Elevated sodium chloride concentrations enhance the bystander effects induced by low dose alpha-particle irradiation

Previous studies have shown that high NaCl can be genotoxic, either alone or combined with irradiation. However, little is known about the relationship between environmental NaCl at elevated conditions and radiation-induced bystander effects (RIBE). RIBE, which has been considered as non-targeted bystander responses, has been demonstrated to occur widely in various cell lines. In the present study, RIBE under the elevated NaCl culture condition was assessed in AG 1522 cells by both the induction of gamma-H2AX, a reliable marker of DNA double-strand break (DSB) for the early process (<1h post irradiation), and the generation of micronuclei (MN), a sensitive marker for relative long process of RIBE. Our results showed that in the absence of irradiation, NaCl at elevated concentration such as 8.0, 9.0 and 10.0g/L did not significantly increase the frequency of gamma-H2AX foci-positive cells and the number of foci per positive cell comparing with that NaCl at a normal concentration (6.8g/L). However, with 0.2cGy alpha-particle irradiation, the induced fraction of gamma-H2AX foci-positive cells and the number of induced gamma-H2AX foci per positive cell were significantly increased in both irradiated and adjacent non-irradiated regions. Similarly, the induction of MN by 0.2cGy alpha-particle irradiation also increased with the elevated NaCl concentrations. With N(G)-methyl-l-arginine, an inhibitor of nitric oxide synthase, the induced fraction of foci-positive cells was effectively inhibited both in 0.2cGy alpha-particle irradiated and adjacent non-irradiated regions under either normal or elevated NaCl conditions. These results suggested that the cultures with elevated NaCl medium magnified the damage effects induced by the low dose alpha-particle irradiation and nitric oxide generated by irradiation was also very important in this process.     

Reduction of background mutations by low-dose X irradiation of Drosophila spermatocytes at a low dose rate

A sex-linked recessive lethal mutation assay was performed in Drosophila melanogaster using immature spermatocytes and spermatogonia irradiated with X rays at a high or low dose rate. The mutation frequency in the sperm irradiated with a low dose at a low dose rate was significantly lower than that in the sham-irradiated group, whereas irradiation with a high dose resulted in a significant increase in the mutation frequency. It was obvious that the dose-response relationship was not linear, but rather was U-shaped. When mutant germ cells defective in DNA excision repair were used instead of wild-type cells, low-dose irradiation at a low dose rate did not reduce the mutation frequency. These observations suggest that error-free DNA repair functions were activated by low dose of low-dose-rate radiation and that this repaired spontaneous DNA damage rather than the X-ray-induced damage, thus producing a practical threshold.     

Glutathione and lipid peroxide levels in rat liver following administration of methapyrilene and analogs

The possibility was examined that the induction of tumors in rat liver by feeding methapyrilene, which is not mutagenic, is related to effects on glutathione levels and lipid peroxidation. Fischer 344 rats were given single-dose and multiple-dose treatments with the anti-histamine methapyrilene (MP), which is carcinogenic in rats, and with two non-carcinogenic analogs, methafurylene (MF) and thenyldiamine (TD) and the effects on malonaldehyde (MDA) formation and glutathione (GSH) levels in the liver were investigated. After a single dose, MDA levels were increased at 6 h by MF and TD and at 24 h by MP. MDA levels returned to normal after 30 h with MP and MF, but not with TD. Levels of MDA (and other TBA-reactive products) after four daily treatments were most elevated by TD, less elevated by MP, and were lowered by MF. Forty-two hours following treatment with both MP and MF, MDA levels had returned to normal, but in TD-treated animals MDA remained high. GSH levels were highest after MF and MP, and remained high at 42 h, but TD induced only a small increase. There appears to be increased lipid peroxidation in the liver as a result of treatment of rats with MP, MF and TD. The greater response induced by TD, as well as the increased liver GSH levels after repeated administration of all three drugs indicate that lipid peroxidation in rat liver is not a particular effect related to the liver carcinogen methapyrilene.     

Increased glycosylation capacity in regenerating rat liver is paralleled by decreased activities of CMP-N-acetylneuraminate hydrolase and UDP-galactose pyrophosphatase.

In regenerating rat liver the activities of CMP-N-acetylneuraminate hydrolase and UDP-galactose pyrophosphatase were decreased to 40-50% of control values within 35 h after partial hepatectomy. In the same time period the activities of sialyltransferase and galactosyltransferase were increased, and the initial sharp decrease in the carbohydrate content of liver and serum glycoproteins was largely restored. The antiparallel nature of these events is suggestive of an involvement of nucleotide-sugar-hydrolysis enzymes in rat liver glycoprotein biosynthesis.     

