In vitro antioxidant and in vivo xanthine oxidase inhibitory activities of Pandanus amaryllifolius in potassium oxonate‐induced hyperuricemic rats

Xanthine oxidase (XO) plays an important role in the regulation of uric acid and prevents it from being overproduced as in hyperuricemia disease. The combined effects of antioxidant and xanthine oxidase inhibitor would become a promising approach for hyperuricemia treatment. In this research, the antioxidant and xanthine oxidase inhibitory activities of Pandanus amaryllifolius leaf were evaluated. The leaf water extract (PA‐W) showed highest total phenols, and petroleum ether extract (PA‐PE) showed highest total flavonoids contents. The antioxidant activity of DPPH, metal chelating and hydrogen peroxide was highest in PA‐W extract. The treatment of PA‐W extract at 1000 mg kg^?1 body weight in potassium oxonate‐induced hyperuricemic rats showed significant (P < 0.001) decrease in serum uric acid level by 85% and XO activity by 64%, respectively, as compared to the hyperuricemic rats. In conclusion, the P. amaryllifolius possess the dual effect of antioxidant and XO inhibition as potential therapeutic agents in the hyperuricemia treatment.     

Camellia sinensis in asymptomatic hyperuricemia: A meta-analysis of tea or tea extract effects on uric acid levels

Flavanols of Camellia sinensis exhibit uric acid (UA) lowering effect, through the modulation of both xanthine oxidase and urate excretion. In order to investigate the potential benefit of Camellia Sinenis products in asymptomatic hyperuricemia, a meta-analysis of long-term Randomized Controlled Trials (RCT) with tea or tea extract has been conducted. From 20 human intervention studies selected only 5 RCT (13 interventions) were suitable for meta-analysis (n = 472). The current “normal” range set for hyperuricemia fails to identify patients with potential metabolic disorders. Therefore on the basis of the literature data, we fixed cut-off limits for UA baseline levels of 4.5 mg/dl for women, 6.1 mg/dl for men, and 5.5 mg/dl for studies involving mixed populations. Statistically significant effects were not found, but subgroup analysis revealed that the Pooled Estimate effect was different in subjects with baseline levels under [MD (95% CI): 0.1078 (?0.0528 to 0.2684)] and over the cut-off [MD (95% CI): ?0.0239 (0.3311 to 0.2833)]. However, due to the low number of RCT and to the lack of data on bioavailability, it is difficult to draw any firm conclusion and more studies are needed to establish if tea flavanols could be useful in asymptomatic hyperuricemia treatment.     

大麦、麦芽和啤酒酿造中的内源性氧化还原酶

由于大麦和麦芽中存在的内潭性氧化还原酶的作用，使内源性多酚、不饱和脂类等物质被氧化，导致成品啤酒风味稳定性和非生物稳定性的降低。酶促氧化反应可发生在不同的酿造阶段，包括发芽、焙爆和糖化等环节。五种主要的内源性氧化还原酶中，超氧化物歧化酶是最为重要的抗氧化酶，可防止超氧阴离子自由基的危害；而过氧化氢酶可催化具有活性的H2O2生成如，由此构成了清除活性氧的初级抗氧化酶体系。过氧化物酶和多酚氧化酶分别在H2O2和O2存在的情况下，可催化内源性酚类底物生成具有活性的醌类物质，所产生的次级氧化产物可改变啤酒的品质。脂肪酸氧化酶可氧化不饱和脂肪酸生成可挥发性的醛类物质，是导致啤酒风味老化的关键酶。酶促氧化的结果在成品啤酒上主要表现为老化异昧的出现、形成混浊、苦味和收敛性的改变，以及色泽的加深等。本文综述了这五种酶的基本性质，在制麦和糖化过程中的变化及其影响，并探讨了对啤酒酿造的影响。     

朝鲜蓟叶提取物的体外抗氧化作用

对朝鲜蓟叶提取物(ALE)进行体外抗氧化实验,评价其抗氧化功能。采用4种不同的体外抗氧化评价体系对ALE进行抗氧化功能的评价,结果以IC50来表示。ALE在4种系统中表现出不同的抗氧化能力。其中以NH2OH-Xan-XOD系统的IC50值最低,为16.5μg/mL,二酪氨酸/酪氨酸系统的IC50值最高,为310μg/mL。ALE具有抗氧化作用,且存在剂量依赖效应。     

