Lipid quinones

Cancer as a disease of old age: changing mutational and microenvironmental landscapes

Why do we get cancer mostly when we are old? According to current paradigms, the answer is simple: mutations accumulate in our tissues throughout life, and some of these mutations contribute to cancers. Although mutations are necessary for cancer development, a number of studies shed light on roles for ageing and exposure-dependent changes in tissue landscapes that determine the impact of oncogenic mutations on cellular fitness, placing carcinogenesis into an evolutionary framework. Natural selection has invested in somatic maintenance to maximise reproductive success. Tissue maintenance not only ensures functional robustness but also prevents the occurrence of cancer through periods of likely reproduction by limiting selection for oncogenic events in our cells. Indeed, studies in organisms ranging from flies to humans are revealing conserved mechanisms to eliminate damaged or oncogenically initiated cells from tissues. Reports of the existence of striking numbers of oncogenically initiated clones in normal tissues and of how this clonal architecture changes with age or external exposure to noxious substances provide critical insight into the early stages of cancer development. A major challenge for cancer biology will be the integration of these studies with epidemiology data into an evolutionary theory of carcinogenesis, which could have a large impact on addressing cancer risk and treatment.

Quinone specificity of complex I

This review considers the interaction of Complex I with different redox acceptors, mainly homologs and analogs of the physiological acceptor, hydrophobic Coenzyme Q. After examining the physical properties of the different quinones and their efficacy in restoring mitochondrial respiration, a survey ensues of the advantages and drawbacks of the quinones commonly used in Complex I activity determination and of their kinetic properties. The available evidence is then displayed on structure-activity relationships of various quinone compounds in terms of electron transfer activity and proton translocation, and the present knowledge is discussed in terms of the nature of multiple quinone-binding sites in the Complex.

Ubiquinone biosynthesis in Leishmania major promastigotes

Promastigotes of Leishmania major contain a ubiquinone which has a side chain made up of nine isoprene subunits (UQ9). Incorporation of radioactivity from [14C] acetate and [14C] mevalonate into ubiquinone as well as the identification of hydroxymethylglutaryl coenzyme A reductase (HMG CoA reductase), and mevalonate kinase indicate that the isoprenoid portion of the molecule is synthesized by the acetate-mevalonate pathway as in mammalian cells. Incorporation of [14C] tyrosine into ubiquinone is low, but [14C] parahydroxybenzoic acid is readily incorporated. Distribution of radioactivity from [14C] acetate indicates that about 60-80% is associated with the side chain and about 20% with the ring. Label from parahydroxybenzoic acid is, however, incorporated preferentially into the ring. L. major is capable of synthesizing the aromatic ring of ubiquinone from acetate, parahydroxybenzoate being an important intermediate. In this behaviour it resembles procaryotes. Ubiquinone biosynthetic pathway in L. major thus shares characteristics with mammalian and bacterial systems.

Preparation and physicochemical characterization of aqueous dispersions of coenzyme Q10 nanoparticles

The present study describes a novel pharmaceutical formulation of coenzyme Q10, viz. submicron-sized dispersions of the substance prepared by emulsification of molten coenzyme Q10 in an aqueous phase. Photon correlation spectroscopy reveals mean diameters of 60 to 300 nm depending on process parameters. Coenzyme Q10 nanoparticles remain stable on storage for more than 30 months. Lipophilic drugs can be incorporated into the nanoparticles demonstrating their potential use as a drug carrier system. Transmission electron micrographs of freeze-fractured replica show spherical particles with an amorphous core. Cryo-electron microscopy reveals the coexistence of small unilamellar vesicles in phospholipid stabilized dispersions. Thermoanalysis and X-ray studies indicate that the dispersed and emulsified coenzyme Q10 does not recrystallize even at 4 degrees C over 30 months. These agree with 1H NMR data which demonstrate that coenzyme Q10 molecules have a high mobility when formulated as nanoparticles and that colloidally dispersed coenzyme Q10 remains in the state of a supercooled melt. Despite the high melting point of the bulk material, coenzyme Q10 dispersions represent no suspensions but O/W emulsions according to the IUPAC definition (1).

