Synthesis of potent cyclic hexapeptide NK-1 antagonists. Use of a minilibrary in transforming a peptidal somatostatin receptor ligand into an NK-1 receptor ligand via a polyvalent peptidomimetic

The endogenous peptides somatostatin (SRIF) and substance P comprise very different structures. Although both bind G-protein-coupled receptors, the SRIF receptors (SSTR 1-5) recognize SRIF and related peptides which retain its beta-turn such as the potent cyclic hexapeptide SRIF agonist L-363,301 (6a), but not substance P. Conversely the NK-1 receptor binds substance P but not the above ligands. In contrast, the beta-D-glucosides 1 and 2, designed to mimic the beta-turn of 6a, bind both receptors. This observation led us to attempt the conversion of 6a into the first potent, selective cyclic hexapeptide ligand for the NK-1 receptor. To this end, we combined design with a minilibrary approach. The goal was accomplished with surprising ease, leading to the NK-1 receptor antagonist 9 (IC50 2.0 +/- 0.4 nM). This demonstrates that peptidomimetics, incorporating in this case the promiscuous beta-D-glucose scaffold, can provide valuable clues about receptor similarities not revealed by their endogenous ligands. In addition, this work suggests that the use of libraries and rational design need not be mutually exclusive approaches to lead discovery.

Vectorially oriented monolayers of detergent-solubilized Ca(2+) -ATPase from sarcoplasmic reticulum

A method for tethering proteins to solid surfaces has been utilized to form vectorially oriented monolayers of the detergent-solubilized integral membrane protein Ca(2+) -ATPase from the sarcoplasmic reticulum (SR). Bifunctional, organic self-assembled monolayers (SAMs) possessing "headgroup" binding specificity for the substrate and "endgroup" binding specificity for the enzyme were utilized to tether the enzyme to the substrate. Specifically, an amine-terminated 11-siloxyundecaneamine SAM was found to bind the Ca(2+)-ATPase primarily electrostatically. The Ca(2+)-ATPase was labeled with the fluorescent probe 5-(2-[(iodoacetyl)amino]ethyl)aminonaphthalene-1-sulfonic acid before monolayer formation. Consequently, fluorescence measurements performed on amine-terminated SAM/enzyme monolayers formed on quartz substrates served to establish the nature of protein binding. Formation of the monolayers on inorganic multilayer substrates fabricated by molecular beam epitaxy made it possible to use x-ray interferometry to determine the profile structure for the system, which was proved correct by x-ray holography. The profile structures established the vectorial orientation of the Ca(2+)-ATPase within these monolayers, to a spatial resolution of approximately 12 A. Such vectorially oriented monolayers of detergent-solubilized Ca(2+)-ATPase from SR make possible a wide variety of correlative structure/function studies, which would serve to elucidate the mechanism of Ca(2+) transport by this enzyme.

Omega-conotoxin GVIA-resistant neurotransmitter release in postganglionic sympathetic nerve terminals

Intracellular recording techniques were used to study neurotransmitter release in the guinea-pig isolated vas deferens. Low concentrations of the irreversible and selective N-type calcium channel blocker omega-conotoxin GVIA have previously been shown to block excitatory junction potentials evoked by low frequencies (< or = 1 Hz) of nerve stimulation. Here we report a component of action potential-evoked release which is insensitive to high concentrations of omega-conotoxin GVIA. We have termed this component "residual release" and show (i) it is positively frequency-dependent, (ii) its magnitude is dependent on both the train length and interval between trains, (iii) "residual release" can be modulated through prejunctional alpha 2-adrenoceptors and (iv) "residual release" is insensitive to many calcium entry blockers but abolished by omega-grammotoxin SIA and cadmium ions. Although noradrenaline is released by nerve action potentials, residual excitatory junction potentials were abolished by alpha,beta-methylene-ATP and therefore resulted entirely from the actions of neuronally released ATP acting through postjunctional P2x-purinoceptors. The results suggest that calcium entry through a novel, pharmacologically uncharacterized voltage-dependent calcium channel is responsible for "residual release" in sympathetic nerve terminals. It seems that in response to single or short trains of nerve action potentials, N-type calcium channels dominate the release process. However, at higher frequencies other voltage-dependent calcium channels are recruited and these may have an important role to play in triggering the mechanisms underlying frequency-dependent facilitation.

