RESUMEN
The production of reactive oxygen species (ROS), especially superoxide anions (O2 (·-)), is enhanced in many normal and tumor cell types in response to ionizing radiation. The influence of ionizing radiation on the regulation of ROS production is considered as an important factor in the long-term effects of irradiation (such as genomic instability) that might contribute to the development of secondary cancers. In view of the increasing application of carbon ions in radiation therapy, we aimed to study the potential impact of ionizing density on the intracellular production of ROS, comparing photons (X-rays) with carbon ions. For this purpose, we used normal human cells as a model for irradiated tissue surrounding a tumor. By quantifying the oxidization of Dihydroethidium (DHE), a fluorescent probe sensitive to superoxide anions, we assessed the intracellular ROS status after radiation exposure in normal human fibroblasts, which do not show radiation-induced chromosomal instability. After 3-5 days post exposure to X-rays and carbon ions, the level of ROS increased to a maximum that was dose dependent. The maximum ROS level reached after irradiation was specific for the fibroblast type. However, carbon ions induced this maximum level at a lower dose compared with X-rays. Within â¼1 week, ROS decreased to control levels. The time-course of decreasing ROS coincides with an increase in cell number and decreasing p21 protein levels, indicating a release from radiation-induced growth arrest. Interestingly, radiation did not act as a trigger for chronically enhanced levels of ROS months after radiation exposure.
Asunto(s)
Inhibidor p21 de las Quinasas Dependientes de la Ciclina/metabolismo , Fibroblastos/metabolismo , Fibroblastos/efectos de la radiación , Iones Pesados , Especies Reactivas de Oxígeno/metabolismo , Transducción de Señal/fisiología , Isótopos de Carbono , Línea Celular , Relación Dosis-Respuesta en la Radiación , Humanos , Recién Nacido , Dosis de Radiación , Transducción de Señal/efectos de la radiaciónRESUMEN
To gain a better understanding of the light-induced reduction of protochlorophyllide (PChlide) to chlorophyllide as a key regulatory step in chlorophyll synthesis, we performed transient infrared absorption measurements on PChlide in d4-methanol. Excitation in the Q-band at 630 nm initiates dynamics characterized by three time constants: τ1 = 3.6 ± 0.2, τ2 = 38 ± 2, and τ3 = 215 ± 8 ps. As indicated by the C13'=O carbonyl stretching mode in the electronic ground state at 1686 cm⻹, showing partial ground-state recovery, and in the excited electronic state at 1625 cm⻹, showing excited-state decay, τ2 describes the formation of a state with a strong change in electronic structure, and τ3 represents the partial recovery of the PChlide electronic ground state. Furthermore, τ1 corresponds with vibrational energy relaxation. The observed kinetics strongly suggest a branched reaction scheme with a branching ratio of 0.5 for the path leading to the PChlide ground state on the 200 ps timescale and the path leading to a long-lived state (>>700 ps). The results clearly support a branched reaction scheme, as proposed previously, featuring the formation of an intramolecular charge transfer state with â¼25 ps, its decay into the PChlide ground state with 200 ps, and a parallel reaction path to the long-lived PChlide triplet state.