- Email: [email protected]
Influence of chelating agents on the gastrointestinal absorption of lead
TOXICOLOGYAND APPLIED PHARMACOLOGY34259-263
Influence
of Chelating
Agents
(1975)
on the Gastrointestinal of Leadlt2
SLOBODAN JUGO,~ TEA MALJKOVIC, Department
for Mineral
Received
Metabolism, Zagreb 41000,
February
26,1975;
Absorption
AND KRISTA KOSTIAL
Institute Yugoslavia accepted
for Medical May
Research,
16,1975
Influence of Chelating Agents on the Gastrointestinal Absorption of Lead. JUGO, S., MALJKOVIC, T. AND KOSTIAL, K. (1975). Toxicol. Appl. Pharmacol. 34, 259-263. The effect of chelating agents given orally and parenterally in therapeutic doses (0.2 mmol/kg) on the gastrointestinal absorption of lead (50 mg/kg and 0.5 mg/kg) wasinvestigated in female, 5- to 7week-old rats using a method of radioactive zo3Pblabeling. Intraperitoneal administration of calcium disodium ethylenediaminetetraacetate and 2,3dimercaptopropanol increased significantly the intestinal lead absorption. Sodium citrate, D-penicillamine, calcium disodium ethylenediaminetetraacetate, and 2,3-dimercaptopropanol given orally caused an increase in the lead absorption from the bowel. The amount of lead retained in the body in this experiment was also increased by all chelating agents except calcium disodium ethylenediaminetetraacetate. Despite some findings (Castellino and Aloj, 1965; Garber and Wei, 1974), it is generally accepted that the oral administration of calcium disodium ethylenediaminetetraacetate (Ca-EDTA) can increase the absorption of lead from the intestine (Rieders, 1960; Byers, 1959; Kehoe, 1955; Chisolm, 1968) by forming a Pb-EDTA chelate that is readily absorbed (Selander, 1967). Byers (1959) suggested that even the intravenous administration of Ca-EDTA may promote lead absorption from the bowel and, therefore, emptying the intestinal tract by enemata may be an important preliminary to treatment with chelating agents in acute oral lead intoxications. Catsch (1961) also indicated that the parenteral injection of chelating compounds can increase the intestinal absorption of metals since an increased resorption of radiometals from contaminated wounds after Ca-EDTA treatment was observed. It was experimentally shown that parenteral administration of chelating compounds can increase absorption of iron (Nigrovid et al., 1967) and strontium (Kostial et al., 1967) from the intestine. However, there are no experimental data about increased intestinal lead absorption after a parenteral injection of chelating agents and thus it was proposed not to waste time with an enema and to institute chelation therapy as soon as possible (Chisolm, 1968). 1 This work was partially supported by a research grant from the U.S. Public Health Service and the U.S. Environmental Protection Agency. 2 Presented in part at the 8th Congress of the Yugoslav Physiological Society, September 24-28, 1973, Opatija Yugoslavia, and at the 1st Congress of the Yugoslav Toxicological Society, October 6-9, 1974, Herceg-Novi, Yugoslavia. 3 Present address: Coney Island Hospital, Surgical Services, 2601 Ocean Parkway, Brooklyn, N.Y. 11235. Copyright CQ 1975 by Academic Press, Inc. 259 All rights of reproduction in any form reserved. Printed
in Great
Britain
260
JUGO,
MALJKOVIC
AND
KOSTIAL
We attempted to establish whether chelating compounds given parenterally in therapeutic doses have any influence on intestinal lead absorption. We also determined the absorbability of some lead chelates from the gastrointestinal tract. METHODS
