Incorporation of plastoquinone and ubiquinone into liposome membranes studied by HPLC analysis. The effect of side chain length and redox state of quinone

Exploring Ubiquinone Biosynthesis Inhibition as a Strategy for Improving Atovaquone Efficacy in Malaria

Atovaquone (AV) acts on the malaria parasite by competing with ubiquinol (UQH₂) for its union to the mitochondrial bc₁ complex, preventing the ubiquinone-8 and ubiquinone-9 (UQ-8 and UQ-9) redox recycling, which is a necessary step in pyrimidine biosynthesis. This study focused on UQ biosynthesis in Plasmodium falciparum and adopted proof-of-concept research to better elucidate the mechanism of action of AV and improve its efficacy. Initially, UQ biosynthesis was evaluated using several radioactive precursors and chromatographic techniques. This methodology was suitable for studying the biosynthesis of both UQ homologs and its redox state. Additionally, the composition of UQ was investigated in parasites cultivated at different oxygen saturations or in the presence of AV. AV affected the redox states of both UQ-8 and UQ-9 homologs by increasing the levels of the respective reduced forms. Conversely, low-oxygen environments specifically inhibited UQ-9 biosynthesis and increased the antimalarial efficacy of AV. These findings encouraged us to investigate the biological importance and the potential of UQ biosynthesis as a drug target based on its inhibition by 4-nitrobenzoate (4-NB), a 4-hydroxybenzoate (4-HB) analog. 4-NB effectively inhibits UQ biosynthesis and enhances the effects of AV on parasitic growth and respiration rate. Although 4-NB itself exhibits poor antimalarial activity, its 50% inhibitory concentration (IC₅₀) value increased significantly in the presence of a soluble UQ analog, p-aminobenzoic acid (pABA), or 4-HB. These results indicate the potential of AV combined with 4-NB as a novel therapy for malaria and other diseases caused by AV-sensitive pathogens.

CoQ0-induced mitochondrial PTP opening triggers apoptosis via ROS-mediated VDAC1 upregulation in HL-60 leukemia cells and suppresses tumor growth in athymic nude mice/xenografted nude mice

Coenzyme Q (CoQ) analogs with variable numbers of isoprenoid units have been demonstrated as anticancer and antioxidant/pro-oxidant molecules. This study examined the in vitro and in vivo antitumor and apoptosis activities of CoQ₀ (2,3-dimethoxy-5-methyl-1,4-benzoquinone, zero isoprenoid side-chains) through upregulation of the Voltage-dependent anion channel 1 (VDAC1) signaling pathway on human promyelocytic leukemia. CoQ₀ (0-40 μg/mL) treatment significantly reduced HL-60 cell viability, and up-regulated mitochondrial VDAC1 expression. CoQ₀ treatment triggers intracellular ROS generation, calcium release, ΔΨm collapse and PTP opening in HL-60 cells. CoQ₀ treatment induced apoptosis, which was associated with DNA fragmentation, cytochrome c release, caspase-3 and PARP activation, and Bax/Bcl-2 dysregulation. Annexin V-PI staining indicated that CoQ₀ promotes late apoptosis. Furthermore, the blockade of CoQ₀-induced ROS production by antioxidant NAC pretreatment substantially attenuated CoQ₀-induced apoptosis. The activation of p-GSK3β expression, cyclophilin D inhibition, and p53 activation through ROS are involved in CoQ₀-induced HL-60 apoptotic cell death. Notably, ROS-independent p38 activation is involved in CoQ₀-mediated apoptosis in HL-60 cells. In addition, the silencing of VDAC1 also prevented CoQ₀-induced mitochondrial translocation of Bax, activation of caspase-3, and reduction in Bcl-2. Intriguingly, VDAC1 silencing did not prevent ROS production induced by CoQ₀, which in turn indicates that CoQ₀ induced ROS-mediated VDAC1 and then mitochondrial apoptosis in HL-60 cells. In vivo results revealed that CoQ₀ is effective in delaying tumor incidence and reducing the tumor burden in HL-60-xenografted nude mice. Taken together, CoQ₀ could be a promising anticancer agent for the treatment of human promyelocytic leukemia through upregulation of VDAC1 signaling pathways.

