Biomedical subjects

P Amodeo

Publications and source records attributed to P Amodeo.

At least 19 recordsLinked to original sources

PubMed1995

Conformational analysis of potent and very selective delta opioid dipeptide antagonists.

The delta selectivity and antagonism of peptides containing L-tetrahydro-3-isoquinoline carboxylic acid (Tic) in second position can be attributed mainly to the Tyr-Tic unit. These properties can be further enhanced by substituting Tyr1 with 2,6-dimethyl-L-tyrosyl (Dmt). Dmt-Tic-NH2, Dmt-Tic-OH, Dmt-Tic-Ala-NH2 and Dmt-Tic-Ala-OH are all more active and/or selective than the corresponding [Tyr1]-parent peptides. In fact the selectivities of Dmt-Tic-OH and Dmt-Tic-Ala-OH are the highest ever recorded for opioid molecules. 1H NMR spectra in a DMSO/water mixture at 278 K reveal the presence of two similar conformers, characterised by a cis or trans Dmt-Tic bond, in all four peptides. A detailed conformational analysis in solution of Dmt-Tic-NH2 shows that these conformers have a shape very similar to that of the bioactive conformation of Tyr-Tic-NH2 and to that of naltrindole.

Dipeptides↗

PubMed1995

Assignment and secondary-structure determination of monomeric bovine seminal ribonuclease employing computer-assisted evaluation of homonuclear three-dimensional 1H-NMR spectra.

Monomeric bovine seminal ribonuclease (mBS-RNase), the subunit of dimeric bovine seminal ribonuclease (BS-RNase), is an unusual monomer: for its structural stability, its catalytic activity, which is even higher than that of the parent dimeric enzyme, and for its role as an intermediate in the refolding of dimeric BS-RNase. Here we present the proton NMR assignment and secondary-structure determination of mBS-RNase, with a comparison of its structure to the structure of its parent protein, and to the structure of RNase A, a homologue with more than 80% identity in amino acid sequence. Proton NMR assignment was performed using a computer-assisted procedure, through a partially automated analysis of homonuclear three-dimensional spectra [Oschkinat, H., Holak, T. A. & Cieslar, C. (1991) Biopolymers 31, 699-712]. The secondary structures of mBS-RNase, of the A chain of dimeric BS-RNase, and of RNase A, are found to be similar. Significant differences are found instead, between mBS-RNase and RNase A in the more flexible stretches of the molecule, where a higher number of substitutions is present. Furthermore, a preliminary tertiary-structure model is reported, showing that the overall folding of mBS-RNase is closer to that of RNase A rather than that of (dimeric) BS-RNase.

Amino Acid Sequence↗

PubMed1994

Multiple conformations and proline cis-trans isomerization in salmon calcitonin: a combined nuclear magnetic resonance, distance geometry, and molecular mechanics study.

The relationship between multiple conformations and proline cis-trans isomerization in salmon calcitonin (sCT) has been investigated by 1H-NMR, distance geometry, and molecular mechanics. In different solvents, the isomerization of Pro23 induces resonance heterogeneity for amino acids adjacent to it. NOESY experiments have related such heterogeneity to two different isoforms of the hormone, which interconvert into each other in polar solvents as well as in SDS micelles. The cis-trans ratio was found to depend upon the structure of the hormone. In water, the random-coil sCT showed a 35% cis population, while 16% cis was observed in the folded SDS-bound hormone. Such a decrease contributes, per se, a Gibbs free energy stabilization of 3.10 kJ mol-1. Except for the 21-25 region, a common NOE pathway was found for both isomers. This is in agreement with the common secondary structure for both isoforms: a central helix and an extended C-terminal segment interacting with it. Calculations indicated that while the trans isomer is helical in the Thr6-Tyr22 region, a shorter helix (Thr6-Lys18) is present in the cis isoform. It is concluded that isomerization of Pro23 does not alter the three-dimensional structure of the hormone, although trans structures show a lower average NOE root mean square deviation and a higher relative stability. Both cis and trans structures satisfactorily reproduce the experimental data, although they do not fulfill the whole set of NOE restraints, pointing out the danger involved in structure calculation whenever the cis-trans equilibrium does not affect the global fold.

Amino Acid Sequence↗

PubMed1994

Conversion of enkephalin and dermorphin into delta-selective opioid antagonists by single-residue substitution.

