Chelation of lead during co-exposure to ethanol

Efficacy of calcium disodium EDTA, D-penicillamine (DPA), 2,3 dimercaptosuccinic acid (DMSA), and alpha-mercapto-beta-(2-furyl) acrylic acid (MFA) to reduce the body burden of lead and restore the altered biochemical variables in lead or lead + ethanol administered rats was investigated. The investigation was aimed to suggest suitable prophylaxis of lead intoxication prevalent among workers co-exposed to lead and alcohol ingestion. Administration of lead (10 mg/kg, oral, once daily for 8 weeks) produced a significant inhibition in the activity of blood delta-aminolevulinic acid dehydratase (ALAD), elevation in the blood zinc protoporphyrin (ZPP) and urinary elimination of lead and delta-aminolevulinic acid (ALA). Lead contents of blood, liver, kidney and brain were also significantly higher than the normal control. The above changes were more marked in animals co-exposed to lead + ethanol (20% in drinking water) compared to lead alone. All the chelators were effective in increasing the urinary lead elimination, reducing the above biochemical alterations and lead contents of tissues. The order of effectiveness being DMSA greater than Calcium disodium EDTA greater than DPA greater than MFA. However, the protection was more noticeable in animals treated with lead alone than with lead and ethanol.     

Decrease of hepatic delta-aminolevulinate dehydratase activity in an animal model of fatigue

Fatigue can be defined physiologically as inability to maintain the expected power output. At present, no standard of fatigue are yet available. In order to find biomarkers of fatigue, we investigated the level of delta-aminolevulinic acid (ALA), the first intermediate metabolite in the heme biosynthetic pathway, in the plasma and urine of an animal model of fatigue. To prepare fatigued animals, we kept rats for 5 days in a cage filled with water to a height of 1.5 cm. As a result, the plasma and urinary ALA levels were increased in the fatigued animals as compared with those in the control animals. One day after the rats had been returned to their normal cages, these increased levels were restored to the control ones. We also examined the activity of the enzyme ALA dehydratase (ALAD), which is the second enzyme in the heme biosynthetic pathway, and ALAD gene expression during the fatigue and its recovery sessions. The ALAD activity, as well as its gene expression, in the liver of the fatigued animals was decreased as compared with those of the control animals. Both activity and gene expression of ALAD were recovered to their respective control levels after the rats had been allowed to rest in their normal cages for 1 day. Furthermore, the activity of ALA synthase (ALAS), the rate-limiting enzyme in the heme biosynthesis, in the liver was increased after the fatigue session for 5 days. Although this level of increase in the plasma concentration of ALA may not induce fatigue, increase in plasma and urinary ALA levels can be biomarkers of fatigue.     

Relationship between lead absorption and iron status and its association with oxidative stress markers in lead-exposed workers

BackgroundThe emission of lead (Pb) occurring during the extraction, processing and industrial applications of this element remains a significant environmental risk factor. The absorbability of lead in humans is strongly associated with the general health status of exposed individuals. Existing mineral deficiencies are considered being a predisposition to an increased Pb uptake. Both, iron deficiency and lead poisoning are the major causative factors responsible for the prevalence of anemia within the vulnerable population, especially in children. Although some of the intervention programs of counteracting lead poisoning by iron supplementation proved to be effective in the Pb-exposed population, the exact mechanisms of this interaction still require further studies. The objective of the presented study was to examine the association of iron level on oxidative stress measures and its effects on the severity of lead toxicity in the exposed population.MethodsThe analyzed population consisted of 270 male workers from the lead-zinc smelter. The studied population was divided into two sub-groups based on the serum iron concentration: low iron level group (L-Fe; Fe < median value) and high iron level group (H-Fe; Fe > median value). Measured traits comprised of blood lead (PbB), serum Fe and zinc protoporphyrin (ZPP) levels as well as a blood count and oxidative stress markers.ResultsNo significant correlation between serum iron concentration and PbB in the tested cohort was found. On the contrary, the analysis of ZPP levels (long-term marker related to a hematologic toxic effect of Pb) within the subgroups differing in serum Fe level shown that ZPP was 12.3 % lower (p = 0.043) in subjects classified within the H-Fe group. A positive correlation of serum Fe and total antioxidant capacity (TAC) was found (R = 0.1999). The conducted 3-D PCA analysis showed that individuals classified within the H-Fe group were characterized by the co-occurrence of higher Fe levels, lower ZPP, and higher TAC value.ConclusionThese results support the existing evidence providing that maintaining the optimal status of Fe may play a significant role in preventing the lead poisoning and alleviating harmful effects of Pb on the oxidative balance in humans.     

