The influence of insulin infusion on the metabolism of amyloid β peptides in plasma

Abstract

BackgroundAccumulating body of evidence suggests pathophysiologic links between Alzheimer’s disease and diabetes mellitus (DM). For example, the two crucial peptides playing a role in both degenerative disorders, amyloid β (Aβ) and insulin, are metabolized by the same enzyme, insulin degrading enzyme. Euglycemic hyperinsulinemic clamp is a method of estimating insulin sensitivity, based on the assumption that during steady-state hyperinsulinemic euglycemia, glucose infusion rate equals tissue glucose uptake, that is, the higher the glucose infusion rate, the higher the insulin sensitivity. ObjectiveThe aim of this study was to analyze the influence of insulin on the plasma concentrations of Aβ peptides. MethodsBlood samples were collected from 20 healthy young male volunteers before insulin infusion (clamp) and then at 120 and 360 minutes. In the second protocol, insulin was accompanied by Intralipid, which is mainly a mixture of triacylglycerols, and heparin, given as an activator of lipoprotein lipase, inducing insulin resistance. Analyses of plasma Aβ1-42, Aβx-42, Aβ1-40, and Aβx-40 were performed with multiplexing technology. Furthermore, concentrations of the Aβ peptides in healthy persons were compared with those in 16 type 1 DM patients receiving chronic insulin therapy. ResultsWhen applied alone (i.e., without Intralipid), insulin infusion increased concentrations of Aβ42 (full length and N-terminally shortened) but not of Aβ40. When combined with Intralipid, infusion of insulin resulted in increased concentrations of all peptides (nonsignificant tendency in case of Aβx-40). We did not observe differences between Aβ peptide concentrations in healthy subjects and those in type 1 DM patients. ConclusionInfusion of insulin in nonphysiologic high doses increases plasma concentrations of Aβ peptides; in case of Aβ40, only when applied together with Intralipid, which perhaps might be explained by hypothetical shift of insulin degrading enzyme activity from degradation of Aβ peptides to the degradation of insulin.