A single amino acid substitution confers high cinchonidine oxidation activity comparable with that of rabbit to monkey aldehyde oxidase 1.

Aldehyde oxidase 1 (AOX1) is a major member of the xanthine oxidase family belonging to the class of complex molybdo-flavoenzymes and plays an important role in the nucleophilic oxidation of N-heterocyclic aromatic compounds and various aldehydes. The enzyme has been well known to show remarkable species differences. Comparing the rabbit and monkey enzymes, the former showed extremely high activity toward cinchonidine and methotrexate, but the latter exhibited only marginal activities. In contrast, monkey had several times greater activity than did rabbit toward zonisamide and (+)-4-(4-cyanoanilino)-5,6-dihydro-7-hydroxy-7H-cyclopenta[d]-pyrimidine [(S)-RS-8359]. In this report, we tried to confer high cinchonidine oxidation activity comparable with that of rabbit AOX1 to monkey AOX1. The chimera proteins prepared by restriction enzyme digestion and recombination methods between monkey and rabbit AOX1s indicated that the sequences from Asn993 to Ala1088 of rabbit AOX1 are essential for the activity. The kinetic parameters were then measured using monkey AOX1 mutants prepared by site-directed mutagenesis. The monkey V1085A mutant acquired the high cinchonidine oxidation activity. Inversely, the reciprocal rabbit A1081V mutant lost the activity entirely: amino acid 1081 of rabbit AOX1 corresponding to amino acid 1085 of monkey AOX1. Thus, cinchonidine oxidation activity was drastically changed by mutation of a single residue in AOX1. However, this might be true for bulky substrates such as cinchonidine but not for small substrates. The mechanism of substrate-dependent species differences in AOX1 activity toward bulky substrates is discussed.

Effects of selenium deficiency on aldehyde oxidase 1 in rats.

Selenium deficiency has been reported to result in an extraordinary decrease of glutathione peroxidase (GSH-Px) and, reversely, an increase of detoxifying enzymes such as glutathione-S-transferase (GST), uridine-5'-diphosphate glucuronosyltransferase (UGT), nicotinamide-dependent quinine oxidoreductase (NQO1; DT-diaphorase), and epoxide hydrolase without significantly affecting cytochrome P450 activity. However, little is known about the effects on aldehyde oxidase 1 (AOX1) activity towards various kinds of aldehydes and N-heterocyclic aromatic compounds. The aim of this study is to clarify the effects of selenium deficiency on AOX1 in rats. As expected, selenium deficiency was confirmed by the extremely low activity of GSH-Px along with the increased activities of GST and DT-diaphorase. AOX1 activity towards vanillin and (S)-RS-8359 was increased by selenium deficiency, and that corresponded to an increase of AOX1 protein level but not to a decreased AOX1 mRNA level. It has been documented that the assembly of the catalytically active holoenzyme forms of the molybdo-flavoenzyme family is very complex and is controlled through transcriptional and translational events by many gene products. In addition, selenium deficiency has been known to cause oxidative stress that leads to an increase of AOX1 activity. Furthermore, aldehyde oxidase homolog 1 (AOH1) with properties similar to AOX1 is present in rodent liver. All the reports suggest that the mechanisms by which selenium deficiency increases AOX1 activity are highly complicated and investigated from different points of view.

Functional analysis of aldehyde oxidase using expressed chimeric enzyme between monkey and rat.

Aldehyde oxidase (AO) is a homodimer with a subunit molecular mass of approximately 150 kDa. Each subunit consists of about 20 kDa 2Fe-2S cluster domain storing reducing equivalents, about 40 kDa flavine adenine dinucleotide (FAD) domain and about 85 kDa molybdenum cofactor (MoCo) domain containing a substrate binding site. In order to clarify the properties of each domain, especially substrate binding domain, chimeric cDNAs were constructed by mutual exchange of 2Fe-2S/FAD and MoCo domains between monkey and rat. Chimeric monkey/rat AO was referred to one with monkey type 2Fe-2S/FAD domains and a rat type MoCo domain. Rat/monkey AO was vice versa. AO-catalyzed 2-oxidation activities of (S)-RS-8359 were measured using the expressed enzyme in Escherichia coli. Substrate inhibition was seen in rat AO and chimeric monkey/rat AO, but not in monkey AO and chimeric rat/monkey AO, suggesting that the phenomenon might be dependent on the natures of MoCo domain of rat. A biphasic Eadie-Hofstee profile was observed in monkey AO and chimeric rat/monkey AO, but not rat AO and chimeric monkey/rat AO, indicating that the biphasic profile might be related to the properties of MoCo domain of monkey. Two-fold greater V(max) values were observed in monkey AO than in chimeric rat/monkey AO, and in chimeric monkey/rat AO than in rat AO, suggesting that monkey has the more effective electron transfer system than rat. Thus, the use of chimeric enzymes revealed that 2Fe-2S/FAD and MoCo domains affect the velocity and the quantitative profiles of AO-catalyzed (S)-RS-8359 2-oxidation, respectively.

