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Biomedical subjects

J R Amberg

Publications and source records attributed to J R Amberg.

At least 19 recordsLinked to original sources
PubMed1993

Cloning in a bacteriophage lambda vector for the display of binding proteins on filamentous phage.

We have combined the efficiency and ease of use of bacteriophage lambda vectors with the power of phage display screening technology to create SurfZAP. The use of bacteriophage lambda allows the construction of large lambda expression libraries, which are rapidly and efficiently converted to stable plasmid libraries by mass excision. In SurfZAP, clones are expressed as fusions with amino acids 198-406 of the M13 minor coat protein (cpIII) and are displayed on the surface of filamentous phage. When produced with helper phage proteins, the fusion proteins are incorporated into the surface of phagemid particles. We demonstrate the utility of biopanning by isolating tetanus toxoid-binding mouse Fab clones from SurfZAP libraries. Approximately 10-100-fold enrichment of specific clones was observed after each panning round. The ability to create a large library of genotypes and screen the phenotypes by activity may be a potent methodology for basic research and drug discovery.

Animals↗
PubMed1993

Value of brominated fluorocarbons for the radiographic diagnosis of small-bowel obstruction: comparison with other contrast agents in rats.

OBJECTIVE: The disadvantages of water-soluble gastrointestinal contrast agents include high osmolality, contrast dilution, and severe toxicity if aspirated. Perfluorocarbons are nontoxic in the lung and peritoneal cavity. Because perfluorocarbons are immiscible with water, they have no osmotic effect and cannot be diluted. Because these properties offer theoretical advantages over traditional gastrointestinal contrast agents, we compared two perfluorocarbons with barium and ionic and nonionic iodinated contrast material in a rat model of small-bowel obstruction. MATERIALS AND METHODS: Twelve groups of six rats each had ligation of the terminal ileum (obstruction model) or of the terminal ileum and mesenteric artery (obstruction with ischemia model). Each rat received 3 ml of barium, meglumine sodium diatrizoate, iohexol, neat perfluorooctyl bromide, neat perfluorohexyl bromide, or saline (control animals). Contrast media were given at the recommended concentrations, and their progression was evaluated on serial radiographs by an observer who was not aware of the model or the contrast medium given. When one contrast material reached the point of obstruction, all rats in the group were sacrificed and a final radiograph was obtained. Three radiologists, who were not aware of the contrast medium given, on two separate occasions independently reviewed the radiographs and ranked the contrast agents for their relative radiopacity, mucosal definition, speed of transit, gastric retention, and bowel distension. RESULTS: When data from both models were combined, perfluorocarbons were judged on the final image to be the most radiodense, to provide the sharpest mucosal detail, to have the least gastric retention, and to have faster progression than barium. Whereas meglumine sodium diatrizoate and iohexol reached the point of obstruction more rapidly than the perfluorocarbons and barium, they had the greatest gastric retention, caused the most bowel distension, and were the least radiopaque. CONCLUSION: Our results show that the radiopaque perfluorocarbons are suitable as gastrointestinal contrast agents and have favorable radiographic characteristics in this animal model. When these results are combined with the low-toxicity profile of perflubron, clinical evaluation of this agent for the radiographic assessment of bowel obstruction is warranted.

Absorption↗
PubMed1992

Expression of a heterodimeric Fab antibody protein in one cloning step.

A new method is presented for creating antibody expression libraries in Escherichia coli. Rather than perform two cloning steps to express the heavy and light chains of the antigen binding domain, we have used a fusion-PCR method to link the coding regions for heavy and light chain sequences in a single DNA molecule prior to vector ligation. This greatly simplifies the construction of antibody expression clones.

Amino Acid Sequence↗
PubMed1990

Identification of human antibody fragment clones specific for tetanus toxoid in a bacteriophage lambda immunoexpression library.

