Coenzyme Q biosynthesis inhibition induces HIF-1α stabilization and metabolic switch toward glycolysis.

Coenzyme Q10 (CoQ, ubiquinone) is a redox-active lipid endogenously synthesized by the cells. The final stage of CoQ biosynthesis is performed at the mitochondrial level by the 'complex Q', where coq2 is responsible for the prenylation of the benzoquinone ring of the molecule. We report that the competitive coq2 inhibitor 4-nitrobenzoate (4-NB) decreased the cellular CoQ content and caused severe impairment of mitochondrial function in the T67 human glioma cell line. In parallel with the reduction in CoQ biosynthesis, the cholesterol level increased, leading to significant perturbation of the plasma membrane physicochemical properties. We show that 4-NB treatment did not significantly affect the cell viability, because of an adaptive metabolic rewiring toward glycolysis. Hypoxia-inducible factor 1α (HIF-1α) stabilization was detected in 4-NB-treated cells, possibly due to the contribution of both reduction in intracellular oxygen tension and ROS overproduction. Exogenous CoQ supplementation partially recovered cholesterol content, HIF-1α degradation, and ROS production, whereas only weakly improved the bioenergetic impairment induced by the CoQ depletion. Our data provide new insights on the effect of CoQ depletion and contribute to shed light on the pathogenic mechanisms of ubiquinone deficiency syndrome.

Statin treatment and new-onset diabetes: a review of proposed mechanisms.

New-onset diabetes has been observed in clinical trials and meta-analyses involving statin therapy. To explain this association, three major mechanisms have been proposed and discussed in the literature. First, certain statins affect insulin secretion through direct, indirect or combined effects on calcium channels in pancreatic ß-cells. Second, reduced translocation of glucose transporter 4 in response to treatment results in hyperglycemia and hyperinsulinemia. Third, statin therapy decreases other important downstream products, such as coenzyme Q10, farnesyl pyrophosphate, geranylgeranyl pyrophosphate, and dolichol; their depletion leads to reduced intracellular signaling. Other possible mechanisms implicated in the effect of statins on new-onset diabetes are: statin interference with intracellular insulin signal transduction pathways via inhibition of necessary phosphorylation events and reduction of small GTPase action; inhibition of adipocyte differentiation leading to decreased peroxisome proliferator activated receptor gamma and CCAAT/enhancer-binding protein which are important pathways for glucose homeostasis; decreased leptin causing inhibition of ß-cells proliferation and insulin secretion; and diminished adiponectin levels. Given that the magnitude of the risk of new-onset diabetes following statin use remains to be fully clarified and the well-established beneficial effect of statins in reducing cardiovascular risk, statins remain the first-choice treatment for prevention of CVD. Elucidation of the mechanisms underlying the development of diabetes in association with statin use may help identify novel preventative or therapeutic approaches to this problem and/or help design a new generation statin without such side-effects.

Lovastatin prevents carcinogenesis in a rat model for liver cancer. Effects of ubiquinone supplementation.

AIM: This study tests the hypothesis that statins (HMGCoA reductase inhibitors) inhibit carcinogenesis and that this effect may be mediated by the statin-induced inhibition of ubiquinone synthesis. MATERIALS AND METHODS: The effects of lovastatin, with and without addition of ubiquinone, were studied in a rat model for chemically induced hepatocarcinogenesis. Intermediates in the mevalonate pathway were measured. RESULTS: Lovastatin treatment reduced the volume fraction of liver nodules by 50% and the cell proliferation within the liver nodules was reduced to one third. Ubiquinone (Q10) treatment reversed the statin-induced inhibition of cell proliferation. Lathosterol levels were reduced significantly in the statin-treated rats, indicating inhibition of the mevalonate pathway, but cholesterol levels were not affected. CONCLUSION: Lovastatin inhibits carcinogenesis in a rat model for liver cancer, despite unaffected cholesterol levels. The statin-induced inhibition of cell proliferation may, at least in part, be explained by the inhibition of ubiquinone synthesis.

HMG-CoA reductase inhibitors and coenzyme Q10.

The most concerning adverse reaction with HMG-CoA reductase inhibitors (statins) is myotoxicity. Statins inhibit the production of mevalonate, a precursor of both cholesterol and coenzyme Q10, a compound believed to be crucial for mitochondrial function and the provision of energy for cellular processes. There is speculation that a reduction in coenzyme Q10 concentrations may promote the myopathies that have been associated with statin treatment as a result of mitochondrial damage. Although studies have repeatedly demonstrated a reduction in circulating coenzyme Q10 concentrations with statin therapy, it is unclear as to whether tissue levels of coenzyme Q10 are significantly affected. Coenzyme Q10 supplementation has been shown to reverse statin-induced decreases in circulating coenzyme Q10 concentrations, although the effect of supplementation on tissue coenzyme Q10 concentrations and any resulting clinical benefit has not been adequately assessed. Although there is not much of a safety concern with coenzyme Q10 supplementation, there is also not enough evidence to support its routine use for preventing the adverse effects of statin therapy, and it is therefore not recommended for this purpose at this time.

Bioenergetics in clinical medicine. III. Inhibition of coenzyme Q10-enzymes by clinically used anti-hypertensive drugs.

Background data revealed that some American and Japanese patients with essential hypertension, including many who were not being treated with any anti-hypertensive drug, had a deficiency of coenzyme Q10. Eight clinically used anti-hypertensive drugs have now been tested for inhibition of two mitochondrial coenzyme Q10-enzymes of heart tissue, succinoxidase and NADH-oxidase. Diazoxide and propranolol significantly inhibited the CoQ10-succinoxidase and CoQ10-NADH-oxidase, respectively. Metoprolol did not inhibit succinoxidase, and was one-fourth as active as propranolol for inhibition of NADH-oxidase. Hydrochlorothiazide, hydralazine, ans clonidine also inhibited CoQ10-NADH-oxidase. Reserpine did not inhibit either CoQ10-enzyme, and methyldopa was a very eak inhibitor of succinoxidase. The internationally recognized clinical side-effects of propranolol may be due, in part, to inhibition of CoQ10-enzymes which are indispensable in the bioenergetics of cardiac function. A pre-existing deficiency of coenzyme Q10 in the myocardium of hypertensive patients could be augmented by subsequent treatment with propranolol, possibly to the "life-threatening" state described by others.