Antioxidant activity of anacardic acids

Anacardic acids, 6-pentadec(en)ylsalicylic acids isolated from the cashew Anacardium occidentale L. (Anacardiaceae) nut and apple, were found to possess preventive antioxidant activity while salicylic acid did not show this activity. These anacardic acids prevent generation of superoxide radicals by inhibiting xanthine oxidase (EC 1.1.3.22, Grade IV) without radical-scavenging activity. Notably, the inhibition kinetics of anacardic acids do not follow hyperbolic dependence of enzyme inhibition on inhibitor contents (Michaelis–Menten equation) but follow the Hill equation instead. Anacardic acid (C_15:1) inhibited the soybean lipoxygenase-1 (EC 1.13.11.12, Type 1) catalyzed oxidation of linoleic acid with an IC₅₀ of 6.8 μM. The inhibition is a slow and reversible reaction without residual enzyme activity. The inhibition kinetics indicate that anacardic acid (C_15:1) is a competitive inhibitor and the inhibition constant, K_I, was 2.8 μM. Anacardic acids act as antioxidants in a variety ways, including inhibition of various prooxidant enzymes involved in the production of the reactive oxygen species and chelate divalent metal ions such as Fe²⁺ or Cu²⁺, but do not quench reactive oxygen species. The C₁₅-alkenyl side chain is largely associated with the activity.     

Content of polyphenolic constituents and antioxidant activity of some Stachys taxa

Seven Croatian Stachys taxa (S. alpina, S. officinalis, S. palustris, S. recta subsp. recta, S. recta subsp. subcrenata, S. salviifolia and S. sylvatica) have been investigated in order to determine their content of biologically active compounds (polyphenols, tannins, phenolic acids and flavonoids) as well as their antioxidant activity. All taxa tested had a high content of total polyphenols, medium content of total phenolic acids, and a rather low content of tannins and flavonoids. The total phenolic acids content correlated significantly with total polyphenols content and the content of polyphenols unadsorbed on hide powder. A low correlation between plant phenolic acids and tannins was observed. Methanolic, ethanolic and dichloromethane extracts were investigated using DPPH, lipid peroxidase and xanthine oxidase assays. The extracts showed no inhibitory effects against lipid peroxidation and xanthine oxidase, but they had the ability to scavenge DPPH. The most effective in the DPPH assay were methanolic extracts of S. recta sub. recta and S. palustris whose radical scavenging activity was higher then that of the reference rutin. A low correlation between radical scavenging capacities of extracts with total flavonoids content was observed. The results indicate that investigated Stachys taxa exhibit potent antiradical activity and therefore could be a potential material for extracting free radical scavengers.     

Antioxidant and anticholinesterase evaluation of selected Turkish Salvia species

Since Salvia species (Lamiaceae) have been recorded to be used against memory loss in European folk medicine, we herein examined in vitro anticholinesterase and antioxidant activities of 56 extracts prepared with petroleum ether, chloroform, ethyl acetate and methanol obtained from 14 Salvia species (Salvia albimaculata Hedge and Hub, Salvia aucheri Bentham var. canescens Boiss and Heldr, Salvia candidissima Vahl. ssp. occidentalis, Salvia ceratophylla L., Salvia cryptantha Montbret and Bentham, Salvia cyanescens Boiss and Bal., Salvia frigida Boiss, Salvia forskahlei L., Salvia halophilaHedge, Salvia migrostegia Boiss and Bal., Salvia multicaulis Vahl., Salvia sclarea L., Salvia syriaca L., Salvia verticillata L. ssp. amasiaca) growing in Turkey. The antioxidant activities were assessed by both chemical and enzymatic methods against 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging and xanthine/xanthine oxidase (XO) system generated superoxide anion radical inhibition. Anticholinesterase effect of the extracts was tested against both acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) at concentrations of 0.2 and 1 mg/ml using a microplate-reader assay based on the Ellman method. Most of the extracts did not show any activity against AChE at 0.2 mg/ml, while the chloroform extracts had noticeable inhibition against BChE between 47.7% and 74.7%. The most active extracts at 1 mg/ml for AChE inhibition were observed to be petroleum ether extract of Salvia albimaculata (89.4%) and chloroform extract of Salvia cyanescens (80.2%), whereas ethyl acetate extracts of Salvia frigida and Salvia migrostegia, chloroform extracts of Salvia candidissima ssp. occidentalis and Salvia ceratophylla, as well as petroleum ether extract of Salvia cyanescens were found to inhibit potently BChE (92.2%, 89.6%, 91.1%, 91.3%, and 91.8%, respectively). Particularly, the ethyl acetate and methanol extracts were observed to be highly active against both DPPH and XO. Our data indicates that nonpolar extracts of Salvia species for anticholinesterase activity and the polar extracts for antioxidant activity are worth further phytochemical evaluation for identifying their active components.     

