Arsenic induced blood and brain oxidative stress and its response to some thiol chelators in rats

Chronic arsenic toxicity is a widespread problem, not only in India and Bangladesh but also in various other regions of the world. Exposure to arsenic may occur from natural or industrial sources. The treatment that is in use at present employs administration of thiol chelators, such as meso 2,3-dimercaptosuccinic acid (DMSA) and sodium 2,3-dimercaptopropane 1-sulfonate (DMPS), which facilitate its excretion from the body. However, these chelating agents are compromised with number of limitations due to their lipophobic nature, particularly for their use in cases of chronic poisoning. During chronic exposure, arsenic gains access into the cell and it becomes mandatory for a drug to cross cell membrane to chelate intracellular arsenic. To address this problem, analogs of DMSA having lipophilic character, were examined against chronic arsenic poisoning in experimental animals. In the present study, therapeutic efficacy of meso 2,3-dimercaptosuccinic acid (DMSA), sodium 2,3-dimercaptopropane 1-sulfonate (DMPS), monoisoamyl DMSA (MiADMSA) were compared in terms of reducing arsenic burden, as well as recovery in the altered biochemical variables particularly suggestive of oxidative stress. Adult male Wistar rats were given 100-ppm arsenic for 10 weeks followed by chelation therapy with the above chelating agents at a dose of 50 mg/Kg (orally) once daily for 5 consecutive days. Arsenic exposure resulted in marked elevation in reactive oxygen species (ROS) in blood, inhibition of ALAD activity and depletion of GSH. These changes were accompanied by significant decline in blood hemoglobin level. MiADMSA was the most effective chelator in reducing ROS in red blood cells, and in restoring blood ALAD compared to two other chelators. Brain superoxide dismutase (SOD) and glutathione peroxidase (GPx) decreased, while ROS and TBARS increased significantly following arsenic exposure. There was a significant increase in the activity of glutathione-S-transferase (GST) with a corresponding decline in its substrate i.e. glutathione. Among all the three chelators, MiADMSA showed maximum reduction in the level of ROS in brain. Additionally, administration of MiADMSA was most effective in counteracting arsenic induced inhibition in brain ALAD, SOD and GPx activity. Based on these results and in particular higher metal decorporation from blood and brain, we suggest MiADMSA to be a potential drug of choice for the treatment of chronic arsenic poisoning. However, further studies are required for the choice of appropriate dose, duration of treatment and possible effects on other major organs.     

Combined administration of iron and monoisoamyl-DMSA in the treatment of chronic arsenic intoxication in mice

Co-administration of iron in combination with monoisoamyl dimercaptosuccinic acid (MiADMSA) against chronic arsenic poisoning in mice was studied. Mice preexposed to arsenic (25 ppm in drinking water for 6 months) mice were treated with MiADMSA (50 mg/kg, intraperitoneally) either alone or in combination with iron (75 or 150 mg/kg, orally) once daily for 5 days. Arsenic exposure led to a significant depletion of blood δ-aminolevulinic acid dehydratase (ALAD) activity, hematocrit, and white blood cell (WBC) counts accompanied by small decline in blood hemoglobin level. Hepatic reduced glutathione (GSH) level, catalase and superoxide dismutase (SOD) activities showed a significant decrease while, oxidized glutathione (GSSG) and thiobarbituric acid-reactive substances (TBARS) levels increased on arsenic exposure, indicating arsenic-induced hepatic oxidative stress. Liver aspartate and alanine transaminases (AST and ALT) activities also decreased significantly on arsenic exposure. Kidney GSH, GSSG, catalase level and SOD activities remained unchanged, while, TBARS level increased significantly following arsenic exposure. Brain GSH, glutathione peroxidase (GPx), and SOD activities decreased, accompanied by a significant elevation of TBARS level after chronic arsenic exposure. Treatment with MiADMSA was marginally effective in reducing ALAD activity, while administration of iron was ineffective when given alone. Iron when co-administered with MiADMSA restored blood ALAD activity. Administration of iron alone had no beneficial effects on hepatic oxidative stress, while in combination with MiADMSA it produced significant decline in hepatic TBARS level compared to the individual effect of MiADMSA. Renal biochemical variables were insensitive to any of the treatments. Combined administration of iron with MiADMSA also had no additional beneficial effect over the individual protective effect of MiADMSA on brain oxidative stress. Interestingly, combined administration of iron with MiADMSA provided more pronounced depletion of blood arsenic, while no additional beneficial effects on tissue arsenic level over the individual effect of MiADMSA were noted. The results lead us to conclude that iron supplementation during chelation has some beneficial effects particularly on heme synthesis pathway and blood arsenic concentration.     

