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Biomedical subjects

J W Eaton

Publications and source records attributed to J W Eaton.

At least 19 recordsLinked to original sources
PubMed1995

Hazards of antioxidant combinations containing superoxide dismutase.

Oxygen free radical scavengers protect against ischemia/reperfusion injury of the kidney in vivo and against hypoxia/reoxygenation (H/R) injury of renal cells in several in vitro systems. In an attempt to maximize renal protection we tested several antioxidants in combination; the individual components had previously reduced reoxygenation injury of hypoxic renal epithelial cells. Both glutathione (GSH; 1 mM) and Cu,Zn-SOD provided significant protection against posthypoxic injury. Surprisingly, the combination of Cu,Zn-SOD plus GSH eliminated protection entirely and was highly toxic to normoxic cells. The toxicity of Cu,Zn-SOD+GSH was not prevented by the iron chelator deferoxamine and was only slightly reduced by the hydroxyl scavenger DMTU. Catalase reversed the toxicity of Cu,Zn-SOD+GSH and provided net protection. Direct measurement of intracellular peroxides using 2,7-dichlorofluorescein quantitated by laser cytometry also revealed enhanced generation of peroxides by cells during H/R when Cu,Zn-SOD+GSH was present. GSSG was less toxic than GSH when combined with Cu,Zn-SOD. Importantly, the combination of Mn-SOD+GSH provided superior protection to either agent alone. In the presence of added GSH, heated or autoclaved Cu,Zn-SOD was still toxic, whereas SOD free of chelatable Cu++ was benign. In the presence of GSH, Cu++ derived from SOD may promote the formation of toxic thionyl radicals, metal-centered radicals, and/or H2O2, thereby causing cell injury. Great care should be used in designing and interpreting studies employing combinations of antioxidants.

Aerobiosis↗
PubMed1995

Inflammatory responses to biomaterials.

Implanted biomedical devices are of increasing importance in modern medical care. However, surprisingly little is known of the factors that determine biocompatibility of the materials used in these devices. These materials, although generally inert and non-toxic, can mediate a variety of adverse reactions, including inflammation, fibrosis, coagulation, and infection. This brief review focuses on the inflammatory responses (including fibrosis) that commonly occur around implanted biomaterials. Host proteins that spontaneously associate with implant surfaces are important determinants of the acute inflammatory response. In this regard, adsorbed fibrinogen appears particularly pro-inflammatory. Chronic inflammatory processes, in many cases in response to fragments of implanted biomaterials, may cause implant failure. In the case of silicone-filled mammary prostheses, the extravasation of silicone gel has been held responsible for a number of complications, including silicone granuloma, synovitis, connective-tissue disease, and lymphadenopathy. In some instances, material-mediated inflammatory responses may even cause degradation of the material itself (via oxidative products released by implant-associated inflammatory cells). Overall, there is insufficient knowledge of the determinants and mechanisms of host: implant responses. A clear understanding of tissue:biomaterial interactions will be required both to explain the pathogenesis of many implant-mediated complications and to aid in the development of more biocompatible materials for implantable devices.

Biocompatible Materials↗
PubMed1994

Heme and the vasculature: an oxidative hazard that induces antioxidant defenses in the endothelium.

Heme proteins transport oxygen and facilitate redox reactions. Heme, however, may be dangerous, especially when free in biologic systems. For example, iron released from hemoglobin-derived heme can catalyze oxidative injury to neuronal cell membranes and may be a factor in post-traumatic damage to the central nervous system. We have shown that heme catalyzes the oxidation of low density lipoproteins which can damage vascular endothelial cells. The endothelium is susceptible to damage by oxidants generated by activated phagocytes, and this has been invoked as an important mechanism in a number of pathologies including the Adulte Respiratory Distress Syndrome (ARDS), acute tubular necrosis, reperfusion injury and atherosclerosis. Because of its highly hydrophobic nature, heme readily intercalates into endothelial membranes and potentiates oxidant-mediated damage. This injury is dependent on the iron content of heme and is completely blocked when concomitant hemopexin is added. Ferrohemoglobin, when added to cultured endothelial cells, is without deleterious effects, but if oxidized to ferrihemoglobin (methemoglobin), it greatly amplifies oxidant damage. Methemoglobin, but not ferrohemoglobin, releases its hemes which can then be incorporated into endothelial cells. Cultured endothelial cells, when exposed to methemoglobin but not ferrohemoglobin, cytochrome c or metmyoglobin, potentiate this oxidant injury. Stabilization of the methemoglobin by cyanide, haptoglobin or capture of the heme by hemopexin abrogates this effect. Paradoxically, more prolonged exposure of endothelium to heme or methemoglobin renders them remarkably resistant to oxidant challenge. Endothelium defends itself from heme by induction of the heme degrading enzyme heme oxygenase and the concomitant production of large amounts of the iron binding protein ferritin.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Albumin binding surfaces for biomaterials.

