Effect of cyclodextrins on biological membrane. I. Effect of cyclodextrins on the absorption of a non-absorbable drug from rat small intestine and rectum

The effects of three kinds of cyclodextrins (CyDs), alpha-, beta- and gamma-CyD on biological membranes were investigated by changes in absorption of a non-absorbable drug, sulfanilic acid (SA), from the rat small intestine and rectum using an in situ perfusion technique. The absorption of SA from the intestine was slight and was not affected by the addition of CyDs. After pretreatment with a mucolytic agent, N-acetyl-L-cysteine (N-Ac), the absorption of SA was increased compared with SA alone in the presence of only beta-CyD. Similar treatment with sodium deoxycholate (SDC) and sodium lauryl sulfate (SLS) to gastro-intestinal membrane showed the enhanced absorption of SA by the addition of beta-CyD. The mucin layer on the surface of the gastro-intestinal membrane may play an important role in the absorption of drugs. On the other hand, enhanced absorption of SA from the rat rectum was not induced by beta-CyD with or without pretreatment with N-Ac, SDC or SLS. Simultaneously, the release of neutral sugars in the perfusate after treatment with adjuvants was also observed with N-Ac, SDC and SLS. These results indicate that the mucin layer works as a barrier to the increased absorption of SA by beta-CyD.     

High-performance liquid chromatographic separation of physiological folate monoglutamate compounds. Investigation of absorption and conversion of pteroylglutamic acid in the small intestine of the rat in situ

A new high-performance liquid chromatographic method to investigate many folate monoglutamate compounds was developed. This method employed a Cosmosil 5-Ph column eluted with 10 mM potassium phosphate buffer (pH 7.0) containing 1% methanol at a flow-rate of 1.0 ml/min. Under these conditions, almost all of the physiological folate monoglutamate compounds were effectively separated and determined within 22 min. By applying this method to investigate the absorption and conversion of pteroylglutamic acid in the rat small intestine, it was demonstrated that pteroylglutamic acid was converted into 5-methyltetrahydrofolic acid during absorption, and that the conversion was a saturable process, whereas unchanged pteroylglutamic acid was absorbed almost linearly in proportion to the initial amount administered.     

Effect of the interaction of drug-beta-cyclodextrin complex with bile salts on the drug absorption from rat small intestinal lumen

This investigation was concerned with the change of the bioavailability of a drug owing to the interaction of the drug-beta-cyclodextrin complex with bile salts in rat intestinal lumen. The absorption of sulfamethizole (SMZ) from rat intestinal lumen after administration of SMZ-beta-cyclodextrin complex was determined by a closed-loop method in the presence or absence of bile. The blood level of SMZ after administration of SMZ-beta-cyclodextrin complex was significantly decreased in comparison with that after administration of SMZ alone in bile duct-ligated rats. On the other hand, the blood level of SMZ after SMZ-beta-cyclodextrin administration in intact rats (bile duct non-ligated) or on the addition of sodium cholate was similar to the level in the case of SMZ alone. Thus, bile salts were found to act as a competing agent in the gastrointestinal tract.     

Interaction of toxic lectin ricin with epithelial cells of rat small intestine in vitro.

To clarify the mechanism of oral toxicity of ricin, the interaction of ricin with the epithelial cells isolated from rat small intestine was compared in vitro with those of other plant lectins by two different determinations, i.e., viability and cytotoxicity. After incubation of the cells for 1 h at 37 degrees C with ricin, B-chain, castor bean hemagglutinin (CBH), soybean agglutinin (SBA), wheat germ agglutinin (WGA), concanavalin A (Con A), and peanut agglutinin (PNA), respectively, followed by staining with trypan blue, ricin and ricin B-chain as well as CBH and SBA were found to have effectively reduced the number of viable cells. On the contrary, only ricin inhibited protein synthesis in the cells and the effect was blocked by D-galactose. Additional experiments employing [125I]-labeled ricin strongly suggested that ricin was first bound via its B-chain to the galactosyl residues on the cell surface followed by internalization into cells as the whole 62 kDa molecule. These results infer first that ricin, as well as other lectins mentioned above, was able to reduce viability of the epithelial cells of rat small intestine by direct binding to the cell surface. The second effect, specific to ricin, was the inhibition of cellular protein synthesis.