Effect of gamma knife irradiation on relaxation and contraction responses of the common carotid artery in the rat

α- and ϵ-Protein Kinase C Activity during Smooth Muscle Cell Apoptosis in Response to γ-Radiation

The use of gamma-radiation in treatment of pelvic cancer is associated with injury of healthy surrounding tissues and disorders of intestinal motility; however, the cellular mechanisms involved are unclear. We tested the hypothesis that exposure of visceral smooth muscle cells (SMCs) to gamma-radiation induces apoptosis via activation of specific protein kinase C (PKC) isoforms. Cultured SMCs and slices from guinea pig ileum smooth muscle longitudinal layer (GPISMLL) were exposed to 10 to 50 Gy. Flow cytometry in gamma-radiated SMCs showed increased percentage of cells in the sub-G(0)/G(1) phase, a hallmark of apoptosis. gamma-Radiation-induced reduction in cell survival was partially but significantly alleviated with the PKC inhibitors. Sections of gamma-irradiated GPISMLL showed DNA fragmentation and apoptotic bodies analyzed by the terminal deoxynucleotidyl transferase dUTP nick-end labeling method, whereas the plasma and nuclear membranes were preserved. Confocal microscopy in gamma-radiated SMCs labeled with annexin V-fluorescein showed an increase in apoptotic cells and phosphatidylserine externalization. Contraction of GPISMLL strips in response to KCl and acetylcholine was reduced in tissues exposed to 30 and 50 Gy. gamma-Radiation of GPISMLL caused an increase in PKC activity in the particulate fraction, a decrease in the cytosolic fraction, and increased particulate/cytosolic PKC activity ratio. Western blot analysis revealed significant amounts of alpha- and epsilon-PKC in the cytosolic fraction of control GPISMLL. gamma-Radiation caused an increase in the amount of alpha- and epsilon-PKC in the particulate fraction and a decrease in the cytosolic fraction. Data suggest that gamma-radiation induces apoptosis, growth arrest, and contractile dysfunction in visceral SMCs of GPISMLL via activation and translocation of alpha- and epsilon-PKC isoforms.

Poly(ADP-ribose) polymerase inhibition reverses vascular dysfunction after gamma-irradiation

PURPOSE

The generation of reactive oxygen species during gamma-irradiation may induce DNA damage, leading to activation of the nuclear enzyme poly(adenosine diphosphate [ADP]-ribose) polymerase (PARP) culminating in endothelial dysfunction. In the present study, we assessed the effect of PARP inhibition on changes in vascular function after acute and short-term irradiation.

METHODS AND MATERIALS

In the acute experiments, aortic rings were exposed to 20 Gy of gamma-irradiation. The aortae were harvested after 1 or 7 days. Two additional groups received the ultrapotent PARP inhibitor, INO-1001, for 1 or 7 days after irradiation. The aortic rings were precontracted by phenylephrine and relaxation to acetylcholine and sodium nitroprusside were studied.

RESULTS

The vasoconstrictor response to phenylephrine was significantly lower both acutely and 1 and 7 days after irradiation. Vasorelaxation to acetylcholine and sodium nitroprusside was not impaired acutely after irradiation. One and seven days after irradiation, vasorelaxation to acetylcholine and sodium nitroprusside was significantly enhanced. Treatment with INO-1001 reversed vascular dysfunction after irradiation.

CONCLUSION

Vascular dysfunction was observed 1 and 7 days after irradiation, as evidenced by reduced vasoconstriction, coupled with endothelium-dependent and -independent hyperrelaxation. PARP inhibition restored vascular function and may, therefore, be suitable to reverse vascular dysfunction after irradiation.

Time-dependent astroglial changes after gamma knife radiosurgery in the rat forebrain

OBJECTIVE

Using an experimental rat model and a clinically relevant treatment dose, we performed gamma knife radiosurgery to define the hyperacute radiation effects in normal rat forebrain, the time dependence of the astrocytic reaction, and the participation of astrocytes in the healing process after single-dose gamma radiation injuries.

METHODS

Seventy-one rats underwent radiosurgical treatment (4-mm collimator) of the caudate-putamen nucleus (single-fraction maximal dose of 100 Gy) and were killed at times ranging from 3 hours to 90 days. Serial cryostat brain sections were processed with the immunohistochemical avidin-biotin complex technique, using anti-glial fibrillary acidic protein as the primary antibody (to identify astrocytes).

RESULTS

Vascular changes, including endothelial hyperplasia and vessel wall thickening, were identified as the earliest postradiation manifestations and continued throughout the observation period. Astrocytes reacted to the radiation injury with hyperplasia and hypertrophy. At earlier time points (3-24 h), proliferation was the predominant reaction. The expression of glial fibrillary acidic protein in the proliferating and hypertrophic astrocytes formed an initial peak in the adjacent corpus callosum 3 days after radiosurgery and peaked within the target site between 14 and 30 days. Astrocytic proliferation and hypertrophy were also observed in distant cortices (frontal, parietal, insular, and piriform cortices) and in the hippocampus. No necrosis was observed less than 30 days after irradiation. By Day 90, necrotic lesions with a mean diameter of 4 mm were identified, with glial scar at their peripheries. Astrocytic morphological features varied according to the distance from the necrosis. The irradiated side contained more glial fibrillary acidic protein-containing cells than did the nonirradiated contralateral side.

CONCLUSION

During the early phase after radiation, vasculopathy was the first morphological change and may serve as the initiating factor for subsequent changes. Reactive astrocytes appeared not only at the target site but also in the surrounding regions; the severity of injury was determined by the distance from the target.