The Study Of Oral Drug Delivery System With Insulin-Adsorbed Porous Microspheres

Hydroxyapatite (HA), is the main mineral constituent of the hard tissues in human body. So synthesized HA has been widely applied as hard tissue replacement implants because of its excellent biocompatibility and non-toxicity. With its high recovery of biomolecules with unaltered physicochemical properties, HA has also been used successfully as adsorbent for separation and purification of proteins, DNA and RNA.The mechanism of separation and purification by HA has been deduced: Two types of adsorbing surface, the a (or b) and the c crystal surface, generally appear on HA particle. The acidic proteins (and also nucleic acids including other nucleotides) are mainly adsorbed on the a (or b) surface by using their carboxyl groups (and/or phosphate groups) during adsorption process. The adsorbed acidic protein molecules can be replaced by competing phosphate ions during desorption process. The basic proteins are mainly adsorbed on the c surface by using their e-amino groups (and/or guanidinyl groups) during adsorption process. The adsorbed basic protein molecules can be replaced by competing ions such as sodium, potassium, or/and calcium ions etc. during desorption process.In pharmaceutics, oral delivery of peptides and proteins is preferredroute of administration to injection because of its convenience and high patient compliance, a great deal of research has been focused on the development of oral dosage forms for the past few decades. HA has been reported to enhance the absorption of various peptides across the mucosal barrier. Meantime, HA can carry peptides or proteins by adsorption and release them by desorpion. So it would be feasible to introduce HA to oral proteinic delivery system..In this study, five steps have been accomplished: ① HA crystallites with 10-50 nm in width and 200-500 nm in length were obtained by precipitation method. Afterwards, spray-drying method was applied to prepare porous HA microspheres (PHAMS), and several technical parameters (i.e. the concentration of HA slurry, atomizer rotation, slurry feeding rate etc.) which could effect the sizes of microspheres have been investigated. Porous HA microspheres (PHAMS) with the size range 9-80 μm in diameter have been obtained with specific condition. (2) An acidic peptide, insulin (PI=5.3-5.4), has been chosen as model drug in this study. In adsorption experiment of PHAMS, many factors (i.e. incubation temperature, incubation duration, pH and concentration of insulin solution) had influences on insulin adsorption on obtained microspheres. More than 92% insulin in solution could be loaded with optimized condition and drug loading of more than 3.2% could be achieved. In desorption experiment, the concentration of K2HPO4 solution in many effecting factors had greatest influence on insulin release from insulin-adsorpted microspheres (IAMS). More than 90% loaded-insulin could bereleased at K2HPO4 solution at concentration around 10 mM.. ③ IAMS were microencapsulated into Eudragit(?) L-100 by modified emulsion-solvent evaporation technique. The influence of several technical parameters (i.e. the amount of anti-aggregation, the volume of solvent and magnetic stirring speed, etc.) on IAMS coated with Eudragit(?) L-100 (IAMSCE) have been studied. IAMSCE with d50 being 482.03 μm in diameter, drug loading being 0.493% and encapsulation efficiency being 84.48% have been obtained with specific condition. ④ In vitro experiment of drug release, no release was observed in acidic medium. However, more than 96% encapsulated insulin was released within 4 h in phosphate buffer solution (PBS, 0.05 M, pH 6.8). ⑤ In vivo experiment of biological activity, IAMSCE could reduce the blood glucose level (BGL) of streptozocin-induced diabetic rats for more than 3 h with maximal value of 34.7% at 2 h after administration, showing statistically significant effect (P<0.05). Compared to subcutaneous injection of insulin, IAMSCE demonstrated bioavailability of 4.3%.In conclusion, the obtained IAMSCE presented advantageous behaviors in vitro drug release experiment and improved significantly the bioavailability of orally administered insulin. These results suggested that HA could be applied for fabrication of oral proteinic drug delivery system.