The properties of di- and tri-peptides containing 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid (Tic) in second position suggest that the message domain of opioid peptides can be composed of only two residues [Temussi, P. A., Salvadori, S., Amodeo, P., Guerrini, R., Tomatis, R., Lazarus, L. H., Picone, D. & Tancredi, T. (1994) Biochem. Biophys. Res. Commun. 198, 933-939]. As a crucial test of the possibility that the Tyr-Tic segment be a message domain in longer peptide sequences, we have inserted it in the sequences of two typical opioid peptides: [Leu]enkephalin, a non-selective agonist, and dermorphin, a selective mu agonist. Here we report the synthesis and biological activity of [L-Tic2]enkephalin, [L-Tic2]dermorphin, [L-Tic2]dermorphin carboxylic acid and [D-Tic2]dermorphin: all [L-Tic2]peptides were converted from agonists to delta-selective antagonists. The NMR conformational study in a dimethylsulfoxide/water cryoprotective mixture at low temperature shows diagnostic side-chain--side-chain NOEs in the spectra of all [L-Tic2]peptides and hints that the 90 degrees arrangement of the the two aromatic rings found in the cis-Tyr-L-Tic moiety, typical of N-methyl naltrindole and other delta-selective opiate antagonists, is responsible for the antagonist activity of all these peptides.

Amino Acid Sequence↗

PubMed1994

Selective opioid dipeptides.

The surprising change of selectivity induced by the change of chirality in peptides containing the tetrahydro-3-isoquinoline carboxylic acid (Tic) in second position, interpreted as a conformational preference induced on the Tyr-Xaa-Phe domain, can instead be attributed to the Tyr-Tic message domain. The relative spatial disposition of the aromatic ring of delta-selective non peptidic opiates is compatible with a message domain, in opioid peptides, of only two residues. This hypothesis was tested through the synthesis of Tyr-L-Tic-NH2, Tyr-D-Tic-NH2, Tyr-L-Tic-Ala-NH2, Tyr-L-Tic-Ala-OH and Tyr-D-Tic-Ala-NH2. Peptides containing Tyr-L-Tic- behave as very selective delta antagonists and those containing Tyr-DTic- as non selective agonists. This is the first case of opioid peptides containing a two-residue message domain and of opioid dipeptides with substantial opioid activity.

Amino Acid Sequence↗

PubMed1994

Solution conformation of c-[Gln-Trp-Phe-Gly-Leu-Met], a NK-2 tachykinin antagonist.

The conformation of cyclo-[Gln-Trp-Phe-Gly-Leu-Met], a potent tachykinin antagonist selective for the NK-2 receptor, has been studied by 1H NMR spectroscopy in DMSO-d6 and in a DMSO-d6/H2O cryoprotective mixture in the temperature range 280-320 K. The NMR data cannot be interpreted on the basis of a single ordered conformation. An exhaustive search, based mainly on missing NOEs among skeleton protons, yields a description of the conformational state in solution consisting of a few interconverting structures that can explain all observed NMR parameters. The relative position of the side chains of key residues may be interpreted in terms of bioactive conformations.

Amino Acid Sequence↗

PubMed1993

Solution structure of casokefamide.

Casokefamide (Tyr-D-Ala-Phe-D-Ala-Tyr-NH2) is a synthetic peptide derived from the beta-casomorphin sequence, designed to increase the resistance to gastric proteases. Casokefamide binds to both mu and delta-opioid receptors, while beta-casomorphins and its fragments are typical mu-opioid receptor agonists. Furthermore, casokefamide can affect gastric acid and pancreatic exocrine secretions and also gastrointestinal motility. We have undertaken a conformational study on this peptide based on NMR measurements in a DMSOd6/H2O cryomixture at 265 K and energy calculations. The predominant conformation is characterised by the absence of regular structures and intramolecular hydrogen bonds. The conformation of the message domain is reminiscent of the shape of several peptidic and non peptidic opiates, with the D-Ala2CH3 group sandwiched between Tyr1 and Phe3 aromatic rings.

Amino Acid Sequence↗

PubMed1993

Solution conformation of CCK9, a cholecystokinin analog.

Cholecystokinin (CCK) is a peptide hormone endowed with several important biological activities, both in the central and peripheral nervous system. Previous conformational studies have dealt mainly with its C-terminal octapeptide fragment (CCK8), which represents the shortest fully circulating form of this hormone. We have undertaken a detailed NMR conformational study in a DMSOd6/H2O cryomixture at 278 K of the CCK analog H-Arg-Asp-Tyr(SO3H)-Thr-Gly-Trp-Nle-Asp-PheNH2 (CCK9) which retains all the bioactivities of CCK8, but was found to be remarkably more stable in acidic media and unaffected by air oxidation due to Met replacements. The predominant conformation contains a gamma-turn centered on Thr4, separated by Gly5 from a helical segment that comprises the C-terminal residues.

Amino Acid Sequence↗

PubMed1993

Synthesis, biological activity, and conformational analysis of [pGlu6,N-MePhe8,Aib9] substance P (6-11): a selective agonist for the NK-3 receptor.