Antitumor properties of Coenzyme Q0 against human ovarian carcinoma cells via induction of ROS-mediated apoptosis and cytoprotective autophagy

Coenzyme Q0 (CoQ0, 2,3-dimethoxy-5-methyl-1,4-benzoquinone) has been reported to exert anticancer properties against human breast/lung cancer cells. This study investigated the in vitro and in vivo anticancer properties of CoQ0 on human ovarian carcinoma (SKOV-3) cells and xenografted nude mice, and revealed the underlying molecular mechanism. CoQ0 induced G2/M arrest through downregulation of cyclin B1/A and CDK1/K2 expressions. CoQ0-induced autophagy as a survival mechanism was evidenced by increased accumulation of LC3-II, GFP-LC3 puncta, AVOs formation and Beclin-1/Bcl-2 dysregulation. Increased TUNEL-positive cells and Annexin-V/PI stained cells indicated CoQ0-induced late apoptosis. Both mitochondrial (caspase-3, PARP and Bax/Bcl-2 dysregulation) and ER stress (caspase-12 and Hsp70) signals are involved in execution of apoptosis. Interestingly, CoQ0-induced apoptosis/autophagy is associated with suppression of HER-2/neu and PI3K/AKT signalling cascades. CoQ0 triggered intracellular ROS production, whereas antioxidant N-acetylcysteine prevented CoQ0-induced apoptosis, but not autophagy. Inhibition of apoptosis by Z-VAD-FMK suppressed CoQ0-induced autophagy (diminished LC3-II/AVOs), indicates CoQ0-induced apoptosis led to evoke autophagy. Contrary, inhibition of autophagy by 3-MA/CQ potentiated CoQ0-induced apoptosis (increased DNA fragmentation/PARP cleavage). Furthermore, CoQ0 treatment to SKOV-3 xenografted nude mice reduced tumor incidence and burden. Histopathological analyses confirmed that CoQ0 modulated xenografted tumor progression by apoptosis induction. Our findings emphasize that CoQ0 triggered ROS-mediated apoptosis and cytoprotective autophagy.

Configuration of polyisoprenoids affects the permeability and thermotropic properties of phospholipid/polyisoprenoid model membranes

The influence of α-cis- and α-trans-polyprenols on the structure and properties of model membranes was analyzed. The interaction of Ficaprenol-12 (α-cis-Prenol-12, α-Z-Prenol-12) and Alloprenol-12 (α-trans-Prenol-12, α-E-Prenol-12) with model membranes was compared using high performance liquid chromatography (HPLC), differential scanning calorimetry (DSC) and fluorescent methods. l-α-Phosphatidylcholine from egg yolk (EYPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) as the main lipid components of unilamellar (SUVs) and multilamellar (MLVs) vesicles were used. The two-step extraction procedure (n-pentane and hexane, respectively) allowed to separately analyze the fractions of polyprenol as non-incorporated (Prenol(NonInc)) and incorporated (Prenol(Inc)) into liposomes. Consequently, distribution coefficients, P', describing the equilibrium of prenol content between phospholipid (EYPC) membrane and the aqueous phase gave different logP' for α-cis- and α-trans-Prenol-12, indicating that the configuration of the α-terminal residue significantly alters the hydrophobicity of the polyisoprenoid molecule and consequently the affinity of polyprenols for EYPC membrane. In fluorescence experiments α-trans-Pren-12 increased up to 1.7-fold the permeability of EYPC bilayer for glucose while the effect of α-cis-Pren-12 was almost negligible. Considerable changes of thermotropic behavior of DPPC membranes in the presence of both prenol isomers were observed. α-trans-Pren-12 completely abolished the pretransition while in the case of α-cis-Pren-12 it was noticeably reduced. Furthermore, for both prenol isomers, the temperature of the main phase transition (T(m)) was shifted by about 1°C to lower values and the height of the peak was significantly reduced. The DSC analysis profiles also showed a new peak at 38.7°C, which may suggest the concomitant presence of more that one phase within the membrane. Results of these experiments and the concomitant occurrence of alloprenols and ficaprenols in plant tissues suggest that cis/trans isomerization of the α-residue of polyisoprenoid molecule might comprise a putative mechanism responsible for modulation of the permeability of cellular membranes.

