Determination of urinary 2,5-hexanedione concentration by an improved analytical method as an index of exposure to n-hexane

Irreversible Protein Labeling by Paal-Knorr Conjugation

The application of new chemical reactions in a biological context has advanced bioconjugation methods for both fundamental research and commercial arenas. Recent adaptations of reactions such as Huisgen 1,3-dipolar or Diels-Alder cycloadditions have enabled the labeling of specific residues in biomolecules by the attachment of molecules carrying azides, alkynes, or strained alkenes. Although these are fundamental tools, there is a need for the discovery of reactions that can label native proteins. We report herein the adaptation of the Paal-Knorr reaction to label lysine residues in proteins via pyrrole linkages.

Biological exposure indices of pyrrole adducts in serum and urine for hazard assessment of n-hexane exposure

BACKGROUND

Pyrrole adducts might be used as a biomarker for monitoring occupational exposure to n-hexane, but the Biological Exposure Indices of pyrrole adducts in serum and urine are still unknown. The current study was designed to investigate the biological exposure limit of pyrrole adducts for hazard assessment of n-hexane.

METHODS

Male Wistar rats were given daily dose of 500, 1000, 1500, 2000, 4000 mg/kg bw n-hexane by gavage for 24 weeks. The levels of pyrrole adducts in serum and urine were determined at 8, 24 hours postdose once a week. The Biological Exposure Indices was evaluated by neurological evaluation and the levels of pyrrole adducts. The difference in pyrrole adducts formation between humans and rats were estimated by using in vitro test.

RESULTS

Dose-dependent effects were observed between the doses of n-hexane and pyrrole adducts in serum and urine, and the levels of pyrrole adduct in serum and urine approached a plateau at week 4. There was a significantly negative correlation between the time to paralysis and the level of pyrrole adducts in serum and urine, while a positive correlation between gait score and levels of pyrrole adducts in serum and urine was observed. In vitro, pyrrole adducts formed in human serum was about two times more than those in rat serum at the same level of 2,5-HD.

CONCLUSION

It was concluded that the BEIs of pyrrole adducts in humans were 23.1 ± 5.91 nmol/ml in serum 8 h postdose, 11.7 ± 2.64 nmol/ml in serum 24 h postdose, 253.8 ± 36.3 nmol/ml in urine 8 h postdose and 54.6 ± 15.42 nmol/ml in urine 24 h postdose.

Biomarker research in neurotoxicology: the role of mechanistic studies to bridge the gap between the laboratory and epidemiological investigations

There is an increasing interest in the development and validation of biomarkers for use in biochemical/molecular epidemiological studies. Though the area of neurotoxicology has received much attention in the past several years, it still lags behind with regard to the development of biomarkers, particularly those of health effects and susceptibility. This review discusses several aspects of biomarker research as it relates to neurotoxic compounds and focuses on selected agents (organophosphorus insecticides, styrene, n-hexane, carbon disulfide, acrylamide), which have been the subject of a number of investigations in animals and humans. While traditional biomonitoring approaches and novel techniques (e.g., hemoglobin adducts) provide several measurements for monitoring exposure to neurotoxic chemicals, potential markers of genetic susceptibility have been seldom investigated in a neurotoxicology context. Furthermore, the complexity of the nervous system, together with the multiplicity of end points and the limited knowledge of the exact mechanism(s) of action of neurotoxicants, has led to only limited advancements in the development of biomarkers for neurotoxic effects. Significant progress in this area will depend upon an increased understanding of the cellular, biochemical, and molecular targets directly involved in neurotoxicity.

Monitoring of exposure to methylpentanes by diffusive sampling and urine analysis for alcoholic metabolites

OBJECTIVES

To investigate the possibilities of personal ambient monitoring and biological monitoring for methylpentane isomers.

METHODS

The performance of activated carbon cloth to absorb 2- and 3-methylpentane was studied by experimental vapour exposure followed by solvent extraction and gas chromatography (GC). Urine from workers and rats exposed to 2- and 3-methylpentane was analysed by GC with or without acid or enzymatic hydrolysis.