A highly potent and selective agonist to the tachykinin NK-3 receptor, [pGlu6,N-MePhe8,Aib9] substance P (6-11) (I), was synthesized via the solid phase method. The ED50 of I was 4 nM in the guinea pig ileum in the absence of atropine (NK-1+NK-3 receptors) and this agonist was 5000-fold less potent in the presence of atropine (NK-1 receptor). The analogue was virtually inactive in the rat vas deferens (NK-2 receptor). A detailed analysis of the solution conformation of this analogue in DMSO-d6 and in a DMSO-d6/H2O cryomixture was carried out by a combination of 1H-nmr 2D techniques (DQF-COSY, TOCSY, NOESY and ROESY) and model building based on empirical energy calculations. Peptide I exists as a mixture of isomers containing cis and trans Phe-N-MePhe peptide bonds. The main isomer, containing a cis Phe-N-MePhe peptide bond, shows a preferred folded conformation characterized by a type VI beta-turn with Phe and N-MePhe in the i + 1 and i + 2 positions. The turn is followed by a helical segment extending to the C-terminal. This conformation is compared to previously reported conformations of other selective tachykinin agonists and may be a promising lead for the design of novel NK-3 agonists with additional conformational constraints.

Amino Acid Sequence↗

PubMed1992

Solution conformation of tuftsin.

Tuftsin, a natural linear tetrapeptide (Thr-Lys-Pro-Arg) of potential antitumor activity, has been studied in DMSO-d6 solution by 2D NMR spectroscopy. 1H and 13C spectra show the presence of two families of conformations characterized by a trans or cis Lys-Pro bond, respectively. The family of conformers containing the cis peptide bond is a mixture of extended structures as expected for a short linear peptide. On the contrary, the trans isomer appears to be a rigid, folded conformer, as indicated by crucial NOEs and by the exceptionally low temperature coefficient of Arg NH. Analysis of the solution data by means of energy calculations leads to a unique structure, characterized by a Lys-Pro inverse gamma-turn.

Amino Acid Sequence↗

PubMed1992

Structural determination of the active site of a sweet protein. A 1H NMR investigation of pMNEI.

pMNEI, a single chain sweet protein related to monellin, has been studied by means of 1H NMR at 500 MHz. A partial sequential assignment performed by means of the MCD method allowed the determination of the secondary structure of a large portion of the beta-sheet of pMNEI that contains a likely 'sweet finger': the loop connecting the beta-strands from residue 59 to residue 78, corresponding to segment 16-35 of the A chain of monellin. The detailed three-dimensional structure of the loop (Tyr66-Ala67-Ser68-Asp69), determined from several interresidue and intraresidue NOEs and subsequent energy minimization, shows that the side chains of Tyr66 and Asp69 fit our model of the sweet receptor in a manner very similar to that of the side chains of Phe and Asp of aspartame.

Amino Acid Sequence↗

PubMed1992

Conformational analysis of an opioid peptide in solvent media that mimic cytoplasm viscosity.

Many neuropeptides exert their action between the presynaptic vesicles and postsynaptic transmembrane receptors, crossing different layers of specialized cytoplasm. Biomimetic media usually employed to study bioactive peptides do not reproduce the physico chemical environment of cytoplasm--in particular, the high viscosity of this biological fluid. Here we describe a conformational study of a delta-selective opioid peptide, deltorphin I, at variable temperatures in several biocompatible media characterized by varying values of viscosity and dielectric constant. It was found that only viscosity, among these parameters, induces ordered conformations; that is, it acts as a conformational sieve. This finding suggests that the high viscosity of the intersynaptic fluid contributes, in addition to the membrane catalysis proposed by Schwyzer, in overcoming the so-called entropic barrier to the transition state of peptide-receptor interaction by selecting ordered conformations prior to receptor interaction. The folded conformer found in the 80:20 (v:v) DMSOd6/H2O cryoprotective mixture at 265 K has a shape consistent with those of rigid nonpeptidic opiates.

Amino Acid Sequence↗

PubMed1991

New insights on mu/delta selectivity of opioid peptides: conformational analysis of deltorphin analogues.

