Biomedical subjects

W Zeng

Publications and source records attributed to W Zeng.

131 records · Page 8Linked to original sources

PubMedDate not supplied

Natural peptides as building blocks for the synthesis of large protein-like molecules with hydrazone and oxime linkages.

Methods are known for the production of synthetic protein-like molecules of nonlinear architecture with molecular masses in the 10-20 kDa range. To synthesize such compounds of higher molecular mass and complexity, chemoselective ligation of natural (as opposed to synthetic) peptide building blocks was studied. In preliminary experiments with model peptides, conditions for the formation of peptide oximes were investigated, and their stability at alkaline pH was examined, to resolve a literature controversy. It was found that low pH (down to 2.1) was suitable for polyoxime formation and that the oxime bond was stable for up to 65 h at pH 8 and for more than 2 h at pH 9. Then, using natural peptides, it was found to be possible to synthesize, and characterize by mass spectrometry, nine-component species with molecular masses > 48 kDa. This is about twice the size of homogeneous artificial proteins previously described. Such complex molecules of defined structure are beginning to find applications as vaccine candidates, as radioimmunodiagnostic agents, and as nonviral gene therapy delivery vehicles.

Chromatography, High Pressure Liquid↗

PubMedDate not supplied

New cyclization reaction at the amino terminus of peptides and proteins.

Mild oxidation with periodate of the 1-amino-2-ol moiety of N-terminal seryl or threonyl peptides and proteins leads to a terminal aldehyde function O=CH-CO- which usually may be exploited for bioconjugate formation (e.g., via oximation with an O-alkyl hydroxylamine). We report that, when followed by a prolyl residue, the O=CH-CO- group can undergo a rapid cyclization and dehydration reaction through nucleophilic attack by the amide nitrogen of the third amino acid residue of the chain. We have characterized the resulting heterocycle, which is stable in aqueous acid, by mass spectrometry and NMR. Quantitative oximation can nevertheless be achieved in such cases by performing a one-pot oxidation-oximation without isolation of the intermediate aldehyde, as is demonstrated with cholera toxin B subunit.

Aldehydes↗

PubMedDate not supplied

Histamine receptor type coupled to nitric oxide-induced relaxation of guinea-pig nasal mucosa.

1 The aim of this study was to characterize the histamine receptor type mediating relaxation of the vascular bed of the nasal mucosa from the guinea-pig, and to determine the role of cyclo-oxygenase products and nitric oxide in this relaxant response to histamine. These studies were performed in isolated nasal mucosae examined in vitro to obtain potencies of histamine receptor-type selective agonists in causing vasorelaxation and to determine affinities of histamine receptor antagonists for inhibiting histamine-induced relaxation. 2 After contraction of nasal mucosae with noradrenaline, histamine caused a maximal relaxation response that was 75 +/- 6% of the contraction caused by noradrenaline with a mean EC50 value of 4.3 +/- 0.5 microM. Neither dimaprit (H2-receptor selective) nor R-alpha-methylhistamine (H3-receptor selective) caused significant relaxation of nasal mucosae. In contrast, betahistine (H1-receptor selective) caused an 81 +/- 7% relaxation of noradrenaline-induced tone with an EC50 value of 15 +/- 1 microM. 3 pA2 experiments were performed to obtain KB values of chlorpheniramine (H1-receptor selective) and diphenhydramine (H1-receptor selective) for blocking histamine-stimulated relaxation of nasal mucosae. KB values for chlorpheniramine (0.87 nM) and diphenhydramine (7.4 nM) were consistent with their interaction at the H1-receptor type. Additionally, neither 10 microM cimetidine (H2-receptor selective) nor 1 microM thioperamide (H3-receptor selective) had any effect on the relaxation curve for histamine. 4 In the presence of 10 microM indomethacin (cyclo-oxygenase inhibitor), histamine caused a maximal relaxation response of 73 +/- 5% of the noradrenaline-induced tone with an EC50 value of 2.9 +/- 0.2 microM, which was not different from control values (EC50 = 5.0 +/- 0.4 microM; maximal relaxation = 71 +/- 6%). In contrast, 200 microM NG-nitro-L-arginine (nitric oxide synthase inhibitor) completely inhibited histamine-induced relaxation of nasal mucosae. 5 In conclusion, data from the present study suggest only the H1-receptor type mediates relaxation of nasal mucosal blood vessels to histamine, and histamine-induced relaxation of nasal mucosae is entirely dependent on nitric oxide production.

Adrenergic alpha-Agonists↗

PubMedDate not supplied

Characterization of beta-adrenergic receptors in DiFi and HT-29 cells.

The beta-adrenergic receptors present in two human colorectal adenocarcinoma cell lines were characterized by measuring specific binding of [125I]-cyanopindolol (CYP). Whole, cultured, DiFi (derived from a familial adenomatous polyposis [FAP] patient) and HT-29 cells were used in radioligand binding assays. Scatchard analysis of specific 125I-CYP binding gave KDS of 38.6 +/- 5.7 pM in DiFi cells and 54 +/- 9.1 pM in HT-29 cells. However, binding site density (Bmax) in the DiFi cells was greater than that in HT-29 cells. In DiFi cells, the kinetically determined KD was similar to that calculated from Scatchard analysis. Studies in DiFi cells of the displacement of specific 125I-CYP binding by nonselective (propranolol), beta 1-selective (metoprolol and atenolol), and beta 2-selective (ICI 118-551) antagonists revealed only a single class of beta 2-adrenergic receptors. This provides the first evidence that colorectal adenocarcinoma cell lines contain beta-adrenergic receptors and shows that only beta 2-adrenergic receptors are present in DiFi cells. Mechanisms possibly affecting beta-adrenergic-receptor expression in such cells are discussed in relation to colon carcinogenesis.

Adenocarcinoma↗

PubMedDate not supplied

The role of spermatozoa in the pathogenesis of Chlamydia trachomatis salpingitis in a primate model.

BACKGROUND AND OBJECTIVES: The role of spermatozoa in carrying microorganisms from the cervix to the fallopian tubes and promoting infection was examined in eight pig-tailed macaques. GOAL OF THIS STUDY: The aim of this study was to determine whether spermatozoa play a role in the transport of Chlamydia trachomatis into the upper reproductive tract and in the pathogenesis of chlamydial salpingitis. STUDY DESIGN: Five monkeys were inoculated with Chlamydia trachomatis in the cervix and mated, and three other monkeys were infected in the cervix but not mated. RESULTS: Culture positive results were obtained for cervical samples from all animals. After cervical inoculation, no mated animals and one unmated animal had positive culture results for samples from the fallopian tubes. After mating, no spermatozoa examined in samples taken from the upper tract or cul de sac had elementary bodies (EBs) on their surfaces, and only one sample obtained from the cervix showed C. trachomatis attached to the spermatozoa, as determined by fluorescent antibody (FA) staining. Two of the mated monkeys became pregnant; one spontaneously aborted late in gestation, and the other delivered a normal female infant. The fallopian tubes of all eight monkeys were challenged directly with serovar D and examined for evidence of salpingitis. Repeat laparoscopy was performed to monitor the inflammatory response. Tubal specimens for isolation and polymerase chain reaction (PCR) were obtained. Hysterectomies were performed between 3 and 4 weeks after tubal inoculation. Histopathologic examination of the fallopian tubes revealed widespread inflammation consisting of focal collections of lymphocytes and plasma cells in the submucosa. Peritubal adhesions were observed in four of five mated monkeys and in two of three unmated monkeys. CONCLUSION: This study failed to confirm that spermatozoa play a role in the pathogenesis of C. trachomatis infection.

Animals↗