Efficacy of various dithiol compounds in acute As2O3 poisoning in mice

Metabolism and toxicity of arsenicals in mammals

Arsenic (As) is a metalloid usually found in organic and inorganic forms with different oxidation states, while inorganic form (arsenite As-III and arsenate As-v) is considered to be more hazardous as compared to organic form (methylarsonate and dimethylarsinate), with mild or no toxicity in mammals. Due to an increasing trend to using arsenicals as growth promoters or for treatment purposes, the understanding of metabolism and toxicity of As gets vital importance. Its toxicity is mainly depends on oxi-reduction states (As-III or As-v) and the level of methylation during the metabolism process. Currently, the exact metabolic pathways of As have yet to be confirmed in humans and food producing animals. Oxidative methylation and glutathione conjugation is believed to be major pathways of As metabolism. Oxidative methylation is based on conversion of Arsenite in to mono-methylarsonic acid and di-methylarsenic acid in mammals. It has been confirmed that As is only methylated in the presence of glutathione or thiol compounds, suggesting that As is being methylated in trivalent states. Subsequently, non-conjugated trivalent arsenicals are highly reactive with thiol which converts the trivalent arsenicals in to less toxic pentavalent forms. The glutathione conjugate stability of As is the most important factor for determining the toxicity. It can lead to DNA damage by alerting enzyme profile and production of reactive oxygen and nitrogen species which causes the oxidative stress. Moreover, As causes immune-dysfunction by hindering cellular and humeral immune response. The present review discussed different metabolic pathways and toxic outcomes of arsenicals in mammals which will be helpful in health risk assessment and its impact on biological world.

α-Lipoic acid protects against arsenic trioxide-induced acute QT prolongation in anesthetized guinea pigs

Clinical use of arsenic trioxide (As₂O₃), which can induce the remission of relapsed or refractory acute promyelocytic leukemia, is often limited because of its cardiotoxicity. Symptoms of cardiotoxicity include acute cardiac conduction disturbances, such as QT prolongation. The present study was undertaken to evaluate the effects of α-lipoic acid (LA) on acute As₂O₃-induced ECG abnormalities (QTc interval prolongation) in anesthetized guinea pigs. Intravenous injection of As₂O₃ in guinea pigs caused QTc interval prolongation, which was significantly attenuated by co-treatment with LA (0.35, 3.5 and 35 mg/kg) in a dose-dependent manner. In isolated guinea pig cardiomyocytes, the decrease in IKs current induced by As₂O3 (1 μM) was rapidly restored to the basal level by the addition of LA (10 μM). Consistent with this finding, the As₂O₃-induced QTc interval prolongation was also improved rapidly by post-treatment with LA in guinea pigs. Electrospray ionization time-of-flight mass spectrometry analysis detected an expected peak of arsenic-LA complex in vitro, indicating that LA and As₂O3 form a new compound in vivo. In addition, pre-treatment with a chelating agent, British anti-Lewisite (BAL, 3.5 or 35 mg/kg), also attenuated the As₂O₃-induced QTc interval prolongation. In this study, co- and post-treatments with LA and pre-treatment with BAL ameliorated As₂O₃-induced acute QT prolongation in anesthetized guinea pigs. Because LA and probably BAL may bind to As₂O₃, these agents may exert protective effects through their chelating activity. Further studies are needed to determine whether LA is beneficial as a prophylactic or rescue agent for acute promyelocytic leukemia patients treated with As₂O₃.

In vitro and in vivo reduction of sodium arsenite induced toxicity by aqueous garlic extract

BACKGROUND

Arsenic is ubiquitous in the environment, and chronic or acute exposure through food and water as well as occupational sources can contribute to a well-defined spectrum of disease. Despite arsenic being a health hazard and a well-documented human carcinogen, a safe, effective and specific preventive or therapeutic measure for treating arsenic induced toxicity still eludes us.

OBJECTIVE

This study was undertaken to evaluate the therapeutic efficacy of aqueous garlic (Allium sativum L.) extract (AGE) in terms of normalization of altered biochemical parameters particularly indicative of oxidative stress following sodium arsenite (NaAsO(2)) exposure and depletion of inorganic arsenic burden, in vitro and in vivo.

