Allantoin in human plasma, serum, and nasal-lining fluids as a biomarker of oxidative stress: avoiding artifacts and establishing real in vivo concentrations

Metabolomics-based search for lung cancer markers among patients with different smoking status

Tobacco smoking is the main etiological factor of lung cancer (LC), which can also cause metabolome disruption. This study aimed to investigate whether the observed metabolic shift in LC patients was also associated with their smoking status. Untargeted metabolomics profiling was applied for the initial screening of changes in serum metabolic profile between LC and chronic obstructive pulmonary disease (COPD) patients, selected as a non-cancer group. Differences in metabolite profiles between current and former smokers were also tested. Then, targeted metabolomics methods were applied to verify and validate the proposed LC biomarkers. For untargeted metabolomics, a single extraction-dual separation workflow was applied. The samples were analyzed using a liquid chromatograph-high resolution quadrupole time-of-flight mass spectrometer. Next, the selected metabolites were quantified using liquid chromatography-triple-quadrupole mass spectrometry. The acquired data confirmed that patients' stratification based on smoking status impacted the discriminating ability of the identified LC marker candidates. Analyzing a validation set of samples enabled us to determine if the putative LC markers were truly robust. It demonstrated significant differences in the case of four metabolites: allantoin, glutamic acid, succinic acid, and sphingosine-1-phosphate. Our research showed that studying the influence of strong environmental factors, such as tobacco smoking, should be considered in cancer marker research since it reduces the risk of false positives and improves understanding of the metabolite shifts in cancer patients.

Identification of Bacterial Metabolites Modulating Breast Cancer Cell Proliferation and Epithelial-Mesenchymal Transition

Breast cancer patients are characterized by the oncobiotic transformation of multiple microbiome communities, including the gut microbiome. Oncobiotic transformation of the gut microbiome impairs the production of antineoplastic bacterial metabolites. The goal of this study was to identify bacterial metabolites with antineoplastic properties. We constructed a 30-member bacterial metabolite library and screened the library compounds for effects on cell proliferation and epithelial-mesenchymal transition. The metabolites were applied to 4T1 murine breast cancer cells in concentrations corresponding to the reference serum concentrations. However, yric acid, glycolic acid, d-mannitol, 2,3-butanediol, and trans-ferulic acid exerted cytostatic effects, and 3-hydroxyphenylacetic acid, 4-hydroxybenzoic acid, and vanillic acid exerted hyperproliferative effects. Furthermore, 3-hydroxyphenylacetic acid, 4-hydroxybenzoic acid, 2,3-butanediol, and hydrocinnamic acid inhibited epithelial-to-mesenchymal (EMT) transition. We identified redox sets among the metabolites (d-mannitol-d-mannose, 1-butanol-butyric acid, ethylene glycol-glycolic acid-oxalic acid), wherein only one partner within the set (d-mannitol, butyric acid, glycolic acid) possessed bioactivity in our system, suggesting that changes to the local redox potential may affect the bacterial secretome. Of the nine bioactive metabolites, 2,3-butanediol was the only compound with both cytostatic and anti-EMT properties.

Screening method for the simultaneous determination of allantoin and uric acid from dried blood spots

Uric acid and its oxidation product allantoin are excellent biomarkers of oxidative stress in humans. Currently, there are high requirements not only for tests monitoring oxidative stress but also for screening laboratory tests in general. The highest demand is imposed on the simplest sampling, easy transport of the sample, and the shortest possible analysis time. The possible solution how to fulfil the requirements is sampling by dried blood spot technique with subsequent HPLC-MS/MS analysis. A fast, sensitive, and reliable HPLC-MS/MS method for the simultaneous determination of uric acid and allantoin from dried blood spots using stable isotopically labelled analogs as internal standards was developed. The separation took place in the reversed phase within 3 min, with protein precipitation and extraction in a one-step procedure. The analytical parameters of the method were satisfactory with an excellent linear range. The presented method was used to determine allantoin and uric acid levels in dried blood spot samples from 100 healthy volunteer donors. The median uric acid concentration in the cohort was 239.3 µmol/L and the median allantoin concentration was 5.6 µmol/L. The presented analytical protocol and method are suitable for screening and monitoring allantoin and uric acid levels as biomarkers of oxidative stress in clinical practice.

Reflections of an Aging Free Radical Part 2: Meeting Inspirational People

Significance: During my long career in the field of redox biology, I met many inspiring people, especially Lester Packer. Recent Advances: This special issue of Antioxidants & Redox Signaling is dedicated to Lester Packer. Critical Issues: In this short review, I explore how Lester and other pioneers helped to develop the redox biology field and how I interacted with them. Future Directions: In our research to advance the field of redox biology, we stand on the shoulders of giants, including Lester Packer.

