caa a22 4500 477128165 CHVBK 20180405111656.0 cr unu---uuuuu 170330e19970201xx s 000 0 eng 10.1023/A:1012092409216 doi (NATIONALLICENCE)springer-10.1023/A:1012092409216 Effect of Restricted Conformational Flexibility on the Permeation of Model Hexapeptides Across Caco-2 Cell Monolayers [Elektronische Daten] [Franklin Okumu, Giovanni Pauletti, David Vander Velde, Teruna Siahaan, Ronald Borchardt] Purpose. To determine how restricted conformational flexibility of hexapeptides influences their cellular permeation characteristics. Methods. Linear (Ac-Trp-Ala-Gly-Gly-X-Ala-NH2; X = Asp, Asn, Lys) and cyclic (cyclo[Trp-Ala-Gly-Gly-X-Ala]; X = Asp, Asn, Lys) hexapeptides were synthesized, and their transport characteristics were assessed using the Caco-2 cell culture model. The lipophilicities of the hexapeptides were determined using an immobilized artificial membrane. Diffusion coefficients used to calculate molecular radii were determined by NMR. Two-dimensional NMR spectroscopy, circular dichroism, and molecular dynamic simulations were used to elucidate the most favorable solution structure of the cyclic Asp-containing peptide. Results. The cyclic hexapeptides used in this study were 2−3 times more able to permeate (e.g., Papp = 9.3 ± 0.3 × 10−8 cm/sec, X = Asp) the Caco-2 cell monolayer than were their linear analogs (e.g., Papp = 3.2 ± 0.3 × 10−8 cm/sec, X = Asp). In contrast to the linear hexapeptides, the flux of the cyclic hexapeptides was independent of charge. The cyclic hexapeptides were shown to be more lipophilic than the linear hexapeptides as determined by their retention times on an immobilized phospholipid column. Determination of molecular radii by two different techniques suggests little or no difference in size between the linear and cyclic hexapeptides. Spectroscopic data indicate that the Asp-containing linear hexapeptide exists in a dynamic equilibrium between random coil and β-turn structures while the cyclic Asp-containing hexapeptide exists in a well-defined compact amphophilic structure containing two β-turns. Conclusions. Cyclization of the linear hexapeptides increased their lipophilicities. The increased permeation characteristics of the cyclic hexapeptides as compared to their linear analogs appears to be due to an increase in their flux via the transcellular route because of these increased lipophilicities. Structural analyses of the cyclic Asp-containing hexapeptide suggest that its well-defined solution structure and, specifically the existence of two β-turns, explain its greater lipophilicity. Plenum Publishing Corporation, 1997 peptide delivery nationallicence conformation nationallicence Caco-2 cells nationallicence membrane permeability nationallicence NMR nationallicence CD nationallicence Okumu Franklin aut Pauletti Giovanni aut Vander Velde David aut Siahaan Teruna aut Borchardt Ronald aut Pharmaceutical Research Kluwer Academic Publishers-Plenum Publishers 14/2(1997-02-01), 169-175 0724-8741 14:2<169 1997 14 11095 https://doi.org/10.1023/A:1012092409216 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1023/A:1012092409216 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Okumu Franklin aut NATIONALLICENCE 700 1- Pauletti Giovanni aut NATIONALLICENCE 700 1- Vander Velde David aut NATIONALLICENCE 700 1- Siahaan Teruna aut NATIONALLICENCE 700 1- Borchardt Ronald aut NATIONALLICENCE 773 0- Pharmaceutical Research Kluwer Academic Publishers-Plenum Publishers 14/2(1997-02-01), 169-175 0724-8741 14:2<169 1997 14 11095 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer