succimer and lewisite

Chelation for heavy metal intoxication began more than 70 years ago with the development of British anti-lewisite (BAL; dimercaprol) in wartime Britain as a potential antidote the arsenical warfare agent lewisite (dichloro[2-chlorovinyl]arsine). DMPS (unithiol) and DMSA (succimer), dithiol water-soluble analogs of BAL, were developed in the Soviet Union and China in the late 1950s. These three agents have remained the mainstay of chelation treatment of arsenic and mercury intoxication for more than half a century. Animal experiments and in some instances human data indicate that the dithiol chelators enhance arsenic and mercury excretion. Controlled animal experiments support a therapeutic role for these chelators in the prompt treatment of acute poisoning by arsenic and inorganic mercury salts. Treatment should be initiated as rapidly as possible (within minutes to a few hours), as efficacy declines or disappears as the time interval between metal exposure and onset of chelation increases. DMPS and DMSA, which have a higher therapeutic index than BAL and do not redistribute arsenic or mercury to the brain, offer advantages in clinical practice. Although chelation following chronic exposure to inorganic arsenic and inorganic mercury may accelerate metal excretion and diminish metal burden in some organs, potential therapeutic efficacy in terms of decreased morbidity and mortality is largely unestablished in cases of chronic metal intoxication.

Topics: Animals; Arsenic Poisoning; Arsenicals; Chelating Agents; Chelation Therapy; Humans; Mercury Poisoning; Succimer; Treatment Outcome; Unithiol

Lewisite is a potent chemical warfare arsenical vesicant that can cause severe skin lesions. Today, lewisite exposure remains possible during demilitarization of old ammunitions and as a result of deliberate use. Although its cutaneous toxicity is not fully elucidated, a specific antidote exists, the British anti-lewisite (BAL, dimercaprol) but it is not without untoward effects. Analogs of BAL, less toxic, have been developed such as meso-2,3-dimercaptosuccinic acid (DMSA) and have been employed for the treatment of heavy metal poisoning. However, efficacy of DMSA against lewisite-induced skin lesions remains to be determined in comparison with BAL. We have thus evaluated in this study the therapeutic efficacy of BAL and DMSA in two administration modes against skin lesions induced by lewisite vapor on SKH-1 hairless mice. Our data demonstrate a strong protective efficacy of topical application of dimercapto-chelating agents in contrast to a subcutaneous administration 1h after lewisite exposure, with attenuation of wound size, necrosis and impairment of skin barrier function. The histological evaluation also confirms the efficacy of topical application by showing that treatments were effective in reversing lewisite-induced neutrophil infiltration. This protective effect was associated with an epidermal hyperplasia. However, for all the parameters studied, BAL was more effective than DMSA in reducing lewisite-induced skin injury. Together, these findings support the use of a topical form of dimercaprol-chelating agent against lewisite-induced skin lesion within the first hour after exposure to increase the therapeutic management and that BAL, despite its side-effects, should not be abandoned.

Topics: Administration, Topical; Animals; Arsenic Poisoning; Arsenicals; Chelating Agents; Dermatitis; Dimercaprol; Injections, Subcutaneous; Male; Mice; Mice, Hairless; Succimer; Volatilization

The cytotoxicity of the arsenical vesicant Lewisite was assessed in first passage cultures of proliferating neonatal human skin keratinocytes. Both munitions grade and distilled Lewisite were extremely toxic with LC(50) values in the low ng/ml range, with no significant differences between them. This similarity in toxicity was also mirrored with respect to their toxic effects on hairless guinea pig skin. Two-, 4- and 6-min vapour exposures of these agents resulted in similar and severe skin injury that was obvious by 3-5h post-exposure and almost maximal at 24h. The toxicity of Lewisite in culture was temperature dependent, with a >10-fold reduction in 24h LC(50) values as the incubation temperature was reduced from 37 to 25 degrees C. However, this cooling induced protection was not persistent. In contrast, cooling of Lewisite exposed hairless guinea pig skin at approximately 10 degrees C for as little as 30 min post-exposure resulted in dramatic and permanent protection, with 4h of cooling almost completely eliminating Lewisite induced skin injury. Further, significant protection was also evident even when cooling was delayed for as long as 2h post-Lewisite exposure. In an effort to investigate whether cooling might also increase the window in which chelation therapy against this vesicant agent would be useful, we examined the protective effects of the heavy metal chelator dimercaptosuccinic acid (DMSA). Topical application to Lewisite exposed skin was extremely protective, even when delayed for 2h after Lewisite. Cooling of Lewisite exposed skin for 2h, followed by DMSA topical application resulted in decreased skin injury compared to either treatment in isolation. It appears that the simple and non-invasive application of cooling measures may provide not only significant therapeutic relief to Lewisite exposed skin, but that it may also increase the therapeutic window in which medical countermeasures against this vesicant agent are useful.