Involvement of cytochrome P450-mediated metabolism in tienilic acid hepatotoxicity in rats.

Tienilic acid is reported to be converted into electrophilic metabolites by cytochrome P450 (CYP) in vitro. In vivo, however, the metabolites have not been detected and their effect on liver function is unknown. We previously demonstrated that tienilic acid decreased the GSH level and upregulated genes responsive to oxidative/electrophilic stresses, such as heme oxygenase-1 (Ho-1), glutamate-cysteine ligase modifier subunit (Gclm) and NAD(P)H dehydrogenase quinone 1 (Nqo1), in rat liver, as well as inducing hepatotoxicity by co-treatment with the glutathione biosynthesis inhibitor l-buthionine-(S,R)-sulfoximine (BSO). In this study, for the first time, we identified a glutathione-tienilic acid adduct, a stable conjugate of putative electrophilic metabolites with glutathione (GSH), in the bile of rats given a single oral dose of tienilic acid (300mg/kg). Furthermore, a tienilic acid-induced decrease in the GSH level and upregulation of Ho-1, Gclm and Nqo1 were completely blocked by pretreatment with the CYP inhibitor 1-aminobenzotriazole (ABT, 66mg/kg, i.p.). The increase in the serum ALT level and hepatocyte necrosis resulting from the combined dosing of BSO and tienilic acid was prevented by ABT, despite a low hepatic GSH level. These findings suggest that the electrophilic metabolites of tienilic acid produced by CYP induce electrophilic/oxidative stresses in the rat liver and this contributes to the hepatotoxicity of tienilic acid under impaired GSH biosynthesis.

Properties of 130 kDa subunit of monkey aldehyde oxidase.

We previously demonstrated the existence of a minor 130 kDa subunit in the sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE)/Western blot analysis of monkey liver cytosol and expressed monkey aldehyde oxidase (AO) in Escherichia coli. In contrast, the 130 kDa subunit was not observed in rat AO. In the current study, the properties of the 130 kDa subunit were investigated from the viewpoint of species differences in the presence of the subunit and AO activity. Monkey AO with His-tag at the N- and C-terminus were expressed, and were immunoanalyzed with anti-AO and anti-His-tag antisera. The results revealed that the minor 130 kDa subunit was produced by cleavage at the N-terminal side of the 150 kDa subunit. The cleavage point was shown to be located between 188Leu and 189Pro of 150 kDa AO subunit by the Edman degradation method. The two amino acids related to the cleavage are contained in the linkage between the 2Fe-2S and FAD domains in AO of human and monkey, but not in AO of rat and mouse. As a fact, the 130 kDa subunit was observed in AO of human and monkey, but not in AO of rat and mouse, suggesting the two amino acids might be one reason of a species difference in the formation of the 130 kDa subunit. However, the existence of the 130 kDa subunit is not associated with the species differences in AO activity, because the cleavage results in the loss of 2Fe-2S cluster domain essential for exertion of AO activity.

Construction and expression of mutant cDNAs responsible for genetic polymorphism in aldehyde oxidase in Donryu strain rats.

We demonstrated the genetic polymorphism of aldehyde oxidase (AO) in Donryu strain rats: the ultrarapid metabolizer (UM) with nucleotide mutation of (377G, 2604C) coding for amino acid substitution of (110Gly, 852Val), extensive metabolizer (EM) with (377G/A, 2604C/T) coding for (110Gly/Ser, 852Val/Ala), and poor metabolizer (PM) with (377A, 2604T) coding for (110Ser, 852Ala), respectively. The results suggested that 377G > A and/or 2604C > T should be responsible for the genetic polymorphism. In this study, we constructed an E. coli expression system of four types of AO cDNA including Mut-1 with (377G, 2604T) and Mut-2 with (377A, 2604C) as well as naturally existing nucleotide sequences of UM and PM in order to clarify which one is responsible for the polymorphism. Mut-1 and Mut-2 showed almost the same high and low activity as that of the UM and PM groups, respectively. Thus, the expression study of mutant AO cDNA directly revealed that the nucleotide substitution of 377G > A, but not that of 2604C > T, will play a critical role in the genetic polymorphism of AO in Donryu strain rats. The reason amino acid substitution will cause genetic polymorphism in AO activity was discussed.

