Torsion angle based design of peptidomimetics: a dipeptidic template adopting beta-I turn (Ac-Aib-AzGly--NH(2))

We have attempted to design a model dipeptide (acetyl dipeptide amide, Ac-CA1-CA2--NH(2)) that can adopt specifically typical torsion angles of the beta-I turn (phi(i+1), psi(i+1), phi(i+2), psi(i+2)=-60 degrees, -30 degrees, -90 degrees, 0 degrees ). The key of the design is the combination of constrained amino acids that prefer to adopt the desired torsion angles. We chose Aib (aminoisobutyric acid) as the first residue of which phi and psi angles must be -60 degrees and -30 degrees, respectively. Then, we selected an azaamino acid as the second residue since previous studies have indicated that they prefer to adopt +/-90 degrees of phi angle and 0 degrees or 180 degrees of psi angle. The conformational preference of the resulting Ac-Aib-AzGly--NH(2) is investigated using ab initio methods. The conformations implying beta-I and beta-I' turns are energetically most favorable, as we expected. Thus, we synthesized the designed molecule on the solid phase considering the future generation of combinatorial libraries using an automatic peptide synthesizer. Then, NMR spectroscopy was carried out to confirm their conformational preference in solution was carried out. The results indicated that the Ac-Aib-AzGly--NH(2) adopt beta-I or beta-I' turns in solution forming an intramolecular hydrogen bonding between Ac--C(O) and terminal NH(2). We believe that such a small peptidomimetic template is highly useful for the design of drug candidates and molecular devices.

Novel voltage-dependent non-selective cation conductance in murine colonic myocytes

1. Two components of voltage-gated, inward currents were observed from murine colonic myocytes. One component had properties of L-type Ca(2+) currents and was inhibited by nicardipine (5 x 10(-7) M). A second component did not 'run down' during dialysis and was resistant to nicardipine (up to 10(-6) M). The nicardipine-insensitive current was activated by small depolarizations above the holding potential and reversed near 0 mV. 2. This low-voltage-activated current (I(LVA)) was resolved with step depolarizations positive to -60 mV, and the current rapidly inactivated upon sustained depolarization. The voltage of half-inactivation was -65 mV. Inactivation and activation time constants at -45 mV were 86 and 15 ms, respectively. The half-recovery time from inactivation was 98 ms at -45 mV. I(LVA) peaked at -40 mV and the current reversed at 0 mV. 3. I(LVA) was inhibited by Ni(2+) (IC(50) = 1.4 x 10(-5) M), mibefradil (10(-6) to 10(-5) M), and extracellular Ba(2+). Replacement of extracellular Na(+) with N-methyl-D-glucamine inhibited I(LVA) and shifted the reversal potential to -7 mV. Increasing extracellular Ca(2+) (5 x 10(-3) M) increased the amplitude of I(LVA) and shifted the reversal potential to +22 mV. I(LVA) was also blocked by extracellular Cs(+) (10(-4) M) and Gd(3+) (10(-6) M). 4. Warming increased the rates of activation and deactivation without affecting the amplitude of the peak current. 5. We conclude that the second component of voltage-dependent inward current in murine colonic myocytes is not a 'T-type' Ca(2+) current but rather a novel, voltage-gated non-selective cation current. Activation of this current could be important in the recovery of membrane potential following inhibitory junction potentials in gastrointestinal smooth muscle or in mediating responses to agonists.

[Drug sensitivity, conjugative R plasmids and plasmid profiles of Salmonella isolated from humans with infectious enteritis]

