Evidence of hepatic endogenous hydrogen peroxide in bile of selenium-deficient rats

Effects of loading a magnetic field longitudinal to the linear particle-beam track on yields of reactive oxygen species in water

The effects of a magnetic field longitudinal to the ion beam track on the generation of hydroxyl radicals (•OH) and hydrogen peroxide (H₂O₂) in water were investigated. A longitudinal magnetic field was reported to enhance the biological effects of the ion beam. However, the mechanism of the increased cell death by a longitudinal magnetic field has not been clarified. The local density of •OH generation was estimated by a method based on the EPR spin-trapping. A series of reaction mixtures containing varying concentrations (0.76‒2278 mM) of DMPO was irradiated by 16 Gy of carbon- or iron-ion beams at the Heavy-Ion Medical Accelerator in Chiba (HIMAC, NIRS/QST, Chiba, Japan) with or without a longitudinal magnetic field (0.0, 0.3, or 0.6 T). The DMPO-OH yield in the sample solutions was measured by X-band EPR and plotted versus DMPO density. O₂-dependent and O₂-independent H₂O₂ yields were measured. An aliquot of ultra-pure water was irradiated by carbon-ion beams with or without a longitudinal magnetic field. Irradiation experiments were performed under air or hypoxic conditions. H₂O₂ generation in irradiated water samples was quantified by an EPR spin-trapping, which measures •OH synthesized from H₂O₂ by UVB irradiation. Relatively sparse •OH generation caused by particle beams in water were not affected by loading a magnetic field on the beam track. O₂-dependent H₂O₂ generation decreased and oxygen-independent H₂O₂ generation increased after loading a magnetic field parallel to the beam track. Loading a magnetic field to the beam track made •OH generation denser or made dense •OH more reactive.

Effects of LET on oxygen-dependent and-independent generation of hydrogen peroxide in water irradiated by carbon-ion beams

Linear energy transfer (LET) dependence of yields of O₂-dependent and O₂-independent hydrogen peroxide (H₂O₂) in water irradiated by ionizing radiation was investigated. The radiation-induced hydroxyl radical (•OH) generation in an aqueous solution was reported to occur in two different localization densities, the milli-molar (relatively sparse) and/or molar (markedly-dense) levels. In the milli-molar-level •OH generation atmosphere, •OH generated at a molecular distance of ∼7 nm are likely unable to interact. However, in the molar-level •OH generation atmosphere, several •OH were generated with a molecular distance of 1 nm or less, and two •OH can react to directly make H₂O₂. An aliquot of ultra-pure water was irradiated by 290-MeV/nucleon carbon-ion beams at the Heavy-Ion Medical Accelerator in Chiba (HIMAC, NIRS/QST, Chiba, Japan). Irradiation experiments were performed under aerobic or hypoxic (<0.5% oxygen) conditions, and several LET conditions (13, 20, 40, 60, 80, or >100 keV/μm). H₂O₂ generation in irradiated samples was estimated by three methods. The amount of H₂O₂ generated per dose was estimated and compared. O₂-independent H₂O₂ generation, i.e. H₂O₂ generation under hypoxic conditions, increased with increasing LET. On the other hand, the O₂-dependent H₂O₂ generation, i.e. subtraction of H₂O₂ generation under hypoxic conditions from H₂O₂ generation under aerobic conditions, decreased with increasing LET. This suggests that the markedly-dense •OH generation is positively correlated with LET. High-LET beams generate H₂O₂ in an oxygen-independent manner.

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.

A quantitative analysis of carbon-ion beam-induced reactive oxygen species and redox reactions

The amounts of reactive oxygen species generated in aqueous samples by irradiation with X-ray or clinical carbon-ion beams were quantified. Hydroxyl radical (^•OH), hydrogen peroxide (H₂O₂), and the total amount of oxidation reactions, which occurred mainly because of ^•OH and/or hydroperoxy radicals (HO₂ ^•), were measured by electron paramagnetic resonance-based methods. ^•OH generation was expected to be localized on the track/range of the carbon-ion beam/X-ray, and mM and M levels of ^•OH generation were observed. Total ^•OH generation levels were identical at the same dose irrespective of whether X-ray or carbon-ion beam irradiation was used, and were around 0.28-0.35 µmol/L/Gy. However, sparse ^•OH generation levels decreased with increasing linear energy transfer, and were 0.17, 0.15, and 0.09 µmol/L/Gy for X-ray, 20 keV/µm carbon-ion beam, and >100 keV/µm carbon-ion beam sources, respectively. H₂O₂ generation was estimated as 0.26, 0.20, and 0.17 µmol/L/Gy, for X-ray, 20 keV/µm carbon-ion beam, and >100 keV/µm carbon-ion beam sources, respectively, whereas the ratios of H₂O₂ generation per oxygen consumption were 0.63, 0.51, and 3.40, respectively. The amounts of total oxidation reactions were 2.74, 1.17, and 0.66 µmol/L/Gy, respectively. The generation of reactive oxygen species was not uniform at the molecular level.