Cloning, expression, and characterization of male cynomolgus monkey liver aldehyde oxidase.

In this study, we investigated the properties of monkey liver aldehyde oxidase directed toward the clarification of species differences. The aldehyde oxidase preparation purified from male cynomolgus monkey liver cytosol showed a major 150 kDa Coomassie brilliant blue (CBB)-stained band together with a minor 130 kDa band using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Both bands were identified as being aldehyde oxidase by a database search of the MS data obtained with nano-liquid chromatography, quardrupole time of flight, mass spectrometry (nano-LC Q/TOF MS). Based on the sequence coverage, the 130 kDa protein was presumed to be deficient in 20-30 kDa mass from the N-terminus. Full male cynomolgus monkey aldehyde oxidase cDNA was cloned and sequenced with the four degenerate primers designed by considering the peptide sequences containing the amino acids specific for monkey aldehyde oxidase. The deduced amino acid sequences had 96% amino acid identity with those of human enzyme. The aldehyde oxidase expressed in Escherichia coli also exhibited two immunoreactive bands on SDS-PAGE/Western blot analysis. Further, the biphasic pattern was observed for Eadie-Hofstee plots of the (S)-enantiospecific 2-oxidation activity of RS-8359 with the expressed and cytosolic monkey liver aldehyde oxidase. The results suggested that two forms of aldehyde oxidase in monkey were the expression products by a single gene. In contrast, the similarly expressed rat aldehyde oxidase showed only one immunoreactive protein and monophasic pattern. The biphasic phenomenon could be caused by the existence of two aldehyde oxidase isoforms or two active sites in a single enzyme or some other reasons. Further studies on the problems of the biphasic pattern and species differences in aldehyde oxidase are needed.

Lack of formation of aldehyde oxidase dimer possibly due to 377G>A nucleotide substitution.

In addition to the many articles reporting on the marked differences in species and large differences in rat strains in response to aldehyde oxidase (AO), individual differences in some rat strains have also been reported. However, little has been clarified about any related molecular biological mechanisms. We previously revealed that nucleotide substitutions of 377G>A and 2604C>T in the AO gene might be responsible for individual differences in AO activity in Donryu strain rats. By using native polyacrylamide gel electrophoresis/Western blotting in this study, the lack of formation of the AO dimer protein, which is essential for catalytic activity, was shown in poor metabolizer Donryu rats, and this could be a major reason for the individual differences. Rat strain differences were also verified from the same perspectives of nucleotide substitutions and expression levels of a dimer protein. Rat strains with high AO activity showed nucleotide sequences of (377G, 2604C) and a dimer protein. In the case of those with low AO activity, the nucleotide at position 2604 was fixed at T, but varied at position 377, such as G, G/A, and A. An AO dimer was detected in the liver cytosols of rat strains with (377G, 2604T), whereas a monomer was observed in those with (377A, 2604T). These results suggest that the lack of formation of a dimer protein leading to loss of catalytic activity might be due to 377G>A nucleotide substitution. Individual and strain differences in AO activity in rats could be explained by this 377G>A substitution, at least in the rat strains used in this study.

Influence of cytochrome P450 (CYP) 3A5 polymorphisms on the pharmacokinetics of lansoprazole enantiomers in CYP2C19 extensive metaboliser renal transplant recipients.