Animals. Experiments were performed on 5- to 7-week-old female albino rats weighing 90-140 g. Animals were placed into individual metabolic cages and fed stock laboratory diet and water ad libitum. Stable andradioactive lead. Lead, as the acetate, was used in doses of 50 and 0.5 mg/kg labeled with radioactive zo3Pb (Gustav Werner Institute, Uppsala, Sweden). Each animal received about 15 &i of 203Pb. Chelating agents. Ca-EDTA (Koch-Light Laboratories Ltd., Colnbrook, Bucks, England) was given in a dose of 75 mg/kg (0.2 mmol/kg) which is widely accepted as a maximal safe dose for human use (Chisolm, 1968). 2,3-Dimercaptopropanol (BAL) Pliva, Zagreb, Yugoslavia) was used as well as other chelating agents in an equimolar concentration to EDTA, 25 mg/kg. D-Penicillamine (Trolovol-Substanz-Bayer, Bayer-Leverkusen, Germany) was given in a dose of 30 mg/kg and sodium citrate in a dose of 60 mg/kg. First experiment. A dose of 50 mg/kg of lead as the acetate labeled with zo3Pb was given by stomach tube. Immediately after the lead had been given, the animals were divided into three groups and two were injected intraperitonealiy with Ca-EDTA or BAL. Whole-body retention and cumulative urinary excretion of zo3Pb were determined with a twin crystal assembly (Tobor, Nuclear Chicago) 6 days after the lead and chelating agents were given, a time at which all unabsorbed lead has been eliminated from the bowel (Kostial et al., 1973). Secondexperiment. Animals received by stomach tube 0.5 mg/kg lead in the form of lead acetate or in a chelated form (Pb-EDTA, Pb-BAL, Pb-citrate, and Pb-n-penicillamine) labeled with 203Pb. Chelates were prepared before administration by mixing lead acetate and the chelating agents in a molar ratio of 1: 83. Whole-body retention and cumuiative urinary excretions were measured 6 days later as previously described. Determination of intestinal lead absorption. The percentage of lead absorbed was calculated by adding the total 6-day urinary excretion to the amount of lead remaining in the body after 6 days. This method has been also used by others (Harrison et al., 1969; Baxter and Sullivan, 1972). Fecal excretion was neglected. Statistics. The results are expressed as a percentage of the dose of lead given &SE. The significance of the difference between the means of control and treated animals was calculated by Student’s t test. RESULTS
The results presented in Table 1 show that chelating agents given intraperitoneally do not decrease the body retention of orally administered 203Pb. On the contrary, a slight increase in body retention in the treated groups can be seen although the difference relative to controls is not statistically significant. The urinary excretion of 203Pb was much higher in animals receiving chelation therapy than in control (P < 0.001). The
CHELATINGAGENTSAND
261
LEAD ABSORPTION
gastrointestinal absorption of lead was significantly increased in treated animals (p < 0.01). As an explanation of these results, it was suggested that the biliary excreted fraction of the parenteral dose of chelating compounds may chelate lead intraluminally in the bowel and thus promote absorption (Jugo, 1973). To support this presumption it was TABLE 1 ~N~LUENCEOFINTRAPERITONEALADMINISTRATIONOFCALCIUMDISODIUMETHYLENEDIAMINETETRAACETATE (EDTA) AND&~-DlMERCAPTOPROPANOL (BAL) INEQUIMOLAR CONCENTRATION (0.2 mmol/kg) ON ABSORPTION, WHOLE-BODY RETENTION, AND TOTAL URINARY EXCRETION OF SINGLE ORAL DOSE OF 203P~ GIVEN WITH STABLE LEAD (50mg/kg) ACETATE'
Group Control
Ca-EDTA BAL
Number of animals
Whole-body retention
Total urinary excretion
Absorptionb
18 20 20
1.05 -f: 0.14 1.41 + 0.24 1.60 +- 0.28
0.13 * 0.02 1.54 +_ 0.29 1.45 5 0.24
1.19 +_ 0.15 3.01 c 0.50 3.05 f 0.49
a The results are expressed as a percentage of dose (mean + SE) 144 hr after lead and chelating agent administration. * Absorption was calculated by adding total urinary excretion to whole body retention.
