A Neuroprotective Sericin Hydrogel As an Effective Neuronal Cell Carrier for the Repair of Ischemic Stroke

Ischemic stroke causes extensive cellular loss that impairs brain functions, resulting in severe disabilities. No effective treatments are currently available for brain tissue regeneration. The need to develop effective therapeutic approaches for treating stroke is compelling. A tissue engineering approach employing a hydrogel carrying both cells and neurotrophic cytokines to damaged regions is an encouraging alternative for neuronal repair. However, this approach is often challenged by low in vivo cell survival rate, and low encapsulation efficiency and loss of cytokines. To address these limitations, we propose to develop a biomaterial that can form a matrix capable of improving in vivo survival of transplanted cells and reducing in vivo loss of cytokines. Here, we report that using sericin, a natural protein from silk, we have fabricated a genipin-cross-linked sericin hydrogel (GSH) with porous structure and mild swelling ratio. The GSH supports the effective attachment and growth of neurons in vitro. Strikingly, our data reveal that sericin protein is intrinsically neurotrophic and neuroprotective, promoting axon extension and branching as well as preventing primary neurons from hypoxia-induced cell death. Notably, these functions are inherited by the GSH's degradation products, which might spare a need of incorporating costly cytokines. We further demonstrate that this neurotrophic effect is dependent on the Lkb1-Nuak1 pathway, while the neuroprotective effect is realized through regulating the Bcl-2/Bax protein ratio. Importantly, when transplanted in vivo, the GSH gives a high cell survival rate and allows the cells to continuously proliferate. Together, this work unmasks the neurotrophic and neuroprotective functions for sericin and provides strong evidence justifying the GSH's suitability as a potential neuronal cell delivery vehicle for ischemic stroke repair.

Formation, Removal, and Reformation of Surface Coatings on Various Metal Oxide Surfaces Inspired by Mussel Adhesives

Mussels survive by strongly attaching to a variety of different surfaces, primarily subsurface rocks composed of metal oxides, through the formation of coordinative interactions driven by protein-based catechol repeating units contained within their adhesive secretions. From a chemistry perspective, catechols are known to form strong and reversible complexes with metal ions or metal oxides, with the binding affinity being dependent on the nature of the metal ion. As a result, catechol binding with metal oxides is reversible and can be broken in the presence of a free metal ion with a higher stability constant. It is proposed to exploit this competitive exchange in the design of a new strategy for the formation, removal, and reformation of surface coatings and self-assembled monolayers (SAM) based on catechols as the adhesive unit. In this study, catechol-functionalized tri(ethylene oxide) (TEO) was synthesized as a removable and recoverable self-assembled monolayer (SAM) for use on oxides surfaces. Attachment and detachment of these catechol derivatives on a variety of surfaces was shown to be reversible and controllable by exploiting the high stability constant of catechol to soluble metal ions, such as Fe(III). This tunable assembly based on catechol binding to metal oxides represents a new concept for reformable coatings with applications in fields ranging from friction/wettability control to biomolecular sensing and antifouling.

Evaluation of Cholecystokinin (CCK-8) Peptide Thermal Stability for Use as Radiopharmaceutical by Means Isothermal and Nonisothermal Approaches

The purpose of this research was to study the thermal stability of cholecystokinin octapeptide (CCK-8) in aqueous solution at pH 12 and ionic strength 0.01 M, which were kept as constants, by using isothermal and nonisothermal methods. The isothermal decomposition of CCK-8 was investigated as a function of temperature (40 degrees C to 70 degrees C). Nonisothermal stability studies were performed using a linear increasing temperature program. Two different nonisothermal studies were carried out at 0.25 degrees K and 0.5 degrees K per hour, and the temperature interval varied from 40 degrees C to 82 degrees C. The degradation of CCK-8 followed first-order kinetics, obeying the Arrhenius equation in the experimental temperature range. This indicated that the degradation mechanism of CCK-8 could be the equal within the temperature range studied. The nonisothermal approach resulted in activation energy (Ea) and shelf-life (t90%) values that agree well with those obtained by the isothermal method. The level of uncertainty in the estimates of t90% and Ea values is determined mainly by the extent of drug degradation and temperature change during the experiment. Therefore, nonisothermal experiments save time, labor and materials (i.e. the amount of drugs necessary to conduct the experiment) compared to the classic isothermal experiments, if they are performed using a suitable experimental design and a precise analytical method.

Nanostructures by self-assembling peptide amphiphile as potential selective drug carriers

The self-assembling behavior, at physiological pH, of the amphiphile peptide (C18)(2)L5CCK8 in nanostructures is reported. Stable aggregates presenting a critical micellar concentration of 2 x 10(-6) mol kg(-1), and characterized by water exposed CCK8 peptide in beta-sheet conformation, are obtained. Small angle neutron scattering experiments are indicative for a 3D structure with dimensions > or =100 nm. AFM images confirm the presence of nanostructures. Fluorescence experiments indicating the sequestration of pyrene, chosen as drug model, and the anticancer Doxorubicin within the nanostructures are reported.

Transmembrane segment peptides can disrupt cholecystokinin receptor oligomerization without affecting receptor function

Oligomerization of the G protein-coupled cholecystokinin (CCK) receptor has been demonstrated, but its molecular basis and functional importance are not clear. We now examine contributions of transmembrane (TM) segments to oligomerization of this receptor using a peptide competitive inhibition strategy. Oligomerization of CCK receptors tagged at the carboxyl terminus with Renilla luciferase or yellow fluorescent protein was quantified using bioluminescence resonance energy transfer (BRET). Synthetic peptides representing TM I, II, V, VI, and VII of the CCK receptor were utilized as competitors. Of these, only TM VI and VII peptides disrupted receptor BRET. Control studies established that the beta2-adrenergic receptor TM VI peptide that disrupts oligomerization of that receptor had no effect on CCK receptor BRET. Notably, disruption of CCK receptor oligomerization had no effect on agonist binding, biological activity, or receptor internalization. To gain insight into the face of TM VI contributing to oligomerization, we utilized analogous peptides with alanines in positions 315, 319, and 323 (interhelical face) or 317, 321, and 325 (external lipid-exposed face). The Ala317,321,325 peptide eliminated the disruptive effect on CCK receptor BRET, whereas the other mutant peptide behaved like wild-type TM VI. This suggests that the lipid-exposed face of the CCK receptor TM VI most contributes to oligomerization and supports external contact dimerization of helical bundles, rather than domain-swapped dimerization. Fluorescent CCK receptor mutants with residues 317, 321, and 325 replaced with alanines were also prepared and failed to yield significant resonance transfer signals using either BRET or a morphological FRET assay, further supporting this interpretation.

