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D Fiorentini

Publications and source records attributed to D Fiorentini.

27 records · Page 2Linked to original sources
PubMed1991

Ubiquinol prevents alpha-tocopherol consumption during liposome peroxidation.

In this study we investigated whether alpha-tocopherol can be spared by ubiquinol-3 during autoxidation of multilamellar liposome. A lipophilic azocompound, 2,2'-azobis-(2,4-dimethyl-valeronitrile), was chosen to initiate liposome autoxidation. The effect of either alpha-tocopherol, ubiquinol-3, or a mixture of them was compared. Rates of conjugated diene formation and concomitant disappearance of the two antioxidants was measured. Since the inhibition rate constant for the scavenging of peroxyl radical for alpha-tocopherol was higher than that for quinol-3, it was concluded that alpha-tocopherol is regenerated by ubiquinol-3.

Free Radicals↗
PubMed1990

Inhibition of autoxidation of egg yolk phosphatidylcholine in homogenous solution and in liposomes by oxidized ubiquinone.

The aim of this study was to obtain a quantification of the antioxidant activity of ubiquinone. To this purpose the oxidation of egg yolk phosphatidylcholine both in solvent and in liposomes initiated by an azocompound has been studied either in the absence or in the presence of ubiquinone-3, using alpha-tocopherol as a reference antioxidant. The two experimental systems gave similar results. In the presence of ubiquinone-3 the oxidation rate was reduced with respect to control experiments but was faster than that in the presence of alpha-tocopherol. The amount of ubiquinone required to decrease the autoxidation rate was so high as to prevent detection of the induction period. The stoichiometric factor was greater than 2 and the rate constant of inhibition was two orders of magnitude lower than that of alpha-tocopherol. It is concluded that high concentrations of ubiquinone are required to exhibit significant antioxidant activity. A possible mechanism compatible with the stoichiometric factor larger than 2 for the inhibiting effect of ubiquinone is also suggested.

Liposomes↗
PubMed1989

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.

Animals↗
PubMed1989

Buffers can modulate the effect of sonication on egg lecithin liposomes.

When model membranes are prepared by ultrasonic irradiation of polyunsaturated phospholipids, radical production can induce a partial degradation of the polyunsaturated fatty acyl chains and the formation of lipid hydroperoxides. A suitable buffer employed during liposome preparation, like Hepes or Tris, is able to exhibit a protective effect against lipid peroxidation. Hepes has been found to be the most effective: a 10 mM concentration provides a 70% protection after 30 min sonication. Tris, in the same conditions, exhibits a 50% protection. These findings may be explained on the basis of the rate constants of these organic buffers with hydroxyl radicals.

Buffers↗
PubMed1989

Lipid peroxidation. Definition of experimental conditions for selective study of the propagation and termination phases.

To find experimental conditions to selectively study the propagation phase of lipoperoxidation we studied the lipoperoxidation, catalyzed by FeCl2, of liposomes in a buffering condition where Fe2+ autoxidation and oxygen active species generation does not occur. Liposomes from egg yolk phosphatidylcholine, prepared by vortex mixing, do not oxidize Fe2+; on the contrary they oxidize Fe2+ when prepared by ultrasonic irradiation. Dimyristoyl phosphatidylcholine liposomes prepared by ultrasonic irradiation do not oxidize Fe2+. During sonication polyunsaturated fatty acid residues autoxidize and lipid hydroperoxides (LOOH) are generated. Only when LOOH are present in the liposomes Fe2+ oxidizes and its rate of oxidation depends on the amount of LOOH in the assay. The reaction results in the generation of both LOOH and thiobarbituric acid reactive material (TBAR); it is inhibited by butylated hydroxytoluene and has a acidic pH optimum; it is not inhibited by catalase and OH scavengers. The reaction studied, thus, appears to be the chain branching and propagation phase of lipoperoxidation. When we studied the dependence of Fe2+ oxidation, LOOH and TBAR generation on FeCl2 concentration, we observed that at high FeCl2 concentrations the termination phase of lipoperoxidation was prevalent. Thus, by selecting the appropriate FeCl2 concentration the proposed experimental system allows study of either the propagation or the termination phase of lipoperoxidation.

Ferrous Compounds↗
PubMed1988

Effect of AD6 (8-monochloro-3-beta-diethylamino-ethyl-4-methyl-7-ethoxycarbonylme tho xy coumarin) on cyclic nucleotide phosphodiesterases in human platelets.

The effect of AD6 (8-monochloro-3-beta-diethylamino-ethyl-4-methyl-7-ethoxycarbonylmeth oxy coumarin), an inhibitor of platelet aggregation, on cyclic nucleotide metabolism was investigated. AD6 inhibited selectively human platelet cyclic GMP phosphodiesterase, which was separated from cyclic AMP phosphodiesterase by DEAE-cellulose chromatography. Addition of AD6 to washed platelets increased cyclic GMP levels significantly in two minutes. These results could be useful in elucidating the action of AD6 on intact platelets.

3',5'-Cyclic-GMP Phosphodiesterases↗
PubMedDate not supplied

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.

Antioxidants↗
PubMedDate not supplied

Reactions of oxygen radicals with the quinone ring of coenzyme Q.

Coenzyme Q, besides its role in electron transfer reactions, may act as a radical scavenger. The effect of oxygen radicals produced by ultrasonic irradiation on the quinone ring was investigated. Aqueous solutions of a Q homologue, completely lacking the side chain, were irradiated and the modifications were spectrophotometrically followed. The experimental results show that both degradation and reduction of the benzoquinone ring took place when the irradiation was performed in water. Data obtained when ultrasonic irradiation was carried out in the presence of OH. scavengers, as formate, organic and inorganic buffers, suggest: a) the responsible species for most the ubiquinol generated by sonication appeared to be the superoxide radical b) addition reactions of OH. radicals with the aromatic ring led probably to the degradation of Coenzyme Q molecules.

Formates↗