The surfaces of medical devices may promote both coagulation and infections caused by adherent microorganisms. In the case of polymeric elastomers, these iatrogenic effects are likely intermediated by absorbed host proteins that spontaneously bind to the device surface, promoting both bacterial adherence and thrombotic events. We earlier attempted to produce biomaterial surfaces that would selectively bind host albumin because albumin-coated surfaces were known to diminish both coagulation and bacterial adherence. To this end, an albumin-binding high molecular weight dextran:Cibacron blue adduct was bulk incorporated into polyetherurethane (Keogh et al., J Biomed Mater Res 1992;26:441). The modified material bound albumin selectively and reversibly and showed evidence of enhanced biocompatibility. However, approximately 30% of the surface of this material was evidently unmodified and still capable of exerting the above adverse effects. In the present work, we have covalently surface-modified polyetherurethane with sequential additions of acrylamide, amino-propylmethacrylamide, dextran, and Cibacron blue. This derivatized polyurethane preferentially and reversibly binds albumin, even from complex mixtures of proteins such as plasma. Furthermore, this material inhibits the clotting of nonanticoagulated whole human blood (for > 16 hours at room temperature), perhaps by virtue of binding and activation of antithrombin III by the sulfonic acid residues on the surface-immobilized Cibacron blue. Finally, such surfaces, especially when bearing bound albumin, diminish the adherence of Staphylococcus epidermidis, a pathogen frequently associated with device-centered infections. We conclude that similar albumin-affinity surfaces may hold promise for the development of more biocompatible materials for implantation and blood contact applications.

Anticoagulants↗
PubMed1994

Free fatty acids enhance hypochlorous acid production by activated neutrophils.

Activated polymorphonuclear neutrophils (PMNs) may contribute to the genesis of chronic obstructive lung disease in long-term cigarette smokers. However, it is not presently known which elements in smoke are important in triggering this progressive pulmonary damage or in affecting the activities of inflammatory cells such as PMNS. We earlier found substances in organic concentrates of cigarette smoke that bound ferrous iron and transferred the metal into organic phases. These substances were later identified as saturated free fatty acids, predominantly palmitic and stearic acids (16:0 and 18:0). We now report investigations of the effects of fatty acids on the oxidative metabolism of PMNs. In accord with most earlier reports, we find that saturated fatty acids have little direct effect on PMN oxidative metabolism. However, micromolar amounts of free fatty acids will more than double production of hypochlorous acid (HOCl) by PMNs stimulated with small amounts of phorbol myristate acetate. Similar fatty acid-mediated increases in HOCl production also occur when PMNs are stimulated with 1,2-dioctanoyl-sn-glycerol and 1-oleoyl-2-acetyl-sn-glycerol (also thought to be agonists of protein kinase C) but not when cells are stimulated with the calcium ionophore A23187, the formylated tripeptide f-met-leu-phe, or opsonized zymosan. Fatty acid-mediated enhancement of PMN HOCl production evidently arises from increased release of myeloperoxidase from stimulated PMNs. Furthermore, in the presence of free fatty acids, stimulated PMNs are much more cytotoxic toward cultured mink lung epithelial cells, a toxicity that is blocked by scavengers of HOCl. These results suggest that the relatively large amounts of free fatty acids present in tobacco smoke may act to amplify PMN-mediated oxidative damage to the lungs of smokers.