Nucleotides and their degradation products during processing of dry-cured ham, measured by HPLC and an enzyme sensor

The aim of this work was to study how nucleotide degradation during the processing of dry-cured ham is affected when using three types of salting (100% NaCl; 50% NaCl and 50% KCl; 55% NaCl, 25% KCl, 15% CaCl₂ and 5% MgCl₂). Divalent salts in the salting mixture depressed the breakdown rate from the beginning of the process (salting and post-salting) up to the ripening stage (7 months) when the inosine (Ino), hypoxanthine (Hx) and xanthine (X) concentrations matched for the three treatments. The evolution of Hx and Hx + X were analysed by HPLC and an enzyme sensor, respectively, during processing. Time and temperature conditions during the curing time did not affect Hx stability. The usefulness of the enzyme sensor was confirmed and it is a practical tool to determine Hx + X in dry-cured ham, as an index of minimum curing time. A good correlation between enzyme sensor and HPLC data was observed.     

Evaluation of xanthine derivatives in chocolate – nutritional and chemical aspects

 Organic substances containing nitrogen are widespread throughout the whole of the natural world. Also included amongst these are the methylxanthine derivatives caffeine, theobromine and theophylline. These are very closely related and are to be found in extremely varying contents in different plants. Because of their pharmacological effect, which is fundamentally of a stimulative nature, methylxanthines have been significant since time immemorial as luxury, non-essential foodstuffs and as medication. These substances are often referred to as alkaloids. Theobromine is the major alkaloid in cacao (Theobroma cacao). Caffeine, on the other hand, is only to be found in cacao in very small quantities and theophylline only in trace amounts. Methylxanthines are said to contribute towards the typically bitter taste of cacao. In addition they represent important analytical parameters with regard to the evaluation of the quality of cacao-containing and chocolate products. The amount of methylxanthines in cacao depends on various influencing factors, the most essential ones being processing procedures, genotype, geographical origin and cacao bean weight. By determining the amount of theobromine and caffeine in cacao and/or cacao products, the amount of fat-free dry cacao can also be estimated. There are various methods available for the detection and determination of methylxanthines. UV-spectrophotometric determination and analysis using HPLC have attained major significance here. With regard to human nutrition, cacao and cacao products are the main natural sources of theobromine, but significantly less so with regard to caffeine. The presence of methylxanthines in cacao products leads to that they are sometimes the subject of consumer criticism, particularly because they are considered as luxury foodstuffs. The concluding evaluation of methylxanthines by dieticians and toxicologists reveals that plants that contain methylxanthines have been consumed for as long as can be remembered without having led to damage to health. Scientific research has shown that the consumption of these substances has no consequence whatsoever, as long as consumption is not excessive, which is the case for all foodstuffs. Methylxanthines in cacao products have no negative effects on the health of humans because their amounts in chocolates and other processed foodstuffs containing cacao are so low that they account for only a very small proportion of the whole of the human diet. Received: 15 November 1996 / Revised version: 22 January 1997     

Improvement in the remaining activity of freeze-dried xanthine oxidase with the addition of a disaccharide–polymer mixture

