The role of free radical reactions with haemoglobin and thalassaemia

It is well known that all living systems depend on iron to transport (haemoglobin), store (myoglobin) and utilize (cytochromes, cytochrome oxide) oxygen for respiration. Iron is an essential component in the active sites of the enzyme that protects against oxidation, such as the iron superoxide dismutase, in bacteria and plants. In normal human plasma almost all iron loading of transferrin is 20-30% maximum. In this presentation we review and summarize recent developments in our understanding of iron transport and storage in living systems.     

Hydralazine-dependent carbon dioxide free radical formation by metabolizing mitochondria

The addition of hydralazine (1-hydrazinophthalazine) to rat liver mitochondria metabolizing malate/glutamate causes formation of a carbon-centered free radical which was spin-trapped with phenyl-t-butylnitrone (PBN) or dimethylpyrrolidine-N-oxide (DMPO). The coupling constants of the spin-trapped free radical were AN = 16.1, AH beta = 4.6 G for PBN and AN = 15.9, AH beta = 18.9 G for DMPO-trapped radical in aqueous solution. The spin-trapped free radical was shown to be the carbon dioxide anion free radical by independent synthesis, high pressure liquid chromatography separation, and electron paramagnetic resonance characterization. The amount of carbon dioxide anion free radical produced was absolutely dependent upon the presence of hydralazine and varied depending on mitochondrial substrate, with by far the highest amount produced by pyruvate. Studies with 13C-labeled pyruvate demonstrated that the carbon dioxide free radical came from C-1 of this compound.     

The role of free radical processes and redox-signalization in adaptation of the organism to changes in oxygen level

Data are presented on participation of free-radical oxygenation in development of the organism adaptation. The redox-signalization concept is discussed in the aspect of its responsibility for the initial stage of external signal transmission to the cell genetic apparatus. The pro- and antioxidant system ratio is noted as important for assessment of formation of the cell structure and the tissue resistance. A protective effect of periodic hyperoxia was shown as well as regularities of its development similar formation of adaptation to the periodic hyperoxia.     

The role of free radical generation in increasing cerebrovascular permeability

The brain endothelium constitutes a barrier to the passive movement of substances from the blood into the cerebral microenvironment, and disruption of this barrier after a stroke or trauma has potentially fatal consequences. Reactive oxygen species (ROS), which are formed during these cerebrovascular accidents, have a key role in this disruption. ROS are formed constitutively by mitochondria and also by the activation of cell receptors that transduce signals from inflammatory mediators, e.g., activated phospholipase A₂ forms arachidonic acid that interacts with cyclooxygenase and lipoxygenase to generate ROS. Endothelial NADPH oxidase, activated by cytokines, also contributes to ROS. There is a surge in ROS following reperfusion after cerebral ischemia and the interaction of the signaling pathways plays a role in this. This review critically evaluates the literature and concludes that the ischemic penumbra is a consequence of the initial edema resulting from the ROS surge after reperfusion.     

Depolymerization of xanthan by iron-catalysed free radical reactions

It is demonstrated using gamma-radiolytic and photolytic techniques that, when O₂?- is produced in the presence of catalytic amounts of iron(II) and iron(III) complexes depolymerization of xanthan in aqueous solution occurs. The use of these techniques also allows a quantitative measurement of the efficiency of conversion of O₂^?- to ?OH in these systems to be made, with the assumption that ?OH is the most likely depolymerizing species present. Using pulse radiolysis and oxidative-reductive depolymerization, the effects of some common anions on the degradation process have been correlated with the reactivities of their related free radicals with xanthan. The effects of other parameters such as ionic strength and temperature on xanthan depolymerization are also detailed     

Enhanced intraarticular free radical reactions in adjuvant arthritis rats

One of the reasons of rheumatoid arthritis (RA) development is widely recognized the relation of free radical reactions in tissue injuries. The aim of this study was to evaluate the location where in vivo free radical reactions was enhanced in adjuvant arthritis (AA) model rats using in vivo electron spin resonance (ESR)/nitroxyl spin probe technique. The signal decay after intravenous injection of spin probe was enhanced in AA than that in control and suppressed by the pre-treatment of dexamethasone (DXT). Interestingly, the decay in joint cavity occurred prior to paw swelling of AA and suppressed by a simultaneous injection of free radical scavengers, indicating that the enhancement of free radical reactions in joint cavity of AA rats. This technique would be useful tool to determine the location of the enhanced free radical reactions and evaluate the activity of antioxidant medicine with non-invasive real-time measurement.     

