Effects of temporary rearing with organic selenium on the muscle flavor and texture properties of largemouth bass (Micropterus salmonides).

In this study, the influences of organic selenium (Se, 0.002 mg/L) on the muscle flavor and texture properties of Micropterus salmonides under fasting temporary rearing (8 weeks) was investigated. Electronic nose and headspace solid-phase microextraction-gas chromatography-mass spectrometry analysis suggested that organic Se regulated the types and contents of volatile compounds, especially aldehydes and ketones, which were increased in the early temporary rearing but decreased in the late stage. Organic Se significantly increased the content of 5'-inosine monophosphate by approximately 15 % (p < 0.05), and decreased the content of hypoxanthine and hypoxanthine ribonucleoside by more than 20 % (p < 0.05). After the 8th temporary rearing week, muscle hardness and springiness increased by at least 10 % (p < 0.01), resilience and gumminess improved by at least 18 % (p < 0.05) and 5.9 % (p < 0.05), respectively. In conclusion, organic Se ameliorates the flesh quality of M. salmonides during long-term temporary rearing.

Identification of Sputum Biomarkers Predictive of Pulmonary Exacerbations in COPD.

BACKGROUND: Improved understanding of the pathways associated with airway pathophysiologic features in COPD will identify new predictive biomarkers and novel therapeutic targets. RESEARCH QUESTION: Which physiologic pathways are altered in the airways of patients with COPD and will predict exacerbations? STUDY DESIGN AND METHODS: We applied a mass spectrometric panel of metabolomic biomarkers related to mucus hydration and inflammation to sputa from the multicenter Subpopulations and Intermediate Outcome Measures in COPD Study. Biomarkers elevated in sputa from patients with COPD were evaluated for relationships to measures of COPD disease severity and their ability to predict future exacerbations. RESULTS: Sputum supernatants from 980 patients were analyzed: 77 healthy nonsmokers, 341 smokers with preserved spirometry, and 562 patients with COPD (178 with Global Initiative on Chronic Obstructive Lung Disease [GOLD] stage 1 disease, 303 with GOLD stage 2 disease, and 81 with GOLD stage 3 disease) were analyzed. Biomarkers from multiple pathways were elevated in COPD and correlated with sputum neutrophil counts. Among the most significant analytes (false discovery rate, 0.1) were sialic acid, hypoxanthine, xanthine, methylthioadenosine, adenine, and glutathione. Sialic acid and hypoxanthine were associated strongly with measures of disease severity, and elevation of these biomarkers was associated with shorter time to exacerbation and improved prediction models of future exacerbations. INTERPRETATION: Biomarker evaluation implicated pathways involved in mucus hydration, adenosine metabolism, methionine salvage, and oxidative stress in COPD airway pathophysiologic characteristics. Therapies that target these pathways may be of benefit in COPD, and a simple model adding sputum-soluble phase biomarkers improves prediction of pulmonary exacerbations. TRIAL REGISTRY: ClinicalTrials.gov; No.: NCT01969344; URL: www. CLINICALTRIALS: gov.

Using follicular fluid metabolomics to investigate the association between air pollution and oocyte quality.

BACKGROUND AND AIM: Our objective was to use metabolomics in a toxicological-relevant target tissue to gain insight into the biological processes that may underlie the negative association between air pollution exposure and oocyte quality. METHODS: Our study included 125 women undergoing in vitro fertilization at an academic fertility center in Massachusetts, US (2005-2015). A follicular fluid sample was collected during oocyte retrieval and untargeted metabolic profiling was conducted using liquid chromatography with ultra-high-resolution mass spectrometry and two chromatography columns (C18 and HILIC). Daily exposure to nitrogen dioxide (NO2), ozone, fine particulate matter, and black carbon was estimated at the women's residence using spatiotemporal models and averaged over the period of ovarian stimulation (2-weeks). Multivariable linear regression models were used to evaluate the associations between the air pollutants, number of mature oocytes, and metabolic feature intensities. A meet-in-the-middle approach was used to identify overlapping features and metabolic pathways. RESULTS: Of the air pollutants, NO2 exposure had the largest number of overlapping metabolites (C18: 105; HILIC: 91) and biological pathways (C18: 3; HILIC: 6) with number of mature oocytes. Key pathways of overlap included vitamin D3 metabolism (both columns), bile acid biosynthesis (both columns), C21-steroid hormone metabolism (HILIC), androgen and estrogen metabolism (HILIC), vitamin A metabolism (HILIC), carnitine shuttle (HILIC), and prostaglandin formation (C18). Three overlapping metabolites were confirmed with level-1 or level-2 evidence. For example, hypoxanthine, a metabolite that protects against oxidant-induced cell injury, was positively associated with NO2 exposure and negatively associated with number of mature oocytes. Minimal overlap was observed between the other pollutants and the number of mature oocytes. CONCLUSIONS: Higher exposure to NO2 during ovarian stimulation was associated with many metabolites and biologic pathways involved in endogenous vitamin metabolism, hormone synthesis, and oxidative stress that may mediate the observed associations with lower oocyte quality.