We have applied a molecular biology approach to the identification of human monoclonal antibodies. Human peripheral blood lymphocyte mRNA was converted to cDNA and a select subset was amplified by the polymerase chain reaction. These products, containing coding sequences for numerous immunoglobulin heavy- and kappa light-chain variable and constant region domains, were inserted into modified bacteriophage lambda expression vectors and introduced into Escherichia coli by infection to yield a combinatorial immunoexpression library. Clones with binding activity to tetanus toxoid were identified by filter hybridization with radiolabeled antigen and appeared at a frequency of 0.2% in the library. These human antigen binding fragments, consisting of a heavy-chain fragment covalently linked to a light chain, displayed high affinity of binding to tetanus toxoid with equilibrium constants in the nanomolar range but did not cross-react with other proteins tested. We estimate that this human immunoexpression library contains 20,000 clones with high affinity and specificity to our chosen antigen.

Amino Acid Sequence↗
PubMed1986

Efficacy of radiologic studies in the detection of Barrett's esophagus.

Esophageal radiography using two different air-contrast techniques was used to examine 30 patients with Barrett's esophagus and 18 controls. All patients had upper gastrointestinal endoscopy and biopsy of the esophagus. The radiographs were randomized, masked, and then interpreted by two radiologists blinded to the endoscopic and biopsy diagnosis. Depending upon the diagnostic strategy of the radiologist, sensitivity varied from 0.36 to 0.83 and specificity from 0.56 to 1.00. A typical receiver-operating-characteristic curve was generated. Esophageal radiography is effective in identifying those patients who have stricture and ulceration as a complication beyond the epithelial transformation. However, because of low sensitivity, it is not a satisfactory method for identifying most cases of Barrett's esophagus.

Adult↗
PubMed1984

Pyloric and duodenal motor contributions to duodenogastric reflux.

The motor mechanisms of duodenogastric reflux were identified in 4 healthy, conscious dogs using electromyographic and fluoroscopic recordings of stomach, duodenum and upper jejunum. A barium suspension was injected via a pre-placed cannula in the orad jejunum, during the interdigestive period. Under normal conditions, reflux was uncommon. It was produced by duodenal segmental contractions occurring when the pylorus was open, or forced open by the duodenal contractions. Reflux was more common during retrograde electrical pacing of the duodenal pacesetter potential. It was then also produced by duodenal segmental contractions associated with an open, or opening, pylorus. During intravenous administration of apomorphine, reflux occurring early in the vomiting complex, was again produced by duodenal segmental contractions associated with an open, or opening, pylorus. The major apomorphine reflux event, however, occurred later when an emetic antiperistaltic contraction, originating in the duodenum or orad jejunum swept the contents before it into the stomach.

Animals↗
PubMed1980

Comparison of oral cholecystopaques: iopronic acid vs. iopanoic acid.

A new oral cholecystopaque, iopronic acid, was compared to iopanoic acid. This was a double blind, randomized study of 260 subjects. A 4.5-G dose of iopronic acid produced a similar degree of gallbladder opacification as 3.0 g of iopanoic acid. Adverse reactions to the contrast media were generally mild, but were significantly less with iopronic acid. The present study is criticized because it was not designed to help the radiologist determine the better contrast medium under optimal clinical conditions.

Cholecystography↗
PubMed1977

Colonic polyp detection: role of roentgenography and colonoscopy.

In order to determine the relative yields of colonoscopic and radiologic examinations of the colon, the following guidelines are suggested: (a) prospective data collection; (b) a standard, effective colon cleansing regimen; (c) colonoscopic and radiologic examiners of comparable expertise; (d) examiners should be unaware of each other's findings; (e) a suitable method for demonstrating false-negative findings and for resolving conflicting findings between the two examinations; and (f) indexing of the study findings as to lesion size, lesion location, quality of colon cleansing, and examiner's level of confidence. The two examinations should be used as complementary diagnostic procedures.

Colon↗
PubMed1975

Metastatic disease involving the stomach.

Metastatic disease involving the stomach is an unusual and difficult clinical problem. A review of 1010 autopsies of patients with cancer disclosed 17 cases of gastric metastases (an incidence of 1.7%), with breast cancer, lung cancer, and melanoma being the most frequent primaries. The clinical manifestations of epigastric pain, melena, and anemia are nonspecific, necessitating radiographic examination of the gastrointestinal tract. The radiographic findings are usually sufficient to suggest the diagnosis.

Breast Neoplasms↗