Age-related changes in plasma coenzyme Q10 concentrations and redox state in apparently healthy children and adults
Introduction
Coenzyme Q10 (CoQ) is an endogenous enzyme cofactor that is produced in most living cells in humans, is distributed in cellular membranes, is an essential component of the mitochondrial respiratory chain, and may provide protective benefits as an antioxidant [1], [2]. Coenzyme Q10 is a redox molecule (2,3-dimethoxy, 5-methyl, 6-decaprenyl benzoquinone), which exists in biochemically reduced CoQ (ubiquinol) and oxidized CoQ (ubiquinone) forms in biological tissues [1]. Because of its important role in mitochondrial and membrane functions, the redox state of CoQ (ubiquinol/ubiquinone ratio) has been suggested to be a useful biomarker of oxidative stress [3], [4].
The development of mitochondrial abnormalities, increased production of free radicals, and the cumulative effects of oxidative stress upon the body have been proposed as the mitochondrial theory of aging [5]. The hypothesis that mitochondria are both a source and a target of cellular free radicals and the knowledge of the important role of CoQ in mitochondrial function have led others to propose that CoQ may be linked with aging mechanisms [6]. The common assumption has been that CoQ levels generally decline with aging [7], but data supporting this postulate are limited. Interestingly, Hara et al. [8] reported low ubiquinol concentrations, redox ratio, and total CoQ plasma concentrations in apparently healthy neonates during the first 5 days after birth.
CoQ reference ranges are needed to support CoQ research and clinical monitoring in pediatric populations. The objectives of this study are twofold: to determine if age-related changes in ubiquinol, ubiquinone, and CoQ redox state (ubiquinol/ubiquinone ratio) occur in healthy individuals between childhood and old age; and to establish reference intervals for these analytes in healthy children.
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Materials and methods
This study was approved by the Institutional Review Board of the Cincinnati Children's Hospital Medical Center (CCHMC), Cincinnati, OH. Informed consent was obtained from all subjects or their parents. Adult participants in the study were drawn from the ongoing Princeton Follow-up Study, a 28-year follow-up of former students and their parents from the Princeton Lipid Research Clinics (LRC) Study. The Princeton LRC Study has been described previously [9], [10], [11]. Adults provided a medical
Results
Demographic characteristics and lipid profiles of population samples are summarized in Table 1. Age-related increases in BMI, total cholesterol (TC), high density lipoprotein (HDL), and low density lipoprotein (LDL) are evident (Table 1). No significant differences in total plasma CoQ or ubiquinol concentrations are found between younger children and adults (Table 2). Younger children have increased mean lipid-adjusted total CoQ concentrations compared with adults (Table 2). CoQ redox ratios
Discussion
CoQ deficiency states have been associated with many diseases and conditions in pediatric and adult populations [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25]; however, in a recent study, age-related CoQ changes were not evident in healthy adults ranging from 28 to 80 years [26]. In this study, comparison of CoQ measures in younger adults (29–50 years) vs. older adults (53–78 years) also shows no significant age-related differences (data not shown). Review of previous
Acknowledgements
This study was supported in part by NIH grant HL62394.
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