Antidotal Efficacy of Newly Synthesized Dimercaptosuccinic Acid (DMSA) Monoesters in Experimental Arsenic Poisoning in Mice

The efficacy of four newly synthesized monoesters of meso-2,3-dimercaptosuccinicacid (DMSA), mono-i-arnyl- (Mi-ADMS), mono-n-amyl- (Mn-ADMS),mono-i-butyl- (Mi-BDMS), and mono-n-butyl-meso-2,3-dimercaptosuccinate(Mn-BDMS) in increasing survival and arsenic elimination inexperimental arsenic poisoning was investigated. Male mice (strainNMRI) received arsenite sc (survival study: 130 µmol/kg,7 mice/group; elimination study: 85 µmol/kg (LD5) togetherwith a tracer dose of⁷³ As(III), 6 mice/group). After 30 minmice were treated with 0.7 mmol/kg of DMSA or a monoester ipor via gastric tube (ig). Control animals received saline ip.In the survival study mice were observed for 30 days. In theelimination study, the 73-arsenic content of several organs(blood, liver, heart, lung, kidneys, spleen, testes, brain,small intestine, large intestine, muscle, and skin) was measured0.5, 2, 4, 6, and 8 hr after the arsenic injection using a gammacounter. Survival increased correspondingly well with the increaseof arsenic elimination. DMSA, Mi-ADMS, Mn-ADMS, Mi-BDMS, andMn-BDMS markedly decreased arsenic content in most organs assoon as 1.5 hr after treatment. Only in small and large intestinewere higher arsenic amounts found, indicating a shift in arsenicelimination from the renal to the fecal route, and thereby suggestinga protective effect for the kidneys. Given ip, the monoestersturned out to be similarly as effective as the parent drug DMSA.Following ig treatment, the DMSA monoesters Mi-ADMS and Mn ADMSseemed to be superior to DMSA with regard to survival. The similarefficacy of the various monoesters indicates that the side chainsubstitution did not markedly change bioavailabilty and efficacy.It is concluded that the new DMSA monoesters are effective arsenicantidotes given systemically or orally.     

Protection of mice against lethal effects of sodium arsenite--a quantitative comparison of a number of chelating agents

The LD50 of NaAsO₂ was found to be 0.129 mmol/kg, sc, using white mice. The ip administration of the sodium salt of 2,3-dimercapto-1-propanesulfonic acid (DMPS) or meso-dimercaptosuccinic acid (DMSA) (0.80 mmol/kg) immediately after and 90 min after NaAsO₂ increased the LD50 of NaAsO₂ about 4.2- and 4.4-fold, respectively. Neither d-penicillamine nor N-acetyl-dl-penicillamine affected the LD50 of NaAsO₂ under the same conditions. The LD50 of DMPS and DMSA in mice was found to be 5.22 and 13.58 mmol/kg, ip, respectively. The effective dose 50 for treating mice 10 min after receiving and LD100 of NaAsO₂ (0.15 mmol/kg) was 0.066 mmol/kg for DMPS and 0.065 mmol/kg for DMSA. The therapeutic index of DMSA against 0.15 mmol/kg NaAsO₂ was found to be 209. This was 2.6 times greater than that of DMPS. The explanation for this difference is that although DMSA was as effective as DMPS, it is less toxic. The LD50 of NaAsO₂ was not increased by sodium diethyldithiocarbamate, α-mercaptopropionylglycine, dl-N-acetylhomocysteinethiolactone, or monomercaptosuccinic acid. A series of polymercapto compounds, some having as many as four mercapto groups per molecule, also did not protect against the lethality of NaAsO₂. There is extensive experimental and clinical information about DMPS and DMSA available in the Soviet and Chinese literature where these agents are known as Unithiol or Unitiol and succimer, respectively. It would appear that DMPS and DMSA warrant further experimental studies and eventually clinical trials for the treatment of intoxication by arsenic as well as by certain other heavy metals.     

DMSA,DMPS, and DMPA—as arsenic antidotes

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 > DMPS > DMPA > 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.     