A high-performance liquid chromatography method for hypoxanthine determination in vitreous humour: application to estimation of post mortem interval.

We have developed a new technique to determine the concentration of hypoxanthine [Hx] in a reverse phase column using a modified high-performance liquid chromatography (HPLC) method that is faster and more reliable than those previously described. In this paper we present a formula for estimating the post mortem interval (PMI) based on this HPLC method by applying the inverse prediction method. The regression line obtained by changing the variables gives PMI = 0.183 [Hx] + 0.599 (PMI in hours, [Hx] in micromol/L, R2 = 0.531, P < 0.05).

Hypoxanthine concentrations in normal subjects and patients with solid tumors and leukemia.

Mean plasma hypoxanthine (Hyp) concentrations determined by high-pressure liquid chromatography were 0.56 microM (range, 0.2 to 1.9 microM) in 16 normal subjects, 0.68 microM (range, 0.1 to 1.1 microM) in 10 untreated acute leukemic subjects, and 0.89 microM (range, 0.3 to 2.6 microM) in 14 solid tumor patients. Despite large differences in Hyp concentration between patients, every 4-hr sampling, indicated that diurnal variation in individual patients was small (maximum, 2.3-fold). While the mean plasma and malignant effusion Hyp concentrations did not differ significantly, bone marrow plasma Hyp concentration averaged 4.0-fold greater than that of simultaneously drawn venous plasma. Allopurinol 300 mg p.o. caused a mean 1.5-fold increase in plasma Hyp within 3 hr. In 17 patients with acute leukemia, treatment with allopurinol at 300 mg daily plus initiation of chemotherapy caused a mean 7-fold increase in plasma Hyp to 4.6 microM (range, 1 to 12 microM). The ability of Hyp to modulate the toxicity of antimetabolites affecting purine synthesis (6- diazao -5- oxonorleucine , 6-methylmercaptopurine riboside, 6-mercaptopurine, and 6-thioguanine) was determined in vitro using human B-lymphoblast (WI-L2) and promyelocytic leukemia (HL-60) cell lines. Hyp permitted growth of both cell lines in the presence of clinically achievable concentrations of all 4 drugs, but the initial culture concentrations of Hyp required were above those found in patients. Since Hyp was consumed rapidly during the culture period, the average Hyp concentrations required for the protection of cells were actually much lower. We conclude that, in patients with acute leukemia receiving allopurinol during chemotherapy, plasma Hyp concentrations are significantly elevated; the potential for antagonism of antimetabolite activity is uncertain.

Radiation-induced hydroxyl addition to purine molecules: EPR and ENDOR study of hypoxanthine hydrochloride monohydrate single crystals.

Three radical species were detected in an EPR/ENDOR study of X-irradiated hypoxanthine.HCl.H2O single crystals at room temperature: RI was identified as the product of net H addition to C8, RII was identified as the product of net H addition to C2, and RIII was identified as the product of OH addition to C8. The observed set of radicals was the same for room-temperature irradiation as for irradiation at 10 K followed by warming the crystals to room temperature; however, the C2 H-addition and C8 OH-addition radicals were not detectable after storage of the crystals for about 2 months at room temperature. Use of selectively deuterated crystals permitted unique assignment of the observed hyperfine couplings, and results of density functional theory calculations on each of the radical structures were consistent with the experimental results. Comparison of these experimental results with others from previous crystal-based systems and model system computations provides insight into the mechanisms by which the biologically important purine C8 hydroxyl addition products are formed. The evidence from solid systems supports the mechanism of net water addition to one-electron oxidized purine bases and demonstrates the importance of a facial approach between the reactants.