RESULTS

AGE (2mg/ml) co-administered with 10 microM NaAsO(2) attenuated arsenite induced cytotoxicity, reduced intracellular reactive oxygen species (ROS) level in human malignant melanoma cells (A375), human keratinocyte cells (HaCaT) and in cultured human normal dermal fibroblast cells. Moreover, AGE application in NaAsO(2) intoxicated Sprague-Dawley rats resulted in a marked inhibition of tissue lipid peroxide generation; enhanced level of total tissue sulfhydryl groups and glutathione; and also increased the activities of antioxidant enzymes, superoxide dismutase and catalase to near normal. An increase in blood ROS level and myeloperoxidase activity in arsenic-intoxicated rats was effectively prevented by AGE administration. AGE was also able to counter arsenic mediated incongruity in blood hematological variables and glucose level.

CONCLUSIONS

The restorative property of AGE was attributed to its antioxidant activity, chelating efficacy, and/or oxidizing capability of trivalent arsenic to its less toxic pentavalent form. Taken together, evidences indicate that AGE can be a potential protective regimen for arsenic mediated toxicity.

Effect of Centella asiatica on arsenic induced oxidative stress and metal distribution in rats

Concomitant oral supplementation of Centella asiatica (100, 200 or 300 mg kg(-1), orally once daily) during arsenic exposure (20 ppm in drinking water for 4 weeks) was investigated in rats for its protective value. The animals exposed to arsenic (III) showed a significant inhibition of delta-aminolevulinic acid dehydratase (ALAD) activity, a marginal decrease in glutathione (GSH) and an increase in zinc protoporphyrin (ZPP) level in blood. Hepatic and renal glutathione (GSH) decreased, while oxidized glutathione (GSSG) and thiobarbituric acid reactive substance (TBARS) levels increased significantly in the liver, kidney and brain. The activities of brain superoxide dismutase (SOD) and catalase decreased marginally on arsenic exposure. Concomitant administration of Centella asiatica showed a significant protective action on inhibited blood ALAD activity and restored the blood GSH level, whereas most of the other blood biochemical parameters remained unchanged on Centella asiatica supplementation. Interestingly, most of the hepatic biochemical variables indicative of oxidative stress showed protection. There was, however, a significant protection observed in the altered kidney GSSG level and hepatic and brain TBARS. Only a marginal beneficial effect of Centella asiatica on blood and liver arsenic concentration was noted, particularly at the highest dose studies (300 mg kg(-1)). No effect of Centella asiatica on most of the altered renal biochemical parameters was noted. The results thus lead to the conclusion that simultaneous supplementation of Centella asiatica significantly protects against arsenic-induced oxidative stress but does not influence the arsenic concentration in these organs. It can thus be suggested that co-administration of Centella asiatica protects animals from arsenic-induced oxidative stress but exhibits no chelating property. Further studies are recommended for determining the effect of co-administration of Centella asiatica during chelation therapy with a thiol chelator.

Arsenic trioxide (As(2)O(3)) inhibits peritoneal invasion of ovarian carcinoma cells in vitro and in vivo

OBJECTIVES

To study the role of arsenic trioxide (As(2)O(3)) in regulating peritoneal invasive activity of ovarian carcinoma cells in vitro and in vivo.

METHODS

The effects of As(2)O(3) on human ovarian cancer cell lines (3AO, SW626 and HO-8910PM) migration, invasion and adhesion with tumor cells and human peritoneal mesothelial cells (HPMC) were observed by means of cell migration test, cell invasion test and cell adhesion test. The effects of As(2)O(3) on MMP-2, MMP-9, TIMP-1 and TIMP-2 gene expressions and protein expressions of tumor cells were determined by RT-PCR and ELISA, respectively. In animal experiments, ovarian tumor cells were implanted into abdominal cavity of nude mice and then the nude mice were treated by intraperitoneal injection of different doses As(2)O(3). The foci on the surface of peritoneum were counted.

RESULTS

As(2)O(3) inhibited tumor cells migration, invasion and adhesion with HPMC in a dose-dependent manner, while the same treatment enhanced tumor cell-tumor cell interactions. As(2)O(3) inhibited mRNA and protein expressions of MMP-2, MMP-9 and TIMP-2 of tumor cells. In contrast, As(2)O(3) increased mRNA and protein expressions of TIMP-1. As(2)O(3) could reduce tumor cells peritoneal metastasis in nude mice.

