Yoshiyuki Chiba

Pluronic F-127 gels incorporating highly purified unsaturated fatty acids for buccal delivery of insulin.

The present study investigated the release profiles of insulin from Pluronic F-127 (PF-127) gel containing unsaturated fatty acids such as oleic acid (18:1), eicosapentaenoic acid (20:5) or docosahexaenoic acid (22:6) and the hypoglycemic effect of insulin following the buccal administration of the gel formulations in normal rats. Insulin release from the gels decreased in the presence of unsaturated fatty acids. Remarkable and continuous hypoglycemia was induced by all PF-127 gels (insulin dose, 25 IU/kg) containing unsaturated fatty acids. PF-127 gels containing oleic acid showed the highest pharmacological availability (15.9+/-7.9%). Our finding demonstrate that 20% PF-127 gels containing unsaturated fatty acids are potential formulations for the buccal delivery of insulin.

In vivo effects of highly purified docosahexaenoic acid on rectal insulin absorption.

The purpose of this study was to evaluate the effectiveness and the toxicity of polyunsaturated fatty acid, such as oleic acid, eicosapentaenoic acid (DHA), as potential absorption enhancer for rectal delivery of insulin, using a water-in-oil-in water (W/O/W) multiple emulsion. In a single administration study, rectal insulin absorption was enhanced markedly, and marked hypoglycemia was induced by the emulsion incorporating various fatty acids in an insulin dose-related fashion. The pharmacological availability of the emulsion incorporating 2% oleic acid, EPA and DHA was approximately 7.7, 11.0 and 25.4%, respectively. The insulin absorption enhancement effect was not increased in proportion to the amount of DHA in the emulsion, the mean T(max) value of the serum glucose-time curve could be extended to twice that of the emulsion without PF 127. In a multiple administration study, the mean AUC(glucose) values of the emulsion incorporating DHA showed almost the same value on the first and the tenth day. From the morphological appearance of the mucosal surface, the emulsion incorporating DHA induced no or little mucosal damage. Our findings demonstrated that DHA has a strong insulin permeability enhancement effect and little toxicity. Thus, DHA is an attractive candidate as an absorption enhancer for intestinal delivery of insulin.

Enhanced rectal absorption of insulin-loaded pluronic® F-127 gels containing unsaturated fatty acids

The objective of this study was to prepare and to evaluate Pluronic F-127 (PF127) gel containing unsaturated fatty acids such as oleic acid (18:1), eicosapentaenoic acid (20:5) and docosahexaenoic acid (22:6) as a potential formulation for rectal delivery of insulin. The hypoglycemic effect of insulin was examined following rectal administration of the various formulations in normal rats. Rectal insulin absorption was markedly enhanced, and marked hypoglycemia was induced by all PF127 gels (insulin dose, 5 U/kg) containing different unsaturated fatty acids. PF127 gels containing unsaturated fatty acids presented low tmax mean values indicating that the absorption of insulin occurred very rapidly in the rectum. The relative hypoglycemic efficacy of PF127 gel formulations containing fatty acids such as oleic acid, eicosapentaenoic (EPA) and docosahexaenoic (DHA) were 28.4+/-8.1, 26.8+/-14.3 and 23.1+/-5.7%, respectively. The finding demonstrated that 20% PF127 gels containing unsaturated fatty acids are potential formulations for rectal delivery of insulin.

The dose-related hypoglycemic effects of insulin emulsions incorporating highly purified EPA and DHA.

The dose-related pharmacological effects of insulin emulsion incorporating highly purified eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) were investigated. Water-in-oil-in-water multiple emulsions (insulin dose, 0, 10, 25 and 50 IU/kg) incorporating 2% DHA or EPA were administered directly into the colonic and rectal loops in situ. Serum insulin levels rose and serum glucose levels decreased in an insulin dose-related fashion. The relationship of insulin dose and C(max) or AUC(insulin) was linear at the rectum, but a non-linear relationship was observed at the colon. The trend was more predominant in DHA. In the in vivo rectal absorption experiment using emulsions incorporating 2% DHA, 5 IU/kg of insulin emulsion produced a rapid, transitory increase in serum insulin levels and strong reduction of serum glucose levels. The pharmacological availability determined from the dose-response curve by s.c. administration of insulin reached 43.2+/-26.3% (mean+/-S.D.). Mucosal irritation caused by administration of emulsions incorporating 2% EPA or DHA was evaluated by a lactate dehydrogenase (LDH) release study, and compared with those of the emulsion incorporating 2% oleic or linolenic acid. Only when emulsion incorporating 2% oleic acid was applied in the intestine did significant LDH release into the mesenteric veins occur. Our results indicate that emulsion incorporating highly purified long-chain polyunsaturated fatty acid, especially DHA, has the potential of becoming the formulation for enteral delivery of insulin.

Enhanced enteral bioavailability of vancomycin using water-in-oil-in-water multiple emulsion incorporating highly purified unsaturated fatty acid.

The aim of this study was to evaluate the potential of an emulsion incorporating unsaturated fatty acids to improve the mucosal absorption of poorly absorbed drugs from rat intestinal loops in situ, using a water-in-oil-in-water (W/O/W) multiple emulsion. Vancomycin hydrochloride (VCM) was used as a model drug with low oral bioavailability. The entrapment efficiency of VCM in the emulsion was approximately 60% and remained constant over storage for 1 month at 4 degrees C. The emulsion incorporating C18 unsaturated fatty acids or docosahexaenoic acid (DHA) markedly enhanced VCM absorption after colonic and rectal dosing. The effectiveness of DHA on VCM colonic absorption improvement was the same as that of oleic acid, and less than that of linoleic and linolenic acids. For rectal dosing, bioavailability was similar among various emulsions, in the range 40-50%. The effect of the emulsion incorporating oleic acid or DHA on improving VCM enteral bioavailability was not increased proportional to the incorporated amount. The electrical resistance of membranes was not changed by the incorporation of various fatty acids in emulsions. Our results indicated that W/O/W emulsions incorporating C18 unsaturated fatty acid or DHA were useful carriers for improving the absorption of poorly absorbable drugs via the intestinal tract without gross changes to tight junction function.

Induction of angiotensin-converting enzyme inhibitory activity by acid-limited proteolysis of glyceraldehyde 3-phosphate dehydrogenase

Angiotensin-converting enzyme (ACE) inhibitors were excised from glyceraldehyde 3-phosphate dehydrogenase (GAPDH) preparations of tuna and porcine muscles by heating at 120 degrees C for 5 min in 1 M AcOH-20 mM HCl. The inhibitors were then purified by successive chromatographies. The final product from tuna was identified as Pro-Thr-His-Ile-Lys-Trp-Gly-Asp, which was the ACE inhibitor obtained from tuna muscle [Kohama et al. (1988) Biochem. Biophys. Res. Commun. 155, 332-337]. The porcine ACE inhibitor was found to be Pro-Ala-Asn-Ile-Lys-Trp-Gly-Asp, which was identical to the porcine muscle GAPDH peptide 79-86. These results strongly suggested that the ACE inhibitory octapeptides derived from GAPDH proteins by acid-limited proteolysis at Asp-Pro and Asp-Ala peptide bonds.