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Comparison of coenzyme Q10 plasma levels in obese and normal weight children
Clinica Chimica Acta 349 (2004) 121 – 127 www.elsevier.com/locate/clinchim
Comparison of coenzyme Q10 plasma levels in obese and normal weight children Thomas Menke*, Petra Niklowitz, Gideon de Sousa, Thomas Reinehr, Werner Andler Vestische Kinderklinik Datteln, Universita¨t Witten/Herdecke, Dr.-Friedrich-Steiner-Str. 5, D-45711 Datteln, Germany Received 14 April 2004; received in revised form 9 June 2004; accepted 11 June 2004
Abstract Background: Childhood obesity is associated with lower plasma levels of lipophilic antioxidants which may contribute to a deficient protection of low-density lipoproteins (LDL). An increased plasma level of oxidized LDL in obese people with insulin resistance has been demonstrated. The lipophilic antioxidant coenzyme Q10 (CoQ10) is known as an effective inhibitor of oxidative damage in LDL as well. The aim of the present study was to compare the CoQ10 levels in obese and normal weight children. Methods: The CoQ10 plasma concentrations were measured in 67 obese children (BMIN97th percentile) and related to their degree of insulin resistance. Homeostasis model assessment (HOMA) was used to detect the degree of insulin resistance. The results were compared to a control group of 50 normal weight and apparently healthy children. The results of the CoQ10 levels were related to the plasma cholesterol concentrations. Results: After adjustment to plasma cholesterol, no significant difference in the CoQ10 levels between obese and normal weight children could be demonstrated. Furthermore, there was no difference between insulin-resistant and non-insulin-resistant obese children. Conclusion: CoQ10 plasma levels are not reduced in obese children and are not related to insulin resistance. D 2004 Elsevier B.V. All rights reserved. Keywords: Obesity; Insulin resistance; Childhood; Coenzyme Q10; Oxidative stress; Arteriosclerosis
Abbreviations: IQR, interquartile range; CoQ10, coenzyme Q10; Redox status, percentage of ubiquinone in total CoQ10; Ubiquinone-10, oxidized form of CoQ10; Ubiquinol-10, reduced form of CoQ10; LDL, low-density lipoprotein; VLDL, very lowdensity lipoprotein; NIDDM, non-insulin-dependent diabetes mellitus; HOMA, homeostasis model assessment; SDS-BMI, standard deviation score of body mass index. * Corresponding author. Tel.: +49 2363 9750; fax: +49 2363 64211. E-mail address: [email protected] (T. Menke). 0009-8981/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.cccn.2004.06.015
1. Introduction Hyperlipidemia based on insulin resistance in obesity is thought to play a pivotal role in the development of arteriosclerosis [1–3]. Insulin resistance resulted in an increased lipolysis and production of lipoproteins (VLDL/LDL) [1–3]. The delayed clearance and prolonged residence of the lipoproteins in the bloodstream lead to an increased susceptibility to
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oxidative modification. An increased plasma level of oxidized LDL in obese people with insulin resistance has been demonstrated [4]. The oxidative modification of LDL is thought to represent a key step in the development of arteriosclerosis [5]. The polyunsaturated fatty acids in the LDL are susceptible to oxidative damage [6]. They are protected by several lipophilic antioxidants [6]. Obesity in children and adults is associated with lower levels of lipophilic antioxidants like a-tocopherol and h-carotene [7–9]. This may contribute to a deficient protection of LDL and to the resulting risk of the development of arteriosclerosis. The lipophilic antioxidant coenzyme Q10 (CoQ10) is an effective inhibitor of oxidative damage [10]. This antioxidant is present in lipoproteins and lipophilic cell particles and originates from endogenous synthesis as well as from food intake [11]. Ubiquinol-10, the reduced form of CoQ10, inhibits lipid peroxidation by scavenging peroxyl radicals [10]. The oxidized form of CoQ10 is known as ubiquinone10. The regenerative and antioxidative efficiency of CoQ10 is highly dependent on the reduction rate of ubiquinone-10. At the tissue level, several enzymes have been found to have activity to regenerate the oxidized form [12]. Ubiquinol-10 is the first lipophilic antioxidant to be oxidized when LDL are exposed to oxidants [13]. Therefore, it has been proposed that in particular the ubiquinol-10/ubiquinone-10 ratio may be a sensitive marker for studying disturbances in the prooxidant–antioxidant balance in human blood [14– 16]. A decreased ubiquinol-10/ubiquinone-10 ratio has been reported in diseases associated with oxidative damage [17–24]. The CoQ10 levels in childhood are poorly examined. The aim of the present study was to compare the CoQ10 levels in obese and normal weight children. Therefore, the CoQ10 redox status as a proposed marker of oxidative damage and the CoQ10 plasma concentrations were measured in obese children and related to their degree of insulin resistance. The results were compared to a control group of normal weight and apparently healthy children.
