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Biomedical subjects

S Chang

Publications and source records attributed to S Chang.

At least 361 records · Page 20Linked to original sources
PubMed1986

Experimental chelation therapy in chromium, lead, and boron intoxication with N-acetylcysteine and other compounds.

The usefulness of N-acetylcysteine (NAC) as a chelating agent was studied for the toxin potassium dichromate, lead tetraacetate, and boric acid. Mature Sprague-Dawley rats were intoxicated with these substances and placed in metabolic cages. Urinary excretion rates of intoxicant and total urine volume were determined during treatment with N-acetylcysteine, calcium EDTA, and/or dimercaptosuccinic acid, N-acetylcysteine proved to be the most effective agent at increasing the excretion of chromium and boron and was also able to reverse the oliguria associated with these toxins. Dimercaptosuccinic acid was most effective at the chelation of lead. NAC did not increase the excretion of lead. We conclude that NAC may be useful in intoxications due to chromate and borate and is effective at reversing the oliguria associated with these intoxicants.

Acetylcysteine↗
PubMed1986

Effects of Ro 16-0521 on cholesterol metabolism in the rat.

Ro 16-0521 is a newly synthesized benzodiazepine derivative which is devoid of reactivity with the brain benzodiazepine receptor. The effects of this drug on plasma lipids and lipoproteins and hepatic cholesterol metabolism have been examined in the cholesterol-fed rat. Drug therapy was associated with dose-related falls in plasma cholesterol concentration, liver cholesterol content, and the activity of the liver enzyme Acyl-CoA cholesterol acyltransferase. Drug therapy abolished the lipid and lipoprotein changes induced by cholesterol feeding, including those associated with a diet supplemented with olive oil to facilitate cholesterol loading. Drug therapy was also associated with an increased activity of the enzyme HMG-CoA reductase and reduced hepatic microsomal cholesterol content. It is suggested that the cholesterol-fed rat will be a suitable model for further mechanistic studies.

Animals↗
PubMed1986

Analysis of 6-keto PGF1 alpha, 5-HETE, and LTC4 in rat lung: comparison of GM/MS, RIA, and EIA.

The recent availability of fast and sensitive radioimmunoassay (RIA) and enzyme immunoassay (EIA) procedures to measure icosanoids has led to utilization of these techniques by many investigators. A major concern has been that techniques based on immunoreactivity may lack specificity, in particular if complex biologic fluids or tissue extracts are evaluated. The purpose of this investigation was the comparison of icosanoid measurements obtained either with EIA or RIA with those obtained by gas chromatography/mass spectrometry (GC/MS). Rats were injected with Salmonella enteritidis endotoxin, killed at various times after the injection and the lung extract assayed for 6-keto-PGF1 alpha, 5-HETE and LTC4. By EIA lung tissue was found to contain large quantities of 6-keto-PGF1 alpha after endotoxin stimulation. Comparisons made between EIA and GC/MS analysis showed good correlation between 6-keto-PGF1 alpha amounts in lung as determined by each technique. It was also determined that little purification of lung extract was needed to obtain reliable quantitation of 6-keto-PGF1 alpha, probably due to the specificity of the antibody and the large quantity of this prostaglandin produced. Crudely purified (Sep-Pak) lung extracts gave 5-HETE levels by RIA which were highly correlated with GC/MS values, but RIA values were 70% higher than those obtained by GC/MS. The presence of other components in lung extract which cross react with this 5-HETE antibody was probably responsible for the higher values obtained by RIA. LTC4 was measured by immunoassay in crude lung extracts, as well as after Sep-Pak purification and HPLC purification. LTC4 levels were identical in unpurified lung extract and after Sep-Pak purification, but decreased substantially after HPLC purification. Thus, by validating the icosanoid immunoassays, we have found that they can give accurate and reproducible results in lung tissue, although LTC4 and 5-HETE must be purified prior to analysis.