Identification of haptoglobin as a natural inhibitor of trypanocidal activity in human serum

Trypanosomes are protozoan parasites of medical and veterinary importance. Trypanosoma brucei rhodesiense and Trypanosoma brucei gambiense infect humans, causing African sleeping sickness. However, Trypanosoma brucei brucei can only infect animals, causing the disease Nagana in cattle. Man is protected from this subspecies of trypanosomes by a toxic subtype of high density lipoproteins (HDLs) called the trypanosome lytic factor (TLF). The toxic molecule in TLF is believed to be the haptoglobin-related protein that when bound to hemoglobin kills the trypanosome via oxidative damage initiated by its peroxidase activity. The amount of lytic activity in serum varies widely between different individuals with up to a 60-fold difference in activity. In addition, an increase in the total amount of lytic activity occurs during the purification of TLF, suggesting that an inhibitor of TLF (ITLF) exists in human serum. We now show that the individual variation in trypanosome lytic activity in serum correlates to variations in the amount of ITLF. Immunoblots of ITLF probed with antiserum against haptoglobin recognize a 120-kDa protein, indicating that haptoglobin is present in partially purified ITLF. Haptoglobin involvement is further shown in that it inhibits TLF in a manner similar to ITLF. Using an anti-haptoglobin column to remove haptoglobin from ITLF, we show that the loss of haptoglobin coincides with the loss of inhibitor activity. Addition of purified haptoglobin restores inhibitor activity. This indicates that haptoglobin is the molecule responsible for inhibition and therefore causing the individual variation in serum lytic activity.

Killing of trypanosomes by the human haptoglobin-related protein

African trypanosomes cause disease in humans and animals. Trypanosoma brucei brucei affects cattle but not humans because of its sensitivity to a subclass of human high density lipoproteins (HDLs) called trypanosome lytic factor (TLF). TLF contains two apolipoproteins that are sufficient to cause lysis of T. b. brucei in vitro. These proteins were identified as the human haptoglobin-related protein and paraoxonase-arylesterase. An antibody to haptoglobin inhibited TLF activity. TLF was shown to exhibit peroxidase activity and to be inhibited by catalase. These results suggest that TLF kills trypanosomes by oxidative damage initiated by its peroxidase activity.

A combined morphological and molecular phylogeny for sea urchins (Echinoidea: Echinodermata)

Phylogenetic relationships of higher taxa of echinoids have been investigated using a 163 character morphological data base and molecular sequences from large and small subunit (LSU and SSU) ribosomal RNA (rRNA) genes. The complete SSU rRNA gene has been sequenced for 21 taxa, with representatives from nine of the 14 extant orders of Echinoidea. Partial LSU sequences, representing the first 400 base pairs (b.p.) from the 5' end were also sequenced for three taxa to complement an existing data base of ten taxa. The two molecular sequences provided a total of 371 variable sites, of which 143 were phylogenetically informative (compared to 145 phylogenetically informative sites from morphological data). Morphological, LSU and SSU data have been analysed separately and together. Morphological and SSU sequence data generate topologies that are not significantly in conflict (under Templeton's test), but the strong signal pairing arbaciids with clypeasteroids in the LSU derived tree marks the LSU sequence data as anomalous for this taxon. A 'total evidence' approach derived a tree very similar in topology to that derived from morphological data. Rooted on the stem group echinoid Archaeocidaris, our total evidence tree suggested relationships of higher taxa as follows: Cidaroida (Phormosomatidae (Echinothuriidae (Diadematidae ((Spatangoida (Clypeasteroida, Cassiduloida)) ((Calycina, Arbacioida) (Stomopneustidae (Glyphocidaridae (Temnopleuridae (Echinometridae (Echinidae, Stronglyocentridae)))))))))). Phylogenetic analyses run both with and without key fossil taxa yielded slightly different topologies. It is important to include fossil taxa in a phylogenetic analysis where there are long stem-group branches or where the crown group is highly derived.

