Protection of mice against the lethal effects of sodium arsenite by 2,3 dimercapto-1-propane-sulfonic acid and dimercaptosuccinic acid

The role of chelation in the treatment of arsenic and mercury poisoning

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.

Topical efficacy of dimercapto-chelating agents against lewisite-induced skin lesions in SKH-1 hairless mice

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.

Chelation for heavy metals (arsenic, lead, and mercury): protective or perilous?

Despite clinical experience that spans more than half a century, chelation for toxic heavy metals represents one of the most controversial and misapplied interventions in clinical toxicology. The prompt use of chelating agents to treat acute, life-threatening intoxication is an indication that is largely supported by experimental animal data and limited clinical research. Although chelating agents administered for chronic intoxication may accelerate the excretion of heavy metals, their therapeutic efficacy in terms of decreased morbidity and mortality is largely unestablished. Recent investigations suggest that their use in such settings might be associated with deleterious effects. Careful attention to risk-benefit issues is warranted, particularly in clinical situations in which the etiological role of heavy metals in the patient's illness is in question.

Increased urinary excretion of carnitine and acylcarnitine by mercuric chloride is reversed by 2,3-dimercapto-1-propanesulfonic acid in rats

This investigation was aimed to study the effect of 2,3-dimercapto-1-propanesulfonic acid (DMPS) on mercuric chloride (HgCl(2))-induced alterations in urinary excretion of various carnitine fractions including free carnitine (FC), acylcarnitine (AC), and total carnitine (TC). Different groups of Wistar male rats were treated with HgCl(2) at the doses of 0.1, 0.5, 1.0, 2.0, and 3.0 mg/kg body weight, and the animals were sacrificed at 24 hours following HgCl(2) injection. A separate batch of animals received HgCl(2) (2 mg/kg) with or without DMPS (100 mg/kg) and sacrificed at 24 or 48 hours after dosing. Administration of HgCl(2) resulted in statistically significant and dose-dependent increase in the urinary excretion of FC, AC, and TC in rats. However, the ratio of urinary AC:FC was significantly decreased by HgCl(2). Pretreatment with DMPS offered statistically significant protection against HgCl(2)-induced alterations in various urinary carnitine fractions in rats.

Therapeutic efficacy of new dimercaptosuccinic acid (DMSA) analogues in acute arsenic trioxide poisoning in mice

The therapeutic efficacy of six newly synthesized analogues of dimercaptosuccinic acid (DMSA) was investigated in acute arsenic trioxide poisoning in mice. Meso-2,3-di(acetylthio)succinic acid (DATSA) and meso-2,3- di(benzoylthio)succinic acid (DBTSA) are analogues of DMSA with protected thiol groups ("prodrugs"), and DMDMS, DEDMS, DnPDMS, and DiPDMS are various di-esters of DMSA with methyl, ethyl, n-propyl, and isopropyl alcohols, respectively. Thirty minutes after s.c. injection of an LD80 of arsenic trioxide (65 mumol/kg) male NMRI mice were treated with a single equimolar dose (0.7 mmol/kg) of DMSA i.p. or one of the analogues i.p. or via gastric tube (i.g.). Control animals received arsenic trioxide and saline 30 min later. The survival rate was recorded for 30 days. All of the animals treated with DMSA i.p. survived and all controls died within 2 days. Administered i.g., DATSA and DBTSA increased the survival rate to 29% and 43%, and injected i.p. to 86%. Treatment with DMDMS i.p. and i.g., and with DEDMS, DnPDMS, and DiPDMS i.g. did not reduce lethality. Given i.p., DnPDMS increased the survival rate to 72%, and DEDMS and DiPDMS to 86%, respectively. To investigate the efficacy of the DMSA analogues in reducing the tissue content of arsenic, male NMRI mice received an s.c. injection of an LD5 of arsenic trioxide containing a tracer dose of 73-As(III) (42.5 mumol/kg body wt). Thirty minutes later, saline (controls) or a single equimolar dose (0.7 mmol/kg) of DMSA i.p., or one of the analogues i.p. or i.g. was administered. The arsenic content of various organs (blood, liver, kidneys, heart, lungs, spleen, small intestine, large intestine, brain, testes, skeletal muscle, and skin) at 30 min, 2 h, 4 h, 6 h, and 8 h after the arsenic injection was measured using a gamma counter.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute effects of the heavy metal antidotes DMPS and DMSA on circulation, respiration, and blood homoeostasis in dogs

