In vivo distribution of single chain variable fragment (scFv) against atherothrombotic oxidized LDL/β₂-glycoprotein I complexes into atherosclerotic plaques of WHHL rabbits: Implication for clinical PET imaging

Background Oxidized LDL (oxLDL) can exist as a complex with β₂-glycoprotein I (β₂GPI) in plasma/serum of patients with non-autoimmune atherosclerotic disease or antiphospholipid syndrome (APS). Nonetheless, direct in vivo evidence supporting the pathophysiological involvement of oxLDL/β₂GPI complexes and specific autoantibody against the complexes in developing atherothrombosis has yet been established. In the present study, we demonstrated in vivo distribution of single chain variable fragment of IgG anti-oxLDL/β₂GPI complexes (3H3-scFv) in Watanabe heritable hyperlipidemic (WHHL) rabbits by PET/CT imaging. Methods An antibody-based PET probe, ⁶⁴Cu-3H3-scFv, was established, and WHHL rabbits were applied for a non-autoimmune atherosclerotic model to demonstrate in vivo distribution of the probe. Results 3H3-scFv has exhibits specificity towards β₂GPI complexed with oxLDL but neither a free form of β₂GPI nor oxLDL alone. Post-intravenous administration of ⁶⁴Cu-3H3-scFv into WHHL rabbits has demonstrated a non-invasive approach for in vivo visualization of atherosclerotic lesion. The imaging probe achieved ideal blood clearance and distribution for optimal imaging capacity in 24 h, significantly shorter than that of an intact IgG-based imaging probe. ⁶⁴Cu-3H3-scFv targeted on atherosclerotic plaques in aortas of WHHL rabbits where extensive accumulation of lipid deposits was observed by lipid staining and autoradiography. The accumulation of ⁶⁴Cu-3H3-scFv in aortic segments of WHHL rabbits was 2.8-folds higher than that of controls (p = 0.0045). Conclusions The present in vivo evidence supports the pathophysiological involvement of oxLDL/β₂GPI complexes in atherosclerotic complications of WHHL rabbits. ⁶⁴Cu-3H3-scFv represents a novel PET imaging probe for non-invasive pathophysiological assessment of oxLDL/β₂GPI complexes accumulated in atherosclerotic plaques.