Desferrioxamine as a lipid chain-breaking antioxidant in sickle erythrocyte membranes

Guanidinylated bioactive chitosan-based injectable hydrogels with pro-angiogenic and mechanical properties for accelerated wound closure

Wound healing is a complex process involving the concerted action of many genes and signaling pathways, with angiogenesis being crucial for expediting wound closure. Dressings that possess pro-angiogenic properties are increasingly recognized as attractive candidates for wound care. Drawing inspiration from the active closure of wounds in embryos, we have developed a thermo-responsive hydrogel with mechanoactive properties, combining vascular regeneration and skin wound contraction to accelerate healing. The significant improvement in vascular reconstruction is attributed to the synergistic effect of arginine and deferoxamine (DFO) released from the hydrogels. Additionally, the contraction force of the hydrogel actively promotes skin closure in wounds. Remarkably, groups treated with hydroxybutyl chitosan methacrylate combined with arginine (HBC_m_Arg/DFO) exhibited increased vascularization, and greater wound maturity, leading to enhanced healing. These results highlight the synergistic impact of pro-angiogenic and mechanical properties of the HBC_m_Arg/DFO hydrogel in accelerating wound healing in rats.

Design of a water-soluble chitosan-based polymer with antioxidant and chelating properties for labile iron extraction

Loosely bound iron, due to its contribution to oxidative stress and inflammation, has become an important therapeutic target for many diseases. A water-soluble chitosan-based polymer exhibiting both antioxidant and chelating properties due to the dual functionalization with DOTAGA and DFO has been developed to extract this iron therefore preventing its catalytic production of reactive oxygen species. This functionalized chitosan was shown to have stronger antioxidant properties compared to conventional chitosan, improved iron chelating properties compared to the clinical therapy, deferiprone, and provided promising results for its application and improved metal extraction within a conventional 4 h hemodialysis session with bovine plasma.

Ultraviolet Light Protection: Is It Really Enough?

Our current understanding of the pathogenesis of skin aging includes the role of ultraviolet light, visible light, infrared, pollution, cigarette smoke and other environmental exposures. The mechanism of action common to these exposures is the disruption of the cellular redox balance by the directly or indirectly increased formation of reactive oxygen species that overwhelm the intrinsic antioxidant defense system, resulting in an oxidative stress condition. Altered redox homeostasis triggers downstream pathways that contribute to tissue oxinflammation (cross-talk between inflammation and altered redox status) and accelerate skin aging. In addition, both ultraviolet light and pollution increase intracellular free iron that catalyzes reactive oxygen species generation via the Fenton reaction. This disruption of iron homeostasis within the cell further promotes oxidative stress and contributes to extrinsic skin aging. More recent studies have demonstrated that iron chelators can be used topically and can enhance the benefits of topically applied antioxidants. Thus, an updated, more comprehensive approach to environmental or atmospheric aging protection should include sun protective measures, broad spectrum sunscreens, antioxidants, chelating agents, and DNA repair enzymes.

Effect of prooxidants and chelator Desferal on the oxidative status and sperm motility of Muscovy semen

This study aimed to establish the sensitivity of Muscovy duck semen to oxidative stress (OS) and the effect of Desferal, applied as an antioxidant. The effect of three prooxidant systems in presence and absence of Desferal were tested on the motility and kinetic parameters (determined using CASA system), as well as the level of lipid peroxidation (LPO) and glutathione (tGSH) of Muscovy semen. The semen was diluted (1:3 v/v) with four extenders (saline solution, IMV Canadyl, HIA-1, and AU) and stored at 4 °C for 6 h. The cooled semen was divided into aliquots (50 × 106 sperm cells/mL), which were incubated at 37 °C for 30 min with one of the following prooxidative agents: ferrous sulfate (FeSO4, 0.1 mM), hydrogen peroxide (H2O2, 1 mM), and Fenton system (FeSO4(Fe2+), 0.1 mM + H2O2, 1 mM), in the presence or absence of Desferal (0.1 mM). The addition of FeSO4 + H2O2 or FeSO4 regardless of the used extender, as well as the addition of H2O2 to the diluted semen with saline solution significantly increased the levels of LPO (P < 0.05). With the lowest prooxidant effect was H2O2. The application of Desferal reduced significantly (P < 0.05) the LPO levels induced by FeSO4 + H2O2 or FeSO4 and in a weaker degree by H2O2. Among all prooxidants, FeSO4 + H2O2 decreased in the greatest extent the tGSH concentration in semen diluted with each used extenders in comparison to the relevant control. The addition of Desferal in semen diluted with HIA-1 extender and incubated with FeSO4, and H2O2, showed the best restoration of tGSH level, close to that of respectively controls. The studied prooxidants significantly reduced total, progressive, and kinetic sperm motility (P < 0.05). Although the inclusion of Desferal reduced the sperm OS, it did not improve the impaired by OS sperm motility.

Deferoxamine accelerates endothelial progenitor cell senescence and compromises angiogenesis

Senescence reduces the circulating number and angiogenic activity of endothelial progenitor cells (EPCs), and is associated with aging-related vascular diseases. However, it is very time-consuming to obtain aged cells (~1 month of repeated replication) or animals (~2 years) for senescence studies. Here, we established an accelerated senescence model by treating EPCs with deferoxamine (DFO), an FDA-approved iron chelator. Four days of low-dose (3 μM) DFO induced senescent phenotypes in EPCs, including a senescent pattern of protein expression, impaired mitochondrial bioenergetics, altered mitochondrial protein levels and compromised angiogenic activity. DFO-treated early EPCs from young and old donors (< 35 vs. > 70 years old) displayed similar senescent phenotypes, including elevated senescence-associated β-galactosidase activity and reduced relative telomere lengths, colony-forming units and adenosine triphosphate levels. To validate this accelerated senescence model in vivo, we intraperitoneally injected Sprague-Dawley rats with DFO for 4 weeks. Early EPCs from DFO-treated rats displayed profoundly senescent phenotypes compared to those from control rats. Additionally, in hind-limb ischemic mice, DFO pretreatment compromised EPC angiogenesis by reducing both blood perfusion and capillary density. DFO thus accelerates EPC senescence and appears to hasten model development for cellular senescence studies.

How to Improve the Antioxidant Defense in Asphyxiated Newborns-Lessons from Animal Models

Oxygen free radicals have been implicated in brain damage after neonatal asphyxia. In the early phase of asphyxia/reoxygenation, changes in antioxidant enzyme activity play a pivotal role in switching on and off the cascade of events that can kill the neurons. Hypoxia/ischemia (H/I) forces the brain to activate endogenous mechanisms (e.g., antioxidant enzymes) to compensate for the lost or broken neural circuits. It is important to evaluate therapies to enhance the self-protective capacity of the brain. In animal models, decreased body temperature during neonatal asphyxia has been shown to increase cerebral antioxidant capacity. However, in preterm or severely asphyxiated newborns this therapy, rather than beneficial seems to be harmful. Thus, seeking new therapeutic approaches to prevent anoxia-induced complications is crucial. Pharmacotherapy with deferoxamine (DFO) is commonly recognized as a beneficial regimen for H/I insult. DFO, via iron chelation, reduces oxidative stress. It also assures an optimal antioxidant protection minimizing depletion of the antioxidant enzymes as well as low molecular antioxidants. In the present review, some aspects of recently acquired insight into the therapeutic effects of hypothermia and DFO in promoting neuronal survival after H/I are discussed.

