Membrane lipid peroxidation by UV-A: mechanism and implications

UV-A produced a dose-dependent linear increase of lipid peroxidation in liposomal membrane, as detected by the assay of (i) conjugated dienes, (ii) lipid hydroperoxides, (iii) malondialdehydes (MDA), and (iv) the fluorescent adducts formed by the reaction of MDA with glycine and also a linear dose-dependent increase of [14C]glucose efflux from the liposomes. UV-A-induced MDA production could not be inhibited by any significant degree by sodium formate, dimethyl sulfoxide, EDTA, or superoxide dismutase but was very significantly inhibited by butylated hydroxytoluene, alpha-tocopherol, sodium azide, L-histidine, dimethylfuran, and beta-carotene. MDA formation increased with an increase in the D2O content in water, leading to a maximal amount of nearly 50% enhancement of lipid peroxidation in 100% D2O vis-à-vis water used as dispersion medium. The experimental findings indicate the involvement of singlet oxygen as the initiator of the UV-A-induced lipid peroxidation.     

The induction of lipid peroxidation in liposomal membrane by ultrasound and the role of hydroxyl radicals

Ultrasonic radiation produced a dose-dependent linear increase in lipid peroxidation in the liposomal membrane as reflected in the measurements of conjugated dienes, lipid hydroperoxides, and malondialdehydes (MDA). Production of MDA was confirmed by spectrophotometric and spectrofluorometric methods including the detection of excitation (360 nm) and emission (435 nm) maxima characteristic of the MDA-glycine adduct formed after addition of glycine in the system. Ultrasound of frequencies 20 kHz (used for laboratory purposes) and 3.5 MHz (used for clinical purposes) produced MDA in an identical manner. Ultrasound-induced lipid peroxidation was enhanced synergistically by 2.5 X 10(2) microM ascorbic acid but inhibited significantly by 10(4) microM ascorbic acid. Ultrasound-induced production of MDA could not be inhibited to any significant degree by superoxide dismutase, histidine, dimethylfuran, or beta-carotene but was very significantly inhibited by cholesterol (93%), butylated hydroxytoluene (88%), alpha-tocopherol (85%), sodium benzoate (80%), dimethyl sulfoxide (80%), sodium formate (64%), and EDTA (64%). The scavenger studies indicated the functional role of OH radicals in the initiation of ultrasound-induced lipid peroxidation.     

Effect of antiperoxidative drugs on gastric damage induced by ethanol in rats

Lesion formation due to oral administration of absolute ethanol could be prevented by parenteral pretreatment with antiperoxidative drugs such as butylated hydroxytoluene (BHT), quercetin and quinacrine. Also effective were allopurinol and oxypurinol, inhibitors of xanthine oxidase, but not superoxide dismutase (SOD) and hydroxyl radical scavengers, such as sodium benzoate and dimethyl sulfoxide (DMSO). BHT, quercetin, quinacrine and sulfhydryl compounds such as reduced glutathione and cysteamine which offer gastroprotection in vivo against ethanol inhibited lipid peroxidation induced in vitro by ferrous ion in porcine gastric mucosal homogenate, but SOD, sodium benzoate, DMSO, allopurinol and oxypurinol did not. These results suggest the possibility that an active species, probably derived from free iron mobilized by the xanthine oxidase system, other than oxygen radicals such as hydroxyl radicals, contributes to lipid peroxidation and lesion formation in the gastric mucosa after absolute ethanol administration.     

Phospholipid peroxidation induced by the catechol-Fe3+(Cu2+) complex: a possible mechanism of nigrostriatal cell damage

Ferric or cupric ions significantly promoted a peroxidative cleavage of unsaturated phospholipids in liposomes in vitro after coordinating with dopa and dopamine. Either alpha-tocopherol or desferrioxamine completely abolished the dopa-Fe3+ complex-induced phospholipid peroxidation, while superoxide dismutase, catalase, or sodium benzoate did not. A ferroxidase, ceruloplasmin, significantly inhibited the lipid peroxidation induced by the dopa-Fe3+ complex, indicating the importance of the reduction of the iron moiety in the complex for the lipid peroxidation. A possible mechanism of dopa-Fe3+ complex-induced phospholipid peroxidation is that oxene complexes, such as Fe(V) = O and Fe(IV) = O, produced abstract hydrogen atoms in unsaturated phospholipids to initiate lipid peroxidation.     