Inactivation of SARS-CoV-2 and COVID-19 Patient Samples for Contemporary Immunology and Metabolomics Studies

Due to the severity of COVID-19 disease, the U.S. Centers for Disease Control and Prevention and World Health Organization recommend that manipulation of active viral cultures of SARS-CoV-2 and respiratory secretions from COVID-19 patients be performed in biosafety level (BSL)3 laboratories. Therefore, it is imperative to develop viral inactivation procedures that permit samples to be transferred to lower containment levels (BSL2), while maintaining the fidelity of complex downstream assays to expedite the development of medical countermeasures. In this study, we demonstrate optimal conditions for complete viral inactivation following fixation of infected cells with commonly used reagents for flow cytometry, UVC inactivation in sera and respiratory secretions for protein and Ab detection, heat inactivation following cDNA amplification for droplet-based single-cell mRNA sequencing, and extraction with an organic solvent for metabolomic studies. Thus, we provide a suite of viral inactivation protocols for downstream contemporary assays that facilitate sample transfer to BSL2, providing a conceptual framework for rapid initiation of high-fidelity research as the COVID-19 pandemic continues.

Serum Metabolites Responding in a Dose-Dependent Manner to the Intake of a High-Fat Meal in Normal Weight Healthy Men Are Associated with Obesity

Although the composition of the human blood metabolome is influenced both by the health status of the organism and its dietary behavior, the interaction between these two factors has been poorly characterized. This study makes use of a previously published randomized controlled crossover acute intervention to investigate whether the blood metabolome of 15 healthy normal weight (NW) and 17 obese (OB) men having ingested three doses (500, 1000, 1500 kcal) of a high-fat (HF) meal can be used to identify metabolites differentiating these two groups. Among the 1024 features showing a postprandial response, measured between 0 h and 6 h, in the NW group, 135 were dose-dependent. Among these 135 features, 52 had fasting values that were significantly different between NW and OB men, and, strikingly, they were all significantly higher in OB men. A subset of the 52 features was identified as amino acids (e.g., branched-chain amino acids) and amino acid derivatives. As the fasting concentration of most of these metabolites has already been associated with metabolic dysfunction, we propose that challenging normal weight healthy subjects with increasing caloric doses of test meals might allow for the identification of new fasting markers associated with obesity.

Mechanisms of Oxidative Stress and Therapeutic Targets following Intracerebral Hemorrhage

Oxidative stress (OS) is induced by the accumulation of reactive oxygen species (ROS) following intracerebral hemorrhage (ICH) and plays an important role in secondary brain injury caused by the inflammatory response, apoptosis, autophagy, and blood-brain barrier (BBB) disruption. This review summarizes the current state of knowledge regarding the pathogenic mechanisms of brain injury after ICH, markers for detecting OS, and therapeutic strategies that target OS to mitigate brain injury.

Reflections of an aging free radical

In this mini-reflection, I explain how during my doctoral work in a Botany Department I first became interested in H2O2 and later in my career in other reactive oxygen species, especially the role of "catalytic" iron and haem compounds (including leghaemoglobin) in promoting oxidative damage. The important roles that H2O2, other ROS and dietary plants play in respect to humans are discussed. I also review the roles of diet-derived antioxidants in relation to human disease, presenting reasons why clinical trials using high doses of natural antioxidants have generally given disappointing results. Iron chelators and ergothioneine are reviewed as potential cytoprotective agents with antioxidant properties that may be useful therapeutically. The discovery of ferroptosis may also lead to novel agents that can be used to treat certain diseases.

Oral dextrose reduced procedural pain without altering cellular ATP metabolism in preterm neonates: a prospective randomized trial

OBJECTIVE

To examine the effects of 30% oral dextrose on biochemical markers of pain, adenosine triphosphate (ATP) degradation, and oxidative stress in preterm neonates experiencing a clinically required heel lance.

STUDY DESIGN

Utilizing a prospective study design, preterm neonates that met study criteria (n = 169) were randomized to receive either (1) 30% oral dextrose, (2) facilitated tucking, or (3) 30% oral dextrose and facilitated tucking 2 min before heel lance. Plasma markers of ATP degradation (hypoxanthine, uric acid) and oxidative stress (allantoin) were measured before and after the heel lance. Pain was measured using the premature infant pain profile-revised (PIPP-R).

RESULTS

Oral dextrose, administered alone or with facilitated tucking, did not alter plasma markers of ATP utilization and oxidative stress.

CONCLUSION

A single dose of 30% oral dextrose, given before a clinically required heel lance, decreased signs of pain without increasing ATP utilization and oxidative stress in premature neonates.

Immobilization of Allantoinase for the Development of an Optical Biosensor of Oxidative Stress States

Allantoin, the natural end product of purine catabolism in mammals, is non-enzymatically produced from the scavenging of reactive oxygen species through the degradation of uric acid. Levels of allantoin in biological fluids are sensitively influenced by the presence of free radicals, making this molecule a candidate marker of acute oxidative stress in clinical analyses. With this aim, we exploited allantoinase—the enzyme responsible for allantoin hydrolization in plants and lower organisms—for the development of a biosensor exploiting a fast enzymatic-chemical assay for allantoin quantification. Recombinant allantoinase was entrapped in a wet nanoporous silica gel matrix and its structural properties, function, and stability were characterized through fluorescence spectroscopy and circular dichroism measurements, and compared to the soluble enzyme. Physical immobilization in silica gel minimally influences the structure and the catalytic efficiency of entrapped allantoinase, which can be reused several times and stored for several months with good activity retention. These results, together with the relative ease of the sol-gel preparation and handling, make the encapsulated allantoinase a good candidate for the development of an allantoin biosensor.