Protease-catalyzed synthesis of the tripeptide CCK26–28, a fragment of CCK-8

Two enzymatically synthetic strategies of the tripeptide derivative PhAc-Asp(OMe)-Tyr-Met-OAl are reported. The second strategy gains the advantage of more economical starting materials, less reaction steps and a higher overall isolated yield of this tripeptide fragment over the first strategy. The effect of the acyl-donor ester concentration and structure, the C-alpha protecting group of the nucleophile, reaction media, enzyme and the carrier on the tripeptide derivative synthesis were studied. This tripeptide selected is a fragment of the cholecystokinin C-terminal octapeptide (CCK-8), a potential therapeutic agent in the control of gastrointestinal function and also a drug candidate for the treatment of epilepsy.

The difference in mRNA expressions of hypothalamic CCK and CCK-A and -B receptors between responder and non-responder rats to high frequency electroacupuncture analgesia

The present study was performed to determine whether the expression levels of the hypothalamic cholecystokinin (CCK) and its receptors are associated with the responsiveness to high frequency electroacupuncture (EA) analgesia in rats. EA stimulation (100 Hz, 0.5 ms pulse width, 0.2-0.3 mA) was delivered to the Zusanli (ST36) acupoint of male Sprague-Dawley rats for 20 min without anesthetics or holder restraint. The analgesic effect of EA was quantified using a tail flick latency test, and subsequently animals were allocated to responder or non-responder groups. The hypothalamus of rats in each group was dissected and RNA was purified. The mRNA expressions of CCK, and CCK-A and -B receptor were determined by real-time RT-PCR. CCK mRNA levels were not significantly different in the two groups, whereas both CCK-A and -B receptors were significantly more expressed in non-responders. These results suggest that the level of CCK receptor mRNA expression in the hypothalamus, rather than CCK mRNA, has an important relationship with the individual variations to high frequency EA analgesia in rats.

Anthranilic Acid Based CCK1 Receptor Antagonists and CCK-8 Have a Common Step in Their “Receptor Desmodynamic Processes”

The interaction between the 1-47 N-terminus of the CCK(1)-R and the anthranilic acid based antagonists has been investigated by fluorescence spectroscopy. These antagonists interact with W39 of the N-terminal domain of the CCK(1)-R like that of the endogenous ligand CCK-8. This specific interaction was not found in other nonpeptide ligands of the CCK(1)-R. Conformational studies, using NMR and energy minimization procedures, have allowed formulation of a new hypothesis on the CCK(1)-R binding mode of the anthranilic antagonists.

“Dipeptoids”: From the Chemical Structure of the Endogenous Peptide to the Design of Peptidomimetics

The present review details the rational multi-step process followed for the discovery of a family of non-peptide CCK receptor ligands ("dipeptoids"), starting from the structure of the endogenous peptide, CCK(8). Emphasis will be made on the N- and C-terminal modifications, on the singular effects of the stereochemical changes and the incorporation of conformational constraints into the structure of "dipeptoids", and on the modifications directed to improve the pharmacological profile of these compounds to afford valuable clinical candidates.

Physicochemical properties of mixed micellar aggregates containing CCK peptides and Gd complexes designed as tumor specific contrast agents in MRI

New amphiphilic molecules containing a bioactive peptide or a claw moiety have been prepared in order to obtain mixed micelles as target-specific contrast agents in magnetic resonance imaging. The first molecule, C(18)H(37)CONH(AdOO)(2)-G-CCK8 (C18CCK8), contains a C18 hydrophobic moiety bound to the C-terminal cholecystokinin octapeptide amide (CCK 26-33 or CCK8). The second amphiphilic compound, C(18)H(37)CONHLys(DTPAGlu)CONH(2) (C18DTPAGlu) or its gadolinium complex, (C18DTPAGlu(Gd)), contains the same C18 hydrophobic moiety bound, through a lysine residue, to the DTPAGlu chelating agent. The mixed aggregates as well as the pure C18DTPAGlu aggregate, in the presence and absence of Gd, have been fully characterized by surface tension measurements, FT-PGSE-NMR, fluorescence quenching, and small-angle neutron scattering measurements. The structural characterization of the mixed aggregates C18DTPAGlu(Gd)-C18CCK8 indicates a spherical arrangement of the micelles with an external shell of approximately 21 A and an inner core of approximately 20 A. Both the DTPAGlu(Gd) complexes and the CCK8 peptides point toward the external surface. The measured values for relaxivity in saline medium at 20 MHz proton Larmor frequency and 25 degrees C are 18.7 mM(-)(1) s(-)(1). These values show a large enhancement in comparison with the isolated DTPAGlu(Gd) complex.

Prediction of peptide conformation using a scale-transformed entropy sampling algorithm

An algorithm for predicting the lowest energy structure of a peptide has been developed. High-energy barriers on an energy surface can be easily overcome by logarithmically transforming the energy space. For efficient optimizations, the energy space is searched using a scale-transformed entropy sampling method, and conformations specific to a primary structure of the peptide are sampled with large weights. The efficiency of the present method is demonstrated by calculations on cholecystokinin octapeptide (CCK-8).

Total enzymatic synthesis of cholecystokinin CCK-5

This paper describes the enzymatic synthesis of the C-terminal fragment H-Gly-Trp-Met-Asp-Phe-NH2 of cholecystokinin. Immobilized enzymes were used for the formation of all peptide bonds except thermolysin. Beginning the synthesis with phenylacetyl (PhAc) glycine carboxamidomethyl ester (OCam) and H-Trp-OMe by using immobilized papain as biocatalyst in buffered ethyl acetate, the dipeptide methyl ester was then coupled directly with Met-OEt.HCl by alpha-chymotrypsin/Celite 545 in a solvent free system. For the 3+2 coupling PhAc-Gly-Trp-Met-OEt had to be converted into its OCam ester. The other fragment H-Asp(OMe)-Phe-NH2 resulted from the coupling of Cbo-Asp(OMe)-OH with H-Phe-NH2.HCl and thermolysin as catalyst, followed by catalytic hydrogenation. Finally PhAc-Gly-Trp-Met-Asp-Phe-NH2 was obtained in a smooth reaction from PhAc-Gly-Trp-Met-OCam and H-Asp(OMe)-Phe-NH2 with alpha-chymotrypsin/Celite 545 in acetonitrile, followed by basic hydrolysis of the beta-methyl ester. The PhAc-group is removed with penicillin G amidase and CCK-5 is obtained in an overall isolated yield of 19.6%.

