Autoxidation and antioxidant activity of ubiquinol homologues in large unilamellar vesicles

The antioxidant activity of ubiquinol homologues with different side-chain length such as ubiquinol-3 and ubiquinol-7 was compared with that of alpha-tocopherol when peroxidation was induced by the water-soluble initiator 2,2'-azobis-(2-amidinopropane hydrochloride). In large unilamellar vesicles containing equal amounts of alpha-tocopherol, ubiquinol-3 and ubiquinol-7 the rates of inhibition were very similar but the stoichiometric factor of quinols was approximately 1. To explain this low value, which is one-half of that found when the autoxidation was performed in apolar solvents (Chem. Phys. Lipids (1992) 61, 121-130), the oxidation of alpha-tocopherol and ubiquinol-3 initiated by the azocompound was studied both in methanol and in dimiristoyl-lecithin vesicles. The results obtained show that the ubiquinol homologues undergo a radical chain reaction taking place at the polar interface and suggest that the average preferred location of both quinol headgroups is near to the outer surface of the bilayer.

Relative susceptibility of the thymus and thymocytes to lipid peroxidation

Thymus and thymocytes peroxidizability was studied in well defined conditions where lipid hydroperoxide dependent peroxidation occurs. The results show that: (i) lipid peroxidation is very low in thymocytes notwithstanding the higher content of arachidonic acid; (ii) the amounts of lipophilic chain-breaking antioxidants is higher in thymocytes; (iii) the thymus contains more total lipids and phospholipids. Thus the higher sensitivity to peroxidation of the thymus can be due to the replacement of thymus parenchyma by fatty tissue not correlated to an increase of lipophilic antioxidants.

Phospholipid polar heads affect the generation of oxygen active species by Fe2+ autoxidation

The possibility that phospholipid polar heads may influence Fe2+ reaction with molecular oxygen and, thus, the generation of oxygen active species was investigated. Dipalmitoyl phosphatidylcholine (DPPC) and DPPC/dipalmitoyl phosphatidic acid (DPPA) were utilized as model liposomes. Fe2+ oxidation, oxygen consumption, nitro blue tetrazolium reduction and 2-deoxyribose degradation were the parameters evaluated. Comparison of the results obtained clearly shows that the two types of polar heads differently affect iron chemistry. DPPC liposomes are ineffective. By contrast, Fe2+ oxidation by oxygen occurs in the presence of DPPC/DPPA liposomes. During this reaction, species able to reduce nitro blue tetrazolium and to degrade 2-deoxyribose are generated. The results obtained indicate that the polar heads of phospholipids, by influencing Fe2+ autoxidation, generate dangerous oxygen species which may exert an active role in the oxidation of the associated hydrophobic components of the phospholipids.

Extraction of lipids and lipophilic antioxidants from fish tissues: a comparison among different methods

1. Lipids, phospholipids and lipid soluble antioxidants were extracted from Sparus auratus liver and white muscle by three different methods and the yields obtained were compared. 2. None of the three procedures can recover the above components with the same efficiency. 3. For comparison the methods were also applied to rat liver homogenates. 4. The choice of the extraction procedures depends on the tissue investigated and on specific research requirements.

The influence of phospholipid polar head on the lipid hydroperoxide dependent initiation of lipid peroxidation

In a buffer (Mes) and at a pH (6.5) where Fe2+ is very stable, we have studied the peroxidation of liposomes catalyzed by FeCl2. The liposomes studied, prepared by sonolysis, contained either phosphatidylcholine or 1:1 molar ratio of phosphatidylcholine and phosphatidic acid. The presence of the negatively charged phospholipid causes: 1) rapid Fe2+ oxidation and oxygen consumption; 2) increased generation of lipid hydroperoxides; 3) decreased generation of thiobarbituric acid-reactive materials; 4) very low inhibition of Fe2+ oxidation and lipid hydroperoxide generation by BHT; 5) inhibition of the termination phase of lipid peroxidation at high FeCl2 concentrations. A hypothesis is proposed to explain the results obtained.

Coenzyme Q-3 as an antioxidant. Its effect on the composition and structural properties of phospholipid vesicles

Coenzyme Q-3 incorporated into the lipid bilayer at physiological concentration provided an 80% inhibition of the lipid peroxidation induced by ferrous ions. In coenzyme Q-containing vesicles, the fluorescence lifetime and the fluorescence anisotropy decay of the probe, 1,6-diphenyl-1,3,5-hexatriene, were measured in order to find out if the presence of the quinone can cause variations in the membrane organization. Our data show that two distinct populations of the probe were present and that both populations were available to quenching by coenzyme Q. The overall effects of coenzyme Q on the static and dynamic properties of the model membranes were: a very small effect in the ordering of the fatty acid chain, and a more noticeable decrease of the probe correlation time and, therefore, an increase in membrane fluidity at increasing quinone concentration. When vesicles were peroxidized in the absence of the coenzyme Q, the fluidity markedly decreased; in its presence, the fluidity was nearly unchanged. The results suggest that the antioxidant properties of coenzyme Q can be ascribed to its ability to react with free radicals. The effect on the fluidity of the lipid bilayer might imply that a requisite for a molecule to act as an efficient antioxidant could be its ability to readily diffuse within the membrane.

