The role of oxygen radicals in experimental acute pancreatitis

Oxygen-derived free radicals mediate an important step in the initiation of experimental acute pancreatitis. Thereby, it seems that these reactive oxygen metabolites are generated at an early stage of disease. The source of the enhanced production of oxygen radicals still remains unclear. Experimentally, the efficiency of scavenger treatment varied between different models, whereby these differences depended on the experimental model and not on the form of pancreatitis which was induced. Most studies pretreated the experimental animals before inducing acute pancreatitis. This does not mirror the clinical reality, since patients are admitted to the hospital after onset of the disease. It was shown in Cerulein pancreatitis, however, that scavenger treatment also mitigated the pancreatic tissue damages after induction of acute pancreatitis. Moreover, antioxidant treatment also attenuated the extrapancreatic complications, thus improving the final outcome of the disease. The first indirect observations also suggest that in human acute recurrent and chronic pancreatitis, oxygen free radicals are generated and add to the damages seen. Therefore, well-defined controlled clinical studies with patients suffering from acute pancreatitis are needed to validate the role of oxygen radicals in this disease.     

The role of free radicals in cold injuries

Cold injury is a tissue trauma produced by exposure to freezing temperatures and even brief exposure to a severely cold and windy environment. Rewarming of frozen tissue is associated with blood reperfusion and the simultaneous generation of free oxygen radicals. In this review is discussed the current understanding of the mechanism of action of free oxygen radicals as related to cold injury during rewarming. Decreased energy stores during ischaemia lead to the accumulation of adenine nucleotides and liberation of free fatty acids due to the breakdown of lipid membranes. On rewarming, free fatty acids are metabolized via cyclo-oxygenase and adenine nucleotides are metabolized via the xanthine oxidase pathway. These may be the source of free oxygen radicals. Leukocytes may also play a major role in the pathogenesis of cold injury. Oxygen radical scavengers, such as superoxide dismutase and catalase, may help to reduce the cold induced injury but their action is limited due to the inability readily to cross the plasma membrane. Lipid soluble antioxidants are likely to be more effective scavengers because of their presence in membranes where peroxidative reactions can be arrested.     

Diving seals, ischemia-reperfusion and oxygen radicals

The cardiovascular adaptations of seals that contribute to their ability to tolerate long periods of diving asphyxial hypoxia result in episodic regional ischemia during diving and abrupt reperfusion upon termination of the dive. These conditions might be expected to result in production of oxygen-derived free radicals and other forms of highly reactive oxygen species. Seal organs vary during dives with respect to the degree and persistence of ischemia. Myocardial perfusion is reduced and intermittent; kidney circulation is vigorously vasoconstricted. Heart and kidney tissues from ringed seals (Phoca hispida) and domestic pigs (Sus scrofa) were compared in reactions to experimental ischemia. Resulting production of hypoxanthine, indicative of ATP degradation, was higher in pig than in seal tissues. Activity of superoxide dismutase (SOD), an oxygen radical scavenger, was higher in seal heart. We suggest that these results indicate enhanced protective cellular mechanisms in seals against the potential hazard of highly reactive oxygen forms. SOD activity was unexpectedly higher in pig kidney.     

The reactivity of carotenoid radicals with oxygen

The possibility that carotenoid radicals react with oxygen to form chain-carrying peroxyl radicals has been postulated to account for the reduction in antioxidant effetiveness displayed by some carotenoids at high oxygen concentrations. The primary objective of the work described in this paper was to measure the rate constants for oxygen addition to a series of carotenoid radicals and to examine any influence of carotenoid structural features on these rate constants. Laser flash photolysis has been used to generate long-lived carotenoid radicals (PhS-CAR^√) derived from radical addition reactions with phenylthiyl radicals (PhS^√) in benzene. The PhS-CAR^√ radicals are scavenged by oxygen at rates that display a moderate dependence on the number of conjugated double bonds (n_db) in the carotenoid. The rate constants range from ∼10³ to ∼10⁴ M^- 1 s^- 1 for n_db = 7-11. The data also suggest that the presence of terminal cyclic groups may cause an increase in the rate constant for oxygen addition.     

Serum immunoglobulin levels in human hydatidosis

Serum IgG, IgM, IgA and IgD levels of 83 patients with hepatic or pulmonary hydatidosis and 15 postoperative individuals with no cysts were compared with the mean values of 80 healthy Lebanese controls. A significant increase of IgG was present in all patients. An increase in the mean IgM and IgA levels was significant only in pulmonary cases. There was no significant correlation between the titres of antibodies as detected by haemagglutination and complement-fixation tests and the respective serum IgG and IgM immunoglobin levels. Mean IgD levels were not different between patients and controls. Elevated IgE levels were detected in 77% of 21 hydatid patients. A persistent hyperglobulinemia was observed in postoperative follow-ups.     