Tert-Butyl Hydroperoxide Stimulated Apoptosis Independent of Prostaglandin E2 and IL-6 in the HTR-8/SVneo Human Placental Cell Line

Significant gaps exist in our knowledge of how cellular redox status, sometimes referred to as oxidative stress, impacts placental trophoblasts. The present study used tert-butyl hydroperoxide (TBHP) as a known generator of reactive oxygen species (ROS) in the extravillous trophoblast cell line HTR-8/SVneo to examine the role of cellular redox disruption of prostaglandin E₂ (PGE₂) and the cytokine IL-6 in cell death. Cells were exposed to 0, 12.5, 25, or 50 μM TBHP for 4, 8, and 24 h to ascertain effects on cell viability, caspase 3/7 activity, PGE₂ release, PTGS2 mRNA expression, and IL-6 release. Experiments with inhibitors included the cyclooxygenase inhibitor indomethacin, mitogen-activated protein kinase inhibitors (PD169316, U0126, or SP600125), or treatments to counter expected consequences of TBHP-stimulated generation of ROS (deferoxamine [DFO], butylated hydroxyanisole [BHA], and N,N'-diphenyl-1,4-phenylenediamine [DPPD]) using 24-h exposure to 50 μM TBHP. Cell viability, measured by ATP content, decreased 24% relative to controls with a 24-h exposure to 50 μM TBHP, but not at lower TBHP concentrations nor at earlier time points. Exposure to 50 μM TBHP increased caspase 3/7 activity, an indicator of apoptosis, after 8 and 24 h. Antioxidant treatment markedly reduced TBHP-stimulated caspase 3/7 activity, PGE₂ release, and IL-6 release. TBHP-stimulated IL-6 release was blocked by PD169316 but unaltered by indomethacin. These data suggest that TBHP-stimulated IL-6 release and caspase 3/7 activation were independent of PGE₂ yet were interrupted by treatments with known antioxidant properties, providing new insight into relationships between PGE₂, IL-6, and apoptosis under conditions of chemically induced cellular oxidation.

Quantifying Intranasally Administered Deferoxamine in Rat Brain Tissue with Mass Spectrometry

Deferoxamine, a metal chelator, has been shown to be neuroprotective in animal models of ischemic stroke, traumatic brain injury and both subarachnoid and intracerebral hemorrhage. Intranasal deferoxamine (IN DFO) has also shown promise as a potential treatment for multiple neurodegenerative diseases, including Parkinson's and Alzheimer's. However, there have been no attempts to thoroughly understand the dynamics and pharmacokinetics of IN DFO. We developed a new high-performance liquid-chromatography electrospray-tandem mass spectrometry (HPLC/ESI-MS²) method to quantify the combined total levels of DFO, ferrioxamine (FO; DFO bound to iron), and aluminoxamine (AO; aluminum-bound DFO) in brain tissue using a custom-synthesized deuterated analogue (DFO-d₇, Medical Isotopes Inc., Pelham NH) as an internal standard. We applied our method toward understanding the pharmacokinetics of IN DFO delivery to the brain and blood of rats from 15 min to 4 h after delivery. We found that IN delivery successfully targets DFO to the brain to achieve concentrations of 0.5-15 μM in various brain regions within 15 min, and decreasing though still detectable after 4 h. Systemic exposure was minimized as assessed by concentration in blood serum. Serum concentrations were 0.02 μM at 15 min and no more than 0.1 μM at later time points. Compared to blood serum, brain region-specific drug exposure (as measured by area under the curve) ranged from slightly under 10 times exposure in the hippocampus to almost 200 times exposure in the olfactory bulb with IN DFO delivery. These findings represent a major step toward future method development, pharmacokinetic studies, and clinical trials for this promising therapeutic.

Deferoxamine: An Angiogenic and Antioxidant Molecule for Tissue Regeneration

Deferoxamine (DFO) has been in use for half a century as a Food and Drug Administration-approved iron chelator, but recent studies indicate a variety of properties that could expand this drug's application into the fields of tissue and regenerative engineering. DFO has been implicated as an angiogenic agent in studies on ischemia, wound healing, and bone regeneration because of its ability to upregulate hypoxia-inducible factor-1 alpha (HIF-1α) and other key downstream angiogenic factors. DFO has also demonstrated antioxidant capabilities unrelated to its iron-chelating properties, making it a potential modulator of the oxidative stress involved in the inflammation response. Together, these properties make DFO a potential bioactive molecule to promote wound healing and enhance tissue integration of biomaterials in vivo. Impact Statement Deferoxamine (DFO) is approved by the Food and Drug Administration as an iron chelator and is been used to treat iron overload. Recent studies indicate that DFO may have important applications in the growing field of tissue regeneration because of its unique properties of downregulating inflammation while promoting vascularization, thereby enhancing wound healing in vivo.

Ciprofloxacin-induces free radical production in rat cerebral microsomes

In the presence of ciprofloxacin (CPFX), free radical adduct formation was demonstrated in rat cerebral microsomes using a spin trap α-(4-pyridyl-1-oxide)-N-tert-butyl-nitrone by electron spin resonance spectroscopy. Active microsomes, dihydronicotinamide-adenine dinucleotide phosphate, and ciprofloxacin were necessary for the formation of a spin trap/radical adduct. Adduct formation increased dose-dependently at 0.5-1 mM CPFX concentration for 180 min, and 0.3-1 mM concentration level for 240 min. The addition of SKF 525A, ZnCl₂ or desferrioxamine to the incubation system caused complete inhibition of the radical formation. However, pretreatment of microsomal system with superoxide dismutase (SOD) did not induce any protective effect. Induction of lipid peroxidation, and depletion of thiol levels by CPFX were also shown in the system. These results strongly suggested that CPFX produces free radical(s) in the cerebral microsomes of rats.