Possible degradative process of cholecystokinin analogs in rabbit jejunum brush-border membrane vesicles

Our recent work on the intestinal metabolism and absorption of cholecystokinin analogs, sulfated C-terminal octapeptide (CCK8; Asp-Tyr(SO(3)H)-Met-Gly-Trp-Met-Asp-Phe(NH(2)) = DY(SO(3)H)MGWMDF(NH(2))) and tetrapeptide (CCK4; Trp-Met-Asp-Phe(NH(2)) = WMDF(NH(2))), was extended to investigate the degradative process of these analogs using rabbit jejunum brush-border membrane vesicles and to find a better enzyme-inhibitor system for intestinal absorption of peptide drugs. Various enzyme inhibitors and a lower pH buffer were applied to discover the major enzyme(s) involved in each process. Metabolic pathways showing degradative processes were proposed for both analogs. The major cleavage site occurs at the W(1)-M(2) for CCK4. At least three metabolic pathways occur independently for CCK8 and appear at peptides bonds between G(4)-W(5), M(6)-D(7), and D(7)-F(NH(2))(8). Many different enzymes of aminopeptidase, endopeptidase, angiotensin-converting enzyme, metalloenzyme, and others were involved in each process. Identification of more specific yet safe enzyme inhibitors and co-administration of various these inhibitors may lead to further enhancement in intestinal peptide absorption when administered orally.

Differences in receptor binding and stability to enzymatic digestion between CCK-8 and CCK-58

INTRODUCTION AND AIMS

It has been proposed that distinct tertiary structures of the C-terminus of CCK-8 and CCK-58 result in differences in stimulation of pancreatic amylase secretion. Binding of CCK-8 and CCK-58 to CCK-A and CCK-B receptors and stability to enzymatic digestion were used as independent probes for tertiary structure of the C-terminus.

METHODOLOGY

Canine CCK-58 was purified from intestinal extracts and CCK-8 was purchased. Their amounts were determined by amino acid analysis. The effect of tertiary structure on receptor binding at CCK-A receptors and CCK-B receptors was evaluated using membrane preparations from mouse pancreas and brain. The influence of C-terminal tertiary structure on stability to enzymatic digestion was evaluated by reacting CCK-8 and CCK-58 with endopeptidase 24:11.

RESULTS

CCK-58 was three times more potent than CCK-8 for binding mouse pancreatic membrane CCK-A receptors and equipotent to CCK-8 for binding mouse brain CCK-B receptors. CCK-8 was readily digested by endopeptidase 24:11, whereas CCK-58 was not.

CONCLUSIONS

The results strongly support the hypothesis that differences in tertiary structure of the carboxyl terminus of CCK-8 and CCK-58 influence receptor binding and stability to enzymatic digestion.

NMR evidence for different conformations of the bioactive region of rat CCK-8 and CCK-58

Sulfated CCK-58 and CCK-8 have identical bioactive C-terminal primary sequences but distinct C-terminal solution structures and different bioactivities. To examine structural differences in greater detail, rat CCK-58 and -8 were synthesized with isotopic enrichment of C-terminal residues with (15)N at alpha-amino nitrogens. Proton and nitrogen chemical shift assignments of peptide solutions were obtained by homo- and heteronuclear NMR methods. These data show that the tertiary structure ensembles of C-terminal CCK-8 and CCK-58 differ significantly. Thus, distinct solution conformations may explain differences in CCK(A) and CCK(B) receptor interactions of large and small molecular forms of CCK.

NMR studies of CCK-8/CCK1 complex support membrane-associated pathway for ligand-receptor interaction

The interaction of peptide ligands with their associated G-protein-coupled receptors has been examined by a number of different experimental approaches over the years. We have been developing an approach utilizing high-resolution NMR to determine the structural features of the peptide ligand, well-designed fragments of the receptor, and the ligand-receptor complexes formed upon titration of the peptide hormone. The results from these investigations provide evidence for a membrane-associated pathway for the initial interaction of peptide ligands with the receptor. Here, our results from the investigation of the interaction of CCK-8 with the CCK1 receptor are described. Our spectroscopic results clearly show that both CCK-8 and the regions of CCK1 with which it interacts are closely associated with the zwitterionic interface of the lipids utilized in our solution spectroscopic studies.

Fluorescence studies on the binding between 1-47 fragment of cholecystokinin receptor CCK(A)-R(1-47) and nonsulfated cholecystokinin octapeptide CCK8

The interaction between the 1-47 N-terminus fragment of the cholecystokinin receptor and the nonsulfated cholecystokinin octapeptide, CCK8, is monitored by fluorescence emission. Quenching of the fluorescence intensities is observed on binding. Dissociation constants calculated by these data are in the same submicromolar range as found for the binding of linear CCK8 analogues to B-type receptors. Although detailed structural information cannot be obtained, fluorescence emission is more sensitive than other techniques and permits fast detection of receptor-ligand interaction.

Synthesis and solution characterization of a porphyrin-CCK8 conjugate

In this paper we report the synthesis and a detailed NMR solution characterization of a new CCK8 analogue and its indium(III) complex, PK-CCK8 and In-PK-CCK8. The new compounds contain a porphyrin moiety covalently bound through an amide bond to the side chain of a Lys residue introduced at the N-terminus of CCK8. A molecular dynamics simulation, based on the NMR structure of the complex between CCK8 and the N-terminal extracellular arm of the CCK(A) receptor, is also reported. Both the NMR study and the molecular dynamics simulation indicate that the porphyrin-peptide conjugate might be able to bind to the CCK(A) receptor model. The results of the molecular dynamics calculations show that the conformational features of the CCK8/CCK(A) receptor model complex and of the PK-CCK8/CCK(A) receptor-model complex are similar. This evidence supports the view that the introduction of the porphyrin-Lys moiety does not influence the mode of ligand binding to the CCK(A) receptor model. The NMR structure of PK-CCK8 in DMSO consists of a well defined pseudo-helical N-terminal region, while the C-terminal region is flexible. Moreover, the absence of NOE contacts between the porphyrin and the peptide indicates that the macrocyclic ring is directed away from the peptide region involved in the binding with the receptor.

Small molecule peptidomimetics containing a novel phosphotyrosine bioisostere inhibit protein tyrosine phosphatase 1B and augment insulin action

Protein tyrosine phosphatase 1B (PTP1B) attenuates insulin signaling by catalyzing dephosphorylation of insulin receptors (IR) and is an attractive target of potential new drugs for treating the insulin resistance that is central to type II diabetes. Several analogues of cholecystokinin(26)(-)(33) (CCK-8) were found to be surprisingly potent inhibitors of PTP1B, and a common N-terminal tripeptide, N-acetyl-Asp-Tyr(SO(3)H)-Nle-, was shown to be necessary and sufficient for inhibition. This tripeptide was modified to reduce size and peptide character, and to replace the metabolically unstable sulfotyrosyl group. This led to the discovery of a novel phosphotyrosine bioisostere, 2-carboxymethoxybenzoic acid, and to analogues that were >100-fold more potent than the CCK-8 analogues and >10-fold selective for PTP1B over two other PTP enzymes (LAR and SHP-2), a dual specificity phosphatase (cdc25b), and a serine/threonine phosphatase (calcineurin). These inhibitors disrupted the binding of PTP1B to activated IR in vitro and prevented the loss of tyrosine kinase (IRTK) activity that accompanied PTP1B-catalyzed dephosphorylation of IR. Introduction of these poorly cell permeant inhibitors into insulin-treated cells by microinjection (oocytes) or by esterification to more lipophilic proinhibitors (3T3-L1 adipocytes and L6 myocytes) resulted in increased potency, but not efficacy, of insulin. In some instances, PTP1B inhibitors were insulin-mimetic, suggesting that in unstimulated cells PTP1B may suppress basal IRTK activity. X-ray crystallography of PTP1B-inhibitor complexes revealed that binding of an inhibitor incorporating phenyl-O-malonic acid as a phosphotyrosine bioisostere occurred with the mobile WPD loop in the open conformation, while a closely related inhibitor with a 2-carboxymethoxybenzoic acid bioisostere bound with the WPD loop closed, perhaps accounting for its superior potency. These CCK-derived peptidomimetic inhibitors of PTP1B represent a novel template for further development of potent, selective inhibitors, and their cell activity further justifies the selection of PTP1B as a therapeutic target.