Combined Therapeutic Potential of meso-2,3-Dimercaptosuccinic Acid and Calcium Disodium Edetate on the Mobilization and Distribution of Lead in Experimental Lead Intoxication in Rats

Asymptomatic lead poisoning remains a serious public healthproblem in developed and developing countries. Chelation therapyparticularly with calcium disodium ethelenediamine tetra-aceticacid (CaNa₂EDTA) is often used therapeutically to reduce thebody burden of lead. This chelating drug has serious side effectsand drawbacks primarily related to redistribution of lead, nephrotoxicity,and essential metal depletion. The present study was plannedto determine the effectiveness of CaNa₂EDTA and meso-2,3-dimercaptosuccinicacid (DMSA) used in combination. Both drugs, when administeredindividually, resulted in significant urinary excretion of leadand lowered the tissue lead burden. Combined treatment withCaNa₂EDTA and DMSA elicits an additive response in promotingurinary lead elimination, depleting body lead burden, and restoringaltered lead-sensitive biochemical variables. Further, no redistributionof lead to brain or any other soft organ following combinedDMSA-CaNa₂EDTA treatment was observed indicating a definiteadvantage of combined therapy over the conventional treatmentwith CaNa₂EDTA or DMSA alone. However, an elevation of serumtransaminase activity, creatinine level, and depletion of bloodzinc level may limit the usefulness of this combined treatment.     

Subchronic Oral and Intravenous (iv) Safety Evaluation and Pharmacokinetics in Rats and Dogs of Ipazilide Fumarate (Win 54, 177-4), an Antiarrhythmic Agent

Ipazilide fumarate (Win 54,177-4) is a chemically novel antiarrhythmicagent that prolongs ventricular refractoriness and possessesantiectopic activity. Subchronic (29 days) nonclinical safetyevaluation of ipazilide was conducted following oral and ivadministration in Sprague-Dawley rats (20–320 mg/kg oraland 1.25–10 mg/kg iv) and 14 and 28 days in beagle dogs(3–30 mg/kg oral and 2.5–20 mg/kg iv). The pharmacokineticparameters of ipazilide indicate that ipazilide is absorbed(t_max 1 hr) in fasted rats and dogs following single and repeatedoral administrations. The apparent elimination half-life inthe two species is approximately 1 hr (except in rats at a dosageof 320 mg/kg), suggesting rapid clearance. Increases in liverweights (rats 320 mg/kg) accompanied by the observation of centrilobularhypertrophy of hepatocytes were considered an expression ofan adaptive metabolic response of the liver to ipazilide andmay be associated with the induction of microsomal enzymes.Duodenal villous atrophy and epithelial hyperplasia (rats, 80and 320 mg/kg) were interpreted to represent an irritant responseto the drug. Local irritation was also observed at the injectionsite in rats and dogs. Dogs tolerated the oral and the iv administrationof ipazilide at dosages of up to 30 and 20 mg/kg, respectively.Despite emesis (oral dogs), which was reduced in frequency followingrepeated treatment over several weeks, plasma levels in treateddogs (i.e., C_max 4–5 µg/ml) were approximately twicethat required to convert spontaneous arrhythmias in the conscious dog model 24 hr after myocardial infarction. Moreover,plasma levels (C_max 6–7 µg/ml) of iv-treated dogswere approximately three times higher than the efficacious levelsin the dog model and did not cause adverse effects except emesis.Electrocardiographic changes (i.e., increased P wave and QRSdurations, and T wave alterations) in dogs were transient andrepresented an extension of the pharmacological effects of ipazilide.In summary, since ipazilide, at multiple therapeutic dosages,was well tolerated in rats and dogs, it may be considered anappropriate drug for clinical evaluation of safety and efficacyin humans as a potential antiarrhythmic agent. The safety profileof ipazilide in clinical trials is currently ongoing.     