Adult↗
PubMed1993

Fibrin(ogen) mediates acute inflammatory responses to biomaterials.

Although "biocompatible" polymeric elastomers are generally nontoxic, nonimmunogenic, and chemically inert, implants made of these materials may trigger acute and chronic inflammatory responses. Early interactions between implants and inflammatory cells are probably mediated by a layer of host proteins on the material surface. To evaluate the importance of this protein layer, we studied acute inflammatory responses of mice to samples of polyester terephthalate film (PET) that were implanted intraperitoneally for short periods. Material preincubated with albumin is "passivated," accumulating very few adherent neutrophils or macrophages, whereas uncoated or plasma-coated PET attracts large numbers of phagocytes. Neither IgG adsorption nor surface complement activation is necessary for this acute inflammation; phagocyte accumulation on uncoated implants is normal in hypogammaglobulinemic mice and in severely hypocomplementemic mice. Rather, spontaneous adsorption of fibrinogen appears to be critical: (a) PET coated with serum or hypofibrinogenemic plasma attracts as few phagocytes as does albumin-coated material; (b) in contrast, PET preincubated with serum or hypofibrinogenemic plasma containing physiologic amounts of fibrinogen elicits "normal" phagocyte recruitment; (c) most importantly, hypofibrinogenemic mice do not mount an inflammatory response to implanted PET unless the material is coated with fibrinogen or the animals are injected with fibrinogen before implantation. Thus, spontaneous adsorption of fibrinogen appears to initiate the acute inflammatory response to an implanted polymer, suggesting an interesting nexus between two major iatrogenic effects of biomaterials: clotting and inflammation.

Ancrod↗
PubMed1993

Degradation of biomaterials by phagocyte-derived oxidants.

Polymers used in implantable devices, although relatively unreactive, may degrade in vivo through unknown mechanisms. For example, polyetherurethane elastomers used as cardiac pacemaker lead insulation have developed surface defects after implantation. This phenomenon, termed "environmental stress cracking," requires intimate contact between polymer and host phagocytic cells, suggesting that phagocyte-generated oxidants might be involved. Indeed, brief exposure of polyetherurethane to activated human neutrophils, hypochlorous acid, or peroxynitrite produces modifications of the polymer similar to those found in vivo. Damage to the polymer appears to arise predominantly from oxidation of the urethane-aliphatic ester and aliphatic ether groups. There are substantial increases in the solid phase surface oxygen content of samples treated with hypochlorous acid, peroxynitrite or activated human neutrophils, resembling those observed in explanted polyetherurethane. Furthermore, both explanted and hypochlorous acid-treated polyetherurethane show marked reductions in polymer molecular weight. Interestingly, hypochlorous acid and peroxynitrite appear to attack polyetherurethane at different sites. Hypochlorous acid or activated neutrophils cause decreases in the urethane-aliphatic ester stretch peak relative to the aliphatic ether stretch peak (as determined by infrared spectroscopy) whereas peroxynitrite causes selective loss of the aliphatic ether. In vivo degradation may involve both hypohalous and nitric oxide-based oxidants because, after long-term implantation, both stretch peaks are diminished. These results suggest that in vivo destruction of implanted polyetherurethane involves attack by phagocyte-derived oxidants.

Animals↗
PubMed1992

Ferritin: a cytoprotective antioxidant strategem of endothelium.

Phagocyte-mediated oxidant damage to vascular endothelium is likely involved in various vasculopathies including atherosclerosis and pulmonary leak syndromes such as adult respiratory distress syndrome. We have shown that heme, a hydrophobic iron chelate, is rapidly incorporated into endothelial cells where, after as little as 1 h, it markedly aggravates cytotoxicity engendered by polymorphonuclear leukocyte oxidants or hydrogen peroxide (H2O2). In contrast, however, if cultured endothelial cells are briefly pulsed with heme and then allowed to incubate for a prolonged period (16 h), the cells become highly resistant to oxidant-mediated injury and to the accumulation of endothelial lipid peroxidation products. This protection is associated with the induction within 4 h of mRNAs for both heme oxygenase and ferritin. After 16 h heme oxygenase and ferritin have increased approximately 50-fold and 10-fold, respectively. Differential induction of these proteins determined that ferritin is probably the ultimate cytoprotectant. Ferritin inhibits oxidant-mediated cytolysis in direct relation to its intracellular concentration. Apoferritin, when added to cultured endothelial cells, is taken up in a dose-responsive manner and appears as cytoplasmic granules by immunofluorescence; in a similar dose-responsive manner, added apoferritin protects endothelial cells from oxidant-mediated cytolysis. Conversely, a site-directed mutant of ferritin (heavy chain Glu62----Lys; His65----Gly) which lacks ferroxidase activity and is deficient in iron sequestering capacity, is completely ineffectual as a cytoprotectant. We conclude that endothelium and perhaps other cell types may be protected from oxidant damage through the iron sequestrant, ferritin.

