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Prevention of oxidant-induced cell death by intralysosomal iron binding
Linköping University, Department of Medicine and Care, Pulmonary Medicine. Linköping University, Department of Neuroscience and Locomotion, Speech and Language Pathology. Linköping University, Faculty of Health Sciences.
2003 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The lung is particularly prone to oxidative stress by its exposure to ambient oxygen and inhaled environmental oxidants. Abnormal assimilation and accumulation of iron are found in many lung disorders, which in redox-active form will exacerbate oxidative tissue damage. It may be that the most important cellular pool of redox -active iron exists within lysosomes. As a result, these organelles are very vulnerable to oxidative stress and may burst due to peroxidative membrane destabilization. Support for the importance of intralysosomal iron in cellular oxidant damage includes the observation that the iron chelator, desferrioxamine, which almost exclusively localizes within the lysosomal compartment, will protect cells against oxidati ve challenge. Iron chelators targeted to the lysosomes may therefore be a particularly efficient therapeutic strategy for cells under conditions of substantial oxidative stress.

The present study, employing cultures of human respiratory epithelial cells and murine macrophage-like cells, explores the protective effects by iron binding agents upon H202 and gamma radiation-induced lysosomal damage and cell death. Using these in vitro models, the present study shows: (1) that chelation of intralysosomal iron efficiently prevents lysosomal rupture and ensuing cell death induced by either H202 or gamma radiation; (2) that cell permeable lysosomotropic iron-chelators are much more efficient than those being internalized by endocytosis; (3) that intralysosomal iron is the most important cellular pool of redox-active iron for chelation therapy; (4) that ironcatalyzed peroxidative lysosomal destabilization is a decisive and early event in the apoptotic machinery.

Although apoferritin and desferrioxarnine suppress the reactivity of lysosomal iron, their efficacy is considerably restrained by their uptake by fluid-phase endocytosis. Apoferritin is digested intralysosomally which further decreases its iron sequestering potential, while desferrioxamine by its intralysosomal retention may disturbe normal cellular functions and cause iron-starvation. Amongst cell permeable iron-binding agents we tested a-lipoic acid, alipoamide, and a synthetic amine derivative of α-lipoarnide, α-lipoic acid-plus (5-[1,2] dithiolan-3-yl-pentanoic acid (2-dimethylamino-ethyl) amide). The large difference in the protective potential of these cell permeant iron-chelators derives from their being localized in different cellular compartments, which lends further support that lysososomes contain the most important pool of chelatable redox-active iron. Indeed, a-lipoic acid-plus by its lysosomotropism was by all means the most efficient iron chelator. On a molar basis α-lipoic acid-plus was 4,000 to 5,000 times more effective than desferrioxamine to prevent lysosomal rupture and cell death induced by H202 or gamma radiation.

We conclude that iron chelating therapy targeted to the lysosomes is an efficient strategy to protect oxidatively stressed cells in vitro. A corresponding efficacy of such treatment in vivo, and in iron dependent pulmonary disorders in particular, needs to be explored.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet , 2003. , 60 p.
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 812
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:liu:diva-27537Local ID: 12194ISBN: 91-7373-502-7 (print)OAI: oai:DiVA.org:liu-27537DiVA: diva2:248089
Public defence
2003-10-23, Victoriasalen, Universitetssjukhuset, Linköping, 13:15 (Swedish)
Opponent
Available from: 2009-10-08 Created: 2009-10-08 Last updated: 2012-10-05Bibliographically approved
List of papers
1. Novel cellular defenses against iron and oxidation: ferritin and autophagocytosis preserve lysosomal stability in airway epithelium
Open this publication in new window or tab >>Novel cellular defenses against iron and oxidation: ferritin and autophagocytosis preserve lysosomal stability in airway epithelium
2001 (English)In: Redox report, ISSN 1351-0002, E-ISSN 1743-2928, Vol. 6, no 1, 57-63 p.Article in journal (Refereed) Published
Abstract [en]

