Enhanced permeability of insulin across the rat intestinal membrane by various absorption enhancers: Their intestinal mucosal toxicity and absorption-enhancing mechanism of n-lauryl-beta-D-maltopyranoside

T. Uchiyama et al., Enhanced permeability of insulin across the rat intestinal membrane by various absorption enhancers: Their intestinal mucosal toxicity and absorption-enhancing mechanism of n-lauryl-beta-D-maltopyranoside, J PHARM PHA, 51(11), 1999, pp. 1241-1250
Citations number
Categorie Soggetti
Pharmacology & Toxicology
Journal title
ISSN journal
0022-3573 → ACNP
Year of publication
1241 - 1250
SICI code
We have examined the in-vitro permeability characteristics of insulin in th e presence of various absorption enhancers across rat intestinal membranes and have assessed the intestinal toxicity of the enhancers using an in-vitr o Ussing chamber method. The absorption enhancing mechanism of n-lauryl-bet a-D-maltopyranoside was studied also. The permeability of insulin across the intestinal membranes was low in the absence of absorption enhancers. However, the permeability was improved in the presence of enhancers such as sodium glycocholate and sodium deoxychola te in the jejunum, and sodium glycocholate, sodium deoxycholate, n-lauryl-b eta-D-maltopyranoside, sodium caprate and ethylenediaminetetraacetic acid ( EDTA) in the colon. Overall, the absorption enhancing effects were greater on the colonic membrane than on the jejunal membrane. The intestinal membra ne toxicity of these enhancers was characterized using the release of cytos olic lactate dehydrogenase from the colonic membrane. A marked increase in the release of lactate dehydrogenase was observed in the presence of sodium deoxycholate and EDTA. The release of lactate dehydrogenase in the presenc e of these absorption enhancers was similar to that seen with sodium dodecy l sulphate (SDS), used as a positive control, indicating high toxicity of t hese enhancers to the intestinal membrane. In contrast, sodium glycocholate and sodium caprate caused minor releases of lactate dehydrogenase, similar to control levels, suggesting low toxicity. In addition, the amount of lac tate dehydrogenase in the presence of n-lauryl-beta-D-maltopyranoside was m uch less than that seen with sodium deoxycholate, EDTA and SDS. Therefore, sodium glycocholate, sodium caprate and n-lauryl-beta-D-maltopyranoside are useful absorption enhancers due to their high absorption enhancing effects and low intestinal toxicity. To investigate the absorption enhancing mechanisms of n-lauryl-beta-D-malto pyranoside, the transepithelial electrical resistance (TEER), voltage clamp experiments and the circular dichroism spectra were studied. n-lauryl-beta -D-maltopyranoside decreased the TEER values in a dose-dependent manner, su ggesting that the enhancer may open the tight junctions of the epithelium, thereby increasing the permeability of insulin via a paracellular pathway. This speculation was supported by the findings that 20 mM n-lauryl-beta-D-m altopyranoside produced a greater increase in the paracellular flux rate th an in the transcellular flux rate by the voltage clamp studies. Evaluating the circular dichroism spectra we found that insulin oligomers were not dis sociated to monomers by the addition of n-lauryl-beta-D-maltopyranoside, bu t dissociation did occur with the addition of sodium glycocholate. Thus, th e dissociation of insulin was not a major factor in the absorption enhancin g effect of n-lauryl-beta-D-maltopyranoside. These findings provide basic information to select the optimal enhancer for the intestinal delivery of peptide and protein drugs including insulin.