Adenine, guanine, and inosine nucleotides of chick growth cartilage: relationship between energy status and the mineralization process.

The major aim of this investigation was to measure the nucleotide content of the developing chick epiphysis and to relate changes in nucleotide levels to chondrocyte maturation and the development of mineralization. Using a cryostat, sections of cartilage were isolated from the proximal head of the tibial growth cartilage, care being taken to preserve the metabolic integrity of the tissue. Sections were identified microscopically, pooled, and the nucleotide and nucleoside content of each sample determined by HPLC. Procedures used for the study were shown to minimize degradation of nucleotides. Their effectiveness was assessed through an evaluation of the rapid freezing technique and by examination of the effects of apatite on the recovery of endogenous and added nucleotides. Analysis of nucleotide levels in the growth cartilage indicated that chondrocytes undergo a profound change in energy metabolism during development and maturation. Thus, in the premineralized resting and proliferative zones, ATP and, to a lesser extent, GTP values were high, suggesting that the chondrocytes obtained metabolic energy through both glycolytic and mitochondrial oxidative processes. In the hypertrophic zone and in calcified cartilage, there was a profound decrease in the ATP concentration and a corresponding fall in the energy charge and the ATP/ADP ratios. The nucleotide levels in this zone indicated that there was increased reliance on nonoxidative metabolism. Measurement of nucleoside levels in premineralized cartilage suggested that there was little resynthesis of nucleotides through the salvage pathway. These observed changes in nucleotide values are consistent with earlier observations concerning chondrocyte redox and the low pO2 tension of the hypertrophic zone.2+off

Increased brain interstitial fluid adenosine concentration during hypoxia in newborn piglet.

The effects of arterial hypoxia on interstitial fluid adenosine concentrations were studied in the frontal cortex and thalamus by the brain dialysis technique and in CSF from the cisterna magna of the newborn piglet. Acute hypoxia (PaO2 = 20 +/- 1 mm Hg) increased the interstitial fluid adenosine concentrations significantly from 0.68 +/- 0.29 (SEM) to 1.60 +/- 0.35 microM in the frontal cortex and from 1.03 +/- 0.32 to 2.60 +/- 0.86 microM in the thalamus (n = 8). Interstitial fluid inosine and hypoxanthine also increased significantly during hypoxia. In separate groups of piglets, the adenosine concentration in the cisterna magna CSF under normoxic conditions was 0.04 +/- 0.01 microM (n = 5), which increased significantly to 0.17 +/- 0.04 microM (n = 6) with hypoxia (PaO2 = 4.7 +/- 1.2 mm Hg). Cisterna magna CSF inosine levels did not change significantly during the severe hypoxia. Adenosine concentrations found in the interstitial space and CSF of newborn piglets under normoxic and hypoxic conditions are within the vasodilator range. These results thus suggest that in the neonatal brain adenosine may play a role in regulating blood flow during hypoxia.

DNA damage in human respiratory tract epithelial cells: damage by gas phase cigarette smoke apparently involves attack by reactive nitrogen species in addition to oxygen radicals.

Treatment of human respiratory tract tracheobronchial epithelial cells with gas-phase cigarette smoke led to dose-dependent DNA strand breakage that was highly correlated with multiple chemical modifications of all four DNA bases. The pattern of base damage suggests attack by hydroxyl radicals (OH.). However, by far the most important base damage in quantitative terms was formation of xanthine and hypoxanthine, presumably resulting from deamination of guanine and adenine respectively. Hence, DNA damage by cigarette smoke may involve reactive nitrogen species as well as reactive oxygen species.

Enhanced restoration of adenine nucleotides in rat liver following extended preservation in UW solution by provision of adenosine during reperfusion.

The extensive reduction of adenine nucleotides during preservation coupled with the loss of salvageable precursors during initial reflow may exacerbate recovery of adenine nucleotides in allograft liver following transplantation. The objective of this study was to assess whether provision of adenosine during reperfusion of rat liver stored for 20 hr in University of Wisconsin solution could enhance adenine nucleotide restoration. ATP and total adenine nucleotide content of livers perfused with an oxygenated Krebs/fluorocarbon solution containing 1 mM adenosine were restored to levels in vivo within 30 min of perfusion. Adenine nucleotide recovery in livers perfused without adenosine was only 65% of normal. Acute nutritional deprivation of the donor rats had no effect on adenine nucleotide restoration. These results indicate that a conditional deficiency of intracellular nucleotide precursors exists during initial reperfusion of liver subjected to extended storage in UW solution. Provision of supplemental adenosine to the allograft liver during initial reflow appears warranted to promote full and rapid restoration of adenine nucleotide content following extended preservation ex vivo.