Comparative Toxicokinetics of Methanol in the Female Mouse and Rat

The toxicokinetics of methanol in female CD-1 mice and Sprague-Dawleyrats were examined to explore the possibility of species differencesin the disposition of the compound. Mice received a single doseof 2.5 g/kg methanol either po (by gavage) or iv (as a 1-mminfusion). Rats received a single oral dose of 2.5 g/kg methanol.As expected, the disposition of methanol was nonlinear in bothspecies. Data obtained after iv administration of methanol tomice were well described by a one-compartment model with Michaelis-Mentenelimination. Blood methanol concentration-time data after oraladministration could be described by a one compartment (mice)or two-compartment (rats) model with Michaelis-Menten eliminationfrom the central compartment and biphasic absorption from thegastrointestinal tract Kinetic parameters (V_max for elimination,apparent volume of the central compartment [V_e first-order rateconstants for intercompartmental transfer [k₁₂ and k₂₁ and first-orderabsorption rate constants for fast [k_AF] and slow [k_AS] absorptionprocesses) were compared between species. When normalized forbody weight, mice evidenced a higher maximal elimination ratethan rats (V_max=117±3 mg/hr/kg vs 60.7±1.4 mg/hr/kgfor rats). The contribution of the fast absorption process tooverall methanol absorption also was larger in the mouse thanin the rat.     

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.     

Toxicity of the Protein Kinase C Inhibitor Safingol Administered Alone and in Combination with Chemotherapeutic Agents

Safingol [(2S,3S)-2-amino-1,3-octadecanediol] potentiates thetoxicity of doxorubicin (DOX) and cisplatin (CIS) against tumorcells in vitro and in vivo. The present studies were conductedin rats and dogs to evaluate safingol toxicity when administerediv as a single agent and to evaluate safingol's ability to potentiatethe toxicity of established chemotherapeutic agents to normaltissues in vivo. In an escalating dose study, dogs were administeredsafingol iv at 5, 10, 20, 30, 40, and 75 mg/kg on Days 1 through6. Necropsies were performed on Day 7. Red urine was observedat 10 mg/kg and higher. Icterus was observed following 40 mg/kgwith additional signs of hypoactivity and anorexia occurringafter 75 mg/kg. Clinical and microscopic pathology revealedmarked hepatotoxicity, venous degeneration and necrosis at injectionsites, and evidence of intra-vascular hemolysis. Doses of 5,20, or 40 mg safingol/kg were utilized in single iv dose ratand dog studies. No evidence of adverse systemic toxicity wasseen up to 20 mg/kg in either species [for rats: C_max = 12,600(males) or 17,133 (females) ng/ml, AUC = 3853 (males) or 4365(females) ng x hr/ml; for dogs: C_max = 2533 ng/ml, AUC = 2851ng x hr/ml (no sex differences)]. Local effects of venous irritationor intravascular hemolysis were observed at all doses in ratsand at 20 and 40 mg/kg in dogs. A dose of 40 mg/kg [for rats:C_max = 31,233 (males) or 91,300 (females) ng/ml, AUC = 11,519(males) or 18,620 (females) ng x hr/ml; for dogs: C_max = 9033ng/ml, AUC = 11,094 ng x hr/ml (combined sex)] was associatedwith clinical pathologic and renal histomorphologic changesconsidered consequent to intravascular hemolysis in both species,lethality and testicular toxicity in rats, and clinical biochemicalchanges indicative of hepatobiliary injury in dogs. Studiesindicated that hemolysis occurred during infusion, was not causedby circulating levels of safingol, and was a function of doseconcentration and vein of delivery. Safingol at 10 or 20 mg/kgwas administered iv to rats 30–60 min prior to myelosuppressiveiv doses of DOX, CIS, or cyclophosphamide (CYP). Hematology,plus renal function and morphology for CIS-treated animals,was assessed 4 and 14 days later. Safingol did not potentiateDOX-, CIS-, or CYP-mediated leukopenia/thrombocytopenia. A minimalenhancement of CIS-mediated decrease in GFR and increase increatinine was observed at 20 mg safingol/kg. Dogs were administered20 mg safingol/kg iv followed 60 min later by 0.5 or 1.25 mgDOX/kg or 0.75 or 2.0 mg CIS/kg. A complete toxicologic assessment4 and 29 days postdose failed to show potentiation of DOX toxicityby safingol or vice versa. A renal lesion was inferred in dogsadministered 20 mg/kg safingol and 2 mg/kg CIS based on minimalto slight renal tubular regeneration observed 4 weeks post-treatment.There were no effects of safingol on the pharmacokinetic profilesof DOX or CIS or vice versa.     

