Heme-regulated eukaryotic initiation factor 2α kinase—A molecular indicator of haemolytic anemia

Abstract

The heme-regulated enkaryotic initiation factor-2α (eIF-2α) kinase, also called the heme-regulated inhibitor (HRI), is a key regulator of protein synthesis in mammalian reticulocyte. HRI is almost undetectable in blood samples of normal rabbits and it increases by 12–15-fold in the reticulocytes of anemic rabbits. In order to determine if such an increase in the quantity of HRI is gradual during anemia, and if it could be an indicator of anemia, we have carried out a detailed analysis on the expression of HRI and its eIF-2α kinase activity in rabbit reticulocyte lysates during various stages of acetylphenylhydrazine (APH)-induced anemia. In a 9-day schedule of induction of anemia, using an anti-HRI monoclonal antibody, HRI was detectable immediately after completion of fourth injection (day 5) and it increased gradually during the entire period reaching its maximum (24-fold) on day 9. Furthermore, when rabbits recovered from anemia due to individual response to the drug, quantity of HRI decreased significantly. Northern blot analysis results were similar to those of the Western blot. The other parameters that are generally used to monitor anemia in human patients, namely, reticulocyte count, haematocrit level and haemoglobin content although changed at the onset of anemia, did not change significantly during its progression. These results thus indicate that HRI could be a more appropriate and sensitive indicator of drug-induced anemia.