Elevation of ubiquinone content by peroxisomal inducers in rat liver during aging

Secondary CoQ10 deficiency, bioenergetics unbalance in disease and aging

Coenzyme Q₁₀ (CoQ₁₀ ) deficiency is a rare disease characterized by a decreased accumulation of CoQ₁₀ in cell membranes. Considering that CoQ₁₀ synthesis and most of its functions are carried out in mitochondria, CoQ₁₀ deficiency cases are usually considered a mitochondrial disease. A relevant feature of CoQ₁₀ deficiency is that it is the only mitochondrial disease with a successful therapy available, the CoQ₁₀ supplementation. Defects in components of the synthesis machinery caused by mutations in COQ genes generate the primary deficiency of CoQ₁₀ . Mutations in genes that are not directly related to the synthesis machinery cause secondary deficiency. Cases of CoQ₁₀ deficiency without genetic origin are also considered a secondary deficiency. Both types of deficiency can lead to similar clinical manifestations, but the knowledge about primary deficiency is deeper than secondary. However, secondary deficiency cases may be underestimated since many of their clinical manifestations are shared with other pathologies. This review shows the current state of secondary CoQ₁₀ deficiency, which could be even more relevant than primary deficiency for clinical activity. The analysis covers the fundamental features of CoQ₁₀ deficiency, which are necessary to understand the biological and clinical differences between primary and secondary CoQ₁₀ deficiencies. Further, a more in-depth analysis of CoQ₁₀ secondary deficiency was undertaken to consider its origins, introduce a new way of classification, and include aging as a form of secondary deficiency.

Coenzyme Q homeostasis in aging: Response to non-genetic interventions

Coenzyme Q (CoQ) is a key component for many essential metabolic and antioxidant activities in cells in mitochondria and cell membranes. Mitochondrial dysfunction is one of the hallmarks of aging and age-related diseases. Deprivation of CoQ during aging can be the cause or the consequence of this mitochondrial dysfunction. In any case, it seems clear that aging-associated CoQ deprivation accelerates mitochondrial dysfunction in these diseases. Non-genetic prolongevity interventions, including CoQ dietary supplementation, can increase CoQ levels in mitochondria and cell membranes improving mitochondrial activity and delaying cell and tissue deterioration by oxidative damage. In this review, we discuss the importance of CoQ deprivation in aging and age-related diseases and the effect of prolongevity interventions on CoQ levels and synthesis and CoQ-dependent antioxidant activities.

Physical activity affects plasma coenzyme Q10 levels differently in young and old humans

Coenzyme Q (Q) is a key lipidic compound for cell bioenergetics and membrane antioxidant activities. It has been shown that also has a central role in the prevention of oxidation of plasma lipoproteins. Q has been associated with the prevention of cholesterol oxidation and several aging-related diseases. However, to date no clear data on the levels of plasma Q during aging are available. We have measured the levels of plasmatic Q10 and cholesterol in young and old individuals showing different degrees of physical activity. Our results indicate that plasma Q10 levels in old people are higher that the levels found in young people. Our analysis also indicates that there is no a relationship between the degree of physical activity and Q10 levels when the general population is studied. However, very interestingly, we have found a different tendency between Q10 levels and physical activity depending on the age of individuals. In young people, higher activity correlates with lower Q10 levels in plasma whereas in older adults this ratio changes and higher activity is related to higher plasma Q10 levels and higher Q10/Chol ratios. Higher Q10 levels in plasma are related to lower lipoperoxidation and oxidized LDL levels in elderly people. Our results highlight the importance of life habits in the analysis of Q10 in plasma and indicate that the practice of physical activity at old age can improve antioxidant capacity in plasma and help to prevent cardiovascular diseases.

Metabolism and function of coenzyme Q

Coenzyme Q (CoQ) is present in all cells and membranes and in addition to be a member of the mitochondrial respiratory chain it has also several other functions of great importance for the cellular metabolism. This review summarizes the findings available to day concerning CoQ distribution, biosynthesis, regulatory modifications and its participation in cellular metabolism. There are a number of indications that this lipid is not always functioning by its direct presence at the site of action but also using e.g. receptor expression modifications, signal transduction mechanisms and action through its metabolites. The biosynthesis of CoQ is studied in great detail in bacteria and yeast but only to a limited extent in animal tissues and therefore the informations available is restricted. However, it is known that the CoQ is compartmentalized in the cell with multiple sites of biosynthesis, breakdown and regulation which is the basis of functional specialization. Some regulatory mechanisms concerning amount and biosynthesis are established and nuclear transcription factors are partly identified in this process. Using appropriate ligands of nuclear receptors the biosynthetic rate can be increased in experimental system which raises the possibility of drug-induced upregulation of the lipid in deficiency. During aging and pathophysiological conditions the tissue concentration of CoQ is modified which influences cellular functions. In this case the extent of disturbances is dependent on the localization and the modified distribution of the lipid at cellular and membrane levels.