Adrenocortical Toxicity of 3-Methylsulfonyl-DDE in Mice: II. Mitochondrial Changes following Ecologically Relevant Doses

Transmission electron microscopy was used to characterize earlyultrastructural lesions in the adrenal zona fasciculata of femaleC57BL mice given a single ip injection of the adrenocorticolyticDDT-metabolite 3- methylsulfonyl-DDE (MCSO₂-DDE Following 3mg/kg, mitochondrial changes were observed 6 hr after dosing.At 12 and 24 hr the mitochondrial changes were conspicuous,with disorganization and disappearance of central cristae. Atdoses of 6, 12, and 25 mg/kg body wt initial (6 hr) mitochondrialvacuolization was observed, followed by disappearance of mitochondria(6–12 mg/kg) or cellular necrosis (25 mg/kg). The metabolicactivation and binding of MeSO₂-[¹⁴C]DDE in adrenal homogenateswere determined in vitro. The irreversible binding of MeSO₂-[¹⁴C]to the mitochondria-containing adrenal S-9 pellet fraction was50 times higher than that to the postmitochondrial S-12 supernatantfraction. The apparent K_m was 2.1 µM and the apparentV_max was 104 pmol/mg protein/30 mm for the binding of MeSO₂-[¹⁴C]to S-0.3 supernatants. The irreversible protein binding wasinhibited by metyrapone (K₁=1 µM) and 11-deoxycorticosterone(K₁=3 µM). In conclusion, the adrenal metabolic activationof MeSO₂-[¹⁴C]DDE is suggested to be mediated by a mitochondrialcytochrome P450 form, presumably P450 (11ß). A primarymitochondrial lesion develops and subsequently leads to degenerationand necrosis of the zona fasciculata.     

Disposition of [14C]Dimercaptosuccinic Acid in Mice

Disposition of [¹⁴C]Dimercaptosuccinic Acid in Mice. LIANG,Y.-Y., MARLOWE, C., AND WADDELL, W. J. (1986). Fundam. Appl.Toxicol. 6, 532–540. Dimercaptosuccinic acid labeled with¹⁴C ([¹⁴C]DMSA) was administered to mice iv; the mice were frozenby immersion in dry ice/hexane at 6 and 20 min and 1, 3, 9,and 24 hr after injection. The frozen mice were sectioned andprocessed for whole-body autoradiography for soluble substances.The radioactivity was highly localized in extracellular fluidssuch as the subcutaneous, intrapleural, intraperitoneal, andperiosteal spaces. There was a pronounced accumulation in theperiosteal fluid above that in other fluids during the firsthour after injection. Most of the radioactivity was eliminatedby the kidney and liver. Pretreatment of a mouse with HgCl₂subcutaneously 1 hr before [¹⁴C [¹⁴C]DMSA produced an increasein radioactivity in the liver and decrease in lung. A high concentrationof radioactivity was seen at the subcutaneous site of injectionof the HgCl₂. The results are interpreted to indicate that mostof the DMSA is in the extracellular space but that it can crosscellular membranes to some extent. The pronounced accumulationin periosteal fluid may be an interaction of DMSA with Ca²⁺in this space. No tissue had a pronounced retention of the compound,but lung retained more than most other tissues.     

Mobilization of cadmium by liposome-encapsulated meso-2,3-dimercaptosuccinic acid in pre-exposed mice.

meso-2,3-Dimercaptosuccinic acid (DMSA) treatment in free of liposome-encapsulated form was given to mice pre-exposed to cadmium as CdCl2 (2 intraperitoneal injections; 0.5 mg Cd/kg along with 5 microCi 109CdCl2 in 4 ml volume within 24 h). Both treatments removed cadmium from liver, spleen, testis and blood with liposomal DMSA exhibiting higher efficacy in mobilizing cadmium not only from whole organs but also from liver proteins. It also resulted in higher excretion of cadmium via urine as compared with free DMSA or saline treatment. Whereas this treatment eliminated significantly higher amounts of cadmium via the fecal route throughout the period examined, free DMSA responded only 48 h after treatment and was less effective. The results suggest mobilization of cadmium from intracellular sites of deposition. However, DMSA in the dose administered (24 mumol/kg i.v.) in either form was ineffective in decorporating cadmium from the kidney, the critical organ in cadmium intoxication.     