BACKGROUND AND OBJECTIVE: Lansoprazole is extensively metabolised by cytochrome P450 (CYP) 2C19 and CYP3A4. The purpose of this study was to evaluate the effects of CYP3A5 polymorphism (A6986G) on the pharmacokinetics of lansoprazole enantiomers in renal transplant recipients who are CYP2C19 extensive metabolisers (EMs). METHODS: Among 40 Japanese CYP2C19 EMs, 20 had the CYP3A5*1 allele (*1/*1 in two subjects and *1/*3 in 18 subjects) and 20 had the CYP3A5*3/*3 genotype. After repeated oral doses of racemic lansoprazole 30mg once daily for 28 days, plasma concentrations of lansoprazole enantiomers were determined using high performance liquid chromatography. RESULTS: The mean area under the plasma concentration-time curves from 0 to infinity (AUC(infinity)) of (R)- and (S)-lansoprazole in recipients with the CYP3A5*1 allele were 3145 and 384 ng * h/mL, respectively, compared with 4218 and 587 ng * h/mL in recipients with the CYP3A5*3/*3 genotype. The AUC(infinity) and the maximum plasma concentration of (R)- and (S)-lansoprazole in subjects with the CYP3A5*3/*3 genotype were greater than subjects with CYP3A5*1/*1 + *1/*3 alleles. The mean R/S ratio for AUC of lansoprazole in each CYP3A5 genotype group was the same (12.6). CONCLUSION: Our findings show that CYP3A5 genotype is not an important determinant of enantioselective disposition of lansoprazole. Based on our results and those of previous studies, the enantioselective disposition of lansoprazole appears to be primarily influenced by enantioselective metabolism by CYP2C19 rather than by CYP3A.

Genetic polymorphism of aldehyde oxidase in Donryu rats.

One of major metabolic pathways of [(+/-)-4-(4-cyanoanilino)-5,6-dihydro-7-hydroxy-7H-cyclopenta[d]-pyrimidine] (RS-8359), a selective and reversible monoamine oxidase type A inhibitor, is the aldehyde oxidase-catalyzed 2-hydroxylation at the pyrimidine ring. Donryu rats showed a dimorphic pattern for the 2-oxidation activity with about 20- to 40-fold variations in the Vmax/Km values between a low and a high activity group. The rats were classified as extensive metabolizers (EM) and poor metabolizers (PM) of RS-8359, of which ratios were approximately 1:1. One rat among the EM rats of each sex showed extremely high activity, and they were referred to as ultrarapid metabolizers. There was no significant difference in the expression levels of mRNA of aldehyde oxidase between the EM and PM rats. Analysis of nucleotide sequences showed four substitutions, of which the substitutions at 377G>A and 2604C>T caused 110Gly-Ser and 852Ala-Val amino acid changes, respectively. Amino acid residue 110 is located very near the second Fe-S center of aldehyde oxidase. Its change from nonchiral Gly to chiral Ser may result in a conformational change of aldehyde oxidase protein with the shift of isoelectric point value from 5.0 in the EM rats to 6.2 in the PM rats. The 110Gly-Ser amino acid substitution (377G>A) may be primarily responsible for the variations of aldehyde oxidase activity observed in Donryu rats, in addition to the difference of expression levels of aldehyde oxidase protein. If a new drug candidate is primarily metabolized by aldehyde oxidase, attention should be given to using a rat strain with high aldehyde oxidase activity and small individual variation.

Substrate selectivity of monoamine oxidase A, monoamine oxidase B, diamine oxidase, and semicarbazide-sensitive amine oxidase in COS-1 expression systems.

The substrate selectivity of monoamine oxidase A (MAO-A), monoamine oxidase B (MAO-B), diamine oxidase (DAO), and semicarbazide-sensitive amine oxidase (SSAO) was investigated in the absence of chemical inhibitors using the COS-1 cells expressed with respective amine oxidase. Serotonin (5-hydroxytryptamine), 1-methylhistamine, and histamine were preferentially oxidized by MAO-A, SSAO, and DAO, respectively, at a low substrate concentration. In contrast, benzylamine, tyramine, and beta-phenylethylamine served as substrates for all of MAO-A, MAO-B, and SSAO. Each amine oxidase showed broad substrate selectivity at a high substrate concentration. The cross-inhibition was remarkable in MAO-A and MAO-B, especially in MAO-A, but not in SSAO and DAO. A study of the substrate selectivity of amine oxidases should include consideration of the effects of substrate concentration and specific chemical inhibitors.

Chiral inversion of RS-8359: a selective and reversible MAO-A inhibitor via oxido-reduction of keto-alcohol.

