Detection of free radicals in blood by electron spin resonance in a model of respiratory failure in the rat

Dietary selenium augments sarcoplasmic calcium release and mechanical performance in mice

Background

As an essential trace element selenium plays a significant role in many physiological functions of the organs. It is found within muscles as selenocystein in selenoprotein N, which is involved in redox-modulated calcium homeostasis and in protection against oxidative stress.

Methods

The effects of two different selenium compounds (selenate and NanoSe in 0.5 and 5 ppm concentration for two weeks) on muscle properties of mice were examined by measuring in vivo muscle performance, in vitro force in soleus (SOL) and extensor digitorum longus (EDL) muscles and changes in intracellular Ca²⁺ concentration in single fibers from flexor digitorum brevis (FDB) muscle.. Western-blot analysis on muscle lysates of EDL and SOL were used to measure the selenoprotein N expression. Control mice received 0.3 ppm Se.

Results

While the grip force did not change, 5 ppm selenium diets significantly increased the speed of voluntary running and the daily distance covered. Both forms of selenium increased significantly the amplitude of single twitches in EDL and SOL muscle in a concentration dependent manner. Selenate increased fatigue resistance in SOL. The amplitude of the calcium transients evoked by KCl depolarization increased significantly from the control of 343 ± 44 nM to 671 ± 51 nM in the presence of 0.5 ppm selenate in FDB fibers. In parallel, the rate of calcium release during short depolarizations increased significantly from 28.4 ± 2.2 to 45.5 ± 3.8 and 52.1 ± 1.9 μM/ms in the presence of 0.5 ppm NanoSe and selenate, respectively. In 0.5 ppm concentration both selenium compounds increased significantly the selenoprotein N expression only in EDL muscle.

Conclusions

Selenium supplementation augments calcium release from the sarcoplasmic reticulum thus improves skeletal muscle performance. These effects are accompanied by the increased selenoprotein N expression in the muscles which could result in increased oxidative stress tolerance in case of long lasting contraction.

Electronic supplementary material

The online version of this article (doi:10.1186/s12986-016-0134-6) contains supplementary material, which is available to authorized users.

Dynamic changes in parameters of redox balance after mild heat stress in aged laying hens (Gallus gallus domesticus)

In order to evaluate the metabolic responses of laying hens induced by high temperature at later laying stage, nine 60-wk-old laying hens (Gallus gallus domesticus) were employed in the present study. The hens were exposed to 32 degrees C for 21 d and blood samples were obtained before and at 1, 7, 14 and 21 d of heat exposure. The reactive oxygen species (ROS) formed in blood during heat exposure were estimated by the ex vivo spin-trapping method. Body temperature and plasma concentrations of glucose, urate, creatine kinase (CK), triiodothyronine (T(3)), thyroxine (T(4)), corticosterone (CORT), thiobarbituric acid reacting substances (TBARS), ferric/reducing antioxidant power (FRAP) and superoxide dismutase (SOD) activity were measured. Plasma levels of glucose, CK and CORT were not significantly influenced by heat exposure at any time point. The circulating concentrations of T(3) were decreased while plasma T(4) levels changed in the opposite way. The formation of ROS was significantly augmented by heat exposure in laying hens though the body temperature was not significantly altered. The enhanced enzymatic and non-enzymatic antioxidant systems acted in concert to alleviate the heat stress evoked oxidative damage.

Oxidative study of patients with total body irradiation: effects of amifostine treatment

In patients undergoing bone marrow transplant (BMT), reactive oxygen species (ROS) are released as a consequence of the events related to the preparative regimen. Total body irradiation (TBI), which is known to generate ROS, is a routine preconditioning procedure prior to BMT. Several studies have demonstrated that amifostine protects normal tissues. In the present report, we investigated the oxidative state of plasma and erythrocytes in 21 patients with hematological malignancies undergoing TBI. The dose fraction was 160 cGy, twice daily (eight sessions). For ROS detection, we used electron spin resonance spectroscopy and spin-trapping technique. In all, 15 patients received amifostine prior to the irradiation and six did not. No free radical signal was detected in the plasma samples spectrum of 15 amifostine-treated patients, and five of six samples of nontreated patients showed ROS signal. Only two of 15 treated patients had mucositis degree higher than 2, whereas five of six nontreated patients suffered this complication. The average hospitalization days in treated and nontreated patients were 23.5 and 29.7, respectively. This work represents an original observation; we found by direct measurements of free radicals that ROS are released during TBI, and confirmed the amifostine radical scavenger activity.

