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Biomedical subjects

S C Chang

Publications and source records attributed to S C Chang.

At least 307 records · Page 17Linked to original sources
PubMed1988

Mutagenicity and polycyclic aromatic hydrocarbons analysis of airborne particulate matters from Taipei City.

The mutagenic activity of dichloromethane extracts of 147 air particulate samples collected from 8 stations during December 1986-June 1987 in Taipei city was consistently higher in S. typhimurium strain TA 98 than in strain TA 100 in the presence of S9 mixture. Among the 8 stations, Nan Kang Police Station, Fu Hsing Elementary School, and Chung Hsing University which were located in the industrial district, downtown area, and heavy traffic zone, respectively, had significantly higher levels of PAHs than the other stations. In contrast, the levels of PAHs were much lower in the suburban station, near Pei Tou Elementary School. However, PAH contents of the air particulate samples collected from these stations did not show good correlation with their mutagenicity. The air particulates collected at some stations on Sunday when the traffic changed from heavy to light showed lower mutagenicity and PAH contents as compared with the other weekdays at the same stations. On the contrary, the samples collected at Pei Tou station in a suburban area where the traffic changed from light to heavy on Sunday showed higher mutagenicity and PAH contents. The monthly average of PAHs of air particulate samples collected over a 7-month period from 8 stations in Taipei city was lower than the average in 1980. Moreover, when compared with other countries, such as U.S.A., the Netherlands, West Germany, Italy, Norway, and Japan, the levels of PAHs and mutagenicity of air particulate matters in Taipei city were similar or slightly lower. The mutagenicity and contents of PAHs of air particulates collected from burnt ABS were significantly higher than those of burnt PVC. One sample PT-6-3 was collected while a nearby garbage collection area was on fire. The mutagenicity of that sample increased 3 to 16 fold and contained an 11 to 33 times higher content of the six PAHs (BaP, BeP, BbF, BaA, Chr, and DbA) as compared with the other samples collected at the same location at a different time. The higher mutagenicity and PAH contents of that sample might be due to the pollution of the air from combustion of the garbage containing products made of ABS.

Air Pollutants↗
PubMed1988

Low dose O-butyryl timolol improves the therapeutic index of timolol in the pigmented rabbit.

The degree of enhancement in the ocular absorption of timolol afforded by its O-butyryl prodrug and the possibility of reducing its systemic absorption through a proportional reduction in its instilled dose were investigated in the pigmented rabbit. A reversed phase HPLC procedure was used to assay for timolol and O-butyryl timolol in the aqueous humor and plasma over 120 min post-instillation of 25 microliter of drug solutions. We found that the ocular absorption of the O-butyryl prodrug of timolol from a 15 mM solution was 5.5 times greater than that of the parent drug while the systemic absorption was comparable. When a lower concentration of the prodrug (3.75 mM) was used the therapeutic index as assessed by the ratio of aqueous humor to plasma concentrations seemed to improve fifteenfold. Therefore, it is possible to significantly reduce the systemic absorption of timolol without reducing its ocular absorption by using a low dose of its O-butyryl prodrug.

Absorption↗
PubMed1987

Hydrogen sulfide poisonings in hot-spring reservoir cleaning: two case reports.

The potential hazards to maintenance personnel cleaning hot-spring reservoirs are reported following two severe and unusual episodes of acute hydrogen sulfide poisoning involving seven workers. In the first episode, five victims lost consciousness immediately after climbing down a manhole to the bottom of a reservoir disregarding a strong odor of rotten eggs. One of them died immediately. Of the four who lived, three developed hemorrhagic keratoconjunctivitis and aspiration pneumonia, but no sequelae were observed 2 years later. In the second episode, two workers had been cleaning the reservoir for about 2 hours when one collapsed and his companion went to seek help. Both died of acute respiratory distress syndrome due to pulmonary edema within 12 hours. Since hot-spring bathing is a popular recreation in Taiwan, other accidents of hydrogen sulfide poisoning may have occurred but have not been reported. Such clinical information is helpful to enable regulators to initiate proper precautions to safeguard those workers involved.