The heavy metal antidotes sodium-2,3-dimercaptopropane-1-sulfonate (DMPS) and meso-2,3-dimercaptosuccinic acid (DMSA) were investigated in anaesthetized dogs for their effects on a variety of physiological variables and parameters. In addition, the influence of both dithiols on oxygen consumption and ferrihaemoglobin production was studied in blood and red blood cells in vitro. DMPS (15 and 75 mg/kg i.v.) did not affect respiration, central venous pressure, left ventricular pressure or cardiac output and showed only marginal, statistically non-significant effects on aortic and effective perfusion pressure. In contrast to the slight, non-significant changes due to DMPS (15 mg/kg i.v.), an equimolar dose of DMSA (12 mg/kg i.v.) led to a slight transient decrease in femoral blood pressure with strong reflex tachycardia and increase in blood flow. The higher DMPS dose (75 mg/kg i.v.), however, caused marked decreases in femoral blood pressure and blood flow, strong changes in blood gases and pH, and lactacidosis. Most of the physiological variables and parameters did not return to the initial level by 60 min. The R-spike of the electrocardiogram decreased, and the T-wave increased. Experiments on the denervated hind leg indicate that DMPS may be a direct vasodilator. The fall of blood pressure due to DMPS was markedly reduced when 30% ferrihaemoglobin had been formed by 4-dimethylaminophenol.HCl (DMAP). The highest DMPS dose (150 mg/kg i.v.) provoked circulatory failure and respiratory arrest. Artificial ventilation with room air restored spontaneous respiration, but one of three animals did not survive this dose for more than 90 min. DMPS and DMSA reacted with oxygen.(ABSTRACT TRUNCATED AT 250 WORDS)

Meso-2,3-dimercaptosuccinic acid (DMSA) affects maternal and fetal copper metabolism in Swiss mice

Meso-2,3-dimercaptosuccinic acid (DMSA) is a chelating agent used to treat heavy metal intoxication. DMSA has been reported to be teratogenic in the mouse, and it has been suggested that this teratogenicity may be secondary to DMSA-induced alterations in Zn metabolism. In the present study, 0, 400 or 800 mg DMSA/kg body weight were administered on gestation days 6-15 to pregnant Swiss mice by gavage (PO) or subcutaneous injection (SC). Mice were fed a diet containing 14 micrograms Zn, 10 micrograms Cu, 120 micrograms Fe, 1175 micrograms Mg and 6.8 mg Ca/g diet. A sub-group of mice in the 800 mg DMSA/kg SC group was fed a diet containing 250 micrograms Zn/g. DMSA administration did not result in overt maternal toxicity. There was no effect of the drug on fetal or placental weight, or on crown-rump length. However, some fetuses from DMSA-treated dams were characterized by skeletal abnormalities including supernumerary ribs, unossified anterior phalanges and malformed sternebrae. Drug exposure was not associated with consistent changes in tissue Zn, Fe, Ca or Mg levels. Supplemental Zn had no marked effects on the fetus. Fetal liver Cu concentrations exhibited dose-dependent decreases with increasing DMSA dose. This finding suggests that the developmental toxicity of DMSA may be mediated through disturbed maternal/fetal copper metabolism.

Antidotal effects of dimercaptosuccinic acid

Dimercaptosuccinic acid (DMS), HOOC-CH(SH)-CH(SH)-COOH, was first developed in China as an effective antidote for poisoning from many heavy metals, such as Pb, Hg, As, Cd, Sb, Tl, Au, Zn, Ni, Pt, Ag, Co and Sn. DMS increases the excretion of Ce, Pm, Sr and Po from the body. Hundreds of patients suffering from hepatolenticular degeneration (Wilson's disease) have been treated successfully with DMS. Recently, DMS was found to be effective also in treating certain non-metallic intoxications, like some of the new non-phosphate pesticides and mushroom poisonings.

