Aki Kitagawa

Insulin-loaded biodegradable PLGA microcapsules: initial burst release controlled by hydrophilic additives

We investigated the controlled release of human insulin at an initial stage from poly(DL-lactic-co-glycolic acid) (PLGA, M(w) 6600) spherical matrices. PLGA microcapsules were prepared by the novel solvent evaporation multiple emulsion process. When the crystalline insulin was dispersed in dichloromethane as solid-in-oil (S/O) dispersion, it was found that most of insulin molecules were inlaid on the surface of PLGA microcapsules. Consequently, insulin-loaded PLGA microcapsules exhibited marked rapid release of insulin within several hours in both in vivo and in vitro experiments. On the other hand, the addition of glycerol or water in the primary dichloromethane dispersion results in drastically suppressed initial release. It was found by SEM observation that water- or glycerol-in-oil (W/O or G/O) type mini-emulsion droplets with a mean diameter of 300-500 nm were formed in this primary solution. This phenomenon can be theoretically presumed to occur because insulin and PLGA molecules, having amphiphilic properties, converge on the interface between the hydrophilic additive and dichloromethane. Hence, insulin molecules heterogeneously located in the inside of PLGA microcapsules, not on the surface, would be gradually released with PLGA hydrolytic decomposition. As an additional effect of glycerol, the initial burst was further suppressed due to the decrease of the glass transition temperature of PLGA from 42.5 to 36.7 degrees C. Since the annealing of PLGA molecules took place at around 37 degrees C, the porous structure of microspheres immediately disappeared after immersion in PBS or subcutaneous administration. The insulin diffusion through the water-filled pores would be effectively prevented. The strict controlled initial release of insulin from the PLGA microsphere suggested the possibility of utilization in insulin therapy for type I diabetic patients who need construction of a basal insulin profile.

A novel sustained-release formulation of insulin with dramatic reduction in initial rapid release.

To ensure a strictly controlled release of insulin, a preparation method for insulin-loaded microcapsules was designed. Microcapsules were prepared with an injectable, biodegradable polymer composed of co-poly(D,L-lactic/glycolic) acids (PLGA) (mean molecular weight 6600, LA/GA ratio 50:50). Morphological examination using scanning electron microphotography demonstrated spherical particles with a main diameter of 15-30 microm. When 3% insulin-loaded PLGA microcapsules were administered subcutaneously as a single dose (250 U/kg) to streptozotocin-induced hyperglycemic rats, plasma insulin levels increased and were sustained at levels showing hypoglycemic effects. When glycerin, ethanol, or distilled water was used throughout the preparation procedure, the resultant microcapsules dramatically reduced the initial burst. The formulation in which glycerin was added to an oil phase containing PLGA, insulin, and ZnO increased plasma insulin levels to 86.7, 108.4, and 84.9 microU/ml at 1, 2, and 6 h, respectively. The levels remained at 36.2-140.7 microU/ml from day 1 to day 9. The AUC(0-24 h)/AUC(0-336 h) ratio was calculated to be 9.7%. The formulation prepared without additives gave such a rapid insulin release that animals receiving it became transiently hypoglycemic.

Marked hypotensive and blood flow-increasing effects of a new lipo-PGE1 (lipo-AS013) due to vascular wall targeting

Lipo-AS013 is being developed as an improved formulation of lipo-PGE(1), which is widely used in clinical practice in Japan and some Asian countries. We have previously reported that lipo-AS013, which is a lipid microsphere (LM) preparation of a chemically stable and lipophilic PGE(1) prodrug (AS013, Fig. 1), slowly releases small amounts of the active ingredient (AS013) in human plasma. In the present study, to estimate the vascular wall targeting ability and efficacy of lipo-AS013, we determined the hypotensive and blood flow-increasing effects of lipo-AS013, lipo-PGE(1), PGE(1)CD, and AS013. Lipo-AS013 was found to have longer-lasting hypotensive and blood flow-increasing effects than the other agents. The two LM preparations, lipo-PGE(1) and lipo-AS013, had a markedly stronger effect than PGE(1)CD and AS013 alone, demonstrating the benefit of drug delivery using LM. In spontaneously hypertensive rats (SHR), lipo-AS013 also had a significant hypotensive effect. To confirm vascular wall targeting by lipo-AS013, the localization of PGE(1) in the aorta and neovascular capillaries of rat was investigated by immunostaining. The results indicated that lipo-AS013 was more efficient at delivering the active ingredient (AS013) to the vessel wall. In conclusion, lipo-AS013 could supersede lipo-PGE(1) and PGE(1)CD in clinical use.

A novel insulin formulation can keep providing steady levels of insulin for much longer periods in-vivo

We have recently succeeded in preparing insulin‐loaded microcapsules that release the insulin in a strictly controlled manner with little initial rapid release in‐vitro or in‐vivo. We show here the superiority of the best formulation prepared with co‐poly(d,l‐lactic/glycolic) acids (PLGA) (mean MW 5800, L/G ratio 50:50) with a main diameter of 15 ˜ 30 μm in‐vivo. When 3.2% insulin‐loaded PLGA microcapsules were subcutaneously given as a single dose to streptozotocin‐induced hyperglycaemic rats (250 U kg−1), plasma insulin levels gradually increased and constant levels (30.3–94.1 μL−1) were sustained. Rats receiving the formulation once a week showed not only steady plasma insulin levels, but also gained weight at a similar speed to normal rats. Meanwhile, daily treatment with Humulin U (25 U kg−1) caused a transient high insulin level (2723.9 μU mL−1 at 1 h) in plasma, but the body weight of the rats was little changed. A pharmacological study in female Cynomolgus monkeys also revealed that the microcapsular formulation provided a flat release of insulin for longer periods and showed no immunogenic activity. In the near future, therefore, this insulin formulation could become very beneficial as a provider of basal insulin levels for insulin‐dependent diabetic patients.

Administration of Optimum Sustained-Insulin Release PLGA Microcapsules to Spontaneous Diabetes-Prone BB/WorTky Rats

To show the possibility of sustained-release insulin formulation composed of PLGA, the optimum one was administered to BioBreeding rat, a model of spontaneous type I diabetes mellitus (IDDM). Every 2 weeks subcutaneous administration made their blood glucose level depend on the insulin release and food intake. However, all of them kept alive with little change or rather a little gain in body weight. Furthermore, some of pregnant rats with intermittent treatment bore fetuses, although additional insulin therapy seemed necessary. Therefore, the formulation could become a new tool as a provider of basal insulin for IDDM patients.