Evidence that a β-N-glucuronide of 4,4'-methylenebis(2-chloroaniline) (MbOCA) is a major urinary metabolite in man: implications for biological monitoring

Abstract

Urine samples from workers exposed to 4,4'-methylenebis(2-chloroaniline) (MbOCA) contain a labile metabolite(s) that, on hydrolysis, yields the parent compound at concentrations two to three times those of free MbOCA. Evidence has now been obtained that the major labile metabolic is an N-glucuronide of MbOCA. The N-glucuronide of MbOCA was synthesised chemically, characterised by thermospray mass spectrometry, and found to have a pseudomolecular (M + 1) ion at m/z 443/445. MbOCA and [14C] uridine diphosphoglucuronic acid ([14C]UDPGA) were incubated with liver microsomes from rats induced with polychlorinated biphenyls. The stoichiometry of the reaction product was about 1:1 (MbOCA:UDPGA). This product, the chemically synthesised glucuronide, and the labile urinary metabolite had identical chromatographic and hydrolytic (heat and β-glucuronidase) properties. These studies show that the major labile conjugate of MbOCA in the urine of workers exposed to this compound is probably the mono N-glucuronide. In view of the lability of this compound and the fact that its concentration in urine is two to three times that of free MbOCA, it is essential that any strategy for the biological monitoring of exposed workers takes into account the N-glucuronide.