Reactive Oxygen Molecules Research Articles

Glucocorticoid and ACTH regulation of rat peritoneal phagocyte chemiluminescence and nitric oxide production in culture.

In order to study the adrenocortical regulation of monocyte/macrophage functions further, leucocytes from the rat peritoneum were incubated in vitro with glucocorticoid concentrations up to 10 mumol L-1 and with adrenocorticotropic hormone (ACTH) up to 100 micrograms mL-1. The monocyte/macrophage production of reactive oxygen molecules was measured by luminol amplified chemiluminescence, and the production of nitric oxide (NO) was measured as nitrite (NO2-). Dexamethasone in vitro in nanomolar concentrations inhibited monocyte/macrophage chemiluminescence and also nitric oxide production; the potency was dexamethasone > methylprodnisolone > prednisolone. ACTH enhanced both activated chemiluminescence and endotoxin-induced nitric oxide production, but only at concentrations about 20-100 micrograms mL-1, and there was no significant effect of physiological concentrations. In summary, the results of the present study further confirm and substantiate that glucocorticoids in low pharmacological concentrations have a general inhibitory effect on monocyte/ macrophage production of reactive oxygen molecules through the specific glucocorticoid receptors, while the stimulatory effect of ACTH is only observed by very high, non-physiological concentrations. Furthermore, since low concentrations of glucocorticoids inhibited the production of these reactive oxygen molecules in vitro, indirect mechanisms involving hormones and other elements outside the immune system are not essential for the effect of glucocorticoids on monocytes/macrophages.

Reactive oxygen species and calcium homeostasis in cultured human intestinal smooth muscle cells.

Reactive oxygen species (ROS) significantly alter cell function. We examined the effects of hydrogen peroxide (H2O2) and xanthine/xanthine oxidase (X/XO) on isolated intestinal muscle cells. We assessed cell viability with the exclusion dye trypan blue and assayed the effects of H2O2 and X/XO on the intracellular redox state with the fluorescent probe 2',7'-dichlorofluorescein. Intracellular calcium concentration was measured in cells loaded with fura 2-acetoxymethyl ester, and we recorded whole membrane currents with conventional patch-clamp methods. Cells remained viable after a 5-min exposure to H2O2 and X/XO. H2O2 and X/XO led to a significant rise of the intracellular concentration of ROS. H2O2 (270 microM to 2.7 mM) as well as X/XO (0.25-16 mU; 0.5 mM xanthine) significantly increased intracellular calcium concentrations. Depletion of intracellular calcium with ryanodine or thapsigargin did not abolish the effect of ROS on the intracellular calcium concentration. In the absence of external calcium or in the presence of the calcium channel blocker nifedipine, H2O2 and X/XO still increased the intracellular calcium level. Thus calcium influx and calcium release from internal stores contributed to this rise in cytosolic calcium. Catalase and superoxide dismutase blunted or completely abolished the changes in calcium concentration elicited by H2O2 and X/XO. Exposure to ROS resulted in a rapid decline of the membrane resistance without significant changes in voltage-sensitive ion currents. We conclude that ROS disrupt the calcium homeostasis of cells at concentrations that do not lead to immediate cell death. The resulting elevation in cytosolic free calcium will activate a variety of biochemical reactions and may thus contribute to the cytotoxicity of reactive oxygen molecules.

Effect ofin vivocorticosterone and acute food deprivation on rat resident peritoneal cell chemiluminescence after activation ex vivo

