Reduction of hypervalent states of myoglobin and hemoglobin to their ferrous forms by thymoquinone: the role of GSH, NADH and NADPH.

Reduction of hypervalent states of myoglobin and hemoglobin to their ferrous forms by thymoquinone: The role of GSH, NADH and NADPH K.H. Khalife, G. Lupidi ⁎ Department of Molecular, Cellular, and Animal Biology, University of Camerino, Via Camerini 2, 62032 Camerino MC Italy Received 29 August 2007; received in revised form 30 November 2007; accepted 17 December 2007 Available online 23 December 2007 Abstract The reactivity of thymoquinone towards different redox states of hemoglobin and myoglobin in the presence of GSH, NADH, and NADPH was evaluated by optical spectral analysis. Thymoquinone reduces the ferryl forms (HbIV/MbIV) of both met-hemoglobin (HbIII) and metmyoglobin (MbIII) to oxy-hemoglobin (HbIIO2) and oxy-myoglobin (MbIIO2) under physiological conditions. The reaction is mediated by the intermediate quinone forms of TQ, that is, glutathionyl-dihydrothymoquinone (DHTQ-GS) and dihydrothymoquinone (DHTQ), formed from direct interaction of TQ with GSH or NADH (NADPH). In vitro incubation of oxidized human erythrocytes with TQ, DHTQ, and the GSH/TQ mixture reduces the intracellular met-Hb at different rates. In the present study, we report that TQ and its reduced derivatives can also prevent lipid peroxidation induced by the MbFeIII/H2O2 system. In this system, lipid peroxidation is induced by MbIV or a putative MbIV/•MbVI composite; it is plausible that the antioxidant function of TQ derivatives is related to their ability to reduce these oxidizing species. This is of particular biological significance, as natural quinones may participate in reducing processes that lead to recovery of hemoglobin and myoglobin during oxidative stress. Biochimica et Biophysica Acta 1780 (2008) 627–637