Intermolecular interactions between cholecystokinin-8 and the third extracellular loop of the cholecystokinin A receptor

The interaction of the C-terminal octapeptide of cholecystokinin, CCK-8, with the third extracellular loop of human cholecystokinin-A receptor, CCK(A)-R(329-357), has been probed by high-resolution NMR and extensive computer simulations. The structure of CCK(A)-R(329-357) in the presence of dodecylphosphocholine micelles consists of three alpha-helices, with the first and third corresponding to the extracellular ends of transmembrane (TM) helices 6 and 7. The central helix, residues W335-R345, is found to lie on the zwitterionic surface. Titration with CCK-8 produces a stable complex with a number of intermolecular NOEs between the C-terminus of the ligand (Trp(30), Met(31), Asp(32)) and the interface of TM6 and the third extracellular loop (N333, A334, Y338) of the receptor fragment. The mode of ligand binding based on these intermolecular NOEs is in agreement with a number of published findings from receptor mutagenesis and photoaffinity cross-linking. Utilizing these ligand/receptor points of interaction, the structural features of CCK(A)-R(329-357), and also the structures of CCK-8 and CCK(A)-R(1-47) previously determined, extensive molecular dynamics simulations of the CCK-8/CCK(A)-R complex were carried out. The results provide unique insight into the molecular interactions and forces important for the binding of CCK-8 to CCK(A)-R.

Reciprocal effect of unsulfated and sulfated forms of cholecystokinin-octapeptide on gastric acid secretion in the rat

The sulfated and unsulfated forms of cholecystokinin-octapeptide (CCK-8) were compared, with respect to their effect on gastric acid secretion, in the rat. Unsulfated CCK-8 stimulated acid secretion in a dose-dependent manner, while the sulfated form was without stimulatory effect; thus, sulfation of the tyrosine residue in the seventh position from the C terminus completely abolished the gastrin-like action of CCK-8. Compared with pentagastrin and human gastrin II, unsulfated CCK-8 gave lower calculated maximal response. While sulfated CCK-8 given alone had no effect on acid secretion, it caused marked inhibition of the plateau response to submaximal pentagastrin. This inhibition was surmountable with higher doses of pentagastrin, suggesting a competitive type of inhibition. It is, therefore, concluded that lack of sulfation of the tyrosine residue in the seventh position does not exclude CCK-8 from occupying the gastrin receptor; but does prevent the hormone-receptor interaction that leads to the secretory response. These observations in the rat are different from those in the dog where desulfation of tyrosine renders the CCK analog, caerulein, ineffective in its ability to stimulate acid secretion.

Neuropeptides of the cholecystokinin group: effects and mechanisms of action on the gastro-intestinal and gall bladder motility

The neuropeptides of the cholecystokinin (CCK) group belong to the substances usually referred to as "brain-gut" neuropeptides. They are synthesized in neurons of the central nervous system, in the peripheral and in the autonomous nervous systems, in endocrine cells (types "I", "K" and "A"), as well as in the enteric nervous system of the gastro-intestinal tract and of the pancreas. The CCK-group peptides realize their effects via several different mechanisms (Fig. 1): endocrine or neuroendocrine (classic hormonal mechanism)--the peptide, released by the endocrine cell or by the nerve terminal, is carried by the circulation to the remote target organs; paracrine or neuroparacrine--the peptide, released in the intercellular space, reaches the target effector cells via diffusion. Similarly to the classic neurotransmitters, CCK and its analogues could play a neurotransmitter role, also modulating the release of acetylcholine (ACh) and of other neurotransmitters in enteric and CNS neurons. In the present review article some smooth-muscle and neuromodulatory effects of CCK are described and compared to the results of the authors' studies on the problem.

Identical primary sequence but different conformations of the bioactive regions of canine CCK-8 and CCK-58

The C-terminal bioactive regions of CCK-8 and CCK-58 are identical (DY*MGWMDF-NH(2), Y* denotes a sulfated tyrosine residue), but these peptides have different patterns of bioactivity. Specifically, CCK-58 binds more avidly to the CCK(A) receptor while CCK-8 is more potent for stimulation of amylase secretion from pancreatic acini. We postulate that these seemingly contradictory observations reflect a stable conformational change in CCK-58 that enhances binding, but diminishes activation of second messenger. We used CD and NMR spectra to evaluate postulated structural differences between CCK-8 and the carboxy-terminus of synthetic CCK-58. The CD spectra indicate the presence of turns in CCK-8 but a mixture of helical and random coil structures for CCK-58. Comparisons of partial NMR chemical shift assignments of CCK-58 and full assignments for CCK-8 also indicate differences in the backbone conformations for these residues. The data support the hypothesis that these peptides have different, stable, carboxy-terminal structures that may influence bioactivity.

N-terminal glycation of cholecystokinin-8 abolishes its insulinotropic action on clonal pancreatic B-cells

Monoglycated cholecystokinin octapeptide (Asp(1)-glucitol CCK-8) was prepared under hyperglycaemic reducing conditions and purified by reverse phase-high performance liquid chromatography. Electrospray ionisation mass spectrometry and automated Edman degradation demonstrated that CCK-8 was glycated specifically at the amino-terminal Asp(1) residue. Effects of Asp(1)-glucitol CCK-8 and CCK-8 on insulin secretion were examined using glucose-responsive clonal BRIN-BD11 cells. In acute (20 min) incubations, 10(-10) mol/l CCK-8 enhanced insulin release by 1.2-1.5-fold at 5.6-11.1 mmol/l glucose. The stimulatory effect induced by 10(-10) mol/l CCK-8 was abolished following glycation. At 5.6 mmol/l glucose, CCK-8 at concentrations ranging from 10(-11) to 10(-7) mol/l induced a significant 1.6-1.9-fold increase in insulin secretion. Insulin output in the presence of Asp(1)-glucitol CCK-8 over the concentration range 10(-11)-10(-7) mol/l was decreased by 21-35% compared with CCK-8, and its insulinotropic action was effectively abolished. Asp(1)-glucitol CCK-8 at 10(-8) mol/l also completely blocked the stimulatory effects of 10(-11)-10(-8) mol/l CCK-8. These data indicate that structural modification by glycation at the amino-terminal Asp(1) residue effectively abolishes and/or antagonises the insulinotropic activity of CCK-8.