Animals↗
PubMed1992

Multicellular oxidant defense in unicellular organisms.

Although catalase is thought to be a major defense against hydrogen peroxide (H2O2), the catalase activity within individual Escherichia coli fails to protect against exogenous H2O2. Contrary to earlier reports, we find that dilute suspensions of wild-type and catalase-deficient E. coli are identical in their sensitivity to H2O2, perhaps because even wild-type, catalase-positive E. coli cannot maintain an internal/external concentration gradient of this highly diffusible oxidant. However, concentrated suspensions or colonies of catalase-positive E. coli do preferentially survive H2O2 challenge and can even cross-protect adjacent catalase-deficient organisms. Furthermore, high-density catalase-positive--but not catalase-negative--E. coli can survive and multiply in the presence of competitive, peroxide-generating streptococci. These observations support the concept that bacterial catalase may defend colonial, but not individual, E. coli against environmental H2O2. Group protection by the activity of enzymes that mitigate oxidative stress may have been a driving force in the evolution of multicellular organisms.

Biological Evolution↗
PubMed1992

Albumin-binding surfaces for implantable devices.

Surfaces of implantable and blood contact-devices accumulate adsorbed and denatured proteins. This anomalous layer of proteins may help trigger unwanted events such as activation of coagulation systems and, perhaps, chronic inflammation. Because, in many experimental systems, the purposeful coating of surfaces with albumin will biologically "passivate" materials, we have attempted to develop polymers which, when exposed to blood or body fluids, will spontaneously, selectively, and reversibly adsorb host albumin. We report here a novel derivatization technique for increasing the albumin affinity of implantable polyetherurethane (PU). The technique is based on the incorporation of high-molecular-weight dextran to which the albumin-binding dye Cibacron Blue is covalently attached. Somewhat surprisingly, the amounts of human albumin adsorbed by Blue Dextran-modified and unmodified PU are quite similar. There are, however, important differences. First, the binding of albumin to derivatized PU is specific and not readily blocked by proteins in albumin-depleted human serum. Second, the majority of albumin associated with derivatized PU appears to be reversibly bound. Third, the binding of albumin to derivatized PU evidently is mediated primarily through ligand-specific binding of the protein to the albumin-binding dextran-dye conjugate. We conclude that it is possible to produce implantable polymers having surfaces which display albumin-binding dyes that selectively and reversibly bind albumin. Materials with this property, when implanted or exposed to blood, should form an infinitely renewable coating of albumin derived from physiologic fluids. This surface modification strategy may spawn a new generation of implantable materials with improved biologic compatibility.

Adsorption↗
PubMed1991

Spirohydantoin inhibitors of aldose reductase inhibit iron- and copper-catalysed ascorbate oxidation in vitro.

Transition metal-catalysed oxidations have been implicated in the complications of diabetes. We report here that some experimental inhibitors of the enzyme aldose reductase (implicated in diabetes mellitus via its ability to catalyse glucose reduction to sorbitol) are also potent inhibitors of transition metal-catalysed ascorbate oxidation. The inhibition appears to be dependent upon the presence of a spirohydantoin group. It is conceivable that the copper- and iron-binding capacity of these compounds may contribute to some of their observed biological effects and may provide a starting point for a new generation of experimental drugs for the treatment of diabetes mellitus.