Reductions in Postprandial Plasma Allantoin Concentrations With Increasing Doses of Polyphenol Rich Curry Intake - A Randomized Crossover Trial

While dietary or supplementary antioxidants are thought to inhibit or delay oxidation of biological molecules, their utility in vivo has been marred by equivocal evidence. Consumption of polyphenol rich foods has been thought to alleviate postprandial oxidative stress and/or improve endothelial function. Although, previous studies suggested the utility of allantoin as a biomarker of oxidative stress, controlled dose response studies with dietary antioxidants to test this in humans have been limited. We therefore investigated the effects of 2 doses of polyphenol rich curry consumption on postprandial plasma concentrations of allantoin, allantoin to uric acid ratio, F2-isoprostanes using liquid chromatography-tandem mass spectrometry (LCMS-MS) and measured endothelial function using peripheral arterial tonometry (endoPAT). In a randomized controlled crossover trial in 17 non-smoking, healthy, Chinese men, aged 23.7 ± 2.4 years and BMI 23.1 ± 2.3 kg/m², the volunteers consumed 3 test meals in a random order, consisting of either non-curry Dose 0 Control (D0C, 0 g spices), or Dose 1 Curry (D1C, 6 g spices) or Dose 2 Curry (D2C, 12 g spices), after overnight fast. There were significant reductions in postprandial allantoin concentrations (p < 0.001) and allantoin to uric acid ratio (p < 0.001) at 2 h and 3 h following test meal consumption, indicating improvements in postprandial redox balance with increasing curry doses, although there were no differences between treatments on F2-isoprostane concentrations or on RHI (measured at 2 h only). Allantoin may have a utility as a biomarker of redox balance, in an acute setting. The study was registered at www.clinicaltrials.gov (Identifier No. NCT02599272).

Pre-clinical Pharmacokinetic and Metabolomic Analyses of Isorhapontigenin, a Dietary Resveratrol Derivative

Background: Isorhapontigenin (trans-3,5,4'-trihydroxy-3'-methoxystilbene, ISO), a dietary resveratrol (trans-3,5,4'-trihydroxystilbene) derivative, possesses various health-promoting activities. To further evaluate its medicinal potentials, the pharmacokinetic and metabolomic profiles of ISO were examined in Sprague-Dawley rats. Methods: The plasma pharmacokinetics and metabolomics were monitored by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and gas chromatography-tandem mass spectrometry (GC-MS/MS), respectively. Results: Upon intravenous injection (90 μmol/kg), ISO exhibited a fairly rapid clearance (CL) and short mean residence time (MRT). After a single oral administration (100 μmol/kg), ISO was rapidly absorbed and showed a long residence in the systemic circulation. Dose escalation to 200 μmol/kg resulted in higher dose-normalized maximal plasma concentrations (C_max/Dose), dose-normalized plasma exposures (AUC/Dose), and oral bioavailability (F). One-week repeated daily dosing of ISO did not alter its major oral pharmacokinetic parameters. Pharmacokinetic comparisons clearly indicated that ISO displayed pharmacokinetic profiles superior to resveratrol as its C_max/Dose, AUC/Dose, and F were approximately two to three folds greater than resveratrol. Metabolomic investigation revealed that 1-week ISO administration significantly reduced plasma concentrations of arachidonic acid, cholesterol, fructose, allantoin, and cadaverine but increased tryptamine levels, indicating its impact on metabolic pathways related to health-promoting effects. Conclusion: ISO displayed favorable pharmacokinetic profiles and may be a promising nutraceutical in view of its health-promoting properties.

LC-MS/MS Analysis of Lipid Oxidation Products in Blood and Tissue Samples

Oxygenated lipid products of non-cyclooxygenase derivatives, namely, prostanoids such as, isoprostanes and isofurans, are formed in vivo through lipid autoxidation. Insofar it has been marked as novel biomarkers of oxidative stress in the biological systems. Elevations of these oxidized products are associated with several diseases. This chapter describes the preparation and measurement of the products, including newly identified F₂-dihomo-isoprostanes and dihomo-isofurans, from plasma and tissue samples using the liquid chromatography-tandem mass spectrometry approach.

Administration of Pure Ergothioneine to Healthy Human Subjects: Uptake, Metabolism, and Effects on Biomarkers of Oxidative Damage and Inflammation

AIM

We investigated the uptake and pharmacokinetics of l-ergothioneine (ET), a dietary thione with free radical scavenging and cytoprotective capabilities, after oral administration to humans, and its effect on biomarkers of oxidative damage and inflammation.