Direct identification of the agonist binding site in the human brain cholecystokininB receptor

In investigating the agonist binding site of the human brain cholecystokininB receptor (CCKBR), we employed the direct protein chemical approach using a photoreactive tritiated analogue of sulfated cholecystokinin octapeptide, which contains the p-benzoylbenzoyl moiety at the N-terminus, followed by purification of the affinity-labeled receptor to homogeneity. This probe bound specifically, saturably, and with high affinity (KD = 1.2 nM) to the CCKBR and has full agonistic activity. As the starting material for receptor purification, we used stably transfected HEK 293 cells overexpressing functional CCKBR. Covalent labeling of the WGA-lectin-enriched receptor revealed a 70-80 kDa glycoprotein with a protein core of about 50 kDa. Identification of the agonist binding site was achieved by the application of subsequent chemical and enzymatical cleavage to the purified receptor. A radiolabeled peptide was identified by Edman degradation amino acid sequence analysis combined with MALDI-TOF mass spectrometry. The position of the radioactive probe within the identified peptide was determined using combined tandem electrospray mass spectrometry and peptide mapping. The probe was covalently attached within the sequence L52ELAIRITLY61 that represents the transition between the N-terminal domain and predicted transmembrane domain 1. Using this interaction as a constraint to orientate the ligand within the putative receptor binding site, a model of the CCK-8s-occupied CCKBR was constructed. The hormone was found to be placed in a binding pocket built from both extracellular and transmembrane domains of CCKBR with its N-terminus mainly interacting with residues Arg57 and Tyr61.

Release and endogenous actions of the gastrin/cholecystokinin (CCK) family in the chicken

The regulation of cholecystokinin (CCK) and gastrin release in the chicken and their endogenous actions are summarized. Both dietary protein and amino acids stimulated CCK releases. Among dietary fat sources, medium-chain triacylglycerol (MCT) was a potent stimulator of CCK release compared with long-chain triacylglycerol (LCT). However, it is difficult to explain that endogenous CCK released by those stimulators has an important role in the avian gastrointestinal physiology. Luminal acids may be an important regulator in pancreatic enzyme and fluid secretion. Gastrin (a regulator of luminal acid secretion) release was stimulated by food components, strongly by MCT, but not by LCT, and weakly by some amino acids, and was inhibited by luminal acids. Luminal acids controlled food passage from the crop. In conclusion, gastrointestinal physiology may be directly regulated by luminal acid rather than by the gastrin/CCK family in the chicken.

Glycated cholecystokinin-8 has an enhanced satiating activity and is protected against enzymatic degradation

Monoglycated cholecystokinin octapeptide (CCK-8) (glucitol-Asp1 adduct) modified at the NH2-terminus was prepared under hyperglycemic conditions, purified by high-performance liquid chromatography, and characterized by mass spectrometry (Mr 1228.4 Da) and peptide sequencing. CCK-8 (100 nmol/kg, i.p.) significantly (P < 0.001) reduced voluntary food intake of fasted mice for up to 30 min after its administration, compared with saline-administered controls. Glycated CCK-8 reduced food intake at 30-120 min (P < 0.01 to P < 0.001) and significantly reduced feeding compared with CCK-8 from 60 to 120 min (P < 0.01). In vitro plasma degradation studies indicated that glycated CCK-8 was resistant to the normal rapid enzymatic conversion to CCK fragments. This study demonstrated that CCK-8 is a potent short-term inhibitor of food intake, and that structural modification of this peptide by amino-terminal glycation leads to enhanced satiating activity, partially due to increased resistance to serum aminopeptidase degradation.

Prohormone convertase 1 (PC1) when expressed with pro cholecystokinin (pro CCK) in L cells performs three endoproteolytic cleavages which are observed in rat brain and in CCK-expressing endocrine cells in culture, including the production of glycine and arginine extended CCK8

Pro CCK was expressed in an L cell line engineered to express PC1 and the products secreted into the media were characterized by a combination of RIA, gel filtration and HPLC. PC1 released from L cells, cleaved pro CCK generating the amino terminal pro peptide. PC1 also generated a peptide which after carboxypeptidase B treatment, was detected with an antiserum specific for CCK Gly. Neither of these peptides was found in media from L cells expressing pro CCK alone. This CCK Gly immunoreactive peptide was similar in size to CCK 8, and after treatment with arylsulfatase and carboxypeptidase B, it co-eluted on HPLC with unsulfated CCK 8 Gly. These results agree with previous studies which support a role for PC1 in generation of CCK 8. This is the first demonstration that PC1 acting alone is able to cleave pro CCK liberating the amino terminal pro peptide and a glycine and arginine extended CCK 8 which is the immediate precursor of CCK 8 amide.

Reaction engineering for consecutive enzymatic reactions in peptide synthesis: application to the synthesis of a pentapeptide

A single-pot enzymatic synthesis of Z-CCK5 (4-8) is presented in this work, employing Z-Gly-Trp-OBzl as acyl donor, under kinetic control. The first goal of the work is the development of a synthetic strategy allowing the use of the same medium for two reactions catalyzed by immobilized alpha-chymotrypsin, discriminating between simultaneous and consecutive addition systems. The second goal is the maximization of the pentapeptide yield as a function of the molar excess of both nucleophiles employed. A maximum yield of 36% was obtained, and the addition strategy as well as the optimal initial concentrations of substrates have been determined.

Effects of C-terminal fragments of cholecystokinin on plasma insulin and glucagon concentrations in sheep

The effects of three C-terminal fragments of cholecystokinin (CCK) (CCK-8-sulphated form [SF], CCK-8-non-sulphated form [NSF] and CCK-4) on insulin and glucagon secretion were examined in sheep in vivo. Each CCK fragment was injected intravenously at a wide range of doses (1 pmol to 3 x 10(5) pmol kg-1). CCK-8(SF) had the lowest threshold dose (10 pmol kg-1) and a maximal response dose of 10(3) pmol kg-1 for increasing plasma insulin concentration; the respective threshold doses of CCK-8(NSF) and CCK-8 for increasing plasma insulin were 30 and 100 times greater than that of CCK-8(SF). A maximal insulin response was not obtained at the highest doses of CCK-8(NSF) or CCK-4 tested (3 x 10(3) and 3 x 10(5) pmol kg-1, respectively). These results indicate that CCK-A type receptors rather than CCK-B receptors may be involved in CCK-induced insulin secretion in sheep. None of the CCK fragments affected plasma glucagon concentration. The lack of a glucagon response to exogenous CCK-fragments may be one of the characteristics of the endocrine pancreatic responses of ruminant species.

