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Ubiquinol decreases monocytic expression and DNA methylation of the pro-inflammatory chemokine ligand 2 gene in humans
© Fischer et al.; licensee BioMed Central Ltd. 2012
- Received: 3 April 2012
- Accepted: 20 September 2012
- Published: 1 October 2012
Coenzyme Q10 is an essential cofactor in the respiratory chain and serves in its reduced form, ubiquinol, as a potent antioxidant. Studies in vitro and in vivo provide evidence that ubiquinol reduces inflammatory processes via gene expression. Here we investigate the putative link between expression and DNA methylation of ubiquinol sensitive genes in monocytes obtained from human volunteers supplemented with 150 mg/ day ubiquinol for 14 days.
Ubiquinol decreases the expression of the pro-inflammatory chemokine (C-X-C motif) ligand 2 gene (CXCL2) more than 10-fold. Bisulfite-/ MALDI-TOF-based analysis of regulatory regions of the CXCL2 gene identified six adjacent CpG islands which showed a 3.4-fold decrease of methylation status after ubiquinol supplementation. This effect seems to be rather gene specific, because ubiquinol reduced the expression of two other pro-inflammatory genes (PMAIP1, MMD) without changing the methylation pattern of the respective gene.
In conclusion, ubiquinol decreases monocytic expression and DNA methylation of the pro-inflammatory CXCL2 gene in humans. Current Controlled Trials ISRCTN26780329.
- Coenzyme Q10
- Gene expression
- DNA methylation
Coenzyme Q10 (CoQ10) is a key component of the mitochondrial respiratory chain where it is mainly known for its role in oxidative phosphorylation. The reduced form of CoQ10, ubiquinol, serves as a potent antioxidant in mitochondria, lipid membranes and plasma lipoproteins [1, 2] as well as a regenerator of other lipid soluble antioxidants (e.g. vitamin E) [3, 4]. Several studies in vitro[5–7], in SAMP1 mice  and in humans  indicate that ubiquinol is involved in inflammatory processes and lipid metabolism via gene expression.
Gene expression as well as DNA methylation processes are affected by various dietary supplements and food nutrients [10–13]. Furthermore, DNA methylation is one of the epigenetic modifications that per se is able to determine the gene expression by regulating the chromatin organization [10, 14]. During methylation of mammalian DNA a methyl group is attached at the 5-position of the cytosine residue within the cytosine-guanine dinucleotides (CpG) resulting in the formation of 5-methylcytosine, which is designated as the fifth base of DNA . Although most genomic DNA in mammals is deficient in CpG sites, clusters of CpG dinucleotides (CpG islands) were described to be primarily located at promoter regions of genes . Here we investigated the effect of ubiquinol on the expression and methylation of CpG island promoter regions of pro-inflammatory genes in humans.
Materials and methods
Participants and study design
Sample characteristics of subjects and study design have been described lately . Briefly: fifty-three healthy male volunteers, 21–48 years of age, received 150 mg of the reduced form of CoQ10 (Q10H2, ubiquinol, KANEKA Corporation, Japan) daily in form of three capsules with each principal meal for 14 days. Fasting blood samples were taken before (T0) and after (T14) supplementation. The participants had an average Body Mass Index (BMI) of 24.1 ± 2.5 kg/m2, no history of gastrointestinal, hepatic, cardiovascular or renal diseases, a habit of non- or occasional smoking and maintenance of usual nutrition habits. The study was approved by the ethics committee of the Medical Faculty of Kiel University, Germany, and was conformed to Helsinki Declaration. All volunteers gave written informed consent.
Microarray-based gene expression analysis and qRT-PCR
Microarray experiment using the Affymetrix human genome U133 plus 2.0 GeneChip® were performed as described previously  with RNA samples from CD14-positive monocytes obtained from three volunteers before (T0) and after (T14) supplementation with ubiquinol. Based on microarray data, expression levels of selected genes including the CXCL2, MMD and PMAIP1 gene were verified by real-time qRT-PCR. Primer sequences for real-time qRT-PCR experiments were designed with Primer Express® Software 3.0 (Applied Biosystems, Darmstadt, Germany). Primer pairs were obtained from MWG Biotech AG (Ebersberg, Germany). cDNA synthesis with subsequent PCR amplification procedure has been described before .
