A. Petkau

Radioprotective effect of superoxide dismutase on model phospholipid membranes

1. Hydroperoxide formation in model membranes was measured via the net increase in absorbance at 232 nm after exposure to X-rays or 137Cs gamma rays in the presence and absence of bovine superoxide dismutase and other radical scavengers. 2. Membranes X-irradiated in air to 4200 rad at 210 rad/min exhibited a large increase in absorbance, a major portion of which was O2--mediated since active superoxide dismutase at 1 mug/ml reduced it by more than 80% to the level observed in N2O. In N2 the change in absorbance was smaller than in N2O but not in proportion to the halving in OH production. 3. The net absorbance of membranes exposed to a constant dose from 137Cs increased with decreasing dose rate. A minor component of this effect was due to exposure protraction with decreasing dose rates while the major component was attributed to long chain reactions initiated by ionizing radiation. A corollary effect was also observed, namely, that with reducing dose rate the dose required to elicit a constant absorbance change decreased. Both aspects were abolished by superoxide dismutase at 1 mug/ml. 4. The enzyme protected membranes after an acute exposure and from low level radiation at natural background while its inactivated form sensitized.

Radioprotection of mice by superoxide dismtuase

Summary The distribution in sensitivity to X-rays of female Swiss mice was log-normal following a single intravenous injection of superoxide dismutase at 35 μg/g body weight. The X-ray dose required to kill 50% of the enzyme-treated mice within 30 days (LD50(30)) was 700 rads as compared to 627 rads for the saline-injected control group of mice which exhibited a normal distribution in sensitivity to radiation. Inactivated superoxide dismutase, when given intravenously in the amount of 35 μg/g, did not produce a significant radioprotective effect on mouse survival.

RADIATION PROTECTION BY SUPEROXIDE DISMUTASE

Abstract— Protection of X‐irradiated mice by bovine superoxide dismutase is enhanced when the enzyme is given intravenously both before and after the exposure. With the combined treatment, the LD50(30) dose is increased from 734 ± 8 to 1144 ± 15rad for a dose reduction factor of 1.56 ± 0.04. This protection occurs in a dose range where hematological damage is an important contributor to animal lethality. The proliferative capacity of bone marrow stem cells, X‐irradiated in air, is protected by exogenous superoxide dismutase. The enzyme increased the D0 from 105 ± 6 to 290 ± 34rad, an increase that represents 83% of the oxygen enhancement ratio of 3.3. In N2 and N2O, the D0 of the stem cells is 348 ± 50 and 327 ± 55 rad, respectively, and the enzyme does not significantly change these values.

Radioprotection of bone marrow stem cells by superoxide dismutase

Abstract In mouse bone marrow cells the radioactivity from intravenously injected 125I-superoxide dismutase reached its maximum level 1 h later. The 1 h interval was used while examining the effect of the unlabelled enzyme on the proliferative capacity of X-irradiated hematopoietic stem cells, as measured by their ability to form colonies in host spleens. When administered to donor mice in the amount of 35 μg/g body weight, the enzyme protected the cells, exposed to 350 rads, by a factor of 2.16 ±0.18. At doses of 15, 70, and 100 μg/g, this factor was reduced to 1.44 ± 0.18, 1.15 ± 0.15, and 0.7 ± 0.1, respectively. The value of 2.16 at 35 μg/g was increased to 2.5 by giving an additional therapeutic dose of the same size 1 h after the X-irradiation.

Protection by superoxide dismutase of white blood cells in X-irradiated mice

In x-irradiated mice the loss of white blood cells increases exponentially with dose. The dose x/sub 0/, which reduces the cell number to 1/e, is 115 +- 15, 205 +- 30, 108 +- 5, and 235 +- 18 rad for leucocytes, granulocytes, lymphocytes and platelets, respectively. The x/sub 0/ value increases with the amount of endogenous superoxide dismutase per cell. Intravenous bovine superoxide dismutase has no effect on the x/sub 0/ for granulocytes and platelets but increases it to 145 +- 15 and 143 +- 20 rad for leucocytes and lymphocytes, respectively. The exogenous enzyme also shortens the delay in recovery of the white blood cells, particularly after x-ray doses of 550 and 675 rad. The earlier hematological recovery is attributable to the known radioprotective effect of the enzyme on bone marrow stem cells.

Purification of human copper, zinc superoxide dismutase by copper chelate affinity chromatography.

Copper, zinc superoxide dismutase was isolated from human red blood cell hemolysate by DEAE-Sepharose and copper chelate affinity chromatography. Enzyme preparations had specific activities ranging from 3400 to 3800 U/mg and recoveries were approximately 60% of the enzyme activity in the lysate. Copper chelate affinity chromatography resulted in a purification factor of about 60-fold. The homogeneity of the superoxide dismutase preparation was analyzed by sodium dodecyl sulfate-gel electrophoresis, analytical gel filtration chromatography, and isoelectric focusing.

Protective effect of superoxide dismutase on erythrocytes of X-irradiated mice

Abstract Following X-ray doses of 550 and 675 rad, the erythrocyte count and percentage reticulocytes in mice first decline and then gradually recover. Bovine superoxide dismutase, injected intravenously at 35 μg/g body weight 1 h before and after the X-irradiation, did not significantly affect the initial phase but hastened the recovery such that at 22 days post-exposure, the erythrocyte count and percentage reticulocytes were both significantly different from the control values. It is estimated that the circulating red cell gains approximately 10 molecules of enzyme per injection. Almost all of it is in the cytoplasm.

Radioprotection by superoxide dismutase of macrophage progenitor cells from mouse bone marrow

X-ray survival of cultured macrophage progenitor cells from mouse bone marrow was represented by a two-component curve, both in the absence and presence of superoxide dismutase. Protection by the enzyme was limited to the radiosensitive fraction, for which a dose modifying factor of 2.8 +/- 0.7 was obtained. Catalase did not protect. Survival of the radiosensitive fraction, with and without exogenous superoxide dismutase, was temperature-dependent, whereas that of the radioresistant fraction was not. In the former case, the energy required for the enzyme-treated cells was approximately 13kJ/mol.

Bovine superoxide dismutase: A radioimmunoassay

Abstract Rabbit antibodies to bovine superoxide dismutase have been produced and used to develop a double-antibody solid phase radioimmunoassay for the enzyme. The assay is sensitive and highly specific for the bovine enzyme, showing no cross-reactivity with the murine or human superoxide dismutases. It has been applied to the quantitation of exogenous enzyme in serum and extracts of mouse cells and tissues.

Variation in distribution of membrane particles in Acholeplasma laidlawii B with pH

Freeze-fracture electron microscopy was used to examine the redistribution of particles in Acholeplasma laidlawii B cell membranes in response to a change in the H+ concentration after growth. At pH 6.0 the distribution was more heterogeneous than at pH 7.5 or 9.0. The mean values from a number of experiments for the nearest-neighbor interparticle distances were within the range of 70.4–72.9, 88.8–92.1, and 101.7–105.4 nm for pH 6.0, 7.5, and 9.0, respectively.