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.     

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.     

The popular herbal antimalarial, extract of Cryptolepis sanguinolenta, is potently cytotoxic.

The aqueous root extract of Cryptolepis sanguinolenta (CSE) is a popular antimalarial in West African ethnomedicine. Cryptolepine (CLP), the major alkaloid of the plant, is a cytotoxic DNA intercalator that has promise as an anticancer agent. To date the aqueous root extract, the traditional antimalarial formulation, has not been evaluated for toxicity. In this study, we have examined the in vitro toxicity of CSE and CLP using V79 cells, a Chinese hamster lung fibroblast frequently used to assess genetic toxicity, and a number of organ-specific human cancer cell lines. CSE and CLP caused a dose- and time-dependent reduction in viability of the V79 cell line. Flow cytometric analysis of CSE- and CLP-treated (24 h) asynchronously growing V79 cells using propidium iodide (PI) staining revealed an accumulation of cells (up to 55%) in the sub-G1 phase of the cell cycle, indicative of cell death. The V79 cells and almost all the organ-specific human cancer cell lines exposed to CSE and CLP were profoundly growth inhibited, as measured in a clonogenicity assay. In a V79 cell mutation assay (hprt gene), CSE (5-50 microg/ml) only induced mutation at the highest dose employed (mutation frequency approximately 4 and 38 mutant clones per 10(6) cells for control and CSE, respectively), but CLP (0.5-5.0 microM) was not mutagenic. These results indicate that CSE and CLP are very cytotoxic and may be weak mammalian mutagens and/or clastogens. The poor genotoxicity of CSE and CLP coupled with their potent cytotoxic action support their anticancer potential.     

Stereospecific oxidation of the (S)-enantiomer of RS-8359, a selective and reversible monoamine oxidase A (MAO-A) inhibitor,by aldehyde oxidase

In a previous paper by the authors on RS-8359, a new selective and reversible monoamine oxidase A (MAO-A) inhibitor, it was reported that the (S)-enantiomer of RS-8359 is rapidly eliminated from rats, monkeys and humans as a result of the formation of a 2-oxidative metabolite. The present study investigates the properties of the enzyme responsible for the 2-oxidation of RS-8359. Subcellular localization, cofactor requirement and the inhibitory effects of typical compounds were studied using rat liver preparations. In addition, the enzyme was purified from rat liver cytosol for further characterization. The enzyme activity was localized in the cytosolic fraction without the need for any cofactor and was extensively inhibited by menadione, chlorpromazine and quinacrine. The purified enzyme was also a homodimer with a monomeric molecular weight of 140?kDa and it had an A₂₈₀/A₄₅₀ ratio of 5.1 in the absorption spectrum. The results suggest that the enzyme responsible for the biotransformation of RS-8359 to give the 2-keto derivative is aldehyde oxidase (EC 1.2.3.1). The reaction of aldehyde oxidase is highly stereoselective for the (S)-configuration of RS-8359 and the (9R)-configuration of cinchona alkaloids.     

Interference of aldehyde metabolizing enzymes with diamine oxidase/histaminase/activity as determined by 14C putrescine method.

The Δ¹ pyrroline formation, as an indicator of diamine oxidase activity according to Okuyama and Kobayashi ¹⁴C putrescine test [1], has been investigated in several tissue homogenates. When guinea pig liver homogenate was used as a source of enzyme in the presence of aldehyde dehydrogenase inhibitors chloral hydrate and acetaldehyde the level of formation Δ¹ pyrroline was strongly increased in a dose-dependent manner. Also inhibition of aldehyde reductase by phenobarbital enhanced Δ¹ pyrroline formation, but to a lesser degree. In other tissues, with very high initial diamine oxidase activity (rat intestine, dog kidney) or with very low diamine oxidase activity (guinea pig skin, dog liver) the influence of these inhibitors was only slight. Pyrazole, an inhibitor of alcohol dehydrogenase exerted only a small effect on Δ¹ pyrroline formation. All aldehyde-metabolizing enzymes inhibitors, except pyrazole, were without effect on purified pea seedling and hog kidney diamine oxidases. The use of aldehyde-metabolizing enzymes inhibitors may help to reveal the real values of diamine oxidase activity, when tissues homogenates are used as a source of enzyme.     

