties during culture in vitro. Intracellular GABA and glutamate levels were measured along with measurement of the release of GABA and glutamate into the culture medium, glutamine uptake from the culture medium, and the specific effects of Mn on the enzymes directly responsible for the synthesis and degradation of GABA, glutamate decarboxylase (GAD) and GABA transaminase (GABA-T). Our results demonstrate that Mn had no effect on the activities of GAD or GABA-T. Similarly, low-level Mn treatment of AF5 cultures had only a small effect on intracellular GABA levels (114% of control) and no effect on the release of GABA. In contrast, intracellular and extracellular glutamate levels were enhanced to 170 and 198% of control during Mn treatment, respectively, while extracellular glutamine decreased to 73% of controls. Together, these results suggest that glutamate homeostasis may be preferentially affected over GABA in AF5 cells during low-level Mn treatment, suggesting a novel mechanism by which Mn-induced excitotoxicity might arise.

Temporal responses in the disruption of iron regulation by manganese

Manganese (Mn) is an essential trace element, though at elevated exposures it is also a neurotoxicant. Several mechanisms underlying manganese toxicity have been investigated, although a consistent mechanism(s) of action at low exposures has not been fully elucidated. Here we systematically evaluated the effects of in vitro manganese exposure on intracellular iron (Fe) homeostasis and iron-regulatory protein (IRP) binding activity in undifferentiated PC12 cells over a range of manganese exposure concentrations (1, 10, 50, and 200 microM MnCl(2)) and exposure durations (12, 24, 36, and 48 hr), to test the hypothesis that moderately elevated manganese exposure disrupts cellular iron regulation. Results demonstrate that manganese exposure produces a rapid and sustained dose-dependent dysregulation of cellular iron metabolism, with effects occurring as early as 12 hr exposure and at manganese doses as low as 1 microM. Manganese exposure altered the dynamics of IRP-1 binding and the intracellular abundance of IRP-2, and altered the cellular abundance of transferrin receptor, ferritin, and mitochondrial aconitase protein levels. Cellular levels of labile iron were significantly increased with manganese exposure, although total cellular iron levels were not. The overall pattern of effects shows that manganese produced an inappropriate cellular response akin to iron deficiency, to which the cells were able to mount a compensatory response. Consistent with our previous studies, these data indicate that even low to moderate exposures to Manganese in vitro significantly disrupt cellular iron metabolism, which may be an important contributory mechanism of manganese neurotoxicity.

Monensin improves the effectiveness of meso-dimercaptosuccinate when used to treat lead intoxication in rats

Among divalent cations, the ionophore monensin shows high activity and selectivity for the transport of lead ions (Pb2+) across phospholipid membranes. When coadministered to rats that were receiving meso-dimercaptosuccinate for treatment of Pb intoxication, monensin significantly increased the amount of Pb removed from femur, brain, and heart. It showed a tendency to increase Pb removal from liver and kidney but had no effect of this type in skeletal muscle. Tissue levels of several physiologic (calcium, cobalt, copper, iron, magnesium, manganese, molybdenum, zinc) and nonphysiologic (arsenic, cadmium, chromium, nickel, strontium) elements were also determined after the application of these compounds. Among the physiologic elements, a number of significant changes were seen, including both rising and falling values. The size of these changes was typically around 20% compared with control values, with the largest examples seen in femur. These changes often tended to reverse those of similar size that had occurred during Pb administration. Among the nonphysiologic elements, which were present in trace amounts, the changes were smaller in number but larger in size. None of these changes appears likely to be significant in terms of toxicity, and there were no signs of overt toxicity under any of the conditions employed. Monensin may act by cotransporting Pb2+ and OH- ions out of cells, in exchange for external sodium ions. The net effect would be to shuttle intracellular Pb2+ to extracellular dimercaptosuccinic acid thereby enhancing its effectiveness. Thus, monensin may be useful for the treatment of Pb intoxication when applied in combination with hydrophilic Pb2+ chelators.

