Intestinal absorption and analgesic activity of aminopeptidase-resistant cellobiose-coupled leucine enkephalinamide

Leucine enkephalinamide (LEamide), aminopeptidase-degradable opioid peptide , was coupled with cellobiose (cellobiose-coupled LEamide, CcpLEamide). Ccp LEamide was absorbed from the rat small intestine in vitro, whereas LEamide was not. CcpLEamide on the mucosal side was more stable than aminopeptidas e-resistant cellobiose-coupled leucine enkephalin (CcpLE) in the presence o f inhibitors of enkephalinase and angiotensin converting enzyme, and much m ore stable than LEamide. The absorption rate (clearance) of CcpLEamide was comparable with that of CcpLE in the presence of these peptidase inhibitors . Analgesic activities of these enkephalins were tested by the acetic acid writhing assay and hot-plate assay after subcutaneous administration to mic e. Both assays indicated CcpLEamide-induced analgesia. On the other hand, t he analgesic activity of LEamide was not observed, but preheatment with ama statin (a peptidase inhibitor) produced LEamide-induced analgesia. These re sults indicate that CcpLEamide is stable in the body and has analgesic effe cts without pretreatment with peptidase inhibitors, and was stable enough t o be absorbed from the small intestine. We propose CcpLEamide as an orally active analgesic peptide candidate. (C) 1998 John Wiley & Sons, Ltd.