Metabolism of isovanillin by aldehyde oxidase, xanthine oxidase, aldehyde dehydrogenase and liver slices

Aromatic aldehydes are good substrates of aldehyde dehydrogenase activity but are relatively poor substrates of aldehyde oxidase and xanthine oxidase. However, the oxidation of xenobiotic-derived aromatic aldehydes by the latter enzymes has not been studied to any great extent. The present investigation compares the relative contribution of aldehyde dehydrogenase, aldehyde oxidase and xanthine oxidase activities in the oxidation of isovanillin in separate preparations and also in freshly prepared and cryopreserved liver slices. The oxidation of isovanillin was also examined in the presence of specific inhibitors of each oxidizing enzyme. Minimal transformation of isovanillin to isovanillic acid was observed in partially purified aldehyde oxidase, which is thought to be due to residual xanthine oxidase activity. Isovanillin was rapidly metabolized to isovanillic acid by high amounts of purified xanthine oxidase, but only low amounts are present in guinea pig liver fraction. Thus the contribution of xanthine oxidase to isovanillin oxidation in guinea pig is very low. In contrast, isovanillin was rapidly catalyzed to isovanillic acid by guinea pig liver aldehyde dehydrogenase activity. The inhibitor studies revealed that isovanillin was predominantly metabolized by aldehyde dehydrogenase activity. The oxidation of xenobiotic-derived aromatic aldehydes with freshly prepared or cryopreserved liver slices has not been previously reported. In freshly prepared liver slices, isovanillin was rapidly converted to isovanillic acid, whereas the conversion was very slow in cryopreserved liver slices due to low aldehyde dehydrogenase activity. The formation of isovanillic acid was not altered by allopurinol, but considerably inhibited by disulfiram. It is therefore concluded that isovanillin is predominantly metabolized by aldehyde dehydrogenase activity, with minimal contribution from either aldehyde oxidase or xanthine oxidase.     

An iminium ion metabolite hampers the production of the pharmacologically active metabolite of a multikinase inhibitor KW‐2449 in primates: irreversible inhibition of aldehyde oxidase and covalent binding with endogenous proteins

We previously reported that KW‐2449, (E)‐1‐{4‐[2‐(1H‐Indazol‐3‐yl)vinyl]benzoyl}piperazine, a novel multikinase inhibitor developed for the treatment of leukemia patients, was oxidized to an iminium ion intermediate by monoamine oxidase B (MAO‐B) and then converted to its oxo‐piperazine form (M1) by aldehyde oxidase (AO). However, it was found that the significant decrease in the pharmacologically active metabolite M1 following repeated administration of KW‐2449 in primates might hamper the effectiveness of the drug. The mechanism underlying this phenomenon was investigated and it was found that the AO activity was inhibited in a time‐dependent manner in vitro under the co‐incubation of KW‐2449 and MAO‐B, while neither KW‐2449 nor M1 strongly inhibited MAO‐B or AO activity. These results clearly suggest that MAO‐B catalysed iminium ion metabolite inhibited AO, prompting us to investigate whether or not the iminium ion metabolite covalently binds to endogenous proteins, as has been reported with other reactive metabolites as a cause for idiosyncratic toxicity. The association of the radioactivity derived from ¹⁴C‐KW‐2449 with endogenous proteins both in vivo and in vitro was confirmed and it was verified that this covalent binding was inhibited by the addition of sodium cyanide, an iminium ion‐trapping reagent, and pargyline, a MAO‐B inhibitor. These findings strongly suggest that the iminium ion metabolite of KW‐2449 is highly reactive in inhibiting AO irreversibly and binding to endogenous macromolecules covalently.     

Metabolism of azoxy derivatives of procarbazine by aldehyde dehydrogenase and xanthine oxidase.