Using 92 Salmonella strains isolated from patients suspected of having infectious diseases of the intestinal tract who visited 13 hospitals in Japan during the six years between 1991 and 1996, we investigated the drug susceptibility, prevalence of conjugative R plasmid, and the plasmid profiles. 1) Of the bacterial isolates tested, 52.2% showed drug-resistance. Regarding the drug-resistance patterns, 70.8% of the isolates were resistant to a single drug, while 29.2% were multi drug-resistant. 2) Dividing the resistance patterns by the serotypes, among Salmonella Enteritidis isolates, single-drug resistance to SM was the most frequent, being detected in 27 isolates. Single-drug resistance to NA and two-drug resistance to SM/TC were the second-most frequent, each being detected in isolates. Among Salmonella Hadar isolates, four isolates showed two-drug resistance to SM/TC, and one isolate showed single-drug resistance to TC. Among Salmonella Typhimurium isolates, one isolate each showed three-drug resistance to ABPC/CER/KM and KM/TC/CP. Among Salmonella Agona isolates, one isolate each showed two-drug resistance to SM/TC and single-drug resistance to SM. Among Salmonella Derby isolates, two isolates showed single-drug resistance to SM. 3) The prevalence of conjugative R plasmid was investigated in 48 drug-resistant isolates, and six isolates (12.5%) contained the plasmid. 4) The prevalence of the plasmid was investigated in 29 drug-resistant S. Enteritidis isolates, and 22 isolates (75.9%) contained the plasmid. These isolated were classified by the plasmid profiles into types H1 to H7. 5) Regarding the plasmid profiles of the S. Enteritidis isolates, a position corresponding to 60 Kbp was the most frequently detected in 90.5%.

Dynamic hemicarcerands and hemicarceplexes

The reversible nature of the imine bond formation in CDCl(3) solution has been exploited to exchange substituted for unsubstituted m-phenylenediamine (MPD) units in hemicarcerand octaimines. Moreover, acid-catalyzed imine exchange has been shown to provide a novel mechanism whereby ferrocene (Fc) can be released as an entrapped guest from the hemicarceplex C(2)B(4)&crcldt;Fc dissolved in CDCl(3) to give the hemicarcerand C(2)B(4) when excess of both MPD and trifluoroacetic acid are present.

Role of azaamino acid residue in beta-turn formation and stability in designed peptide

The structural perturbation induced by C(alpha)-->N(alpha) exchange in azaamino acid-containing peptides was predicted by ab initio calculation of the 6-31G* and 3-21G* levels. The global energy-minimum conformations for model compounds, For-azaXaa-NH2 (Xaa=Gly, Ala, Leu) appeared to be the beta-turn motif with a dihedral angle of phi= +/- 90 degrees, psi=0 degrees. This suggests that incorporation of the azaXaa residue into the i+2 position of designed peptides could stabilize the beta-turn structure. The model azaLeu-containing peptide, Boc-Phe-azaLeu-Ala-OMe, which is predicted to adopt a beta-turn conformation was designed and synthesized in order to experimentally elucidate the role of the azaamino acid residue. Its structural preference in organic solvents was investigated using 1H NMR, molecular modelling and IR spectroscopy. The temperature coefficients of amide protons, the characteristic NOE patterns, the restrained molecular dynamics simulation and IR spectroscopy defined the dihedral angles [ (phi i+1, psi i+1) (phi i+2, psi i+2)] of the Phe-azaLeu fragment in the model peptide, Boc-Phe-azaLeu-Ala-OMe, as [(-59 degrees, 127 degrees) (107 degrees, -4 degrees)]. This solution conformation supports a betaII-turn structural preference in azaLeu-containing peptides as predicted by the quantum chemical calculation. Therefore, intercalation of the azaamino acid residue into the i+2 position in synthetic peptides is expected to provide a stable beta-turn formation, and this could be utilized in the design of new peptidomimetics adopting a beta-turn scaffold.

Water extract of Helicobacter pylori stimulates interleukin-8 secretion by a human gastric epithelial cell line (JR-St) through protein tyrosine phosphorylation

BACKGROUND

Infection by Helicobacter pylori induces cytokine production in gastric mucosal cells. Production of interleukin-8 (IL-8) is known to be markedly increased and is believed to play an important role in gastric mucosal inflammation. The aim of this study was to elucidate the effects of soluble factors of H. pylori on IL-8 production in a gastric epithelial cell line, JR-St.

METHODS

JR-St cells were cocultured with a H. pylori water extract, live H. pylori or culture medium supernatant for 24 h, then the IL-8 secreted into the culture medium was assayed. The effects of three different inhibitors; (i) an inhibitor of protein kinase C (PKC); (ii) an inhibitor of PKC and protein kinase A (PKA); and (iii) an inhibitor of protein tyrosine kinase (PTK) were also compared. Specific induction of IL-8 mRNA was also examined.