6-Ketoprostaglandin F1 alpha↗
PubMed1986

Lithium treatment of mania: clinical characteristics, specificity of symptom change, and outcome.

The effects of lithium treatment and prediction of response in 18 manic patients were studied as part of the National Institute of Mental Health Collaborative Study of the Psychobiology of Depression. Patients were rated using the Mania Diagnostic and Severity Scale (MADS) and an additional battery of behavioral constructs developed for measurement of state and drug response in depressed patients. About 67% of the patients had good treatment outcome after 26 days of lithium treatment. Responders did not differ from nonresponders before treatment with respect to delusions, hallucinations, or irritable-paranoid symptoms. Nonresponders were rated as more anxious than responders before treatment and had higher scores on the Hamilton Rating Scale for Depression. Improvement on the MADS, however, did not correlate with pretreatment behavioral ratings. Patients with relatively high ratings for aspects of behavior not specific to mania tended to improve in these regardless of change in MADS score. Manic patients who were also depressed (44%) had higher mania ratings than manic patients who were not depressed. Patients with concomitant depression and mania had significantly worse overall treatment outcome, although their depression ratings improved during lithium treatment.

Adult↗
PubMed1986

Hot hydrogen atom reactions moderated by H2 and He.

Photolysis experiments were performed on the H2-CD4-NH3 and the He-CD4-NH3 systems. The photolysis (1849 angstoms) involved only NH3. Mixtures of H2:CD4:NH3 included all combinations of the ratios (200,400,800):(10,20,40):4. Two He:CD4:NH3 mixtures were examined where the ratios equalled the combinations 100:(10,20):4. Abstraction of a D from CD4 by the photolytically produced hot hydrogen from ammonia was monitored by mass spectrometric determination of HD. Both experiment and semiempirical hot-atom theory show that H2 is a very poor thermalizer of hot hydrogens with excess kinetic energy of about 2 eV. Applications of the hard-sphere collision model to the H2-CD4-NH3 system results in predicted ratios of net HD production to NH3 decomposition that were two orders of magnitude smaller than the experimental ratios. On the other hand, helium is found to be a very efficient thermalizer; here, the classical model yields reasonable agreement with experiments. Application of a semiempirical hot-atom program gave quantitative agreement with experiment for either system.

Ammonia↗
PubMed1986

Identification of a positive retroregulator that stabilizes mRNAs in bacteria.

A positive retroregulator that enhances the expression of an upstream gene(s) has been identified. It resides within a 381-base pair (bp) restriction fragment containing the transcriptional terminator of the crystal protein (cry) gene from Bacillus thuringiensis vs. Kurstaki HD-1. This fragment was fused to the distal ends of either the penicillinase (penP) gene of Bacillus licheniformis or the interleukin 2 cDNA from the human Jurkat cell line. In both cases, the half-lives of the mRNAs derived from the fusion genes were increased from approximately equal to 2 to 6 min in both Escherichia coli and Bacillus subtilis. Synthesis of the corresponding polypeptides in the bacteria carrying the fusion genes was also increased correspondingly. The enhancement of expression of the upstream genes was independent of the insertional orientation of the distal cry terminator fragment. Deletion analysis showed that the locus conferring the enhancing activity coincided with the terminator sequence and was located within a 89-bp fragment that includes an inverted repeat, the 19-bp upstream-, and the 27-bp downstream-flanking sequences. We propose that transcription of the retroregulator sequence leads to the incorporation of the corresponding stem-and-loop structure at the 3' end of the mRNA; the presence of this structure protects the mRNAs from exonucleolytic degradation from the 3' end and, thereby, increases the mRNA half-life and enhances protein synthesis of the target genes.

Bacillus subtilis↗
PubMed1986

Processing of Bacillus licheniformis penicillinases lacking a lipoprotein modification site in Escherichia coli.