outpatient clinic in our hospital, entered this study (37 males, 30 females). The control group consisted of 50 apparently healthy and normal weight children who were hospitalized for minor surgery (25 males, 25 females). There was no difference in age between study group and control group (Table 2). There was no difference in CoQ10 plasma levels and the CoQ10 redox status with respect to gender in the control group and in the study group. Children with endocrine or metabolic disorders were excluded from the study. Smokers and children taking any medication, including oral contraceptives, were excluded, as well. Further criteria for exclusion were mitochondriopathies and encephalopathies which represent clinical situations where a CoQ10 deficiency has been described [25]. The criteria for exclusion are summarized in Table 1. Children taking oral CoQ10 supplementation were excluded, too. The performed diet records of the obese children showed no difference concerning food items with high CoQ10 content (e.g. pork heart, beef, fish, broccoli [11]) if compared to nutritional habits of healthy children in Germany [26]. The study was approved by the Human Ethic Committee of the Medical Faculty, University of Witten/Herdecke. Blood samples from the obese children were obtained with a routine blood puncture in the endocrinological outpatient clinic. The blood samples of the control group were collected with the routine preoperative investigations. All blood samples were collected after overnight fasting and stored at 84 8C until preparation for analysis. Ubiquinol-10 and ubiquinone10 were measured simultaneously by HPLC with electrochemical detection and internal standardization. The analytical procedures have already been published in detail [15]. The results for CoQ10 were expressed as molar concentration (pmol/Al plasma). Lipophilic Table 1 Criteria for exclusion of the study Cardiac diseases Metabolic diseases
2. Materials and methods
Cerebral diseases Neuromuscular diseases
A total of 67 obese children (BMI N97th percentile), who were referred to the endocrinological
Mitochondriopathies
(haemodynamic vitium, cardiomyopathy, myocarditis) (diabetes, organoacidopathies, storage diseases, lipid metabolism diseases) (seizures, neurodegenerative diseases, cerebral dysmorphism) (spinal muscular atrophy, muscular dystrophy)
T. Menke et al. / Clinica Chimica Acta 349 (2004) 121–127 Table 2 CoQ10 plasma level and CoQ10 redox status in obese and normal weight childrena Number Age (years) SDS-BMI Total CoQ10 (pmol/Al) Cholesterol (mmol/l) CoQ10/Chol (Amol/mol) Ubiquinone (pmol/Al) CoQ10 redox status (% oxidized/total CoQ10) a b
Obese
Non-obese
67 11.1 (9.2–13.0) 2.43 (2.04–2.81) 0.883 (0.731–1.15) 4.07 (3.37–4.63) 224 (198–270) 0.076 (0.053–0.122) 8.85 (7.9–11.3)
50 12.6 (10.9–13.3) 0.52 (0.49–1.01) 0.789 (0.620–0.950) 3.66 (3.18–4,21) 226 (180–248) 0.065 (0.057–0.088) 9.3 (6.5–11.7)
p=valueb 0.136 0.00001 0.007 0.006 0.321 0.241 0.627
Results are given as median and IQR (in parentheses). Mann–Whitney U-test.