Acute Disease↗
PubMed1987

Rat gene encoding the 78-kDa glucose-regulated protein GRP78: its regulatory sequences and the effect of protein glycosylation on its expression.

The 78-kDa glucose-regulated protein GRP78 is a stress-inducible protein ubiquitously expressed in animal cells. In this paper we show that the first exon of this endoplasmic reticulum-localized protein consists of an 18 amino acid leader sequence rich in hydrophobic residues, followed by a highly acidic mature N-terminus and an 11 amino acid domain that is shared by members of the 70-kDa heat shock protein family. The end of this shared domain also marks the beginning of the first intron of this gene. A DNA region upstream of the promoter element important for induction by calcium ionophore and by a temperature-sensitive mutation was identified by deletion analysis. Our results indicate that a region spanning from 85 to 480 nucleotides upstream of the major transcription initiation site is important for both induction conditions. With evidence suggesting that perturbations in protein glycosylation may be one of the common stimuli involved in transcription activation of the GRPs, we measured the rate of glycosylation during A23187, glucose starvation, and temperature-shift induced conditions. The inverse correlation observed between the rate of glycosylation and the steady-state level of the GRP78 transcripts lends support to this hypothesis.

Amino Acid Sequence↗
PubMed1987

Nasal and conjunctival contributions to the systemic absorption of topical timolol in the pigmented rabbit: implications in the design of strategies to maximize the ratio of ocular to systemic absorption.

The primary purpose of this study was to determine the relative contribution of the nasal and the conjunctival mucosae to the systemic absorption of topically applied timolol in the pigmented rabbit. The nasal mucosa was found to be about 2.5 times more efficient than the conjunctival mucosa in contributing to systemic timolol absorption, which occurred to the extent of 74% of the instilled dose. In addition, a minimum of 5-10 min prolongation of ocular contact time was determined to be necessary for significantly reducing systemic drug absorption and indirectly enhancing ocular drug absorption. The pharmaceutical implication of this finding is that ophthalmic vehicles such as polymeric inserts and gels would provide more favorable ocular to systemic drug absorption ratios than vehicles such as aqueous solutions and low-viscosity polymer solutions.

Absorption↗
PubMed1987

Lower lung field tuberculosis.

Sixty-five patients with lower lung field tuberculosis were found, representing 5.1 percent of the total admissions with pulmonary tuberculosis over a period of five years. Unlike previous reports, the disease affects more within the old age and female groups. The most common symptoms were cough, followed by chills, fever and hemoptysis. Bilateral or bilobar involvement was infrequent. Common basal segments and middle lobe were the most commonly affected locations. Chest x-ray film showed consolidation in most cases. Sputum smear for AFB was positive in 37 patients. Endobronchial involvement was proved by bronchoscopy in 32 of 42 patients who received the diagnostic procedure. The major bronchoscopic findings were ulcerative granuloma, fibrostenosis, and submucosal infiltration. In rare instances, final diagnosis could be made only after exploratory thoracotomy. Besides its diagnostic merit in lower lung field tuberculosis, bronchoscopy can assess the severity of the endobronchial lesion and provide a guide to early surgical intervention in patients with severe fibrostenosis.

Adult↗
PubMed1987

Bacteriology of viridans streptococcal bacteremia.

In order to assess the species distribution and the antibiotic susceptibility of viridans streptococci in various human infections, we reviewed 164 cases of viridans streptococcal bacteremia seen at the National Taiwan University Hospital between May 1981 and April 1987. The organisms were isolated from 83 patients with endocarditis. Among 81 nonendocarditis patients, only 54 had clinically recognizable foci of suppurative inflammation. Mainly based on API 20 STREP system of species identification, S. sanguis II accounted for 24.4%; S. mitis, 20.7%; S. sanguis I, 20.1%; and S. milleri 2, 11.6% of the 164 cases studied. Of 83 endocarditis patients, 27.7% were S. sanguis I; 21.7%, S. sanguis II; and 16.9%, S. mitis. In nonendocarditis bacteremia with known suppurative lesions, 3 most often isolated organisms were S. sanguis II (24.0%), S. mitis (24.0%), and S. milleri 2 (24.0%). In nonendocarditis bacteremia without suppurative infection, the most frequent isolates were S. sanguis II (33.3%) and S. mitis (25.9%). In terms of relative frequency between endocarditis and nonendocarditis cases, S. mutan, S. sanguis I, and S. bovis had the highest frequency ratio of 7:1, 3.5:1, and 1.5:1, respectively. All isolates were susceptible to penicillin G, ampicillin, and cephalothin. Tetracycline resistance, however, were observed in 35.4% of the isolates; oxacillin resistance, 11.0%; and erythromycin resistance, 9.1%.

