Simultaneous determination of the major metabolites of styrene and acetaminophen, and of unchanged acetaminophen in urine by ion-pairing high-performance liquid chromatography

Isolation and Culture of Porcine Hepatocytes for Artificial Liver Support

The primary requirement of cells in a liver support system is the preservation of the in vivo metabolic functions that prevent or decrease the progress of hepatic encephalopathy (HE) by providing interim support to liver failure patients. While rodent hepatocytes offer a model for liver assist device (LAD) research, their limited number per animal prohibits direct scale up to human devices. Healthy human liver cells are seldom available in adequate numbers to support clinical LAD use; consequently, a large animal source of liver cells is needed. The study presented here explored the potential of porcine hepatocytes to proliferate and maintain metabolic function in vitro. Porcine hepatocytes were isolated from ~12 kg swine by a modification of Seglen's method. Hepatocytes cultured up to 10 days were shown to metabolize ammonia and maintain both Phase I and II detoxification functions. In addition, the cultures showed proliferative activity both as an increase in total protein content and by thymidine incorporation. Immunocytochemical staining identified cell proliferation through Day 4 to be primarily hepatocytes while Days 6 and 10 showed nonparenchymal cells to be increasing. The detoxification functions measured showed peak activity on Day 4 and gradually declined through Day 10. The ability of porcine hepatocytes to proliferate and maintain a diversity of hepatic functions in culture strongly suggests their potential for use as the biological component of artificial LADs.

Chiral separations of mandelic acid by HPLC using molecularly imprinted polymers

Styrene is used in a variety of chemical industries. Environmental and occupational exposures to styrene occur predominantly through inhalation. The major metabolite of styrene is present in two enantiomeric forms, chiral R- and S- hydroxy-1-phenyl-acetic acid (R-and S-mandelic acid, MA). Thus, the concentration of MA, particularly of its enantiomers, has been used in urine tests to determine whether workers have been exposed to styrene. This study describes a method of analyzing mandelic acid using molecular imprinting techniques and HPLC detection to perform the separation of diastereoisomers of mandelic acid. The molecularly imprinted polymer (MIP) was prepared by non-covalent molecular imprinting using (+) MA, (-) MA or (+) phenylalanine, (-) phenylalanine as templates. Methacrylic acid (MAA) and ethylene glycol dimethacrylate (EGDMA) were copolymerized in the presence of the template molecules. The bulk polymerization was carried out at 4ºC under UV radiation. The resulting MIP was grounded into 25~44¼m particles, which were slurry packed into analytical columns. After the template molecules were removed, the MIP-packed columns were found to be effective for the chromatographic resolution of (±)-mandelic acid. This method is simpler and more convenient than other chromatographic methods.

Growth and metabolic activity of immortalized porcine hepatocytes in extracorporeal hollow-fiber liver assist devices

The development of a cell based extracorporeal liver assist device offers a promising clinical approach to bridge individuals suffering from acute liver failure to transplant. However, a major drawback of the existing technology is the lack of a continuous supply of well differentiated hepatocytes. Although some investigators have used primary porcine cells, this approach demands costly, labor-intensive isolation procedures and yields cells with inconsistent detoxification capacity. The limitations of primary cells led us to develop the HepLiu immortalized porcine hepatocyte cell line for use in liver assist devices (LADs). HepLiu cells are nontumorigenic and exhibit multiple hepatic detoxification functions including diazepam and acetaminophen metabolism. To investigate the suitability of HepLiu cells for artificial liver support, morphology, as well as xenobiotic metabolism, was studied in perfused polysulfone hollow-fiber LADs. HepLiu cells were cultured in the intercapillary space of a prototype LAD, and the metabolism of diazepam, acetaminophen, and 7-ethoxycoumarin was evaluated over 25 days in culture. Our results indicated that HepLiu cells proliferated rapidly following inoculation of the LAD until Day 10 when proliferation appeared to cease. Ultrastructural analysis demonstrated that HepLiu cells retained many of the features of primary hepatocytes including desmosomes that sealed bile canalicular-like structures and junctional complexes (intermediate, gap junctions) that appeared concentrated in the paracanalicular areas. Unlike primary porcine hepatocytes, HepLiu cells retained drug metabolic function throughout the 25 day culture period. Diazepam metabolism by HepLiu cells was consistently higher than that of primary cells. Acetaminophen metabolism persisted throughout the 25 day period albeit at a much lower level than the primary cells exhibited on Days 1 or 2. In conclusion, we have shown that HepLiu cells proliferate to occupy the intercapillary space of perfused hollow-fiber LADs following inoculation, and retain their metabolic capacity for Phase I and Phase II detoxification reactions in perfusion culture. Our findings suggest that HepLiu cells may provide an alternative to primary porcine hepatocytes as the cellular component of bioartificial liver support systems.

