Abstract
[d-Ala2]deltorphins are enzymatically stable, amphibian heptapeptides that have a higher affinity and selectivity fordelta-opioid receptors than any endogenous mammalian compound known. This study investigated the in vitroblood-brain barrier permeability, using primary bovine brain microvessel endothelium culture, and the resistance to enzymatic degradation, in mouse 15% brain membrane homogenates and 100% plasma, of [d-Ala2]deltorphin I, [d-Ala2]deltorphin II and several analogues. Derivatives were designed with the addition of N-terminal neutral and basic amino acids or with alterations of the amino acids present within the deltorphin sequences. The results indicated that the N-terminal sequence and the amino acids in position 4 and 5 are critical to deltorphin analogue BBB permeability and biological stability,i.e., t½ brain; 4.8 hr- [d-Ala2]deltorphin I; >15 hr- [d-Ala2,Ser4,d-Ala5]deltorphin. Although, no analogue was found to increase the BBB permeability coefficient (PC; ×10−4 cm/min) of the parent compounds ([d-Ala2]deltorphin II, PC = 23.49 ± 2.42) analogues were identified: [Arg0,d-Ala2]deltorphin II, PC = 19.06 ± 3.73 and [Pro−1,Pro0,d-Ala2]deltorphin II, PC = 22.22 ± 5.93; which had similar permeability coefficients, even though they had larger molecular weights and, in the case of the cationic pro-drug, a significantly lower lipophilicity. These analogues provide directions in the development of future pro-drugs for the treatment of pain and this study further clarifies the structure-activity relationship of the deltorphins.
Footnotes
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Send reprint requests to: Dr. Thomas P. Davis, Department of Pharmacology, University of Arizona, 1609 N. Warren St., Tucson, AZ 85724.
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↵1 This work was supported by NIDA DA-06284.
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↵2 Current address: Sherrington School of Physiology, UMDS St. Thomas Hospital Campus, Lambeth Palace Road, London SE1 7EH, United Kingdom.
- Abbreviations:
- BBB
- blood-brain barrier
- BMEC
- brain microvessel endothelial cells
- PC
- permeability coefficient
- RP-HPLC
- reverse phase high-performance liquid chromatography
- k′
- capacity factor
- Abu
- α-aminobutyric acid
- HOBt
- N-hydroxybenzotriazole
- BOP
- benzotriazol-1-yl-oxy-tris-dimethylamino-phosphonium
- TFA
- trifluroacetic acid
- Received October 15, 1996.
- Accepted January 15, 1997.
- The American Society for Pharmacology and Experimental Therapeutics
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