Adsorbed to a variety of particles, iron may be carried to the lungs by inhalation thereby contributing to a number of inflammatory lung disorders. Redox-active iron is a potent catalyst of oxidative processes, but intracellularly it is bound primarily to ferritin in a non-reactive form and probably is catalytically active largely within the lysosomal compartment. Damage to the membranes of these organelles causes the release to the cytosol of a host of powerful hydrolytic enzymes, inducing apoptotic or necrotic cell death. The results of this study, using cultured BEAS-2B cells, which are adenovirus transformed human bronchial epithelial cells, and A549 cells, which have characteristics similar to type II alveolar epithelial cells, suggest that the varying abilities of different types of lung cells to resist oxidative stress may be due to differences in intralysosomal iron chelation. Cellular ferritin and iron were assayed by ELISA and atomic absorption, while plasma and lysosomal membrane stability were evaluated by the acridine orange uptake and trypan blue dye exclusion tests, respectively. Normally, and also after exposure to an iron complex, A549 cells contained significantly more ferritin (2.26 ± 0.60 versus 0.63 ± 0.33 ng/μg protein, P <0.001) and less iron (0.96 ± 0.14 versus 1.48 ± 0.21 ng/μg protein, P <0.05) than did BEAS-2B cells. Probably as a consequence, iron-exposed A549 cells displayed more stable lysosomes (P <0.05) and better survival (P <0.05) following oxidative stress. Following starvation-induced autophagocytosis, which also enhances resistance to oxidant stress, the A549 cells showed a significant reduction in ferritin, and the BEAS-2B cells did not. These results suggest that intralysosomal ferritin enhances lysosomal stability by iron-chelation, preventing Fenton-type chemistry. This notion was further supported by the finding that endocytosis of apoferritin, added to the medium, stabilized lysosomes (P <0.001 versus P <0.01) and increased survival (P <0.01 versus P <0.05) of iron-loaded A549 and BEAS-2B cells. Assuming that primary cell lines of the alveolar and bronchial epithelium behave in a similar manner as these respiratory cell lines, intrabronchial instillation of apoferritin-containing liposomes may in the future be a treatment for iron-dependent airway inflammatory processes.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-25287 (URN)10.1179/135100001101536049 (DOI)9727 (Local ID)9727 (Archive number)9727 (OAI)
Available from: 2009-10-07 Created: 2009-10-07 Last updated: 2017-12-13Bibliographically approved
2. α-lipoic acid and α-lipoamide prevent oxidant-induced lysosomal rupture and apoptosis
Open this publication in new window or tab >>α-lipoic acid and α-lipoamide prevent oxidant-induced lysosomal rupture and apoptosis
2001 (English)In: Redox report, ISSN 1351-0002, E-ISSN 1743-2928, Vol. 6, no 5, 327-334 p.Article in journal (Refereed) Published
Abstract [en]

α-Lipoic acid (LA) and its corresponding derivative, α-lipoamide (LM), have been described as antioxidants, but the mechanisms of their putative antioxidant effects remain largely uncharacterised. The vicinal thiols present in the reduced forms of these compounds suggest that they might possess metal chelating properties. We have shown previously that cell death caused by oxidants may be initiated by lysosomal rupture and that this latter event may involve intralysosomal iron which catalyzes Fenton-type chemistry and resultant peroxidative damage to lysosomal membranes. Here, using cultured J774 cells as a model, we show that both LA and LM stabilize lysosomes against oxidative stress, probably by chelating intralysosomal iron and, consequently, preventing intralysosomal Fenton reactions. In preventing oxidant-mediated apoptosis, LM is significantly more effective than LA, as would be expected from their differing capacities to enter cells and concentrate within the acidic lysosomal compartment. As previously reported, the powerful iron-chelator, desferrioxamine (Des) (which also locates within the lysosomal compartment), also provides protection against oxidant-mediated cell death. Interestingly, although Des enhances the partial protection afforded by LA, it confers no additional protection when added with LM. Therefore, the antioxidant actions of LA and LM may arise from intralysosomal iron chelation, with LM being more effective in this regard.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-47165 (URN)10.1179/135100001101536472 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13Bibliographically approved
3. Prevention of oxidant-induced cell death by lysosomotropic iron chelators
Open this publication in new window or tab >>Prevention of oxidant-induced cell death by lysosomotropic iron chelators
Show others...
2003 (English)In: Free Radical Biology & Medicine, ISSN 0891-5849, E-ISSN 1873-4596, Vol. 34, no 10, 1295-1305 p.Article in journal (Refereed) Published
Abstract [en]