CCK-58: a novel reagent for studying the regulation of cholecystokinin bioactivity

CCK-58 has been shown to be the major circulating form of the hormone in the dog and human. To date, there have been no reports on its biological activity in vivo. We report here that CCK-8 and CCK-58 were equipotent in decreasing gastric motor function after bolus doses and in stimulating protein secretion after continuous infusion in urethane-anesthetized rats. The present results are the first on the in vivo activity of CCK-58, and indicate that because CCK-58 is equipotent to CCK-8, and because it is a major released and circulating form, it may be considered as a major contributor to the expression of cholecystokinin bioactivity.

Whole body autoradiography of CCK-8 in rats

Rats were given i.v., intranasal or intraperitoneal doses of CCK-8 (sulfated) labelled with 125I-labeled Bolton and Hunter reagent. Radioactivity was found mainly in the liver, kidney, and the intestinal contents. No radioactivity was detected in the brain. In animals dosed i.v., specific localization occurred in the tissue of the pyloric region of the stomach, and in the pancreas. Label persisted within the pyloric region of the stomach for longer than 30 min, in spite of the reported half-life of CCK-8 in plasma of approximately 1 min. Intranasal and intraperitoneal doses had limited bioavailability. The binding to the sites in the pyloric region of the stomach, which required systemic delivery, may have identified receptors associated with appetite control.

[Synthesis of protected active peptide analogues of cholecystokinin and study of their biological activities]

A number of protected active peptide analogues of Cholecystokinin were prepared in solution by N-end stretching method with active esters. In the synthesis t-butoxycarbonyl (Boc-) and benzyloxycarbonyl (Z-) were applied as protecting groups. Six oligopeptides which contained protecting groups have not yet been reported in literature. Their structures were identified by amino acid analysis, opticity, IR and FAB-MS. The results of preliminary pharmacological tests show all the samples have biological activities in various degrees.

Synthesis and biological evaluation of cholecystokinin analogs in which the Asp-Phe-NH2 moiety has been replaced by a 3-amino-7-phenylheptanoic acid or a 3-amino-6-(phenyloxy)hexanoic acid

Boc-Tyr(SO3H)-Nle-Gly-Trp-Nle-Asp-2-phenylethyl ester (JMV180), an analog of the C-terminal octapeptide of cholecystokinin (CCK-8), shows interesting biological activities behaving as an agonist at the high-affinity CCK binding sites and as an antagonist at the low-affinity CCK binding sites in rat pancreatic acini. Although we did not observe any major hydrolysis of the ester bond of Boc-Tyr(SO3H)-Nle-Gly-Trp-Nle-Asp-2-phenylethyl ester in our in vitro studies, we were aware of a possible and rapid cleavage of this ester bond during in vivo studies. To improve the stability of Boc-Tyr(SO3H)-Nle-Gly-Trp-Nle-Asp-2-phenylethyl ester, we decided to synthesize analogs in which the ester bond would be replaced by a carba (CH2-CH2) linkage. We synthesized the 3-amino-7-phenylheptanoic acid (beta-homo-Aph) with the R configuration in order to mimic the Asp-2-phenylethyl ester moiety and the 3-amino-6-(phenyloxy)hexanoic acid (H-beta-homo-App-OH), an analog of H-beta-homo-Aph-OH in which a methylene group has been replaced by an oxygen. (R)-beta-Homo-Aph and (R)-H-beta-homo-App-OH were introduced in the CCK-8 sequence to produce Boc-Tyr(SO3H)-Nle-Gly-Trp-Nle-(R)-beta-homo-Aph-OH and Boc-Tyr(SO3H)-Nle-Gly-Trp-Nle-(R)-beta-homo-App-OH. Both compounds were able to recognize the CCK receptor on rat pancreatic acini (IC50 = 12 +/- 8 nM and 13 +/- 5 nM, respectively), on brain membranes (IC50 = 32 +/- 2 nM and 57 +/- 5 nM, respectively), and on Jurkat T cells (IC50 = 75 +/- 15 nM and 65 +/- 21 nM, respectively). Like Boc-Tyr(SO3H)-Nle-Gly-Trp-Nle-Asp-2-phenylethyl ester, both compounds produced maximal stimulation of amylase secretion (EC50 = 6 +/- 2 nM and 4 +/- 2 nM, respectively) with no decrease of the secretion at high concentration indicating that these compounds probably act as agonists at the high-affinity peripheral CCK-receptor and as antagonists at the low-affinity CCK-receptor. Replacing the tryptophan by a D-tryptophan in such analogs produced full CCK-receptor antagonists. All these analogs might be more suitable for in vivo studies than Boc-Tyr(SO3H)-Nle-Gly-Trp-Nle-Asp-2-phenylethyl ester.

Models for the A- and B-receptor-bound conformations of CCK-8

Energy calculations were performed for CCK-8 (Asp26-Tyr(SO3)27-Met28-Gly29- Trp30-Met31-Asp32-Phe33-NH2, I) and [desaminoTyr(SO3)27, Nle28,31]CCK-7 (II), which are nonselective ligands of CCK receptors, and for the CCK-A selective analog [desaminoTyr(SO3)27, Nle28,31, N-Me-Asp32]CCK-7 (III) and the CCK-B selective analog [desaminoTyr(SO3)27, Nle28, N-Me-Leu31]CCK-7 (IV). The geometrical shapes of the obtained low energy backbone conformers were then compared with each other, searching for similar spatial arrangements of specific atomic centers. The comparisons were performed separately for peptides with high affinity towards CCK receptors of the A type (compounds I, II and III) and for peptides with high affinity towards CCK receptors of the B type (compounds I, II and IV). Possible models for CCK "A"- and "B"-receptor-bound conformations were then developed. The proposed CCK "B-conformation" has a distorted beta-III turn at the C-terminal Gly-Trp-Met-Asp fragment, the Phe33 residue and the C-terminal amide being directed outward from the turn. The CCK "A-conformation" has two reversals of the peptide chain so that the C alpha-atoms of the C-terminal pentapeptide appear at the corners of a nearly regular pentagon, and a distinct beta-II turn is centered at the N-terminal Tyr-Met-Gly-Trp fragment, the planes of the turn and the pentagon being almost perpendicular. The proposed models are consistent with the results of biological testing for CCK related peptides including cyclic analogs and CCK-A selective tetrapeptides.

