Diagnostic chelation challenge with DMSA: a biomarker of long-term mercury exposure?

Failure of chelator-provoked urine testing results to predict heavy metal toxicity in a prospective cohort of patients referred for medical toxicology evaluation

INTRODUCTION

Provoked urine testing (PUT), involving chelating agent administration prior to measuring urine metal excretion levels, is used by some alternative health care practitioners to diagnose patients with heavy metal poisoning. Multiple medical societies have advised against this practice due to its presumed unreliability, expense, and lack of validation. However, no prospective study of the predictive value of PUT for heavy metal poisoning has been undertaken.

METHODS

This study utilized the Toxicology Consortium's prospective case registry to evaluate the reliability of PUT for diagnosing heavy metal poisoning. Inclusion criteria were toxicology clinic patients with PUT results who were subsequently evaluated by a board-certified medical toxicologist and had a determination made regarding whether their signs and symptoms were likely related or unrelated to toxicologic exposures. The primary outcome was the positive predictive value of PUT for heavy metal toxicity as diagnosed by the evaluating medical toxicologist. Patients presenting to participating toxicology clinics without PUT served as a comparison group.

RESULTS

74 of 106 cases presenting with PUT results met inclusion criteria and were analyzed. 15 cases were determined by the examining toxicologist to be likely related to a toxicologic exposure. Only three cases were found to be related to heavy metal exposure, giving a positive predictive value of 4.3%. 20.2% of patients with PUT were found to have signs or symptoms related to any toxicologic exposure, compared to 14.3% of clinic patients without PUT. Demographics of toxicology clinic patients with and without PUT results were not significantly different except for age.

DISCUSSION

Our results provide empiric support that PUT is an inaccurate predictor of a diagnosis of heavy metal poisoning by a board-certified medical toxicologist. Given the inability to properly interpret PUT results along with the increased cost burden and risk of false positives, PUT should not be performed.

Laboratory tests commonly used in complementary and alternative medicine: a review of the evidence

It is increasingly easy for the general public to access a wide range of laboratory tests. Tests can be ordered online with little or no input from a health professional. The complementary and alternative medicine (CAM) community promote and sell a wide range of tests, many of which are of dubious clinical significance. Many have little or no clinical utility and have been widely discredited, whilst others are established tests that are used for unvalidated purposes. They range from the highly complex, employing state of the art technology, e.g. heavy metal analysis using inductively coupled plasma-mass spectrometry, to the rudimentary, e.g. live blood cell analysis. Results of 'CAM tests' are often accompanied by extensive clinical interpretations which may recommend, or be used to justify, unnecessary or harmful treatments. There are now a small number of laboratories across the globe that specialize in CAM testing. Some CAM laboratories operate completely outside of any accreditation programme whilst others are fully accredited to the standard of established clinical laboratories. In this review, we explore CAM testing in the United States, the United Kingdom and Australia with a focus on the common tests on offer, how they are reported, the evidence base for their clinical application and the regulations governing their use. We will also review proposed changed to in-vitro diagnostic device regulations and how these might impact on CAM testing.

Fluorescent theranostic agents for Hg2+detection and detoxification treatment

Two novel small-molecule based theranostic agents encompassing the dual functions of detection and detoxification of mercury ion poisoning are developed.

Clinical description of toxic neuropathies

Toxic neuropathy, although rare, is an important consideration in the setting of a known or suspected toxic exposure in the workplace or other environment. This chapter discusses the clinical and electrodiagnostic evaluation of peripheral neuropathies, highlighting findings that direct further workup and may point to specific toxins as etiology. The difficulty of establishing causality of a toxin in relation to peripheral neuropathy is discussed; guidelines for establishing causality are presented. Examples of common industrial toxins are listed, including their typical industrial uses and their mechanisms of action in producing neuropathy. Characteristic clinical presentations of specific toxic neuropathies are highlighted with selected case studies.

