Iron-induced lipid peroxidation

Fe(iii)Adr causes lipid peroxidation and induces DNA damage in vitro in the presence of reductants. In cells, the cleavage of DNA by Adr is inhibited under iron-deficient conditions, but is insensitive to the presence of added catalase. In contrast, Fe(iii)Adr causes DNA strand scission that is largely eliminated by the addition of catalase. The first result extends the iron-dependence of cytotoxicity described above to a particular site of reaction. The second shows that, at least when Fe(m)Adr is used, DNA strand scission results from a cascade of reactions leading to oxyradical formation, which can be interrupted by the dismutation of H2O2 to O2 and H2O by catalase. 

In studies in Alzheimer s brain, in vitro induction of lipid peroxidation by iron is more intense than in control cortical samples (Andorn et al., 1990 Subbarao et nL, 1990 McIntosh et al., 1991). The 21-aminosteroid U-74500A has been shown to effectively inhibit iron-induced lipid peroxidation in Alzheimer s brain samples (Subbarao et al., 1990). 

Treatment with iron chelators and a-tocopherol protect against lipid p>eroxidation and hepatocellular injury in iron-overloaded rats (Sharma etal., 1990). When hepatocytes are isolated from rats, which have been pretreated with a-tocopherol, there is a significant reduction in iron-induced lipid peroxidation and improvement in cell viability in vitro (Poli et al., 1985). Similar effects were seen when hepatocytes were incubated with iron chelators (Bacon and Britton, 1990). Treatment of moderately, but not heavily, iron-loaded rats with desferrioxamine in vivo inhibits the pro-oxidant activity of hepatic ultrafiltrates (Britton et al., 1990b). 

Younes, M. and Wess, A. (1990). The role of iron in t-butyl hydroperoxide-induced lipid peroxidation and hepatotoxicity in rats. J. Appl. Toxicol. 10, 313-317. 

The phenothiazines, chlorpromazine and promethazine, have been described as inhibitors of CCU-induced lipid peroxidation at relatively high concentrations in rat liver microsomes (Slater, 1968). Structural modifications of chlorpromazine were undertaken to try to increase antioxidant activity and maintain molecular lipophilicity. The 2-N-N-dimethyl ethanamine methanesulphonate-substituted phenothiazine (3) was found to be a potent inhibitor of iron-dependent lipid peroxidation. It was also found to block Cu -catalysed oxidation of LDL more effectively than probucol and to protect primary cultures of rat hippocampal neurons against hydrogen peroxide-induced toxicity in vitro (Yu et al., 1992). 

To study the effects of iron overloading on inflammatory cells, Muntane et al. [186] investigated the effect of iron dcxtran administration on the acute and chronic phases of carrageenan-induced glanuloma. It was found that iron dcxtran increased the iron content in plasma and stores, and enhanced lipid peroxidation and superoxide production by inflammatory cells. At the same time, iron dcxtran had a beneficial effect on recovery from the anemia of inflammation. It has been suggested that iron overload may affect nitric oxide production in animals. For example, alveolar macrophages from iron-overloaded rats stimulated with LPS or interferon-7 diminished NO release compared to normal rats [187]. 

As a rule, oxygen radical overproduction in mitochondria is accompanied by peroxidation of mitochondrial lipids, glutathione depletion, and an increase in other parameters of oxidative stress. Thus, the enhancement of superoxide production in bovine heart submitochondrial particles by antimycin resulted in a decrease in the activity of cytochrome c oxidase through the peroxidation of cardiolipin [45]. Iron overload also induced lipid peroxidation and a decrease in mitochondrial membrane potential in rat liver mitochondria [46]. Sensi et al. [47] demonstrated that zinc influx induced mitochondrial superoxide production in postsynaptic neurons. 

Colquhoun and Schumacher [98] have shown that y-linolcnic acid and eicosapentaenoic acid, which inhibit Walker tumor growth in vivo, decreased proliferation and apoptotic index in these cells. Development of apoptosis was characterized by the enhancement of the formation of reactive oxygen species and products of lipid peroxidation and was accompanied by a decrease in the activities of mitochondrial complexes I, III, and IV, and the release of cytochrome c and caspase 3-like activation of DNA fragmentation. Earlier, a similar apoptotic mechanism of antitumor activity has been shown for the flavonoid quercetin [99], Kamp et al. [100] suggested that the asbestos-induced apoptosis in alveolar epithelial cells was mediated by iron-derived oxygen species, although authors did not hypothesize about the nature of these species (hydroxyl radicals, hydrogen peroxide, or iron complexes ). 

The efficiency of vitamin E in the suppression of free radical-mediated damage induced by iron overload has been studied in animals and humans. Galleano and Puntarulo [46] showed that iron overload increased lipid and protein peroxidation in rat liver. Vitamin E supplementation successfully suppressed these effects and led to an increase in a-tocopherol, ubiquinone-9, and ubiquinone-10 contents in liver. Important results were obtained by Roob et al. [47] who found that vitamin E supplementation attenuated lipid peroxidation (measured as plasma MDA and plasma lipid peroxides) in patients on hemodialysis after receiving iron hydroxide sucrose complex intravenously during hemodialysis session. These findings support the proposal that iron overload enhances free radical-mediated damage in humans. 

