title: Elucidation of the mechanism of ribose conjugation in a pyrazole-containing compound in rodent liver.
abstract: 1. Here we report on the mechanism of ribose conjugation, through NADH as a cofactor, of a pyrazole-containing compound (PT). Incubation of PT in rat liver microsomes supplemented with NADP⁺/H, NAD⁺/H, and β-nicotinamide mononucleotide (NMN) resulted in complete conjugation to the adenine dinucleotide phosphate conjugate (ADP-C), adenine dinucleotide conjugate (AD-C), and 5-phosphoribose conjugate (Rib-C1), respectively. In hepatocytes, PT predominantly formed three ribose conjugates: Rib-C1, the ribose conjugate (Rib-C2), and the carboxylic acid of Rib-C2 (Rib-C3). 2. Phosphatase inhibitors were added to hepatocyte incubations. AD-C was detected in this reaction, which suggests that one of the major pathways for the formation of the ribose conjugates is through NAD⁺/H. When AD-C was incubated with phosphatase, Rib-C1 and Rib-C2 formed. 3. To understand the in vivo relevance of this metabolic pathway, rats were dosed with PT and Rib-C2 was found in the urine. 4. Structure-activity relationship shows that replacement of the distal thiazole group in the PT to a phenyl group abolishes this conjugation. Three amino acid residues in the active site preferentially interact with the sulfur atom in the thiazole of PT. 5. In summary, PT forms direct AD-C in hepatocytes, which is further hydrolyzed by phosphatase to give ribose conjugates.
authors.affiliation: Department of Drug Metabolism and Pharmacokinetics, Genentech, Inc., South San Francisco, CA, USA.
authors.forename: Hoa
authors.initials: H
authors.lastname: Le
authors.forename: Kevin A
authors.initials: KA
authors.lastname: Ford
authors.forename: S Cyrus
authors.initials: SC
authors.lastname: Khojasteh
authors.forename: Peter W
authors.initials: PW
authors.lastname: Fan
mesh_terms: D036002:ADP Ribose Transferases / Q000378:metabolism; D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D000469:Alkaline Phosphatase / Q000037:antagonists & inhibitors / Q000378:metabolism; D000818:Animals; D020134:Catalytic Domain; D002852:Chromatography, Ion Exchange; D022781:Hepatocytes / Q000201:enzymology; D006801:Humans; D006868:Hydrolysis; D008099:Liver / Q000378:metabolism*; D008297:Male; D008862:Microsomes, Liver / Q000378:metabolism; D008958:Models, Molecular; D011720:Pyrazoles / Q000378:metabolism*; D012266:Ribose / Q000378:metabolism* / Q000652:urine; D012377:Rodentia / Q000378:metabolism*; D013347:Subcellular Fractions / Q000378:metabolism; D013379:Substrate Specificity; D013816:Thermodynamics
chemical_list: D011720:Pyrazoles; D000246:Adenosine Diphosphate Ribose; C031280:pyrazole; D012266:Ribose; D036002:ADP Ribose Transferases; D000469:Alkaline Phosphatase