Recommendations for provoked challenge urine testing

"Urine mobilization test," "challenge test," and "provoked urine test" are all terms used to describe the administration of a chelating agent to a person prior to collection of their urine to test for metals. There is no standard, validated challenge test. Despite recommendations by professional and government organizations against the use of provoked urine testing, the tests are still commonly used and recommended by some practitioners. Challenge testing utilizes a variety of chelating agents, including dimercaptosuccinic acid (DMSA), dimercaptopropanesulfonate (DMPS), and ethylenediaminetetraacetic acid (EDTA). The agents are given by a variety of routes of administration, doses used are inconsistent, and urine collection procedures vary. Additional problems with challenge tests include comparison of results to inappropriate reference ranges and creatinine correction of urine obtained within hours of chelator administration. Human volunteer studies demonstrate that mercury is detected in the urine of most people even in the absence of known exposure or chelator administration, and that urinary mercury excretion rises after administration of a chelator, regardless of exposure history and in an unpredictable fashion. Studies also demonstrate that challenge testing fails to reveal a "body burden" of mercury due to remote exposure. Chelating agents have been associated with adverse reactions. Current evidence does not support the use of DMPS, DMSA, or other chelation challenge tests for the diagnosis of metal toxicity. Since there are no established reference ranges for provoked urine samples in healthy subjects, no reliable evidence to support a diagnostic value for the tests, and potential harm, these tests should not be utilized.

Heavy metal chelation in neurotoxic exposures

Metals such as iron and copper are critical to living organisms, whereas other metals such as lead and arsenic have no known biologic role. Any metals in large amounts may cause toxicity. Many metals cause pervasive systemic effects involving the nervous system, which can be subtle in some cases. Although challenging, the diagnosis and treatment of metal poisoning can be made based on history, physical examination, and the proper use of metal testing. This article focuses on the use, and misuse, of chelation in the diagnosis and management of metal intoxication.

Urine mercury excretion following meso-dimercaptosuccinic acid challenge in fish eaters

CONTEXT

Public awareness of methylmercury in fish has caused patients to seek testing for mercury poisoning. In some patients, the diagnosis of mercury poisoning has been made based on urine mercury excretions following oral dosing of meso-dimercaptosuccinic acid (DMSA), a metal chelator. However, studies comparing urine mercury excretion following DMSA in healthy non-fish eaters with healthy fish eaters could not be located.

OBJECTIVES

To describe urinary mercury excretion before and after DMSA in healthy fish eaters and non-fish eaters, and to determine whether urine mercury excretion after DMSA would rise above baseline levels to a greater extent in fish eaters.

DESIGN

A total of 24 healthy physicians were assigned to 1 of 3 groups based on fish consumption: non-fish eaters; 1 to 2 fish servings per week; and 3 or more servings per week. Blood mercury concentrations and 12-hour urine mercury and creatinine excretions were measured before and after oral ingestion of 30 mg of DMSA per kilogram of body weight.

RESULTS

A total of 24 subjects completed the study, and 2 subsequently were excluded. No difference in baseline urinary mercury excretion was detected between groups. All groups demonstrated an increase in urinary mercury excretion following DMSA, which was higher in fish eaters (P = .04). Multiple linear regression found that the best predictor of a rise in urine mercury excretion following DMSA challenge was the prechelation blood mercury concentration.

CONCLUSIONS

In this study of healthy physicians, oral DMSA produced a rise in urine mercury excretion both in non-fish eaters and fish eaters. The increase in chelated mercury excretion was higher in fish eaters. A simple rise in chelated mercury excretion over baseline excretion is not a reliable diagnostic indicator of mercury poisoning.

N-acetylcysteine as a potential antidote and biomonitoring agent of methylmercury exposure

BACKGROUND

Many people, by means of consumption of seafood or other anthropogenic sources, are exposed to levels of methylmercury (MeHg) that are generally considered to be quite low, but that may nevertheless produce irreversible brain damage, particularly in unborn babies. The only way to prevent or ameliorate MeHg toxicity is to enhance its elimination from the body.

OBJECTIVES

Using N-acetylcysteine (NAC), we aimed to devise a monitoring protocol for early detection of acute exposure or relatively low MeHg levels in a rodent model, and to test whether NAC reduces MeHg levels in the developing embryo.

RESULTS

NAC produced a transient, dose-dependent acceleration of urinary MeHg excretion in rats of both sexes. Approximately 5% of various MeHg doses was excreted in urine 2 hr after injection of 1 mmol/kg NAC. In pregnant rats, NAC markedly reduced the body burden of MeHg, particularly in target tissues such as brain, placenta, and fetus. In contrast, NAC had no significant effect on urinary MeHg excretion in preweanling rats.

