Effective portal insulin delivery with enzyme-protected capsules in pancreatectomized pigs

Eudragit S100-Coated Chitosan Nanoparticles Co-loading Tat for Enhanced Oral Colon Absorption of Insulin

In order to improve oral absorption of insulin, especially the absorption at the colon, Eudragit S100® (ES)-coated chitosan nanoparticles loading insulin and a trans-activating transcriptional peptide (Tat) were employed as the vehicle. In vitro releases of insulin and Tat from ES-coated chitosan nanoparticles had a pH-dependant characteristic. A small amount of the contents was released from the coated nanoparticles at pH 1.2 simulated gastric fluid, while a fairly fast and complete release was observed in pH 7.4 medium. Caco-2 cell was used as the model of cellular transport and uptake studies. The results showed that the cellular transport and uptake of insulin for ES-coated chitosan nanoparticles co-loading insulin and Tat (ES-Tat-cNPs) were about 3-fold and 4-fold higher than those for the nanoparticles loading only insulin (ES-cNPs), respectively. The evaluations in vivo of ES-Tat-cNPs were conducted on diabetic rats and normal minipigs, respectively. The experimental results on rats revealed that the pharmacodynamical bioavailability of ES-Tat-cNPs had 2.16-fold increase compared with ES-cNPs. After oral administration of nanoparticle suspensions to the minipigs, insulin bioavailability of ES-Tat-cNPs was 1.73-fold higher than that of ES-cNPs, and the main absorption site of insulin was probably located in the colon for the two nanoparticles. In summary, this report provided an exploratory means for the improvement of oral absorption of insulin.

Oral colon delivery of insulin with the aid of functional adjuvants

Oral colon delivery is currently considered of importance not only for the treatment of local pathologies, such as primarily inflammatory bowel disease (IBD), but also as a means of accomplishing systemic therapeutic goals. Although the large bowel fails to be ideally suited for absorption processes, it may indeed offer a number of advantages over the small intestine, including a long transit time, lower levels of peptidases and higher responsiveness to permeation enhancers. Accordingly, it has been under extensive investigation as a possible strategy to improve the oral bioavailability of peptide and protein drugs. Because of a strong underlying rationale, most of these studies have focused on insulin. In the present review, the impact of key anatomical and physiological characteristics of the colon on its viability as a protein release site is discussed. Moreover, the main formulation approaches to oral colon targeting are outlined along with the design features and performance of insulin-based devices.

Immunohistochemical localization of insulin-degrading enzyme along the rat intestine, in the human colon adenocarcinoma cell line (Caco-2), and in human ileum

Insulin-degrading enzyme (IDE) has been implicated in the intracellular degradation of insulin in insulin target cells. Knowledge of the existence of this enzyme in the intestine will be beneficial to the achievement of clinical oral efficacy of insulin. A comparative study was conducted with rat intestine, human colon adenocarcinoma (Caco-2) cells, and human ileum. Confocal microscopy analysis using the anti-IDE antibody showed that IDE was localized in the mucosal cells of rat and human intestines, as well as in Caco-2 cells. Immunostaining of this enzyme was homogeneous throughout the cell excluding nucleus, indicating a typical cytosolic distribution in rat and human enterocytes and in Caco-2 cells.

Development and validation of a pig model for colon-specific drug delivery

The purpose of this investigation was to develop a pig model for colonic drug delivery and to validate the model by determining whether the physiology of the pig colon had been significantly altered after the surgical implantation of a gut cannula into the terminal ileum of the pig. A fistula was created in the terminal ileum of the pig, and a cannula fitted for the purpose of directly administering drug formulations to a point just anterior to the ileocaeco-colonic valve of the gastrointestinal tract. The cephalic vein of the pig was also cannulated to enable continued blood sampling. Sulphasalazine was used as the model drug for the validation study. In the intact colon, sulphasalazine is metabolized by the gut microflora to sulphapyridine which is then absorbed. Sulphasalazine was administered orally to non-fistulated and fistulated pigs and then ileally, via the gut cannula, to fistulated pigs. Absorption of sulphapyridine was monitored by HPLC analysis of plasma samples. There was no significant difference in the absorption obtained for the three groups. Thus it is demonstrated that the colon physiology had not been altered. The colonic pig model is ideal for studying factors affecting the colonic absorption of drugs and as a means for developing drug delivery systems with improved absorption properties.

Colonic absorption of insulin-like growth factor I in vitro

Colonic absorption of recombinant human insulin-like growth factor I (rhIGF-I) was measured in vitro using both rat and minipig colon. The permeability coefficients were 8.03 +/- 1.03 and 4.75 +/- 0.43 x 10(-8) cm sec-1 in the rat and minipig, respectively. The steady-state flux in rat colon was linearly related to the donor concentration over the range 1 to 10 mg/mL. rhIGF-I was metabolically stable in contact with both mucosal and serosal surfaces of washed colon for 5 hr. The amount of IGF-I permeating through the tissue was quantitated by radioimmunoassay and the identity and integrity of the permeating species were confirmed by reverse-phase HPLC, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and Western blotting. In all cases the permeant was identical to authentic rhIGF-I. The integrity of the colonic tissue in vitro was demonstrated by the maintenance of electrophysiological parameters, a secretory response to serosal theophylline, and the ability of sodium azide, a metabolic inhibitor, to abolish the barrier properties and cause a large increase in flux.