Synthesis of human CCK26-33 and CCK-33 related analogues on 2,4-DMBHA and TMBHA

New analogues of human cholecystokinin in which the Tyr(SO3H) has been replaced by Phe(p-CH2SO3Na), methionines by norleucines, and tryptophan by 2-naphthylalanine([Phe(p-CH2- SO3Na)27,Nle28,31,Nal30]-CCK26-33 and [Phe(p-CH2SO3Na)27,Nle7,28,31,Nal30]-CCK-33) were synthesized by Fmoc solid phase methodology on two different resins (2,4- dimethoxybenzhydrylamine- and 4-(benzyloxy)-2',4'-dimethoxybenzhydrylamine resins, 2,4-DMBHA and TMBHA resins, respectively). While the syntheses on the TMBHA appeared to be more sluggish than those carried out on the 2,4-DMBHA, both final crude products were of equivalent relative purity and after purification gave approximately the same final yields of analogues estimated to have a purity greater than 93% using RPHPLC and CZE. The peptides were further characterized by amino acid analysis and LSIMS. Phe(p-CH2SO3Na)27,Nle7,28,31,Nal30]-CCK-33 was submitted to 33 Edman cycles and shown to be the desired product with less than 3% preview. Both analogues were tested for their ability to stimulate amylase release from isolated rat pancreatic acini. In this assay, [Phe(p-CH2SO3Na)27,Nle28,31,Nal30]-CCK26-33 and Phe(p-CH2SO3Na)27,Nle7,28,31,Nal30]-CCK-33 were 10 and 30 times less potent than CCK-8, respectively.

Development of potent and selective CCK-A receptor agonists from Boc-CCK-4: tetrapeptides containing Lys(N epsilon)-amide residues

A series of Boc-CCK-4 derivatives represented by the general structure Boc-Trp-Lys(N epsilon-COR)-Asp-Phe-NH2, where R is an aromatic, heterocyclic, or aliphatic group, are potent and selective CCK-A receptor agonists. These amide-bearing compounds complement the previously described urea-based tetrapeptides (Shiosaki et al. J. Med. Chem. 1991, 34, 2837-2842); structure-activity studies revealed parallel as well as divergent trends between these two series. A significant correlation was observed between pancreatic binding affinity and the resonance constant R of the phenyl substituent in one particular series of derivatives. Sulfation of phenolic amides appended onto the epsilon-amino group of the lysine did not affect affinity for the CCK-A receptor in contrast to the 500-fold increase in binding potency observed upon sulfation of CCK-8, suggesting that the lysine appendage and the sulfated tyrosine in CCK-8, both key structural elements that impart high affinity for the CCK-A receptor, are interacting differently with the receptor. The amide-bearing tetrapeptides are full agonists relative to CCK-8 in stimulating pancreatic amylase release while being partial agonists in eliciting phosphoinositide (PI) hydrolysis. Both effects were blocked by selective CCK-A receptor antagonists.

Structure activity of C-terminal modified analogs of Ac-CCK-7

Previous work indicates that both the C-terminal phenylalanine amide and the tryptophan moieties of cholecystokinin (CCK) are critical pharmacophores for interaction with either the A or B receptor subtypes. We have examined a series of analogs of Ac-CCK-7 [Ac-Tyr(SO3H)-Met-Gly-Trp-Met-Asp-Phe33-NH2] (2) in which the phenyl ring of the C-terminal Phe-NH2 has been modified. Compounds were assessed in binding assays using homogenated rat pancreatic membranes and bovine striatum as the source of CCK-A and CCK-B receptors respectively and for anorectic activity after intraperitoneal administration to rats. Substitution of a number of cycloalkyl or bicyclic aryl moieties for the phenyl ring of phenylalanine33 including cyclopentyl (20), cyclohexyl (21), cyclooctyl (23), 2-(5,6,7,8-tetrahydro)naphthyl (26), 2-naphthyl (27), and 1-naphthyl (29) led to analogs with 10-70 times the anorectic potency of 2. The anorectic activity of 21 was blocked by the specific CCK-A receptor antagonist MK-329. Other bulky aliphatic groups in place of the phenylalanine33 aromatic ring such as isopropyl, 2-adamantyl and cyclohexylmethyl gave derivatives similar to 2 in potency. While most of the new compounds were comparable to CCK in binding assays, 23, 26, 27 and 29 were exceptionally potent with IC50s 10(-11)-10(-14) M in the pancreas. Compounds 23 and 29 were further evaluated for their ability to stimulate amylase secretion and found to have potencies similar to that of CCK. The dissociation between potency in the binding and amylase secretion assays suggests that they may interact with a high affinity binding site which is not coupled to amylase secretion. We conclude that CCK receptors possess a generous hydrophobic pocket capable of accommodating large alkyl groups in place of the side chain of phenylalanine33 and that the pharmacological profile of CCK analogs can be tailored by appropriate exploitation of this finding.

Structure activity studies of tryptophan30 modified analogs of Ac-CCK-7

Cholecystokinin represents a family of gut hormones which among other activities, have been proposed to participate in satiety signaling. Ac-CCK-7[Ac-Tyr(SO3H)-Met-Gly-Trp30-Met-Asp-Phe-NH2 (2)] possesses the full spectrum of activity and potency of the intact hormone; thus analogs of 2 may be useful as anorectic agents. A series of derivatives has been prepared in which the tryptophan indole moiety of 2 has been modified. The new compounds were assayed in CCK binding assays using homogenated rat pancreatic membranes and bovine striatum as a source of CCK-A and CCK-B receptors respectively and in vivo in rats for anorectic activity. Although previous studies have concluded that the indole ring of Trp30 is a critical pharmacophore for the interaction of CCK with both its A and B type receptors, we find 2-Nal30-Ac-CCK-7 (20) to be nearly equipotent to 2 in both CCK binding and as an anorectic agent sensitive to blockade by the Merck CCK-A receptor antagonist MK-329. The extreme structural sensitivity of this anorectic activity is illustrated by the 1-naphthylalanine30 (19) and (benzo[b]thien-2-yl)alanine30 (21) analogs which are 30 and 100 times less potent than 2 respectively. Other mono- and bicyclic Trp30 replacements, including substituted phenylalanines, 3-quinolinylalanine, and 2-(5,6,7,8-tetrahydro)naphthylalanine, gave inactive compounds.

Isolation and amino acid sequences of opossum vasoactive intestinal polypeptide and cholecystokinin octapeptide

Evolutionary history suggests that the marsupials entered South America from North America about 75 million years ago and subsequently dispersed into Australia before the separation between South America and Antarctica-Australia. A question of interest is whether marsupial peptides resemble the corresponding peptides of Old or New World mammals. Previous studies had shown that "little" gastrin of the North American marsupial, the opossum, is identical in length to that of the New World mammals, the guinea pig and chinchilla. In this report, we demonstrate that opossum cholecystokinin octapeptide, like that of the Australian marsupials, the Eastern quoll and the Tamar wallaby, is identical to the cholecystokinin octapeptide of Old World mammals and differs from that of the guinea pig and chinchilla. However, opossum vasoactive intestinal polypeptide differs from the usual Old World mammalian vasoactive intestinal polypeptide in five sites: [sequence; see text].