Assessment of purine metabolism in human renal transplantation.

Cortical levels of nucleotides and their degradation products from 42 transplanted human kidneys have been studied. Biopsies were performed during renal harvesting just before cooling, at the end of cold storage, and following reinstallment of renal blood circulation. ATP levels fell, and AMP and degradation products (inosine monophosphate [IMP], inosine, adenosine, and hypoxanthine) increased during cold storage and returned to near-normal values 30 min after recirculation. The major degradation product found was hypoxanthine, indicating very poor xanthine oxidase activity in human kidneys. The sum of adenine nucleotides (ATP+ADP+AMP) did not significantly decrease after cold storage, but adenylate energy charge (ATP+1/2ADP/ATP+ADP+AMP) was reduced to half, being recovered in implanted kidneys. The sum of adenine nucleotides was significantly reduced after implantation. The rate of acute tubular necrosis was higher in kidneys preserved for more than 30 hr. Kidneys with acute tubular necrosis had significantly lower levels of the total pool of adenine nucleotides at reperfusion, but there was no correlation between incidence of acute tubular necrosis and ATP or other metabolite levels in the kidneys before or during cold preservation. The success of human kidney transplantation does not seem to depend only on the pool of residual nucleotides at the end of cold storage but on other factors that determine the ability of the cell to recover a normal energy state after reperfusion.

The effects of gamma-glutamylcysteine ethyl ester, a prodrug of glutathione, on ischemia-reperfusion-induced liver injury in rats.

This study was designed to clarify the effects of changes in liver tissue glutathione (GSH) concentration on postischemic liver injury together with the effects of gamma-glutamylcysteine ethyl ester (GCE), a prodrug of GSH, and GSH. Rats were pretreated with GSH (50 mg/kg, i.v.), or GCE (50 mg/kg, i.v.), or untreated. In each rat, liver was isolated, and liver mitochondria were prepared after 2 h of ischemia or 1 h of reperfusion following 2 h of ischemia. Mitochondrial function was measured polarographically. Liver adenine nucleotide concentrations were also determined using high-performance liquid chromatography. Liver tissue GSH, an oxidized form of glutathione (GSSG) concentrations, and activities of GSH peroxidase and GSSG reductase were determined enzymatically. Liver hypoxanthine and xanthine concentrations were determined by HPLC. Liver tissue concentration of lipid peroxide was measured. Leakages of aspartate aminotransferase (AST), alanine aminotransferase (ALT), lactate dehydrogenase (LDH), and adenine nucleotides into the hepatic vein after reperfusion were also measured. Administration of GCE improved the recovery of mitochondrial function and maintained tissue GSH concentration concomitantly. Increases in liver lipid peroxide concentration after reperfusion, and leakage of liver cell enzymes and adenine nucleotides were mitigated by administration of GCE. Administration of GSH itself failed to maintain tissue GSH concentration and had no protective effects. From these results, it is concluded that in the postischemic process, free radical formation might be enhanced, and the radical scavenging system deteriorated. To enhance the radical scavenging system is a possible maneuver to prevent radical-related cell damage associated with reperfusion, because pharmacological reduction of breakdown of ATP to hypoxanthine and xanthine seems to be difficult. GCE maintained liver GSH concentrations and mitigated postischemic liver injury, concomitantly. Clinical use of GCE might be recommended.

Elevated levels of hypoxanthine in vitreous humor indicate prolonged cerebral hypoxia in victims of sudden infant death syndrome.

Hypoxanthine levels in vitreous humor from 32 infants who died of sudden infant death syndrome (SIDS) were determined and compared with levels found in eight children who died of trauma, drowning, or hanging and with levels from seven neonates dying suddenly without long-standing antemortem hypoxia. Determination of hypoxanthine level was done with either a PO2 electrode method or high-performance liquid chromatography. The results obtained by both methods were significantly correlated; therefore they were pooled. The median hypoxanthine level in victims of SIDS (380 mumol/L) was significantly higher (P less than .001) than in the children who died violently (118 mumol/L). Moreover, the levels from the SIDS victims were significantly higher (P less than .001) than those from the neonates who died without long-standing hypoxia (53 mumol/L). It is concluded that SIDS is probably not a sudden event but may be preceded by a relatively long period of respiratory failure and hypoxia.