Adrenoglucocorticoid regulation of rat peritoneal monocyte/macrophage function was studied by exposing rats to corticosterone (CS) in the drinking water, and to fast (48 h). Production of reactive oxygen metabolites was measured by luminol amplified chemiluminescence (CL) in preparations of peritoneal cells activated by serum treated zymosan (STZ). Administration of CS which led to an increase in plasma CS from 31 (controls) to 46 ng mL-1, reduced CL (per cell) by 31%. Fast, which did not change plasma CS or ACTH, also had an inhibitory effect on CL (-25%), while the combination of CS administration and fast strongly inhibited the CL (-89%), indicating that plasma CS and fast reduced CL in a synergistic way. Similar effects on cell number were observed: CS-administration, fast and the combination reduced macrophage numbers (-13, -19.7 and -55%), while no significant effect was observed on the number of monocytes. The effect of adrenalectomy (adx) was studied in another series of experiments; adx induced no significant change in peritoneal leucocyte number or composition, while cells from adx animals had significantly higher chemiluminescence reaction than cells from sham operated animals. CS substitution in adx animals reduced CL by 30% while sham operated animals had 49% lower CL in adx. The data from adx animals also suggest that endogenous levels of CS are inhibitory for CL, but the results are not conclusive for the effect of very low doses of CS since other mechanisms than elimination of CS could prime the chemiluminescence reaction after adx. In conclusion, a moderate elevation of CS after systemic administration in vivo reduced the total number of mononuclear phagocytes in rat peritoneum, reduced the relative number of macrophages compared with monocytes, and suppressed the function of monocytes/macrophages by reducing the production of reactive oxygen molecules in activated cells. Furthermore, the effect of corticosterone was also dependent on the physiological situation, since the effects of fast and corticosterone were synergistic.

In vitro cytotoxicity of the chlorinated naphthoquinone dichlone to human endothelial ECV304 cells

The cytotoxicity of the pro-oxidant fungicide dichlone (2,3-dichloro-1,4-naphthoquinone), to the human endothelial cell line, ECV304, was evaluated. The sensitivity of these cells to dichlone was intermediate between that of human hepatoblastoma HepG2 cells (least sensitive) and that of human GMO5757 fibroblasts. The midpoint cytotoxicity values for a 24-hr exposure to dichlone was about 0.02 m m when evaluated with the neutral red, acid phosphatase, and XTT tetrazolium assays. Lactic acid dehydrogenase leakage, after a 4-hr exposure, occurred initially at 0.05 m m dichlone. As with other naphthoquinones, cellular metabolism of dichlone presumably could proceed either by a one- or a two-electron reduction reaction. The enhancement of potency of dichlone towards ECV304 cells pretreated with the glutathione-depleting agents, dl-buthionine-[ S,R]-sulfoximine, 1-chloro-2,4-dinitrobenzene, and 1,3-bis(chloroethyl)-1-nitrosourea; the reduction in potency of dichlone to cells pretreated with (−)-2-oxo-4-thiazolidine carboxylic acid; the decrease in intracellular glutathione on exposure to dichlone; the subtle damage to the plasma membrane of dichlone-treated cells (as detected by the leakage of lactate dehydrogenase from these cells); and the lack of potentiation of dichlone toxicity by pretreatment with dicoumarol, are all consistent with the one-electron reduction reaction as the dominant pathway and with the subsequent generation of reactive oxygen molecules. The ECV304 cell line proved to be a useful research tool to study cytotoxic injury to endothelial cells.

The pH-dependent reduction of Adriamycin catalysed by NADH:cytochrome b5 reductase

Adriamycin is a redox active antineoplastic antibiotic that upon reduction can, in the presence of oxygen, redox cycle to form reactive oxygen species, while in anaerobiosis can generate a reactive quinone methide. NADH:cytochrome b 5 reductase catalysed the reduction of adriamycin at pH 6.6 with an apparent K m of 1.8 μM; at pH 7.6, no measurable reduction of adriamycin occurred. Aerobically, in the presence of enzyme and NADH, adriamycin stimulated oxygen consumption and concomitant accumulation of hydrogen peroxide. At pH 7.6, no discernible oxygen consumption nor detectable hydrogen peroxide generation was observed. The findings demonstrate that NADH:cytochrome b 5 reductase is capable of reducing adriamycin, in a pH-dependent manner, to species that can redox cycle in the presence of oxygen to form reactive oxygen molecules and thus may contribute to the generation of oxidative stress, a phenomenon suggested to be involved in both the toxicity and the antineoplastic activity of adriamycin.