TABLE 2 ABSORPTION, WHOLE-BODY RETENTION, AND TOTAL URINARY EXCRETION OF 203P~, 144hr AFTERASINGLEORALDOSEOFSOMELEADCHELATESTORATS~ Number of animals
Control (Pb-acetate) Pb-EDTA Pb-citrate
Pb-penicillamine Pb-BAL
8
10 9 7
10
Whole-body retention
Total
urinary
excretion
Absorptionb
0.70 c 0.15
0.31 + 0.05
1.01 + 0.20
0.43 2.30 1.87 3.39
1.39 +_ 0.13 0.61 +_ 0.10 1.22 LO.10 6.62 + 0.96
1.82 ?I 0.14 2.94 + 0.57
+ + rt +
0.04 0.48 0.19 0.44
3.09 + 0.28 9.94 f 1.31
a Dose of stable lead was 0.5 mg/kg, and doses of chelating agents were 0.2 mmol/kg. The results are expressed as a percentage of dose (mean + SE). b Absorption was calculated by adding total urinary excretion to whole body retention.
necessary to show experimentally that lead in chelated form is much more readily absorbed from the bowel than unchelated lead. Therefore, a second experiment was performed and the results are presented in Table 2. All lead chelates were absorbed in greater amounts than unchelated lead (p < 0.001) All chelating agents, except CaEDTA
also caused an increase
in the whole-body
retention
amount of lead retained in the body after oral Pb-EDTA
of lead (p < 0.001).
The
was not significantly affected.
262
JUGO,
MALJKOVIC
AND
KOSTIAL
The urinary excretion of zo3Pb was markedly enhanced in all groups receiving chelating agents @ < 0.001). DISCUSSION In the first experiment (Table 1) we showed that the parenteral application of chelating agents such as Ca-EDTA and BAL can increase intestinal lead absorption. Thus the presumptions of Byers (1959) and Catsch (1961) were experimentally demonstrated. The mechanism of this action of the chelating compounds is not clear. One of the possible mechanisms could be stated as follows: A certain quantity of the parenteral dose of chelating agents is excreted by the biliary tract. The presence of the chelating agent in the intestinal content would result in the chelation of unabsorbed lead. If the chelated lead is absorbed more readily than the unchelated lead, the intestinal absorption of lead will increase. Such a mechanism could explain the effect of BAL but is less likely to in the case of Ca-EDTA. Namely, BAL is eliminated rapidly by both the biliary and urinary tract (Peters et al., 1947) and our results (Table 2) indicate that the Pb-BAL chelate is absorbed from the intestine in an amount 10 times higher than unchelated lead. Contrary to this, only 3% of the parenteral dose of Ca-EDTA is excreted into intestine (Foreman et al., 1953) and such a small quantity of Ca-EDTA could provide a means for increase of lead absorption only if the absorbability of Pb-EDTA chelate is much greater than shown by our experiment (Table 2). A nonspecific increase in intestinal permeability after Ca-EDTA treatment had been reported (Aronson and Rogerson, 1972; Schanker and Johnson, 1961) but the doses that were used were toxic and much higher than those used here. Although the mechanism of such action remains to be elucidated, the increased absorption of lead from the intestine induced by the parenteral injection of chelating agents may explain the clinical experience of deterioration in some cases of lead encephalopathy after chelation therapy has been instituted (Chisolm, 1968). According to our results, this phenomenon may be related to enhanced intestinal lead absorption with an elevation of circulating lead concentrations and consequent toxic effects. It is concluded that in acute oral lead intoxication, especially if it is severe, the use of an enema for removal of unabsorbed lead from the bowel before instituting chelating agents may be an essential step in the therapeutic regime. In the part of this work that dealt with the influence of oral chelating agents on gastrointestinal lead absorption, we showed that all chelating agents used enhanced the amount of lead absorbed. This finding is of considerable importance since the intestinal tract is a major route for burdening the human population with lead (National Academy of Sciences, 1972), and some chelating compounds are widely used as food additives or may occur as natural food constituents (Furia, 1968). Our results are in agreement with the recent report of Garber and Wei (1974) who found that sodium citrate increased the intestinal absorption of lead in mice. The same authors failed to find our effect of Ca-EDTA, probably because they neglected urinary excretion in calculating the amount of lead absorbed. According to our results, D-penicillamine which is used as an oral drug for lead poisoning (Selander, 1967; Goldberg et al., 1963; Chisolm, 1968) can enhance lead absorption and therefore we would like to recommend that oral D-penicillamine be avoided if a significant amount of unabsorbed lead in the bowel is suspected.