RESULTS

After oral administration, ET is avidly absorbed and retained by the body with significant elevations in plasma and whole blood concentrations, and relatively low urinary excretion (<4% of administered ET). ET levels in whole blood were highly correlated to levels of hercynine and S-methyl-ergothioneine, suggesting that they may be metabolites. After ET administration, some decreasing trends were seen in biomarkers of oxidative damage and inflammation, including allantoin (urate oxidation), 8-hydroxy-2'-deoxyguanosine (DNA damage), 8-iso-PGF2α (lipid peroxidation), protein carbonylation, and C-reactive protein. However, most of the changes were non-significant.

INNOVATION

This is the first study investigating the administration of pure ET to healthy human volunteers and monitoring its uptake and pharmacokinetics. This compound is rapidly gaining attention due to its unique properties, and this study lays the foundation for future human studies.

CONCLUSION

The uptake and retention of ET by the body suggests an important physiological function. The decreasing trend of oxidative damage biomarkers is consistent with animal studies suggesting that ET may function as a major antioxidant but perhaps only under conditions of oxidative stress. Antioxid. Redox Signal. 26, 193-206.

Administration of Uric Acid in the Emergency Treatment of Acute Ischemic Stroke

Oxidative stress is one of the main mechanisms implicated in the pathophysiology of inflammatory and neurodegenerative diseases of the central nervous system (CNS). Uric acid (UA) is the end product of purine catabolism in humans, and it is the main endogenous antioxidant in blood. Low circulating UA levels have been associated with an increased prevalence and worse clinical course of several neurodegenerative and inflammatory diseases of the CNS, including Parkinson's disease and multiple sclerosis. Moreover, the exogenous administration of UA exerts robust neuroprotective properties in experimental models of CNS disease, including brain ischemia, spinal cord injury, meningitis, and experimental allergic encephalitis. In experimental brain ischemia, exogenous UA and the thrombolytic agent alteplase exert additive neuroprotective effects when administered in combination. UA is rapidly consumed following acute ischemic stroke, and higher UA levels at stroke admission are associated with a better outcome and reduced infarct growth at follow-up. A recent phase II trial demonstrated that the combined intravenous administration of UA and alteplase is safe and prevents an early decrease of circulating UA levels in acute ischemic stroke patients. Moreover, UA prevents the increase in the circulating levels of the lipid peroxidation marker malondialdehyde and of active matrix metalloproteinase (MMP) 9, a marker of blood-brain barrier disruption. The moderately sized URICOICTUS phase 2b trial showed that the addition of UA to thrombolytic therapy resulted in a 6% absolute increase in the rate of excellent outcome at 90 days compared to placebo. The trial also showed that UA administration resulted in a significant increment of excellent outcome in patients with pretreatment hyperglycemia, in females and in patients with moderate strokes. Overall, the encouraging neuroprotective effects of UA therapy in acute ischemic stroke warrants further investigation in adequately powered clinical trials.

The ratio of oxidized and reduced forms of selected antioxidants as a possible marker of oxidative stress in humans

Oxidative stress is an imbalance between reactive oxygen species exposure and the ability of organisms to detoxify the reactive intermediates and to repair the oxidative damage of biologically important molecules. Many clinical studies of oxidative stress unfortunately provide conflicting and contradictory results. The ability of antioxidant systems to adequately respond to oxidative stress can be used in laboratory diagnostics. In the present review, methods using the ratio of reduced and oxidized forms of uric acid, ascorbic acid, glutathione and coenzyme Q10 as suitable indicators of oxidative stress are discussed. From the mentioned publications it is evident that suitable sample preparation prior to analysis is crucial.

Urinary Allantoin Is Elevated in Severe Intraventricular Hemorrhage in the Preterm Newborn

Germinal matrix intraventricular hemorrhage (IVH) is the most common type of intracranial hemorrhage observed in preterm neonates. It is a precursor of poor neurocognitive development, cerebral palsy, and death. The pathophysiology is not well defined, but damage to the fragile germinal matrix vasculature may be due to free radicals generated during inflammation and as a consequence of ischemia followed by reperfusion. Assessment of the oxidative stress status in these infants is therefore important. Urinary allantoin concentration was measured in preterm neonates as a marker of oxidative stress associated with IVH. Urine was collected from 44 preterm neonates at four time points between 24 and 72 hours of life (HOL), and the allantoin content was determined by gas chromatography mass spectrometry (GCMS). Records were retrospectively reviewed, and the incidence and severity of IVH was categorized as follows: no IVH (n = 24), mild (grade 1-2) IVH (n = 13), and severe (grade 3-4) IVH (n = 7). Neonates with severe IVH showed significantly elevated allantoin levels vs subjects with no IVH from 36 HOL (0.098 ± 0.013 μmol and 0.043 ± 0.007 μmol, respectively, p = 0.002). The allantoin concentration remained elevated even at 72 HOL (0.079 ± 0.014 μmol and 0.033 ± 0.008 μmol, respectively, p = 0.021). There were no significant differences in allantoin levels in the no IVH and mild IVH groups. IVH was diagnosed by head imaging on average at about 11th postnatal day. Urinary allantoin levels were significantly elevated during the first 3 days of life in the neonates subsequently diagnosed with severe IVH, suggesting that oxidative stress might be a crucial factor in IVH pathogenesis. Further studies are needed to assess the usefulness of urinary allantoin in early identification of preterm infants at risk for or with severe IVH and monitoring of the response to interventions designed to prevent or treat it.