Endogenous tumor necrosis factor functions as a resistant factor against adriamycin

One of the mechanisms of cytotoxicity by tumor necrosis factor (TNF) and heat is the induction of reactive oxygen molecules. Cells producing endogenous tumor necrosis factor (enTNF) show resistance to the cytotoxicity of exogenous TNF and heat by inducing manganous superoxide dismutase (MnSOD) to scavenge the reactive oxygen molecules. Intracellular hydroxyl radical production is also involved in adriamycin-induced cytotoxicity. In this study, we therefore examined the possibility that enTNF may act as a protective protein against adriamycin-induced cytotoxicity in a manner similar to that in which it protects against exogenous TNF and heat. Adriamycin-sensitive L-M (mouse tumorigenic fibroblast) cells, originally expressing no enTNF, were transfected with an expression vector which directs the synthesis of non-secretory-type human TNF (enTNF). The stable transformants became resistant to adriamycin with increased levels of MnSOD. Conversely, when HeLa (human uterine cervical cancer) cells, which originally produce an appreciable amount of enTNF, were transfected with an anti-sense TNF mRNA expression vector to inhibit enTNF synthesis, their intracellular MnSOD activity was suppressed and adriamycin sensitivity was enhanced. However, no alterations in expression of multidrug-resistant gene products--P-170 glycoprotein, glutathione S-transferase pi (GST-pi) and the intracellular concentrations of glutathione (GSH)--were observed in these transfectants as compared to their parent cells. These results indicate that enTNF exerts its intracellular protective effect against adriamycin-induced cytotoxicity by the same mechanism as that against exogenous TNF and heat, namely scavenging reactive oxygen with induced MnSOD.

Oxidative modification of low-density lipoproteins by mesangial cells.

Because hypercholesterolemia and mesangial cell proliferation may be important in the pathogenesis of glomerulosclerosis, the effects of low-density lipoprotein (LDL) on human mesangial cell proliferation were evaluated. Native LDL (20 to 200 micrograms/mL) caused a dose-dependent increase in (3H)thymidine incorporation and increased mesangial cell numbers over 96 h. The mitogenic effect of LDL was partially blocked by the inhibition of cytochrome P-450, but not by the inhibition of cyclooxygenase or lipoxygenase pathways. Higher LDL concentrations (1,000 to 2,000 micrograms/mL) inhibited (3H)thymidine incorporation and reduced cell numbers, possibly as a result of the oxidative modification of LDL, indicated by an increase in thiobarbituric reactive substances. This peroxidation of LDL involved superoxide, because superoxide dismutase and butylated hydroxytoluene prevented it, whereas hydroxyl radical scavengers were without effect. Native LDL subjected to chemical oxidation by copper sulfate also inhibited mesangial cell proliferation. These results suggest that low concentrations of LDL may stimulate human mesangial cell proliferation, which may, in turn, cause the production of reactive oxygen molecules. Moreover, the oxidative modification of LDL may mediate the toxic effects of high LDL concentrations on human mesangial cells.

Solid-atomic particle charge transfer effects in atomic-like Auger electron emission

We report a direct observation of the solid-atomic particle charge transfer effects on atomic-like Auger electron emission from both projectile and target species during ion bombardment on solid surfaces. Upon chemisorption of reactive oxygen molecules or physisorption of inert argon atoms on a clean Al surface, the intensity ratio between the atomic-like Al autoionization and Auger transition peaks is dramatically reduced and four new transition lines can be clearly resolved. The Ar L-shell spectra also show a gradual increase of the L 23M 23−M 23 3 peak intensity relative to that of the L 23M 23M 23 feature as the Ar layer condensed on substrate thickens.

Taurine attenuates renal disease in chronic puromycin aminonucleoside nephropathy

Repeated administration of low doses of puromycin aminonucleoside (PAMN) to rats induces a proteinuric renal disease that resembles focal segmental glomerulosclerosis (FSGS). Reactive oxygen molecules may be involved in the progressive course of this nephropathy. Therefore we evaluated whether taurine, an endogenous antioxidant, could limit the extent of renal injury. Sprague-Dawley rats received low-dose injections of PAMN, 2 mg/100 g body wt, over a 12-wk period. Two groups were studied: 1) controls given tap water (n = 23), and 2) an experimental group that drank 1% taurine-supplemented water (n = 22). Taurine-treated nephrotic rats had a reduction in albuminuria, as assessed by the urinary albumin-to-creatinine ratio (26 +/- 4 vs. 44 +/- 4, P less than 0.0001). After 12 wk, creatinine clearance was 0.33 +/- 0.03 (experimental) vs. 0.17 +/- 0.03 ml.min-1.100 g body wt-1 (control) (P less than 0.001), and inulin clearance (n = 6 pairs) was 0.26 +/- 0.04 (experimental) vs. 0.13 +/- 0.02 ml.min-1.100 g body wt-1 (control) (P less than 0.025). Administration of taurine reduced the percentage of segmentally sclerosed glomeruli (9.8 +/- 1.7 vs. 16.2 +/- 1.8%, P less than 0.02) and the tubulointerstitial injury score (1.36 +/- 0.19 vs. 2.61 +/- 0.25, P less than 0.0025) in experimental vs. control rats. Taurine treatment normalized the elevated renal cortical malondialdehyde level in rats with PAMN nephropathy (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Methods of assessing oxidant injury in renal tubular epithelial cells in vitro

