Effect of X-irradiation on erythrocyte membrane proteins. Primary radicals

The compound effect of irradiation and familial pseudohyperkalemia on potassium leak from red blood cells

BACKGROUND

Familial pseudohyperkalemia (FP) is a rare asymptomatic condition characterized by an increased rate of potassium leak from red blood cells (RBC) on refrigeration. Gamma irradiation compromises RBC membrane integrity and accelerates potassium leakage. Here, we compared the effect of irradiation, applied early or late in storage, on FP versus non-FP RBC.

STUDY DESIGN

Five FP and 10 non-FP individuals from the National Institute for Health Research Cambridge BioResource, UK, and three FP and six non-FP individuals identified by Australian Red Cross Lifeblood consented to the study. Blood was collected according to standard practice in each center, held overnight at 18-24°C, leucocyte-depleted, and processed into red cell concentrates (RCC) in Saline Adenine Glucose Mannitol. On Day 1, RCC were split equally into six Red Cell Splits (RCS). Two RCS remained non-irradiated, two were irradiated on Day 1 and two were irradiated on Day 14. RBCs were tested over cold storage for quality parameters.

RESULTS

As expected, non-irradiated FP RCS had significantly higher supernatant potassium levels than controls throughout 28 days of storage (p < .001). When irradiated early, FP RCS released potassium at similar rates to control. When irradiated late, FP RCS supernatants had higher initial post-irradiation potassium concentration than controls but were similar to controls by the end of storage (14 days post-irradiation). No other parameters studied showed a significant difference between FP and control.

DISCUSSION

FP does not increase the rate of potassium leak from irradiated RBCs. Irradiation may cause a membrane defect similar to that in FP RBCs.

Effect of stereotactic radiosurgery on lipids and proteins of normal and hypoperfused rat brain homogenates: A Fourier transform infrared spectroscopy study

PURPOSE

The effect of stereotactic radiosurgery on lipids and proteins of normal and hypoperfused rat brain was investigated to see if hypoxic areas are really more resistant to radiation effects or not.

MATERIALS AND METHODS

Rat brain samples from control, stereotactically irradiated and chronically hypoperfused plus stereotactically irradiated groups were homogenized separately with saline phosphate buffer, and centrifuged at 125,000 g for 15 min. Membrane rich parts (pellet) of these homogenates were used for Fourier Transform Infrared (FTIR) spectroscopy studies. Mann-Whitney U tests were performed on the groups, two by two, to test the significance of the differences between the control group and stereotactically irradiated group as well as the control group and chronically hypoperfused plus stereotactically irradiated group.

RESULTS

After a single high dose of X-rays to healthy rat brain, the lipid concentration increased slightly, protein content decreased significantly (p < 0.05) and protein-to-lipid ratio decreased slightly. The secondary structure of the proteins was altered in the irradiated brain samples such that the content of a-helical structure decreased significantly (p < 0.01) and random coil increased dramatically (p < 0.05). The effect of radiation on the content of a-helical structure was not found to be significant in the hypoperfused group, but the decrease in the content of random coil was significant (p < 0.01).

CONCLUSION

Stereotactic radiosurgery of the brain increased the lipid concentration, decreased the protein concentration and consequently resulted in a decrease in the protein to lipid ratio compared to un-irradiated brain. Radiation also altered the secondary structure of protein. The variations in lipid and protein content and the resulting lipid to protein ratio imply that chronically hypoperfused brain is more vulnerable to radiation than non-hypoperfused brain and suggests chronic hypoperfusion does not prevent cerebral damage caused by irradiation. However, irradiation of hypoperfused brain resulted in less alteration in protein structure than in non-hyperfused brain, suggesting higher resistance to irradiation using this endpoint.

The cell membrane as a biosensor of oxidative stress induced by radiation exposure: a multiparameter investigation

The role of biological membranes as a target in biological radiation damage remains unclear. The present study investigates how the biochemical and biophysical properties of a simple biological model, i.e. human erythrocyte membranes, are altered after exposure to relatively low doses of (60)Co gamma rays. Lipid peroxidation increased in the hours after radiation exposure, based on measurements of MDA and on the lipid peroxidation index after parinaric acid incorporation. Protein carbonyl content also increased rapidly after radiation exposure. An imbalance between the radiation-mediated oxidative damages and the antioxidant capacity of the erythrocytes was observed in the hours after radiation exposure. Antioxidant enzyme activities, mainly catalase and glutathione peroxidase, were found to decrease after irradiation. The development of a radiation-induced oxidative stress probably explains the reorganization of the fatty acid pattern 72 h after radiation exposure. The phosphatidylethanolamine (PE) fatty acids of the (n-3) and (n-6) series decreased, while the PE saturated fatty acid content increased. All these modifications may be involved in the variation of the biophysical properties of the membranes that we noted after radiation exposure. Specifically, we observed that the lipid compartment of the membrane became more fluid while the lipid-protein membrane interface became more rigid. Taken together, these findings reinforce our understanding that the cell membrane is a significant biological target of radiation. Thus the role of the biological membrane in the expression and course of cell damage after radiation exposure must be considered.

Irradiation of Langmuir-Blodgett multilayer preparations of phospholipids and a fatty acid. 2: Effect of X-radiation

X-irradiation of Langmuir-Blodgett (LB) preparations of stearic acid with doses up to a few thousand Gy produced no change of measured electrical conductance in the direction perpendicular to the stacked monolayers. However, irradiation of LB preparations of phospholipids resulted in increased conductance. The effect depended on dose, but not on dose rate and, unlike the corresponding effect of UV-radiation, did not reverse at room temperature. For doses up to about 2 kGy the increased conductance fell away over some tens of minutes if the temperature was raised above 45 degrees C. For doses between 2 and 60 kGy the conductance increased linearly, but less rapidly than the initial rise and the increase was only partly reversible by heating. The rate of increase of conductance rose again for doses above about 60 kGy and for these doses the increase could not be reversed on heating. It is suggested that X-irradiation left molecules in a damaged but reversible state similar to that found after UV irradiation; and that subsequent excitation and ionization damaged the molecules irreversibly.