After haemin treatment intracellular non-haem iron increases prior to haem oxygenase-1 induction: A study in human monocytic cell line THP-1.

Background: Iron overload is a major health concern for transfusion-dependent patients. Repeated transfusions result in the loading of large amounts of haem-derived iron on macrophages, in turn, inducing cell death. We previously demonstrated that haemin-induced cell death in human monocytic THP-1 cells is consistent with ferroptosis, an iron-dependent cell death regulation mechanism. However, direct measurement of iron after haemin treatment has not yet been conducted. In this study, we measured intracellular non-haem iron concentration and haem oxygenase levels after haemin treatment. Material and methods: Human monocytic THP-1 cells were treated with haemin, and the cell lysate was prepared. Non-haem iron concentration of the cell lysate was measured using the Nitroso-PSAP method. Expression of haem oxygenase-1 (HO-1) and haem oxygenase-2 (HO-2) was quantified by western blotting. Results: We measured intracellular non-haem iron and the expression of haem oxygenases post-haemin treatment. Concentration of non-haem iron post-haemin treatment increased dependently with time and dose. HO-1 expression was detected 4 h after haemin treatment, whereas HO-2 expression was constitutive. Discussion: Increase in non-haem iron prior to induction of HO-1 expression suggests the involvement of HO-2 in haem-induced cytotoxicity. (184 words)