antioxidants are carried by circulating lipoproteins in the plasma. The positive correlation between plasma lipids and plasma levels of lipophilic antioxidants is well-established [27,28]. Therefore, the CoQ10 results were related to plasma cholesterol concentrations (Amol/mol cholesterol) and to plasma LDL concentrations (pmol/mg LDL). LDL-cholesterol was measured by an enzymatic test (LDL-C PlusR). The CoQ10 redox status was calculated as the percentage of ubiquinone-10 within the total concentration of CoQ10 (ubiquinol-10 plus ubiquinone-10). Homeostasis model assessment (HOMA) was used to detect the degree of insulin resistance [29]. The resistance can be assessed from the fasting glucose and insulin concentrations by the formulae: resistance (HOMA)=(insulin [mU/l]glucose [mmol/l])/22.5. Insulin was measured by microparticle enzyme assay (AbbothR). Blood glucose was determined by colorimetric test (Vitros GLU-Analysepl7ttchenR). Intraassay and interassay coefficients of variation were b4.0% in all methods. CoQ10 plasma levels, CoQ10 redox status and cholesterol-related CoQ10 plasma levels in obese children and in the control group were calculated and compared. Furthermore, the obese children were divided into two groups according with their HOMA values (HOMAN4 and HOMAV4). The cut-off point
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of 4 was used since in normal weight subjects the lower limit of the top quintile of HOMA distribution values is below 4 and prospective analyses over years have demonstrated HOMAb4 in subjects without appearance of non-insulin-dependent diabetes mellitus (NIDDM) in contrast to converters to NIDDM [30,31]. CoQ10 plasma levels, CoQ10 redox status, cholesterol- and LDL-related CoQ10 plasma levels in both groups of obese children were calculated and compared. Data were reported as median and interquartile range (IQR). Differences between the groups were tested for significance by Mann–Whitney U-test. The Spearman test was used for calculating the correlation between the CoQ10 plasma levels and the cholesterol and LDL plasma levels. A p-value lower than 0.05 was considered as significant.
3. Results The comparison of CoQ10 plasma levels and redox status in obese and normal weight children is presented Table 3 CoQ10 plasma level and CoQ10 redox status in obese children with high and low HOMA valuesa Number Age (years) SDS-BMI HOMA Total CoQ10 (pmol/Al) Cholesterol (mmol/l) CoQ10/Chol (Amol/mol) LDL (mg/dl) CoQ10/LDL (pmol/mg) Ubiquinone (pmol/Al) CoQ10 redox status (% oxidized/total CoQ10) a b
HOMA V 4
HOMA N 4
41 9.6 (7.55–11.8) 2.27 (2.01–2.65) 2.33 (1.62–3.38) 0.900 (0.716–1.234) 4.00 (3.48–4.76) 224 (180–275) 117 (88–140) 678 (540–910 0.077 (0.057–0.118) 9.5 (7.2–11.1)
26 11.8 (10.2–13.6) 2.65 (2.14–2.98) 6.27 (4.92–7.82) 0.870 (0.777–1.049) 4.00 (3.26–4.41) 224 (200–261) 114 (92–135) 800 (670–910) 0.066 (0.048–0.124) 7.4 (5.1–13.2)
p=valueb 0.001 0.03 0.000001 0.524 0.578 0.768 0.882 0.236 0.236 0.627
Results are given as median and IQR (in parentheses). Mann–Whitney U-test.
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in Table 2. In the obese children, the plasma levels of CoQ10 and cholesterol were significantly higher than in the control group. After adjustment to the plasma cholesterol, however, there was no significant difference in the CoQ10 levels between obese and normal weight children. There also was no significant difference in the CoQ10 redox status between the groups. The comparison of CoQ10 plasma levels and redox status in obese children with high (HOMAN4) and low (HOMAV4) values is presented in Table 3. There was no significant difference in the CoQ10 levels and CoQ10 redox status between the groups. LDL and cholesterol related CoQ10 values showed no significant difference either. The Spearman test showed positive correlations between the CoQ10 plasma levels and the cholesterol plasma levels in the control group (r=0.480, p= 0.0005) and the study group (r=0.585, p=0.0008). In obese children CoQ10 plasma levels were positively correlated with the LDL plasma levels (r=0.612, pb0.00001).
