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S J Shields

Publications and source records attributed to S J Shields.

10 recordsLinked to original sources
PubMed2001

Synthesis and spectroscopic characterization of site-specific 2-amino-1-methyl-6-phenylimidazo.

The aim of the present study is to determine the chemical structure and conformation of DNA adducts formed by incubation of the bioactive form of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), N-acetoxy-PhIP, with a single-stranded 11mer oligodeoxyribonucleotide. Using conditions optimized to give the C8-dG-PhIP adduct as the major product, sufficient material was synthesized for NMR solution structure determination. The NMR data indicate that in duplex DNA this adduct exists in equilibrium between two different conformational states. In the main conformer, the covalently bound PhIP molecule intercalates in the helix, whilst in the minor conformation the PhIP ligand is probably solvent exposed. In addition to the C8-dG-PhIP adduct, at least eight polar adducts are found after reaction of N-acetoxy-PhIP with the oligonucleotide. Three of these were purified for further characterization and shown to exhibit lowest energy UV absorption bands in the range 342-347 nm, confirming the presence of PhIP or PhIP derivative. Accurate mass determination of two of the polar adducts by negative ion MALDI-TOF MS revealed ions consistent with a spirobisguanidino-PhIP derivative and a ring-opened adduct. The third adduct, which has the same mass as the C8-dG-PhIP oligonucleotide adduct, may contain PhIP bound to the N2 position of guanine.

Base Sequence↗
PubMed2001

Clinical outcome of the use of enteral stents for palliation of patients with malignant upper GI obstruction.

BACKGROUND: The endoscopically placed enteral stent has emerged as a reasonable alternative to palliative surgery for malignant intestinal obstruction. This is a report of our experience with the use of enteral stents for nonesophageal malignant upper GI obstruction. METHODS: Data on all patients who had undergone enteral stent placement were reviewed. Those with a diagnosis of pancreatic cancer were compared with another similar cohort of patients who underwent palliative gastrojejunostomy. RESULTS: Thirty-one procedures were performed on 29 patients (mean age 67.7 years). Thirteen (45%) were men and 16 (55%) women. The diagnoses were gastric (13.8%), duodenal (10.3%), pancreatic (41.4%), metastatic (27.6%), and other malignancies (6.9%). Malignant obstruction occurred at the pylorus (20.7%), first part of duodenum (37.9%), second part of duodenum (27.6%), third part of duodenum (3.5%), and anastomotic sites (10.3%). Twenty-nine (93.5%) procedures were successful and good clinical outcome was achieved in 25 (80.6%). Re-obstruction by tumor ingrowth occurred in 2 patients after a mean of 183 days. The median survival time for patients with pancreatic cancer who underwent enteral stent placement compared with those who underwent surgical gastrojejunostomy was 94 and 92 days, charges were $9921 and $28,173, and duration of hospitalization was 4 and 14 days, respectively (latter 2 differences with p value < 0.005). CONCLUSION: Endoscopic enteral stent placement of nonesophageal malignant upper GI obstruction is a safe, efficacious, and cost-effective procedure with good clinical outcome, lower charges, and shorter hospitalization period than the surgical alternative.

Adult↗
PubMed2000

Fragmentation chemistry of [M + Cu]+ peptide ions containing an N-terminal arginine.

[M + Cu]+ peptide ions formed by matrix-assisted laser desorption/ionization from direct desorption off a copper sample stage have sufficient internal energy to undergo metastable ion dissociation in a time-of-flight mass spectrometer. On the basis of fragmentation chemistry of peptides containing an N-terminal arginine, we propose the primary Cu+ ion binding site is the N-terminal arginine with Cu+ binding to the guanidine group of arginine and the N-terminal amine. The principal decay products of [M + Cu]+ peptide ions containing an N-terminal arginine are [a(n) + Cu - H]+ and [b(n) + Cu - H]+ fragments. We show evidence to suggest that [a(n) + Cu - H]+ fragment ions are formed by elimination of CO from [b(n) + Cu - H]+ ions and by direct backbone cleavage. We conclude that Cu+ ionizes the peptide by attaching to the N-terminal arginine residue; however, fragmentation occurs remote from the Cu+ ion attachment site involving metal ion promoted deprotonation to generate a new site of protonation. That is, the fragmentation reactions of [M + Cu]+ ions can be described in terms of a "mobile proton" model. Furthermore, proline residues that are adjacent to the N-terminal arginine do not inhibit formation of [b(n) + Cu - H]+ ion, whereas proline residues that are distant to the charge carrying arginine inhibit formation of [b(n) + Cu - H]+ ions. An unusual fragment ion, [c(n) + Cu + H]+, is also observed for peptides containing lysine, glutamine, or asparagine in close proximity to the Cu+ carrying N-terminal arginine. Mechanisms for formation of this fragment ion are also proposed.