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.     

Prolonged Oral Treatment with Two Monoesters of meso-2,3-Dimercaptosuccinic Acid for Depleting Inorganic Mercury Retention in Suckling Rats

Abstract: Two monoesters of meso-2,3-dimercaptosuccinic acid (DMSA), monoisoamyl meso-2,3-dimercaptosuccinate (Mi-ADMS) and mono-n-hexyl meso-2,3-dimercaptosuccinate (Mn-HDMS) were compared to DMSA in their efficiency to mobilize ²⁰³Hg in mercury-laden suckling rats. Seven-day-old pups were given ²⁰³Hg (18.5 kBq) with a dose of 0.5 mg Hg/kg/day as HgCl₂ for five days. Seven days after the beginning of Hg loading a ten-day oral treatment with DMSA, Mi-ADMS, or Mn-HDMS was administered at a dose of 0.25 mmol/kg/day. At the end of experiment, radioactivity was measured in the whole body, liver, both kidneys, and brain. Monoesters of DMSA were superior to DMSA in decreasing body and organ Hg retention. The highest reduction in comparison to controls in groups treated with DMSA, Mi-ADMS, or Mn-HDMS occurred in the kidneys (48%, 97%, and 96%), followed by reduction in the liver (24%, 84%, and 83%), and in the brain (8%, 23%, and 23%, respectively). For both, Mi-ADMS and Mn-HDMS, the reductions in the whole body and organs were significantly greater than in controls or DMSA-treated rats. No difference between the efficiency of the two DMSA-monoesters was found.     

Functional Assessment of Rabbit Alveolar Macrophages following Intermittent Inhalation Exposures to Sulfuric Acid Mist

Functional Assessment of Rabbit Alveolar Macrophages followingIntermittent Inhalation Exposures to Sulfuric Acid Mist. SCHLESINGER,R. B. (1987). Fundam. Appl. Toxicol. 8, 328–334. Sulfuricacid (H₂SO₄) aerosols are common in both ambient and occupationalenvironments. This study examined the numbers and selected invitro functional properties of alveolar macrophages recoveredfrom rabbits undergoing inhalation exposure to 0.5 mg/m³ submicrometer(0.3 µm) H₂SO₄ for 2 hr/day. Bronchoalveolar lavage wasperformed on Days 3, 7, and 14 during the exposure period (specifically,24 hr after either 2, 6, or 13 exposures). Total cell numbersand macrophage counts were increased on Day 3, but returnedto control levels by Day 7; no change in polymorphonuclear leukocyteswas observed at any time point. Macrophage substrate attachmentwas not affected by exposures to H₂SO₄, but random mobilitywas severely depressed at Days 7 and 14. The numbers of phagocyticallyactive macrophages and the level of such activity were increasedon Day 3, but became depressed by Day 14. These results demonstratesignificant alterations in important functional properties ofalveolar macrophages due to short-term intermittent exposuresto H₂SO₄ aerosols; these changes have implications for the abilityof the lungs to maintain adequate defense against depositedviable and nonviable particles.     

