Flow Injection Determination of Xanthine Oxidase Inhibitory Activity and Its Application to Food Samples

Abstract

In humans, a given amount of oxygen taken in by the body is always converted to ROS, such as O2 -, H2O2 and hydroxyl radical (OH·) by various enzymatic metabolism systems. 1 Because of their high reactivity, ROS affects various molecular components of the cell, like fatty acids, proteins and DNA, and an excess of ROS leads to cell degeneration and death.2 When the amount of ROS exceeds the limit of defense mechanism of the body, many serious diseases may be induced, such as: cancer, arteriosclerosis, gout, Alzheimer's disease, Werner syndrome, and various age-related diseases. 1 Among the enzymes concerning oxidation, XOD has been recognized as a key oxidative enzyme in pathology, such as hypertension and ischemia-reperfusion. The enzyme catalyses the oxidation of many substrates, including purines, pteridines, aldehydes and heterocyclic molecules. 3 XOD catalyzes the following reactions, which produce both superoxide anion and hydrogen peroxide directly:Xanthine + H2O + 2O2 → Uric acid + 2O2 -+ 2H + ,Xanthine + H2O + O2 → Uric acid + H2O2.However, about 20% of the reduction of oxygen is univalent and the rest is divalent. 3 Superoxide anion, which is very reactive, spontaneously dismutates into oxygen and hydrogen peroxide, if it does not react with some other species, 2O2 -+ 2H + → H2O2 + O2.The overproduction and/or underexcretion of uric acid leads to hyperuricemia, such as gout. 4 Thus, one of the treatments of gout is the use of XOD inhibitors that block the production of uric acid.In the human body, XOD is normally found in the liver, and is not free in the blood. During oxidative stress, the enzyme XOD increases. There are five different mechanisms known to increase superoxide generation by XOD during ischemiareperfusion: firstly, superoxide and hydrogen peroxide production are enhanced due to increased conversion of xanthine dehydrogenase to XOD; secondly, mRNA levels of xanthine dehydrogenase and XOD are upregulated; thirdly, when the liver becomes ischemic and hepatocellular damage occurs, the liver releases XOD in the bloodstream, this superoxide-producing enzyme thus being transported throughout the body (thus, a blood assay for XOD is a way to determine if liver damage has happened); furthermore, XOD can bind to endothelial cells, and cell-bound XOD has been reported to produce radicals; finally, during ischemia, ATP is degenerated to xanthine and hypoxanthine, thereby increasing the XOD substrate levels, which leads to increased superoxide production. 5 To protect the body from highly toxic ROS, the human body requires anti-oxidative stress mechanisms, including superoxide dismutase (SOD), which catalyses dismutation of two O2 -into H2O2 and O2 (have lower activity). SOD plays an important role in the defense against oxygen toxicity. However, XOD inhibitors, which effectively suppress the production of ROS created by xanthine-XOD, can be substitute for SOD.Among the XOD inhibitory agents, allopurinol (Fig. 1) is an allosteric XOD inhibitor that is structurally related to xanthine, and is oxidiz...

Simultaneous spectrophotometric determination of phenanthridine, phenanthridinone and phenanthridine N-oxide using multivariate calibration methods

“…methods have been reported for the determination of phenanthridine and its metabolites [4,8,9]. The separation and determination of phenanthridine and its metabolites are achieved by chromatographic methods which are usually inconvenient, expensive and timeconsuming [8,9].…”

“…The separation and determination of phenanthridine and its metabolites are achieved by chromatographic methods which are usually inconvenient, expensive and timeconsuming [8,9]. The simultaneous determination of several components in a mixture, in particular in the biological matrices, can be a difficult task, especially when their analytical characteristics are not very different, which is the case with phenanthridine and its metabolites.…”

KAEMPFEROL FROM STELECHOCARPUS BURAHOL, (BL.) HOOK F. & TH. LEAVES AND XANTHINE OXIDASE INHIBITION ACTIVTY

“…10). According to Lam et al (2006) [27], allopurinol (positive control) has an activity of inhibiting xanthine as an allosteric inhibitor of XO by reducing the reactive groups on the XO (Massey et al, 1970) [28].…”