CONCLUSION

As(2)O(3) inhibits in vitro and in vivo peritoneal invasive activity of ovarian carcinoma cells in a dose-dependent manner. Its anti-invasive activity may be the results of reduced cell motility, inhibited attachment of tumor cells to HPMC and enhanced tumor cell-tumor cell interaction, as well as down-regulation of MMP-2 and MMP-9 levels and up-regulation of TIMP-1 level.

Chronic arsenic poisoning in the rat: treatment with combined administration of succimers and an antioxidant

The influence of the coadministration of vitamin C or vitamin E on the efficacy of two thiol chelators, meso-2,3-dimercaptosuccinic acid (DMSA) or monoisoamyl DMSA, in counteracting chronic arsenic toxicity was investigated in rats. Vitamin C and vitamin E were only mildly effective when given alone or in combination with the above chelators in mobilizing arsenic from the target tissues. However, combined administration of vitamin C plus DMSA and vitamin E plus MiADMSA led to a more pronounced depletion of brain arsenic. The supplementation of vitamins was significantly effective in restoring inhibition of blood delta-aminolevulinic acid dehydratase (ALAD) oxidative stress in liver, kidneys, and brain as reflected by reduced levels of thiobarbituric acid reactive substance and oxidized and reduced glutathione levels. The results thus lead us to suggest that coadministration of vitamin E or vitamin C may be useful in the restoration of altered biochemical variables (particularly the effects on heme biosynthesis and oxidative injury) although it has only a limited role in depleting arsenic burden.

Acute arsenic poisoning treated by intravenous dimercaptosuccinic acid (DMSA) and combined extrarenal epuration techniques

Arsenic poisoning was diagnosed in a 26-year-old man who had been criminally intoxicated over the last two weeks preceding admission by the surreptitious oral administration of probably 10 g of arsenic trioxide (As2O3). The patient developed severe manifestations of toxic hepatitis and pancreatitis, and thereafter neurological disorders, respiratory distress, acute renal failure, and cardiovascular disturbances. In addition to supportive therapy, extrarenal elimination techniques and chelating agents were used. Dimercaprol (BAL) and dimercaptosuccinic acid (DMSA or succimer) were used simultaneously as arsenic chelating agents for two days, and thereafter DMSA was used alone. DMSA was administered by intravenous (20 mg/kg/d for five days, then 10 mg/kg/d for six days) and intraperitoneal route. Intravenous DMSA infusion was well tolerated and resulted in an increase in arsenic blood concentration immediately after the infusion. Continuous venovenous hemofiltration combined with hemodialysis, and peritoneal dialysis were proposed to enhance arsenic elimination. It was calculated that over an 11-day period 14.5 mg arsenic were eliminated by the urine, 26.7 mg by hemodialysis, 17.8 mg by peritoneal dialysis, and 7.8 mg by continuous venovenous hemofiltration. These amounts appeared negligible with regard to the probable ingested dose. The patient died on day 26 from the consequences of multiple organ failure, with subarachnoid hemorrhage and generalized infection caused by Aspergillus fumigatus.

Randomized placebo-controlled trial of 2,3-dimercapto-1-propanesulfonate (DMPS) in therapy of chronic arsenicosis due to drinking arsenic-contaminated water

BACKGROUND

Chronic arsenic toxicity, producing various clinical manifestations, is currently epidemic in West Bengal, India, Bangladesh, and other regions of the world. 2,3-Dimercapto-1-propanesulfonate, a chelating agent, increases excretion of arsenic in urine to several times the prechelation concentration but the therapeutic efficacy of 2,3-dimercapto-1-propanesulfonate in the management of chronic arsenic toxicity has been incompletely evaluated. We investigated the clinical use of 2,3-dmercapto-1-propanesulfonate in such patients.