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.     

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.     

Response of lead-induced oxidative stress and alterations in biogenic amines in different rat brain regions to combined administration of DMSA and MiADMSA

The present study was planned to investigate if combined administration of meso-2,3-dimercaptosuccinic acid (DMSA) and monoisoamyl DMSA (MiADMSA) could achieve better recovery in the altered biochemical parameters suggestive of brain oxidative stress and depletion of lead from blood and brain following acute lead exposure. Male Wistar rats were exposed to lead nitrate (50 mg/kg, i.p., once daily for 5 days) followed by treatment with the above chelating agents using two different doses of 25 or 50 mg/kg (orally) either alone and in combination once daily for five consecutive days. Lead exposure resulted in the significant inhibition of δ-aminolevulinic acid dehydratase activity and depletion of glutathione (GSH) in blood. These changes were accompanied by significant reduction in blood hemoglobin, RBC levels and superoxide dismutase and catalase activities. Significant increase in blood reactive oxygen species (ROS) and thiobarbituric acid reactive substances (TBARS) levels were noted. We observed marked increase in brain ROS level while GSH/oxidized glutathione ratio showed significant decrease accompanied by a significant increase in blood and brain lead concentration. The levels of norepinephrine, dopamine and serotonin in different brain regions were also altered on lead exposure. Co-administration of DMSA and MiADMSA particularly at the lower dose was most effective in the recovery of lead-induced changes in the hematological variables and oxidative stress and resulted in more pronounced depletion of lead from blood and brain compared to monotherapy with these chelators. On the other hand, combined administration of MiADMSA (50 mg/kg) in combination with DMSA (25 mg/kg each) had additional beneficial effect over the individual effect of chelating agent in the recovery of altered levels of brain biogenic amines. The study suggests that administration of MiADMSA is generally a better lead chelator than DMSA while combined administration of DMSA and MiADMSA might be a better treatment option compared to monotherapy at least in the removal of lead from the target tissues.     

Response of arsenic-induced oxidative stress,DNA damage,and metal imbalance to combined administration of DMSA and monoisoamyl-DMSA during chronic arsenic poisoning in rats

Arsenic and its compounds cause adverse health effects in humans. Current treatment employs administration of thiol chelators, such as meso-2,3-dimercaptosuccinic acid (DMSA) and sodium 2,3-dimercaptopropane 1-sulfonate (DMPS), which facilitate its excretion from the body. However, these chelating agents are compromised by number of limitations due to their lipophobic nature, particularly in case of chronic poisoning. Combination therapy is a new approach to ensure enhanced removal of metal from the body, reduced doses of potentially toxic chelators, and no redistribution of metal from one organ to another, following chronic metal exposure. The present study attempts to investigate dose-related effects of two thiol chelators, DMSA and one of its new analogues, monoisoamyl dimercaptosuccinic acid (MiADMSA), when administered in combination with the aim of achieving normalization of altered biochemical parameters suggestive of oxidative stress and depletion of inorganic arsenic following chronic arsenic exposure. Twenty-five adult male Wistar rats were given 25 ppm arsenic for 10 weeks followed by chelation therapy with the above chelating agents at a dose of 0.3 mmol/kg (orally) when administered individually or 0.15 mmol/kg and 0.3 mmol/kg (once daily for 5 consecutive days), respectively, when administered in combination. Arsenic exposure led to the inhibition of blood δ-aminolevulinic acid dehydratase (ALAD) activity and depletion of glutathione (GSH) level. These changes were accompanied by significant depletion of hemoglobin, RBC and Hct as well as blood superoxide dismutase (SOD) acitivity. There was an increase in hepatic and renal levels of thiobarbituric acid-reactive substances, while GSH:GSSG ratio decreased significantly, accompanied by a significant increase in metallothionein (MT) in hepatocytes. DNA damage based on denaturing polyacrylamide gel electrophoresis revealed significant loss in the integrity of DNA extracted from the liver of arsenic-exposed rats compared to that of normal animals. These changes were accompanied by a significant elevation in blood and soft-tissue arsenic concentration. Co-administration of DMSA and MiADMSA at lower dose (0.15 mmol/kg) was most effective not only in reducing arsenic-induced oxidative stress but also in depleting arsenic from blood and soft tissues compared to other treatments. This combination was also able to repair DNA damage caused following arsenic exposure. We thus recommend combined administration of DMSA and MiADMSA for achieving optimum effects of chelation therapy.     

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.     

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.     

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.     

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.     

