[Measurement of contents in organs of selenium- or vitamin E-deficient rat using instrumental neutron activation analysis]

Effects of selenium deficiency on biological results of X-ray and carbon-ion beam irradiation in mice

The impact of radiation-induced hydrogen peroxide (H₂O₂) on the biological effects of X-rays and carbon-ion beams was investigated using a selenium-deficient (SeD) mouse model. Selenium is the active center of glutathione peroxidase (GSH-Px), and SeD mice lack the ability to degrade H₂O₂. Male and female SeD mice were prepared by feeding a torula yeast-based SeD diet and ultrapure water. Thirty-day survival rates after whole-body irradiation, radiation-induced leg contracture, and MRI-based redox imaging of the brain were assessed and compared between SeD and normal mice. Thirty-day lethality after whole-body 5.6 Gy irradiation with X-rays or carbon-ion beams was higher in the SeD mice than in the normal mice, while SeD did not give the notable difference between X-rays and carbon-ion beams. SeD also did not affect the maximum leg contracture level after irradiation with carbon-ion beams, but delayed the leg contraction rate. In addition, no marked effects of SeD were observed on variations in the redox status of the brain after irradiation. Collectively, the present results indicate that SeD slightly altered the biological effects of X-rays and/or carbon-ion beams. GSH-Px processes endogenous H₂O₂ generated through mitochondrial respiration, but does not have the capacity to degrade H₂O₂ produced by irradiation.

Preparation of an experimental mouse model lacking selenium-dependent glutathione peroxidase activities by feeding a selenium-deficient diet

Relatively young (4-week-old) selenium deficient (SeD) mice, which lack the activity of selenium-dependent glutathione peroxidase (GSH-Px) isomers, were prepared using torula yeast-based SeD diet. Mice were fed the torula yeast-based SeD diet and ultra-pure water. Several different timings for starting the SeD diet were assessed. The weekly time course of liver comprehensive GSH-Px activity after weaning was monitored. Protein expression levels of GPx1 and 4 in the liver were measured by Western blot analysis. Gene expression levels of GPx1, 2, 3, 4, and 7 in the liver were measured by quantitative real-time PCR. Apoptotic activity of thymocytes after hydrogen peroxide (H2O2) exposure was compared. Thirty-day survival rates after whole-body X-ray irradiation were estimated. Pre-birth or right-after-birth starting of the SeD diet in dams was unable to lead to creation of SeD mice due to neonatal death. This suggests that Se is necessary for normal birth and healthy growing of mouse pups. Starting the mother on the SeD diet from 2 weeks after giving birth (SeD-trial-2w group) resulted in a usable SeD mouse model. The liver GSH-Px activity of the SeD-trial-2w group was almost none from 4 week olds, but the mice survived for more than 63 weeks. Protein and gene expression of GPx1 was suppressed in the SeD-trial-2w group, but that of GPx4 was not. The thymocytes of the SeD-trial-2w group were sensitive to H2O2-induced apoptosis. The SeD-trial-2w group was sensitive to whole-body X-ray irradiation compared with control mice. The SeD-trial-2w model may be a useful animal model for H2O2/hydroperoxide-induced oxidative stress.

The effect of long-running severe selenium-deficiency on the amount of iron and zinc in the organs of rats

The amounts of selenium (Se), iron (Fe), and zinc (Zn) in the liver, kidney, and spleen as a function of age of rats measured using instrumental neutron activation analysis were compared between Se-deficient (SeD) rats and normal rats. The SeD model rats can live for more than 50 weeks. The effect of Se-deficinecy in rats might be weak, compared to the marked malfunction of GSH-Px. The SeD rats can be considered as a model of non-lethal chronic oxidative stress. Fluctuations of Fe and Zn in the liver of Se-deficient rats were observed. The amount of redox-relating minerals, such as Fe and Zn, in SeD rat organs is changeable depending on the age.

Importance of volume limitation for tissue redox status measurements using nitroxyl contrast agents: a comparison of X-band EPR bile flow monitoring (BFM) method and 300 MHz in vivo EPR measurement

Methods proposed for in vivo redox status estimation, X-band (9.4 GHz) electron paramagnetic resonance (EPR) bile flow monitoring (BFM) and 300 MHz in vivo EPR measurement, were compared. The spin probe 3-carbamoyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl (carbamoyl-PROXYL) was utilized for both methods, due to its suitable lipophilicity. EPR signal decay of a nitroxyl spin probe in the bile flow and in the liver region (upper abdomen) of several rat groups with different selenium status were measured by both the BFM and the in vivo EPR method, respectively. The nitroxyl radical clearance measured with in vivo EPR method may be affected not only by the redox status in the liver but also by information from other tissues in the measured region of the rat. On the other hand, the time course of nitroxyl radical level in the bile flow of rats was found to be a reliable index of redox status. Measurement site and/or volume limitation, which was achieved by the BFM method in this paper, is quite important in estimating reasonable EPR signal decay information as an index of tissue/organ redox status.

Correlation between Keton Body Level in Selenium-Deficient Rats and Oxidative Damages

The age dependence of ketone body levels (KBLs) and oxidative damages in selenium-deficient (SeD) and normal rats were compared. The feeding SeD diets gave ketogenesis and higher KBLs especially in younger rats. However, KBLs in SeD rats seemed to decrease with their age. Feeding 0.1 mg/kg Se in water with SeD diet did not affect the KBLs in young (8 week old) rats, whereas the addition of Se reduced the KBLs in older (20 week old) rats. Blood KBLs showed some correlations with tissue damage. TBARSs showed no correlations with the tissue damages and KBLs when the values were compared between the same age, while better correlation was obtained between urinary KBLs of 6-20 week old normal rats and the liver TBARSs of 4-16 week old normal rats. The oxidative injury might induce liver damage with some delay. SeD rat kidney TBARS levels normalized by protein had some correlations with BUN and blood KBL. Kidney may be sensitive to the oxidative stresses and/or injuries. Tissue damages of SeD rats decreased with age. In contrast, oxidative injuries might be gradually accumulated in normal rat tissue. Oxidative stress can be visible by gradual accumulation of small damages during the aging, while large stress in young rats can be buffered and masked. The aging based accumulation of oxidative injuries might also be correlated with KBLs, while it might not give notable tissue damages.

Effect of hydrogen peroxide in redox status estimation using nitroxyl spin probe

A procedure for estimating in vivo redox status using EPR and a hydrogen peroxide (H(2)O(2))-dependent spin probe method is described. The mechanism of decreasing spin clearance in the selenium-deficient (SeD) rat is discussed. The in vivo decay constant of the nitroxyl spin probe in the liver region of SeD rats appeared to be slightly lower that of the selenium-adequate control (SeC) group, and was significantly smaller than that of normal rats. Bile H(2)O(2) levels in normal rats were significantly lower than those in SeD rats. The in vivo decay constant of the spin probe in SeD rats depended on the bile H(2)O(2) level. Furthermore, H(2)O(2) was detected in the bile in all SeD rats, whereas bile H(2)O(2) could be detected in only half of the normal rats. It was found that the in vivo decay constant of the spin probe in normal rats also depended on whether bile H(2)O(2) was detected or not. In vivo decay constants were smaller in rats subjected to the surgical operation than in the nonoperated groups. The EPR signal of the nitroxyl radical in the liver homogenate was increased by addition of H(2)O(2), which was administered 30 min before the rat was killed. It appears that H(2)O(2) can oxidize the hydroxylamine formed following reduction of the spin probe in the liver.