CHELATINGAGENTSAND
LEAD
ABSORPTION
263
REFERENCES ARONSON, A. L. AND ROGERSON,K. M. (1972). Effect of calcium and chromium chelates of ethylenediaminetetraacetate on intestinal permeability and collagen metabolism in the rat. Toxicol. Appl. Pharmacol.
21,440-453.
BAXTER,D. W. ANDSULLIVAN,M. F. (1972). Gastrointestinalabsorption and retention of plutonium chelates.Health Phys. 22,785-786. BYERS, R. K. (1959).Leadpoisoning.Review of the literature and report on 45 cases. Pediatrics 23,585~603. CASTELLINO, N. ANDALOJ, S. (1965)Effects of calcium sodiumethylenediaminetetra-acetate on the kineticsof distribution and excretion of leadin the rat. Brit. J. Znd. Med. 22, 172-180. CATSCH,A. (1961).Radioactive metal mobilization. Fed. Proc. Fed. Amer. Sot. Exp. Biol. 20 (Suppl. lo), 206-219. CHISOLM, J. J., JR. (1968).The useof chelatingagentsin the treatment of acute and chronic lead intoxication in childhood. J. Pediut. 73, l-38. FOREMAN, H., VIER, M. AND MAGEE,M. (1953). The metabolismof C14-labeledethylenediaminetetraaceticacid in the rat. J. Biol. Chem. 203, 1045-1053. FURIA,T. E. (1968).Handbook of Food Additives, pp. 263-266,289-312. ChemicalRubber PublishingCo., Cleveland,Ohio. GARBER,B. T. ANDWEI, E. (1974).Influenceof dietary factors on the gastrointestinalabsorption of lead. Toxicol. Appl. Pharmacol. 27,685-691. GOLDBERG, A., SMITH, J. A. AND LOCHHEAD, A. C. (1963).Treatment of lead poisoningwith oral penicillamine.Brit, Med. J. 1, 1270-1275. HARRISON, G. E., CARR,T. E. F., SUTTON,A., HUMPHREYS, E. R. ANDRmoo, J. (1969). Effects of alginateon the absorptionof lead in man. Nature (London) 224,1115-l 116. JUGO,S. (1973)Influence of Some Chelating Agents on Lead Metabolism in Relation to Age. MSc. thesis,pp. 82-87. University of Zagreb, Yugoslavia. KEHOE,R. A. (1955).Misuseof edathamilcalciumdisodiumfor prophylaxis of leadpoisoning. J Amer. Med. Ass. 157, 341-342. KCSTIAL,K., VOJVODI~,S.ANDMALJKOVIC,T. (1967).Influenceof somecomplexingagentson radiostrontium metabolism.Arh. Hig. Rada. 18, 111-123. KOSTIAL,K., KELLO,D. ANDHARRISON, G. H. (1973).Comparative metabolismof lead and calciumin young and adult rats. Znt. Arch. Arbeitsmed. 31, 159-161. National Academy of Sciences(1972).Lead. Airborne Lead in Perspective, pp. 47-70. National Academy of Sciences,WashingtonD.C. NIGROVIC,V., SPRENG, P. ANDBOHNE,F. (1967). Untersuchungenzur Frage der enteralen Eisenresorption.In Radioisotope in der Gastroenterologie (G. Hoffmann, Ed.), pp. 147-l 50. F. K. Schattauer-Verlag,Stuttgart. PETERS,R. A., SPRAY,G.H.,STOCKEN,L. A.,COLLIE,C. H., GRACE,M. A. AND WHEATLEY, G. A. (1947).The useof British anti-Lewisitecontainingradioactive sulfur for metabolism investigations.Biochem. J. 41, 370-373. RIEDERS, F. (1960). Current conceptsin the therapy of lead poisoning.In Metal-Binding in Medicine (M. J. Seven,Ed.), pp. 143-145.Lippincott, Philadelphia. SCHANKER, L. S. ANDJOHNSON, J. M. (1961).Increasedintestinalabsorptionof foreign organic compoundsin the presenceof ethylenediaminetetraacetic acid (EDTA). Biochem. Pharmacol. ii, 4214122. I SELANDER, S.(1967).Treatment of leadpoisoning.A comparisonbetweenthe effectsof sodium calciumedetateand penicillamineadministeredorally and intravenously. Brit. J. Znd. Med. 24,272-281.