4. Discussion To the author’s knowledge, this is the first study concerning CoQ10 plasma levels in obese children. Strauss et al. [7] demonstrated that plasma levels of lipophilic antioxidants like a-tocopherol and h-carotene are significantly decreased in obese children. It has been suggested that antioxidant uptake, distribution, and metabolism may be altered in obesity [32,33]. Increased adipose tissue pools in obese children may trap lipophilic antioxidants and thereby affect their availability to other tissues and plasma lipoproteins. The present study demonstrated that CoQ10 plasma levels are not reduced in obese children. In contrast to a-tocopherol and h-carotene, CoQ10 originates from endogenous synthesis as well as from food intake [11]. Plasma CoQ10 levels correlated significantly to cholesterol concentration in obese children, as was proven for a normal and for a diabetic adult population [34]. The plasma levels of both parameters were elevated in comparison to the control group of normal weight children. The diet records of the obese children in this study showed no preference of food items with high CoQ10 content. If the elevated CoQ10 plasma level in obese children
were caused by an increased fat consumption, the plasma level of other lipophilic antioxidants like carotene and tocopherol would have to be elevated as well. This may indicate that endogenous CoQ10 synthesis may compensate the greater demand of lipophilic antioxidants in the plasma in situations like obesity where plasma lipids are increased. Since ubiquinol, the reduced form of CoQ10, is easily oxidized to ubiquinone in lipoproteins, it has been suggested that the CoQ10 redox status may be used as an early marker for the detection of oxidative LDL modification [19,35]. Recent reports demonstrated an altered CoQ10 redox status with an increased percentage of ubiquinone in total CoQ10 in patients with certain conditions [17–24], including hyperlipidemia [36] leading to arteriosclerosis. The present data showed no difference in the CoQ10 redox status between obese children with high HOMA values and obese children with normal HOMA values. This may indicate that the recycling of this antioxidant by the reduction enzymes of the body is so efficient, that an increased consumption of the reduced CoQ10 in LDL protection is not reflected by its redox status. Therefore, the CoQ10 redox status in the plasma may not reflect the risk for arteriosclerosis in obesity in childhood. Further research has to elucidate whether other methods are more useful for quantifying oxidative damage to LDL in obese children. In accordance with other authors, this study demonstrated that obese children with high HOMA values are significantly older and show significantly higher standard deviation score of body mass index (SDS-BMI) scores than children with low HOMA values [37]. There was no correlation between age and CoQ10 values in the study group and in the control group. Furthermore, there was no difference in cholesterol-related CoQ10 values between obese and normal weight children. Therefore, age and SDS-BMI score are without any influence on the CoQ10 state if the groups with high and low HOMA values are compared. It is well known that childhood obesity is associated with an approximately doubled risk of developing arteriosclerosis and cardiovascular diseases in adulthood [38–42]. Therefore, the enrichment of the LDL with lipophilic antioxidants to prevent oxidative modification may offer new concepts in prevention. In this study, the plasma concentration and redox status of CoQ10 in obese and normal weight children were
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within the normal range if compared to studies in healthy children and adults [14,43,44]. Reduced CoQ10 is the first lipophilic antioxidant consumed when freshly isolated LDL is exposed to antioxidants while other lipophilic antioxidants like h-carotene and a-tocopherol decrease after depletion of reduced CoQ10 [13,45]. Therefore, this substance is a first line of lipophilic antioxidant defense in lipoproteins. This might explain, why supplementation of h-carotene and a-tocopherol has only little effect on the development of cardiovascular diseases in intervention trials [46– 48]. Up to now, no study has examined the effect of dietary CoQ10 supplementation on atherogenesis in humans. The antioxidative efficiency of this substance in CoQ10-enriched LDL in vitro has been demonstrated [49]. The attenuating effect of CoQ10 on arteriosclerosis in an animal model using apoE knockout mice has been shown as well [50]. CoQ10 supplementation leads to increased plasma levels and the CoQ10 redox status remains constant during the supplementation period [51]. This indicates that sufficient reducing potential is available to keep circulating CoQ10 in the reduced form under supplementation. Whether the supplementation of CoQ10 reduces the risk of arteriosclerosis in obese children is therefore still a question needing further research. In summary, the data of this study showed that the CoQ10 plasma levels are not decreased and the CoQ10 redox status is not altered in obese children. The results suggest that both parameters are not suitable as early markers for a deficient protection and oxidative modification of LDL in obesity in childhood. In vitro studies and animal studies suggest that CoQ10 seems to represent an efficient antioxidant defense for lipoproteins. There is still a need for further research into the relationship between the CoQ10 state, its antioxidant efficiency and the risk of cardiovascular diseases in obese children.
Acknowledgements This work was supported by the patient self-help groups bElterninitiative Tumorkranker Kinder e.V. der Vestischen Kinderklinik DattelnQ, Germany, and by the bPeter und Ruth Wirth StiftungQ, Switzerland. The technical assistance of A. Frau, Pracejus is gratefully acknowledged.
