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Biomedical subjects

C N Ong

Publications and source records attributed to C N Ong.

At least 19 recordsLinked to original sources
PubMed1992

High-performance liquid chromatographic method for routine determination of vitamins A and E and beta-carotene in plasma.

A simple and reliable reversed-phase high-performance liquid chromatographic (HPLC) method for the routine determination of vitamins A and E and beta-carotene in plasma (or serum) with wavelength-programmed ultraviolet-visible absorbance detection is described. A 200-microliters aliquot of serum or plasma sample, after deproteinization with ethanol, and containing tocopherol acetate as internal standard, was extracted with butanol-ethyl acetate. Sodium sulphate was added for dehydration. Analytes of extracted samples were found to be stable for at least four days. A 10-microliters aliquot of this organic extract was used for HPLC analysis. The mobile phase was methanol-butanol-water (89.5:5:5.5, v/v) and the flow-rate was set at 1.5 ml/min. The analytes of interest were well separated from other plasma constituents within 22 min at 45 degrees C. The lowest detection limits of vitamins A and E and beta-carotene were 0.02, 0.5 and 0.1 microgram/ml, respectively. The recovery and reproducibility of the present method were around 90%. The method is sensitive, specific and can be used for epidemiological studies and for routine determination of vitamin deficiency. Several important factors that may affect the analysis are also discussed in this paper.

Carotenoids↗
PubMed1992

Separation of globins using free zone capillary electrophoresis.

This paper describes the use of high-performance capillary electrophoresis for the separation of globin chains. Adult and newborn haemolysates from normal individuals and children suspected of having thalassaemia were analysed using free zone electrophoresis. Separation of globins was accomplished using a 25 mM phosphate buffer at pH 11.8. Distinct peaks of alpha-, beta- and gamma-chains were resolved within 8 min. The coefficient of variation for within-day and between-day runs was 4.1% and 5.7%, respectively. This method is simple and rapid, and it can be used to screen for thalassaemia and for the clinical study of various haemoglobinopathies.

Carrier State↗
PubMed1992

Medical students' exposure to formaldehyde in a gross anatomy dissection laboratory.

The authors studied 150 first-year medical students exposed to formaldehyde during the dissection of cadavers in a gross anatomy laboratory. As a reference group, they used 189 third- and fourth-year medical students matched for sex, ethnic group, and age. Environmental and personal samples were collected to determine the exposure to formaldehyde among the first-year students. The mean concentration of formaldehyde in parts per million (ppm) in the area was 0.50 ppm (range = 0.40-0.60 ppm) and the personal sample was 0.74 ppm (range = 0.41-1.20 ppm). No significant differences were noted in the pre- and post-exposure mean FEV1 (forced expiratory volume in 1 second) and FVC (forced vital capacity) among the 22 randomly selected exposed male and female subjects. Significant differences, however, were observed in the exposed group for symptoms of decreased ability to smell, eye irritation, throat irritation, and dry mouth in comparison with the reference group. These symptoms were also significantly related to the time and place of occurrence. Medical schools should take more concrete measures to reduce students' exposure to formaldehyde. Meanwhile, although it is not now the practice in most medical schools, students should have ready access to goggles and respirators when working in dissection laboratories.

Air Pollutants, Occupational↗
PubMed1992

Renal tubular function of cadmium exposed workers.

The kidney is considered the critical organ following long term occupational or environmental exposure to cadmium. Tubular dysfunction in the form of low molecular weight proteinuria is the earliest manifestation of cadmium nephrotoxicity. The current acceptable critical concentration of cadmium in the urine is 10 ug Cd/g creatinine. The aim of this paper is to identify the presence of tubular dysfunction among workers with less than 10 ug Cd/g creatinine. The exposed group of 92 workers were from a nickel-cadmium battery factory. The control group of 122 workers were factory and sedentary office workers with no known history of exposure to nephrotoxic agents. The urinary excretion of N-acetyl-D-glucosaminidase (NAG), beta-2-microglobulin (beta 2m) and alpha-1-microglobulins (alpha 1m) were measured from morning spot urine samples. The age, sex and race adjusted NAG and alpha 1m showed increasing trend with rising urinary cadmium levels. Levels were significantly raised when the urinary cadmium was above 5 ug Cd/g creatinine. A similar trend was seen with increasing length of exposure. Renal tubular dysfunction is present among cadmium exposed workers with levels below the current critical concentration.