RESULTS

Water extract of H. pylori increased IL-8 secretion 7.72-fold, more than the control. The increase was concentration dependent. Live bacteria, supernatant and water extract significantly stimulated IL-8 secretion. Addition of live bacteria increased IL-8 secretion most strongly, while the effect of water extract was small (22% that of live bacteria). Secretion was not inhibited by the PKC inhibitor staurosporine or the inhibitors of PKA and PKC H7. However, secretion was significantly reduced by the PTK inhibitor herbimycin in a dose-dependent manner. Furthermore, 24 h exposure to water extract increased IL-8 mRNA expression, suggesting water extract increased production of IL-8.

CONCLUSIONS

Some soluble factors of H. pylori can stimulate IL-8 production by JR-St cells. Stimulation was not dependent on PKA or PKC but was, at least partially, dependent on protein tyrosine phosphorylation. This suggests that soluble factors of H. pylori can play an important role in mediating the inflammatory response of H. pylori gastritis.

Stimulatory effect of growth in the presence of alcohols on biotransformation of penicillin G into cephalosporin-type antibiotics by resting cells of Streptomyces clavuligerus NP1

Growth of Streptomyces clavuligerus NP1 in the presence of methanol or ethanol resulted in a marked increase in production of cephalosporin(s) from penicillin G by resting cells. The mycelium produced in alcohol-supplemented medium was fragmented and dispersed as compared with growth in control medium. HPLC analysis showed that at least two products were present in the biotransformation supernatant fluid after 1 h incubation. One of them has been identified as deacetoxycephalosporin G (DAOG).

Conformational studies of irreversible HIV-1 protease inhibitors containing cis-epoxide as an amide isostere

We have carried out NMR and molecular modeling studies of peptidomimetic HIV-1 protease inhibitors, LB71116: Qc-Asn-Phepsi[(1R,2S)-cis-epoxide]Gly-NH-CH(isopropyl)2 where Qc stands for quinaldic acid and LB71148: Qc-(SMe)Pen(O)2-Phepsi[(1R,2S)-cis-epoxide]Gly-NH-CH(isoprop yl)2 where (SMe)Pen(O)2 stands for S-methyl-S-dioxo-penicillamine. Through conformational calculations and NMR data analysis, we have obtained preferred conformations of the two inhibitors in solution. To our knowledge, this work is one of the first extensive conformational studies of peptidomimetics containing cis-epoxide amide isostere. The resulting preferred conformations contain extended structures. In these conformations, the psi of Phe(cep) is maintained about 130 degrees and the phi angle of (cep)Gly prefers +/- 150 degrees [where Phe(cep) and (cep)Gly are the residues generated by the replacement of the Phe-Gly peptide bond with cis-epoxide]. Two conformations were commonly observed in the preferred conformations of each inhibitor. Through restrained molecular dynamics simulating the hydrogen bond formation between our inhibitor and a water molecule ('flap water'), one of the conformations is assumed as the conformation which can bind to the enzyme without large conformational changes. Recently, we had the opportunity to compare the selected preferred conformation with the binding conformation of LB71116 observed from the X-ray studies of the complex between LB71116 and HIV-1 protease. These two conformations are surprisingly similar to each other. Thus, we can explain high activity and selectivity of our inhibitors to the HIV-1 protease by the similarity between the preferred conformations in solution and the binding conformation.

Concentrations of C-reactive protein in normal monkeys (Macaca irus) and in monkeys inoculated with Bordetella bronchiseptica R-5 and measles virus

The concentrations of C-reactive protein (CRP) in serum from normal crab-eating monkeys (Macaca irus) were measured by means of a monkey-specific turbidimetric immunoassay (TIA), and the changes in the serum CRP concentrations in crab-eating monkeys inoculated with Bordetella bronchiseptica R-5 and measles virus (Ichinose or NK 3 strain) were also examined. The CRP concentrations in sera from 54 normal crab-eating monkeys ranged from 0 to 8.3 microg/ml (mean 2.2 +/- 1.9). No significant difference was found in the CRP concentrations between males and females (p > 0.05). The concentrations of CRP in the sera from four crab-eating monkeys inoculated intrabronchially with 10(9) live B. bronchiseptica increased gradually to a peak at 2 days after inoculation. The peak concentrations of CRP were from 102.4 to 313.2 microg/ml, 54-96 times the preinoculative values of 1.9-5.6 microg/ml. When the same four crab-eating monkeys were inoculated intrabronchially with measles virus 34 days after inoculation of B. bronchiseptica, the serum CRP concentrations did not increase. Monitoring of CRP is useful for assessing monkeys with acute B. bronchiseptica infection and will probably be of value in the diagnosis of other bacterial infections.

