Effect of allyl alcohol on xanthine dehydrogenase activity in the perfused rat liver

Xanthine oxidase has been implicated in the production of reactive oxygen species and cell injury produced by various toxic compounds. Since allyl alcohol injuries the liver by an oxygen-dependent mechanism, we examined the actions of this hepatotoxicant on the conversion of xanthine dehydrogenase into xanthine oxidase in perfused livers. A microassay for NAD(+)-dependent xanthine dehydrogenase, based on measuring the production of NADH fluorometrically under anaerobic conditions, was developed and used to examine the actions of allyl alcohol on this activity in periportal and pericentral regions of the liver lobule. The oxygen-dependent activity, xanthine oxidase, was monitored in whole liver homogenates by uric acid formation at 302 nm under aerobic conditions. Perfusion of the liver with allyl alcohol (350 microM) increased xanthine oxidase and decreased xanthine dehydrogenase in whole liver consistent with the hypothesis that allyl alcohol enhanced calcium-dependent proteolytic conversion of the NAD(+)-dependent to the O2-dependent form. Xanthine dehydrogenase was higher in pericentral than in periportal regions of the liver lobule and tended to decrease selectively in periportal zones of livers exposed to allyl alcohol. O2 uptake was stimulated transiently by allyl alcohol followed by subsequent inhibition of respiration. These results are consistent with the idea that conversion of NAD(+)-dependent xanthine dehydrogenase to xanthine oxidase is involved in the zone-specific hepatotoxicity of allyl alcohol.     

Effect of heat-treated ceruloplasmin on the hepatic xanthine oxidase activity and type conversion

The effect of ceruloplasmin or copper ion on hepatic xanthine oxidase activity and type conversion was investigated using rat liverin vitro. It was observed that ceruloplasmin increased xanthine oxidase type conversion depending on duration of its storage. Xanthine oxidase (type O) activity and type conversion in incubation mixture was increased by the addition of heated celuroplasmin in a temperature dependent manner. The type conversion of xanthine oxidase induced by heated ceruloplasmin was retumed to normal by the treatment with DTT or penicillamine. The effect of copper ion on type conversion of xanthine oxidase was similar to that of heated ceruloplasmin.     

An updated patent review: xanthine oxidase inhibitors for the treatment of hyperuricemia and gout (2011-2015)

Introduction: Xanthine oxidase (XO) is a versatile molybdoflavoprotein, widely distributed, occurring in milk, kidney, lung, heart, and vascular endothelium. Catalysis by XO to produce uric acid and reactive oxygen species leads to many diseases. Anti hyperuricemic therapy by xanthine oxidase inhibitors has been mainly employed for the treatment of gout.

Area covered: This review covers the patent literature (2011–2015) and also presents the interesting strategies/rational approaches employed for the design of xanthine oxidase inhibitors reported recently.

Expert opinion: Recent literature indicates that various non purine scaffolds have been extensively investigated for xanthine oxidase inhibition. The significant potential endowed by heteroaryl based compounds, in particularly fused heterocycles clearly highlights their clinical promise and the need for detailed investigation. Studies by various research groups have also revealed that the flavone framework is open for isosteric replacements and structural modifications for yielding potent non purine xanthine oxidase inhibitors. In addition, various plant extracts recently reported to possess significant xanthine oxidase inhibitory potential presents enough promise to initiate a screening program for the identification of other plant extracts and phytoconstituents possessing inhibitory potential towards the enzyme.     

以黄嘌呤氧化酶为靶点的新型非嘌呤类抗痛风及高尿酸血症药物研究进展

黄嘌呤氧化酶（XO）催化黄嘌呤生成尿酸及次黄嘌呤生成黄嘌呤的过程,是抗高尿酸血症或痛风药物研究的关键靶点。黄嘌呤氧化酶抑制剂由于作用机制明确、疗效显著而倍受关注,研发新型XO抑制剂具有广阔的应用前景。XO的结构生物学及分子模拟技术为新一代非嘌呤类XO抑制剂的合理药物设计奠定了基础。本文综述了以黄嘌呤氧化酶为靶标的新型非嘌呤类小分子杂环化合物及天然产物来源的活性分子在抗高尿酸血症或痛风药物研究领域中的进展。     

Oxidation of selected pteridine derivatives by mamalian liver xanthine oxidase and aldehyde oxidase.