Reactive oxygen molecules mediate renal injury in several diseases including glomerulonephritis, ischemic-reperfusion injury, and toxic nephropathies. Several in vivo animal studies document a role for reactive oxygen molecules in causing tissue injury. In vitro methods to determine the mechanisms and effects of reactive oxygen molecule injury will further aid in understanding the pathogenesis of several renal diseases. We describe methods to study cell injury in an in vitro cell culture system of renal tubular epithelial cells exposed to reactive oxygen molecules generated by hypoxanthine-xanthine oxidase or glucose-glucose oxidase. Methods to determine ATP levels and [3H]adenine release as an early response (15 to 90 min) to oxidant stress are described.51Chromium release representing cell detachment and cell lysis which are late responses (3 to 5 h) are also detailed. Methods of assessing oxidant injury in in vitro systems will allow the precise mechanisms of cell injury to be determined and will allow for the potential development of strategies to prevent or alleviate such injury.

Mechanism for candidacidal activity in macrophages activated by recombinant gamma interferon

Candidacidal activity in macrophages activated by recombinant gamma interferon was examined kinetically in relation to acidification of phagolysosomes. In resident peritoneal macrophages (PMPs) of BALB/c mice, enhanced killing activity against Candida albicans was demonstrated after incubation with 100 U of gamma interferon per ml for 24 h but not after incubation for 48 to 72 h. Conversely, increased generation of H2O2 was exhibited in PMPs incubated from 48 to 72 h but not in PMPs incubated for 24 h. In normal PMPs, fusion of lysosomes to candida-containing phagosomes was readily accomplished and phagosome-lysosome fusion was not enhanced further by activation. The candidacidal substance was extracted from granule-rich fractions of either normal or activated PMPs by using citric acid (pH 2.7) in equal amounts; the substance showed a noncationic, heat-stable protein nature. In addition, when phagolysosomal pH was determined by flow cytometry of intraphagolysosomal fluorescein isothiocyanate-labeled C. albicans, phagolysosomes with low pH (less than 4.0) were detected in about 40% of PMPs activated for 24 h but not in those activated for 72 h or in normal PMPs. Moreover, increasing the intralysosomal pH with NH4Cl resulted in a significant reduction of candidacidal activity in activated PMPs. These results indicate that the candidacidal activity of gamma interferon-activated PMPs correlates well with enhanced acidification of their phagolysosomes and suggest that the candidacidal activity of activated PMPs is independent from reactive oxygen molecules and is mediated by proteinaceous substance(s) generated only in a strong acidic milieu of phagolysosomes by activation.

Reactive oxygen molecules, oxidant injury and renal disease

Oxidant injury has been implicated in the pathogenesis of inflammatory, metabolic and toxic insults, in ischemic-reperfusion injury, and in carcinogenesis, aging and atherosclerosis. Oxidant injury is initiated by free radicals and reactive oxygen molecules which are generated by activated neutrophils, monocytes, and mesangial cells, during normal and abnormal metabolic processes, and from the metabolism of exogenous drugs and toxins. When cells and organs are exposed to oxidant stress, several different antioxidant defense mechanisms operate to prevent or limit oxidant injury. When antioxidant defense mechanisms are decreased, or when the generation of reactive oxygen molecules is increased, oxidant injury results from the shift in the oxidant/antioxidant balance. Oxidant-induced alterations of proteins, membranes, DNA, and basement membranes leads to cell and organ dysfunction. Several renal diseases including glomerulonephritis, vasculitis, toxic nephropathies, pyelonephritis, acute renal failure, and others are likely to be mediated at least in part by oxidant injury. In the future, mechanisms to decrease the generation of reactive oxygen molecules and/or antioxidant therapy may develop into new avenues of therapeutic intervention.

