Comparison of human liver and small intestinal glutathione S-transferase-catalyzed busulfan conjugation in vitro.
The apparent oral clearance of busulfan has been observed to vary as much as 10-fold in the population of children and adults receiving high-dose busulfan. The only identified elimination pathway for busulfan involves glutathione conjugation. The reaction is predominantly catalyzed by glutathione S-transferase (GST) A1-1, which is present in both liver and intestine. The purpose of this study was to compare busulfan Vmax/Km in cytosol prepared from adult human liver and small intestine. Tetrahydrothiophenium ion formation rate per milligram of cytosolic protein was constant along the length (assessed in 30-cm segments) of three individual small intestines. A 30-cm-long intestinal segment 90-180 cm from the pylorus was chosen to be representative of intestinal cytosolic busulfan conjugating activity. Busulfan Vmax/Km (mean +/- SD) in cytosol prepared from 23 livers and 12 small intestines was 0.166 +/- 0.066 and 0.176 +/- 0.085 microl/min/mg cytosolic protein, respectively, in incubations with 5 microM busulfan, 1 mM glutathione, and 2 mg of cytosolic protein. The relative content of GSTalpha (A1-1, A1-2, and A2-2) was compared for human liver and intestinal cytosol using Western blot. The levels of GSTalpha in liver and intestinal cytosol were 1.12 +/- 0.56 and 1.36 +/- 0.32 integrated optimal density units/5 microg cytosolic protein, respectively. Busulfan conjugation in vitro was comparable per milligram of cytosolic protein in liver and intestinal cytosol.
Gibbs
J P
JP
Department of Pharmaceutics, University of Washington, Seattle, WA 98195-7610, USA.
Yang
J S
JS
Slattery
J T
JT
D002066:Busulfan / Q000737:chemistry / Q000378:metabolism*; D002384:Catalysis; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D004136:Dinitrobenzenes / Q000378:metabolism; D005982:Glutathione Transferase / Q000378:metabolism / Q000494:pharmacology; D006801:Humans; D007421:Intestine, Small / Q000737:chemistry / Q000201:enzymology*; D007700:Kinetics; D008099:Liver / Q000737:chemistry / Q000201:enzymology*; D011506:Proteins / Q000737:chemistry / Q000378:metabolism; D013876:Thiophenes / Q000378:metabolism
D004136:Dinitrobenzenes; D011506:Proteins; D013876:Thiophenes; D005982:Glutathione Transferase; D002066:Busulfan