Considerable information is available concerning the oxidation of pteridine derivatives by bovine milk xanthine oxidase, but few investigations have been carried out on the oxidation of such compounds by mammalian liver xanthine oxidase and the related aldehyde oxidase. Xanthine oxidase, obtained from rat liver, oxidizes a variety of substituted amino- and hydroxypteridines in a manner identical to that previously observed for milk xanthine oxidase. For example, 2-aminopteridine and its 4- and 7-hydroxy derivatives were oxidized efficiently to 2-amino-4,7-dihydroxypteridine (isoxanthopterin) by the rat liver enzyme, and 4-aminopteridine and its 2- and 7-hydroxy derivatives were oxidized to 4-amino-2,7-dihydroxypteridine.4-Hydroxypteridine and the isomeric 2- and 7-hydroxypteridines were oxidized by rat liver xanthine oxidase to 2,4,7-trihydroxypteridine. Rabbit liver aldehyde oxidase, but not rat liver xanthine oxidase, was able to catalyze the oxidation in position 7 of 2,4-diaminopteridine and its 6-methyl and 6-hydroxymethyl derivatives. 2-Aminopteridine and 4-aminopteridine were both oxidized to the corresponding 7-hydroxy derivatives in the aldehyde oxidase system; 2-amino-4-hydroxypteridine appeared to be a minor product in the oxidation of 2-aminopteridine by rabbit liver aldehyde oxidase. Both aldehyde oxidase and xanthine oxidase were able to catalyze the oxidation of 2-amino-6,7-disubstituted pteridines to the corresponding 4-hydroxy derivatives; 4-hydroxy-6,7-disubstituted pteridines were oxidized in position 2 by both enzymes. 4-Amino-6,7-disubstituted pteridines were not oxidized by either enzyme. 2-Amino-4-methylpteridine was oxidized in position 7 by aldehyde oxidase but was not an effective substrate for xanthine oxidase; 2-hydroxypteridine and 7-hydroxypteridine were not oxidized to a detectably extent by aldehyde oxidase. All oxidations mediated by xanthine oxidase were strongly inhibited by allopurinol (4-hydroxypyrazolo[3,4-d]pyrimidine), and all oxidations mediated by aldehyde oxidase were inhibited by menadione (2-methyl-1,4-naphthoquinone). Rat liver xanthine oxidase and, to a lesser extent, rabbit liver aldehyde oxidase were inhibited by 4-chloro-6,7-dimethylpteridine; 2-amino-3-pyrazinecarboxylic acid inhibited xanthine oxidase but not aldehyde oxidase. The oxidations of 2- and 4-aminopteridines by aldehyde oxidase resulted in concomitant reduction of cytochrome c.     

Contribution of aldehyde oxidase, xanthine oxidase, and aldehyde dehydrogenase on the oxidation of aromatic aldehydes

Aliphatic aldehydes have a high affinity toward aldehyde dehydrogenase activity but are relatively poor substrates of aldehyde oxidase and xanthine oxidase. In addition, 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 substituted benzaldehydes in separate preparations. The incubation of vanillin, isovanillin, and protocatechuic aldehyde with either guinea pig liver aldehyde oxidase, bovine milk xanthine oxidase, or guinea pig liver aldehyde dehydrogenase demonstrated that the three aldehyde oxidizing enzymes had a complementary substrate specificity. Incubations were also performed with specific inhibitors of each enzyme (isovanillin for aldehyde oxidase, allopurinol for xanthine oxidase, and disulfiram for aldehyde dehydrogenase) to determine the relative contribution of each enzyme in the oxidation of these aldehydes. Under these conditions, vanillin was rapidly oxidized by aldehyde oxidase, isovanillin was predominantly metabolized by aldehyde dehydrogenase activity, and protocatechuic aldehyde was slowly oxidized, possibly by all three enzymes. Thus, aldehyde oxidase activity may be a significant factor in the oxidation of aromatic aldehydes generated from amines and alkyl benzenes during drug metabolism. In addition, this enzyme may also have a role in the catabolism of biogenic amines such as dopamine and noradrenaline where 3-methoxyphenylacetic acids are major metabolites.     