The influence of polyunsaturated fatty acids on spermine inhibition of lipoperoxidation. Studies on liposomes prepared with microsomal and mitochondrial phospholipids of sea bass (Dicentrarchus labrax L.) and rat liver

1. Composition of phospholipids extracted from different organelles of European sea bass liver was determined and compared with that of phospholipids extracted from the same organelles of rat liver. 2. Spermine binding to the vesicles prepared from microsomal and mitochondrial phospholipids and their aggregation was studied: these parameters indicate that only the presence of acidic phospholipids and not their unsaturation was essential for polyamine action. 3. No correlation exists between polyunsaturated fatty acid and spermine inhibition of lipid peroxidation. In fact microsomal phospholipids, which have a low content of acidic phospholipids, and a prevalent presence of phosphatidylinositol, are not protected by spermine. 4. Mitochondrial phospholipids, which have high content of cardiolipin, elicit the capability of spermine to inhibit lipid peroxidation.

Iron oxidation in Mops buffer. Effect of phosphorus containing compounds

Fe2+ autoxidation in Mops buffer both in absence and presence of substoichiometric concentrations of EDTA, H2O2 and of Fe3+ is greatly affected by phosphorus containing compounds. They increase the lag phase, characteristic of Fe2+ oxidation in this buffer, and decrease the rate of the reaction. This effect is due to the phosphates of the molecule. The ability of the different compounds tested to affect Fe2+ oxidation, however, appears to be influenced also by the rest of the molecule. The concentration of the different phosphorus containing compounds that inhibits 50% of Fe2+ oxidation is rather different. The effect exerted appears to be the result of an equilibrium between an inhibitory effect on the pathway of Fe2+ oxidation that occurs in Mops buffer and the onset of a different oxidation pathway of Fe2+ similar to that occurring in Na phosphate buffer. A hypothesis is proposed that the phosphorus containing compounds inhibit Fe2+ oxidation by binding Fe3+ and decreasing its ability to accelerate Fe2+ autoxidation. It is suggested that the presence in vitro and in vivo of phosphorus containing compounds may modify Fe2+ autoxidation and thus the production of oxygen active species.

Antioxidant behaviour of ubiquinone and beta-carotene incorporated in model membranes

Experiments with model membranes, in which ubiquinone was incorporated, were performed in order to clarify the mechanism by which ubiquinone can prevent or control chain lipid peroxidation in biomembranes. Comparing the behavior of ubiquinone-containing vesicles with beta-carotene containing vesicles we suggest that a possible explanation of the ubiquinone antioxidant effect could be to scavenge singlet oxygen and to affect structurally the lipid bilayer inhibiting hydroperoxide decomposition.

Incorporation of ubiquinones into lipid vesicles and inhibition of lipid peroxidation

Ubiquinone incorporation into vesicles to evaluate its antioxidative effect on lipid peroxidation has been studied. Only sonication and not vortication allows comparable incorporation patterns of the various ubiquinone homologues into lipid vesicles. The measure of malondialdehyde, a convenient index for determining the extent of autoxidation, shows that both the naturally occurring homologues and synthetic shorter-chain ones, also in the oxidized form, possess similar antioxidant efficiency.

Determination of the polyamine content of rat heart mitochondria by the use of heparin-sepharose

Heparin-sepharose has been utilized to remove polyamines adsorbed to the cytoplasmic surface of rat heart mitochondria. The results obtained can be summarized as follows: Heparin-sepharose removes 90% of the spermine, 98% of the spermidine, and 98% of the putrescine adsorbed. Polyamine contents of chromatographed mitochondria amount to 2.66 and 0.36 nmol spermine and spermidine, respectively, per mg of mitochondrial protein.

Antioxidative effect of ubiquinones on mitochondrial membranes

Peroxidation of mitochondria occurs extensively in ubiquinone-depleted membranes. Reincorporation into the membranes of either the physiological ubiquinone or a short-chain homologue protects mitochondria against peroxidation. The ability to prevent this phenomenon is more evident in mitochondria that have incorporated ubiquinone-3 and might be ascribed to an ordering structural effect on the lipid bilayer.

