Coenzyme Q10 (CoQ10) has a number of vital functions in all cells, both mitochondrial and extramitochondrial. In addition to its key role in mitochondrial oxidative phosphorylation, CoQ10 serves as a lipid soluble antioxidant, plays an important role in fatty acid, pyrimidine and lysosomal metabolism, as well as directly mediating the expression of a number of genes, including those involved in inflammation. In view of the central role of CoQ10 in cellular metabolism, it is unsurprising that a CoQ10 deficiency is linked to the pathogenesis of a range of disorders. CoQ10 deficiency is broadly classified into primary or secondary deficiencies. Primary deficiencies result from genetic defects in the multi-step biochemical pathway of CoQ10 synthesis, whereas secondary deficiencies can occur as result of other diseases or certain pharmacotherapies. In this article we have reviewed the clinical consequences of primary and secondary CoQ10 deficiencies, as well as providing some examples of the successful use of CoQ10 supplementation in the treatment of disease.

Coenzyme Q10 (CoQ10) has a number of important roles in the cell that are required for optimal functioning of the immune system. These include its essential role as an electron carrier in the mitochondrial respiratory chain, enabling the process of oxidative phosphorylation to occur with the concomitant production of ATP, together with its role as a potential lipid-soluble antioxidant, protecting the cell against free radical-induced oxidation. Furthermore, CoQ10 has also been reported to have an anti-inflammatory role via its ability to repress inflammatory gene expression. Recently, CoQ10 has also been reported to play an important function within the lysosome, an organelle central to the immune response. In view of the differing roles CoQ10 plays in the immune system, together with the reported ability of CoQ10 supplementation to improve the functioning of this system, the aim of this article is to review the current literature available on both the role of CoQ10 in human immune function and the effect of CoQ10 supplementation on this system.

Post-viral fatigue syndrome (PVFS) encompasses a wide range of complex neuroimmune disorders of unknown causes characterised by disabling post-exertional fatigue, myalgia and joint pain, cognitive impairments, unrefreshing sleep, autonomic dysfunction, and neuropsychiatric symptoms. It includes myalgic encephalomyelitis, also known as chronic fatigue syndrome (ME/CFS); fibromyalgia (FM); and more recently post-COVID-19 condition (long COVID). To date, there are no definitive clinical case criteria and no FDA-approved pharmacological therapies for PVFS. Given the current lack of effective treatments, there is a need to develop novel therapeutic strategies for these disorders. Mitochondria, the cellular organelles responsible for tissue energy production, have recently garnered attention in research into PVFS due to their crucial role in cellular bioenergetic metabolism in these conditions. The accumulating literature has identified a link between mitochondrial dysfunction and low-grade systemic inflammation in ME/CFS, FM, and long COVID. To address this issue, this article aims to critically review the evidence relating to mitochondrial dysfunction in the pathogenesis of these disorders; in particular, it aims to evaluate the effectiveness of coenzyme Q10 supplementation on chronic fatigue and pain symptoms as a novel therapeutic strategy for the treatment of PVFS.

Mitochondrial dysfunction is a common factor known to be involved in the pathogenesis of a number of neurological disorders, including Parkinson’s disease, Alzheimer’s disease, and amyotrophic lateral sclerosis. Given the importance of coenzyme Q10 (CoQ10) in promoting normal mitochondrial function, and the deficiency of CoQ10 reported in such neurological disorders, there is a rationale for investigating the potential therapeutic role of supplementary CoQ10. However, while there is evidence for the efficacy of CoQ10 supplementation in animal models of the above disorders, randomised controlled clinical trials supplementing CoQ10 in PD, AD, or ALS have had disappointing outcomes. This in turn may be a reflection of the current uncertainty as to whether CoQ10 can access the blood–brain barrier in human subjects. In an attempt to further elucidate the disparity in outcomes of such preclinical and clinical studies, in this article we have reviewed evidence from the peer-reviewed literature to establish the ability of CoQ10 to access the brain via the BBB.

Mitochondria are primary targets for environmental toxic chemicals; these typically disrupt the mitochondrial electron transport chain, resulting in reduced ATP production, increased reactive oxygen free radical species (ROS)-induced oxidative stress, increased apoptosis, and increased inflammation. This in turn suggests a rationale for investigating the potential role of coenzyme Q10 (CoQ10) in mediating such chemical-induced mitochondrial dysfunction, given the key roles of CoQ10 in promoting normal mitochondrial function, and as an antioxidant and anti-apoptotic and anti-inflammatory agent. In the present article, we have, therefore, reviewed the potential role of supplementary CoQ10 in improving mitochondrial function and mediating adverse effects following exposure to a number of environmental toxins, including pesticides, heavy metals, industrial solvents, endocrine-disrupting agents, and carcinogens, as well as pharmacological drugs and lifestyle toxicants.

Intracellular signalling pathways provide a mechanism to connect events at a cell surface to the nucleus and are of fundamental importance to normal cell functioning. Intracellular signalling pathways control many aspects of cell metabolism, including mitochondrial function, oxidative stress, inflammation, and apoptosis/ferroptosis. Randomised controlled clinical trials supplementing coenzyme Q10 (CoQ10) have reported significant clinical improvements in a number of disorders, in turn associated with the action of CoQ10 to promote normal mitochondrial function, reduce oxidative stress and inflammation, and mediate apoptosis and ferroptosis. However, the precise mechanisms by which CoQ10 facilitates beneficial changes in the above factors is not completely understood. In the present article, the evidence we have reviewed provides a supporting rationale that the beneficial role of CoQ10 in the above disorders occurs via mediation of major intracellular signalling pathways, including the Nrf2/NQO1, NF-κB, P13/AKT/mTOR, MAPK, JAK/STAT, WNT/B-catenin, AMPK-YAP-OPA1, and hedgehog (Hh) pathways; the clinical consequences of such mediation are also reviewed.