Ultrasonic radiation induced lipid peroxidation in liposomal membrane

Summary Ultrasonic radiation produced a dose dependent linear increase in lipid peroxidation (MDA formation) in the liposomal membrane. The yield of MDA was significantly inhibited by butylated hydroxytoluene (BHT), the antioxidant, sodium formate, the OH radical scavenger, and EDTA, the metal ion chelator. Ascorbic acid at low concentration increased the ultrasonic induced MDA formation while high concentrations inhibited lipid peroxidation. A mechanism of ultrasound induced lipid peroxidation is suggested.     

An approach towards understanding the genesis of sunlight-induced skin cancer

The molecular basis of the sunlight-induced skin carcinogenesis has been elucidated. Of the two ultraviolet components of sunlight that reach the earth's surface the UV-B is known to be carcinogenic but the mode of action of UV-A, the predominant component of sunlight, is ill understood. Using the liposomes as a model system, it has been shown here that UV-A causes dose-dependent lipid peroxidation as estimated by measurements of conjugated dienes, lipid hydroperoxides, malondialdehydes and the fluorescent adducts (Schiff bases) produced by the reaction of MDA with glycine. Direct exposure to sunlight has also been shown to cause dose-dependent lipid peroxidation. The UV-A induced lipid peroxidation has also been shown to be dependent on dose rate. While the sodium formate, dimethyl sulphoxide, superoxide dismutase and EDTA do not have any significant effect, sodium azide, histidine, beta-carotene and dimethylfuran were shown to inhibit significantly the UV-A induced lipid peroxidation, thereby providing significant evidence of the involvement of singlet oxygen (1O2) as the initiating agent. The use of D2O in place of H2O as the liposome dispersing medium enhanced to great extent the UV-A induced lipid peroxidation, thereby lending additional support to the finding that singlet oxygen was the initiating agent. The possible mode of formation of 1O2 on exposure to UV-A was discussed. This study also highlighted the role of environmental factors on the sunlight-induced cutaneous damage. Finally, the relation between lipid peroxidation, DNA damage and carcinogenesis has been discussed in a way to suggest the possible link between sunlight exposure and causation of skin cancer.     

Influence of superoxide generating system, vitamin E, and superoxide dismutase on radiation consequences.

During studies of the mechanism by which hemolysis is induced in irradiated human erythrocytes in vitro, several inducements of membrane lipid peroxidation and protective effects of vitamin E (V.E) and superoxide dismutase (SOD) were investigated. Findings were: (1) Before hemolysis, K+ release from erythrocytes induced by radiation stimulated hemolysis but was inhibited by V.E or SOD. (2) Lipid peroxidation of mitochondria induced by Fe3+, ADP, and superoxide (O2-) generating system, and lipid peroxidation of microsome induced by O2- generating system, were also inhibited by V.E or SOD. (3) X-ray or 60Co gamma-ray radiation stimulated lipid peroxidation of liver homogenate, microsome, and liposome. Some of this peroxidation was inhibited by V.E. or SOD. These results suggest that O2- and/or OH formation by radiation induces membrane lipid peroxidation, which causes deterioration of membrane resulting in change of ion permeability and consequent hemolysis.     

Arsenite-induced lipid peroxidation in Saccharomyces cerevisiae

The ability of sodium arsenite at concentrations of 10(-2), 10(-4), and 10(-6) M to induce lipid peroxidation in Saccharomyces cerevisiae cells was studied. Arsenite at the concentrations 10(-2) and 10(-4) M enhanced lipid peroxidation and inhibited the growth of yeast cells. Enhanced lipid peroxidation likely induced oxidative damage to various cellular structures, which led to suppression of the metabolic activity of cells. Arsenite at the concentration 10(-6) M did not activate lipid peroxidation in cells. All of the tested arsenite concentrations inhibited the activity of alpha-ketoglutarate dehydrogenase and pyruvate dehydrogenase in cells. The inference is made that the toxicity of arsenite may be related to its stimulating effect on intracellular lipid peroxidation.     

