Abstract
In previous studies, it was shown that liver microsomes from rabbit, rat, pig, and human are involved in the reduction of N-hydroxylated amidines, guanidines, and amidinohydrazones of various drugs and model compounds (Drug Metab Rev 34: 565–579). One responsible enzyme system, the microsomal benzamidoxime reductase, consisting of cytochrome b5, its reductase, and a cytochrome P450 isoenzyme, was isolated from pig liver microsomes (J Biol Chem 272:19615–19620). Further investigations followed to establish whether such enzyme systems are also present in microsomes of other organs such as brain, lung, and intestine. In addition, the mitochondrial reduction in human and porcine liver and kidney preparations was studied. The reductase activities were measured by following the reduction of benzamidoxime to benzamidine, guanoxabenz to guanabenz, and Ro 48-3656 ([[1-[(2S)-2-[[4-[(hydroxyamino)iminomethyl]benzoyl]amino]-1-oxopropyl]-4-piperidinyl]oxy]-acetic acid) to Ro 44-3888 ([[1-[(2S)-2-[[4-(aminoiminomethyl)benzoyl]amino]-1-oxopropyl]-4-piperidinyl]oxy]-acetic acid). Interestingly, preparations of all tested organs were capable of reducing the three compounds. The highest specific rates were found in kidney followed by liver, brain, lung, and intestine, and usually the mitochondrial reduction rates were superior. From the determined characteristics, similarities between the enzyme systems in the different organs and organelles were detected. Furthermore, properties of the benzamidoxime reductase located in the outer membrane of pig liver mitochondria were studied. In summary, these results demonstrate that in addition to the microsomal reduction, mitochondria are involved to a great extent in the activation of amidoxime prodrugs. The importance of extrahepatic metabolism in the reduction of N-hydroxylated prodrugs is demonstrated.
Footnotes
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Financial support was provided by the Deutsche Forschungsgemeinschaft (DFG, Cl 56/6-3) and the Fonds der Chemischen Industrie. Preliminary results were presented in Arch Pharm332 (Suppl 2):31 and Arch Pharm333 (Suppl 1):12.
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Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.
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doi:10.1124/dmd.105.005249.
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ABBREVIATIONS: HPLC, high-performance liquid chromatography; Ro 48-5656, amidoxime (free acid); Ro 48-3656, [[1-[(2S)-2-[[4-[(hydroxyamino)iminomethyl]benzoyl]amino]-1-oxopropyl]-4-piperidinyl]oxy]-acetic acid; Ro 48-3888, [[1-[(2S)-2-[[4-(aminoiminomethyl)benzoyl]amino]-1-oxopropyl]-4-piperidinyl]oxy]-acetic acid; P450, cytochrome P450; MOPS, 3-(N-morpholino)propanesulfonic acid; BSA, bovine serum albumin; DTT, dithiothreitol; OMV, outer membrane vesicle(s); p-HMB p-hydroxymercuribenzoic acid.
- Received April 21, 2005.
- Accepted August 22, 2005.
- The American Society for Pharmacology and Experimental Therapeutics
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