Human Hemoglobin Shares Bioactivities Ascribed to Human Tumor Necrosis Factor‐α

Abstract

Hemoglobin mediated cytotoxicity and apoptosis has been evaluated in Tumor necrosis factor‐α (TNF‐α) sensitive cell line, U937 and compared with TNF‐α. Both species of hemoglobin, Hemoglobin A2 and Hemoglobin A0 induced apoptosis and cytotoxicity in U937 cell as measured by flow cytometry and 3‐(4,5‐dihydro‐6‐(4‐(3,4‐dimethoxybenzooyl)‐1‐piperazinyl)‐2(1H)‐quinoline (MTT) assay respectively. Different concentration of Hemoglobin A0 (4 ng/mL to 4000 ng/mL) induced apoptosis ranging from 9% to 16% in U937 cells. 4000 ng/mL hemoglobin A0 showed maximal apoptotic cells. TNF‐α showed 87% apoptotic U937 cells at concentration of 1 pg/mL. HbA0 displayed cytotoxicity in U937 cell line at higher concentration in comparison to TNF‐α. 4000 ng/mL of hemoglobin A0 showed optimal cytotoxic response in U937 cells. A dose response curve was also observed with varying doses of hemoglobin A0. U937 cells pretreated with serum activated LPS for 1 hr and incubated with different concentration of hemoglobin or human TNF‐α for 24 h reduced the cytotoxic effect on U937. Dexamethasone treatment of U937 cells helped in protecting the HbA0 and HbA2 mediated cytotoxicity and anti‐TNF‐α antibody neutralized the hemoglobin mediated apoptosis and cytotoxicity. It is therefore apparent that human hemoglobin shares some of the bioactivities previously ascribed to TNF‐α. Sharing of bioactivities of TNF‐α by hemoglobin is interesting and suggests that cell free hemoglobin can mimic TNF‐α functionally.