Representative applications of heparin-sepharose in the removal of polyamines from biological materials

Many experimental systems would greatly benefit from the availability of a simple and effective technique to remove polyamines from biological materials. We have examined the possibility of utilizing heparin-sepharose in the removal of polyamines from rat heart mitochondria, DNA-spermine complex, and fetal calf serum. Heparin-sepharose removes 90% of spermine adsorbed to the cytoplasmic surface of rat heart mitochondria. Heparin-sepharose almost totally removes spermine from DNA-spermine complex, leaving less than 0.003 mol spermine/mol DNA phosphorus. Heparin-sepharose is highly effective in removing spermine and spermidine (99.5 and 95% adsorbed, respectively) from fetal calf serum. Under the same experimental conditions only 50% of putrescine is adsorbed. A higher amount of resin corresponding to an increased capacity for putrescine must be used to achieve a satisfactory removal of putrescine.

On the mechanism of inhibition of NADH oxidase by ubiquinone-3

The combined effects of rotenone and ubiquinone-3 on the kinetics of NADH dehydrogenase and NADH oxidase have been investigated. The two inhibitors do not show additivity; on the other hand, ubiquinone-3, when preincubated with the enzyme, partially removes rotenone sensitivity. The inhibition of NADH oxidase by ubiquinone-3 is the result of at least two combined effects: the competition of the less active ubiquinone-3 with endogenous ubiquinone-10 in the acceptor site of the dehydrogenase, and a nonspecific action on the structure of complex I. The latter effect is perhaps mediated by a physical change of the phospholipid bilayer similar to that observed with agents such as butanol, perturbing lipid-protein interactions in the membrane.

Lipid protein interactions in mitochondria. VII. A comparison of the effects of lipid removal and lipid perturbation of the kinetic properties of mitochondrial ATPase

We investigated the kinetics of mitochondrial ATPase in bovine heart mitochondria and submitochondrial particles upon treatment with phospholipase A2, or upon addition of n-butanol to perturb the lipid protein interactions. The changes observed are the following: (1) Lipid removal or perturbation with butanol is accompanied by loss of ATPase activity with decrease of both V and of the KM for ATP. (2) There are changes of activation energy of ATPase activity at temperatures above the discontinuity normally observed for membrane-bound enzymes in mitochondria. In particular, butanol abolishes the discontinuity, and induces a constant activation energy of about 32 kcal/mol in the range 8--37 degrees C. (3) Butanol modifies the pH dependence of ATPase shifting the pH optimum from around 10 to less alkaline values. The optimum for Mg2+ concentrations is increased by the solvent. (4) Treatment with phospholipase A2 results in a removal of oligomycin-sensitive ATPase, whereas butanol addition prevents oligomycin inhibition of ATPase. (5) In beef heart mitochondria, a spin-labelled analog of the inhibitor, dicyclohexyl carbodiimide, did not show any change in environment upon butanol addition, unlike that found in mitochondria from Saccharomyces cerevisiae.

A role of ubiquinone in energy conservation in mitochondria

Short chain ubiquinones (Q-3) uncouple oxidative phosphorylation in rat heart mitochondria, as shown by polarimetric experiments, and abolish P:O ratios in succinate driven oxidative phosphorylaton. The uncoupling is reversed by long chain ubiquinones (Q-7). Furthermore, short chain ubiquinones abolish oligomycin sensitivity of ATPase; the inhibition is restored by Q-7. The extraction of endogenous ubiquinone from mitochondria reversibly lowers oligomycin sensitivity of ATPase.

Fromation and stoichiometry of a lysozyme-phospholipid-mitochondrial protein ternary complex

Mitochondrial membranes reconstituted from lipid-depleted mitochondria and aqueous phospholipid dispersions still have the phospholipid negative charges available for ionic interaction with the basic protein, lysozyme. The stoichiometry of the binding is of about 6 nmoles of lysozyme per 100 nmoles of phospholipid in membranes reconstituted with Asolectin, and of 10 nmoles of phospholipid phosphorus in membranes reconstituted with cardiolipin. Unextracted submitochondrial particles ETP also bind lysozyme (about 3 nmoles per 100 nmoles of phospholipid). These observations indicate that the phospholipid anionic groups are not completely shielded by the mitochondrial proteins, which might occupy areas between the nonpolar groups of the lipid molecules.

Lipid metabolism in fatty liver of lysine- and threonine-deficient rats

Rats were fed a low protein diet deficient in and supplemented with lysine and threonine. Liver lipids contained more lecithin, sphingomyelin, and free fatty acids, and less amino phospholipids in the deficient rats. No variations in fatty acid composition of choline- and ethanolamine-containing phospholipids were found; only palmitic acid was increased in the serine-containing phospholipids of the deficient animals. The incorporation of acetate-(14)C into phospholipids, but not into other liver lipids, was lower in deficient rats. In the plasma of deficient rats the concentration of esterified fatty acids and phospholipids was lower, of free fatty acids higher, than in the controls. The fatty acid composition of depot fat differed from that of liver neutral fat both in deficient and supplemented animals. The results presented establish that multiple metabolic defects resulting from lysine and threonine deficiency accompany the fatty liver. The design of the experiments does not permit conclusions to be drawn regarding the causal relationship between the various alterations in lipid metabolism and the fatty liver.