An exploration of the effects of L- and D-tetrahydroisoquinoline-3-carboxylic acid substitutions at positions 2,3 and 7 in cyclic and linear antagonists of vasopressin and oxytocin and at position 3 in arginine vasopressin

We have investigated the effects of mono-substitutions with the conformationally restricted amino acid, 1,2,3,4 tetrahydroisoquinoline-3-carboxylic acid (Tic) at position 3 in arginine vasopressin (AVP), at positions 2, 3 and 7 in potent non-selective cyclic AVP V₂/V_1a antagonists, in potent and selective cyclic and linear AVP V_1a antagonists, in a potent and selective oxytocin antagonist and in a new potent linear oxytocin antagonist Phaa-D -Tyr(Me)-Ile-Val-Asn-Orn-Pro-Orn-NH₂ (10). We report here the solid-phase synthesis of peptide 10 together with the following Tic-substituted peptides: 1, [Tic³]AVP; 2, d(CH₂)₅[D -Tic²]VAVP; 3, d(CH₂)₅[D -Tyr(Et)²Tic³]VAVP; 4, d(CH₂)₅[Tic²Ala-NH₂⁹]AVP; 5, d(CH₂)₅[Tyr(Me)², Tic³, Ala-NH₂⁹]AVP; 6, d(CH₂)₅ [Tyr(Me)², Tic⁷]AVP; 7, Phaa-D -Tyr(Me)-Phe-Gln-Asn-Lys-Tic-Arg-NH₂; 8, desGly-NH₂,d(CH₂)₅[Tic²,Thr⁴]OVT; 9, desGly-NH₂d(CH₂)₅[Tyr(Me)²Thr⁴, Tic⁷]OVT; 11, Phaa-D-Tic-Ile-Val-Asn-Orn-Pro-Orn-NH₂, using previously described methods. The protected precursors were synthesized by the solid-phase method, cleaved, purified and deblocked with sodium in liquid ammonia to give the free peptides 1–11 which were purified by methods previously described. Peptides 1–11 were examined for agonistic and antagonistic potency in oxytocic (in vitro, without Mg²⁺) and AVP antidiuretic (V₂-receptor) and vasopressor (V_1a-receptor) assays. Tic³ substitution in AVP led to drastic losses of V₂, V_1a and oxytocic agonistc activities in peptide 1.L - and D -Tic² substitutions led to drastic losses of anti-V₂/anti-V_1a and anti-oxytocic potencies in peptides 2, 4, 8 and 11 (peptide 2 retained substantial anti-oxytocic potency; pA₂ = 7.25 ± 0.25). Whereas Tic³ substitution in the selective V_1a antagonist d(CH₂)₅[Tyr(Me)², Ala-NH₂⁹]APV(C) led to a drastic reduction in anti-V_1a potency (from anti-V_1a pA₂) 8.75 to 6.37 for peptide 5, remarkably, Tic³ substitution in the V₂/V_1a antagonist d(CH₂)₅[D -Tyr(Et)²]VAVP(B) led to full retention of anti-V₂ potency and a 95% reduction in anti-V_1a potency. With an anti-V₂ pA₂ = 7.69 ± 0.05 and anti-V_1a pA₂ = 6.95 ± 0.03, d(CH₂)₅[D -Tyr(Et)²,Tic³]VAVP exhibits a 13-fold gain in anti-V₂/anti-V_1a selectivity compared to (B). Tic⁷ substitutions are very well tolerated in peptides 6, 7 and 9 with excellent retention of the characteristic potencies of the parent peptides. The findings on the effects of Tic³ substitutions reported here may provide promising leads to the design of more selective and possibly orally active V₂ antagonists for use as pharmacological tools and as therapeutic clinical agents for the treatment of the syndrome of the inappropriate secretion of antidiuretic hormone (SIADH).     

Distribution and possible interrelationships of pathogenic and nonpathogenicAcanthamoeba from aquatic environments

Among the more recently discovered agents of human disease are small, free-living amebae belonging to the generaNaegleria andAcanthamoeba. An overview of the distribution ofAcanthamoeba in recent surveys of the near shore waters of the northeastern United States is presented. There appears to be a particular association between the presence ofAcanthamoeba in marine sediments and the sites of oceanic sludge dumping. Amebae belonging to the genusNaegleria have not been isolated from these marine sediments which routinely yieldedAcanthamoeba. Starch gel electrophoretic analysis of enzymes suggests that some isolates ofAcanthamoeba from oceanic sludge dump-sites are not members of previously recognized pathogenic species.     

Cytotoxicity of pilosulin 1, a peptide from the venom of the jumper ant Myrmecia pilosula

The synthetic peptide pilosulin 1, corresponding to the largest defined allergenic polypeptide found in the venom of the jumper ant Myrmecia pilosula, inhibited the incorporation of [methyl-³H]thymidine into proliferating Epstein–Barr transformed (EBV) B-cells. The LD₅₀ was four-fold lower in concentration than melittin, a cytotoxic peptide found in honey bee venom. Loss of cell viability was assessed by flow cytometry by measuring the proportion of cells that fluoresced in the presence of the fluorescent dye 7-aminoactinomycin D. Examination of proliferating EBV B-cells indicated that the cells lost viability within a few minutes exposure to pilosulin 1. Partial peptides of pilosulin 1 were less efficient in causing loss of cell viability and the results suggest that the 22 N-terminal residues are critical to the cytotoxic activity of pilosulin 1. Normal blood white cells were also labile to pilosulin 1. T- and B-lymphocytes, monocytes and natural killer cells, however, were more labile than granulocytes. Analysis of pilosulin 1 using circular dichroism indicated that, in common with melittin and other Hymenoptera venom toxins, it had the potential to adopt an α-helical secondary structure.     

Peptide and peptidomimetic libraries

Various techniques for generation of peptide and peptidomimetic libraries are summarized in this article. Multipin, tea bag, and split-couple-mix techniques represent the major methods used to make peptides and peptidomimetics libraries. The synthesis of these libraries were made in either discrete or mixture format. Peptides and peptidomimetics combinatorial libraries were screened to discover leads against a variety of targets. These targets, including bacteria, fungus, virus, receptors, and enzymes were used in the screening of the libraries. Discovered leads can be further optimized by combinatorial approaches.     

Unilateral naris occlusion and the rat accessory olfactory bulb

Blocking airflow through half of the nasal cavity during early life results in a 25% reduction in the size of the ipsilateral main olfactory bulb. The present study indicates that the size of the accessory bulb is relatively unaffected by the procedure.