Potential Developments in Systemic Delivery of Insulin

Prolonged hypoglycemic effect of insulin-loaded polybutylcyanoacrylate nanoparticles after pulmonary administration to normal rats

Insulin-loaded polybutylcyanoacrylate nanoparticles were prepared by emulsion polymerization. The mean diameter of the nanoparticles was 254.7 nm with a polydispersity of 0.064. The associating ratio of insulin to the nanoparticles reached 79.1%. Studies on in vitro release kinetics showed that release profiles can be modeled using a biexponential function and the burst effect was obvious. After various doses of insulin-loaded nanoparticles were intratracheally given to normal rats, significant decrease of glucose level was achieved at each dose group from 5 to 20 IU kg-1. The minimum blood glucose concentration reached 46.9%, 30.4% and 13.6% of the initial level after pulmonary delivery of 5, 10 and 20 IU kg-1 insulin-loaded nanoparticles to normal rats, respectively. The time to reach the minimum blood glucose level (Tmin) was 4, 4 and 8 h for three doses, respectively. The duration of glucose level below 80% of insulin-loaded nanoparticles was much longer than that of insulin solution at every dose. Relative pharmacological bioavailability of insulin-loaded nanoparticles by pulmonary administration was 57.2% over the same formulation by subcutaneous administration.

Efficacy, safety and mechanism of cyclodextrins as absorption enhancers in nasal delivery of peptide and protein drugs

Cyclodextrins are used in nasal drug delivery as absorption enhancing compounds to increase the intranasal bioavailability of peptide and protein drugs. The most effective cyclodextrins in animal experiments are the methylated derivatives, dimethyl-beta-cyclodextrin and randomly methylated beta-cyclodextrin, which are active at low concentrations ranging between 2% and 5%. However, large species differences between rats, rabbits and humans exist for the nasal absorption enhancement by cyclodextrins. Based on toxicological studies of the local effects of cyclodextrins on the nasal mucosa dimethyl-beta-cyclodextrin and randomly methylated beta-cyclodextrin are considered safe nasal absorption enhancers. Their effects were quite similar to controls (physiological saline), but smaller than those of the preservative benzalkonium chloride in histological and ciliary beat frequency studies. In these studies, and in a study of the release of marker compounds after nasal administration, methylated beta-cyclodextrins were less toxic than sodium glycocholate, sodium taurodihydrofusidate, laureth-9 and L-alpha-phosphatidylcholine. Systemic toxicity after nasal cyclodextrin administration is not expected, because very low doses of cyclodextrins are administered and only very small amounts are absorbed. The mechanism of action of cyclodextrins may be explained by their interaction with the nasal epithelial membranes and their ability to transiently open tight junctions.

Efficacy of insulin eyedrops

Systemic absorption of insulin delivered via eyedrops has been studied in rats made transiently hyperglycemic by anesthesia with xylazine/ketamine. Insulin at a concentration of 2 mg/ml was not absorbed significantly when saline alone was used as the formulation for the eyedrops (0.04 ml). When various emulsant agents were added to the eyedrop formulation, systemic insulin levels were increased and concomitantly, blood D-glucose levels were decreased. Saponin, Brij-78, BL-9 and several alkylglycosides all increased the systemic absorption of insulin following delivery in eyedrops. Not all surfactant agents were effective in promoting systemic insulin absorption from eyedrops, as evidenced by the failure of some non-ionic surfactants to increase insulin absorption. Similar results were obtained when nosedrops containing insulin plus non-ionic surfactants were administered to rats. In conclusion, systemic insulin absorption was greatly accelerated by the addition of certain emulsants to the eyedrop formulation and physiologically important levels of insulin could be delivered systemically following eyedrop administration.

Delivery of hormones: some new concepts

Some new concepts in the delivery of hormones are described. Transmucosal or transdermal penetration of hormones can be facilitated, often by the use of absorption enhancers. Studies of nasal insulin delivery are described. Recently developed iontophoretic delivery devices can be useful for pulsatile transdermal administration of peptide hormones. A self-regulating delivery system releasing insulin in response to glucose levels is described. A vaginal ring releasing ethinylestradiol and 3-ketodesogestrel is a new concept in long-acting contraception. A nasal estradiol formulation, containing the absorption enhancer dimethyl-beta-cyclodextrin, is an interesting alternative to oral and transdermal delivery of female sex hormones.