High postmortem levels of hypoxanthine in the vitreous humor of premature babies with respiratory distress syndrome.

To test whether or not premature babies at risk for retinopathy of prematurity have elevated hypoxanthine levels in the eye, the vitreous humor of 13 premature babies who died of severe respiratory distress syndrome and lung failure, was analyzed for hypoxanthine. Their hypoxanthine level was 459 +/- 171 mumol/L (mean +/- SD) compared with 54 +/- 71 mumol/L in seven newborn babies who died suddenly (P less than .001). In 53 adults who died suddenly, the hypoxanthine concentration was 136 +/- 119 mumol/L (P less than .001 when compared with babies with respiratory distress syndrome). Babies with respiratory distress syndrome underwent a significantly longer period with arterial PO2 levels less than 40 mm Hg (5.3 kPa) and they required supplementation with 100% oxygen significantly longer than control babies. The hypoxanthine concentration was correlated with the time during which the arterial PO2 was lower than 40 mm Hg (5.3 kPa) before death, and a significant positive correlation was found (R = .59, P less than .12). The study shows that high levels of hypoxanthine are found in vitreous humor of premature babies with respiratory distress syndrome. Because hypoxanthine is a potential oxygen radical generator and premature babies might have lower levels of antioxidants than full-term babies, it is suggested that the hypoxanthine accumulation in the eyes of premature babies with respiratory distress syndrome could play a pathogenetic role in the development of retinopathy of prematurity.

Hypoxanthine levels in vitreous humor: evidence of hypoxia in most infants who died of sudden infant death syndrome.

Postmortem changes of the hypoxanthine in vitreous humor in humans were investigated. Hypoxanthine is formed from hypoxic degradation of adenosine monophosphate. Repeated sampling was performed in 13 deceased adults. Keeping the bodies at +6 degrees C, the increase of the hypoxanthine levels was estimated to 3.5 mumol/L per hour when sampling was started more than 12 hours after death (range 2.8 to 5.6 mumol/L per hour). Results of hypoxanthine measurements from vitreous humor in 73 infants with sudden infant death syndrome, 17 infants and children who died sudden violent deaths, and 6 neonates who died suddenly without hypoxemia prior to death were corrected according to the expected postmortem hypoxanthine increase. The time between death and autopsy was similar in the three groups studied. The corrected median hypoxanthine level in the group with sudden infant death syndrome was 227 mumol/L, which is significantly higher than in the other groups; 22 mumol/L in the group who had violent deaths (P less than .01), and 0 mumol/L in the neonate group (P less than .01). The findings seem to confirm that sudden infant death is preceded by a relatively long period of tissue hypoxia in most cases.

Purine composition of the crystalline cytoplasmic inclusions of Paramecium tetraurelia.

Crystalline cytoplasmic inclusions were isolated by differential centrifugation from mass cultures of Paramecium tetraurelia feeding on Klebsiella pneumonia. Physical and chemical measurements of intact and solubilized crystals determined that they consist primarily of guanine and hypoxanthine with traces of xanthine. Crystals from the mutant sombre consist primarily of xanthine, suggesting there is a disorder of purine metabolism in this mutant.

Effects of nucleoside transport inhibition on long-term ex vivo preservation of canine hearts.