Influence
of Chelating
Agents
(1975)
on the Gastrointestinal of Leadlt2
SLOBODAN JUGO,~ TEA MALJKOVIC, Department
for Mineral
Received
Metabolism, Zagreb 41000,
February
26,1975;
Absorption
AND KRISTA KOSTIAL
Institute Yugoslavia accepted
for Medical May
Research,
16,1975
Influence of Chelating Agents on the Gastrointestinal Absorption of Lead. JUGO, S., MALJKOVIC, T. AND KOSTIAL, K. (1975). Toxicol. Appl. Pharmacol. 34, 259-263. The effect of chelating agents given orally and parenterally in therapeutic doses (0.2 mmol/kg) on the gastrointestinal absorption of lead (50 mg/kg and 0.5 mg/kg) wasinvestigated in female, 5- to 7week-old rats using a method of radioactive zo3Pblabeling. Intraperitoneal administration of calcium disodium ethylenediaminetetraacetate and 2,3dimercaptopropanol increased significantly the intestinal lead absorption. Sodium citrate, D-penicillamine, calcium disodium ethylenediaminetetraacetate, and 2,3-dimercaptopropanol given orally caused an increase in the lead absorption from the bowel. The amount of lead retained in the body in this experiment was also increased by all chelating agents except calcium disodium ethylenediaminetetraacetate. Despite some findings (Castellino and Aloj, 1965; Garber and Wei, 1974), it is generally accepted that the oral administration of calcium disodium ethylenediaminetetraacetate (Ca-EDTA) can increase the absorption of lead from the intestine (Rieders, 1960; Byers, 1959; Kehoe, 1955; Chisolm, 1968) by forming a Pb-EDTA chelate that is readily absorbed (Selander, 1967). Byers (1959) suggested that even the intravenous administration of Ca-EDTA may promote lead absorption from the bowel and, therefore, emptying the intestinal tract by enemata may be an important preliminary to treatment with chelating agents in acute oral lead intoxications. Catsch (1961) also indicated that the parenteral injection of chelating compounds can increase the intestinal absorption of metals since an increased resorption of radiometals from contaminated wounds after Ca-EDTA treatment was observed. It was experimentally shown that parenteral administration of chelating compounds can increase absorption of iron (Nigrovid et al., 1967) and strontium (Kostial et al., 1967) from the intestine. However, there are no experimental data about increased intestinal lead absorption after a parenteral injection of chelating agents and thus it was proposed not to waste time with an enema and to institute chelation therapy as soon as possible (Chisolm, 1968). 1 This work was partially supported by a research grant from the U.S. Public Health Service and the U.S. Environmental Protection Agency. 2 Presented in part at the 8th Congress of the Yugoslav Physiological Society, September 24-28, 1973, Opatija Yugoslavia, and at the 1st Congress of the Yugoslav Toxicological Society, October 6-9, 1974, Herceg-Novi, Yugoslavia. 3 Present address: Coney Island Hospital, Surgical Services, 2601 Ocean Parkway, Brooklyn, N.Y. 11235. Copyright CQ 1975 by Academic Press, Inc. 259 All rights of reproduction in any form reserved. Printed
in Great
Britain
260
JUGO,
MALJKOVIC
AND
KOSTIAL
We attempted to establish whether chelating compounds given parenterally in therapeutic doses have any influence on intestinal lead absorption. We also determined the absorbability of some lead chelates from the gastrointestinal tract. METHODS
