Category: Formulation and Quality
Purpose: Currently, insulin is administered mainly by parenteral routes to treat diabetes mellitus. To improve patient compliance, many non-invasive methods of administration of insulin have been explored. Amongst these, however, very limited literature is available to understand sublingual administration of insulin. Owing to hydrophilicity and large molecular weight of insulin, in order to achieve satisfactory membrane permeability, the use of permeation enhancer becomes a prerequisite for any insulin formulation for sublingual administration. Therefore, in this current investigation, HPβCD (2-hydroxypropyl-β-cyclodextrin) and poloxamer 188 were being explored as permeation enhancers.
Methods: In vitro performance of insulin solutions with and without combination of HPβCD and poloxamer 188 were evaluated using MatTek tissue model, MDCK cell line, rat esophagus, and porcine esophagus, respectively. Briefly, the in vitro permeation of insulin (10 IU/mL) with and without the permeation enhancers was evaluated using side-by-side permeation apparatus along with rat and porcine esophagus, respectively. On the other hand, to evaluate in vitro permeation of insulin across MatTek tissue model and MDCK cell line, the set protocols were used. Furthermore, insulin was administered sublingually to Sprague-Dawley rats at dose of 0, 5, 10, and 15 IU/kg, respectively, along with the permeation enhancers. Following the administration of insulin, blood glucose levels were measured at predetermined time intervals using glucometer (Accucheck-Aviva). To serve as control groups, sublingual saline and insulin solutions (15 IU/kg) as well as subcutaneous insulin solution (1 IU/kg), respectively, were administered to rats. Finally, the combination effect of of HPβCD and poloxamer 188 at various concentration levels was explored using Box-Behnken design (BBD) to optimize the permeation of insulin solution. In this design, the independent (X1: concentration of insulin, X2: concentration of HPβCD, and X3: concentration of poloxamer 188) and dependent (Y1: cumulative amount of insulin permeated at 60 min and Y2: insulin permeation flux) variables were used to generate BBD using FusionPro software (S-Matrix Corporation). As a result, fifteen formulations were generated and subjected to in vitro permeation evaluation using cellulose acetate membrane. Upon analyzing the relationship among the independent and dependent variables by FusionPro software, models were generated for Y1and Y2, respectively. Based on the generated Y1 and Y2 models, an optimized formulation and two checkpoint formulations were obtained and subjected the same permeation evaluation to validate the prediction accuracy of generated models.
Results: It was observed that the cumulative amount of insulin permeated at 60 min (Q60), in presence of the combination of permeation enhancers was higher as compared to insulin alone across MatTek tissue model, MDCK cell line, rat esophagus, and porcine esophagus, respectively. Due to the physiological relevance and feasibility, porcine esophagus was found to be a potential tool for in vitro permeation studies. Based on the comparison of blood glucose profiles following administration of insulin solution at various doses shown in Fig. 1A, it was observed that the mean maximum decrease in glucose levels was 23.4%, 31.5%, and 36.5% (n = 3-6) for insulin dose at 5, 10, and 15 IU/kg, respectively. In addition, results in this study indicate that significantly lower maximum decrease in glucose levels in presence of the combination of permeation enhancers as compared to insulin alone (Fig. 1B). Since there was no significant decrease in the maximum decrease in glucose levels observed from sublingual administrations of saline and insulin at 0 IU/kg in presence of permeation enhancers, the inclusion of excipients (e.g., permeation enhancers) in the solution formulations did not have any hypoglycemic effect. Finally, based on regression analysis, the models were generated for Y1 (Models 1 and 2) and Y2 (Models 3 and 4), as shown in Figure 2 and 3, respectively.
Conclusion: The present investigation suggests use of permeation enhancer, such as HPβCD and poloxamer 188, is suitable for development of insulin solution for sublingual administration.