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.     

Inhibitory action of quercetin on xanthine oxidase and xanthine dehydrogenase activity

Quercetin is an equally good inhibitor of xanthine oxidase (type O, oxygen-reducing enzyme) and xanthine dehydrogenase (type D, NAD+-reducing enzyme) activity of a preparation of the xanthine-oxidizing enzyme partially purified from rat liver. The inhibition seems competitive with the oxidase form and non-competitive (mixed-type) with the dehydrogenase form of the enzyme. These inhibitory properties should be referred to the flavonoid structure of quercetin rather than to its antioxidant power. The antioxidant properties of quercetin and its inhibitory effect on the xanthine-oxidizing enzyme are discussed with reference to hyperuricemic and ischemic states.     

The reduction of 6-N-hydroxylaminopurine to adenine by xanthine oxidase.

The genotoxic and mutagenic compound 6-N-hydroxylaminopurine (HAP) can be detoxified in vitro by enzymatic N-reduction to adenine. This reaction is catalysed by both rat and rabbit liver cytosolic fractions. The formation of adenine was monitored using HPLC. Subcellular distribution of the activity, kinetic parameters and the influence of various cofactors and inhibitors were determined. The N-reduction required NADH or hypoxanthine or xanthine and was strongly inhibited by allopurinol. These observations suggested that the N-reductase activity is due to xanthine oxidase (EC 1.2.3.2). Moreover, the involvement of xanthine oxidase is supported by the observation that purified cow milk xanthine oxidase also catalysed this reaction. The N-reduction of HAP was inhibited only weakly by oxygen. In addition, the formation of adenine is catalysed by either the oxidase or dehydrogenase form of xanthine oxidase. Thus, this reaction should be significant for the in vivo detoxification of HAP.     

Synthesis and enzymic activity of some novel xanthine oxidase inhibitors. 3-Substituted 5,7-dihydroxypyrazolo(1,5-alpha)pyrimidines.

A series of 3-substituted 5,7-dihydroxypyrazolo[1,5-alpha]pyrimidines containing various aromatic [phenyl- (3e), 3-pyridyl- (3f), p-bromophenyl- (3g), p-chlorophenyl- (3h), p-acetamidophenyl- (3i), p-tolyl- (3j), m-tolyl- (3k), 3,4-methylenedioxyphenyl- (3m), or naphthyl- (3n)] or nonaromatic [hydrogen- (3a), nitro- (3b), bromo- (3c), or chloro- (3d)] substituents in the 3 position was synthesized and tested as inhibitors of xanthine oxidase. The compounds (3a-m) were synthesized by condensation of the appropriate 3-amino-4-substituted pyrazole with diethyl malonate in alcoholic sodium methoxide and neutralization of the resulting enol sodium salts. As inhibitors of xanthine oxidase, 3e-n greater than 3a,c,d congruent to allopurinol greater than 3b. The 3-aryl-substituted compounds 3e-n were 30-160 times better xanthine oxidase inhibitors than allopurinol using hypoxanthine as substrate and 10-80 times better using xanthine as substrate, as evidenced by a comparison of Ki values. The inhibition by all compounds (3a-n) was totally reversible and of the noncompetitive or mixed type. A study of the pH dependence of xanthine oxidase inhibition by 3a,e,g and allopurinol indicated that the 3-aryl substituents facilitated binding to the enzyme. These and the above results show that the compounds reported here inhibit xanthine oxidase by a mechanism which is significantly different from that of allopurinol.     

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.     