The message domain of dermorphin (Tyr-D-Ala-Phe), a natural mu-opioid heptapeptide, has long been considered the main cause of the high mu selectivity of this peptide and of its analogues. The recent discovery, in the skin of Phyllomedusa sauvagei (i.e., the same natural source of dermorphin) and of Phyllomedusa bicolor of deltorphins, challenges this belief. Deltorphins, in fact, are three heptapeptides characterized by a message domain typical of mu-selective peptides, but endowed of an extremely high delta selectivity, the highest of all natural opioid peptides. A conformational analysis of dermorphin and deltorphins, based on nmr studies in DMSO and cryoprotective mixtures and internal energy calculations, showed that the enormous differences in receptor selectivity can be interpreted on the basis of receptor models for mu and delta opioids that recognize the same beta-turn in the N-terminal part, but discriminate for the conformation and polarity of the C-terminal part. Here we present the synthesis, biological activity, and conformational analysis in solution of three deltorphin analogues with very similar constitution, but with different net charge, different location of negative residues, or even without negative residues, which confirm these hypotheses and show that His4 can play a specific structural role.

Amino Acid Sequence↗

PubMed1984

Effect of preoperative irradiation on healing of low colorectal anastomoses.

The effect of preoperative irradiation on the healing of low colorectal anastomoses was studied experimentally. In 12 dogs in whom preoperative irradiation of 4,000 rads was given before low colorectal stapled anastomosis was performed, anastomotic leakage occurred in 66 percent. More than half of the anastomotic leaks were associated with either severe sepsis or death. In a matched group of control animals that underwent stapled anastomoses without irradiation, no anastomotic complications occurred. The clinical implications of this study are that stapled anastomoses in irradiated colon are at serious risk of anastomotic dehiscence and, therefore, should be protected with a proximal colostomy.

Animals↗

PubMed1984

Effects of choledochojejunostomy with Roux-en-Y exclusion on dimethylhydrazine induced neoplasms in rats.

The role of biliary secretions was studied in the development of neoplasms in the small intestine and colon of rats treated with 1,2-dimethylhydrazine (DMH). Sixty-eight female Sprague-Dawley rats underwent either no operative procedure or choledochojejunostomy with or without a Roux-en-Y exclusion. All animals then received weekly subcutaneous injections of DMH at 20 mg/kg for 26 weeks and were subsequently sacrificed. The largest number of neoplasms was found in the proximal duodenum, within 3 cm distal to the pylorus, in the control as well as both operative groups. In addition, only six neoplasms developed in relation to the choledochojejunostomy site in rats undergoing choledochojejunostomy only, and no neoplasms were noted at this location in the animals undergoing choledochojejunostomy with Roux-en-Y exclusion. These results suggest that the distribution of enteric neoplasms in DMH treated rats does not depend on excretion of active carcinogen in bile.

1,2-Dimethylhydrazine↗

PubMed1984

Surgical procedures in nonagenarians.

During the hospital course of 225 nonagenarian patients who underwent 285 major operations-80% on the general, vascular, orthopedic and urologic services-overall morbidity was 37% and mortality 7.5%. The 100 emergency operations were associated with a higher morbidity and mortality rate. Nonsurvivors were more likely to have associated cardiac or cerebral medical conditions, higher utilization of intraoperative invasive hemodynamic monitoring and greater use of surgical intensive care units. Compared with all surgical patients, the nonagenarians were admitted twice as often to the surgical intensive care unit, required twice the number of hospital days, underwent intraoperative hemodynamic monitoring twice as frequently and incurred 200% greater hospital charges. We conclude that with careful evaluation and management, a nonagenarian patient presenting with a surgical condition can safely undergo necessary operative procedures.

Aged↗

PubMed1983

Melanosis coli. Changes in appearance when associated with colonic neoplasia.

In 30 cases of colonic neoplasia associated with melanosis coli, proliferating or neoplastic colonic epithelium was notable within the melanotic colons by virtue of a striking absence of pigmentation. Microscopically this characteristic was found to be due to an absence or diminution of pigment-laden macrophages in the lamina propria underlying such lesions. Therefore, the absence of pigment-laden macrophages can be considered a marker for abnormally proliferating epithelium. This characteristic may denote a cellular or humoral change mediated by macrophages in association with neoplastic epithelium.

Colonic Diseases↗

PubMed1983

Comparative tissue reactivity to topical hemostatic agents in the periureteral area.

Application of the topical hemostatic agents microfibrillar collagen hemostat (Avitene), oxidized cellulose (Surgicel), and absorbable gelatin sponge (Gelfoam) to the periureteral regions in dogs did not incite an adverse inflammatory or fibrotic reaction when used in standard, recommended fashion. No instances of ureteral obstruction resulted from such application. The addition of a small amount of sterile urine in the same area with the topical agent did not influence the degree of reaction. We concluded that these useful hemostatic agents, when used properly, are absorbed with only slight or no residual tissue reaction. The adverse tissue reaction occasionally reported probably can be ascribed to either improper use of the hemostatic agent, other concomitant noxious influences such as infection, or admixture with abnormal collections of body fluids.

Administration, Topical↗