CONCLUSIONS

Because NAC causes a transient increase in urinary excretion of MeHg that is proportional to the body burden, it is promising as a biomonitoring agent for MeHg in adult animals. In view of this and because NAC is effective at enhancing MeHg excretion when given either orally or intravenously, can decrease brain and fetal levels of MeHg, has minimal side effects, and is widely available in clinical settings, NAC should be evaluated as a potential antidote and biomonitoring agent in humans.

Molecular mechanisms triggered by mercury

Mercury is an ubiquitous environmental toxin that causes a wide range of adverse health effects in humans. Three forms of mercury exist: elemental, inorganic and organic. Each of them has its own profile of toxicity. Exposure to mercury typically occurs by inhalation or ingestion. Mercury can be an indoor air pollutant, however industry emission remains the most important source of inhaled mercury. Furthermore, fresh water and ocean fish may contain large amounts of mercury and dental amalgam can be another important source of inorganic and mercury vapor. The present review discusses the current information on mercury toxicity and the distinct toxicologic profile of the three forms of mercury. The existing therapeutics, new therapeutics development or agents for treating mercury poisoning will also discussed. Since in general low levels of mercurial are tolerable, herein, we also discuss the defensive mechanisms developed by the cell to protect itself against mercury injury. This aspect may be useful to provide a biological protection against toxic effects exerted by mercury or by specific forms of mercury in view of a medicinal purposes.

The role of thiols, dithiols, nutritional factors and interacting ligands in the toxicology of mercury

Mercury has been a known as a toxic substance for centuries. Whilst the clinical features of acute mercury poisoning have been well described, chronic low dose exposure to mercury remains poorly characterised and its potential role in various chronic disease states remains controversial. Low molecular weight thiols, i.e. sulfhydryl containing molecules such as cysteine, are emerging as important factors in the transport and distribution of mercury throughout the body due to the phenomenon of "Molecular Mimicry" and its role in the molecular transport of mercury. Chelation agents such as the dithiols sodium 2,3-dimercaptopropanesulfate (DMPS) and meso-2,3-dimercaptosuccinic acid (DMSA) are the treatments of choice for mercury toxicity. Alpha-lipoic acid (ALA), a disulfide, and its metabolite dihydrolipoic acid (DHLA), a dithiol, have also been shown to have chelation properties when used in an appropriate manner. Whilst N-acetyl-cysteine (NAC) and glutathione (GSH) have been recommended in the treatment of mercury toxicity in the past, an examination of available evidence suggests these agents may in fact be counterproductive. Zinc and selenium have also been shown to exert protective effects against mercury toxicity, most likely mediated by induction of the metal binding proteins metallothionein and selenoprotein-P. Evidence suggests however that the co-administration of selenium and dithiol chelation agents during treatment may also be counter-productive. Finally, the issue of diagnostic testing for chronic, historical or low dose mercury poisoning is considered including an analysis of the influence of ligand interactions and nutritional factors upon the accuracy of "chelation challenge" tests.

Lead and mercury exposures: interpretation and action

Lead and mercury are naturally occurring elements in the earth's crust and are common environmental contaminants. Because people concerned about possible exposures to these elements often seek advice from their physicians, clinicians need to be aware of the signs and symptoms of lead and mercury poisoning, how to investigate a possible exposure and when intervention is necessary. We describe 3 cases of patients who presented to an occupational medicine specialist with concerns of heavy metal toxicity. We use these cases to illustrate some of the issues surrounding the investigation of possible lead and mercury exposures. We review the common sources of exposure, the signs and symptoms of lead and mercury poisoning and the appropriate use of chelation therapy. There is a need for a clear and consistent guide to help clinicians interpret laboratory investigations. We offer such a guide, with information about population norms, lead and mercury levels that suggest exposure beyond that seen in the general population and levels that warrant referral for advice about clinical management.

24-Hour Provoked Urine Excretion Test for Heavy Metals in Children with Autism and Typically Developing Controls, a Pilot Study

INTRODUCTION

The complementary and alternative medicine practice of prescribing chelators to children with autism is based on the premise that the chronic symptoms of autism can be ameliorated by reducing heavy metal body burden. However, there has not been definitive evidence, published to date, to support the assertion that children with autism are at increased risk of an excess chelatable body burden of heavy metals. The oral chelator meso-2,3-dimercaptosuccinic acid (DMSA) can be used diagnostically to mobilize heavy metals from extravascular pools, enhancing the identification of individuals who have a chelatable body burden.