New developments in therapeutic chelating agents as antidotes for metal poisoning

An examination of the studies on therapeutic chelating agents that have been carried out during the last decade reveals that extensive efforts have been made to develop compounds superior to those previously available for the treatment of acute and chronic intoxication by many metals. These metals include primarily iron, plutonium, cadmium, lead, and arsenic, but also many other elements for which acute and chronic intoxication is less common. These studies have revealed the importance of several additional factors of importance in the design of such compounds and have led to many new compounds of considerable clinical promise. An additional development has been the introduction of previously developed chelating agents for use with certain metals on a broader scale.

Efficacy of various dithiol compounds in acute As2O3 poisoning in mice

The efficacy of DL-dimercaptopropanol (British Anti-Lewisite, BAL), DL-dimercaptopropanesulfonate (DMPS), and meso-dimercaptosuccinic acid (DMSA) was compared in reducing the acute As2O3 toxicity in mice. Mice were treated with a single equimolar dose of a dithiol compound (0.7 mmol/kg i.p.) 0.5 or 30 min after the s.c. injection of various doses of As2O3. Both DMPS and DMSA were significantly (p less than or equal to 0.05) more effective in mice treated 0.5 min after the poisoning if compared to BAL on an equimolar level. The highest potency ratio (PR) (LD50 with treatment/LD50 without treatment) was found in animals injected with DMSA (PR = 8.6). The corresponding value for DMPS was 4.2, and for BAL 2.1, respectively. In animals treated 30 min after poisoning the efficacy of DMPS (PR = 2.6) was similar to the efficacy of DMSA 2.4, both being only slightly superior to BAL 2.0. DMPS and DMSA were found to be much less toxic than BAL. The LD50 of arsenic was 0.057 mmol/kg. The efficacy of BAL, DMPS, and DMSA in reducing the tissue content of arsenic following acute As2O3 poisoning was investigated in mice (n = 6/group) and guinea pigs (n = 3-4/group). The animals were injected s.c. with 0.043 mmol/kg As2O3 (containing a tracer dose of 74As(III)). Thirty minutes later the antidotes were administered i.p. (0.7 mmol/kg). From 2 to 4 h after As2O3 poisoning bile was collected from guinea pigs. Four h after As2O3 injection the content of 74As in blood, liver, kidneys, spleen, heart, lungs, brain, testes, skeletal muscle, and skin in mice and guinea pigs was measured.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of the developmental toxicity of 2,3-dimercapto-1-propanesulfonate (DMPS) in mice. Effect on mineral metabolism

The sodium salt of 2,3-dimercapto-1-propanesulfonic acid (DMPS), a potent chelating agent used in the treatment of inorganic and organic heavy metal intoxications was evaluated for developmental toxicity in pregnant Swiss mice. DMPS was administered by gavage at doses of 0, 75, 150 and 300 mg/kg per day on gestational days 6-15. Females were evaluated for body weight gain, food consumption, appearance and behavior, survival rates and reproduction data. Cesarean sections were performed on gestation day 18. There were no maternal toxic effects, and no treatment-related changes were recorded in the number of total implants, resorption, the number of live and dead fetuses, fetal body weight or fetal sex distribution data. Gross external, soft tissue and skeletal examination of the DMPS-treated fetuses did not show significant differences at any dose in comparison with the controls. Mineral analysis of maternal and fetal tissues revealed slight effects of DMPS on metabolism of calcium, magnesium, zinc, copper and iron. The results of this study in mice indicate that DMPS is not a developmental toxicant at levels up to 300 mg/kg per day.

Evaluation of the developmental effects on mice after prenatal, or pre- and postnatal exposure to 2,3-dimercaptopropane-1-sulfonic acid (DMPS)

The sodium salt of 2,3-dimercaptopropane-1-sulfonic acid (DMPS), a water soluble metal complexing agent, was administered to four groups of pregnant Swiss mice at 0, 70, 210, and 630 mg/kg/day by two dosing schedules: gestation day 14 until birth (prenatal exposure), and gestation day 14 until postnatal day 21 (pre- and postnatal section). Dams were allowed to deliver and the number of live and dead pups recorded. Each pup was sexed and weighed on days 0, 4, 14, and 21. Also, pinna detachment, incisor eruption and eye opening were monitored. No adverse effects on offspring survival or development were evident in either exposures at doses employed in this study. The "no observable effect level" (NOEL) for health hazard to the developing fetus or pup was 630 mg DMPS/kg/day. This dose is much higher than the amounts of DMPS usually administered in human heavy metal poisoning.