Progress towards the discovery of xanthine oxidase inhibitors

Xanthine oxidase (XO) is a highly versatile flavoprotein enzyme, ubiquitous among species (from bacteria to human) and within the various tissues of mammals. The enzyme catalyses the oxidative hydroxylation of purine substrates at the molybdenum centre (the reductive half-reaction) and subsequent reduction of O(2) at the flavin centre with generation of reactive oxygen species (ROS), either superoxide anion radical or hydrogen peroxide (the oxidative half-reaction). Many diseases, or at least symptoms of diseases, arise from a deficiency or excess of a specific metabolite in the body. For an example of an excess of a particular metabolite that produces a disease state is the excess of uric acid which can led to gout. Inhibition of XO decreases the uric acid levels, and results in an antihyperuricemic effect. Allopurinol, first synthesised as a potential anticancer agent, is nowadays a clinically useful xanthine oxidase inhibitor used in the treatment of gout. There is overwhelming acceptance that xanthine oxidase serum levels are significantly increased in various pathological states like hepatitis, inflammation, ischemia-reperfusion, carcinogenesis and aging and that ROS generated in the enzymatic process are involved in oxidative damage. Thus, it may be possible that the inhibition of this enzymatic pathway would be beneficial. In this review the State of the Art will be presented, which includes a summary of the progress made over the past years in the knowledge of the structure and mechanism of the enzyme, associated pathological states, and in the efforts made towards the development of new xanthine oxidase inhibitors.     

On-chip assay for determining the inhibitory effects and modes of action of drugs against xanthine oxidase

Xanthine oxidase (XO) is a key enzyme that can catalyze the conversion of xanthine to uric acid, causing various diseases in humans. We have developed a high-throughput chip-based assay that uses a photodiode array (PDA) microchip system to explore the inhibitory effects of drug analogs on XO. Inhibitory activities of cyclosporin A, aminoglutethimide, dithranol and naringenin against XO were assessed using this chip-based xanthine assay in the presence or absence of the antioxidant enzyme, superoxide dismutase (SOD). In addition, the mechanism of drug action was also disclosed by monitoring the combined effect of respective drug analogs and SOD on XO in the assay. The assessment was based on the red light absorption property of nitroblue tetrazolium (NBT) formazan, formed by free radical-mediated NBT reduction. Compared to naringenin (50 and 100 μM; a known XO inhibitor), cyclosporin A (5 and 10 μM) exhibited similar XO inhibitory activity, whereas dithranol (1 and 3 μM) and aminoglutethimide (2.5 and 5 mM) showed minimum XO inhibition. Low standard deviation obtained during the assay demonstrates the preciseness and accuracy of the developed approach. Compared to the existing methods, the developed approach is advantageous due to its simplicity and compatibility with high-throughput screening procedures. Furthermore, this approach can be applied to the early phase of drug discovery screening to explore various drug analogs for their XO inhibitory activities.     

Human and bovine xanthine oxidases. Inhibition studies with oxipurinol

Oxipurinol inhibited human xanthine oxidase and bovine xanthine oxidases by very similar mechanisms. It bound to an electronically reduced form of human xanthine oxidase in a manner similar to that previously discerned from its interactions with the bovine enzyme [review article: Spector, Biochem. Pharmac. 26, 355 (1977)]. Xanthine was a good source for the reducing equivalents because it did not compete with oxipurinol for binding to reduced enzyme. The inhibition of the rate of urate production progressively increased with time. Studies of the effect of the concentration of oxipurinol on the rate constant of the development of this inhibition revealed that a complex was rapidly formed between oxipurinol and reduced bovine or human xanthine oxidases (KD of about 8 microM). At 37 degrees these complexes were converted to stable complexes at a maximum rate of about 1.6 min-1. The rate constant was highly temperature dependent with an energy of activation of 30 kcal/mole (cf. 13 kcal/mole for the energy of activation for catalysis). These data support the earlier conclusions that the formation of stable complexes probably reflects a massive rearrangement of the initial complexes. The isolated oxipurinol-xanthine oxidase complexes spontaneously reverted to active enzyme with a rate constant of 0.02 min-1 at 37 degrees. The energy of activation for the "reactivation" was similar to that for the formation of the stable complexes. The rates of "reactivation" could be stimulated by high concentrations of xanthine: 2.4-fold at 50 microM and 3.4-fold at 100 microM. The constant for the overall inhibition by oxipurinol was approximately 100 nM with both enzymes.     

Antioxidant,antihyperuricemic and xanthine oxidase inhibitory activities of Hyoscyamus reticulatus

Context:?Xanthine oxidase (XO) is a key enzyme in the pathophysiological homeostasis of hyperuricemia. It catalyzes the oxidation of hypoxanthine to xanthine and then to uric acid, the reaction involves the formation of free radical intermediates and superoxide byproducts.