The evidence for conjugated mandelic and phenylglyoxylic acids in the urine of rats dosed with styrene

Male Wistar rats were dosed intraperitoneally with styrene (400 mg/kg). Urine samples were collected over phosphate buffer, pH 6.5 for 24 h. Excretion of mandelic (MA) and phenylglyoxylic acid (PGA) amounted to 1.66 +/- 0.62 and 5.21 +/- 2.44% of dose, respectively, as determined by ion-pair HPLC. After acidic hydrolysis, the amount of MA and PGA found in urine increased to 2.10 +/- 0.84 and 6.81 +/- 3.20% (mean +/- S.D.; n = 7), respectively. A similar increase was observed after alkaline hydrolysis of urine samples. Differences between hydrolysed and non-hydrolysed samples were significant in the paired t-test (P < 0.05). Further, urine samples were fractionated by HPLC. Fractions were subjected to acidic hydrolysis and analysed by HPLC and GC/MS. Both MA and PGA were detected in the fraction which did not contain any of these metabolites before hydrolytic treatment. Thus, MA and PGA, which are used as biomarkers of exposure to styrene, form hydrolysable conjugates in the rat. At least a minor part of the total urinary MA and PGA is bound in these conjugates.

Isolation and culture of porcine hepatocytes for artificial liver support

The primary requirement of cells in a liver support system is the preservation of the in vivo metabolic functions that prevent or decrease the progress of hepatic encephalopathy (HE) by providing interim support to liver failure patients. While rodent hepatocytes offer a model for liver assist device (LAD) research, their limited number per animal prohibits direct scale up to human devices. Healthy human liver cells are seldom available in adequate numbers to support clinical LAD use; consequently, a large animal source of liver cells is needed. The study presented here explored the potential of porcine hepatocytes to proliferate and maintain metabolic function in vitro. Porcine hepatocytes were isolated from approximately 12 kg swine by a modification of Seglen's method. Hepatocytes cultured up to 10 days were shown to metabolize ammonia and maintain both Phase I and II detoxification functions. In addition, the cultures showed proliferative activity both as an increase in total protein content and by thymidine incorporation. Immunocytochemical staining identified cell proliferation through Day 4 to be primarily hepatocytes while Days 6 and 10 showed nonparenchymal cells to be increasing. The detoxification functions measured showed peak activity on Day 4 and gradually declined through Day 10. The ability of porcine hepatocytes to proliferate and maintain a diversity of hepatic functions in culture strongly suggests their potential for use as the biological component of artificial LADs.

Determination of the urinary metabolites of styrene: estimation of the method evaluation function and evaluation of reference values in Danish subjects

A European study on styrene exposure was initiated in 1989 to evaluate the health effects of environmental and occupational exposure. A part of this study included the development of an analytical method for use in a biological monitoring program. The urinary metabolites of styrene, mandelic acid (MA) and phenylglyoxylic acid (PGA) were quantitated by a direct and convenient high-performance liquid chromatography method. Urine samples were diluted with eluent and analysed by HPLC with a C8 reversed-phase column and a buffer to acetonitrile (9:1) eluent with a counterion added. The detector used was a variable UV detector and the wavelength was lambda = 210 nm. The method was statistically evaluated by a method evaluation demonstrating no systematic error. The uncertainty was 23.8 mumol/l and 11.5 mumol/l for MA and PGA, respectively. The limit of detection (LOD) of MA is 71.4 mumol/l and the LOD of PGA is 34.5 mumol/l, sufficiently low for the measurement of styrene exposure at a low exposure level. The present study indicates that reference values for MA and PGA are low. The fraction of reference values below LOD was 0.80 for MA and 0.66 for PGA; consequently, the reference values were described by a non-parametric one-sided tolerance interval. The 95% one-sided upper tolerance limits calculated for MA and PGA were 31.0 mumol/mmol creatinine and 20.1 mumol/mmol creatinine, respectively, with the coverage 0.95 +/- 0.045 for both metabolites. The method has been used for biological monitoring in several studies of environmentally and occupationally exposed subjects in concentrations up to 200 mumol/mmol creatinine for MA and 150 mumol/mmol creatinine for PGA.

