Tatsumi, K; Kitamura, S; Kato, M; Hiraoka, K
Sodium nifurstyrenate [Beta-(5-nitro-2-furyl)-p-carboxystyrene sodium salt, NSA- Na] is an antibacterial nitrofuran which has been widely used for prevention and treatment of bacterial infections in fish in Japan. When NSA-Na was anaerobically incubated with rabbit liver cytosol and 2-hydroxypyrimidine, 1-(p-carboxyphenyl)-5-cyano-3-oxo-1,4-pentadiene (cyano-pentadienone), 1-(p-car- boxyphenyl)-5-cyano-3-oxo-1-pentene (cyano-pentenone), and 1-(p-carboxyphenyl)-5 -cyano-3-pentanone (cyano-pentanone) were isolated and identified as the metabolites of the nitrofuran. In addition, when cyano-pentenone and cyano-pentanone were aerobically incubated with the liver preparation and NADPH, 1-(p-carboxyphenyl)-5-cyano-3-hydroxy-1-pentene (cyano-pentenol) and 1-(p-carboxyphenyl)-5-cyano-3-pentanol (cyano-pentanol) were also isolated and identified as the metabolites of the nitrofuran in its further metabolism, respectively. The anaerobic incubation of NSA-Na with rat liver cytosol and 2-hydroxypyrimidine resulted in the formation of cyano-penta-dienone and cyano-pentanone. In this case, however, cyano-pentenone not detectable. On the other hand, when NSA-Na was anaerobically incubated with sea bream liver cytosol and NADPH, the formation of cyano-pentenone, cyano-pentanone, and cyano-pentenol, but not cyano-pentadienone, was observed. Furthermore, cyano-pentanone was metabolized to cyano-pentanol by the fish liver preparation with NADPH under aerobic conditions. When NSA-Na was given orally to rabbits, cyano-pentanone, cyano-pentenol, cyano-pentanol, and beta-(acetamido-2-furyl)-p-carboxystyrene (acetamidofuran) were identified as the urinary metabolites of the nitrofuran. In rats, cyano-pentanone and acetamidofuran, but not cyano-pentenol and cyano-pentanol, were also identified as the urinary or fecal metabolites of the nitrofuran. On the other hand, when goldfish were bathed in NSA-Na solution, only cyano-pentanone was identified as the in vivo metabolite of the nitrofuran in the fish. These NSA-Na metabolites except cyano-pentenone and acetamidofuran are new types of nitrofuran metabolites. In rabbits and rats, the conversion of NSA-Na to cyano-pentadienone is catalyzed by a liver cytosolic 2-hydroxypyrimidine-linked enzyme (probably aldehyde oxidase). The double bond reduction is due to cytosolic NAD(P)H-linked enzymes, one of which is NADPH-linked alpha,beta-ketoalkene double bond reductase. NADH-linked carbonyl reductase activity exists in rabbit liver, but not in rat liver. In sea breams, the conversion of NSA-Na to cyano-pentenone is catalyzed by microsomal and cytosolic NADPH-linked enzymes. NAD(P)H-linked double bond reductase and NADPH-linked carbonyl reductase activities reside in the liver cytosol. However, goldfish appears to be unable to reduce the carbonyl group. Mutagenic activities of cyano-pentenone and cyano-pentanone were examined using Salmonella typhimurium TA 100 and TA 98. These metabolites showed only very weak activities against either tester strain in the presence or absence of S-9 Mix.