RS-8359, (+/-)-4-(4-cyanoanilino)-5,6-dihydro-7-hydroxy-7H-cyclopenta[d]-pyrimidine is a selective and reversible MAO-A inhibitor. The (S)-enantiomer of RS-8359 has been demonstrated to be inverted to the (R)-enantiomer after oral administration to rats. In the current study, we investigated the chiral inversion mechanism and the properties of involved enzymes using rat liver subcellular fractions. The 7-hydroxy function of RS-8359 was oxidized at least by the two different enzymes. The cytosolic enzyme oxidized enantiospecifically the (S)-enantiomer with NADP as a cofactor. On the other hand, the microsomal enzyme catalyzed more preferentially the oxidation of the (S)-enantiomer than the (R)-enantiomer with NAD as a cofactor. With to product enantioselectivity of reduction of the 7-keto derivative, it was found that only the alcohol bearing (R)-configuration was formed by the cytosolic enzyme with NADPH and the microsomal enzyme with NADH at almost equal rate. The reduction rate was much larger than the oxidation rate of 7-hydroxy group. The results suggest that the chiral inversion might occur via an enantioselectivity of consecutive two opposing reactions, oxidation and reduction of keto-alcohol group. In this case, the direction of chiral inversion from the (S)-enantiomer to the (R)-enantiomer is governed by the enantiospecific reduction of intermediate 7-keto group to the alcohol with (R)-configuration. The enzyme responsible for the enantiospecific reduction of the 7-keto group was purified from rat liver cytosolic fractions and identified as 3alpha-hydroxysteroid dehydrogenase (3alpha-HSD) via database search of peptide mass data obtained by nano-LC/MS/MS.

Enantioselective 2-hydroxylation of RS-8359, a selective and reversible MAO-A inhibitor, by cytochrome P450 in mouse and rat liver microsomes.

RS-8359, (+/-)-4-(4-cyanoanilino)-5,6-dihydro-7-hydroxy-7H-cyclopenta[d]-pyrimidine is a racemic compound with a selective and reversible monoamine oxidase A (MAO-A) inhibition activity. The substrate and product enantioselectivity with respect to 2-hydroxylation of RS-8359 enantiomers was studied using mouse and rat liver microsomes. In mice, the (S)-enantiomer was transformed to the cis-diol metabolite, whereas the (R)-enantiomer to the trans-diol metabolite. The Vmax/Km value for the formation of the cis-diol metabolite from the (S)-enantiomer was sevenfold greater than that for the formation of the trans-diol metabolite from the (R)-enantiomer. The greater Vmax/Km value for the (S)-enantiomer was due to the tenfold smaller Km value compared to that for the (R)-enantiomer. The results were in fair agreement with the previously reported low plasma concentrations of the (S)-enantiomer and the high recovery of the cis-diol metabolite derived from the (S)-enantiomer in urine after oral administration of RS-8359 to mice. Similarly to mice, in rats the (R)-enantiomer was transformed to the trans-diol metabolite, whereas the (S)-enantiomer yielded the cis-diol and trans-diol metabolites. The Vmax/Km value for the (R)-enantiomer was larger than that for the (S)-enantiomer in rats, indicating that the low plasma concentration of the (S)-enantiomer in rats might be caused by a metabolic reaction other than P450-dependent hydroxylation. CYP3A was shown to be responsible for the trans-diol formation from the (R)-enantiomer.

Rat strain differences in stereospecific 2-oxidation of RS-8359, a reversible and selective MAO-A inhibitor, by aldehyde oxidase.

Aldehyde oxidase catalysed 2-oxidation activity of the (S)-enantiomer of RS-8359, a selective and reversible monoamine oxidase A (MAO-A) inhibitor, was investigated in liver cytosolic fractions from ten rat strains. Remarkably large strain differences were observed with approximately a 230 variation between the highest activity in the Wistar-Imamichi strain and the lowest activity in the Slc:Wistar strain. The activities of Crj:SD and Slc:SD strain rats were considerably low, and that of the F344/DuCrj strain was very low. Among six Wistar strains, Crj:Wistar, Slc:Wistar, WKY/Izm, WKAH/Hkm, Jcl:Wistar and Wistar-Imamichi, the Slc:Wistar strain rats showed exceptionally low 2-oxidation activity that was comparable to that of the F344/DuCrj strain. The rat strain differences in the catalytic activity of aldehyde oxidase could correlate in part with the expressed levels of protein based on the mRNA of aldehyde oxidase. However, no small discrepancy existed in the almost negligible catalytic activity and the fairly high expression levels of protein and mRNA in the F344/DuCrj and Slc:Wistar strain rats. Some genetic factors might possibly be one of reasons for the discrepancy.

Metabolism of nicotine in rat lung microvascular endothelial cells.

