Effect of Antibody-Mediated Crosslinking of Insulin on Its Bioactivity and Receptor Binding^*

Abstract

Precipitating anti-insulin antibodies or anti-insulin IgG/anti-IgG complexes bind insulin in a highly aggregated form and thus should preferably be capable of inducing receptor aggregation, which has recently been suggested to be a precondition for insulin bioactivity. We, therefore, studied the influence of antibody-mediated crosslinking of insulin on the glucose conversion into CO2 in rat fat cells and glycogen synthesis in rat liver cells. As far as possible receptor-bound insulin was measured in parallel. Insulin bound to antibodies with low insulin precipitating capacity had no or little bioactivity and receptor reactivity on fat cells. The bioactivity, however, could be restored in part by addition of a second antibody. On liver cells, second antibody-mediated crosslinking of insulin-antibody complexes resulted in an enhancement of receptor reactivity, and insulin bioactivity of such crosslinked immune complexes was demonstrable. An insulin-precipitating antiserum was shown to form insulin-antibody complexes with significant bioactivity in fat cells which correlated with their receptor binding. In each case antibodies had no or little effect in the absence of insulin. Our data suggest that insulin neutralization by antibodies can be compensated by crosslinking the insulin-antibody complexes or by formation of big complexes precipitating by themselves. This is probably due to the induction of receptor aggregation.

The Role of Insulin Antibodies in Insulin Treatment of Type I Diabetes

“…In the whole group neutralization of insulin by insulin antibodies, which is clearly detectable in vitro (Keilacker et al, 1985;Ziegler et al, 1972) could not be recognized by any relationship of insulin binding parameters and insulin requirement. Demonstration of that relationship seems to be only possible if a large number of subjects are being employed (Kerp et al, 1968;Mincu et al, 1981;Ortved Andersen, 1972) or while changing the insulin preparations from conventional to highly purified insulin or vice versa (Mustaffa et al, 1977;Walford et al, 1982).…”

Ligand-binding characteristics of feline insulin-binding immunoglobulin G

“…If the polyclonal insulin-binding IgGs bind to multiple insulin epitopes, insulin-binding IgG may crosslink with insulin and form a macromolecule complex of insulin and IgGs. Reports by Keilacker et al [ 8 ] and Shechter et al [ 20 ] described the possibility that the macromolecule complex of polyclonal anti-insulin antibodies and insulin induced aggregation of receptors on the cell membrane, and the complex might enhance the bioactivity of insulin through the combination with many receptors. However, the effect of formation of a macromolecule complex on bioactivity of insulin is unknown in cats.…”

Measurement Of Insulin in Human Sera Using a New RIA Kit. 2. Determination of Free and Total Insulin — Correlations to Insulin Antibody Levels1)

“…Most insulin-treated diabetics develop insulin antibodies which influence insulin action (Keilacker et al, 1982; and insulin pharmacodynamics (Kurtz et aI., 1977;Havford and Thompson, 1982;Francis et al, 1985;Waldhäusl et al, 1985;Madsbad et al, 1985;Sodoyez et al, 1984). In these patients injected insulin distributes between an antibody-bound and a non-bound compartment (free insulin), the latter being considered as representing the biologically active form of the administered insulin, although, under certain conditions, antibody-bound insulin may also act on target cells (Keilacker et al, 1985). Accordingly, in insulin-treated patients serum insulin is determined as either free insulin in polyethylene glycol extracted serum (Nakagawa et al, 1973;Gennaro and van Norman, 1975;Kuzuya et al, 1976) or total (free plus bound) insulin in ethanol (Ohneda et al, 1970;Heding, 1972;Ziegler et al, 1975;Martin and Russe!, 1974;Davidson and Deal, 1976) or polyethylene glycol (Nakagawa et al, 1973;Gennaro and van Norman, 1975;Kuzuya et al, 1976) extracted serum after preceding acidification.…”