Mikhail Kisel

Radiation-induced peroxidation and fragmentation of lipids in a model membrane

Purpose : To ascertain the possibility of fragmentation processes in lipid membranes when acted upon with γ-radiation under various conditions, and to evaluate fragmentation processes quantitatively in comparison with the lipid peroxidation processes. Materials and methods : Phospholipids as components of multilamellar liposomes exposed to 137 Cs γ-rays at dose-rates of 0.06 and 0.33 Gy s -1 in the dose range 0-18 kGy. Peroxidation products were determined spectrophotometrically and fragmentation products were analysed using thin-layer chromatography and GLC methods. Results : Phosphatidylglycerol containing unsaturated fatty acid residues and free hydroxyl groups underwent both peroxidation and fragmentation when its aqueous dispersions were treated with ionizing radiation. γ-Radiolysis of multilamellar liposomes led to the formation of peroxidation products, as well as phosphatidic acid and hydroxyacetone, fragmentation products of the initial lipid. Comparable radiation-chemical yields of conjugated-diene products and phosphatidic acid indicate that the probabilities of oxidation and fragmentation processes to occur are approximately equal in this case. In contrast to lipid peroxidation, lipid fragmentation is not accelerated but suppressed by oxygen and appears to be a prevailing process in de-aerated solutions. The phosphatidic acid formed as a result of phosphatidylglycerol fragmentation can intensify the lipid peroxidation. Conclusions : Treatment of lipid membranes with ionizing radiation leads to the destructive processes within both hydrophobic and hydrophilic moiety of lipids.

Formation of phosphatidic acid in stressed mitochondria.

Mitochondria are an important intracellular source of ROS as well as a sensitive target for oxidative damage under certain pathological conditions such as iron or copper overload. Mitochondrial membranes are rich in the tetraacyl phospholipid cardiolipin. Its integrity is important for efficient oxidative phosphorylation. Mouse liver mitochondria were subjected to oxidative stress by the Cu(2+)(Fe(2+))/H(2)O(2)/ascorbate system. Phosphatidic acid was detected in oxidized mitochondria, but not in unperturbed mitochondria. The Cu(2+)/H(2)O(2)/and (or not) ascorbate system caused the formation of phosphatidic acid and phosphatidylhydroxyacetone in cardiolipin liposomes. These products proceed via an HO*-radical induced fragmentation taking place in the polar moiety of cardiolipin. Mass spectrometry analysis of phosphatidic acid newly formed in mitochondria revealed that it has been derived from fragmentation of cardiolipin. Thus, free-radical fragmentation of cardiolipin in its polar part with the formation of phosphatidic acid is a likely mechanism that damages mitochondria under conditions of oxidative stress.

Synthesis and Properties of 11-(3,5-Di-tert-butyl-2- hydroxyphenylcarbamoyl)undecanoic Acid, a New Amphiphilic Antioxidant

Based on the membrane addressing concept, designing and synthesis of 11-(3,5-di-tert-butyl-2-hydroxyphenylcarbamoyl)undecanoic acid have been carried out. Antioxidant properties of the prepared compound were investigated in comparison with its non-amphiphilic analogues.

γ- and UV-radiation-induced degradation of sphingomyelin, lysosphingomyelin, and related compounds

The experimental data on the formation of final products in the radiolysis of 2-aminoglycerol and lysosphingomyelin (sphingosine phosphocholine) and in the photolysis of N-(2-hydroxypropyl)hexanamide and sphingomyelin suggest the occurrence of the radiation-induced degradation of the above substances with C-C bond cleavage. It was hypothesized that this process occurs by the formation and subsequent degradation of the N-centered radicals of the substrates.

Dopamine and iron mediated fragmentation of galactocerebroside and cardiolipin in micelles

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and thin-layer chromatography (TLC) have been used to study dopamine and iron mediated free-radical transformation of lipids in their hydrophilic parts. It has been shown that the action of the dopamine/Fe2+ system on galactocerebroside or cardiolipin, which are the components of mixed micelles, results in formation of ceramide or phosphatidic acid and phosphatidylhydroxyacetone, respectively. These data, when combined with results obtained using the ascorbate/Fe2+/H2O2 oxidizing system with the same substrates, demonstrate that the formation of these products proceeds via an OH-radical induced fragmentation taking place in polar moiety of the starting lipids.

Effect of structure of polar head of phospholipids on their fragmentation during γ-irradiation of model membranes

The ability of phospholipids with different structures of the polar head (phosphatidylpropandiol, phosphatidylglycerol, phosphatidylinositol, and cardiolipin) to sustain radiation-induced fragmentation was studied. It was shown by thin-layer chromatography and MALDI-TOF mass spectroscopy that all test lipids entering the composition of model membranes subjected to γ-irradiation suffered fragmentation yielding phosphatidic acid. The radiation-chemical yield of phosphatidic acid increased in this phospholipid series on passing from phosphatidylpropanediol to cardiolipin.

Effect of calcium(II) ions on the radiation-induced free-radical fragmentation of dimyristoyl phosphatidylglycerol as a constituent of model membranes

The effect of Ca2+ ions on the radiation-initiated reaction of free-radical fragmentation of dimyristoyl phosphatidylglycerol arranged as monolamellar and multilamellar liposomes was examined. It was found that the formation of the reaction products dimyristoyl phosphatidic acid and hydroxy acetone was considerably reduced in the presence of Ca2+ ions at all γ-irradiation doses examined regardless of the type of model membranes.