We have previously shown that the penP Ser-27 prepenicillinase is processed into two forms, Ser-35-penicillinase and Asn-29 penicillinase. Two new penicillinase mutants, penP Ser-27 Pro-28 and penP Ser-27,23' (Pro-Asp)24', were derived from the penP Ser-27 mutant by oligonucleotide-directed site-specific mutagenesis. The penP Ser-27 Pro-28 mutant prepenicillinase was also processed into two forms, Ser-35-penicillinase and Gly-26-penicillinase. On the contrary, the penP Ser-27,23' (Pro-Asp)24' mutant prepenicillinase is unprocessed.

Bacillus↗
PubMed1986

Control of lysogeny and immunity of Bacillus subtilis temperate bacteriophage SP beta by its d gene.

The d gene from the Bacillus subtilis temperate bacteriophage SP beta was isolated. When introduced into an SP beta-sensitive strain of B. subtilis, the cloned d gene directed the synthesis of a 22-kilodalton protein and conferred on the host immunity to SP beta phage. A frameshift mutation, designated d2, was introduced into the cloned d gene, and it was subsequently crossed back into the SP beta phage genome. The resulting SP beta phage grew lytically and formed clear plaques on sensitive bacteria. Although the cloned d gene confers immunity to the host, we could not detect complementation of the d gene by mixed infection with SP beta d2 and various SP beta c mutants. The nucleotide sequence of the 1,033-base-pair PstI-to-EcoRI fragment containing the d gene was determined; it includes an open reading frame that could potentially encode a protein of 227 amino acids. The gene was mapped within the PstI H fragment on the phage genome, which positions the d gene about 25 kilobases from the right end of the phage genome. It is transcribed from right to left.

Amino Acid Sequence↗
PubMed1985

Purification and characterization of GDP-D-mannose 4,6-dehydratase from porcine thyroid.

The enzyme GDP-D-mannose 4,6-dehydratase has been purified 1500-fold from porcine thyroid tissue. The enzyme exhibits a molecular mass of 251000 Da as determined by sedimentation techniques. Its subunit size was determined as 41500 Da by dodecyl sulfate gel electrophoresis. The enzyme has a Km of 3.3 microM with respect to GDP-D-mannose and appears specific with respect to this substrate. The enzyme appears to be inhibited by guanine nucleotides and by guanine nucleotide sugars. It is particularly susceptible to inhibition by GDP-L-fucose. It is suggested that this compound may have a physiological function as an end-product feedback inhibitor.

Animals↗
PubMed1985

Identification of prolipoprotein signal peptidase and genomic organization of the lsp gene in Escherichia coli.

The product of the lsp gene of Escherichia coli, i.e. the prolipoprotein signal peptidase, was identified by both in vivo pulse labeling experiments using a high expression lambda PL promoter vector and by an in vitro transcription/translation coupled system. The molecular weight of prolipoprotein signal peptidase was estimated to be approximately 18,000 by its mobility on polyacrylamide gel electrophoresis and was found to be the same as that of SPase II purified from the wild-type cells. Analysis of SPase II activities in strains containing various subclones, deletion derivatives generated from plasmid pMT521, and analysis of protein products in a strain harboring an ileS-lsp-fused gene indicated that ileS and lsp genes are transcribed on the same mRNA. This was further supported by the observation that Tn5 insertions in the ileS gene resulted in a reduced expression of the lsp gene. In addition to an upstream promoter shared by the ileS and lsp genes, these analyses also revealed the presence of an internal promoter for the lsp gene within the coding region of the ileS gene.

Bacterial Outer Membrane Proteins↗
PubMed1985

Modification and processing of internalized signal sequences of prolipoprotein in Escherichia coli and in Bacillus subtilis.

