Radiobiologic response of CHO-KI cells treated with vitamin A

Health risks of space exploration: targeted and nontargeted oxidative injury by high-charge and high-energy particles

SIGNIFICANCE

During deep space travel, astronauts are often exposed to high atomic number (Z) and high-energy (E) (high charge and high energy [HZE]) particles. On interaction with cells, these particles cause severe oxidative injury and result in unique biological responses. When cell populations are exposed to low fluences of HZE particles, a significant fraction of the cells are not traversed by a primary radiation track, and yet, oxidative stress induced in the targeted cells may spread to nearby bystander cells. The long-term effects are more complex because the oxidative effects persist in progeny of the targeted and affected bystander cells, which promote genomic instability and may increase the risk of age-related cancer and degenerative diseases.

RECENT ADVANCES

Greater understanding of the spatial and temporal features of reactive oxygen species bursts along the tracks of HZE particles, and the availability of facilities that can simulate exposure to space radiations have supported the characterization of oxidative stress from targeted and nontargeted effects.

CRITICAL ISSUES

The significance of secondary radiations generated from the interaction of the primary HZE particles with biological material and the mitigating effects of antioxidants on various cellular injuries are central to understanding nontargeted effects and alleviating tissue injury.

FUTURE DIRECTIONS

Elucidation of the mechanisms underlying the cellular responses to HZE particles, particularly under reduced gravity and situations of exposure to additional radiations, such as protons, should be useful in reducing the uncertainty associated with current models for predicting long-term health risks of space radiation. These studies are also relevant to hadron therapy of cancer.

Should supplemental antioxidant administration be avoided during chemotherapy and radiation therapy?

Despite nearly two decades of research investigating the use of dietary antioxidant supplementation during conventional chemotherapy and radiation therapy, controversy remains about the efficacy and safety of this complementary treatment. Several randomized clinical trials have demonstrated that the concurrent administration of antioxidants with chemotherapy or radiation therapy reduces treatment-related side effects. Some data indicate that antioxidants may protect tumor cells as well as healthy cells from oxidative damage generated by radiation therapy and some chemotherapeutic agents. However, other data suggest that antioxidants can protect normal tissues from chemotherapy- or radiation-induced damage without decreasing tumor control. We review some of the data regarding the putative benefits and potential risks of antioxidant supplementation concurrent with cytotoxic therapy. On the basis of our review of the published randomized clinical trials, we conclude that the use of supplemental antioxidants during chemotherapy and radiation therapy should be discouraged because of the possibility of tumor protection and reduced survival.

Reversible changes in radiation response induced by all-trans retinoic acid

PURPOSE

The aim was to establish a model of reversible radiosensitization in human tumor cell lines by all-trans retinoic acid without influencing cell cycle or differentiation.

METHODS AND MATERIALS

Three human carcinoma cell lines (one bladder and two lung lines) were incubated in medium containing delipidized serum with or without varying concentrations of all-trans retinoic acid for a range of time periods, and their acute response to radiation measured by clonogenic assay. Cell phenotype was monitored using growth rates, morphology, and intermediate filament expression.

RESULTS

Two of the three cell lines (those in which cell kill was predominantly through reparable damage beta in control cultures) showed an increase in radiosensitivity with retinoic acid, at a concentration with no discernable effect on phenotype (10(-7) M). No significant change in alpha values was observed. The values for beta increased from 0.057 to 0.109 and from 0.039 to 0.075, corresponding to dose modification factors of 1.59 and 1.67. When retinoic acid was removed prior to irradiation, cell survival returned to control levels by 48 h.

CONCLUSION

Radiosensitization occurred at retinoic acid concentrations that did not otherwise perturb the cells; the effect may be due to inhibition of DNA repair in cells usually competent at repair. The model provides a method of altering radiosensitivity in selected cell lines without genetic mutation, which may enable investigation of DNA repair mechanisms.