Influence of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors on mitochondrial respiration in rat liver during ischemia

Effects of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors, pravastatin and simvastatin, on mitochondrial respiration in ischemic rat liver were examined. Either vehicle, pravastatin (2 or 4 mg/kg per day), or simvastatin (1 or 2 mg/kg per day) was orally administered for 3 weeks. Liver ischemia was induced by cessation of the systemic circulation for 60 min. Liver mitochondria were isolated and the respiration was determined by polarography using glutamate and succinate as substrates. In the vehicle-treated group, ischemia drcreased ZO3, respiratory control index (RCI: QO3/QO4), and ADP/O ratio. Pretreatments with pravastatin and simvastatin enhanced the decreases in QO3 measured with either glutamate or succinate, and in ADP/O ratio measured with succinate. Because of decreasing QO4, HMG-CoA reductase inhibitors did not modify the changes in RCI due to ischemia. There were no significant differences in respiratory indices between pravastatin- and simvastatin-treated groups. In conclusion, HMG-CoA reductase inhibitors may enhance respiratory impairment of liver mitochondria under pathophysiological conditions, such as ischemia.

Steady-state kinetics of ubiquinol-cytochrome c reductase in bovine heart submitochondrial particles: diffusional effects

In an attempt to establish the relative importance of diffusional and chemical control in the reactivity of the two of the two substrates, ubiquinol and cytochrome c, we have undertaken as extensive characterization of the steady-state kinetics of ubiquinol-cytochrome c reductase (EC 1.10.2.2) when present in open submitochondrial particles from bovine heart. The kinetic pattern follows a Ping Pong mechanism; contrary to the situation found with the isolated enzyme [Speck and Margoliash (1984) J. Biol. Chem. 259, 1064-1072, and confirmed in our laboratory], no substrate inhibition by oxidized cytochrome c was observed with the membrane-bound enzyme. Endogenous oxidized ubiquinone-10 is unable to exert product inhibition under the conditions employed. In the Ping Pong mechanism for this enzyme, the reaction scheme can be clearly divided into two parts, and the Kmin. (kcat./km) value for one substrate is independent of the rate constant for the second substrate. Both ubiquinol-1 and ubiquinol-2 can be used as electron donors reacting with the enzyme from within the lipid bilayer [Fato, Castelluccio, Palmer and Lenaz (1988) Biochim. Biophys. Acta 932, 216-222]; the kmin. values for ubiquinols, when calculated on the basis of their membranous concentrations, are significantly lower than the kmin. for cytochrome c. The temperature-dependence of the kinetic parameters was investigated by titrating each of the substrates under quasi-saturating concentrations of the second substrate. Arrhenius plots of Vmax. extrapolated from both cytochrome c and ubiquinol titrations were linear, when care was taken to verify the quasi-saturating concentrations of the fixed co-substrate. The Arrhenius plots for the kmin. values for both ubiquinol and cytochrome c were linear, but the activation energy was much higher for the former, particularly when calculated for ubiquinol dissolved in the lipid phase; the very low value of activation energy of the kmin. for cytochrome c is strong support for diffusion control being present in the reaction of cytochrome c with the membranous enzyme. In contrast to the soluble enzyme, ubiquinone titrations of submitochondrial particles at low cytochrome c concentrations deviated from hyperbolic behaviour. Changing the medium viscosity with either poly(ethylene glycol) or sucrose had a strong effect on the cytochrome c kmin., whereas the change in the ubiquinol kmin. was much smaller. From the viscosity studies the extent of diffusional control could be calculated, revealing that the reaction with cytochrome c was mostly diffusion-limited. The viscosity of the membrane was changed by incorporating cholesterol; no significant effect on the ubiquinol kmin. ascribable to diffusion control could be recognized.(ABSTRACT TRUNCATED AT 400 WORDS)

Decrease of oxidative activities in brown adipose tissue mitochondria of cold acclimated rats on short term exposure to heat stress

