Thymoquinone provides structural protection of human hemoglobin against oxidative damage: Biochemical studies

Hydroxyl radicals (OH^.) are one of the most active reactive oxidants recognized for their deleterious effects to cause protein oxidative damage. Thymoquinone, a monoterpene molecule abundantly present in black cumin and known for its pharmacological activities, but its activity against the OH^.-induced protein oxidative damage has never been explored. This study determined the therapeutic potential of thymoquinone against OH^.-induced oxidative human hemoglobin damage. Novel data demonstrated that thymoquinone provides structural protection of hemoglobin against oxidative damage. Treatment of hemoglobin with OH^. induces hypochromicity at 280 and 405 nm, whereas thymoquinone reversed these hypochromic effects. In addition, OH^. cause significant reduction in tryptophan fluorescence, however thymoquinone also reversed these damaging effects. Thymoquinone also reduces OH^.-induced hydrophobicity and also reduces OH^.-induced carbonylation. Moreover, it also inhibits thermal stabilization of OH^.-hemoglobin complex. SDS-PAGE of unmodified hemoglobin showed four bands, which disappeared upon OH^. treatment and these changes were also retained by thymoquinone. In conclusion, this is the first study that shows the therapeutic potential of thymoquinone against OH^.-induced oxidative damage in human hemoglobin.