Procarbazine, a 1,2-disubstituted hydrazine, is employed therapeutically in the treatment of Hodgkin's disease and a limited number of other neoplasias. The isomeric azoxy metabolites of procarbazine have recently been identified as the precursors of species responsible for both the anti-cancer efficacy and toxic effects mediated by this drug. This study demonstrates that cytosolic enzymes are involved in the metabolism of the azoxy metabolites of procarbazine. Two azoxy procarbazine oxidase activities were resolved by diethylaminoethyl (DEAE)-cellulose chromatography. The activity which did not bind to this column was purified to homogeneity and was identified as a phenobarbital-inducible form of cytosolic aldehyde dehydrogenase. This protein fraction was shown to metabolize only the azoxy 2 procarbazine isomer to yield N-isopropy-p-formylbenzamide (ALD) in a reaction which did not require NAD+ as cofactor. The ALD product formed was also a substrate for a subsequent NAD(+)-dependent reduction reaction catalyzed by that purified protein. The azoxy 2 procarbazine isomer and ALD were shown to be potent inhibitors of both the dehydrogenase and esterase activities of aldehyde dehydrogenase. The second azoxy procarbazine oxidase activity which was retained by the DEAE-cellulose column co-eluted with xanthine oxidase activity. Both the xanthine dehydrogenase/oxidase and azoxy procarbazine oxidase activities of this protein fraction were inhibited by allopurinol, a specific inhibitor of xanthine dehydrogenase. Xanthine dehydrogenase/oxidase was partially purified by an alternative procedure and was shown to metabolize both the azoxy 2 procarbazine isomer and ALD, ultimately producing N-isopropylterephthalamic acid. The ability of xanthine oxidase to metabolize azoxy 2 procarbazine and ALD was confirmed using commercial, purified milk xanthine oxidase.     

Determination of pKa and forced degradation of the indoloquinoline antimalarial compound cryptolepine hydrochloride

The study was aimed at determining the acid dissociation constant of cryptolepine hydrochloride and its degradation under stressed conditions. The pKa was determined using buffers in the pH range 10.4–11.6 by spectrophotometry at controlled measurement temperature (20?±?0.5°C). The stability of the compound was investigated under various stressed conditions including neutral, acid, alkaline, light, dry heat and oxidation at different temperatures. Degradation products were analysed by HPLC. The calculated pKa values (uncorrected and corrected for ionic strength) were 11.09?±?0.03 and 10.99?±?0.05, respectively. A graphical approach yielded an uncorrected pKa value of 11.07. Degradation of the compound in water, 0.1?M HCl, 0.1?M NaOH and 3% hydrogen peroxide followed a first order reaction. With proper temperature control and maintenance of uniform ionic strength, a reproducible pKa of cryptolepine is obtainable by spectrophotometry. The compound was found to be highly susceptible to oxidation and relatively stable in neutral and acidic conditions but less so in a basic medium. There were no significant changes in concentration of samples exposed to light and dry heat at 60°C over the study period.     

Metabolism of zaleplon by human liver: evidence for involvement of aldehyde oxidase

1. The metabolism of Zaleplon (CL-284,846; ZAL) has been studied in precision-cut human liver slices and liver cytosol preparations. 2. Human liver slices metabolized ZAL to a number of products including 5-oxo-ZAL (M2), N-desethyl-5-oxo-ZAL (M1) and N-desethyl-ZAL (DZAL), the latter metabolite being known to be formed by CYP3A forms. 3. Human liver cytosol preparations catalysed the metabolism of ZAL to M2. Kinetic analysis of three cytosol preparations revealed mean (+/- SEM) K(m) and V(max) of 93 +/- 18 mm and 317 +/- 241 pmol/min/mg protein, respectively. 4. Using 16 individual human liver cytosol preparations a 33-fold variability in the metabolism of 80 micro M ZAL to M2 was observed. Correlations were observed between M2 formation and the metabolism of the aldehyde oxidase substrates phenanthridine (r(2) = 0.774) and phthalazine (r(2) = 0.460). 5. The metabolism of 80 micro M ZAL to M2 in liver cytosol preparations was markedly inhibited by the aldehyde oxidase inhibitors chlorpromazine, promethazine, hydralazine and menadione. Additional kinetic analysis suggested that chlorpromazine and promethazine were non-competitive inhibitors of M2 formation with K(i) of 2.3 and 1.9 micro M, respectively. ZAL metabolism to M2 was also inhibited by cimetidine. 6. Incubations conducted with human liver cytosol and H(2)(18)O demonstrated that the oxygen atom incorporated into ZAL and DZAL to form M2 and M1, respectively, was derived from water and not from molecular oxygen. 7. In summary, by correlation analysis, chemical inhibition and H(2)(18)O incorporation studies, ZAL metabolism to M2 in human liver appears to be catalysed by aldehyde oxidase. With human liver slices, ZAL was metabolized to products dependent on both aldehyde oxidase and CYP3A forms.     

