Decreased carbon centered and hydrogen radicals in skeletal muscle of vitamin E supplemented rats

Attenuation of changes in capillary fine structure and leukocyte adhesion improves muscle performance following chronic ischaemia in rats

Acute ischaemia-reperfusion disrupts capillary fine structure and increases leukocyte adhesion in postcapillary venules. We determined whether chronic muscle ischaemia has similar consequences, and whether it is possible to ameliorate its effect on muscle performance. Following ischaemia (unilateral ligation, common iliac artery) rat hindlimb muscles were examined without other intervention or following treatment with an xanthine oxidase inhibitor (allopurinol), a Na(+)/H(+) exchange blocker (amiloride), or an oxygen free radical scavenger (vitamin E). No significant leukocyte adhesion or rolling, nor changes in capillary fine structure were observed 3 days postsurgery, when limb use was limited. However, leukocyte rolling and adhesion almost trebled by 7 days (P < 0.001), when normal gait was largely restored. Capillary fine structure was disturbed over a similar time course, e.g. relative endothelial volume (control 46%, 7 days 61%; P < 0.05), that resolved by 5 weeks. Where activity was increased by mild electrical stimulation 3 days after ligation muscles showed enhanced capillary swelling (endothelial volume 66% versus 50%, P < 0.005), but improved fatigue index (52% versus 16%, P < 0.001) as a result of greater blood flow. Muscle fatigue after ligation was related to the extent of contraction-induced hyperaemia (R(2) = 0.725), but not capillary swelling. Amiloride, and to a lesser extent allopurinol but not vitamin E, significantly decreased leukocyte rolling and adhesion, as well as capillary endothelial swelling. We conclude that increased activity of ischaemic muscles on recovery is likely to accentuate acidosis accompanying changes in microcirculation and contribute to enhanced muscle fatigue, whereas formation of oxygen free radicals may be attenuated by endogenous protective mechanisms.

Spin-trapping of oxygen free radicals in chemical and biological systems: new traps, radicals and possibilities

The choice of the spin-trap that is to be applied in any EPR study represents the crossroad between a comprehensive investigation and an "ordinary" quantification of production of radicals. So, the scope of our study was to compare the performance of different spin-traps for qualitative analysis of radical-generating systems, and their ability to recognize previously unnoticed radicals. In addition, we present a brief account of the difficulties involved in the detection of oxygen-centered radicals in chemical and biological systems accompanied by the rationale for using the EPR spin-trapping technique in quantitative studies of such reactive species. Certain technical aspects of EPR experiments related to efficient trapping of free radicals in biochemical systems are also discussed. As an example we present here results obtained using EPR spectroscopy and the spin-trap DEPMPO, which show that the Fenton reaction, as well as various biological systems generate a previously unappreciated hydrogen (*H) atom.

Effects of dietary functional ingredients and packaging methods on sensory characteristics and consumer acceptance of irradiated turkey breast meat

Raw and cooked breast patties from turkeys fed 8 different diets [control; 200 IU/kg of vitamin E (VE); 0.3 mg/kg of Se; 2.5% conjugated linoleic acids (CLA); 200 IU/kg of VE + 0.3 mg/kg of Se; 200 IU/kg of VE + 2.5% CLA; 0.3 mg/kg of Se + 2.5% CLA; and 200 IU/kg of VE + 0.3 mg/kg of Se + 2.5% CLA] were treated with 2 irradiation doses (0 and 1.5 kGy) and 2 packaging methods (vacuum and aerobic). Raw and cooked samples from 32 treatments were tested by 8 trained sensory panelists for turkey aroma and irradiation off-aroma. Based on the sensory scores, the 3 dietary treatments producing the most and the least off-aroma were selected and used for a consumer acceptance study. Sensory results of raw meat showed that turkey aroma was intense in aerobically packaged meat, whereas irradiation off-aroma was intense with vacuum packaging. Raw meats from dietary treatments containing CLA (CLA, VE + CLA, Se + CLA, VE + Se + CLA) had greater turkey aroma scores, whereas those containing VE (VE and VE + Se) had lower scores than the control. Dietary treatments containing VE (VE, VE + Se, VE + Se + CLA) significantly lowered (P < 0.05) irradiation off-aroma in raw turkey breast meat, whereas CLA increased it, especially when the meats were packaged aerobically. In cooked meat, however, irradiation and packaging had no effect on turkey meat aroma and irradiation off-aroma. Cooked meat from turkeys supplemented with VE (VE and VE + Se) had less (P < 0.05) irradiation off-odor than other dietary treatments. Dietary CLA increased the irradiation off-aroma in cooked meat, which could not be reduced, even when VE and Se were combined in the diet. Irradiation off-aroma of raw meat was not pleasant for most consumers, and dietary supplementation of VE and VE + Se improved consumer acceptance of irradiated raw meat. For cooked meat samples, consumers preferred both color and flavor of irradiated meat to nonirradiated meat.