Acetylglucosaminidase↗
PubMed1992

Sudden unexplained death syndrome. A review and update.

Sudden unexplained death syndrome (SUDS) among young healthy Thai construction workers in Singapore has been given much publicity recently. From May 1982 to July 1990, 226 SUDS were reported among them. In this article we review and compare studies on SUDS in the United States and South-east Asia. So far, studies to identify the causal factors have been inconclusive and they cannot explain the male preponderance and occurrence of death during sleep. Current hypotheses about the cause of SUDS have included stress, genetic factors, dietary deficiency (particularly thiamine), potassium deficiency, melioidosis and sleep disorders. The following areas are suggested for further research: epidemiological investigations on SUDS at its source; in-depth case studies of families with and without SUDS; role of dietary factors, biochemical studies with respect to thiamine, pyruvate and potassium metabolism in the victims and susceptibles; and histopathological studies of cases and controls.

Adolescent↗
PubMed1992

Sero-prevalence of hepatitis B infection among dental professionals.

Dental employees in government institutions in a State in Peninsular Malaysia were screened for exposure to hepatitis B virus (HBV) in 1989. Almost all (96.8%) of the 217 employees responded. One quarter (24.8%) was positive for at least one serological markers to HBV; 2.4% had hepatitis B surface antigen (HBsAg) and 22.4% had anti-body to HBsAg (anti-HBs). The presence of HBsAg was unrelated to age, sex, ethnicity, geographical locality and occupations of the subjects. The prevalence of anti-HBs increased with age and was highest for ethnic Chinese (53.6%), followed by Indians (25%), compared to Malays (14.9%) (p less than 0.001) and were increased among dentists (53.1%) and assistant nurses (33.3%). The overall prevalence of HBsAg and anti-HBs were similar to the situation in the community. However, dentists and their chairside assistant nurses, with a higher proportion of Chinese, had higher anti-HBs prevalences compared with that of the general population.

Adult↗
PubMed1991

Determination of thiamine and its phosphate esters by gradient-elution high-performance liquid chromatography.

A high-performance liquid chromatographic method for the determination of thiamine and its phosphate esters using gradient elution is presented. Chromatography was performed on an octadecyl C18 column with post-column derivatization using potassium ferricyanide: thiamine was oxidized to thiochrome, which was detected fluorimetrically. The gradient system avoids the use of a modifier and an ion-pairing reagent. The proposed method enables the separation of thiamine triphosphate, thiamine pyrophosphate, thiamine monophosphate and free thiamine, at concentrations of ca. 2 nM, within 10 min The within-assay precision for blood and serum total thiamine was less than 2 and 5%, respectively, and the between-day variation was less than 3 and 5%, respectively. The method is simple and rapid, and it can be used for screening of thiamine deficiency and for clinical study of various diseases related to vitamin B1 deficiency.

Chromatography, High Pressure Liquid↗
PubMed1991

Biological monitoring of occupational exposure to methyl ethyl ketone.

This study was conducted to evaluate the usefulness of three commonly used methods of biological monitoring for worker exposed to methyl ethyl ketone (MEK) under field conditions using blood, breath and urine. Environmental MEK exposures were measured by personal sampling with carbon-felt dosimeters. The correlation coefficient (r) between the time-weighted average (TWA) MEK concentration in air and the MEK concentration in blood collected at the end of the work shift was 0.85. The correlation coefficient between the TWA MEK level in air and the concentration exhaled in the breath of workers at the end of the work shift was 0.71. The end-of-shift urinary MEK excretion correlated best with the environmental concentration (r = 0.89). Correlations became lower after urine samples had been corrected for urinary creatinine (r = 0.83) or specific gravity (r = 0.73). After 8 h exposure to 200 ppm MEK, the corresponding end-of-shift urinary excretion was 5.1 mumol/l or 4.11 mg/g creatinine. This value is higher than that previously found in some studies, the difference probably being due to the physical activities of the present workers and their extensive skin contact with the solvent. The kinetics of inhaled MEK was also studied in eight subjects. Breath and urine samples were collected during the 8-h work shift on 2 consecutive Mondays. The results showed that urinary MEK excretion rose steadily until the end of exposure, whereas the MEK concentration in exhaled air varied markedly throughout the day.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1991

Biological monitoring for occupational exposure to toluene.