Influence of zinc-saccharide complexes on some haematological parameters in rats

The effects of three recently synthesized zinc-saccharide complexes (zinc-fructose, zinc-galactose and zinc-glucose) on blood -aminolevulinic acid dehydratase (ALAD) activity, glutathione (GSH), zinc-protoporphyrin (ZPP) and urinary -aminolevulinic acid (ALA) levels have been investigated to ascertain the utility of these complexes as zinc supplements and as preventive agents against lead intoxication in rats.     

Blood lead concentration and delta-aminolevulinic acid dehydratase activity in adult Bufo arenarum

The effects of sublethal doses of lead (as acetate) on blood parameters of adult male Bufo arenarum were studied. Toads received one single injection with 10, 25, 50 or 100 mg/kg of body weight, equivalent to approximately 1/90-1/10 of the 120 h-LD50; seven days after the injections, the hematocrit and the blood delta-aminolevulinic acid dehydratase (ALAD) activity were measured. Hematocrit of lead-injected animals did not exhibit significant changes respective to controls that received sodium acetate (range 29.8-38.8%). Blood lead concentrations were positively and significantly correlated with the injected metal doses. Blood ALAD activity declined proportionately to the doses of the metal as well as to its whole blood concentration. Because of its sensitivity and specificity, it was concluded that the activity of delta-ALAD may be adopted as a reliable biomarker of Bufo arenarum experimental lead intoxication.     

Influence of dietary deficiency of nicotinamide on lead toxicity in young rats

The influence of dietary nicotinamide deficiency on lead intoxication in young developing rats was investigated. The Pb induced an increase in brain dopamine and noradrenaline, inhibition in blood δ-aminolevulinic acid dehydratase activity, an elevation in urinary excretion of δ-aminolevulinic acid and blood and tissue uptake of Pb were significantly more marked in animals maintained on a nicotinamide-deficient diet than those fed a nicotinamide-sufficient diet. The nicotinamide deficiency may enhance the susceptibility to Pb intoxication possible by enhancing the absorption of Pb and altering nicotinic acid metabolism.     

Increased lead uptake and inhibition of ALAD-activity in isolated rat hepatocytes incubated with lead-diethyldithiocarbamate complex

Dithiocarbamates can form lipid soluble complexes with lead and are known to markedly increase tissue uptake of lead and potentiate toxic effects of lead in rats. Cellular effects of the interactions between lead and diethyldithiocarbamate were studied in primary cultures of rat hepatocytes. The cells were incubated with lead acetate (PbAc) or lead-diethyldithiocarbamate complex (Pb(DTC)2), labelled with 203Pb. The lipid soluble Pb(DTC)2 was rapidly taken up in the cells and after 30 min incubation the cellular levels of lead were approximately 40 times higher in cells incubated with Pb(DTC)2 than in cells incubated with a similar concentration of PbAc. The maximal cellular uptake of lead was reached after 4 h incubation with Pb(DTC)2, while incubation with PbAc caused a slow continuously increasing uptake of lead during the 20 h incubation. The enzyme delta-aminolevulinic acid dehydratase (ALAD) was inhibited to a much higher extent by Pb(DTC)2 compared to PbAc after incubations with similar concentrations of lead. Maximal inhibition of ALAD activity was reached at a cellular concentration of 0.5-1 nmol Pb/mg protein, irrespective of which form of lead was used in the incubation. Pb(DTC)2 was shown to inhibit ALAD activity also in vitro when incubated with purified ALAD enzyme. The rapid and high intracellular uptake and cellular response of Pb(DTC)2, shown in the present study, may explain the drastic effects of dithiocarbamates on lead distribution and toxicity previously shown in vivo.     