We have cloned the Escherichia coli lipoprotein structural gene (lpp) into a shuttle vector and studied its expression in both E. coli and in Bacillus subtilis. Using in vitro gene fusion techniques, the lpp gene was placed under the control of the promoter for the erythromycin-resistance (ery) gene. This fusion gene directed the synthesis of Braun's prolipoprotein which can be subsequently processed into the mature lipoprotein. In addition to the prolipoprotein, two ery-lpp hybrid proteins containing a 45- and a 22-amino acid extension preceding the NH2 terminus of prolipoprotein, respectively, are also synthesized in E. coli. The synthesis of these three proteins appears to involve the utilization of three distinct translation initiation sites. In B. subtilis, only two proteins are synthesized, the hybrid protein with a 45-amino acid extension and the prolipoprotein. In both E. coli and B. subtilis, the precursor forms of the hybrid proteins are lipid-modified, and they are processed to mature lipoprotein in vivo. These results indicate that internalized signal sequence containing the prolipoprotein modification and processing site (Leu-Ala-Glys-Cys) can function normally and permit the modification of hybrid proteins to lipid-modified precursors which can be subsequently processed by the globomycin-sensitive prolipoprotein signal peptidase.

Amino Acid Sequence↗
PubMed1985

Synthesis and incorporation of human ribosomal protein S14 into functional ribosomes in human-Chinese hamster cell hybrids containing human chromosome 5: human RPS14 gene is the structural gene for ribosomal protein S14.

In Chinese hamster ovary cells, mutations in the RPS14 gene (which was previously designated emtB) render cells resistant to normally cytotoxic concentrations of the protein synthesis inhibitor, emetine. Several lines of evidence indicate the RPS14 gene in Chinese hamster is the structural gene for ribosomal protein S14, including the finding that mutants with alterations in this gene produce an electrophoretically altered form of this protein. A human gene which complements the defect in CHO RPS14 mutants and renders them sensitive to emetine has previously been assigned to the long arm of chromosome 5. The analysis of ribosomal proteins extracted from CHO Emtr X human cell hybrids, which contain human chromosome 5 and are emetine sensitive, demonstrated the presence of both the normal human and altered hamster forms of ribosomal protein S14. Human chromosome 5, the emetine-sensitive phenotype, and the human form of ribosomal protein S14 segregate concordantly from hybrids, confirming that the human gene in question is the structural gene for this protein. In addition, the results indicate that in interspecific cell hybrids, the human form of S14 is either incorporated into functional ribosomes more efficiently than the altered hamster protein or the human gene is overexpressed relative to the corresponding hamster gene.

Animals↗
PubMed1985

An assay for GDP-D-mannose-4,6-dehydratase.

The mechanism of GDP-D-mannose-4,6-dehydratase action with respect to loss of the C5 hydrogen has been established using GDP-D-[5-3H]-mannose as a substrate. This observation has been incorporated into a rapid assay for the enzyme based on the equilibration of 3H with the aqueous medium.

Guanosine Diphosphate Mannose↗
PubMed1985

Perfluorocarbon gases in vitreous surgery.

Fifty-six patients with complicated retinal detachments were managed with vitreous surgery and one of two perfluorocarbon gases. These gases are capable of greater expansion and greater longevity compared to sulfur hexafluoride. Forty-five patients received perfluoropropane (C3F8), eleven received perfluoroethane (C2F6). The retinas of 31 patients (55.4%) were attached at six months after the disappearance of the gas. In many instances, operations performed with air-sulfur hexafluoride mixtures had failed and the retina was subsequently reattached with the use of the perfluorocarbon gases. The major complications were increased intraocular pressure, which was usually transient, and gas-induced lens opacities.

Fluorocarbons↗
PubMed1985

Therapeutic ultrasound in the treatment of glaucoma. II. Clinical applications.

Focused, high-intensity therapeutic ultrasound was used to treat 69 selected patients with uncontrollably elevated intraocular pressure (IOP). This new technique selectively thins scleral collagen, and produces focal damage to the ciliary epithelium. These tissue modifications provide a reduction in IOP pressure to 25 mmHg or less in 83% of patients with a minimum three-month follow-up period.

Ciliary Body↗