The role of radical reactions in organomercurials impact on lipid peroxidation

The organomercury compounds RHgX and R(2)Hg are broad-spectrum biocidal agents acting via diverse mechanisms in biological systems. Despite the enormous amount of studies carried out in last decades to elucidate the detailed mechanisms of organomercurials toxicity their biomolecular mode of action is still under debate. Among various toxicity mechanisms the action of RHgX and R(2)Hg at the membrane level due to the lipophilic properties of their molecules is discussed. Organomercurials are supposed to induce membrane associated oxidative stress in living organism through different mechanisms including the enhancement of the lipid peroxidation and intracellular generation of reactive oxygen species (ROS), H(2)O(2), O(2)(-), HO(). The perturbation of antioxidative defense system and the peroxidation of unsaturated fatty acids in membrane lipid bilayer are consequences of this impact. On the other hand, the involvement of organomercurials in radical and redox biochemical processes is manifested in carbon to metal bond cleavage that leads to the generation of reactive organic radicals R(). This pathway is discussed as one of the multiple mechanisms of organomercurials toxicity. The goal of this review is to present recent results in the studies oriented towards the role of organomercurials in the xenobiotic-mediated enhancement of radical production and hence in the promotion of lipids peroxidation. The application of natural and synthetic antioxidants as detoxification agents is presented.     

Enhanced intraarticular free radical reactions in adjuvant arthritis rats

One of the reasons of rheumatoid arthritis (RA) development is widely recognized the relation of free radical reactions in tissue injuries. The aim of this study was to evaluate the location where in vivo free radical reactions was enhanced in adjuvant arthritis (AA) model rats using in vivo electron spin resonance (ESR)/nitroxyl spin probe technique. The signal decay after intravenous injection of spin probe was enhanced in AA than that in control and suppressed by the pre-treatment of dexamethasone (DXT). Interestingly, the decay in joint cavity occurred prior to paw swelling of AA and suppressed by a simultaneous injection of free radical scavengers, indicating that the enhancement of free radical reactions in joint cavity of AA rats. This technique would be useful tool to determine the location of the enhanced free radical reactions and evaluate the activity of antioxidant medicine with non-invasive real-time measurement.     

The role of carbon dioxide in glucose metabolism of Bacteroides fragilis

The effect of CO₂ concentration on growth and glucose fermentation of Bacteroides fragilis was studied in a defined mineral medium. Batch culture experiments were done in closed tubes containing CO₂ concentrations ranging from 10% to 100% (with appropriate amounts of bicarbonate added to maintain the pH at 6.7). These experiments revealed that CO₂ had no influence on growth rate or cell yield when the CO₂ concentration was above 30% CO₂ (minimum available CO₂–HCO ₃ ^- , 25.5 mM), whereas a slight decrease in these parameters was observed at 20% and 10% CO₂ (available CO₂–HCO ₃ ^- , 17 and 8.5 mM, respectively). If CO₂–HCO ₃ ^- concentrations were below 10 mM, the lag phase lengthened and a decrease in maximal growth rate and cell yield were observed. The amount of acetate made decreased, while d-lactate concentration increased. A net production of CO₂ allowed growth under conditions of extremely low concentrations of added CO₂.When B. fragilis was grown in continuous culture with 100% CO₂ or 100% N₂, the dilution rate influenced the concentrations of acetate, succinate, propionate, d-lactate, l-malate and formate formed. Decreasing the dilution rate favored propionate and acetate production under both conditions. When the organism was grown with 100% N₂, the amount of propionate formed was greater than the amount of succinate formed at all dilution rates. Except at slow dilution rates the reverse was true when 100% CO₂ was used. B. fragilis was unable to grow at dilution rates faster than 0.154 h^-1 when grown with 100% N₂; the Y _glc ^max was 67.9 g DW cells/mol glucose and m _s was 0.064 mmol glucose/g DW·h. If the gas atmosphere was 100% CO₂ the organism was washed out of the culture when the dilution rate exceeded 0.38 h^-1; the Y _glc ^max was 59.4 g DW cells/mol glucose and m _s was 0.094 mmol glucose/g DW·h.Measurement of the phosphoenolpyruvate (PEP) carboxykinase (E.C. 4.1.1.49) with whole, permeabilized cells of B. fragilis showed an increase of specific enzyme activity with decreasing CO₂ concentrations. The mechanisms used by B. fragilis to adjust to low levels of CO₂ are discussed.     

