Peroxynitrite-induced structural alterations render human fibrinogen more immunogenic: A possible mechanism of auto-immune response that acts as a proatherogenic marker

Abstract

Aberrant protein structure and aggregation trigger humoral and cellular immunological responses. Persistent exposure to toxic endogenous metabolites may trigger heightened autoantibody production and chronic inflammation. The pathophysiology of atherosclerosis (AS) is linked to inflammation, transitioning into a chronic state of robust antibody responses against self-macromolecules. The molecular mechanisms of atherosclerotic inflammation are still not fully deciphered; moreover, identifying a biomarker would help link the molecular findings with clinics, thereby reducing the burden of cardiovascular complications. Fibrinogen (Fg) is an abundant plasma protein with a well-defined hemostatic role. Apart from this, Fg is also recognised as an acute-phase protein, vulnerable to changes in the oxidant-antioxidant status of plasma. Like other proteins, Fg aggregation is associated with interference in proteostasis and vital cellular processes. This study aims to understand the nitro-oxidation of human Fg and its role in the pathophysiology of inflammatory AS. Molecular docking demonstrated a stable interaction between Fg and peroxynitrite (PON). Spectroscopic results confirmed the structural changes in Fg due to modifications at aromatic amino acid residues. An enhancement of carbonyl content was observed, leading to an α-helix to β-sheet transition and the exposure of the hydrophobic core, ultimately resulting in aggregation. Immunization of experimental animals demonstrated that PON-modified Fg (PON-Fg) has much higher immunogenicity than its native equivalent. PON-Fg exhibited strong interactions with IgGs isolated from AS patients. Binding affinities differed for the initial and late stages of AS. Therefore, it can be hypothesized that anti-PON-Fg-IgGs from AS patients may serve as a biomarker for atherogenic proinflammatory progression. More in-depth investigations may aid in and strengthen the identification of patients prone to atherogenic inflammatory progression.

Keywords: Atherosclerosis; Human fibrinogen; Nitrosative stress; Peroxynitrite.