METHODS

Twenty-one consecutive patients with chronic arsenicosis were individually randomized into 2 groups: 11 patients (9 males and 2 females, age 30.63+/-11.4 years) received 2,3-dimercapto-1-propanesulfonate 100-mg capsules 4 times a day for 1 week and repeated in the 3rd, 5th, and 7th week with no drug during the intervening period. The other 10 patients (5 males and 5 females, age 34.4+/-14.41 years) were given placebo capsules (resembling 2,3-dimercapto-1-propanesulfonate) in the same schedule. The consumption of arsenic-contaminated water was terminated by all 21 subjects. Initial and posttreatment urinary arsenic excretion was determined in all cases. Sequential excretion of urinary arsenic was determined during the treatment of 2 drug- and 1 placebo-treated cases. The clinical features were evaluated by an objective scoring system before and after treatment. Routine investigation including liver function test and skin biopsy were also done before and after the treatment. Drug-associated toxicity was tabulated.

RESULTS

Therapy with 2,3-dimercapto-1-propanesulfonate caused significant improvement in the clinical condition of chronic arsenicosis patients as evidenced by significant reduction of total clinical scores from 8.90+/-2.84 to 3.27+/-1.73; p < 0.0001. Exposure cessation alone with placebo treatment also reduced clinical scores (8.50+/-1.96 to 5.40+/-2.12; p < 0.003), but the posttreatment total clinical score of 2,3-dimercapto-1-propanesulfonate-treated patients (3.27+/-1.73) was significantly lower than that of placebo-treated patients (5.40+/-2.12; p < 0.01). The most significant improvement was noted in regard to the clinical scores of weakness, pigmentation, and lung disease. No difference was noted between groups in the hematological and biochemical parameters (which were normal) and skin histology before and after treatment. No 2,3-dimercapto-1-propanesulfonate-related adverse effects were noted. Total urinary excretion of arsenic in 2,3-dimercapto-1-propanesulfonate-treated cases increased significantly following drug therapy, with no increase in placebo-treated cases.

CONCLUSION

2,3-Dimercapto-1-propanesulfonate treatment caused significant improvement in the clinical score of patients suffering from chronic arsenic toxicity. Increased urinary excretion of arsenic during the period of therapy is the possible cause of this improvement.

Randomized placebo-controlled trial of 2,3-dimercaptosuccinic acid in therapy of chronic arsenicosis due to drinking arsenic-contaminated subsoil water

INTRODUCTION

Chronic arsenic toxicity producing various clinical manifestations is currently epidemic in West Bengal, India, Bangladesh, and other regions of the world. Animal studies have indicated that 2,3-dimercaptosuccinic acid can be used as an oral chelating agent. A prospective, double-blind, randomized controlled trial was carried out to evaluate the efficacy and safety of 2,3-dimercaptosuccinic acid for chronic arsenicosis due to drinking arsenic-contaminated (> or = 50 micrograms/L) subsoil water in West Bengal.

METHOD

Twenty-one consecutive patients with chronic arsenicosis were individually randomized (random number; assignment made by individual not evaluating patients) into 2 groups: 11 patients (10 male, age 25.5 +/- 8 years) received 2,3-dimercaptosuccinic acid 1400 mg/d (1000 mg/m2) in the first week and 1050 mg/d (750 mg/m2) during the next 2 weeks with a repeat course 3 weeks later. The other 10 patients (all male, age 32.2 +/- 9.7 years) were given placebo capsules for the same schedule. The clinical features were evaluated by an objective scoring system before and after treatment. Routine investigations including liver function tests, arsenic concentrations in urine, hair, and nails, and skin biopsy evaluations were also completed.

RESULTS

Though there was improvement in the clinical score of 2,3-dimercaptosuccinic acid-treated patients, similar improvement was observed in the placebo-treated group. There were no statistical differences in the clinical scores between the 2 groups at the beginning and at the end of treatment. Similarly, no differences were found for the other investigated parameters.

CONCLUSION

Under the conditions of this study, 2,3-dimercaptosuccinic acid was not effective in producing any clinical or biochemical benefit or any histopathological improvement of skin lesions in patients with chronic arsenicosis.

Are we ready to replace dimercaprol (BAL) as an arsenic antidote?

