Open AccessZn2+ chelation by serum albumin improves hexameric Zn2+-insulin dissociation into monomers after exocytosis
Author(s) -
José A. G. Pertusa,
Trinidad León–Quinto,
Genoveva Berná,
Juan R. Tejedo,
Abdelkrim Hmadcha,
Francisco J. Bedoya,
Franz Martı́n,
Bernat Soria
Publication year - 2017
Publication title -
plos one
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.99
H-Index - 332
ISSN - 1932-6203
DOI - 10.1371/journal.pone.0187547
Subject(s) - insulin , albumin , chemistry , medicine , islet , endocrinology , serum albumin , bovine serum albumin , biochemistry , biology
β-cells release hexameric Zn 2+ -insulin into the extracellular space, but monomeric Zn 2+ -free insulin appears to be the only biologically active form. The mechanisms implicated in dissociation of the hexamer remain unclear, but they seem to be Zn 2+ concentration-dependent. In this study, we investigate the influence of albumin binding to Zn 2+ on Zn 2+ -insulin dissociation into Zn 2+ -free insulin and its physiological, methodological and therapeutic relevance. Glucose and K + -induced insulin release were analyzed in isolated mouse islets by static incubation and perifusion experiments in the presence and absence of albumin and Zn 2+ chelators. Insulin tolerance tests were performed in rats using different insulin solutions with and without Zn 2+ and/or albumin. Albumin-free buffer does not alter quantification by RIA of Zn 2+ -free insulin but strongly affects RIA measurements of Zn 2+ -insulin. In contrast, accurate determination of Zn 2+ -insulin was obtained only when bovine serum albumin or Zn 2+ chelators were present in the assay buffer solution. Albumin and Zn 2+ chelators do not modify insulin release but do affect insulin determination. Preincubation with albumin or Zn 2+ chelators promotes the conversion of “slow” Zn 2+ -insulin into “fast” insulin. Consequently, insulin diffusion from large islets is ameliorated in the presence of Zn 2+ chelators. These observations support the notion that the Zn 2+ -binding properties of albumin improve the dissociation of Zn 2+ -insulin into subunits after exocytosis, which may be useful in insulin determination, insulin pharmacokinetic assays and islet transplantation.