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Biomedical subjects

J S Chou

Publications and source records attributed to J S Chou.

12 recordsLinked to original sources
PubMed1999

Detection of methyl ethyl ketone in urine using headspace solid phase microextraction and gas chromatography.

Headspace solid-phase microextraction coupled with gas chromatography/flame ionization detection was developed to measure urinary methyl ethyl ketone (MEK). A fused silica fiber coated with 75 microns carboxen/polydimethylsiloxane was used to extract urinary MEK. The optimal extraction conditions were obtained when temperature was 50 degrees C, extraction time was 15 minutes, and ammonium sulfate concentration was 0.5 g/mL. The optimal desorption temperature and time were 200 degrees C and 5 minutes, respectively. The concentration range of calibration curves was 27 to 8000 ng/mL of MEK. The within-day and between-day pooled coefficients of variation (9 concentrations, triplicate samples) were 5.4% and 8.8%, respectively. The limit of detection and limit of quantitation were 4.2 ng/mL and 21.6 ng/mL, respectively. The recovery (+/- standard deviation) of MEK was 100.2% +/- 8.6% (n = 3). MEK in urine was stable for at least 1 month when stored at -20 degrees C. This method proved to be applicable for the analysis of urinary MEK of exposed workers in a plastic material printing plant. We concluded that this new method is sensitive, inexpensive, simple, and reliable for measuring the occupational exposure of MEK.

Adult↗
PubMed1999

Correlation between urinary 2-methoxy acetic acid and exposure of 2-methoxy ethanol.

OBJECTIVES: To examine the correlation between airborne 2-methoxy ethanol (ME) exposures and the urinary 2-methoxy acetic acid (MAA) and to recommend a biological exposure index (BEI) for ME. METHODS: 8 Hour time weighted average (TWA) personal breathing zone samples and urine samples before and after the shift were collected from Monday to Saturday for 27 workers exposed to ME and on Friday for 30 control workers. RESULTS: No correlation was found between airborne exposure to ME and urinary MAA for nine special operation workers due to the use of personal protective equipment. For 18 regular operation workers, a significant correlation (r = 0.702, p = 0.001) was found between urinary MAA (mg/g creatinine) on Friday at the end of the shift and the weekly mean exposures of ME in a 5 day working week. The proposed BEI, which corresponds to exposure for 5 days and 8 hours a day to 5 ppm, extrapolated from the regression equation is 40 mg MAA/g creatinine. A significant correlation was also found between the weekly increase of urinary MAA (Friday after the shift minus Monday before the shift) and the weekly mean exposures of ME (r = 0.741). The recommended value of the weekly increase of urinary MAA for 5 days repeated exposures of 5 ppm ME is 20 mg/g creatinine. No urinary MAA was detected in workers in the non-exposed control group. CONCLUSIONS: The Friday urinary MAA after the shift or the weekly increase of urinary MAA is a specific and a good biomarker of weekly exposure to ME.

Acetates↗
PubMed1999

Improved method to measure urinary alkoxyacetic acids.

OBJECTIVES: To simplify the current preparation of samples, and to improve the specificity and reliability of the conventional analytical methods to measure urinary alkoxyacetic acids. METHODS: Samples containing alkoxyacetic acids including methoxy, ethoxy, and butoxyacetic acids (MAA, EAA, and BAA) were acidified with HCl and extracted with a mixed solvent of methylene chloride and isopropyl alcohol, then analysed by gas chromatography/mass spectrometry (GC/MS). RESULTS: Optimal results were obtained when pH was 1.05-1.45, the ratio of methylene chloride and isopropyl alcohol was 2:1, and when extraction time was 10 minutes. Over the concentration range 0.3-200 micrograms/ml, MAA, EAA, and BAA could be determined with a pooled coefficient of variation (nine concentrations, six replicate samples) of 5.55%, 6.37%, and 6.41%, respectively. Urine samples were stable for at least 5 months and 3 freeze-thaw cycles at -20 degrees C. The limits of detection of MAA, EAA, and BAA were 0.055, 0.183, and 0.009 microgram/ml, respectively. The matrix effect of urine samples was negligible for MAA and EAA, but were marginally significant for BAA. The average recoveries of alkoxyacetic acids were 99%-101%. In urine samples MAA from 15 exposed workers showed a strong linear correlation (r = 0.999, slope = 1.01) between the new GC/MS method and Sakai's GC method. CONCLUSIONS: The simplified non-derivatisation pretreatment of samples coupled with GC/MS can provide a specific, sensitive, simple, safe, and reliable method for the biological monitoring of occupational exposure of ethylene glycol ethers.

