Tracking oxidation-induced alterations in fibrin clot formation by NMR-based methods

Abstract

Plasma fibrinogen is an important coagulation factor that is susceptible to post-translational modification by oxidants. We have reported altered fibrin polymerization and increased methionine oxidation in fibrinogen after exposure to hypochlorous acid (HOCl), and similarly in the fibrinogen of severely injured trauma patients. Molecular dynamics suggests that methionine oxidation offers a mechanistic link between oxidative stress and coagulation through fibrin protofibril lateral aggregation by disruption of AαC domain structures. However, experimental evidence explaining how HOCl oxidation impairs fibrinogen structure and function has not been demonstrated. We used polymerization studies and two dimensional-nuclear magnetic resonance spectrometry (2D-NMR) to test the hypothesis that HOCl oxidation alters fibrinogen conformation in the prefibrillar state and T2 water surface relaxation of fibrin fiber assemblies. We found that both HOCl oxidation of purified fibrinogen and addition of HOCl-oxidized fibrinogen to plasma disrupted fibrin polymerization similarly to competitive inhibition of polymerization using a recombinant AαC fragment (AαC 419–502). DOSY NMR measurement of 1H fibrinogen at 25oC demonstrated that fibrinogen oxidation increased translational diffusion coefficient by 17.4%, suggesting a more compact and rapidly translational motion of the protein with oxidation. 2D-NMR analysis of control plasma fibrin gels indicated that water existed in two states, namely intermediate (T2i) in the hydration shell of fibrin fibers, and bulk (T2) within the gel. T2 relaxation of bulk water protons was decreased 2-fold in oxidized fibrin gels and was inversely proportional to gel fiber density (T2). The fast exchange of water protons between hydration shell (T2i) and bulk water, indicating oxidation increased fiber hydration and formed densely packed fibrin gels. We have confirmed experimentally that HOCl oxidation affected native fibrinogen and fibrin gel structures and have demonstrated that NMR can serve as a valuable tool to probe the oxidative rearrangement of fibrin clot structure.