A Monitoring of Allantoin, Uric Acid, and Malondialdehyde Levels in Plasma and Erythrocytes After Ten Minutes of Running Activity

Uric acid is the final product of human purine metabolism. It was pointed out that this compound acts as an antioxidant and is able to react with reactive oxygen species forming allantoin. Therefore, the measurement of allantoin levels may be used for the determination of oxidative stress in humans. The aim of the study was to clarify the antioxidant effect of uric acid during intense exercise. Whole blood samples were obtained from a group of healthy subjects. Allantoin, uric acid, and malondialdehyde levels in plasma and erythrocytes were measured using a HPLC with UV/Vis detection. Statistical significant differences in allantoin and uric acid levels during short-term intense exercise were found. Immediately after intense exercise, the plasma allantoin levels increased on the average of 200 % in comparison to baseline. Plasma uric acid levels increased slowly, at an average of 20 %. On the other hand, there were no significant changes in plasma malondialdehyde. The results suggest that uric acid, important antioxidant, is probably oxidized by reactive oxygen species to allantoin. Therefore allantoin may be suitable candidate for a marker of acute oxidative stress.

Metabolic Profiling of Green Tea Treatments in Zucker Diabetic Rats Using 1H NMR

This study has investigated the metabolic effects of catechin-rich green tea (GT) and its formulation with ascorbic acid (AA) on the Zucker rat model of type 2 diabetes. AA is used to protect the GT catechins during digestion and increase bioavailability. Thirty two Zucker diabetic fatty (ZDF) rats were randomly divided into four groups (n=8 in each group) and treated with water, GT, AA and GT+AA respectively for five weeks. Urinary metabolic profiles were determined using ¹H NMR spectroscopy. Fourteen metabolites were identified and their 24-hr excretions were quantified. Changes in the 14 metabolites demonstrated differential treatment effects on the metabolism of ZDF rats. GT and AA were found to be able to independently reduce urinary excretions of most metabolites that were over-excreted in the control diabetic rats, such as oxidative stress marker metabolites and TCA cycle metabolites. GT showed a great potential in controlling metabolic acidosis by suppressing the excretion of lactic acid and acetic acid from diabetic rats and GT+AA showed a remarkably stronger suppression than GT while AA was unable to suppress these two acids. Further investigation is needed to better understand the role of GT and/or formulated GT in altering the metabolic pathways in the diabetic animal model as well as in humans.

Oral sucrose for heel lance increases adenosine triphosphate use and oxidative stress in preterm neonates

OBJECTIVE

To examine the effects of sucrose on pain and biochemical markers of adenosine triphosphate (ATP) degradation and oxidative stress in preterm neonates experiencing a clinically required heel lance.

STUDY DESIGN

Preterm neonates that met study criteria (n = 131) were randomized into 3 groups: (1) control; (2) heel lance treated with placebo and non-nutritive sucking; and (3) heel lance treated with sucrose and non-nutritive sucking. Plasma markers of ATP degradation (hypoxanthine, xanthine, and uric acid) and oxidative stress (allantoin) were measured before and after the heel lance. Pain was measured with the Premature Infant Pain Profile. Data were analyzed by the use of repeated-measures ANOVA and Spearman rho.

RESULTS

We found significant increases in plasma hypoxanthine and uric acid over time in neonates who received sucrose. We also found a significant negative correlation between pain scores and plasma allantoin concentration in a subgroup of neonates who received sucrose.

CONCLUSION

A single dose of oral sucrose, given before heel lance, significantly increased ATP use and oxidative stress in premature neonates. Because neonates are given multiple doses of sucrose per day, randomized trials are needed to examine the effects of repeated sucrose administration on ATP degradation, oxidative stress, and cell injury.

Amide-mediated hydrogen bonding at organic crystal/water interfaces enables selective endotoxin binding with picomolar affinity

Since the discovery of endotoxins as the primary toxic component of Gram-negative bacteria, researchers have pursued the quest for molecules that detect, neutralize, and remove endotoxins. Selective removal of endotoxins is particularly challenging for protein solutions and, to this day, no general method is available. Here, we report that crystals of the purine-derived compound allantoin selectively adsorb endotoxins with picomolar affinity through amide-mediated hydrogen bonding in aqueous solutions. Atom force microscopy and chemical inhibition experiments indicate that endotoxin adsorption is largely independent from hydrophobic and ionic interactions with allantoin crystals and is mediated by hydrogen bonding with amide groups at flat crystal surfaces. The small size (500 nm) and large specific surface area of allantoin crystals results in a very high endotoxin-binding capacity (3 × 10(7) EU/g) which compares favorably with known endotoxin-binding materials. These results provide a proof-of-concept for hydrogen bond-based molecular recognition processes in aqueous solutions and establish a practical method for removing endotoxins from protein solutions.