Mobilisation of Cadmium by meso‐ and racemic‐2,3‐Dimercaptosuccinic Acid (DMSA) in Rats

A higher efficiency of cadmium binding with racemic than with meso‐2,3‐dimercaptosuccinic acid (rac‐DMSA; meso‐DMSA) was found in an in vitro speciation model by Fang et al. (1996). This finding has not yet been tested in vivo. This paper presents results on mobilisation of cadmium by meso‐ and rac‐DMSA in rats. Cadmium chloride was administered as the radioactive isotope ¹⁰⁹Cd intraperitoneally to all animals. One group was an untreated control and two groups were treated with meso‐ and rac‐DMSA, respectively. Treatment with chelators was applied twice, immediately after ¹⁰⁹Cd and 24 hr afterwards intraperitoneally at the dose of 1 mmol/kg, each. Six days later radioactivity was measured in the liver and kidneys. Whole‐body counting was carried out on days 1, 2, 3 and 6 of the experiment. At the end of the experiment, both treatments caused a decrease in ¹⁰⁹Cd whole‐body retention with rac‐DMSA being more efficient (decrease from 83% in control to 74% and 64% in groups treated with meso‐ and rac‐DMSA, respectively). The same reduction of ¹⁰⁹Cd was obtained by both chelators in the liver (from 57% to about 47%). In the kidney only rac‐DMSA produced significant reduction of ¹⁰⁹Cd (from 5.3% to 3.5%). In conclusion, these results show modest reduction of cadmium in the body by two isoforms of DMSA with rac‐DMSA being slightly more efficient than meso‐DMSA.     

Induction of Renal Mixed Function Oxidases in the Rat and Mouse: Correlation with Ultrastructural Changes in the Proximal Tubule

Induction of Renal Mixed Function Oxidases in the Rat and Mouse:Correlation with Ultrastructural Changes in the Proximal Tubule.RUSH, G. F., PRATT, I. S., LOCK, E. A., AND HOOK, J. B. (1986).Fundam. Appl. Toxicol. 6, 307–316. Rats and mice werepretreated with ß-naphthoflavone (BNF) at 100 mg/kg/day,ip, for 4 days, or polybrominated biphenyl (PBB) as a singleip dose at 150 mg/kg, and the temporal changes in renal mixedfunction oxidase (MFO) activity and ultrastructural changesin the proximal tubule were examined. Rat renal cytochrome P-450(P), ethoxycoumarin-O-deethylase (ECOD), and ethoxyresorufin-O-deethylase(EROD) were increased 5 days following the first dose of inducer.P-450 content and enzyme activity peaked on Day 5 to Day 10and returned to control values by Day 15. BNF and PBB causedproliferation of smooth endoplasmic reticulum (SER) in onlythe S₃ segment of the rat proximal tubule. Histologic analysisindicated that there was a close correlation between the temporalchanges in renal MFO activity and proliferation of SER in theS₃ segment of the proximal tubule. In contrast to the rat, mouserenal P-450 and ECOD were not induced by either BNF or PBB norwas there any significant proliferation of SER in any segmentof the proximal tubule. Mouse renal EROD was slightly increasedon Day 5 but not Day 10 or 15 by BNF; PBB had no effect. Inaddition to proliferation of SER, these inducers also causedproliferation of peroxisomes in the rat and mouse proximal tubule.These results demonstrate a temporal relationship between inductionof rat renal MFOs and proliferation of SER in specific sectionsof the proximal tubule and thus suggest that induction of theserenal enzymes may also be restricted to specific cell populationsof the kidney. A species difference apparently exists sinceproliferation of SER was not observed in the mouse.     

Oral meso-2,3-dimercaptosuccinic acid in pregnant Sprague-Dawley rats: teratogenicity and alterations in mineral metabolism. I. Teratological evaluation

meso-2,3-Dimercaptosuccinic acid (DMSA), an effective antagonist for the treatment of lead, arsenic, mercury, and cadmium poisoning, was evaluated for developmental toxicity in pregnant Sprague-Dawley rats. DMSA was administered by gavage on d 6-15 of gestation at doses of 0, 100, 300, or 1000 mg DMSA/kg/d. At termination on d 20 of gestation, fetuses were examined for external, visceral, and skeletal malformations and variations. Maternal toxicity was observed at all doses, as evidenced by a significant decrease in body weight gain. There were no effects with respect to hematology or clinical chemistry. Increased early resorptions, increased percentage postimplantation loss, and reduced fetal body weight per litter were observed at 100, 300, and 1000 mg/kg/d. Examination of fetuses for gross external abnormalities, visceral and skeletal malformations, or ossification variations revealed that DMSA did not produce teratogenicity at any dosage level. However, significant fetotoxicity was observed at 100, 300, and 1000 mg/kg/d. The no-observable-effect level (NOEL) for maternal and developmental toxicity was less than 100 mg DMSA/kg/d.     

