In vitro and in vivo opioid activity of [DPro(6)]dermorphin, a new dermorphin analogue.

To study the effects of inducing stereo-chemical modifications in the structure of dermorphin (DM) so as to improve its mu-opioid receptor affinity and its resistance to C-terminal enzymatic degradation, in the Institute of Molecular Genetics of Moscow, we synthesized a new DM analogue ([DPro(6)]DM) and analyzed the changes induced in the biological activities of DM by substituting the Pro(6) residue with DPro(6). We compared the activity of the new DM analogue and DM in in vitro assays and in in vivo tests of analgesia, thermoregulation, heart rate recordings, and gastrointestinal motility in rats. In the in vitro tests, guinea pig ileum (GPI) and mouse vas deferens (MVD), although the opioid activities of [DPro(6)]DM indicated that the peptide was always less potent than DM, its lower IC(50) ratios (mu/delta) showed that it had higher mu-opioid receptor selectivity. In the in vivo analgesic test, [DPro(6)]DM, when injected intraperitoneally (i.p.) (0.5-5 and 10mg/kg) in rats, had the same antinociceptive efficacy as DM and when injected intranasally (i.n.) (0.005 and 0.02 mg/kg) it induced a more stable and long-lasting analgesia than DM (the AUC was about 91% higher for [DPro(6)]DM than for DM). Moreover, these data confirm that the intranasal route is advantageous for peripheral drug administration. In the heart rate study, [DPro(6)]DM and DM (0.5mg/kg, i.p.), induced a similar, weak bradycardia. The only difference was that [DPro(6)]DM induced a longer-lasting effect than DM. Conversely, in body temperature regulation [DPro(6)]DM induced weaker inhibitory activity than DM (56% of the DM-induced response); it did so only in a cold environment and at the maximal used dose (0.5mg/kg, i.p.) without inducing vasomotor effects. In the gastrointestinal study, [DPro(6)]DM and DM (0.005, 0.05, and 0.5mg/kg, i.p.) significantly slowed upper gastrointestinal transit of a charcoal meal and inhibited colonic propulsion. Comparison of the ED(50) values of [DPro(6)]DM (0.03 mg/kg) and DM (0.009 mg/kg) showed that the DM analogue was about three times less potent than DM in slowing gastrointestinal and colonic transit. In conclusion, all these data overall suggest that structural maneuvering in the Pro(6)-residue of the DM molecule changes its affinity for mu-opioid receptor subtypes and confirms the usefulness of experimental studies involving structural modifications in obtaining new therapeutic agents.

Degradation of ACTH/MSH(4-10) and its synthetic analog semax by rat serum enzymes: an inhibitor study.

Degradation of the behaviorally active peptide ACTH/MSH(4-10) and its synthetic analog semax was studied in serum in the presence of several specific peptidase inhibitors. Bestatin and puromycin were used to inhibit aminopeptidase activity, lisinopril for angiotensin-converting enzyme, phosphoramidon for neutral endopeptidase 24.11, and Z-Pro-prolinal for prolyl endopeptidase. Bestatin inhibited up to 66%, puromycin about 33%, and lisinopril about 15% of total degrading activity against both ACTH/MSH(4-10) and semax. Involvement of neutral endopeptidase and prolyl endopeptidase in hydrolysis of the two peptides was less definitive. These studies showed that aminopeptidases and angiotensin-converting enzyme are responsible for the major part of the hydrolysis of ACTH/MSH(4-10) and semax in rat serum.

Use of tetrabutylammonium salts of amino acids in peptide synthesis.

Tetrabutylammonium (TBA) salts of amino acids and peptides have increased solubility, as compared with that of alkali metals salts, in organic solvents. We have compared the reaction rates for tripeptide formation in methylene chloride from Boc-Gly-Phe activated with various phenols, N-oxysuccinimide and azide, and TBA-salt of tryptophan, as well as Trp-OCH3. H-Trp-O-.TBA+ as an amino component significantly accelerates the rate of reaction. Although a significant degree of racemization has been found, the use of TBA-salt of amino acids and peptides is justified in many cases due to high conversion rates.

N-terminal degradation of ACTH(4-10) and its synthetic analog semax by the rat blood enzymes.

Degradation of a regulatory peptide ACTH(4-10) and its synthetic analog semax in rat blood and serum was studied using high-performance liquid chromatography. About one third to one half of the serum degrading activity could be ascribed to bestatin-sensitive aminopeptidase which cleaved first and second N-terminal residues Met and Glu producing relatively stable intermediates. Comparable areas under the degradation/accumulation curves for intact peptides and intermediates implied that the latter can contribute to effects of intact peptides. Semax turned out to be more stable than ACTH(4-10) against the action of other enzymes that took part in degradation.