Efficacy of iron and/or zinc supplementation on cognitive performance of lead-exposed Mexican schoolchildren: a randomized, placebo-controlled trial

OBJECTIVE

Lead exposure in children has been associated with both global and specific cognitive deficits. Although chelation therapy is advised for children with blood lead concentrations of >44 microg/dL, treatment options for children with lower blood lead values are limited. Because lead absorption is related to children's nutritional status, micronutrient supplements may be 1 strategy for combating low-level, chronic lead exposure. This study was designed to test the efficacy of iron and zinc supplementation for lowering blood lead concentrations and improving cognitive performance in schoolchildren who live in a lead-contaminated city.

METHODS

This randomized, double-blind, placebo-controlled field trial was conducted in public elementary schools in Torreón, an industrialized city in northern Mexico. A metal foundry, located close to the city center and within 3.5 km of 9 schools, was the main source of lead exposure. A total of 602 children who were aged 6 to 8 years and regularly attending first grade in the study schools were enrolled. Children were given 30 mg of iron, 30 mg of zinc, both, or a placebo daily for 6 months. A total of 527 completed the treatment, and 515 were available for long-term follow-up, after another 6 months without supplementation. Eleven cognitive tests of memory, attention, visual-spatial abilities, and learning were administered at baseline and each follow-up.

RESULTS

There were no consistent or lasting differences in cognitive performance among treatment groups.

CONCLUSIONS

Daily supplementation with iron and/or zinc may be of limited usefulness for improving cognition in lead-exposed schoolchildren. However, these treatments may be effective in settings with higher prevalence of nutritional deficiencies or in younger children.

Effect of chelation therapy on the neuropsychological and behavioral development of lead-exposed children after school entry

OBJECTIVE

Some children in the United States continue to be exposed to levels of lead that increase their risk for lowered intellectual functioning and behavior problems. It is unclear whether chelation therapy can prevent or reverse the neurodevelopmental sequelae of lead toxicity. The objective of this study was to determine whether chelation therapy with succimer (dimercaptosuccinic acid) in children with referral blood lead levels between 20 and 44 microg/dL (0.96-2.12 micromol/L) at 12 to 33 months of age has neurodevelopmental benefits at age 7 years.

METHODS

The Treatment of Lead-Exposed Children (TLC) study is a randomized, double-blind, placebo-controlled trial that was conducted between September 1994 and June 2003 in Philadelphia, PA; Newark, NJ; Cincinnati, OH; and Baltimore, MD. Of 1854 referred children who were between the ages of 12 to 33 months and screened for eligibility, 780 were randomized to the active drug and placebo groups stratified by clinical center, body surface area, blood lead level, and language spoken at home. At 7 years of age, 647 subjects remained in the study. Participants were randomly assigned to receive oral succimer or placebo. Up to 3 26-day courses of succimer or placebo therapy were administered depending on response to treatment in those who were given active drug. Eighty-nine percent had finished treatment by 6 months, with all children finishing by 13 months after randomization. All participants received residential lead hazard control measures before treatment. TLC subjects also received a daily multivitamin supplement before and after treatment(s) with succimer or placebo. Scores on standardized neuropsychological measures that tap cognition, behavior, learning and memory, attention, and neuromotor skills were measured.

RESULTS

Chelation therapy with succimer lowered average blood lead levels for approximately 6 months but resulted in no benefit in cognitive, behavioral, and neuromotor endpoints.

CONCLUSION

These new follow-up data confirm our previous finding that the TLC regimen of chelation therapy is not associated with neurodevelopmental benefits in children with blood lead levels between 20 and 44 microg/dL (0.96-2.17 micromol/L). These results emphasize the importance of taking environmental measures to prevent exposure to lead. Chelation therapy with succimer cannot be recommended for children with blood lead levels between 20 and 44 microg/dL (0.96-2.12 micromol/L).