Urinary biomarkers of oxidative status

Oxidative damage produced by reactive oxygen species (ROS) has been implicated in the etiology and pathology of many health conditions, including a large number of chronic diseases. Urinary biomarkers of oxidative status present a great opportunity to study redox balance in human populations. With urinary biomarkers, specimen collection is non-invasive and the organic/metal content is low, which minimizes the artifactual formation of oxidative damage to molecules in specimens. Also, urinary levels of the biomarkers present intergraded indices of redox balance over a longer period of time compared to blood levels. This review summarizes the criteria for evaluation of biomarkers applicable to epidemiological studies and evaluation of several classes of biomarkers that are formed non-enzymatically: oxidative damage to lipids, proteins, DNA, and allantoin, an oxidative product of uric acid. The review considers formation, metabolism, and exertion of each biomarker, available data on validation in animal and clinical models of oxidative stress, analytical approaches, and their intra- and inter-individual variation. The recommended biomarkers for monitoring oxidative status over time are F₂-isoprostanes and 8-oxodG. For inter-individual comparisons, F₂-isoprostanes are recommended, whereas urinary 8-oxodG levels may be confounded by differences in the DNA repair capacity. Promising urinary biomarkers include allantoin, acrolein-lysine, and dityrosine.

Ergothioneine; antioxidant potential, physiological function and role in disease

Since its discovery, the unique properties of the naturally occurring amino acid, L-ergothioneine (EGT; 2-mercaptohistidine trimethylbetaine), have intrigued researchers for more than a century. This widely distributed thione is only known to be synthesized by non-yeast fungi, mycobacteria and cyanobacteria but accumulates in higher organisms at up to millimolar levels via an organic cation transporter (OCTN1). The physiological role of EGT has yet to be established. Numerous in vitro assays have demonstrated the antioxidant and cytoprotective capabilities of EGT against a wide range of cellular stressors, but an antioxidant role has yet to be fully verified in vivo. Nevertheless the accumulation, tissue distribution and scavenging properties, all highlight the potential for EGT to function as a physiological antioxidant. This article reviews our current state of knowledge. This article is part of a Special Issue entitled: Antioxidants and Antioxidant Treatment in Disease.

Biochemical measurement of neonatal hypoxia

Neonatal hypoxia ischemia is characterized by inadequate blood perfusion of a tissue or a systemic lack of oxygen. This condition is thought to cause/exacerbate well documented neonatal disorders including neurological impairment. Decreased adenosine triphosphate production occurs due to a lack of oxidative phosphorylation. To compensate for this energy deprived state molecules containing high energy phosphate bonds are degraded. This leads to increased levels of adenosine which is subsequently degraded to inosine, hypoxanthine, xanthine, and finally to uric acid. The final two steps in this degradation process are performed by xanthine oxidoreductase. This enzyme exists in the form of xanthine dehydrogenase under normoxic conditions but is converted to xanthine oxidase (XO) under hypoxia-reperfusion circumstances. Unlike xanthine dehydrogenase, XO generates hydrogen peroxide as a byproduct of purine degradation. This hydrogen peroxide in combination with other reactive oxygen species (ROS) produced during hypoxia, oxidizes uric acid to form allantoin and reacts with lipid membranes to generate malondialdehyde (MDA). Most mammals, humans exempted, possess the enzyme uricase, which converts uric acid to allantoin. In humans, however, allantoin can only be formed by ROS-mediated oxidation of uric acid. Because of this, allantoin is considered to be a marker of oxidative stress in humans, but not in the mammals that have uricase. We describe methods employing high pressure liquid chromatography (HPLC) and gas chromatography mass spectrometry (GCMS) to measure biochemical markers of neonatal hypoxia ischemia. Human blood is used for most tests. Animal blood may also be used while recognizing the potential for uricase-generated allantoin. Purine metabolites were linked to hypoxia as early as 1963 and the reliability of hypoxanthine, xanthine, and uric acid as biochemical indicators of neonatal hypoxia was validated by several investigators. The HPLC method used for the quantification of purine compounds is fast, reliable, and reproducible. The GC/MS method used for the quantification of allantoin, a relatively new marker of oxidative stress, was adapted from Gruber et al. This method avoids certain artifacts and requires low volumes of sample. Methods used for synthesis of MMDA were described elsewhere. GC/MS based quantification of MDA was adapted from Paroni et al. and Cighetti et al. Xanthine oxidase activity was measured by HPLC by quantifying the conversion of pterin to isoxanthopterin. This approach proved to be sufficiently sensitive and reproducible.

Oral zinc supplementation does not improve oxidative stress or vascular function in patients with type 2 diabetes with normal zinc levels

OBJECTIVE

There is considerable controversy about what constitutes optimal zinc intakes in patients with type 2 diabetes mellitus. Several studies suggest that higher zinc intakes improve vascular function and decrease oxidative damage. We aimed to assess the effects of zinc supplementation using a range of reliable biomarkers of oxidative damage and vascular function in patients with type 2 diabetes.