Antistress effects of vitamin E and dimethylsulfoxide during their combined administration in low doses

Low doses of vitamin E (5 mg/kg body weight) and dimethyl sulfoxide (50 mg/kg) given simultaneously orally to albino rats prevented the disturbances of the behaviour and vegetative functions induced by chronic emotional painful stress. The adaptive effect of vitamin E or dimethyl sulfoxide given alone was much lower or altogether absent. The antioxidant combination used decreased the intensity of lipid peroxidation in the brain and blood serum as well as cholesterol content in brain lipids and activated brain superoxide dismutase and nonenzymatic superoxide scavenging activity of the serum. The results obtained suggest that the combination of vitamin E with dimethyl sulfoxide may be used for the treatment of pathological conditions accompanied by lipid peroxidation syndrome.     

Cholate solubilization of liver microsomal membrane components which promote NADPH-supported lipid peroxidation.

NADPH-supported lipid peroxidation monitored by malondialdehyde (MDA) production in the presence of ferric pyrophosphate in liver microsomes was inactivated by heat treatment or by trypsin and the activity was not restored by the addition of purified NADPH-cytochrome P450 reductase (FPT). The activity was differentially solubilized by sodium cholate from microsomes, and the fraction solubilized between 0.4 and 1.2% sodium cholate was applied to a Sephadex G-150 column and subfractionated into three pools, A, B, and C. MDA production was reconstituted by the addition of microsomal lipids and FPT to specific fractions from the column, in the presence of ferric pyrophosphate and NADPH. Pool B, after removal of endogenous FPT, was highly active in catalyzing MDA production and the disappearance of arachidonate and docosahexaenoate, and this activity was abolished by heat treatment and trypsin digestion, but not by carbon monoxide. The rate of NADPH-supported lipid peroxidation in the reconstituted system containing fractions pooled from Sephadex G-150 columns was not related to the content of cytochrome P450. p-Bromophenylacylbromide, a phospholipase A2 inhibitor, inhibited NADPH-supported lipid peroxidation in both liver microsomes and the reconstituted system, but did not block the peroxidation of microsomal lipid promoted by iron-ascorbate or ABAP systems. Another phospholipase A2 inhibitor, mepacrine, poorly inhibited both microsomal and pool-B'-promoted lipid peroxidation, but did block both iron-ascorbate-driven and ABAP-promoted lipid peroxidation. The phospholipase A2 inhibitor chlorpromazine, which can serve as a free radical quencher, blocked lipid peroxidation in all systems. The data presented are consistent with the existence of a heat-labile protein-containing factor in liver microsomes which promotes lipid peroxidation and is not FPT, cytochrome P450, or phospholipase A2.     

Lipid peroxidation induced by phenylbutazone radicals

Lipid peroxidation was investigated to evaluate the deleterious effect on tissues by phenylbutazone (PB). PB induced lipid peroxidation of microsomes in the presence of horseradish peroxidase and hydrogen peroxide (HRP-H2O2). The lipid peroxidation was completely inhibited by catalase but not by superoxide dismutase. Mannitol and dimethylsulfoxide had no effect. These results indicated no paticipation of superoxide and hydroxyl radical in the lipid peroxidation. Reduced glutathione (GSH) efficiently inhibited the lipid peroxidation. PB radicals emitted electron spin resonance (ESR) signals during the reaction of PB with HRP-H2O2. Microsomes and arachidonic acid strongly diminished the ESR signals, indicating that PB radicals directly react with unsaturated lipids of microsomes to cause thiobarbituric acid reactive substances. GSH sharply diminished the ESR signals of PB radicals, suggesting that GSH scavenges PB radicals to inhibit lipid peroxidation. Also, 2-methyl-2-nitrosopropan strongly inhibited lipid peroxidation. R-Phycoerythrin, a peroxyl radical detector substance, was decomposed by PB with HRP-H2O2. These results suggest that lipid peroxidation of microsomes is induced by PB radicals or peroxyl radicals, or both.     

Lipid peroxidation associated protein damage in rat brain crude synaptosomal fraction mediated by iron and ascorbate

In crude synaptosomal fractions from rat brain exposed to iron and ascorbate, enhanced lipid peroxidation (more than 3-fold compared to control), loss of protein thiols up to the extent of 40% compared to control, increased incorporation of carbonyl groups into proteins (more than 4.5-fold compared to control) and non-disulphide covalent cross-linking of membrane proteins have been observed. The phenomena are not inhibited by catalase or hydroxyl radical scavengers like mannitol or dimethyl sulphoxide. However, chain breaking antioxidants like alpha-tocopherol and butylated hydroxytoluene prevent both lipid peroxidation and accompanying protein oxidation. It is suggested that in this system lipid peroxidation propagated by the decomposition of preformed lipid hydroperoxides by iron and ascorbate is the primary event and products of the peroxidation process cause secondary protein damage. In view of high ascorbate content of brain and availability of several transition metals, such ascorbate mediated oxidative damage may be relevant in the aetiopathogenesis of several neurodegenerative disorders as well as ageing of brain.     