Objectives:?This study was undertaken to investigate the antioxidant, antihyperuricemic, and xanthine oxidase inhibitory potentials of Hyoscyamus reticulatus L. (Solanaceae) extract.

Materials and methods:?The antioxidant potency was measured using the ABTS^?+ scavenging capacity system, which includes Trolox as a standard. The xanthine oxidase inhibitory activity of the extract was quantitated in vitro by measuring the decline in the catalytic rate of xanthine oxidase following incubations with the plant extracts and using xanthine as a substrate. The hypouricemic potential of the extract was evaluated using an in vivo model for hyperuricemia. We tested three different doses of the extract and allopurinol was used as standard antihyperuricemic positive control.

Results:?H. reticulatus aqueous extract exhibited significant antioxidant scavenging properties (533.26 μmol TE/g dry extract weight) and inhibitory effect on xanthine oxidase activity (IC₅₀ 12.8 μg/mL). Furthermore, oral administration of the aqueous extract significantly reduced serum urate levels in oxonate-induced hyperuricemic mice in a dose-dependent manner.

Discussion and conclusion:?Our results suggest that the aqueous extract of H. reticulatus aerial parts might have great potential as an antioxidant and a hypouricemic agent. Our lab is currently identifying the active compounds in the extract to which the biological activities could be attributed.     

Studies on the mechanism of inhibition of xanthine oxidase by 5-diazoimidazole-4-carboxamide and related thioazoimidazole carboxamides

The mechanism of inhibition of milk xanthine oxidase by 5-diazoimidazole-4-carboxamide (diazo-ICA) and by five related thioazoimidazole carboxamides (thioazo-ICAs) was studied. The extent of inhibition of xanthine oxidase by diazo-ICA and thioazo-ICAs decreased greatly when these compounds were preincubated in a buffer before the addition of substrate and enzyme. In 0.1 M Tris-HCl buffer, pH 7.5, thioazo-ICAs were converted to 2-azahypoxanthine, a cyclized product of diazo-ICA, which inhibits xanthine oxidase slightly. The inhibition of xanthine oxidase by thioazo-ICAs is probably due to this diazo-ICA. With xanthine as a variable substrate, diazo-ICA caused uncompetitive, irreversible inhibition. The inhibition of xanthine oxidase by diazo-ICA was reduced by simultaneous addition of a sulfhydryl compound, such as cysteine, cysteamine or reduced glutathione, but not other amino acids. Diazo-ICA inactivated the enzyme more significantly and rapidly than other sulfhydryl reagents. The inhibitory activity of diazo-ICA was potentiated strongly by Fe²⁺, Mn²⁺, Co²⁺ and Cu²⁺, and slightly by Mo⁵⁺. Treatment of milk xanthine oxidase with diazo-ICA changed the absorption spectrum of the enzyme.     

Monochloramine produces reactive oxygen species in liver by converting xanthine dehydrogenase into xanthine oxidase

In the present study, we assessed the influence of monochloramine (NH₂Cl) on the conversion of xanthine dehydrogenase (XD) into xanthine oxidase (XO) in rat liver in vitro. When incubated with the partially purified cytosolic fraction from rat liver, NH₂Cl (2.5-20 μM) dose-dependently enhanced XO activity concomitant with a decrease in XD activity, implying that NH₂Cl can convert XD into the reactive oxygen species (ROS) producing form XO. The NH₂Cl (5 μM)-induced XD/XO interconversion in the rat liver cytosol was completely inhibited when added in combination with an inhibitor of NH₂Cl methionine (25 μM). A sulfhydryl reducing agent, dithiothreitol at concentrations of 0.1, 1 and 5 mM also dose-dependently reversed the NH₂Cl (5 μM)-induced XD/XO interconversion. These imply that NH₂Cl itself acts on the XD/XO interconversion, and that this conversion occurs at the cysteine residues in XD. Furthermore, using the fluorescent probe 2′,7′-dichlorodihydrofluorescein diacetate, it was found that NH₂Cl could increase ROS generation in the cytoplasm of rat primary hepatocyte cultures, and that this increase might be reversed by an XO inhibitor, allopurinol. These results suggest that NH₂Cl has the potential to convert XD into XO in the liver, which in turn may induce the ROS generation in this region.     