Reactive oxygen molecule-mediated injury in endothelial and renal tubular epithelial cells in vitro

To investigate renal tubular epithelial cell injury mediated by reactive oxygen molecules and to explore the relative susceptibility of epithelial cells and endothelial cells to oxidant injury, we determined cell injury in human umbilical vein endothelial cells and in four renal tubular epithelial cell lines including LLC-PK1, MDCK, OK and normal human kidney cortical epithelial cells (NHK-C). Cells were exposed to reactive oxygen molecules including superoxide anion, hydrogen peroxide and hydroxyl radical generated by xanthine oxidase and hypoxanthine. We determined early sublethal injury with efflux of 3H-adenine metabolites and a decline in ATP levels, while late lytic injury and cell detachment were determined by release of 51chromium. When the cells were exposed to 25, 50, and 100 mU/ml xanthine oxidase with 5.0 mM hypoxanthine, ATP levels were significantly lower (P less than 0.001) in LLC-PK1, NHK-C and OK cells compared to MDCK cells while ATP levels were significantly lower (P less than 0.01) in endothelial cells compared to all tubular cell lines. A similar pattern of injury was seen with efflux of 3H-adenine metabolites. When the cells were exposed to 50 mU/ml xanthine oxidase with 5.0 mM hypoxanthine for five hours, total 51chromium release was significantly (P less than 0.001) greater in LLC-PK1, NHK-C and OK cells compared to MDCK cells, while total 51chromium release was significantly (P less than 0.001) greater in endothelial cells compared to all tubular cells. However, lytic injury was the greatest in LLC-PK1 cells and NHK-C cells while cell detachment was the greatest in endothelial cells. MDCK cells were remarkably resistant to oxidant-mediated cell detachment and cell lysis. In addition, we determined ATP levels, 3H-adenine release and 51chromium release in LLC-PK1, NHK-C and endothelial cells in the presence of superoxide dismutase to dismute superoxide anion, catalase to metabolize hydrogen peroxide, DMPO to trap hydroxyl radical and DMTU to scavenge hydrogen peroxide and hydroxyl radical. We found that catalase and DMTU (scavengers of hydrogen peroxide) provided significant protection from ATP depletion, prevented efflux of 3H-adenine metabolites and cell detachment while DMPO (scavenger of hydroxyl radical) prevented lytic injury. In addition, we found that the membrane-permeable iron chelator, phenanthroline, and preincubation with deferoxamine prevented cell detachment and cell lysis, confirming the role of hydroxyl radical in cell injury.(ABSTRACT TRUNCATED AT 400 WORDS)

Photodynamic therapy

AbstractIn the wide field of laser applications in medicine, the photodynamic therapy is a very fascinating method for cancer diagnosis and therapy. The essential part of this treatment is the photosensitizer used, its selectivity, toxicity and phototoxicity. The first photosensitizer has been haematoporphyrinderivative (HPD); meanwhile a lot of potential dyes have been tested and the run for the “ideal” sensitizer is still going on. Also the reaction mechanisms are probably different, and depend on the dye. The last step in the reaction is the creation of the reactive oxygen molecule, which destroys the tumor cell. The selectivity of this reaction, the higher concentration of the dye in the tumor (cells and the vascular system) compared to the normal tissue, considerably depends on the type of the tumor. Beside this, the parameters of laser irradiation for a successful treatment are very critical. Laser‐tissue interactions limit the applications up to now to special tumor types and tumor stages. Nevertheless, photodynamic therapy will become increasingly important in the future, also in combination with conventional techniques.

Co-administration of ascorbic acid with cyclophosphamide (CPA) to pregnant mice inhibits the clastogenic activity of CPA in preimplantation murine blastocysts.