Adolescent↗
PubMed1987

Improved corneal penetration of timolol by prodrugs as a means to reduce systemic drug load.

A major problem in the use of timolol in glaucoma therapy is its relatively high incidence of cardiovascular and respiratory side effects. This report presents preliminary evidence for the feasibility of a prodrug approach to minimize systemic absorption of timolol using a reduced topical dose made possible by improved corneal drug penetration. The results indicate that the O-acetyl, propionyl, butyryl, and pivalyl ester prodrugs of timolol were virtually completely hydrolyzed between 30 and 150 min when incubated with plasma, aqueous humor, and ocular tissue homogenates of pigmented rabbits. Moreover, the in vitro corneal penetration of all but the O-pivalyl prodrug was 2-3 times higher than timolol. This was accompanied by a four- to sixfold increase in aqueous humor concentration at 5 and 30 min post-instillation of 15 mM solutions, although the plasma timolol concentration at the same time points was either unaltered or slightly reduced. Collectively, these preliminary findings suggest that at least a twofold reduction in the topical dose of timolol is possible by using prodrugs, thereby reducing timolol concentration in the systemic circulation and possibly the incidence of cardiovascular and respiratory side effects.

Animals↗
PubMed1986

Evidence for a delayed, integral, and proportional phase of glucocorticoid feedback on ACTH secretion in normal human volunteers.

To investigate the mechanisms responsible for glucocorticoid feedback on nonstress-induced ACTH secretion in normal subjects, 24 volunteer subjects (14 males and 10 females, 21 to 43 years) were divided into six groups in a randomized fashion and studied. Each subject received a single midnight dose of 30 mg/kg per body weight of metyrapone and then cortisol was administered according to different protocols in the next morning to provide extreme variations of the input signal. It was found that no obvious inhibition in plasma ACTH levels was shown during the first 15 min despite the fact that cortisol was given at rather larger doses and short time intervals. However, a significant suppression in plasma ACTH levels began to manifest approximately 30 min after cortisol administration in each study group and it became apparent that the degree of inhibition of ACTH level at 75 min correlated with the plasma cortisol concentrations at the same moment (r = 0.97, P less than 0.01) as well as with the dosage of cortisol during this time, whatever administered (r = 0.99, P less than 0.01). In summary, our data provided evidence for a delayed, proportional, and integral phase of glucocorticoid feedback on nonstress-induced ACTH secretion in normal human volunteers.

Adrenocorticotropic Hormone↗
PubMed1986

A calcium ionophore-inducible cellular promoter is highly active and has enhancerlike properties.

We examined the regulatory/promoter sequence of a calcium ionophore-inducible gene isolated from the rat genome. Whereas the promoter of this ubiquitously expressed gene is active under noninduced conditions, after induction by calcium ionophore A23187 this promoter is 10- to 25-fold more active than the simian virus 40 early promoter, as measured by chloramphenicol acetyltransferase activities. Within this regulatory/promoter region, we have identified a DNA fragment with enhancer-like properties immediately 5' to the TATA sequence. This 291-nucleotide fragment acts in cis to enhance expression of the neomycin phosphotransferase (neo) gene driven by the herpes simplex virus thymidine kinase promoter in an orientation-independent manner. In addition, this fragment can confer A23187 inducibility to the neo gene and effectively compete for positive regulatory factors involved in A23187 induction. Sequence analysis of this promoter reveals homology with viral core enhancer sequences, and the apparent organization of direct repeat domains is similar to those observed in viral enhancers.

Animals↗