Synthesis of novel benzimidazole acrylonitriles for inhibition of Plasmodium falciparum growth by dual target inhibition

Antimalarial drug resistance has emerged as a threat for treating malaria, generating a need to design and develop newer, more efficient antimalarial agents. This research aimed to identify novel leads as antimalarials. Dual receptor mechanism could be a good strategy to combat developing drug resistance. A series of benzimidazole acrylonitriles containing 18 compounds were designed, synthesized and evaluated for cytotoxicity, heme binding, ferriprotoporphyrin IX biomineralisation inhibition, and falcipain‐2 enzyme assay. Furthermore, in silico docking and MD simulation studies were also performed.The tests revealed quite encouraging results. Three compounds, viz. R‐01 (0.69 μM), R‐04 (1.60 μM), and R‐08 (1.61 μM), were found to have high antimalarial activity. These compounds were found to be in bearable cytotoxicity limits and their biological assay suggested that they had inhibitory activity against falcipain‐2 and hemozoin formation. The docking revealed the binding mode of benzimidazole acrylonitrile derivatives and MD simulation studies revealed that the protein‐ligand complex was stable. The agents exhibit good hemozoin formation inhibition activity and, hence, may be utilized as leads to design a newer drug class to overcome the drug resistance of hemozoin formation inhibitors such as chloroquine.     

线粒体乙醛脱氢酶2在心肌缺血后处理中的作用

目的探讨线粒体乙醛脱氢酶2(aldehyde dehydrogen-ase 2,ALDH2)在离体大鼠心肌缺血后处理中的保护作用。方法采用离体大鼠心脏Langendorff灌流方法 ,局部结扎冠状动脉左前降支30min,复灌120min模拟心肌缺血/复灌模型。缺血后处理采用复灌初期立即给予反复6次的10s复灌/10s全心缺血的循环。测定心室动力学指标和复灌期间冠脉流出液中乳酸脱氢酶(lactate dehydrogenase,LDH)含量。实验结束后TTC染色法测定心肌梗死面积。RT-PCR测定左心室前壁心尖组织线粒体ALDH2、Bcl-2和Bax mR-NA的表达。结果与单纯缺血/复灌组相比,缺血后处理明显促进左室发展压、左室做功的恢复,降低复灌期冠脉流出液中LDH的释放和心肌梗死面积,ALDH2 mRNA表达增高,Bcl-2/Bax mRNA比值增高。ALDH2阻断剂氨基氰减弱了缺血后处理的作用。结论缺血后处理部分通过增强线粒体乙醛脱氢酶2的表达发挥心肌保护作用。     

反相高效液相色谱法测定胃炎片中原儿茶醛的含量

目的建立胃炎片中原儿茶醛的含量测定方法。方法采用反相高效液相色谱法测定胃炎片中原儿茶醛的含量。采用日本Sil C18色谱柱,以甲醇-1%醋酸水溶液(13∶87)为流动相,流速为1ml/min,检测波长280nm。结果原儿茶醛在0．0762～0．4572μg线性关系良好,r=0．9999,平均回收率为101．1%, RSD=0．70%。结论该方法简便、灵敏、准确,可作为胃炎片的质量控制方法。     

醛脱氢酶2与人类疾病的关系及其小分子激动剂研究

醛脱氢酶2（ALDH2）是人体内重要的抗氧化应激损伤因子之一，而较高比例的东亚人携带ALDH2失活突变基因。与ALDH2密切相关的疾病有很多，如心血管疾病、神经退行性疾病和肝脏疾病等。近期研究还发现ALDH2与铁死亡也有联系。正因如此，ALDH2逐渐成为上述相关疾病治疗的潜在靶点，研究者报道了其多个类型的小分子激动剂，展现出一定的应用前景。本文重点介绍ALDH2的结构、功能、与人类疾病的关系以及其激动剂的研究进展。     

Plasmodium falciparum: binding studies of peptide derived from the sporozoite surface protein 2 to Hep G2 cells