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Comparison of coenzyme Q10 plasma levels in obese and normal weight children Thomas Menke*, Petra Niklowitz, Gideon de Sousa, Thomas Reinehr, Werner Andler Vestische Kinderklinik Datteln, Universita¨t Witten/Herdecke, Dr.-Friedrich-Steiner-Str. 5, D-45711 Datteln, Germany Received 14 April 2004; received in revised form 9 June 2004; accepted 11 June 2004
Abstract Background: Childhood obesity is associated with lower plasma levels of lipophilic antioxidants which may contribute to a deficient protection of low-density lipoproteins (LDL). An increased plasma level of oxidized LDL in obese people with insulin resistance has been demonstrated. The lipophilic antioxidant coenzyme Q10 (CoQ10) is known as an effective inhibitor of oxidative damage in LDL as well. The aim of the present study was to compare the CoQ10 levels in obese and normal weight children. Methods: The CoQ10 plasma concentrations were measured in 67 obese children (BMIN97th percentile) and related to their degree of insulin resistance. Homeostasis model assessment (HOMA) was used to detect the degree of insulin resistance. The results were compared to a control group of 50 normal weight and apparently healthy children. The results of the CoQ10 levels were related to the plasma cholesterol concentrations. Results: After adjustment to plasma cholesterol, no significant difference in the CoQ10 levels between obese and normal weight children could be demonstrated. Furthermore, there was no difference between insulin-resistant and non-insulin-resistant obese children. Conclusion: CoQ10 plasma levels are not reduced in obese children and are not related to insulin resistance. D 2004 Elsevier B.V. All rights reserved. Keywords: Obesity; Insulin resistance; Childhood; Coenzyme Q10; Oxidative stress; Arteriosclerosis
Abbreviations: IQR, interquartile range; CoQ10, coenzyme Q10; Redox status, percentage of ubiquinone in total CoQ10; Ubiquinone-10, oxidized form of CoQ10; Ubiquinol-10, reduced form of CoQ10; LDL, low-density lipoprotein; VLDL, very lowdensity lipoprotein; NIDDM, non-insulin-dependent diabetes mellitus; HOMA, homeostasis model assessment; SDS-BMI, standard deviation score of body mass index. * Corresponding author. Tel.: +49 2363 9750; fax: +49 2363 64211. E-mail address: [email protected] (T. Menke). 0009-8981/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.cccn.2004.06.015
1. Introduction Hyperlipidemia based on insulin resistance in obesity is thought to play a pivotal role in the development of arteriosclerosis [1–3]. Insulin resistance resulted in an increased lipolysis and production of lipoproteins (VLDL/LDL) [1–3]. The delayed clearance and prolonged residence of the lipoproteins in the bloodstream lead to an increased susceptibility to
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oxidative modification. An increased plasma level of oxidized LDL in obese people with insulin resistance has been demonstrated [4]. The oxidative modification of LDL is thought to represent a key step in the development of arteriosclerosis [5]. The polyunsaturated fatty acids in the LDL are susceptible to oxidative damage [6]. They are protected by several lipophilic antioxidants [6]. Obesity in children and adults is associated with lower levels of lipophilic antioxidants like a-tocopherol and h-carotene [7–9]. This may contribute to a deficient protection of LDL and to the resulting risk of the development of arteriosclerosis. The lipophilic antioxidant coenzyme Q10 (CoQ10) is an effective inhibitor of oxidative damage [10]. This antioxidant is present in lipoproteins and lipophilic cell particles and originates from endogenous synthesis as well as from food intake [11]. Ubiquinol-10, the reduced form of CoQ10, inhibits lipid peroxidation by scavenging peroxyl radicals [10]. The oxidized form of CoQ10 is known as ubiquinone10. The regenerative and antioxidative efficiency of CoQ10 is highly dependent on the reduction rate of ubiquinone-10. At the tissue level, several enzymes have been found to have activity to regenerate the oxidized form [12]. Ubiquinol-10 is the first lipophilic antioxidant to be oxidized when LDL are exposed to oxidants [13]. Therefore, it has been proposed that in particular the ubiquinol-10/ubiquinone-10 ratio may be a sensitive marker for studying disturbances in the prooxidant–antioxidant balance in human blood [14– 16]. A decreased ubiquinol-10/ubiquinone-10 ratio has been reported in diseases associated with oxidative damage [17–24]. The CoQ10 levels in childhood are poorly examined. The aim of the present study was to compare the CoQ10 levels in obese and normal weight children. Therefore, the CoQ10 redox status as a proposed marker of oxidative damage and the CoQ10 plasma concentrations were measured in obese children and related to their degree of insulin resistance. The results were compared to a control group of normal weight and apparently healthy children.