Chelation in metal intoxication XVIII: Combined effects of thiamine and calcium disodium versenate on lead toxicity

Calcium disodium ethylenediaminetetraacetate (Ca-Na2EDTA; Versenate) was more effective than thiamine (vitamin B1) in enhancing the urinary excretion of lead, reducing tissue lead and restoring lead induced biochemical alterations in rats. However, the combination of CaNa2EDTA and vitamin B1 enhanced the beneficial effect of CaNa2EDTA in lead intoxication and was particularly effective in reducing the brain concentration of lead.     

Effects of individual and combined exposure to sodium arsenite and sodium fluoride on tissue oxidative stress, arsenic and fluoride levels in male mice

Arsenic and fluoride are potent toxicants, widely distributed through drinking water and food and often result in adverse health effects. The present study examined the effects of sodium meta-arsenite (100 mg/l in drinking water) and sodium fluoride (5 mg/kg, oral, once daily), administered either alone or in combination for 8 weeks, on various biochemical variables indicative of tissue oxidative stress and cell injury in Swiss albino male mice. A separate group was first exposed to arsenic for 4 weeks followed by 4 weeks of fluoride exposure. Exposure to arsenic or fluoride led to a significant depletion of blood delta-aminolevulinic acid dehydratase (ALAD) activity and glutathione (GSH) level. These changes were accompanied by increased level of blood and tissues reactive oxygen species (ROS) level. An increase in the level of liver and kidney thiobarbituric acid reactive substance (TBARS) along with a concomitant decrease in the activities of superoxide dismutase (SOD), catalase, and glutathione peroxidase (GPx) and reduced GSH content were observed in both arsenic and fluoride administered mice. The changes were significantly more pronounced in arsenic exposed animals than in fluoride. It was interesting to observe that during combined exposure the toxic effects were less pronounced compared to the effects of arsenic or fluoride alone. In some cases antagonistic effects were noted following co-exposure to arsenic and fluoride. Arsenic and fluoride concentration increased significantly on exposure. Interestingly, their concentration decreased significantly on concomitant exposure for 8 weeks. However, the group which was administered arsenic for 4 weeks followed by 4 weeks of fluoride administration showed no such protection suggesting that the antagonistic effect of fluoride on arsenic or vice versa is possible only during interaction at the gastro intestinal sites. These results are new and interesting and require further exploration.     

Interrelationship between iron deficiency and lead intoxication (part 1)

The influence of lead exposure, iron deficiency, or their combination on certain biochemical parameters in blood, plasma, and urine of rats was investigated in an attempt to identify the specific diagnostic tests of the two conditions and to draw a possible interrelationship between the two factors. The decrease in blood-glutathione peroxidase activity, -packed cell volume, plasma-ceruloplasmin, and-Fe levels and increase in urinary excretion of delta-aminolevulinic acid, plasma-cholesterol, and-total Fe binding capacity occur under Fe deficiency as well as Pb intoxication. However, increase in the activity of blood delta-aminolevulinic acid dehydratase (ALAD) without any change in blood zinc protoporphyrin (ZPP) level appears to be a specific effect of Fe deficiency that could be distinguished from Pb intoxication, a condition characterized by the inhibition in blood ALAD activity accompanied by an increase in blood ZPP level. The linear regression analysis of the data showed that the blood Pb and plasma free cholesterol levels increase with the decrease in plasma Fe level.     

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.     

Essential Metal Status, Prooxidant/Antioxidant Effects of MiADMSA in Male Rats: Age-related Effects

Thiols are known to act as protectants in the biological system for their involvement in a number of metabolic regulations. In this study, we investigated the effect of a new and potent thiol-chelating agent, monoisoamyl 2,3-dimercaptosuccinic acid (MiADMSA), an analog of meso 2,3-dimercaptosuccinic acid, to find out if it could act as a prooxidant (because of its lipophilic character) or antioxidant (because of thiol moiety) that could supplement its chelating properties in different age groups of male rats (young, adult, and old rats) and produce effective clinical recoveries in the treatment of metal intoxication. Animals were treated with 25, 50, and 100 mg/kg of MiADMSA, i.p, once daily for 1 week to assess the effect on the antioxidant system in major organs based on sensitive biochemical variables indicative of oxidative stress. Results suggested that MiADMSA administration increased the activity of d-aminolevulinic acid dehydratase in all the age groups and increased blood glutathione (GSH) levels in young rats. MiADMSA also potentiated the synthesis of metallothioneine in liver and kidneys and GSH levels in liver and brain. Apart from this it also significantly reduced the glutathione disulfide levels in tissues. However, administration of MiADMSA caused some concern over the copper loss. MiADMSA was found to be safe in rats of all ages.     