Effects of combined administration of captopril and DMSA on arsenite induced oxidative stress and blood and tissue arsenic concentration in rats

We compared the therapeutic efficacy of captopril and a thiol chelating agent, meso 2,3-dimercaptosuccinic acid (DMSA) either individually or in combination against arsenite induced oxidative stress and mobilization of metal in rats. Animals were exposed to 100 ppm arsenite as sodium arsenite in drinking water for six weeks followed by treatment with DMSA (50 mg/kg, orally), captopril (50 mg/kg, intraperitoneally) either alone or in combination, once daily for 5 consecutive days. Arsenite exposure led to a significant depletion of blood delta-aminolevulinic acid dehydratase (ALAD) activity, glutathione and platelet levels while significantly increased the level of reactive oxygen species (in RBCs). Hepatic reduced glutathione (GSH) level showed a significant decrease while, thiobarbituric acid reactive substances (TBARS) levels increased on arsenite exposure indicating arsenite induced hepatic oxidative stress. Kidney GSH, GSSG, catalase and TBARS remained unchanged on arsenite exposure. Treatment with DMSA was effective in increasing ALAD activity while, captopril was ineffective when given alone. Captopril when co-administered with DMSA also provided no additional beneficial effect on blood ALAD activity but significant brought altered platelet counts back to the normal value. In contrast, administration of captopril alone provided significant beneficial effects on hepatic oxidative stress, and in combination with DMSA provided a more pronounced recovery in the TBARS level compared to the individual effect of DMSA and captopril. Renal biochemical variables remained insensitive to arsenite and any of the treatments. Interestingly, combined administration of captopril with DMSA had a remarkable effect in depleting total arsenic concentration from blood and soft tissues. These results lead us to conclude that captopril administration during chelation treatment had some beneficial effects particularly on the protection of inhibited blood ALAD activity, and depletion of arsenic level. The study supports our earlier conclusion that a co-administration of an antioxidant is more beneficial than monotherapy with the chelating agents, in order to achieve optimal effects of chelation in arsenite toxicity.     

delta-Aminolevulinic acid dehydratase: effects of succinylacetone in rat liver and kidney in an in vivo model of the renal Fanconi syndrome.

Succinylacetone (SA) is a known inhibitor of the heme biosynthetic pathway in liver. We have demonstrated previously the SA enhancement of delta-aminolevulinic acid dehydratase (ALAD) in renal tubules, while this enzyme is known to be impaired by SA in the liver. The present studies, based on in vivo treatment of animals with SA, show equivalent degree of inhibition of specific ALAD activity in liver and kidney. Both tissues evidenced an ability to restore enzyme activity with time, the recovery occurring much more slowly in kidney than in liver. The discrepant in vitro and in vivo effect of SA on renal ALAD may be due to differences between a direct inhibitor-enzyme interaction and inhibitor actions in the living cell, respectively. Persistent tissue levels of SA, consistent with demonstrated SA in plasma and urine, might account for continuing inhibition, with the greatest tissue accumulation in kidney where the substance must be cleared for excretion.     

Delta-aminolevulinic acid dehydratase (ALAD) activity in blood of Bufo arenarum (Anura)

The aim of the present investigation was to standardize a method for measuring delta-aminolevulinic acid dehydratase (ALAD) activity in circulating red blood cells of adult Bufo arenarum kept in controlled environmental conditions, and to obtain reference basal values suitable for environmental monitoring of lead exposure. The normal ALAD activity for B. arenarum was 131.86 +/- 14.47 U per liter of red blood cells (n = 38, mean +/- SEM; interval 72.98-236.33). In animals exposed to lead, ALAD activity decreased as lead dose increased.     

Lead-induced oxidative stress and hematological alterations and their response to combined administration of calcium disodium EDTA with a thiol chelator in rats

