Effect of gamma irradiation on liver metallothionein synthesis and lipid peroxidation in rats.

Several studies have recently shown that metallothionein (MT), a protein characterized by a high thiol content and that binds Zn2+ and Cu+, might be involved in the protection against oxidative stress and can act as a free radical scavenger. Oxidative stresses, such as irradiation, increase lipid peroxidation (LP) and subsequent tissue damage through free radical production. The induction of hepatic MT synthesis by gamma-irradiation (20 Gy) at 8, 24, 30 and 48 hrs. post-irradiation in two different age groups of Sprague-Dawley rats (39-40 and 48-49 days old) was studied. LP measured by the thiobarbituric acid reactive substances (TBARS) assay and Cu and Zn levels in liver have also been determined. In the younger group, the gamma-irradiation induced hepatic MT synthesis and increased LP that peaked 24 hrs. after irradiation. During the first 30 hrs. post-irradiation, a positive and statistically significant correlation between hepatic MT content and LP level in liver was found. In the older group, liver MT synthesis was only increased 1.7-fold and LP levels were not altered at 24 hrs. post-irradiation compared with sham-irradiated rats.Therefore it appears that LP is not necessary for induction of MT synthesis by gamma-irradiation.     

Changes of lipofuscin-like pigments in erythrocytes and spleen after whole-body gamma irradiation of rats

Whole-body gamma irradiation of rats induced the formation of lipofuscin-like pigments in erythrocytes. Erythrocytes that were damaged by oxidation were scavenged in the spleen, and lipofuscin-like pigments were transferred from erythrocytes to the spleen during this process. The time course of lipofuscin-like pigments in erythrocytes and spleen indicates that the pigments were not induced by the action of free radicals produced by ionizing radiation but rather were a sequela of postirradiation metabolic changes.     

Micronucleus induction after whole-body microwave irradiation of rats

Adult male Wistar rats were exposed for 2 h a day, 7 days a week for up to 30 days to continuous 2,450 MHz radiofrequency microwave (rf/MW) radiation at a power density of 5-10 mW/cm(2). Sham-exposed rats were used as controls. After ether anesthesia, experimental animals were euthanized on the final irradiation day for each treated group. Peripheral blood smears were examined for the extent of genotoxicity, as indicated by the presence of micronuclei in polychromatic erythrocytes (PCEs). The results for the time-course of PCEs indicated significant differences (P<0.05) for the 2nd, the 8th and the 15th day between control and treated subgroups of animals. Increased influx of immature erythrocytes into the peripheral circulation at the beginning of the experiment revealed that the proliferation and maturation of nucleated erythropoietic cells were affected by exposure to the 2,450 MHz radiofrequency radiation. Such findings are indicators of radiation effects on bone-marrow erythropoiesis and their subsequent effects in circulating red cells. The incidence of micronuclei/1,000 PCEs in peripheral blood was significantly increased (P<0.05) in the subgroup exposed to rf/MW radiation after eight irradiation treatments of 2 h each in comparison with the sham-exposed control group. It is likely that an adaptive mechanism, both in erythrocytopoiesis and genotoxicity appeared in the rat experimental model during the subchronic irradiation treatment.     

Micronucleus induction after whole-body microwave irradiation of rats

Adult male Wistar rats were exposed for 2 h a day, 7 days a week for up to 30 days to continuous 2450 MHz radiofrequency microwave (rf/MW) radiation at a power density of 5–10 mW/cm². Sham-exposed rats were used as controls. After ether anesthesia, experimental animals were euthanized on the final irradiation day for each treated group. Peripheral blood smears were examined for the extent of genotoxicity, as indicated by the presence of micronuclei in polychromatic erythrocytes (PCEs). The results for the time-course of PCEs indicated significant differences (P<0.05) for the 2nd, the 8th and the 15th day between control and treated subgroups of animals. Increased influx of immature erythrocytes into the peripheral circulation at the beginning of the experiment revealed that the proliferation and maturation of nucleated erythropoietic cells were affected by exposure to the 2450 MHz radiofrequency radiation. Such findings are indicators of radiation effects on bone-marrow erythropoiesis and their subsequent effects in circulating red cells. The incidence of micronuclei/1000 PCEs in peripheral blood was significantly increased (P<0.05) in the subgroup exposed to rf/MW radiation after eight irradiation treatments of 2 h each in comparison with the sham-exposed control group. It is likely that an adaptive mechanism, both in erythrocytopoiesis and genotoxicity appeared in the rat experimental model during the subchronic irradiation treatment.     