Disturbed hypoxic responses as a pathogenic mechanism of diabetic foot ulcers

Diabetic foot ulceration (DFU) is a chronic complication of diabetes that is characterized by impaired wound healing in the lower extremities. DFU remains a major clinical challenge because of poor understanding of its pathogenic mechanisms. Impaired wound healing in diabetes is characterized by decreased angiogenesis, reduced bone marrow-derived endothelial progenitor cell (EPC) recruitment, and decreased fibroblast and keratinocyte proliferation and migration. Recently, increasing evidence has suggested that increased hypoxic conditions and impaired cellular responses to hypoxia are essential pathogenic factors of delayed wound healing in DFU. Hypoxia-inducible factor-1 (HIF-1, a heterodimer of HIF-1α and HIF-1β) is a master regulator of oxygen homeostasis that mediates the adaptive cellular responses to hypoxia by regulating the expression of genes involved in angiogenesis, metabolic changes, proliferation, migration, and cell survival. However, HIF-1 signalling is inhibited in diabetes as a result of hyperglycaemia-induced HIF-1α destabilization and functional repression. Increasing HIF-1α expression and activity using various approaches promotes angiogenesis, EPC recruitment, and granulation, thereby improving wound healing in experimental diabetes. The mechanisms underlying HIF-1α regulation in diabetes and the therapeutic strategies targeting HIF-1 signalling for the treatment of diabetic wounds are discussed in this review. Further investigations of the pathways involved in HIF-1α regulation in diabetes are required to advance our understanding of the mechanisms underlying impaired wound healing in diabetes and to provide a foundation for developing novel therapeutic approaches to treat DFU.

Transdermal deferoxamine prevents pressure-induced diabetic ulcers

There is a high mortality in patients with diabetes and severe pressure ulcers. For example, chronic pressure sores of the heels often lead to limb loss in diabetic patients. A major factor underlying this is reduced neovascularization caused by impaired activity of the transcription factor hypoxia inducible factor-1 alpha (HIF-1α). In diabetes, HIF-1α function is compromised by a high glucose-induced and reactive oxygen species-mediated modification of its coactivator p300, leading to impaired HIF-1α transactivation. We examined whether local enhancement of HIF-1α activity would improve diabetic wound healing and minimize the severity of diabetic ulcers. To improve HIF-1α activity we designed a transdermal drug delivery system (TDDS) containing the FDA-approved small molecule deferoxamine (DFO), an iron chelator that increases HIF-1α transactivation in diabetes by preventing iron-catalyzed reactive oxygen stress. Applying this TDDS to a pressure-induced ulcer model in diabetic mice, we found that transdermal delivery of DFO significantly improved wound healing. Unexpectedly, prophylactic application of this transdermal delivery system also prevented diabetic ulcer formation. DFO-treated wounds demonstrated increased collagen density, improved neovascularization, and reduction of free radical formation, leading to decreased cell death. These findings suggest that transdermal delivery of DFO provides a targeted means to both prevent ulcer formation and accelerate diabetic wound healing with the potential for rapid clinical translation.

Towards the prevention of potential aluminum toxic effects and an effective treatment for Alzheimer's disease

In 1991, treatment with low dose intramuscular desferrioxamine (DFO), a trivalent chelator that can remove excessive iron and/or aluminum from the body, was reported to slow the progression of Alzheimer's disease (AD) by a factor of two. Twenty years later this promising trial has not been followed up and why this treatment worked still is not clear. In this critical interdisciplinary review, we provide an overview of the complexities of AD and involvement of metal ions, and revisit the neglected DFO trial. We discuss research done by us and others that is helping to explain involvement of metal ion catalyzed production of reactive oxygen species in the pathogenesis of AD, and emerging strategies for inhibition of metal-ion toxicity. Highlighted are insights to be considered in the quests to prevent potentially toxic effects of aluminum toxicity and prevention and intervention in AD.

Xanthine oxidase-induced neuronal death via the oxidation of NADH: prevention by micromolar EDTA

The oxidation of xanthine by xanthine oxidase (XO) or xanthine dehydrogenase represents an important source of reactive oxygen species (ROS), which contribute to the damaging consequences of cerebral ischemia, inflammation, and neurodegenerative disorders. However, both enzymes are also able to act on reduced nicotinamide adenine dinucleotide (NADH). The FAD binding site to which NADH binds is distinct from that of the xanthine binding site. We report that the combination of xanthine oxidase and NADH is toxic to cultures of cerebellar granule neurons. Protection by superoxide dismutase (Cu,Zn-SOD or Mn-SOD) or catalase indicates mediation of the toxicity by superoxide and hydrogen peroxide. In addition, pre-incubating XO with EDTA at concentrations as low as 2 microM, prevented the toxicity, indicating that a metal contaminating XO is involved in producing the toxic effects of XO/NADH. It is possible that such a metal might play a role in the toxicity of XO in vivo.

High susceptibility of activated lymphocytes to oxidative stress-induced cell death

The present study provides evidence that activated spleen lymphocytes from Walker 256 tumor bearing rats are more susceptible than controls to tert-butyl hydroperoxide (t-BOOH)-induced necrotic cell death in vitro. The iron chelator and antioxidant deferoxamine, the intracellular Ca2+ chelator BAPTA, the L-type Ca2+ channel antagonist nifedipine or the mitochondrial permeability transition inhibitor cyclosporin A, but not the calcineurin inhibitor FK-506, render control and activated lymphocytes equally resistant to the toxic effects of t-BOOH. Incubation of activated lymphocytes in the presence of t-BOOH resulted in a cyclosporin A-sensitive decrease in mitochondrial membrane potential. These results indicate that the higher cytosolic Ca2+ level in activated lymphocytes increases their susceptibility to oxidative stress-induced cell death in a mechanism involving the participation of mitochondrial permeability transition.

Desferrioxamine (DFX) induces apoptosis through the p38-caspase8-Bid-Bax pathway in PHA-stimulated human lymphocytes

Desferrioxamine (DFX) induces apoptosis in human lymphocytes, although the mechanism leading to cell death is unclear. Therefore, we investigated the signaling pathways implicated in DFX-induced apoptosis in lymphocytes. DFX treatment activated caspase-9, caspase-3, and caspase-8. DFX-induced apoptosis was inhibited by both z-IETD-fmk and z-DEVD-fmk. DFX treatment also enhanced caspase-8 activity, Bid cleavage, and the conformational activation of Bax. DFX treatment activated two MAPKs, p38 and JNK, and induced the phosphorylation of two proteins in the p38 pathway, MKK3 and MKK6. DFX treatment also increased the phosphorylation of two downstream targets of p38, ATF-2 and MAPKAPK2, indicating that DFX promotes p38 activity. In addition, the selective p38 inhibitor SB203580 suppressed DFX-induced apoptosis and caspase-8 activation, whereas the JNK inhibitor, SP600125, and the ERK inhibitor, PD98059, had no effect. Our results suggest that DFX-induced apoptosis is mediated by the p38 pathway and a caspase-8-dependent Bid-Bax pathway in human lymphocytes.