The therapeutic efficacy of calcium disodium ethylenediaminetetracetic acid (CaNa(2)EDTA) and the two thiol chelators, 2,3-dimercaptopropane 1-sulfonate (DMPS) and monoisoamyl dimercaptosuccinic acid (MiADMSA) was studied, both individually and in combination, in reducing lead concentration in blood and soft tissues and in restoring lead induced altered biochemical variables in rats. Exposure to subacute dose of lead implicated a critical role of reactive oxygen species (ROS) and oxidative stress in altering the normal values of these variables. Exposure to lead caused a significant inhibition of blood delta-aminolevulinic acid dehydratase (ALAD), an important enzyme in the haem synthesis pathway and glutathione (GSH) level. These changes were also accompanied by inhibition of ALAD activity in kidney, delta-aminolevulinic acid synthase (ALAS) activities in liver and changes in platelet counts in whole blood suggesting disturbed haem synthesis pathway. Lead exposure also led to a pronounced depletion of brain GSH contents, superoxide dismutase (SOD) activity, an increase in thiobarbituric acid reactive substances (TBARS), and activity of glutathione S-transferase (GST). Specific activities of membrane-bound enzymes, acetylcholinesterase (AChE) and monoamine oxidase (MAO), were significantly inhibited on lead exposure. These biochemical changes were correlated with increased uptake of lead in blood and soft tissues. Post lead exposure treatment with MiADMSA in particular provided significant recovery in altered biochemical variables besides significant depletion of tissue lead burden. Treatment with CaNa(2)EDTA and DMPS individually had only moderate beneficial effects on tissue oxidative stress, although they were equally effective in the removal of tissue lead burden. Tissue zinc and copper levels did not depict any significant depletion, although changes like marked depletion of zinc following CaNa(2)EDTA and copper after MiADMSA administration were of some concern. Combined administration of CaNa(2)EDTA, particularly with MiADMSA, was the most effective treatment protocol compared to all other treatments. It can be concluded from our present results that combined therapy with CaNa(2)EDTA and MiADMSA proved significantly better in restoring biochemical and clinical variables over monotherapy with these chelating agents against subacute lead exposure in adult rats.     

Beneficial effect of combined administration of some naturally occurring antioxidants (vitamins) and thiol chelators in the treatment of chronic lead intoxication

Ameliorative effects of few naturally occurring antioxidants like ascorbic acid (vitamin C), alpha-tocopherol (vitamin E) either alone or in combination with meso-2,3-dimercaptosuccinic acid (DMSA) or monoisoamyl DMSA (MiADMSA), on parameters indicative of oxidative stress in the liver, kidney, brain and blood of lead-exposed rats were studied. Male Wistar rats were exposed to 0.1% lead acetate in drinking water for 3 months and treated thereafter with DMSA or its analogue MiADMSA (50 mg/kg, intraperitoneally), either individually or in combination with vitamin E (5 mg/kg, intramuscularly) or vitamin C (25 mg/kg, orally) once daily for 5 days. The effects of these treatments in influencing the lead-induced alterations in haem synthesis pathway, hepatic, renal and brain oxidative stress and lead concentration from the soft tissues were investigated. Exposure to lead produced a significant inhibition of delta-aminolevulinic acid dehydratase (ALAD) activity from 8.44+/-0.26 in control animals to 1.76+/-0.32 in lead control, reduction in glutathione (GSH) from 3.56+/-0.14 to 2.57+/-0.25 and an increase in zinc protoporphyrin level from 62.0+/-3.9 to 170+/-10.7 in blood, suggesting altered haem synthesis pathway. Both the thiol chelators and the two vitamins were able to increase blood ALAD activity towards normal, however, GSH level responded favorably only to the two thiol chelators. The most prominent effect on blood ALAD activity was, however, observed when MiADMSA was co-administered with vitamin C (7.51+/-0.17). Lead exposure produced a significant depletion of hepatic GSH from 4.59+/-0.78 in control animals to 2.27+/-0.47 in lead controls and catalase activity from 100+/-3.4 to 22.1+/-0.25, while oxidized glutathione (GSSG; 0.34+/-0.05 to 2.05+/-0.25), thiobarbituric acid reactive substance (TBARS; 1.70+/-0.45 to 5.22+/-0.50) and glutathione peroxidase (GPx) levels (3.41+/-0.09 to 6.17+/-0.65) increased significantly, pointing to hepatic oxidative stress. Altered, reduced and oxidized GSH levels showed significant recovery after MiADMSA and DMSA administration while, vitamins E and C were effective in reducing GSSG and TBARS levels and increasing catalase activity. Administration of MiADMSA alone and the combined administration of vitamin C along with DMSA and MiADMSA were most effective in increasing hepatic GSH levels to 4.88+/-0.14, 4.09+/-0.12 and 4.30+/-0.06, respectively. Hepatic catalase also reached near normal level in animals co-administered vitamin C with DMSA or MiADMSA (82.5+/-4.5 and 84.2+/-3.5, respectively). Combined treatments with vitamins and the thiol chelators were also able to effectively reduce lead-induced decrease in renal catalase activity and increase in TBARS and GPx level. Combination therapy, however, was unable to provide an effective reversal in the altered parameters indicative of oxidative stress in different brain regions, except in catalase activity. The result also suggests a beneficial role of vitamin E when administered along with the thiol chelators (particularly with MiADMSA) in reducing body lead burden. Blood lead concentration was reduced from 13.3+/-0.11 in lead control to 0.3+/-0.01 in MiADMSA plus vitamin E-treated rats. Liver and kidney lead concentration also showed a most prominent decrease in MiADMSA plus vitamin E co-administered rats (5.29+/-0.16 to 0.63+/-0.02 and 14.1+/-0.21 to 1.51+/-0.13 in liver and kidney, respectively). These results thus suggest that vitamin C administration during chelation with DMSA/MiADMSA was significantly beneficial in reducing oxidative stress however, it had little or no additive effect on the depletion of lead compared with the effect of chelators alone. Thus, the co-administration of vitamin E during chelation treatment with DMSA or MiADMSA could be recommended for achieving optimum effects of chelation therapy.     