2,3-Dimercaptosuccinic acid treatment of heavy metal poisoning in humans

14 patients with heavy metal poisoning received 2,3-dimercaptosuccinic acid (DMSA). 12 subjects were given 30 mg/kg/day for 5 days; 1 subject was started on a lower dose because of a history of atopy; another subject was treated for 15 days because of very high initial blood lead concentrations. In the 9 subjects who had lead poisoning, DMSA decreased blood lead concentrations by 35 to 81%, and induced a 4.5- to 16.9-fold increase in mean daily urinary excretion of the metal. In the acutely arsenic-poisoned case, the plasma arsenic concentration on day 7 was half the pretreatment value, while no clear decrease was observed in a chronically exposed subject. In 3 mercury cases, DMSA increased daily mercury urinary excretion 1.5-, 2.8- and 8.4-fold, respectively, while blood mercury concentrations remained below detection limits. No serious side effects were observed and 3 weeks after administration of the drug the clinical condition of all subjects was either stable or improved. These results indicate the efficacy of DMSA for lead poisoning in humans and provide a rationale for further investigating its usefulness in mercury and arsenic poisoning cases.

Meso-2,3-dimercaptosuccinic acid in the diagnosis and treatment of lead poisoning

Lead poisoning remains one of the hazards of industrialized civilization. CaNa2 EDTA and dimercaprol, the usual therapeutic measures, have many side effects and can be given by parenteral route alone. The authors present a case of chronic lead poisoning caused by ingestion of contaminated flour ground in a primitive flour mill. The diagnosis was confirmed by the CaNa2 EDTA provocative test. Dimercaptosuccinic acid (DMSA) was given orally as a further provocation and resulted in an 11-fold increase in urinary lead excretion. A 5-day course of treatment with DMSA was instituted, during which symptoms abated, urinary lead excretion increased and the blood lead level decreased. No side effects were noticed. There has been no relapse over several months of follow-up. The authors conclude that the oral use of DMSA is effective, safe and convenient both as a provocative test in establishing the diagnosis of lead poisoning and as a therapeutic tool.

Dimercaptan metal-binding agents influence the biotransformation of arsenite in the rabbit

The urinary metabolites of sodium arsenite have been investigated in rabbits given sodium arsenite and water-soluble dimercaptans. Rabbits injected sc with NaAsO2 (1 mg As/kg) were given, im 1 hr later, either saline, 2,3-dimercapto-1-propanesulfonic acid (DMPS), mesodimercaptosuccinic acid (DMSA), or N-(2,3-dimercaptopropyl)phthalamidic acid (DMPA) at 0.2 mmol/kg. Arsenic metabolites in urine collected from treated rabbits were isolated by combined anion-cation-exchange chromatography. Column fractions were acid-digested and analyzed for arsenic by direct hydride-flame atomic absorption spectrophotometry. The relative amounts of inorganic arsenic, methylarsonate, and dimethylarsinate found in 0 to 24 hr urine of rabbits given only sodium arsenite agreed closely with those reported for human subjects given arsenite po. This finding suggests that the rabbit biotransforms arsenite in a manner very similar to that of man. The urinary excretion of total arsenic between 0 and 24 hr was elevated after dimercaptan administration, but urinary excretion of total arsenic between 0 and 48 hr was unaffected. This result indicates that the action of these dimercaptans occurs early after treatment. In addition, the dimercaptans influenced differently the amounts of the arsenic metabolites excreted in the urine between 0 and 24 hr. DMPS, DMSA, or DMPA increased arsenite excretion but decreased dimethylarsinate excretion. DMPS or DMPA treatment increased methylarsonate excretion but DMSA did not. Arsenate excretion increased after DMPS or DMSA treatment but was not affected by DMPA treatment. These results suggest that the dimercaptans, in addition to increasing arsenic excretion, also influence the biotransformation of arsenite to less toxic species. The different effects on the urinary excretion of arsenic metabolites suggest that these dimercaptan metal binding agents have mechanisms of action in addition to simple chelation of inorganic arsenic.