Abstract: Plasmodium falciparum sporozoite surface protein 2 (Pf SSP2), also called thrombospondin related anonymous protein (TRAP), is involved in the process of sporozoite invasion of hepatocytes. Pf SSP2/TRAP possesses two different adhesion domains sharing sequences and structural homology with von Willebrand factor A‐domains and human repeat I thrombospondin (TSP). Pf SSP2/TRAP has also been implicated in sporozoite mobility and in mosquito salivary gland invasion processes. We tested 15‐mer long synthetic peptides having five overlapping residues covering the complete protein Pf SSP2 sequence in binding assays to Hep G2 cells. In these 57 peptides, 21 high‐activity binding peptides (HABPs) were identified; five were in the adhesion domains already described and 16 were in two regions toward the protein's carboxy and middle terminal part. Six HABPs showed conserved amino acid sequences: 3243 (²¹FLVNGRDVQNNIVDE³⁵), 3279 (²⁰¹FLVGCHPSDGKCNLY²¹⁵), 3287 (²⁴¹TASCGVWDEWSPCSV²⁵⁵), 3289 (²⁵¹SPCSVTCGKGTRSRK²⁶⁵), 3327 (⁴⁴¹ERKQSDPQSQDNNGNY⁴⁵⁵) and 3329 (⁴⁵¹DNNGNRHVPNSEDREY⁴⁶⁵). The HABPs show saturable binding and dissociation constants between 140 and 900 nm with 40 000–855 000 binding sites per cell. The 3279 (²⁰¹FLVG CHPSDGKC NLY²¹⁵), 3323 (⁴²¹NDKS DRYIPYSP LSP⁴³⁵) and 3331 (⁴⁶¹SEDRE TRPHGR NNENY⁴⁷⁵) HABPs have B epitopes in their sequences; these have previously been recognized by antibodies partially inhibiting hepatocyte invasion and development of the hepatic state. The 3287 (²⁴¹TASCGVWDEWSPCSV²⁵⁵) and 3289 (²⁵¹SPCSVTCGKGTRSRK²⁶⁵) HABPs share common sequences with the Pf SSP2/TRAP region II plus, which is present in a great number of adhesion proteins. Based on this information, six new peptides covering the high binding regions identified previously were synthesized and, using a competition assay, the amino acid involved in the binding were determined.     

HPLC测定心可宁胶囊中原儿茶醛的含量

目的　采用高效液相色谱法测定心可宁胶囊中原儿茶醛的含量。方法　InertsilC1 8柱 (5 μm ,1 5 0mm× 4 .6mm) ;流动相为甲醇 - 0 .0 5mol·L-1 磷酸二氢钾缓冲液 (磷酸调pH 3.0 ) (2 0∶80 ) ;检测波长为 2 80nm。结果　原儿茶醛进样量在 0 .0 5 5 3～2 .2 1 30 μg范围内线性关系良好 (r=0 .9999) ;平均加样回收率为 99.7% (n =9) ;方法精密度RSD =0 .5 0 % (n =6 )。 结论　本方法操作简便、准确、重复性好 ,可作为该制剂中原儿茶醛的含量测定方法     

人类乙醛脱氢酶II及其激动剂的研究进展

人类乙醛脱氢酶Ⅱ(aldehyde dehydrogenasesII,ALDH2)具有脱氢酶和酯酶等多种酶的功能,ALDH2活性的增强将减轻因酒精、缺血等多种因素引起的肝脏、心肌损伤及某些癌症的发生。本文通过对国内外文献的分析、整理和归纳,较为全面的介绍了ALDH2及其激动剂的研究现状。     

Lack of dimer formation ability in rat strains with low aldehyde oxidase activity

Aldehyde oxidase (AO) is a homodimer with a molecular weight of 300?kDa. To clarify the reasons for the well-known differences in rat strains, we set out to study the relationship between AO activity and the expression levels of its dimer. AO-catalyzed 2-oxidation activity of (S)-RS-8359 was measured in liver cytosols from ten rat strains. The expression levels of AO dimeric protein were evaluated by the native-PAGE/Western blot. Rat strains with low AO activity showed only a monomer, whereas strains with high activity overwhelmingly exhibited a dimer. Exceptionally, one strain in the high AO activity group displayed complex mixed expression patterns of low and high AO activity groups. However, there was a good relationship between AO activity and the expression levels of a dimer, but not of a monomer. The results suggest that rat strains with low AO activity lack the ability to produce a dimer necessary for catalytic activity, and AO differences in rat strains should be discussed in terms of the expression levels of the dimer itself.