outpatient clinic in our hospital, entered this study (37 males, 30 females). The control group consisted of 50 apparently healthy and normal weight children who were hospitalized for minor surgery (25 males, 25 females). There was no difference in age between study group and control group (Table 2). There was no difference in CoQ10 plasma levels and the CoQ10 redox status with respect to gender in the control group and in the study group. Children with endocrine or metabolic disorders were excluded from the study. Smokers and children taking any medication, including oral contraceptives, were excluded, as well. Further criteria for exclusion were mitochondriopathies and encephalopathies which represent clinical situations where a CoQ10 deficiency has been described [25]. The criteria for exclusion are summarized in Table 1. Children taking oral CoQ10 supplementation were excluded, too. The performed diet records of the obese children showed no difference concerning food items with high CoQ10 content (e.g. pork heart, beef, fish, broccoli [11]) if compared to nutritional habits of healthy children in Germany [26]. The study was approved by the Human Ethic Committee of the Medical Faculty, University of Witten/Herdecke. Blood samples from the obese children were obtained with a routine blood puncture in the endocrinological outpatient clinic. The blood samples of the control group were collected with the routine preoperative investigations. All blood samples were collected after overnight fasting and stored at 84 8C until preparation for analysis. Ubiquinol-10 and ubiquinone10 were measured simultaneously by HPLC with electrochemical detection and internal standardization. The analytical procedures have already been published in detail [15]. The results for CoQ10 were expressed as molar concentration (pmol/Al plasma). Lipophilic Table 1 Criteria for exclusion of the study Cardiac diseases Metabolic diseases
2. Materials and methods
Cerebral diseases Neuromuscular diseases
A total of 67 obese children (BMI N97th percentile), who were referred to the endocrinological
Mitochondriopathies
(haemodynamic vitium, cardiomyopathy, myocarditis) (diabetes, organoacidopathies, storage diseases, lipid metabolism diseases) (seizures, neurodegenerative diseases, cerebral dysmorphism) (spinal muscular atrophy, muscular dystrophy)
T. Menke et al. / Clinica Chimica Acta 349 (2004) 121–127 Table 2 CoQ10 plasma level and CoQ10 redox status in obese and normal weight childrena Number Age (years) SDS-BMI Total CoQ10 (pmol/Al) Cholesterol (mmol/l) CoQ10/Chol (Amol/mol) Ubiquinone (pmol/Al) CoQ10 redox status (% oxidized/total CoQ10) a b
Obese
Non-obese
67 11.1 (9.2–13.0) 2.43 (2.04–2.81) 0.883 (0.731–1.15) 4.07 (3.37–4.63) 224 (198–270) 0.076 (0.053–0.122) 8.85 (7.9–11.3)
50 12.6 (10.9–13.3) 0.52 (0.49–1.01) 0.789 (0.620–0.950) 3.66 (3.18–4,21) 226 (180–248) 0.065 (0.057–0.088) 9.3 (6.5–11.7)
p=valueb 0.136 0.00001 0.007 0.006 0.321 0.241 0.627
Results are given as median and IQR (in parentheses). Mann–Whitney U-test.