Lipid diffusion in sperm plasma membranes exposed to peroxidative injury from oxygen free radicals

Unsaturated lipids in sperm plasma membranes are very susceptible to peroxidation when exposed to reactive oxygen species (ROS). In this investigation we have incubated ram spermatozoa in the presence of two ROS generating systems, ascorbate/FeSO4 and potassium peroxychromate (K3CrO8), and examined their effects on membrane fluidity by measuring fluorescence recovery after photobleaching (FRAP) of a lipid reporter probe 5-(N-octadecanoyl)-aminofluorescein (ODAF). Peroxidation was monitored by malonaldehyde formation and changes in fluorescence emission of 4,4-difluoro-5-(4-phenyl-1,3-butadienyl)-4-bora-3a,4a-diaza-s-indacene-3-undecanoic acid (C11-BODIPY(581/591)). Ascorbate/FeSO4-induced peroxidation was inhibited by Vitamin E, butylated hydroxyanisole (BHA), 1,4-diazobicyclo(2,2,2)octane (DABCO), and to a lesser extent by ethanol. Added superoxide dismutase (SOD), gluthathione peroxidase (GPX), and catalase were ineffective scavengers. K3CrO8 induced very rapid peroxidation that could be delayed, but not prevented, by Vitamin E, BHT, DABCO, ethanol, and mannitol; once again SOD, GPX, and catalase were ineffective scavengers. Neither peroxidation with ascorbate/FeSO4 nor K3CrO8, or added H2O2 or malonaldehyde perturbed ODAF diffusion in any region of the sperm plasma membrane. Vitamin E tended to enhance diffusion rates. Exogenous cumene hydroperoxide, however, reduced ODAF diffusion to low levels on the sperm head. These results suggest that the adverse effects of ROS on spermatozoa are more likely to be caused by direct oxidation of proteins and membrane permeabilisation than disturbance of lipid fluidity.     

Gut-associated immune effector responses in immunocompetent and immunocomprimised mice with Giardia lamblia

Abstract Significantly higher Giardia lamblia trophozoites load in the intestine of infected mice accompanied pronounced influx of suppressor/cytotoxic T cells (Lyt 2.2⁺), T cells (Thy 1.2⁺) and significant reduction in IgA-containing cells in the gut during the establishment and peak phases of infection. The induction of helper/inducer T cells (Lyt 1.1⁺) and significant enhancement of IgA-containing cells in gut resulted in the decline of the trophozoite loads. However, the prior treatment of animals with dexamethasone alone resulted in significant reduction in helper/inducer T cells (Lyt 1.1⁺) and the IgA-containing cells in the gut; the percents of suppressor/cytotoxic T cells (Lyt 2.2⁺) and IgM-containing cells remained unaltered. Although the G. lamblia infection in such animals further significantly increased the influx of suppressor/cytotoxic T cells, the late response of helper/inducer T cells and IgA-containing cells was abrogated during the decline phase of infection. The significant reduction in the trophozoite load — despite immuno-suppressive therapy — appeared to be due to unaltered IgM response in such animals which probably took over the function of IgA in defense against G. lamblia . The data of the investigation thus suggested a role of helper/inducer T cells and antibodies producing cells in gut as important effector cells resulting in the termination of primary G. lamblia infection.     

The rate of oxygen utilization by cells

The discovery of oxygen is considered by some to be the most important scientific discovery of all time—from both physical-chemical/astrophysics and biology/evolution viewpoints. One of the major developments during evolution is the ability to capture dioxygen in the environment and deliver it to each cell in the multicellular, complex mammalian body—on demand, i.e., just in time. Humans use oxygen to extract approximately 2550 calories (10.4 MJ) from food to meet daily energy requirements. This combustion requires about 22 mol of dioxygen per day, or 2.5 × 10^− 4 mol s^− 1. This is an average rate of oxygen utilization of 2.5 × 10^− 18 mol cell^− 1 s^− 1, i.e., 2.5 amol cell^− 1 s^− 1. Cells have a wide range of oxygen utilization, depending on cell type, function, and biological status. Measured rates of oxygen utilization by mammalian cells in culture range from < 1 to > 350 amol cell^− 1 s^− 1. There is a loose positive linear correlation of the rate of oxygen consumption by mammalian cells in culture with cell volume and cell protein. The use of oxygen by cells and tissues is an essential aspect of the basic redox biology of cells and tissues. This type of quantitative information is fundamental to investigations in quantitative redox biology, especially redox systems biology.     

