In vitro skin penetration and degradation of enkephalin, elcatonin and insulin

Measurement of Protein Diffusion Through Poly(d,l-Lactide-Co-Glycolide)

A novel method was developed for studying the diffusion of proteins through poly(D,L-lactide-co-glycolide) (PLG), using a diffusion cell. To develop improved formulations for the controlled release of encapsulated drugs it is important to understand the underlying release mechanisms. When using low-molecular-weight PLG as the release-controlling polymer, diffusion through the pores is often proposed as the main release mechanism. The experimental set-up and method of determining the diffusion coefficient were thoroughly evaluated with regard to the reliability and the influence of the stirring rate. A procedure for spraying thin films of PLG onto a filter, which could be placed in the diffusion cell, was optimized. The method was then applied to the determination of the diffusion coefficient of human growth hormone (hGH) through a PLG film. The results show that the method enables measurements of the diffusion coefficient through the polymer film. Neither the stirring rate nor the concentration of hGH influenced the diffusion coefficient. The diffusion coefficient of hGH through degraded PLG films was 5.0 x 10(-13) m2/s, which is in the range that could be expected, i.e., several orders of magnitude smaller than its the diffusivity in pure water. The reproducibility was good, considering the dynamic properties of PLG, i.e., the difference in diffusion coefficients, at, for example, different stages of degradation and for different compositions of PLG, is expected to be much higher. The variation is probably also present in PLG films used for controlled-release formulations. Although the PLG film contains a large amount of water, a considerable time elapsed before pores of sufficient size formed and diffusion through the film started. In two-component diffusion experiments, the difference in diffusion rate did not correspond to the difference in molecular weight of the solutes, indicating a size exclusion effect. This method can be used to study the effect of changes in the formulation specification. By studying the change in the diffusion coefficient through the degradation process of PLG, or similar polymers, a better understanding of diffusion and, thus, also release mechanisms can be obtained.

Effect of cholic acid and its keto derivatives on the analgesic action of lidocaine and associated biochemical parameters in rats

This study examined the effect of the structure and concentration of cholic acid and its keto derivatives on the local analgesic action of lidocaine in rats, measured by an analgesimetric method. The increase in bile acid concentrations in the administered lidocaine solution increased the duration of local anesthesia. It was found that the introduction of keto groups into the cholic acid molecule yielded derivatives with lower promotory action, i.e. decreased the duration of local anesthesia. The biochemical parameters investigated indicated that the keto derivatives of cholic acid exhibited no toxicity compared to that of cholic acid itself.

Transdermal delivery of CaCO3-nanoparticles containing insulin

BACKGROUND

This study evaluates the pharmacokinetic and pharmacodynamic effects of a transdermally delivered insulin using novel CaCO(3)-nanoparticles in normal mice and those with diabetes.

METHODS

CaCO3-nanoparticles encapsulating insulin (nanoinsulin) were transdermally applied to the back skin of normal ddY mice and dB/dB and kkAy mice with diabetes after fasting for 1 h. Serum insulin levels of ddY mice were analyzed by enzyme immunoassay, and blood glucose of normal mice and those with diabetes was monitored.

RESULTS

Maximum serum insulin was 67.1 +/- 25.9 microIU/mL at 4 h with 200 microg of transdermal nanoinsulin in ddY mice, whereas that after subcutaneous injection of 3 microg of monomer insulin was 462 +/- 20.9 microIU/mL at 20 min. Transdermal nanoinsulin decreased glucose levels in a dose-dependent manner. A maximum decrease in blood glucose of 48.3 +/- 3.9% (ddY), 32.5 +/- 9.8% (dB/dB), and 26.2 +/- 7.6% (kkAy) after 6 h was observed with 200 microg of transdermal nanoinsulin, compared with 64.1+/-1.0% (ddY), 57.9 +/-3.4% (dB/dB), and 24.1 +/- 6.7% (kkAy) after 1 h with 3 microg of subcutaneous monomer insulin. Insulin bioavailability until 6 h with transdermal nanoinsulin in ddY mice was 0.9% based on serum insulin level and 2.0% on pharmacodynamic blood glucose-lowering effects.

CONCLUSIONS

This CaCO(3)-nanoparticle system successfully delivered insulin transdermally, as evidenced by a significant sustained decrease in blood glucose in normal mice and those with diabetes. These results support the feasibility of developing transdermal nanoinsulin for human applications.