Characterisation of RC-proteoliposomes at different RC/lipid ratios

Reconstitution of membrane proteins in phospholipid vesicles allows the investigation of such macromolecules in a biomimetic simplified environment. The often employed micelle-to-vesicle-transition method for proteoliposome preparation is a fast and reproducible technique. In this, communication is shown that the lipid/protein ratio influences the size of the proteoliposomes and the actual protein reconstitution. The results indicate that for photosynthetic reaction centres, the best conditions for ligand-interaction experiments are achieved with a lipid/protein value of 1000:1, while for complete protein incorporation, the 2000:1 ratio should be chosen.

Isolation of lipids from photosystem I complex and its characterization with high performance liquid chromatography/electrospray ionization mass spectrometry

A method for simultaneous analysis of lipids extracted from photosystem I complex was developed with high performance liquid chromatography/electrospray ionization mass spectrometry. The photosystem I complex was firstly solubilized and separated using deoxycholate polyacrylamide gel electrophoresis method after ultrasonic treatment of the sample (leaves of pea, Pisum sativum L.). The Photosystem I complexes were electrophoretically eluted from the deoxycholate polyacrylamide gel electrophoresis bands containing them, and the electron transport activity of the eluent measured as confirmation. Lipids, which were isolated from the complex having photosystem I activity, were separated and characterized with high performance liquid chromatography/electrospray ionization mass spectrometry. Five lipids, monogalactosyldiacylglycerol, digalactosyldiacylglycerol, phosphatidylglycerol, sulphoquinovosyldiacylglycerol and phosphaditylcholine were found combining with photosystem I complex. Different species of these lipids were found in the ESI mass spectra and the compositions of the acyl groups in them were determined.

Influence of the chain length of ubiquinones on their interaction with DPPC in mixed monolayers

The thermodynamic behavior of representative short (UQ2), middle (UQ4 and UQ6) and long-chain (UQ10) ubiquinones (UQ) mixed with dipalmitoyl-phosphatidylcholine (DPPC) was studied in monolayers at the air-water interface. The influence of isoprenoid chain-length of UQ on miscibility of both lipids was investigated by analysis of surface pressure-area isotherms and using fluorescence microscopy. Analysis of excess areas (A(ex)) and free energies of mixing (DeltaGm), calculated from compression isotherms in the full range of ubiquinones concentrations, has given evidences for UQ-rich constant-size (UQ6, UQ10) or less growth limited (UQ2, UQ4) microdomains formation within mixed films. Fluorescence microscopy observation revealed that ubiquinones are preferentially soluble in the expanded phase. When lateral pressure increased, concomitant evolutions of A(ex) and DeltaGm parameters, and composition dependence of collapse surface pressures, argue for an evolution towards a total segregation, never reached due to expulsion of ubiquinones from the film. The possible significance of these observations is discussed in relation to ubiquinones organization and similar chain length effects in membranes.

