RESUMO
Phosphorylation of l-serine-containing enkephalin analogs has been explored as an alternative to glycosylation in an effort to increase blood-brain barrier permeability and CNS bioavailability of peptide pharmacophores. Two enkephalin-based peptides were modified for these studies, a set related to DTLES, a mixed µ/δ-agonist, and one related to DAMGO, a highly selective µ-agonist. Each unglycosylated peptide was compared to its phosphate, its mono-benzylphosphate ester, and its ß-d-glucoside. Binding was characterized in membrane preparations from Chinese hamster ovary cells expressing human µ, δ and κ-opiate receptors. Antinociception was measured in mice using the 55 °C tail-flick assay. To estimate bioavailability, the antinociceptive effect of each opioid agonist was evaluated after intracerebroventricular (i.c.v.) or intravenous administration (i.v.) of the peptides. Circular dichroism methods and high-field nuclear magnetic resonance were used in the presence and absence of sodium dodecylsulfate to understand how the presence of a membrane might influence the peptide conformations.
