Oral absorption enhancement of dipeptide L‐Glu‐L‐Trp‐OH by lipid and glycosyl conjugation

Abstract

In recent years, the conjugation of sugar moieties and lipoamino acids has been extensively investigated as a mean to enhance the stability towards enzymatic degradation and the permeability across biological membranes of poorly orally available drugs, including peptides. In this prospect, a library of novel derivatives of the dipeptide L-Glu-L-Trp, a naturally occurring thymic immunomodulator with high hydrophilic character and low membrane permeability, was designed and synthesised by conjugating 2-amino-dodecanoic acid (C(12)) and/or 1-amino-beta-D-glucuronic acid (GlcAN), beta-D-glucuronic acid (GlcA) and N-beta-D-glucopyranosylamine succinamic acid (GlsNS) residues to the Glu-Trp scaffold, using an Fmoc solid-phase peptide synthesis strategy on trichlorotrityl resin. A cellobiose derivative was also prepared in solution. The synthesized peptides showed no sign of toxicity to red blood cells at 200 microM (haemolysis assay) and their resistance against enzymatic hydrolysis, assessed in Caco-2 homogenates, was usually significantly increased, particularly for the C-terminal conjugates. Several derivatives also saw their apparent permeability values greatly enhanced and one of the conjugates tested proved to be able to release the initial dipeptide after penetrating Caco-2 monolayers. An initial in vivo experiment was then carried out in male Wistar rats to examine the effect of conjugation on the absorption rate and bioavailability.

Modern lipid‐, carbohydrate‐, and peptide‐based delivery systems for peptide, vaccine, and gene products

“…The determination of which type of lipid should be conjugated to a specific peptide in order to improve its membrane permeability must be experimentally determined. Further conjugation of carbohydrates to generate a liposaccharide-based peptide delivery system 33,34 offers a great potential to resolve water solubility problems. Membrane proteins that function to transport carbohydrates, such as glucose transport proteins, allow for the uptake of specific carbohydrates, so conjugation of carbohydrates to lipidated peptides offers the potential to utilize specific, active, or facilitated transport pathways to deliver peptides across biological barriers.…”

“…32 The conjugation of lipids to peptide drugs may improve the permeability of peptides across the gastrointestinal tract and blood-brain barrier. 33,34 Lipo-, glyco-, and glycolipidconjugates of Leu-enkephalin (an endogenous opioid that regulates pain and nociception) have been assessed for their ability to improve peptide stability (resistance to intra and extracellular peptidases), as well as their permeability. 36 The conjugation of a single lipoamino acid to the C-terminus of Leu-enkephalin was shown to maintain (slight increase) the biological activity of the parent drug.…”

Peptides As Therapeutics with Enhanced Bioactivity

“…Examples of modifications were the use of N-pyroglutamate, C-amidation, acetylation [74], pegylation (PEG) [75] and conjugation of carbohydrate moieties [76][77][78]. Examples of modifications were the use of N-pyroglutamate, C-amidation, acetylation [74], pegylation (PEG) [75] and conjugation of carbohydrate moieties [76][77][78].…”

“…Lipidation of hydrophilic compounds has been used extensively to improve absorption by passive diffusion across epithelial barriers, notably in the gastrointestinal tract and the central nervous system [76,98]. Lipid moieties coupled to peptides conferred the characteristics essential for intestinal delivery [99].…”

“…Liposaccharide-based delivery systems were designed to improve bioactive peptides [76,98] and were shown to enhance their bioavailability [77,98,103,104]. Somatostatin, a peptide with poor pharmacokinetics, was modified with lipids and with or without a monosaccharide moiety.…”