Noninvasive Markers of Oxidative DNA Stress, RNA Degradation and Protein Degradation Are Differentially Correlated With Resting Metabolic Rate and Energy Intake in Children and Adolescents

0031-3998/08/6403-0246 PEDIATRIC RESEARCH Copyright © 2008 International Pediatric Research Foundation, Inc. Vol. 64, No. 3, 2008 Printed in U.S.A. Noninvasive Markers of Oxidative DNA Stress, RNA Degradation and Protein Degradation Are Differentially Correlated With Resting Metabolic Rate and Energy Intake in Children and Adolescents HEINRICH TOPP, GERHARD FUSCH, GERHARD SCHÖCH, AND CHRISTOPH FUSCH Neonatology [H.T., G.F., C.F.], University Children’s Hospital, 17487 Greifswald, Germany; Business Unit Parenteral Nutrition [H.T.], Fresenius Kabi Deutschland GmbH, 61440 Oberursel, Germany; Research Institute for Child Nutrition [G.S.], 44225 Dortmund, Germany highly significant correlations between the excretion of 8-oxodG/creatinine and the specific metabolic rate (25). However, we have found no such close association when comparing the 8-oxodG excretion and the resting metabolic rate (RMR) between 18-y-old humans and 320-g rats; RMR/d/kg BW of the latter was higher by a factor of 4 times but the excretion of 8-oxodG was similar in both species (26). In that study, RMR was estimated via BWs by using an empirical formula or a figure from literature in the case of humans and rats, respectively (26), and RMR represented the specific metabolic rate under fasting and more inactive conditions. Hence, our results in man and rat were different to those reported in the abovementioned studies (24 –25). However, our results of a similar 8-oxodG excretion in man and rat are consistent with corresponding results published by Helbock et al. (4). In a recent study performed in 14 children (median age 11 y) and 16 adults (median age 30 y) of both genders, we found also no significant correlation between RMR per 24 h per kg lean body mass (RMR/d/kg LBM), as measured by indirect calorimetry and dual-energy x-ray absorptiometry, and excretion of 8-oxodG/d/kg LBM (27). In contrast, in a subgroup (four children, six adults) of the latter study, strong correlations were found between RMR and RNA turnover, as measured by whole-body degradation rates of tRNA and rRNA, when related to LBM (27). In this study, the degradation rate of tRNA was determined by measuring the urinary excretion of the tRNA-specific catabolite N2, N2-dimethylguanosine (m22G). The degradation rate of rRNA was determined on the basis of the excretion of pseudouridine (␺), as described in detail elsewhere (28). From these and former findings in different other mammalian species of various BWs (29,30), it may be concluded that noninvasively determined degradation rates of t- and rRNA as well as the excretion rate of ␺ seem to be appropriate indicators of RMR at least in healthy subjects (27,28). ABSTRACT: Urinary excreted RNA and DNA catabolites are used as noninvasive markers for metabolic processes: 8-oxo-2⬘deoxyguanosine (8-oxodG) potentially represents oxidative stress to DNA/deoxyribonucleotidetriphosphate pool, modified ribonucleoside pseudouridine (␺) originating mainly from degraded rRNA and tRNA reflects RNA turnover. Modified amino acid ␥-carboxyglutamic acid (Gla) stems from degraded proteins reflecting turnover of proteins. Aim of the present study was to investigate (44 healthy males, 3–18 y) how excretion rates of 8-oxodG, ␺, and Gla are related to resting metabolic rate and energy intake. Excretion rates of 8-oxodG (pmol/kg/d), ␺ (␮mol/kg/d), and Gla (␮mol/kg/d) were significantly correlated with resting metabolic rate (kJ/kg/d): r2 ⫽ 0.108 (p ⫽ 0.029), 0.691 and 0.552 (p ⬍ 0.0001), respectively. Excretion rates of 8-oxodG, ␺, and Gla were also significantly correlated with energy intake (kJ/kg/d): r2 ⫽ 0.108 (p ⫽ 0.036), 0.602 and 0.462 (p ⬍ 0.0001). 8-oxodG and Gla excretion was significantly correlated with ␺ excretion: r2 ⫽ 0.174 (p ⫽ 0.005) and 0.709 (p ⬍ 0.0001). These results indicate close relationships between whole-body RNA and protein degradation and metabolic rate. The relationship between 8-oxodG excretion and metabolic rate, however, is less strong suggesting that factors other than metabolic rate considerably affect the oxidative stress to DNA. (Pediatr Res 64: 246–250, 2008) 8 -oxo-2⬘-deoxyguanosine (8-oxodG) can be formed in DNA by reactive oxygen species (ROS). Renal excretion of 8-oxodG has been considered as a noninvasive marker of oxidative DNA damage in (patho-) physiologic and nutritional studies (e.g., Refs.1–19). The respiratory chain in mitochondria is one source for the formation of ROS (20 –22) and it may be hypothesized that the formation and urinary excretion of 8-oxodG is related to consumption of O2. Indeed, a close association between 24-h O2 consumption and 8-oxodG excretion has been described in a group of 33 smoking and nonsmoking premenopausal women (23). Another study of the same research group described a close association between the urinary excretion rate of 8-oxodG and the metabolic rate in four various mammalian species (24). Also subsequently performed investigations in six different species ranging in body weight (BW) from 0.02 (mouse) to 75 kg (human) showed Abbreviations: BW, body weight; dG, deoxyguanosine; dNTP, deoxyribonucleotidetriphosphate; EI, energy intake by food; Gla, ␥-carboxyglutamic acid; LBM, lean body mass; 8-oxodG, 8-oxo-2⬘-deoxyguanosine (8-oxo-7,8dihydro-2⬘-deoxyguanosine); 8-oxoGua, 8-oxoguanine (8-oxo-7,8-dihydroguanine); ␺, pseudouridine; RMR, resting metabolic rate; ROS, reactive oxygen species Received January 2, 2008; accepted April 10, 2008. Correspondence: Christoph Fusch, M.D., University Children’s Hospital, Soldmannstrasse 15, D-17475 Greifswald, Germany; e-mail: 246 247 NONINVASIVE MARKERS AND METABOLISM Whole-body protein turnover as measured using stable isotope techniques was also shown to be strongly correlated with calculated RMR in different mammalian species of various BWs (31). Furthermore, it could be shown in various mammals and in humans that calculated RMR was strongly related to the degradation rate of muscle protein and proteins containing the modified amino acid ␥-carboxyglutamic acid (Gla), namely prothrombin, blood coagulation factors VII, IX, and X, proteins C, S, and Z as well as matrix Gla protein and osteocalcin (29,30,32). The degradation of muscle protein and Gla-containing proteins was also determined noninvasively by measuring urinary excretion of the modified amino acids 3-methylhistidine and Gla, respectively (29,32). Whereas, strong correlations between RMR and wholebody RNA and protein degradation rates have been concordantly described (27–32), the results concerning 8-oxodG excretion and metabolic rate are somewhat controversial (23– 27). Therefore, the aim of the present basic research study was to compare in different groups that were fairly homogenously composed with respect to age, gender, lifestyle, etc. (see “Discussion”) the correlations of urinary excretion of 8-oxodG (potential marker for oxidative stress to DNA and deoxyribonucleotidetriphosphate (dNTP) pool, cf. discussion), ␺ (...truncated)