Animals. Experiments were performed on 5- to 7-week-old female albino rats weighing 90-140 g. Animals were placed into individual metabolic cages and fed stock laboratory diet and water ad libitum. Stable andradioactive lead. Lead, as the acetate, was used in doses of 50 and 0.5 mg/kg labeled with radioactive zo3Pb (Gustav Werner Institute, Uppsala, Sweden). Each animal received about 15 &i of 203Pb. Chelating agents. Ca-EDTA (Koch-Light Laboratories Ltd., Colnbrook, Bucks, England) was given in a dose of 75 mg/kg (0.2 mmol/kg) which is widely accepted as a maximal safe dose for human use (Chisolm, 1968). 2,3-Dimercaptopropanol (BAL) Pliva, Zagreb, Yugoslavia) was used as well as other chelating agents in an equimolar concentration to EDTA, 25 mg/kg. D-Penicillamine (Trolovol-Substanz-Bayer, Bayer-Leverkusen, Germany) was given in a dose of 30 mg/kg and sodium citrate in a dose of 60 mg/kg. First experiment. A dose of 50 mg/kg of lead as the acetate labeled with zo3Pb was given by stomach tube. Immediately after the lead had been given, the animals were divided into three groups and two were injected intraperitonealiy with Ca-EDTA or BAL. Whole-body retention and cumulative urinary excretion of zo3Pb were determined with a twin crystal assembly (Tobor, Nuclear Chicago) 6 days after the lead and chelating agents were given, a time at which all unabsorbed lead has been eliminated from the bowel (Kostial et al., 1973). Secondexperiment. Animals received by stomach tube 0.5 mg/kg lead in the form of lead acetate or in a chelated form (Pb-EDTA, Pb-BAL, Pb-citrate, and Pb-n-penicillamine) labeled with 203Pb. Chelates were prepared before administration by mixing lead acetate and the chelating agents in a molar ratio of 1: 83. Whole-body retention and cumuiative urinary excretions were measured 6 days later as previously described. Determination of intestinal lead absorption. The percentage of lead absorbed was calculated by adding the total 6-day urinary excretion to the amount of lead remaining in the body after 6 days. This method has been also used by others (Harrison et al., 1969; Baxter and Sullivan, 1972). Fecal excretion was neglected. Statistics. The results are expressed as a percentage of the dose of lead given &SE. The significance of the difference between the means of control and treated animals was calculated by Student’s t test. RESULTS
The results presented in Table 1 show that chelating agents given intraperitoneally do not decrease the body retention of orally administered 203Pb. On the contrary, a slight increase in body retention in the treated groups can be seen although the difference relative to controls is not statistically significant. The urinary excretion of 203Pb was much higher in animals receiving chelation therapy than in control (P < 0.001). The
CHELATINGAGENTSAND
261
LEAD ABSORPTION
gastrointestinal absorption of lead was significantly increased in treated animals (p < 0.01). As an explanation of these results, it was suggested that the biliary excreted fraction of the parenteral dose of chelating compounds may chelate lead intraluminally in the bowel and thus promote absorption (Jugo, 1973). To support this presumption it was TABLE 1 ~N~LUENCEOFINTRAPERITONEALADMINISTRATIONOFCALCIUMDISODIUMETHYLENEDIAMINETETRAACETATE (EDTA) AND&~-DlMERCAPTOPROPANOL (BAL) INEQUIMOLAR CONCENTRATION (0.2 mmol/kg) ON ABSORPTION, WHOLE-BODY RETENTION, AND TOTAL URINARY EXCRETION OF SINGLE ORAL DOSE OF 203P~ GIVEN WITH STABLE LEAD (50mg/kg) ACETATE'
Group Control
Ca-EDTA BAL
Number of animals
Whole-body retention
Total urinary excretion
Absorptionb
18 20 20
1.05 -f: 0.14 1.41 + 0.24 1.60 +- 0.28
0.13 * 0.02 1.54 +_ 0.29 1.45 5 0.24
1.19 +_ 0.15 3.01 c 0.50 3.05 f 0.49
a The results are expressed as a percentage of dose (mean + SE) 144 hr after lead and chelating agent administration. * Absorption was calculated by adding total urinary excretion to whole body retention.