Chromatographic determination of volatile solvents and their metabolites in urine for monitoring occupational exposure

The determination of volatile solvents and their metabolites in biological materials such as expired air, blood or urine allows the estimation of the degree of exposure of these chemicals. Chromatographic methods are now universally employed for this purpose and numerous analytical procedures are available for the determination of the most commonly used volatile solvents and their metabolites in urine. GC methods appear well adapted to the determination of the parent volatile solvents in blood and urine and may be used for the determination of their urinary metabolites, but these methods often require several prechromatographic steps. However, HPLC is becoming a powerful tool for the accurate and easy determination of urinary metabolites of volatile solvents, considering its decisive advantages for routine monitoring. Further, recent developments in HPLC could widen the usefulness of this method for most complex analytical problems that could be encountered during this measurement. However, despite the relative neglect of planar chromatography in this area of concern and considering the great interest in methods that could permit the simultaneous assay of numerous samples often required by routine monitoring, new approach using improved methods such as overpressured TLC could be very fruitful in the future.

Analysis and stability of phenylglyoxylic and mandelic acids in the urine of styrene-exposed people

In this work a high-performance liquid chromatographic method is described that is reliable and practical for use in routine biological monitoring of exposure to styrene. The method uses a modern diode array detection technique by which mandelic and phenylglyoxylic acids can be measured simultaneously using different wavelengths. The liquid chromatographic method was compared to a gas chromatographic method developed for the analysis of mandelic, phenylglyoxylic and para-hydroxymandelic acids. The methods gave results consistent with each other. These two methods were then used to check the stability of the main metabolites of styrene, especially of phenylglyoxylic acid, in urine samples stored at +6 degrees C or at -18 degrees C for periods up to 70 days. None of the frozen samples showed any significant decrease in the phenylglyoxylic acid concentration, whereas at 6 degrees C one of the samples showed a reduction of 46% after 1 month.

Evaluation of biological monitoring parameters for occupational exposure to toluene

A survey was conducted in a rotogravure printing plant with inhalatory and percutaneous exposure to toluene. Workers (n = 9) were followed for 2 consecutive days and the frequency and duration of skin contact with toluene were monitored. In order to assess percutaneous absorption an airstream helmet was worn during one day. Urine and exhaled air samples were collected simultaneously 5 times each day for toluene (urine and breath) and hippuric acid (urine). The mean (personal air sampling) exposure concentration was between 30 mg/m3 and 600 mg/m3. The best biological monitoring parameter of external exposure (without a helmet) was the concentration toluene in exhaled air 8 h after work (r = 0.99). While wearing the airstream helmet the relationship between external exposure (measured in the helmet) and concentrations in exhaled air and urine deviated from the preceding relations. This was likely the result of the high body burden and not of skin contact with toluene. Skin contact with toluene (usually by cleaning of the hands) was limited to 0-30 minutes a day, with an average of about 5 minutes. During experimental exposure (n = 6) in which the hands were washed with toluene for 5 minutes the toluene in exhaled air (max after 1040 min) clearly demonstrated skin absorption of toluene. The next morning 0.1 mg/m3 toluene was still detectable; this was less than the concentration measured the next morning in exhaled air of workers: between 0.5 and 10 mg/m3.

Determination of paracetamol and its four major metabolites in mouse plasma by reversed-phase ion-pair high-performance liquid chromatography

A reversed-phase ion-pair high-performance liquid chromatographic method has been used for the separation of paracetamol and its four major metabolites (glucuronide, sulphate, cysteine and mercapturate conjugates) in mouse plasma samples. An ODS column was used and the mobile phase consisted of an aqueous solution of 0.01 M tetrabutylammonium chloride and 0.01 M Tris buffered to pH 5.0 with phosphoric acid, with methanol as the organic solvent. The gradient elution started with 30% methanol. After a delay of 0.5 min the methanol concentration was increased linearly to 75% over 7.5 min. The column was returned to the initial conditions after a delay of 1 min. A methanol solution of theophylline was added to the mouse plasma sample, centrifuged and immediately injected into the chromatographic system. The advantages of this method include good and rapid separation (last metabolite detected at 6.86 min), well resolved peaks, only a small amount of sample required for assay, adequate precision (no coefficient of variation was greater than 10% for paracetamol metabolites) and a high sensitivity (particularly for unchanged paracetamol and the cysteine conjugate).