Unique in vivo applications of spin traps

The ultimate goal of in vivo electron spin resonance (ESR) spin trapping is to provide a window to the characterization and quantification of free radicals with time within living organisms. However, the practical application of in vivo ESR to systems involving reactive oxygen radicals has proven challenging. Some of these limitations relate to instrument sensitivity and particularly to the relative stability of these radicals and their nitrone adducts, as well as toxicity limitations with dosing. Our aim here is to review the strengths and weaknesses of both traditional and in vivo ESR spin trapping and to describe new approaches that couple the strengths of spin trapping with methodologies that promise to overcome some of the problems, in particular that of radical adduct decomposition. The new, complementary techniques include: (i) NMR spin trapping, which monitors new NMR lines resulting from diamagnetic products of radical spin adduct degradation and reduction, (ii) detection of *NO by ESR with dithiocarbamate: Fe(II) "spin trap-like" complexes, (iii) MRI spin trapping, which images the dithiocarbamate: Fe(II)-NO complexes by proton relaxation contrast enhancement, and (iv) the use of ESR to follow the reactions of sulfhydryl groups with dithiol biradical spin labels to form "thiol spin label adducts," for monitoring intracellular redox states of glutathione and other thiols. Although some of these approaches are in their infancy, they show promise of adding to the arsenal of techniques to measure and possibly "image" oxidative stress in living organisms in real time.

Methods to assess free radicals and oxidative stress in biological systems

Oxidative stress results from a disruption of the prooxidant/antioxidant cellular balance and monitoring free radical status becomes an interesting challenge in animal and human nutrition. In the present work, merits and limitations of different analytical techniques (HPLC, GC-MS, fluorometric and colourometric assays, ELISA, gel electrophoresis) for the measurement of radical mediated alterations in the cellular integrity of lipids (malondialdehyde, hydrocarbon gases, F2-isoprostanes) proteins (protein carbonyls, 3-nitrotyrosine) and DNA (8-hydroxy-2'-deoxyguanosine) are discussed. Besides these indirect methods, owing to the fact that free radicals are paramagnetic, electron paramagnetic resonance spectroscopy combined with spin trapping has become a valuable tool to directly assess and to better understand the mechanisms of free radical reactions. With this approach a radical that is too short-lived to be detected, adds to a spin-trapping agent to form a relatively long-lived radical adduct. Information obtained from the hyperfine splitting of the spin-trapped adduct can provide identification and quantification of the originally generated free radicals.

Adrenocorticotropin counteracts the increase in free radical blood levels, detected by electron spin resonance spectrometry, in rats subjected to prolonged asphyxia

We investigated the influence of the adrenocorticotropic fragment 1-24 [ACTH-(1-24)] on the blood levels of highly-reactive free radicals in a rat model of prolonged asphyxia. Anesthetized animals were endotracheally intubated and mechanically ventilated with room air; after a 10 min stabilization period, the ventilator was turned off to induce asphyxia for 5 min; then, the ventilator was turned back on, and, simultaneously, the rats were intravenously treated with either ACTH-(1-24) (160 microg/kg in a volume of 1 ml/kg) or equivolume saline. Free radicals were detected in arterial blood by electron spin resonance spectrometry using an ex vivo method that avoids injection of the spin-trapping agent employed (alpha-phenyl-N-tert-butylnitrone). Arterial pressure, electrocardiogram (ECG) and electroencephalogram (EEG) were monitored for the 60 min observation period, or until prior death. At the end of the 5 min period of respiratory arrest, blood levels of free radicals were about four times higher than those of the basal, pre-asphyxia condition, arterial pressure had dramatically decreased, ECG showed marked bradycardia and signs of ischemic damage and the EEG had become isoelectric. Treatment with ACTH-(1-24) produced an immediate normalization of the blood levels of free radicals, associated with a restoration of cardiovascular function and full recovery of EEG within 30-45 min; all the saline-treated rats, on the other hand, died within 6.89 +/- 0.96 min. These results provide direct evidence that in a severe condition of prolonged asphyxia there is a rapid and massive production of highly-reactive free radicals and suggest that the resuscitating effect of adrenocorticotropin fragments in severe hypoxic conditions may be largely due to the inhibition of free radical overproduction during tissue reoxygenation.