In order to improve the remaining activity of a practically important freeze-dried enzyme, xanthine oxidase (XOD), the effects of disaccharide (sucrose and trehalose), polymer (bovine serum albumin: BSA and dextran) and a mixture of them on the loss of XOD activity during freeze-drying and subsequent storage were investigated. All samples were amorphous solids and their glass transition temperatures (T_g) were evaluated by using differential scanning calorimetry. Although dextran showed no stabilizing effect on the freeze-dried XOD, the others protected XOD from the activity loss during freeze-drying to a certain extent. It was found that the mixture of disaccharide (sucrose or trehalose) and BSA improved the XOD activity synergistically. The XOD activity of the samples decreased gradually during storage at a temperature range of between 25 and 60 °C. Samples stored at temperatures below the T_g showed a lower loss of XOD activity than those stored at just the T_g.     

Inhibition of xanthine oxidase activity by an oxathiolanone derivative of quercetin

An oxathiolanone derivative of rutin could be produced in the stomach after the ingestion of rutin containing foods, and the oxathiolanone derivative could be hydrolysed to an oxathiolanone derivative of quercetin (quercetin-oxathiolanone) in the intestine. Quercetin-oxathiolanone as well as quercetin inhibited xanthine oxidase. Approximately 0.05 μM quercetin-oxathiolanone inhibited the activity by 50%, whereas 50% inhibition by quercetin was observed at approximately 0.4 μM. The results suggested that quercetin-oxathiolanone can be used as an effective inhibitor of xanthine oxidase and that the ingestion of rutin-rich foods may be useful to prevent the increase in the blood concentration of uric acid.     

Xanthine oxidase inhibitory activity of alkyl gallates

A series (C1-C12) of alkyl gallates was examined for their effects on the activity of xanthine oxidase. Octyl (C8), decyl (C10), and dodecyl (C12) gallates competitively inhibited uric acid formation generated by xanthine oxidase, and the inhibition increased upon increasing the alkyl chain length. Interestingly, neither menthyl nor bornyl gallates inhibited uric acid formation. These data indicate that the hydrophobic alkyl portion is associated with the xanthine-binding site in the Mo-binding domain. It is likely that the linear alkyl portion interacts with the hydrophobic domain close to the binding site, and the hydrophobic interaction is crucial to inhibit the xanthine oxidase reaction. On the other hand, all of gallic acid and its esters equally suppress superoxide anion generation catalyzed by xanthine oxidase at low concentration. The suppression is not due to scavenging activity of these gallates but due to reduction of xanthine oxidase by these gallates. The reduced enzyme catalyzes the reaction to generate hydrogen peroxide and uric acid.     

高效液相色谱法定量尿酸、黄嘌呤和次黄嘌呤在人体血清中的浓度

目的: 建立高效液相色谱法测定尿酸、黄嘌呤和次黄嘌呤在人体血清中的浓度。方法: 用Agilent ZORBAX SB-Aq column色谱柱,ZORBAX-Extend C₁₈预柱,以甲醇和 47 mmol/L KH₂PO₄水溶液作为流动相,流速:1.0 mL/min,检测波长为 260 nm。结果: 血清中尿酸、黄嘌呤和次黄嘌呤的线性范围分别是(1.667~166.667)×10³ ng/mL (r=0.9995)、(0.033~3.338)×10³ ng/mL(r=0.9994)和 (0.033~3.338)×10³ ng/mL (r=0.9996),日间与日内精密度均<15%。结论: 该法灵敏度高,精密度和准确度佳,能满足非布司他体内药效学研究。     

黄嘌呤氧化酶抑制剂研究进展及发展前景

别嘌呤醇是治疗高尿酸血症及痛风的主要药物之一,可是该药物不但会引发皮肤炎症,还引其发热和多器官受损,甚至有引起死亡的报道。其安全性受到质疑。天然产物来源的黄嘌呤氧化酶抑制剂毒性小,安全性高,不易引起过敏反应且来源广,有的甚至可以用于日常饮食。本文对黄嘌呤氧化酶具有抑制作用的天然产物的研究进展及发展前景进行综述。