Scavenging effect of tea catechins and their epimers on superoxide anion radicals generated by a hypoxanthine and xanthine oxidase system

Catechins are a major group of polyphenolic compounds contained in abundance in green tea. Using electron spin resonance spectroscopy along with a spin‐trapping agent, the scavenging effect of tea catechins and their corresponding epimers against superoxide anion radicals generated by a hypoxanthine and xanthine oxidase reaction system was evaluated. The presence of 3′,4′,5′‐trihydroxyl groups attached to the B‐ring of the flavan skeleton of tea catechins elevated their radical‐scavenging efficiency in comparison to those with 3′,4′‐dihydroxyl groups. There were no significant differences between the four dominant tea catechins and their corresponding epimers with regard to radical‐scavenging ability. Under the different spin‐trapping agent concentrations, the sigmoid curves of reducing spin‐trapping adducts produced by tea catechins were shifted leftward, suggesting that a likely possible action of tea catechins is to scavenge superoxide anion radicals directly, not to inhibit the function of xanthine oxidase. Although caffeine is also known as a major ingredient of tea, its superoxide anion radical‐scavenging effect was much weaker than that of the catechin family. It is concluded that tea catechins and their epimers serve as powerful antioxidants for directly eliminating superoxide anion radicals, and may be useful in the prevention of diseases relating to in vivo oxidative stress. © 2000 Society of Chemical Industry     

Antioxidative activities of bran extracts from twenty one pigmented rice cultivars

Ethanol–water (70:30, v/v) extracts from the bran of rice seeds from twenty one pigmented and one nonpigmented rice cultivars were evaluated for antioxidative activities using the following tests: inhibition of peroxidation of linoleic acid; inhibition of peroxidation of rabbit lipid erythrocyte membranes; reduction of potassium ferricyanide, and scavenging of superoxide anions and hydroxyl radicals. With some exceptions, extracts from the pigmented rice seeds had higher antioxidative activity than did the nonpigmented variety. The following pigmented cultivars had the highest antioxidative activities in all tests: Jumlalocal-1, Parnkhari 203, DZ78, LK1-3-6-12-1-1, and Elwee. A significant correlation was also noted between reducing power, inhibition of erythrocyte ghost membrane peroxidation, and superoxide anion and hydroxyl radical scavenging. The results suggest that: (a) ferricyanide reducing power might be a useful and simple index for large-scale evaluation of antioxidative potencies of natural products present in rice; (b) pigmented rice varieties with high antioxidative activities provide a source of antioxidants and a genetic resource to develop new health-promoting rice cultivars.     

3种黄酮对黄嘌呤氧化酶活性的抑制作用

采用分子对接技术结合体外酶活性测定技术,从200个天然活性小分子中筛选出香叶木素(Dio)、漆黄素(Fis)和金雀异黄酮(Gen)3种黄酮类化合物。采用紫外光谱、拉曼光谱和分子动力学等方法分析它们的互作机制。结果表明,Dio、Fis、Gen均结合在XO的FAD活性位点附近,主要作用力是氢键和范德华力。紫外光谱分析表明:3种黄酮对XO都有抑制作用,作用强弱排序为Dio>Fis>Gen。拉曼光谱分析表明:Dio、Fis、Gen使XO刚性结构(α-螺旋和β-折叠)含量由55.3%分别增加到59.4%,59%和58.7%,无规则卷曲消失。DSC、粒径和电位测定表明:Dio、Fis、Gen使XO变性温度Tm分别提高了3.62,1.60,4.52 ℃,粒径减小且电位绝对值增加。分子动力学分析结果:3种黄酮通过影响酶活性位点附近色氨酸残基的微环境使酶收缩,形成更加紧密、稳定的构象。结论:3种黄酮使XO结构收缩形成更加稳定的构象,从而抑制酶的活性。氨基酸残基LEU257、ILE353和VAL259起关键性作用。研究结果对新型XO抑制剂的开发利用具有重要意义。     

Mechanisms of Enzyme-Catalyzed Reduction of Two Carcinogenic Nitro-Aromatics, 3-Nitrobenzanthrone and Aristolochic Acid I: Experimental and Theoretical Approaches

