In vivo relationship between bound and free insulin in patients with diabetes having anti-insulin antibodies

Objective: The Scatchard plot of anti-insulin antibodies is curvilinear, indicating heterogeneity in binding sites. However, the relationship between bound insulin (B) and free insulin (F) in patients with anti-insulin antibodies has not yet been elucidated. This study aimed to determine this relationship. Methods: We studied two insulin-treated patients with diabetes who had high titers of anti-insulin antibodies. The B and F levels were measured using daily blood samples. Assuming that the law of mass action is applicable to the reactions between insulin and anti-insulin antibody forms, we plotted the bound-to-free ratio (B/F) vs. B using patient data. We also performed an equilibrium binding assay in vitro. Results: Some of the B/F vs. B plots of the daily variation showed an approximately linear relationship, while the Scatchard plots of in vitro data became curvilinear. Conclusion: Our study suggests that the one-site (high-affinity site) of anti-insulin antibodies accounts, for the most part, for insulin pharmacokinetics within physiological insulin concentrations.