The aim of this study was to examine whether cultured rat lung microvascular endothelial cells (LMECs), which constitute the gas-blood barrier, have the ability to metabolize nicotine. Nicotine was biotransformed to cotinine and nicotine N'-oxide by cytochrome 450 (CYP) and flavin-containing monooxyganase (FMO), respectively, in rat LMECs. The intrinsic clearance (Vmax1/Km1) for the cotinine formation was about 20 times as high as that for the trans-nicotine N'-oxide formation in the low-Km phase, indicating that oxidation by CYP was much higher than that by FMO. On the other hand, as shown in Eadie-Hofstee plots, the formation of cis-nicotine N'-oxide was monophasic, whereas the plot for the trans-nicotine N'-oxide formation was clearly biphasic. These results suggest that nicotine N'-oxide was stereoselectively metabolized to cis and trans forms. However, in the high-Km phase there was no significant difference in N'-oxidation between the cis and trans forms. Moreover, we suggest that CYP2C11 and CYP3A2 are key players in the metabolism to cotinine of nicotine in rat LMECs using the respective enzyme inhibitors (tranylcypromine and troleandomycine). On the other hand, methimazole (5 microM) caused 73 and 45% decreases in the formation of N'-oxides of cis- and trans- enantiomers, respectively, demonstrating the presence of FMO in rat LMECs. These results suggest that rat LMEC enzymes can convert substrates of exogenous origin such as nicotine for detoxication, indicating LMECs are an important barrier for metabolic products, besides hepatic cells.

Species differences in enantioselective 2-oxidations of RS-8359, a selective and reversible MAO-A inhibitor, and cinchona alkaloids by aldehyde oxidase.

The 2-oxidation activity on the pyrimidine ring of RS-8359, a MAO-A inhibitor, is the major metabolic pathway catalysed by aldehyde oxidase. This study investigated the species differences in the 2-oxidation activity by using liver cytosolic fractions from rats, mice, guinea-pigs, rabbits, dogs, monkeys and humans. The Vmax/Km value for the (S)-enantiomer of RS-8359 was extremely high in monkeys and humans, moderate in guinea-pigs, and low in rats and mice. Dogs were deficient in 2-oxidation activity. The (R)-enantiomer was only oxidized at a very low rate in guinea-pigs, monkeys and humans, and not oxidized in rats, mice and rabbits. Thus, marked species differences and enantioselectivity were obvious for the 2-oxidation of the (S)-enantiomer of RS-8359. The in vitro results were in good accordance with previously reported in vivo excretion data of the 2-keto metabolite and the non-detectable plasma concentrations of the (S)-enantiomer in monkeys and humans after administration of racemic RS-8359. Enantioselectivity was also observed for the oxidation of cinchona alkaloids catalysed by aldehyde oxidase. Among the four cinchona alkaloids studied, the oxidation activity of cinchonidine, which has no substituents at the 6-hydroxy group but bears (8S,9R)-configurations, was highest. As opposed to the (S)-enantiomer, an extremely high catalytic activity of cinchonidine was confirmed in rabbits, but not in monkeys or humans. Rabbit liver aldehyde oxidase was suggested to have characteristic properties around the active site.

Molecular cloning and characterization of rat semicarbazide-sensitive amine oxidase.

Semicarbazide-sensitive amine oxidase (SSAO) (EC 1.4.3.6) is widely distributed in nature and catalyzes the oxidative deamination of primary amines. Although SSAO full-length cDNA sequences have been reported for some mammalian species, only a partial 5'-terminal sequence has been confirmed in the rat. In this study we isolated full-length SSAO cDNA from rat aorta and examined its mRNA expression in various rat tissues by real-time PCR, as well as the subcellular and tissue distributions of SSAO activity. The deduced amino acid sequence showed 91% and 80% identity with mouse and human SSAO, respectively. The mRNA was expressed in many rat tissues. Those findings were supported by the broad distribution of SSAO in the body. Thus, a high level of SSAO was shown in adipocytes by both mRNA expression and enzyme activity measurement. The results suggest that SSAO may play an important role in the degradation of biologically active amines in adipocytes.

Stereoselective pharmacokinetics of RS-8359, a selective and reversible MAO-A inhibitor, by species-dependent drug-metabolizing enzymes.