Replacement of Tyr-SO3H by a p-carboxymethyl-phenylalanine in a CCK8-derivative preserves its high affinity for CCK-B receptor

The sulfated tyrosine present in the sequence of CCK8 Asp26-Tyr(SO3H)-Met-Gly-Trp-Met-Asp-PheNH2, seems to play a critical role in the recognition of CCK-A binding sites. In this work, we have investigated whether the presence of an anionic charge on the tyrosine moiety is strictly necessary and whether the sulfate moiety interacts with a divalent cation in the receptor subsite. For this purpose, the novel amino acids (L,D)Phe(p-CH2CO2H) and (L,D) Phe(p-CH2CONHOH), as well as their L-resolved forms were introduced into the sequence of Ac[X27, Nle28, Nle31]-CCK27-33 by solid phase method. The biological activities of these new derivatives were compared to two almost equiactive analogues of CCK8, Ac[Phe(p-CH2SO3H)27, Nle28, Nle31]-CCK27-33 and Boc[Nle28, Nle31]-CCK27-33 (BDNL) and to the nonsulfated analogue of the latter peptide (BDNL NS). All these new CCK-related analogues behave as agonists in stimulating pancreatic amylase release and display high affinity for brain binding sites (KI approximately 3-11 nM) but the only peptides which retain affinity for CCK-A receptors (KI approximately 20 nM) are those containing a p-carboxymethyl phenylalanine. Thus, introduction of this amino acid under an esterified form on the side chain, into specific and potent CCK-B agonists could allow compounds endowed with good bioavailabilities to be obtained.

Application of 2-chlorotrityl resin in solid phase synthesis of (Leu15)-gastrin I and unsulfated cholecystokinin octapeptide. Selective O-deprotection of tyrosine

The carboxyl terminal dipeptide amide, Fmoc-Asp-Phe-NH2, of gastrin and cholecystokinin (CCK) has been attached in high yield through its free side chain carboxyl group to the acid labile 2-chlorotrityl resin. The obtained peptide resin ester has been applied in the solid phase synthesis of partially protected (Leu15)-gastrin I utilising Fmoc-amino acids. Quantitative cleavage of this peptide from resin, with the t-butyl type side chain protection intact is achieved using mixtures of acetic acid/trifluoroethanol/dichloromethane. Under the same conditions complete detritylation of the tyrosine phenoxy function occurs simultaneously. Thus, the solid-phase synthesis of peptides selectively deprotected at the side chain of tyrosine is rendered possible by the use of 2-chlorotrityl resin and Fmoc-Tyr(Trt)-OH. The efficiency of this approach has been proved by the subsequent high-yield synthesis of three model peptides and the CCK-octapeptide.

Hyperstimulation pancreatitis in mice induced by cholecystokinin octapeptide, caerulein, and novel analogues: effect of molecular structure on potency

Acute pancreatic oedema with hyperamylasaemia was induced in mice by subcutaneous administration of cholecystokinin octapeptide (CCK8). Comparison with effect of caerulein showed that cholecystokinin is less potent in vivo. To investigate the observed difference in response, threonine3 CCK8 and methionine5 caerulein were synthesised and evaluated. Comparison of these peptides suggests that difference in bioactivity is related to possession of extra N-terminal residues rather than substitution of threonine for methionine.

Synthetic CCK8 analogs with antagonist activity on pancreatic receptors: in vivo study in the rat, compared to non-peptidic antagonists

The cholecystokinin octapeptide (CCK8)-derived synthetic peptides Boc-Tyr(SO3H)-Nle-Gly-DTrp-Nle-Asp-O-CH2-CH2-C6H5 (JMV179) and Boc-Tyr(SO3H)-Nle-Gly-DTrp-Nle-Asp-NH-CH2-CH2-C6H5 (JMV167) are antagonists of peripheral cholecystokinin (CCK) receptors in vitro. In the present study, antagonist activity of these peptides was studied on rat pancreatic secretion in vivo, and compared to those of other peptidic molecules and to the non-peptidic antagonists L364718, D-, L-, DL-lorglumide, and proglumide. The decreasing order of antagonist potencies on amylase release in vitro was L364718 greater than JMV179 greater than lorglumide greater than JMV167 greater than proglumide; JMV179 was 25 times less potent than L364718 and 300 times more potent than JMV167. The decreasing order of antagonist potencies on protein output in pancreatic juice in vivo was L364718 greater than JMV167 greater than JMV179 greater than lorglumide greater than proglumide; JMV167 was two times more potent than JMV179 and only 8 times less potent than L364718. Increased potency of JMV167, relative to JMV179 under in vivo conditions, is probably due to the slower rate of catabolism of the phenylethylamide group, relative to the phenylethylester group, since the metabolite issued from hydrolysis of the ester bond was totally inactive. This study shows that it is possible to obtain peptidic CCK antagonists, which are active and potent in vivo, and provides a quantitative measurement of potency changes occurring in vivo for several peptidic and non-peptidic antagonists.

Solid phase synthesis of a fully active analogue of cholecystokinin using the acid-stable Boc-Phe (p-CH2) SO3H as a substitute for Boc-Tyr(SO3H) in CCK8

Substitution of the -OSO3H group in the sulfated-tyrosine by the non-hydrolyzable-CH2SO3H group was the first described modification of the sulfate ester that does not affect CCK8 activity. In addition to its capacity to mimic the sulfated tyrosine residue, the amino acid Phe(p-CH2SO3Na) was shown to be stable in acidic media, including HF containing mixtures. The synthesis of Boc-Phe(p-CH2SO3Na)-OH in racemic and resolved forms and its introduction into the sequence of CCK8 by solid phase using standard Boc/benzyl synthesis conditions and BOP as coupling reagent is now reported. The two CCK8 analogues containing the L- or the D-Phe(p-CH2SO3Na) residue, obtained in satisfactory yields, were separated by HPLC and the stereochemistry of Phe(p-CH2SO3Na) residue in each peptide was established by NMR spectroscopy and confirmed by a separate solid phase synthesis in which the pure L isomer was used. Both CCK8 analogues displayed high affinities for peripheral and central receptors (KI approximately 1 nM) and proved to be full agonists in the stimulation of pancreatic amylase secretion. The "stabilized-CCK8 peptide", easily prepared by solid phase, could replace the native peptide in biochemical and pharmacological studies. Moreover the modified amino acid Phe (p-CH2SO3Na) could also be used in solid phase synthesis to prepare a wide variety of CCK analogues and more generally, peptides analogues containing the acid-labile O-sulfated tyrosine.

Effects of a new cholecystokinin antagonist (GE 410) on the smooth muscle of the guinea pig ileum

Suc-Tyr-(SE)-Met-Gly-Trp-Met-Asp-beta-phenethylamide (GE 410) competitively antagonized the contractions of smooth muscle strips from guinea pig ileum (pA2 = 7.6, n = 0.95) induced by cholecystokinin-octapeptide (CCK8). GE 410 inhibited the electrically-induced cholinergically mediated contractile responses and the [3H]ACh release in the ileum, as well as the CCK-stimulated electrical contractile responses and the [3H]ACh release in the cholinergic nerve terminals. The results suggest the existence of CCK-receptors not only in the smooth muscles but also on the neurons.