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), Î±-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 Î´-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.