Effect of seminal plasma antioxidant on lipid peroxidation in spermatozoa, mitochondria and microsomes

Seminal plasma antioxidant inhibited ascorbate/iron-induced lipid peroxidation in spermatozoa, brain and liver mitochondria. The concentration required to produce inhibition in brain and liver mitochondria was high. Denaturation of spermatozoa resulted in complete loss of antioxidant action. Maintenance of native structure was essential for action of seminal plasma antioxidant in spermatozoal lipid peroxidation. The antioxidant inhibited NADPH, Fe3+-ADP induced lipid peroxidation in microsomes and consequences of lipid peroxidation such as glucose-6-phosphatase inactivation were prevented by presence of antioxidant. It did not inhibit microsomal lipid peroxidation induced by ascorbate and iron and xanthine-xanthine oxidase.     

Inhibitory effects of calcium antagonists on mitochondrial swelling induced by lipid peroxidation or amchidonic acid in the rat brain in vitro

Inhibitory effects of calcium antagonists, efonidipine (NZ-105), nicardipine, nifedipine, nimodipine and flunarizine, on mitochondrial swelling induced by lipid peroxidation or arachidonic acid in the rat brain in vitro were investigated. Mitochondrial swelling and lipid peroxidation induced by FeSO₄ and ascorbic acid system showed a close and significant relationship. Mitochondrial swelling and lipid peroxidation induced by FeSO₄ and ascorbic acid were inhibited by all of calcium antagonists tested. The order of inhibition was: flunarizine>nicardipine>efonidipine>nimodipine>nifedipine. This result suggests that calcium antagonists tested have antiperoxidant activities resulting in protection of mitochondrial membrane damage and that each moiety of these structures would play an important role in appearance of anti-peroxidant activities. Furthermore, flunarizine and efonidipine inhibited mitochondrial swelling induced by arachidonic acid, which is not associated with lipid peroxidation. In contrast, nicardipine, nifedipine, and nimodipine did not inhibited this swelling. It is possible that flunarizine and efonidipine could directly interact with mitochondrial membrane. In conclusion, it is capable that calcium antagonists tested may protect from the membrane damage induced by lipid peroxidation and that flunarizine and efonidipine could stabilize the membrane, which is attributed to a direct interaction with the membrane.     

Inhibition of lipid peroxidation by a novel compound (CV-2619) in brain mitochondria and mode of action of the inhibition

Lipid peroxidation in rat brain mitochondria was induced by NADH in the presence of ADP and FeCl3. CV-2619 inhibited the lipid peroxidation in a concentration-dependent manner; the concentration giving 50% inhibition (IC50) was 84 microM. In addition, the inhibitory effect of CV-2619 was strongly enhanced by adding substrates of mitochondrial respiration; when succinate, glutamate, or succinate plus glutamate was added, the IC50 of CV-2619 was changed to 1.1, 10, or 0.5 microM, respectively. Metabolites of CV-2619 also inhibited the lipid peroxidation. The inhibitory effect of CV-2619 on mitochondrial lipid peroxidation disappeared when TTFA, an inhibitor of complex II in mitochondrial respiratory chain, was added. The results indicate that in mitochondria CV-2619 is changed to its reduced form which inhibits lipid peroxidation.     

Polyunsaturated fatty acids promote 8-hydroxy-2-deoxyguanosine formation through lipid peroxidation under the glutamate-induced GSH depletion in rat glioma cells

It has been reported that glutamate decreased the intracellular glutathione (GSH) concentration and thereby induced cell death in C6 rat glioma cells. Polyunsaturated fatty acids such as arachidonic acid, gamma-linolenic acid, and linoleic acid enhanced lipid peroxidation promoting 8-hydroxy-2'-deoxyguanosine (8-OH-dG) formation under the glutamate-induced GSH-depletion. The enhancement of lipid peroxidation by polyunsaturated fatty acids was species-dependent. Some antioxidants capable of scavenging oxygen and lipid radicals and some iron or copper scavengers inhibited both the lipid peroxidation and the 8-OH-dG formation, consequently protecting against cell death induced by glutamate-induced GSH depletion. These results suggest that GSH depletion caused by glutamate induces lipid peroxidation and consequently 8-OH-dG formation and that polyunsaturated fatty acids enhance lipid peroxidation associated with mediated 8-OH-dG formation through a chain reaction.     

