The Oxidative Status of Valinomycin-Resistant Normal and Thalassemic Red Cells (RBCs).

Normal high-K + , low-Na + RBCs, suspended in low-K + media and permeabilized to K + with valinomycin, become dehydrated from net loss of KCl and water. A very small fraction of light, normal RBC and larger fractions of light, sickle cell anemia (SCA) and beta-thalassemia RBC were found to be “valinomycin-resistant” ( val-res ) due to their Na + /K + gradient dissipation (PNAS2000;97: 8050; BLOOD2000;96:24b). In thalassemia and SCA, although the primary lesions involve the globin genes, the major damage to the RBC membranes is mediated by oxidative stress. We previously showed (Cytometry2004;60:73) that thalassemic RBC have higher reactive oxygen species (ROS) and lower reduced glutathione (GSH) levels than normal RBC before or after in vitro oxidant stress (treatment with hydrogen peroxide). Here, we examined the oxidative status of val-res RBC from normal and beta-thalassemia major blood. RBC suspended in a plasma-like buffer containing 15 mM KCl and 10 mM valinomycin for 45 min were then layered on arabinogalactone (Larex) with density δ=1.091, and spun at 15,000 g for 30 min. Val-res cells were identified as the low density (δ val-res RBC in beta-thalassemic samples ( n = 10), was 84-fold higher (4.2 ± 0.4% (mean ± SD), range 2.5 to 6.0%) than in normal samples (0.05 ± 0.06%, range 0.02 to 0.1%) ( n =10). To determine the oxidative status of the RBC, the cells were washed with PBS and stained for intracellular contents of ROS and GSH, using 2′-7′-dichlorofluoresein and Mercury Orange, respectively. RBC were analyzed by flow cytometry, using gating based on size and granularity. The Mean Fluorescence Channel (MFC) for each fluorochrome was computed. The results showed that valinomycin treatment, per se, did not affect ROS and GSH contents: MFC of the stained un-fractionated RBC was similar before and after treatment with valinomycin, indicating that large changes in MCHC had little or no effect on these measurements. In addition, the unfractionated RBC had ROS and GSH values comparable to those of the high density ( val-sensitive) RBC which were recovered from the pellet of valinomycin-treated RBC following Larex fractionation. Measurements on six normal and six beta-thalassemic blood samples indicated that in each case val-res RBC had higher ROS (3.5-10 fold) and lower GSH (2.5-8 fold) levels than the unfractionated RBC or the val-sensitive RBC of the same sample. Compared with val-res cells from normal blood, thalassemic val-res RBC had higher capacity to produce ROS (1.7-fold) and had a lower GSH level (1.5-fold) compared with normal val-res RBC. These results confirm that, as with SCA, beta-thalassemia blood contains a higher percent of val-res RBC than normal blood. They show, further, that (i) both normal and thalassemic val-res RBC have higher oxidative status than other cells ( val-sensitive ) in the same sample; and that (ii) thalassemic val-res RBC have higher oxidative status than val-res RBC in normal blood. The present results are consistent with the possibility that oxidative stress may contribute to the generation of val-res RBCs, but do not establish a cause-effect relationship. Further studies will be needed to elucidate the origin and significance of these cells.