Production and oxidation of indole by Haemophilus influenzae

During growth in high concentrations of iron nitrate, H. influenzae produces compounds reactive in biochemical assays for hydroxamates. Mixing experiments established that nitrate was responsible for inducing these compounds. Analysis by 1H and 13C NMR and high resolution mass spectrometry identified the active species as 2,2-bis(3'-indolyl)indoxyl. Bacterial production of the latter compound has been previously observed only in Pseudomonas aureofaciens. A mutant defective in the production of 2,2-bis(3'-indolyl)indoxyl was constructed by marker insertion. The formation of indole and 2,2-bis (3'-indolyl)indoxyl was quantitated by reverse-phase high pressure liquid chromatography during growth in high concentrations of nitrate. The mutant produced high concentrations of indole, but only minimal amounts of 2,2-bis(3'-indolyl)indoxyl, and also proved to be defective in nitrate reduction. These data suggest that indole may function as an electron donor for nitrate reductase in H. influenzae.

Design and synthesis of nonpeptide peptidomimetic inhibitors of renin

The desire to replace the amide backbone of renin inhibitors with a new scaffold led us to explore vinylogous amides (enaminones). An initial attempt proved unsuccessful, a result explained after the fact via docking experiments. Based on this lesson, we designed a different vinylogous amide scaffold which incorporated one or more pyrrolinone rings into the backbone. Three of the four compounds gave IC50S in the 0.6 to 18 microM range. These compounds did not inhibit HIV-1 protease. Taken together, the results reported herein provide insights into the role of hydrogen bonding and steric interactions for binding to renin.

Factors affecting the life span of peripheral intravenous lines in hospitalized infants

A study was undertaken to identify the effect of insertion site, cannula size and brand type, blood, and unit setting on the life span of IVs in hospitalized infants. A comparative descriptive design was used to study 250 data sets gathered from charts of infants 12 months of age and under, in the NICU, PICU, and general pediatric units at a children's medical center in the Southwest. Analysis revealed no significant difference in life span of nonelectively discontinued IVs by insertion site, cannula size, or brand type. A statistical difference was found in the life span of IVs regarding blood infusion: IVs in which blood had infused lasted longer than those without blood products. A statistical difference in IV life span was also found between the unit settings, with a longer life span for IVs on the general pediatric units than for those on the NICU. Research-based knowledge about factors that influence the life span of IVs in infants could be helpful in making practice decisions and in parent teaching.

Cancer mortality patterns among female and male workers employed in a cable manufacturing plant during World War II

A cohort mortality study was conducted among 9028 (3042 women, 5986 men) workers potentially exposed to chlorinated naphthalenes (chloracnegens structurally similar to dioxins) and asbestos in the manufacture of Navy cable during World War II. Based on mortality through December 31, 1985, standardized mortality ratios (SMRs) for all cancers was 1.03 in women (95% confidence interval [CI] = 0.9 to 1.17) and 1.18 in men (95% CI = 1.10 to 1.26). There were no significant elevations in causes of death hypothesized a prior to be associated with chlorinated naphthalene exposure (malignant neoplasms [MN] of connective tissue, liver, and lymphatic and hematopoietic organs). An excess of MN of the connective tissue was suggested for workers with over 1 year of exposure and 25 years of latency (SMR = 3.54; 95% CI = 0.97 to 9.07). Among cancer sites not hypothesized to be related a priori, three showed concordant excesses among both genders (MN of stomach; rectum; and trachea, bronchus, and lung). No significant elevations occurred in hormonally related cancers among women. Cancer mortality among 460 individuals with chloracne (431 men, 29 women) was similar to that of the entire cohort, although the chloracne subcohort showed significant excesses in two rare causes of death (MN of esophagus, SMR = 3.26; "benign and unspecified neoplasms," SMR = 4.93). Use of county referent rates decreased SMRs for stomach, rectal, and buccal cavity cancer, suggesting a role for nonoccupational risk factors. It is difficult to draw conclusions about carcinogenicity of chlorinated naphthalenes because of study limitations, most importantly, concomitant asbestos exposure and the relatively short duration of exposure to chlorinated naphthalenes among most of the cohort.