Solid phase synthesis of azapeptides using an automatic synthesizer

Peptides containing azaglycine located terminally or within the backbone have been prepared in the solid phase by means of an automatic synthesizer.

Increased serum levels and sinusoidal expression of thrombomodulin in acute liver damage

Thrombomodulin (TM) is a surface glycoprotein of endothelial cells involved in both anticoagulation and antifibrinolysis. In this study, we assessed the clinical significance of TM in acute liver damage by using a rat model induced by intraperitoneal injection of D-galactosamine (Gal-N). Serum TM levels were measured with enzyme immunoassay utilizing rabbit anti-rat TM antibody. Simultaneously, immunohistochemical examination was performed using the same antibody. Serum TM levels increased significantly after the injection of Gal-N compared with preinjection levels, peaking from 48 to 72 hours after injection and normalizing by 168 hours. Changes in parenchymal damage were synchronized with changes of TM, and changes of TM levels mirrored changes of liver weight. In immunohistochemical examination, TM immunoreactivity was observed only on the endothelial surfaces of both the artery and portal vein within Glisson's sheath in controls. After injection of Gal-N, TM immunoreactivity was gradually intensified, especially around the necrotic area and the central veins. These findings disappeared with improvement of parenchymal damage. Both the increase of serum TM levels and intensified TM immunoreactivity in the liver were synchronized with acute liver parenchymal damage induced by Gal-N. These findings on TM are related to endothelial damage with parenchymal necrosis and liver regeneration interacting with both homeostasis of microcirculation and healing of parenchymal damage.

Interleukin-8 enhances tetragastrin-stimulated acid secretion in vivo

Recent studies have demonstrated a relationship between cytokines and gastric acid secretion. However, details of the mechanism underlying that relationship have not been elucidated. For this study, an in vivo experiment was undertaken to investigate the possibility that IL-8 would be involved in the mechanism of gastric acid secretion. Gastric lumen-perfused rats were prepared and the stomachs were perfused with a saline solution. The effluent was collected at 15-min intervals and assayed for titratable acid against 0.01 M NaOH. IL-8 (200 ng/rat) given intravenously did not influence basal acid output in rats. However, when IL-8 was administered by injection during continuous tetragastrin infusion (4 microg/kg/hr) acid output increased significantly (P < 0.01). The acid output during the first hour following IL-8 injection was 43.6% higher than prior to the injection. Acid output during the second hour was lower than during the first hour. However, successive injection of IL-8 again increased tetragastrin-stimulated acid output by 23.4% (P < 0.05). IL-8 injection did not change histamine-stimulated acid output. The results indicate that IL-8 has the effect of enhancing gastrin-stimulated acid secretion and might have an important role in the pathophysiology of gastric acid secretion in vivo.

NMR and topochemical studies of peptidomimetic HIV-I protease inhibitors containing a cis-epoxide amide isostere

NMR and topochemical studies of irreversible HIV-1 protease inhibitors containing a cis-epoxide as amide isostere have been carried out to identify conformational preference of the inhibitors in solution. The inhibitors prefer to adopt extended conformations similar to the beta-strand in solution.

Solution and solid phase combinatorial synthesis of peptidomimetic library containing diversified alpha-methylated amino acids

A combinatorial peptidomimetic library containing diversified alpha-methylated amino acids was generated by the Ugi four component condensation (4cc) reaction from acids, amines, isocyanides and ketones in both solution and solid phase synthetic procedures. This one-pot methodology overall gave fair to good yields, which compare well with multi-step syntheses.

Plasma from patients with cirrhosis increases tissue plasminogen activator release from vascular endothelial cells in vitro

AIMS/BACKGROUND

In patients with severe liver disease, blood levels of many coagulation and fibrinolytic factors are lowered due to a diminished synthetic capability in the liver. Tissue plasminogen activator (t-PA) is synthesized by the vascular endothelial cells, however, and is increased in such patients.