Coenzyme Q2 induced p53-dependent apoptosis

Coenzyme Q functions as an electron carrier and reversibly changes to either an oxidized (CoQ), intermediate (CoQ.-), or reduced (CoQH2) form within a biomembrane. The CoQH2 form also acts as an antioxidant and prevents cell death, and thus has been successfully used as a supplement. On the other hand, the value of the CoQ/CoQH2 ratio has been shown to increase in a number of diseases, presumably due to an anti-proliferative effect involving CoQ. In the present study, we examined the effect of CoQ and its isoprenoid side chain length variants on the growth of cells having different p53 statuses. Treatment with CoQs having shorter isoprenoid chains, especially CoQ2, induced apoptosis in p53-point mutated BALL-1 cells, whereas treatment with longer isoprenoid chains did not. However, CoQ2 did not induce apoptosis in either a p53 wild-type cell line or a p53 null mutant cell line. These results indicated that the induction of apoptosis by CoQ2 was dependent on p53 protein levels. Moreover, CoQ2 induced reactive oxygen species (ROS) and the phosphorylation of p53. An antioxidant, l-ascorbic acid, inhibited CoQ2-induced p53 phosphorylation and further apoptotic stimuli. Overall, these results suggested that short tail CoQ induces ROS generation and further p53-dependent apoptosis.

Reproductive Fitness and Quinone Content of Caenorhabditis elegans clk-1 Mutants Fed Coenzyme Q Isoforms of Varying Length

Caenorhabditis elegans clk-1 mutants lack coenzyme Q9 and accumulate the biosynthetic intermediate demethoxy-Q9. A dietary source of ubiquinone (Q) is required for larval growth and development of the gonad and germ cells. We considered that uptake of the shorter Q8 isoform present in the Escherichia coli food may contribute to the Clk phenotypes of slowed development and reduced brood size observed when the animals are fed Q-replete E. coli. To test the effect of isoprene tail length, N2 and clk-1 animals were fed E. coli engineered to produce Q7, Q8, Q9, or Q10. Wild-type nematodes showed no change in reproductive fitness regardless of the Qn isoform fed. clk-1(e2519) fed the Q9 diet showed increased egg production; however, this diet did not improve reproductive fitness of the clk-1(qm30) animals. Furthermore, animals with the more severe clk-1(qm30) allele become sterile and their progeny inviable when fed Q7-containing bacteria. The content of Q7 in the mitochondria of clk-1 animals was decreased relative to Q8, suggesting less effective transport of Q7 to the mitochondria, impaired retention, or decreased stability. Additionally, regardless of E. coli diet, clk-1(qm30) animals contain a dysfunctional dense form of mitochondria. The gonads of clk-1(qm30) worms fed Q7-containing food were severely shrunken and disordered. The differential fertility of clk-1 mutant nematodes fed Q isoforms may result from changes in Q localization, altered recognition by Q-binding proteins, and/or potential defects in mitochondrial function resulting from the mutant CLK-1 polypeptide itself.

Anisotropy measurements of intrinsic fluorescence of prenyllipids reveal much higher mobility of plastoquinol than alpha-tocopherol in model membranes

As an alternative to a fluorescent probe approach, the intrinsic fluorescence of reduced forms of prenylquinones has been exploited, which offers a convenient means of determining directly motional properties of these molecules. The steady-state fluorescence anisotropy measurements of plastoquinols (PQH(2)) and alpha-tocopherol (alpha-Toc) incorporated into phospholipid liposomes have been performed. The effect of prenyllipid concentration, PQH(2) side chain length and the composition of the membranes has been studied. For the data interpretation, the fundamental anisotropy of alpha-Toc, PQH(2), ubiquinol-10 and alpha-tocopherolquinol, as well as the angles between the absorption and emission transition moments have been also determined. It was concluded that alpha-Toc shows very low mobility in the lipid bilayer, whereas PQH(2)-9 displays significant motional freedom in dipalmitoylphosphatidylcholine vesicles and even higher in egg yolk lecithin membranes.

