Effects of protein phosphorylation on the sulphonylurea receptor of the pancreatic beta-cell

Visualization of the specific interaction of sulfonylurea-incorporated polymer with insulinoma cell line MIN6

A derivative of sulfonylurea (SU) that mimics glibenclamide in chemical structure was synthesized and incorporated into a water-soluble polymeric backbone as a biospecific polymer for stimulating insulin secretion. In this study, a backbone polymer fluorescence-labeled with rodamine-B isothiocyanate was found to be strongly adsorbed onto MIN6 cells, probably due to its specific interaction mediated by SU receptors on the cell membrane. The intensity of fluorescence on the cells was significantly increased by increasing the incubation time and polymer concentration. To verify the specific interaction between the SU (K(+) channel closer)-incorporated copolymer and MIN6 cells, the cells were pretreated with diazoxide, an agonist of the ATP-sensitive K(+) channel (K(+) channel opener), before adding the polymer to the cell culture medium. This treatment suppressed the interaction between SU and MIN6 cells. A confocal laser microscopic study confirmed this effect. The results of this study provide evidence that SU-incorporated copolymer stimulates insulin secretion through the specific interactions of SU moieties in the polymer with MIN6 cells.

Enhanced effect of sulfonylurea (SU) in copolymer comprising a sugar moiety and SU derivative as double ligands on insulin secretion from MIN6 cells

Copolymers composed of sulfonylurea (SU) as an antagonist of ATP-sensitive K+ channel and sugar moieties as double ligands were synthesized. Insulin secretion from MIN6 cells (insulinoma cell line) in contact with the copolymers was evaluated. MIN6 cells attached to the poly(N-p-vinylbenzyl-D-maltonamide-co-SU) [P(VMA-co-SU)]-coated dishes were in the more aggregated form as compared to other polymer-coated surfaces. By introducing SU into the sugar bearing homopolymer, an enhanced effect on insulin secretion from MIN6 cells was observed due to the specific interaction between SU ligands and SU receptors on the beta-cell membrane. P(VMA-co-SU) composed of SU and non-reducing glucose moieties demonstrated enhanced insulin secretion from MIN6 cells and faster proliferation of MIN6 cells as compared to poly(N-p-vinylbenzyl-D-lactonamide-co-SU) [P(VLA-co-SU)] probably owing to the glucose transporters presence on the MIN6 cell membrane. Insulin secretion from MIN6 cells pretreated with diazoxide as an agonist of ATP-sensitive K+ channel was suppressed.

Interaction of sulfonylurea-conjugated polymer with insulinoma cell line of MIN6 and its effect on insulin secretion

A carboxylated derivative of sulfonylurea (SU), an insulinotropic agent, was synthesized and grafted onto a water-soluble polymer as a biospecific and stimulating polymer for insulin secretion. To evaluate the effect of the SU-conjugated polymer on insulin secretion, its solution in dimethyl sulfoxide was added to the culture of insulinoma cell line of MIN6 cells to make 10 nM of SU units in the medium and incubated for 3 h at 37 degrees C. The culture medium was conditioned with glucose concentration of 3.3 or 25 mM. To verify the specific interaction between the SU (K+ channel closer)-conjugated polymer and MIN6 cells, the cells were pretreated with diazoxide, an agonist of adenosine triphosphate-sensitive K+ channel (K+ channel opener), before adding the SU-conjugated polymer to the cell culture medium. This treatment suppressed the action of SUs on MIN6 cells. Fluorescence-labeled polymer with rodamine-B isothiocyanate was used to visualize the interactions, and we found that the labeled polymer strongly absorbed to MIN6 cells, probably owing to its specific interaction mediated by SU receptors on the cell membrane. The fluorescence intensity on the cells significantly increased with an increase in incubation time and polymer concentration. A confocal laser microscopic study further confirmed this interaction. The results from this study provided evidence that SU-conjugated copolymer stimulates insulin secretion by specific interactions of SU moieties in the polymer with MIN6 cells.