Arsenic excretion after treatment of arsenic poisoning with DMSA or DMPS in mice

The effects of 2,3-dimercaptosuccinic acid (DMSA) and 2,3-dimercaptopropane-1-sulfonic acid, Na salt (DMPS) on arsenic excretion in arsenic poisoning were studied using ICR mice. One group of mice was given arsenic trioxide (5 mg As/kg, s.c.) and another two groups were given DMSA or DMPS (100 mg/kg, i.p.) immediately after administration of the arsenic (5 mg/kg, s.c.). Arsenic excretion in urine and feces was determined by atomic absorption spectrophotometry. Results obtained showed a marked arsenic excretion in the urine collected at the first 12 hr in the group treated with DMSA. Further remarkable arsenic excretion in the feces was seen in the group treated with DMPS, suggesting that arsenic might have been excreted in the bile.     

人脐静脉内皮细胞水通道蛋白9磷酸化与砷耐受性的关系

目的探讨人脐静脉内皮细胞株ECV-304和抗砷性ECV-304(AsRE)细胞株中水通道蛋白AQP9的表达及其磷酸化水平以及其对亚砷酸钠(NaAsO2)耐受性之间的关系。方法 采用CCK8法测定NaAsO22.5～40μmo.l L-1作用24 h对ECV-304和AsRE细胞株的毒性。NaAsO22.5～20μmol.L-1处理ECV-304和AsRE细胞株2 h,实时定量PCR法测定AQP9 mRNA表达水平,Western印迹法检测AQP9和p38蛋白表达水平;免疫印迹法检测AQP9蛋白磷酸化水平;电感耦合等离子体质谱仪(ICP-MS)法测定细胞内砷含量。结果 NaAsO2在AsRE和ECV-304细胞的IC50分别为12.59和4.06μmol.L-1。在NaAsO2同浓度下,AsRE细胞内砷摄入量均低于ECV-304细胞(P<0.05)。NaAsO2处理ECV-304和AsRE细胞后,AQP9 mRNA表达水平均有所下调,但在AsRE细胞中的下调幅度显著高于ECV-304细胞(P<0.05);AQP9蛋白水平在AsRE细胞呈浓度增加而下降,而ECV-304细胞中则无明显变化;ECV-304细胞中AQP9磷酸化水平随浓度有所上升,AsRE细胞中AQP9磷酸化水平则一直维持在更高的表达水平。NaAsO2处理后,p38蛋白及其磷酸化水平在两个细胞株间无明显变化。结论 AsRE细胞中AQP9的磷酸化水平与砷耐受性有明显相关性,其可能机制是AQP9通过影响细胞对砷的摄入影响砷的耐受性。     

Influence of 2,3-dimercaptosuccinic acid on gastrointestinal lead absorption and whole-body lead retention

2,3-Dimercaptosuccinic acid (DMSA) is a new orally active heavy metal chelator for the treatment of childhood Pb intoxication on an outpatient basis. The influence of DMSA, as well as other chelating agents, on gastrointestinal 203Pb absorption and whole-body 203Pb retention was examined. Groups of Sprague-Dawley rats (230-260 g) were gavaged with a solution containing approximately 25 mg/kg Pb [as Pb(NO3)2] plus 15 microCi 203Pb. Some groups were then immediately given 0.11 mmol/kg of either DMSA, CaNa2EDTA, D-penicillamine, or BAL by oral gavage, while other groups received the same drugs by ip injection. Control groups received solutions of the drug vehicles po or ip. Whole-body Pb retention and gastrointestinal Pb absorption (whole body retention + urinary Pb excretion) were significantly decreased in rats that received DMSA po. This finding implies that the use of DMSA to treat childhood lead intoxication on an outpatient basis is not associated with a risk for increased Pb absorption.