Topics: Animals; Arsenicals; Cell Survival; Cells, Cultured; Chelating Agents; Chemical Warfare Agents; Guinea Pigs; Humans; Hypothermia, Induced; Keratinocytes; Male; Skin Diseases; Succimer

Lewisite is a highly toxic arsenic compound which can cause skin damage. In the present study effects of Lewisite on cell membrane integrity and energy metabolism as well as antidotal effects of DL-2,3-dimercaptopropanesulfonate (DMPS), and meso-2,3-dimercaptosuccinic acid (m-DMSA) were investigated in a keratinocyte derived cell line (SCL II) and primary human keratinocytes (HK). Cells were incubated in Lewisite (60 microM) containing medium for 5 min. During the following 6 h lactate dehydrogenase (LDH) activity in the supernatant, intracellular ATP content, tetrazolium reduction, glucose consumption and lactate formation were measured. Glucose consumption and lactate production were decreased in both cell lines after Lewisite exposure. In SCL II cells an increase of LDH activity in the supernatant, a decrease of ATP content, and an impaired ability to reduce tetrazolium was found 3 h after Lewisite exposure. In HK cultures tetrazolium reduction was significantly decreased already after 2 h, whereas LDH increase in the supernatant and ATP content decrease occurred only at 6 h after Lewisite exposure. When DMPS or m-DMSA was added directly after Lewisite exposure to SCL II cells, glucose consumption and lactate formation were restored and LDH leakage was prevented. SCL II cells might be more prone to membrane damage whereas in keratinocytes mitochondrial impairment seems to be the predominant effect of Lewisite.

Topics: Adenosine Triphosphate; Arsenicals; Cell Membrane Permeability; Cell Survival; Chelating Agents; Energy Metabolism; Formazans; Glucose; Humans; Keratinocytes; L-Lactate Dehydrogenase; Lactic Acid; Succimer; Tetrazolium Salts; Time Factors; Tumor Cells, Cultured; Unithiol

The efficacy of three chelating agents, BAL, DMPS and DMSA has been evaluated in rabbits as treatments for systemic dichloro(2-chlorovinyl)arsine [lewisite] poisoning by the percutaneous route. Chelating agent treatment reduced the incidence and severity of pathological liver changes following lewisite poisoning. There was no marked difference between the three chelating agents for protection against lethality when screened at an equimolar dose of 40 mumol kg-1. The results indicated DMPS and DMSA may prolong survival time compared with BAL. The low toxicity of DMPS and DMSA compared to BAL enabled doses of 160 mumol kg-1 on a more prolonged dosing schedule to be used for DMPS and DMSA. This schedule showed DMPS and DMSA to give a significant improvement in protection against the lethal effects of percutaneous lewisite compared to that of BAL. It was concluded that DMPS and DMSA have significant advantages over BAL for use as treatment for systemic lewisite poisoning.

Topics: Administration, Topical; Animals; Arsenic Poisoning; Arsenicals; Chelating Agents; Chemical and Drug Induced Liver Injury; Dimercaprol; Gallbladder; Lethal Dose 50; Liver; Lung; Male; Rabbits; Succimer; Sulfhydryl Compounds; Unithiol

1 The standard drug for the treatment of arsenic poisoning is BAL (dimercaprol). BAL possesses marked side-effects and a low safety ratio, drawbacks which new BAL analogues, DMPS and DMSA, do not possess. 2 The efficacy of three chelating agents, BAL, DMPS and DMSA, has been evaluated as a treatment for systemic organic arsenic poisoning, induced by intravenous dichloro(2-chlorovinyl)arsine (lewisite) administration to rabbits. Equimolar dosing schedules were used based upon realistic doses for the most toxic agent, BAL. 3 It was concluded that all three dimercapto chelating agents provided significant protection against the lethal systemic effects of lewisite, and, under the test conditions reported here, there was no significant difference between them in therapeutic efficacy. 4 The cause of mortality following intravenous lewisite in treated and untreated rabbits was pulmonary damage. 5 It is considered that DMPS and DMSA are worthy of further study as replacements for BAL in the treatment of systemic poisoning by lewisite.