Effects of calcium disodium EDTA and meso-2,3-dimercaptosuccinic acid on tissue concentrations of lead for use in treatment of calves with experimentally induced lead toxicosis

OBJECTIVE

To compare the efficacy of calcium disodium EDTA (CaNa2EDTA) and meso-2,3-dimercaptosuccinic acid (DMSA) in reducing concentrations of lead in selected tissues for use in treatment of calves with experimentally induced lead toxicosis.

ANIMALS

19 sexually intact male Holstein calves that weighed 35 to 60 kg.

PROCEDURE

Calves were randomly assigned to 1 of 5 treatment groups: group 1, control calves; group 2, lead only; group 3, lead and EDTA; group 4, lead and DMSA; and group 5, lead, EDTA, and DMSA. Calves in groups 2 to 5 were dosed daily with lead (5 mg/kg, PO) for 10 days. Doses of EDTA (100 mg/kg) and DMSA (25 mg/kg) were administered IV once daily for 4 consecutive days beginning on day 11. Effects of the chelators on lead concentrations in the liver, kidneys, testes, muscles, bones, and brain were compared among the various groups.

RESULTS

Compared with the effects of EDTA, DMSA greatly reduced lead concentrations in renal and hepatic tissues. We did not detect significant differences for the effects of EDTA or DMSA on lead concentrations in the testes; there was an adverse interaction of EDTA with DMSA that caused an increase in lead concentrations in the testes.

CONCLUSIONS AND CLINICAL RELEVANCE

DMSA is much more effective than EDTA in removing lead from renal and hepatic tissues in calves. Use of DMSA in calves with lead intoxication appears to be a viable treatment option. Combining DMSA and EDTA as a treatment modality in calves did not offer any advantages.

Alterations in cellular IRP-dependent iron regulation by in vitro manganese exposure in undifferentiated PC12 cells

Manganese (Mn) may interfere with iron regulation by altering the binding of iron regulatory proteins (IRPs) to their response elements found on the mRNA encoding proteins critical to iron homeostasis. To explore this, the effects of 24-h in vitro manganese exposure (1, 10, 50, and 200 microM Mn) on: (i) total intracellular and labile iron concentrations; (ii) the cellular abundance of transferrin receptor (TfR), H- and L-ferritin, and mitochondrial aconitase proteins; and (iii) IRP binding to a [32P](-) labeled mRNA sequence of L-ferritin were evaluated in undifferentiated PC12 cells. In vitro manganese exposure altered the cellular abundance of TfR, H-/L-ferritin, and m-aconitase, resulting in an increase in labile iron. This latter effect led to a decrease in IRP binding activity at the lower (10 and 50 microM) manganese exposures. In contrast, 200 microM manganese exposure increased IRP binding, in spite of the significant increase in labile iron. These data indicate that at lower exposures, manganese directly interfered with IRP-dependent translational events, producing an increase in labile iron, which in turn signaled a decrease in IRP binding at 24 h. At higher exposures, the intracellular burden of manganese resulted in overt cytotoxicity and appeared to compromise the normal compensatory response to increased labile iron, producing increased IRP binding. We conclude that low to moderate manganese exposure interferes with cellular iron regulation, and thus may serve as a contributory mechanism underlying manganese neurotoxicity.

Elevated blood lead resulting from maxillofacial gunshot injuries with lead ingestion

PURPOSE

The purpose of this study was to identify the contribution of ingested lead particles to elevated blood lead concentrations in victims of gunshot injury to the maxillofacial region.

PATIENTS AND METHODS

As part of a larger study of the effects of retained lead bullets on blood lead, a retrospective review of study findings was completed on 5 of 8 patients who sustained injuries to the maxillofacial region. These 5 patients were recruited into the larger study within 11 days of injury and showed a penetration path for the projectile that engaged the upper aerodigestive tract. All subjects were recruited from patients presenting for care of their gunshot injuries to a large inner-city trauma center with a retained bullet resulting from a gunshot injury. An initial blood lead level was measured for all recruited patients and repeated 1 to 17 weeks later. Medical history was taken along with a screening and risk factor questionnaire to determine other potential or actual sources (occupational/recreational) of lead exposure. (109)Cd K-shell x-ray fluorescence determinations of bone lead were completed to determine past lead exposure not revealed by medical history and risk factor questionnaire. Radiographs taken of the abdomen and chest, required as a part of the patient's hospital care, were retrospectively reviewed for signs of metallic fragments along the aerodigestive tract.

