RT Journal Article
SR Electronic
T1 Sulfhydryl-Dependent Biotransformation and Macromolecular Binding of 1,2-Dibromo-2,4-Dicyanobutane in Blood
JF Drug Metabolism and Disposition
JO Drug Metab Dispos
FD American Society for Pharmacology and Experimental Therapeutics
SP 1001
OP 1007
VO 26
IS 10
A1 Jingqi Bao
A1 John-Michael Sauer
A1 Richard L. Smith
A1 Robert K. Kuester
A1 Margaret J. Kattnig
A1 I. Glenn Sipes
YR 1998
UL http://dmd.aspetjournals.org/content/26/10/1001.abstract
AB 1,2-Dibromo-2,4-dicyanobutane (BCB) is a broad-spectrum microbicide used commercially in consumer products. The objectives of this study were to elucidate the biotransformation of BCB, characterize its ability to covalently bind macromolecules, and predict the possible toxicological ramifications of such events. After iv administration of [14C]BCB to male Fischer 344 rats,14C-equivalents were observed to bind gradually to blood constituents. By 48 hr, approximately 12% of the total dose was covalently bound. At no time was parent compound detected in the blood. However, the debrominated BCB metabolite 2-methyleneglutaronitrile (MGN) was observed. In vitroexperiments revealed that BCB was extremely labile and was readily debrominated in fresh whole blood, erythrocyte preparations, and buffered glutathione (GSH) solutions. In each case, the formation of MGN was inhibited by the alkylation of free sulfhydryls withN-ethylmaleimide (NEM). For every 1 mol of BCB converted to MGN, 2 mol of GSH were oxidized to glutathione disulfide (GSSG) (BCB + 2 GSH → MGN + GSSG + 2 HBr). The oxidation of free sulfhydryls during the conversion of BCB to MGN caused erythrocyte hemolysis (EC50 ∼ 1 mM) in isolated preparations. Hemolysis was increased by coincubation of BCB with NEM (EC50 ∼ 0.3 mM) and was decreased by coincubation with GSH (EC50 > 3 mM). However, MGN did not cause hemolysis of erythrocytes, even at concentrations 10-fold higher than the EC50 of BCB. In vitro experiments also demonstrated that incubation with either BCB or MGN resulted in significant macromolecular binding to the erythrocyte fraction of the blood (∼80%). Incubation with NEM resulted in a significant decrease in binding for both BCB (11.3% bound) and MGN (29.5% bound). Because BCB is rapidly debrominated in whole blood, it appears that MGN is the reactive species responsible for macromolecular binding. From these studies, we conclude that the conversion of BCB to MGN is mediated by a free sulfhydryl-dependent biotransformation pathway. Furthermore, BCB biotransformation is required for erythrocyte binding, and the consumption of free sulfhydryls associated with the biotransformation of BCB is responsible for hemolysis. The American Society for Pharmacology and Experimental Therapeutics