Distribution and breakdown of labeled coenzyme Q10 in rat

Radioactive coenzyme Q(10) ([(3)H]CoQ) was synthesized in a way that the metabolites produced retained the radioactivity. Administration of the lipid to rats intraperitoneally resulted in an efficient uptake into the circulation, with high concentrations found in spleen, liver, and white blood cells; lower concentrations in adrenals, ovaries, thymus, and heart; and practically no uptake in kidney, muscle, and brain. In liver homogenate most [(3)H]CoQ appeared in the organelles, but it was also present in the cytosol and transport vesicles. Mitochondria, purified on a metrizamide gradient, had a very low concentration of [(3)H]CoQ, which was mainly present in the lysosomes. All organs that took up the labeled lipid also contained water-soluble metabolites. The majority of metabolites excreted through the kidney and appeared in the urine. Some metabolites were also present in the feces, which further contained nonmetabolized [(3)H]CoQ, excreted through the bile. The major metabolites were purified from the urine, and the mass spectrometric fragmentation showed that these compounds, containing the ring with a short side chain, are phosphorylated. Thus, the results demonstrate that CoQ is metabolized in all tissues, the metabolites are phosphorylated in the cells, transported in the blood to the kidney, and excreted into the urine.

Regulation of coenzyme Q biosynthesis and breakdown

All animal cells synthesize sufficient amounts of coenzyme Q (CoQ) and the cells also possess the capacity to metabolize the lipid. The main product of the metabolism is an intact ring with a short carboxylated side chain which glucuronidated in the liver and excreted mainly into the bile (Nakamura et al., Biofactors 9 (1999), 111-119). In other cells CoQ is phosphorylated, transferred into the blood and excreted through the urine. The biosynthesis of this lipid is regulated by nuclear receptors. PPARalpha is not required for the biosynthesis, or induction upon cold exposure, but it is necessary for the elevated CoQ synthesis during peroxisomal induction. RXRalpha is involved in the basal synthesis of CoQ and also in the increased synthesis upon cold treatment but is not required for peroxisomal induction. Dietary CoQ in human appear in the blood and it is taken up by mononuclear but not polynuclear cells. The former cells display a specific phospholipid modification, an increase of arachidonic acid content. In monocytes the CoQ administration leads to a significant decrease of the beta2-integrin CD11b and the complement receptor CD35. CD11b is one of the adhesion factors regulating the entry of these cells into the arterial wall which demonstrates that the anti-atherogenic effect of CoQ is mediated by other mechanisms beside its antioxidant protection.

Regulation of ubiquinone metabolism

Interest in ubiquinone (UQ) has increased during recent years, mainly because of its antioxidant function and its use as a dietary supplement. However, our knowledge of the biosynthesis, catabolism, and regulation of this lipid in mammalian tissues is quite limited. UQ exhibits a high rate of turnover in all tissues indicating that cells possess efficient metabolic pathways for handling this compound and controlling its tissue levels. Besides reviewing the generally accepted metabolic pathway, alternative synthetic mechanisms are described. The lack of data concerning catabolism and regulation of this compound is emphasized. Reasons for the rather limited uptake of dietary UQ are discussed and alternative mechanisms for its beneficial effects on organ function are suggested. Since appropriate tissue uptake of dietary UQ probably only occurs in deficient states, the definition of partial UQ deficiency and its consequences is urgently needed. The possibility of raising tissue UQ levels by drug treatment or natural metabolites is raised as a choice of preference for the future.

Induction of endogenous coenzyme Q biosynthesis by administration of peroxisomal inducers

A large number of chemical compounds have been identified which cause peroxisomal proliferation and induce a number of enzymes, mainly those participating in lipid metabolism. Administration of these drugs/chemicals to rats increased coenzyme Q levels in the blood and most of the organs. Levels were raised in all cellular membranes of such organs. The extent of induction of this lipid was 8-fold in young animals but decreased during aging and was absent at 1.5 year of age. One of the regulating factors of the mevalonate pathway is farnesol, which is produced by dephosphorylation of farnesyl-PP and eliminated by phosphorylation including two kinases. Future research will involve a search for modified intermediary metabolites, which increase coenzyme Q synthesis and thereby efficiently elevate the level of this lipid in conditions of deficiency.