Regular ArticleThe Effects of 21-Aminosteroids on the Redox Status of Iron in Solution
Abstract
The effects of two 21-aminosteroids (U-74500A and U-74006F) on the oxidation and reduction of iron were investigated. U-74500A completely prevented ADP: Fe(II) autoxidation whereas U-74006F had only a slight inhibitory effect. The inhibition of Fe(II) oxidation by U74500A was concentration dependent, with 100% inhibition occurring at concentrations equal to or greater than 25 μM in systems containing 50 μM Fe(II). When the Fe(II)-speciflc chelator Ferrozine was ndded to incubations containing U-74500A and ADP:Fe(II), formation of the Ferrozine:Fe(II) chromophore was slow, suggesting that U-74500A chelates Fe(II) with substantial affinity. Temporally, 20 min were required for complete formation of the Ferrozine-Fe(II) chromophore in the presence of U-74500A, whereas complexation in its absence was instantaneous. This phenomenon was not observed with U-74006F, Desferal, or ascorbate. In a system containing 25 μM ADP:Fe(II), U-74500A (25 μM) and U-74006F (25 μM) acted as iron reductants, reducing the iron at rates of approximately 2, and 0.1 μM/min, respectively. In addition, U-74500A fluorescence was quenched in a concentration-dependent manner upon the addition of Fe(III), further demonstrating interactions between this compound and iron. The substructures of U-74500A consist of a steroid (U-76911) and a complex amine (U-82902E). When these compounds were assayed individually, it was found that U-82902E exhibited activities similar to those of U-74500A, whereas the free steroid had no effect. Studies employing cyclic voltammetry revealed that U-74500A had a relatively low oxidation potential (E = 228 mV), whereas U-74006F was much less susceptible to oxidation (E = 810 mV). Taken together, these data suggest that subtle effects on iron redox chemistry, which would in turn inhibit or eliminate the initiation of undesired oxidative reactions, may contribute to the potent antioxidant activities of U-74500A and U-74006F.
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Protection of U937 cells against oxidative injury by a novel series of iron chelators
1998, Free Radical Biology and MedicineA new series of iron chelators designed to protect tissues against iron-catalysed oxidative damage is described. These compounds are aminocarboxylate derivatives bearing pendant aromatic groups. They were designed to have a relatively low affinity for both ferrous and ferric iron and to be site-specifically oxidizable by hydrogen peroxide through intramolecular aromatic hydroxylation into species with strong iron binding capacity which do not catalyse hydroxyl radical formation. Thus, at the cellular level, oxidative injury is used to convert weak iron chelators into strong iron chelators in order to promote cell survival. The purpose of this local activation process is to minimise toxicity compared to strong iron chelators which may interfere with normal iron metabolism. Compounds within this series were evaluated in vitro in view of their capacity to undergo intramolecular hydroxylation and to protect cultured cells against oxidative injury. Results show that the intramolecular aromatic hydroxylation capacity is critically dependent upon the amino carboxylate chelating moieties and the substituents of the aromatic rings. Cell protection against oxidative injury is only observed with compounds possessing sufficient lipophilicity. The monohydroxylation product of N,N′-dibenzylethylenediamine N,N′-diacetic acid, protects cells against both H2O2 and tBuOOH toxicity with IC50’s of 12 and 60 μM, respectively, in agreement with the oxidative activation concept. These results represent the first step toward the development of a new strategy to safe iron chelation for the prevention of oxidative damage.
Antioxidant activities of isoflavones and their biological metabolites in a liposomal system
1998, Archives of Biochemistry and BiophysicsGenistein and daidzein, the two major soy isoflavones, principally occur in nature as their glycosylated or methoxylated derivatives, which are cleaved in the large intestine to yield the free aglycones and further metabolites. The objective of this study was to compare the antioxidant activities of genistein and daidzein with their glycosylated and methoxylated derivatives and also those of their human metabolites. The abilities of these compounds to inhibit lipid peroxidation in a liposomal system were evaluated using fluorescence spectroscopy, and structural criteria that enhance antioxidant activity were established. The peroxidation initiators employed in the study were Fe(II) and Fe(III) metal ions and aqueous-phase, azo-derived peroxyl radicals. Both the parent isoflavonoids and their metabolites were more effective at suppressing metal-ion-induced peroxidations than the peroxyl-radical-induced peroxidation. Antioxidant activities for the isoflavone metabolites were comparable to or superior to those for the parent compounds. Equol and its 4-hydroxy and 5-hydroxy derivatives were the most potent antioxidants in the study, suggesting that absence of the 2,3-double bond and the 4-oxo group on the isoflavone nucleus enhances antioxidant activity. Additionally, the number and position of hydroxyl groups were determining factors for isoflavonoid antioxidant activity, with hydroxyl substitution being of utmost importance at the C-4′ position, of moderate importance at the C-5 position, and of little significance at the C-7 position.
Background. Lazaroids (21-aminosteroids) are a novel class of compounds that have been shown to limit experimental ischemic injury of varied causes. The mechanism of action is uncertain but may include scavenging of lipid peroxy radicals, iron binding, or direct membrane interaction. The purpose of these experiments was to evaluate the capacity of the lazaroids U-74500A and U-74389F to modify ischemia/reperfusion injury of skeletal muscle in a well-characterized model of high-grade partial ischemia.
