Differences between initial and final hippuric acid concentrations were compared by Student's t-test.
Environmental toluene and urinary hippuric acid levels.
The GM of the urinary hippuric acid at the beginning and the end of a work shift were 0.
First, toluene levels in work area air and hippuric acid levels in urine were measured for each subject, and these data were individually associated with the subject's CYP2E1 mRNA data.
Hippuric acid has been used extensively as a toluene exposure biomarker, but this metabolite may occur in the diet, that is, via some fruits and food preservatives (Kawamoto et al.
The associations of peripheral lymphocyte CYP2E1 mRNA content with environmental toluene or urinary hippuric acid were statistically significant.
Each batch of substrate was checked for the presence of free hippuric acid by assaying a sample blank (10 [micro]L of distilled water added to 40 [micro]L of substrate).
For the calibration procedure, four 1000-[micro]L aliquots of the hippuric acid calibrator solution (22.
The carboxypeptidase activity (U/L) was calculated using the mean ratio of the peak heights of hippuric acid and the peak heights of the internal standard of the sample, blank, and calibrator.
Activity was measured with the substrate Hip-Arg, and the released hippuric acid was determined by HPLC.
Detection of the enzyme-produced product is simple, fast (separation of hippuric acid and the substrate within 3 min), and can be partly automated.