Cyclophosphamide (CPA) administered at a dose of 15 mg/kg body weight to pregnant inbred CBA/CaH mice 60 h after copulation significantly elevated the incidence of structural chromosomal aberrations and sister-chromatid exchanges in 96 h blastocysts. When ascorbic acid (800 mg/kg body weight) was co-administered with CPA (15 mg/kg) using different injection sites, the incidence of structural chromosomal aberrations and the number of aberrant metaphases were significantly lower as compared to the CPA-exposed embryos, but still significantly higher than untreated controls. Sister-chromatid exchanges were not significantly different in embryos exposed to CPA only when compared to those exposed to CPA and ascorbic acid. In terms of the developmental potential of embryos, pregnant mice injected with both CPA and ascorbic acid had significantly fewer resorptions per mouse, and a significantly higher number of viable fetuses retrieved on the 18th day of gestation when compared to mice injected with CPA alone. The data in this study demonstrate that the co-administration of ascorbic acid with CPA to pregnant mice ameliorates the CPA-induced clastogenicity and improves the developmental potential of these embryos. This study suggests that some of the CPA-induced genotoxicity is due to the generation of reactive oxygen molecules, but further research is necessary before this can be firmly concluded.

Mutagenic and lethal effects of near-ultraviolet radiation (290-400 nm) on bacteria and phage.

Despite decades of study of the effect of near-ultraviolet radiation (NUV) on bacterial cells, insights into mechanisms of deleterious alterations and subsequent recovery are just now emerging. These insights are based on observations that 1) damage by NUV may be caused by a reactive oxygen molecule, since H2O2 may be a photoproduct of NUV; 2) some, but not all, of the effects of NUV and H2O2 are interchangeable; 3) there is an inducible regulon (oxyR) that responds to oxidative stress and is involved in protection against NUV; 4) a number of NUV-sensitive mutants are defective either in the capacity to detoxify reactive oxygen molecules or to repair DNA damage caused by NUV; and 5) recovery from NUV damage may not directly involve induction of the SOS response. Since several distinctly different photoreceptors and targets are involved, it is unknown whether NUV lethality and mutagenesis result from an accumulation of damages or whether there is a particularly critical photoeffect. To fully understand the mechanisms involved, it is important to identify the chromophore(s) of NUV, the mechanism of toxic oxygen species generation, the role of the oxidative defense regulon (oxyR), the specific lesions in the DNA, and the enzymatic events of subsequent repair.

Role of endothelial cells and their products in the modification of low-density lipoproteins

A majority of the LDL preparations from various donors could be modified by incubation with endothelial cells from human arteries, veins and microvessels. These alterations comprise changes in electrophoretic mobility, buoyant density and lipid composition of LDL, the generation of thiobarbituric acid reactive substances in the medium, and a decrease in primary amino groups of LDL. Furthermore, the association of endothelial cell proteins with LDL was demonstrated by [ 35S]methionine incorporation and trichloroacetic acid precipitation of reisolated endothelial cell-modified LDL. After SDS-polyacrylamide gel electrophoresis of the reisolated modified LDL particles, radioactivity was mainly found at a molecular mass of 48 kDa and at one or two bands with a molecular mass of more than 100 kDa. The 48 kDa protein was identified as a latent plasminogen activator inhibitor. Cell viability was necessary for the cell-mediated LDL modification, which indicates that endothelial cells are actively involved in this process. The Ca 2+ ionophore A23187 and monensin did not influence LDL modification. LDL modification was markedly inhibited by antioxidants. It was not prevented by cyclooxygenase and lipoxygenase inhibitors, which indicates that non-enzymatic lipid peroxidation is involved. Transition metal- (copper-) induced lipid peroxidation results in similar physicochemical alterations of the LDL particle as found with endothelial cells; it is prevented by the presence of superoxide dismutase. In contrast, endothelial cell LDL modification was not influenced by superoxide dismutase. Catalase or singlet oxygen and hydroxyl radical scavengers also did not affect it. We suggest that yet unidentified radicals or lipid peroxides are generated in the cells or on the cell membrane and that these reactive molecule(s) will react with LDL after leaving the cell. HDL and lipoprotein-depleted serum prevented LDL modification markedly, and to a larger extent than that by copper ions. We speculate that LDL modification by endothelial cells will only occur under those conditions in which the balance between the generation of reactive oxygen molecules and the cellular protection against these reactive species is disturbed.

