Super-porous Hydrogel Complexes Containing Of Carbopol ~ (?) (sphcc) Carrier Insulin Novel Oral Drug Delivery Systems

Carbopol?-containing superporous hydrogel composites (SPHCc) as novel vehicles for drug administration were investigated. Insulin being used as model drug, the peroral delivery systems based on SPHCc for protein and peptide drugs and their absorption mechanism in the GI tract were studied.1 Stability of insulin in gastrointestinal (GI) tractThe concentration of insulin solution was chosen according to the circular dichroism spectra. Effects of various pH and proteolytic enzymes on the stability of insulin, including pepsin, trypsin, chymotrypsin, enzymes in the content of GI tract, as well as in the intestinal mucosa, were investigated. The results demonstrated that most of the insulin stayed in the presence of monomer when the concentration of solution was 100μg.ml^-1. No obvious change of the contents and hypoglycemic effects of insulin took place within 3h in the physiological pH environment of GI tract. Insulin was degraded when incubated with any kind of proteolytic enzymes, thus the contents and hypoglycemic effects reduced with the increase of the incubation time. Insulin was strongly degraded by pepsin, trypsin, chymotrypsin, proteases in the gastrointestinal lumen, and enzymes in the cytosol in comparison with weak degradation by proteases in the brush border membrane vesicles. The different chromatographic behavior of degraded products revealed that various proteolytic enzymes cleaved insulin molecule at different sites. The correlation between the contents and hypoglycemic effects of degraded products by the proteases primarily indicated that they were loss of bioactivities.2 Absorption and transport of insulin through the intestine, colon and Caco-2 cell monolayersWith the in situ perfusion and closed loop method, the absorption of insulin in the duodenum, jejunum, ileum, and colon was studied. With the use of the Valia-Chien diffusion chambers, the permeability of insulin across various intestinal sites and colon was investigated. Caco-2 cell monolayer model being used, the transport of insulin between AP to BL and BL to AP and transport pathway were investigated. The order of hypoglycemic effects was colon > ileum > jejunum > duodenum in in vivo absorption test. The rank of in vitro apparent permeability coefficients was ileum > jejunum > colon >duodenum. Under the grounds of abovementioned results, the distal intestine may be an advantageous region for oral delivery of insulin. The apparent permeability coefficient of insulin across Caco-2cell monolayer model was higher than that in the duodenum and lower than that in the jejunum and ileum. The transport of insulin between AP to BL and BL to AP showed no significant difference, which indicated that the p-glycoprotein may be not involve in the insulin transport. The FITC-insulin being dispersed in the paracellular localization confirmed that like other hydrophilic macromolecules, the transport of insulin was mainly in the paracellular route.3 Preparation and characterization of SPHCcThe effects of pH of acrylic acid solution, acrylic acid/acrylamide ratio, concentration of initiator, and amount of Carbopol? and water on the preparation of Carbopol?-containing superporous hydrogel composites (SPHCc) were respectively investigated. SPHCc were characterized by SEM, density, and swelling ratio. The results demonstrated that the pH 5.0 of acrylic acid solution, 2:3 of the acrylic acid/acrylamide ratio (v/v), 16.7% of TEMED, and suitable amount of Carbopol? and water help to obtain homogeneous SPHCc from free radical copolymerization using APS and TEMED as initiator system. It was approved by SEM that the SPHCc possessed lots of pores interconnected with each other. The low density SPHCc could swell rapidly and possess higher swelling ratio.4 Toxicity of SPHCcThe acute toxicity of SPHCc and the damage of intestinal mucosa and Caco-2 cell monolayer after application of the SPHCc were studied. The maximum tolerance amount was high. The sections of the intestinal mucosa demonstrated that the rat intestinal villi of the control and refresh group was intact and that of experiment group was intact as well. The damage after application of SPHCc was little. The cells were able to exclude trypan blue as well as propidium iodide after incubation with SPHCc. The damage of Caco-2 cell monolayer was little5 Swelling kinetics of SPHCc and in vitro drug releaseThe influences of the Carbopol? content in the SPHCc, the pH of swelling medium, the ion strength of swelling medium, and the apparent surface area on the swelling kinetics were respectively studied. The swelling ratios decreased with the increase of the Carbopol? content. As the pH of swelling medium was between 3.0 and 7.4, it had no influence on the swelling ratios. When the pH of swelling medium was lower than 2.0, SPHCc shrank and the swelling ratios reduced with the decrease of pH. When the ion strength was O.OOOlmoH'1 and O.OOlmoH"1, it had no effect on the swelling ratios and the maximum swelling ratios of SPHCc were obtained. Whilethe ion strength of swelling medium surpassed 0.00lmoH"1, the swelling ratio enhanced with the decrease of ion strength. The time to equilibrium swelling ratio was shortened with the increase of ion strength. The effect of apparent surface area on swelling kinetics was insignificant.Insulin was loaded into SPH polymers by the immersion method. The results indicated that the amount loading insulin reached (4.78 + 0.13) % (wt) . The cumulative release amount of insulin from SPHCc with 0.072 of Carbopol?/monomer reached 90% during the first 15min. The FTIR spectra demonstrated no new absorption peak in FTIR spectrum after loading SPHCc with insulin. Insulin did not covalently bind to the SPHCc and interacted only physically with SPHCc.6 Insulin delivery via GI tract with SPHCcThe enteric-coat capsules containing the SPHCc loaded with insulin were administrated via intrajejunum in the anaesthetized rats and via ig in the conscious rats, respectively. In the anaesthetized rats, the hypoglycemic effect was significant and enhanced with the increase of the dose. When the dose was 35u-kg'] and 70ukg"1, the blood glucose level decreased down to about 60% of their initial values between 2h and 4h and 40% of their initial values between 2h and 5h, respectively. Intrajejunal administration of insulin solution and capsules containing only SPHCc as controls did not result in a significant decrease of blood glucose concentrations. In the conscious rats, the hypoglycemic effect was observed. When the dose was 35ukg'' and 70u-kg"1, the lowest blood glucose level decreased down to about 80% and 60% of their initial values, respectively. Intragastric administration of capsules containing insulin or only SPHCc as controls did not result in a significant hypoglycemic effect.7 Enhancement mechanism of SPHCc for the intestinal absorption of insulinSPHCc had in vitro adhesive capacity and an increase in Carbopol? content gave a rise of adhesive force in every polymer tested. SPHCc with fast swelling mechanically fixed to the absorption sites in the intestine. In the presence of SPHCc, the degradation of insulin decreased significantly. This indicated that SPHCc were able to inhibit to some extent the activity of trypsin and a-chymotrypsin and their inhibition was stronger as compared to SPH. After SPHCc was put in situ closed loops pre-washed with saline, the insulin solution was administrated and the blood glucose levels decresed down to about 30% of their initial values at 30min after...