RESULTS

All 5 patients retained multiple lead pellets or fragments at the site of injury, sustained fractures of the facial bones, and showed increases in blood lead. Three of the 5 study subjects who sustained maxillofacial gunshot injuries involving the mouth, nose, or throat region showed metallic densities along the gastrointestinal tract indicative of ingested bullet fragments. Each patient with ingested bullet fragments showed rapid elevation of blood lead exceeding 25 microg/dL and sustained increases well beyond the time when all ingested fragments were eliminated. A 3-year follow-up on these 3 patients showed significantly sustained elevation of blood lead but less than that observed during the initial 6 months after injury. None of the 5 study subjects showed any evidence of metallic foreign bodies within the tracheobronchial regions indicative of aspiration.

CONCLUSION

Ingestion of lead fragments can result from gunshot injuries to the maxillofacial region and may substantially contribute to a rapid increase in blood lead level. Prompt diagnosis and elimination of ingested lead fragments are essential steps necessary to prevent lead being absorbed from the gastrointestinal tract. Increased blood lead in victims after gunshot injuries must be fully evaluated for all potential sources, including recent environmental exposure, absorption of lead from any remaining bullets in body tissues, and the possibility of mobilization of lead from long-term body stores such as bone.

Effects of dietary lead and/or dimercaptosuccinic acid exposure on regional serotonin and serotonin metabolite content in rainbow trout (Oncorhynchus mykiss)

The lead (Pb) chelator, meso-2,3-dimercaptosuccinic acid (DMSA) may be effective in reversing some of the adverse effects of Pb exposure. Pb-induced behavioral deficits observed in fish are due to disruptions in the integrative functioning of the medulla, cerebellum, and optic tectum. Pb exposure increased serotonin (5-HT) content in all three brain regions without an effect on 5-hydroxy-3-indoleacetic acid (5-HIAA). Pb exposure followed by no Pb in the diet increased 5-HT and 5-HIAA content in all three brain regions. The replacement of dietary Pb with DMSA had no effect on 5-HT and increased 5-HIAA content. DMSA increased 5-HIAA content in all three brain regions and increased 5-HT content only the optic tectum. Treatment with DMSA may be more effective than removal of Pb from the diet in reversing Pb-induced alterations in 5-HT.

Reversal of lead-induced oxidative stress by chelating agent, antioxidant, or their combination in the rat

The influence of N-acetyl cysteine (NAC), an antioxidant, on the therapeutic efficacy of meso-2,3-dimercaptosuccinic acid (DMSA), a hydrophilic, and its ester, monoisoamyl 2,3-dimercaptosuccinate (MiADMS), a lipophilic, both soft tissue lead mobilizers, was investigated in lead-preexposed rats. The subsequent treatment of lead-exposed animals with DMSA, MiADMS, or NAC reversed the lead-induced alterations in blood delta-aminolevulinic acid dehydratase, catalase, malondialdehyde (MDA), reduced glutathione, oxidized glutathione, and brain MDA levels. The combined treatment with DMSA and NAC was more effective than that with MiADMS and NAC in enhancing the restoration of all these parameters indicative of lead-induced oxidative stress. These reversals were consistent with the lead-removing ability of DMSA and MiADMS but not that of NAC. As the reversal of these parameters by NAC was independent of its lead-mobilizing capability, this ought to be mainly due to its strong antioxidant property. The increase in blood and brain zinc levels upon lead exposure appears to be the result of the redistribution of endogenous zinc due to lead. Subsequent treatment with DMSA, MiADMS, NAC, or their combination decreased the brain zinc as its excretable complexes with a transient increase in blood zinc level. The ideal treatment of lead poisoning seems to be a combination of a lead chelator and an antioxidant.