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

Abstract

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.

Figure 1. The structure of the pyrrole adduct.

A: 2,5-dimethylpyrrole adducts, B: cross-linked pyrrole adducts.

Figure 2. Effects of n-hexane on rats body weight, gait score and the rate of paralysis of rats.

The data were expressed as mean±S.D. (n = 8).

Figure 3. Changes of pyrrole adducts levels in serum and urine of rats exposed to n-hexane for 24 weeks.

The data were expressed as mean ± S.D. (n = 8). A: pyrrole adducts in serum 8 hours postdose; B: pyrrole adducts in urine 8 hours postdose; C: pyrrole adducts in serum 24 hours postdose; D: pyrrole adducts in urine 24 hours postdose.

Figure 4. Correlations between the time to paralysis and the pyrrole adducts levels in serum and urine at time of paralysis.

A: pyrrole adducts in serum 8 hours postdose; B: pyrrole adducts in urine 8 hours postdose; C: pyrrole adducts in serum 24 hours postdose; D: pyrrole adducts in urine 24 hours postdose.

Figure 5. Correlations between the gait score and the pyrrole adducts levels in serum and urine in week 8.

A: pyrrole adducts in serum 8 hours postdose; B: pyrrole adducts in urine 8 hours postdose; C: pyrrole adducts in serum 24 hours postdose; D: pyrrole adducts in urine24 hours postdose.

Figure 6. Difference in pyrrole adducts formation between the human serum and rat serum.

*P<0.05 versus human serum.