1 Dimercaprol (BAL), 2,3-dimercaptopropanesulphonate sodium (DMPS) and meso-2,3-dimercaptosuccinic acid (DMSA) are effective arsenic antidotes, but the question which one is preferable for optimal therapy of arsenic poisoning is still open to discussion. Major drawbacks of BAL include (a) its low therapeutic index, (b) its tendency to redistribute arsenic to brain and testes, for example, (c) the need for (painful) intramuscular injection and (d) its unpleasant odour. 2 The newer antidotes DMPS and DMSA feature low toxicity and high therapeutic index. They can be given orally or intravenously due to their high water solubility. While these advantages make it likely that DMPS and DMSA will replace BAL for the treatment of chronic arsenic poisoning, acute intoxication-especially with lipophilic organoarsenicals-may pose a problem for the hydrophilic antidotes, because their ionic nature can adversely affect intracellular availability. 3 This article focuses on aspects dealing with the power of BAL, DMPS, and DMSA to mobilize tissue-bound arsenic in various experimental models, such as monolayers of MDCK (= Madin-Darby canine kidney) cells from dog kidney, isolated perfused liver from guinea-pigs, and perfused jejunal segments from rat small intestine. 4 The results show that hydrophilic DMPS and DMSA may fail to rapidly and completely remove arsenic that has escaped from the extracellular space across tight epithelial barriers. However, owing to their low toxicity, which allows larger doses to be applied, and the potential modification of their pharmacokinetics by means of inert oral anion-exchange resins, DMPS and DMSA may advantageously replace BAL whenever intervention time is not critical. With severe intoxication by organic arsenicals, when the point-of-no-return is a limiting factor, BAL may still have a place as an arsenic antidote.

Effect of DMPS and various adsorbents on the arsenic excretion in guinea-pigs after injection with As2O3

The present experiments were performed to test the possibility of interrupting the enterohepatic circulation of arsenic (As). Therefore the efficacy of adsorbents to bind As and/or As-DMPS adducts in vitro and their effect on the excretion of As into the feces and urine in vivo were investigated after injection of As2O3 and DMPS in guinea-pigs. The adsorbents bentonite, activated charcoal or colestyramine, respectively, were tested. Only slight binding of 73As (< 5% of the 73As dose) was observed to all adsorbents in vitro. After addition of DMPS, a good binding was found for 73As to colestyramine (50%) or activated charcoal (60%), respectively. However, the 73As-DMPS adduct was removed from the activated charcoal during washing. In the first in vivo experiment, male guinea-pigs (n = 4/group) received As2O3 [0.02 mmol As(III)/kg s.c. labelled with a tracer dose of 73As(III) (0.14 kBq/g)], 30 min later DMPS (0.1 mmol/kg i.p.) and by gastric tube (10 ml/kg body wt) either saline, bentonite (1 g/kg), activated charcoal (1 g/kg) or colestyramine (0.2 g/kg), respectively. Urine and feces were collected for 24 h. No increase in 73As excretion into the feces was observed after administration of DMPS and all adsorbents, compared to control animals. In the second in vivo experiment male guinea-pigs (n = 4/group) received the same As2O3 (+ 73As)- and DMPS dose. In addition, with a gastric tube (10 ml/kg) saline, colestyramine (0.2 g/kg), DMPS (0.1 mmol/kg), or the combination of DMPS (0.1 mmol/kg) + colestyramine (0.2 g/kg) were administered according to the scheme given in the following table. The amount of feces excreted did not differ between groups. Excretion of 73As within the feces during the first 12 h after As injection is shown in the following table (mean +/- SEM). The same amount of 73As (34% of the 73As dose) was excreted into the urine from animals in groups 4 and 5 during this time. Obviously, the combined oral administration of DMPS + colestyramine markedly enhanced fecal excretion of As mobilized by DMPS i.p. It is suggested that interruption of enterohepatic circulation of As may be a valuable adjunct in the treatment of As poisoning.