antioxidants are carried by circulating lipoproteins in the plasma. The positive correlation between plasma lipids and plasma levels of lipophilic antioxidants is well-established [27,28]. Therefore, the CoQ10 results were related to plasma cholesterol concentrations (Amol/mol cholesterol) and to plasma LDL concentrations (pmol/mg LDL). LDL-cholesterol was measured by an enzymatic test (LDL-C PlusR). The CoQ10 redox status was calculated as the percentage of ubiquinone-10 within the total concentration of CoQ10 (ubiquinol-10 plus ubiquinone-10). Homeostasis model assessment (HOMA) was used to detect the degree of insulin resistance [29]. The resistance can be assessed from the fasting glucose and insulin concentrations by the formulae: resistance (HOMA)=(insulin [mU/l]glucose [mmol/l])/22.5. Insulin was measured by microparticle enzyme assay (AbbothR). Blood glucose was determined by colorimetric test (Vitros GLU-Analysepl7ttchenR). Intraassay and interassay coefficients of variation were b4.0% in all methods. CoQ10 plasma levels, CoQ10 redox status and cholesterol-related CoQ10 plasma levels in obese children and in the control group were calculated and compared. Furthermore, the obese children were divided into two groups according with their HOMA values (HOMAN4 and HOMAV4). The cut-off point
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of 4 was used since in normal weight subjects the lower limit of the top quintile of HOMA distribution values is below 4 and prospective analyses over years have demonstrated HOMAb4 in subjects without appearance of non-insulin-dependent diabetes mellitus (NIDDM) in contrast to converters to NIDDM [30,31]. CoQ10 plasma levels, CoQ10 redox status, cholesterol- and LDL-related CoQ10 plasma levels in both groups of obese children were calculated and compared. Data were reported as median and interquartile range (IQR). Differences between the groups were tested for significance by Mann–Whitney U-test. The Spearman test was used for calculating the correlation between the CoQ10 plasma levels and the cholesterol and LDL plasma levels. A p-value lower than 0.05 was considered as significant.
3. Results The comparison of CoQ10 plasma levels and redox status in obese and normal weight children is presented Table 3 CoQ10 plasma level and CoQ10 redox status in obese children with high and low HOMA valuesa Number Age (years) SDS-BMI HOMA Total CoQ10 (pmol/Al) Cholesterol (mmol/l) CoQ10/Chol (Amol/mol) LDL (mg/dl) CoQ10/LDL (pmol/mg) Ubiquinone (pmol/Al) CoQ10 redox status (% oxidized/total CoQ10) a b
HOMA V 4
HOMA N 4
41 9.6 (7.55–11.8) 2.27 (2.01–2.65) 2.33 (1.62–3.38) 0.900 (0.716–1.234) 4.00 (3.48–4.76) 224 (180–275) 117 (88–140) 678 (540–910 0.077 (0.057–0.118) 9.5 (7.2–11.1)
26 11.8 (10.2–13.6) 2.65 (2.14–2.98) 6.27 (4.92–7.82) 0.870 (0.777–1.049) 4.00 (3.26–4.41) 224 (200–261) 114 (92–135) 800 (670–910) 0.066 (0.048–0.124) 7.4 (5.1–13.2)
p=valueb 0.001 0.03 0.000001 0.524 0.578 0.768 0.882 0.236 0.236 0.627
Results are given as median and IQR (in parentheses). Mann–Whitney U-test.
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in Table 2. In the obese children, the plasma levels of CoQ10 and cholesterol were significantly higher than in the control group. After adjustment to the plasma cholesterol, however, there was no significant difference in the CoQ10 levels between obese and normal weight children. There also was no significant difference in the CoQ10 redox status between the groups. The comparison of CoQ10 plasma levels and redox status in obese children with high (HOMAN4) and low (HOMAV4) values is presented in Table 3. There was no significant difference in the CoQ10 levels and CoQ10 redox status between the groups. LDL and cholesterol related CoQ10 values showed no significant difference either. The Spearman test showed positive correlations between the CoQ10 plasma levels and the cholesterol plasma levels in the control group (r=0.480, p= 0.0005) and the study group (r=0.585, p=0.0008). In obese children CoQ10 plasma levels were positively correlated with the LDL plasma levels (r=0.612, pb0.00001).