Tissue distribution of the molybdenum hydroxylases, aldehyde oxidase and xanthine oxidase, in male and female guinea pigs

The activity of the molybdenum hydroxylase, aldehyde oxidase, was determined in crude homogenates and (NH4)2SO4 fractions prepared from guinea pig liver, lung, kidney, intestine, spleen and heart. Xanthine oxidase was also measured in (NH4)2SO4 fractions. In each case, xanthine oxidase levels were lower than those of aldehyde oxidase; activity of the latter enzyme was highest in the liver, whereas xanthine oxidase was predominant in the small intestine. There was no significant difference in the activity of either molybdenum hydroxylase between tissues taken from male and female guinea pigs.     

2-苯基-5-吡啶基-1,3,4-噁二唑类化合物的合成及黄嘌呤氧化酶抑制活性

目的 设计合成2-苯基-5-吡啶基-1,3,4-噁二唑类化合物,并对其黄嘌呤氧化酶抑制活性进行初步评价。方法 以对羟基苯甲酸甲酯为原料,经烃化、肼解、环合等反应合成目标化合物。以非布司他为阳性对照药,采用牛源的黄嘌呤氧化酶对目标化合物的抑制活性进行评价。结果 共合成了15 个未见文献报道的目标化合物,结构经核磁共振氢谱、飞行时间质谱和红外光谱确证。目标化合物均表现出一定的黄嘌呤氧化酶抑制活性,其中化合物 4m（IC₅₀=1.04 µmol·L^-1）活性最好,但低于阳性对照药非布司他（IC₅₀=0.024 µmol·L^-1）。结论 2-苯基-5-吡啶基-1,3,4-噁二唑类化合物作为新型黄嘌呤氧化酶抑制剂,其构效关系值得进一步研究。     

Phenylacetaldehyde oxidation by freshly prepared and cryopreserved guinea pig liver slices: the role of aldehyde oxidase

Phenylacetaldehyde is formed when the xenobiotic and biogenic amine 2-phenylethylamine is inactivated by a monoamine oxidase-catalyzed oxidative deamination. Exogenous phenylacetaldehyde is found in certain foodstuffs such as honey, cheese, tomatoes, and wines. 2-Phenylethylamine can trigger migraine attacks in susceptible individuals and can become fairly toxic at high intakes from foods. It may also function as a potentiator that enhances the toxicity of histamine and tyramine. The present investigation examines the metabolism of phenylacetaldehyde to phenylacetic acid in freshly prepared and in cryopreserved guinea pig liver slices. In addition, it compares the relative contribution of aldehyde oxidase, xanthine oxidase, and aldehyde dehydrogenase in the oxidation of phenylacetaldehyde using specific inhibitors for each oxidizing enzyme. The inhibitors used were isovanillin for aldehyde oxidase, allopurinol for xanthine oxidase, and disulfiram for aldehyde dehydrogenase. In freshly prepared liver slices, phenylacetaldehyde was converted mainly to phenylacetic acid, with traces of 2-phenylethanol being present. Disulfiram inhibited phenylacetic acid formation by 80% to 85%, whereas isovanillin inhibited acid formation to a lesser extent (50% to 55%) and allopurinol had little or no effect. In cryopreserved liver slices, phenylacetic acid was also the main metabolite, whereas the 2-phenylethanol production was more pronounced than that in freshly prepared liver slices. Isovanillin inhibited phenylacetic acid formation by 85%, whereas disulfiram inhibited acid formation to a lesser extent (55% to 60%) and allopurinol had no effect. The results in this study have shown that, in freshly prepared and cryopreserved liver slices, phenylacetaldehyde is converted to phenylacetic acid by both aldehyde dehydrogenase and aldehyde oxidase, with no contribution from xanthine oxidase. Therefore, aldehyde dehydrogenase is not the only enzyme responsible in the metabolism of phenylacetaldehyde, but aldehyde oxidase may also be important and thus its role should not be ignored.