Methods. Nonfasted male Sprague-Dawley rats were anesthetized, a tracheostomy tube was placed, and the carotid artery and jugular vein were cannulated. Animals received heparin (1 unit/gm) and crystalloid (1 ml/hr) intravenously. The baseline group (n=6) was allowed a 30-minute equilibration period, after which resting transmembrane potential (Em) was measured in a hindlimb muscle. Muscle biopsy specimen was obtained; conjugated diene and thiobarbituric acid reactive substances were measured as indexes of lipid peroxidation. Spectrophotometric determination of plasma iron and unsaturated iron-binding capacity were performed (total iron-binding capacity and percent saturation were calculated). Animals received U-74389F (2 mg/kg, n=7), U-74500A (2 mg/kg, n=6), or vehicle only (0.02 mol/L citrate acid/citrate; n=7)) intraarterially before infrarenal aortic clamping was performed for 120 minutes. An additional group of animals received U-74389F (2 mg/kg, n=7), U-74500A (2 mg/kg, n=7), or vehicle (n=11) intraarterially before infrarenal aortic clamping was performed for 120 minutes, followed by reperfusion for 30 minutes.
Results. Depolarization of resting Em was noted during ischemia, with partial repolarization on reperfusion, which was enhanced by either lazaroid. As expected, iron delocalization occurred during ischemia and persisted on reperfusion, with U-74500A effectively binding iron, whereas U-74389 did not. Vehicle but not the 21-aminosteroids inhibited lipid peroxidation.
Conclusions. High-grade partial ischemia of skeletal muscle is associated with iron delocalization, which persists on reperfusion. Each lazaroid achieved a similar “membranoprotective” effect during reperfusion only despite lack of iron binding by U-74389F, suggesting a direct interaction with the cell membrane. These data support the concept that ischemic injury and reperfusion injury occur through fundamentally different mechanisms.
Advances in the development of pharmaceutical antioxidants
1996, Advances in Drug ResearchThis chapter attempts to narrow the gap where antioxidant pharmacology meets with organic chemistry. It is intended to serve as a reference to substances that have been described, designed, or developed as therapeutically relevant antioxidants. It is obvious that the present contribution cannot cover more than a limited number of examples of antioxidants from the large variety of structural classes that have been studied as possible drug candidates. For this purpose, it most fruitful to cover compounds that have emerged from in vitro experimentation and structure–activity studies. The chapter discusses antioxidant effects in molecular and structural terms. The synthetic compounds have been classified chemically, rather than by therapeutic area, as the latter, in most instances, is a matter of the preference of the researchers rather than inherent properties of the substances. Some ranges regarding dose or concentration have been included to indicate the approximate potencies of compounds, especially when standard in vitro assays have been utilized. The enzyme systems that are devoted to detoxification of reactive and potentially pathological oxygen metabolites have also been thoroughly treated by others, and will be mentioned to provide a basis for the discussion of synthetic enzyme mimics. The chapter attempts to present the various conceivable approaches that are at hand for attenuating oxidative tissue injury and the harmful effects that are ascribed to free radicals.
Potential Use of Iron Chelators against Oxidative Damage
1996, Advances in PharmacologyIron is critically involved in dioxygen transport and in a wide variety of cellular events ranging from respiration to DNA synthesis. The physical properties those enable iron to be an essential factor for a wide range of proteins involved in controlled redox reactions also allow iron to be toxic when not carefully handled by proteins and shielded from surrounding media. In systemic iron overload, excess iron saturates the binding sites of transferrin, allowing free iron to circulate and oxidize heart muscle cells ultimately leading to heart failure. Systemic iron overload is associated with several diseases such as hereditary hemochromatosis and thalassemia major, which is characterized by a defective production of the globin chain of hemoglobin. This leads to anemia and is treated by repetitive blood transfusions. In most of this systemic iron overload situations; treatment by iron chelators such as desferrioxamine is the only effective way to remove excess iron. This chapter focuses on the potential use of iron chelators for the treatment of conditions involving oxidative damage or local disturbance of iron homeostasis, with a special emphasis on the possible side effects related to interactions of the chelators with normal iron metabolism. Discussed are iron homeostasis, iron release during oxidative stress from ferritin and other sites, and the consequences of iron release. The chapter also details the design of iron chelators, its interaction with normal iron metabolism, catalysis of fenton chemistry, the main classes of iron chelators, the oxidative stress-activatable iron chelators, protective effect of iron chelators against oxidative damage, and in vivo situations unrelated to systemic iron overload such as inflammatory diseases, post-ischemic/reperfusion injury, intoxication by xenobiotics, atherosclerosis, and neurodegenerative diseases. The “oxidative stress activation” concept described in this chapter could provide a rational approach to minimize side effects and therefore allow chelation therapy for long periods of time.
Effects of estrogens on the redox chemistry of iron: A possible mechanism of the antioxidant action of estrogens
1995, SteroidsThe preventive effects of estrogens on FeSO4-induced lipid peroxidation are closely correlated with their inhibition of Fe(II) oxidation during peroxidation. Estrogens affected the redox status of iron in aqueous solution with varying degrees of effectiveness. 2-Hydroxyestradiol substantially decreased the oxidation of Fe(II) and was the most potent Fe(III) reductant. Diethylstilbestrol and 4-hydroxyestradiol also exhibited reduction properties, whereas the phenolic estrogens 17β-estradiol, estrone, and 17α-ethynylestradiol displayed slighter or no effects. Present results demonstrate that catecholestrogens and diethylstilbestrol directly alter the iron redox chemistry, this fact probably being involved in the antioxidant effects of these molecules.