Early changes in the lymphocyte surface membrane of rats after whole-body irradiation with neutrons and gamma rays

Biochemical changes in lymphocyte plasma membranes were studied 3 and 18 h after whole-body exposure of rats to neutrons and gamma-rays at doses from 2 to 6 Gy. It was shown that fast neutrons, with an average energy of 1.5-2.0 MeV, increased the rate of lipid peroxidation more markedly than gamma-rays did. In addition, there was an increase in the number of free aminogroups on the thymocyte surface. Dose- and time-dependent parameters of changes in the aminogroup content on the cellular surface were quantitatively different after the effect of radiation with different LET.     

Lysosomal lipolytic enzymes,lipid peroxidation,and injury

Summary We have used highly purified lysosomes to investigate three models of hydrolytic injury by lysosomal phospholipases. Lysosomes, enriched up to 70-fold in marker enzyme activities, can be isolated from homogenized hepatic tissue by differential centrifugation and subsequent free flow electrophoresis. These organelles remain latent and can also be utilized to obtain lysosol, the soluble fraction of the lysosomes tissue containing acid active phospholipases. The first model investigated the effect of lysosol on non-lysosomal membranes. When this soluble fraction was incubated with plasmalemma (sarcolemma) from cardiac cells, selective hydrolysis of the phospholipids was observed: phosphatidylcholine, phosphatidylethanolamine, and sphingomyelin were the preferred substrates, and only lysophosphatidylcholine and lysophosphatidylethanolamine accumulated in significant amounts. Hydrolysis of sphingomyelin was enhanced significantly by Triton-X-100. In the second model, when intact lysosomes were incubated at acid pH, hydrolysis of phospholipids by the endogenous lipases was observed. Once again this lipolysis was specific for phosphatidylcholine, phosphatidylethanolamine, and sphingomyelin: significant amounts of lysophospholipids also accumulated in this model. Concurrent with these lipid changes, an increase in lysosomal permeability also occurred and pH 5.0 was optimal for this lipolytic activity. However, no phospholipase activity was detected when lysosomes were incubated at pH ranges found in acidotic tissue (pH 6.0 or higher). In the third model, lysosomes were incubated at pH 6.0 in the presence of exogenously generated free radicals (dihydroxyfumarate-FeADP). A rapid loss of membrane phospholipids was observed, and most of this loss could be contributed to peroxidation of membrane phospholipids; the production of malondialdehyde preceded loss of N-acetylglucosaminidase from the lysosome. However, significant accumulation of lysophospholipids, from 2% at control time to 6.6 and 8.7% at 10 and 20 minutes, suggested that lysosomal phospholipase were hydrolyzing lysosomal phospholipids. Thus, we hypothesize that this free radical-induced lipolysis is a result of peroxidized phospholipids serving as preferred substrate for phospholipases at pH 6.0.     

Hypodontia in the beagle after perinatal whole-body 60Co gamma irradiation

As part of a long-term study to evaluate health effects of pre- and postnatal irradiation, dental development was examined. Beagles were irradiated in utero at 8, 28, or 55 days postcoitus or postnatally at 2, 70, or 365 days postpartum. Whole-body 60Co gamma radiation doses ranged from 0 to 3.8 Gy. There was an age-dependent dose-related increase in premolar hypodontia for animals irradiated at 55 days postcoitus or 2 days postpartum with doses of 0.83 Gy or higher and for those irradiated at 28 days postcoitus with 1.2 Gy or higher.     

Histological changes in rat duodenum mucosa after whole-body gamma irradiation.

In order to understand the mechanisms of intestinal injuries due to ionizing radiation, various groups of rats have been whole-body irradiated by gamma-rays at two dose rates (1 Gy/min and 1 Gy/hr), three doses (1, 2 and 4 Gy) and two post-irradiation times (24 and 48 hr). Duodenum samples of the animals were prepared for light microscopy, according to classical methods for histology and TUNEL reaction. A small number of morphological differences were observed within the mucosa between the two dose rates used. The extent and the number of lesions were more important at the slower dose rate (1 Gy/hr) and increased with the total dose. Clear cavities were seen inside the lamina propria which appeared like capillaries free of blood cells. The mitotic index calculated from crypt cells showed a regular decrease with the dose, which was exacerbated at 48 hr post-irradiation. On the other hand, the apoptotic index increased with the dose and the postirradiation time. Our results lead to hypothesize another mechanism of intestinal mucosa renewal allowing to explain mucosa denudations observed after radiotherapy. Thus we propose a new concept in which the duodenal mucosa renewal may occur by whole villi shedding into the duodenal lumen.     