Oxidative stress promotes degradation of the Irr protein to regulate haem biosynthesis in Bradyrhizobium japonicum

The haem proteins catalase and peroxidase are stress response proteins that detoxify reactive oxygen species. In the bacterium Bradyrhizobium japonicum, expression of the gene encoding the haem biosynthesis enzyme delta-aminolevulinic acid dehydratase (ALAD) is normally repressed by the Irr protein in iron-limited cells. Irr degrades in the presence of iron, which requires haem binding to the protein. Here, we found that ALAD levels were elevated in iron-limited cells of a catalase-deficient mutant, which corresponded with aberrantly low levels of Irr. Irr was undetectable in wild-type cells within 90 min after exposure to exogenous H2O2, but not in a haem-deficient mutant strain. In addition, Irr did not degrade in response to iron in the absence of O2. The findings indicate that reactive oxygen species promote Irr turnover mediated by haem, and are involved in iron-dependent degradation. We demonstrated Irr oxidation in vitro, which required haem, O2 and a reductant. A truncated Irr mutant unable to bind ferrous haem does not degrade in vivo, and was not oxidized in vitro. We suggest that Irr oxidation is a signal for its degradation, and that cells sense and respond to oxidative stress through Irr to regulate haem biosynthesis.     

Influence of delta-aminolevulinic acid dehydratase (ALAD) polymorphism on the frequency of sister chromatid exchange (SCE) and the number of high-frequency cells (HFCs) in lymphocytes from lead-exposed workers

In this study, the cytogenetic response to lead exposure in storage battery manufacturing workers carrying different alleles of delta-aminolevulinic acid dehydratase (ALAD 1 and ALAD 2) was evaluated. The cytogenetic response was measured by analysis of the frequency of sister chromatid exchange (SCE) and the number of high-frequency cells (HFCs) in peripheral blood lymphocytes from workers occupationally exposed to lead. A total of 71 voluntary male workers were enrolled in the study. According to our genotype analysis, 50 workers had the ALAD 1-1 genotype and 21 workers had the ALAD 1-2 genotype. In spite of the statistically insignificant difference in mean values of SCE per cell between ALAD 1-1 and ALAD 1-2 workers, the percentage of HFC (HFC (%)) was statistically (chi2-test, P<0.05) higher in ALAD 1-1 workers. The control group was selected among voluntary male office workers (n = 20) and genotyping was also performed for this group in order to rule out the possibility that ALAD 1-1 subjects had a higher HFC (%) than ALAD 1-2 carriers, independent of the exposure to lead. Accordingly, 11 control workers had the ALAD 1-1 genotoype and 9 workers had ALAD 1-2. The differences in mean values of SCE per cell and HFC (%) were not statistically significant when the two genotypes in the control group were compared. On the basis of this result we suggest that ALAD 1-1 subjects might be more susceptible to cytogenetic effects of lead exposure than ALAD 1-2 subjects. There were no ALAD 2-2 subjects in the exposed and control groups.     

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.     

Changes in certain hematological and physiological variables following single gallium arsenide exposure in rats

Gallium arsenide (GaAs), a group III-VA intermetallic semiconductor, possesses superior electronic and optical properties and has a wide application in electronic industry. Exposure to GaAs in the semiconductor industries could be a possible occupational risk. The aim of the present study was to determine the dose-dependent effect of single oral exposure to GaAs (500, 1000, or 2000 mg/kg) on some biochemical variables in heme synthesis pathway and few selected physiological variables at d 1, 7, and 15 following administration. The results indicate that GaAs produced a significant effect on the activity of δ-aminolevulinic acid dehydratase (ALAD) in blood and heart (particularly at d 7) following exposure to 2000 mg/kg, whereas urinary δ-aminolevulinic acid (ALA) excretion was elevated only at d 7. No marked influence of GaAs on blood hemoglobin, zinc protoporphyrin, and packed cell volume was noticed. Blood glutathione (GSH) was significantly reduced at d 7, but remained unchanged at two other time intervals. On the other hand, heart GSH contents remained uninfluenced on GaAs exposure. Most of the physiological variables, viz. blood pressure, heart and respiration rate, and twitch response, remained unchanged, except for some minor alterations observed at d 7 and 15 following exposure to GaAs at a dose of 2000 mg/kg. Blood gallium concentration was not detectable in normal animals and rats exposed to 500 mg/kg GaAs. Blood arsenic concentration was, however, detectable even at the a lower dose level and increased in a dose-dependent manner. All these changes showed a recovery pattern at d 21, indicating that the alterations are reversible.     

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.