METHODS

Amounts of t-PA secreted were determined by immunosorbent assay after plasma from patients with cirrhosis was added to cultured human umbilical vein endothelial cells to determine whether a plasma factor directly enhanced t-PA secretion from vascular endothelial cells.

RESULTS

Release of t-PA was significantly higher with exposure to plasma from patients with decompensated cirrhosis than when plasma from patients with compensated cirrhosis or normal subjects was used (p < 0.01 and p < 0.05, respectively). Plasminogen activator inhibitor 1 (PAI-1) concentrations were measured similarly but did not differ among the three groups.

CONCLUSIONS

Our results indicate that factors in plasma from patients with decompensated cirrhosis directly stimulate t-PA release from the vascular endothelial cells, while any increased PAI-1 release observed in comparable in vivo situations is probably an indirect response to an increase of t-PA or a result of impaired hepatic clearance.

Solid phase synthesis of benzamidine and butylamine-derived hydantoin libraries

We have constructed a number of benzamidine- and butylamine-based hydantoin compounds by means of an efficient route using solid phase synthesis in which neat diisopropylamine was employed for a novel cyclization/traceless cleavage step. All library compounds were obtained in excellent yield and high purity.

Characterization of the spinal antinociceptive activity of constrained peptidomimetic opioids

We examined the in vitro and in vivo bioactivities of several families of peptidomimetic opioids including: constrained linear enkephalin (n = 12 analogs), dermorphin (n = 9 analogs) and morphiceptin (n = 17 analogs). The biological activities were assessed in vitro by examining the inhibitory effects of these agents on the electrically evoked contractions of the guinea pig ileum (GPI) and the mouse vas deferens (MVD) preparations. The in vivo bioactivities were determined from the antinociceptive activity of these agents on the 52.5 degrees C hot-plate test after spinal administration of rats with chronically placed spinal catheters. Examination of the effect of cyclization, incorporation of retro-inverso bonds and substitutions of D- or constrained amino acids reveals systematic changes in the activity of these agents. There was a significant correlation between the potency of these agents in the hot-plate bioassay and their activity in the GPI and, to a lesser extent, in the MVD tests. Examination of the ability of naltrindole (a delta selective antagonist) to reverse the drug action and the respective potency on the GPI and MVD, showed that a correlation exists with actions on the MVD, but not on the GPI, consistent with the likelihood that agents with high MVD/GPI ratios in vitro act at the mu sites, whereas those with low MVD/GPI ratios act at the delta receptor in the spinal cord. The close correlations between activity in the GPI and spinal cord suggest that the structural requirements for potency in the smooth muscle and in the spinal cord are essentially the same as those mu receptors that mediate nociceptive transmission.

[Changes in plasma tissue plasminogen activator (t-PA) and plasminogen activator inhibitor 1 (PAI-1) by the interferon treatment for chronic hepatitis C]

To determine the effects of interferon (IFN) treatment for chronic hepatitis C on vascular endothelium, we measured the concentrations of tissue plasminogen activator (t-PA) and its inhibitor (PAI-1) in the plasma from patients before and after IFN treatment for 14 consecutive days. The plasma t-PA and PAI-1 levels were measured before and after treatment. The plasma t-PA level was significantly increased after IFN treatment (p < 0.01) but no significant difference in plasma PAI-1 level was observed before and after treatment. The ratio of t-PA/PAI-1 was significantly increased after IFN treatment (p < 0.05). These changes may be caused by the effect of IFN on endothelium, leading to an activation of the endothelium derived fibrinolysis factors. Increase in plasma t-PA concentration may induce hyperfibrinolysis which may be one of the causes of suborbital hemorrhage. Further study on the fibrinolysis pathway in the blood is necessary to elucidate the mechanisms of the many side effects observed during IFN treatment.

