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

Neuropeptide pharmaceuticals have potential for the treatment of neurological disorders, but the blood-brain barrier (BBB) limits entry of peptides to the brain. Several strategies to im-prove brain delivery are currently under investigation, including glycosylation. In this study we investigated the effect of O-linked glycosylation on Ser6 of a linear opioid peptide amide 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 and mouse by high-performance liquid chromatography. BBB transport properties were investigated by rat in situ perfusion. Tail-flick analgesia studies were per-formed on male ICR mice, injected i.v. with 100 g of peptide ligand. Glycosylation of Ser6 of the peptide led to a significant increase in enzymatic stability in both serum and brain. Glyco