4. Discussion To the author’s knowledge, this is the first study concerning CoQ10 plasma levels in obese children. Strauss et al. [7] demonstrated that plasma levels of lipophilic antioxidants like a-tocopherol and h-carotene are significantly decreased in obese children. It has been suggested that antioxidant uptake, distribution, and metabolism may be altered in obesity [32,33]. Increased adipose tissue pools in obese children may trap lipophilic antioxidants and thereby affect their availability to other tissues and plasma lipoproteins. The present study demonstrated that CoQ10 plasma levels are not reduced in obese children. In contrast to a-tocopherol and h-carotene, CoQ10 originates from endogenous synthesis as well as from food intake [11]. Plasma CoQ10 levels correlated significantly to cholesterol concentration in obese children, as was proven for a normal and for a diabetic adult population [34]. The plasma levels of both parameters were elevated in comparison to the control group of normal weight children. The diet records of the obese children in this study showed no preference of food items with high CoQ10 content. If the elevated CoQ10 plasma level in obese children
were caused by an increased fat consumption, the plasma level of other lipophilic antioxidants like carotene and tocopherol would have to be elevated as well. This may indicate that endogenous CoQ10 synthesis may compensate the greater demand of lipophilic antioxidants in the plasma in situations like obesity where plasma lipids are increased. Since ubiquinol, the reduced form of CoQ10, is easily oxidized to ubiquinone in lipoproteins, it has been suggested that the CoQ10 redox status may be used as an early marker for the detection of oxidative LDL modification [19,35]. Recent reports demonstrated an altered CoQ10 redox status with an increased percentage of ubiquinone in total CoQ10 in patients with certain conditions [17–24], including hyperlipidemia [36] leading to arteriosclerosis. The present data showed no difference in the CoQ10 redox status between obese children with high HOMA values and obese children with normal HOMA values. This may indicate that the recycling of this antioxidant by the reduction enzymes of the body is so efficient, that an increased consumption of the reduced CoQ10 in LDL protection is not reflected by its redox status. Therefore, the CoQ10 redox status in the plasma may not reflect the risk for arteriosclerosis in obesity in childhood. Further research has to elucidate whether other methods are more useful for quantifying oxidative damage to LDL in obese children. In accordance with other authors, this study demonstrated that obese children with high HOMA values are significantly older and show significantly higher standard deviation score of body mass index (SDS-BMI) scores than children with low HOMA values [37]. There was no correlation between age and CoQ10 values in the study group and in the control group. Furthermore, there was no difference in cholesterol-related CoQ10 values between obese and normal weight children. Therefore, age and SDS-BMI score are without any influence on the CoQ10 state if the groups with high and low HOMA values are compared. It is well known that childhood obesity is associated with an approximately doubled risk of developing arteriosclerosis and cardiovascular diseases in adulthood [38–42]. Therefore, the enrichment of the LDL with lipophilic antioxidants to prevent oxidative modification may offer new concepts in prevention. In this study, the plasma concentration and redox status of CoQ10 in obese and normal weight children were
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within the normal range if compared to studies in healthy children and adults [14,43,44]. Reduced CoQ10 is the first lipophilic antioxidant consumed when freshly isolated LDL is exposed to antioxidants while other lipophilic antioxidants like h-carotene and a-tocopherol decrease after depletion of reduced CoQ10 [13,45]. Therefore, this substance is a first line of lipophilic antioxidant defense in lipoproteins. This might explain, why supplementation of h-carotene and a-tocopherol has only little effect on the development of cardiovascular diseases in intervention trials [46– 48]. Up to now, no study has examined the effect of dietary CoQ10 supplementation on atherogenesis in humans. The antioxidative efficiency of this substance in CoQ10-enriched LDL in vitro has been demonstrated [49]. The attenuating effect of CoQ10 on arteriosclerosis in an animal model using apoE knockout mice has been shown as well [50]. CoQ10 supplementation leads to increased plasma levels and the CoQ10 redox status remains constant during the supplementation period [51]. This indicates that sufficient reducing potential is available to keep circulating CoQ10 in the reduced form under supplementation. Whether the supplementation of CoQ10 reduces the risk of arteriosclerosis in obese children is therefore still a question needing further research. In summary, the data of this study showed that the CoQ10 plasma levels are not decreased and the CoQ10 redox status is not altered in obese children. The results suggest that both parameters are not suitable as early markers for a deficient protection and oxidative modification of LDL in obesity in childhood. In vitro studies and animal studies suggest that CoQ10 seems to represent an efficient antioxidant defense for lipoproteins. There is still a need for further research into the relationship between the CoQ10 state, its antioxidant efficiency and the risk of cardiovascular diseases in obese children.
Acknowledgements This work was supported by the patient self-help groups bElterninitiative Tumorkranker Kinder e.V. der Vestischen Kinderklinik DattelnQ, Germany, and by the bPeter und Ruth Wirth StiftungQ, Switzerland. The technical assistance of A. Frau, Pracejus is gratefully acknowledged.
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