Intralysosomal iron powerfully synergizes oxidant-induced cellular damage. The iron chelator, desferrioxamine (DFO), protects cultured cells against oxidant challenge but pharmacologically effective concentrations of this drug cannot readily be achieved in vivo. DFO localizes almost exclusively within the lysosomes following endocytic uptake, suggesting that truly lysosomotropic chelators might be even more effective. We hypothesized that an amine derivative of α-lipoamide (LM), 5-[1,2] dithiolan-3-yl-pentanoic acid (2-dimethylamino-ethyl)-amide (α-lipoic acid-plus [LAP]; pKa = 8.0), would concentrate via proton trapping within lysosomes, and that the vicinal thiols of the reduced form of this agent would interact with intralysosomal iron, preventing oxidant-mediated cell damage. Using a thiol-reactive fluorochrome, we find that reduced LAP does accumulate within the lysosomes of cultured J774 cells. Furthermore, LAP is approximately 1,000 and 5,000 times more effective than LM and DFO, respectively, in protecting lysosomes against oxidant-induced rupture and in preventing ensuing apoptotic cell death. Suppression of lysosomal accumulation of LAP (by ammonium-mediated lysosomal alkalinization) blocks these protective effects. Electron paramagnetic resonance reveals that the intracellular generation of hydroxyl radical following addition of hydrogen peroxide to J774 cells is totally eliminated by pretreatment with either DFO (1 mM) or LAP (0.2 μM) whereas LM (200 μM) is much less effective.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-27105 (URN)10.1016/S0891-5849(03)00106-0 (DOI)11752 (Local ID)11752 (Archive number)11752 (OAI)
Available from: 2009-10-08 Created: 2009-10-08 Last updated: 2017-12-13Bibliographically approved
4. Chelation of intralysosomal redox-active iron protects against ionizing radiation damage
Open this publication in new window or tab >>Chelation of intralysosomal redox-active iron protects against ionizing radiation damage
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The mechanisms involved in cellular injury and death caused by ionizing radiation remain incompletely understood. Although DNA damage - especially to actively dividing cells - is certainly a critical component, other types of damage may also be important. Ionizing radiation generates reactive oxygen species (ROS) and 'loose' (i.e., redox-active) iron amplifies the damaging effects of ROS. The major pool of reactive intracellular iron may reside within the acidic vacuolar compartment (lysosomes and late endosomes). Lysosomes are responsible for the continuous digestion of ferruginous materials such as fenitin, mitochondria, and various metalloproteins. We have investigated the possible importance of intralysosomal iron and lysosomal rupture in radiation-induced cellular injury using macrophage-like J774 cells. We find: (i) Gamma radiation of cells greatly enhances the intracellular pool of reactive iron, which increase ≈ 5-fold 24 hours following a non-lethal single dose of radiation (40 Gy). (ii) Using a special staining procedure (the sulfide-silver method or auto-metallography), we find that most redox-active iron resides within the lysosomal compartment both before and after radiation. The dramatically increased intralysosomal iron following radiation probably derives from reparatin· autophagocytosis, whereby damaged iron-containing cellular constituents are digested intralysosomally. (iii) This increased lysosomal iron sensitizes cells to a second dose of radiation (20 Gy), which results in lysosomal rupture and ensuing apoptosis or necrosis. The enhanced sensitivity to radiation-induced lysosomal rupture is very likely linked to lysosomal iron: two chemically distinct iron chelators, HMW-DFO and LAP, which specifically localize within the lysosomal compartment, stabilize lysosomes and prevent cell death. These observations provide a biological rationale for fractionated radiation, in that a primary dose of radiation causes increased intralysosomal iron and synergizes the damage from a second dose of radiation. The resultant lysosomal rupture may not only lead directly to cell death, as we have proposed elsewhere, but iron released from lysosomes may relocate to the nucleus, intensifying radiation-mediated DNA damage. These findings should be useful in the design of more effective regimens of fractionated radiation and in designing new therapeutic modalities for the prevention of incidental radiationinduced death of normal tissues.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-84369 (URN)
Available from: 2012-10-05 Created: 2012-10-05 Last updated: 2012-10-05Bibliographically approved

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