TABLE 2 ABSORPTION, WHOLE-BODY RETENTION, AND TOTAL URINARY EXCRETION OF 203P~, 144hr AFTERASINGLEORALDOSEOFSOMELEADCHELATESTORATS~ Number of animals
Control (Pb-acetate) Pb-EDTA Pb-citrate
Pb-penicillamine Pb-BAL
8
10 9 7
10
Whole-body retention
Total
urinary
excretion
Absorptionb
0.70 c 0.15
0.31 + 0.05
1.01 + 0.20
0.43 2.30 1.87 3.39
1.39 +_ 0.13 0.61 +_ 0.10 1.22 LO.10 6.62 + 0.96
1.82 ?I 0.14 2.94 + 0.57
+ + rt +
0.04 0.48 0.19 0.44
3.09 + 0.28 9.94 f 1.31
a Dose of stable lead was 0.5 mg/kg, and doses of chelating agents were 0.2 mmol/kg. The results are expressed as a percentage of dose (mean + SE). b Absorption was calculated by adding total urinary excretion to whole body retention.
necessary to show experimentally that lead in chelated form is much more readily absorbed from the bowel than unchelated lead. Therefore, a second experiment was performed and the results are presented in Table 2. All lead chelates were absorbed in greater amounts than unchelated lead (p < 0.001) All chelating agents, except CaEDTA
also caused an increase
in the whole-body
retention
amount of lead retained in the body after oral Pb-EDTA
of lead (p < 0.001).
The
was not significantly affected.
262
JUGO,
MALJKOVIC
AND
KOSTIAL
The urinary excretion of zo3Pb was markedly enhanced in all groups receiving chelating agents @ < 0.001). DISCUSSION In the first experiment (Table 1) we showed that the parenteral application of chelating agents such as Ca-EDTA and BAL can increase intestinal lead absorption. Thus the presumptions of Byers (1959) and Catsch (1961) were experimentally demonstrated. The mechanism of this action of the chelating compounds is not clear. One of the possible mechanisms could be stated as follows: A certain quantity of the parenteral dose of chelating agents is excreted by the biliary tract. The presence of the chelating agent in the intestinal content would result in the chelation of unabsorbed lead. If the chelated lead is absorbed more readily than the unchelated lead, the intestinal absorption of lead will increase. Such a mechanism could explain the effect of BAL but is less likely to in the case of Ca-EDTA. Namely, BAL is eliminated rapidly by both the biliary and urinary tract (Peters et al., 1947) and our results (Table 2) indicate that the Pb-BAL chelate is absorbed from the intestine in an amount 10 times higher than unchelated lead. Contrary to this, only 3% of the parenteral dose of Ca-EDTA is excreted into intestine (Foreman et al., 1953) and such a small quantity of Ca-EDTA could provide a means for increase of lead absorption only if the absorbability of Pb-EDTA chelate is much greater than shown by our experiment (Table 2). A nonspecific increase in intestinal permeability after Ca-EDTA treatment had been reported (Aronson and Rogerson, 1972; Schanker and Johnson, 1961) but the doses that were used were toxic and much higher than those used here. Although the mechanism of such action remains to be elucidated, the increased absorption of lead from the intestine induced by the parenteral injection of chelating agents may explain the clinical experience of deterioration in some cases of lead encephalopathy after chelation therapy has been instituted (Chisolm, 1968). According to our results, this phenomenon may be related to enhanced intestinal lead absorption with an elevation of circulating lead concentrations and consequent toxic effects. It is concluded that in acute oral lead intoxication, especially if it is severe, the use of an enema for removal of unabsorbed lead from the bowel before instituting chelating agents may be an essential step in the therapeutic regime. In the part of this work that dealt with the influence of oral chelating agents on gastrointestinal lead absorption, we showed that all chelating agents used enhanced the amount of lead absorbed. This finding is of considerable importance since the intestinal tract is a major route for burdening the human population with lead (National Academy of Sciences, 1972), and some chelating compounds are widely used as food additives or may occur as natural food constituents (Furia, 1968). Our results are in agreement with the recent report of Garber and Wei (1974) who found that sodium citrate increased the intestinal absorption of lead in mice. The same authors failed to find our effect of Ca-EDTA, probably because they neglected urinary excretion in calculating the amount of lead absorbed. According to our results, D-penicillamine which is used as an oral drug for lead poisoning (Selander, 1967; Goldberg et al., 1963; Chisolm, 1968) can enhance lead absorption and therefore we would like to recommend that oral D-penicillamine be avoided if a significant amount of unabsorbed lead in the bowel is suspected.
CHELATINGAGENTSAND
LEAD
ABSORPTION
263
REFERENCES ARONSON, A. L. AND ROGERSON,K. M. (1972). Effect of calcium and chromium chelates of ethylenediaminetetraacetate on intestinal permeability and collagen metabolism in the rat. Toxicol. Appl. Pharmacol.