Flavonoid baicalein, which is believed to be one of the most important components of Japanese Kampo (traditional herbal) medicine, was found to be an effective scavenger of superoxide and hydroxyl radicals and the inhibitor of iron-induced in vivo lipid peroxidation in gerbils [122],... 

In 1989, we showed [142] that the Fe2+(rutin)2 complex is a more effective inhibitor than rutin of asbestos-induced erythrocyte hemolysis and asbestos-stimulated oxygen radical production by rat peritoneal macrophages. Later on, to evaluate the mechanisms of antioxidant activities of iron rutin and copper-rutin complexes, we compared the effects of these complexes on iron-dependent liposomal and microsomal lipid peroxidation [165], It was found that the iron rutin complex was by two to three times a more efficient inhibitor of liposomal peroxidation than the copper-rutin complex, while the opposite tendency was observed in NADPH-dependent microsomal peroxidation. On the other hand, the copper rutin complex was much more effective than the iron rutin complex in the suppression of microsomal superoxide production, indicating that the copper rutin complex indeed acquired additional SOD-dismuting activity because superoxide is an initiator of NADPH-dependent... 

There are other synthetic and natural thiolic compounds possessing antioxidant activity. One such compound is tetradecylthioacetic acid (TTA), which inhibited the iron-ascorbate-induced microsomal lipid peroxidation [234]. Its Se analog exhibited even a more profound antioxidative effect. 

High antioxidative activity carvedilol has been shown in isolated rat heart mitochondria [297] and in the protection against myocardial injury in postischemic rat hearts [281]. Carvedilol also preserved tissue GSL content and diminished peroxynitrite-induced tissue injury in hypercholesterolemic rabbits [298]. Habon et al. [299] showed that carvedilol significantly decreased the ischemia-reperfusion-stimulated free radical formation and lipid peroxidation in rat hearts. Very small I50 values have been obtained for the metabolite of carvedilol SB 211475 in the iron-ascorbate-initiated lipid peroxidation of brain homogenate (0.28 pmol D1), mouse macrophage-stimulated LDL oxidation (0.043 pmol I 1), the hydroxyl-initiated lipid peroxidation of bovine pulmonary artery endothelial cells (0.15 pmol U1), the cell damage measured by LDL release (0.16 pmol l-1), and the promotion of cell survival (0.13 pmol l-1) [300]. SB 211475 also inhibited superoxide production by PMA-stimulated human neutrophils. 

Thus, the mechanism of MT antioxidant activity might be connected with the possible antioxidant effect of zinc. Zinc is a nontransition metal and therefore, its participation in redox processes is not really expected. The simplest mechanism of zinc antioxidant activity is the competition with transition metal ions capable of initiating free radical-mediated processes. For example, it has recently been shown [342] that zinc inhibited copper- and iron-initiated liposomal peroxidation but had no effect on peroxidative processes initiated by free radicals and peroxynitrite. These findings contradict the earlier results obtained by Coassin et al. [343] who found no inhibitory effects of zinc on microsomal lipid peroxidation in contrast to the inhibitory effects of manganese and cobalt. Yeomans et al. [344] showed that the zinc-histidine complex is able to inhibit copper-induced LDL oxidation, but the antioxidant effect of this complex obviously depended on histidine and not zinc because zinc sulfate was ineffective. We proposed another mode of possible antioxidant effect of zinc [345], It has been found that Zn and Mg aspartates inhibited oxygen radical production by xanthine oxidase, NADPH oxidase, and human blood leukocytes. The antioxidant effect of these salts supposedly was a consequence of the acceleration of spontaneous superoxide dismutation due to increasing medium acidity. 

Overproduction of free radicals by erythrocytes and leukocytes and iron overload result in a sharp increase in free radical damage in T1 patients. Thus, Livrea et al. [385] found a twofold increase in the levels of conjugated dienes, MDA, and protein carbonyls with respect to control in serum from 42 (3-thalassemic patients. Simultaneously, there was a decrease in the content of antioxidant vitamins C (44%) and E (42%). It was suggested that the iron-induced liver damage in thalassemia may play a major role in the depletion of antioxidant vitamins. Plasma thiobarbituric acid-reactive substances (TBARS) and conjugated dienes were elevated in (3-thalassemic children compared to controls together with compensatory increase in SOD activity [386]. The development of lipid peroxidation in thalassemic erythrocytes probably depends on a decrease in reduced glutathione level and decreased catalase activity [387]. 

Figure 2. NO inhibits iron-induced lipid peroxidation. The rate of Oj consumption of HL-60 cells (5 X 10 /ml) was detennined using a YSI O2 monitor. Fe (20 pM) was added at the first arrow and subsequently NO (0.45 pM) was added (other arrows). When NO was added, the O2 consumption was inhibited for a period of a few min, then it resumed at near its initial rate until the reintroduction of additional NO. Also shown (lower dashed line) is a control of HL-60 cells subjected to Fe -induced oxidative stress in the absence of NO addition. The background rate of O2 uptake of the HL-60 cell suspension before the addition of Fe was 10 nM/sec. Upon the addition of 20 pM Fe, this rate increased to 220 nM/sec. The addition of NO resulted in a decrease in O2 consumption to <10 nM/sec. (From Kelley, E.E., Wagner, B.A., Buettner, G.R., and Bums, C.P., 1999, Arch. Biochem. Biophys. 370 97-104).

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