Pediatric arsenic ingestion

Acute arsenic toxicity is rare, and there have been no pediatric cases of acute arsenic poisoning in the recent literature. We report a pediatric case of acute arsenic ingestion treated initially with British antilewisite (BAL) and D-penicillamine (DP), and later with dimercaptosuccinic acid (DMSA). A 22-month-old girl ingested 1 oz 2.27% sodium arsenate and developed immediate vomiting and diarrhea. The patient presented to a community emergency department with the following vital signs: blood pressure 96/72 mm Hg, pulse 160 beats/min, respirations 22 breaths/min. She was pale and lethargic. Gastric lavage was performed, and abdominal X-ray was normal. She continued to have gastrointestinal symptoms and received 3 mg/kg BAL. Sinus tachycardia persisted, with heart rate increasing to 200 beats/min. In 12 hours, she was asymptomatic and was started on oral DP. On day 1, 24-hour urine arsenic was 4,880 micrograms/L. She remained asymptomatic and was discharged on day 6 on oral DP. She did well except for a rash that could have been a side effect of DP. On day 8, when the day 5 24-hour urine arsenic level was returned at 650 micrograms/L, the patient was readmitted and started on DMSA. After 4 days on DMSA, the 24-hour urine arsenic level was 96 micrograms/L. White blood cell count and renal and hepatic function remained normal. The excretion half-life was approximately 2.5 days, which is at least 2 to 3 times faster than the spontaneous excretion half-life expected in adults. Long-term follow-up was unavailable.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of various antidotes on the biliary and intestinal excretion of arsenic in situ and into the feces in vivo in guinea-pigs after injection of As2O3

The effect of various antidotes on the excretion of arsenic into the feces in vivo and on the biliary and enteric excretion in situ was investigated on segments of jejunum and colon in anesthetized guinea-pigs using the pendular perfusion technique, according to Henning and Forth (1982). In the in situ experiments guinea-pigs received As2O3 (0.02 mmol As(III)/kg) and 30 min later, British-Anti-Lewisite (BAL), dimercaptopropanesulfonic acid (DMPS), dimercaptosuccinic acid (DMSA) or 2,3-bis-(acetylthio)propanesulfonamide (BAPSA) (0.1 or 0.7 mmol/kg each) into the jugular vein. In the in vivo experiments guinea-pigs received As2O3 s.c. (same dose as above) and 30 min later the same antidotes (0.1 mmol/kg i.p.). The feces were collected for 24 h and the arsenic content measured. During the 60-min perfusion period the amount of arsenic excreted into the jejunum or colon was only 3% or 0.4% of the dose administered, respectively. Of the arsenic dose, 8% was found in the bile. None of the antidotes had an effect on the arsenic excretion into the jejunum or colon. No change in biliary excretion was found in animals treated with BAL, 0.1 or 0.7 mmol/kg, respectively. DMSA, BAPSA or DMPS, 0.1 mmol/kg, increased the biliary excretion of arsenic to 14, 33, or 43% of the dose administered and after 0.7 mmol/kg to 29, 37, or 42%, respectively. Furthermore, a significant increase (P > 0.05) was found for the bile/blood concentration ratio in the following order: control < BAL < DMSA < BAPSA approximately DMPS.(ABSTRACT TRUNCATED AT 250 WORDS)

A chemical hypothesis for arsenic methylation in mammals

The toxicology of arsenic is complicated by its ability to convert between oxidation states and organometalloidal forms. These processes cause differences in the relative tissue-binding affinities of the various arsenic species, and they determine both the intoxication and the detoxification mechanisms. In this review, a chemical hypothesis of arsenic biomethylation is developed from an examination of data and observations presented by researchers who conducted numerous in vivo and in vitro experiments. It is likely that a combination of pathways is actually used during methylation of arsenic in vivo, and that the principal mechanism depends on various factors affecting the cellular environment. Despite these uncertainties, several observations can be made: (i) glutathione (GSH) is required for reduction of arsenic(V) to arsenic(III) species in preparation for enzyme-catalyzed oxidative methylation; (ii) GSH is not involved in monomethylation once arsenite is formed, but GSH is involved in dimethylation by reducing methylarsonic acid [MMA(V)] to methylarsonous acid [MMA(III)]; (iii) GSH is also required in the methylation of arsenic by stabilizing the reductive nature of the cell; (iv) a different methyltransferase is used in each methylation step; (v) dithiols (either a cofactor or the methyltransferases) are required for both mono- and dimethylation and (vi) where dithiols are involved, oxidative methylation reduces the stability of the arsenic-sulfur complex and permits dissociation of the arsenic species. This lower affinity of the pentavalent organoarsenic species for dithiols is part of the reason why methylation of arsenic can be a detoxification mechanism when the As(III) intermediates are not permitted to accumulate.