Cloning and kinetic characterization of Arabidopsis thaliana solanesyl diphosphate synthase

trans -Long-chain prenyl diphosphate synthases catalyse the sequential condensation of isopentenyl diphosphate (C(5)) units with allylic diphosphate to produce the C(30)-C(50) prenyl diphosphates, which are precursors of the side chains of prenylquinones. Based on the relationship between product specificity and the region around the first aspartate-rich motif in trans -prenyl diphosphate synthases characterized so far, we have isolated the cDNA for a member of trans -long-chain prenyl diphosphate synthases from Arabidopsis thaliana. The cDNA was heterologously expressed in Escherichia coli, and the recombinant His(6)-tagged protein was purified and characterized. Product analysis revealed that the cDNA encodes solanesyl diphosphate (C(45)) synthase (At-SPS). At-SPS utilized farnesyl diphosphate (FPP; C(15)) and geranylgeranyl diphosphate (GGPP; C(20)), but did not accept either the C(5) or the C(10) allylic diphosphate as a primer substrate. The Michaelis constants for FPP and GGPP were 5.73 microM and 1.61 microM respectively. We also performed an analysis of the side chains of prenylquinones extracted from the A. thaliana plant, and showed that its major prenylquinones, i.e. plastoquinone and ubiquinone, contain the C(45) prenyl moiety. This suggests that At-SPS might be devoted to the biosynthesis of either or both of the prenylquinone side chains. This is the first established trans -long-chain prenyl diphosphate synthase from a multicellular organism.

Ubiquinol inhibition of neutral sphingomyelinase in liver plasma membrane: specific inhibition of the Mg2+-dependent enzyme and role of isoprenoid chain

In this work, the specificity of ubiquinol as inhibitor of the neutral sphingomyelinases present at the plasma membrane (Mg(2+)-dependent and -independent) and structural requirements for such inhibition have been studied. Our results have shown that ubiquinol specifically inhibits Mg(2+)-dependent neutral sphingomyelinase activity in isolated liver plasma membranes, but no significant participation of the Mg(2+)-independent enzyme was observed. Both the reduction state of the (hydro)quinone ring and the length of the hydrophobic side chain were important determinants in neutral sphingomyelinase inhibition. Ubiquinols inhibited the nSMase more efficiently than ubiquinones, and hydrophobic homologs with six or nine isoprene units were the most effective inhibitors. Inhibition of nSMase by ubiquinols displayed similarities with inhibition by manumycin and the hydroquinones F11334's, suggesting that these compounds could act as structural analogs of ubiquinol. Beyond its participation in mitochondrial energy metabolism, and as antioxidant, this novel role for ubiquinol as a neutral sphingomyelinase inhibitor should be considered an important factor to regulate lipid signaling at the plasma membrane that could be related to its beneficial effects on cells, tissues, and organisms.

The influence of structure and redox state of prenylquinones on thermotropic phase behaviour of phospholipids in model membranes

Our study was aimed to investigate the significance of the isoprenoid side chain size as well as redox state of the quinone ring for interaction of two main classes of prenylquinones: plastoquinones (PQ) and ubiquinones (UQ) with lipid bilayers. By use of differential scanning calorimetry (DSC) we have followed the thermotropic behaviour of multilamellar vesicles prepared from dipalmitoylphosphatidylcholine (DPPC) upon incorporation of increasing amount (1.3-12 mol%) of quinone (quinol) molecules. Our studies reveal that as the side chain is shorter (from 9 to 2 isoprenoid units) the height of the calorimetric profiles is reduced and the temperature of the main transition of DPPC (T(m)) decreases (T(m)=39.4 degrees C for a sample with 12 mol% of PQ-2), and then increases up to 39.8 degrees C for PQ-1. For the samples containing quinols the effect is more pronounced even at lower concentration. The greater influence of the added prenylquinones on the pretransition demonstrates a stronger distortion of the DPPC packing in the gel state. It seems that this is the isoprenoid side chain length rather than the redox state of prenylquinones that determines their effectiveness in perturbation of thermotropic properties of lipid bilayer.