RESULTS

Carbon cloth absorbed 2- and 3-methylpentane linearly to exposures up to eight hours and to 400 ppm, and was sensitive enough to detect a 15 minute peak of exposure. The two isomers were clearly separated from hexane on a DB-1 column. For analysis of the urine, enzymatic hydrolysis was superior to acid hydrolysis. Exposure of rats to methylpentane vapours showed that 2-methyl-2-pentanol and 3-methyl-2-pentanol were excreted in urine in proportion to the dose of 2-methylpentane and 3-methylpentane, respectively. 2-Methyl derivatives of 1-, 3-, and 4-propanol, 2-methylpentane-2,4-diol, and 3-methyl-2-pentanol were minor metabolites. Analysis of urine from the exposed workers showed that 2-methyl- and 3-methyl-2-pentanol are leading urinary metabolites after exposure to the corresponding methylpentane.

CONCLUSIONS

Diffusive sampling is applicable to monitor 2- and 3-methylpentane vapours as is the case for hexane vapour. 2-Methyl-2-pentanol and 3-methyl-2-pentanol will be markers of occupational exposure to 2-methylpentane and 3-methylpentane, respectively. Also, 2-methylpentane-2,4-diol might be a marker of exposure to 2-methylpentane.

Interlaboratory quality control and status of n-hexane biological monitoring in Japan

This paper reports the problem of interlaboratory quality control and the actual condition of biological monitoring of n-hexane among the seven major laboratories specializing in clinical chemistry tests, where more than 80% of the total urine specimens in Japan have been analyzed after the beginning of biological monitoring of n-hexane in 1989. First, transportation conditions of urine specimens and transportation effects on measurement results were studied. The seven major laboratories carried urine specimens at distances of more than 450 km from the University of Occupational and Environmental Health (UOEH) to the respective laboratories and had at least one transit terminal where specimens from various areas were collected and transferred to the analytical laboratories. All laboratories used cooler boxes with dry ice or ice bars and stored the specimens in freezers or refrigerators. Specimens arrived at the final destinations within 24 hours. The transportation from institutes for health examination to the laboratories did not affect the measurement results of 2,5-hexanedione (HD), a determinant of n-hexane biological monitoring. Interlaboratory cross-checks were performed among the seven major laboratories and four institutes for occupational health examination that have their own analytical laboratories. All of the laboratories analyzed HD by acid hydrolysis (pH < 1.0); interlaboratory differences were recognized at the first cross-check. After some laboratories intensified gas chromatography (GC) maintenance and changed to a new column, the interlaboratory variation lessened.(ABSTRACT TRUNCATED AT 250 WORDS)

Modification of metabolism and neurotoxicity of hexane by co-exposure of toluene

The effects of co-exposure of hexane and toluene were investigated in field surveys and animal experiments. One field survey suggested that increase of hexane content in adhesives might have caused an outbreak of polyneuropathy in a vinyl sandal manufacture in Japan. The animal experiments proved that co-exposure of hexane and toluene decrease hexane neurotoxicity and urinary excretion of hexane metabolites in rats. The results also suggested that toluene might inhibit metabolism of hexane. Another recent field survey indicated that the ratio of urinary 2,5-hexanedione to hexane exposure in the workers co-exposed to hexane and toluene decreased in parallel with in more crease of toluene concentration. The results indicated that urinary excretion of 2,5-hexanedione could be depressed by co-exposure of toluene even in the workers exposed to relatively low concentrations. These above-mentioned results suggest that co-exposure of hexane and toluene could inhibit hexane metabolism and decrease hexane neurotoxicity in both experimental animals and workers. Although metabolism of hexane could be easily modified by toluene or other solvents and might not be a good indicator for hexane exposure in mixed exposure, urinary 2,5-hexanedione might be a good indicator for neurotoxicity of hexane even in mixed exposure.