Peptidase activity on the surface of the porcine buccal mucosa

Peptide drugs in buccal bioadhesive delivery systems are exposed to the surface of the buccal mucosa at high concentrations over long periods of time. The peptidase activity on the surface of the buccal mucosa has not been evaluated as a barrier to peptide buccal delivery. The in vitro stability of various synthetic substrates on the surface of intact porcine buccal mucosa was determined. No carboxypeptidase or dipeptidyl peptidase IV activity was detected on the buccal mucosa, while aminopeptidase N activity was detected using Leu-p-nitroanilide. No endopeptidase activity was observed towards the peptide substrates. Insulin and insulin B-chain were intact at the 2 h time point at 37 degrees C, while the percent of parent Leu-enkephalin remaining was 18+/-9 (mean+/-S.D., n=9). In the presence of aminopeptidase inhibitors, amastatin, sodium deoxycholate and EDTA, the degradation of Leu-enkephalin was dramatically reduced. This work suggests that the buccal route maybe advantageous for the delivery of peptides that are susceptible to such activities. The inclusion of aminopeptidase inhibitors in buccal bioadhesive delivery systems could improve buccal bioavailability of Leu-enkephalin. We suggest that compared with the existing in vitro metabolism methods, the analysis of peptide or protein metabolism on intact buccal mucosa could better predict the degradation of the drug as it crosses the tissue.

Transdermal delivery of insulin from a novel biphasic lipid system in diabetic rats

Noninvasive transdermal insulin delivery could provide diabetic patients with sustained physiological levels of basal insulin in a pain-free manner. We have developed a novel transdermal lipid-based system (Biphasix) suitable for macromolecule delivery across the skin. The objective of this study was to evaluate the pharmacological effects of the Biphasix-insulin delivery system in a diabetic rat model. Transdermal patches (one per animal) containing Biphasix-insulin formulation (10 mg of recombinant human insulin dose) were applied to the shaved abdominal skin of streptozotocin-induced diabetic rats for 48 h. Blood glucose was monitored every 2-4 h using a Lifescan glucose meter. Serum insulin levels were analysed by enzyme-linked immunosorbent assay. A decrease in blood glucose of 43.7 +/- 3.8% (mean +/- SEM, n = 25) was observed compared with initial blood glucose levels. The duration of the response was 51.5 +/- 3.7 h (mean +/- SEM, n = 25). Serum insulin after application of the transdermal Biphasix-insulin patch was 20.08 +/- 5.44 micro IU/mL (mean +/- SEM, n = 13) during the steady state, which was not statistically different from the insulin levels obtained 2 h after subcutaneous injection of 1 mg of recombinant human insulin solution. Insulin bioavailability from the transdermal Biphasix-insulin patches was 21.5 +/- 6.9% (mean +/- SEM, n = 13) based on serum insulin and 39.5 +/- 8.5% (mean +/- SEM, n = 25) based on the pharmacodynamic blood glucose-lowering effects. The Biphasix system successfully delivered insulin transdermally, as evidenced by a significant sustained decrease in blood glucose in diabetic rats, with a corresponding increase in serum insulin. These results support the feasibility of developing a transdermal insulin patch for human applications.

Oral delivery of synthetic eel calcitonin, elcatonin, in rats

This study was designed to develop an oral dosage form of elcatonin (EC), a hypocalcemic peptide. The EC absorption was estimated by the reduction in plasma calcium concentrations. When EC was orally coadministered with nitroso-N-acetyl-D,L-penicillamine (SNAP, 4.0 mg) and 0.02% Carbopol solution or with taurocholate (20 mM) and 0.02% Carbopol solution, the lowering effect was increased compared with that after EC alone, but the F values (0.32 and 0.30%) were extremely small. The oral administration of the mucoadhesive emulsion, which was prepared by coating the W/O/W emulsion with 0.1% Carbopol, enhanced the calcium lowering effect, with the F value of 0.43%. The strong mucoadhesion of the mucoadhesive emulsion to the gastrointestinal mucosa was observed. A capsule containing EC (500 microg), taurocholate (6 mg) and lyophilized Carbopol (3.5 mg) administered orally gave a sustained but comparatively small calcium lowering effect. In the in vitro enzymatic hydrolysis experiment, EC was more rapidly hydrolyzed in the intestinal fluid than in the mucosal extract. The combination of 20 mM taurocholate with 0.02% Carbopol showed the greatest inhibitory effect in both fluid and extract. These data indicated that EC was effectively absorbed through the intestinal wall, but the peptide was dominantly degraded by proteolytic enzymes in the GI tract. These results will offer a potential approach to the oral delivery of EC.