Stereoselective glucuronidation and hydroxylation of etodolac by UGT1A9 and CYP2C9 in man.

1. In vitro metabolic studies with etodolac were performed. S- and R-etodolac were converted to the acylglucuronide and hydroxylated metabolites by UDP-glucuronosyltransferase (UGT) and cytochrome P450 in microsomes. However, the stereoselectivities of UGT and P450 for the isomers were opposite. S-etodolac was glucuronidated preferentially than R-etodolac by UGT. In contrast, R-etodolac was hydroxylated preferentially than S-etodolac by P450. 2. Of several human P450 enzymes, CYP2C9 had the greatest activity for hydroxylation of R-etodolac. Sulfaphenazole, an inhibitor of CYP2C9, and anti-CYP2C9 antibody inhibited the hydroxylation of R-etodolac in human liver microsomes. CYP2C9 therefore contributes to the stereoselective hydroxylation of R-etodolac. 3. Of several human UGT enzymes, UGT1A9 had the greatest activity for glucuronidation of S-etodolac. Propofol and thyroxine, inhibitors of UGT1A9, inhibited the glucuronidation of S-etodolac in human liver microsomes. Therefore, UGT1A9 is mainly responsible for the stereoselective glucuronidation of S-etodolac. 4. Because S-etodolac was metabolized more rapidly than R-etodolac in human cryopreserved hepatocytes, the stereoselectivities of UGT1A9 for etodolac substantially influenced the overall metabolism of S- and R-etodolac in man.

Paraoxonase has a major role in the hydrolysis of prulifloxacin (NM441), a prodrug of a new antibacterial agent.

NM441 is a prodrug of the new quinolone carboxylic acid antibacterial agent NM394. A rat serum enzyme (NM441-hydrolase) that catalyzes the hydrolysis of NM441 to NM394 was purified by ultracentrifugation, heparin-Sepharose column chromatography, and HPLC with a Mono Q anion exchange column. The enzyme showed a single protein band after sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Its molecular mass was estimated as 46 kDa. The amino-terminal sequence and two internal amino acid sequences of the NM441-hydrolase resemble those of mouse, rabbit, and human serum paraoxonases. Moreover, its enzymatic characteristics (optimum pH, calcium requirement, and molecular mass) were similar to those of the paraoxonases. These findings identify the NM441-hydrolase as rat serum paraoxonase. To determine whether the paraoxonase catalyzes the hydrolysis of NM441 to NM394 in human serum, we investigated whether the paraoxonase and NM441-hydrolase activities were correlated. There was a positive correlation (r = 0.653, p < 0.005) found in the sera of 67 healthy volunteers, indicating that paraoxonase is responsible for the conversion of NM441 to NM394 in humans. Human paraoxonase shows polymorphism. There was a 9-fold variation in paraoxonase activity but only a 2-fold variation in NM441-hydrolase activity. These findings show that paraoxonase polymorphism does not cause marked interindividual variation in NM441-hydrolase activity and is substrate dependent.

Pharmacokinetics of (+/-)-4-diethylamino-1,1-dimethylbut-2-yn-1-yl 2-cyclohexyl-2-hydroxy-2-phenylacetate monohydrochloride monohydrate. 2nd communication: tissue levels and enzyme activity in rats after repeated administration, and placental and milk transfer after single administration.

The absorption, distribution and excretion of radioactivity in rats were studied during and after repeated oral administration of 30 mg/kg of NS-21 ((+/-)-4-diethylamino-1, 1-dimethylbut-2-yn-1-yl 2-cyclohexyl-2-hydroxy-2-phenylacetate monohydrochloride monohydrate, CAS 129927-33-4) once a day for 21 days. The plasma concentrations of radioactivity 24 h after each administration of 14C-NS-21 reached a steady state on the 5th day. 48 h after the 21st administration, the plasma concentrations of radioactivity were under the detection limit. The plasma concentrations of the radioactivity after the 7th oral administration of 14C-NS-21 was higher than that after the single administration, but similar to those after the 14th and 21st administrations. There were no marked differences in the elimination half-lives after each administration. The urinary and fecal excretion of the radioactivity was 21.5 and 81.3%, respectively, within 168 h after the 21st administration. In most tissues, no radioactivity was observed 336 h after the 21st administration. Repeated oral administration of 30 and 100 mg/kg of NS-21 once a day for 7 days had no effect on the cytochrome P-450 content, aniline hydroxylase and aminopyrine N-demethylase activity in rat liver. The transfer of radioactivity into fetuses and milk was investigated after single oral administration of 14C-NS-21 to female rats. In the 18th day pregnant rats, the radioactivity concentrations were lower in most fetal tissues than in the maternal plasma. After oral administration of 14C-NS-21 to lactating rats, the concentrations of radioactivity were higher in the milk than in the maternal plasma during an 8-h period. No radioactivity was observed in milk 48 h after administration.

Cloning and nucleotide sequence of the carboxynorspermidine decarboxylase gene from Vibrio alginolyticus.

The gene (nspC) encoding carboxynorspermidine decarboxylase (CANS DC), the last enzyme in norspermidine biosynthesis, in Vibrio alginolyticus was isolated by immuno-screening and its complete nucleotide sequence was determined. Sequence analysis of the subcloned fragment (2.0 kb) revealed an ORF of 1131 bp encoding a protein of 377 amino acids with a calculated molecular mass of 42,008 Da. The sequence of 20 N-terminal amino acids of purified CANS DC was found to be identical to that predicted from the nspC gene. A putative ribosome binding sequence was observed 8 bp upstream from the translation start site (ATG), and promoter- and terminator-like sequences were detected upstream and downstream of the ORF, respectively. Database searches identified no similar proteins, but the deduced amino acid sequence contained a putative pyridoxal 5'-phosphate binding region similar to those of the bacterial meso-2,6-diaminopimelate decarboxylases and eukaryotic ornithine decarboxylases. Another full ORF was found on the opposite strand downstream from the nspC gene. It encoded a protein of 69 amino acids with a calculated molecular mass of 7441 Da, which exhibited some weak similarity to ScrR, a repressor protein of V. alginolyticus, in the helix-turn-helix DNA binding domain, but did not appear to be expressed in the host cells.

Purification and characterization of L-2,4-diaminobutyrate decarboxylase from Acinetobacter calcoaceticus.

Acinetobacter calcoaceticus ATCC 23055 produces a large amount of 1,3-diaminopropane under normal growth conditions. The enzyme responsible, L-2,4-diaminobutyrate (DABA) decarboxylase (EC 4.1.1.-), was purified to electrophoretic homogeneity from this bacterium. The native enzyme had an M(r) of approximately 108,000, with a pI of 5.0, and was a dimer composed of identical or nearly identical subunits with apparent M(r) 53,000. The enzyme showed hyperbolic kinetics with a Km of 1.59 mM for DABA and 14.6 microM for pyridoxal 5'-phosphate as a coenzyme. The pH optimum was in the range 8.5-8.75, and Ca2+ gave a much higher enzyme activity than Mg2+ as a cationic cofactor. N-gamma-Acetyl-DABA, 2,3-diaminopropionic acid, ornithine and lysine were inert as substrates. The enzyme was different in subunit structure, N-terminal amino acid sequence and immunoreactivity from the DABA decarboxylase of Vibrio alginolyticus previously described.