A study was undertaken to examine the relationship between exposure of workers to toluene in the work environment and biological indicators of toluene exposure. The biological indicators studied were toluene in expired air, toluene in blood obtained by the finger prick method, and urinary hippuric acid. The study was undertaken in a factory in Singapore that manufactures speakers for audio systems. A total of 86 female workers exposed to toluene at the workplace and a control group of workers not exposed to toluene were examined. All of them were teetotalers, were nonsmokers, and gave no history of chronic drug usage. The 8-hr time-weighted average exposure level of toluene ranged from 1.6 ppm to 263 ppm. The study showed the expected toluene levels in finger prick blood was 1.4 micrograms/mL after an 8-hr exposure to 100 ppm of toluene. Toluene concentration in expired air of 16 ppm after an 8-hr exposure to 100 ppm compared favorably with other studies. The toluene in blood/expired air ratio was observed to be lower than in other studies. In this study, the expected urinary hippuric acid level for a 100-ppm exposure to toluene was 2.7 g/g creatinine. This level is higher than that recorded in other studies. The results showed that at low levels of toluene, urinary hippuric acid is not a valuable indicator of exposure. Toluene in expired air is the most reliable biological indicator of exposure to toluene.

Air Pollutants, Occupational↗
PubMed1991

Male endocrine functions in workers with moderate exposure to lead.

Evidence for the effect of occupational exposure to lead on the male endocrine system is conflicting. This study evaluated the primary (testicular) and secondary (hypothalamo pituitary testicular) effects of exposure to lead in 122 current lead workers and 49 non-exposed workers. The mean current blood lead concentration was 35.2 (range 9.6-77.4) micrograms/dl in the exposed workers, and 8.3 (range 2.6-14.8) micrograms/dl in the non-exposed workers. Concentrations of plasma luteinising hormone (LH) and follicle stimulating hormone (FSH) were both significantly higher in the exposed workers, but testosterone (T) was not significantly different between the two groups. In older exposed workers, however (greater than or equal to 40 years), plasma T concentrations were significantly lower, but LH and FSH concentrations were not significantly different. Compared with non-exposed workers, those exposed for less than 10 years had significantly raised LH and FSH and normal T concentrations whereas those exposed for 10 or more years had significantly lower T, and normal LH and FSH concentrations. The concentrations of LH and FSH showed a moderate increase in relation to blood lead concentrations in the range of 10 micrograms/dl to 40 micrograms/dl and thereafter reached a plateau or declined. No apparent trend for plasma T concentrations occurred. No significant difference in prolactin (PRL) concentration was noted. It is concluded that moderate exposure to lead was associated in dose related fashion with small but measurable changes in male endocrine functions that reflected both primary and secondary effects of lead on the testes and the hypothalamo pituitary testicular axis.

Adolescent↗
PubMed1991

Biological monitoring of occupational exposure to tetrahydrofuran.

Occupational exposure to tetrahydrofuran (THF) was studied by analysis of environmental air, blood, alveolar air, and urine from 58 workers in a video tape manufacturing plant. Head space gas chromatography (GC) with an FID detector was used for determination of THF concentration in alveolar air, urine, and blood. Environmental exposure to THF was measured by personal sampling with a carbon felt passive dosimeter. When the end of shift urinary THF concentrations were compared with environmental time weighted average (TWA) values, urinary THF concentration corrected for specific gravity correlated well with THF concentration in air (r = 0.88), and uncorrected urinary THF concentration gave a similar result (r = 0.86). Correction for creatinine in urine weakened the correlation (r = 0.56). For exposure at the TWA concentration of 200 ppm the extrapolated concentration of THF was 33 mumol/l in blood and 111.9 mumol/l (61 mumol/g creatinine) or 109 mumol/l at a specific gravity of 1.018 in urine. The correlation between exposure to THF and its concentration in exhaled breath and blood was low (r = 0.61 and 0.68 respectively). Laboratory methodological considerations together with the good correlation between urinary THF concentration and the environmental concentration suggest that THF concentration in urine is a useful biological indicator of occupational exposure to THF.

Adult↗
PubMed1991

Monitoring of exposure to cyclohexanone through the analysis of breath and urine.