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.

Changes in the components of biliary and plasma lipids in selenium-deficient rats

We constructed a chronic oxidative stress model in which Se-deficient diet was fed to male Wister rats for 8 weeks. As expected, effects of oxidative damage, including Fe accumulation and increase in peroxidized lipids, were identified in the liver owing to the lack of glutathione peroxidase. Although the oxidative stress caused Fe accumulation in the liver, the Fe concentration in bile of the SeD rat was almost the same as that in the control rats. The constant excretion of Fe into bile supported the Fe accumulation in the liver. No differences were observed in the principal components of biliary lipids, i.e., bile acids, phospholipids, and cholesterol, between the two groups; moreover, these trends were also reflected in the plasma. Due to the trapping of reactive oxygen species, only bilirubin concentrations in the bile and plasma were decreased in the SeD group, when compared with those in the control group. Measurement of bilirubin concentration may be used as a supplemental oxidative stress marker.

Hydroxymethylglutaryl-coenzyme A reductase inhibitors and osteoporosis: a meta-analysis

Studies determining the association between hydroxymethylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors (statins) and bone metabolism are mixed. We conducted a systematic review to assess the potential impact of statins on fractures, bone mineral density and bone markers. We searched Medline, Embase, the Cochrane Library, and Federal Research in Progress (FEDRIP). Inclusion criteria consisted of human studies with measurable outcomes, which were rated as good or fair according to the United States Preventive Services Task Force (USPSTF) criteria. The effects of statins on bone mineral density (BMD), bone markers and fracture risk were independently extracted by two reviewers and were combined by use of a random-effects model. The 31 analyzed studies included 24 observational studies and seven randomized controlled trials. Overall, statin use was associated with fewer hip fractures (OR 0.60, 95% CI 0.45-0.78) and improved hip BMD (Z score 0.12, 95% CI 0.05-0.19), with a non-significant reduction in vertebral fractures and no effect on vertebral BMD. In subgroup analysis of studies that involved only women there was a reduction in hip fractures (OR 0.75, 95% CI 0.60-0.95) and improvement in hip BMD (Z score 0.11, 95% CI 0.04-0.18). Vertebral BMD was unchanged, and only one study reported on vertebral fractures, finding improvement. Statins had only small effects on bone markers, with a decrease in alkaline phosphatase [standardized mean difference (SMD) -0.18, 95% CI -0.34 to -0.01], an increase in NTX (SMD 0.39, 95% CI 0.07-0.71), with no effect on osteocalcin or CTX. The statistically significant improvement in hip fracture risk was seen only in case-control trials, not in either the eight prospective trials or the two randomized controlled trials (RCTs). Statins may have a beneficial impact on bone metabolism and fracture risk; randomized controlled trials are needed to explore this association.

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.

Evaluation of oxidative damage in the liver of selenium-deficient rats

Previous studies have implied a relationship between Se-deficiency and oxidative stress. In the present study, the occurrence of oxidative stress due to Se-deficiency was investigated by evaluating the age dependence of growth and indices of oxidative damage for the liver of Se-deficient (SeD) rats. The ratios of liver weight to body weight of the SeD rats were greater than those of the normal rats. The values of AST and ALT (clinical indices of liver damage) were higher in the SeD rats than the normal ones especially in the young (6-12 weeks of age). The TBARS level of the 4-week-old SeD group were higher than the normal group while the level decreased with age. Conversely, the TBARS level of the normal group gradually increased and became higher than SeD group in older rats (12-20 weeks of age). Vitamin E rather than vitamin C may be consumed during oxidative stress due to Se-deficiency. Damage induced by Se-deficiency may be related to growth and the mechanisms of this damage may alter with age.