Reversible Oxidant-Induced Increases in Albumin Transfer Across Cultured Endothelium: Alterations in Cell Shape and Calcium Homeostasis

To determine whether reactive oxygen molecules could directly and reversibly increase the transfer of albumin across an endothelial barrier, we measured albumin transfer across monolayers of endothelium cultured on micropore filters before and after exposure to xanthine and xanthine oxidase. Xanthine and xanthine oxidase increased endothelial albumin transfer in a dose-dependent fashion. Parallel phase contrast and fluorescence microscopy demonstrated retraction of adjacent cells from one another and disruption of the actin filaments. The oxidant-induced increases in albumin transfer and changes in cell shape were reversed by removing xanthine oxidase and then incubating the monolayers for 3 1/2 hours in tissue culture media enriched with fetal bovine serum. However, incubation in tissue culture media without serum resulted in progressive injury and cell death. Hence, the brief exposure to oxidants initiated a progressive injury process that was reversed by incubation in serum. Because intracellular and extracellular calcium are important determinants of cell shape, and because some oxidized membrane lipids act as calcium ionophores, we asked whether oxidants altered endothelial calcium homeostasis. Xanthine-xanthine oxidase increased release of 45Ca++ from preloaded cells. The calcium antagonist lanthanum chloride prevented xanthine-xanthine oxidase increases in endothelial albumin transfer and prevented the changes in cell shape; chelation of extracellular calcium inhibited lysis of endothelium by xanthine-xanthine oxidase; and the calcium ionophore A23187 increased endothelial albumin transfer and mimicked the oxidant-induced changes in cell shape. Lanthanum chloride inhibited these effects of A23187. These data suggest that oxygen radicals can reversibly increase endothelial permeability to macromolecules, that this is associated with reversible changes in endothelial cell shape and actin filaments, and that the changes in cell shape are related to oxidant-induced changes in endothelial calcium homeostasis.

Reversible oxidant-induced increases in albumin transfer across cultured endothelium: alterations in cell shape and calcium homeostasis

To determine whether reactive oxygen molecules could directly and reversibly increase the transfer of albumin across an endothelial barrier, we measured albumin transfer across monolayers of endothelium cultured on micropore filters before and after exposure to xanthine and xanthine oxidase. Xanthine and xanthine oxidase increased endothelial albumin transfer in a dose-dependent fashion. Parallel phase contrast and fluorescence microscopy demonstrated retraction of adjacent cells from one another and disruption of the actin filaments. The oxidant- induced increases in albumin transfer and changes in cell shape were reversed by removing xanthine oxidase and then incubating the monolayers for 3 1/2 hours in tissue culture media enriched with fetal bovine serum. However, incubation in tissue culture media without serum resulted in progressive injury and cell death. Hence, the brief exposure to oxidants initiated a progressive injury process that was reversed by incubation in serum. Because intracellular and extracellular calcium are important determinants of cell shape, and because some oxidized membrane lipids act as calcium ionophores, we asked whether oxidants altered endothelial calcium homeostasis. Xanthine-xanthine oxidase increased release of 45Ca++ from preloaded cells. The calcium antagonist lanthanum chloride prevented xanthine- xanthine oxidase increases in endothelial albumin transfer and prevented the changes in cell shape; chelation of extracellular calcium inhibited lysis of endothelium by xanthine-xanthine oxidase; and the calcium ionophore A23187 increased endothelial albumin transfer and mimicked the oxidant-induced changes in cell shape. Lanthanum chloride inhibited these effects of A23187. These data suggest that oxygen radicals can reversibly increase endothelial permeability to macromolecules, that this is associated with reversible changes in endothelial cell shape and actin filaments, and that the changes in cell shape are related to oxidant-induced changes in endothelial calcium homeostasis.

Antioxidant activity of some antiproteases.

Proteolytic enzymes and reactive oxygen molecules participate in the pathogenesis of models of acute inflammation, and antiproteases have been used to determine proteolytic participation in these models. However, antiproteases have been demonstrated to directly inhibit inflammatory cells. In this report, significant antioxidant effects of antiproteases are described. These effects involve both scavenging of oxygen radicals and direct inhibition of enzymes capable of producing oxygen radicals. These results suggest using caution in implicating proteolytic mechanisms solely on the basis of antiprotease inhibition of expected phenomena.