Occupational exposure to cyclohexanone was studied for 59 workers through the analysis of environmental air, alveolar air, and urinary cyclohexanol. Environmental cyclohexanone exposure was measured by personal sampling with a carbon-felt passive dosimeter. Cyclohexanone in alveolar air and cyclohexanol in urine were determined with gas chromatography with a flame ionization detector. The end-of-shift urinary cyclohexanol levels correlated well with the time-weighted average environmental cyclohexanone values (r = 0.66). Urinary cyclohexanol corrected for creatinine correlated best with cyclohexanone in air (r = 0.77); when corrected for specific gravity, it gave a similar correlation coefficient (r = 0.73). When the time-weighted average of the exposure was 25 ppm, the corresponding calculated concentration for urinary cyclohexanol was 54.5 mg/1, 23.3 mg/g of creatinine, or 43.5 mg/l at a specific gravity of 1.018. The relationship between cyclohexanone exposure and its concentration in exhaled breath was found to be poorer than that for cyclohexanone exposure and the urinary metabolite (r = 0.51).

Adolescent↗
PubMed1991

Ethnic differences in blood lead concentration among workers in a battery manufacturing factory.

Blood lead levels of two ethnic groups (11 Chinese and 25 Malays) of workers in a factory manufacturing lead accumulator battery were studied. The mean adjusted (for environmental lead levels, age, exposure duration and stick-years of smoking by analysis of covariance) blood lead level of the Malays was 34.8 micrograms/dl as compared to 22.4 micrograms/dl for the Chinese. This difference was significant (p less than 0.02). Oral ingestion of lead, through eating of food with hands contaminated by lead compound, among the Malay workers was suggested as a possible cause for the difference in the mean blood lead levels. Preventive measures and recommendations to overcome the problem among this particular group of workers were discussed.

Adult↗
PubMed1990

Biological monitoring of workers exposed to lead stearate.

This study was conducted to examine the usefulness of some of the commonly used biological parameters for monitoring of workers exposed to lead stearate. Forty-two lead stearate workers from a lead stabilizer factory and 26 workers exposed to inorganic lead compounds were involved in this study. Although the workers had similar blood lead values (PbB), subjects exposed to lead stearate were found to have a significantly higher concentration of lead in plasma (PbP), 1.0 +/- 0.57 micrograms dl-1) than workers exposed to inorganic lead compounds (0.42 +/- 0.3). The ratio of PbP to PbB was ca. 2.5 times higher for lead stearate workers (0.38) than the inorganic lead workers (0.15). These data suggest that the different chemical properties of lead stearate may result in different distributional patterns of the metal in different blood components. On the other hand, the activity of delta-aminolevulinic acid dehydratase (ALAD), an enzyme highly sensitive to lead, was not so much depressed among the lead stearate workers as that of workers handling inorganic lead. A poor correlation was also observed between PbB and ALAD activity of the stearate workers. These findings indicate that PbB and ALAD are not good biological indicators for evaluating the toxicological effect of lead stearate exposure.

Chemical Industry↗
PubMed1990

Urinary levels of proteins and metabolites in workers exposed to toluene. A cross-sectional study.

We measured urinary excretion of albumin and retinol-binding proteins to investigate the occurrence of early renal dysfunction in 45 paint workers exposed principally to toluene, and in the same number of unexposed control subjects matched individually for sex and age. Two biological indicators of personal toluene absorption, namely urine hippuric acid and o-cresol, were also measured in the exposed subjects. A significantly higher level and increased prevalence of elevated retinol-binding protein in the urine of exposed workers was found, whereas no significant difference in urinary albumin concentration was seen between the two groups. Urinary concentrations of retinol-binding protein was correlated (r = 0.399, P less than 0.006) with that of o-cresol, but not with hippuric acid or employment duration. The results suggest a dose-dependent early tubular effect due to toluene exposure that might be useful for monitoring individuals exposed to toluene at work.

Adult↗
PubMed1990

The in vitro and in vivo effects of lead on delta-aminolevulinic acid dehydratase and pyrimidine 5'-nucleotidase.

The in vitro and in vivo effects of lead on the activity of pyrimidine-5'-nucleotidase (P5N, E. C. 3.1.3.5) and delta-aminolevulinic acid dehydratase (ALA-D, E.C. 4.2.1.24) were studied. Incubation of blood with lead at concentrations of up to 3 mumol/l (about 60 micrograms/dl) did not appear to affect the activity of P5N, while the activity of ALA-D decreased dose-dependently with lead. Administration of lead caused a marked and rapid suppression of ALA-D in rats. The suppression of lead on P5N appeared to be a rather slow process. The decrease of its activity only came into effect 20 days after administration with lead. these findings suggest that lead induced P5N inhibition is a slow process while the suppression of ALA-D activity occurs much earlier.

5'-Nucleotidase↗