远紫外辐射对紫杉幼苗针叶膜脂过氧化及内源保护系统的影响

实验室条件下用远紫外线(UV-BC)光源照射紫杉幼苗,随照射时间延长,针叶的离子渗出率、膜脂过氧化水平、组织自动氧化速率及H₂O₂含量显著增加,可溶性蛋白、抗坏血酸、类胡萝卜素和叶绿素含量下降,叶绿体光系统II电子传递活性显著下降,外源活性氧清除剂苯甲酸钠和抗坏血酸对针叶膜脂过氧化有抑制作用;甲基紫精和DDC对针叶膜脂过氧化有促进效果,远紫外线引起的紫杉伤害可能和针叶树的越冬光氧化伤害有类似之处.紫杉苗对紫外辐射的抗性远高于一般农作物.     

Lipoxygenase may be involved in cationic liposome-induced macrophage apoptosis

The purpose of this study was to determine the source of reactive oxygen species (ROS) generation and the contribution of ROS to the apoptosis of RAW264.7 cells induced by cationic liposomes. Cationic liposome-induced apoptosis was inhibited by lipoxygenase inhibitors, but not inhibitors of NADPH-oxidase, xanthine oxidase or cyclooxygenase. ROS generation induced by cationic liposomes was also inhibited by the lipoxygenase inhibitor NDGA. Furthermore, lipid peroxidation was observed following liposome treatment, but the apoptosis was not inhibited by the antioxidant alpha-tocopherol. These findings suggested that lipoxygenase is responsible for ROS generation, and ROS but not lipid peroxidation acts as a key mediator in the progress of apoptosis induced by cationic liposomes.     

The antioxidant action of ketoconazole and related azoles: comparison with tamoxifen and cholesterol

The azole antifungal drug ketoconazole was found to inhibit Fe(III)-ascorbate dependent lipid peroxidation using either rat liver microsomes or ox-brain phospholipid liposomes as the substrate. It also inhibited microsomal peroxidation induced by the Fe(III)-ADP/NADPH system. The related azoles, miconazole and clotrimazole, were much weaker inhibitors than ketoconazole. Ketoconazole was approximately equipotent with the triphenylethylene anticancer drug tamoxifen in the microsomal system and was almost as effective as 4-hydroxytamoxifen in the liposomal system. Ketoconazole introduced into phospholipid liposomes during their preparation inhibited Fe(III)-ascorbate induced lipid peroxidation to a greater extent than similarly introduced cholesterol, ergosterol or tamoxifen. Miconazole and clotrimazole were again poor inhibitors of lipid peroxidation in this system. These antioxidant effects of ketoconazole may be due to membrane stabilization in the systems used. The implications of our findings for the clinical applications of these drugs are discussed.     

Role of hydroxyl radical in superoxide induced microsomal lipid peroxidation: Protective effect of anion channel blocker

Treatment of bovine pulmonary artery smooth muscle microsomes with the superoxide radical generating system hypoxanthine plus xanthine oxidase stimulated iron release, hydroxyl radical production and lipid peroxidation. Pretreatment of the microsomes with deferoxamine or dime thy lthiourea markedly inhibited lipid peroxidation, and prevented hydroxyl radical production without appreciably altering iron release. The superoxide radical generating system did not alter the ambient superoxide dismutase activity. However,addition of exogenous superoxide dismutase prevented superoxide radical induced iron release,hydroxyl radical production and lipid peroxidation. Simultaneous treatment of the microsomes with deferoxamine, dimethylthiourea or superoxide dismutase prevented hydroxyl radical production and liqid peroxidation. While deferoxamine or dimethylthiourea did not appreciably alter iron release, superoxide dismutase prevented iron release. However, addition of deferoxamine, dimethylthiourea or superoxide dismutase even 2 min after treatment did not significantly inhibit lipid peroxidation, hydroxyl radical production and iron release. Pretreatment of microsomes with the anion channel blocker 4,4’- dithiocyano 2,′- disulphonic acid stilbine did not cause any discernible change in chemiluminiscence induced by the superoxide radical generating system but markedly inhibited lipid peroxidation without appreciably altering iron release and hydroxial radical production.