Reactions of desferrioxamine with peroxynitrite-derived carbonate and nitrogen dioxide radicals

The iron chelating agent desferrioxamine inhibits peroxynitrite-mediated oxidations and attenuates nitric oxide and oxygen radical-dependent oxidative damage both in vitro and in vivo. The mechanism of protection is independent of iron chelation and has remained elusive over the past decade. Herein, stopped-flow studies revealed that desferrioxamine does not react directly with peroxynitrite. However, addition of peroxynitrite to desferrioxamine in both the absence and the presence of physiological concentrations of CO2 and under excess nitrite led to the formation of a one-electron oxidation product, the desferrioxamine nitroxide radical, consistent with desferrioxamine reacting with the peroxynitrite-derived species carbonate (CO3*-) and nitrogen dioxide (*NO2) radicals. Desferrioxamine inhibited peroxynitrite-dependent free radical-mediated processes, including tyrosine dimerization and nitration, oxyhemoglobin oxidation in the presence of CO2, and peroxynitrite plus carbonate-dependent chemiluminescence. The direct two-electron oxidation of glutathione by peroxynitrite was unaffected by desferrioxamine. The reactions of desferrioxamine with CO3*- and *NO2 were unambiguously confirmed by pulse radiolysis studies, which yielded second-order rate constants of 1.7 x 10(9) and 7.6 x 10(6) M(-1) s(-1), respectively. Desferrioxamine also reacts with tyrosyl radicals with k = 6.3 x 10(6) M(-1) s(-1). However, radical/radical combination reactions between tyrosyl radicals or of tyrosyl radical with *NO2 outcompete the reaction with desferrioxamine and computer-assisted simulations indicate that the inhibition of tyrosine oxidation can be fully explained by scavenging of the peroxynitrite-derived radicals. The results shown herein provide an alternative mechanism to account for some of the biochemical and pharmacological actions of desferrioxamine via reactions with CO3*- and *NO2 radicals.

Oxidative insult in sheep red blood cells induced by T-butyl hydroperoxide: the roles of glutathione and glutathione peroxidase

Three different types of red blood cells (RBC) were used: (i) RBC from sheep having genetically high GSH (ii) RBC from sheep with genetically low GSH and (iii) RBC from high-GSH sheep treated with CDNB to deplete GSH. Incubation of these RBC with t-butyl hydroperoxide (tBHP, 3 mM) for 10 min caused the formation of TBARS, oxidation of haemoglobin and degradation and aggregation of membrane proteins in RBC from low-GSH sheep and GSH-depleted RBC. By contrast, RBC from high-GSH sheep (normal RBC) did not show the degradation and aggregation of membrane proteins within the first 10 min. Dithiothreitol (DTT) was highly effective in preventing the tBHP-mediated oxidation of haemoglobin, the formation of TBARS and the degradation and aggregation of membrane proteins in both normal RBC and low-GSH RBC. However, DTT did not provide protection in GSH-depleted RBC or normal RBCs in the presence of 1.5 mM mercaptosuccinate (MCS), a potent inhibitor of GSH peroxidase (GSHPx). The ability of GSH to prevent the oxidation of haemoglobin and the degradation and aggregation of membrane proteins was abolished in the presence of MCS. These results indicate that the protective function of DTT involves a GSH-dependent mechanism. Both GSH and GSHPx play key roles in this enzymatic system. In the light of the complete protection of RBC against oxidation induced by tBHP in the presence of DTT or GSH, the GSH/GSHPx system appears to act directly as a tBHP scavenger. The activities of four well-known antioxidants, Butylated hydroxytoluene, ascorbate, alpha-tocopherol and desferrioxamine were also tested in this study to cast further light on the role of free radical scavenging in protection from tBHP mediated free radical insult.

Sickle cell anemia: a potential nutritional approach for a molecular disease

A certain population of red blood cells in patients with sickle cell anemia has an elevated density and possesses an abnormal membrane. These "dense cells" have a tendency to adhere to neutrophils, platelets, and vascular endothelial cells, and, thus, they could trigger vasoocclusion and the subsequent painful crisis from which these patients suffer. We developed a laboratory method of preparing such dense cells and found that nutritional antioxidant supplements, hydroxyl radical scavengers, and iron-binding agents could inhibit the formation of dense cells in vitro. The concentrations at which effective nutritional supplements could inhibit dense cell formation by 50% were 4.0 mg/mL for aged garlic extract, 0.38 mg/mL for black tea extract, 0.13 mg/mL for green tea extract, 0.07 mg/mL for Pycnogenol, 930 microM for alpha-lipoic acid, 270 microM for vitamin E, 45 microM for coenzyme Q(10), and 32 microM for beta-carotene. Both an ex vivo study and a pilot clinical trial demonstrated that a cocktail consisting of daily doses of 6 g of aged garlic extract, 4-6 g of vitamin C, and 800 to 1200 IU of vitamin E may indeed be beneficial to the patients.

Effect of N-acetylcysteine and deferoxamine on endogenous antioxidant defense system gene expression in a rat hepatocyte model of cocaine cytotoxicity

In the present study we investigated on cultures of hepatocytes from phenobarbital-pretreated rats, the effect of the antioxidants, 0.5 mM N-acetylcysteine (NAC) or 1.5 mM deferoxamine (DFO), previously incubated for 24 h and coincubated with cocaine (0-1000 microM) for another 24 h. Cocaine cytotoxicity was monitored by either the lysis of the cell membranes or apoptosis. Lysis of the cell membranes was evidenced by lactate dehydrogenase leakage, apoptosis was observed by detecting a hypodiploid peak (<2C) in DNA histograms obtained by flow cytometry, peroxide production was quantified with 2', 7'-dichlorodihydrofluorescein diacetate and gene expression of the antioxidant enzymes: Mn- and Cu,Zn-superoxide dismutases, catalase and glutathione peroxidase were measured by Northern blot analysis. NAC and DFO significantly decreased the extent of lysis of cell membranes and apoptosis, and the antiapoptotic effect was parallel to peroxide generation. By the effect of NAC and DFO, significant increases were detected in the levels of mRNA of catalase, manganese superoxide dismutase and glutathione peroxidase. From these results we conclude that NAC or DFO, when incubated in the presence of cocaine, exerted a protective effect against cocaine toxicity at the level of both lysis of the membranes and apoptosis. This protective effect, in the case of NAC, was directed towards an increase in antioxidant enzyme expression, and in the case of DFO against reactive oxygen species generation.

Dopamine induces cell death, lipid peroxidation and DNA base damage in a catecholaminergic cell line derived from the central nervous system

Dopamine can be autoxidized to superoxides and quinones. Superoxides can form hydroxyl radicals that are highly reactive with lipids, proteins and DNA leading to neuronal damage and cell death. We used a clonal catecholaminergic cell line (CATH.a) derived from the central nervous system to evaluate the effects of dopamine on cell death, lipid peroxidation and DNA base damage. Dopamine produces cell death in CATH.a cells and this is associated with an increase in annexin binding, which is an early indicator of apoptosis. Incubation of CATH.a cells with deferoximine, an iron chealator, partially antagonizes dopamine-induced cell death. In CATH.a cells, dopamine produces an increase in both lipid peroxidation, as measured by cis-parinaric acid fluorescence, and DNA oxidative base damage, as measured by 8-hydroxy-2'-deoxyguanosine formation. Cell death was inhibited 84-92% by the hydrophilic antioxidants, dithiothreitol, L-cysteine, and N-acetylcysteine. The lipophilic vitamins, retinol and vitamin E and the vitamin E analog, Trolox, inhibited dopamine-induced cell death by 18-33%. The lipophilic antioxidants probucol, propyl glycol and butylated hydroxyanisone had no inhibitory effect on dopamine-induced cell death. These data suggest that damage to DNA and lipids may be partially responsible for dopamine-induced cell death in CATH.a cells.

