Metabolism of sulphobromophthalein I: positional isomers of sulphobromophthalein monoglutathione conjugate

Abstract

Abstract Three positional isomers of sulphobromophthalein glutathione monoconjugate (BSP-mGSH) were detected using a paired-ion HPLC method that employs triethylamine phosphate (TEA-H3PO4) as a pairing agent. To confirm that these compounds were glutathione (GSH) conjugates, sulphobromophthalein (BSP) was incubated with a four-fold volume of GSH under alkaline ammonium hydroxide. At least 6 metabolites (3 di-GSH conjugates and 3 isomers of mono-GSH conjugates) were produced under these conditions. The three mono-GSH conjugates were each purified and identified as compounds with a molecular weight of 1020 according to FAB mass spectrometry results. Positional isomers of BSP-GSH were provisionally distinguished via the addition of the symbols α, β and δ to the end of each abbreviation, to reflect the amount of isomers present. Thus, the isomer present in the largest quantity was termed BSP-mGSH(α), the second most abundant isomer was termed BSP-mGSH(β) and the third was termed BSP-mGSH(δ). Interestingly, a species difference was recognized in that rat cytosol GSH S-transferase (GST) primarily produced BSP-mGSH(α), whereas guinea-pig cytosol generated BSP-mGSH(δ), BSP-mGSH(α) and BSP-mGSH(β) equally and rabbit cytosol mainly produced BSP-mGSH(β).