Biochemical and hematological effects of lead ingestion in nestling American kestrels (Falco sparverius)

One-day old American kestrel (Falco sparverius) nestlings were orally dosed daily with 5 microliters/g of corn oil (controls), 25, 125 or 625 mg/kg of metallic lead in corn oil for 10 days. Forty per cent of the nestlings receiving 625 mg/kg of lead died after 6 days and growth rates were significantly depressed in the two highest lead dosed groups. At 10 days hematocrit values were significantly lower in the two highest lead treated groups, and hemoglobin content and red blood cell delta-aminolevulinic acid dehydratase (ALAD) activity was depressed in all lead treated groups. Plasma creatine phosphokinase decreased in the two highest treatment groups. Brain, liver and kidney ALAD activities, brain RNA to protein ratio and liver protein concentration decreased after lead exposure whereas liver DNA, DNA to RNA ratio and DNA to protein ratio increased. Brain monoamine oxidase and ATPase were not significantly altered. Measurements of the ontogeny of hematological variants and enzymes in normal development, using additional untreated nestlings, revealed decreases in red blood cell ALAD, plasma aspartate amino transferase, lactate dehydrogenase, brain DNA and RNA and liver DNA, whereas hematocrit, hemoglobin, plasma alkaline phosphatase, brain monoamine oxidase, brain ALAD and liver ALAD increased during the first 10 days of posthatching development. Biochemical and hematological alterations were more severe than those reported in adult kestrels or precocial young birds exposed to lead. Alterations may be due in part to delayed development.     

Influence of L-lysine and zinc administration during exposure to lead or lead and ethanol in rats

Influence of lysine and zinc administration on the lead-sensitive biochemical parameters and the accumulation of lead during exposure to lead or lead and ethanol was investigated in rats. The lead exposure inhibited blood δ-aminolevulinic acid dehydratase (ALAD) activity, increased blood zinc protoporphyrin (ZPP), urinary δ-aminolevulinic acid (ALA), serum glutamic oxalacetic transaminase (SGOT), serum glutamic pyruvic transaminase (SGPT), blood and tissue lead levels, and decreased blood and hepatic glutahione (GSH) contents. Some of these effects were enhanced on coexposure to ethanol. The simultaneous administration of lysine and zinc reduced tissue accumulation of lead and most of the lead-induced biochemical alterations irrespective of exposure to lead alone or lead and ethanol. The depletion of endogenous calcium and magnesium owing to lead or ethanol exposure was also prevented by co-administration of lysine and zinc.     