N-(2,3-dimercaptopropyl)phthalamidic acid: protection, in vivo and in vitro, against arsenic intoxication

The ip LD50s of N-(2,3-dimercaptopropyl)phthalamidic acid (DMPA) and British Anti-Lewisite (BAL) were 0.819 and 1.48 mmol/kg, respectively, in male albino mice. The ip ED50 of DMPA and BAL for prevention of the lethal effects of 0.15 mmol NaAsO2/kg was 0.022 and 0.169 mmol/kg, respectively. DMPA increased the LD50 of sodium arsenite by approximately 2.5-fold following two ip injections of 0.20 mmol DMPA/kg. The effectiveness of DMPA in reducing the toxicity of NaAsO2 was further demonstrated by its reversal of the sodium arsenite inhibition of pyruvate dehydrogenase multienzyme complex (PDH) activity in vitro. Similarly, in an in vivo experiment in which mice received 0.10 mmol NaAsO2/kg, and 30 min later were given 0.05 or 0.10 mmol/kg DMPA, there was a rapid recovery of PDH activity. The distribution of 74As in the tissues of male New Zealand rabbits was altered following im injection of 0.20 mmol/kg DMPA. Under these conditions, the tissue concentration of 74As was significantly decreased. For all tissues tested, the 74As content decreased by at least 50% as compared to that of untreated controls. DMPA was effective also in increasing both urinary and fecal excretion of arsenic. The stability of aqueous solutions of DMPA varies with the pH of the solution. DMPA is more stable in acid solution.

Evaluation of the effect of BAL (2,3-dimercaptopropanol) on arsenite-induced teratogenesis in mice

The effect of the chelating agent dimercaprol (BAL) on the embryotoxic and teratogenic effects of arsenite (As3+) was determined. BAL (sc, 30 mg/kg) was administered to pregnant CD-1 mice, either 8 and 4 hr prior to or 4 and 8 hr after a 12-mg/kg ip dose of arsenite; other females received a single sc injection of 60 mg/kg BAL concurrently with the arsenite. Treatments were given on Gestation Day 9 or 12 (copulation plug = Day 1). Controls received sc corn oil or ip H2O, with or without arsenite or BAL. Arsenite treatment caused gross and skeletal malformations and prenatal deaths, while controls were unaffected. When BAL was given prior to arsenite on Day 9, incidences of prenatal mortality and skeletal malformation were significantly diminished, and on Day 12, BAL protected against fetocidal effects of arsenite when given concurrently with the arsenite. No other significant protective effects against arsenite toxicity were seen due to BAL; however, concurrent BAL treatment on Day 9 appeared to result in decreased fetal mortality and a decline in skeletal malformations. BAL given following arsenite on Day 9 afforded no significant protection against the arsenic, although an apparent decrease in gross and skeletal malformations was suggestive of such an effect. According to these results, BAL is unlikely to have a practical beneficial effect on the arsenite exposed conceptus, because it must be administered prior to the teratogen (or perhaps simultaneously with it) to be effective.

Chelation of lead by dimercaptopropane sulfonate and a possible diagnostic use

The mobilization of lead (Pb) from Pb-exposed rats was examined following administration of dimercaptopropane sulfonate (DMPS). A dose-response study showed that the highest dose of DMPS (200 mumol/kg, ip) removed Pb from kidneys, liver, and bone, while the lower doses (25 and 50 mumol/kg) chelated Pb only from the kidneys. In experiments where DMPS was repeatedly injected to Pb-exposed rats, the maximum urinary excretion of Pb was observed within 24 hr after the first injection, with little effect in subsequent injections. Discontinuation of DMPS after the first injection (at a dose of 50 mumol DMPS/kg) caused renal Pb levels to increase until further injection of DMPS, several days later, which again mobilized Pb only from the kidneys. A single oral administration of 150 mumol DMPS/kg (a dose adjusted for specific chelation from the kidney) to rats, previously exposed to different doses of Pb resulted in a significant decrease of renal Pb in groups injected with more than 0.5 mg Pb/kg. A linear relationship was observed between renal Pb burden and urinary Pb excretion following chelation (r = 0.94, p less than 0.01). Thus, the specific removal of Pb from the kidney by DMPS treatment suggests a potential use of DMPS, a relatively nontoxic drug, for the estimation of renal Pb burden and also for treatment of Pb poisoning. Unlike other chelating agents, DMPS can be administered orally.