METHODS

Seventeen children with autism and five typically developing children were enrolled in a pilot study to test for chelatable body burden of Arsenic (As), Cadmium (Cd), Lead (Pb), and Mercury (Hg). Evaluation included a questionnaire regarding potential exposure to heavy metals, diet restrictions, a baseline 24-hour urine collection, and a DMSA-provoked urine collection. Urine collections were sent for As, Cd, Pb, and Hg quantification by Inductively Coupled Plasma-Mass Spectrometry. Unprovoked reference ranges were used in the interpretation of all collections.

RESULTS

Fifteen autistic children and four typically developing children completed the study. Three autistic subjects excreted one metal in greater quantity during the provoked excretion than baseline. Two of these were very close to the limit of detection. In the third case, the provoked excretion of mercury was between the upper limit of normal and lower limit of the potentially toxic reference range. Fish was removed from this child's diet for greater than one month, and the provoked excretion test repeated. The repeat excretion of mercury was within the normal range.

CONCLUSION

In the absence a proven novel mode of heavy metal toxicity, the proportion of autistic participants in this study whose DMSA provoked excretion results demonstrate an excess chelatable body burden of As, Cd, Pb, or Hg is zero. The confidence interval for this proportion is 0-22%.

Mercury exposure: evaluation and intervention the inappropriate use of chelating agents in the diagnosis and treatment of putative mercury poisoning

Public awareness of the potential for mercury to cause health problems has increased dramatically in the last 15 years. It is now widely recognized that significant exposure to all forms of mercury (elemental/metallic and both inorganic and organic compounds) can result in a variety of adverse health effects, including neurological, renal, respiratory, immune, dermatologic, reproductive, and developmental sequellae. And while the various media have made the general population cognizant of the need to avoid unnecessary exposure to this naturally occurring element, there has also evolved a growing tendency to attribute unexplainable neurologic, as well as other, signs and symptoms to mercury, whether or not significant exposure to mercury has actually occurred. For the physician, making a diagnosis of mercury intoxication can be difficult, because many of the clinical signs and symptoms of mercury exposure can also be attributed to any number of causes, including undiagnosed neurological diseases, pharmacotherapy, vitamin or mineral deficiencies, and psychological stress. The physician must be able to recognize the clinical manifestations of mercury intoxication, and understand the importance of biological markers in making a definitive diagnosis of mercury poisoning. In a desire to treat the patient complaining of symptoms similar to some that can be caused by mercury, a growing number of physicians, particularly those in alternative medicine fields, result to chelation to "rid" the body of the mercury, believed to be the cause of the ailments. And although the use of chelation is increasing, controlled studies showing that this procedure actually improves outcome are lacking. If chelation therapy is considered to be indicated, the attending physician should communicate the risks of chelation to the patient before beginning treatment with metal-chelating drugs.

Effects of mercury and selenite on delta-aminolevulinate dehydratase activity and on selected oxidative stress parameters in rats

The present study evaluates the effects of Na(2)SeO(3) and HgCl(2) on kidney and liver of adult rats. In vivo, HgCl(2) (17 micromol/kg, sc) reduced ascorbic acid levels in liver ( approximately 15%), whereas in kidney it reduced ALA-D activity ( approximately 60%) and ascorbic acid levels ( approximately 35%) and increased TBARS content ( approximately 50%). Na(2)SeO(3) (17 micromol/kg, sc) exposure increased the content of nonprotein thiol groups in liver (35-60%) and kidney ( approximately 50-160%), partially prevented mercury-induced ALA-D inhibition in kidney, and completely prevented a mercury-induced increase of TBARS content and decrease of ascorbic acid levels in kidney. In vitro, HgCl(2) and Na(2)SeO(3) inhibited renal and hepatic ALA-D, while HgCl(2) increased TBARS in renal and hepatic tissue preparations. Na(2)SeO(3) increased the rate of glutathione oxidation in vitro. Results indicated that Na(2)SeO(3) protected against HgCl(2) effects in vivo (prevention of mercury interaction with thiol groups and of mercury-induced oxidative damage). In vitro, Na(2)SeO(3) did not prevent mercury effects, but potentiated ALA-D inhibition by mercury, probably due to its ability to oxidize thiol groups.