RS-8359, (+/-)-4-(4-cyanoanilino)-5,6-dihydro-7-hydroxy-7H-cyclopenta[d]pyrimidine selectively and reversibly inhibits monoamine oxidase A (MAO-A). After oral administration of rac-RS-8359 to rats, mice, dogs, monkeys, and humans, plasma concentrations of the (R)-enantiomer were greatly higher than were those of the (S)-enantiomer in all species studied. The AUC((R)) to AUC((S)) ratios were 2.6 in rats, 3.8 in mice, 31 in dogs, and 238 in monkeys, and the (S)-enantiomer was almost negligible in human plasma. After intravenous administration of RS-8359 enantiomers to rats, the pharmacokinetic parameters showed that the (S)-enantiomer had a 2.7-fold greater total clearance (CL(t)) and a 70% shorter half-life (t(1/2)) than those for the (R)-enantiomer but had no difference in distribution volume (V(d)). No significant difference in the intestinal absorption rate was observed. The principal metabolites were the 2-keto form, possibly produced by aldehyde oxidase, the cis-diol form, and the 2-keto-cis-diol form produced by cytochrome P450 in rats, the cis-diol form in mice, RS-8359 glucuronide in dogs, and the 2-keto form in monkeys and humans. Thus, the rapid disappearance of the (S)-enantiomer from the plasma was thought to be due to the rapid metabolism of the (S)-enantiomer by different drug-metabolizing enzymes, depending on species.

Protein identification by peptide mass fingerprinting and peptide sequence tagging with alternating scans of nano-liquid chromatography/infrared multiphoton dissociation Fourier transform ion cyclotron resonance mass spectrometry.

We have developed a method for protein identification with peptide mass fingerprinting and sequence tagging using nano liquid chromatography (LC)/Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). To achieve greater sensitivity, a nanoelectrospray (nano-ES) needle packed with reversed-phase medium was used and connected to the nano-ES ion source of the FTICR mass spectrometer. To obtain peptide sequence tag information, infrared multiphoton dissociation (IRMPD) was carried out in nano-LC/FTICR-MS analysis. The analysis involves alternating nano-ES/FTICR-MS and nano-ES/IRMPD-FTICR-MS scans during a single LC run, which provides sets of parent and fragment ion masses of the proteolytic digest. The utility of this alternating-scan nano-LC/IRMPD-FTICR-MS approach was evaluated by using bovine serum albumin as a standard protein. We applied this approach to the protein identification of rat liver diacetyl-reducing enzyme. It was demonstrated that this enzyme was correctly identified as 3-alpha-hydroxysteroid dehydrogenase by the alternating-scan nano-LC/IRMPD-FTICR-MS approach with accurate peptide mass fingerprinting and peptide sequence tagging.

Stereoselective transport of histidine in rat lung microvascular endothelial cells.

The transport characteristics of L- and D-histidine through the blood-lung barrier were studied in cultured rat lung microvascular endothelial cells (LMECs). L-Histidine uptake was a saturable process. The addition of metabolic inhibitors [2,4-dinitrophenol (DNP) and rotenone] reduced the uptake rate of L-histidine. Ouabain, an inhibitor of Na(+)-K(+)-ATPase, also reduced uptake of L-histidine. Moreover, the initial L-histidine uptake rate was reduced by the substitution of Na(+) with choline chloride and choline bicarbonate in the incubation buffer. The system N substrate, L-glutamic acid gamma-monohydroxamate, also inhibited uptake of L-histidine. However, system N-mediated transport was not pH sensitive. These results demonstrated that L-histidine is actively taken up by a system N transport mechanism into rat LMECs, with energy supplied by Na(+). Moreover, the Na(+)-independent system L substrate, 2-amino-2-norbornanecarboxylic acid (BCH), had an inhibitory effect on L-histidine uptake in Na(+) removal, indicating facilitated diffusion by a Na(+)-independent system L transport into the rat LMECs. These results provide evidence for there being at least two pathways for L-histidine uptake into rat LMECs, a Na(+)-dependent system N and Na(+)-independent system L process. On the other hand, the uptake of D-histidine into rat LMECs was not reduced by the addition of DNP, rotenone, or ouabain, or by Na(+) replacement. Although the uptake of D-histidine was reduced in the presence of BCH, the addition of L-glutamic acid gamma-monohydroxamate did not significantly decrease uptake of D-histidine. These results suggest that the uptake of D-histidine by rat LMECs has different characteristics compared with its isomer, L-histidine, indicating that system N transport did not involve D-histidine uptake.