Prooxidant activity of ferrioxamine in isolated rat hepatocytes and linoleic acid micelles

The complex iron-desferrioxamine (ferrioxamine) is considered chemically unreactive, and not able to participate in redox cycle reactions. Desferrioxamine-dependent toxicity is, however, described in both human and animal studies. The aim of this work was to test the possibility that chelated iron, under certain circumstances, could enter redox reactions, giving an explanation of desferrioxamine side effects. Carefully prepared ferrioxamine, to obtain a 1:1 desferrioxamine:iron ratio, was added to isolated rat hepatocytes and to linoleic acid micelles. A strong prooxidant and cytotoxic effect was observed in the cells, also potentiating tert-butyl hydroperoxide-induced lipid peroxidation. In micelles, the prooxidant effect was observed only in the presence of ascorbate, which is oxidized during the process, giving rise to ascorbyl radical. Ferrioxamine, under the experimental conditions used, did not release iron, indicating that the prooxidant effect was due to iron redox cycling. The addition of desferrioxamine prevented both ferrioxamine- and tert-butyl hydroperoxide-induced lipid peroxidation and cytotoxicity. Concurrently, a nitroxide radical was detected, an indication of the radical scavenger activity of the hydroxamic moiety. No radical species was observed when ferrioxamine was added to the same system. The prooxidant effect of ferrioxamine gives a possible explanation of the reported human and animal desferrioxamine toxicity. When, in compartmentalized regions, the ratio of desferrioxamine:metal reaches 1:1, ferrioxamine is formed. In the absence of metal-free desferrioxamine, ferrioxamine can participate in redox cycling reactions, initiating lipid peroxidation and cytotoxicity.

Inhibition of skeletal sarcoplasmic reticulum Ca2+-ATPase activity by deferoxamine nitroxide free radical

Deferoxamine is an inhibitor of iron-dependent free radical reactions. Despite the antioxidant roles, prolonged clinical use of the chelator is far from benign, and paradoxically, deferoxamine has been shown to promote lipid peroxidation. The possible toxicity of the drug's metabolites, such as deferoxamine nitroxide free radical, deserves attention. We, therefore, tested the hypothesis that deferoxamine nitroxide radicals produced as a result of enzymatic one-electron oxidation of deferoxamine by horseradish peroxidase in the presence of H2O2 are capable of inactivating Ca2+-ATPase of skeletal sarcoplasmic reticulum microsomes as a model system with which to explore the effect of the radical on a biological membrane. Ca2+-ATPase activity of sarcoplasmic reticulum was depressed by exposure to Fenton's reagent (H2O2/FeSO4); the observed effect was significantly enhanced by deferoxamine. We found that the Fenton reaction produced hydroxyl radical, as determined by electron spin resonance spectroscopy. The formation of hydroxyl radical was completely inhibited by deferoxamine; instead, under the same experimental conditions (in the presence of sarcoplasmic reticulum vesicles with or without FeSO4 but without spin trap 5, 5-dimethyl-1-pyrroline N-oxide), the spectral shape and hyperfine coupling constants of electron spin resonance signals confirmed to be long-lived deferoxamine radical were obtained. Furthermore, exposure of sarcoplasmic reticulum vesicles to deferoxamine radical formed by horseradish peroxidase via reaction with H2O2 caused an inhibition of the Ca2+-ATPase activity. The findings show that the sarcoplasmic reticulum vesicles can act as peroxidases and suggest that deferoxamine enhances the decreased Ca2+-ATPase activity afforded by H2O2/FeSO4 due to formation of its metabolites, possibly deferoxamine nitroxide free radical.

The role of iron in neurodegeneration: prospects for pharmacotherapy of Parkinson's disease

Although the aetiology of Parkinson's disease (PD) and related neurodegenerative disorders is still unknown, recent evidence from human and experimental animal models suggests that a misregulation of iron metabolism, iron-induced oxidative stress and free radical formation are major pathogenic factors. These factors trigger a cascade of deleterious events leading to neuronal death and the ensuing biochemical disturbances of clinical relevance. A review of the available data in PD provides the following evidence in support of this hypothesis: (i) an increase of iron in the brain, which in PD selectively involves neuromelanin in substantia nigra (SN) neurons; (ii) decreased availability of glutathione (GSH) and other antioxidant substances; (iii) increase of lipid peroxidation products and reactive oxygen (O2)species (ROS); and (iv) impaired mitochondrial electron transport mechanisms. Most of these changes appear to be closely related to interactions between iron and neuromelanin, which result in accumulation of iron and a continuous production of cytotoxic species leading to neuronal death. Some of these findings have been reproduced in animal models using 6-hydroxydopamine, N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), iron loading and beta-carbolines, although none of them is an accurate model for PD in humans. Although it is not clear whether iron accumulation and oxidative stress are the initial events causing cell death or consequences of the disease process, therapeutic efforts aimed at preventing or at least delaying disease progression by reducing the overload of iron and generation of ROS may be beneficial in PD and related neurodegenerative disorders. Current pharmacotherapy of PD, in addition to symptomatic levodopa treatment, includes 'neuroprotective' strategies with dopamine agonists, monoamine oxidase-B inhibitors (MAO-B), glutamate antagonists, catechol O-methyltransferase inhibitors and other antioxidants or free radical scavengers. In the future, these agents could be used in combination with, or partly replaced by, iron chelators and lazaroids that prevent iron-induced generation of deleterious substances. Although experimental and preclinical data suggest the therapeutic potential of these drugs, their clinical applicability will be a major challenge for future research.

Inflammatory responses to ischemia and reperfusion in skeletal muscle

Skeletal muscle ischemia and reperfusion is now recognized as one form of acute inflammation in which activated leukocytes play a key role. Although restoration of flow is essential in alleviating ischemic injury, reperfusion initiates a complex series of reactions which lead to neutrophil accumulation, microvascular barrier disruption, and edema formation. A large body of evidence exists which suggests that leukocyte adhesion to and emigration across postcapillary venules plays a crucial role in the genesis of reperfusion injury in skeletal muscle. Reactive oxygen species generated by xanthine oxidase and other enzymes promote the formation of proinflammatory stimuli, modify the expression of adhesion molecules on the surface of leukocytes and endothelial cells, and reduce the bioavailability of the potent antiadhesive agent nitric oxide. As a consequence of these events, leukocytes begin to form loose adhesive interactions with postcapillary venular endothelium (leukocyte rolling). If the proinflammatory stimulus is sufficient, leukocytes may become firmly adherent (stationary adhesion) to the venular endothelium. Those leukocytes which become firmly adherent may then diapedese into the perivascular space. The emigrated leukocytes induce parenchymal cell injury via a directed release of oxidants and hydrolytic enzymes. In addition, the emigrating leukocytes also exacerbate ischemic injury by disrupting the microvascular barrier during their egress across the vasculature. As a consequence of this increase in microvascular permeability, transcapillary fluid filtration is enhanced and edema results. The resultant increase in interstitial tissue pressure physically compresses the capillaries, thereby preventing microvascular perfusion and thus promoting the development of the no-reflow phenomenon. The purpose of this review is to summarize the available information regarding these mechanisms of skeletal muscle ischemia/reperfusion injury.