Peptide synthesis catalyzed by an antibody containing a binding site for variable amino acids

Monoclonal antibodies, induced with a phosphonate diester hapten, catalyzed the coupling of p-nitrophenyl esters of N-acetyl valine, leucine, and phenylalanine with tryptophan amide to form the corresponding dipeptides. All possible stereoisomeric combinations of the ester and amide substrates were coupled at comparable rates. The antibodies did not catalyze the hydrolysis of the dipeptide product nor hydrolysis or racemization of the activated esters. The yields of the dipeptides ranged from 44 to 94 percent. The antibodies were capable of multiple turnovers at rates that exceeded the rate of spontaneous ester hydrolysis. This achievement suggests routes toward creating a small number of antibody catalysts for polypeptide syntheses.

Vectorially oriented membrane protein monolayers: profile structures via x-ray interferometry/holography

X-ray interferometry/holography was applied to meridional x-ray diffraction data to determine uniquely the profile structures of a single monolayer of an integral membrane protein and a peripheral membrane protein, each tethered to the surface of a solid inorganic substrate. Bifunctional, organic self-assembled monolayers (SAMs) were utilized to tether the proteins to the surface of Ge/Si multilayer substrates, fabricated by molecular beam epitaxy, to facilitate the interferometric/holographic x-ray structure determination. The peripheral membrane protein yeast cytochrome c was covalently tethered to the surface of a sulfhydryl-terminated 11-siloxyundecanethiol SAM via a disulfide linkage with residue 102. The detergent-solubilized, photosynthetic reaction center integral membrane protein was electrostatically tethered to the surface of an analogous amine-terminated SAM. Optical absorption measurements performed on these two tethered protein monolayer systems were consistent with the x-ray diffraction results indicating the reversible formation of densely packed single monolayers of each fully functional membrane protein on the surface of the respective SAM. The importance of utilizing the organic self-assembled monolayers (as opposed to Langmuir-Blodgett) lies in their ability to tether specifically both soluble peripheral membrane proteins and detergent-solubilized integral membrane proteins. The vectorial orientations of the cytochrome c and the reaction center molecules were readily distinguishable in the profile structure of each monolayer at a spatial resolution of 7 A.

Tremorgenic indole alkaloids potently inhibit smooth muscle high-conductance calcium-activated potassium channels

Tremorgenic indole alkaloids produce neurological disorders (e.g., staggers syndromes) in ruminants. The mode of action of these fungal mycotoxins is not understood but may be related to their known effects on neurotransmitter release. To determine whether these effects could be due to inhibition of K+ channels, the interaction of various indole diterpenes with high-conductance Ca(2+)-activated K+ (maxi-K) channels was examined. Paspalitrem A, paspalitrem C, aflatrem, penitrem A, and paspalinine inhibit binding of [125I]charybdotoxin (ChTX) to maxi-K channels in bovine aortic smooth muscle sarcolemmal membranes. In contrast, three structurally related compounds, paxilline, verruculogen, and paspalicine, enhanced toxin binding. As predicted from the binding studies, covalent incorporation of [125I]ChTX into the 31-kDa subunit of the maxi-K channel was blocked by compounds that inhibit [125I]ChTX binding and enhanced by compounds that stimulate [125I]ChTX binding. Modulation of [125I]ChTX binding was due to allosteric mechanisms. Despite their different effects on binding of [125I]ChTX to maxi-K channels, all compounds potently inhibited maxi-K channels in electrophysiological experiments. Other types of voltage-dependent or Ca(2+)-activated K+ channels examined were not affected. Chemical modifications of paxilline indicate a defined structure-activity relationship for channel inhibition. Paspalicine, a deshydroxy analog of paspalinine lacking tremorgenic activity, also potently blocked maxi-K channels. Taken together, these data suggest that indole diterpenes are the most potent nonpeptidyl inhibitors of maxi-K channels identified to date. Some of their pharmacological properties could be explained by inhibition of maxi-K channels, although tremorgenicity may be unrelated to channel block.

