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Abstract
α1-Microglobulin is a 26 kDa plasma and tissue glycoprotein that belongs to the lipocalin protein superfamily. Recent reports show that it is a reductase and radical scavenger and that it binds heme and has heme-degrading properties. This study has investigated the protective effects of α1-microglobulin against oxidation by heme and reactive oxygen species in the human erythroid cell line, K562. The results show that α1-microglobulin prevents intracellular oxidation and up-regulation of heme oxygenase-1 induced by heme, hydrogen peroxide and Fenton reaction-generated hydroxyl radicals in the culture medium. It also reduces the cytosol of non-oxidized cells. Endogeneous expression of α1-microglobulin was up-regulated by these oxidants and silencing of the α1-microglobulin expression increased the cytosol oxidation. α1-microglobulin also inhibited cell death caused by heme and cleared cells from bound heme. Binding of heme to α1-microglobulin increased the radical reductase activity of the protein as compared to the apo-protein. Finally, α1-microglobulin was localized mainly at the cell surface both when administered exogeneously and in non-treated cells. The results suggest that α1-microglobulin is involved in the defence against oxidative cellular injury caused by haemoglobin and heme and that the protein may employ both heme-scavenging and one-electron reduction of radicals to achieve this.
| Abbreviations | ||
| ABTS | = | 2,2′-azino-bis(3-ethylbenzo-thiazoline-6-sulphonic acid)diammonium salt |
| α1m | = | α1-microglobulin |
| AGP | = | α1-acid glycoprotein |
| DTT | = | dithiothreitol |
| G3DPH | = | glyceraldehyde-3-phosphate dehydrogenase |
| Hb | = | haemoglobin |
| H2DCFDA | = | 2′,7′-dichlorodihydrofluorescein diacetate |
| NEM | = | N-ethylmaleimide |
| PI | = | propidium iodide |
| ROS | = | reactive oxygen species |
| t-α1m | = | truncated α1-microglobulin |
| 5-IAF | = | 5-iodoacetamido-fluorescein |
| Abbreviations | ||
| ABTS | = | 2,2′-azino-bis(3-ethylbenzo-thiazoline-6-sulphonic acid)diammonium salt |
| α1m | = | α1-microglobulin |
| AGP | = | α1-acid glycoprotein |
| DTT | = | dithiothreitol |
| G3DPH | = | glyceraldehyde-3-phosphate dehydrogenase |
| Hb | = | haemoglobin |
| H2DCFDA | = | 2′,7′-dichlorodihydrofluorescein diacetate |
| NEM | = | N-ethylmaleimide |
| PI | = | propidium iodide |
| ROS | = | reactive oxygen species |
| t-α1m | = | truncated α1-microglobulin |
| 5-IAF | = | 5-iodoacetamido-fluorescein |