D-galactosamine induced changes in rat liver plasma membranes lipid composition and some enzyme activities

The influence of D-galactosamine administration on rat liver plasma membranes lipid composition, fluidity and some enzyme activities was investigated. D-Galactosamine was found to induce an increase of the total phospholipids, the cholesterol level and membrane rigidity. In liver plasma membranes of D-galactosamine-treated rats the exogenous phospholipase A2 activity was enhanced about 2 fold, whereas the endogenous activity was slightly decreased. No alteration of the neutral sphingomyelinase activity was observed.     

Investigation of lipid peroxidation in liposomes induced by heavy ion irradiation

Lipid peroxidation induced by heavy ion irradiation was investigated in 1,2-dilinoleoyl-sn-glycero-3-phosphocholine (DLPC) liposomes. Lipid peroxidation was induced using accelerated heavy ions that exhibit linear energy transfer (LET) values between 30 and 15 000 keV/μm and doses up to 100 kGy. With increasing LET, the formation of lipid peroxidation products such as conjugated dienes, lipid hydroperoxides, and thiobarbituric acid-reactive substances decreased. When comparing differential absorption spectra and membrane fluidity following irradiation with heavy ions and x-rays (3 Gy/min), respectively, it is obvious that there are significant differences between the influences of densely and sparsely ionizing radiation on liposomal membranes. Indications for lipid fragmentation could be detected after heavy ion irradiation. Received: 6 March 1997 / Accepted in revised form: 31 March 1998     

Increased autophagocytosis induced by colchicine in rat sympathetic neurons

The effect of colchicine was followed up in the superior cervical ganglion of rats. An increase was observed in the number of autophagocytosis vacuoles in the neurons, especially three and four hours after the intraperitoneal injection of colchicine (0.05 mg/100 g.b.w.). These vacuoles presented very various ultrastructural characters due to their different content and stage of degradation. Their high number is explained by the action of colchicine upon cytoplasmic microtubules, the secondary inhibition of the intracellular movement, and the blockage or reduction of the fusion of primary lysosomes with the autophagic vacuoles, which are continuously formed in the neuron cytoplasms, as well as in other cells.     

Inhibition by polyamines of lipid peroxide formation in rat liver microsomes.

Both NADPH- and ascorbic acid-dependent lipid peroxidations were inhibited by spermine, the degree of inhibition being greater with the former peroxidation. The effective concentration of spermine required for inhibition was higher when larger amounts of microsomes were used. However, the activities of NADPH-cytochrome c reductase and NADPH-peroxidase were not influenced by spermine. These results suggest that spermine inhibits lipid peroxidation by binding to phospholipids in the microsomes.     

Increased uncoupling proteins and decreased efficiency in palmitate-perfused hyperthyroid rat heart

The physiological role of mitochondrial uncoupling proteins (UCPs) in heart and skeletal muscle is unknown, as is whether mitochondrial uncoupling of oxidative phosphorylation by fatty acids occurs in vivo. In this study, we found that UCP2 and UCP3 protein content, determined using Western blotting, was increased by 32 and 48%, respectively, in hyperthyroid rat heart mitochondria. Oligomycin-insensitive respiration rate, a measure of mitochondrial uncoupling, was increased in all mitochondria in the presence of palmitate: 36% in controls and 71 and 100% with 0.8 and 0.9 mM palmitate, respectively, in hyperthyroid rat heart mitochondria. In the isolated working heart, 0.4 mM palmitate significantly lowered cardiac output by 36% and cardiac efficiency by 38% in the hyperthyroid rat heart. Thus increased mitochondrial UCPs in the hyperthyroid rat heart were associated with increased uncoupling and decreased myocardial efficiency in the presence of palmitate. In conclusion, a physiological effect of UCPs on fatty acid oxidation has been found in heart at the mitochondrial and whole organ level.     

Increased cerebrospinal fluid levels of S100B protein in rat model of mania induced by ouabain

Bipolar disorder is a chronic and severe mental disorder. Recently, new animal models have emerged to further investigate underlying mechanisms of bipolar disorder such as ouabain-induced hyperactivity in rats. In this study, we investigated the cerebrospinal fluid levels of S100B protein as a putative marker of astrocytic activity in bipolar mania induced by intracerebroventricular administration of ouabain in rats. Ouabain induced a two-fold increase in crossing responses in the open field test and increased 30% the cerebrospinal fluid concentration of S100B, as compared to vehicle group. Our findings reinforce the role of astroglial cells in the pathogenesis of bipolar disorder and S100B protein as a marker of bipolar mania.     