Methylation analysis of genomic regions of CXCL2, MMD and PMAIP1 gene
The presence of CpG islands within the CXCL2, MMD and PMAIP1 genes was predicted using the European Molecular Biology Open Software Suite CpGplot, respectively. Quantitative methylation analysis was performed on the MassARRAY® system (Sequenom, Hamburg, Germany) at BioGlobe (Hamburg, Germany) applying the MassCLEAVETM (hMC) biochemistry after bisulfit treatment of DNA samples and MALDI-TOF mass spectrometry for analyte detection. All reactions were performed according to the standard protocols recommended by the supplier. Genomic DNA was extracted from human monocytes obtained from five volunteers (H1/H1_1 to H5/H5_1) before (T0, H1-H5) and after (T14, H1_1-H5_5) using the DNeasy Tissue Kit (Quiagen). Analysis was carried out from both, forward and reverse strand.
The protocol starts with a bisulfit treatment of provided genomic DNA sample, which converts native cytosine (“C”) nucleotides into uracil (“U”), whereas 5-methyl-protected cytosine residues remain as “C”. The resulting artificial sequence variation is conserved during PCR amplification using methylation independent primers. One primer for each PCR is tagged with T7 RNA polymerase promoter sequence facilitating the transformation of double stranded PCR product into single stranded RNA together with a second level of amplification. The in vitro transcription product is “U-specific” cleaved with RNase A. The generated fragments represent unique portions of the amplified region of interest and are displayed based on their molecular weight in the mass spectrum, which is acquired after sample conditioning with a MassARRAY® Analyzer Compact. Automated data analysis was performed with EpiTyper Software.
Results and discussion
Ubiquinol supplementation reduces the expression of low and high abundant mRNA steady-state levels of pro-inflammatory genes in human monocytes
Normalized steady-state mRNA expression levels (AU) of the CXCL2, PMAIP1 and MMD gene in monocytes of human volunteers before (T 0 ) and after (T 14 ) supplementation with ubiquinol
(T0 vs. T14)
1271 ± 35
578 ± 106
147 ± 30
85 ± 19
1150 ± 865
93 ± 30
Ubiquinol supplementation reduces the methylation status of six adjacent CpG islands within the promoter of the CXCL2 gene
Position, length and number of CpG islands of amplicons covering the analysed genomic regions of the human CXCL2, PMAIP1 and MMD gene
left primer (+Tag)
right primer (+Tag)
The effect of ubiquinol on DNA methylation seems to be rather gene specific and might depend on the extent of ubiquinol induced alteration of gene expression
Our study provides a first hint towards a modifying effect of ubiquinol on DNA methylation in humans. This effect is in line with another human study demonstrating that a supplementation with a mixture of CoQ10, niacin and riboflavin reduces DNA methylation of the tumor suppressor gene RASSF1A in breast cancer patients undergoing tamoxifen therapy . Moreover, literature indicates that global methylation patterns are affected by several other dietary supplements and micronutrients [27–32]. The effect of ubiquinol on DNA methylation seems be rather gene specific because we identified two genes (PMAIP1, MMD) which are regulated by ubiquinol without changing DNA methylation. A recent SAMP-mice study from our group  found that ubiquinol alters hepatic expression of PPARα target genes without influencing DNA methylation in the respective gene promoters.
The effect of ubiquinol on DNA methylation might be linked to the extent of ubiquinol dependent alteration of gene expression. In the case of the CXCL2 gene, ubiquinol reduces its expression more than 10-fold accompanied by a reduced methylation status within certain CpG islands. This finding seems to be contradictory to common models of gene expression, because increased DNA methylation of a gene leads to reduced expression levels , whereas demethylation correlates with the transcription of the gene . On the other hand there is evidence, especially in cancer cells, that DNA methylation status does not correlate with gene expression [36, 37]. However, the mechanism regarding effects of ubiquinol on DNA methylation and expression remains unclear and has to be studied in the future. The reduced expression of pro-inflammatory genes under ubiquinol supplementation supports recent findings from our lab [5, 6, 8, 9, 38–41] and other groups [42, 43] suggesting that CoQ10 displays anti-inflammatory properties. As a summary, we found in a human intervention study that ubiquinol decreases expression and DNA methylation of the pro-inflammatory CXCL2 gene in monocytes. Further studies will be necessary to investigate the mechanistic link between ubiquinol dependent gene expression, DNA methylation and inflammation.
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