Topics: Animals; Arsenic; Arsenic Poisoning; Arsenicals; Body Weight; Chelating Agents; Dimercaprol; Gallbladder; Lethal Dose 50; Liver; Lung; Male; Rats; Succimer; Unithiol

Proton nuclear magnetic resonance spectroscopy was used to determine relative binding constants for several arsenical-antidote adducts. It was found that BAL (2,3-dimercaptopropanol) and DMPS (2,3-dimercaptopropanesulfonic acid) had a higher affinity than DMSA (2,3-dimercaptosuccinic acid) for the two organic arsenicals studied.

Topics: Antidotes; Arsenicals; Dimercaprol; Magnetic Resonance Spectroscopy; Solvents; Stereoisomerism; Succimer; Unithiol

meso-Dimercaptosuccinic acid (DMSA), 2,3-dimercapto-1-propanesulfonic acid, Na salt (DMPS), and N-(2,3- dimercaptopropyl )- phthalamidic acid (DMPA) are water soluble analogs of 2,3-dimercapto-1-propanol (BAL). The relative effectiveness or therapeutic index of these dimercapto compounds in protecting mice from the lethal effects of an LD99 of sodium arsenite is DMSA greater than DMPS greater than DMPA greater than BAL in the magnitude of 42:14:4:1, respectively. DMPS, DMPA, or DMSA will mobilize tissue arsenic. BAL, however, increases the arsenic content of the brain of rabbits injected with sodium arsenite. These results raise the question as to the appropriateness of BAL as the treatment for systemic arsenic poisoning. Either DMSA or DMPS, when given sc or po, will protect rabbits against the lethal systemic effects of subcutaneously administered Lewisite . DMPS and DMSA have promise as prophylactics for the prevention of the vesicant action of Lewisite . The sodium arsenite inhibition of the pyruvate dehydrogenase (PDH) complex can be prevented and reversed in vitro or in vivo by DMPS, DMSA, DMPA, or BAL. Of them all, DMPS is most potent and BAL appears to be the least potent. The usefulness of all these dimercapto compounds would be enhanced by a careful study of their metabolism and biotransformation. These dimercapto compounds are in a great many respects orphan drugs. At this stage of their development, it is very difficult for the clinician to obtain funds to study them clinically even though they appear to be useful for treatment of poisoning by any one of the heavy metals.

Topics: Animals; Antidotes; Arsenates; Arsenic; Arsenic Poisoning; Arsenicals; Arsenites; Brain; Dimercaprol; Guinea Pigs; Male; Mice; Organ Size; Phthalic Acids; Pyruvate Dehydrogenase Complex; Rabbits; Sodium Compounds; Succimer; Sulfhydryl Compounds; Unithiol

Meso-dimercaptosuccinic acid (DMSA) and the sodium salt of 2,3-dimercapto-1-propanesulfonic acid (DMPS) are analogous in chemical structure to dimercaprol (BAL, British Anti-Lewisite). Dimercaprol was among the first therapeutically useful metal chelating agents and was developed originally as an anti-lewisite agent. Either DMSA or DMPS protects rabbits from the lethal systemic action of dichloro(2-chlorovinyl)arsine (29.7 mumols/kg, also known as lewisite. The analogs are active in this respect when given either sc or po. The stability of each of the three dimercapto compounds in distilled H2O, pH 7.0 at 24 degrees, has been examined for seven days. DMSA retained 82% of its mercapto groups, but no titratable mercapto groups remained in the DMPS or BAL solutions. At pH 5.0, however, there was no striking difference in the stability of the three dimercapto compounds (78-87%) over a seven day period. DMSA and DMPS warrant further investigation as water soluble metal binding agents in both in vivo and in vitro experiments.

Topics: Administration, Oral; Animals; Arsenic Poisoning; Arsenicals; Dimercaprol; Dose-Response Relationship, Drug; Drug Stability; Hydrogen-Ion Concentration; Injections, Subcutaneous; Male; Rabbits; Succimer; Unithiol