The accumulation of lipid peroxidation products in the eye structures of mice under whole-body x-ray irradiation

In studying the effect of whole-body X-irradiation on the accumulation of lipid peroxidation products (conjugated dienes, TBA-active products, and Schiff bases) in retina and retinal pigmented epithelium of pigmented and nonpigmented mice it was shown that irradiation of dark-pigmented mice does not cause even a slight accumulation of lipid peroxidation products as compared to that in the controls. Albino mice exhibited a marked increase in the level of lipid peroxidation products which was manifested soon after irradiation and persisted for at least 3 months after irradiation. Melanine is suggested to participate in protecting eye structures against pro-oxidizing action of ionizing radiation.     

Dynamic changes in kidney function after the whole-body gamma irradiation of rats at a dose of 7.4 Gy

In experiments on female Wistar rats it was shown that whole-body gamma-irradiation (7.4 Gy) impairs the hemodynamics and function of kidneys, particularly their filtering capacity, the dynamics of which was of an undulatory character. The most pronounced changes occurred during the first 30 days following irradiation, later on the functional status normalized.     

Blood-brain barrier permeability after gamma whole-body irradiation: an in vivo microdialysis study

The effects of total-body irradiation on the permeability of rat striatal blood-brain barrier (BBB) to [3H]alpha-aminoisobutyric acid (AIBA) and [14C]sucrose were investigated using the microdialysis technique. Seven days, 3 and 6 weeks, and 3, 5, and 8 months after gamma exposure at a dose of 4.5 Gy, no modification of the permeability to both [3H]AIBA and [14C]sucrose was observed. But, in the course of the initial syndrome, we observed a significant but transient increase in the BBB permeability to the two markers between 3 and 17 h after exposure. A secondary transient "opening" of the BBB to [14C]sucrose was noticed about 28 h following irradiation without the corresponding increase in BBB permeability to [3H]AIBA. On the contrary, the transport of [3H]AIBA through the BBB was decreased between 33 and 47 h postradiation. In conclusion, our experiments showed early modifications of BBB permeability after a moderate-dose whole-body exposure. Confirmation of these results with other tracers, in another experimental model or in humans, would have clinical applications for designing appropriate pharmacotherapy in radiotherapy and treatment of accidental overexposure.     

Influence of ginger rhizome (Zingiber officinale Rosc) on survival, glutathione and lipid peroxidation in mice after whole-body exposure to gamma radiation

The radioprotective effect of the hydroalcoholic extract of ginger rhizome, Zingiber officinale (ZOE), was studied. Mice were given 10 mg/kg ZOE intraperitoneally once daily for five consecutive days before exposure to 6-12 Gy of gamma radiation and were monitored daily up to 30 days postirradiation for the development of symptoms of radiation sickness and mortality. Pretreatment of mice with ZOE reduced the severity of radiation sickness and the mortality at all doses. The ZOE treatment protected mice from GI syndrome as well as bone marrow syndrome. The dose reduction factor for ZOE was found to be 1.15. The optimum protective dose of 10 mg/kg ZOE was 1/50 of the LD50 (500 mg/kg). Irradiation of the animals resulted in a dose-dependent elevation in the lipid peroxidation and depletion of GSH on day 31 postirradiation; both effects were lessened by pretreatment with ZOE. ZOE also had a dose-dependent antimicrobial activity against Pseudomonas aeruginosa, Salmonella typhimurium, Escherichia coli and Candida albicans.     

Time course of lipid peroxidation during incomplete ischaemia followed by reperfusion in rat brain

The time course of lipid peroxidation was studied in the rat brain cortex after ischaemia and reperfusion. The ischaemia was induced by 4-hour occlusion of both common carotid arteries and was followed by reperfusion of different duration (10, 30 or 60 min). The extent of lipid peroxidation was determined by measurement of conjugated dienes (CD) and TBA reactive products. Maximal values of CD and TBA reactive products were found after 10- and 30-minute reperfusion. This indicated the most suitable time interval for studying the effect of antioxidants and oxygen radical scavengers in this model of brain ischaemia.