New modes of action of desferrioxamine: scavenging of semiquinone radical and stimulation of hydrolysis of tetrachlorohydroquinone

Desferrioxamine (DFO) is a common drug used in the treatment of iron overload. In addition to its iron-chelation, other properties have been identified. Alas, DFO has demonstrable effects which cannot be explained by its classically established properties; i.e., DFO protects against DNA single strand breaks induced by tetrachlorohydroquinone (TCHQ), while other iron chelators such as DTPA (diethylenetriaminepentaacetic acid) do not. The autooxidation process of TCHQ yielding the tetrachlorosemiquinone radical (TCSQ.) intermediate, was studied here in the presence of chelators. DFO led to a marked reduction in both concentration and life span of TCSQ. via formation of DFO-nitroxide radical (DFO.). In contrast, DTPA had no detectable effect on TCHQ autooxidation. Present studies indicate that the protective effects of DFO on TCHQ-induced DNA damage were not due to the binding of iron, but rather to scavenging of the reactive TCSQ. and the formation of the less reactive DFO.. An additional mode of action of DFO was identified, via stimulation of the hydrolysis (dechlorination) of tetrachloro-1,4-benzoquinone (chloranil), which is the oxidation product of TCHQ, to form 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone (chloranilic acid). The results of this study demonstrate two new modes of action for DFO: the scavenging of deleterious semiquinone radical, and the stimulation of the hydrolysis of halogenated substituents on the quinone structure. Both modes might prove highly relevant to the biological activities of DFO.

Desferrioxamine and vitamin E protect against iron and MPTP-induced neurodegeneration in mice

To elucidate the neuroprotective effects of the iron chelator desferrioxamine (DFO) and the antioxidant vitamin E on excessive iron-induced free radical damage, a chronic iron-loaded mice model was established. The relationship between striatal iron content, oxidized to reduced glutathione ratio, hydroxyl radical (.OH) levels and dopamine concentrations were observed in DFO or vitamin E pretreated iron-loaded/1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated C57BL/6 mice. The results demonstrated that both DFO and vitamin E inhibit the iron accumulation and thus reverses the increase in oxidized glutathione (GSSG), oxidized to reduced glutathione ratios, .OH and lipid peroxidation levels. The striatal dopamine concentration was elevated to normal value. Our data suggested that: (1) iron may induce neuronal damage and thus excessive iron in the brain may contribute to the neuronal loss in PD; (2) iron chelators and antioxidants may serve as potential therapeutic agents in retarding the progression of neurodegeneration.

Peroxidative damage in sickle-cell erythrocyte ghosts: protective effect of allopurinol

1. Malondialdehyde (MDA) levels of erythrocyte membranes of sickle-cell disease patients were measured as an indicator of peroxidative damage and allopurinol was used as a lipid peroxide scavenger. 2. Incubating sickle-cell erythrocytes with allopurinol significantly reduced MDA levels of erythrocyte membranes compared with before-treatment values. 3. Allopurinol seems to reduce the peroxidative damage in sickle-cell erythrocytes, but the mechanism is still unknown.

Desferrioxamine inhibition of the hydroxyl radical-like reactivity of peroxynitrite: role of the hydroxamic groups

Nitric oxide reacts with superoxide to form peroxynitrite, a strong oxidizing species. Peroxynitrite can either directly oxidize molecules such as thiols or protonate to peroxynitrous acid, which can yield an oxidant with a reactivity similar to that of hydroxyl radical in a transition metal-independent mechanism. This oxidative chemistry of peroxynitrite, however, is inhibited by the metal chelator desferrioxamine. Indeed, desferrioxamine, was a potent inhibitor of dimethylsulfoxide, hydrogen peroxide, 5,5-dimethyl-1-pyrroline-N-oxide, and luminol oxidation, whereas the metal chelator diethylenetriaminepentaacetic acid, and ferrioxamine, the iron complex of desferioxamine, were not. Two other hydroxamates, acetohydroxamate and salicylhydroxamate, were also effective inhibitors. Stopped-flow experiments showed that there is no direct reaction between peroxynitrite anion or cis-peroxynitrous acid with desferrioxamine. Electron paramagnetic resonance (EPR) studies showed the formation of the desferrioxamine nitroxide radical in incubations containing desferrioxamine, but not ferrioxamine, indicating that the hydroxamic group acts as a one-electron donor to peroxynitrite-derived oxidants. Taken together, our results led us to propose that desferrioxamine can inhibit the oxidative chemistry of peroxynitrite by reaction of the hydroxamic acid moieties with trans-peroxynitrous acid.

Oxidised low density lipoproteins induce iron release from activated myoglobin

Recent reports have detected the presence of iron in human atherosclerotic lesions [Biochem. J. 286 (1992) 901-905]. This study provides evidence for a biochemical mechanism whereby iron is released from myoglobin by low density lipoprotein (LDL) which has become oxidised by the ferryl myoglobin species. The haem destabilisation and iron release are inhibited by monohydroxamate compounds and desferrioxamine through their ability to inhibit the propagation of LDL oxidation. Thus, iron may derive from the myoglobin released from ruptured cells in the oxidising environment of the atherosclerotic lesion.

Current status of antioxidant therapy

There is evidence that free radical damage contributes to the aetiology of many chronic health problems such as emphysema, cardiovascular and inflammatory diseases, cataracts, and cancer. In this review we are not concerned with tissue damage in vivo induced directly by radicals from exogenous sources, such as air pollutants and tobacco smoke, high-pressure oxygen, irradiation, or through the metabolism of certain solvents, drugs, and pesticides. Rather, we address some of the disease states associated with increased oxidative stress from endogenous sources and the possible therapeutic advantage of the antioxidant treatment. This raises the question of the antioxidant status of individuals and its role in protection against amplification of certain disease processes. We have chosen to concentrate mainly on coronary heart disease, reperfusion injury, and organ storage for transplantation.

