Investigation On The Design Of Insulin Embedded Microsphere With Acidic Buffer As Stabilizer & Its Hypoglycemic Effects For Diabetes Rats

There are two primary obstructions for insulin to pass through cellular gap of intestinal mucosa after oral administration.One is that the insulin can be inactive because of protease in gastrointestinal tract.The other is that it cannot pass through mucous layer and physical barrier of epithelium tight junction.We devoted to solve the two problems above.Firstly,we prepared sustained release microsphere of insulin by spray drying.In the process,hyaluronic acid/citric acid buffer system was used to inhibit activity of trypsin and chitosan to open the epithelium tight junction and adhere intestinal mucosa.The microsphere was then filled into enteric capsules.In vitro and in vivo tests showed that hydrogen ion released by hyaluronic acid/citric acid buffer system in microsphere inhibited activity of proteases and protected insulin released simultaneously from the proteases before passing through intercellular space into general circulation.By measuring the activity of trypsin in different PH conditions,the author found out that when the PH decreased to 4.3 from 7.6,the activity of trypsin increased by 130 times.The buffering capacity in vitro experiments showed: the insulin sustained-release microspheres can reduce the PH of agarose gel plates to and maintain at 3.1 from 6.8 within 4 hours.Furthermore,it can also reduce and maintain the PH at between 3.1 and 4.4 within 2 hours.The results show that: the insulin sustained-release microspheres prepared in our paper can provide weakly acidic microenvironments which can protect the activity of insulin from the impact by inhibiting the activity of trypsin.Oral hypoglycemic diabetic rats experimental results show that 50u/kg oral insulin loaded microspheres and 50u/kg subcutaneous insulin solution have no significant difference in the effect of lowering blood glucose in addition to the absorption peak of 1 hour.But 50u/kg oral insulin loaded microspheres has more obvious hypoglycemic effect than blank microspheres formulation which confirms the result that the hypoglycemic effect from the release microspheres active insulin instead of the carrier material.In addition,the effect of the insulin loaded microspheres without chitosan and hyaluronic acid decreases the diabetic rats' blood glucose is significantly lower than the slow-release microspheres containing these two materials,the result confirms that when the oral insulin slow-release microspheres are taken orally,the absorption of insulin in the body and its hypoglycemic effect root in the inhibition on trypsin and the protection of insulin from hyaluronic acid and its low PH buffer system.In this work,sustained release buffer system of weak-acid was used to inhibit the activity of trypsin,which could protect the activity of insulin from the damage of trypsin.Compared with the existing method of adding enzyme inhibitors,the design concept of this study had three aspects of advantages as follows.Firstly,the inhibition of weak-acid sustained release buffer system to the activity of trypsin was reversible,which then had no effect on the normally physiological mechanism of gastrointestinal tract.Secondly,it was different from the uncertainty of exposed in the environment of enzyme inhibitors,the activity of insulin in the environment of weak-acid was not affected.Finally,the suppression of enzyme inhibitors to protease activity was often restricted by external factors,while the buffering capacity of weak-acid sustained release buffer system could perform normally always.The research program and acquired results in this study provided a simply and feasibly new idea for the research and development of the oral preparations of insulin and other protein/polypeptide drugs.