Effects of coenzyme Q10 on gene expression and inflammation : results from in silico, in vitro and in vivo studies
CoQ10 acts as an obligatory cofactor in the electron transport in the respiratory chain. Additionally, CoQ10 is required for the biosynthesis of pyrimidine nucleotides and the function of uncoupling proteins (UCPs). The reduced form of CoQ10 (Q10H2) serves as a potent antioxidant of lipid membranes. More recently, CoQ10 has been identified as a modulator of gene expression in vitro. This established function of CoQ10 was investigated in the present thesis on the molecular, cellular and physiological level by the use of bioinformatics and cell culture models as well as animal and human studies. Based on text mining analysis, a functional connection of CoQ10-sensitive genes was performed. Through signalling pathways of G-protein coupled receptors, JAK/STAT and integrin, 17 genes were functionally connected as previously published in Caco-2 cells. Moreover, promoter regions of genes related to inflammation revealed binding sites for the pivotal inflammatory transcription factor NFκB. To evaluate the data from the in silico analysis in an experimental context, monocytic cells were either treated with the oxidized (Q10) or reduced (Q10H2) form of CoQ10. Subsequently, the LPS-induced release of NFκB-dependent cytokines and chemokines was determined in cell-free supernatants. Finally, both for Q10- and Q10H2-incubated cells reduced secretion levels of the pro-inflammatory mediators TNFα, RANTES and MIP-1α have been observed. On the basis of the in vitro results, indicating slight differences in the anti-inflammatory properties of Q10 and Q10H2, redox-dependent gene expression patterns were hypothesized. To test this assumption in vivo, a genome-wide expression profiling was performed in various tissues (liver, kidney, heart and brain) of SAMP1 mice. Animals were either supplemented with Q10 or Q10H2 (500 mg/kg BW/d) for 6 (6 M) or 14 (14 M) months, respectively. In doing so, liver seemed to be the main target tissue of CoQ10 intervention, followed by kidney, heart and brain. In comparison to Q10, Q10H2 supplementation was more effective to increase total CoQ10 levels in liver tissues of SAMP1 mice. Evaluation of the array data also indicated a stronger impact on gene expression by Q10H2 when compared to Q10. Gene expression analysis in the liver of 14 M SAMP1 mice identified 11 Q10H2-sensitive genes primarily involved in cholesterol and lipid metabolism as well as inflammation and cell differentiation. Results from text mining revealed a functional connection of these genes in PPARα signalling pathways. Interestingly, these genes were not regulated in liver tissues of Q10-treated mice. Moreover, a key regulator gene in cholesterol metabolism, CYP51, was significantly down-regulated in the Q10H2-treated group, but became up-regulated in Q10-supplemented animals. Hence, the redox sensitivity of the identified genes might be a possible explanation for the observed differences in liver cholesterol levels of Q10H2- and Q10-supplemented mice. For further verification of the results obtained from in vitro experiments, 53 healthy male volunteers were supplemented with Q10H2 (150 mg/d) for 2 weeks. Based on microarray data and stringent selection criteria, 7 Q10H2-sensitive genes related to inflammatory and apoptotic processes were identified in isolated monocytes. For the identified Q10H2-sensitive genes, text mining analysis revealed a functional connection in NFκB and PPAR signalling pathways. As PPARs are known key players in lipid metabolism and cell differentiation, in addition to the transcriptional effects, a putative impact on physiological parameters such as LDL cholesterol and blood cell count was determined. Thereby, Q10H2 supplementation showed a significant reduction of LDL serum cholesterol levels. Additionally, due to the significant differences in the count of maturated red blood cells (erythrocytes) and immature reticulocytes, effects on cell differentiation processes were hypothesized. In summary, the results from the in silico, in vitro and in vivo studies show anti-inflammatory properties of Q10H2 as well as a regulatory role in cholesterol metabolism and cell differentiation processes. These effects could be explained, at least in part, by a modulatory impact of Q10H2 on redox-sensitive NFκB/PPARα dependent gene expression.