The effect of nucleoside transport inhibition on 24-hour preservation of canine hearts was studied in 36 hearts arrested either with a cold hyperkalemic cardioplegic solution without (group I) or with supplementation of a specific nucleoside transport inhibitor (R75231, 1 mg/L) (groups II and III). The hearts were excised and stored for 24 hours at 0.5 degrees C. Then they were reperfused for 3 hours with use of a closed perfusion system primed with normal blood (groups I and II) or with blood supplemented with the same nucleoside transport inhibitor (0.32 mg/L) (group III). Serial biopsy specimens for determination of myocardial purines were taken. Creatine kinase and heat-stable lactate dehydrogenase release from the myocardium were examined during reperfusion. Recovery of function was studied during reperfusion by measurement of isometric contraction in a fluid-filled intraventricular balloon. After 24 hours of preservation, without the use of the drug, myocardial inosine and hypoxanthine accumulated to, respectively, 4.05 +/- 1.18 and 0.28 +/- 0.08 mumol/gm dry weight. In the drug-treated groups (II and III pooled), significantly less inosine and hypoxanthine accumulated (1.68 +/- 0.33 and 0.05 +/- 0.02 mumol/gm dry weight, respectively) (p < 0.05 versus group I). Upon reperfusion, intramyocardial adenosine was lost in the control hearts and maintained in the drug-treated hearts. Hypoxanthine accumulated significantly (p < 0.05) during reperfusion in group I (1.08 +/- 0.43 versus 0.16 +/- 0.13 in group II and 0.03 +/- 0.03 mumol/gm dry weight in group III). The rate of creatine kinase and heat-stable lactate dehydrogenase release was significantly lower (p < 0.05) in group III (that is, pretreatment and posttreatment with the drug) than in the control group. Functional recovery of hearts in group III was superior to that in group II (p < 0.05), while hearts in group I showed no recovery at all. We conclude that nucleoside transport inhibition improves long-term preservation of the heart and that the mechanism of this protection may be related to an increase in endogenous adenosine and reduction of myocardial hypoxanthine content.

Vitreous humour and cerebrospinal fluid hypoxanthine concentration as a marker of pre-mortem hypoxia in SIDS.

AIMS: To assess the rate at which premortem hypoxia occurs in sudden infant death syndrome (SIDS) when compared with death in early childhood. METHODS: The hypoxanthine concentration was measured as a marker of premortem hypoxia in vitreous humour and cerebrospinal fluid samples obtained at necropsy from 119 children whose ages ranged from 1 week to 2 years. RESULTS: Increasing interval between death and necropsy was accompanied by an increase in the hypoxanthine concentration of vitreous humour for the first 24 hours, at a rate of 8.3 mumol/l/hour. Thereafter, there was little change with time, and the results wer corrected to 24 hours according to a regression equation. Cerebrospinal fluid concentrations showed no significant change with time following death. Patients were divided into three groups according to the cause of death: SIDS, cardiac or pulmonary disease, and others. Median values for the cerebrospinal fluid hypoxanthine concentrations were not significantly different among the groups and no difference could be shown between the vitreous humour hypoxanthine concentration in cases of SIDS and those children dying from other causes. Patients with established cardiac or pulmonary disease had a significantly reduced vitreous humour hypoxanthine concentration which may have reflected the premortem use of artificial ventilation. CONCLUSIONS: The results of this study do not support the view that pre-mortem hypoxia is a common feature in SIDS when compared with other causes of death.

Role of conversion of xanthine dehydrogenase to oxidase in ischemic rat liver cell injury.

This study was undertaken to determine whether hepatic ischemia and the subsequent reflow of blood have any effect on the conversion of xanthine dehydrogenase to xanthine oxidase (XO). Ischemia of the liver for 90 or 120 minutes did not permit survival of the animals. XO represented 15% of the total xanthine dehydrogenase plus XO activity in the control liver. XO activity remained unchanged even after 90 minutes of hepatic ischemia, although a marked increase in lipid peroxide in the liver tissue was observed during the reperfusion. When hepatic ischemia was prolonged for 6 hours (animals were dead), XO activity rose to 35% of the total activity. Incubation of the liver at 37 degrees C resulted in a definite change in XO activity dependent on the length of incubation period. Although no significant changes occurred in XO activity during the first 2 hours of incubation, a marked XO conversion was observed between 2 and 4 hours, and a maximal conversion was achieved after 6 hours of incubation. These results suggest that XO newly generated during ischemia has a very limited role in oxygen free radical production after resuming perfusion.

Fibre-optic biosensor for hypoxanthine and xanthine based on a chemiluminescence reaction.

Fibre-optic biosensors were constructed for determination of hypoxanthine and xanthine. Xanthine oxidase and peroxidase were immobilized on different preactivated membranes which were subsequently mounted onto the tip of a fibre-optic bundle. The H2O2 generated by the reaction of hypoxanthine and xanthine oxidase was measured by chemiluminescence (CL) detection using luminol and peroxidase. A linear calibration curve of the sensors in the range of 1-316 microM hypoxanthine and 3.1-316 microM xanthine, respectively, with a detection limit of 0.55 microM hypoxanthine was obtained. Recovery of hypoxanthine ranged between 91 and 102%.