Red blood cells in thalassemics have morphologic abnormalities, which result in increased susceptibility of thalassemic red cells to the exogenous peroxidant threat. Two mechanisms for inadequate peroxidant defense in thalassemics are insufficient vitamin E levels in red blood cells and plasma, and decreased activity of several enzymes including SOD and GPX, which are the first line of defense against oxidant stress[7
According to the results (), mean serum levels of vitamin E in all groups at beginning of the study were lower than the normal range[27
Vitamin E deficiency in thalassaemias is attributed to its increased consumption pursuant to the oxidative stress[5
]; Chronic hepatic iron overloads, while causing a substantial reduction of serum lipids, can also lead to concurrent reduction of serum vitamin E[28
]. Some studies have reported a serum zinc deficiency in beta thalassemia patients, which was related to hyperzincuria resulted from the release of Zn from hemolyzed red cells[18
In our studied subjects, 16% had a serum zinc deficiency (data are not shown); however, mean serum zinc was not low. Similarly, Mehdizadeh et al also did not report a zinc deficiency in beta thalassemic patients[29
Absence of predominant zinc deficiency in our patients may have resulted from regular transfusion therapy.
Our findings indicate that supplementation with Zn, vitamin E or both of these causes a significant increase in serum level of zinc in the first group, increased serum vitamin E in the second group, and increased serum zinc and vitamin E levels in the third group with no significant difference in the control group. Therefore, these interventions, especially vitamin E supplementation had favorable effects on serum vitamin E levels in patients, considering that base level of vitamin E in serum of all studied groups was lower than the normal limit.
Oxidative stress is the result of an imbalance between free radical production and reduced degradation[30
]. An increased oxidant stress and a decreased antioxidant status promote peroxidative damage to cell and organelle membranes. It is well documented that disturbances of oxidant-antioxidant balance occur in hemoglobinopathies, especially in thalassemia and sickle cell diseases[31
]. Removal of toxic oxygen metabolites is the putative function of antioxidant enzymes such as SOD and GPX. It has already been demonstrated that oxidative stress induces antioxidative enzymes, including SOD and GPX[5
]. Our findings confirm this. As indicated in , prior to interventions, SOD and GPX activities in all groups were much higher than in those of healthy subjects[31
]. Significant increase in catalytic activities of SOD and GPX also were found in beta-thalassemic erythrocytes of beta-thalassemic carriers in the study of Filiz et al[31
The increased activity of SOD in beta thalassemia may be involved in scavenging the superoxide radical (O2-), thereby producing more hydrogen peroxide in the erythrocytes.
The increased activity of GPX in beta-thalassemia may be involved in detoxifying hydroxyl radical (OH-
). This finding suggests that high iron produces an oxidative stress in cells, which respond by increasing their antioxidant defenses. The increase of intracellular antioxidant enzymes might be hypothesized to be a direct effect of increased intracellular iron on gene expression[5
Based on our results (), SOD and GPX activities in subjects were also higher than normal limits at the end of the study. However, GPX activity showed a significant reduction in all treated groups. Therefore, all three types of interventions had protective effects on this enzyme, and were effective in elevating the antioxidant status. These findings confirm the results of other studies[31
]. Pfeifer et al reported that after vitamin E administration, thalassemic patients presented a significant reduction in levels of erythrocyte RBC-reactive oxygen species (ROS) and serum thiobarbituric acid reactive substances (TBARS), and concluded that it could be useful for reducing oxidative damage in other target organs of beta-thalassemia intermediate patients[33
]. Mei-ling Cheng et al demonstrated that supplementation with vitamin E prevents oxidative damage to low-density-lipoprotein (LDL) and erythrocytes in beta thalassemia patients[34
In addition to vitamin E, it was established that zinc can reduce the iron-mediated oxidation of lipids (including red blood cells), proteins, and DNA[35
]. The precise antioxidant role of zinc is unclear, but two mechanisms were proposed; first the competitive effect of zinc with iron and copper on the surface of cell membrane for special protein binding which is specific for preventing the production of the toxic OH radical. The second one is binding to the –SH groups in some proteins and preventing them from oxidation[36
]. Sidhu et al found that in zinc and protein deficient rat the activities of GPX, catalase, and peroxidation of lipids were increased[37
]. Our results confirmed antioxidant effect of zinc (), as seen in zinc supplemented group GPX activity also reduced significantly.
According to the results () SOD activity in groups did not change significantly after supplementation. The study of Rahul Naithani, et al in beta-thalassemia major patients showed that SOD increases significantly, and it may be a compensatory mechanism to keep formation of superoxide anions checked to combat the oxidative stress[32
]. Kessab-Chekir, et al observed that iron, ferritin, SOD, GPX and TBARS were increased in 56 beta-thalassemic patients; however, vitamin E and TRAP reduced considerably[5
]. Meral, et al reported that because of increased lipid peroxidation in beta thalassemic patients a compensatory increase will be seen in SOD and GPX activity[38
Our findings confirmed the results of above mentioned study, and showed higher SOD activities in patients. Similar to our findings, Carpino et al indicated despite the increased activity of SOD in transfusion dependent thalassemics, TAC did not change[39
Dissayabutra et al reported despite vitamin E and vitamin C supplementation in beta-thalassemia major patients, TAC did not change during the study period[40
]. It was suggested that various methods, including TAC, developed to measure the total antioxidant capacity of serum, have been indicated as useful tools to predict the risk of free radical-induced tissue damage.
Nevertheless, with thalassaemia patients, such an approach appears unsuitable. Changes in contributors such as uric acid and bilirubin, the levels of which increase in thalassaemia because of hemolysis, may mask marked changes in other essential antioxidants[28
]. It seems that these conditions also contributed to unchanged SOD activity and TAC in our subjects.
Low BMI in beta-thalassemic patients is common[41
]. According to findings () BMI of all treated subjects increased significantly, which was indicative of well-being of patients and positive effect of supplementation. Similar results were seen in Das et al study[12
It should be noticed that, we did not evaluate other components of the cellular antioxidant defense system such as catalase, glutathione, uric acid, bilirubin, vitamin C, etc. If more enzymatic and non enzymatic antioxidants were measured, we could have a complete evaluation of the antioxidant status in these patients. So, they are considered as limitations of our study.