Highly potent side chain-main chain cyclized dermorphin-deltorphin analogues: an integrated approach including synthesis, bioassays, NMR spectroscopy and molecular modelling

Our continuing efforts to study structure-activity relationships of peptide opioids have resulted in the synthesis of a series of cyclic opioids related to dermorphins and deltorphins. The biological activities of the compounds have been determined and the conformational analyses carried out using 1H-NMR spectroscopy and molecular modelling. The three compounds in the series Tyr-c[D-Orn-Phe-Ala], Tyr-c[D-Lys-Phe-Ala], and Tyr-c[A2bu-Phe-Ala-Leu] are cyclized via a lactam bridge from the side-chain of the residue at the second position with the carboxyl terminus of each compound. The molecules incorporate 12-, 13- and 14-membered rings, respectively. They include a phenylalanine at the third position which is a distinguishing characteristic of dermorphins and deltorphins. The guinea pig ileum and mouse vas deferens assays show that the compounds are highly active at both mu- and delta-opioid receptors. The compounds are all highly effective antinociceptive agents as measured by the intrathecal rat hot plate test. Conformational analyses of the molecules indicate that they can adopt topochemical arrays required for bioactivity at both mu- and delta-receptors which explains their high activity in both guinea pig ileum and mouse vas deferens in vitro assays. The results support our models for mu- and delta-receptor activity for constrained peptide opioids.

A topochemical approach to explain morphiceptin bioactivity

A topochemical model to explain the bioactivity of morphiceptin (Tyr1-Pro2-Phe3-Pro4-NH2) was developed by taking account of accessible conformations around rotatable bonds which define relative spatial arrangements of opioid pharmacophores, the amine and phenolic groups of tyrosine and the aromatic ring of phenylalanine, necessary for receptor recognition. For this purpose, 1H-NMR measurements and computer simulations were extensively carried out on 10 stereoisomeric analogs related to morphiceptin: Tyr-Pro-(L and D)-Phe- (L and D)-Pro-NH2; Tyr-Pro-(L and D)-(NMe)Phe-(L and D)-Pro-NH2; Tyr-(NMe)Ala-Phe-D-Pro-NH2; and Tyr-Ala-Phe-D-Pro-NH2. These analogs are structurally close to one another but display various opiate potencies from highly active to inactive. The conformation of each rotatable bond has been specifically identified by measuring accessible space for the analogs, in which the difference in composition is observed in the specific site affecting only the conformation around the target bond. The most interesting characteristic of the model is a requirement of a cis amide bond linking residues 1 and 2. The model also requires the side chains in a trans conformation (chi 1 = 180 degrees) for the Tyr and Phe residues. The distances between the three pharmacophores, d1 (Tyr N to Tyr OH), d2 (Tyr N to the center of the aromatic ring of the third residue), and d3 (Tyr OH to the center of the aromatic ring of the third residue), were found to be approximately 8, approximately 7, and approximately 11-13 A, respectively. This model should aid in pharmaceutical design of peptide and nonpeptide ligands with opioid potencies.

Topochemical design of bioactive peptides and peptidomimetics

For the studies of bioactive peptides, our laboratories have been employed an integrated approach including synthesis, bioassays, and conformational analysis. To obtain highly potent, selective and metabolically stable analogs, peptidomimetics such as peptide backbone modifications (retro-inverso structures), constrained amino acids, and cyclic structures have been incorporated into many bioactive peptide sequences. The conformational studies of the resulting analogs have led to topochemical models for the bioactivities of those peptides. This lecture will be focused on the results of such studies on opioids and somatostatin. We have synthesized numerous opioid analogs with various peptidomimetics based on three classes: enkephalins, dermorphin-deltorphins, and morphiceptins. Many of these analogs exhibit high potency, selectivity, and metabolic stability. Conformational studies of these analogs have enabled us to define the structural characteristics necessary for bioactivities of morphiceptins, dermorphins, enkephalins, and deltorphins. From these results, we can propose conformational models responsible for bioactivities at the mu- and delta-receptors. Our studies of cyclic somatostatin analogs are based on the highly active Merck analog c(-Pro6-Phe7-D-Trp8-Lys9-Thr10-Phe11-) (where the superscripts denote position in native somatostatin). To investigate the topochemical preference of backbone and side chains, unusual amino acids, including beta-methylphenylalanine7 or 11, beta-methyltryptophan8, as well as backbone modifications such as retro-inverso structures have been incorporated. The bioactivity profiles of these peptidomimetic molecules provide much information on the effects of backbone and side chain constraints on bioactivity.