Arginine↗
PubMed2000

Endoscopic detection of dysplasia in patients with Barrett's esophagus using light-scattering spectroscopy.

BACKGROUND & AIMS: We conducted a study to assess the potential of light-scattering spectroscopy (LSS), which can measure epithelial nuclear enlargement and crowding, for in situ detection of dysplasia in patients with Barrett's esophagus. METHODS: Consecutive patients with suspected Barrett's esophagus underwent endoscopy and systematic biopsy. Before biopsy, each site was sampled by LSS using a fiberoptic probe. Diffusely reflected white light was spectrally analyzed to obtain the size distribution of cell nuclei in the mucosal layer, from which the percentage of enlarged nuclei and the degree of crowding were determined. Dysplasia was assigned if more than 30% of the nuclei exceeded 10 microm and the histologic findings compared with those of 4 pathologists blinded to the light-scattering assessment. The data were then retrospectively analyzed to further explore the diagnostic potential of LSS. RESULTS: Seventy-six sites from 13 patients were sampled. All abnormal sites and a random sample of nondysplastic sites were reviewed by the pathologists. The average diagnoses were 4 sites from 4 different patients as high-grade dysplasia (HGD), 8 sites from 5 different patients as low-grade dysplasia (LGD), 12 as indefinite for dysplasia, and 52 as nondysplastic Barrett's. The sensitivity and specificity of LSS for detecting dysplasia (either LGD or HGD) were 90% and 90%, respectively, with all HGD and 87% of LGD sites correctly classified. Decision algorithms using both nuclear enlargement and crowding further improved diagnostic accuracy, and accurately classified samples into the 4 histologic categories. CONCLUSIONS: LSS can reliably detect LGD and HGD in patients with Barrett's esophagus.

Aged↗
PubMed1998

Characterization of proteins utilized in the desulfurization of petroleum products by matrix-assisted laser desorption ionization time-of-flight mass spectrometry.

Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI/TOF/MS) with delayed extraction is utilized in linear, reflected-ion and post-source decay (PSD) modes to directly characterize enzymes being developed for use in a petroleum desulfurization process. The DNA sequence for the genes isolated from Rhodococcus sp. strain IGTS8 that produce three of the four enzymes under study had been previously reported with a discrepancy in residue assignments for one of the enzymes, dsz-C. The use of proteolytic digests followed by MALDI/TOF/MS with delayed extraction in the reflected-ion mode provided sequence-specific information with mass accuracies exceeding 40 ppm over a range of masses and signal-to-noise values. Peptide mapping of >80% of the residues was accomplished for all four proteins. The use of PSD established the true sequence for dsz-C, resolving the discrepancy in the literature. A posttranslational loss of N-terminal methionine was observed for each of the four proteins in linear MALDI/MS and was reconfirmed by peptide mapping for three of the proteins.

Amino Acid Sequence↗
PubMed1996

Sphincterotomy techniques and risks.

Endoscopic sphincterotomy has revolutionized the approach to numerous biliary and pancreatic diseases. The indications, technique, and complications of endoscopic sphincterotomy are covered in detail in this article.

Biliary Tract Diseases↗
PubMed1992

Arterioportal fistula: a role for pre-TIPSS arteriography and hepatic venous pressure measurements.

A 70-yr-old male presented with massive upper gastrointestinal bleeding secondary to esophageal varices. Because the bleeding was not controlled by sclerotherapy or vasopressin and nitroglycerin, the patient was evaluated for a transjugular intrahepatic portosystemic shunt. Preprocedure arteriography was performed because the etiology of the portal hypertension was uncertain. The arteriogram revealed a hepatic artery to portal vein fistula. Hepatic venous pressure measurements documented an elevated hepatic venous pressure gradient, which diminished dramatically upon embolization of the fistula. Rebleeding from the varices was associated with reestablishment of the fistula via collaterals and elevation of the hepatic venous pressure gradient. The case is presented to establish a role for arteriography prior to transjugular intrahepatic portosystemic shunting, especially in patients with unexplained portal hypertension, and to establish the potential value of hepatic venous pressure measurements in the treatment of arterioportal fistulas.

Aged↗