METHODS

Forty male type 2 diabetic patients were supplemented either with 240 mg/day of zinc as zinc gluconate (n=20) or with placebo (n=20) for 3 months. Blood and spot urine samples were taken at baseline, days 3 and 7, months 1, 2 and 3 during supplementation and 1 month after cessation. Serum zinc, reliable biomarkers of oxidative damage (F(2)-isoprostanes, neuroprostanes, cholesterol oxidation products, allantoin) as well as hydroxyeicosatetraenoic acid products and vascular-related indices (augmentation index, pulse wave velocity and aortic pressure) were measured.

RESULTS

Despite significantly higher levels of serum zinc in the treatment group, markers of oxidative damage, levels of hydroxyeicosatetraenoic acid products and vascular indices were unchanged by zinc supplementation during the four-month study period.

CONCLUSION

Improving the zinc status in patients with type 2 diabetes with normal zinc levels did not have any impact on oxidative damage and vascular function, and such supplementation may not be generally beneficial in these individuals.

Biomarkers of oxidative damage in cigarette smokers: which biomarkers might reflect acute versus chronic oxidative stress?

Cigarette smoking predisposes to the development of multiple diseases involving oxidative damage. We measured a range of oxidative damage biomarkers to understand which differ between smokers and nonsmokers and if the levels of these biomarkers change further during the act of smoking itself. Despite overnight abstinence from smoking, smokers had higher levels of plasma total and esterified F(2)-isoprostanes, hydroxyeicosatetraenoic acid products (HETEs), F(4)-neuroprostanes, 7-ketocholesterol, and 24- and 27-hydroxycholesterol. Levels of urinary F(2)-isoprostanes, HETEs, and 8-hydroxy-2'-deoxyguanosine were also increased compared with age-matched nonsmokers. Several biomarkers (plasma free F(2)-isoprostanes, allantoin, and 7β-hydroxycholesterol and urinary F(2)-isoprostane metabolites) were not elevated. The smokers were then asked to smoke a cigarette; this acute smoking elevated plasma and urinary F(2)-isoprostanes, plasma allantoin, and certain cholesterol oxidation products compared to presmoking levels, but not plasma HETEs or urinary 8-hydroxy-2'-deoxyguanosine. Smokers showed differences in plasma fatty acid composition. Our findings confirm that certain oxidative damage biomarkers are elevated in smokers even after a period of abstinence from smoking, whereas these plus some others are elevated after acute smoking. Thus, different biomarkers do not measure identical aspects of oxidative stress.

Using isoprostanes as biomarkers of oxidative stress: some rarely considered issues

The measurement of F2-isoprostanes by methods utilizing mass spectrometry is widely regarded as the best currently available biomarker of lipid peroxidation. F2-isoprostanes and their metabolites can be measured accurately in plasma, urine, and other body fluids using mass spectrometric techniques, and detailed protocols have been published in several papers. However, many clinical studies and intervention studies with diets or supplements, have employed single "spot" measurements of F2-isoprostanes on either plasma/serum or urine to estimate "oxidative stress." This review examines the validity of the common assumption that plasma and urinary F2-isoprostane measurements are equivalent. It identifies scenarios where they may not be and where "spot" measurements can be misleading, with examples from the literature. We also discuss the controversial issue of whether and how F2-isoprostane levels in plasma should be standardized against lipids, and, if so, which lipids to use.

Effects of ozone blood treatment on the metabolite profile of human blood

Metabonomic characterization of the effects caused by ozone and other stressors on normal human blood was performed. Samples of blood obtained from healthy subjects were treated ex vivo with increasing concentrations of ozone and/or with UV radiation and heat. (1)H-NMR analysis of plasma samples after treatments showed the quantitative variation of some metabolites and the formation of new metabolites normally absent. Both the increment of some metabolites like formate, acetoacetate, and acetate and the decrement of pyruvate were of particular interest. Moreover, the oxidation of ascorbic acid and the transformation of uric acid into allantoin after ozonation within the therapeutic concentration range were observed. In the ozonated spectra, 2 unidentified peaks appeared at 2.82 ppm and 8.08 ppm. They are related to the direct antioxidant activity of albumin in the presence of ozone and they could be considered as specific markers of the blood ozonation.

Urinary biomarkers of oxidative status in a clinical model of oxidative assault

BACKGROUND

We used doxorubicin-based chemotherapy as a clinical model of oxidative assault in humans.

METHODS

The study recruited newly diagnosed breast cancer patients (n = 23). Urine samples were collected immediately before (T0) and at 1 hour (T1) and 24 hours (T24) after i.v. administration of treatment. Measurements included allantoin and the isoprostanes iPF(2alpha)-III, iPF(2alpha)-VI, and 8,12-iso-iPF(2alpha)-VI along with the prostaglandin 2,3-dinor-iPF(2alpha)-III, a metabolite of iPF(2alpha)-III. All biomarkers were quantified using liquid chromatography-tandem mass spectrometry.

