Protective potential of thymoquinone against peroxynitrite induced modifications in histone H2A: In vitro studies

Peroxynitrite (ONOO^-) is a reactive oxidant involved in numerous pathological conditions. Thymoquinone (TQ) is an active constituent of Nigella sativa and is reported to have anti-disease activities, but its role on ONOO^- has never been investigated. This study was undertaken to investigate the role of TQ on ONOO^--induced damage of histone-H2A. Our novel data showed TQ significantly inhibited ONOO^--induced oxidative damage in histone-H2A. ONOO^- induces UV-hypochromicity of histone-H2A, whereas TQ reversed this effect to hyperchromicity. Tyrosine fluorescence was significantly reduced by ONOO^- and was significantly increased upon TQ treatment. TQ reduces ONOO^--induced hydrophobicity in histone-H2A and also reduces thermal stability of ONOO^--histone H2A complex. SDS-PAGE of native histone-H2A showed a single band, which disappeared when treated with ONOO^- alone. This changed was retained when protein samples were treated with TQ. Similar protective effects of TQ were found when protein carbonyl contents were estimated. In conclusion, this is the first study that shows the potential of TQ against ONOO^--induced damaged of histone-H2A. TQ inhibits oxidative modification of tyrosine, lysine, arginine, proline and threonine in histone-H2A. These results have importance for the development of novel therapeutic strategies for the treatment of disorders, where ONOO^- plays a role.