Oxidation of desferrioxamine to nitroxide free radical by activated human neutrophils

Human neutrophils activated by PMA were found to induce the formation of a nitroxide radical from DFO. The presence of SOD was necessary to permit the formation of the DFO radical. The inactive phorbol ester did not induce DFO radical, and DL-sphinganine suppressed the radical produced by the active phorbol ester. Other cell stimuli (Zymocel and the chemotactic peptide) also induced the formation of the DFO radical, although radical concentration was very much lower than with PMA. Participation of NO, OH or 1O2 was ruled out by the inability of NG-methyl-L-arginine, NG-nitro-L-arginine, DMSO, mannitol, histidine, and methionine to inhibit the formation of DFO radical produced by PMA-activated cells. Furthermore, PMA-activated cells did not produce detectable levels of NO2-, a stable oxidation product of NO, and D2O, which enhances the lifetime of singlet oxygen, did not modify the intensity or the lifetime of DFO radical. The involvement of cell MPO was suggested by the inhibition of the DFO radical observed after treatment with catalase or with antihuman MPO antibodies. Also, HOCl was found to induce the DFO radical in cell-free reactions, but our data indicate that the reaction leading to DFO radical formation by neutrophils involves the reduction of MPO compound II back to the active enzyme (ferric-MPO). Anti-inflammatory drugs strongly increased the DFO radical produced by activated neutrophils. On the contrary, none of these drugs was able to increase the DFO radical produced by HOCl. Histidine and methionine that inhibited the DFO radical intensity in cell-free reactions, were shown to act directly on HOCl. Experiments with MPO-H2O2 in SOD- and Cl(-)-free conditions showed the formation of DFO radical and confirmed the hypothesis of the involvement of compound II. The conversion of compound II to ferric MPO by DFO optimized the enzymatic activity of neutrophils, and in the presence of monochlorodimedon (compound II promoting agent) we measured an increased HOCl production. When DFO was modified by conjugation with hydroxyethyl starch, it lost the ability to produce the radical either by neutrophils or by MPO-H2O2 and did not increase HOCl production. The inability of these DFO derivatives to produce potentially toxic species might explain their reported lower toxicity in vivo.

The efficacy of monohydroxamates as free radical scavenging agents compared with di- and trihydroxamates

Desferrioxamine, the therapeutic iron chelator, is limited in its usage by its short half-life in plasma and lack of oral activity, its side-effects and its slow penetration into cells. Several studies have emerged recently demonstrating the ability of this trihydroxamate compound to act as a radical scavenger, in addition to and independently of its iron-chelating properties. These include the interaction of desferrioxamine with the superoxide radical and ferryl myoglobin radical, as well as its action as a chain-breaking antioxidant in peroxidizing erythrocyte membranes. We have synthesized recently a series of monohydroxamate compounds and investigated their efficacy as radical scavenging antioxidants in comparison with desferrioxamine and rhodotorulic acid, a naturally occurring dihydroxamate compound. The results show that the relative rates of reaction of these hydroxamate derivatives with ferryl myoglobin are N-methyl-N-hexanoyl hydroxylamine > N-methyl-N-benzoyl hydroxylamine > N-methyl-N-acetyl hydroxylamine > desferrioxamine > rhodotorulic acid > N-methyl-N-butyryl hydroxylamine.

Free radical-lipid interactions and their pathological consequences

In this review we have tried to present the current thinking on the consequences for lipids of their interactions with free radicals and the pathological implications. In particular, atherosclerosis and cancer have been addressed. In the case of the former, it is not clear whether the initial oxidative event is an enzymic or free radical-mediated process as yet. However, the importance of the antioxidants in controlling LDL oxidation, macrophage uptake of oxidatively modified LDL and progression of atheroma in animal models certainly suggests an important propagative role for free radical-mediated events. With regard to cancer, oxidative modification of cell lipids has potential consequences for tumour cell proliferation. Whilst lipid hydroperoxides can serve as an origin of prostaglandins with tumour inhibitor (or immunosuppressive) properties, they may also influence cellular growth regulatory proteins normally dependent on membrane lipid integrity. Alternatively, they may function as a source of aldehydic breakdown products capable of 'down-regulating' cell proliferation through covalent modification of regulatory proteins. Oils rich in n-3 polyunsaturated fatty acids have toxic effects towards tumour cells. This toxicity is not mediated by prostaglandins but rather through the capacity of such agents to elevate the levels of lipid peroxides. This may be enhanced by active oxygen species released constitutively from tumour cells.

Impairment of macrophage functions after ingestion of Plasmodium falciparum-infected erythrocytes or isolated malarial pigment

Human monocyte-derived macrophages ingest diamide-treated red blood cells (RBC), anti-D immunoglobulin (Ig)G-opsonized RBC, or Plasmodium falciparum ring-stage parasitized RBC (RPRBC), degrade ingested hemoglobin rapidly, and can repeat the phagocytic cycle. Monocytes fed with trophozoite-parasitized RBC (TPRBC), which contain malarial pigment, or fed with isolated pigment are virtually unable to degrade the ingested material and to repeat the phagocytic cycle. Monocytes fed with pigment display a long-lasting oxidative burst that does not occur when they phagocytose diamide-treated RBC or RPRBC. The phorbol myristate acetate-elicited oxidative burst is irreversibly suppressed in monocytes fed with TPRBC or pigment, but not in monocytes fed with diamide-treated or IgG-opsonized RBC. This pattern of inhibition of phagocytosis and oxidative burst suggests that malarial pigment is responsible for the toxic effects. Pigment iron released in the monocyte phagolysosome may be the responsible element. 3% of total pigment iron is labile and easily detached under conditions simulating the internal environment of the phagolysosome, i.e., pH 5.5 and 10 microM H2O2. Iron liberated from pigment could account for the lipid peroxidation and increased production of malondialdehyde observed in monocytes fed with pigment or in RBC ghosts and liposomes incubated at pH 6.5 in presence of pigment and low amounts of H2O2. Removal of the labile iron fraction from pigment by repeated treatments with 0.1 mM H2O2 at pH 5.5 reduces pigment toxicity. It is suggested that iron released from ingested pigment is responsible for the intoxication of monocytes. In acute and chronic falciparum infections, circulating and tissue-resident phagocytes are seen filled with TPRBC and pigment particles over long periods of time. Moreover, human monocytes previously fed with TPRBC are unable to neutralize pathogenic bacteria, fungi, and tumor cells, and macrophage responses decline during the course of human and animal malaria. The present results may offer a mechanistic explanation for depression of cellular immunity in malaria.

The chelation of nonheme iron within sickle erythrocytes by the hydroxypyridinone chelator CP094

Nonheme, nonferritin iron has been detected in membrane preparations from sickle erythrocytes and has been suggested to catalyze free radical reactions in these cells contributing to the development of membrane oxidation. In this study the hydroxypyridinone iron chelator, CP094, currently being evaluated as a potentially therapeutic chelator, and desferrioxamine have been studied for their abilities to chelate the nonheme iron within intact sickle erythrocytes under physiological conditions. The results suggest that CP094 can enter sickle erythrocytes, chelate nonheme iron and suppress membrane lipid peroxidation within a timescale in which desferrioxamine does not enter the cells. Suppression of lipid peroxidation showed no protective effect in an in vitro system inducing the formation of irreversibly sickled cells.

