Conjugates of insulin with copolymers of N-(2-hydroxypropyl) methacrylamide: effects on smooth muscle cell proliferation

Novel hydrogels as supports for in vitro cell growth: poly(ethylene glycol)- and gelatine-based (meth)acrylamidopeptide macromonomers

Conversion of amine groups with vinyl-functional azlactones occurs at room temperature under physiological conditions to afford (meth)acrylamidopeptide-functional macromonomers. Such macromonomers based upon alpha,omega-bisaminopropyl-terminated poly(ethylene glycol) and gelatine were prepared and copolymerized to produce novel hydrogel networks. Compression modulus was inversely proportional to the water content (EWC), which was controlled primarily by the PEG macromonomers with non-modified gelatine, the covalent attachment of gelatine to the hydrogel network gave substantially improved performance with respect to both, adhesion and growth of human fibroplasts.

Surface characterization and in vitro blood compatibility of poly(ethylene terephthalate) immobilized with insulin and/or heparin using plasma glow discharge

Poly(ethylene terephthalate)(PET) film was exposed to oxygen plasma glow discharge to produce peroxides on its surfaces. These peroxides were then used as catalysts for the polymerization of acrylic acid (AA) in order to prepare a carboxylic acid group-introduced PET (PET-AA). Insulin and heparin co-immobilized PET (PET-I-H) was prepared by the grafting of poly(ethylene oxide) (PEO) on to PET-AA, followed by reaction first with insulin and then heparin. These surface-modified PETs were characterized by attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, electron spectroscopy for chemical analysis (ESCA), and a contact angle goniometer. The concentration of the heparin (1.23 microg/cm2) bound to the PEO-grafted PET (PET-PEO) was higher than that (0.77 microg/cm2) on the insulin-immobilized PET (PET-In). The blood compatibilities of the surface-modified PETs were examined using in vitro thrombus formation, plasma recalcification time (PRT), activated partial thromboplastin time (APTT), and platelet adhesion and activation. In the experiment with plasma proteins, the PRT and APTT were significantly prolonged for both the heparin-immobilized PET (PET-He) and the PET-I-H, suggesting the binding of immobilized heparin to antithrombin III. The percentage of platelet adhesion slightly increased with the introduction of AA on the PET surfaces, decreased with the introduction of PEO and insulin, and decreased further with the immobilization of heparin. The release of serotonin was highly suppressed on PET-He and PET-I-H, and on surface-modified PETs the percentage of its release increased with an increase in platelet adhesion.

Insulin-like growth factor-1 receptors mediate infragenicular vascular smooth muscle cell proliferation in response to glucose and insulin not by insulin receptors

PURPOSE

Vascular smooth muscle cell (VSMC) proliferation is an early event in the pathogenesis of atherosclerosis. Insulin and glucose are known to stimulate the growth of VSMC. Cell membrane receptors play an important role in the proliferation of VSMC in response to growth factors. Insulin and insulin-like growth factor-1 (IGF-1) have demonstrated a cross reactivity for receptor binding and function. By using monoclonal antibodies directed against insulin (IRA) and IGF-1 (IGF-1RA) receptors, we attempt to further delineate the mechanism for the proliferation of VSMC in response to insulin and glucose.

METHODS

Human infragenicular VSMC isolated from diabetic patients undergoing below-knee amputations were used. Cells from passages 3 to 6 were grown in serum-free media with a glucose concentrations of 0.1% or 0.2%, both with and without insulin (100 ng/mL). The baseline cell density was 4,635 +/- 329 cells/mL. IRA or IGF-1RA was added to the media, with the control group receiving neither antibody. Cells were grown in 5% CO2 at 37 degrees C for 6 days. Analysis of variance was used for statistical analysis, with P <0.05 considered significant. In addition, DNA synthesis was measured using thymidine incorporation assays in the same groups of cells receiving IRA, IGF-1RA, and no antibody.

RESULTS

IGF-1RA prevented the proliferation of VSMC in response to insulin and glucose, while IRA had no effect on cell growth. There was no significant growth when IGF-1RA was added to the media, while the control group and the group receiving IRA demonstrated significant growth compared with the baseline concentration of 4,635 +/- 329 cells/mL at all concentrations of insulin and glucose. [3H]thymidine incorporation assays confirmed the cell count results.

CONCLUSIONS

These results suggest that the mitogenic effects of insulin and glucose on infragenicular VSMC are due to stimulation of the IGF-1 receptor. VSMC antiproliferative strategies employing receptor blockade should be directed against the IGF-1 receptor, not the insulin receptor.

Bioactive surfaces via immobilization of self-assembling polymers onto hydrophobic materials

Conjugation of proteins to copolymers from poly(acrylic acid) grafted onto PEO-PPO-PEO backbone (Pluronic-PAA) following adsorption of the conjugates onto hydrophobic surfaces is reported. Insulin-Pluronic-PAA conjugates show negligible internalization of insulin into human uterine smooth muscle cells as well as enhancement of mitogenic activity. Glucose-induced release of glycated albumin complexed with a Pluronic-PAA-concanavalin conjugate and adsorbed onto polystyrene nanospheres may provide a model for a glucose-responsive protein delivery system or a heterogeneous diagnostic device.

Extending insulin action in vivo by conjugation to carboxymethyl dextran

The biochemical and pharmacological properties of bioactive peptides and proteins can be altered by conjugation with polymers. This report describes site-specific attachment of insulin to activated carboxyl groups of carboxymethyl dextran (CMD, MW=51000) through the GlyA1 insulin amino group. On average, three or four insulin molecules were grafted to a CMD linear chain. Coupled insulin molecules were properly folded, and the bioactivity of conjugated insulin in the blood glucose depression assay was 9.6 IU/mg, which was only 2.6 times less than that for native insulin. The cell growth study indicated that the CMD-insulin conjugate was as mitogenic as insulin on vascular smooth muscle cells, whereas the starting CMD polymer was not. The insulin receptor binding constant of the conjugate (3.6 x 10[9] M[-1]) compared well with that of native insulin (7.6 x 10[9] M[-1]), indicating that the CMD chain does not present any major constraints to binding. Plasma clearance of CMD-insulin obeyed a two-compartment pharmacokinetic (PK) model with a CMD-insulin conjugate plasma elimination half-life of 114.1 min, which was significantly longer than that of soluble Zn-insulin (12.4 min). In contrast, pharmacodynamic (PD) profiles (blood glucose lowering effects) after intravenous (iv) administration of the conjugate or insulin in rats were not different. Subcutaneous (sc) administration of the conjugate resulted in a significantly prolonged plasma profile with a noncompartmental PK parameter mean residence time (MRT) of 103.5 min which was significantly longer than that of soluble Zn-insulin (40.5 min). This was reflected in the protracted PD effect of sc administered conjugate with time needed to reach minimum glucose concentration Tnadir of 95.7 min, which was significantly longer than that of insulin (62 min). We conclude that the conjugation of insulin to CMD leads to a bioactive conjugate with a delayed sc PD profile showing prolonged response, resembling intermediate acting insulin preparations.