The regulatory role of oxygen radicals in myocardial cells

The paper reviews participation of primary active forms of oxygen in the processes of regulation of intracellular metabolism. Action of the primary forms of oxygen upon the myocardium contractile function depends on their concentration: their moderate increase enhances the rate and strength of contractions whereas higher concentrations diminish the contraction strength by inhibiting Ca2+ inflow from without. For NO the latter effect might be compensated by absence of coronary vessels dilatation. The level of the active forms of oxygen in the cells is subsidiary to the antioxidant system, and loss of the latter's components might trigger the apoptosis process and, consequently, some diseases.     

Free radicals in reperfusion-induced arrhythmias: Study with EUK 8, a novel nonprotein catalytic antioxidant

Oxyradicals have been implicated as a possible cause of postischemic reperfusion arrhythmias (RA). However, the ability of enzymatic scavengers such as superoxide dismutase and/or catalase to reduce RA remains controversial. The purpose of the present work was to determine whether a nonprotein catalytic antioxidant, EUK 8, may limit RA in isolated heart preparations. The catalytic dismutation of H₂O₂ by EUK 8 was demonstrated using a Clark electrode. EUK 8's ability to scavenge oxyradicals was studied in vitro by electron spin resonance (ESR) in presence of superoxide-anion generating system. ESR concentration-effect curves obtained led us to use EUK 8 at 50 μmol/l in isolated heart preparations. Isolated rat hearts were submitted to 10 min regional ischemia induced by left coronary artery ligation. Reperfusion was achieved by releasing the coronary ligation, and the incidence and duration of early ventricular arrhythmias were then investigated. In the treated-group, EUK 8 was added to the perfusion fluid (50 μmol/1) 90 s before reperfusion. Our results show that EUK 8 significantly reduced the severity of RA as assessed by the arrhythmia score measurement (control: 3.46 ± 0.21 vs. EUK 8:2.73 ± 0.27, p < .05). In conclusion, EUK 8 is able to limit RA in our experimental model. This effect might be related to the catalytic antioxidant properties of this complex.     

Formation of activated oxygen in the hypoxic rat liver

The biliary GSSG efflux rate of normoxic perfused rat liver was 1.5 +/- 0.2 nmol/min/g liver wet weight. The GSSG efflux rate as indicator for the flux through the glutathione peroxidase reaction and, therefore, for an oxidative loading increased with the extent of hypoxia. 2.6 +/- 0.5 nmol/min/g were released from the severely hypoxic liver. The hydroxyl radical scavenger formate as well as the xanthine oxidase inhibitor allopurinol reduced the efflux rate of GSSG. GSH was released from the perfused liver at a rate of 15.5 nmol/min/g which was nearly unchanged in severe hypoxia. The high rate of glucose liberation from the hypoxic liver declined to almost that of the normoxic organ in the presence of formate. There is an 'oxidative stress' during hypoxic liver perfusion which probably originates from increased generation of activated oxygen species in the degradation of purine nucleotides.     

Hydroxyl radicals mediate injury to endothelium-dependent relaxation in diabetic rat

The purpose of this study was to determine the radical species which mediates the toxic effects of exogenous oxygenderived free radicals on endothelial function of chronic diabetic rat aorta. Endothelium-dependent relaxation to acetylcholine was impaired in diabetic vessels. Exposure to the exogenous free radical generating system of xanthine plus xanthine oxidase selectively impaired endothelium-dependent relaxation to acetylcholine in control and diabetic aorta with relaxations essentially abolished in diabetic aorta. The loss of relaxation to acetylcholine in diabetic aorta was prevented or attenuated by pretreatment with catalase, dimethylthiourea or desferrioxamine, but not by mannitol or superoxide dismutase. These results suggest that hydroxyl radicals play an important role in the endothelial injury produced by oxygen-derived free radicals in chronic diabetic rat aorta. Furthermore, the site of the injury is likely due to intracellular generation of hydroxyl radicals.     