[Relation of bile hydrogen peroxide level and liver super oxide dismutase activity in selenium-deficient rats]

The relationship of hydrogen peroxide (H2O2) levels in bile with liver SOD and GSH-Px activity in selenium (Se)-deficient rats is discussed. Normal rats and 7 groups of rats fed a Se-deficient diet with different feeding periods were examined. H2O2 levels in bile were measured using the spin-trapping method with electron spin resonance (ESR). Bile H2O2 levels in the initial stage (20-60 min from start of the cannulation) of measurement were increased depending on the length of the feeding period with the Se-deficient diet and absence of Se. Bile H2O2 levels in the later stage (60-120 min) of measurement first increased with the length of feeding with the Se-deficient diet and then decreased with longer feeding periods. Bile H2O2 levels immediately after the operation were relatively low in almost all cases. The operation may result in oxidative stress to generate H2O2. Liver GSH-Px activity decreased depending on the length of the feeding period with the Se-deficient diet and existence of Se. Liver SOD activity increased in Se-deficient groups. It is suggested that the H2O2 levels in bile are related to decreased GSH-Px activity, SOD activity, and also the oxidative stress caused by surgery. Therefore the H2O2 levels in bile can be used as an index of sensitivity to oxidative stress. Although severe oxidative stress may decrease SOD activity, Se deficiency can induce liver SOD activity.

[Noninvasive detection of dynamics of various elements in the upper abdomen of selenium-deficient rat using multitracer analysis technique]

The advantages of a technique as a diagnostic tool for examining the distribution of bio-trace elements in the living body are discussed. Time courses of the distribution of Be, V, Mn, Fe, Co, Zn, As, Se, Rb, Sr, and Y in the upper abdomen of living selenium-deficient rats were examined using the in vivo multitracer analysis technique. The dynamics of the elements were estimated by comparison with the distribution of As. Almost all As was taken up by red blood cells. The present findings of a decrease in Se and increase in Co in the liver of Se-deficient rats are in good agreement with the previous data that showed a decrease in Se and increase in Co uptake into the liver cell fraction of Se-deficient rats. Although the normalized uptake rate and the relative distribution of Co 48 h after administration increased in Se-deficient rats, the early level of the relative distribution of Co was not lower compared with that in the normal group. This suggests that the high level of the normalized uptake rate and the relative distribution of Co in Se-deficient rats were affected by the decreasing excretion rate rather than by the increasing uptake rate of Co. The plateau level of relative distribution of Se in the Se-deficient rats is lower than that in normal rats, suggesting that the lower levels of the normalized uptake rate and relative distribution of Se in Se-deficient rats were due to the decreased uptake rate of the element.

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

The contents of iron (Fe), cobalt (Co), zinc (Zn), and selenium (Se) in the organs (liver, kidney, spleen, heart, lung, and brain) and the liver cell fractions (nuclear, mitochondrial, microsomal, and cytosolic fractions) of Se- or vitamin E (VE)-deficient rats were measured using instrumental neutron activation analysis (INAA). The contents of Fe in the liver of Se-deficient rats, and in the liver and the spleen of VE-deficient rats were increased compared with those in normal rats. Fe contents increased mainly in the microsomal fraction. Contents of Co in the organs and liver cell fractions of Se- and VE-deficient rats were markedly low, reflecting the Co contents in both diets. Contents of Zn in the organs and liver cell fractions of Se- and VE-deficient rats decreased to 60-80% of the contents in normal rats. The Se contents in Se-deficient rat organs except for the kidney, spleen, and brain were below the detectable level under the present conditions. Se contents in VE-deficient rat decreased to 50-80% of those in normal rats in all organs and fractions. It is suggested that oxidative stress due to Se- or VE-deficiency affects the dynamics of Fe and Zn.

Contents and uptake rates of Mn, Fe, Co, Zn, and Se in Se-deficient rat liver cell fractions

The contents of manganese (Mn), iron (Fe), cobalt (Co), zinc (Zn), and selenium (Se) in nuclear (NU), mitochondrial (MT), microsomal (MC), and cytosolic (CS) fractions of liver homogenates of normal and selenium-deficient (SeD) rats were determined by instrumental neutron activation analysis (INAA). The uptake rates of these elements in the liver cell fractions of both groups of rats were determined by multitracer analysis (MTA). The results indicated that Se-deficiency caused a significant increase in the content of Fe in the MC fractions. The MTA showed that the uptake rate of Fe was highest in the MC fraction, and that the uptake rate in the fraction was similar between the SeD and normal rats.