Anti-lewisite activity and stability of meso-dimercaptosuccinic acid and 2,3-dimercapto-1-propanesulfonic acid

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.

Interactions of the chelating agent 2,3-dimercaptopropane-1-sulfonate with red blood cells in vitro. I. Evidence for carrier mediated transport

Uptake of the water soluble 1,2-dimercaptopropanol (BAL) derivative 2,3-dimercapto-1-sulfonate (DMPS) into human red blood cells was found in vitro and the mode of penetration studied in detail. The compound entered erythrocytes in a concentration dependent manner. In contrast to sealed ghosts where inside and outside concentrations reached the same value, DMPS accumulated in intact erythrocytes. Since no binding of DMPS could be detected, the reason for accumulation was assumed to be a conversion of DMPS into chelates or metabolites which penetrated the membrane in a slower rate. A facilitated transport of DMPS mediated by the anion carrier protein was concluded on the basis of the following similarities with the anion transport: inhibition of [14C]DMPS-uptake by N-ethylmaleimide (NEM), tetrathionate (90%), sulfate (50%), 5,5'-dithio bis(2-nitrobenzoic acid) (DTNB) (25%); inhibition of uptake and efflux by 4,4'-diisothiocyano-2,2'-stilbene disulfonate (DIDS) (80%), dipyridamole (55%); temperature dependency (activation energy 24 Kcal/mol); pH-dependency (pH optimum about 6.9); counter-transport; activation of uptake by preincubation with DMPS (transmembrane effect).

Biological chelation: 2,3-dimercapto-propanesulfonic acid and meso-dimercaptosuccinic acid

Water soluble analogs of British Anti-Lewisite that are active orally and less toxic than BAL are now available. These agents are 2,3-dimercapto-1-propanesulfonic acid and meso-dimercaptosuccinic acid. Evidence for their effectiveness in preventing the lethal effects of sodium arsenite in mice and lewisite in rabbits is presented. These analogs can be expected to replace BAL in the treatment of heavy metal poisoning.

Inducible plasmid-determined resistance to arsenate, arsenite, and antimony (III) in escherichia coli and Staphylococcus aureus

Plasmids in both Escherichia coli and Staphylococcus aureus contain an "operon" that confers resistance to arsenate, arsenite, and antimony(III) salts. The systems were always inducible. All three salts, arsenate, arsenite, and antimony(III), were inducers. Mutants and a cloned deoxyribonucleic acid fragment from plasmid pI258 in S. aureus have lost arsenate resistance but retained resistances to arsenite and antimony, demonstrating that separate genes are involved. Arsenate-resistant arsenite-sensitive S. aureus plasmid mutants were also isolated. In E. coli, plasmid-determined arsenate resistance and reduced uptake were additive to that found with chromosomal arsenate resistance mutants. Arsenate resistance was due to reduced uptake of arsenate by the induced plasmid-containing cells. Under conditions of high arsenate, when some uptake could be demonstrated with the induced resistant cells, the arsenate was rapidly lost by the cells in the absence of extracellular phosphate. Sensitive cells retained arsenate under these conditions. When phosphate was added, phosphate-arsenate exchange occurred. High phosphate in the growth medium protected cells from arsenate, but not from arsenite or antimony(III) toxicity. We do not know the mechanisms of arsenite or antimony resistance. However, arsenite was not oxidized to less toxic arsenate. Since cell-free medium "conditioned" by prior growth to induced resistant cells with toxic levels of arsenite or antimony(III) retained the ability to inhibit the growth of sensitive cells, the mechanism of arsenite and antimony resistance does not involve conversion of AsO2- or SbO+ to less toxic forms or binding by soluble thiols excreted by resistant cells.