The role of the reactions of NO with superoxide and oxygen in biological systems: A kinetic approach

In this study we calculate the half-life of ^·NO in its reactions with superoxide and with oxygen under various conditions using the known rate constants for these reactions. The measured half-life of ^·NO in biological systems is 3–5 s, which agrees well with the calculated value for intracellular ^·NO, but not for extracellular ^·NO under normal physiological conditions. The autoxidation of ^·NO to yield NO₂ as a final product cannot be responsible for such a short measured half-life under normal as well as pathologic conditions. Therefore, if there is direct evidence for the occurrence of the reaction of ^·NO with O₂ in the medium, one has to assume that the steady state concentrations of free ^·NO are much lower than those measured. The very low concentrations of free ^·NO in biological systems may result from its reversible strong binding to biological molecules. Simulation of the mechanism of the autoxidation of ^·NO indicates that the binding constants of ^·NO to O₂ or to another ^·NO are too small to account for the very low concentration of free ^·NO in biological systems. Nevertheless, the reaction of ^·NO with oxygen cannot be neglected in biological systems if the intermediate ONOO· reacts rapidly with a biological target. The biological damage caused by ONOO′ is expected to be due to the radical itself and to peroxynitrite, which is most probably formed via the reaction of ONOO· with the biological molecule.     

活性氧、自由基与植物的衰老

介绍近 1 0年来有关活性氧、自由基的产生 ,对植物的伤害及植物对活性氧、自由基清除的研究进展。     

轮状病毒四价灭活疫苗的制备及在小鼠的免疫原性研究

制备轮状病毒四价灭活疫苗,观察其在小鼠体内的抗体应答情况。实验采用轮状病毒原液经凝胶过滤层析纯化,灭活后配制四价疫苗,肌肉注射免疫小鼠,ELISA法测定小鼠血清IgA、IgG。将单价G1、G2、G3、G4型灭活病毒原液及四价轮状病毒灭活疫苗免疫小鼠后,均可刺激产生针对RV的高水平的特异性IgG抗体,但IgA应答较弱。表明四价轮状病毒灭活疫苗在小鼠中具备很好的免疫原性。     

天然免疫分子在糖基化异常IgA致肾小球足细胞损伤中的免疫调节作用

IgA肾病(IgA nephropathy,IgAN)位居各类肾小球疾病之首,是一组以IgA为主的免疫球蛋白在肾小球系膜区沉积为特征的免疫介导性肾小球疾病,也是引起患者终末期肾衰竭最常见的病因之一。足细胞是继系膜细胞与IgA肾病关系的新近关注热点,其系一类位于基底膜最外层的上皮细胞,并是构成肾小球滤过屏障的核心成份。目前认为,足细胞损伤及其生物学行为在IgA肾病等疾病起始进展乃至终末期肾衰中起关键作用。近年伴随着对上皮细胞尤其细胞转分化(EMT)现象在足细胞损伤机制中重要意义的认识,人们注意到糖基化异常IgA在足细胞EMT发生中的诱发作用,以及足细胞EMT过程中的病生理调控机制与IgA肾病等肾小球疾病发生发展的关系。为此,该文进一步基于足细胞的生物学特性以及免疫调节新的视角,探讨天然免疫分子在糖基化异常IgA致足细胞损伤中的调控作用,拟为进一步阐释IgA肾病发病机制及其相关研究乃至临床治疗提供新的思路。     

Modification of contractile proteins by oxygen free radicals in rat heart

This study was undertaken to investigate the effects of oxygen free radicals on myofibrillar creatine kinase activity. Isolated rat heart myofibrils were incubated with xanthine+xanthine oxidase (a superoxide anion radical-generating system) or hydrogen peroxide and assayed for creatine kinase activity. To clarify the involvement of changes in sulfhydryl groups in causing alterations in myofibrillar creatine kinase activity, 1) effects of N-ethylmaleimide (sulfhydryl groups reagent) on myofibrillar creatine kinase activity, 2) effect of oxygen free radicals on myofibrillar sulfhydryl groups content, and 3) protective effects of dithiothreitol (sulfhydryl groups-reducing agent) on the changes in myofibrillar creatine kinase activity due to oxygen free radicals were also studied. Xanthine+xanthine oxidase inhibited creatine kinase activity both in a time-and a concentration-dependent manner. Superoxide dismutase (SOD) showed a protective effect on the depression in creatine kinase activity caused by xanthine+xanthine oxidase. Hydrogen peroxide inhibited creatine kinase activity in a concentration-dependent manner; this inhibition was prevented by the addition of catalase. N-ethylmaleimide reduced creatine kinase activity in a dose-dependent manner. The content of myofibrillar sulfhydryl groups was decreased by xanthine+xanthine oxidase; this reduction was protected by SOD. Furthermore, the depression in myofibrillar creatine kinase activity by xanthine+xanthine oxidase was protected by the addition of dithiothreitol. Oxygen free radicals may inhibit myofibrillar creatine kinase activity by modifying sulfhydryl groups in the enzyme protein. The reduction of myofibrillar creatine kinase activity may lead to a disturbance of energy utilization in the heart and may contribute to cardiac dysfunction due to oxygen free radicals.