Dithiothreitol improves recovery from in vitro diaphragm fatigue

There is increasing evidence that reactive oxygen species are produced during strenuous skeletal muscle work and that they contribute to the development of muscle fatigue. Although the precise cellular mechanisms underlying such a phenomenon remain obscure, it has been hypothesized that endogenously produced reactive oxygen species may down-regulate force production during fatigue by oxidizing critical sulfhydryl groups on important contractile proteins. To test this hypothesis, we fatigued rat diaphragm strips in vitro for 4 min at 20 Hz stimulation and a duty cycle of 0.33. Following fatigue, the tissue baths were drained and randomly replaced with either physiologic saline or physiologic saline containing the disulfide reducing agent, dithiothreitol (DTT) at varying doses (0.1-5.0 mM). Force-frequency characteristics were then measured over a 90-min recovery period. At the 0.5 and 1.0 mM doses, DTT treatment was associated with significantly greater force production in the recovery period. DTT's effects were observed at most frequencies tested, but appeared more prominent at the higher frequencies. The beneficial effects of DTT were not evident at the 0.1 or 5.0 mM doses and appeared to be specific for fatigued muscle. These recovery-enhancing effects of a potent disulfide reducing agent suggest that important contractile proteins may be oxidized during fatigue; such changes may be readily reversible.

Influence of ACTH-(1-24) on free radical levels in the blood of haemorrhage-shocked rats: direct ex vivo detection by electron spin resonance spectrometry

1. The influence of ACTH-(1-24) on the blood levels of highly reactive free radicals in haemorrhagic shock was studied in rats. 2. Volume-controlled haemorrhagic shock was produced in adult rats under general anaesthesia (urethane, 1.25 g kg-1 intraperitoneally) by stepwise bleeding until mean arterial pressure stabilized at 20-23 mmHg. Rats were intravenously (i.v.) treated with either ACTH-(1-24) (160 micrograms kg-1 in a volume of 1 ml kg-1) or equivolume saline. Free radicals were measured in arterial blood by electron spin resonance spectrometry using an ex vivo method that avoids injection of the spin-trapping agent (alpha-phenyl-N-tert-butylnitrone). 3. Blood levels of free radicals were 6490 +/- 273 [arbitrary units (a.u.) ml-1 whole blood, before starting bleeding, and 30762 +/- 2650 after bleeding termination (means +/- s.e. mean of the values obtained in all experimental groups). All rats treated with saline died within 30 min, their blood levels of free radicals being 35450 +/- 5450 a.u. ml-1 blood, 15 min after treatment. Treatment with ACTH-(1-24) produced a rapid and sustained restoration of arterial pressure, pulse pressure, heart rate and respiratory function, with 100% survival at the end of the observation period (2 h); this was associated with an impressive reduction in the blood levels of free radicals, that were 12807 +/- 2995, 10462 +/- 2850, 12294 +/- 4120, and 10360 +/- 2080 a.u. ml-1 blood, 15, 30, 60 and 120 min after ACTH-(1-24) administration, respectively. 4. These results provide a direct demonstration that (i) in haemorrhagic shock there is a rapid and massive production of highly reactive free radicals, and that (ii) the sustained restoration of cardiovascular and respiratory functions induced by the i.v. injection of ACTH-(1-24) is associated with a substantial reduction of free radical blood levels. It is suggested that ACTH-(1-24) prevents the burst of free radical generation during blood mobilisation and subsequent tissue reperfusion, and this may be an important component of its mechanism of action in effectively preventing death for haemorrhagic shock.