Exposure of rats to the cold (4-5 degrees C) caused large (2-3-fold) increases in the mass of interscapular brown adipose tissue (BAT), its mitochondrial content and the basal metabolic rate of the animals. The rate of substrate oxidation by BAT mitochondria also increased about 3-fold. When cold-acclimated animals were exposed to heat (37 degrees C), the BMR decreased by half in 3 h, the earliest time interval tested. Mitochondrial substrate oxidation, as well as substrate-dependent H2O2 generation, showed a proportionate decrease in rates. In these mitochondria, activities of cytochrome c reductases, but not dehydrogenases with NADH, alpha-glycerophosphate and succinate as substrates, also showed a significant decrease. The concentration of cytochromes aa3 and b, but not cytochrome c, also decreased in BAT mitochondria from 12-h heat-exposed animals, while the change in concentration of cytochrome b alone was found as early as 3 h of heat exposure. These results identify the change in cytochromes as a mechanism of regulation of oxidative activities in BAT mitochondria under conditions of acute heat stress.

The role of ubiquinones in the regulation of lipid metabolism in rat thymocytes

The effect of ubiquinones Q-1, Q-2, Q-8 and Q-9 on lipid metabolism in rat thymocytes in vitro was studied. The cells were incubated in a medium containing ubiquinones within the concentration range from 1 to 100 microM. A 2-fold decreased cholesterol synthesis was observed in thymocytes incubated with ubiquinone Q-9 at a concentration of exogenous ubiquinone of no less than 40 microM. Incubation of thymocytes with ubiquinones UQ-1 and UQ-2 that are characteristic of rats (40 microM and 100 microM) resulted in a decrease of cholesterol synthesis. Ubiquinone-8 had a tendency to inhibit the cholesterogenesis in rat thymocytes.

Nonpolar lipid methylation-identification of nonpolar methylated products synthesized by rat basophilic leukemia cells, retina and parotid

Incorporation of radioactivity from [3H- or 14C-methyl] methionine into nonpolar lipids had been investigated in rat basophilic leukemia (RBL) cells, retina, and rat parotid gland. These nonpolar methylated lipids were extracted into heptane and characterized by thin-layer chromatography, high performance liquid chromatography, gas chromatography, and mass spectrometry. The major methylated nonpolar lipid product in the RBL cells themselves was ubiquinone-9, which accounted for about 90% of the nonpolar lipid and 20-30% of the total radioactive lipid formed. There was a modest increase in the methylation of nonpolar lipids upon stimulation of the RBL cells with IgE and anti-IgE, but the significance of this change is uncertain. In contrast to whole cells, RBL membrane fractions (incubated with [3H-methyl]-S-adenosylmethionine) incorporated radioactivity primarily into fatty acid methyl esters and not ubiquinone. A third product, 2-(methylthio)-benzothiazole, was formed by RBL cells, retina and minced parotid upon incubation in enriched media. This product was formed enzymatically, apparently by the known enzyme S-thiolmethyltransferase, using the thiol substrate which contaminates these media. Evidence suggest that the enzyme may reside, at least in part, on the surface of the cells.

Lipids of Thermoplasma acidophilum

Cells of Thermoplasma acidophilum contain about 3% total lipid on a dry weight basis. Total lipid was found to contain 17.5% neutral lipid, 25.1% glycolipid, and 56.6% phospholipid by chromatography on silicic acid. The lipids contain almost no fatty acid ester groups but appear to have long-chain alkyl groups in ether linkages to glycerol. The phospholipid fraction includes a major component which represents about 80% of the lipid phosphorus and 46% of the total lipids. We believe this component to be a long-chain isopranol glycerol diether analogue of glycerolphosphoryl monoglycosyl diglyceride. The glycolipids appear to contain isopranol diether analogues. Several components of the complex, neutral lipid fraction have been identified as hydrocarbons, vitamin K(2)-7, and isopranol glycerol diether analogues. Sterols are present in the neutral lipids but do not appear to be synthesized by the organism.