Detection of radicals produced by reaction of hydroperoxides with rat liver microsomal fractions

EPR spin trapping using the spin traps 5,5-dimethyl-1-pyrroline N-oxide (DMPO) and 3,5-dibromo-4-nitrosobenzene sulphonic acid (DBNBS) has been employed to examine the generation of radicals produced on reaction of a number of primary, secondary and lipid hydroperoxides with rat liver microsomal fractions in both the presence and absence of reducing equivalents. Two major mechanisms of radical generation have been elucidated. In the absence of NADPH or NADH, oxidative degradation of the hydroperoxide occurs to give initially a peroxyl radical which in the majority of cases can be detected as a spin adduct to DMPO; these radicals can undergo further reactions which result in the generation of alkoxyl and carbon-centered radicals. In the presence of NADPH (and to a lesser extent NADH) alkoxyl radicals are generated directly via reductive cleavage of the hydroperoxide. These alkoxyl radicals undergo further fragmentation and rearrangement reactions to give carbon-centered species which can be identified by trapping with DBNBS. The type of transformation that occurs is highly dependent on the structure of the alkoxyl radical with species arising from beta-scission, 1,2-hydrogen shifts and ring closure reactions being identified; these processes are in accord with previous chemical studies and are characteristic of alkoxyl radicals present in free solution. Studies using specific enzyme inhibitors and metal-ion chelators suggest that most of the radical generation occurs via a catalytic process involving haem proteins and in particular cytochrome P-450. An unusual species (an acyl radical) is observed with lipid hydroperoxides; this is believed to arise via a cage reaction after beta-scission of an initial alkoxyl radical.

Thiol compounds as protective agents in erythrocytes under oxidative stress

The potential for the thiol-containing drugs, N-acetyl cysteine and N-mercaptopropionyl glycine, to act as antioxidants intracellularly has been studied in erythrocytes under oxidative stress. The effects have been compared with that of the glutathione peroxidase inhibitor, mercaptosuccinate. The results show differential responses of sickle and normal erythrocytes to the thiol compounds. N-acetyl cysteine is the more efficacious with no toxic effects in these systems. N-Mercaptopropionyl glycine is not only limited in its ability to demonstrate antioxidant capacity in erythrocytes but also exerts deleterious effects.

The role of free radicals in asbestos-induced diseases

Asbestos exposure causes pulmonary fibrosis and malignant neoplasms by mechanisms that remain uncertain. In this review, we explore the evidence supporting the hypothesis that free radicals and other reactive oxygen species (ROS) are an important mechanism by which asbestos mediates tissue damage. There appears to be at least two principal mechanisms by which asbestos can induce ROS production; one operates in cell-free systems and the other involves mediation by phagocytic cells. Asbestos and other synthetic mineral fibers can generate free radicals in cell-free systems containing atmospheric oxygen. In particular, the hydroxyl radical often appears to be involved, and the iron content of the fibers has an important role in the generation of this reactive radical. However, asbestos also appears to catalyze electron transfer reactions that do not require iron. Iron chelators either inhibit or augment asbestos-catalyzed generation of the hydroxyl radical and/or pathological changes, depending on the chelator and the nature of the asbestos sample used. The second principal mechanism for asbestos-induced ROS generation involves the activation of phagocytic cells. A variety of mineral fibers have been shown to augment the release of reactive oxygen intermediates from phagocytic cells such as neutrophils and alveolar macrophages. The molecular mechanisms involved are unclear but may involve incomplete phagocytosis with subsequent oxidant release, stimulation of the phospholipase C pathway, and/or IgG-fragment receptor activation. Reactive oxygen species are important mediators of asbestos-induced toxicity to a number of pulmonary cells including alveolar macrophages, epithelial cells, mesothelial cells, and endothelial cells. Reactive oxygen species may contribute to the well-known synergistic effects of asbestos and cigarette smoke on the lung, and the reasons for this synergy are discussed. We conclude that there is strong evidence supporting the premise that reactive oxygen species and/or free radicals contribute to asbestos-induced and cigarette smoke/asbestos-induced lung injury and that strategies aimed at reducing the oxidant stress on pulmonary cells may attenuate the deleterious effects of asbestos.

Desferrioxamine enhances the reactivity of vanadium (IV) and vanadium (V) toward ferri- and ferrocytochrome c

Ligands, especially desferrioxamine, affect the rate at which vanadium reduces or oxidizes cytochrome c. Whether reduction or oxidation occurs, and how fast, depends on the nature of the ligand, the state of reduction of the vanadium, the pH (6.0, 7.0, or 7.4), and the availability of oxygen. In general, oxidation of ferrocytochrome c was favored by (1) low pH, (2) an oxidized state of the vanadium, (3) the presence of oxygen, and (4) more strongly binding ligands (desferrioxamine much greater than histidine = ATP greater than EDTA greater than albumin greater than aquo). Thus, at pH 6.0, desferrioxamine accelerated the V(V)-catalyzed ferrocytochrome c oxidation 160-fold aerobically, and 3500-fold anaerobically. In general, strongly binding ligands slowed oxidations, especially at higher pH. Desferrioxamine was unique among the five ligands in that it not only accelerated oxidation of ferrocytochrome c at pH 6.0, but at pH 7.4 the redox balance shifted to the point where it paradoxically reduced ferricytochrome c. V(V) is an improbable electron donor, but desferrioxamine will reduce cytochrome c, and V(V) accelerates this process. Oxidation of cytochrome c by V(V):desferrioxamine was faster anaerobically, and reduction by V(IV):desferrioxamine was faster aerobically. Although V(V) did not oxidize ferrocytochrome c at pH 7.4, V(IV) did, provided oxygen and desferrioxamine were both present. V(IV):desferrioxamine almost completely reduced ferricytochrome c, and this reduction was followed by a slow, progressive oxidation. This latter oxidation of cytochrome c is mediated by active species generated in the reaction between V(IV):desferrioxamine and oxygen, because none of these reagents alone can induce oxidation at a comparable rate. The mediating species were transient, and generated in reactions with oxygen.(ABSTRACT TRUNCATED AT 250 WORDS)

The formation of free radicals by cardiac myocytes under oxidative stress and the effects of electron-donating drugs

The interaction of myoglobin with H2O2 leads via a two-electron oxidation process to the formation of ferryl myoglobin. Metmyoglobin is more readily activated than oxymyoglobin to the ferryl states, which are capable of inducing peroxidative damage to membranes. E.p.r. and optical spectroscopic studies show that the thiol-containing compounds N-(2-mercaptopropionyl) glycine and N-acetylcysteine and the trihydroxamate desferrioxamine attenuate these processes by reducing the ferryl myoglobin species to metmyoglobin, with the formation of thiyl radicals and the desferrioxamine nitroxide radical respectively. Biochemical investigations of the potential for myoglobin in ruptured myocytes to be involved in radical generation, when under oxidative stress, and of the nature of the resulting species, were also undertaken. E.p.r. spectroscopic studies revealed the formation of a radical species which is capable of inducing membrane lipid peroxidation. The interaction of the thiol compounds and desferrioxamine with components of myocardial tissue under these conditions results in the generation of thiol-derived radical species and the desferrioxamine nitroxide radical respectively. These data, along with those obtained using optical spectrocopy, support the assignment of the identity of the radical species generated from the myocytes as the ferryl myoglobin radical.