Comparison of sex hormone dependent induction of delta-aminolevulinic acid dehydratase in chick liver and oviduct

1. Comparative study on induction of hepatic and oviduct delta-aminolevulinic acid dehydratase (EC 4.2.1.24, ALAD) was performed following estradiol-17 beta and/or testosterone administration in immature female chicken (Gallus domesticus). 2. The lowest amount of estradiol for maximal induction of hepatic and oviduct ALAD activity was 2 mg/day/bird. 3. When estradiol of 2 mg/day/bird was administered for 15 days successively, induction extent of oviduct ALAD molecule was markedly larger and became approximately 144-fold in comparison with that of liver. Testosterone (2 mg/day/bird) alone did not induce both hepatic and oviduct ALAD activity. 4. Synergistic and antagonistic effect of testosterone on estradiol-induced total ALAD activity in oviduct was dependent on testosterone amount administered, whereas testosterone antagonized the inductive effect of estradiol on liver ALAD activity, independently of its amount.     

Quercetin Administration During Chelation Therapy Protects Arsenic-Induced Oxidative Stress in Mice

We studied the efficacy of quercetin and a thiol chelating agent, monoisoamyl 2, 3-dimercaptosuccinic acid (MiADMSA) either individually or in combination against arsenic-induced oxidative stress and mobilization of metal in mouse. Animals were chronically exposed to 25 ppm arsenite as sodium arsenite in drinking water for 12 months followed by treatment with MiADMSA (0.2 mmol/kg, orally), quercetin (0.2 mmol, orally) either alone or in combination, once daily for 5 consecutive days. Arsenic exposure led to a significant depletion of blood δ-aminolevulinic acid dehydratase (ALAD) activity, glutathione, white (WBC) and red blood cell (RBC) counts, and an increase in platelet levels while significantly increasing the level of reactive oxygen species (in RBCs). Hepatic reduced catalase (CAT) and glutathione peroxidase activities showed a depletion, whereas thiobarbituric acid reactive substances (TBARS) levels increased on arsenic exposure indicating arsenite-induced oxidative stress in blood and liver. Kidney CAT activity showed a depletion, whereas TBARS levels increased on arsenic exposure. These biochemical changes were accompanied by an increase in blood, liver, and kidney arsenic concentration. Treatment with MiADMSA was effective in increasing ALAD activity, whereas quercetin was ineffective when given alone. Quercetin when co-administered with MiADMSA also provided no additional beneficial effect on blood ALAD activity but significantly brought altered platelet counts nearer to the normal value. In contrast, administration of quercetin alone provided significant beneficial effects on hepatic oxidative stress and kidney TBARS levels. Renal biochemical variables remained insensitive to arsenic and any of the treatments. Interestingly, combined administration of quercetin with MiADMSA had a remarkable effect in depleting total arsenic concentration from blood and soft tissues. These results lead us to conclude that quercetin administration during chelation treatment had some beneficial effects particularly on the protection of inhibited blood ALAD activity and depletion of arsenic level from target organs. The study supports our earlier conclusion that a co-administration of an antioxidant particularly flavonoids more beneficial than monotherapy with the chelating agents to achieve optimal effects of chelation in arsenite toxicity.     

Inhibition of delta-aminolevulinic acid dehydratase in human red blood cells by lead and activation by zinc or cysteine.

Inhibition of blood delta-aminolevulinic acid dehydratase(ALA-D) activity by lead was studied in vivo and in vitro. In vivo, a negative linear correlation (r = -0.85) was found between the logarithmic values of ALA-D activity and blood lead levels. In vitro the inhibitory effect of lead on blood ALA-D activity increased both with contact time and contact temperature of lead with blood before ALA-D assay. Maximum enzyme inhibition occurred after 14 h of contact at 25 degrees C. Inhibition of ALA-D activity by lead, in vivo as well as in vitro, is suppressed by the addition of zinc or cysteine. The logarithmic values of the activity ratios increase linearly with blood lead concentrations. The increase in ALA-D activity brought about by the addition of zinc or cysteine can be used to identify cases of low enzyme activity with no lead intoxication involved. The same technique can also detect cases in which ALA-D inhibition may be concealed by a presumably high initial enzyme activity as observed in some patients.     

Metal constitution of metallothionein influences inhibition of delta-aminolaevulinic acid dehydratase (porphobilinogen synthase) by lead.