Design of in vivo cadmium-mobilizing agents: synthesis and properties of monobenzyl meso-2,3-dimercaptosuccinate

A novel method for the synthesis of monoesters of meso-2,3-dimercaptosuccinic acid (DMSA) is presented which utilizes the reaction of the vicinal sulfhydryl-protected anhydride with the corresponding alcohol in the presence of a base. The product is then treated successively with mercuric chloride to remove the protecting group and form the mercuric complex, and hydrogen sulfide to regenerate thiol groups by removal of mercury as HgS. This strategy was exploited to synthesize monobenzyl meso-2,3-dimercaptosuccinate (MBzDMS), C6H5CH2O(O)CCH(SH)CH(SH)C(O)OH, and demonstrates a feasible synthesis of monoesters difficult to obtain by direct esterification, via the use of the reactive anhydride. The resultant compound was found to be an effective cadminum-mobilizing agent when used with cadmium-exposed rats or mice and when administered by any one of several routes (ip, iv, po). This monobenzyl ester (MBzDMS) of DMSA was found to be somewhat less effective than the corresponding monoisoamyl ester (Mi-ADMS) in mobilizing cadmium from such cadmium deposits. The ability of MBzDMS to mobilize cadmium into the urine is significantly decreased by the coadministration of p-aminobenzoic acid, in support of the hypothesis that MBzDMS enters renal cells via an anion transport system. An analysis of the structural features of vicinal dithiols examined as antagonists for chronic cadmium intoxication allows a hypothesis to be formulated indicating essential features required for the design of effective new cadmium antagonists of this type.

Effect of chelate treatments on kidney, bone and brain lead levels of lead-intoxicated mice

The effects of chelating agent treatment with meso-2,3-dimercaptosuccinic acid (DMSA), Na2CaEDTA, Na2ZnEDTA, and Na3ZnDTPA on the organ lead levels of lead-loaded mice have been determined. At 1 mmol/kg/day i.p., all caused reductions in the lead levels of the kidney after four injections, but only Na2CaEDTA produced a significant reduction in brain lead. All chelating agents caused significant reductions in kidney and brain lead levels when administered at a daily dose of 1 mmol/kg/day for eight days, but only DMSA reduced the bone lead level. In animals given 50 mg Pb/kg or 100 mg Pb/kg, the administration of Na2CaEDTA or DMSA at 1 mmol/kg/day x 8 produced significant reductions in kidney, bone and brain lead levels, but DMSA produced greater reductions of bone lead in both groups and of kidney lead in the group given 100 mg Pb/kg. An examination of published data describing the effect of chelating agent treatment on brain lead levels indicates that DMSA produces a reduction in brain lead levels under all conditions examined to date.

Unexpected Square Symmetry Seen by Atomic Force Microscopy in Bilayer Films of Disk-Like Molecules

Thin films of disk-shaped molecules are expected to display anisotropic optical and transport properties, leading to applications in optical display or sensor technologies. Bilayer Langmuir-Blodgett films of monomeric triphenylene mesogens have been studied by atomic force microscopy. The triphenylene cores of the constituent molecules tend to promote the formation of columnar structures in the plane of the substrate and along the direction of deposition of the film. Atomic force microscopy images of bilayer Langmuir-Blodgett films revealed two types of structure, one corresponding to an aligned columnar structure and the other to an unusual square lattice, which may result from the superposition of columnar structures in adjacent layers that intersect at near right angles. Annealing such bilayers near the melting point of the bulk compound improved the structural ordering by reducing the angular spread of orientations associated with the well-developed columnar structure in some areas and by producing a more distinct square lattice in other areas of the sample.

Cadmium mobilization by monoaralkyl- and monoalkyl esters of meso-2,3-dimercaptosuccinic acid and by a dithiocarbamate

Syntheses and relative cadmium mobilizing properties are described for three new monoaralkyl esters (HOOCCH(SH)CH(SH)COOR, where R = phenylethyl ((CH2)2C6H5), MPhEDMS; R = 3-phenylpropyl ((CH2)3C6H5), MPhPDMS; and R = 2-phenoxyethyl ((CH2)2OC6H5). MPhOEDMS) of meso-2,3-dimercaptusuccinic acid. These were prepared by the reaction of the corresponding alcohol with meso-2,3-dimercaptosuccinic acid (DMSA) in aqueous HCl. When administered intraperitoneally to cadmium-loaded mice at 0.50 mmol/kg/day for four consecutive days, all induced significant reductions in the whole body cadmium levels. MPhEDMS, 60%; MPhPDMS, 66%; and MPhOEDMS, 58% in comparison with control levels. At the same dosage monoisoamyl meso-2,3-dimercaptosuccinate (Mi-ADMS) and a dithiocarbamate, sodium N-benzyl-4-O-(beta-D-galactopyranosyl)-D-glucamine-N-carbodithioate++ + (BLDTC) induced reductions of 65% and 57%, respectively. Hepatic and renal cadmium were also depleted significantly, while brain cadmium levels were unchanged. These compounds induced a significant reduction in the cadmium levels of the spleen, and one, MPhOEDMS, produced a 10% decrease in pancreatic cadmium. The manner in which the later injections removed smaller fractions of the total body cadmium is consistent with a bodily distribution of these compounds by which they are concentrated primarily in the kidneys and the liver, with much smaller amounts reaching other organs. It is proposed that these compounds enter renal and hepatic cells through an anion transport system.

