Improved blood-brain barrier penetration and enhanced analgesia of an opioid peptide by glycosylation

Neuropeptide pharmaceuticals have potential for the treatment of neurologic al disorders, but the blood-brain barrier (BBB) limits entry of peptides to the brain. Several strategies to improve brain delivery are currently unde r investigation, including glycosylation. In this study we investigated the effect of O-linked glycosylation on Ser(6) of a linear opioid peptide amid e Tyr-D-Thr-Gly-Phe-Leu-Ser-NH2 on metabolic stability, BBB transport, and analgesia. Peptide stability was studied in brain and serum from both rat a nd mouse by high-performance liquid chromatography. BBB transport propertie s were investigated by rat in situ perfusion. Tall-flick analgesia studies were performed on male ICR mice, injected i.v. with 100 mug of peptide liga nd. Glycosylation of Ser(6) of the peptide led to a significant increase in enzymatic stability in both serum and brain. Glycosylation significantly i ncreased the BBB permeability of the peptide from a value of 1.0 +/- 0.2 mu l . min(-1) . g(-1) to 2.2 +/- 0.2 mul . min(-1) . g(-1) (p < 0.05), withou t significantly altering the initial volume of distribution. Analgesia stud ies showed that the glycosylated peptide gave a significantly improved anal gesia after i.v. administration compared with nonglycosylated peptide. The improved analgesia profile shown by the glycosylated peptide is due in part to an improvement in bioavailability to the central nervous system. The bi oavailability is increased by improving stability and transport into the br ain.