RESULTS

In all subjects, the levels of the biomarkers increased at T1: allantoin by 22% (P = 0.06), iPF(2alpha)-III by 62% (P < 0.05), iPF(2alpha)-VI by 41% (P < 0.05), 8,12-iso-iPF(2alpha)-VI by 58% (P < 0.05), and 2,3-dinor-iPF(2alpha)-III by 52% (P < 0.05). At T24, the F2-isoprostanes returned to their baseline levels; the levels of allantoin continued to increase, although the T24-T0 difference was not statistically significant.

CONCLUSIONS

These results indicate that urinary F2-isoprostanes are valid biomarkers and allantoin is a promising biomarker of oxidative status in humans.

IMPACT

The levels of biomarkers change quickly in response to oxidative assault and can be used to monitor oxidative status in humans in response to treatments related either to generation of free radicals (chemotherapy and radiation therapy) or to antioxidants (inborn metabolic diseases and Down syndrome).

Quantitative metabolomics by H-NMR and LC-MS/MS confirms altered metabolic pathways in diabetes

Insulin is as a major postprandial hormone with profound effects on carbohydrate, fat, and protein metabolism. In the absence of exogenous insulin, patients with type 1 diabetes exhibit a variety of metabolic abnormalities including hyperglycemia, glycosurea, accelerated ketogenesis, and muscle wasting due to increased proteolysis. We analyzed plasma from type 1 diabetic (T1D) humans during insulin treatment (I+) and acute insulin deprivation (I-) and non-diabetic participants (ND) by (1)H nuclear magnetic resonance spectroscopy and liquid chromatography-tandem mass spectrometry. The aim was to determine if this combination of analytical methods could provide information on metabolic pathways known to be altered by insulin deficiency. Multivariate statistics differentiated proton spectra from I- and I+ based on several derived plasma metabolites that were elevated during insulin deprivation (lactate, acetate, allantoin, ketones). Mass spectrometry revealed significant perturbations in levels of plasma amino acids and amino acid metabolites during insulin deprivation. Further analysis of metabolite levels measured by the two analytical techniques indicates several known metabolic pathways that are perturbed in T1D (I-) (protein synthesis and breakdown, gluconeogenesis, ketogenesis, amino acid oxidation, mitochondrial bioenergetics, and oxidative stress). This work demonstrates the promise of combining multiple analytical methods with advanced statistical methods in quantitative metabolomics research, which we have applied to the clinical situation of acute insulin deprivation in T1D to reflect the numerous metabolic pathways known to be affected by insulin deficiency.

Markers of oxidative damage are not elevated in otherwise healthy individuals with the metabolic syndrome

OBJECTIVE

The role of oxidative damage in the pathogenesis of metabolic syndrome is poorly understood.

RESEARCH DESIGN AND METHODS

A detailed cross-sectional study was performed to assess the relationship between lipid oxidation products, gamma-glutamyltransferase, high-sensitivity C-reactive protein (hs-CRP), and phospholipase activities with respect to the metabolic status in a cohort of otherwise healthy individuals.

RESULTS

A total of 179 individuals (87 men and 92 women) aged 43 +/- 14 years (mean +/- SD) participated in this study. There were no differences in the levels of plasma F(2)-isoprostanes, hydroxyeicosatetraenoic acids, cholesterol oxidation products, and phospholipase activities in individuals with features of metabolic syndrome. In multivariate analyses, serum hs-CRP was a consistent independent predictor of metabolic syndrome.

CONCLUSIONS

Minimal changes were observed in multiple markers of oxidative damage in a well-characterized cohort of individuals with features of metabolic syndrome.

A metabolomics approach using juvenile cystic mice to identify urinary biomarkers and altered pathways in polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited kidney disease and affects 1 in 1,000 individuals. Ultrasound is most often used to diagnose ADPKD; such a modality is only useful late in the disease after macroscopic cysts are present. There is accumulating evidence suggesting that there are common cellular and molecular mechanisms responsible for cystogenesis in human and murine PKD regardless of the genes mutated, and, in the case of complex metabolomic analysis, the use of a mouse model has distinct advantages for proof of principle over a human study. Therefore, in this study we utilized a urinary metabolomics-based investigation using gas chromatography-time of flight mass spectrometry to demonstrate that the cystic mouse can be discriminated from its wild-type counterpart by urine analysis alone. At day 26 of life, before there is serological evidence of kidney dysfunction, affected mice are distinguishable by urine metabolomic analysis; this finding persists through 45 days until 64 days, at which time body weight differences confound the results. Using functional score analysis and the KEGG pathway database, we identify several biologically relevant metabolic pathways which are altered very early in this disease, the most highly represented being the purine and galactose metabolism pathways. In addition, we identify several specific candidate biomarkers, including allantoic acid and adenosine, which are augmented in the urine of young cystic mice. These markers and pathway components, once extended to human disease, may prove useful as a noninvasive means of diagnosing cystic kidney diseases and to suggest novel therapeutic approaches. Thus, urine metabolomics has great diagnostic potential for cystic renal disorders and deserves further study.