Chelation of intralysosomal redox-active iron protects against ionizing radiation damage
(English)Manuscript (preprint) (Other academic)
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.
Medical and Health Sciences
IdentifiersURN: urn:nbn:se:liu:diva-84369OAI: oai:DiVA.org:liu-84369DiVA: diva2:558827