Abstract

Since 1–2% of the red cell’s oxyhemoglobin undergoes spontaneous heterolytic dissociation into metHb and superoxide every day, and superoxide is readily converted to H2O2 by superoxide dismutase, the red cell is unavoidably exposed to high levels of reactive oxygen species (ROS). We have used a series of gene-disrupted mice to examine the oxidative defenses of the red cell. Work with glutathione peroxidase deficient [GSHPx(−/−)] red cells has been reported earlier. We here add results with red cells from mice that were catalase deficient (−/−), catalase heterozygotes (+/−), double knockouts [GSHPx(−/−) and catalase (−/−)], or peroxiredoxin II deficient. Catalase(−/−) cells were readily oxidized by exogenous H2O2, as monitored by methemoglobin formation, but no methemoglobin was formed when these cells were exposed to organic peroxides. Catalase heterozygotes were not distinguishable from wild type cells in these assays. This is consistent with the clinical finding that partial catalase deficiency is a benign condition. Red cells lacking both GSHPx and catalase exhibited more metHb formation in response to an H2O2 generating system than did either single knockout, indicating that both enzymes contribute to the defense against exogenous H2O2. Adding catalase deficiency to GSHPx deficiency did not increase Hb oxidation by organic peroxides. With peroxiredoxin-deficient cells, PrxII(−/−), preliminary results found an increased flux of the endogenously generated H2O2 through catalase, which could be detected using 3-amino-1,2,4-triazole (3-AT) inhibition. Earlier work (

Lee et al,
Blood
101
:
5033
,
2003
) has demonstrated increased ROS with cell and membrane damage in PrxII(−/−) red cells, but exposure to a flux of H2O2 generated by glucose oxidase produced no increase in metHb formation over that seen in wild type cells. Thus, Hb may be less sensitive to oxidation than is the cell membrane. Prx(−/−) red cells were not more sensitive than wild type red cells to Hb oxidation by organic peroxides. These findings show that all three oxidant defense enzymes play multiple roles in the erythrocyte. All participate in detoxifying endogenously generated H2O2. Calculations with a model of erythrocyte oxidative reactions (
Johnson et al,
Free Rad. Biol. Med.
39
:
1407
,
2005
) are consistent with the experimental findings, predicting H2O2 disposal by all three enzymes. Thus, it is not accurate to identify any one of these enzymes as the sole oxidant defense mechanism in the erythrocyte, as all participate in H2O2 removal. GSHPx in addition has a unique role in detoxifying organic peroxides. The data indicate that peroxiredoxin plays a minor role in the red cell’s defense against Hb oxidation. However, PrxII(−/−) mice are anemic, in contrast with the hematologically normal GSHPx(−/−) and catalase(−/−) mice. This suggests that the primary role of PrxII in the red cell may lie in protecting the cell membrane against oxidative damage.

Author notes

Disclosure: No relevant conflicts of interest to declare.