21,440-453.
BAXTER,D. W. ANDSULLIVAN,M. F. (1972). Gastrointestinalabsorption and retention of plutonium chelates.Health Phys. 22,785-786. BYERS, R. K. (1959).Leadpoisoning.Review of the literature and report on 45 cases. Pediatrics 23,585~603. CASTELLINO, N. ANDALOJ, S. (1965)Effects of calcium sodiumethylenediaminetetra-acetate on the kineticsof distribution and excretion of leadin the rat. Brit. J. Znd. Med. 22, 172-180. CATSCH,A. (1961).Radioactive metal mobilization. Fed. Proc. Fed. Amer. Sot. Exp. Biol. 20 (Suppl. lo), 206-219. CHISOLM, J. J., JR. (1968).The useof chelatingagentsin the treatment of acute and chronic lead intoxication in childhood. J. Pediut. 73, l-38. FOREMAN, H., VIER, M. AND MAGEE,M. (1953). The metabolismof C14-labeledethylenediaminetetraaceticacid in the rat. J. Biol. Chem. 203, 1045-1053. FURIA,T. E. (1968).Handbook of Food Additives, pp. 263-266,289-312. ChemicalRubber PublishingCo., Cleveland,Ohio. GARBER,B. T. ANDWEI, E. (1974).Influenceof dietary factors on the gastrointestinalabsorption of lead. Toxicol. Appl. Pharmacol. 27,685-691. GOLDBERG, A., SMITH, J. A. AND LOCHHEAD, A. C. (1963).Treatment of lead poisoningwith oral penicillamine.Brit, Med. J. 1, 1270-1275. HARRISON, G. E., CARR,T. E. F., SUTTON,A., HUMPHREYS, E. R. ANDRmoo, J. (1969). Effects of alginateon the absorptionof lead in man. Nature (London) 224,1115-l 116. JUGO,S. (1973)Influence of Some Chelating Agents on Lead Metabolism in Relation to Age. MSc. thesis,pp. 82-87. University of Zagreb, Yugoslavia. KEHOE,R. A. (1955).Misuseof edathamilcalciumdisodiumfor prophylaxis of leadpoisoning. J Amer. Med. Ass. 157, 341-342. KCSTIAL,K., VOJVODI~,S.ANDMALJKOVIC,T. (1967).Influenceof somecomplexingagentson radiostrontium metabolism.Arh. Hig. Rada. 18, 111-123. KOSTIAL,K., KELLO,D. ANDHARRISON, G. H. (1973).Comparative metabolismof lead and calciumin young and adult rats. Znt. Arch. Arbeitsmed. 31, 159-161. National Academy of Sciences(1972).Lead. Airborne Lead in Perspective, pp. 47-70. National Academy of Sciences,WashingtonD.C. NIGROVIC,V., SPRENG, P. ANDBOHNE,F. (1967). Untersuchungenzur Frage der enteralen Eisenresorption.In Radioisotope in der Gastroenterologie (G. Hoffmann, Ed.), pp. 147-l 50. F. K. Schattauer-Verlag,Stuttgart. PETERS,R. A., SPRAY,G.H.,STOCKEN,L. A.,COLLIE,C. H., GRACE,M. A. AND WHEATLEY, G. A. (1947).The useof British anti-Lewisitecontainingradioactive sulfur for metabolism investigations.Biochem. J. 41, 370-373. RIEDERS, F. (1960). Current conceptsin the therapy of lead poisoning.In Metal-Binding in Medicine (M. J. Seven,Ed.), pp. 143-145.Lippincott, Philadelphia. SCHANKER, L. S. ANDJOHNSON, J. M. (1961).Increasedintestinalabsorptionof foreign organic compoundsin the presenceof ethylenediaminetetraacetic acid (EDTA). Biochem. Pharmacol. ii, 4214122. I SELANDER, S.(1967).Treatment of leadpoisoning.A comparisonbetweenthe effectsof sodium calciumedetateand penicillamineadministeredorally and intravenously. Brit. J. Znd. Med. 24,272-281.