This study was undertaken to evaluate the effect of Zn and Cd pretreatment on the inhibition of delta-aminolaevulinic acid dehydratase (ALAD; porphobilinogen synthase, EC 4.2.1.24) by Pb. Male CD rats were pretreated with 200 mumol of Zn/kg s.c. (subcutaneously) or 18 mumol of Cd/kg s.c., 48 and 24 h before assay of ALAD. Pretreatment with Zn resulted in activation of hepatic and renal ALAD and attenuated the inhibition of this enzyme by Pb in vitro. Pretreatment with Cd increased hepatic ALAD activity, and the inhibitory effect of Pb on the hepatic enzyme was attenuated in this group. In contrast with the situation in liver, pretreatment with Cd did not affect the activity of renal ALAD and did not alter the inhibitory effect of Pb on the renal enzyme. The Pb IC50 (concentration causing half-maximal inhibition) values for hepatic and renal ALAD in Zn-pretreated rats and for hepatic ALAD in Cd-pretreated rats were increased above control, whereas the IC50 for renal ALAD in Cd-pretreated rats was unchanged. Cytosolic binding patterns for the three metals were assessed by gel-filtration chromatography and disclosed that 203Pb was co-eluted with Zn and Cd bound to liver and kidney Zn-thioneins and liver Cd,Zn-thionein, although minimal binding of 203Pb to kidney Cd,Zn-thionein was observed. Estimation of the molar ratio of metals bound revealed Cd/Zn ratios of 2 and 5 for Cd,Zn-thioneins from liver and kidney respectively. The inhibition of purified ALAD by Pb was also attenuated by addition of purified Zn-thioneins and Cd,Zn-thioneins from liver and kidney in the following order: liver Zn-thionein = kidney Zn-thionein greater than liver Cd,Zn-thionein much greater than kidney Cd,Zn-thionein. Thus liver and kidney Zn-thioneins and liver Cd,Zn-thionein with a low Cd/Zn ratio readily decrease the free pool of Pb available to interact with ALAD. These data also demonstrate that the capacity of metallothionein to alter the intracellular distribution of Pb and mediate the inhibition of ALAD by Pb is dependent on the tissue source and relative metal constitution of the metallothionein.     

Combined administration of N-acetylcysteine and monoisoamyl DMSA on tissue oxidative stress during arsenic chelation therapy

The present study deals with the therapeutic potential of combined administration of N-acetylcysteine (NAC) along with monoisoamyl DMSA (MiADMSA) against chronic arsenic poisoning in guinea pigs. Animal were exposed to 50 ppm arsenic in drinking water for 8 mo and subsequently treated for 5 consecutive days with 100 mg/kg NAC (orally) and MiADMSA (intraperitoneally), individually or in combination (50 mg/kg each). Arsenic exposure produced a significant depletion of blood δ-aminolevulinic acid dehydrate (ALAD) activity, increased the blood zinc protoporphyrin (ZPP) level, and reduced blood and liver glutathione (GSH) levels in guinea pigs. Hepatic oxidized glutathione (GSSG) and thiobarbituric acid reactive substance (TBARS) levels showed a marked increase, whereas hepatic alkaline phosphatase (ALP) activity decreased and acid phosphatase (ACP) activity increased on arsenic exposure. Significant depletion of liver transaminase activities on arsenic exposure suggests organ injury. Administration of MiADMSA, alone and in combination with NAC after arsenic exposure, was able to significantly enhance hepatic GSH and to reduce GSSG and TBARS levels compared to the arsenic control. Biochemical variables indicative of liver injury generally remained insensitive to any of these treatments. The recoveries in parameters indicative of oxidative stress were more marked in guinea pigs treated with combined administration of NAC and MiADMSA than monotherapy. Interestingly, there was a more pronounced depletion of arsenic from blood and tissues after combined treatment with NAC plus MiADMSA than MiADMSA. Blood and tissues copper, zinc, iron, and calcium concentrations showed a significant increase after arsenic exposure, which showed improvement, particularly after combined administration of MiADMSA and NAC. Based on these data, a proposal can be made that greater effectiveness in chelation treatment against chronic arsenic poisoning (i.e., turnover in the oxidative stress and removed of arsenic from the system) could be achieved by combined administration of an antioxidant (preferably having a thiol moiety) with MiADMSA.