The potential role of carbon dioxide in the neuroimmunoendocrine changes following cerebral ischemia

Carbon dioxide (CO(2)) interacts in complex ways with the brain and the endocrine and immune systems. Arterial CO(2) may be elevated or decreased following cerebral ischemia-reperfusion injury or stroke. The aim of the present review is to delineate potential changes in the neuroimmunoendocrine system following cerebral ischemia-reperfusion injury and to provide evidence for the modulatory role of carbon dioxide in this setting. It appears that lesions of the right and left cerebral hemispheres are associated with different patterns of immune activation and cytokine release. Changes in arterial CO(2) can profoundly alter the neuroimmunoendocrine system, especially the hypothalamic-pituitary-adrenal (HPA) axis and the production of pro-inflammatory cytokines. Hypercapnia activates the HPA axis, exerts antiinflammatory and antioxidant effects, and can alter the secretion and function of various brain neurotransmitters. There is conflicting evidence surrounding arterial CO(2): its effects on the ischemic brain may be either beneficial or deleterious. Mild hypercapnia may exert some neuroprotection following cerebral ischemia, but severe hypercapnia may aggravate neuronal injury by extra- and intra-cellular acidification and/or impairment of cellular calcium hemostasis. Future studies are required to delineate the potential relationship between arterial CO(2) and prognosis and long-term survival following cerebral ischemia-reperfusion injury. "Therapeutic hypercapnia" seems to be a promising approach to the treatment of stroke patients, and its use should be justified by further experimental and clinical studies.     

The carbon cycle and carbon dioxide over Phanerozoic time: the role of land plants

A model (GEOCARB) of the long-term, or multimillion year, carbon cycle has been constructed which includes quantitative treatment of (1) uptake of atmospheric CO₂ by the weathering of silicate and carbonate rocks on the continents, and the deposition of carbonate minerals and organic matter in oceanic sediments; and (2) the release of CO₂ to the atmosphere via the weathering of kerogen in sedimentary rocks and degassing resulting from the volcanic-metamorphic-diagenetic breakdown of carbonates and organic matter at depth. Sensitivity analysis indicates that an important factor affecting CO₂ was the rise of vascular plants in the Palaeozoic. A large Devonian drop in CO₂ was brought about primarily by the acceleration of weathering of silicate rock by the development of deeply rooted plants in well-drained upland soils. The quantitative effect of this accelerated weathering has been crudely estimated by present-day field studies where all factors affecting weathering, other than the presence or absence of vascular plants, have been held relatively constant. An important additional factor, bringing about a further CO₂ drop into the Carboniferous and Permian, was enhanced burial of organic matter in sediments, due probably to the production of microbially resistant plant remains (e.g. lignin). Phanerozoic palaeolevels of atmospheric CO₂ calculated from the GEOCARB model generally agree with independent estimates based on measurements of the carbon isotopic composition of palaeosols and the stomatal index for fossil plants. Correlation of CO₂ levels with estimates of palaeoclimate suggests that the atmospheric greenhouse effect has been a major factor in controlling global climate over the past 600 million years.     

The measurement of free radical reactions in humans. Some thoughts for future experimentation

The question as to whether free radical reactions are a major cause of tissue injury in human disease, or merely an accompaniment to such injury, is very difficult to answer because of lack of adequate experimental techniques. New techniques that are becoming available are discussed, with specific reference to their use in humans.     

The role of dark carbon dioxide fixation in root nodules of soybean

The magnitude and role of dark CO₂ fixation were examined in nodules of intact soybean plants (Harosoy 63 × Rhizobium japonicum strain USDA 16). The estimated rate of nodule dark CO₂ fixation, based on a 2 minute pulse-feed with ¹⁴CO₂ under saturating conditions, was 102 micromoles per gram dry weight per hour. This was equivalent to 14% of net nodule respiration. Only 18% of this CO₂ fixation was estimated to be required for organic and amino acid synthesis for growth and export processes. The major portion (75-92%) of fixed label was released as CO₂ within 60 minutes. The labeling pattern during pulse-chase experiments was consistent with CO₂ fixation by phosphoenolpyruvate carboxylase. During the chase, the greatest loss of label occurred in organic acids. Exposure of nodulated roots to Ar:O₂ (80:20) did not affect dark CO₂ fixation, while exposure to O₂:CO₂ (95:5) resulted in 54% inhibition. From these results, it was concluded that at least 66% of dark CO₂ fixation in soybean may be involved with the production of organic acids, which when oxidized would be capable of providing at least 48% of the requirement for ATP equivalents to support nitrogenase activity.