Acetates↗
PubMed1993

Molecular cloning and sequence analysis of the cDNA for ancrod, a thrombin-like enzyme from the venom of Calloselasma rhodostoma.

The 1.54 kb cDNA for ancrod, a thrombin-like enzyme, was cloned from a lambda ZAP cDNA library derived from the venom glands of Calloselasma (Agkistrodon) rhodostoma. The cDNA sequence reveals that ancrod is synthesized as a pre-zymogen of 258 amino acids, including a putative secretory peptide of 18 amino acids and a proposed zymogen peptide of 6 amino-acid residues. The amino-acid sequence of the predicted active form of the enzyme exhibits a high degree of sequence similarity to those of mammalian serine proteases (trypsin and pancreatic kallikrein) and other thrombin-like enzymes (batroxobin and flavoxobin). Key amino-acid residues (His43, Asp88, Ser182 and Asp176) that are thought to be involved in the substrate cleavage and in the substrate-binding reaction are conserved. Ancrod contains 13 cysteine residues. Based on alignment with the amino-acid sequences of trypsin and batroxobin, six disulphide bridges can be predicted to be present in the ancrod protein. The existence of a free cysteine, which changes the common sequence surrounding the Ser182 active site from Gly-Asp-Ser-Gly-Gly-Pro to Cys-Asp-Ser-Gly-Gly-Pro, is unusual for a serine protease.

Amino Acid Sequence↗
PubMed1993

Nucleotide sequence of a full-length cDNA encoding a common precursor of platelet aggregation inhibitor and hemorrhagic protein from Calloselasma rhodostoma venom.

The nucleotide sequence of a full-length cDNA encoding the common precursor of a platelet aggregation inhibitor, rhodostomin and a hemorrhagic protein from Calloselasma rhodostoma snake venom is presented. The 1.98-kb cDNA contains an open reading frame encoding 478 amino acid residues. The complete structure of the precursor protein encoded by the cDNA is elucidated.

Amino Acid Sequence↗
PubMedDate not supplied

Evaluation and implantation of a teledioptric lens system for cataract and age-related macular degeneration.

The teledioptric lens implant, with a high-minus central zone, was evaluated on an optical bench and implanted in the eyes of 50 patients with both cataract and age-related macular degeneration. In vitro testing demonstrated slightly reduced contrast and modulation-transfer-function as compared with a standard intraocular lens. The lens implant functions ideally with a 1.9-millimeter diameter on the high-minus portion. Lens implantation was proven safe in the clinical study. When used with spectacles as a part of a teledioptric system, the resulting visual field was 2.6 times larger than that achieved with an external telescope. Postoperative visual acuity initially improved in more than 65% of patients. After 1 year, due to disease progression, only 20% had improved acuity.

Aged↗
PubMedDate not supplied

Aging and urinary excretion of epidermal growth factor.

The aging process in man leads to some loss of kidney mass and function. The kidney produces epidermal growth factor (EGF), a polypeptide involved in the repairing process of epithelial cells. Human urine contains high concentrations of EGF, derived from its production in the kidney. It is not known if aging alters urinary EGF production in humans. This study investigates the possibility of decreased urinary EGF in elderly people. Urine samples were collected from 70 healthy subjects of various ages and measured for EGF by the technique of radioimmunoassay. The studied urine samples were divided into five age groups (3 to 10, 11 to 20, 21 to 60, 61 to 70, and 71 to 80 years). Urinary EGF (corrected for the urine creatinine concentration and measured as ng per mg creatinine) was highest in the two youngest groups, 78.5 +/- 14.3 and 76.2 +/- 18.8 (mean +/- standard error of the mean), respectively, and decreased with age so that the lowest urinary EGF was observed in the oldest group (27.0 +/- 8.8 ng per mg creatinine). In addition, a significant inverse relationship exists between urinary EGFD in all 79 subjects and their respective age (P < 0.001). These findings show that normal values of urinary EGF should take age into account. The reduced production of EGF by the kidney in the elderly may have functional significance in retarding the repair process in the kidney.

Adolescent↗