Design and synthesis of sulfur-free cyclic hexapeptides which contain the RGD sequence and bind to the fibrinogen GP IIb/IIIa receptor. A conformation-based correlation between propensity for imide formation and receptor affinity

The Arg-Gly-Asp (RGD) sequence is the key recognition site in many adhesive interactions. To probe the structural and conformational requirements for potential antithrombotic agents, we have designed and synthesized three cyclic hexapeptides (1, 5 and 6) containing the RGD sequence. In the ELISA GP IIb/IIIa-fibrinogen receptor assay, 1, 5 and 6 bound with IC50 values of 1, 0.1 and 0.016 microM, respectively. All three peptides completely displaced fibrinogen from the receptor. No potent, sulfur-free cyclic hexapeptide had heretofore been described as a fibrinogen receptor antagonist. The enhanced binding affinity of 6, distinguished by the presence of two D-amino acids, is likely to reflect an increased conformational resemblance to the natural peptide ligands. Cyclization of H-Asp(OFm)-DSer-Phe-DPhe-Arg-Gly-OH with DPPA and NaHCO3 in DMF to afford 6 was attended by subsequent aspartimide formation with generation of 9-fluorenylmethanol. Interestingly, imide formation was not observed with any of the three linear hexapeptides (3, 8 and 9), with the all-L-cyclic peptide 1, nor with 5, which contains only Ser-1 in the D-configuration. The observed imide formation led us to use catalytic transfer hydrogenation rather than piperidine to remove the 9-fluorenylmethyl ester protecting group at the beta-carbonyl of aspartic acid. Further investigation revealed that imide formation was minimized by careful exclusion of water, reducing dissolution of NaHCO3. Thus the distinguishing conformational features of 6 express themselves both in receptor affinity and chemical propensity toward imide formation.

meso-2,3-dimercaptosuccinic acid monoalkyl esters: effects on mercury levels in mice

Seven monoesters of meso-2,3-dimercaptosuccinic acid (DMSA) were evaluated for relative activities in mobilizing and promoting excretion of mercury in mercury-laden mice. Compounds assessed were the ethyl (M-EDMS), n-propyl (Mn-PDMS), isopropyl (Mi-PDMS), n-butyl (Mn-BDMS), isobutyl (Mi-BDMS), n-amyl (Mn-ADMS), and isoamyl (Mi-ADMS) esters. 2,3-Dimercaptopropane-1-sulfonate (DMPS) and DMSA were used as positive controls. After the first oral dose of each compound at 0.5 mmol/kg, DMSA and DMPS reduced the corporal mercury burden 16% and 24%, respectively, compared to controls, while the monoesters effected reductions of 35% (M-EDMS) to 49% (Mi-ADMS). After the second treatment at the same dose, the respective reductions produced by DMSA and DMPS were 24% and 38%, and those conferred by the monoesters ranged from 52% (M-EDMS) to 61% (Mn-BDMS). Determination of the comparative dose-response relationships of DMSA and Mi-ADMS on corporal and renal mercury concentrations revealed the monoester to be more active than DMSA on both parameters at each dose used. The cumulative amount of mercury excreted in urine by control mice over a 3-day period was 7.08 micrograms; this was increased 22%, 85%, and 94% by daily i.p. injections of DMSA, DMPS, and Mi-ADMS, respectively, at a daily dose of 0.1 mmol/kg. The respective cumulative 3-day totals recovered in feces from control mice and from mice treated with DMSA, DMPS, and Mi-ADMS were 9.76, 8.21, 10.44, and 11.73 micrograms. Parallel daily measurements of retained whole body radioactivity from 203Hg in mice were in good agreement with the values calculated from the excretion data.