Aldehyde Reductase↗
PubMed1991

A spectrophotometric assay for chlorine-containing compounds.

Determinations of hypochlorous acid and chloramine compounds are important in a number of areas. Several techniques are now available for such analyses, but most require unstable reagents and/or multiple steps in the analytical procedure. We have developed a simple, one-step spectrophotometric assay for reactive chlorine-containing compounds involving the oxidation of ascorbic acid by hypochlorous acid or chloramines. There is no interference from other nonhalide oxidants such as hydrogen peroxide or hypothiocyanous acid. Because small amounts of ascorbic acid will not damage biological materials, this method also allows continuous measurements of the generation of chlorine-containing compounds by activated neutrophils. This simple assay permits precise analysis of as little as 1 nmol of HOCl.

Ascorbic Acid↗
PubMed1991

Is the lens canned?

The ocular lens somehow remains pellucid despite bombardment by ultraviolet radiation and endogenous hydrogen peroxide (present in the humoral fluids which bathe this tissue). The lens and adjacent aqueous and vitreous humors contain exceptionally high concentrations of reducing substances, particularly ascorbic acid, thought to be important in lenticular oxidant defense. However, in the presence of traces of transition metals, or when exposed to ultraviolet radiation, ascorbic acid readily reacts with oxygen, yielding hydrogen peroxide, and damaging lens crystallins. We propose the alternative hypothesis that the real antioxidant function of ascorbic acid, particularly that in the aqueous and vitreous humors, may be effecting the conversion of oxygen to water. Because the lens lacks a blood supply, coupled reactions of ascorbic acid with oxygen in the humoral fluid spaces should produce a metabolically sustained anaerobiosis. If so, nature may have preinvented the process of canning, wherein food (or in this case, the lens) is preserved by a combination of sterility and anoxia.

Animals↗
PubMed1991

Iron translocation by free fatty acids.

Organic extracts of cigarette smoke and uncombusted tobacco contain substances capable of translocating iron from aqueous solutions into immiscible organic solvents. Such extracts will also effect the organic solvation of iron present in ferruginous forms of asbestos such as amosite and crocidolite (Qian and Eaton, Arch Biochem Biophys 1989, 275:280). These substances, previously detected by their iron-translocating properties, have now been purified and identified by mass spectroscopy as saturated fatty acids, predominantly stearic and palmitic acids. Organic extracts of tobacco smoke, as well as the pure fatty acids, also transfer ferrous iron into both isolated red cell membranes and intact human erythrocytes. The increased membrane iron may enhance cellular susceptibility to exogenous oxidants; erythrocyte membranes subject to fatty acid-mediated iron accumulation show elevated peroxidation of endogenous polyunsaturated fatty acids. These observations may help explain the phlogistic effects of tobacco use and suggest, in a broader context, that free fatty acids may act as physiologic and pathologic mediators of metal translocation.

Biological Transport↗
PubMed1990

Antimalarial activity of diethyldithiocarbamate. Potentiation by copper.

The antimalarial activity of diethyldithiocarbamate (DDC) in vitro was potentiated by subtoxic concentrations of copper. DDC was also more potent in the presence of an intracellular source of copper, such as when parasites were grown in superoxide dismutase (SOD)-loaded erythrocytes. These data suggest that DDC forms a complex with copper, either intracellularly or extracellularly, which is toxic to malarial parasites. The exact cause of this toxicity is not known, but may be due to a membrane effect, since DDC and copper, in combination, exert a potent lytic effect on normal human erythrocytes.

Animals↗
PubMed1990

Antioxidant functions of phytic acid.

Phytic acid is a natural plant antioxidant constituting 1-5% of most cereals, nuts, legumes, oil seeds, pollen and spores. By virtue of forming a unique iron chelate it suppresses iron-catalyzed oxidative reactions and may serve a potent antioxidant function in the preservation of seeds. By the same mechanism dietary phytic acid may lower the incidence of colonic cancer and protect against other inflammatory bowel diseases. Its addition to foods inhibits lipid peroxidation and concomitant oxidative spoilage, such as discoloration, putrefaction, and syneresis. A multitude of other industrial applications are based on the antioxidant function of phytic acid.

Animals↗