Letter Cite This: Environ. Sci. Technol. Lett. XXXX, XXX, XXX−XXX
pubs.acs.org/journal/estlcu
Allantoin as a Marker of Oxidative Stress: Inter- and Intraindividual Variability in Urinary Concentrations in Healthy Individuals Maria-Pilar Martinez-Moral† and Kurunthachalam Kannan*,†,‡ †
Downloaded via SAM HOUSTON STATE UNIV on April 13, 2019 at 06:20:31 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.
Wadsworth Center, New York State Department of Health, and Department of Environmental Health Sciences, School of Public Health, State University of New York at Albany, Empire State Plaza, P.O. Box 509, Albany, New York 12201-0509, United States ‡ Biochemistry Department, Faculty of Science and Experimental Biochemistry Unit, King Fahd Medical Research Center, King Abdulaziz University, Jeddah 21589, Saudi Arabia S Supporting Information *
ABSTRACT: Altered systemic oxidative stress is a consequence of environmental exposures and diseases, among other stress factors. The extent of oxidative stress in humans is assessed through the analysis of oxidative stress biomarkers (OSBs) in biospecimens such as urine. Allantoin is an OSB, a specific product of the oxidation of uric acid, that is measurable in urine. In this study, concentrations and inter- and intraindividual variability in urinary concentrations of allantoin were determined in healthy individuals. The results were compared with those found for other OSBs of lipids, proteins, and DNA in the same set of samples. Allantoin was found in all urine samples (N = 515), at concentrations that ranged from 0.88 to 41.7 mmol mol−1 creatinine (0.90 to 112 μg mL−1 urine). The intraclass correlation coefficient (ICC) of urinary allantoin measured in samples collected longitudinally for over a month from 19 individuals (0.74 for creatinine corrected and 0.80 for volumetric concentrations) showed an excellent reliability and notable interindividual variability. Among eight biomarkers measured in the same set of urine samples, allantoin was the predominant one, and it was positively and significantly correlated with urinary creatinine and other OSBs of lipids, proteins, and DNA. We suggest that urinary allantoin is a suitable biomarker of oxidative stress because of its requirement for simple and rapid analysis and long-term reliability/reproducibility as determined by high ICC values.
■
urable in biospecimens such as serum4−6 and urine.7−9 Allantoin is stable in urine after storage or freeze−thaw cycles.8 For these reasons, allantoin has been used as a specific biomarker of oxidative stress in humans. Allantoin has been used as a biomarker of oxidative stress in studies on people with diabetes,4,10 inflammation,11,12 cystic fibrosis,13 response to exercise,14 and smoking.15 Nevertheless, concentrations and inter- and intraindividual variability in urinary allantoin in healthy individuals have not been studied. Information on longitudinal variability in urinary concentrations of biomarkers (such as allantoin) in individuals is important to assess the validity/reliability of such OSBs in toxicological and epidemiological studies.7 Allantoin was traditionally analyzed by Rimini−Schryver colorimetric assay.16 However, due to its high polarity, colorimetric methods of analysis of allantoin are challenging and typically require long sample processing steps involving
INTRODUCTION The exposure to environmental contaminants, incidence of diseases, and other stress factors increase the levels of reactive oxygen species (ROS) in an organism. When the ROS concentration exceeds that of antioxidant capacity of a cell, cellular biomolecules (such as DNA, lipids, and proteins) get oxidized, resulting in the production of compounds that can be used as biomarkers of oxidative stress. Measurements of oxidative stress biomarkers (OSBs) of lipids, proteins, and DNA in urine or other biospecimens have been commonly used in the evaluation of extent of oxidative damage.1 Biomonitoring of effect biomarkers such as OSBs is important for the assessment of adverse effects from chemical exposures. Uric acid is produced in humans as an end product of purine metabolism and is an endogenous antioxidant that can scavenge ROS such as singlet oxygen and peroxyl and hydroxyl radicals.2 The oxidation of uric acid results in the formation of allantoin, which is produced by enzymatic oxidation in most mammals other than humans. However, urate oxidase is silenced in humans by several mutations, and therefore, allantoin is only produced by nonenzymatic oxidation of uric acid.3 Uric acid levels in human serum or urine are not correlated with allantoin concentrations.4 Allantoin is meas© XXXX American Chemical Society
Received: Revised: Accepted: Published: A
March 3, 2019 April 9, 2019 April 9, 2019 April 9, 2019 DOI: 10.1021/acs.estlett.9b00142 Environ. Sci. Technol. Lett. XXXX, XXX, XXX−XXX
Letter
Environmental Science & Technology Letters
Figure 1. Schematic showing formation of OSBs by the reaction of excess ROS with proteins, lipids, DNA, and uric acid in organisms under oxidative stress.
(Columbia, MD) with a binary pump and a Luna 3 μm C18 (4.6 × 150 mm) column from Phenomenex (Torrance, CA) and API 3200 MS/MS (ABSciex, Redwood City, CA) were used for the quantification of allantoin in urine. Urine Samples. A total of 515 urine samples were collected from 19 healthy nonsmoking participants daily for over a month. Information with regard to urine sample collection and demographic characters of the study participants are detailed elsewhere.25 Briefly, participants (58% male) provided early morning void urine daily for a month, while following their normal activities. All individuals were from the Albany area of New Yok State, USA. The BMI of 84% of the participants was
