Cerebellar Ataxia and Coenzyme Q Deficiency through Loss of Unorthodox Kinase Activity.

The UbiB protein kinase-like (PKL) family is widespread, comprising one-quarter of microbial PKLs and five human homologs, yet its biochemical activities remain obscure. COQ8A (ADCK3) is a mammalian UbiB protein associated with ubiquinone (CoQ) biosynthesis and an ataxia (ARCA2) through unclear means. We show that mice lacking COQ8A develop a slowly progressive cerebellar ataxia linked to Purkinje cell dysfunction and mild exercise intolerance, recapitulating ARCA2. Interspecies biochemical analyses show that COQ8A and yeast Coq8p specifically stabilize a CoQ biosynthesis complex through unorthodox PKL functions. Although COQ8 was predicted to be a protein kinase, we demonstrate that it lacks canonical protein kinase activity in trans. Instead, COQ8 has ATPase activity and interacts with lipid CoQ intermediates, functions that are likely conserved across all domains of life. Collectively, our results lend insight into the molecular activities of the ancient UbiB family and elucidate the biochemical underpinnings of a human disease.

4-Nitrobenzoate inhibits coenzyme Q biosynthesis in mammalian cell cultures.

Coenzyme Q (Q) is an electron transporter in the respiratory chain and a lipid-soluble antioxidant that decreases in humans with age. Here we show that 4-nitrobenzoate inhibited 4-hydroxybenzoate:polyprenyl transferase (Coq2) in a competitive manner and dose-dependently decreased Q in mammalian cells without accumulation of Q intermediates. As 4-nitrobenzoate neither interfered with mitochondrial respiration nor induced oxidative stress, it should prove a valuable tool for studies on both Q deficiency and Q supplementation.

Farnesol is glucuronidated in human liver, kidney and intestine in vitro, and is a novel substrate for UGT2B7 and UGT1A1.

Farnesol is an isoprenoid found in many aromatic plants and is also produced in humans, where it acts on numerous nuclear receptors and has received considerable attention due to its apparent anticancer properties. Although farnesol has been studied for over 30 years, its metabolism has not been well characterized. Recently, farnesol was shown to be metabolized by cytochromes P450 in rabbit; however, neither farnesol hydroxylation nor glucuronidation in humans have been reported to date. In the present paper, we show for the first time that farnesol is metabolized to farnesyl glucuronide, hydroxyfarnesol and hydroxyfarnesyl glucuronide by human tissue microsomes, and we identify the specific human UGTs (uridine diphosphoglucuronosyltransferases) involved. Farnesol metabolism was examined by a sensitive LC (liquid chromatography)-MS/MS method. Results indicate that farnesol is a good substrate for glucuronidation in human liver, kidney and intestine microsomes (values in nmol/min per mg). Initial analysis using expressed human UGTs indicated that UGTs 1A1 and 2B7 were primarily responsible for glucuronidation in vitro, with significantly lower activity for all the other UGTs tested (UGTs 1A3, 1A4, 1A6, 1A9 and 2B4). Kinetic analysis and inhibition experiments indicate that, in liver microsomes, UGT1A1 is primarily responsible for farnesol glucuronidation; however, in intestine microsomes, UGT2B7 is probably the major isoform involved, with a very-low-micromolar K(m). We also show the first direct evidence that farnesol can be metabolized to hydroxyfarnesol by human liver microsomes and that hydroxyfarnesol is metabolized further to hydroxyfarnesyl glucuronide. Thus glucuronidation may modulate the physiological and/or pharmacological properties of this potent signalling molecule.

Coenzyme Q-responsive Leigh's encephalopathy in two sisters.

A 31-year-old woman had encephalopathy, growth retardation, infantilism, ataxia, deafness, lactic acidosis, and increased signals of caudate and putamen on brain magnetic resonance imaging. Muscle biochemistry showed succinate:cytochrome c oxidoreductase (complex II-III) deficiency. Both clinical and biochemical abnormalities improved remarkably with coenzyme Q10 supplementation. Clinically, when taking 300mg coenzyme Q10 per day, she resumed walking, gained weight, underwent puberty, and grew 20cm between 24 and 29 years of age. Coenzyme Q10 was markedly decreased in cerebrospinal fluid, muscle, lymphoblasts, and fibroblasts, suggesting the diagnosis of primary coenzyme Q10 deficiency. An older sister has similar clinical course and biochemical abnormalities. These findings suggest that coenzyme Q10 deficiency can present as adult Leigh's syndrome.

beta2-Integrin and lipid modifications indicate a non-antioxidant mechanism for the anti-atherogenic effect of dietary coenzyme Q10.

Dietary supplementation with coenzyme Q (CoQ) has been proposed to have anti-atherogenic effects by virtue of its antioxidant capacity. To investigate this question, the leukocyte status of 5 males and 5 females (52-68 years) was evaluated before and after supplementation with 200mg CoQ/day for 5 and 10 weeks. CoQ was selectively taken up by mononuclear cells and alpha-tocopherol increased in polynuclear and mononuclear cells. The expression of beta2-integrin CD11b and complement receptor CD35 on the plasma membrane of resting and stimulated monocytes was significantly decreased upon dietary CoQ. Fatty acid and aldehyde analysis revealed that there was a selective increase of arachidonic acid and plasmalogens in only mononuclear cells. These selective lipid changes are not consistent with a general improvement in antioxidant status and indicate that CoQ most likely inhibits a phospholipase A2. Thus, these results strongly suggest that the anti-atherogenic effects of CoQ be mediated by other mechanisms beside its antioxidant protection.