Contractile response of skeletal muscle to low peroxide concentrations: myofibrillar calcium sensitivity as a likely target for redox-modulation

Endogenous peroxides and related reactive oxygen species may influence various steps in the contractile process. Single mouse skeletal muscle fibers were used to study the effects of hydrogen peroxide (H2O2) and t-butyl hydroperoxide (t-BOOH) on force and myoplasmic Ca2+ concentration ([Ca2+]i). Both peroxides (1010 to 105 M) decreased tetanic [Ca2+]i and increased force during submaximal tetani. Catalase (1 kU/ml) blocked the effect of H2O2, but not of t-BOOH. The decrease in tetanic [Ca2+]i was constant, while the effect on force was biphasic: A transitory increase was followed by a steady decline to the initial level. Myofibrillar Ca2+ sensitivity remained increased during incubation with either peroxide. Only the highest peroxide concentration (10 mM) increased resting [Ca2+]i and slowed the return of [Ca2+]i to its resting level after a contraction, evidence of impaired sarcoplasmic reticulum Ca2+ re-uptake. The peroxides increased maximal force production and the rate of force redevelopment, and decreased maximum shortening velocity. N-ethylmaleimide (25 mM, thiol-alkylating agent) prevented the response to 1 mM H2O2. These results show that myofibrillar Ca2+ sensitivity and cross-bridge kinetics are influenced by H2O2 and t-BOOH concentrations that approach those found physiologically, and these findings indicate a role for endogenous oxidants in the regulation of skeletal muscle function.

Biological methane activation involves the intermediacy of carbon-centered radicals

The spin-trapping technique has demonstrated that carbon-centered radicals are produced during soluble-methane-monooxygenase catalysis of the hydroxylation of several different types of substrate. The resulting spin-adducts were identified from the hyperfine splitting constants in their EPR spectra. Isotopic labelling showed unequivocally that the trapped radicals were derived from substrate. The carbon-centered substrate radicals are believed to result from hydrogen-atom abstraction by a ferryl species in a cytochrome-P-450-like mechanism. No hydroxy radical nor an oxygen-based radical of any kind was detected in any of the spin-trapping experiments.

Brown fat thermogenesis and exercise: two examples of physiological oxidative stress?

Both brown fat tissue (BAT) and skeletal muscle experience large increases of oxygen consumption and oxygen radical generation during activation. This, together with the relatively low activities of antioxidant enzymes in these two tissues and the high lipid content and free fatty acid liberation of BAT, can produce a physiological oxidative stress. Increases of in vivo or in vitro (BAT) lipid peroxidation have been described in these tissues after activation. They react to this oxidative stress in an adaptive way after chronic stimulation. Cold acclimation increases antioxidant enzymes, ascorbate, and especially reduced glutathione (GSH) in BAT. There is controversy about the variations of antioxidants in skeletal muscle after acute exercise. Nevertheless, exercise training seems to increase muscle antioxidant enzymes and GSH. Many reports show that vitamin E levels decrease in the muscle and increase in plasma during exercise. Studies of vitamin E deficiency and supplementation strongly suggest that this vitamin is of protective value during exercise.

The threshold of age in exercise and antioxidants action

Physical activity and exercise are important factors in determining the quality of life in old animals and humans. With age there is a slow but significant reduction in muscle mass and ability to perform certain physical activities. This may be due to changes with the age of muscle composition and protein turnover, as well as decrease of trophic influence in neural control of muscles of old individuals. Exercise in general was shown to improve muscle performance even in old age. However a concept of threshold of age in exercise was advanced forward in the 1970s. Accordingly, the idea was that for a given exercise of a particular duration and intensity there is a certain age beyond which this exercise may not have a positive influence, but can become detrimental to the exercising animal or human. Recent studies on the effect of antioxidants such as Vitamins C and E and selenium have shown that these agents could decrease the free radical associated muscle damage caused by extensive exercise. Thus, administration of these antioxidants especially vitamins C and E may reduce the oxidative damage due to exercise, and may alter the threshold of age by delaying it to an older age.