Mercury exposure aboard an ore boat

Two maritime academy interns (X and Y) were exposed to mercury vapor after spilling a bottle of mercury on the floor in an enclosed storeroom while doing inventory aboard an ore boat. During a 3-day period, intern Y suffered transient clinical intoxication that resolved after he was removed from the environment and he showered and discarded all clothing. His initial serum mercury level dropped from 4 ng/mL to < 0.05 ng/mL. Intern X had an initial level of 11 ng/mL, which continued to rise to a maximum of 188.8 ng/mL. He complained of tremulousness, insomnia, and mild agitation and was hospitalized. He had showered and discarded all clothing except his footwear earlier than intern Y. Intern X's continued exposure due to mercury in the contaminated boots during the 2 weeks before hospitalization was presumed to be the cause. Removing his footwear led to resolution of his toxic symptoms and correlated with subsequent lowered serum mercury levels. Chelation was initiated as recommended, despite its uncertain benefit for neurologic intoxication. Mercury is used in the merchant marine industry in ballast monitors called king gauges. New engineering is recommended for ballast monitoring to eliminate this hazard.

[Chronic occupational metallic mercurialism]

This is a review on current knowledge of chronic occupational mercurialism syndrome. Major scientific studies and reviews on clinical manifestation and physiopathology of mercury poisoning were evaluated. The search was complemented using Medline and Lilacs data. Erethism or neuropsychological syndrome, characterized by irritability, personality change, loss of self-confidence, depression, delirium, insomnia, apathy, loss of memory, headaches, general pain, and tremors, is seen after exposure to metallic mercury. Hypertension, renal disturbances, allergies and immunological conditions are also common. Mercury is found in many different work processes: industries, gold mining, and dentistry. As prevention measures are not often adopted there is an increasing risk of mercury poisoning. The disease has been under diagnosed even though 16 clinical forms of mercury poisoning are described by Brazilian regulations. Clinical diagnosis is important, especially because abnormalities in the central nervous, renal and immunological systems can be detected using current medical technology, helping to develop the knowledge and control measures for mercurialism.

The pitfalls of hair analysis for toxicants in clinical practice: three case reports

Hair analysis is used to assess exposure to heavy metals in patients presenting with nonspecific symptoms and is a commonly used procedure in patients referred to our clinic. We are frequently called on to evaluate patients who have health-related concerns as a result of hair analysis. Three patients first presented to outside physicians with nonspecific, multisystemic symptoms. A panel of analytes was measured in hair, and one or more values were interpreted as elevated. As a result of the hair analysis and other unconventional diagnostic tests, the patients presented to us believing they suffered from metal toxicity. In this paper we review the clinical efficacy of this procedure within the context of a patient population with somatic disorders and no clear risk factors for metal intoxication. We also review limitations of hair analysis in this setting; these limitations include patient factors such as low pretest probability of disease and test factors such as the lack of validation of analytic techniques, the inability to discern between exogenous contaminants and endogenous toxicants in hair, the variability of analytic procedures, low interlaboratory reliability, and the increased likelihood of false positive test results in the measurement of panels of analytes.

Mercury exposure: current concepts, controversies, and a clinic's experience

In the context of controversies surrounding fish consumption, amalgams, and commercial hair testing, we reviewed all cases from an occupational and environmental medicine clinic that had undergone mercury testing. Sixty-nine of 71 (97%) patients had no known mercury exposures other than diet or amalgams. Of these 69, 48 had blood mercury tested and 58 had urine testing. Regular-to-heavy fish consumption explained 10 of 11 cases with blood mercury concentrations > 15 micrograms/L (19 to 53 micrograms/L). Six of these 10 individuals reported regular swordfish consumption. For the 31 patients with adequate dietary history, there was a significant relationship between fish consumption and blood mercury concentration (P < 0.001). Higher blood mercury concentrations were, however, not associated with specific patterns of health complaints. Ninety-eight percent (57 of 58) of urine values were < 10 micrograms/L. Fourteen patients were evaluated because they were labeled as mercury toxic by other practitioners after unconventional commercial testing. Using standard tests of blood and urine, we could not document evidence of mercury toxicity in any of these 14 cases. We conclude that consumption of commercially available fish can lead to elevated blood mercury concentrations. A recognized exposure source is a better predictor of significant mercury concentrations in biologic media than any particular symptom constellation. Unconventional commercial panels that test hair or urine for multiple metals have questionable validity. Clinicians should use standard blood and urine tests to evaluate mercury exposure.