Effects of iron salts and haemosiderin from a thalassaemia patient on oxygen radical damage as measured in the comet assay

Abstract

Thalassaemia is a group of genetic diseases where haemoglobin synthesis is impaired. This chronic anaemia leads to increased dietary iron absorption, which develops into iron overload pathology. Treatment through regular transfusions increases oxygen capacity but also provides iron through the red cells' haemoglobin. An essential treatment, in parallel with transfusions, is the use of chelating agents to remove the excess iron deposited in tissues. These deposits are found in the liver, spleen, heart, and pancreas and are associated with cardiac failure and diabetes. The deposits in these tissues of patients have been isolated as haemosiderin. Thalassaemia patients are particularly at risk of free radical induced damage. Thus, the present study has investigated, as a model system, human cells in vitro in the Comet assay in the presence of free radicals. This assay measures DNA damage, particularly DNA strand breakage. The effects of iron overload on cells oxidatively stressed with hydrogen peroxide (H(2)O(2)) have been determined as well as the effect of the chelating agent, deferoxamine. Iron overload was simulated with ferric (FeCl(3)) and ferrous chloride (FeCl(2)), ferrous sulphate (FeSO(4)) and haemosiderins. Both human lymphocytes from a male and a female donor and human adenocarcinoma colonic cells showed an increase in DNA damage in the Comet assay after treatment with H(2)O(2). Ferric chloride produced an increase in DNA damage in human colonic cells, but little or no damage in human lymphocytes. Ferrous chloride also produced weak DNA damage in human lymphocytes, but ferrous sulphate produced a dose-related response. Deferoxamine produced no DNA damage. When H(2)O(2) was combined with FeCl(3), FeCl(2), or FeSO(4), the DNA damage produced was as least as great as or slightly greater than with H(2)O(2) alone. When deferoxamine was combined with H(2)O(2) and FeSO(4) there was a consistent decrease in response. There was little or no decrease in response when deferoxamine was combined with H(2)O(2) and FeCl(3) or FeCl(2), but at high (100-300microm) doses there were changes in the appearance of cellular DNA from Comet tails to dense centres surrounded by a diffuse area. This was probably as a consequence of chelation processes. Haemosiderin produced no damage. The three fractions of haemosiderin examined were of three different densities and from a Thai patient where the oxyhydroxide phase is the ferrihydrite. The colour change was similar to that for FeCl(3), but the level of the ferric ion in the haemosiderin was possibly too low in the sample to produce a response. The next stage is to examine peripheral lymphocytes from thalassaemic patients, with and without chelation therapy, whose cells may be more sensitive to simulated iron overload and to lower levels of haemosiderin. Teratogenesis Carcinog. Mutagen. 20:11-26, 2000.

Flow cytometric analysis of the oxidative status of normal and thalassemic red blood cells

“…The excess iron deposits in the liver, spleen, heart, pancreas etc, and results in organ failure. Iron chelation is therefore an essential treatment, particularly for polytransfused patients (43). Excess iron has also been described in the thalassemic RBC itself, probably due to increased uptake and/or exposure of the heme moiety due to instability of abnormal hemoglobin molecules (44), such as the ␣-globin tetrameres in ␤-thalassemia (19,24).…”

Intracellular iron overload leading to DNA damage of lymphocytes and immune dysfunction in thalassemia major patients

“…28 Hemosiderins isolated from thalassemic patients induced DNA damage in lymphocytes from healthy donors. 29 In the present study, it was also shown that free iron induced oxidative stress in thalassemic lymphocytes, but this effect was not observed for normal lymphocytes (Figure 4). For NTBI to mediate oxidative DNA damage in lymphocytes, it must enter the cells.…”

Effect of antioxidant flavonoids and a food mutagen on lymphocytes of a thalassemia patient without chelation therapy in the Comet assay

“…In previous studies [6,7], it has been shown that lymphocytes from a thalassemia patient were more sensitive to damage from oxygen radicals and iron salts. Because of the Fenton-type chemistry involved, and iron overload that results from dietary absorption, it was considered that, with other dietary agents such as food mutagens and antioxidant flavanoids, the lymphocytes of the thalassemia patient might also show increased sensitivity to the effect of these agents.…”