This review summarizes the results found in studies investigating the enzymatic activation of two genotoxic nitro-aromatics, an environmental pollutant and carcinogen 3-nitrobenzanthrone (3-NBA) and a natural plant nephrotoxin and carcinogen aristolochic acid I (AAI), to reactive species forming covalent DNA adducts. Experimental and theoretical approaches determined the reasons why human NAD(P)H:quinone oxidoreductase (NQO1) and cytochromes P450 (CYP) 1A1 and 1A2 have the potential to reductively activate both nitro-aromatics. The results also contributed to the elucidation of the molecular mechanisms of these reactions. The contribution of conjugation enzymes such as N,O-acetyltransferases (NATs) and sulfotransferases (SULTs) to the activation of 3-NBA and AAI was also examined. The results indicated differences in the abilities of 3-NBA and AAI metabolites to be further activated by these conjugation enzymes. The formation of DNA adducts generated by both carcinogens during their reductive activation by the NOQ1 and CYP1A1/2 enzymes was investigated with pure enzymes, enzymes present in subcellular cytosolic and microsomal fractions, selective inhibitors, and animal models (including knock-out and humanized animals). For the theoretical approaches, flexible in silico docking methods as well as ab initio calculations were employed. The results summarized in this review demonstrate that a combination of experimental and theoretical approaches is a useful tool to study the enzyme-mediated reaction mechanisms of 3-NBA and AAI reduction.     

Modeling of Anopheles minimus Mosquito NADPH-Cytochrome P450 Oxidoreductase (CYPOR) and Mutagenesis Analysis

Malaria is one of the most dangerous mosquito-borne diseases in many tropical countries, including Thailand. Studies in a deltamethrin resistant strain of Anopheles minimus mosquito, suggest cytochrome P450 enzymes contribute to the detoxification of pyrethroid insecticides. Purified A. minimus CYPOR enzyme (AnCYPOR), which is the redox partner of cytochrome P450s, loses flavin-adenosine di-nucleotide (FAD) and FLAVIN mono-nucleotide (FMN) cofactors that affect its enzyme activity. Replacement of leucine residues at positions 86 and 219 with phenylalanines in FMN binding domain increases FMN binding, enzyme stability, and cytochrome c reduction activity. Membrane-Bound L86F/L219F-AnCYPOR increases A. minimus P450-mediated pyrethroid metabolism in vitro. In this study, we constructed a comparative model structure of AnCYPOR using a rat CYPOR structure as a template. Overall model structure is similar to rat CYPOR, with some prominent differences. Based on primary sequence and structural analysis of rat and A. minimus CYPOR, C427R, W678A, and W678H mutations were generated together with L86F/L219F resulting in three soluble Δ55 triple mutants. The C427R triple AnCYPOR mutant retained a higher amount of FAD binding and increased cytochrome c reduction activity compared to wild-type and L86F/L219F-Δ55AnCYPOR double mutant. However W678A and W678H mutations did not increase FAD and NAD(P)H bindings. The L86F/L219F double and C427R triple membrane-bound AnCYPOR mutants supported benzyloxyresorufin O-deakylation (BROD) mediated by mosquito CYP6AA3 with a two-to three-fold increase in efficiency over wild-type AnCYPOR. The use of rat CYPOR in place of AnCYPOR most efficiently supported CYP6AA3-mediated BROD compared to all AnCYPORs.     

Syntheses of 1,2,4-triazolo[4,3-c]pteridines. Potential substrates for xanthine oxidase

A synthetic route for the preparation of 9-phenyl-1,2,4-triazolo[4,3-c]pteridines 8 is described. Their reactivities towards xanthine oxidase from Arthrobacter M-4 are determined and compared with the pteridine derivatives 6-phenylpteridin-4[3H]-thione 5, 6-phenyl-4-thiomethylpteridine 6, 4-hydrazino-6-phenylpteridine 7, 3-N-methyl-6-phenylpteridin-4[3H]-thione 19, 4-amino-6-phenylpteridine 22 and 1-N-methyl-6-phenylpteridin-4[1H]-one 24, in order to inspect a possible influence of pyrimidine ring substitution pattern on their interaction with the bacterial enzyme. It has been suggested that a planar structure of the pteridine moiety and the substituents could be an important factor that so far has been overlooked when considering the enzyme activity. Some literature data are also discussed in view of revision of structure assignment of the compounds 12, 14, and 17. This revised version was published online in August 2006 with corrections to the Cover Date.