Induction of radio-adaptive response in colony formation by low dose X-ray irradiation.

In this study, we examined the induction of a radio-adaptive response to cell death using a colony formation test in m5S, G401.2/6TG.1 and HeLa cells. When m5S cells were subjected to priming irradiation of 0.05 to approximately 0.15 Gy 4 hr before being irradiated with 4.5 Gy, the survival ratios increased significantly to 39 to approximately 42%. The priming irradiation effect was also observed when G401.2/6TG.1 cells were subjected to priming irradiation of 0.025 to approximately 0.1 Gy 4 hr before being irradiated with 0.8 Gy. This effect showed a two-phasic characteristic, where the first peak was reached at 0.025 Gy, and the second peak was reached at 0.075 Gy. The first peak showed a survival ratio of 56%, while the second peak was at 55%. However, in HeLa cells, this priming irradiation effect was not observed. These results indicated that induction of the radio-adaptive response did not depend on whether cells are normal or cancerous. One of the differences in these cells is that m5S and G401.2/6TG.1 cells have gap-junctional intercellular communication, but HeLa cells do not. Induction of the radio-adaptive response may be related to gap-junctional intercellular communication.     

Cadmium induced lipid peroxidation in rat testes and protection by selenium

The main goal of this study was to investigate the role of cadmium in the promotion of lipid peroxidation in the homogenates of rat testes and the effect of selenium on lipid peroxidation in testes of rats after cadmium injection. Treatment of rats with cadmium resulted in a time- and dose-related accumulation of the metal ions in testes. The concentrations of cadmium, copper, zinc, selenium and iron in the tissues were determined by an atomic absorption spectrophotometer and lipid peroxidation in testes was measured by a spectrophotometer. Cadmium produced enhanced lipid peroxidation in testes. These cadmium-induced changes were accompanied by a significant increase of iron and copper, and a decrease of zinc in testes. Concurrent treatment with selenium and cadmium reduced the cadmium-induced alterations in lipid peroxidation and essential metal levels. Data suggest that lipid peroxidation was associated with cadmium toxicity in testes and that the addition of selenium was found to be effective in attenuation of this effect.     

Low levels of clustered oxidative DNA damage induced at low and high LET irradiation in mammalian cells

DNA double-strand breaks (DSBs) and locally multiply damaged sites (LMDS) induced by ionizing radiation (IR) are considered to be very genotoxic in mammalian cells. LMDS consist of two or more clustered DNA lesions including oxidative damage locally formed within one or two helical turns by single radiation tracks following local energy deposition. They are thought to be frequently induced by IR but not by normal oxidative metabolism. In mammalian cells, LMDS are detected after specific enzymatic treatments transforming these lesions into additional DSBs that can be revealed by pulsed-field gel electrophoresis (PFGE). Here, we studied radiation-induced DSBs and LMDS in Chinese hamster ovary cells (CHO-K1). After addition of the iron chelator deferoxamine (DFO) or the antioxidant glutathione (GSH) to the cell lysis solution, we observed reduced spontaneous DNA fragmentation and a clear dose-dependent increase of radiation-induced DSBs. LMDS induction, however, was close to background levels, independently of dose, dose rate, temperature and radiation quality (low and high LET). Under these experimental conditions, artefactual oxidative DNA damage during cell lysis could not anymore be confounded with LMDS. We thus show that radiation-induced LMDS composed of oxidized purines or pyrimidines are much less frequent than hitherto reported, and suggest that they may be of minor importance in the radiation response than DSBs. We speculate that complex DSBs with oxidized ends may constitute the main part of radiation-induced clustered lesions. However, this needs further studies.     

Application of conventional and FPG staining for the analysis of chromosome aberrations induced by low levels of dose in human lymphocytes

Human peripheral lymphocytes were irradiated with 0.05-0.5 Gy of 220 keV X-rays. After application of either a conventional or the fluorescence plus Giemsa (FPG) staining technique, the dose response for dicentrics and acentrics was studied. The analysis of exclusively first-division cells (M1), carried out by the FPG method, revealed significantly higher aberration yields as compared with the results of the conventional method. The data from M1 cells support the assumption of a linear dose response for both dicentrics and acentrics. The results are discussed with regard to the application of chromosome analyses for a cytogenetic dosimetry after exposure to low levels of ionizing radiation.