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)

Effects of acute sodium arsenite administration on the pulmonary chemical metabolizing enzymes, cytochrome P-450 monooxygenase, NAD(P)H:quinone acceptor oxidoreductase and glutathione S-transferase in guinea pig: comparison with effects in liver and kidney

Tissue specific changes in the cytochrome P-450 (P-450) monooxygenase system were observed following a single subcutaneous dose of sodium arsenite (75 mumol/kg), a known inducer of stress proteins. P-450 monooxygenase activities were assayed with several isozyme selective substrates; 7-ethoxyresorufin, 7-pentoxyresorufin, 4-aminobiphenyl and erythromycin. Both tissue selective and isozyme selective changes in monooxygenase activity were noted. For example, the rate of 4-aminobiphenyl N-hydroxylation (ABH) was increased by arsenite administration in lung but not in liver. Arsenite inhibited 7-ethoxyresorufin O-deethylation (ERF) in all tissues of control animals, but to a lesser extent in lung. However, increases of ERF activity occurred after arsenite treatment in lung of beta-naphthoflavone (beta NF)-treated guinea pigs whereas arsenite decreased ERF activities in the kidney and liver of these animals. These complex effects on ERF activity may in part be modulated by induction of heme oxygenase, whose activity was increased 2.5-3.5-fold in these organs by arsenite. The highest heme oxygenase activity was found in kidney with lower activities being present in liver and lung, respectively. These data are consistent with the decreased P-450 content observed in kidney and liver microsomes of arsenite treated guinea pigs. On the other hand there was either no change or a slight increase (about 2-fold) in the pulmonary microsomal P-450 content of these animals. A complex pattern of induction for the non-heme, Ah locus associated enzyme, NAD(P)H:quinone acceptor oxidoreductase (QOR) was also observed. With menadione as substrate arsenite treatment increased QOR activity in all tissues studied. However, with dichlorophenolindophenol (DCPIP) as substrate a significant arsenite effect was observed only in the kidney. Significant differences between the QOR substrates were also observed in beta NF-treated guinea pigs and control animals. Our results are consistent with the presence of more than one form of QOR in the guinea pig. Arsenite treatment also caused an increase in glutathione S-transferase activity, with 2,4-dinitro-1-chlorobenzene (DNCB) as substrate, of guinea pig kidney but not liver or lung.

Effect of various antidotes on biliary excretion of arsenic in isolated perfused livers of guinea pigs after acute experimental poisoning with As2O3

The effect of the dithiols British Anti-Kewisite (BAL), dimercaptopropanesulfonic acid (DMPS), dimercaptosuccinic acid (DMSA) and a new metal binding agent 2,3-bis-(acetylthio)- propanesulfonamide (BAPSA) on the biliary excretion of arsenic in perfused livers of guinea pigs after acute experimental poisoning with As2O3 was investigated. Guinea pigs received As2O3, 10.0 mg/kg subcutaneously at 9 a.m. as a single injection. One hour after the injection the livers were perfused (2.5 ml x min.-1 x g-1 liver) with Krebs-Henseleit buffer and glucose for 80 min. After 40 min. of saline perfusion (control) 0.1 or 0.7 mmol/l BAL, DMSA, DMPS, or BAPSA were added to the perfusate and arsenic elimination in the bile and effluent perfusate was measured. The biliary excretion of arsenic in control livers between 40 and 80 min. was 0.7% of the total arsenic liver content before perfusion (= arsenic liver content after perfusion + portion excreted in the bile+perfusate). After antidote addition (0.1 mmol/l) the excretion was 0.2% for livers perfused with BAL, 6.8% for DMSA, 10.6% for DMPS, and 11.1% for BAPSA, respectively. After 0.7 mmol/l antidote the excretion of arsenic was 0.1% in livers perfused with BAL, 9.6% for DMSA, 12.3% for DMPS, and 13.3% for BAPSA, respectively. Except BAL, all compounds and most effectively BAPSA increased biliary excretion of arsenic. This indicates that excretion of arsenic which normally is mainly renal is shifted towards faecal excretion by the dithiols.